PRINCIPLES OF 
 STRATIGRAPHY 
 
COMPANION VOLUMES OF THIS WORK 
 
 North American Index Fossils 
 
 (Invertebrates) 
 
 By AMADEUS W. GRABAU, Professor of Palaeontology 
 in Columbia University, and HERVEY WOODBURN Sm- 
 MER, Assistant Professor of Palaeontology in the Massa- 
 chusetts Institute of Technology. 2 vols. Vol. I, 1909, 
 853 pages and 1210 text figures; Vol. II, 1910, 909 
 pages and 727 text figures. 
 
 The volumes contain brief descriptions of the genera 
 and species of North American fossils most important 
 for the determination of geological horizons, and keys 
 for the determination of the genera. They are suitable 
 for class work in Palaeontology, and as an aid to the 
 worker, in determining his fossils and finding his hori- 
 zons. Owing to the widely scattered condition of the 
 literature, a comprehensive treatise like the present 
 becomes an indispensable adjunct to the geologist's 
 equipment. The Stratigraphic Appendices, the Glos- 
 sary of Terms, Directions for Collecting and Preserving 
 Fossils, and the extensive bibliography will also prove 
 of great value. 
 
 Large octavo, cloth bound, $12.00 net, for the two 
 volumes. 
 
 In preparation 
 
 Manual of Stratigraphy 
 
 By PROFESSOR AMADEUS W. GRABAU. 
 A discussion of the geological formations, with espe- 
 cial reference to North America and Europe. An appli- 
 cation of "Principles of Stratigraphy." 
 
 A. G. SEILER & Co., 1224 Amsterdam Ave., New York 
 
PRINCIPLES OF 
 STRATIGRAPHY 
 
 BY 
 
 AMADEUS W. GRABAU, S.M., S.D. 
 
 PROFESSOR OF PALAEONTOLOGY IN COLUMBIA UNIVERSITY 
 
 NEW YORK 
 A.. G. SEILER AND COMPANY 
 
 1913 
 
COPYRIGHT, 1913, BY 
 A. W. GRABAU 
 
 All rights reserved 
 
ERRATA 
 
 Part changed in italic 
 
 PAGE 
 
 54, 7 lines from top, change Egglest^on to Egleston 
 
 56, 1 6 lines from top, change Pumpelli to Pumpelly 
 
 86, 7 lines from top, change silvestris to sylvestris 
 
 90, 1 6 lines from top, change primogenius to prirm'genius 
 
 97, reference 96, change Tolman, C. E., to Tolman, C. F. 
 
 224, 26 lines from top, change Skagar to Skager 
 
 236, 17 lines from top, change Barent to Barents 
 
 268, reference 66, change Sorbey to Sorby 
 
 294, 23 lines from top, change Philipps to Phi//is 
 
 296, 6 lines from top, for shatter marks put chatter marks 
 
 299, reference 23, change Philipps to Phillips 
 
 310, 10 and ii lines from bottom, change Abyssolyth to Abyssoh'th 
 
 377, 14 lines from top, change Pterigotus to Pterygotus 
 
 392, 4 lines from top, change Woods Holl to Woods Hole 
 
 474, 15 lines from bottom, change Cymapolia to Cymopolia 
 
 534, 4 lines from bottom, change Yantzi to Yangtse 
 
 543, 5 and 7 lines from bottom, change Solefluction to Solifluction 
 
 554, 7 lines from top, change Askabad to As&kabad 
 
 591, 14 lines from bottom, change Molasse to Mo//asse 
 
 614, 2 lines from bottom, change Dantzig to Dawzig 
 
 639, reference 45, change Philipps to Phillips 
 
 684, 1 6 lines from bottom, change Reed to Reeds 
 
 689, reference 80, change Reed to Reeds 
 
 743, 3 lines from top, initial letter c to be capital C 
 
 830, 3 lines from top, change Chonoplain to conoplain 
 
 893, bottom line, change Equador to Ecuador 
 
 905, 4 lines from bottom, change R. D. Chamberlin to R. T. Chamberlin 
 
 941, 8 lines from bottom, change Dadoxylen to Dadoxylon 
 1034, 4 lines from top, change Bothryolepis to Bothn'olepis 
 1038, top line, change ^Epyornys to .^Epyorms 
 1051, 8 lines from top, change Orinoko to Orinoco 
 1076, 7 lines from bottom, change Chili to Chile 
 1086, 7 lines from bottom, change Valient to Valiant 
 1096, reference 22, change Roth, I. to Roth, /. 
 1099, Foot note I, 2 lines from bottom, change Philips to Philips 
 1 1 08, column headed Founder, change Conybear to Conybeare 
 
 271728 
 
TO 
 
 JOHANNES WALTHER 
 
 A LEADER IN THE 
 
 FIELDS OF KNOWLEDGE 
 
 HEREIN EXPLORED 
 
ACKNOWLEDGMENTS. 
 
 To the many among my colleagues and students who have ren- 
 dered assistance in the production of this work I zvish to tender 
 heartiest acknowledgments. Of those whose helpful attitude aided 
 the early stages of my labors 1 want especially to mention Alpheus 
 Hyatt and Robert Tracy Jackson, leaders in American Paleon- 
 tology, and further, William Otis Crosby, Nathaniel Southgate 
 Shaler, William Morris Davis and Jay Backus Woodworth, masters 
 all of inorganic geology, and known as such in both hemispheres. 
 More recently my colleagues at Columbia University, Professors 
 James F. Kemp, Douglas Wilson Johnson, and especially Charles 
 Peter Berkey have put me under obligations by helpful suggestions 
 and criticisms. My graduate students, too, during the last ten years 
 have aided me more than many of them perhaps realise, for only a 
 teacher can know the help and inspiration that comes from daily 
 contact with eager and, above all, inquiring minds, such as our 
 splendid body of American graduate students furnishes. May these 
 pages recall to them the many spirited discussions, in which they 
 usually bore their part so zvell. 
 
 To one of them. Miss Marjorie O'Connell, A.M., instructor in 
 Geology in Adelphi College, Brooklyn, my special thanks are due 
 for the careful and critical attention given for a period of a full 
 year or over to both manuscript and proof, and to the verification of 
 the literary references, and the endeavor, by patient library re- 
 search, to make the bibliographies as serviceable as possible. To 
 her prolonged search of the literature for available material, I also 
 owe many important references which I would otherwise have 
 missed. And, finally, she has to her credit the very complete index 
 of this volume. One other I may mention by name, Mr. George L. 
 Cannon, of Denver, Colorado, whose broad conceptions of the prin- 
 ciples of classification have rendered our discussions highly prof- 
 itable. 
 
 Finally, I cannot forbear to mention my many foreign friends 
 who, by word of mouth or by their writings, have led me into paths 
 replete with interest and profitable adventure. To their willingness 
 to guide me in my studies within their home-lands, and to discuss 
 the problems which interested us in common, I owe many stimulat- 
 ing hours. Some, like Kittl of Vienna, Koken of Tubingen, and 
 Holzapfel of Strassburg, have since passed away, and I may think 
 of them here in sorrow. To the many, however, who still hold 
 high the torch of learning, these pages bring a greeting from the 
 land which has yet much to learn from the culture, and the devo- 
 tion to Pure Science, so characteristic of the European leaders in 
 the Earth Sciences. And he, to whom these pages are inscribed, 
 will know that the days spent in his inspiriting companionship in 
 field and study are among the potent influences which helped to 
 shape the character of this book. 
 
 vi 
 
PREFACE 
 
 This book is written for the student and for the professional 
 geologist. It aims to bring together those facts and principles 
 which lie at the foundation of all our attempts to interpret the his- 
 tory of the earth from the records left in the rocks. Many of 
 these facts have been the common heritage of the rising genera- 
 tion of geologists, but many more have been buried in the litera- 
 ture of the science, especially the works of foreign investigators, 
 and so have generally escaped the attention of the student, though 
 familiar to the specialist. Heretofore there has been no satisfac- 
 tory comprehensive treatise on lithogenesis in the English language, 
 and we have had to rely upon books in the foreign tongue for such 
 summaries. It is the hope of the author that the present work 
 may, in a measure, supply this need. 
 
 The book was begun more than fifteen years ago, and the ma- 
 terial here incorporated has been collected and sifted during this 
 interval. From time to time certain phases of the work have been 
 published, and these in a revised form have been included in the 
 book. The first of these, on Marine Bionomy, appeared in 1899, 
 the latest, on Ancient Deltas, in 1913. Much of the material has, 
 however, not appeared in print before. The principles and data 
 herein treated have for years been considered and discussed in a 
 course of lectures on the "Principles of Geology," given jointly 
 by Professor Berkey and myself at Columbia University. Some 
 of the problems which have taken form during these discussions 
 have been chosen as subjects for more extensive investigations by 
 members of the classes, and the results of a number of these have 
 already appeared in print. 
 
 My own interest in the problems, and especially the principles 
 of Orogenesis and Geodynamics, goes back to the days when, as a 
 student, I listened to the illuminating expositions of that versatile 
 and accomplished exponent of rational geology, Professor William 
 Otis Crosby, at the Massachusetts Institute of Technology. It was 
 at this time also that Alpheus Hyatt and the other eminent natural- 
 ists who foregathered at the fortnightly meetings of the Boston 
 Society of Natural History, discussed the problems of Biogenesis, 
 and evolved the working principles which have since guided the in- 
 
 vii 
 
viii PREFACE 
 
 vestigations of the "Hyatt School" of Palaeontologists. Later, at 
 Harvard University, under the leadership of the unforgettable 
 Shaler, and guided by that keenest of analysts, William Morris 
 Davis, and by the others of that brilliant coterie of Harvard Ge- 
 ologists and Palaeontologists Wolf, Woodworth, Jackson, Ward, 
 Daly, Jaggar, and others the principles of Lithogenesis. Glypto- 
 genesis, and Biogenesis formed daily topics of discussion, and 
 many of that group of eager students, who took part in these dis-, 
 cussions, here laid the foundations for subsequent achievements in 
 these fields. It was at this time also that we in America first be- 
 came acquainted with those monumental contributions to Litho- 
 genesis and Biogenesis, that had been and were being made by the 
 then Haeckel Professor of Geology and Palaeontology at Jena, Dr. 
 Johannes Walther, now Professor of Geology and Palaeontology at 
 Halle. The Einleitung in die Geologic als historische IVissenschaft 
 had appeared only a few years before, and its influence in shaping 
 geologic thought; especially among the younger men, was just be- 
 ginning to be felt. The Lithogenesis der Gegenwart presented such 
 a wealth of facts concerning the origin of sedimentary rocks, that 
 attention began to be diverted from the problems of the igneous 
 rocks which had heretofore almost exclusively occupied petrog- 
 raphers, and "Sediment-Petrographie," or the petrography of the 
 sedimentary rocks, attracted more and more of the younger geolo- 
 gists, especially in Germany and France. In the latter country the 
 works of Cayeux and Thoulet led the way, while in Britain Mackie 
 and Goodchild applied the principles of eolian deposition to the in- 
 terpretation of British strata, and Sorby, Phillips and many others 
 accumulated a wealth of facts and inferences. 
 
 It was at this period, too, that the attention of geologists and 
 especially stratigraphers was first seriously directed toward the 
 desert regions of the world and the phenomena of extensive sub- 
 aerial deposition. Here, again, Walther led the way in that classic, 
 Die Denudation in der Wiiste, followed in 1900 by his epoch-mak- 
 ing book, Das Gesetz der Wilstenbildung, which, in its revised 
 second edition, appeared in 1912. It is, of course, true, that impor- 
 tant studies of desert regions were made earlier, notably those of 
 von Zittel on the Libyan desert (1883), but the significance of the 
 desert deposits in terms of stratigraphy was first fully appreciated 
 within the last decade. That the importance of the desert as a 
 geological factor has become widely recognized, is shown by the 
 numerous recent studies, especially those on the Kalahari by Pas- 
 sarge, and those on the Asiatic deserts, by Sven Hedin, Pumpelly, 
 Huntington, and others. 
 
PREFACE ix 
 
 It is during this same decade that the Sciences of Glyptogenesis 
 and Geomorphology have come into being, notably through the 
 labors of Davis in America, and of Suess and Penck in Europe. 
 Suess's Antlits der Erde began to appear, it is true, in 1883, but it 
 is only in recent years that this work has been readily accessible to 
 most American students, through the medium of the English trans- 
 lation by Sollas and Sollas (1904-1909). Penck's Morphologic der 
 Erdoberflache appeared in 1894, but did not become well known 
 in this country until much later. It was, however, Davis's publica- 
 tions in this country, chiefly during the early nineties of the last 
 century, which gave the great impetus to the study of land forms, 
 and especially of the influence of erosion on their production. The 
 concept of the peneplain, of the cycle of erosion, of the sequential 
 development of rivers and erosion forms on the coastal plain and 
 on folded strata, and others chiefly due to him, have become of 
 incalculable value to the stratigrapher. The more recent develop- 
 ment of the idea of desert planation by Passarge and Davis, has 
 opened further promising fields to the stratigrapher, who seeks to 
 interpret the record in the strata by the aid of modern results 
 achieved by universal processes. 
 
 The science of earth deformations, or Orogenesis, also received 
 renewed impetus, during the last decade, in the work of Bailey 
 Willis in this country (Mechanics of Appalachian Structure, 1893), 
 and the researches of the European geologists on the deformations 
 of the Alps and other great mountain chains. True, this field had 
 been opened up in a masterful way by Heim, when in 1878 he 
 published his Mechanismus der Gebirgsbildung, and by Suess in his 
 earlier studies, but such work was of the nature of pioneer investi- 
 gations. In the Face of the Earth, too, emphasis is laid on de- 
 formation as the principal agent in the production of the diversi- 
 fied surface features of the earth. 
 
 In the field of Correlative Stratigraphy the past decade has like- 
 wise seen striking advances. The publication of the Lethaea falls 
 into this period, and so .does Marr's comprehensive little volume, 
 The Principles of Stratigraphical Geology, not to mention the elab- 
 orate recent texts of Haug, Kayser, and others, or the numerous 
 publications of Government surveys, and of individual contributors. 
 That questions of correlation have reached an acute stage in 
 American Geology is manifested by such recent publications as the 
 Outlines of Geological History and Ulrich's Revision of the Palcco- 
 zoic Systems, and the numerous papers accompanying or called 
 forth by these. Finally, Palaeogeography, as a science, is of very 
 recent development, most of the works of importance having ap- 
 
x PREFACE 
 
 peared in the last five years. In America Schuchert and Bailey 
 Willis are the acknowledged leaders, while in Europe many able 
 minds have -attacked the problems of Palaeogeography from all 
 angles. 
 
 It is thus seen that this book was conceived during the period 
 of initial reconstruction of our attitude toward the problems of 
 geology, and that its birth and growth to maturity fell into that 
 tumultuous epoch when new ideas crowded in so fast that the task 
 of mastering them became one of increasing magnitude and, finally, 
 of almost hopeless complexity. To summarize and bring together 
 the ideas of the past decade, and focus them upon the point of view 
 here essayed, is probably beyond the power of one individual. 
 Nevertheless, the attempt to present the essentials of the new ge- 
 ology for the benefit of those who, grown up with it, have perhaps 
 treated it with the lack of consideration usually bestowed on a con- 
 temporary, as well as for those who will carry on the work during 
 the next decade or two, cannot but serve a useful purpose. May 
 this attempt be adjudged 'not unworthy of its predecessors, nor 
 unfit to stand by the side of its contemporaries. 
 
 Scarsdale, New York, 
 The first of November, 
 One thousand nine hundred and thirteen. 
 
TABLE OF CONTENTS 
 
 CHAPTER I. 
 
 PAGE 
 
 GENERAL INTRODUCTORY CONSIDERATIONS : i 
 
 The Earth as a Whole i 
 
 I. The Atmosphere i 
 
 II. The Hydrosphere 2 
 
 Transgression and Regression 3 
 
 The Terrestrial Part of the Hydrosphere 4 
 
 III. The Lithosphere 5 
 
 The Mean Sphere Level (6) ; The Continental Block (7); Isostacy 
 (9); Thickness of the Earth's Crust (10); Material of the 
 Earth's Crust (12); Deformation of the Earth's Crust (Dias- 
 
 trophism) 6-12 
 
 IV. The Pyrosphere 12 
 
 V. The Centrosphere 13 
 
 Temperature of the Earth's Interior (13); Increase of Density. .13-15 
 
 VI. The Organic or Biosphere 16 
 
 Interaction of the Spheres 16 
 
 Sculpturing Processes 16 
 
 Definition and Subdivision of Geology 19 
 
 Table of Division of Geological Time 22 
 
 Bibliography 1 22 
 
 A. THE ATMOSPHERE. 
 CHAPTER II. 
 
 CONSTITUTION, PHYSICAL CHARACTERISTICS, AND MOVEMENTS OF THE 
 
 ATMOSPHERE; GEOLOGIC WORK OF THE ATMOSPHERE 24 
 
 Composition of the Atmosphere 24 
 
 Nitrogen; Oxygen; Argon; Carbon Dioxide; Water Vapor (25) ; 
 Absolute and Relative Humidity (26) ; Source of Water Vapor 
 
 (27) ; Impurities 25-27 
 
 Optical Characters of the Atmosphere 28 
 
 Light; Diffusion of Daylight 28 
 
 xi 
 
xii TABLE OF CONTENTS 
 
 PAGE 
 
 Temperature of the Atmosphere 29 
 
 Distribution of Heat within the Earth's Atmosphere 30 
 
 Geological Work of Heat and Cold Changes in Temperature 
 
 (31); Insolation and Radiation; Frost Work 31-34 
 
 Chemical Work of the Atmosphere 34 
 
 Oxidation (35) ; Red and Yellow Colors of Soil due to Oxidation 
 
 (36) ; Oxidation of Organic Compounds 35~37 
 
 Hydration; Kaolinization (37); Dehydration; Carbonation 
 (38); Laterization (39); Influence of Temperature on Rock 
 
 Decomposition 37~4O 
 
 Movements of the Atmosphere. Winds 40 
 
 Isobars; Direction of Movements of the Air (41); Influence of 
 Continents on Winds (44); Sea Breezes; Land Breezes; Mon- 
 soons 41-45 
 
 Cyclones and Anticyclones (46) ; Whirlwinds and Tornadoes 46-47 
 
 The Influence of Mountains on Winds (47); Mountain and 
 Valley Winds (50) ; Velocities of Wind 47~5o 
 
 Eolation or Mechanical Work of the Atmosphere 51 
 
 Wind Erosion and Translocation 52 
 
 Corrasion (52); Facetted Pebbles (54); Deflation (55); Character 
 and Amount of Deflational Denudation (57); Distance of Eolian 
 Transportation (58); Volume of Dust Falls (60); Sorting and 
 Rounding of Sand Grains by Wind 52-61 
 
 Condensation and Precipitation of Atmospheric Moisture 62 
 
 Dew, Frost, Clouds and Fogs; Rain, Snow and Hail 62-63 
 
 Amount of rainfall (63); Relation of Evaporation to Rain- 
 fall (65); Influence of Winds and Topography on Rainfall 
 (66) ; The Equatorial Belt of Calms and Variable Winds 
 (67); Latitude and Precipitation; Periodicity of Rainfall. .63-71 
 
 Electrical Phenomena of the Atmosphere 72 
 
 Fulgurites 72 
 
 Climate; Climatic Zones, Present and Past 74 
 
 Solar Climates, Climatic Belts or Zones 74 
 
 Physical Climate 75 
 
 I. Marine or Oceanic Climate; 2. Coast or Littoral Climate; 
 3. Interior Continental Climate; 4. Desert Climate; 5. 
 Mountain Climate 75~77 
 
 Climatic Provinces (77) ; Climatic Types based on Separate Atmo- 
 spheric Factors and on Agents (78); Climatic Zones of the Past 
 (78); Neumayr's Climatic Zones of the Jurassic (79); Discussion 
 of the subject of Climatic Zones 77~79 
 
 Rhythm of Climatic Changes (82) ; Indication of Climatic Changes 
 (83); Topographic Evidence of Change of Climate (83); Strati- 
 graphic Evidence of Change of Climate (84); Organic Evidence 
 of Change of Climate (85); i. Plants; 2. Animals 82-87 
 
 Displacement of the Earth's Axis as a Cause of Climatic Changes . 90 
 
 Origin of the Atmosphere 92 
 
 Bibliography II 92 
 
TABLE OF CONTENTS xiii 
 
 B. THE HYDROSPHERE. 
 CHAPTER III. 
 
 PAGE 
 
 MORPHOLOGY AND SUBDIVISION OF THE HYDROSPHERE 99 
 
 A. The Marine Division of the Hydrosphere 99 
 
 Regional Subdivisions of the Sea 99 
 
 I. Intercontinental Seas or Oceans 100 
 
 Bathymetric Zones of the Sea (too) ; Conformation of the Ocean 
 Floor (101); Features and Extent of the Continental Shelves 
 (103); Table Showing Distribution Area and Depth of the Prin- 
 cipal Continental Shelves (103); Subordinate Features of the 
 Continental Shelf (104); Features of the Suboceanic Elevations 
 and Depressions 100-105 
 
 II. Intracontinental Seas 106 
 
 A. Independent Seas (107); i. The Mediterraneans (107); Inter- 
 oceanic Mediterraneans (109); 2. Epicontinental Seas (109); 
 
 B. Dependent Seas, Funnel Seas 107-1 12 
 
 Summary of Classification 113 
 
 B. The Continental Division of the Hydrosphere 115 
 
 III. Continental Seas or Lakes 115 
 
 Classification of Lakes and Lake Basins. ....... 1 16 
 
 Classification of Lake Basins 1 16 
 
 A. Deformational or Tectonic Basins 118 
 
 B. Constructional Basins (120); Volcanic Basins ; Chemi- 
 cal Basins; Organic Basins; Detrital Basins 120-121 
 
 C. Destruction^! Basins (122); Volcanic; Chemical; 
 Fluviatile; Glacial; Deflation; Artificial 122-123 
 
 D. Obstructional or Barrier Basins (124); Tectonic; Vol- 
 canic; Chemical; Ice; Organic; Detrital 124-126 
 
 Classification of Lakes as a Whole 128 
 
 IV. Rivers 129 
 
 Simple or Monogene Rivers 130 
 
 I. Consequent Streams; II. Insequent Streams; III. Over- 
 flow Streams; IV. Glacial Streams; V. Subterranean 
 Streams , . 130-133 
 
 Polygene Rivers 133 
 
 Relative Ages of Rivers and River Systems 135 
 
 Aging of Rivers by Accident; Revival and Rejuvenation 
 
 of Rivers I35~I37 
 
 V. Underground Water (Ground Water) 138 
 
 Classification of Ground Water (138); General Course of 
 Meteoric Water (139); Porosity of .Rocks (140); The Water 
 Table; Depth and Quantity of Ground Water 138-141 
 
 Bibliography III 143 
 
xiv TABLE OF CONTENTS 
 
 CHAPTER IV. 
 
 PAGE 
 
 COMPOSITION AND PHYSICAL CHARACTERS OF THE HYDROSPHERE 145 
 
 Composition of the Hydrosphere 145 
 
 I. Salinity of the Sea 145 
 
 Table Showing the Salinity of the Sea (146); Variation in the 
 Distribution of the Salt Content of the Oceans and Intra- 
 continental Seas (149) ; Variation in Salinity in Bay of Danzig 
 (151); Table Showing the Bathymetric Variations of Salinity 
 
 in the Sea 146-152 
 
 II. Composition of Lake Waters 154 
 
 Table of Salinity of Various Lakes (154); Table Showing Ver- 
 tical Range of Salinity in Dead Sea (156); Analyses of Types 
 of Lake Water (157); Table in Percentage of Total Solids of 
 Composition of Various Types of Natural Waters (158); 
 Composition of Saline Lakes in Percentage of Total Solids 
 (159); Table of Average Composition of Lake Waters. 154-161 
 
 III. Composition of River Water 161 
 
 Table Showing the Amounts in Permille of the Principal 
 Elements and Compounds occurring in Various River Waters 
 (162); Table Showing Salinity of other Rivers (162); Table 
 of Total Solids carried in Solution in Tons per Year (164); 
 Table Showing the Amounts of the Different Salts carried in 
 Solution in one Cubic Mile of Average River Water 162-164 
 
 IV. Composition of Spring Water 165 
 
 Table of Composition of Rain Water near London (165); 
 Impurities in Rain Water; Solids in Rain Water (166); 
 
 Composition of Spring Water from the Sahara 165-167 
 
 Classification of Natural Waters; Gases and Organic Matter in 
 
 Natural Waters 169 
 
 Table of Analyses of Spring and Well Waters (170); Com- 
 position of Dissolved Air in Rain Water at Different Tem- 
 peratures (170); Gases in a Liter of pure Water 170-171 
 
 Organic Matter (172); Table of Organic Matter in Various 
 
 Streams in Percentage of the Total Solids 172-173 
 
 Chemical Work of the Natural Waters 174 
 
 Solution; Cementation; Hydration; Oxidation; Carbonation. . 175-179 
 
 Density and Specific Gravity of the Hydrosphere 179 
 
 Variation in Osmotic Pressure in the Sea Water 180 
 
 Temperature of the Hydrosphere 181 
 
 Freezing Point of Water; Heat Capacity of Water 181 
 
 Warming of the Water Body; Average Surface Tempera- 
 ture; Vertical variation of Temperature 182-183 
 
 Temperature of the Sea 184 
 
 Horizontal and Vertical Distribution of the Temperature in 
 the Three Great Oceans (184); Temperature of the Mediter- 
 raneans and Epicontinental Seas Dependent on the Large 
 Oceans (189); Temperatures of Dependent Seas (191); 
 Temperatures of the Arctic Ocean and its Dependencies 
 (192); Mean Temperatures of the Oceans and Intraconti- 
 nental Seas; Eutectic Temperatures (193); Range of Tem- 
 perature of the Oceans 184-194 
 
TABLE OF CONTENTS xv 
 
 PAGE 
 
 Temperatures of the Terrestrial Waters 195 
 
 Temperatures of Lakes, etc. (195); Classification of Lakes 
 According to Temperature (196); Freezing of Lakes (197); 
 Normal and Excessive Temperatures of Streams and of 
 Ground Water (199); Freezing of Rivers; Freezing of 
 Ground Water (200) ; Mechanical Work of Freezing Ground 
 Water (200) ; Thermal Springs (200) ; Magmatic or Juvenile 
 
 Waters 195-201 
 
 Optics of the Water . 204 
 
 Bibliography IV 206 
 
 CHAPTER V. 
 
 MOVEMENTS OF THE HYDROSPHERE AND THEIR GEOLOGICAL EFFECTS 209 
 
 Waves 209 
 
 Table Showing Relationships Between Wind Velocities and 
 Wave Height (213); Table Showing Relationship Between 
 Mean Wave and Wind Velocities (214); Relation Between 
 Length and Height of Wave (214); Classification of Waves 
 (214); The Swell or Ground Swell (215); Depth of Wave 
 Activity (216) ; Waves in Shallow Water (217) ; Destructive 
 Work of Waves (220) ; Rounding and Sorting of Detritus 
 
 by Wave Action 213-226 
 
 Tides 226 
 
 Comparison of Tides and Waves (228); Interference of 
 Tides; Tidal Scour and Transportation 228-231 
 
 Marine Currents 231 
 
 Currents of the Oceans (231); The Atlantic Ocean; the Arctic 
 Ocean; the Pacific Ocean; the Indian Ocean 231-238 
 
 Currents in Mediterraneans and Epicontinental Seas 239 
 
 Marine Currents in Relation to Migration and Dispersal, Past 
 and Present (243); Depth of Current Action 243-244 
 
 Lake Currents 244 
 
 River Currents 244 
 
 Velocities of River Currents (245); Erosive Power of 
 Rivers (246); Rate of Erosion; Transporting Power of 
 River Currents 245-247 
 
 Table Showing Transportation of Material by Rivers 
 (248); Table of Velocities Required to stir up Bottom 
 Material (248) ; Table Showing the Size of Rock Frag- 
 ments Moved by Different Velocities of Currents 248-249 
 
 Sorting Power of Rivers (252) ; Rounding of Sand Grains. . 252-253 
 
 Table Showing Coefficient of Psephicity of Minerals in 
 , Air and Water (255) ; Table Showing Rounding of Sands 
 of Moray Firth (256); Table Showing Rounding of 
 Sands of Culbin Dunes 255-256 
 
 Movement of Underground Waters 257 
 
 The Underflow (258) ; Rate of Flow of Underground Water 
 (259); Table Showing Permeability of Various Soils (259); 
 Pervious and Impervious Strata (260) ; The Deeper Zones 
 of Flow 258-260 
 
 Springs 261 
 
xvi TABLE OF CONTENTS , 
 
 PAGE 
 
 Water in the Solid Form 261 
 
 Kinds of Movement of Solid Water (262); Rate of Move- 
 ment; Wasting of the Glaciers; Erosive Work of Ice; 
 
 Transportation by Ice 262-265 
 
 Bibliography V 265 
 
 C. THE LITHOSPHERE. 
 CHAPTER VI. 
 
 CLASSIFICATION OF THE ROCKS OF THE EARTH'S CRUST 269 
 
 Subdivision of rocks 269 
 
 I. The Endogenetic Rocks 271 
 
 1. The Pyrogenic or Igneous Rocks (Pyroliths) 274 
 
 Composition Groups (274); Textural Groups (275); Water 
 
 and Ice as Igneous Rocks (278); Metamorphic Derivatives 
 
 of Igneous Rocks 274-279 
 
 2. The Atmogenic or Atmospheric Rocks (Atmoliths) 279 
 
 I. Snow; II. Firn or Neve; III. Snow Ice or Glacial Ice. . 279 
 
 3. The Hydrogenic Rocks (Hydroliths) 280 
 
 4. The Biogenic Rocks (Bioliths) 280 
 
 Caustobioliths (281); Sapropelites, Humus and Humuliths, 
 
 Liptobioliths 281 
 
 Subdivision of Hydrogenic and Biogenic Rocks 281 
 
 Textures of Amorphous Hydrogenics (281); Textures of 
 Biogenic Rocks (281); Table of the Principal Types of 
 
 Hydrogenic and Biogenic Rocks 281-282 
 
 Spherytes, Granulytes and Pulverytes , 283 
 
 Ooliths, Pisoliths, Rogensteine, etc 283 
 
 II. The Exogenetic"or Clastic Rocks 284 
 
 Textural Groups (285) ; Size of Grain (286) ; Table of Stand- 
 ard Sizes of Rock Fragments (287); Types of Sands Based on 
 
 Origin (288); Composition of Clastic Rocks 285-290 
 
 i. The Pyroclastics (290); 2. The Autoclastics (291); 3. The 
 Atmoclastics (292); 4. The Anemoclastics (293); 5. The Hy- 
 
 droclastics (294); 6. The Bioclastics 290-296 
 
 Summary of "Sedimentary Rocks " 296 
 
 The Cosmoclastic Rocks 297 
 
 Special Rock Terms 297 
 
 Rock Terms Emphasizing Composition (297); Autoch- 
 thonous and Allochthonous Deposits 297-298 
 
 Bibliography VI 298 
 
 CHAPTER VII. 
 STRUCTURAL OR TECTONIC FEATURES OF ROCK MASSES. ORIGINAL 
 
 STRUCTURES AND LITHOGENESIS OF THE PYROGENIC ROCKS 301 
 
 The Pyrogenic Rocks 301 
 
 Intrusive Igneous Bodies 302 
 
 Igneous Versus Sedimentary Contact (309); Contacts of 
 subterranean or abyssal masses (309); Contacts of hypa- 
 byssal or injected masses 309-310 
 
TABLE OF CONTENTS xvii 
 
 PAGE 
 
 Effusive Igneous Masses 311 
 
 Features of Basal Contact of Lava Sheets (311); Features 
 of Upper Surfaces of Lava Flows (313); i. Basic Lavas; 
 
 2. Acid Lavas 311-317 
 
 Minor Structural Characters of Volcanic Rocks 317 
 
 Flow Structure; Stratification of Flows; Columnar Struc- 
 ture; Variation in Grain 317-319 
 
 Bibliography VII 320 
 
 CHAPTER VIII. 
 
 STRUCTURE AND LITHOGENESIS OF THE ATMOGENIC ROCKS 322 
 
 Snow 322 
 
 Height of Snow-line (322) ; Altitude of Snowfall and of Snow- 
 line (323) ; Conversion of Snow into Ice 322-323 
 
 Glaciers (Kinds and Character) 323 
 
 Stratification of Ice (326) ; Shear Zones and Flow Struc- 
 ture 326-327 
 
 Bibliography VIII 327 
 
 CHAPTER IX. 
 
 ORIGINAL STRUCTURES AND LITHOGENESIS OF THE TRUE AQUEOUS OR HY- 
 
 DROGENIC ROCKS 329 
 
 Oceanic Precipitates 330 
 
 Chemical Deposits of the Deep Sea 330 
 
 Chemical Lime and Magnesia Deposits 33 1 
 
 Chemical Precipitation of Carbonate of Lime and Magnesia in 
 the Ocean (331); Table Showing Proportion of Dolomites to 
 Limestones in the Geological Series (333) ; Oolites and Pisolites 
 
 of Chemical or purely Hydrogenic Origin 331-336 
 
 Deposits in Enclosed or Nearly Enclosed Basins 338 
 
 Chemical Limestone Deposits of Lakes in Arid Regions (338); 
 
 Older Deposits of this Type 338-341 
 
 Limestone Deposits from Rivers 341 
 
 Deposits of Lime by Springs (342);' The Onyx Marble 342-344 
 
 Underground Deposits of Lime 345 
 
 Method of Deposition of Lime from Solution 346 
 
 Deposits of Marine Gypsum and Salt 347 
 
 Experiments of Usiglio (348) ; Table Showing the Order of 
 
 Separation of Salts from Sea Water 348-349 
 
 The Bar Theory of Ochsenius (350); The Bitter Lakes of 
 
 Suez an Example (352); The Karabugas Gulf 350-354 
 
 Natural Salt Pans (354); Evaporation of Cut-offs from the 
 
 Sea 354-355 
 
 Non-calcareous Terrestrial Precipitates 356 
 
 Salt Lakes and Salinas (356); The "Salitrales" of Patagonia 356-360 
 
 Deposits of Sodium Sulphate and Carbonate 361 
 
xviii TABLE OF CONTENTS 
 
 Table Showing Successive Crystallization resulting from 
 
 the Evaporation of the Waters of Owens Lake 362 
 
 Borax and Borates (363) ; Deposits of Nitrates (364) ; Other Min- 
 erals Deposited under Desert Climates 363-365 
 
 Origin of the Saline Deposits 365 
 
 Sources of Sodium Chloride (366); Marine; Leaching of Salt 
 from Older Formations and its Segregation (366); Sources of 
 Calcium Sulphate (368); Sources of Alkaline Carbonates 
 (369); Sources of Boric Acid and Borates and of Nitrates. .366-370 
 
 Summary 370 
 
 Ancient Salt Deposits 37 l 
 
 The Stassfurt Salts (371); The Siluric Salts of North America 
 
 (376) ; The Salt Domes 37i~379 
 
 Bibliography IX 380 
 
 CHAPTER X. 
 MORPHOLOGY AND LITHOGENESIS OF THE TRUE ORGANIC OR BIOGENIC 
 
 ROCKS. ZOOGENIC DEPOSITS 3 8 4 
 
 Coral and Other Reefs 3$5 
 
 Characters and Development of Modern Coral Reefs 386 
 
 Types of Modern Coral Reefs 386 
 
 Factors Limiting the Distribution of Modern Coral Reefs (389) ; 
 Depth of Water; Intensity of Light; Temperature; Other Phys- 
 ical Conditions 389-392 
 
 Composition and Structure of the Reef (393); Materials Com- 
 posing the Reef (393) ; Structure of Coral Reefs (396) ; Cavernous 
 character of reefs (401); Characters of Epicontincntal reefs. .393-402 
 Theories of Origin of Types of Coral Reefs (407); Subsidence 
 Theory of Darwin (408); Evidence of Subsidence (409); The 
 Spreading Ring Theory of Murray (410); Multiple Origin of 
 
 Reefs 407-41 1 
 
 Rate of Growth of Reef Organisms 411 
 
 Compacting Agents of the Coral Reef 413 
 
 Destruction of the Coral Reefs (414); Formation of Coral and 
 
 other Organic Lime-Sand and Mud 414 
 
 Fossil Coral and Stromatopora Reefs 417 
 
 Cambric and Pre-Cambric (417); Ordovicic 417-418 
 
 Siluric (418) ; Niagaran Reefs of Wisconsin (418) ; Siluric Reefs of 
 
 Gotland (420); Upper Siluric Reefs of North America 418-422 
 
 Devonic Coral Reefs (423) ; Lower Devonic Reefs of Konjepruss, 
 Bohemia (423) ; The Onondaga Reefs of New York (424) ; Middle 
 Devonic Reefs of Michigan (426) ; Devonic Reefs of the Attawa- 
 pishkat River, Canada (430) ; Middle Devonic Reefs of the Eifel 
 
 and Belgium 423-430 
 
 Mississippi Reefs (431); Mississippi Reefs of Belgium; Missis- 
 
 sippic Reefs of Great Britain 43i~432 
 
 Fossil Reefs of Bryozoa and other Organisms 433 
 
 Bryozoan Reefs of the German Zechstein (433) ; The Triassic 
 Reefs of the Tyrol (434) ; The Jurassic Reefs of Solnhofen (437) ; 
 The Sponge Reefs of the Swabian Jura (442); Miocenic Reefs of 
 the Austro-Russian Border (442); Pliocenic Bryozoa Reefs of 
 Kertch 433~443 
 
TABLE OF CONTENTS xix 
 
 PAGE 
 
 Bedded Reefs 444 
 
 Loss of Structure through Alteration of Reef Limestones 445 
 
 Ball-stone Reefs 446 
 
 Structures Formed by the Growth of Shell Colonies 447 
 
 Tepee Buttes (447) ; Other Examples 447-449 
 
 Bedded Zoogenic Deposits 449 
 
 Crinoidal Limestones" (449) ; Shell Limestones (449) ; Calcareous 
 and Siliceous Oozes . : 449-450 
 
 1. The Calcareous Oozes (450); Recent Foraminiferal Oozes 
 (450); Fossil Foraminiferal Oozes (453); Zoogenic Oolites 
 (455); Recent Pteropod Oozes; Fossil Pteropod Oozes ; Ento- 
 mostracan Oozes; Coccolith and Rhabdolith Oozes 450-456 
 
 2. The Siliceous Oozes (457); Radiolarian Oozes (457); The 
 Jurassic Radiolarite of the Alps (459) ; Recent Diatomaceous 
 Oozes (460) ; Fossil Diatomaceous Earths of both Fresh and 
 Salt Water Origin 457-461 
 
 Phosphate Deposits; Guano 461 
 
 Bibliography X 461 
 
 CHAPTER XI. 
 
 CHARACTER AND LITHOGENESIS OF ORGANIC OR BIOGENIC ROCKS (CON- 
 TINUED). PHYTOGENIC DEPOSITS. 467 
 
 Acaustophytoliths '. 467 
 
 Deposits formed by Lime-Secreting Algae 467 
 
 Modern Marine Forms (467) ; Order Cyanophyceae or Blue-Green 
 Algae (467); Phytogenic Oolites (467); Order Chlorophyceae 
 or Green Algae (469) ; Order Phaeophyceae or Brown Algae (470) ; 
 Order Rhodophyceae or Floridae; Red Algae (470); Lime-secret- 
 ing Algae of Fresh Water 467-471 
 
 Fossil Phytoliths of Algous Origin 471 
 
 Fossil Ooliths (471); Rogensteine of the Bunter Sandstein 
 
 (472); Alteration of Oolites 471-473 
 
 Sphasrocodium and Girvanella Deposits; Fossil Nullipores; 
 
 Fossil Chara 474-475 
 
 Travertine and Siliceous Sinter formed by Algae in Hot Springs . . . 475 
 
 Method of Lime Deposition by Plants 475 
 
 Separation of Siliceous Sinter by Plants 476 
 
 Vegetal Deposits (Caustophytoliths) 478 
 
 Petrographical Types of Vegetal Deposits 478 
 
 Sapropeliths (478); Petroleum (480); Sapanthraconyte or Cannel 
 Coal (481); Jet (482); Black Shales (483); Sapropelcalcilyths 
 
 Sapropelsilicilyth and Sapropel-ferrilyths 480-484 
 
 Recent Humuliths 485 
 
 Marine Marshes (487); Conversion of Salt Peat into Coal 
 
 (493) ; Mangrove Marshes 487-494 
 
 Fresh Water Swamps (494); Lake Swamps (495); Rivers and 
 
 Estuarine Swamps 494~497 
 
 Terrestrial Bogs (501); Forest Moors; Upland Bogs or High 
 Moors; the Arctic Tundras 501-507 
 
xx TABLE OF CONTENTS 
 
 PAGE 
 
 Peat in the Tropics 509 
 
 Fossil Humuliths 510 
 
 Lignite; Brown coal; Bituminous Coal; Anthracite; Graph- 
 ite 510-511 
 
 Ancient Moors (511); Black Soil and Shales of Humulithic 
 Origin (513); Burial of Peat Deposits (514); Liptobioliths . .511-517 
 Allochthonous Vegetal Deposits (518); Marine Vegetal Deposits 518 
 Bibliography XI 519 
 
 CHAPTER XII. 
 
 ORIGINAL CHARACTERS^ AND LITHOGENESIS OF THE EXOGENETIC ROCKS. 
 
 THE PYROCLASTICS AND THE AUTOCLASTICS 524 
 
 Pyroclastic Rocks 524 
 
 Modern Pyroclastics (524) ; Organic Remains of Modern Pyro- 
 
 clastics (525); Older Pyroclastic Deposits 524-525 
 
 Autoclastic'JRocks 527 
 
 Classification of Autoclastic Rocks 527 
 
 Fault Breccias (528); Intraformational Breccias (529); Fractur- 
 ing and Piling up of Material; Distortion of Layers in Gliding. .528-530 
 Glacial Deposits (531); Character of Modern and Pleistocenic 
 Glacial Deposits (531); Ancient Glacial Deposits (534); The 
 Pre-Cambric Tillite of Canada; Cambric Glacial Deposits; the 
 
 Permic Glacial Deposits '. . 531-535 
 
 Endolithic Brecciation 536 
 
 Bibliography XII 537 
 
 CHAPTER XIII. 
 
 ORIGINAL STRUCTURE AND LITHOGENESIS OF THE ATMOCLASTIC AND ANEMO- 
 CLASTIC ROCKS 540 
 
 A. Atmoclastic Rocks 540 
 
 Characteristics and Occurrence of Modern Atmoclastic Forma- 
 tions 541 
 
 Texture of Atmoclastic Rocks (542) ; Movement of Atmoclastic 
 Material (543); Slow Movements of Rock and Soil; Rock and 
 Soil Creep; Solifluction or Rock Flow (543); Rock Slides and 
 
 Falls (545); Rock Slides Started by Earthquakes 542-546 
 
 Ancient Examples of Rock Streams and Slides (546); Mackinac 
 
 Limestone Breccia 546-547 
 
 Residual Soils 548 
 
 B. Anemoclastic or Eolian Deposits. Anemoliths. 549 
 
 Source of Material of Eolian Deposits 549 
 
 Textural Types of Anemoliths; General Characteristics of Modern 
 Eolian Deposits 551 
 
 Sorting of Material according to Size and Specific Gravity; 
 
 Size of Grain in Eolian Deposits; Rounding of Sand Grains; 
 
 Stratification and Cross-bedding of Eolian Deposits 552-554 
 
TABLE OF CONTENTS xxi 
 
 Sand Dunes, their Origin and Form 555 
 
 Types of Sand Dimes; (i) Strand Dunes; (2) Lake Shore 
 Dunes; (3) River Flood Plain and River Bottom Dunes; 
 
 (4) Inland or Desert Dunes 557~56i 
 
 The Forms of Dunes (563) ; Origin of Intercalated Dust and 
 Clay Layers, and of Clay Balls in Sand Dunes ; Peat and Lig- 
 nite Deposits in Sand Dunes (564) ; Transgressive Relation of 
 
 Dune Sands to Subjacent Formations 563-565 
 
 Examples of Older Eolian Deposits 565 
 
 The Loess as an Example of a Dust Deposit; Fossils and 
 Concretions in the Loess ; Cenozoic and Mesozoic Loess-like 
 
 Deposits; Palaeozoic Loess-like Deposits 565-569 
 
 Older Deposits of Dune Types 570 
 
 Volcanic Dust Deposits 572 
 
 Special Indicators of Eolation 572 
 
 Calcareous and Other Non-Siliceous Eolian Sands (573); Recent 
 and Tertiary Examples (573); Older Examples (577); Possible 
 
 Application to the Chalk Beds (577) ; Dunes of Gypsum 573~578 
 
 Bibliography XIII 57 
 
 CHAPTER XIV. 
 
 ORIGINAL STRUCTURE AND LITHOGENESIS OF THE CONTINENTAL HYDRO- 
 
 CLASTICS 582 
 
 River-laid Clastics or Potamoclastics 582 
 
 Alluvial Fans (583) ; Form and Extent of Modern Alluvial 
 
 Fans (583) ; Basins Filled by River-washed Waste 583-587 
 
 River Flood Plains 588 
 
 Cross-bedding of Torrential Sediments (590); Thickness 
 and Composition of River Deposits (590) ; Depth of Com- 
 pound Continental Deposits (592); Chatter or Percussion 
 Marks (592) ; Organic Remains in Torrential Deposits (592) ; 
 Distance to which Material may be Carried by Rivers (594) ; 
 Purity and Rounding of Fluviatile Deposits (594); Form 
 of River Pebbles (595); Overlap Relations of River De- 
 posits 590-597 
 
 Flood Plains of Glacial Streams (597) ; River and Flood Plain 
 
 Deposits from Continental Ice-sheets 597~598 
 
 i. Torrential Moraine or Kame Deposits; 2. The 
 Frontal or Apron Plain; 3. The Esker; 4. Glacial 
 
 Sand Plains 598-600 
 
 Consolidated Sand Plains; The Nagelfluh of Salzburg. ... 60 1 
 Playasor Takyrs and Salinas (602); Preservation of Footprints, 
 etc., in Subaerial Deposits (604) ; Other Structural Characters . 602-605 
 
 Normal Paludal and Lacustrine Clastic Deposits 605 
 
 Deltas 607 
 
 Form and Rate of Growth of Deltas (608) ; Thickness or 
 Depth of Deltas (609); Delta Slopes (610); The Bird-foot 
 Delta of the Mississippi (610); Structure and Composition 
 of the Delta (612); Organisms of the Delta (615); Gaseous 
 Emanations of Deltas (615) ; Cementation of Delta Deposits 
 
xxii TABLE OF CONTENTS 
 
 (616); Modification of the Delta Surfaces (616); Relation 
 of Delta-building to Crustal Movements (617); Effect of 
 Subsidence (618); Effect of Elevation (619); Deltas Merg- 
 ing into Desert Deposits 608-619 
 
 Colors of Continental Clastics 620 
 
 Alternation of Red Beds with Those of Other Colors; Ori- 
 ginal Red Color of Sediments 623-625 
 
 Examples of Older Continental Hydroclastics 626 
 
 Cenozoic or Tertiary Examples 626 
 
 Mesozoic Examples of Continental Hydroclastics 631 
 
 The Potomac Formation; The Red Beds of North America; 
 Triassic Red Beds of Eastern North America, and of 
 
 Europe 631-633 
 
 Palaeozoic Delta Deposits 635 
 
 Bibliography XIV 637 
 
 CHAPTER XV. 
 
 STRUCTURAL CHARACTERS AND LITHOGENESIS OF THE MARINE HYDRO- 
 CLASTICS 641 
 
 Subdivision of the Areas of Marine Deposition 643 
 
 I. The Littoral District; 2. The Bathyal District; 3. The 
 
 Deep Sea or Abyssal District 643 
 
 Murray and Renard's Classification of Marine Deposits 
 (643); Krummers Classification of Marine Deposits (644); 
 
 A New Classification of Marine Deposits 643-545 
 
 Discussion of the Marine Clastics 646 
 
 The Littoral District and Its Deposits 646 
 
 The Shore Zone (Inter Co-tidal Zone; Littoral Zone in a 
 
 Restricted Sense) 647 
 
 Facies of the Shore Zone (648) ; i. Rocky Cliff Facies 
 (648); 2. Bouldery Facies (648); 3. Gravel Facies (649); 
 v Organic Remains in Pebble Beds (650) ; 4. Sandy Facies 
 (651); Marine Arkoses (652); Sorting of Sands and Gravels 
 by Waves (653); Organic Remains in Marine and Lacus-. 
 trine Sands (654); 5. Muddy Facies (655); Flocculation 
 and the Conditions of Mud Deposition (655); Table Show- 
 ing Rate of Settlement of Solid Matter in Fresh and Salt 
 
 Water (656) ; 6. Organic Facies 648-657 
 
 Subaqueous Solifluction (657); Accessory Features of Sub- 
 aqueous Gliding 657-660 
 
 The Permanently Submerged or Neritic Zone (Flachsee, 
 
 Shallow Water or Thalassal Zone) 661 
 
 I. The Estuary (66 1) ; 2. The Marginal Lagoon or Barachois 
 (665); 3. The Epicontinental Seas and Mediterraneans 
 
 (666); 4. The Ocean Littoral or the Neritic Zone 661-667 
 
 Deposits of the Bathyal District 668 
 
 Table Showing Kinds and Distribution of Bathyal De- 
 posits (668) ; .Table of Analyses of Muds, of Terrigenous 
 and of Volcanic Origin 668-669 
 
TABLE OF CONTENTS xxiii 
 
 PAGE 
 
 The Blue or Slate Colored Mud; The Red Mud; The Green 
 Mud; Green Sand; Table of Analyses of Glauconite from 
 
 Various Horizons 668-670 
 
 Deposits on Lee Banks and at the Edge of the Continental 
 
 Shelf 673 
 
 Abyssal Deposits 674 
 
 Abyssal Deposits of Pelagic Origin (674) ; Abyssal Deposits of 
 Terrigenous Origin (676); The Red Clay (676); Analyses of 
 Deep Sea Deposits (677); Table of Analyses of Deep Sea 
 Deposits (677) ; Older Deposits that have been Considered of 
 Deep Sea Origin (678); Concretions of the Deep Sea (678); 
 Cosmic Deposits of the Deep Sea (679) ; Submarine Volcanic 
 
 Deposits . 674-679 
 
 Interruptions of Marine Sedimentation 680 
 
 Persistence and Variation in Thickness of Marine Strata 682 
 
 Comprehensive Formations 684 
 
 Bibliography XV 685 
 
 CHAPTER XVI. 
 
 CHARACTERS AND LITHOGENESIS OF THE BIOCLASTIC ROCKS 691 
 
 Work of Herds of Animals in the Present and the Past ; Work of Burrow- 
 ing Animals; Destructive Work of Fish and Marine Invertebrates; 
 Work of Earthworms and Lobworms; Work of Ants and Termites; 
 Comparison of Work of Earthworms and Ants; Summary of Work of 
 
 Ants in Soil and Subsoil; Destructive Work of Plants 691-695 
 
 Bibliography XVI 695 
 
 CHAPTER XVII. 
 
 SUMMARY OF ORIGINAL FEATURES OF CLASTIC ROCKS 696 
 
 1. Stratification; Definitions of Stratum; Types of Stratifica- 
 tion 697-700 
 
 2. Cross Bedding 7 O1 
 
 a. Delta Type (702); b. Cross-bedding of Torrential Deposits 
 (702); Cross -bedding of Eolian Deposits (703); c. Comparison 
 
 of Types (704) 701-704 
 
 3. Beach Cusps (706); Fossil Beach Cusps (707); 4. Wave 
 Marks (708); 5. Rill Marks 706-708 
 
 6. Mud-cracks, Sun Cracks or Desiccation Fissures 709 
 
 Playa Surface (709); Permanent Lake Surface (709); 
 River Flood Plains (710); The Shore Zone (710) 709-710 
 
 7. Clay Galls (Thon-gallen) (711); 8. Clay Boulders (711); 
 9. Rain Prints (712); 10. Ripple Marks (712); n. Impressions 
 
 of Animals and Plants in Transit 711-714 
 
 12. Application of these Structures in Determining Position of 
 Strata 7*5 
 
 13. Rounding and Sorting of Sand Grains and Wearing of 
 Pebbles.. 7'5 
 
xxiv TABLE OF CONTENTS 
 
 14. Characteristics of Inclusions in Sand Grains 7*6 
 
 15. Organic Remains 717 
 
 16. Concretions 718 
 
 Accretions (719); Intercretions (719); Excretions (720); 
 Incretions (720) 719-720 
 
 17. Secretions 721 
 
 Bibliography XVII 721 
 
 CHAPTER XVIII. 
 
 OVERLAP RELATIONS OF SEDIMENTARY FORMATIONS 723 
 
 Progressive Overlap 723 
 
 A. Marine Progressive Overlap 723 
 
 I. Rising Sea-level or Positive Diastrophic Movement 724 
 
 1. Transgressive Movement 725 
 
 a. Rate of Depression Equals Rate of Supply (725) ; Older 
 Examples (728) ; b. Rate of Depression Exceeds Rate of Sup- 
 ply 725-731 
 
 2. Regressive Movements 732 
 
 c. Rate of Depression is Exceeded by Rate of Supply 732 
 
 II. Stationary Sea-level 733 
 
 III. Falling Sea-level 733 
 
 Characteristics of Regressive Deposits (734); Burial of Re- 
 treatal Sandstone by Subsequent Transgrossive Movement . 734-735 
 Examples of Intercalated Sandstones from the Palaeozoic and 
 
 Mesozoic; Formations of North America 738 
 
 The Saint Peter Sandstone (738) ; The Dakota Sandstone . 738-739 
 
 B. Non-marine Progressive Overlap 739 
 
 The Pottsville Series, a typical Example of Non-marine Progressive 
 
 Overlap 741 
 
 C. Replacing Overlap -. 743 
 
 Bibliography XVIII 744 
 
 CHAPTER XIX. 
 
 METAMORPHISM OF ROCKS 746 
 
 General Definitions (746); The Forces Producing Metamorph- 
 ism (746); The Region of Metamorphism (747); Character- 
 istics of the Zones of Metamorphism (747); Kinds of Meta- 
 morphism 746-748 
 
 Static Metamorphism or Diagenism 750 
 
 I. Lithification or Induration 750 
 
 Lithification or Induration of Clastic Rocks (751); I. Welding 
 (751); 2. Cementation (753); Quartzites and Novaculites (755); 
 Lithification of Clastics Largely a Supra-marine Process. . . .751-755 
 
 II. Recrystallization 755 
 
 Pressure Phenomena due to Recrystallization (Enterolithic 
 Structure) 756 
 
TABLE OF CONTENTS xxv 
 
 III. Dolomitization of Limestones 759 
 
 IV. Replacement of Limestone by Silica, Iron Oxide, etc. (762); 
 V. Desalinification (763); VI. Formation of Concretions (763); 
 
 VII. Hydration and Dehydration . . 762-765 
 
 Contact Metamorphism or Aethoballism 765 
 
 i. Pyrometamorphism (765); 2. Hydrometamorphism (766); 
 
 3. Atmometamorphism (767); 4. Biometamorphism ...765-768 
 
 Dynamic or Pressure Metamorphism, or Symphrattism 768 
 
 The Terms Slate, Schist and Gneiss (770); General Terms 
 for Metamorphic Rocks (771); Variation in Metamorphism 
 
 of Strata (772); Age of Metamorphic Rocks 77o~773 
 
 Bibliography XIX 773 
 
 CHAPTER XX. 
 
 DEFORMATION OF ROCK MASSES 776 
 
 Endogenetic Deformations 777 
 
 i. Endolithic Brecciation (777); 2. Enterolithic Structure 
 
 (778); 3. Contraction Joints, Basaltic Jointing 777~778 
 
 Deformation Due to Extraneous Causes Exogenetic Deformations. . 779 
 
 A. Gravitational Deformation 779 
 
 a. Structures due to Movements 779 
 
 4. Intraformational Brecciation 779 
 
 5. Subaquatic Gliding Deformation 780 
 
 Examples of Fossil Subaqueous Solifluction (781) A. 
 Miocenic Sublacustrine Glidings of Oeningen (781); 
 
 B. Jurassic Deformations (781); C. Triassic Examples 
 (782); D. Devonic Examples (782); E. Ordovicic Ex- 
 amples (783); F. A Cambric or Earlier Example 781-784 
 
 6. Surface deformations Due to Creep 785 
 
 b. Deformations due to Vertical Pressure of Overlying Rock 
 Masses (785); 7. Squeezing Out of Layers; 8. Shaliness; 9. 
 Slatiness 785-786 
 
 c. Of Complex Origin (786); 10. Pressure Sutures and Sty- 
 lolites (786); ii. Cone in Cone 786-788 
 
 B. Tectonic or Orogenic Deformations 789 
 
 d. Deformations Resulting in Fractures and Related Struc- 
 tures 789 
 
 12. Joints (789); Minor Characters of Joints; Feather 
 Fractures; Dendritic Markings; Widening of Joints. . . .789-791 
 
 13. Earthquake Fissures (792); 14. Slaty Cleavage (793); 
 15. Fissility (794); 16, Schistosity (794); 17- Gneissoid 
 Structure 792-795 
 
 e. Deformation due to Folding and to Folding and Erosion. . . 795 
 18. Folding (795); a. Anticlines (795); b. Synclines (795); 
 
 c. Isoclines (796); d. Fan Folds (798); e. Monoclines (798); 
 Anticlinoria and Synclinoria (799); Geosyncline and Fore- 
 deep 795-799 
 
 Relation of Dip Strike and Outcrop (800); Strike as 
 Affected by Pitching Axis of Folds (806); Folding as 
 Indications of Unconformity (815); The trend of the 
 Appalachian Folds 800-807 
 
xxvi TABLE OF CONTENTS 
 
 PAGE 
 
 ig. Domes and Basins 808 
 
 f. Deformation due to Dislocation of Strata. Faulting 810 
 
 20. Faults 810 
 
 Features Shown in Section of Faults (812); Features 
 Shown in Surface Appearance of Faults, i.e. Map Fea- 
 tures of Faults (813); Classification of Faults (813); 
 With Reference to Direction; With Reference to Move- 
 ment; With Reference to Cause 812-814 
 
 Terms Applied to Rock Masses Formed by, or Bounded 
 by Faults, but not Topographically Distinguishable 
 from Surrounding Masses (815); Terms Applied to the 
 Topographic Expression of Faults 815 
 
 Secondary Features due to Erosion (816); Strati- 
 graphic Significance of Faults (817); Faults as Indica- 
 tions of Unconformity (819); Relation of Folds, Faults, 
 Cleavage, Fissility and Joints 816-819 
 
 C. Contact Deformations 820 
 
 21. Prismatic Joints due to Contact with Igneous Masses 
 (820) ; 22. Insolation joints 820-821 
 
 D. Struc cures in Part due to Deformation and in Part to Erosion. 821 
 
 23. Disconformity and Unconformity (821); Disconformity 
 (Parun conformity, Paenaccordanz) (822); Unconformity 
 (Clinunconformity; Discordanz) (824) 821-824 
 
 Bibliography XX 826 
 
 i j 
 
 CHAPTER XXI. 
 THE PRINCIPLES OF GLYPTOGENESIS OR THE SCULPTURING OF THE EARTH'S 
 
 SURFACE 829 
 
 The Cycle of Erosion 829 
 
 A. Erosion Features in Undisturbed Strata 830 
 
 1. The Coastal Plain 830 
 
 Dissection of the Coastal Plain (831); Deposition in Dis- 
 sected Coastal Plain; Effect of Dissection and Peneplana- 
 tion of Coastal Plain Strata on Outcrop 831-833 
 
 Ancient Coastal Plains Showing Cuesta Topography 835 
 
 Minor Erosion Forms of Horizontal Strata 839 
 
 B. Erosion Features in Disturbed Strata 846 
 
 2. The Monocline (840); 3. Erosion Features of the Structural 
 Dome (841); 4. Erosion Features of the Anticline (843); 5. The 
 Basin (846); 6. The Syncline (847); 7. Erosion Features in Faulted 
 Strata (847); 8. The Completion of the Cycle (847) 840-847 
 
 The Peneplain (847); The Relation of the Peneplain to Sedi- 
 mentation; Dissection of the Peneplain; Age of the Peneplain; 
 High-level Plains of Arid Regions 847-852 
 
 C. Minor Erosion Features 856 
 
 Bibliography XXI 857 
 
TABLE OF CONTENTS xxvii 
 
 D. THE PYROSPHERE. 
 CHAPTER XXII. 
 
 PAGE 
 
 GENERAL SUMMARY OF PYROSPHERIC ACTIVITIES 859 
 
 Volcanic Activities 859 
 
 Types of Volcanic Activities 859 
 
 Subdivision with Reference to Location 859 
 
 Explosive Eruption (860) ; Terrestrial Type (860) ; The Cinder 
 Cone; Material of the Cinder Cone; The Forms of the Cinder 
 Cones; Consolidation of Cinder Cone; Submarine Explosive 
 Eruptions 860-863 
 
 Ext ravasative Eruptions (865); Terrestrial Type; Fissure 
 Eruption; The Lava Dome; Acid Lava Domes; The Spine of 
 Pel<e 865-870 
 
 Composite Lava and Cinder Cones (870); Submarine Cones; 
 Mud Volcanoes 870-872 
 
 Dissection of Volcanoes (874) ; Special Erosion Features 874-875 
 
 Formation of the Lava 876 
 
 Bibliography XXII 878 
 
 E. THE CENTROSPHERE OR BARYSPHERE. 
 CHAPTER XXIII. 
 
 DlASTROPHISM, OR THE MOVEMENTS TAKING PLACE WlTHIN THE EARTH'S 
 CRUST AND THEIR CAUSES 880 
 
 Classification of Earth Movements 880 
 
 Classification of Seismic Disturbances (881); The Volcanic or 
 Pyroseismic Type of Earthquake; The Tectonic or Dislocation 
 (Baryseismic) Earthquake 882 
 
 Surface Manifestations of Baryseismic Disturbances 883 
 
 Rifting (883) ; Filling of the Fissures, Sandstone Dikes (884) ; 
 Craterlets (885); Fossil Examples (886); Slipping (887); 
 Block Movement (887); Disruptive Effects of Earthquakes 
 (888) ; Effects of Earthquakes on Topography (888) 883-888 
 
 Submarine Earthquakes and Seaquakes (889); Airquakes (891); 
 Periodicity of Earthquakes (891) 889-891 
 
 Movements due to Displacement or Migration of the Poles 
 (891); The Pendulation Theory (892); Determined Migrations 
 of the Poles 891-899 
 
 Earth Movements and Geosynclines (900) ; Geosynclines, the Sites 
 of Orogenic Disturbance (902); Foreshortening of the Crust (903); 
 Height of the Folds (903) ; Character and Thickness of the De- 
 formed Mass 900-904 
 
 Changes due to Extra-Telluric Influences 96 
 
 Bibliography XXIII 908 
 
xxviii TABLE OF CONTENTS 
 
 F. THE BIOSPHERE. 
 CHAPTER XXIV. 
 
 PAGE 
 
 SUBDIVISION OF THE BIOSPHERE. CLASSIFICATION AND GENERAL MORPHO- 
 LOGICAL CHARACTERS OF ORGANISMS 910 
 
 Plants and Animals as Indicators of the Age of the Period in 
 
 Which They Occur 911 
 
 Classification of Plants and Animals 912 
 
 Naming of Genera and Species (912); Pryority and Syn- 
 onymy (914); Synonymy (915); Manuscript Names, List 
 Names ; Nomina Nuda (917); Generic Names as Synonyms, 
 
 912-917 
 Types (918); Terms Used for Specific Types (918); Generic 
 
 Types 918-920 
 
 Selection of the Genotype or Type Species of a Genus (920) ; 
 Union of Genera into Group of Higher Taxonomic Value. .920-921 
 Sub-families; Families: Super-families; Sub-orders; Orders; 
 
 Groups of Higher Rank; Faunas and Floras 921-922 
 
 Table I, Subdivisions of the Plant Kingdom (922); Table 
 
 II, Subdivisions of the Animal Kingdom 922-925 
 
 Brief Summary of the Morphological Characters of the Phyla of 
 Plants and Animals 933 
 
 A. Plants (933) ; Phylum I, Protophyta (933) ; Phylum II, Thallo- 
 phyta (934); a. Algae (935); b. Fungi (937); c. Lichens (937); 
 Phylum III, Bryophyta (937); Phylum IV, Pteridophyta (938); 
 Phylum V, Spermatophyta (941) 933~94i 
 
 B. Animals (942); Phylum I, Protozoa (942); Phylum II, Porifera 
 (Sponges) (942); Phylum III, Ccelenterata (942); Phylum IV, 
 Molluscoidea (943); Phylum V, Mollusca (944); Phylum VI, 
 Platyhelmintha and Phylum VII, Vermes (946); Phylum VIII, 
 Arthropoda (947); Phylum IX, Echinodermata (949); Phylum X, 
 Protochorda (950); Phylum XI, Vertebrata (950); Pisces (951); 
 Amphibia (952); Reptilia (952); Aves (954); Mammalia (955). .942-955 
 
 Bibliography XXIV 956 
 
 CHAPTER XXV. 
 
 BIOGENETIC RELATIONS OF PLANTS AND ANIMALS 958 
 
 The Conception of Species 958 
 
 The Mutations of Waagen 960 
 
 Mutation Theory of De Vries 962 
 
 Orthogenesis and the Concept of Species 963 
 
 Acceleration and Retardation in Development (Tachygenesis 
 
 and Bradygenesis) 964 
 
 Illustrations of Orthogenetic Development (964); Origin 
 and Development of Characters the Important Question; 
 
 Rectigradations and Allometrons 964-970 
 
 Nomenclature of Stages in Development 970 
 
 Ontogenetic Stages and Morphic Stages (970); Simple 
 Organisms (970) ; Colonial Forms 97O~973 
 
TABLE OF CONTENTS xxix 
 
 PAGE 
 
 Intracolonial Acceleration and Retardation (973); Atavism or 
 
 Reversion 973~974 
 
 Parallelism and Convergence in Development (Homceogenesis) . . 976 
 Bibliography XXV 979 
 
 CHAPTER XXVI. 
 
 PHYSICAL CHARACTERISTICS OF THE INHABITABLE EARTH. BIONOMIC 
 
 CHARACTERS OF THE ENVIRONMENT 982 
 
 I. The Littoral District 983 
 
 A. Marine (983); B. Fresh Water (987); C. Terrestrial 
 
 (988) 983-988 
 
 II. The Pelagic District 988 
 
 A. Marine (988); B. Fresh Water (988); C. Terrestrial 
 
 (989) 988-989 
 
 III. The Abyssal Life District 990 
 
 A. Marine; B. Fresh Water and C. Terrestrial 990 
 
 Bibliography XXVI 990 
 
 CHAPTER XXVII. 
 
 BIONOMIC CLASSIFICATION- OF PLANTS AND ANIMALS 991 
 
 Subdivisions (991); Primary Divisions; Secondary Divisions.... 991 
 
 A. Haloplankton 992 
 
 I. Holoplankton (992); 2. Meroplankton (993); 3. Pseudo- 
 plankton (994); 4. Epiplankton (994); B. Halonekton (996); 
 
 C. Halobenthos (996) 992-996 
 
 D. Limnoplankton (997); E. Limnonekton (Helionekton, 
 Potamonekton) ; F. Limnobenthos (Heliobenthos, Pota- 
 
 mobenthos) 997-998 
 
 G. Atmoplankton ; H. Atmonekton; I. Atmobenthos 998 
 
 Bibliography XXVII 999 
 
 CHAPTER XXVIII. 
 
 BIONOMIC CHARACTERISTICS OF PLANTS AND ANIMALS 1000 
 
 A. Bionomic Characters of Plants 1000 
 
 Protophyta (1000); Thallophyta (1001); (Alga, Fungi, Lichens); 
 
 Bryophyta and Pteridophyta (1003) 1000-1003 
 
 Spermatophyta 1004 
 
 Ecology and Ecological Adaptations of Spermatophytes 1005 
 
 I. Hydrophytes and Hemihydrophy tes ; 2. Xerophytes; 
 
 3. Bog Xerophytes; 4. Tropophytes; 5. Hygrophytes; 
 
 6. Sciophytes; 7. Halophytes; 8. Calcicole and Calcifuge 
 
 Plants 1006 
 
 B. Bionomic Characteristics of Animals 1007 
 
 I. Protozoa (1007); (Foraminifera; Radiolaria) ', II. Porifera (1008); 
 III. Ccelenterata (1009) (Hydrozoa; Anthozoa); IV. Molluscoidea 
 (1014) (Bryozoa; Brachiopoda) ; V. Mollusca (1015); (Pelecypoda; 
 Scaphapoda and Amphineura; Gastropoda; Pteropoda; Cephalo- 
 poda) 1007-1023 
 
xxx TABLE OF CONTENTS 
 
 VI. Platyhelmintha; VII. Vermes. 1023 
 
 VIII. Arthropoda (1025); Crustacea (1025); (Trilobita; Phyllo- 
 poda; Copepoda; Ostracoda; Cirrepedia; Phyllocarida; Schizopoda; 
 Stomatopoda; Sympoda; Decapoda; Arthrostraca); Acerata (1028); 
 (Merostomata; Arachnida; Pantapoda); Myriopoda and Insecta 
 (1030) 1025-1030 
 
 IX. Echinodermata (1031); Cystoidea and Blastoidea; Crinoidea; 
 Asteroidea; Ophiuroidea; Eckinoidea; Holothuroidea 1031-1033 
 
 X. Protochordata i33 
 
 XI. Vertebrata (1033); Osiracoderma (1033); Pisces (1034); 
 Amphibia (1035); Reptilia (1036); Aves (1037); Mammalia 
 (1038) 1033-1038 
 
 Bibliography XXVIII 1038 
 
 CHAPTER XXIX. 
 
 CHOROLOGY OR THE PRINCIPLES OF THE GEOGRAPHICAL DISTRIBUTION OF 
 
 PLANTS AND ANIMALS 1040 
 
 Dispersal and Migration (1041); Barriers to Migration and Dis- 
 persal (1042) ; Faunal Groups 1041-1044 
 
 Factors Governing Dispersal and Migration 1044 
 
 Inorganic Factors; the Medium 1044 
 
 Composition of Medium (1044); Stenohalinity and Eury- 
 halinity; Quantity of Air (1045); Volume of Water (1047), 
 
 1044-1047 
 
 Climate 1047 
 
 Climate and Temperature (1047); Currents (1048); Topog- 
 raphy (1051) 1047-1051 
 
 The Organic Factors 1052 
 
 Biogeographical Provinces 1053 
 
 Marine Provinces (1055); Former Marine Geographic Prov- 
 inces (1057); Present and Former Biogeographic Provinces 
 of the Land (1058) ; Fresh Water Biotic Provinces (1059) . 1055-1059 
 Relicts (1062); Relict Faunas and Lakes (1062); Marine Relicts, 
 
 Bipolar Faunas (1065); Terrestrial Relicts (1066) 1062-1066 
 
 Dwarf Faunas and Micro-Faunas 1066 
 
 Bibliography XXIX. . . . .* 1069 
 
 CHAPTER XXX. 
 
 FOSSILS, THEIR CHARACTER AND MODE OF PRESERVATION 1073 
 
 Definition and Limitation of the Term Fossil 1073 
 
 Fossilization 1075 
 
 Types of Fossil 1076 
 
 I. Actual Remains 1076 
 
 Preservation of Soft Tissues (1076); Preservation of Hard 
 
 Structures and of Petrified Remains 1078 
 
 Petrifaction of Non-mineral Substances (1080); a. Re- 
 placement of Soft Animal Tissue; b. Petrification of 
 
 Plants 1080 
 
TABLE OF CONTENTS x*xi 
 
 Petrifaction of Mineral Structures (1082); a. Protozoa 
 (1082); b. Sponges and Hydrozoans (1082); c. Silicifica- 
 tion of Corals (1083); d. The Brachiopod Shell (1083); 
 e. Shells of Molluscs (1084); f. Crustaceans Merostomes, 
 Insects, etc. (1086); g. Echinoderms (1086); h. Verte- 
 brates (1088) 1082-1088 
 
 Excessive silicification 1089 
 
 Molds and Casts 1089 
 
 2. Tracks, Trails and Burrows of Animals 1090 
 
 3. Artificial Structures 1093 
 
 4. Coprolites 1093 
 
 Mechanical Deformation of Fossils 1094 
 
 Index Fossils 1094 
 
 Bibliography XXX 1095 
 
 G. PRINCIPLES OF CLASSIFICATION AND CORRELATION OF 
 GEOLOGICAL FORMATIONS. 
 
 CHAPTER XXXI. 
 
 NOMENCLATURE AND CLASSIFICATION OF GEOLOGIC FORMATIONS 1097 
 
 Development of Classifications 1097 
 
 Selection of the Type Section 1 100 
 
 Time Scale and Formation Scale 1 102 
 
 Subdivision of Time and Formation Scales (1103); I. Inter- 
 national Geological Congress (1104); II. Dana's System 
 
 (1106); III. United States Geological Survey 1103-1106 
 
 Unification of Terminology (i 107) ; Local Stages and Substages 1 107 
 Principles Governing the Naming of Formations (1109); Selection 
 
 of Names for Systems, Series and Stages (Groups) 1109-1 1 1 1 
 
 Mapping (1112); Mapping on Formational Basis (1112); Mapping 
 on Faunal Basis (1113); Mapping of Discontinuous Formations 
 
 (1113) , 1112-1113 
 
 Types of Geological Maps (1115); Formation and System 
 Maps (1115); Intermediate Maps (1115); Notation of Forma- 
 tions on Map (1116); Legend (1116) 1115-1116 
 
 Continuous and Discontinuous Mapping 1117 
 
 Sections; Types of Sections 1117 
 
 The Length of Geological Time 1 1 18 
 
 Bibliography XXXI 1119 
 
 CHAPTER XXXII. 
 
 CORRELATION, ITS CRITERIA AND PRINCIPLES. PAL^EOGEQGRAPHY 1121 
 
 Correlation 1121 
 
 History of Development of Methods of Correlation 1121 
 
 Chronological Equivalency; Contemporaneous and Homo- 
 taxial Formations (1124); Contemporaneity of Faunas 
 
 (1125); Prenuncial Faunas; Colonies 1124-1126 
 
 Standard or Type Section (i 127) ; A Double Standard . 1 127-1 129 * 
 
xxxii TABLE OF CONTENTS 
 
 PAOK 
 
 Methods of Correlation 1 129 
 
 i. Superposition (1129); 2. Stratigraphic Continuity 
 (1131); 3. Lithic Character (1132); 4. Organic Contents 
 
 (i 133) 1 129-1 133 
 
 a. Index Fossils (i 133) ; b. Grade of Index Fossil (i 134) ; 
 c. Correlation by Equivalent Stages in Development 
 (1135); d. Correlation by Faunas and Floras. Repre- 
 sentative Species (1136) 1133-1136 
 
 5. Correlation by Unconformities and Disconformities 
 (1137); 6. Correlation by Regional Metamorphism 
 
 (H39); 7- Correlation by Diastrophism 1139-1141 
 
 Palaeogeography and Palaeogeographic Maps 1 144 
 
 Types of Palaeogeographic Maps (1145); Construction of 
 
 Palasogeographic Maps 1 145-1 146 
 
 Bibliography XXXII 1 148 
 
 Index 1151 
 
PRINCIPLES OF STRATIGRAPHY 
 
 CHAPTER I. 
 GENERAL INTRODUCTORY CONSIDERATIONS. 
 
 STRATIGRAPHY in its broadest sense may be defined as the inor- 
 ganic side of Historical Geology, or the development through the 
 successive geologic ages of the earth's rocky framework or litho- 
 spliere. Its relation to other branches of geologic science may be 
 made clear by a few brief considerations regarding the earth as a 
 whole, and a short survey of the science of geology and its subdi- 
 visions. 
 
 THE EARTH AS A WHOLE. 
 
 The earth as a whole may be viewed as a central mass or sphere 
 of unknown material surrounded by a number of envelopes. For 
 convenience sake in discussion, these envelopes may be considered 
 as continuous shells or hollow spheres, the outer ones more or less 
 intimately interwoven with the upper part of the rocky crust. They 
 may be grouped into the inorganic and the organic spheres. Begin- 
 ning with the outermost of the inorganic, the following are recog- 
 nized : I. Atmosphere or sphere of gas and vapor; II. Hydro- 
 sphere or sphere of water; III. Lithosphere or the rock sphere or 
 solid part of the earth. Below the known crust of the earth is the 
 zone of volcanic activities and the seat of lava formation. This is 
 called the Pyrosphere, IV, and it merges upward into the litho- 
 sphere (III) and downward into the Centra- or Barysphere, V, 
 which occupies the unknown center of the earth and the nature 
 of which is in doubt. Permeating more or less all of these spheres, 
 except the last two, is the organic or Biosphere, VI, the living en- 
 velope of the earth. A brief summary of each may first be given. 
 
 I. THE ATMOSPHERE. This consists of a mechanical mix- 
 ture of nitrogen about 79 parts, and of oxygen about 21 parts (by 
 volume), with small quantities of carbon dioxide (about 0.03 part of 
 the whole) and some of the rarer elements. Besides this it nearly 
 always contains a variable amount of aqueous vapor together with 
 other impurities, such as dust, organic matter, etc. Its weight at 
 
2 PRINCIPLES OF STRATIGRAPHY 
 
 sea- level is about 15 pounds ( 14.7 pounds)* per square inch, or about 
 a ton per square foot, and this is spoken of as the normal at- 
 mospheric pressure or one atmosphere. It becomes more tenuous 
 upward ; above 50 miles from the earth's surface it becomes so ex- 
 cessively thin that it is incapable of producing measurable pres- 
 sure, or of deflecting perceptible amounts of sunlight. CDavis- 
 6:/j.)f Above 100 miles it practically ceases to exist so far as ob- 
 servations have been made, though it is supposed that it might ex- 
 tend in an excessively attenuated state to the limit of the earth's 
 gravitative control, which is at about 620,000 miles from the sur- 
 face of the lithosphere. (Chamberlin and Salisbury-4, i:d.) 
 
 II. THE HYDROSPHERE. This is a fairly continuous en- 
 velope, concentrated chiefly in the larger depressions of the litho- 
 sphere, where it constitutes the oceans, but also permeating the 
 upper part of the earth's crust as a more or less continuous layer. 
 The surficial extent of the sea water on the earth is estimated at 
 361.1 million square kilometers, while the total land surface is esti- 
 mated at 148.8 million square kilometers. This makes a ratio of 
 land surface to sea surface of i : 2.43 or 29.2% land and 70.8% 
 sea (Kriimmel-17, i :#),: or in round numbers the sea surface is 
 2.5 times that of the land. When taken in hemispheres, the 
 northern one has 60.7% water and the southern 80.9% 
 (17, i:/j). The greatest known depth, that of the Xero deep, 
 opposite the island of Guam in the Ladrone Islands east of the 
 Philippines, is 9,636 meters (5,269.13 fathoms or 31,615 feeti. 
 The area of the ocean bottom below 4,000 meters comprises about 
 185 million square kilometers, that below 5,000 meters of depth 72 
 million square kilometers or about half the area of the dry land 
 (i/5th of the sea surface) ; that below 6,000 meters about 5.4 
 million square kilometers or about the area of European Russia. 
 Among the greater deeps, which are more circumscribed, we have 
 that of the Marian depression opposite the Marian or Ladrone 
 Islands (in which the Xero deep occurs) with an area of 49,000 
 square kilometers (equal in area to Sardinia and Sicily) below 
 7,000 meters and about 22.500 square kilometers below 8,000 
 
 * I -333 kgm. per sq. cm., or the weight at sea-level of a column of mercury 
 760 mm. (29.921 inches) high. 
 
 t The Arabic figure refers to the number of the article in the bibliography 
 at the end of the chapter, the italicized number refers to the page. 
 
 % Penck in Scobel's Geographisches Handbuch makes the surface area of the 
 water 366 million square kilometers, and that of the land 144 million square 
 kilometers, including the Antarctic continent, which has an estimated area of 
 8 to 9 million square miles, giving in percentages 71.8% water and 28.2 r c 
 land, a ratio approximately of 2.5 : i. 
 
THE EARTH AS A WHOLE 3 
 
 meters. In the southern Pacific the Tonga deep has an area of 
 123.000 square kilorreters below 7,000 meters, and 63,000 square 
 kilometers below 8,000 meters, while the Kermadec deep to the 
 south of it has 137,000 square kilometers below 7,000 meters, and 
 78,000 square kilometers below 8,000 meters. The maximum 
 depths of these two depressions are 9427 and 9,413 meters, re- 
 spectively. (Krummel-i7, 1:6*5.) The total area of the oceanic de- 
 pressions below 6,000 meters is given by Penck as 10.6 million 
 square kilometers, and by Krummel as 5.4 million square kilo- 
 meters. Taking .the area of the seas as a whole at 361,100,000 
 square kilometers, and evening out the irregularities of the bot- 
 tom, so as to obtain a mean depth, we find this to be approximately 
 3,680 meters or 2,012 fathoms (see further under lithosphere). 
 Various estimates as to the volume of the sea water as a whole 
 have been made. The most recent of these, given by Krummel, 
 places it at 1,330 million cubic kilometers. The weight of the sea 
 water may be calculated from this by taking its average density, 
 increased in the deeper portions by pressure, as 1.04, the result 
 being 1.3832 X 10 18 metric tons or in round numbers 138 X io 18 
 metric tons.* 
 
 Transgressions and Regressions. Two types of alternation of 
 the level of the hydrosphere are recognized : the local and the uni- 
 versal. The former is due to slight up or down warpings or fault- 
 ings of parts of a continent with resulting local retreat or advance 
 of the sea. The effects of such a change will be noticed only locally 
 and will at best be of slight amount. An example of this is shown 
 in the periodic rising and sinking of the land in the Gulf of Naples 
 as recorded in the ruins of the temple of Jupiter Serapis, near 
 Pozzuoli (Lyell-i8, ii Chapter XXX) ; or, in the Scandinavian 
 region, where, during the last century, an area of 300,000 square 
 kilometers rose on the average 0.7 meter, making a total elevated 
 mass of 210 cubic kilometers. 
 
 The second type of change is one that affects the entire surface 
 of the ocean, and is best explained by a bulging up or a sinking down 
 of the sea bottom, the result of which will be a universal rise of 
 the sea-level and transgression over, or fall and retreat from the 
 edge of the land. For these latter movements Suess (27, \i\68o\ 
 28, 11:534) nas proposed the term: "Eustatfc Movements." The 
 sinking of the sea bottom and consequent lowering of the level and 
 withdrawal of the water from the land constitute negative eustatic 
 movements, while elevation or bowing up of the sea bottom with 
 
 *The metric ton contains 1,000 kilograms, equivalent to 2,204.6 pounds 
 avoirdupois. 
 
4 PRINCIPLES OF STRATIGRAPHY 
 
 accompanying rise and transgression cause positive eustatic move- 
 ments. A third type of movement must be considered. If we re- 
 gard the continents "as crustal blocks of a lighter specific gravity 
 than the suboceanic crustal blocks, the former being squeezed 
 upward by the downward pressure of the suboceanic blocks, it 
 is conceivable that a single continental block like that of the 
 Americas might be squeezed upward, while the other conti- 
 nental blocks would remain stationary, and yet at the same time 
 there need be no marked change in the altitude of the suboceanic 
 blocks with reference to the stationary continental blocks. As a 
 result there will be a widespread emergence, or negative move- 
 ment of the sea, so far as the rising land block is concerned, while 
 at the same time the resultant displacement of the water will 
 cause a transgressive or positive movement of the sea with refer- 
 ence to the stationary blocks. Thus a retreatal movement in one 
 continent may be correlated with a transgressive one in another 
 continent. Such differential movements may even affect different 
 parts of the same continental block, if the movement is an unequal 
 or tilting one, and this would account for transgression of the sea 
 over one section of a continent at a time when retreatal move- 
 ments characterized another part. 
 
 THE TERRESTRIAL PART OF THE HYDROSPHERE. The terrestrial 
 or extra-oceanic part of the hydrosphere is chiefly found in the 
 ground water and in the streams, lakes and ponds of the earth's 
 surface. Since the porosity of the rocks constituting the earth's 
 surface region varies greatly, the quantitative distribution of the 
 water also varies. The ground water is probably chiefly confined 
 to the upper six miles of the earth's crust, and here w r e have a 
 diminishing porosity from 5 per cent, or over at the surface to 
 zero at the depth of six miles. It has been estimated on this basis 
 that the rock of the earth's surface contains enough water to form 
 a layer nearly 800 feet deep (Chamberlin and Salisbury -4:^7), 
 but other estimates make this layer much thicker, that of Slichter 
 being 3,000 to 3,500 feet (25:15). Van Hise, on the other hand, 
 has shown that the amount is much less, and is, according to his 
 estimate, sufficient to make a layer only 69 meters or 226 feet 
 thick over the continental area (30:128-129, 5/0-577). Kemp has 
 called attention to the fact that in the deep mines no water is en- 
 countered below a moderate depth. "In several important in- 
 stances of this class, as well as in many mines of smaller depth, 
 it is possible to impound all the water within a short distance, it 
 may be within 500 feet of the surface. Below this level the work- 
 ings are dry, and in not a few cases dusty." (15:16.) He con- 
 
THE EARTH AS A WHOLE 5 
 
 eludes that something like 2,000 feet appears to be the limit to 
 which ground water descends, while in some regions it ceases at 500 
 feet. From this it is estimated that the amount of water present 
 would produce a layer over the surface of the earth between 50 
 and loo feet deep. Fuller (7:61, 62, 72) calculates the exact figure 
 at 96 feet, which would be acceptable were it proven that the data 
 on which his calculations are based are ascertained with equal 
 exactness. 
 
 III. THE LITHOSPHERE. This is the solid framework of 
 the earth. It is a nearly perfect oblate spheroid with a polar di- 
 ameter of 12,713.5 kilometers (7,899.7 miles) and an equatorial 
 diameter of 12,756.5 kilometers (7,926.5 miles), corresponding to a 
 meridional circumference of about 40,008 kilometers (24,860 miles), 
 an equatorial circumference of 40,076 kilometers (24,902 miles), 
 and a surface area of 510 million square kilometers (196,940,700 
 square miles). As already noted, the land surface is something 
 over 29 per cent, of this, or about 148.8 million square kilometers. 
 The greatest elevation of the land above sea-level (Mt. Everest) is 
 8,840 meters, which is nearly 800 meters less than the greatest 
 known depth of the sea (9,636 meters). Of the entire earth's sur- 
 face not over three million square kilometers of area lie more than 
 4,000 meters, nor over half a million square kilometers more than 
 5,000 meters above sea-level. The following table shows the per- 
 centages of land within successive strata of 100 meters (Penck- 
 21/1:145): 
 
 Between o and 200 meters, each interval of 100 meters contains 14.6 % 
 
 of the land, or a total of '; 29 . 2 % 
 
 Between 200 and 500 meters, each interval of 100 meters contains 
 
 9.0 % of the land, or a total of 27.0 % 
 
 Between 500 and 1,000 meters, each interval of 100 meters contains 
 
 3.8 % of the land, or a total of 19.0 % 
 
 Between 1,000 and 2,000 meters, each interval of 100 meters contains 
 
 1.7 % of the land, or a total of 17.0 % 
 
 Between 2,000 and 3,000 meters, each interval of 100 meters contains 
 
 0.4 % of the land, or a total of 4.0 % 
 
 Between 3,000 and 4,000 meters, each interval of 100 meters contains 
 
 o.i % of the land, or a total of I .o % 
 
 Between 4,000 and 8,840 meters, each interval of 100 meters contains 
 
 0.04 % of the land, or a total of 1.9 % 
 
 99-1 % 
 
 It is thus seen that more than one-half of the earth's surface (56 
 per cent.) lies below the 5OO-meter contour, and that more than 
 half this lies below the 2oo-meter contour. Very different values 
 
6 PRINCIPLES OF STRATIGRAPHY 
 
 have been reached by de Lapparent, Heiderich and Murray, as 
 shown in the following table (Penck-2i, i 1/50) : 
 
 
 
 
 
 
 
 
 
 Percentage of 
 land surface 
 
 Below 
 o m. 
 
 From 
 o- 
 
 200 
 
 m. 
 
 From 
 200- 
 500 
 
 m. 
 
 From 
 500- 
 
 1,000 
 
 m. 
 
 From 
 1,000- 
 
 2,000 
 
 m. 
 
 From 
 
 2,000- 
 
 3,000 
 m. 
 
 Above 
 3,000 
 m. 
 
 de Lapparent 
 
 
 1 8 oo 
 
 20 oo 
 
 4.7 o 
 
 Hoo 
 
 
 
 
 
 
 
 
 
 
 
 Heiderich 
 Murray 
 
 0.08 
 o oo 
 
 I3-40 
 
 14. 60 
 
 37-96 
 ^8 oo 
 
 28.5 
 25 8 
 
 17.81 
 
 IQ 8O 
 
 i-95 
 
 I 4-O 
 
 0.30 
 o 40 
 
 
 
 
 
 
 
 
 
 The mean elevation for all continents is given by Sir John Mur- 
 ray as 2,250 feet (686 meters), and the mean or average depth 
 of the ocean as 3,840 meters (2,100 fathoms). Penck (21:157; 
 22:17), on the other hand, finds the mean elevation of the conti- 
 nents and islands to be 735 meters and the mean depth of the 
 ocean 3,650 meters. The mean depth of the ocean has more re- 
 cently been calculated as 3,680 meters (precisely 3,681 meters) by 
 Krummel (17:144), who also assumes the mean altitude of the 
 land at approximately 700 meters. More recently still Penck has 
 given these figures as 3,680 meters and 710 meters, respectively 
 (22:1^5). With a land area of 148.8 million square kilometers, the 
 volume of the land mass above sea-level becomes 104.2 million 
 cubic kilometers. From these figures the following ratios are de- 
 duced : mean height of land to mean depth of sea = 700 : 3,680 = 
 1:5.25; area of land to sea= 148.8:361. 2 i :2.43 ; volume of 
 land to sea= 1 04.2 -.1,330.0=: i :i2.8. Thus (Krummel-i7, 1:147) 
 it would take nearly 13 times the volume of the land rising above 
 sea-level to fill the sea, three times that volume to fill the Atlantic 
 Ocean, 2% times that volume to fill the Indian Ocean, and 6 l / 2 
 times to fill the Pacific Ocean. 
 
 THE MEAN SPHERE LEVEL. If we regard the land mass as a 
 whole, we may represent it by a prismatic block (tetragonal) com- 
 posed of that portion which lies above mean ocean depth, plus that 
 portion rising above sea-level, giving a height of 3,680-1-700= 
 4,380 meters, a base of 148.8 million square kilometers, the present 
 area of the land surface, and a volume of 651.8 million cubic kilo- 
 
THE EARTH AS A WHOLE 7 
 
 meters ; * while the sea may be represented by a prismatic block 
 (tetragonal) having twice that volume (1,330.0-1-651.8=2.04). If, 
 then, we were to flatten out all irregularities of the sea bottom by 
 cutting down the land block sufficiently to fill them, or, in other 
 words, if we distribute the land block of 651.8 million cubic kilo- 
 meters over the entire surface of the earth, 509,950,000 square 
 kilometers, according to Bessel, it would raise the mean level of 
 the ocean floor by the quotient of 651.8-^509.9=1.278 kilo- 
 meters. The level of the earth's crust would therefore be 
 3,681-1-1,278= 2,403 meters, or approximately 2,400 
 meters ( 1,313 fathoms) below the present sea-level. This is 
 called the mean sphere level (mittlere Krustenniveau) , which Penck 
 originally placed at 2,500 meters ( 1,367 fathoms), but more 
 recently at 2,400 meters (22:125). Mill (19:183), using the fig- 
 ures of Sir John Murray for height of land and depth of ocean 
 cited above, finds the mean sphere level to be 2,560 meters or 
 1,400 fathoms, while Romieux (24:994) from the same data 
 finds it to be approximately 2,360 meters ( 1,290 fathoms). 
 For the whole earth, 222 million square kilometers lie above this 
 mean sphere level and 288 million square kilometers below it. If 
 we assume a smooth lithosphere, the surface of which would cor- 
 respond to the mean sphere level, and the available sea water 
 (1,330 million cubic kilometers) were uniformly spread over this 
 surface, we would have an approximate but uniform depth of 2,600 
 meters (1,422 fathoms) for the universal ocean (1,330.0-1-509.0 
 2.608 kilometers). The oceanic areas below this depth of 2,400 
 meters (or approximately 1,300 fathoms) constitute the abysmal 
 areas; those above this to the edge of the continental shelf (200- 
 meter or approximately 100- fathom line) the transitional areas 
 (die aktischen Regionen of Penck) and those above this level 
 ( 200 meters to -(-8,840 meters) as the continental area 
 ( Penck ).f 
 
 THE CONTINENTAL BLOCK. The conception of a continental 
 block was introduced by H. Wagner (31 '.749) for the mass of land 
 (222 million square kilometers in basal area) which rises above 
 the mean crustal level. This he divides into: I. The continental 
 slope (Kontinentalabhang), between the median sphere level and the 
 
 * If we represent the continental mass as a prismatic block with a square 
 base of 148,800,000 square kilometers of area, a side of 12,198.36 kilometers, 
 and a height of 4,380 kilometers, on the scale of i/j, 000,000, we would have a 
 block of square base 12.2 meters on the side, and 4.38 mm. in height and nearly 
 one-fifth of this or 0.83 mm. would represent the part above sea-level. 
 
 f In the original classification by Dr. Hugh Robert Mill, the line between the 
 transitional and the continental areas was drawn at sea-level. 
 
8 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 edge of the continental shelf, i. e., between 200 and 2,400 
 meters depth. 2. The continental platform (Kontinentaltafel) , be- 
 tween 200 meters below and -{-1,000 meters above sea-level; 
 and 3. The culminating land region (Kulminationsgebiet) from 
 1,000 meters to 8,840 meters above sea-level. The abysmal regions 
 are divided into (a) the deep sea platform (Tiefseetafel), between 
 the median sphere level ( 2,400 meters) and 5,000 meters 
 depth ; and (b) the depressed region (Depressionsgebiet) , below 
 
 Land 
 ^Median Height of Land 
 
 Sea. Let/el 
 
 Meter 
 
 Mean, J/>/iere Lei/eJ 
 
 Mean Depth of S 
 
 MOO 
 4009 
 MOO 
 
 Million square kilometers. 
 
 FIG. i. Hypsographic curve, showing subdivisions of the heights of the land 
 and of the depths of the sea. (After Krummel ) 
 
 5,ooo meters. A more satisfactory dividing line is placed by 
 Krummel at 5,500 meters. (Fig. I.) The continental block has 
 roughly the form of a star surrounding the north pole, and ex- 
 tending its rays southward. (Penck-22:/^i.) Two principal 
 divisions of these rays are recognizable, the Old World and the 
 New World, of which the first is divided into three continents, 
 Eurasia, Africa, and Australia, and the other into two : North 
 America and South America. The divisions are brought about by 
 deep indentations from the sea, constituting the mediterraneans. 
 Besides the five continents mentioned, there is the continent of 
 Antarctica, still little known, but larger than Australia in area. 
 The two main divisions of the continental block are separated by 
 the "arctic mediterranean." 
 
THE EARTH AS A WHOLE 9 
 
 In some respects, as has already been stated, it might serve our 
 purpose better to consider the main land groups as three separate 
 continental blocks, namely; the Old World block, comprising the 
 continents of Eurasia, Africa and Australia ; the New World block 
 or the two Americas, and the Antarctic block. On the basis of 
 such division we may consider that we have four great oceans 
 separating these blocks one from another, namely, the Atlantic, the 
 Pacific and the Arctic * separating the Old and the New World 
 blocks, and the Indian Ocean separating the Old World from the 
 Antarctic block. These oceans would then be the intercontinental 
 divisions of the sea, while the divisions of these masses into conti- 
 nents, as ordinarily understood, would be accomplished by mediter- 
 raneans, which may then be regarded as w^racontinental in char- 
 acter. 
 
 Isostasy. Carrying out this idea, we have to consider the sea 
 
 FIG. 2. Diagram illustrating the relationships between the denser suboceanic 
 crustal blocks A and D and the light or terrestrial crustal blocks 
 B, C, when in static equilibrium. (After Penck.) 
 
 as divided into four great blocks corresponding to the four oceans, 
 including the Arctic. If we divide the crust into continental and 
 suboceanic masses or crustal blocks, we must consider that these 
 masses are in static equilibrium, due to the greater density of the 
 material of the suboceanic masses, as shown by pendulum experi- 
 ments. Penck (22 -.125-126) illustrates these relations by compar- 
 ing these masses with boards of equal thickness, but of different 
 weights floating upon water. Those of heavier wood will sink 
 deeper than those of lighter wood, and may be taken to represent 
 the suboceanic masses. This static equilibrium of the blocks of the 
 earth's crust constitutes the phenomenon of isostasy, and indicates 
 
 * It must, on the other hand, be considered that the Arctic Ocean has the 
 character of a mediterranean, in that its abyssal portion is everywhere separated 
 from that of the sea as a whole. In fact, at the present time, not only is the 
 2,4oo-meter line continuous within the Arctic, but this is equally true of the 
 i,ooo-meter line, the depths between North America, Greenland, Iceland, and 
 Northern Europe not going below this. That the Arctic Ocean is one independent 
 depressed earth block similar to those forming the three great oceans can hardly 
 be doubted. The peculiarities which differentiate it from the other oceans are 
 due largely to its location at the earth's axis, and to its extensive covering of ice. 
 
TO 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 that these differences are of fundamental value, and that hence the 
 great relief features of the earth's surface have been persistent 
 since the earliest time (Fig. 2). Where the isostatic equilibrium is 
 disturbed by erosion of the higher less dense masses, and by the 
 transference of the product to the denser block, a compensatory 
 deep-seated transference of material by flow must occur, from the 
 denser to the lighter, which is accompanied by a sinking of the 
 upper part and surface of the denser block and a corresponding 
 rise above the level of compensation of the upper part and surface 
 of the less dense block. (Hayford-i3 :/pp.) 
 
 'THICKNESS OF THE EARTH'S CRUST. In considering the top of 
 the lithosphere as representing the surfaces of a series of elevated 
 and depressed crustal blocks, we naturally assume that the thick- 
 
 SURF4CE 
 
 SEA LEVEL 
 OCEAN BOTTOM 
 
 y 
 
 COLUM-M A 
 
 DEPTH 
 
 DEPTH Of COMPENSATION 
 
 FIG. 3. Diagram illustrating the conception of isostatic equilibrium and its 
 adjustment with change in surface. (After Hayford.) 
 
 ness of the crust is measured by the height of these blocks. Since 
 they are considered to be in a state of isostasy, it follows that, if 
 these masses were divided into prismatic columns of equal basal 
 area, the pressure due to gravity at the bases of these columns 
 would be the same. The depth at which this state of equilibrium 
 is found is the depth of compensation. From calculations made by 
 the Coast and Geodetic Survey on numerous observations scattered 
 over the United States, the conclusion has been drawn that the 
 most probable depth of compensation is 76 miles, and that it is 
 practically certain that it is not less than 62 nor more than 87 miles. 
 (Hayford-i2 177- 7$; 13:^00.) This assumes a uniform position of 
 the level of compensation with reference to depth. In Fig. 3, 
 adapted from Hayford, columns A and B have been assumed to 
 contain equal masses. There is complete isostatic equilibrium and 
 
THE EARTH AS A WHOLE 11 
 
 the pressures at the bases of the two columns are equal. But, since 
 the heights of the columns are unequal, it follows that their densi- 
 ties must also be unequal, the shorter column, B, having the greater 
 density. If the mass is unequal in the two columns, isostatic com- 
 pensation is incomplete. At any plane, as x, above the level of 
 compensation, the pressure of the two columns will not be the 
 same, since the mass above this point differs. The mass of column 
 A will be greater than that of column B, and hence the pressure of' 
 A at x will be greater than that of B. If now, through erosion, 
 material from the higher column A is transferred to the lower col- 
 umn B, the height of the two columns will be changed, and hence 
 the pressure at their bases will not be the same, but greater in B 
 than in A. So long as A remains higher than B, any plain, as y, 
 cutting A and B near the top, will leave A heavier than B. If, 
 then, the weight of B becomes greater than A at the base, owing to 
 the loading of B, while at y it is still less than A, owing to its lesser 
 mass, it follows that at some intermediate point, as at x, it will be 
 uniform. This is the "neutral level," which, however, rises as the 
 load on B increases and as A is lowered by erosion. Below the 
 neutral level x there will be an excess of pressure in the column 
 B over that of column A, and this excess of pressure will increase 
 as the neutral level rises, through continued erosion and deposition. 
 When the pressure becomes greater than the natural resistance of 
 the material can balance, a transference or flow of the material from 
 B to A will take place below the neutral level. This transfer of 
 material will be accompanied by an elevation of the upper part and 
 surface of A, and a sinking of the upper part and surface of B, 
 unless there is a compensatory change in volume of material. 
 Chemical changes in the mass relieved by erosion may cause further 
 expansion in volume, and consequent further rise of the surface, but 
 lowering of temperature throughout the entire block, due to the 
 lowering of the surface by erosion and the invasion of surface tem- 
 peratures into regions originally below the surface and therefore 
 of much higher temperatures, will cause a slow, but continued 
 shrinking of the mass. Hayford assumes an approximate shrink- 
 ing from this cause of the crustal column of 76 miles, to the amount 
 of 30 feet for every 1,000 feet eroded (13:^04). In like man- 
 ner, blanketing of the mass by deposition will cause a rise in tem- 
 perature and consequent expansion and increase in volume. If the 
 changes due to variations in the temperature overbalance those due 
 to the causes with opposite effects, as may be the case in the course 
 of a long time, the regions of erosion may subside, as in the event 
 of the submergence of a peneplain, while regions of former deposi- 
 
12 PRINCIPLES OF STRATIGRAPHY 
 
 tion may rise. It thus appears that the adjustments within the 
 earth's crust and the forces responsible for the geological changes 
 recognizable on the surface of the earth are confined to the upper 
 76 miles of the earth's mass, or about 1/53 of the radius. This we 
 may, therefore, regard as the crust of the earth, bearing in mind, 
 however, that there is no marked line of separation between the 
 crust and the subcrustal part. It is within this crust, and chiefly 
 within its upper part', that we find the seat of vulcanism; that the 
 minor disturbances recorded as earthquakes, etc., occur; that the 
 ground water circulates, and that the crushing and flowage of rocks 
 take place, and it is by changes in the crust as thus defined that 
 the rise and fall of land masses and sea bottoms take place. It is 
 of course possible that the source of some of our basic volcanic 
 rocks is deeper than 75 miles. Thus the density increase in the earth 
 cited below suggests that basalts are derived from depths of 105 to 
 137 miles. 
 
 MATERIAL OF THE EARTH'S CRUST. Only the material of the 
 lighter blocks of the earth's crust, i. e., those constituting the con- 
 tinental masses, is open to observation, and constitutes the "rocks 
 of the earth's crust." The average specific gravity of this material 
 is 2.2 to 3 (average 2.6), while that of the earth as a whole is 
 about 5.6. This difference is accounted for by assuming that the 
 material constituting the interior of the earth (centrosphere) has 
 a higher specific gravity than the earth as a whole. It is clear that 
 if the continental and suboceanic crustal blocks are in the condition 
 of static equilibrium, the latter must consist of heavier or denser 
 material than that of the known surface. 
 
 DEFORMATION OF THE EARTH'S CRUST. (Diastrophism.) The 
 larger deformations of the earth's crust consist in the sinking of 
 the suboceanic crustal blocks, or the rise of the continental blocks, 
 or vice versa. These are designated epeiro genie (continent-mak- 
 ing) movements. Minor diastrophic changes result from local 
 warpings, either up or down, from faultings, or foldings of the 
 strata. These are designated as orogenic (mountain-making) 
 movements, resulting in the formation of mountains. Local rising 
 of the land, even though unaccompanied by visible foldings, must be 
 considered as bowing or folding on a large scale, and it often pre- 
 cedes the formation of folded mountains, as shown by the suc- 
 cessive elevations of the Appalachian Old Land (recorded in the 
 successive continental fans), which preceded the folding of the 
 strata at the end of Palaeozoic time. 
 
 IV. THE PYROSPHERE. This is an indefinite region in the 
 lower part of the earth's crust, or below it, and designated as dis- 
 
THE EARTH AS A WHOLE 13 
 
 tinct because it is the zone of fusion and of the formation of vol- 
 canic matter. Its existence is revealed by the manifestation of vol- 
 canic phenomena, and it passes insensibly on the one hand into the 
 Lithosphere and on the other into the Centrosphere, of which it 
 may indeed be a part. Its depth varies for different rocks, and it 
 cannot be regarded as constituting a continuous sphere, as do the 
 others so far discussed. Its consideration as a distinct sphere is 
 rather more for the sake of convenience of discussion. 
 
 V. THE CENTROSPHERE. So far as actual observation is 
 concerned, the greater part of the geosphere is unknown to us. Be- 
 yond the relatively insignificant thickness represented by the known 
 part of the earth's crust or lithosphere open to observation, and the 
 inferred pyrosphere, there is the vast mass of the earth's interior, 
 forever withdrawn from direct observation and approachable only 
 in an indirect manner. This is the centrosphere which may be the 
 ultimate storehouse of the earth's internal heat. The following 
 diagram (Fig. 4), adapted from Crosby,* will serve to illustrate the 
 relation between the known and the unknown parts of the earth. 
 The diagram represents a sector of the earth, two degrees or about 
 140 miles broad. It is drawn to a radius of 75 inches, or a scale of 
 53 j/3 miles to the inch. Assuming the crust to have a thickness of 75 
 miles, and the greatest depth of the atmosphere at 100 miles, these 
 would be represented by i^ and ij^ inches, respectively. The 
 extreme depth of the ocean is taken as 31,600 feet (o.n inches), 
 the mean depth as 12,000 feet (0.043 inches), the mean height of 
 land as 2,300 feet (0.009 inches) and the greatest height of land 
 as 29,000 feet (0.03 inches). The length of radius on this scale 
 being 75 inches, it follows that the two radii will meet at that 
 distance from the surface of the water line, i. e., the distance 
 to the center of the earth on this scale is 6 l /4 feet from the line 
 representing sea-level. This shows well the relative insignificance 
 of the surface features as compared with the size of the earth as a 
 whole. 
 
 TEMPERATURE OF THE EARTH'S INTERIOR. (Giinther-10, 1:328.) 
 From observations in deep mines, artesian wells, etc., it appears 
 that there is an increase in temperature downward, this being about 
 1 Fahrenheit for every 53 feet vertical descent, or, in round num- 
 bers, 100 per mile. (2.5 to 3 C. per 100 meters, or about one 
 degree for every 40 meters.) Considerable variation is, however, 
 shown in different mines or wells. Thus the Sperenberg bore hole 
 in North Germany (south of Berlin), which went to a depth of 
 
 * Collections of Dynamic and Structural Geology in the Museum of the Bos- 
 ton Society of Natural History. 
 
PRINCIPLES OF STRATIGRAPHY 
 
 1,273 meters (3,492 feet), showed a rate of increase of i F. in 
 51.5 feet depth; the bore at Schladebach, Saxony (west of Leipzig), 
 extending to a depth of 1,748 meters (5,630 feet), showed a rate of 
 increase of i F. in 67.1 feet, while the Calumet and Hecla mine 
 
 HEIGHT OF ATMOSPHERE, 
 too 
 
 FIG. 4. Diagram illustrating the relation of the superficial features of the 
 earth to the entire mass. Scale i inch = 53 1-3 miles. Drawn 
 to radius of 75 inches (=4,000 miles). 
 
 . 
 
 of Northern Michigan, with a depth of 4,939 feet, showed a rate of 
 increase of i F. in 103 feet depth, though between 3,324 feet and 
 4,837 feet the rate of increase was as high as i F. in 93.4 feet. 
 Other bores and mines show intermediate values.* In the Witwa- 
 
 * The deepest well yet completed is at Paruschowitz, Province of Silesia, 
 which reached a depth of 2,003 meters (6,571.5 feet). 
 
THE EARTH AS A WHOLE 15 
 
 tersrand mines, South Africa, the general rate of increase was i F. 
 for 250 feet, the temperature at 1,000 feet being 68.75 F., and at 
 8,000 feet 102.35 (32:^0). These observations, however, are re- 
 stricted to the thin outer layer or shell of the earth's crust, which 
 does not exceed 1/4000 of the earth's radius, and hence we are 
 scarcely justified in extending this rate over the whole interior of 
 the earth. If continued at the known rate, enormous temperatures 
 would be met with at a depth of only a few miles. With a regular 
 increase of one degree F. in 60 feet, we would get at the center of 
 the earth a temperature of 348,000 F., while at the regular rate of 
 increase of one degree F. in 100 feet, we would get a temperature 
 of 209,000 F. at the center. (4:571.) On the other hand, we 
 may, with Crosby (5:9), consider it as more likely that the in- 
 crease in temperature is at a constantly diminishing rate, so that the 
 interior temperatures do not exceed those with which we are ac- 
 quainted on the surface. 
 
 INCREASE OF DENSITY. As already noted, the density of the 
 earth as a whole is 5.6, while the median density of the known 
 rocks of the earth's crust or lithosphere is only 2.6. Assuming a 
 regular and steady increase in density, Helmert (14:475) has cal- 
 culated that the density of the center of the earth is 11.2. From 
 this it is possible to calculate the depth at which any given density 
 of rocktf should prevail, according to the formula: 
 
 h= 
 
 where is the given density, h is the depth sought, and r the radius 
 of the earth (r (equatorial) =3,959 miles or 6,375 kilometers). 
 (21, 1:442.) According to this formula (21, i:^/j), andesites and 
 trachytes with a specific gravity of 2.7 2.8 would be derived from a 
 depth of 73 to 117 kilometers, basalts with a specific gravity of 
 2.9 3, from a depth of 169 to 221 kilometers. According to this 
 calculation, rock-melting temperatures (1,200 C.) must exist at 
 a depth of 73 kilometers, which would require a rate of increase of 
 i C. in 61 meters. That the rocks at the depth at which the tem- 
 perature of 1,200 C. exists are not in a molten condition, is due 
 to the fact that they are under the weight of the superincumbent 
 rock mass, and that pressure raises the fusing point. Thus, ac- 
 cording to the experiments of Carl Barus, as summarized by Clar- 
 ence King (16:7), basalt, which will melt at the earth's sur- 
 face at a temperature of 1,170 C., will require a temperature of 
 76,000 C. (136,800 F.) to fuse it at the center of the earth. This 
 
16 PRINCIPLES OF STRATIGRAPHY 
 
 raising of the fusing point by increased pressure has led to the as- 
 sumption that, in spite of the great heat, the earth's interior is a solid 
 mass. Dana and Crosby suggested that the earth might be re- 
 garded as a mass of solid iron from the center to within 500 miles 
 of the surface; others, however, still hold to the fluid theory of the 
 earth's interior, more or less universally accepted at the beginning 
 of the last century, while still others hold to the theory of a gase- 
 ous interior (i:jp5; 9 '.58; 10:554; 33) with a zone of liquid mat- 
 ter transitional to the solid crust. 
 
 VI. THE ORGANIC OR BIOSPHERE. This is the sphere 
 of living matter which permeates the atmo- and hydrospheres, and 
 to some extent the upper strata of the lithosphere. Its two main 
 divisions, the plants and the animals, are familiar. The first forms 
 a nearly continuous mantle over the land and the shallower ocean 
 bottoms, and may be spoken of as the phytosphere; while the sec- 
 ond forms a less continuous, though more universally present animal 
 sphere or shell, which may be designated the zoo sphere. 
 
 INTERACTION OF THE SPHERES. 
 
 Of the known spheres, the lithosphere is the most stable, and the 
 one retaining in a more or less permanent form the impressions re- 
 ceived through the mutual interaction of the spheres upon each 
 other. The cycle of change, as it affects the lithosphere, has been 
 divided (11:12) into: I. Lithogenesis, or the origin and develop- 
 ment of the rocks; 2. Orogenesis, or their deformation (diastro- 
 phism, including epeirogenic elevations), and 3. Glyptogenesis, or 
 the sculpturing of the lithosphere. In lithogenesis all the other 
 spheres participate. Deformation or orogenesis may be referred 
 especially to the influence of the centrosphere and to gravitative 
 forces; while glyptogenesis is largely accomplished by the at- 
 mosphere and hydrosphere, with minor contributions of the bio- 
 sphere and pyrosphere. 
 
 Sculpturing Processes. 
 
 It will be convenient to treat the sculpturing processes while 
 discussing the characteristics of the spheres most actively engaged 
 therein, leaving the larger aspects of the subject, i. e., the land 
 forms due to sculpture, until we have considered in detail the 
 processes of lithogtnesis and orogenesis. 
 
 In its broadest aspects the sculpturing processes may be di- 
 
INTERACTION OF THE SPHERES 17 
 
 vided into the three phases : Erosion, Transportation, and Deposi- 
 tion. Erosion consists of ClastattOH* or the breaking up of the rock 
 masses in situ ; and Ablation, or the separation of material from the 
 main mass. The first process is accomplished to a large extent 
 by atmospheric forces and hence is called weathering. It affects 
 only the upper zone of the earth's crust, which is termed the 
 zone or belt of weathering, while the zone beneath it is termed the 
 belt of cementation. The processes of erosion may be tabulated as 
 follows: (8; 34:573.) 
 
 EROSION. 
 
 I. CLASTATION (breaking up of rock material). 
 
 A. PHYSICAL OR DISINTEGRATION. 
 
 1. Atmospheric (generally included under weather- 
 
 ing). 
 
 a. Insolation and radiation. 
 
 b. Frost shattering. 
 
 c. Electrical (lightning) shattering, etc. 
 
 2. Hydrospheric, wave shattering, etc. 
 
 3. Pyrospheric, shattering by volcanic explosion. 
 
 4. Centrospheric, shattering by earthquakes. 
 
 5. Biospheric, shattering by growing organisms, by 
 
 man, etc. 
 
 B. CHEMICAL OR DECOMPOSITION. 
 
 1. Atmospheric (weathering in the narrower sense; 
 
 oxidation, hydration, carbonation, etc.). 
 
 2. Hydrospheric (hydration, oxidation, etc.). 
 
 3. Pyrospheric (decomposition through the activities 
 
 of eruptive masses; of fumaroles, etc.). 
 
 4. Biospheric (decomposition under influence of liv- 
 
 ing matter, probably rare.) 
 
 II. ABLATION (separating off, or removal of material). 
 
 A. MECHANICAL. 
 
 i. Denudation, removal of weathered or loose ma- 
 terial, i. e., mantle rock. 
 
 a. by wind = deflation. 
 
 b. by streams = fluvial ablation. 
 
 c. by glaciers = exaration. 
 
 d. by waves, shore currents, etc. 
 
 e. by organisms. 
 
 * From Gr. KXewrds = broken, and ation. 
 
i8 PRINCIPLES OF STRATIGRAPHY 
 
 2. Corrasion, a filing process. 
 
 a. by wind = eolian corrasion. 
 
 b. by running water=river corrasion. 
 
 c. by ice = glacial corrasion. 
 
 d. by waves = abrasion. 
 
 e. by organisms= gnawing, etc. 
 
 3. Quarrying (closely related to physical clastation). 
 
 a. by wind (rare) undermining (decapitation of 
 
 erosion monuments), etc. 
 
 b. by running water = undermining (recession 
 
 of Niagara). 
 
 c. by ice=plucking, sapping. 
 
 d. by waves = tunneling and undermining. 
 
 e. by organisms, plant-wedging, plucking, etc., 
 
 man's work. 
 B. CHEMICAL. 
 
 4. Corrosion. 
 
 a. by air or evaporation (snow, ice). 
 
 b. by water (aqueous corrosion) or solution. 
 
 c. by heat igneous corrosion or melting. 
 
 d. by organisms. 
 
 TRANSPORTATION. 
 
 I. MECHANICAL. 
 
 A. IN SUSPENSION (in, and moving with the mass). 
 
 1. Atmospheric by wind: eolian transport. 
 
 2. Hydro spheric. 
 
 a. by waves, ocean and lake currents, tidal cur- 
 
 rent, undertow, etc. 
 
 b. by rivers (fluviatile transport). 
 
 c. by ice, englacial till ; ground moraine, etc. 
 
 d. carried by floating host such as : 
 
 (1) floating dead organisms (stones held by 
 floating trees, etc.). 
 
 (2) icebergs, shore ice, etc. 
 
 (3) rafts, ships, etc. 
 
 3. Pyrospheric suspended in molten lava. 
 
 4. Biospheric transported by animals either ex- 
 
 ternally or internally. 
 
 B. BASALLY, by shoving, rolling, sliding, etc. 
 
 i. Atmospheric rolling by wind, as sand of sand 
 dune, etc. 
 
INTERACTION OF THE SPHERES 19 
 
 2. Hydrospheric 
 
 a. by water currents. 
 
 b. by ice, terminal moraines, etc. 
 
 c. by snowslides, etc. 
 
 3. Centra spheric purely under the influence of gravi- 
 
 tation. 
 
 4. Biospheric by man, and more rarely other ani- 
 
 mals. 
 II. CHEMICAL: In solution. 
 
 1. Atmospheric dissolved in air, as water-vapor, 
 
 gases, etc. 
 
 2. Hydrospheric dissolved in water, e. g. } salt. 
 
 3. Pyrospheric in igneous solution. 
 
 4. Biospheric as body constituents, etc. 
 
 DEPOSITION. 
 
 A. MECHANICAL. 
 
 1. Atmospheric by wind, etc. Atmoclastic and ane- 
 
 moclastic deposits. 
 
 2. Hydrospheric by water. Hydroclastic deposits. 
 
 3. Pyrospheric by igneous action. Pyroclastic de- 
 
 posits. 
 
 4. Biospheric by animals, including man. Bioclastic 
 
 deposits. 
 
 B. CHEMICAL. 
 
 1. Atmospheric atmogenic deposits snow, etc. 
 
 2. Hydrospheric hydrogenic deposits, salt, gypsum, 
 
 etc. 
 
 3. Pyrospheric pyrogenic or igneous deposits. 
 
 4. Biospheric biogenic deposits (coral rock), etc. 
 
 DEFINITION AND SUBDIVISIONS OF GEOLOGY. 
 
 Geology is the science of the entire earth. The common im- 
 pression of the layman, that geology is the study of the lithosphere 
 alone, is a misconception, based on the fact that the geologist con- 
 cerns himself largely with the crust of the earth, since here he finds 
 the record of the history he seeks to read. According to the division 
 of the earth as a whole into a series of spheres, as already set forth, 
 we may divide the science of geology as a whole into the following 
 branches : 
 
20 PRINCIPLES OF STRATIGRAPHY 
 
 Inorganic 
 Atmology (Meteorology) 
 
 t Oceanography (Oceanology) 
 Hydrology \ Limnology 
 
 I Potamology 
 
 Geology 
 
 Lithology (Petrology, Geology in the narrow sense) 
 
 Pyrogeology (Vulcanology) 
 Organic 
 
 r Zoology (including palseozoology) 
 Biology | Phytology (Botany) including palaso- 
 
 < botany 
 
 Since no direct study of the Centrosphere is possible, no corre- 
 sponding science has been developed. (See, however, Chapter 
 XXIII.) 
 
 Each branch or science may again be treated under the follow- 
 ing headings : dynamics, structure, and history or genetics. Dynami- 
 cal geology in the broadest sense deals with the physical and chemi- 
 cal forces and their working. In the narrow sense, dynamical 
 geology is dynamical lithology, or the working of the physical and 
 chemical forces in and upon the earth's crust. Dynamical biology is 
 designated physiology. Hydrology and atmology (meteorology) are 
 largely a treatment from the dynamic point of view of the water 
 and the atmosphere, respectively, dealing especially with the move- 
 ments of these. Volcanic manifestations illustrate the dynamics of 
 the pyrosphere, or p^ro dynamics, while earthquakes illustrate the 
 dynamics of the centrosphere, or rather their effect upon the litho- 
 sphere. The interaction of the spheres upon one another must here 
 be considered as developing the exogenous dynamic forces. Thus 
 the action of the atmosphere, hydrosphere, biosphere, and pyro- 
 sphere upon the lithosphere furnishes the exogenous dynamic prod- 
 ucts which are manifested chiefly in the clastic rocks ; while the en- 
 dogenous dynamic forces reside within the material of the earth's 
 crust, and are manifested in chemical combinations, in crystalliza- 
 tion, etc. 
 
 From the point of view of structure, structural lithology (struc- 
 tural geology in the narrower sense) deals with the composition 
 and arrangement of the material of the earth's crust, and comprises : 
 i, elements; 2, minerals (mineralogy) ; 3, rocks (petrology, petrog- 
 raphy, lithology in the narrower sense) ; 4, large structural fea- 
 tures (geotectology or the study of the architecture of the earth's 
 crust) ; 5, the surface features (lithomorphology, physical geogra- 
 phy). Structural biology comprises the study of: i, the cell (cytol- 
 ogy) ; 2, the tissues (histology) ; 3, the larger structures (anatomy) ; 
 
SUBDIVISIONS OF GEOLOGY 21 
 
 4, the form (biomorphology), etc. Structural hydrology comprises 
 the study of composition (hydrochemistry), classification according 
 to form (hydromorphology), such as oceans, lakes, rivers, etc., each 
 of which has developed a special science to which are applied the 
 names oceanography (oceanology, thalassography), the hydrology 
 of oceans; limnology, the hydrology of the lakes; and potamology, 
 or the hydrology of the rivers. Structural atmology-or meteorology 
 considers the composition of the atmosphere, its density, etc. The 
 composition and structure of the Pyrosphere is only indirectly as- 
 certainable, while those of the Centrosphere fall into the realm of 
 speculation. 
 
 The historic or genetic aspect of these sciences likewise affords 
 an interesting series of parallels. Thus historical or genetic lithol- 
 ogy, or the science of lithogenesis in its broadest sense, deals with 
 the origin not only of the rocks as such, but also of the structures 
 they exhibit, and must necessarily take account of the conditions 
 under which they were formed. The study of the genesis of the 
 stratified rocks is stratigraphy, which, however, is closely bound up 
 with the other branches of the earth science, and cannot be made 
 independent of them. Historical biology or the science of bio- 
 genesis is the science of organic evolution. It may be considered 
 from the botanical side (phylogenesis), or from the zoological side 
 (zoo genesis), with reference to the individual (ontogenesis) or 
 to the race (phylogenesis). Palaeontology, or the science of the 
 past life of the earth, traces the phylogeny back through the suc- 
 cessive geologic periods, and is, therefore, the complement of 
 neobiology, or the science of modern life, and further demonstrates 
 the intimate relationship between the organic and the inorganic 
 sciences. Hydrogenesis, atmogenesis, and pyrogenesis are branches 
 of historical geologic science as yet little developed. 
 
 While stratigraphy is thus more especially the science of the 
 genesis of the stratified series of rocks, it necessarily includes and 
 is based upon the study of the rocks themselves, of their arrange- 
 ment or structures, and of the morphology of the earth's surface 
 during their formation. Thus it comprises the subject of Palce- 
 ogeography, or the geography of former times, and it furthermore 
 takes careful account of the physical conditions of the land and sea 
 as indicated by the organic remains entombed in the strata. Nor 
 can it leave out of consideration the various diastrophic movements 
 and their results, during all the geologic periods ; while igneous 
 activities, in so far as they affected the strata of the earth's crust, 
 also belong to the field of legitimate inquiry for the stratigrapher. 
 In other words, stratigraphy is the science of the evolution of the 
 
22 PRINCIPLES OF STRATIGRAPHY 
 
 lithosphere since the formation of the Archaean rocks. The follow- 
 ing table gives the larger divisions of this evolutionary history : 
 
 TABLE or THE DIVISIONS OF GEOLOGICAL TIME. 
 
 -~ . ,-\ j.- f Recent or Holocenic 
 
 Psychozoic or Quaternary time 1 Heist 
 
 Pliocenic 
 
 ~ , . Miocenic 
 
 Cenozoic or Tertiary time ~ r 
 
 Ohgocemc 
 
 Eocenic 
 Cretacic 
 
 Mesozoic or Secondary time . . , . C manchlc 
 
 Jurassic 
 
 Triassic 
 
 Permic 
 
 Carbonic 
 
 Mississippic 
 
 Palaeozoic or Transition time , 
 
 Devonic 
 
 Siluric 
 Ordovicic 
 Cambric 
 
 Proterozoic (Eozoic) or Primary time (in j Keweenawic 
 part) Algonkian I Huronic 
 
 Azoic (Archaeozoic) or Primary time (in part) j Keewatic 
 Archaean 1 Laurentic 
 
 BIBLIOGRAPHY I. 
 
 1. ARRHENIUS, SVANTE. 1900. Geol. Foren. Forhandl. Vol. XXII. 
 
 2. BARUS, CARL. 1891. The Contraction of Molten Rock. American 
 
 Journal of Science, 3rd ser., Vol. XLII, pp. 498-499. 
 
 3. BARUS, CARL. 1892. The Relation of Melting to Pressure in Case of 
 
 Igneous Rock Fusion. Ibid. Vol. XLIII, pp. 56-57. 
 
 4. CHAMBERLIN, THOMAS C., and SALISBURY, ROLLIN D. 1906. 
 
 Geology, Vol. I. 
 
 5. CROSBY, WILLIAM OTIS. 1892. Dynamical Geology and Petrog- 
 
 raphy. 
 
 6. DAVIS, WILLIAM MORRIS. 1899. Elementary Meteorology. 
 
 7. FULLER, MYRON L. 1906. Water Supply and Irrigation Paper, 
 
 No. 1 60. 
 
 8. GREGORY, J. W. 1911. The Terms Denudation, Erosion, Corrosion, 
 
 and Corrasion. Geographical Magazine, Feb. 1911, pp. 189-195. 
 
 9. GUNTHER, SIEGMUND. 1891. Lehrbuch der Physicalischen Geog- 
 
 raphic. Stuttgart. 
 
BIBLIOGRAPHY I 23 
 
 10. GtiNTHER, SIEGMUND. 1897. Handbuch der Geophysik. 2nd 
 
 edit. Stuttgart. 2 volumes. 
 
 11. HAUG, EMILE. 1907. Traite" de Geologic. T.I. 
 
 12. HAYFORD, JOHN F. 1909. The Figure of the Earth and Isostasy 
 
 (and Supplementary Investigation). U. S. Coast and Geodetic Survey. 
 
 13. HAYFORD, JOHN F. 1911. Vice-presidential address before section D 
 
 of A. A. A. S. The Relation of Isostasy to Geodesy, Geophysics, and 
 Geology. Science, N. S., Vol. XXXIII, Feb. 10, pp. 199-208. 
 14.. HELMERT, F. R. 1884. Theorien der hoheren Geodesie. Leipzig, Vol. II. 
 
 15. KEMP, JAMES FURMAN. 1901. The Role of the Igneous Rocks in * 
 
 the Formation of Veins. American Institute of Mining Engineers. 
 Richmond Meeting. 
 
 16. KING, CLARENCE. 1893. The Age of the Earth. American Journal v 
 
 of Science, 3rd ser., Vol. XLV, pp. 1-20. 
 
 17. KRUMMEL, OTTO. 1907. Handbuch der Ozeanographie. Band i, 
 
 2nd edit. 
 
 1 8. LYELL, CHARLES. 1875. Principles of Geology. Twelfth edition, 
 
 Vol. II. 
 
 19. MILL, HUGH ROBERT. 1890. The Vertical Relief of the Globe. v 
 
 Scottish Geographic Magazine. Vol. VI, pp. 182-187, with map. 
 
 20. MURRAY, JOHN. 1888. On the Height of the Land and the Depth of v 
 
 the Ocean. Scottish Geographic Magazine. Vol. IV, p. I et seq. 
 
 21. PENCK, ALBRECHT. 1894. Morphologic der Erdoberflache, Vol. I. 
 
 22. PENCK, ALBRECHT. 1908. Die Erdoberflache in Scobel's Geographi- 
 
 sches Handbuch. 
 
 23. PENCK, A., and SUPAN, A. 1889. Mittheilung liber Murray's "Die 
 
 Mittlere Hohe des Landes und die Mittlere Tiefe des Meeres." Peter- 
 mann's Mittheilungen, Bd. XXXV, pp. 17-21. 
 
 24. ROMIEUX, A. 1890. Relations entre la deformation actuelle de la 
 
 croute terrestre et les densities moyennes des terres et des Mers. Comptes 
 Rendus des Seances de 1' academie des Sciences. Paris, T. CXI. 
 
 25. SLIGHTER, CHARLES S. 1902. Water Supply and Irrigation Paper, 
 
 No. 67. U. S. G. S. 
 
 26. STAPFF, F. M. 1894. Ueber die Zunahme der Dichtigkeit der Erde 
 
 nach ihrem Innern. Gerland's Beitrage zur Geophysik, Vol. II. 
 
 27. SUESS, EDUARD. 1888. Das Antlitz der Erde, Bd. II. 
 
 28. SUESS, EDUARD. 1906- The Face of the Earth, Vol. II. 
 
 29. TUMLIRZ, O. 1892. Die Dichte der Erde, berechnet aus der Schwer- 
 
 rebeschleunigung und der Abplattung. Sitzungsberichte K. Acad. d. 
 Wiss. Wien. Math. Nat. Klasse. CI, Abh, Ha, pp. 1528-1536. 
 
 30. VAN HISE, CHARLES R. 1904. A Treatise on Metamorphism. 
 
 United States Geological Survey, Monograph, Vol. XLVII. 
 
 31. WAGNER, HERMANN. 1894. Areal und Mittlere Erhebung der 
 
 Landflachen sowie der Erdkruste. In Gerland's Beitrage zu Geophysik 
 Bd. II. 
 
 32. WATSON, THOMAS L. 1911. Underground Temperatures. Science, 
 
 N. S., Vol. XXXIII, pp. 828-831. 
 
 33. WOODWARD, R. S. 1889. Mathematical Theories of the Earth. Pro- 
 
 ceedings of the American Association for the Advancement of Science, 
 pp. 59-63; American Journal of Science, 3rd ser. Vol. XXXVIII, pp. 
 337 et seq. 
 
 34. WALTHER, JOHANNES. 1893-4. Einleitung in die Geologie als histor- 
 
 ische Wissenschaft. 
 
A. THE ATMOSPHERE. 
 
 CHAPTER II. 
 
 CONSTITUTION, PHYSICAL CHARACTERISTICS AND MOVEMENTS 
 OF THE ATMOSPHERE; GEOLOGIC WORK OF THE ATMOS- 
 PHERE. 
 
 COMPOSITION OF THE ATMOSPHERE. 
 
 As already noted, the atmosphere consists of a mechanical mix- 
 ture of oxygen and nitrogen with some argon, the proportion in 
 pure dry air being: 
 
 By weight. By volume. 
 
 Oxygen 23.024 20.94! 
 
 Nitrogen 75-539 
 
 Argon 1-437 
 
 100.000 100.000 
 
 Air is always impure, water vapor and carbon dioxide, as well as 
 various organic and inorganic impurities being generally present in 
 variable quantities. The average volumetric composition of the 
 gases of the atmosphere in parts per 10,000 is as follows (29:860) : 
 
 Oxygen 2,065 94 Ozone 0.015 
 
 Nitrogen 7,711 .600 Aqueous vapor 140.000 
 
 Argon (about) 79.000 Nitric acid 0.080 
 
 Carbon dioxide 3 . 360 Ammonia o . 005 
 
 In addition to this there is often found free hydrogen, up to one 
 part in 5,000 by volume (Gautier), methane, benzine and its homo- 
 logues, etc. Other compounds are formaldehyde (2 to 6 gr. per 
 loo cu. meters), and sulphur compounds, especially H 2 S, which be- 
 comes oxidized to SO 2 . Sulphur dioxide is also derived from vol- 
 canoes and the combustion of coal, and has been found at Lille 
 (France) to the extent of 1.8 cu. cm. of SO 2 in i cu. meter of air. 
 It is returned to the ground as H 2 SO 4 in rain water. So universally 
 
 24 
 
COMPOSITION OF THE ATMOSPHERE 25 
 
 are water vapor and CO 2 present, that we can speak of a triple at- 
 mosphere, one an intimate mixture of oxygen and nitrogen, and 
 the other two of water vapor and CO 2 , respectively, diffused through 
 the pure air atmosphere. 
 
 NITROGEN is the inactive element, though animals and plants ap- 
 propriate it through the formation of nitrogenous compounds. 
 
 OXYGEN, the active element of the atmosphere, is consumed by 
 all animals and taken either directly from the air, or, in the case of 
 water-living animals, from the water in which it is dissolved. De- 
 caying organic matter consumes oxygen, and so do some minerals 
 during the process of oxidation. Oxygen is supplied to the air by 
 the growth of plant life, which breaks up CO 2 , using the carbon 
 and setting part of the oxygen free. Volcanic vents also supply 
 oxygen, while another source of supply is found in the deoxidation 
 of minerals. Thus the quantity of oxygen withdrawn from the air 
 is balanced by that supplied, so that the relative amount remains 
 practically constant. 
 
 ARGON, first separated from the nitrogen of the air in 1895, is 
 like that element exceedingly inert, its power of combining with 
 other elements being even less than that of nitrogen. It forms about 
 0.94 per cent, by volume, or 1.44 per cent, by weight, of the at- 
 mosphere. Other previously unknown gases in the atmosphere are : 
 helium, i to 2 parts per million ; neon, i to 2 parts per hundred 
 thousand; krypton, I part in 20 millions; xenon, i part in 170 mil- 
 lions. These are as inert as argon. 
 
 CARBON DIOXIDE (CO 2 ). This is a relatively constant constitu- 
 ent of the air, making about 0.03 per cent, by volume, or three parts 
 in 10,000 of the entire atmosphere. It is supplied to the atmosphere 
 by the burning or decay of organic matter, by the respiration of ani- 
 mals, as well as by volcanic emanations and other agents. Artifi- 
 cial consumption of coal and other burnables furnishes a large sup- 
 ply of CO 2 to the atmosphere, a ton of bituminous coal (75 per cent, 
 of carbon) furnishing about 2^4 tons of CO 2 ( Salisbury-83 15 15) . 
 Since the amount of CO 2 in the air remains relatively constant, a 
 quantity equal to that supplied [estimated at several billion tons a 
 year (Salisbury)] must be removed from the air. The chief agents 
 active in abstracting CO 2 from the air are chlorophyll-forming 
 plants, which, as already remarked, find in it the source of carbon 
 for their tissues. Carbonization of mineral matter, or the com- 
 bination of the CO 2 with other elements, is another cause of the 
 reduction of the amount of CO 2 in the air. 
 
 WATER VAPOR. The water vapor of the atmosphere varies with 
 temperature and other local conditions, and with the amou^- sup- 
 
26 PRINCIPLES OF STRATIGRAPHY 
 
 plied. It is precipitated in the form of dew, rain, snow, frost, 
 etc., and is constantly returned to the atmosphere by evaporation. 
 In damp countries near the equator the amount of water vapor in 
 the air may be 3 or even 4 per cent, by volume of the whole air. 
 Thus at Batavia (Java), where the vapor pressure is 21 mm., the 
 amount of water in the air is 2.8 per cent, by volume. The com- 
 position of the air here is: N 76.8%, O 20.4%, H 2 O 2.8% and 
 a few hundredths of a per cent, of CO 2 . At Allahabad (Persia) 
 during the rainy season, 4 per cent, of water vapor by volume has 
 been found in the air (calculated from the vapor pressure, which 
 was 30.7 mm.). In central Europe, even in summer, with a vapor 
 pressure of about 10 mm., the volume of water in the air amounts 
 to only 1.3 per cent. (Hann-4o:7^.) 
 
 Absolute and Relative Humidity. Expressed in weight of wa- 
 ter, the amount which one cubic foot of air can hold is as follows : 
 one-half grain of water at o F., 5 grains at 60 F., and II grains 
 at 80 F. At 60 the amount which the air of a room 4Ox4<Dx 15 
 ft. can hold is nearly 20 pounds, or almost enough to fill a common 
 water pail. The amount of moisture which the air contains is its 
 absolute humidity. The percentage of moisture which the air con- 
 tains at a given temperature, of that which it would contain at that 
 temperature if it were saturated, is its relative humidity, which is 
 50 when the air contains only half the amount which it could con- 
 tain at saturation at that temperature. In the latter state the hu- 
 midity is 100. The average relative humidity of the air on the land 
 is perhaps 60 per cent., and over the ocean about 85 per cent. Be- 
 low 65 per cent, the air becomes dry. In semiarid regions it ranges 
 around 45 per cent., and in desert regions it ranges around 25 or 30 
 per cent. 
 
 At Ghadames (Hann-4O:/5/), western Tripoli, the relative hu- 
 midity for July is 27 per cent, and for August 33 per cent. The 
 oasis of Kufra, in the heart of the Libyan desert, has a relative 
 humidity of 27 per cent, in August, 33 per cent, in September, and 
 17 per cent, for the 3 P.M. August mean. The oasis of Kauar, in 
 the heart of the Sahara, has a mean relative humidity of 27 per 
 cent, in August. In the Punjab district of India, the relative mean 
 humidity in May is 31 per cent, at Lahore, while at Agra, in the 
 northwest province, it is 36 per cent. It must, of course, be borne 
 in mind that the observations made in the inhabitable portions of 
 the desert regions, i. e., the oases, give a much higher relative 
 humidity than occurs in the open desert itself. 
 
 In the semiarid regions of southwestern United States, the fol- 
 lowing humidities occur: 
 
COMPOSITION OF THE ATMOSPHERE 
 
 27 
 
 
 Mean 
 
 Mean 
 
 
 
 annual 
 
 monthly 
 
 
 Place 
 
 relative 
 
 minimum 
 
 Month 
 
 
 humidity 
 
 humidity 
 
 
 Yuma, Arizona 
 
 42.0% 
 
 74 7% 
 
 June 
 
 Santa Fe, New Mexico 
 
 44.8% 
 
 28.7% 
 
 June 
 
 Pueblo, Colorado 
 
 46 2% 
 
 VI 6% 
 
 April 
 
 
 
 
 
 )eath Valley, California, a typical American desert, showed a mean 
 relative humidity of 23 per cent, for the five months from May to 
 September in 1891. In regions of summer rain the relative humidity 
 is high, even far inland. Thus at Dorpat, Baltic Provinces of Rus- 
 sia, the mean relative humidity in summer is 73 per cent. ; at Yeni- 
 seisk, Central Siberia, it is 70 per cent. 
 
 Source of Water Vapor. Evaporation is the chief source of the 
 water vapor of the air. All exposed moist surfaces furnish water 
 vapor to the atmosphere, the conversion of water into vapor con- 
 stituting evaporation. Evaporation is, of course, most marked over 
 large water surfaces, such as the oceans, the ultimate source of the 
 water vapor, and over lakes, ponds, etc. It is estimated that the 
 average amount of evaporation from the surface of the earth 
 amounts to a layer 30 or 40 inches deep each year. (Some esti- 
 mates make it 60 inches.) At this rate, if the water were not re- 
 turned to the sea, the oceans would be dried up in from 3,000 to 
 4,000 years, while the lakes of the earth would probably.be ex- 
 hausted in a single year. The water evaporatipn from the surface 
 of the Mediterranean and Black Seas is estimated as more than 
 226 cubic miles per annum. Evaporation may be going on from an 
 approximately dry land surface, the moisture being drawn from 
 beneath the surface. By such processes mineral matter held in 
 solution within the pores of the rock is drawn to the surface, and 
 there left on evaporation. Such is the origin of the brown desert 
 varnish on rock surfaces, and- the efflorescence of salt and alum 
 found on many rocks. Snow and ice also evaporate, at a tempera- 
 ture below the melting point, for snow and ice slowly disappear, 
 even in temperatures below 32 F. 
 
 Other sources of water vapor are animal and plant respiration, 
 and volcanic ejections, the latter often adding an appreciable 
 amount. 
 
 IMPURITIES. The impurities of the atmosphere are in large 
 part inorganic particles or dust. Organic matter, such as spores of 
 plants, bacteria, etc., also abounds, but the dust is by far the most 
 
28 PRINCIPLES OF STRATIGRAPHY 
 
 prevalent. In dust storms the amount is, of course, extreme, but 
 ordinary air sometimes carries a surprising amount. Thus, in Eng- 
 land, during the fogs of February, 1891, the amount of dust de- 
 posited on the previously washed glass roofs of the plant house at 
 Kew was 30 grams to 20 square yards, while at Chelsea 40 grams 
 were deposited over the same area. This represents 22 pounds to 
 the acre, or six tons to the square mile. Of this amount, uncon- 
 sumed carbon (soot) formed 42.5 and 39 per cent., respectively, 
 and 41.5 and 33.5 per cent, was other mineral matter, including 
 some metallic iron. (Hann-4o:/7; Russell-8i.) 
 
 OPTICAL CHARACTERS OF THE ATMOSPHERE. 
 
 LIGHT. The three chief effects produced by the energy of the 
 sun's rays are optical, thermal, and chemical.' We may thus speak 
 of light rays, heat rays, and chemical or actinic rays, bearing in 
 mind that the difference of effect does not lie in the differences of 
 the rays, but in the nature of the surface on which they fall. 
 
 The rays of the most importance to vegetal life are the luminous 
 or light rays, i. e., the components of radiation near the red end of 
 the visible spectrum, rather than at the blue and violet end. Experi- 
 ments with monochromatic light on Mimosa pudica have shown 
 that the plant thrives best in red light and least in blue. "The red 
 and the yellow rays are the most active in promoting the respira- 
 tion and the transpiration of the leaves and the assimilation of car- 
 bonic acid/' (C. Flammarion, quoted by Hann~4o:jd.) 
 
 Diffusion of daylight. The sunlight on penetrating our atmo- 
 sphere is scattered or diffused by the particles of dust in the air, 
 and thus the illumination of the whole atmosphere on the sunny 
 side of the earth is produced. If it were not for the dust, it is 
 probable that the sky would be black, the stars visible by day, and 
 darkness prevail in all shady places, while those exposed to the sun 
 would be illumined with dazzling brilliancy. The color of the sky 
 and the sunset and sunrise tints are largely due to the presence of 
 the dust. The very brilliant sunset effects of the autumn and winter 
 of 1883 were due to the large amount of volcanic dust in all parts 
 of the upper air, derived from the explosion of the volcano Kraka- 
 toa (between Sumatra and Java) from May to August, 1883. (See 
 the illustrations in Hann (39), opposite page 50.) 
 
 Diffused sunlight is of the greatest importance to plant life. It 
 is the diffused light which pours over all portions of the plant 
 equally, which benefits the plant as a whole by benefiting all its parts. 
 
TEMPERATURE OF THE ATMOSPHERE 29 
 
 Plants need less light as the temperature rises, and more as it 
 falls. 
 
 TEMPERATURE OF THE ATMOSPHERE. 
 
 The chief source of atmospheric heat is the sun, while of much 
 less significance is the internal heat of the earth. Other local 
 causes, such as friction in landslides, etc., volcanic activities, fires, 
 organic decay, etc., and movements of the atmosphere itself, locally 
 warm the air, but these are generally of almost negligible signifi- 
 cance. 
 
 The amount of heat received by the earth from the sun each 
 year would, if equally distributed, melt a layer of ice about 141 feet 
 thick over the entire surface of the earth, or evaporate a layer of 
 water 18 feet deep; yet the amount received is less than 1/2,000,- 
 000,000 of the heat given off by the sun. The space outside of our 
 atmosphere is believed to have a temperature of 273 C. 
 ( 459 F.), which would be the winter temperature (coldest 
 month) of the polar regions of the earth if there were no at- 
 mosphere. The winter temperature of the equator would be about 
 -(-56 C. (4-164.8 F.). The estimated summer temperature at 
 the poles under the same condition would be +82 C. (4-211.6 F.), 
 while that at the equator at the same time would be only 4~67 C. 
 (4-184.6 F.), since the polar regions, owing to their continuous day 
 in summer, would receive a greater amount of total heat. The 
 minimum observed temperature is 60 C. and the maximum 
 4~ 80 C. The chief agents in retaining the sun's heat within the 
 earth's atmosphere are the carbon dioxide and the water vapor, 
 which act as thermal blankets. It has been estimated by Arrhenius 
 (2) that if the amount of CO 2 in the atmosphere were in- 
 creased 2.5 to 3 times its present value, the temperature in the 
 arctic regions must rise 8 to 9 C. and produce a climate as mild 
 as that of Eocenic time, so that magnolias would again grow in 
 Greenland. On the other hand, if the CO 2 were decreased to an 
 amount ranging from 0.62 to 0.55 of its present value, a fall of 
 from 4 to 5 C. would result and glacial conditions would again 
 overspread the northern parts of the continents. These estimates 
 have been seriously questioned, but the general fact that both CO 2 
 and water vapor act as thermal blankets is established. Chamber- 
 lin (13, 14, 15) has discussed in detail the bearing of these facts 
 on former continental glaciation, his argument being that the ab- 
 straction of the CO 2 from the atmosphere during the periods of ex- 
 tensive vegetal growth, i. e., the periods of coal formation, tended 
 
30 PRINCIPLES OF STRATIGRAPHY 
 
 to refrigerate the climate. The amount of CO 2 taken from the air 
 in the known geologic periods and locked up in the coals and lime- 
 stones of the earth has been variously estimated at from 20,000 to 
 200,000 times the present atmospheric content, or even more. An- 
 other factor favoring the consumption of CO 2 is the extensive sub- 
 terranean decomposition of the rocks following a period of elevation 
 with its attendant fissuring of the rock and the deepening of the 
 zone of circulation of surface waters. These, supplied with CO 2 at 
 the surface, are active in the carbonation of the decomposing rocks. 
 The solution of limestones and other carbonates is a further source 
 of abstraction of CO 2 from the atmosphere, since the original mono- 
 carbonates are changed to bicarbonates in the process of solution, the 
 second molecule of CO 2 being derived from the atmosphere. This 
 is, however, a temporary abstraction, for on the redeposition of the 
 limestone, either by chemical or organic agencies, the second mole- 
 cule of CO 2 is set free again. Hence periods of extensive limestone 
 deposition must be periods of extensive supply of CO 2 to the atmos- 
 phere, and this would have the effect of ameliorating the climate. 
 It is important to note that extensive coal formation is dependent on 
 the great expanse of land areas, while extensive limestone formation 
 depends on the expanse of the sea. Extension of the land is accom- 
 panied further by an extension of the deep-seated circulation, and by 
 decomposition and carbonation of the crystalline rocks, as well as by 
 periods of solution of the carbonates. The two periods of great 
 land expansion, followed by well-authenticated glacial periods, are 
 the close of the Palaeozoic and that of the Cenozoic. Other periods 
 are the pre-Cambric, the close of the Siluric and the opening of the 
 Devonic, the close of the Jurassic and opening of the Comanchic, 
 and the end of the Cretacic. Periods of marine extension, on the 
 other hand, with the formation of much limestone and the accom- 
 panying 1 setting free of CO 2 , were the middle and early upper 
 Ordovicic, the early Siluric (Niagaran), the Mississippic, the upper 
 Jurassic, the mid-Cretacic, and in some regions the Eocenic and 
 Oligocenic. Much evidence exists that these periods of extensive 
 limestone formation were periods of mild and equable climates, very 
 nearly uniform for all latitudes. 
 
 Distribution of Heat Within the Earth's Atmosphere. The sun's 
 heat is distributed through the atmosphere by radiation, conduction, 
 and convection. The heat which the earth receives from the sun is 
 returned to the atmosphere by radiation. These non-luminous heat 
 waves are much more readily absorbed by the air than the luminous 
 ones which reach it from the sun. The atmosphere in contact with 
 the land is further heated by conduction, provided the surface of the 
 
TEMPERATURE OF THE ATMOSPHERE 31 
 
 land is warmer than the air, and this warmer air will be distributed 
 by the setting in of convection currents. The heated air expands 
 and rises, while the heavier, colder air from above sinks down to 
 take the place of that which has risen, pushing upward and out- 
 ward, at the same time, the lighter air which still remains. Vertical 
 and horizontal convection currents thus come into existence, and 
 distribute the heated air in the atmosphere. The surface of the land 
 is heated four or five times as fast as the surface of the water, due 
 partly to the greater specific heat of the latter, the more ready ab- 
 sorption of heat by the land and its reflection by the water. The 
 land radiates its heat more readily than the water, in which convec- 
 tion currents tend to distribute it, while at the same time the heat 
 of the sun's rays penetrates more deeply into it than into the land, 
 and a given amount of heat is distributed through a thicker layer of 
 water than of land. All this shows that the temperature of the air 
 over the land is heated more highly than that over the water, and 
 conversely it is cooled more quickly than that over the water. Hence 
 continental climates show greater annual extremes than those of the 
 sea. As an example, two points in 62 N. latitude are given, one at 
 Thorshaven on the Faroe Islands, where the mean annual range is 
 7.9 C. (+3.0 C. in March, +10.9 C. in July) the other at Ya- 
 kutsk, Siberia, where the range is 61.6 ( 42.8 C. in January, 
 + 18.8 C. in July). 
 
 GEOLOGICAL WORK OF HEAT AND COLD CHANGES IN TEMPERATURE. 
 
 This may be grouped under the heads of (a) insolation, or the 
 exposure to the influence of the sun's rays by day; (b) radiation, 
 or the loss of heat at night through cooling; and (c) congelation, or 
 the work of frost. 
 
 Insolation and Radiation. Heating in general causes expansion 
 of rock masses and decreasing density, while cooling causes contrac- 
 tion and an increase of density. Even water follows this rule down 
 to a temperature of +4 C., when it reaches its maximum density, 
 after which it expands. Naked rock surfaces may be highly heated 
 by exposure to the sun during the day, especially in the rarefied air 
 of high altitudes. This heating will affect the outer part only, 
 owing to the poor conductivity of rock, and the resulting expansion 
 will cause a surface layer to scale off from the cooler, less expanded 
 mass below. On cooling at night, the outer layer loses its heat most 
 rapidly, and the accompanying contraction causes the rock to break. 
 Where changes of temperature are great and regular, as on exposed 
 mountain summits, the surface may be characterized by scaling-off 
 
32 PRINCIPLES OF STRATIGRAPHY 
 
 layers, as in Mt. Starr-King, California, or Mt. Monadnock, New 
 Hampshire; or by breaking off of fragments of all sizes, which 
 cover the mountain. top to the frequent exclusion of solid ledges, as 
 on Pike's Peak, Colorado; Mt. Adams, New Hampshire; Sugar 
 Loaf Mountain, Brazil ; Ben Nevis, Scotland ; and most mountain 
 summits. Such fragments, supplemented by those broken off by 
 frost action, accumulate at the foot of every cliff and on every 
 steep slope, forming the talus, the surface angle of which varies 
 with the coarseness of the material. (See Chapter XIII.) 
 
 The best illustration of such disruption of rocks is seen in 
 desert regions, where changes of temperature are very great. Liv- 
 ingston has described the disruption, with ringing sound, of the basalt 
 masses in South Africa. Other examples are cited from Brazil and 
 the Atacama desert of Chile, where the temperature in winter ranges 
 from 12 C. at 7 A.M. to +37 C. at n A.M., and the summer 
 temperature from +5 C. to +55 C. From tropical west Africa 
 Pechuel-Loesche has recorded temperature ranges of 60 to 84 C. 
 ( Walther-iO4 -.28 et seq. ; also 103 :55<5-557 and literature there 
 cited.) Walther has found this shattering of rocks through insola- 
 tion in limestone, flint, sandstone, porphyry, granite, gneiss, quartz, 
 and other rocks. The crack penetrates gradually into the depths of 
 the rock, so that half-broken pebbles are not infrequently found. 
 Such cracks are visible in rocks of all sizes, from fragments as large 
 as a nut to blocks of the dimensions of a house. In limestone and 
 granites, Walther often found peripheral cracks which permitted the 
 separation of concentric shells, varying in thickness from that of a 
 sheet of paper in some limestones to shells 10 cm. thick in some 
 granites. In Brazil the range of temperature is considerably more 
 than 100 F., while in the northern United States it is 150 F. 
 ( 30 to +125) in half a year, with a diurnal variation often 
 amounting to half that. (Shaler.) 
 
 Changes of temperature in like manner affect the individual 
 mineral constituents of the rock, as well as their association in the 
 rock. Since each mineral has its normal coefficient of expansion and 
 contraction under a given influence of heat or cold, it follows that 
 irregular stresses and strains are set up within a rock mass of rela- 
 tively coarse-grained minerals such as a granite, and that this must 
 lead to a slipping back and forth of the minerals upon each other 
 with ultimate disruption or disintegration of the mass as a whole. 
 Walther regards the difference of color of these minerals as of 
 especial significance (103:556), and Branner (10) has also called 
 attention to the fact that coarse texture likewise favors this type of 
 disintegration. This is well shown in coarse granites of sub-arid 
 
WORK OF THE ATMOSPHERE 33 
 
 regions such as Pike's Peak, the granite countries along the Colo- 
 rado River in Arizona, the peaks of Mount Sinai, and many other 
 mountain tops where taluses or screes of crystalline sand, made up 
 of dissociated minerals of the granite, characterize the exposed 
 mountain sides and fill up all the hollows. The feldspar of this 
 sand is generally fresh and unclouded, the original crystals being 
 scarcely altered. Such sands, reconsolidated with little assortment, 
 give rise to peculiar arkoses in which the fresh feldspar crystals 
 form the most striking feature, and may even cause the rock to be at 
 first mistaken for an unaltered granite. Examples of this kind are 
 found in certain parts of the Torridon sandstone (pre-Cambric) of 
 the west of Scotland, and in other rocks. Granite bosses, wherever 
 exposed, are generally marked by rounded surfaces, intersected per- 
 haps by joint cracks into which the disintegration products have 
 been washed, and which alone support vegetation, the granite sur- 
 face being bare. Granite boulders exposed to the same forces will 
 crumble into heaps of crystalline sand. Since the corners and 
 angles of rock fragments are their most exposed portions, the first 
 being attacked from three sides, it follows that disintegrating blocks 
 will soon assume a rounded outline. Concentric exfoliation of the 
 disintegrated outer portions of such rock masses is observable, the 
 rock becoming a boulder formed in situ and often embedded in a 
 mass of disintegrated and partly decomposed residual sand and soil. 
 Branner,, discussing the effect of these temperature changes on the 
 rocks of Brazil, remarks : "The unequal contraction and ex- 
 pansion of the minerals composing the rock tend to disintegrate the 
 entire mass, while the even annual and diurnal changes and the 
 approximately even penetration of these changes cause the rock 
 to exfoliate or to spall off in layers of even thickness, like the coats 
 of an onion, while the crevices opened in the rocks admit acids and 
 gases and set up a train of reactions that sooner or later disinte- 
 grate and decompose the entire rock mass." (10:281.) 
 
 The individual minerals themselves may likewise be affected by 
 this change in temperature., since there is differential expansion 
 along the different crystal axes. A cleavable mineral like feldspar 
 may thus become potentially shattered, innumerable fine rifts form- 
 ing along the cleavage planes, which, though insufficient to cause 
 the mineral to crumble, yet admit air and moisture and permit 
 chemical decomposition within the crystal. In moist climates this is 
 seen in the clouding of a feldspar crystal along the fine cleavage 
 lines as seen in a thin section under the microscope. 
 
 Disintegration, as here described, is always associated with a 
 greater or less amount of chemical alteration, such as oxidation, 
 
34 PRINCIPLES OF STRATIGRAPHY 
 
 hydration, etc., according to the state of the atmosphere. Where 
 Jittle moisture exists in the air, as in arid regions, the chief process 
 by which the destruction of rock masses is effected is disintegration, 
 supplemented, of course, by the mechanical work of the wind. 
 
 Branner (10:281) has observed that the mica of Brazilian 
 gneisses is an element of weakness, tending, both on account of its 
 low conductivity and its form, to develop crevices along which the 
 rocks exfoliate more readily. 
 
 Frost Work. Water, on freezing, expands one-tenth of its vol- 
 ume, and so becomes a powerful agent in destroying rock masses. 
 The expansion of water in fissures on freezing is capable of prying 
 off huge masses of rock, and in some cases much of the talus at the 
 foot of the cliff is to be referred to frost action. Rock surfaces may 
 by radiation cool below the freezing point (o C. or 32 F.), so 
 that moisture coming in contact with them freezes at once. This is 
 often seen in high altitudes where moisture-laden winds strike a cold 
 rock wall or cairn, with the result that the moisture is precipitated 
 as ice. An interesting, case of freezing in contact with cold rocks 
 has been observed on the coast of Newfoundland, where the lime- 
 stone cools more rapidly at the beginning of the winter than the sea- 
 water, which penetrates all the fissures at high tide, freezing there 
 in contact with the cold rock and shattering the mass during the re- 
 treat of the tide. The constant repetition of this phenomenon re- 
 sults in covering the beach with freshly broken, angular fragments. 
 (Thoulet, Walther-i03i55p.) 
 
 The creep of the soil on sloping surfaces has also been referred 
 to frost action, the water in the soil freezing and converting the 
 mass into an "earth glacier" (Kerr~54:j^5). The creeping down- 
 hill of this mass results in the bending over of the ends of the ver- 
 tical or steeply inclined strata. 
 
 CHEMICAL WORK OF THE ATMOSPHERE. 
 
 The chemical activities of the atmosphere penetrate the upper 
 layers of the lithosphere to the level of the ground water. This 
 averages perhaps from 30 to 50 meters below the surface, though in 
 many regions it is at the surface, while again, in arid regions it may 
 be so much as 1,000 meters or more beneath the surface. The belt 
 thus produced, between the average level of the ground water and 
 the surface, is the belt of deniorphism, or in general the Belt of 
 Weathering. It is here that the chemical work of the atmosphere 
 is most marked in destroying the rocks, this work consisting, so far 
 
WORK OF THE ATMOSPHERE 35 
 
 as the atmosphere is concerned, in oxidation, hydration, and car- 
 bonation. Solution, which also goes on actively here, is to be re- 
 garded as the work of the ground water, rather than that of atmo- 
 spheric moisture. The two agents are, however, so intimately re- 
 lated that it is impossible to draw a sharp line between them and 
 their respective accomplishments. 
 
 Carbonation of silicates is on the whole the most characteristic 
 reaction. This takes place on a vast scale, producing carbonates 
 from the silicates, and setting free, thereby, silica or colloidal silicic 
 acid. Hydration is the most extensive single reaction in this belt, 
 while oxidation is very pronounced, owing to the free access of 
 oxygen to the pores, from the absence of water. Solution removes 
 many of the products of decomposition from this belt of weathering, 
 and carries it away over ground or under ground. As a result of 
 this, the volume of rock in the belt of weathering becomes greatly 
 reduced, the resultant material in the end occupying only a small 
 fraction of the volume it once had. 
 
 OXIDATION. "The oxygen is chiefly utilized in the oxidation of 
 iron, surphur, and organic material. In the upper part of the belt 
 [of weathering], where oxygen is abundant, large amounts of hema- 
 tite and limonite may be produced by the oxidation of the ferrous 
 particles, but for the greater part of the belt of cementation, where 
 oxygen is somewhat deficient, the ferrous oxide is oxidized only to 
 the form of magnetite, since this requires, per unit of iron, only two- 
 thirds as much oxygen as to produce hematite and limonite." (Van 
 Hise-ioordod.) Magnetite may be directly oxidized, into hematite, 
 involving an increase in volume of 2.5 per cent. Hydration may 
 occur simultaneously, changing the mineral to limonite with a cor- 
 responding increase in volume of 64 per cent. Iron carbonates, are 
 oxidized to ferric oxide, with a corresponding decrease in volume, 
 owing to loss of CO 2 . This is 49 per cent., if hematite is the result, 
 but only 18 per cent., if the carbonate is changed to limonite. Sul- 
 phides are oxidized to sulphites and sulphates. Sulphurous and sul- 
 phuric acids are formed, which may enter into various combinations. 
 Sulphuretted^ hydrogen is a common 'result of the oxidation of iron 
 pyrites, and, from the further oxidation of this, pure sulphur may 
 be precipitated. 
 
 Some of the changes occurring may be expressed in the follow- 
 ing formula (for others see Van Hise-ioo :.?//) : FeS 2 -|-6O=: 
 FeSO 4 -|- SO... If the water is present, we may have : 
 
 FeS,+3O+H 2 O=FeSO 4 -fH 2 S. 
 The ferrous sulphate may be removed in solution or may fur- 
 
36 PRINCIPLES OF STRATIGRAPHY 
 
 ther be oxidized into hydrated sesquioxide of iron or limonite and 
 sulphuric acid, thus : 
 
 . In each of these reactions heat is liberated. Where H 2 S is 
 liberated, this may be further oxidized, especially in the presence of 
 bacteria, and sulphur may result thus : H 2 S-|-O=H 2 O-|-S. The 
 sulphur may later be oxidized to sulphuric acid. 
 
 The change from sulphides to oxides without hydration involves 
 a diminution in volume. A change to magnetite means a decrease in 
 volume of 24 to 39 per cent., oxidation and hydration of pyrite, how- 
 ever, result in a total increase in volume of 3 per cent., while the 
 increase in the case of pyrrhotite is 25 per cent. 
 
 Red and Yellow Colors of Soil Due to Oxidation. Within the 
 zone of active flock weathering, the iron compounds are transformed 
 to ferric oxide or hydrate, if- the amount of oxygen is sufficient. 
 These iron compounds will impart their characteristic color to the 
 soil, which will be yellow or red, according to the simultaneous 
 occurrence or non-occurrence of hydration. Dehydration of ferric 
 hydrates may likewise change the color of yellow soil to red, as is 
 shown in brick-making, when the yellow clay on burning changes to 
 a red brick. Crosby has attributed the contrast of the color of soils 
 of high and low latitudes to the process of dehydration of the latter, 
 partly due to the greater heat of the southern latitudes and partly to 
 the greater age of the products of decomposition. He calls at- 
 tention to the /act that the red color is mostly a superficial feature, 
 varying usually from two to five feet in depth, and rarely exceeding 
 ten feet. The color is "usually reddest at, or near, the surface, 
 changing downward gradually, more rarely abruptly, through vari- 
 ous shades of orange to yellow ; while occasional complete sections 
 show the yellow changing through paler tints to gray or the color 
 of the underlying hard rocks." (Crosby-2o ://.) Russell has 
 shown that the grains of the rock are encrusted by a ferruginous 
 clay which contains both, ferric oxide and alumina. 
 
 In Nicaragua, east of the continental divide, the - red color is 
 from 3 to 10 meters deep. (Hayes-45 :/,?#, I2 9-} Tne abundant 
 vegetation here causes a transpiration of the moisture so that the 
 soil is not saturated with water.. On the* western side of Nicaragua 
 the color of the clay soil is blue, the iron being in the ferrous form. 
 Here dry seasons alternate with wet ones, and the deeply cracked 
 soil of the dry season is filled with the remains of vegetation, which 
 thus become a powerful reducing agent within the zone of weather- 
 ing. 
 
CHEMICAL WORK OF THE ATMOSPHERE 37 
 
 The red color of desert sands has frequently been remarked 
 upon. It is due to a coating of iron oxide over the rounded quartz 
 grains. Phillips (76) has determined the total amount of iron 
 oxide of the coating of the sands in the Nefud desert of Arabia to 
 be 0.21 per cent, while the -sand itself, after the solution of the 
 coating, still contained 0.28 per cent, of .iron oxide, 0.88 per cent, of 
 clay and 98.53 per cent, of silica. Walther holds that the iron of 
 the crust was also originally in the sand and has found its way to 
 the surface of the grain under the intense heating of these grains 
 from exposure to the sun. Similar conditions are rather wide- 
 spread within the arid belt of the earth, and such coating of quartz 
 sand grains may be considered as typical of desert sands, whether 
 of recent origin or preserved in older formations. 
 
 Oxidation of Organic Compounds. (Van Hise-ioo:^<5i.) In 
 the presence of water and bacteria, cellulose and other organic sub- 
 stances are oxidized with the production of a number of organic 
 acids, such as humic, ulmic, crenic, etc. (See Chapter IV.) Fur- 
 ther oxidation of these acids results in the production of carbon 
 dioxide and water. The artificial oxidation of carbon in the form of 
 coal and other combustibles has become a factor of great impor- 
 tance. It is estimated that at the present time 1 ,000,000,000 metric 
 tons of coal are oxidized each year, and this, with an average of 
 80 per cent, of carbon, would produce a total of 2,933,333,000 
 metric tons of CO 2 to be passed into the atmosphere each year. 
 This is 0.1233 per cent, of the total amount of CO 2 at present in 
 the atmosphere. Continuing this rate of consumption of coal for 
 812 years, the amount of CO 2 in the atmosphere would be doubled. 
 (Van Hise-ioo '.464.) The oxidation of nitrogen to ammonium 
 nitrites and nitrates takes place in the presence of water and with 
 the aid of bacteria. It is most marked in the tropics, where the 
 nitrates of the soil sometimes amount to 30 per cent, of the 
 mass. 
 
 HYDRATION. The chemical union of water with minerals is 
 hydration, and the results are hydroxides. So far as hydration of 
 minerals by atmospheric moisture is concerned, the process is a 
 superficial one, but within the belt of weathering of the lithosphere 
 it is a very extensive process due to the percolation of the ground 
 water. It will be further considered under that heading. A com- 
 paratively low temperature favors hydration of minerals, a temper- 
 ature above 1 10 C. at ordinary conditions of pressure will stay the 
 process or even reverse it, dehydration being the result. 
 
 KAOLIN IZATION. The ordinary effect of the atmospheric mois- 
 ture on the rocks is the attack upon the feldspars producing kaolin 
 
38 PRINCIPLES OF STRATIGRAPHY 
 
 or clay. This commonly takes place in the presence of CO 2 , the 
 formula for the alteration of orthoclase into kaolin and quartz being 
 (Van Hise-i 00:389) : 
 
 2KAlSi 3 O 8 +2H 2 O+CO 2 =H 4 Al 2 Si 2 O 9 +4SiO 2 +K 2 CO 3 . 
 
 The change to kaolin is accompanied by a volume decrease of 
 54.44 per cent. ; the change to kaolin and quartz, as in the above 
 reaction, by a decrease of 12.57 P er cent - The change by hy- 
 dration of hematite to limonite is accompanied by an increase in 
 volume of 60.72 per cent., and may be expressed by the formula : 
 2Fe 2 O 3 -j- 3H 2 O = 2Fe 2 O 3 .3H 2 O. Hydration under the atmos- 
 phere often goes on so rapidly as to suggest slaking of quicklime. 
 This has been observed by Merrill in the granitic rocks of the Dis- 
 trict of Columbia (66 :i88), and by Derby in the sedimentary rocks 
 of railway cuttings in Brazil (Branner-6). In both cases the 
 rocks exposed at the surface soon break into powder, al- 
 though in fresh exposures they may be so strong as to require 
 blasting. 
 
 DEHYDRATION. The loss of combined water or dehydration is a 
 phenomenon of regions of high temperature and low humidity. It 
 probably occurs on the largest scale in regions of alternating wet 
 and dry climate combined with high temperature. Such dehydra- 
 tion tends to change the limonite or gothite of the soil to hematite, 
 with a corresponding change in color from ochery to red. Crosby, 
 Dana, and Russell have attributed the red color of the soil of south- 
 ern regions to this process of dehydration under the influence of high 
 temperature and, to some extent, under that of age. Partial dehy- 
 dration of such compounds as the zeolites, colloidal silicic acid, 
 aluminum hydroxide, etc., may take place on a considerable scale in 
 regions of high temperature and little moisture. 
 
 CARBONATION. The atmosphere furnishes much of the CO 2 
 which combines with the bases to form carbonates, either directly or 
 indirectly through the mediation of plants. Like oxidation, it is 
 thus a superficial phenomenon. As we have seen, the oxidation 
 (decay) of the vegetable matter on the surface of the earth liber- 
 ates much CO 2 , which may be taken up by the waters entering the 
 soil and used for carbonation. The air, as already noted, contains 
 about 3.4 parts by volume in 10,000 (4.5 by weight). Rain water 
 contains from 0.22 to 0.45 per cent. (Merrill-66 :/7p) of the vol- 
 ume of the water or 0.00044 to 0.00089 P er cent - by weight. In the 
 pore spaces of soils much more CO 2 exists, as shown by the follow- 
 ing table by Boussingault and Lewy copied from Merrill (66:77$) : 
 
CHEMICAL WORK OF THE ATMOSPHERE 39 
 
 CO 2 in 10,000 parts 
 
 by weight. 
 
 Air from sandy subsoil in forest 38 
 
 Air from loamy subsoil in forest 124 
 
 Air from surface soil of forest 130 
 
 Air from surface soil of vineyard 146 
 
 Air from pasture soil 270 
 
 Air from soil rich in humus 543 
 
 The union which goes on continually of the CO 2 with the min- 
 erals of the Belt of Weathering in the earth's crust is rather an 
 accompaniment of the processes set going by the ground water, than 
 a direct activity of the atmosphere. The use of CO 2 in solution 
 of limestones likewise belongs there. On liberation in the process 
 of decarbonation, the CO 2 commonly returns to the atmosphere. 
 
 LATERIZATION. Laterite (Meigen-64; Clarke-i7) is the prod- 
 uct of rock decay in pluvial tropical regions, and is especially 
 characterized by the high content of iron oxide. Its color is mostly 
 a deep red, the iron being often so abundant as to form concretions 
 of brown or red iron ore. The depth to which the laterite extends 
 may be very great, being over 300 feet in Brazil. Its areal extent 
 is likewise great ; thus, according to the estimates of von Tillo, it 
 covers 49% of the surface of Africa, 16% of Asia and 43% of 
 South America. 
 
 Typical laterite is characterized by the formation, during the 
 process of decomposition, of a considerable amount of hydrous oxide 
 of aluminum, chiefly in the form of Hydrargillite (A1 2 O 3 .3H 2 O), 
 whereas the ordinary products of rock decay in moist temperate 
 climates are the hydrous silicates of aluminum, kaolinite (H 4 A1 2 - 
 Si 2 O 9 ), or its ferric equivalent, nontronite (H 4 Fe 2 Si 2 O 9 ). Often 
 the laterite still shows the form or structure of the gneisses or other 
 crystalline rocks from which it is derived. 
 
 The diminution or total disappearance of the silicic acid in com- 
 bination with bases is one of the characteristic features of lateriza- 
 tion. Thus the laterization of a dolerite near Bombay, India, in- 
 volves a loss of SiO 2 from 50.4% in the fresh to 0.7% in the 
 weathered, while at the same time there is a proportional increase 
 in the A1 2 O 3 from 2.2.2% in the fresh to 50.5% in the weathered 
 rock, and an increase in Fe 2 O 3 from 9.9% to 23.4%. In the 
 kaolinization of an English dolerite in South Staffordshire, the 
 change from the fresh to the altered rock includes a change in SiO 2 
 from 49.3% to 47.0%, in A1 2 O 3 from 17.4% to 18.5%, of Fe 2 O 3 
 from 2.7% (+8.3% FeO) to 14.6%, and so forth. Laterization 
 
40 PRINCIPLES OF STRATIGRAPHY 
 
 must be regarded as a further step in the decomposition of rocks, 
 the silica being separated out and deposited elsewhere as agate 
 or chalcedony. The-alkalies likewise are carried away and the sep- 
 aration and redeposition of the iron, if present, also take place at 
 an early moment. 
 
 While in the temperate climates the abundance of humus brings 
 about the reactions which result in the kaolinization of the feld- 
 spars, the absence of this humus tends to subject the feldspars to 
 the attack of non-acidulated waters, which under the influence of 
 tropical heat produce a hydrolytic separation of the silicates with 
 the formation of aluminum hydrate and alkali silicate, which sepa- 
 rates further into alkali hydroxide and free silica. 
 
 Influence of Temperature on Rock Decomposition. 
 
 The influence of temperature on the decomposition of rocks is 
 well shown by the fact that beneath the ever-moist moss cushions 
 of Finland and the northern Urals, the granite shows undecom- 
 posed surfaces, solution being the only process active here, (von 
 Richthofen^Srptf.) This is due to the prevailing high degree of 
 cold. The same thing is seen on the Kerguelen and the Crozet is- 
 lands in the South Indian Ocean, where the cold humid climate has 
 produced but little soil, whereas in tropical regions, as in the Samoan 
 Islands, a deep brilliant red soil, the terra rossa, is produced. The 
 soil of the Samoan Islands is deep and rich and is produced by the 
 decomposition of a basaltic rock similar to that of the Kerguelen 
 Islands, which there, however, is unaffected. (Russell 80.) 
 
 MOVEMENTS OF THE ATMOSPHERE. 
 
 WINDS. The movements of the atmosphere are inaugurated 
 by the inequalities in atmospheric pressure and are controlled to a 
 large extent by the rotation of the earth. The normal atmospheric 
 pressure at sea-level, or one atmosphere, is sufficient to balance the 
 weight of a column of mercury in the barometer 30 inches, or 760 
 millimeters, high. As the pressure decreases the mercury falls, as it 
 increases the mercury rises. At an elevation of 5,910 feet above sea- 
 level the mercury stands at 24 inches, at 10,550 feet at 20 inches, and 
 at 16,000 feet above sea-level it stands at 16 inches. (Davis- 
 26:13.) When air is heated it expands and so becomes lighter, 
 and the same is true when air becomes saturated with moisture. 
 Though temperature and humidity are causes of varying pressure, 
 high temperature and high humidity, producing areas of low pres- 
 sure, and conversely low temperature and humidity, producing areas 
 
MOVEMENTS OF THE ATMOSPHERE 41 
 
 of high pressure, the distribution of these over the earth's surface 
 depends on a variety of factors, and is not coincident with regions 
 of corresponding temperature and humidity. Areas of high pres- 
 sure may also be produced by the crowding of warm rising air 
 against the cooler upper layers, as is the case in the higher atmos- 
 phere of the equatorial belt. 
 
 ISOBARS. If the points of equal atmospheric pressure, due to 
 unequal heating, at a given time were united into a series of con- 
 tinuous surfaces, they would form a series of superposed planes 
 warped and dented into domes and ridges, and basins and troughs, 
 in a more or .less conformable manner. So far as the layers are 
 affected by the heating, those representing the highest pressure 
 would lie below, and the successive surfaces upward would repre- 
 sent a regularly decreasing pressure. The elevations in these sur- 
 faces cover the areas of high pressure on the earth's surface, and 
 these elevations, when localized, would be dome-like. The depres- 
 sions similarly cover the areas of low pressure. Since pressures 
 both higher and lower than 30 (30 inches of mercury) are found at 
 sea-level, this surface must be regarded as a horizontal plane cutting 
 the warped isobaric surfaces. The resulting lines of intersection are 
 the isobars, and it will be observed that, where the sea-level cuts a 
 local area of low pressure, i. e., a depressed area in the isobaric sur- 
 faces, the resulting isobars will be irregular closed curves of decreas- 
 ing value toward the center, and crowded in proportion to the steep- 
 ness of the slope or gradient, whereas a local high pressure area 
 (a convex surface) will show closed curves of increasing value 
 toward the center. Over much of the earth's surface the isobars 
 are long, more or less parallel lines conforming in a general way 
 to the direction of the parallels of latitude. The winds are the 
 movements of the atmosphere from the regions of high to those of 
 low barometric pressure, at the same level. This may be regarded 
 as a movement down the isobaric slopes, and most readily and 
 strongly down the steepest gradient. 
 
 DIRECTIONS OF MOVEMENT OF THE AIR. Since the lower air of 
 the equatorial regions is heated more than that of the polar regions 
 by the direct action of the sun (insolation), it must expand most 
 at the equator and, rising, produce a belt of low pressure around 
 the globe. Into this will flow the winds from the region of greater 
 pressure to north and south, along the bottom of the atmosphere, 
 while at the same time the rising air crowds against the higher 
 layers of the equatorial atmosphere which are not heated, and so 
 produces a surface of high pressure in the upper part of the equa- 
 torial belt, with a poleward gradient down which the air will move. 
 
42 PRINCIPLES OF STRATIGRAPHY 
 
 Thus a poleward movement of the upper air and an equatorial 
 movement of the lower air are established, with a rising of the air at 
 the equator and a descent in the polar regions. (Fig. 5.) This is the 
 fundamental type of circulation of the atmosphere. This simple type 
 of circulation is greatly modified, however, at any rate so far as the 
 lower part of the atmosphere is concerned, by various factors, chief 
 among which may be counted the rotation of the earth, the distribu- 
 tion of land and sea, the lateral pressure exerted by the expanding 
 warm air of the equatorial region, and the crowding from the 
 descent of the air in high latitudes, the subsidiary motions set going 
 
 FIG. 5. Diagrammatic section 
 of the earth and the en- 
 closing atmosphere, illus- 
 trating the fundamental 
 type of circulation in the 
 lower atmosphere, estab- 
 lished by unequal heating, 
 as a result of differences 
 in latitude. (After Salis- 
 buryPhysiography. ) 
 
 FIG. 6. Diagram showing the general 
 movements which would take place 
 in the lower air if there were no 
 rotation. (After Salisbury.) 
 
 by the aspiratory action of the larger currents, etc. Considering 
 that in each hemisphere there is, on the equatorial side, a rising 
 mass of air, which turns poleward, while on the poleward side an 
 equivalent current descends, and then flows equatorward, we have 
 an intermediate area around which this circulation takes place, and 
 these areas are belts of high pressure. Their location is approxi- 
 mately in latitudes 30 N. and S., a location determined in part 
 by the rotation of the earth. The center of this high pressure belt 
 in the northern hemisphere is in 30 N. lat., or a little less in Jan- 
 uary, with great expansion of the belt northward on the land. In 
 July this center shifts north to about lat. 35 and the belt is inter- 
 rupted on land. The reverse is true for the southern hemisphere, 
 where the summer conditions exist in January, with the center of 
 
MOVEMENTS OF THE ATMOSPHERE 
 
 43 
 
 the high pressure belt in about lat. 35 S., while in July the center 
 shifts to 30 or less. (Fig. 7.) The shifting of the center of high 
 pressure is, therefore, in harmony with the apparent motion of the 
 sun. 
 
 The general distribution of pressure areas is somewhat as fol- 
 lows : i, an equatorial belt of low pressure; 2, two belts of high 
 pressure in about latitudes 30 N. and 30 S., respectively; and 3, 
 two high latitude areas of low pressure. In general there should 
 thus be a horizontal movement of air in the lower part of the atmos- 
 phere from the extra-tropical belts of high pressure, both poleward 
 
 FIG. 7. Diagram illustrating 
 the seasonal shifting of 
 the wind zones. (After 
 Davis.) 
 
 FIG. 8. Generalized diagram illustrating 
 the deflection of the winds at the 
 bottom of the atmosphere, due to 
 rotation of the earth. (After Salis- 
 bury.) 
 
 and equatorward. (Fig. 6.) This motion is modified by the rota- 
 tion of the earth, which causes a deflection of all currents to the 
 right in the northern hemisphere and to the left in the southern. 
 (Salisbury-83 : doj, Fig. 8.) As a result, the poleward winds in 
 each hemisphere are turned toward the east, and so become westerly 
 winds, or southwest winds, in the northern hemisphere, and north- 
 west winds in the southern hemisphere. The winds blowing equa- 
 torward will be deflected to the west, and so become easterly winds, 
 northeast winds in the northern and southeast in the southern hemi- 
 sphere. These are the most constant winds and are known as the 
 trade winds. Where these currents meet at the equator, we have 
 the zone of equatorial calms, characterized chiefly by rising air 
 
44 PRINCIPLES OF STRATIGRAPHY 
 
 currents. The center of this zone shifts with the sun, but remains 
 near the equator. The prevailing winds or planetary ivinds thus 
 produced belong strictly to the lower part of the atmosphere. This 
 is especially true of the trade winds, which appear to be confined 
 to the lower 10,000 feet, as shown by observations on the Peak of 
 Teneriffe in the Canary Islands (lat. 28). The westerly winds of 
 the higher latitudes, however, coincide with the general movement 
 of the upper air, which, being poleward, is deflected to the east. 
 Thus, as shown by the movement of the upper clouds, the direction 
 of the upper winds is toward the east, and so a circumpolar whirl 
 is instituted. 
 
 Influence of Continents on Winds. 
 
 Sea-Breezes. The chief disturbing factor of the planetary winds 
 is the unequal heating of the atmosphere over the land and the 
 water, as explained on p. 31, which, in fact, is itself a cause of 
 local winds. As the land, after the rising of the sun, is more quickly 
 warmed in summer than the water, the air above the land expands 
 upward, crowding against the upper air and so producing a seaward 
 barometric gradient down which the air will flow. The resulting 
 pressure over the sea and the relief of pressure over the land will 
 cause a lower return current, the sea-breezt, to flow landward. The 
 velocity increases from the morning (8 or 9 A.M.) to the afternoon, 
 reaching its maximum at the time of greatest air temperature. At first 
 the sea-breeze blows, in general, at right angles to the coast, but 
 as the air is drawn from greater distances off-shore, it comes under 
 the influence of the deflective force of the earth's rotation and is 
 turned to the right in the northern hemisphere and to the left in the 
 southern hemisphere. Thus a sea-breeze on the eastern coast will 
 change to a southeast wind in the northern and a northeast wind in 
 the southern hemisphere, while a sea-breeze on the western coast 
 changes to a northwest and a southwest wind in the northern and 
 southern hemispheres respectively. Where the sea-breeze has the 
 direction of the prevailing winds it often increases in the afternoon 
 to the velocity of a gale. At Valparaiso "pebbles are torn up 
 from the walks and whirled about the street" and business and 
 shipping are interrupted. (Maury-63.) At evening the calm 
 suddenly succeeds the uproar. Measurements on the Massachu- 
 setts coast have shown the velocity of the sea-breeze to be at first 
 from 5 to 13 km. per hour, reaching its greatest velocity of 16 to 
 30 km. late in the afternoon. At Boston the average velocity is 
 23 km. per hour at 3 P. M. on sea-breeze days. The height of the 
 
MOVEMENTS OF THE ATMOSPHERE 
 
 45 
 
 sea-breeze at Coney Island, New York, was found to be 150 meters 
 in August, with a distinct seaward motion of the air at 200 meters. 
 At Toulon, in the middle of October, 1893, it was found to be 400 
 meters, with a distinct off-shore current at 600 meters. On the 
 coast of California its height is about 2,500 meters. 
 
 Land-Breezes. These are generally much weaker than sea- 
 breezes. They result from the more rapid cooling of the land at 
 night, involving a decrease in the pressure of the higher air and an 
 inflow of warm air from the sea. This lowers the surface pressure 
 over the sea and increases that over the land, with the result that a 
 surface current flows seaward from the land. As the land winds 
 increase in length they will fall under the deflective action of the 
 
 r* r 
 
 FIG. 9. The isobars of India for Jan- FIG. 10. Wind directions in India in 
 uary. (After Bartholomew; winter. (After Koppen; from 
 
 from Salisbury.) Salisbury.) 
 
 earth's rotation, and the breeze on the east coast will become a 
 northwest wind on the northern and a southwest wind on the south- 
 ern coast, while the land-breezes on the west coast will become 
 southeast and northeast winds, respectively. The .large lakes in like 
 manner influence the formation of land- and lake-breezes, though 
 not to the extent that oceans do. 
 
 Monsoons. These are the seasonal winds, brought about by the 
 heating of the land during the summer and the cooling during the 
 winter. These winds may be regarded as sea- and land-breezes act- 
 ing continuously for nearly half a year each, and hence attaining 
 great velocity. In the middle and higher latitudes of the northern 
 hemisphere these, seasonal winds may even entirely overcome the 
 prevailing or planetary circulation, at least so far as the lower 
 atmosphere is concerned, and may further exert a powerful influ- 
 ence on ocean currents. 
 
PRINCIPLES OF STRATIGRAPHY 
 
 A glance at a chart of isobaric lines for January shows that 
 Eurasia is a center of high pressure, and hence of air depression. 
 The Indian Ocean us an area of low pressure and hence strong con- 
 tinental winds flow southward, and by the rotation of the earth are 
 deflected to the west. Hence, over India we have northeast conti- 
 nental winds which harmonize with the trade winds and augment 
 their effectiveness. In summer, on the other hand, Eurasia is a 
 center of low pressure, centering in July over northwestern India, 
 and hence the direction of the winds is a northward one, deflected 
 to the northeast by the rotation of the earth. This is diametrically 
 opposed to the direction of the northeast trade winds, which become 
 
 FIG. IT. Isobars of India for August 
 (After Bartholomew; from Sal- 
 isbury.) 
 
 FIG. 12. Winds of India in midsum- 
 mer. (After Koppen; from Sal- 
 isbury.) 
 
 displaced by this more powerful southwest monsoon. The influ- 
 ence of these changes on the ocean currents will be noted later. 
 Spain, which lies in the zone of westerly winds, furnishes another 
 illustration of the importance of seasonal winds or monsoons. In 
 winter the central plateau is characterized by low temperature and 
 high pressure, and the winds blow outward, while in summer the 
 reverse is true, the winds blowing toward the center. The impor- 
 tance of such winds in affecting the relative humidity of the climate 
 and corresponding sedimentary deposits must not be overlooked. 
 
 CYCLONES AND ANTICYCLONES. 
 
 An area of high barometric pressure produces an anticyclonic 
 movement of the air, which passes out in all directions from it. In 
 the northern hemisphere these winds are. deflected to the right, 
 making a clockwise circulation, while in the southern hemisphere 
 deflection to the left produces a counter-clockwise circulation. Con- 
 versely, the low pressure areas are characterized by a cyclonic cir- 
 
MOVEMENTS OF THE ATMOSPHERE 47 
 
 culation, the winds flowing inward. In the northern hemisphere 
 the course of the winds is counter-clockwise, the deflection being 
 again to the right, while in the southern hemisphere the direction 
 of the circulation is clockwise, the deflection being to the left. 
 
 WHIRLWINDS AND TORNADOES. 
 
 These are due to ascending air currents of a localized character 
 caused by excessive heating of the air at one place. In desert re- 
 gions these whirls often reach a height of 1,000 feet or more, as 
 shown by the whirling columns of dust. Rains of exceptionally 
 heavy character, called cloudbursts, often result from the expan- 
 sion of the air above and the consequent cooling. Tornadoes are 
 whirlwinds of unusual strength and very small diameter. The air 
 pressure at the center of the tornado is sometimes a fourth less than 
 that of the surrounding region, while the velocity of the winds has 
 been estimated at from 400 to 500 miles per hour. Tornadoes are 
 thus of exceptionally destructive character. 
 
 THE INFLUENCE OF MOUNTAINS ON WINDS. The air move- 
 ments are locally modified to a considerable extent by mountains, 
 which give them special characters, significant in their influence on 
 climate. As an example, the foehn of Switzerland may be men- 
 tioned. (Hann-4O:j^5.) This is a warm dry wind which blows 
 down from the crest of the Alps with great violence from a south- 
 easterly, southerly, or, less frequently, a southwesterly direction, ac- 
 cording to the trend of the valleys. The main valleys which trend 
 southeast and northwest or south and north on the northern side 
 of the central chain of the Alps are the most exposed to the foehn, 
 while east and west valleys are seldom or never visited by it. The 
 greatest frequency of these winds is between Geneva and Salzburg, 
 where in the valleys the velocity of the wind, the rise in temper- 
 ature, and the dryness are the greatest. In the upper portions of 
 the valleys of the Rhine, the Linth, the Reuss, and the lower Rhone, 
 the foehn sometimes attains the velocity of a gale. As it recedes 
 from the mountains its violence decreases, and over the main part of 
 the Swiss highland and the Jura, and along the northern frontier of 
 Switzerland, it causes only a slight rise in temperature and corre- 
 sponding decrease in humidity. These winds are most frequent in 
 spring, when the snow disappears before their hot breath, and least 
 so in summer. T^n years' observations at Innsbruck give the aver- 
 age number of foehn wind days for spring 17, summer 5, autumn 
 II. i, and winter 9.5 ; a total of 42.6 for the year. 
 
 While (40:349) the foehn is blowing north of the Alps, there 
 
4 8 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 is a calm on their southern side, with little if any increase in tem- 
 perature, and with high humidity. In most cases also, a few hours 
 after the foehn has begun to blow, rain and snow begin to fall on 
 the southern slopes and the summits of the Alps, the precipitation 
 being often extraordinarily heavy; exceptional precipitation on the 
 south often coinciding with extreme violence of the foehn on the 
 north. The following table, copied from Hann, shows the average 
 weather conditions which prevailed simultaneously at Milan, on the 
 southern side, at Bludenz, Austria, in a tributary alpine valley of the 
 Rhine, and at Stuttgart in the northern plains, during twenty winter 
 days on which there were foehn winds. (40:550.) 
 
 
 Temperature 
 
 Relative humidity 
 
 
 
 in degrees C. 
 
 in per cent. 
 
 
 Station 
 
 
 
 Weather 
 
 
 A.M. 
 
 P.M. 
 
 Eve. 
 
 A.M. 
 
 P.M. 
 
 Eve. 
 
 
 Milan 
 
 3-2 
 
 5-i 
 
 3-9 
 
 96 
 
 93 
 
 96 
 
 Rain on 1 6 days. 
 
 
 
 
 
 
 
 
 
 Variable 
 
 
 
 
 
 
 
 
 winds. 
 
 Bludenz 
 
 ii i 
 
 14. O 
 
 ii ^ 
 
 2Q 
 
 22 
 
 28 
 
 S E 5-8 foehn 
 
 Stuttgart 
 
 i 4 
 
 8 8 
 
 c o 
 
 84 
 
 72 
 
 81 
 
 Rain on lodays 
 
 
 
 
 
 
 
 
 Variable 
 
 
 
 
 
 
 
 
 winds. 
 
 The high temperature of the wind and its dryness do not exist 
 on the alpine summits, but are acquired during the descent on the 
 northern side. They are not imported from the region to the south 
 of the Alps. This is shown by the observations on the weather 
 along the St. Gotthard Pass during the foehn of January 3i-Feb- 
 ruary I, 1869, as shown in the following table. (Hann~4o:j5O.) 
 
 Station 
 
 Altitude 
 (meters) 
 
 Temperature, 
 degrees C. 
 
 Relative 
 humidity, 
 per cent. 
 
 Wind 
 
 Bellinzona 
 
 22Q 
 
 + 1 o 
 
 80 
 
 N. (rain) 
 
 San Vittore 
 
 26Q 
 
 + 2 q 
 
 85 
 
 S and S W 
 
 Airolo . 
 
 1,172 
 
 -4- O Q 
 
 
 N and S 
 
 St Gotthard 
 
 2 IOO 
 
 4 5 
 
 
 S 2-1 
 
 Andermatt. . . . 
 
 1,448 
 
 4-25 
 
 
 S W 2 
 
 Altdorf 
 
 454 
 
 4-14. 5 
 
 28 
 
 S (Foehn). 
 
 
 
 
 
 
MOVEMENTS OF THE ATMOSPHERE 49 
 
 The foehn winds are explained by the development of south- 
 erly winds which flow toward a region of low pressure in western 
 Europe, because of the advance of barometric depressions or storm 
 centers from the Atlantic. The air of the Alpine valleys is likewise 
 drawn toward this region, and to replace it the air rushes in from 
 the summits, the wall of the Alps preventing any direct supply, and 
 keeping the air calm on the south side of the Alps. Air carried up 
 and expanding is cooled at the rate of i C. for every 100 meters, 
 this loss of heat being the thermal equivalent of the work done by 
 the air in increasing its volume against the pressure of the sur- 
 rounding air. Conversely, air drawn down from a region of less to 
 one of greater pressure will be compressed, and at the same time 
 warmed at the rate of i C. for every 100 meters (or more ex- 
 actly 0.99 C. for every 100 m.). Since the average rate of de- 
 crease of temperature with increase in altitude is in winter 0.45 C. 
 for every 100 meters, the air coming down from the mountains 
 increases in temperature 0.54 C. in every 100 meters. This would 
 give 13.5 C. for a descent of 2,500 meters. The increase in tem- 
 perature readily explains the fall in relative humidity, since the 
 capacity of the air for moisture is greatly increased with but slight 
 actual additions. Foehn winds of less magnitude sometimes occur 
 on the south side of the Alps when the conditions are reversed. 
 Similar winds have been recorded from the western coast of Green- 
 land, where a warm, dry easterly or southeasterly wind blows across 
 the ice-covered interior of Greenland and down onto the fiords of 
 the western coast, raising the temperature on the average 12 to 
 20 C. above the mean in winter, and about 11 in spring and 
 autumn. Iceland, New Zealand, Japan, and other countries have 
 foehn winds, and the chinook wind, which blows eastward from the 
 Rocky Mountains of North America in Wyoming, Montana, Al- 
 berta, and the Saskatchewan country, has a similar origin. The 
 siroccos of Sicily (Palermo), the Algerian coast, the north coast "of 
 Spain, etc., are other examples of foehn winds, but the sirocco of 
 Italy and the Dalmatian coast is a damp, muggy south or southeast 
 wind in striking contrast with the cold, dry northerly winds of 
 that region. These winds, the bora, rushing down from the high 
 plateau of the Istrian and Dalmatian coasts and then down the 
 southerly slope of the Caucasus to the Black Sea (at Novors- 
 siisk, Russia), are ice-cold blasts which apparently are not warmed 
 by their descent. This is only apparent, however, since the initial 
 temperature of these winds' is so low that, in spite of the increase 
 during the descent, they reach the warm coast of the Adriatic or 
 the Black Sea as a cold blast. The bora occurs only where the 
 
50 PRINCIPLES OF STRATIGRAPHY 
 
 back country is very cold as compared with the coast. The mistral, 
 a stormy northwest wind blowing from the Cevennes in southern 
 France, has a similar origin, descending from the cold central plateau 
 to the warm Mediterranean coast. 
 
 Mountain and Valley Winds. Where the general air movements 
 are not too strong, a regular daily alternation of winds is observ- 
 able in mountain regions, blowing up the valleys by day and down 
 by night. Though not confined to valleys on the mountain sides, 
 they attain their best development there. In the Himalayas, the 
 winds blow up the valleys from 9 A. M. to 9 P. M. and down the 
 remainder of the night. Where the valleys open out into the plains, 
 the winds often blow with great violence, particularly in winter. 
 The upward flow during the day is explained by the increase of 
 pressure at points distant from the slope, owing to the warming and 
 rising of the air beneath these points and the expansion of the air 
 at the same level on the mountain slope. This causes a movement 
 of the air toward the mountain which must result in an upward 
 flow of the current on the mountain side. At night the cool wind 
 naturally flows down the slope, attaining its greatest velocity where 
 it leaves narrow, cool valleys and enters broader, well-warmed ones. 
 
 VELOCITIES OF WIND. The velocity of the wind current varies 
 enormously, from the frightful rate of 400 or 500 miles per hour 
 obtaining in some tornadoes, to the gentle zephyr breeze of a frac- 
 tion of a mile per hour. The average velocity for the winds* of the 
 United States has been estimated at about 9.5 miles per hour (4.25 
 meters per second), and for Europe 10.3 miles per hour (4.60 
 meters per second). It is greater over the sea than over the land, 
 where friction retards it, and greater in the upper air than at the 
 earth's surface. The average velocity of the wind is also greatest 
 in about latitude 50. The following wind scale gives the velocities 
 of the various types of wind according to Hann (40) : 
 
 Number 
 
 Name 
 
 Velocity 
 
 Meters per second 
 
 Miles per hour 
 
 o 
 
 i 
 
 2 
 
 3 
 
 Calm. 
 Light air. 
 Light breeze. 
 Gentle breeze. 
 
 
 
 i-7 
 3-i 
 
 4.8 
 
 4.0 
 7.0 
 10.5 
 
 * For comparison see velocities of streams given on p. 245. 
 
MOVEMENTS OF THE ATMOSPHERE 
 
 
 
 Velocity 
 
 Number 
 
 Name 
 
 
 
 
 
 Meters per second 
 
 Miles per hour 
 
 4 
 
 Moderate breeze, 
 
 6-7 
 
 15.0 
 
 5 
 
 Fresh breeze. 
 
 8.8 
 
 20.0 
 
 6 
 
 Strong breeze. 
 
 10.7 
 
 24.0 
 
 7 
 
 Moderate gale. 
 
 12.9 
 
 29.0 
 
 8 
 
 Fresh gale. 
 
 15-4 
 
 34-5 
 
 9 
 
 Strong gale. 
 
 18.0 
 
 40.0 . 
 
 10 
 
 Whole gale. 
 
 21.0 
 
 47.0 
 
 ii 
 
 Storm. 
 
 30.0 
 
 67.0 
 
 12 
 
 ^ Hurricane. 
 
 50.0 
 
 112. 
 
 The following table by Mohn (67 : 121) gives the range in 
 velocities and also the corresponding pressure. The values are 
 somewhat different from those in the table by Hann. 
 
 Type of wind 
 
 Velocity in 
 meters 
 per second 
 
 Pressure in kilo- 
 grams per 
 square meter 
 
 o. Calm 
 
 o to o 5 
 
 o to o 15 
 
 i. Light 
 
 O 5 to 4. O 
 
 o 15 to i 87 
 
 2. Moderate 
 
 4 to 7 
 
 I 87 to 5.96 
 
 3. Fresh 
 
 7 to 1 1 
 
 5Q6 to 1 5 27 
 
 4. Strong 
 
 ii to 1 7 
 
 1C 27 to 1,4. T,^ 
 
 5. Storm 
 
 17 to 28 
 
 1A. 1^ to Q 6 . 4. 
 
 6. Hurricane . 
 
 above 28 
 
 above OS 4. 
 
 
 
 
 EOLATION OR MECHANICAL WORK OF THE 
 ATMOSPHERE. 
 
 The mechanical work of the wind is expressed by the term eola- 
 tion, which is the process of the earth sculpture by wind, the scour- 
 ing by wind-driven sand, dust, and other substances, and the 
 transportation and deposition of rock material by wind. It may be 
 summarized as wind erosion or corrosion, as wind transportation or 
 deflation, and as eolian sedimentation. The last will be especially 
 dealt with in Chapter XIII. 
 
52 PRINCIPLES OF STRATIGRAPHY 
 
 WIND EROSION AND TRANSLOCATION. 
 
 Walther (102, 104) has repeatedly insisted upon the importance 
 of distinguishing the twofold process of denudation performed by 
 the wind, namely, corrasion, or the abrasive proces-s, and deflation, 
 or the process of denuding by removal of mineral particles loosened 
 by weathering. The latter is by far the more effective process, and 
 applies not only to the immediate products of weathering, but to 
 all the loose material of the earth's surface, fine enough to be sub- 
 ject to wind transportation. 
 
 CORRASION. Wind corrasion is accomplished by means of the 
 material carried by the wind. Sand grains are tlje commonest and 
 most effective agent in this respect, though blown snow crystals have 
 a similar though less violent effect. Wind-corraded rocks usually 
 have a smooth and highly polished surface, which, however, is fre- 
 quently irregular, with the harder minerals or bands projecting, or 
 with cavities due to corrasion of the soft parts. Hard limestones 
 often have their otherwise obscure bedding emphasized by the wear- 
 ing of the softer layers; while hard fossils or concretions will ap- 
 pear in relief by the filing away of the surrounding softer rock. In 
 the Libyan desert the blocks of Tertiary Operculina limestone are 
 corraded by the wind in such a manner that the somewhat harder 
 Foraminifera are filed out in relief, each resting on a pyramid or a 
 needle of limestone, the latter often 2 cm. long, and sometimes 
 giving the rock the aspect of a pincushion stuck full of long pins. 
 (Waltrfer-io6: 414.) On the Libyan limestone plateau, where the 
 surface is formed by an exceptionally hard siliceous lower Eocenic 
 limestone bed, wind-carved furrows have been discovered, which 
 extend in a N.N.W. S.S.E. direction and vary in depth up to a 
 meter. These were carved by the sand-laden winds which for thou- 
 sands of years swept across this surface, with little or no variation 
 of direction. (Walther-io6: 413, and Martonne-62, pi. XXXIII, 
 b.) Similar furrows, a foot or more wide, but shallow, occur in 
 the surface of the late Siluric Anderdon limestone of western On- 
 tario, and probably represent wind erosion under desert conditions 
 during Lower Devonic time. They are covered with Middle De- 
 vonic sands, both siliceous and calcareous, about 12 feet thick, ap- 
 parently free from fossils, and probably representing the somewhat 
 reworked calcareous sands drifted across the old limestone plateau. 
 These lower beds, chiefly brown dolomitic rocks, fill the fissures 
 above referred to. (Grabau and Sherzer 36: 44.) The yardangs 
 of Central Asia (47) are groove-like hollows, sculptured out of ar- 
 
WIND CORRASION 
 
 53 
 
 gillaceous rock surfaces, and separated by more or less fluted 
 ridges. (Fig. 13.) 
 
 Such structures in an early stage are also found in the region 
 near Biggs, Oregon. What may be a similar structure is seen in 
 the contact of the Upper Cambric Olenus limestones with the high- 
 est bed of the Ceratopyge limestone in central Sweden, the lower 
 
 FIG. 13. Diagrammatic section of yardangs of Central Asia, the deeper de- 
 pressions filled by sand. (After Sven Hedin.) 
 
 limestone surface being grooved irregularly, sometimes for a depth 
 o*f a few centimeters, and the succeeding limestone filling the 
 crevices. Other eolian erosion features are seen in the Bad Land 
 topography of western North America, the remarkable sandstone 
 pillars of the Bastei, in Saxony, the equally remarkable stone pillars 
 
 . 
 
 FIG. 14. Erosion columns in sandstone. The result of eolian erosion. 
 Monument Park, Colorado. (After Hayden.) 
 
 of Tertiary sandstone, capped by harder iron-cemented layers, found 
 in Monument Park, Colorado, and the similar erosion pillars or 
 gour (singular gar a) of Egypt. In part these are probably due to 
 deflation of material previously disintegrated. (Fig. 14.) 
 
 The natural sand-blast in the San Bernardino Pass, in southern 
 California, is so powerful that the modern telegraph poles of the 
 Southern Pacific Railway are greatly damaged and have to be pro- 
 
54 PRINCIPLES OF STRATIGRAPHY 
 
 tected by piles of rock and supplementary pieces placed on the wind- 
 ward side of the affected poles. The telegraph wires of the Trans- 
 Caspian Railway -between Aidin and Bala-ischem had to be renewed 
 after eleven years, because their diameter had been diminished one- 
 half by the sand-blast corrasion. (Walther-iO4: 52.) Even dust 
 from the city streets blown against the tombstones of cemeteries 
 will in time efface their inscriptions. ( Eggleston-28 : 654-658. ) 
 
 Facetted Pebbles. A highly significant and interesting result of 
 sand corrasion on loose stones is the facetted pebble or windkanter. 
 This generally has three or more faces ground flat, by the sand 
 blown over it at different times, and these faces meet in sharp 
 angles. These angles do not represent the direction of the wind 
 at the time of cutting, but rather the more or less accidental meeting 
 of faces cut at different times. Walther (106) describes "Ein- 
 kanter," Irregular "Windkanter," "Dreikanter," and "Parallel- 
 kanter" from the Libyan desert, all formed by wind blowing in one 
 direction only. The einkanter are arranged with the ridge at right 
 angles to the wind direction, the single wind-cut face being nor- 
 mal to and inclined toward that direction. This Walther regards 
 as the normal type. The polyfacetted condition is brought about 
 by the fact that the sand-laden wind-currents along the bottom of 
 the atmosphere wind in and out among the pebbles strewn over the 
 surface, cutting one here and another there, and so producing faces 
 and angles which have no definite orientation. In some cases the 
 undermining of a pebble on which one face has been cut and its sub- 
 sequent rolling over, expose a new surface to the wind. (Davis- 
 24.) Of between 300 and 400 specimens observed by Wade (101) 
 in the eastern desert of Egypt, 78 per cent, were set at right angles 
 to the direction of the wind. He found the ridge to be more gener- 
 ally a curved one, and the face presented to the wind not a plane sur- 
 face, but a gently curved one. Measurements taken on over fifty 
 specimens showed that this surface makes an angle with the vertical, 
 which varies between 40 and 50, most usually approximating 
 45. Wade determined to his own satisfaction that the air currents 
 were driven upward, carrying the sand against the pebble face. 
 Undermining and consequent change of position of the pebble were 
 found to be the cause of the cutting of the several facets, as postu- 
 lated by Davis. 
 
 The presence of these pebbles in undisturbed condition in older 
 formations is a reliable indication of the subaerial origin of the 
 deposit. Davis (24) has used them to prove the undisturbed sub- 
 aerial character of the apron plains of Cape Cod. They have also 
 been found in the pre-Cambric Torridon sandstone of Scotland, the 
 
DEFLATION 
 
 55 
 
 basal Cambric sands of Sweden, the Rothliegende of Germany, the 
 Buntersandstein of Thuringia and elsewhere. 
 
 DEFLATION. This is by far the most important work of the wind, 
 and its geological significance can scarcely be overestimated. The 
 lifting of the material from the surface is largely the work of 
 eddies and irregularities of movement of the wind, including many 
 conflicting cross-currents. (Langley-57; 58.) The most important 
 are, of course, the whirling eddies of whirlwinds and tornadoes, but 
 many minor currents, due, in part, at least to the irregularities of 
 the surface are active in lifting the dust and fine sand. The ordi- 
 nary convection currents of the atmosphere carry this finer material 
 up to great heights. The force (Free-33 : 35) which moves the par- 
 ticle is due to the direct impact of the wind plus the friction along 
 its surface. The force of the direct impact varies with the velocity 
 of the wind, and for a given velocity with the cross-section of the 
 particle in the plane perpendicular to the direction of the wind, as 
 well as with the orientation of the particle, and it is of course most 
 efficient when a smooth plane is opposed to the wind. The resistance 
 of the particle varies with its mass, i. e., its size and specific gravity, 
 and to some extent its form. In general the velocity of the wind 
 necessary to carry a spherical particle of given specific gravity 
 varies as the square of the radius, and conversely the radius of a 
 particle which can be supported by wind varies as the square root 
 of the velocity. Thoulet (94; 95) found that a uniform upward 
 current of air will keep suspended quartz grains, the size of which 
 varied with the velocity as follows : 
 
 Velocity in meters per second 
 
 Diameter of 
 quartz grain 
 in mm. 
 
 o. so. . 
 
 0.04 
 
 I OO . 
 
 o 08 
 
 2.OO 
 
 o. 16 
 
 * OO 
 
 o 25 
 
 4. ^O 
 
 o. ^5 
 
 S.oo. . 
 
 0.41 
 
 6 oo 
 
 O.4Q 
 
 7.OO. . 
 
 0.57 
 
 8 oo 
 
 O.6S 
 
 Q.OO 
 
 0.73 
 
 10 . oo 
 
 0.81 
 
 1 1 . OO 
 
 0.89 
 
 12. OO " 
 
 0.97 
 
 11. OO. 
 
 i .05 
 
 
 
56 . PRINCIPLES OF STRATIGRAPHY 
 
 From this Free deduced the formula V Kr, where K is a con- 
 stant for the conditions of experiment and r the radius of the 
 particle. 
 
 From numerous measurements Udden concluded that the "aver- 
 age largest size of quartz particles that can be sustained in the air 
 by ordinary strong winds is about o.i mm. in diameter" (Udden- 
 97), but the largest particle that can be transported (not held in 
 suspension) is nearer 2 mm. in diameter, while gravel the size of 
 peas may in rare cases be carried along by the wind. This, how- 
 ever, represents the limit of ordinary deflation. (Walther-iO4: 
 97.) Much larger fragments, nevertheless, are rolled along by the 
 wind, and sometimes even lifted and carried for some distance. 
 Stones as large as a man's fist have been observed blown along by 
 wind in the deserts of Sahara (Rohlfs), and Gobi (Przhevalsky), 
 and Pumpelli saw stones 2 inches across blown by a storm in Tur- 
 kestan. (Pumpelli-77 :joj.) A wind-blown pebble 2 cm. in di- 
 ameter was collected from the snows of Ben Nevis after a severe 
 storm. (Murray and Renard-69 : 590, also Theobold-93 : 534- 
 535.) A remarkable case is reported by St. Meunier (66a : 440; 73 : 
 247-248) of a "rain" of limestone pebbles, whose diameter ranged 
 from 25 to 35 mm., which fell on June 6, 1891, in the Department of 
 Aube, France. These pebbles are believed to have been transported 
 150 km. Other pebble falls are recorded by various observers. Or- 
 ganisms, often of some size, are also known among the remark- 
 able "solid" rains. Thus a fall of lichens was reported from Persia 
 by De Candolle. Falls of small live fish have been reported from 
 Madras, India, and were also observed at Singapore, in the Malay 
 peninsula; at Winter Park, Florida, in June, 1893; and at Tillers 
 Ferry, South Carolina, in 1901. A turtle 6 inches by 8 inches, and a 
 stone fragment y 2 inch by ^4 inch, both incased in ice, fell at Vicks- 
 burg, Mississippi, on May n, 1894. (Abbe cited by Free-33-) 
 
 Sokolow gives the following table of quartz sand grains moved 
 by varying wind velocities, as derived from his experiments 
 
 Strength of wind in meters Maximum diameter of 
 
 per second. sand grains per mm. 
 
 4-5 6.7 ...................................... 0.25 
 
 6.78.4 ...................................... 0.5 
 
 9.8 11.4 ...................................... i.o 
 
 11.413.0 ..................... . ................ 1.5 
 
 These results are only approximate. Sokolow holds that eolian 
 deposits with grains above 4 to 5 mm. in diameter are not known. 
 
 ' 
 
DEFLATION 57 
 
 Character and Amount of Deflational Denudation. On the sea- 
 shore and in the deserts all the dust and fine sand grains are blown 
 away, leaving only the coarser sands and the rock fragments. The 
 latter are characteristic of the stony desert, the Hamada type, which 
 is found in many deserts the world over. The pebbles are generally 
 smooth from wind wear, and may resemble water-laid deposits. 
 That some pavements of this kind are due to water work is be- 
 lieved to be the case by some observers ( Free-33 : j^, and works 
 cited there). Not infrequently the surface of the pebbles is covered 
 with the brown desert varnish, indicating that corrasion has come to 
 an end for the time being. The desert varnish is a brown to black, 
 often highly polished coating of iron oxide or hydrate, or of man- 
 ganese oxide, which covers the stones and ledges of arid regions. 
 The amount of the coating, which is seldom more than a small 
 fraction of a millimeter thick, increases with the increase in aridity. 
 Often it is developed only on the upper, exposed side of the stones 
 of the Hamada, the under surfaces remaining uncoated. Chem- 
 ically, the material forming the rind is a mixture varying from pure 
 iron oxide to nearly pure manganese oxide, with all intermediate 
 combinations. The formation of the rind begins with the absorp- 
 tion of moisture by the porous rock and the formation of various 
 compounds, through the substances present in the rock or derived 
 from without. The solutions formed are drawn to the surface by 
 capillarity, and under the intense heat of the desert they evaporate, 
 leaving the coating of oxide upon the surface. What appears to be 
 a case of desert varnish in Palaeozoic rocks is found in a layer of 
 pebbles at the base of the Siluric iron ore deposit of Wisconsin. 
 These rest upon an eroded surface of Ordovicic shale, and are suc- 
 ceeded by the iron ore. 
 
 A marked characteristic of many desert surfaces is the wealth of 
 fossil organisms which are left behind after the disintegration and 
 deflation of the rock mass originally containing them. Even if the 
 original rock is only sparingly fossiliferous, a long-continued defla- 
 tion will result in the concentration of a considerable number of 
 specimens on the desert surfaces. (Walther-iO4: j#.) 
 
 Extensive eolian erosion, referable almost entirely to deflation 
 of materials loosened by other agencies, is shown in the plateau 
 country of western North America. The Jurassic sandstone of 
 Utah shows this especially well, numerous isolated remnants or 
 buttes testifying to the great extent of this work. The buttes them- 
 selves often show striking features, as in the case of Casa Colorado 
 and Looking Glass Rock in Dry Valley, Utah. In the latter a large 
 alcove or cavern has been hollowed out by the wind, a feature not 
 
58 PRINCIPLES OF STRATIGRAPHY 
 
 uncommon in these sandstones where some parts are very friable. 
 (Cross-2i : pi. 4, fig. 2.) Hollows of this type are very common in 
 sandstones, especially Vhere concretionary segregation of this iron 
 oxide has left some of the sands in an unconsolidated condition. 
 (See Chapter XVII.) Deflational erosion of rocks in moist tem- 
 perate regions is shown by the classical example of the Heidelberg 
 Schloss. The western tower of this castle, built in 1533 and partly 
 blown up in 1689, shows a narrow passageway, through which the 
 wind blows with considerable force. The wall of this passage is 
 built of heavy sandstone blocks, some of which have been hollowed 
 out for a depth of 10 cm., entirely by the blowing away of the 
 disintegrated sand grains, the situation being such as to exclude 
 corrasion. 
 
 Eolian erosion over wide areas is well shown in the Kalahari 
 Desert of South Africa, where, according to Passarge, extensive 
 plains have been produced by this agent, the amount of deflational 
 work being often indicated by the butte-like "Inselberge" still ris- 
 ing above the plain as unconsumed remnants. (Bornhardt-8 :J7.) 
 A similar origin has been advocated for a part at least of the desert 
 plains or "bolsons" of southwestern United States. (Hill-5o; 
 Keyes-56.) That some of the extensive depressions of the earth's 
 crust occupied by deserts owe their character to deflational work of 
 the wind seems quite certain. In the Inselberg-landscape of South 
 Africa the country rock is a crystalline rock, mostly biotite gneiss, 
 biotite muscovite gneiss, garnet gneiss, and amphibolite. The resid- 
 ual peaks are harder rocks, chiefly pegmatite dikes and other rocks 
 high in quartz. The individual Inselberge are separated by dis- 
 tances varying up to 25 km. and over; the differences in height of 
 various parts of this plain are 'not great, 80 meters having been 
 found in a distance of over 150 km. Sometimes the floor of the 
 plain seems as smooth as a table top, the minor depressions being 
 filled in by eolian deposits. Near the Inselberge, sometimes at their 
 very bases, are heavy masses of talus, consisting of the products of 
 recent rock decay, inaugurated probably by a change in climate to 
 a more pluvial one. (Hecker-46.) 
 
 Distance of Eolian Transportation. Only the finest dust par- 
 ticles remain more or less permanently suspended in the air, or until 
 washed out by rains. Most of the wind-borne particles travel by 
 means of leaps and bounds of varying magnitude.. The length 
 of the leap depends upon the size and shape of the particles, the wind 
 velocity, and to some extent on the topography of the country. 
 From a number of analyses of wind-transported material Udden has 
 constructed the following table of approximate maximum distances 
 
EOLIAN TRANSPORTATION 
 
 59 
 
 over which quartz particles of different dimensions may be lifted by 
 moderately strong winds in single leaps. (Udden~99: 65.) 
 
 Gravel (diameter from 8-1 mm.)* A few.feet. 
 
 Coarse and medium sand (diameter i-J^ mm. 1-0.25) Several rods. 
 
 Fine sand (diameter i/4- 1 /^ mm. 0.25 0.125) Less than a mile. 
 
 Very fine sand (diameter i^-Vio mm - 0.125-0.0625) A few miles. 
 
 Coarse dust (diameter I/LQ -1/32 mm. 0.0625-0.03125) 200 miles. 
 
 Medium dust (diameter %2~%4 mm - 0.03125-0.015625).. . 1,000 miles. 
 
 Fine dust (diameter % 4 mm. 0.015625 and less) Around the globe. 
 
 These theoretical distances are probably never realized, owing to 
 the complex character of the wind currents and other factors. 
 
 Dust storms may often cover extensive areas and be the means of 
 distant transportation of materials. Udden (98:196) records 
 storms extending 300 and 400 miles in their longest observed direc- 
 tion. A Chinese dust storm is known to have existed simultane- 
 ously from Hankow to Chin-kiang, or over a distance of more than 
 450 miles, and for an unknown distance beyond in either direction. 
 (Guppy-38.) On February 6 and 7, 1895, dust fell in Mis- 
 souri which must have come from western Kansas and Nebraska, 
 since all the intervening country was covered with snow and ice. 
 On April 2, 1892, a yellow dust carried from the interior of China 
 fell on the deck of a ship 95 miles west by south of Nagasaki, at 
 least 1,000 miles from its source; and dust storms from Australia 
 have sometimes reached New Zealand, having been transported 
 some 1,500 miles. Dust believed to have been brought from the 
 Sahara has been observed in northern Germany, and in England, 
 some 2,000 miles distant. This is the so-called sirocco or trade- 
 wind dust, which, however, has little or no relation to the true si- 
 rocco. Volcanic dust carried to the upper air is likewise trans- 
 ported over great distances. Thus the dust formed by the eruption 
 of Krakatoa in 1883 was projected so high into the air that, caught 
 by the currents of the upper air, it was carried around the world 
 repeatedly before settling. Some of this dust is said to have com- 
 pleted the circuit of the earth in 15 days. (Chamberlin and Salis- 
 bury-i6 :<?/.) This dust settled slowly all over the world and 
 became incorporated in all contemporaneous deposits. Beds of vol- 
 canic dust in places 30 feet thick are known in Kansas and Ne- 
 braska, hundreds of miles distant from volcanoes which could have 
 supplied the material. ( Salisbury-82. ) The following summary of 
 volcanic dust transport is taken from Free (33:149-150) : "Vol- 
 canic dust from Iceland has several times fallen in Scandinavia, in 
 
 * See table of sizes of sand grains, etc., in Chapter VI, page 287. 
 
60 PRINCIPLES OF STRATIGRAPHY 
 
 northern Great Britain, and in Holland. Dust from Tomboro fell 
 on Sumatra, a thousand miles away. Krakatoa ashes fell inches 
 deep at distances of 'nearly 1,000 miles from the volcano, and small 
 quantities fell even in Holland. Dust from Colima in Mexico fell 
 in February and March, 1903, at points over 200 miles north and 
 east of the volcano, and the ash from Santa Maria in Guatemala in 
 October, 1902, covered all the northern part of that country and 
 most of the states of Tabasco, Veracruz, and Oaxaca in southern 
 Mexico. At Tapachula, 40 miles away, the ashes were 19.5 centi- 
 meters thick. 
 
 "Ash from Coseguina in Nicaragua in 1835 covered an area of 
 1,500,000 square miles and even reached Jamaica, more than 750 
 miles away. The dust from the eruption of Cotopaxi in Equador 
 in 1877 fell at Guayaquil, 150 miles away, to the amount of 315 
 kilograms on every square kilometer during the first thirty hours 
 of the fall. Once 209 kilograms fell in twelve hours. The dust 
 ejected by this same volcano in 1888 amounted to more than 2,000,- 
 ooo tons. On this occasion the dust cloud traveled 85 miles in six 
 hours. At the eruption of Tarawera in New Zealand in 1886, 
 1,960,000,000 cubic yards of dust were discharged in five or six hours 
 and covered a land area of over 6,000 square miles. Much more 
 dust fell into the sea. Dust from the eruptions of La Soufriere and 
 Pelee in 1902 fell plentifully all over the West Indies and especially 
 at Barbados, 130 miles from Pelee and 225 from La Soufriere. 
 Dust from the eruption of Pelee in 1812 is said to have reached the 
 Azores. Dust from Vesuvius has been observed in Greece, in 
 France, and in Austria." 
 
 Volume of Dust Falls. In 1863 a rain of dust occurred on the 
 Canary Islands, the volume of which was estimated at 3,944,000 
 cubic meters. (Fritsch-34: 212.) Free (33:9$) reduces this to 
 5,900,000,000 kgm. or 6,500,000 tons. The dust fall in Eng- 
 land on February 22, 1903, is said to have furnished 9,100,000,000 
 kilograms or 10,000,000 tons of material, but the data are not wholly 
 reliable. The great dust storm of March 9-12, 1901, however, 
 brought to Europe 1,782,200,000 kilograms or 1,960,420 tons of dust, 
 while North Africa received 1,500,000,000 kilograms or 1,650,000 
 tons. This dust deposit thus covered at least 300,000 square miles 
 of land surface, and 170,000 square miles of ocean, and, accord- 
 ing to Walther, traveled in part at least a distance of 4,000 kilo- 
 meters or 2,500 miles. Altogether 3,282,200,000 kilograms or 
 3, "6 1 0,420 tons of dust fell. For the European area (437,500 square 
 kilometers or 168,437 square miles), the fall averaged a layer of 
 dust 0.239 mm. thick. Assuming the usual dust falls together with 
 
EOLIAN TRANSPORTATION 61 
 
 the exceptional ones to average this amount for every period of five 
 years, we would get a deposit 4.78 mm. thick in a century, while dur- 
 ing the three thousand odd years during which such storms have 
 been recorded, the total amount would be 143.4 mm. or over $ l / 2 
 inches of material brought from the desert. Dust fogs are charac- 
 teristic of the Red Sea at certain seasons and are known on parts 
 of the Atlantic reached by the winds from the desert. If dust-laden 
 winds reach a district of more rainfall, or if their velocity is dimin- 
 ished, they will be relieved of their burden, and the dust will settle. 
 This occurs in the steppe surrounding the desert, where the further 
 transport of the material is in large measure prevented by the grassy 
 vegetation. Thus the surface of the steppe is gradually built up by 
 deposits of fine material derived often from great distances. Skele- 
 tons of terrestrial animals may readily be buried where accumulation 
 is rapid, while along the water courses leaves and shells of fresh 
 water or land molluscs may become entombed. The loess, discussed 
 more at length below, is believed to be an accumulation of this sort, 
 and older deposits of this type are coming to be more generally 
 recognized. 
 
 Sorting and Rounding of Sand Grains by Wind. The sands 
 picked up by the winds on the shores ordinarily travel only at a 
 slow and probably constantly diminishing rate inland. But the 
 finer dust particles are blown away rapidly. If the sand consists of 
 or contains minerals which are readily ground into dust, this dust 
 will be blown away and the destructible minerals are thus removed 
 from the dune sand. It is due to this destruction of other minerals 
 that the dune sand of some coasts consists almost entirely of pure 
 quartz grains. 
 
 During this movement, these dry sand particles are not only ac- 
 tively engaged in abrading whatever rocks or other objects are in 
 their path, but they themselves are well rounded through mutual 
 attrition. So perfect is this rounding of the grains in some wind- 
 blown sands that even the lens will reveal no irregularities. (Wal- 
 ther-iO3 : 795.) Since particles o.i mm. or less in diameter are not 
 reduced by mutual attrition in water, it follows that rounded grains 
 below this size must in general be 'regarded as wind-worn grains. 
 (The relative efficacy of wind and water as agents of rounding will 
 be discussed in Chapter V.) The glassy character is, moreover, 
 dimmed by this attrition, and the surface of the grains takes on the 
 character of ground glass. Such sands may later be worked over 
 by the waves of a transgressing sea or lake, and so become well- 
 stratified waterlaid deposits with remains of aquatic organisms. Not 
 infrequently shells are driven far up on the shore by the winds, 
 
62 PRINCIPLES OF STRATIGRAPHY 
 
 and become buried in the sand dunes. (See, further, Chapter 
 XIII.) Wind is a better sorter than water, hence pure quartz sands 
 will be more commonly formed from crystalline rocks in arid 
 regions. When the rock destroyed is a marine or other sandstone, 
 the resulting sand requires comparatively little purification. 
 
 The sands of the Libyan desert are believed to have been de- 
 rived from the destruction of the Nubian sandstone to the south, 
 whence they were transported by wind to their present position on 
 the Cretacic limestone plateaus of the desert. Grains of lime rock 
 from the underlying foraminiferal limestones are noted in this sand, 
 but otherwise it is pure quartz and well assorted as to size. 
 
 CONDENSATION AND PRECIPITATION OF AT- 
 MOSPHERIC MOISTURE.* 
 
 The moisture of the atmosphere is condensed and precipitated in 
 the form of frost or of clouds and fogs, rain, snow, or hail. Air is 
 brought to the point of condensation of its moisture by being car- 
 ried to regions of lower temperature, i. e., up the sides of mountains 
 or to higher latitudes, by the influx of a cooler wind, by radiation, 
 and by expansion. Convection currents will carry the air upward 
 to cooler regions, or to regions where it can expand. Such cur- 
 rents are characteristic of the tropical belt of calms where precipi- 
 tation occurs almost daily. 
 
 DEW. When the temperature of the air is lowered to such a 
 point that, with a given absolute humidity, the relative humidity 
 rises to 100, the next step in cooling will cause the precipitation or 
 condensation of some of the moisture. The temperature at which 
 this takes place in any given case is the dew point. According to the 
 absolute amount of water in the air, the dew point will vary in tem- 
 perature, being high when there is a large amount of water in the 
 air, and low when the amount is small. Radiation on clear nights 
 may reduce the temperature of the rocks and vegetation to such an 
 extent below that of the air, that moisture will condense in the form 
 of dew, if the condensation temperature is above 32 F. (o C), 
 or in the form of ice particles if the temperature is below that point. 
 Moisture thus condensed has been observed by the author to cover 
 the rocks and vegetation of the summits of the White Mountains 
 with ice crystals in early August, these crystals, six inches long, jut- 
 ting out into the teeth of the moisture-laden wind from the vertical 
 
 * For composition of rain water see Chapter IV. 
 
ATMOSPHERIC MOISTURE 63 
 
 surface of the rock cairn. Similar crystals 18 inches long have been 
 reported from these summits. 
 
 FROST. Frost results from a condensation of the atmospheric 
 moisture at a temperature below the freezing point, in contact with 
 cold objects. It has the same relation to dew that snow has to rain. 
 The atmospheric moisture freezing in the finer rock crevices becomes 
 a powerful agent in causing rock disruption. The freezing of water 
 in these fissures likewise acts as a powerful wedging agent (see, 
 further, Chapter IV.) 
 
 CLOUDS AND FOGS. Clouds are the condensed atmospheric vapor 
 remaining suspended in the air, and fogs are clouds resting upon 
 the surface of the earth. When condensation takes place above the 
 freezing point, the clouds and fogs will consist of water particles ; 
 if below that point, they will be ice particles, constituting air frost. 
 Clouds form an effective thermal blanket, preventing radiation and 
 the cooling of rock surfaces. In regions of much cloudiness, shat- 
 tering of rocks by insolation is reduced to a minimum. The diame- 
 ter of the droplets of water in clouds and fogs has been estimated 
 at 0.0085 mm., and it is owing to this small size that they remain 
 suspended. The types of forms which clouds assume are : cumulus, 
 thick clouds with horizontal base and more or less dome-shaped up- 
 per surface ; stratus, horizontal sheets of lifted fog ; nimbus, or rain 
 clouds, of thick layers of dark clouds with ragged edges ; and cirrus, 
 high, thin, feathery, or fibrous clouds, often consisting of particles 
 of snow or ice. Intermediate types are also recognized. 
 
 RAIN, SNOW, AND HAIL. The moisture of the atmosphere is 
 precipitated as rain, snow, or hail, when the particles become heavy 
 enough to fall. If they begin as frozen particles of snow in the 
 upper air, they may melt on passing through a stratum of warmer 
 lower air and so change to rain, or, if the air is dry, even evaporate. 
 Thus snow may fall on the mountain top and rain in the valley, 
 or no precipitation occur in the valley, while rain "or even snow 
 falls on the summits. When water falling as rain passes through 
 a colder stratum of air, it may freeze, and hail will result. Hail 
 also results from the enlargement of snow crystals which pass 
 through a very moist atmosphere and so surround themselves with 
 layers of ice. 
 
 Amount of Rainfall. Sir John Murray (68) estimates the total 
 annual rainfall of the globe at 29,350 cubic miles. Of this amount 
 2,243 cubic miles of rain falls on the inland drainage areas of the 
 globe, such as the Caspian, the Sahara, and similar districts. Of 
 this the Sahara alone gets 728.9 cubic miles, or an average of 
 31,106,860 cubic feet per square mile of area, while the Kalahari 
 
64 PRINCIPLES OF STRATIGRAPHY 
 
 desert gets 14.4 cubic miles, making an average of 34,261,500 cubic 
 feet per square mile. . The inland drainage areas of Eurasia aver- 
 age 25,125,040 cubic feet and those of Australia only 23,986,540 
 cubic feet per square mile. The total of these inland drainage areas 
 comprises about 11,486,350 square miles, giving an average of 
 28,729,760 cubic feet of rain per square mile of area. None of the 
 water falling there reaches the sea. Most or all of this amount is 
 returned to the atmosphere and often more, as shown by the shrink- 
 age of inland lake basins such as Great Salt Lake of Utah. When 
 the annual rainfall is under 10 inches, desert conditions will prevail, 
 and a "rainless" condition is assumed to exist. Thus the average 
 precipitation along the Mexican boundary of the lower Colorado 
 district is about 8 inches; on the Yuma and Colorado deserts it is 
 only 2 or 3 inches. The total area of land thus affected at the 
 present time is about 12,200,000 square miles, and corresponds very 
 closely in extent and position to the inland drainage areas of the 
 world. These areas are distributed as follows : 
 
 Continent 
 
 Area in square 
 miles with less 
 than 10 inches of 
 rainfall 
 
 Percentage of 
 total area of 
 continent 
 
 Australia and Tasmania 
 
 I 1 06 2^0 
 
 -7Q 8 
 
 Asia 
 
 5, 802, 2^O 
 
 ^6 ^ 
 
 Africa 
 
 2 221 OOO 
 
 28 2 
 
 North America 
 
 I 4.72 4.OO 
 
 17 O 
 
 South America 
 
 Wl,O*,O 
 
 A 7 
 
 Europe 
 
 J7.Q ISO 
 
 37 
 
 Antarctica 
 
 
 
 
 
 
 Total 
 
 1221 s ? ^OO 
 
 21 2% total land 
 
 
 
 area * 
 
 The highest rainfall is recorded in Asia, where 437,500 square 
 miles, or 2.7 per cent, of its total area, receive over 75 inches an- 
 nually (averaging 113 inches), and in South America, where 1,444,- 
 ooo square miles, or 20.5 per cent, of its total area, receives 100 
 inches or over. The distribution of areas receiving over 75 inches 
 of rainfall annually is as follows : 
 
 * Taking the total area of the land (see ante) as 148.8 million square kilo- 
 meters or 57,460,777 square miles- 
 
QUANTITY OF RAINFALL 65 
 
 Square miles. 
 Asia 
 
 Mean of 85 inches 46,450 
 
 Mean of 90 inches 92,900 
 
 Mean of 100 inches 7,75 
 
 Mean of 120 inches 58,100 
 
 Mean of 170 inches 232,300 
 
 Africa 
 
 Mean of 100 inches 201,300 
 
 Mean of 1 10 inches 209,050 
 
 Java, mean of 1 10 inches 54,200* 
 
 Sumatra, mean of 130 inches 185,800* 
 
 Celebes, mean of 120 inches 77,400* 
 
 Borneo, mean of 100 inches 290,350* 
 
 Philippines, mean of 90 inches 123,900* 
 
 Formosa, mean of 85 inches 15,500* 
 
 Japan, mean of 80 inches 46,450 
 
 North America 
 
 Mean of 85 inches 92,900 
 
 Mean of 90 inches 69,700 
 
 South America 
 
 Mean of 100 inches 185,800 
 
 Mean of 120 inches 1,122,700 
 
 Mean of 130 inches I35,5o 
 
 Total area over 75 inches of rainfall annually 2,810,550 
 
 The rainfall of Europe does not exceed 75 inches, nor does that 
 of Australia and Tasmania. The rainfall of the Antarctic ranges 
 from 25 to 50 inches, that of Greenland from 10 to 50, and that of 
 Iceland from 25 to 75 inches. 
 
 Relation of Evaporation to Rainfall. Measurements of rainfall 
 and evaporation made in Russia have shown a steady decrease of 
 the former from the coast to the interior, and a corresponding 
 rapid increase of the evaporation. Thus at Kiev the rainfall is 53 
 cm., while the evaporation is 48 cm. At Astrakhan the precipita- 
 tion is 1 6, and at Petro-Alexandrovsk it is only 6 cm., while the cor- 
 responding evaporation at the two points is 74 cm. and 232 cm., re- 
 spectively. The following table (p. 66), compiled by Murray, 
 shows the annual rainfall and annual discharge for 33 rivers in dif- 
 ferent parts of the world, the difference between these representing 
 the mean annual amount evaporated. Over the total area of the 
 drainage basins of these rivers, comprising 13,272,000 square miles, 
 the annual evaporation amounts to about 8,000 cubic miles of water. 
 
 * Total area of the islands. 
 
66 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Position 
 of 
 mouth 
 of 
 river 
 
 
 
 River 
 
 Drainage 
 area 
 in 
 square 
 miles 
 
 Annual 
 rainfall 
 in . 
 cubic 
 miles 
 
 Mean 
 annual 
 discharge 
 in cubic 
 miles 
 
 Mean 
 ratio 
 
 5o-6o N 
 
 Rhine 
 
 1,2,600 
 
 IO-5OO 
 
 IO. IOO 
 
 2 Od.Q 
 
 
 Oder .... 
 
 51,100 
 
 14.700 
 
 2 . 5OO 
 
 5 SO'* 
 
 
 Niemen 
 
 36,450 
 
 10.355 
 
 3.783 
 
 2 7^7 
 
 
 Vistula 
 
 65,800 
 
 10.008 
 
 5 657 
 
 T co8 
 
 40-50 N. 
 
 St. Lawrence 
 
 565,200 
 
 338.967 
 
 87.^12 
 
 T. 004 
 
 
 Danube 
 
 ^2O,^OO 
 
 108 7^6 
 
 67 SI I 
 
 2 7/16 
 
 
 Po 
 
 27,100 
 
 2^.887 
 
 11. 122 
 
 I 7Q4 
 
 
 Volga 
 
 592,300 
 
 152.384 
 
 4^.7^6 
 
 T. 4.84 
 
 
 Seine 
 
 2^,25O 
 
 10.266 
 
 5 460 
 
 I 877 
 
 
 Rhone 
 
 34,850 
 
 22 .439 
 
 14.066 
 
 I 724 
 
 
 Dnieper 
 
 107,4. co 
 
 56 ^84 
 
 22 105 
 
 2 527 
 
 
 Loire . . 
 
 42,600 
 
 18.210 
 
 7 810 
 
 2 112 
 
 
 Dniester 
 
 30,950 
 
 8.792 
 
 ^.274 
 
 2 685 
 
 -4.o N 
 
 Yang-tse-kiang 
 
 680,100 
 
 408 872 
 
 12 S OA^ 
 
 ^421 
 
 
 Hoang-ho 
 
 Nile 
 
 387,150 
 
 I 20^ CKO 
 
 117.711 
 
 892 I 20 
 
 28.591 
 
 24 ^4 
 
 4-159 
 
 ^6 008 
 
 2o-3o N. 
 
 Pei-ho 
 Mississippi 
 
 65,000 
 1,285,300 
 
 22.354 
 
 673 . 064 
 
 1.650 
 I25.6o^ 
 
 13.551 
 5 446 
 
 
 Rio Grande 
 
 2^2 1OO 
 
 11^ 655 
 
 12 676 
 
 8 966 
 
 
 Indus . . 
 
 ; 60,050 
 
 104.416 
 
 26 032 
 
 4 886 
 
 * 
 
 Ganges 
 
 cg8 450 
 
 cj.8 70 1 
 
 4^ 26^ 
 
 1 6 169 
 
 I0-20 N 
 
 Magdalena . . 
 
 Q2.QOO 
 
 116 746 
 
 50 451 
 
 I 064 
 
 
 Irawadi .... 
 
 l8l,Q5O 
 
 180.849 
 
 82 200 
 
 2 256 
 
 
 Kistna 
 
 Godavery . . 
 
 8l,300 
 1^4,8^0 
 
 61.025 
 05 024 
 
 14.766 
 16 841 
 
 4.137 
 
 5 7o8 
 
 o-io N. 
 
 Orinoco . . 
 
 42Q.7OO 
 
 60^ . 1Q7 
 
 122.242 
 
 4- Q^6 
 
 Eouator 
 
 Amazon 
 
 2 22Q QOO 
 
 2 811 8^0 
 
 527 051 
 
 8 OOQ 
 
 o-io S. 
 
 San Francisco 
 Congo 
 
 212,900 
 1,540,800 
 
 218.459 
 1,213.044 
 
 22.197 
 419.291 
 
 9,842 
 
 1.211 
 
 20-30 S. 
 
 Orange 
 
 267 I SO 
 
 50 oi i 
 
 21 875 
 
 2 ^7 
 
 10-40 S. 
 
 Olifant . 
 
 14,^00 
 
 2 .472 
 
 o 670 
 
 1 &1Q 
 
 
 De la Plata 
 
 QQ4. QOO 
 
 QO4. 687 
 
 I 88 740 
 
 6 OQI 
 
 
 Uruguav . . 
 
 151 ,000 
 
 i^d 800 
 
 ^2 1^6 
 
 4 O7^ 
 
 
 
 
 
 
 
 
 Total 
 
 n, 272,000 
 
 10,186.460 
 
 2,182 485 
 
 
 
 
 
 
 
 
 Influence of Winds and Topography on Rainfall. Winds 
 blowing from higher to lower latitudes, i. c., from cooler to warmer 
 regions, have their capacity for moisture increased and hence be- 
 come drying winds. This is illustrated by the trade winds, which 
 take up moisture from the oceans and the lowlands over which 
 they blow. The Sahara, parts of Asia, and large parts of Aus- 
 
DISTRIBUTION OF RAINFALL 67 
 
 tralia, South Africa, and southern South America present such 
 lowlands in the trade-wind zones, and hence are deserts. Indeed 
 most of the great deserts of the modern world lie in the belts of 
 lowland country swept by the trades outside the poleward limit of 
 the equatorial rain belt, or roughly between latitudes 20 and 30. 
 On the leeward western coasts of Australia, South America, and 
 South Africa, these deserts extend directly to the edge of the sea. 
 If these winds are forced to rise to greater altitudes, as is the case 
 when a mountain range stretches across their path, they are cooled, 
 and the moisture is condensed and may fall as rain or snow. Thus 
 the windward sides of these mountains will be characterized by 
 heavy rainfall, as illustrated by the eastern slope of the Andes 
 Mountains. The southeastern trades of this region first lose a part 
 of their moisture over the comparatively low Sierras of the east 
 coast, where the rainfall is over 80 inches a year. Then, as they 
 sweep over the Brazilian plains, the rainfall is less (between 40 and 
 80 inches per annum), to be increased again to over 80 inches as 
 they rise in the Andes. After crossing the Andes, they descend, and 
 being warmed both by compression during the descent (see page 
 49, foehn), and by contact with the warm surface of the lower 
 region, they become drying winds, with the result that the nar- 
 row Pacific coastal strip, to leeward of the Andes, is a pronounced 
 desert from near the equator to about latitude 30 S. Cold ocean 
 waters and prevailing southerly (drying) winds along shore further 
 contribute to this result. The leeward sides of the mountains in the 
 path of the trade winds are thus a region of little precipitation, dry 
 savannas or deserts occurring, while the windward sides support a 
 luxuriant vegetation. If the eastern coast mountains were higher, 
 the winds after passing over them would become drying winds, and 
 the plains of Brazil would be arid, rainfall becoming abundant again 
 only as the winds rose over the Andes. Corresponding to such a 
 distribution of rainfall, one would expect densely wooded areas on 
 the eastern side and heavy torrent-laid deposits on the western bor- 
 ders of the two mountain chains, with semiarid or desert conditions 
 between them. The latter might be characterized either by eolian 
 erosion, or by deposition of wind-transported material, or by both. 
 Some of the lofty islands of the Hawaiian group which lie in the 
 northeast trade wind belt furnish other good examples of rainy 
 windward and dry lee slopes, the latter in some cases being of a 
 desert character. 
 
 The equatorial belt of calms and variable winds, i. e., the dol- 
 drums, is a region of exceptionally abundant rainfall, being one of 
 the rainiest regions of the world, its average being about 100 inches 
 
68 PRINCIPLES OF STRATIGRAPHY 
 
 per year. The cause of this rainfall is the rising and expansion of 
 the air warmed near the surface, and the consequent cooling- and 
 condensation of its moisture. These precipitations are almost daily 
 accompanied by thunderstorms, especially in the afternoon and even- 
 ing. The belt shifts north and south with the position of the sun. 
 Two maxima occur, one in April and one in November, lagging 
 thus somewhat behind the vertical sun, the April maximum being 
 the principal one. The minima between these are seldom rainless. 
 This constitutes the equatorial type of rainfall. The tropical belt 
 of calms, situated in about latitude 30, but likewise shifting with 
 the position of the sun, is a region of descending and hence com- 
 pressing winds, which thus become warmed and have a drying ef- 
 fect. 
 
 From the shifting nature of the tropical rain belt with the change 
 in position of the sun, the regions near its margin (or more than 
 10 to 12 from the equator) are subject to regular alternations of 
 one wet and one dry season, the two rainy seasons having become 
 merged, owing to the short interval between the periods of vertical 
 sun in summer. This is followed by a single dry winter season. 
 During this period the trade winds produce their drying effect, 
 which continues until the equatorial rain belt again encroaches. This 
 type of alternating abundant rainfall and draught is called the 
 tropical type. The dry (winter) season lasts eight months in 
 typical cases ; the lowlands become parched and vegetation withers 
 away, whereas during the shorter wet season grass and flowers will 
 grow in abundance and all life take on new activity. The Soudan, 
 between the Sahara and the equatorial forest of Africa, partakes 
 alternately of the character of each ; vegetation grows actively when 
 the doldrums are over it (May to August), but when the trade 
 winds blow the ground is dry and parched (December to March). 
 The llanos of Venezuela have a dry season when the trade winds 
 blow, i. e., during the northern winter, and an abundant rainfall 
 from May to October. The reverse is the case in the canipos of 
 Brazil, situated south of the equator, where the rain falls from 
 October to April, while the remainder of the year is dry. The 
 overflow of the Nile results from the abundant rainfall in the Abys- 
 sinian Mountains when the equatorial rain belt migrates northward. 
 
 In the monsoon belts the rains follow the vertical sun, and there 
 is thus a simple annual period similar to that of the tropical type. 
 In summer the warm air flows inland from the sea, bringing much 
 moisture, which is condensed and precipitated as the winds are 
 forced to rise over mountains or highland plateaus. The heaviest 
 precipitation in India is in the Khasi Hills (Assam) at the head of 
 
CAUSES OF RAINFALL 69 
 
 the Bay of Bengal, and at an altitude of 4,455 feet. Here the mean 
 annual rainfall is between 400 and 500 inches. Along the southern 
 base of the Himalayas it is 60 to 100 inches, on the bold western 
 coast 80 to 1 20 inches and over, and on the mountains of Burma 
 160 inches. (See map of Indian winds, Figs. 10 and 12.) The pre- 
 vailing direction of the rain-bringing monsoon of India is from 
 the southwest, that of the Pacific coast of Asia from the southeast. 
 In general, the eastern coasts in the tropics are the rainiest, though 
 there are notable exceptions to this rule. 
 
 The westerly winds of both hemispheres (southwesterly in the 
 northern and northwesterly in the southern), which blow poleward 
 above the latitudes of 30, have a corresponding effect on the rain- 
 fall, the precipitation occurring on the westerly side of the mountain 
 ranges, while corresponding dryness prevails on the eastern. In 
 general, bold west coasts on the polar side of latitude 40 are very 
 rainy, the precipitation being 100 inches or more a year in the most 
 favorable situations. The interior of the continents, on the other 
 hand, especially when well enclosed by mountains, or open only to 
 the cool ocean winds which become warmed as they proceed, have 
 only a slight rainfall of from 10 to 20 inches or less. The eastern 
 coasts are drier than the western, but wetter than the interiors of 
 the continents. The maximum rainfall occurs in winter over the 
 oceans, islands, and west coasts of the continents, this being the 
 season of strong westerly winds, when cyclonic storms are most 
 numerous and best developed. The cold lands, too, have a chilling 
 effect on the inflowing damp air. In the interior of the continents 
 high pressure prevails and the winds flow outward, while their 
 low temperature at the start makes them drying winds as they pro- 
 ceed outward to warmer regions. This season is, therefore, the 
 driest for the interior of the continents. 
 
 The greater part of the United States lies within this zone of 
 prevailing westerlies, the direction for almost all the country being 
 from the southwest. In winter these winds from the Pacific yield 
 their moisture on reaching the cool lands, this occurring even at 
 low altitudes, as a result of which the lowlands of California have 
 a wet season. This condition also exists in summer in Washington 
 and Alaska, while southern California has its dry season. Rising 
 over the mountains back of the coast, the winds yield more mois- 
 ture, so that all the regions west of the crest of the coast ranges are 
 well supplied with rain and snow in winter. Beyond this range, and 
 beyond the Sierras and Cascade Mountains further north, the winds 
 descend and become warmer and drier, and here lie the semiarid 
 lands of eastern Oregon and Washington, and the Great Basin with 
 
70 PRINCIPLES OF STRATIGRAPHY 
 
 Great Salt Lake, the shrunken remnant of Lake Bonneville. In 
 southern California the Mohave and Colorado deserts lie just east 
 of the Coast Range. In the. higher parts of the Rocky Mountains 
 these winds again yield some moisture, but beyond these ridges 
 they once more become drying winds, with corresponding semi- 
 aridity of the climate. The winds would continue so, and arid con- 
 ditions would prevail throughout the entire interior of the conti- 
 nent, were it not for the aperiodic cyclonic winds which, passing 
 over the country from east to west, cause moist air to flow from 
 the Gulf northward to cooler latitudes. 
 
 If the south winds from the Gulf were shut out by a mountain 
 range, the region to the northeast of it would likewise be of an arid 
 nature. Such conditions seem to have existed in Triassic time in 
 North America and western Europe. In North America the newly 
 formed Appalachian ranges shut in the land on the Atlantic side, 
 and their westward continuation in Arkansas, Oklahoma, and Texas 
 formed a barrier against the winds from the south. Continuing 
 through the region of the present Basin ranges, as the Palseo-Cor- 
 dilleran Mountains, they formed the western arm of the system 
 which embraced interior North America. To the south and west 
 extended the Triassic sea with its marine limestone accumulations. 
 Rising over the Palseo-Cordillerans in the southern region (Arizona, 
 New Mexico), these winds became drying winds, as a result of 
 which semiarid continental deposits were formed on the leeward 
 side of these mountains. These are now found as extensive red 
 sandstone deposits, partly of torrential, but perhaps more largely 
 of eolian character, extending from Texas to Montana and Canada. 
 They are heaviest in the Arizona region and extend eastward and 
 northward into Colorado and Dakota, dipping under the Cretacic 
 deposits of the Great Plains. They come to an end before reach- 
 ing the Mississippi Valley, where Cretacic beds rest disconformably 
 upon Permic. Over the whole eastern half of North America, west 
 of the newly made Appalachian Mountains, no Triassic deposits are 
 known, and erosion rather than deposition seems to have been ac- 
 tive. This erosion probably was in part eolian, similar to that known 
 in the Kalahari desert, but near the mountains precipitation was 
 again abundant, so that river erosion characterized the mountain 
 regions. Much of the drainage from these mountains must have es- 
 caped toward the northwest, where an arm of the sea entered during 
 part of Triassic and later Jurassic time. Some of the continental de- 
 posits formed over the crystalline region of Canada and northern 
 United States may have subsequently been reworked into the con- 
 
PERIODICITY OF RAINFALL 71 
 
 tinental Kootanay and Cretacic deposits, especially the widespread 
 Dakota sandstone. As the west-winds descended on the eastern side 
 of the new Appalachians, they again produced semiarid conditions, 
 which favored the deposition of the continental Newark and Con- 
 necticut Valley sandstones and their extensions north and south, 
 formations which to-day are represented only by fragments of what 
 must have been formerly a very extensive piedmont deposit. South- 
 ward the condition seems to have been one of less aridity, possibly 
 because the mountains were lower, or south winds from the Atlantic 
 acted as modifiers, for here we find plant beds and coal deposits as- 
 sociated with the upper part of the formation. These same south- 
 westerlies were also responsible for the extensive continental de- 
 posits of the Trias of western Europe. A mountain chain, the Ar- 
 morican, extended northwestward from central France through 
 Brittany, southern England and Ireland, thus lying directly in the 
 path of the southwesterly winds. A second chain, the Variscian, ex- 
 tended eastward through southern Germany, around the Bohemian 
 Mass on the north, and thence to the present Carpathians. These 
 chains thus completely enclosed northern Europe on the south, and 
 to the north of them were formed the extensive New Red sandstone 
 deposits of England and the Bunter Sandstein with its desert fea- 
 tures in Germany. 
 
 Latitude and Precipitation. Rain and snow decrease progres- 
 sively from the equator polewards, the precipitation being compara- 
 tively slight, owing to the smaller capacity of the air for water- 
 vapor at the prevailing low temperature, and to the absence of local 
 convectional storms. The western coast of Norway is an exception, 
 since the rainfall is here much heavier. The precipitation is mostly 
 in the form of snow, though rain falls in summer sometimes prob- 
 ably at all points. The snow of the polar regions is fine and dry; 
 flakes are not formed at low temperatures, but the atmosphere is 
 full of fine, glittering ice needles, which gradually descend to the 
 
 ^arth even on clear days. 
 Periodicity of Rainfall. In a number of places, as for example 
 ndia, observations have shown an apparent fluctuation in rainfall 
 nd temperature for a period of eleven years, corresponding to the 
 un-spot period or the periodicity of the earth's magnetic phe- 
 nomena. A thirty-five-year period of Oscillation has also been dis- 
 covered and elaborated by Professor Bruckner (12) (Bruckner 
 cycle). The cycle varies from 20 to 50 years, but 35 is the average. 
 The fluctuations of the rainfall between the dry and wet periods are 
 most marked in the interior of the continents. 
 
72 PRINCIPLES OF STRATIGRAPHY 
 
 ELECTRICAL PHENOMENA OF THE ATMOSPHERE. 
 
 By thunderstorms, or other electrical discharges in the atmos- 
 phere, some of its oxygen is probably converted into the allotropic 
 modification ozone. Hydrogen dioxide and oxides of nitrogen are 
 further formed, the latter yielding, with the moisture of the air, 
 nitric and nitrous acids, which, when brought to the earth by rains, 
 become agents of corrosion of the rocks. Both ozone and hydrogen 
 dioxide are powerful oxidizing agents, and will transform organic 
 matter suspended in the air into carbon dioxide, water, and probably 
 ammonium nitrate. 
 
 Lightning may further act as a disrupter of rock masses. In 
 Fetlar, one of the Shetland Islands, a solid mass of rock 105 feet 
 long, 10 feet broad, and in some places more than 4 feet high, was 
 in an instant torn from its bed by lightning and broken into three 
 large and several small fragments. "One of these, 28 feet long, 
 17 feet broad, and 5 feet in thickness, was hurled across a high 
 point of rock to a distance of 50 yards. Another broken mass, 
 about 40 feet long, was thrown still farther, but in the same direc- 
 tion, and quite into the sea. There were also many lesser fragments 
 scattered up and down." ( Hibbard-49 : j#p. ) 
 
 FULGURITES. When the electric spark strikes loose sand or rock, 
 a coating of fused vitreous material may be formed, or a mass of 
 vitreous drops or bubbles. More generally, slender tubes of fused 
 material mark the path of the electric spark, especially in loose 
 sand. These tubes, known as fulgurites * consist of fused grains, 
 and range up to 2^/2 inches in diameter. They descend vertically 
 or obliquely into the rock or sand, occasionally branch, and dimin- 
 ish in size to a point. The summit of Little Ararat, which is ex- 
 posed to frequent thunderstorms, is riddled with fulgurites, which 
 here occur in a porous andesite and consist of irregular tubes hav- 
 ing an average diameter of 3 centimeters, and being lined with a 
 blackish-green glass. Humboldt obtained these fulgurites from 
 trachyte peaks in Mexico, and found that in two cases at least the 
 fused mass overflowed from the tubes onto the surrounding sur- 
 face. Other cases of lightning-fused rocks have been reported in 
 hornblende schist of Mont Blanc (De Saussure) ; in mica schist 
 and limestones from the Pyrenees (Ramond; Arago) ; in basalt of 
 Mount Thielson, Oregon, and Mount Shasta, California (Diller) ; 
 in glaucophane schist of Monte Viso (J. Eccles) ; in gneiss of Lake 
 
 * For extended bibliography including the cases cited, see the article by 
 Barrows (5) 1910. 
 
ELECTRICAL PHENOMENA 73 
 
 Champlain (Hallock), etc. Fulgurites in sand have been frequently 
 described. These have been found in the sands of the Libyan desert 
 (Giimbel), as well as in the sand and soil of moist climates. In 
 Silesia, near Olkusz, 26 tubes were found in an area of 200 by 100 
 feet, most of them associated in groups. In Cumberland, England, 
 near Drigg, fulgurites of exceptional size were found. Three of 
 these tubes were found in a sand hillock within an area of fifteen 
 square yards. One of them was traced perpendicularly to a depth of 
 40 feet, the basal part being much contorted and branched, owing to 
 the presence of many small pebbles in the soil. The maximum 
 diameter of this tube was 2^2 inches. 
 
 The finer structure of the glass lining of the tube has been espe- 
 cially investigated by Julien (53). He finds that the bubbles which 
 occur in such large numbers in the clear amorphous glass of the 
 tube contain no water, these bubbles probably being formed by the 
 expansion of heated air. The vesicles are elongated, and their 
 longer axes disposed radially. All sand grains within a radius of 
 a few millimeters were suddenly and completely fused. The inner 
 wall is practically free from bubbles, and is a clear, shining glass, 
 streaked and spotted with black and brown, according to the abun- 
 dance of iron-bearing minerals. Externally the form is very rough, 
 corrugated longitudinally and coated with partially fused sand 
 grains. The outline is an irregularly branching one, due to the 
 forking of the electric spark. The thickness of the wall varies from 
 o.i cm. or less to 0.5 cm. or more, and the vesicles from less than 
 0.002 mm. to 1.2 mm. or over. The cross section is often nearly 
 circular ; at other times it is irregular. Sometimes the round hole is 
 merely lined by a network of fused materials. 
 
 Of exceptional interest is a fulgurite described by Barrows (5) 
 from the Raritan sands of New Jersey. It was found in a mass of 
 sand fifty feet thick, resting on the South Amboy fire clay, and oc- 
 curred 15 to 20 feet above the clay or from 45 to 55 feet from the 
 surface formed by the Pensauken outwash gravels of Pleistocenic 
 age. The fulgurite ran at a low angle to the horizontal for about 
 15 feet parallel to the face of the bank. The length was about 19 
 feet, including branches, and the diameter of the tube varied from 
 3.2 cm. to 0.3 cm. The position of this tube suggests that it was 
 formed after part of the sand had been deposited and before the 
 laying down of the upper part of the sand. If this is the case, these 
 sands would have to be regarded as dune sands, since fulgurites will 
 form only in comparatively dry media. This interpretation is not 
 inconsistent with the character of the formation as a whole, which 
 is of continental rather than of marine origin. Of course the tube 
 
A 
 
 74 PRINCIPLES OF STRATIGRAPHY 
 
 may have resulted from a discharge entering the bank of sand since 
 digging has exposed it, but it is difficult to understand why the dis- 
 charge should run parallel to the face of the cliff. 
 
 It is obvious that fulgurites found in the older formations may 
 have such relationships that they must be regarded as contemporane- 
 ous in age with the formation, in which case they would form valu- 
 able evidence for the continental origin of such formations. 
 
 CLIMATE. CLIMATIC ZONES, PRESENT AND PAST. 
 
 Climate is the average or sum total of weather conditions normal 
 to a given region, while weather is only a single occurrence or event 
 in that series of conditions, and of short duration. Climate may be 
 classified as solar and physical, the latter comprising continental, 
 marine, and mountain climates. 
 
 SOLAR CLIMATES. CLIMATIC BELTS OR ZONES. 
 
 If the earth had a homogeneous land surface and no atmosphere, 
 solar climate alone would prevail, the distribution of heat being 
 solely according to latitude. Five zones of solar climate are recog- 
 nized: the torrid or tropical, limited by the tropics of Cancer and 
 Capricorn and divided by the equator, the two temperate zones, lim- 
 ited poleward by the arctic and antarctic circles, and the two frigid 
 or polar zones centering at the poles. The torrid or tropical zone 
 has the least annual variation in insolation, and may be called the 
 zone of perpetual summer, while the polar zones have the greatest 
 variation between summer and winter, and may be called the winter 
 zones, summer being so short and cool that it may be neglected. The 
 intermediate zones have about an equal distribution of seasons, 
 summer in the northern corresponding to winter in the southern 
 hemisphere. A somewhat different delimitation of the zones has 
 been proposed by Supan, who suggests that the hot belt be limited by 
 the two mean annual isotherms of + 68 F. (-f- 20 C.) (the ap- 
 proximate polar limit of the trade-wind belts, and the polar limit of 
 palms), and the polar limits of the temperate zones, by the two 
 isotherms of -f- 50 F. (+ 10 C.) for the warmest month (the ap- 
 proximate northern limit of the cereals and forest trees). This 
 limit in the north is very near the northern boundary of the conti- 
 nent of North America and Eurasia, while in the south it passes 
 through the southern extremity of South America. Africa lies al- 
 most wholly within the hot belt, and so does the greater part of 
 South and all of Central America. The smaller size of the north 
 
CLIMATE 75 
 
 polar climatic cap is due to the expansion of the land in that 
 hemisphere. The greatest expanse of land lies in the north tem- 
 perate zone. 
 
 PHYSICAL CLIMATE. 
 
 This is the climate produced through modification of the solar 
 climate by the physical characters of the earth's surface. The prin- 
 cipal kinds to be considered are: i, The marine or oceanic; 2, the 
 coast or littoral ; 3, the continental or interior ; 4, the desert, and 5, 
 the mountain and plateau climates. Each of these has its peculiari- 
 ties which in turn influence the distribution of plant and animal life. 
 (See Chapter XXIX.) 
 
 1. Marine or Oceanic Climate. Owing to the slow changes of 
 temperature which the ocean water undergoes, the seasonal tem- 
 perature changes are comparatively slight, while the times of oc- 
 currence of maxima and minima are retarded, a cool spring and 
 warm autumn resulting. Relatively greater humidity, cloudiness, 
 and heavier rainfall than is found on the land, are further charac- 
 teristic of marine climates ; and are explained by the greater evap- 
 oration over the sea. In the winter within the middle latitudes, 
 there is excessive precipitation over the, oceans, but the continental 
 interiors are relatively dry. Air over the water is also purer and 
 in more active motion than that over the land. 
 
 2. Coast or Littoral Climate. The coastal region shows the 
 transition from the" marine to the interior continental type of cli- 
 mate, and may alternately partake of both, according to whether 
 the prevailing wind is from the sea or from the land. The wind- 
 ward coasts are usually well supplied with rainfall, especially in 
 the tropics, while the leeward coasts, notably those in the trade- 
 wind zones, are usually dry; and the deserts may extend clear 
 to the coast. This is the condition on the west coasts of South 
 America, Africa and Australia. The cold shore currents and the 
 prevailing long-shore winds further prevent precipitation. An ex- 
 ception to this general character of wet eastern and dry western 
 coasts in the trade-wind zone is seen in the regions of the monsoons. 
 Thus the west coast of India is abundantly watered by the wet 
 southwest monsoon. A peculiarity of these monsoon countries is 
 the threefold division of the climate such as characterizes India. 
 In the winter little precipitation occurs, and the temperature is low, 
 the monsoons blowing offshore. Then follows the hot transition 
 period, which in turn is succeeded by the cooler and wet summer 
 season, when the monsoon blows onshore. The monsoons of the 
 
7 6 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 eastern coast of Asia, the most northerly of such, likewise produce 
 these results, the weather being cold, clear and dry in winter, and 
 cool, cloudy and damp in summer. 
 
 3. Interior Continental Climates. In the interior of continents 
 climatic changes are for the most part very pronounced. The an- 
 nual temperature ranges become greater with increased distance 
 from the shore, the coldest and warmest months in the northern 
 hemisphere being January and July, respectively. There being less 
 cloudiness over the land, the diurnal changes are greater than over 
 the sea. These ranges are well shown by a comparison of the Janu- 
 ary and July temperatures of coast and inland stations in low and 
 high latitudes. 
 
 
 January 
 temperature 
 
 July-August 
 temperature 
 
 C. 
 
 F. 
 
 C. 
 
 F. 
 
 Low Latitudes: 
 Bagdad, Asia Minor (continental) 
 
 Funchal, Island of Madeira (ma- 
 rine) 
 
 + ii.5 
 
 ' +53 
 +60 
 
 +34 
 +22.5 
 
 + 22 
 
 + 16 
 
 _ 
 
 +93 
 
 + 15-5 
 
 High Latitudes: 
 Nertschinsk, E. Siberia (conti- 
 nental) 
 
 +72.5 
 
 -32 
 + 7-5 
 
 Valentia, southwest Ireland (ma- 
 rine) 
 
 -25-6 
 
 + 71-6 
 
 
 +45-5 
 
 +60.8 
 
 . 
 
 
 
 The mean range of many observations in widely distributed sta- 
 tions is 8.2 C. for marine, and 39.0 C. for continental climates. 
 (Hann-4o: 142.) 
 
 The relative humidity of continental interiors is of course much 
 lower than that over the sea or on the coast, but even in arid regions 
 it may reach 20 per cent, or 30 per cent. The rainfall decreases in 
 amount and frequency as we proceed inland, except where local 
 topographic features act as modifiers. The winds average lower 
 in velocity, and calms are more frequent over the land than over 
 the sea. Continental winds are sometimes so well developed as to 
 become monsoons. 
 
TYPES OF CLIMATE 77 
 
 4. Desert Climate. This is characterized by excessive dryness, 
 by great heat during the day, with accompanying strong convection 
 currents resulting in high winds, and by relatively cool, clear and 
 calm nights. The peculiarities of temperature and aridity are un- 
 favorable to the growth of vegetation, except certain adapted forms, 
 and the general absence of plants further intensifies the climatic 
 conditions. Rains are infrequent; parts of the Sahara are known 
 to have been without rains for 10 or 15 years, and when they occur 
 they are apt to be sudden downpours of great floods of water. Dust 
 storms are characteristic of the daytime, when high winds blow, and 
 it is then that deflation and the mechanical wear by drifting sands 
 are chiefly accomplished. The rivers resulting from the sudden 
 rainfalls, or fed by springs in the mountains, wither away, the water 
 sinking into the parched ground or evaporating. Brackish sinks 
 and lakes abound, and temporary playa-lakes suddenly come into 
 existence and disappear by evaporation, leaving behind a charac- 
 teristic, hard, mud-cracked surface. The plants protect themselves 
 against animals by thorns, and guard against excessive evaporation 
 by a reduction in the size of the leaves. The roots penetrate deep 
 into the dry soil and subdivide extensively to obtain all the available 
 moisture. 
 
 5. Mountain Climate. This is distinctive in all zones, and always 
 contrasts strongly with that of the neighboring lowlands. There is 
 a decrease in temperature, pressure and absolute humidity, and an 
 increase in intensity of insolation and radiation, and generally an in- 
 crease in the frequency and amount of precipitation. Pressure is re- 
 duced to about one-half that at sea-level, at an altitude of about 
 16,000 feet, while the zone of maximum rainfall lies at about 6,000 
 to 7,000 feet in intermediate latitudes. Inversions of temperature 
 characterize mountains at night and during the colder months, the 
 cold air flowing down the mountain sides to collect in the valleys 
 below, and being replaced by warmer air above. Thus the diurnal 
 and annual ranges of temperature are lessened, mountain summits 
 having in this respect a climate more nearly resembling the marine. 
 
 CLIMATIC PROVINCES. 
 
 Detailed consideration of climates leads to the recognition of a 
 number of climatic types for the entire earth, the characters of these 
 types being brought about by combinations of distinct climatic ele- 
 ments. Supan has established thirty-five types arranged in thirty- 
 five provinces as follows (91 '.232) : 
 
78 PRINCIPLES OF STRATIGRAPHY 
 
 I. EASTERN CONTINENTS AND ISLAND REGIONS with the follow- 
 ing provinces : 
 
 i West European ; 2 East European ; 3 West Siberian ; 4 East 
 Siberian ; 5 Kamtschatka ; 6 Chinese-Japanese ; 7 Asiatic highland ; 
 8 Aral; 9 Indus; 10 Mediterranean; n Sahara; 12 Tropical Africa; 
 13 Kalahari; 14 Cape (of Good Hope); 15 East Indo-Australian 
 monsoon province; 16 Australian lake province; 17 Southwest Aus- 
 tralia; 18 East Australian; 19 New Zealand; 20 Polynesia (trop- 
 ical) ; 21 Hawaii. 
 
 II. AMERICAN REGIONS with the following provinces : 
 
 I Hudson Bay ; 2 Northwest Coast ; 3 California ; 4 Highlands ; 
 5 Atlantic ; 6 West Indian ; 7 Tropical Cordilleran ; 8 Tropical 
 South America; 9 Peruan; 10 North Chilean; n South Chilean; 12 
 Pampas. 
 
 III. ARCTIC REGIONS with only one province : 
 I Arctic province. 
 
 IV. ANTARCTIC REGIONS with only one province: 
 i Antarctic province. 
 
 CLIMATIC TYPES, BASED ON SEPARATE ATMOSPHERIC FACTORS AND 
 
 ON AGENTS. 
 
 In considering the principal atmospheric factors, we may recog- 
 nize several distinct types, which, however, vary with change in 
 local conditions. The principal types based on factors are : ( i ) 
 moist and (2) dry, (3) cold .and (4) warm, (5) pluvial and (6) 
 arid. Based on the agent influenced by these factors, we may dis- 
 tinguish : (i) glacial climates, when glacial conditions become 
 widespread, and (2) interglacial climates, when glaciers dwindle; 
 (3) fluvial and lacustrine climates, when there is an increase in pre- 
 cipitation and consequently a rise in streams and an extension of 
 lakes, and (4) interfluvial and interlacustrine, or desert climates, 
 when the reverse is true, lakes and rivers shrink and vegetation dries 
 up. These terms are useful in discussing the prevailing character of 
 ancient climates. 
 
 CLIMATIC ZONES OF THE PAST. 
 
 The existence of climatic zones in the past was first suggested by 
 Jules Marcou in 1860, who postulated their occurrence in Jurassic 
 time to explain the "homozooidal belts" of that period. The Aus- 
 trian geologist, Melchior Neumayr (70), attempted to prove this 
 theory by palseontological and geological evidence, and his conclu- 
 
CLIMATIC ZONES 79 
 
 sions have been widely accepted in some quarters, and combated in 
 others. 
 
 NEUM AYR'S CLIMATIC ZONES OF THE JURASSIC. These from the 
 north southward are as follows : 
 
 1. Boreal Zone. Characterized by the presence of the ammonite 
 genera, Cardioceras, Oxynoticcras, and Virgatites, the belemnite 
 Cylindrotcuthis, and the pelecypod Aucella; also by the absence of 
 reef-building corals, and of the ammonite genera: Phylloceras, 
 Lvtoceras, Simoceras, and Lissoceras, and the scarcity of the 
 genera : Oppelia, Hecticoceras, Peltoceras, and Aspidoceras. The 
 boundary between this and the next zone was placed at latitude 45 
 in the Pacific, but further north in the Atlantic and Europe. 
 
 2. North Temperate Zone. This comprised especially the prov- 
 inces of Central Europe, and was characterized by the rarity of the 
 ammonite genera which attained their maximum in the two adjoin- 
 ing zones; and also by the appearance of reef corals, and the 
 predominance of the ammonite genera : Oppelia, Reineckia, Pel- 
 toceras, and Aspidoceras. The boundary between this and the next 
 zone was placed at latitude 32 N. in the Pacific, but oscillated about 
 latitude 40 N. in the Atlantic and in Eurasia. 
 
 3. Equatorial Zone. This comprised in Europe the Mediter- 
 ranean province and was characterized by the abundance of the am- 
 monite genera Phylloceras, Lytoceras, and Simoceras, the belem- 
 nites Belemnopsis and Duvalia, and the brachiopod, Pygope. The 
 boundary between this and the next zone was placed at about lati- 
 tude 32 S. 
 
 4. South Temperate Zone. This reproduced the characters of 
 the north temperate zone. 
 
 DISCUSSION OF THE SUBJECT OF CLIMATIC ZONES. 
 
 Of the zones mentioned above, the colder or boreal zone appears 
 to be well established, but the differentiation of the warmer belt 
 into three distinct zones is less generally supported by the evidence. 
 In Europe the north temperate province of Neumayr represents, 
 according to Haug (42), the shallow water zone of the warm belt, 
 while the equatorial zone corresponds in general with the open and 
 deep Thetys sea. The distribution of the genera in these provinces 
 is due more to this difference in depth and the corresponding differ- 
 ence in temperature than to zonal distinctness. That annual 
 changes of temperature existed in Jurassic time is shown by the de- 
 velopment of annual growth rings in the stems of Abietinese of 
 that period found on King Charles Land. (78 N. lat.) (Gotan- 
 
80 PRINCIPLES OF STRATIGRAPHY 
 
 35:44.) (See, further, under Chapter XXIX.) Although the 
 distribution of the genera of ammonites, as well as of corals, does 
 not follow so rigidly the belt-like arrangement in extra-European 
 countries as held by Neumayr, and although much of the distribu- 
 tion js explainable by difference in depth, still the probability of 
 differentiation of the earth's surface into climatic zones is not to be 
 altogether discarded. A part of the anomalous distribution of 
 ammonites may certainly be explained by floatation (see Chapter 
 XXVIII), while the deflection of the zonal boundaries, due to conti- 
 nental expansions or contractions, must also be considered. Finally, 
 the influence of ocean currents in modifying the temperature of the 
 water must not be neglected. Ortmann (71:267} especially em- 
 phasizes the occurrence of reef-building corals in the Russian Jura, 
 in a region included in Neumayr's boreal zone, and insists that 
 these indicate a tropical climate, but Neumayr contended that such 
 occurrence was not sufficient evidence against his theory. 
 
 That climatic zones existed during Mesozoic times, if not ear- 
 lier, is not at all an improbable supposition, though it may perhaps 
 be questioned whether the differences between successive zones 
 were always as great as now. That the air temperature as a whole 
 was higher at times than now, probably through an increase in the 
 carbon dioxide content and the consequent trapping of solar heat, 
 is highly probable, and indeed seems far more reasonable than the 
 assumption of a uniform climate over the entire earth. A universal 
 rise in temperature of the air would permit a wider distribution of 
 those marine types now restricted to the tropical water of to-day, 
 for the present tropical temperatures would extend to higher lati- 
 tudes. Even though the tropics under such conditions would be 
 much more highly heated, it is questionable if the waters would be 
 too hot for the existence of life. It would only be necessary for 
 organisms living in the tropics to descend to greater depths, so as 
 to escape the excessive surface temperatures. Nor must the pos- 
 sibility be overlooked that stenothermal modern forms may have 
 had eurythermal ancestors ; that, in other words, the descendants 
 of once widely adapted classes of organisms, capable of existing 
 under a great range of 'temperature, have now become restricted to 
 a limited range, in the warmer waters of to-day. 
 
 It is a universally recognized fact that climatic conditions of 
 greater severity existed in the recent geologic past, so that exten- 
 sive portions of the northern continents became glaciated. The 
 very fact that these glaciers extended over only part of the earth's 
 surface shows the existence of climatic zones, the limit of glacia- 
 tion marking the poleward limit of a milder belt. The southern 
 
ANCIENT CLIMATES 81 
 
 limit of Pleistocenic glaciation in North America was at latitude 
 37 3' m the Mississippi valley, while in Europe it did not extend 
 below about 53, though the Alps and other great mountain ranges 
 were heavily glaciated. The high mountain areas of Asia (Leb- 
 anon, the Caucasus, the Himalayas and the mountains of Man- 
 churia) were heavily glaciated, these glaciers reaching down to 
 4,500 feet A. T. in latitude 26 in Bengal, and to 2,000 or 3,000 
 feet in the western Himalayas. (Coleman- 19:34$.) The Atlas 
 Mountains of Africa and the lofty peaks under the equator all show 
 an advance of the glaciers of several thousand feet lower than at 
 present. A similar extent of glaciation of the southern hemisphere 
 would not have reached any of the continents, except the southern 
 end of South America and perhaps New Zealand. The greater 
 expanse of ocean, however, with its more moderate climate, would 
 favor a less extent of the Atlantic ice; and it may be questioned if 
 the ice sheet which is known to have been much more extensive 
 over the Antarctic continent extended much beyond its border. 
 Patagonia, it is true, was widely glaciated south of latitude 37, 
 the ice reaching the sea. This may have been purely local, however. 
 In the Andes, further north, even within the tropics, are old mo- 
 raines, showing the extent of these glaciers 800 to 900 meters below 
 their present position. 
 
 The now incontrovertible evidence pointing to glacial periods at 
 various times during the geologic history of the earth from pre- 
 Cambric time on, indicates not only repeated periods of greater cold 
 in the earth's atmosphere, explainable by the reduction in the 
 amount of CO 2 , but also the existence of warmer and colder zones, 
 as shown by the limited extent of these glacial deposits. Indeed, 
 it may be questioned if zonal arrangement of temperature has not 
 always been the normal state of the atmosphere, and that the 
 changes have only been toward a greater universal increase or de- 
 crease in temperature, the former permitting expansion of tropical 
 types of organisms, the latter the expansion of the cooler types, 
 and culminating in many cases in periods of glaciation. Evidence 
 of early glaciation has now been recorded from the Lower Huronian 
 of Ontario, Canada (Coleman-i9), the pre-Cambric (?) of 
 Varanger Fjord, Norway (Reusch, Strahan~9O, etc.), and Spitz- / 
 bergen (Gregory-37), the basal Cambric or pre-Cambric of the \f 
 Yangtse canyon of China (Willis-io8), of South Australia (How- 
 chin, David-23, etc.), and Tasmania; of South Africa (Griqua- 
 town series, Rogers-79) and less definitely from North America 
 and North Asia. The extent in the southern hemisphere was north- 
 ward to 29 in South Africa, and to 32 or 33 in South Australia, 
 
82 PRINCIPLES OF STRATIGRAPHY 
 
 the movement being northward and the ice reaching sea-level. The 
 evidence of Permo-Carbonic glaciation is even more firmly estab- 
 lished. This has been recognized in India, Australia and Tasmania, 
 South Africa (Dwyka conglomerate and tillite) and South Amer- 
 ica. In India the indications of glacial occupancy have been traced 
 .from lat. 16 or 17 to lat. 34 or 35, and in Australia from lat. 
 20 30' to lat. 43 S. In the eastern Urals of Russia a Permic 
 boulder conglomerate suggests glacial origin (Karpinsky) and a 
 conglomerate of similar age in England has been regarded by Ram- 
 say as glacial, though this has been disputed by others. In Prince 
 Edward Island (F. Bain~3), Colorado (Cross), and eastern Mas- 
 sachusetts (Shaler) conglomerates of this age occur, which sug- 
 gest a glacial origin. In the Antarctic region glacial deposits of 
 this age have recently been found in the Falkland Islands (Halle- 
 41*64). 
 
 It is a remarkable fact that a center of Permic glaciation in the 
 Old World seems to have been near the tropics, perhaps in the In- 
 dian Ocean (the old Gondwana land), for the movement in South 
 Africa seems to have been southward, and in India northward, the 
 movement in both cases being away from the equator. The evi- 
 dence of transported rocks in eastern Massachusetts is, however, 
 from the north and similar in extent to that of the Pleistocenic 
 glacial transportation. So far as the evidence goes, a general re- 
 frigeration of the climate of world-wide extent may have occurred, 
 and the development of an ice sheet in the tropics may be in part 
 due to the great elevation of the land of that time and in part to 
 the nature of supply of moisture to feed the ice sheet. (Philippi- 
 75.) For another suggested explanation, see Chapter XXIII. 
 
 RHYTHM OF CLIMATIC CHANGES. 
 
 The course of climatic changes during geologic time passes from 
 a rhythmically pulsating state, a climatic "strophe," to one of rela- 
 tive torpidity, the climatic "interstrophe." ( Huntington-5 1 1362.) 
 The pulsations of the strophe comprise a series of accentuations of 
 certain climatic characters, such as glacial,- fluvial, vegetal (when 
 plant life spreads widely), or pluvial (when much rain falls). Each 
 accentuation forms an arsis of the climatic strophe, the time of such 
 accentuation being an arsial epoch. The thesis, or thesial epoch of 
 the strophe, is the depression between the accented epochs, as in 
 the case of interglacial or intern 1 uvial epochs, intervegetal or inter- 
 pluvial epochs. The growth in strength of the arses and theses of 
 the strophe is a gradual one to the point when the acme is reached, 
 
CLIMATIC CHANGES 83 
 
 after which a diminution will set in. The interval between two 
 thesial epochs constitutes a short or strophic cycle, while the in- 
 terval from the center of one interstrophe to that of another consti- 
 tutes a grand or climatic cycle. (See diagram, Fig. 15.) 
 
 INDICATION OF CLIMATIC CHANGES. 
 
 TOPOGRAPHIC EVIDENCE OF CHANGE IN CLIMATE. Since the 
 angle of slope assumed by waste under arid conditions is much 
 steeper than that assumed under pluvial climates (see posted Chap- 
 ter XIV) and the material of the former is much coarser than that 
 of the latter, it follows that traces of such conditions in a region 
 now well watered suggest a former greater aridity. This is seen in 
 alluvial fans of great radius and steepness of slope, such as those 
 of the region near San Bernardino with radii of ten, twelve, or 
 
 ARSIS INTER . STROPHE f STROPHE ">, 
 
 ^^yN/v/V/YVv^-^^--. 
 
 'HESIS 
 
 I CYCLE 
 
 FIG. 15. Diagram illustrating progress of changes of climate during geologic 
 time. (After Huntington.) 
 
 fourteen miles, and an elevation, at the head, of four, six, or seven 
 hundred feet above the frontal margin. Such fans are characteris- 
 tic of arid mountain regions, and their essential features will be 
 recognizable in the topography of a region become more moist. The 
 clogging by waste of deep-cut valleys, formed during a moist cli- 
 matic period, as well as the formation of fans on the much dis- 
 sected mountain slopes, is evidence of change from moist to dry 
 climate. In the same manner the dissection of steeply graded val- 
 ley floors and waste slopes shows a change from dry to moist cli- 
 mate, provided these features do not indicate increased elevation 
 of the region. In lakes of a dry region the water would be low and 
 their shores lined by alluvial fans, against which, on the change of 
 the climate to moister conditions, the waters of the expanded lake 
 would come to lie. This was the case in Lake Bonneville, the wa- 
 ters of which rested against the alluvial fans of the pre-Bonneville 
 dry period. The present dry period is again characterized by the 
 formation of such alluvial fans. The outlets of these lakes are fur- 
 ther marked by the features of topographic youth. Evidences of 
 
84 PRINCIPLES OF STRATIGRAPHY 
 
 former extensive sand dunes now covered over by vegetation must 
 further be regarded as indicative of a change of climate. 
 
 STRATIGRAPIIIC EVIDENCE OF CHANGE OF CLIMATE. A careful 
 consideration of the lithic characters of the strata of a given region 
 may furnish evidence of changes of climate in the successive geo- 
 logic epochs. Thus ancient alluvial fans and delta deposits inter- 
 calated between marine sediments are not only evidence of eleva- 
 tion followed by subsidence, but may also indicate a change in cli- 
 matic conditions. This is especially the case when such alluvial 
 fans are characterized by coarse waste, or by red color. The red 
 color of such continental deposits as the Longwood shale of the 
 late Siluric, the Catskill and Old Red sandstones of the Devonic, 
 the Mauch Chunk of the Mississippic, and the Newark and Red beds 
 of the Trias, have been regarded as indicating more or less arid con- 
 ditions during the formation of those deposits. Huntington (51) 
 has described the alternations of red and green strata exposed in 
 the uplifted and dissected bottom of the Pleistocenic lake Seyistan 
 in eastern Persia. The red or pink strata are thick beds of clays, 
 silts, and fine brown sands of a very continuous and uniform char- 
 acter, traceable for miles, even though varying in minor details. 
 They show evidence of exposure to the air, under conditions which 
 prevented extensive development of vegetation. The white or 
 greenish layers, on the other hand, are solid beds of clay, lined above 
 and below by somewhat more sandy films. These green clays were 
 deposited during the periods of expansion of the lake, while the red 
 beds indicate exposure to a dry climate followed by oxidation dur- 
 ing periods of retreat, when arid conditions prevailed. There are 
 here indicated ten epochs of expansion of the lake (the arsial 
 epochs) and ten of contraction (the thesial epochs). The Moen- 
 copie beds of Utah and Arizona (Permic) show a similar alterna- 
 tion of red and greenish beds and indicate a similar pulsation of the 
 climate of the Permic. 
 
 Arid conditions are also shown by the arkose character of many 
 rocks, as, for example, the Torridon sandstone of western Scotland, 
 where the feldspar crystals are scarcely weathered, and the Newark 
 sandstone beneath the Palisades of the Hudson. Arid conditions 
 are further indicated by the occurrence of beds of salt and gypsum, 
 and the same thing is shown by extensive deposits of wind-blown, 
 cross-bedded sands such as are found in the White River beds (Ju- 
 rassic) of Arizona. The extensive development of coal swamps and 
 marshes may indicate a change to cooler and moister climate, while 
 tillites, coarse boulder conglomerates and striated rock and boul- 
 der surfaces indicate glacial conditions. 
 
CLIMATIC CHANGES 85 
 
 ORGANIC EVIDENCE OF CHANGE OF CLIMATE. This is in many 
 respects the most reliable, since organisms are the most sensitive 
 indicators of climatic conditions. 
 
 i. Plants. Coal swamp vegetation, as indicative of cooler and 
 moister climates, has already been referred to. The various types 
 of swamp vegetation preserved in the peats of different coun- 
 tries, serve as an excellent index to the gradual change of climatic 
 conditions since the last glacial period. Thus for Germany it has 
 been ascertained that the first floral mantle following the retreat of 
 the ice was of the tundra type without any true arboreal growths 
 whatever. In many places a lower horizon, with the mountain or 
 arctic dryas, Dryas octopetala, and the arctic dwarf willow, Salix 
 polaris, and a higher one, with Salix phylicifolia and S. rcticulata, 
 besides Dryas octopetala, can be determined. Aquatic plants are 
 rare in this period, but several species of Potamogeton occur regu- 
 larly in the upper beds, together with Myriophyllum spicatwn, Hip- 
 puris vulgaris and Batrachimn aquatile confervoides. During the 
 Dryas period, even in the earliest epoch, the climate could not have 
 been an arctic one in North Germany, for the aquatic plants require 
 a July temperature of approximately 6 C, and need 4 to 5 months 
 with a temperature of at least 3 C. in order that their seeds may 
 ripen. The rapid amelioration of the climate during the Dryas 
 period is shown by the presence of Phragmites communis in the 
 upper layers formed during this period, followed by heavy deposits 
 of decayed vegetation, indicating a rapid increase in the plant and 
 animal life of the waters. With this appears the first arboreal vege- 
 tation with birches and pines. 
 
 The two epochs of arctic floras, i. e., the earlier colder one with 
 Salix polaris and the later milder one with Salix reticulata, are rec- 
 ognized in many regions in Scania and elsewhere in southern 
 Sweden. In Finland the arctic Dryas flora (Dryas, Salix polaris, 
 Betula nana, Batrachium confervoides) and the moss Sphccro- 
 cephalus turyidus, characteristic of the modern arctic region, to- 
 gether with the arctic beetle Pterostichus vermiculosus, occur in a 
 sandy deposit between Lake Ladoga and the Gulf of Finland, in- 
 dicating a climate, during the period of the melting of the ice, com- 
 parable to that now found in northern Russia and the neighbor- 
 hood of the polar sea. The Salix polaris flora has also been found 
 in Norway and Denmark, this arctic flora everywhere forming the 
 first or tundra type of flora to appear during the period of melting 
 of the glaciers. Gunnar Andersson lays especial stress on the oc- 
 currence of an aquatic flora with these arctic plants, which, though 
 consisting of few species, is nevertheless rich in numbers. He con- 
 
86 PRINCIPLES OF STRATIGRAPHY 
 
 eludes that "already in^a period immediately after the melting of the 
 ice ... the vegetation period was four months [in length] and 
 the July temperature about -f- 6 C. This increased; during the 
 period of the tundras, to a season of five months' vegetation and 
 a July temperature of + 9 C." ( Andersson-i : xxv.) The arctic 
 flora of these countries was followed by forests in which three trees, 
 the pine (Pinus silvestris), the birch (Betula odorata), and the 
 asp or poplar (Populus tremula) became the dominant types. The 
 July temperature at this time averaged probably 10 to 12 C. 
 These first forest trees were, however, not uniformly distributed. 
 Thus in the western regions the pines were absent, the birch and 
 poplar alone predominating. This corresponds to the distribution 
 of the trees in the present arctic region where Betula odorata forms 
 the dominant forest tree around the fjords of South Greenland, in 
 Iceland, the whole of Scandinavia and the peninsula of Kola to the 
 White Sea. This may be explained by the greater humidity of this 
 region. In Finland and North Germany the birch and pine oc- 
 curred together in the first post-glacial forests, which represented 
 the drier, more continental type of arctic forest, such as is found 
 to-day in the remainder of the arctic regions, where forests, consist- 
 ing primarily of pines (Pinus), spruces (Picea) and larches 
 (Larix), abut against the treeless arctic plains. 
 
 With the increase in temperature, the coniferous woods were re- 
 placed by those requiring a higher summer temperature, such as 
 small leaf lindens (Telia europcca), hazel (Corylus avellana}, 
 maple (Acer platanoides) , elm (Ulnius montana), etc. Finally, 
 the oak (Quercus pedunculata) made its appearance, and displaced 
 the pines almost entirely. Gunnar Andersson and others have fur- 
 nished evidence from the former distribution of the hazel, oak, 
 linden and several aquatic plants, to the effect that the increase in 
 warmth culminated in a period of higher temperature than the pres- 
 ent over the whole of western Scandinavia, and less markedly over 
 North Germany. In northern Sweden the temperature during the 
 warmer period averaged 2.5 C. higher than now, though the win- 
 ter temperature could not have been higher than the present, for 
 plants requiring a warmer winter apparently did not extend fur- 
 ther north than they do now. In the central parts of southern 
 Norway, Holmboe finds that the border line of the fir was once 
 about 300 meters higher than at present. In general, the appear- 
 ance of the spruce (Picea excelsa) in the northern and the beech 
 (Fagus silvatica) in the southern part of the glaciated' region seems 
 to indicate a gradual deterioration of the climate of Europe since 
 the maximum of post-glacial temperature. 
 
CLIMATIC CHANGES 87 
 
 A similar succession of floras seems to have occurred in North 
 America, but the evidence has not been fully gathered. Over the 
 great plains of Canada, between the international boundary and 
 the forest region which stretches northwestward through Manitoba 
 and Saskatchewan and westward across Alberta, the climate on the 
 melting of the glaciers was probably much like that of the barren 
 lands farther north at the present time, where the mean summer 
 temperature is below 10 C., with permanently frozen subsoil and 
 consequently a complete absence of trees. As the climate became 
 warmer on the disappearance of the ice, it also became drier, so that 
 forests were unable to grow and Sphagnum swamps unable to form. 
 
 Evidence of a warmer climate preceding the present has been 
 obtained from the Atlantic coast, where the Talbot formation of 
 Maryland and Virginia, believed to be post-glacial in age, holds a 
 flora which is more characteristic of southern portions of the same 
 region. Thus the bald cypress (Tax odium distichum), found fossil 
 as far north as Long Branch, New Jersey, has its present northern 
 limit in southern Delaware and on the eastern shore of Maryland ; 
 the loblolly pine (Pinus tceda), also found at Long Branch, does 
 not extend north of southern New Jersey at the present time, with 
 its maximum development west of the Mississippi; the tupelo 
 (Nyssa biflora), found fossil in New Jersey, ranges to-day from 
 North Carolina to Louisiana. 
 
 2. Animals. Marine and fresh-w r ater mollusca are among the best 
 available indicators of climatic changes, so far as species are con- 
 cerned, which are still existing, and the geographic range of which is 
 known. In the marine species it must, however, always be borne in 
 mind that bathymetric distribution may counteract the influences of 
 climate and that hence the evidence must be carefully scrutinized. 
 Even better indications of change of climate are furnished by the 
 distribution of land animals, especially insects and mammals, though 
 this evidence is generally less readily available. Examples showing 
 changes of fauna, most probably due to change of climate, have 
 been obtained in numerous late glacial and post-glacial deposits. 
 A highly significant section of these deposits has been studied by 
 Jensen and Harder on the west coast of Greenland in the Orpiksuit 
 fjord, Disko Island (about lat. 70 N.). In the lowest clays occurs 
 a fossil fauna with Balanus hameri, indicating a period during 
 which the climate was not high arctic, but rather resembled that 
 of the present time. This is followed by a series of clay beds 
 averaging 10 meters in thickness, with a rich fauna, among which 
 Mya truncata cf. ovata and Yoldia arctica must be noted, indicating 
 that the climate gradually refrigerated until high arctic conditions 
 
88 PRINCIPLES OF STRATIGRAPHY 
 
 existed. This period seems to have been characterized by subsi- 
 dence. A period of elevation followed, with an increase in warmth, 
 which reached its maximum when the land stood approximately 10 
 meters higher than at present. This is shown by the boreal mol- 
 luscs Zirphcca crispata and Anomia ephippium, together with Mytilus 
 edulis, Tellina baltica, Littorina rudis, and L. palliata, mostly forms 
 now common on the New England coast. With still greater eleva- 
 tion the climate again cooled, until it resembled that of the present 
 time, the maximum elevation being 50 meters above the present sea- 
 level. The first two formations probably were deposited during 
 glacial time, while the succeeding deposits represent post-glacial time. 
 The warm-water fauna has a wide distribution in the arctic, espe- 
 cially recognizable by the shells of Mytilus edulis, and often by 
 Cyprina islandica and Littorina littorea. Some of the arctic locali- 
 ties where this fauna has been found fossil are the Franz Josef 
 fjord, East Greenland, Spitzbergen, King Charles Land and Franz 
 Josef Land. It has not yet been found in arctic North America. 
 
 Another fauna, found in parts of the arctic where it is now ex- 
 tinct, and indicating warmer conditions than now, is the Purpura 
 fauna, with P. lapillus, Pecten islandicus, Zirphcea crispata, Cy- 
 amium minutum and Skenea planorbis. This has been found in 
 northwestern Iceland, in a formation resting in some cases directly 
 upon the peat beds with remains of the arctic birch, Betula odorata. 
 
 In North Germany a climate similar to the arctic one is indicated 
 by late glacial or early post-glacial deposits, carrying the molluscs, 
 Vertigo paracedentata, Succinea schumacheri, Planorbis arcticus, 
 P. stroemi, Sphcerium duplicatum and Anodonta mutabilis. Arctic 
 conditions in Denmark and Sweden, while the ice still occupied a 
 part of the land, are indicated by deposits containing at the base a 
 fauna with the arctic molluscs, Yoldia arctica, Tellina torelli, and 
 T. loveni, which at present are restricted to seas where the tem- 
 perature in the depths at which the species live scarcely rises above 
 2.5 C. and frequently remains below o, even in the warmest 
 months of the year. This corresponded to the time of the Salix 
 polaris flora in Denmark. Higher up, together with a flora in which 
 the birches predominate, occurs Anodonta cygnea, which has been 
 held to indicate a July temperature of 13 to 15 C. Still higher 
 follows the fauna with Zirphcea crispa, Mytilus edulis, Cyprina 
 islandica, etc. 
 
 In northern New England and eastern Canada, the glacial till 
 is followed by the lower Leda clays, the fauna of which (Leda sp., 
 Saxicava rugosa, etc.) indicates a climate like that of southern 
 Labrador. These are followed by the upper Leda clays and sands 
 

 
 CLIMATIC CHANGES 89 
 
 with Macoma fusca, which indicate a climate like that of the pres- 
 ent St. Lawrence valley. The occurrence of relict colonies of 
 Ostrea virginiana var. borealis and Venus mercenaria at various 
 places in the maritime provinces, and in shell heaps along the New 
 England coast as far as Casco Bay, Maine, indicates a period of 
 warmer climate than the present, since these species are now limited 
 in their northward migration by Cape Cod. The extinction of this, 
 and the character of the present fauna indicate a return to cooler 
 conditions. Warmer water conditions inland are also indicated by 
 the occurrence of Unios and other fresh-water molluscs in the 
 gravels of Goat Island and the banks near the Falls of Niagara, 
 some of which (Unio clavus, U. occidens, and U. solidus and the 
 Margaritana) live to-day only in tributaries of the Mississippi to the 
 south. Evidence of change of climate during Pliocenic times in 
 Japan is indicated by the succession of molluscan faunas (Yoko- 
 yama-no). From beds regarded as of middle Pliocenic age, a 
 molluscan and brachiopod fauna of decidedly boreal character has 
 been obtained. In the Upper Pliocenic near Tokyo was obtained 
 a molluscan fauna less boreal in character, though indicating still 
 colder conditions than exist at the present time. Still higher beds, 
 referred to the Pleistocenic (Diluvial), contain a molluscan and 
 coral fauna, many species of which are now found only in much 
 more southern localities, the China Sea, the Philippines, and the 
 tropical portions of the Pacific and Indian oceans. If the identifica- 
 tions of these formations as Pliocenic and Pleistocenic, respectively, 
 are correct, the remarkable conclusion would have to be drawn that 
 Japan actually had a warmer climate than to-day, while Europe and 
 America were suffering glacial conditions. In order to bring Japan 
 into harmony with the western world, we would have to assume 
 that the deposits called Pliocenic on the basis of numerical pre- 
 ponderance of living species are actually later in age, i. e., are all 
 Pleistocenic. Such an assumption is not unwarranted. 
 
 The Pliocenic or Crag faunas of England show a progressive 
 refrigeration of the climate. The mollusca of the lowest of these, 
 the Coralline Crag, still bears the stamp of a more genial climate 
 than the present, in spite of the admixture of a few boreal types. In 
 the next division, the Red Crag, the number of boreal species in- 
 creases so as to form 10%, while the succeeding Norwich Crag 
 has a still greater percentage of northern forms. Finally, the high- 
 est, the Chillesford and Wegbourne Crags, have a really boreal or 
 arctic molluscan fauna, including Tellina baltica, Saxicava arctica, 
 Mya arenaria, M. truncata, Cyprina islandica, Astarte compressa, 
 A. sulcata, A. borealis, Turritella terebra, Trophon antiquus, Pur- 
 
go PRINCIPLES OF STRATIGRAPHY 
 
 pura lapillus, Littorina littorea, Buccinum undatum, etc., most of 
 which still exist in arctic and subarctic regions. 
 
 The mammals of North America have furnished some evidence 
 of the change in climate (Hay-43). Along the cold margin of the 
 ice sheet ranged the northern Rangifer, Bodtheriinn and Symbos, 
 as shown by their remains. The giant beaver Casteroides lived with 
 the now extinct horses, tapirs, mastodons, elephants, mylodon, and 
 magalonyx in the southern States and continued there during the 
 Pleistocenic period. It moved northward after the melting of the 
 ice. The peccaries, apparently always lovers of a mild if not warm 
 climate, now range from Arkansas to Patagonia. In the Pliocenic 
 a species lived in Texas, while after the melting of the ice repre- 
 sentatives of the family moved northward, their remains having 
 been found in three localities upon the Wisconsin drift sheet, viz. : 
 northern Indiana; near Columbus, Ohio, and at Rochester, New 
 York. The hairy mammoth, Elephas primogenius, seems to have 
 always lived near the margin of the ice sheet, but the Columbian 
 elephant, E. colmnbi, was a denizen of warmer climates, yet its 
 remains have also been found in deposits overlying the Wisconsin 
 drift. The same is true of the mastodon, M. americanus, a denizen 
 of mild climates, which has not only left its remains over the south- 
 ern States, but which roamed northward during the warm post- 
 glacial period. The mammals also indicate a period of warmer cli- 
 mate, during which they ranged farther north than at present, which 
 is a period of somewhat lower temperatures. This reduction, while 
 fatal to many forms, was the cause of the survivors moving south- 
 ward again. 
 
 DISPLACEMENT OF THE EARTH'S Axis AS A CAUSE OF 
 CLIMATIC CHANGES. 
 
 That a change in the position of the earth's axis would bring 
 about a change in climate, cannot be questioned, and this explanation 
 has been suggested for the glacial conditions in Pleistocenic time. 
 Davis (25) has outlined the climatic consequences of displacing the 
 poles in such a way that the north pole would be located at Iceland, 
 in latitude 70 N. on the meridian of 20 W., the following being 
 some of the effects : "First, a rearrangement of shore lines in con- 
 sequence of the adoption of new locations of polar flattening and 
 equatorial bulging. . . . Second, alteration in the paths of ocean 
 currents, of which one of the most important would be the dimi- 
 nution of the volume of warm water transferred from the southern 
 to the northern hemisphere by the oblique cross-equator current of 
 
CAUSES OF CLIMATIC CHANGES 91 
 
 the Atlantic, and thus the great loss of importance in the extension 
 of the Gulf Stream into the North Frigid zone. Third, a change 
 in the location of the wind and rain belts, their boundaries being 
 shifted twenty degrees southward, in the meridian of Iceland, the 
 same amount northward on the opposite meridian which passes 
 somewhat east of New Zealand, and remaining essentially un- 
 changed at the halfway points, which are located near the meridians 
 of Ceylon and the Galapagos." 
 
 Such rearrangement of wind and rain belts "would tend not only 
 to glaciate northwestern Europe and northeastern America, but 
 would also place arid trade-wind climates on the northern side of 
 the belt now occupied by the equatorial rains of Africa and South 
 America, and at the same time place the equatorial rains on the 
 northern margin of the arid land areas now found in the southern 
 parts of these continents. On the adoption of the present location 
 of the poles, the change would be reversed." The northern side of 
 the equatorial rain belt in Africa and South America should then 
 be found to possess topographic records of a wet climate recently 
 succeeding a dry climate, and the features of the region south of 
 the same belt should indicate a dry climate following a wet climate. 
 
 Professor Simroth, of Leipzig, in his book, Die Pendulations 
 Theorie, 1907 (86) has tried to explain some peculiar distributions 
 of organisms in the present period by oscillations of the poles along 
 the meridian of 10 E. latitude (170 W. lat). With an oscilla- 
 tion of 20 back and forth this would bring the north pole at one 
 time near Behring Strait, and at the other extreme in the Arctic 
 Ocean, west of the northern end of Norway. If the former posi- 
 tion was held in Pliocenic times, the Pacific side would be cool and 
 gradually become warmer, with the change of the pole to the oppo- 
 site position ; while on the Atlantic side the change would be from 
 warmer to cooler conditions terminated by glacial climates. Such 
 conditions seem actually to have occurred, as shown by the gradual 
 change from a warmer climate than at present at the beginning of 
 Pliocenic time in Europe, to the glacial conditions in Pleistocenic 
 time, and by a gradual increase in warmth on the Pacific side as 
 shown by the Pliocenic deposits of Japan, until in the Pleisto- 
 cenic the sun shone in the region of Noma (35 N. lat.), "with 
 about the same intensity as it now shines at least on the Ryukyus 
 or the Bonin Islands." (Lat. 27 N.) This explanation has 
 found its most recent advocate in the brilliant palaeontologist of the 
 Imperial University of Tokyo, Professor Matajiro Yokoyama (Yo- 
 koyama-no://<5). Investigating this problem, G. H. Darwin (22) 
 came to the conclusion that, if the earth is quite rigid, the pole may 
 
92 PRINCIPLES OF STRATIGRAPHY 
 
 have moved about 3 from its original position. If, however, the 
 earth is plastic, as seems to be the case to a certain degree, so that it 
 could readjust itself to the form of equilibrium, then there is a pos- 
 sibility of a cumulative effect, and the pole may have wandered 10 
 or 15 from its original position. This subject is more fully dis- 
 cussed in Chapter XXIII. 
 
 ORIGIN OF THE ATMOSPHERE. 
 
 According to the nebular hypothesis of earth origin, the atmos- 
 phere is merely the residuum of uncombined gases which were left 
 behind when the globe assumed its solid form. To this are added 
 various supplies, chief among which is the carbon dioxide from 
 volcanic eruptions, the decay of organic matter, and the burning of 
 coal. The Planetesimal hypothesis of Chamberlin, on the other 
 hand, considering the earth as made up of aggregations of small 
 solid bodies coming from space, derives the atmosphere from the 
 small quantities of entangled or occluded atmospheric matter 
 brought by these planetesimals. The pressure of the accumulating 
 cold matter eventually produced sufficient internal heat to expel 
 these gases. If the conception of an internal gaseous centrosphere 
 can be entertained, the possibilities of addition to the atmosphere 
 are greatly enhanced. 
 
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94 PRINCIPLES OF STRATIGRAPHY 
 
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 Congres Geologique International. Compte Rendu. loth Session, 
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BIBLIOGRAPHY II 95 
 
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 46. HECKER, OSKAR. 1905. Zur Entstehung der Inselberglandschaften 
 
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 I75-I79- 
 
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 Quoted by Geikie, Text Book of Geology, 3rd edition, p. 328; 4th 
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 50. HILL, ROBERT T. 1908. Growth and Decay of the Mexican Plateau. / 
 
 Engineering and Mining Journal, Vol. LXXXV, pp. 681-688. 
 
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 53. JULIEN, ALEXIS A. 1901. A Study of the Structure of Fulgurites. 
 
 Journal of Geology, Vol. IX, pp. 673-693. 
 
 54. KERR, W. C. 1 88 1. On the Action of Frost in the Arrangement of 
 
 Superficial Earthy Material. American Journal of Science, third series, 
 Vol. XXI, article XLIV, pp. 345-360. 
 
 55. KEYES, CHARLES R. 1908. Rock Flour of the Intermont Plains of 
 
 the Arid Regions. Bulletin of the Geological Society of America, 
 Vol. XIX, pp. 63-92, pi. 5. 
 
 56. KEYES, CHARLES R. 1911. Mid-Continental Eolation. Bulletin of 
 
 the Geological Society of America, Vol. XXII, pp. 687-714. 
 
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 Smithsonian Contributions, 27, No. 884, 30 pages. 
 
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 59. MANSON, MARSDEN. 1899. The Evolution of Climates, Separate 
 
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 American Geologist, Vol. XXXIII, pp. 44-57. 
 
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 developpement et leurs causes. Congres Ge"ologique International. 
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96 PRINCIPLES OF STRATIGRAPHY 
 
 62. MARTONNE, E. DE. 1909. Traite" de Geographic Physique. 
 
 63. MAURY, M. F. 1874. The Physical Geography of the Sea. 
 
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BIBLIOGRAPHY II 
 
 97 
 
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98 PRINCIPLES OF STRATIGRAPHY 
 
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B. THE HYDROSPHERE. 
 
 CHAPTER III. 
 MORPHOLOGY AND SUBDIVISIONS OF THE HYDROSPHERE. 
 
 The hydrosphere consists of the oceans and their prolongations 
 into the land blocks, the lakes, the rivers, and the ground water. 
 The oceans and their extensions into the land blocks constitute the 
 marine portion of the hydrosphere; the lakes, rivers, and ground 
 waters constitute the non-marine or continental portion. In the 
 present chapter their morphological characteristics will be discussed, 
 and an attempt will be made to outline a natural classification of the 
 various subdivisions, based primarily on origin. 
 
 A. THE MARINE DIVISION OF THE HYDROSPHERE. 
 
 REGIONAL SUBDIVISIONS OF THE SEA. The classifica- 
 tion of oceans and minor subdivisions of the sea has attracted the 
 interest of geographers from the earliest times. Many and varying 
 systems of classification have been proposed, based on size, form, 
 position with reference to the land, composition, origin, etc. Otto 
 Krummel (23 :^p) has published a very comprehensive system of 
 the seas, in which he recognizes as primary divisions: (i) The 
 independent, and, (2) the dependent types; the former comprising 
 the oceans, the latter the mediterraneans subdivided into (a) inter- 
 continental, and (b) intracontinental mediterraneans and the mar- 
 ginal seas. Added to these are: (3) the gulfs or bays, and (4) the 
 straits. Two other subdivisions are made on the basis of ingression 
 of the sea into existing depressions, with the subsidence of the land, 
 forming ingression seas, gulfs, or straits ; or, on the partial breaking 
 down of the surface and sinking of fault blocks, permitting the sea 
 to enter the land and forming tectonic seas, gulfs, or straits. 
 
 In a natural subdivision of the sea into basins, its relation to the 
 continental blocks must be considered of primary importance, since 
 
 99 
 
ioo PRINCIPLES OF STRATIGRAPHY 
 
 it is on this relationship that the other characteristics are, in a large 
 measure, dependent. As shown in the introductory chapter, the 
 most natural view to take of the land mass as a whole is that it 
 constitutes three continental blocks the American; the Old World, 
 comprising Europe, Asia, Africa, and Australia ; and the Antarctic. 
 These three great blocks are separated one from the other by the 
 great divisions of the sea, the oceans, which, therefore, have an 
 intercontinental location. These continental blocks and dividing 
 oceans have certainly been distinct since the Mesozoic, and it is 
 probable that they have been distinct since much earlier, possibly 
 Palaeozoic, time. It is, of course, true that America has at different 
 times been united with Europe or with Asia on the north, and 
 with Antarctica on the south, either by land bridges or by shallow 
 submarine banks. But this does not, therefore, destroy the essen- 
 tial independence of the three great blocks. If, then, we regard 
 the oceans as the intercontinental bodies of sea water, and consider 
 America and the Old World as distinct blocks, we have the follow- 
 ing four: 
 
 I. INTERCONTINENTAL SEAS OR OCEANS. 
 
 1. Pacific between all three blocks, with a superficial area * of 166 
 
 million square kilometers. 
 
 2. Atlantic between all three blocks, with a superficial area * of 82 
 
 million square kilometers. 
 
 3. Indian between Old World and Antarctica, with a superficial 
 
 area of 73 million square kilometers. 
 
 4. Arctic between Old and New World, with a superficial area of 
 
 about 14 million square kilometers. * 
 
 If, on the other hand, we consider, with Wagner, Penck, and 
 others, the Old and New World together as one block, we must take 
 the Arctic Sea from the list of oceans and place it as an intra- 
 continental body among the mediterraneans. 
 
 BATHYMETRIC ZONES OF THE SEA. A strip of shallow sea sur- 
 rounds each of the four great oceans and constitutes the belt of 
 transition from the sea to the land. This is the littoral belt, the 
 width of which corresponds to the width of the continental shelf. 
 Similarly, a littoral belt outlines each group of oceanic islands, 
 though this is generally very narrow. The depth of the littoral belt 
 does not, perhaps, greatly exceed 200 meters (roughly, ioo fathoms), 
 and it corresponds very closely with the depth to which sunlight 
 
 * Exclusive of marginal bodies. 
 
THE OCEANS 101 
 
 ordinarily penetrates. The littoral belt is, therefore, the submerged" 
 edge of the continental area, and most of it forms the margins of 
 the great oceans. The remainder of the oceans constitutes the 
 abysmal or abyssal area, in the discussion of which we may include 
 the steep transitional slopes between 200 meters and 2,400 me- 
 ters (see ante}. The upper zone of the ocean as a whole, irrespec- 
 tive of the position of the sea floor, forms the pelagic district, of 
 especial importance in marine bionomy, under which heading it and 
 the abyssopelagic zone will be more fully considered. (See Chap- 
 ter XXVI.) 
 
 CONFORMATION OF THE OCEAN FLOOR. The ocean floor is char- 
 acterized by elevations and depressions, often of great extent and 
 
 Andes 
 
 FIG. 16. (a) Diagrammatic cross-section of the Pacific Ocean near lat. 20 S., 
 showing two fore-deeps, the Tonga and the Atacama. 
 (b) A similar section across the South Atlantic and Indian oceans 
 near lat. 24 S. The Mid-Atlantic Rise is shown in section in the 
 Atlantic. (After Haug.) 
 
 diversity. (Fig. 16.) The following terminology has been de- 
 veloped for these irregularities by the International Commission for 
 submarine nomenclature 
 
 /. Grand or Major Features, or Those of Wide Extent. 
 
 1. Continental Shelf (G. Schclf, Fr. socle or plateau continental). 
 
 The submerged border of the continents to the loo-fathom or 
 2oo-meter line, where the descent is abrupt. 
 
 2. Sub-oceanic Depressions. 
 
 a. Basin (G. Becken, Fr. bassin). Approaching a circular 
 
 form. 
 
 b. Trough (G. Mulde, Fr. valid e). Elongated and broad de- 
 
 pressions with gradually sloping sides. 
 
 c. Trench (G. Graben, Fr. ravin}. Long but narrow depres- 
 
 sions along the continental border, with steep sides, of 
 which the continental is higher than the marine. 
 
102 PRINCIPLES OF STRATIGRAPHY 
 
 d. Prolongations of the basins or trough, comprising: 
 
 (1) Embayment (G. Bucht, Fr. golfe). Semicircular 
 
 to triangular indentations of the land or of sub- 
 marine elevations. 
 
 (2) Gully (G. Rinne, Fr. chenal). Elongated indenta- 
 
 tions of like character. 
 
 3. Sub-oceanic elevations, either independent, or submarine pro- 
 
 longations of the land. 
 
 a. Rise (G. Schwellen, Fr. seuil). With very gradually as- 
 
 cending sides. 
 
 b. Ridge (G. Riicken, Fr. crete). Prolonged elevations with 
 
 steep sides. 
 
 c. Plateau (G. Plateau, Fr. plateau). Elevations with steep 
 
 sides and longitudinal and transverse dimensions of sim- 
 ilar extent. 
 
 4. Deep (G. Tief, Fr. fosse). Abrupt depressions of the sea 
 
 floor, e. g., Nero deep. 
 
 5. Height (G. Hoh, Fr. haut). Abrupt elevations, generally on 
 
 rises, ridges, or plateaus. 
 
 //. Minor Features, or Those of Limited Extent. 
 
 1. Elevations. 
 
 a. Ridge (G. Riicken, Fr. crcte). Long ridges of minor 
 
 character, generally with an irregular surface, rising and 
 falling. 
 
 b. Submarine hill or peak. 
 
 (1) Dome (G. Kuppe, Fr. dome). Small, steep-sided 
 
 elevations in depths "of more than 200 meters. 
 
 (2) Bank (G. Bank, Fr. bane). Elevations above 200 
 
 meters but below 1 1 meters, e. g., Porcupine Bank 
 west of Ireland ; Grand Bank south of Newfound- 
 land. 
 
 (3) Reef or Shoal (G. Riff, Fr. recif or haut fond). 
 
 Elevations to within n meters or less of the 
 surface. 
 
 2. Depressions. 
 
 a. Caldron (G. Kessel, Fr. caldeira). Steep-sided depres- 
 
 sions of slight extent. 
 
 b. Furrow (G. Furche, Fr. sillon). Canal-like depressions 
 
 in the continental shelf, and more or less transverse to it, 
 e. g. } Ganges furrow. 
 
THE OCEANS 
 
 103 
 
 Features and Extent of the Continental Shelves. 
 
 Among the more prominent parts of the continental shelves we 
 may mention the following (Krummel-23 :uj) : 
 
 Table showing distribution area and depth of the principal 
 continental shelves. 
 
 Name and location 
 
 Area in sq. km. 
 
 Depth 
 
 I. Atlantic Ocean: 
 I. America 
 
 145,000 
 
 150-200 m. 
 
 Florida-Texas shelf 
 
 185 ooo 
 
 mostly less than 
 
 Campeche shelf, Central America 
 
 170,000 
 
 50 m. 
 
 do. 
 
 Guiana shelf South America 
 
 485 ooo 
 
 do. 
 
 South Brazil shelf 
 
 770,000 
 
 do. 
 
 Patagonia shelf 
 
 060,000 
 
 50-100 m. 
 
 2. Africa 
 Agulhas shelf, South Africa 
 
 75,000 
 
 mostly over 
 
 3. Europe 
 British shelf, including North Sea to 
 Cape Skagen, Denmark, and south to 
 Biarritz Bay of Biscay 
 
 i 050 ooo 
 
 100 m. 
 mostly under 
 
 II. Arctic Ocean: 
 Norwegian shelf 
 
 Q l.OOO 
 
 loom. 
 200-300 m. 
 
 Iceland-Faroe shelf 
 
 IIS OOO 
 
 200300 m. 
 
 Barent shelf. 
 
 810,000 
 
 200-300 m. 
 
 North Siberian shelf (Nova Zembla to 
 155 W Long ) 
 
 I ^O OOO 
 
 one-half under 
 
 III. Indian Ocean: 
 I. Africa 
 Zambesi shelf, mouth of Zambesi River . . 
 
 2. Asia 
 Bombay shelf, India 
 
 55,000 
 2^0 ooo 
 
 50 m. 
 
 mostly under 
 50 m. 
 
 50-100 m. 
 
 Birma shelf, India 
 
 200,000 
 
 mostly under 
 
 3. Australia 
 Northwest Australian shelf (N. W. Cape 
 to Melville Island) 
 
 500,000 
 
 loo m. 
 50-100 m. 
 
 South Australian shelf 
 
 320,000 
 
 50-100 m. 
 
 
 
 
IO4 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Table showing distribution area and depth of the principal 
 continental shelves Continued. 
 
 Name and location 
 
 Area in sq. km. 
 
 Depth 
 
 IV. Pacific Ocean: 
 i. Australian coast 
 Tasmania shelf 
 
 1 60 ooo 
 
 50100 m 
 
 Queensland shelf 
 
 IQO OOO 
 
 mostly under 
 
 Arafura shelf, North Australia 
 
 Q-JQ OOO 
 
 100 m. 
 50-100 m. 
 
 2. Austral-Asian coast 
 Borneo- Java shelf 
 
 i 850 ooo 
 
 50100 m. 
 
 3. Asiatic coast 
 Tonkin-Hong Kong shelf (facing South 
 China Sea) 
 
 4-7 c OOO 
 
 mostly under 
 
 Tung hai shelf (from Straits of Formosa 
 to Straits of Korea) 
 
 a I E; OOO 
 
 loom. 
 
 do. 
 
 Okhotsk-Sachalin shelf 
 
 7 T e OOO 
 
 50100 m 
 
 Behring shelf 
 
 I T2O OOO 
 
 one-half under 
 
 
 
 50 m. 
 
 Along the East Pacific {West American) border the continental 
 shelf is extremely narrow ; no specially defined portion of any size 
 being recognizable. 
 
 Subordinate Features of the Continental Shelf. These are the 
 minor elevations and depressions of which the banks and furrows 
 are the most important. Of the former, the banks at the mouth 
 of the English and St. George's channels are characteristic, the 
 largest of these, the Labadie-Cockburn bank, having a length of 280 
 kilometers. These banks are submarine continuations of the old 
 folds of southern Ireland, and on their surfaces are often found 
 the shells of shore Mollusca, which do not live in the depth of water 
 now covering the banks, showing a comparatively recent subsidence. 
 On the other parts of the British shelf we have the great Dogger 
 Bank in the North Sea. Bones of mammoth, rhinoceros, bison, 
 urochs, and wild horse are not infrequently brought up from this 
 bank, this, together with other facts, indicating depression, prob- 
 ably in glacial time, of a former land area. The Silver Pit furrow 
 in this bank has been regarded by Jukes-Brown as the ancient con- 
 tinuation of the Rhine. 
 
 Examples of banks and furrows on the American coast are the 
 Newfoundland banks, Great Bahama banks, Campeche bank, etc., 
 and the St. Lawrence and Hudson furrows. 
 
THE OCEANS 
 
 105 
 
 Features of the Sub-Oceanic Elevations and Depressions. 
 
 Among the great sub-oceanic elevations the most extensive is the 
 Mid-Atlantic Rise (Supan-38, plate 12), which extends from Ice- 
 land, over the Azores, southward to Tristan da Cunha, a distance of 
 14,000 kilometers and an area of 10 million square kilometers. It 
 is bounded by the 4,ooo-meter line, and its width in the South At- 
 lantic is approximately indicated by the longitudes of Ascension and 
 St. Helena islands. From the temperatures found in the depres- 
 sions on either side, and especially from the high temperature of the 
 south African trough, it is thought that the axis of this rise nowhere 
 
 Guam 
 
 MedinilJa 
 
 
 FIG. 17. Two cross-sections of the Marian Trench, a fore-deep in the 
 western Pacific. The upper is east from Guam, and passes 
 through the Nero Deep, 9,636 meters. The lower is east from 
 Medinilla, and passes through lesser deeps, north of the preced- 
 ing, and also shows a "ridge" east of the trench. (After Kriim- 
 mel.) 
 
 falls below 3,000 meters. North of the equator it is less continuous 
 than south of it. With its branches it divides the Atlantic Ocean 
 bottom into a number of great depressions: a North American 
 basin of 13 million square kilometers area, a Brazilian and an Ar- 
 gentine basin with a combined area of 16 million square kilometers, 
 a North African basin of 9 million square kilometers area, and a 
 West African trough of n million square kilometers area. This 
 great Mid- Atlantic swell does not join the Antarctic continent, but 
 between 30 and 40 S. lat. it has two branches a northwestern 
 one, the Rio Grande rise, nearly separating the Argentine and Brazil 
 basins, and a western one, the Whales rise, which extends from 
 Tristan da Cunha island /to the South African continent, and ef- 
 
io6 PRINCIPLES >F STRATIGRAPHY 
 
 fectively cuts off the South African trough from the Antarctic cold 
 waters. In the Pacific, west of South America, is the great Easter 
 Island rise, with an- area exceeding that of Africa. The South 
 Indian Ocean shows two great swells or rises : the Kerguelen rise, 
 from Antarctica and Australia, and the Crozet swell, or rise, ex- 
 tending southward from Africa. As examples of trenches, or 
 Graben, may be mentioned the Marian trench with the Nero deep, 
 and the Japan trench with the Tuscarora deep. They are regarded 
 as submarine fault or rift valleys, just as are those upon the land 
 (e. g., Rhine Graben). The two cross-sections of the Marian trench 
 here reproduced show their general characteristics (Fig. 17). 
 Ridges are illustrated by the Wyville-Thomson ridge, between 
 North Britain and the Faroe Islands, and the Faroe Island ridge, 
 which separates the deep Arctic waters of the East Greenland Sea 
 from the North Atlantic. The Wyville-Thomson ridge has its 
 lowest point within 576 meters of the sea-level, and shows a num- 
 ber of notches of the wind-gap type, which suggest that it is a part 
 of an old land ridge. The floor of the Faroe-Shetland gully, which 
 terminates in this ridge, has a fairly uniform depression of 1,170 
 to 1,189 meters. As an example of a plateau may be mentioned the 
 Blake Plateau, a nearly flat submerged tableland averaging 700 to 
 800 meters below sea-level, and bounded on the west by the steep 
 slope rising to the Florida-Carolina shelf, and on the east by the 
 equally steep slope descending to the North American basin. From 
 this basin rises the small isolated Bermuda plateau, while the Pacific 
 has in its central part the equally steep-sided Hawaiian plateau, 
 both of which are well shown on Supan's map, above cited. The 
 Pourtales plateau, south of Florida, with a depth of 90 to 300 
 fathoms (165 to 549 meters), is an example of a small plateau bor- 
 dering the continent. 
 
 II. INTRACONTINENTAL SEAS. 
 
 The continental blocks are divided into continents by arms of 
 the sea penetrating deep into the land, or indented by shallow or 
 deep marginal seas more or less land-locked or enclosed by islands. 
 These are the intracontinental seas, among which two types can be 
 distinguished : the independent,* and dependent. Independent 
 seas are more or less distinct from the oceans, lying in depres- 
 sions which are independent of the main ocean basins, and sepa- 
 rated from them by a rim, which may be largely submerged or 
 may rise above sea-level, leaving only a slight superficial connection 
 
 * Not in the sense of Kriimmel. See ante. 
 
INTRACONTINENTAL SEAS 107 
 
 with the ocean. These seas would become wholly independent if 
 the surface of the ocean were lowered sufficiently, or, at the most, 
 would remain connected with the oceans only by very narrow chan- 
 nels. Dependent seas are merely arms of the ocean extending 
 into the land, without marginal rim, becoming progressively nar- 
 rower and shallower the further they penetrate into the land. 
 Seas of this type would merely become shorter on the lowering of 
 the sea-level, but would always maintain their open connection with 
 the oceans. 
 
 In each of these groups we may further distinguish a subordi- 
 nate group in which an abyssal area is present, and another in which 
 it is absent. Independent intracontinental seas with an abyssal area 
 are called mediterraneans (Mittelmeere) , while the shallow type, 
 without the abyssal area, constitutes the true epicontinental sea.* 
 Each of these types may further be divided into marginal seas, i. e., 
 those largely enclosed by islands rising from a submerged rim, and 
 land-locked seas, or those largely surrounded by the mainland. 
 
 A. Independent Seas. 
 
 i. The Mediterraneans. The land-locked mediterraneans are the 
 most typical of this kind, and by some they are regarded as the only 
 true mediterraneans. Examples of these are the Roman mediter- 
 ranean (the Mediterranean of geographers ; in reality, a double one, 
 the western descending to 3,151 meters off the coast of Sardinia, 
 and the eastern to 4,404 meters south of Greece) ; the Black Sea, 
 an extreme type with a maximum depression of 2,244 meters ; the 
 Red Sea, 2,271 meters ; and the Mexican mediterranean, or Gulf of 
 Mexico, 3,809 meters. An intermediate type between the land-locked 
 and the marginal is seen in the Caribbean Sea, partly enclosed by 
 islands, and in the group of Austral-Asian mediterraneans.! This 
 group comprises a number of distinct mediterraneans, each one of 
 which, considered separately, would be classed as of the marginal 
 type. The chief of these are: the South China Sea, with a maxi- 
 mum depth of 4,226 meters; the Celebes Sea, 5,112 meters; and the 
 Banda Sea, 5,226 meters. An example of an abnormal marginal 
 mediterranean is found in the Tung-Hai, or East China Sea. This 
 descends regularly from the shore to below the 2OO-meter line, 
 
 * This term was proposed by Professor Chamberlin, and made to include the 
 littoral zone of the open ocean, which by no stretch of meanings can be classed 
 as a distinct sea. The present restriction of the term was proposed by the 
 author in 1907 (18). 
 
 t Classed by Krummel as a typical intercontinental mediterranean. 
 
io8 PRINCIPLES OF STRATIGRAPHY 
 
 and then rises abruptly in the chain of Lu-Tschu Islands, which 
 bound it on the southeast. Its littoral belt occupies more than two- 
 thirds the width of the sea on the west or continental side, but is 
 extremely narrow on the east or oceanic side, where the islands 
 rise abruptly. The maximum depth within the chain is 914 meters. 
 Typical marginal mediterraneans are found in the Japan Sea, 3,731 
 meters; in Okhotsk Sea, 3,370 meters; and in Behring Sea, 5,369 
 meters all on the east coast of Asia. The last of these is an ex- 
 ample of a mediterranean in which the rim is in large part sub- 
 merged, only islands bounding it on the south, east, and north. An 
 example of a still more extreme marginal mediterranean is .the Coral 
 Sea, east of Australia, the deepest part of which descends to 4,663 
 meters, but of which the southeastern margin is largely composed 
 of submerged reefs and shoals with deep channels between. From 
 this a further step takes us to the oceanic deeps, already mentioned, 
 as the extremes in one direction, while the land-locked type leads 
 through the Black Sea type of nearly cut-off bodies to the com- 
 pletely enclosed deep continental seas or lakes, such as the Cas- 
 pian. A subordinate type is found in the Adriatic, which is a de- 
 pendent, not of an ocean, but of the Roman mediterranean. Only a 
 small part of its bottom falls below the 2OO-meter line, its greatest 
 depth being 1,589 meters. It is thus transitional to the epicontinen- 
 tal seas. 
 
 It is noteworthy that marginal mediterraneans, so characteristic 
 of the western or Asiatic border of the Pacific, are wanting on the 
 eastern or American border. On the west Atlantic (east American) 
 coast we have the Caribbean and Mexican mediterraneans already 
 mentioned, and between them the smaller Yucatan basin, which de- 
 scends to 6,269 meters south of Grand Cayman Island. The ridge 
 between this and the Caribbean lies between Pedro and Rosalind 
 banks and has a maximum depth of nearly 1,300 meters. The Wind- 
 ward Canal between Haiti and Cuba has a maximum depth of 1,284 
 meters and the Mona passage between Porto Rico and Haiti, one of 
 the entrances to the Caribbean, only 583 meters, though the main 
 entrance, the Anegada Straits, between the Virgin Islands and Som- 
 brero in the Lesser Antilles, is less than 2,000 meters, while the 
 greatest depth of the Caribbean is 5,201 meters. The Florida Canal, 
 the exit from the Mexican mediterranean, has a maximum depth of 
 803 meters. On the northern Atlantic we have Baffin Bay (5,249 
 meters), which, though also open to the Arctic Ocean, has its 
 broader connection with the North Atlantic. On the East Atlantic 
 coast no mediterraneans except the Roman, with its dependents the 
 Adriatic and Black seas, occur, ' but epicontinental seas abound. 
 
INTRACONTINENTAL SEAS 109 
 
 The Indian Ocean has only the Red Sea as a contributory land- 
 locked marginal mediterranean, in addition to which there is a very 
 open and incomplete marginal mediterranean, the Burma or Anda- 
 man Sea, between the Malay peninsula and the Andaman and Nico- 
 bar Island groups. The maximum recorded depth here is 4,177 
 meters, but much of its deeper part lies between 2,000 and 3,000 
 meters below sea-level. Whether or not mediterraneans exist off the 
 southern borders of the three great oceans is at present unknown. 
 The Arctic Ocean has only one large marginal mediterranean, but 
 several epicontinental seas. The mediterranean type is represented 
 by the East Greenland Sea, lying between Greenland and Scandi- 
 navia, and Iceland and Spitzbergen. This has a maximum known 
 depth of 4,846 meters between North Greenland and Spitzbergen, its 
 connection with the Arctic being by channels 2,000 meters deep. 
 The deepest part of its submerged southern border is 550 meters 
 in Denmark Straits, but much of this border is shallow. (Fig. 18.) 
 Interoceanic mediterraneans. The East Greenland Sea and Baf- 
 fin Bay are interoceanic mediterraneans, i. e., lying between the 
 Atlantic and the Arctic, one belonging to each. Behring Sea is an 
 interoceanic mediterranean which lies between the Arctic and the 
 Pacific, but belongs to the latter. The Austral-Asian group is inter- 
 oceanic between the Pacific and the Indian oceans, while the Red 
 Sea has been artificially made interoceanic between the Indian and 
 Atlantic systems by the building of the Suez Canal, and the Carib- 
 bean mediterranean will soon be placed in this class also. 
 
 In general, mediterraneans may be considered in the light of mi- 
 nute oceans, with the essential bathymetric zones found in these, 
 i. e., abyssal, littoral, and pelagic. The characteristic independent 
 ocean currents are, however, wanting, though parts or branches of 
 these currents may occur, as, for example, the Gulf Stream in the 
 Central American mediterraneans, and the branch streams entering 
 the Roman mediterranean. 
 
 2. Epicontinental Seas. These are the shallow independent seas, 
 the greatest depth of which does not pass much below 200 fathoms, 
 or, if so, in only a few isolated spots. These have, therefore, only 
 a littoral and a pelagic zone, the abyssal being absent. Both land- 
 locked and marginal epicontinental seas occur; the former, when 
 situated in a region of normal pluvial climate, generally falling in 
 percentage of salinity below that of the open sea, owing to the 
 abundant influx of fresh water. Examples of the land-locked epi- 
 continental seas are Hudson Bay in North America, and the Baltic 
 with its branches, the Bothnian and the Finnish gulfs, in Europe. 
 Both of these are tributary to the Atlantic system. Hudson Bay 
 
no 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 has a maximum depth of 228 meters in one spot, but otherwise is 
 less than 200 meters deep; while the maximum depth of the Baltic 
 is 249 meters east of Gotland, that of the Bothnian Gulf 294 meters 
 
 FIG. 18. Bathymetric chart of the Arctic Ocean. The deepest shade (solid) 
 shows depths below 3,000 meters; the next (cross-hatching) be- 
 tween 3,000 -and 1,000 meters; the next lighter (horizontal lining) 
 shows depths between 1,000 and 200 meters, while the white 
 color shows everything above the 2OO-meter line, including the 
 lands. The character of East Greenland mediterraneans and the 
 location of the Wyville-Thomson Faroe-Iceland and Denmark- 
 Strait ridges is recognizable. The dotted circle is the Arctic circle. 
 (After Nansen and Haug.) 
 
 opposite Hernosand, Sweden, and that of the Finnish Gulf 124 
 meters near its mouth. In each case these maxima lie in small 
 depressions below the main floor of the water body. The deeper 
 portions of the main floor of the Baltic average 150 to 170 meters, 
 
INTRACONTINENTAL SEAS in 
 
 while much of the depth is less than TOO meters. In the Bothnian 
 Gulf the deeper parts lie between 100 and 160 meters, while the 
 greater part has a depth of less than 90 meters. Finally, the Finnish 
 Gulf, with the exception noted, does not reach the loo-meter line, 
 while much of it has a depth of less than 50 meters. The Persian 
 Gulf, with a maximum depth of 90 meters, is the only land-locked 
 epicontinental sea tributary to the Indian Ocean, but several other 
 Eurasian epicontinental seas of the land-locked type are tributary to 
 the Arctic Ocean. The larger of these are the White Sea, with a 
 maximum depth of 329 meters, but mostly above 200 meters, and 
 the Gulf of Obi in Siberia. In the Pacific the only land-locked epi- 
 continental sea is the Huang-hai or Yellow Sea, of China. This sea 
 has a rather broad opening into the East Chinese Sea and its margin 
 does not rise perceptibly above the general level of its floor, which 
 is from 80 to 90 meters below sea-level. Still there are a few de- 
 pressions of a little more than 100 meters, the maximum being 106 
 meters, opposite the southern end of the Korean peninsula. The 
 Gulf of Carpentaria in North Australia is another epicontinental sea 
 partly land-locked, but with ,a broad opening toward the north. The 
 average depth is from 50 to 60 meters, and this continues north- 
 ward in the shallow Arafura Sea between Australia and New 
 Guinea. Among the islands which separate this sea from the 
 Banda mediterranean on the northwest are several deep holes, some 
 of them descending below the 2,ooo-meter line. 
 
 On the eastern shore of the Pacific, Cook Inlet in Alaska and 
 Georgia Straits in British Columbia are examples of land-locked 
 epicontinental seas of very small size. The latter has a hole 316 
 meters deep opposite Vancouver, but is generally quite shallow, as 
 is also Cook Inlet. Another small water body of this type is San 
 Francisco Bay, while marginal epicontinental seas of small size also 
 occur on the coast of British Columbia and Alaska. An aberrant 
 type of the marginal epicontinental sea is found in the Rann of 
 Cutch, Bombay, west coast of India. This is very shallow, and as 
 it lies within the belt of great evaporation, it has practically been 
 converted into a salina or salt pan. 
 
 In the Arctic Ocean system are several epicontinental seas of 
 the marginal type, besides the land-locked types already mentioned 
 (White Sea and Gulf of Obi). Melville Sound in Arctic North 
 America is probably to be classed here, though its central area 
 descends below the 2OO-meter line. The Kara Sea, behind Nova 
 Zembla, is another but more open marginal sea, though in its west- 
 ern end a hole 730 meters deep is recorded. The largest sea of this 
 class connected with the Arctic Ocean is the East Spitzbergen, or 
 
ii2 PRINCIPLES OF STRATIGRAPHY 
 
 Barents Sea, lying between Spitzbergen on the west, Nova Zembla 
 on the east, the North European coast on the south, and nearly 
 closed on the north by the island group of Franz Josef Land. It 
 has some depths as great as 370 meters, but is shallow for the most 
 part, so that it is best classed as an epicontinental sea. 
 
 The North Sea and the Irish Sea are examples of marginal 
 epicontinental seas on the North Atlantic border. The former is 
 for the most part less than 100 meters deep, but has some depths as 
 great as 187 meters off the Orkneys, while the latter has a maximum 
 depth of 124 meters, much of its bottom lying between 50 and 100 
 meters. The English Channel is an extreme case, approaching the 
 dependent type; still it has a few deep holes descending to a 
 maximum of 172 meters north of the Channel Isles. Its opening 
 into the great North Sea' at Dover Straits gives it, however, a 
 peculiarity not possessed by other marginal bodies of this kind. In 
 the South Pacific the Tasmanian Sea, between Australia and Tas- 
 mania, may be classed as a shallow, flat-bottomed, rather open epi- 
 continental sea of the marginal type. Its greatest reported depth 
 is 88 meters. , 
 
 B. Dependent Seas Funnel Seas. 
 
 A typical example of a dependent sea is found in the Gulf of 
 California, between the Peninsula of Lower California and Mexico. 
 The floor of this water body descends from zero at the head to 
 2,600 meters below sea-level at the mouth, the descent being a 
 regular one. At the same time the channel widens so that the form 
 is that of a narrow funnel split lengthwise. This Funnel Sea 
 (Trichter See, mare tuyau), as it may be called, will never become 
 distinct, no matter how much the surface of the, ocean is lowered; 
 it will simply be shortened until, when the level has been lowered 
 2,600 meters, it becomes extinct. In form it resembles a broad 
 river valley; indeed, if it were shorter and shallower it might be 
 regarded as the estuary of the Colorado River, which enters its 
 head. 
 
 An example of a broader funnel sea is found in the Bay of 
 Biscay, which descends to near 5,000 meters at the mouth. Here a 
 few deeper depressions may occur inside of the mouth, but the form 
 is in all essentials that of a funnel sea. 
 
 The Bay of Fundy on the Atlantic is a shallow funnel sea, not 
 descending below 200 meters at the mouth. It may be regarded as 
 the littoral type of the narrow funnel seas, just as the Californian 
 Sea may be regarded as the littoral-abyssal type of the same class. 
 
INTRACONTINENTAL SEAS 113 
 
 Of the broader, or Biscayan type, on the east Pacific border, only 
 the Gulf of Panama need be mentioned as of sufficient size and 
 importance. This descends to 3,665 meters. On the Atlantic bor- 
 der, besides the Biscayan, may be noted the Gulf of Guinea (to 
 4,000 meters), off the African coast. Of a special type is the Gulf 
 of Cadiz (3,000 to 4,000 meters), as the funnel sea between Spain 
 and Morocco is called. This has all the characters of a typical 
 funnel sea of the Biscayan type, but opens by the Straits of Gibral- 
 tar into the Roman Mediterranean, making it more truly a funnel 
 than Biscay. Of a similar type, though in form related to the 
 Californian Sea, is the Gulf of Oman, connecting the Persian Gulf 
 with the Indian Ocean (3,292 meters) and the Gulf of Aden, the 
 continuation of the Red Sea (to 3,584 meters). 
 
 An extreme case of the Fundy type is seen in the estuary of the 
 Rio de la Plata, which has a depth of only 26 meters at the mouth. 
 Neither the Arctic nor the West Pacific furnishes examples of 
 dependent seas. 
 
 Examples of subordinate funnel seas, situated on a mediter- 
 ranean instead of an ocean, are found in the Golfe di Taranto, 
 southern Italy, and the .Golfe du Lion, southern France. Both 
 descend approximately to 2,000 meters at the mouth. Of the same 
 character is the Gulf of Sidra on the north coast of Africa. All 
 of these are of the Biscayan type. The Gulf of Suez at the head 
 of the Red Sea may be taken as an example of a subordinate funnel 
 sea of the Fundy type, though its channel is rather narrow and 
 tortuous. The Gulf of Akabah, on the other hand, forming the 
 east branch of the head of the Red Sea, is a subordinate mediter- 
 ranean of the land-locked type. 
 
 An example of a complex funnel sea, approaching in some of its 
 characters a mediterranean of the marginal type, is seen in the Gulf 
 of St. Lawrence the mouth of the river of that name. This 
 descends regularly to 572 meters, but rises again from Cabot Straits 
 outward to 410 meters before falling off to deep water. It has two 
 arms, one from north of Anticosti, the other separating Labrador 
 and Newfoundland. A continuous deep channel is said to exist, 
 however, and the valley is explained as a Tertiary erosion valley. 
 
 SUMMARY OF CLASSIFICATION. 
 
 The classification of seas may be summarized as follows : 
 I. Intercontinental seas or oceans. 
 
 Zones: Pelagic, littoral, abyssal. 
 Examples: Pacific, Atlantic, Indian, Arctic. 
 
114 PRINCIPLES OF STRATIGRAPHY 
 
 II. Intracontinental seas. 
 
 A. INDEPENDENT SEAS. 
 
 1. MEDITERRANEANS. 
 
 Zones: Pelagic, littoral, abyssal. 
 
 a. LAND-LOCKED. 
 
 Atlantic system: Roman, Black, Mexican. 
 Indian system: Red Sea. 
 Subordinate: Adriatic, Akabah. 
 
 b. MARGINAL. 
 
 Pacific system: Australasian group, East 
 China Sea, Japan Sea, Okhotsk Sea, 
 Behring Sea. 
 
 Atlantic system: Caribbean. 
 
 Indian system: Andaman. 
 
 Arctic system: East Greenland Sea. 
 
 2. EPICONTINENTAL SEAS. 
 
 Zones: Pelagic, littoral. 
 
 a. LAND-LOCKED. 
 
 Pacific system: Yellow Sea. 
 
 Atlantic system: Hudson Bay, Baltic 
 
 group. 
 
 Indian system: Persian Gulf. 
 Arctic system: White Sea, Sea of Obi. 
 
 b. MARGINAL. 
 
 Pacific system: Tasmanian Sea, Carpen- 
 taria Gulf. 
 
 Atlantic system: North Sea, Irish Sea, 
 English Channel. 
 
 Arctic system: East Spitzbergen Sea. 
 Kara Sea, Melville Sound. 
 
 B. DEPENDENT SEAS. Funnel seas. 
 
 i. CALIFORNIAN TYPE. 
 
 Zones: Pelagic, littoral, abyssal. 
 
 a. CLOSED HEAD. 
 
 Pacific system: Calif ornian Gulf. 
 Atlantic system: Gulf of St. Lawrence. 
 
 b. OPEN HEAD. 
 
 Indian system: Gulf of Aden, Gulf of 
 Oman. 
 

 CONTINENTAL SEAS 115 
 
 2. BISCAYAN TYPE. 
 
 Zones: Pelagic, littoral, abyssal. 
 
 a. CLOSED HEAD. 
 
 Atlantic system: Bay of Biscay, Gulf of 
 
 Guinea. 
 Subordinate: Gulf of Taranto, Gulf of 
 
 Lyons, Gulf of Sidra. 
 
 b. OPEN HEAD. 
 
 Atlantic system: Gulf of Cadiz. 
 
 3. FUNDYAN TYPE. 
 
 Zones: Pelagic, littoral. 
 
 a. CLOSED HEAD. 
 
 Atlantic system: Bay of Fundy, Rio de 
 la Plata. 
 
 b. OPEN HEAD. 
 
 Indian system (Subordinate) : Gulf of 
 Suez. (Head artificially opened.) 
 
 B. THE CONTINENTAL DIVISION OF THE 
 HYDROSPHERE. 
 
 III. CONTINENTAL SEAS OR LAKES. 
 
 Inland seas or lakes, i. e., water bodies entirely enclosed by 
 land, may be classed as continental. They are either salt or fresh, 
 depending on their location within the arid or the pluvial belts and 
 on the relative amount of evaporation and precipitation. Salt lakes 
 lying near the sea often have their surface below that of the ocean, 
 as in the case of the Caspian Sea, the surface of which lies 26 
 meters below the level of the Black Sea, less than 500 kilometers 
 distant; while the Dead Sea is 394 meters below the level of the 
 Roman mediterranean, which is only 75 kilometers distant. The 
 Sea of Aral, however, another salt sea in the same belt, is 48 
 meters above the Black Sea, with a maximum depth of 66 meters; 
 while Balchash Sea, in the Great Steppe farther east, has an eleva- 
 tion of 274 meters, with a depth of 25 meters. In the region 
 bounded by the Caspian, the Black, and the Mediterranean 
 (Roman), are several small salt lakes varying from 940 meters to 
 1,925 meters in elevation. In North America, Great Salt Lake has 
 an elevation of 1,283 meters above the sea. 
 
 Fresh-water lakes all have their surfaces above or just at sea- 
 level, though some of them have their bottoms far below sea-level. 
 
ii6 PRINCIPLES OF STRATIGRAPHY 
 
 Such is the case with Lake Baikal in Siberia, which has an eleva- 
 tion of 520 meters and a depth of 1,430 meters, its floor, therefore, 
 descending 910 meters below sea-level. 
 
 Among the* great American lakes, Ontario descends 150 meters 
 below sea-level, Huron 52 meters, Michigan 88 meters, and Superior 
 114 meters. The American Great Lakes drain their surplus waters 
 through the St. Lawrence system into the Atlantic, and Lake Baikal 
 through the Angara River into the Arctic. Lake Tanganyika, of 
 East Africa, 780 meters above sea-level, has only an interrupted 
 outward drainage, the removal of surplus water being by evapora- 
 tion ; but Lake Nyassa, 480 meters above sea-level, drains by the 
 Schire and the Zambesi into the Indian Ocean. This lake has a 
 maximum known depth of 786 meters (430 fathoms), its floor thus 
 descending 300 meters below sea-level. Its length is about 350 
 miles and its average width about 40 miles. Lake Tanganyika also 
 passes below sea-level in its deeper portion. On the American 
 continent, Lake Tahoe in the Sierras, with a depth of 1,654 feet, 
 is second only to Crater Lake, Oregon, which has a depth of 1,975 
 feet. Lake Superior has a maximum depth of only 1,008 feet, while 
 Lake Maggiore (1,004 feet) and Lake Como (1,354 feet), on the 
 south side of the Alps, compare favorably with the American lakes 
 in depth. 
 
 CLASSIFICATION' OF LAKES AND LAKE BASINS. A genetic classi- 
 fication of lake basins differs from a classification of lakes as a 
 whole because it deals only with the depression in which the lake 
 is situated. Depressions of exactly similar characters, but without 
 water, may exist, and would have to be taken account of in the 
 classification of basins. Such "dry lakes" are, however, of no sig- 
 nificance to the limnographer or to the bionomist. Again, the 
 character of the water, whether salt or fresh, is largely a matter of 
 climate, and has no relation to the lake basin. This is also true of 
 the outlet or effluent, for if the number of affluents is small and 
 evaporation lowers the lake sufficiently, it will lose its outlet, just as 
 it may through a rise of the rim or other tectonic change. Such 
 excess of evaporation generally brings about the salinifying of the 
 water by the concentration of the mineral solute. (Davis-7; also 
 Salisbury-33.) 
 
 Classification of Lake Basins. 
 
 In a natural classification of lake basins the agent active in 
 their production is of first importance, and lake basins may, there- 
 fore, be classified in the first place as A. Lakes of Deformation, or 
 
CLASSIFICATION OF LAKE BASINS 117 
 
 Tectonic Lakes, B. Lakes of Construction, C. Lakes of Destruction, 
 and D. Lakes of Obstruction. The further subdivision is as fol- 
 lows : 
 
 A. DEFORMATIONAL OR TECTONIC BASINS. 
 
 1. Fault basins. 
 
 2. Folded basins. 
 
 3. Warp basins. 
 
 4. Complex basins, great basins. 
 
 B. CONSTRUCTIONAL BASINS. 
 
 1. Volcanic: a. Crater lakes; b. depressions in lava flows. 
 
 2. Chemical : Hot spring and geyser basins. 
 
 3. Organic : a. Vegetal or swamp ; b. coral reef lagoon. 
 
 4. Detrital : (Reconstructional). 
 
 a. Marine : ( i ) Coastal plain depressions. 
 
 b. Lacustrine. 
 
 c. Fluviatile : (i) River flood plain lakes (oxbows) ; 
 
 (2) delta lakes; (3) fan lakes. 
 
 d. Glacial: (i) Morainal kettle lakes ; (2) drift sheet 
 
 kettle lakes. 
 
 e. Atmospheric: (i) Land-slip basins; (2) dune 
 
 lakes. 
 
 f . Artificial : Human constructions, etc., e. g., built- 
 
 up reservoirs. 
 
 C DESTRUCTIONAL BASINS. 
 
 1. Volcanic: Pit craters, volcanic subsidence hollows. 
 
 2. Chemical : 
 
 a. Solution hollows and sink-holes. 
 
 b. Disintegration hollows. 
 
 3. Fluviatile : 
 
 a. Waterfall lakes. 
 
 b. Pot-hole lakes. 
 
 4. Glacial : Ice excavated rock tarns. 
 
 5. Deflation lakes, or wind excavated hollows. 
 
 6. Artificial excavations : Man-made excavations ; mud 
 
 wallows. 
 
 D. OBSTRUCTIONAL BASINS. Formed by damming a pre- 
 existing valley. 
 I. Tectonic barrier basins. 
 
 a. Warp barrier. 
 
 b. Fold barrier. 
 
n8 PRINCIPLES OF STRATIGRAPHY 
 
 2. Volcanic barriers 
 
 a. Volcanoes. 
 
 b. Lava flows. 
 
 3. Chemical : Tufa barrier basin. 
 
 4. Ice barrier basin. 
 
 5. Organically built barrier. 
 
 a. Coral reef barrier. 
 
 b. Vegetal growths. 
 
 6. Detrital barrier basin. 
 
 a. Marine and lacustrine (barrier beach). 
 
 b. Fluviatile, or river-built : Fan-delta barriers ; mar- 
 
 ginal barriers (drift-wood barriers, etc.). 
 
 c. Glacial, or ice-built : Drift and morainal barriers. 
 
 d. Atmospherically built. 
 
 (1) Land-slip barrier. 
 
 (2) Dune barrier. 
 
 e. Artificial (built by organisms from foreign sub- 
 
 stances). 
 
 (1) Beaver dams. 
 
 (2) Man-made dams. 
 
 While pure types of these basins probably exist, the majority 
 of lake basins are of a more complex order, falling under more 
 than one class. 
 
 A. Deformational or tectonic basins. 
 
 These are due to faulting, folding, or warping, so as to produce 
 a closed depression, i. Fault basins are not uncommon, the best 
 examples being Albert and Summer Lakes of Oregon (Fig. 19), 
 and perhaps Lakes Tanganyika and Nyassa of Africa (Fig. 20). 
 2. Lakes due only to folding or the formation of mountain troughs 
 are rare, but those in which iolding takes a part are not uncommon 
 in young mountain regions. Here belong, in part at least, Lake 
 Baikal of Asia, Lake Nicaragua, and the western end of Lake Supe- 
 rior in Central and North America, respectively. 3. Basins due 
 wholly to warping are unknown, but Lake Ontario is a warped river 
 valley which is partly closed by drift deposits. 4. Great basins are 
 produced when mountains arise all around a less disturbed area by 
 combined folding, faulting, and warping, and thus leave this area 
 surrounded by a rim, and in condition to become a lake. The size 
 of this lake, when below the maximum possible for the lowest 
 
DEFORMATIONAL LAKE BASINS 
 
 119 
 
 outlet, is determined by the relation between rainfall and evapora- 
 tion. A typical example is found in the extinct Lake Bonneville 
 (Gilbert-i5), which extended along the western base of the 
 Wasatch range for 300 miles. Its surface covered 19,750 square 
 miles at the highest stage, and its hydrographic basin had an area 
 
 -~-^~^- ^ ::LV- S";-Ji ^fif^-j3^^^=r ^ * 
 
 FIG. 19. Sketch of Albert Lake, Oregon, a fault-basin lake. (After Russell.) 
 
 of 52,000 square miles. By evaporation it has now been reduced 
 to a body of salt water which in 1850 was 1,750 square miles in 
 area, with a maximum depth of 36 feet the Great Salt Lake of 
 Utah. Another example in the same region is the extinct Lake 
 Lahontan, which lay in what is now northwestern Nevada, with an 
 arm extending into California, and with a length of 260 miles, 
 
 FIG. 20. Section through Lakes Tanganyika and Rukwa, from northeast to 
 southwest. Vertical scale exaggerated five times. (After Moore.) 
 
 and enclosed an island 126 miles long and 50 miles broad. Most 
 of the valleys occupied by the arms of this lake are deserts now, 
 but some contain small lakes of more or less saline or alkaline 
 waters, but not of concentrated brines. (Russell 31.) What ap- 
 pears to have been an enormous inland sea or lake of this type, 
 but beginning as a cut-off from the sea, occupied, according to 
 
120 PRINCIPLES OF STRATIGRAPHY 
 
 Walther (4574-79), the greater part of Germany during the 
 Middle Zechstein period (Permic), extending from the Urals on 
 the east to the Armorican chain in Franee, Belgium, South Eng- 
 land and Ireland on the west, and bounded on the south by the 
 Bohemian mass, and the mountain chain (Vindelician) correspond- 
 ing to the present Danube plain. In this sea the great salt deposits 
 of North Germany were laid down from the complete evaporation 
 of the waters. Fault depressions accompanying earthquakes also 
 belong to this class. 
 
 B. Constructional basins. 
 
 1. Volcanic (pyrogenic) basins. These include a. crater 
 lakes, where water is enclosed by the built-up rim of the crater, and 
 b. depressions in a lava sheet produced at cooling and occupied by 
 water. Examples of the former are Crater Lake of Oregon (in 
 part a broken-down cone), the Soda Lakes of Nevada, and Lakes 
 Albano and Nemi, near Rome, and Agnano and Averno, near 
 Naples. Other lakes of this type occur in the Auvergne district of 
 France, about Auckland, New Zealand, and in other volcanic 
 regions. (Davis-7:j#o.)* Sometimes these lakes are hot, or con- 
 tain gases fatal to animal life. In the Caucasus a lake of this class 
 (Elbruz) lies at an elevation of 18,500 feet above the sea. Lakes in 
 depressions in lava flows are probably not common, and when they 
 are found they are mostly small. 
 
 2. Chemical (hydrogenic) basins. This class is limited to 
 small ponds, or basins built by tufas in hot spring and geyser 
 regions. The small tufa basins in mammoth Hot Springs of the 
 Yellowstone region are typical examples. Examples of large size 
 are so far unknown. (See Fig. 67, page 343.) 
 
 3. Organic (biogenic} basins, a. Basins built by the growth 
 of vegetation in moist climates are not an uncommon feature in 
 the peat bog regions of northern countries, though the larger ones 
 of this class may be in part of the barrier type, the vegetable 
 growth merely damming back waters in a preexisting valley. A 
 more perfect example of a phytogenetic or vegetal basin is seen in 
 Lake Drummond in the Dismal Swamp of Virginia and North 
 Carolina. (41.) This lake was originally 22 feet above sea-level 
 and 16 feet deep. It is completely surrounded and enclosed by a 
 mass of peat and vegetable material with a maximum thickness of 
 20 feet. At present the lake is only 6 feet deep and only about 16 
 
 * Pavis places them among obstruction lakes. 
 
CONSTRUCTIONAL LAKE BASINS 121 
 
 feet above sea-level, owing to artificial drainage. The lake decreases 
 to a few inches in the woods surrounding it. Although originally 
 believed to have started in a depression in the underlying stratum, 
 it is now entirely enclosed by, and owes its continuance to, a rim of 
 vegetal material, and so is typical of this class. Lakes and ponds 
 of this type due wholly to the growth of vegetation, abound in the 
 tundra of Alaska, where they occur even on hillsides, which other- 
 wise would be freely drained. (Russell-3O :/<?#.) b. Lake basins 
 of animal or zoogenic origin are less common, but are represented 
 by coral island lagoons, when their connection with the sea ceases 
 or is reduced to a minimum. An elevation of the coral island or 
 atoll would result in complete separation of the basin from the 
 ocean, and a freshening of the water. Lakes apparently of this 
 type have been reported from the coral islands of the Pacific. 
 
 4. Detrital (clastic) basins. These are built up by detrital 
 material, which, though it is the product of rock destruction else- 
 where, nevertheless produces constructional basins similar to the 
 volcanic and the chemical, the material for the building of which is 
 obtained from within the earth, and to the organic, the material for 
 which is obtained from the air or the water. They may also be 
 called reconstructional, since the material of old land forms is 
 reconstructed into the new. 
 
 a. Marine detrital basins are depressions on the subcoastal 
 plain, due to irregularity of arrangement of material. On emergence 
 these will carry shallow lakes. Such are the lakes on the coastal 
 plain of Buenos Ayres. (Davis-7 :j/^.) b. Lacustrine detrital basins 
 are those left in the irregular detrital deposits on the floors of large 
 extinct lakes. Here belong many lakes remaining in the Great 
 Basins, such as the successors of Lake Lahontan and Lake Bonne- 
 ville and others, c. Fluviatile detrital basins comprise (i) those 
 formed on river flood plains by irregular deposition, though these 
 are always complicated by erosion, as in the case of oxbow lakes ; 
 (2) those formed by irregular deposition of deltas; and (3) those 
 formed by irregular deposition on alluvial fans. Lake Pontchar- 
 train, near the mouth of the Mississippi, is of the delta-lake type. 
 It has a surface of twenty by forty miles, but a depth of only 27 
 feet. Others are found on the Mississippi delta, the deltas of the 
 Rhine, and elsewhere. (Davis-7.) Oxbows and other flood-plain 
 lakes occur on most large rivers, while delta-fan basins, though 
 small, are not uncommon. A combination of flood plain and delta 
 basin is seen in the lakes of the great alluvial plains of China, 
 d. Morainal and drift kettle holes are common in the region affected 
 by the PJeistocenic ice sheet. They are mostly small, though often 
 
122 PRINCIPLES OF STRATIGRAPHY 
 
 proportionately deep for their size. Though mostly due to irregu- 
 larity of deposition, many owe their chief characteis to the caving- 
 in of the sand upon the melting of an included ice block, e^ Land- 
 slip basins are rare and small, forming in irregularities or depres- 
 sions in the land-slide surface. e 2 . Hollows between dunes are com- 
 mon, but these, as a rule, hold no water, owing to the porousness of 
 the sands. Examples of lakes held up by sand dunes are, however, 
 abundant in Cherry county and elsewhere in the sand-dune region 
 of Nebraska, f. Finally, artificial structures, such as built-up (not 
 excavated or dammed) reservoirs, belong here. 
 
 C. Destructional basins. 
 
 1. Volcanic destructional. Of this type the most characteristic 
 are the pit craters, or the more or less circular hollows produced 
 by volcanic explosions, without the building up of a crater, or by 
 subsidence. The Maare of the Eifel and elsewhere in Germany are 
 typical examples, the largest of this type being the Laacher See, 
 near Coblenz, with a diameter of a mile and a half and a depth of 
 about 200 feet. Other examples are found in the Auvergne. Where 
 the surrounding region is strewn with the pyroclastic ejectamenta, 
 the basin may be regarded as due to explosion, as in the case of the 
 Maare of the Eifel in general. In other cases subsidence after the 
 removal of rock matter below may be the cause of the depression. 
 Lake Balaton (Flatten See) in Hungary is regarded as of this 
 type. It is 50 miles long, 3 to 10 miles wide and 40 feet deep. 
 
 2. Chemical basins of the destructional type include (a) solu- 
 tion basins, where limestone or gypsum has been removed by 
 solution; some of the lakes in Florida may have originated in this 
 way. Sink-holes, due to caving-in of the surface over caverns, also 
 belong here. These are common in limestone regions. Lakes due to 
 solution of underground salt deposits and to the caving-in of the 
 surface are also of this type. An example of a recently formed 
 lake of this class is the intensely saline Lake Illyes or Medve Lake, 
 near Szovata, Hungary. Temporary solution lakes on glacier sur- 
 faces must also be included in this group, (b) Decomposition and 
 disintegration hollows. These are of little significance, since they 
 can be cleared out only by wind, ice, or other agency. 
 
 3. Fluviatile destructional basins are never of great size, for 
 rivers cannot excavate large hollows, their chief work resulting in 
 free drainage channels. Pot-holes, however, and the depressions 
 gouged out by retreating waterfalls, are rock basins of this type. 
 Pot-holes are mostly small, though exceptional cases have a diameter 
 
DESTRUCTIONAL LAKE BASINS 123 
 
 of 20 feet and a depth of 40 feet. Waterfall hollows also are 
 limited in size. At Niagara a hollow nearly 200 feet deep, over 
 three miles in length, and a thousand feet or more broad has been 
 gouged out by the Horseshoe Falls. When Niagara goes dry, this 
 will remain as a lake. A typical example of an existing lake of 
 this type is Lake Thaxter of the St. Croix Dalles region in Minne- 
 sota. Along the course of most rivers are deeper reaches which 
 represent stronger scour, and these may be converted into lakes. 
 This is the case in some of the branches of the Nile, where, during 
 the dry season, these pools contain water. In old river courses 
 like that of the Oxus, an affluent of the Caspian, and the old course 
 of the Huang-ho, such lakes are sometimes a characteristic feature. 
 
 4. Glacial rock basins. When a glacier gouges out the floor of 
 its valley above the mouth, so as to leave the frontal rim actually 
 higher than some other parts of the basin, the conditions for the 
 formation of a destructional lake basin are- furnished. Such lakes 
 are common in areas of recent glaciation and many of the lakes 
 in the region of the Pleistocenic ice sheet invasion owe their exist- 
 ence partly to this cause. The Finger Lakes of New York are 
 believed to be in part glacial rock-basins, and in part due to ob- 
 struction. 
 
 5. Deflation basins. These result from the removal, by wind, 
 of sand and dust from a disintegrating surface, in such manner as to 
 leave a complete rock rim surrounding the area of removal. This 
 area will be deepened to the extent determined by the power of the 
 wind to remove disintegrated material. Desert basins, in so far as 
 they are not tectonic depressions, owe their character to this agent, 
 since no other force (excepting man) can remove soil or sand from 
 the enclosed basin. Playa lakes may occupy temporarily the lower 
 depressions of these basins. Hollows excavated by wind carrying 
 sand, though insignificant, should nevertheless be mentioned. 
 
 6. Artificial excavations. These are included for completeness 
 sake, but need no further comment. Mud wallows, on the other 
 hand, may be briefly discussed. In desert areas where elephants 
 and other large creatures wallow about in pools, they produce hol- 
 lows several meters deep. Rains washing down the sandy sides of 
 these hollows widen the area affected. Thus if the hollow left after 
 the filling is still i meter deep its diameter may be 25 in. Continued 
 wallowing will result in the formation of a depression 5 meters 
 deep and 120 to 150 meters in diameter, such as are found in abun- 
 dance at the present time in the drier districts. Their formation by 
 animal erosion is often observed in the Kalahari and other deserts. 
 
 Where salty marl surfaces are covered by sand, these retain 
 
124 PRINCIPLES OF STRATIGRAPHY 
 
 the moisture to which the buried salt surface is relatively impervi- 
 ous. Efflorescences of salt on the surface attract herds of animals 
 who stamp the soil jnto powder, which then is carried away by 
 wind. Water may gather in the resulting shallow depression, and 
 this will attract more animals, and by their trampling of the soil 
 and the deflation of the material large hollows are formed, which 
 will be permanent lakes when the ground water level is reached. 
 Such lakelets abound in the northern Kalahari. Where the surface 
 of the Kalahari is formed by a porous limestone with efflorescence 
 of salt, it is broken up by the hoofs of animals and blown away by 
 wind. As water accumulates in the shallow depressions, the ani- 
 mals coming to drink trample the rock into fragments. The finest 
 particles are separated out by the water and settle as a layer of fine 
 mud which, on the drying of the pool curls up, is powdered by the 
 hoofs of the animals and blown away by the wind. 
 
 In a region where, through increasing aridity, vegetation dies 
 out, the roots are grubbed after by animals, which thus begin the 
 formation of a hollow, later subject to enlargement. 
 
 D. Obstructional or barrier basins. 
 
 These in all cases arise by an obstruction or dam placed across 
 a valley which, but for this obstruction, would have free drainage. 
 The principal types are the following. (Davis-7.)* 
 
 1. Tectonic barrier basins. These are brought about by warp- 
 ing, by folding, or by faulting. Warp barrier basins are produced 
 by the deformation of an entire valley area by warping so as to 
 reduce it from its continuous slope to a depression. Lake Ontario 
 owes its existence in part to such warping, which has carried the 
 upper part of the ancient river valley below sea-level, leaving the 
 lower part considerably above it. (Grabau- 17:49.) Valleys 
 dammed by folding are not uncommon in the Alps. Laggo Mag- 
 giore, Lake Lucerne and others have been classed here. 
 
 2. Volcanic barrier basins. These are formed by the growth of 
 volcanoes so as to cut off a preexisting valley, or by the damming 
 of such a valley by a lava flow. Lake Kivu in the great rift valley 
 of Africa is a good example of the first type. Formerly this 
 drained northward into the Albert Edward Nyanza and the Albert 
 Nyanza, with the valleys of which its own is continuous. A 
 group of modern volcanoes, the Mfumbiro Mountains, dammed it 
 
 * Davis includes as obstructional many of those here classed as constructional, 
 especially the detrital section. 
 
OBSTRUCTIONAL LAKE BASINS 
 
 125 
 
 on the north and raised its level 2,000 feet, until it began to over- 
 flow southward across the gneiss rim into Lake Tanganyika. The 1 
 watershed on the north has been raised by these (in part) still active 
 volcanoes to something over 7,000 feet, while individual peaks of 
 the barrier rise to great altitudes, the peak of Karisimbi reaching 
 14,000 feet and being often snow-capped. (Moore-26:#/.) 
 (Fig. 21.) The valley of Lake Kivu is of tectonic origin. The 
 extinct Tertiary Lake Florissant of Colorado was due to a lava 
 dam. Lakes of this type are usually long lived. Navahoe Lake of 
 Utah is held by a flow of scoriaceous lava. 
 
 3. Chemical (Hydrogenic) or tufa barrier basins are probably 
 always of small size. Some of the smaller lakes of the Yellowstone 
 
 FIG. 21. Sketch of Lake Kivu and the Mfumbiro Mountains of Africa. The 
 lake lies in the great rift valley of Africa, and is dammed by 
 volcanoes of. recent origin. (After Moore.) 
 
 region appear to owe their existence, in part at least, to damming of 
 valleys by hot springs or geyser deposits. The Plitvicer seas of 
 Croatia are small lakes in a Karst valley dammed by tufa deposits. 
 The same may be true of Lac de Brenets of the French Jura, which 
 has a depth of 31.5 meters. (Penck-28: 288.) 
 
 4. Ice barrier basins. Of these the Merjelen See in Switzer- 
 land is the best known existing example. An example of one now 
 extinct is seen in Glen Roy (Agassiz-i :jj) in the Highlands of 
 Scotland. Here only the old wave-cut shore-lines remain in the 
 "Parallel Roads," marking the successive changes in level of the 
 lake which was held up by the glacier occupying the valley to which 
 Glen Roy is tributary. Ice barrier lakes were abundant toward 
 the close of the Pleistocenic ice age, when the continental glacier 
 blocked northward draining valleys and converted them into tern- 
 
126 PRINCIPLES OF STRATIGRAPHY 
 
 porary lakes. Examples of these are Lake Agassiz (Upham-4o) 
 on the Minnesota-Canadian border; Lake Passaic (Salisbury-33) 
 of eastern New Jersey; Lakes Bouve (Grabau-i6), Charles (Clapp- 
 3), Nashua (Crosby-4), etc., in eastern Massachusetts; and Lake 
 Shaler (Wilson-46) in the Cape Cod region; and the glacial 
 Genesee and other lakes of New York (Fairchild-i3). Additional 
 examples are found in Scotland, Scandinavia, the north of Ger- 
 many, etc. Ice-barrier lakes are as a rule very short-lived. 
 
 5. Organic barriers. The growth of vegetal material at the 
 mouth of a river may serve directly to choke drainage and so 
 transform the district into a lake, and indirectly it will serve this 
 purpose by inviting deposition of fine detritus where the current is 
 checked. The growth of coral reefs may also form a barrier across 
 an indentation of the shore, which may then be transformed into 
 a lake. According to Davis (7), the lakes of the Everglades in 
 southern Florida are examples of this type. 
 
 6. Detrital barrier basins. These are perhaps the most com- 
 mon barrier basins, and to them by far the largest part of the 
 barrier lakes now existing belong. 
 
 (a) Barrier beach basins. A barrier beach may cut of! a 
 valley or embayment from the ocean or from other lakes and so 
 convert it into a separate lake basin. So long as the free connec- 
 tion with the parent body is maintained, so that water flows into 
 the new basin from the sea or lake to which it belongs, it cannot 
 be considered distinct, but only as an arm of the parent body. In 
 some cases the opening remaining is so small as practically to pro- 
 hibit the entrance of the water from the parent body. This seems 
 to be largely the case in the Frische Haff and the Kurische Haff 
 on the Prussian coast (2) ; and to a large extent also in the 
 Black Sea. Occasionally the cut-off from the sea becomes brackish 
 or fresh, as in the case of some ponds along the Massachusetts 
 coast, and those of the coast of Pomerania, while in others exces- 
 sive evaporation may cause the extinction of the lake, unless the 
 barrier is broken, as in the salt lakes of Bessarabia on the north- 
 west coast of the Black Sea. 
 
 (b) Fan delta basins. These are formed by the damming of a 
 valley by the dry delta or fan of a tributary. Lake Pangkong in 
 the Himalayas, back of Kashmir, represents this type. Its drain- 
 age is now entirely by seepage, the water being slightly brackish. 
 Another example is Tulare Lake, a shallow sheet of water with 
 indefinite marshy shores, situated along the San Joaquin River in 
 the Valley of California. The upper tributaries of this stream have 
 been ponded back by the alluvial fan of King River, which rises 
 
OBSTRUCTIONAL LAKE BASINS 127 
 
 in the Sierra Nevada range. Lakes Brienz and Thun are divided 
 by a delta or fan on which Interlaken stands, and other examples 
 are found in the Alps, in the Mississippi region, and elsewhere. 
 Marginal lakes also come into existence when the main stream 
 aggrades its valley, thus damming the tributaries. The lakes along 
 the Red River of Louisiana have been regarded as due to this 
 process, but organic accumulations or "rafts" played an extensive 
 part in the ponding of the tributaries. (Veatch-44.) These 
 organic accumulations are to be regarded as detrital material, just 
 as are the inorganic materials swept together. 
 
 (c) Moraine and drift-barrier basins. These are numerous 
 in all glaciated regions, but are generally accompanied by some 
 deepening of the basin through glacial scour. This is the condition 
 of many of the Alpine lakes and it is also the condition of the 
 Finger Lakes of New York. A typical example of a drift barrier 
 lake now extinct is found in the Upper Genesee valley from Por- 
 tageville southward. This was dammed by drift at Portageville, 
 and the resulting lake overflowed southward for a time, until a 
 gorge was cut through the rock to drain the waters northward. 
 The drainage here was originally southward, but was inverted by 
 depression of the land on the north. Slight glacial overdeepening 
 also occurred. (Fairchild-13 ; Grabau-iQ.) Drift damming accom- 
 panied by warping is shown in the Great Lakes of North America. 
 It must be clearly understood that only lakes formed in valleys 
 dammed by drift or moraines belong to this class. Lakes formed 
 in depressions in the drift itself, i. e., kettle lakes, are construc- 
 tional, not obstructional. Morainal lakes are generally short-lived, 
 although those blocked by great drift sheets may fairly be called 
 permanent. 
 
 (d) A tmo clastic barriers are either land-slip barriers or dune 
 sand barriers, (i) Land-slip barriers originate when a landslide 
 dams a mountain valley. They are mostly short-lived, for the 
 drainage across the barrier will result in their rapid extinction. 
 Lake St. Laurent, 10 kilometers long, in the Oisans, western 
 Alps, was created by a land slip in 1181. It existed about 40 years, 
 during which period the farmers of the valley became fishermen, 
 and it was destroyed by the breaking of the drift dam. (Reclus- 
 29:5^.) In September, 1893, a great landslide, lasting three days 
 and bringing down 800,000,000 'tons of rock, dammed the deep 
 valley of one of the upper branches of the Ganges in the Himalayas, 
 150 miles above the city of Hardwar, which lies at the mouth of 
 the valley. The dam made was nearly 1,000 feet deep and the 
 
128 PRINCIPLES OF STRATIGRAPHY 
 
 lake behind it grew to a length of four miles before it overflowed, 
 a year after the slide. "The flood occurred at midnight, August 
 26-27, 1894. In four hours about 400,000,000 cubic yards of water 
 were discharged, cutting down the dam nearly 400 feet, flooding 
 the valley to a depth of from 100 to 170 feet, and rushing forward 
 with a velocity of 20 miles an hour. . . . Every vestige of habita- 
 tion was destroyed in villages along the Ganges above Hardwar. 
 But so well was the notice of danger given that only one man lost 
 his life, and that because he would not heed the warning." (Davis- 
 11:182, 183.) (2) Dune sand barriers may give rise to marshes 
 and small ponds, and more rarely to lakes of some size. These 
 will, however, rarely be deep, for seepage will keep down the 
 level. 
 
 (e) Detrital dams built by organisms. Dams built by organisms 
 of detritus are typically represented by beaver dams, and by the 
 artificial dams built by man. Neither of these requires more than 
 a passing notice. 
 
 Classification of Lakes as a Whole. 
 
 From a bionomic and stratigraphic point of view, lakes must be 
 classified irrespective of the origin of the basin in which they are 
 held. The most natural division from such a viewpoint should be 
 based on the -character of the water, for, since this is the medium 
 in which life exists or sediments are deposited, its composition 
 exercises a more or less controlling influence. Waters may be 
 classed as fresh, salt or alkaline. Fresh waters do not on the aver- 
 age carry much over 0.2 part per thousand of dissolved mineral 
 matter, of which only about 2 per cent, is sodium chloride. (See 
 tables in Chapter IV.) With an increase in the percentage of 
 sodium chloride, the water becomes brackish and then salt. Alkaline 
 waters contain a large percentage of alkali carbonates. Lakes may 
 next be divided into deep lakes, i. e., those in which an abyssal as 
 well as a littoral region is distinguishable, and shallow lakes, those 
 in which the abyssal district is wanting. The shallow lakes include 
 permanent and temporary ones, the latter sometimes being ex- 
 tremely shallow, as in the case of playa lakes, which may not 
 exceed six inches in depth. The* presence or absence of an outlet 
 or effluent is also of significance, and its permanent or intermittent 
 character, when marked, must be considered. These features may 
 be tabulated as follows: 
 
RIVERS 129 
 
 Classification of Continental Seas or Lakes. 
 
 A. Saline (without effluent). 
 
 1. Deep, with pelagic, littoral, and abyssal zones. (Cas- 
 
 pian, Dead Sea.) 
 
 2. Shallow, with pelagic and littoral zones. (Aral, Great 
 
 Salt Lake.) 
 
 B. Alkaline (without effluent). 
 
 1. Deep. 
 
 2. Shallow, with pelagic and littoral zones. (Albert and 
 
 Summer Lakes, Oregon; Mono Lake, California, etc.) 
 
 C. Fresh. 
 
 1. Without effluent or with only temporary one. 
 
 a. Deep, with pelagic, littoral, and abyssal zones. 
 
 (Tanganyika.) 
 
 b. Shallow, with pelagic and littoral zones. (Eifeler 
 
 Maare; Silver Lake, Oregon; Eagle Lake, 
 California; many ponds.) 
 
 2. With effluent. 
 
 a. Deep, with pelagic, littoral, and abyssal zones. 
 
 (Lake Superior, Lake Nyassa, Lake Geneva, 
 Lake Baikal.) 
 
 b. Shallow, with pelagic and littoral zones. (Lake 
 
 Erie; most of the fresh water lakes of the 
 world.) 
 
 IV. RIVERS. 
 
 In the genetic classification of rivers we must recognize at the 
 outset that we are dealing with two distinct things, the rivers them- 
 selves and their drainage basins. Either may be simple or compli- 
 cated. A simple type of river may be conceived of as existing in 
 a complicated drainage basin (see antecedent, superimposed con- 
 sequents, and consequents on a peneplain surface) ; or the reverse 
 may be conceived of, a complicated (polygene) river existing in a 
 drainage basin of simple structure, as on a coastal plain. Consid- 
 ering rivers alone, we may class them with reference to their 
 development as simple or monogene and complicated or polygene; 
 and with reference to their relation to the structure of the region 
 as antecedent, or existing before the structure, and postcedent, 
 coming into existence after the structure. Most rivers belong to 
 the latter class. Rivers generally, by growth, capture and the acci- 
 
130 PRINCIPLES OF STRATIGRAPHY 
 
 dents brought about by outside agencies, become polygenetic, i. e., 
 become a union of originally separate rivers, but all of them begin 
 as simple types. 
 
 Simple or Monogene Rivers. 
 
 Five simple or monogene types can be recognized. I. Conse- 
 quent streams, II. Insequent streams. III. Overflow streams, IV. 
 Glacial streams, V. Subterranean streams. 
 
 I. Consequent Streams. These are the streams which come 
 into existence upon a new land surface. Such a land surface may 
 be young or rejuvenated, but so far as the river is concerned, it is 
 a new land. The mode of origin may be A. by origination (de 
 novo), B. by extension, and C. by inheritance. In all cases the 
 consequent is distinguished from the insequent type by the fact 
 that -it starts upon a sloping land surface and cuts primarily 
 downward rather than headward, although this latter also occurs. 
 From the other types it is distinguished by not having primarily a 
 stored supply at its head, as in the overflow river from a lake, or 
 in the stream supplied by the melting of a glacier. Its supply of 
 water is derived from the run-off and the ground water. 
 
 A. Ne^vly originated consequents may be classed as principal 
 and as tributary, the former entering the sea or receiving basin 
 direct, the others being tributary to other consequents, which may 
 ,or may not be principal ones. Calling the principal type the conse- 
 quent of the first order, its consequent branches would be those of 
 the second order, their consequent branches would represent the 
 third order, and so forth. These streams may next be divided 
 according to the type of land they come into existence on, the three 
 types being: I. Constructional surface consequents, 2. Destruc- 
 tional surface consequents, and 3. Deformational surface conse- 
 quents. The consequents arising on constructional surfaces may 
 be divided into (a) coastal plain consequents, or those originating 
 on a newly emerged coastal plain, elevated by purely epeirogenic 
 movements of the land" or by negative eustatic movements of the sea, 
 or by the drainage of an elevated water basin; (b) fan delta conse- 
 quents, or those originating on dry deltas of other streams or on 
 landslides; (c) moraine and till surface consequents, or those com- 
 ing into existence on a sloping surface of deposition of glacial 
 detritus; and (d) lava and volcanic cone consequents, or those orig- 
 inating on the slopes of volcanoes or on lava flows. Consequents 
 arising on a surface of destruction, upon simple elevation, are almost 
 wholly represented by peneplain consequents, i. e., those developing 
 
 
CLASSIFICATION OF RIVERS 131 
 
 on an uplifted, slightly tilted peneplain or plain of subaerial denuda- 
 tion. Streams originating on a newly ice-scoured surface may be 
 noted as of this class, but of minor importance. If surfaces of purely 
 marine denudation are of sufficient extent to have streams originate 
 on them on elevation, these would also be classed here. Finally, 
 consequents arising on a surface of deformation include several 
 types : those formed on a simple dome, those formed on a series of 
 anticlines and synclines, and those formed on tilted fault blocks. 
 In the first case we have radial consequents of the n th +'i order 
 tributary to another consequent of the n th order which may be the 
 first (principal consequent) or any higher order. In rare cases 
 domes of deformation rise directly out of the sea, when the radial 
 consequents are of the first order, n being zero. In the anticlinal 
 and synclinal folds we have transverse consequents flowing down 
 the limbs of the anticline, and longitudinal consequents flowing in 
 the synclines. The first belong to the n th + i order, the second to 
 the n th . In exceptional cases a transverse consequent may flow into 
 the sea, the shore of which may be formed by an anticline, or the 
 syncline may be filled by an arm of the sea or by a lake. Conse- 
 quents flowing down the back slopes of inclined fault blocks are in 
 all essentials like those flowing down the limbs of anticlines. 
 
 B. Extended consequents are streams of an older type which 
 become extended across the newly emerged coastal plain. These 
 streams do not differ from those originating on the coastal plain, 
 except in their greater volume of water and hence greater erosive 
 power. They will, therefore, cut deeper than the others, becoming 
 the master streams of their respective regions, and directing to a 
 large extent the further development of their drainage system. 
 Streams extended across a dry delta may also be classed here, as 
 are those extended across a plain of glacial deposition. In so far 
 as the older part of the stream is concerned it may be simple or 
 complex, monogene or polygene. 
 
 C. Inherited consequents. These are consequents which are 
 superimposed upon a complex terrane by learning to flow upon a 
 coastal plain which once covered the complex rocks, and which 
 directed the course of the river, though long since removed by 
 erosion. Superimposed consequents are believed to be illustrated 
 by the lower courses of the Housatonic and Connecticut rivers in 
 southern New England. The coastal plain strata which apparently 
 once extended over this area have been entirely removed by erosion. 
 (Dodge-i2.) The coastal plain strata may be replaced by layers of 
 volcanic ash (Gunnison River), by drift, by river, or eolian deposits, 
 or, in exceptional cases, by glacial ice. 
 
132 PRINCIPLES OF STRATIGRAPHY 
 
 II. Insequent Streams. These are essentially distinct from the 
 preceding type in that they originate upon the side of a preexisting 
 valley of erosion or dislocation, and in that their chief mode of 
 development is by headward gnawing instead of downward cutting. 
 Nevertheless, there are times when it might be difficult to dis- 
 tinguish this type from a consequent originating on an erosion 
 surface, or one flowing down the back-slope of a fault block. For 
 the question would arise, when is the erosion slope steep enough 
 to support insequents instead of tributary consequents? In the 
 case of the fault block, we may consider that the streams on the 
 back slope are consequents and those on the fault scarps are inse- 
 quents. Of course this merely emphasizes the fact that in any 
 natural classification of inorganic, as well as of organic things, sharp 
 lines do not exist, but the classes are connected by gradations. 
 
 Most insequent streams are classifiable into a. erosion-bluff and 
 b. fault-scarp insequents. The former comprise ( i ) wave-cut cliffs 
 (marine and lacustrine), (2) river-cut cliffs, (3) ice-cut cliffs, (4) 
 wind-cut cliffs, and (5) artificially-cut cliffs, while the second 
 includes scarps due to faulting and to local subsidences, such as 
 kettle-holes in moraines, etc., sink-holes over caverns and others. 
 A third but rare type c. forms on the margins of pit or explosion 
 craters, while a fourth type d. is seen in embankment insequents, 
 where cliffs of construction or artificial embankments are gullied. 
 This type approaches the consequent type developed on dry river 
 deltas or alluvial fans, since it develops on a constructional surface. 
 
 Simple subsequent streams. Insequent streams, near the head 
 of a coastal plain, may open out a lowland parallel to the strike of 
 the strata on an underlying softer substratum. Such enlarged 
 insequents have been termed subsequents, and in a young region 
 these may be of simple type. In most cases, however, subsequents 
 become compound through capture. Axial subsequents open up 
 longitudinal valleys on the crests or axes of anticlines, and by 
 sliding downward occupy the monoclinal valleys. (See chapter 
 XXI.) 
 
 Obsequent streams. These are insequents peculiar on account 
 of their location on the inface of a cuesta, as a result of which 
 their course is in an opposite direction from that of the consequents. 
 Rivers on the fault face of tilted blocks would also come under this 
 category. 
 
 III. Overflow Streams. These are the spillways from stand- 
 ing water bodies and as such include all effluents of lakes. Such 
 effluents may be terminal, carrying the waters of the lake directly 
 to the sea or into a trunk stream which flows into the sea without 
 
CLASSIFICATION OF RIVERS 133 
 
 further laking; or inter lacustrine, spilling over from one lake into 
 another. The St. Lawrence River is a good example of the former 
 type, and the Niagara of the latter. Overflow streams are charac- 
 terized by little or no sediment, this being all left behind in the 
 lake. They may, however, pick up sediment on the way from their 
 bed and banks, or from tributaries, and so obtain tools for erosion. 
 Niagara is a good example of such a stream, free from sediment in 
 its upper part and accomplishing its erosion work by undermining 
 at the cataract and drilling on the floor. 
 
 IV. Glacial Streams. These have their water supplied by the 
 melting ice mass, which also furnishes detrital material. Hence 
 these streams are distinct from all others. Streams originating on 
 the ice, i. e., superglacial streams, have the consequent habit, and 
 might be classed as an extreme type of that group. But sub- 
 glacial streams are unlike all others. Their peculiar position under 
 the ice cover and subject to hydrostatic pressure, often forces them 
 to flow across obstacles no normal river could surmount, or actually 
 to flow for a part of their course uphill. Such abnormal courses 
 of ancient subglacial streams are indicated by the position of the 
 eskers which they have built. In many characters, subglacial 
 streams approach subterranean streams. 
 
 V. Subterranean Streams. These are often of great extent and 
 diversity, following enlarged joints in limestone strata, and forming 
 caverns along their paths, which are subsequently more or less 
 filled up again by stalactic deposits. Underground drainage may 
 develop to the complete absorption of surface drainage, giving the 
 peculiar Karst type of landscape so characteristic of the west side 
 of the Balkan peninsula, and also seen in the Barren lands of 
 Kentucky and Tennessee, in the plateau of the Cevennes in southern 
 France, in the German Jura, and in many other regions. (Cvijic-5; 
 Neumayr-27 .-500-5/0.) 
 
 Polygene Rivers. 
 
 Under this heading may be grouped the three types denomi- 
 nated by Davis: i. compound rivers, 2. composite rivers, and 3. 
 complex rivers. (Davis-8:/#j; 9:10^.) Davis defines a compound 
 river as one "which is of different ages in its different parts," and 
 cites as examples "certain rivers of North Carolina which have old 
 headwaters rising in the mountains and young lower courses tra- 
 versing the coastal plain." These are the extended consequents of 
 our classification. The term should be made to cover streams 
 which by capture have enlarged their drainage basin at the expense 
 
134 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 of other streams Extended consequents, by reason of their greater 
 water supply, are apt to become compound or at least their principal 
 branches will be affected in this manner. This is especially the case 
 with the subsequent type of stream. The present Moselle of 
 western Europe i& an example of a compound river, having ac- 
 quired by capture some of the headwaters of the Meuse. (Davis, 
 10:229-230.) (Figs. 22, 23.) 
 
 A composite stream is defined by Davis as one including in its 
 basin, drainage areas of different structure. In so far as the differ- 
 
 Hypothetical sketch map of the 
 
 Meuse and Moselle rivers, 
 
 France, before capture. (After 
 Davis.) 
 
 FIG. 23. Map of the Meuse and the I 
 selle after capture. (Davis. 
 
 ence in structure affects the stream, causing it to modify its course, 
 this definition may stand. We must, however, bear in mind that we 
 are dealing with two distinct things, the river and the drainage 
 basin. A simple consequent on a destructional surface (peneplain) 
 or a superimposed consequent on a much folded older terrane may 
 flow across regions of different structure -in different parts, i. e., 
 have a composite drainage basin and yet be of simple character. 
 
 The third type of polygene river is the complex. This is defined 
 by Davis as a river which "has entered a second or later cycle of 
 development." Rivers inherited by an uplifted peneplain from the 
 previous cycle are typical examples of this class. They will differ 
 from simple consequents upon a peneplain in that they have ac- 
 
AGE OF RIVERS 135 
 
 quired a meandering course, while the peneplain was low, and this 
 will be in a large measure retained, so that the inherited stream will 
 be characterized by deeply incised meanders, whereas the new con- 
 sequent will generally be straight. A more pronounced complexity 
 is produced when by warping, partial damming and division a river 
 enters locally on a new cycle, while other parts remain compara- 
 tively unchanged. An example of such a river is the Genesee, which 
 at present occupies the valleys of two formerly distinct streams of 
 diverse origin. This is really the case with the St. Lawrence drain- 
 age system as a whole, the affluents of the lakes, which belong to 
 this system, having a varied history, as already noted in the case 
 of the Genesee. 
 
 RELATIVE AGES OF RIVERS AND RIVER SYSTEMS. In discussing 
 the relative ages of rivers and river systems, we must distinguish 
 between the age of the river or river system and the age of the dis- 
 trict it inhabits. Thus a young stream may exist in a young country, 
 as in the case of new streams on a young coastal plain, or it may 
 exist in a mature or old country. The age -of the land must be 
 considered distinct from the age of the river. (Johnson-2i.) 
 Only the latter will be considered here. Streams are classed as 
 young, mature and old, according to the degree of their develop- 
 ment. No conception of actual time is involved, for of two rivers 
 born at the same time one may reach maturity while the other is still 
 very youthful. Young rivers are characterized by rapids and falls, 
 and by steep-sided, narrow gorges. Lakes may further interrupt 
 the course of the drainage. A river is mature when it has destroyed 
 its lakes and falls, and reduced its valley sides to graded slopes, and 
 broadened its floor so that it may swing upon it in great meanders. 
 A mature river is able to carry away all the load that it receives, 
 but generally has no power to do further erosion. A river system 
 is mature when all the branches have become mature, but generally 
 youthful branches are found long after the trunk stream has become 
 mature. Old rivers are those which move sluggishly along across 
 a flat, much-encumbered valley bottom. Their grade is so low that 
 they cannot carry away the rock waste, and so they aggrade their 
 beds, or stagger about in them by avoidance of the debris. In a 
 river system the main stream may grow old, while its branches are 
 still mature or even youthful. 
 
 Aging of Rivers by Accident. Rivers may grow old rapidly 
 through various accidents. Among these are mutilation, sudden 
 overloading, and drowning. The first of these produces perma- 
 nent senescence, and may be compared to the permanent aging of 
 an animal body through a severe illness or accident. The second is 
 
136 PRINCIPLES OF STRATIGRAPHY 
 
 only temporary, for as soon as the supply ceases the river will re- 
 vive and begin active cutting again. This may be compared to a 
 temporary depression or weakening from overwork, which pro- 
 duces temporarily a weariness akin to that of old age, but from 
 which recovery is usually certain, on cessation of the excess of 
 work. The third'may be of long duration with ultimate revival, or 
 it may lead to extinction. It may be compared with a serious ill- 
 ness, from which recovery is doubtful. 
 
 1. Mutilation. When a river has its headwaters or branches 
 cut off by capture or diversion, it quickly begins to age. From a 
 youthful, cutting or degrading stream it changes to a mature one, 
 where graded conditions are maintained. By further reduction, old 
 age is reached, when the river begins to aggrade its valley, by drop- 
 ping what debris is brought to it. The river Bar, an affluent of the 
 Meuse, is such an old river, aged by mutilation, which resulted 
 in the loss of its headwaters. It now staggers through a debris- 
 clogged valley, which is out of proportion to its present size. 
 The Meuse itself may be considered at least a submature river, 
 just able to maintain its course, which in this case means cut- 
 ting through the rising ground, which is equivalent to carrying 
 away all the debris brought to it without cutting, in a stationary 
 region. 
 
 2. Sudden overloading of a mature or submarine river may also 
 produce the phenomena of old age, by causing the river to aggrade 
 its floor. This may occur while the river valley is still a long way 
 from entering upon the state of old age. The gravel terraces of the 
 Allegheny, Monongahela and other Pennsylvania rivers, which rise 
 about 200 feet above the present stream channel, have been ex- 
 plained as remnants of high flood-plains due to aggrading of the 
 valleys by the overloaded Allegheny in early glacial time. The 
 debris was largely supplied to the river by the melting ice. Even 
 the tributary streams were forced to aggrade their valleys from the 
 mouth upward. Since then the rivers have cut down again through 
 this old flood plain, leaving the terraces on either side to mark its 
 former elevation. (Shaw, 35.) Similar examples are found in 
 New England rivers. 
 
 3. Drowning of rivers also brings on the phenomena of old age. 
 This drowning may be due to overflow of a lake to which the river 
 is affluent, or to subsidence of the coast or to other causes. Ex- 
 amples of drowned coastal rivers are the Hudson, the lower St. 
 Lawrence, and numerous other rivers of the North Atlantic coast. 
 No erosion is accomplished by these rivers ; they have no apprecia- 
 ble current of their own, the movements of the water being regu- 
 
REVIVAL OF RIVERS 137 
 
 lated by the tides, and they deposit all the debris furnished to them. 
 They are justly called old rivers, though their old age is premature, 
 and they may be situated in young valleys. Partial drowning re- 
 sults when, through damming by drift, a portion of a river valley is 
 converted into a lake, as was the case in the upper Genesee River. 
 (Fairchild-i3.) 
 
 Revival and Rejuvenation of Rivers. Rivers which have be- 
 come prematurely old, or which have grown old in the normal cycle 
 of development, may be revived or rejuvenated by an uplift of the 
 land or by a removal of the cause of senescence. The overloaded 
 stream is most easily revived by the removal of the cause of senes- 
 cence, i. e., the excessive supply of material. This is better spoken 
 of as a recovery. Drowned coastal rivers may be revived by eleva- 
 tion until they have again reached the condition prior to drowning. 
 If further elevation occurs they will become rejuvenated and enter 
 upon a new cycle of erosion as youthful streams. Partly or wholly 
 drowned rivers, through damming by drift or otherwise, may be re- 
 vived by removal of the dam, or, what is more often the case, 
 by the cutting of a new outlet. This will result in a complex stream, 
 in which the outlet portion is youthful, while the rest is mature or 
 older. The narrow gorges with rapids and waterfalls connecting 
 the present upper and lower Genesee valleys are examples of 
 young connecting portions interpolated between revived mature 
 portions. 
 
 Rivers which in the course of their normal development have 
 reached a state of old age, may be rejuvenated by a favorable 
 change of the environment, through an uplift of the land, or a low- 
 ering of the base-level of erosion, i. e., the local level to which ero- 
 sion proceeds; or by an infusion of new life, in the case of certain 
 rivers, through a change in climatic conditions, which will greatly 
 increase the amount of water, and hence the power of work of the 
 stream. The Great Falls of the Missouri in eastern Montana occur 
 in a rejuvenated valley, i. e., a valley now in its second or later 
 cycle (n th -f- i cycle, where n may be the first or any later cycle). 
 (Davis.) The rivers of the Piedmont district of Virginia, and all 
 rivers which incised themselves into uplifted peneplains which 
 they had helped to make, are examples of rejuvenated rivers, now 
 in their n th -f- i cycle. These rivers are generally characterized by 
 well-entrenched meanders, which differ strikingly from the crooked 
 curves of young streams. Such meanders are shown by the Seine in 
 the Normandy upland, the Moselle and the Rhine in the old Rhine 
 uplands of western Germany, the Susquehanna in the old Appa- 
 lachian upland, and by many other streams. 
 
138 PRINCIPLES OF STRATIGRAPHY 
 
 V. UNDERGROUND WATER (GROUND WATER). 
 
 Ground water is that part of the hydrosphere enclosed within 
 the pores of the rock of the earth's crust, and either circulating by 
 slow movements within the crust, or remaining stagnant within its 
 pores. 
 
 Classification of Ground Waters. 
 
 According to the mode of origin, ground water may be divided 
 into three types. 
 
 A. Meteoric or Pluvial Waters, or those derived from rain or 
 snow and penetrating into the crust from above. These form the 
 vadose circulation. 
 
 B. Connate Waters, or those buried originally with the sedi- 
 ments in which they occur, and varying according to their derivation 
 from fresh to marine waters. This is the fossil water, and to be 
 conserved must remain stagnant within the pores of the rock. 
 
 C. Magmatic or Juvenile Waters, or those given off by cooling 
 magmas and in a sense generated anew by the combining of gases 
 from the igneous mass. 
 
 Some observers, notably Van Hise and his followers, would re- 
 gard all ground water as of meteoric origin, and consider the high 
 temperature and mineral content of such waters, originally cool and 
 nearly pure, as due to a descent into regions of high temperature 
 within the depths of the earth, or their coming in contact with 
 heated igneous masses, and the consequent impartation of heat and 
 thermal solvent power, so that both their temperature and mineral 
 content are acquired properties. Other workers in this field, notably 
 Eduard Suess and J. F. Kemp, have insisted on the magmatic ori- 
 gin of many if not most of the heated and mineral-laden waters, 
 the temperature and mineral content of which are, therefore, pri- 
 mary or a part of their original character. It is this class of waters 
 which is believed to be responsible for most of the ore deposits 
 within the older rocks, and to such an origin may perhaps also be 
 traced most of the hot and mineral springs of the present day. Re- 
 cent experiments at Kilauea have resulted in the actual condensation 
 of water from gases given off by the lavas. 
 
 The term connate waters was proposed by Lane (24:50^), who 
 calls attention to a class of waters which has been much neglected. 
 Walther, more than any other writer, has insisted on the signifi- 
 cance of fossil sea waters as an important source of salts concen- 
 trated from them by surface agencies under arid climatic conditions. 
 
GROUND WATER 139 
 
 The amount of such water preserved in the rocks depends, of 
 course, on the volume of the pore space (see below, p. 140), 
 which may be as high as 60% of the volume of the sediment, though 
 of course it is much less in the majority of clastic deposits. 
 
 Lane has called attention to the role played by connate waters in 
 preventing the downward passage of the meteoric waters, which 
 will tend in a measure to dilute some of these stagnant waters. 
 While the meteoric waters circulate freely in the upper zone of 
 the earth's crust (the belt of weathering), the zone of permanent 
 ground water is one of more or less stagnation, and one in which 
 deposition of the mineral matter of these waters in the pores of the 
 rock will take place. We have, therefore, beneath the zone of 
 weathering and free circulation, one of cementation, and thus a 
 barrier to the further downward progress of the meteoric waters 
 is formed. This at the same time forms a barrier against the es- 
 cape of the imprisoned connate waters, which will thus be con- 
 served until erosion of the rocks sets them free once more. Lane 
 was led by such considerations, and by the study of the composition 
 of the deep-seated waters, to conclude that a large part of the 
 ground water attributed by Van Hise and others to a meteoric ori- 
 gin was in reality connate, i. e., the imprisoned water of former 
 oceans. 
 
 General Course of Meteoric Waters. 
 
 Rain falling upon the land is disposed of in several ways. A 
 part of it runs off down the slopes (the run-off), a part sinks into 
 the ground (the absorp), and a part evaporates, returning to the air 
 (the evaporate). The part that sinks into the ground becomes the 
 ground water, while the run-off starts the development of surface 
 drainage. The quantitative relation between run-off, evaporate and 
 absorp depends upon (i) the character of the surface, i. e., its 
 topography or slope, porosity of material, state of saturation, 
 amount of vegetable covering, etc., (2) the rate of rainfall or melt- 
 ing of snow, and (3) the subsequent dryness of the atmosphere, 
 and perhaps other local features. Very porous soil holding little 
 water will greedily absorb the rain if it falls not too heavily. In 
 this latter case much will run off, as the rate of absorption cannot 
 keep pace with the rate of supply. In a very dry atmosphere much 
 will evaporate before it has time to sink in, while much more will 
 be evaporated from the upper layers of the soil before it has de- 
 scended far, or will be taken up by vegetation to be ultimately re- 
 turned to the air. 
 
140 PRINCIPLES OF STRATIGRAPHY 
 
 Porosity of Rocks. 
 
 The porosity of a rock or soil mass is determined by the frac- 
 tional part of the mass occupied by open spaces or voids. (Slichter- 
 37:/d.) If a cubic foot of sandstone holds, on saturation, one- 
 quarter of a cubic foot of water, the porosity of the sandstone is 25 
 per cent. The following table of tests made by Dr. E. R. Buckley, 
 State Geologist of Wisconsin, shows the variation in the porosity of 
 various building stories of that state: 
 
 Kind of rock, and locality 
 
 Average porosity 
 
 of two specimens 
 
 per cent. 
 
 Granite from Montello, Wis 
 
 Granite from Berlin, Wis 
 
 Niagara limestone from Marblehead, Wis 
 
 Sandstone, Ableman, Wis ; 
 
 Niagara limestone, Wauwatosa, Wis ._ 
 
 Lower Magnesian limestone, Bridgeport, Wis 
 
 Sandstone, Ashland, Wis 
 
 Sandstone, Dunville, Wis 
 
 0.237 
 
 0.384 
 
 0.770 
 
 5.600 
 
 6.400 
 
 13.190 
 
 20.700 
 
 28.260 
 
 The porosity of quartz sand usually varies between 30 and 40 
 per cent., and that of clay loams between 40 and 50 per cent., de- 
 pending on the variety of size of grains in the mixture, and on the 
 manner of packing the particles. (Slichter, 34, p. 17.) The pore 
 space of fresh, strong granite varies from 0.2 to 0.5 per cent., the 
 absorption of water being 0.08 to 0.20 per cent, by weight. Ordi- 
 nary compact limestone varies from 2.5 to 12.5 per cent, (absorp- 
 tion i to 5 per cent, by weight of water), although the more porous 
 limestone can absorb 10 per cent, by weight of water, corresponding 
 to a pore space of 25.0 per cent. The more compact types of lime- 
 stones, however, fall as low as 0.55 per cent, of pore space. Sand- 
 stones generally have a pore space ranging from 5 to 28 per cent. 
 Chalk has been credited with the ability to absorb 20 per cent, by 
 weight of water corresponding to a pore space of about 41 per cent. 
 (Van Hise-43 : 125.) The pore space of an organic limestone from 
 the^Gulf of Naples was over 35 per cent. (Walther), while recent 
 sediments of the Mississippi delta contained, according to Hilgard, 
 a pore space ranging from 23 to 61 per cent. The actual size of the 
 grains is of less importance in influencing the porosity of the mass 
 than the variation in size within the same mass, or the arrangement 
 
GROUND WATER 141 
 
 
 
 or mode, of packing. Thus, if a quantity of shot be poured into a 
 glass, and the quantity of water required to fill the pores be 
 measured, it will be found that the porosity varies greatly if different 
 methods be used in filling the glass, each producing a different 
 arrangement, but that the same values may be obtained with small 
 shot as with large. (Slichter-37 :<?/.) Slichter has determined that 
 the minimum porosity of a mass of spheres, packed'in the most com- 
 pact manner, is 25.95 P er cen t- of the whole space occupied by the 
 spheres, while the maximum porosity is 47.64 per cent, of the whole 
 mass. ( Slichter-38 ^95. ) 
 
 The pores between the grains are both larger in diameter and 
 shorter in length for a packing of spheres having a large porosity 
 than they are for a packing of low porosity. As already noted, 
 slight variations in the shape of the grains make little difference in 
 the porosity of the mass, but variations in size within the mass 
 make a great difference. Thus a mass of sand of uniform-sized 
 grains will have a greater porosity than one in which the grains 
 vary greatly. Many rocks of originally great porosity have suffered 
 a considerable reduction in this respect by the filling of the pores 
 by secondarily introduced mineral matter. 
 
 The Water Table. 
 
 The level beneath which the soil is completely saturated is called 
 the level of groundwater, or the water table or water plane. This 
 is also the summit plane of the true groundwater, that between it 
 and the surface of the lithosphere constituting the subsurface water. 
 This latter plays an important part in the influence it has on the soil 
 and on plant growth. 
 
 The depth of the water table varies greatly both regionally and 
 seasonally. Where the rainfall is heavy it usually lies only a few 
 feet below the surface, but in arid regions its depth may be several 
 hundred feet. In general the surface of the water table corre- 
 sponds to the surface of the land, but the irregularities are less pro- 
 nounced (Fig. 24.) Where the water table lies deep, it can be 
 reached only by deep wells, and springs are wanting. Where it co- 
 incides with the surface of the ground, the region is a swamp or 
 marsh. 
 
 Depth and Quantity of Ground Water. 
 
 According to Van Hise (42:595; 43:16*9), at a depth of about 
 6 miles (about 10,000 meters) below the surface, the rock pressure 
 
142 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 is so enormous as to close effectively all cavities and pores. This 
 is the limit of the zone of rock fracture, the zone below it being 
 that of rock flowage. This is, then, the depth to which ground 
 water can penetrate, though by far the largest quantity exists con- 
 siderably above this. More recently the experiments of Adams and 
 King have shown that pore spaces may exist at greater depths, even 
 down to eleven 'miles. (Kemp-22.) 
 
 Slichter, assuming that the geologic limit of the existence of 
 ground water is at an average depth of six miles below the surface 
 of the land, and five miles below the floor of the sea, estimates the 
 entire amount of ground water to be about 565,000 million million 
 cubic yards, or about 430,000 million million cubic meters. This is 
 nearly one-third the amount of the water of the sea as a whole. Ac- 
 
 River 
 
 Flood plain 
 
 FIG. 24. Diagrammatic section illustrating the position of the water table. 
 (After Slichter.) 
 
 cording to these estimates the total amount of ground water is suffi- 
 cient to cover the entire surface of the earth to a uniform depth of 
 from 3,000 to 3,500 feet. (Slichter-37.) These estimates are 
 based on the selection of an average pore space for all rocks of 
 10 per cent., which Slichter himself regards as too large rather 
 than too small. 
 
 It has, however, been shown by Kemp that, according to the ex- 
 perience in deep mines, ground water of meteoric origin is limited 
 to the upper 1,000 feet of the earth's crust. This makes the total 
 amount of ground water much less than that given by the estimates 
 above cited. Kemp concludes that this ground water is sufficient 
 to cover the earth's surface with a layer of water from only 50 to 
 loo feet deep. Fuller subsequently made more close calculations, 
 concluding therefrom that the layer of water would be 96 feet deep. 
 (Fuller-i4:5p-7^.) See the preliminary discussion on pp. 4 and 5 
 and further under thermal springs, their possible relation to mag- 
 matic waters, etc. (pp. 200-203). Finally movements of ground 
 water, pp. 257-261. 
 
THE HYDROSPHERE 143 
 
 BIBLIOGRAPHY III. 
 (See also references under Chapters II and IV.) 
 
 1. AGASSIZ, LOUIS. 1876. The Parallel Roads of Glen Roy. Geological 
 
 Sketches. 2nd series, pp. 32-76. 
 
 2. BERENDT, G. 1869. Geologie des kurischen Haffes, Erlauterung zu 
 
 Section 2, 3, 4, der geologischen Karte von Preussen, Konigsberg. 
 
 3. CLAPP, F. C. 1902. Geological History of the Charles River in Massa- 
 
 chusetts. American Geologist, Vol. XXIX, pp. 218-233. 
 
 4. CROSBY, WILLIAM OTIS. 1899. Geological History of the Nashua 
 
 Valley during the Tertiary and Quaternary Periods.. Technology 
 Quarterly, Vol. XII, No. 4, pp. 288-324, 4 plates. 
 
 5. CVIJIC, J. 1893. Das Kartsphanomen. Geographische Abhandlungen, 
 
 Vol. Ill, Wien. 
 
 6. DANA, JAMES D. 1872. Corals and Coral Islands. 
 
 7. DAVIS, WILLIAM MORRIS. 1882. On the Classification of Lake Ba- 
 
 sins. Proceedings of the Boston Society of Natural History, Vol. 
 
 xxi, pp. 315-381. 
 
 8. DAVIS, W. M. 1889. The Rivers and Valleys of Pennsylvania. Nation- 
 
 al Geographic Magazine, Washington, Vol. I, pp. 183-253. 
 
 9. DAVIS, W. M. 1890. The Rivers of Northern New Jersey with Notes 
 
 on the Classification of Rivers in General. Ibid., Vol. II, pp. 81-110. 
 
 10. DAVIS, W. M. 1896. The Seine, the Meuse, and the Moselle. Ibid., 
 
 Vol. VII, pp. 189-238. 
 
 11. DAVIS, W. M. 1899. Physical Geography. Boston, Ginn and Com- 
 
 pany. 
 
 12. DODGE, R. E., and others. 1902. Physiography. United States 
 
 Geological Survey, New York City Folio. No. 83. 
 
 13. FAIRCHILD, H. L. 1899. Glacial Genesee Lakes. Bulletin of the 
 
 Geological Society of America, Vol. X, pp. 27-68. 
 
 14. FULLER, MYRON L. 1906. Total Amount of Free Water in the Earth's 
 
 Crust. Water Supply and Irrigation Paper, No. 160. United States 
 Geological Survey. 
 
 15. GILBERT, G. K. 1890. Lake Bonneville. United States Geological 
 
 Survey Monograph, Vol. I. 
 
 16. GRABAU, AMADEUS WILLIAM. 1900. Lake Bouve, an Extinct 
 
 Glacial Lake in the Boston Basin. Occasional Papers of the Boston 
 Society of Natural History, Vol. IV, Pt. Ill, pp. 564-600, map. 
 
 17. GRABAU, A. W. 1901. Geology and Palaeontology of Niagara Falls and 
 
 Vicinity. Bulletin of the New York State Museum of Natural History, 
 No. 45, Vol. IX. 
 
 1 8. GRABAU, A. W. 1907. The Geographical Classification of Marine 
 
 Life Districts. Science, N. S. Vol. XXV, NO. 631, p. 185. Feb. i, 
 1907. 
 
 19. GRABAU, A. W. 1908. Preglacial Drainage in Central Western New 
 
 York. Science, N. S., Vol. XXVIII, No. 720, pp. 527-534. 
 
 20. HAGUE, ARNOLD. 1912. Origin of Thermal Waters of Yellowstone. 
 
 Bulletin of the Geological Society of America, Vol. XXII, No. i, pp. 
 
 IO2-I22. 
 
 21. JOHNSON, DOUGLAS W. 1905. Youth, Maturity and Old Age of 
 
 Topographic Forms. American Geographical Society, Bulletin XXXVII, 
 pp. 648-653; 3 figs. 
 
i 4 4 PRINCIPLES OF STRATIGRAPHY 
 
 22. KEMP, JAMES F. 1913. The Ground Waters. Transactions of the 
 
 American Institute of Mining Engineers, pp. 603-624. 
 
 23. KRUMMEL, OTTO. 1907. Handbuch der Ozeanographie, Band I. 
 
 24. LANE, ALFRED C. 1909. Mine Waters and Their Field Assay. Bulle- 
 
 tin of the Geological Society of America, Vol. XIX, pp. 501-512. 
 
 25. LINCOLN, F. C. 1907. Magmatic Emanations. Economic Geology. 
 
 Vol. II, pp. 258-274. 
 
 26. MOO^-E, J. E. S. 1903. The Tanganyika Problem. London. 
 
 27. NEUMAYR, MELCHIOR. 1895. Erdgeschichte, Vol. I. Leipzig und 
 
 Wien. 
 
 28. PENCK, ALBRECHT. 1894. Morphologic der Erdoberflache. Vol. I. 
 
 29. RECLUS, JEAN JACQUES ELISEE. 1867. La Terre, Vol. I. 
 
 30. RUSSELL, ISRAEL COOK. 1885. Geological History of Lake Lahon- 
 
 tan. United States Geological Survey Monograph, Vol. XI. 
 
 31. RUSSELL, I. C. 1890. Notes on the Surface Geology of Alaska. Bul- 
 
 letin of the Geological Society of America, Vol. I, pp. 99-162. 
 
 32. RUSSELL, I. C. 1898. Rivers of North America. New York, Putnam. 
 
 33. SALISBURY, ROLLIN D. 1907. Physiography. New York, Henry 
 
 Holt and Company. 
 
 34. SALISBURY, R. D., and others. 1902. The Glacial Geology of New Jer- 
 
 sey. Geological Survey of New Jersey, Final Report, Vol. V. 
 
 35. SHAW, E. W. 1911. High Terraces and Abandoned Valleys in Western 
 
 Pennsylvania. Journal of Geology, Vol. XIX, pp. 140-156. 
 
 36. SLIGHTER, C. S. 1899. Theoretical Investigations of the Motion of 
 
 Ground Waters. I9th Annual Report of the United States Geological 
 Survey, Pt. II, pp. 295-384, pi. xvii, figs. 54-89. 
 
 37. SLIGHTER, C. S. 1902. The Motions of Underground Waters. Water 
 
 Supply and Irrigation Papers, No. 67. 
 
 38. SUPAN, ALEXIS. 1899. Die Bodenformen des Weltmeeres. Peter- 
 
 manns, Mittheilungen, Vol. XLV, pp. 177-188, with map 12. 
 
 39. SUPAN, A. 1903. Terminologie der wichtigsten unterseeischen Boden- 
 
 formen. Ibid., Vol. XLIX, pp. 151-152. 
 
 40. UPHAM, WARREN. 1895. The Glacial Lake Agassiz. United States 
 
 Geological Survey Monograph XXV. 
 
 41. UNITED STATES GEOLOGICAL SURVEY, Norfolk Folio, No. 80. 
 
 42. VAN HISE, CHARLES R. 1896. Principles of North American Pre- 
 
 cambrian Geology. i6th Annual Report of the United States Geological 
 Survey, Pt. I, pp. 581-872. 
 
 43. VAN HISE, C. R. 1904. A Treatise on Metamorphism. United States 
 
 Geological Survey Monographs, Vol. XLVII. 
 
 44. VEATCH, A. C. 1906. Geology and Underground Water Resources of 
 
 Northern Louisiana and Southern Arkansas. United States Geological 
 Survey, Professional Paper No. 46. 
 
 45. WALTHER, JOHANNES. 1910. Lehrbuch der Geologic von Deutsch- 
 
 land. Leipzig. 
 
 46. WILSON, J. HOWARD. 1906. The Glacial History of Nantucket and 
 
 Cape Cod. Columbia University Geological Series, Vol. I. 
 
CHAPTER IV. 
 
 COMPOSITION AND PHYSICAL CHARACTERS OF THE HYDRO- 
 SPHERE. 
 
 COMPOSITION OF THE HYDROSPHERE. 
 
 The hydrosphere is never pure H 2 O, but always includes dis- 
 solved salts and gases. The former are most abundant in sea wa- 
 ter and in the waters of salt lakes, the latter in some underground 
 waters. The composition of the larger divisions of the hydrosphere, 
 the oceans and the intracontinental seas, the lakes, rivers and 
 ground water, will be considered in turn. The totality of dissolved 
 salts constitutes the salinity of the water, though in the open sea 
 less than 80 per cent, of this is common salt (NaCl). The totality 
 of mineral matter is determined in parts (by weight) per 1,000 
 parts of water, or the number of grams in 1,000 grams (i liter) of 
 water. This amount is expressed as so many permille (/ 00 ) of 
 salts. Thus a salinity of 35 permille exists when each 1,000 grams 
 (or approximately each liter) of sea water contain 35 grams of 
 salts, as in average ocean water. (For details and corrections of 
 method see Krummel-2o: 221-222.) 
 
 I. SALINITY OF THE SEA. 
 
 The salinity of the sea as a whole has been calculated at 34.49 
 permille, but that of. individual divisions varies greatly. The fol- 
 lowing table adapted from Krummel gives the mean surface salinity 
 for the principal divisions, to which is added the mean salinity of 
 the entire volume. (Krummel-2o : 333, 361.) 
 
 The seven important elements which form most of the salts con- 
 tained in solution in the sea water are: Chlorine (Cl), Bromine 
 (Br), Sulphur (S), Potassium (K), Sodium (Na), Calcium (Ca), 
 and Magnesium (Mg). 
 
146 
 
 PRINCIPLES OF STRATIGRAPHY 
 Table Showing the Salinity of the Sea. 
 
 
 Surface 
 salinity 
 in 
 permille 
 
 Mean 
 total 
 temperature 
 C. degrees 
 
 Volume 
 salinity 
 in 
 permille 
 
 A. OCEANS. 
 I Atlantic Ocean 
 
 35. 37 
 
 4.02 
 
 
 2 Indian Ocean 
 
 74 8l 
 
 3 82 
 
 
 3 Pacific Ocean . . 
 
 74 QI 
 
 ^ 7^ 
 
 
 Average for the three large oceans 
 (or 3 5 per cent by weight) 
 
 7C O3 
 
 3 83 
 
 
 4 Arctic Ocean 
 
 25. 50 (?) 
 
 0.66 
 
 34 80 
 
 B. MEDITERRANEANS. 
 a. Land Locked. 
 
 e Roman mediterranean 
 
 74 85 
 
 13 35 
 
 ^6 10 
 
 6. Red Sea mediterranean 
 7 Mexican mediterranean. ... . "1 
 
 38.80 
 
 22.69 
 
 39.00 
 
 8. Yucatan mediterranean r 
 
 35-95 
 
 6.60 
 
 35.30 
 
 9. Caribbean mediterranean J 
 10 Black Sea mediterranean 
 
 18.30 
 
 
 22.04 
 
 b. Marginal. 
 1 1 Austral- Asian group . 
 
 33.87 
 
 6.9O 
 
 34.00 
 
 12. Andamanian mediterranean 
 
 31 .50 
 
 IO.O9 
 
 33.00 
 
 13. East Chinese mediterranean 
 
 32.10 
 
 9.29 
 
 34.00 
 
 14 Japanese mediterranean 
 
 34. 10 
 
 0.90 
 
 34.00 
 
 15. Okhotsk mediterranean 
 1 6 Behring Sea mediterranean 
 
 30.90 
 30.30 
 
 1.50 
 2 .OO 
 
 33-50 
 32.00 
 
 C. EPICONTINENTAL SEAS. 
 a. Land Locked. 
 
 17 Hudson Bay . . . . 
 
 26.00 (?) 
 
 1. 00 (?) 
 
 30.00 (?) 
 
 18. Baltic Sea 
 
 7.80 
 
 3.91 
 
 10.00 
 
 19 Persian Gulf 
 
 36.70 
 
 24.00 
 
 37.00 
 
 20. Sea of Azov 
 
 b. Marginal. 
 21 British group 
 
 10.50-10.70 
 
 34 80 
 
 0.77 
 
 10.50-10.70 
 35.00 
 
 22. North Sea 
 
 34.2O 
 
 7.72 
 
 35.00 
 
 23 Tasmanian Sea 
 
 35. SO 
 
 12 5O 
 
 35- 5O 
 
 D. FUNNEL SEAS. 
 24 Californian funnel sea . 
 
 35 5O 
 
 9. 12 
 
 35.50 
 
 25. Laurentian funnel sea 
 
 3O. 5O 
 
 2.18 
 
 33-00 
 
 
 
 
 
COMPOSITION OF SEA WATER 
 
 147 
 
 From a total of 77 very complete analyses of samples of ocean 
 water obtained by the Challenger Expedition, Dittmar (2: 189, 204; 
 Krummel-2O : 219) has calculated the following average composi- 
 tion of* the salt content of the sea. The calculations are in percent- 
 ages of the total solids, in grams per thousand grams of sea water 
 (permille) and in British tons per cubic mile of sea water. The 
 total of the solids is taken at 35 permille, or 3.5 per cent, by weight 
 of the sea water. The earliest calculations of Forchhammer (7), 
 
 
 +J 
 
 
 
 
 
 
 I 
 
 & 
 
 3 
 
 a g^ 
 
 ^ C w 
 
 ,s 
 
 
 ! 
 
 I 
 
 a 
 
 -8 2 6 
 
 rt M g 
 
 VH j-j W) . 
 
 s l 
 
 
 1 
 
 O 
 
 4J 
 
 c . 
 
 '~ ! 
 
 ri . 
 
 
 "3 
 
 
 
 D tn 
 
 '1 s ^ ^ 
 
 .y <3 
 
 
 * 
 
 & 
 
 I 1 
 
 i 1 * 1 
 
 S * 
 
 i Sodium chloride (NaCl) 
 
 c8 5 
 
 2 17 
 
 77 7c8 
 
 
 117,434,000 
 
 2. Magnesium chloride (MgCl 2 ) . 
 
 O" O 
 
 95-3 
 
 / 
 
 2.18 
 
 / / / O 
 
 10.878 
 
 3.807 
 
 16,428,000 
 
 3. Magnesium sulphate (MgSO) 
 
 120.4 
 
 2.6 5 
 
 4-737 
 
 1.658 
 
 7,154,000 
 
 4. Calcium sulphate (CaSO 4 ) . . . 
 
 136.1 
 
 2.97 
 
 3.600 
 
 1.260 
 
 5,437,000 
 
 5. Potassium sulphate (K 2 SO ) . . 
 
 174. i 
 
 
 2 4.6^ 
 
 o 86^ 
 
 7 727 OOO 
 
 6. Calcium carbonate (CaCO,)f. 
 
 / rr 
 100. 
 
 2.72 
 
 * . i|.V^^ 
 
 0-345 
 
 *f"O 
 
 0.123 
 
 O > / w I v -' v/vy 
 
 521,000 
 
 7. Magnesium bromide (MgBr 2 ) . 
 
 184-3 
 
 
 0.217 
 
 0.076 
 
 328,000 
 
 Total 
 
 
 
 IOO.OOO 
 
 35 .000 
 
 151,025,000 
 
 
 
 
 
 
 
 based on more than 150 analyses of sea water, gave : NaCl 78.32% 
 of the total solids, or a salinity of 26.862 permille; MgCL, 9.44%, 
 or 3.239 permille; MgSO 4 , 6.4.0%, or 2.196 permille ; CaSO 4 , 3.94%, 
 or 1.350 permille. The K is calculated as KC1, 1.69% of the 
 total solids, or a salinity of 0.582 permille, no K 2 SO 4 , MgBr 2 
 or CaCO 3 being given. A residue of 0.21% or 0.070 permille 
 is left, making a total of 100% solids, or a salinity of 34.299 
 permille. 
 
 Calculated in percentages- of ions, we have (Tolman-39) : 
 
 * One British ton equals 2,240 pounds avoirdupois; one metric ton equals 
 i, ooo kilograms, or 2,204.6 pounds avoirdupois. One cubic mile of sea water 
 (density 1.026) weighs 4,315,000,000 tons. 
 
 f Including all traces of other salts,. 
 
148 PRINCIPLES OF STRATIGRAPHY 
 
 Per cent. Grams per liter.* 
 
 Cl 55-292 19 . 68 
 
 Br o.i 88 0.07 
 
 SO 4 7.692 2.74 
 
 CO 3 o . 207 o . 08 ' 
 
 Na 30-593 10-89 
 
 K 1.105 0.40 
 
 Mg.., 3-725 i-33 
 
 Ca i .197 0.43 
 
 99-999 35-62 
 
 Besides the predominating seven elements in the sea, there are 
 traces of numerous others, the quantity of which, precipitated as salts 
 in the evaporation, are figured in the above table of Dittmar with the 
 calcium carbonate. The following additional elements have been de- 
 tected (for details see Krummel--2O : 216, 218) : Aluminium (Al), 
 Arsenic (As), Barium (Ba), Boron (B), Caesium (Ce), Cobalt 
 (Co), Copper (Cu), Fluorine (F), Gold (Au), Iodine (I), Iron 
 (Fe), Lead (Pb), Lithium (Li), Manganese (Mn), Nickel (Ni), 
 Phosphorus (P), Rubidium (R), Silicon (Si), Silver (Ag), 
 Strontium (Sr), Zinc (Zn), together with dissolved Oxygen (O), 
 Nitrogen (N), and Carbon dioxide (CO 2 ), % the latter estimated at 
 1 8 times the amount contained in the atmosphere. (Chamberlin 
 and Salisbury-3 : 5^5) . 
 
 The weight of the sea water, as a whole, being taken at 
 138 X IO IG metric tons (Chapter I, p. 3), and the average per- 
 centage of salts by weight as 3.5, we obtain for the total amount of 
 salt in the sea the product of 4.84 X io lc metric tons. The volume 
 of salt, resulting from a complete evaporation of the oceans, would 
 depend on the average specific gravity of the salt, which may be 
 
 4.84 
 taken at 2.22. This would give us X io 36 or 2.18 X io 16 cubic 
 
 meters, or 21.8 million cubic kilometers, a quantity sufficient, if 
 spread over a level sea bottom of 361 million square kilometers, to 
 make a layer more than 60 meters thick. Of this 47.5 meters would 
 represent sodium chloride or common salt, 5.8 meters magnesium 
 chloride, 3.9 meters would represent magnesium sulphate, 2.2 
 meters calcium sulphate, and 0.6 meter the remaining salts. The 
 total quantity of salts forms a mass three times as great as the con- 
 tinent of Europe, or a little more than half the volume of land in 
 Asia, which has 41.6 million cubic kilometers. 
 
 * With the average salinity taken as 35.6 permille. 
 
COMPOSITION OF SEA WATER 149 
 
 Variation in the Distribution of the Salt Content of the Oceans and 
 Intracontinental Seas. 
 
 The distribution of salts in the surface layers of the oceans 
 varies with the degrees of latitude. Thus, for the Atlantic it is 
 32.80 permille between 70 and 65 N. lat. (Schott-36: -?//). It in- 
 creases to 37.00 permille between 30 and 20 N. lat., and decreases 
 to 35.07 permille at the equator. Then it increases again to 36.52 
 permille between 20 and 25 S. lat., after which it decreases to 
 33 permille at 70 S. lat. There are thus two maxima in the At- 
 lantic. In the Pacific we have a salinity of 31.72 permille at 60 
 N. lat., increasing to 35.42 permille between 30 and 25 N. lat., 
 and decreasing again to 34:36 permille at 10 north of the equator. 
 Then it increases to its second maximum of 36.18 permille between 
 15 and 20 S. lat., after which it decreases again to 33.00 permille 
 at 70 S. lat. In the Indian Ocean the first maximum of 35.37 per- 
 mille lies near the equator, and the second between 25 and 30 S. 
 lat. (35.88 permille). The minimum of 34.55 permille between these 
 two lies about 10 south of the equator. Southward the decrease is 
 similar to that in the other oceans, to 33 permille at 70 S. lat. ; but 
 northward from the equator the change is oscillatory. (Kriim- 
 mel-2o: 334.) The causes of this variation are to be sought chiefly 
 in the varying rate of evaporation from the surface of the ocean, 
 and the consequent increase in salinity. Evaporation is a func- 
 tion of the temperature, wind velocity and relative humidity. 
 ( Schott-36 : 218. ) Opposing factors are the amount of precipi- 
 tation, and the addition of fresh water by streams, melting ice- 
 bergs, etc. Displacement of waters of a certain salinity through 
 currents also must be considered. The following table gives the re- 
 sults of Marzelles' experiments in this direction ( Schott-36 : 218) : 
 
 I. Average evaporation in 24 hours with varying temperatures 
 without considering wind velocity or humidity. 
 
 At i C 0.80 mm. At 19 C ...1.52 mm. 
 
 At 11 C 0.97 mm. At 27 C 2.96 mm. 
 
 II. Evaporation in 24 hours with the temperature of the air 
 about 20 C. and varying wind velocity. 
 
 With velocity of 0.3 meter per second 1.21 mm. 
 
 With velocity of 4.2 meters per second i . 90 mm. 
 
 With velocity of 7.5 meters per second 2.97 mm. 
 
 With velocity of 10.3 meters per second 4.01 mm. 
 
150 PRINCIPLES OF STRATIGRAPHY 
 
 III. Evaporation in 24 hours with varying humidity and a tem- 
 perature of the air of 20 C. 
 
 Relative humidity 81-85 % I 2 3 
 
 Relative humidity 71-75 % i . 44 
 
 Relative humidity 61-65 % 2 6 
 
 Relative Jiumidity 5 1-55 % 2 . 66 
 
 Relative humidity 41-45 % 2.97 
 
 Experiments by Schott have given the following results in con- 
 centration of normal sea water through evaporation at a tempera- 
 ture of the air ranging around 25 C. and an average velocity of the 
 wind of 7.5 meters per second. The measurements were made on 
 the Atlantic from the 5th to the 8th of September, 1892, at 8 o'clock 
 each morning, on 10 liters of sea water, in a vessel giving 600 
 square centimeters surface, and fully exposed to the wind. 
 
 Salinity Height of water 
 
 Date (8 A. M.) permille column in cm. Volume c. c. 
 
 Sept. 5 36.3 16.5 10.000 
 
 Sept. 6 38.5 16.2 
 
 Sept. 7 40.3 15.9 
 
 Sept. 8 42.1 15.6 9.360 
 
 Thus in three days the decrease in volume was about 6 per cent., 
 while the increase in salinity was nearly 6 permille. 
 
 B at hy metric Variation. Besides the regional variation, there is 
 a bathymetric variation in the different water bodies. In rare cases 
 is the salinity uniform throughout (homalinc); it is commonly vari- 
 able (heterohaline). A decreasing salinity downward constitutes an 
 anohaline arrangement (ah) ; an increasing one is a katohaline 
 (kh) condition. A decreasing followed by an increasing salinity 
 downward constitutes a dichohaline (dh) condition, while the re- 
 verse, an increasing followed by a decreasing salinity downward, 
 constitutes a mesohaline condition (nih), the most saline layers being 
 in the middle. (Krummel, 20:554.) These relations may be sum- 
 marized graphically as follows : 
 
 Decreasing Increasing 
 
 salinity salinity 
 
 Homohaline J 
 
 C Anohaline ,/ &' ff 
 
 Katohaline . . \ cu C 
 
 Heterohaline i T\ t_ t_ V* f> 3 
 
 Dichohaline / ^ & 
 
 [ Mesohaline \ & 
 
COMPOSITION OF SEA WATER 151 
 
 The following table copied from Krummel shows the variation 
 in salinity with depth, and the seasonal variations in the Bay of 
 Danzig on the southern border of the Baltic. (20 : J5J.) 
 
 Variation in Salinity. Bay of Danzig, 1902-1906. 
 
 Depth in meters. . . . 
 
 
 
 10 
 
 20 
 
 30 
 
 40 
 
 50 
 
 75 
 
 105 
 
 February 
 
 7. 1O 
 
 7. 11 
 
 7- ^i 
 
 7- ^4 
 
 7. 12 
 
 7.16 
 
 7.86 
 
 II 17 
 
 May 
 
 7 I ^ 
 
 7 1^ 
 
 7 10 
 
 7 2Q 
 
 7 ^ 
 
 7 ^.^i 
 
 8 04 
 
 II 72 
 
 August 
 
 7 22 
 
 7.2^ 
 
 7.21 
 
 7.20 
 
 7.26 
 
 7 11 
 
 7 QQ 
 
 1 1 QQ 
 
 November 
 
 7.2A 
 
 7.21 
 
 7.2^ 
 
 7.21 
 
 7.26 
 
 7.27 
 
 Q. 17 
 
 II 74 
 
 
 
 
 
 
 
 
 
 
 Average 
 
 7.22 
 
 7.22 
 
 7.24 
 
 7.26 
 
 7.29 
 
 7-32 
 
 8.49 
 
 11.66 
 
 In the Arctic Ocean the variation in the salt content has been 
 found by the Fram to average as follows ( Krummel-20 : 
 
 Depth in meters: 
 
 o 
 
 40 
 
 250 
 
 45 
 
 1,000 . . 
 
 2,000 
 
 3,000 
 
 Parts per 1,000 
 
 by weight 
 
 21 .00 
 
 33-26 
 
 34-97 
 35-02 
 
 35-07 
 35-oS 
 35-12 
 
 The increase is rapid at first owing to the fact that the surface 
 strata are diluted by river waters and melting ice. A slight irregu- 
 larity is shown by the fact that at one locality the salt content was 
 35.19 at 2,500 meters' depth. In the East Greenland Mediterranean 
 Sea, between Spitzbergen and the Faroe Islands, the bottom layers, 
 below 800 or 1,000 meters in depth, have a homohaline character, 
 the salinity being 34.91 permille. A homothermal character of 
 - 1.2 C. also prevails. Along the Norwegian coast the upper lay- 
 ers, of 200 to 300 meters, have a uniform salinity of something over 
 35.2 permille, south of 70 north latitude, while north of that it 
 decreases. 
 
 The following table gives some of the variations in salinity in the 
 Atlantic Ocean (Krummel-2o: 338*341) : 
 
152 PRINCIPLES OF STRATIGRAPHY 
 
 Table Showing Bat hy metric Variations of Salinity in the Sea. 
 
 Depth in 
 meters 
 
 Parts by weight in 1,000 parts of sea water (permille) 
 
 Bay of 
 Biscay 
 
 43 7' 
 N. Lat. 
 
 19 43' 
 W. Long. 
 
 Azores 
 
 S. W. 
 Cape 
 Verde 
 Islands 
 
 South 
 Atlantic 
 
 23 33' 
 S. Lat. 
 20 51' 
 W. Long. 
 
 Off Cape 
 of 
 Good 
 Hope 
 35 52' 
 S. Lat, 
 13 8' 
 E. Long. 
 
 o 
 
 100 
 2OO 
 500 
 600 
 692 
 800 
 900 
 1,000 
 I,2OO 
 1,500 
 2,OOO 
 
 3,000 
 4,000 
 
 4,777 
 4,957 
 5,045 
 5,900 
 
 6,035 
 
 35-78 
 
 35-90 
 
 35-90 
 
 36.40 
 35-70 
 
 36.77 
 36.60 
 
 35-43 
 34-55 
 
 35-50 
 
 35-72 
 35-6o 
 
 
 35-75 
 
 
 34-50 
 
 35-45 
 
 35-40 
 
 
 
 ^s 10 
 
 
 
 35-6o 
 
 
 
 
 
 
 
 
 
 34-33 
 34-43 
 
 34-73 
 
 34-36 
 
 35-53 
 
 35.65 
 
 35-40 
 
 
 
 34-58 
 34-60 
 
 35-51 
 
 35-34 
 35-08 
 
 
 
 35-10 
 35-oo 
 
 35-00 
 
 
 f 35-12 
 to. 
 I 35-69 
 
 
 
 
 
 
 34-77 
 
 
 
 
 
 
 
 
 34-72 
 
 
 
 
 
 T.A 67 
 
 
 
 34-90 
 
 
 
 
 
 
 35-8i 
 
 
 
 
 
 
 
 
 In the Indian Ocean (35 S. lat., 74 E. long.) the salinity de- 
 creases from 35.3 at the surface to 34.38 at 900 meters, increasing 
 again to 34.45 at 1,500 meters and 34.65 at the bottom. It is thus a 
 strictly dichohaline arrangement. A similar condition exists in the 
 South Pacific, where a minimum of 34.2 to 34.3 is found at a depth 
 of 730 meters. 
 
 The salinity of the Roman Mediterranean may be taken as an 
 example of the conditions in the nearly landlocked types. In this 
 the increase in salinity of the surface waters is from the west east- 
 ward. At the Straits of Gibraltar, where the Atlantic water enters, 
 the salinity is 36.35 permille; at Cape Gata, Spain, it is 37.83 ~per- 
 
SALINITY OF SEA WATER 153 
 
 inille; between Greece and Barca (Africa) 38.46 permille, and about 
 halfway between the islands of Rhodes and Cyprus (long. 30 18' 
 E., lat. 35 49' N.) it is 39.40 permille. The salinity varies strongly 
 with depth. Thus at the Straits of Gibraltar the following changes 
 occur : 
 
 Surface 36 . 35 permille The denser water flows out as an 
 
 25m 36 . 56 permille undercurrent and affects the salinity 
 
 50 m 37 .00 permille of the deeper strata of the Gulf of 
 
 100 m 38-07 pcrniille Cadiz for a long distance out. The 
 
 200 m 38 . 30 permille density of 38.46 found at 400 meters 
 
 400 m 38.46 permille depth in the Gibraltar Straits is 
 
 found between Malta and Pantel- 
 
 leria at a depth of 200 meters and south of Greece at the surface. 
 In the eastern region (Cyprus district) the surface salinity was 
 found in the summer to be from 0.2 to 0.4 permille greater than 
 at the bottom (2,000 to 2,950 meters). This change occurs in the 
 upper 100 meters, and is believed to be due to the rapid evapora- 
 tion on the surface. The seasonal change in the salinity of surface 
 waters, due to the influx of fresh water through the streams, is 
 well shown in the Adriatic, where in the spring the salinity sinks to 
 18 or even 16 permille in the neighborhood of the land, while in 
 the winter the salinity is 38 permille even at the mouths of streams. 
 This freshening of the surface waters extends, however, to the 
 depth of only about one meter. Throughout the year salt water 
 ascends the streams along their bottoms ; in the Natissa River at the 
 head of the Adriatic, it ascends as far as Aquileja, 10 kilometers 
 from the coast. (Krummel-20 : 555.) 
 
 The Sea of Marmora, between the Black and Roman mediter- 
 raneans, has a surface layer, of n meters or more, of low salinity 
 (22 to 25 permille), followed by a rapid increase to a depth of 
 25 meters where the salinity is 28.5 permille. Beyond this follows 
 a slow increase to a depth of 200 to 300 meters, where the salinity 
 is 38.1 permille, increasing later to 38.4 permille, after which it 
 remains constant to the bottom (1,400 meters). 
 
 The surface stratum of low salinity is again seen in the Black 
 Sea, where, according to Wrangell and Spindler, the upper 40 or 45 
 meters have a homohaline character of 18.3 permille. Downward this 
 slowly increases to 19.7 at 90 m., to 21.4 at 180 m., 22.0 at 350 m., 
 and 22.4 to 22.5 from 900 m. to 2,000 m. The Sea of Azov is an epi- 
 continental sea, being very shallow, and, as a result, it is usually 
 homohaline, with 10.5 to 10.7 (more rarely ii.o) permille. In the 
 
154 PRINCIPLES OF STRATIGRAPHY 
 
 northeast, where fresh-water streams enter the basin, the salinity 
 may be as low as 7 permille. In the Straits of Kertch, connecting 
 the Azov and Black seas, the upper 5 meters of 10 permille salinity 
 flow outward, while the remainder (2 to 3 meters) represents the 
 inflowing water from the Black Sea, with 16 to 17 permille, the 
 isohaline surfaces lying higher in the east than in the west. In the 
 Red Se# the salinity decreases on the surface from 40.43 in the 
 north to 37.77 in the south. In the northern section the salinity 
 increases downward from 40.43 to 40.55 permille at the bottom (547 
 meters), and in the southern, from 37.77 to 40.41 permille at the 
 bottom (1,120 meters). In the greatest depth (2,160 meters) near 
 the middle, the salinity is 40.68 permille. 
 
 II. COMPOSITION OF LAKE WATERS. 
 
 The composition of the waters of enclosed basins varies greatly, 
 as does also the absolute salinity, which is much greater than that of 
 the ocean in many cases, and less in still more numerous cases. 
 
 The following table (Russell-29, table C; Clarke-4) gives the 
 salinity of the surface layers of a number of enclosed waters in 
 permillages.* For comparison it should be remembered that the 
 permillage of average ocean water is 35. 
 
 Table of Salinity of Various Lakes. 
 
 A. Saline and Alkaline. 
 
 Permille. 
 
 1. Tinetz Lake, a residue lake of the Caspian 289 . ooo 
 
 2. Karaboghas (Karabugas) Gulf 285 . ooo 
 
 3. Elton Lake, Russiaf. .' 270 . 627 
 
 4. Indevsk Lake 261 . 530 
 
 5. Bogdo Lake, Russia 256.750 
 
 6. Illyes Lake, Hungary 233 . 747 
 
 7. Great Salt Lake, Utah (1892) 230.355 
 
 8. Owen's Lake, Cal., 1905 (triple alkali) 213 . 700 
 
 9.. Urmiah Lake, Persia 205 . 500 
 
 10. Black Lake, Hungary 195 . 300 
 
 11. Dead Sea (maximum) I9 2 - 153 
 
 12. Great Salt Lake, Utah (1889) 167 . 160 
 
 3. Lake Domoshakovo, Siberia 145.500 
 
 14. Great Salt Lake, Utah (1877) i37-9o 
 
 15. Soda Lake, near Ragtown, Nevada (triple alkali). . H3- 6 44 
 
 16. Goodenough Lake, British Col. (alkali carbonate) 103.470 
 
 17. Sevier Lake, Utah 86 . 403 
 
 18. Borax Lake, Cal. (alkali, carbonate-chloride) 76 . 560 
 
 * Equivalent to grams per liter of water, 
 t Average of 3 analyses. 
 
COMPOSITION OF LAKE WATERS 155 
 
 Table of Salinity of Various Lakes Continued. 
 
 A. Saline and Alkaline. Continued 
 
 Permille. 
 
 19. Owen's Lake, Cal. 1876 (sp. gr. 1.051) 60.507 
 
 20. Mono Lake, Cal. (triple alkali) . . 49 . 630 
 
 21. Albert Lake, Oregon, 1890 (alkali) 39 . 172 
 
 22. Albert Lake, Oregon, 1883 (sp. gr. 1.02317) 27.357 
 
 23. Van Lake 22 . 600 
 
 24. Caspian Sea* (1878) 12 .940 
 
 25. Lake Koko-Nor, Tibet 1 1 . 100 
 
 26. Aral Sea 10 . 842 
 
 27. Lake Biljo, Siberia 8 . 800 
 
 28. Chichen Kanab (Little Sea), Yucatan 4-446 
 
 29. Natron Lake, near Thebes, Egypt (alkali, carbonate-chloride). . . 4.407 
 
 30. Winnemucca Lake, Nevada (alkali, carbonate-chloride) 3 . 603 
 
 31. Issyk-Kul, Siberia 3 . 574 
 
 32. Pyramid Lake, Nevada (alkali, carbonate-chloride) 3.486 
 
 33. Walker Lake, Nevada (triple alkali) 2 . 562 
 
 34. Palic Lake, Hungary 2 - 2I 5 
 
 35. Humboldt Lake,t Nevada (alkali, carbonate-chloride) 0.929 
 
 36. Laacher See, Germany (alkaline sodium carbonate) 0.213 
 
 B. Fresh Water Lakes. 
 
 37. Lake Erie at Buffalo^ o . 134 
 
 38. Lake Michigan* o. 1 16 
 
 39. Lake Huron f o. 105 
 
 40. Croton Reservoir, New York o . 084 
 
 41 . Lake Baikal, Siberia o . 069 
 
 42. Lake Champlain* 0.067 
 
 43. Lake Superior* o . 058 
 
 As will be seen by a comparison inter se of the analyses made in 
 1876 and 1905 of the waters of Owen's Lake, California, a lake of 
 triple alkaline waters, and those of the Great Salt Lake, Utah, made 
 in 1877, 1889 and 1892, a difference of salinity, amounting in the 
 case of Owen's Lake to 153.2 permille, and in that of Great Salt 
 Lake to 116.7 permille, obtained between the extreme dates. This 
 shows the variation in concentration of the smaller salt lakes. In 
 both cases it is seen that the concentration has been a progressive 
 bne in time. For Great Salt Lake, successive analyses show the 
 following concentration, which, with the exception of the first, 
 
 shows a regular progression. 
 
 
 
 * Average of 5 analyses. 
 
 t Average of 4 analyses. 
 | Average of 6 analyses. 
 
156 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Permille. 
 
 1869 149-94 
 
 1877 137.90 
 
 1879 156.71 
 
 Permille. 
 
 1885 167.16 
 
 1889 I95-58 
 
 1892 230.36 
 
 Elton Lake, Russia, gave in April a salinity of 255.6 permille; 
 in August 264.980 permille, and in October 291.300 permille, the 
 specific gravity in the last case being 1.273. 
 
 The vertical range in salinity is well shown by a number of 
 analyses of the waters of the Dead Sea, which are here tabulated. 
 (Terreild, in Clarke, 4.) 
 
 Table Showing Vertical Range in Salinity in the Dead Sea. 
 
 Depth 
 
 Salinity 
 permille 
 
 Specific 
 gravity 
 
 a Surface, Ras Dale 
 
 25.700 
 
 i .0216 
 
 b. Surface, north end ". 
 
 IQ2. I S3 
 
 I . 1647 
 
 c At 20 meters 5 miles east of Wady Mrabba 
 
 2O7 OQO 
 
 
 d. At 42 meters, near Ras Mersed 
 
 242 6^0 
 
 
 e. At depth of 120 meters (393 ft.), 5 miles east of 
 Ras Feschkah 
 
 24C 7-10 
 
 i 2225 
 
 f. At 200 meters (656 ft.), same locality as e. ... 
 g. At 300 meters, same locality as c 
 
 251. ioo 
 
 2 SO -08O 
 
 i . 2300 
 
 
 
 
 The salinity of the River Jordan, flowing into the Dead Sea, is 
 only i. 6 1 permille. Its carbonates and gypsum are precipitated 
 when it enters the lake, and its contribution consists almost entirely 
 of chlorides, derived from the Cretacic salt- and gypsum-bearing 
 strata of the region. Soda Lake, Nevada, at one foot below the sur- 
 face, where the specific gravity was i.ioi, gave a salinity of 113.644 
 permille, a large part being carbonate and sulphate of sodium. At a 
 depth of ioo feet the salinity was 113.651 permille. 
 
 The waters of salt and alkaline lakes may be divided into several 
 fairly well-defined groups (Clarke-4: 134-138}. Among the salt 
 lakes we have first a group of normal chloride waters, characterized 
 mainly by sodium chloride, and having a close resemblance to 
 oceanic water. They may represent remnants of the ocean water, 
 or the salts may be due to leaching of ancient marine deposits carry- 
 ing oceanic salt. The analyses of the waters of Great Salt Lake 
 (Aj) and of Illyes Lake, Hungary (A 2 ) may be taken as examples. 
 The second group is that of Natural Bitterns derived from the pre- 
 
COMPOSITION OF LAKE WATERS 157 
 
 ceding, but having its magnesium salts concentrated from prolonged 
 evaporation, sodium chloride having crystallized out. The Dead 
 Sea (Bj) and Elton Lake, Russia (B 2 ), are examples. The third 
 group is characterized by sulphate waters, there being, however, no 
 distinct line of demarcation between this and the last group. Sevier 
 Lake, Utah (Q), and Lake Domoshakovo, Siberia (C 2 ), show ex- 
 tremes. A somewhat different group comprises the sulphate- 
 chloride waters of the Caspian and the Aral Sea (DJ, which show 
 a falling off of the alkaline metals and an increase in calcium and 
 magnesium, while the sulphates approach the chlorides. The bit- 
 terns of this type differ from the natural or normal bitterns 
 (B , B 2 ) in the proportion of sulphates. This is shown in the analy- 
 ses of the waters of the Karabugas Gulf (D 2 ) and of Issyk-Kul 
 Lake (D 3 ), Siberia. An extreme case representing a subgroup is 
 shown in Lake Chichen-Kanab, Yucatan (D 4 ). 
 
 The alkaline lakes comprise, first, a group in which the car- 
 bonates are largely in excess of all other salts, constituting the 
 typical carbon waters. Goodenough Lake, British Columbia (Ej), 
 and Palic Lake, Banat, Hungary (E 2 ), are examples. A second 
 group of alkaline waters is the carbonate-chloride group, these two 
 salts predominating, while sulphates are present in subordinate 
 quantity. Humboldt Lake, Nevada (FJ, Albert Lake, Oregon 
 (F 2 ), and Pyramid Lake, Nevada (F 3 ), are examples of this type. 
 "Triple" waters, in which chlorides, sulphates and carbonates are 
 present in notable quantities, constitute the next group. Owens 
 Lake, Cal. (Gj), and Soda Lake, Nevada (G 2 ), are examples of this 
 type. Finally, the waters of two sulphate-chloride lakes of a mod- 
 erate alkaline character, Lake Biljo (HJ and Lake Koko-Nor (H 2 ), 
 are included, and the corresponding constituents of the sea are also 
 given (I). (Clarke-4 : 118-138.) 
 
 Analyses of Types of Lake Water. 
 
 i. Saline Lakes. 
 
 Ai Great Salt Lake (1877) normal chloride waters. 
 A 2 Illeyes Lake, Hungary, normal chloride waters. 
 BI Dead Sea, natural bittern. 
 B 2 Elton Lake, Russia, natural bittern. 
 Ci Sevier Lake, Utah, sulphate waters. 
 C 2 Lake Domoshakovo, Siberia, sulphate waters. 
 DI Aral Sea, sulphate-chloride waters. 
 D 2 Karabugas Gulf, sulphate-chloride bittern. 
 D 3 Issyk-Kul Lake, Siberia, sulphate-chloride bittern. 
 D 4 Lake Chichen Kanab, Yucatan, sulphate-chloride bittern. 
 
158 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Analyses of Types of Lake Water Continued. 
 
 2. Alkaline Lakes. 
 
 EI Goodenough Lake, British Columbia, carbonate waters. 
 E 2 Palic Lake, Hungary, carbonate waters. 
 FI Humboldt Lake, Nevada, carbonate-chloride waters. 
 F 2 Albert Lake, Oregon, carbonate-chloride waters. 
 Fa Pyramid Lake, Nevada (mean of four concordant analyses), 
 
 carbonate-chloride waters. 
 
 F4 Borax Lake, Lake Co., California, carbonate-chloride waters. 
 Gi Owen's Lake, California, " Triple" waters (1965). 
 G 2 Soda Lake, Nevada, " Triple" waters. 
 HI Lake Biljo, Siberia, alkaline sulphate-chloride waters. 
 H 2 Lake Koko-Nor, Tibet, alkaline sulphate-chloride waters. 
 
 For Comparison 
 I Ocean water. 
 
 TABLE, IN PERCENTAGES, OF TOTAL SOLIDS, OF 
 
 
 Normal 
 chloride 
 
 Natural 
 bittern 
 
 Sulphate 
 waters 
 
 Sulphate chloride 
 waters 
 
 A! 
 
 .Ai 
 
 Bi 
 
 B 2 
 
 Ci 
 
 C 2 
 
 D! 
 
 D 2 
 
 D 3 
 
 D 4 
 
 Cl 
 
 56.21 
 
 60. 18 
 tr. 
 0.44 
 0.04 
 
 65.81 
 2.37 
 0.31 
 
 tr. 
 
 64.22 
 
 'o 82 
 o 04 
 
 52.66 
 'io!88 
 
 3.71 
 tr. 
 63.62 
 0.08 
 0.07 
 
 35-40 
 0.03 
 30.98 
 0.85 
 
 53.32 
 0.06 
 17-39 
 
 15.64 
 0.03 
 55-94 
 i .26 
 
 8.14 
 
 Br 
 
 SO4 
 
 6.89 
 0.07 
 
 58.64 
 
 COs 
 
 NOs 
 
 
 
 PO4 
 
 
 
 
 
 * 
 
 
 O.O2 
 
 
 Li 
 
 
 
 11.65 
 I.8 S 
 
 4-73 
 13.28 
 
 tr. 
 
 II 27 
 
 
 
 
 
 
 
 B40 7 
 Na 
 
 33^45 
 
 39-02 
 
 
 
 
 
 33-33 
 
 30.61 
 0-59 
 
 .0.58 
 0.74 
 
 tr. 
 tr. 
 
 22.62 
 0.54 
 
 O.O2 
 4.02 
 5-50 
 
 o.o4f 
 
 11.51 
 1.83 
 0.06 
 
 15*83' 
 
 11.76 
 
 1.85 
 
 H.99 
 0.43 
 
 K 
 Rb 
 
 0. IO 
 
 17.55 
 
 0. 12 
 3-01 
 
 Ca 
 Mg 
 Si0 2 
 AhOs.. .. 
 p e2 O3 
 
 O.2O 
 
 3.18 
 
 0.25 
 0.03 
 0.04 
 
 tr 
 
 0.94 
 12.50 
 
 tr. 
 
 13-49 
 7.31 
 
 * 
 
 MnzOs 
 S. sulphide 
 As2Os . . . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 o 6 
 
 
 
 
 
 
 
 
 
 
 
 
 Total %... 
 
 Salinity 
 permille . 
 
 
 
 
 
 
 
 
 IOO.OO 
 
 IOO.OO 
 
 IOO.OO 
 
 100.00 
 
 IOO.OO 
 
 IOO.OO 
 
 IOO.OO 
 
 IOO.OO 
 
 100.00 
 
 100.00 
 
 137.90 
 
 233.747 
 
 192.15 
 
 265.00 
 
 86.40 
 
 145.50 
 
 10.84 
 
 285.00 
 
 3-574 
 
 4.446 
 
 The composition of saline lakes in percentage of total solids is 
 given in the following partial analyses of the waters of Great Salt 
 Lake, a normal chloride water ; of the Dead Sea, a natural bittern ; 
 and of the Caspian Sea, a sulphate-chloride water. The composi- 
 
COMPOSITION OF LAKE WATERS 
 
 159 
 
 Composition of Saline (and Alkaline Saline) Lakes, in Percentage 
 
 of Total Solids. 
 
 * 
 
 Koko-Nor 
 
 Caspian 
 
 Dead 
 
 Great Salt 
 
 Sodium chloride (NaCl) 
 
 64 4 
 
 6-z QI 
 
 29 oo 
 
 8l 71 
 
 Magnesium chloride (MgCU) 
 
 
 
 65 oo 
 
 O* /O 
 
 6 U 
 
 Magnesium sulphate (MgSO4) . . 
 Calcium sulphate (CaSO 4 ) 
 
 8-7 
 
 23.29 
 
 -zoo 
 
 0.40 
 
 "Oo 
 2.26 
 3C7 
 
 Potassium sulphate (K^SC^) 
 
 
 
 
 371 
 
 Sodium sulphate (Na2SO4) 
 
 16.1 
 
 
 
 
 Calcium carbonate (CaCOs) .... 
 
 4-4 
 
 2.66 
 
 
 
 Magnesium carbonate (MgCOs) . 
 
 4.0 
 
 1.46 
 
 
 
 Calcium chloride (CaCl 2 ) 
 
 
 4.. 6S 
 
 
 
 
 
 
 
 
 tion, in like manner, of a moderately alkaline sulphate-chloride wa- 
 ter is given in the analysis of the waters of Lake Koko-Nor, Tibet. 
 
 COMPOSITION OF VARIOUS NATURAL WATERS. 
 
 Carbonate 
 waters 
 
 Carbonate chloride 
 waters 
 
 Triple 
 waters 
 
 Sulphate chlo- 
 ride waters 
 
 Ocean 
 
 Ei 
 
 E 2 
 
 Fi 
 
 Fs 
 
 F 3 
 
 F 4 
 
 G I 
 
 G 2 
 
 H! 
 
 H 2 
 
 I 
 
 7.64 
 
 7.08 
 41.41 
 
 0.62 
 
 15-68 
 
 2.92 
 41.02 
 
 31.82 
 
 3-27 
 21.57 
 
 36.04 
 
 41.04 
 
 32.27 
 
 o 04 
 
 24.82 
 
 36.51 
 
 9.91 
 
 40.05 
 0.04 
 17.84 
 5-55 
 
 55-29 
 0.19 
 7.69 
 
 0.21 
 
 1.90 
 
 20.67 
 
 5-25 
 14.28 
 
 0.13 
 
 22.47 
 
 O 02 
 
 9-93 
 
 24-55 
 0.45 
 
 O II 
 
 10.36 
 13.78 
 
 52.33 
 
 6.22 
 
 1.07 
 
 
 0.07 
 
 
 
 o 02 
 
 
 
 
 5.05 
 38.10 
 1.52 
 
 0.03 
 0.14 
 38.09 
 1.62 
 
 tr. 
 
 O.O2 
 O.OI 
 
 o. 14 
 } 0.04 
 
 
 
 
 
 tr. 
 36.17 
 6.65 
 
 O.O2 
 O.O4 
 O.O4 
 0-33 
 
 35-75 
 
 29-97 
 6.54 
 
 
 
 0.25 
 36.63 
 
 2.01 
 
 0.22 
 
 0.24 
 
 
 
 
 39-33 
 1.44 
 
 33-84 
 
 2. II 
 
 21.83 
 0.87 
 
 0.43 
 7.28 
 
 0.03 
 0.03 
 
 30.60 
 1. 08 
 0.04 
 1.77 
 2.90 
 0.09 
 
 30.59 
 I. II 
 
 0.66 
 3-35 
 0.27 
 
 1-35 
 1.88 
 3-53 
 
 0.62 
 
 0.25 
 
 2.28 
 
 0.95 
 
 0.03 
 0.35 
 
 O.OI 
 [ O.OI 
 
 I. 2O 
 3-72 
 
 
 o 35 
 
 
 
 
 O.O2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 100.00 
 
 100.00 
 
 IOO.OO 
 
 100.00 
 
 100.00 
 
 100 . 00 
 
 100.00 
 
 100 . 00 
 
 100.00 
 
 100 . 00 
 
 IOO.OO 
 
 103.470 
 
 2.215 
 
 0.929 
 
 39.172 
 
 3.486 
 
 76.560 
 
 213.70 
 
 113.70 
 
 8.80 
 
 II. 10 
 
 35-00 
 
 * Included with SiO 2 . t Including PO 4 and Fe 2 O 3 . 
 
 The quantitative composition of a typical alkaline lake is shown 
 by the following analysis made in 1883 by F. W. Taylor of the 
 water of Albert Lake, Oregon, a carbonate water (sp. gr. 1.02317). 
 (Russell-29: 454.) 
 
i6o 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Silica in solution (SiC^) 
 
 Sodium chloride (NaCl) 
 
 Potassium chloride (KC1) 
 
 Potassium sulphate (K 2 SO 4 ) 
 Potassium carbonate (K 2 CO 3 ) . . 
 Magnesium carbonate (MgCO 3 ) . 
 
 Total. 
 
 Grams per liter 
 
 of the water 
 
 0.065 
 
 7.219 
 
 8.455 
 
 o . 92 1 
 
 10.691 
 
 o . 006 
 
 27.357 
 
 The following analyses of the waters of Pyramid Lake, another 
 carbonate-chloride lake, show variation vertically as well as hori- 
 zontally. ( Rtissell-30 : 57, 58. ) 
 
 
 Probable combination in grams per liter 
 
 South of Anaho Isl. 
 
 North of Anaho Isl. 
 
 i foot 
 below 
 surface* 
 
 200 feet 
 below 
 surface** 
 
 i foot 
 below 
 surf ace f 
 
 350 feet 
 below 
 surface! 
 
 Silica (SiO 2 ) 
 
 o . 0425 
 o . 2632 
 
 0-1374 
 
 2 . 2466 
 0.2621 
 0.4940 
 
 0.0300 
 0.2912 
 
 0.4212 
 0.2800 
 0.0447 
 0.1474 
 2.2411 
 0.2667 
 0.4738 
 
 . 0200 
 0.2818 
 0.0447 
 O.I38I 
 2.2550 
 0.2737 
 0.4756 
 
 Magnesium carbonate (MgCOa) 
 Calcium carbonate (CaCO 3 ) .... 
 Potassium chloride (KC1) 
 Sodium chloride (NaCl) 
 
 0.1387 
 2.2428 
 0.2757 
 0.4834 
 
 Sodium sulphate (Na 2 SO 4 ) 
 Sodium carbonate (Na2COs) .... 
 
 Total 
 
 3-4458 
 
 3.4618 
 
 3-4949 
 
 3.4889 
 
 
 Nearly all the fresh water entering Pyramid Lake, which is 
 without outlet, is delivered at the southern end by Truckee River, 
 near the mouth of which the water is fresh enough for camp pur- 
 poses. At the northern end of the lake the water is unfit for human 
 consumption, but animals may drink it without injury. 
 
 3. Fresh-water Lakes. Water absolutely free from mineral mat- 
 
 * 99- 2 3 per cent, of total solids accounted for. 
 ** 99.19 per cent, of total solids accounted for. 
 f 99.94 per cent, of total solids accounted for. 
 I Error of 0.15 per cent, in excess. 
 
COMPOSITION OF RIVER WATERS 
 
 161 
 
 ter does not exist in nature. That of lakes and rivers suitable for 
 drinking purposes (by man) always contains in the neighborhood of 
 o.i permille of mineral matter, especially calcium carbonate. Wa- 
 ter above 0.15 or 0.2 permille cannot be considered potable, espe- 
 cially if the percentage of sodium chloride is high. (Bibliography 
 V-44.) The average composition of fresh-water lakes is shown by 
 the following analyses of the waters of Lake Baikal, the American 
 Great Lakes and Lake Champlain. (Clarke-4: 61, 81.) 
 
 Table of Average Composition of Lake Waters. 
 
 
 Lake 
 Baikal 
 
 Lake 
 Superior 
 
 Lake 
 Michigan 
 
 Lake 
 Huron 
 
 Lake 
 Erie 
 
 Lake 
 Cham- 
 plain 
 
 CO 3 
 SO 4 
 
 49.85 
 6 93 
 
 45.26 
 4- 33 
 
 48.82 
 5.67 
 
 48.99 
 5.64 
 
 45 64 
 9.48 
 
 45.8i 
 ii .03 
 
 Cl 
 
 2.44 
 
 1 .69 
 
 2 .OI 
 
 2. 19 
 
 5-4 
 
 1.78 
 
 NO 3 
 
 O.2I 
 
 0.56 
 
 0.22 
 
 0.30 
 
 0. 12 
 
 
 POi 
 
 O 72 
 
 
 
 
 
 
 Ca 
 
 23.42 
 
 25.78 
 
 23.42 
 
 23. ii 
 
 23.79 
 
 21 . 19 
 
 Mg.. 
 
 3-57 
 
 4.96 
 
 6.94 
 
 6-35 
 
 5.51 
 
 4.21 
 
 Na 
 
 S 85 | 
 
 
 
 
 
 
 K 
 
 3.44 
 
 4.96 
 
 3-65 
 
 3.21 
 
 4.84 
 
 8.80 
 
 NH 4 
 
 o 08 
 
 
 
 
 
 
 SiO 2 
 
 2 Ol 
 
 12 T.T, 
 
 Q 22 
 
 10. 14 
 
 5. 14 
 
 5.58 
 
 Fe 2 O 3 
 A1 2 O 3 
 
 1.46 
 
 0.13 
 
 0.05 
 
 0.07 
 
 0.08 I 
 
 1.60 
 
 
 
 
 
 
 
 
 Total... 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 IOO.OO 
 
 III. COMPOSITION OF RIVER WATER. 
 
 The composition of river water varies in accordance with the 
 character of the rock, over or in which the river flows, and the na- 
 ture of the supply. Though different rivers show varying amounts 
 in the totality of solids, this is never very high, while at the same 
 time the relative preponderance of the salts does not change greatly. 
 The following table gives the totality of solids in a number of rivers, 
 together with the predominant element or compounds in each. 
 (Russell-30, Table A; Clarke-4 160-82. ) 
 
162 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Table Showing the Amounts in Permille of the Principal 
 
 
 
 Total 
 
 Cal- 
 cium 
 Ca 
 
 Mag- 
 nesium 
 Mg 
 
 I. 
 
 2. 
 
 Rio de los Papagayos, Argentina 
 San Lorenzo River, California 
 
 9.18500 
 4 68500 
 
 0.73572 
 o 23472 
 
 0.03307 
 o 11609 
 
 3- 
 
 Pecos River, New Mexico; average of 6 analyses 
 
 . 2 . 83400 
 
 o . 40999 
 
 o . 10259 
 
 4- 
 5. 
 6. 
 
 7. 
 
 Arkansas River, Rocky ford, Colorado 
 Salt River, at Mesa, Arizona; aver, of 6, anal 
 Brazos River, Waco, Texas 
 Mono Creek California; aver, of 3 anal 
 
 2 . I34OO 
 I . 23400 
 I . 06600 
 I O040O 
 
 0.27273 
 0.09193 
 
 o. 10170 
 o 14889 
 
 0.08024 
 0.03319 
 0.02175 
 
 8 
 
 Arkansas River, Little Rock 
 
 0.7940O 
 
 0.06034 
 
 o . 01326 
 
 9- 
 10. 
 
 Red River of the North below Assiniboine 
 Red River of the North at Fargo, N. Dakota 
 
 0.55IOO 
 O.39800 
 
 0.07102 
 0.07375 
 
 0.04402 
 
 1 1. 
 
 Humboldt at Battle Mt., Nevada 
 
 o . 36150 
 
 0.04890 
 
 o 01240 
 
 12. 
 
 Jordan Utah Lake, Utah 
 
 o 30600 
 
 o 05580 
 
 o 01860 
 
 13- 
 
 14. 
 
 Los Angeles, Los Angeles (hydrant; 
 Rhine at Strassburg 
 
 0.24475 
 
 0.23200 
 
 0.01750 
 0.05869 
 
 0.02097 
 o . 00142 
 
 \l' 
 
 Genesee at Rochester, New York 
 Rhine at Cologne 
 
 o. 19526 
 o. 17800 
 
 0.04170 
 0.04870 
 
 0.00896 
 o . 00991 
 
 17- 
 T 
 
 Bear River at Evanston, Wyoming 
 Walker Mason Valley Nevada 
 
 0.18450 
 o 18000 
 
 0.04320 
 o 02280 
 
 0.01250 
 o 00380 
 
 IQ. 
 2O. 
 21. 
 22. 
 23. 
 
 Mississippi at New Orleans 
 Lower Nile; average of 12 monthly samples 
 St. Lawrence, Pt. de Cascades, S. side 
 Rio Grande del Norte, Fort Craig, New Mexico 
 Mohawk, Utica, New York : 
 
 0.16990 
 o. 16800 
 0.16055 
 o. 15760 
 o. 15250 
 
 0.03720 
 0.03377 
 0.03233 
 0.01633 
 0.03180 
 
 0.00674 
 0.00585 
 0.00123 
 o . 00690 
 
 24- 
 25. 
 
 Hudson, Hudson, New York 
 Cumberland, Nashville, Tennessee 
 
 o. 14238 
 0.13786 
 
 O.O222O 
 O.O2987 
 
 0.00465 
 0.00280 
 
 26. 
 27. 
 
 Passaic, 4 miles above Newark, New Jersey 
 Sacramento Sacramento California 
 
 0.13267 
 o 11484 
 
 O.OI459 
 
 o 01279 
 
 o . 00404 
 
 O OOI2I 
 
 ^8 
 
 Maumee Ohio 
 
 o 10971 
 
 o 02645 
 
 o 00443 
 
 29. 
 30. 
 
 Croton, New York City 
 Moldau above Prague 
 
 0.08433 
 o 07400 
 
 o . 00905 
 
 O OIOOI 
 
 0.00336 
 o 00361 
 
 31- 
 32. 
 
 Truckee, Lake Tahoe, Nevada 
 James, Richmond, Virginia 
 
 0.07300 
 o 07246 
 
 0.00930 
 o 01284 
 
 0.00300 
 o 00377 
 
 33- 
 
 Delaware, Trenton, New Jersey 
 
 o 06795 
 
 o 01104 
 
 o 00435 
 
 34- 
 
 Ottawa Montreal Canada 
 
 o 06116 
 
 o 00992 
 
 o 00161 
 
 
 
 
 
 
 The following table gives the total salinity of a number of addi- 
 tional rivers, as quoted by Penck (26:509) and Clarke (4). 
 
 Table Showing Total Salinity of Other Rivers. 
 
 35. Rio Saladillo, Argentine 
 
 36. Cheliff near Orleansville, Africa 
 
 37. Colorado River, Argentine, South America. . . 
 
 38. Thames, above London (average) 
 
 39. Elbe, above Hamburg 
 
 40. Nile at Cairo * 
 
 41. La Plata, near Buenos Ayres 
 
 42. Vistula, near Culm 
 
 43. Dwina, Russia , 
 
 44. Danube at Budapest (average) 
 
 45. Rhone at Lyons (average) 
 
 46. Rio Negro, above Mercedes, South America . . 
 
 47. Parana, 5 miles above its entry into La Plata 
 
 48. La Plata, 5 miles above Buenos Ayres 
 
 Permille. 
 1.213 
 0.780 
 0.651 
 0.289 
 0.237 
 0.231 
 0.206 
 
 0.201 
 0.187 
 0.187 
 
 0.145 
 0.132 
 O.098 
 O.O9I 
 
COMPOSITION OF RIVER WATERS 
 
 163 
 
 Elements and Compounds Occurring in Various River Waters 
 
 Potas- 
 sium 
 K 
 
 Sodium 
 Na 
 
 Carbonic 
 acid 
 CO, 
 
 Sulphuric 
 acid 
 SO* 
 
 Chlorine 
 Cl 
 
 Other substances present 
 
 0.04501 
 
 2.43219 
 
 0.00551 
 
 2.92535 
 
 2.99707 
 
 S 
 
 o . 06044 
 
 1.07204 
 
 0.14477 
 
 2.20710 
 
 0.77209 
 
 
 0.02182 
 
 o. 14226 
 
 o . 04364 
 
 1.23911 
 
 0.63835 
 
 Si0 2 , A1 2 3 , Fe 2 3 
 
 0.00597 
 
 0.30943 
 
 0.56650 
 
 1.29512 
 
 0.10435 
 
 Si0 2 
 
 i .70292 
 
 0.32553 
 
 o. 11858 
 
 0.01430 
 
 0.51305 
 
 SiO2, A1 2 O 3 , Fe 2 Oa 
 
 0.2/ 
 
 806 
 
 0.24806 
 
 0.22109 
 
 0.35935 
 
 Si0 2 , Fe 2 3 
 
 trace 
 
 o . 10893 
 
 0.18875 
 
 0.45863 
 
 0.03614 
 
 SiO 2 , A1 2 O 3 , Fe 2 O 3 
 
 0.00588 
 
 0.20580 
 
 0.08575 
 
 0. IOOI2 
 
 o . 30609 
 
 Si0 2> A1 2 3 , Fe 2 0, 
 
 0.00650 
 
 0.05328 
 
 0.17340 
 
 0.12155 
 
 0.04838 
 
 SiO 3 , (AlFe) 2 O3 
 
 0.01485 
 
 0.22348 
 
 0.00346 
 
 0.00394 
 
 (AlFe) 2 3 
 
 O.OIOOO 
 
 0.04670 
 
 0.15440 
 
 0.04770 
 
 0.00750 
 
 SiO 2 , A1 2 O 3 
 
 
 o . 01780 
 
 o . 06080 
 
 o . 13060 
 
 o . 01240 
 
 SiO 2 
 
 
 o . 02968 
 
 o . 05635 
 
 o . 05724 
 
 O OIO.44 
 
 SiO 2 , Al 2 Os, FeCOs, MnCOs, NH4, 
 
 
 
 
 
 u **AW|^, 
 
 organic matter 
 
 0.00153 
 
 0.00503 
 
 0.08373 
 
 0.01888 
 
 O.OOI2O 
 
 SiO 2 , A1 2 O 3 , Fe 2 O 3 , NOs 
 
 0.00230 
 
 o . 00440 
 
 o . 06460 
 
 0.04310 
 
 O.OO24O 
 
 SiO 2 , A1 2 O 3 , Fe 2 O 3 , organic matter 
 
 
 0.00479 
 
 0.08377 
 
 0.02244 
 
 O.OO742 
 
 SiO 2 , A1 2 O 3 , Fe 2 O 3 , PO< 
 
 
 o . 00820 
 
 o . 09820 
 
 o . o 1050 
 
 o 00490 
 
 SiO 2 
 
 trace 
 
 0.03180 
 
 0.05760 
 
 0.02840 
 
 0.01310 
 
 Si0 2 
 
 
 0.03100 
 
 o . 03830 
 
 
 
 Carbonates and sulphates of K Na Me 
 
 0.01329 
 
 0.00511 
 
 0.00613 
 
 0.02929 
 
 0.0075 
 
 Si0 2 , Fe 2 3 
 
 0.00115 
 
 0.00513 
 
 0.06836 
 
 0.00831 
 
 0.00242 
 
 Si0 2 
 
 o . 00063 
 
 0.03220 
 
 0.01025 
 
 0.04700 
 
 o . 03604 
 
 Organic mattef , traces of other minerals 
 
 o . 00090 
 
 0.00360 
 
 0.05690 
 
 0.01870 
 
 0.00230 
 
 SiO 2 , A1 2 O 3 , Fe 2 Os, organic matter 
 
 0.00058 
 
 0.00243 
 
 0.07278 
 
 0.01257 
 
 0.00581 
 
 SiO 2 , Fe 2 O 3 , A1 2 O3, H, organic matter 
 
 0.00050 
 
 0.01032 
 
 0.05727 
 
 0.00563 
 
 0.00299 
 
 SiO 2 , HNO 3 , Fe 2 O 3 , Al 2 Os, organic matter 
 
 0.00163 
 
 0.02357 
 
 0.02634 
 
 0.01716 
 
 0.03192 
 
 SiO 2 , A1 2 O 3 , Fe 2 O 3 
 
 
 O.002OO 
 
 0.00887 
 
 0.00397 
 
 
 H 3 P0 4 , Si0 2 , A1 2 3 , FeCOa, MnCO 3 , NaCl, 
 
 
 
 
 
 
 Na 2 S0 4 
 
 o . 00309 
 
 0.00162 
 
 0.04438 
 
 0.01401 
 
 0.00250 
 
 SiO 2 , Fe 2 O 3 , organic matter 
 
 0.00154 
 
 0.00298 
 
 0.02248 
 
 0.00441 
 
 0.00213 
 
 SiO 2 , Fe 2 O 3 , A1 2 O 3 , organic matter 
 
 0.00384 
 
 0.00756 
 
 0.00243 
 
 0.00843 
 
 0.00793 
 
 Si0 2 , (AlFe)j, 3( P0 4 
 
 0.00330 
 
 0.00730 
 
 0.02870 
 
 0.00540 
 
 0.00230 
 
 Si0 2 
 
 0.00251 
 
 0.00234 
 
 0.02954 
 
 0.00363 
 
 0.00105 
 
 HNOs, Si0 2 , AU03, Fe 2 3 Mn 2 O 3 , NH 4 , or- 
 
 
 
 
 
 
 ganic matter 
 
 0.00178 
 
 0.00072 
 
 0.02552 
 
 0.00175 
 
 O.OOI2I 
 
 H 3 PO4, SiO 2 . A1 2 O 3 , Fe 2 O 3 , organic matter 
 
 0.00139 
 
 0.00239 
 
 0.02255 
 
 0.00194 
 
 0.00076 
 
 SiO 2 ; traces of other substances 
 
 Table Showing Total Salinity of Other Rivers. Continued. 
 
 Permille. 
 
 49. Uruguay, above Fray Bentos 0.066 
 
 50. Amazon, between the Narrows and Santarem o . 059 
 
 51. Xingu, South America o . 045 
 
 52. Tapajis, South America o . 038 
 
 53. Amazon at Obidos o . 037 
 
 In most of the rivers calcium is in excess, probably in the form 
 of the bicarbonate. Jn some cases, however, as in the Jordan River, 
 Utah, the calcium is chiefly in the form of the sulphate. 
 
 From the analyses of the waters of twenty American rivers 
 (United States and Canada), it has been found that the average 
 total amount of solids carried in solution is 0.15044 permille, of 
 which 0.056416 permille is calcium carbonate (Russell-^.i/o 3 ). 
 Forty-eight analyses of the waters of European rivers tabulated by 
 Bischof give the average total solids in solution as 0.2127 permille 
 with an average of 0.1139 permille of CaCO 3 , while forty analyses 
 
164 PRINCIPLES OF STRATIGRAPHY 
 
 gave Roth an average total of 0.2033 permille and of cakium car- 
 bonate 0.009598 permille (Russell-33 : 79). For both American 
 and European rivers the above data give an average of total solids 
 in solution of 0.1888 permille, of which 0.088765 permille, or 47 
 per cent, of the total solids, represents calcium carbonate. 
 
 The annual total transport of mineral matter in solution was 
 compiled for a number of rivers by Russell (31 : 79), and is given 
 in the following rearranged and supplemented 
 
 Table of Total Solids Carried in Solution, in Tons per Year* 
 
 1. Mississippi 112,832,170 
 
 2. Danube 22,521,430 
 
 3. Nile 16,950,001 
 
 4. Rhone 8,290,464 
 
 5. Arkansas 6,828,350 
 
 6. Rhine 5,816,804 
 
 7. Thames , 613,930 
 
 8. Hudson : 438,005 
 
 9. Croton 66,795 
 
 Total for nine rivers i?4>357>949 
 
 Sir John Murray (22: 76) has computed the number of tons of 
 different salts carried in solution in a cubic mile of river water; 
 the average of which for nineteen of the principal rivers of the 
 world is given in the following table (Russell-33 :8o) : f 
 
 Table Showing the Amounts of the Different Salts Carried in Solu- 
 tion in One Cubic Mile of Average River Water. 
 
 British tons in 
 Constituents. one cubic mile.J 
 
 Calcium carbonate (CaCO 3 ) 326,710 
 
 Magnesium carbonate (MgCQa) 1 12,870 
 
 Calcium phosphate (Ca 3 P 2 O8) 2,913 
 
 Calcium sulphate (CaSO 4 ) 34,36i 
 
 Sodium sulphate (Na 2 SO 4 ) 31,805 
 
 Potassium sulphate (K 2 SO 4 ) 20,358 
 
 Sodium nitrate (NaNO 3 ) 26,800 
 
 Sodium chloride (NaCl) 16,657 
 
 Lithium chloride (LiCl) 2,462 
 
 Ammonium chloride (NH 4 C1) 1,030 
 
 Silica (SiO 2 ) 74,577 
 
 Ferric oxide (Fe 2 O 3 ) 13,006 
 
 Alumina (A1 2 O 3 ) 14,315 
 
 Manganese oxide (Mn 2 O 3 ) 5>73 
 
 Organic matter , 79,020 
 
 Total dissolved matter 762,587 
 
 * See other tables cited by Clarke~4 : 80- 
 
 | Acids and bases combined according to the principles indicated by Bunsen. 
 
 j One cubic mile of fresh water weighs about 4,205,650,000 British tons of 
 2,240 pounds each. 
 
COMPOSITION OF SPRING WATER 165 
 
 Murray has further computed that the volume of water flowing 
 into the sea in one. year, for all the land areas of the earth, totals 
 about 6,524 cubic miles, which, with the average composition given 
 above, results in the grand total of 4,975,117,588 British tons of 
 mineral matter carried in solution into the sea annually. Large as 
 the amount is, when compared with the total mineral matter in the 
 sea, it dwindles in proportion. Of calcium carbonate alone 2,131,- 
 455,940 tons are carried into the sea annually, of magnesium car- 
 bonate 736,363,880 tons, or a total of carbonates of 2,867,819,820 
 tons, or, in round numbers, 2,868 million British tons, or 2,823 mil- 
 lion metric tons.* (Krummel figures out only 2,460 million metric 
 tons of carbonates, using Penck's estimate [26:310] of 4,100 mil- 
 lion metric tons of mineral matter carried into the sea annually, or 
 1/6000 of the total amount of the water flowing into the sea. The 
 percentage of carbonates dissolved in river water is taken as 60.) 
 Although the percentage of carbonates in the sea may be as low as 
 0.2, the absolute quantity is 99.4 X io 12 metric tons, or 39,000 times 
 as much as the yearly supply by streams, according to Krummers 
 estimate. On these same estimates it appears that of sulphates there 
 is 9 million times the amount by weight, while of chlorides there is 
 17 million times the amount by weight brought into the sea annually 
 by all the rivers of the world. (Krummel-2o: 228.) 
 
 IV. COMPOSITION OF SPRING WATER. 
 
 Rain water is not absolutely pure H 2 O, but always contains im- 
 purities gathered in its passage through the lower strata of the 
 atmosphere. An analysis of rain water collected near London, Eng- 
 land, gave the following composition : 
 
 Table of Composition of Rain Water near London. 
 
 Permille. 
 
 Organic carbon o . 00099 
 
 Organic nitrogen o . 00022 
 
 Ammonia o . 00050 
 
 Nitrogen as nitrates and nitrites o . 00007 
 
 Chlorine o . 00630 
 
 Other impurities 0.03142 
 
 Total 0.03950 
 
 * One metric ton equals 1,000 kilograms, equals 2,204.6 pounds avoirdupois; 
 I British ton equals 2,240 pounds avoirdupois. 
 
i66 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 This is 39.50 grams in one thousand liters of rain water. At 
 Troy, New York, the mean chlorine content of the rain water for 
 one year was found to be 0.00164 permille, or 1.64 grams per 1,000 
 liters. 
 
 At Lincoln, New Zealand, the impurities of the rain water were 
 found by Gray to average during two years as follows : 
 
 Impurities of Rain Water. 
 
 Permille 
 
 Cl 0.00774 
 
 SO 3 o . 00201 
 
 N in NH 3 0.00012 
 
 N in nitrates o . 00014 
 
 N albuminoid o . 00009 
 
 Other matter 0.01350 
 
 Total dissolved matter o . 02360 
 
 The following solids, in pounds per acre per annum, have been 
 determined as brought by the rain in various localities. (Clarke- 
 4:46-47.) 
 
 Solids in Rain Water. (Pounds per acre per year.) 
 
 
 
 Nitrogen 
 
 
 
 
 
 Ammonia- 
 cal 
 
 Nitric 
 
 Total 
 
 Chlorine 
 
 Sodium 
 chloride 
 
 Rothamsted, England* 
 Barbados 
 
 2.823 
 I ooq 
 
 0.917 
 2.441 
 
 3-740 
 1.452 
 
 14.400 
 116 980 
 
 24 . ooo 
 
 British Guiana 
 
 I . 151 
 
 2.190 
 
 3.541 
 
 108.613 
 
 
 
 
 
 
 
 
 From the soil the rain water takes CO 2 and humus acids derived 
 from both living and decaying vegetation, and these, with the acids 
 derived from the atmosphere, will exercise a solvent power upon 
 the rocks through which the water passes. Several of them are 
 good solvents of silica, and the streams passing through bogs are 
 generally rich in this constituent. Thus the Ottawa drains a region 
 occupied chiefly by crystalline rocks, covered by extensive forests 
 and marshes, and its percentage of silica is 33.7 of the total in- 
 organic solids.f 
 
 *Average of five years. 
 
 t For a full discussion of the Geological action of the Humus Acids see Julien 
 (17). For a correlation between compositions of river water and source of the 
 water see Hanamann (12). 
 
COMPOSITION OF SPRING WATERS 167 
 
 The ordinary spring or vadose water will thus have a certain 
 type of composition, though varying greatly within that type. The 
 leading acid ions in its mineral content are CO 2 and SO 3 , and lime 
 and magnesia are the leading bases, except in granitic countries or 
 in arid regions. Lane thinks that the salinity is not commonly over 
 i permille, that saturation with bicarbonates (0.238 permille of 
 CaCO 3 ) seems to be a very common goal, and that the specific grav- 
 ity of such waters is not greater than i. Analysis A on page 170 
 may be taken as a type of such waters. 
 
 Waters regarded by Lane as showing large proportions of bur- 
 ied sea water were obtained from Sheboygan, Wisconsin. These 
 have a salinity of 589.2536 grains per U. S. gallon (8.782 grams per 
 liter, or 8.782 permille), of which 52.1% is NaCl. Others have 
 been obtained from Bowling Green, Ohio, which had a salinity of 
 3,297.93 grains per U. S. gallon (49.154 grams per liter, or 49.154 
 permille), of which 72.3% is NaCl. 
 
 Magmatic waters obviously have the greatest range of variabil- 
 ity in composition. Still it would not be proper to hold that all wa- 
 ters varying beyond the limits ordinarily set for meteoric waters or 
 for connate waters are to be regarded as of magmatic origin. Such 
 an assumption would disregard the evident ability of meteoric 
 waters to take up mineral matter in their passage through the rocks. 
 Since magmatic waters are essentially thermal, they will be more 
 fully discussed under the section dealing with the temperature of 
 the water. (See page 201.) Analyses of spring waters from the 
 Algerian Sahara gave the following extremes of composition (Rol- 
 land quoted by Walther-43 : 57) : 
 
 Composition of Spring Water from the Sahara. 
 
 Permille 
 
 SiO 2 0.012 to 0.068 
 
 NaCl 0.039104.030 
 
 KC1 o . 005 to o . 307 
 
 CaCO 3 o . 076 to o . 294 
 
 MgCO 3 0.005 to 0.052 
 
 Fe 2 CO 3 o . 004 to o . 013 
 
 CaSO 4 0.008 to 1.851 
 
 MgSO 4 o.ioo to 0.916 
 
 Na 2 SO 4 0.025 to i - 2I 4 
 
 Total amount of solids o. 274 to 8 . 745 
 
 In the table on pp. 170-171 a number of analyses of the waters 
 of springs and wells are given to show their variations and general 
 
i68 PRINCIPLES OF STRATIGRAPHY 
 
 character. For a more extensive tabulation the student is referred 
 to Clarke's Data of Geochemistry. As with the waters of lakes, so 
 here a number of divisions are made, but no hard-and-fast line can 
 be drawn between end members of adjoining groups. The follow- 
 ing springs are given: 
 
 A. Spring near Magnet Cove, Arkansas ordinary (Car- 
 bonate) spring water. 
 
 B. Spring near Mount Mica, Paris, Maine ordinary (sul- 
 phate) spring water. 
 
 C. Artesian well, Cincinnati chloride waters. 
 
 D. Upper Blue Lick Springs, Kentucky chloride waters. 
 
 E. Utah hot springs, 8 miles north of Ogden, Utah chloride 
 waters. 
 
 F. The Kochbrunnen, Wiesbaden chloride waters. 
 
 G.* Well, 2,667 f eet deep at Conneautsville, Pa. chloride wa- 
 ters. 
 
 H.* Boiling spring, Savu-Savu, Fiji chloride waters. 
 
 I.f Congress Spring, Saratoga chloride waters. 
 
 J.f Steamboat Springs, Nevada chloride waters. 
 
 K. Bitter Spring Laa, Austria sulphate waters. 
 
 L. Cruzy, Herault, France sulphate waters. 
 
 M. Pine Creek Valley Spring, near Atlin, British Columbia 
 carbonate waters. 
 
 N. Orange Spring, Yellowstone National Park mixed waters. 
 
 O. The Sprudel, Carlsbad, Bohemia mixed waters. 
 
 P. Chalybeate waters, Mittagong, New South Wales mixed 
 waters. 
 
 Q. Old Faithful Geyser, Upper Geyser Basin siliceous wa- 
 ters. 
 
 R. Excelsior Geyser, Midway Basin siliceous waters. 
 
 S. Great Geyser, Iceland siliceous waters. 
 
 T. Hot Spring, Sulphur Bank, Clear Lake, Cal. borate water. 
 
 U. Viry, Seine-et-Oise, France phosphate water. 
 
 V. Holy Well, Zem Zem, Mecca nitrate water. 
 
 W. Tuscarora Sour Spring, 9 miles south of Brantford, Can- 
 ada acid water. 
 
 X. Solfatara at Pozzuoli, Italy (volcanic) acid water. 
 
 Y. Hot Lake, White Island, Bay of Plenty, New Zealand 
 (a 10% solution of HC1) acid water. 
 
 * With much calcium. f Notable quantities of other acid radicles present. 
 
COMPOSITION OF SPRING WATERS 169 
 
 CLASSIFICATION OF NATURAL WATERS. 
 
 Clarke (4: 757) has summarized the characters of natural wa- 
 ters in the following classification : 
 
 I. Chloride waters. Principal negative ion Cl. 
 
 A. Principal positive ion sodium. 
 
 B. Principal positive ion calcium. 
 
 C. Waters rich in magnesium. 
 
 II. Sulphate waters. Principal negative ion SO 4 . 
 
 A. Principal positive ion sodium. 
 
 B. Principal positive ion calcium. 
 
 C. Principal positive ion magnesium. 
 
 D. Waters rich in iron or aluminum. 
 
 E. Waters containing heavy metals such as zinc. 
 
 III. Sulphato-chloride waters, with SO 4 and Cl both abundant. 
 
 IV. Carbonate waters. Principal negative ion CO 3 or HCO 3 . 
 
 A. Principal positive ion sodium. 
 
 B. Principal positive ion calcium. 
 
 C. Chalybeate waters. 
 
 V. Sulphato-carbonate waters SO 4 and CO 3 both abundant. 
 
 VI. Chloro-carbonate waters Cl and CO 3 both abundant. 
 
 VII. Triple waters, containing chlorides, sulphates and car- 
 bonates in equally notable amounts. 
 
 VIII. Siliceous waters. Rich in SiO 2 . 
 
 IX. Borate waters. Principal negative radicle B 4 O 7 . 
 
 X. Nitrate waters. Principal negative ion NO 3 . 
 
 XI. Phosphate waters. Principal negative ion PO 4 . 
 
 XII. Acid waters. Contain free acids. 
 
 A. Acid chiefly sulphuric. 
 
 B. Acid chiefly hydrochloric. 
 
 While this emphasizes the essential types, it must be borne in 
 mind that many waters are intermediate in character between these 
 types, and their classification with one or the other may be a matter 
 of opinion. 
 
 GASES AND ORGANIC MATTER IN NATURAL WATERS. 
 
 Besides the dissolved mineral matter found in the natural wa- 
 ters of the world, there exist various dissolved gases and a varying 
 proportion of organic matter. The relative quantity of different 
 gases varies according to the temperature, as shown in the follow- 
 ing table prepared by R. W. Bunsen and quoted by Clarke (4: 45) : 
 
170 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Table of Analayses of 
 
 
 A 
 
 B 
 
 C 
 
 D 
 
 E 
 
 F 
 
 G 
 
 H 
 
 I 
 
 J 
 
 K 
 
 L 
 
 Cl 
 Br, I, F... 
 S0 4 
 COs 
 POi 
 
 1.35 
 
 - 3'40 
 53.59 
 
 trace 
 
 60^97 
 6.22 
 
 55.83 
 0.07 
 3.12 
 2.63 
 
 53.08 
 0.53 
 6.03 
 2.34 
 
 58.79 
 trace 
 0.94 
 0.61 
 
 56.58 
 0.04 
 0.78 
 3.13 
 trace 
 
 62.31 
 0.54 
 0.03 
 0.27 
 
 57.91 
 
 '3^38 
 trace 
 trace 
 
 42.00 
 1.15 
 
 0.08 
 18.59 
 trace 
 
 35.00 
 
 '4^58 
 5.08 
 03 
 
 0.57 
 
 69 ^ 87 
 4.75 
 
 3.73 
 
 74J6 
 0.03 
 
 NO S 
 B 4 07 
 
 
 
 
 
 
 
 
 
 trace 
 
 8 88 
 
 
 
 H 2 S0 4 free. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 HNOafree. 
 HClfree... 
 As0 4 
 BOs .. 
 
 
 
 
 
 
 trace 
 01 
 
 
 
 
 
 
 
 Na 
 K.. 
 
 1.08 
 0.63 
 
 4.32 
 0.21 
 
 33.09 
 0.27 
 
 31.47 
 0.96 
 
 30.38 
 3.76 
 
 32.60 
 1.16 
 
 18.35 
 1.55 
 
 16.65 
 0.93 
 
 27.62 
 0.78 
 
 30.35 
 3.79 
 
 2.99 
 0.35 
 
 4.50 
 0.03 
 
 Li 
 NH 4 
 
 
 
 
 
 trace 
 
 0.04 
 07 
 
 0.04 
 23 
 
 
 0.08 
 
 0.27 
 
 6 22 
 
 
 Ca 
 
 Sr 
 
 30.95 
 
 22.37 
 
 3.72 
 
 3.56 
 
 4.90 
 
 4.05 
 12 
 
 13.86 
 
 18.34 
 
 6.03 
 trace 
 
 0.25 
 
 7.63 
 
 0.02 
 
 Ba... 
 
 
 
 
 
 
 0.01 
 
 
 
 0.09 
 
 
 
 
 Mg 
 Mn 
 
 3.45 
 
 2.62 
 
 1.13 
 
 1.57 
 
 0.40 
 
 0.61 
 
 1 A. 
 
 2.53 
 
 0.04 
 
 3.41 
 
 0.01 
 
 13.18 
 
 17.45 
 
 Fe" 
 Fe'" 
 
 
 
 
 
 
 > 0.04 
 
 
 
 
 
 
 
 Fe 
 FesOa 
 
 
 '6'49 
 
 6!66 
 
 
 
 
 
 0.25 
 
 trace 
 
 '6'03 
 
 trace 
 
 
 \ 0.02 
 
 'oioi 
 
 AhO, 
 Al 
 
 
 
 
 
 0.02 
 
 
 6 02 
 
 0.54 
 43 
 
 trace 
 
 0.01 
 
 
 
 SiO* 
 Cd.Zn Cu 
 
 5.55 
 
 2.80 
 
 0.08 
 
 0.16 
 
 0.20 
 
 0.76 
 
 0.02 
 
 1.78 
 
 
 11.41 
 
 0.42 
 
 0.07 
 
 S.As.Sb.Hg 
 
 
 
 
 
 
 
 
 
 
 0.34 
 
 
 
 
 Total solid. 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 Permille 
 of total . 
 
 0.224 
 
 0.606 
 
 10.589 
 
 11.068 
 
 23.309 
 
 8.241 
 
 309.175 
 
 7.813 
 
 12.022 
 
 2.850 
 
 62.371 
 
 101.000 
 
 The HNOs is found in some waters not included in this table. It is listed here on account of its interest as 
 
 Composition (in Percentages of Total Gases) of Dissolved Air in 
 Rain Water at Different Temperatures. 
 
 
 
 
 5 
 
 10 
 
 15 
 
 20 
 
 Nitrogen (N 2 ) 
 
 63.20 
 
 63 35 
 
 63 4Q 
 
 63 62 
 
 63.60 
 
 Oxygen (O 2 ) 
 
 33 88 
 
 T.T. 07 
 
 -IA O5 
 
 T.A 12 
 
 ^4. 17 
 
 Carbon dioxide (CO 2 ) .... 
 
 2.92 
 
 2.68 
 
 2.46 
 
 2.26 
 
 2.14 
 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100. OO 
 
 100.00 
 
 The absolute amounts of the different gases vary more markedly 
 with different temperatures. Thus a liter of pure surface water, 
 under a normal barometric pressure of 760 mm., contains the fol- 
 lowing absolute and percental amounts of dissolved gases in c. c. 
 (Krummel-2o: ^pj; Forel-8:p5 gives somewhat different val- 
 
 ues.)* 
 
 * See also Cyrus F. Tolman (39). 
 
COMPOSITION OF SPRING WATERS 
 Spring and Well Waters 
 
 171 
 
 M 
 
 N 
 
 
 
 P 
 
 Q 
 
 R 
 
 s 
 
 T 
 
 u 
 
 V 
 
 W 
 
 X 
 
 Y 
 
 0.03 
 
 'i!ai 
 
 67.56 
 trace 
 
 10.07 
 trace 
 32.80 
 20.76 
 
 11.52 
 0.03 
 31.19 
 19.15 
 0.01 
 
 27.34 
 36:58 
 
 31.64 
 0.25 
 1.30 
 8.78 
 
 20.91 
 trace 
 1.31 
 25.01 
 trace 
 
 13 52 
 
 '9 6i 
 
 10 16 
 
 16.49 
 0.03 
 trace 
 21.96 
 
 5.11 
 
 Y74 
 19.46 
 22.41 
 6.33 
 
 16.44 
 
 iiioi 
 
 12.78 
 24^ 62 
 
 22.il 
 trace 
 
 0.34 
 55:68 
 
 11.69 
 
 io'.ei 
 
 L91 
 
 trace 
 
 
 
 
 1.19 
 
 1.34 
 
 
 25.61 
 
 
 
 69:62 
 
 16.62 
 
 trace 
 
 
 
 
 
 
 
 
 
 
 
 
 
 65 42 
 
 
 
 
 
 24 
 
 29 
 
 
 
 
 
 
 
 
 'ijs 
 
 0.26 
 '2:54 
 
 Yes 
 
 3.78 
 0.10 
 
 17:50 
 
 32:49 
 1.35 
 
 '2:23 
 01 
 
 7^3 
 8.96 
 
 "4:25 
 
 26: 42 
 1.93 
 0.40 
 trace 
 0.11 
 
 3L34 
 2.43 
 0.15 
 trace 
 0.17 
 
 i^ri 
 
 1.88 
 6:28 
 
 24:99 
 trace 
 
 '7'88 
 trace 
 
 '3'.32 
 trace 
 trace 
 
 36:38 
 
 12^6 
 6.67 
 
 '8^70 
 
 '6:26 
 0.44 
 
 '3:76 
 
 trace 
 0.57 
 
 0:58 
 
 2.91 
 
 '6:75 
 0.59 
 
 '2:36 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 25.03 
 
 4.09 
 
 0.65 
 0.01 
 
 5.89 
 
 0.04 
 trace 
 
 0.17 
 trace 
 
 0.08 
 
 trace 
 
 1.21 
 
 2.70 
 
 0.50 
 2 17 
 
 0.55 
 trace 
 3 47 
 
 0.34 
 trace 
 
 
 
 
 
 
 
 
 
 
 
 
 
 5.98 
 
 
 
 02 
 
 15 85 
 
 
 13 
 
 
 
 
 
 
 
 
 21 
 
 
 
 
 
 
 
 
 
 
 
 
 
 0.14 
 
 'L79 
 
 0.13 
 '3J2 
 
 trace 
 1.34 
 
 
 0.12 
 27! 58 
 
 0.17 
 i(L58 
 
 45:64 
 
 0.40 
 
 Y.ei 
 
 "I'M 
 
 L39 
 
 'i:20 
 
 Yie 
 12:72 
 
 '0^5 
 
 6:03 
 
 
 
 
 
 
 
 So 32 
 
 
 
 
 
 trace 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 100.00 
 
 7.829 
 
 1.612 
 
 5.431 
 
 0.225 
 
 1.388 
 
 1.336 
 
 1.131 
 
 5.343 
 
 0.490 
 
 3.455 
 
 6.161 
 
 2.477 
 
 158.051 
 
 another free acid in natural waters. 
 
 Gases in a Liter of Pure Water. 
 
 Absolute amounts 
 in c. c. per liter 
 
 Tem- 
 pera- 
 ture 
 
 Nitro- 
 gen 
 
 Oxy- 
 gen 
 
 Argon 
 
 Carbon 
 dioxide 
 (C0 2 ) 
 
 Total 
 
 
 
 18.32 
 
 10.26 
 
 0-54 
 
 0.51 
 
 29-63 
 
 30 
 
 10.46 
 
 5-47 
 
 0.31 
 
 0.20 
 
 16.44 
 
 Percentage of total 
 absorbed gases t 
 
 
 
 61.8 
 
 34-6 
 
 1.8 
 
 i-7 
 
 100.00 
 
 30 
 
 63-6 
 
 33-3 
 
 19 
 
 I .2 
 
 100.00 
 
 * Compare with table of absorbed gases in rain water, p. 1 70. 
 
172 PRINCIPLES OF STRATIGRAPHY 
 
 The amount of dissolved gases depends directly on the pressure 
 on the water. Thus a lake lying in lowlands contains more dis- 
 solved gases than a mountain lake, where the pressure is less. With 
 rising barometer and sinking temperature the upper strata of water 
 of a lake will absorb more gases, while with falling pressure and 
 rising temperature gases will be given off. Change in temperature 
 is, however, more important than change in pressure. With a rise 
 from o to 25 C. the power of water for absorption of gases de- 
 creases from 30 to 40%, while the extremes of pressure bring about 
 a change in absorption of only about 6%. The surface waters of 
 lakes are generally saturated with atmospheric gases, though the 
 presence of living animals and plants and the decay of organic mat- 
 ter tend to disturb the normal balance. In the deeper strata of the 
 waters of lakes the power to absorb gases is much greater, owing 
 to the increased pressure, but as a matter of fact the actual amounts 
 correspond more nearly to those obtained in surface waters during 
 periods of low temperature. This is due to the fact that the deeper 
 waters depend for their atmospheric gases upon the amount fur- 
 nished them by the upper layers, when supersaturated, this amount 
 being greatest in the cold period ; or upon the amount carried down 
 to the deeper strata by surface waters acting as convection cur- 
 rents, when the temperature of the surface has sunk to that of 
 the deeper strata. In the deeper strata of lake waters a deficit in 
 oxygen and an increase in CO 2 may further develop through the 
 physiological activities of bottom organisms or the decay of organic 
 matter. This change is less marked in surface waters, owing to the 
 balancing effect of chlorophyll-bearing plants, which are absent in 
 the deeper waters. (See Chapter XL) 
 
 From the tables above given it is clear that the proportion of 
 oxygen to nitrogen is much higher in the absorbed air of water 
 than in the normal atmosphere. The latter has 21 parts of oxygen 
 to 78 parts of nitrogen, the proportion being in round numbers as 
 1:4. In the absorbed air of pure fresh water the proportion of O 
 to N at o is as 34.6:61.8, and at 30 as 33.3:63.6, or, in round 
 numbers, in either case as 1:2. In applying this fact, however, to 
 the available oxygen for aqueous plant and animal life, it must be 
 borne in mind that, though the proportion of oxygen to nitrogen 
 is greater in water than in air, the absolute amount of oxygen per 
 liter of the medium in which the organism breathes is vastly greater 
 in air than in water, being 210 c. c. for each liter of air, and only 
 10 c. c. for each liter of water. 
 
 ORGANIC MATTER. This is present in solution in many waters, 
 especially those of rivers and lakes. Calculated in percentages of 
 
ORGANIC MATTER IN STREAMS 
 
 173 
 
 total solids, we find that it rises in sonic of the tropical streams to 
 more than fifty per cent. The variation is shown in the following 
 table (Clarke-4:^) : 
 
 Table of Organic Matter in Various Streams in Percentages of the 
 
 Total Solids. 
 
 Danube 3.25 
 
 James 4. 14 
 
 Maumee 4 . 55 
 
 Nile 10.36 
 
 Hudson 1 1 . 42 
 
 Rhine 1 1 . 93 
 
 Cumberland 12 .08 
 
 Thames 12.10 
 
 Genesee.. . 12.80 
 
 Amazon 15-03 
 
 Mohawk 15 .34 
 
 Delaware 16 . oo 
 
 Lough Neagh, Ireland. ... 16.40 
 
 Xingu 20 ~63 
 
 Tapajos 24 . 16 
 
 Plata 49-59 
 
 Negro 53.89 
 
 Uruguay 59 . 90 
 
 In the tropical streams at the end of the list the high percentage 
 is due to the contributions formed by tropical swamps through which 
 they flow. Lough Neagh, Ireland, derives its organic matter in part 
 from peat bogs. 
 
 Among the vegetable acids present are Humic acid (C 20 H 10 O G ), 
 Geic acid (C 20 H 12 O 7 ),* and Ulmic acid (C 20 H 14 O 6 ),* derived 
 from peat or soil richly charged with decaying vegetation. They 
 form various compounds or salts, such as ammonium humate, so- 
 dium and potassium humates, calcium humate, magnesium humate, 
 ferric humate, etc. The alkaline salts are easily soluble in water, but 
 those of the alkaline earths and metallic oxides are not soluble or 
 only with great difficulty, but these are soluble in aqueous alkalies, 
 especially ammonia and its carbonate. Humic acid itself dissolves in 
 8 >333 P arts of water at 6 C. and in 625 parts at 100 C. It is in- 
 soluble in water free from nitrogen or air. Among the products of 
 higher oxidation of these acids are the more soluble crenic acid 
 (C 24 H 30 O 19 Wurtz), or Quellsaure, and apocrenic acid (C 24 H 14 O 13 
 Wurtz), or Quellsalzsaure. The former occurs in the waters of 
 probably all springs, rivers, lakes, etc., and in rain water, rotten 
 wood, peat, and tilled soil, and in bog ore, ochre, etc. It is easily 
 soluble in water; its alkali salts (ammonium crenate, etc.) are, how- 
 ever, soluble to a less degree. Some of the salts of the alkaline 
 earths (calcium crenate) require much water, while others (mag- 
 nesium crenate) are easily soluble. The salts of metals are insoluble 
 (aluminium crenate, ferric crenate) or slightly soluble (ferrous 
 crenate, manganese crenate). Apocrenic acid also occurs in the 
 
 * Formulas according to Mulder, others give different formulas. (See Julien- 
 
174 PRINCIPLES OF STRATIGRAPHY 
 
 waters of springs and rivers, and in tilled soil, peat, decaying wood, 
 and bog ores ; it easily dissolves in water. The salts of the alkalies 
 and alkaline earths are soluble, the latter to a less degree. Some 
 of the apocrenates of the metals are soluble, others insoluble. 
 
 f he solvent action of these acids on siliceous rocks is of con- 
 siderable importance. Humic acid is said to decompose silicates. 
 The various humous acids absorb nitrogen from the air and form 
 azohumic acids, which, in the presence of alkaline carbonates, are 
 capable of dissolving silica, especially when it is in the amorphous 
 state, though even quartz is corroded. From this it follows that a 
 stream well supplied with these organic acids may acquire a high 
 percentage of silica in solution, unless the solvent power is neu- 
 tralized in some way. Since tropical streams carry the highest per 
 cent, of organic matter they are likely to be rich in dissolved silica. 
 Thus the Uruguay River, with 59.9% of the total solids as organic 
 matter contains 46.22% of the remainder, or 18.53% f the whole, 
 of SiO 2 , though the total salinity (inorganic) is only 0.04 permille. 
 In the St. Lawrence, along the borders of which "the granite of the 
 main and islands is almost everywhere covered with peat, full of 
 stagnant ponds of dark bog water" (Hunt), SiO 2 forms 23% of its 
 total dissolved inorganic matter, while the Ottawa, which "drains 
 a region occupied chiefly by crystalline rocks, covered by extensive 
 forests and marshes" (Hunt-i6: 126] Julien-i 7:555), has 33.7% 
 of its total dissolved inorganic matter as SiO 2 . 
 
 CHEMICAL WORK OF THE NATURAL WATERS. 
 
 The chemical work of the natural waters is chiefly that of the 
 ground water, and is primarily confined to that zone or belt within 
 the earth's crust which is permanently occupied by this water, i. e., 
 that zone extending from the level of the ground water or the water 
 table to the greatest depth to which such water extends. This belt, 
 for which Van Hise estimates the great depth of 10,000 or 12,000 
 meters, but which others believe to be much less (see ante), con- 
 stitutes the belt of cementation, in contradistinction to the belt of 
 weathering, which forms the upper zone of the lithosphere above 
 the level of the ground water. In this latter belt the activities 
 are largely those of the atmosphere, but the ground water in passing 
 through it also performs a considerable amount of both chemical 
 and mechanical work, of which solution is the most pronounced. 
 
 The chief chemical processes going on in the belt of cementa- 
 tion are solution and redeposition, hydration, carbonation and oxida- 
 
CHEMICAL WORK OF WATER 175 
 
 tion. Reduction or deoxidation may also go on at times, and so 
 may decarbonation and silicatiqn. Solution is less characteristic 
 than in the belt of weathering, while deposition becomes of the 
 greatest significance. Hydration and carbonation are important re- 
 actions, but oxidation is confined to the upper layers. 
 
 SOLUTION. This is most active in the belt of weathering. Lime- 
 stone, gypsum, and salt beds are dissolved by the underground 
 water, with the production of caverns sometimes of very limited 
 duration. The rate of solution may be estimated from the amount 
 of dissolved matter discharged by the springs of a given region, and 
 some data are available for this determination. Thus the warm 
 springs of Bath, England (mean temperature of 120 F.), discharge 
 annually a quantity of dissolved sulphates of calcium and sodium, 
 and chlorides of sodium and magnesium, sufficient to make a square 
 column of mineral matter 9 feet in diameter and 140 feet high 
 (Ramsay, quoted by Geikie-io : 477} . The St. Lawrence spring at 
 Loueche, Switzerland, discharges every year 1,620 cubic meters 
 (2,127 cubic yards) of dissolved sulphate of lime, which is equiv- 
 alent to lowering a bed of gypsum one square kilometer (0.3861 
 square miles) in extent, more than 16 decimeters (upward of 5 
 feet) in a century (Reclus; Geikie-io: 477). It is estimated 
 that the Solnhofen limestone is reduced I meter in thickness in 
 72,000 years (Pfaff), and that of the Nittany Valley I meter in 30,- 
 ooo years (Ewing-6: 51). T. Mellard Reade has calculated that 
 throughout the entire globe there is removed annually in solution 
 96 tons (about 86 metric tons or tonneaux) of material per square 
 mile, divided as follows: Calcium carbonate, 50 tons (45 ton- 
 neaux) ; calcium sulphate, 20 tons (18 tonneaux) ; sodium chloride, 
 8 tons (7.2 tonneaux) ; silica, 7 tons (6.3 tonneaux) ; alkaline car- 
 bonates, and sulphates, 6 tons (5.4 tonneaux) ; magnesium car- 
 bonate, 4 tons (3.6 tonneaux) ; oxide of iron, i ton (0.9 tonneaux) 
 (quoted by Van Hise-4i : 486). 
 
 The rate of solution is strongly influenced by the temperature of 
 the solvent. "At temperatures above 100 C, and especially above 
 185 C., the activity of water may increase to an amazing degree." 
 (Van Hise-4i : 79.) It thus follows that solvent action of water is 
 greater at the equator than in the arctic regions, where it is prac- 
 tically at a standstill when the temperature is below o C. Solution 
 at any temperature goes on until saturation is reached, which is 
 much sooner at high than at low temperatures. 
 
 Through continued solution extensive underground channels and 
 grottos are produced within the upper zone of the earth's crust in 
 limestone regions. The presence of these is marked on the surface 
 
i ;6 PRINCIPLES OF STRATIGRAPHY 
 
 by sink-holes, and sometimes by depressions filled intermittently 
 with water. That all large caverns are the result of solution of 
 solid limestone masses has been seriously questioned. Walther 
 (42:560) has called attention to the fact that large dome-like cham- 
 bers 'are commonly found in reef-like masses of limestone and that 
 these are covered with stalactic deposits, showing that deposition and 
 not solution has been active here for a long period of time. He sug- 
 gests that many of these may be original hollows in the reef masses, 
 such as are known to occur in structures of this type. 
 
 No minerals are wholly insoluble in the ground water solutions, 
 even quartz, the most resistant, being at times attacked by moisture- 
 carrying solvents. (Hayes-i4.) 
 
 FIG. 25. Karren or lapias (rascles) topography of the Sentis formed by solu- 
 tion by surface streams on a limestone plateau. (After Heim.) 
 
 . 
 
 While solution is most characteristic of the belt of weathering, it 
 is, nevertheless, not confined to it. Active solution goes on in the 
 belt of permanent ground water, but it is here balanced by equally 
 active deposition. Streams and rain water form a rough solution 
 topography on limestone plateaus. These are illustrated by the 
 Karren or lapiaz of the Sentis. (Fig. 25.) 
 
 CEMENTATION. This is of equal importance with solution in the 
 belt of cementation, forming one of the characteristic processes of 
 this belt. It is practically unknown in the belt of weathering. The 
 material deposited is largely derived from the belt of weathering, 
 and the result of such deposition is the partial closing of the pore 
 spaces in the rock below the level of ground water. The expan- 
 sion of the minerals on hydration further tends to close up these 
 pores. The ultimate result of these processes will be the induration 
 
 
CHEMICAL WORK OF WATER 177 
 
 or lithification of the rock masses. (See the section on diagenesis 
 of rock masses, Chapter XIX.) 
 
 Not only are the pores in the rock masses filled, but fissures are 
 closed up by the formation of mineral veins. Large cavities, either 
 originally due to some disturbance, or solution-caves, brought into 
 the belt of cementation by a rise of the ground water level, will be 
 slowly filled by crystallized mineral matter. In the lead and zinc 
 district of Missouri such caverns were slowly filling with crystals of 
 calcite before the last change in ground-water level. These crystals 
 have the form of huge scalenohedrons, some of them half a meter or 
 more in length, and they project from the walls in the manner of 
 crystals from the walls of a geode. The ordinary deposits of cav- 
 erns, stalactites and stalagmites, characteristic of the zone of weath- 
 ering, are wholly absent from these caverns, which were but recently 
 exposed, by the lowering, through pumping, of the ground-water 
 level, from a few meters to a depth of 45 to 60 meters (Van Hise- 
 
 The temperature of the water within the belt of cementation may 
 be greatly raised by the presence of masses of hot igneous rock, 
 the time of cooling for which is much greater than that required 
 at the surface. The juvenile waters given off by such lava sheets 
 are likewise in a highly heated state, and so accomplish much solu- 
 tion. 
 
 HYDRATION. This is the chief reaction in the belt of cementa- 
 tion, and is second in importance only to deposition or cementation. 
 Since water is everywhere present, the minerals are constantly ex- 
 posed to it, and hydration as well as solution must result. It is in 
 this belt that the great group of hydrous silicates and oxides, such 
 as the hydromicas, chlorites, zeolites, serpentine, epidote, limonite, 
 and gibbsite form most abundantly. Kaolin and talc also form here, 
 though they are more characteristic of the belt of weathering. Gyp- 
 sum is altered to anhydrite, in the belt of weathering, whereas hy- 
 dration may change anhydrite to gypsum. The change in the proc- 
 ess of hydration involves an increase in volume of from 30 to 50 
 per cent. 
 
 OXIDATION. Water entering the soil commonly carries oxygen 
 in solution, the amount varying with the porosity of the soil, lack of 
 vegetation, atmospheric pressure, etc. Oxidation goes on through- 
 out the belt of weathering, but affects only the upper layers of the 
 permanently saturated belt, for the supply of oxygen is quickly ex- 
 hausted, and its replenishing is a slow process. Normally the depth 
 below ground-water level to which oxidation is restricted is not more 
 than a few meters, but in exceptional cases this may go much far- 
 
178 PRINCIPLES OF STRATIGRAPHY 
 
 ther. Thus in the Lake Superior mining region it has gone to a 
 depth of 100 meters on an extended scale, while in a few exceptional 
 cases the depth affected has been 500 to 700 meters. In the San 
 Juan district of Colorado it is marked at a depth of 600 meters, and 
 occasionally is noted at 1,000 meters. In the Missouri-Kansas lead 
 and 'zinc district, on the other hand, oxidation scarcely extends be- 
 neath the level of ground water. 
 
 In the belt of weathering, and to some extent in that of cementa- 
 tion, hematite and limonite are the common products of oxidation of 
 iron compounds. Throughout the remainder of the belt where oxi- 
 dation occurs, magnetite is the common product of oxidation of iron, 
 since this requires a smaller amount of oxygen in its production. 
 Oxidation of the sulphur of pyrite and marcasite produces a ferrous 
 sulphate of ferric oxide, and sulphuric acid, in the belts where oxy- 
 gen is abundant. In the major part of the belt of cementation, 
 where oxygen is not abundant, magnetite and sulphurous acid are 
 more likely to be formed. 
 
 The oxidation of organic matter produces carbon dioxide and 
 water, which join the circulating ground- water, producing carbon- 
 ates in the belt of cementation. When the oxygen is all exhausted, 
 organic and other compounds may be taken into solution, and so 
 give the waters a reducing quality. Waters which have made long 
 underground journeys are especially likely to be in this state. Oxi- 
 dation of carbonates, and the liberation of CO 2 , may cause a consid- 
 erable decrease in volume, amounting in some instances to 50 per 
 cent. This may counterbalance the increase from oxidation of inor- 
 ganic compounds, which, in some cases, is as much as 64 per cent. 
 (Van Hise-4i:<5oS.) 
 
 CARBONATION. Carbon dioxide is produced in abundance in 
 regions of luxuriant vegetation, through the oxidation of the carbon, 
 and hence the waters entering the soil here will be rich in CO 2 , but 
 poor in oxygen. Conversely, in regions of little vegetation carbon 
 dioxide will be lacking, but oxygen may be carried in considerable 
 quantity by the water sinking into the ground. If this water en- 
 counters buried carbon in the form of coal beds or of other types, 
 the oxygen will be used up and carbon dioxide produced. The same 
 result is caused by the decomposition of carbonates in the zone of 
 cementation. Carbon dioxide is also produced in enormous quanti- 
 ties in the zone beneath the ground water (the zone of anamorphism, 
 see Chapter XIX) by silication or the union of silicic acid with the 
 bases of the carbonate rocks, and the simultaneous liberation of the 
 CO 2 (Van Hise-4i). 
 
 The process of carbonation, or the union of CO 2 with bases, 
 
DENSITY OF THE HYDROSPHERE 179 
 
 within the belt of cementation is a slow one, and much of the CO 2 
 therefore remains unused and issues again on the surface. The 
 mineral springs of the Auvergne district of France alone furnish an 
 amount of CO 2 , estimated by Lecoq at 7,000,000,000 cubic meters 
 per year, and these represent only a small fraction of the carbonated 
 waters of the world. Carbonation, or the production of carbonates, 
 is, on the whole, one of the most important chemical reactions within 
 the zone permanently occupied by the ground water. 
 
 DENSITY AND SPECIFIC GRAVITY OF 
 THE HYDROSPHERE. 
 
 Pure water (distilled) has its greatest density at a temperature 
 of 4 C., and this is taken as the unit of measurement, or i. (Its 
 salinity is o, and this may be expressed by S', while that of any 
 other water is expressed by S.) The addition of dissolved substances 
 increases the density of the water, which in the case of normal sea 
 water of 35 permille salinity (35 gr. of salts in 1000 gr. of sea water) 
 at o C. becomes 1.02812. This is expressed by the following 
 
 S o 1.02812 
 formula: ^7 3 = - = 1.02812, where S o represents the 
 
 o 4- i 
 
 density of the water in question at o C. and S' 4 that of pure water 
 at 4 C. For convenience sake we may transform the above formula 
 
 (Q O v 
 
 -~7 i J , and express the result by the symbol <T O . 
 
 Thus for normal sea water of 35 permille salinity <T O = 28.12, while, 
 if the salt were NaCl only, o- would be 26.67. If wholly MgSO 4 , <T O 
 
 (S t \ 
 oT~8 i ) 
 
 where t = the temperature at which the density of the water in 
 question is taken. For sea water where o- = 28 *, <r 4 = 27.68, 0-15 = 
 25.87, 0-15.5 = 25.76 (approx.), 0-26 = 23.24. 15 is the temperature 
 for which the hydrometers used in foreign laboratories are usually 
 graduated, while those of English and American use are graduated 
 for 60 F. (15.56 C.). Many of the newer instruments are arranged 
 for the more usual temperature of laboratories, which is 25 C. or 
 77 F. For the same temperatures, distilled water has the following 
 densities: o C. (32 F.) 0.99987, 4 C. (39.20 F.) i.ooooo, 15 C. 
 (59.00 F.) 0.99913, 25 C. (77 F.) 0.99707. (See the table given 
 in Krummel-2o, 232-233.) When the salinity is known <r may be 
 
 *28 instead of 28.12 is used, since the tables of Knudsen given by Krumme 1 
 
i8o PRINCIPLES OF STRATIGRAPHY 
 
 calculated from the following formula devised by Martin Knudsen 
 (Krummel-2o, 237), where S represents the salinity in permille. 
 
 o- = 0.093 + 0.8149 S 0.000482 S 2 -f- 0.0000068 S 3 
 According to this formula the density of the waters of the Kara- 
 bugas Gulf, which has a salinity of 285 permille, should be 1.353329 
 at o C. or O-Q = 353.329, though since the salts are not those of 
 normal sea water this figure is not wholly correct. While the 
 maximum density of distilled water (i) is at + 4 C. (+ 3.947 C.), 
 i. e., a density when v e = 0.00, that of sea water of different con- 
 centration varies greatly. 
 
 The temperature at which any given water is at its greatest 
 density may be designated 6. Substituting this in the general 
 
 formula we have = 1000 (- ). When the salinity is .35 
 
 \ S 40 / 
 
 permille, equals 3.524 C., and = 28.22 as compared with 
 CT O = 28.12. 
 
 VARIATION IN OSMOTIC PRESSURE IN SEA WATER. 
 
 By osmotic pressure is meant that pressure which causes diffusion 
 between the solution of a substance and its solute, or between solu- 
 tions differing in concentration. It varies directly with the concen- 
 tration of the solution, and increases with the temperature. Thus 
 for Baltic water with a salinity of 7.5 /oo, at a temperature of 
 1 8 C. the osmotic pressure is 4.9 atmospheres; in water of the Red 
 Sea, with 40 /oo salinity and a temperature of 30 C., it is 26.7 
 atmospheres. Normal sea water with a salinity of 35 /oo has an 
 osmotic pressure of 23.12 atmospheres at o C. For water of i /oo 
 salinity at o C. the osmotic pressure is 0.66 atmosphere (Krummel= 
 20, table, p. 241). In general for each increase of one permille of 
 salinity there is an increase of 2/3 atmosphere in osmotic pressure, 
 equivalent to the pressure of a mercury column 500 mm. long. 
 
 Osmosis may be considered either as Exosmosis, or that tendency 
 of the fluid within a submerged body to pass into the surrounding 
 fluid, and Endosmosis, the tendency for the outer fluid to pass into 
 the space occupied by the inner; or that action of the fluid which 
 passes with greater rapidity into the other. The effect on organisms 
 of the different osmotic pressures is very marked. Thus a frog 
 placed into sea water loses, by exosmosis, which commences at once, 
 a considerable quantity of water, and in a short time its weight is 
 diminished by one-fifth. On the other hand, a salt-water fish placed 
 suddenly into fresh water suffers through rapid increase by endos- 
 mosis of the water in its body, which results in swelling and death. 
 
TEMPERATURE OF WATER 181 
 
 (Regnard-28.'4j7.) A direct passage of organisms from the fresh 
 waters to the sea or the reverse is thus attended with great dangers 
 to the organisms, and can be safely accomplished only through the 
 intracontinental waters of intermediate salinity. 
 
 TEMPERATURE OF THE HYDROSPHERE. 
 FREEZING POINT OF WATER. 
 
 The freezing point of pure water is o C. or 32 F. With addition 
 of salts the freezing point is lowered as shown in the following 
 table, condensed from Krummel (20:241). 
 
 Salinity I permille, freezing point o . 055 C. 
 
 Salinity 5 permille, freezing point o . 267 C. 
 
 Salinity 10 permille, freezing point . o. 534 C. 
 
 Salinity 15 permille, freezing point o. 802 C. " 
 
 Salinity 20 permille, freezing point 1 . 074 C. 
 
 Salinity 25 permille, freezing point 1 . 349 C. 
 
 Salinity 30 permille, freezing point i .627 C. 
 
 Salinity 35 permille, freezing point _ 1 .910 C. 
 
 Salinity 40 permille, freezing point 2 . 196 C. 
 
 Ordinary sea water of 35 permille salinity will therefore freeze at 
 a temperature of 1.9 C. or +28.58 F. when its density (o- t ) is 
 28.21. According to the formula given by Krummel, the surface 
 water of the Black Sea, with a salinity of 18.5 permille, will freeze 
 at a temperature of 0.99 C. (+30.2 F.), that of Behring Sea 
 (30 permille) at 1.6 C. (+29.12 F.), while the water of the Baltic 
 (7.8 permille) would freeze at about 0.4 C. (+31.28 F.) If o- 
 is known (see formula p. 180) then the freezing point r of water may 
 be calculated according to the following empirical formula devised 
 by H. J. Hansen of Copenhagen (Krummel-2o:^o). 
 
 r = 0.0086 0.064633 <r 0.0001055 o-Q 2 .* 
 
 According to this formula the waters of the Karabugas Gulf where 
 "o = 353.329 would freeze at a temperature of 36.016 C or 
 32.836 F. if it were of the composition of normal sea water. 
 
 HEAT CAPACITY OF WATER. 
 
 The heat required to raise a gram of pure water from 14.5 to 
 15.5 C. is the unit of measurement of the heat capacity or specific 
 heat of water, and is called the small calorie or gram-calorie. Saline 
 waters have a smaller heat capacity than pure water, i. e., it takes 
 less heat to raise a gram one degree. The following table is given 
 
 * The formula as printed in Krummel is incorrect, the second term of the 
 right-hand member is there given as 0.0064633^. 
 
1 82 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 by Krummel for the heat capacity of waters of different salinity 
 at 17.5 C. (20:272): 
 
 Salinity in permille 
 
 o 
 
 5 
 
 10 
 
 15 
 
 20 
 
 25 
 
 30 
 
 35 
 
 40 
 
 Heat capacity 
 
 i .000 
 
 0.982 
 
 0.968 
 
 0.958 
 
 0-95 1 
 
 0-945 
 
 0-939 
 
 0.932 
 
 0.926 
 
 Warming of the Water Body. The heat conductivity of water 
 is very low. It has been calculated that a mass of water 5,000 
 meters deep, and of a uniform temperature of o C., would, if in 
 contact with a heat source of 30 C. at the surface, experience the 
 following rate of warming, providing no other factor, such as con- 
 vection currents, etc., entered in : In 100 years no appreciable in- 
 crease in temperature would be found at a depth of 100 meters ; in 
 1,000 years not one per cent, of the surface warmth is to be found at 
 a depth of 300 m., while it takes 10,000 years to carry this fraction 
 of the surface warmth to a depth of 1,000 m., and one million years 
 to carry it to a depth of 4,900 m. After 1,000 years the temperature 
 at a depth of 100 m. will be 7.3 C., while at 200 m. it will be only 
 0.6 C. The temperature of 15 C. descends in a half year 1.3 
 meters, in a year 1.85 m., in 10 years 5.8 m. Thus daily or yearly 
 variation of temperature is of little significance for great depths so 
 far as conductivity of water is concerned. 
 
 Warming of the water is, however, produced by the absorption 
 of the sun's rays, which penetrate to a certain depth, and through 
 vertical convection currents. The latter are in part due to the 
 evaporation on the surface and the consequent increase in density, 
 which brings about a readjustment between the denser surface and 
 the lighter, deeper waters. In the tropical waters of the Indian 
 Ocean the average evaporation during the day is ^4 to ^3 mm. 
 per hour, which, for a surface layer of I mm., with a temperature 
 of 26 C. and a salinity of 35 permille at the beginning, would re- 
 sult in an increase of 13 to 16 permille at the end of the hour, or 
 an increase in density from 1.023 to 1.033, or I -37> which would 
 cause this water to sink, carrying with it its temperature of 26. Of 
 course, the water begins to sink long before it has reached that 
 density, in fact, as soon as it becomes slightly heavier through in- 
 creased salinity. 
 
 Average Surface Temperature. The average temperature of the 
 surface of the oceans varies from 1.7 C. at the poles to 27.4 C. 
 at 5 N. latitude, the latitude of maximal surface temperature. It 
 varies in the different oceans, where the maximum is 26.83 C. in 
 the Atlantic, 27.88 C. in the Indian, 27.20 C. in the Pacific. In all 
 
TEMPERATURE OF THE HYDROSPHERE 183 
 
 cases there is an abrupt increase between 45 and 35 both north 
 and south latitude, where the temperature is sometimes nearly 
 doubled in going toward the equator. Of course, the sur- 
 face temperature is not divisible into a series of regular zonal belts, 
 but is in reality quite irregularly distributed owing to the influence 
 of currents, etc. Considering average surface temperatures as a 
 whole, it appears that the Pacific is the warmest of the four oceans, 
 its mean -being 19.1 C, whereas the mean of the Atlantic is only 
 16.9 C. The mean of the Indian Ocean is only 17 C. in spite of its 
 high maximum of 27.88. The Pacific is the great tropical ocean, 
 so far as surface temperatures are concerned, owing to its great 
 expanse in the equatorial region, where the Atlantic experiences its 
 greatest contraction. Of the total surface of the Pacific 59.5 per 
 cent., or about 3/5, lies between 30 N. and 30 S. latitude. This is 
 well brought out by the wide distribution of coral reefs in the Pacific 
 as compared with their occurrence in the Atlantic Ocean ; these reef- 
 building coral polyps being confined to relatively shallow waters. 
 A similar difference is shown in the temperature of the air over the 
 two oceans, as noted by von Tillo, who found the temperature of the 
 air over the Atlantic 2.6 lower than that over the Pacific. As will 
 be noted later, the waters of the Atlantic, taken as a whole, are 
 warmer than those of the other oceans. 
 
 Vertical Variation of Temperature. As has been noted above, 
 the heat conductivity of water is very low, and were it not for the 
 absorption of the sun's rays by the deeper strata of water, and the 
 existence of vertical convection currents, there would be little change 
 in the temperature of the deeper waters. Kriimmel has introduced 
 terms to designate the downward changes in temperature, for all 
 heterothermal water bodies, i. e., those in which the temperature is 
 not uniform throughout, or homothermal. When the temperature of 
 the water decreases downward we have the anothermal arrange- 
 ment which normally prevails in the open ocean and in some intra- 
 continental seas of low latitudes ; when, on the other hand, it in- 
 creases downward, we have the katothermal arrangement, which is 
 generally associated with a katohaline state. This condition exists 
 in the intracontinental seas of higher latitudes during winter. A 
 dichothermal arrangement, with a colder stratum between warmer 
 upper and lower strata, is characteristic of such seas during the 
 summer months, while the reverse, a mesothermal arrangement, with 
 warmer strata enclosed between upper and lower colder layers, is 
 found in polar waters, and may even extend into the other oceans. 
 
 In the anothermal arrangement of the ocean waters the decrease 
 is, in general, comparatively rapid and uniform for the first 500 
 
184 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 fathoms (915 meters) or more, after which the rate of decrease 
 becomes a slower one. Thus the Challenger Expedition found at 
 one of its stations in the South Atlantic (35 59' S., i 34' E.) a 
 drop from 13.4 to 13.0 in the first 100 fathom's, i. e., a decrease of 
 only 0.4 then a rapid drop to about 4.5 C. at 400 fathoms, or a de- 
 crease of about 8.5 in 300 fathoms, after which the decrease was 
 a slow one again to nearly 2 at 1,500 fathoms, or 6.5 in 1,100 
 fathoms (Fig. 26). In general, the temperature of the deeper 
 
 - I4 C 
 
 io!L 
 
 500 
 
 915 
 
 1000 
 1830 
 
 1500F 
 2745 HI. 
 
 FIG. 26. Diagram illustrating the rate of decrease of temperature from the 
 surface to 1,500 fathoms. Challenger station, South Atlantic, 
 35 58' S. i 34' E. (After Krummel.) 
 
 parts of the oceans becomes relatively uniform below 1,000 meters, 
 so that where the average depth is 4,000 m. only the upper *4 is 
 affected. The other % f the ocean are generally below 3 C., 
 and near the bottom the temperature, even in many parts of the 
 tropics, is but little above o C. 
 
 TEMPERATURE OF THE SEA. 
 
 HORIZONTAL AND VERTICAL DISTRIBUTION OF THE TEMPERATURE 
 IN THE THREE GREAT OCEANS. Leaving the Arctic Ocean for sep- 
 
 
TEMPERATURE OF THE HYDROSPHERE 185 
 
 arate consideration, we must first note the principal sources of the 
 hot and cold waters of the three great oceans, and then note their 
 distribution. It need scarcely be repeated that the chief source of 
 warm waters is the sinking warm surface water of the tropical 
 regions of the ocean. The chief source of the cold waters, especially 
 in the deeper parts, must be sought in the antarctic extensions of the 
 three great oceans, though the cold waters of the Arctic Ocean to 
 a considerable extent modify the surface layers of the North Atlan- 
 tic and North Pacific. 
 
 The cooling of the surface waters of the antarctic extensions and 
 the formation of ice, with the corresponding extrusion of the salts, 
 greatly increase the density of the water, which will sink and carry 
 the low surface temperatures with it. The following temperatures 
 have been recorded for the antarctic extensions of the three great 
 oceans, showing in each case a mesothermal arrangement. In the 
 Atlantic at 61 S. latitude off the coast of South America (63 W. 
 long.) the Belgica found surface temperatures of +3.2 C, which at 
 75 meters depth had fallen to i.o and at 125 meters to the cool- 
 est, 1.4 C. Rising beyond this the temperature reached +0.4 C. 
 at 175 meters, +1.9 between 500 and 1,000 meters, and then fell 
 again to +0.6 C. at the bottom, 3,690 meters. At the other side 
 of the Atlantic, in 70 30' south latitude, off the South African 
 coast (94 W. long.), the same vessel found surface temperatures of 
 
 1.8 C., which increased downward more or less regularly to 
 +0.3 at 175 meters, and to +1.7 C. at 400 meters, after which 
 it decreased to the bottom (1,750 meters), where it was -j-o.8 C. 
 In the antarctic extension of the Indian Ocean the Gauss found at 
 65^ S. lat, 8$ l /2 E. long, surface temperatures of 1.80 C, 
 increasing to 1-75 C. at 75 meters, and then decreasing again to 
 
 1.90 C. between 175 and 200 meters. This is followed by an 
 increase to +0.35 at 1,000 meters, and a decrease to 0.20 at the 
 bottom of 2,821 meters. At 62 S. lat. and 56 E. long, the 
 Valdivia found surface temperatures of 1.0 decreasing to 1.6 
 at 75 meters depth, and rising again more or less regularly to +1.7 
 C. at 300 m. After this a decrease with some irregularity to 0.4 
 C. at 4,636 meters occurs. For the Pacific, the Belgica found at 
 61 S. lat. and 63 W. long, surface temperatures of 1.8 C, in- 
 creasing downward, though with some irregularity, to -j-i.7 C. at 
 400 meters, after which a slow decrease followed to -f-o.8 C. at the 
 bottom, of 1,750 meters. 
 
 Turning, now, to the intercontinental portion of the three great 
 oceans, we find that the temperature distribution in the upper 100 
 meters is largely affected by the seasonal variations, which for the 
 
i86 PRINCIPLES OF STRATIGRAPHY 
 
 surface are shown by the isobars of February and August on tem- 
 perature maps. At a depth of 100 meters the surface influence 
 is still visible to some extent. The Indian and West Pacific 
 are strongly contrasted with the Atlantic. The zone of tem- 
 peratures exceeding 25 C. comprises the West Pacific, west of 
 125 W. long, and between 18 N. and S. lat., and continues 
 through the Banda and Flores seas into the Indian, extending north- 
 westward to Ceylon, and westward beyond the Maldives (to 65 E. 
 long). In the Atlantic, on the other hand, only a small area in the 
 Brazilian current reaches this mean temperature. Along the whole 
 western border of tropical America, as well as tropical Africa, the 
 temperature of the water does not rise above 20 C. at a depth of 
 100 meters, though higher temperatures exist at the surface. No 
 temperatures of o are known at a depth of 100 meters in the 
 North Atlantic or North Pacific, except at the south end of Green- 
 land and in Denmark and Davis Straits and close to the southeast 
 coast of Kamtchatka, where the cold currents enter from the Arc- 
 tic. In Davis Straits, near the Arctic circle, the surface tempera- 
 ture varies from +1.15 C. to +2.6 C., whereas in Denmark 
 Straits the surface temperature as well as that at 100 meters is 
 0.7 C., but at 50 meters it is 1.5 C., rising to +1.5 C. at 150 
 m. and to + 3.1 C. at 200 m. At a depth of 200 meters the tempera- 
 ture distribution becomes greatly modified, the chief feature being 
 the distribution of the warmer portions of this stratum in the three 
 great oceans, which, instead of lying in the equatorial region, are 
 now pushed to the north and south of the same, an arrangement 
 which becomes still more pronounced at a depth of 400 meters. At 
 this depth the zone of highest temperature, over 18 C., lies in the 
 West Atlantic below the Florida stream, at about 30 N. lat. Be- 
 tween 22 and 40 N. lat. the temperature at this depth is every- 
 where above 17 C. in the western half of the North Atlantic. In 
 the South Pacific a temperature of 16 was found only near the 
 Fiji Islands at this depth, 14 or even 12 being the more usual 
 maximum temperature. At a depth of 600 meters the area of 
 maximum temperatures in the North Atlantic spreads eastward 
 (between 20 and 40 N. lat.) and shows a height of over 10, in- 
 creasing in some cases to 16.8 (northwest of the Bermudas), while 
 under the equator the temperatures are only 5 or 5.5. Maximum 
 temperatures of over 10 C. are found besides in the South Pa- 
 cific in scattered areas, and in the Indian Ocean at this depth. At 
 1 ,000 meters the mid North Atlantic is bounded by the 7 isotherm, 
 which is deflected northward to the North British coast. Tempera- 
 tures of 8 occur in two areas, between 30 and 40 N. lat. and 40 
 
TEMPERATURE OF THE HYDROSPHERE 187 
 
 and 80 W. long., and in an eastward broadening area in the Span- 
 ish Sea, which nearer the land becomes 9 or more and in the Gulf 
 of Cadiz 11, thus showing the influence of the undercurrent of 
 warmer Mediterranean waters. At 2,000 meters in the southwestern 
 part of the South Atlantic, the southern part of the Indian, and the 
 whole Pacific, the temperature lies between 2 and 3 C. It rises to 
 something over 3 in the other parts of the Atlantic, except in the 
 southwest part of the Sargasso Sea region and in the Spanish Sea 
 between the tropic of Cancer and Cape Finisterre on the north 
 coast of Spain, where it is something over 4 C. Temperatures 
 above 3 C. are also found at this depth in the two northern exten- 
 sions of the Indian Ocean the Bay of Bengal and the Arabian Sea, 
 the latter having temperatures as high as 5 or 6 C. 
 
 At 3,000 m. the Pacific has a uniform temperature of 1.6 to 2.2 
 C., except where depressions surrounded by higher rims occur, as in 
 the Fiji * basin and tire Coral basin, where the temperatures rise 
 from 2 to 2.7 C. In the Indian Ocean at this depth great uni- 
 formity of 1.3 to 1.9 C. occurs with but few exceptions, notably 
 beneath the Arabian and Bengal gulfs, where it rises sometimes to 
 2.9 C. In the Atlantic the temperatures are somewhat higher, 
 falling nowhere below 2 C. north of 40 S. lat., and rising more 
 often to 2.2 or even 2.9 C. Only below the eastern part of the 
 Guinea current, and the Sargasso Sea, are the temperatures more 
 than 3 C., reaching a maximum of 3.7 C. 
 
 At 4,000 meters and lower the temperature of the North Pacific 
 is nearly uniform at 1.6 to 1.7 C, even in depths of 6,000 
 meters. The same temperature occurs in the various depressions 
 southwest of the Hawaiian Islands, except in the deeps, like the 
 Tonga and Kermadec deeps, where temperatures as low as 1.1 C. 
 have been obtained. Near the border of the Antarctic continent the 
 Belgica found temperatures of about 0.6 C., while in the Atlantic- 
 Indian Polar basin, which descends below 5,000 meters, a tempera- 
 ture of o to 0.5 obtains. This cold bottom water flows north- 
 ward in the west Atlantic trough, for in the basins composing it 
 bottom temperatures of 0.1 to 0.4 are found. The mid-Atlantic 
 and the Whale swells, or rises, however, cut off the east Atlantic or 
 South African trough from these cold waters to the south, for, 
 although this descends to depths of 5,000 to 5,600 meters, the lowest 
 bottom temperatures found are + 2.2 to + 2.6 C. 
 
 In the Cape trough to the south of the Whale ridge the tempera- 
 ture at 4,800 m. is 0.9 C. This shows that the Whale ridge can- 
 
 * Some .lower temperatures occur in this basin also, suggesting that it is not 
 completely closed. 
 
i88 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 not fall below 3,000 m., for the temperature of 2.4 C. is that of the 
 2,950 m. depth (Fig. 27). The mid- Atlantic rise is broken in the 
 equatorial region just west of the great Romanche deep by cross 
 channels descending to 5,000 m. Through these channels the cold 
 wafers of the Brazil basin (derived from the Antarctic) find access 
 
 Sea Level 
 
 SOUTH AFRICAN TROUGH 
 
 2.91 
 
 vypT/. 
 
 3000 M. OR LESS 
 
 ilwHALE RIDGE; 
 
 CAPE TROUGH 
 E.4--C. 
 
 FIG. 27. Diagrammatic section of the Whale Ridge in the South Atlantic, 
 showing the differences of temperature on opposite sides. 
 
 to the North African basin, but this trans-passage is a mild one, ow- 
 ing, probably, to the narrow character of the cross channel, for its 
 effects are no longer noticeable beyond 2 
 normal bottom temperatures of 2.2 to 2.6 
 North African basin are found. 
 
 or 3 N. lat., where the 
 characteristic of the 
 
 s.o. 
 
 N.E. 
 
 (T 
 
 500 m 
 
 4000" 
 
 2000 m 
 
 FIG. 28. Diagrammatic transverse section of the Wyville-Thomson Ridge 
 in the North Atlantic, showing its effect as a thermal barrier. 
 (After Prouvot and Haug.) 
 
 In the North Atlantic the bottom temperatures of 2.0 to 2.6 
 are preserved through the barring of the cold waters of the Arctic 
 Ocean by the Wyville-Thomson and Faroe -Iceland and Denmark 
 Straits ridges, which completely divide the two oceans below a depth 
 of 550 to 580 meters. To the north of these ridges the temperature 
 $inks as low as 1.2 C. in 2,222 meters (Fig. 28). 
 
TEMPERATURE OF. THE HYDROSPHERE 189 
 
 TEMPERATURES OF THE MEDITERRANEANS AND EPICONTINENTAL 
 SEAS DEPENDENT ON THE LARGE OCEANS. As a general chracteris- 
 tic of mediterraneans may be noted the deep homothermal bottom 
 layer, which, as a rule, has a somewhat higher temperature than 
 that of the neighboring ocean at the same depth. Thus the Roman 
 mediterranean has a temperature of 12.8 between 200 m. and 2,600 
 m., while the layers above this show a gradual increase to 25.0 at 
 the surface. The temperature of the Atlantic in the Bay of Cadiz 
 at 1,000 meters depth is normally not over 8, though the outflow of 
 the warm mediterranean bottom water raises it to 11, whereas in 
 depths of 2,000 m. the temperature of this part of the Atlantic is 
 only a little over 4 C. The Sea of Marmora below a depth of 220 
 to 350 m. to the bottom of 1,403 m. has a homothermal temperature 
 of 14.2, which is the approximate winter temperature of the sur- 
 face water of the ^Egean Sea. While thus the Marmora Sea has 
 a higher bottom temperature than the Mediterranean, the Black 
 Sea shows a much lower. Here, in summer, we have a typical dicho- 
 thermic stratification, the minimum temperature of 6.3 in the north- 
 ern part lying at 75 m., while the bottom at 131 m. has a temperature 
 of 8.3 C. In the central area the minimum temperature is 7.3 
 and lies only 45 m. below the surface, while between 100 and 2,012 
 m. the bottom temperature rises from 8.5 to 9.1 C. In the 
 southern part the minimum temperature of 6.2 lies at 65 m., 
 the bottom temperature at 366 m. having risen to 8.9. The South 
 China Sea shows a fall of 10 at 200 m. from the surface tempera- 
 ture of 24 characteristic of the upper 50 m. At 1,000 m. the tem- 
 perature is 3.9, at 1,500 m. 2.6, but below i, 600 m. to the bottom 
 (3,480 m.) a homothermal temperature of 2.5 obtains, which is the 
 average temperature of the Pacific at 1,500 meters. That the 
 deeper strata of the China Sea are uninfluenced by the correspond- 
 ingly colder waters of the Pacific, which sink to 1.6 at 3,000 m., 
 indicates that the submarine barrier of this sea is nowhere below 
 i ,600 m. Similar conditions are found in the Celebes Sea, where a 
 homothermal state exists below 1,500 m., with a temperature of 
 3.67 C. In the Philippine waters, on the other hand, a homother- 
 mal condition with 10.9 exists from 500 m. to the bottom (1,280 
 meters), and in the neighboring Sulu Sea a temperature of 10.3 
 characterizes the water from 730 m. to the bottom at 4,070 m. Here, 
 then, a greater separation from the Pacific is shown. The Red Sea 
 offers some striking features owing to its situation in the tropical 
 belt. It has the highest bottom temperatures of all mediterraneans, 
 this being, according to J. Luksch, uniformly at 21.5 from 700 m. 
 to its greatest depth at 2,200 m. This is associated with a salinity of 
 
PRINCIPLES OF STRATIGRAPHY 
 
 from 40.5 permille to 40.7 permille. The elevation of the marginal 
 rim in the Straits of Bab-el-Mandeb, which rises to within 185 m. 
 of the surface, prevents the cooler and less saline waters of the 
 Indian Ocean from entering. These waters in the Arabian Sea and 
 Gulf of Aden have a temperature, at 800 m., of 11 to 13. This 
 is 4 above the normal and is due to the outflow of the warm waters 
 of the Red Sea. At 2,000 m. the temperature of the Arabian Sea is 
 5 to 6, whereas that of the Red Sea at this depth remains at 21.5 
 (Fig. 29). 
 
 The three Central American mediterraneans, the Mexican, Yuca- 
 tan, and Caribbean, show homothermal conditions below 1,700 m., 
 from which depth the temperature of 4.2 C. continues to the great- 
 est depth at 6,269 m. In the corresponding depths of the Atlantic 
 the temperature ranges from 4 to 2. 
 
 RED SEA 
 
 I Pvel GUL ' r ofr ADEN 
 
 Hornotherwal 2,1. 5*C 
 ....E200M... 
 
 FIG. 29. Diagrammatic cross-section of the ridge dividing the Red Sea and 
 the Gulf of Aden, to show temperature differences. 
 
 Among the epicontinental seas the Baltic may serve as an ex- 
 ample of a special type of low salinity. The surface temperature 
 varies, of course, greatly with the season, the minimal temperature 
 ranging in the Danzig Bay region from 1.6 to 2.8 C., according 
 to the rigor of the winter. This temperature extends through the 
 upper 40 to 60 m., which are also homohaline. The maximum 
 density of water of the salinity of the Baltic (7^2 permille) is 
 reached at 2.4 C. Hence cooler waters will remain at the surface. 
 The freezing point of this water is, moreover, at 0.4 C. Down- 
 ward the temperature increases, so that at the bottom of the Danzig 
 Bay temperatures of 5.68 and 5.88 C. have been found in Febru- 
 ary, while those of August range from 3.82 to 4.90. In the Alands 
 deep, near the mouth of the Bothnian Gulf, surface temperatures 
 of 0.2 C. extending to a depth of 20 meters were found in Feb- 
 ruary, 1903, and below this an increase to 3.07 at 273 meters. In 
 the summer months the temperature of the upper layers, varying 
 in different years from 20 to 45 m., ranges from 15 to 18 or over 
 
TEMPERATURE OF THE HYDROSPHERE 191 
 
 on the surface and from 14 to nearly 16 at the bottom. Below 
 this surface layer a sudden drop occurs, a feature characteristic of 
 fresh-water lakes. Thus east of Bornholm observations by F. L. 
 Ekman in July, 1877, showed a surface temperature of 15.7 C. 
 slowly decreasing to 14 at 18 meters depth, followed by a sudden 
 drop to 8 at 20 meters, decreasing regularly to 5 at 25 meters. 
 The salinity here was 7.5 permille down to 30 meters, where it rose 
 to 7.6 permille. Such abrupt changes are found only in water 
 bodies of slight wave and current activities. 
 
 So far as measurements have been made in Hudson Bay, a nearly 
 homothermal condition seems to be indicated, with temperatures 
 between 0.3 and 1.7, to a depth of 365 m. The North Sea 
 is a typical and well-studied example of a marginal epicontinental 
 sea. Southwest of the Dogger bank the strong wave activity and 
 tides produce a homothermal arrangement which in winter has a 
 temperature of 5 to 6. Northward and eastward this decreases to 
 4 or even 3. After a period of quiet days a surface layer of less 
 salinity may form from the influx of fresh waters, and with this a 
 low temperature occurs. Thus, while the salinity of the surface at 
 the German station 15 (lat. 55 2' N., long. 7 30' E.) fell to 32.5 
 permille on February 24, 1906, the temperature fell to 2.89 ; both 
 salinity and temperature- increased downward, being at 24 meters 
 32.18 permille and 3.20, respectively. A typical kathothermal condi- 
 tion for February is shown by measurements off the mouth of the 
 Moray Firth (Scottish station 25, lat. 58 n' N., long. o 32' W.) 
 on February 18, 1904, when the temperature rose from 6.63 at the 
 surface to 6.77 at no m., and the salinity from 35.10 permille to 
 35.14 permille at the same depths. In the summer the reverse is 
 true, the surface temperature (18) being slightly higher than the 
 bottom, 7.6, at 35 m., except where after storms a homothermal 
 and homohaline condition prevails. A sharply defined stratification 
 may occur even here, as shown by observations in the open North 
 Sea in August, 1905 (lat. 55 22' N., long. 4 18' E.), when it 
 was found that the temperature decreased slowly from 15.74 on the 
 surface to 15.67 at 20 meters, then fell to 11.38 at 25 meters, and 
 to 8.26 at 30 meters, and 8.25 at 43 meters. On the west side of 
 the Great Fisher bank the observations for 1903 show a sudden drop 
 from 12.24 at 30 m. to 6.52 at 40 m., with but little decrease be- 
 low this. Such a condition is general north of the Dogger bank. 
 
 TEMPERATURES OF DEPENDENT SEAS. In the Funnel seas with 
 closed head the conditions of the ocean to which they are dependent 
 prevail, and this is true of the Biscayan as well as of the California 
 type. Where the head is open, leading into a mediterranean, the 
 
192 PRINCIPLES OF STRATIGRAPHY 
 
 generally warmer bottom waters of this sea will influence the tem- 
 peratures of the adjoining funnel sea. This is shown in the ab- 
 normally high temperatures of the Gulf of Cadiz and that of Aden. 
 
 TEMPERATURES OF THE ARCTIC OCEAN AND ITS DEPENDENCIES. 
 Through the entrance over the Wyville-Thomson ridge of the warm 
 waters of the gulf stream, the eastern part of the Greenland Sea has 
 a surface temperature of +6 to +7 m summer and something 
 over +7 in winter. On reaching the latitude of Spitzbergen the 
 main branch, much cooled, sinks beneath the cold but less dense ice- 
 bearing East Greenland stream and turning southwestward pro- 
 duces the mesothermal stratification of this part of the waters as 
 far as the ridge in Denmark Straits, across which the warm water 
 still is able to pass. Midway between Spitzbergen and Greenland 
 (78 13' N. lat, 2 58' W. long.) the temperature is still 3.1 and 
 decreases more or less regularly to 1.3 C. at the bottom (2,690 
 m.). Seven degrees farther south, near the center of the East 
 Greenland Sea (71 N. lat, 5 9' W. long.), a thin surface layer 
 of warmer water has a temperature decreasing from -j-4-6 at the 
 surface to +2.0 at 25 meters, below which lies arctic water from 
 1.6 at 50 m. to 1.9 at 75 m., and decreasing to 1.3 at 
 1,516 meters. On the east coast of Greenland (74 38' N. lat, 15 
 3' W. long.), in the cold East Greenland stream, the surface tem- 
 perature of 0.95 decreases to i-53 at 50 m. depth, and then 
 increases again at the bottom (277 m.) to -(-0.70, showing the in- 
 fluence of the warm submerged Gulf Stream drift from 180 m. 
 downward. In Denmark Straits w r est of Iceland and a little below 
 the Arctic circle (66 25' N. lat., 25 50' W. long.) the surface 
 temperature of -f 1.7 sinks to 1.4 at 20 m., to 1.6 at 30 m., 
 and rises again to 0.8 at 40 m., these temperatures representing 
 the East Greenland stream. Then at 50 meters the temperature sud- 
 denly rises to +5.3, increases to +6.3 between 75 and 100 m., and 
 then sinks again to +5- at 300 m., then more rapidly to 0.5 
 at 600 m., and to 1.1 at 650 m., the bottom. Where the water is 
 strongly and normally influenced by the Gulf Stream drift only an 
 anothermal arrangement occurs, as north of the Faroe Islands (63 
 22' N. lat., 5 29' W. long.), where the temperature sinks from 
 + 10.0 C. at the surface to 1.2 at 2,222 fathoms. The measure- 
 ments above given were made in the summer ; for the winter months 
 the temperature in the upper 100 meters is much lower, the differ- 
 ence amounting at the surface, between July and April, to six 
 degrees. 
 
 In general the temperature of the East Greenland Sea below 
 600 m. is down to o, while from 800 or 1,000 m. to 3,800 m. homo- 
 
TEMPERATURE OF THE HYDROSPHERE 193 
 
 thermal conditions at 1.2 to 1.3 C. exist. In the Central 
 Polar Sea, the temperatures of the upper strata (themselves of a 
 dichothermic arrangement) are mostly below 1 C. and range 
 from 1 60 m. to 200 m. in depth, where the temperatures sometimes 
 are as high as 0.2. A second stratum of mesothermal character 
 ranges from -(-0.2 to -(-1.2 and lies between 200 and 800 meters 
 in depth, while a third deeper, nearly homothermal, one of 0.7 
 to 0.8 extends to depths of 3,000 and 3,800 meters, though the 
 actual temperature of 0.7 is not reached above 1,400 to 2,000 
 meters depth. Of the other dependencies of the Arctic Ocean the 
 shallow White Sea has winter temperatures of 1.9 to 1.6, 
 which range throughout and are associated with a salinity of 34.85 
 permille and 30.08 permille, respectively. In the summer months 
 the temperature rises to over + 13 on the surface, but below 30 m. 
 the temperature is under o, while below 120 m. it is 1.6, as in 
 winter. This does not hold for the very shallow bays, however, 
 where temperatures of 8 to 9 and over are still found at the bot- 
 tom of 30 to 35 meters. 
 
 MEAN TEMPERATURES OF THE OCEANS AND INTRACONTINENTAL 
 SEAS. The mean temperatures of the four oceans have been de- 
 termined to be as follows (Krummel-2o:^p5), see, ante, p. 146: 
 Arctic," 0.66 ; Pacific, +3.73 ; Indian, +3.82 ; Atlantic, +4.02 ; 
 mean of three larger oceans, -)-3.86. This shows that, taken as a 
 whole, the Atlantic is warmer than the other oceans, this being due 
 to the comparatively high bottom temperatures. As already noted, 
 when surface temperatures alone are considered those of the Pacific 
 are higher than those of the other oceans. Of the mediterraneans, 
 the Red Sea has the highest (22.69) an d the Japanese the lowest 
 (0.90) mean temperature. In the latter only the surface waters 
 down to 100 or 150 m. are warm, the western side being cooler 
 owing to the cold southward-flowing current. The deeper waters 
 of the central basin have a temperature of 0.7 to 0.3. Among the 
 epicontinental seas the Persian Gulf has, as might be expected from 
 its location, the highest mean temperature (24), while Hudson Bay 
 has the lowest (1.0). 
 
 EUTECTIC TEMPERATURES. This term is applied to the tempera- 
 ture at which salts are separated from cooling waters holding them 
 in solution by the simultaneous crystallization of the salt and water. 
 This temperature is always lower than the temperature of freezing 
 water, and differs for the different salts in the following order, as 
 shown by Pettersson (27:501, see also Krummel-2o:5oj) ; Na^SO 4 
 (-0.7) ; KC1 (-n.r ).; NaCl (-21.9) ; MgCl a (-33-6) ; CaCl 2 
 ( 55). With progressive cooling the salts would thus be sep- 
 
 
194 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 arated out in the above order, sodium sulphate first and calcium 
 chloride last. Owing to the presence of the other salts in sea water, 
 however, Na 2 SO 4 does not separate out at its eutectic temperature 
 of 0.7, but only at 8.2. When the entire mass is frozen, a 
 mixture of ice and salt crystals results, the so-called cryohydrate, 
 which may be compared with graphic granite (pegmatite), the best 
 known eutectic among rocks. The following table shows the results 
 of Ringer's experiment in freezing 1,000 grams of sea water of 
 35.05 permille salinity (Krummel-2o:50^) : 
 
 At temperature of 
 
 5 
 
 8.2 
 
 10 
 
 15 
 
 23 
 
 
 
 
 
 
 
 Liquid remains, grams 
 
 420. 5 
 
 281.5 
 
 2^4.0 
 
 186.1 
 
 114.0 
 
 Solid occurs, mostly ice, in grams .... 
 Solid Na2SC>4 in grams in above solid . 
 
 570-5 
 o.o 
 
 718-5 
 
 o.o 
 
 766.0 
 
 1.84 
 
 813.9 
 3.09 
 
 865.1 
 
 3-68 
 
 Temperatures lower than 8.2 C. exist in the drift ice itself 
 near the surface (at depth of 40 cm.) from October to May in- 
 clusive, falling close to 24 in January. At a greater depth the 
 temperature is invariably higher in the cold months and lower in the 
 warm. Thus at 200 cm. depth the January temperature, which at 40 
 cm. was 23.9, was 10.6, while the July temperature, which at 
 40 cm. was 0.5, was at 200 cm. 1.4 C. In all cases the ice in 
 winter is warmer than the air above it. The water, however, retains 
 a nearly constant temperature of 1.5 to 1.7 C. From the above 
 considerations it appears that sea ice is likely to be richer in sul- 
 phuric acid (SO 3 -f~ H 2 O) than normal sea water, while sea water 
 coming in contact with ice at a temperature below 8.2 C. will 
 have its SO 3 extracted and so become poorer in this substance. On 
 the other hand, portions of the ocean where the sea ice melts will 
 be richer in SO 3 than normal sea water. The normal, according to 
 Dittmar, is 11.576 parts of SO 3 to 100 Cl; according to Forchham- 
 mer, it is n.88; and, according to Schmelck, it is 11.46. Pack ice 
 melted by Irvine gave 10.84, H-97, an d H-93 for different samples, 
 two of them higher than the highest figure for normal sea "water. 
 One piece of ice melted by Hamburg gave a proportion of SO 3 of 
 57.4 or 5 times as much as normal sea water. This, however, had 
 only 0.05 permille of chlorine. 
 
 RANGE OF TEMPERATURE OF THE OCEANS. The annual range of 
 temperature of the waters is of greater bionomic significance than 
 the absolute temperature itself. Sir John Murray has mapped these 
 
TEMPERATURE OF THE HYDROSPHERE 195 
 
 for the oceans (23) and from his maps the following general facts 
 may be taken: For tropical waters, the range is small (less than 
 10 F. or 5.55 C.) in the Pacific between the tropics of Cancer and 
 Capricorn, except off the west coast of South America, where the 
 range increases to 15 or even 20 F. (11.11 C.). In the Atlantic 
 this small range of less than 10 F. occupies about the same position, 
 except off the North African coast and the Gulf of Guinea. A sim- 
 ilar low range occurs in the Indian and Australian waters between 
 20 N. and S. lat., except in the Madagascar region, where a greater 
 range exists. Similar small ranges, but for low temperatures, exist 
 in the Arctic Ocean, except where the Gulf Stream carries warmth 
 to Iceland, and in the southern parts of the other oceans below 50 
 or 60 S. lat. Ranges of 20 or over exist in the North Pacific 
 north of 40 N. lat. and in the North Atlantic between 30 and 55 
 N. lat., likewise in the South Atlantic and Indian between 30 and 
 50 S. lat., from South America to New Zealand. The greatest 
 ranges of temperature, more than 50 F., or 27.78 C., are found in 
 the west Atlantic, eastward from the New England coast, and in 
 the western part of the Philippine Sea. Ranges from 30 to 40 F. 
 (16.66 to 22.22 C.) are found off the Rio de la Plata, and in the 
 Roman Mediterranean, the Black, Caspian, and Baltic seas and in 
 part of the North Sea, and in the northern ends of the Red Sea and 
 Arabian Gulf, as well as the western North Atlantic and the western 
 or Asiatic Pacific. 
 
 Shifting of the areas of great range of temperature may be 
 brought about by storms or by change in currents or otherwise, and 
 such a shifting may be lateral or vertical. This results generally in 
 the wholesale destruction, of animal life adapted to a smaller range, 
 as illustrated by the enormous destruction of Tile fish off the New 
 England coast in 1882, which exceeded in estimation the number of 
 one billion, and covered the floor of the ocean in this region to a 
 depth estimated at six feet with the bodies of dead Tile fish. The 
 influence of the changes in temperature on the destruction of life 
 will be more fully discussed in a subsequent chapter. 
 
 TEMPERATURES OF THE TERRESTRIAL WATERS. 
 
 TEMPERATURES OF LAKES, ETC. Since lakes are mostly shallow 
 the seasonal variations in temperature are more pronounced through- 
 out than in the oceans or mediterraneans. The chief source of heat 
 is the sun, whose rays are absorbed to a greater or less extent. Re- 
 flection from the surface, however, greatly reduces the amount 
 
196 PRINCIPLES OF STRATIGRAPHY 
 
 which would otherwise go to heat the water, this reflection being in 
 some instances with the sun near the horizon as high as 68% of 
 the total radiation received (Dufour-5). The heat taken up by the 
 water is chiefly absorbed by the upper layers; and absorption is 
 greatest in water containing much sediment in suspense. Contact 
 with warm air further warms the upper layers of the water. Trans- 
 portation of the superficial heated layers to cooler depths occurs by 
 convection as well as by wind or by currents. Loss of heat from the 
 upper layers occurs through radiation, and through conduction or 
 contact of the surface with cold air. Fresh water has its maximum 
 density at +4 C. (+39.2 F.) and this may serve as a dividing 
 line between warm and cold fresh water, the former being above, the 
 latter below this temperature (Forel-8: 105). The densest layers 
 sink, of course, to the bottom, and so warm water will show an ar- 
 rangement of strata progressively cooler downward, i. e., an ano- 
 thermal arrangement. This has been called direct stratification. 
 Cold water, on the other hand, i. e., that below 4 C., will have a 
 reversed stratification, the warmer but denser layers, i. e., those at 
 or near 4 C., lying at the bottom, and the colder above. The tem- 
 perature arrangement will be katothermal. For saline lakes, the 
 temperature corresponding to their maximum density must be 
 chosen as the dividing point. 
 
 Classification of Lakes According to Temperature. From the 
 viewpoint of temperature three types of lakes may be recognized : 
 a. tropical, where the water is always above the maximum density 
 temperature (4 C. for fresh water) ; b. temperate, where it alter- 
 nately rises above and falls below this temperature; and, c. polar, 
 where it is always below the maximum density temperature. These 
 lakes are, however, not restricted to the corresponding geographic 
 zones of the earth. Tropical lakes always have a direct thermal 
 stratification, or an anothermal arrangement. In spring and sum- 
 mer the stratification becomes increasingly marked, while in fall 
 and winter it decreases until homothermic conditions are approached 
 in winter. Examples of such lakes are the great lakes of upper 
 Italy, i. e., Lake Geneva (Germ. Genfer See, Fr. Lac Leman), etc. 
 
 Polar lakes always have a reversed thermal stratification, or 
 katothermal arrangement, the warmest water (not above 4 C., how- 
 ever) lying at the bottom. Here the stratification becomes most pro- 
 nounced in fall and winter, decreasing in the spring and approaching 
 homothermal conditions in summer. Such lakes occur in the polar 
 regions and in the mountains of the temperate regions. 
 
 Temperate lakes assume a tropical habitus in summer and au- 
 tumn, the stratification being pronounced in the former and tending 
 
TEMPERATURE OF THE HYDROSPHERE 197 
 
 to disappear in the latter, only to appear in reversed order as win- 
 ter approaches, when the polar type of reversed stratification is 
 pronounced. This will disappear again in spring and give place to 
 the tropical type. The minimum and maximum surface tempera- 
 tures of fresh-water lakes are : for tropical lakes -j- 4 C. and 
 + 25 C. to +30 C; for polar lakes o and +4 C. ; and for 
 temperate lakes below + 4 in winter, and above + 4 m summer, 
 seldom rising, in the deeper lakes of the temperate zone, above 25 
 C. In all cases the temperature of the surface waters is 'lower than 
 that of the air immediately above it in summer, and higher in 
 winter. The depth to which the seasonal variation penetrates is 
 about 100 meters. 
 
 Differences of temperature also exist between the littoral and 
 open lake or pelagic district, the former being warmer in summer 
 and colder in winter than the latter. As has already been indi- 
 cated, the bottom temperatures of tropical lakes are generally above 
 4 C., though those of subtemperate ones may be at times as low as 
 4 C. Temperate lakes, even those inclining toward either extreme, 
 i. e., subtropical and subpolar, have a normal bottom temperature of 
 4, though the former may at times be greater than 4 and the lat- 
 ter less. Polar lakes have a normal bottom temperature lower than 
 4 C., though the subtemperate ones may occasionally have as high 
 a bottom temperature as 4. Lake Geneva, having a depth of 309 
 m. (surface elevation 375 m.), is beyond the influence of seasonal 
 variation (100 m.), nevertheless a difference of from 0.1 to 0.3 
 between seasons has been observed in the deepest layers. This is 
 regarded as chiefly due to the sinking down of sediment-bearing 
 waters of higher ^emperature. The actual temperatures at the bot- 
 tom of this lake are from -f- 4 to + 5 C., while the temperature 
 of the littoral belt varies from + 15 to + 25 C. in summer, that 
 of the inflowing Rhone being -f- 10 to + I 5- I n winter the tem- 
 perature of the littoral region sinks to +4.5 or to +5-5 in dif- 
 ferent years; only near the shore, in the shallow littoral region, 
 does the temperature fall below 4 and may fall to o with the 
 formation of ice. This results in the formation of a reversed ther- 
 mal stratification, whereas that of the littoral region is normal or 
 direct, as shown in the accompanying diagram (Fig. 30), copied 
 from Forel. The line along which the densest water of 4 tem- 
 perature reaches the surface has been called the thermal barrier. 
 
 Freezing of Lakes. Where reversed thermal stratification ex- 
 ists the temperature on the surface may sink to o, and ice will be 
 formed. This is normal in polar lakes, usual during the colder 
 months in temperate lakes, and may occur in the shallow littoral belt 
 
198 PRINCIPLES OF STRATIGRAPHY 
 
 of tropical lakes, where a thermal barrier separates this from the 
 littoral zone, as in the above illustration from Lake Geneva. In 
 quiet lakes, where the surface water has reached o, a slight lower- 
 ing of the temperature, as during a still, clear night, will cause the 
 formation of a uniform, continuous, though thin sheet of ice over 
 the entire surface, which, if not melted -during the succeeding day, 
 will thicken the following night by addition of ice on its under side, 
 until a thick crust is formed. The increase in thickness is, however, 
 at a diminishing rate, owing to the low conductivity of ice. 
 
 In disturbed waters ice floes are formed, a method of ice forma- 
 tion characterizing the sea and rivers as well. These pancake 
 masses (Fr. glaqons-gateaux, Ger. Kuchschollen) result from the 
 union of the ice needles tossed about by the waves, these needles 
 often forming suddenly in the super-cooled mass, through agita- 
 
 FIG. 30. Diagram representing thermal barrier of 4 between the littoral and 
 pelagic districts of Lake Geneva in winter. The barrier is in reality a 
 vertical sheet. (After Forel-8.) 
 
 tion, or through the dropping in of snowflakes, analogous to the 
 formation of crystals in a supersaturated solution on agitation or 
 on dropping in of a crystal. The round form of the pancake floes is 
 due to the constant friction they undergo. The density of ice is 
 about 0.92, while that of pure water at o is 0.9998676 and that of 
 normal sea water is 1.028. (Pure water at 4 [or better 3.947 ],- 
 its maximum density, is taken as I.) It is, therefore, evident that 
 ice will float on fresh as well as on salt water of the temperature 
 permitting its formation. Owing to the addition of ice fragments 
 and crystals on the margins of the cakes where they are thrown by 
 the waves, the weight of the mass will increase until it sinks suffi- 
 ciently to be covered by a thin stratum of water, which will cause 
 further addition to the ice mass on its surface, while at the same 
 time it grows marginally as well as on its under side. The ice mass 
 eventually acquires the form of a plano-convex lens, with the con- 
 vex side downward and a thickness of a meter or more. The ice 
 floes will freeze together when heaped up by waves or currents or 
 when coming in contact after the water has quieted down. 
 
TEMPERATURE OF THE HYDROSPHERE 199 
 
 As the temperature of ice sinks below zero, especially at night, 
 further contraction takes place, and thus cracks are formed in the 
 ice sheet, which may extend for hundreds if not thousands of 
 meters in length and cross each other at various angles. Water 
 rising in these fissures freezes, and so prevents the closing of the 
 old fissures on the expansion of the ice during the day. A powerful 
 lateral pressure is thus inaugurated which, if the whole lake is 
 frozen, will cause the ice to move up on the shore, carrying ma- 
 terials with it and building a shore wall of ice-shoved boulders, 
 while at the same time it may scratch the underlying rock layers 
 and produce the effect of glaciation. Such boulder walls and ridges 
 may also be built by the ice floes resulting from the breaking up 
 of the ice in spring. These floes are driven onto the shelving shores 
 by wind and carry stones up with them. This action is pronounced 
 in northern lakes like those of Labrador. Tyrrell (40:64 B.) has 
 described such ridges around Lake Winnipegasie, and Russell men- 
 tions their occurrence on other Canadian and northern United 
 States lakes, where they are found "40 or 50 feet from the water's 
 edge, are 20 feet high, and broad enough to furnish convenient 
 roadways." (Russell-3i '.52.) The same lateral pressure through 
 expansion of the ice causes the buckling of the ice masses in the 
 center of the lake. Only in very shallow water bodies will the ice 
 extend to the bottom. Owing to the greater density of water at 
 4 C., this will sink to and remain at the bottom, and the slow con- 
 ductivity of both water and ice will prevent the reduction of the 
 bottom temperature during the cold season. It is in this way that 
 organisms can survive under the frozen surface of a lake. 
 
 NORMAL AND EXCESSIVE TEMPERATURES OF STREAMS AND OF 
 GROUND WATER. The temperature of streams in a given area varies 
 according to the season, but also with the volume of water and with 
 its source, the length of the stream, the character of its bottom and 
 banks, etc., so that different streams within the same region and at 
 the same time may have different temperatures. Thus streams re- 
 sulting from melting glaciers will always be cold, although, as they 
 proceed in their course, the waters may be warmed to a certain ex- 
 tent by contact with the warm air. If much sediment is carried 
 in suspension by a stream, its temperature will be proportionally 
 higher. A stream flowing through a lake will, after leaving the 
 lake, have in general the temperature of the surface waters of that 
 body, which alone are carried out. Underground effluents in like 
 manner have the temperature of the layers of water in which they 
 originate. 
 
 Spring waters vary less in temperature, for their sources are 
 
200 PRINCIPLES OF STRATIGRAPHY 
 
 generally below the influence of the seasonal variation, which in 
 temperate regions may extend to a depth of 50 feet. The normal 
 temperature of spring water lies in general between 47 and 51 F. 
 
 Freezing of Rivers. Rivers of comparatively gentle current will 
 freeze over after the manner of lakes, but rivers of strong current 
 will freeze over only under exceptional circumstances. In all cases 
 the current continues under the ice. 
 
 Freezing of Ground Water. The ground water will sometimes 
 freeze to an astonishing depth. Thus in the Tundras of Alaska and 
 Siberia the permanently frozen soil often extends to a great depth, 
 that of Yakutsk, Siberia, having been given as 382 feet. (K. E. von 
 Baer, quoted by Russell~3i :/Jo.) Sands saturated with glacial 
 waters may freeze throughout and then behave like solid rock. In 
 this manner faulting, crumpling, and other structures normal only to 
 solid rock have been formed in the otherwise unconsolidated glacial 
 sands and clays of the glacial period. (Berkey & Hyde-i : 223- 
 
 #*.) 
 
 Mechanical work cf freezing ground water. ( Salisbury-34 : 
 208.) The upper layers of the lithosphere in high latitudes are 
 subject to periodic refrigeration below the freezing point of the 
 ground water. This is especially true of the soil layer, which may 
 be affected to a depth varying considerably with the latitude, the 
 intensity, and above all the duration of the period of cold. When 
 the soil is frozen, erosion is retarded, and where the subsoil is 
 permanently frozen, as in the northern regions of the larger con- 
 tinents, the arboreal type of vegetation is absent as already noted. 
 The freezing of the soil also disturbs the solid particles in it. Thus 
 stones and boulders work their way up through the soil to the 
 surface, producing constantly recurring stony surfaces, leading 
 sometimes to the belief that stones "grow." Foundation walls of 
 buildings which do not extend below the zone of freezing are like- 
 wise disturbed in this manner. 
 
 Moisture rising from the soil through capillary attraction may 
 freeze as it reaches the surface and so form ice crystals which push 
 upward by addition from below. These may be two or three inches 
 in length, and they will raise leaves, sticks and stones. 
 
 Where the soil is thin the water may freeze in the crevices of 
 the rock beneath the soil cover, and so shatter the rocks. This is 
 especially effective where moisture is abundant, and where there is 
 a frequent change of temperature from above to below the freezing 
 point. (On the depth of frost in the Arctic regions see Wood- 
 ward-45.) 
 
 Thermal Springs. Heated waters reaching the surface in the 
 

 TEMPERATURE OF THE HYDROSPHERE 201 
 
 form of hot springs either represent the meteoric waters, which, as 
 ground water, descended to sufficient depth to be heated to a high 
 temperature, or which by contact with unexposed igneous masses 
 became heated; or it is juvenile or magmatic water newly formed 
 and liberated from the molten rock. The temperatures of the hot 
 springs and geysers of Yellowstone National Park and of Iceland 
 have been regarded as due to the contact with igneous masses, 
 though Suess holds that they are due to the gaseous emanations of 
 lava masses lying at moderate depths below the surface, cooling to 
 a certain degree reducing them to the liquid state. Surface or 
 vadose waters may find access to these newly formed or juvenile 
 (magmatic) waters and so form a mixed product. 
 
 In non-volcanic countries the water probably comes from great 
 depths. This is believed to be the case with the Bakewell Buxton, 
 warm springs of England, which range in temperature from 60 to 
 82 F., and the three hot springs of Bath, which have a temperature 
 varying from 104 to 120, and yield an estimated quantity of about 
 half a million gallons daily. Prestwich estimates that the water 
 rises from a depth of about 3,500 feet. The Mountain Home hot 1 
 springs of Idaho have temperatures ranging from 103 to 167 F., 
 and Russell estimates that the depth at which this temperature would 
 be found in that region is about 5,000 feet below the surface. The 
 Hot Springs of Arkansas have a temperature ranging from 95 
 upward, and, if not magmatic, probably owe their temperature to 
 contact with young igneous rocks still hot. 
 
 In the Yellowstone Park there are more than 3,000 hot springs 
 and about 100 geysers. The geysers are intermittently eruptive hot 
 springs, throwing their waters into the air at intervals, sometimes to 
 a height of 200 feet or more. The eruption is believed, by those who 
 hold to the vadose origin of the waters, to be due to the superheat- 
 ing of a long column of water in a tube with hot walls. If this 
 results in the formation of steam in the lower part of the tube this 
 may lift the column, causing an overflow of the water at the top 
 and a corresponding relief of pressure. This permits a sudden 
 expansion of the superheated waters into steam on the relief of 
 pressure, and a consequent eruption of the entire mass. In the 
 change of the water to steam it expands about 1,700 times. (See 
 Hague-n.) (Fig. 31.) 
 
 MAGMATIC OR JUVENILE WATERS. The steam clouds accom- 
 panying volcanic eruptions, and formerly regarded as due to infiltra- 
 tion of surface or vadose waters into the volcanic regions, are now 
 held by many geologists to be the result of gaseous emanations from 
 the lava itself and their cooling and condensation into steam and 
 
2O2 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 FIG. 31. The Giant Geyser of the Yellowstone. (After Hayden.) 
 
 later water. Such waters are designated as juvenile or magmatic 
 waters. Suess holds that, instead of volcanoes being fed by infiltra- 
 tions from the sea (directly or indirectly), the sea receives additions 
 through each eruption. (38.) He believes that the oceans and the 
 whole body of vadose water were separated from the cooling litho- 
 
TEMPERATURE OF THE HYDROSPHERE 203 
 
 sphere, in the form of emanations. Tschermak, Reyer, de Lap- 
 parent, Kemp and others have actively, supported the view of the 
 importance of such magmatic waters, especially as causes in ore 
 deposition, a view advocated by lie de Beaumont before 1850. 
 (Kemp-iQ: 610-618 \ Lincoln-2i : 258-274.) Armand Gautier (9) 
 has shown that when powdered igneous rocks (granites, porphyries, 
 trachytes, gneisses, gabbros, etc.) are raised to a red heat in a 
 vacuum they give off water and gases among which hydrogen and 
 carbon dioxide predominate. This is 'not water taken in by the 
 rock, but water of constitution. The quantity of water lost at red 
 heat varies from 7 grams per kilogram in granite to nearly 17 
 grams per kilogram in Iherzolite. With the water is driven off 
 from 3 to 1 8 times its volume of gases which are only -in small part 
 included gases, being produced mainly by the action of the ferrous 
 salts in the rock upon vapor of water at a red heat. These gases 
 are similar to volcanic gases, being rich in free hydrogen and CO 2 . 
 The great eruption of Etna in 1865 supplied 11,000 metric tons of 
 water a day for 200 days, or a total of over 2,000,000 tons for this 
 critical period. A cubic kilometer of granite would furnish at red 
 heat, from 25 to 30 million tons of water, one-fourth of which would 
 be sufficient to supply a volume like that given out by Etna during 
 the whole eruption of 1865. "De Laumy estimates that the princi- 
 pal thermal springs of France discharge a total of 700,000 hecto- 
 liters of water in 24 hours. The water which issues from a single 
 cubic kilometer of granite raised to a temperature of 600 or 700 
 C. would suffice to keep all these springs running for a year with a 
 flow of 48,500 liters a minute." ( Gautier-o, : 692. ) Suess regards 
 the springs of Carlsbad, Bohemia, as having their source in 'mag- 
 matic emanations, and he also places the hot waters of Iceland and 
 the Yellowstone under this category. In fact, if we accept the con- 
 clusions of Kemp and others that the meteoric water is limited to 
 the upper 2,000 feet or less of the earth's crust, we are forced to 
 regard most thermal springs as newly originated or magmatic waters 
 emanating from a not too deeply buried igneous mass which has not 
 yet wholly expired. "Thermal springs," says Armand Gautier, 
 "may be explained as a kind of gentle distillation of crystalline 
 rocks in a region so hot that water of constitution tends to escape 
 upon a slight increase in temperature." (9-603.) The view is 
 also held to some extent by geologists that mineral veins owe their 
 origin to just such emanations, the magmatic waters carrying with 
 them in solution the mineral matter to be deposited in the fissures 
 penetrated by these waters. (See Kemp-i9 for summary of most 
 recent opinions; also Schneider~35 and Hague-n.) 
 
204 PRINCIPLES OF STRATIGRAPHY 
 
 OPTICS OF THE WATER. 
 
 Of the greatest importance to organisms living in the sea or in 
 fresh water is the depth to which sunlight penetrates. It is to this 
 depth only that chlorophyll-generating plant life occurs, which in 
 turn determines the depth to which animal life subsisting on it may 
 penetrate. Thus the Characea exist in Lake Geneva to depths of 
 25 m., while Hypnum lehmanie has been found as deep as 60 m. (a 
 single case.) Diatoms extend in summer to a depth of 20 m., in 
 winter to 80 m. 
 
 The transparency of water varies greatly. Thus in tropical seas 
 the animal and plant life can easily be seen at a depth of 20 meters 
 or more, while 45 meters has been recorded near the Philippine 
 Islands as a depth at which corals were still visible. A white plate 
 submerged by von Kotzebu in tropical waters of the North Pacific 
 was still visible at 50 meters, while Wilkes found that the depth at 
 which such an object became invisible varied in the same region 
 from 31 to 59 meters. Observations on the Gazelle showed that 
 the visibility depth of other colors was less than that of white, the 
 depth at which yellow disappeared being 88% of that at which white 
 disappeared, while for red it was 77% and for green 67%. Ex- 
 periments with submerged lights gave for the Lake of Geneva the 
 following results : 
 
 Depth 
 visible. 
 
 1. Moderator lamp with vegetable oil (July 18, 1884) ..41.3 m. 
 
 2. Edison lamp, 7 candle power (March 15, 1886) . . . .50.9111. 
 
 3. Arc light (August 8, 1885) 88.0 m. 
 
 tit 
 A small electric lamp of 8 candle power was submerged in the 
 
 Black Sea, where the depth was over 2,000 meters. The depth at 
 which the point of light disappeared varied from 3.7 m. to 40 m., 
 that at which the light disappeared entirely varied from 43 to 
 77 m., according to the locality. Measurements made by expos- 
 ing photographic plates at various depths showed that the influence 
 of the light still extended to 500 or 550 m. depth. From various 
 measurements it appears, however, that in the sea only the upper 
 300 meters receive light throughout the day, while at 350 meters 
 depth light is present for only 8 hours. 
 
 In fresh water the depths beyond which photographic plates are 
 no longer affected appear to be much less. Thus in Lake Geneva 
 F. A. Forel found that silver chloride plates were affected in sum- 
 
OPTICS OF THE WATER 205 
 
 mer to depths of 45 m. only after exposure for a full day, while in 
 winter the depth increased to no meters. Lake Constance (Boden- 
 see) gave a depth for the same phenomena of 30 m. in summer and 
 less than 50 m.. in winter. Sensitive plates coated with silver bro- 
 mide and exposed for a whole day in the Lake of Zurich were 
 affected to a depth of 100 meters in August, 1881, and in the 
 Walensee to a depth of 140 m. in October, 1891. In the Lake of 
 Geneva after 10 minutes' exposure Fol and Sarasin found in August 
 that the plates were faintly affected at 113 m. and not at all at 237 
 m. In September very faint results were shown at 170 m. and in 
 March, 1885, at 192 m., while at 235 m. no effect was obtained. 
 In the next year, however (March, 1886), slight results were ob- 
 tained at 240 m. From these facts Forel concludes that the limit 
 of light effect for silver bromide is between 200 and 240 meters, 
 varying with the season and the water body, while at the same 
 time the depth varies for different substances sensitive to light. 
 (S:i 34 .) 
 
 The recent work in the North Atlantic by the Michael Sars has 
 brought out some very interesting results. A series of measure- 
 ments of the intensity of the light at various depths was made, by 
 a photometer carrying panchromatic plates and gelatine color filters. 
 Near the Azores the light strongly affected the plates at 100 meters' 
 depth, the red rays being weakest and the blue and violet strongest. 
 At 500 meters the blue and violet rays still made distinct impres- 
 sions, the violet and ultra violet still affecting the plate at 1,000 
 meters. At 1,700 meters, however, not the faintest trace of light 
 effect occurred after 2 hours' exposure. Observations in several 
 latitudes showed equal intensity of light as follows : 
 
 In 33 N. lat. at about 800 meters depth. 
 In 50 N. lat. at about 500 meters depth. 
 In 67 N. lat. at about 200 meters depth. 
 
 These depths correspond to those which were found to be the 
 upper limit of the red pelagic crustaceans (Acanthephyra), as well 
 as that of certain black pelagic fish (Gastrostomus, Cyema) in the 
 same latitudes, so that these organisms are found only where during 
 the daytime the chemically effective rays from the violet portion 
 of the spectrum are alone active, or at depths where the red forms 
 are as invisible as the black ones. It is only at night that they 
 rise into the upper strata of the sea. (Hjort-i5; Murray and 
 
206 PRINCIPLES OF STRATIGRAPHY 
 
 BIBLIOGRAPHY IV 
 
 See Also References Under Chapters III and V. 
 
 . I. BERKEY, CHARLES P., and HYDE, JESSE E. 1911. Original Ice 
 Structures Preserved in Unconsolidated Rocks. Journal of Geology, 
 Vol. XIX, No. 3, pp. 223-231. 
 
 2. CHALLENGER REPORTS, PHYSICS AND CHEMISTRY, Vol. I. 
 
 3. CHAMBERLIN, THOMAS C., and SALISBURY, ROLLIN D. 1906. 
 
 Geology, Vol. I. 
 
 4. CLARKE, FRANK -W. 1908. Data of Geochemistry. United States 
 
 Geological Survey Bulletin, No. 330, Second Edition, Bulletin 491, 1911. 
 
 5. DUFOUR, LOUIS. 1873. Bulletin de la Societe Vaudoise. Sciences 
 
 Naturelles, XII, i. Lausanne. 
 
 6. EWING, A. L. 1885. An Attempt to Determine the Amount of Chemi- 
 
 cal Erosion, etc., in the Limestone Valley of Centre County, Pennsylvania. 
 American Journal of Science, 3rd series, Vol. XXIX, pp. 29-31. 
 
 7. FORCHHAMMER, GEORG. 1865. On the Composition of Sea-Water 
 
 in the Different Parts of the Ocean. Royal Society of London, Philosophi- 
 cal Transactions, Vol. CLV, No. 4, pp. 203-262. 
 
 8. FOREL, F. A. 1901. Handbuch der Seenkunde. Stuttgart. 
 
 9. GAUTIER, ARM AND. 1906. The Genesis of Thermal Waters and 
 
 Their Connection with Vulcanism. English Abstract by F. L. Ransome, 
 Economic Geology, Vol. I, No. 7. July-August. 
 
 10. GEIKIE, ARCHIBALD. 1903. Text Book of Geology, Fourth Edition, 
 
 Vol. I. 
 
 11. HAGUE, ARNOLD. 1912. Origin of Thermal Waters of Yellowstone. 
 
 Bulletin of the Geological Society of America, Vol. XXII, No. i, pp. 
 
 102-122. 
 
 12. HAN AM ANN, J. 1894. Archiv der Naturwissenschaftlichen Landes- 
 
 durchforschung von Bohmen, Prague. Vol. IX, No. 4; 1898, Vol. X, 
 No. 5. 
 
 13. HARRISON, J. B., and WILLIAMS, JOHN. 1897. The Proportions of 
 
 Chlorine and of Nitrogen as Nitric Acid and as Ammonia in Certain 
 Tropical Rainwaters. Journal of the American Chemical Society, Vol. 
 XIX, pp. 1-9. 
 
 14. HAYES, C. W. 1879. Solution of Silica under Atmospheric Conditions. 
 
 Bulletin of the Geological Society of America, Vol. VII, pp. 214-217. 
 
 15. HJORT, JOHN. 1911. The Michael Sars North Atlantic Deep-Sea 
 
 Expedition, 1910. Geographical Journal (London) April and May. 
 
 16. HUNT, T. STERRY, 1878. Chemical and Geological Essays. Second 
 
 Edition. 
 
 17. JULIEN, ALEXIS A. 1880. On the Geological Action of the Humus 
 
 Acids. Proceedings of the American Association for the Advancement 
 of Science, Vol. XXVIII, pp. 311-410. 
 
 1 8. KEMP, JAMES F. 1908. Waters Meteoric and Magmatic. Mining and 
 
 Scientific Proceedings, May 23, 1908. 
 
 19. KEMP, J. F. 1913. The Gound Waters. Transactions of the American 
 
 Institute of Mining Engineers. New York Meeting, Feb., 1913, pp. 
 603-624. 
 
 2 0. KRUMMEL, OTTO. 1907. Handbuch der Ozeanographie. Band I. 
 
BIBLIOGRAPHY IV 207 
 
 21. LINCOLN, F. C. 1907. Magmatic Emanations. Economic Geology, 
 
 Vol. II, No. 3, pp. 258-274. 
 
 22. MURRAY, SIR JOHN. 1887. On the Total Annual Rainfall on the Land 
 
 of the Globe, and the Relation of Rainfall to the Annual Discharge of 
 Rivers. Scottish Geographical Magazine, Vol. Ill, pp. 65-77. 
 
 23. MURRAY, SIR JOHN. 1899. On the Temperature of the Floor of the 
 
 Ocean and of the Surface Waters of the Ocean. Geographical Journal, 
 Vol. XIV, pp. 34-51, 3 maps. 
 
 24. MURRAY, SIR JOHN, and HJORT, JOHAN. 1912. The Depths of 
 
 the Ocean. Macmillan. 
 
 25. PALMER, CHASE. 1911. The Geochemical Interpretation of Water 
 
 Analyses. Bulletin 479 U. S. Geological Survey, 1911, 31 pp. 
 
 26. PENCK, ALBRECHT. 1894. Morphologic der Erdoberflache. Band I. 
 
 27. PETTERSSON, SVEN OTTO. 1883. On the Properties of Water and 
 
 Ice. Vega Expeditionens Vetenskapliga lakttagelser, Band II, Stock- 
 holm, pp. 247-323. 
 
 28. REGNARD, PAUL. 1891 Physique biologique: Recherches experimen- 
 
 tales sur les conditions physiques de la vie dans les eaux. Paris. 
 
 29. RUSSELL, ISRAEL COOK. 1882-83. A Geological Reconnaissance in 
 
 Southern Oregon. Fourth Annual Report of the L T nited States Geo- 
 logical Survey. 
 
 30. RUSSELL, I. C. 1885. Geological History of Lake Lahontan, a Quater- 
 
 nary Lake of Northwestern Nevada. Monograph United States Geo- 
 logical Survey, No. XI. 
 
 31. RUSSELL, I. C. 1890. Notes on the Surface Geology of Alaska, Bul- 
 
 letin of the Geological Society of America, Vol. I, pp. 99-162, pi. 2. 
 
 32. RUSSELL, I. C. 1895. Lakes of North America. Boston, Ginn and 
 
 Company. 
 
 33. RUSSELL, I. C. 1898. Rivers of North America. New York, Putnam. 
 
 34. SALISBURY, ROLLIN D. 1907. Physiography. Henry Holt. 
 
 35. SCHNEIDER, KARL. 1913. Beitrage zur Theorie der heissen Quellen. 
 
 Geologische Rundschau. Zeitschrift fur allgemeine Geologic, Band 
 IV, Heft 2, pp. 65-102. 
 
 36. SCHOTT, GERHARD. 1902. Die Verteilung des Salzgehalts im Ober- 
 
 flachenwasser der Ozeane. Petermanns' Mittheilungen., Vol. XLVIII, 
 
 pp. 217-218. 
 37- SCHOTT, GERHARD. 1912. Geographic des atlantischen Ozeans. 
 
 Hamburg, C. Boyson. 
 38. SUESS, EDUARD. 1902. Ueber heisse Quellen, Verhandlungen der 
 
 Gesellschaft Deutscher Naturforscher und Aerzte, allgemeiner Theil. 
 39- TOLMAN, CYRUS F. 1890-91. Carbon Dioxide of the Ocean and its 
 
 Relation to the Carbon Dioxide of the Atmosphere. Journal of Geology, 
 
 Vol. VII, pp. 585-620. 
 
 40. TYRRELL, J. BURR. 1893. Report on Northwestern Manitoba, with 
 
 portions of the adjacent districts of Assiniboia and Saskatchewan. Geol- 
 ogy and Natural History Survey of Canada, Annual Report, Vol. V, 
 new series, part i, Report E, 231 pp. 
 
 41. VAN HISE, CHARLES R. 1904. A Treatise on Metamorphism. 
 
 United States Geological Survey Monograph XLVII. 
 
 42. WALTHER, JOHANNES. 1893. Einleitung in die Geologic als his- 
 
 torische Wissenschaft. Jena. 
 
208 PRINCIPLES OF STRATIGRAPHY 
 
 43. WALTHER, JOHANNES. 1900. Das Gesetz der Wiistenbildung, First 
 
 Edition. Jena. 
 
 44. WALTHER, JOHANNES. 1912. Ibid. Second Edition. Leipzig. 
 
 45. WOODWARD, R. S. 1890. Communication on the Depth of Frost in 
 
 the Arctic. In Russell, Bulletin of the Geological Society of America, 
 f Vol. I, pp. 130-132. 
 
CHAPTER V. 
 
 MOVEMENTS OF THE HYDROSPHERE AND THEIR GEOLOGICAL 
 
 EFFECTS. 
 
 The movements of the hydrosphere are manifested in the waves, 
 the tides and seiches, the ocean and river currents, and the move- 
 ments of ground waters. The effects of these movements upon the 
 lithosphere are seen in mechanical erosion and the transportation 
 of eroded material, and to a less degree in chemical solution and 
 decomposition of the rock. Diminution or cessation of motion is 
 followed by the deposition of the material in suspension.- Deposi- 
 tion of material in solution at a distance from the source of origin 
 is a further result of the movements of water. The effect of the 
 motion upon the biosphere is shown by the increase in the supply 
 of oxygen in the water and the transportation of food. The dis- 
 tribution of organisms is also affected to a considerable degree by 
 the currents. 
 
 WAVES. 
 
 These are the undulatory motions of water produced by wind 
 blowing over its surface. In the open sea, the motion of the water 
 is an orbital one; the particles move in curves, and only the wave 
 form advances. The top of the wave is its crest, the bottom the 
 trough, the lines of both lying at right angles to the direction of the 
 wind. The distance from crest to crest is the wave length, which in 
 stormy weather in the open ocean varies between 60 and 150 meters 
 (200 and 500 feet). Swells may in some cases reach nearly twice 
 this length, however. The rapidity with which wave crests travel 
 is the velocity of the wave, which varies from 10 to 15 meters per 
 second (22 to 33.5 miles per hour, and may be as high as 60 miles 
 per hour). The time taken by a crest to travel a wave length is 
 the period of the wave, which in storm waves varies from 6 to 10 
 seconds or over. The vertical distance between the top of the crest 
 and the bottom of the trough is the height of the wave, and its mag- 
 nitude depends on the strength of the wind. In the open sea the 
 average height of the waves varies between 2 m. (6 l / 2 feet) and 5 
 
 209 
 
210 PRINCIPLES OF STRATIGRAPHY 
 
 meters (nearly i6j/2 feet), while storm waves may have a height of 
 30 feet or over (10-11.5 meters), reaching 50 feet (15+ meters) in 
 exceptional cases. On the shore the breaking wave or the surf 
 may be as high as 100 feet, or even higher. In mediterraneans the 
 waves are as a rule smaller than in the open ocean. In the Roman 
 mediterranean the maximum height is probably not over 5 meters 
 (16.38 feet). A height of 4 meters is regarded as the usual maxi- 
 mum for storm waves in the North Sea, though a maximum height 
 of 6 meters, a length of 45 meters, and a period of 9 seconds have 
 been reported. 
 
 The orbits in which the water particles of a given wave move 
 have a diameter corresponding to the height of the wave, while 
 the time required for the completion of the circuit by the water 
 
 FIG. 32. Diagrams to illustrate wave form, and its change with change in 
 size of orbit, strength of wind, etc. The heavy arrows indicate 
 the wind direction and the direction of wave-form advance. The 
 smaller (curved) arrows indicate the movements of the water par- 
 ticles. (Original.) 
 
 particle corresponds to the period of the wave. Thus when a par- 
 ticle has moved from the top of the orbit, where it forms a part of 
 the crest of the wave, to the bottom, a trough has replaced the crest, 
 the crest has moved half a wave length forward, or half the wave 
 period has been completed, corresponding to half the revolution of 
 the particle in its orbit. By the time the entire orbit has been 
 completed the wave crest has traversed the entire wave length ; the 
 period is completed. The length of a wave period varies ordinarily 
 for ocean waves from 5.8 to 9.5 seconds, corresponding to an 
 orbital velocity of i.i to 2.3 m. per second, and may sometimes 
 exceed 4 m. per second. The orbital velocity (v) is obtained from 
 
 the formula, v = , where h is the height of the wave (or 
 
 the diameter of the orbit) and r the wave period. ( = 
 3.14159265359+; 3.1416 approximately.) 
 
WAVES 2ii 
 
 The preceding diagrams represent these movements and the 
 resultant waves. (Fig. 32.) They show clearly the relation be- 
 tween the wave height and amplitude of the orbits, and that, with 
 the same wave length, the increase in the size of the orbit brings 
 about a corresponding increase in the height of the wave. At the 
 same time it will be noted that the crest becomes sharper, the slopes 
 being steeper and the angle more acute. If the velocity of the 
 moving particle remains the same with an increase in the size of the 
 orbit, the period must lengthen, because the particles have a longer 
 path to travel before they return to their starting point. If, on the 
 other hand, the period remains the same, or is shortened, giving 
 the same or greater velocity for the wave progress, the orbital 
 velocity of the particles must increase. This is also true when the 
 wave increases in height by an increase in the size of the orbit, as 
 is the case near shore. With the same size of orbit an increase in 
 the wave length brings about a reduction in the sharpness of the 
 crest. The change in wave length is brought about by a relative 
 change in the spacing of particles whose position in the orbit differs 
 by a uniform degree. Thus if, as in Fig. 32b, we have particles 
 selected from the wave surface revolving in immediately adjoining 
 orbits, of the size indicated and spaced so that they are just 45 
 apart, we have the wave length AB, and the form given in the 
 dotted line. This means that the velocity of the wind is such that it 
 not only produces the orbit shown, but also reaches and sets in 
 motion the second particle at the moment the first particle has com- 
 pleted y$ of its revolution. If, now, the velocity of the wind in- 
 creases, so that, when it reaches the next particle, the first one has 
 completed only 1/16 of its revolution, the wave length with the 
 same size orbit would become twice as great and correspondingly 
 flatter. But increased velocity of wind means an increase in the 
 size of the orbit, which in turn means an increase in the height of 
 the wave, and a sharpening of the crest. As the wave length in- 
 creases the period would lengthen correspondingly, since the dis- 
 tance to travel increases, unless the wave velocity also increases, 
 which means a great augmentation of the orbital velocity of the 
 moving particles. The period does increase in length, but not in 
 proportion to the increase in wave length. (See formula i, page 
 212.) Thus a wave with a length of 500 feet may have a period 
 of 10 seconds, which corresponds to a wave velocity of about 34 
 miles per hour. On increasing to 1,500 feet, the period will increase 
 to between 17 and 18 seconds, corresponding to a wave velocity of 
 about 56 miles per hour. If the wave velocity had remained the 
 same, the period would have been 30 seconds. The disproportional 
 
212 PRINCIPLES OF STRATIGRAPHY 
 
 increase in the length of the period, therefore, means an increase in 
 the orbital velocity, which, if the wave height also increases, must 
 increase still further.* 
 
 Wave velocity (Davis-i7 : 123} does not depend so much on 
 the orbital velocity as on the rate at which the crest position is 
 assumed by successive parts of the water, and this rate depends 
 chiefly on the depth to which orbital oscillations are felt in the 
 water body, so that the progress of the wave increases with the 
 increase in the depth affected. 
 
 * The following f ormula? copied from Krummel (42 : 0) serve to show the 
 relationship which exists between height and length of wave, its period, orbital 
 and translatory velocity in deep water. In all these: 
 
 r = radius of orbit of water particles. 
 
 h = half the wave height, i. e., its height above mean surface. 
 
 H = entire wave height (bottom of trough to top of crest). 
 
 v = orbital velocity of water particles in meters per second 
 
 Z = depth of water (in meters) from mean surface. 
 
 \ = wave length in meters. 
 
 c = translatory velocity or wave velocity (meters per second) 
 
 T = wave period in seconds. 
 
 if = 3.1416. 
 
 g = velocity of a free falling body at the end of the first second (9.81 m.). 
 
 I The relation between the period of the wave T and the wave length X 
 
 . / 2 7T 
 
 is T - V T 
 
 TI The relation between the wave velocity c and the period r is 
 
 2 IT 
 
 T = C 
 
 g 
 
 III The relation between wave velocity c and wave length X is 
 
 e , t -/~-\: 
 y TT 
 
 IV The relation between wave velocity and size (radius) of the orbit r is 
 
 c = \/g r 
 
 V The relation between wave period r and the radius of the orbit r is 
 
 = 27r v ~g 
 
 VI The relation between velocity c and period r is 
 
 " 27T 
 
 VII Given velocity or period the wave length is therefore 
 
 x== ^: c2or JL T2 
 
 g 2 7T 
 
 VIII The orbital velocity v is found according to the formula 
 
 h 
 v 
 
WAVES 
 
 213 
 
 The height of the waves increases until the resistance awak- 
 ened by the orbital motion throughout the mass of water affected, 
 balances the wind work on the surface. As increase in length 
 depends on the increase in the spacing of particles, i. e., the in- 
 crease in rapidity with which adjoining particles are affected, it is 
 seen that the wave length may increase even after the height no 
 longer increases. Thus while the height of hurricane waves or 
 great "seas" is seldom over thirty or forty feet and their length 
 perhaps 500 feet, the latter may increase to 1,500 feet, or three 
 times, while the height does not, or but rarely, reach 50 feet. The 
 velocity of such waves varies from 20 to 60 miles an hour, and their 
 period from 10 to 20 seconds. 
 
 The height of the waves depends not only on the strength of 
 the wind causing them, but also on the size of the water body, 
 especially the diameter of the surface along the path of the wind. 
 Wind velocity is greater over the open sea than along the coast or 
 inland, and this, together with their smaller size, makes the waves 
 of inland lakes less pronounced than those of the sea, and hence 
 lake shores suffer less erosion than the sea-coast. In a small water 
 body the wave height is proportional to the square root of its diam- 
 eter (Stevenson, Th.-68 '.358) . As soon as the wave height ex- 
 ceeds 0.8 m., it may be determine^ according to the following for- 
 mula (modified from Stevenson), when H is the wave height in 
 meters, d the diameter of the water body in kilometers (Penck- 
 $2:466): 
 
 H = H~3+ 0.8 -H~d 
 
 In the ocean the waves rise quickly to a height of 5 meters, but 
 also decrease rapidly, as soon as the wind producing them ceases. 
 The maximum height of waves in the open ocean, with a given 
 wind velocity, is shown in the following approximate table, ab- 
 stracted from Krummel (42:75). 
 
 Table shoiving relationships between wind velocities 
 and zvave height. 
 
 Wind velocity in 
 meters per second 
 (w). 
 
 i 
 
 2 
 
 3 
 
 4 
 
 5 
 
 10 
 
 15 
 
 20 
 
 25 
 
 30 
 
 40 
 
 Maximum height 
 of waves in me- 
 ters (Hm). 
 
 O.I 
 
 0-3 
 
 0.5 
 
 0.8 
 
 I.O 
 
 3-5 
 
 6-7 
 
 10.9 
 
 13-3 
 
 15-0 
 
 17.0 
 
214 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 With increase in the strength of the wind, the length of the 
 waves increases more rapidly than their height ; the former may 
 increase threefold before the latter is doubled. Lieutenant Paris 
 noted, east of the Cape of Good Hope, that during strong westerly 
 storms, extending over four days with remarkable uniformity, the 
 height of the waves rose only from 6 to 7 meters, while the length 
 increase threefold before the latter is doubled. Lieutenant Paris 
 
 i. e., changed from 18.84 to 33.57. 
 H 
 
 This increase in length 
 
 means an increase in the velocity of the wave, which may rise to 
 exceed that of the wind itself. The following table shows the 
 mean velocity of the waves compared with that of the wind in the 
 several oceanic bodies (Krummel-42 :8o) : 
 
 Table showing relationships between mean wave and wind velocities. 
 
 Mean Mean 
 
 velocity of velocity of 
 
 wind in waves in 
 
 meters per meters per 
 
 second second 
 
 Atlantic Trade Wind 5.9 11.2 
 
 South Atlantic West Wind 10.9 14.0 
 
 Indian Ocean West Wind 12 . 5 15.0 
 
 Indian Ocean Trade Wind . . . 7.0 12.6 
 
 Chinese Sea 11.3 11.4 
 
 West Pacific Region 8.2 12.4 
 
 Relation between Length and Height of Wave. This may be 
 
 expressed by the formula and varies greatly according to 
 
 H 
 
 the age of the waves. In young waves it may be 10 or less, i. e., 
 if the height of the waves is I meter its length would be 10 meters 
 
 As the wave grows the quotient increases until it 
 
 H 
 
 or less. 
 
 is 50 or over. The following classification of waves was made by 
 Paris ( Krummel-42 -.83 ): 
 
 Classification of waves. 
 
 Type of 
 
 Waves 
 
 Very 
 High Sea 
 
 High 
 Sea 
 
 Rough 
 Sea 
 
 Moder- 
 ate Sea 
 
 High 
 Swell 
 
 Ordinary 
 Swell 
 
 77 Mean 
 
 19. i 
 
 21 .O 
 
 21.6 
 
 38.7 
 
 20 T. 
 
 -72 S 
 
 rl 
 " Maximum 
 
 22. S 
 
 21. O 
 
 30. o 
 
 80.0 
 
 48.6 
 
 6-5 3 
 
 " Minimum 
 
 IS 4- 
 
 IS O 
 
 1^ 1 
 
 21 6 
 
 18 4. 
 
 1C -I 
 
 
 
 
 
 
 
 
WAVES 215 
 
 We have seen that the higher the wave with a given length, the 
 sharper the crest, or, what amounts to the same thing, the increase 
 of length without or with but moderate increase of height flattens 
 the crest, and this flattening lessens the destructiveness of the 
 waves in the open sea. In sharp-crested waves the crest water 
 "tends to roll forward faster than the front is built up, and this 
 tendency is increased by the forward brushing of the wind. Sharp 
 waves of moderate height break in 'white caps'; great seas gain 
 curling or combing crests, which capsize small boats and break 
 with dangerous force on the decks of large vessels." (Davis- 
 
 The Swell or Ground Swell. "Waves spread rapidly from the 
 gales in which they are formed. As they advance they decrease 
 in height, but retain length, velocity and period unchanged. Their 
 long, flat undulation is called 'swell.' [German, Diinung; French, 
 houle.] It may swing for thousands of miles across the ocean, 
 fading as it goes. The glassy water of calm weather in the equa- 
 torial 'doldrums' is always slowly heaving and sinking with passing 
 swells." (Davis-i"7: 124-5.} The swell or ground swell of great 
 hurricanes may break with destructive force on a coast a thousand 
 miles or more distant. Davis states that "landing in the harbor 
 of St. Helena is sometimes impossible on account of surf from 
 swell that originates in winter gales in the North Atlantic, thou- 
 sands of miles away." (126.) 
 
 Swells are much longer than true waves. The longest were 
 measured by the French Admiral Mottez in the Atlantic, just north 
 of the equator, and had a length of 824 meters (2,703.5 feet), a 
 period of 23 seconds, or a velocity of 35.8 m. (117.5 ^ eet P er sec ~ 
 ond). 
 
 On the coast of Ascension Island, Buchanan (6:234) observed 
 in March, 1886, a rhythmic breaking of the swell at intervals of 
 16 seconds, this being the period (T) of the swell wave. These 
 great "rollers" represented waves originating south of Newfound- 
 land, and their length after traveling this great distance is deter- 
 mined from their period to be 400 meters. At Bournemouth, on 
 the south coast of England, Dr. Cornish (10) found the mean 
 period of continuous series of 139 breakers to be 19.35 seconds, cor- 
 responding to a wave length of 585 meters. Breakers with periods 
 of 15 to 17 seconds are common at certain seasons of the year on 
 the Channel and the Atlantic coast of England and Ireland, where 
 they are known as "Death Waves" and regarded as indications of 
 coming storms. The origin of these waves is in the Gulf Stream 
 
2l6 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 region, where their period is probably not over 8 to 1 1 seconds, and 
 their length from 100 to 200 meters. 
 
 Depth of Wave Activity. The orbital radius of wave particles 
 in the open sea decreases downward in geometrical progression, so 
 that for each descent in depth equal to 1/9 of the wave length the 
 diameter of the orbit decreases by one-half. (Krummel-42 : 6.) 
 Thus: 
 
 For depths equal to 
 
 
 
 
 
 
 
 
 
 the following frac- 
 
 
 
 
 
 
 
 
 
 tions of the wave 
 
 
 
 
 
 
 
 
 
 length, X 
 
 o 
 
 1/9 
 
 2/9 
 
 3/9 
 
 4/9 
 
 5/9 
 
 8/9 
 
 9/9 
 
 
 
 
 
 
 
 
 
 
 The diameter of the 
 
 
 
 
 
 
 
 
 
 orbit (2 p) is equal 
 
 
 
 
 
 
 
 
 
 to the following 
 
 
 
 
 
 
 
 
 
 fraction of the wave 
 
 
 
 
 
 
 
 
 
 height (2h) ... . 
 
 i 
 
 1/2 
 
 i/4 
 
 1/8 
 
 1/16 
 
 1/32 
 
 1/256 
 
 1/512 
 
 
 
 
 
 
 
 
 
 
 be 
 
 At twice the depth of the wave length the orbital diameter will 
 part of the wave height at the surface. A wave of 90 
 
 ,144 
 
 meters in length and 3 m. high (a not uncommon size in the open 
 ocean, during strong winds) will show the following decrease of 
 the orbits in which the particles move. 
 
 Depth 
 
 o. 
 
 lorn. 
 
 20 m. 
 
 50 m. 
 
 100 m. 
 
 200 m. 
 
 Approximate size of 
 orbit (2 p) . 
 
 ^ m. 
 
 1.5 m. 
 
 0.75 m. 
 
 91.5 mm. 
 
 2.79 mm. 
 
 .002725 mm. 
 
 
 
 
 
 
 
 
 Thus with a wave length of 1,500 ft. and a height of 50 ft. the orbital 
 motion, which at the surface is 50 ft., will at a depth of 1500 ft. 
 be 50/512 ft. or 1.17 inches, while at a depth of 3,000 ft. (500 fathoms) 
 it is 50/262,144 ft. or 0.0023 of an inch, or 0.058 millimeter or 
 practically nothing. At 100 fathoms, a wave 600 feet in length on 
 the surface and with a height of 30 ft. (i. e. an orbital diameter 
 (2p) of 30 ft.) will be represented by orbital movements of 0.7 inch in 
 diameter. 
 
WAVES 217 
 
 The radius of the orbit p may be calculated according to the follow- 
 ing formula of Bertin (quoted by Krummel-42 :6) 
 
 O 7 
 
 he " A or log = 2 TT m 
 h A 
 
 where h is the half height of the waves (radius of orbit on surface) ; 
 e the basis of the natural logarithms (2.718); z the depth of water 
 in meters from the mean surface, A. the wave length and m the 
 modulus of the common system of logarithms (0.4342944819)^11^6 
 TT = 3.1416. 
 
 Waves in Shallow Water. "When waves run into shoaling 
 water their period remains unchanged, their height increases, and 
 their velocity and length decrease. The height increases because the 
 wave energy at any given point is spent upon a lessening depth of 
 water. The velocity decreases because the forward propagation 
 
 FIG. 33. Diagrams showing the change in the orbit described by the moving 
 particles of the waves as they approach the shore, and their direc- 
 tion of movement. (After Davis.) 
 
 of wave disturbance is slower in shallow than in deep water. The 
 wave length decreases because the forward waves are more re- 
 tarded than the following waves. The period is unchanged because, 
 at any given point, one wave is as much delayed in arrival as 
 another. 
 
 "On a steep-sloping beach the waves may wash up and down 
 without breaking; then the orbit is a narrow ellipse, much inclined 
 forward ; directly on the beach the orbit is practically a line coinci- 
 dent with the slope of the beach; and here the water rises as it 
 advances and falls as it recedes. This relation of rise and fall to 
 forward and backward motion is not found where the orbit is an 
 oval. If the orbit is a vertical ellipse, rise goes with the last half 
 of recession and the first half of advance; fall goes with the last 
 half of advance and the first half of recession." This is illustrated 
 by the "square frames" fitted to different forms of orbit in the 
 above diagrams (Fig. 33) given by Davis. 
 
 "On a gradually shoaling bottom, swell changes to surf or break- 
 ers close to shore. The height of the wave increases, its front 
 
218 PRINCIPLES OF STRATIGRAPHY 
 
 becomes steeper than its back, its crest curls forward and at last 
 plunges into the trough ahead of it, splashing and surging up the 
 beach. Just at the time of breaking, the water may be seen ascend- 
 ing in the concave front of the wave and curling forward at the 
 crest. Breaking is therefore the result of normal orbital move- 
 ment at a place where the water is so shallow that there is not 
 enough of it to build up the front of the wave." Davis thinks that 
 this is a more effective cause than the "drag" of the waves on the 
 bottom in shallow water, and their consequent retardation. 
 
 In general the critical point at which breaking of waves occurs 
 is found where the depth is equal to the height of the wave, or the 
 diameter of the orbit in which the water particles move. This is, 
 however, complicated by the ground swell over submerged banks, 
 such as the Dogger bank, the Newfoundland banks, the Agulhas 
 banks, etc., where the shoaling of the water results in the breaking 
 of waves over water several times deeper than the height of the 
 visible waves. Thus waves have been known to break in water 
 25 to 30 meters deep, on the north coast f Spain, in 48 meters 
 near Terceira, in the Azores; 46-57 meters off Punta Robanal, 
 North Spain, and at 84 meters on the Syrian coast. During heavy 
 tidal runs at Faira Island, north of the Orkneys, heavy surf was 
 found, according to Stevenson, in water 70 meters deep, and Airy 
 mentions surf on the outer margin of the "Grounds" at the mouth 
 of the English Channel where the water was 180 to 200 meters deep 
 (100 fathoms). Again heavier and shorter seas have been observed 
 over the Wyville Thomson ridge between Faroe and Scotland 
 than on either side of it, although the ridge culminates at a depth of 
 300 to 500 meters below the surface of the ocean. 
 
 On the Banks of Newfoundland the water is often stirred to 
 the bottom, although the depth is 50 meters and over. Heavy waves 
 breaking on the decks of the vessels in water 20 to 25 meters deep 
 often leave there sand stirred up from the bottom. The stirring up 
 of the bottom is also shown by the fact that the remains of Mya 
 truncata, which lives buried at a depth of 20 to 25 cm. in the sandy 
 bottom, are found in the stomachs of bottom-feeding fish, which 
 could have obtained them only after they were dug up by the 
 waves. 
 
 The sand and mud of the bottom of the North Sea is kept in 
 constant motion by the waves and the tides, so that no seaweeds 
 can become attached, except on the rocky cliffs of the coast. Meas-> 
 urements made in Lake Ontario showed that stirring of the sand 
 at the bottom by storm waves does not extend down to 20 feet. 
 Four empty boxes were anchored in the sloping sand bed of the 
 
WAVES 219 
 
 lake bottom "at equal distances over a length of 650 yards, in 
 depths .of 6 feet, 12 feet, 18 feet and 20 feet. After storms it was 
 found that the first box in the shallow water became filled with 
 sand; the box in 12 feet of water half-full; in the one at 18 feet 
 there was very little sand ; and at 20 feet there was no sand in the 
 box." (Wheeler-73: jo.) 
 
 In the open Atlantic ripple marks have been found at a depth 
 of 200 meters, but in the English Channel they occur only down to 
 depths of 40 meters, and to depths of 50 meters in the Roman 
 mediterranean. Off the Florida coast, too, Agassiz has noted dis- 
 turbances to a depth of 200 meters. 
 
 Destructive wave work, however, does not extend to such depths, 
 especially in the more protected water bodies. Thus submarine con- 
 structions in the Mediterranean scarcely suffer damage from storms 
 at a depth of 5 meters, and the coarse sand at the bottom of the 
 Bay of Biscay in less than 10 fathoms of water is scarcely dis- 
 turbed. (Delesse-2i.) A great oceanic swell may, on reaching 
 a coast, break more than once. The first surf line will occur at 
 about the point where the shoaling water becomes equal in depth to 
 the wave height. If this is far from shore the water mass, after 
 breaking, will roll forward as a wave of diminished height, and 
 this will break again where the further shoaling demands it, and 
 this may be repeated several times. The resultant piling up of 
 the waters on the coast will induce a strong seaward-tending bot- 
 tom current or undertow, which will carry the less heavy substances 
 out along the bottom. 
 
 The height to which a breaking wave may be thrown, or the 
 height of the surf, is sometimes surprising. Lighthouses and even 
 rock cliffs have been destroyed at a height of 100 feet above sea- 
 level. The lighthouse of Unst, the northernmost of the Shetland 
 Islands, which stands nearly 60 meters above sea-level, repeatedly 
 has had its windows broken by the high-dashing surf. "During 
 northeasterly gales the windows of the Dunnet Head lighthouse [on 
 the north coast of Caithness in Scotland], at a height of upwards 
 of 300 feet above high-water mark, are said to be sometimes broken 
 by stones swept up the cliffs by sheets of sea water, which then 
 deluge the building." (Geikie-26 : 561.) 
 
 The surf from the ground swell alone will, "even when no wind 
 is blowing, often cover the cliffs of North Scotland with sheets of 
 water and foam up to heights of 100 or even nearly 200 feet." 
 ( Geikie-26 :5<5/.) 
 
 As the waves advance on the shore, they tend to become more 
 and more nearly parallel to the shore line, mainly as a result of the 
 
220 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 differential decrease in velocity. Where the shore projects into 
 headlands or points, the energy from a considerable crest line is 
 C9ncentrated, resulting in intensive destructional work. In bays, 
 on the other hand, the energy of a small portion of the crest line is 
 stretched, as it were, over a broad area, and hence becomes rela- 
 tively weak. This is shown in Fig. 34, copied from Davis, where 
 the energy of the crest line D F is concentrated on d f, whereas 
 at A C only the energy of the short portion of the crest lying 
 between a c is felt. The bay head thus becomes a place of relative 
 safety for vessels and a region of slight erosion. 
 
 FIG. 34. Map showing concentration of energy from a considerable crest 
 line upon a narrow headland and its diffusion in the bay or 
 harbor. (After Davis.) 
 
 An on-shore wind produces a shoreward "drift" of the water 
 aside from the movement due to waves. The "undertow" is the 
 return current flowing outward at the bottom. This is, of course, 
 greatly increased during strong wave action. When the wave 
 strikes the shore obliquely, a movement parallel to the shore is inau- 
 gurated, and this is the longshore or littoral current, the chief 
 agent in the transportation of material along the shore. 
 
 Destructive Work of the Waves. Wherever the waves beat 
 upon a shore, erosional work of some kind is going on. If the 
 shore is sandy, the waves may only stir up the sand, which will then 
 be carried seaward by the undertow, or along the coast by the 
 
WAVE EROSION 221 
 
 longshore currents. The actual impact of the waves upon a sandy 
 or rocky shore produces comparatively little effect. By compress- 
 ing the air in the caves or joint cracks, completely closed by the 
 water, or by hydraulic pressure, the waves may succeed in ulti- 
 mately shattering the rocks or loosening large masses. The most 
 effective wave erosion work is, however, accomplished by hurling 
 pebbles and even boulders or ice blocks against the cliffs, and so 
 undermining them and by removing the pieces broken off by this 
 process, by frost action or otherwise. 
 
 The force of the waves in great storms is often surprising. 
 Measurements with a dynamometer made by Stevenson on the 
 north coast of Scotland gave a force of impact equal to about 
 3,000 kgm. per square meter in summer (611 Ib. per square foot), 
 and more than 10,000 kgm. per square meter in winter (2,086 Ib. 
 per square foot), while in exceptional storms the force may exceed 
 30,000 kgm. per square meter. "The greatest result yet obtained 
 at Skerryvore was during the heavy westerly gale of 2Qth of March, 
 1845, when a pressure of 6,083 Ibs. per square foot was registered. 
 The next highest is 5,323 Ibs." (Stevenson-67 1^5.) At Cher- 
 bourg, on the coast of France, and at Algiers, on the north coast of 
 Africa, similar measurements gave a force 3,000 to 3,500 kgm. to 
 the square meter, while at Civitavecchia, on the west coast of Italy, 
 a force of 16,000 kgm. per square meter has been obtained. 
 
 Observations on the transporting powers of waves are also avail- 
 able. Rock masses weighing 100 tons have been known to be 
 moved by the great waves of winter storms on the north British 
 coast. Many times blocks weighing five tons or over have been 
 torn from the ledges or from foundations and dragged many yards 
 by the waves. At Plymouth, during a severe storm in November, 
 1824, granite blocks up to 14,000 pounds were broken from the 
 harbor embankment, and pushed uphill in some cases for 60 yards. 
 
 "On more than one occasion at Plymouth during the construc- 
 tion of the breakwater large blocks of stone, some of them weigh- 
 ing 7 to 9 tons, were removed from the sea slope of the break- 
 water at the level of the low water, carried over the top a distance 
 of 138 feet, and piled up on the inside. In one night 200,000 tons 
 [British] of stones were thus removed; and on another occasion 
 9,000 tons." (Wheeler-73:/#.) At the Peterhead breakwater 
 waves 30 feet in height and 500 to 600 feet long have on three 
 occasions displaced blocks weighing over 40 tons each at levels 
 from 17 to 36 feet below tide, and at Cherbourg over 200 blocks 
 weighing each about 4 tons were lifted over the top of the break- 
 water, while blocks weighing over 12 tons were turned upside down. 
 
222 PRINCIPLES OF STRATIGRAPHY 
 
 Murchison and Stevenson noted in the Bound Skerries, the 
 eastern ramparts of the Shetland Islands, a gneiss block weighing 
 jy 2 tons at a height of about 7 meters above sea-level, which shortly 
 before, during a southerly storm, had been dragged over a ragged 
 surface from a position 22 meters nearer the sea, and at the same 
 elevation, by the waves which broke over these cliffs. The path 
 along which the boulder was dragged was clearly marked by the 
 splinters left by the way, and the block itself showed the marks 
 of the concussions during passage. Blocks from 6 to 13 tons in 
 weight were elsewhere seen to have been transported inland at a 
 height of 20 m. above the sea. The most noteworthy case on 
 record is, however, that of the dislocation of the breakwater in the 
 harbor of Wick in North Scotland by an unusually heavy eastern 
 storm in December, 1872. The depth of water in the bay is more 
 than 10 meters, while just outside it is over 30 meters. The break- 
 water consisted, above the foundation, of three large blocks, weigh- 
 ing 80 to 100 tons each, across which a huge concrete monolith 
 weighing over 800 tons was cast in situ, and firmly anchored to the 
 blocks by iron anchors. The total mass weighed 1,350 tons, and 
 yet this mass was torn from the foundations by the successive wave 
 impacts, and hurled into the inner harbor a distance of 10 to 15 
 meters, the monolith and the three foundation stones remaining 
 anchored together and being moved as a single mass. 
 
 Shingle has been thrown from the beach to the roadway, 18 feet 
 above high water, at Brighton, England, by southwest gales. Sir 
 John Coode found that "on one occasion . . . 3^4 million tons of 
 shingle had been torn down from the Chesil Bank and carried sea- 
 ward by the waves ; and on another occasion 4^2 million tons were 
 scoured out, three-fourths of which was removed back after the 
 gale ceased." (Wheeler-73 : 77.) On this same bank a laden 
 sloop of 100 tons burden became stranded during a heavy gale in 
 1824, and was cast to the top of the bank, where it was more than 
 30 feet above ordinary high water. "At Hove [England] it was 
 calculated that 27,000 tons of shingle were removed from the beach 
 in a heavy gale during one set of spring tides, and that 10,000 tons 
 were drifted along the beach in two tides on another occasion." 
 Entire shingle banks may be removed in a single storm. "In the 
 Solent, near Hurst Castle [England], a shingle bank two miles long 
 and 12 feet high, consisting principally of flints resting on a clay 
 base, was moved forward in a northeasterly direction 40 yards, 
 during a storm in 1824." (Wheeler-73 : 77.) 
 
 Rock fragments weighing from 10 to 150 Ibs. have been rolled 
 along the shore of Barnstable Bay, England, between Hartland 
 
WAVE EROSION 223 
 
 Point, a cliff of Carbonic rock, and Abbotsham, 12 miles distant; 
 the boulders have been rolled "for a distance of from 10 to 15 
 miles and piled up into banks of from 100 to 150 feet wide and 20 
 feet high, the top being from 6 to 9 feet above high water." 
 (Wheeler-7 3 :i;.) 
 
 The progress of wave erosion on a cliff of uniform exposure 
 depends in a large measure upon the relative hardness or resistance 
 of the rock in question. Unconsolidated material is readily re- 
 moved, even in sheltered places. Berkey (4) has estimated from 
 observations extending over a year that the cutting back of a cliff of 
 glacial sand and fine gravel near Port Jefferson, at the 'head of a 
 narrow enclosed bay on the north shore of Long Island, New 
 York, proceeds at the rate of 10 feet per hundred years. On the 
 exposed outer shore of Cape Cod, the unconsolidated glacial sands 
 and older clays are cut back at a rapid rate, as shown by the neces- 
 sity of repeated removal of the lighthouses at the three Nauset 
 Lights. 
 
 The Island of Sylt, on the west coast of Schleswig-Holstein, fur- 
 nishes an instructive example of rapid erosion. The sand dunes 
 which protected this island from the sea began to move eastward, 
 in the middle of the eighteenth century, and the sea followed. The 
 church of the village of Rantum had to be taken down, and in 
 thirty years the sand hills had passed the site, and the waves had 
 swallowed the foundations of the church. Fifty years later the 
 former site of the church was nearly 300 yards from the shore. 
 (Andresen-2.) 
 
 Many striking examples of the advance of the sea on a low 
 coast are recorded in the district of the Landes on the west coast of 
 France. This region between the Gironde and the mouth of the 
 Adour, is believed by many to be subsiding, while others hold the 
 advance of the sea as due to wave and current erosion entirely. 
 The retreat of the coast near the Garonne is estimated at not less 
 than 2 meters per year ; the lighthouse of Cordonan, -formerly situ- 
 ated on the coast, is at present separated from the mainland by an 
 inlet 7 kilometers in width. On many portions of the coast the 
 dunes are washed away by the constant advance of the sea. 
 
 On the south coast of the North Sea subsidence with encroach- 
 ment of the sea through erosion is abundantly illustrated. The 
 Zuidersee, originally a marsh, then a coastal lake, finally became an 
 arm of the sea, and is constantly increasing in depth, being navi- 
 gable to-day by much larger vessels than in the former centuries. 
 In many places the sea now covers sites of villages which flourished 
 thirty years ago. A structure built by the Romans under Caligula, 
 
224 PRINCIPLES OF STRATIGRAPHY 
 
 which sank into the sea anno 860, was discovered in the last cen- 
 tury at a distance of 4,710 meters off the west coast of Katwijk, in 
 south Holland, while the remains of another structure swallowed 
 earlier by the sea now lie at a distance of a mile from the coast. 
 The dunes at Gravenzande, north of the Meuse mouth, which in 
 1726 had a width of 640 meters, had been entirely removed by the 
 sea near the end of that century, making an average retreat of the 
 coast for this section of 10 meters per year. 
 
 On the west coast of Denmark, erosion of the coast proceeds at 
 a rapid rate, accompanied by subsidence. At Agger, near the west- 
 ern end of the Lumfjord, a strip of coast 141 meters in width dis- 
 appeared between the years 1815 and 1839, making an annual re- 
 treat of more than 5.6 meters. Even more extended was the loss be- 
 tween the years 1840 and 1857, during which time the sea devoured 
 a strip 157 meters broad, the coast thus retreating at a rate of 
 more than 9.4 meters per year. In many places along the coast of 
 the North Sea submarine forests are found, with many stems still 
 erect, while numerous structures built in historic times are now 
 beneath the water. 
 
 The cliffs of glacial sand, gravel and boulder clay which form 
 the coast of Yorkshire, England, for 36 miles from Flamborough 
 head to the mouth of the Humber furnish numerous examples of 
 rapid erosion by the sea. The process is generally a removal of 
 the loose material at the foot of the cliffs, by the waves, with a 
 partial undermining of the cliff, followed by the slipping of a large 
 mass into the sea. The cliff faces the opening of the Skagar 
 Rack on the opposite shore of the North Sea, 400 miles away, and 
 so is exposed to the full force of the waves of this turbulent epi- 
 continental sea during northeast gales. The ordinary rise of the 
 spring tides is 16 feet, the water reaching the foot of the cliff 
 throughout a great part of the length, in some places rising 2 to 3 
 feet above the foot. At low tide the beach is 150 to 300 yards 
 wide. "The waste of the cliff has been estimated at 2 miles since 
 the time of the Romans, a mile of which has gone since the Nor- ' 
 man Conquest." (Wheeler-73 : 222.) Phillips (54) and others 
 have estimated a loss of 2^ yards annually, equal to 30 acres a 
 year over the 36 miles of coast, the average height being taken at 
 40 feet. On one part of the coast a recession of 215 feet occurred 
 in the 37 years between 1852 and 1889, according to the estimates 
 of Captain Kenny, while Captain Salversen estimated the erosion 
 on 12 miles of the coast to be 132 feet in 40 years, or a loss of 204 
 acres. From the record of old maps it appears that whole town- 
 ships have been devoured by the sea, while others have lost churches, 
 
WAVE EROSION 225 
 
 houses and the greater part of their land. "Kilnsea church fell in 
 1826-36, and the village was removed. Nearly the whole of this 
 parish has been washed away during the last century. Aldborough 
 church is far out at sea and Thorpe parish has been reduced from 
 690 to 148 acres. Of Ravenser and Ravenserodd, once a seaport 
 town at the mouth of the Humber, not a vestige is left." ( Wheeler- 
 73 : 222.} Wheeler has estimated that the total quantity of material 
 falling from this cliff each year is 1,615,680 cubic yards, of which 
 969,408 cubic yards is alluvial matter carried away in suspension. 
 This occurs only for about two hours before and two hours after 
 high water of spring tides, or about four hours 260 tides a year. 
 Thus each tide would carry away about 3,728 cubic yards. (73 : 
 
 -) 
 
 The progress of erosion of steep rocky coasts is strikingly illus- 
 
 FIG. 35. Diagrammatic view of the Island of Helgoland (direction S. W. 
 by N. E.), showing the great erosion platform, especially in the 
 southwest side, where the beds dip into the island. The rock 
 is Bunter Sandstein) (Triassic) much faulted. (After Walther.) 
 
 trated by the numerous sea stacks found on nearly every coast, and 
 so familiar from the illustrations in the basaltic cliffs of Nova 
 Scotia, the chalk cliffs of Yorkshire and the Isle of Wight in Eng- 
 land, the Old Red Sandstone cliffs of North Britain, the Zechstein 
 cliffs of the Sunderland coast, the Buntsandstein of Helgoland, etc. 
 On these coasts the erosion is seen to progress at an almost visible 
 rate, changes in outline being perceptible often from year to year. 
 Perhaps the most noted example is the island of Helgoland, the 
 position of which, off the mouth of the Elbe, makes it such an 
 important strategic possession for the German Empire that they 
 obtained it in 1890 from England by relinquishing Zanzibar. In 
 1570 this island extended eastward across the present dune, where 
 it formed the Wittecliff of Muschelkalk, which had the height of 
 the present Helgoland. Destruction of these limestone banks by 
 the Helgolanders made it possible for the great flood of 1712 to 
 separate the entire mass of Muschelkalk and chalk from the main 
 mass of Helgoland. In the nineteenth century the last remnant of 
 this mass was a little island covered by dunes, which was threat- 
 
226 PRINCIPLES OF STRATIGRAPHY 
 
 ened with complete destruction by the great storm flood of Christ- 
 mas, 1894, and is at present protected from the waves by artificial 
 constructions. (Fig. 35.) 
 
 Rounding and Sorting of Detritus by Wave Action. Wave work 
 on sand grains is limited to those of larger size*. Shaler (63) has 
 called attention to the fact that between the smaller grains of sand 
 on the beach a cushion of water exists, due to capillary attraction, 
 and that to this the wet beach sand owes its firmness. It is this 
 cushion of water which prevents the sand grains from rubbing 
 against each other, and thus the finer grains remain angular. Ex- 
 periments by Daubree (16:256) showed that granules o.i mm. in 
 diameter will float in feebly agitated water, and that hence grains 
 of this size and less could not be mechanically rounded by water. 
 Destructible material, such as feldspar grains, is slowly eliminated 
 in wave-churned sands. On the shores of eastern Moray the sands 
 contained only 10 per cent, of feldspar, whereas, at the river mouths 
 which furnished the sands, 18 per cent, of feldspar grains is still 
 found. The rounding, purity and assortment according to size is 
 never as great as in the case of wind-blown sand, but probably in 
 most cases better than river sands. (See the tables and discussion 
 on p. 256.) 
 
 Pure sands, i. e., sands consisting of one mineral generally 
 quartz are sometimes found on the seashore, though, as a rule, 
 other minerals are present. An unusually pure beach sand is found 
 at West Palm Beach, on the Atlantic coast of Florida, nearly every- 
 thing but quartz being eliminated. The grains are, however, 
 mostly subangular, though the material has been transported for 
 many miles along shore from the Piedmont region to the north. 
 Shaler (63) calls attention to the fact that these sands, though some- 
 what rounded, are not much smaller than those in the region of 
 that coast about Cape Hatteras, whence they come. 
 
 Large rock fragments, on the other hand, are rapidly rounded 
 by the waves. At Cape Ann, cubes of granites of a kind which 
 forms excellent blocks for paving city streets are worn by the surf 
 in the course of a year to spheroidal forms, with an average loss of 
 more than an inch from their peripheries (Shaler-63 : 208), while 
 fragments of hard-burned bricks are reduced to half their size by 
 a year of moderate beach-wearing. 
 
 TIDES. 
 
 Tides are the periodic rise and fall of the ocean waters, due to 
 combined attraction of sun and moon, and occur twice in every 
 
TIDES 227 
 
 24 hours and 52 minutes. At flood tide the water is high, at ebb 
 tide, low. Twice each month, at new moon and at full moon, the 
 tides are exceptionally high, owing to the relative position of sun 
 and moon at these times, when they exert a combined influence of 
 the same character upon the waters. Such tides are called Spring 
 Tides. Twice a month also, at the period of first quarter and last 
 quarter of the moon, the interval between high and low water is at 
 its lowest, since at such times the moon and sun act in contrary 
 direction upon the waters, each tending to neutralize the force of 
 attraction of the other. This constitutes the Neap Tides. 
 
 In the open ocean the rise is estimated to be 2 or 3 feet, but 
 along coasts this is generally greatly increased. This is especially 
 the case where the water is crowded into narrowing bays, as illus- 
 trated by the Bay of Fundy, a funnel sea, with the highest known 
 tides of the world. The mouth of this bay is 48 miles wide and 
 its depth at this point from 70 to no fathoms. The bottom rises 
 at the rate of 4 feet per mile for 145 miles, when the head of the 
 bay is reached. Near the mouth the spring tides vary from 12 to 
 1 8 feet, while at its head, in Cobequid Bay, the range is as high 
 as 53 feet, that of the neap tide being 31 feet. The tide runs up 
 the Petit-Codiac River from the head of the bay, presenting a more 
 or less perpendicular wall. This is the tidal bore which is seen in a 
 number of rivers, such as the Severn and the Wye of England, the 
 Seine of France, the Hugh of India, and the Tsien-Tang of 
 China, where it is sometimes 25 feet high and very destructive. 
 According to the observations of Captain Moor, ij4 million tons 
 of water rushed past a point in the river in a minute. Up river 
 the tides are often felt for a considerable distance. Thus its influ- 
 ence is felt up the Hudson as far as Troy, New York, up the 
 Delaware nearly to Trenton, and 70 miles up the St. John's River 
 in New Brunswick, where it is felt at an elevation of 14 feet above 
 mean sea-level. The salt water does not actually run up the 
 rivers to the distances mentioned, the waters of the Hudson, for 
 example, being fresh above Poughkeepsie. The tidal influence is 
 felt rather in a backing up of the river water, which is of course 
 accompanied by a checking of the current, a condition favoring the 
 deposition of material held in suspension. 
 
 Where tides pass through narrow channels, tidal currents or 
 races are produced, which are generally effective agents in scouring 
 the channels or preventing deposition. Where bars or other obstruc- 
 tions retard the entrance of the tide into a narrow bay or estuary, 
 it may not reach its full height before the setting in of ebb tide, 
 and thus the rise and fall will be less than on the unprotected shore. 
 
228 PRINCIPLES OF STRATIGRAPHY 
 
 The removal of such a bar would cause a greater rise and fall of 
 the tide on the shores of the bay, and so produce the appearance of 
 subsidence of the land. Johnson (35; 37) has used this explana- 
 tion to account for many apparent indications of recent subsidence 
 along the Atlantic and other shores. 
 
 Comparison of Tides and Waves. Tides may be regarded as 
 huge waves sweeping successively around the earth from east to 
 west, their theoretical period being a* little over 12 hours and 26 
 minutes. If lines were drawn connecting the points which have 
 the same high tide at the same moment, these cotidal lines would 
 mark the crests of the tide waves. Normally there would be two 
 such cotidal crest lines on opposite sides of the earth, and between 
 them would be the cotidal trough line. If the earth were covered 
 by a universal ocean of uniform depth, the cotidal lines would be 
 great circles, and the period of the tide waves would be exactly 12 
 hours and 26 minutes. The velocity at the equator would be equal 
 to that of the rotation of the earth, and is approached by the tides 
 of the deep and open sea. The continents, however, greatly inter- 
 fere with this movement of the tides, and this is especially the case 
 in bays or funnel seas, where we have not only an increase in the 
 height of the wave, but also a change in interval between high and 
 low water, or between the crest and trough of the wave. As the 
 bay na'rrows, low water occurs nearer the following than the 
 preceding high tide, the rise being more rapid than the fall. In 
 some estuaries the duration of rise is to the duration of fall as one 
 is to ten or twenty. In such cases we have the production of the 
 tidal bore already mentioned, the water rushing up the estuary as a 
 visible wall of water with a speed of ten or more miles per hour. 
 
 The tidal currents (flood and ebb) likewise- suffer a striking 
 change. In the ocean "the flood begins three hours and six minutes 
 before high water, attains its greatest velocity at high water, and 
 ceases three hours and six minutes later." (Davis-i?: J^p.) Like- 
 wise, in the ebb tide, slack water occurs at mid-interval between 
 high and low tides. This is illustrated by the tides in the center of 
 the English Channel, where the current flows up the channel (toward 
 Dover) for three hours before high tide, and down the channel for 
 three hours after. This phenomenon is understood when we com- 
 pare the movement of the waters of the tidal wave with that of 
 the ordinary wave. Rise and fall of the tide is brought about by 
 the vertical component of the orbital movement of the water, while 
 the back and forward currents are due to the horizontal compo- 
 nent. The change in the latter occurs at mid-tide, which is the 
 period of slack water. 
 
TIDES 229 
 
 The conformation of the coast line and the relation of the tidal 
 wave to it modify this interrelation of current and tide. Thus at 
 the mouth of the Elbe, at Cuxhaven, the reversal of the current 
 occurs i hour and 30 minutes after low water, and i hour and 25 
 minutes after high water. Thus during the first hour and a half 
 of falling tide a current still runs up the Elbe, and during the 
 same interval of rising tide the current still runs down. On Lon- 
 don Bridge one may observe that in the center of the Thames the 
 current still runs up stream, even after the water has fallen 2 feet, 
 while at the mouth of the Thames, at the Mouse lightship, the re- 
 versal of the current occurs 2 hours after high and low water. 
 
 At the heads of small bays, and on shores where the tide comes 
 on broadside, slack water agrees with high and low tides ; all the 
 rising tide having a flood current, all the falling tide an ebb current. 
 This is, however, not the case when the tide progresses obliquely 
 along the shore. 
 
 Interference of Tides. In bays or channels open in two direc- 
 tions, remarkable interferences may occur by the meeting of high 
 and low tides or by cross tides. "At New York high tide entering 
 from the harbor reaches the rocky narrows of Hell Gate when a 
 low tide arrives through Long Island Sound, and six hours later a 
 low tide from the harbor meets a high tide from the Sound." 
 (Davis-i8:#7.) This produces a rapid back and forth flowing 
 current or tidal race, which made this passage a dangerous one to 
 vessels until the channel was widened by blasting away the rocks. 
 
 Even more complicated interferences occur in the English Chan- 
 nel, especially near the Dover Straits, where the tides from the 
 Atlantic and the North Sea meet, with the production of the famil- 
 iar strong series of currents and waves. In the Irish Sea the meet- 
 ing of two tides of equal height from opposite directions, and with 
 a difference of phase of 12 hours, produces excessive tides (5 to 7 
 meters), but, owing to the direct opposition of movements of the 
 two tidal streams, complete slack water results, as is the case at 
 the Isle of Man. When, on the other hand, the phase difference is 
 6 hours, no rise or fall of the tide will occur, since a crest ap- 
 proaching, say, from the right, balances a trough approaching from 
 the left. In both the movement is to the left, that of the crest 
 being forward and that of the trough being backward, and so a 
 current of double strength will alternately flow in the one and the 
 other direction, slack water being halfway between high and low 
 water time. 
 
 Where the waters are crowded in narrow channels, as between 
 islands or headlands, the tidal stream likewise becomes greatly 
 
230 PRINCIPLES OF STRATIGRAPHY 
 
 strengthened. Between the cliffs of the Pentland fjord the tidal 
 stream known as the Roost has a velocity of 10 to n knots, and 
 even steamers which have a speed of more than n knots avoid 
 steaming against this stream when the wind favors it. Between the 
 Orkneys and the north coast of Scotland, tidal streams of 8 to 10 
 knots are normal during spring tides. In such tidal races irregu- 
 larities of the coast will produce whirlpools such as the one off 
 Mosken and Varo, among the Lofoten Islands, famous for centuries 
 as the "Maelstrom" ; or the even more dangerous "Saltstrom" at 
 the mouth of the Saltenfjord on the Norwegian mainland oppo- 
 site. The whirlpool known since the days of Homer as the 
 Charybdis, in the Straits of Messina, and the fainter but equally 
 noted maelstroms at Scilla, on the Italian coast of the Straits, owe 
 their peculiarities to the meeting in the narrow passage of the tides 
 from the Tyrrhenian and Ionian seas, which have a phase differ- 
 ence of 6 hours, and thus high water approaches from one and low 
 water from the other side, the differences being adjusted by the 
 strong currents generated which change in direction every six 
 hours. Owing to the conformation of the borders and bottom of 
 the passage, strong whirls of water are produced, which bring the 
 colder and more saline waters from the deeper parts and with it 
 deep water organisms, such as the larval form of the eel, etc. 
 
 Tidal currents extend to much greater depth than that reached 
 by wave motion. North of the Dogger bank, in water 73 meters 
 deep, the maximum tidal current in the upper 10 meters of water, 
 measured at intervals of six hours, was 15.9, 20.4 and 20.1 cm. per 
 second, and in 70 meters' depth or 3 meters above the bottom, the 
 corresponding velocities were 8.9, 13.2 and 10.2 cm. per second. 
 The tidal wave in this case was not over i meter high ; deep water 
 waves of this height would be imperceptible at a depth of 70 
 meters, while the tidal stream still retained 56, 65 and 51 per cent, 
 respectively, of its surface velocity. 
 
 Tides and tidal streams are not as pronounced in the mediter- 
 raneans as in the open sea, and this difference becomes emphasized 
 when the outlet of the mediterranean is narrow, as in the case of 
 the Straits of Gibraltar. The Gulf of Mexico (Mexican mediter- 
 ranean), with a wider opening, still illustrates this phenomenon, the 
 range of the tide at Galveston, Texas, being less than i foot. 
 
 Tides independent of the Atlantic tides and more nearly com- 
 parable to the seiches in lake basins also occur. In still more 
 enclosed basins, as in the Black Sea, tides are wanting altogether. 
 In large lakes a periodic rise and fall of the water of slight extent 
 has been observed and compared with the tides. These lake tides 
 
MARINE CURRENTS 231 
 
 are very small, that of Lake Michigan, for example, having an 
 interval of only 2 inches. More irregular oscillations of the entire 
 water body of lakes are found in the seiches, which are due to 
 some disturbance of the water as a whole, as in the case of sudden 
 barometric changes, .in storms, etc., and may be compared to the 
 oscillation of the water in a basin which has been lifted on one side 
 and suddenly dropped. Such oscillations will continue for some 
 time after the cessation of the disturbing force. 
 
 Tidal Scour and Transportation. Wherever the tide passes 
 through a narrow channel so as to produce a race, considerable 
 scouring of the bottom results. Thus the tidal stream channels in 
 salt marshes are kept open by this tidal scour, and not infrequently 
 harbors are benefited by such scour. Transportation of sand and 
 mud by tidal currents is often extensive. Sand grains i/ioo inch 
 (about 0.25 mm.) will be moved in a state of semisuspension by 
 tidal currents of 3 or 4 knots. The movement is, however, princi- 
 pally a forward, backward movement, the sands carried away by 
 ebb tide being brought back during flood. This is illustrated by 
 the case of a vessel which sank at the mouth of the Gironde, 
 opposite Verdun, where she rested on her keel at the bottom of the 
 channel in 6 fathoms of water at low tide. "At the end of the ebb 
 tide the sand was so scoured as to leave a space under the keel at 
 both ends, leaving the hull only supported in the middle; at the 
 end of the flood tide the vessel was again completely buried in the 
 sand, the sand bed extending- 100 yards fore and aft of the vessel 
 and 50 yards from each side." (Partiot~5o and Wheeler-73 :i6.) 
 
 MARINE CURRENTS.* 
 
 CURRENTS OF THE OCEANS. Ocean currents are due to a com- 
 bination of causes, which may be classed either as primary or as 
 secondary stream constituents. The primary causes are the active 
 producers of the currents, and as such may be noted (i) internal 
 or endogenetic causes, existing within the water itself, such as 
 local differences in density, due to variation in temperature and 
 salinity under the influence of varying sunshine, evaporation, rain- 
 fall, or melting of snow and ice; (2) external or exogenetic causes, 
 such as variation in air pressure, and especially the winds. Among 
 the secondary causes which act chiefly in modifying the current 
 may be noted, I, friction, 2, the rotation of the earth on its axis,f and 
 
 * In this section I have followed Krummel closely. 
 
 f This operates to deflect all moving particles on the surface of the Northern 
 Hemisphere to the right, and to the left in the Southern. 
 
232 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 3, the configuration of the basins. It is this latter, i. e., the presence 
 of continental masses .in the path of the currents, which causes a 
 piling up of the waters on the coast against which it is driven by 
 the primary causes, and a potential depression of the surface from 
 which it flows away. In the one case, then, .the heaped-up water 
 must flow away, and in the other compensating streams originate, 
 drawing the water into the space whence removal has taken place. 
 In a symmetrical ocean reaching from pole to pole and covering 
 
 80 
 
 FIG. 36. Schematic representation of ocean currents in an ideal ocean. (After 
 Kriimmel.) 
 
 a meridional distance of 90, we would have a symmetrical ar- 
 rangement of currents as shown in the annexed diagram repro- 
 duced from Krummel (Fig. 36). On both sides 'of the equator, 
 at 10 north and south latitudes, the equatorial streams would flow 
 westward and on approaching the western shores, bending respec- 
 tively northward and southward and crossing eastward again in 
 50 north and south latitude, would approach the equator again 
 along the eastern border of the sea, thus constituting the principal 
 north and south circulation. Between the equatorial currents set- 
 ting westward is an. eastward-setting equatorial counter current, 
 
OCEAN CURRENTS 233 
 
 while two polar currents also exist, each flowing westward and 
 forming a complete circulation with the eastward-flowing northern 
 arm of the main circulation. The configurations of the lands are 
 largely responsible for the course of the currents in the different 
 oceans. Broadly outlined, the currents of the several oceans and 
 its main dependencies are as follows : 
 
 The Atlantic Ocean. The North Equatorial current is somewhat 
 variable in its position, its southern border ranging from 6 north 
 latitude in March to 12 north latitude in September, and with an 
 average velocity of 15 to 17 nautical miles per day, or from 32 to 
 36.5 cm. per second, 1.15 to 1.3 km. per hour,* the maximum 
 rising to 2.4 km. per hour or over. The direction of this current 
 is west-southwest to west, east of longitude 35, then turns due 
 west and becomes west-northwest at the Lesser Antilles. 
 
 The South or principal Equatorial current is of a very constant 
 character, and crosses the equator diagonally. Its southward ex- 
 tent is near 15 south latitude, while its northern border is already 
 i north latitude in the meridian of Greenwich during the winter 
 and spring months. Its average velocity in June, July and August is 
 20 to 24 nautical miles in 24 hours, or from 1.58 to 1.85 km. or 
 more per hour, while velocities as high as 72 nautical miles per 24 
 hours (5.55 kilometers per hour) occur. The current divides at 
 Cape St. Roque, the eastern point of South America, one arm 
 passing southward to become 'the Brazil current and the other 
 uniting with the North Equatorial current to produce the Guiana 
 current, which later becomes the Gulf Stream. The velocity of 
 this northern arm near Cape St. Roque is not infrequently from 
 30 to 60 nautical miles per 24 hours (2.3 to 4.6 kilometers per 
 hour). The Guiana stream is continued as the Caribbean stream, 
 with a velocity of 24 to 72 nautical miles per day (1.85 to 5.55 
 km. per hour). It here becomes a veritable sea in motion rather 
 than a single stream. In the Gulf of Mexico it bends eastward and 
 leaves between Florida and Cuba as the warm Gulf Stream, flowing 
 at first eastward, then turning northward between Florida and the 
 Bahama banks, and then crosses the North Atlantic as the Gulf 
 Stream or West-wind drift. At the Florida Straits the average 
 annual velocity is 72 nautical miles per day (5.55 km. per hour), 
 
 * The nautical or geographic mile (Seemeile) as defined by the United States 
 Coast Survey is "equal to one-sixtieth part of the length of a degree on the 
 great circle of a sphere whose surface is equal to the surface of the earth." This 
 makes the value of a nautical mile 6,080.27 ft. or 1,853.248 meters. The Brit- 
 ish admiralty knot is 6,080 ft. The German Seemeile, in terms of which the 
 following measurements are given, is equal to 1.852016 km. or 6079.55 ft. 
 
234 PRINCIPLES OF STRATIGRAPHY 
 
 but rises to 100 or 120 nautical miles in the colder and warmer 
 seasons, i. e., 1.5 to 2.5 meters per second, a velocity which com- 
 pares favorably with that of many great rivers in their lower 
 reaches during high water. 
 
 The western border of the Gulf Stream follows pretty closely 
 the edge of the continental shelf and remains more or less sharply 
 defined. It is often abruptly outlined by the rising of a wall of 
 cold water, the temperature of which in different seasons is from 
 10 to 20 lower than that of the Florida stream. This so-called 
 "cold wall" is an effective barrier to migration, and its displace- 
 ment by strong winds brings about anomalous bionomic results. 
 Eastward the current widens from 30 nautical miles in the straits 
 to twice that at Cape Canaveral, and becoming from 120 to 150 
 nautical miles wide opposite Charleston. It constantly increases 
 northward. Southeast of New York the average velocity has be- 
 come reduced to from 30 to 48 nautical miles per day, though some- 
 times it rises to 72 nautical miles. The stream as such cannot 
 be traced beyond the meridian of the eastern border of the Great 
 Newfoundland banks, before reaching which it already begins to 
 break up into a series of separate streams of varying temperature. 
 The velocity of the West-wind drift becomes reduced to an average 
 of 12 or 15 nautical miles in mid-ocean, though as much as 4$ 
 nautical miles per day has been observed. The well-known mild 
 temperatures of the British Isles, especially Ireland, where flowers 
 bloom in January, though the latitude is that of Labrador, are due 
 to the impingement against the coast of a branch of this warm 
 West-wind drift. Dividing on the British co^st, both arms of this 
 branch enter the North Sea, one by way of the English Channel 
 and Dover Straits, and the other around the north coast, the Hebri- 
 des and Orkneys, while sending a third arm along the Norwegian 
 coast. A large part of the West-wind drift or "Irish Stream," 
 however, turns northward to Iceland, passing to the west of the 
 Faroe Islands and turning westward and southwestward as the 
 Irminger current, running parallel to the cold East Greenland 
 current and sending a branch around Cape Farewell into Davis 
 Straits. Throughout this course the velocity of the current is prob- 
 ably less than 21 cm. per second. From the west coast of Davis 
 Straits the cold southward-flowing Labrador current runs past the 
 Newfoundland coast and the eastern border of the Grand Banks 
 and disappears on reaching the Gulf Stream. This disappearance 
 has been regarded as due to a "swallowing" of the cold water by 
 the warm, or to a submergence of the cold beneath the warm, but 
 is probably due rather to dispersal as suggested by Krummel. Part 
 
OCEAN CURRENTS 235 
 
 of the cold water passes westward and southwestward into the 
 St. Lawrence Gulf and Cabot Straits, and bathes the eastern coast 
 of the United States to Cape Cod (Cabot current). It is probably 
 recognizable in the "cold wall" bordering the Florida current. An- 
 other part turns eastward and even northeastward, occasionally 
 carrying iceberg fragments to the North British coast. 
 
 The southern arm of the West-wind drift forms the Canary 
 current, which flows southward between Madeira and the Cape 
 Verde Islands, to join the North Equatorial current. Flowing from 
 higher to lower latitudes, it is a relatively cool current, varying in 
 velocity from 8 to 30 nautical miles per day (0.62 to 2.3 km. per 
 hour). 
 
 The Equatorial Counter current of the Atlantic is especially well 
 developed off the African coast, where it is known as the Guinea 
 current. Its position varies with the seasons, but it is always a 
 warm current. It is not traceable over the entire mid-Atlantic, 
 being formed by recurring branches of the two equatorial currents. 
 In March its western end lies near 25 west latitude, and in Sep- 
 tember near 40 west latitude, and in other months it lies between 
 these. It broadens westward, gaining an average velocity of per- 
 haps 1 8 nautical miles per day, though velocities as high as 40 or 50 
 may occur, while at Cape Palmas a velocity of 85 nautical miles per 
 day has been recorded. Owing to the conformation of the West 
 African coast, an arm of the Guinea current is deflected northward, 
 though its main mass enters the Gulf of Guinea. This is especially 
 the case in the summer months. 
 
 In the South Atlantic the principal warm stream is the Brazil 
 current, which follows the South American coast to latitude 49 or 
 50, before reaching which it has turned eastward and united with 
 the cold Cape Horn current, forming .the South Atlantic connecting 
 current, which varies in velocity between 6 and 33 nautical miles 
 per 24 hours. The northern part of this connecting stream has a 
 higher temperature than the southern, as is to be expected from 
 the double origin of this current. An arm of the Cape Horn cur- 
 rent turns northward along the Patagonian coast, forming the cold 
 Falkland current, which is always at least 3 to 4 cooler than the 
 neighboring Brazil current. 
 
 Where the cold West-wind drift of the South Atlantic meets the 
 West African coast, it turns northward and becomes the cold 
 Benguelan current, with a velocity of generally more than 12, but 
 seldom more than 30, nautical miles per day, a velocity sufficient 
 to deflect the red-brown water of the Congo northward and cause 
 the floating mangrove islands and tree trunks furnished by this 
 
236 PRINCIPLES OF STRATIGRAPHY 
 
 stream to be carried northeastward, far out into the Atlantic. Of 
 the two great current rings thus formed in the Atlantic, that of the 
 Nprth Atlantic turns clockwise, that of the South Atlantic counter 
 clockwise. The areas enclosed by them are relatively free from 
 currents, both air and water, and mark a region of high air pressure. 
 The northern is filled with the floating seaweed forming the Sar- 
 gasso Sea, while the southern is relatively free from accumulated 
 drift material. Transportation of floating material (plankton) 
 from one circle to the other occurs sometimes, but generally these 
 circles remain distinct. 
 
 The Arctic Ocean. In this ocean the chief current is the 
 continuation of the Gulf or Atlantic stream, which, after giving 
 off a branch to the southeast into the North Sea around the North 
 British coast, continues past the Shetland Islands along the Nor- 
 wegian coast to beyond North Cape, where it splits into a number 
 of minor streams, one of which, the North Cape current, turns east 
 along the north coast into the Barent Sea, to the south coast of 
 Nova Zembla, with a branch north to Franz Josef Land. Another 
 arm continues northward to Spitzbergen, where it can be recognized 
 beyond 80 north latitude. All along its course, driftwood from 
 tropical regions has been observed, the most noted example being 
 the bean of the West Indian Entada gigalobium, one of the com- 
 monest drift materials of the Gulf Stream, which was found by 
 Otto Torell in latitude 80 8' north, longitude 17 40' east, the 
 western point of North East Land. The cold currents most pro- 
 nounced are the East Greenland current already noted and its 
 branch, the East Iceland current. This meeting with the warm 
 water of the Gulf Stream extension produces a series of compli- 
 cated whirls, which have a decided influence on the distribution 
 of the temperature, the salinity, and, with these, the planktonic life. 
 (See the maps given by Helland Hansen and F. Nansen~3o; 
 Krummel-42 : 652.) Various other cold streams have been charted, 
 such as the cold Bear Island stream, issuing from the Barent 
 Straits, another issuing from Kara Straits and passing along the 
 south and west coast of Nova Zembla, one between Nova Zembla 
 and Franz Josef Land, and one between the latter and Spitzber- 
 gen, flowing southward and westward. All these are branches of a 
 general southward drift of the cold surface waters of relatively low 
 salinity, which result from the inpouring and excessive precipitation 
 of fresh waters, and give the arctic waters in general a higher level 
 than that of the neighboring oceans. On the Atlantic side the out- 
 lets are on the two sides of Spitzbergen, especially between Spitz- 
 bergen and Greenland. Another line of outflow is from the waters 
 
OCEAN CURRENTS 237 
 
 of the Parry Archipelago, eastward to Baffin Bay, and south to 
 Davis Straits, where it becomes part of the Labrador current, 
 which is further fed by recurving waters of the West Greenland 
 current. (See maps, Krummel-42 : 663.) 
 
 The Pacific Ocean. The currents of this ocean conform more 
 nearly to the typical arrangement sketched at the beginning than do 
 those of any other terrestrial ocean. The North Equatorial stream, 
 driven by the northeast trade winds, crosses the entire ocean from 
 east to west (S. 87 W.), a distance of 7,500 nautical miles, with an 
 average velocity of 14.5 nautical miles in 24 hours, 31.08 cm. per 
 second or 1.12 km. per hour, and with a high percentage of stability. 
 The southern border of this stream lies 10 north of the Equator in 
 summer, and 5 in winter. East of the Philippines, the current 
 turns north, increasing its velocity to 30 or even 50 nautical miles 
 per day. The main body goes north to form the Kuroshiwo or 
 Japan current, which, skirting Japan, gives rise to the North 
 Pacific West-wind drift and bends southward again on the West 
 American coast as the California current. This replaces the waters 
 carried westward in the North Equatorial current under the influ- 
 ence of the northeast trade wind, and corresponds to the Canaries 
 current of the North Atlantic. A smaller part of the North Equa- 
 torial stream bends off through the Ballingtang channel north of the 
 Philippines into the China Sea, where, especially in winter, during 
 the period of the northeast monsoon, it adds a considerable amount 
 to the cyclonal circulation of that mediterranean. Finally, large 
 parts of the current become reversed, especially in summer, to form 
 part of the Equatorial Counter current. The South Equatorial cur- 
 rent is much stronger than the northern, velocities of 20 nautical 
 miles per day being normal, velocities of 40 or 50 not uncom- 
 mon in all seasons, while occasional velocities of 70, 80, or even 
 more than 100 nautical miles in 24 hours have been recorded. The 
 greatest velocity is in its northern part, near or north of the 
 Equator, especially in the eastern region, and here the rapid move- 
 ment brings about a welling up of the colder, deeper waters as 
 clearly indicated by the tongue-like drawing out of the isotherms 
 west of the Galapagos Islands on the temperature chart of the 
 Pacific. The length of this stream is about 8,500 nautical miles; 
 its northern border may reach to i or 2 north of the Equator. 
 Opposite the Molucca Straits the northern part of the stream bends 
 northward and, recurving, produces its part of the Equatorial 
 Counter current. The greater part, however, flows southward along 
 the Australian coast, and constitutes the East Australian current. 
 This in part disposes of the excess of water driven against this 
 
238 PRINCIPLES OF STRATIGRAPHY 
 
 coast by the southeast trades, as the South Equatorial current, and 
 in part becomes a compensating current to replace the eastward- 
 flowing waters of the great South Pacific West-wind drift. This 
 finally turns northward as the Peruvian current, with an average 
 velocity of 15 nautical miles per day, which velocity is greatly 
 increased as it nears and finally joins the South Equatorial stream, 
 which has the effect of an aspirator. Cold waters well up between 
 the Peruvian current and the South American coast, and these were 
 formerly regarded as Antarctic waters flowing northward. 
 
 The Equatorial Counter current crosses the entire Pacific from 
 west to east, being especially strong during the northern summer, 
 when it occupies the zone between 5 and 10 north latitude, 
 though in winter it shrinks to a narrow band between 5 and 7. 
 With the varying season the strength of the current fluctuates. 
 Thus in winter it is from 5 to 8 nautical miles per day, while in 
 summer it rises to 9 or 12 nautical miles. 
 
 The Indian Ocean. The currents of this ocean are subject to 
 semiannual variation induced by the alternate dominance of the 
 winter or summer monsoons. During the winter or northeast mon- 
 soons the currents correspond in a measure to those of the Atlantic 
 and Pacific. Two westward-flowing currents separated by an east- 
 ward-flowing counter current occur. The South Equatorial is the 
 most pronounced, its boundaries being between 10 and 27 south 
 latitude, while the counter current lies between 2 and 5 south 
 latitude. This latter has a strength of 20 to 60 nautical miles per 
 day. During the northern summer, when the southwest monsoon 
 prevails, the southern westward-flowing current is broadened to 
 near 5 south latitude, the counter current as such has disap- 
 peared, while the movement of the waters north of the equator is 
 eastward. 
 
 Against Madagascar the impinging South Equatorial current 
 divides, a large part passing southward as the Mozambique cur- 
 rent, and later becoming the Agulhas stream, which bathes the coast 
 of Cape Colony in South Africa outside of the continental shelf, 
 where velocities ranging from 50 to no nautical miles per day 
 have been noted. South of the Cape of Good Hope the Agulhas 
 current meets the southern continuation of the cold West-wind drift 
 of the South Atlantic, which causes it to splinter into numerous 
 fingers, the spaces between which are taken by the cold fingers of 
 the eastward-flowing stream. In addition to carrying off the waters 
 of the South Equatorial current, the Agulhas stream further acts in 
 a compensatory manner to supply the water carried eastward by 
 the strong west winds of the southern latitudes. This south Indian 
 
OCEAN CURRENTS 239 
 
 West-wind drift is again continued in part in the northward-flowing 
 West Australian current, the close analogue of the Benguelan cur- 
 rent of the South Atlantic. The velocity of this current generally 
 ranges from 1 8 to 36 nautical miles per day, though sometimes it is 
 scarcely perceptible. The main part of the West-wind drift, how- 
 ever, continues eastward past Cape Leeuwin and along the South 
 Australian coast past Tasmania to the Pacific, forming part of the 
 great circumpolar current of the Antarctic region. That this great 
 eastward drift around the antarctic continent is a reality has been 
 shown by many tests with floating bottles, one of which, thrown 
 overboard December 16, 1900, off the Patagonian coast (long. 60 
 W.), was picked up June 9, 1904, on the north coast of New 
 Zealand (long. 172) having traveled in 1,271 days a distance of 
 10,700 nautical miles, or nearly 2/3 the circumference of the earth, 
 between latitude 40 and 50 south, a distance equal to that from 
 pole to pole, or an average of Sy 2 nautical miles per day. (Map, 
 Krummel-42 '.677.) 
 
 A characteristic accompanying feature of the wind-drift cur- 
 rents is a vertical compensatory movement, the upwelling of the 
 colder, deeper waters where the velocity of the surface stream is 
 such that the lateral compensation is insufficient. An example of 
 this has already been cited in the tongue of deep-green, colder wa- 
 ter extending westward from the Galapagos into the blue warm 
 water of the South Equatorial current of the Pacific. A similar 
 phenomenon occurs along the west American coast, where the Cali- 
 fornia current draws up the colder, deeper water on its landward 
 side. This is likewise the case in the Canary and Benguelan 
 streams, as well as along the west coast of South America. The 
 upwelling follows the wind, while a compensating downward move- 
 ment of the warmer water must occur before the wind. This ex- 
 plains the phenomenon that a persistent land breeze will cause the 
 upwelling along the coast of the colder waters, the warmer being 
 blown out to sea, while a sea breeze brings the warmer surface wa- 
 ters. Thus it is observed at the bathing beaches on the North Ger- 
 man coast that the north winds cause a warming, but south winds 
 a distinct cooling of the water. 
 
 CURRENTS IN MEDITERRANEANS AND EPICONTINENTAL SEAS. 
 The currents of intracontinental water bodies are generally mere 
 branches of the main oceanic circulation, and sometimes indeed, as 
 in the case of the Caribbean and Mexican seas, are an integral part 
 of it. The circulation of the North Sea is a southward-bending 
 branch from the Gulf Stream, and the main currents of the East 
 Greenland mediterranean are also a part of this larger circulation. 
 
240 PRINCIPLES OF STRATIGRAPHY 
 
 The currents of the Arabian Sea and the Bengal Bay are clearly a 
 part of the circulation of the Indian Ocean, while the circulation 
 of the China Sea is in part a branch of the North Equatorial cur- 
 rent of the Pacific. In general, the circulation of the mediter- 
 raneans is a cyclonal one, and it becomes more individualized the 
 more the water body is separated from the ocean's adjoining. 
 
 The Roman Mediterranean, which is connected with the At- 
 lantic only by the narrow Gibraltar Straits, nevertheless receives a 
 small branch of the northern West-wind drift. This stream, 
 though subject to modification by local winds, is recognizable 
 throughout, and influences the migration of the sands of the bot- 
 toms and coasts. It passes eastward along the north coast of Al- 
 giers, through the narrows between Tunis and Sicily, with a veloc- 
 ity of 5 to 10.5 nautical miles per day, and south of Malta toward 
 Barca (Africa), causing eddies in the Gulf of Sidra, turning north- 
 ward on the Syrian coast, and westward on the south coast of Asia 
 Minor, around Crete into the Ionian Sea, then north along the Dal- 
 matian, and south along the east Italian coasts, making a counter- 
 clockwise circulation in the Adriatic. In the Tyrrhenian Sea it con- 
 tinues northwestward, then west in the Ligurian and southwest 
 along the Spanish coast, thus completing the counter-clockwise cir- 
 culation. This circulation takes place largely under the influence of 
 the local winds, and is not always constant. 
 
 Both the Adriatic and ^Egean seas have practically independent 
 circulations in a counter-clockwise direction, and a similar circula- 
 tion exists in the Black Sea, though a part of the water moving 
 along the west coast of this body passes -out as a strong stream 
 through the Bosphorus, the Sea of Marmora, and the Dardanelles 
 into the ^Egean Sea. To compensate this outflow, a deeper lying 
 current enters from the yEgean and the Marmora Sea. At Con- 
 stantinople the outflowing stream of the Bosphorus has a velocity of 
 123 cm. per second at the surface, and rapidly decreases to nothing 
 at 20 meters' depth. At 25 meters' depth the inflowing stream is at 
 its maximum with a velocity of 73 cm. per second with moderate 
 diminution downward, its strength at 40 m. depth being still 43 cm. 
 per second. Makaroff has estimated that the outflowing stream car- 
 ries 10,530 cb. m. per second, while the inflowing carries only 5,700 
 cb. m. per second. This makes a yearly deficit of 152 cb. km., the 
 excess carried out over the inflow, and this has to be replaced by the 
 annual precipitation and afflux of water from the drainage basin. 
 A similar out- and influx take place through the Straits of Kertch 
 between the Sea of Azov and the Black Sea. Just the- reverse mo- 
 tion is seen at the mouth of the Roman Mediterranean and that of 
 
CURRENTS IN MEDITERRANEANS 241 
 
 the Red Sea. Here the ocean waters are of less salinity than those 
 of the mediterraneans, and they flow in on the surface, while the 
 more saline waters from the mediterraneans escape below the sur- 
 face to the oceans, influencing the salinity of the adjoining parts of 
 the sea. In the Straits of Bab-el-Mandeb the surface waters enter 
 the Red Sea with a velocity of 2 to 2^4 nautical miles per 'hour, ex- 
 tending down with diminishing velocity to 130 or 140 meters, below 
 which the outflowing stream ranges in velocity from i to 3 nauti- 
 cal miles per hour. 
 
 An outflowing surface stream, the Baltic Stream, carries the 
 weakly saline waters of the Baltic through the Ore Sound and con- 
 tinues along the Swedish coast of the Kattegat, where it is driven 
 by the prevailing west wind and the rotation of the earth. Its 
 velocity at a distance of 4 to 6 miles from shore is 24 to 48 nautical 
 miles per day in calm weather. Turning westward along the Nor- 
 wegian coast, it may reach a velocity of 80 to 100 nautical miles in 
 24 hours. It normally flows against the prevailing wind, which 
 must reach great strength before it is able to reverse the current 
 even temporarily. This stream has its greatest strength in the 
 spring and early summer months, when the influx of fresh water 
 into the Baltic is at its maximum. 
 
 The currents of the Baltic and its branches are largely dependent 
 on the wind and are further complicated by the tidal currents and 
 the relative amount of influx and evaporation. In the spring 76 
 per cent, of all currents flows westward, owing to the strong influx 
 of land waters and the pronounced east winds. In summer this 
 drops to 60.5 per cent., when evaporation over the Baltic becomes 
 strong and west winds prevail, while during autumn and winter 71 
 per cent, and 69 per cent, of all currents of the Baltic flows west- 
 ward. The strength of the outflowing streams may reach 3 to 4 
 nautical miles per hour in the narrows of the western part, or Belt 
 Sea. The Finnish Gulf, which is scarcely separated from the Bal- 
 tic, and has therefore much the structure of a funnel sea, is charac- 
 terized by a westward-flowing surface stream of fresher water and 
 an eastward-flowing compensating stream of greater salinity at some 
 depth below the surface. The Bothnian Gulf, on the other hand, 
 has a more independent circulation in the counter-clockwise direc- 
 tion, and this corresponds to its greater distinctness from the Bal- 
 tic. The current flows into the gulf east of the Aland Islands, and 
 out on the west, except when interfered with by strong winds. 
 
 The circulation of other northern intracontinental seas, like Hud- 
 son Bay, St. Lawrence Gulf and Kara Sea, is a cyclonal one in the 
 counter-clockwise direction. A similar circulation exists in the Red 
 
242 PRINCIPLES OF STRATIGRAPHY 
 
 Sea, where the current sets north on the Arabian and south on the 
 African coast. Here, however, the strong monsoons act as modi- 
 fiers of this general circulation. Similar conditions exist in the Per- 
 sian Gulf, but here, as in epicontinental seas generally, the circula- 
 tion is strongly modified by winds and tidal streams. The marginal 
 mediterraneans of the West Pacific coast show the cyclonic circu- 
 lation in the counter-clockwise direction characteristic of the 
 northern hemisphere, but more or less modified by the inflowing cir- 
 culation of the North Pacific itself. The Japan Sea may be taken 
 as typical. Here a branch of the warm and highly saline Kuro- 
 shiwo current enters through the Straits of Korea, and follows the 
 west coast of Japan northeastward. It sends branches out to the 
 Pacific through the several straits, and then turns into the Gulf of 
 Tartary, where it unites with the counter current from the north, 
 the low temperature and salinity of which strongly influence the 
 Asiatic coast, which it follows to the east coast of Korea. The cir- 
 culation within the sea of Okhotsk, and to a less extent in Behring 
 Sea, follows the same plan, though in the latter the influence of the 
 warm Kuroshiwo in summer causes marked modifications such as a 
 northward flowing warm surface stream in the western half to 
 Behring Straits. 
 
 The Australian group of mediterraneans is of especial interest, 
 as it lies on bath sides of the equator and so partakes alternately 
 of both systems of circulation. At the time of the northeast mon- 
 soon the counter-clockwise circulation normal for the northern 
 hemisphere exists in the China Sea, the water running W. S. W. 
 along the Chinese coast with a velocity of 20 to 40 nautical miles 
 toward the coast of Anam, where it reaches velocities of 50 to 
 80 nautical miles per day, turns south and east, and then to the 
 northeast, along the west coast of Borneo, Palawan Island and the 
 Philippines, with velocities of 15 to 25 nautical miles per day. The 
 currents of the Java, Flores and Banda seas flow prevailingly east- 
 ward with southward flowing branches through the straits between 
 the small Sunda Islands and on both sides of Timor. The reverse 
 direction is taken by the circulation in the time of the southwest 
 monsoon. Along the coast of Cochin China, the stream flows 
 northeastward, reaching a strength of 40 to 70 nautical miles at 
 Cape Pedaran ; along the Anam coast it flows north, and off the 
 South Chinese coast in general eastward. Along the coast of Pala- 
 wan and Borneo the movement is southwestward, the circle being 
 closed by a northward stream from the Natuna to the Condore 
 islands. In the Java, Flores and Banda seas the main direction of 
 the flow is westward. It thus appears that the circulation in med- 
 
CURRENTS AND MIGRATION 243 
 
 iterraneans and epicontincntal seas of the northern hemisphere, 
 when not a part of the main oceanic circulation, as in the American 
 mediterraneans, is normally a singly cyclonic movement in counter- 
 clockwise direction, while the movement of the main oceanic circu- 
 lation of this hemisphere is clockwise. Only in the case of the seas 
 lying on the Equator does a reversal of conditions occur when the 
 sun crosses to the north of the Equator during the northern summer 
 or the period of southwest monsoons. 
 
 The type of currents found in funnel seas of the California!! type 
 is illustrated by that water body. During the cooler months the 
 prevailing northwest winds drive the surface waters southward, 
 while in summer the monsoon-like southeast winds drive the surface 
 waters into the gulf. At a depth of 50 meters the stream flows 
 again southward. 
 
 MARINE CURRENTS IN RELATION TO MIGRATION AND DISPERSAL, 
 PAST AND PRESENT. As will be more fully set forth in Chapter 
 XXIX, ocean currents are among the important factors in influenc- 
 ing migration of organisms, and they are the chief cause of the dis- 
 persal of the plankton or floating matter, organic and inorganic, of 
 the sea. The numerous records of the wide dispersal of floating 
 matter, such as sealed bottles, purposely thrown into the sea, wrecks 
 of known date, tree trunks brought by tropical rivers to the sea, 
 and carried by the ocean currents to the arctic regions, and others 
 have indeed been one of the chief sources of our knowledge of the 
 direction of these currents. Taking our cue from these dispersals 
 in the modern sea, we may look for similar evidence of currents 
 in the past. In such determination the dispersal of the holo- 
 planktonic organisms serves perhaps as the best guide. In the early 
 Palaeozoic, the graptolites seem to furnish reliable indications of the 
 general course of the currents, and they have been so used in the 
 construction of Palseogeographic charts. (Ruedemann-6o: 488', 
 Grabau-29; Map figs. /, 2, 7, 8.) Sometimes the direction of the 
 current can be found by the position which the rhabdosomes of the 
 graptolites assumed in the strata, as in the case cited by Ruedemann 
 from the Utica shales of Dolgeville, New York, where not only the 
 rhabdosomes of the graptolites, but also the spicules of sponges, 
 fragments of byozoans and shells of Endoceras proteifonne have a 
 parallel arrangement, indicating an east-northeast by south-south- 
 west direction of the currents. "That the flow came from N. 78 
 E. and ran toward S. 78 W., can be inferred from the appearance 
 of the mud-flow structure, the drift ridges behind the fossils (En- 
 doceras), the eastward pointing of the apices of the Endoceras 
 shells, and often also of the sicular ends of the graptolites. . . . 
 
244 PRINCIPLES OF STRATIGRAPHY 
 
 Gastropods have been noticed with transversally arranged frag- 
 ments, which apparently were arrested by the immovable shell, on 
 the .east side, and with a drift ridge of longitudinally arranged 
 fragments on the west side." ( Ruedemann-59 : 380-381.) Since 
 the general direction of the great ocean currents seems to have been 
 to the northeast, this indication of a southwestward flow estab- 
 lishes a secondary recurving current of the type common at the 
 present time. 
 
 DEPTH OF CURRENT ACTION. The depth of current action can 
 often be ascertained by the scouring which it accomplishes on the 
 bottom, sweeping off all fine sediment, and leaving a ''hard bottom." 
 T. M. Reade has recorded such bottoms between Gran Canaria and 
 Teneriffe in the Canary Islands in depths of 2,000 meters. (T. M. 
 Reade 56.) This is, however, to be regarded as more properly the 
 work of a tidal current. In the Florida straits, at depths of 160 to 
 550 meters, the bottom is kept clean, the fine mud being swept be- 
 yond the edge of the Pourtales Plateau, which consists of recent 
 organic material consolidated into a hard breccia. The bottom of 
 the Straits of Gibraltar is swept clean and smooth through the out- 
 ward flowing bottom current. 
 
 LAKE CURRENTS. 
 
 Lakes, owing to their usually small size, are not influenced in 
 the same manner by the primary current-producing agents as are 
 the larger water bodies. It is true that on the large lakes, like those 
 of North America, longshore currents, due to prevailing winds, 
 are of considerable significance, not only in navigation, but in the 
 transportation of material along the beach, and the building of 
 bars, sandspits, etc. In general, however, the movements of lake 
 waters induced by wind partake of the nature of a vortical circu- 
 lation. The wind blowing steadily across the surface of a lake 
 forces the water to the opposite shore, where it sinks, while the com- 
 pensatory streams behind the wind rise from below. This produces 
 an under current flowing in the opposite direction from that on the 
 surface, and at a depth depending on the temperature, density, etc., 
 of the water and the configuration of the basin. (Forel-24 : 81-83.) 
 
 RIVER CURRENTS. 
 
 Rivers are currents of water confined between banks of rock or 
 soil, and they differ from currents in water bodies in that typically 
 their movement is due to gravity alone. While the whole mass of 
 
RIVER CURRENTS 245 
 
 water of the river is in motion, nevertheless there is to be found 
 in each cross-section of a river a point of maximum motion. This 
 is generally a short distance below the surface, and in a symmetrical 
 section, near the center. This .fast-moving portion of the river is 
 especially designated the "current," and its course in a winding river 
 is always more curving than that of the river itself. As a result, 
 it impinges alternately upon the right and left bank of the river, 
 which points become the centers of maximum erosion. The bank 
 against which the current impinges will be kept vertical by under- 
 mining, and the river at the same time will be deepest at that point. 
 The opposite side is shallow, the bank sloping, and deposition rather 
 than erosion occurs. 
 
 Velocities of River Currents. The velocity of a river depends 
 on a number of factors, first among which may be mentioned the 
 slope of the river bed, and next the volume of water. The width of 
 the channel is also an important factor, this varying from the in- 
 definite width of the sheet floods of Arizona and Mexico (Mc- 
 Gee-45) to the narrow canyons of a youthful topography. The 
 slope may vary from nearly horizontal to vertical; in the one case, 
 a nearly stagnant stream results; in the other, the extreme of a 
 waterfall is produced. The most variable of these factors is the 
 volume, and hence the velocity of a given current may change 
 greatly between low and high water. Sudden changes in volume 
 due to sudden precipitation of vast amounts of water, as in semi- 
 arid regions, may produce a marked change in the slope or 
 width of the channel, and so affect the strength of the current in 
 a more permanent manner. Within the same stream velocities vary 
 according to slope, or width and depth of the channel. Thus the 
 velocity of the Rhine, during medium height of water, has been 
 found to be 3.42 m. per second at the Bingerloch, 0.63 m. at Wert- 
 hausen and 1.5 m. at Mannheim, while high water at Coblenz gave 
 a velocity of 1.88 m. per second. The Vistula (Weichsel) during 
 high water has a velocity of 1.2 to 1.9 m. per second. The Neckar 
 above Mannheim at medium water has a velocity of 0.9 m., but at 
 high water over 3 m. The Danube at Vienna has a velocity of 1.94 
 m. per second during high water, while the maximum velocity of 
 the Mississippi between the mouths of the Ohio and the Arkansas 
 is 1.91 m. and between Bayou la Fourche and the forking is 1.76 m. 
 per second. ( Krummel-42 : 575, footnote.) 
 
 Perhaps the best example of local changes due to change in the 
 bed of the river is furnished by Niagara. This river is placid and 
 calm from its head near Lake Erie to within a half mile or more 
 of the falls, the fall being 14 feet in something over 20 miles, and 
 
246 PRINCIPLES OF STRATIGRAPHY 
 
 the current very slight. Then a sudden change in the slope of the 
 river bed, causing a descent of 55 feet in less than half a mile, trans- 
 forms the river into a rushing torrent the rapids above the falls 
 culminating in a drop of 160 feet at the cataracts, over which 22,- 
 400,000 cubic feet of water fall per minute. Below the falls strong 
 currents and eddies continue for a while, due to the disturbance of 
 the water at the falls. Then, however, the river becomes relatively 
 calm again with moderate current, easily navigable for about two 
 miles. The channel is from 1,200 to 1,300 feet wide at the top, and 
 the water from 160 to 190 feet deep. At Suspension Bridge the 
 channel suddenly contracts to 700 or 750 feet at the top, while the 
 water is not over 35 feet deep. In this narrow and shallow gorge 
 the whirlpool rapids are situated, the great volume of water rushing 
 through it with indescribable force, far exceeding that of the upper 
 rapids. The descent at the same time is slightly more than 50 feet 
 in a distance of about a mile, or about half the descent of the 
 upper rapids. The curious eddy of the whirlpool is entirely due to 
 the conformation of the channel, wnich here bends at right angles. 
 A second narrowing at Fosters Flats again produces rapids, but be- 
 low this the river becomes relatively quiet and placid again, and 
 navigable for seven miles of its lower course. 
 
 Erosive Power of Rivers. The erosive power of a river, i. e., 
 the ability to overcome cohesion, varies as the square of its velocity. 
 Pure water does little or no actual erosion, this being accomplished 
 by the transported material. The rock fragments carried by the 
 stream corrode its bed, while at the same time they abrade each 
 other. In the part of a stream bed unsupplied by new material 
 from tributaries it is noticeable that there is a progressive diminu- 
 tion in size of the fragments downstream, the reduction being pro- 
 portional to the weight of the rock in water and the distance trav- 
 eled. The following measurements made on the river Mur show 
 the progressive reduction in average size of the fragments in ac- 
 cordance with distance (Hochenburger-33 153, quoted by Penck- 
 51 -.292} : 
 
 At Graz 224 cb. cm. 
 
 At Gossendorf ( 10 km. below Graz) 184 cb. cm. 
 
 At Wildon (26 km. below Graz) 132 cb. cm. 
 
 At Landscha ( .43 km. below Graz) 1 17 cb. cm. 
 
 At Unterschwarza (56 km. below Graz) 81 cb. cm. 
 
 At Dippersdorf (71 km. below Graz) 60 cb. cm. 
 
 At Leitersdorf (83 km. below Graz) 50 cb. cm. 
 
 At Mauth-Eichdorf . . . . (101 km. below Graz) 33 cb. cm. 
 
 At Wernsee (112 km. below Graz) 37 cb. cm. 
 
 At Unter-Mauthdorf . . . (120 km. below Graz) 21 cb. cm. 
 
EROSION BY RIVERS 247 
 
 The distance necessary for rock fragments to travel before they 
 become completely destroyed varies with the character of the rock, 
 as shown in the following table : 
 
 Rhaetic sandstone (Average weight, 40 grams) 15 km. 
 
 Clay slate (Average weight, 24 grams) 42 km. * 
 
 Orthoceras limestone . . (Average weight, 61 grams) 64 km. 
 
 Granular limestone .... (Average weight, 40 grams) 85 km. 
 
 Granite (Average weight, 36 grams) 278 km. 
 
 Rate of erosion. From the known area of the hydrographic 
 basin of a river, and the measured amount of transportation of the 
 material in the river, it is possible to arrive at a reasonably accurate 
 estimate of the rate of erosion of the river system in question. 
 Thus the Mississippi system, with a hydrographic basin 1,244,000 
 square miles in area and an annual discharge of sediment of 
 7,471,411,200 cubic feet of sediment, erodes at the rate of one foot 
 in 4,640 years ; while the Ganges system, with a hydrographic basin 
 of only 400,000 square miles and an estimated annual discharge of 
 sediment of 6,368,000,000 cubic feet, erodes its basin one foot in 
 1,751 years. Other estimates make it I meter in 7,781 years, or I 
 foot in about 2,628 years. The greater efficiency of the Ganges is 
 attributable in large part to heavy rainfall during six months of the 
 year, and to the steeper slopes of the basin. 
 
 Le Conte (43:11), using the Mississippi basin as more typical 
 than the Ganges for the earth's surface as a whole, concludes that 
 the continent is probably lowered at the rate of one foot in 5,000 
 years. 
 
 Transporting Poiver of River Currents. Streams move solid 
 material either by rolling it along the bottom or by carrying it in 
 suspension. Suspension of fine material is favored by minor up- 
 ward currents in the main current, while others carry it down again 
 or against the side of the channel. Suspended material is repeat- 
 edly dropped and picked up again, the solid particles making their 
 journey down the river with many interruptions. The total amount 
 of material transported by rivers is often very great. Thus the 
 Mississippi River carries more than 400,000,000 tons of sediment 
 each year to the Gulf of Mexico, or more than a million tons a day. 
 The exact volume, according to the measurements of Humphreys 
 and Abbot (34:148-150), is 7,471,411,200 cubic feet, a mass suffi- 
 cient to cover an area of one square mile to a depth of 268 feet. 
 The amount carried to the sea by all the rivers of the earth has been 
 estimated at perhaps 40 times this quantity. (Salisbury-62 : 122.) 
 
 The following table (Kayser-39: 545) gives the amounts of ma- 
 
248 PRINCIPLES OF STRATIGRAPHY 
 
 terial carried in suspension or rolled along the bottom of some of 
 the larger streams of the world, according to the investigations 
 of Guppy and T. Mellard Reade. 
 
 Table showing the transportation of material by rivers. 
 
 TTT , . Material 
 
 Water in 
 
 Stream cu. meters 
 
 in cu. meters 
 per sec. 
 
 per year 
 
 Amazon 69,580 
 
 Congo 50,970 
 
 Yangtsekiang 21,810 182,000,000 
 
 La Plata 19,820 44,000,000 
 
 Mississippi 17,500 21 1,500,000 
 
 Danube 8,502 35,540,000 
 
 Ganges 5,762 18,030,000 
 
 Indus 5,649 
 
 Nile 3,680 
 
 Huang-ho 3,285 472,500,000 
 
 Rhine i,974 
 
 Po 1,735 11,480,000 
 
 Pei-ho 220 2,266,000 
 
 Thames 65 528,300 
 
 The ability of a current to transport material varies in general 
 as the sixth power of its velocity. Thus, if the velocity is doubled, 
 the carrying power is increased 64 times. A current having a 
 velocity of 3 feet (or approximately I meter) per second (about 
 2 miles per hour) will move ordinary rock fragments of the size of 
 a hen's egg and weighing about 3 ounces. From the law of varia- 
 tion it follows that a current of ten miles per hour will carry rocks 
 weighing one and one-half tons, while a torrent of 20 miles per hour 
 will carry rock masses 100 tons in weight. Taking the varying spe- 
 cific gravities of different rocks into consideration, the table on page 
 249 has been constructed by T. E. Blackwell (5; cited by Beard- 
 more~3:7; Penck~5i : 281) to show the size of the various rock 
 masses transported by currents of varying velocity. 
 
 According to the experiments of Forbes (23 : 474) made in a 
 shallow trough, the following velocities were required to stir up 
 various sediments from the bottom : 
 
 Table of -velocities required to stir up bottom material. 
 
 Moist brick clay at a velocity of 0.077 m. per sec. 
 
 Fine fresh-water sand at a velocity of 0.213 m. per sec. 
 
 Sea sand at a velocity of -337 m - P er sec- 
 Gravel, pea size, at a velocity of 0.610 m. per sec. 
 

 
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 249 
 
250 PRINCIPLES OF STRATIGRAPHY 
 
 Recent experiments by Sorby (66 : 180) indicate that a current 
 of about 6 inches per second is sufficient to slowly drift along 
 granules of common sand having a diameter of about a hun- 
 dredth of an inch. No rippling of the sand was produced until the 
 velocity was somewhat greater. In the bed of the River Rhine at 
 Breisbach the following measurements were made by Suchier 
 (71 : jji ; Penck-5i : 283} to ascertain the velocity at which various 
 sediments begin to move, (i) through the influence of the cur- 
 rent alone, and (2) after the sediments on the bottom are stirred 
 up: 
 
 A. With stream bed covered by fine sediment. 
 
 Under action of current alone, no movement found, with 
 
 bottom velocity at 0.694 m - P er sec- 
 After being stirred up, the movement of the sediment be- 
 gan for fragments of the size of beans, when bottom 
 velocity reached 0.897 m - P er sec- 
 Fragments of the size of hazelnuts, when bottom velocity 
 
 reached 0.923 m. per sec. 
 
 Fragments of the size of walnuts, when bottom velocity 
 
 reached 1.062 m. per sec. 
 
 Fragments of the size of a pigeon egg, when bottom 
 
 velocity reached 1.123 m. per sec. 
 
 B. With river bottom free from sediment, the smallest particles 
 
 are moved when the current velocity reaches at 
 
 bottom 1.180 m. per sec. 
 
 Pebbles of pea and hazelnut size move freely under a 
 
 velocity of 1.247 m. per sec. 
 
 With noticeable noise at 1 .300 m. per sec. 
 
 Pebbles of walnut size are moved without stirring and 
 such of 250 gr. weight after stirring up, with current 
 
 at i .476 m. per sec. 
 
 Pebbles of 1,000 gr. wt. rolled at 1.589 m. per sec. 
 
 C. General movements of pebbles: 
 
 Up to the size of pigeon eggs, at i .623 m. per sec. 
 
 Up to the size of hens' eggs, at 1.71? m. per sec. 
 
 (including such of 1,500 gr.) 
 
 Pebbles of less than 2,500 gr. wt. are moved at 1.800 m. per sec. 
 
 All pebbles moved at 2.063 m. per sec. 
 
 It is evident that it requires a much greater velocity to start the 
 movement than is required to keep it up. This is shown by the fol- 
 lowing comparison : 
 
TRANSPORTATION BY RIVERS 251 
 
 Velocity re- Velocity re- 
 
 Size of pebbles quired to move quired to start 
 
 after stirring up motion 
 
 Hazelnut size , 0.923 m. per sec. 1.35 m. per sec. 
 
 Walnut size 1.062 m. per sec. 1.39 m. per sec. 
 
 Pigeon egg size 1.123 m. per sec. 1.45 m. per sec. 
 
 The transportation of the coarser detritus in streams is chiefly 
 by rolling along the bottom, more rarely by pushing along. The 
 entire river bed may be in motion, forming a waste stream saturated 
 with water, which in the case of the Rhine at Ragaz and the Birsig 
 at Basel has been found to possess a depth of more than three 
 meters (Pestalozzi-53 :vi) and of four meters in the Danube at 
 Vienna. This phenomenon is, however, ordinarily restricted to 
 mountain streams in flood. 
 
 The sands of the river bottoms generally assume the arrange- 
 ment of a series of low banks, alternating in position on opposite 
 sides of the stream. Opposite each low bank is a deep channel with 
 steep sides, harboring the main current of the river. These banks, 
 which in general have a triangular outline, their bases against the 
 river banks, slowly wander downstream, through removal of the 
 sand on the upstream side, its passage across the bank and deposi- 
 tion against the downstream side. On the middle Rhine such banks 
 move at the rate of 200 to 400 meters per year downstream, this 
 being increased to three times that amount in years of high water. 
 In seven years a bank may thus reach the former position of the 
 one next downstream on the same side. (Grebenau, cited by Penck- 
 51 -.286.) In the regulated reaches of the Danube at Vienna, the 
 sand banks have wandered in seven years from 700 to 1,000 meters 
 downstream. (Penck~5i -.286.) In the Loire the sand banks mi- 
 grate at the rate of 1.72 to 3.61 meters per day in summer and 2.37 
 to 18.65 m - P er day m winter, according to the varying angle of 
 fall of the water, which is from 0.28 permille to 0.45 permille. This 
 also shows the great difference between the transport in summer 
 and winter, the latter being the season of floods and high water gen- 
 erally. In all cases the motion of the waste matter is much slower 
 than that of the water, and the amount of water passing a given 
 point may be a thousand times the amount of sediment carried 
 past that point in the same period. Thus the Rhine above Germers- 
 heim carries nearly 7 cu. cm. of waste for every cubic meter of wa- 
 ter, while the Danube at Vienna carries on the average 13 cu. cm. 
 in every cubic meter of water. That sands and pebbles can be trans- 
 ported in the course of time to great distances by river currents 
 
252 PRINCIPLES OF STRATIGRAPHY 
 
 is shown in the great delta of the Huang-ho, which extends for 300 
 miles or more from the mountains which have furnished the sedi- 
 ment. The sands and round quartz pebble conglomerate at the 
 base of the Carbonic of North America (Pottsville) have been 
 spread over an area of more than 400 miles radius. With progres- 
 sive transport a constant decrease in the size of the fragments oc- 
 curs, owing to the grinding processes which they undergo. [See the 
 table given above for the reduction of the sediments of the Mur 
 River (p. 246).] 
 
 Sorting Power of Rivers. When sands and gravel consist of a 
 variety of material, a gradual assorting and elimination of the more 
 destructible matter will result by river transportation, as well as 
 wave action. This sorting of sands by rivers and by the waves 
 along the shore is, however, always much slower and generally less 
 complete than when it is done by the wind. The gravels of the 
 River Saale at Jena, derived from the Thuringer Wald, consist 
 chiefly of fragments of the Culm and Cambric formations. The 
 Siluric, Devonic, Zechstein and Buntsandstein formations of this 
 region are scarcely represented in the Saale gravels on account of 
 the preponderance of soft shales, sandstones, limestones and dolo- 
 mites, which in the course of transportation are destroyed. (Keil- 
 hack~40 : 15. ) 
 
 Analyses (Mackie-46: 149) of the sands of the River Spey de- 
 rived from the fundamental gneiss of Scotland showed at Cromdale 
 1 8 per cent, of feldspar and I per cent, of mica, while further down 
 the river at Orton the percentage of feldspar was only 12. That 
 of the River Findhorn above Dulsie bridge showed 42 per cent, of 
 feldspar, while between Forres bridge and the sea the percentage 
 was reduced to twenty-one. This shows the gradual washing out 
 by rivers of the feldspar and mica. On the seashore, as already 
 noted, further assorting takes place. Thus the average per cent. 
 of feldspar in the sand furnished by the four principal rivers of 
 Eastern Moray (Spey, Lossie, Findhorn, Nairn) was 10, whereas 
 in the rivers themselves, near their mouths, the average per cent, 
 was 1 8. Prolonged sorting by either waves or river currents may 
 thus produce nearly pure quartz sand by the removal of the other 
 destructible minerals. The distance traveled by river gravels is often 
 very great. Pebbles from the hills bordering the Red Sea have 
 been found in the Nile Delta, 400 miles away. (See Chapter XIV.) 
 There are reasons for believing that the well-rounded quartz peb- 
 bles of the Sharon (Upper Pottsville) conglomerate of Ohio and 
 western Pennsylvania and the Olean of southern New York have 
 traveled over 400 miles from their original source. 
 
EROSION BY RIVERS 253 
 
 Rounding of Sand Grains. (Goodchild-27; Mackie-47: 500.) 
 The chief factors concerned in the rounding of sand grains by 
 attrition are : 
 
 1. The size of the particles. 
 
 2. Their specific gravity. 
 
 3. Their hardness. 
 
 4. The distance over which they had traveled. 
 
 5. The agent by which they had been transported. 
 
 The amount of rounding of a particle varies directly as i, 2 and 
 4, and indirectly as 3. Particles transported by wind are more 
 rounded than those transported an equal distance by water. 
 
 A cube, with the side measuring I inch, presents an area of 6 
 square inches, while a sphere of one inch diameter presents a sur- 
 face of only 3.14159 + square inches. Now, since the surface area 
 of bodies of similar figure, but different in size, varies as the square 
 of their linear dimensions, a doubling of the linear dimensions of 
 the cube would increase its surface area to 24 square inches. If 
 the diameter of the sphere is doubled, the surface area becomes 
 12.566 + square inches. On the other hand, reducing the cube 
 from a linear dimension of one inch to one of half an inch by the 
 side, the area of its surface is reduced from 6 square inches to one 
 and one-half square inches. In like manner the reduction of the 
 diameter of the sphere to one-half inch reduces its surface area to 
 0.78539 square inch. 
 
 The volumes of bodies of similar figure, however, increase as 
 the cube of their respective linear dimensions, or decrease as the 
 cube root of those dimensions. Thus, while the sphere reduced 
 from one inch to one-half inch diameter changes in area from 
 3.1416 square inches to 0.78539 square inch, its volume will change 
 from 0.5236 cubic inch to 0.06545 cubic inch. That is, while 
 the superficial area is decreased to one-fourth, the volume is de- 
 creased to one-eighth its original amount. Since the weight of an 
 object depends on its volume, it follows that the decrease in weight 
 is greater than the decrease in surficial area, and, since adhesion 
 (surface tension or the adhesion between the object and the medium 
 in which it is immersed) is dependent on the surficial area of the 
 object, it follows that in the wearing down of a sand grain the de- 
 crease in weight is always greater than the decrease of surface ten- 
 sion. Thus, with the progressive wearing down of a sand grain, a 
 stage will be reached when the surface tension will balance the 
 gravitational force, and further wearing of the grain becomes im- 
 possible in that medium. So, with a given medium and strength 
 
254 PRINCIPLES OF STRATIGRAPHY 
 
 of current, grains below a certain size will not be rounded. Since 
 the buoyancy or surface tension (adhesion between water and sand) 
 of salt water is greater than that of fresh water, the smallest 
 rounded grain of the former should be somewhat larger than that 
 of the latter, other things being equal. Again, since the surface 
 tension of air is very much less than that of water, very much 
 smaller grains will be rounded by wind than by water. In other 
 words, wind-blown sands of even extremely small size will come in 
 contact with each other and with stationary objects, and so become 
 worn and rounded. The fact that all grains below a certain size 
 show angularity, and that the transition from rounded to angular 
 grains is not a gentle but an abrupt one, is readily noticeable in 
 both modern sands and ancient sandstones. Moreover, grains of 
 materials of different specific gravity, but of the same size, will 
 show a greater rounding with higher specific gravity. (Mackie- 
 47: 298.} Ziegler (75) noted from experiments that quartz par- 
 ticles less than i mm. in diameter showed repulsion due to the 
 viscosity of the liquid. He concludes that it is impossible that 
 grains less than 0.75 mm. in diameter could be well rounded under 
 water, but if rounded must be wind-worn. 
 
 Since mineral particles have less w r eight in water than in air, it 
 follows that particles of the same size and material will suffer more 
 erosion in air on this account also. 
 
 Hardness and the distance over which the material is trans- 
 ported are likewise factors in the rounding of grains, the amount 
 of rounding varying indirectly as the former and directly as the 
 latter. Mackie has reduced the variability of the rounding (R) of 
 particles to the following formula : 
 
 size X the specific gravity X distance 
 
 Roc 
 
 hardness 
 
 Distance (d) traveled may be expressed by the number of times 
 the body turns on its axis. This number of times for a cube with 
 
 side measuring x will be - and since the weight of such a cube is 
 
 4X 
 
 expressed by x 3 X sp. gr. (i. e. the size or volume x multiplied by its 
 sp. gr.) we have 
 
 x 3 spg. 
 
 _. 4X x 2 spg.d x 2 spg.d 
 
 Roc 2 = - _or generally - 
 
 h 4h mh 
 
 where m varies with the outline of the figure, being 4 in a cube, and 
 3.1416 in a sphere, with proportional values for other forms. Since 
 
ROUNDING OF SAND GRAINS 255 
 
 sand grains weigh less in water than in air, a corresponding correction 
 must be made (47), the formula being according to Mackie for water: 
 
 Roc *'(*Pfr-')d 
 
 mh 
 
 On making a comparison (Mackie 47:510) of the relative efficiency 
 of wind and water as rounding agents, we have from the formulas 
 
 for wind Roc x ' Spg<d and for water Roc x " ( s Pg--D d 
 mh mh 
 
 the following relationships : 
 
 wind agency spg. . . , . 2.6$ 
 
 s i = - _ which for quartz = 
 
 water agency spg. 1 i . 65 
 
 or wind = 1.6 times water, but since average wind velocities are 
 always greater than average water velocities, it follows that the result 
 attained by wind will be much greater than that given. Mackie 
 has calculated that with a wind velocity of 8 miles an hour, and a 
 water velocity of 2 miles an hour, the ability of the wind to round 
 a given quartz particle (sp. 2.65) is nearly 29 times as great as that 
 of water. Mackie concludes that "under the conditions stated, 
 particles less than one-fifth the diameter of those rounded by water 
 will be rounded to an equal degree by wind" (47:510). Mackie has 
 calculated the values of the coefficient of roundability or psephicity 
 for various minerals a few of which are given (Mackie~4 7:502). 
 
 Table showing coefficient of psephicity of minerals in air and water. 
 In air In water 
 
 Quartz ) ' = 0.38 - = 0.23 
 
 n n 
 
 = 0.29 
 = 0.30 
 = 0.39 
 = 0.39 
 = o-45 
 = 0.70 
 = 0.76 
 = 0.86 
 
 Examination of a sample of sand from the River Spey at 
 Craigellachie, Scotland, at a point where it could not be contami- 
 nated by admixture of particles derived from the sandstones 
 showed, according to Mackie (47:506), no appreciable rounding of 
 the quartz grains, "though they certainly did not all of them pre- 
 sent the marked angularity of the quartz grains in most boulder 
 clays." The feldspars also were angular, though some of them, be- 
 
 Orthoclase ' 
 
 = 0.40 
 
 Tourmaline ' 
 
 = 0.43 
 
 Garnet 
 
 = 0.53 
 
 Hornblende ' 
 
 = 0.57 
 
 Zircon 
 
 = 0.59 
 
 Biotite 
 
 = 1.05 
 
 Chlorite 
 
 = 1.20 
 
 Muscovite ' 
 
 = 1.30 
 
PRINCIPLES OF STRATIGRAPHY 
 
 ing kaolinized in a high degree, exhibited considerable blunting of 
 their angles. The chlorite flakes were generally rounded, though 
 with frayed, irregular edges, the muscovite and biotite were some- 
 what rounded on their prominent angles, but generally of irregular 
 outline. The hornblende and garnets were angular, as was also the 
 zircon, though showing occasionally ground-glass surfaces. Mackie 
 concludes that these sands had traveled not less than 70 miles. 
 
 A specimen of sand from the seashore, midway between Lossie- 
 mouth and Covesea on the south coast of the Moray Firth, gave 
 Mackie the following results : 
 
 Table showing rounding of sands of Moray Firth. 
 
 Mineral Particles 
 
 No. 
 ob- 
 served 
 
 Rounded 
 
 Sub- 
 angu- 
 lar 
 
 Angular 
 
 Average 
 round- 
 ing* 
 
 Hornblende 
 
 10 
 
 
 c 
 
 c 
 
 I c 
 
 Kyanite 
 
 2 
 
 
 I 
 
 I 
 
 I c 
 
 Biotite 
 
 16 
 
 7 
 
 7 
 
 6 
 
 1.8 
 
 Opaque iron ore 
 
 -I 
 
 I 
 
 I 
 
 i 
 
 2 O 
 
 Chlorite 
 
 4 
 
 I 
 
 2 
 
 i 
 
 2 O 
 
 Muscovite 
 
 2O 
 
 7 
 
 9 
 
 4 
 
 2 .2 
 
 Quartz** 
 
 18 ' 
 
 6 
 
 i^ 
 
 10 
 
 I 7 
 
 Feldspar** 
 
 26 
 
 8 
 
 13 
 
 5 
 
 2.1 
 
 Average rounding represented by 
 
 A sample from the sand dunes of Culbin, in the same region, 
 gave the following: 
 
 Table showing rounding of sands of Culbin dunes. 
 
 Mineral Particles 
 
 No. 
 ob- 
 served 
 
 Rounded 
 
 Sub- 
 angu- 
 lar 
 
 Angular 
 
 Average 
 round- 
 ing 
 
 Staurolite 
 
 2 
 
 
 
 2 
 
 I O 
 
 Kyanite . .... 
 
 2 
 
 
 i 
 
 i 
 
 I C 
 
 Garnet 
 
 45 
 
 Ii 
 
 14 
 
 18 
 
 I .9 
 
 Hornblende . . 
 
 K 
 
 7 
 
 i 
 
 i 
 
 2 4 
 
 Tourmaline 
 
 IT. 
 
 8 
 
 4 
 
 
 2 . S 
 
 Opaque iron ore 
 
 IO 
 
 7 
 
 T. 
 
 
 2 7 
 
 Sphene 
 
 q 
 
 8 
 
 
 r 
 
 2 8 
 
 Zircon 
 
 
 7 
 
 
 
 T. O 
 
 Feldspar 
 
 16 
 
 IO 
 
 e: 
 
 I 
 
 2 6 
 
 Quartz 
 
 16 
 
 6 
 
 9 
 
 i 
 
 2.3 
 
 Average rounding represented by 2.27 
 
 * Obtained by counting 3 for a round, 2 for a subangular, and i for an angular 
 particle and dividing the sum by the number of particles in each group. 
 
 ** A proportion of these evidently derived from the sandstones of the coast. 
 
MOVEMENTS OF GROUND WATER 257 
 
 Comparing this with the sea sands, it is at once apparent that 
 the rounding is much more pronounced, though the sands were car- 
 ried only a few miles. These sands have a common origin and are 
 of about the same degree of fineness. 
 
 MOVEMENT OF UNDERGROUND WATERS. 
 
 The movement of underground water depends on the nature of 
 the material through which it flows and the space available for this 
 flow. Underground channels or tunnels may allow the water to 
 flow as readily as it does upon the surface. If the channel is filled 
 completely, the water is under hydrostatic pressure, and it may be 
 forced up a rising slope. Such a stream may act as an aspirator, 
 drawing water or air through fissures past which it flows, and caus- 
 ing currents to flow toward it by suction, and even causing water 
 to rise from a lower to a higher level. This has been regarded by 
 Penck and others as the cause of the currents flowing from the 
 ocean into the land at the island of Cephalonia, Greece, the water 
 replacing that which is drawn up by suction of a strong under- 
 ground stream, which completely fills its channel. For these cur- 
 rents, which formerly drove the "sea mills of Cephalonia," Crosby 
 and Crosby (14) and Fuller (25) have offered other explanations. 
 Underground streams of this kind are further illustrated by some 
 subglacial streams, which, being confined in a tunnel-like tube, often 
 flow uphill, as shown by the eskers which mark their former course. 
 (Grabau-28.) 
 
 Water flowing through a porous soil has of course a vastly lower 
 rate of motion under the same gravitational influence on account 
 of friction. The rate of movement of water through such a porous 
 medium depends on the following factors : 
 
 1. Size of pores in the water-bearing medium. 
 
 2. Porosity of material, i. e., the relative abundance of pores. 
 
 3. Pressure gradient, or change in pressure or head, per unit of 
 length, measured in the direction of the motion. 
 
 4. Temperature of water. 
 
 In general the rate of flow varies with the variation in all of 
 these factors, the law governing this rate of flow or velocity (v) 
 
 being expressed by the formula of Darcy, v = k ^, where p is the 
 
 difference in pressure at the ends of the column of soil (measured 
 by height of water column), // the length of the column and k a 
 constant depending upon the determinable characters of the soil, 
 
258 PRINCIPLES OF STRATIGRAPHY 
 
 especially the size of the grains. The following formula of Allen 
 Hazen (32:5^7) takes more factors into consideration and serves 
 
 for- experimental purposes, v=c d 2 - (0.70-1-0.03^), v being the 
 
 velocity of the water in meters per day in a solid column of the same 
 area as that of the sand, c a constant factor found empirically to 
 approximate 1,000; d is the "effective size"* of sand grains in 
 mm., which is such that 10 per cent, of the material is of smaller 
 grains and 90 per cent, of larger grains than the size given ; h is 
 the loss of head; / is the thickness of sand through which water 
 passes, and t is the temperature on the centigrade scale. The loss 
 of head is measured from points just inside the ends of the column 
 of sand or soil. (See, further, King-4i:5p; and Slichter-64 '.322, 
 329; 65:79, 22.) 
 
 The quantity of water transmitted by a column of sand depends 
 upon the length of the column and the head of water, and further- 
 more varies with the effective size of the soil grain, the tempera- 
 ture of the water and with the porosity of the soil. The flow varies 
 as the square of the size "of the soil grain, and doubling the size of 
 the grain will quadruple the flow of water. Thus the flow through a 
 soil whose effective size of grain is I mm. is 10,000 times the flow 
 through a soil whose effective size of grain is o.oi mm. The flow 
 at 70 F. is about double that at 32 F. 
 
 The Underflow. This is the moving sheet of water beneath the 
 bed and banks of a stream through the porous medium. This may 
 be so concentrated as to produce a subterranean stream, scores of 
 feet in depth and miles in breadth. It naturally follows a line of 
 depression in the surface of the sustaining impervious layer the 
 Thalweg and the rapidity of flow will depend in a very large 
 measure upon the texture of the material forming the river bed. 
 Where this is fine the water will be stored, but a considerable un- 
 derflow is impossible. Where the material is coarse sand and 
 gravel, however, as near the mountains, the water will readily flow 
 through it. In arid regions, the lower reaches of the surface 
 streams often disappear altogether, by sinking into the ground. 
 They are then continued by the underflow, and only occasionally 
 after a heavy storm are the "dry washes" filled again by a rushing 
 surface torrent. In general, the underflow follows the trend indi- 
 cated by the surface branches, which may extend as dry washes 
 
 * Determined by experiment to be the mean diameter of the grains, or the 
 one which, if all the grains corresponded to that size, would give the soil the 
 porosity it actually has. 
 
MOVEMENTS OF GROUND WATER 
 
 259 
 
 across the alluvial fan built up by the dropping of the stream-trans- 
 ported material. 
 
 Rate of Floiv of Underground Water. The following table 
 adapted from Slichter (65 : ^7) shows the theoretical rate of flow 
 and amount of transmission determined by experiment for various 
 kinds of soil, with a porosity of 32 per cent., and at the temperature 
 of 50 F. and with pressure gradients of i : i, and 100 feet to I 
 mile.* 
 
 Table showing permeability of various soils. 
 
 
 Diam- 
 
 Velocities 
 pery 
 
 in miles 
 -ear 
 
 Maximum 
 
 
 eter of 
 grains 
 
 Pressure 
 gradient 
 1:1 
 
 Pressure 
 gradient 100 
 ft. to i mile 
 
 cubic feet 
 per min. 
 
 Silt 
 
 f O.OI 
 
 0.0113 
 
 o . 00026 
 
 o . 000036 
 
 Very fine sand ... 
 
 10.04 
 
 f 0.05 
 
 0.1807 
 0.2823 
 
 o . 00408 
 o . 00638 
 
 0.000577 
 0.000901 
 
 . ,, : ..v^~v; : v-' v /. : 
 Fine sand 
 
 10.09 
 f o. 10 
 
 0.9147 
 I . 1290 
 
 o . 02066 
 
 0.02551 
 
 o . 002920 
 o . 003605 
 
 Medium sand . . . 
 
 \ O.2O 
 
 (0.25 
 
 4.5180 
 7.0580 
 
 O.I02IO 
 0.15940 
 
 0.014420 
 0.022530 
 
 Coarse sand . . 
 
 10.45 
 (0.50 
 
 22.8700 
 28.2300 
 
 0.51650 
 0.63770 
 
 o . 073000 
 0.090120 
 
 Very coarse sand . . 
 
 10.95 
 
 I OO 
 
 101 .9000 
 
 112 9OOO 
 
 2 . 30200 
 2 SSI OO 
 
 0.325300 
 o 360500 
 
 or 
 Very fine gravel 
 
 2 OO 
 
 4 SI 8OOO 
 
 I O 21 OOO 
 
 I 442000 
 
 Fine gravel . . . 
 
 / 3-oo 
 
 IOI6.OOOO 
 
 22 . 96000 
 
 3 . 244000 
 
 
 I5oo 
 
 2823.OOOO 
 
 63 . 77000 
 
 9.012000 
 
 Note. The last figures (o) in the higher numbers are approximate. 
 
 Direct observations on the underflow of water to the Loup 
 River, Nebraska, have indicated a rate of one-third of a mile per 
 
 * The number in italics gives the value just before the upper limit of each 
 grade is reached. Compare table, p. 287, Chapter VI. . 
 
260 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 day, a rate so high (120 -(- miles per year, compare column 4 of ta- 
 ble) that the observations are probably erroneous. Observations on 
 seepage of water from canals, etc. (Slichter-65 142), have given 
 rates of 0.2074, 0.2500, 0.3000, and 1.0369 miles per year, values 
 closely in accord with those received by experiment. 
 
 Pervious and Impervious Strata. Strata which, from their por- 
 osity, permit a flow of water through them are called pervious, 
 while those not so constituted are impervious. Quartz sandstones, 
 especially those of uniform grain, are usually the most pervious, 
 and shales the most impervious of stratified rocks. Limestones are 
 generally impervious, owing to the filling of their pores by secondary 
 deposit, a change much less characteristic of quartz sandstones, 
 though also found here. Some limestones are, however, porous 
 enough to be good water bearers, such as chalk and partly consoli- 
 
 FIG. 37. Cross-section through South Dakota artesian basin. Elevations 
 above sea-level. Vertical scale much exaggerated over the hori- 
 zontal. (After Slichter.) 
 
 dated shelly limestone (coquina, etc.) ; limestones rendered porous 
 in the belt of weathering by solution ; and limestones rendered 
 porous by dolomitization through replacement of some of their cal- 
 cite by magnesium carbonate. 
 
 The Deeper Zones of Flow. Pervious strata confined between 
 impervious ones may, from their position, carry surface waters to 
 great depths and constitute a deeper zone of flow. In thus being 
 confined between impervious layers it differs from the surface zone, 
 which is bounded below by an impervious layer, but above is not 
 confined, but formed merely by the upper limit of ground water. 
 Whereas the subsurface flow follows the slope of the region, that of 
 the deeper zone depends on geologic structure. The deeper zone 
 also draws its supply from great distances and is independent of the 
 local drainage level, while that of the subsurface zone is local. 
 An example of such a pervious bed is the Dakota sandstone of the 
 Front Range and the Great Plains, which is capped by the impervi- 
 
SPRINGS' 261 
 
 ous Benton clay of the Cretacic. The water enters along the outcrop 
 of this formation more than 3,000 feet above sea-level. Over parts 
 of the Great Plains the Dakota has descended near to or even below 
 sea-level, while perhaps 2,000 feet of other strata are piled above 
 it. When tapped by artesian wells the water will rise to within 2,400 
 to 1,500 feet above sea-level, according to the distance from the 
 mountains. As the surface over most of the country is lower than 
 this, the result is the formation of actively flowing artesian wells 
 (see Fig. 37). 
 
 Springs. 
 
 Springs are the escape of ground water at the surface of the 
 lithosphere. By surface of the lithosphere is here meant any point 
 where the lithosphere is in contact with a mass of water or air; 
 thus we have sublacustrine springs and springs formed in subterra- 
 nean channels, in wells, etc. 
 
 Springs commonly issue where the contact between a pervious 
 and an impervious lower layer is exposed in section. In the Helder- 
 berg Mountains the spring line is at the base of Siluric or Devonic 
 limestones, where they rest upon impervious clays (Brayman), or 
 unconformably upon the Hudson River beds. Along the line of 
 contact between the Devonic Onondaga limestone, a porous rock, 
 and the Siluric Monroe limestone, a compact, impervious one in 
 western New York, Canada, and Michigan, occurs a line of copious 
 springs. The contact line here is a disconformity, and the water 
 sometimes gushes out in great volume. The contact between the 
 Lockport dolomite and Rochester shales along Niagara gorge and 
 the whole front of the Niagara escarpment constitutes another such 
 spring line, and so does the upper surface of the Black Shale 
 throughout the southern Appalachians. Where the section is made 
 only into the pervious layer, as in a well, a general seeping or 
 "welling" of the ground water takes place ; where the surface is de- 
 pressed to the ground-water level, or below it, a similar "welling" 
 of the ground water takes place. Swamps are formed in this way, 
 which may be regarded as natural wells on a large scale. 
 
 WATER IN THE SOLID FORM. 
 
 Snow and ice may, on the one hand, be considered as water in 
 the solid state, and so referred to the hydrosphere ; or, on the other 
 hand, as a rock, solid only at low temperatures. In the latter case 
 it belongs either to the igneous or pyrogenic rocks when due to 
 
262 PRINCIPLES OF STRATIGRAPHY 
 
 solidification of water, or to the atmogenic when precipitated as snow 
 and snow ice. Ice is thus a substance intimately uniting the hydro- 
 sphere and lithosphere, just as water in the form of vapor unites 
 tHe hydrosphere and atmosphere. The freezing of water has been 
 dealt with to some extent under the heading of temperature influence 
 on the hydrosphere. As a rock it will be dealt with in Chapter VI 
 and its larger structural features will be taken up in Chapter VIII. 
 Glacial deposits naturally fall under the heading of autoclastic rocks 
 and are discussed in Chapter XII, while deformation due to glacial 
 motion is considered in Chapter XX. Finally, the results of glacial 
 sculpture are treated under the head of glyptogenesis, or the land 
 forms produced by the sculpturing agents. In the present chapter a 
 brief preliminary summary of the movement of water in the solid 
 form and its geological effects will be given. 
 
 Kinds of Movement of Solid Water. Water in the solid state 
 may become translocated either ( I ) passively by transportation, or, 
 (2) actively by movements due to its own gravitative and internal 
 readjustments. Transportation may be either by wind, as in the 
 case of snowflakes and ice crystals, or by water, as icefloes or ice- 
 bergs. Wind-transported snowflakes and ice crystals may accom- 
 plish a certain amount of geological work by corrasion, as noted 
 in Chapter II, and they may be heaped up in dunes or deposited in 
 strata, which may be temporary, or may endure for a long time, with 
 gradual metamorphosis into crystalline ice. One result of wind- 
 transported snow is a special distribution, and consequently the 
 placing of sources of water supply in positions which might prob- 
 ably not be accessible to them in any other way. Water-transported 
 ice blocks often act as powerful agents in erosion and destruction, 
 and they may be responsible for groovings and markings on rock 
 surfaces not otherwise explainable. Extensive deposits of trans- 
 ported material frozen into the ice block or resting on its back 
 are also sometimes formed, as in the case of the Grand Banks of 
 Newfoundland, where the debris brought by the icebergs from the 
 north is dropped upon their melting and so embedded in and made 
 part of contemporaneous marine sediments, boulder conglomerates 
 here accumulating beneath the zone of wave activity. The anomal- 
 ous occurrence of erratics or strayed rock masses in marine forma- 
 tions is also accounted for by floating icebergs. Such ice-rafted 
 erratics have been found in the Caney shale of Oklahoma (Car- 
 bonic) (Woodworth-74). 
 
 Ice masses, moving over the surface of the land constitute the 
 glaciers, which may be either glacial streams or glacial sheets. 
 Their motion is due to a variety of causes, among which partial 
 
MOVEMENT OF GLACIERS 263 
 
 melting and refreezing of the ice crystals constituting the mass are 
 at least important ones. (See the discussion by Chamberlin and 
 Salisbury-9:j7j-j<?j.) Observations on glaciers flowing in valleys 
 have shown that motion is faster at the center than at the sides, 
 and near the top than at the bottom. A current analogous to that 
 found in water streams is thus produced, which also meanders more 
 strongly than does the ice stream as a whole. In broad glaciers, 
 formed by the union of a number of branches, several lines of rapid 
 motion may exist, with lines of weaker movement between. Up- 
 ward currents within the ice also exist, which bring debris from the 
 bottom to the surface at the sides. In this manner lateral moraines 
 of rock and soil are formed on the surface of the valley glacier. 
 This morainal material, augmented by that falling from the cliffs 
 between which the glacier flows, is left at the foot of the ice with 
 much that is carried along the bottom, there to constitute the termi- 
 nal moraine. 
 
 Rate of Movement. Movement of glaciers is, as a rule, greater 
 in summer than in winter. . Some of the glaciers of Greenland 
 move 50, 60, or even more feet per day in summer time, while a 
 case of 100 feet per day has been noted (Chamberlin & Salisbury-9). 
 In this case the movement in April was only 34 feet. Such rapid 
 movements occur only where the ice of large inland areas crowds 
 down into comparatively narrow- fjords. In Switzerland the rate 
 of motion ranges from I or 2 inches to four feet or more per day, 
 while the Muir glacier of Alaska has been found to move 7 feet or 
 more per day (Reid). The causes affecting rate of movement 
 of the ice are: I, thickness and volume of the ice sheet; 2, slope 
 of the land surface ; 3, slope or gradient of upper surface of the ice ; 
 4, character and relief of the rock bed ; 5, temperature ; 6, quantity 
 of water falling on or reaching the glacier. 
 
 Wasting of the Glaciers. Glaciers waste away by melting at 
 their surface, front and sides, and to some extent at the bottom, 
 where heat is generated through friction and compression as well as 
 by the rise of the earth's heat through conduction under cover of a 
 thick ice sheet. Glaciers also waste away by evaporation, the ice 
 changing directly to the form of vapor. The wasting of glaciers on 
 the surface is generally spoken of as ablation. 
 
 Erosive Work of Ice. The erosive work of ice may be twofold : 
 denudation, or the removal of material formed through decomposi- 
 tion and disintegration of the rock surface, and the active removal 
 of fresh rock material by scraping, plucking, etc., or glacial corra- 
 sion. The general process of erosion by ice has been termed execra- 
 tion by Walther (from arare, to flow). This word might be re- 
 
264 PRINCIPLES OF STRATIGRAPHY 
 
 stricted to glacial denudation, i. e., the removal and transport of 
 weathered material. (See ante, Chapter I.) 
 
 The first step in glacial erosion is generally ablation, or the 
 taking up of the weathered material on the surface of the land. 
 When ice accumulates through a long period of gradual refrigera- 
 tion, punctuated by intervals of partial melting, the waterlogged 
 soil, the product of pre-glacial weathering, is incorporated as an in- 
 tegral part into the base of the glacier or ice sheet and carried 
 away with it when movement begins. Through shearing and 
 through formation of ascending ice currents this material may be 
 carried upward, and, from being subglacial, becomes successively 
 englacial and then super glacial. The part remaining in the bottom 
 of the ice is used as a tool for the corrasion of the rock surface, 
 which soon is worn down to the undecomposed layers and becomes 
 smoothed, polished, and marked by parallel striae, the direction of 
 which indicate the direction of ice movement. The material held 
 in the base of the ice sheet (the product of denudation plus material 
 which may have descended from the surface) is likewise polished 
 and striated, this in the flatter fragments of rock usually being con- 
 fined to two faces. 
 
 The heat generated by friction over the rock surfaces, aug- 
 mented by the rising heat of the earth, owing to the ice blanketing, 
 may result in melting the basal portion of the ice sheet, or glacier, 
 whereupon a layer of basally transported material or till is deposited 
 on the previously eroded surface, protecting it from further erosion. 
 If the direction of motion of the ice is subsequently changed, it may 
 not again remove this material, but leave it to protect the striae 
 made during the early period of movement (Crosby). That ice is 
 able to move over unconsolidated material without actively eroding it 
 is shown by many observations (Fairchild-22). Glacial grooves of 
 exceptional size are sometimes formed, the best known being those 
 of Kelley's Island in Lake Erie. The most effective work of cor- 
 rasion by glaciers seems to occur somewhere above the lower end of 
 the glacier, so that deepening of the valley above its mouth results. 
 Both glaciers and ice sheets effect little or no erosion at their front 
 or margins. At the head of the glacier, i. e., at the Bergschrund, 
 plucking or pulling out of loose blocks occurs, resulting in the 
 formation of cirques. Plucking also occurs on the lee side of pro- 
 jecting rock masses which on their stoss side are eroded by corra- 
 sion, the result being a rock mass with smooth upper surface, grad- 
 ually rising in the direction of ice movement, and terminating in a 
 rough cliff downstream. These structures are known as roches mou- 
 
TRANSPORTATION BY ICE 265 
 
 tonnees. Combined erosion by glaciers and subglacial streams is 
 called fluvioglacial erosion. 
 
 Transportation by Ice. As already noted, much material may 
 be transported by floating icebergs or floes and so become incor- 
 porated in marine sediments. Land ice transports rock debris on its 
 surface as superglacial drift, within its mass as englacial drift, and 
 at its bottom as subglacial drift. In form the superglacial material 
 generally constitutes lateral and median moraines. (See posted 
 Chapter XII.) The englacial is likely to be scattered, and the sub- 
 glacial is often in the form of a more or less continuous sheet. 
 Changes from one position to another are constantly effected, the 
 subglacial rising by shearing and upward currents to become en- 
 glacial or superglacial, the englacial becoming subglacial by basal 
 melting of the ice or superglacial by surface ablation, and the super- 
 glacial material becoming englacial or subglacial through the action 
 of descending currents or by falling through fissures or crevasses. 
 By melting on reaching the sea this material may be incorporated 
 with marine sediments, or by advancing over forests and swamps it 
 may be deposited on organic accumulations (future coal beds), and 
 finally, by taking up material from the bottom of the shallow sea 
 over which it passes, the ice may incorporate remains of marine 
 organisms in continental sediments, as in the case of the fossils of 
 Tertiary or younger age included in the drumlins of Boston Harbor 
 and the moraine of Cape Cod. (Crosby and Ballard-i3, Crosby-n.) 
 
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 Proceedings of the Boston Society of Natural History, Vol. XX, pp. 
 136-140. 
 
266 PRINCIPLES OF STRATIGRAPHY 
 
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 able Age of the Fossil Shells in the Drumlins of the Boston Basin. 
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 1 8. DAVIS, W. M. 1899. Physical Geography. Boston, Ginn & Co. 
 
 19. DAVIS, W. M. 1905. Illustrations of Tides by Waves. The Journal 
 
 of Geography, Vol. IV, pp. 290-294. 
 
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 the Geological Society of America, Vol. XVI, pp. 13-74, pis. 12-23. 
 
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 477- 
 
 24. FOREL, F. A. 1901. Handbuch der Seenkunde. Stuttgart. 
 
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 28. GRABAU, A. W. 1900. Lake Bouve. An extinct Glacial Lake in the 
 
 Boston Basin. Occasional Papers of the Boston Society of Natural 
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 America during Ordovicic, Siluric and early Devonic time, Chapter IV 
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 Hydroegraphie, Bd. II, Sept. 3, p. 338. Revue by W. Bremeche. 
 Annales de Hydrologie, 1900, p. 353. 
 
 31. HANSEN, HELLAND, and NANSEN, FR. 1913. Remarks on the 
 
 Oceanographical Investigations carried out by the "Fram" in the North 
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 . 32. HAZEN, ALLEN. 1892. Some Physical Properties of Sands and Gravels. 
 
 Report of the Massachusetts State Board of Health, 1892, p. 541. 
 33. HOCHENBURGER. 1886. Ueber Geschiebsbewegung und Eintiefung 
 fliessender Gewasser. Leipzig. 
 
BIBLIOGRAPHY V 267 
 
 34. HUMPHREYS, A. G., and ABBOTT, H. L. 1861. Report upon the 
 
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 mouths. Philadelphia, 1861, Washington, 1867. 
 
 35. JOHNSON, D. W. 1910. The Supposed Recent Subsidence of tne Massa- 
 
 chusetts and New Jersey Coasts, Science, N. S., Vol. XXXII, pp. 721-723. 
 
 36. JOHNSON, D. W. 1911. Botanical Evidence of Coastal Subsidence. 
 
 Science, New Ser., Vol. XXXIII, pp. 300-302. 
 
 37. JOHNSON, D. W. 1912. Fixite de la cote Atlantique de 1'Amerique du 
 
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 38. JOHNSON, D. W. 1913. The Shoreline of Cascumpeque Harbor, Prince 
 
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 39. KAYSER, E. 1905. Allgemeine Geologic, 2nd ed. 4th ed. 1912 Stuttgart. 
 
 40. KEILHACK, K. 1908. Lehrbuch der praktischen Geologic, 2nd edition. 
 
 Stuttgart. 
 
 41. KING, F. H. 1899. Principles and conditions of the movements of 
 
 Ground Water. Nineteenth Annual Report, U. S. Geological Survey, 
 pt. II, pp. 59-94- 
 
 42. KRUMMEL, O. 1911. Handbuch der Ozeanographie. Bd. II. Stuttgart. 
 
 43. LE CONTE, JOSEPH. 1893. Elements of Geology, 3rd edition. 
 
 44. McGEE, W. J. 1893. Potable Waters of Eastern United States. Four- 
 
 teenth Annual Report, U. S. Geological Survey, pt. II, pp. 1-47. 
 
 45. McGEE, W. J. 1897. Sheet flood erosion. Bulletin of the Geological 
 
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 46. MACKIE, WILLIAM. 1897. The sands and sandstones of Eastern 
 
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 47. MACKIE, WILLIAM. 1897. On the Laws That Govern the Rounding 
 
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 48. NANSEN, FRIDJOF. 1902. Oceanography of the North Polar Basin. 
 
 Kristiana. 
 
 49. OCHSENIUS, CARL. 1893. Ueber unterirdische Wasseransammlungen. 
 
 Zeitschrift f. praktische Geologic, Bd. I, pp. 36-40. 
 
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 Gefalle der Gebirgsfliisse, Progr. der eidgenossischen. Polytechnischen 
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 Part I. The Yorkshire Coast. 
 
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268 PRINCIPLES OF STRATIGRAPHY 
 
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C. THE LITHOSPHERE 
 
 CHAPTER VI. 
 CLASSIFICATION OF THE ROCKS OF THE EARTH'S CRUST. 
 
 As has been outlined in the introductory chapter, the stratig- 
 rapher deals with the genesis of the rocks of the earth's crust and 
 considers their structure and composition, or the petrographical 
 characters of rocks, chiefly from the point of view of their bearing 
 on lithogenesis. The dynamic forces active in the production of 
 rocks are likewise considered by him in their bearing upon this 
 subject. Naturally, those rocks which bear the most satisfactory 
 evidence of chronological succession, i. e., the stratified rocks, re- 
 ceive most attention, for it is the business of the stratigrapher to 
 establish the events in the history of the earth in the order of their 
 occurrence. 
 
 SUBDIVISION OF ROCKS. 
 
 Numerous subdivisions of rocks have been proposed, most of 
 them being largely or entirely artificial in character. The most 
 familiar divisions are: igneous, aqueous, ceolian, and organic. The 
 last three are commonly classed together as stratified or sedimentary, 
 as opposed to the unstratified or igneous rocks. Metamorphic rocks 
 are generally grouped by themselves, though in the beginning they 
 were grouped with the stratified (6). The chief objection to this 
 classification lies in the fact that, under the aqueous as well as 
 under the organic groups, rocks of chemical and of mechanical 
 origin are included. Nor are all of the rocks so classed truly sedi- 
 mentary or stratified. One of the earliest attempts at a rational 
 classification based on origin was that of Carl Friedrich Naumann, 
 who, in the second edition of his Lehrbuch der Geogn.osie, 1858 
 (21), recognized two classes in which all rocks are included. These 
 are: I, The Protogenous, or original; and II, the Deuterogenous, 
 or derived, terms corresponding essentially to the endogenetic and 
 
 269 
 
PRINCIPLES OF STRATIGRAPHY 
 
 exogenetic divisions used in this book. Naumann's terms have been 
 adopted in the latest of French text-books by Hang (14), but in a 
 more restricted meaning. He, first of all, divides all rocks into roches 
 exogenes, or those formed on the outside of the earth, i. e., the sedi- 
 mentary rocks ; and into the roches endogcnes, or those having their 
 origin from within the lithosphere, i. e., the volcanic rocks. The exo- 
 gene rocks are then divided into roches protogcnes, comprising (a) 
 the chemical and (b) the organic deposits, and roches deutogcnes, or 
 the elastics. The old notion of a primary distinction between igne- 
 ous and sedimentary rocks still prevails in this classification, but 
 Haug recognizes the important distinction between elastics and non- 
 clastic sediments. Zirkel (31), too, used similar subdivisions of 
 primary rank when he divided rocks into : A, Original crystalline, 
 and B, Clastic rocks; terms used by Naumann in the first edition 
 of his Lehrbuck, 1850. The term for the first group was not well 
 chosen, since it included rocks which were not crystalline, i. e., ob- 
 sidian, etc. For this reason Zirkel substituted the term non-clastic 
 in 1873. Both Naumann and Zirkel included metamorphic rocks in 
 their class of Protogene or non-clastic (crystalline) rocks. H. 
 Rosenbusch (24), in 1877, on the other hand, included metamor- 
 phic rocks in his class of stratified rocks (Geschichtete Gesteine), 
 which, with the class of massive rocks (Massige Gesteine) the 
 igneous rocks of our present classifications constituted the two ma- 
 jor divisions of rocks. In 1898 (25), however, he made the three fol- 
 lowing classes: I, Eruptive rocks (Eruptivgesteine). These are 
 the igneous rocks of other authors and they are divided into : a, 
 deep-seated rocks, or Tiefengesteine (Plutonic rocks of other classi- 
 fications) ; b, dike rocks, or Ganggesteine; and, c, effusive rocks, or 
 Ergussgesteine, i. e., volcanic rocks of later classifications. II, 
 Stratified rocks (Schichtige Gesteine). These include clastic sedi- 
 ments and chemical precipitates from water; rocks of organic 
 origin and the porphyroid rocks. The latter, though bedded, are 
 clearly out of place in this division, as the author himself recognizes, 
 since they never were sediments nor are such now, but are meta- 
 morphic derivatives of igneous rocks. Siliceous rocks of organic 
 (biogenic) and those of aqueous (hydrogenic) origin are grouped 
 together by Rosenbusch in this classification, and the same is true 
 for calcareous rocks. Coals and other combustibles are placed in 
 a separate subdivision or appendix. Under argillaceous rocks are 
 included the phyllites and other more or less altered or metamor- 
 phosed clay rocks ; under sandstones he includes quartzites, and 
 under calcareous rocks he places marbles, but other- metamorphic 
 rocks are placed in the third main division. Altogether the grouping 
 
ENDOGENETIC ROCKS 271 
 
 within this class is as illogical and unsatisfactory as it well could be. 
 Ill, Crystalline slates (Krystalline Schiefer), This includes the 
 gneisses, mica schists, talc schists, chlorite schists, amphibole and 
 pyroxene rocks, serpentines, the metamorphic calcareous, mag- 
 nesian, and iron rocks, and emery. These, then, include metamorphic 
 sedimentaries as well as metamorphic igneous rocks, and this group- 
 ing can be excused only on the ground of convenience. Rosenbusch, 
 indeed, tries to separate these metamorphics of diverse origin by 
 proposing the prefix ortho for those derived from igneous, and para 
 for those derived from sedimentary rocks. To the above three 
 groups is added a fourth, that of the original crust of the earth, 
 Erste Erstarrungs Kruste. We owe to Johannes Walther (30) the 
 first comprehensive attempt at a truly genetic classification of all 
 rocks. One of the essential features of this system is the recognition 
 of the fact that metamorphic rocks belong with the rocks from 
 which they are derived. He proposed four main divisions, namely : 
 I, mechanical or clastic; II, chemical precipitates and sublimates; 
 III, organic; and, IV, volcanic rocks, or consolidated lavas. 
 
 This is essentially the classification adopted in this book, except 
 that a stronger distinction is made between the first group, the 
 E.voyenctic, or clastic, and the others which are classed as Endo- 
 genetic (Grabau-9). The Endogenetic are those formed by agents 
 acting from within, i. e., by agents intimately associated with the 
 rock mass forming; they produce rocks by solidification, precipita- 
 tion or extraction of the mineral matter from the states of igneous 
 fusion, aqueous solution or vaporization. The Exogenetic rocks, on 
 the other hand, are those formed by agents acting from without 
 upon already existing rock matter, reducing it to a finer condition 
 either by mechanical or by chemical means, while still leaving it in 
 a solid state. They are, in fact, the clastic rocks of earlier writers, 
 while the Endogenetic rocks are the non-clastic. 
 
 I. THE ENDOGENETIC ROCKS. 
 
 These are best understood when we approach them through a 
 consideration of the material of the earth as a whole, and the con- 
 ditions under which it appears to us. Aside from the solid state, 
 three general conditions may be conceived of under which : the ma- 
 terial of the earth's crust may exist. These are: -r/the molten con- 
 dition, or state of igneous fusion and solution ; 2,, the state of solu- 
 tion in water; and, 3, the state of vapor or incorporation in the air. 
 A molten magma is not merely produced by a change of condition 
 
272 PRINCIPLES OF STRATIGRAPHY 
 
 from the solid to the liquid state through a rise in temperature 
 (i. e., snow or ice to water), though this is undoubtedly to be re- 
 garded as the simplest state of fusion. A much more complex state, 
 however, exists in the fusion of compound materials such as the 
 rock magmas consist of. These are to be regarded as solutions of 
 the silicates one in another or several in one, under a condition of 
 high temperature. Solutions of salts in water are not actually dif- 
 ferent in kind from these "igneous solutions," though they take 
 place at a lower temperature. Since, however, such a large part of 
 the earth's surface consists of water in the liquid state, it is con- 
 venient to consider solution in water as distinct from igneous solu- 
 tions. This conception makes it possible to identify the three states 
 of the material from which the lithosphere is to be formed, re- 
 spectively, with the pyrosphere, hydrosphere, and atmosphere. By 
 a direct crystallizing out from the three states (or precipitation in 
 the amorphous state), we have three groups of endogenetic rocks 
 composing the lithosphere, namely: I, the pyrogenic, or igneous; 2, 
 the atmogenic, or atmospheric; and, 3, the hydrogenic, or aqueous 
 (in a restricted sense). By the physiological activities of the organ- 
 isms which constitute the biosphere, the biogenic or truly organic 
 rocks are formed and these may be divided into zoogenic, or animal- 
 formed, and phytogenic, or plant-formed. These four types of 
 endogenetic rocks may then be tabulated as follows : 
 
 1. Pyrogenic, or igneous, rocks Pyroliths. 
 
 2. Atmogenic, or atmospheric, rocks--Atmoliths. 
 
 3. Hydrogenic, or aqueous, rocks (in a restricted sense) 
 Hydroliths. 
 
 4. Biogenic, or organic, rocks (in a restricted sense) Bioliths. 
 The origin and interrelations of these types are shown in the 
 
 following diagram (Fig. 38). 
 
 The first of these groups comprises the Igneous rocks of most 
 current classifications, the other three are commonly included with 
 the clastic rocks as sedimentaries. Metamorphic rocks, though gen- 
 erally considered independently for convenience sake, belong strictly 
 with the unaltered rocks from which they are derived, and of which 
 they constitute modifications. The chief practical difficulty in plac- 
 ing them with their unaltered prototypes in a scheme is found in 
 the impossibility of determining the precise types from which they 
 have been derived (see further below). 
 
 The further subdivisions of the Endogenetic rocks are pri- 
 marily based on chemical composition, and secondarily on texture. 
 As a rule, composition is most readily expressed in terms of the 
 minerals composing the rock if they can be ascertained, and this is 
 
ENDOGENETIC ROCKS 
 
 273 
 
 a simple matter in all but the pyrogenic rocks. In refined work 
 the chemical composition of the latter is by some subjected to a 
 recalculation into the minerals which satisfy the composition (Cross, 
 Iddings, Pirsson, etc.-4), though this at best seems an artificial 
 procedure. 
 
 Texture and structure have been used with rather indefinite 
 limitations. In general, texture is the fine structure or microstruc- 
 ture, concerned especially with minute arrangement of the compo- 
 
 Fic. 38. Interrelations of the Endogenetic Rocks. 
 
 "The material of the earth may be in three states before solidification, 
 i. e., that of fusion, of solution in water, and that of vapor. From these states 
 by direct deposition (endogenetically) we get the three types of fundamental 
 rocks the Igneous, or Pyrogenic; the Aqueous, or Hydrogenic; and the 
 Atmospheric, or Atmogenic (snow and snow-ice). By the physiological ac- 
 tivities of organisms we have formed the Organic, or Bio genie, rocks, the 
 material of which is derived either from the atmosphere (chiefly through 
 plants Phytogenic, though also in a minor degree through animals, as indi- 
 cated by the heavy dotted line) ; or from the water (chiefly through animals 
 Zoogenic, though also in a minor degree through plants). The lighter 
 arrows show to which states the rocks finally return, the dotted lines indicating 
 the less likely change. Biogenic rocks are either vaporized or dissolved, hence 
 the return arrows rise from the center. Pyro-atmogenic rocks, half way 
 between Pyro- and Atmogenic are illustrated by sublimates, and Pyro-hydro- 
 genic rocks, half way between Pyro- and Hydrogenic, by pegmatites." 
 
274 PRINCIPLES OF STRATIGRAPHY 
 
 nent particles, while structure is the coarser arrangement. It might 
 be serviceable to retain structure as a general term, and to speak 
 of the finer structure of rocks, i. e., that which can be seen in a 
 hand specimen, as texture, while the coarser structural features, 
 generally, visible only in the field, come under the heading of 
 geotectonics, or earth architecture. 
 
 The texture of Endogenetic rocks is either crystalline or amor- 
 phous, each of these having a number of subordinate phases, pecu- 
 liar to one or other of the classes of endogenetic rocks. A type 
 of texture or aggregation of a higher order approaching structure 
 may also be observed at times in the endogenetic rocks, which give 
 them a resemblance to rocks of clastic origin. The three types of 
 these aggregates, spherites, granulites, and pulverites, will be dis- 
 cussed at the end of the section on endogenetic rocks. A brief de- 
 scription of each class follows: 
 
 i. THE PYROGENIC OR IGNEOUS ROCKS (Pyroliths). These 
 rocks result from the cooling of a molten magma, and are crystal- 
 line or glassy, or of intermediate character. The following groups, 
 based on the composition of the magma, are most generally met 
 with: 
 
 Composition Groups. 
 
 I. Granite group, where the composition is that of granite, which 
 when fully crystallized out would result in the formation 
 of quartz and orthoclase with hornblende and biotite or 
 muscovite generally present. 
 
 II. Syenitic group, where the composition is that of syenite, re- 
 sulting on crystallization in the formation of orthoclase 
 and hornblende, with other accessory minerals generally 
 present. 
 
 III. Dioritic group, where the composition is that of diorite, i. e., 
 
 resulting in the crystallizing out of plagioclase and horn- 
 blende, frequently with some orthoclase, biotite, and other 
 minerals, and sometimes with sufficient silica to form free 
 quartz. 
 
 IV. Gabbroitic group, with the composition of gabbro, which on 
 
 crystallization will yield pyroxene and plagioclase, with or 
 without basic minerals, as olivine, etc. 
 
 V. Ultra Basic group, the component minerals being ferromag- 
 nesian silicates, without feldspar, and in the more basic 
 with olivine. 
 
 The first of these constitutes the acid group with the percentage 
 of silica (SiO 2 ) 68 or over, the second and third constitute the in- 
 
PYROGENIC ROCKS 275 
 
 termediate group with the percentage of silica (SiO 2 ) between 
 50* and 68; while the fourth and fifth constitute the basic group, 
 with 'the percentage of SiO, below 50. That this classification is 
 only approximate appears from the fact that some gabbros have a 
 percentage of SiO 2 approaching 55, while some granites fall as 
 low as 62 per cent. Each of these groups may be subdivided ac- 
 cording to texture as follows : 
 
 Textural Groups. 
 
 I. Crystalline Division. 
 
 A. Holo crystalline, or Granitic. Also called phaneritic, 
 
 with the minerals all crystallized out, and the lead- 
 ing minerals visible magascopically, as in granite. 
 They may occasionally exhibit a rude porphyritic 
 structure. The crystals may be in part idiomorphic 
 (automorphic), each having its own form, or allo- 
 trionwrphic (xenomorphic), having their outline 
 determined by the surrounding crystals, or both. In 
 basic igneous rocks, of either holo- or cryptocrys- 
 talline texture, an ophitic structure may occur, in 
 which the crystals of pyroxene have the character of 
 large plates, separated and penetrated by fine needles 
 and crystals of feldspar. The pyroxene has crystal- 
 lized around the feldspar, as shown by the fact that 
 the pyroxene is in optical continuity on both sides 
 of the obstruction. Orbicular structure may also 
 occur in basic igneous rocks, and consists of an 
 abundance of spheroidal aggregates ranging in size 
 up to that of a walnut or over, and composed of 
 silicates with radial or concentric arrangements. In 
 the well known napoleonite from Corsica they con- 
 sist of concentric shells with a radial structure and 
 composed of hornblende and feldspar alternately. 
 The Finnish granite, known as Rapakiwi, belongs 
 here. (Harris-i3.) 
 
 B. Cryptocrystalline, also called aphanitic, with a consid- 
 
 erable proportion of the mineral constituents not 
 visible magascopically. When larger crystals (pheno- 
 crysts) are scattered through the main mass (ground 
 mass) the rock is said to be porphyritic or porphyry. 
 
 * 55, according to some. 
 
276 PRINCIPLES OF STRATIGRAPHY 
 
 When the ground mass predominates, the pheno- 
 crysts being few, the rock is spoken of as porphy- 
 ritic rhyolite, trachyte, etc. But if the phenocrysts 
 abound then the rock is called a rhyolite porphyry, 
 trachyte porphyry, andesite porphyry, etc. 
 
 Porphyries (Cross, etc.~4) may, in a general way, 
 be divided into light-colored, or leucophyres, and 
 dark-colored, or melaphyres, and, according to 
 the character of the phenocrysts, into Quartz-leu- 
 cophyres, Feldspar-leucophyres, Quartz-melaphy- 
 res, Feldspar-melaphyres, etc. When intermediate 
 as to color the names quartz-porphyry or quart- 
 zophyres, feldspar-porphyry or feldspar -phyres, 
 hornblende porphyries, or hornblendophyres, etc., 
 are useful. 
 
 Cryptocrystalline texture may be original or second- 
 ary through a process of devitrification of lavas orig- 
 inally glassy or acrystalline. They may be divided 
 as follows : 
 
 B-i. With Trachytic texture, the ground mass 
 consisting of an aggregate of little rods of 
 feldspar in parallel arrangement. This is 
 sometimes visible to the unaided eye. 
 B-2. With Felsitic texture (lithoidal), when the 
 ground mass is so dense as to appear 
 acrystalline except under the microscope, 
 where it is seen to consist of minute quartz 
 and feldspar grains with some glass. 
 B-3. Vesicular and Ainygdaloidal, with a crypto- 
 crystalline ground mass, but with numer- 
 ous vesicles or steam holes which may be 
 filled with mineral matter (amygdaloidal 
 texture). 
 II. Amorphous Division. 
 
 C. Acrystalline, or glassy, the greater part of the mass be- 
 ing an amorphous glass, without crystalline charac- 
 ter even under the microscope. It may be divided 
 into: 
 
 C-i. Vitreous, or obsidianic, when a uniform 
 
 glass as in obsidian. 
 
 C-2. Perlitic with spheroidal structure due to con- 
 centric cracks from contraction in cooling. 
 Ex. Perlite. 
 
PYROGENIC ROCKS 277 
 
 -3. Vesicular, or pumiceous and scoriaceous. 
 When rendered light and cellular by the 
 abundance of steam holes due to expansion 
 of the steam during solidification. The 
 commoner, rougher type constitutes the 
 scoriaceous texture. These vesicles may 
 characterize the entire mass or be limited 
 to layers or streaks. In the basic rocks the 
 scattered vesicles may become filled by min- 
 eral matter either during or subsequent to 
 the volcanic period, and so produce an 
 amygdaloidal structure. 
 
 -4. Spherulitic, micro spherulitic, variolitic, etc. 
 Containing globes or spherules made up of 
 extremely delicate fibers of feldspar, ar- 
 ranged radially and embedded in a mass 
 consisting chiefly of aggregates of tridy- 
 mite or quartz. In size these spherulites 
 may range to several inches. Microspheru- 
 lites are very minute Spherulitic bodies, 
 often occurring in great numbers in bands 
 or affecting the entire ground mass. The 
 large spherulites of older acid lavas are 
 often partly or totally replaced by flint or 
 quartz. In basic rocks a similar structure 
 is known as variolitic. Lithophysce are 
 spherulitic structures varying up to a foot 
 or more in diameter, and consisting of con- 
 centric shells separated by interspaces. 
 (For illustrations, see Iddings-i5; pis. xli 
 and xliii.) 
 
 Cryptocrystalline and Acrystalline rocks may also exhibit a 
 banded texture, i. e., flow structure on a small scale (see beyond). 
 From the combination of any member of the composition group 
 with members of the texture group we get the common types of 
 pyrogenic rocks, as follows* : 
 
 * For a more detailed discussion of the pyrogenic rocks the student is referred 
 to the Hand Book of Rocks, by J. F. Kemp, and to the work of Cross, Iddings, 
 Pirsson and Washington, on Quantitative Classification -of Igneous Rocks, cited 
 in the Bibliography. See also Harker, A Natural History of the Igneous 
 Rocks, and for a brief treatise, his Petrology for Students, Cambridge. 
 
278 PRINCIPLES OF STRATIGRAPHY 
 
 I. The Granite magma, when holocrystalline constitutes granite, 
 when cryptocrystalline, rhyolite, quarts felsite (petro- 
 silex) or quarts porphyry; when glassy, (i) rhyolite ob- 
 sidian, (2) per lite, or (3) rhyolite pumice. 
 
 II. The Syenitic magma when becoming holocrystalline consti- 
 tutes syenite; when cryptocrystalline, trachyte felsite, or 
 trachyte porphyry; when glassy, (i) syenite obsidian, (2) 
 perlite, or (3) syenite pumice. 
 
 III. The Dioritic magma when becoming holocrystalline consti- 
 
 tutes diorite or quarts diorite (free quartz present) ; when 
 cryptocrystalline, andesite, andesite felsite, or andesite 
 porphyry and dacite, dacite felsite, or dacite porphyry; 
 when glassy, (i) andesite obsidian, or (2) andesite pumice. 
 
 IV. The Gabbroitic magma when holocrystalline constitutes gab- 
 
 bro and olivine gabbro; when cryptocrystalline, augite an- 
 desite or augite andesite prophyry, and basalt or basalt 
 porphyry; when glassy, (i) basalt obsidian, or (2) scoria. 
 V. The Ultra basic (non-feklspathic) magmas, when holocrystal- 
 line constitute pyroxenite, and peridotites (with olivine) ; 
 when cryptocrystalline, augitite and limburgite (with cor- 
 responding porphyrys) ; and, when glassy, basic obsidians 
 and scorias. 
 
 The following may further be noted : 
 
 Dolerite, a field name to be used for a holocrystalline rock, either 
 a diorite or a gabbro, in which the ferromagnesian minerals 
 cannot be determined at sight. (Chamberlin and Salisbury 2 : 
 
 Trap, a field name for a cryptocrystalline, non-porphyritic, dark 
 rock, of either dioritic or gabbroitic composition. 
 
 Diabase, a holocrystalline rock of gabbroitic composition, but with 
 a diabasic (ophitic) texture, the plagioclase feldspar crystals be- 
 ing lath-shaped and fully crystallized (idiomorphic), while the 
 augite between them is allotriomorphic. It occurs chiefly as a 
 dike rock or in sills. 
 
 Hornblendite, a holocrystalline rock composed of hornblende with- 
 out feldspar. 
 
 Water and Ice as Igneous Rocks. 
 
 Water solidifying into ice by a lowering of temperature must be 
 referred to the igneous rocks. Its texture may be holocrystalline, 
 but is more commonly cryptocrystalline, or glassy. It must be 
 
ATMOGENIC ROCKS 279 
 
 placed at the ultra basic end of the scale, being entirely free from 
 SiO 2 when pure. (See Kemp-i7.) 
 
 Metanwrphic Derivatives of Igneous Rocks. 
 
 These comprise : ( I ) Gneisses, which include granite gneiss, 
 syenitic gneiss, dioritic gneiss, gabbroitic gneiss, pyroxenitic gneiss, 
 peridotitic gneiss, according to the nature of the pyrogenic rock 
 from which they have been derived. (2) Schists, including some 
 mica schists due to crushing and shearing of acid igneous rocks, 
 hornblende schists derived from basic igneous rocks ; chlorite and 
 perhaps talc schists. (3) Serpentines and some soapstones derived 
 from basic igneous rocks. The weathering products of igneous 
 rocks will be discussed at some length in a later chapter. 
 
 2. THE ATMOGENIC OR ATMOSPHERIC ROCKS (Atmoliths). This 
 group is represented by snow and snow ice,* which are precipitates 
 from the atmosphere, as rock salt and gypsum are precipitates from 
 the water. It forms a surface rock of considerable extent at the 
 present time in the Polar regions, while at various periods in the 
 earth's history it has extended widely over regions now for the 
 most part freed from it. The importance of snow ice in stratigraphy 
 is emphasized by the preservation in it of animals in an almost un- 
 altered condition and by the glacial deposits to which it has given 
 rise in various geologic periods. In composition ice is simple, con- 
 sisting throughout of a single mineral mass, and in texture it is 
 granular crystalline, though appearing compact with conchoidal frac- 
 ture. The types here comprised are : I., Snow ; II., Firn ; and, III., 
 Glacier Ice. 
 
 I. Snoiv. This is a loose aggregate of needles and flakes of crys- 
 talline form and structure, precipitated in this state from the atmos- 
 phere in which the material was held as water vapor. The crystal- 
 line form is soon lost through partial melting and evaporation, a fine 
 granular powder resulting. This is the first step in metamorphism 
 (diagenism). 
 
 II. Firn, or Neve. This is an aggregate of snow grains, either 
 loosely held together or united by ice cement. These aggregates are 
 full of air bubbles. Firn is formed below the snow line and repre- 
 sents a further step in metamorphism of the snow. 
 
 III. Snow Ice, or Glacier Ice. This is a granular crystalline 
 mass in which the individual crystalline ice grains range from the 
 
 * Water ice which is to be considered an igneous rock resulting from the 
 cooling of a magma is of little stratigraphic importance. (See above, p. 278.) 
 
280 PRINCIPLES OF STRATIGRAPHY 
 
 size of a pea near the firn border to that of a hen's egg. The crys- 
 tals are intimately united, so that in fresh ice they cannot be dis- 
 tinguished. 
 
 3. THE HYDROGENIC ROCKS (Hydroliths). These are the only 
 true aqueous rocks and they are wholly of chemical origin. Though 
 often forming beds of considerable extent, they do not generally 
 enclose evidence of their age, though in some cases organic re- 
 mains are found. As a rule, however, the age of a bed of rock salt 
 or gypsum can be determined only by the age of the enclosing 
 rocks. Chemically formed, or hydrogenic limestones, on the other 
 hand, may include organic remains, as is the case in calcareous tufa 
 and cave deposits. Many great limestone beds which are sparingly 
 fossiliferous have frequently been considered of chemical (hydro- 
 genic) origin, but it is not improbable that many, if not most, of 
 these will prove to be of clastic origin. Among hydrogenic 
 rocks of less stratigraphic importance are siliceous sinters and 
 their alteration products and the various ferrites or iron ore 
 deposits, which owe their precipitation from water to inorganic 
 reactions. 
 
 4. THE BIOGENIC ROCKS (Bioliths). These are the only true 
 organic rocks, i. e., those due directly to the physiological activities 
 of organisms. They are among the most important rocks with 
 which the stratigrapher has to deal, for they are the rocks richest 
 in organic remains. As examples may be mentioned the organic 
 limestones, such as coral and shell rock ; and the organic oozes, 
 whether calcareous or siliceous. Here also belong the deposits of 
 coals and vegetable materials in all stages of carbonization, from 
 peat to anthracite. 
 
 Bioliths may be divided into Zooliths, or those of animal origin, 
 and Phytotttks, or those of vegetal origin. The latter include two 
 important types, those formed by the direct accumulation of vegetal 
 matter, such as peat, coals, etc., which, from their burnable nature, 
 have been called caustobiolitJis * (Potonie, see Chapters x and xi), 
 or better caustophytoliths; and those forming pure accumulations 
 of mineral matter, either silicia (diatoms) or lime (nullipores, etc.). 
 These are the acaustophytoliths. Caustobioliths may also be of 
 zoogenic origin (caustozooliths), but these are rare (some oils, etc.). 
 Finally, caustoliths of non-organic origin are also known, such as 
 chemically formed petroleum, asphalt, graphite, and sulphur. Caus- 
 tobioliths have been divided into three groups, according to their 
 mode of origin. These are: 
 
 * Kau<rr6y, verbal adjective of Ket/etv burn. 
 
BIOGENIC ROCKS 281 
 
 Caustobioliths. 
 
 i. Sapropelites, ouTrpos (sapros), rotten; m;Xos (pelos), slime, 
 mud; "T/S (ites), derived from. These are derived from the 
 decaying organic matter of water organisms, both animal and plant, 
 algae, etc.* (sapropel, Faulschlamm, decay ooze, putrid slime). 
 When formed into rock they constitute sapropeliths or sapropelites.f 
 They differ from the humus rocks in their greater content of fat 
 and protein. 
 
 2. Humus and Humulith. These are deposits derived from de- 
 caying land plants, including those of swamps and marshes. Car- 
 bohydrates are an important product of the decay of the higher 
 plants. All peat and coal deposits belong here. Lithified, they form 
 humus rock or chamaeliths (x a ^ MU on the ground, Greek equiva- 
 lent of humus; the Latin would be humulith). 
 
 3. Liptobiolith, Xewrw (leipo), Aewrros (leiptos, Latinized, Up- 
 tos, left behind, residual and biolith). These comprise the resins 
 and gums, amber, copal, etc., which, from their greater resistance to 
 decay remain behind after the destruction of the plants containing 
 them. 
 
 SUBDIVISION OF HYDROGENIC AND BIOGENIC ROCKS. In both 
 hydrogenic and biogenic rocks the chemical division is most readily 
 made on the basic elements of the salts. In texture hydrogenic 
 rocks are both crystalline and amorphous while in biogenic rocks the 
 amorphous texture predominates. 
 
 Textures of Amorphous Hydrogenics. Among the amorphous 
 hydrogenics the following subtextures are most marked : 
 
 (a) Botryoidal, with grape-like, rounded surfaces. 
 
 (b) Pisolitic, of large spherules. 
 
 (c) Oolitic, of small spherules, also characteristic of the bio- 
 
 genic rocks. 
 
 (d) Banded, as in stalactic deposits (stalactites and stalagmites). 
 
 (e) Laminated, or scaly. 
 
 (f) Fibrous. 
 
 (g) Concretionary. 
 
 (h) Tufaceous, as in calcareous and siliceous, tufa or sinter. 
 Textures of Biogenic Rocks. Among the biogenic rocks we note 
 the following subtextures : 
 
 * Mineral structures, such as shells and skeletons, are of course excluded, 
 t The termination pelite should be restricted to oozes or slimes of endogenetic 
 origin, leaving the termination lutyte for oozes of exogenetic or clastic origin. 
 
282 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 (a) Granular, the texture of the fine organic oozes. 
 
 (b) Oolitic, consisting of minute spherules or oolite grains. 
 (c) Earthy texture. 
 
 (d) Compact conchoidal, as in coal, etc. 
 
 The following table gives some of the principal hydrogenic and 
 biogenic rocks (Grabau~9) : 
 
 Table of the principal types of hydrogenic and biogenic rocks. 
 
 Class 
 
 
 
 Composition 
 
 
 
 
 (a) 
 
 (b) 
 
 (c) 
 
 (d) 
 
 (e) 
 
 
 Alkali, 
 
 Calcare- 
 
 Siliceous 
 
 Ferru- 
 
 Carbona- 
 
 
 ous 
 
 ous 
 
 
 ginous 
 
 ceous 
 
 
 
 Chemical 
 
 
 
 
 
 
 Limestone, 
 
 Siliceous 
 
 
 
 
 Rock Salt, 
 
 Stalactic 
 
 Sinter, 
 
 Bog Ore, 
 
 
 HYDROLITHS 
 
 Etc. 
 
 Deposits, 
 
 Vein 
 
 Limonites, 
 
 
 Original 
 
 Natural 
 
 Calcareous 
 
 Quartz, 
 
 Siderites, 
 
 
 
 Soda 
 
 Tufa, Gyp- 
 
 Flint, 
 
 etc. 
 
 
 
 
 sum, An- 
 
 Chert 
 
 
 
 
 
 hydrite, 
 
 
 
 
 
 
 etc. 
 
 
 
 
 
 
 
 
 Specular 
 
 
 Metamorphic 
 
 
 Marble, 
 
 Quartz 
 
 Hematites, 
 
 
 
 
 Alabaster 
 
 Rocks 
 
 Magnet- 
 
 
 
 
 
 
 ites, etc. 
 
 
 
 
 
 Siliceous 
 
 
 Peat, Lig- 
 
 
 
 Organic 
 
 Organic 
 
 
 nite, Bitu- 
 
 
 
 Limestones 
 
 Oozes, 
 
 
 minous 
 
 BlOLITHS 
 
 Phosphate 
 
 Coral Rock 
 
 Diatoma- 
 
 Limonites 
 
 coal, some 
 
 Original 
 
 Rocks 
 
 Shell beds, 
 
 ceous 
 
 (organic) 
 
 Anthracites 
 
 
 
 (organic 
 
 Earth 
 
 
 etc. (Caus- 
 
 
 
 oozes, etc.) 
 
 Tripolite, 
 
 
 tobioliths) 
 
 
 
 
 etc. 
 
 
 
 
 
 
 
 Specular 
 
 Certain an- 
 
 
 
 
 Quartz 
 
 hematites 
 
 thracites, 
 
 Metamorphic 
 
 
 Marble 
 
 Rock 
 
 spathic 
 
 Native 
 
 
 
 
 or 
 
 and mag- 
 
 coke, Bitu- 
 
 
 
 
 Quartzites 
 
 netic 
 
 mens, etc. 
 
 
 
 
 
 iron ores 
 
 Graphite 
 
 
 
 
 
 
 in part 
 

 ENDOGENETIC SANDS 283 
 
 SPHERYTES, GRANULYTES, AND PULVERYTES (pelytes). These 
 names have been suggested (Grabau-io) for rocks composed of 
 aggregates of constructional origin simulating in texture destruc- 
 tional or clastic rocks and having many features in common with 
 them, such as stratification, etc. The textures which characterize 
 these rocks are spherytic, granulytic, and pulverytic, corresponding 
 to the textures rudaceous, arenaceous, and lutaceous among the clas- 
 tic rocks. Thus a rock formed of volcanic bombs would be a 
 spheryte, one formed of lapilli or oolitic grains a granulyte, and one 
 formed of diatom frustules, or minute radiolaria or foraminifera, a 
 pulveryte. The last three types would be of biogenic origin, and 
 therefore would constitute biopulverytes, two of them being bio- 
 silicipulverytes, the material being silica, the third a biocalci- 
 pulveryte, the material being calcite. A pulverytic rock of hydro- 
 genie origin would be a hydropulveryte. As suggested above, the 
 term pelyte (from the Greek 707X05, slime) might well be restricted 
 to muds and slimes of endogenetic origin, and so be used instead 
 of the word pulveryte. Thus, instead of pyro-, atmo-, hydro-, and 
 biopulverytes, we may use the terms, pyropelytes, atmopelytes, hy- 
 dropelytes, and biopelytes. 
 
 Chemically formed oolites are hydrocalcigranulytes, or, if of 
 silica, hydrosilicigranulytes. The oolitic iron ores of Wisconsin 
 (Siluric) are probably hydro ferrogranulytes. Organically formed 
 oolites are biocalcigranulytes ; granular snow (firn) is an atmo- 
 granulyte, and volcanic lapilli form a pyrogranulyte. A bed of vol- 
 canic bombs is a pyrospheryte, and one of unworn coral or Girva- 
 nella heads a biospheryte (biocalcispheryte). All of these rocks are 
 of endogenetic or nonclastic origin. 
 
 OOLITHS, PlSOLITHS, ROGENSTEINE, ETC. Rocks Composed of 
 
 spherical grains of either hydrogenic or biogenic origin are called 
 Oolites or Ooliths when the grains are small, and Pisolites or 
 Pisoliths (Pea grits) when they have the size of a pea or over. 
 Rogensteine are ooliths or pisoliths in which the grains (ooids) 
 are held together by a more or less argillaceous cement. In typical 
 ooliths, so named from their resemblance to fish-roe, each grain 
 consists of successive concentric shells of carbonate of lime, and has, 
 moreover, commonly an internal radiating fibrous structure, which 
 gives a black cross between crossed nicols. The lime is often de- 
 posited around some foreign body, but also often without such a 
 body, forming a sphere hollow at the center. The granules consist 
 sometimes of aragonite, sometimes of calcite, or they are formed 
 by an intermediate substance, ktypeit. Great variation in size occurs. 
 
284 PRINCIPLES OF STRATIGRAPHY 
 
 The giant pisoliths * of Zepce, Bosnia, range from 2 to 13.5 centi- 
 meters in diameter, but ordinary ooliths do not range much above 
 "1.5 mm. In the Bosnian examples the kernal is magnesite and the 
 surrounding shells dolomite. Both concentric and radial structure 
 is shown in these and they are believed to have been formed in hot 
 springs, similar to the pisoliths of the Carlsbad Sprudel. 
 
 True ooliths and pisoliths are precipitations (hydrogenic or bio- 
 genie) and their spherical form is an original structure. Rocks 
 of clastic or worn calcite grains or fragments of shells, etc., may 
 resemble ooliths, and are indeed often mistaken for them. To such 
 Bornemann has applied the term pseudo-ooliths, and they belong 
 to the category of exogenetic rocks, unless, indeed, they are subse- 
 quently enlarged by deposition of lime about them. Concretions 
 may also assume the form of ooliths or pisoliths, but they are 
 secondary or diagenetic structures. Three modes of origin have 
 been most widely discussed by geologists and one or the other has 
 frequently been regarded as the sole mode. These are : i. Chemical, 
 or hydrogenic ; 2. animal, or zoogenic ; and, 3. plant, or phytogenic. 
 Each of these will be discussed under its appropriate heading in 
 succeeding chapters. 
 
 II. THE EXOGENETIC, OR CLASTIC ROCKS 
 
 In discussing next the clastic rocks, the agent active in the 
 production of their present characteristics will be considered as of 
 primary importance in making the larger divisions. It is not always 
 possible to determine what was the cause of the clastic condition 
 of a given rock, since other agents subsequently active have pro- 
 duced those features which give the rock its most characteristic 
 aspects. Thus a sand mass may owe its origin in part to atmos- 
 pheric disintegration and in part to the mechanical activity of the 
 water. Its final form, however, may be given by aeolian action, 
 the mass becoming finally by diagenism a consolidated sand-dune. 
 It will, however, be observed that the agent last active, and there- 
 fore the one whose characteristics were most strongly impressed 
 upon the mass, i. e., the wind, is not only responsible for the form 
 and structure which the deposit eventually takes on, but also, in part 
 at least, modifies the original form of the component grains. Thus 
 without overlooking the claims of the other agents those of the wind 
 may be considered as greatest and the rock is therefore placed under 
 the division of wind-formed elastics, or anemoclastics. 
 
 * These should be classed as hydrospherytes. 
 
EXOGENETIC ROCKS 285 
 
 The relative claims of the various agents active in the production 
 of a given clastic rock once determined provided there is more 
 than one agent it will be found that most rocks fall under one of 
 five groups, though some rocks may fall so precisely half way be- 
 tween two groups that it becomes a matter of individual opinion 
 where it should be placed. The five principal groups are : 
 
 1. Pyroclastic rocks, or pyroclasts. 
 
 2. Autoclastic rocks, or autoclasts. 
 
 3. Atmoclastic rocks, or atmoclasts. 
 
 4. Anemoclastic rocks, or anemoclasts. 
 
 5. Hydroclastic rocks, or hydroclasts. 
 
 6. Bioclastic rocks, or bioclasts. 
 
 The interrelations of these rocks are shown in the following 
 diagram (Fig. 39), on page 286. 
 
 
 
 Textural Groups. 
 
 In these divisions the grain of the rock or its texture is of 
 greater importance than the composition, for, although the latter is 
 often the prime cause of selective destruction of rocks, yet this is 
 generally only on a minor scale, and the destruction of the different 
 rocks by the same agent, especially when mechanical, goes on with- 
 out much reference to the composition. On the other hand, the size 
 of the grain is generally directly proportional to the intensity of ac- 
 tion of the agent (aided of course by the composition and struc- 
 ture of the original rock), and so naturally takes a higher classi- 
 ficatory rank. These types of texture or grain of clastic rocks are 
 recognized : 
 
 1. Rudaceous * texture, or that of the rubble rocks, in which the 
 grain is larger than that of a sand grain. Consolidated rocks 
 of this texture are Rudytes (psephytes of many authors). 
 
 2. Arenaceous f texture or that of sand rocks, irrespective of 
 composition, in which the size of the grain varies from being 
 barely visible to that of a grain of rice. Consolidated rocks 
 of this texture are Arenytes (Psammytes of some authors). 
 
 3. Lutaceous % texture or that of impalpable powder or rock 
 flour. Consolidated rocks of this type are Lutytes (i. e., 
 mud rocks). (Pelytes in part of some authors.) 
 
 * From rudus, Lat. for rubble, 
 t From arena, Lat for sand. 
 I From lutum, Lat. for mud. 
 
286 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Size of Grain. In recent years attempts have been made to es- 
 tablish a more precise mode of designation of the various types 
 based on size of grain. The following is the standard adopted by 
 the New York City aqueduct commission and may well be adopted 
 as a general standard with the emendations given beyond. 
 
 FIG. 39. Diagram showing the interrelations of the exogenetic rocks. ABC 
 represent the crust of the earth or lithosphere. From within this 
 shell, but still external so far as the crust is concerned, the volcanic 
 explosions produce the pyroclastic rocks on the surface of the 
 earth. Within the crust itself are formed the autoclastic rocks. 
 From without the shell the attack by atmosphere, hydrosphere and 
 biosphere produce, respectively, atmoclastic (and anemoclastic), 
 hydroclastic and bioclastic rocks. The final result of the destruc- 
 tive activities of the various agents is the return of the material 
 either to the air as vapor or to the water in solution, or more 
 rarely to assimilation by the biosphere (salt, etc.). Fusion may 
 transfer some of the material to the realm of the pyrosphere. The 
 cycle of change is thus complete and redeposition will be as endo- 
 genetic rocks. 
 
 /, Coarse gravel above 5. mm. ; 2, fine gravel 5 to I mm. ; 5, 
 coarse sand I to 0.5 mm. ; 4, medium sand 0.50 to 0.25 mm. ; 5, fine 
 sand 0.25 to o.io mm.; 6, superfine sand o.io to 0.05 mm.; 7, rock 
 flour (silt, Merrill) 0.05 to o.oi mm. ; 8, superfine flour (fine silt, 
 Merrill) o.oio to 0.005 mm - J 9> C ^ a 7 s ^ ze O-OO5 to o.oooi mm. 
 
EXOGENETIC ROCKS 
 
 287 
 
 Eventually this classification was published by Merrill in 1898 
 (20:56*0), the only difference being that he gives the range of fine 
 gravel as between 2 and i millimeter, and classes everything above 
 2 mm. as gravel. Crosby (3*^05) has given a somewhat different 
 valuation for some of the types as follows : 
 
 Fine sand : 0.45 mm. ; superfine sand : 0.28 mm. ; quartz flour : 
 o.i 6 mm. ; superfine quartz flour : 0.08 mm. 
 
 Keilhack ( 16:5^% 528) gives the following classification, accord- 
 ing to size of grain : i, grains above 2 mm. diameter : gravel; 2, 
 grains from 2 to i mm. diameter : very coarse sand; 3, grains from i 
 to 0.5 mm. diameter: coarse sand; 4, grains from 0.5 to 0.2 mm. 
 diameter: medium sand; 5, grains from 0.2 to o.i mm. diameter: 
 fine sand; 6, grains from o.i to 0.05 mm. diameter: superfine sand; 
 7, grains from 0.05 to o.oi diameter : dust; 8, grains smaller than 
 o.oi mm. diameter: finest dust. Nos. 2 to 6 inclusive were classed 
 merely as sands ; the varietal names are here added. 
 
 It will be seen that the subdivisions of the sands here given cor- 
 respond very closely to those selected by the New York engineers, 
 who, however, place the grains above i mm. in diameter into the 
 category of gravel. No. 7, rock flour of the engineer's table, also 
 corresponds to No. 7, dust of Keilhack's table. 
 
 From these analyses, we may construct the following table, 
 which may serve as a standard for comparison : 
 
 Table of standard sizes of rock fragments. 
 
 1 . Boulders above 1 50 . oooo mm. 
 
 2. Cobbles 150.000 to 50.0000 mm. 
 
 3. Very coarse gravel .... 50.000 to 2 5. oooo mm. 
 
 4. Coarse gravel 25 . ooo to 5 . oooo mm. 
 
 5. Fine gravel 5 . ooo to 2 . 5000 mm. 
 
 6. Very coarse sand (or 
 
 very fine gravel) ... 2 . 500 to i . oooo mm. 
 
 7. Coarse sand i .000 to 0.5000 mm. 
 
 8. Medium sand 0.500 to 0.2500 mm. 
 
 9. Fine sand 0.250 to o. 1000 mm. 
 
 10. Superfine sand o. 100 to 0.0500 mm. 
 
 11. Rock flour 0.050 to o.oioo mm. 
 
 12. Superfine flour o.oio to 0.0050 mm. 
 
 13. Clay size 0.005 to o.oooi mm. 
 
 Texture rudaceous; on 
 consolidation forming 
 rudytes. 
 
 Texture arenaceous; on 
 consolidation forming 
 arenytes. 
 
 Texture lutaceous; on 
 consolidation forming 
 lutytes. 
 
 Orth (22), Laufer (18) and Wahnschaffe (29) are in essential 
 agreement with Keilhack, and so is E. Wollny. Orth calls material 
 from i mm. to 3 mm. very coarse sand and fragments, above 3 mm. 
 
288 PRINCIPLES OF STRATIGRAPHY 
 
 pebbles. Laufer and Wahnschaffe call grade 4 of Keilhack's scale 
 fine sand and both 5 and 6 very fine sand. Wollny makes his 
 medium sand from 0.5 to 0.25 and his fine sand 0.25 to o.i. From 
 o.i to 0.05 he calls coarse silt, from 0.05 to 0.025 medium silt, from 
 the last to 0.005 mm. fine silt, and below that to o.ooi mm. colloidal 
 clay. Orth, Laufer, etc., call 0.05 to o.oi mm. dust, and everything 
 below that finest dust. Wollny calls fragments from 5 to 2 mm. 
 medium gravel, from 10 to 5 coarse gravel and above 10 mm. stones. 
 
 Thoulet has given these dimensions, gravel: coarse, 9.0 mm. ; 
 medium 4.5 mm.; fine 3.0 mm.; sand: coarse (a) 1.32 mm., (b) 
 0.89; medium (a) 0.67, (b) 0.54, (c) 0.45 ; fine (a) 0.39, (b) 0.34, 
 (c) 0.30, (d) 0.26 mm.; very fine 0.04 mm. Silt below 0.04 mm.* 
 
 It will be seen that Crosby and Thoulet differ most from the 
 others, and also from each other. Their definite sizes are less sat- 
 isfactory than the ranges given by the others. f 
 
 Types of Sands Based on Origin. 
 
 Sherzer (26) has recently proposed to subdivide sands according 
 to their mode of origin into 7 groups, each with a number of sub- 
 groups. They are herewith given, separated into clastic and non- 
 clastic sands, and each is referred to its proper place in the classifi- 
 cation adopted in this book. Three additional types are added to 
 make the series complete (Grabau-io: 1006). 
 
 A. Clastic sands (Exo genetic). 
 
 1. Glacial sand typej Autoclastic = autoarenyte 
 
 2. Volcanic sand type Pyroclastic = pyroarenyte 
 
 3. Residual sand, type Atmoclastic = atmoarenyte 
 
 4. Aqueous sand type Hydroclastic = hydroarenyte 
 
 5. ^Eolian sand type Anemoclastic = anemoarenyte 
 
 6. Artificial sands (added) Bioclastic = bioarenyte 
 
 B. Non-clastic sands (endogenetic, see page 283). 
 
 7. Organic sand type Biogenic sand (biogranulyte) 
 
 8. Concentration sand type Hydrogenic sand (hydrogranulyte) 
 
 9. Snow and firn sand (added) Atmogenic sand (atmogranulyte) 
 
 10. Lapilli or igneous sand (added) Pyrogenic sand (pyrogranulyte) 
 
 * These grades are numbered 1,2, etc., by Thoulet. 
 
 t For further analyses see the table given under wind transportation, p. 59. 
 
 t In this he includes the material resulting in the manufacture of talus in 
 avalanches, rock slides, rock and mud flows, and earth movements along joint 
 planes. All except the first, which is atmoclastic, belong under the autoclastic 
 group with the glacial sand type. 
 
EXOGENETIC ROCKS 289 
 
 Sherzer designates as subtypes sands of one type modified by 
 another agency and calls them by a compound term. Thus an 
 ague o -residual sand (hydro-atmoclastic sand) is one in which the 
 granules have been produced by the various residual agencies, and 
 are subsequently more or less modified by water action. Again a 
 residua-aqueous sand (atmo-hydroclastic) is one in which water- 
 rounded grains have been subjected to the agencies of weathering, 
 and give more or less evidence of such action. The principal sub- 
 types or intermediate types may be grouped as follows : 
 
 aeolo-aqueous or anemohydroclastic 
 aeolo-residual or anemoatmoclastic 
 seolo-volcanic or anemopyroclastic 
 aeolo-glacial, etc. or anemoautoclastic 
 aqueo-aeolian or hydroanemoclastic 
 aqueo-residual or hydroatmoclastic 
 aqueo-volcanic or hydropyroclastic 
 aqueo-glacial, etc. or hydroautoclastic 
 residuo-aeolian or atmoanemoclastic 
 resi duo-aqueous or atmohydroclastic 
 residuo-volcanic or atmopyroclastic 
 residuo-glacial or atmoautoclastic 
 glacio-aeolian or auto-anemoclastic 
 glacio-aqueous or auto-hydroclastic 
 glacio-residual or auto-atmoclastic 
 glacio-volcanic or auto-pyroclastic 
 
 In all cases the agent last modifying the type is placed first, the 
 agent producing the original type last. The organic elastics or bio- 
 elastics are of such recent origin that reworking by other agents has 
 not occurred on an extensive scale. When it occurs, the coupling 
 of the respective prefix with bioclastic will designate it. Reworking 
 of other sands by volcanic agencies is of so rare an occurrence that 
 such types may be neglected, although in a complete classification 
 they must be included. 
 
 The organic (biogenic) and concentration or chemical (hydro- 
 genie) sand types may also be reworked, producing seoloorganic 
 and aeolo-concentration types, aqueo-organic and aqueo-concentra- 
 tion types, etc. i. e., the wind- or water-worn and the weathered 
 biogenic and hydrogenic sands. The characters of the undisturbed 
 endogenetic sands will be more fully dealt with in later chapters. 
 The principles of classification applied to sands may equally be ap- 
 plied to the coarser or rudaceous material and the finer or lutaceous 
 matter. 
 
290 PRINCIPLES OF STRATIGRAPHY 
 
 Composition of Clastic Rocks. 
 
 In composition clastic rocks may be pure or impure, simple or 
 complex. If one mineral type predominates, such as lime or quartz, 
 this fact may be combined with the corresponding textural term 
 into a compound word expressive of both. Thus, if the material of 
 the clastic rock is pure lime, the rock becomes a calcirudyte, a cal- 
 carenyte or a calcilutyte, according to the texture. If quartz, the 
 rock becomes a silicirudyte, a silicarenyte, or a silicilutyte, accord- 
 ing to the texture. If the rock is impure it will still be possible to 
 designate it, keeping in mind that the dominant mineral constitu- 
 ent furnishes the name. Thus we may have siliceous calcirudytes, 
 calcarenytes, calcilutytes or calcareous silicirudytes, silicarenytes, 
 silicilutytes. Or the impurities may be iron, carbon, clay, etc., in 
 which case we use the prefixes ferruginous, carbonaceous, argil- 
 laceous, etc. 
 
 Lutytes are most generally formed among the argillaceous or 
 clay rocks, but pure argillutytes are not very common. Generally 
 they are siliceous, calcareous or carbonaceous argillutytes, all of 
 which are more familiarly known by the structural terms shales or 
 slates, which terms, however, express nothing definite in regard to 
 the composition. 
 
 Clastic rocks of complex composition, as, for example, those 
 formed from the reconsolidation of disintegrated granites (ark- 
 oses), can be spoken of simply as rudytes, arenytes, or lutytes, 
 without attempt at defining their composition. 
 
 Examples of elastics under each group are as follows : 
 
 i. THE PYROCLASTICS. In composition these are seldom simple, 
 being mostly complex siliceous rocks shattered by volcanic 
 explosions. The more or less indefinite terms tuff, volcanic 
 breccia and agglomerate are, commonly used. The essential 
 types are : 
 
 Pyrorudytes: coarse, chiefly angular volcanic blocks and 
 bombs, loose or recemented by finer material volcanic 
 breccias and agglomerates. 
 
 Pyr arenytes: coarse tuffs where the grain is not above the 
 size of the ordinary sand grain (2 mm.). They gener- 
 ally show rude stratification and may contain organic re- 
 mains. (Vide, the buried cities and human remains in 
 the tuffs of Vesuvius and other volcanoes.) 
 Pyrolutytes: fine tuffs composed of volcanic dust and 
 ashes. Stratified, and enclose remains, as in the case of 
 pyrarenytes. 
 
PYROCLAST1CS AND AUTOCLASTICS 291 
 
 Volcanic sand is characterized by irregular and sharply angular 
 outline, giving no evidence of erosion except in the case of the 
 larger particles, where partial rounding from mutual attrition dur- 
 ing suspension occurs. The sands are comparatively well sorted, 
 according to size, the finest material being often carried far 
 away. More or less well defined crystals are generally visible un- 
 der the microscope, but as a rule much of the material is amorphous, 
 showing flow structure or vesicular character. (26 : 629, with refer- 
 ences.) Subsequent modification and rounding by water or air 
 gives us hydropyroclastics and anemopyro elastics, while weathering 
 produces atmopyro elastics. When water laid, remains of marine or 
 fresh- water organisms may be enclosed in these strata, or drifted 
 land organisms may be entombed, as in the case of the Tertiary 
 "Lake beds" of Florissant, Colorado. 
 
 2. THE AUTOCLASTICS. This group comprises all rocks shat- 
 tered or crushed within the earth either by pressure of one 
 mass upon the other, or by movement of rocks over each 
 other. Fault-breccias and the material of the "crush zones" 
 must be classed here, as well as fragments produced by 
 avalanches. Earthquake-shattered rocks may also be in- 
 cluded, though they may likewise be considered transitional 
 to the pyroclastics. By far the most important autoclastic 
 products, however, are those resulting from glacial erosion. 
 Ice, including all the material frozen in it, is a part of the 
 earth's crust while it exists, and hence any material ground 
 up between the ice and the rock on which it moves is of the 
 type of the material crushed between other moving rock 
 masses (ex. fault breccia). Furthermore, since all ice-trans- 
 ported material has received its most characteristic features 
 from that agent, we may with propriety include such material 
 in this group, even though it was originally broken by atmos- 
 pheric agencies. Such rocks, if determinable, would come 
 under the compound heading, auto-atmoclastic. 
 
 Fault breccias or autorudytes partake of the composition of the 
 rocks from which they were formed, with probably slight changes 
 due to secondary modifications. In limestones there may thus occur 
 pure autocalcirudytes, while among pure quartz rocks autosilici- 
 rudytes may occur. In general, however, the composition of auto- 
 clastic rocks is quite impure, and this is particularly the case in the 
 autorudytes and other types which result from the consolidation of 
 glacial deposits. The latter are of the most importance to the 
 stratigrapher, for there can be little doubt that they are represented 
 
292 PRINCIPLES OF STRATIGRAPHY 
 
 in many of the geologic periods of the earth's' history. Autorudytes 
 of glacial origin, when unaffected by other agents, are characterized 
 by the polished and striated surfaces of the boulders, larger pebbles 
 and cobbles. Flat blocks generally have only two sides striated, 
 while the margins may remain angular. The characteristic striation 
 Js soon lost through subsequent wear by streams from the ice, the 
 material thus becoming hydroclastic (potamoclastic). The charac- 
 teristics of glacial sands, whether derived from the crushing of 
 igneous or of clastic rocks, lie chiefly in their angularity and fresh- 
 ness of grain, unless subsequent weathering has attacked these. If 
 the material is derived through crushing of igneous or other crystal- 
 line rocks, it will show a variety of mineral grains. The quartz 
 grains will be sharp-edged and pointed, with strongly vitreous and 
 conchoidal surfaces, while the cleavable minerals will show fresh 
 cleavage faces as well as sharp outlines. (Sherzer-26:d?j.) 
 When pure clastic rocks such as sandstones are crushed by ice the 
 resulting material will be pure, with sharply angular grains, which 
 may or may not be derived from originally rounded grains. 
 
 Glacial boulders and sands are frequently reworked by the 
 glacial streams and so become hydroautoclastic or aqueo-glacial 
 (Sherzer). The finer rock flour, etc., may be reworked by wind 
 and so become anemo-autoclastic or aeolo-glacial (ex. loess). See 
 further, Chapters XII and XIII. 
 
 3. THE AT^OCLASTICS. These comprise rocks broken in situ, 
 either by chemical or mechanical means, and recemented 
 without further rearrangement by wind or water. Most of 
 the rocks of this type are of complex composition, and there 
 is a characteristic angularity in the coarser material which 
 shows the absence of water. Stratification also is coarse or 
 absent altogether. Characteristic examples are found in talus 
 breccias, which when consolidated form typical atmorudytes ; 
 in the extensive subaerial accumulations of waste along 
 slopes of most mountains, and in many of the Tertiary and 
 earlier subaerial deposits, which were neither windlaid nor 
 deposited in water bodies. Remains of land plants and 
 animals are often characteristic of these rocks. The kaolinite 
 and laterite, i. e., decomposition products which mantle the 
 rock in unglaciated regions, when consolidated, also form 
 typical examples of atmoclastic rocks. 
 
 The composition of atmoclastic rocks varies, of course, greatly, 
 according to the nature of the rock from which they are derived, 
 and the complication of the atmospheric processes involved. Under 
 
ATMOCLASTICS AND ANEMOCLASTICS 293 
 
 * 
 
 arid climatic conditions mechanical disintegration will predominate, 
 especially in the case of crystalline rocks. Through differential ex- 
 pansion and contraction under heat and cold the minerals of the 
 rock will become separated and a mixed sand results, in which the 
 minerals have sharp outlines, owing to splintering along cleavage 
 planes. Reconsolidation of such, a sand produces arkoses, which, 
 as in the case of the Torridon sandstone of Scotland, may have 
 all the appearance of an igneous rock. In moist climates chemical 
 alteration or decomposition of the feldspars (Mackie-iQ:^//^) and 
 other decomposable minerals will set in, resulting eventually in the 
 production of clay, etc., in which quartz and mica abound. The 
 chief processes in this chemical destruction or decomposition 'of 
 rock minerals consist of oxidation (and deoxidation), hydration 
 (and dehydration), and carbonation; silication and desilication may 
 also occur and solution of minerals also belongs here. (Van Hise- 
 28:461.) Under rainy or pluvial conditions the clay and mica will 
 be removed, the latter suffering mechanical destruction, while the 
 quartz will become mechanically concentrated. When not modified 
 by subsequent water or wind activities, the quartz and other resist- 
 ant mineral grains will be found fresh and angular, without evi- 
 dence of subsequent rounding, while complete crystals of idio- 
 morphic minerals of the crystalline rock are among the resulting 
 constituents. When modified by subsequent agents, various sub- 
 types are produced, namely, hydro-atmoclastic, anemo-atmoclas- 
 tic, etc. 
 
 4. THE ANEMOCLASTICS. These are the wind-laid deposits 
 which are often of great extent, and are of great importance 
 to the stratigrapher. Anemorudytes are probably unknown, 
 but anemoarenytes and anemolutytes are widely distributed. 
 Some familiar examples are anemosilicarenytes represented 
 by solidified sand dunes of quartz sand; anemocalcarenytes, 
 such as the consolidated wind-blown or seolian rocks of Ber- 
 muda in which the sand grains are wholly calcium carbon- 
 ate; and the complex anemolutytes forming extensive de- 
 posits of aeolian dust, chiefly of volcanic matter, in the Ter- 
 tiary strata of North and South America, and in which some 
 of the best preserved remains of mammals have been found. 
 These deposits approach and grade into the pyrolutytes which 
 form in volcanic regions, and in fact it becomes a matter of 
 opinion where the line between the two is to be drawn. The 
 wind-laid loess is also a good example of an impure anemo- 
 lutyte. 
 
294 PRINCIPLES OF STRATIGRAPHY 
 
 In form, anemoclastic sand grains are apt to be more thor- 
 oughly rounded and worn than similar grains worn by water. In 
 .general, rounding of superfine sand, i. e., grains below o.i mm., is 
 not accomplished by water (Chamberlin and Salisbury i '.24.6 >; 
 Daubree-5 '.256} , but such grains may readily be rounded in air. 
 As shown by Mackie (see Chapter V), particles of quartz sand, 
 less than one-fifth the diameter of those rounded by water, will be 
 rounded to an equal extent by wind. Pitting and frosting of the 
 surface is another characteristic result of aeolian activity, as is 
 also- assortment according to size of grain and specific gravity of 
 mineral, so that in a typical seolian sand the grains are of approxi- 
 mately uniform size, and of the same mineral throughout, generally 
 quartz. 
 
 Most seolian sand and dust is derived from some other type of 
 sand, such as residual material (anemoatmoclastic), glacial sand 
 (anemoautoclastic), river or beach sand (anemohydroclastic), or 
 volcanic sand (anemopyroclastic). Extensive deposits of anemobio- 
 clastic sands may accumulate around quarries, etc., especially where 
 stone is crushed for road material. Where the reworking by wind 
 has been extensive, the evidence of the original character may be 
 destroyed. ^Eolian sand in a state of rest may have its grains 
 coated with iron oxide, as in the case of the red sand of the 
 Arabian desert. (Philipps-23 :uo.) 
 
 5. THE HYDROCLASTICS. These comprise by far the larger num- 
 ber of clastic rocks. They are the water-laid deposits and 
 include the following common types : 
 
 a. Hydrorudytes, or conglomerates of variable compo- 
 
 sition. 
 
 b. Plydrosilicirudytes, or pure quartz conglomerates, and 
 
 various varieties due to admixture of simple mineral 
 matter. 
 
 c. HydrocalcirudyteSf or pure lime conglomerates and the 
 
 varieties due to iron, silica or other simple impurities 
 in the paste. 
 
 d. Hydrarenytes, or water-laid sandstones of variable com- 
 
 position. 
 
 e. Hydrosilicarenytcs, or pure quartz sandstones with va- 
 
 rieties due to simple admixtures in the paste. 
 
 f. Hydrocalcarenytes, or pure lime sandstones with vari- 
 
 eties as above. 
 
 g. Hydrolutytes, or water-laid mud beds of variable com- 
 
 position. 
 
HYDROCLASTICS 295 
 
 h. Hydrargillutytes, or pure clay beds and varieties due to 
 the presence in small amounts of silica, lime, iron, or 
 carbon. 
 
 i. Hydrosilicilutytes, or pure quartz-mud rocks, with their 
 varieties due to a slight admixture of argillaceous, 
 calcareous, carbonaceous, glauconitic, or ferruginous 
 matter. 
 
 j. Hydrocalcilutytes, or pure lime-mud rocks, with their 
 varieties due to a slight admixture of argillaceous, 
 siliceous, carbonaceous or ferruginous matter. 
 
 The prefix "hydro" in all these cases is omitted when it is 
 understood that the rocks are water-laid deposits. This is the class 
 of rocks with which the stratigrapher has most to deal, for they 
 comprise by far the largest portion of the sedimentary rocks, and 
 they most commonly contain organic remains in greater or less 
 abundance. In general, hydrorudytes have their pebbles rounded, 
 the degree of rounding depending on the length of time that the 
 pebbles have been subject to water wear, the character of the mate- 
 rial, the intensity of the abrading force, etc. Extensive and pro- 
 longed wave or current action will further result in eliminating 
 much if not all of the perishable mineral matter, so that a much- 
 worked-over conglomerate will consist largely or wholly of quartz 
 pebbles. The same is true of the arenytes, although the sorting 
 here is not so pronounced as that by the wind. Pure hydroclastic 
 quartz sands do occur, however, as at Escambia, on the Gulf coast 
 of Florida, in which scarcely a fragment of mineral other than 
 quartz is found. The granules of this sand range in size from o.i 
 to i.o mm. (fine to coarse sand, averaging 0.25 to 0.50 mm. (me- 
 dium sand). At West Palm Beach, on the Atlantic coast of Flor- 
 ida, a similar pure sand occurs which apparently has been trans- 
 ported along the shore from the Piedmont region to the north. In 
 both of these cases the grains are subangular. The finest sand and 
 the rock flour and clays will retain their angular outlines unim- 
 paired, for, as Daubree has shown, quartz and other mineral par- 
 ticles of o.i mm. or less diameter will float in faintly agitated 
 water. 
 
 In the broader considerations of hydroclastic rocks it is impor- 
 tant that current or river-worn elastics be distinguished from 
 marine or other wave- formed elastics. The former may be spoken 
 of as fluvio-clastic (potamoclastic*) deposits, and the latter as kymo- 
 clastic.f So far as grain is concerned, no marked distinction exists 
 
 * From 7roTa/*6s, a river and K\eurr6s, broken, 
 t From KW/UCI, a wave and K\a<rr63, broken. 
 
296 PRINCIPLES OF STRATIGRAPHY 
 
 in the lutaceous and arenaceous types, but the rudaceous sediments 
 of fluvio-clastic origin may often be distinguished from those of 
 * wave-laid origin by minor characters of the component material. 
 Thus exceedingly well-rounded boulders of moderate size are more 
 characteristic of river than of wave work. The remarkable percus- 
 sion or shatter marks (Schlagnarben) found on fine-grained boul- 
 ders transported by torrents are further to be noted. They consist 
 of semicircular or crescent-shaped slits, appearing as if made by a 
 thumb nail, and crossing each other or interlocking in an indeter- 
 minate manner. They are due to a sudden blow upon the smooth 
 surface from a rounded pebble or boulder of equally hard rock. 
 6. THE BIOCLASTICS. These are the clastic rocks which owe 
 their essential character to organisms. The only class of 
 great importance is that for which man is responsible. Thus 
 bricks (as material), plaster, concrete, cement, etc., are no 
 mean portion of the material composing the uppermost lay- 
 ers of the earth's crust, and are all to be included with the 
 bioclastic division of rocks. 
 
 SUMMARY OF "SEDIMENTARY ROCKS." 
 
 The following table shows the more familiar types of "sedi- 
 mentary" rocks, with the more important species included under 
 each: 
 i. Conglomerates "j f Hydrorudytes 
 
 or -j Hydrosilicirudytes 
 
 Puddingstones. J I Hydrocalcirudytes 
 
 Pyrorudytes (agglomerates) 
 Autorudytes 
 Autosilicirudytes 
 Autocalcirudyt.es 
 Atmorudytes 
 Atmosilicirudytes 
 Atmocalcirudytes 
 . Biorudytes (artificial rubble rock) 
 
 Autoarenytes 
 
 Autosilicarenytes 
 
 Atmosilicarenytes 
 
 2. Breccias. 
 
 3. Sandstones. 
 
 Anemosilicarenytes 
 Hydrarenytes 
 Hydrosilicarenytes 
 ; Bioarenytes (artificial sandstones) 
 
SUMMARY OF SEDIMENTARY ROCKS 
 
 297 
 
 Slates. 
 Shales. 
 Mud rocks 
 
 and 
 
 Clay stones 
 (argillytes) ., 
 
 5. Tuffs. 
 
 6. Limestone 
 (calcilytes) 
 
 and 
 Dolomites. 
 
 Autolutytes (argillaceous) 
 
 Autosilicilutytes (argillaceous) 
 
 Autoargillutytes (pure, siliceous, cal- 
 careous or carbonaceous) 
 
 Atmolutytes (argillaceous) 
 
 Atmoargillutytes (pure, siliceous, cal- 
 careous, or carbonaceous) 
 
 Anemolutytes (argillaceous) 
 
 Anemoargillutytes (pure, siliceous, 
 calcareous, or carbonaceous) 
 
 Anemosiliciluty tes ( argillaceous ) 
 
 Hydrolutytes (argillaceous) 
 
 Hydrargillutytes (pure, siliceous, cal- 
 careous, or carbonaceous) 
 
 Pyrarenytes 
 Pyrolutytes 
 
 Hydrogenic calc-rocks (Hydrocalci- 
 
 lytes) (chemical limestones) 
 Biogenic calc-rocks (Biocalcilytes) 
 
 (coral rock, shell rock, oozes, 
 
 etc.) 
 Autocalcirudytes, 
 
 calcilutytes 
 Atmocalcirudytes, calcarenytes, and 
 
 calcilutytes 
 
 Anemocalcarenytes and calcilutytes 
 Hydrocalcirudytes, calcarenytes, and 
 
 calcilutytes 
 
 calcarenytes, and 
 
 THE COSMOCLASTIC ROCKS. 
 
 This term has been proposed by. Prof. H. L. Fairchild for the 
 original rocks of the earth, which, according to the Planetesimal 
 hypothesis of earth origin, were formed through accretion of frag- 
 ments derived from space. (Fairchild-8; Chamberlin and Salis- 
 bury-2, ii, Chapter I.) 
 
 SPECIAL ROCK TERMS. 
 
 Rock Terms Emphasising Composition. It is often necessary 
 or desirable to emphasize the composition of a rock rather than its 
 
298 PRINCIPLES OF STRATIGRAPHY 
 
 texture or origin. This is already done in the familiar terms 
 limestone, claystone, ironstone, etc. While these terms are good 
 and useful, more euphonious technical terms might be found pref- 
 erable in some cases. Such terms should end in ith, or yte, to 
 signify that they refer to rock masses rather than minerals. Thus 
 rocks composed chiefly of the mineral calcite, or whatever origin, 
 i. e., limestones, may be termed calciliths or calcilytes. 
 Thus we may have : 
 
 quartz rocks or siliciliths or silicilytes 
 
 limestones or calciliths or calcilytes 
 
 dolomite rock or dolomiths (dolomiliths) or dolomytes (dolomilytes) 
 
 gypsum rock or gypsolith or gypsolytes 
 
 claystones or rocks or argilliths or argillytes 
 
 iron stones or ferriliths or ferrilytes 
 
 carbon rocks (coals, peats, etc.) or carbonoliths or carbonolytes 
 
 rock salt or haliliths or halilytes 
 
 Autochthonous* and Allochthonous^ Deposits. These terms 
 were first introduced by Giimbel in 1883 to designate : the first, 
 deposits (especially coal) formed in situ, and the second, deposits 
 made from transported material. The first comprises all hydro- 
 genie and many biogenic deposits, although deep-sea oozes are al- 
 lochthonous. Coal formed from vegetation in situ is autochtho- 
 nous, while transported vegetal matter forms allochthonous coal. 
 Clastic deposits are typically allochthonous. 
 
 BIBLIOGRAPHY VI. 
 
 1. CHAMBERLIN, T. C., and SALISBURY, R. Preliminary paper on the 
 
 driftless area of the Upper Mississippi Valley. Sixth annual report, 
 U. S. Geological Survey, pp. 199-322. 
 
 2. CHAMBERLIN, T. C., and SALISBURY, R. 1906. Geology, Vols. I 
 
 and II. 
 
 3. CROSBY, W. O. 1908. Report of the State Water Supply Commission. 
 
 Progress Report for 1907, p. 205. 
 
 4. CROSS, WHITMAN ; IDDINGS, JOSEPH P. ; PIRSSON, LOUIS, V., and 
 
 WASHINGTON, HENRY S. 1903. Quantitative Classification of 
 igneous rocks based on chemical and mineral characters, with a systematic 
 nomenclature. 
 
 5. DAUBREE, A. 1879. Etudes Synthetiques de Geologie Experimentale. 
 
 Paris. 
 
 * avTfc (autos), self; x0(6w (chthon), the earth; i.e., belonging to the same 
 earth. 
 
 f axXos (allos), another; xOuw (chthori), the earth, i. e., from another region. 
 
BIBLIOGRAPHY VI 299 
 
 6. DE LA BECHE, HENRY T. 1833. Geological Manual, 3rd edition. 
 
 7. DILLER, JOSEPH S. 1898. The Educational Series of Rock Specimens. 
 
 U. S. Geological Survey, Bulletin 150. 
 
 8. FAIRCHILD, H. L. 1904. Geology under the Planetesimal Hypothesis 
 
 of Earth Origin. Bulletin of the Geological Society of America, Vol. 
 XV, pp. 243-266. 
 
 9. GRABAU, A. W. 1904. On the Classification of Sedimentary Rocks. 
 
 American Geologist, Vol. XXXIII, pp. 228-247. 
 
 10. GRABAU, A. W. 1911. On the Classification of Sand Grains. Science, 
 
 N. S., Vol. XXXVII, pp. 1005-1007. 
 
 11. HARKER, ALFRED. 1902. Petrology for Students. 3d edition, Cam- 
 
 bridge Natural Science Manuals. 
 
 12. HARKER, ALFRED. 1909. The Natural History of the Igneous Rocks. 
 
 New York, Macmillan Co, 
 
 13. HARRIS, G. F. 1898. Narrative of a Geological Journey through Russia 
 
 (Rapakiwi described.) Geological Magazine, Vol. XXXV, pp. 11-13. 
 
 14. HAUG, EMILE. 1907. Traite de Geologic. I. Les Phenomenes geo- 
 
 logiques. Paris, Armand Colin. 
 
 15. IDDINGS, J. P., and Others. 1899. Descriptive Geology, Petrography, etc., 
 
 of the Yellowstone National Park. U. S. Geological Survey, Monograph 
 XXXII, pt. II. 
 
 16. KEILHACK, KONRAD. 1908. Lehrbuch der praktischen Geologic, 
 
 2te Auflage. Stuttgart, Ferdinand Enke. 
 
 17. KEMP, JAMES F. 1900. A Handbook of Rocks, without the Microscope. 
 
 New York, D. Van Nostrand & Co. Second edition. 191 1, 5th ed. 
 
 18. LAUFER, E.,und WAHNSCHAFFE, F. 1879. (Classification of Sands.) 
 
 Abhandlungen zur geologischen Special Karte von Preussen. Bd. Ill, i, 
 p. 24. 
 
 19. MACKIE, WILLIAM. 1897. The feldspars present in sedimentary 
 
 rocks as indicators of the conditions of contemporaneous climate. Trans- 
 actions of the Edinburgh Geological Society, Vol. VII, pp. 443-468. 
 
 20. MERRILL, GEORGE P. 1898. Mechanical analysis of residual sand 
 
 of diabase and of washed kaolin. Bulletin 150, U. S. Geological Survey, 
 pp. 380 and 383. 
 
 21. NAUMANN, CARL FRIEDRICH. 1850. Lehrbuch der Geognosie. 
 
 Second edition 1858. 
 
 22. ORTH. 1875. Bezeichnung des Sandes nach der Grosse des Kornes. 
 
 Neues Jahrbuch fur Mineralogie, Volume for 1875, p. 551. 
 
 23. PHILIPPS, J. ARTHUR. 1882. The sands of the Arabian Desert. 
 
 Quarterly Journal of the Geological Society of London, Vol. XXXVIII, 
 pp. 110-113. 
 
 24. ROSENBUSCH, H. 1877. Mikroskopische Physiographic der Massigen 
 
 Gesteine. Stuttgart. Schweizerbart'sche Verlagshandlung. 4th edition 
 in 1908. 
 
 25. ROSENBUSCH, H. 1898. Elemente der Gesteinslehre. Stuttgart. 
 
 Schweizerbart'sche Verlagshandlung. 
 
 26. SHERZER, W. H. 1910. Criteria for the recognition of the various types 
 
 of sand grains. Bulletin Geological Society of America, Vol. XXI, 
 pp. 628-662, pis. 43-4- 
 
 27. THOULET, J. 1 88 1. Etude mineralogiquc d'au sable de Sahara. Bul- 
 
 letin de la Socie'te' Mineralogique de France, T. IV, pp. 262-268. 
 
 28. VAN HISE, C. R. 1904. A treatise on metamorphism. Monograph 
 
 U. S. Geological Survey, No. XLVII. 
 
300 PRINCIPLES OF STRATIGRAPHY 
 
 29. WAHNSCHAFFE, F. 1903. Anleitung zur Wissenschaftlichen Boden- 
 
 untersuchung. Berlin. With literature. 2 te Auflage. 
 
 30. ' WALTHER, JOHANNES. 1897. Versuch einer classification der Ge- 
 
 steine auf Grund der Vergleichenden Lithogenie. Congres Geologique 
 International. Compte Rendu de la VII me session, St. Petersburg, 1897, 
 3 me partie. pp. 9-25. 
 
 31. ZIRKEL, FERDINAND VON. 1866. Lehrbuch der Petrographie. 2nd 
 
 ed. 1893, Leipzig. 
 
 Supplementary. 
 
 32. FINLAY, GEORGE I. 1913. Introduction to the Study of Igneous 
 
 Rocks. McGraw Hill Book Co., New York. 
 
CHAPTER VII. 
 
 STRUCTURAL OR TECTONIC FEATURES OP ROCK MASSES. 
 ORIGINAL STRUCTURES AND LITHOGENESIS OF THE PYRO- 
 GENIC ROCKS. 
 
 When rock masses are considered on a large scale, certain struc- 
 tural features are seen which furnish a clue to the geological his- 
 tory of the region. These can generally be observed only in the 
 field. Two classes of such structural or tectonic features are recog- 
 nized : (i) original structures and (2) secondary or later struc- 
 tures. To the first belong all those accompanying the phenomena 
 of rock formation, features of essential significance in the study of 
 the origin of the formation which they characterize. To the second 
 belong all structures due to subsequent disturbances such as faults, 
 folds, cleavage, and the like, as well as metamorphism, or the alter- 
 ation of rocks. While all these need to be carefully considered in 
 working out the stratigraphy of any region, they have not the im- 
 portance possessed by the original structures, which alone furnish 
 clues to the method of formation of the rock possessing them. In 
 this and the next eleven chapters the Original Structures of rocks 
 will be discussed; the secondary ones will be taken up in Chapters 
 XIX and XX. Since each class of endogenetic rocks has its own 
 mode of origin, the original structures of each must be of corre- 
 sponding individuality. 
 
 THE PYROGENIC ROCKS. 
 
 Pyrogenic or igneous rock masses naturally fall into two great 
 divisions, (a) the intrusive and (b) the effusive. The former 
 solidify within the crust of the earth, appearing as a part of the 
 surface only through subsequent erosion of the overlying masses, 
 while the latter reach the surface in a molten condition, and on 
 solidifying form the uppermost crust of the earth at that point. 
 In otherwise undisturbed regions intrusive igneous masses are al- 
 ways younger than the enclosing rocks, while effusive igneous 
 
 301 
 
302 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 masses are younger than the subjacent, but older than the super- 
 jacent strata. 
 
 INTRUSIVE IGNEOUS BODIES. 
 
 The classification of intrusive igneous bodies as structural fea- 
 tures must be based primarily on their origin, form, and relation 
 to enclosing rock masses, while size and attitude with reference to 
 horizontal plane are criteria of minor significance. (Daly 7:505.) 
 
 A A A 
 
 A A A A A Olorlt * 
 
 FIG. 40. Diagrammatic map and section of Ascutney Mountain, Vermont, 
 illustrating a composite stock of successive intrusions, in stock or 
 boss form, of diorite, syenite, and granite. A small boss of 
 syenite (shown in black) cuts the diorite. These bodies cut crys- 
 talline schists, the attitude of which is shown by the dip-strike 
 symbols. (After Daly.) 
 
 From the point of view of origin, or method of intrusion, two 
 great divisions of igneous intrusive masses may be recognized, (a) 
 the abyssal, deep-seated, or plutonic (Tiefengesteine) , the method 
 of intrusion of which may be either a process of eating into the 
 enclosing rocks (einfressen) , or a pushing aside of the surround- 
 ing rocks, and (b) the injected masses, the Ganggesteine of Rosen- 
 busch, the Hypabyssal division of Brogger. The abyssal division 
 
INTRUSIVE IGNEOUS BODIES 303 
 
 includes two types, i. The Batholith and 2. the Stock and Boss. 
 The distinction between these two groups is largely one of size. 
 Batholiths are large intruded masses of granitic or other holocrys- 
 talline pyrogenics, such as form the central granite core of mountain 
 masses. Suess holds that these masses are intruded through the 
 adjacent formations as a result of fusion, constituting thus a 
 transfusion mass or Durchschmelsungsmasse. A boss (Fig. 40) is 
 a subterranean intrusive mass of moderate size with a circular or 
 subcircular ground plan. The term has been used for such masses 
 up to several miles in diameter, but is best restricted to the smaller 
 
 \ - -* * 
 .'"'I: , \\\ 
 
 FIG. 41. Ideal section of the Holmes Bysmalith (after Iddings). 
 
 masses of this type. A stock, on the other hand, is characterized by 
 irregularity of shape, and often by smaller size than that of the 
 boss. 
 
 The Hypabyssal intrusives may be divided into : 
 
 I. The transverse or those injected across the planes of stratifi- 
 cation of the invaded formation, and 
 
 II. The parallel or those injected along the planes of stratification 
 of the invaded formation. (Daly~7 : 507.) 
 
 The first of these groups includes, I. Dikes, 2. Eruptive veins, 
 3. Apophyses or tongues, 4. Bysmaliths, 5. Necks, and 6. Chono- 
 liths. A dike (Fig. 44) is characterized by nearly or quite paral- 
 lel walls, relatively close together, and may cut the planes of strati- 
 
304 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 fication at any angle except parallelism. Dikes may be simple or 
 complex. In the latter case, they are multiple when successive in- 
 trusions of the same material occur in the same fissure; and com- 
 posite when showing successive injections of different material in 
 the same fissure. Eruptive veins are injections into irregular branch- 
 ing cracks, while apophyses are tongues of igneous matter pro- 
 jecting irregularly into the rock from a larger intrusive mass. A 
 bysmalith (Iddings-i7 :?o8) (Fig. 41) is an injected mass of 
 
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 Basalt 
 
 TKalk 
 
 FIG. 42. Section of a typical volcanic neck. (After Geikie, Ancient Volcanoes 
 of Great Britain, Vol. II.) 
 
 igneous rock filling a more or less circular cone or cylinder in 
 strata, and having the form of a plug. This plug may reach the 
 surface or may end against a domed roof of strata, simulating a 
 laccolith in appearance. It differs from other masses of this type 
 in that the enclosing strata have been displaced by faulting, a solid 
 block of nearly horizontal strata being lifted at one time by the 
 force of the intrusions. The Holmes bysmalith of the Yellowstone 
 is a typical example. With laccoliths this type agrees in having a 
 more or less well-defined floor of other rock on which it rests. 
 Necks (Fig. 42) are the solid plugs of lava filling old volcanic 
 vents. They are generally regular in outline and section. Chono- 
 liths (Daly-7:^p#) (Fig. 43) are the intrusive masses injected 
 into actual or potential cavities formed by dislocation of rock 
 formations such as is brought about during mountain building, and 
 not classifiable as dikes, sills, or laccoliths, bysmaliths, or necks. 
 They are of irregular form, and show a complex relation to the 
 invaded formation. In the process of injection they may crowd 
 aside and mash the country rock, intruding irregularly into all the 
 fissures thus formed. Of the intruded igneous masses this is per- 
 haps the commonest kind. 
 
 The second group or that of the parallel hypabyssal igneous 
 masses comprises, I. Intrusive sheets, II. Laccoliths, and III. 
 Phacoliths. The first of these includes (a) sills, and (b) interfor- 
 
INTRUSIVE IGNEOUS BODIES 
 
 305 
 
 inational sheets. Sills are sheets intruded between parallel strata. 
 They have essentially the characters of dikes, except that they are 
 
 X' X X X X 
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 X X X X X 
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 Confluence o 
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 reek 
 
 1 mile 
 
 SCALE 
 
 International Boundary 
 
 FIG. 43. Diagrammatic map of a Tertiary "chonolith" of thombenporphyry 
 (crosses), cutting intensely folded Palaeozoic sediments (broken 
 lines) and Tertiary sandstones and conglomerates (white) Kettle 
 River, British Columbia. (After Daly.) Late Tertiary lava caps 
 (dots) cover the porphyry in the north. The Tertiary sediments 
 are tilted and faulted, the intrusions occurring at the same time 
 or immediately after. 
 
 bounded by parallel strata. Like dikes, they may be simple, mul- 
 tiple or composite. (Figs. 44, 45.) Interformational sheets differ 
 from sills in that they are intruded along a line of unconformity, 
 
 FIG. 44. Section of an intrusive sheet or sill (s) and connecting dike (d). 
 
 and that therefore the subjacent strata are not parallel to it, though 
 the superjacent ones are. 
 
3o6 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Laccoliths differ from sheets in being lens-like in mass, thick in 
 the center and dying away laterally. In the process of intrusion 
 
 W. by M. 
 
 E. by 9. 
 
 Sta-lmtl 
 
 FIG. 45. Section of a composite sill, Island of Skye (after Marker). The 
 stratified Lias was cut by the sill of basalt ; a later sill, of grano- 
 phyre, was intruded along the middle plane of the basic sill the 
 latter itself may have been double. 
 
 the overlying strata are arched. Laccoliths may be simple or com- 
 pound, when divided by strong beds of the invaded formation. 
 (Judith Mountains.) They may be multiple or composite (Fig. 46), 
 
 FIG. 46. Section of a composite laccolith. (After Weed and Pirsson.) The 
 laccolith cuts heavy-bedded lava flows. Its maximum thickness is 
 150 feet. Black: basalt; white: granophyre. 
 
 as in dikes and sills. Like sills, they may also be interformational. 
 (Fig. 47.) In form they may be symmetric or asymmetric. These 
 variations are illustrated in Fig. 51. 
 
 FIG. 47. Section of an interformational laccolith. (After Weed and Pirsson.) 
 The floor of the porphyry laccolith (in black) is composed of pre- 
 Cambric crystalline schists; the cover, of Palaeozoic sediments. 
 The length of the section represented is about ten miles. 
 
INTRUSIVE IGNEOUS BODIES 
 
 307 
 
 Phacoliths (Harker-i5 :?6) are intrusions of igneous rocks 
 between strata which have been folded and occupying the points of 
 
 N.W. 
 
 FIG. 48. Lenticular intrusion (phacolith) in anticline of Ordovicic strata, 
 Corndon, Shropshire, England. (After Lapworth and Watts.) 
 A. Flags and shales; B. ashes and andesite; D. dolerite. 
 
 greatest pressure relief, as in the crests and troughs of a simply 
 folded series of strata. (Figs. 48, 49.) As Marker points out, they 
 
 FIG. 49. Diagram to illus- 
 trate phacolith intrud- 
 ed in connection with 
 folding. (After 
 Harker.) 
 
 FIG. Soa. Hypothetical development of a 
 folded laccolith. ist stage. 
 (After Baltzer.) 
 
 differ from laccoliths, in that they are a consequence of folding, 
 instead of the cause of the uplift as in laccoliths. Their distinction 
 from the Chonoliths of Daly lies in their parallelism to the strata 
 
 FIG. sob. The same as Fig. 503, in the 
 second stage (Baltzer). 
 
 FIG. 500. The same, in the third stage 
 (Baltzer). 
 
 between which they are intruded, while chonoliths are irregular, 
 commonly, in part at least, transverse. A typical example of a 
 phacolith is seen in the accompanying section from Corndon, Shrop- 
 
3 o8 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 shire. (Lapworth and Watts-20 : 342. ) A remarkable modifica- 
 tion of such intrusions through later folding is described by Balt- 
 zer (i) from the Aarmassive, in the Alps. In the Aletschhorn 
 (4,198 meters high) he finds that the schists which form the summit 
 of the mountain rest discordantly upon the surface of the granite, 
 
 FIG. 51. Diagrams illustrating intrusive masses. A. Laccolith (Mt. Holmes, 
 Henry Mts., Utah). B. Compound laccolith (El Late Mountains, 
 Colorado). C. Laccolith with subsidiary sheets (Judith Mts. 
 type, Montana). D. Laccolith with broken cover (Ragged Top 
 Mt., Black Hills, S. Dakota). E. Interformational laccolith 
 (Deadwood Gulch, Black Hills). F. Compound laccolith cedar- 
 tree type (La Plata Mts., Colorado). G. Abruptly protuberant 
 laccolith (Mt. Hillers, Henry Mts.). H. Asymmetric laccolith 
 (Mt. Marcellina, West Elk Mts., Colorado). K. Intrusion in 
 Little Rocky Mts. (Montana). L. Intrusion in volcanic vents 
 (Island Skye). M. Bysmalith (Mt. Holmes). N. Plutonic plug 
 (Ideal). (After Harker.) 
 
CONTACTS OF INTRUSIVE MASSES 309 
 
 i. e., the relation is like an inverted unconformity. This relation is 
 believed to be due to subsequent folding of the entire mass. The 
 process is illustrated in the three diagrams on page 307. (Figs. 
 5oa-5oc.) 
 
 The end result is an intrusive mass which appears to cut across 
 folded strata and so is indistinguishable from the Chonoliths of 
 Daly. 
 
 Igneous versus Sedimentary Contact. It is of the greatest im- 
 portance that the nature of the contact between igneous and non- 
 igneous formations be determined. Three types of contacts may 
 be recognized, i. Fault contacts, 2. Igneous contacts, and 3. Sedi- 
 mentary contacts. Fault contacts are secondary contacts and will 
 be considered in a subsequent section, as they have no direct bearing 
 on the history of the igneous mass. Igneous and sedimentary con- 
 tacts, on the other hand, are primary and intimately connected with 
 the origin of one or the other of the formations in contact. The 
 igneous contact stamps the igneous mass as the younger, while the 
 sedimentary contact shows the sedimentary formation to be the 
 younger of the two. As a rule, when exposures are sufficiently 
 good, the nature of the contact is not difficult to determine unless 
 both igneous and sedimentary mass have subsequently become meta- 
 morphosed. Sometimes the subsequent intrusion of igneous ma- 
 terial along the contact of an older igneous with a sedimentary for- 
 mation obscures the nature of the original contact. 
 
 The chief criteria for use in determining relative ages of igneous 
 intrusive bodies in contact with sediments are the following : 
 
 Contacts of subterranean or abyssal masses. 
 
 (1) If the granitoid boss, stock or batholith is in contact with 
 sediments of known age, and these sediments have been metamor- 
 phosed or partly remelted by the igneous rock, which may even 
 enclose fragments of the sediment, then the igneous rock is of 
 younger age than the sediments, which were there before the molten 
 magma ate its way into them. 
 
 (2) If sediments of a known age rest unconformably upon a 
 granitoid mass (granite, syenite, diorite, gabbro, etc.), worn frag- 
 ments of which are included in the sediments next adjoining the 
 igneous mass, the age of the igneous mass is very much greater 
 than that of the adjacent strata, for the igneous mass was exposed 
 by erosion before the sediments now resting upon it were laid down. 
 In such case the igneous mass has not metamorphosed the sedi- 
 
3 io PRINCIPLES OF STRATIGRAPHY 
 
 ments. Such contacts may be sharp, where the surface of the 
 igneous mass has been swept clean before the deposition of the 
 sediments, as in the case of the pre-Cambric granite floor of the 
 Manitou region in Colorado (Crosby-6), upon which abruptly 
 appear the clean-washed sands of the basal Palaeozoic of that 
 region (Fig. 52), or it may be a transition contact where the old 
 igneous mass has been much decomposed, while the subsequent 
 sediment is made up of the partly reworked upper layers of the 
 old regolith. An example of this is found in the contact of the 
 Lake Superior sandstone of the Marquette region with the altered 
 peridotites of pre-Cambric age, where it is often impossible to 
 
 M. 
 
 ... ^^^^^^ff^^^^^^^^^i 
 
 ;X?0$^yj&2* 
 
 linch lOfeet. 
 
 FIG. 52. Irregularities in sedimentary contact, of basal Palaeozoic sandstones 
 on pre-Cambric granite in Williams Canyon, Colorado. The gen- 
 eral character of the contact is a sharp and, for the most part, 
 very smooth one. (After Crosby.) The granite mass is part of 
 an abyssolith. 
 
 determine the precise line of contact. Great difference in age may 
 exist between these two. 
 
 For such an ancient igneous mass, which has been uncovered by 
 erosion, and subsequently covered by sediments, with which it is in 
 sedimentary contact, the name Abyssolyth is proposed. Such an 
 abyssolyth is seen in the granite mass of Pikes Peak, the contact 
 of which, with the Palaeozoics, is a sedimentary one. (Fig. 52.) 
 
 Contacts of hyp abyssal or injected masses. 
 
 Dikes, sills, laccoliths, etc., are younger than the strata which 
 they cut, or which they have metamorphosed. Their proximal age 
 limit is, however, not determined by the strata in which they occur, 
 unless some of these strata should contain erosion fragments of 
 the intrusives, when the latter must be considered as very much 
 older than the strata containing such fragments, and which are in 
 sedimentary cpntact with the igneous masses. 
 
EFFUSIVE IGNEOUS MASSES 311 
 
 In general terms : Strata underlying igneous masses, parallel 
 with them, are always older than those masses, but strata lying 
 directly upon such igneous rocks must be considered older only if 
 they have been altered or in any way affected by the igneous mass 
 while the latter was still hot, but younger if they are not affected 
 and especially if they contain worn fragments of the igneous rock. 
 An exception must, however, be made in the case of strata de- 
 posited upon a hot laval stream, the heat of which later affects the 
 strata of younger age. In such a case evidence within the strata 
 or the igneous mass will generally furnish the clue to the respective 
 ages of each. Misinterpretation of the contact between adjoining 
 formations may result in grave errors regarding the relative ages 
 of these formations. Thus up to within very recent times the great 
 granitic and gneissic masses of the Canadian shield known as the 
 Laurentian were believed to represent the oldest known rocks of 
 the earth's crust, the metamorphosed rocks now called the Keewatin 
 series being regarded as the next younger, and representing ancient 
 sediments resting unconformably upon the Laurentian. It is now 
 known, however, that in many instances at least the contact between 
 the Laurentian and the Keewatin is an igneous contact, the former 
 being intruded into the latter, and hence younger than it. 
 
 EFFUSIVE IGNEOUS MASSES 
 
 Effusive masses, i. e., volcanic flows or sheets are always 
 younger than the strata on which they rest and older than the 
 strata which overlie them. Volcanic sheets are distinguished from 
 sills, which are younger than both the enclosing strata, by the fact 
 that only the stratum underlying the flow is metamorphosed, while 
 the overlying one generally contains fragments of the flow. Fur- 
 thermore, the upper portion of the flow shows generally a more or 
 less vesicular structure which indicates the exposed surface of the 
 old lava sheet. 
 
 Features of the Basal Contact of Lava Sheets. The basal con- 
 tact of lava sheets may furnish important evidence of the physical 
 condition of a region prior to its invasion by the lava flow. Thus a 
 land area, bare or covered by soil either dry or with a comparatively 
 small content of water, will give a relatively smooth and uniform 
 contact line with the overflowing lava sheet. A saturated soil, or 
 one covered by water, will give a very different kind of contact. 
 The conversion of the water into steam will cause a violent ebul- 
 lition along the line of contact, accompanied by an inter-kneading 
 
3 I2 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 of the igneous and non-igneous rocks, and not infrequently a trans- 
 formation of the basal part of the flow. Such features have been 
 described from the base of the Newark trap sheets of the Paterson 
 region of New Jersey by Fenner (n). He finds that in places 
 "along the contact for a width of ten feet or more the trap and 
 mud show evidence of having experienced the most violent agita- 
 tion" the two being mixed and kneaded together in a surprising 
 manner. "The mud has boiled through and through the seething 
 
 FIG. 53. Bonldery structure, with in- 
 cluded sand masses brought 
 from below. Trap sheet 
 near Paterson, N. J. (After 
 Fenner. ) 
 
 FIG. 54. Bouldery structure in 
 lower part of extruded 
 trap sheet, near Pater- 
 son, N. J. (After 
 Fenner.) 
 
 body of lava until particles of mud of every size from minute specks 
 to large masses have become incorporated in the pasty flow. Both 
 lava and mud are full of blowholes, steam vents, and other forms 
 of irregular pipes and cavities which attest the violent escape of 
 gases." (iiijij.) The amount of injected mud decreases up- 
 ward and the vesicular character gradually gives way to purer 
 igneous rock. In structure this is still very peculiar, showing the 
 effect of escaping gases through the mass. A boulder-like structure 
 is produced, the "boulders" being of dense trap with crusts of dark 
 
EFFUSIVE IGNEOUS MASSES 313 
 
 glass. (Figs. 53, 54.) Between these "boulders" lie vugs of min- 
 erals especially rich in zeolites. 
 
 Emerson (10:61) has described inclusion of "mud drops" or 
 mud amygdules in the upper part of the Triassic trap of the Hoi- 
 yoke region in the Connecticut Valley, where occur also the gray 
 laminated shales confusedly mingled in the trap, and appearing 
 under the microscope as an intimate mixture or "complete emulsion 
 of the two non-mixing fluids," the lava and the mud. He finds that 
 the base of the sheet has similar pronounced mud inclosures in 
 one place, while at another, a hundred rods north, "along the base 
 of the same sheet the black compact aphanitic trap rests on the 
 same coarse sandstone, and contains .only a few long steam holes." 
 Emerson regards the basal layer as the underolled top layer. 
 
 The Carbonic lava flows of the coast of Fife, Scotland, show 
 in their bases a series of pipes or funnels which were evidently 
 formed by the steam generated when the lava flowed over the wet 
 sands. These pipes extend vertically into the lava and generally 
 are filled with zeolites or with calcite. 
 
 The rhyolitic flows of the Yellowstone National Park rest in 
 places upon a deposit of well-laminated rhyolite dust, while the 
 basal part of the flow itself along the contact is marked by a thin 
 layer of perlitic glass. (Iddings-i8: 358.) In the Grand Canyon 
 of the Yellowstone the bottom contact of a younger flow of rhyo- 
 lite on a thick mass of basalt shows a tuffaceous character passing 
 upward into denser material which in turn passes up into porphy- 
 ritic glass, and this into lithoidal lava. (i8:jpo.) Another small 
 sheet of rhyolite on Saddle Mountain has its basal contact on basal- 
 tic breccia, marked by white rhyolitic tuff, followed by fissile light 
 gray lithoidal rhyolite with small phenocrysts, passing up into dark- 
 colored spherulitic and glassy rhyolite with lithophysse and small 
 phenocrysts. ( 18 : jp^. ) 
 
 Features of the Upper Surfaces of Lava Flows. The upper 
 surfaces of lava streams vary with the nature of the lava itself and 
 the conditions under which it is extravasated. 
 
 i. Basic lavas. These are well illustrated in the character of 
 the extravasations of the Hawaiian Islands. The kinds of sur- 
 faces represented by these lavas may be classified as (a) ropy, 
 (b) the pillowy or pahoehoe and the rough or aa. 
 
 The ropy lava, the least common, has the aspect of irregular 
 coarse pieces of rope, generally intertwined in an extreme manner, 
 the strands moreover being longitudinally ridged. The rock is 
 moderately vesicular. The pillowy or pahoehoe (pr. pah-hoy-hoy 
 literally, with satiny surface) has been compared with the pitch 
 
314 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 dumped from a large number of enormous caldrons and allowed 
 partly to run out, some masses running together and some advanc- 
 ing over preceding masses. (Fig. 55.) (Duton-g; Dana-8:o; 
 Hitchcock-i6:^o.) These hummocks form a rolling surface, with 
 fine wrinklings which produce the satin aspect. The pillowy masses 
 have sometimes a glassy exterior half an inch or less thick, forming 
 tachylite, in which a variolitic texture may sometimes be found. 
 The rough or aa lava presents a striking contrast with the pahoehoe. 
 "It consists mainly of clinkers, sometimes detached, sometimes par- 
 tially agglutinated together, with a bristly array of sharp, jagged, 
 
 FIG. 55. Pahoehoe lava of Mauna Loa, Hawaiian Islands. (After Button.) 
 
 angular fragments of a compact character projecting up through 
 them." (9: 95.) The breaking up of the lava occurs during the 
 flow. The masses are sometimes piled together in confused heaps 
 to a height of 25 to 40 feet above the general surface. The individ- 
 ual fragments vary in size from an inch to ten feet, or even much 
 more. In texture the lava is usually less vesiculated than the 
 pahoehoe, not scoreaceous, but cavernous exteriorly. Large pro- 
 jecting masses of jagged lava occur, some having been noted on 
 southern Hawaii, of slablike form and very compact "twenty feet 
 or more long, eight feet high and three to ten inches thick, standing 
 vertically together, with a curving over at the top somewhat like 
 gigantic shavings." (8:10.) Associated with aa lava are lava 
 balls or pseudobombs of concentric structure, sometimes wrongly 
 taken for bombs. "These lava balls are smoothish exteriorly, more 
 
FEATURES OF LAVA FLOWS 315 
 
 or less rounded and boulder-like, and vary in size from an inch or 
 less to ten feet or more." (Dana-8: 10.) 
 
 Peach and Home have described and figured the lava surfaces 
 of the Ordovicic rocks of the south of Scotland. (21.) One of 
 their striking characteristics is the pillow-shaped or sack-like form 
 which they present. "On a weathered face they sometimes look 
 like a pile of partially filled sacks heaped on each other, the promi- 
 nences of one projecting into corresponding hollows of the other." 
 (Geikie-i3 :/pj.) The rocks are finely amygdaloidal, the vesicles 
 being grouped in lines parallel to the outer surface of the pillow-like 
 block in which they occur. 
 
 The spaces between the subspheroidal masses are sometimes 
 filled with fine sediment, sometimes with fossiliferous limestone, 
 and again with radiolarian chert, these being deposited upon the 
 surface flow after cooling or sometimes before. Some of the radio- 
 larian cherts, however, appear to be deposited contemporaneously 
 with the lava, for they are intercalated with it. These lavas are 
 believed to represent submarine eruptions, at successive periods, 
 while between these periods, normal sedimentation took place. 
 Structures of this kind have been found in the lower Ordovicic 
 (Arenig) lavas of Cader Idris, Merionethshire, North England. 
 
 A similar structure occurs in the post-Carbonic (Tertiary) vari- 
 olitic diabase of the Mont Genevre district in the French-Italian 
 border. (Cole and Gregory-^.) The structure of this lava is 
 spheroidal on a large scale, most commonly "resembling -pillows or 
 soft cushions pressed upon and against one another." As shown in 
 the cliffs, they appear as swelling surfaces with curving lines of 
 junction. (Fig. 56.) Small vesicles occur in the rude spheroids, 
 especially toward the margin, while in some places the whole rock 
 becomes vesicular and slaggy. The surfaces of these masses are 
 covered by a crust of variolite, from I to 7 or 8 centimeters thick, 
 the variolites being grouped or drawn out in bands parallel to the 
 surface and varying from almost microscopic to a diameter of 
 5 cm. 
 
 Ransome finds a structure of this character in the basic lava of 
 Point Bonita, Marin County, California, and comes to the conclu- 
 sion that it is essentially a flow structure and that hence the rock in 
 question is an extravasated lava. (23.) He regards the structure 
 as indicating a lava of intermediate viscosity between that pro- 
 ducing the pahoehoe and that resulting in the aa surface. 
 
 Crosby has described structures of this type from the Carbonic 
 lavas of the Nantasket region of eastern Massachusetts. (5.) 
 While the careful study of these structures in the cases cited has 
 
PRINCIPLES OF STRATIGRAPHY 
 
 led the observers to the conclusion that such features are reliable 
 as indications of surface flows, yet there are cases in which these 
 surfaces have such an intimate relation with marine sediments as 
 to suggest the possibility of intrusion. An example of this kind is 
 described by Fox and Teall (12:211) from the Greenstone of the 
 Lizard and Mullion Island, where intimate association 1 with radio- 
 larian cherts suggested that the lava was intruded between the 
 sheets of chert near the surface of the sea bed upon which they 
 were being deposited. This intimate association with radiolarian 
 cherts also found in the Arenig lavas of Great Britain seems at 
 
 FIG. 56. Spheroidal or pillow lava with variolitic selvages. North end of 
 Le Chenaillet Ridge, above the Durance Mont Genevre region, 
 France. (After Cole and Gregory.) 
 
 present the only good indication of the probable submarine origin 
 of the lava. So far as the pahoehoe type of surface is concerned, 
 it appears to be equally characteristic of subaqueous and subaerial 
 extravasations. That constant and reliable minor differences exist 
 between subaerial and subaqueous lava surfaces is scarcely to be 
 doubted, but at present such differences appear to be unrecognized. 
 The aa type of lava has also been recognized in older formations. 
 In the pre-Cambric rocks of the Vermilion iron-bearing district of 
 Minnesota occur bunches of igneous rocks having a concentric 
 
MINOR STRUCTURES OF VOLCANICS 317 
 
 structure. They have been referred to the pseudo bombs of the 
 aa. (Clements-2.) Some of the Triassic extrusives near Green- 
 field, Massachusetts, have been referred to this type by Hitchcock. 
 (16:283.) 
 
 2. Acid lavas. These are as a rule very viscous and slow 
 moving, and may solidify before they spread far. The surface is 
 generally rough or ropy, the former being a feature of some acid 
 lava flows of Vulcano in the Lipari group (obsidian), the other 
 being illustrated by lavas of Vesuvius. As shown in the Vesuvian 
 stream of 1858; which was very viscous and slow moving, the sur- 
 face has been wrinkled and folded in quite a remarkable manner, 
 some of the folds closely resembling coils of rope. This is the sur- 
 face feature seen in artificial slags, flowing from a furnace. The 
 cause of this appears to be the wrinkling of the chilled surface 
 crust through the continued onward movement of the liquid mass 
 below. Sometimes the breaking of the lava crust produces a heap 
 of large and small fragments or blocks, so that the lava stream 
 looks like a huge mass of broken fragments confusedly piled to- 
 gether. (Block lava, Schollenlava.) Sometimes lavas of the more 
 acid type are very liquid and flow rapidly. In such cases a rough 
 and ragged cindery surface is produced suggestive of aa lava. The 
 surface suggests the solidification of a boiling, squirting mass 
 (spratzige Lava). Such a surface is seen in the lava stream of 
 1872 on Vesuvius. In rapidly cooling lavas the surface of the 
 stream may be covered with a crust of hard slaggy material which, 
 breaking and rolling under at the front of the moving lava stream, 
 forms a slaggy floor on which the more compact lava comes to rest. 
 This crust of slag is responsible for the relatively little effect which 
 the lava of a submarine volcano produces on coming in contact with 
 the water, or for the phenomenon of a lava stream flowing across a 
 snowfield without completely melting it. (Credner-4 1/50.) 
 
 MINOR STRUCTURAL CHARACTERS OF VOLCANIC ROCKS. 
 
 Flow Structure. A banding of igneous rocks is often noted, this 
 banding sometimes simulating stratification, for which it has at 
 various times been mistaken. It is produced by the disposition of 
 the crystals, vesicles or other recognizable structures in more or 
 less parallel lines, which, however, are constantly interrupted by 
 obstacles around which the lines curve in such a manner as to show 
 that it was due to the flowing of the viscous mass around the ob- 
 stacle. Flow structure is not confined to surface flows, but also 
 
PRINCIPLES OF STRATIGRAPHY 
 
 occurs in injected masses such as dikes, sills, etc., where it is often 
 very well developed. It is more marked in acid than in basic 
 rocks, especially in obsidians, rhyolites and felsites, etc. The flow 
 structure of basic rocks is more generally seen on a large scale 
 in the orientation of porphyritic crystals or the arrangement of 
 vesicles into line.- 
 
 Stratification of Flows. A succession of surface flows in a 
 given region will produce true stratification of the lavas in which 
 
 FIG. 57. Columnar structure in basalt near Fingal's Cave, Island of Staffa, 
 W. Scotland. 
 
 each layer becomes in turn the top of the lithosphere at that point. 
 (See p. 697.) Such volcanic strata may be distinguished by differ- 
 ences in texture if not composition. 
 
 Columnar Structure. This is a contraction phenomenon in 
 which prismatic columns commonly with six uniform faces form 
 on the cooling of the magma. In general the prisms form at right 
 angles to the enclosing walls. In dikes the prisms thus are hori- 
 zontal or nearly so, while in flows and intruded sheets the columns 
 stand upright. (Ex., Fingal's Cave [Fig. 57] ; Giants' Causeway, 
 etc.) Sometimes they are curved, as in Clamshell Cave, Staffa. 
 Often the columns or prisms are non-persistent through the bed, 
 but die out one into the other, with a wavy, irregular shape. (Geikie- 
 
MINOR STRUCTURES OF VOLCANICS 
 
 319 
 
 13 : 2 5-) Though most common in basic rocks, this structure is 
 also found in the acid types, as is well shown by the columnar 
 obsidian and other rhyolites of the Yellowstone National Park. 
 (Iddings-i8.) (Fig. 58.) 
 
 FIG. 58. Columnar structure in obsidian. Obsidian cliff, Yellowstone Na- 
 tional Park. (After Iddings.) 
 
 Variation in Grain. In both effusive and intrusive masses a 
 variation in the coarseness of texture or size of grain is observable 
 between the outer faces of the mass and its interior. In general 
 there is a regular increase in coarseness toward the center, due to 
 less rapid chilling of the inner portion of the mass. Queneau (22) 
 has been able to establish a table for determining distance from 
 
320 PRINCIPLES OF STRATIGRAPHY 
 
 wall by size of grain in such rocks as the trap of the Palisades. 
 (Lane-i9. See also the various minor structures of pyrogenic 
 rocks referred to in Chapter VI.) 
 
 BIBLIOGRAPHY VII. 
 
 1. BALTZER, A. 1903. Die granitischen Intrusions-massive des Aarmas- 
 
 sives. Neues Jahrbuch fur Mineralogie. Beilage Band XVI, pp. 292- 
 
 3 2 5. 
 
 2. CLEMENT, J. MORGAN. 1903. Vermilion Iron-bearing District of 
 
 Minnesota. Monograph XL, U. S. Geological Survey, 1890. 
 
 3. COLE, G. A. J., and GREGORY, J. W. 1890. The Variolitic Rocks of 
 
 Mt. Genevre. Quarterly Journal of the Geological Society, London. 
 Vol. XLVI, pp. 295-332. 
 
 4. CREDNER, HERMANN. 1897. Elemente der Geologic. 8te Auflage. 
 
 Leipzig. Wilhelm Engelmann. 
 
 5. CROSBY, W. O. 1893. Geology of the Boston Basin, Nantucket and 
 
 Cohasset. Occasional Papers of the Boston Society of Natural History, 
 IV, Vol. I, pt. i. 
 
 6. CROSBY, W. O. 1899. The Archaean Cambrian Contact near Manitou, 
 
 Colorado. Bulletin of the Geological Society of America, Vol. X, pp. 
 141-164. 
 
 7. DALY, REGINALD R. A. .1905. Classification of Igneous Intrusive 
 
 Bodies. Journal of Geology, Vol. XIII, 485-508. 
 
 8. DANA, JAMES D. 1891. Characteristics of Volcanoes. New York, 
 
 Dodd, Mead & Co. 
 
 9. DUTTON, C. E. 1884. Hawaiian Volcanoes. 4th Ann. Rept., U. S. 
 
 Geological Survey, pp. 81-219. 
 
 10. EMERSON, B. K. 1897. Diabase pitchstone and sand inclosures of 
 
 the Triassic trap of New England. Geological Society of America, Bul- 
 letin, Vol. VIII, pp. 59-86, pis. 3-9. 
 
 11. FENNER, C. N. 1908. Features indicative of physiographic conditions 
 
 prevailing at the time of the trap extrusions in New Jersey. Journal of 
 Geology, Vol. XVI, pp. 299-327. 
 
 12. FOX, HOWARD and TEALL, J. J. 1893. On a Radiolarian chert from 
 
 Mullion Island. Quarterly Journal Geology Society, London, Vol. XLIX, 
 
 pp. 211-220, pi. IV. 
 
 13. GEIKIE, A. 1897. Ancient Volcanoes of Great Britain, Vol. I. London, 
 
 Macmillan & Co. 
 
 14. GEIKIE, A. Ibid. Vol. II. 
 
 15. HARKER, ALFRED. 1909. The Natural History of Igneous Rocks. 
 
 New York, Macmillan Co. 
 
 16. HITCHCOCK, CHARLES H. 1909. Hawaii and its Volcanoes. Hawai- 
 
 ian Gazette Co. 
 
 17. IDDINGS, J. P. Bismalith. Journal of Geology, Vol. VI, 1898, pp. 704- 
 
 710. 
 
 18. IDDINGS, J. P., and Others. 1899. Geology of the Yellowstone 
 
 National Park. Monograph U. S. Geological Survey, XXXII, pt. II. 
 w 19. LANE, ALFRED C. 1905. The Coarseness of Igneous Rocks and its 
 Meanings. American Geologist, Vol. XXXV, pp. 65-72. 
 
BIBLIOGRAPHY VII 
 
 321 
 
 20. LAPWORTH CH. and WATTS. 1894. Proceedings of the Geologists' 
 
 Association, Vol. XIII. 
 
 21. PEACH, BENJAMIN N., and HORNE, J. 1899. The Silurian Rocks 
 
 of Great Britain. Memoirs of the Geological Survey of the United 
 Kingdom. Vol. I, Scotland. 
 
 22. QUENEAU, A. L. 1902. Size of grain in igneous rocks in relation to the 
 
 distance from the cooling wall. Columbia School of Mines Quarterly, 
 Vol. XXIII, pp. 181-195, 6 plates. 
 
 23. RANSOME, F. LESLEY. 1893. The Eruptive Rocks of Point Bonita. 
 
 Bulletin of the Department of Geology of the University of California. 
 Vol. I, pp. 71-114, plates 6 and 7. 
 
CHAPTER VIII. 
 
 STRUCTURE AND LITHOGENESIS OF THE ATMOGENIC ROCKS 
 
 SNOW. 
 
 Snow is a direct condensation of the moisture of the air, when 
 the temperature falls below 32 F. (o C.). This occurs in high 
 latitudes throughout much of the year, but in low latitudes, during 
 the summer season, only in high altitudes. It is in these regions of 
 more or less continuous precipitation of snow that it remains as a 
 permanent cover of the surface throughout the year, constituting 
 the permanent snow fields. The lower limit of the permanent snow 
 fields constitutes the snow-line. The snow-line may be considered 
 under two aspects: (a) Its dependence primarily on climatic con- 
 ditions, giving the climatic snow-line, and (b) its dependence pri- 
 marily on orographic features, giving the orographic snow-line. 
 The climatic snow-line depends in the first place upon the course of 
 the mean summer isotherm of o C. (32 F.), but there are other 
 climatic factors which modify this, as, for example, the amount of 
 precipitation of snow during the winter months, exposure to the 
 sun, and warm and dry winds from the land; the steepness of the 
 mountain sides, and their altitude, etc. The orographic snow-line 
 is the lower limit of both snow fields and separate neve patches, 
 which owe their permanent preservation mainly to favorable oro- 
 graphic surroundings. They may thus occur in ravines and gullies 
 far below the true snow-line. 
 
 Height of Snow-line. The snow-line is always higher than the 
 lower limit of snowfall, and it is of course much higher in the 
 equatorial than in northern regions. Thus in the Bolivian Andes, 
 near the equator, it is 5,500 meters (18,500 feet) on the west side 
 and 4,876 meters (16,000 feet) on the east side, while in latitude 
 70 N. (Lapland) it is about 915 meters (3,000 feet), and in 
 Greenland (6o-7o N. lat.) about 670 meters (2,200 feet). From 
 numerous observations Humboldt obtained the following table of 
 
 322 
 
SNOW. GLACIERS 323 
 
 relationship between latitude, the lower limit of snowfall, and 
 the snow-line. (Hantt 4:3/3.) 
 
 Altitude of Snowfall and of Snozv-line (Meters). 
 
 Lower Lower limit 
 
 Latitude limit of of eternal Differences 
 
 snowfall snow 
 
 o 4,000 4,800 800 
 
 20 3,ooo 4,600 i, 600 
 
 40 o 3,ooo 3,ooo 
 
 These figures are approximate and represent average condi- 
 tions. Many temporary and local variations from these averages 
 occur. 
 
 The equatorial limits of regular snowfall (at sea-level) are as 
 follows, the figures in parentheses giving the range of occasional 
 snowfall: On the west coast of America, 45 (34) N. to 45 
 (34) S. ; east coast, 35 (29) N. to 44 (23?) S. Interior, 30 
 (19) N. to near tropics in South America. For the Old World, 
 on the west coast of Europe, 45 (33) N., .on the east coast of 
 Asia, 30 (22.5) N.; on east and south coast of Australia, 34 S. 
 (occasional). For the interior of Asia snow falls to 24 (22) N. 
 latitude; on the Mediterranean to 37 (29) N. latitude, while 
 in the interior of South Africa it falls occasionally at 24 S. lati- 
 tude. (Hann-4: 314.) That the distribution of snow and ice 
 resulting from it was different in former geologic periods is shown 
 by the extent of former glaciation. 
 
 Conversion of Snow into Ice. The deeper portions of the 
 snowfield are gradually converted into snow ice through the inter- 
 mediate state of Urn or neve. The process of transformation of 
 snow into ice involves the partial melting and regelation of the 
 granules and the cementation of the remainder by the reconsoli- 
 dated snow water. This is a process of diagenetic metamorphism 
 or diagenesis. 
 
 GLACIERS. 
 
 When the mass of ice resulting from the consolidation of snow 
 begins to spread, creeping or flowing away from the center of 
 accumulation, it gives rise to glaciers. From their mode of occur- 
 rence, glaciers may be divided into, A. true glaciers or glacier 
 streams, and B. ice caps, or glacier sheets. True glaciers are com- 
 
3^4 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 parable to streams, and, like them, are confined in more or less 
 definite channels. Their length may be ten miles or more. The 
 most typical form is that of the valley glacier or alpine glacier, 
 extending from the mountain flanks or from a plateau through a 
 well-defined valley. They may be simple throughout or multiple 
 in the upper reaches, where several streams unite to form one 
 master stream of ice. At the foot of the valley they may spread 
 
 Moraines 
 Forests 
 S3 Glactens 
 
 Pacific Ocean, 
 
 r *- * 
 
 FIG. 59. Map of the Malaspina Glacier and of Yakutat Bay, Alaska; the 
 type of a piedmont glacier. (After Russell.) 
 
 out into glacier fans or piedmont glaciers, which may be simple, 
 i. e. } resulting from a single glacier, or compound, when formed by 
 the confluence of two or more glaciers from adjoining valleys. 
 (Example, Malaspina glacier, generally regarded as a typical pied- 
 mont glacier. Fig. 59.) Of secondary* rank among true glaciers 
 are cliff glaciers (Gehangegletscher), resting in the depressions at 
 the foot of cliffs on the mountain flanks, and never descending to 
 a valley; cirque glaciers (Kargletscher) in deep mountain hollows 
 or cirques surrounded by high peaks, and ravine glaciers (Schlucht- 
 gletscher), resting in deep gorges with precipitous walls. 
 
GLACIAL SHEETS 
 
 325 
 
 Ice caps, or glacial sheets, are expansions of ice, covering and 
 concealing the underlying topography, to which their surfaces do 
 not correspond. They may be compared to a flood, not confined 
 within banks, but spreading over and uniformly submerging hills 
 and valleys alike. The smaller glaciers of this type are the plateau 
 glaciers, such as are found in Iceland, parts of Scandinavia, etc., 
 while the larger constitute the continental glaciers or ice sheets. 
 
 FIG. 60. Map of Greenland, showing the ice cap and the ice-free borders. 
 (After Stieler, from Chamberlin and Salisbury.) 
 
 Of these the great ice cap of Greenland, with an area of nearly 
 2,000,000 square kilometers, is a well-known example. (Fig. 60.) 
 Another example of a little explored ice sheet is the continental ice 
 sheet of Antarctica, which ends seaward in ice cliffs 50 meters or 
 more in height, (i.) In Pleistocenic time several huge ice caps 
 covered the northern part of North America. (Fig. 61.) They 
 were contiguous along their margins, where they interfered the one 
 with the others in respect to freedom of movement, interferences 
 now expressed in the distribution of their transported material and 
 frequently by the absence of erosion along the line of contact. 
 From the margins of the ice caps of the present day numerous 
 glaciers descend, many of them into the sea, where their ends may 
 break off and become icebergs. In continental glaciers no bounding 
 rock walls hem in the ice, though occasionally in the thinner mar- 
 
326 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 ginal portion one of the higher peaks may project through the ice 
 as a tmnatack* 
 
 Stratification of Ice. Since the ice of the snow fields and of 
 
 FIG. 61. Map of North America in Pleistocenic time, showing four centers of 
 dispersion of the ice. I., Cordilleran ; II., Keewatin ; III., Labra- 
 doran ; IV., Newfoundland. (After Wilson.) 
 
 glaciers is the product of successive deposits of snow in more or 
 less continuous sheets, each of which at the time forms the surface 
 layer of the earth at that point, it follows that snow ice has a 
 
 * For types of glacial deposits see Chapter XII. 
 
STRUCTURE OF GLACIAL ICE 
 
 327 
 
 stratified structure. This may not always be visible, but, on the 
 other hand, it may be very prominent. It is especially well marked 
 where layers of wind-blown dust or sand were spread over the 
 older layer before the deposition of the new one. 
 
 FIG. 62. Diagram illustrating lateral upturning of ice layers in a glacier. 
 The bottom line is sea level. (Chamberlin and Salisbury.) 
 
 Shear Zones and Flow Structure. Instead of moving uni- 
 formly as a mass, lines of more rapid movement within the ice 
 may develop, as the result of which a shear structure will come 
 into existence. This may simulate stratification, especially when, as 
 is commonly the case, debris from the bottom is carried up into 
 the ice along the shear zones. Though a secondary structure, it 
 may be mentioned here for purposes of comparison. 
 
 FIG. 63. Diagram illustrating compound or double glacier, with debris-laden 
 layers rising laterally and medially, forming corresponding 
 moraines. The bottom line is sea-level. (Chamberlin and Salis- 
 bury.) 
 
 Flow structure is developed within many glaciers. This is most 
 pronounced near the front of the ice and along its sides. The 
 layers near the front turn up and the debris within the ice thus 
 gradually reaches the surface. Along the sides the movement is 
 also from below upward, and where two valley glaciers have joined 
 into a single trunk glacier, the current of each still remains dis- 
 tinct, and we have upward moving currents from both sides in the 
 center as well as on each side. (Figs. 62, 63.) 
 
 BIBLIOGRAPHY VIII. 
 
 1. AMUNDSEN, ROALD. 1913. The South Pole. 2 volumes. London' 
 
 John Murray. New York, Lee Keedick. 
 
 2. CHAMBERLIN, T. C. 1885-1886. The Rock Scouring of the Great Ice 
 
 Invasion. Seventh Annual Report of the Director of the U. S. Geological 
 Survey, pp. 155-254. 
 
 3. CHAMBERLIN and SALISBURY. 1909. Geology, Vol. I. 2nd edition, 
 
 pp. 321-22. Extended bibliography on glacier motion, with summary. 
 
328 PRINCIPLES OF STRATIGRAPHY 
 
 , 
 
 4. HANN, JULIUS. 1903. Handbook of Climatology. Translated by R. 
 
 de Courcy Ward. New York, Macmillan Co. 
 
 5. HOBBS, WILLIAM H. 1911. Characteristics of existing Glaciers. 
 
 New York, The Macmillan Company. 
 
 6. PENCK, ALBRECHT, and BRUCKNER, EDUARD. 1901-1909. 
 
 Die Alpen im Eiszeit-alter. 3 Bande. Leipzig. 
 
 7. REID, HARRY FIELDING. 1895-1913. The Variation of Glaciers. 
 
 I-XVIII. Journal of Geology, Vols. III-XXI. 
 
 8. REID, H. F. 1896. The Mechanics of Glaciers. I. Journal of 
 
 Geology, Vol. IV, pp. 912-928. 
 
 9. REID, H. F. 1901. De la progression des glaciers, leur stratification et 
 
 leurs veines bleues. Congres Geologique International, Compte Rendu, 
 VIII me Session, pp. 749-755. 
 
 10. REID, H. F. 1905. The flow of Glaciers and their Stratification. Ap- 
 
 palachia, Vol. II, pp. 1-6, 2 pis., I fig. 
 
 11. REID, H. F. 1907. Ibid. Johns Hopkins University Circular, new 
 
 series, No. 7, pp. 24-26 [612-614], l % 
 
 12. REID, H. F. 1908. On the Internal and Basal Melting of the Ice of 
 
 Glaciers. Zeitschrift fur Gletscherkunde, Bd. Ill, H. I, pp. 68-70. 
 
 13. REID, H. F. 1909. The Relation of the Blue Veins of Glaciers to the 
 
 Stratification, etc. Congres Geologique International, IX me Session, 
 pp. 703-706. 
 
 14. RUSSELL, I. C. 1883-1884. Existing glaciers of the United States, 
 
 5th Annual Report of U. S. Geological Survey, pp. 309-362. 
 
 15. RUSSELL, I. C. 1897. Glaciers of North America. Boston and Lon- 
 
 don, Ginn & Co. 
 
CHAPTER IX. 
 
 ORIGINAL STRUCTURES AND LITHOGENESIS OF THE TRUE 
 AQUEOUS OR HYDROGENIC ROCKS. 
 
 True aqueous or hydrogenic deposits, i. e., precipitates from 
 solution in water, may be grouped under a number of divisions, ac- 
 cording to the mode of origin. The principal groups are : 
 
 1. Marine, or oceanic (halmyrogenic, halogenic,* or thalasso- 
 genicf). 
 
 2. Lacustrine (limnogenic J), including those of lakes, ponds, 
 marshes, salinas, and playa lakes. 
 
 3. Fluvial (potamogenic ). 
 
 4. Terrestrial, including those of springs, both cold and hot, of 
 geysers, the deposits in caverns, mineral veins, etc. They comprise 
 deposits of both vadose and magmatic waters. Under this head 
 must also be placed the salitrales of Patagonia and other regions. 
 
 Chemical deposits of the open sea when not alteration products 
 are practically limited to carbonates of lime and of magnesia, though 
 these are rare in the modern ocean. In enclosed mediterraneans or 
 other cut-offs from the ocean, deposits of calcium carbonate are 
 formed, while gypsum and salt may be precipitated on evaporation 
 of the water. Complete evaporation may result in the deposition of 
 the rarer salts, especially those of potash. 
 
 In lakes chemical deposits are chiefly confined to the carbonates 
 of lime, which may be extremely abundant. Complete evaporation, 
 however, may result in the deposition of a variety of salts, including 
 chlorides, nitrates, borates, sulphates, carbonates, etc. Chemical de- 
 posits of fluvial origin are chiefly limited to the carbonates of lime, 
 though deposits of iron oxides and carbonates may also be formed. 
 Finally, the terrestrial deposits of this type include carbonate of 
 lime and silica, as well as a large variety of additional mineral 
 
 *d\s = salt. 
 
 f 0a\aff<ra = the sea. 
 
 = a marsh, lake, pond. 
 river. 
 
 329 
 
330 PRINCIPLES OF STRATIGRAPHY 
 
 substances which fill up fissures and other cavities, forming veins 
 and other types of deposits. Chief attention will here be given to 
 the deposits of carbonate of lime and magnesia, to gypsum and an- 
 hydrite, and to chloride of sodium and some other common salts. 
 
 OCEANIC PRECIPITATES. 
 
 CHEMICAL DEPOSITS OF THE DEEP SEA. Purely hydrogenic 
 rocks, i. e., precipitates, are practically unknown in the open 
 ocean, but chemical deposits, in part alteration products, are 
 found. Here belong the manganese concretions, which are found 
 widely distributed over the floor of the abyssal portion of 
 the Pacific Ocean and elsewhere. They generally enclose foreign 
 objects, pieces of pumice, the teeth of sharks often of extinct Ter- 
 tiary species the ear-bones of whales, etc., or even fragments of 
 siliceous or calcareous sponges. The encrusting material is dis- 
 posed in concentric layers and consists of manganese oxide up to 
 63 per cent, and iron oxide up to 45 per cent., the iron in some cases 
 even exceeding the manganese. Clay and silica make up the re- 
 mainder, one or the other having been found to approach 50 per 
 cent, of the mass. Copper, nickel, lead, cobalt, molybdenum, and 
 traces of zinc, lithium and thallium have also been found in these 
 concretions. The source of the manganese has been thought to be 
 the sea water, in which it occurs as the bicarbonate, which, when 
 coming in contact with the oxygen of the air, is precipitated as the 
 peroxide. The small quantity of this salt found in the sea water 
 has, however, cast doubt on this explanation, and others have sought 
 for the source of the manganese in the decomposition products of 
 basic volcanic rocks in the sea, or in submarine volcanic eruptions 
 or in mineral springs. (See summary by Potonie-46:/(5d.) An- 
 other alteration product is found in the crystals of Phillipsite, a 
 hydrous silicate of aluminium, calcium and potassium, found 
 abundantly in the deeper portions of the Pacific and Indian oceans. 
 They not infrequently occur in the form of crossed twins. These 
 are also regarded as due to precipitation of decomposition products 
 of submarine volcanic rocks, taken into solution in the water of the 
 deep sea. 
 
 Glauconite, too, may be mentioned here. It accumulates in the 
 shallower portions of the sea, being more largely confined to the 
 littoral district, i. e., the continental shelf. Since this mineral is, 
 however, more properly to be regarded as an alteration product 
 of the finer marine sediments, its discussion is best deferred until 
 these sediments have been considered. (See Chapter XV.) 
 
PRECIPITATION OF LIME IN THE SEA 331 
 CHEMICAL LIME AND MAGNESIA DEPOSITS. 
 
 CHEMICAL PRECIPITATION OF CARBONATE OF LIME AND MAG- 
 NESIA IN THE OCEAN. In the modern oceans the chemical precipi- 
 tation of lime and magnesia as limestones and dolomites is almost 
 unknown. It is true that crystals of dolomite grow in vugs and 
 cavernous openings of coral reefs (Skeats~5o), and calcite and 
 aragonite crystals were found abundantly in the cavities between the 
 organic fragments composing the coral rock in the deeper portions 
 of the Funafuti core, but those deposits belong rather to the cate- 
 gory of diagenetic modifications. This general absence in the 
 modern sea of such deposits is not a safe argument for the similar 
 freedom of the ancient sea from these deposits. Indeed, there are 
 many horizons where limestones and dolomites occur, which, from 
 the absence of organic remains, are difficult to explain as of other 
 than chemical origin. This is especially the case with the pre- 
 Cambric limestones, for which Daly (12:163) advocates a chemical 
 history. He suggests that the lime of the pre-Cambric ocean was 
 precipitated on the ocean floor by the agencies of decaying organic 
 matter. This accumulated in quantity owing to the absence of the 
 bottom scavengers which had not then come into existence, and 
 which now keep the sea bottom free from organic matter to a 
 large extent. Furthermore, the low temperatures of our sea bot- 
 toms permit only a very slow putrefaction of the organic matter 
 which does remain. In earlier seas, however, temperatures may 
 have been much higher, permitting such putrefaction on a large 
 scale. 
 
 During putrefaction ammonium carbonate is given off in large 
 volumes. This converts the chloride and sulphate of calcium into 
 carbonate, which is then precipitated, the reactions being: 
 
 CaSO 4 + (NH 4 ) 2 CO 3 = CaCO 3 + (NH 4 ) 2 SO 4 
 CaCU + (NH 4 ) 2 C0 3 = CaC0 3 + 2 NH 4 C1. 
 
 Experiments (Irvine and Woodhead-3O :/p. Quoted by Daly- 
 II : 101) have shown that sea water is readily modified by putre- 
 fying organic matter or effete substances derived from living ani- 
 mals. Four small crabs, weighing 90.72 grams, were placed in sea 
 water absolutely free from carbonate of lime. After twelve months 
 they produced an alkalinity in the water equal to the production of 
 45-36 grams of calcium carbonate. This was due to the decom- 
 position of calcium sulphate by the uric acid and other effete 
 matter. In a second experiment, with temperatures ranging from 
 
332 PRINCIPLES OF STRATIGRAPHY 
 
 60 to 80 degrees Fahrenheit, the decomposition of urine mixed with 
 sea water precipitated practically all the sulphate of lime present in 
 seventeen days. The complete putrefaction after death of nine 
 small crabs in 2 liters of sea water, at temperatures varying from 
 70 to 80 F., resulted in the precipitation of all the lime salts in 
 the form of carbonates. 
 
 One objection that has been raised against this theory of lime 
 deposition is that in the decay of organic matter carbon dioxide is 
 likewise generated, and that this would tend to keep the lime in 
 solution. This is indeed the accepted explanation for the absence 
 of calcareous deposits in the deep sea, where only red clay is 
 deposited (see beyond, Chapter XV). Natterer emphasizes the 
 importance of the abundant ammonia resulting from the decay of 
 the organic matter on the sea bottom, and holds that this must.be 
 capable of precipitating lime and magnesia from the sea as car- 
 bonates, but only when there is no free CO 2 present. The reaction 
 of ammonium carbonate and sodium carbonate resulting from 
 organic decay (Steinmann-5i : /pp) with the calcium sulphate re- 
 sults in the precipitation of calcium carbonate, which, according to 
 Linck (33:500) is aragonite and not calcite. Magnesium carbon- 
 ates and dolomites, however, are not directly separated from sea 
 water through the reactions with ammonium and sodium carbon- 
 ates (Philippi-45 : 432), but will separate after an interval of 
 time, especially if the calcium salts are first removed. Murray and 
 Irvine (36: 104) found that a mixture of sea water and urine after 
 standing several days furnished the precipitate under A of the fol- 
 lowing table, the urine decomposing and furnishing the alkaline car- 
 bonate. After filtering out this precipitate and permitting the liquid 
 to stand ten days longer the precipitate given under B was obtained. 
 
 A B 
 
 Water and organic matter (containing 7.38 % 
 
 ammonia in A) 31.81 20.25 
 
 Carbonate of lime 4-85 75-35 
 
 Phosphate of magnesia and ammonia 51 . 10 
 
 Phosphate of lime 12 . 24 
 
 Carbonate of magnesia 1 . 02 
 
 Phosphate of magnesia 3-38 
 
 IOO.OO 100.00 
 
 The carbonate of magnesia was precipitated only after much, 
 and perhaps nearly all, of the calcium was precipitated as carbonate 
 A considerable amount of the precipitating alkali, i. e., the am- 
 
PRE-CAMBRIC LIMESTONES 
 
 333 
 
 monia, was removed from the mixture in the first precipitate. From 
 the experiments cited, it appears that hydrous carbonate of mag- 
 nesium can be precipitated by ammonium carbonate emitted from 
 decaying animal remains, the precipitation being much slower than 
 in the case of calcium carbonate, and being retarded by the pres- 
 ence of calcium salts in the solution. If the pre-Cambric ocean was 
 nearly limeless, as argued by Daly, the proportion of precipitated 
 magnesium carbonate would be high, even possibly approaching the 
 ratio of true dolomite. The general proportion of dolomites to 
 limestones in the various formations of the earth's crust is shown 
 in the following table. (Daly-i2 : 165.) 
 
 Table showing proportion of dolomites to limestones in the 
 geological series. 
 
 4 
 
 Period 
 
 i 
 
 No. of 
 analyses 
 averaged 
 
 2 
 
 Ratio of 
 CaCO 3 to 
 MgCO 3 
 
 3 
 
 Ratio of 
 Ca to Mg 
 
 Pre-Cambric: 
 a. From North America except those in b . 
 b. From Ontario (Miller) 
 c Average of a and b 
 
 28 
 
 33 
 61 
 
 i .64:1 
 4.92:1 
 
 2 QVI 
 
 2.30: 
 6.89: 
 
 4IO* 
 
 d. Best general average. 
 
 4.0 
 
 2 58:1 
 
 1 61: 
 
 Cambric (including 17 of the Shenandoah 
 limestone) 
 
 ?O 
 
 2 96"! 
 
 4 14' 
 
 Ordovicic 
 
 Q-I 
 
 2 72*1 
 
 T, 81: 
 
 Siluric 
 
 208 
 
 2 oo:i 
 
 2 .a*;: 
 
 
 
 
 
 All pre-Devonic 
 
 T.Q2 
 
 2 ^Q'l 
 
 7 IS: 
 
 Devonic . 
 
 1 06 
 
 4 4Q:I 
 
 6 20: 
 
 Carbonic (including Mississippic) 
 
 2^8 
 
 8.80:1 
 
 12. 4S: 
 
 Cretacic 
 
 77 
 
 40 . 2 -\ : I 
 
 56.32: 
 
 Tertiary 
 
 26 
 
 V7 Q2:I 
 
 SVO9: 
 
 Quaternary and Recent 
 
 26 
 
 25 oo:i 
 
 ^S.oo: 
 
 
 
 
 
 Total . . . 
 
 86s 
 
 
 
 
 
 
 
 
 This table shows that the ratio of calcium to magnesium is 
 fairly constant for all pre-Devonic rocks (shown by 392 analyses 
 chiefly from North America), the average being 3.35:1. In the 
 DevoniC the ratio rises abruptly and increases rapidly in the Car- 
 bonic. The Cretacic shows an apparent maximum, but might be 
 
334 PRINCIPLES OF STRATIGRAPHY 
 
 exceeded by Tertiary and later formations if more analyses were 
 available. Daly points out that the ratio of calcium to magnesium 
 in all pre-Devonic formations is significantly close to the same 
 ratio in the rivers now draining pre-Cambric terranes, as shown by 
 the Ottawa River, where the average ratio is 3.69: i. From this 
 he suggests that during pre-Devonic time the river-borne magne- 
 sium and calcium were wholly precipitated, after diffusing, to the 
 sea bottom. Daly holds that the study of the grain of unmeta- 
 morphosed Cambric and pre-Cambric carbonate rocks convincingly 
 shows that they are not of clastic origin nor of direct organic origin 
 through accumulation of shells or skeletons. Microscopic exami- 
 nations of typical specimens from a mass more than 7,000 feet 
 thick seem to indicate that neither horizon nor distance from the 
 old shore lines affects the singularly monotonous grain of the 
 rocks. "The constituent particles are either idiomorphic and 
 roughly rhombohedral, or anhedral and faintly interlocking. The 
 former are everywhere of nearly uniform average diameter, rang- 
 ing from o.oi mm. to 0.03 mm., with an average of about 0.02 mm. 
 The anhedral grains range from 0.005 mm. to 0.03 mm., averaging 
 about 0.015 mm. in diameter." (Daly-i2 : 168.) A similar uni- 
 formity of grain was found in the Archaean dolomites of Idaho, in 
 the magnesian limestones and dolomites of the Belt terrane with 
 Beltina danai, in the Clarke range, and in the Siyeh and Sheppard 
 siliceous limestones of northwestern Montana (Middle Cambric). 
 Similar fine-grained dolomites have been found by Vogt in Nor- 
 way, and are believed to be chemical precipitates. (Vogt-55, 
 quoted by Daly-i2 : 168.) An apparently good case of lime 
 deposition in the sea by chemical separation, through the influence 
 of decaying organic matter, is found in the fine calcareous and 
 magnesian mud at the bottom of the Bay of Naples. (Walther and 
 Schirlitz-67:jjd) This, mud is relatively poor in organic remains, 
 and seems to have been separated from the lower strata of water, 
 which are poorer in lime and magnesia than the upper. Stony 
 crusts consisting chiefly of calcium carbonate, of ferruginous clay, 
 of double silicates of sodium and potassium holding manganese, of 
 silica, and of carbonate of magnesia are found at the bottom of 
 several mediterraneans, as, for example, the Roman Mediterranean 
 between Crete and Africa on the one hand, and Crete and Asia 
 Minor on the other. Also between Crete and Greece and in parts 
 of the ^Egean Sea, as well as in the Red Sea, where they are com- 
 mon, and the bottom waters are rich in ammonia ( Phillipi-45 : 
 429.) Calcareous concretions were dredged by the Challenger from 
 a blue clay in 216-255 m - depth west of New Guinea, and these are 
 
MARINE HYDROGENIC LIME DEPOSITS 335 
 
 regarded as of purely chemical origin. The rapid .cementation of 
 lime sands in the deeper sea by the deposition of lime or magnesium 
 carbonate is a further illustration of this phenomenon, as is also 
 the rapid cementation of reef limestones and the sands and rubble 
 on the borders of the reef. Darwin found that the breccias of 
 coral fragments on the outer margins of the reefs were so firmly 
 cemented that it was difficult to chop off a fragment, even with a 
 chisel. The Pourtales plateau, south of Florida, is a hard limestone 
 surface of recent origin. All loose material not cemented by lime 
 deposits is swept off the plateau by the Gulf Stream. Similar sub- 
 marine banks are found between the Canaries and the South Afri- 
 can coast (the Seine-Dacia and Josephine banks), the Campeche 
 banks of Yucatan, the Mosquito bank of the east' coast of Nica- 
 ragua and elsewhere. 
 
 What is true of modern coral reefs and banks is equally ap- 
 plicable to older deposits of this character. The cementation of the 
 organic (biogenic) limestone of the reefs of the various geological 
 periods is undoubtedly due to precipitation of lime from the sea 
 water. This, however, is always of minor importance, and the reef 
 deposits must be classed with biogenic rocks. A rapid cementation 
 of detrital lime sands and muds seems to be indicated in many 
 limestone banks. It has been especially described for the Mus- 
 chelkalk (Philippi-45 '.438), and is suggested by certain features in 
 a number of limestone beds, and is to be explained as due to rapid 
 chemical deposition of lime between the grains of the calcareous 
 clastic material. 
 
 Among the indications of rapid hardening of such banks is the 
 attachment of crinoids by flat, disk-like expansions, which is pos- 
 sible only on a hard bottom ; by the attachment of molluscs and 
 other hard-bottom-loving organisms, and by channelings and bor- 
 ings which may be filled by the immediately succeeding materials. 
 Such rapid hardening makes possible the formation of conglomerate 
 or of brecciated layers which contain fragments of the underlying 
 limestone layer. Such intraformational conglomerates have been 
 described by Walcott from Lower Cambric limestones of eastern 
 New York and Pennsylvania and from Virginia and Tennessee (57; 
 58 134), and by Wagner from the Muschelkalk of the vicinity of 
 Jena (56; Fig. j). Here the lower bed represents a worn surface 
 and many fissures which are filled by the material of the succeeding 
 layer. This upper layer is also characterized by a basal conglom- 
 erate with pebbles of the lower rock. That the upper layer was 
 also rapidly cemented is shown by the occurrence of a large En- 
 crinus root and a rich molluscan fauna over its surface. Much care, 
 
336 PRINCIPLES OF STRATIGRAPHY 
 
 however, is needed to distinguish such conglomerates from the basal 
 conglomerates marking" a disconformity between the two layers. 
 The Cretacic chalk of western Europe has also been regarded as in 
 part made up of chemical precipitates. This refers especially to the 
 cement which unites the shells of foraminifera, etc. The chemical 
 part of the cement consists of microscopic calcite rhombohedrons 
 and less regular calcite grains, a large part of these originating from 
 the recrystallization of organic aragonite (Cayeux-Q). Walther 
 regards the cementing material of the fine calcilutytes of the Soln- 
 hofen region as due to chemical precipitation (64:212). 
 
 Oolites and Pisolites of Chemical or Purely Hydrogenic Origin. 
 These have been described from a number of localities, occurring 
 both in recent formations and in older geological deposits. The fa- 
 miliar pisolite of the Carlsbad Springs in Bohemia is a typical ex- 
 ample, formed by the encrustation of minute particles of quartz or 
 feldspar, held in suspension by the rising waters, and turned in all 
 directions, so as to produce uniform encrustations. Gas and air 
 bubbles likewise may form the nuclei of such encrustations, which 
 in that case have a hollow center. The usual composition is CaCO 3 , 
 with a small quantity of FeCO 3 (Zirkel-7o :-/##; Hochstetter- 
 24:6*5), but the mineral is neither calcite nor aragonite, but a third 
 modification "Ktypeit," convertible by heat into calcite. On the 
 shores of seas, the water of which holds much lime, particles of 
 broken shells, grains of igneous rocks, etc., are encrusted by CaCO 3 
 forming a rock of typical oolitic appearance. On the shores of 
 the Island of Gran Canaria in the Canary Islands, between Las 
 Palmas and Isleta, encrustations of carbonate of lime are found, 
 according to L. von Buch, around fragments of broken molluscs, 
 and small sand grains of trachyte and basalt. This sand becomes 
 consolidated into a porous rock, which is quarried at low tide. The 
 water of the waves throughout the greater part of the year has a 
 temperature of more than 20 C, and seems to be abundantly able 
 to dissolve lime and redeposit it around the grains of sand, forming 
 a "Rogenstein." In the Mexican lagoons oolites are formed, ac- 
 cording to Virlet d'Ooust, by the encrustation with lime of insect 
 eggs, and these oolites closely resemble those from the Jurassic. 
 
 On the coast of Ascension Island recent oolites are formed, ac- 
 cording to Darwin, by the encrustation of rounded fragments of fos- 
 sils. Similarly, fragments of shells and grains of coral sand on the 
 north coast of Tahiti are coated with lime, according to Dana 
 (13:57^), and transformed into oolites. Other examples are cited 
 from the coast of the Sinai peninsula at Wadi Deheese, and in 
 the Reede of Suez (Walther-59 :/). These last two examples 
 
HYDROGENIC OOLITES 337 
 
 are, however, regarded by Rothpletz as of algous origin (see be- 
 yond). Linck (33:49$) has obtained for these recent oolites an 
 aragonite reaction, while the fossil oolites are by him referred to 
 calcite. 
 
 Linck (33:506) has experimented with the chemical precipita- 
 tion of lime from artificial sea water with results leading to the fol- 
 lowing conclusions : 
 
 The maximum solubility of calcium carbonate in sea water is 
 about 0.0191% CaCO 3 . If this maximum is exceeded deposition 
 of CaCO 3 occurs, in the form of calcite in temperate climates and 
 of aragonite in tropical climes, but without the formation of 
 sphaeruliths. The same thing is true of solutions of calcium car- 
 bonate otherwise free from salts. If the calcium sulphate of the 
 water is precipitated as carbonate by sodium or ammonium car- 
 bonate, it is always aragonite and of sphserulithic form. These re- 
 agents will precipitate calcite from solutions of calcium sulphate 
 otherwise free from salts, both at 40 C. and at 18 C. The solu- 
 bility of aragonite is thus shown to be greater in solutions which 
 are poor in or free from other salts than in those rich in such 
 salts, and that it is greater in colder than in warmer solutions. For 
 calcite just the reverse holds true, and hence, at a given tempera- 
 ture, sea water will hold in solution more calcium carbonate than 
 fresh water, but there may be circumstances under which arago- 
 nite and calcite are soluble in equal degree, and so may be formed 
 simultaneously. Both calcium carbonate and calcium sulphate are 
 more readily soluble in sea water than in fresh water. Applying 
 his results to the elucidation of the question of the origin of 
 marine oolites, Linck finds that the under saturation of sea water 
 precludes deposition of lime without the intervention of a precipi- 
 tating reagent, and this he finds in the sodium and ammonium car- 
 bonate resulting from the decay of organic matter. The precipi- 
 tated material is usually in the form of sphseruliths or concretions 
 of aragonite with or without an inner grain. The latter is found in 
 the neighborhood of coasts, where the lime is deposited around 
 fragments of shells or coral, grains of quartz or other sand, foram- 
 inifera, etc., while in the open sea they are without central kernel. 
 Linck considers that all oolites and pisolites are of inorganic or 
 chemical origin, and that, whenever organic remains occur in the 
 mass, these are mechanically enclosed, or, in the case of unicellular 
 algae, the oolite grains serve as a basis for attachment. In the 
 open sea the sphseruliths sink to the bottom in time, while near the 
 shore they are piled up into sand dunes and assorted, according to 
 size, with more or less mechanical wear. In the course of time the 
 
338 PRINCIPLES OF STRATIGRAPHY 
 
 aragonite spheres are converted into calcite, with often complete 
 retention of structure. The opinion of Rothpletz, who regards most 
 of these oolites as of organic (phytogenic) origin, will be given 
 later (Chapter XI). 
 
 DEPOSITS IN ENCLOSED OR NEARLY ENCLOSED BASINS. The 
 Black Sea (Andrussow-4) is characterized by relatively slight ver- 
 tical currents, owing to the superficial layer of water. of less salin- 
 ity. This layer, 125 fathoms deep, is alone furnished with oxygen 
 from the surface, while below that the water is poisoned by the 
 gases resulting from the putrefaction of the dead animal bodies 
 which have sunk to the bottom from the surface layers, and which, 
 in the absence of scavengers, were left to decompose in the relatively 
 high bottom temperatures. Only anaerobic bacteria, especially Bac- 
 terium hydrosulfuricum ponticum, live in the lower strata of these 
 waters. At a depth of about 100 fathoms begins the separation of 
 H 2 S. by these bacteria, the quantity being 33 c.c 4 ! to 100 liters of 
 water, and rapidly increasing until at 500 fathoms it is 570 c.c. to 
 100 liters of water. Further down the increase is less rapid. Am- 
 monium carbonate is also produced in large quantities. The black 
 mud between 300 and 717 fathoms is charged with an abundant 
 separation of iron sulphide (FeS), according to the following reac- 
 tions (Murray and Irvine-36 : pj, modified by Daly-n : xoj) : 
 
 RSO 4 + 2C = 2COo + RS 
 RS + 2CO 2 +H 2 O = H S + RCO 3 CO, 
 RS + RCO 3 CO 2 + H 2 O = 2RCO, + H 2 S 
 Fe 2 O 3 + 3H 2 S = 2FeS + S + 3H 2 O 
 
 With the iron sulphide and free sulphur there is also formed a 
 powdery precipitate of CaCO 3 , which at a distance from shore, 
 where mechanical detritus is less abundant, forms layers and thin 
 banks of fine-grained limestone, whereas nearer the shore the 
 powdery lime is mixed with fine detritus. Shells of the planktonic 
 young of pelecypods and the frustules of pelagic diatoms are 
 likewise abundant in these deposits (Andrussow-4). 
 
 CHEMICAL LIMESTONE DEPOSITS OF LAKES IN ARID REGIONS. 
 While chemical precipitation of lime is found in the sea only under 
 exceptional conditions, and is of merely local significance, tie 
 chemical precipitation of lime from drying lakes in arid or semiarid 
 regions becomes a matter of greater import. The site of the former 
 Lake Lahontan in the Great Basin region (western Nevada) was 
 characterized by calcareous deposits of great extent, as was also 
 Lake Bonneville, the predecessor of Great Salt Lake. Three types 
 
LIME PRECIPITATES IN LAKES 
 
 339 
 
 of hydrogenic lime are recognized by Russell (47:^/7; 48) in the 
 basin of Lake Lahontan, where they covered the surfaces of nearly 
 all the rocks, on the shores and bottom of the old lake. The oldest 
 deposit is the Lithoid tufa. It is compact, gray, sometimes form- 
 ing a cement for the ancient gravels, and not infrequently contain- 
 
 FIG. 64. A group of crystals of thinolite, or thinolithic tufa. Lake Lahontan 
 basin, Nevada. (After Russell.) 
 
 ing the shells of fresh-water gastropods. After an interval of ex- 
 posure the second type, or Thinolithic tufa, was deposited over the 
 first. It consists of orthorhombic prisms 6 to 8 inches in length 
 and almost half an inch thick (Fig. 64). These have a peculiar in- 
 ternal structure, and were at first considered pseudomorphs after 
 gaylussite, but their structure does not agree with that of any 
 known mineral. The entire layer is from 6 to 8 feet thick where 
 
340 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 best developed. Similar crystals are found in the deposit of the ex- 
 tinct lake of Mono Valley, California. The last deposit is the 
 Dendritic tufa, and it is also the most abundant. Its greatest depth 
 is more than twenty feet, and may be as much as fifty. (Fig. 65.) 
 Between Wadsworth and Pyramid lakes, the old floor of Lake La- 
 hontan is completely covered over an area of several square miles 
 by dome-shaped masses of this tufa, commonly spreading in mush- 
 
 FIG. 65. Tufa domes, shore of Pyramid Lake, Nevada. A remnant of Lake 
 Lahontan. The deposit is of dendritic tufa. (After Russell.) 
 
 room fashion, and up to 5 or 6 feet in diameter. (Fig. 66.) In- 
 terference with one another's growth produces polygonal outlines. 
 This is the case on Carson River, where they sometimes form a 
 pavement of hexagonal blocks, each about 2 feet in diameter. The 
 dendritic character of this tufa is seen on weathered surfaces. 
 Where embedded in the gravel or silt deposits of the lake or the 
 interpolated river sediments, these tufa deposits form definite lime- 
 stone horizons, with or without fossils, these limestones horizons be- 
 ing indicative of desert conditions, under which they were chemi- 
 cally precipitated. 
 
LIME PRECIPITATES OF RIVERS 341 
 
 Older Deposits of This Type. What appears to be a deposit 
 closely related to the last type is found in the upper Permic Mag- 
 nesian Limestone series of Durham, England. Here many of the 
 beds are composed of more or less spherical masses of dolomite 
 having a radiating structure and varying greatly in size and form; 
 pisolitic, botryoidal, reniform and large globular masses being com- 
 mon. 
 
 LIMESTONE DEPOSITS FROM RIVERS. Throughout the limestone 
 region of torrid America, especially on the margins of the bolson 
 plains of Mexico, a deposit of limestone is forming as a white 
 superficial crust, sometimes comparatively free from foreign ma- 
 terial, at others forming the cement of conglomerates. This con- 
 
 FIG. 66. Spheroids of dendritic tufa. Basin of Lake Lahontan. 
 (After Russell.) 
 
 centrate of lime is called tepetate, and consists of material dissolved 
 from the limestone surfaces, and transported in solution by the tor- 
 rential rivers. 
 
 The Catinga limestone of Bahia, Brazil (Branner-6: /pj), is a 
 good example of a river-deposited limestone. The material is de- 
 rived from the older Salitre (Jurassic) or other limestones, and the 
 deposition probably began as far back as the Tertiary, and still con- 
 tinues. The attitude of the beds is generally horizontal, and their 
 thickness ranges up to nearly 100 feet. 
 
 The deposition of this rock is due to the partial evaporation of 
 the lime-saturated stream waters as they leave the limestone regions, 
 and to the liberation" of the carbon dioxide during the warming 
 under the semitropic sun. The deposition of lime usually begins at 
 
342 PRINCIPLES OF STRATIGRAPHY 
 
 falls or cataracts, and proceeds both upstream and downstream, rill- 
 ing the shallow parts first, because of the greater exposure of the 
 water at those places. "Any downstream slope of the stream bed 
 that causes a rippling of the water exposes it to the air, liberates 
 more carbon dioxide, and thus causes an increased deposition of 
 lime on the downstream side." Barriers are thus built up in time. 
 Embankments formed in this way vary in height from half a meter 
 to four meters. The rock is hard at the upper surface, more or 
 less overhanging and cavernous on the downstream side. Where 
 streams spread out to form arms or embayments, the floors of these 
 are covered with soft, marly limestone. The same is true over the 
 flat portions of the limestone valleys. In the low grounds water 
 often remains stagnant in broad, shallow pools, especially in some 
 of the sink-hole depressions. The deposit here formed is always 
 soft and marly when fresh, but becomes as hard as a normal lime- 
 stone on ageing. "At many places these lime deposits, both the 
 newer and older ones, contain plant impressions and enclose the re- 
 mains of land shells." Sometimes the shells are cemented together 
 into a hard-shell limestone, the species being those still existing in 
 the region. Angular as well as water-worn fragments of all kinds 
 of rock are not infrequently found embedded in this limestone. 
 
 "When a broad, gentle and rather even slope carries the lime- 
 charged waters in shallow sheets toward a channel, the lime is pre- 
 cipitated more rapidly along the edge of the plain, where, on ac- 
 count of a change to a steeper grade, the water breaks into ripples 
 or spray. This causes the bluff to encroach steadily on the low 
 ground, and the process must eventually lead to the low ground be- 
 ing entirely filled up." The bluffs thus formed curve over at the 
 top, and are full of caverns due to the irregularity of the deposit. 
 The roofs of the caverns are hung with stalactites. "Often the 
 travertine is deposited in masses of such shape that they break 
 from their own weight and form a talus slope at the base of the 
 bluff, and this, too, in time is covered over by later deposits, and is 
 incorporated in the great limestone sheet." Some of these bluffs are 
 from 25 to 30 meters high, which is, therefore, the thickness of the 
 great limestone thus forming on dry land. The process is one of 
 chemical aggradation. 
 
 DEPOSITS OF LIME BY SPRINGS. Calcareous tufa is a common 
 deposit by springs emerging from limestone formations. The de- 
 posit of lime here is due largely to the relief of pressure and the 
 escape of CO 2 , which held the lime in solution (see posted). Or- 
 ganic bodies, such as leaves, sticks, etc., are commonly encrusted by 
 this lime, which at first is a fine slime, but soon hardens on ex- 
 
LIME PRECIPITATES OF SPRINGS 
 
 343 
 
 posure to the air. Much lime is also precipitated upon certain liv- 
 ing mosses (Hypnum, etc.) by what appears to be the physiological 
 activity of the plant itself (see p. 475). The calcium carbonate de- 
 posits of the hot springs of the Yellowstone, etc., are probably due 
 to organic activities. Nevertheless a considerable part of the cal- 
 careous tufa or travertine is a purely hydrogenic deposit. (Fig. 67.) 
 At the Baths of San Vignone in Tuscany the travertine is de- 
 posited at the rate of six inches a year, while at San Filippo, Sicily, 
 
 FIG. 67. The Mammoth Hot Springs of the Yellowstone National Park, 
 showing the formation of calcareous deposits by hot springs. 
 (After Hay den.) 
 
 it is one foot in four months, the deposit having grown to a height 
 of at least 250 feet, and forming a hill a mile and a quarter long 
 and a third of a mile broad. (Lyell-34 : 402.) The deposits at 
 Narni, Italy, increase proportionally to the rate of flow, little lime 
 being deposited in stagnant water. The amount also increases with 
 distance from source and consequent length of exposure to the air, 
 and with decrease in temperature. Percolating ground water often 
 deposits lime in the pores of clastic strata and so cements them. 
 This is shown by the lime-sand dunes of the Bermudas, which are 
 
344 PRINCIPLES OF STRATIGRAPHY 
 
 consolidated in this manner and by the formation of conglomerates 
 with a limestone matrix or cement within deposits of the Pleisto- 
 cenic ice sheet, the lime in this case being commonly derived from 
 the solution of limestone fragments included in the deposit. 
 
 The Onyx Marble. A remarkable type of spring deposit is the 
 so-called onyx marble or Mexican onyx so extensively used for 
 decoration and other purposes. (Merrill-35.) This is a compact, 
 highly crystalline and commonly beautifully variegated deposit of 
 calcium carbonate, which occurs interbedded with breccias, or with 
 ordinary porous tufas in many localities. In Yavapai County, Ari- 
 zona, these have been found on the side of ravines in crystalline 
 schists which stand on edge and are penetrated by basic dikes. 
 The deposit occurs interbedded with breccias made of the country 
 rock, and forms irregular, somewhat concentric layers, from a frac- 
 tion of an inch to two or more feet in thickness, and lying essen- 
 tially horizontal. The massive layers are separated from one an- 
 9ther by porous cellular ones. At Cave Creek, Arizona, large 
 blocks of the onyx up to 4 feet or more in diameter are embedded 
 in tufaceous material. In Mexico, whence the original supply came, 
 this rock is found in masses up to ten feet or more in diameter in a 
 tough, reddish or dark-brown clay, overlying a closely cemented 
 conglomerate. In one instance (at Antigua Salines) it is found in 
 a hard, flint-like country rock, and appears to be a regular vein 
 formation. Similar onyx deposits are found in western Utah. 
 
 In Lower California this onyx marble occurs in the desert region 
 near the Gulf coast. It is found here in layers, slabs and blocks 
 20 inches to 3 or more feet thick, interstratified with tufaceous beds 
 and ancient lake bed material, and shows a most surprising variety 
 of delicate colors and tints. Elsewhere in lower California on the 
 steep slopes of Tule Arroyo, a deep canyon in dark mica schist and 
 blue-gray silicified limestones and quartzites standing on end, simi- 
 lar deposits of these onyx marbles were made by former springs. 
 At first a cellular travertine was formed cementing the angular 
 fragments of the older rocks, with which the slopes were strewn, into 
 a coarse breccia. After several feet of such deposits, the compact 
 onyx marble succeeded, probably through a change in the constitu- 
 tion of the spring or the conditions of deposition. "In time the 
 onyx-forming action ceased and for a period no calcareous deposi- 
 tion whatever took place, the slopes becoming once more covered 
 with angular particles of the older rocks from higher up, these in 
 their turn becoming cemented into breccias when the springs re- 
 sumed their work. In this way were built up the alternating layers 
 of breccia, tufa and onyx, until finally all deposition practically 
 
LIME DEPOSITS OF CAVERNS 345 
 
 ceased, and spasmodic but fiercely rushing streams cut the arroyo 
 to its present depth, exposing in either wall the irregularly alter- 
 nating beds described." (Merrill-35 : 548.) Two highly carbonated 
 springs still occur in the bottom of the canyon, building small beds 
 of tufaceous material. 
 
 Considering the nature of the country rock in this and the Ari- 
 zona localities, and the highly carbonated character of the springs 
 still remaining, one is led to regard the water as magmatic or juve- 
 nile, bringing its burden of lime from greater depth. 
 
 In Algeria, North Africa, province of Oran, deposits of this 
 type occur, covering an estimated area of about 12 acres. The 
 formation consists of strata varying from 6 inches to 4 feet in thick- 
 ness and separated by beds of compact travertine. The deposits are 
 of Quaternary age, resting unconformably upon Middle Miocenic 
 limestones and sandstones. Similar deposits are also found in 
 Persia. 
 
 A significant fact bearing on the mode of deposition of these 
 formations is that these deposits occur in regions of comparatively 
 recent volcanic activity, and it is highly probable that the onyx 
 marbles were deposited in heated waters and possibly under the 
 surface of a pool or shallow lake, which would prevent too rapid loss 
 of CO 2 , resulting in ordinary porous travertine. Such travertine 
 was formed after the periodic draining of the lakes. 
 
 UNDERGROUND DEPOSITS OF LIME. Caverns are especially noted 
 for the extent and variety of their deposits of calcium carbonate. 
 In certain Missouri caverns once submerged by a rising of the 
 ground water, i. e., caverns formerly situated within the belt of 
 cementation, lime was deposited as crystals of calcite, lining the 
 walls, as in huge geodes (ante, p. 177). Caverns within the belt 
 of weathering and hence not filled by the ground water are charac- 
 terized by the deposition of stalactites and stalagmites normal to 
 such caverns. These are formed by the water percolating through 
 the limestone of the roof of the cavern and becoming suspended in 
 drops. Partial evaporation of the water in the dry air, or the 
 escape of the CO 2 which held the lime in solution, results in the 
 formation of a ring of lime for each drop, from the base of each of 
 which a second drop becomes suspended, with the subsequent addi- 
 tion of a second calcareous ring at the bottom of the first one. By 
 this process a hollow tube is formed, which grows by addition be- 
 low, and increases in thickness by successive layers added by the 
 water flowing on the outside of the tube. After a time the external 
 deposits increase to such an extent that they will cover the opening 
 of the tube, or this may become closed by deposits within it. The 
 
346 PRINCIPLES OF STRATIGRAPHY 
 
 stalactite then grows after the manner of an icicle by external addi- 
 tions, and may become of great size. By the confluence of a series 
 of stalactites, banded sheets of lime are formed, which hang from 
 the roof of the cavern, a curtain of stone screening nooks and cham- 
 bers. Stalagmites are formed on the floor of the caverns from the 
 lime still contained within the water after it drops from the stalac- 
 tite. They may be sheet-like, forming a solid floor for the cavern, 
 or they may grow up into mounds. In the latter case they are 
 often in the form of successive caps, one above the other, their 
 edges frequently fringed with stalactites, which give the surface of 
 the stalagmite mound a fluted appearance. 
 
 Cavern deposits may sometimes form on such a scale that the 
 cavern is filled again by crystallized marble, which is often beautiful 
 enough to be sought for commercial purposes. In the Southern 
 Appalachians, and in Missouri and Arkansas, broken-down caverns 
 have made possible the quarrying of the stalagmitic deposits for 
 onyx marble. There are similar deposits in clefts and caverns in 
 the Eocenic limestones of the Nile valley in Egypt. These have 
 been extensively used for architectural and other purposes. In 
 Italy, too, at many localities such cavern deposits occur, and have 
 been worked since ancient times. 
 
 METHOD OF DEPOSITION OF LIME FROM SOLUTION. 
 
 According to Fresenius, carbonate of lime is soluble in pure 
 water, in the proportion of I part in 10,800 of cold, and I part in 
 8,875 parts of boiling water, while others have placed the proportion 
 at much less. "In carbonated waters the neutral carbonate of lime 
 unites with the carbonic acid to form the bicarbonate of lime, which 
 is readily dissolved in water to the extent of 0.88 gram per liter 
 in water saturated with carbonic acid gas at the ordinary at- 
 mospheric pressure and a temperature of 10 degrees centigrade." 
 (Weed-68 :(5j7.) With increased pressure the solubility increases, 
 with corresponding increase in the amount of CO 2 absorbed, until 
 the maximum is reached, which is about 3 grams per liter. When 
 the waters are free from carbonic acid, but contain alkaline and 
 earthy salts, the formation of unstable supersaturated solutions of 
 carbonate of lime is favored. From this the lime is gradually pre- 
 cipitated, the precipitation being more rapid when the salts in solu- 
 tion are the chlorides of the alkalies and alkaline earths than when 
 they are the sulphates of these same bases. Magnesium sulphate 
 and sodium sulphate form solutions with a certain amount of sta- 
 
GYPSUM AND SALT 347 
 
 bility ; but, according to T. Sterry Hunt, the lime is all precipitated 
 in eight to ten days. 
 
 When the water is saturated with carbonic acid, the chlorides of 
 the alkalies and alkali earths will form unstable supersaturated 
 solutions, from which the lime crystallizes out at low temperature 
 as the hydrous carbonate. The solution then retains only 0.8 
 gram of carbonate of lime per liter, corresponding to that dis- 
 solved by the CO 2 . If, however, sodium and magnesium sulphates 
 are present in the solution in carbonated waters, the capacity of 
 these waters for carbonate of lime is nearly doubled. Thus car- 
 bonated water holding either of these sulphates in solution in the 
 proportion of I to 100 or less will take into permanent solution, 
 under ordinary temperature and pressure, a quantity of pure car- 
 bonate of lime equal to 1.56 to 2. grams in a liter. Thus only when 
 free CO 2 is present in pure or mineral waters will CaCO 3 be held in 
 permanent solution. The precipitation of this lime may be brought 
 about by an abstraction of the carbonic acid necessary to hold it in 
 permanent solution. The abstraction may be caused by (Weed- 
 68 : 640) : 
 
 1. Relief of pressure. 
 
 2. Diffusion of the CO 2 by exposure to the atmosphere. 
 
 3. Evaporation. 
 
 4. Heating. 
 
 5. Influence of plant and animal life. 
 
 The first of these is mainly active in nature where springs issue 
 on the surface, while the second occurs on a more extended scale, 
 as in the formation of stalactites and stalagmites and in the encrus- 
 tations formed in petrifying springs. Here diffusion of the CO 2 is 
 facilitated by increase of surface of exposure, and in such cases 
 evaporation generally accompanies diffusion. The deposition of 
 lime through evaporation is illustrated by the tufa deposits of Lake 
 Lahontan. Deposition through heat, illustrated by the encrustation 
 in boilers, is of little significance in nature. Precipitation through 
 the influence of plant and animal life belongs under the head of 
 deposits of Biogenic type, and will be more fully discussed later. 
 
 DEPOSITS OF MARINE GYPSUM AND SALT. 
 
 GYPSUM AND SALT OF MARINE ORIGIN. Gypsum and salt 
 are as a rule the products of similar physical conditions of pre- 
 cipitation, though they do not by any means always occur together. 
 
348 PRINCIPLES OF STRATIGRAPHY 
 
 Both are notably absent from the open ocean and the ordinary type 
 of mediterranean. In the marginal portions of the more enclosed 
 mediterraneans in the arid belts of the earth such deposits often 
 abound. Examples of these are found on the borders of the Black 
 Sea, to a moderate extent on the borders of the Red Sea, and in 
 the Rann of Cutch on the west coast of India. 
 
 Experiments of Usiglio. The precipitation of salt on the evapo- 
 ration of sea water was studied by Usiglio at Cette (52) on the 
 Mediterranean. He began with 5 liters of water, which at 12.5 C. 
 had a density of 1.0258 and a salinity of 38.45 permille, and by evap- 
 oration in the air obtained the results given in the accompanying 
 table, reduced to grams per liter of volume. No salt was deposited 
 until the water had been reduced by evaporation to nearly one-half 
 its volume (53.3 per cent.) and a density of 1.0506,* when slight de- 
 posits consisting chiefly of CaCO 3 and ferric oxide were made. 
 When, on further evaporation, the density had increased to 1.1304, 
 hydrated calcium sulphate (gypsum) began to deposit, this contin- 
 uing until a density of 1.2627 was reached. During the change in 
 the density from 1.13 to 1.208, 84.34 per cent, of all the CaSO 4 was' 
 precipitated as gypsum. After this NaCl was deposited mixed with 
 a little magnesium chloride and sulphate, and this continued until 
 the density was 1.2627, when all the sulphate of lime had been de- 
 posited together with 78.23 per cent, of the total quantity of NaCl. 
 After this 12.38 per cent, of the total NaCl was precipitated without 
 any gypsum. At a density of 1.2444 a little sodium bromide had 
 begun to deposit. Thus between densities 1.0506 and 1.208, only 
 0.1583 per cent, of the total solids had been deposited, and this 
 chiefly as lime sulphate and carbonate and as iron, but between 
 densities 1.221 and 1.318 the following mixture was precipitated: 
 
 Calcium sulphate o . 2828 o/oo 
 
 Magnesium sulphate o . 6242 o/oo 
 
 Magnesium chloride o . 1532 o/oo 
 
 Sodium chloride 27 . 1074 o/oo 
 
 Sodium bromide o . 2224 o/oo 
 
 Total 28 . 3900 o/oo 
 
 Of this 28.3900 permille of total solids, 27.1074 permille, or 
 about 95 per cent., was sodium chloride. The volume had now 
 been reduced to 1.62 per cent, of the original volume of 5 liters 
 
 * The values here given are taken from the table. Slightly different values for 
 intermediate densities are often given. (See the article on Salt in Encyclopaedia 
 Britannica, also Clarke-io.) 
 
ATION AT THE SUCCESSIVE DENSITIES IN GRAMS 
 
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 349 
 
350 PRINCIPLES OF STRATIGRAPHY 
 
 (0.081 liter), and this, the mother liquor, still contained the follow- 
 ing quantities of salts : 
 
 NaCl 2 . 5885 grams per liter, or 12 .9425 grams in 5 liters 
 
 MgSO 4 i . 8545 grams per liter, or 9 . 2725 grams in 5 liters 
 
 MgCl 2 3 . 1640 grams per liter, or 15 . 8200 grams in 5 liters 
 
 NaBr 0.3300 gram per liter, or 1 .6500 grams in 5 liters . 
 
 KC1 o . 5339 gram per liter, or 2 . 6695 grams in 5 liters 
 
 8 . 4709 grams per liter, or 42 . 3545 grams in 5 liters 
 
 Up to this point the separation of the salt had been fairly regu- 
 lar, but now the difference of temperature between night and day 
 became an influencing factor. At night nearly pure magnesium sul- 
 phate was deposited ; by day this was mixed with sodium and potas- 
 sium chloride. With the mother liquor at a specific gravity of 
 1.3082 to 1.2965, there was formed a very mixed deposit of mag- 
 nesium bromide and chloride, potassium chloride and magnesium 
 sulphate, with the double magnesium and potassium sulphate, cor- 
 responding to the kainite of Stassfurt, Germany. A double chlo- 
 ride of magnesium and potassium similar to the carnallite of Stass- 
 furt was also deposited. The mother liquor, which had again risen 
 to specific gravity of 1.3374, contained only pure magnesium 
 chloride. 
 
 The Bar Theory of Ochsenius. In 1877 Carl Ochsenius (37), 
 following 'a previous suggestion of G. Bischof, sought to explain 
 the formation of extensive salt deposits of great thickness by as- 
 suming that they were formed in a nearly enclosed lagoon or bay 
 cut off from the main water body by a barrier beach or bar, across 
 which the water was just able to pass. Concentration of the water 
 within the lagoon and over the bar proceeds by evaporation, and 
 as the water over the bar becomes denser and heavier it sinks and 
 flows down the bar and into the lagoon. If the surface evaporation 
 over the lagoon equals the inflow of salt-bearing waters, it is evi- 
 dent that precipitation of salt must result from the constant in- 
 crease in salinity, and the depth of the salt deposit will depend on 
 the original depth of the lagoon and on the length of time that these 
 conditions obtain. The constant addition of salts to the water of 
 the lagoon, brought about by the influx of sea water and its evapo- 
 ration from the surface of the lagoon, would result in the same con- 
 centration that is produced by evaporation of a given quantity of 
 sea water, as in Usiglio's experiments. The same result would be 
 obtained. In Usiglio's experiments, NaCl began to deposit when 
 one liter of the water was evaporated to 0.095, or about one-tenth 
 
BAR-THEORY OF OCHSENIUS 351 
 
 of its original volume. At that time there were 38.45-1.58 or 36.87 
 grams of salts in 0.095 liters of water, which corresponds to 388 
 grams in I liter, or a salinity of 388 permille. The most saline 
 body of water given in the list of salt lakes on p. 154, i. e., Tinetz 
 Lake, has a salinity of only 289 permille, while the next body, 
 the Karabugas Gulf, has a salinity of only 285 permille. It is evi- 
 dent that neither of these waters is saline enough to deposit salts, 
 and this is known to be the case (Andrussow-3). On the other 
 hand, 38.38 grams in 0.190 liter, or a salinity of 202 permille, marks 
 the point at which calcium sulphate will be deposited. It is evident 
 that such precipitation can take place in both the above water bod- 
 ies, and that it may indeed take place in all of the nine lakes cited 
 first in the list on page 154. That it does not so take place is in 
 all probability due to the variation in composition of these bodies 
 from normal sea water. Many of these lakes deposit magnesium or 
 other sulphates, and some of them have deposited sodium chloride 
 at a former time of greater salinity. 
 
 Calcium sulphate is a usual accompaniment of salt deposits oc- 
 curring as gypsum or anhydrite, and forming alternating layers 
 with the salt, as in the so-called annual rings (Jahresringe) of the 
 Stassfurt and other salts, or as mixtures recognizable only on analy- 
 sis. Only in rare cases is gypsum or anhydrite absent, as in the 
 great deposits of Miocenic age at Wieliczka, where the salt is ab- 
 solutely pure. As seen from the table of Usiglio, pure calcium 
 sulphate is deposited first, and then sodium chloride with small ad- 
 mixtures of calcium and magnesium sulphate and some magnesium 
 chlorides. If now, after a period of salt precipitation, the salinity 
 of the water should become reduced by an unusual influx of sea 
 water, salt deposition will cease, and after a while gypsum or anhy- 
 drite will form to be again succeeded by salt deposits. If, however, 
 the bar remains closed for a period after the precipitation of all 
 the calcium sulphate, only pure salt will be deposited, and this will 
 continue until the mother liquor is nearly depleted of sodium 
 chloride (see the table). After this no more deposition is possible 
 except through renewal of the water across the bar, and so it 
 is evident that the deposition of pure salt is limited in thickness. It 
 is apparent that very thick deposits of pure salt cannot be explained 
 in this manner. 
 
 The influx of much water across the bar may bring with it silt, 
 and this will be deposited first, the succession becoming, from below 
 up, silt, gypsum and salt. With the silt the organisms of the ad- 
 joining sea may enter the bay, but, owing to the rapid increase in 
 
352 PRINCIPLES OF STRATIGRAPHY 
 
 density of the water, they will soon die, and their remains become 
 embedded within the layer of silt. 
 
 The Bitter Lakes of Sues an example. A characteristic exam- 
 ple of this type of deposit was formed in the Bitter Lakes on the 
 Isthmus of Suez, and which before 600 B. C. formed the Heroopo- 
 lite Gulf, a continuation of the present Gulf of Suez and the Red 
 Sea. After the gulf became separated by silting up to such an ex- 
 tent that the supply of water from the Red Sea just balanced the 
 evaporation from the surface of the gulf, and the salinity was of 
 corresponding magnitude, salt began to deposit, and continued until 
 some time after complete separation from the Gulf of Suez, and 
 transformation into the Bitter Lakes, when only the intensely saline 
 mother liquor remained. When in 1861-1863 the present canal 
 was cut through these lakes, a mass of salt 13 km. long, 6 km. broad 
 and averaging 8 m. in thickness, was found. In the center of Great 
 Bitter Lake, this salt mass was estimated at 20 meters in thickness. 
 The salt was of course quickly dissolved by the fresher waters of 
 the canal which pass through these lakes, but until 1869 the salt 
 beds were still covered by a layer of mother liquor. 
 
 When discovered (Bader 4), the salt mass consisted of parallel 
 layers of varying thickness separated by thin layers of earthy mat- 
 ter and gypsum. Soundings to a depth of 2.46 m. snowed 42 lay- 
 ers of similar composition and varying from 3 to 18 cm. in thick- 
 ness, while the earthy layers between them were only a few milli- 
 meters in thickness. At a depth of 1.47 m. from the surface were 
 found a bed of mixed powdery gypsum and clay 0.112 m. thick and 
 a bed of pure powdery gypsum 0.07 meter thick. The clay layers 
 were as a rule richly fossiliferous, containing the shells of numer- 
 ous genera and species of .molluscs now living in the Red Sea. 
 
 There is here illustrated a long succession of flooding and par- 
 tial drying up of these Bitter Lakes. On the influx of the waters 
 from the Red Sea, mud was deposited, followed quickly by de"posi- 
 tion of gypsum. After this the salt crystallized out, with an admix- 
 ture of magnesium sulphate. As the waters became concentrated, 
 the animals perished and their shells sank to the bottom, where 
 they became embedded in the growing deposit. 
 
 The amount of bittern salts in the mother liquor which covered 
 the salt beds of these lakes until 1869 was insufficient for the quan- 
 tity of salt found deposited in these lakes. It must therefore be 
 assumed that on the successive inundations from the Red Sea the 
 mother liquor then present was partly carried out in diluted form, 
 and that the quantity last found represented only the residue since 
 the last flooding of the lakes and the closing of the bar. The 
 
BITTER LAKES AND KARABUGAS GULF 353 
 
 amount of evaporation since that time was sufficient to lower the 
 surface of the Bitter Lakes appreciably below that of the Red Sea 
 
 FIG. 68. Map of the Karabugas Gulf. (After von Seidlitz, Globus, 1899.) 
 
 (high water), two thousand million cubic meters of water being 
 necessary to raise the surface to the level of the canal. (Ochsenius- 
 38: 164.) 
 
354 PRINCIPLES OF STRATIGRAPHY 
 
 The Karabugas Gulf. The Karabugas Gulf on the eastern bor- 
 der of the Caspian Sea is frequently cited as a typical example of 
 the salt lagoon, cut off from the main body of the Caspian Sea by 
 a long, partly submerged bar. Ochsenius himself used it as an 
 illustration. As we have seen, the salinity of this body of water, 
 while sufficient for the deposition of gypsum, is not great enough for 
 the deposition of salt. As will be seen by a reference to the analysis 
 of the water of the Karabugas (p. 158), which is an example of 
 a sulphate chloride bittern, magnesium entirely replaces the cal- 
 cium. This is also shown in the deposits at the bottom of this 
 basin, where over an area of 1,300 square miles a deposit of Epsom 
 salts, (sulphate of magnesia) is formed, 7 feet thick and amounting 
 to an estimated total of 1,000,000,000 tons. (Fig. 68.) 
 
 This gulf further illustrates the enormous destruction of organ- 
 isms due to the intense salinity, a destruction which would render all 
 salt deposits of such a gulf highly fossiliferous. Andrussow calls 
 attention to the large number of fish which are carried across the 
 bar into the Karabugas, where they perish. "Their carcasses float 
 about as long as the water flowing into the gulf moves them, after 
 which they either sink to the bottom, or are driven onto the shore. 
 The carcasses of Clupea, Atherina, Cyprinus, Luciopercoy Acipemer 
 and Sygnathus piled upon the shores are partly eaten by the native 
 birds, and the quantities of dead fish which lie upon these shores in 
 March can be measured by the fact that the gulls at this season of 
 the year feed only on the eyes of the fish, and do not even take the 
 trouble to turn over the fish to get at the other eye." (Andrussow- 
 3 :<?p ; and Walther-62 #5.) 
 
 Among other organisms killed in the saline waters of this gulf, 
 Cardium edule should be mentioned. This euryhaline organism 
 abounded in the gulf before it reached the stage at which sulphates 
 were deposited. The shells of this species occur in enormous num- 
 ber on the shores of the Karabugas. (Andrussow-3 155.) 
 
 It is a significant fact that all deposits of salt along the borders 
 of the present seas, as well as inland, are found in regions of rela- 
 tive aridity; that, in other words, salt deposition demands a suffi- 
 ciently dry climate to allow an excess of evaporation over precipi- 
 tation or influx. Thus salt deposits of all ages and occurrence are 
 indicative of dryness of climate. 
 
 Natural Salt Pans. 
 
 Of the natural salt pans in the vicinity of the seashore, the 
 Rann of Cutch on the northwestern coast of India is perhaps the 
 
NATURAL SALT PANS 355 
 
 best known. (Walther-6i : 76*9.) This is a low-lying coastal area, 
 flooded during the southwest monsoon period in some parts to the 
 depth of i meter. The Rann is the true salt plane; it covers an 
 area 300 km. long and 100 km. broad. It merges into flat planes 
 free from vegetation, the so-called Put, and is surrounded and 
 diversified by the sand-dune region, the so-called Thurr. Here the 
 dunes are 25 to 130 meters high, with flat areas often carrying 
 lakes up to 20 meters in depth, and this region is inhabited chiefly 
 by foxes, jackals, wolves, rats, snakes, etc. In the region of the 
 Rann proper animal life, as well as plant life, is exceedingly scarce. 
 The smooth, flat surface of the Rann is composed of sandy clay, 
 which is constantly kept moist by the included salt. The shallow 
 pools scattered about on its surface are covered in winter by crusts 
 of pure salt, generally only about 10 cm., but occasionally over a 
 meter in thickness. 
 
 The Nile delta, too, is characterized by a large number of salinas 
 or natural salt pans. These extend along the coast from Abu Sir 
 to Sheik Zayed, and owe their salt to the flooding from the Medi- 
 terranean and the rapid evaporation due to the desert climate of the 
 coast. The salt is often covered by wandering sand dunes, which 
 when they reach a great thickness become filled through efflores- 
 cence with crystals of gypsum 3-5 cm. long. These unite into 
 heads I to 4 meters broad and from 0.5 to i meter in thickness. 
 
 On the borders of the Red Sea are a number of salinas. One, 
 west of Amfila (Hanfela) Bay on the Abyssinian border, lies below 
 sea-level, and is surrounded by a wall of gypsum. The streams 
 flowing from the East Abyssinian Mountains into this depression 
 evaporate, adding their contribution to the saline deposits. At 
 Allolebod, on the southern coast of the Red Sea, the deposits in the 
 natural pans show regular interstratification by layers of gypsum, 
 similar to the annual rings of the Stassfurt salt. These layers mark 
 the periodic inundation of the salt pans. Though extensive, these 
 salt deposits can in no wise be compared with those of past geologic 
 periods. (Grabau-i9.) 
 
 Evaporation of Cut-offs from the Sea. 
 
 When, in an arid region a portion of an indentation of the sea 
 is cut off, by tectonic movements, by delta deposits, or otherwise, 
 the waters thus separated may evaporate, leaving a salt sea or salina 
 in which the salt of the original water body becomes concentrated. 
 The Salton-sink region in the Lower Colorado Basin of California 
 is an example of such a cut-off. The delta built by the Colorado 
 
356 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 River into the former upper end of the Gulf of California, cut off 
 the head of this water body from the remainder of the Gulf, convert- 
 ing it into a separate lake. This was at first converted into a fresh or 
 brackish water lake by the continued influx of the river water, with 
 a corresponding rise of the level as indicated by the traces of old 
 shore-lines 40 feet or so above the present sea-level, the deposit of 
 calcium carbonate and the presence of numerous shells of fresh or 
 brackish water molluscs. The Colorado repeatedly changed its 
 mouth, discharging at intervals into the Gulf of California. When- 
 ever this occurred the lake began to shrink, the waters evaporating 
 under the drying influence of the Westerlies descending from the 
 high coastal ranges. The Salton-sink represents the present concen- 
 
 FIG. 69. Sketch map of the Salton Sink Region. (After Davis.) 
 
 tration of these waters, the bottom of this lake being 273.5 feet 
 below mean sea-level (Freeman and Bolster-i 7:46-51). Before the 
 recent overflows of the Colorado (1891, 1905, 1906-07) the waters 
 of the Salton Lake were intensely saline and its shores were fringed 
 with broad belts covered with white crusts of salt. The author 
 (19:5, 4) has estimated that the salt resulting from the complete 
 evaporation of the sea waters originally cut off from the head of the 
 Gulf of California would form a bed 12.5 m. thick over the area 
 of the present Salton Lake. (Fig. 69.) 
 
 NON-CALCAREOUS TERRESTRIAL PRECIPITATES. 
 SALT LAKES AND SALINAS. 
 
 Salt lakes and salinas are characteristic features' of the arid re- 
 gions of the earth, and they occur in nearly every country. Those 
 of the drainless basin of the Caspian have long been well known. 
 
SALT LAKES AND SALINAS 357 
 
 Of these, Elton Lake, a natural Bittern with a salinity of 271 per- 
 mille, furnishes a good example. It lies in the flat clayey steppe, 
 has clay banks, a length of 18 km. and a width of 14 km. As 
 shown by the analyses in the table (p. 158, 62), it contains only o.i 
 per cent, of Ca, but 17.55 P er cent - f Mg, while the sodium is only 
 11.27 per cent. This is due to the fact that a part of the sodium 
 has crystallized out as NaCl, from a liquor formerly of much higher 
 salinity. Two layers of salt are found at the bottom of the lake, 
 the lower 2.5 cm., the upper 4 to 5 cm. thick. Analyses of these 
 salts gave the following: 
 
 Upper Bed Lower Bed 
 
 NaCl 87.08 90.50 
 
 MgCl 2 3-25 2.17 
 
 MgSO 4 0.53 0.47 
 
 CaSO 4 1.13 1.49 
 
 H 2 O '. .; 6.85 3.51 
 
 99.84 98.14 
 
 Into this lake flows a small stream, the Chara Zacha, which an- 
 nually carries enough salt into the lake to make a crust 4 cm. in 
 thickness. 
 
 Baskunchak Lake (Walther-6i :7#/0, also in the Astrakhan dis- 
 trict of Russia, north of the present Caspian, is another example. 
 It lies on the eastern border of the Volga and has a length of 16 km. 
 and a breadth of 9 km. Analysis by Goebel (i) and Nikitinsky 
 (2) gave the following composition of the brine: 
 
 (I) (2) 
 
 NaCl 72 . 72 , 73 . 6 1 
 
 MgCl 2 20 . 80 22 . 32 
 
 CaCl 2 3-40 2.43 
 
 KC1 0.76 
 
 MgSO 4 0.22 
 
 MgBr 2 o . 023 
 
 CaSO 4 o.io o.io 
 
 97 . 803 98 . 68 
 
 In the center of the lake was found a salt bed averaging 160 cm. in 
 thickness, the thickness at 500 meters from shore being considerably 
 over 2 meters. Eight distinct layers are recognizable, separated 
 by layers of clay. The upper layer contained 91 per cent. NaCl, 
 the second 95.4 per cent. NaCl, the fourth 97.2 per cent., the eighth 
 
358 PRINCIPLES OF STRATIGRAPHY 
 
 97.82 per cent., and below this lies a coarsely crystalline salt 1.5 m. 
 thick and of perfect transparency containing 98.7 per cent. NaCl. 
 The upper layers consist of small crystals which are dissolved dur- 
 ing the spring rains. The larger crystals of the deeper layers re- 
 main undissolved and further increase in size during the summer, 
 and thus the deeper layers are constantly becoming poorer in mag- 
 nesium chloride and as the salt becomes purer it also increases in 
 density. 
 
 This region is characterized by more than a hundred lakes of 
 varying salinity, many of which deposit very pure rock salt. Many 
 of these are covered by drifted sands which have dried up the lakes 
 and drawn away the bitterns, so that the salt under the sand is per- 
 fectly dry and very pure. Some of these lakes of the Astrakhan 
 district deposit magnesium chloride, others magnesium or sodium 
 sulphate, and others still, gypsum. 
 
 South of the Caspian, in Persia, is an extensive desert nearly 800 
 miles in length and in places over 200 miles in width, covered with 
 salinas and dry salt, and dune sand areas. Of the salinas, that of 
 Darya in Namak may be noted. For 2 km. from the margin 
 of the salina the ground is muddy and contains the skeletons of 
 animals which probably died of thirst ; beyond this a zone of earthy 
 salt follows, with the appearance of a frozen swamp during a thaw. 
 Six to eight kilometers from the border begins the pure salt, in the 
 form of irregular polygonal masses 20 to 90 cm. in length. The 
 crust of salt beyond this extends for 40 km. and is from 2 to 3 
 meters thick, and very hard. 
 
 The Great Salt Plain of Lop, in Eastern Turkestan, is described 
 by Huntington (28) as resembling "the choppiest sort of sea with 
 whitecaps a foot or two high ; and frozen solid." He says : "When 
 we camped in what we hoped was a soft spot and tried to drive in 
 the iron tent-pegs, most of them bent double. We had to use an 
 axe to hew down hummocks of rock salt a foot high before we 
 could get places smooth enough for sleeping" (p. 251). The rough- 
 ness of this salt plain is explained as follows: "During the long- 
 continued process of drying up the ancient lake of Lop deposited 
 an unknown thickness of almost pure rock salt. When the salt 
 finally became dry it split into pentagons from five to twelve feet 
 in diameter, the process being similar to that which gives rise to 
 mud-cracks. The wind, or some other agency, apparently de- 
 posited dust in the cracks ; when rain or snow fell, the moisture 
 brought up new salt from below ; and thus the cracks were solidly 
 filled. When next the plains became dry the pentagons appeared 
 again. This time the amount of material was larger and the penta- 
 
SALT LAKES AND SALINAS 359 
 
 gons buckled up on the edges and became saucer-shaped. By count- 
 less repetitions of this process, or of something analogous to it, the 
 entire lake-bed became a mass of pentagons with ragged, blistered 
 edges." (Huntington-28:^5^-j.) In the salt of this plain Hunt- 
 ington found 4< a half-buried plover, dead for centuries ever since 
 the time when the bottom of the lake was still soft." Aside from 
 this, and from a few deeply buried roots of some reeds, Huntington 
 found no signs of life for nearly a hundred miles of his journey 
 in this region. 
 
 In the African deserts salinas are equally characteristic. Those 
 of the Bilma and Kalala oases in the Sahara supply much of Central 
 Africa with salt. A new crust of salt several inches thick forms 
 over these lakes in a few days after the harvesting of the preceding 
 salt crop. 
 
 Salt deposited by Katwee Lake north of Albert Edward Nyanza 
 Lake in Central Africa contains 81.7% NaCl, 5.32% Na 2 SO 4 , 
 8.43% K 2 SO 4 , 2.46% Na,CO 3 , 0.15% Fe 2 O 3 , and 0.82^ H 2 O. In 
 the Kalahari, salinas are a characteristic feature. (Passarge 43.) 
 
 Calcium sulphate in the form of gypsum or anhydrite is, as 
 we have seen, a frequent accompaniment of the deposits of sodium 
 chloride in the cut-off lagoons of the sea and in normal salt lakes. 
 Gypsum of undoubted marine origin has been found on some small 
 coral islands in the Pacific, where it constitutes a residue formed by 
 the evaporation of lagoons, and may reach a thickness of 2 feet. 
 Gypsum may also be deposited by concentrated lake water, as in 
 the case of Lake Chichen-Kanab in Yucatan. Gypsum likewise 
 forms on an extensive scale in the playas or sebchas of desert 
 regions. At Fillmore, Utah, such a deposit covers an area of 2 
 square miles and has been opened to a depth of 6 feet without 
 reaching bottom. (Russell-48 -.84.) In general it accumulates in 
 the center of the basin in the form of gypsum, rendering the bot- 
 tom and sides of the basin impervious and so forming a foundation 
 on which the salt may accumulate, above which, in turn, is formed 
 the impervious cover of anhydrite. Such deposits in desert regions 
 are often of considerable thickness. The great depression of the 
 Ued Rir, which merges from the south into the Schott Mel Rir, 
 carries a flooring of gypsum which extends at least to a depth of 
 50 meters, and beneath which is often a great accumulation of 
 water under strong hydrostatic pressure. Piercing of one of these 
 gypsum floors in South Tunis in 1885, at a depth of 90 m., dis- 
 covered a well of water which rushed up with such force as to hurl 
 blocks weighing 12 kgm. into the air. (Ochsenius-4i :j#.) 
 
 In many sections the salinity is not sufficient to produce solid 
 
360 PRINCIPLES OF STRATIGRAPHY' 
 
 salt beds whereupon crystals of salt form in the clayey deposits left 
 on drying of the water bodies. Salt crystals or the molds they occu- 
 pied are common in many ancient deposits, for which a similar origin 
 may be assumed. 
 
 Salt is deposited in the shallow marginal portions of the great 
 Salt Lake of Utah in spite of the fact that the salinity of the lake 
 as a whole is only 230.4 permille. Greater concentration exists, of 
 course, in the shallow marginal pools. In South America salinas are 
 extensively developed in Patagonia and elsewhere. Darwin (14:76) 
 describes one of these as consisting in winter u of a shallow lake of 
 brine, which in summer is converted into a field of snow-white 
 salt. The layer near the margin is from four to five inches thick, 
 but toward the center its thickness increases. This lake was two and 
 a half miles long and one broad. Others occur in the neighborhood 
 many times larger, and with a floor of salt, two and three feet in 
 thickness, even when under water during the winter." Analysis of 
 this salt gave only 0.26 per cent, of gypsum and 0.22 per cent, of 
 earthy matter. The borders of these salinas are formed of mud in 
 which crystals of gypsum up to three inches in length occur. 
 , Crystals of sulphate of soda lie scattered about on the surface, and 
 among these the mud was thrown up by numbers of some kind of 
 worm, upon which the flamingos, which frequent these salinas, seem 
 to feed. As already noted, this salt is extensively deposited on the 
 floor of the Karabugas Gulf, where a layer seven feet thick covers 
 an area of 1,300 square miles. Shunett Lake of Siberia also de- 
 posits this salt. 
 
 The "Salitrales" of Patagonia. These should be mentioned in this 
 connection. They are most abundant near Bahia Blanca. "The salt 
 here, and in other parts of Patagonia, consists chiefly of sulphate of 
 soda with some common salts. As long as the ground remains moist 
 in the salitrales (as the Spaniards improperly call them, mistaking 
 this substance for saltpetre), nothing is to be seen but an extensive 
 plain composed of a black, muddy soil, supporting scattered tufts 
 of succulent plants. On returning through one of these tracts, after 
 a week's hot weather, one is surprised to see square miles of the 
 plain white, as if from a slight fall of snow, here and there heaped 
 up by the wind into little drifts. This latter appearance is chiefly 
 caused by the salts being drawn up, during slow evaporation of the 
 moisture, round blades of dead grass, stumps of wood, and pieces of 
 broken earth, instead of being crystallized at the bottoms of the 
 puddles of water. The salitrales occur either on level tracts elevated 
 only a few feet above the level of the sea, or on alluvial land bor- 
 dering rivers." (Darwin 14, Chapter IV.) At a distance of some 
 
DEPOSITS OF SODA, ETC. 361 
 
 miles from the sea the incrustations on the plain consist chiefly of 
 sulphate of soda, with only seven per cent, of common salt, while 
 nearer to the coast the common salt increased to 37 parts in a hun- 
 dred. 
 
 DEPOSITS OF SODIUM SULPHATE AND CARBONATE. 
 
 In the Great Basin region of North America soda lakes are not 
 uncommon. In Wyoming lakes of this type form deposits on their 
 floors which contain 40 to 45 per cent, sodium sulphate, alternating 
 with clay layers. The Donney lakes contain a bed of soda 2 to 3 
 meters thick. At Wilmington a bed of natural soda more than four 
 meters thick was found at the bottom of the lake. Similar sedi- 
 ments are found in Mono Lake, California; Albert Lake, Oregon; 
 and Owens Lake, California. Sevier Lake, Utah, was covered in 
 January, 1880, by a crust of salt 10 to 12 cm. thick, beneath which 
 the following sediments occurred in descending order : 
 
 Sodium sulphate 5 cm. 
 
 Sodium sulphate with NaCl 2 cm. 
 
 Sodium sulphate / 5 cm. 
 
 Gray clay with wood fibers 5 cm. 
 
 Fine sand with fresh water shells 15 cm. 
 
 This lake is at times entirely dry. Other lakes depositing sodium 
 sulphate are Altai Beisk, Domoshakovo, Kisil-Kull, and Schunett 
 lakes in Siberia. Great Salt Lake likewise deposits sodium sulphate 
 during the winter, even casting it up in heaps upon the shore (Gil- 
 bert-i8). Lakes depositing alkaline carbonates are also common. 
 They occur in Hungary, Egypt, Armenia, Venezuela, and in Utah, 
 California, and Nevada, especially in the playas of the last named 
 state. Those of the Soda Lakes near Ragtown, Nevada, may be 
 taken as typical, they having been worked for commercial pur- 
 poses. The sodium carbonate of these lakes is but slightly con- 
 taminated by sodium sulphate and chloride. These soda lakes gave 
 the following analyses, the first from Big, the others from Little 
 Soda Lake, the last being market soda (Clarke-ior/p/; 226) : 
 
 (i) (2) (3) 
 
 Na 2 CO 3 45.05 44.25 52.20 
 
 NaHCO 3 34-66 34 . 90 25 . 05 
 
 Na 2 SO 4 1.29 0.99 5.10 
 
 NaCl 1.61 1. 10 3.31 
 
 SiO 2 0.27 
 
 Insoluble .80 2.81 
 
 H 2 16.19 15-95 14.16 
 
 99.60 100.00 100.09 
 
3 62 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 These soda lakes also deposit crystals of gaylussite(CaCO 3 .Na 2 CO 3 - 
 5H 2 O), although the analysis of the water shows no calcium, the 
 minute quantities of this element brought in by springs, etc., prob- 
 ably combining at once to form this mineral (Clarke-io:/p/; 227). 
 The carbonates deposited by these lakes are probably three in num- 
 ber: thermonatrite (Na 2 CO 3 .H,O), natron (Na 2 CO 3 .ioH 2 O), and 
 trona or urao (Na 2 CO 3 .NaHCO 3 .2H 2 O). The proportion of these 
 varies, but the third is the most important. This is the first salt 
 crystallizing out on fractional crystallization of the waters of Owens 
 Lake, Inyo County, California, where sodium carbonate is manu- 
 factured on a commercial scale. The following analysis shows the 
 composition of the salts of successive crystallizations which took 
 place during the experiments (Chatard, quoted by Clarke-io:/p^; 
 228) : 
 
 Table showing successive crystallisation, resulting from the evap- 
 oration of the zvaters of Ozvens Lake. 
 
 Stage of Crystallization 
 
 Nat'l 
 Waters 
 
 First 
 Crop 
 
 Second 
 Crop 
 
 Third 
 Crop 
 
 Fourth 
 Crop 
 
 Fifth 
 Crop 
 
 Specific gravity of water or 
 mother liquor 
 At temperature (C) 
 Salinity in permille 
 
 1.062 
 
 25 
 77 OQ8 
 
 1.312 
 27.9 
 
 78S 4Q 
 
 1.312 
 
 25 
 
 I-3I5 
 26.25 
 
 1.327 
 
 35-75 
 
 1.30 
 13-9 
 
 Volume 
 
 I .OO 
 
 O.2O 
 
 
 
 
 
 Composition: 
 H 2 O. 
 
 
 14 SI 
 
 4 ^ 
 
 7 47 
 
 2 24. 
 
 1 1 O^ 
 
 Na 2 CO 3 
 
 34 -OS 
 
 AT. . 7S 
 
 22.84 
 
 18. 19 
 
 12 SI 
 
 SS 04 
 
 NaHCO 3 
 
 7 4-O 
 
 ^O 12 
 
 IO S^ 
 
 406 
 
 } 88 
 
 4 OO 
 
 Na 2 SO 4 
 
 14.38 
 
 3.18 
 
 2S 44 
 
 26 70 
 
 10 oi 
 
 S 7O 
 
 NaCl 
 
 18 16 
 
 7 44 
 
 ^s 06 
 
 4S SO 
 
 60 oo 
 
 19 16 
 
 Na 2 B 4 O 7 . . . . . 
 
 o 63 
 
 
 
 
 
 
 NaBO 2 
 KC1 
 
 4. O7 
 
 I O7 
 
 I 12 
 
 I 14 
 
 I 21 
 
 2.01 
 2 Q"* 
 
 (CaMg) CO 3 
 
 0.08 
 
 O 14 
 
 
 
 
 
 (AlFe) 2 O 3 
 
 o os 
 
 O OI 
 
 
 
 O OI 
 
 O O2 
 
 SiO 2 . . 
 
 0.28 
 
 o 055 
 
 O OQ 
 
 o 06 
 
 O OS 
 
 o 16 
 
 Organic matter 
 Insoluble 
 
 
 0.032 
 o 078 
 
 
 
 
 
 
 
 
 
 
 
 
 Total 
 
 IOO OO 
 
 TOO ^8s 
 
 QQ 41 
 
 OQ 17 
 
 00 QO 
 
 ioo 14 
 
 
 
 
 
 
 
 
 In Egypt there are 9 soda lakes, the largest 10 km. long, 3 km. 
 broad, and 6 meters deep (Walther-6i :/po). The salt forming on 
 
BORAX AND BORAXES 363 
 
 the bottom of these lakes consists of a lower bed 5 meters thick 
 with much sodium carbonate in its composition and an' upper layer 
 also 5 meters thick composed largely of sodium chloride. The 
 smaller lakes generally dry up, only salt encrustations remaining, 
 while the sand of the surrounding desert is underlain by a dark gray 
 clay containing gypsum and sodium salts. 
 
 BORAX AND BORAXES. 
 
 Borates are deposited by some lakes of which Borax Lake, Lake 
 County, California, is a typical example. The analysis of the water 
 is given on p. 159, F4, the mineral contents of the water being chiefly 
 sodium carbonate and sodium chloride, with borax (Sodium bi- 
 borate, Na 2 B 4 O 7 ) next in importance. The bed of the lake is oc- 
 cupied by a large mass of crystallized borax of great purity. A 
 neighboring smaller lake, Hachinchama, furnished a larger supply 
 of borax, which probably came from neighboring hot springs. 
 
 Deposits of borates are forming in a number of ''marshes" or 
 playa lakes of Nevada and California. Rhodes' marsh, Esmeralda 
 County, Nevada, has a central area of common salt surrounded by 
 a deposit of sodium sulphate, outside of which borax and ulexite 
 (NaCaB 5 O 2 .8H 9 O) occur. According to M. R. Campbell (8:401) 
 these salts of similar lakes in California are leached from beds of 
 Tertiary sediments. Searles's marsh or borax lake, in San Berna- 
 dino County, California, has furnished the following succession 
 through borings (De Groot-i5 1535 ; Clarke-io: ipp; <?J5) : 
 
 Surface 
 
 1. Salt and thenardite (Na 2 SO 4 ) 2 feet 
 
 2. Clay and volcanic sand, with some Tianksite: Na 22 K(SO 4 )9 
 
 (CO 3 ) 2 C1-. 4 feet 
 
 3. Volcanic sand and black clay, with bunches of trona NasH- 
 
 (CO 8 ) 2 . 2H 2 8 feet 
 
 4. Volcanic sand, containing glauberite Na 2 Ca(SO 4 ) 2 ; then- 
 
 ardite, and a few crystals of hanksite 8 feet 
 
 5. Solid trona overlain by a thin layer of very hard material 28 feet 
 
 6. Mud, smelling of hydrogen sulphide and containing layers 
 
 of glauberite, soda, and hanksite 20 feet 
 
 7. Clay, mixed with volcanic sand and permeated with hydro- 
 
 gen sulphide 230 + feet 
 
 Borax is chiefly found in the top crust or crystallized in the water 
 which sometimes accumulates in the depressions of the bed (Clarke 
 10). The layer is reproduced by slow degrees, through capillary 
 action, which brings up the soluble salts from below. Some 20 dis- 
 
364 PRINCIPLES OF STRATIGRAPHY 
 
 tinct mineral species have so far been obtained from the deposits 
 (see Clarker-io :ipp-<?oo; ^55), mostly sulphates, borates, and carbon- 
 ates, with some chlorides, soda niter (NaNO 3 ), and ammonium salts. 
 In the southern part of San Bernardino County, California, near Dag- 
 gett, occurs a solid bed of colemanite (CagBgOj^HgO) from 5 to 30 
 feet in thickness, highly crystalline, and interstratified with lake 
 sediments. At one end it is much mixed with sand, gypsum, and 
 clay, suggesting that it had been laid down at the edge of an evapor- 
 ating sheet of water. Colemanite was originally obtained from 
 Death Valley Desert, California. The Mohave Desert, on the 
 borders of California and Nevada, and the Atacama desert of South 
 America have in recent times been the chief sources of boron com- 
 pounds, the boron in these deposits having probably been supplied 
 by hot springs and solfataras of volcanic origin. In the South 
 American region, the principal mineral is ulexite (NaCaB 5 O 9 . 
 8H 2 O). 
 
 In Tuscany deposits of borates are formed on an extensive scale 
 from emanations of fumaroles or jets of steam issuing from the 
 ground. The deposits concentrate in lagoons, forming orthoboric 
 acid or sassolite (H 3 BO 3 ), ammonium borate or larderellite 
 ((NH 4 ) 2 B 8 O 13 4H 2 O) ; borocalcite or bechilite (CaB 4 O 7 4H 2 O), the 
 hydrous ferric borate; lagonite (Fe'" 2 B 6 O 12 .3H 2 O), and the am- 
 monium compound boussingaultite ( (NH 4 ) 2 Mg(SO 4 ) 2 .6H 2 O). In 
 the most concentrated of the lagoons the orthoboric acid (H 3 BO 3 ) 
 amounted to 19.3 grams per liter. 
 
 From Tibet borax deposits have been known since very early 
 time. In the lake plain of Pugha, in Ladakh, the deposits occur at 
 an elevation of 15,000 feet above the sea. The deposit covers an 
 area of about 2. square miles and has an average depth of 3 feet. It 
 is formed by hot springs which issue at this elevation with a tem- 
 perature ranging from 54 to 58 C. The deposit is impure, other 
 minerals, including gypsum, occurring with it. 
 
 DEPOSITS OF NITRATES. 
 
 Soda niter, or Chili saltpeter (NaNO 3 ), is found in the deposits 
 of Searles's Marsh and in various other parts of southern Califor- 
 nia, especially around Death Valley, and along the boundary between 
 Inyo and San Bernardino counties, forming beds associated with 
 the later Eocenic clays. In Searles's Marsh it is associated with the 
 borates, and the same holds true for the occurrences in the Atacama 
 and Tarapaca deserts, northern Chile. Here are found the largest 
 known deposits of nitrates in the world, the amount being officially 
 
ORIGIN OF SALINE DEPOSITS 365 
 
 estimated at 2,316 millions of metric quintals (254,760,000 short 
 tons). The niter fields lie between 50 and 100 miles from the coast, 
 and at elevations exceeding 2,000 feet. The crude sodium nitrate 
 or "caliche" occurs in deposits scattered over a large area and is 
 associated with salt and ulexite. A section of one of the "calichera" 
 or niter deposits in the Atacama Desert, 50 miles west of Taltal, 
 shows (Clarke-io:^o7; 242) : 
 
 1. Sand and gravel o ft. 1/2 inch 
 
 2. " Chusca, " a porous, earthy gypsum o ft. 6 inches 
 
 3. A compact mass of earth and stones 2 to 10 ft. 
 
 4. "Costra, " a low grade caliche, containing 
 
 much sodium chloride, feldspar and earthy m 
 matter ' I to 3 ft. 
 
 5. "Caliche" itoaft. 
 
 6. " Coba, " a clay +3 inches 
 
 The caliche varies in its percentage of NaNO 3 from 31.9 to 56.25. 
 Sometimes it contains up to 7% CaSO 4 , at others up to 10% or over 
 MgSO 4 , and again up to 34.6% Na 2 SO 4 . Insoluble impurities may 
 range as high as 45% or over. No potassium salts appear in these 
 deposits, but anhydrite, gypsum, epsomite, halite and other minerals 
 are associated with the nitrates. 
 
 In the Tarapaca desert the bed of "caliche" is from 4 to 12 feet 
 thick. Other localities are known in South America, but they are 
 of much less importance. Potassium nitrate, or saltpeter, is found 
 as an immense deposit near Cochabamba, Bolivia, associated with 
 borax. It contains 60.7% KNO 3 , 30.7% Na 2 B 4 O 7 , and traces of 
 NaCl, N 2 O and some organic matter. 
 
 OTHER MINERALS DEPOSITED UNDER DESERT CLIMATES. 
 
 Among the minerals known to be found under conditions of in- 
 adequate rainfall is carnotite, a more or less impure hydrated vana- 
 date of uranium and potash. It is found as a yellow crystalline 
 powder or in loosely coherent masses, and contains radium. It oc- 
 curs somewhat abundantly in Montrose County and elsewhere in 
 Colorado, and has been found in the Mauch Chunk red shale of 
 Pennsylvania a formation formed under comparatively arid condi- 
 tions. (Wherry-69.) 
 
 ORIGIN OF THE SALINE DEPOSITS. 
 
 The source of the various 'saline deposits is a subject of consid- 
 erable importance, since it promises to throw light on the condition 
 
366 PRINCIPLES OF STRATIGRAPHY 
 
 of accumulation of ancient deposits of this type, and hence to fur- 
 nish a clue to the physiographic characters of the region at the 
 time of such deposition. In general, we may divide the deposits of 
 salts into those abstracted from the hydrosphere, either directly de- 
 posited from the water or secondarily redeposited after leaching, and 
 those of chemical origin, i. e., formed by reactions of salts with each 
 other. 
 
 Sources of Sodium Chloride. 
 
 Marine. Practically all deposits of sodium chloride may 
 be traced back to the ocean water as their original source. 
 Direct deposition by evaporation and concentration of sea water 
 is, however, not the only mode of origin of such salts, al- 
 though many authors, following Ochsenius, have so regarded it. 
 The bar theory has already been discussed, and its application to 
 the origin of many saline deposits has been indicated. It has been 
 shown that such deposition can take place only in arid regions, 
 where evaporation concentrates the sea water within a nearly cut-off 
 basin, to the extent required for the deposition of the salts, and 
 holds it at such a state by removing a quantity of water equal to 
 that brought by the feeding current from the sea. In order that 
 such a feeding may be accomplished, it is necessary that the salt- 
 depositing bay be in the vicinity of a constant source of supply, i. e., 
 the ocean or an inland saline sea of vast dimensions, like the Cas- 
 pian. In such an ocean or inland sea, deposits of clastic and or- 
 ganic character would accumulate, so that for every great salt de- 
 posit formed in the neighborhood of the sea by concentration of 
 sea water, there should be a corresponding fossiliferous series of 
 normal marine type of sediments. Furthermore, as shown by the 
 deposits in the Bitter Lakes of Suez, and the Karabugas Gulf, the 
 deposits formed within the natural salt pan will be highly fossilifer- 
 ous, full of the remains of the organisms of the contemporaneous 
 sea from which the supply of salt water was derived. These two 
 criteria are the most significant, and when they fail, as in the case 
 of the salt deposits of the Mid-Siluric (Salman) of North America, 
 these deposits cannot be regarded as the results of direct evapora- 
 tion of sea water. (Grabau-iQ.) 
 
 Leaching of Salt from Older Formations and Its Segregation. 
 Extensive salt deposits may form by the leaching of the salt of an 
 older saliferous formation and its redeposition within a drainless 
 basin by concentration through evaporation. That such salt deposits 
 are now going on is believed to be the case in a number of regions. 
 
SOURCES OF SODIUM CHLORIDE 367 
 
 A large part of the salt of the Dead Sea is said to be derived 
 through leaching of an older salt bed. 
 
 A far more important, because more universal, source of salt is 
 found in the imprisoned or connate waters of the older marine sedi- 
 ments. When sediments carrying such water are exposed by erosion, 
 their saline contents will be drawn to the surface by capillarity and 
 the evaporation of the water. It is obvious that this can proceed on 
 an extended scale only in arid districts, where meteoric waters play 
 but a minor part. The salt from the fossil sea water will form an 
 efflorescence on the surface of the rocks, where it will remain until 
 removed by the wind or rain. If the region is a drainless basin the 
 salt redissolved by the rain will be carried to the center of a neigh- 
 boring depression, where it will accumulate on evaporation of the 
 water. Salt carried by wind may be deposited anywhere within or 
 without the basin. 
 
 The quantity of salt which is furnished by various ancient ma- 
 rine sediments depends to a large degree upon the pore space of the 
 rock. As we have seen (page 140), this is sometimes as high as 
 60% or over, but more generally falls below 40. If we take 35% 
 as an average measure, and take the salinity of the former ocean as 
 equal to that of to-day, i. e., 35 permille, we can readily see that 
 marine sediments include about i% of sea salt, which is three- 
 fourths NaCl. A marine formation, which has a thickness of 1,000 
 meters, as in the case of the Jura of Europe, could furnish a bed of 
 salt approximately 10 meters thick and extending over the entire 
 area covered by such a formation. If such salt becomes concen- 
 trated into a smaller area, the deposit will, of course, be of a pro- 
 portionally greater thickness. 
 
 Analyses of modern marine sediments have shown an even 
 greater salt content, due to electrolytic separation of the salt from 
 sea water. Thus the deep-sea red clay contained from 6.8 to 8% 
 of salt. Diatomaceous ooze contained $.4% ; Antarctic glacial clay, 
 1.9 to 3.7%; Globigerina ooze, i.o to 3.4%. These differences in 
 amount are due to differences in absorption power of the various 
 sediments. (Andree-2 1355.) 
 
 The leaching of the connate salts from old sediments furnishes 
 the rivers with their load of salt in solution ; as an example may be 
 quoted the high percentage of chlorine which rises to 32.63% in 
 the Rio de los Papagayos of Argentina. In this same river the 
 water carries 26.48% of sodium,* its total salinity being 9.185 per- 
 mille. This water runs into the ocean, but if similar water runs into 
 
 *This percentage is of the total solids, corresponding to 2.997 and 2.432 
 permille, respectively. See table pp. 162-3. 
 
3 68 PRINCIPLES OF STRATIGRAPHY 
 
 a drainless basin it is evident that the salt will be deposited on 
 evaporation of the water, and that such deposits are limited in 
 thickness only by the depth of the basin and the continuation of 
 erosion of the tributary area. Salts deposited in this manner will, 
 of course, be free from marine organic remains, though terrestrial 
 organisms or brine animals may be enclosed. The area tributary to 
 this basin will show extensive erosion during the period of forma- 
 tion of the salt deposits, while the salt beds themselves rest on the 
 formation elsewhere eroded, and will be covered by a formation 
 which elsewhere rests on the eroded surface of the formation below 
 the salts, or on an earlier one. 
 
 Besides the segregation of the salts in desert regions through 
 streams, due credit must be given to the wind. Where rock sur- 
 faces are covered with an efflorescence of salt, the dry wind may 
 sweep it away and redeposit the salt particles mixed with clay or 
 dust. In rare cases large particles of salt may be picked up by the 
 wind and dropped elsewhere, as in the case of the remarkable salt 
 hail which fell near the Lucendro bridge of the Gotthard road on 
 August 30, 1870, at ii A. M. (Kengott, quoted by Walther-6o.) 
 Saline clays may be deposited at any altitude by the wind, while 
 playa surfaces may be dusted over with a layer of salt particles, 
 which adhere to the surface rendered damp by the presence in the 
 clay of hygroscopic salts. 
 
 Shallow salt lakes or playas may be dried by a covering of 
 desert sands, which will sponge up the mother liquor and so leave 
 only the pure salt behind. On reaching the surface of the covering 
 sand dunes through capillary action, the efflorescing salts may be 
 scattered far and wide by the winds. Desert salts are probably, as 
 a rule, free from the potash salts. 
 
 These mother liquor salts crystallize, as a rule, only at very 
 high or very low temperatures. Thus kieserite (MgSO 4 .H 2 O) 
 crystallizes out in the laboratory only on evaporation of the solution 
 at temperatures above 100 C., while a solution of carnallite 
 (KMgCl 3 .6H 2 O) first loses its water at a temperature of 120 C. 
 This same substance, however, has been found to crystallize out 
 at a low winter temperature, such as can readily be produced in 
 continental areas, or where snow is mixed with the brine. 
 
 Sources of Calcium Sulphate. 
 
 Gypsum, like salt, is deposited from sea water direct, or from 
 concentrated lake waters or in playas. It may be said to have the 
 
SOURCES OF ALKALINE CARBONATES 369 
 
 same source as the sodium chloride, being one of the constituents 
 of the sea water whether recent or fossil. Gypsum forms as an ef- 
 florescence or incrustation in caves, and it is also produced exten- 
 sively by the alteration of other rocks. Oxidation of pyrite in 
 calcareous rock often results in the formation of this mineral and 
 so does the double decomposition between other metallic sulphates 
 and calcium carbonate. 
 
 Sources of Alkaline Carbonates. 
 
 The origin of the alkaline carbonates deposited by many waters 
 has been attributed to the leaching of volcanic rocks. Near Owens 
 Lake some of the seepage waters percolate through beds of vol- 
 canic ash, and contain even a higher proportion of alkaline carbon- 
 ates than the lake^ itself. The rocks from which these salts were 
 originally derived seem to have been mainly rhyolites, andesites, and 
 others rich in alkalies and relatively poor in lime. (Clarke-io, 2d 
 ed. 1229.) 
 
 Other sources of alkaline carbonates in natural waters and soils 
 are found in the double decomposition between calcium bicarbonate 
 and alkaline sulphates (T. Sterry Hunt) or alkaline chlorides (E. 
 von Kvassay) and in the reduction of alkaline sulphates by organic 
 matter and the subsequent absorption of CO 2 from the air (E. Sick- 
 enberger). Finally, Ochsenius suggested that alkaline carbonates 
 are formed by the action of CO 2 , commonly of volcanic origin, on 
 the mother liquor salts. In Egypt, Chile, and Bolivia he finds also a 
 lack of association of lime and sodium carbonate, but he notes the 
 occurrence of eruptive rocks as sources of CO 2 exhalations. In 
 Utah and in the Sahara he finds an association of lime with the 
 mother liquor salts, but no sodium carbonate, because eruptive rocks, 
 the sources of CO 2 , are absent. Finally, in Nevada he finds the 
 mother liquor salts associated with eruptive rocks and much soda. 
 He concludes, therefore, that an association of lime with the mother 
 liquor salts alone produces no alkaline carbonates, but that CO 2 
 emanations from volcanic sources (with or without the presence 
 of lime reaction on these salts) will produce the alkaline carbonates. 
 The widespread occurrence of sodium carbonate in the soils of arid 
 regions is attributed by Hilgard (23) to the reaction between al- 
 kaline salts and calcium bicarbonate. When by excessive irriga- 
 tion these salts are dissolved they rise to the surface by capillary 
 attraction to form the crusts of "alkali." 
 
370 PRINCIPLES OF STRATIGRAPHY 
 
 Sources of Boric Acid and B orates and of Nitrates. 
 
 Boric acid and saline borates are commonly formed by volcanic 
 activities, as in the case of the Tuscan fumaroles, where ammonium 
 salts also occur, an association found in undoubted volcanic vents. 
 Leaching of rocks containing borosilicates (tourmaline, axinite, dato- 
 lite, etc.), as in the case of granites, mica schists, etc., also probably 
 accounts for some of the deposits of borates, and more rarely such 
 deposits originate from sea water, though Ochsenius and some other 
 writers attempt to refer all such deposits to a marine origin. When 
 the origin is undoubtedly a marine one, magnesium borates are the 
 result, while lake deposits, like those of California and Chile, con- 
 tain calcium borates, with nitrates near by. Volcanic waters and 
 fumaroles, on the other hand, yield ammonium compounds along 
 with the borates. The sodium nitrate deposits of Chile and other 
 regions and the extensive potassium nitrate beds of Bolivia are like- 
 wise regarded by Ochsenius, Penrose, and others as of marine 
 origin, either directly or indirectly. Ochsenius derives the Chilean 
 nitrates from the mother liquors of salts deposited in the Andes, 
 which, flowing downward to the plains, have their chlorides partly 
 converted to carbonates by CO 2 of volcanic origin. The nitrogen 
 is brought as ammoniacal dust from guano beds upon or near the 
 sea coast, the heavier phosphatic particles being left behind. The 
 sufficiency of the amount of ammoniacal dust thus carried has been 
 questioned, and it has been pointed out that carbonates are com- 
 paratively rare in the nitrate regions. 
 
 Penrose (44 :i6) regards the nitrate fields as a former ocean bot- 
 tom and likewise derives his nitrogen from guano, the iodine from 
 decomposing sea weeds or from mineral springs and the accompany- 
 ing borates from the decomposition of rocks, containing boron-bear- 
 ing minerals. A volcanic origin has also been suggested for the 
 nitrogen (Clarke-io, 2d ed. -.246). 
 
 SUMMARY. 
 
 To sum up, it is apparent that salt deposits of to-day, when 
 not referable to a volcanic source, are only to a slight extent due to 
 direct evaporation of the water on the sea coast, but that by far 
 the more prominent mode of formation is a secondary one, the salt 
 being derived from the enclosed connate waters ,of marine sediments 
 or from the products of alteration. In all cases a relatively arid 
 climate is necessary to permit extensive evaporation, so that salt 
 
THE STASSFURT SALTS 371 
 
 deposits may legitimately be considered as indices of dry climates 
 during the period of their formation. Since most modern salt de- 
 posits are of continental origin, a similar origin may have obtained 
 for the deposit of past geologic periods. 
 
 ANCIENT SALT DEPOSITS. 
 
 Salt deposits are found in most geological formations from the 
 Cambric (?*) to the Present, and in all cases they are associated 
 with other evidence of continental expansion. Until recently the 
 salt range of India was supposed to hold the oldest salt deposits, 
 these underlying marine strata of Lower Cambric age. It is now 
 held, however, that these salt deposits are of much later age, perhaps 
 even as late as Tertiary time, and that the Cambric strata owe their 
 present position above the salt beds to an overthrust. The thickness 
 of many of the ancient salt deposits is very great, individual beds 100 
 feet thick having been found in the Siluric deposits of Michigan. 
 Deposits of much greater thickness are known, but these are either 
 complicated by intercalated anhydrite or polyhalite layers, or they 
 are in the form of salt domes, a formation of limited extent, and of 
 secondary origin. 
 
 THE STASSFURT SALTS. The extensive salt beds of Upper 
 Permic (Zechstein) age in North Germany in the Stassfurt, or more 
 properly the Magdeburg-Halberstadt region, may be taken as an ex- 
 ample of a complex deposit in which the strata have, on the whole, 
 suffered little alteration or rearrangement. The Border of succession 
 is as follows, in descending order (Walther-65) : 
 
 1. Lower Buntsandstein (capping rock) 
 
 2. Red clay with concretions of anhydrite and salt 
 
 cavities abt. 20 m. 
 
 3. Anhydrite layer (Anhydrite IV) abt. 4 m. 
 
 4. Rock Salt abt. 40 m. 
 
 5. Anhydrite III (Pegmatitanhydrit) abt. 5 m. 
 
 6. Red clay abt. 10 m. 
 
 7. Younger Rock Salt, with about 400 annual rings 
 
 ** of Polyhalite abt. 80 m. 
 
 8. Main anhydrite (Hauptanhydrit) Anhydrite II 
 
 varying from 30 to 80 m. 
 
 9. Salt clay, averaging from 5 to 10 m. 
 
 10. Carnallite zone from 15 to 40 m. 
 
 This is sometimes overlain by a layer of rock salt, at others by a kainite layer 
 followed by one of "sylvinite" or "hartsalz" and that by one of schoenite before 
 reaching the salt clay. 
 
 * The Indian salt deposits are the only ones of significance which have been 
 referred to the Cambric. 
 
372 PRINCIPLES OF STRATIGRAPHY 
 
 n. Kieserite zone averaging 18 m. 
 
 12. Polyhalite zone averaging 35 m. 
 
 13. Older Rock Salt with about 3,000 "annual" rings 
 
 of anhydrite averaging 245 m. 
 
 Nos. n, 12, and 13 have a combined thickness 
 
 ranging from 150 to perhaps 1,000 meters.* 
 
 ~ The "annual" rings of anhydrite form layers 
 
 averaging 7 millimeters thick, separating the 
 
 salt into sheets of 8 or 9 millimeters. 
 
 14. Older anhydrite and gypsum (Anhydrite I) 
 
 averaging 100 m. 
 
 15. Zechstein limestone or dolomite 
 
 1 6. Kupferschiefer 
 
 17. Zechstein conglomerate 
 
 1 8. Upper Rothliegende (base of section) 
 
 The lower members, beginning with Anhydrite I and ending with 
 the carnallite zone (and sometimes the kainite, sylvinite and schoen- 
 ite zones), form one depositional series, the last being the salts from 
 the mother liquor. This is followed by a protecting layer of clay. 
 Apparently a second depositional series began with the second or 
 main anhydrite and the Younger Rock Salt, but lacks the mother 
 liquor salts. 
 
 Altogether more than thirty saline minerals are found in the 
 Stassfurt deposit. Of these some of the more prominent besides the 
 halite and anhydrite are : 
 
 Carnallite KMgCl 3 .6H 2 O 
 
 Kieserite MgSO 4 .H 2 O 
 
 Polyhalite 2CaSO4.MgSO 4 .K 2 SO4.2H 2 O 
 
 Kainite MgSO 4 .KCl. 3 H 2 O 
 
 Sylvite KC1 (Sylvinite is a mixture of sylvite and rock salt; 
 
 Hartsalz contains these substances together with 
 
 Kieserite). 
 Schoenite MgSO 4 .K 2 SO 4 .6H 2 O 
 
 Borates, especially boracite (Mg 7 Cl 2 B 16 O 30 ), occur with the carnal- 
 lite and in the overlying zone. A noteworthy fact is that these de- 
 posits are absolutely unfossiliferous, in spite of the fact that organic 
 remains would here have a chance for perfect preservation. 
 
 These deposits have been commonly regarded as illustrations of 
 the Bar Theory, but against this interpretation strong objections 
 have been urged, especially by Walther (62:63) and by Erdmann 
 (16). Walther uses as his main arguments against such an origin 
 the absolute want of organic remains in these deposits, and the fur- 
 
 * This is probably the result of thickening through subsequent diagenetic 
 processes, the average of the salt deposits in undisturbed regions being about 
 350 meters. 
 
THE STASSFURT SALTS 373 
 
 ther fact that anhydrite is the first deposit and not gypsum, as would 
 be the case for evaporating sea water. The second series of deposits 
 above the mother liquor salts again begins with anhydrite instead 
 of gypsum. Walther (65) regards these deposits as due to evapora- 
 tion of a shallow late Permic or Zechstein sea, entirely cut off from 
 the ocean, and surrounded by a country changing gradually from 
 pluvial to desert conditions. This old sea extended from the Urals 
 in Russia, on the east, over North Germany, and the region of the 
 North Sea to the center of England. On the south its boundary 
 was partly formed by the Bohemian mass, and the old Vindelician 
 and Armorican Mountain chains, the former in the region of the 
 present Danube plain, the latter extending through France, Belgium, 
 South England, and Ireland. In the north, and on the southeast, 
 the separation was caused by the development of extensive broad 
 marsh lands. During the gradual evaporation of this sea, the salt 
 deposits accumulated in the deeper areas of the basin, where to-day 
 they cover scarcely the fiftieth part of the original area of the salt 
 sea. As partial areas were laid bare the salt deposited there was 
 again dissolved by the streams and carried to the pools which still 
 existed, and thus the concentration became more and more pro- 
 nounced. Under the influence of changing temperature and mois- 
 ture with the change of seasons, the nature of the precipitate varied, 
 and thus the salt beds are separated at regular intervals by layers of 
 anhydrite or polyhalite, forming the annual rings. Their number 
 suggests that the deposition of the Stassfurt salt occupied a period 
 of about 10,000 years. Erdmann ( 16) holds that the amount of an- 
 hydrite in the deposits is too great to be derived solely from the 
 drying up of this sea, and he therefore supposes that additional 
 amounts of calcium sulphate were brought into it by the streams 
 from the surrounding regions. 
 
 According to Van't Hoff and Weigert (54 11140) anhydrite forms 
 from gypsum in sodium chloride solutions at 30 C. (+86 F.), 
 while in the sea water this transformation takes place at 25 C. 
 (+77 F.). At ordinary temperatures, according to Vater, calcium 
 sulphate crystallizes from a saturated solution of salt in the form of 
 gypsum. Such high temperatures are not to be found in water of 
 bays still in connection with the sea, especially in the present latitude 
 of the Stassfurt salt deposit, unless indeed the temperature of the 
 whole earth was higher. The Red Sea, which to-day has the highest 
 temperature of any mediterranean, has a bottom temperature of 
 21.5 C, its mean temperature being 22.69 C. The Persian Gulf, 
 on the other hand, has a mean temperature of 24, owing to its 
 greater shallowness (see Chapter IV). Where influx of cooler 
 
374 PRINCIPLES OF STRATIGRAPHY 
 
 ocean water is prevented, however, the temperature of the entire 
 body may easily rise to the required degree. When the deeper 
 layers had become a concentrated brine the successive influxes of 
 calcium sulphate, probably during the rainy period when the streams 
 brought this mineral in solution from the surrounding country, were, 
 on passing through these layers of brine, deposited directly as anhy- 
 drite, in alternate layers with the salt deposits. That these influxes 
 of calcium sulphate were not due to successive ingressions of the 
 open sea is shown by the utter lack of marine organic remains in 
 these strata. In this manner were formed the 3,000 or more layers 
 of anhydrite which divide the older rock salt. With the progress of 
 concentration, the supernatant solution became a bittern -rich in mag- 
 nesium salts, whereupon the calcium sulphate united with these salts, 
 forming polyhalite (2CaSO 4 .MgSO 4 .K 2 SO 4 .2H 2 O). The polyhalite 
 stratum of Stassfurt is essentially a bed of rock salt, containing, 
 with other impurities, from 6 to 7 per cent, of polyhalite. With 
 further concentration of the mother liquor, kieserite (MgSO 4 .H 2 O) 
 was deposited, this requiring a temperature above 72 C. for its dep- 
 osition. The zone named after it contains about 17% of this min- 
 eral, together with 13 of carnallite, 3 of bischofite. 2 of anhydrite, 
 and 65 of rock salt. At this stage polyhalite was no longer de- 
 posited. 
 
 The final step in the concentration of the mother liquor produced 
 the carnallite zone. The average composition of this zone is 55 
 per cent, of carnallite, 25 of rock salt, 16 of kieserite, and 4 of 
 various other minerals. The carnallite (KMgC\^.6H 2 O) was formed 
 from the chlorides which had hitherto remained in solution, and it 
 represents the more or less complete drying up of the bittern lake. 
 The protecting layer of clay must have been formed by winds, for 
 water would have caused a resolution of the carnallite. 
 
 The reestablishment of the conditions of deposition, first for anhy- 
 drite and later for rock salt, which produced the "younger succes- 
 sion," suggests a renewed invasion of the sea. This is negatived, 
 however, by the absence of organic remains either in the salt clay 
 or in the succeeding anhydrite. This younger series may, therefore, 
 be wholly of continental origin, the anhydrite and salt being both 
 derived from connate waters. 
 
 The change to a dry climate over the region of North Germany 
 is understood when we take into consideration the fact that at the 
 beginning of Permic time the Armorican Mountain chain began to 
 rise, extending from the region of what is now central France north- 
 westward to the present Irish Isle. This placed a barrier directly 
 across the path of the prevailing Westerlies, which then were ap- 
 
ORIGIN OF STASSFURT SALTS 375 
 
 parently much as they are to-day. As a result, rainy conditions 
 prevailed on the windward side of these mountains, where the old 
 mediterranean or Thetis Sea of that day was situated, but arid 
 conditions were produced over the region beyond these mountains 
 by these winds, which on crossing the mountains became aridifiers. 
 As a result of this change in climate the region of North Germany, 
 Belgium, etc., previously one of much moisture and characterized 
 by the formation of luxurious coal swamps, became the theatre of 
 deposition of the red sands of the lower Permic or Rothliegende. 
 The lower division of this deposit forms a transition from the coal- 
 bearing formations preceding and contains at first some coal and 
 plant remains. Extensive forests of calamites, ferns, and conifers 
 covered the rising lands, for at first the barrier was not sufficient to 
 keep the moist winds out. The progressive development of the 
 mountain system finally involved some of the earlier Rothliegende 
 deposits, so that the later division, mostly free from plant remains, 
 rests unconformably, in part on the folded and eroded lower divi- 
 sion. There is thus indicated a progressive aridification of the 
 region, due no doubt to the continued growth of the Armorican 
 Mountain system which became more and more effective as a bar- 
 rier for the moisture-laden southwest winds. 
 
 The Rothliegende desert was invaded by the Zechstein Sea from 
 the North Russia region, marked at first by invading channels with 
 a marine fauna, while elsewhere sand-dunes, now forming the 
 Weissliegende, covered the lowlands. Then followed the peculiar 
 conditions producing the Kupferschiefer, which were probably due 
 to a separation of the early waters from the ocean to the north, to 
 form a shallow, brackish lake into which streams from the sur- 
 rounding old land, the Harz, Frankenwald, Erzgebirge, and rhein- 
 ische Schiefergebirge, carried mineral matter in solution. The abun- 
 dant fish fauna of this lake eventually succumbed to the gradual 
 fouling of these stagnant waters and the carcasses were buried in 
 the black muds, which also enclosed the metallic precipitates. The 
 renewed invasion of this area by the Russian Sea then led to the 
 formation of the marine Zechstein with its Bryozoa reefs and rich 
 fauna, and for a long time the conditions of an open sea existed 
 over North Europe. That the winds from the southwest still main- 
 tained their drying characteristic is shown by the deposits of western 
 England, which remained of the arid type, and extended down to, 
 and perhaps partly into, the Zechstein (Magnesian limestone) Sea. 
 The marine fauna of the Zechstein found conditions of existence 
 more favorable where the old Kupferschiefer muds were absent, as 
 around the margins of the old lands and the projecting islands of 
 
376 PRINCIPLES OF STRATIGRAPHY 
 
 older rock. Here the fauna is richest, and the reefs often rest di- 
 rectly upon the eroded old land. Over the floor of the sea, however, 
 underlain by the black muds, conditions of existence were less 
 favorable, probably because the gases resulting from the decay of 
 the vast number of fishes in these muds were constantly rising, and 
 so the fauna is much poorer as well as more or less dwarfed in 
 species and in individuals. 
 
 With the persistence of the aridifying winds it required only a 
 second closing of the inlet of the North Russian waters to convert 
 the Zechstein Sea into a salt pan, through the gradual evaporation 
 of the water. It is probable that the connection with the sea was 
 temporarily reestablished at least once during this period, this being 
 indicated by the formation of the upper salt series. With the pro- 
 gressive drying up of this sea, the red continental sands encroached, 
 and eventually covered the entire region of the former Zechstein 
 Sea, forming the Bunter Sandstein, the base of the Trias. Thus 
 actual desert conditions were established over Northwest Europe 
 and continued until the invasion of the Muschelkalk Sea. 
 
 THE SILURIC SALTS OF NORTH AMERICA. These present a rather 
 different type of deposit. In southern Michigan this formation 
 reaches a thickness of nearly a thousand feet. It includes nine 
 separate salt beds, several of them 100 feet thick, while the lowest 
 one is 160 feet thick (Lane~32:pl. xl). The annual rings character- 
 istic of the Stassfurt salt seem to be wholly wanting here, and the 
 same is true for the potash salts. The various beds of salt are 
 separated by layers recorded in the wells as shale or limestone, some 
 of which, however, are most probably gypsum or anhydrite. In cen- 
 tral New York the following succession is shown in descending 
 order : 
 
 BERTIE WATER LIME Upper Monroe 60 ft. 
 
 SALINA GROUP: 
 
 Camillas shales and gypsum 250-300 ft. 
 
 Syracuse salt 100-470 ft. 
 
 Vernon red shales 200-525 ft. 
 
 Pittsford shales 41 ft. 
 
 GUELPH dolomite of the Niagaran 
 
 The salt series (Syracuse) is thinner than in Michigan. In the 
 well sunk at Ithaca, New York, it has a thickness of only 470 feet 
 and includes seven salt beds ranging in thickness from 17 to 54 feet, 
 with shale partings ranging from 6 to 82 feet in thickness. Where 
 actually exposed, as in the Livonia and other salt shafts, something 
 akin to the annual rings of Stassfurt is seen, in thin intercalated 
 layers of gypsum and shaly material. These are, however, discon- 
 
SILURIC SALTS OF AMERICA 377 
 
 tinuous and only locally developed. The beds are all horizontal and 
 in rare cases are any of the layers distorted as is so commonly the 
 case in the North German salt deposits. Pieces of rock, either shale 
 or limestones are not uncommonly embedded in the salt ; sometimes 
 these pieces are large, and seem to represent a broken-up cover of 
 clay or lime, which subsequently sank into the upper salt layers, or 
 was buried by the new formed strata. 
 
 The Pittsford shale at the base of the series represents a change 
 from the preceding Niagaran (Guelph) sea to the continental con- 
 ditions under which the salt was deposited. The shale alternates 
 with dolomitic layers which contain the last survivors of the Guelph 
 fauna. Near the middle of the mass occur a few black shale layers 
 crowded with fragments and molts of entire individuals of six spe- 
 cies of Eurypterida, including the genera Eurypterus, Pterigotus, 
 and Hughmilleria, and several species of Phyllocarida, and at least 
 one Synxiphosuran (Pseudoniscus roosevelti). Followed eastward 
 for two hundred miles, this fauna is found in black shale layers 
 in the Shawangunk conglomerate of eastern New York and Penn- 
 sylvania, which is interpreted as a great continental fan formed 
 along the rising Appalachians during the same period, and form- 
 ing part of the upward movement of the North American continent 
 of that time, which resulted in the complete withdrawal of the 
 Niagaran sea of that period. (Grabau-2o.) 
 
 The close of the Pittsford shale epoch marks the period of de- 
 struction of the animal life of the Siluric sea in North America, the 
 red Vernon shales, a distinct continental type of deposit 400 feet or 
 more in thickness, succeeding in central New York. These can like- 
 wise be traced eastward, where they swell enormously, forming the 
 Longwood shales of New Jersey some 2,000 feet thick, and through- 
 out of continental origin. While the red Vernon shales of central 
 New York were depositing, salt formed in the deeper basin of south- 
 ern Michigan. Some of this may have resulted from the final evap- 
 oration of the waters of the Niagaran sea, for the salt there lies fre- 
 quently directly upon the limestone. No gypsum or anhydrite has 
 been recorded, but, as before noted, it is not improbable that some 
 of the limestone beds recorded in the well sections are in reality 
 anhydrite. The salt of central New York was probably derived 
 altogether from connate waters enclosed in the recently formed 
 marine Niagaran and earlier strata which underlay and surrounded 
 the salt basins and which suffered extensive erosion during this pe- 
 riod. While these salt deposits were forming, red sedimentation 
 was still going on in eastern New York, New Jersey, and Pennsyl- 
 vania. The centra] New York salt basin extends from the Oatka 
 
378 PRINCIPLES OF STRATIGRAPHY 
 
 valley in Wyoming county to Morrisville in Madison county and 
 southward for an undetermined distance. Western New York is 
 free from salt, which was either not deposited, or was removed 
 by erosion during Upper Siluric time. 
 
 Immediately above the red Vernon shales the salt is coarsely 
 crystallized, the crystals being commonly embedded in the mud. 
 Limestone, shale and gypsum occur as fragments mixed with the 
 clear salt crystals, the whole forming a brecciated mass. Sometimes 
 in the basal salt beds there is an abundance of layers and irregular 
 masses of shale and limestone, while in other localities the salt is 
 almost pure. At Livonia this basal layer is succeeded by 8 feet of 
 stratified marlyte grading upward into impure magnesian limestones, 
 both shales and limestones being full of seams and veins of salt, 
 often with columnar structure in the larger veins. Overlying the 
 limestone is the main salt bed. It is often very pure and well 
 stratified. Shaly matter and gypsum occur in thin streaks, but, on 
 the whole, the impurities are not more than two or three per cent. 
 of the entire bed. Non-continuous layers of limestone or shale 
 several inches thick sometimes occur. The crystals of salt are much 
 smaller than those of the mixed salt, and vary considerably in size 
 in the different layers. The salt is again capped by a layer of mixed 
 salt like that found below. Gypsous shales are common here, these 
 containing more or less disseminated salt. Irregular and more per- 
 sistent layers of dark magnesian limestone also occur in the upper 
 part of the salt bed. They are up to two or three feet in thickness 
 and full of salt seams and grains, and have the appearance of having 
 been formed above the salt and of having settled down into it. The 
 roof of the salt bed likewise consists of large and small blocks of 
 gypsous shale, the spaces between the blocks, sometimes several 
 inches in width, being filled with salt. These salt veins sometimes 
 extend upward into the overlying rock for 200 feet, though, as a 
 rule, they are much shorter. 
 
 The total thickness of the salt beds of central New York, in- 
 cluding the shale layers, ranges from 100 to 190 feet, but southward 
 it thickens to 470 feet, in the Ithaca well. The limestone layers in 
 this formation show evidence of exposure to the air during their 
 formation, by the abundance of mudcracks which are filled by salt, 
 gypsum or black mud. They are entirely unfossiliferous, as is this 
 whole series of deposits. 
 
 The Camillus shales overlying the salt are gray, often containing 
 beds of magnesian limestone and great masses of gypsum, together 
 with some anhydrite. This gypsum has been regarded as an altera- 
 tion product, being formed from impure limestones of the water lime 
 
ORIGIN OF SALINA SALTS 
 
 379 
 
 type. Numerous hopper-shaped cavities formerly occupied by salt 
 crystals occur in the shalier beds. 
 
 When we consider the former extent of the Niagaran strata, 
 from central New York to the Rocky Mountains and from the Ohio 
 or southward to Hudson Bay, and its thickness, which in Wisconsin 
 is still over 800 feet, and realize that much of this was worn away 
 during Salina time by the streams flowing into the Salina basins of 
 New York, Michigan, and Canada West, we can understand that 
 the connate sea water held in these strata was quite sufficient to 
 
 FIG. 70. Map and cross-section of Rhang-el-Melah, a salt dome in Algeria. 
 (After M. Ville.) 
 
 furnish all the salt of the Salina deposits. The intercalated lime- 
 stone and shale layers likewise had their origin in the erosion prod- 
 ucts obtained from these Niagaran formations. The fact that all 
 around the Salina area the Upper Siluric strata rest on Niagaran 
 except where the continental deposits of Salina time intervene, and 
 the further fact that no undoubted marine equivalents of the Salinan 
 are known in North America, greatly strengthen the argument for 
 the wholly continental origin of these salt deposits. 
 
 THE SALT DOMES. These should be briefly mentioned here, as 
 accumulations of salt in circumscribed areas, often to a thickness of 
 
380 PRINCIPLES OF STRATIGRAPHY 
 
 several thousand feet. They are of all ages and owe their form to 
 rearrangement of the salt mass through the force of crystal growth 
 inherent in the salt, and in this process they have often seriously 
 disturbed the enclosing strata. (Hahn-2i; Harris-22; see further 
 under diagenesis, Chapter XX.) (Fig. 70.) 
 
 BIBLIOGRAPHY IX. 
 
 1. ANDERSON, W. S. 1890. The Solubility of Carbonate of Lime in 
 
 Fresh and Salt Water. Proceedings of the Royal Society of Edinburgh, 
 Vol. XVI, pp. 319-324- 
 
 2. ANDREE, KARL. 1912. Ueber Sedimentbildung am Meeresboden, iter 
 
 Teil. Geologische Rundschau, Bd. Ill, Heft 5-6, pp. 324-360. 
 
 3. ANDRUSSOW, N. 1897. Der Adschi-darja, oder Karabugas-Busen. 
 
 Petermanns Mittheilungen, Bd. XLIII, pp. 25-34. 
 
 4. ANDRUSSOW, N. 1897. La Mer Noire, Guide des Excursions du 
 
 VII me . Congres Geologique International, No. 29. 
 
 5. BADER, H. 1869. Ueber die Bitterseen des Suezkanals. Verhandlungen 
 
 der kaiserlich-koniglichen geologischen Reichsanstalt, pp. 287-289, 311. 
 
 6. BRANNER, J. C. 1911. Aggraded Limestone Plains of the Interior of 
 
 Bahia and the Climatic Changes'Suggested by Them. Bulletin Geological 
 Society of America, Vol. XXII, No. 2, pp. 187-206. 
 
 7. CAMPBELL, M. R. 1902. Reconnaissance of the borax deposits of 
 
 Death Valley and Mohave Desert [California]. Bulletin U. S. Geological 
 Survey, No. 200. 
 
 8. CAMPBELL, M. R. 1903. Borax Deposits of Eastern California, Bul- 
 
 letin U. S. Geological Survey, No. 213, pp. 401-405. 
 
 9. CAYEUX, L. 1897. Contribution a I'EJtude de micrographie des terrains 
 
 sedimentaires. Lille. 
 10. CLARKE, F. W. 1908-1911. The Data of Geochemistry, ist edition. 
 
 Bulletin 330, U. S. Geological Survey, 2nd edition Bulletin 491. (Unless 
 
 otherwise stated the pages of both editions are given.) 
 U. DALY, REGINALD A. 1907. The Limeless Ocean of Pre-Cambrian 
 
 Time. American Journal of Science. 4th series. Vol. XXIII, pp. 93-115. 
 
 12. DALY, R. A. 1909. First Calcareous Fossils and the Evolution of the 
 
 Limestones. Geological Society of America, Bulletin XX, pp. 153-170. 
 
 13. DANA, JAMES D. 1872. Corals and Coral Islands. New York, Dodd 
 
 & Mead. 
 
 14. DARWIN, CHARLES. 1841. Voyage of the Beagle. 
 
 15. DE GROOT, HENRY. 1890. The Searles Borax Marsh. loth Report, 
 
 California State Mineralogist, pp. 534-539. 
 
 16. ERDMANN, E. 1908-09. Die Entstehung der Kalisalzlagerstatten Zeit- 
 
 schrift fur Angewandte Chemie, Vol. XXI, pp. 1685, 1702, also Demon- 
 stration von Salzmineralien, Ibid., Vol. XXII, pp. 238-239. 1909. 
 
 17. FREEMAN, W. B., and BOLSTER, R. H. 1910. Surface Water Supply 
 
 of the United States, 1907-08. Colorado River Basin, U. S. Geological 
 Survey Water Supply Paper, No. 249, pt. 9. 
 
 1 8. GILBERT, G. K. 1890. Lake Bonneville. Monograph U. S. Geological 
 
 Survey, Vol. I. 
 
 19. GRABAU, A. W. 1912. The Origin of Salt Deposits with Special Refer- 
 
 ence to the Siluric Salt Deposits of North America. Bulletin No. 57, 
 Mining and Metallurgical Society of America. 
 
BIBLIOGRAPHY IX 381 
 
 20. GRABAU, A.W. 1913. Early Palaeozoic Delta Deposits of North America. 
 
 Bulletin of the Geological Society of America, Vol. XXIV, pp. 399528. 
 
 21. HAHN, F. F. 1912. The Form of Salt Deposits. Economic Geology, 
 
 Vol. VII, pp. 120-135. 
 
 22. HARRIS, G. D. 1909. The Geological Occurrence of Rock Salt in 
 
 Louisiana and East Texas. Economic Geology, Vol. IV, pp. 12-34. 
 
 23. HILGARD, E. W. 1896. The Geologic Efficacy of Alkali Carbonate 
 
 Solutions. American Journal of Science, 4th ser., Vol. II, pp. 100-107. 
 
 24. HOCHSTETTER, F. V. 1856. Karlsbad, seine Geognostische Ver- 
 
 haltnisse und seine Qucllen, Karlsbad. 
 
 25. HUBBARD, LUCIUS L. 1893. Origin of Salt, Gypsum and Petroleum. 
 
 Geological Survey of Michigan, Vol. V, pt. II, Introduction, pp. i-xxiv. 
 
 26. HUNT, T. STERRY. 1859. On some Reactions of the Salts of Lime 
 
 and Magnesia and on the formation of Gypsum and Magnesian rocks. 
 American Journal of Science, 2nd ser., Vol. XXVIII, pp. 170-187, 365-383. 
 
 27. HUNT, T. S. 1866. Further Contributions to the History of Lime and 
 
 Magnesium Salts. American Journal of Science, 2nd ser., Vol. XLII, pp. 
 49-67. 
 
 28. HUNTINGTON, ELLSWORTH. 1907. The Pulse of Asia. Houghton 
 
 Mifflin & Co. 
 
 29. IRVINE, ROBERT, and YOUNG, GEORGE. 1889. On the Solubility 
 
 of Carbonate of Lime under Different Forms in Sea- water. Proceedings 
 of the Royal Society of Edinburgh, Vol. XV, pp. 316-320. 
 
 30. IRVINE, ROBERT, and WOODHEAD, G. SIMS. 1889-90. On the 
 
 Secretion of Carbonate of Lime by Animals. Proceedings of the Royal 
 Society of Edinburgh, Vol. XV, pp. 308-316, Vol. XVI, pp. 324-354, Vol. 
 XVII, pp. 79-108. 
 
 31. KNOP, A. 1874. Ueber Kieselsaureabscheidungen und Oolithbildung. 
 
 Neues Jahrbuch fur Mineralogie, etc., 1874, PP- 281-288. 
 
 32. LANE, ALFRED C. 1893. The Geology of Lower Michigan with Refer- 
 
 ence to Deep Borings. Michigan Geological Survey, Vol. V, pt. II. 
 
 33. LINCK, G. 1903. Die Bildung der Oolithe und Rogensteine. Neues 
 
 Jahrbuch fur Mineralogie, Beilage Band XVI, pp. 495-513. 
 
 34. LYELL, CHARLES. 1875. The Principlesof Geology, I2th edition, Vol. I. 
 
 London, John Murray. 
 
 35. MERRILL, GEORGE P. 1895. The Onyx Marbles: Their Origin, 
 
 Composition and Uses, Both Ancient and Modern. Smithsonian Insti- 
 tution, U. S. National Museum. Report for 1893, pp. 541-585. 
 
 36. MURRAY, JOHN, and IRVINE, ROBERT. 1891. On Coral Reefs and 
 
 Other Carbonate of Lime Formations in Modern Seas. Proceedings of 
 the Royal Society of Edinburgh, Vol. XVII, pp. 79-109. 
 
 37. OCHSENIUS, KARL. 1877. Die Bildung der Steinsalzlager und ihrer 
 
 Mutterlaugensalze. Halle. 
 
 38. OCHSENIUS, KARL. 1878. Beitrage zur Erklarung der Bildung von 
 
 Steinsalzlagern und ihrer Mutterlaugensalze. Nova Acta der kaiserlich- 
 Leopoldish-Carolinischen deutschen Akademie der Naturforscher, Bd. XL, 
 No. 4, pp. 121-166. 
 
 39. OCHSENIUS, KARL. 1888. On the formation of rock salt beds and 
 
 mother liquor salts. Philadelphia Academy of Sciences, Proceedings, 
 1888, pt. 2, pp. 181-187. 
 
 40. OCHSENIUS, KARL. 1893. Bedeutung des orographischen Elementes 
 
 "Barre" in Hinsicht auf Bildungen und Veranderungen von Lagerstatten 
 und Gesteinen. Zeitschrift fur Praktische Geologic, Bd, I, May, June. 
 
382 PRINCIPLES OF STRATIGRAPHY 
 
 41. OCHSENIUS, K. 1893. Ueber unterirdische Wasseransammlungen, 
 
 Zeitschrift f . Praktische Geologic, I, pp. 36-40. 
 
 42. OCHSENIUS, K. 1902. Review das Gesetz der Wustenbildung von 
 
 Johannes Walther, Centralblatt fur Mineralogie, Geologie u. Palaeontologie, 
 PP- 551-590, 620-633. 
 
 43. PASSARGE, SIEGFRIED. 1904. Die Kalahari. Versuch einer phys- 
 
 isch-geographischen Darstellung der Sandfelder der sudafrikanischen 
 Becken. Berlin, Dietrich Reimer. 
 
 44. PENROSE, R. A. P., Jr. 1910. The Nitrate Deposits of Chile. Journal of 
 
 Geology, Vol. XVIII, pp. 1-32. 
 
 45. PHILIPPI, E. 1907. Ueber Dolomitbildung und Chemische Abschcid- 
 
 ung von Kalk an heutigen Meeren. Neues Jahrbuch f. Mineralogie, 
 etc. Festband, pp. 397-445. 
 
 46. POTONIE, H. 1906. Naturwissenschaftliche Wochenschrift, Bd. V. 
 
 47. RUSSELL, ISRAEL C. 1881-82. Sketch of the geological history of 
 
 Lake Lahontan. A Quaternary lake of northwestern Nevada. 3rd 
 Annual Report, U. S. Geological Survey, pp. 189-235. 
 
 48. RUSSELL, I. C. 1885. Geological history of Lake Lahontan, a Quater- 
 
 nary lake of northwestern Nevada. Monograph, U. S. Geological Sur- 
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 49. SEIDLITZ, N. VON. 1899. Der Karabugas-Meerbusen des Kaspischen 
 
 Meers. Globus, Vol. LXXVI, pp. 13-17. 
 
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 Mus. Comp. Zool., XLII, pp. 53- 126 - 
 
 51. STEINMANN, GUSTAV. 1889. Ueber Schalen und Kalksteinbildung. 
 
 Bericht der Naturwissenschaftlichen Gesellschaft. Freiburg. 
 
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 France. Annales chem.phys.,3rd ser., Vol. XXVII, pp. 92-107; 172-191. 
 
 53. VAN'T HOFF, J. H. 1905. Zur Bildung der Ozeanischen Saltzablagerung- 
 
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 54. VAN'T HOFF and WEIGERT, F. 1901. Untersuchungen iiber die 
 
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 January, February, Vol. VI, pp. 4-16; 43-52. 
 
 56. WAGNER, R. Abhandlungen der koniglich-preussischen Geologischen 
 
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 U. S. Geological Survey, No. 134. 
 
 59. WALTHER, JOHANNES. 1888. Die Korallenriffe der Sinaihalbinsel. 
 
 Abhandlungen der koniglich-sachsischen Gesellschaft der Wissenschaf- 
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BIBLIOGRAPHY IX 383 
 
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 69. WHERRY, E. T. 1908. Communication on the occurrence of Carnotite 
 
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CHAPTER X. 
 
 MORPHOLOGY AND LITHOGENESIS OF THE TRUE ORGANIC 
 OR BIOGENIC ROCKS. ZOOGENIC DEPOSITS. 
 
 Biogenic rocks, or Bioliths as Chr. G. Ehrenberg has termed 
 them, are deposits of organic material, or material formed through 
 the physiological activities of the organisms. In general, Bioliths 
 may be divided into those in which the organic matter is preserved 
 in the form of carbon or compounds of carbon, and those in which 
 only the inorganic mineral matter, abstracted from the food or 
 the medium in which the organism lives (air, water, or soil), is 
 preserved. The former are almost wholly restricted to plant- 
 formed (phytogenic) deposits, or phytoliths, and the latter are 
 best represented by animal-formed (zoogenic) deposits or zooliths. 
 As the organic carbon deposits, whether plant or animal, all have 
 the property of combustibility, they have been designated causto- 
 bioliths,* while the non-combustible organic deposits of purely min- 
 eral character are designated acaustobioliths. 
 
 The following classification of the types of biogenic deposits, 
 or Bioliths (Biolites), may be made: 
 
 A. Zoogenic Deposits or Zooliths. 
 
 1. Coral reefs. 
 
 2. Sponge reefs. 
 
 3. Bryozoa reefs. 
 
 4. Shell colonies. 
 
 5. Shell limestones. 
 
 6. Crinoidal limestones. 
 
 7. Calcareous oozes. 
 
 a. Foraminiferal oozes. 
 
 b. Pteropod oozes. 
 
 c. Cyprid oozes. 
 
 *From Kau<m/c6s = capable of burning, Bios, life, \l0os, stone. Caustoliths of 
 inorganic origin also exist: e. g., sulphur deposits. 
 
 384 
 
CORAL REEFS 385 
 
 8. Siliceous oozes. 
 
 a. Radiolarian oozes. 
 
 b. Sponge spicule oozes. 
 
 9. Phosphate (guano) deposits. 
 B. Phytogenic Deposits or Phytoliths. 
 
 1. Nullipore reefs and limestones. 
 
 2. Algous travertine. 
 
 3. Phytogenic oolites. 
 
 4. Chara marls and limestones. 
 
 5. Diatomaceous oozes. 
 
 6. Caustophytoliths. 
 
 a. Sapropeliths. 
 
 b. Peat. 
 
 c. Lignites, brown coal, etc. 
 
 d. Coals. 
 
 e. Deep sea vegetal deposits. 
 
 In the present chapter only the zoogenic deposits will be dis- 
 cussed, the phytogenic being referred to the next chapter. 
 
 CORAL AND OTHER REEFS. 
 
 Coral reefs have been formed in all geological periods, from the 
 Cambric to the present, and recent investigations seem to indicate 
 the existence of archaeocyathid corals in reef-like association during 
 the pre-Cambric (Animikie) in the Canadian region. Reefs are 
 complex structures, and corals often play only a minor part in their 
 construction. Calcareous algae, or Nullipores, are commonly among 
 the most important reef organisms (Marshall Howe~5o), while 
 Hydrocorallines are equally abundant. In fossil reefs Sponges and 
 Bryozoa are often the most important reef organisms. The term 
 coral will be used here in its more general or comprehensive sense, 
 so as to include the hydrocorallines, both the recent millepores and 
 their fossil representatives, the Stromatoporoids. Among the corals 
 proper two classes are represented : Madreporaria, or stone corals, 
 and the Alcyonarla. The latter, however, furnish only a small con- 
 tribution to the reef. Many other lime-secreting organisms occur 
 besides corals and nullipores. They are, however, of secondary 
 significance, and, on the whole, contribute only a fraction of its 
 mineral matter to the reef. 
 
 The general characteristics of modern coral reefs will first be 
 discussed, and this will be followed by a review of reefs of the past. 
 
3 86 PRINCIPLES OF STRATIGRAPHY 
 
 CHARACTERS AND DEVELOPMENT OF MODERN CORAL REEFS. 
 
 TYPES OF MODERN CORAL REEFS. Three types of coral reefs 
 are recognized in the modern seas : the fringing reef, barrier 
 reef, and atoll The Fringing Reef, or shore reef (Figs. 71-2), is 
 a platform of coral rock closely bordering a continent or island of 
 earlier rigin and extending some distance from the shore. Sea- 
 ward the platform of coral rock is often somewhat higher than 
 the inner end, rising into low ridges or mounds of living or dead 
 coral and coral sand often awash at low tide. It is intersected by 
 channels and a pronounced but shallow channel extends between it 
 and the shore. Its seaward side is often rather steep, but it descends 
 into comparatively shallow water. This is the zone of active coral 
 growth as well as destruction, for here wave activity is most marked. 
 Within the outer rim conditions of life are less favorable, since 
 
 FIG. 71. Island with fringing reef, 
 and submarine platform over 
 which the surf breaks. (After 
 Le Conte.) 
 
 FIG. 72. Diagrammatic cross-section 
 of the island and reef shown in 
 preceding figure. a, a, Dead 
 coral material added to island. 
 (After Le Conte.) 
 
 here the water is more stagnant, and the channels are scoured out 
 by the tidal currents and the solvent action of the water. The 
 influx of fresh water and clastic sediment from the land also hin- 
 ders coral growth to a considerable extent within the outer rim of 
 the fringe. Typical examples of fringing reefs are found on the 
 borders of the Sandwich, Solomon, Friendly, and Navigator islands, 
 the New Hebrides and Mariana islands and many others, all in the 
 Pacific, also in the Seychelles and Nicobar islands and in Mau- 
 ritius, as well as parts of the coast of Madagascar and Mozambique 
 in the Indian Ocean. In the Red Sea they occur on both the 
 Arabian and African shores, and in the Atlantic on the coast of 
 Florida and around nearly the whole of the islands of the West 
 Indies. 
 
 The Barrier Reef (Figs. 73-4) is situated further from shore 
 and consequently has a greater depth of water both between it and 
 the land and on the seaward side. It may be formed from the 
 fringing type by the subsidence of the land and the simultaneous up- 
 ward growth of the corals on the outer border of the reef (Darwin) ; 
 
MODERN CORAL REEFS 
 
 387 
 
 by the seaward growth of the front of the reef and the enlargement 
 by solution of the channel between the reef and the land without sub- 
 sidence (Murray, Agassiz), and, finally, by the independent upward 
 growth of the corals into reefs on a suitable platform at a distance 
 from the shore. The Great Barrier Reef on the northeast coast 
 of Australia extends for 1,250 miles from Torres Strait in 9.5 S. 
 lat. to Lady Elliott Island in 24 S. lat. At Cape York the sea- 
 
 FIG. 73. Barrier reef around cen- 
 tral island. The surf (white) 
 shows the location of the reef, 
 which is dotted with small coral 
 islands. (After Le Conte.) 
 
 FIG. 74. Diagrammatic section of the 
 island shown in the preceding 
 figure, showing location of reefs 
 (dotted). (After Le Conte.) 
 
 ward edge of this reef is nearly 90 miles distant from the coast and 
 it descends to a depth often exceeding 1,800 feet. It represents "a 
 great submarine wall or terrace, fronting the whole northeast coast 
 of Australia, resting at each end in shallow water, but rising from 
 very great depths about the center. Its upper surface forms a pla- 
 teau, covered by 10 to 30 fathoms of water, but studded all over 
 with steep-sided block-like masses which rise up to low water 
 level." ( Jukes-Browne-53 ; 54.) These individual reefs are espe- 
 
 FIG. 75. An atoll formed of discon- 
 nected' coral islands arising from 
 a submerged reef which is out- 
 lined by surf (white). (After 
 Le Conte.) 
 
 FIG. 76. Diagrammatic section of an 
 atoll, showing depth of central 
 lagoon, and relation of the islands 
 to the reef. (After Le Conte.) 
 
 cially numerous along the edge of the bank and protect the com- 
 paratively shallow water over the reef, as well as the numerous 
 inner reefs scattered over the surface, from the effects of the waves 
 of the open ocean. In most barrier reefs, the outer edge is in 
 places often awash at low tide and islands and bars of dead coral 
 and sand are formed. These may coalesce and in time become cov- 
 ered with vegetation. Thus a strip of land is formed, lying some 
 hundred yards or less from the extreme outer edge of the reef. 
 
388 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Where the barrier reef is not far from land, gaps always occur in it 
 opposite the mouths of rivers. 
 
 Other examples of barrier reefs occur in the Pacific, where 
 they encircle some of the Society Islands, including Tahiti, the 
 Fiji Islands, and New Caledonia. The last is 400 miles long and 
 about ten miles distant from shore. The Pelew Islands and the 
 Comoro Isles in the Mozambique Channel are surrounded by bar- 
 rier reefs and other examples occur in the middle of the Red Sea. 
 
 The Atoll is an elliptical, oval or roundish ring of coral, its 
 continuity broken here and there by channels which lead into the 
 central lake-like expanse of water, the lagoon. The outside water 
 is commonly very deep, while the water of the atoll is shallow. 
 Thus, off the Cocos-Keeling atoll, the depth sounded at a distance 
 
 FIG. 77. The atoll of Whitsunday Island. (From Le Conte.) 
 
 of 2,200 yards from the reef's edge was 1,200 fathoms, while the 
 depth of the lagoon is only from two to seven fathoms (3.5 to 13 
 meters). In the atolls of the Low Archipelago the depth varies 
 from 35 to 70 meters (20 to 38 fathoms), in the Marshall group 
 from 50 to 60 meters (30-35 fathoms), and in the Maldive group 
 up to 90 meters (45 to 49 fathoms). (Figs. 75-77.) 
 
 The openings in the reefs are always on the leeward side, and so 
 the water within the lagoon is seldom much disturbed. In it live 
 swarms of organisms of all kinds, including fishes and, preeminently, 
 sharks. The calcareous alga Halimeda grows abundantly over the 
 floor of the lagoon of Funafuti in the Ellis group, and of many 
 other atolls in the Pacific, and it has been collected in quantity in 
 the lagoon of Diego Garcia in the Chagos group in the Indian 
 Ocean and elsewhere. 
 
 Atolls are especially abundant in the Pacific and the Indian 
 
MODERN CORAL REEFS 389 
 
 oceans. Of the Pacific atolls the largest group forms the Low 
 Archipelago in the center of the Pacific, south of the equator, and 
 next the Caroline Archipelago in the western part of the Pacific, 
 north of the equator. The Marshall group, the Gilbert Islands, the 
 Ellis Island group with Funafuti, and a number of scattered atolls, 
 lie between the two first mentioned archipelagoes. In the Indian 
 Ocean the Laccadives, the Maldives, the Chagos, and the Sava de 
 Malha groups form the largest of the associations of atolls. The 
 Cocos-Keeling islands may also be mentioned as isolated but typical 
 atolls in the eastern part of the Indian Ocean (lat. 12 S., long. 
 96 E.). 
 
 From the geological point of view, a classification based on the 
 relationship of the reef to the continental block is perhaps of even 
 more fundamental significance. On such a basis reefs may be di- 
 vided into oceanic, those encircling oceanic islands or resting on 
 oceanic platforms, and epicontinental or neritic, those growing upon 
 or on the border of the continental shelf and around the islands per- 
 taining thereto. Each group may be represented by fringing and 
 barrier reefs, as well as by atolls, though the latter are more com- 
 monly confined to the oceanic type. 
 
 In general only the epicontinental type is represented in the 
 older deposits of the known earth's crust, though some of these may 
 well have had deep, marginal depressions similar to those found off 
 many of the western Pacific reefs. The dolomite reefs of the Tyrol 
 have, however, been regarded as atolls. Of existing examples of 
 epicontinental reefs the Great Barrier Reef of Australia may be 
 considered the best representative. In their composition and in- 
 ternal structure and in the factors influencing their distribution, all 
 reefs are more or less alike. 
 
 FACTORS LIMITING THE DISTRIBUTION OF MODERN CORAL REEFS. 
 The geographic distribution of modern coral reefs falls within that 
 portion of the oceans lying approximately between 28 north and 
 south latitudes, in those depths in which the mean annual tempera- 
 ture does not fall below + 68 F. (+ 20 C), nor rise very much 
 above that point. Most of the existing coral reefs are found in the 
 Pacific Ocean, whose average surface temperature is the highest of 
 the four oceans (19.1 C, 66.38 F., maximum 27.60 C., 80.69 
 F.). (See Chapter IV.) The Indian Ocean comes next with a 
 mean annual temperature of 17 C, 62.6 F. (27.88 C, 82.18 F. 
 maximum), and it is next in importance with reference to the dis- 
 tribution of coral reefs. The Atlantic (mean annual temperature 
 16.9 C., 62.42 F., maximum 26.83 C., 80.38 F.), finally, is sur- 
 prisingly poor in coral reefs, though numerous fringing reefs occur 
 
390 PRINCIPLES OF STRATIGRAPHY 
 
 in the West Indies, off the coast of Florida and on the coast of 
 Brazil. This is clearly due to the fact that the tropical belt is most 
 contracted in the Atlantic. The Bermuda Islands are a remarkable 
 exception to the general law of distribution of coral reefs, for they 
 are found in the latitude 32 N., and are therefore the farthest re- 
 moved from the equator of any modern coral reefs. Their occur- 
 rence in such a position is favored by the Gulf Stream, which brings 
 the warm waters of the tropics. No coral reefs are known in the 
 eastern part of the Atlantic. 
 
 The eastern part of the Pacific is likewise free from reefs, and 
 this is to be correlated with the fact that the cooler ocean currents 
 from north and south converge here, as in the east Atlantic, to form 
 the equatorial currents. The coral reef area of the Pacific lies west 
 of the i2Oth meridian (E.), the greatest area lying between 130 E. 
 and 145 W. longitude and between 15 N. and 25 S. latitude. 
 The most extensive eastern group is that of the Low Archipelago 
 with Ducie Island, its eastern outpost. The largest western group 
 is that of the Caroline Archipelago, but many scattered atolls and 
 fringing reefs occur to the west of this, notably in the China Sea, 
 where the Paracelle group forms an extensive cluster of atolls in 
 lat. 112 W., long. 17 N. The fringing reefs of the Sandwich 
 Islands form a large single and isolated group in the mid-Pacific 
 north of the equator. 
 
 The coast of the mainland and the islands of the western Pacific 
 within the coral zone are generally bordered by reefs either fringing 
 or barrier, beginning with the Great Barrier Reef on the south, and 
 extending to the fringing reefs of the Loo Choo group. 
 
 The Indian Ocean is generally lined by fringing reefs, which ex- 
 tend with interruptions from Madagascar north along both sides of 
 the Red Sea, in the Persian Gulf around Ceylon and the Nicobar 
 Islands and south along the coast of Sumatra and Java to Australia. 
 In the western half lies the great group of atolls, the Maldives and 
 Laccadives, extending from the equator north to lat. 13 and the 
 Chagos and Sava de Malha groups. The fringing reefs of the 
 Seychelles and of Mauritius also fall in this half of the Indian 
 Ocean. The eastern half contains only the Cocos-Keeling group 
 and some atolls off the northwest coast of Australia. 
 
 In general, then, reefs of various kinds occur in the three larger 
 oceans, but are mainly confined to the western half of these oceans. 
 The Indian Ocean alone has representatives in the eastern half, but 
 they are far less abundant than in the western. The Atlantic has 
 no typical atolls, though the Bermudas come near to representing 
 them. 
 
MODERN CORAL REEFS 391 
 
 Depth of Water. The greatest depth at which reef -building 
 corals flourish is 20 to 25 fathoms, though occasionally reef-build- 
 ing species may extend down to 40 or 45 fathoms. At this depth 
 Madrepora has been found growing on the Macclesfield and Tizard 
 banks of the China Sea. These corals were, however, as a rule, of 
 much slighter build than those found in shallow water. The depth 
 here given is of course not the downward limit of corals as a whole, 
 for some species are known to extend to great depths (see Chap- 
 ter XXVIII). Reef corals, however, flourish best in shallow water, 
 their most luxuriant growth being above 15 or 10 fathoms and to 
 just below low-tide level. Indeed many coral reefs luxuriate in 
 spite of the fact that they are exposed at exceptionally low tides, 
 as shown in Great Barrier Reef of Australia (Saville-Kent-77). 
 The alcyonarian Heliopora and the hydrocoralline Millepora, how- 
 ever, are active reef builders at 35 and 40 fathoms, and nullipores 
 extend to a depth of 35 fathoms. 
 
 Intensity of Light. That the range in depth is in part to be cor- 
 related with the intensity of the sunlight is shown by the fact that 
 species of reef corals placed in a light-proof life car die after the 
 light has been excluded for several weeks. At Fort Jefferson in the 
 Tortugas, reef corals grow on the peripheral piles of the govern- 
 ment wharf, but are absent from the permanently shaded portions. 
 (Vaughan-87 -.240.) 
 
 Now, as has been shown by the investigations of the optics of 
 sea water (see ante, p. 204), the visible depth in the open ocean 
 in 33 north latitude is roughly 50 meters (27^3 fathoms), and in 
 50 north latitude it is 40 meters (22 fathoms). In the tropics 
 the depth is even greater, and it thus appears that the reef-building 
 species flourish within the zone of visibility and therefore of great- 
 est intensity of the sunlight. 
 
 Temperature. As long ago shown by Dana, the minimum an- 
 nual temperature of the water must be 68 F. (20 C.), or the mean 
 annual temperature must be above 70 F. (21.2 C.). (Murray-68: 
 25-27.) All the principal coral-reef regions lie within the equatorial 
 belt where the range of temperature is not over 10 Fahrenheit 
 (5-5 C.), and recent observations and experiments have shown 
 that the precipitation of carbonate of lime both by organisms and by 
 inorganic agencies is most active at high temperatures. Saville- 
 Kent (77:p), indeed, insists that reef building is influenced by 
 temperature much more than by the species of corals, for he finds 
 that the same species which build the reefs in tropical waters are not 
 reef-building in extratropical regions. He further holds that it is 
 only in the shallower water where precipitation of lime is caused 
 
392 PRINCIPLES OF STRATIGRAPHY 
 
 by evaporation that coral conglomerates and limestones occur. 
 Corals as such are, however, by no means restricted to the tropics. 
 Astrangea dance grows on the southern shore of Massachusetts at 
 Woods Holl, and Lophohelia prolifera and Dendrophyllia ramea 
 form dense beds at a depth of from 100 to 200 fathoms off the 
 coasts of Norway, Scotland and Portugal. 
 
 Other Physical Conditions. For the successful growth of reef 
 corals it is further necessary that the water should be generally in a 
 state of agitation, the stagnation of the inner marginal waters of the 
 reefs or the lagoons being for the most part unfavorable to the 
 growth of coral. This is chiefly due to the fact that still water per- 
 mits fine sediment to be deposited, and this quickly kills the polyps. 
 On the other hand, very powerful surf is equally deleterious to the 
 coral polyps, for it will throw the shingles against the soft polyps 
 and so destroy them. Moreover, the heavy breakers will tear off 
 the branching madrepores, and loosen even the massive maean- 
 drinas, owing to the fact that the dead base of the colony is often 
 so much riddled by boring organisms that it easily succumbs to the 
 onslaught of the waves. When such a great mass of coral is 
 loosened, it will be rolled along the reef, rounding and grinding the 
 other corals in its course. (Bourne-i4: 440.) 
 
 A strong current likewise seems to be unfavorable to the growth 
 of corals, if it sets directly against them. Thus at Diego Garcia, 
 and especially at the east end of East Islet in the Chagos group, 
 strong direct currents strike the reef, which is barren here and suf- 
 fering rapid erosion, where the whole force of the current falls 
 directly upon them. "As the current parts and flows round the 
 obstacle one meets with a reef covered with debris, but barren of 
 live coral ; further on, as the current moderates in force, one finds 
 a few growing heads of coral ; and finally, at the further end of the 
 reef, where the current has abated its force considerably, there is a 
 luxuriant bed of living corals and Alcyonaria." (Bourne-i4.) The 
 same facts have been observed at Celebes, and the conclusion seems 
 to be supported by many observations "that direct and strong cur- 
 rents are unfavorable to coral growth, that moderate tangential 
 currents are extremely favorable, and sluggish or still water again 
 unfavorable." A hard rock bottom is furthermore a necessity for 
 good coral growth, these organisms finding it impossible to become 
 attached to muddy or silty bottoms. 
 
 A normal composition of sea water is required, and the normal 
 salinity of 35 permille seems to be most favorable, as in the open 
 oceans, but a surface salinity decreased to 32.1 permille, as in the 
 China Sea (volume salinity 34 permille), or even 31.5 permille, as 
 
MATERIALS OF CORAL REEFS 393 
 
 In the Andamanian marginal mediterranean (volume salinity 33 
 permille) does not prevent their growth. On the other hand, a 
 surface salinity of 38.8 permille, that of the Red Sea (39 permille 
 volume salinity), is not too high for their development. 
 
 COMPOSITION AND STRUCTURE OF THE REEF. Our knowledge of 
 the composition and structure of the deeper parts of a modern coral 
 reef has been obtained from examination of the accessible parts of 
 reefs and from a deep boring made on the atoll of Funafuti in the 
 Ellis Island group, for the purpose of ascertaining these facts. 
 Three attempts were made, beginning in 1896, and the depth finally 
 reached was 1,114 feet ( l &5 fathoms). (David-22.) This boring 
 passed only through pure limestone of organic origin to the depth 
 reached, without trace of any other rock. The organic remains 
 found were chiefly corals, calcareous algse and Foraminifera, be- 
 sides other types. A boring made from the deck of a ship into the 
 floor of the lagoon, where the water was 17 fathoms deep, showed 
 a deposit consisting of the calcareous alga Halimeda opuntia, with 
 an abundant admixture of Foraminifera, and having a thickness of 
 over 100 feet. At a depth of 245 feet, Madrepora, Porites and 
 Heliopora were encountered, forming a solid mass of coral rock. 
 As these corals are shallow-water types, it is evident that subsi- 
 dence has taken place and that the lagoon of Funafuti has been 
 filled up to a depth of at least 245 feet (nearly 41 fathoms). 
 
 Materials Composing the Reef. 
 
 The most important of the reef corals of modern reefs are the 
 branching Madrepores, Pocilloporas and Porites and the heads of 
 Astrseans and Maeandrinas. Among the hydrozoans Millepora is 
 very abundant, the common species being M. complanata and M. 
 alcicornis. In addition to the corals a number of species of nulli- 
 pores occur on the reefs, and often become as important as, if not 
 more so than, the corals themselves. This is the case with the reefs 
 of Christmas Island, of Fiji and Funafuti, where, besides, a promi- 
 nent part is taken by Foraminifera, Echinodermata, Bryozoa, Pele- 
 cypoda and other organisms. 
 
 Within the lagoon of some atolls corals flourish in abundance. 
 At Diego Garcia in the Chagos group the more delicate branching 
 species of the Madreporaria flourish in considerable numbers, and 
 true reef-building species of Porites, Maeandrina, Pocillopora and 
 others are also found. "Many of the species growing in the lagoon 
 at a distance of five miles and upward from its outlet are identical 
 
394 PRINCIPLES OF STRATIGRAPHY 
 
 with those growing on the outer reef. In addition to them are nu- 
 merous species such as Seriatopora stricta, Mussa corymbosa, 
 Favia lobata, Fungia dentata, and many others that are not found 
 on the outside." This is due to the fact that these corals are either 
 free (Fungia) or attached by such slender stems that they could 
 not maintain themselves in the strong surf and currents of the open 
 ocean. 
 
 Within the lagoon these species grow close together and form 
 knolls and patches, which, together with the clastic debris washed 
 into the lagoon, tends to fill it up completely. The distribution of the 
 organisms in the atoll of Funafuti in the Ellis Island group (long. 
 179 E. and lat. 8 30' S.) may be taken as representative (Firickh- 
 31). "On the ocean side up to as far in as the wash of the waves 
 reaches at low-water spring tide, the reef platform is densely cov- 
 ered with vigorously growing organisms." A thinly branching 
 Lithothamnion is the most abundant, appearing in small, isolated 
 shrub-like clusters, from I to 5 inches in diameter and varying simi- 
 larly in height. Between these grow small Madrepora loripes, 
 Brook. On the outer edge of the platform lichenous and knobby 
 Lithothamnia occur, but no Porites nor Heliopora cccrulea. None 
 of these species forms patches of great size, owing to the intense 
 intraspecific struggle for existence which takes place here, though 
 eventually Lithothamnion seems to be the victor over the corals and 
 hydrocorallines. This vigorous growth extends for only 2 or 3 
 feet downward at the edge of the reef below the level of low-water 
 spring tide, below which the reef becomes comparatively destitute of 
 organisms. 
 
 The Lithothamnion zone is dissected by a large number of nar- 
 row cross channels, which give it a fringed appearance. The edge 
 is generally somewhat raised and rough on account of the Litho- 
 thamnion growth, and the encrustation of the surface by Foramin- 
 ifera, like Carpenteria and Polytrema. This feature is less marked 
 or wholly absent on the lagoon side of the coral reef platform. Dif- 
 ferent species of Lithothamnion characterize this fringe in differ- 
 ent parts of the atoll. Thus in the eastern or windward portion a 
 lichenous form abounds, while in the western or leeward portion 
 of the lagoon rim a thinly branching species and another lichenous 
 form with stony knobs entirely replace the first species. 
 
 Next to the Lithothamnion, the branching nullipore Halimeda 
 abounds on the reef, both on the lagoon and ocean slopes. It lives 
 to the 45-fathom level, while the Lithothamnion has been found 
 alive at 200 fathoms' depth. The hydrocorallines are chiefly repre- 
 sented by the branching Millepora alcicornis and the more massive 
 
ORGANISMS OF CORAL REEFS 395 
 
 M. complanata. The first is restricted to the lagoon side, the second 
 also occurs on the ocean side. Among the corals Hcliopora ccerulea 
 is by far the most important, but is scarcely found on the outer rim 
 of the atoll. It occurs on the lagoon side, where it often forms the 
 chief lime contributor next to the algae. The yellow Porites limosa 
 and a purple species of Forites also occur on the lagoon side, but 
 seem to be rare or absent on the ocean side. Large blocks of rock 
 made of dead Porites abound in some sections, showing this coral 
 to have been formerly of great importance. Besides these species, 
 the branching Madrepora loriceps abounds on the western rim of 
 the atoll, but is rare elsewhere. Pocillopora of several species also 
 occurs. Astrsean corals seem of far less importance at Funafuti 
 than at other coral reefs. The reef platform has a width of 1,300 
 yards where it supports the islet of Fualopa, but it is mostly much 
 narrower. It consists of a smooth, barren surface formed on dead 
 Lithothamnion coral sand, and coral fragments, generally overlying 
 a basal stratum of dead Helipora ccerulea, Porites or both. In 
 many cases this old Helipora reef still forms the surface of the 
 platform within the Lithothamnion fringe, the islet being built upon 
 it by the accumulation of coral and Lithothamnion sand and breccia. 
 A dense growth of sea weed is characteristic of the submerged por- 
 tion of the platform. 
 
 In general, the ocean rim of the leeward portion of the atoll 
 is characterized by the enormous quantity of branching Litho- 
 thamnion with its vivid coloration, the great abundance of Madre- 
 pora loriceps, the general small size of all the species and the ab- 
 sence of Heliopora cocrulea and Millepora alcicornis. The plat- 
 form is smooth and not divided into zones, while the transverse 
 channels are short and shallow. 
 
 On the windward side, the branching and knobby forms of 
 Lithothamnion are wholly absent, while the lichenous form present 
 has a dark color. Corals are scarce, Madrepora loriceps, Heliopora 
 carulea and Millepora alcicornis being wholly wanting, while Pocil- 
 lopora grandis, though rare, is the predominant type. No large 
 masses of coral are, however, found. The platform is divided into 
 erosion, corrosion, seaweed and Lithothamnion zones, while trans- 
 verse channels are numerous, deep and long. 
 
 From the platform surface rise the islands built by the calcare- 
 ous debris derived from the destruction of the corals and nulli- 
 pores and the old reef rock. As might be expected, the islets are 
 most abundant on the windward side of the atoll, where by far the 
 greatest part of the rim is covered by them, while on the leeward 
 side they are few and much smaller. The leeward islets consist of 
 
396 PRINCIPLES OF STRATIGRAPHY 
 
 the debris of the reef organisms with plentiful Halimeda sands, but 
 the windward islets are largely composed of the material torn from 
 the reef platform, and sand is scarce. 
 
 In places where the islets are absent, the leeward rim passes 
 gradually from an area covered by living organisms nearest the 
 ocean into a central portion of perfectly bare and smooth Litho- 
 thamnion rock. Thence to the edge next to the lagoon the condi- 
 tions of the ocean face of the reef repeat themselves, but on a 
 smaller scale. 
 
 On the lagoonward slopes sands abound, consisting either wholly 
 of Halimeda fragments or of these mixed with Foraminifera and 
 shell fragments. On the seaward side the platform generally ends 
 in a cliff or vertical wall, one or two fathoms deep, beyond which 
 the general submarine slope of the atoll begins. 
 
 Structure of Coral Reefs. 
 
 In most modern coral reefs it is found that the lens-shaped clus- 
 ters of growing corals or reef mounds are scattered over the foun- 
 dation platform "like tufts of vegetation in a sandy plain" (Dana- 
 20: 174), and that they are surrounded and connected by coral sand 
 resulting from the destruction of the reefs by the waves and by 
 organisms. The individual reef mound generally rises as an iso- 
 lated lens-like mass above the sea bottom to near the surface of the 
 water, and is composed of coral heads and branching forms, between 
 which coral sand and shells and shell fragments of molluscs, echino- 
 derms and other organisms accumulate. The form varies from a 
 shallow lens, which is almost a layer, to that with lateral slopes as 
 high as 45 degrees or over. A peculiar variety known as "cha- 
 peiros" were described by Professor Hartt (46: ipi, ipp-^oo) from 
 the coast of Brazil. These grow in small, scattered patches, "and, 
 without spreading much, often rise to the height of forty to fifty 
 feet or more, like towers, and sometimes attain the level of low wa- 
 ter ... at the top they are usually very irregular, and some- 
 times spread like mushrooms or ... umbrellas. Some of these 
 chapeiros are only a few feet in diameter." They grow thickly 
 scattered over considerable areas in those waters. According to 
 Dana, "the rock of these submerged coral heads is but a loose ag- 
 gregation of coral in the position of growth, except possibly in their 
 lower portion, where the open spaces may be filled with sand and 
 fragments cemented together." 
 
 Except where reefs rise from great oceanic depths, their sub- 
 
STRUCTURE OF CORAL REEF 397 
 
 merged slopes are generally low, frequently falling much below 10 
 degrees. This is particularly the case in the Bermudas, where the 
 slopes are very gentle. The following are given for Hamilton 
 Island in this group. (Dietrich, quoted by Walther-o/D : 905. ) 
 Westward the shallow reef extends for 19.4 kilometers, then for the 
 next 8.9 kilometers the slope averages 21 degrees 50 minutes, carry- 
 ing the depth to 3,566 meters. Then for the next n kilometers it 
 rises again at an average angle of one degree 20 minutes to a 
 depth of 3,310 meters, falling again for the next 36 kilometers at an 
 average angle of 2 degrees 27 minutes to 4,846 meters in depth. On 
 the same island the slope to the south-southwest, after passing the 
 reef which extends for 4.3 kilometers, averages 3 degrees 22 min- 
 
 150 Yards 
 
 FIG. 78. Section of Keeling atoll, drawn from the outer coast at low water, 
 across one of the small islands to the lagoon. A Level of the sea 
 at low water. At A the depth is 25 fathoms, and the distance 
 rather more than 150 yards from the edge of the reef. B Outer 
 edge of flat part of reef, which dries at low water ; the edge either 
 consists of a convex mound, as represented, or of rugged points, 
 like those a little farther seaward, beneath the water. C A flat 
 coral rock covered at high tide. D A low projecting ledge of 
 brecciated coral rock washed by the waves at high water. E A 
 slope of loose fragments, reached by the sea only during gales; 
 the upper part, which is from six to twelve feet high, is clothed 
 with vegetation. The surface of the islet gently slopes to the 
 lagoon. F Level of the lagoon at low water. (After Darwin.) 
 
 utes for a distance of 20.5 kilometers, carrying the depth to 1,234 
 meters. Then it rises again at an angle of 3 8' for the next 5.5 
 kilometers until the depth is only 933 m. Following this a slope of 
 3 55' for 8 km. carries the depth again to 1,481 meters, beyond 
 which for the next 26.7 km. the average angle increases to 4 9', 
 carrying the depth to 3,420 meters. Southward after passing the 
 reef (2-9 km. from shore), the margin of the reef falls at an angle 
 of 8 n' to a depth of 3,328 meters, which is reached 23.1 km. 
 from the edge of the reef. On the north side of David Island the 
 reef extends for 15.35 km., then falls at an angle of 10 8' to a 
 depth of 2,798 meters, reached at a distance of 15.65 km. from the 
 edge of the reef. On the Bermudas the angle of slope of the edge 
 of the reef varies from 3 22' toward the S.S.W. to 8 11' toward 
 the S., 10 8' to the north and 21 50' to the west. 
 
398 PRINCIPLES OF STRATIGRAPHY 
 
 Of 41 slopes determined on the Bahama Islands the lowest is 
 o and the highest 28 18'. Seventy-five per cent, of the slopes are 
 below 10, while one-third of the entire number of determined 
 slopes falls below 5. 
 
 On Keeling Island, on the other hand, only a few slopes fall be- 
 low 10. Nearly half the number of slopes recorded by Dietrich 
 lie between 30 and 43 degrees, one being as high as 63 21'. 
 
 A section made by Darwin on this reef showed that "the water 
 deepens for a space between one and two hundred yards wide, very 
 gradually to 25 fathoms (45.72 meters), beyond which the sides 
 plunge into the unfathomable ocean at an angle of 45. To the 
 depth of ten or twelve fathoms (18-22 meters) the bottom is ex- 
 ceedingly rugged, and seems formed of great masses of living coral 
 similar to those on the margin." (Darwin-2i : 22.) The corals 
 and Hydrozoa growing here were Millepora alcicornis, Madrepora 
 cf . corymbosa, Porites and Astneans. The madrepore was not found 
 in the shallow part of the reef nor in the lagoon, and this and the 
 Astraeans seem to be restricted to the outer slope. Below 12 
 fathoms and especially at a depth greater than 20 fathoms, the bot- 
 tom was covered with coral sand, while at 200 to 300 fathoms, and 
 even at 360 fathoms, the floor consisted of finely triturated frag- 
 ments of stony zoophytes, particles of the lamelliform genera not 
 being recognized, while shell fragments were rare. (Fig. 78.) 
 
 At a distance of 2,200 yards from the breakers, no bottom was 
 found with a line 7,200 feet in length, hence the submarine slope 
 of this coral island is steeper than that of any volcanic cone. (Dar- 
 win.) Submarine cliffs are also indicated. 
 
 In the shallow part of the reef Porites in places forms nearly 
 the entire floor in great, irregular, rounded masses from four to 
 eight feet broad and little less in thickness. These mounds are sep- 
 arated from each other by narrow, crooked channels about six feet 
 deep, generally intersecting the reef at right angles. On the upper 
 surface of these masses the polyps were often dead, but growth oc- 
 curred around the margin. This was due to the exposure of these 
 corals at lowest tides, the upward limit of growth having been 
 reached. Further seaward the entire mass was alive. The same 
 is true of the Millepora. Closely within the line marked by these 
 partly dead polyps, and thus above the zone of coral growth, flourish 
 three species of nullipores, one thin like a lichen, one with stony 
 knobs as thick as a man's finger, and one moss-like, with thin, rigid 
 branches. These also require the breakers, for they do not exist in 
 any abundance in the protected hollows in the back part of the reef. 
 They thus form only a fringe about 20 yards in width, but located 
 
STRUCTURE OF CORAL REEF 399 
 
 where they form an effective protection against the breakers. They 
 form an artificial breakwater rising about 3 feet higher than the 
 rest of the reef. This is a very common occurrence in modern 
 reefs. Steep slopes are found around many modern atolls, and it 
 appears that where the currents run with greatest force near the 
 reef the slopes are steeper. In the Maldive and Chagos atolls such 
 steep slopes are common. At Heawandoo Pholo 50 and 60 fathoms 
 were found close to the edge of the reef, and at 300 yards' dis- 
 tance no bottom was obtained with a 3OO-yard line. On Egmont 
 Island a slope of 45 was found, while the slopes on the Cardoo 
 atoll were so great that no bottom was obtained with a line 200 
 fathoms long at only sixty yards from the reef. 
 
 The general character of the slopes on the Low Archipelago 
 closely corresponds to that found on the Keeling atoll, the slope a 
 short distance beyond the edge of the reef being 45. In some 
 cases, however, the slope is that of a vertical cliff. Perpendicular 
 or even overhanging cliffs are, however, also found in the quiet 
 water of the lagoon, while in other cases, where the water is gen- 
 erally tranquil, though not always so, as on the leeward side of 
 Mauritius, the slope is a very gentle one. 
 
 The shores of the lagoons within the atolls also vary greatly. 
 At Keeling atoll (Fig. 78) they shelve gradually where the bottom 
 is of sediment, and irregularly or abruptly where there are coral 
 reefs. In the Marshall group, on the other hand, the slope is often 
 abrupt so that we pas's directly "from a depth of two or three 
 fathoms to twenty or twenty-four, and you may pursue a line in 
 which on one side of the boat you may see bottom, and on the other 
 the azure blue deep water." (Chamisso, quoted by Darwin 21.) 
 In the Matilda atoll of the Low Archipelago the surface of the great 
 exterior reef slopes gently toward and beneath the surface of the 
 lagoon, and then ends abruptly in a little cliff 3 fathoms deep. At 
 its foot a ledge forty yards wide extends, shelving gently inward 
 like the surface reef, and is terminated by a second little cliff 5 
 fathoms deep, beyond which the bottom of the lagoon slopes off 
 to twenty fathoms, its average central depth. The ledges appear 
 to be formed of coral rock, often porous, so that the sounding lead 
 descends several fathoms through holes in them. Some lagoons, 
 on the other hand, have gentle slopes to the center. 
 
 Sections made by Captain Maclear, R. N., of the small island 
 of Masamarhu in the Red Sea show not only the nature of the 
 slopes of a coral island, but also give indisputable proof of sub- 
 sidence since the commencement of the growth. "In each case the 
 surface of the fringing reef, after shelving very gently downward 
 
400 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 to a depth of about three or four fathoms, is bounded by a sub- 
 marine cliff. This in one section (No. i) continues almost un- 
 broken to a depth of about 500 feet, except that a kind of edge or 
 terrace is clearly indicated at a depth of rather less than 100 feet. 
 In the other section the foot of the great submarine cliff is 
 found at about 500 feet, but . . . the cliff is distinctly divided into 
 two precipices by a shelving bank of coral and sand, which begins at 
 a depth of about 140 feet and reaches the brow of the lower preci- 
 pice at about 260 feet. This bank is covered by 'sand and coral.' At 
 
 No. I. 
 
 Soalt of feet 
 
 Is/ant 
 
 FIG. 79. Section i of Masamarhu Island in the Red Sea, showing the char- 
 acters of the slopes according to Captain Maclear. (After Saville- 
 Kent.) 
 
 this depth in each section the island is, as it were, defended by a 
 deep and narrow ditch, the edge of its steep glacis being formed by 
 a sharp arete of coral which in one case rises into soundings of 
 about 250 feet." (Bonney-i3.) From this the first section rapidly 
 falls to a second ditch, the bottom of which is more than 1,200 feet 
 below sea-level, while its counterscarp rises more than 300 feet. 
 Beyond this, after a level stretch, the slope descends at about 30 
 degrees. The second ditch is wanting in the second section. Coral 
 and sand are found in the bottom of the ditches, and the two 
 aretes are formed by coral apparently grown in situ. This would 
 
STRUCTURE OF CORAL REEFS 
 
 401 
 
 indicate subsidence from about 25 fathoms to the present depth of 
 these points. (Figs. 79, 80.) 
 
 Cavernous character of reefs. Observation on modern reef 
 knolls shows that the mass as a whole is often cavernous, large, 
 empty spaces remaining where branching corals reach across to 
 form a solid canopy. These caverns are the favorite haunts of the 
 echinoderms, Mollusca and Crustacea which inhabit the reefs, and 
 through the openings by which they communicate with the open sea 
 the pelagic fish of the reefs find constant in- and egress. Such 
 
 No. II. 
 
 FIG. 
 
 SKETCH 01 MA&AMARHU I 
 
 Shan" nf approtimate 
 
 ositioner Sectifas ' 
 
 Section 2 of Masamarhu Island in the Red Sea. The small map 
 shows the location of the sections. (After Saville-Kent.) 
 
 caverns may be preserved after the coral rock is uplifted into dry 
 land, and Walther (90:91,?) has argued for such an initial origin of 
 many limestone caverns in earlier geological formations. 
 
 In general the structure and form of barrier reefs around 
 oceanic islands differ in no essential from those of the atolls, so that 
 the designation of such a barrier as an atoll with high land rising 
 within the lagoon (Balbi) is quite applicable. Such are the reefs 
 of Tahiti and others in the Society Archipelago, of Vanikoro and 
 of others. The distance from shore of the reef is from one to one 
 and a half, and occasionally even more than three miles, in the 
 Society Archipelago (Ellis). In the few cases where encircled 
 highlands exist in the Caroline Archipelago greater distances are ob- 
 
402 PRINCIPLES OF STRATIGRAPHY 
 
 served. Thus on the south side of Hogoleu this is no less than 20 
 miles, 6 miles on the east and 14 miles on the south. 
 
 The central mountains in the Society and other groups are gen- 
 erally bordered by a fringe of flat and often marshy, alluvial land, 
 from one to four miles in width, and consisting of coral sand and 
 detritus thrown up from the lagoon channel, and of soil washed 
 down from the hills. These island hills vary greatly in height and 
 character. At Tahiti the height is 7,000 feet, though the maximum 
 diameter of the reef is only thirty-six miles. At Maurua the cen- 
 tral peak is about 800 feet high, and the maximum diameter only 
 a little more than two miles. In other cases it is much lower; at 
 Manouai only 50 feet. In most cases the rock is that of an old 
 volcano, while in some cases it is old crystalline rock and in others 
 raised coral reef rock. The number of peaks varies from one to 
 nearly a dozen (Hogoleu). 
 
 What has been said of barrier reefs around oceanic islands also 
 applies to the fringing reefs of such islands. These differ from the 
 encircling barriers only in the narrowness of the dividing water 
 channel or moat. Thus on the western side of Mauritius the reef 
 generally lies at a distance of about half a mile from the shore, 
 though in some parts it is distant from one to two and even three 
 miles. In general, the fringing reef rests on the gently sloping sub- 
 merged portion of the island mass, which in most cases does not de- 
 scend, within the limits of the reef, to depths greater than those at 
 which coral polyps flourish. Where such a greater depth exists it is 
 to be accounted for either by progressive subsidence and upbuilding 
 of the reef, or by outward growth upon a basis of coral detritus, 
 which forms a talus in front of the growing reef. Fringing reefs 
 are breached by passages in front of every river and streamlet 
 which descends from the enclosed land. Such breaches are found 
 in barrier reefs only in front of the larger streams where the width 
 of the lagoon channel is not too great. The width of the reef varies 
 with the inclination of the substratum. 
 
 Characters of Epicontinental Reefs. Reefs resting for the main 
 part upon the continental shelf or its margin are found to-day in 
 the western portions of the three oceans covering the tropical belt, 
 namely, the Pacific, Indian and Atlantic. The largest and most char- 
 acteristic are those of the western Pacific, the Great Barrier Reef 
 of Australia occupying the first place among these. This, as already 
 noted, extends with a few interruptions for about a thousand miles ; 
 its average distance from the land is between twenty and thirty 
 miles, while in some parts this distance increases to between fifty 
 and seventy miles. It encloses a great lagoon strip which varies in 
 
EPICONTINENTAL REEFS 403 
 
 depth from ten to twenty-five fathoms, and has a sandy bottom. 
 Southward, where the reef increases in distance from the shore, 
 the depth of the lagoon increases to forty and in some places more 
 than sixty fathoms. Just outside of the reef the water descends 
 to profound depths. 
 
 The surface of the reef consists of a hard, white agglomerate of 
 many kinds of corals with numerous projecting points. The outer 
 rim is highest, and is traversed by narrow gullies, and is breached 
 at rare intervals by ship canals. 
 
 In form the Great Barrier Reef is a triangular wedge, widening 
 gradually from the shore outward for a distance of from 30 to 90 
 miles. Just outside of the reef the descent to abyssal depths is 
 abrupt, the outer face of the reef forming a great wall in some cases 
 exceeding 1,800 feet in height, and fronting the whole northeast 
 coast of Australia. Along the outer edge of the platform produced 
 by the reefs is the true barrier, a linear series of reefs breached by 
 narrow passages. Inside the barrier is a clear and broad channel 
 generally from 15 to 20 fathoms deep, with its bottom covered by 
 unconsolidated lime sand or by a sand largely composed of the 
 foraminiferan Orbitolites, these remains in some cases also making 
 up the whole sand of the beach either of the coral islets or the neigh- 
 boring shores. Outside, in the deep sea, the dredge obtained only 
 a fine-grained, impalpable, pale, olive-green mud, which was wholly 
 soluble in dilute hydrochloric acid, and when dried had the charac- 
 ter and consistency of chalk. 
 
 Great masses of Porites and Maeandrina flourish on the outer 
 border of the reef, and these when detached from their anchorage 
 are rolled about by the waves and worn, while at the same time 
 grinding down the rock mass beneath until the whole coral head is 
 reduced to fine sand or mud. Such rounded detached masses of 
 Mseandrina 6 or 8 feet in diameter are common among the loose 
 blocks rolled up from the outer slope onto the reef. They may be 
 seen just inside the surf at low water, extending for some miles, 
 and are known as "Turks' heads." Madrepora, Millepora and 
 other genera also characterize the outer reef together with numer- 
 ous species of astrseans. Inside the channel mentioned lie the "in- 
 ner reefs" separated from each other by narrow waterways through 
 which the tide rushes with great force. Sometimes these tidal cur- 
 rents continue in the same direction even for two or three days, es- 
 pecially after great storms have driven Jarge volumes of water into 
 the reef area. Between the inner reefs and the mainland of old rock 
 lies a shallow channel, mostly free from coral growth. 
 
 Among the inner reefs are many, which are to a large extent 
 
404 PRINCIPLES OF STRATIGRAPHY 
 
 composed of one type of coral. Thus on the Organ Pipe Reef of 
 Thursday Island Tubipora musica predominates, while another reef 
 of this island is largely composed of the blue Heliopora coerulea. 
 Other important contributors to the Great Barrier Reef material 
 are Euphyllia, Galaxea, Mussa, Trachyphyllia, Symphyllia, Gonias- 
 traea, Prionastnea, Favia, Fungia, etc. ; none of these are, however, 
 as important as are the various species of Porites and Madrepora. 
 The hydrocorallines, Millepora and the red Distichopora also add 
 materially to the lime of the great series of reefs. 
 
 The reefs on the eastern coast of Africa are of the fringing 
 type, extending for a distance of nearly forty miles, from lat. i 
 15' to i 45' S., and with an average distance from shore of some- 
 what more than a mile. The depth of the lagoon is very slight, and 
 this continues for some distance outside of the reef, where it is only 
 from 8 to 14 fathoms at a distance of a mile and a half from the 
 reef. The external margin of the reef is formed of projecting 
 points, within which there is a space from 6 to 12 feet deep with 
 patches of living coral on it. At Mombas (lat. 4 S.) a reef fringes 
 the coast for thirty-six miles, at a distance of from half a mile to 
 one mile and a quarter from the shore. The channel within this 
 reef, ranging in depth from 6 to 15 feet, is navigable for canoes 
 and small craft. Outside of the reef the depth is about 30 fathoms 
 at a distance of nearly half a mile. Part of this reef is very sym- 
 metrical, with a uniform breadth of 200 yards (Darwin-2i). 
 
 The reefs of the Florida coast form an interesting example of 
 the fringing type on a shallow continental platform. The southern 
 coast of Florida rises from 12 to 15 feet above the sea-level, in the 
 form of a curving ridge, which encloses an extensive fresh-water 
 swamp, the Everglades. The surface of this lies only two or three 
 feet above sea-level, and is dotted over with small islands, the so- 
 called hummocks. Some distance outside of the southern border 
 of the land lies a row of small islands or "keys" of dead coral 
 rock and sand, ranging from 5 to 30 miles distant from shore and 
 continued westward in a curved line far beyond the western coast 
 of the peninsula. The islands are low and of limited extent, that of 
 Key West near the western end of the line being less than 4 miles 
 long, while the longest of the islands is only 15 miles in length. 
 The keys slope toward their northern shore, and present a steep 
 face to the south, where they are separated from the living reefs 
 by an open channel. Between the keys and the southern coast of 
 the mainland the water is very shallow and navigable only to the 
 smallest boats. This lagoon is, moreover, dotted with small, low 
 mangrove islands. The mangrove trees growing here extend their 
 
FLORIDA REEFS 
 
 405 
 
 aerial roots in all directions, forming a tangle, which becomes effi- 
 cient in checking sediment-laden currents and causes them to de- 
 
 FIG. 81. Map of Florida, showing the keys and reefs. (After Le Conte.) a 
 Southern coast; a' keys; a" living reef; d-d' older coral rock; 
 e everglades; e' shoal water; e" ship channel; GSS Gulf 
 Stream. 
 
 posit their load. Hence the inner lagoon will gradually silt up, and 
 this has already progressed so far that a considerable portion of the 
 area forms mud flats at low tide. (Figs. 81, 82.) Here, then, a 
 
 FIG. 82. Diagrammatic section of Florida along the line N.S. in the preceding 
 figure, showing the relative position of the various parts, lettering 
 the same. The dotted lines indicate hypothetical former condi- 
 tions. (After Le Conte.) 
 
406 PRINCIPLES OF STRATIGRAPHY 
 
 clastic mud sediment rich in organic matter rests directly upon the 
 ancient coral reef now represented by the keys, a relationship ex- 
 pressed in the rocks of the older geological periods by the super- 
 position of a black carbonaceous shale above an earlier coral lime- 
 stone. * 
 
 Outside of the line of keys and from 3 to 15 miles distant from 
 it is a line of living coral reefs, consisting of mounds made up of 
 branching madrepores, Porites, etc., besides many smaller genera 
 such as Manicina, Agaricia, etc. Corallina and Lithothamnion also 
 add a large percentage of calcareous material to the reef. 
 
 These reefs are for the most part submerged, rising only here 
 and there to the surface. Between them and the keys lies the outer 
 lagoon, a long, narrow channel five to six fathoms deep and naviga- 
 ble for small vessels. Here the sedimentation consists of coral 
 sand and of the shells of marine organisms, thus producing a nor- 
 mal marine limestone, which is either in the form of a coral breccia 
 or a more or less oolitic calcarenyte. Outside the living reef, the 
 bottom rapidly descends to the abyssal depths of the Florida Straits 
 (2,916 feet). 
 
 While nullipores, or the stony algae, luxuriate in the outer zone 
 of the reef, where they form a distinct Nullipore zone in the face 
 of the strong surf, the more delicate branching and brittle corallines 
 are confined to the channels and lagoons within the reef, where 
 they often form thick carpets in the quiet water. Thus the shallow 
 parts of the bottom of the ship channel between the living Florida 
 reefs and the old reefs or keys are covered with the so-called "coun- 
 try grass," one of these calcareous algae. This is especially notice- 
 able between Fowey Rocks, Triumph Reef and Long Reef on the 
 one side, and Soldier Key and Ragged Keys on the inside ( Agassiz- 
 2 : 126, 127) . The floor of Hawk Channel, which has a depth of 
 from 6 to 7 fathoms, is covered with disintegrated corals and coral- 
 lines (Pourtales; Dana-2O :<?//), while some of the keys in the Dry 
 Tortugas and Marquesas are wholly composed of fragments of 
 corallines bound together into a solid mass. Among these coral- 
 lines a large species of Opuntia is especially noticeable. 
 
 It has been shown by Agassiz that the keys, the southern rim 
 of the mainland, and a strip including the north shore of the Ever- 
 glades and extending as far north on the eastern shore as St. Au- 
 gustine, are of coral-reef origin. When this last strip was the living 
 reef, the platform in front was being built out into the sea by the 
 accumulations of the shells of organisms which lived in abundance 
 in the genial waters of the Gulf Stream border. When the platform 
 was sufficiently extended a new line of reefs came into existence, 
 
THEORIES OF ORIGIN OF REEFS 407 
 
 forming a barrier reef at a distance from shore where now lies the 
 outer rim of the Florida mainland. The lagoon behind this new 
 reef was of the character of the present outer lagoon, and received 
 normal marine sediments, until with progressive upbuilding the 
 outer reef was converted into a series of dead keys and a new line 
 of reefs came into existence upon the meanwhile extended sub- 
 marine platform. This new line was subsequently converted into 
 the present line of keys, the preceding row became the southern 
 coastal rim, and the old lagoon behind it was converted by suc- 
 cessive steps into the present Everglades. The present inner lagoon 
 channel between the mainland and the keys is gradually approach- 
 ing the same fate, and it and the line of keys will in turn be added 
 to the mainland, while the present living reef will gradually emerge 
 as a line of islands and the lagoon behind it suffer filling up. It is 
 not likely that a new line of reefs will form outside of the present 
 one, as the force of the Gulf Stream will prevent further extension 
 on the Pourtales Plateau of the submarine platform which serves as 
 the foundation of the reef.. (Le Conte-59; 60.) 
 
 It is to be noted that as the building of the new reef progresses, 
 leading to the extinction of the preceding inner reef, a new type 
 of sedimentation the mud-flat type will come into existence be- 
 hind the older reef, while contemporary calcareous deposits will 
 accumulate in the outer lagoon and on the reef. Thus the top of 
 the limestone series formed by these shell accumulations and reefs 
 will rise progressively seaward, while mud-flat and later continental 
 conditions will progressively replace the marine conditions from 
 the landward side outward. Precisely such conditions existed in the 
 Onondaga (Middle Devonic) period of New York and Pennsyl- 
 vania, where the coral- forming conditions progressed toward the 
 northwest, while the black Marcellus muds replaced them on the 
 south and east. 
 
 THEORIES OF ORIGIN OF TYPES OF CORAL REEFS. Of all the 
 reef types, the fringing reef alone requires no special explanation 
 of origin, since here the corals grow in shallow water under normal 
 conditions of habitat. All continental or island shores in the tropics, 
 in which the submarine slope is a moderate one, are suitable for 
 coral reef development, provided mechanical detritus is absent or of 
 negligible amount and the other necessary conditions, clearness and 
 saltiness of the sea, absence of large streams, sufficient wave activi- 
 ties, absence of cooling currents, sufficiency of food supply, etc., 
 concur. Corals will grow under such conditions out to the zone of 
 depth limit (20-25 fathoms). Where the submerged platform on 
 which the corals grow is increased in. extent seaward by the accumu- 
 
408 PRINCIPLES OF STRATIGRAPHY 
 
 lation of organic or other debris, as in the case of the Florida 
 region, coral reefs may progressively develop seaward in what was 
 originally water of too great a depth for normal coral growth. 
 
 Oceanic barrier reefs and atolls, on the other hand, rise from 
 depths greater than those at which reef corals flourish, and so these 
 types need further explanation. Two principal theories have been 
 proposed for their explanation: the subsidence theory of Darwin, 
 elaborated and strengthened by Dana, and the spreading ring theory 
 proposed by Murray and elaborated by Alexander Agassiz. 
 
 Subsidence Theory of Darzvin. Fringing reefs surrounding 
 oceanic islands may be progressively converted into barrier reefs 
 and finally into atolls by a constant subsidence sufficiently slow to 
 permit the reef corals to grow upward and maintain themselves in 
 a relatively uniform depth within the normal limit. By such a sub- 
 sidence the older dead coral masses are carried constantly to lower 
 depths, while the top of the reef flourishing on this foundation 
 of dead coral constantly keeps near to the surface of the sea. The 
 channel between the reef and the rock island will become wider as 
 more of this island is submerged, while at the same time it becomes 
 filled by the coral sand, and broken coral masses thrown over the 
 reef and the land-derived detritus supplied by the streams from 
 within. Growing nullipores and other organisms will likewise help 
 in filling the constantly widening lagoon. When subsidence has pro- 
 gressed so far that the central land mass has become entirely sub- 
 merged, the barrier reef has changed to the atoll and the ring lagoon 
 to the open lake-like body of water within the ring of coral reefs 
 and islets. 
 
 This explanation readily accounts for the observed gradation be- 
 tween the fringing reefs and atolls noted in the islands of the Pa- 
 cific, where every stage seems to be represented. It accounts for the 
 steep slopes and the occasional cliffs of the outside of the reef 
 which descend to abysmal depths, as well as the occurrence of dead 
 reef corals at depths where they cannot live corals which have 
 been carried by subsidence of their foundation beyond their normal 
 depth and drowned. This theory accounts also in a satisfactory way 
 for the remarkable distribution of the various kinds of reefs in the 
 Pacific, as shown by Dana. In the middle of the atoll area of the 
 Pacific there is an extensive area 2,000 miles long by 1,000 miles 
 wide free from islands. This is roughly surrounded by a belt of 
 small atolls, outside of which occurs the region of large or grouped 
 atolls, then a belt in which the reefs are mostly barriers and finally 
 the belt of fringing reefs. This distribution is of course to be 
 traced only in a general way. Outside of the last belt there is even 
 
THEORIES OF ORIGIN OF REEFS 409 
 
 some evidence of elevation. The subsidence theory accounts for 
 this distribution by assuming that the central area has gone down 
 so fast that the corals, could not gain a foothold or were drowned 
 out completely. The small atolls show a rapid and great sub- 
 mergence, but not sufficient to prevent coral growth entirely, the 
 upward growth barely keeping pace with the subsidence, and with 
 no opportunity for spreading. The successive belts show the de- 
 crease in the amount of subsidence, so that we ,pass progressively 
 from large atolls to barrier reefs and finally to fringing reefs, where 
 the zone of no subsidence is reached, beyond which the movement 
 seems to have been in the opposite direction and dead, fringing 
 reefs cling to the sides of high islands often at a considerable ele- 
 vation above the present sea-level. 
 
 Evidence of subsidence. The most convincing proof of the cor- 
 rectness of this theory for the explanation of at least some of the 
 coral reefs of the Pacific is furnished by the deep boring on the 
 atoll of Funafuti, which showed organic limestone consisting of 
 corals, Foraminifera, calcareous algae and other organisms to a 
 depth of 1,114 feet, the extent of the boring. The boring made in 
 the lagoon showed the existence of solid masses of shallow-water 
 corals (Porites, Madrepora, Heliopora) at a depth of 245 feet un- 
 der a layer of calcareous algae (Halimeda opuntia) and Forami- 
 nifera, more than a hundred feet thick. Other evidence of sub- 
 sidence is furnished by sacred structures erected by the natives on 
 certain coral islands. These now stand in the water, and the paths 
 worn by the feet of the devotees are at present passages for ca- 
 noes. (Dana-2O.) 
 
 Davis has recently shown (23) that Dana furnished con- 
 vincing proof of the theory of subsidence in the region of some 
 coral atolls. This lies in the fjord-like bays which indent much 
 eroded mountain islands, around which coral reefs grow. If no 
 subsidence has taken place, these valleys would be more or less 
 filled by alluvial deposits, since clastic material is constantly brought 
 into the sea by the wash from the mountain. Where, however, the 
 valleys are unobstructed embayments, and continue as such under the 
 water, the evidence of progressive subsidence with corresponding en- 
 croachment of the sea up the valleys seems clear. As Dana says : 
 "The very features of the land, the deep indentations, are sufficient 
 evidence of subsidence to one who has studied the character of the 
 Pacific islands." And, again : "When ... we find the several val- 
 leys continued on beneath the sea, and their enclosing ridges stand- 
 ing out in long, narrow points, there is reason to expect that the land 
 has subsided after the formation of the valleys. For such an island 
 
4io 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 as Tahiti could not subside even a few scores of feet without chang- 
 ing the even outline into one of deep coves or bays, the ridges pro- 
 jecting out to sea on every side. . . . The absence of such coves, 
 on the contrary, is evidence that any subsidence which has taken 
 place has been comparatively small in amount." (Davis-23 : i#j.) 
 The following diagram (Fig. 83), illustrating this principle, is 
 copied from Davis. 
 
 The Spreading .Ring Theory of Murray. Sir John Murray's 
 theory of coral reef formation is an elaboration of the early expla- 
 nation of the forms of coral reefs propounded by the poet-natu- 
 
 FIG. 83. Block diagram illustrating the effects of subsidence of a much dis- 
 sected island around the borders of which grow coral reefs. The 
 effect of subsidence is produced by adding to the surface of each 
 successive block an amount equal to the postulated -subsidence. 
 The deep embayments in^the middle block, from which terrigenous 
 sediment is absent, can be produced only by subsidence. (After 
 Davis.) 
 
 ralist Adalbert von Chamisso. It is based on the existence of sub- 
 marine banks of volcanic or other origin, rising to within a moderate 
 depth beneath the surface of the sea. The existence of such banks 
 has been abundantly shown by soundings of the Challenger and 
 other exploring expeditions. Such submerged surfaces afford a 
 habitat for lime-secreting organisms, such as deep-sea corals, echino- 
 derms, molluscs, crustaceans, etc., and their shells and skeletons will 
 gradually raise the surface of the submerged bank until it comes 
 within the zone of reef-coral growth. As pointed out by Chamisso, 
 the corals on the outer side of a growing mass are situated most 
 favorably with regard to wave activity, food supply, etc., and so the 
 reef will rise to the surface as an atoll. The nearer it approaches 
 the surface, the more unfavorable will become the atoll for the 
 
THEORIES OF ORIGIN OF REEFS * 411 
 
 growth of corals, and these eventually die out on the interior, while 
 they continue to flourish vigorously on the exterior of the atoll. By 
 the accumulation of coral debris on the outer slope of the reef a 
 foundation is formed for the spreading of the coral ring, as in the 
 case of the Florida reefs, and so the diameter of the atoll increases, 
 while at the same time the solvent action of the water in the lagoon 
 and the scouring action of the tide will enlarge the area of the en- 
 closed water body. It may, however, be questioned if the great 
 depth of some lagoons, 40 to 50 fathoms, can be accounted for in 
 this way, especially as in many cases the tendency is to fill up the 
 lagoon by nullipore growth and accumulation of debris. 
 
 That such an origin must be accepted for certain atoll reefs is 
 shown by the observations of Guppy (41) on certain uplifted 
 islands of the Solomon group. On Ugi, Santa Anna, Treasury and 
 Stirling islands, he found unmistakable evidence of a nucleus of 
 volcanic rock, which was covered by an earthy, stratified deposit of 
 mixed foraminiferal and volcanic material similar to the deep-sea 
 muds, several hundred feet thick, and highly fossiliferous, contain- 
 ing the remains of pteropods, pelecypods and echinoderms. On the 
 flanks of these elevated beds are found deposits of coralline lime- 
 stone varying from 16 to 100 feet in thickness, and representing the 
 reef deposits now elevated above the sea-level. Santa Anna has the 
 form of an uplifted lagoon, the coral rock 80 feet in thickness and 
 resting on a friable, somewhat argillaceous rock resembling a deep- 
 sea deposit.' Here we have, then, a clear example of reefs growing 
 on a platform, built up of foreign material, and similar features are 
 shown on the Fiji Islands and the Great Barrier Reef, and on the 
 reefs of the Bahamas, Florida and the Bermudas in the West At- 
 lantic. All of these areas show either stationary conditions or 
 actual evidence of recent elevation. 
 
 Multiple Origin of Reefs. On the whole, the subsidence theory 
 seems to be applicable to many, though far from all, oceanic reefs, 
 where at the same time spreading of the coral ring by outward 
 growth may have cooperated. Epicontinental reefs, on the other 
 hand, or those forming on the margins of the continents and around 
 continental islands, are probably in all cases to be explained by 
 growth on suitable foundations, without subsidence, the reef ex- 
 panding as the platform on which it grows expands. Such an ori- 
 gin is almost certain for the Great Barrier Reef of Australia, and 
 for the Florida reefs, and such an origin is to be postulated for 
 most of the older reefs, which all or nearly all belong to the epi- 
 continental type. 
 
 RATE OF GROWTH OF REEF ORGANISMS. Comparatively little is 
 
4 i2 PRINCIPLES OF STRATIGRAPHY 
 
 known regarding the rate of growth of the organisms forming the 
 reefs. Experiments and observations on Funafuti reef organisms 
 showed that the lichenous forms of Lithothamnion grow very 
 slowly, no appreciable increase in size occurring in five months. 
 When, however, the alga was killed by too long exposure to the 
 sun at low tide, turning white as a result, a resubmergence caused 
 the pink color to reappear in a few days by the spreading from a 
 center where some cells still remained alive. Halimeda, however, 
 the alga producing the greatest amount of calcareous debris, grows 
 more rapidly, a cluster 3 inches in height and of equal thickness, 
 and weighing 14.38 grains after it was dried, growing in a period 
 of six weeks. 
 
 The rate of increase of Millepora on Funafuti was found to be 
 16.5 per cent, per annum for the massive M. complanata, while the 
 branching M. alcicornis showed an average increase in size of I 
 inch in 34.7 weeks. The latter species also covers objects entangled 
 in its mass, and fragments of Halimeda and other corallines may 
 thus be enclosed. Of the corals, Porites limosa was found to in- 
 crease in weight at the regular rate of 47.27 per cent, per annum. 
 The encrusting coral Hydnophora microcona was found to spread 
 at the rate of one inch in 39 months. Astraopora ocellata, though 
 forming new calices between the old ones, showed no measurable 
 increase in size during the period of observation. Pocillopora 
 grandis increased in all directions at a rate of one inch in 13.5 
 weeks ; while small pieces of P. verrucosa were found to increase in 
 weight at the startling rate of 150 per cent, per annum. This, how- 
 ever, was partly due to the expansion of the living matter over the 
 broken surface, and the formation of new calices there, a feature not 
 normal under natural conditions. A similar large increase was 
 found for P . paucistellata. The mushroom coral Montipora in- 
 cognita showed a rate of growth in one direction of half an inch in 
 three months, and an average increase in three directions measured 
 one inch in 35.7 weeks. 
 
 An extensive growth of the coral Orbicella annularis took place 
 upon a bell olive jar and decanter recovered in 1857 f rom the wreck 
 of a vessel supposed to be the British frigate Severn, lost off Turk's 
 Island in the West Indies in 1793. These specimens are now pre- 
 served in the Museum of the Boston Society of Natural History. 
 (Crosby, 18:^09; Verrill-88.) During the 64 years of submerg- 
 ence Orbicella annularis attached to the bell spread out on all sides. 
 The thickness at the center is about 8 inches and the breadth 15. 
 The olive jar and glass decanter are cemented together by a similar 
 mass of the same species. The wreck lay in from three to ten 
 
RATE OF GROWTH OF REEF ORGANISMS 413 
 
 fathoms of water, and it was covered astern of the middle by thick- 
 branching Madrepora, the branches of which were twelve inches in 
 diameter and sixteen feet in height. This makes a rate of growth 
 for this coral of three inches per year. 
 
 Darwin cites some experiments made on the east coast of Mada- 
 gascar in December, 1830, by Dr. Allan, of Forres. Twenty corals 
 were weighed and placed apart on a sand bank in water 3 feet deep 
 at low tide, each of them reaching in the following July nearly to 
 the surface and being quite immovable, while some had grown over 
 the others. A block of concrete taken at Fort Jefferson, Tortugas, 
 and which had been in the water only twenty years, had a specimen 
 of Mceandrina labyrinthica growing on it, which measured a foot in 
 diameter and four inches thick in the most convex part. (Dana- 
 20: 124.) At Key West, a Mseandrina had grown to a radius of 
 six inches in twelve years. An Oculina diffusa planted as a germ 
 in this same region grew in 14 years to a height of four inches and 
 a breadth of 8 inches, while a M&andrina clivosa in the same time 
 reached a height of two and a quarter inches and a breadth of seven 
 and a half inches. 
 
 The rate of growth of coral reefs is, however, much slower than 
 the rate of growth of the corals and other organisms composing 
 them, since these grow only in isolated patches. Estimates on the 
 rate of increase in height of reefs allow two hundred years for every 
 foot of increase. 
 
 COMPACTING AGENTS OF CORAL REEFS. The isolated coral heads 
 of the reefs do not of themselves produce the solid limestone 
 masses characteristic of these structures, unless they are bound 
 together either by chemical precipitation of lime in the interstices 
 or by organic agencies. Qn Funafuti (74: 147) it is the lichenous 
 Lithothamnion which performs this office most effectively, cement- 
 ing the coral masses to each other and to the reef as a whole. 
 This nullipore will attack both living and dead corals and will cause 
 every interstice as well as every space between the branches, if 
 present, to be transformed into one solid mass. Thus the coral mass 
 will be permanently added to the reef, enlarging it by the amount 
 of its bulk when taken possession of by the Lithothamnion. Obser- 
 vations show that a coral once attacked by the nullipore will remain 
 stunted, and thus the amount of addition to the reef depends on 
 the period of growth reached by the coral when attacked by the 
 Lithothamnion. 
 
 On the Great Barrier Reef it was found that reef forming was 
 less a function of the species of coral than of the temperature, for 
 the same species forming solid reefs in the warmer portions of the 
 
4 i4 PRINCIPLES OF STRATIGRAPHY 
 
 reef-area remained unconsolidated in the southern part, where the 
 temperature was lower. 
 
 A characteristic feature of the closing stages of reef formation 
 at any locality seems to be the production of coarse oolitic sands. 
 Dana (20 '.156) points out that such oolitic beds "appear to be con- 
 fined to the superficial formation of a reef, that is, to the beach 
 and wind-drift accumulations." The same thing was shown by 
 Agassiz. 
 
 DESTRUCTION OF THE CORAL REEF. 
 
 Formation of Coral and Other Organic Lime Sand and Mud. 
 The agents at work destroying the reef rock are both inorganic and 
 organic. (74:140.) The most effective inorganic agent is the 
 surf which constantly beats against the outer edge of the reef. 
 Alone, however, it is of little effect, unless it succeeds in breaking 
 off branches of the corals, which may then be hurled up onto the 
 reef, or over it into the lagoon. Coral polyps seem to flourish best 
 
 FIG. 84. Organic limestone of corals, corallines, serpula tubes, echinoderm 
 fragments, etc. Pourtales plateau. (After A. Agassiz.) 
 
 where the surf is strongest, so that we have the anomaly of a rock 
 mass growing into the very teeth of one of the most powerful 
 agents of rock destruction. Wherever the surf encounters loose 
 blocks of stone, such as volcanic bombs, or coral heads torn from 
 their foundations, it at once assumes all of its force as an agent of 
 destruction, ior it will roll about these rock masses and so grind the 
 coral rock beneath them to powder. On the Florida reefs boulders 
 
DESTRUCTION OF CORAL REEFS 415 
 
 of coral occur formed from the heads of large maeandrinas and 
 astrseans torn by the waves from their anchorage and rolled about, 
 grinding down the rock beneath them and also being worn them- 
 selves. 
 
 Perhaps by far the largest contribution of coral sand and mud 
 is made by the activities of organisms. Darwin found that two 
 species of the Parrot fish (Scarus), "one inhabiting the surf outside 
 the reef and the other the lagoon, subsist entirely ... by browsing 
 on the living polypifers." (21.) On opening several of these fish, 
 he found their intestines distended by small pieces of coral and 
 finely ground calcareous matter, which must pass daily from them 
 as the finest sediment. On Funafuti, on the other hand, no evi- 
 dence of such destruction of coral rock by fish was found, though 
 they apparently fed to some extent on the Lithothamnion. In like 
 manner the reported destruction of' coral masses by holothurians 
 found no confirmation on Funafuti, where these echinoderms live 
 wholly on the organic matter of the sand and mud. Worms, mol- 
 luscs and crustaceans, however, appear to be active destroyers of 
 coral rock, though at Funafuti the molluscs were found to live 
 among the coral masses without interfering with them. On these 
 reefs, however, the Lithothamnion rock was found riddled by 
 Gephyrean worms and an Aspidosiphon "from two to three inches 
 in length, but very thin, and possessing a long retractile proboscis, 
 by which it is seen at low tide to feed off the Lithothamnion-cov- 
 ered rock immediately surrounding its abode. ... A small piece 
 of reef rock, a few inches in diameter, when broken off, will show 
 as many as 10 or 15 of these animals." Echinoderms also dwell 
 in cavities which they have hollowed out of the reef rock, and 
 which, except for the recuperative growth of the Lithothamnion, 
 they would rapidly destroy. Among the most efficient coral de- 
 stroyers are probably the Crustacea, and they are generally credited 
 with the production of much of the coral sand. Not only the corals 
 themselves, but the shells of molluscs and the tests of echinoderms 
 are ground up by these voracious feeders, the resultant being a 
 mixture of lime sand and flour, which by the sorting action of the 
 waves is distributed in beds around the reef. 
 
 Much coral sand will become lodged in the interstices of the 
 reefs between the growing coral masses, thus binding the whole 
 into a solid mound. One of the marked features of this mound 
 of coral rock is the absence of stratification, and when solidified the 
 mound will be an irregular, structureless, often lens-shaped mass 
 of lime rock embedded in stratified calcarenytes and calcilutytes. 
 Along the margin of the reef the clastic lime rocks will be deposited, 
 
4 i6 PRINCIPLES OF STRATIGRAPHY 
 
 generally with a steep inclination dependent on the slope of the 
 reef itself, but it will form nearly horizontal beds at a distance from 
 the reef. Close to the reef the clastic material is often a rudyte, 
 consisting of worn fragments of coral embedded in the sand. Cal- 
 carenytes are, ho\vcver, the most characteristic clastic sediments 
 around the reef, while calcilutytes or lime-mud rocks are deposited 
 at a distance, where the fine lime mud settles in deeper and more 
 quiet water. Around modern coral reefs the water after a storm 
 is milky for great distances, owing to the presence in suspension of 
 the lime-rock flour. Agassiz has noticed this fine sediment in sus- 
 pension at a distance of 12 to 20 kilometers from the reef. After 
 a prolonged storm 4 to 5 centimeters of coral mud were laid down 
 between two tides. (Agassiz-2.) 
 
 In the lagoon of Keeling atoll the fine lime debris resulting 
 from the erosion of the reef appears like chalk, but when dry is 
 seen to be very fine sand. Finer grained, purely calcareous lime 
 mud forms large soft banks from the southeast shore of the lagoon, 
 covered with a thick growth of Fucus. Similar material is obtained 
 from the Bermuda reefs and has often been mistaken for true 
 chalk. Dunes of these sands are not infrequently heaped up on 
 the higher parts of the reef, and the steep, submerged slopes are 
 covered with them, even where the angle of the slope is as high as 
 55. Similar white lime sands and muds are deposited along the 
 Brazilian coast for a space of 1,300 miles, from the Abrolhos Islands 
 to Maranhao. 
 
 The sand and rolled coral heads soon become cemented into a 
 hard platform of coral rock more or less structureless in character, 
 this being accompanied in many cases by the growth of Lithotham- 
 nion. In Keeling atoll this flat submerged platform "varies in 
 width from 100 to 200, or even 300, yards, and is strewed with a 
 few large fragments of coral torn up during gales." (Darwin 21.) 
 This platform is uncovered only at low water, and Darwin found 
 the rock so well cemented that he could break off a piece only with 
 the aid of a chisel. Calcarenytes composed of the rounded par- 
 ticles of shells, corals, spines of echini, and other calcareous struc- 
 tures occur with the rocks of pure coral mud. These sands are 
 found even where the slopes are as high as 50. The reef rock 
 itself is often so altered in its older portion that no organic struc- 
 ture can be ascertained in it. 
 
 Close to the reef there is often an interlocking of organic and 
 clastic lime rock, for at intervals the reef organisms will extend 
 outward over the region previously covered by the coral sand, after 
 which this sand may again overwhelm the fringe of the reef. 
 
FOSSIL REEFS: CAMBRIC 417 
 
 FOSSIL CORAL AND STROMATOPORA REEFS. 
 
 CAMBRIC AND PRE^-CAMBRIC. The oldest reef-forming organisms, 
 the Archccocyathida, were originally referred to the sponges, and 
 more recently to the primitive perforate madreporarian corals, of 
 which group they probably form a distinct order. They have been 
 reported from a number of localities in the Cambric, including both 
 Western United States (California, Nevada) and the eastern part 
 of North America (Newfoundland, Labrador), Sardinia, Spain, 
 Northern Siberia and Australia. In a number of these localities 
 they have been found to constitute layers or strata of which they 
 formed the principal portion, but they did not build massive reefs 
 comparable to those of the present day. Since they were all simple 
 corals, and of a very porous character of skeleton, they were not 
 especially adapted to the formation of reefs. Nevertheless, they 
 constituted an important limestone builder of this period, forming 
 in the straits of Belle Isle, Labrador, beds of coral limestone 
 varying in thickness from 25 to 50 feet. In many cases evidence of 
 shallow water, such as conglomerates, ripple marks, trails, etc., are 
 found in association with the beds of Archaeocyathidoe. In Sardinia 
 (Bornemann) and in Australia similar extensive reefs of these 
 corals are found, in some cases extending up into the Ordovicic. 
 
 The recent finding of archaeocyathid fossils forming limestone 
 masses in the Animikie of Canada makes this one of the oldest if 
 not the oldest reef-building coral. The probabilities are that these 
 corals lived in shallow and comparatively warm waters. 
 
 The Hydrocoralline, Cryptozoon, formed an important reef 
 builder in the upper Cambric and lower Ordovicic of North Amer- 
 ica. It always occurs in layers which often have a considerable 
 extent. The individual heads are spherical, from i to 2 feet in 
 diameter, or plate-like, with a thickness of one or two feet, and 
 from 5 to 100 feet in horizontal extent. These are not reefs as we 
 apply the term to such structures in the modern sea, though super- 
 ficially they must have had the appearance of a platform of coral 
 heads not dissimilar to some parts of the broader portion of the 
 Great Barrier Reef of Australia. They may perhaps be referred to 
 as "bedded reefs," and their distribution is probably synchronous 
 with that of the stromatoporoid and other hydrocoralline genera. 
 
 These types apparently also formed similar bedded reefs in the 
 pre-Cambric sediments of North America. Walcott has figured a 
 "reef" of Cryptozoon ( ?) frequcns ( ?C. occidental, Dawson) 
 from the Algonkian limestone (Belt terrane) of northwestern Mon- 
 tana, where it forms beds from 6 inches to 3 feet or more in thick- 
 
4 i8 PRINCIPLES OF STRATIGRAPHY 
 
 ness. (Walcott-89, pi. n.) It also occurs in similar beds in 
 Alberta and British Columbia, and in Arizona. 
 
 ORDOVICIC. Reefs of the bedded type have been reported from 
 the Lower Ordovicic, Cryptozoon minnesotensis forming the chief 
 reef builder. Little is known about the detail of occurrence, thick- 
 ness, and extent of these reef masses, which have been found in 
 many localities in the eastern United States and Canada. In the 
 Middle Ordovicic (Chazyan) the genera Stronmtocerium and Sty- 
 laraca form similar developments in New York, Tennessee, Ken- 
 tucky and Oklahoma. In the Black River horizon Stromatocerium 
 is reenforced by Columnaria and Tetradium, in Tennessee and 
 Kentucky, and these genera also form reef-like associations in the 
 Cincinnatian of these states. These same genera, together with 
 Beatricia, Labechia, Calapcecia, etc., form reef-like associations in 
 the Richmond of North America from Baffin Land and Anticosti 
 to the Mississippi Valley and also in Colorado, Nevada, Wyoming 
 and Alaska. (Vaughan-87 1244.) None of these is to be regarded as 
 a typical reef, these structures being rather of the type of plate-like 
 expansions or bedded reefs, often of not more than a single layer 
 of hydrocorallines. They were undoubtedly an important source 
 of the lime sands and lime muds of the formations in which they 
 occur, though in many cases they seem to lie in undisturbed position 
 as of growth. It is not improbable, however, that the corals an^ 
 hydrocorallines of one section were ground up to form the sand 
 which covers undisturbed layers of the same horizon. 
 
 SILURIC. Coral reefs are well developed in the Siluric, where 
 typical Palaeozoic reef builders Favosites, Heliolites, Halysites, 
 Syringopora, etc. among the corals, and stromatoporoids among 
 the hydorcorallines abound. They have been especially described 
 from Wisconsin and from the Island of Gotland in the Baltic Sea. 
 Others occur in the Upper Siluric of western Ontario and Michi- 
 gan, in the Louisville limestone of the Falls of the Ohio, the Lewis- 
 town limestone of Pennsylvania, and in the Wenlock of England 
 and in Bohemia. 
 
 Niagaran Reefs of Wisconsin. The Siluric strata of south- 
 eastern Wisconsin are characterized by typical coral reefs which 
 form mounds almost entirely composed of coral and Stromatopora 
 masses, and separated from each other by interspaces of some 
 extent, in which the coral sand and mud were deposited in stratified 
 layers. (Chamberlin-i5 '.364; Grabau-4o.) These mounds stand 
 out in relief, owing to the peculiar resistance of the structureless 
 reef rock to erosion, while the bedded strata of calcarenyte and 
 calcilutyte between them more easily suffered denudation. In the 
 
FOSSIL REEFS: SILURIC 419 
 
 older days quarries were opened in these reefs, but, owing to the 
 absence of stratification planes or seams, the operations were more 
 difficult and costly, and the old quarries were abandoned when the 
 bedded strata were discovered. 
 
 The exposed face of the old quarry is generally thoroughly 
 weathered, and it shows an all but structureless surface^ the chief 
 characteristic of which is the total absence of stratification. The 
 reefs consist largely of stromatoporoids, among which the genus 
 Clathrodictyon seems to abound. The reefs as exposed are gen- 
 erally several hundred feet in diameter, with a height of perhaps 
 50 feet. They thus constitute a series of independent reef mounds 
 rising from a platform which is sometimes composed of organic 
 accumulations and at others of clastic material. On the borders 
 of the reef mounds the material consists of coral sand, consolidated 
 into calcarenyte, and this dips away from the reef in all directions. 
 This dip is not due to any tectonic deformations, but is the original 
 dip of the clastic material on the flanks of the reef. The dips 
 observed in the Shoonmaker quarry near Wauwatosa range as high 
 as 54 degrees close to the reef, while dips of 28 to 34 degrees 
 are more common, and others as low as 18 degrees occur. Further 
 away the strata become practically horizontal. (Grabau~4O.) At 
 the Distillery quarry in Milwaukee (foot of Twenty-ninth Street) 
 dips of 40 degrees toward the east and west and of 20 degrees and 
 more to the south have been observed. The two reefs mentioned 
 and a third in the grounds of the National Military Asylum form 
 a triangle, in the center of which quarries have been opened to a 
 great depth in evenly bedded, rather fine-grained calcarenyte, this 
 being the coral and crinoid sand derived from the reef and swept 
 together in even-bedded strata in the inter-reef spaces. These 
 limestones are sparingly fossiliferous, the roving orthoceratitic 
 cephalopods alone occurring in abundance. The strongest possible 
 contrast existed between the reef mounds, on the one hand, on the 
 borders of which flourished a rich fauna of corals, bryozoans, 
 brachiopods, molluscs, trilobites, and crinoids, and the nearly bar- 
 ren sandy bottoms of the comparatively shallow sea on the other; 
 desert areas surrounding luxuriant oases of animal and plant life. 
 
 A typical reef mound exposed by quarrying operations near 
 Cedarburg, 20 miles north of Milwaukee (Grabau~4o), shows a 
 thickness of about 30 or 40 feet of coral rock, though the full 
 measure is not exposed. The diameter of the old reef mound was 
 perhaps 300 feet from north to south. Much of the reef rock has 
 become dolomitizecl, and in many of the bedded strata the corals 
 have been dissolved out. The central part of the reef consists of 
 
420 PRINCIPLES OF STRATIGRAPHY 
 
 stromatoporoids, with perhaps a moderate development of Favo- 
 sites and other corals. On the flanks of the reef numerous smaller 
 corals are found, together with an abundance of crinoids, brachio- 
 pods, molluscs, and some trilobites. The peripheral dips of the 
 bedded strata are of the usual character, and here, as in the other 
 reefs, a repeated interfmgering of the reef rock and the .bordering 
 clastic strata is marked. Several miles from Groth's quarry, just 
 described, is Anschiitz quarry, on the road to Grafton. Here the 
 bedded strata on the flanks of the reef are well shown, their char- 
 acter being that of a typical calcarenyte locally known as sand- 
 stone. The general arrangement of the Siluric reef mounds of 
 Wisconsin is in more or less linear series parallel to the old shore 
 of the period, but probably at a considerable distance from that 
 shore. (Chamberlin-i5.) The arrangement appears to have been 
 that of a barrier reef, the eastward extent of which can be traced 
 through northern Michigan, where an abundant coral fauna, prob- 
 ably in reef association, is found on Drummond Island and else- 
 where. Its eastern extent appears to have been in the vicinity of 
 Lockport, New York, but neither there nor in Michigan have actual 
 reef structures been observed. Farther south occurred independent 
 reefs, remains of which are now found at Louisville, Kentucky, at 
 the Falls of Ohio. Probably many other reefs of this age exist in 
 the Hudson Bay region, where strata of this age still await detailed 
 exploration. 
 
 Siluric Reefs of Gotland. One of the finest exhibitions of Palae- 
 ozoic coral reefs is found on the western coast of the Island of 
 Gotland in the Baltic Sea. (Wiman-93; Hedstrom-47 ; Munthe- 
 65.) Here the erosion by the waves both at the present altitude 
 and during a former period of higher water has exposed a series of 
 wonderful sections through the ancient reefs such as are probably 
 not to be found anywhere else in the world, though equally fine 
 sections of Mesozoic and later reefs are well known. There appear 
 to be two main horizons in which the reefs occur, separated by a 
 disconformity, one series being best exposed in the northern and 
 the other in the southern part of the island. 
 
 In general aspect the "reefs" are lenticular mounds locally 
 known as "klintar." They stand out as bold cliffs on the shore, 
 their massive, structureless character offering great resistance to 
 both wave and atmospheric erosion, whereas the bedded enclosing 
 strata are more rapidly reduced by both agencies, and so produce 
 indentations and reentrants in the coast line. (Fig. 85.) 
 
 Unlike the Siluric reefs of Wisconsin, those of Gotland are 
 practically unaltered by subsequent dolomitization, and hence their 
 
FOSSIL REEFS: SILURTC 
 
 421 
 
 structural character and composition can be readily ascertained. 
 The materials of which they consist are partly corals, among which 
 are Halysites and Favosites, both massive and branching forms, 
 Striatopora, Pachypora and Syringopora, which latter is especially 
 adapted by its loose method of growth to retain the coral sand pro- 
 duced by the erosion of the reef. Stromatopora heads are like- 
 wise common in these reefs, and often of large size, and with them 
 occur calcareous algae (Sphaerocodium) and Spongiostroma, which 
 sometimes constitute as much as 50 per cent, of the reef-building 
 types, though when occurring alone they form beds instead of 
 reefs. 
 
 On the borders of the Gotland reefs characteristic interfmgering 
 of the organic and detrital limestone is often well shown, as for 
 instance at the cliff of Hoburgen in the southern part of the island. 
 Often masses of stratified sand appear to be included in the reef 
 mass, a phenomenon also observed in the reefs of Wisconsin. The 
 
 FIG. 85. Diagram of the reef structure at Gotland, and the relation of the 
 reefs to the bedded formations. (After Wiman.) 
 
 detrital lime sand is thickest on the border of the reef, and it is 
 often well stratified, dipping away from the reef as in the Wiscon- 
 sin examples. Overturned coral heads are common on the border of 
 the reef, these being torn from their original anchorage and rolled 
 about by the waves of the Siluric sea, which used them as mill- 
 stones to grind the coral and other organic rock into sand and 
 mud, which was either deposited within the interstices of the reef 
 or swept outward to form bedded strata of limestone. The detrital 
 lime sand is in part the result of such destruction of the corals and 
 the brachiopod and molluscan shells, but to a large extent it is 
 derived from the dismemberment of crinoids, the stems and calices 
 of which yield an abundance of discs and plates through the natu- 
 ral dissociation of these components on the maceration of the 
 dead organism. Much of this crinoidal detritus is already of suffi- 
 ciently small grain to be directly included among the stratified 
 sediments forming outside the reef. Crinoidal conglomerates, 
 formed of the discs of the larger crinoid stems, as well as coral 
 conglomerates, are of common occurrence on the borders and sum- 
 mits of the reefs. 
 
422 PRINCIPLES OF STRATIGRAPHY 
 
 The Gotland reefs often rest on marly clay beds or on oolitic 
 sands. When the latter is the case, it appears that these oolitic 
 sands immediately succeed a shallow-water, if not terrestrial quartz 
 sandstone, and are themselves of very shallow-water origin, show- 
 ing an abundance of wave activities. The reefs were thus evidently 
 built in water of no considerable depth, as is further shown by the 
 structure of the reef borders themselves. Where the reef rests on 
 the marl shales, the latter show evidence of relative plasticity at 
 the time of reef formation, for the reefs, with growing size and 
 weight, sank into the marly muds to some extent, forcing the 
 mud away in either direction or causing the layers to bend down 
 under the reef. 
 
 The reefs of this section apparently formed a barrier parallel 
 to the old Scandinavian land, in part of which graptolite-bearing 
 shales seem to have been deposited at the same time. The earlier 
 reef series shows its proximity to the land by the fact that, in the 
 lagoons between the reef mounds, terrestrial or semiterrestrial 
 organisms, the eurypterid Pterygotus and the scorpion Palaeophonus, 
 were found together with marine organisms. It is highly probable 
 that the reef was dotted with islets, and that perhaps even fresh- 
 water lagoons existed, and this would serve to explain the exist- 
 ence of these continental organisms. It is noteworthy that the 
 Pterygotus beds occur at the lower boundary of a distinct hiatus, 
 which marks a period of land condition for the entire island, and 
 was probably of much greater extent. 
 
 Upper Siluric Reefs of North America. Reef structures are 
 known from the Upper Siluric (Monroan) formation of western 
 Ontario and Michigan and the equivalent Lewistown limestone of 
 Pennsylvania. They probably occur in formations of similar age 
 in northwest Canada. The best example of these reefs occurs in the 
 Anderdon limestone quarry, about a mile northeast of Amherst- 
 burg, Ontario. (Sherzer and Grabau-8o: 43.) Its thickness is 
 only from 6 to 8 feet, but its horizontal extent is unknown. It is 
 probably of the nature of a series of lenses of organic limestone, 
 surrounded by and passing into the finest lime mud strata (cal- 
 cilutytes) derived from the destruction of the reef. The organisms 
 of the reef are mainly stromatoporoids, Stromatopora galtense and 
 Clathrodictyon ostiolatum predominating. With these occurs the 
 small branching stromatoporoid, Idiostroma nattressi, which was es- 
 pecially adapted to capture the coral sand and mud produced by the 
 grinding action of rolled Stromatopora heads. Corals of the genera 
 Favosites, Diptophyllum and Cladopora, all well adapted to capture 
 coral sand, on account of their loosely branching habit, and simple 
 
FOSSIL REEFS: DEVONIC 423 
 
 corals of less importance as reef builders also occur. Brachiopods 
 and molluscs appear to be rare, however. A remarkable feature of 
 this reef is the enclosing rock, which is a calcilutyte and wholly 
 unfossiliferous so far as exposed, except in the upper layers. Or- 
 ganisms seem to have been confined entirely to the reef, while the 
 surrounding area was the site of the deposition of the finest lime 
 mud. It is highly probable that the fineness of this mud explains 
 the absence of macroscopic forms of life, because few animals can 
 exist in muddy water such as this must have been. 
 
 Elsewhere in this horizon reef structures ,of similar type are 
 developed. They are well shown in the Lewistown limestone of 
 central Pennsylvania, where, near Tyrone, they consist almost wholly 
 of stromatoporoids of the same species as at Anderdon, together 
 with the Favosites, Cladopora and Diplophyllum found there. In 
 the Manlius limestone of New York State similar Stromatopora 
 reefs are found. These are more especially of the bedded type, 
 consisting of one or more layers of Stromatopora heads of various 
 sizes and belonging to a number of genera and species. Other or- 
 ganisms are rare, and the enclosing strata are mostly calcilutytes. 
 
 It is a common fact that such bedded Stromatopora reefs are 
 enclosed in calcilutytes, and this seems to be due in part to the 
 absence of other organisms which could furnish lime sand. The 
 mutual attrition of the massive Stromatopora heads seems to have 
 resulted chiefly in the formation of lime mud. If so, the progress 
 of sedimentation here must have been an exceedingly slow one. 
 
 DEVONIC CORAL REEFS. The Devonic formations abound in 
 coral reefs both in North America and Europe. They occur in the 
 lower Devonic of Konjepruss, Bohemia, in the Onondaga of New 
 York, and the Falls of Ohio, the Traverse group of Michigan, the 
 Devonic of. Canada, of Belgium, the Eifel and elsewhere. The 
 details of the reef structure of only a few of these have been inves- 
 tigated, and these will be discussed at some length. 
 
 Lower Devonic Reefs of Konjepruss, Bohemia. As exposed in 
 the quarries near Konjepruss, the lower Devonic limestone of Bo- 
 hemia (F 2 of Barrande) shows a massive, structureless reef facies, 
 in which the zoogenic limestone is largely composed of massive 
 Favosites and stromatoporoids, while brachiopods, molluscs, trilo- 
 bites and small corals also abound, especially on the margin of the 
 reef. Laterally this reef limestone merges into a stratified, coralline 
 limestone (see Kayser and Holzapfel-55). The reefs are under- 
 lain by the Upper Siluric platey limestones and black graptolite 
 shales, but whether they rest directly on these deposits or arc 
 preceded by shell layers has not been ascertained. 
 
424 PRINCIPLES OF STRATIGRAPHY 
 
 The Onondaga Reefs of New York. The Onondaga limestone 
 of the State of New York is a good example of an ancient 
 formation resulting from the growth of numerous coral reefs and 
 the accumulation of their attendant deposit of clastic lime sands. 
 (Grabau-40.) The formation varies in thickness from about 50 
 feet in the eastern part of the state to about 200 feet in the western, 
 and is in part continued westward into Ohio and Michigan by the 
 Columbus and Dundee limestones, the age of which, however, ap- 
 pears to be somewhat younger. Throughout this extent the forma- 
 tion rests upon an old land surface, or the deposits of continental 
 origin formed during that period, and partly reworked by the trans- 
 gressing sea. At first more or less siliceous limestones containing 
 shells of molluscs and brachiopods were formed (Schoharie grit, 
 Decewville beds), and on this foundation the corals began to 
 grow. It appears that the corals formed a series of barrier reefs 
 roughly parallel to the old coast line, which passed through New 
 Jersey, southeastern Pennsylvania, central Maryland and West Vir- 
 ginia. Close to the shore in the northern part clastic deposits, 
 chiefly grits, were forming, but the southern section is marked by 
 the accumulation of black muds (Romney shale) with a depau- 
 perate fauna of few species. The conditions were much the same 
 as we find now in Florida, where the inner lagoon is a region of 
 black mud deposits with a mingling of marine and fresh-water 
 organisms. In Pennsylvania and in New York a succession of 
 reefs was apparently formed paralle4 to this southeastern shore, 
 each series progressively farther removed to the north and west 
 from this coast. The gradual advance of the inner lagoon con- 
 ditions toward the northwest is shown by the progressive creeping 
 out of the black mud deposits over the old dead reefs, the Onondaga 
 limestone being progressively covered by the black Marcellus muds, 
 which are to a large extent the lagoon equivalents of the reef 
 limestone farther seaward. In most localities the deposits formed 
 immediately over the dead reefs continue to be of lime sands 
 derived, no doubt, from the still-living reefs farther out to sea. 
 These lime sands were, however, abundantly charged with silica, 
 probably in the form of sponge spicules and diatoms, and these 
 gave rise to the layers of chert found in these upper rocks in such 
 abundance in some localities, and on which account this rock early 
 received the name of Corniferous limestone. These corniferous de- 
 posits swell between the reefs, where most probably the lagoons 
 were situated, and they are buried in turn by the encroaching black 
 mud deposits which represent conditions of deposition unlike those 
 found in the open sea. That the deposits of black mud were pro- 
 
FOSSIL REEFS: DEVONIC 425 
 
 gressively replacing the deposits of limestone is shown by the fact 
 that the highest layer of these rocks in western New York, the 
 Agoniatite limestone, extended eastward during a temporary east- 
 ward transgression of the sea, and rests on 50 feet of these black 
 muds in eastern New York, where the Onondaga is only 50 feet 
 thick, and on 175 feet of black muds in Maryland, where the Onon- 
 daga limestone is absent. In western New York, where the Onon- 
 daga is about 200 feet thick, it consists of reefs in the lower part, 
 followed by -shell limestones and cherty beds in the upper. This in 
 turn is followed by over 50 feet of black shale practically barren 
 of fossils except in a few localities, and there sometimes including 
 the remains of eurypterids and other arthropods adapted to brack- 
 ish or fresh waters and rarely found except in the deposits of shal- 
 low coastal lagoons, protected embayments or fresh-water lakes or 
 rivers. In Ohio and southern Michigan the deposits of limestones 
 of the Onondaga type began much later, and also continued much 
 
 FIG. 86. Diagram showing successive advances of the coral reefs and accom- 
 panying clastic lime sands and the covering muds of the inner 
 lagoons. 
 
 later, so that the overwhelming black muds reached that part of the 
 sea only toward the close of the deposition of black Marcellus muds 
 in western New York. (Fig. 86.) 
 
 Few of the actual reefs have been located and described, this 
 being due more to lack of attention directed toward their structure 
 than to their non-exposure. It is also important to bear in mind 
 that modern quarrying operations are carried on in the bedded 
 strata of inter-reef origin, and that the structureless reefs, so diffi- 
 cult to operate in, are avoided. This is strikingly shown by the 
 quarries opened in these limestones in western New York (Wil- 
 liamsville), two of which are found on opposite flanks of a reef 
 several hundred feet in diameter; the reef itself being untouched. 
 ( Grabau~4O '-340. ) In the quarries the various dips away from the 
 reef are shown, these, however, not often exceeding 10. (Fig. 87.) 
 On one side the sloping floor of the quarry is formed by the 
 upper surface of the reef, and here the composition of the reef 
 can be ascertained. Enormous heads of branching Syringoporas, 
 
426 PRINCIPLES OF STRATIGRAPHY 
 
 Eridophyllum, Synaptophyllum and Diplophyllum occur here, their 
 interstices rilled in with coral sands. Favosites likewise abound, 
 the heads being often of enormous size. Large Cystiphyllums and 
 Cyathophyllums also occur, and crinoid stems are equally abundant. 
 In the bedded limestones near the reef, fragments of Favosites 
 abound, and sometimes heads of great size occur, but they are 
 partly worn, and very commonly overturned. Here we have the 
 coral breccia formed of the dead coral heads on the borders of the 
 reef, enclosed in the coral sand derived from the reef by the grind- 
 ing action of the waves which rolled about these fragments of 
 coral and used them as tools for their destructive work. Brachio- 
 pods, bryozoans, molluscs and other lime-secreting organisms are 
 also plentiful on the borders of the reef, while the remains of giant 
 placoderm fishes found in these deposits further complete the 
 
 FIG. 87. Section of a reef in the Onondaga limestone of Williamsville, N. Y. 
 Two quarries have been opened in this section, one on either side 
 of the reef. The left-hand (eastern) quarry does not quite touch 
 the reef, but the floor of the right-hand (western) quarry rests 
 partly upon the reef and exposes the low secondary reef-mound. 
 
 faunal list and show us some of the organic agents influential in the 
 destruction of the coral reef and the production of the coral sand. 
 These fishes are especially abundant in the later deposits of this 
 series in Ohio and Michigan, from which 19 species have been 
 obtained as against 8 species from the Onondaga of New York. 
 
 In some portions of the Ohio limestones small globular bodies, 
 Calcisph&ra robusta, abound, sometimes making up the limestone. 
 These resemble the spore capsules of the fresh-water lime-secreting 
 alga, Chara, and may be part of a plant, or more probably a foram- 
 iniferan, of the kind living abundantly to-day in the quiet waters 
 of the lagoons within the coral reefs. (See description of Funa- 
 futi.) 
 
 Reefs of this age are likewise found in southern Indiana and 
 adjacent portions of Kentucky (Jeffersonville limestone of the 
 Falls of the Ohio). 
 
 Middle Devonic Reefs of Michigan. In the Hamilton or Trav- 
 erse group of Michigan reefs are well developed, and almost every 
 
FOSSIL REEFS: DEVONIC 
 
 427 
 
 characteristic of the structure of Palaeozoic reefs is shown. The best 
 examples are found in the eastern area of the northern part of the 
 Southern Peninsula in the vicinity of Alpena. Here their occur- 
 rence is marked in the topography by low mounds or swellings which 
 rise above the general level of the country, a feature observed in 
 Siluric coral reefs as well, as, for example, in the neighborhood of 
 Visby, on the Island of Gotland, where such knolls form a marked 
 feature of the topography, many of them being surmounted by 
 windmills. 
 
 The Alpena reefs (Grabau~4o) are mostly well exposed in the 
 quarries which are extensively opened up in this rock, the purity of 
 which makes it desirable for chemical and other purposes. Analyses 
 of the reef rock have given over 99% of calcium carbonate. The 
 
 FIG. 88. Diagram of the reef structure in the Traverse (Middle Devonic) 
 limestones of Alpena, Mich. The black masses represent corals 
 (Favosites, Acervularia, etc.) and stromatoporoids. The dip of 
 the calcarenytes and calcilutytes on the margin of the reefs and 
 the interfmgering of the reef and clastic formations are shown. 
 
 reef mounds are of the usual lens shape, the height averaging 35 
 feet, while their diameter at the base is several hundred feet. The 
 chief reef-builders are large heads of Favosites, Acervularia, and 
 stromatoporoids, many of them three or four feet in diameter, 
 while occasional stromatoporoids up to 10 feet in diameter also 
 occur. Branching species of Favosites are common, and bryozoans, 
 crinoids and brachiopods help to swell the organic content of the 
 reef. Between these organisms the coral sand abounds, binding the 
 whole into a solid, structureless mass, in which lines of stratification 
 are entirely wanting. Even where the coral sand fills extensive 
 cavities in the reef mass, no stratification is shown. In such cases 
 the coral heads may be found wholly enclosed in the sand, and 
 often overturned. For the most part, however, the coral heads lie 
 in their normal position of growth, successive heads growing; on a 
 foundation of older corals embedded in crystalline sand. ( Fig. 88L) 
 On the borders of the reef-mounds the clastic lime sand forms 
 beds which are often steeply inclined. Close to one of the mounds, 
 
428 PRINCIPLES OF STRATIGRAPHY 
 
 for example, the dip was 28, then rapidly changed to 14, and then 
 -more gradually to 2. The sand here is finer than that filling the 
 cavities in the reef, but it often includes fragments and partly worn 
 heads of Favosites, Stromatopora, etc., lying in all positions. Occa- 
 sionally the material is a coral breccia, but for the most part it is 
 a calcarenyte. Farther away from the reef-mound it frequently 
 becomes a calcilutyte or rock made up of the finest lime flour. 
 Throughout the marginal zone there is an interlocking of organically 
 formed and fragmental lime rock, indicating a periodic spreading 
 outward of the reef and a subsequent overwhelming of each ex- 
 panded rim by fragmental deposits. These spreading fringes of the 
 reef consist mainly of the smaller branching corals and of bryozo- 
 ans, which at times extend far out on the foundation of coral 
 sand. ' These expanded rims, formed when erosion temporarily 
 ceased, extend outward to form the dividing planes between the 
 successive strata of the bedded limestones, where they are often 
 replaced by films of silty or even clayey material. These periodic 
 cessations of erosive activity on the reef and the spreading of the 
 reef fauna over the surrounding beds of unfossiliferous coral sand 
 must be due to the local protection of the reef mass from the 
 waves. This may be brought about by the becoming effective of 
 some outer barrier formed by the slow growth of an outer reef 
 which has become of sufficient height to break the force of the 
 waves, or by the building of a temporary sand or shell bar. At 
 such times the various minor organisms of the reef fauna find it 
 possible to spread in all directions in the relatively quiet water, and 
 so form a layer of fossiliferous material between the thicker layers 
 of coral sand limestone. It is on these dividing planes, as every 
 collector knows, that the largest number of specimens is found, the 
 limestones themselves only rarely carrying unworn fossils. 
 
 In some cases, however, the dividing planes close to the reef 
 mark a period of especial destructiveness, when the smaller corals 
 and other organisms torn from the reef are rolled outward and 
 come to rest in more or less worn conditions as a bed of organic 
 conglomerate upon the uniformly grained clastic limestones. In 
 some cases the spreading organic rims are marked by the death of 
 the corals, especially the simple types, and by their partial solu- 
 tion. The cyathophylloid corals often have their epithecas dis- 
 solved away. On such a partly corroded surface Bryozoa and other 
 attached organisms grow, showing that conditions unfavorable to 
 the true corals did not affect some of the other organisms. These 
 conditions are well shown in the upper part of the reefs near 
 Alpena. 
 
FOSSIL REEFS: DEVONIC 429 
 
 On the western side of the State of Michigan, in the Petoskey 
 and Traverse Bay regions, at present only the marginal portions of 
 the reefs are shown in the outcrops and cuttings ; here the rock is 
 made up of fragments of Acervularia davidsoni, Favosites and 
 stromatoporoids embedded in the crystalline sand, these often form- 
 ing a veritable coral conglomerate, such as is found on the flanks of 
 modern coral reefs. Farther away from the reef the coral frag- 
 ments cease, once the rock becomes a well-stratified calcarenyte or 
 calcilutyte. That the waters in which these beds were deposited 
 were shallow is shown by the occasional cross-bedding and the ripple 
 marks found in these strata, as well as by the repeated phenomenon 
 of contemporaneous erosion and deposition, and the wedging out of 
 certain strata and the thickening of others. Not infrequently 
 seams of carbonaceous material separate some of the layers of the 
 limestone, and in these layers plant remains are not uncommon. 
 
 The sections exposed below the city of Petoskey in the Traverse 
 Bay region are very instructive in this connection. As stated, they 
 represent the marginal portions of the reefs and show a succession 
 of erosion planes dividing the entire mass into strata from a few 
 feet to 10 or 20 feet in thickness. These strata show successive 
 accumulations of coral sand with worn pebbles of corals or stroma- 
 toporoids, generally of the size of a man's fist or larger, and ar- 
 ranged in strata which in some cases are horizontal, in others dip 
 in various directions at low angles. There is a certain succession 
 of remains in the various strata, those of the higher beds being dis- 
 tinct from those of the lower. In the upper beds the branching 
 stromatoporoid Idiostroma ccespitosum is the chief organism, and 
 this is often found in the position of growth, its finger-like branches 
 spreading to capture the coral sand. Most of this coral sand has 
 since been dolomitized with the result that the mass is rendered 
 porous. The coral pebble strata are often traceable for miles with- 
 out apparent change in character. 
 
 These successive erosion planes suggest that periodic subsi- 
 dence was going on here during the growth of the reef, each stratum 
 being eroded when its growth had brought it to within the level 
 of wave activity. The change in fauna with the change in the 
 growth of the reef is analogous to the changes in fauna found at 
 successive steps in the building of modern reefs. A striking fea- 
 ture of the clastic strata of this region is the frequent intercalation 
 of calcilutytes made from the finest lime flour. These and the 
 equally pure beds of calcarenyte are in some cases separated by 
 layers of carbonaceous shales indicating a period of plant growth, 
 and probably even local terrestrial conditions in the form of vege- 
 
43 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 tation-covered islets, such as are characteristic of coral reefs to-day. 
 Devonic Reefs of the Attawapishkat River, Canada. In the 
 southern part of the Province of Keewatin, in Canada, reef struc- 
 tures occur in the Devonic limestones. (Bell-i2:,?7G, ?8G.} These 
 have been exposed in natural sections by the Attawapishkat River, 
 an affluent of James Bay. These reefs have the character of great 
 spongy and cavernous limestone masses often occupying the full 
 height of the cliffs, which is about 40 feet. They are structureless 
 masses of rudely lens-like character and "largely made up of fos- 
 sils, although the number of species does not appear to be great." 
 The principal forms are brachiopods (Meristella, Stropheodonta), 
 a trilobite and corals. Stromatoporoids are probably also among 
 the abundant reef-builders. The thinly bedded limestones which 
 enclose the reefs dip away from them at various angles, and are 
 sparingly fossiliferous. These beds are more easily removed by 
 
 FIG. 89. Reef mounds enclosed in bedded 
 formations of Devonic age. Atta- 
 wapishkat River, Canada. (After Bell.) 
 
 FIG. 90. A single reef mass 
 left by erosion of the 
 bedded rocks. Attawa- 
 pishkat River, Canada. 
 (After Bell.) 
 
 erosion, with the result that the reef masses stand out in bold relief 
 like the Klintar of Gotland. The numerous islets in the Attawap- 
 ishkat River "appear to consist of single masses," each of these 
 reef-cores being left in relief by the removal of the surrounding 
 strata. They are locally known as wigwams by the native Indians. 
 (Figs. 89, 90.) 
 
 Middle Devonic Reefs of the Eifel and Belgium. The Middle 
 Devonic Stringocephalus beds of the Eifel show in many sections 
 a typical reef structure similar to that already described for the 
 Devonic of North America. As in other cases, the reef masses 
 stand out in relief, forming high cliffs of structureless limestone 
 often dolomitized. The structure and topography are in many 
 cases modified by the eruption through these limestones of Tertiary 
 volcanic rocks. The chief reef-building organisms in these de- 
 posits are Favosites, Cyathophyllum, Endophyllum, Stromatopora 
 and Actinostroma. Brachiopods, gastropods, pelecypods and ceph- 
 alopods are also characteristic and sometimes abundant. The usual 
 
FOSSIL REEFS: MISSISSIPPI 431 
 
 inclined marginal strata have been noted in a number of sections 
 in the Eifel, and the character of the reefs is not unlike that of 
 the more massive American reefs, such as that of the Niagaran of 
 Wisconsin. The reef masses rest upon a foundation of crinoidal 
 limestone. 
 
 The corresponding Middle Devonic Calcaire de Givet (Givetien) 
 of Belgium has the reef structure well developed. (Dupont-27.) 
 The reefs have at first impression the appearance of amorphous 
 limestone, passing into more or less saccharoidal rock. On weath- 
 ered surfaces a somewhat brecciated structure appears, together 
 with numerous outlines of corals or sponges, slightly left in relief 
 by the solution of the enclosing limestone. Stromatoporoids make 
 up a large part of the reef, but they have been profoundly altered, 
 so that it is difficult now to separate the Stromatoporoids along their 
 laminae or structure planes even with a hammer. It is only on 
 weathered surfaces that the true composition of the reef is shown, 
 the fresh surfaces showing only a compact rock often with con- 
 choidal fracture, full of cavities, but without trace of the Stroma- 
 toporoids or other organic content. As in other cases, the reef is 
 structureless, no stratification being visible. The reef-formers be- 
 side the Stromatoporoids (Stromatactis and Pachystroma), include 
 Favosites, Alveolites and more rarely cyathophylloids. Cyatho- 
 phyllum cccspitosum occurs on the margin of some of the reefs in 
 crowded heads from 1.5 to 2 meters in diameter. -The flanking beds 
 of clastic limestone show well-marked stratification, and between 
 the reef knolls these clastic limestones often contain beds of crin- 
 oidal fragments, and others largely composed of shells. 
 
 Dupont deduces from the arrangement of the reef masses that 
 they constituted fringing reefs to the land of that period, and he 
 has found indications of a breach in the reef line in the Frasnien 
 reef north of the Couvin, which is analogous to the interruptions in 
 the reef opposite the mouths of streams coming from the fringed 
 land. Reef structures of similar character are found in the Devonic 
 of the Karnic Alps on the Austro-Italian border. (Frech-34; 35.) 
 The reefs are chiefly in the Middle Devonic, and composed of Alve- 
 olites, Heliolites, Stromatoporas, etc., while Stringocephalus and 
 other brachiopods are among the other characteristic organisms of 
 the reefs. The reefs themselves rest on bedded Lower Devonic 
 (Konjeprussian) limestones composed of an abundance of brachio- 
 pods and crinoids, of corals and of other organisms. 
 
 MISSISSIPPI REEFS. These are less abundant and are not so 
 widespread as the Devonic reefs. None have as yet been described 
 from America, though they are known to exist in some sections. 
 
432 PRINCIPLES OF STRATIGRAPHY 
 
 Mississippic Reefs of Belgium. In the Mississippic (Tour- 
 nasien and Viseen) of Belgium occurs a distinct reef facies known 
 as "Calcaire de Waulsort" and belonging in part to both of the 
 above subdivisions. This limestone is a massive, structureless ag- 
 glomeration of the stromatoporoids Stromatocus bulbaceus Dupont 
 and Ptylostroma fibrosa Dupont. To the surfaces of these hydro- 
 corallines adhere numerous fronds of the bryozoan Fenestella. 
 Corals play only a small part in these reefs, including Amplexus 
 coralloides and a few other rare types. The reefs are in the form 
 of small massive heaps or islets scattered through the bedded lime- 
 stones which surround them and are marginally entangled with 
 them. These limestones are of diverse character, and chiefly 
 marked by the clearness of their stratification. Two varieties of 
 this limestone may be distinguished, the amorphous and the crin- 
 oidal. The latter, formed from the dissociated joints of crinoid 
 columns, commonly fill the channels in the reef mass proper. As in 
 the case of the Devonic reefs, these also are disposed in fche form 
 of fringing reefs parallel to the old shore, and separated from it 
 by a lagoon canal of greater or less width. In one case the reef 
 has been followed for a distance of 60 kilometers. 
 
 Mississippic Reefs of Great Britain. In the Mountain limestone 
 of Great Britain certain structures occur which have been inter- 
 preted by Tiddeman (84; 85) as reefs, but this interpretation was 
 challenged by Marr (62). The structures in question occur in 
 the Craven district of Yorkshire, on the south side of the Craven 
 fault system, in the Pendleside and Clitheroe limestones. "The 
 form and the system of arrangement of the white limestones [of 
 the knolls] are peculiar. The stratification of the deposits is usu- 
 ally somewhat obscure, and the masses rise in the form of conical 
 or ovoid eminences up to a height of 300 or 400 feet. The change 
 of thickness occurs in a very limited horizontal extent. These 
 eminences ordinarily present upon their sides strata which dip 
 away from the mass in all directions; but when the rocks of the 
 eminences have been quarried, or denuded by atmospheric agents, 
 one sees that the stratification, rough as it is, preserves its hori- 
 zontality or agrees with the direction of inclination of the sur- 
 rounding country. . . ." (Tiddeman-85 -.321 ; Marr's transla- 
 tion-62.) 
 
 "At the foot of these mounds, or reef knolls, as I would call 
 them, we have in many places a breccia formed of fragments of 
 the limestone, which, I take it, have been broken off the reef above 
 between wind and water, and have subsequently been covered up 
 by the mud of the Bowland shales and compacted into a breccia. 
 
FOSSIL REEFS: PERMIC 433 
 
 Fragments of limestone similarly consolidated occur, though more 
 rarely, on the sides of these knolls themselves. I would call these 
 reef-breccias." (Tiddeman-84:<5o<?.) The knolls are crammed 
 with brachiopods, pelecypods, crinoids, corals, etc., many fairly 
 perfect. This, however, is true only in a general sense, for in 
 places the limestone is apparently entirely devoid of fossils, though 
 this, as in the case of many of the other reefs cited, may be due 
 to obliteration of the organic structure. 
 
 Marr (62) has pointed out the abundant evidence of folding 
 and thrusting in the rocks of this region, and he would explain 
 these knolls as due wholly to tectonic movements, the thickening 
 of the limestone being due to folding and thrusting. That the 
 region has been much disturbed is clearly evident from the facts 
 given by Marr, but that the knolls are wholly due to tectonic causes 
 seems doubtful. The original reefs of the limestones would serve 
 as centers of resistance in which the cumulative effects of the 
 thrusts would be most strongly marked. 
 
 FOSSIL REEFS OF BRYOZOA AND OTHER ORGANISMS. 
 
 BRYOZOAN REEFS OF THE GERMAN ZECHSTEIN. In the Zech- 
 stein of the southeastern district of Thuringia in Germany reef 
 structure is well developed. The reef-forming organisms here are, 
 however, no longer corals but Bryozoa. These bryozoan reefs form 
 large block-like masses of structureless dolomite which lies scattered 
 within the normal bedded Zechstein strata. When erosion has 
 carved away the enclosing bedded strata, the reef mass stands out 
 in relief, forming frequently isolated bastion-like mounds, not un- 
 commonly surmounted by a castle or an ancient burg. The reef- 
 forming organisms are chiefly closely crowded masses of Acanth- 
 ocladia anceps, 'Fenestella retiformis, Phyllopora and other Bryo- 
 zoa. Corals are wholly absent, but brachiopods are well represented 
 by Productus horridus, Strophalosia goldfussi, Terebratula elon- 
 gata, and Spiriferina cristata, while the pelecypods are represented 
 by Pseud omonotis speluncaria and Prospondylus liebeamus. The 
 most abundant organism, however, is a lime-secreting sponge or 
 hydrocoralline, Evinospongia, which covered the cliffs up to the 
 level of the sea. These reefs grew upon the cliffs of older rocks 
 which projected as islands and as lines of crags above the floor of 
 the early Zechstein sea. They extended along the southern border 
 of the Harz old land and the East Thuringian peninsula, from 
 Kostritz past Possneck, where they are especially well developed, 
 
434 PRINCIPLES OF STRATIGRAPHY 
 
 past Saalfeld to Eisenach and southward around the peninsula to 
 Laebenstein. The floor of the Zechstein sea had previously been 
 covered with the black Kupferschiefer mud rich in decaying organic 
 matter, chiefly the carcasses of dead fish and decomposing algae, and 
 in which the copper now obtained from it was precipitated. These 
 deposits did not cover the ledges upon which the reefs subsequently 
 grew when normal marine conditions were established. These reefs 
 grew to the height of 40 to 100 meters, with steep sides which, how- 
 ever, often show the interfmgering with the clastic limestone which 
 surrounds their flanks. This limestone is often almost devoid of 
 organic remains, forming a dark "Stinkstein" or a blue compact 
 
 FIG. 91. Dolomite reefs of South Tyrol. Richthofen reef on left with tongue- 
 like extensions into the contemporaneous marls. Sett Sass on 
 right. C D Structureless Schlern-dolomite. (Kayser.) 
 
 lime, both well stratified, and succeeded by a porous dolomitic 
 "Rauchwacke." The growth of the reefs came to an end with the 
 closing of the outlet from the open ocean to this epicontinental sea, 
 and the beginning of gypsum and salt deposition (referred to in 
 the preceding chapter), the reefs being eventually buried under 
 hydrogenic or clastic deposits. 
 
 THE TRIASSIC REEFS OF THE TYROL. The dolomites of the 
 southern Tyrol are regarded by many geologists as examples of 
 fossil reefs on a gigantic scale. They consist of huge, structure- 
 less and more or less circumscribed masses of limestone or dolo- 
 mite representing a distinct facies of the mid-Triassic, which is 
 elsewhere represented by the bedded and often highly fossiliferous 
 Cassian, and underlying Wengen and Buchensteiner divisions of the 
 
FOSSIL REEFS: TRIASSIC 435 
 
 Ladinian. The masses are often of great thickness, that of the 
 Schlern-dolomite reaching over 3,000 feet (1,000 meters), and they 
 are commonly of limited horizontal extent. Tongue-like offshoots 
 of the "reef rock" extend into the surrounding bedded strata as is 
 the case with modern coral reefs. The reef character of these 
 masses was first pointed out by von Richthofen (72), and they 
 were subsequently more fully described by Mojsisovics (64). 
 This author calls attention to the fact that the position which these 
 isopic masses occupy with reference to the heteropic strata enclosing 
 them is that of a reef mass growing upon a basis of volcanic or 
 other origin, but rising above the level of the sea floor on which 
 the heteropic deposits were forming. The latter, therefore, have 
 their bases at a lower level than the reef masses, which always 
 project above the synchronous bedded deposits surrounding them. 
 
 8W. 
 
 SO. 
 
 FIG. 92. Section of the Schlern-massif, showing the relationship of the dolo- 
 mite "reef rock" to the bedded formations, South Tyrol. (After 
 Mojsisovics.) 
 
 The chief structural characters pointing to the reef origin of these 
 masses are : the resemblance of the isolated dolomite masses to 
 upraised reefs ; the great concentration of the dolomite masses 
 thousands of feet thick tailing off laterally into marly deposits of 
 much less thickness, but formed during the same interval of geo- 
 logic time and often showing inclined bedding near the reef; the 
 absence of bedding in the "reef masses" ; and the occurrence of 
 interfingering masses and of blocks of the dolomite material on the 
 slopes of the "reefs" and apparently intercalated among the sur- 
 rounding sedimentary deposits. (Figs. 91, 92.) On the other hand, 
 many observers (Ogilvie-7o, Diener and Artharber-24 and others) 
 hold that the structural features are due to faulting and that the 
 dolomite masses are fragments of once continuous deposits of 
 marine origin. They do not deny, however, that they constitute 
 distinct facies of the Cassian, Wengen and Buchenstein or even 
 earlier beds. 
 
 Corals are very rare in the dolomite, calcareous algse and echino- 
 derms constituting the chief organic remains. This has forced the 
 
436 PRINCIPLES OF STRATIGRAPHY 
 
 advocates of the reef theory to regard these deposits as more strictly 
 nullipore reefs, in which corals played only a secondary part. The 
 organisms of these massive dolomites have for the most part been 
 destroyed during the alteration of the deposit, but it has been possi- 
 ble to ascertain that the chief lime contributors were a coral, 
 Thecosmilia subdichotoma, and a coralline alga, Diplopora annu- 
 lata. The abundance of this and other calcareous algae is the cause 
 for the frequent interpretation of this mass as a nullipore reef. 
 Brachiopods (Koninckina leonhardi, Rhynchonella faucensis), pele- 
 cypods (Daonella parthanensis) and cephalopods (Ptychites acutus, 
 Gymnites palmai, Japonites ganghoferi, Hungarites bavaricus, etc.) 
 occur at a few points, as for example, in the massif of the Zug- 
 spitze, but are as a rule very rare. Large gastropods (Chemnitzia) 
 occur at many localities in the reef masses. The bordering heter- 
 opic limestones sometimes consist largely of Diplopora fragments, 
 and as a rule are very rich in organic remains, especially close to 
 the reef. 
 
 Recently the problem has been attacked by Professor Skeats 
 (82) from the chemical and petrographical side. He started with 
 the ascertained facts that in modern coral islands remote from land 
 areas and volcanic rocks the amount of insoluble residue in the reef 
 rock is negligible. The same is true also of many coral rocks asso- 
 ciated with volcanic rocks, though those in the proximity of the vol- 
 canic masses were found to contain a considerable quantity of in- 
 soluble material, amounting in some cases to 4 per cent, or over. 
 With this as a basis, he made numerous analyses of the dolomites, 
 which showed the prevailing purity of the rock, the percentage of 
 insoluble residue being in the majority of cases less than one per 
 cent., and frequently almost zero. Where residue is present, it can 
 generally be attributed to association with contemporaneous vol- 
 canic rocks, as is the case in the raised coral reefs of Fiji. 
 
 Taking the purity of the rock, the absence of structure and its 
 occurrence as enormously thick masses in the surrounding clastic 
 strata into consideration, there appears to be no other mode of ori- 
 gin than that due to the growth of corals, with an abundance of cal- 
 careous algae, foraminifera and echinoderms, such as are found in 
 some modern coral reefs. These Triassic reefs formed a barrier 
 reef to the land mass lying to the north, whose main axis consisted 
 of the crystalline rocks now forming the central chain of the Alps. 
 In the beginning of Triassic time continental sediments spread north 
 from these highlands, forming the Bunter Sandstein deposits of Ger- 
 many. In mid-Triassic time, however, a marine invasion from the 
 north caused the deposition of the Muschelkalk, only to be fol- 
 
FOSSIL REEFS: JURASSIC 437 
 
 lowed again by non-marine sedimentation in later Middle and Upper 
 Triassic time. While the period during which reefs were forming 
 corresponds largely to that during which the Wellenkalk and 
 Muschelkalk were forming north of the Alps, it probably continued 
 to some extent into the time when the continental sedimentation be- 
 gan in the north. 
 
 In view of this relationship of the reef to the old coast line, the 
 development of certain accessory features becomes of interest. 
 Thus the interfingering, the cross-bedding and the irregular over- 
 lapping structure characteristic of the more or less inclined beds 
 on the flanks of the reef (Uebergussschichtung) with their irregu- 
 lar swelling and the union and separation of layers, are confined to 
 the parts of the reefs farthest away from the old shore, i. e., the 
 southern or outer side of the reef, where it was exposed to the 
 wave destruction and where it rose steeply from the sea. The 
 lagoon side, on the other hand, is characterized by the abundance of 
 Diplopora related to the modern Cymopolia, delicate, branching 
 corallines, which abound only in the protected waters of the lagoons, 
 and do not occur on the outer side of the reef, where the stony 
 nullipores find a congenial habitat. 
 
 In the upper bedded strata of the Cassian formation, coarse 
 oolites are common in the eastern part of the reefs, a feature asso- 
 ciated with the closing stages of reef formation at the present day. 
 The Raibler beds overlying the reefs also are oolitic, and contain 
 many layers of calcarenytes. A remarkable feature of these dolo- 
 mite reefs is the accompanying eruptive series of augite porphyry 
 lavas, which began after the reef had already assumed massive pro- 
 portions. The reef masses thus appear to have set a limit to the 
 extent of these lava flows in one direction, and they spread over the 
 submerged flanks on which the clastic sediments, formed by the 
 destruction of the reef, had accumulated. The result was the 
 formation of a remarkable limestone tuff breccia, which is com- 
 monly found at the base of these flows. 
 
 THE JURASSIC REEFS OF SOLNHOFEN. In the Jurassic beds of 
 the Solnhofen district in Bavaria, famous for its lithographic stones 
 and the beautifully preserved fossils found in it, reef structures are 
 well developed and have recently been fully described by Walther 
 (91). The thin-bedded lithographic layers (calcilutytes) are found 
 to rest in shallow basins in a coarse, unstratified or rudely stratified 
 limestone with which they interfinger at the margin of the basins, 
 and which even rises above the level of the youngest of the litho- 
 graphic stones (Figs. 93-95). These coarse, unstratified limestones 
 are reefs on a large scale, composed chiefly of sponges, corals and 
 
438 PRINCIPLES OF STRATIGRAPHY 
 
 bivalve molluscs, among which large and coarse types, such as oys- 
 ters, Pecten, Hinnites, Lima and especially the curiously twisted 
 Disceras predominate. The last is so abundant in some places, e. g., 
 Kelheim, that the beds have become known as the "Disceras lime- 
 stones." These molluscs flourished on the margin of the reefs, 
 where the wave activities were strong, and food plentiful. Large 
 and coarse gastropods were also plentiful, including Nerinea, Ceri- 
 thium, Turbo, Pleurotomaria and others. With these also occur 
 large brachiopods (Terebratula and Waldheimia), which occupied 
 the cavities in the reefs, and sea urchins, which had heavy skeletal 
 parts and crawled about on the reefs. All these are now incor- 
 porated in the coarse reef rock which constitutes a large portion of 
 this formation. These organisms are best preserved on the margins 
 of the reefs, the main portion having more commonly the appear- 
 ances of a structureless limestone or dolomite (Franken dolomite, 
 
 FIG. 93. Section through the reef region (Jurassic) of the Altmiihl, in the 
 Pappenheim-Eichstadt region (near Solnhofen) in Bavaria. The 
 reef rock is structureless, the thin bedded "Plattenkalke" or litho- 
 graphic beds are shown in the lagoon-like depressions in the reef. 
 (After Walther.) 
 
 Kelheim limestone). This rock is well shown in the gorge of the 
 Danube at Kelheim, and in numerous other natural and artificial ex- 
 posures in Franken. As a rule, the reef masses stand out in relief 
 in the present topography, while the inter-reef portion, occupied by 
 the thin-bedded calcilutytes (Plattenkalke), is often worn out into 
 a hollow or depression. The individual knolls seem to have had an 
 arrangement suggestive of atolls, though on the whole this series of 
 reefs is more properly to be regarded as forming a barrier reef to 
 the old Jurassic land. (Fig. 93.) 
 
 The reef-rocks of the Swabian Alb have recently been studied by 
 Dr. Fritz Berckhemer,* who finds that the Hydrozoan Ellipsactinia 
 is one of the principal reef-builders, holding the place of the stro- 
 matoporoids of the Palaeozoic, and of the milleporoids of later time. 
 These, together with nullipores and the lime-sand derived from 
 
 * Fritz Berckhemer. Eine vorlaufige Mitteilung tiber den Auibau des 
 Weissen Jura c (Quenstedt) in Schwaben. Jahreshefte d. Vereins f. Vaterl. 
 Naturkunde in Wurtemberg, 69 Jahrgang, 1913 pp. Ixxvi-lxxii. 
 
FOSSIL REEFS: JURASSIC 439 
 
 the destruction of the reef, make up the "reef masses" which sur- 
 round the basins in which the platy limestones (Plattenkalke) were 
 deposited. In many cases, these Hydrozoa reefs rest upon or over 
 the sponge reefs of a lower horizon. 
 
 The presence of islands on these reefs is shown by the eolian 
 more or less oolitic limestones with pronounced eolian cross-bed- 
 ding, shown in the quarries of Schnaitheim and Zandt. These have 
 precisely the structure of the eolian rocks of Bermuda. Walther 
 suggests that the organisms of the reefs near Nattheim were 
 abruptly killed and preserved by the mud spread over them, and so 
 they escaped the usual fate of the coral reef organisms, which are 
 destroyed by boring organisms, and changed to structureless dolo- 
 mite. Subsequent silicification has resulted in the wonderful preser- 
 vation of this coral fauna, for which this region has become famous. 
 
 The basins containing the fine and thin-bedded lithographic rock 
 form the strongest possible contrast to the enclosing reef mass. In 
 
 /' i . r . \^ ' 
 
 ' f.'.XA, OV /,..\, ' ' 
 
 FIG. 94. Diagrammatic section of a lagoon in reef-rock, with lithographic 
 limestone layers of extreme thinness (Plattenkalke) occupying the 
 depressions. (After Walther.) 
 
 these sediments of impalpable lime mud the most delicate organisms 
 were preserved with a marvelous perfection. The feathers of the 
 ancient bird, Archseopteryx ; the wing membrane of the flying 
 saurians, the dragon-flies and other insects, with the veining of their 
 wings perfectly retained, are wonderfully well preserved, and even 
 the delicate jellyfish left its impressions in marvelous perfection. 
 Sometimes secondary reefs occur in the midst of the basin, indicat- 
 ing a temporary encroachment of the reef builders, which later on 
 were again overwhelmed by the fine mud which produced the litho- 
 graphic calcilutytes. The strata are often very thin, and very uni- 
 formly bedded. The heavier bedded ones are used for lithographic 
 purposes, the thin ones for roofing and flagging purposes. At inter- 
 vals argillaceous layers occur, and some of the beds retain a mud- 
 crack structure. The evidence adduced by Walther goes to show 
 
440 PRINCIPLES OF STRATIGRAPHY 
 
 that the clayey beds are due to deposition of terrigenous dust, and 
 in them the terrestrial insect fauna was buried. 
 
 It appears, then, that these lagoon-like depressions or basins in 
 the coral reefs of the Jurassic sea of that region were slowly filled 
 by the fine lime mud derived from the destruction of the reefs, by 
 terrestrial dust brought by the strong winds from the distant land 
 and by chemical precipitation of lime. Thus were formed the fine- 
 grained lime deposits, which reach in places a thickness approaching 
 a hundred feet. In the more clayey beds and between the layers 
 were preserved the insects and plants blown from the mainland or 
 the marine types brought there during the flooding of the lagoons. 
 Walther has shown from the position of these remains that with 
 
 FIG. 95. Section of the reef rock (Franken dolomite, Jurassic) of Kelheim, 
 Bavaria. The thin bedded "Plattenkalke" are shown by horizontal 
 lining. Those in the upper left-hand portion show distortion 
 through gliding. ("Krumme Laage," see page 781.) (After 
 Walther.) 
 
 few exceptions they were brought there dead, and left as stranded 
 carcasses on the ooze of the lagoon bottom, which was mostly cov- 
 ered by little water if not altogether exposed. The repeated evi- 
 dence of shallow water, and even complete exposure of the lagoons 
 to the air, suggests that these deposits were accumulating during a 
 slow subsidence of the region and that the filling of the lagoons in 
 general kept pace with the sinking of the reefs. The absolute uni- 
 formity of the entire series of thin-bedded limestones further shows 
 that the physical conditions remained uniform during their deposi- 
 tion. Walther assumes that the old shore of the Vindelician land 
 was some 20 km. to the south, but no clastic mud was carried by the 
 currents to these reefs. Instead, the terrigenous dust incorporated in 
 the thin sediments represents wind-blown material. It is in these 
 dust-bearing layers that most of the fossils are found, especially the 
 insects, of which there are 72 genera and 103 species, 35 per cent. 
 
FOSSIL REEFS: JURASSIC 441 
 
 of these being dragon-flies. The peculiar character of the fauna, 
 and the indications which it furnishes of having been stranded on 
 surfaces of calcareous mud, suggest that the lagoon was nearly dry 
 and flooded only during exceptionally high tides or during storms, 
 after which the water soon ran off again. (Walther-9i.) (Fig. 96.) 
 Some such conditions are represented to-day by the lagoons of Lil 
 and Mejt, in the Marquesas Archipelago, where the water is brackish, 
 and poor in organisms, while at Jabor and Jaluit the lagoons have 
 become fresh. (Agassiz-8: ji, 273, 284.) Where abundant rain 
 
 FIG. 96. A horseshoe crab (Limulus) and the marks of its death struggles, 
 showing that it was left stranded on the mud forming the lagoon 
 deposits. (After Walther.) 
 
 water dissolves some of the limestones, the eolian sand is soon solidi- 
 fied by the redeposition of this lime in the interstices, as in the case 
 of the Bermuda sands. Moreover, some of this dissolved lime may 
 be reprecipitated in the lagoon, a process believed by Walther to 
 have taken place in the lagoons of the Solnhofen region. As a re- 
 sult of these and other chemical activities in the lagoons of these 
 reefs, we have not only the rapid and complete encasement of the 
 dead organisms and their perfect preservation in consequence, but 
 also the remarkable preservation of the muscle fibers of reptiles, 
 fishes, etc., which have been transformed into a rock containing 
 70% of Ca 3 P 2 O 8 , 12% of CaCO 3 , 3.5% of CaSO 4 , 6.5% of CaFl 2 , 
 3% of Na 3 PO 4 and 0.5% each of Mg 3 P 2 O 8 and K 3 PO 4 , together 
 with small quantities of water and organic substances. 
 
 The lagoon in which the Plattenkalke were formed was thus 
 apparently a great lifeless surface, on which the carcasses of land 
 and sea animals, cast there during storms or brought by the wind, 
 or, as in the case of the flying reptiles and the early bird, Archae- 
 opteryx, dropped there on the death of the animal, were so quickly 
 enclosed by the fine, chemically precipitated lime ooze that the usual 
 forces of destruction, scavengers, bacteria, etc., did not succeed in 
 destroying them or dissociating their parts. They were entombed in 
 a hermetic and antiseptic mud case, and thus preserved in all their 
 perfection of form and delicacy of structure which, until the re- 
 
442 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 cent discoveries of the wonderfully preserved Cambric fauna of 
 British Columbia, had not its equal the world over. 
 
 Conditions like those which existed in the Solnhofen region dur- 
 ing Jurassic time are unknown in any modern coral reef ; neither 
 were they repeated in any of the numerous reefs known from the 
 Palaeozoic, Mesozoic or Cenozoic periods of the earth's history. 
 They remain an example of a unique type of reef resulting through 
 a remarkable concatenation of topographic, climatic, lithologic and 
 faunistic conditions not met before, nor since attained. 
 
 THE SPONGE REEFS OF THE SWABIAN JURA. In the Upper or 
 White Jura of Swabia, massive, structureless limestones and dolo- 
 mites are found, which prove to be reefs built largely of lime-secret- 
 
 FIG. 97. "Sponge Reef" of the lower White Jura of Swabia. (E. Fraas.) 
 R Structureless reef limestone, a, /3, 7, associated bedded Juras- 
 sic limestones, marls, etc. S. Talus. (From Kayser.) 
 
 ing sponges. These reefs from their massive character stand out in 
 relief through the erosion of the softer enclosing rock, and so form 
 pinnacles, buttresses or even isolated outliers of the Swabian Alb, 
 which since the earliest days have formed the favorite site of castles 
 and other strongholds. These sponge reefs sometimes extend 
 through several subdivisions of the Upper (White) Jura, as shown 
 in the accompanying figure (Fig. 97), after E. Fraas, where the 
 reef is surrounded by bedded sediments of the stages a, ft and y- 
 The reef contains many other well-preserved organisms besides 
 sponges, among which latter the genus Cnemidiastrum predomi- 
 nates. On the flanks of the reef a breccia of reef rock is found 
 with some clay, and this passes into the normal bedded strata of 
 clastic limestones. 
 
 MIOCENIC REEFS OF THE AUSTRO-RUSSIAN BORDER. The low 
 
FOSSIL REEFS: TERTIARY 443 
 
 ranges of hills known as "Mjodoboren" in Galicia (Austria), and as 
 "Toltry" in Podolia across the border in Russia, and which extend 
 northward into Volhynia and southward into Bessarabia, have com- 
 monly been explained as representing Bryozoa reefs (Hieber-48; 
 Teisseyre-83) of Upper Miocenic (Sarmatian) age. In reality they 
 represent reefs of earlier Miocenic age (Mediterranstufe) covered 
 by bryozoan layers of Sarmatian age (Michalski). The Toltry 
 reefs consist chiefly of corals and Vermetus masses, and form a 
 structureless limestone, which eastward and westward passes into 
 stratified clastic limestones and nullipore beds. These are on the 
 whole horizontal, but in the neighborhood of the reefs have an ir- 
 regular and often inclined position, similar to the overlap and inter- 
 lap structure on the borders of modern reefs. The reef limestone, 
 called Vermetus limestone, rises above the level of the enclosing 
 bedded limestones and constituted a barrier reef parallel to the 
 Miocenic shore which existed several kilometers to the east. Upon 
 these mid-Miocenic reefs settled in later Miocenic (Sarmatian) time 
 the Bryozoa Leprailia terebrata Sinz, and the worm tubes Serpula 
 gregalis Eichw., which formed structureless limestone masses cover- 
 ing the older reefs. Over the clastic limestones enclosing the older 
 reefs and in the depressions in the Vermetus limestones were 
 formed oolitic and conglomeratic limestones containing Ervilia 
 podolica, Cardium obsoletum, Trochus, etc. 
 
 PLIOCENIC BRYOZOA REEFS OF KERTCH. The peninsula of 
 Kertch, which partly separates the Black Sea and the Sea of Azov, 
 has been famous for more than a century for its remarkable reef 
 limestones, first described as composed of Bryozoa by Pallas in 1803. 
 They form picturesque hillocks and stacks along both the Azov and 
 Black Sea coasts, many of them dissociated by erosion from the 
 mainland and rising as partly submerged towers and stacks from 
 the shallow waters. They are developed in a less degree on the 
 opposite peninsula of Taman, where the same formations are repre- 
 sented by more clastic and argillaceous deposits. These reefs have 
 been described and illustrated in great detail in a monograph de- 
 voted to them by Andrussow ( 1 1 ) . They form knolls or tower-like 
 masses of unstratified limestone, consisting almost wholly of the 
 Bryozoan Membranipora (Pleuropora) lapidosa (Pallas), and are 
 embedded in stratified clastic limestones and argillaceous beds be- 
 longing to the Maotic stage of the Pliocenic. Many of these beds 
 are largely composed of molluscan shells, chiefly Modiola volhynica 
 Eichw. var. minor Andrussow, while others are fragmental layers 
 in which the material is largely broken shells, mingled with Bryo- 
 zoa and Serpula fragments. Where these layers meet the reef 
 
444 PRINCIPLES OF STRATIGRAPHY 
 
 knolls, they are commonly inclined, and an interlapping of the clastic 
 layers with layers composed of Membranipora and Serpula masses 
 is common. 
 
 The reef itself consists of a cavernous limestone composed of 
 knolls of Membranipora with the intervening areas largely filled by 
 a small Spirorbis shell. The surface is commonly marked by wind- 
 ing channels and irregular depressions, in which Maotic mollusc 
 shells abound. Especially numerous is the shell Sphenia cimmeria 
 Andrus. which makes up masses of shell limestone, sometimes in 
 cavities within the reef itself. The sides of the reef masses are 
 commonly very steep, often vertical and at times overhanging, and 
 the surface of the reef at all stages of growth possessed a higher 
 hypsometric * niveau than did the surrounding bedded material. 
 The height of the reef masses ranges up to 30 meters. Sometimes 
 they are embedded in argillaceous layers, derived probably from the 
 neighboring land. 
 
 BEDDED REEFS. 
 
 A type of reef differing from the lenticular one described is found 
 in a number of Palaeozoic rocks, where stromatoporoids are the 
 chief or only reef organism. Instead of forming local aggregations 
 built up into lens-like mounds, the heads of the stromatoporoids are 
 evenly distributed in beds of slight thickness, but of wide horizontal 
 extent. They grew apparently on a shallow sea bottom, at a con- 
 siderable distance from the shore, as shown by the frequent worn 
 character or overturned position of the heads, and by the scarcity 
 or absence of siliceous sediment. Sometimes the reef consists of 
 a single layer of "heads," which may measure up to 5 or 6 feet in 
 diameter ; at other times it consists of superimposed heads or frag- 
 ments of heads, forming beds twenty or more feet in thickness and 
 traceable for several thousand feet or even, with some interrup- 
 tions, for miles. Sometimes this sheet reef contains only a small 
 number of heads more or less worn, and embedded in calcarenyte 
 derived from the wear of the stromatoporoids, and sometimes it is 
 entirely replaced, for a short distance, by the coral sand. Chan- 
 nels, filled with the coral sand, are characteristic features, and 
 these and the larger interruptions of the continuity of the reef pro- 
 
 * Andrussow has proposed the term Palfeohypsometric to express the relative 
 position which the deposits had at the time of formation, while folding and dis- 
 location may have entirely changed this relationship, the present hypsometric 
 position of such deposits not being the same as that which they possessed at 
 the time of their formation. 
 
ALTERATION OF REEF ROCK 445 
 
 duce a varied aspect in the sections where they are exposed. Char- 
 acteristic examples of sheet reefs of this type are found in the up- 
 permost Siluric beds (Manlius) of central and eastern New York 
 and in the mid-Devonic limestones (Transverse group) of western 
 Michigan. 
 
 Loss OF STRUCTURE THROUGH ALTERATION OF REEF LIMESTONES. 
 
 In many of the foregoing examples of fossil reefs the organic 
 structure of the limestone has been wholly or almost completely de- 
 stroyed through subsequent alteration of the rock. In the Niagara 
 reefs of Wisconsin the stromatoporoid structure is scarcely recog- 
 nizable, except in a few cases on weathered surfaces. The same is 
 true of the Devonic and Carbonic reefs of Belgium, and especially 
 of the dolomites of the Tyrol. In all these cases dolomitization is 
 one of the chief factors in the destruction of the organic structure, 
 while recrystallization of the undolomitized limestones has had a 
 similar effect. Such changes are not uncommonly observed in mod- 
 ern coral limestones, where the hard parts, composed of aragonite, 
 as in reef-forming corals (Madreporaria), gastropoda and some 
 calcareous algae are rendered unrecognizable by recrystallization as 
 calcite, and where dolomitization obliterates the structure of even 
 the more stable calcite organisms. Sections of modern coral lime- 
 stones have shown that three types of mineral structure may be 
 recognized, due to different degrees of alteration of the rock. 
 (Skeats-8i : 105; 82 : 128; Cullis-iQ : 404.) 
 
 1. Limestones consisting largely of calcite, but containing also 
 organisms with hard parts of aragonite, while not infrequently sec- 
 ondary aragonite has been deposited in crystallographic continuity 
 with the aragonite of the organism. 
 
 2. Limestones produced from gradual alteration and recrystal- 
 lization of the first type of limestone, thus resulting in a rock in 
 which organic remains and matrix alike consist entirely of calcite. 
 
 3. Limestones produced from either the first or second type by 
 the replacement of some of the calcium carbonate by magnesium 
 carbonate, resulting in the occurrence in the rock of generally idio- 
 morphic crystals of dolomite; continued replacement will result in 
 the complete change of the limestone to dolomite. When the rock 
 is completely clolomitized, it becomes usually quite structureless, 
 the crystals of dolomite being almost entirely allotriomorphic.* 
 
 * See, further, dolomitization in Chapter XIX. 
 
446 PRINCIPLES OF STRATIGRAPHY 
 
 BALLSTONE REEFS. 
 
 In the Siluric (Clinton and Lockport) horizons of western New 
 York and the Wenlock of western England, reef-like accumulations 
 of an impure argillaceous calcilutyte occur, of a lens-like or ball- 
 like form, and embedded in shales or fragmental limestones, which 
 arch more or less around them. They vary from two to fifty feet 
 in diameter, though one in the Lockport has a length of no feet. 
 When not spherical, they range in thickness from one to fifteen 
 feet. In England these have long been known as Ball Stones, but 
 their origin has not heretofore been described. While in large part 
 composed of fine, calcareous mud, the structural groundwork of 
 these lenses is formed by branching and fan-like types of Bryozoa 
 or other organisms which grew upon the sea bottom in colonies, 
 and which captured the fine sediment from the water and formed 
 a suitable medium for its retention. On these reefs, as rich feeding 
 grounds, lived a multitude of brachiopods, molluscs, trilobites and 
 other organisms, whose remains are now found in or around these 
 lenses, while many of them are comparatively rare or unknown in 
 the adjoining strata. In western New York ( Grabau~39 :pp ; 
 Sarle~76) these ball reefs are found in the upper Clinton limestone 
 (Irondequoit limestone), and are either entirely embedded in this 
 otherwise clastic lime rock (calcarenyte) or lie in its upper portion, 
 partly enclosed in the overlying Rochester shales. More rarely are 
 reefs of this type found in the higher Lockport dolomite. They 
 are generally in the form of flattened lenses due to the cessation of 
 growth before they had reached their full size. These reefs are 
 often closely crowded, so that it has been possible to step from 
 one reef knoll to the others in places where erosion has exposed 
 their upper surfaces. The bryozoans forming the foundation of 
 these structures are several species of fistuliporoids, these some- 
 times being the only organic material found in the reefs. Tri- 
 lobites, especially the cephala and pygidia of Illsenus, abound near 
 the margin, and brachiopods are also -common, most abundant 
 among them being Whitfieldella nitida. The silt captured by these 
 organisms was exceedingly fine, so that the rock is a typical argil- 
 laceous calcilutyte, and breaks with a conchoidal fracture. On fresh 
 surfaces the bryozoans are not visible, except when their epithecal 
 surface is exposed, but weathering generally brings out their struc- 
 ture. 
 
 The Wenlock Ballstones are generally more spherical than those 
 of New York, in which the lens form prevails. They are found at 
 various levels in the thin-bedded limestones of Wenlock Edge in 
 
SHELL COLONIES 
 
 447 
 
 Shropshire, and, according to the observations of the author of this 
 volume, are in all essentials similar to those of the New York 
 Siluric. They form a marked contrast to the surrounding rock, 
 which is generally a well-bedded calcarenyte, not only by their struc- 
 tureless form, but by the compactness and fineness of the material 
 composing them. The foundation of those balls appears to be 
 formed by a branching coral, while other organisms seem to be 
 rare. 
 
 STRUCTURES FORMED BY THE GROWTH OF SHELL 
 
 COLONIES. 
 
 TEPEE BUTTES. Gilbert and Gulliver have described a series of 
 buttes or erosion hills of conical outline carved from the Cretacic 
 Pierre shales along the Arkansas River and some of its tributaries 
 in Colorado. (Gilbert and Gulliver-38.) From their resemblance 
 
 
 FIG. 98. 
 
 View of a group of Tepee-Buttes near Canyon City, Colorado. 
 (After Gilbert and Gulliver.) 
 
 to the Indian "tepee" or conical hut, they have applied the name of 
 tepee buttes to them. (Figs. 98, 99.) The buttes have an irregularly 
 cylindrical core of limestone, varying from 2, to 24. feet in diameter 
 in different examples. The average diameter is, however, 10 to 15 
 feet, while the height is unknown. (Fig. 100.) This limestone core 
 consists of an aggregation of shells, "embedded in a matrix which is 
 composed of fragments of shell, water-worn grains of calcite, foram- 
 inifera and clay." The shells are mostly those of Lucina occi- 
 dentalis var. ventricosa, which makes up by far the larger part of the 
 core. With these occur other characteristic marine Cretacic species. 
 The core is enclosed in the Pierre shales, the passage from the 
 limestone to the shale being abrupt. There is, however, a certain 
 
448 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 amount of interpenetration of the limestone and shale. "Processes 
 of the limestone embrace portions of the shale, and the contiguous 
 shale contains outlying lumps of the limestone." The best exposed 
 cores have a stratified appearance, with beds from one to three feet 
 in thickness, and separated by more or less continuous horizontal 
 
 FIG. 99. A single tepee-butte, showing the top of the limestone core. (After 
 Gilbert and Gulliver.) 
 
 partings of shale. The presence of these shale partings indicates 
 that the core was not built any faster than the surrounding de- 
 posits of mud. 
 
 Various explanations have been offered by the authors cited for 
 the origin of these cores. The best of these, and the one favored 
 by the authors, regards these accumulations of shells as colonies, 
 
 FIG. loo. Ideal section of a tepee-butte, showing the core of organic lime- 
 stone, the enclosing bedded shales, and the cover of talus. (After 
 Gilbert and Gulliver.) 
 
 which, having begun in a given place, continued there through a 
 long period of deposition, the later organisms living on the shell 
 heaps of their dead predecessors without migrating much outward 
 onto the surrounding muddy ocean bottom. Professor Shaler has 
 suggested that Lucina may have had a byssus, by means of which 
 it would attach itself to the dead shells of earlier genera- 
 tions, which would readily explain the localization of these deposits. 
 On these shell heaps would be the best feeding ground for other 
 
CRI-NOIDAL LIMESTONE 449 
 
 animals, whose remains would thus become incorporated with the 
 Lucina. 
 
 OTHER EXAMPLES. On the modern coast we sometimes find 
 colonies of Mytilus edulis growing in isolated spots, surrounded by 
 black mud deposits. As the colony increases the young individuals 
 will attach themselves to the older shells, remaining chiefly within 
 the circumscribed area occupied by the original colony, since any 
 transgression outside this area would be checked by the soft mud, 
 which offers no means of attachment. In this manner, on a slowly 
 subsiding bottom, a core of shell limestone may be formed, sur- 
 rounded by mud, in which only occasional shells are found. 
 
 Some of the "Reef Knolls" described by Tiddeman (85) from 
 the Carbonic limestones of the Clitheroe district, England, appear 
 to be due to colonies of shell-building animals, more than to the 
 growth of reef corals. Their structure, however, is more like the 
 coral reefs than the tepee butte cores. 
 
 BEDDED ZOOGENIC DEPOSITS. 
 
 CRINOIDAL LIMESTONES. Among the limestones of all geologic 
 formations, beds composed largely or wholly of crinoid remains are 
 common. These remains are generally the stem joints, and they 
 vary greatly in size, from that of a pin head or smaller to those 
 over one inch or more in diameter. Generally the fragments of each 
 bed are more or less uniform in size, this latter depending on the 
 species of crinoid which has flourished in that region. Crinoids 
 are admirably adapted to the formation of limestone beds, because, 
 on the death of the animal, the long stems, as well as the calices and 
 arms, readily separate into their component ossicles, and thus with 
 little rearrangement furnish the material in proper size of grain for 
 a limestone bed. Kirk (56) has recently brought forward much 
 evidence to show that many crinoids separate from their anchorage 
 and become more or less planktonic in later life. Thus schools of 
 floating crinoids may be washed into shallow water, there to accu- 
 mulate as crinoidal limestones. The crinoidal character of an an- 
 cient limestone is not always noticeable on the fresh surface, but 
 on weathering this structure is brought out. When accumulations 
 occur within the zone of wave activity, cross-bedding and other 
 shallow water structures may result. 
 
 SHELL LIMESTONES. Beds of unbroken shells or coquina are 
 likewise found in different geologic horizons. Often great beds of 
 limestone occur, in which one species of shell predominates to the 
 
45 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 practical exclusion of others. Such are the great beds of Pen- 
 tamerus oblongus extending widely through the Siluric of Gotland 
 and New York; the beds of Anoplotheca in the Clinton of the 
 Rochester region, and those composed of Exogyra or other shells 
 in the Cretacic of Texas ; the limestones entirely made up of Tur- 
 rit ella mortoni in the Eocenic of Virginia, and numerous other ex- 
 amples. Rocks of this type generally form thin beds among the 
 clastic sediments. From the nature of the material, these beds can 
 be only rudely stratified, and irregularities in thickness may be ex- 
 pected where wave action has not been strong. 
 
 CALCAREOUS AND SILICEOUS OOZES. These often form beds of 
 considerable thickness, as in the case of the chalk. These accumu- 
 lations when pure always indicate either a remoteness of the shore, 
 with perhaps deep-water conditions, or a very low relief of the land, 
 which has been peneplaned to such an extent that no clastic sedi- 
 ments are derived from it. The oozes formed in the modern ocean 
 include the following types: 
 
 1. Calcareous: a, Foraminiferal; b, Pteropod; c, Entomostra- 
 can ; d, Coccolith, and e, Rhabdolith ooze. 
 
 2. Siliceous: a, Radiolarian; b, Diatom. 
 
 i. The Calcareous Oozes. 
 
 Recent Foraminiferal Oozes. These are represented in the mod- 
 ern sea by the Globigerina ooze (Fig. 105), so named from the pre- 
 ponderance of the shells of Globigerina, which is represented by ten 
 
 FIG. 101. Globigerina bulloides. x 40. 
 (After Wyville Thomson.) 
 
 FIG. 102. Orbulina unvversa. x 40. 
 (After Wyville Thomson.) 
 
 species, while Pulvinulina is represented by five species. The total 
 number of species of foraminifera making up this ooze is only 21, 
 distributed in 9 genera, but only four species are of great impor- 
 tance in the making of this ooze. These are Globigerina bulloides 
 
GLOBIGERTNA OOZE 451 
 
 (Fig. 101), in the northern hemisphere and most of the tropical 
 seas ; Globigerina dutertrei, for the higher southern latitudes ; and, 
 further, Orbulina unwersa (Fig. 102) and Hastigerina pelagica. 
 The foraminifera of this ooze all inhahit the upper 200 meters of 
 the ocean, leading a planktonic existence (Chapter XXVIII). It is 
 only on the death of these organisms that their shells sink to the bot- 
 tom and become incorporated in contemporaneous sediments of other 
 origin, or, if this is rare or absent, to accumulate as extensive, more 
 or less pure deposits of shells. The ooze is never absolutely com- 
 posed of foraminiferal shells, for the shells of other planktonic or- 
 ganisms also enter into the composition. Among these are the 
 shells of pelagic molluscs, such as the pteropods arid heteropods, 
 both often of considerable size; ostracods (Crithe producta, Cy- 
 thcre dictyon) ; minute planktonic algae, Coccolithophores or coc- 
 
 FIG. 103. Pulvinulina. A multicham- FIG. 104. Coccolithophora. (After 
 bered foraminiferal shell (after A. Agassiz.) x 600. 
 
 Murray) much enlarged. 
 
 eoliths (Fig. 104) and rhabdoliths. These pelagic admixtures are 
 further supplemented by those of sea-bottom or benthonic origin, 
 among which bottom-living Foraminifera may constitute as high as 
 3 per cent, of the mass. Furthermore there are clastic lime and 
 other fragments; spines of echinoderms, shells pf molluscs; worm 
 tubes; deep-sea corals; Bryozoa, etc. In all, these never make up 
 more than 25% of the mass, and, according to Murray and Re- 
 nard, on the average only 9%. From the amount of pelagic cal- 
 careous organisms in these deposits, Murray and Renard have cal- 
 culated that there are at least sixteen tons of floating carbonate of 
 lime in one square mile of water surface, distributed through the 
 upper 100 fathoms of the sea. The clastic material is often less 
 than i% and averages 3.3% in the 118 samples obtained by the 
 Challenger expedition. In depth the Globigerina ooze is most abun- 
 dant between 2,500 and 4,500 meters, its mean depth being 3,660 
 
452 PRINCIPLES OF STRATIGRAPHY 
 
 meters. The 118 samples obtained by the Challenger expedition 
 were distributed as follows : 
 
 Percent- 
 age of 
 CaC0 3 
 
 Less than 1,000 fathoms (1,830 m.) 5 j 
 
 Between 1,000 and 1,500 fathoms (1,830-2,750 m.) 13 \ 60-70% 
 
 Between 1,500 and 2,000 fathoms (2,750-3,660 m.) 35 J 
 
 Between 2,000 and 2,500 fathoms (3,660-4,570 m.) 49 62% 
 
 Below 2,500 fathoms (4,570 m.) 16 50% 
 
 118 
 
 It will be observed that the percentage of CaCO 3 in the oozes 
 decreases with depth, being only 50% in the samples from the 
 greater depths. The average of the 118 samples gave 64.5% of 
 CaCO 3 , 30.6% of non-calcareous silt, 3.3% mineral particles, and 
 1.6% siliceous organisms. The lime was distributed as follows: 
 ; 
 
 Remains of pelagic organisms 53 . 1 % 
 
 Remains of benthonic organisms 2.1% 
 
 Remains of other organisms 9 . 3% 
 
 64.5% 
 
 Among the mineral matter other than lime associated with the 
 Globigerina oozes may be mentioned glauconite, and phosphate and 
 manganese concretions. 
 
 Sir John Murray concluded from experiments made that it takes 
 the dead foraminiferal shells from three to six days to sink to a 
 depth of 4,500 meters, the rate being slowest in the deeper water. 
 Solution of the lime of the shells by the sea water increases rapidly 
 with depth, owing to the increase in pressure. Thoulet found that 
 the rate varied greatly with the size of the shells and particles, 
 those averaging 0.75 mm. in diameter taking 1.09 days to reach a 
 depth of 4,500 meters, while those having a diameter of only 0.12 
 mm. required 7.47 days for the same distance. 
 
 Not infrequently fragments and blocks of terrestrial rocks are 
 found in the Globigerina deposits, as, for example, fossiliferous 
 Palaeozoic rocks marked by glacial scratches, and found by the 
 French expedition northeast of the Azores, 1,100 km. from the Euro- 
 pean coast, carried there by drift ice probably during the last glacial 
 period; and the coarse fragments of crystalline rock found in the 
 South Atlantic between Tristan da Cunha and Kapstadt, in 35 to 
 36 S. lat., and others from the Indian Ocean. 
 
 The areal distribution of the Globigerina ooze is a considerable 
 
FOSSIL FORAMINIFERAL OOZES 453 
 
 one, being in round numbers 105 million square kilometers or 29.2 
 per cent, of the entire oceanic surface (Krummel-57: 188). Its 
 principal distribution is, however, in the Atlantic Ocean, where it 
 occupies more than 44 million square kilometers, overshadowing all 
 the other deep-sea sediments. In the Indian Ocean 31 million 
 square kilometers of bottom are covered by this deposit, but in the 
 Pacific it covers only 30 million square kilometers, a comparatively 
 small percentage of the bottom of that ocean. 
 
 Fossil Foraminiferal Oozes. Typical foramini feral oozes are 
 found in fossil form mainly in the chalk of the west of Europe and 
 
 FIG. 105. Globigerina ooze, x 20. (After Murray and Renard.) 
 
 elsewhere. Deposits of foraminiferal shells, of large benthonic 
 types, are, however, developed in other horizons. Such are the Fu- 
 sulina limestones of the Carbonic and Permic, and the Nummulite 
 and Orbitoidal limestones of the Tertiary. These are best classed 
 as shell rocks. Chalk, on the other hand, is a distinct foraminiferal 
 ooze, a calcipulverite, but, unlike the Globigerina rock, it is not 
 formed of pelagic, but of benthonic or bottom types. (Fig. 106.) 
 Among these the biserial Textularia holds the same position that 
 Globigerina does in the modern deposit, while another benthonic 
 form, Rotalia, is also common. Pelagic forms, however, are not 
 wholly absent, nor should we expect them to be. Nineteen species 
 have been recognized as found both in the modern Globigerina ooze 
 and the Cretacic chalk, but this identification of species is largely 
 due to the lack of distinctive characteristics. Coccoliths also are 
 
454 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 common in the chalk, and diatoms, Radiolaria and sponge spicules 
 probably were as plentiful in the chalk as in the modern deposits, 
 but these siliceous structures have since been dissolved, and the sil- 
 ica redeposited as flint. Among the clastic admixtures quartz is also 
 common, indicating the neighborhood of land. 
 
 The principal species of the chalk is Tcxtularia globulosa (Fig. 
 1 06, a), which lives to-day in the estuary of the Dee near Chester, 
 but of course forms no extensive foraminiferal deposits there. 
 (Murray-671477.) 
 
 In the island of Malta, Oligocenic limestones (Aquitanien) oc- 
 cur which are made up largely of pelagic Globigerina, and nearly 
 
 B 
 
 Fia 106. Preparation of white chalk, showing the foraminifera, etc. (After 
 Zittel.) A Chalk from Sussex, Eng. B Chalk from Farafrah, 
 Libyan desert. Both x 60. a Textularia globulosa; b Rotalia 
 (Discorbina) marginata. C dried residue of milky chalk water 
 with coccoliths. x 700. 
 
 40 per cent, of the species of this rock still live in the neighboring 
 Mediterranean. These beds further contain phosphate concretions 
 and green sands such as characterize the modern sea bottom .in 
 depths from 500 to 2,000 meters, and also sharks' teeth similar to 
 those found by the Challenger in the greater oceanic depths. The 
 percentage of lime in the Globigerina deposits of Malta ranges 
 from 95 to 98.6. These deposits appear to have been formed in 
 the greater depths of a mediterranean rather than in the open sea. 
 Similar foraminiferal deposits have been obtained from the Plio- 
 cenic of Sicily and Calabria. 
 
 In this connection it must be noted that foraminiferal limestones 
 are not necessarily deep-sea or even submarine deposits, for the 
 
CALCAREOUS OOZES 455 
 
 shells of littoral species may be washed up onto the shore, where 
 they form an extensive foramini feral sand, as in the case of the 
 Orbiculina shells of the Bahamas. These shells may then be blown 
 inland to form beds of foraminiferal limestone often of great purity, 
 at a distance from the shore on the dry land. Such is the case 
 with the limestone of Junagarh on the Kathiawar peninsula, West 
 India (see Chapter XIII), and the foraminiferal limestones of 
 Jamaica may have a similar history. 
 
 Zoogenic oolites. Among the numerous theories advanced to 
 explain the origin of the oolites is that of their zoogenic origin, the 
 role of oolite-former being commonly assigned to Foramini f era. 
 Thus Ehrenberg regarded the oolites of the Jura of many locali- 
 ties as formed by the more or less recrystallized shells of Melonites 
 
 FIG. 107. Pteropod ooze, x 10. (After Murray and Renard.) 
 
 (Mikrogeologie). The oolite-forming organism described by 
 Bornemann as Siphonema incrustans and referred to alg^e was 
 relegated by Nicholson to the Foraminifera on account of its re- 
 semblance to the recent foramini feran Syringamnina fragilissima 
 Brady, while Sorby and Withered also regard it as a foraminiferan, 
 the former finding its resemblance closest to Hyperamnina vagans 
 Brady. This organism forms oolites in the Siluric and Devonic. 
 The oolites of the Muschelkalk regarded by Bornemann as due to 
 algous growths are referred by Frantzen to zoogenic origin, as lime 
 separated by acid of the animal organisms. By others these same 
 oolites have been regarded as of purely hydrogenic origin. 
 
 Recent Pteropod Ooze. (Fig. 107.) This is found in only a few 
 tropical and subtropical regions resting like the foraminiferal oozes 
 upon the swells and submarine ridges. In all there are known 6 
 
456 PRINCIPLES OF STRATIGRAPHY 
 
 genera and 35 species of planktonic pteropods in this ooze, but only 
 three genera, Limacina, Clio and Cavolinia, are abundantly repre- 
 sented. With these occur the heteropods Carinaria, Atlanta and 
 Oxygyrus. These shells make up from one-quarter to one-half the 
 entire mass, the remainder being chiefly Foraminifera. The depth at 
 which these delicate shells occur is between 1,000 and 2,700 meters; 
 below this they give way to purer Globigerina ooze. In the Atlantic 
 these deposits occur especially around the Azores, on the outside 
 of the Antilles, west of the Canary Islands, and on the South At- 
 lantic rise between Ascension and Tristan da Cunha. In the Indian 
 Ocean they occur off the African coast from the equator to Soko- 
 tora, and to the west of Cape Comorin near the Nicobar and Men- 
 tawie Islands. In the Pacific they surround the Fiji Islands, occur 
 east of the Great Barrier Reef, around the Kermadec and Hawaiian 
 Islands, and especially in the region of the Paumota or Low Archi- 
 pelago. The total area covered by these deposits does not exceed 
 one and a half million square kilometers. 
 
 Fossil Pteropod Oozes. These are known from various hori- 
 zons ; in the Upper Devonic of New York State occurs a lime- 
 stone composed almost entirely of Styliolina fissurella, embedded in 
 dark shales, which are sparingly or not at all fossiliferous. The 
 limestone varies in thickness from 6 inches to a few feet, and has 
 been traced from the Genesee Valley to Lake Erie, a distance of 
 over sixty miles. Clarke has estimated that 40,000 individuals oc- 
 cur on the average in a cubic inch of the rock ( 16 115) . In the Cam- 
 bric, beds of limestones, largely composed of Hyolithes and Ortho- 
 theca, occur, and some Upper Siluric horizons carry layers formed 
 of Tentaculite shells (Manlius limestone of New York, etc.). 
 
 Entomostracan Oozes. These are seldom of great purity as 
 oceanic deposits. The Ostracoda, Crithe and Cythere are abun- 
 dant among the plankton of the ocean, and their shells are found 
 mingled with Foraminifera and pteropods. No pure marine ostra- 
 cod ooze has been obtained from the deep sea. These organisms 
 also occur in salt pools (Cypris salina, etc.), in the estuaries of 
 rivers (Cypris, Potamocypris, Pontocypris, Cythere, etc.) and in 
 fresh-water lakes and pools. At the Ayin Musa Springs near Suez, 
 calcareous deposits are formed by the abundant accumulation of 
 the shells of Cypris delecta (Fraas-32 : 182). Limestones of Cypris 
 shells have also been found in the fresh-water Tertiary deposits of 
 western America. Eolian deposits of this type are also known. 
 
 Coc eolith and Rhabdolith Oozes. Coccoliths are the minute 
 oval plates of lime which cover the planktonic Coccolithophora, 
 small algae of the order Calcocytea, while rhabdoliths are slender 
 
SILICEOUS OOZES 457 
 
 rods, radially arranged in the Rhabdosphaera. Both are members 
 of the family Coccolithophoridae, of the order Chrysomondacese, 
 minute organisms referred by some to the algae, and by others to 
 the Flagellata among the Protozoa. (See Chapter XXIV.) They 
 make up an important part of the Globigerina ooze of the present 
 day, and their remains also abound in older deposits. In the North 
 Atlantic certain dredgings in 4,004 m. brought up ooze in which 
 coccoliths formed 68 per cent, of the sediment. Certain chalks 
 have also been found to consist almost wholly of coccoliths and 
 rhabdoliths. The size of the individual coccolith plates ranges 
 from o.ooi to 0.003 mm - i n diameter, and Huxley has divided them 
 into two groups : discoliths, disk-shaped, convex on one side and 
 concave on the other, and cyatholiths, of a form somewhat resem- 
 bling that of a shirt stud. Minute calcareous disks of this kind are 
 separated out of a solution of lime sulphate or lime chloride by the 
 action of ammonia generated by the decomposition of organic mat- 
 ter, and from this it has been inferred that coccoliths are of inor- 
 ganic origin. 
 
 2. The Siliceous Oozes. 
 
 These comprise the radiolarian and diatomaceous oozes, the first 
 animal and the second plant structures. 
 
 Radiolarian Oozes. (Fig. 108.) These are typically abyssal de- 
 posits ; the shells, owing to the resistance which they offer to solu- 
 tion, can sink into depths below those at which foraminiferal shells 
 dissolve, and so they are typically found associated with the deep- 
 sea red mud. Indeed, the deposit is seldom if ever free from the 
 red mud, which forms a sort of medium in which the radiolarian 
 shells are embedded. When more than 20 per cent, of the sediment 
 is made up of Radiolaria, it is called a Radiolarian ooze. The most 
 abundantly represented and best preserved of these planktonic 
 Radiolaria are the Nessellaria and Spumellaria, while the Phaeo- 
 daria are more sparingly and the Acantharia not at all represented 
 in the deposits, though abundant in the plankton. This is due to 
 the fact that the skeletons of the last group are not siliceous, but 
 consist of acanthin, which, like chitin, is readily destroyed after the 
 death of the organism. 
 
 The Challenger found this ooze in its deepest soundings in the 
 western Marian deep in 8,184 meters. It contained 54.4 per cent, 
 of Radiolaria and other siliceous organisms, 3.1 per cent, of pelagic 
 and o.i per cent, of benthonic Foraminifera, 0.8 per cent, of other 
 
458 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 lime-secreting organisms, 1.7 per cent, mineral matter and 40 per 
 cent, of the fine red mud. 
 
 The geographic distribution of this deposit is much less than 
 that of the Foraminifera, the total area covered by it being only 
 something over 12 million square kilometers, or 3.4 per cent, of the 
 total ocean bottom. It seems to be entirely wanting in the Atlantic, 
 and restricted to the region around the Cocos and Christmas 
 islands in the Indian Ocean. In the Pacific it finds its greatest dis- 
 tribution between 5 and 15 north latitude, and between Central 
 America and 165 west longitude. A few other isolated patches in 
 the Pacific contain this deposit. 
 
 
 
 FIG. 108. 
 
 Radiolarian ooze from the Indian Ocean, x 40. (After Kriim- 
 mel.) i. Tricyrtida; 2. Dicyrtida; 3. Discoidea; 4- Prunoidea; 
 5. Larcoidea; 6. Coronida; 7. Sphseroida ; 8. Chaetoceras (Dia- 
 tom) ; 9. Sponge-spicules. 
 
 Fossil radiolarian oozes also occur, but in most cases it may be 
 questioned whether they are really deep-sea deposits. An example 
 is the radiolarian rock described by Rust (75:181), which has been 
 regarded as of deep-sea origin, but Walther has insisted that the 
 high content of Carbonaceous material and the quantity of littoral 
 sediments oppose this view. The island of Barbados also furnishes 
 a colored clay which contains an abundance of radiolaria (Barbados 
 earth), and this has been regarded as a deep-sea deposit similar 
 to that found in the Pacific at 5,000 m. and now brought to the 
 surface by a local elevation. Limestones similar to the modern 
 Globigerina ooze also occur on this island. 
 
RADIOLARITES . 459 
 
 Radiolaria have been found in cherts of various ages from the 
 Ordovicic on, and some of these cherts are believed to be due to 
 the segregation of silica furnished by the Radiolaria and other silica- 
 secreting organisms. 
 
 The Jurassic Radiolarite of the Alps. In certain portions of the 
 Austrian Alps, a remarkable deposit of radiolarian mud is found 
 in the upper Jura. (Hahn-43, i:j#p.) This radiolarite, as it is 
 called, consists of intensely blood-red, more rarely greenish, jaspery 
 layers, alternating with dense, brown-red or greenish gray quartz- 
 ose and argillaceous marls, the total having a thickness varying from 
 i o to 25 m., the increase being due to increase in the marly layers. 
 Under the microscope it appears as an extremely fine-grained, al- 
 most homogeneous mud rock, filled with minute spherical crystal 
 bodies, referable to Radiolaria. The original ornamentation of these 
 bodies is seldom preserved in the argillaceous layers, but the jasper 
 contains Spumellarians in a wonderful state of preservation. This 
 rock thus appears to be of the type of radiolarites which represent 
 the deep-sea radiolarian oozes, and are found to-day in depths of 
 from 3,000 to 7,000 meters. 
 
 These radiolarites rest on Upper Lias, or on variegated am- 
 monite limestone or breccias of Middle Liassic age. Some indica- 
 tions point to a disconformable relation with the underlying rock, 
 there being apparently ah absence of Dogger and part of the Malm. 
 This would suggest land conditions with erosion prior to sub- 
 mergence, the sinking being a rapid one down to the depths at 
 which such ooze will accumulate. 
 
 Upward the radiolarite passes into gray calcilutytes with 
 Aptychus of Tithonic age. This indicates a gradual shoaling of the 
 water, which culminated in land conditions in the next succeeding 
 period. 
 
 Similar deposits of Radiolarite have been described from the 
 Lower Carbonic beds of the Rhine district ( Wilckens-92 : J5^) and 
 from various parts of Great Britain. These examples of older 
 radiolarites are believed to be of shallow-water origin. Such cherts 
 are well shown in the Carboniferous (Mississippic) limestone series 
 of Gower in western England (Dixon and Vaughan-25 : 521). They 
 are finely and sharply laminated, many of the laminae being lenticu- 
 lar or wedge-shaped. They are also found in the lower Culm of 
 Devon (Codden Hill beds), from which they were first described 
 by Hinde and Fox, who, however, regarded them as deep-sea de- 
 posits. From the nature of the deposits themselves, as well as from 
 the character of the including rocks, others have come to the con- 
 
460 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 elusion that these rocks are of shallow-water or lagoon origin 
 (Dixon and Vaughan-25 '.522. ) 
 
 The Onondaga coral reefs of western New York are succeeded 
 and sometimes replaced by very cherty limestones, and it is not im- 
 possible that the chert layers in the so-called Corniferous limestone 
 represent shallow-water radiolarites accumulated in the lagoon be- 
 hind the coral reefs. 
 
 Recent Diatomaceous Ooze. (Fig. 109.) This is a phytogenic 
 deposit, but is best considered in this connection. It is most abundant 
 in the ocean in the higher latitudes of both hemispheres, and origi- 
 nates from the phytoplankton of the colder and less saline waters 
 of the polar regions. The diatom frustules of the ooze obtained in 
 the southern hemisphere belong to a number of genera (Navicula, 
 Coscinodiscus, Fragillaria, Synedra, Asteromphalus, Rhizosolenia, 
 
 FIG. 109. Diatom ooze, x 200. (After C. Chun.) 1-5. Coscinodiscus; 6 
 Asteromphalus ; 7. Fragilaria antarctica ; 8, 9. Synedra ; 10. Rhiz- 
 osolenia; ii. Chaetoceras; 12. Navicula (?); 13, 14. Dictyochi and 
 Radiolaria. 
 
 etc.), and associated with them are fragmentary frustules, Radio- 
 laria, sponge spicules, lime particles, etc. 
 
 These sediments form a circumpolar belt in the southern hemi- 
 sphere, and likewise form a band across the northern Pacific. The 
 southern area comprises nearly 22 million square kilometers. In the 
 tropical regions diatomaceous sediments also occur. They have 
 been found to constitute a veritable tripolite or infusorial earth at 
 depths from 2,700 to 5,200 meters under the Peru stream between 
 Callao and Galapagos. Between the Marian and Philippine Islands 
 the floor of the Pacific is covered in patches by the frustules of Cos- 
 cinodiscus rex, one of the largest known forms, with a diameter of 
 0.8 mm. This occurs in depths ranging from 4,500 to 6,000 meters. 
 Altogether about 23 million square kilometers of the ocean bottom, 
 
DIATOM AND PHOSPHATE DEPOSITS 461 
 
 or about 6.4 per cent, of the entire sea floor, are covered with this 
 deposit. 
 
 Diatoms likewise live in fresh water and deposits of diatomace- 
 ous ooze may form under such conditions. 
 
 Fossil Diatomaceous Earths of Both Fresh and Salt Water 
 Origin. These are widely distributed over the world, especially in 
 Tertiary deposits. They ordinarily go under the name of Infusorial 
 earth or Tripolite, so named from the deposits at Tripoli in North 
 Africa. The most extensive is that found at Richmond, Virginia, 
 which extends for many miles, and is in some places at least 40 feet 
 in thickness. Other deposits are found in the Great Basin in Ne- 
 vada, Oregon, and California, where they form beds of great thick- 
 ness usually interstratified with volcanic material. 
 
 PHOSPHATE DEPOSITS. 
 
 Guano. A subordinate type of zoogenetic rock is the guano, 
 formed from the droppings of innumerable birds which inhabit iso- 
 lated islands and promontories on the sea coast. Near Iquique, 
 Province of Tarapaca, Chile, such a deposit with a thickness of 10 
 meters is known, and it is estimated that it may have formed in 
 1,100 years. The deeper strata of these formations are generally 
 darker in color and more crystalline. Deposits of the excrements of 
 seals sometimes alternate with those of birds in certain places on the 
 coast of Tarapaca. Here these deposits contain numerous smooth 
 fragments of porphyry from 3 to 10 cm. in length, derived from the 
 stomach content of these seals. (Tschudi in Walther-Qor^j.) 
 
 A number of distinct phosphate minerals are found in guano. 
 
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 Section VIII, pp. 160-164. 
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464 PRINCIPLES OF STRATIGRAPHY 
 
 
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 53. JUKES-BROWNE, A. J. Voyage of H. M. S. Fly, Vol. I, Chapter XIII. 
 
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BIBLIOGRAPHY X 465 
 
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 TIDDEMAN, R. H. 1891. Ibid. Congres Geologique International 
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 VAUGHAN, T. W. 1911. Physical conditions under which Palaeozoic 
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 VERRILL, A. E. 1867. Boston Society of Natural History. Report 
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 WALCOTT, C. D. 1906. Algonkian Formations of Northwestern Mon- 
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466 PRINCIPLES OF STRATIGRAPHY 
 
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 Doppel-Mulde. Zeitschrift der deutschen Geologischen Gesellschaft, 
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CHAPTER XL 
 
 CHARACTER AND LITHOGENESIS OF ORGANIC OR BIOGENIC 
 ROCKS (CONTINUED). PHYTOGENIC DEPOSITS. 
 
 Phytoliths, or rocks formed from the remains of plants, may 
 be classed with reference to their material as acaustophytoliths and 
 caustophytoliths. The latter comprise the peats, coals, bitumens, 
 etc., while the former include calcareous or siliceous mineral matter 
 secreted by the growing organism. With reference to their source 
 of origin, phytoliths may be classed as autochthonous, or such as 
 are deposited where they grew, or allochthonous, those brought 
 from other localities and so deposited in foreign soil. 
 
 Autochthonous acaustophytoliths have been mentioned in the 
 preceding- chapter, in the growth of nullipores on coral reefs, and 
 allochthonous acaustophytoliths have been described in the diatoma- 
 ceous oozes. In this chapter we shall discuss more fully the two 
 classes of phytoliths, beginning with those depositing mineral mat- 
 ter other than carbon. 
 
 ACAUSTOPHYTOLITHS. 
 
 DEPOSITS FORMED BY LIME-SECRETING ALGJE. Among the plants 
 belonging to the comparatively low division of algae are a number 
 which secrete carbonate of lime or silica and deposit it either as a 
 coating on the exterior or within their tissues. 
 
 MODERN MARINE FORMS. Among the lime- and silica-secret- 
 ing algae of the modern ocean the following may be especially men- 
 tioned. 
 
 Order Cyanophycea, or Blue-Green Alg<z. 
 
 This order contains several lime-secreting members, some of 
 which become important as rock builders. 
 
 Phytogenic Oolites. On the shores of Great Salt Lake, Utah, 
 
 467 
 
468 PRINCIPLES OF STRATIGRAPHY 
 
 Rothpletz (36) has noted that the genera Glceocapsa and Glceo- 
 thece, which are rich lime-secreters, form snow-white oolite grains 
 which are scattered among the sand and pebbles of the low shores, 
 and blown landward into dunes ranging up to 6 feet in height. 
 "The cells of the Gloeocapsa are 2 ^ * in diameter and spherical, 
 those of the Glceothece 2 to 3 /x thick and 4 to 5 //, long. The lime 
 is enclosed in the alga-body in the form of rounded tubercles, which 
 often mass themselves together into larger irregular tubercular 
 bodies. It is a fine-grained aggregate of calcite which always en- 
 closes numerous dead alga cells that have already lost their green- 
 ish coloring." Three forms were recognized: ist, irregular tuber- 
 cular bodies, several millimeters in diameter ; 2nd, spherical or oval 
 forms, about one-third millimeter in diameter; and, 3rd, thin rods, 
 about half a millimeter long and one-tenth millimeter broad. These 
 oolites are forming day by day through the secretion of lime by 
 these algae. 
 
 Since analysis of the water of Great Salt Lake (see Chapter 
 IV) shows only a small quantity of calcium chloride or sulphate 
 and no carbonate, no lime would be precipitated from the lake it- 
 self, except for the activities of these minute plants. When it is 
 considered, however, that the streams tributary to this lake bring 
 in quantities of carbonate of lime, all of which is precipitated as 
 oolite grains, it becomes a question whether the algous growth is 
 so active as to use up all this lime or whether "the strong brine of 
 the lake seems to be incapable of holding calcium carbonate in solu- 
 tion" (Clarke-8:/4<5) and it is therefore precipitated chemically.f 
 
 Similar oolites are forming on the shores of the Red Sea, where 
 they are widely distributed along the west coast of the Sinai penin- 
 sula. Here they are drifted inland often for many kilometers, or 
 even days' marches distant from the shore, and constitute white 
 dune sands of oolitic material, a continental formation built of 
 material of marine origin. These grains generally contain vermi- 
 form and often branching canals, more or less filled with calcite. 
 
 * i fj. = o.ooi mm., called a micron. 
 
 t Of the rivers tributary to Great Salt Lake, the following may be noted 
 with their percentage of CO 3 and Ca (Clarke-8:J45): 
 
 CO 3 Ca 
 
 A. Bear River at Evanston, Wyoming 52 . 68 23 . 69 
 
 B. Bear River at Corrine, Utah ' 21 . 53 10. 12 
 
 C. Jordan River at intake of Utah and Salt Lake 
 
 Canal 2 . 67 7 . 59 
 
 D. Jordan River near Salt Lake City trace 10.26 
 
 E. City Creek, Utah 52-57 24 . 19 
 
 F. Ogden River at Ogden, Utah 33 .68 16.05 
 
 G. Weber River at mouth of Canyon 40 . oo 18.19 
 
PHYTOGENIC OOLITES 469 
 
 These are believed to be due to the presence of thread-like algae 
 living symbiotically on the lime-secreting species and being encased 
 by the deposits of lime. 
 
 In the low coastal tract in the further environs of Suez, Quater- 
 nary oolites of this type are found, built up subaerially into beds 
 and dunes and frequently consolidated into hard oolitic limestones 
 (Bauermann). These oolites, however, generally contain a foreign 
 sand grain, but the lime surrounding them has the structure of the 
 oolites of Great Salt Lake and on solution leaves the organic resid- 
 uum found in these. 
 
 Some observers contend that the oolites of the Red Sea region 
 have a radial structure, but this is denied by others. Linck, more- 
 over, holds that this radial structure, when it occurs, does not indi- 
 cate organic growth. He interprets the rods as minute crystals of 
 aragonite deposited in a purely hydrogenic manner. 
 
 Oolites regarded as due to the growth of algae have been de- 
 scribed from the salt lakes of the Kalahari desert of Africa. 
 (Kalkowsky-26.) From his studies Rothpletz concludes that the 
 "majority of the marine calcareous oolites with regular zonal and 
 radial structure are of plant origin ; the product of microscopically 
 small algae of very low rank, capable of secreting lime." (Roth- 
 pletz-Cragin~36:^7p.) On the other hand, Linck, who' approached 
 the subject from the experimental point of view, is equally positive 
 that these oolites are 'wholly of chemical origin, deposited either 
 freely or upon a foreign nucleus, under the influence of chemical 
 reaction, as aragonite (really ktypeit) and that when organic re- 
 mains, such as algae, etc., were enclosed they lived upon the growing 
 shells of inorganic origin or were mechanically enclosed by the 
 chemical deposit. The algous rods (Algenstabchen) of Rothpletz 
 he regards as minute crystals of aragonite. The aragonite oolites 
 are subsequently altered to calcite, which is the condition of most 
 fossil oolites. (See further under fossil oolites, posted, p. 471, and 
 oolites of chemical origin, ante, p. 336, Chapter IX.) 
 
 Order Chlorophycece, or Green Alga. 
 
 In this division the chief lime-secreting algae of the modern 
 sea are the genera Halimeda and Udolea of the group Siphonales. 
 These grow in the shallower portion of the coral reefs connecting 
 dead coral masses. (Agassiz-i :&?.) Halimeda opuntia and H. tri- 
 dens form masses of lime on the shores of St. Thomas. (Challen- 
 ger Narrative-7:/^7.) It is a jointed plant and readily broken up 
 into small lime rods. An analysis of Halimeda gave CaCO 3 , 90.16%, 
 
470 PRINCIPLES OF STRATIGRAPHY 
 
 MgCO 3 , S-S% ; CaSO 4 and SiO 2 , 0.5% ; organic matter 3.8%. This 
 alga forms extensive limestone deposits within the lagoons of coral 
 atolls, as in the case of Funafuti, and in the Red Sea. 
 
 Order Phceophycece or Brown Algce. 
 
 This division, which contains the great algae (Laminaria, Ma- 
 crocystis), the floating Sargassum, and the attached rock weed or 
 Fucus, has no important lime-secreting members, but the diatoms, 
 important on account of their siliceous frustules, belong here. Their 
 general character and importance have already been discussed in 
 the preceding chapter. 
 
 Order Rhodophycece or Floridecc Red Alga. 
 
 This division contains several very important types which act 
 in part as rock-builders. These include the genera Corallina, Jania, 
 Melobesia, Lithothamnion, and Lithophyllum and they are dis- 
 tributed from the equator to the arctic regions. The living plant 
 often contains as much as 85% CaCO 3 and many of the more mas- 
 sive ones (Lithothamnion, etc.) build heavy barriers on the outer 
 zone of coral reefs, where wave activity is most pronounced. Litho- 
 thamnion fasciatum occurs in the Arctic Sea on the coast of Nor- 
 way at a depth of 70 m., on the Russo-Lapland coast from 10 
 to 55 meters, at Spitzbergen, 18-36 m., and at Nova Zembla in 45 
 meters. L. polymorphic and Corallina officinalis are found on 
 the Great Banks in 22 m. (Walther). L. racemus forms masses of 
 the size of a fist in the Gulf of Naples on the Secca di Gajola in 
 25 meters depth, while the smaller L. ramolosum abounds in 45 to 
 60 meters on the Secca di Benda Palummo, or pigeon bank. (Wal- 
 ther-5o :^.?p ; 52:47.) 
 
 In the Caribbean Sea nullipores occur down to depths of 284 m. 
 (Agassiz-2:/^/) and in the Gulf of Naples Lithothamnion, Coral- 
 lina and Lithophyllum occur at depths of 30 to 65 m. (Wal- 
 ther 50 :22p. ) The name "Nullipore" is generally applied to all 
 these lime-secreting algae. It is derived from the old Lamarckian 
 genus Nullipora, which included four species of calcareous organ- 
 isms, all probably belonging to the family Corallinaceae of the re( 
 algae. 
 
 The name Lithothamnion was generally applied to the unseg- 
 mented coralline algae, but has more recently been restricted, while 
 other generic groups Lithophyllum, Goniolithon, Phyinatolithon, 
 etc. have been separated from the original group. 
 
CHARA MARLS; FOSSIL OOLITES 471 
 
 The nullipores are often the most important lime-contributors 
 to the coral reefs, far more important than the corals themselves. 
 This has been found to be the case in Funafuti reef (Finckh), the 
 Fiji reefs (Gardiner), the Chagos group (Gardiner), etc. In all 
 these, animal, especially coral life is relatively unimportant, while 
 plant life (nullipores) flourishes luxuriantly. (See the photograph 
 of a Lithothamnion reef in Nature, Vol. LXXII, pp. 571, 572.) 
 
 In Bermuda, too, corals play a subordinate part in the reef 
 formation, Lithothamnion taking its place among the principal reef 
 builders (Agassiz-3). Nullipores also grow on the Challenger Bank, 
 raising the surface from considerable depths to within the zones of 
 coral growth. (Howe-24.) 
 
 LIME-SECRETING ALG.E OF FRESH WATER. These are chiefly 
 represented by Chlorophycese of the family of the Stoneworts or 
 Characea, and they are widely distributed in the fresh-water lakes 
 of the temperate regions, and form extensive deposits of marl. 
 Analyses of Chara from the fresh-water lakes of Michigan showed 
 that something over 0.61 gram of soluble mineral matter occurs in 
 an average plant. This mineral matter is nearly 94% CaCO 3 and 
 is deposited as an encrustation on the outside of the plant. This 
 encrustation renders the stems and branches of the alga almost 
 white, and very brittle. On the average from 50 to 80 plants were 
 found on a square decimeter of lake bottom. Extensive beds of 
 marl or bog lime have in this manner accumulated at the bottoms 
 of ponds and small lakes. (Davis-i4.) Marl beds composed 
 chiefly of the remains of Chara hispida have been found in various 
 parts of Scotland and elsewhere. Extensive deposits of "Characese- 
 lime" have been formed in the lakes of Denmark by the growth of 
 Chara. (Wesenberg-Lund-56 1/55- 156. ) Such deposits are also 
 known among the older rocks. The organs of fructification of the 
 Characeae sometimes accumulate in such quantities as to form parts 
 of extensive beds of limestones in both recent and earlier forma- 
 tions. 
 
 In the Devonic of Ohio, and in other formations, occur lime- 
 stones often to a large extent composed of small spherical and 
 fluted bodies described under the name of Calcisph&ra robusta Wil- 
 liams. These have also been regarded as the organs of fructifica- 
 tion of one of the Characeae. 
 
 FOSSIL PHYTOLITHS OF ALGOUS ORIGIN. 
 
 FOSSIL OOLITES. These occur in all geological horizons either 
 as autochthonous or as allochthonous deposits. The latter generally 
 
472 PRINCIPLES OF STRATIGRAPHY 
 
 show evidence of wind transportation, as in the case of modern 
 oolite dunes of the Florida coast, the shores of the Great Salt Lake 
 of Utah, and the coast of the Arabian Sea. Such transported ma- 
 terial generally shows eolian cross-bedding, a feature very com- 
 monly associated with fossil oolites. This is well shown in the 
 Siluric oolites of Gotland and better still in the Jurassic oolites 
 of England, where remarkably fine examples of wind bedding are 
 seen. 
 
 The oolites of the Upper Siluric (Monroan) of Michigan have 
 been referred by Sherzer (43) to an origin similar to that of the 
 Great Salt Lake oolites. Rothpletz regards those from the Lias and 
 the Triassic Wetterstein Kalk of the northern Alps as due to algous 
 growths. From the Carbonic of England, oolites have been de- 
 scribed and referred to algous origin. The same is true of the 
 well-known oolites of the Jurassic of England which have given 
 many of the formations their local names (Superior oolite, Great 
 oolite, etc.) These oolites show, according to Wethered (58; 59), 
 organic structures similar to those described by Nicholson and 
 Etheridge as Girvanella problematica from the upper Siluric of the 
 Girvan district of Ayrshire. Both oolites and pisolites of these hori- 
 zons show often a concentric encrustation of organic fragments by 
 organisms forming flexuous or contorted tubules. Several species 
 have been distinguished by Wethered (58), among them Girvanella 
 pisolithica, which forms the Peagrit of the Inferior oolite and 
 coralline oolite. 
 
 Rogensteine of the Bunter Sandstein. The remarkable ooliths 
 of the Bunt Sandstein of North Germany known as Rogensteine 
 have been described in great detail by Kalkowsky (27). This 
 author restricts the name oolith to the rock having an oolitic struc- 
 ture, and proposes the term "ooid" for the individual grains. The 
 diameter of the ooids never falls below o.i mm., though smaller 
 grains occur (0.1-0.5 mm.), which he regards as ooids in the mak- 
 ing "embryonic ooids.*' The maximum size is 7 mm., only one 
 case exceeding that having been known. He finds in all cases for- 
 eign bodies forming the nuclei of the ooids, these bodies being 
 commonly small crystals of calcite, or again scales and rods of a 
 fine-grained clay slate. Kalkowsky finds the following structures 
 represented : 
 
 1. Concentric structure, layers of clear calcite of varying width, 
 alternating with more or less opaque calcite layers carrying im- 
 purities of clay. 
 
 2. Fine radial structure, produced by radial arrangement of 
 fine threads of CaCO 3 . 
 
FOSSIL OOLITES 473 
 
 3. Spindle structure, the concentric layers are traversed by 
 elongated spindles which become pointed toward the periphery and 
 the center of the ooid, the structure of the spindles being an ir- 
 regular mass of calcite grains. 
 
 4. Cone shaped, conical bodies traverse the concentric layers, 
 their points at the center of the ooid. These cones are built up of 
 concentric layers of a radius often somewhat smaller than that of 
 the ooid itself, and separated by interradii containing clay and 
 sand and having a somewhat radial structure. 
 
 By a combination of these structural groups, eight or nine differ- 
 ent ooid types were produced. Special types among these are the 
 roller form, the hemiooids, the polyooids, and the cystiform ooids. 
 These ooids are held together by a cement of CaCO 3 . Kalkowsky 
 regards these structures as due to secretion of lime by minute algae 
 of low organization, all traces of which are destroyed by recrystal- 
 lization. 
 
 Walther (53:^0) suggests that the Rogensteine of the Bunt 
 Sandstein of North Germany may have been formed in salt seas 
 in the desert, similar to those now forming through algous growth 
 in the Great Salt Lake of Utah, and in the Salt Lakes of the Kala- 
 hari desert. 
 
 The stromatoliths of Kalkowsky are large masses of calcareous 
 material having a stratified as well as fibrous structure. He re- 
 gards them as structures similar to the ooids, only vastly larger 
 and growing chiefly in one direction, i. e., upward. In size they 
 are found up to one meter in diameter, and they often form beds 
 of considerable extent. 
 
 Alteration of Oolites. Linck (Chapter IX) finds that recent 
 oolites consist or have consisted of aragonite, and that fossil oolites, 
 so far as investigated, are calcite, from which he concludes that al- 
 teration to calcite is a change which all oolites undergo with lapse of 
 time. It may also be briefly noted that oolites of chemical as well as 
 organic (phytogenic) origin may be altered by replacement by other 
 minerals. Thus siliceous as well as iron oolites are known, both 
 probably due to replacement of calcareous oolites. Of the former 
 a good example is found in silicified oolites of the salt seas of the 
 Kalahari desert in Africa (Kalkowsky-26), and in the Ordovicic 
 limestones of central Pennsylvania (Ziegler-6i). Of the latter a 
 typical example occurs in the basal iron ores of the Siluric in Wis- 
 consin where the grains are regular pellets of uniform character, 
 probably of phytogenic origin. Linck holds that original oolites 
 (chemically formed) of aragonite are saturated with iron solutions, 
 
474 PRINCIPLES OF STRATIGRAPHY 
 
 so that the aragonite is changed to iron carbonate which subse- 
 quently alters to iron oxide as outlined by Sorby and others. 
 
 SPH^ROCODIUM AND GIRVANELLA DEPOSITS. In the Palaeozoic 
 and later limestones of many countries are found rounded masses of 
 lime ranging in size up to several centimeters and referred to the 
 genera Sphaerocodium and Girvanella. These often occur in suf- 
 ficient abundance to constitute a large part of the rock mass, as in 
 the case of the Sphaerocodium beds of the Siluric of Gotland. 
 Sphaerocodium forms rounded masses generally coating foreign 
 bodies and consists of a simple network of unicellular threads, which 
 result in the formation of successive shells of calcareous tissue. 
 The genus has been -found abundantly represented in the Siluric of 
 Sweden and in the Triassic of the Alpine region. 
 
 Girvanella consists of irregularly twisted, tubes and forms ir- 
 regular knobby or rod-like masses, also, as a rule, adhering to 
 foreign bodies. It has been found in the Ordovicic of England and 
 America and in the Carbonic limestone (Mississippic), the Superior 
 oolite and the Coralline oolite of England. 
 
 Other algous types of the Palaeozoic, with similar mode of 
 growth, are Siphonema, found in the Ordovicic, and Zonotrichites 
 from the Rhaetic. (Rothpletz-35 ; 37.) Algae have also been de- 
 scribed from the Trenton limestone of New York. (Ruede- 
 mann-38. ) 
 
 FOSSIL NULLIPORES. The fossil nullipores are well represented 
 in older geological formations. As already noted, the Triassic reefs 
 of the Tyrol are regarded by many as chiefly of nullipore origin. 
 The leading alga is a coralline, Diplopora, which occurs largely as 
 dissociated joints of the branches. These algae are closely related 
 to the living Cymapolia, which, like Halimeda, is a jointed siphona- 
 ceous member of the Chlorophyceae or green algae. The red algae 
 (Rhodophyceae) are also well represented from the Jura to the 
 Pliocenic, some fifteen or more species being known in a fossil state. 
 Sometimes they formed extensive encrustations on the shores and 
 islands of ancient seas, as in the case of the Miocenic Leythakalk 
 of the Vienna basin, formed chiefly by Lithothamnion ramossimum 
 Reuss. This nullipore forms bundles and mats of numerous short, 
 wart-like or club-shaped branches from 2 to 5 mm. in diameter. As 
 the lime is in the form of calcite, it is commonly well preserved to- 
 gether with other calcite structures, while associated fossils of 
 aragonite are for the most part dissolved away and the lime re- 
 deposited as calcite among the algous masses. (See Mojsisovics 
 29:498.) 
 
 FOSSIL CHARA, Fossil stems and fruits of Chara are responsible 
 
METHOD OF LIME DEPOSITION 475 
 
 for many fresh-water limestones, as long ago pointed out by Lyell. 
 Such a fresh-water limestone was described by him from a com- 
 paratively recent deposit in Forfarshire. In the Eocenic of the Paris 
 Basin, Char a lyelli is rock- forming. Chara-like bodies have also 
 been discovered in abundance in Devonic limestones of Ohio, as 
 above noted. 
 
 TRAVERTINE AND SILICEOUS SINTER FORMED BY 
 IN HOT SPRINGS. 
 
 In the waters of hot springs, the world over, algae of various 
 types have been observed to grow, in temperatures ranging from 
 below 100 to 200 F. (55). In the hot springs of the Yellow- 
 stone National Park they occur in waters between the temperature 
 of 90 and 185 F., more having been found in warmer waters; 
 but in California they have been found in waters of a temperature 
 of 200 F. These algse through their physiological activities sep- 
 arate lime or silica from the waters of these hot springs, producing 
 extensive deposits of travertine, or of siliceous sinter, according 
 to the nature of the spring and its water. Not all the deposits of 
 travertine or siliceous sinter are due to this cause ; many are of 
 purely hydrogenic origin, being precipitated from the water by loss 
 of pressure, by diffusion or by abstraction of the solvent gases, by 
 evaporation, or by chemical reaction. In widely separated regions, 
 however, plants have been found active in the separation of these 
 mineral matters from the water examples being the travertine de- 
 posits of the Carlsbad Sprudel in Bohemia, and the hot springs 
 of Yellowstone National Park, in the United States, and the geyser- 
 ite or siliceous sinter deposits of the latter region. The extensive 
 sinter deposits of Iceland and New Zealand are probably also in 
 large part due to algous growth. 
 
 METHOD OF LIME DEPOSITION BY PLANTS. 
 
 We have seen above that lime carbonate is held in solution by 
 the excess of CO 2 in the water and that any agent which causes 
 the abstraction of the CO 2 also causes the precipitation of much of 
 the calcium carbonate. Plants obtain the carbon of which their 
 tissues are built by decomposing the carbon dioxide derived either 
 from the air or from the water, according to the mode of life of 
 the plant. It is thus obvious that where aquatic life is abundant, 
 much CO 2 will be abstracted from the water, and thus deposition 
 
476 PRINCIPLES OF STRATIGRAPHY 
 
 of the lime carbonate is brought about. Algae are most effective 
 in this respect, different algae accomplishing the separation in differ- 
 ent ways. According to Dr. Colin (10), who studied in detail 
 the algous limestones of the Carlsbad Sprudel, the lime is deposited 
 first in minute crystals in the slime between the vegetable threads 
 and upon their surface. At first these crystals are separate, but 
 continued growth in numbers produces star-like clusters which by 
 enlargement grow into grains of calcareous sand. Further growth 
 results in the union of the grains into a solid mass of travertine. 
 
 "The exact relation of the crystals and grains of carbonate of 
 lime varies in the different species of algae. In the Oscillaria: of 
 Carlsbad, and allied species, the crystals form in the slimy intercel- 
 lular tissue ; in Halimcda, the carbonate of lime forms a sieve-like 
 cover about the tips of the algae filaments; and, in Acetularia it 
 occurs as a tube about the stalk of the plant. In the Charae the lime 
 is separated and deposited in the cells and cell walls of the back 
 alone, while in the Corallines [Corallina, Lithothamnion, etc.] it 
 is found only within the cells." (Weed-55 :<5//j.) In the last men- 
 tioned types, especially in Lithothamnion and allied forms, the 
 surface layer alone is living, the lime occupying the successive 
 strata of dead cells beneath. In this manner thick masses of lime- 
 stone are built up. Solution of the lime in acid sets free the dead 
 cell walls which will either remain behind as a tangled mass of fila- 
 ments, or float as pellicles on the surface of the solution. Rothpletz 
 found this to be the case in the green fission-algae secreting the lime 
 of the oolites as well as in the red algae, which form extensive lime- 
 stone deposits. 
 
 Where calcium carbonate is absent, as in the Great Salt Lake, or 
 occurs only in small quantities, as in sea water, the lime-secreting 
 plants decompose the calcium chloride, phosphate or sulphate and 
 deposit it within their tissues as carbonate. The same is believed to 
 be true of many animals, which take the lime from the sea water 
 in the form of the sulphate, but deposit it in their shells and skele- 
 tons as carbonate. The reaction is brought about through the 
 formation of ammonium carbonate as a decomposition product, 
 which in turn, precipitates the calcium in the form of carbonate 
 from the solution within the dead cells. 
 
 SEPARATION OF SILICEOUS SINTER BY PLANTS. 
 
 The silica is at first deposited in and upon the plants in the 
 form of a gelatinous substance, often quite brilliantly colored, in 
 
SEPARATION OF SILICEOUS SINTER 477 
 
 golden-yellow, orange, or red, and in the hottest waters pale flesh- 
 pink or even white. "These algae are often so thickly encrusted 
 by silica that the plant structure is not recognizable even under the 
 microscope, and their presence is often only to be distinguished by 
 the color." (Weed-55 idj/.) The color varies with the temperature, 
 so that in the differently heated portions different colors obtain. The 
 order of color from progressive cooling is white, pale flesh-pink, 
 bright orange, yellowish-green, emerald. The most luxuriant growth 
 exists in the pools into which the waters flow, where leathery sheets 
 of tough gelatinous material with .coralloid and vase-shaped form 
 abound. In some cases, the algae twelve to fifteen inches long unite 
 their tops into a solid roof, which may become the floor of a second 
 story of algous growth in a new basin. "The exact manner in 
 which the algae of these waters eliminate the silica from solution 
 is not known, but the process appears to be due to the vital growth 
 of the plant, for both the algae filaments and their slimy envelope 
 are formed of gelatinous silica. Upon the death of the algae which 
 have separated this jelly from the spring waters there is a loss of a 
 large part of its water and a change to a soft, cheesy, but more 
 permanent form. This dehydration is carried still farther if the 
 silica be removed from the water and dried, but if allowed to 
 remain in the cold water pools there is a further separation of silica, 
 possibly due to organic acids, formed by the decaying vegetation 
 reacting upon the silica salts of -the water. This hardens the exist- 
 ing structures, in certain cases, and generally covers the pillars with 
 a frost-like coating of silica." (Weed-55 -.664.) 
 
 It is in the inner dead layers of the algous mass that the gelatine 
 hardens first into silica, the outer layer continuing alive. Fibrous 
 varieties of sinter are formed in many of the Yellowstone and New 
 Zealand hot springs by the growth of the algae CalothrLv, Mastigo- 
 nema, and Leptothrix, the first two producing a "furry" sinter in 
 strata from a sixteenth of an inch to half an inch thick, the last 
 forms fibrous, straw-like masses. 
 
 Mosses and diatoms have also been found active in separating 
 out the silica of the hot springs of the Yellowstone. The moss 
 (Hypnum a dun cum var. grasilescens, Br. & Sch.) grows on the 
 lower parts of the slopes where the water is cooled to blood heat, 
 and has lost much of its lime and part of its silica. The silica is 
 abstracted from the water by the physiological activities of the 
 plant and, in turn, encloses and buries the moss. Diatoms are espe- 
 cially active in the tepid marshes, Denticula valida being the pre- 
 dominant type, though a number of other species occur. Extensive 
 beds of diatomaceous earth are formed by their siliceous skeletons. 
 
478 PRINCIPLES OF STRATIGRAPHY 
 
 VEGETAL DEPOSITS. (CAUSTOPHYTOLITHS.) 
 
 The actual accumulations of vegetal matter in the strata of the 
 earth's crust are perhaps of even greater significance than the lime 
 and silica deposits caused by plants. There are few horizons which 
 have not some kind of plant deposit in the form of carbonaceous 
 material. They occur even in the Algonkian, where a bed of an- 
 thracite two meters thick is found in the upper part of the middle 
 Algonkian or Jatulian formation north of Lake Onega in Finland. 
 
 As already noted, Caustophytoliths have been divided into those 
 formed from plants living where their remains are found to-day, 
 autochthonous Caustophytoliths, and those transported to their pres- 
 ent place of occurrence, or allochthonous. Autochthonous caus- 
 tophytoliths may be terrestrial or aquatic, according to the condition 
 of life of the plants, i. e., whether land or aquatic plants. Alloch- 
 thonous Caustophytoliths are primarily allochthonous, when the ma- 
 terial of which they were made was transported in the living, or at 
 least undecomposed, condition to the place where it is now found, 
 and secondarily allochthonous, when transportation occurred after 
 the plant had become a caustophytolith. 
 
 Modern autochthonous deposits of vegetal matter are found in 
 the sea, especially in enclosed bodies of sea water, in marine 
 marshes, fresh water swamps, and in bogs and wet woods. Alloch- 
 thonous deposits may be found embedded in marine, lacustrine,' flu- 
 viatile or even aeolian deposits. 
 
 PETROGRAPHICAL TYPES OF VEGETAL DEPOSITS. 
 As noted in Chapter I, vegetal deposits may occur in one or another 
 of the following types: I, Sapropeliths ; 2, Humuliths; and, 3, 
 Liptobioliths. Each of these groups will be considered at some 
 length. 
 
 SAPROPELITHS. 
 
 These are accumulations of the decaying organic tissues of 
 aquatic animals and plants at the bottom of the sea, or in fresh 
 water lakes and ponds. In the unconsolidated state it is a foul or- 
 ganic slime (Faulschlamm) , or slime of decomposing organic mat- 
 ter derived from the water. In so far as plants contribute to this 
 slime, it is of algous origin, since any deposit formed by higher 
 plants normally belongs to the next type, the humuliths. The chief 
 chemical difference between such sapropelitic material and that 
 formed by land and swamp plants is the higher fat and protein 
 content of the former. Sapropeliths accumulate only in relatively 
 
SAPROPELITHS 479 
 
 quiet waters, since strong agitation of the water results in the 
 inclusion of much oxygen and the consequent complete oxidation of 
 the organic matter a feature observed in strongly agitated lakes. 
 
 The decaying vegetal matter rarely accumulates in any great 
 quantity as an absolutely pure caustobiolith. Most commonly inor- 
 ganic or organic mineral impurities are present in greater or less 
 quantity. Among them clay or mud is often a very important 
 constituent, forming argillaceous sapropeliths (if the clay is of 
 small amount) or more commonly sapropelargilliths or in general 
 sapropellutytes. Lime of clastic or organic origin may form the 
 admixture producing sapropelcalc rocks (sapropelitic calcilutytes, 
 sapropelitic calcipulverytes, etc.), while silica, especially that of 
 diatoms, produces a siliceous or diatom sapropelith. Marine sapro- 
 pelargillites are common on many shallow sea coasts, especially in 
 protected areas, where they constitute deposits of black mud. These 
 mud flats exposed at low tide are extensive generators of hydrogen 
 sulphide, which leads to the precipitation of sulphides, especially 
 those of iron. In this way the foundations are laid for the forma- 
 tion of highly carbonaceous lutytes or black shales rich in iron 
 pyrites and with the remains of a more or less depauperate fauna. 
 Such deposits are forming in the estuaries along the Atlantic coast, 
 and in a fossil state these seem to be represented in part at least by 
 the Devonic Genesee shale of New York State. They are further 
 forming in the lagoons behind the coral reefs of Florida, and in a 
 fossil state these are represented by the Middle Devcnic Marcellus 
 shale of New York, and perhaps to a certain extent by the Utica 
 shales of eastern North America. Again they are forming to-day 
 in the depths of the Black Sea, and this type appears to be repre- 
 sented by the Permic Kupferschiefer of Thuringia, and possibly 
 the oil shales of the Calciferous series (Lower Carbonic) of Scot- 
 land. The Posidonia shales of the Jurassic of Europe, and 
 some of the Upper Devonic (Portage) shales of New York have 
 also been interpreted on this basis. (Pompeckj-3i and Clarke-Q.) 
 This interpretation is, however, questionable. The black shales of 
 southern United States, i. e., the Chattanooga, are probably more 
 nearly referable to the class of argillaceous humuliths. The various 
 fossil sapropellutytes furnish oil on distillation and may in part be 
 the source of the petroleum in the underlying rocks. 
 
 Purer sapropeliths from the Tertiary are known as Dysodil 
 (Greek <W<o8r;s = ill-smelling), on account of their bad odor on 
 burning. Carbonic sapropeliths are represented by Cannel coal, a 
 characteristic of which is that it burns with a bright flame. Both 
 Dysodil and Cannel coal are, however, commonly impure, the im- 
 
480 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 purity or "ash" being primary, i. e., due to the non-burnable mineral 
 matter originally a part of the plants, or secondary, due to the ad- 
 mixture of foreign material, either mechanical sediment or chemi- 
 cal precipitate. Though rare, absolutely pure sapropelitic deposits 
 occur. According to the stage of consolidation and age, these have 
 received distinct names, as shown in the first columns of the sub- 
 joined table after Potonie (32:55). 
 
 Pure 
 Sapropeliths 
 
 With admixture of organic 
 lime or silica 
 
 With admixture of clastic 
 material, clay or sand 
 
 
 Sapropelite 
 (unconsolidated) 
 
 (sapro +pel) 
 
 Saprocollyte 
 (hardened sapro- 
 lite) 
 
 (sapro+colla, glue) 
 
 Calcareous sapro- Diatom- 
 pelite pelite 
 Sapropelitic cal- 
 ciliths 
 
 Argillaceous (and arena- 
 ceous) sapropelite and 
 sapropelitic argillyte 
 or microarenyte 
 
 Recent and subfossil 
 sapropeliths 
 
 Diatomaceous-calc sapro- 
 pelite and Diatomaceous 
 sapropelcalcilith (often 
 also containing clayey 
 sediment, etc.) 
 
 Saprodittyte 
 (pure Dysodil) 
 
 (sapro + odemeis, 
 odor) 
 
 SapantTiraconyte 
 (sapro -1- anthrax, 
 coal = sapropelite 
 coal, *. e., purest 
 cannel coal 
 
 Bituminous marl, shales, 
 etc. 
 
 Most bituminous calcilytes 
 
 Most bituminous argillites 
 and argillaceous lutytes 
 (ex. Jurassic Posidonia, 
 shales) 
 
 Zechstein Marl shales 
 (Kupferschiefer) 
 
 Fossil sapropeliths 
 
 In the purest state largely or almost entirely 
 biogenic and therefore aquatic autochtho- 
 nous formations, i- e., produced through 
 autochthonous sedimentation. 
 
 Allochthonous, with ref- 
 erence to the lutaceous 
 or finely arenaceous con- 
 stituents, but autoch- 
 thonous, with reference 
 to the organic constitu- 
 ents, therefore produced 
 by allochthonous and 
 autochthonous sedimen- 
 tation. 
 
 Petroleum. Among the fossil sapropelytic substances petroleum 
 takes the first rank. It is, however, to be regarded as a diagenetic 
 
CANNEL COAL 481 
 
 product from sapropelytes, the result of distillation. Both animal 
 and plant remains, especially algae, are now generally regarded as 
 the material from which petroleum is distilled, and the rocks rich 
 in such deposits, namely, the sapropelytic rocks, must therefore 
 form the mother rock of petroleum of organic origin. 
 
 Sapanthraconyte or Cannel Coal. This has an amorphous 
 structure and a clull luster of a greasy or silky character, quite dis- 
 tinct from the luster of true coal. The contrast is well shown by 
 the carbonized remains of the rhizomes of plants preserved in the 
 fossil slimes of ancient marsh bottoms. Thus stigmaria embedded 
 in cannel coal will show the bright luster of true coal in contrast 
 with the duller cannel coal. The vertebraria or rhizomes of Glos- 
 sopteris occurring in the Petroleum shales of the Southern Per- 
 mic show a similar Contrast. Cannel coal is found in America in 
 the Carbonic of Ohio, Indiana, and especially eastern Kentucky, 
 where Breckenridge is a noted locality. It is especially valuable 
 for the manufacture of gas on account of its abundance of volatile 
 hydrocarbons. Remains of fishes, crustaceans (Cypris), meros- 
 tomes (eurypterids), etc., and more rarely amphibians, are found 
 in some localities, these in most cases being fresh-water species. 
 At Linton, Ohio, more than 50 species of fishes and amphibians 
 were found in the cannel coal. Analyses of cannel coal gave the 
 following results. (Dana-n 1662.) 
 
 (For comparison analyses of anthracite and of bituminous coal 
 are given) : 
 
 Locality C H O N S Ash 
 
 Cannel coal from Brecken- 
 ridge, Hancock Co., Ky. . 68.13 6.49 5.83 2.27 2.48 12.30 
 
 Cannel coal from Wigan. .. 80.07 5-53 8 - IQ 2 - 12 i-5<> 2.70 
 
 Cannel coal or "Torbanite" 
 
 from Scotland 64 . 02 8 . 90 5 . 66 0.55 o . 50 20 . 32 
 
 Anthracite coal from Penn- 
 sylvania 92.59 2.63 1.61 0.92 .... 2.25 
 
 Bituminous "non- caking" 
 
 coal from Brier Hill, Ohio. 78.94 5.92 11.50 1.58 0.56 1.45 
 
 Microscopic algae are often well preserved in cannel coals. Pol- 
 len of Cordaites spores, wood and numerous algae were found, to- 
 gether with fish remains, Crustacea and coprolites in the "Boghead" 
 or Permic cannel coal of Autun (Bertrand-4). Cannel coal and 
 ordinary (humus) coal are often associated, the sapropelites form- 
 ing the foundation for the growth of land or swamp plants. Thus 
 a layer of cannel coal will often underlie one of bituminous or of 
 
482 PRINCIPLES OF STRATIGRAPHY 
 
 anthracite coal, and, moreover, the two may become interstratified, 
 the one or the other predominating, according to the length of time 
 during which the conditions responsible for either existed. Where 
 the beds are relatively thin the coal is spoken of as banded cannel 
 or bituminous coal, as the case may be. A section from Reckling- 
 hausen in Westphalia illustrates a complex relationship. In de- 
 scending order we find : 
 
 5. Bituminous coal about 10 cm. 
 
 4. Banded coal about 95 cm. 
 
 3. Cannel coal about 8-15 cm . 
 
 2. Banded coal about 10 cm. 
 
 i. Cannel coal about i . 3 m. 
 
 This section shows, first, a water body in which algse and other 
 truly aqueous plants lived and accumulated as decomposition slime, 
 followed by marshy conditions with growth of higher plants, but 
 with repeated inundations to furnish the decomposition slime from 
 which the bands of cannel coal were formed. This is followed by a 
 second period of complete submergence, with the formation of can- 
 nel coal. Then the alternating conditions were repeated, with the re- 
 sult that more banded coals were formed, and the area was finally 
 converted into a marsh or moor with the formation of pure bitumi- 
 nous or gas coal. 
 
 The algous origin of cannel coals has, however, been seriously 
 questioned by Jeffrey (25). He finds, on the basis of numerous 
 well-prepared microscopic sections from widely separated regions, 
 that the organisms found in abundance in boghead coals are not 
 of the nature of colonial gelatinous algae, as has been asserted by 
 Renault, Bertrand and Potonie, but are spores of vascular 
 cryptogams. This, Jeffrey holds, also overthrows the algal hy- 
 pothesis of the origin of petroleum and similar substances, these in- 
 stead having been mainly derived from the waxy and resinous 
 spores of vascular cryptogams laid down on the bottoms of shal- 
 low lakes during the coal period. 'These lacustrine layers, either 
 as cannels, bogheads, or bituminous shales, according to the sporal 
 composition and the admixture of earthy matter, are the mother 
 substance of petroleum. Pressure and temperature either separ- 
 ately or combined, in the presence of permeable strata, have brought 
 about the distillation of petroleum from such deposits." (Jeffrey- 
 25:^90.) 
 
 Jet (Ger. Gagat, Fr. jais, and jayet). This mineral, for which 
 Giimbel suggested the name gagatite, is a sapropelith obtained in 
 black sapropelargillytes of Mesozoic and younger formations. What 
 
JET; BLACK SHALES 483 
 
 are perhaps the most important deposits are found in the Liassic 
 rocks (zone of Ammonites serpentinus) of Yorkshire, England, 
 being especially obtained near Whitby, where it is mined and 
 wrought into all sorts of ornaments and toys, and, together with 
 the famous ammonites of the same formation, sold as native curiosi- 
 ties. -The jet here occurs in thin lenticular masses between the 
 layers of the hard bituminous shale (sapropelargillyte) and occa- 
 sionally shows under the microscope the structure of coniferous 
 wood, referred to araucarians. Scales of fish and other organisms 
 of jet rock are frequently impregnated with this bituminous matter, 
 which may replace the original tissues. Drops of liquid bitumen are 
 also found in the cavities of some of the fossils. Petroleum and 
 inflammable gases are likewise associated with jet deposits and iron 
 pyrite occurs, often replacing the fossils. The Lias of Wiirttem- 
 berg in Germany also furnishes jet, especially the Posidonia shale, 
 which is of the age of the Whitby beds. Of the same age is the 
 shale furnishing the original deposits on the river Gagas in ancient 
 Lycia, Asia Minor. Jet has also been obtained from Tertiary de- 
 posits. 
 
 Jet is characterized by its hardness, which is greater than that 
 of asphalt, its conchoidal fracture, and by the fact that it is less 
 brittle than anthracite, and is susceptible of a high polish. Its com- 
 mon association with driftwood leads to the supposition that its 
 chief source is carbonized wood enriched by secondary impregnation 
 with bituminous matter obtained from sapropelite. Analysis of the 
 jet from Holznaden, Wiirttemberg, gave C 71.0%, H 7.7%, O 
 2 3-3%> N trace, S trace, Ash 0.9-2.9%. 
 
 Black Shales. 
 
 Many black or blackish blue shales of various horizons show 
 characters which stamp them as sapropelargillites. The best known 
 of these is the Posidonia shale of the West European Upper Lias 
 (Lias ). This shale, so named from the abundance of the pe- 
 lecypod Posidonia bronni, Voltz, is typically developed in Wiirttem- 
 berg, where especially the locality of Holzmaden near Stuttgart 
 has become famous on account of the wonderful preservation of the 
 great marine saurians found in these shales. Other localities are 
 Whitby and Lyme Regis in England. The wide distribution of this 
 formation, as well as its organic contents, proves it to be of marine 
 origin, though from the nature of the occurrence of the fauna, as 
 
484 PRINCIPLES OF STRATIGRAPHY 
 
 well as the character of the rock, it must be assumed that the 
 regions were not open sea, but a coast lagoon or perhaps a marginal 
 epicontinental sea, laid bare to some extent at low tide with the 
 formation of extensive mud flats on which were stranded animals 
 and plants drifted in from the sea, and washed from the land. The 
 fact that the lower side of the fossils is generally better preserved 
 than the upper shows that the organisms were partly embedded and 
 corroded on the exposed surfaces by the acids generated on the 
 mud flats from the decaying organic matter. Had the water been 
 deep, the carcasses of the Ichthyosaurians, etc., could not have been 
 stranded in the mud, but would probably have continued to float 
 until they were cast on the shore or until decay had brought 
 about the dissociation of the skeletal elements, which would then 
 become scattered on the bottom. Instead of this, not only are they 
 intact, but the skin of the Ichthyosaurians has been found as a car- 
 bonaceous film surrounding the skeleton in its normal relationship. 
 Besides these saurians numerous well preserved Pentacrini are 
 found which were carried into those water bodies attached to drift- 
 wood. Gastropods, worms, cephalopods, and crustaceans also occur, 
 and fish are likewise common and well preserved. Land plants, 
 conifers, and cycads abound, and land animals, especially insects 
 and pterosaurs, also occur. The driftwood is commonly trans- 
 formed into jet, by the secondary enrichment of the decaying wood 
 by bituminous matter from the mud. Besides these macroscopic 
 remains, the shale abounds in microscopic fossils of sponges (?) 
 (Phymatoderma), Foraminifera, coccoliths, and diatoms ( ?). Other 
 black shales of a similar origin are probably found in the Devonic 
 Ohio black shale with its rich fish fauna, and the Upper Devonic 
 black shales of New York. The Marcellus shale of New York has 
 already been referred to as a similar sapropelargillyte, but formed 
 in the lagoons behind the Onondaga coral reef. The oil shales of 
 Australia, with the rhizomes of Glossopteris, the so-called "vertebra- 
 ria" often replaced by or transformed into jet, also belong here. 
 Finally, it must be emphasized that black shales also are formed 
 by the decay of land and swamp plants and that these, therefore, 
 belong more truly with the true coals and other humuliths. (See 
 page 513.) 
 
 Sapropelcalcilyths, Sapropelsilicilyths, and Sapropelferrilyths. 
 
 Bituminous or asphaltic limestones are formed when lime sands 
 or muds or organic calcipelytes are deposited along with much 
 
HUMULITHS 485 
 
 organic matter, either animal or plant. Fusulina limestones often 
 contain asphaltic material in abundance, and the same is true to a 
 certain extent of Stromatopora limestones, where the organic matter 
 may be represented by concentric films of asphaltum or other bitu- 
 minous matter. Nummulitic as well as nullipore limestones may, in 
 like manner, have a bituminous constituency. The finest calcilutytes 
 are often impregnated with bituminous matter, especially if, as in 
 the Upper Cambric of Sweden, they are intercalated in bituminous 
 shales (sapropelargyllites). Such rocks when struck with a ham- 
 mer give out a fetid odor which causes them to be classed as fetid 
 limestones, or "stinkkalk." Metamorphism of limestones o'f this 
 type would result in the production of graphitic marbles. Sapro- 
 pelites in which silica forms the leading accessory constituent are 
 represented by diatomaceous oozes in which the decay of the or- 
 ganic matter has produced the bitumen. The Eocenic Menilite 
 shales of the Paris basin and the Oligocenic Menilite shales of 
 Galicia are typical examples. The latter might perhaps be regarded 
 as the source of the petroleum of that region. Sapropelferrilytes 
 are bituminous iron carbonates such as are deposited under certain 
 conditions in some bogs. 
 
 RECENT HUMULITHS. 
 
 These are formed by the growth in situ of plants, either such 
 as grow on the land or those living in marshes and swamps (autoch- 
 thonous) or formed from material rafted or drifted together (al- 
 lochthonous). Marshes, swamps, and bogs are the chief sites of 
 accumulation of such deposits at the present time, and a consid 
 eration of these must precede the discussion of the older deposits of 
 humuliths, i. e., the coals. 
 
 In general we may adopt the word moor for all the surfaces 
 of land, whether high or low, which, with more or less wetness, are 
 covered by successive growths of vegetation, the remains of which 
 accumulate to form beds of peat. Three kinds of moor may be 
 distinguished : the marine low moor, or marsh ; the fresh water 
 low moor, or swamp; and the upland moor, or bog. The restric- 
 tion of the terms here given, and in part at least advocated by 
 Shaler many years ago, will prove useful and make for precision. 
 Shaler (42:264} has given us a useful classification of modern 
 moorlands which, with some slight changes, chiefly ^rearrange- 
 ments, is as follows (Parsons~3o) : 
 
46 PRINCIPLES OF STRATIGRAPHY 
 
 f Below mean tide. . .(\ 
 A , , . , 12. Mud banks 
 
 A. Marine marshes ..... < ; 
 
 [ Above mean tide. ... 1 3- Grass marshes 
 
 \ 4. Mangrove marshes 
 
 f Lake swamps . . ; / ' Lake margin swamps 
 
 B. Fresh-water swamps . I 6 " Q uakm S bo & or swam P s 
 
 ( River swamps ....... J 7- Terrace swamps 
 
 \ 8. Estuarine or delta swamps 
 
 r Upland bogs ........ \ 9. Climbing bogs 
 
 C. Terrestrial Bogs ..... J / 10. Wet wood bogs 
 
 L Ablation bogs 
 
 A more recent classification of peat moors, adopted by the 
 students of the West European peat deposits, has reference to the 
 succession of plant types found in the moors. It applies to the 
 fresh-water swamps and terrestrial bogs only. Three types are 
 recognized : a, Low moor, or flat moor (Flachmoor, Verlandungs- 
 moor) ; b, Intermediate or Transition moor (Zwischenmoor, Ueber- 
 gangsmoor) ; and, c, High moor or Upland moor (Hochmoor). 
 
 The transition moors are less well characterized than the low 
 and high moors, and the tendency of some authors is to eliminate 
 them altogether. A further group, however, the forest moor, or 
 dry peat moor, is separated by most modern authors. For pur- 
 poses of mapping, the following divisions of modern fresh-water 
 or terrestrial deposits of caustobioliths have been recognized in 
 Germany (Ramann-33 : 
 
 I. Slime deposits (fresh-water sapropelytes). 
 
 II. Flat or low moor deposits Terrigenic moor deposits (Ver- 
 landungsmoorablagerungen) comprising : 
 
 A. Peat: formed by 
 
 1. Reed association or a Phragmitetum * (Phrag mites, 
 
 America; Arundo, Europe). 
 
 2. Sedge association or Cyperacetum or Caricetum 
 
 (Cyperus, Car ex, etc.), including: 
 
 a. Magnocaricetum or tall sedge plantation. 
 
 b. Parvocaricetum or low sedge plantation. 
 
 3. Moss association or Hypnetum (Hypnum and certain 
 
 species of Sphagnum, etc.). 
 
 B. Mold. 
 
 III. Forest peat (dry peat). 
 
 IV. Highmoor peat. 
 
 * The ending etum designates a plantation, grove or association in which the 
 plant to whose name it is suffixed forms the principal type. 
 
MARINE MARSHES 487 
 
 The reed association or phragmitetum is not wholly restricted to 
 the low moors, but also occurs, though more sparingly, on the high 
 moors. The same may be said of certain sedge associations or 
 cyperacetes. Among the mosses certain species of Hypnum (as, for 
 example, H. fluitans, giganteum, and trifarium, in Europe, and cer- 
 tain Sphagnums) occur with the reed associations, partly forming 
 floating mats or growing among the reeds. The sphagnums are 
 most characteristic of the high moors. 
 
 The following classification comprises the important subdivi- 
 sions of the areas of deposition of modern caustobioliths : 
 
 A. Marshes Marine. 
 
 1. Sapropelite region submerged. 
 
 a. Eel grass marsh. 
 
 b. Mud flat region. 
 
 2. Humulite region emerged. 
 
 a. Grass or Spartina marsh. 
 
 b. Mangrove marsh. 
 
 B. Swamps Fresh Water. 
 
 1. Sapropelite region. 
 
 2. Humulite region. 
 
 a. Moss or Hypnetum zone. 
 
 b. Sedge or Cyperacetum zone. 
 
 c. Reed or Phragmitetum zone. 
 
 d. Tree or arboretum zone. 
 
 (1) Alder or Alnetum zone. 
 
 (2) Cypress or Taxodetum zone. 
 
 (3) Tupelo or Nyssetum zone. 
 
 C. Bogs Terrestrial. 
 
 1. Forest moors. 
 
 2. Upland bogs (High Moors). 
 
 Marine Marshes. 
 
 The development of marine marshes proceeds in the following 
 manner (Shaler-4i : 359; Davis, W. M.-i6) : An off-shore sand 
 bar is built by the waves on the gently sloping sandy sea-bottom, 
 or a barrier beach is built between two projecting headlands. The 
 scouring action of the tides will keep open a channel through this 
 beach so that a connection between the sea and the lagoon is always 
 maintained. Bars may be built in water from 20 to 30 feet in depth, 
 and are due to the breaking of the large waves off shore, which 
 then pile up in front of them the detritus which they have dug up 
 
488 PRINCIPLES OF STRATIGRAPHY 
 
 from the sea-bottom. The bar grows until at last it rises above the 
 level of ordinary tides, and thus becomes a barrier beach. Mean- 
 while, at low tide, the sun dries out the upper portion of the sand, 
 which then becomes mobile, and is piled up into shoreward advanc- 
 ing sand-dunes. Thus a barrier-beach of some breadth may be 
 formed. While this is going on, deposition of sediments within the 
 lagoon behind the beach takes place, for here the water is mostly 
 quiet, while sediment is carried in both by streams from the land 
 and by the tide. As soon as an accumulation of mud or fine sand 
 over the bottom has begun, it is taken possession of by eel grasses 
 (Zostera marina, etc.), which soon cover the bottom with a dense 
 growth. These plants, belonging to the pond-lily family, have be- 
 come adapted to a marine habitat, and cannot live outside of the 
 salt water. Wherever these plants grow sufficiently near the sur- 
 face they form at low tide a tangle, passage through which is ac- 
 complished only with difficulty by the swimmer or the oarsman. 
 "A tidal current of two miles an hour, swift enough to carry much 
 sediment, is* almost entirely deadened in this tangle of plants.'' 
 (Shaler-4i.) As a result, the sediment will sink down between the 
 leaves of the plant and there will rapidly accumulate a bottom de- 
 posit of mud, which encloses the vertical stems of the plants. With 
 the fine sediment, fronds of sea-weed are carried by the current, 
 and these with pebbles or shells attached to their bases will settle 
 to the bottom and become buried in the mud. The presence of 
 decaying vegetal and animal matter gives a characteristic color 
 and odor to these deposits which may readily be observed wher- 
 ever the mud flats are exposed at low tide. Wliere the mud is cal- 
 careous, extensive beds of calcilutytes may be formed in this man- 
 ner, which may even retain the vertical impressions of the plants or 
 other organisms which have "combed" out the mud from the sea 
 water. What appears to be a good example of this kind is found 
 in the Ordovicic (Lowville) limestone of the Black River valley, 
 etc., in New York, where the remains of the vertical stems form a 
 characteristic feature of the rock, the appearance on cross-section 
 having given rise to the term "Bird's Eye," by which the rock is 
 commonly known. 
 
 Where the mud has accumulated to such an extent that at low 
 water the flat is uncovered the eel grass will die, and its place is 
 gradually taken by the marsh grasses. For a time mussels will 
 occupy patches of the mud flat surface, and a mussel bed of some 
 thickness may be formed on the substratum of black mud. Micro- 
 scopic examination of the mud will show that it consists of ill- 
 assorted and generally angular grains. The marsh grasses com- 
 
MARINE MARSHES 489 
 
 monly push their growth from the shore outward. Their roots 
 and stems, partly submerged at each tide, readily entangle sediment 
 and so the level of the deposits is rapidly raised to where it will 
 be covered only at the highest tide. At this stage portions of the 
 marsh are sometimes inhabited by enormous numbers of the fiddler 
 crab (Gelasimus). At this point the process is generally arrested 
 except for the decay of the older vegetation and the growth of 
 new crops. The appearance of the marsh and its structure are 
 shown in the following map and section, copied from Shaler (Figs, 
 no, noa.) In cases where much sand is carried into the lagoon by 
 the tidal currents, the eel-grass-mud-flat stage may be entirely 
 omitted, the marsh-grass stage following directly upon the sandy 
 filling of the lagoon. 
 
 The salt marsh vegetation consists chiefly of grasses and sedges. 
 
 IIMUMHMHBHHHMi 
 
 A. Bed rock. B. Sand and gravel. C. Eel grass layer. D. Upper marsh. 
 
 FIG. no. Ideal section of a salt marsh formed behind barrier beaches. 
 (After Shaler.) 
 
 Among the former the genus Spartina leads with seven species, 
 not all of which are, however, of marine habitat. Some species 
 are of world-wide distribution, while others occupy a restricted 
 area. In vertical range the species also vary. In the lowest zone 
 occupied by those plants, i. e., the zone limited downward very 
 nearly by half tide and upward by ordinary high tide, the tall, 
 coarse, rank-smelling salt thatch, Spartina glabra Muhl., var. altcrni- 
 flora Loisel and Merr, is the sole representative of these grasses, 
 except for occasional stragglers from the zone above. This plant 
 has large, hollow, jointed stems, broad, yellowish-green leaves, and 
 grows from two to four or even six feet high. It produces numer- 
 ous seeds, and sends strong, thick and very characteristic under- 
 ground stems in all directions into the substratum on which it 
 grows. From these, at nodal intervals, spring the long, fibrous, 
 much branched roots. The underground stems, and those parts of 
 the aerial branches buried in the mud are the most frequently pre- 
 served, and these are readily distinguished from other plants by 
 their size and straw color, which is retained for a long time. The 
 aerial parts of the plant, i. e,, the leaves and stems, become very 
 brittle at the end of the growing season and are broken off by 
 
490 PRINCIPLES OF STRATIGRAPHY 
 
 the waves and shore ice. They often accumulate along the high- 
 water line or are carried out to sea. 
 
 This plant, which is thus submerged for about half the time, 
 is especially abundant in the banks of the tidal creeks. The deposits 
 which it forms are rich in mineral matter, they themselves rarely 
 forming accumulations approximating in purity those due to the 
 species growing at a higher level. Above the salt thatch zone is 
 the peat zone proper, which is submerged by salt water only from 
 i to 4 hours each day. Many species grow here, sedges (Carex) 
 as well as grasses, but only two are common on the northern coast, 
 Spartina patens Muhl. and Distichlis spicata (L.) Greene. These 
 salt marsh grasses are both short, from 6 to 12 or 14 inches tall, 
 with rather slender, tough, wiry stems, and dull grayish-green, slen- 
 der, involute leaves. Their root stocks are slender, tough and numer- 
 ous, their roots long, fibrous, and branching. The peat formed by 
 these plants cannot be mistaken for that of any other form of vege- 
 table deposit with which it is likely to be associated. "It differs 
 from the turf formed by sedges in the persistence with which the 
 underground stems retain their form and individuality instead of 
 collapsing and flattening, in the lack of the remains of leaves and 
 aerial branches, in color, in the absence of definite lamination, in 
 the amount of silt generally contained, and, more than all else, in 
 the presence of the white or light-colored finely branching roots, 
 which penetrate the mass in every direction and make up the great 
 bulk of the material." (Davis-i5 '.632.) 
 
 The leaves and stems of these two salt marsh grasses are more 
 persistent than those of the salt thatch, but they also are largely 
 removed during the winter by ice, wind, and tides. A fresh water 
 species, S. cynosuroides Willd. with a culm 2 to 6 feet high and 
 narrow leaves 2 to 4 feet long and a half inch or less in width 
 below and tapering to a slender point, inhabits the banks of rivers 
 and lakes, or occurs in rich soil from the Atlantic to the Pacific. 
 
 Sedges, Carex salina and Carex maritima, are also characteristic 
 of the salt marshes, and often add a considerable part to the peat 
 formed. 
 
 The tidal marshes are dissected by meandering channels through 
 which the salt water ebbs and flows twice a day. These channels 
 are generally narrow and deep, the width being determined by 
 various factors, chief among which is the scouring force of the 
 tidal current, and the resisting force and growing power of the 
 marsh vegetation. 
 
 During the slow conversion of the lagoon into a marsh the 
 sand dunes from the beach commonly advance over the growing 
 
MARINE MARSHES 
 
 491 
 
 mass, while at the same time the waves may cut back the beach 
 line. Thus it may happen that a section of a marsh is exposed 
 along the shore, below the cover of dune sand. Examples of such 
 old marshes showing on the coast may be seen at Cape Cod, near 
 the Nausett Lights, on the coast of Nantucket, along the western 
 coast of Long Island (near Bath Beach), and elsewhere. 
 
 The sequence of events thus outlined would lead to the forma- 
 tion of the following succession of deposits (Davis, C. A.- 
 15:626-7}: At the bottom the section should show sand, silt, or 
 mud up to about twelve feet below low-water mark; between this 
 level and that of low water should occur silt surrounding the easily 
 recognizable remains of the eel grass and mingled with it should 
 
 FIG. noa. Map of the Plum Island (Massachusetts) marshes, dissected by 
 meandering tidal streams. (After Shaler.) 
 
 be the shells of molluscs and the remains of other marine organisms. 
 Above this should occur another layer of silty mud up to the level 
 above which the salt water grasses grow. The next higher stratum 
 should contain the remains of these plants in constantly increasing 
 numbers, until they form the bulk of the stratum. This would 
 result from the observed fact that there is a level above the low-tide 
 mark below which these plants do not go, while, at the greatest 
 depth at which they do grow, the number of individuals is small 
 compared with that found higher up, where these grasses find their 
 most favorable conditions for growth. "At the top of the section 
 should be a distinct turf, formed of the characteristic plants grow- 
 ing on the surface, which, because of the very definite fixed habits 
 of these species, would be, relatively, very thin." (Davis-i5.) 
 
492 PRINCIPLES OF STRATIGRAPHY 
 
 Considerable variation from this normal section is to be ex- 
 pected, for salt marsh building may be interrupted at any stage by 
 blowing sands, and the whole may be greatly complicated by sub- 
 sidence or elevation of the coast. In some cases studied, as on the 
 Massachusetts coast, the structure of the marsh does not conform 
 to this succession in some of its major features, showing that the 
 history here has been quite different from that outlined. "In many 
 cases . . . the deposits below the surface, instead of contain- 
 ing eel grass and salt thatch remains, was entirely composed of the 
 very different and definitely recognizable sort of vegetation that 
 never grows where salt water reaches, i. e,, the deposits were 
 largely of fresh water origin." These deposits often show consid- 
 erable accumulation of woody material, including stumps of large 
 pine trees, near the surface and for a few feet below. "The struc- 
 ture of these marshes also often showed salt water intrusion in 
 varying degree in different parts of the same area, the deposit of 
 the salt marsh material being progressively thicker as the ocean was 
 approached." (Davis-i5.) In the case of these marshes, the salt 
 water deposits were made up of the species of plants which grow 
 at or near high-tide level, while eel grasses and species which can 
 stand partial submergence were rare or absent. Even where no 
 fresh water peat was found underlying the salt peats the species 
 making up the latter were those growing at present at high tide 
 level or above, although the peat formed by these was often below 
 present low-water level. This, if not due to compacting, indicates 
 subsidence of the coast during or since the formation of the peaty 
 deposits. Oscillation of the coast, or at any rate of the tidal range, 
 is indicated by the intercalation in some cases of fresh water peat 
 between layers of salt marsh peat. Salt marshes of this type must 
 be interpreted as follows : On a flat coastal plain, above the reach 
 of tide, owing to the moist climatic conditions and probably to the 
 growth of trees .preventing free drainage, are formed swampy areas 
 in which an accumulation of fresh water peat goes on to an in- 
 definite extent. By a slight but constant progressive subsidence 
 of this coast the sea enters in, kills the fresh water peat, and be- 
 gins to cover more or less permanently a part of the coastal strip of 
 this plain. Since the growth of marsh grasses on the open exposed 
 coast is ordinarily an impossibility, owing to the violent wave work, 
 it follows that the first step in the conversion of the fresh to the 
 salt marsh is the building of the barrier beach. If the barrier 
 beach is built far enough from the shore, owing to the gradual 
 shoaling of the water, a broad lagoon of salt water will be left be- 
 tween it and the shore, and in this the salt peat may gradually form, 
 
MARINE MARSHES 493 
 
 as outlined above in Shaler's hypothesis. Such marsh' deposits are 
 now forming" on the Long Island and New Jersey coasts. As the 
 coast slowly subsides the marsh grasses will encroach upon the 
 dead fresh water swamps, and since the subsidence is a slow one 
 only the plants growing at high water level or above will enter into 
 the constitution of this deposit. Among these on the Massachu- 
 setts coast, the grass Spartina patens Muhl. is the chief type, which 
 will form successive layers if the subsidence is slow, and so a pro- 
 gressive overlap of the Spartina patens layer over the fresh water 
 peat will take place, with the result that this peat thickens seaward 
 because in that direction deposition began earlier. During all this 
 time the lagoon beyond the area of the fresh water peat deposit 
 may be slowly rilling up and the ordinary salt peat would form, 
 beginning with the more euryhaline species of salt grasses, such as 
 Spartina glabra, and followed by the more stenohaline species, such 
 as S. patens. Progressive erosion and landward migration of the 
 outer bar would eventually result in the entire removal of the 
 purely marine peat series, so that, as in the case of the Massachu- 
 setts marshes, the only part remaining behind the bar is the com- 
 pound peat mass, commonly of fresh water peat at the bottom and 
 salt water peat on top. 
 
 In such cases as these the bar has successively migrated shore- 
 ward until it has reached if not transgressed the original shore 
 which existed at the time that the fresh water peat was forming on 
 the coastal plain. 
 
 If the subsidence is more rapid than the upbuilding of the 
 Spartina patens peat, the more frequent submergence of the surface 
 will kill that species and its place is taken by the more euryhaline 
 5". glabra, which, in turn, may be succeeded by a mussel bed or 
 mud flat. 
 
 Conversion of salt peat into coal. The burial of a salt peat 
 marsh under silts of marine or terrestrial origin would tend to its 
 preservation and ultimate conversion into coal. Such coal will, 
 however, be very high in ash, for the high tides, especially during 
 stormy periods, will spread much silt over them, while wind-blown 
 sand from the shore may also add a quantity of mineral matter. 
 Hydrogen sulphide is generated in great abundance in peat beds 
 to which salt water has access. This is apparently due to the action 
 of certain bacteria on the sulphates contained in the water. By 
 reaction with iron compounds of the silt and other mineral mat- 
 ter iron sulphides are formed, which are deposited as iron pyrite. 
 This mineral is abundant in the inorganic constituent of the salt 
 marsh peat. Such formation of hydrogen sulphide does not occur 
 
494 PRINCIPLES OF STRATIGRAPHY 
 
 in fresh water peats, unless these are subsequently submerged by 
 marine waters. 
 
 Mangrove Marshes. 
 
 These occur in the tropics and take the place of the salt grass 
 marshes of temperate climes. The mangroves comprise some 
 twenty species, characterized by numerous slender trunks varying 
 from five to sixty feet in height. These rise to just above the level 
 of high tide, and are crowned with heavy foliage, which, when the 
 tide is full, appears to float upon the water. From the crown, 
 stolonal processes are sent off and these, in turn, give rise to de- 
 scending roots, which, after reaching the sea-floor, become fixed and 
 serve to support the trees against the effects of the tides and waves. 
 Shaler believes that the mangrove thickets may advance over the 
 sea-floor at the rate of twenty or thirty feet in a century. Their 
 seaward extent is limited by the deepening of the water and the 
 force of the waves, and by fish which feed upon the growing ex- 
 tremities of the roots. The densely interwoven stems and roots of 
 the mangrove form an effective barrier for the retention of silt. 
 The flow of water from the land is checked, and sediment deposited, 
 until the roots and stems are completely buried, when the plants die 
 and give way to other types of vegetation. Commingled with these 
 buried trunks and roots we find a considerable littoral fauna, a 
 part of which was directly attached to the bases of the mangrove 
 or crawled about on them, and another part which lived on or in 
 the mud which accumulated between the stems. (See further, Chap- 
 ter XXVIII.) 
 
 Fresh Water Swamps. 
 
 The sapropelite region of swamps is largely confined to the 
 deeper parts of the lakes where planktonic fresh water algae sink 
 to the bottom upon their death and where Characese grow and pro- 
 duce a layer of sapropelcalcilite or marl. The formation of sapro- 
 pelite is, probably, far less extensive than in marine waters, for 
 terrestrial vegetation will take root in all shallow waters or push 
 out as floating mats from the shore, the deposits resulting being, 
 therefore, chiefly humuliths. Floating algae are rare in all except 
 the smaller, more stagnant, lakes or pools, and thus the chief de- 
 posits of this type on the deeper lake bottoms are the Chara marls. 
 Fresh water swamps may be subdivided into lake swamps, river 
 swamps, and estuarine swamps, which merge into the marine 
 marshes. 
 
FRESH-WATER SWAMPS 
 
 495 
 
 Lake Swamps. Around the margins of lakes and fresh water 
 ponds a variety of plants are found more or less submerged. The 
 number of species of flowering plants having such a habitat is com- 
 paratively small, the endogenous plants predominating, with the 
 water lily family, especially Potamogeton, as the leading class. Of 
 the flowerless plants Hypnum and Sphagnum, two mosses, and the 
 alga Chara are the most significant. The depth at which seed plants 
 will grow ranges from 15 to 25 feet, very few, such as the water 
 lilies, being able to establish themselves in depths greater than 10 
 feet. As the 25-foot limit is approached the number of species 
 rapidly diminishes, this being apparently due to the decrease in 
 light and heat available. Of the plants growing in deeper water, 
 the algae, especially the species of Chara, should be mentioned as 
 
 7 c s- 
 
 FIG. TII. Diagram of plant zones in small lake near Merryman's Lake, Mich- 
 igan. (After Davis.) o, Chara; i, floating bladder worts ; 2, 
 yellow pond lily; 3, lake bulrush; 4, Sartwell's sedge; 5, 
 bottle sedge; 6, spike rush; 7, cat-tails. 
 
 significant, These are instrumental in raising the bed of the lake 
 or pond by the formation of marl (ante, p. 471). Floating or 
 planktonic plants also abound in most fresh water ponds and lakes, 
 especially in the stagnant portions. The most important of these 
 are the Bladderworts (Utricularia), of which there is a number 
 of species, and Myriophyllum which may cover whole surfaces of 
 the ponds. 
 
 The most important species of peat-forming plants in lakes do 
 not grow in water over two feet in depth. These comprise, among 
 others, the cat-tail flags (Typha), the Bur reeds (Sparganium), the 
 Water Plantain (Alisma), the Arrow-heads (Sagittaria), some 
 grasses (Zizania), the wild or Indian rice (Phragmites), Reed 
 grass, and several sedges, in addition to the pond lilies. Hypnum 
 and Sphagnum grow near the surface. 
 
 In lakes more than 25 feet in depth, filling by the formation of 
 
496 PRINCIPLES OF STRATIGRAPHY 
 
 marl or sapropelite from floating plants has to occur to bring the 
 bottom to the required level where the higher plants can gain a 
 foothold. These will slowly build up the floor of the lake by partly 
 decayed vegetal matter, the rate increasing with progressive shoal- 
 ing, owing to the increase in the number of plant species and their 
 greater luxuriance. The succession of types is shown in the pre- 
 ceding diagram (Fig. in), copied from Davis. 
 
 In the rilling of lakes by vegetal growth a prominent part is taken 
 by the plants which build floating mats from the shore outward. 
 Chief among these in our temperate climes is the sedge Carex fili- 
 fonnis L., which forms a mat of felted and interwoven stems and 
 roots, making a buoyant structure capable of supporting consider- 
 able weight. This sedge may grow with its rhizomes submerged a 
 foot or more below the surface of the water and its roots extending 
 much farther downward. These mats may be from a few inches 
 to two feet in thickness near their lakeward end, while toward the 
 shore they become more and more solid and eventually no longer 
 float. The solid portion gradually extends lakeward, partly by the 
 accumulation of more or less decayed vegetal matter beneath the 
 mat, and the pond thus becomes filled. The sedge is sometimes 
 largely replaced by the cat-tail Typha latifolia, which likewise aids 
 in the building of the mat. As the surface of the mat approaches 
 the level of the water, dense growths of the moss Hypnum will 
 occur ; other plants follow, including ferns and the Sphagnum moss, 
 and, finally, the tamaracks and spruces will begin to migrate out- 
 ward, and the pond passes from the quaking bog stage to the more 
 or less wooded tamarack swamp (see Fig. 112). As the forest ad- 
 vances the sedges begin to die, being unable to flourish in the shade. 
 The ground becomes covered by a heavy growth of Sphagnum 
 moss, which may grow to some extent in the water, but more com- 
 monly forms a surface growth which may reach a thickness of 
 several feet. The stumps and trunks of dead and fallen trees are 
 gradually embedded in this growing mass of vegetal material, be- 
 coming an integral part of the accumulating peat deposit. As the 
 Sphagnum forms the most conspicuous part of the surface of the 
 swamp and is a vigorously growing plant, it has commonly been 
 credited with being the chief agent in the production of swamp 
 peat, the plant itself being known as the peat moss. It appears, 
 however, that this moss must be regarded as only a contributor 
 so far as swamp peat is concerned. 
 
 In a consideration of lake swamps we must not neglect the fact 
 that lake basins come into existence in a great variety of ways (see 
 ante, p. 116), and that in some cases these basins may from the 
 
FRESH-WATER SWAMPS 497 
 
 outset be so shallow as to quickly assume the character of a swamp 
 or bog, without passing through all the stages described. Further- 
 more, it has been shown that lakes may actually be produced by the 
 growth of vegetation, as in an upland moor, this forming either a 
 barrier or an enclosing rim. In such a case the bog precedes the 
 lake, which may subsequently be rilled by the development and en- 
 croachment of the swamp vegetation. 
 
 River and Estuarine Swamps. These are produced where the 
 borders of the rivers with broad flood plains are raised through the 
 building of natural levees by the overflowing stream. The vegeta- 
 tion growing on the borders of a river will tend to arrest the sedi- 
 ment carried by the rising water in times of flood, when the flood 
 plains on either side are inundated. These higher marginal ridges 
 will therefore separate the lower flood plain from the river, and 
 thus the waters resulting from the overflow of the river will find 
 
 FIG. 112. Diagram showing how plants fill depressions from the sides and 
 top. (i) zone of Chara and floating aquatics; (2) zone of pond- 
 weeds or potamogetons ; (3) zone of water-lilies; (4) floating 
 sedge mass; (5) advance plants of conifers and shrubs; (6) 
 shrub and sphagnum zone; (7) zone of tamarack and spruce; 
 (8) marginal fosse. (After Davis.) 
 
 it impossible to return to the river on its subsidence. Thus exten- 
 sive swampy lands are formed over the inundated parts of the 
 flood plain, which may also enclose an extensive series of shallow 
 lakes. The back Swamps of the Mississippi are examples of this 
 sort of occurrence. 
 
 Delta surfaces may be covered with swamps in the same manner 
 that lakes are formed on deltas, through irregular deposition and 
 obstruction of drainage. At the heads* of estuaries, fresh-water 
 swamps may likewise form which further out may merge into or 
 pass beneath grass marshes due to encroachment of the sea. 
 
 From a consideration of the succession of plant associations dur- 
 ing the gradual filling of a lake, it must be apparent that in the re- 
 sulting deposits there will be noticeable a stratification, due to the 
 superposition of successive types of dead vegetal matter. In gen- 
 eral, these may be grouped according to their decreasing hygro- 
 phylous characters into the following divisions : I, limnic; 2, tel- 
 
498 PRINCIPLES OF STRATIGRAPHY 
 
 matic; 3, semiterrestric, and, 4, terrestric. The needs of the plant 
 associations in mineral food also vary with the development of the 
 swamp or bog, the earliest plants deriving their food from the 
 water or the bottom on which they grow, while the succeeding 
 groups must depend more and more upon the older plant deposits 
 for their mineral nourishment, and this becomes less and less in 
 amount. We have thus a series with decreasing demand on the 
 substratum for food, and these are classed in descending order, as 
 eu-j meso- and oligotraphent types, and they may be found among 
 various hygrophylous types. From the deposition of these types of 
 vegetation we get eu-, meso- and oligotrophic types of peat deposits, 
 
 FIG. 113. Ideal section, showing the approximate relation (i) of the different 
 types of peat, and (2) the plant societies at Algal Lake, northern 
 Michigan. (After C A. Davis.) The succession of plant asso- 
 ciations from without inward is: (i) Tamarack-spruce-cedar 
 swamp, with young tamarack at the inner border; (2) open 
 sedge marsh, with islands of tamarack wood; (3) swamp loose- 
 strife (Decodon verticillatum) gradually advancing lakeward, and 
 forming "stools" on which grow mosses, ferns, sedges and 
 shrubs, finally killing the loosestrife; (4) cat-tail flags; (5) 
 potamogeton. The peat formed by these plants thickens away 
 from the lake, and is humus peat. Below this, and forming the 
 lake bottom, is a mass of sapropelitic peat, composed of green 
 algae, with diatoms, and an abundance of pollen-grains of conifers, 
 forming a structureless mass. 
 
 the last of which normally occurs in the upper part of the stratified 
 series. 
 
 It is, however, apparent that in the gradual closing of a lake by 
 vegetal deposits, those formed near the shore will have the largest 
 supply of mineral food, especially where affluents bearing such food 
 enter, and that the waters within the growing rivers of eutrophic 
 vegetation will become poorer and poorer in foodstuff, so that the 
 inward succession of plant associations will take on successively a 
 meso- and an oligotraphent character, and the deposits of peat in 
 such a basin, when completely filled, will be eutrophic peat around 
 the margin, mesotrophic next within, while in the center it will be 
 oligotrophic, and thus of a distinct character. Thus within the same 
 
FRESH-WATER SWAMPS 
 
 499 
 
 horizontal section there will be a marked change in the peats filling 
 a single basin. Such differences are frequently observed in single 
 basins, and also between adjoining basins, where slight differences 
 in the physical characters may bring about marked variation in the 
 result. The range of variation is enormously increased under the 
 influence of fluctuating climatic conditions such as nearly every 
 country experiences sooner or later. 
 
 An inverted order of superposition may result from a raising 
 of the water level, often due to the growth of a retaining rim of peat, 
 
 V'V 
 
 -/-/ - i - 1 - 
 
 O'. . o 
 
 ':&".-. 
 
 i Younger Sphagnetum Peat 
 
 "5cheucherteto- 5phacrnetu.*m Peat 
 
 "i'f Boundary horizon-- LriophoretuTn Peat 
 
 I (E.v agin at urn callunetum Peat) 
 3 - Older Sph.agTietu/m Peat 
 
 JScheuchzerietum Peat, Car iceto-SphagnetajTi or 
 I Erlophoretum Peat (E.vaqiTmtum etc.) 
 5 1 PiTieto-BetaletaTnPeat;Ui|erof pine stamps In upper 
 6 L part,and beneath that of ten lor i barnt surfaces 
 Almeium Peat 
 
 7. Phracpitetiun Peat 
 
 8 Peat mud 
 
 a Liver- colored mad (Lebbermudde) 
 
 IQ Lime mud 
 " Clay mud 
 12 Diluvial bottom 
 
 Semi terrestrial 
 
 Teltnatic or 
 5envterrestrial 
 Terrestrial 
 
 Semiterres trial 
 feUatic 
 
 Limnic 
 Formation 
 
 FIG. 114. Section through a North German peat bog, showing the succession 
 of strata. (After Ramann.) 
 
 or through sinking of a floating mat. A floating mat is composed of 
 interlacing roots and stolons of hygrophytes, above which form 
 semiterrestrial or even oligotrophic peats. When the weight be- 
 comes too great, the floating mat sinks with its load, and the meso- 
 trophic and eutrophic deposits will again form. Thus a layer of 
 oligotrophic peats may occur interpolated between layers of eutro- 
 phic peat deposits. 
 
 A section seven meters deep through a North German peat 
 series in which the peat- forming processes had come to an end gave 
 the succession shown in the above diagram (Fig. 114). 
 
500 PRINCIPLES OF STRATIGRAPHY 
 
 In general, the three principal zones given on p. 486 (the reed 
 or Phragmitetum, the sedge or Cyperacetum and the moss or Hyp- 
 netum zones) may be recognized as those which tend to succeed each 
 other in the process of filling the lake or pond, though one or an- 
 other of them may at times be absent. Toward the last the water- 
 loving trees begin to migrate into the swamp, among which in our 
 northern climes are the alders (Alnus incana, A. sermlata, A. mari- 
 tima near the coast, and A. glutinosa in western Europe), forming 
 the Alnetum zone. Elsewhere in the United States the tamarack 
 (Larix americana) takes the place of the alders, forming the Lare- 
 tum. In the southern states the Cypress (Taxodiwn distichum) or 
 the Tupelo (Nyssa uniflora) occupies this zone, forming, respec- 
 tively, a Taxodetum and a Nyssetum. Under and among these trees 
 a rich herbaceous flora flourishes, including ferns, sedges, the 
 Equisetum ftuviatile, the pitcher plant, Saracenia, violets, Galium, 
 Impatiens and a host of others. Sphagnum, however, is absent. In 
 the cypress swamps of Florida ( Stevenson-46 : 144, etc.) and the 
 Gulf Coast, logs and woody roots are common. At New Orleans 
 the cypress and other trees were found superimposed one upon the 
 other, in an upright position, with their roots as they grew. A 
 cypress swamp dissected in cutting a canal from Lake Pontchartrain 
 showed three tiers of stumps in the 9 feet excavated, these ranging 
 one above the other. The earlier trees apparently rotted away at the 
 level of the ground before the later ones grew over the same site. 
 The peat in the cypress swamp is formed by an accumulation of 
 the forest litter, the swamps themselves being due for the most part 
 to impeded drainage on an almost level surface. The depth of the 
 material has been reported as in some cases more than 150 feet. 
 Among the largest swamps on our coastal plain are : Okefenoke 
 Swamp in southern Georgia, and the smaller Dismal Swamp of 
 Virginia and North Carolina, which covers about 500 square miles. 
 
 In Okefenoke Swamp, which lies 50 miles from the ocean and 
 115 feet above the mean tide, the peat is about 10 feet thick, and 
 cypress stumps abound. The wetter portions are often free from 
 trees and show a luxuriant growth of cane, pickerel weed and water 
 lilies, but little or no Sphagnum. (Harper-23.) 
 
 The Dismal Swamp (49) is only a few feet above sea-level, 
 and has a peaty deposit at least fifteen feet deep (C. A. Davis), 
 resting on Pliocenic sands. Lake Drummond lies on its western 
 border (see ante, p. 120). Sphagnum plays only a small part in 
 the peat formation of this swamp, the canes, a grape, the bald 
 cypress (Tax odium distichum) and the junipers (Juniperus vir- 
 giniana) being the chief peat- forming plants. Of these the junipers 
 
TERRESTRIAL BOGS 501 
 
 occupy the drier spots, but the others generally grow in the water. 
 The projecting knees of cypress and the arched roots of Nyssa are 
 much in evidence. The knees are formed only where the cypress 
 grows in water, and serve as a sort of breathing organ or pneuma- 
 tophore. They are excrescences from the roots, rising above the 
 water, of a subcylindrical form, and crowned by a cabbage-shaped 
 expansion of bark, rough without and often hollow within. When 
 through a rise of water these knees are submerged the trees will 
 die. 
 
 Extensive cedar swamps (Chamcccyparis thyoides) occur on the 
 Atlantic coastal plain of the United States north of Florida. The 
 peat increases in thickness inward from the shore to perhaps 15 
 feet, and is full of tree trunks buried at all depths, these having 
 either rotted away or become uprooted. The peat is very pure, con- 
 taining only 3.35 per cent, of ash. The trees on the surfaces of 
 these marshes have broad, spreading roots, which do not penetrate 
 very far into the ground, but rely upon the great horizontal extent 
 of their shoots, which penetrate very deeply. 
 
 Terrestrial Bogs. 
 
 These include the forest bogs or moors and the high moors. 
 They may be the regular successors of the lake and river swamps, 
 but more often they develop independently upon a rocky or sandy 
 substratum. Such are the familiar upland moors, covering the hill- 
 sides in Great Britain and Scandinavia, as well as large parts of 
 northern Germany, and broad areas of northern Asia, and of Can- 
 ada and the northern United States. 
 
 Forest Moors. Beeches, pines and spruces succeed the tamarack 
 and alders, and form the transition to the high moors. Here the 
 ground is dry, and a wood flora appears, often characterized by 
 orchids. In these woods dry peat or forest peat results from the 
 falling and partial decay of the trunks, branches and leaves of the 
 trees. The character of the resulting peat varies with the type of 
 vegetation, especially with the predominant arboreal types. Decay 
 is partly accomplished through the influence of microorganisms. 
 The destruction of the dry peat and its conversion into earthy mold 
 or its entire decay are furthered by the growth of a number of 
 grasses, especially the common hair-grass, Deschampsia flexiiosa 
 Trin. The growth of peat mosses among the trees in the transition 
 of the bogs to the high moor type will result in killing these trees 
 through increasing moisture. Decay at the point of exposure above 
 
5 2 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 the moss will result in the breaking off of the trunk at that point, 
 and the subsequent complete embedding of the stumps in the peat. 
 Such old pine and other stumps are common features of the upland 
 bogs. 
 
 Upland Bogs, or High Moors. These are built up by the re- 
 
 
 FIG. 115. Section through a mature peat deposit near Hermansville, Menom- 
 inee Co., Michigan. (After Davis.) i, Surface vegetation; 2, 
 layer containing roots and coarse vegetable debris ; 3, fully de- 
 composed dark peat ; 4, light-colored structureless peat. 
 
 mains of peat mosses, especially the Sphagnum mosses and related 
 types. These form the bulk of the peat in the upland bogs, though 
 in some cases they are largely replaced by one or more members of 
 the pondweed family, especially Scheuchseria palustris, or of the 
 sedge family, notably the cotton grass, Eriophoruni vaginatum L., 
 
TERRESTRIAL BOGS 503 
 
 and the bulrush, Scirpits caspitosus, L., and other species. Thus 
 in the upland bogs of Great Britain, Sphagnum is of little impor- 
 tance as a peat-maker, its place being taken by Scirpus cccspitosus 
 and Eriophorum vaginatum. Other types, such as the heather, 
 Calluna vulgaris and Erica tetrali.v, are among those dominant in 
 some localities. The Scandinavian and north German moors, on 
 the other hand, are chiefly made up of species of Sphagnum. Where, 
 however, the Sphagnum is exposed during the winter for lack of 
 snow covering, as along the coast of Norway, it disappears, and its 
 place is taken by the bulrush, Scirpus cccspitosus. Heather peat, 
 formed by Calluna vulgaris, is also found in the high moors of 
 North Germany, as is also Molinia peat, formed by Molinia cccru- 
 Ica. Both Sphagnum peat and peat formed by the Scheuchzeria, 
 the cotton grass and by Scirpus cccspitosus are found in Canada 
 and the northern United States. The place of the heather is taken 
 by Vaccinium (blue berries, cranberries, etc.), Andromeda and 
 other members of the Heath family. 
 
 In northern Germany (Ramann-34: ijp) the high moors gen- 
 erally consist of an older, strongly decayed Sphagnum peat and a 
 newer, little decomposed, more porous Sphagnum peat, the two be- 
 ing separated by a dividing layer of peat formed by Eriophorum 
 vaginatum and Calluna vulgaris (Eriophoretum and Callunetum, 
 see the section, Fig. 114). Overlying these is a peat layer formed 
 of the most recent growths, the heaths, lichens, etc. The double 
 character of the Sphagnum peat is explained by the gradual diminu- 
 tion of the water raised in the peat bog by capillarity, so that, as the 
 bog rises by continuous growth, a time will come when the amount 
 of water is too small for further Sphagnum growth. Then other 
 plants take the place of the moss, until by decomposition the latter 
 has been reduced again in volume, and as a result become less 
 permeable to surface waters. Moist conditions wiH then return, 
 and a new growth of Sphagnum begins. Owing to the fact that 
 the old Roman roads were built upon the dividing layer of terres- 
 trial peat, it becomes possible to measure the rate of growth of the 
 upper peat layer, which must have accumulated during the past two 
 thousand years. 
 
 The external form of the high moor is domed, and permits the 
 run-off of the rain water, which produces moist margins, where 
 hygrophytes of various kinds will grow. 
 
 The upland peat bogs of Great Britain generally occur on un- 
 dulating and sloping ground. When the slopes of the surface do not 
 exceed 10, the peat generally grows to considerable thickness, but 
 where these slopes are greater the peat is also much thinner. 
 
504 PRINCIPLES OF STRATIGRAPHY 
 
 Marshes ("flows") seldom occur, since lakes and pools were rare 
 in the original surface. The peat rests either directly on the rock 
 surfaces or on the surface of glacial deposits, the contact being a 
 sharp one. In the Pennines the peats cover elevations like the 
 Cross Fell, whi-ch rises to 879 meters. It here sometimes has a 
 thickness of 4.5 meters. The peat is largely formed from the com- 
 mon reed, Phragmites communis. Sphagnum is scarce in this peat, 
 as already noted for the whole of Great Britain. In places the peat 
 contains an old forest bed, sharply marked off from the other de- 
 posits and at an altitude not exceeding 780 m. A section of a peat 
 bog in this district gave ( Samuelson-40 : 200) : 
 
 c. Scirpus caspitosus peat, yellow brown in color, very rich in 
 humus, not moldered, containing remains of dwarf shrubs. 
 Washing gave only numerous small specimens of Cenococcum 
 geophilum 125 cm. 
 
 b. Phragmites- Car ex peat, containing numerous large stools, 
 stems, twigs, and roots of birch. The finer f material con- 
 sists to a great extent of wood detritus. No coal found. 
 Nutlets of Ajuga reptans and seeds of Viola sp. were 
 washed out from a peat sample. Pollen grains of elm, 
 hazel and pine, spores of ferns and leaves of Sphagnum 
 were also found 75 cm. 
 
 a. Boulder clay. 
 
 This peat, as that of other regions of northern Europe, espe- 
 cially Fennoscandia, shows the occurrence of an Alpine vegetation 
 during the period of formation of the early peat. In the Cross Fell 
 the remains of these are not found in situ, however. Then followed 
 a period when the region was an extensive reed swamp, and this 
 was succeeded by wet birch forests, which in turn were replaced by 
 the wet moorland. 
 
 A section of a peat moor in the southern Uplands of Scotland 
 gave the following succession in descending order, the altitude being 
 about 300 meters above sea-level (Samuelson-4o:.?o/) : 
 
 6. Scirpus caspitosus peat, mixed with Eriophorum va'ginatum, 
 and also containing solitary Calluna stems. Pollen grains 
 of alder, birch, grasses, hazel, pine, Typha latifolia, etc. 
 and spores of Poly podium vulgar e and Sphagnum occur. . . 100 cm. 
 
 5. A sharply marked layer of pine " stools" with individuals 
 sometimes exceeding 50 cm. in diameter; rarely burnt 
 surrounding peat highly moldered and contains numerous 
 stems of Calluna and birch twigs; a hazelnut also found. . 30 cm. 
 
 4. Eriophorum vaginatum peat, rich in humus, containing some 
 birch fragments very likely the roots penetrating from 
 above washing gave Cenococcum geophilum, some Calluna 
 shoots, stones of Empetrum nigrum pollen grains of birch, 
 hazel, pine, etc., also found 45 cm. 
 
TERRESTRIAL BOGS 505 
 
 3. Eriophorum vaginatum peat very little moldered, Sphagnum 
 rare, Empetrum stems numerous few small birch twigs. 
 Stones of Empetrum, numerous, achenes of Potentilla 
 comarum, etc., also pollen of birch, pine, etc., and spores 
 and leaves of Sphagnum and brown fungus hyphas 20 cm. 
 
 2. Forest peat, rather rich in humus, hard and firm. Fine 
 material consists chiefly of wood detritus. In the peat 
 are numerous trunks and twigs of birch no coal wash- 
 ing gave achenes of Potentilla comarum, seeds of Viola and 
 numerous fruits of different Carex species. No determin- 
 able microorganisms 45 cm. 
 
 The two forest beds (2 and 5) appear to be of wide extent over 
 the Scottish uplands, the peat layers between varying in thickness 
 and to some extent in composition. The lowest bed always consists 
 of the remains of a birch forest. The dividing peat generally con- 
 tains arctic plants. 
 
 In the Grampians, Carex peat (150 cm.) rests directly upon the 
 boulder clay, or sometimes has a stratum of Sphagnum peat at the 
 base. Scirpus cccspitosus peat or Eriophorum vaginafiim peat fol- 
 lows this. 
 
 In the northwest Highlands of Scotland similar successions are 
 met with. In Coire Bog, in Easter Ross, the following section oc- 
 curs (Lewis quoted by Samtfelson-4o) : 
 
 DOMINANT PLANT ACCOMPANYING PLANT 
 
 1 . Scirpus Sphagnum 3 ft. 
 
 2. Pinus sylvestris L 
 
 3. Sphagnum 1-3 ft. 
 
 4. Pinus sylvestris L 
 
 5. Eriophorum 5 ft. Calluna (abundant in upper layers) 
 
 6. Betula alba L 2-3 ft. Menyanthes trifoliata L. 
 
 Eriophorum vaginatum L. 
 
 7. Empetrum nigrum L iJ4ft. Eriophorum, Polytrichum 
 
 8. Salix arbuscula L Betula nana. L. (abundant in upper 
 
 layers). Dry as octopetala L. Po- 
 tentilla comarum, Nestl. (abundant 
 in the lower layers). 
 
 Total peat 13-16 ft. 
 
 9. Sand 
 
 10. Closely packed stones 
 
 While most Swedish and many German authors refer the strat- 
 ification of the peat to successive changes in the level of ground wa- 
 ter as outlined above, other authors follow James Geikie, who re- 
 fers this alternation of vegetation to changes in climatic conditions 
 
506 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 accompanying changes in physical outline of Great Britain. His 
 succession of late glacial and interglacial stages in Scotland is as 
 follows : 
 
 5. Upper Turbarian or Sixth Glacial Stage. 
 
 High-level corrie glaciers, with snow line at 3,500 feet; peat overlying 
 Upper Forest; raised beaches at 25 to 30 feet; somewhat cold and wet 
 climate. 
 
 4. Upper Forestian or Fifth Interglacial Stage. 
 
 Upper Forest overlying lower peat; relatively dry and genial climate; 
 land area somewhat more extensive than now. 
 
 3. Lower Turbarian or Fifth Glacial Stage. 
 
 Valley-glaciers, with average snow-line at 2,400 to 2,500 feet; Lower 
 Peat overlying Lower Forest; raised beaches at 45 to 50 feet; cold and 
 wet climate. 
 
 2. Lower Forestian or Fourth Interglacial Stage. 
 
 Lower Forest overlying morainic accumulations of Fourth Glacial 
 stage; genial climate; land area of greater extent than now. 
 
 I. Mecklenburgian or Fourth Glacial Stage. 
 
 District ice-sheets and large valley glaciers of Highlands and Southern 
 Uplands; raised beaches at 100 to 135 feet; Arctic climate, with snow- 
 line ranging from 1,000 feet in west and northwest to 1,500 feet or 
 thereabout in Central Scotland. 
 
 The typical succession of strata of the Scottish peat bogs agrees 
 with this series of changes, this being as follows : 
 
 \ 
 
 Peat Deposits 
 
 Blytt's Climatic Period 
 
 Geikie's Climatic Period 
 
 5. Upper Peat Deposits 
 
 The Subatlantic Period 
 
 Upper Turbarian 
 
 
 (moist and cold) 
 
 
 4. Upper Forest Bed 
 
 The Subboreal Period 
 
 Upper Forestian 
 
 pine or birch re- 
 
 (warm and dry) 
 
 
 placed in the Shet- 
 
 
 
 lands by a Calluna 
 
 
 
 layer 
 
 
 
 3. Middle Peat Deposit 
 
 The Atlantic Period 
 
 Lower Turbarian 
 
 commonly with a 
 
 (warm and moist) 
 
 
 thin layer near the 
 
 
 
 middle containing 
 
 
 
 arctic plants (second 
 
 
 
 arctic bed) 
 
 
 i 
 
 2. Lower Forest Bed 
 
 The Boreal Period 
 
 Lower Forestian 
 
 chiefly of birch re- 
 
 (warm and dry) 
 
 
 mains 
 
 
 
 i. Lower Peat Deposit 
 
 The Subarctic and Arctic 
 
 Arctic Tundra time, at 
 
 containing the re- 
 
 Periods 
 
 close of Mecklenburg- 
 
 mains of the first 
 
 
 ian ice age 
 
 arctic flora (first 
 
 
 
 arctic bed) 
 
 
 
THE TUNDRA 507 
 
 The Arctic Tundras. The permanently frozen areas of 
 northern Europe, Asia and America are covered for the most part 
 by a growth of peat which rises in the form of rounded hills or 
 banks of approximately uniform height. Frozen solid in winter, 
 they are thawed out on the surface during the summer months. 
 Throughout northern Europe the old peat vegetation, which con- 
 sisted largely of Sphagnum, has perished, only on the borders of 
 the natural drainage channels are cotton grass and Sphagnum still 
 found growing. The causes of this widespread destruction of the 
 peat moss and of the consequent cessation of peat formation are 
 the rising of the permanently frozen ground-level beneath the moss, 
 and the overgrowing of the moss by lichens, especially Lecanora 
 tartarea, which covers both living and dead organisms with a uni- 
 form mantle. The peat protects the ice beneath it from melting, so 
 that in Lapland ice exists the year round under peat only. Melt- 
 ing of the peat bogs proceeds down to a depth of 30 to 40 cm. 
 With the increase in thickness of the peat, the ice is more protected 
 and its surface rises, the result being that the plants are less and less 
 supplied with moisture. This eventually leads to their destruction. 
 The tundra of Alaska covers the whole surface, except the faces of 
 steep cliffs, along the borders of Behring Sea and the Arctic Ocean. 
 It is typically "a swampy, moderately level country, covered with 
 mosses, lichens and a great number of small but exceedingly beauti- 
 ful flowering plants, together with a few ferns. The soil beneath 
 the luxuriant carpet of dense vegetation is a dark humus, and at a 
 depth exceeding about a foot is always frozen." (Russell-39 : /^J.) 
 Lakelets and ponds abound in the level parts, and they occur even 
 on the hillsides, where, except for the spongy retaining vegetation, 
 no such accumulation would be possible. The dense vegetation ex- 
 tends up the mountainsides wherever conditions are favorable and 
 covers even steep crags. "On the steep slopes, as in the swamps, 
 the vegetation is always water-soaked, owing to the extreme hu- 
 midity of the climate in which it thrives." Mosses and lichens char- 
 acterize the flora with a notable absence of trees. "Cryptogamic 
 plants make more than nine-tenths of its mass. On their power to 
 grow above as they die and decay below depends the existence of 
 the tundra." Two species of Equisetum flourish with rank luxur- 
 iance over great areas along the Yukon. Excavations show "that 
 the fresh luxuriant vegetation at the surface changed by insensible 
 gradations to dead and decaying matter a few inches below and 
 finally became a black, peaty humus, retaining but few indications 
 of its vegetable origin." (Russell-39: 126.) The depth of the 
 humus layer at St. Michaels is about two feet. A mile east of the 
 
508 PRINCIPLES OF STRATIGRAPHY 
 
 village it is about twelve feet. "In the delta of the Yukon a depth 
 of over fifteen feet was seen at one locality. A depth of 150 to 300 
 feet has been assigned by several observers to the tundra, where it 
 is exposed in a sea cliff on Eschscholtz Bay, at the head of Kotzebue 
 Sound." Here the surface layer of humus is rich in mammalian 
 remains. It is evident that the conditions here differ from those 
 found in North Europe, where the rising ground ice eventually puts 
 a stop to further peat formation. Russell thinks that in Alaska 
 "there is apparently no reason why this process [of growth above, 
 decay below, and conservation of the partly decayed vegetation by 
 freezing] might not continue indefinitely, so as to store up vegetable 
 matter in a way that is only paralleled in the most extensive coal 
 fields." (39:^70 
 
 "On the flood plains of the larger rivers, and generally through- 
 out all the lowlands of Alaska, peaty deposits are forming in the 
 same manner as on the tundra, modified, however, by the growth of 
 arborescent vegetation and by the intrusion of sand and clay in 
 places that are flooded during the high-water stage of the rivers. 
 
 "At many localities along the Yukon, sections of peaty deposits 
 are exposed often eight or ten feet thick and several long. The 
 bluffs . . . are from fifteen to twenty feet high . . . and nearly 
 always frozen solid. . . . Some of the vegetable layers are in- 
 terstratified with sand and clay; others at the surface are still in- 
 creasing in thickness and have a dense forest growing on them. 
 Not infrequently there is a stratum of clear ice interbedded with 
 the layers of peat, sand and clay." (Russell-39.) 
 
 The moist, cool climate prevailing over eastern , Canada has also 
 been conducive to the extensive growth of peat bogs, which cover 
 all the, area around the St. Lawrence and the Ottawa, as well as 
 on Newfoundland and on the smaller islands off the coast. On 
 Anticosti Island in the Gulf of St. Lawrence there are peat beds 
 covering in some cases areas from one hundred to more than a 
 thousand acres in extent, with a thickness of ten feet or over. 
 (Twenhofel-48: 66.) The peat rests on sands and gravels, some- 
 times with Mya arenaria, and at other times it rests directly upon 
 the eroded limestone surface of early Palaeozoic age. The lower 
 peat deposits often contain tests of sea urchins (Strongylocentrotus 
 drobachiensis) , fragments of lobsters and crabs, gastropods, etc., 
 which are brought there by birds, chiefly crows, or which have been 
 washed up by unusually high waves and tides. These marine or- 
 ganic remains are often very abundant. In the wooded areas, 
 where trees have only a slight foothold owing to the shallowness of 
 
PEAT IN THE TROPICS 509 
 
 the soil, fallen trees abound and are entombed in the growing and 
 only partially decaying vegetation. 
 
 The temperature of Anticosti ranged, during the six years from 
 1897 to 1902, from 4-26 C, which occurred once, to 39 C, 
 which occurred twice. The average temperature for June, July and 
 August is about + 12.5 C., that of the winter months about 10 
 C., or an annual average of about'-f 2 C. Precipitation during the 
 three months of the growing season varies from 23 to 28 centi- 
 meters, the mean annual rainfall lying between 50 and 100 cm., 
 but nearer the latter. Cloudiness and fogginess often prevail. 
 (Twenhofel-48.) In southern latitudes peat is more rarely formed 
 from mosses. In the Chonos Archipelago (S. L. 44 to 46) every 
 piece of level ground is covered with Astilia puniata and Donatia 
 magellanica, which by their joint decay compose a thick bed of 
 elastic peat. (Darwin 12 : 24-26.) 
 
 Astilia is the chief peat former of Tierra del Fuego. Fresh 
 'leaves appear constantly around the growing stem, while the lower 
 ones decay. ( Stevenson-46 : 563 (161).) Every plant in the Falk- 
 land Islands becomes converted into peat, but the most important 
 plants are a variety of "crowberry 1 ' also common on Scottish Hills 
 (Empetrum rubrum), a creeping myrtle (Myrtus nummularia), a 
 dwarf species of water marigold (Caltha appendiculata) and some 
 sedges and sedge-like plants. "The roots, preserved almost unal- 
 tered,, may be traced downward in the peat for several feet, but 
 finally all structure is obliterated and the whole is reduced to an 
 amorphous structureless mass." ( Stevenson-46 : 564 
 
 Peat in the Tropics. 
 
 Sphagnum does not occur south of N. L. 29, but peat is formed 
 by a variety of plants south of this line. The cypress swamps of 
 Florida contain thick deposits of peat, with cypresses, grasses, ferns 
 and myrtle making up the bulk of the vegetation. On Bermuda a 
 thickness of at least 50 feet is assigned to the peat in one of the two 
 great peat swamps. "The climate is such that plants of Carbonifer- 
 ous type could grow' well, for the banana thrives, while palms and 
 Indian rubber trees attain great size." ( Stevenson-46 -.567 (165). ) 
 Extensive peat bogs are found in the Amazon region and in the in- 
 terior of Africa. In the region between the Gulf of Guinea and the 
 sources of the Niger, extensive peat deposits are formed by the 
 sedge Eriosporq pilosa Benth. On the Island of Sumatra occurs 
 a large swamp, 90 km. from the coast, on the left bank of the river 
 
5io PRINCIPLES OF STRATIGRAPHY 
 
 Kampar. It has a width of 12 kilometers and an area of more 
 than 80,000 hectares, and is covered by trees rising mostly to a 
 height of 30 m. It contains a peat deposit which has been sounded to 
 a depth of 9 meters. This peat consists largely of decayed woody 
 tissue. The larger roots of trees, with their upward pointing pneu- 
 matophores, form a solid basis in this swamp, which makes tra- 
 versing possible. The numerous varieties of trees have mostly slen- 
 der stems, bearing only a small crown of leaves, but with broad, 
 buttressed roots rising three to four meters above the ground, and 
 with remarkable aerial roots projecting in bundles for a meter or a 
 meter and a half from the trunk. Gymnosperms and monocotyl- 
 edons are wholly wanting among the taller trees of this swamp, 
 these being chiefly composed of dicotyledons. Among the smaller 
 trees and bushes monocotyledons occur, though sparingly. Tree 
 palms are rare, but bushes of this family abound, especially several 
 species of a small Calamus. A small tree fern (Alsophila?) was 
 also found scatteringly. The herbaceous vegetation is sparingly rep- 
 resented both in species and individuals. Grasses and sedges are 
 practically wanting, the ground between the trees, where not occu- 
 pied by the aerial roots or "knees," being strewn with decaying 
 leaves. Sphagnum is wholly wanting, and other mosses, liverworts, 
 lichens and herbaceous Pterydophytes are rare. Epiphytes occur 
 only in the leafy crown of the trees on account of the smooth char- 
 acter of their trunks. Phanerogamous water plants appear to be 
 rare, but thread-like algae were found to be numerous where the 
 forest was lightened through uprooting of trees by the winds. To- 
 ward the margin of this tropical swamp the vegetation gradually 
 changes, merging into that of the surrounding drier land. (Potonie- 
 
 32.) 
 
 FOSSIL HUMULITHS. 
 
 The Humuliths of former geological periods are represented by 
 the following types : 
 
 Lignite, 
 Brown Coal, 
 Bituminous Coal, 
 Anthracite, 
 Graphite. 
 
 Lignite is wood, especially that of coniferous trees, which is in 
 its early stages of alteration, but still shows the woody characters 
 in unmistakable manner. Lignites are found in Mesozoic deposits 
 
FOSSIL HUMULITHS 511 
 
 and are especially abundant in and characteristic of the Tertiary, 
 where they are often associated with brown coal. 
 
 Brown Coal is a compact or earthy, altered peat deposit, espe- 
 cially characteristic of the Tertiary rocks. It represents one of the 
 intermediate stages from peat to mineral coal, and still often shows 
 evidence of its organic origin. It varies from pale brown or yel- 
 low to deep brown or black, though some shade of brown is the 
 prevailing color. It contains from 55 to 75 per cent, of carbon, has 
 a specific gravity of 0.5 to 1.5 and burns easily with a sooty flame 
 and strong odor, leaving a light ash. The most extensive deposits 
 are in the Oligocenic of North Germany, but peat beds altered to 
 Brown coal have also been observed in post-Tertiary deposits. 
 
 Bituminous Coal. This coal, also called soft coal, is found in 
 the Mesozoic and the Carbonic. It is black, compact, usually brit- 
 tle, with cubical or conchoidal cleavage, and has a shiny luster. It 
 contains from 75 to 90 per cent, of carbon and generally some sul- 
 phur. Its specific gravity ranges from 1.2 to 1.35, and it burns 
 with a bright, clear flame. Some varieties cake on burning, others 
 are consumed to ashes. Generally no trace of organic matter is 
 recognizable, except under the microscope. 
 
 Anthracite, or hard coal, is the most highly mineralized form of 
 coal, with a black color, strong, metalloid or vitreous luster and 
 conchoidal fracture. Its specific gravity ranges from 1.35 to 1.7, 
 and it contains over 90 per cent, of carbon. It kindles with diffi- 
 culty, but burns in a strong draught with great heat and without 
 smoke, caking or odor. It occurs in disturbed regions where the 
 volatile matter has been driven off through heat and metamorphism. 
 Some anthracites also originate through extensive loss of the vola- 
 tile gases before entombment. 
 
 Graphite, or pure carbon, is found chiefly in ancient crystalline 
 rocks, such as gneisses, mica schists, metamorphic limestones, etc. 
 When originating from organic matter it is the product of extreme 
 metamorphism, but it may also be formed in purely inorganic 
 manner. 
 
 Ancient Moors. 
 
 Among the moors of past geological time, those of the Anthra- 
 colithic or Carbonic period deserve especial attention, for they have 
 not only furnished a large part of the coal supply of the world, but 
 their wonderful luxuriance of growth and strangeness of type in- 
 vest them with peculiar interest, and make the restoration of 
 these ancient swamps and forests and their subsequent burial a 
 problem full of fascination. 
 
512 PRINCIPLES OF STRATIGRAPHY 
 
 Comparison with modern moors leads to the conclusion that 
 those of Carbonic time were of the flat or low moor variety, or 
 that type in which arboreal vegetation plays a more significant part 
 than it does in our upland bogs. While the seashore or marsh type 
 was not unrepresented, it is apparent from the character of the 
 vegetation that the prevailing moor type of that period, now repre- 
 sented by our coal beds, was of the fresh-water swamp or morass 
 type. The character of the vegetation itself points to this, since 
 the tissues of the Carbonic trees are of coarse-cell type like those 
 of the rapid-growing trees of our swamps, instead of the close- 
 celled type characteristic of upland bogs and due to slower growth. 
 Of all the known modern swamps that of Sumatra, above de- 
 scribed, comes nearest to representing the conditions of the Car- 
 bonic moors, for the character of the vegetation seems to point un- 
 mistakably to a moist, tropical climate for at least part of our Car- 
 bonic coal deposits. 
 
 The place of the modern bulrushes and other reeds was taken 
 in Carbonic time by the gigantic reed-like relatives of the modern 
 Equisetum, i. e., the Calamites. The usual occurrence of these 
 plants in sandstones preceding coal beds indicates that they per- 
 formed much the same land- forming office in those days that the 
 reeds do to-day. They have in common with them the characteris- 
 tic power of sectional repetition of parts which enables the plant 
 to continue growth and putting forth of roots, even though it is 
 progressively buried by the accumulating silt. 
 
 The tree types succeeding the calamites, the Lepidophytes, in- 
 cluding Lepidodendra and Sigillaria, were true swamp plants with 
 horizontally spreading roots, the Stigmaria. These fossil roots have 
 a remarkable similarity to the spreading roots of Pinus and other 
 moor trees of the present day, and, like these, were adapted for 
 growth on wet ground, where firmness of foundation was secured 
 by great horizontal spreading, and where it was not necessary to 
 penetrate into the soil for moisture, as in regions of low-lying 
 ground-water level. A basal enlargement of the trunks of trees, 
 such as characterizes Nyssa uniflora and others of our swamp trees, 
 is also often seen in these Carbonic types. This feature likewise 
 tends to keep the tree erect, owing to the greater weight of the 
 basal portion. Structures suggestive of the cypress knees or pneu- 
 matophores of our subtropical swamps have also been found asso- 
 ciated with the Sigillaria, while structures suggestive of the breath- 
 ing pores or lenticels, so characteristic of the basal portions of the 
 trunks of trees in the tropical swamps, occur in the Carbonic 
 Lepidophytes, where they form the Syringodendron surface. 
 
COALS AND COAL SHALES 513 
 
 The characters of the Ferns and the Sphenophyllaceae of the 
 Carbonic likewise point to moist tropical conditions during that 
 period, and since the coal deposits resulting from the growth of 
 these plants are so widely distributed in regions which to-day have 
 a temperate climate, it is apparent that conditions now characteristic 
 of the equatorial region of the world were during the Carbonic 
 period more widely distributed. In Chapter II a possible cause 
 for the increase in temperature was discussed, this being the greater 
 supply of CO 2 in the atmosphere which would retain the heat and 
 so raise the temperature of the entire earth's surface. The removal 
 of this atmospheric constituent and the storage of the carbon in 
 the tissues of plants would bring about a progressive lowering of 
 the temperature, and this refrigeration of the climate would bring 
 on the glacial conditions known to have existed in Permic time. It 
 is a notable fact that the coal-forming period was preceded by a 
 period of wide and extensive submergence and the building of lime- 
 stones in all parts of the world. This would result in setting free 
 much CO 2 , and hence would supply the conditions favorable to the 
 development of the tropical coal swamp on the emergence of the 
 land.* 
 
 The coals formed during the Mesozoic periods have probably a 
 history similar to that of the Carbonic coals, though seashore con- 
 ditions and those of lagoons and estuaries may have been more 
 common. The Tertiary coals, especially those of northern Europe, 
 appear to have been formed in swamps closely similar to our mod- 
 ern cypress swamps of southern North America. Many of the 
 species found in the brown-coal deposits of North Germany, such as 
 the Magnolias, Liquidambar, Sassafras, Catalpa, Swamp Cypress, 
 etc., are still living in these swamps, though they have become ex- 
 tinct in Europe. The remarkable depth of the brown-coal deposits 
 of North Germany, reaching north of Cologne nearly 100 meters, 
 gives some indication of the length of time required to accumulate 
 such a mass of vegetal material by successive periods of growth and 
 decay. As in the case of the Carbonic deposits, the Tertiary coal 
 period was preceded by extensive limestone deposits and succeeded 
 by a period of gradual refrigeration which culminated in the Pleis- 
 tocenic glaciation. 
 
 Black Soil and Shales of Humulithic Origin. 
 
 Long-continued growth of vegetation produces in some regions 
 a thick accumulation of a dark loam, such as is seen in the black 
 
 * See also p. 90, and the reference to Koken's work in Chapter XXIII. 
 
514 PRINCIPLES OF STRATIGRAPHY 
 
 cotton soil (regur) of India and in the black earth (tchernozom) 
 of Russia. Such deposits may subsequently harden into black, car- 
 bonaceous shales. Examples of such shales are probably to be 
 found in the Chattanooga black shale of eastern Alabama, etc., of 
 Lower Mississippi age. This in places includes thin layers of 
 coal, arid in other respects bears evidence of having been a former 
 residual soil, the black color of which is due to the abundance of 
 partially decayed land vegetation. 
 
 Burial of Peat Deposits. 
 
 Peats formed near the coast, even when of fresh-water or 
 swamp origin, may be buried by a subsidence of the land and a con- 
 sequent transgression of the sea. Such subsidence may be so slow 
 that salt-water or marsh peat may transgress over the fresh-water 
 peat, as in the case of the Massachusetts coast (see ante, p. 493). 
 Where subsidence is more rapid, fresh-water peat may be covered 
 by marine sands, as in the Bay of Morlaix, Brittany (Finistere), 
 where, according to Cayeux, two layers of peat with Arundo 
 phragmites are separated and again covered by marine sands. In 
 the flat, maritime plain of Pas-de-Calais, a section now three meters 
 above the sea-level shows : 
 
 Marine sand with Cardium edule, i meter. 
 
 Marine clay with Hydrobia ulvcc, I meter. 
 
 Peat. 
 
 Marine sand f with Cardium edule. 
 
 In the mouth of the Shelde similar deposits of peat, i to 1.5 
 meters thick, are enclosed between sediments with marine organ- 
 isms. At Cotentin, in Normandy, 20 meters of peat are overlain by 
 marine sands, and similar deposits are found in other parts of 
 France, in Belgium, Holland and elsewhere. As shown, however, 
 by the deposits of Anticosti, the presence of such marine organisms 
 in the strata covering the peat need not always indicate subsidence 
 after the formation of the peat. 
 
 The section made by the river Tay in the Carse lands of south- 
 eastern Scotland shows a peat bog now forming the river bed and 
 covered by about 17 feet of alluvial material, which near the top 
 contains cockles, mussels and other marine forms. The peat of 
 this region rests in part on alluvial sands and in part on marine 
 clays, and is itself of terrestrial origin. It is "highly compressed 
 and splits readily into laminae, on whose surfaces are small seeds 
 and wing cases of insects. As a rule, but not always, it is marked 
 
BURIAL OF PEAT DEPOSITS 515 
 
 off sharply from the overlying clay and silt." The upper layers of 
 the peat represent transported material from farther up the stream, 
 and consist of silt with twigs and branches and trunks of trees. 
 Other examples are cited by Stevenson (46). 
 
 Glacial till ; is not an infrequent cover for peat deposits. Sir 
 William Dawson (17:63) has described an early Quaternary 
 bog in Nova Scotia, where the peat was covered by 20 feet 
 of boulder clay and so compressed that it had almost the hardness 
 of coal. In the New England States such peat buried under gla- 
 cial drift is not uncommon, and it has been observed in widely sep- 
 arated districts in the glaciated area. In Montgomery County, 
 Ohio, a bed of peat, 15 to 20 feet thick, and with its surface formed 
 by Sphagnum grasses and sedges, underlies 90 feet of gravel and 
 sand. The peat contains coniferous wood, bones of elephant, mas- 
 todon and teeth of giant beaver. In southwestern Indiana and 
 part of Illinois an ancient soil, 2 to 20 feet thick, and containing 
 peat, muck, rooted stumps, branches and leaves, lies at a depth of 
 60 to 1 20 feet below the surface. 
 
 Peat deposits on the flood plains and deltas of rivers are likely 
 to be buried under the silt and mud when the river rises, and like- 
 wise, when through a change in climate or other cause a river be- 
 gins to rapidly aggrade its flood plain. In such cases the peat de- 
 posits will be buried under regular strata of sand and clay of con- 
 tinental origin, and it would happen that the trees still standing are 
 gradually^ buried in the silt and sand. "Even the slender canes of 
 the Mississippi delta, killed by salt-water invasion, remain standing 
 after they have been surrounded by several feet of silt." (Steven- 
 son-46.) The filling of the hollow bark of still erect trees, in which 
 the wood has decayed, by sand and mud and so ensuring their pres- 
 ervation in an erect form, is a familiar fact to students of the Coal 
 Measures. The well-known section at South Joggins, Nova Scotia, 
 shows erect Sigillaria and other trees in considerable number. The 
 most important part of the section containing these trees is as fol- 
 lows (Dawson-i8) : 
 
 Sandstone with erect Calamites and Stigmaria roots 6 ft. 6 in. 
 
 Argillaceous sandstone, Calamites, Stigmaria and Alethop- 
 
 teris cuchitica i ft. 6 in. 
 
 Gray shale, with numerous fossil plants, and also Naiadites, 
 
 Carbonia and fish scales 2 ft. 4 in. 
 
 Black coaly shale, with similar fossils I f t. I in. 
 
 Coal with impression of Sigillaria bark o ft. 6 in. 
 
 "On the surface of the coal stand many erect Sigillariae, pene- 
 trating the beds above, and some of them nearly three feet in 
 
PRINCIPLES OF STRATIGRAPHY 
 
 diameter at the base and nine feet in height. In the lower part of 
 many of these erect trees there is a deposit of earthy matter black- 
 ened with carbon and vegetable remains and richly stored with bones 
 of small reptiles, land snails and millipedes." Dawson considers 
 that "on decay of the woody axis and inner bark they must have 
 constituted open cylindrical cavities, in which small animals shel- 
 
 FIG. 116. Buried peat bed near Marquette, Michigan, with bog-iron stratum 
 below and sand dune above. Exposure made by easterly storm. 
 (After Davis.) a, stump of buried tree; b, sand stratum, with 
 roots and other plant remains ; c, e, and g, pine needles ; d, 
 sand with grass remains; f, iron sand; h, pure sand, cross- 
 bedded; i, peat stratum, with standing pine stump; k, bog iron. 
 (Height of section about 15 feet.) 
 
 tered themselves, or into which they fell and remained imprisoned. 
 These natural traps must have remained open for some time on a 
 subaerial surface." Fifteen out of twenty-five erect trees proved 
 to have these contents, in one no less than twelve reptilian skeletons 
 occurring. In a few instances portions of the cuticle, ornamented 
 with horny scales and spines, had been preserved. In these de- 
 posits, it is evident that the trees after being buried up to a certain 
 depth rotted away on the surface or were blown down, and that 
 
BURIAL OF PEAT DEPOSITS 517 
 
 then the inner tissues decayed until only the bark, embedded in up- 
 right position in the mud, remained behind. The bark of fallen 
 trees is generally pressed flat on the decay of the inner tissues by 
 the weight of the superincumbent sediment. In Alaska the Yahtse 
 River, "issuing as a swift current from beneath the glacier, has in- 
 vaded a forest at the east, and has surrounded the trees with sand 
 and gravel to a depth of many feet. Some of the dead trunks, still 
 retaining their branches, project above the mass, but the greater part 
 of them have been broken off and buried in the deposit. Other 
 streams, east from the Yahtse, have invaded forests, as indicated 
 by dead trees standing along their borders. Where the deposit is 
 deepest the trees have already disappeared, and the forest has been 
 replaced with sand flats. The decaying trunks are broken off by 
 the wind, and are buried in prostrate position. This deposit con- 
 solidated would resemble closely a Coal Measure conglomerate." 
 (Russell, cited by Stevenson-46.) 
 
 Modern tree trunks have been found on the coast with their in- 
 terior decayed and rilled with sand down into the roots. (Potonie- 
 32.) Sand dunes advancing over a peat bed will put an effective 
 stop to further peat formation and serve as a factor in preserv- 
 ing the peat so formed. It is not improbable that many of the 
 sandstones which succeed the coal beds of our Carbonic series owe 
 their origin to such covering wind-blown sands. 
 
 In advancing over the peat the sand dunes will likewise advance 
 over the forests associated with the peat and bury them. This can 
 be seen in many regions where only the tops of large trees project 
 above the sands, as on the shores of Lake Michigan, etc. 
 
 In rare cases peat deposits may be buried by landslides, by mud 
 flows, etc. In all cases where the deposit, first spread over the 
 swamp or bog, is a fine one, impressions of the last fallen leaves 
 and branches may be preserved in great detail. In this manner are 
 formed the roof shales with their wonderful wealth of plant im- 
 pressions, which makes it possible for us to-day to reconstruct the 
 vanished flora of the Coal Period. The clay or soil in which the 
 plants had their roots is in most cases preserved as a "fire clay," 
 that is, a clay which can be used for pottery which has to with- 
 stand intense heat. It contains little iron, and is nearly free from 
 lime and alkalies, of which the clay was deprived by the growth of 
 the plants. 
 
 LIPTOBIOLITHS. 
 
 These may be dismissed with a few words. The exudations of 
 resins, gums, wax, etc., from resinous trees are characterized by 
 
518 PRINCIPLES OF STRATIGRAPHY 
 
 relative stability of composition, and are not easily decomposed. 
 They may thus form accumulations of greater or less extent, while 
 the plant tissues which they enclose decay wholly. The subfossil 
 Copal is a typical example, while from older rocks (Oligocenic) of 
 North Germany comes the amber. Many minor types of liptobio- 
 liths occur in nature, but they are of more mineralogical than geo- 
 logical value. 
 
 ^ ALLOCHTHONOUS VEGETAL DEPOSITS. 
 
 Vegetal material transported from other localities and deposited 
 where it did not grow is found frequently at the present time, both 
 upon the land and in the sea. It also occurred in the past. On the 
 Missouri, Mississippi and other rivers, rafts and whole floating 
 islands of vegetation are known, and logs are found scattered 
 widely through deposits to which they are wholly foreign. "These 
 drifted materials are everywhere distinguishable from plants buried 
 in situ, for they have been deprived of all tender parts; of the 
 harder woods in Carboniferous times there are few traces except 
 decorticated stems, casts of the interior, indeterminate forms 
 grouped under Knorria, Sternbergia and some other names." 
 ( Stevenson-46 : 642.) 
 
 "In all extensive deposits of driftwood the trees are battered, 
 stripped of leaves, bark and often of branches ; they are scattered 
 on the strand or piled in irregular loose heaps, where, exposed to 
 the air, they decay; or, if in more favorable conditions, the inter- 
 stices become rilled with sediment, the trees become merely logs in 
 shale or sandstone, even their genus being unrecognizable except by 
 microscopic study of the structure." ( Stevenson-46 : 557. ) 
 
 The coal deposits of the Commentry basin in France have long 
 been held to be a good example of a fossil allochthonous coal. It is 
 now known, however, that this coal is formed in situ, after all. 
 Stigmaria are found in place, while the trees are arranged in all 
 positions, upright, leaning and prostrate. The resemblance to a 
 forest ravaged by a hurricane is very close. 
 
 Marine Vegetal Deposits. Marine plants, owing to the buoyancy 
 which they possess on account of the numerous air spaces in their 
 tissues, will float on the surface of the water until stranded on the 
 shore or on a mud flat. Their presence in the deep sea deposits 
 is not noted, because they will continue to float until decomposed. 
 On the other hand, in the shallower portions of the littoral district 
 marine plants may accumulate in abundance. Spores of plants are 
 not infrequently found in marine sediments. But by far the most 
 
DEEP SEA VEGETAL DEPOSITS 519 
 
 noteworthy deposits of plants in marine sediments are the deep- 
 sea accumulations of leaves and driftwood of terrestrial origin. 
 In the Caribbean, on the lee side of the West Indian Islands, the 
 Blake dredged "masses of leaves, pieces of bamboo and of sugar 
 cane, dead land shells, and other land debris" at a depth of over 
 1,000 fathoms, and ten or fifteen miles from land. ( Agassiz-i : 291.) 
 The Albatross in its dredging expedition on the west coast of Cen- 
 tral America between the Galapagos Islands, the west coast of Mex- 
 ico, and" the Gulf of California, found nearly everywhere a muddy 
 bottom or one composed of Globigerina ooze, and generally con- 
 taining terrigenous matter. Scarcely a single haul of the trawl 
 was made which did not bring up a "considerable amount of de- 
 cayed vegetable matter, and frequently logs, branches, twigs, seeds, 
 leaves, fruits," much as found by the Blake on the east coast, but 
 in vastly greater quantities. Even at a depth of over 2,000 fathoms 
 these remains were found. ( Agassiz-2 : n, 12.) 
 
 The Challenger also found twigs, woods, and seeds at a depth 
 of 800 fathoms near Ki Island, and also within 20 fathoms off the 
 coast of Amboina Island, both west of New Guinea. South of 
 Mindanao, at a depth of 2,150 fathoms, palm fruits, and fragments 
 of wood and bark were found, while about 50 miles off the coast 
 of Luzon at a depth of 1,050 fathoms were dredged fragments 
 of leaves, stems and wood, the latter overgrown with Serpula. 
 
 The distance from shore to which material is carried by flota- 
 tion is often indicated by the state of preservation of the mate- 
 rial. White says : "If the material is macerated, corroded, rolled, 
 defoliated, skeletonized, incrusted, or bears other signs of having 
 been for some time in the water it is liable to have been trans- 
 ported for some distance. ... If long in sea water the frag- 
 ments are likely to bear the marks of abundant marine organisms, 
 particularly if in tropical sea water. On the other hand, the occur- 
 rence of clean, unbroken^ smooth leaves, and particularly of large 
 segments of fern fronds, with their full complement of carbonace- 
 ous residues, is prima facie evidence of minimum exposure to water 
 and of the least subjection to the action of swift currents or waves." 
 (White-60.) 
 
 BIBLIOGRAPHY XI. 
 
 (See also Bibliography X.) 
 
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520 PRINCIPLES OF STRATIGRAPHY 
 
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 Geological Institution of the University of Upsala, Vol. X, pp. 197-260, 
 with literature. 
 
 41. SHALER, N. S. 1885. Preliminary Report on Sea Coast Swamps of the 
 
 Eastern United States. 6th Annual Report of the U. S. Geological 
 Survey, pp. 353-398- 
 
522 PRINCIPLES OF STRATIGRAPHY 
 
 42. SHALER, N. S. 1890. General Account of the Fresh Water Morasses 
 
 of the United States with description of the Dismal Swamp District of 
 Virginia and North Carolina, roth Annual Report of the United States 
 Geological Survey, pt. I, pp. 253-339. 
 
 43. SHERZER, .W. H. 1900. Geology of Monroe County, Michigan. Geo- 
 
 logical Survey of Michigan, Vol. VII, pt. I. 
 
 44. STEINMANN, G. 1889. Ueber Schalen und Kalksteinbildung. Bericht 
 
 der Naturforschenden Gesellschaft zu Freiburg i. B., Bd. IV, p. 288. 
 
 45. STEMME, H. 1909. Das natiirliche System der Brennbaren Organ- 
 
 ogenen Gesteine (Kaustobiolithe). Zeitschr. fur Praktische Geologic, 
 17. Jahrgangang, pp. 4-12. 
 
 46. STEVENSON, JOHN J. 1910-1913. The Formation of Coal-beds. 506 
 
 pages. Published in 4 parts: Part I. Proceedings of the American 
 Philosophical Society, Vol L, pp. 1-116; Part II. ibid., pp. 519-643; 
 Part III, ibid., Vol. LI, pp. 423-553; Part IV, ibid., vol. LII, pp. 31-162. 
 
 47. STOLLE, J. 1910. Die Beziehungen der Nordwest-deutschen Moore zum 
 . Nacheiszeitlichen Klima. Zeitschrift der deutschen geologischen 
 
 Gesellschaft, Bd. LXII, pp. 163-189. 
 
 48. TWENHOFEL, W. H. 1910. Geologic Bearing of the Peat Beds of Anti- 
 
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 49. UNITED STATES GEOLOGICAL SURVEY. 1902. Geological Atlas 
 
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 50. WALTHER, JOHANNES. 1885. Die Gesteinbildenden Kalkalgen des 
 
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 329-357- 
 
 51. WALTHER, JOHANNES. 1893-4. Einleitung in die Geologic als 
 
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 52. WALTHER, JOHANNES. 1910. Die Sedimente der Taubenbank im 
 
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 53. WALTHER, JOHANNES. 1910. Lehrbuch der Geologic von Deutsch- 
 
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 54. WEBER, C. A. 1910. Was lehrt der Aufbau der Moore Norddeutsch- 
 
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 55. WEED, WALTER HARVEY. 1889. Formation of Travertine and Silice- 
 
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 57. WETHERED, EDWARD. 1889. On the Microscopic Structure of the 
 
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 58. WETHERED, EDWARD. 1890. On the Occurrence of the Genus Gir- 
 
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BIBLIOGRAPHY XI 
 
 523 
 
 60. WHITE, DAVID. 1911. Value of Floral Evidence in Marine Strata as 
 
 indication of Nearness of shores. Bulletin of the Geological Society 
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 113-127. 
 
CHAPTER XII. 
 
 ORIGINAL CHARACTERS AND LITHOGENESIS OF THE EXOGENETIC 
 ROCKS. THE PYROCLASTICS AND THE AUTOCLASTICS. 
 
 The original structures of Exogenetic or clastic rocks are mainly 
 those formed during their deposition. Therefore the structures of 
 each division of these rocks will show individual peculiarities, and 
 hence each division will be considered by itself. 
 
 PYROCLASTIC ROCKS. 
 
 MODERN PYROCLASTICS. Tuffs and volcanic breccias (pyrolu- 
 tytes, pyrarenytes, and pyrorudytes) are typically formed about the 
 volcanic vents which have furnished the material. (Their essential 
 lithic characteristics have been described in Chapter VI.) Ordi- 
 narily the distance from the volcano at which the deposit will form 
 will be dependent on the fineness of grain. Thus pyrorudytes will 
 be formed close to the volcano, while the pyrolutytes will often 
 form at great distances from the vent. These latter are often car- 
 ried very far by the winds, and finally deposited as aeolian or wind- 
 blown volcanic ash (anemopyrolutyte). In such cases the structure 
 of the deposit partakes of that of other anemoclastic rocks. Many 
 tuffs are deposited in water, and so become closely allied to typical 
 hydroclastic rocks and partake of their structure. The finer water- 
 laid volcanic tuffs (Hydropyrolutytes) often show a perfect stratifi- 
 cation, and they sometimes are rich in organic remains. An ex- 
 ample of finely bedded pyrolutytes is found in the fine paper shales 
 of volcanic ashes of Florissant, Colorado, where a wealth of beauti- 
 fully preserved insects, leaves, and silicified trees testifies to the 
 adaptability of these deposits to the preservation of fossils. These 
 deposits are commonly referred to a Tertiary lake caused by the 
 damming of a valley by a lava flow. The possibility that the de- 
 posits are those of a river flood plain or playa lake must not be 
 overlooked. The great abundance of insects, spiders, and leaves, 
 the erect tree trunks, and the scarcity of aquatic animals point this 
 
 524 
 
PYROCLASTIC ROCKS 525 
 
 way. The aquatic forms found comprise a thin-shelled Planorbis, 
 always occurring in a crushed condition, a Physa and a single speci- 
 men of a bivalve, and eight species of fishes. Birds' feathers and 
 bones and the skeletons and feathers of entire birds have also been 
 found. Strongly sun-cracked layers point to repeated desiccation 
 
 ! of the shallow lake, and this condition, first recognized by Lesque- 
 
 ! reux, is not excluded by the character of the fish, the water plants, 
 water insects or molluscs. (Scudder-22; 23.) 
 
 Volcanic debris falling on the surface of the land will show 
 little regularity of deposition. The coarser material will exhibit 
 no bedding lines or only the very rudest ones, while volcanic sand 
 or ashes may not infrequently show a moderate stratification, which 
 will generally be more marked in the finer material. Where the 
 ashes come to rest on a slope these stratification planes will be in- 
 clined. 
 
 Organic Remains of Modern Pyroclastics. Organic remains are 
 not infrequent in pyroclastic rocks. They are best preserved in the 
 finer grained deposits. Of these the remains of man and his works 
 are often the most abundant in the modern tuffs, whole cities and 
 their inhabitants having not infrequently been buried. At Hercu- 
 laneum and Pompeii human bodies were completely encased in the 
 fine mud from Vesuvius, which on hardening formed a perfect 
 mold of the body, so that plaster casts could afterward be made 
 from them. 
 
 OLDER PYROCLASTIC DEPOSITS. From South America and from 
 portions of the Great Plains of western North America, Tertiary 
 iieolian tuffs (Anemopyrolutytes) rich in the bones of mammals, 
 have been described. In the Eocenic deposits of the Wind River 
 Basin in Wyoming, a white tuff bed 13 feet in thickness lies 
 
 1 interbedded with the Wind River sands and clays. (Sinclair and 
 Granger-28 :oj et seq. ) It rests on a heavy brown sandstone con- 
 
 ; taining rolled pebbles of tuff and is succeeded by greenish shales. 
 In the upper 4 or 5 feet of tuff occurs much pumice; snow white 
 grains from the size of bird-shot to small peas are found enclosed 
 in a fine-grained gray matrix. The most abundant macroscopic 
 mineral enclosed in the white pumice is biotite, while small frag- 
 ments of feldspar are occasionally found. Under the microscope the 
 fine felt-like mass of volcanic glass of the pumice encloses in the or- 
 der of relative abundance : ( I ) orthoclase, often zonal, sometimes 
 twinned, either with recognizable crystallographic boundaries, more 
 or less broken, or in small laths; (2) plagioclase; (3) olive green 
 biotite; (4) hornblende; and, (5) black opaque grains, probably 
 iron oxide. 
 
526 PRINCIPLES OF STRATIGRAPHY 
 
 The lower part of the tuff consists of a finer grained mass, in 
 which the round mass of felt-like glass fibers and wisps contains 
 angular fragments of feldspar, quartz, biotite, and hornblende in 
 greater abundance than in the upper part. Balls of hard green 
 shale occur in the tuff and these and channel-filling of contempo- 
 raneous origin point to a fluviatile deposition of the material. 
 
 In the Bridger of the same region occurs a white tuff ranging 
 in thickness from 25 to 75 feet which carries frequent lignitic beds 
 varying in thickness from six inches to a foot. No clay, sand or 
 gravel occurs as in tuffs of fluviatile origin, and it is believed that 
 this bed is a lacustrine deposit. In regions where the tuff bed is 
 absent it is replaced by arkose beds with clay pellets and apparently 
 wind-blown pyroclastics, the whole traversed by tubules suggestive 
 of root canals, and representing the terrestrial part of the accumu- 
 lation. 
 
 In the Oligocenic of this region pyroclastic material is more 
 pronounced. In the erosion troughs formed at the close of the 
 Eocenic volcanic mud flows accumulated, beginning with a fine- 
 grained buff-colored tuffaceous shale, in which was found a skull 
 of Titanotherinm heloceras. This was followed by mud flows carry- 
 ing large angular or rounded blocks of hornblende andeSite, up to 
 3 or 4^feet in diameter and consisting of ash, pumice, lapilli and 
 pebbles and cobbles of pre-Tertiary quartz, granite, and gneiss, 
 forming an agglomerate 46 feet in thickness -near Wagon-bed 
 spring. Its distribution was controlled by the preexisting valleys 
 and so it is absent in many localities. Repeated flows seem to be 
 indicated by what appear like channels of erosion in some of the 
 older flows, filled with andesite cobbles embedded in gray ash. 
 The volcanic eruption seems to have continued throughout the 
 lower Oligocenic, showering the surrounding country with ash and 
 dust. This in some localities accumulated to a thickness of over 
 500 feet. Locally this ash is quite unconsolidated, but, as a rule, it 
 shows calcareous cementation and it may pass upward into a 
 tuffaceous limestone. Angular fragments of more or less devitrified 
 pumice, and sharp splinters of isotropic glass, make up more than 
 fifty per cent, of the soft ash. The rest consists of angular frag- 
 ments of plagioclase, orthoclase resembling microcline, hornblende, 
 biotite and some quartz besides some other minerals. The quartz 
 and microcline are believed to have been intermingled wind-blown 
 material, from the gneiss debris which forms alluvial fans elsewhere 
 in this region. Tuffs of volcanoes near or in the sea will commonly 
 enclose remains of marine organisms. Examples of these have 
 
LITHOGENESIS OF EXOGENETIC ROCKS 527 
 
 been described from the Cambric of North America, and from 
 other deposits. (See further, Chapter XXII.) 
 
 AUTOCLASTIC ROCKS. 
 
 We may define an autoclastic rock as made of the fragmental 
 material resulting from the movement of one rock mass over an- 
 other, both contributing from their substance to the clastic material, 
 though, owing to different degrees of hardness, that furnished by 
 one of the masses may be most prominent, while that contributed 
 by the other may be almost if not wholly destroyed during the 
 movements. 
 
 CLASSIFICATION OF AUTOCLASTIC ROCKS. According to the type 
 of movements in the formation of an autoclastic rock we may 
 classify the products as follows : 
 
 1. Exogenous, or those due to external forces, including: 
 
 a. Those due to compressive strains, i. e., thrust-fault brec- 
 
 cias. 
 
 b. Those due to gravitational strains, comprising: 
 
 (1) Breccias, etc., formed by ordinary gravity or normal 
 faulting subsequent to the formation of the strata, a 
 secondary structure, and 
 
 (2) Breccias and brecciated structures formed by slip- 
 ping or gliding of material during the process of ac- 
 cumulation under the influence of gravity, and re- 
 sulting in the production of intraformational brec- 
 cias, or, when the brecciation is incomplete, contorted 
 stratification. Glacial deposits are best placed here. 
 
 2. Endogenous or endolithic structures, or those due to in- 
 
 ternal forces, including: 
 
 c. Those due to movements resulting from solution and re- 
 
 crystallization, as in ice, salt, etc. 
 
 d. Those due to increase or decrease in volume from hydra- 
 
 tion, carbonation, oxidation, etc., or the reverse, as 
 in change of anhydrite to gypsum, or the removal of 
 certain elements, as in dolomitization of limestones. 
 The distortion of salt layers, of gypsum beds, and 
 limestones producing the contorted structure which, 
 from its resemblance to the coiled intestine, has been 
 called enterolithic structure (German, Gekrose), may 
 be cited as illustrations. 
 
 The more important types may be described in detail. 
 
528 PRINCIPLES OF STRATIGRAPHY 
 
 FAULT BRECCIAS. 
 
 So far as understood, fault breccias due to thrusting and those 
 due to gravitational readjustment are not essentially different in 
 character, except that the former may frequently be parallel to the 
 bedding planes of stratified rocks in which such thrusting has taken 
 place, while the latter are likely to cross these planes at an angle. 
 Both are, however, secondary features formed within the rock 
 mass, after its deposition if not its consolidation. In these dynamic 
 movements, autorudytes, autoarenytes, and autolutytes result, and 
 they are often accompanied by the formation of slipping surfaces or 
 slickensides. The coarser rocks of this type often simulate hydro- 
 elastics, owing to the fact that during the movement of the rock 
 masses past each other the angles of the fragments were worn off 
 and have become rounded by mutual friction. (Van Hise-3o:d79.) 
 In this condition the bed may readily be mistaken for a hydroclastic 
 conglomerate (hydrorudyte). Such beds have been termed pseudo- 
 conglomerates. Typical autorudytes or dynamic breccias consist 
 generally of more or less angular fragments embedded in a matrix 
 of crushed material. In all cases the autorudytes are composed, 
 of the material of the enclosing rock with the fragments derived 
 from the most brittle of the beds from which it was formed. Thus 
 an autorudyte formed from interstratified layers of limestone and 
 quartzite will have its fragments mainly composed of the quartzite. 
 
 Since autorudytes so often simulate normal conglomerates, it 
 becomes important to determine the criteria by which the two may 
 be distinguished. For it is obvious that, if the former is mistaken 
 for the latter, it will lead to an entirely erroneous interpretation of 
 the history of that region. This is particularly the case where the 
 autorudyte may be mistaken for a basal conglomerate. Alternating 
 beds of shales or pure lutytes, and fine lutaceous arenytes or gray- 
 wackes, may by deformation be broken up in such a manner that 
 the arenytes yield pebbles, more or less rounded by mutual fric- 
 tion, while the shale flows and fills the spaces between the frag- 
 ments. (Van Hise-3<D.) 
 
 The pseudo-conglomerate thus produced will have "a slate ma- 
 trix and pebbles of graywacke [argillaceous silicarenyte] which, so 
 far as its own characters are concerned, could not be discriminated 
 by any one from a true conglomerate." (Van Hise~3O.) Auto- 
 clastic limestone pebbles of a rounded character are common in the 
 Cambro-Ordovicic rocks of the Taconic region, and in other dis- 
 turbed Palaeozoics in many portions of the world. They are ex- 
 tremely characteristic of pre-Cambric rocks. 
 
AUTOCLASTIC ROCKS 529 
 
 The following criteria are given by Van Hise as aids in dis- 
 criminating between autorudytes and true conglomerates (hydro- 
 rudytes) : 
 
 1. "An autoclastic rock must derive its material mainly from 
 the adjacent formation . . . from the superior formation as 
 well as from the inferior. ... In true basal conglomerates, on 
 the other hand, while the material is very frequently derived in 
 large measure from the immediately subjacent formations, they 
 also usually contain a small proportion of material from various 
 foreign sources, and . . . not . . . from the overlying for- 
 mations, as may the autoclastic rocks." 
 
 2. "In an autoclastic rock, . . . the pebbles . . . will 
 in many cases be found to be less rounded than in a true basal con- 
 glomerate. If ... followed for some distance a considerable 
 variation will frequently be found fragments being here well 
 rounded and there very imperfectly rounded. The well-rounded 
 fragments are concentrated, as are also the angular fragments. A 
 basal conglomerate, on the other hand, has a considerable uniform- 
 ity in the degree of the rounding of its pebbles in passing along 
 the same horizon, but at the same place the large fragments may be 
 angular and the small ones well rounded . . ." 
 
 3. "In many cases the interstices of an autoclastic rock are 
 filled with material of a vein-like character, whereas in a basal 
 conglomerate the filling material is largely fine detritus. But some- 
 times . . . the filling material of an autoclastic rock may be 
 water-worn grains of sand, which have been separated by dynamic 
 action, and are therefore indistinguishable from the ordinary matrix 
 of a true conglomerate." 
 
 4. "In most instances a bed of autoclastic rock, if followed, 
 may be traced into on ordinary brecciated or partly brecciated 
 form. A basal conglomerate, on the other hand, if followed along 
 the strike and dip, may change its character, but it will be a. gradual 
 change into the ordinary mechanical sediments, whereas an auto- 
 clastic rock is likely to have very sudden variations in character." 
 (Van Hise-3o:<5So-<S/.) 
 
 INTRAFORMATIONAL BRECCIAS. 
 
 These are contemporaneous phenomena, formed as one of the 
 sequential divisions of a single rock series. They are almost wholly 
 confined to calcareous rocks, and seem to be most typical of calci- 
 lutytes or fine calcarenytes. Such rocks, composed largely of the 
 
530 PRINCIPLES OF STRATIGRAPHY 
 
 finest lime-mud, accumulate in shallow water or in part even above 
 the normal level of the sea. In form they probably constitute a 
 sort of mud flat delta, the mud being 1 brought and spread out in 
 part at least by streams, which must have derived it from the 
 erosion of earlier limestones. Mud cracks or desiccation fissures 
 testify to the shallow water in which these sediments were accumu- 
 lating. On exposure partial hardening permits the formation of a 
 superficial crust, which may subsequently break or become de- 
 formed by the sliding of the entire mass seaward. Such sliding has 
 been observed in modern deposits as discussed more fully in Chap- 
 ter XX. 
 
 Fracturing and Piling Up of Material. If the surface layers 
 alone slide, a fracturing will result which produces a mass of 
 angular or subrounded flat mud-cakes, which will be piled together, 
 as the result of this sliding, in a confused mass, the fragments most 
 frequently standing on end, but also inclined in all directions. They 
 will be surrounded by the fine still fluid mud which wells up around 
 them and in which these fragments become embedded. Thus is 
 formed an "edgewise conglomerate," as these accumulations have 
 come to be known, a contemporaneous feature abounding in the 
 finer calcilutytes and calcarenytes of all horizons. Both the cakes 
 and the enclosing matrix may contain organic remains ; the former 
 would carry such fine organic fragments as sponge spicules, plant 
 fibers, etc., which may be washed in with the mud or may exist 
 in the water in which it is deposited, while the matrix becomes 
 normally fossil-bearing since it is a part of the submerged deposits. 
 Professor Seeley (24) (Brown-i) has considered the cakes, as a 
 whole, due to organic growth, and described them under several 
 species of the new genus Wingia. The intraformational conglom- 
 erates described by Walcott (31), though mostly of a much coarser 
 character, probably in part represent such gliding conglomerates. 
 Examples where such cakes of lime-mud carrying fossils were 
 formed through fracturing on drying have been described by Hyde 
 (16) from the Coal Measure limestones of Ohio. In these cases, 
 however, no sliding seems to have occurred, the fragments being 
 embedded where formed. These "desiccation conglomerates" will 
 be referred to again in Chapter XX. 
 
 Distortion of Layers in Gliding. If a large mass of rock slides 
 there will be less of fracturing and more of distortion of the layers 
 along the gliding zone and this will be pronounced in proportion to 
 the weight and compactness of the beds overlying the ^gliding plane. 
 Good examples of such distortion are found in the Trenton lime- 
 stone of New York (Hahn-i2) as exposed in the gorge at Trenton 
 
AUTOCLASTIC ROCKS 531 
 
 Falls, where several such layers are visible. It is also well shown 
 in the fine calcilutytes of the Solnhofen beds (Jurassic) of Ba- 
 varia, a formation shown by many characters to be of shallow water 
 origin. (See further, Chapter XX.) 
 
 GLACIAL DEPOSITS. 
 
 If we consider ice as water in the solid form, glacial deposits 
 must be classed under the hydroclastic division of rocks. It is 
 manifest, however, that the essential features of glacial deposits are 
 those which most strongly differentiate them from ordinary hydro- 
 elastics, be they fluvial, lacustrine, or marine. In some characters 
 they may resemble atmbclastic and in others autoclastic deposits, but 
 their most marked characteristics are not shared with any other 
 type. Nevertheless, the method of formation of the most typical 
 glacial elastics is closely analogous to that of autoclastic fault brec- 
 cias. Both are produced by the movement of one rock mass over 
 another, for ice in this relation has the essential characters of a solid 
 rock, and both furnish material for the resulting rudyte or finer 
 rock, though that furnished by the ice is readily destroyed. It is 
 true that material not produced by mutual attrition of the two rock 
 masses, the basal rock and the ice rock, may be, and commonly is, 
 incorporated in the subglacial material, but this merely points the 
 essential peculiarities of this autoclastic rock. It is also true that 
 the movement of glaciers cannot be directly compared with that of 
 rock masses involved in faulting, in so far as it is a gliding partly 
 due to internal forces as well as to gravity. Still the essential fact 
 remains, that clastic material is produced by the movement of one 
 rock mass over another and that both rock masses contribute from 
 their substance to the production of this material. In this respect, 
 then, glacial debris may be compared, on the one hand, with that 
 formed by gravity faulting, and, on the other, with that formed 
 by gliding masses resulting in the production of intraformational 
 breccias. Since the ice also moves by constant internal readjust- 
 ments from recrystallization, the products of such motion may to a 
 certain extent be compared with enterolithic deformations. 
 
 Characters of Modern and Pleistocenic Glacial Deposits. The 
 material resulting from the plucking- and abrasive action of the ice 
 varies in grain from the finest rock flour to boulders of almost 
 unlimited size. Except where disintegration of the rock surface 
 previous to glaciation has occurred, the fine material will all be 
 rock flour with clay notably absent. The arenaceous material also 
 shows in its angularity and sharpness of grain that it has been 
 
532 PRINCIPLES OF STRATIGRAPHY 
 
 produced by mechanical crushing of fresh rocks. Such sand, from 
 the Mer-de-Glace, Switzerland, shows sharp, fresh, angular frag- 
 ments with the barest traces of weathering, and very little wear. 
 The composition is varied, and the assortment very poor. The 
 quartz grains of glacial sands show the characteristic conchoidal 
 fracture, sharp edges and keen points. Cleavable minerals show 
 fresh, clean surfaces and little, if any, trace of internal decomposi- 
 tion. In composition the variation is very great, dependent, of 
 course, upon the original character of the rock ground up by the 
 ice. The assortment according to size is also very marked. 
 
 Till or boulder clay is an intimate mixture of rock flour and 
 glacial sand, together with a varying per cent, of clay derived 
 from rocks decomposed prior to glaciation. Crosby holds that very 
 little of the original residuary soil is incorporated in the till cover- 
 ing New England, for the color of this till is bluish and shows no 
 traces of oxidized material below a certain level, where recent 
 oxidation has been active. "Experiments show that an admixture 
 of a very small proportion of highly oxidized residuary clay, like 
 that of the south, with a typical till, is readily detected in the 
 change of color." (Crosby 7:^5^.) In the most typical till, i. e., 
 that due wholly to glacial erosion of a country from which all 
 decomposed material is absent, the amount of kaolinite is ex- 
 tremely slight, all the finer material being rock flour due to me- 
 chanical crushing. An analysis of till from drumlins of the Boston 
 Basin, from Somerville to Nantasket, gave Crosby the following 
 results expressed in percentages of the total material exclusive of 
 the boulders and other stones over 2 inches in diameter 
 (Crosby-6) : 
 
 i. Coarse 17.08! 
 
 Gravel \ 2. Medium 2 . 99 \ 24 . 90 
 
 3- Fine 4.83] 
 
 4. Coarse 3.33 
 
 Sand -j 5. Medium 9.25 
 
 6. Fine 6 . 93 
 
 Rock Flour. 
 
 7. Coarse 12.80 
 
 8. Medium 6. 52 [ 43-86 
 
 9. Fine 24. 14 
 
 10. Superfine 0.30 
 
 1 1 . First decanting ... o . 86 
 
 Clay \ 12. Second 9 . 13 ^ 11.67 
 
 13. Third 1.78 
 
 99-94 
 
GLACIAL DEPOSITS 533 
 
 Thus, after exclusion of the larger stones the till consists of 
 about 25% of gravel, 20% of sand, 40 to 45% of extremely fine 
 sand or rock flour and only about 12% of clay. (See also 
 Ries-iQ.) 
 
 The intimate admixture of coarse and fine material in the un- 
 modified glacial drift or till renders its pore space of the slightest 
 and so makes it an admirable impervious layer, through which 
 ground water cannot penetrate. This is well shown in the unoxi- 
 dized character of much of the till, its color when freshly ex- 
 cavated being of a bluish slate. Only the surface layers, or some 
 included layers of modified sand or gravel, may show such oxida- 
 tion. Modified till differs mainly in the somewhat worn character 
 of the granules, the progress of weathering in the decomposable 
 minerals and the better assortment of the material* according to 
 size. With this comes increased pore space and consequently pene- 
 tration of ground water accompanied by oxidation, and a change to 
 ochery or brown colors. All gradations may be observed, from 
 the slightly modified drift barely moved by the waters from the 
 melting ice sheet, to the much worn and fairly well-assorted ma- 
 terial of the glacial streams, which quickly assumes all the charac- 
 teristics of water-laid deposits and must be classed with the hydro- 
 elastics. 
 
 The pebbles and boulders of the glacial drift also show dis- 
 tinctive peculiarities. One essential is their imperfectly worn char- 
 acter. Most commonly they are in the form of flattened masses 
 highly polished and striated on the flat faces, but angular or but 
 slightly worn on the other sides. Rounded boulders are the ex- 
 ception. In size they vary enormously, and this is often true for 
 the lithologic character as well. Crosby has found that much of 
 the coarse material of some New England deposits was of compara- 
 tively local origin, these deposits, moreover, having been subject 
 to a certain amount of transportation by water. Of some tons of 
 material coarse enough for ready identification about 50 per cent, 
 came from a belt of rock extending for 13 miles north of the 
 deposit, and 40 per cent, from the next 8 to 10 miles, while only 
 10 per cent, came from distances greater than 23 miles (7:^57-^). 
 
 Transportation of the coarser material by glacial streams results 
 in more or less perfect rounding of the boulders, and the effacement 
 of the striations on the surface. Moreover, the attendant assorting 
 of the material according to size will result in the greater concen- 
 tration of such bouldery deposits, whereas in the true till the 
 boulders are scattered and embedded in the finer material. 
 
 Boulders of ice as well as ice sand derived from the gliding ice 
 
534 PRINCIPLES OF STRATIGRAPHY 
 
 mass are apt to be incorporated in the forming deposit, but such boul- 
 ders are by virtue of their composition subject to speedy destruc- 
 tion. As a result a depression will be formed in the glacial deposit, 
 due to the caving-in of the overlying material into the hollow left 
 by the vanishing ice boulder. Such kettle holes are common in 
 both modified and unmodified glacial deposits and serve to identify 
 them as such. 
 
 Ancient Glacial Deposits. 
 
 Boulder clays and modified glacial deposits are found at a num- 
 ber of geological horizons from the pre-Cambric onward. The 
 rock formed by the consolidation of such deposits is known as 
 tillite and its essential character is found in the heterogeneous mix- 
 ture of the material, the absence of stratification and the striation 
 of the larger blocks, and the fragments of dense texture. Several 
 of the more prominent cases may be discussed in some detail. 
 
 The Pre-Cambric Tillite of Canada. In the Lower Huronian 
 of the Cobalt region in Canada an extensive boulder bed and tillite 
 have been found, indicating glacial origin. (Coleman-2, 3, 4, 5.) 
 The tillite is a consolidated boulder clay or till and the boulders 
 are angular or subangular, and not infrequently striated, but no 
 striation of the underlying rock has yet been observed. The boul- 
 ders are often 2 or 3 feet or more in diameter and distant a couple 
 of miles from the exposures of the rocks. Some of the boulders of 
 this conglomerate are tons in weight, and the areal extent of the 
 mass has been traced over 1,000 miles east and west and 750 miles 
 north and south, while the thickness at Cobalt is about five hundred 
 feet. The boulder clay of this horizon and that of the Permo-Car- 
 bonic and other regions is almost indistinguishable in hand speci- 
 mens or in thin sections under the microscope. Some stratified 
 slaty beds have been found at Cobalt in the great mass of unstrati- 
 fied conglomerate suggesting a possible interglacial period. The 
 glacial origin of these has been questioned by Knight (17) and 
 others. 
 
 Cambric Glacial Deposits. These have been recorded from 
 northern Norway, where in the Varanger fjord an unstratified tillite 
 with striated boulders rests upon a striated rock surface of the pre- 
 Cambric Gaisa series and is succeeded by beds of Cambric age. 
 ( Strahan-29. ) From the Yantzi Canyon in China, lat. 31, Bailey 
 Willis (33) has obtained striated boulders occurring in tillite per- 
 haps 150 feet thick and overlain by Middle Cambric marine deposits. 
 Still more striking and better known are the Cambric tillites of South 
 
ANCIENT GLACIAL DEPOSITS 535 
 
 Australia (lat. 30 to 43 S.). (Howchin-izj., 15; David-8, 9.) 
 They extend for 460 miles from north to south and 250 miles from 
 east to west, and have a thickness of 1,500 feet. Numerous boul- 
 ders and pebbles showing glacial striae have been obtained (see the 
 figures given by Howchin-i5), the character of these boulders in- 
 dicating a southward movement. Intercalated with the tillite are 
 beds of limestone and radiolarian beds. No striations have been 
 found on the underlying rocks. (David-8, 9.) 
 
 In South Africa (lat. 29 S.) tillite of late pre-Cambric or 
 early Cambric age forms a part of the Griquatown series of Cape 
 Colony, occurring over almost 1,000 square miles. It contains 
 typical scratched boulders. 
 
 The Pennic Glacial Deposits. These have been observed in 
 India, Australia, South Africa (Davis-io; Schwartz-2i), and South 
 America (White-32). The South African deposit constitutes the 
 Dwyka conglomerate, the lowest member of the Karoo formation 
 (Davis-ioi^oo). It'varies in thickness up to 1,000 feet or more and 
 extends from the Indian Ocean between 29 and 33^2 south lati- 
 tude northward approximately to Belfast, westward to the Vaal 
 River and thence in latitude 29 to within less than a hundred 
 miles of the Atlantic, and southward to within about 150 miles of 
 Capetown. Its former extent was apparently much greater. "It 
 rests for the most part unconformably on a grooved and striated 
 surface of older rocks, but along its southern border it follows con- 
 formably a series of sandstones and shales. It consists chiefly of 
 an unstratified and consolidated clastic ground mass with sub- 
 angular or rounded scraps, stones, and boulders of many kinds, 
 the finer textured stones and boulders being usually well scratched. 
 It is conformably overlaid by a coal-bearing series of shales and 
 sandstones." (Davis-io^oo.) 
 
 "The glacial origin of the Dwyka formation is as unquestionable 
 as is that of the drift sheets of northeastern America or of north- 
 western Europe; but the Permian ice-sheet, by which the Dwyka 
 was formed, moved in general southward, from the region of the 
 equator toward the region of the pole." (Davis-ioi^o/.) The 
 indications are that the Dwyka ice "was a broad and continuous 
 ice sheet which spread across about 600 miles of country, east and 
 west, and which advanced at least 500 miles poleward from its 
 apparent source. It moved across a region which bore subdued 
 mountains here and there, but which was reduced to moderate relief 
 by previous erosion over large areas." (Davis-ior^/j?.) 
 
 Along its southern margin in latitude 33*^2 south it invaded a 
 water-covered area. A number of fluctuations are recorded, and 
 
536 PRINCIPLES OF STRATIGRAPHY 
 
 upon the final recession a climate favoring a luxuriant growth of 
 plant life succeeded, as testified to by the coals of the overlying 
 Ecca formation. "Demonstrably marine deposits are nowhere asso- 
 ciated with the Dwyka," not even where it "repeatedly reaches the 
 shore of the Indian Ocean" ; but marine Devonic fossils occur in 
 the Bokkeveld s*eries 2,500 feet or more below the basal member of 
 the Dwyka in the Karoo district, while between them lies the con- 
 formable Witteberg series, forming the transition from marine to 
 glacial continental. The structural evidence shows that mountains 
 were absent at this time, though high lands existed which supplied 
 the material of the Karoo formation. 
 
 Davis has presented the facts which show that neither great 
 elevation nor changes in land area or land form were able to produce 
 a glacial climate in subtropical South Africa, nor could any conceiv- 
 able arrangement of ocean currents produce it. General refrigeration 
 alone, either by a decrease of solar radiation or by a change in the 
 constitution of our atmosphere, without shifting of wind belts, 
 would have to be so extreme as to reduce the summer temperature 
 of South Africa to such an extent that the summer rains would be- 
 come summer snows, while the winters would still be dry, and ex- 
 tremely cold. Such a refrigeration would freeze up all the tem- 
 perate lands of the globe and would hardly be in harmony with 
 the rich marine and land life of the Permic deposits found in these 
 regions, nor with the evidence of warm climate furnished by arid 
 deposits of this period in other regions. A shifting of the pole, as 
 elsewhere suggested, to such an extent that it would lie somewhere 
 in the Indian Ocean would account satisfactorily not only for the 
 Dwyka conglomerate, but also for the Talchir glacial formation 
 of northwestern India, the movement of the glaciers forming 
 this being, like those which formed the Dwyka, away from the 
 equator, but in the opposite direction. It would also account for 
 the Muree glacial formation of southeastern Australia. 
 
 Koken (i7a) has discussed this question at length, with special 
 reference to India, and he gives a map of the world showing the 
 possible position of the poles at that time under the theory of 
 polar displacement. He places the North Pole near Tultenango, 
 Mexico (lat. 20 N., long. 100 W., of to-day), and the South Pole 
 in the middle of the Indian Ocean (lat. 20 S., long. 80 E., of 
 to-day). 
 
 ENDOLITHIC BRECCIATION. 
 
 Endolithic brecciation, or the shattering of the strata by forces 
 at work within the rock mass itself, is best shown in formations 
 
ENDOLITHIC BRECCIATION 537 
 
 containing anhydrite, which by hydration is changed to gypsum. 
 This process involves an increase in volume, estimated by some 
 (Credner, Fritsch, Bauer, Geikie) as low as 33 per cent., and by 
 others (Naumann, Zirkel, J. D. Dana) as high as 60 per cent. 
 J. Roth, indeed, has calculated that the increase in volume resulting 
 when anhydrite takes up two molecules of water of crystallization 
 to form gypsum is as high as 62.3 per cent. 
 
 It is probably true that calcium sulphate is largely deposited in 
 the anhydrous state, especially when it originates under arid condi- 
 tions (see ante, Chapter IX). Certain it is that anhydrite abounds 
 in many of the older strata along with gypsum, and it is not im- 
 probable that in such cases the gypsum is the result of hydration of 
 the anhydrite. In view of the great force exerted within the rock 
 mass by the expansion due to this hydration, we would expect to 
 find the results in a shattering and deformation of the enclosing 
 strata. This expectation is commonly realized, for such endolithic 
 brecciation is a frequent if not constant accompaniment of gypsum- 
 bearing strata, especially in the Palaeozoic. Cases have been de- 
 scribed from the Salina and Monroe beds of New York, Ohio, 
 Michigan, and Canada. (Grabau and Sherzer-i i :2p ; Kraus- 
 18:1(57-171.) Brecciation of this type is not uncommon in salt 
 deposits, where through recrystallization a pronounced pressure 
 results, which may even affect the enclosing strata, deforming and 
 disrupting them. This subject will be more fully discussed in the 
 chapter on diagenism. 
 
 BIBLIOGRAPHY XII. 
 
 1. BROWN, THOMAS C. 1913. Notes on the Origin of Certain Palaeozoic 
 
 Sediments, Illustrated by the Cambrian and Ordovician Rocks of Center 
 County, Pennsylvania. Journal of Geology, Vol XXI, pp. 232-250. 
 
 2. COLEMAN, A. P. 1907. A Lower Huronian Ice Age. American Journal 
 
 of Science, 4th series, Vol. XXIII, pp. 187-192. 
 
 3. COLEMAN, A. P. 1908. Ancient Ice Ages and Their Bearing on Astro- 
 
 nomical Theories. Journal of the Astronomical Society of Canada, Vol. 
 II, No. 3, pp. 132-135- 
 
 4. COLEMAN, A. P. 1908. The Lower Huronian Ice Age. Journal of 
 
 Geology, Vol. XVI, pp. 149-158. 
 
 5. COLEMAN, A. P. 1908. Glacial Periods and Their Bearing on Geological 
 
 Theories. Bulletin of the Geological Society of America, Vol. XIX, pp. 
 347-366. 
 
 6. CROSBY, WILLIAM OTIS. 1891. Composition of Till or Boulder 
 
 Clay. Boston Society of Natural History Proceedings, Vol. XXV, pp. 
 115-140. 
 
 7. CROSBY, W. O. 1896. Englacial Drift. American Geologist, Vol. XVII, 
 
 pp. 203-234. 
 
538 PRINCIPLES OF STRATIGRAPHY 
 
 8. DAVID, T. W. EDGEWORTH. 1903. Australasian Association for the 
 
 Advancement of Science. Report of the Ninth Meeting, pp. 199-200. 
 
 9. DAVID, T. W. E. 1906. Glaciation in Lower Cambrian, Possibly in 
 
 Pre-Cambrian Time. International Geological Congress. Compte Rendu, 
 
 Mexico, pp. 271-274; 275-298. 
 10. DAVIS, WILLIAM MORRIS. 1906. Observations in South Africa. 
 
 Bulletin of the Geological Society of America, Vol. XVII, pp. 377-450. 
 n. GRABAU, AMADEUS W., and SHERZER,WILLIAM H. 1910.' Monroe 
 
 Formation of Michigan. Michigan Geological and Biological Survey, 
 
 Publication 2. 
 12. HAHN, F. FELIX 1912. Untermeerische Gleitungen bei Trenton Falls 
 
 (Nord Amerika), und ihr Verhaltniss zu Ahnlichen Storungsbildern. 
 
 Neues Jahrbuch fur Mineralogie, Geologic und Palaeontologie, Beilage 
 
 Band XXXVI, pp. 1-41, pis. I-III. 
 13". HATCHER, J. B. 1900. Sedimentary Rocks of South Patagonia. 
 
 American Journal of Science, 4th Series, Vol. IX, pp. 85-108. 
 
 14. HOWCHIN, WALTER. 1903. Report of South Australian Glacial 
 
 Investigation Committee, Australasian Association for the Advance- 
 ment of Science, Report of the Ninth Meeting; Hobart, Tasmania, 
 1902, pp. 194-199- 
 
 I4a. HOWCHIN, WALTER. 1906. The Geology of the Mount Lofty 
 Ranges, Part II, Transactions and Proceedings and Report of the 
 Royal Society of South Australia, Vol. XXX, pp. 227-262 (especially 
 pp. 228-234). 
 
 15. HOWCHIN, W. 1908. Glacial Beds of Cambrian Age in South Australia. 
 
 Quarterly Journal of the Geological Society of London, Vol. LXIV, pp. 
 234-263, pis. XIX-XXVI. 
 
 / 16. HYDE, JESSE E. 1908. Desiccation Cqnglomerate in the Coal Measure 
 Limestones of Ohio. American Journal of Science, 4th series. Vol. 
 XXV, pp. 400-408. 
 
 17. KNIGHT, CYRIL W. 1909. On the Lower Huronian Ice Age. Canadian 
 
 Mining Journal, Vol. XXX, pp. 727-728. 
 
 I7a. KOKEN, E. 1907. Indisches Perm und die Permische Eiszeit. Neues 
 Jahrbuch fur Mineralogie, etc. Festband, pp. 446-546. Map. 
 
 18. KRAUS, EDWARD H. 1905. On the Origin of the Caves of Put-in- 
 
 Bay Island, Lake Erie. American Geologist, Vol. XXXV, pp. 167-171. 
 
 19. RIES, HEINRICH. 1906^ Clays, Their Occurrence, Properties and 
 
 Uses. John Wylie and Son. 
 
 20. ROGERS, A. W. 1905. An Introduction to the Geology of Cape 
 
 Colony. London. 
 
 21. SCHWARTZ, ERNEST H. L. 1906. The Three Palaeozoic Ice Ages 
 
 of South Africa. Journal of Geology, Vol. XIV, No. 8, pp. 683-691. 
 
 22. SCUDDER, SAMUEL H. 1882. The Tertiary Lake Basin of Florissant, 
 
 Colorado, between South and Hayden Parks. United States Geo- 
 logical and Geographical Survey of the Territories, Vol. VI, pp. 279-300. 
 
 23. SCUDDER, S. H. 1883. Ibid., I2th Annual Report, pp. 271-293. 
 
 24. SEELEY, A. 1906. Geology of Vermont. Report of the State Geologist 
 
 for 1906, pp. 174-78. 
 
 25. SHERZER, W. H. 1910. Criteria for the Recognition of Sand Grains. 
 
 Bulletin of the Geological Society of America, Vol. XXI, pp. 625-662. 
 
 26. SINCLAIR, WILLIAM J. 1906. Volcanic Ash in the Bridger Beds of 
 
 Wyoming. Bulletin of the American Museum of Natural History, 
 Vol. XXII, pp. 273-280, 
 
BIBLIOGRAPHY XII 539 
 
 27. SINCLAIR, W. J. 1909. The Washakie, a Volcanic Ash Formation 
 
 Ibid., Vol. XXVI, pp. 25-27. 
 
 28. SINCLAIR, W. J., and GRANGER, WALTER. 1911. Eocene and 
 
 Oligocene of the Wind River and Big Horn Basins. American Museum 
 of Natural History Bulletin, Vol. XXX, pp, 83-117. 
 
 29. STRAHAN, AUBREY. 1897. The Glacial Phenomena of Palaeozoic 
 
 Age in the Varanger Fjord. Quarterly Journal of the Geological Society 
 of London, Vol. LIII, pp. 137-146, pis. 8-10. 
 
 30. VAN HISE, CHARLES R. 1896. Principles of North American Pre- 
 
 Cambrian Geology. i6th Annual Report of the* United States Geological 
 Survey, part I, pp. 581-872. 
 
 31. WALCOTT, CHARLES D. 1894. Intraformational Conglomerates. 
 
 Bulletin of the Geological Society of America, Vol. V, pp. 191-198. 
 
 32. WHITE, DAVID. 1907. Permo-Carboniferous Climatic Changes in 
 
 South America. Journal of Geology, Vol. XV, pp. 615-633. 
 
 33. WILLIS, BAILEY. 1907. Researches in China, Vol. I, part i. Carnegie 
 
 Institute of Washington Publications. 
 
CHAPTER XIII. 
 
 ORIGINAL STRUCTURE AND LITHOGENESIS OF THE ATMOCLASTIC 
 AND ANEMOCLASTIC ROCKS 
 
 A. ATMOCLASTIC ROCKS. 
 
 Typical atmoclastic rocks owe their origin entirely to disintegra- 
 tion or disruption of older rocks, while the accumulation and ar- 
 rangement of this material are brought about by atmospheric agen- 
 cies under the influence of gravity. The most typical atmoclastic 
 rocks are those produced in situ by subaerial decay and not subse- 
 quently disturbed. Here belong the laterite and kaolinite, the for- 
 mation of which was described in Chapter II, pp. 37, 39. Taken by 
 itself, such rock may show a complete absence of stratification and a 
 gradation in texture from coarse blocks next to the unaltered rock to 
 fine soil and humus at the surface where disintegration and de- 
 composition affect rocks of uniform grain such as granites or other 
 holocrystallines. A downward gradation into the older rock may be 
 pronounced which, if the upper layers are reworked by water or 
 other agencies, forms an apparent transition bed between widely dis- 
 tinct formations. The products of atmospheric disintegration may 
 become rearranged by flowing, sliding or gliding under the influ- 
 ence of gravity. The talus at the foot of a cliff is an example of 
 such rearrangement. The surface gradient of such an accumulation 
 is generally high, varying from 60 degrees or over in the coarsest 
 series to 23 degrees or even less in the fine-grained series. 
 
 Stagnant atmoclastic material is the exception ; in general move- 
 ment to lower levels occurs. When more or less saturated with 
 water, the angle of slope is correspondingly lowered, and the talus 
 approaches more and more the character of an alluvial fan. The 
 atmoclastic sediments then grade into the hydroclastic or aqueous 
 type. If, on the other hand, the wind is a factor in rearrangement 
 and deposition of the material, this becomes an anemoclastic rock 
 and has to be treated as such. 
 
 The waste of the land is on the march to the sea. Everywhere 
 
 540 
 
ATMOCLASTIC ROCKS 541 
 
 the loose rock debris is streaming toward the ultimate repository, 
 the sea, or to the rock-rimmed desert basins of the earth, from 
 which in many cases there is no escape. This great waste stream, 
 as it has been aptly termed, covers much of the surface of the land, 
 and may consist wholly of debris, or of debris and water in varying 
 proportions. As the amount of water increases the fluidity of the 
 mass rises, and the rate of its motion is increased, while the angle 
 at which graded conditions prevail is decreased. Thus where the 
 material is pure waste the angle will commonly be more than 20 
 degrees, and steeper in proportion as the material is coarser. Fur- 
 thermore, the material of the talus heap is constantly undergoing 
 disintegration, and, as it becomes finer, the potential angle of slope 
 is lowered. The actual lowering will be accomplished by a process 
 of "creep," which is often greatly aided by frost action and by tem- 
 porary saturation with water, which may become instrumental in 
 suddenly lowering the angle through landslides. 
 
 The totality of the deposits formed by subaerial agencies on 
 the plains in front of the mountains is classed as piedmont waste 
 deposits. They may be formed wholly by "dry creep" from the 
 mountains, or, as is most generally the case, by combined creep 
 and the wash of mountain streams. Alluvial fans or dry deltas 
 thus form the connecting link between the atmoclastic and the 
 hydroclastic types of deposits, for, though strictly belonging to the 
 fluviatile division of the latter, they partake of many of the charac- 
 teristics of the former, and are indeed partly produced by subaerial 
 creep. (Walther-52; Penck-37 :.?5 ; Barrell-2.) 
 
 CHARACTERISTICS AND OCCURRENCE OF MODERN ATMOCLASTIC 
 
 FORMATIONS. 
 
 Extensive recent formations of atmoclastic origin are found only 
 in the comparatively arid regions of the world, and as these are the 
 last which have come under the detailed observation of the geolo- 
 gist, though they cover about a fifth of the land surface of the earth, 
 their significance with reference to the former history of the earth 
 has been largely overlooked. It is only within recent years that the 
 desert regions of the world have been studied in detail and their 
 phenomena applied toward the interpretation of the genesis of older 
 formations of the earth's crust. So long as the destructive powers 
 of the atmosphere and streams were regarded as their chief at- 
 tributes, while the sea was held to be the chief receptacle of the 
 product of this destructive activity, it was natural that the marine 
 
542 PRINCIPLES OF STRATIGRAPHY 
 
 origin of all formations should be considered axiomatic, except 
 where fossils indicated fresh water, in which case fresh-water lakes 
 or inland seas of any desired magnitude were postulated as the 
 medium in which these formations were deposited. Now, how- 
 ever, that we have the extensive observations on the subaerial origin 
 of formations of great thicknesses, embodied in the epoch-making 
 works of Walther and others, there is no longer any excuse for ac- 
 cepting the time-worn marine or fresh- water lake origin of all the 
 sedimentary formations. It becomes more and more apparent that, 
 where formerly marine conditions were regarded as the only pos- 
 sible ones for the deposition of certain formations, desert con- 
 ditions are often the more probable explanation, while formations 
 generally referred to a lacustrine origin prove in many cases to be 
 subaerial deltas and flood-plain deposits of streams or the accumu- 
 lation of wind-transported material upon a relatively dry land sur- 
 face. It is no longer one of the axioms of the stratigrapher that 
 all stratified deposits were laid down under water ; in fact, we must 
 be prepared to question the subaqueous origin of all formations that 
 do not show by the occurrence of either marine or fresh-water fos- 
 sils throughout that they were formed under water. The possibility 
 of the existence of unfossiliferous subaqueous formations is not ex- 
 cluded, and the subsequent destruction of the organic contents of 
 the formation must be considered. At the same time the possibility 
 of a subaerial origin of all unfossiliferous clastic formations, or of 
 those containing marine or fresh-water fossils only at great inter- 
 vals, must be borne in mind, while the occurrence of remains of 
 terrestrial organisms should be considered as prima facie evidence 
 of subaerial origin of the formations containing them until their 
 subaqueous origin is positively established. 
 
 TEXTURE OF ATMOCLASTIC ROCKS. Among the characters of 
 atmoclastic rocks should first be mentioned their coarseness of 
 grain, especially near the mountains from which the material has 
 been obtained. In the talus region the material will not only be 
 coarse, but the blocks will for the most part be angular. Often the 
 structure is suggestive of morainal accumulations. (Walther-52: 
 1 03.) Large and small, round and angular blocks abound in the 
 sandy ground mass with a total absence of sorting, the result of the 
 indiscriminate piling together of the material by the tremendous 
 flood rains of the desert. The evidence of violent impact is further 
 shown by the abundance of concussion marks and the total absence 
 of the woody vegetation which is ground to fragments and washed 
 away by the floods. Portions of the delta built by less violent floods 
 show interbedded, well-stratified, sandy layers, and these become 
 
ATMOCLASTIC ROCKS 543 
 
 more characteristic at a distance from the mountains, where they 
 also are finer grained and frequently clayey. On the surface of 
 the dry delta the coarse blocks gradually give way to finer, rounded, 
 flat or irregularly worn pebbles, with streams of coarser material 
 between the finer gravel, and with at intervals flat surfaces of luta- 
 ceous material (playas or takyrs) beautifully marked by polygonal 
 sun cracks. 
 
 MOVEMENT OF ATMOCLASTIC MATERIAL. The movement of at- 
 moclastic material is twofold. There is, first, the quiet, more or 
 less continuous creep and flowage of the material under the influ- 
 ence of gravity, and conditioned by the change from coarse to finer 
 material under the disintegrating atmospheric influences. Sec- 
 ondly, there is the sudden movement, exemplified by landslides or 
 rock avalanches. These are very generally conditioned by a satu- 
 ration of the rock debris on a mountainside by water, which thus 
 renders the mass more fluid and lowers the potential angle of sta- 
 bility. A third type of movement may be considered as combining 
 the characteristics of both of the preceding types, and thus repre- 
 senting a compound of gliding and creeping movements. Sliding of 
 rock and soil as the result of earthquakes may also be considered 
 here. 
 
 Slow Movements of Rock and Soil. 
 
 Rock and Soil Creep. The creep of soil is always a slow process. 
 It scarcely affects the surface, which is covered by a blanket of 
 vegetation, beneath which the maximum movement takes place. 
 Gotzinger (18) holds that creep is largely due to the work of satu- 
 rating waters which increase the volume of the mantle rock and set 
 it in motion by forcing the particles upward and outward, this mo- 
 tion being translated into a maximum one down the slope of the 
 surface on which the soil rests. Frost is, of course, an important 
 agent in causing the downhill movement of the soil cover. If such 
 creep takes place over inclined or vertical beds of rock, the upper 
 ends of these beds will suffer overturning or bending in the direc- 
 tion of the creep. 
 
 Solefluction or Rock Flow. To the more rapid movement 
 of the rock debris saturated with large quantities of water, the 
 name solefiuction has been applied (Anderson-i). This was 
 first described from Bear Island in the North Atlantic (lat. 74^ 
 N.), where on account of the hard winters much rock debris is 
 produced by mechanical weathering. The melting of extensive snow 
 masses in spring produces a large quantity of water, which trans- 
 
544 PRINCIPLES OF STRATIGRAPHY 
 
 forms the surface material into a pasty mass, and this under the 
 influence of gravity will move slowly down even gentle slopes, the 
 movement being a flowage at a rate much exceeding that of the 
 slow, subaerial creep. Along the valleys mud streams or mud gla- 
 ciers are formed, the movement of which may be prolonged during 
 a considerable period of time. Such mud streams consist of ma- 
 terial of all sizes from the finest grains to huge, angular blocks. 
 The rapidity of movement of the mud streams of Bear Island is 
 shown by the fact that vegetation rarely gets a foothold on these 
 masses of debris. The width of the mud streams of Bear Island 
 ranges up to 35 meters and the depth to about 2 meters. 
 
 The "stone rivers" of the Falkland Islands form other examples 
 of such atmoclastic accumulations. (Darwin-n.) Valleys here 
 are filled by gray masses of rock debris, with a width of several 
 hundred meters to several kilometers, and having from a distance 
 a glacier-like aspect. Beginning in the uplands, they descend to the 
 low country, several streams uniting, until finally the entire mass 
 debouches into the sea. The streams include vast accumulations of 
 quartzite blocks of irregular form, though parallelepipedal forms 
 predominate. In length they vary from l /z to 7 meters, the width 
 being half as great, while their thickness depends on that of the 
 original beds of the parent rock from which they are derived. 
 These blocks are angular and are piled one above another in an ir- 
 regular manner. It has been held that these streams, which are now 
 mostly covered by vegetation, came into existence when the Falk- 
 land Islands were experiencing a rougher climate, comparable to 
 some extent to that of Bear Island to-day. The original arrange- 
 ment of the strata into hard quartzite beds enclosed in soft layers is 
 considered as having a fundamental influence on the formation of 
 these rock streams, this arrangement being the usual one where such 
 streams are well developed. 
 
 Stone glaciers, a modification of the rock stream phenomenon, 
 have been described from Alaska (Capps-7). They vary in length 
 from one to five kilometers, and in width from 100 to 500 meters. 
 The angle of surface slope varies from 9 to 18 degrees, and the size 
 of the rock fragments averages 20 cm. for porphyry, but more for 
 diorite and limestones and less for slates. Blocks several feet in 
 diameter also occur. In form these stone glaciers resemble true gla- 
 ciers, being thickest in the center, where they also show evidence of 
 more rapid motion. Frontally these glaciers end in a face up to 
 30 meters in height and having a slope generally of 35, the maxi- 
 mum slope of material of such coarseness. The whole aspect of 
 the mass suggests motion. 
 
ROCK GLACIERS 545 
 
 The interstices between the blocks are occupied by ice at a 
 short distance beneath the surface, and the freezing and rethawing 
 are in large part responsible for the present movement. 
 
 The original accumulation of these rock glaciers was believed 
 to be due to a large extent to transportation of the rock masses by 
 true glaciers and their deposition along the path of the glacier, 
 rather than at the front in a moraine. Some modern ice glaciers 
 of this region pass downward into rock glaciers, and furnish a sug- 
 gestion of the mode of origin of those accumulations. Rock streams 
 thought to owe their origin in part to ice glaciers were described by 
 Howe (24) from the San Juan Mountains in Colorado, while others 
 observed in Veta Peak, Colorado, were found to be wholly inde- 
 pendent of ice work. In the San Juan Mountains these streams are 
 found in the valleys in the higher peaks, and they are tongue-like, 
 having a length ranging up .to one kilometer and a width up to 600 
 meters, while the thickness ranges from 20 to 40 meters. The ma- 
 terial is a mixture of large and small angular blocks, the largest 
 having a diameter of 5 meters. A sharp demarcation exists between 
 the stone streams and the talus of the rock walls, from the foot of 
 which the stream starts. The rock stream of Veta Peak is remark- 
 able in that it consists of fragments of a whitish porphyry derived 
 from the summit of the mountain, and, although the rock stream 
 passes down between banks of red shale and sandstone for a dis- 
 tance of 1,700 feet or more, not one particle of any other kind of 
 rock than porphyry is to be seen. The porphyry fragments are of 
 approximately uniform size, fine material being for the most part 
 wanting. Only a few large fragments occur, the average size being 
 from i to 2 feet in diameter, only one over 6 feet having been noted. 
 The length of the stream is something over a mile, while the drop 
 of the surface from the head to the foot of the stream in that 
 distance is about 2,200 feet. The width in the lower part of the 
 stream is 500 feet, but its two feeding branches are each about 1,000 
 feet wide above the junction. The depth is estimated at from 130 
 to 300 feet. 
 
 Rock Slides and Falls. 
 
 These are common in nearly all mountain regions. They may 
 occur in the surface soil and debris which cover the slope, and in the 
 decomposed rock masses of the mountainside, or they may occur in 
 fresh rock. In the former case, saturation by water is commonly 
 a preliminary occurrence, the slide occurring when the inertia and 
 friction of the rock masses are overcome. Such slides leave con- 
 
546 PRINCIPLES OF STRATIGRAPHY 
 
 cave scars in the mountainside and accumulate in convex masses 
 in the valley bottoms. 
 
 Such a rock fall in one of the upper Ganges branches in the 
 Himalayas brought down 800,000,000 tons of rock in three days, 
 filling the narrow valley to a depth of a thousand feet with debris. 
 (See ante, p. 127.) The rock fall here was facilitated by the loos- 
 ening and undermining of the sloping strata of rock. 
 
 A remarkable case of rock fall occurred in the little town of 
 Frank, Alberta, Canada, in 1903, where the Cretacic sandstones and 
 shale of Turtle Mountain suddenly gave way and fell into the val- 
 ley below, forming a huge heap of debris, which spread out in the 
 valley bottom. The cause of the slide was the loosening of the mass 
 through coal-mining operations. 
 
 In 1 88 1 a great rock fall occurred in the village of Elm in 
 Switzerland. Loosened by undermining in a slate quarry, a huge 
 mass of rock broke away on the mountainside and fell onto the 
 plateau in which the quarry was situated. Striking this surface, 
 the mass broke, and numerous large fragments were hurled by the 
 impact through the air, and fell into the valley below, where they 
 formed a rock stream which in all essentials resembles that of the 
 Alaskan region above described. (Heim-2O.) 
 
 In both of the above-mentioned cases of rock falls or slides the 
 fragments showed percussion marks, while chips were sometimes 
 split off as with a hammer. The recent extensive rock slides of the 
 Panama Canal are other examples of such phenomena. 
 
 Rock and Soil Slides Started by Earthquakes. Slides are not in- 
 frequently started by earthquakes, especially where slopes are steep 
 and the material more or less water-soaked. As a result of the 
 earthquake of November 16, 1911, a portion of the shores of the 
 Lake of Constance (Bodensee) sank into the sea. The lake border 
 (Seehalde) was deformed for a total length of about 16 km.; on 
 the left for a distance of 10 km. to the extent of y 2 km., and on 
 the right shore for a distance of 6 km. length to the amount of 
 about iy 2 km. The edge of the sublacustrine shelf was locally 
 translated 2.4 to 18 m. lakeward, the point of abrupt descent 
 (Absturztiefe) was moved between 1.4 to 8 m., the elevations on the 
 border of the break rose from 0.2 to 2 m. In the expansion about 
 9,000 cubic meters of rock and soil material were moved. 
 
 ANCIENT EXAMPLES OF ROCK STREAMS AND SLIDES. 
 
 Many brecciated rock masses occurring in older geological for- 
 mations, of which the explanation is in doubt, may here find an 
 
ANCIENT ROCK STREAMS 
 
 547 
 
 interpretation. Known examples of this type are the Siluro-De- 
 vonic breccias of Mackinac and vicinity in Michigan, the limestone 
 breccias of Gibraltar, the rubble drift of south England and the 
 rock streams of the Ural in the vicinity of the mines of Bakalsk. 
 
 THE MACKINAC LIMESTONE BRECCIA. (Grabau-i8.) This is a 
 remarkable example of a breccia made up of large and small angu- 
 
 FIG. 117. Diagram illustrating the relation of the brecciated limestone to the 
 bedded rocks at St. Ignace, Michigan. The stack is shown again in 
 Fig. 118. The dotted line represents the hypothetical former ex- 
 tent of the brecciated material. 
 
 lar fragments of finely bedded upper Siluric (Monroan) limestones 
 and dolomites, derived from a still intact cliff of this limestone near 
 St. Ignace in the Upper Peninsula. The deposit is best seen in the 
 cliffs of Mackinac Island, nearly the entire mass of which seems to 
 be composed of this rock, which must here have a thickness of be- 
 tween 200 and 300 feet or more. The fragments are of all sizes 
 
 FIG. 118. View of the ancient stack of brecciated limestone at Point St. 
 Ignace. The cliff of bedded strata is to the right of the railroad 
 (lower right-hand corner). (After Hobbs.) 
 
 from that of a pinhead to blocks ten feet or more in diameter, and 
 their position in the breccia is such that the stratification lines of 
 the individual blocks dip in all directions. The distance to which 
 these blocks have been carried from the parent ledges is many 
 miles, and the width of this ancient stream is unknown. At St. 
 Ignace the high ground behind the beach consists of the stratified 
 
548 PRINCIPLES OF STRATIGRAPHY 
 
 Monroe dolomites in undisturbed horizontal position, but in front 
 of these at a level represented in the cliffs by bedded strata are 
 erosion stacks of the brecciated rock, carved from the cliff during a 
 period of higher level of the lakes. The position is such as to indi- 
 cate that these stacks are evidently a part of the rock stream, while 
 the cliffs behind the stacks are a part of the original cliff. In one 
 part of Mackinac Island the breccia is found to be underlain by 
 shales and thin limestones of Monroan (or Salinan?) age. (Figs. 
 117, 118.) 
 
 That the rock stream represented a subaerial flow of the rocks 
 is shown by its character. Fine, rounded quartz grains, blown from 
 a distance, are incorporated in the mass. The age of this stream is 
 Lower Devonic, the Middle Devonic Onondaga strata enveloping and 
 enclosing it and partly incorporating it as a somewhat reworked 
 product. 
 
 RESIDUAL SOILS. 
 
 The product of rock decay in situ, whether of the nature of 
 laterite or kaolinite, pure or. impure, not only furnishes material 
 for other agents to rework, but may also be recomposed in situ 
 without much or any disturbance. The same is true of crystalline 
 sand resulting from disintegration through insolation of granitic and 
 other coarse-grained crystalline rocks. If the upper layers are re- 
 worked by a transgressing sea or by wind or rivers, a perfect 
 gradation from the unaltered crystalline to the overlying stratified 
 rocks may be produced. Such a gradation is seen in the basal 
 arkose of the Lake Superior sandstone, where it rests on the pre- 
 Cambric peridotites. The indistinctness of the contact has led some 
 observers to regard it as of the igneous type. Residual soils of 
 limestone regions would have a sharper contact with the underlying 
 parent rock from which they are derived by solution. They consist 
 of the residual clay left after the removal of the lime in solution. 
 Such clay is rendered carbonaceous, if the old land surface presents 
 obstructed drainage, and swampy conditions prevail as on a pene- 
 plain. In extreme cases layers of coal of the terrestrial (humulith) 
 type may be formed. Eolian dust may be added, and the whole 
 subsequently reworked by a transgressing sea and covered by 
 marine deposits into which it will grade. Thus a complex deposit of 
 dark clay shales will be produced, the age of which ranges from the 
 period of exposure of the region to subaerial solution to the period 
 of resubmergence by the sea. Some of the mid-Palaeozoic black 
 
EOLIAN DEPOSITS 549 
 
 shales of North America, notably the Chattanooga shale of Ten- 
 nessee, seem to have been produced in this manner. 
 
 B. ANEMOCLASTIC OR EOLIAN DEPOSITS. 
 ANEMOLITHS. 
 
 Deposits which owe their location and form to transportation 
 and deposition by wind are commonly known as eolian deposits, 
 and when consolidated become eolian rocks or anemoliths. At first 
 regarded as of relatively little importance, they are being recognized 
 in constantly increasing number among the clastic rocks of the 
 geological column, and their thickness, great horizontal extent and 
 often marked structural characters, as well as the evidence they 
 furnish regarding the former physical geography of the region in 
 which they are found, render them of special significance to the 
 student of earth history. 
 
 SOURCE OF MATERIAL OF EOLIAN DEPOSITS. The ultimate origin 
 of the material entering into eolian deposits is extremely diverse. 
 Only a small part is directly due to the corrasive action of the wind, 
 freighted with sand grains or other material, which act as the tool 
 in the erosive work (see ante, Chapter II). A large part is de- 
 rived from the products of atmospheric decay or is directly pro- 
 duced by insolation, and so is primarily of atmoclastic origin. But 
 the mechanically produced sand and rock flour, whether due to 
 stream or wave work, or derived through the grinding of the rock 
 masses into sand and powder by glaciers, form no mean source of 
 wind-transported material. Not unimportant in this connection is 
 the dust produced by organisms, such as herds of animals pounding 
 a rock mass to powder beneath their hoofs, and, above all, the activi- 
 ties of man in breaking up rocks by mechanical means, and grind- 
 ing to powder the surface of the country under the wheels of his 
 vehicles. The annual amount of dust produced by heavy or rapid 
 traffic over an ordinary road is probably far in excess of the me- 
 chanically formed detritus produced by erosive action of an ordi- 
 nary stream in a bed of similar width. The dust produced in quar- 
 rying and mining operations forms no mean addition to the material 
 furnished for eolian transport, while coal dust, the product of in- 
 complete combustion, sometimes constitutes an important mineral 
 impurity of the air (see ante, Chapter II). Where rocks are ground, 
 as in cement mills or in stone crushers, the air for considerable dis- 
 tances all around is murky with suspended dust. This settles on 
 and around the vegetation of the neighborhood, but may also be 
 
550 PRINCIPLES OF STRATIGRAPHY 
 
 transported for a considerable distance. In the course of long 
 periods of time, deposits of considerable extent and thickness may 
 accumulate, though at present no data are available by which their 
 extent can be measured. 
 
 An important contribution of clastic material available for eolian 
 work is due to the explosive activities of volcanoes. The finer 
 grades of pyroclastics are spread far and wide, and furnish one of 
 the most significant of eolian deposits. As has been shown in an 
 earlier chapter, some of this material is held suspended in the air 
 for a long period of time, and settles far from the place of its pro- 
 duction. The dust from Krakatoa encircled the globe several times 
 before settling. Material which has thus been carried to a distance 
 from the source of production, although in point of origin belong- 
 ing strictly to the pyroclastics, must, in view of its assortment and 
 transportation by wind, be regarded as atmoclastic, since the mode 
 of deposition, more than the mode of production (clastation *), 
 gives the resulting rock mass its chief structural characteristics. 
 
 It should finally be noted that material for eolation is also sup- 
 plied by endogenetic processes. Thus certain pyrogenics, the finer 
 grained lapilli, may be subject to wind transportation and assorta- 
 tion, and on deposition may acquire a typical eolian structure. They 
 would commonly be admixed with and not separable from ordinary 
 eolian pyroclastics. The most typical of atmogenic deposits, snow, 
 is also most commonly exposed to eolian modification, snow dunes 
 or snow drifts being among the common forms assumed by this de- 
 posit. Besides the form, this deposit also shows the other common 
 characters of wind-drifted material, such as uniform size of grains 
 and dune bedding structure, though the latter is brought out only 
 when dust layers alternate with the layers of snow. The ability of 
 the wind-driven snow crystals to act as agents of erosion has been 
 noted in an earlier chapter (p. 52). 
 
 Hydrogenic and biogenic deposits may also be found among the 
 material subject to eolation. Thus salt crystals and gypsum flakes 
 separated from lakes or marginal lagoons may be blown away by the 
 wind. The dune-forming oolites of Great Salt Lake, believed to be 
 of phytogenic origin, and the wind-blown deposits of foramini feral 
 shells in many regions, are examples of the biogenic anemoliths. 
 Finally, accumulations of wind-blown organic fragments, such as 
 seeds, leaves or whole plants, whether microscopic or macroscopic, 
 must be classed among the biogenic anemoliths. These are proba- 
 bly never of great significance. 
 
 See p. 17. 
 
EOLIAN DEPOSITS 551 
 
 The various types of wind-deposited rock material or anemo- 
 liths may, then, be grouped as follows : 
 
 Endogenetic 
 (non clastic) 
 A nemoliths 
 
 1. Pyrogenic 
 
 2. Atmogenic 
 
 3. Hydrogen! c 
 
 4. Biogenic 
 
 a. Zoogenic 
 
 b. Phytogenic 
 
 Exogenetic 
 
 (clastic) 
 Anemoliths 
 
 1. Pyroclastic 
 
 2. Autoclastic 
 
 3. Atmoclastic 
 
 4. Anemoclastic 
 
 5. Hydroclastic 
 
 6. Bioclastic 
 
 The term anemolith in this case refers to deposition by wind, 
 while the origin of the material is indicated by the qualifying term. 
 The immediate sources of the material for sand dunes are the beach 
 sands of sea and lake, the flood plains and terraces of rivers, gla- 
 cial deposits and disintegrating rocks of the region. The dunes of 
 our coast are largely fed by the beach sands. River terraces and 
 flood plains furnish much of the material for the dunes of river 
 valleys, while glacial sands sometimes directly furnish material for 
 dunes, as on the uplands of Cape Cod, and in the North German 
 lowlands. Desert dunes may be derived from disintegrating sand- 
 stones, as in the case of the Libyan and Nebraskan dunes, or from 
 the flood plains of rivers, as in the case of the Kizil Kum and 
 Kara Kum of the Transcaspian deserts. Dry lake bottoms may also 
 form a temporary source of eolian material. 
 
 TEXTURAL TYPES OF ANEMOLITHS. 
 
 Two textural types of anemoliths may be recognized, anemo- 
 lutytes or dust deposits and anemoarenytes or eolian sand-dune de- 
 posits. Anemolutytes will, as a rule, show no, or but little, dis- 
 cernible bedding structure, and this may also be true of the fine 
 grades of anemoarenytes. The loess may be taken as a typical ex- 
 ample of this kind of deposit. Eolian sands (anemoarenytes), es- 
 pecially the coarse types, commonly accumulate in the form of sand 
 dunes, and these will show a typical dune-bedding structure. This 
 is also true of biogenic and atmogenic anemoliths. 
 
 GENERAL CHARACTERISTICS OF MODERN EOLIAN DEPOSITS. 
 
 The chief characters of eolian deposits are their thorough 
 sorting, according to size of grain and mineral material, the round- 
 
552 PRINCIPLES OF STRATIGRAPHY 
 
 ing and pitting of the individual grains, and the kind and character 
 of stratification and cross-bedding. The form of the deposits is of 
 less significance, since that form may be altered or destroyed subse- 
 quently. 
 
 Sorting of Material According to Size and Specific Gravity. A 
 series of experiments was made by J. A. Udden (51) with a cylin- 
 der suspended ninety feet above the ground on a bluff overlooking 
 the Mississippi River, and arranged so as to catch the dust carried 
 by winds of different velocities ranging from 14 miles to 29 miles 
 per hour. From these experiments Udden concluded that "the dif- 
 ferent grades of materials are so far separated from each other 
 in the direction of the wind movement that, even with considerable 
 changes in velocity, the principal area of the deposition of sedi- 
 ments of one grade will not far encroach upon that of the deposi- 
 tion of material much coarser or much finer." Thus, fine gravel 
 or sand will never be carried to the region of the main dust de- 
 posits, and wind-formed sediments will be quite uniform in com- 
 position for any given area. A similar conclusion was reached by 
 von Zittel in reference to the sands of the Libyan desert. (Zittel- 
 
 56.) 
 
 It may thus be stated as the first important character of eolian 
 deposits that they are well sorted, according to size and specific 
 gravity of the material, and this means that the deposits of a given 
 locality will consist, to a very large extent, of one mineral type. 
 Thus, an original mixture of grains of various kinds may by pro- 
 longed eolian action be sorted into nearly pure accumulations of the 
 grains of the different minerals. As will be more fully shown be- 
 yond, calcareous particles are thus separated from others and segre- 
 gated into eolian limestones, while clay and other dust particles are 
 removed from the sands which result from the decomposition of 
 igneous rocks, leaving only pure quartz behind. The clay itself 
 accumulates to form deposits of loess. In the Sinai desert, where 
 the quartz is derived from the decomposition of dark-red granite, 
 it represents approximately one-fourth the volume of the original 
 rock. (Walther-52: 133.) The formation of a dune 10 meters 
 high and 20 meters broad results in the accompanying liberation of 
 perhaps 5,000 cubic meters of finest particles of feldspar and horn- 
 blende, which are carried away by the wind. As most of the quartz 
 sand is probably derived from granites, it is apparent that the 
 amount of fine material produced must be enormous. Much of this 
 is carried as dust by the wind. 
 
 Size of grains in eolian deposits. The size of the grains in 
 eolian deposits varies greatly. According to Sokolow, no undoubted 
 
EOLIAN DEPOSITS 553 
 
 eolian deposits are known in which the diameter of the grains 'ex- 
 ceeds 4 or 5 mm. (48) ; more usually it is less than I mm. The 
 sands of the Libyan desert range from 0.5 mm. to 2.0 mm. in 
 diameter with the grains of a given sample of nearly uniform size. 
 Grains of the Sylvania sandstone of Michigan and Ohio, a fossil 
 eolian deposit, vary in average size in different samples from 0.18 
 to 0.3 mm., though an occasional grain 0.5 mm. or more in diame- 
 ter occurs. Dune sands from Michigan City, Indiana, have an 
 average diameter of grain of nearly 0.3 mm., while various samples 
 from Albuquerque, New Mexico, averaged from this size to 0.13 
 mm. in diameter (Sherzer and Grabau-45 ; The Sylvania Sand- 
 stone~77). Eolian dust deposits range, of course, downward to the 
 finest particles, which will settle out of the atmosphere, or which 
 may be washed out of it by rains or captured by hygroscopic salt- 
 covered surfaces. 
 
 Rounding of Sand Grains. The process of rounding of sand 
 grains has been discussed at length in Chapter V, p. 253, where it 
 was also pointed out that wind-blown sands are more perfectly 
 rounded, especially the finer grades, than grains of similar size sub- 
 jected only to water wear. Besides the wearing off of the corners 
 and the general dulling of the surface from prolonged wear, pitting 
 of the grains also results from the violent impact of grain on grain 
 to which they are all subjected. 
 
 In general it may be stated that sand grains of eolian origin 
 are more or less perfectly rounded, and this together with their 
 well-assorted character makes valuable criteria by which such eolian 
 sands may be recognized. In general, the greater the amount of 
 transportation and the more frequent the rehandling of the sand by 
 the wind, the more perfect will be the rounding, as well as the as- 
 sortment. Sands of parts of the Libyan desert, derived from an 
 older sandstone, the Nubian, and carried in some cases a distance 
 of a hundred miles or more, show a pronounced rounding of grain, 
 as well as perfection of assortment, while sands from the desert 
 near Albuquerque, New Mexico, derived from the not very distant 
 crystallines are poorly assorted, and many of the smaller grains are 
 still angular. Sands of shore dunes such as those derived from the 
 glacial sands of Lake Michigan show only moderate rounding, the 
 transportation and wearing having been of comparatively slight ex- 
 tent. Similar conditions occur in dune sands from the Pacific 
 coast, while a like subangular form also persists in sands from West 
 Palm Beach, Florida. Eolian sands along the Nile valley, derived 
 primarily from the disintegration of the crystallines, are not only 
 very poorly assorted, but they also are mostly angular with only 
 
554 PRINCIPLES OF STRATIGRAPHY 
 
 
 the larger grains rounded. Others, however, carried in from the 
 desert, are well rounded and assorted. 
 
 Stratification and Cross-bedding of Eolian Deposits. Eolian de- 
 posits may or may not be well stratified. Deposits of dust of a 
 loess-like character often show an entire absence of bedding planes, 
 the material being homogeneous throughout. Walther found in the 
 deserts of Turkestan near Askabad layers of loess-like material a 
 meter or more in thickness without apparent bedding, interpolated 
 between layers of stratified sand and gravel. In the steppes sur- 
 rounding the desert, the coarse and rigid stems of the steppe plants 
 check the wind current, which then drops much of its load of dust. 
 Rain will wash the dust from the air and from the leaves of the 
 plants on which it has settled. This accumulates around the plants 
 through which it is protected from further removal by the wind. 
 The same office is performed by the coarse blades of the Buffalo 
 grass (Biichloe dactyloides, Bouteloua oligostachya) and other 
 plants which abound in the semiarid Great Plains east of the Rocky 
 Mountains in North America. As the dust accumulates the mantle 
 of vegetation will rise to a higher level. The roots of the dead 
 plants, however, will continue to penetrate the deposit until their 
 decay leaves a series of vertical tubes, or a series of carbonaceous 
 streaks penetrating the structureless mass. The tubes may subse- 
 quently be filled by mineral matter, as in the case of many loess 
 deposits, where the filling of the tubes is by calcite, and where their 
 presence is believed to be in part the cause of the remarkable ver- 
 tical cleavage of these deposits. Older fossil examples of this type 
 are also known, one of the best being the well-known Portage sand- 
 stone of Devonic age, which is exposed in the banks of the Genesee 
 gorge at Portage, New York. The fine, uniform, structureless tex- 
 ture of this rock makes it an excellent building stone, though the 
 presence of the vertical tubes, described originally as fucoids 
 (Fucoides verticalis), often mars this quality for certain purposes. 
 The loess-like origin of this rock seems undoubted, though the accu- 
 mulation was near the coast, rather than inland. 
 
 Dust carried by wind to regions of more extensive rainfall 
 will be washed from the air by the rain and accumulate as a more 
 or less stratified loess. In like manner dust carried across sur- 
 faces rendered hygroscopic by the presence of salts will adhere to 
 these surfaces and so, as a rule, become finely stratified. 
 
 On the whole, it must, however, be emphasized that regular 
 stratification is not characteristic of eolian deposits. Where strata 
 show fine or uniform bedding water always has played more or less 
 of an active part in its deposition, though the idea of standing wa- 
 
SAND DUNES 555 
 
 ter bodies, passive influence, or receptive waters is not necessarily 
 involved in this concept. Irregular stratification and cross-bedding 
 of a complex type may, however, be regarded as one of the most 
 characteristic structural features of the coarser eolian deposits. 
 
 Eolian cross-bedding is especially characterized by discontinuity. 
 The successive cross-bedded layers or wedges are limited above and 
 below by erosion planes, which are of contemporaneous origin. 
 While deposition goes on in one section of the deposit, erosion of a 
 previously formed one in part supplies the material, or alternate 
 deposition and erosion may characterize any portion of the series. 
 Furthermore, as will be more fully discussed in the summary chap- 
 ter on these structural features, the varying currents will result in 
 the inclination of the cross-bedding in different directions in the 
 successive sections. Horizontal beds will be rare or wanting, a 
 feature readily distinguishing this type from the diagonal bedding 
 due to torrential action. Finally, as Huntington (25) has insisted, 
 the tangency of the inclined beds with reference to the erosion sur- 
 face below, or their gradual bending toward parallelism with this 
 plane as they approach it, is one of the most reliable criteria by 
 which eolian deposits can be recognized. 
 
 SAND DUNES, THEIR ORIGIN AND FORM. 
 
 Wherever along the beach the sun has dried out the sands, 
 they have lost the coherency which they possessed when saturated 
 with water, and are then readily blown about by the winds. As a 
 result, sand dunes are formed along most coasts, these dunes grad- 
 ually traveling inland, and burying forests, fertile lands and build- 
 ings unless their landward march is checked by a barrier, either 
 natural or artificial. The distance to which wind-blown material is 
 carried depends chiefly on the fineness of the material, its specific 
 gravity and the strength of the wind. Examples of such transpor- 
 tation have been given in Chapter II. 
 
 The sand particles move under the direct influence of the wind, 
 and their rate of movement depends on their size and the strength 
 of the wind. According to Sokolow (48:15), when the wind 
 velocity is 4.5 m. per second, quartz sand grains of 0.25 mm. diame- 
 ter will glide only along the surface of the ground without rising 
 freely above it. With a wind velocity of 15 meters per second, 
 however, sand grains of I mm. diameter will be raised some dis- 
 tance into the air. With the wind of no great strength and the sand 
 not very fine, movement of the grains is along the surface of the 
 
556 PRINCIPLES OF STRATIGRAPHY 
 
 ground, or only a few centimeters above it. Since the sand grains 
 of the shore dunes have in large part an irregular, more or less 
 flattened form, their movement is not a rolling, but a gliding one. 
 The larger grains move only by jerks, and only under the influence 
 of strong gusts of wind. A greater force is needed to start the 
 movement of a grain, which then will continue its progress even un- 
 der a diminished wind force. 
 
 While a steady and continuous wind will cause a uniform and 
 constant onward movement of sand grains, with the result that 
 eventually all the finer particles are removed by the wind, a more 
 or less interrupted series of wind gusts or variable winds will re- 
 sult in the irregular movement of the particles and their temporary 
 arrangement into wave-like forms. On a small scale these consti- 
 tute wind ripples, while the larger ones are the dunes. 
 
 Wind ripples are common on sandy surfaces where the irregu- 
 lar motion of the wind creates eddies and cross currents. (See 
 Chapter XVII for formation of ripples.) With a given wind they 
 vary in height and distance apart, according to the size of the sand 
 grains composing them. Sokolow gives the following table of such 
 relationship : 
 
 Size of grain 
 
 Height of 
 ripple 
 
 Distance 
 between ripples 
 
 0.2 mm. 
 1 .0 mm. 
 2 to 3 . o mm. 
 
 10 mm. 
 25 to 40 mm. 
 70 to 100 mm. 
 
 8 to 10 cm. 
 25 to 35 cm. 
 60 to 1 20 cm. 
 
 The form of the ripples is symmetrical, with a gentler windward 
 and a steeper leeward side. Up the windward side the sand grains 
 are rolled or pushed until they reach the crest and roll down the 
 leeward side. In this manner the ripples advance in the direction 
 of wind motion, this advance being at a variable rate dependent 
 on the size of the grain and the strength of the wind. Helman 
 (21 : 384) obtained the following average rates of advance for sand 
 ripples on continental dunes or barchans in the sandy desert of 
 the Khanat of Chiwa in Turkestan : 
 
 Strength of Wind Average advance of ripples 
 (meters per second) in millimeters 
 
 6 9.0 
 
 4 5-2 
 
 3 3-3 
 
 Similar results have been obtained by Sokolow on shore dunes. 
 
SAND DUNES 557 
 
 Types of Sand Dunes. 
 
 Three types of sand dunes are recognized, their characters being 
 largely determined by their location. These are: ist, shore dunes, 
 or those formed from the sands left to dry on the retreat of the 
 water; 2nd, river-bed dunes, and, 3rd, inland or desert dunes. 
 While all of these have fundamental features in common, they, 
 nevertheless, show individual characteristics due to the topographic 
 diversity and structural peculiarities of the respective regions in 
 which they occur. 
 
 ( i ) Strand Dunes. These are a common feature of the coasts, 
 being found on the shores of the sea and of the larger lakes. Typi- 
 cal and well-known examples of seashore dunes are found in the 
 Provincetown region of Cape Cod, Massachusetts, and from there 
 southward along Long Island coast and the sandy coast from New 
 Jersey to Florida. They are further found on the shores of the 
 Baltic, especially on the narrow sand bars which separate off the 
 Kurische and Frische Haff on the east Prussian coast, and on the 
 west coast of Kurland an'd the Gulf of Riga in Russia. (Berendt- 
 4.) Extensive dune areas are also found on the east and south 
 coast of the North Sea, especially in Denmark, and the coast of the 
 Netherlands and Flanders from*the mouth of the Elbe to Pas-de- 
 Calais, while the French coast of the Bay of Biscay bears the most 
 extensive dune accumulations of all. Finally, extensive shore dunes 
 are developed on the eastern and southern coast of Lake Michigan, 
 and to a lesser extent on the shores of the other Great Lakes of 
 North America. Shore dunes are most typically developed where 
 a broad flat zone of sand fronts a low country, as in the examples 
 cited, but they may also occur where such a sand zone lies at the 
 foot of rocky cliffs. In such cases the dunes will accumulate on 
 the summit of the cliff, as on the Normandy coast of France, the 
 west coast of Jutland and. the West Schleswig-Holstein coast, far- 
 ther south, where the height of the cliff in one case (Island of Sylt 
 among the north Friesian islands) was 34 meters and that of the 
 dunes upon it reached a height of 28 meters. They are, however, 
 never found where rocky coasts descend directly into the waters, 
 as on the northern New England coast and the rocky coast of the 
 maritime provinces of Canada, the rocky coasts of Great Britain 
 and of Scandinavia and Finland. The best development of coastal 
 dunes seems to be on a sinking coast, over 90% of the coast dunes 
 of Europe being thus located, according to Sokolow. 
 
 The most important coastal dunes of Europe (Sokolow), if 
 not of the world, are found on the French coast of the Gulf of Bis- 
 
558 PRINCIPLES OF STRATIGRAPHY 
 
 cay, extending without interruption from the mouth of the Adour 
 to that of the Garonne, a distance of over 240 km. They are ar- 
 ranged in parallel rows, ten being the maximum number, covering 
 a strip of coast from 4 to 8 and in some places even 10 km. wide, 
 and approximating an area of 120,000 hectares (296,520 acres). 
 Their height ranges up to 90 meters, making them the highest 
 known coastal dunes. It is true that there are dunes with a height 
 of from 120 to 180 meters on the west coast of Africa between Cape 
 Bojador and Cape Verde, but these appear to be desert dunes which 
 have reached the coast from the Sahara under the influence of pre- 
 vailing northeast winds. 
 
 The country bounded seaward by the great dune belt of the 
 Biscayan dunes is a low, marshy tract known as the Landes, which 
 by many geographers is believed to be subsiding, and the shore of 
 which is retreating at a rapid rate. Near Houtin, in the northern 
 part, the sea advances at a rate estimated at not less than 2 meters 
 per year, while great difficulty is experienced by St. Jean-de-Luz, 
 south of Biarritz, at the southern end of the dune region, from the 
 encroachments of the sea. 
 
 On the south coast of the North Sea along the entire coast of 
 Belgium (Flanders) and the Netherlands, to the mouth of the 
 Elbe, extends a nearly uninterrupted dune belt, which altogether 
 forms a length far exceeding that of the coast of the Landes. These 
 dunes are' not as high as those of the Biscayan coast, averaging 15 
 to 20 meters, with the highest, near Petten, attaining only 35 meters. 
 The coast here is known to subside at a rate where measured of i.i 
 meters per century, and as further indicated by the gradual deep- 
 ening of the Zuidersee, formerly a swamp, but now an embayment 
 of the sea. 
 
 The dunes of the Danish coast of the North Sea are of especial 
 interest on account of their rapid inland advance. This section, 
 together with the coast of Schleswig-Holstein, forms the second 
 largest dune region of Europe, covering an area of 67,000 hec- 
 tares (165,557 acres), many of the dunes reaching a height of 30 
 meters. The retreat of this coast has been discussed in an earlier 
 chapter, but an example may be repeated here to show the rate of 
 dune advance. In 1757 it was found . necessary to tear down the 
 church of the village of Rantum on the Island of Sylt on the west 
 coast of Schleswig-Holstein, because it was reached by the advanc- 
 ing dunes. In 1791 or 1792 the entire dune chain had passed over 
 the church ruins, these then lying on the shore which had advanced 
 to this point. Sixty years later the site of the church was 700 feet 
 from shore, the depth there being 12 feet. The second church has 
 
SAND DUNES 559 
 
 since been buried by the advancing dunes. ( Forchhammer- 1 6 :<?/.) 
 A similar case is shown in the changes produced by migrating dunes 
 on the Kurische Nehrung, in East Prussia, where a church was 
 buried and again resurrected by the advancing dunes between the 
 years 1809 and 1869. 
 
 On the south coast of the Baltic exists another important dune 
 area of Europe, its strongest expression being found on the Ku- 
 rische and Frische Nehrung, two very long narrow sandbars sep- 
 arating off shallow lagoons on the coast of East Prussia. The 
 height of the dunes here reaches 60 meters and more, and hence 
 these are, next to those of the Gascony coast, the most important 
 coastal dunes of Europe. 
 
 Dunes of great size and covering an extended area occur on 
 the North African coast of the Mediterranean, especially on the 
 Great Syrt. Elsewhere on the Mediterranean coast they are of little 
 importance. 
 
 The dunes of the east coast of North America have been studied 
 to a much less extent than those of the European coast. Perhaps 
 the best-known region is that of the extreme tip of Cape Cod at 
 Provincetown, where the dunes reach a height not exceeding 30 or 
 40 meters. This entire section is a region of sandbars and beaches 
 built by the waves and shore currents from material washed from 
 the Truro and Wellfleet coast, a region exposing high cliffs of gla- 
 cial and earlier sands to the open Atlantic. The dunes built at 
 Provincetown slowly advance southward and westward, burying 
 forests and hamlets in their path, though their march has to some 
 extent been arrested in the Provincetown region by artificial means, 
 at an expenditure of $28,000 between the years 1826 and 1838. 
 
 On the Long Island coast the dunes are moderate, but on the 
 New Jersey coast and on that of the Carolinas they reach a consid- 
 erable height and extent, and in their inland march bury forests 
 and even buildings. 
 
 (2) Lake Shore Dunes: These are well illustrated by the dunes 
 so extensively developed on the eastern shore of Lake Michigan 
 from the Straits of Mackinac to the Chicago area. Here extensive 
 glacial sands in part forming beach lines of a subsequent lake stage 
 of greater extent than the present are heaped into sand dunes by 
 the prevailing westerly winds. Some of these sand dunes on the 
 northwest coast of Michigan are grassed over and wooded, but 
 others are still in an active state of movement, advancing upon and 
 burying the forests. In height these dunes range to a hundred feet 
 or more, especially in the southern area, as in Dune Park, In- 
 diana. Near Muskegon, Michigan, occurs one of the largest dunes 
 
560 PRINCIPLES OF STRATIGRAPHY 
 
 in the world. It is several hundred feet high, and from its advance 
 has become known as "Creeping Joe." 
 
 (3) River Flood-Plain and River-Bottom Dunes. Rivers flow- 
 ing through broad, open valleys, especially in semiarid regions, are 
 often accompanied by an extensive development of border dunes, 
 while those rivers flowing through narrow canons are essentially 
 free from such accumulations. In a humid climate dunes are sel- 
 dom formed on river-bottoms, even though these may be broad and 
 supplied with an abundance of sand. In illustration of this it may 
 be noted that river border dunes are not common in western Eu- 
 rope, except in the sunny and somewhat drier regions of southern 
 France and Spain. Thus, while in the North German plains and in 
 England the few dunes which have been formed in the past are 
 low and soon covered with vegetation, the valley of the Gardon in 
 Languedoc shows dunes 10 meters high, while dunes rising to a 
 height of 25 meters are found in the sandy desert region on the 
 right bank of the Guadalquivir in Andalusia in southern Spain. In 
 eastern Europe, on the other hand, river dunes are much more ex- 
 tensively developed. Thus even the smaller streams of the northern 
 half of the Russian regions have dunes rising to a height of 5 
 meters, while southern Russia, with its dry continental climate, 
 shows them extensively developed. A nearly continuous dune belt, 
 reaching sometimes a width of 12 km., and with dunes averaging 10 
 or 12 m. in height, extends along the middle course of the Dnieper 
 below Kief, while the lower course of this stream shows a still 
 more extensive dune area, especially in the government of Taurida. 
 The sands here are found on the left bank of the Dnieper, and ex- 
 tend over an area more than 150 km. long, with a maximum width 
 of 30 km. In the midst of this area, however, are often spots free 
 from sand, while in some parts a broad area of meadow and wooded 
 land separates the sand area and the river. The height of the 
 dunes is mainly from 5 to 7 m,, but exceptional cases, where the 
 height rises to 11.2 m., have been noted. The sand is almost exclu- 
 sively quartz rock, with only a very slight admixture of feldspar 
 and dark grains, probably of iron oxide. The grains are well 
 rounded, often spherical, angular grains being wholly wanting. The 
 color of the dunes as a whole is a light golden yellow. The sands 
 of the middle Dnieper are somewhat coarser, but they do not ex- 
 ceed on the average the diameter of 0.4 mm. In roundness, purity 
 and color the sands of the two areas are much alike. A still greater 
 development of river border dunes is found in the valleys of the 
 Don and the Donetz. In the Don valley the dune zone has a width 
 
SAND DUNES 561 
 
 ranging from 8 to 18 km., the average being 12 or 13 km., while 
 the height of the dunes may reach 30 meters. In the Donetz valley 
 the width of the zone is sometimes 10 km., but the height of the 
 dunes does not as a rule exceed 5 or 7 m. The shores of the 
 Volga in the Kazan district also furnish extensive dunes, which 
 wander far into the steppes. Still more extensive dune develop- 
 ment is found in the river valleys of central Asia, as, for example, 
 along the River Oxus, or Amudaria, and the Jaxartes or Syrdaria, 
 both of which are tributary to the Aral Sea. (Walther-52 ://p.) 
 These streams bring vast quantities of sand and mud from the 
 Tian-Shan, Great Pamir, and Hindu Kush mountains, in which 
 they rise, and spread them over the low ground of their flood plains, 
 which range in width up to 10 km. The thickness of the deposit 
 made by the Oxus was found to be 23 m. at Tschardschui. The 
 rivers rise 3 meters from March to July and overflow the flood 
 plains, depositing the sandy sediment. As the water of the Jax- 
 artes falls, the hot northern winds soon dry the deposit, and carry 
 away all the finer dust particles, leaving only the pure quartz sand, 
 which is heaped into dunes. These wander southward across the 
 Kizil Kum desert, sometimes at a rate of 20 meters during a 
 stormy day, but generally the sand masses move at an average rate 
 of 6 miles per year. Reaching the Oxus, these sands are incor- 
 porated in its sediment, and the operations of sorting the deposits 
 on the flood plain of this river are repeated and the sands again 
 heaped into dunes, which wander southward across the Transcas- 
 pian or Kara Kum desert, until they reach the borders of the 
 Caspian Sea. The activities of the streams are unceasing, and the 
 supply of material in the mountains in which they rise is practically 
 inexhaustible. Thus there is a constant succession of sand dunes 
 wandering southward across these deserts, and layer upon layer of 
 sand accumulates, each showing the characteristic eolian structures, 
 and helping to build up a deposit of pu^e, unfossiliferous sand of 
 almost unlimited thickness. 
 
 In North America dunes are rare and insignificant in the river 
 valleys of the eastern and central region, but are more frequently 
 found in the drier climates of the west. Perhaps the most exten- 
 sive river dune area on this continent is that of the Columbia and 
 Snake rivers in Oregon and Washington between Dallas and 
 Riparia, the sand being derived from the flood plains of the rivers, 
 which are widely exposed during the dry season. 
 
 (4) Inland or Desert Dunes. The largest areas of shifting 
 sands are the deserts. Their occurrence is even more dependent on 
 
562 PRINCIPLES OF STRATIGRAPHY 
 
 aridity of climate than is the case with river dunes, for moisture 
 will permit the growth of vegetation and so check the movements of 
 the sands. Where, however, the cover of vegetation is destroyed by 
 man or other agencies, dunes may occur even in moist climates, as 
 is the case in northern France, Belgium and the North German 
 lowlands. 
 
 The height of continental dunes may range up to 150 or even 
 200 meters, and the area covered by them is often very large. In 
 Hungary the total dune area covers some 13,200 sq. km., with single 
 dunes rising 52 m. in height. Large areas also occur in European 
 Russia, but the greatest dune districts are in the deserts of Asia, 
 Africa and Australia. In the Sahara dunes cover only one-ninth 
 of the total area (Zittel-56), but even so this aggregates a total 
 of 18,000 geographical square miles. Arabia is largely a land of 
 drifting sands. Almost the whole southern area is occupied by the 
 terrible Desert of Roba-el-Khali or the desert Dehna, which is wholly 
 covered by eolian sands and is without the relief of oases. Its 
 length is 150 geographic miles, its width 80. Sands form nearly 
 one-third of the entire surface of Arabia, or not less than 15,000 
 geographic square miles. (Palgrave-35 : pi.) In the northern part 
 of the peninsula is the Nefud desert of red sands, while other sandy 
 deserts of Asia are found in Syria, Iran, Baluchistan, northern In- 
 dia, eastern Turkestan and Mongolia, where continuous sandy 
 desert areas extend for hundreds of kilometers (Przhevalsky-39). 
 In North America extensive sand dune areas of the continental 
 type are found between the Rockies and the Sierra Nevada, in the 
 Colorado and Mohave deserts of southern California and in the 
 Sand Hill region of Nebraska and the adjoining area. In Nebraska 
 this region covers an area of more than 18,000 square miles, or 
 almost one-fourth of the total area of the state. The sand is largely 
 derived from the disintegration of the Tertiary sandstone, and to 
 this is due in part its purity. The size of the grains varies consid- 
 erably, but the average centers around 0.25 to o.i mm., the maxi- 
 mum scarcely rising above i.o mm. 
 
 The sand hills of Nebraska enclose numerous valleys, ranging 
 in size from mere basins. to valleys a mile in width and many miles 
 long. Numerous lakelets generally arranged in groups occur in 
 these valleys, the individual lakes ranging from small ponds a hun- 
 dred yards across to bodies of water a mile or more wide and four 
 or five miles long. In Cherry county fifty or more such lakes form 
 a single group. These lakes exist because the climate is now moist, 
 for which reason also much of the sand-hill region is covered with 
 vegetation, though many bare areas of drifting sand still occur. 
 
SAND DUNES 563 
 
 The chief agent in holding the dunes and making the spread of vege- 
 tation possible is the bunch grass (Andropogon scoparius), though 
 the sand grass (Calamovilfa longifolia} and the needle or silk grass 
 (Stipa coniata) are also important as binders. The most charac- 
 teristic plant next to the bunch grass is the dagger weed (Yucca 
 glauca), which often occurs in great abundance. At the present 
 time hollows or "blow-outs" are more characteristic of these sand 
 hills than new dunes. These blow-outs begin where, from over- 
 grazing or fires, the vegetation is destroyed, and will increase in 
 size until they are from 300 to 900 feet in circumference with sides 
 of bare sand sloping inward at an angle of about 30 degrees to the 
 bottom, which may be from 20 to 75 feet or more beneath the rim. 
 (Pool-38.) In South America continental dunes are best devel- 
 oped in the great Atacama desert of Chile, west of the Andean 
 chain. Finally many of the deserts of Central and West Australia 
 are characterized by dunes of great extent. 
 
 The Forms of Dunes. 
 
 Three main dune forms may be recognized, of which all others 
 constitute more or less divergent modifications. These are: 1st, 
 the conical hill; 2nd, the long ridge, generally occurring in parallel 
 groups, and, 3rd, the crescent-shaped dune or barchan. The cres- 
 cent or barchan type is most characteristic of the inland desert 
 regions. It presents a gently convex surface to the wind, while the 
 lee side is steep and abrupt. The horns of the crescent mark the 
 lateral advance of the sands. Its wide distribution and all but uni- 
 versal presence in the sandy deserts of all continents make this 
 type the normal one for sand hills formed on an open area. In- 
 deed, it is probable that in very many cases the linear ridges are 
 mere modifications of this type, formed by the lateral confluence 
 of many simple barchans. This is often shown in the wavy form of 
 the crest line, as in the case of the dimes of the Transcaspian 
 desert. 
 
 On the coast, barchans, though present, are less characteristic. 
 Here we find the linear series more commonly developed, because 
 a nearly constant and uniform supply of sand is furnished by the 
 parallel coast, and because the sloping coast itself exerts a directing 
 force. Coastal dunes never have a symmetrical cross section, the 
 windward side generally having a gentle slope of from 10 to 20, 
 which may in places be somewhat convex, while the leeward slope is 
 generally much steeper, being often as high as 30. 
 
564 PRINCIPLES OF STRATIGRAPHY 
 
 Origin of Intercalated Dust and Clay Layers, and of Clay Balls in 
 
 Sand Dunes. 
 
 The depressions between the sand dunes when not occupied by 
 standing water, as in the moist sand-hill region of Nebraska, often 
 represent a flat playa or takyr surface, the dried mud bed of a 
 temporary lake, which evaporated soon after its formation under 
 the influence of a dry climate. Such surfaces are common in most 
 desert regions, and they are not infrequently characterized by mud 
 cracks, footprints and trails of various animals. When the sand 
 dunes advance over such a surface a horizontal bed of clay will 
 separate the diagonally bedded eolian sands. This clay bed will 
 of course be of limited extent only, wedging out around the margin 
 of the playa. If the clay layer of the playa surface is very thin 
 (i to 2 cm.), the pieces into which it splits on drying will curl up 
 like shavings, and in such a condition they may be blown by the 
 wind into the dune. Here, on becoming moistened by the winter 
 rains, they will be compressed into flat lenticles of clay and form 
 the "clay galls" so common in modern as well as ancient eolian 
 deposits. 
 
 Clay and dust accumulations are not confined, however, to the 
 depressions between the dunes. A light wind, active for a period of 
 time, may dust over the dune with a coating of argillaceous par- 
 ticles, which then become incorporated in the sand mass as oblique 
 partition layers. Such occurrences are not uncommon in the Trans- 
 caspian (Kara Kum) and other deserts. They appear as steeply 
 inclined sheets of clay penetrating the dunes, and are not infre- 
 quently found in the form of parallel "clay dikes," 10 to 15 meters 
 in length, in the interdune areas, where they may rise a centimeter 
 above the flat surface, representing the residual base of a cross- 
 bedded dune, the top of which has moved onward. 
 
 Peat and Lignite Deposits in Sand Dunes. 
 
 Shore dunes often transgress across peat deposits formed in 
 swamps or marshes behind the dunes. Such peat deposits, some- 
 times with old tree stumps, are found on the shores of Nantucket, 
 and are sometimes buried under deep masses of dune sand, as at 
 the Nauset lights on Cape Cod. They are characteristic of other 
 regions as well. Forests buried by advancing dunes are killed, 
 and the wood, if buried long enough, is converted into lignite. The 
 
OLDER EOLIAN DEPOSITS 565 
 
 same thing is true of coatings of vegetation which are buried by the 
 readvancing sands. In the sand dunes of Cape Cod many such ex- 
 amples are found, and the same is true for the sand hills of Ne- 
 braska. Indeed, this may be seen in almost all coastal dunes where 
 vegetation has gained a temporary foothold. Such sands would 
 thus become lignitic, and the fragments of lignitized and broken 
 wood may be scattered and incorporated in the sands over a wide 
 area. The lignitic sands of the Raritan formation of New Jersey 
 apparently had such a history. 
 
 Transgressive Relation of Dune Sands to Subjacent Formations. 
 
 The southward transgressing dunes of the Kara Kum or Trans- 
 caspian desert spread layers of sand over the older fluvial or marine 
 deposits. The pure quartz sands of the Libyan desert, derived from 
 the disintegration of the Nubian sandstone a hundred miles away, 
 transgress across the floor of Cretacic and Tertiary limestones, and 
 the weathered-out fossils of these formations are enclosed in the 
 basal part of the sands. 
 
 In the profile of the earth's crust many cases of such trans- 
 gressive relation of unfossiliferous sandstones upon fossiliferous 
 marine deposits are found. Examples are the St. Peter on the 
 Beekmantown limestone, the Sylvania on the Monroe dolomites, 
 the Bunter Sandstein upon the marine Zechstein, the Keuper upon 
 the Muschelkalk and many others. Such deposits point strongly to 
 an origin comparable to that of modern desert sands which overlie 
 marine sediments of an earlier age. 
 
 EXAMPLES OF OLDER EOLIAN DEPOSITS. 
 
 The Loess as an Example of a Dust Deposit. The loess is a 
 continental deposit of loosely arranged, angular grains of calcare- 
 ous silt loam, typically intermediate in fineness between sand and 
 clay and of remarkably uniform mechanical composition. Normally 
 it is without stratification, and Breaks off in vertical slabs, with the 
 result that perpendicular cliffs are formed. Loess was first de- 
 scribed from the valley of the Rhine, but is also known from south- 
 eastern Europe, from North America, and especially from China, 
 .where it was fully described by von Richthofen (42). Here the 
 loess sometimes has a thickness of a thousand feet or over, and is 
 believed to be primarily the disintegrated rock material brought by 
 
566 PRINCIPLES OF STRATIGRAPHY 
 
 the winds from the Desert of Gobi in central Mongolia, Evidence 
 of fluvial action is, however, not wanting, many gravel beds of great 
 extent and great distance from their source pointing to river activi- 
 ties. It has been thought (Wright-54) that the distribution indi- 
 cates a vast body of standing water which temporarily occupied the 
 loess-covered area in late Tertiary or Quaternary time, but this in- 
 terpretation does not sufficiently account for the absence of fossils 
 in the loess, nor does it do justice to the ability of rivers and wind 
 to distribute fine sediments in broad level plains. For the whole 
 of Asia the loess-covered area comprises about 1,324,000 square 
 kilometers (511,150 square miles) (v. Tillo), which, with an aver- 
 age estimated thickness of 30 meters, gives a total of nearly 40,000 
 cubic kilometers of loess material. All this material has of course 
 been removed from the rock surfaces of the country where it origi- 
 nated. (Walther-5i 150.) The loess is characteristically pene- 
 trated by vertical tubes, the calcite-filled hollows left by the decay 
 of grasses and roots. These help to produce a vertical splitting of 
 the mass, which otherwise shows no planes of separation, since 
 stratification is for the most part absent. As a result, the walls 
 of loess left on the dissection of the loess area by the Yellow River 
 and its tributaries form vertical bluffs of great height. "Millions 
 of Chinese live on the valley floors of dissected basins of this kind, 
 for the loess is extremely fertile where well watered. Great num- 
 bers of the people inhabit cave-like dwellings excavated in loess 
 bluffs; in a thickly populated district not a house may be seen. 
 The yellowish color of loess prevails everywhere. It gives color 
 and name to the great river of the region and to the sea into which 
 the river flows." (Davis-i3 : 5/7, 318.) The loess of the Mis- 
 sissippi Valley region and of the plains generally, is also commonly 
 interpreted as a deposit of wind-blown material, though indications 
 of aqueous activities are not wanting. The principal evidence for the 
 eolian origin of this "Prairie loess" (Shimek-46) is found (i) in 
 the absence in the deposit of shells belonging to distinctively water 
 species; (2) the presence of land shells of species that live on the 
 shores of ponds; (3) the difficulty of imagining a submergence of 
 the loess-covered area of such character as to account for its pe- 
 culiarities ; for in a permanently standing body of water the uni- 
 formity of distribution of material of the given degree of fineness 
 characteristic of the loess could not be secured; (4) the reasonable 
 influence of vegetation in arresting wind-blown dust. Professor 
 Wright (55'^oj) gives some facts which seem to oppose the eolian 
 origin of the Mississippi valley loess: (i) The distribution of the 
 loess in about equal proportions upon both sides of the Missouri 
 
x - LOESS 567 
 
 River, as well as the presence of the loess where the prevailing 
 winds are least likely to pile it up. (2) The exclusive dependence 
 upon wind for the distribution of the loess leaves out of considera- 
 tion the difficulty of accounting on this basis for the extensive level- 
 topped terraces which frequently occur. (3) The agency of water 
 in the distribution of loess is favored by, or at any rate consistent 
 with, the fact that the loess is quite uniformly found to be thickest on 
 the margin of the streams flowing out of the glaciated region, and 
 that it is of somewhat coarser texture nearer the streams, thinning 
 out at a distance from them, and merging gradually into a more 
 clayey deposit. The stratification of the loess is also considered as 
 indicating deposition by water. Boulders and granitic pebbles have 
 been found in the loess on the Osage River, which can be accounted 
 for only on the supposition that they were 'carried there by floating 
 ice. The source of the material of the Mississippi Valley loess 
 seems to be in close connection with the deposits of the last glacial 
 period. This is shown not only by the distribution, but also by the 
 not infrequent interstratification of loess and marginal glacial drift 
 and till. The close relationship of the Asiatic and European loess 
 to the ice border has also been suggested, but for Asia this is at least 
 somewhat doubtful. Indeed, the source of a part even of the Amer- 
 ican loess is traceable to the nonglaciated arid regions of the west. 
 Our present knowledge of the character of the deposits desig- 
 nated loess leads to the conclusion that the source of the material 
 is various, being in part the dust blown from the deposits in front 
 of the ice sheet, in part the dust derived from deserts and steppes, 
 and in part the silt of river flood plains or other sources. The 
 glacial origin fits best the American and European, and the desert 
 origin the Asiatic deposits, but none are probably of simple char- 
 acter throughout. Though a marine origin has been advocated for 
 the loess by some writers, the consensus of opinion is that the loess 
 is a continental deposit. The evidence, further, points to the wind 
 as the chief agent in distribution, distribution by rivers being of 
 secondary importance. Deposition was for the most part upon dry 
 land, vegetation playing no doubt an important part in the separa 
 tion of the dust from the air, though rain also must be credited 
 to a certain extent with this function. It is, however, essentially 
 a steppe deposit. All such loess is practically without stratification. 
 Some loessic material was no doubt deposited in standing water 
 and more perhaps on river flood plains, but the totality of this was 
 far below that of purely eolian origin. Secondary reworking and 
 redistribution by wind, rivers and waves also occurred, and is going 
 on at the present time. To a certain extent this is also true of the 
 
568 PRINCIPLES OF STRATIGRAPHY 
 
 primary distribution and deposition of loess, for loess is forming to- 
 day in China and Central Asia, and in many other regions of the 
 world.* 
 
 Fossils and concretions in the loess. The fossils of the loess are 
 few and found only at intervals. They are for the most part shells 
 of land snails (Helix, Pupa, Succinea) and of pond and stagnant 
 water types (Planorbis, Paludina, etc.). Bones of land vertebrates 
 are, however, not uncommon in many loessial deposits, while stems 
 and roots of grasses and other plants, more or less replaced or 
 mineralized, are characteristic features in certain regions, espe- 
 cially in China. Curiously formed calcareous concretions known as 
 Loessmannchen, Loesspuppchen, or Loesskindel are also found in 
 many deposits of loess. These often occur in horizontal tiers, giv- 
 ing a semblance of stratification to the deposit. They are, however, 
 of secondary origin, and the arrangement is not necessarily indica- 
 tive of original stratification, but may represent successive levels of 
 ground water. An analysis of the concretions of the German loess 
 gave (Blanck-5) : 
 
 SiO 2 ................... 34-824 MgCO 3 ................. 1.890 
 
 A1 2 3 . K 2 ................... i .048 
 
 Fe 2 3 ' Na 2 ................... 1.202 
 
 CaO ................. . o . 203 P 2 O 5 ................... 0-157 
 
 CaCO 3 ................. 55-294 SO 3 .......... .......... 0.090 
 
 MgO .................. 0.178 H 2 ................... 0.377 
 
 Cenozoic and Mesozoic Loess-like Deposits, Deposits of this 
 type are probably more widespread than is realized at present. The 
 White River clays of Oligocenic age in western North America 
 have been regarded by W. D. Matthew (31) as probably of this 
 type, though the included sandstones are in part at least fluviatile 
 and in part perhaps dune sands. The chief characters stamping 
 these deposits as eolian loess are the fineness of their texture, the 
 lack of stratification and the absence of plants, fish or aquatic rep- 
 tiles or invertebrates, as well as the larger number of land mam- 
 mals. All of these characters are incompatible with the theory of a 
 lacustrine origin of these deposits commonly held for them. A loess- 
 like origin has also been suggested for the Harrison beds of Ne- 
 braska, a Miocenic formation. (Loomis-3o://.) Anemolutytes 
 comparable to the modern loess seem to be represented by the 
 Keuper marls of western Europe. These have been regarded as the 
 loessic deposits 'formed around the borders of the Triassic desert, 
 
 * For a comprehensive bibliography of the loess see Stuntz and Free (50) 
 pp. 124-140. 
 
ANCIENT LOESS-LIKE DEPOSITS 569 
 
 in which the New Red sandstone of Britain was accumulating, 
 partly at least as a sand-dune formation. (Lomas-29.) 
 
 Paleozoic Loess-like Deposits. Unstratified deposits of fine 
 and uniform-grained rocks, free from organic remains and having 
 a general loess-like character, are not uncommon in Palaeozoic and 
 later formations. As already noted, the Nunda or Portage sand- 
 stone of central New York, a formation of Upper Devonic age, has 
 the characteristics of a consolidated loess. This is especially seen 
 in the Genesee Valley near the type locality, where the rock for 
 considerable thicknesses shows a lack of stratification and a fine- 
 ness and uniformity of grain strongly suggestive of these charac- 
 ters in Pleistocenic loess. There is a notable absence of fossils, ex- 
 cept vertical tubes (Fucoides verticals), similar in many respects to 
 those found in more recent loess. The rock, furthermore, splits 
 with a decided vertical tendency, forming slabs of varying thick- 
 ness. This deposit was probably not formed far from the sea, and 
 was succeeded by normal marine sediments. 
 
 Certain portions of the St. Peter sandstone also appear to be 
 of this character, as shown by the fineness and uniformity of grain, 
 absence of stratification and splitting into vertical slabs. Much of 
 this sandstone appears, however, to be of dune origin, subsequently 
 in part reworked by a transgressing sea. 
 
 Many other Palaeozoic formations will probably prove on fur- 
 ther study to have a loess-like origin. This appears to be especially 
 so in the case of those fine-grained, nonstratified deposits which are 
 associated with continental formations of another type, such as 
 fluviatile beds, dune deposits, salt and gypsum beds, etc. Often such 
 loess-like deposits are of a red color, owing to the presence of iron 
 in the ferric oxide stage. The red Vernon shale of eastern New 
 York apparently furnishes a good example of this type of deposit. 
 This formation is of mid-Siluric age, and marks in the opinion of 
 many the beginning of a period of widespread continental sedimen- 
 tation under arid climatic conditions. This red shale in the Syra- 
 cuse area is followed by the salt deposits of Salina age. 
 
 The red color of this formation is due to the presence of de- 
 hydrated ferric oxide, of which 2.25 per cent, occurs in the entire 
 mass. Ferrous oxide of iron is present in small quantities (0.75 
 per cent.) (Miller-34:/5/). The iron is distributed in small quan- 
 tities, but with great uniformity throughout the mass. It is not im- 
 possible that, as Miller argues, the color was not originally red, but 
 yellowish, the iron being in the form of the hydrate. Subsequent 
 dehydration would produce the red color. In this connection it 
 is interesting to know that the ordinary yellow loess commonly con- 
 
570 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 tains a higher percentage of ferric oxide than that found in these 
 red lutytes. Thus of seven analyses of North American loess, the 
 lowest gave Fe 2 O 3 2.52% and FeO 0.31% and the highest Fe,O 3 
 5.22% and FeO 0.35%. Another had Fe 2 O 3 3.74% and FeO 
 1.02%. The average of the seven is 3.35% Fe 2 O 3 and 0.56% FeO. 
 (Clarke-io: 486.) It is thus seen that so far as the red color of 
 the Vernon shale is concerned it is due only to the anhydrous con- 
 dition of the ferric oxide, and not to the greater abundance of this 
 mineral. 
 
 FIG. 119. Cross-bedding in Sylvania Sandstone (Siluric). (After Sherzer 
 and Grabau). Scale i :6o. 
 
 Older Deposits of Dune Type. 
 
 Consolidated deposits showing the characters and structures of 
 dune sands have been obtained from many of the geological hori- 
 zons of the past, and closer attention to the structural details of 
 rock masses will probably reveal their presence in still other forma- 
 tions. Among Tertiary sandstones which have been regarded as 
 of this origin or show evidence pointing that way may be men- 
 tioned the Monument Creek beds of Colorado, while an example of 
 Cretacic sandstones of this type is found in the Nubian sandstone 
 of Egypt, though this is probably not of this character throughout. 
 Certain parts of the Dakota sandstone of the western United States 
 and of the Raritan formation of the east also must be mentioned. 
 Other examples will undoubtedly be found on closer study. In 
 the Jurassic of western North America occurs a sandstone of great 
 thickness and wide areal extent, which shows in a wonderful man- 
 ner the peculiar type of cross-bedding formed by migrating sand 
 
OLDER DUNE-LIKE DEPOSITS 
 
 57 1 
 
 dunes. This is the White Cliff sandstone of southern Utah, the 
 origin of which as a subaerial dune sand deposit can hardly be 
 questioned. 
 
 The Triassic shows many examples of dune sands, commonly 
 much iron-stained, though these are generally associated with fluvia- 
 tile and sometimes lacustrine deposits. They have been recognized 
 in both America and Europe. In the Triassic strata of England 
 and the Elgin sandstone of Scotland this eolian origin seems to be 
 well indicated. 
 
 In the Palaeozoic occur many deposits which bear the earmarks 
 of an eolian or dune origin. Among those that may be cited in this 
 connection are the white dune sands beneath the Magnesian lime- 
 stone of England and the similar beds of "Weissliegende" in Ger- 
 many; the Kanab and Colob formations (probably Permic) of 
 southwestern Utah and northwestern Arizona ; parts of the Old Red 
 sandstone of Britain ; and the Sylvania and St. Peter sandstones of 
 Siluric and Ordovicic age, respectively, in the United States. The 
 Sylvania sandstone may be taken as a typical example of this kind 
 
 FIG. 120. Cross-bedding in Sylvania Sandstone (Siluric). (After Sherzer 
 and Grabau.) Scale i :8o. 
 
 of deposit (Sherzer and Grabau-45 : 72). This rock consists of 
 well-rounded grains of quartz, of nearly uniform size, and seldom 
 carrying over 3 per cent, impurities, these being mainly calcium and 
 magnesium carbonates. In fineness, uniformity of size, roundness 
 of grain and purity of composition it outrivals the most typical 
 modern desert sands, such as are found in various parts of the 
 Libyan and Sahara deserts. Cross-bedding of the eolian type is 
 well developed, as shown by some of the accompanying sketches 
 (Figs. 119, I2oj. Altogether this deposit ranges in thickness up 
 to 300 feet, and is distributed over an area of more than six degrees 
 east and west longitude and four degrees north and south latitude. 
 It may be regarded as one of the best examples of a Palaeozoic 
 dune sand deposit known to us. 
 
572 PRINCIPLES OF STRATIGRAPHY 
 
 VOLCANIC DUST DEPOSITS. 
 
 As has been shown in an earlier chapter (II), the fine dust re- 
 sulting from explosive eruptions of volcanoes is carried far and 
 wide over the surface of the earth and becomes a part of many 
 widespread contemporaneous deposits. Of the 18 cubic kilometers 
 (4.3 cubic miles) of volcanic dust and cinders thrown into the air 
 on the explosion of Krakatoa in 1883, one-third fell at a distance 
 of more than 15 kilometers or 9.4 miles from the seat of disturb- 
 ance. At a distance of 1,000 miles from the volcano ashes still fell 
 inches deep. Shaler has estimated that not less than 300 cubic 
 miles of fine dust have been discharged by the Javanese and 
 Malayan volcanoes since 1770, and more than an equal quantity of 
 such dust has been thrown into the air by other volcanoes of the 
 earth during the same period. The settling of this material all over 
 the surface of the earth forms an important addition tp the eolian 
 rocks of the crust. 
 
 In character this volcanic dust consists of minute angular grains 
 of vitreous or glassy material, often showing by their curved form 
 that they are parts of the walls of glass bubbles. This material has 
 been recognized in deposits of various ages among the stratified 
 series of the earth's crust. Extensive deposits of anemopyrolutytes 
 and pyrarenytes have been found in the Tertiary of South America, 
 especially in Patagonia, where the remains of mammals are found 
 in it. Sinclair (47) has found that the Bridger (Eocenic) beds of 
 Wyoming are largely composed of such material, though cross- 
 bedded fluviatile deposits of sanidine and other sands are likewise 
 characteristic. The fine pyrolutyte of the Florissant basin is an ex- 
 ample of deposition of volcanic dust under playa lake or river flood 
 plain conditions with the entombment of many remains of terrestrial 
 organisms. Pyrolutytes and pyrarenytes are common in many 
 regions of the earth, but the conditions of their deposition are not 
 fully understood in most cases.* 
 
 SPECIAL INDICATORS OF EOLATION. 
 
 Rocks of terrestrial origin are not infrequently characterized by 
 the presence in their mass of wind-carved pebbles or glyptoliths.f 
 These are commonly dreikanter, and they indicate that for a time 
 at least the region containing them was above sea-level and subject 
 
 *See further under pyroclastic rocks, Chapter XII. t Woodworth, 533. 
 
CALCAREOUS ANEMOLITHS 573 
 
 to the sweep of the prevailing winds. These dreikanter may then be 
 buried in deposits of eolian,.fluviatile and even marine origin, but 
 only in the first case are they likely to be left in an undisturbed 
 position. 
 
 Besides being found in abundance in desert and semidesert areas 
 of to-day (see ante, Chapter II), they are also known from a 
 number of older deposits. They have been described by Walther 
 from the pre-Cambric Torridon sandstone of Scotland, and they 
 are not uncommon in the basal Cambric Eophyton sandstone of 
 Sweden. At the other end of the scale they are found in Pleisto- 
 cenic deposits of Germany and North America, where in some 
 cases, as at Cape Cod, Massachusetts, they are buried by subse- 
 quent fluviatile and eolian deposits in the position in which they 
 were formed. (Davis.) They have also been found in the Triassic 
 beds of England, where wind-corraded and polished surfaces, and 
 surfaces showing insolational flaking also occur. 
 
 Accumulations of pebble beds, especially where the pebbles are 
 covered with desert varnish, may in some cases also be traced to 
 extensive eolation, which removed all the finer material and subse- 
 quently buried the residual pebble beds under new accumulations 
 of eolian sands and dust. What seem to be pebbles of this kind 
 buried by dunes of oolites, which have since been changed to iron 
 appear at the base of the Siluric section in Wisconsin. 
 
 CALCAREOUS AND OTHER NONSILICEOUS EOLIAN SANDS. 
 
 Recent and Tertiary Examples. On Bermuda, where siliceous 
 material is wanting, the dunes are composed entirely of calcareous 
 material. This consists in part of fragments of shells and in part of 
 coral sand, while foraminiferal shells (Orbiculina, etc.) frequently 
 make up a considerable portion of the deposit. The older dune 
 sand of the islands has been consolidated into a hard rock (anemo- 
 calcarenyte, Bermudaite), which is locally known as "sandstone/' 
 though nearly pure calcium carbonate. Shells of Helix and Livona 
 are enclosed in this calcarenyte, the former a land shell, the latter 
 marine. These shells of Livona in some cases were carried into the 
 dune sand by the wind, but in others they were buried, together 
 with Area, Chama and Tellina, by the dunes which advanced over 
 the site on which they grew. Below the beds of calcarenytt are 
 finer layers, some of them calcilutytes, and, like the calcarenytes, 
 they generally show wind-drift structure and fine lamination. Eol- 
 ian limestones composed almost wholly of oolite grains are now 
 
574 PRINCIPLES OF STRATIGRAPHY 
 
 forming on the shores of Great Salt Lake in Utah, where oolites are 
 constantly developing through the activities of unicellular algae. 
 Eolian limestones in which the grains are Foraminifera and par- 
 ticles of shells may also be deposited by the wind many miles in- 
 land and often high above the level of the sea. These deposits are 
 stratified and cross-bedded and probably more common than gen- 
 erally assumed, since they are usually taken for marine deposits. 
 The absence of marine organic remains larger than those trans- 
 portable by wind, however, indicates their eolian origin, while the 
 presence of land animals is an additional piece of evidence. Lime- 
 stones of this type have been described from the coast of the 
 Arabian Sea (Evans-i4: $78-580), where they constitute the Milio- 
 litic formation, so called on account of the abundance of the for- 
 aminifer Miliola. The Junagarh limestone overlying the Deccan 
 trap in the Kathiawar Peninsula of western India is a typical ex- 
 ample of this kind of rock. It underlies the city from which it 
 takes its name, at a distance of about 30 miles from the sea, and 
 has a thickness probably exceeding 200 feet. It is mainly formed 
 of calcareous particles derived from shallow-water organisms of re- 
 cent types, each particle being ordinarily surrounded by an en- 
 velope of deposited carbonate of lime, the whole being bound to- 
 gether by a later cement of the same material. Interspersed with 
 the calcareous grains are minute mineral fragments derived from 
 the igneous rocks of the neighborhood, but they constitute only 
 from 6.5 to 12.5 per cent, of the whole. The limestone is divided 
 by horizontal planes into tiers 3 to 4 feet thick, the division planes 
 marking decided breaks in deposition. Between the planes the 
 lamination is very oblique and cut off abruptly, both above and be- 
 low, by the major division planes. Usually the inclination is differ- 
 ent on either side of the plane, the direction, which is generally to 
 the east, remaining constant, or varying even to reversal. The 
 angle of inclination with the horizontal may be anything up to 30, 
 and may vary from point to point of the same division of the rock, 
 though on the whole it is rather regular. 
 
 In other parts of the Kathiawar Peninsula similar conditions ex- 
 ist, and it has been found that the rock is purer in proportion to 
 its distance from the sea, along the border of which it is not infre- 
 quently mixed with much siliceous sand. (Fedden-i5.) Some- 
 times, as on the south coast of the peninsula, the beds are rubbly 
 and earthy f and in them have been found two specimens of Bulimus, 
 two of Helix and one of Cyclotus. On the coast, at Verawal, the 
 Miliolite limestone passes laterally into an open, porous, sandy rock, 
 made up very largely of organic fragments and minute organisms, 
 
EOLIAN LIMESTONES 575 
 
 resembling a raised beach in the vicinity. In the interior the "milio- 
 lite" is stated to occur "capriciously in the gorges of the hills or as 
 patches on their sides like remnants of a snowdrift," while .on 
 Chotila Hill it forms a fringe around the truncated top at a height 
 of 1,173 feet above sea-level. Other more siliceous deposits of this 
 type are known from Cutch, where they form a "concrete" on low 
 ground and at the foot of the hills bordering the Rann, with strong, 
 oblique bedding and with shells of the land snail Buliminus. 
 
 Limestones of the Junagarh type are also well developed on the 
 southeastern seaboard of Arabia, overlying the nummulitic lime- 
 stone or sometimes resting directly on the granite. These form 
 white-domed hills of calcarenyte of unknown thickness and from 
 100 to 200 feet above the level of the sea, extending inland as far 
 as the eye can reach. On the sea border they show scarps up to a 
 hundred feet in height. The rock contains hardly a fossil larger 
 than the size of the grains composing it, though in some localities 
 large shells of Hippopus and Ostrea, as well as corals, are abun- 
 dant in this rock up to 40 feet above sea-level, indicating former 
 submergence to that extent. A small quantity of hyaline quartz and 
 dark specks, probably hornblende, also occur. The calcareous par- 
 ticles are largely remains of minute Foraminifera. ( Carte r-8 :jj, 
 34.) The age of all of these limestones is not older than late Plio- 
 cenic ; indeed, some of them are forming now near the coast. The 
 Junagarh limestone is believed to have been formed from the ma- 
 terial blown inland from the coast, but Evans doubts if it has been 
 carried from the present coast 30 miles away. He holds rather that 
 at the time of the formation of this rock the peninsula stood some 
 150 feet lower than at the present day, and had the character of an 
 island or group of islands. 
 
 Microscopic examination of the foraminferal shells of the 
 Junagarh limestone by Dr. Frederick Chapman shows that they are 
 in most instances worn and polished apparently by eolian action. 
 At 30 miles from the sea the common or frequent forms are Milio- 
 lina trigonula (Lam), M. cf. oblonga (Montagu), Pulvinulina re- 
 panda (F. and M.), Nonionina communis (d'Orb), Polystomella 
 striatopunctata, Amphistegina lessonii (d'Orb). Other rarer 
 genera are Discorbina, Truncatulina, Rotalia and ( ?) Operculina. 
 Some Ostracoda were also present, much worn and polished. 
 
 The Montpelier limestones of Jamaica (Hill-23 : 737) may also 
 belong to this type. They have a thickness of 500 feet, and are 
 almost entirely composed of foraminiferal remains, especially Orbi- 
 toides, Nummulinae, and Miliolidae, all shallow- water forms. There 
 is, however, a total absence of macroscopic fossils, which, if the 
 
576 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 deposit is marine rather than eolian, is at least a surprising fact. 
 Extensive false-bedded limestones composed almost entirely of 
 comminuted marine shells and containing bones of land animals in 
 places occur near Cape Town in South Africa, and belong proba- 
 bly to this type of deposit. (Rogers and Schwartz-43.) Wind- 
 blown calcareous deposits of almost pure foraminiferal shells, and 
 consisting of subglobular Miliolinae and inflated Truncatulina loba- 
 tula, have been found on the Isthmus of Earawalla, between Dog's 
 Bay and Gorteen Bay, on the southwestern coast of Galway, Ire- 
 land. They form low dunes covering an area 1,000 yards from 
 northeast to southwest, and about 350 yards from bay to bay. Land 
 shells occur at intervals, but very few if any marine shells, except 
 such as appear to be derived from kitchen middens in the vicinity, 
 
 FIG. 121. Cross-bedding in Jurrasic oolites of Somersetshire, England. (After 
 De la Beche.) a, a, a, diagonal layers of broken shells, fish-teeth, 
 pieces of wood, and oolite grains, lying in plane of diagonal bed- 
 ding, b, b, b, b, mud layers. 
 
 or have been carried up by birds for food. The surface drift in the 
 North Atlantic, together with local currents, carries an abundance 
 of Foraminifera into Dog's Bay, where every high tide spreads 
 them over the gently sloping strand, together with small Gas- 
 tropoda. They dry rapidly and are carried landward by the wind, 
 the whole surface sometimes being in a state of rolling motion. 
 Foraminifera, Ostracoda, fragments of shells, etc., thus travel 
 across the isthmus, sometimes into the bay on the opposite side. 
 These organisms are not surrounded by an extra coating of lime, 
 as in the case of the Indian examples, probably because such chem- 
 ical deposition of lime is less characteristic of cooler climates. 
 
 Wind-carried Foraminifera have been found in the eastern 
 desert of Egypt, in the sands obtained near the foot of a gully in 
 the hills, about a mile west of the Gulf of Jemsa, on the western 
 side of the Red Sea. On the islands in the Red Sea no siliceous 
 sand is to be found, as a rule. The sands are calcareous, and are 
 chiefly formed from comminuted fragments of corals and shells, as 
 
EOLIAN LIMESTONES 
 
 577 
 
 on Gaysum Island, or of Foraminifera, as on the southern side of 
 Gaysum Island, where Orbitolites complanata is the predominant 
 form. 
 
 Older Examples. Some of the Jurassic oolites of Great Britain 
 appear also to belong in the category of wind-drifted calcareous 
 sands. De la Beche (3) figures a pronounced cross-bedding struc- 
 ture of the Forest marble (oolite) of Somersetshire, here repro- 
 duced. (Fig. 121.) The diagonal layers are "composed of broken 
 shells, fish teeth, pieces of wood and oolitic grains, sometimes mere 
 rounded pieces of shells, the various substances lying in the planes 
 of the diagonal layers, and presenting every appearance of having 
 been shoved or pushed over the more horizontal surfaces formed 
 
 FIGS. I22a and b. Cross-bedding of uniform-grained St. Louis limestone (cal- 
 carenyte), south of St. Louis, Mo. Scale 1:25. 
 
 during the intervals between the mud deposits." The cross-bed- 
 ding is rather more regular than that of wind deposits generally, 
 and suggests the torrential type. De la Beche states that the Bath 
 oolite of Somersetshire is likewise of this type, the rounded frag- 
 ments being drifted together with the true oolite grains. Accord- 
 ing to Evans (14:5^0), the grains of the Great Oolite often show a 
 worn character, suggesting abrasion by the wind, and he holds that 
 the false-bedded oolites which succeed the Stonesfield slates are not 
 improbably of eolian origin. Personal examination of a number of 
 these British oolites has convinced the author of their remarkable 
 resemblance to wind-drifted sands. The cross-bedding figured 
 above (Fig. 122), from the Mississippic calcarenytes of Missouri, 
 also suggests an anemoclastic origin for at least a portion of this 
 rock. 
 
 Possible application to the chalk beds. The remarkable com- 
 position and the structural characters of the White Chalk of west- 
 ern Europe have commonly arrested attention and given rise to 
 speculation regarding its origin and mode of deposition. At first 
 it was thought that the deep-sea Globigerina ooze forms a modern 
 analogue of this deposit, but when it was found that the foraminif- 
 eral shells composing the chalk were very largely of shallow-water 
 
578 PRINCIPLES OF STRATIGRAPHY 
 
 benthonic forms this hypothesis had to be given up. Nor would 
 the character of the adjacent deposits bear out such an interpreta- 
 tion. The absence of stratification in some parts and the fineness, 
 homogeneity, and uniform character of the deposit give it a loess- 
 like aspect. The fossil echinoderms and other macroscopic organ- 
 isms, which are found at intervals, suggest proximity to the sea, 
 with occasional inundations, though dead echini tests might readily 
 be blown inland as well. 
 
 The layers of flints in the chalk have a similar rude horizontality 
 to that assumed by the Loessmdnnchen in Pleistocenic structureless 
 loess, and like these are of secondary origin, and not necessarily 
 evidence of stratification. Such an arrangement may express rather 
 the periodic stand of the ground water as suggested by Potonie. 
 Where regular stratification and an abundance of macroscopic or- 
 ganisms are found, a submarine origin no doubt must be main- 
 tained. 
 
 Dunes of Gypsum. A remarkable type of dune sand has been 
 described from New Mexico. This is the white sand of Otero 
 county which forms a tract of dunes of nearly pure granular gyp- 
 sum covering an area of about 350 square miles. The gypsum sand 
 is derived from the "ribs" of gypsum which rise above the salt flats 
 in successive ridges. These gypsum beds belong to the Red bed 
 series of Permic age. The action of the elements soon breaks up 
 the exposed gypsum crystals into small grains, which are carried 
 away by the wind and piled up into dunes. The salt and alkaline 
 salts forming on the surfaces of the salinas are also driven with the 
 gypsum, but on account of their solubility do not remain in the 
 dunes. (Herrick-22.) 
 
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 52. WALTHER, JOHANNES. 189.1. Die Denudation in der Wuste und 
 
 ihre geologische Bedeutung. Abhandlungen der koniglich sachsischen 
 Gesellschaft der Naturwissenschaften. Bd. XVI, pp. 347-569. 
 
 53. WALTHER, J. 1900. Das Gesetz der Wustenbildung in Gegenwart und 
 
 Vorzeit, Berlin. 2nd edition, 1912, Leipzig. 
 
 53a. WOODWORTH, J. B. 1894. Post-Glacial Eolian Action in Southern 
 New England. American journal of Science, 3rd ser. Vol. XLVIII, 
 pp. 63-71. 
 
 54. WRIGHT, G. FREDERICK. 1902. Origin and Distribution of the Loess 
 
 in Northern China and Central Asia. Bulletin of the Geological Society 
 of America, Vol. XIII, pp. 127-138. 
 
 55. WRIGHT, G. F. 1904. Evidence of the Agency of Water in the Distri- 
 
 bution of the Loess in the Missouri Valley. American Geologist, Vol. 
 XXXIII, pp. 205-222. 
 
 56. ZITTEL, KARL A. VON. 1883. Beitrage zur Geologic und Palaeontologie 
 
 der Libyschen Wuste. Palaeontographica, XXX. 
 
CHAPTER XIV. 
 
 ORIGINAL STRUCTURE AND LITHOGENESIS OF THE CONTI- 
 NENTAL HYDROCLASTICS. 
 
 A very large, perhaps the largest, portion of the stratified elas- 
 tics of the earth's crust consists of water-laid deposits, or hydroclas- 
 tics. By this is not meant that they were deposited in standing 
 water, though this is true of a large portion of them, but that water 
 was influential in the making of the deposit. They therefore include 
 river-laid elastics as well as those formed in the sea or in lakes. 
 
 Hydroclastic rocks may be divided into the following groups : 
 
 1. Stream or river-laid elastics (potamoclastics). 
 
 2. Lake or lacustrine elastics (limnoclastics). 
 
 3. The Delta a transitional deposit. 
 
 4. Marine elastics (haloclastics). 
 
 Each of these will admit of a number of subdivisions. The 
 potamoclastics and limnoclastics, together with the atmoclastics, 
 anemoclastics, pyroclastics, and autoclastics belong to the continen- 
 tal or terrestrial type of elastics, as opposed to the marine or halo- 
 clastics. Seacoast deltas form the transition from the one to the 
 other. The continental hydroclastics, together with the delta de- 
 posits, will be considered in this chapter; the marine hydroclastics 
 being reserved for the next. 
 
 RIVER-LAID CLASTICS, OR POTAMOCLASTICS. 
 
 All along the river course, from near the head to the mouth, 
 clastic deposits may be forming, their character and amount vary- 
 ing with the character of the stream and its environment. Under 
 the latter, the kind of rock material and climate must be mentioned 
 as all-important controlling factors. The amount of weathered 
 rock material available for transport and final deposition is also 
 of the greatest importance. We may consider the clastic river 
 deposits under the following headings: 
 
 582 
 
RIVER-LAID CLASTICS 583 
 
 a. Alluvial fans. 
 
 b. Flood plains. 
 
 c. The playa a temporary expanse of certain rivers. 
 
 Considering" the classes of streams mentioned in Chapter III 
 (p. 129), it may be noted that the deposits of consequents and inse- 
 quents are essentially alike, those of overflow streams may be 
 neglected as insignificant, but deposits of glacial streams, from their 
 abundant supply, are of the greatest importance. Only the residual 
 clays of subterranean streams need to be considered. 
 
 a. ALLUVIAL FANS. Wherever the debris-laden stream leaves 
 its steep mountain bed and debouches upon the piedmont belt, or 
 the floor of a large valley, it changes from a degrading stream, or 
 one just at grade, to an aggrading stream, since the change in the 
 angle of the river bed brings with it decreasing velocity of the 
 current. In its steeper development the alluvial fan grades directly 
 into the talus and other atmoclastic deposits with which, indeed, it 
 forms a continuing sedimentary series, the river portion often being 
 difficult to separate from the purely atmoclastic type. 
 
 Form and Extent of Modern Alluvial Fans. In extent alluvial 
 fans vary from an area of only a few square feet to one covering 
 thousands of square miles. Small alluvial fans are best described 
 as semi-cones with a surface slope which may be as high as 20 
 or even 30. As the fan increases in size its surface angle is 
 lowered, until, in the very large deposits of this type, the surface 
 seems almost to be horizontal. Small cones are seen to rise regu- 
 larly toward the notch in the hills through which the river de- 
 bouches, but in the very large alluvial fans there may result a con- 
 fluence of many adjoining deposits, which will obliterate the effects 
 of regularity. On all large fans, whether simple or confluent, ero- 
 sion channels abound, for the streams building the deposits divide 
 near the head of each fan into numerous distributaries, each of 
 which, when not depositing, will be eroding. Thus a succession of 
 contemporaneous erosion surfaces will result, and later beds will 
 be deposited on the eroded surfaces of the older. In this manner 
 the effect of a disconformity may be repeatedly produced within 
 the depositional unit, and such apparent disconformities might lead 
 to grave misinterpretations of the age and relationships of the ad- 
 joining beds. Should, by subsidence, the sea cover such an alluvial 
 fan of great extent, a decided break would appear between the non- 
 marine and marine strata, the latter gradually encroaching by over- 
 lap upon the eroded surface of the old subaerial fan. 
 
 Among the large alluvial fans or dry deltas of modern times 
 
584 PRINCIPLES OF STRATIGRAPHY 
 
 may be mentioned that of the Merced in California, of the Garonne 
 at the northern base of the Pyrenees, the delta of the Cooper River 
 in the Lake district of South Australia, the great flood plain delta 
 of the Huang-ho or Yellow River of China, and the similar but 
 compound Indo-Gangetic delta plain of northern India. 
 
 The Merced River of California rises in the Sierra Nevadas and 
 carries much waste down their steep western slopes. Reaching the 
 broad open valley of California, which lies between the Sierra and 
 the Coast range, it has built a fan which at present has a radius 
 of about 40 miles. This consists of gravel near the mountain, and 
 of fine silt at a distance. On account of the gentle slope of the 
 surface, the water is turned readily from one channel into the other 
 at the head of the fan. 
 
 "The many rivers issuing from the valleys of the Sierra Ne- 
 vada and the Coast range upon the 'Valley of California' have 
 formed an extensive plain, of which the Merced fan, ... is 
 only a part. The successive fans are so broad and flat that their 
 slightly convex form can hardly be recognized without the aid of 
 surveying instruments. Nearly all the streams run in shallow chan- 
 nels, but little beneath the gently sloping surface of the fans. The 
 fans from the east and west meet in a broad, flat-floored trough." 
 
 River-made plains of this type are formed on both sides of the 
 Alps. Those on-^the south have begun to cut valleys into the old 
 deposits, while those on the north have cut to a depth of 1,000 feet, 
 leaving the former plain as a series of ridges. The river Po flows 
 eastward between the broad plain built by the rivers from the high 
 Alps on the north, and the narrower one built by the streams from 
 the lower Apennines. Where it enters the Adriatic Sea the Po 
 builds a normal delta. 
 
 While the material of this river plain is typically a subaerial 
 deposit, intercalated marine beds are not wanting. They have been 
 reported from the Venetian region where they represent periodic 
 encroachment of the sea. (Penck-4i.) 
 
 One of the most extensive of modern dry deltas is that of 
 Cooper Creek in the Lake district of South Australia. Its area is 
 more than twice that of the Nile delta, its length being nearly 185 
 miles and its width over 170 miles. The water in the river, how- 
 ever, is abundant only after strong rains, the. various distributaries 
 being changeable canals on the surface of the delta. (Peter- 
 mann-43.) 
 
 Even larger than the Cooper Creek alluvial fan is that of the 
 Huang-ho or Yellow River of China. Its head is about 300 miles 
 
ALLUVIAL FANS 585 
 
 from the present shore, and has an elevation of only 400 feet above 
 sea-level. It has thus an average fall of \y$ feet per mile, a slope 
 so gentle that it k imperceptible. Along the coast the fan extends 
 from near Pekin southward for about 400 miles to where it joins 
 the great plains of the Yang-tse-kiang, being interrupted, however, 
 by the mountainous province of Shantung. 
 
 Owing to the very gentle slope of the fan the overflow at its 
 head and the corresponding diversion of a distributary will result 
 in the inundation of vast areas. The mouth of the river has 
 been shifted more than 200 miles north or south, such shiftings 
 having been numerous during Chinese history. "The flood of 1887 
 covered an area estimated at 50,000 square miles, immensely fertile 
 and swarming with villages. The number of people drowned was 
 at least a million and a greater loss followed from famine and 
 disease caused by the flood." (Davis-i8:^po.) Flood plain fans 
 of this type thus furnish excellent examples of the manner of 
 destruction and burial by river silts of terrestrial organisms, and 
 they further illustrate how peat deposits in swamps may be buried 
 to be converted in the course of time into coals. The material 
 carried by the Yellow River is mostly fine silt derived from the 
 loess in the interior, which from its color gives the name to the 
 river. The fineness of the material accounts in part at least for 
 its very gentle slope, for it can be carried to great distances before 
 it settles out. 
 
 Growing steadily but slowly seaward it is, of course, inevitable 
 that marginal marine deposits should be enclosed in the growing 
 fan. Very slight depression of the land would cause a partial 
 flooding by the sea, with accompanying marine deposits. In its sea- 
 ward growth the great delta has annexed the former rocky island, 
 which is now the Province of Shantung. 
 
 The Indo-Gangetic alluvial plain is an example of a river plain 
 formed of many confluent dry deltas and carried -forward by the 
 two great rivers of northern India the Indus on the west and the 
 Ganges, with the tributary Brahmaputra, on the east. Numerous 
 small streams feed these rivers from the south slope of the Hima- 
 layas, carrying an abundance of coarse and fine debris. (Old- 
 ham-4O.) The great alluvial plain extends over an area of about 
 300,000 square miles, and comprises the richest and most populous 
 portion of India. It varies in width from 90 to nearly 300 miles, 
 and entirely separates the lower peninsula of India from the Hima- 
 layas to the north. It rises 924 feet above the sea in its highest 
 portion, and the deepest boring has located these deposits at a depth 
 of nearly a thousand feet below the present sea-level. This is at 
 
586 PRINCIPLES OF STRATIGRAPHY 
 
 Lucknow, which lies approximately midway between the Indus and 
 the Ganges headwaters and about 370 feet above sea-level. It 
 abounds in gravels and conglomerates near the slbping borders, but 
 lutaceous or clayey deposits, more or less arenaceous, prevail over 
 much of the plain, especially near the center, with only subordinate 
 deposits of sand, gravel, and conglomerates. Beds of blown sand 
 of great thickness are found in some regions. Pebbles are scarce 
 at a distance of more than twenty or thirty miles from the enclosing 
 hills. Shells of river and marsh molluscs are occasionally found, 
 and calcareous concretions and nodules of irregular shape, locally 
 known as kankar, are frequent. "The more massive forms 
 are a variety of calcareous tufa, which sometimes forms thick beds 
 in the alluvium and frequently fills cracks in the alluvial deposits, 
 or in older rocks." (Oldham-4o:^J7.) Calcareous tufas also form 
 conglomerates in the stream beds by cementing pebbles derived from 
 the hills. In the clays along the borders and in the shoals of the 
 Jumna River a great variety of vertebrate remains has been found, 
 including elephant, hippopotamus, ox, horse, antelope, crocodile, 
 and various fish. Borings in other regions revealed the presence of 
 peat, forming extensive beds to a depth of 20 to 30 feet below 
 the surface, while a layer of stiff blue clay 15 feet in thickness was 
 found 10 feet below the surface at Calcutta. Clay and variegated 
 sand with calcareous concretions, mica and small pebbles alternated 
 to a depth of 120 feet, below which a quicksand was found. At 
 152 feet this became dark and coarse of grain and intermixed with 
 red water-worn nodules of hydrated iron. At 159 feet a stiff clay 
 was found which, at. 163 feet, became friable and contained much 
 vegetable and ferruginous matter. Lower still fine and coarse sands 
 alternating with clays occur, while at 340 feet a ruminant bone 
 was found, and pieces of tortoise shell at still greater depth. Three 
 hundred and ninety-two feet below the surface pieces of coal, such 
 as are found in the mountain streams, and fragments of decayed 
 wood were found in the sand, while below 400 feet sand and 
 shingle of fragments of primary rocks abounded. The borings 
 also showed wood, remains of terrestrial mammals, fluviatile reptiles, 
 and fresh-water molluscs. No traces of marine fossils have been 
 found. The presence of earthy limestones in these deposits is of 
 especial interest, because it shows that limestones do not necessarily 
 indicate lacustrine or marine conditions. As already noted, in 
 northern Mexico and other tropical regions of America, a super- 
 ficial crust of white lime, often free from foreign material, is 
 formed. This material, called tepetate, has been dissolved from 
 the limestones of the surrounding region, transported in solution by 
 
WASTE-FILLED BASINS 587 
 
 the streams, and then redeposited by evaporation. (Hill and 
 
 Basins Filled by River-Washed Waste. There are many ex- 
 amples of great basins surrounded by mountains and filled to a 
 certain extent by the waste washed from the mountains. The 
 larger of these basins are generally formed by tectonic movements, 
 the process being a downwarping. An example of such a valley 
 holding a "waste lake" is the upper Arkansas valley, back of the 
 Front Range of the Rocky Mountains. As the basin was forming 
 by warping, the rivers deposited their load on its floor, while at the 
 same time the outlet of the Royal Gorge was being cut through the 
 Front Range. The plains of waste within the basin slope forward 
 from the mountainsides, but they have been only slightly dissected 
 so far. Another excellent example is found in the Vale of Kash- 
 mir, enclosed by the front and middle ranges of the Himalayas in 
 northwest India. In area this vale equals that of the Connecticut, 
 being elliptical in form, a hundred miles long from southeast to 
 northwest, and forty or fifty miles broad. It is formed by a down- 
 warping between two lofty mountain ranges, which, for the most 
 part, have very steep sides. The floor of the valley is deeply 
 filled with river-laid waste, coarse near the mountains, but free 
 from pebbles at the center. Its depth is measured probably by thou- 
 sands of feet, while its surface elevation is more than 5,000 feet 
 above sea-level. Across this plain meanders the Jhelam River, 
 which escapes by a deep gorge through the enclosing mountains. 
 Southern Europe furnishes another good example of a waste- 
 floored basin in the oval plain of Hungary, which has a diameter of 
 about 200 miles. Gravelly, sandy and loamy materials brought by 
 the rivers from the enclosing mountains have formed this plain, 
 which rises slightly toward the mountains, where it is formed of 
 gravels, while the level center is a fine silt plain, resembling an 
 abandoned lake bottom. The Danube and its tributaries meander 
 through it and escape by the deep gorge of the Iron Gate cut 
 through the Transylvanian Alps. 
 
 A somewhat similar basin lies in southwestern Wyoming, 
 within the embrace of a series of mountain ranges, the Wasatch on 
 the west, the Uinta on the south, and the Wind River Ranges on 
 the north and east. The Green River flows through this basin and 
 escapes by a deep canyon through the Uinta Mountains. The 
 original deep filling of waste material has now been extensively 
 trenched by the rivers and converted into a dissected upland, with 
 valleys cut into the old waste deposit, in some cases a thousand feet 
 
588 PRINCIPLES OF STRATIGRAPHY 
 
 deep. Other waste basins of this kind are found in Spain, Italy, 
 and elsewhere. 
 
 In arid regions the basins often have an inward drainage and 
 are filled by the combined atmoclastic creep and the river wash. 
 Fans with their heads rising 500 feet or more above their bases 
 and extending 10 or 15 miles outward characterize such basins. 
 The water of the stream evaporates or sinks into the ground be- 
 fore the center of the basin is reached. When such fans become 
 confluent they form huge waste plains of relatively steep grade, 
 filling the valleys and partly burying the mountain slopes. In Utah, 
 Nevada, and Arizona depressions of great depth have thus been 
 wholly filled, while the waste mantle backs up 2,000 or 3,000 feet 
 on the mountain flanks. 
 
 "A great part of Persia consists of large basins enclosed by 
 mountains and without outlet to the sea. Long waste slopes stretch 
 forward 5 or 10 miles with a descent of 1,000 or 2,000 feet, stony 
 near the mountain flanks, and gradually becoming finer-textured 
 and more nearly level. The central depressions are absolute deserts 
 of drifting sands, with occasional saline lakes or marshes. 
 
 "Central Asia repeats the same conditions on a still larger scale. 
 The basin of eastern Turkestan includes many half buried ranges 
 in its central part. It is quite possible that some ranges are com- 
 pletely covered with waste. Many rivers flowing from the moun- 
 tain rim wither on their way toward the chief central depression ; 
 only the largest river (Tarim) reaches it, there spreading out in 
 Lob (Lake) Nor. The chief settlements are near the border of 
 the basin, where the larger rivers come out from the mountains." 
 (Davis-i8:ju.) 
 
 The deposits of these regions must be considered as in part at 
 least of purely atmoclastic and anemoclastic origin. 
 
 RIVER FLOOD PLAINS. River flood plains vary enormously in 
 extent as well as in the character of the material. Streams with 
 relatively steeply sloping beds may have stony flood plains, if they 
 are abundantly supplied with coarse detritus from the head and 
 sides. The flood plain of the Saco in the Intervale is covered with 
 rounded cobbles and boulders, these often forming a regular cobble- 
 stone pavement. The stream is a rushing one, and in flood carries 
 away all the finer material. A large part of the boulders and 
 cobbles is formed of the granite of which this part of the White 
 Mountain region is composed, but a part of the material at least 
 is derived by the rehandling of flood-plain deposits formed during 
 the preceding flooded stage period controlled by the melting ice of 
 the glacial period. 
 
FLOOD PLAIN DEPOSITS 589 
 
 Flood plains of streams of less velocity are made up of fine 
 materials left by the river when it overflows its banks. As most of 
 the deposit is formed near the river the banks on either side are 
 higher than the surface of the plain away from it, there being thus 
 a gentle slope away from the river. In this way the natural levees 
 of the Mississippi are built, which rise considerably above the level 
 of the "back swamps" on either side. Here the slope away from 
 the river east or west is 5 or 10 feet to the mile, while the general 
 southward slope of the entire flood plain is under half a foot to 
 the mile. 
 
 A striking example of a flood plain is afforded by that of the 
 Nile, which flows from a well-watered region through a desert 
 country without receiving a tributary for a thousand miles, except 
 a few small wet weather streams. Entrenched beneath the desert 
 uplands this flood plain holds its own for a length of 500 miles, 
 and maintains a width of from 5 to 15 miles, broadening on the 
 delta to over 100 miles. The annual inundation of the flood plain 
 is caused by the northward movement of the belt of equatorial rains 
 in summer. The flood begins in June and usually rises 25 feet or 
 more at Cairo in the late summer or early autumn. The annual 
 addition of the river silt causes a slow rising of the entire flood 
 plain estimated to amount to 4^ inches a century. 
 
 This region furnishes an instructive example of widely varying 
 contemporaneous deposits within the same general area. On the 
 one hand occur the drifting, cross-bedded, well rounded and pure 
 quartz sands of the desert, and, on the other, the extremely fine, 
 well-stratified muds of the river flood plain. Both enclose the re- 
 mains of organisms or of structures built by man, but there is an es- 
 sential difference between the remains found in each deposit. Aside 
 from ruins of human habitations and other works of man, only 
 occasional remains of animals which were adapted to a dry climate 
 are preserved in the desert sands. These, on the whole, will be 
 rare because burial is often a slow process, and the bones of the 
 dead creatures will crumble unless quickly covered. On the flood 
 plain, on the other hand, aquatic organisms abound, giving a 
 totally different faunal as well as floral association. According to 
 the rash doctrine of the persistence of lithologic units, recently 
 advocated by some geologists, such contemporaneous deposits would 
 be interpreted as of different ages. 
 
 From the nature of deposits on river flood plains, perfect and 
 often very fine stratification is to be expected. This may be con- 
 sidered as characteristic of typical flood plains. 'The plains of the 
 Po and of the Ganges and the great fan of the Huang-ho are very 
 
590 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 largely composed of fine sediments; the proportion of fine to coarse 
 materials in the extensive deposits of these rivers seems to be 
 greater than it is in many of the so-called lake beds of the west 
 [of North America]." (Davis-iQ 1361-362.) 
 
 River flood plains consisting of fine material are especially 
 adapted for receiving the transit impression of organisms as well 
 as sun-cracks, rain-drop impressions, etc. Indeed, almost the only 
 known modern examples of such structures commonly referred to 
 seashore origin are found on river flood plains or on the surfaces 
 of the playas. 
 
 Another feature characterizing many river flood plains is the 
 levelness of their surfaces, which argues well for the close approxi- 
 mation to horizontality of their strata. Many minor irregularities 
 
 FIG. 123. Torrential type of cross-bedding ; seen in modern torrential de- 
 posits. (After Hobbs.) 
 
 will, of course, be found, such as shallow channels, filled by later 
 deposits and other evidence of contemporaneous erosion. 
 
 Cross-Bedding of Torrential Sediments. Whenever sands and 
 gravels are spread by torrential floods, diagonal or cross-bedding on 
 a large scale will result. Between the nearly horizontal layers of 
 finer sands or gravels occur beds inclined at a nearly uniform and 
 relatively large angle with the enclosing layers. Successive cross- 
 bedded strata will have their beds slope in the same direction, 
 which is that of the stream producing them. Such a type of cross- 
 bedding is wholly inconsistent with the theory of wave formation 
 or of currents in a body of water. It has been observed in modern 
 torrential deposits (Hobbs~3i '.291), and is a characteristic feature 
 of many ancient sandstones and conglomerates, the torrential origin 
 of which it indicates (Fig. 123). It is not an infrequent structure 
 in the torrential deposits of the terminal moraine on Long Island. 
 (See further, Chapter XVII.) 
 
 Thickness and Composition of River Deposits. The thickness 
 
TORRENTIAL DEPOSITS 591 
 
 of river deposits is practically unlimited, and depends on the source 
 of supply of material and the depth of the valley in which it is 
 deposited. Where downwarping of a piedmont belt occurs, so as 
 to form a geosyncline, the thickness of the formation may become 
 enormous. Torrential deposits in .Calabria, Italy, have been found 
 1,500 feet or more in thickness and including boulders of many 
 petrographic types, often exceeding a foot in diameter. The Al- 
 hambra formation of Spain is at least 1,000 feet thick and consists 
 mainly of river deposited pebbles distinctly water worn and varying 
 in size from a fraction of an inch to six inches or more "in length. 
 Some of the partly dissected, but still unconsolidated torrential 
 deposits fringing the Front Range of the Rocky Mountain region 
 contain boulders many feet in diameter. Some torrential deposits 
 may be entirely composed of rounded boulders with only enough 
 sand and fine gravel to fill the interstices. Portions of the Old Red 
 sandstone of Scotland furnish splendid examples of fossil boulder 
 beds of this kind. 
 
 The Siwalik formation of India furnishes an excellent example 
 of a sub-recent fluviatile deposit of great thickness. It skirts the 
 southern border of the Himalayas, forming the Siwalik Hills. The 
 strata have been uplifted by the latest movement in this region and 
 exposed by erosion. The thickness of the formation is upward of 
 15,000 feet, and, except at the base, where it is characterized by 
 passage beds from the underlying marine Sirmur group, it is of 
 non-marine origin throughout. In age it is said to range from 
 Miocenic to Quaternary, though most of it belongs to the Pliocenic. 
 In this formation "sandstone immensely predominates . . . 
 and is of a very persistent type from end to end of the region and 
 from top to bottom of the series. Its commonest form is indis- 
 tinguishable from the rock of corresponding age known as Molasse 
 in the Alps, and is of a clear pepper and salt gray, sharp and fine in 
 grain, generally soft, and in very massive beds. The whole Middle 
 and Lower Siwaliks are formed of this rock, with occasional thick 
 beds of red clay and very rare thin, discontinuous bands and 
 nodules of earthy limestone,, the sandstone itself being sometimes 
 calcareous and thus cemented into hard nodular masses. . . . 
 In the Upper Siwaliks conglomerates prevail largely; they are often 
 made up of coarsest shingle, precisely like that in the beds of the 
 great Himalayan torrents. Brown clays occur often with the con- 
 glomerate, and sometimes almost entirely replace it. This clay, 
 even when tilted to the vertical, is indistinguishable in hand speci- 
 mens from that of the recent plains deposit ; and no doubt it was 
 formed in a similar manner, as alluvium. The sandstone, too, of 
 
592 PRINCIPLES OF STRATIGRAPHY 
 
 this zone is exactly like the sand forming the banks of the great 
 rivers, but in a more or less consolidated condition." (Medlicott 
 and Blanford-38:5^.) The fossils of this formation are of fresh 
 water or of terrestrial types exclusively, and they, as well as the 
 nature of the deposit, point the- continental origin of this forma- 
 tion. 'The mountain torrents are now in many cases engaged in 
 laying down great banks of shingle at the margin of the plains, just 
 like the Siwalik conglomerates ; and the thick sandstones and sandy 
 clays of the Tertiary series are of just the same type of form and 
 composition as the actual deposits of the great rivers." (Medlicott 
 and Blanford.) 
 
 In the Salt Range of the Punjab these alternating gray and 
 greenish sandstones and the red and light brownish orange clays 
 "are from seventy to a hundred and twenty feet in thickness, be- 
 ing very frequently about a hundred feet each, but some zones 
 are much thicker." (Wynne-62 :io8.) 
 
 Depth of Compound Continental Deposits. The great amount 
 of material which may accumulate in deserts as the product of 
 combined creep, torrential and eolian deposit is seen from a well 
 boring near Ashkabad, Turkestan (Walther-57 1/05), which pene- 
 trated sands, clays and gravels to a depth of 666 meters without 
 finding rock bottom. No organic remains were found, and the 
 character of the material is similar to that of the surface deposits 
 of the Transcaspian desert, from which it is inferred that this entire 
 mass of over 2,000 feet of sediment accumulated under climatic 
 and topographic conditions similar to those now prevailing. 
 
 Chatter or Percussion Marks. A characteristic feature of many 
 boulder or cobblestone deposits of modern time as well as of 
 former periods is the presence of numerous crescentic chatter or 
 percussion marks on the finer grained and well-rounded pebbles, 
 especially porphyries, quartzites, and the like. These have much 
 the form and size of impressions made by the end of a finger nail 
 in soft clay, and are due to the violent impact of one rounded 
 pebble or boulder upon another. Such marks are plentifully pro- 
 duced by the impact, one upon another of the hard, fine-grained 
 pebbles used for grinding in the revolving cylinders of cement mills 
 and other works. 
 
 Organic Remains in Torrential Deposits. On the whole, or- 
 ganic remains will be few or absent in coarse torrential deposits. 
 Even tough masses of wood will be shattered and completely anni- 
 hilated. As a result, such deposits will be free from organic re- 
 mains, though, of course, with increasing fineness of the sediment 
 the possibility of the preservation of such remains increases. Since 
 
ORGANIC REMAINS IN RIVER DEPOSITS 593 
 
 in semi-arid regions violent floods arise abruptly, sweeping down 
 the previously almost dry river beds, and converting them in a 
 few minutes into raging torrents, it is apparent that organisms may 
 be surprised and suddenly overwhelmed and their remains entombed 
 in the resulting deposits of the flood. We need only recall such 
 disasters as that which recently befell a transcontinental railroad 
 where the sudden flooding of a previously dry wadi swept away 
 a trestle and its load of cars, these with their luckless passengers 
 being buried in the sand and silt of the lower course of the stream. 
 The many unrecorded entombments of cattle and other creatures 
 by just such sudden floods would, if known, form adequate illus- 
 trations of the origin of many-fossiliferous sandstones of the past. 
 
 One of the chief causes of the destruction of animal life on 
 plains of subaerial deposition is found in the periodic droughts 
 affecting these regions. The geologic effects of such droughts 
 have been noted in many tropical countries, especially along the 
 west coast of Africa, in India, and in South America. Darwin 
 (17) has described the "gran seco" or great drought which occurred 
 between the years 1827 and 1830, when, in the northern part of the 
 province of Buenos Ayres (South America) and the southern part 
 of St. Fe, vast numbers of birds and animals perished, the vegeta- 
 tion withered and died, and the brooks became dry, until finally 
 the whole country was turned into a dusty, waterless waste. Dar- 
 win writes : "A man told me that the deer used to come into his 
 courtyard to the well, which he had been obliged to dig to supply 
 his own family with water; and that the partridges had hardly 
 strength to fly away when pursued. The lowest estimation of 
 the loss of cattle in the province of Buenos Ayres alone was taken 
 at one million head. A proprietor at San Pedro had previously 
 to these years 20,000 cattle, at the end not one remained. 
 
 "I was informed by an eye-witness that the cattle in herds of 
 thousands rushed into the Parana, and being exhausted by hunger 
 they were unable to crawl up the muddy banks and thus were 
 drowned. . . . Without doubt several hundred thousand ani- 
 mals thus perished in the river : their bodies when putrid were * 
 seen floating down the stream; and many in all probability were 
 deposited in the estuary of the Plata. All the small rivers became 
 highly saline, and this caused the death of vast numbers in particu- 
 lar spots; for when an animal drinks of such water it does not 
 recover. . . . Subsequently to the drought of 1827 to '32 a 
 very rainy season followed which caused great floods. Hence it is 
 almost certain that some thousands of the skeletons were buried by 
 the deposits of the very next year." Darwin adds very pertinently, 
 
594 PRINCIPLES OF STRATIGRAPHY 
 
 "What would be the opinion of a geologist, viewing such an enor- 
 mous collection of bones, of all kinds of animals and of all ages, 
 thus embedded in one thick earthy mass? Would he not attribute 
 it to a flood having swept over the surface of the land, rather than 
 to the common order of things?" (Darwin-i7, Chapter vii.) 
 These droughts are of frequent occurrence and seem to show an 
 approximate periodicity of about fifteen years. 
 
 Distances to Which Material May Be Carried by Rivers. Wade 
 (55), in his study of the distribution of the gravels derived from 
 the hills of igneous rock facing the western border of the Red 
 Sea, comes to some interesting conclusions regarding the distance 
 to which pebbles may be transported by subaerial agencies. On the 
 eastern side of these ranges the fragments have traveled only a 
 short distance, lying still in the plains at the foot of the hills. On 
 the western side of the Red Sea ranges the gravels appear to have 
 been carried along the main wadis and old lines of drainage* of ten to 
 great distances. "The pebbles have traveled in more or less westerly 
 directions down the wadis, into the important north-and-south wadi 
 which continues the line of the Nile north from Quena. They are 
 abundant for some distance north and south of Quena. Thence 
 they have been carried northward down the Nile Valley. . . . 
 The most interesting occurrences of the rocks, which the Survey 
 geologists say 'could only come from the Red Sea' are at Heluan, 
 a few miles south of Cairo . . . and in the Delta itself, where 
 they were found in the Royal Society's boring at Zagazig. Thus 
 these rocks have been river-borne for at least 400 miles." (Wade- 
 55:^44.) The age of these gravels is Pleistocenic. 
 
 Extensive deposits of apparently river-borne pebbles are found 
 in many older formations. In the Trias of England they have been 
 found 300 miles from their source. The Pottsville conglomerate 
 series of eastern North America extends northwestward for a dis- 
 tance of 400 miles or more, the pebbles of the series throughout be- 
 ing derived from the Appalachians on the southeast. 
 
 Purity and Rounding of Fluviatile Deposits. On the whole, the 
 material of a subaerial fan is very heterogeneous, but by prolonged 
 reworking and the sorting action of running water a considerable 
 assortment into kinds as well as sizes of grain may be effected. 
 In dry climates the disintegration of granitic rocks is not accom- 
 panied by extensive decomposition. Fresh feldspar crystals will 
 remain, and these may be rounded by wind attrition. (Wade-55.) 
 In moister climates, on the other hand, feldspar will decay, forming 
 kaolin or laterite, and by deflation or by flotation these products of 
 finer grain will be swept away. 
 
RIVER PEBBLES 595 
 
 Form of River Pebbles. Rudolf Hoernes (32) has recently 
 insisted upon the distinctive characters possessed by the pebbles 
 subject to prolonged river and wave transport. According to him, / 
 river-borne pebbles are always flat, and more or less wedge-shaped, 
 owing to the fact that the current merely shoves the coarser mate- 
 rial along its bottom. Marine and lacustrine pebbles, on the other 
 hand, are rounded or roller-shaped, because the waves tend to roll 
 the material. 
 
 Eduard Suess in 1862, in describing the fluviatile Belvedere 
 gravels of the Vienna district, says, in effect ($3:64, 65): "A 
 comparison of a considerable quantity of such pebbles shows that 
 they conform more or less to a single typical form, being almost 
 without exception sharpened to a wedge-shaped form on one side. 
 This form distinguishes shoved pebbles from rolled pebbles; it is 
 produced by the pushing along, over the bottom, of the rock frag- 
 ments by the current of the stream. Rolled pebbles, such as are 
 moved to and fro by the surf on the shore, never have the wedge- 
 shaped form, but a uniformly oval or cylindrical ground form." 
 According to J. Lorenz von Liburnau (37:95, 96) the flat river 
 pebbles suffer chiefly a horizontal rotation, so that the top and 
 bottom of the pebbles are rubbed against the overlying and under- 
 lying ones, while at the same time the edges are worn off, the re- 
 sult being a mass of flat, worn cakes with smooth, rounded edges. 
 
 In contradistinction to these observations and deductions, Penck 
 emphatically insists upon the rolling of pebbles on the stream-bed 
 as the chief method of river transport. Such rolling may affect 
 scattered pebbles or the entire mass, in which case the entire sedi- 
 ment on the river bottom is in motion, the individual pebbles roll- 
 ing and striking against one another, with the result that rounded 
 pebbles are produced. In portions of the Rhine bed, such a mass 
 three meters in depth is thus moved along. (Penck 41 1284.) 
 
 It is extremely doubtful if the distinctions made by Suess and 
 Hoernes can be considered of more than local applicability. The ' 
 character of the rock which has furnished the material is probably 
 of much greater significance, as pointed out by Walther. Thus, on 
 the shores of Lake Michigan, where the bed rock is a uniform 
 grained limestone, the pebbles are chiefly of a rounded or roller- 
 shaped character, while on Lake Erie, where the cliffs are of shale, 
 flat gravel predominates, except where glacial deposits have formed 
 a local source of supply. Again, on a relatively steep shore, where 
 wave-work is pronounced, as on the northern Massachusetts coast, 
 the pebbles are well rounded through rolling, while on a shallow 
 coast, where the wash of the waves rushes up and down the beach 
 
596 PRINCIPLES OF STRATIGRAPHY 
 
 as a sheet flood, the pebbles are more often merely moved back- 
 ward and forward without much overturning, or, again, the 
 pebbles are scarcely moved, but polished and worn by the sand 
 carried back and forth across them. 
 
 Pebbles of glacial stream deposits are always rounded, since 
 in such deposits only the more massive rocks escape destruction. 
 The pebbles and coarser rocks of the White Mountain streams are 
 all well rounded, this being especially well shown in the flood plain 
 of the Saco River at Intervale. Destruction of all the weaker 
 type of rocks by prolonged river transport is also imminent, and 
 this is especially the case on large river flood plains or deltas. 
 Prolonged exposure of granitic or other coarse-grained igneous 
 rocks results in their disintegration, and thus by a process of assort- 
 ing, the pebbles may be reduced to a few fundamental lithologic 
 types, such as quartz, porphyry, etc. There are many older quartz 
 conglomerates with well-rounded pebbles, but free from fossils, 
 which appear to represent extreme cases of concentration. The 
 Millstone grit, the Pottsville conglomerate, and the Shawangunk 
 and other conglomerates are almost wholly composed of quartz 
 pebbles. In many cases these quartz pebbles are derived from vein 
 quartz, but in other cases they are probably a highly indurated 
 quartzite in which the individual grains have become obliterated. 
 
 It is difficult to understand how extensive conglomerates, some- 
 times many hundreds or even a thousand feet in thickness, and 
 composed almost entirely of quartz pebbles embedded in quartz 
 sand, can have originated. If the material of the pebbles is vein 
 quartz, an enormous destruction of rock is indicated, since veins 
 form only a small portion of the rock mass carrying them. If 
 the material of the pebbles is an older quartzite, the problem is 
 less difficult. Again, in some cases the pure quartz pebble conglom- 
 erates may be formed of the reworked gravels derived from the de- 
 struction of older conglomerates. Thus the pebbles of the "yellow 
 gravel" of the coastal.plain may be the product of the destruction 
 of the formerly much more extensive Pottsville conglomerate. In 
 this connection it is interesting to record that some of these 
 pebbles are fossiliferous, carrying corals of Siluric age. This may 
 represent a silicified limestone, the silica thus being of secondary 
 origin. Whether any such origin may be postulated for a con- 
 siderable portion of the quartz pebbles is doubtful. 
 
 From our present knowledge of the subject, it seems that 
 no constant differences can be ascertained between river and shore 
 pebbles, both may be round or flat, and both may be well worn or 
 subangular, and form part of a mass of a very uniform lithic char- 
 
OVERLAP OF RIVER DEPOSITS 597 
 
 acter, or one composed of a heterogeneous aggregate. On the 
 whole, destruction of all but the resistant quartz seems more as- 
 sured on the flood plain of large rivers than on the seashore; and 
 certainly the wide transport of such material is more readily ef- 
 fected by streams. 
 
 The sorting action of streams on sands has already been dis-- 
 cussed. (Chapter V, p. 252.) 
 
 Overlap Relations of River Deposits. In a growing subaerial 
 river delta, the later formed portions will progressively overlap 
 the earlier formed parts, coming to rest upon the basement beds, 
 beyond the margin of the older beds of the delta. Since, however, 
 this can be recognized only as an overlap of formations of definite 
 chronologic value, and not an overlap of continuous beds, this sub- 
 ject is better discussed after the simpler type of marine overlap 
 has been described. The general theoretical relationship is ex- 
 pressed by the following diagram (Fig. 124), from which it will 
 be seen that the principal overlap is away from the source of supply. 
 There may, of course, be a slight headward overlap due to aggrada- 
 
 FIG. 124. Diagram showing normal non-marine progressive overlap, each 
 
 later stratum resting upon the old land surface beyond the edge 
 
 of the preceding one. A slight headward overlap is also indi- 
 cated. 
 
 tion of the upper part of the river channels as the grade is lowered. 
 This, as a rule, will be slight and local as compared with the over- 
 lap at the other end, though it is not to be denied that at times 
 such a headward overlap may be considerable. 
 
 Flood Plains of Glacial Streams. These are of exceptional 
 character owing to the abundant supply of detritus as well as water 
 from the melting ice. As already pointed out in Chapter III, p. 136, 
 such streams when overloaded will form extensive deposits in their 
 valleys, aggrading these to a considerable depth. Subsequent change 
 in the character of the stream, either from diminution of supply, 
 
598 PRINCIPLES OF STRATIGRAPHY 
 
 from increase in the amount of water by sudden melting, or from 
 a general uplift of the region, will cause the rivers to entrench 
 themselves in the old flood plains, leaving the remnants as terraces 
 on either side of the valley. Nearly all the streams coming from 
 the glaciated region have such terraces, which mark the greater 
 deposition in periods preceding the present one. Examples of 
 deposits 'of this type now forming are seen in the valleys of the 
 streams coming from the Alaskan and other glaciers. 
 
 River and Flood Plain Deposits from Continental Ice-Sheets. 
 Several types of such deposits are recognized and are noteworthy 
 on account of their peculiarity; among these are: I. the torrential 
 moraine, or kame ; 2. the frontal, or apron plain ; 3. the esker ; and, 
 4. the glacial sand plain, or temporary lake delta. The essential 
 characters of each are as follows : 
 
 1. Torrential moraine or kame deposits. These are irregular 
 hills of semi-stratified sands and gravels, all of the pebbles being 
 water worn. The material was derived from the ice and was 
 dumped by the rivers in front of the ice-sheet. These deposits are 
 commonly of irregular shape, being more or less confluent cones of 
 debris, and often complicated by the formation of kettle holes from 
 the melting of included ice blocks, as in normal moraines. The 
 topography of such a deposit, when extensive, is often a series of 
 knobs and basins. 
 
 2. The frontal or apron plain. This is also a subaerial deposit 
 and consists of the material carried forward from the glacial mo- 
 raine by streams, and spread as a veneer or mantle over the older 
 formations in front of the ice. Where it is spread over a coastal 
 plain, it is generally of uniform thickness, this decreasing from the 
 source outward. The material also becomes finer away from the 
 source of supply. Kettle holes may occur, but they are less fre- 
 quent than in the kame moraine. Cross channels made by the 
 streams from the ice are not uncommon features. Typical examples 
 of such apron plains are found south of the moraine on Cape Cod, 
 and in similar relations to the moraines on Nantucket, Martha's 
 Vineyard, and Long Island. In the Cape Cod sections of this apron 
 plain facetted pebbles or dreikanter have been found in place, in- 
 dicating wind activity and further proving the subaerial origin of 
 this deposit. Such wind work may locally modify the deposit, sub- 
 stituting wind cross-bedding for the horizontal bedding given to 
 them by the water. 
 
 Marine fossils may be locally embedded in such deposits if 
 they are formed near the shore, and when a partial subsidence is 
 succeeded by further deposition by streams from the ice. A fine 
 
GLACIAL DEPOSITS 599 
 
 example is shown by the fossiliferous layers of Sankaty Head on 
 Nantucket, which, however, lie really within the kame-moraine 
 area rather than in the present apron plain. It is probable, however, 
 that the fossiliferous beds themselves belong to an earlier apron 
 plain, for it is known that the Wisconsin ice sheet advanced over this 
 deposit and built its moraine and apron plain further south. (Wil- 
 son-6o:/j.) 
 
 3. The esker. (Swedish os, pi. osars.) This term is applied 
 to long, narrow ridges of sand and gravel with steeply sloping sides 
 and often a sinuous outline. The summit of the esker is generally 
 a narrow, flat space between the sloping sides, the cross-section be- 
 ing very nearly a triangular one. The eskers of the last glacial 
 period run in general parallel with the direction of the ice move- 
 ment and while occurring largely perhaps in the north and south 
 valleys, along which the main drainage lines from the ice discharged, 
 they are not confined to these, but often pass indifferently over hills 
 and through valleys. In height they rarely exceed 100 feet, but in 
 length they may be followed for tens or" in rare cases even hun- 
 dreds of miles. Their best development in this country is in New 
 England, while Scandinavia and Finland furnish some of the best 
 illustrations in the Old World. 
 
 Eskers may be formed in various ways, such as by filling of 
 gorges in the ice, by accumulation of debris in englacial tunnels and 
 by aggradation of their bed by sub-glacial streams. (Grabau-23.) 
 This last is the most characteristic method of formation. Streams 
 originating under the ice are enclosed in a tunnel and, being under 
 an enormous hydrostatic pressure, will fill this tunnel after the 
 .manner of the water in a city main. It may thus be forced up- 
 ward and will discharge at a level much above that of its upper 
 courses, if it is located in a valley sloping against the ice mass, as is 
 so often the case. 
 
 Flowing uphill, such a stream will tend to erode the roof of 
 its tunnel, and simultaneously to aggrade its bottom in the higher 
 (upstream) parts. As the stream rises in the ice by roof erosion, 
 the floor is more and more aggraded until this filling all along the 
 line has reached the level of the outlet, or risen slightly above it. 
 Melting removes the supporting walls on either side of this aggraded 
 river-bed, when the sides will slump, giving the characteristic lateral 
 slopes and the triangular cross-section to the esker. At points 
 where the original deposit is narrow, so much material will be in- 
 volved in the slumping to give the proper angle of repose that the 
 surface of the .esker will be actually lowered. Thus irregularities in 
 height in the esker are readily accounted for. (Woodworth-6i.) 
 
6oo PRINCIPLES OF STRATIGRAPHY 
 
 4. Glacial sand plains. Whenever the ice holds up a tempo- 
 rary body of water between its front or sides and the margins of 
 the valley or basin in which it lies, opportunity for the formation of 
 glacial deltas or sand plains is given. These may be formed around 
 the margins of the lake by streams coming from the land, when 
 they partake of the true delta to be described beyond. Such deltas 
 have been recorded from glacial lakes in New Jersey and else- 
 where. The marginal sand plains of the Upper Hudson Valley 
 were deposited in lakes bordering the ice sheet which occupied 
 the center of that valley. Sand plains formed at the front of the ice 
 of material carried by streams from the ice abound in New Eng- 
 land, especially in eastern Massachusetts, where they have been 
 fully described.* A characteristic feature of these sand plains is 
 their correspondence in height to the elevation of the outlet, which 
 determined the level of the temporary lake. Not infrequently a 
 number of successive sand plains is formed corresponding to a suc- 
 cession of lake levels determined by progressive uncovering oHower 
 outlets. In New England these plains are generally highest in the 
 southern portions of the old northward sloping valleys and become 
 progressively lower toward the north. In Lake Bouve, an extinct 
 glacial lake in the Boston Basin, eight series of such sand plains are 
 known, each series lower than the preceding one on the south. 
 ( Grabau-23 '.580. ) A special example of rather striking character 
 is seen in the sand plains of Wellfleet, Eastham, and Truro on Cape 
 Cod, which were deposited in a lake held in an embayment in the 
 eastern ice lobe, and dammed in part by the terminal moraine of 
 that ice lobe, across which the discharge of the waters occurred. 
 In this case the highest series of plains lies between the two lower 
 series. By the melting of the ice these plains were left without any 
 immediately surrounding land barrier, as isolated sand masses run- 
 ning northward into the ocean from the eastern end of the terminal 
 moraine. (Grabau-24; Wilson-6o '.52-66, pis. 34, 36, 37, 38.) In 
 form the isolated sand plain, revealed on the melting of the ice 
 and the drainage of the temporary lake, consists of a surface slope 
 which is gently forward from the center of origin ; a steeper frontal 
 or delta slope, joining the surface slope abruptly, and having a 
 lobate or scalloped outline, and a still steeper back slope often with 
 concavities between sharp cusps. This latter surface is due to 
 slumping after the supporting ice front against which the delta was 
 built had melted away. Its slope, therefore, represents the angle 
 of repose of the material under the conditions of formation. The 
 gentle surface slope represents the subaerial part of the delta, while 
 
 * See papers by Crosby, Grabau, Clapp, etc., cited in Chapter III. 
 
CONSOLIDATED GLACIAL DEPOSITS 601 
 
 the lobate front is the slope of the front of the original delta where 
 the oblique frontal layers or fore-set beds were added. The loba- 
 tion is due to the division of the stream into a number of spreading 
 fingers or distributaries, each of which builds its own portion of the 
 delta forward. In section it will be seen that the greatest part of 
 the sand plain is composed of the sloping fore-set beds, which are 
 inclined at an angle of 20 or more degrees. The upper ends of 
 the fore-set beds are abruptly truncated, and on these truncated 
 edges rest the coarser, nearly horizontal, top-set beds which con- 
 stitute the subaerial part of the delta. The foot of the fore-set 
 beds generally rests upon a thin series of bottom-set beds of finest 
 material, often of clay or rock flour. All the beds are well stratified 
 and the pebbles are, as a rule, well rounded. 
 
 Consolidated Sand Plains. Sand plains of Pleistocenic age have, 
 in some cases, become consolidated so as to form a rock mass of 
 more or less induration. This is especially the case where many of 
 the pebbles are of limestone, when partial solution and redeposition 
 of the lime in the interstices will occur. A typical example of 
 such a consolidated deposit is seen on the banks of the lower 
 Niagara River, near the railroad station at Lewiston, New York. 
 Here steep fore-set beds are seen dipping at an average angle of 
 15-20 degrees toward the south. The beds are sufficiently well 
 cemented to form a vertical wall, though the material can be broken 
 into its component pebbles by blows of a hammer. The deposit, 
 which is perhaps 30 or 40 feet thick, appears to have formed in a 
 body of water held up against the front of the Niagara escarpment 
 by an ice lobe lying a short distance to the north. Streams from 
 this ice lobe supplied the pebbles and sand which built up the delta. 
 
 This deposit is sufficiently consolidated to resist ordinary erosion, 
 and river, lacustrine, or even marine sediments could be formed over 
 it without disturbing it. Indeed, since the formation of this deposit 
 this region is believed to have been invaded by the sea by way of the 
 Hudson, Lake Champlain, and the St. Lawrence, but this was not 
 of sufficient duration to permit the formation of extensive marine 
 deposits. It is easy to see, however, that these steeply inclined 
 delta beds of coarse material, followed by marine sediments, such 
 as would have been formed had the sea stood here longer, and this 
 in turn by lacustrine deposits, such as would be formed if the 
 present lake should expand, would give a complex succession of 
 formations, the history of which would be decipherable only with 
 considerable difficulty. 
 
 The NagelHuh of Salzburg. (Crammer-13 '.325-334.) The city 
 of Salzburg in the Austrian province of the same name and close 
 
602 PRINCIPLES OF STRATIGRAPHY 
 
 to the Bavarian border furnishes a remarkable example of a con- 
 solidated conglomerate or pebble rock of the type described. This 
 goes by the name of Nagelfluh, from the fact that where the rela- 
 tively small pebbles have fallen out of the matrix a depression 
 like that made ,by the head of a nail is seen. This rock appears 
 in several large erosion remnants within the city ; one of them, 
 the Monchsberg, rises with perpendicular walls (partly artificial) 
 and is pierced by a tunnel through which one of the city streets is 
 carried. Other remnants are the neighboring Rainberg, and the 
 more distant hill of Hellbrunn. All of these are evidently part of a 
 once continuous conglomerate bed, which has since been dismem- 
 bered by erosion. The cohesion of the material is such that old 
 crypts hollowed in this rock and used in the third century as places 
 of secret worship are still in a practically unchanged condition. 
 
 The walls show inclined bedding which indicates the delta char- 
 acter of these deposits (Penck-42 \i6i-i66). According to the 
 opinion of Penck, Crammer, and others, the sand and pebbles were 
 washed into a lake which occupied the Salzburg basin during 
 post-glacial time. The fact that the Nagelfluh rests upon a glacial 
 moraine, as determined by excavations and observations on natural 
 and artificial exposures, seems to indicate that this deposit is of 
 post-glacial age, though other observers have held that the age 
 of the deposit might be greater, perhaps late Tertiary. 
 
 Nagelfluh of similar character, but probably of greater age, is 
 found in a number of localities in South Germany and elsewhere. 
 In some cases, as in Munich, it is used extensively for building 
 purposes. It is, of course, not necessarily true that all conglomer- 
 ates of this type are of non-marine origin, though most of them 
 probably are river deposits. 
 
 PLAYAS OR TAKYRS AND SALINAS. In the low, flat-bottomed 
 depressions of undrained desert basins the rivers at times of flood 
 will spread out into extensive shallow lakes of temporary existence. 
 In the Great Basin region of western North America one such 
 temporary lake reaches a length of about 100 miles by a breadth of 
 12 to 15 miles, but with the water scarcely more than a few inches 
 deep. Here the fine silt of the river is deposited, gradually subsid- 
 ing as the shallow lake evaporates. After complete evaporation a 
 smooth, hard-baked surface remains, .marked by sun-cracks and 
 the tracks of animals which visited the spot before complete harden- 
 ing of the mud had occurred. Raindrop impressions likewise re.- 
 main on such a surface. In structure the material is beautifully 
 and finely stratified, as may be seen on the sides of the sun-crack 
 rifts. This constitutes the playa of the American deserts (Mexico 
 
PLAYAS AND SALINAS 603 
 
 and the southern United States), the takyr or schala of Asia, or the 
 sebcha of Africa. Russell has described a number of such tempo- 
 rary playa lakes from the western United States (49:50). He finds 
 them a characteristic feature of the greater part of the valleys of 
 Nevada, the largest being in the Black Rock Desert in the north- 
 western part of the state. It forms during the winter months and 
 reaches an area of from 450 to 500 square miles, but is seldom over 
 a few inches in depth. Often after storms it is a vast sheet of 
 liquid mud, a characteristic of many playa lakes. In a few hours 
 or a few days the water of the lake may all evaporate, leaving a 
 hard, dry and absolutely barren surface, cracked in all directions 
 as the surface contracts in drying. "The lake beds then have a 
 striking resemblance to tesselated pavements of cream-colored mar- 
 ble, and soon become so hard that they ring beneath the hoof -beats 
 of a galloping horse, but retain scarcely a trace of his foot-prints." 
 Around the margin of the lakes is a belt of plain with desert vege- 
 tation, the transition to which is formed by a marshy tract which 
 in summer is marked by an abundant efflorescence of salts. 
 
 Mechanical analysis has shown that the material of the playa 
 may be 100 per cent, clay, and that laterally it will gradually pass 
 through the addition of sands into the surrounding eolian deposits. 
 In limestone regions where siliceous rocks are wanting the mate- 
 rial of the playa will be largely lime mud, and this may be the 
 origin of some of the finely bedded, sun-cracked calcilutytes of the 
 American Siluric, where the percentage of lime and magnesium 
 carbonates is seventy or less. 
 
 If the playa lake exists for some time it may become stocked 
 with certain forms of organisms, especially types whose eggs or 
 larvae can be transported by wind or by birds. The small crusta- 
 ceans Estheria, Daphnia, and Cypris are characteristic of desert 
 lakes, the first having been found in ponds which are dry for 
 eleven successive months. (Fischer, quoted by Walther~57:p^.) 
 When, as is frequently the case, salts are present in the sediment, 
 these effloresce on the surface, and from their hygroscopic charac- 
 ter keep the surface of the playa sufficiently moist to prevent the 
 removal by the wind of the accumulated material, and further to 
 catch all dust particles carried across the surface by the winds. 
 Thus the surface of the playa becomes dusted over with a fine coat- 
 ing of sand or dust, this process being repeated as the salts rise to the 
 surface of the newly added layer. Where salt is present in great 
 abundance a moist, slippery surface with incrustations of salt re- 
 sults, thus forming salinas. When wet, their surface is impassable, 
 but when dry a crust of hard salt of dazzling whiteness characterizes 
 
604 PRINCIPLES OF STRATIGRAPHY 
 
 the salina. As already noted, the thickness which such a salt 
 deposit may reach is practically limited only by the depth of the 
 basin and the supply of the salt. 
 
 The deeply cleft surface of the dry playa is not infrequently 
 buried by the wandering sands of the desert, while the rifts between 
 the polygonal blocks are filled with wind-blown material, or the 
 mud of the next succeeding inundation, and so preserved. This is 
 made possible by the rapidity with which the playa surface becomes 
 flooded, a case being on record where a lake 10 to 15 kilometers 
 wide and of immeasurable length, though only from an inch and 
 a half to a foot in depth, came into existence in twenty minutes. 
 (Obrutschew, quoted by Walther-57 :iio.) It must, however, be 
 noted that the dried surface of the playa is not infrequently 
 softened on being wetted, and that from swelling and flowage of 
 the mud the cracks may be closed again before they are filled. In 
 this manner many mud-cracked surfaces are again obliterated. 
 From preliminary experiments, Barrell concludes (2:537-53^) that 
 "a mud-cracked loam or silty clay, even when the sand particles 
 are imperceptible to the fingers, is an unfavorable material for the 
 preservation of its detailed surface features, . . . Upon being 
 wet by rain the rapid swelling and disintegration of the surface 
 stratum would turn the surface of such a deposit into a creamy 
 mud. . . ." On the other hand, "a pure clay, slowly subsiding 
 from quiet waters, and wet sufficiently long to become compact 
 upon drying, would retain its mud cracks upon rewetting, either 
 by rain previous to flooding or by the flood waters themselves." 
 When the newly deposited layer is a very thin one it will curl up 
 like shavings on drying and these clay shavings will be blown into 
 the sand dunes, where, upon subsequent softening, they will be 
 compressed into clay lentils or pebbles, and so become a constituent 
 part of an otherwise pure sandstone. 
 
 PRESERVATION OF FOOTPRINTS, ETC., IN SUB AERIAL DEPOSITS. 
 Of the greatest significance is the relative ease with which tracks 
 of animals are preserved in desert deposits. The scarcity of rain 
 permits their almost indefinite retention on suitable surfaces with- 
 out being buried. In the Sahara desert tracks of camels made in 
 1877 were still perfectly recognizable in 1892 (Foureau-2i :/75), 
 the interval of fifteen years having altered them but little. Where- 
 ever ( Walther-57 :##) a temporary accumulation of water after 
 a desert rain attracts the varied desert fauna, or allows animals 
 living on the border of the desert to make extended excursions into 
 the flooded regions, their footprints will be left upon the impres- 
 sionable surface of mud, remaining after such an inundation. These 
 
PALUDAL AND LACUSTRINE CLASTICS 605 
 
 will in time be covered by the shifting sands of the desert and a 
 relief mold will be produced by the covering sands. Such a relief 
 impression will be more readily preserved than the original im- 
 pression, which may be destroyed by the softening of the clay 
 surface of the playa. A single extensive inundation by heavy rains 
 of a desert surface may permit a wide horizontal migration across 
 this surface of animals which never before and never after entered 
 this region. Thus their tracks may be widely preserved in a single 
 horizon in a desert formation, like those of Cheirotherium in the 
 Upper Buntsandstein (Walther-57:<5'#), even though the animal 
 lived during a much longer time period. Repeated floodings, an- 
 nually or at intervals of many years, will permit the formation of 
 successive track-bearing layers, by animals living on the border of 
 the desert. This mode of preservation certainly accords best with 
 the characters of the tracks found in such formations as the Newark 
 sandstone of the eastern United States, whereas the frequent as- 
 sumption that the successive track-bearing beds were made between 
 tides and buried by the sediment brought in by the returning tide 
 does not allow for the obliterating effect of the tide, an argument 
 equally applicable to stream-laid deposits upon the fresh tracks. 
 (Voigt-54:/<5d.) 
 
 The conditions favoring the preservation of footprints in desert 
 regions militate against the preservation of the animals themselves. 
 For, unless the body is buried at once, it is sure to fall a prey to 
 the desert carnivora, while sun and wind will complete the destruc- 
 tion of what remains. This explains the scarcity of remains of the 
 animals in the strata which contain their footprints. 
 
 Other Structural Characters. Ripple marks and rill marks, 
 though usually regarded as typical only of marine formations, are 
 equally, if not more, characteristic of the non-marine deposits. 
 Their discussion is, however, deferred until hydroclastic sediments 
 have been more fully discussed. 
 
 NORMAL PALUDAL AND LACUSTRINE CLASTIC 
 
 DEPOSITS. 
 
 Clastic deposits in swamps (paludal elastics) are of relatively 
 little importance except when associated with vegetal deposits. 
 These latter are by far the most important, the elastics being subor- 
 dinate and confined to the sediments carried in by wet weather 
 streams and rains, or the dust settling out of the air. 
 
 Deposits in ponds and lakes, on the other hand, i. e., in water 
 
606 PRINCIPLES OF STRATIGRAPHY 
 
 bodies free or nearly so from growing vegetation, are of more 
 significance, since they add a decided individualistic note to the'ter- 
 restrial hydroclastic series with which they are commonly asso- 
 ciated. It is true that many of their most pronounced characteris- 
 tics are due to peculiarities in the composition of their waters 
 which will give rise to deposits of special chemical character, such 
 as have been discussed in preceding chapters. In other respects, 
 again, the nature of the sediment is not very different from that of 
 the ocean, except in so far as the absence of the tides, the differ- 
 ence in composition and specific gravity of the water and the 
 difference in size of the water body influence such deposition. The 
 last falls -practically out of consideration in lakes of great size, such 
 as the American Great Lakes. 
 
 The clastic sediment of lakes is chiefly derived from two 
 sources, that resulting from the erosion of its shores by waves, 
 and that brought in by the tributary streams. Erosion is very 
 marked, especially in the larger lakes, such as Erie, Ontario, Huron, 
 etc., and the product is' distributed along the shore as shingle, or 
 heaped up into storm terraces, as on Lake Michigan. Coarse mate- 
 rial is seldom carried far out into the lake, but accumulates along 
 the shores, where it is subject to constant wave attack. The finer 
 sand and mud, however, resulting from such wave attack are 
 carried out from shore and slowly settle all over the lake bottom 
 and sides. This also happens to some of the fine slime brought 
 in by streams, but this tends for the most part to sink to the lake 
 bottom. The coarsest of the river-borne sediments will build up a 
 delta at the shore, but the finer mud, which is held in intimate sus- 
 pension in the stream water, is carried beyond this point. Its 
 presence in the stream water renders that water heavier, and it 
 will, therefore, not mingle with the lighter warm water of the sur- 
 face of the lake, but will sink to the deeper, cooler and denser 
 strata. Thus a mud-laden stream passing into a lake will become 
 submerged, often passing along the lake bottom, and occasionally 
 forming a channel there, bounded by submerged mud banks on 
 either side. The force of the current will finally be dissipated in 
 the deeper waters of the lake and the sediment will slowly sink to 
 the bottom, forming horizontal and well-stratified layers of mud- 
 rock, free from irregularity of bedding and of uniformly fine 
 grain. Mingled with sedime'nts of this type are the muds which 
 were held suspended for a time in the upper waters and which 
 settled all over the lake bottom. 
 
 With the seasonal variation in the strength of the streams there 
 must be a corresponding variation in the grain of the sediment. 
 
LACUSTRINE CLASTICS. DELTAS 607 
 
 Thus when the current is powerful and surcharged with sediment 
 slightly coarser material may be carried to the lake bottom than 
 is the case during the period of lessened river activity. A series of 
 annual layers is thus formed which in any given case may serve to 
 measure the length of time required for the formation of the de- 
 posit. This method has been applied by Berkey (8) for the de- 
 termination of the time required for the deposition of finely bedded 
 clays. 
 
 DELTAS. 
 
 Deltas are the terminal deposits of rivers, and, as such, have 
 an intimate association with the continental elastics. It is true, of 
 course, that a part of the delta of the seacoast is of submarine 
 origin, and its discussion therefore falls more essentially under the 
 heading of marine elastics. Still, deltas are peculiar features of 
 relatively limited distribution, and m no way represent normal 
 marine conditions. Indeed, a part of the delta is always typically 
 non-marine, and the place of the delta is therefore intermediate 
 between true continental and marine elastics. Moreover, deltas 
 are common in lakes, these belonging, of course, entirely to the 
 continental division of the hydroclastics. 
 
 A typical delta may be taken as one that is built into a body of 
 standing water, the level of which is essentially a permanent one. 
 Subsequent drainage of the water body may expose the delta as 
 we have seen, but all such changes bring the delta-building process 
 to an end. On the whole, deltas are more abundant on lakes than 
 on the seashore, partly because lakes are not subject to tidal cur- 
 rents and fluctuation of level, but partly also because wave activity 
 on the sea coast is greater. Fluctuation in level due to tides does 
 not necessarily militate against delta building, as is shown by the 
 Indus delta, which is built where the tidal range is 10 feet, while 
 that of the Ganges is built into a sea having a tidal range of 16 
 feet. Where wave action is strong, however, and especially where 
 long shore transport of material is pronounced, delta building is 
 restricted. Deltas are thus the triumph of river deposition over 
 wave and current destruction, and their location and extent will be 
 determined by the relative importance of the opposing processes. 
 As examples of typical existing deltas on the sea coast may be 
 named that of the Nile, on the Mediterranean; of the Po, on the 
 Adriatic; the confluent deltas of the Rhine and Meuse; and that 
 of the Ems, on the North Sea ; the deltas of the Lena and of the 
 Mackenzie, on the open Arctic Ocean ; those of the Ganges, Brah- 
 
6o8 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 
 maputra and the Indus, on the Indian Ocean ; of the Niger and the 
 Orinoco, on the Atlantic Ocean; and the Mississippi delta on the 
 Gulf of Mexico. Of the numerous deltas on the protected waters 
 of Europe and Asia may be mentioned that of the Danube on the 
 Black Sea, the Volga on the Caspian, and those of the Oxus (Amu- 
 darja) and the Jaxartes (Syr-darja) on the Aral Sea. 
 
 Form and Rate of Growth of Deltas. The^orm of the deltas 
 varies greatly from the typical triangular outline resembling the 
 Greek letter delta (A) characteristic of the Nile delta (the type 
 of deltas; Fig. 125) to the long, narrow estuarine filling of the 
 Mackenzie mouth, on the one hand, and the very broad, but short, 
 cuspate delta of the Tiber, or the still narrower strip-like or stunted 
 delta formed by the Cavonne on the Gulf of Taranto, southern Italy, 
 
 FIG. 125. The Nile Delta. 
 
 on the other. The mouth of the delta-building river may advance 
 singly (unilobate) without dividing into distributaries, as is nearly 
 the case with the Ebro on the northeast coast of Spain, or it may 
 be multilobate with the distributaries pushing each its own narrow 
 lobe forward, which may even become a finger-like extension, as 
 in the remarkable Mississippi delta. If the distributaries are nu- 
 merous, they may form a network of streams, as on the Nile delta, 
 which advances by a continuous, more or less scalloped front. 
 
 In size the deltas of the present day vary from an insignificant 
 deposit at the mouth of a small stream to areas covering many 
 thousands of square miles, as in the deltas of the Nile, the Lena, 
 and the Mississippi. Confluent deltas of several streams occur, 
 making irregular deposits with many lagoons, as in the Rhine- 
 Meuse-Ems delta; while deltas building on a coast with many 
 
CHARACTERISTICS OF DELTAS 609 
 
 islands may gradually annex these to the land by enclosing them 
 in the growing delta. The hilly province of Shantung has thus 
 been enclosed in the great delta of the Huang-ho, and a number 
 of small islands have been included in the delta of the Aspropota- 
 mos in western Greece. 
 
 The rate of growth of deltas varies greatly and is often con- 
 siderable. Thus the Jaxartes increased by 13^4 square miles be- 
 tween 1847 an d 1900. (Andrussow-i :^p.) The delta of the Rhone 
 is said to have lengthened more than 26 kilometers since 400 B. C. 
 The southwest pass of the Mississippi delta grew, according to 
 Captain Talcot, 104 meters in length in 1838, the south pass 85 
 meters, the northeast and southeast passes each 40 meters, and the 
 pass a 1'Outre 92 meters, giving an average of 80 meters per year 
 for each pass. While this holds for the year in question, it is 
 not possible to consider that such an increase occurs in all years. 
 Indeed, often one year destroys what is built in the preceding year. 
 The Po delta has increased between the years 12001600 at an aver- 
 age rate of 25 meters per year, but from 1600 to 1804 its rate of 
 increase was 70 meters per annum. One of the most rapidly grow- 
 ing deltas is that of the Terek, on the Caspian. Within a period of 
 30 years the water has been pushed back 15 kilometers by the 
 growth of the delta, which increased thus at the rate of half a 
 kilometer per year. The other extreme is shown by the delta of 
 the Danube, which at one of its mouths is not over 4 meters per 
 year, though somewhat more rapid at another. The average in- 
 crease of the Nile is about 4 meters 'per year, while the delta of 
 the Tiber is estimated to increase at the low rate of I meter per 
 year. According to Pumpelly, the Huang-ho has increased on the 
 average at a rate of 30 meters per year between B. C. 220 and 
 A. D. 1730. 
 
 Thickness or Depth of Deltas. (Credner-i4.) The depth of 
 delta deposits on modern sea coasts varies greatly, but is, on the 
 whole, comparatively slight. Thus the mud of the Nile delta is 
 not over 10 or 15 meters thick. It rests on loose sea sand. The 
 delta deposits of the Rhine have a thickness of 60 meters, those of 
 the Rhone over 100 meters. In the Po the depth averages 122 
 meters, though near Venice 172.5 meters were penetrated without 
 reaching bottom. The delta deposits of the Ganges and Brahma- 
 putra rest on older sediments and average only 20 meters in thick- 
 ness. The actual delta deposits of the Mississippi range from 9.5 
 to 1 6 meters near New Orleans, increasing to 30 meters at the 
 head of the passes, beyond which the thickness rapidly increases. 
 They rest throughout on a stiff blue clay of earlier age. The Rhone 
 
6io PRINCIPLES OF STRATIGRAPHY 
 
 delta in Lake Geneva has a thickness of 180 to 275 meters and a 
 length of nearly two English miles. 
 
 Delta Slopes. The surface of the delta has always a gentle 
 slope, this being steeper in the smaller deltas than in the larger ones, 
 and steeper also in the deltas of coarse material than in those of fine 
 silts. The frontal slope of the delta is, as a rule, much steeper, 
 being sometimes as high as 25 or 30, or in some cases even 35 
 in the small deltas of Pleistocenic and modern lakes. In the 
 larger deltas, especially those on the sea coast, the frontal slope 
 is much gentler. The strata of the Rhone delta in Lake Geneva 
 are so slightly inclined that they almost take on a horizontal atti- 
 tude. The total thickness of this delta, 180 to 275 meters, is dis- 
 tributed over nearly 2 miles. The frontal slope is i to 18. A 
 much gentler slope is seen in the delta of the same stream in the 
 Mediterranean, where the rate is I in 160, the depth increasing 
 from 4 to 40 fathoms in the distance of 6 or 7 miles from the mouth 
 of the stream. 
 
 Deltas of small lakes often show a steeper inclination for the 
 older coarser beds than for the finer younger ones. Thus the delta 
 of the Aar in the Lake of Brienz shows near the shore an inclina- 
 tion of the beds amounting to 30 degrees. About 300 meters from 
 the shore the grade has decreased to 20 degrees, while at the ex- 
 treme margin of the present delta, 1,100 to 1,200 meters from the 
 shore, the beds are nearly horizontal. The delta of the Dundelbach 
 in the southwest angle of the little Lake of Lungern in Switzer- 
 land shows coarse beds near the margin, sloping at an angle of 35 
 degrees, while the younger layers have a very gentle slope only. 
 
 The Bird-foot Delta of the Mississippi. The lower part of 
 the Mississippi delta has a remarkable form, distinguishing it 
 from all other modern deltas. From Forts Jackson and St. Philip 
 onward for a distance of nearly 25 mile's the river is confined in a 
 narrow channel or "neck" which finally divides at the "Head of the 
 Passes" into three divergent channels, or passes, each bordered 
 by low banks of stiff clay and forming a structure resembling a 
 bird's foot. One of these passes, the Pass a 1'Outre, divides again 
 into the North Pass and the Northeast Pass. The other two, the 
 South Pass and the Southwest Pass, continue, as single narrow fin- 
 gers, the latter for nearly 20 miles. Some distance above the head 
 of the passes a similar channel, the Main Pass, extends northward, 
 and still farther up a group of small channels diverges from the 
 neck. The material composing the banks of the neck and the 
 passes is wholly unlike ordinary river silt, though in general a thin 
 superficial layer of this occurs. Primarily, however, the banks 
 
THE MISSISSIPPI DELTA 
 
 611 
 
 consist of a stiff blue clay not unlike the stiff "Port Hudson clays" 
 (Hilgard-29) which underlie the whole delta. Such mud is brought 
 to the surface in a series of mud volcanoes or mud-lumps which, 
 from time to time, arise on the delta surface. These are believed by 
 Hilgard to be formed of the fine mud brought down by the river 
 and precipitated outside of the delta by flocculation. Over this 
 liquid mud are spread the river sediments, the weight of which and 
 that of the growing marshes and their pressure upon the mud 
 
 FIG. 126. The Mississippi Delta. At the "bird foot" the passes are from 
 ,right to left: North Pass, Northeast Pass (these two unite to 
 form the Pass a 1'Outre), South Pass, Southwest Pass. The 
 Northeast Pass has a small southern branch, the Southeast Pass 
 (not shown), while another group of channels, diverges from the 
 "neck" about five miles above the "head of the passes." 
 
 layers result in local upheavals and formation of mud lumps or 
 craters, as long ago suggested by Lyell. Rod soundings in such 
 a crater have reached a depth of 24 feet, but no solid bottom. 
 The mud flow from these craters varies with the stages of the river, 
 becoming much more lively in times of flood, when great masses of 
 water, or of silt brought down by the river, press upon the layer 
 of liquid mud. Hilgard believes that the banks of the neck and the 
 passes are formed of the disintegrated and redeposited mud from 
 such mud lumps, and that when a mud lump arises in the channel, 
 as has recently occurred, a division is likely to take place. Hilgard 
 
612 PRINCIPLES OF STRATIGRAPHY 
 
 testifies to the tough, resistant character of this clay, which when 
 wet is almost inerodable by pure water. (29.) 
 
 Structure and Composition of the Delta. Theoretically the delta 
 consists of bottom-set, fore-set, and top-set beds. These are all 
 well developed in the small deltas formed in Pleistocenic time in 
 temporary ice-dammed lakes and now open to examination after 
 the draining of these lakes. In the deltas on the sea coast, however, 
 one or the other of these beds is often absent, or two may merge, 
 this being most frequently the case with the fore-set and bottom- 
 set beds. 
 
 The fore-set beds of small or young deltas are generally steeply 
 inclined, as already noted. This is especially the case when the 
 supply of detritus is large. As the delta increases in size the later 
 fore-set beds become more flattened and bend over at the bottom 
 into the horizontal bottom-set beds. The upper ends of the fore- 
 set beds, on the other hand, show more or less of erosion and 
 across their truncated edges are deposited the top-set beds. There 
 may, of course, be at times a bending over of the top-set beds into 
 the fore-set, but in the young delta the contact is more or less sharp. 
 In the larger deltas of fine material, on the other hand, the top-set 
 beds may be more or less continuous with the fore-set, and, indeed, 
 the two may imperceptibly grade into each other, without even a 
 change in angle. 
 
 The top-set beds of small deltas consist of the coarser material 
 laid down in nearly horizontal beds. If we assume that the normal 
 delta begins as a subaqueous detrital cone or semi-cone growing 
 in circumference, it is apparent that fore-set and bottom-set beds 
 alone exist during the earlier stages. As the radius of the cone 
 increases, its summit is invariably truncated by the waves and by the 
 stream itself, which carries the detritus out to the front of the cone. 
 Thus a level plane is formed partly by non-deposition and partly by 
 contemporaneous erosion truncating the fore-set beds. Its surface 
 will be to some extent below water level, the depth depending on 
 the strength of the wave activity. Upon this plane will be deposited 
 the top-set series which the current can no longer carry to the edge 
 of the growing delta. The top-set series will continue to grow in 
 thickness and extent as the delta grows, and its landward part will 
 begin to emerge and become subaerial. The extent to which this 
 subaerial part of the top-set series will grow is determined by 
 the strength of the river and the slope which it can control. In 
 smaller deltas the frontal angle of the delta is also the junction 
 between top-set and fore-set beds and marks 'the extent of sub- 
 mergence of the delta. In larger deltas the top-set beds go deeper. 
 
STRUCTURE OF DELTAS 613 
 
 Examination of deltas permanently or temporarily laid dry 
 shows that the structure is by no means a uniform or simple one 
 throughout. Thus the delta of the Dundelbach, laid open to obser- 
 vation by the partial drying of the Lake of Lungern into which it 
 was built, showed striking variation. Near its head it consists of 
 beds of coarse and fine gravel, sloping at an angle of about 35 
 degrees. Large, flat rock fragments rest with their surfaces on 
 the inclined gravel layers, and a bed of compressed bituminous 
 woods and leaves, six inches in thickness, is interbedded with these 
 gravels in one part of the section. In general, the successive in- 
 clined layers are only a few inches thick; and this thickness does 
 not increase toward the lower end in the coarser layers. In the 
 fine mud layers, however, there is an increase in thickness down- 
 ward before the layers bend over horizontally at the bottom. These 
 finer textured layers rest gently against the steeper, coarser ones, 
 filling especially the angle between the steeper layers and the flat 
 lake bottom. 
 
 The numerous (20 or more) well borings made into the con- 
 fluent deltas of the Po, Etch, and Brenta, in the region about 
 Venice, have revealed the fact that the structure of the delta is an 
 extremely heterogeneous one. While the beds are, in general, 
 horizontal, with only minor undulations, the succession is scarcely 
 the same in any two of the bore holes. This proves that the 
 beds of the delta form a succession of lenticular masses, of very 
 limited extent. Only two sandy layers, carrying water, have 
 proved in any way constant; all other layers quickly wedge out 
 laterally. (See the combination of profiles given by Credner- 
 14: pi. I, Fig. o.) The successive layers comprise brown clays 
 alternating with yellowish sands with lignites and occasionally 
 layers containing marine organisms. The series includes several 
 beds with molluscan remains. Marine molluscs, especially Cardi- 
 acea, abound in the higher fossiliferous layers, while in the deeper 
 beds only occurs the intermingling with these of fresh-water types. 
 In some wells lignites with associated land snails, such as Succinea, 
 Pupa, Helix, etc., were found. Vegetable material occurs at four suc- 
 cessive horizons in the Po delta down to a depth of 100 meters. The 
 material is the same as that now forming marshlands on the coast 
 of the Adriatic. This and the occurrence of the land snails in the 
 lower beds would suggest subsidence since delta-building began 
 here. The borings near Venice show that about one-third of the 
 material making up the upper sixty meters of the delta ground con- 
 sists of lignite and peat. 
 
 Quite a different picture from this is presented by the mud 
 
614 PRINCIPLES OF STRATIGRAPHY 
 
 deposits of the Nile. At low water these are visible in the steep 
 banks which then rise 8 to 10 meters above water level. The hard- 
 ened Nile mud forms a series of horizontal beds varying in thick- 
 ness from a few inches to several feet, and looks more like an an- 
 cient stratified series than like a modern deposit. The material of 
 the Nile mud is a more or less uniformly fine-grained one, the 
 size of the grains varying from 1/13 to i/ioo mm., rarely reaching 
 i/io mm. in size. It is a unique deposit probably not paralleled by 
 any other modern one on the. face of the earth. An analysis of 
 the mud (Clarke-i2 1481) gave: 
 
 SiO 2 45.10 
 
 A1 2 O 3 15-95 
 
 Fe 2 3 13-25 
 
 MgO 2 . 64 
 
 CaO 4.85 
 
 K 2 O 1.95 
 
 Na 2 0.85 
 
 S0 3 0.34 
 
 H 2 15.54 
 
 100.47 
 
 The remarkable fact about this mud is its high iron and low organic 
 content, though some analysts have found the finely divided or- 
 ganic matter as high as 5.53 per cent, or even 7.9 per cent. Some 
 analyses show an admixture of barium carbonate over wide areas. 
 
 In other deltas the organic material is pronounced. The abun- 
 dant admixture of leaves and more or less lignitized wood in some 
 deltas has already been noted. In the Po delta it occurs in four 
 successive horizons. In the Ganges delta such deposits are found 
 between 9 and 15 meters in depth, together with carbonized trunks 
 of trees characteristic of the region, such as Heritiera littoralis, 
 which abounds in the lower part of Bengal. In the lower Mississippi 
 delta driftwood is common, the logs being at times united into 
 floating rafts. Not infrequently erect trunks are found among 
 these, with their roots spreading in all directions, as if while grow- 
 ing there they were submerged by a subsidence. The Mackenzie 
 River delta likewise contains an abundance of carbonized drift- 
 wood, and this is true of many other deltas. 
 
 More striking, however, in some ways is the abundance of 
 finely divided vegetable matter in some deltas. Thus the mud 
 of the Vistula (Weichsel) loses, according to G. Bischof (9) 23.3 
 per cent, on ignition, most of this being organic material. The 
 clay of the Vistula delta in the Bay of Dantzig is so rich in or- 
 ganic material that it has a deep black color, and is locally known 
 
ORGANIC REMAINS OF DELTAS 615 
 
 as pitch, "pech." The bearing of this fact on the origin of some 
 black shales will be considered later. 
 
 Organisms of the Delta. Marine organisms are not uncommon 
 in sea-coast deltas, but they are, as a rule, distributed in certain 
 layers only. Lyell has explained the occurrences of marine molluscs 
 in extensive beds between the fresh water layers of the delta as due 
 to wave work, which casts masses of shells upon the growing delta 
 surface. In some parts of the Rhone delta marine and fresh water 
 shells alternate in the deposit. This is explained by Lyell as probably 
 due to the alternating occupancy of lagoons and channels on the 
 growing delta by salt or by fresh water, according as the prevailing 
 wind or other causes may ordain. As already noted, the delta of 
 the Po also contains fresh water organisms associated with marine 
 shells, but only in the lower beds, while upward the shell deposits 
 become purely marine. Foraminiferal shells often abound in mod- 
 ern deltas. Thus the Mississippi mud was found to contain an 
 abundance of marine Polygastrica and Phytolitharia as well as 
 fresh water Polythalamia. Phytolitharia also abound in the mud of 
 the Nile. Indeed, the range of foraminiferal shell material in the 
 Nile mud is from 4.6 to 10 per cent., while the Ganges carries as 
 high as 12.4 or even 25 per cent, of foraminiferal material. 
 
 Other animal remains have been found, but are less abundant. 
 Remains of arthropods occur in the Po delta sometimes in close as- 
 sociation with the lignites. Remains of river animals also abound 
 in modern deltas, as shown by the presence of turtles and croco- 
 dile remains in the delta deposits of the Ganges and the Zambesi. 
 Terrestrial vertebrate remains have likewise been found in these 
 deltas, among them bones of recent antelope, buffalo, lion, hippo- 
 potamus, and other mammals. 
 
 Gaseous Emanations of Deltas. The gradual decomposition 
 of the organisms in the delta deposits gives rise to gaseous emana- 
 tions which either escape through artificial borings in the delta or 
 find natural passageways through the mud, building up craters 
 as in the mud-lumps of the Mississippi delta. The numerous bor- 
 ings in the delta of the Po have furnished an abundance of inflam- 
 mable gas, the use of which for illuminating purposes has actually 
 been attempted. Sulphuretted hydrogen is also developed, espe- 
 cially where sea water comes in contact with the decaying vege- 
 table matter, as noted in the case of marine marshes (see ante, 
 page 493). In the mud-lumps of the Mississippi delta, the volume 
 of gas emitted is between 1/20 and 1/30 that of the mud flow 
 from these craters. The gas is probably not instrumental in these 
 mud eruptions, but merely an accompaniment of the same. 
 
 
6i6 PRINCIPLES OF STRATIGRAPHY 
 
 Cementation of Delta Deposits. The delta deposits may be 
 compacted merely by pressure, or the component particles may be 
 bound together by the introduction of a cement. The Rhone delta 
 contains much sandstone, the grains of quartz being bound by a 
 calcareous cement, due to the abundance of lime in the stream. 
 The presence of numerous limestone pebbles in glacial deltas also 
 becomes a source of lime which is redeposited among the pebbles 
 and cements them. Such an example is found in the partly con- 
 solidated, gravels of the Pleistocenic delta in the Ontario basin near 
 Lewiston, and a still more extensive one in the Nagelfluh delta of 
 the Salzburg region already referred to. Cementation by infiltrated 
 iron oxides also occurs. 
 
 Deposits of lime are especially abundant in deltas of arid 
 regions, such as the Volga, the Indus, the Nile, and the Colorado. 
 Extensive deposits of massive travertine and caliche have been 
 formed in Arizona and New Mexico. Such deposits are, how- 
 ever, also found where the river water is high in lime content, as 
 in the Rhine delta and in the Rhone delta already mentioned. In 
 the latter case the approach to a semi-arid climate over the delta 
 in the mediterranean is a further factor aiding deposition of lime. 
 The silt of the Rhine delta in the Lake of Constance contains 
 30.76% of CaCO 3 , 1.24% MgCO 3 , and 5.20% FeCO 3 . The other 
 principal constituents are SiO 2 50.14%, A1 2 O 3 4.77%, Fe 2 O 3 2.69%, 
 and small quantities of the oxides of manganese, magnesium, cal- 
 cium, potassium, and sodium. 
 
 Modification of the Delta Surfaces. The chief modifications 
 suffered by the delta are wave and wind erosion, and the forma- 
 tion of deposits over the surface of the delta. Wind erosion affects 
 the surface of the delta, while wave erosion occurs around the 
 margin of the delta when the force of the river no longer is able 
 to continue construction. It is common on a sinking coast, as 
 is shown by the encroachment of the sea on the deltas bordering the 
 North Sea. Wave erosion may also become effective when delta- 
 building has practically come to an end owing to the decrease of 
 supply incident to development of low relief with old age. In such 
 a case the sea may gradually encroach on the delta and plane away 
 the upper layers, until the remaining remnant of the delta is wholly 
 submerged, when normal marine sediments may succeed. In all 
 such cases there is commonly found a fringing belt of dunes at 
 the outer margin of the delta, as in the case of the Rhine delta. 
 Such dunes may also be formed where building is still in progress, 
 as in the Rhone delta, where dunes are formed between the two 
 principal mouths of the stream. Other eolian deposits may form 
 
MODIFICATION OF DELTA 617 
 
 .-* 
 
 on the delta, such as dust brought from a distance and wind- 
 arranged material from the surface of the delta itself. Additional 
 river deposits in the form of natural levees may be built by the 
 overflowing river, which leaves much of its material near the bank, 
 which is thus raised above the surface of the delta on either side. 
 The floor of the channel may also be raised by aggradation, and 
 the river thus flows at a* level much higher than that of the sur- 
 rounding country. Where the levees are artificially raised the 
 river bed may come to occupy a position far above the normal 
 level of the delta or flood plain. Thus the channel of the Po has 
 been elevated in this manner to such an extent that it is said to 
 rise above the tops of the houses in the town of Ferrara (Le Conte- 
 36:^). Where the sea temporarily floods part of the delta, de- 
 posits of salt may occur, as in the Rann of Cutch and other low- 
 lying delta districts. The Nile delta is likewise characterized by 
 saline deposits along the coast, due to evaporation of the sea water 
 which at intervals floods the surface. Over these salt beds sand 
 dunes are seen to wander. Deposits of vegetal material in swamps 
 further characterize many delta surfaces. Such deposits may be 
 marine marsh deposits or fresh water swamp deposits, or both. 
 Salt and gypsum deposits are not uncommon on the lower part of 
 the deltas in arid climates. 
 
 Relation of Delta Building to Crustal Movements. From the 
 known relations of rivers to delta building it would appear that 
 periods of strong river activities are also, as a rule, periods of 
 pronounced delta formation, while, conversely, periods of dimin- 
 ished river work will be, on the whole, periods of slow and com- 
 paratively limited delta building. In general, youthful ungraded 
 conditions of a land with corresponding high relief favor delta 
 building, while mature or graded conditions characteristic'of regions 
 of low relief are correspondingly unfavorable to delta building. 
 There are, however, modifying circumstances which may, to a cer- 
 tain extent, reverse these results, but as a general working proposi- 
 tion they may be confidently accepted. Furthermore, conditions of 
 youth and high relief with active river work are productive of an 
 abundance of coarse waste, which will result in the outward and 
 upward building of deltas with strongly contrasted slopes in fore-set 
 and top-set beds, while the finer waste supplied in lesser quantities 
 by a region of relative maturity will tend to build outward deltas 
 of gently inclined layers and, on the whole, of uniformity 
 of slopes or confluence of top-set, fore-set, and bottom-set beds. 
 In youthful regions of much waste supply the subaerial part of 
 the delta will become a prominent feature, while the reverse will 
 
6i8 PRINCIPLES OF STRATIGRAPHY 
 
 be true in regions past maturity and of slight supply of waste. 
 It is thus readily conceivable that periods of intensive and extensive 
 delta -building may alternate in the earth's history with periods 
 during which deltas are of relatively insignificant extent and the 
 size and number of deltas in one period afford no criterion by which 
 those of another may be measure^. 
 
 Effect of subsidence. While the effect of stationary sea-level 
 will be the rapid outward building of the delta, with pronounced 
 development of the fore-set beds, slow subsidence will result in 
 the extensive development of top-set beds and a restriction in the 
 building of the fore-set beds. If the subsidence is periodic and 
 interrupted, the sea will temporarily encroach on the delta, and 
 the terrestrial top-set beds will be covered by a layer of marine 
 sediments. Continued deposition by the rivers will, however, crowd 
 back the sea, and renewed building of top-set beds will occur. In 
 this manner intercalated marine layers will be formed between the 
 terrestrial deposits. Such layers are found in modern deltas as 
 already noted, and they are also common in older delta deposits, 
 where they are generally taken as indicating the marine origin of 
 the entire formation. That they have no such value is clearly 
 shown by their relation to the continental beds in modern delta 
 deposits. If subsidence were slow and more or less regular, con- 
 tinued deposition by rivers would tend to keep the sea out altogether, 
 and a thick deposit of top-set beds of terrestrial origin would result. 
 Such deposits of considerable thickness are found to characterize 
 the larger modern deltas, which thus appear to occupy sites of 
 continued subsidence. Similar conditions prevailed over the sites 
 of delta deposits of Mesozoic and Palaeozoic time, resulting in the 
 formation of continental deposits of great thickness. 
 
 Subsidence of such a rate as to be in excess of the building 
 power of the streams will put an end to the process of building the 
 deltas and result in their final submergence. This has been brought 
 about in a number of cases where former deltas and parts of 
 deltas are now below sea-level. In earlier geologic periods such 
 complete submergence has resulted in the burial of the delta de- 
 posit beneath a marine series of greater or less thickness. Credner 
 (14) and others have, indeed, held that any subsidence is detri- 
 mental to the process of delta building, and that such stuctures are 
 found only on rising or at least stationary coasts. That subsidence 
 has, however, played a part in the formation of modern deltas is 
 shown by the presence in most of them of terrestrial remains and 
 peat layers, etc., which now lie at a considerable depth beneath 
 sea-level (Fig. 127). 
 
DELTAS, AND CRUSTAL MOVEMENTS 
 
 619 
 
 Effect of elevation. Slight elevation of the delta area results 
 in the destruction by erosion of the top-set series in the upper parts 
 of the delta, and the carrying forward of the material to be added 
 to the subaqueous fore-set series. The zone over which continental 
 deposition takes place will also advance seaward, and thus terres- 
 trial sediments will come to rest on marine deposits. Where the in- 
 clination of the fore-set beds is very gentle these terrestrial beds may 
 come to rest upon them with practically no change in dip. Cessation 
 of elevation or reversal of movement and the resumption of normal 
 delta building will result in the deposition of a new terrestrial 
 series on top of the erosion plane, and a new marine series on top 
 of the terrestrial series nearer the sea. A hiatus and discon- 
 formable relationship will thus appear between the two members of 
 the terrestrial part of the delta, and this disconformity will be re- 
 
 ^'='7c.'^B^^B^>;'V:-^';l-'- Submarine de\fa'<tert&ite. : ?^\ ^^v^--'+^?J 
 
 ''Jf^'^S^fe :/.;: "vf^/.^j^^gp^^V; &*&** 
 
 ^^^^^^^r^rS^ 
 
 /V-.. L:_ L_ I _i- it.- j : i_7r^ *"' -^^^^^^g".-; < .- = . -._ ; -. ,- - .. .. / '.*,;! ~ : . - ~A , *.* : 
 
 ,, _ ..-. ^ 
 
 Conh'nental delta deposiKs. ..F ^v ; 
 
 *E ^ ^^^,^.^^^^-i 
 ~~&l -=~ \#, 
 
 ~ *Vj?'~- -.'?::: = ".^^^^^^m^^^ug^^^^^v- :.'..'.-,. /( Y :.: *''>''* \'i' ' .-"^'-.' 
 
 FIG. 127. Diagrammatic section of a seashore delta, showing the relation 
 of continental and submarine deposits in a region of fluctuating 
 sea-level. (After Barrell.) 
 
 placed seaward by a terrestrial layer interpolated between two 
 marine series. If the delta front is comparatively steep it may, 
 of course, happen that the uplift carries the erosion to the top of 
 the delta front, beyond which deposition will be submarine. In 
 a very large delta slow rising will result in the slow seaward migra- 
 tion of the zones of erosion and the zone of terrestrial deposition, 
 the lowering of the upper part of the delta by erosion progressing 
 steadily, while at the same time the zone of terrestrial deposition 
 extends farther and farther outward. (Barrell-6.) 
 
 Deltas Merging into Desert Deposits. A remarkable combina- 
 tion of a river delta with desert deposits, on the one hand, and 
 marine deposits, on the other, is shown by the Colorado on the 
 Arizona-California and Lower California boundary. This delta was 
 originally built into the Gulf of California, the head of which was 
 by it completely severed from the main part of this funnel sea. 
 The cut-off portion dried out completely under the influence of 
 
620 PRINCIPLES OF STRATIGRAPHY 
 
 the drying westerlies, leaving the arid Coahuila basin north of the 
 delta, the central portion of which is 300 feet below sea-level ; 
 while southward the delta enters the present head of the California 
 Gulf. Occasionally a northwest distributary of the Colorado, the 
 New River, carries water into the basin, which in the past has 
 filled to overflowing, a fresh water lake being thus formed. The dry- 
 ing up of this left saline deposits upon the lacustrine beds, and 
 these, together with the eolian and occasional river deposits, form a 
 complicated series of sediments succeeding the former marine de- 
 posits of the region, all of these changes being brought about 
 without any change in the sea-level. A moderate subsidence or a 
 partial destruction of the delta would let the sea in again, and thus 
 marine deposits would once more succeed the complicated terres- 
 trial series. The area thus affected is somewhere in the neighbor- 
 hood of 5,000 square miles. (Fig. 69, Chapter IX.) 
 
 COLORS OF CONTINENTAL CLASTICS. 
 
 The color of clastic rocks depends to a very large degree upon 
 the states of oxidation of its iron content, and the absence 
 or abundance of carbon. A low state of oxidation gives colors 
 ranging from green to blue, while the higher states of oxidation 
 are marked by yellow, orange, brown, or red colors. According 
 to the carbon content, the color may vary from white, when no 
 carbon is present, through various shades of gray to black. Abun- 
 dant carbon in the strata will prevent oxidation of the iron and 
 will reduce the higher oxides to the lower. Lack of carbon favors 
 high oxidation. 
 
 Sediments deposited on land or in very shallow waters are 
 especially subject to oxidation, unless there is an abundance of 
 organic matter present to prevent such oxidation. In moist or 
 pluvial climates with a moderate amount of vegetation, the soil 
 is apt to be bluish from the prevention of a high degree of oxidation 
 by the vegetation. This is especially true where the vegetation is 
 intimately associated with the soil. The manner in which this is 
 accomplished on the western side of Nicaragua has already been 
 referred to (p. 36). Where black soils are formed, as on 
 swampy surfaces, especially on low alluvial plains or peneplains, 
 oxidation is likewise prevented. The same thing is true of delta 
 deposits rich in carbon. Where, however, vegetation is extremely 
 luxuriant it may prevent the saturation of the soil with moisture 
 through transpiration and likewise prevent a satisfactory commin- 
 
COLORS OF CONTINENTAL CLASTICS 621 
 
 gling of the vegetation with the soil. In such cases oxidation may 
 proceed without hindrance, as in the case of the eastern slopes of 
 Nicaragua, where red soil from 3 to 10 meters deep underlies the 
 dense vegetation. 
 
 In seasons of dryness, when the amount of vegetation is small, 
 the iron of the sediments of deltas and alluvial fans may become 
 thoroughly oxidized. Where dryness prevails for most of the 
 year, and where vegetation is as a result scanty, such oxidation 
 may be especially favored. Thus semiarid or even desert regions 
 would furnish the best conditions for such oxidation. On river 
 flood plains there is always sufficient moisture to result in the 
 formation of hydroxides of iron, and hence the colors of such 
 deposits will range from yellows to ocher and brown. It is only 
 under conditions of intense heat that dehydration will result with 
 a consequent change in color toward the reds. Such change of 
 color may, however, take place as the result of aging of the deposit, 
 as pointed out by Crosby. In such a case dehydration is virtually 
 spontaneous, and "... the color of the deposit, so far as it 
 is due to ferric oxide, is, other things being equal, a function of its 
 geological age." "In other words," says Crosby further, "the color 
 naturally tends with the lapse of time to change from yellow to 
 red; and, although this tendency exists independently of the tem- 
 perature, it is undoubtedly greatly favored by a warm climate." 
 
 (150 
 
 Barrell (4:288) holds that "a still more potent cause exists 
 Ir . . in the dehydration effected by the great increase in pres- 
 sure and moderate rise in temperature which takes place upon 
 the burial of the material to some thousands of feet beneath later 
 accumulations." Under such pressure the tendency would be for 
 the oxide to give up its water with corresponding reduction in 
 volume (see ante, p. 177), just as shales are formed by the giving 
 off of about one-half the combined water by the silicate of alumina, 
 and this at temperatures probably often far below boiling point. 
 
 It is, of course, necessary that organic matter should be absent 
 from such a deposit, for its presence would prevent oxidation in 
 the first place. It is not necessary that the absolute amount of iron 
 should be very large to affect the color of the deposit. The bril- 
 liant red Vernon shales of the eastern New York Siluric carry 
 only 2.25 per cent, of ferric iron and 0.75 per cent, of ferrous iron 
 (Miller-39). The chief desideratum is that the iron should be in 
 an extremely fine state of subdivision and intimately disseminated 
 or diffused through the mud or dust deposits. This fine division 
 and diffusion of the iron have been noted by Dawson for the red 
 
622 PRINCIPLES OF STRATIGRAPHY 
 
 Mississippic beds of Nova Scotia, where the iron has "the aspect 
 of a chemical precipitate rather than of a substance triturated me- 
 chanically" (20:^5). The same thing has been noted by Hilgard 
 with regard to the red tropical soils, where the percentage of 
 ferric oxide is by no means markedly high, but where the oxide 
 is very finely diffused throughout the mass. 
 
 Finely diffused oxide of iron, but in the state of ferric hydrate, 
 is the coloring agent of the yellow loess of China. The total amount 
 of ferric oxide in American loess ranges from 2.50 per cent to 3.74 
 per cent., and in one case to 5.22 per cent., while a limited amount 
 of FeO (from 0.12 to 1.02%) is also present, but organic carbon 
 is very slight, ranging from 0.09 to 0.19 per cent. Dehydration of 
 the iron with age, especially after burial, would result in the forma- 
 tion of fine-grained red deposits, in every respect similar to the 
 Vernon red shales. 
 
 The red Vernon shales, like red shales and sandstones fre- 
 quently, are associated with salt and gypsum deposits. This is 
 an indication of arid conditions during the deposition of the muds 
 from which these shales are formed. Salt and gypsum deposits of 
 the present time are associated with gray and bluish-gray muds 
 and it is only by subsequent oxidation and dehydration that the 
 red color is produced. 
 
 One of the essentials in the production of red rocks by such 
 subsequent oxidation and dehydration appears to be the virtual 
 absence of organic matter which would prevent oxidation. Where 
 the ground water level is high organic matter will accumulate and 
 oxidation is prevented. But where the sands and muds are ex- 
 posed to circulating air in dry seasons, with a low ground water 
 level, more or less complete oxidation of the iron will take place. 
 Such a condition is found in delta deposits of arid regions, as, for 
 example, the Nile delta, in which organic matter seems to be of 
 very small amount, while the iron content is comparatively high. 
 It is probable that the Nile mud on aging would take on a red color. 
 
 There is, however, another factor which may affect the change 
 in color, and that is the lime carbonate content of the deposit. This 
 is high in many delta deposits of arid regions and its presence may 
 prevent the production of a red color by the formation of complex 
 silicates of lime, iron, and alumina. According to Ries (4.7:6, n) 
 a buff or cream color is produced if clay containing three times as 
 much lime as iron or more is burned into bricks. Magnesia has 
 the same coloring effect on the burned ware as lime, while alkalies 
 tend to turn the iron red into a brown. As the Rhine delta in the 
 Lake of Constance has nearly 12 times as much lime carbonate as 
 
COLORS OF CONTINENTAL CLASTICS 623 
 
 iron oxide, it would not produce red bricks, and it is not improb- 
 able that the lime would have the same effect in preventing the 
 formation of a red color with age. 
 
 Alternation of Red Beds with Those of Other Colors. This is 
 a feature often found in older formations and has also been ob- 
 served in modern continental hydroclastics. Huntington (34:36^) has 
 described such deposits of pinkish or reddish sandy clays and sands 
 alternating with whitish or greenish clays from the uplifted and 
 dissected Pleistocenic deposits of the basin of Seyistan in eastern 
 Persia. These layers are well shown in cliffs from 400 to 600 feet 
 high, exposed by recent erosion. The red beds are continuous and, 
 while preserving their general aspect for many miles, they vary 
 greatly in detail. Wedging out layers of sand or even gravel occur, 
 slight erosion disconformities, occasional ripple marks, worm-casts 
 and rain-drops are not uncommon, and the uniform oxidation of 
 these beds indicates long exposure to the air under conditions of 
 aridity. This is further shown by the condition of the modern 
 delta deposits of the region, of which the subaerial part is well 
 drained and aerated and everywhere of a light brown color. On the 
 shores of the modern Lake of Seyistan, where the clayey beds are 
 saturated with water and subject to successive floodings, the brown 
 colors are replaced by light colored soils with black bands. The 
 margin of the present lake supports a dense growth of reeds and 
 the clay deposits on its bottom are greenish and white. The green- 
 ish and whitish beds of the dissected older deposits correspond to 
 these lake sediments. They represent subaqueous deposits formed 
 during the greater extent of the lake, and in continuity and uni- 
 formity, as well as color, they contrast strongly with the pink and 
 red beds formed during the contraction of the lake as subaerial 
 sediments. 
 
 Alternating red and white layers of this type are characteristic 
 of the Moencopie formation of northern Arizona and southern 
 Utah, a deposit of Permic age. The absence of fossils and the 
 general close correspondence between these beds and the series 
 exposed in the dissected basin of Seyistan have led Huntington to the 
 conclusion that both have a similar origin. 
 
 Alternations of gray and green sandstones with red clays are 
 well shown in the Middle Siwalik group, a late Tertiary deposit 
 exposed in the foothills of the Himalayas. As previously noted, 
 this formation represents a fluviatile deposit, of the type now form- 
 ing over the Indo-Gangetic plain. A corresponding Devonic ex- 
 ample is seen in the Catskill formation of eastern New York and 
 Pennsylvania, where, through a thickness of perhaps 5,000 feet, 
 
. 624 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 there is a constant alternation of red shales and greenish sand- 
 stones. The physical characteristics of the deposit and the absence 
 of marine and presence of land and fresh water organisms show 
 that this series was formed under fluviatile conditions similar to 
 those of the Siwalik. 
 
 Lateral variation in color is also a frequent feature of older 
 deposits and can be explained ^by the contemporaneous beds now 
 forming in the Seyistan basin, where the oxidized subaerial de- 
 posits merge laterally into the unoxidized subaqueous or lacustrine 
 ones. The fossiliferous Permic limestones and shales of Kansas 
 may be traced southward into red sandstone and shales of the 
 same age in Oklahoma, the latter being practically unfossiliferous. 
 These red clays may be in part the residual clays from dissolved 
 limestones (Beede-7) and in part of clastic origin. Their high 
 state of oxidation suggests widespread subaerial deposition under 
 sufficiently arid conditions to permit the free influence of the 
 atmosphere. Lateral variation of a more irregular character is 
 shown in some Mesozoic clays, such as the Potomac group of the 
 Atlantic coast, and the Cretacic Atlantosaurus or Como beds of 
 Wyoming, and in the Tertiary beds of the Wind River and Big- 
 horn basins and elsewhere. In the Wasatch and Wind River 
 clays analyses have shown the iron content to be as follows f Sin- 
 clair and Granger-52 11/5) : 
 
 Horizon 
 
 
 
 Total Iron 
 
 
 Total Iron 
 
 
 Phase 
 
 calculated as 
 
 
 
 
 Fe 2 3 
 
 FeO 
 
 Fe 2 O 3 
 
 I. 
 
 Mottled (red and blue) clay, 
 
 
 
 
 
 
 Wind River 
 
 red 
 
 8.16 
 
 o. 19 
 
 7.91 
 
 
 
 blue 
 
 6.67 
 
 0.38 
 
 6.24 
 
 2 
 
 Blue clay, Wasatch 
 
 blue 
 
 -J T.A 
 
 O S2 
 
 2. 77 
 
 3- 
 
 Red clay, Wasatch, same locality 
 
 red 
 
 4.82 
 
 0.58 
 
 4.18 
 
 Sinclair and Granger comment on these analyses as follows : "In 
 all the samples examined, the total iron in the red clays is in excess 
 of that present in the blue by 1.48 per cent, to 1.49 per cent. The 
 amount of ferrous iron in the blue Wasatch clay is less than that 
 present in the red, while in the mottled Wind River clay it is 
 
COLORS OF CONTINENTAL CLASTICS 625 
 
 slightly greater in the blue than in the red phase, but in neither 
 case does it seem possible to ascribe the blue color to ferrous oxide, 
 as this substance is far exceeded in amount by ferric iron, evidently 
 occurring in the blue clay in some other form than ferric oxide 
 (hematite), perhaps as a hydrous silicate. In the Wasatch clay 
 the red contains 1.41% more Fe 2 O 3 than the blue; in the Wind 
 River clay Fe 2 O 3 in the red phase is 1.67% greater than in the blue. 
 If this excess of iron is present in the form of hematite, as the red 
 color seems to show, it is possible that the remaining iron in the 
 red clay may be in the same form as in the blue (a hydrous sili- 
 cate?) and that the blue color has been masked by the red pig- 
 ment." 
 
 'The results of analysis seem to show that the blue color has 
 not been derived from the red by reduction of the iron as ordinarily 
 understood. The red color may have been derived from the blue by 
 conversion of the hypothetical silicate into carbonate by meteoric 
 waters, and the subsequent oxidation of these salts, or by the intro- 
 duction of iron compounds in solution and their concentration and 
 oxidation possibly under drier climatic conditions than existed 
 during the deposition of the blue clays. We favor the latter alterna- 
 tive and regard the coloration of the clays as a phenomenon con- 
 trolled by conditions active during the deposition of each individual 
 stratum (red or blue, as the case may be), and not by subsequent 
 or secondary changes. Under the arid conditions which exist at 
 present over most of the Wind River and Bighorn basins, the 
 blue clays show no tendency to weather red. The layer of weath- 
 ered mud-cracked clay on the surface of bad land slopes cut in the 
 blue clays is yellow from the hydrous oxide, limonite." ( $2 :/ 15, 
 116.) 
 
 Original Red Color of Sediments. Whatever the case above 
 mentioned shows, it must not be overlooked that some sediments 
 when deposited already have a decidedly red color, or that this may 
 be acquired before burial. Soils washed from regions of extensive 
 laterite formation will be deposited as red sediments either on 
 land or in the sea. Such sediments may be carried great distances 
 from regions where they are formed to regions where their pro- 
 duction is prohibited by the local climatic conditions. Russell held 
 that the red sands of the Newark system were deposited with a 
 coating of red iron oxide formed during decomposition. This con- 
 clusion may, however, be questioned. 
 
 Desert sands not infrequently have their grains coated with 
 a thin deposit of iron oxide which often gives the sands a brilliant 
 color, as in the case of the carmine sands of the Nefud desert of 
 
626 PRINCIPLES OF STRATIGRAPHY 
 
 northern Arabia. The source (57:^5) of the iron is believed to be 
 in the sand itself, as shown by analysis, the coating having formed 
 under the influence of the sun's heat, as the desert varnish forms 
 on the larger pebbles and boulders. This latter, however, is 
 subject to destruction owing to the size of the fragments, for 
 Walther has observed that after a hea-vy rain this brown coating 
 is quickly removed by the impact of the rock masses. In like man- 
 ner a coating of iron oxide on sand grains subject to wind trans- 
 port must be destroyed, and this probably accounts for the almost 
 uniform white or golden color of desert sands. The absence of 
 such a coating, then, on the pebbles of ancient desert gravels 
 need not be surprising, and the yellow or white color of gravel 
 and coarse sand beds intercalated between red deposits may not 
 necessarily indicate great climatic differences, but may result rather 
 from the destruction of the color coat in the coarser material. 
 
 EXAMPLES OF OLDER CONTINENTAL HYDRO- 
 CLASTICS. 
 
 Examples of fluviatile and lacustrine deposits have been rec- 
 ognized in nearly all geological horizons, from the pre-Cambric to 
 the present. Not all stratigraphers agree in regarding the forma- 
 tions enumerated below as of unequivocally non-marine origin, but 
 the more obviously fluviatile and glacial formations are recognized 
 as such by most recent students of the subject. 
 
 CENOZOIC OR TERTIARY EXAMPLES. 
 
 Among the Tertiary deposits of the Great Plains regions of the 
 western United States are many beds showing stratification, but 
 composed in large part of alternate pebble and sand beds, with 
 cross-bedding structure well marked. These have commonly been 
 classed as "lake deposits," but, as Davis (19:345) has shown, these 
 are more likely deposits made by running water, and represent 
 outwash plains or alluvial fans, formed by the streams from the 
 mountains. Some of these deposits, as in the case of the Vermillion 
 Creek beds in Wyoming, consist near the mountains from which 
 they have been derived of excessively coarse conglomerates be- 
 tween 3,000 and 4,000 feet thick, nearly structureless, lines of 
 stratification being rarely perceived, "The blocks of which the con- 
 glomerate is chiefly formed range from the size of a pea to masses 
 with a weight of several tons . . ." (King-35 :j<5p.) At some 
 
TERTIARY CONTINENTAL HYDROCLASTICS 627 
 
 distance from the mountains the beds consist of coarse red sand- 
 stones interbedded with clays and arenaceous marls. In the Arapa- 
 hoe and Denver formations of Colorado, basal conglomerates from 
 50 to 200 feet in thickness are succeeded by arenaceous clays, and 
 these, in turn, are followed by 400 feet of eruptive debris, above 
 which are again conglomerates and sands derived from the moun- 
 tains. Cross-bedding and wedging out of layers are common, show- 
 ing a considerable current. In some of the beds "tree stumps in 
 erect position with roots in mud layers and broken trunks in sand 
 or gravel . . ." occur (Cross-i6:id#) and contemporaneous 
 lava flows are interbedded with the sediments. 
 
 In these deposits the remains of terrestrial vertebrates are fre- 
 quently abundant, while fresh water animals are found only where 
 temporary bodies of water existed. Associated with typical atmo- 
 clastic are lacustrine deposits, often rich in remains of fish or 
 other fresh water animals, and eolian deposits (anemoclastics). 
 Not infrequently the atmoclastics extend out covering either lacus- 
 trine or eolian deposits. 
 
 The Eocenic and Oligocenic deposits of the Wind River and 
 Bighorn basins in Wyoming have already been referred to. These 
 deposits consist of clays and sands often well banded and alternat- 
 ing red and bluish in color, of arkose sands, and of conglomerates 
 and occasional fine tuffs or pyrolutytes. They contain land and 
 river vertebrates, such as crocodiles, turtles, garpike, Eohippus, 
 Heptodon, Lambdotherium, etc., and shells of Unio. Microscopic 
 as well as macroscopic study of the deposits has shown that they 
 are derived from the crystalline or other rocks of the enclosing 
 mountains, and their character and mode of occurrence show that 
 they were either wind or river transported. In the coarser sand- 
 stones and arkoses of the Wind River and Bridger ( ?) beds, 
 Archaean granites and Palaeozoic quartzites are readily recognizable. 
 "The well-rounded gravels, found in some of the arkoses, point 
 with equal certainty to running water as the transporting agent, 
 while fluviatile deposition is shown by the frequent channels filled 
 with coarse sandstone which cut irregularly across the finer clays, 
 by the frequent interstratification of sandstone lenses with the clays 
 and by the presence in the latter of fish, crocodiles, and turtles, 
 and occasional beds of Unios. Local swamps are indicated by 
 lignites in the blue clays and sandstones, but never in the red 
 clays." 
 
 Sometimes change in climate or steepening of grade is indi- 
 cated by coarsening of sediments . . . "for instance, the 
 coarse, frequently cross-bedded arkose forming the lower member 
 
628 PRINCIPLES OF STRATIGRAPHY 
 
 of the so-called Bridger of the Beaver Divide appears to represent 
 a series of conjoined alluvial fans spreading out over the banded 
 clays of the Wind River, but it is not possible to say whether the 
 gravels and sands were transported by torrential streams under 
 a dry climate or by streams whose carrying capacity had been in- 
 creased by uplift." (Sinclair and Grange r~52 :uj.) The fresh- 
 ness of the feldspars indicates that they had not been leached by 
 carbonated waters, such as might be expected to occur if they 
 were deposited in a region of high humidity. This also suggests 
 that they have not been derived from the parent rock by ordinary 
 weathering processes, but rather by temperature changes, which 
 shatter the minerals without affecting their freshness. Altogether, 
 the deposits suggest dry, not necessarily arid, climate, with rapid 
 changes of temperature and rapid transportation for short dis- 
 tances and burial beyond the reach of carbonated waters. 
 
 The clays of the Wasatch and Wind River deposits are com- 
 monly banded, alternating beds of red and blue-green clay or of red 
 with mottled clay occurring. "The red clays are frequently streaked 
 with blue-green color along joint cracks or are traversed by anas- 
 tomosing green lines along what may have been the courses of 
 roots. The beds are lenticular in shape, varying from a few 
 inches in thickness, with little horizontal extent, to strata from 18 
 inches to 50 feet in thickness, traceable sometimes for several 
 hundred yards to a mile or more. . . . Lignite is never found 
 in the red clays, but may be present in the blue. . . ." The fos- 
 sils found in the red beds are always fragmentary, "the more re- 
 sistant parts, such as jaws and teeth, predominating. In the blue 
 and mottled clays associated skeletons ... of Coryphodon 
 were found." (Sinclair and Granger-52 1114, -f/5.) The microscope 
 has not revealed any essential difference between the variously 
 colored clays. 
 
 Sinclair and Granger ascribe the color banding to the alternation 
 of moist and dry climatic conditions, though no evidence of exces- 
 sive aridity has been found ; the fauna of the red and blue bands 
 being the same. "The clays cannot owe their color to different 
 sources of supply, for they are microscopically the same and the 
 alternation of color bands is too regular and of too frequent re- 
 currence to permit this inference. The red clay cannot represent 
 upland oxidized wash, for waters swift enough to carry the bone 
 fragments found in the clay would also transport rock fragments 
 of some size, and these are not found." The blue clays of the 
 Wasatch are sometimes lignitic and often afford associated skeletal 
 remains, and this suggests that they were formed during cycles 
 
TERTIARY CONTINENTAL HYDROCLASTICS 629 
 
 of more abundant rainfall, when the surface of the intermontane 
 basin was prevented from drying out rapidly. The red clays, how- 
 ever, appear to have been formed "during the drier cycles, when 
 the carbonaceous matter of decaying plants was completely oxidized, 
 concentration and oxidation of iron compounds occurred, and ani- 
 mal bones exposed at the surface were weathered and broken be- 
 fore entombment." Conditions of this kind seem to have been 
 widespread, as shown by similar color 'banding in the Wasatch in 
 other localities. 
 
 In the Wasatch formation along the contacts of red and blue 
 beds or in many of the red beds themselves great numbers of 
 fragmentary jaws and scattered teeth of vertebrates have been 
 found. The clays appear to represent the deposits on the dry basin 
 floor over which the bones of these creatures were scattered and 
 weathered before being buried. In the blue clays associated skele- 
 tons are common. These are the remains of animals which were 
 either drowned and rapidly covered beneath fluviatile sediments or' 
 were mired in the soft clays. The teeth found in the Wind River 
 area usually have the roots worn away and only the harder enamel- 
 covered crowns are preserved. The Unio beds of the Wasatch are 
 always of limited extent and seem to be confined to the blue clays. 
 The lignite layers in these clays are usually mere dirt bands, but 
 some in the Wind River basin have considerable thickness (52:1/7). 
 
 The Oligocenic beds of this region contain limestone deposits 
 associated with wind-laid volcanic tuffs. These limestones, which 
 are found near the top of the series, are a spring deposit forming 
 sheets of tufaceous limestone, or layers of white nodular masses, 
 calcareous without, but containing more or less silica within. Worn 
 quartz, feldspar, and pink granite pebbles are sometimes found in 
 the limestone, which is also partly replaced by silica in the form 
 of opal or chalcedony. No fossils have been found in the lime- 
 stone, which appears to have been formed under relatively dry 
 climatic conditions. 
 
 These Tertiary deposits on the eastern slopes of the Rockies 
 have thus all the characteristics of deposits formed under semiarid 
 conditions. These conditions prevail to-day in this region under 
 the influence of the westerly winds, which, on crossing the Coast 
 Range, where they leave most of their moisture, become still drier 
 on crossing the Rockies. Greater elevation of the mountain ranges 
 would probably increase .the aridity of the Interment basins in this 
 region and so reestablish the conditions of Tertiary time. 
 
 Hobbs (31) has recently described a typical torrential forma- 
 tion of great thickness from southern Spain. This ranges in age 
 
630 PRINCIPLES OF STRATIGRAPHY 
 
 from Miocenic to the present. Its material is derived from the crys- 
 tallines of the Sierra Nevada, from the northern flanks of which it 
 extends for twenty-five miles, and locally from the Triassic dolo- 
 mite of the Sierra Harana (Alhambra formation). The formation, 
 approaching a thousand feet in thickness, is a conglomerate near 
 the mountains with pebbles varying "from a fraction of an inch to 
 six inches or more in length." Within the various stream valleys 
 local peculiarities of rock material exist, corresponding to the pecu- 
 liarities of the rocks in the respective headwater branches of 
 these streams. At a distance from the mountains fine material 
 prevails, much of it of a loess-like character, indicating wind and 
 playa-lake deposition. Floated plant material, such as roots and 
 brushes, appear to be characteristic of some of the finer deposits. 
 These torrential deposits seem to be intimately related to the 
 semiarid conditions of the interior of Spain, caused by the monsoon 
 winds. These winds blow northward from the Mediterranean in 
 summer, crossing the Sierra Nevada and leaving much of their 
 moisture on the southern slopes. Descending the northern slopes 
 they are relatively drying winds and so permit the formation of 
 these periodic torrential deposits. 
 
 Similar torrential deposits of great thickness and ranging in 
 age from late Tertiary to the present are described from southern 
 Italy (31:^90). A marked pross-bedding structure, already re- 
 ferred to (Fig. 123), so similar to what is commonly found in an- 
 cient sandstones, is characteristic of many of these deposits. The 
 Siwalik formation of India has already been cited as a subaerial 
 deposit of similar character and age. It is of great interest in that 
 it reaches the enormous thickness of 15,000 feet. Here also belongs 
 in part the Mollasse of the Alps. This is a complex series of 
 light-colored sandstones and conglomerates with occasional lime- 
 stones, found in the Alpine forelands, in the south of Germany and 
 in Switzerland. The lower part of the Mollasse is of Oligocenic age 
 and begins as a marine series. In southern Germany this reaches in 
 places a thickness of 600 meters (Bavaria) and is followed by an 
 immense series of fresh water sands and conglomerates approach- 
 ing a thousand meters in thickness. This series shows in part 
 brackish water and in part fluviatile and lacustrine conditions. The 
 brackish water phase contains Cyrena, Cerithium, Cytherea, etc., 
 and the fresh water Limngeus, etc. Numerous leaves and other 
 remains of land plants (Cinnamomum, Juglans, Quercus, Betula, 
 Rhamnus, etc.) are found locally, forming what is known as 
 "Blattermollasse" and forming occasional beds of brown coal, 
 which is extensively exploited in the Bavarian fore-Alps. Red sedi- 
 
TERTIARY CONTINENTAL HYDROCLASTICS 631 
 
 ments forming the "red Mollasse" are frequent in the upper non- 
 marine part of the Oligocenic Mollasse, especially in Switzerland, 
 but occur also in upper Swabia. The red beds are generally fol- 
 lowed by conglomerates with pebbles ranging in size from that of 
 an egg to that of a man's head and locally kown as Nagelfluh. 
 These in places reach a great thickness. Away from the Alps the 
 material becomes finer. The Miocenic Mollasse succeeding this 
 often begins with calcareous beds to a large extent formed of the 
 shells of the land snail, Helix rugulosa (Rugulosa limestones). 
 This is followed by a series of loose sands, glauconitic sandstones 
 and conglomerates (Nagelfluh) several hundred meters thick in the 
 southern part of the region. The lower part of this series is again 
 purely marine, but the upper part is once more brackish and non- 
 marine, beds containing Cardium sociale, Melanopsis, etc., marking 
 the brackish portion ; sands with Paludina, Unio, and Chara fruits, 
 marking the lacustrine and fluviatile. These series constitute the 
 Middle Mollasse. The highest beds finally forming the Upper 
 Mollasse of Upper Miocenic age are again wholly non-marine. 
 They consist of sands, clays, marls, occasional thin beds of brown 
 coal, local volcanic tuffs and especially non-marine limestones. 
 These so-called Sylvana limestones consist of the shells of the land 
 snails Helix sylvana and H. inftexa, of those of the pond and river 
 snails Planorbis, Limnseus, etc. Bones of the mastodon also occur. 
 Other beds contain an abundance of the shells of the river and 
 lake molluscs, Unio, Anodonta, Limnseus, Melania, Melanopsis, 
 etc. Local deposits of thin marly limestones with plant (maple, 
 poplar, etc.) and insect remains also occur, as in the celebrated de- 
 posit of Oningen on the Lake of Constance (Bodensee) and 
 local deposits like those of the Steinheim basin with its sands 
 filled with Planorbis, Helix, and land vertebrates. Remains of 
 terrestrial vertebrates abound in all of these deposits. 
 
 Since the axis of the Alps is parallel to the direction of the rain- 
 bringing winds, both sides receive an abundant rainfall, though 
 within the mountains are dry valleys. The extensive formation of 
 the Mollasse, partly of subaerial origin on the northern side of the 
 Alps, suggests a different condition during Tertiary times, so as to 
 result in a more arid condition on the north, or, at any rate, in con- 
 ditions which would favor the formation of extensive alluvial fans. 
 
 MESOZOIC EXAMPLES OF CONTINENTAL HYDROCLASTICS. 
 
 The Potomac Formation of the Atlantic coast of North America 
 represents a series of delta and flood plain deposits comparable 
 
632 PRINCIPLES OF STRATIGRAPHY 
 
 to those of the Huang-ho and the Indo-Gangetic plain. Extensive 
 torrential deposits are absent here, the series being composed mainly 
 of sands and clays. The series goes back to late Jurassic or early 
 Comanchic time, and comprises four 'main divisions, the Patuxent, 
 Artindel, Patapsco, and Raritan. The organic remains in these 
 deposits are chiefly land plants, while the remains of a land fauna 
 have also been found. No marine organisms are known except in 
 the upper part of the series, the Magothy formation of New Jer- 
 sey, which, however, also contains land plants. Above this series 
 lie sands and clays with an Upper Cretacic marine fauna. These 
 deposits were spread upon a broad coastal belt by rivers coming 
 from the region of Palaeozoic and older strata on the northwest, 
 where peneplanation was in progress. The sea margin at this time 
 must have been some distance farther to the east than the present 
 coast. The rivers were numerous and more or less evenly spaced, 
 so as to produce a continuous series of confluent deltas which ex- 
 tended from Massachusetts to the Gulf of Mexico. Landward the 
 subdivisions of this series are separated by erosion disconformities, 
 marking periodic upwarpings, but seaward they become thicker, 
 and the disconformities probably disappear. Somewhere east of 
 the present coast line these deposits probably pass into a continu- 
 ous marine series, now submerged. 
 
 The fluviatile origin of these deposits is suggested by the dis- 
 continuity of the strata, beds and lenses of clay and gravel occurring 
 in sand and vice versa. Many of the clays are strongly variegated 
 in color, the state of oxidation of the iron varying both horizontally 
 and vertically, while concentrated segregations of the iron also oc- 
 cur. Such variable conditions for oxidation exist on river flood 
 plains, but not in lakes or on the sea bottom. The abundant plant 
 remains, which by their character show little transportation, as 
 well as the absence of marine, brackish or even lacustrine organ- 
 isms, strongly indicate fluviatile -conditions, as do also the bones 
 of dinosaurs, turtles, and crocodiles. 
 
 The Arundel formation appears to have been deposited within 
 stream valleys eroded in the Patuxent, and in this formation gyp- 
 sum has been found. This suggests greater aridity during the 
 period of deposition of this formation than during the time the 
 more widely spread sands and clays of the other divisions accumu- 
 lated. In the Raritan formation feldspathic sands occur, further 
 suggesting an increase in aridity, while lignitic quartz sands alter- 
 nating with highly oxidized sands testify to a variety of conditions. 
 Some of the quartz sands show the characteristics of dune deposits. 
 Upward the occurrence of lignites with Teredo borings marks the 
 
MESOZOIC CONTINENTAL HYDROCLASTICS 633 
 
 beginning of marine invasion, the river building processes being 
 overcome by the invading forces of the sea. (See further, 
 Barrell-6.) 
 
 The Red Beds of North America. The Red Beds of the Rocky 
 Mountain region 'and the similar red sandstones of the Newark 
 formation of the eastern United States are now generally recognized 
 as subaerial deposits, in part of fluviatile and in part of eolian 
 origin, with subordinate lacustrine and rarely estuarine conditions. 
 The source of the western red beds was the old Palseocordilleran 
 chain of mountains formed at the end of the Palaeozoic, and 
 extending northwestward from Arizona to northern California. 
 On the Pacific side of this chain marine Triassic and Jurassic beds 
 were forming, while east of the range a series of alluvial fans ac- 
 cumulated, these being now in part represented by the Red beds. 
 Their highly oxidized character indicates that accumulation was 
 under semi-arid climatic conditions, such as would prevail with a 
 westerly wind sweeping over a mountain chain of sufficient height 
 to deprive it of most of its moisture. That vegetation, neverthe- 
 less, existed in some parts of the mountain slopes is shown by 
 the abundance of the petrified woods preserved in these deposits, 
 into which they were probably carried by torrential streams. Ac- 
 cording to Williston and Case (59) the upper Red beds, from 
 Lander, Wyoming, on the north to New Mexico, Kansas, and Texas, 
 on the south, range from five hundred to possibly a thousand feet 
 in thickness and are ''barren or almost barren measures character- 
 ized by light colors of the sandstone, often of eolian origin, and 
 more or less interspersed or capped with massive beds of gypsum." 
 It may be added, however, that some authors still hold to the ma- 
 rine theory of origin of these beds. (See, especially, Henning-28.) 
 
 Vertebrate fossils of Triassic (Keuper) age are reported from 
 all along the line of outcrop, chiefly comprising phytosaurs and 
 labyrinthodonts, closely agreeing- with species from the European 
 Keuper. Some of the lower Red beds of the southern and western 
 region are of Permic age, and indicate the earlier commencement 
 of this type of sedimentation. 
 
 Triassic Red Beds of Eastern North America and of Europe. 
 The Newark series is likewise best regarded as forming local 
 remnants of a combination of widespread alluvial fans, river flood 
 plain, and eolian deposits, derived from the Appalachians to the 
 west and built out toward the east on the low coastal plain, or into 
 depressions, and under conditions of semi-aridity which permitted 
 pronounced oxidation of the sediments. The beds themselves 
 abound in shrinkage cracks, raindrop impressions and animal foot- 
 
634 PRINCIPLES OF STRATIGRAPHY 
 
 prints. Fish remains and shells of Estheria are found in inter- 
 calated black shales, and terrestrial plant remains are not uncom- 
 mon in some sections. Much feldspar occurs and this together 
 with the oxidation of the iron compounds indicates the relative 
 aridity of the climate. Intrusive sheets and lava flows characterize 
 the northern development, and coal beds the southern. Barrell 
 and Kummel have brought forward evidence in the sediments that 
 a part of the material in Connecticut and in New Jersey was de- 
 rived from the east as well as from the west. They therefore 
 consider the deposits as formed in large basins bounded by faults, 
 rather than accumulations on a coastal plain surface. Until re- 
 cently the Triassic deposits of eastern North America were inter- 
 preted as estuarine accumulations (Russell-48; Chamberlin and 
 Salisbury-n), but the detailed study of the physical characters 
 of the rocks has developed the evidence which shows them to be con- 
 tinental deposits (Barrell-5). Similarly the corresponding Triassic 
 deposits of northern and western Europe, the New Red sandstone 
 of England and the Bunter Sandstein and Keuper of Germany had 
 been regarded as estuarine, tidal, or lake deposits (Reade-46), 
 but their subaerial origin, as sediments deposited by rivers chiefly 
 from the mountains of that period on the south and west, is being 
 more generally recognized. On the Continent the material was 
 chiefly derived from the old Vindelician mountain range which 
 existed where now is the valley of the Danube and separated the 
 Alpine Triassic sea from the North German lowlands. According 
 to Brauhauser (Fraas-22:5/j) the pebbles of the Lower Bunter 
 sandstein of Schramberg are not worn by rolling, but the pebbles 
 of the conglomerate forming the base of the Middle Bunter are 
 well rounded and their size decreases from southeast to northwest. 
 The material is derived from the crystallines and from the Rothlie- 
 gende of the Permic. Wind-cut facetted pebbles also occur, but 
 they have been more or less worn- by subsequent reworking. Wal- 
 ther (58:79) speaks of middle and eastern Europe in Lower 
 Triassic time as a huge desert area supplied with variable detritus 
 by streams from the mountains on the south and west, and covered 
 by endless dunes, interspersed with ponds, and once at least by 
 a large relict sea. Clastic material accumulated to a depth of 400 to 
 600 meters, after which the sea invaded the region from the east 
 and .the marine Muschelkalk was deposited. An earlier temporary 
 and partial invasion of the sea is suggested by fossiliferous hori- 
 zons. The Keuper marks a return to continental sedimentation, 
 which in Switzerland, France, and England was uninterrupted. 
 At the beginning widespread sandstones (Schilf sandstein) were 
 
PALEOZOIC DELTA DEPOSITS 635 
 
 formed, these being- interpreted as flood plain and delta deposits. 
 (Fraas-22:5/<5). The upper sandstone (Stubensandstein) has been 
 interpreted as probably in part a fluviatile and in part an eolian 
 formation, the sandstones representing an accumulation on a flat 
 piedmont area at the foot of the actively eroded Vindelician moun- 
 tain chain. The extensive variegated clays of the Keuper have 
 been regarded by Lang and others as marine sediments, but 
 Philippi (44:465), Fraas (22:5/7), an d Walther (58) consider 
 them rather as aerial sediments especially of eolian origin, repre- 
 senting a sort of loess-like accumulation. This interpretation is 
 suggested by the manner of occurrence in these sediments of the 
 skeletons of phytosaurians, aetosaurians, land turtles, and laby- 
 rinthodonts, with occasional dinosaurs, all lacking evidence of tran- 
 sport or destruction by aquatic animals such as might be expected if 
 the remains were carried into the sea. The prevailing color of 
 these sediments is red except where they were subsequently re- 
 worked by water, and here a gray color predominates. 
 
 PALEOZOIC DELTA DEPOSITS. 
 
 These are numerous, especially in North America, where a 
 whole series has been determined. Thus the entire Coal Measure 
 series and Permic of eastern North America chiefly consist of river 
 deposits with only occasional incursions of the sea. The Pottsville 
 conglomerate at the base of the series is an especially good ex- 
 ample. It was deposited from two centers, one in east central 
 Pennsylvania, the other in southern Virginia. From these points 
 outward the beds progressively overlap away from the source of 
 supply, and apparently upon an old land surface, there being in 
 these sections no marine equivalents. The Pocono sandstone is a 
 similar deposit, and between it and the Pottsville lies the Mauch 
 Chunk red shale, a deposit of river flood plain and eolian origin 
 during a period of relative aridity (Barrell-3). Still earlier in the 
 Devonic a similar deposit, the Catskill, was formed progressively 
 replacing a marine formation (Chemung) westward (Grabau-25). 
 The Oneonta (Portage) sandstone of New York and the upper 
 Hamilton or Ashokan formation is interpreted as of the same char- 
 acter. Still earlier in the Devonic the Esopus grit represents the 
 characters of a sea-level delta built westward by a stream debouch- 
 ing near northern Pennsylvania. The Gaspe sandstone of eastern 
 Canada likewise represents a Devonic dry delta deposit. Still 
 earlier in the Siluric and Ordovicic similar dry deltas were built 
 
636 PRINCIPLES OF STRATIGRAPHY 
 
 to the northwest by streams from an old Appalachian continent, 
 these deposits sometimes replacing marine sediments westward, 
 at others building out upon a dry land or, in one case at least, a 
 desert area. (Grabau-27). * 
 
 A remarkable feature of these deposits is the repeated succes- 
 sion upon light colored pebble deposits, with evidence of torrential 
 origin, of finer red sediments with characters suggesting flood plain 
 and eolian origin. Such are in the Ordovicic the light Bald Eagle 
 conglomerate followed by the red Juniata shales, in the Siluric the 
 Shawangunk conglomerate followed by the red Longwood shales, 
 in the Devonic the Hamilton and Oneonta sands followed by the 
 Catskill red beds, in the Mississippi the Pocono conglomerate and 
 sandstone followed by the red Mauch Chunk shale. This succes- 
 sion seems to indicate conditions which permitted easterly winds 
 to sweep across a more or less elevated land mass (Appalachia), 
 where they were deprived of much of their moisture, thus creating 
 semi-arid conditions on the west of this land mass. Moderate 
 aridity, with periodic torrential rainfalls and swollen streams 
 
 APPALACHIA ' 1 1' I ""'I'/ 1 //////// 
 
 .//'//' ' ' 
 
 FIG. 128. Hypothetical section of Appalachia in Palaeozoic time to show the 
 possible arrangement of the winds, and the corresponding de- 
 
 posits. 
 
 forming alluvial fans of pebbles, seems to have existed repeatedly, 
 but in each case was followed by drier conditions such as would 
 be produced by a renewed elevation of the land, and the consequent 
 deposition in the lee of the land mass of highly oxidized sands and 
 dust as river flood plain and eolian formations, which are now seen 
 in the red beds. The conditions favoring such deposition are illus- 
 trated in the preceding diagram (Fig. 128). 
 
 Deposits of a similar character are found in the Old Red sand- 
 stone of western Europe, and the Siluric deposits of the north 
 of England and the south of Scotland also show much evidence v of 
 deltaic origin. 
 
 One of the most striking examples of a seashore delta of 
 Upper Devonic age seems to be represented in the black shale of 
 Ohio, Michigan, and western New York. To be sure this has also 
 been interpreted as a deep sea deposit, but its peculiarities all point 
 
PALAEOZOIC DELTA DEPOSITS 637 
 
 to a delta-like origin, represented to a certain degree by the modern 
 deposits at the mouth of the Mississippi. The abundance of spores 
 of rhizocarp-like plants, represented to-day by fresh water plants, 
 the presence of tree trunks, and especially the thinning away east- 
 ward and southward, and their interpolation between normal shal- 
 low water marine sediments, all point to the delta origin of these 
 shales. 
 
 NOTE: For a full discussion of the Early Palaeozoic delta deposits of Eastern 
 North America, see Grabau, 27. 
 
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 56. WALTHER, J. 1893-94. Einleitung in die Geologie als Historische Wis- 
 
 senschaft. 
 
 57. WALTHER, J. 1900. Das Gesetz der Wustenbildung in gegenwart 
 
 und Vorzeit. Ed. I (Ed. II, 1912). 
 
 58. WALTHER, J. 1910. Die Bunte Sandwuste. Lehrbuch der Geologic/ 
 
 von Deutschland. Kapitel 13, pp. 79-82. Die Keuperzeit ibid., Kapi- 
 tel 15, pp. 87-90. 
 
640 PRINCIPLES OF STRATIGRAPHY 
 
 59. WILLISTON, SAMUEL W., and CASE, E. C. 1912. The Permo-car- 
 
 boniferous of Northern New Mexico. Journal of Geology, Vol. XX, 
 pp. 3-12. 
 
 60. WILSON, J. HOWARD. 1906. The Glacial History of Nantucket and 
 
 Cape Cod, Chapter IV; Columbia University Press, Geological Series, 
 Vol. I. 
 
 61. WOODWORTH, J. B. Some Typical Eskers of Southern New England. 
 
 Boston Society of Natural History Proceedings, Vol. XXVI, pp. 197-220. 
 
 62. WYNNE, A. B. 1878. The Geology of the Salt Range in Punjab. 
 
 Memoirs Geological Survey of India, Vol. XIV, p. 608. 
 
CHAPTER XV. 
 
 STRUCTURAL CHARACTERS AND LITHOGENESIS OF THE 
 MARINE HYDROCLASTICS. 
 
 Marine hydroclastics are accumulating in nearly every portion 
 of the ocean to-day, and their fossil representatives are among the 
 most widespread of the geological formations. They are most abun- 
 dantly developed in the littoral portion of the seas, including the 
 epicontinental seas, but also occur in the abyssal regions. In gen- 
 eral, we may classify the material with reference to its source, either 
 as terrigenous or land-derived, or as oceanic or derived from purely 
 marine deposits. The latter group is essentially limited to the 
 regions around coral reefs or other organic deposits, and so has a 
 marked uniformity of petrographic character. Viewed as a whole, 
 marine elastics are nearly always well stratified, and they are as a 
 rule fossiliferous. Indeed, it may be seriously questioned if marine 
 elastics are ever wholly free from organic remains, though for con- 
 siderable distances off certain shores organisms may be so rare as 
 to escape detection. Thus Kindle (54) reports dredging off the 
 coast of Alaska for a hundred miles or more along the shore, with- 
 out finding any organic remains whatever. This of course does not 
 prove their absence, but only indicates their scarcity, and indeed at 
 another point of the same coast organisms were abundant. More- 
 over, such dredging affects only the surface layers of the sea floor, 
 and does not prove the absence of remains in somewhat deeper 
 layers. 
 
 It is perfectly well known that marine organisms migrate with 
 the seasons, and that at a certain locality, where life was abundant 
 during one season, it is almost entirely absent in another, the or- 
 ganisms having migrated into deeper water. What is true of sea- 
 sons is also true of longer periods, some regions formerly well 
 stocked with organisms being barren for years at a time, after 
 which a return of the fauna takes place. Such migration up and 
 down the ocean floor is often determined by factors difficult to as- 
 
 641 
 
642 PRINCIPLES OF STRATIGRAPHY 
 
 certain. In the Alaskan case it may be due to the abundance of cold 
 water carried in from the land by the melting of the glaciers, which, 
 as shown by Tarr (92), has recently become very marked through 
 changes which also caused an advance of the glaciers in certain lo- 
 calities. Portions of the glaciers hitherto protected by debris or 
 otherwise have been suffering ablation during July and early 
 August at a rate sufficient to lower the ice surface four inches a 
 day. 
 
 While marine fossils are as a rule a reliable indication of the 
 marine origin of a given series of elastics, this is the case only when 
 the fossils are generally distributed throughout the mass, or when 
 there is no other positive indication of a non-marine origin. As has 
 already been shown, eolian limestones composed almost wholly of 
 marine organisms are forming at the present time, and have formed 
 in the past. Fossils weathering out from a marine series may be 
 incorporated in the next overlying continental formation, as in the 
 case of the Eocenic and other fossils of the rocks forming the floor 
 of the Libyan desert, which are included in the overlying desert 
 sands. Marine organic remains may be carried inland by winds, by 
 birds or in some other manner, and thus become incorporated in 
 terrestrial formations. Finally, deposits of terrestrial character may 
 be at intervals submerged by a momentary encroachment of the sea, 
 as in the case of the Po, the Rhine and other deltas, with the result 
 that intercalated marine sediments are formed. Or, again, the sea 
 may invade a large territory previously the theater of terrestrial 
 deposition, and by reworking the upper layers of the continental de- 
 posits, or in some cases the entire mass, may impress upon it lo- 
 cally a marine character. This has been the case with the St. Peter 
 sandstone, largely an eolian formation; with the upper part of the 
 Sylvania sandstone of similar origin ; with the Dakota and ap- 
 parently also with the Potsdam sandstone, which, in many sections, 
 still shows characters pointing to torrential or eolian origin of a 
 considerable portion of the rock. 
 
 It should of course also be emphasized that the reverse is likely 
 to hold, namely, that absence of marine fossils is not an absolute in- 
 dication of the non-marine character of a formation, though absence 
 over a very large area may probably be taken as a fairly certain 
 guide. The physical characters of the rocks and their relationships 
 must be taken into careful consideration. Among the negative char- 
 acters of marine elastics are : the absence of mud cracks, rain prints, 
 footprint impressions, rill marks, etc., though all of these may 
 occur in the shore zone. 
 
MARINE HYDROCLASTICS 
 
 643 
 
 SUBDIVISIONS OF THE AREAS OF MARINE DEPOSI- 
 TION. TYPES OF MARINE DEPOSITS. 
 
 The following districts and zones or regions of deposition of 
 clastic material may be recognized in the sea : 
 
 1. The Littoral District, or that ranging from the shore to the 
 edge of the continental shelf, that portion of mediterraneans corre- 
 sponding to this, and the whole of the bottoms of epicontinental 
 seas. Deposits formed here are "littoral deposits," and they are 
 among the most varied of their kind. The littoral district is divisi- 
 ble into the shore zone between tides and the permanently sub- 
 merged shallow water or neritic zone* (Flachsec), extending to 
 the isobath of 200 meters. 
 
 2. The Bathyal District (Renevier) is that district lying between 
 the outer limit of the neritic zone, i. e,, the 2OO-meter line, and ap- 
 proximately the isobath of goo, or, in round numbers, 1,000 meters. 
 It represents the steep slope from the edge of the continental shelf 
 to the point- of decreasing angle of slope. This comprises only^ the 
 upper portion of Penck's aktic region, which extends to the mean 
 sphere level of 2,400 meters below sea-level (see Chapter I). (Fig. 
 i, P- 8.) 
 
 3. The Deep Sea or Abyssal District. This, according to Penck 
 and others, begins at the 2,4OO-meter line, but so far as deposition is 
 concerned begins practically at the i,ooo-meter isobath. 
 
 A general classification of oceanic sediments, including all types, 
 was made by Murray and Renard (62: 186), as follows: 
 
 Murray and Renard' s Classification of Marine Deposits. 
 
 i. Deep-sea deposits beyond 
 100 fathoms . . 
 
 2. Shallow- water deposits be- 
 tween low-water mark and 
 100 fathoms 
 
 3. Littoral deposits between 
 high and low- water marks . 
 
 Red clay 
 Radiolarian ooze 
 Diatom ooze 
 Globigerina ooze 
 Pteropod ooze 
 Blue mud 
 Red mud 
 Volcanic mud 
 Coral mud 
 
 f Sand, gravels, 
 { muds, etc. 
 
 Sands, gravels, 
 muds. etc. 
 
 I. Pelagic deposits form- 
 ed in deep water re- 
 moved from lancf 
 
 1 1. 'Terrigenous deposits 
 formed in deep and 
 shallow water, mostly 
 close to land 
 
 * Haug (43 :86) and others have shown a tendency to use neritic in the sense 
 in which littoral is here used, restricting that term to the shore zone or inter- 
 cotidal region. The use here advocated seems the most serviceable. 
 
644 PRINCIPLES OF STRATIGRAPHY 
 
 Otto Kriimmel (55 : /5<?) has made a threefold division of 
 marine sediments; modifying the classification of Murray and 
 Rehard as follows : 
 
 Krummel's Classification of Marine Deposits. 
 
 I. LITTORAL OR NEAR LAND DEPOSITS. 
 
 1. Strand or shore deposits. 
 
 2. Shelf (shallow water) deposits: 
 
 Each comprises boulder, gravel, sand, and mud deposits, which according 
 to their source are clastic, volcanic, biogenic, chemical (halmyrogenic) and 
 glacial. 
 
 II. HEMIPELAGIC OR DEEP SEA TERRIGENOUS DEPOSITS. 
 
 1. Blue and red mud (including volcanic mud). 
 
 2. Greensand and green mud. 
 
 3. Lime sand and lime mud: 
 
 (Subdivisions as under littoral.) 
 
 III. EUPELAGIC DEPOSITS DISTANT FROM LAND. 
 
 A. Epilophic deposits (formed on the submarine ridges and swells). 
 
 (a) Calcareous deep sea ooze. 
 
 1. Globigerina ooze. 
 
 2. Pteropod ooze 
 
 (b) Siliceous deep sea ooze. 
 
 3. Diatomaceous ooze. 
 
 B. Abyssal deposits: 
 
 4. Deep sea red clay 
 
 5. Radiolarian ooze 
 
 Since diatomaceous oozes have been found at depths of 5,000- 
 6,000 meters, and Globigerina ooze is sometimes found in depths 
 greater than that where red clay accumulates, the subdivisions of the 
 Eupekgic deposits as given by Krummel are hardly satisfactory 
 (Philippi-fx)). Andree (4) suggests dividing Krummers Group 
 III into calcareous and noncalcareous (siliceous), the former com- 
 prising Globigerina ooze, with Pteropod ooze as a facies, the latter 
 diatomaceous ooze, and the deep-sea red clay with the radiolarian 
 ooze as a facies of the latter. This entire class, with the exception 
 of the red clay, has been discussed under organic deposits or 
 biogenics (Chapter X). 
 
 The distinction between areas of deposition and types of de- 
 posits 'must be clearly kept in mind. The former, as we have seen, 
 comprise (i) the littoral district, with its two zones, (a) the shore 
 and (b) the neritic zones; (2) the bathyal district and (3) the 
 abyssal district. Oceanic deposits must be classified first as to their 
 
CLASSIFICATION OF MARINE DEPOSITS 645 
 
 origin and next as to their mode of occurrence. Thus we may -make 
 the following classification, taking oceanic deposits as a whole : 
 
 A New Classification of Marine Deposits. 
 
 I MARINE HYDROGENICS (HALMYROGENIC deposits) or chemical precipitates 
 
 from the sea water. (These have been fully discussed in Chapter IX.) 
 
 II MARINE BIOGENICS or organic deposits of marine origin 
 A Benthonic or living on sea bottom 
 
 1 Littoral originating in littoral district 
 
 a Shore zone 
 
 (1) autochthonous or growing in situ 
 
 (2) allochthonous or cast up from deeper water 
 , b Neritic or shallow water zone 
 
 (1) autochthonous growing in situ 
 
 (2) allochthonous transported, usually from shore zone 
 
 2 Bathyal 
 
 (1) autochthonous 
 
 (2) allochthonous transported, usually from littoral zone 
 
 3 Abyssal 
 
 1 i ) autochthonous 
 
 (2) allochthonous transported from the littoral or bathyal 
 regions 
 
 B Pelagic or living in the open ocean and its extension into the shore 
 indentations, either as plankton or nekton. (See Chapter XXVII.) 
 These may settle in the Littoral, Bathyal or Abyssal districts, remain- 
 ing either in place, or more or less rearranged or worked over, especially 
 in shallow water whence they may be cast on shore and even blown 
 inland. 
 
 III MARINE CLASTICS. Fragmental material worn off by or in the sea 
 
 A Hydrcclastics worn off or rearranged by the sea waves or currents 
 
 1 Terrigenous or land-derived 
 
 a from continent including continental islands 
 b from oceanic islands exclusive of coral reefs, and other organic 
 deposits 
 
 2 Thalassigenous ; or sea- derived 
 
 a organic lime sand and mud derived from coral reefs, from 
 
 nullipore reefs, shell deposits, etc. 
 
 b derived from halmyrogenic or chemical deposits. Clastic 
 material derived by destruction by waves of chemical deposits 
 formed by the sea (not known). Chemically formed marine 
 oolites when worn by waves may come under this head 
 B Bioclastics: rock material broken up by marine organisms 
 
 Marine bioclastics. These may, according to the source from which 
 the material was originally derived, be classed as 
 
 1 Terrigenous, from continents and islands 
 
 2 Thalassigenous, from coral reefs, etc. 
 
 IV MARINE DERELICTS, or stragglers from other realms. These may be de- 
 
 posited in the Littoral, Bathyal or Abyssal districts 
 A Land-derived, either from continents or islands 
 I Terrestrial, derived from the land 
 
646 PRINCIPLES OF STRATIGRAPHY 
 
 a Organic: land plants or animals floating out to sea or rafted 
 seaward (as under b) and deposited in the Littoral, Bathyal 
 or Abyssal districts. (Microorganisms blown out to sea with 
 the dust would also be classed here.) 
 
 b Inorganic: rocks, sand, gravel, etc., rafted from land and deposit- 
 ed in the Littoral, Bathyal or Abyssal districts. According to 
 the method of transport we have: 
 
 (1) plant rafted: rocks, etc., held by roots of floating trees etc. 
 
 (2) animal rafted: stones in stomachs of modern sharks, and 
 . seals, and of Jurassic Mystriosaurus and Plesiosaurus as 
 
 well as in the stomachs of many land animals which may 
 float out to sea 
 
 (3) ice rafted: by icebergs and floating ice cakes 
 
 (4) wind rafted: wind-blown dust or sand, and volcanic ma- 
 terial brought from the land 
 
 (5) ship rafted: substances carried out by ships or man-made 
 rafts and cast overboard or deposited on the foundering 
 of the ship 
 
 (6) carried into the sea by slipping or gliding 
 
 2 Aquatic: derived from the rivers and estuaries. This would comprise 
 chiefly river animals and plants which have been carried out to sea 
 
 3 Derived from adjacent higher zone by gliding or thrusting 
 B Atmospherically derived 
 
 Since the chief atmogenic solids, snow and hail, have only a temporary 
 existence, deposits from this source may be neglected. Rare cases 
 of organisms, such as seabirds, which spend most of their lives in the 
 air, might perhaps be included here, but they may as well be classed 
 with terrestrial derelicts 
 
 C Meteoric of Extratelluric origin 
 
 Here belong the cosmic dust and the meteorites 
 
 D Of Subcrustal Origin 
 
 This includes volcanic eruptions beneath the sea and on the coast, 
 so that both pyrogenics and pyroclastics flow or are projected into 
 the sea. The direct pyroclastics merge of course into the wind-trans- 
 ported pyroclastics 
 
 DISCUSSION OF THE MARINE CLASTICS. 
 
 In the following pages the clastic deposits will be discussed with 
 reference to the regions in which they are deposited. Lacustrine 
 elastics will be repeatedly used for parallel illustrations. 
 
 THE LITTORAL DISTRICT AND ITS DEPOSITS. 
 
 The term littoral zone is frequently restricted to the part be- 
 tween high and low-water mark, i. e., the shore, while the term 
 neritic has recently come into use for that portion between low 
 water and the edge of the continental shelf. The term littoral dis- 
 
LITTORAL DEPOSITS 647 
 
 trict is, however, best applied to all that part of the sea above the 
 deep-sea portion, i. e., approximately above the hundred-fathom line. 
 This is in conformity with usage of the term in bionomics (Ort- 
 mann-63 15), where the littoral fauna and flora are those occupying 
 the sea bottom within the illuminated region. It is in this sense 
 that the term littoral will be used throughout this book, while the 
 littoral zone or the zone between high and. low water will be re- 
 ferred to as the shore. 
 
 Littoral deposits are found between the edge of the continental 
 shelf and the high-water edge of the shore. In the shore zone they 
 grade imperceptibly into continental deposits, through the zone of 
 the strand, while at the outermost margin of the littoral district they 
 grade into abyssal deposits. Around the margins of oceanic islands 
 the littoral belt is of greater or less width, according to the slope of 
 the submerged portion of the island. 
 
 It is within the littoral district as here denned that by far the 
 largest proportion of clastic material is deposited. It is here also 
 that the bulk of the hydrogenic and the biogenic deposits of the sea 
 is formed. 
 
 The Shore Zone (Inter Co-tidal Zone ; Littoral Zone 
 in Restricted Sense). 
 
 The separation of the shore zone, or that portion between high 
 and low-water mark, from the portion of the littoral district never 
 uncovered, is of very little significance from the lithogenetic point 
 of view, however much its import biologically. For, although this 
 zone is the focus of the destructive activity of the waves, their work 
 is not limited to this portion. It is known that wave work is very 
 effective at a depth of thirty feet, while at sixty it has still an in- 
 fluence upon the bottom deposits. In fact on a gently sloping coast, 
 the destructive work of the waves is found in the deeper water 
 away from the shore, rather than in the shore zone. Neither has 
 the shore a distinctive type of sediment; not even the pebbly sedi- 
 ment is confined to it, but occurs also at a distance from shore ; nor 
 are sands, muds or even organic deposits excluded from the shore, 
 the sands and muds being often more characteristic than the peb- 
 bles. As for organisms, only stationary or attached types dis- 
 criminate between the shore and the permanently submerged zone, 
 and among these certain ones do not make an absolute distinction. 
 The shore zone is, however, of significance in this respect, that 
 characters typical of continental deposits, such as mud cracks, rain- 
 
648 PRINCIPLES OF STRATIGRAPHY 
 
 prints, footprints, etc., can be impressed upon the exposed sedi- 
 ments, and preserved under favorable circumstances. 
 
 Since the magnitude of tides varies with the moon's phases, the 
 exact limit of the shore zone is never fixed. During spring tides the 
 zone encroaches upon the strand, that indefinite zone just above 
 high water, while the ebb succeeding will lay bare portions of the 
 zone generally submerged. On lakes the shore zone practically dis- 
 appears (it would be wrong, however, to say that there is no littoral 
 district on the lakes) unless the seiche is to be considered as equiva- 
 lent to the tides. 
 
 Fades of the Shore Zone. The shore zone may represent one 
 or more of a variety of fades, or types of material, none of which 
 can be considered as strictly confined to it. The most typical facies 
 of the shore zone are: i, the rocky cliff facies; 2, the bouldery 
 facies; 3, the gravelly facies; 4, the sand facies; 5, the mud flat 
 facies, and 6, the organic facies. Each of these facies has its dis- 
 tinct physical and organic characters. 
 
 i. Rocky cliff facies. 
 
 This is most significant from the point of view of bionomics, as 
 will be more fully discussed in a later chapter. Erosion is active 
 here, and coarse fragments are broken from the cliff and accumu- 
 late as a submarine talus and boulder pavement. Where rock accu- 
 mulation takes place, a rudaceous phase will be found next to the 
 cliff, the material of the rock fragments being that of the cliff from 
 which they are derived. Since in such cases the rock fragments 
 broken from the cliff may fall into water sufficiently deep to prevent 
 much attrition of the fragments, the resultant rudyte may be a 
 breccia, the fragments being in the main angular. Examples of 
 such cliff rudytes are found in the St. Croix formation of the 
 Dalles region of the Wisconsin River, and in the Lake Superior 
 sandstone of Marquette, Michigan. Some of these may of course 
 be old, subaerial talus slopes reworked by the transgressing sea. 
 This appears to be the case with the basal Mid-Devonic limestones 
 (Dundee) of Michigan and western Ontario. (See Chapter XIII.) 
 
 2. Bouldery facies. 
 
 Where a rock cliff fronts the waves, the fragments broken from 
 the cliff by the frost and by the sea are generally ground into 
 
FACIES OF THE SHORE ZONE 649 
 
 pebbles, sand and mud, unless the water at the foot of the cliff is 
 sufficiently deep to render the force of the waves ineffective. Thus 
 boulders will seldom accumulate in such numbers as to make a 
 boulder beach at the foot of a cliff, since the destruction of the cliff 
 proceeds with sufficient slowness to allow the reduction of most of 
 the fragments to pebbles or smaller particles. If, however, the sea 
 eats into a morainal or other bouldery deposit, as is the case of many 
 portions of the New England and Long Island coast of the North 
 Atlantic, a heavy boulder beach arranged in the form of a pave- 
 ment by the close approximation of the boulders through wave and 
 shore-ice work will result. In like manner, when the sea en- 
 croaches upon an old subaerial talus heap, a boulder beach may be 
 formed, the waves being able to round off and arrange the boulders, 
 but not to destroy them. The boulders themselves become a natu- 
 ral barrier, against which the waves beat themselves to pieces with- 
 out accomplishing much erosional work. Where the tides are ex- 
 ceptionally high, as in the Bay of Fundy, the boulders broken from 
 the cliffs by the frost and insolation will be rolled and worn at high 
 tide, but the power of the waves is too small, and the time during 
 which the boulders are subject to their influence too short, to pro- 
 duce any other results. Here the accumulation of boulders is really 
 to be compared with a subaerial talus, which is periodically, but for 
 a short time only, exposed to wave activity. On the whole, boulder 
 beaches other than those due to erosion o drift deposits are of com- 
 paratively rare occurrence, and the same thing may be said of an- 
 cient marine boulder beds. It is doubtful if many such existed, 
 most of the boulder beds of former geologic epochs being probably 
 of continental origin. That boulders of even moderate size may 
 for a long time remain entirely unmoved by the waves is shown on 
 the east coast of Scotland, where the boulders and ledges are cov- 
 ered by living Acmaea or by extensive growth of sea weeds. Even 
 delicate sea anemones are found attached to these boulders, often in 
 such a position that a slight movement of the boulders would grind 
 them to pieces. In other cases the boulders and pebbles are en- 
 crusted by a growth of Lithothamnion or Melobesia. It sometimes 
 happens that in certain zones, or areas, the waves are able to move 
 the boulders, with the result that there they are entirely bare of 
 either vegetation or animal covering. 
 
 3. Gravel fades. 
 
 By far the greater part of the present shore lines of the world is 
 sandy or gravelly, the former predominating. Gravelly beaches or 
 
650 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 beaches of cobbles or shingles are chiefly characteristic of steeply 
 sloping and exposed rocky shores, where the finer product of ero- 
 sion is carried by the undertow to deeper water, the coarser alone 
 remaining. The character of the pebbles will of course partake of 
 that of the cliff from which they are formed, those derived from 
 the more easily shattered rock, as well as the most difficult to grind 
 to powder, predominating. Thus on the north shore of Massachu- 
 setts felsite pebbles predominate, on Lake Michigan limestone peb- 
 bles, and on the shore of Lake Erie flat shale pebbles. These peb- 
 bles are often piled up into extensive terraces, especially after heavy 
 storms. These terraces may show on section a rude and irregular 
 bedding, but the regular cross-bedding (torrential type) found in 
 many old conglomerates was not formed in this manner. 
 
 FIG. 129. Diagram illustrating the deposits in the littoral district of the sea. 
 At the shore gravelly and sandy fades occur, these shading off 
 seaward into lutaceons, and, finally, calcareous sediments. The 
 latter are derived from the coral reef C. R., i. e., they are thalassi- 
 genous, while the others are terrigenous. The overlapping of 
 the formations is also shown. 
 
 Organic remains in pebble beds. On the beach, where the peb- 
 bles undergo much movement, most organic remains, such as shells, 
 bones, etc., are rapidly destroyed. Nevertheless, they are occa- 
 sionally preserved, as is shown by the occurrence of worn shell 
 fragments even in the high gravel terraces. 
 
 That organic remains are common in older boulder and pebble 
 beds has been the experience of many geologists, though some of 
 the so-called conglomerate beds are due to causes other than those 
 active on sea beaches. A comparatively modern example of a pebble 
 and sand beach now abandoned by a slight elevation of the coast 
 is found in eastern Scotland. Near Goldspie on the Moray Firth, 
 the lower of the elevated beach lines abounds in entire shells of 
 Acmsea and other shore forms, as well as in worn fragments of 
 this and other shells. Boulders up to the size of six inches or more, 
 
FACIES OF THE SHORE ZONE 651 
 
 and well worn, are found in this beach. Other examples no doubt 
 occur in other sections of this coast and elsewhere. 
 
 Boulder beds of Tertiary age are not uncommon. In the Mi- 
 ocenic of the Vienna Basin, some of the best preserved pelecypocl 
 and gastropod shells are found in a boulder bed with pebbles up to 
 six inches or more in diameter, and well rounded. The Cretacic 
 boulder beds of South Germany and of Sweden are other examples. 
 In the former well-worn boulders up to several feet in diameter 
 constitute the deposit, while among them abound fragments and en- 
 tire individuals of brachiopods, pelecypods and other organisms 
 often in a remarkable state of preservation. In the Dresden region 
 pothole-like hollows are found in the old porphyries with a depth 
 of 20 feet or more, and these are filled with a coarse boulder con- 
 glomerate of Cretacic age, the individual boulders often a foot or 
 more in diameter, and well worn. Among these boulders sponges, 
 oysters and other organisms occur in abundance. In Scania and 
 elsewhere an Upper Cretacic conglomerate of pebbles and boulders 
 worn or angular contains Belemnites and other fossils of that 
 period, many of them showing no wear. One of the most striking 
 examples of such a conglomerate is found on the present eastern 
 coast of Sutherland, North Scotland, near the village of Helms- 
 dale. The formation occurs as a coastal strip, largely eroded by the 
 present sea, and forming a series of low-lying skerries exposed at 
 low water. The age of the formation is Jurassic, but it is almost 
 wholly composed of large and small fragments of Caithness flags 
 (Lower Old Red sandstone), some, of the fragments reaching the 
 astonishing length of 20 feet or more. The larger fragments lie in 
 irregular positions, their stratification planes dipping in all direc- 
 tions, and they resemble in every respect the fragments now found 
 at the foot of the cliffs of these flags on the exposed Caithness 
 coast. Among the fragments and firmly embedded in the con- 
 glomerate and breccia matrix are worn heads of coral (Isastrea), 
 shells, Belemnites and other Jurassic organisms. Many of the 
 smaller organisms have apparently escaped all wear. 
 
 4. Sandy fades. 
 
 Sand is by far the most typical material of the shore zone, on 
 lakes as well as on the seashore. To a large extent the sand con- 
 sists of quartz grains, since this is the least destructible constitu- 
 ent of rocks. In regions of purely calcareous sources of sand, as in 
 the Bermudas, and on many coral reef islands, the sand is largely or 
 
652 PRINCIPLES OF STRATIGRAPHY 
 
 wholly composed of grains of calcium carbonate, with or without 
 magnesium. 
 
 As Shaler has pointed out, the sand of the seashore is com- 
 pacted into a resistant mass by the films of water which separate 
 the grains and which are held in position by capillary attraction. 
 Whoever has walked on wet beach sand has noted the difference in 
 firmness between the wet and dry sands, the former often con- 
 stituting a hard, level floor. On such a surface the force of the 
 waves is spent; the sands will retain their original angular charac- 
 ter, since the dividing film of water acts as a cushion, which pre- 
 vents the mutual attrition of the grains. Thus the grains of beach 
 sand are normally angular and with fresh surfaces, and this type of 
 sand should be looked for in normal marine sandstones. (Shaler- 
 88.) Shaler cites as an example of marine sands protected in this 
 manner from wearing, the sand of northern Florida . . . "which 
 has traveled southward from the region beyond Cape Hatteras" 
 . ; . and which "is not more rounded than much which is in the 
 inner or landward dunes of the coast within sound of the ocean 
 waves." (88:151.) 
 
 When, through drying, the binding films of water are destroyed, 
 the sands become loosened and are then readily shifted about by 
 the wind, accompanied by mutual attrition of the grains. Here, 
 then, no permanent structural features are formed. ' Both rill and 
 ripple marks left on the retreat of the tide are either obliterated by 
 the wind or washed away by the returning tide, owing to the non- 
 coherency of the material. An exception to this seems to be the 
 wave mark on a very gently sloping sand beach, and the hollows ex- 
 cavated behind pebbles or shells by the return of the wave on such 
 a beach. Examples of these are known from the Upper Medina 
 sandstone in western New York, and in other formations. (Fair- 
 child-32.) 
 
 Marine arkoses. Accumulation of feldspathic sands on the sea 
 coast and their incorporation in marine strata are effected under a 
 peculiar combination of circumstances such as exist to-day in the 
 Gulf of California, as described by McGee (57). The granitoid 
 rocks of this region are subject to disintegration under the arid 
 climatic conditions, due to the interception of the Westerlies by the 
 coast ranges. Decomposition is practically absent, the disintegrated 
 material being transported by sheet floods. These result from ex- 
 ceptional thunderstorms, accompanied by sudden and extensive pre- 
 cipitation. Part of the material is carried into the Gulf and there 
 assorted by the waves, the coarsest and cleanest material being de- 
 posited at the salients of the coast, while in the reentrants much 
 
FACIES OF THE SHORE ZONE 653 
 
 finely comminuted material is deposited with the coarse quartz and 
 feldspar. Quartz- feldspar-mica sandstones are thus produced 
 under conditions permitting the entombment of marine organisms. 
 Sorting of sands and gravels by waves. The conditions under 
 which waves accomplish sorting of sands and gravels according to 
 size and material are given by Bailey Willis (105:481) as the fol- 
 lowing : 
 
 (a) Vigorous wave action, accompanied by strong undertow. 
 
 (b) Prolonged transportation in consequence of deep water 
 
 and continuous currents. 
 
 (c) Moderate volume of sediments. 
 
 On the other hand, the conditions under which sorting is not or 
 but slightly accomplished are, according to Willis : 
 
 (a') Feeble or diffused wave action. 
 
 (b') Concentrated deposition. 
 
 (c') Excessive volume of sediment. 
 
 In general, with a given amount of loose materials to work 
 upon, the waves will accomplish sorting in proportion to their 
 strength and the strength of the undertow. The finest material will 
 be carried out farthest, while only the coarsest material will be left 
 behind. Where the material is all of one kind, as, for example, 
 quartz sand, the sorting will be entirely according to size, while 
 variation in the mineralogical character of the material may lead to 
 a sorting, according to the specific gravity as well. Thus quartz 
 sands may be entirely washed free from mica and clay particles, 
 while garnet and magnetite, two characteristic accompaniments of 
 sands derived from many igneous or metamorphic rocks, will segre- 
 gate through the washing out of all quartz grains. 
 
 This sorting according to size and specific gravity is best accom- 
 plished if, in addition to the strong wave movement which stirs 
 up the sediment, strong currents exist which can transport the ma- 
 terial for long distances. ' The smallest and lightest material may 
 thus be carried much farther away from the point where the 
 coarsest is dropped, the separation being thus most pronounced. 
 In this respect the separation by currents will be analogous to the 
 separation of sediments by wind. A water current of a given 
 velocity is equaled in carrying power only by a wind current of 28 
 times that velocity (Udden-o^rj/p), but wind currents exceeding 
 average ocean currents in velocity by very much more than that are 
 characteristic of. many regions, especially in the upper atmosphere. 
 Thus material projected or carried into the air stands a much better 
 
654 PRINCIPLES OF STRATIGRAPHY 
 
 chance of sorting than does material in the sea. Moreover, material 
 dropped by one air current may be picked up again by another, 
 while sands dropping in deeper water below the reach of the cur- 
 rents are more likely to be left undisturbed by them. 
 
 If the amount of supply of detritus is great, sorting will be im- 
 peded. Flocculation, or the gathering together of particles, will oc- 
 cur, the coarser carrying down with them the finer. Flocculation is 
 less marked in wind-transported material, where the load is always 
 much less per unit of bulk of the carrier than in most waters, and 
 for this reason also the sorting by wind is more pronounced than 
 that by water. Udden thinks that under ordinary circumstances 
 this difference is nearer i to 100,000 than i to 1,000. (99:^5".) 
 The slope of the sea bottom (Willis-io5 : 484) is also a determining 
 factor in the transportation of material by marine currents. Where 
 the slope is a gentle one, sand may be carried for 200 miles or 
 more, as on the Atlantic coast of the United States, where the conti- 
 nental plateau is covered with sands to its outer rim. The trans- 
 porting current here is the undertow, assisted by tides. Since, 
 however, the force of the undertow is largely determined by the 
 strength of .the waves, it follows that in circumscribed and very 
 shallow seas no such extensive transportation is possible. Where 
 the slope is a steep one, as en the west coast of South America, the 
 force of the undertow is dissipated, though pebbles and sand will 
 more readily move down the slope. As a rule, the distance to which 
 sands are transported in such a case is limited. 
 
 Organic remains in marine and lacustrine sands. These are gen- 
 erally common, especially in the sea, though areas free from such 
 remains are known, as in the case of the Alaskan coast, already 
 cited. Such absence is, however, due to purely local causes. Even 
 in the beach sands organic remains abound. Everywhere along our 
 coasts shells in numbers, and crustacean and echinoderm tests to a 
 lesser degree are buried in the sands of the beach, and in those 
 just below the low-water line. In the neritic zone animal life of all 
 kinds abounds on the sandy bottoms (see Chapter XXVIII). 
 Abandoned shores of lakes and of the sea also are rich in organic 
 remains. The higher beaches of the late Pleistocenic stages of the 
 Great Lakes contain numerous shells of fresh- water mollusca, and 
 so do the sands of the old shore lines of Niagara and other rivers. 
 So abundant are shells and other organisms in the sands of the 
 modern sea coast that their entire absence from older sandstones 
 must be looked upon as indicative of conditions of deposition other 
 than normal. It is begging the question to assume the subsequent 
 removal of such remains either by solution or otherwise, for even 
 
FAClES OF THE SHORE ZONE 655 
 
 though percolating waters should dissolve away the shells a mold 
 or impression of the same will remain, which no agent short of 
 metamorphism can obliterate, and that not always. The abundance 
 of organic remains in sandstones of all kinds and colors and of all 
 ages shows that there are no inherent characteristics in sand which 
 prevent the preservation of such remains. In practically all cases 
 when organic remains or their impressions are wanting in sand- 
 stones, we have a right to assume that they were not present at the 
 time of formation of the deposit. Such absence suggests a sub- 
 aerial rather than subaqueous origin -for the deposit, and as such it 
 should be considered unless other unmistakable characteristics point 
 to a subaqueous (marine or lacustrine) origin. (For application to 
 basal beds see Pumpelly-75 :<?//.) 
 
 5. Muddy fades. 
 
 This generally occurs in intimate association with an organic 
 facies in the shore zone. Where sands accumulate in sheltered mar- 
 ginal lagoons, plants (eel grass) and animals commonly contribute 
 their remains to enrich and color the mud. Salt marshes are the 
 normal successors of the mud flat, the organic element here being 
 in the ascendency.. (See ante, Chapter XI.) The purely inorganic 
 structures of such a mud flat are, in addition to stratification, the 
 mud cracks, rain prints and rill marks, and the tracks and trails of 
 animals frequenting the shore. During very high spring tides ex- 
 tensive portions of a very flat shore may be covered with a layer of 
 mud, which on the retreat of the tide may become marked by mud 
 cracks and footprint impressions. Since such areas will be uncov- 
 ered for a fortnight, the clay may become sufficiently hardened to 
 permit the permanent preservation of the mud cracks. It must, 
 however, be borne in mind that when the mud deposit made by 
 one inundation is comparatively thin, as is apt to be the case, this 
 layer will on drying curl up into shaving-like masses and be blown 
 away by the wind. While under exceptional conditions the mud 
 cracks, rill marks and tracks formed in the shore zone may be- pre- 
 served, such preservation is far from being characteristic. 
 
 Flocculation and the conditions of mud deposits. The formation 
 of mud deposits at the mouths of great rivers emptying in the sea, 
 as in the case of the Mississippi, is favored by the presence of the 
 salt in the sea water. Flocculation, or the drawing together of 
 particles, takes place much more extensively in salt than in fresh 
 water, and as a result such particles will sink more quickly in sea 
 
656 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 water than in lakes. Experiments (Brewer-n : 168) have shown 
 that clay which had been in suspension in fresh water for thirty 
 
 FIG. 130. Diagram showing the lateral shading off of the clastic sands and 
 pebbles into calcareous deposits without intervening muddy 
 phase. The successive formations a, b, and c change shoreward 
 into arenytes. An apparently continuous sand bed ; a-c is thus 
 produced resting upon the old land surface. 
 
 months had not settled out as clearly as the same clay from a solu- 
 tion of common salt in less than thirty minutes. These results have, 
 however, been questioned by Wheeler (103), who gives the accom- 
 panying table, showing the rate of settlement in the two media : 
 
 Table Showing Rate of Settlement of Solid Matter in Fresh and 
 
 Salt Water. 
 
 No. 
 
 i 
 
 2 
 
 ' 3 
 4 
 5 
 6 
 
 7 
 8 
 9 
 IO 
 
 ii 
 
 I2T 
 
 13 
 
 14 
 
 No. of 
 
 grains 
 to a 
 lineal 
 inch 
 
 Material 
 
 Time taken 
 to settle 
 
 Water 
 clear 
 
 Ft. 
 per 
 minute 
 
 Remarks 
 
 Fresh 
 
 Salt 
 
 Fresh 
 
 Salt 
 
 m. 
 
 sec. 
 
 m. 
 
 sec. 
 
 h. 
 
 m. 
 
 h. 
 
 m. 
 
 
 
 5 
 
 10 
 20 
 
 20-60 
 
 IOO 
 200 
 
 300 
 
 1,400 
 500 
 1,000 
 2,000 
 
 600 
 
 1,500 
 1, 600 
 1,440 
 
 Small pebbles 
 
 
 
 I 
 T l 
 
 
 
 
 
 
 0.50 
 0.42 
 
 0.21 
 
 o. 13 
 
 5.04 
 2.4O 
 
 Water not 
 discolored 
 do 
 do 
 do 
 do 
 do 
 do 
 do 
 Water scarcely 
 discolored 
 Water turbid 
 do 
 do 
 do 
 do 
 do 
 do 
 do 
 
 Small pebbles 
 
 
 
 
 
 
 
 Coarse sand 
 
 o 
 
 A 
 
 
 
 
 '5 
 
 
 
 o 
 
 
 
 
 Sand 
 
 o 
 
 IO 
 
 
 
 o 
 
 Sand 
 
 o 
 
 25 
 
 
 
 Whiting 
 
 12 
 
 o 
 
 
 Plaster of Paris 
 
 5 
 
 
 
 12 
 2 
 
 8 
 33 
 
 18 
 i? 
 24 
 
 o 
 
 4.5 
 
 
 
 
 
 
 
 
 
 
 o 
 15 
 
 2 
 
 9 
 
 28 
 
 2 
 
 18 
 IS 
 
 
 45 
 
 o 
 o 
 o 
 
 
 
 40 
 
 o 
 o 
 
 22 
 
 o 
 o 
 
 3 
 o 
 
 I 
 7 
 
 
 IO 
 
 I 
 o 
 
 10 
 
 i 
 
 30 
 
 6 
 
 
 
 
 15 
 
 
 
 30 
 43 
 
 
 
 22 
 O 
 O 
 I 
 
 
 9 
 I 
 
 
 
 i 
 
 
 
 
 33 
 30 
 
 1 8 
 
 
 
 o 
 30 
 
 I .20 
 
 O.7O 
 O.42 
 
 O. II 
 0.22 
 0.46 
 0.4O 
 
 0.35 
 
 Warp Trent 
 
 (Fine warp, Dutch river). 
 Silt, salt marsh 
 Warp marsh 
 
 (Alluvium, Boston Dock) 
 (Alluvium, River Parrett) 
 Tilbury Basin 
 
 Brick clay 
 
 Boulder clay 
 
 The phenomena of flocculation have been attributed to chemical 
 reaction, but seem to find a better explanation in the forces of at- 
 
FACIES OF THE SHORE ZONE 657 
 
 traction or tension existing among the fine particles of a solid in 
 suspension. These forces are modified by the existence of the salt 
 in the solution. (Whitney-iO4; Clarke-2O.) According to the ex- 
 periments of G. Bodlander (10), the sodium chloride of the sea 
 water is not so important in this respect, other salts, especially mag- 
 nesium chloride, being more active. Carbon dioxide, which abounds 
 in sea water, also rapidly clears it of suspended clay particles, but 
 temperature changes seem to be of little significance in this re- 
 spect. (Krummel-55 : 152-214.) Even in sea water, however, the 
 finest particles do not settle out completely after several weeks of 
 rest. 
 
 Terrigenous muds extend from the shore to abyssal depths. 
 They will be more fully considered under the neritic zone. 
 
 6. Organic fades. 
 
 This consists of the eel grass and peat marsh areas of the sea 
 coast and of the rush and swamp borders of lakes and ponds. The 
 characteristics of these have been fully described in previous chap- 
 ters, and need not be dwelt upon here at length. Extensive mussel 
 beds such as are forming in many places on our sea coast may also 
 be classed here, though these are as a rule intimately associated 
 with the muddy facies of the flats. Shallow-water coral and Litho- 
 thamnion growths are other examples of this facies, which belongs 
 with the lithogenic rather than the lithoclastic division. 
 
 Subaqueous SoliUuction. 
 
 The movement or gliding of rock material when saturated with 
 water, which under subaerial conditions is called solifluction (see 
 Chapter XIII), also takes place under subaqueous conditions. Ar- 
 nold Heim proposed to distinguish this mode of movement as sub- 
 solifluction (47:141). Such movements have occurred in many 
 regions of the world, both on lakes and on the seashore, but only a 
 few cases have been fu^ly investigated. Among these are the glidings 
 which in 1875 and again in 1877 affected the village of Horgen on 
 the Lake of Zurich (Switzerland), and the one which took place 
 in the village of Zug on the Zuger See in the Canton of Zug 
 (Zoug), north central Switzerland. Both of these were described 
 by Professor Albert Heim and others in special publications, and 
 summarized by Arnold Heim in 1908 (47: 136). 
 
658 PRINCIPLES OF STRATIGRAPHY 
 
 The village of Horgen is situated on the southern shore of the 
 Lake of Zurich. The shore, which is here composed of the sand- 
 stones and marls of the Mollasse, was covered originally by sand, 
 gravel and clay in the upper part; and this, near the shore, was un- 
 derlain by soft muds, which extended lakeward, covering the rocks 
 to the center of the lake. On the ground thus underlain with soft 
 mud rests a part of the railroad, which skirts the southwestern shore 
 of the lake (Zurichseebahn), the Horgen station being built close 
 to the shore. A sea wall was built and the surface raised a slight 
 amount (0.4 to 0.6 meter) by filling-in, but prior to this a number 
 of buildings and a stone-cutting yard were removed, so that on 
 the whole the excess of loading was slight. On February 9, 1875, 
 when the filling in was nearly complete, the new sea wall and the 
 filled area suddenly sank for a length of 135 meters, the lake along 
 the line of the railroad reaching a depth of 7 meters. The examina- 
 tion showed that a part of the bottom layer of soft mud had slid 
 lakeward, so that the more resistant overlying sand and gravel beds 
 came to rest upon the rock surface. The gliding continued until 
 the mud layers had completely bared the rock slopes for a distance 
 of nearly 300 meters lakeward. The most pronounced of these 
 glidings occurred on June 12, 1875, this, however, affecting mainly 
 the sublacustrine mud layers. By filling in a part of the sunken area 
 and carrying the railroad line farther inland, the construction was 
 completed and the line opened for traffic September 20, 1875. The 
 following day was one of heavy rains, and on the morning of the 
 22nd fissures began to open in the made land, the new wall began 
 to crack, and suddenly a part of the wall, 85 meters long, and the 
 station lands and tracks to a width of 23 meters sank beneath the 
 inrushing lake waters. Just before noon a second subsidence took 
 place, a third one followed early in the afternoon, and others fol- 
 lowed on the 23rd and 24th of September. The total area which 
 thus disappeared beneath the water of the lake had a length of 204 
 meters and a width of 48 meters, with an area of 6,560 square me- 
 ters. Subsequent glidings occurred in October and November. 
 
 The gliding began on the steeper slopes at a distance from 
 shore, and was then transferred shoreward. The first effect of the 
 gliding of February 9 was the lowering of the outer slope from 
 31 per cent, to 27 per cent., but the gliding of June 12 caused the 
 complete baring of the rock for a distance of 150 meters or more, 
 and a change of grade back to 30 per cent, or 31 per cent., and 
 even a higher one farther lakeward. This became even more pro- 
 nounced in the glidings of September and later. The total extent 
 of the glidings was 450 meters, and the material was carried out to 
 
SUBAQUEOUS GLIDINGS 659 
 
 a depth of 125 meters. The affected part of the coast extended 
 from Horgen to Kapfnach, a distance of 1.5 km. The material was 
 spread over the lake bottom, raising it from I to 3 meters. In Oc- 
 tober, 1877, another small portion (the Sustplatz) subsided 
 (Frankfurter Zeitung, Beilage zu No. 304, 1877), showing that 
 movements are not ended. More recent glidings if they occurred 
 have not come to our notice. 
 
 The village of Zug has a similar record. As early as 1435, on 
 March 4th, 26 houses on the "Niederen Gasse," in the old part of 
 the village, slipped into the lake, 60 persons perishing at the time. 
 In 1593 the level of the lake was lowered by drainage, and further 
 subsidences occurred. On July 5, 1887, three successive portions 
 of the shore fell into the lake, submerging more than 20 houses. 
 The material which slid into the sea consisted of sandy mud, a delta 
 built by the Lorze when the lake stood at its higher level. A broad 
 stream of mud flowed into the sea, 300 meters from the point of 
 fracture, to a depth of 23 meters, under the lake level, and then con- 
 tinued outward to a distance of about 1,020 meters from shore and 
 a depth of 45 meters below lake level as a broad mud flow 150 to 
 250 meters wide and from i to 4 meters high. The -gliding began 
 in the lakeward region, and migrated landward, as in the case of 
 headward-growing streams. The remarkable fact here is that the 
 average grade of the surface along which the gliding has taken 
 place from the break to the end of the mud stream, a distance of 
 1,020 meters, was only 4.4 per cent. The earlier, smaller move- 
 ment extended for only about 500 meters into the lake and over a 
 grade of 6 per cent. The same rule thus seems to hold for the 
 subaquatic as for the subaerial solifluction, namely, the larger the 
 moving mass the smaller the average slope on which it moves. 
 
 Many similar though less instructive glidings have taken place 
 on the Swiss lakes, among them those of Montreux-Veytaux on 
 Lake Geneva ( Schardt-85 ; 86). Nathorst has also described simi- 
 lar subaquatic glidings in Sweden. 
 
 In 1895 or thereabouts movements of this type occurred at 
 Odessa, where several buildings slid into the Black Sea. The dis- 
 tance to which this mass was carried is unknown, but it was on a 
 much larger scale than that at Zug. 
 
 Submarine glidings of this type are probably common, but no 
 measurements are made of them. Such glidings are often indicated 
 on the steeper slopes by the breaking of the cables. In no case, 
 however, have the magnitude and extent of the glidings been ascer- 
 tained, though dislocations by faulting are known (see page 890). 
 
 It is of course evident that material thus sliding down a sub- 
 
66o 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 marine surface must be piled up to some extent in the deeper areas 
 where it comes to rest. As the result of such gliding the strata must 
 suffer much deformation, especially if they are at all consolidated. 
 Such deformations have all the characters of orogenic disturbances 
 due to lateral pressure, and indeed it has been suggested that some 
 extensive mountain folds and overthrusts may have originated in 
 this manner. These deformations will be more fully discussed in 
 Chapter XX^ 
 
 Accessory Features of Subaqueous Gliding. Among the ac- 
 cessory features produced by subaqueous and especially submarine 
 solifluctions, we may mention in addition to the deformations al- 
 ready noted, and to be more fully discussed in a later chapter, the 
 following phenomena : 
 
 FIG. 131. Diagram illustrating the changes in stratification due to subaquatic 
 gliding. In the shore section strata are eliminated, while farther 
 out duplication occurs. (After Heim.) 
 
 I. Increase of the strata in the lower regions where the shore 
 material is carried by gliding, and where strata are thus repeated by 
 the superposition of portions of the same strata upon one another. 
 2. Reduction of the number of strata in the zone affected by the 
 gliding where the ends of the strata are thus removed, and on the 
 deposition of subsequent beds a local disconformable relation is pro- 
 duced with hiatus signifying no appreciable time interval. 3. Su- 
 perposition of older on younger beds. Thus at Zug, the mass which 
 slid into the sea was more than 99 per cent, formed during the 
 former high-water period of the lake, and came to rest by gliding 
 upon the deposits formed since the present water level was estab- 
 lished (Fig. 131). 4. Displacement of facies. Thus at Zug gravel 
 and even coarse blocks were carried by gliding into the region where 
 they would otherwise be absent. In submarine solifluction shore 
 sediments may be carried out to the neritic belt, or the latter into 
 abyssal regions. A shore breccia may thus come to lie among off- 
 shore marine sediments. 5. Destruction of life. The benthonic and to 
 
NfiRITIC DEPOSITS 66 1 
 
 some extent also the pelagic life will be destroyed by such glidings 
 and the distribution of the fauna will be altered. Such a case has 
 been noted in connection with the rock slide at Elm. Such dis- 
 turbance might result in the sudden destruction of the entire ben- 
 thonic fauna, young and old alike, all stages being found together. 
 Above the mass of material which caused this destruction may come 
 a stratum carrying only remains of planktonic organisms without 
 sedentary benthos, which would return only after a while. (Heim- 
 
 The Permanently Submerged or Neritic Zone (Flachsee, Shallow 
 Water or Thalassal Zone). 
 
 This zone extends from the low-water line of the shore zone, a 
 somewhat variable line, to the edge of the continental shelf. Sev- 
 eral provinces of more or less importance may be recognized, chief 
 of which are : 
 
 1. The estuary. 
 
 2. The marginal lagoon. 
 
 3. Epicontinental seas and mediterraneans. 
 
 4. The ocean littoral. 
 
 i. The Estuary. This is the point of meeting place of the 
 terrestrial and marine realms. It receives on the one hand the sedi- 
 ments and other material brought by the rivers from the land, and 
 on the other it admits the waters of the sea, which for a time at 
 least modify the character of the deposit. Alternately the waters of 
 the land and of the sea predominate, as a result of which the de- 
 posits formed in the estuary will have characteristics typical of both. 
 As a good example, we may consider the estuary of the La Plata in 
 South America. This has a length of 125 miles, and receives the 
 water of the Parana and Uruguay rivers. The currents of these 
 rivers thus come into periodic contention with the tides from the 
 Atlantic. (Willis 105 ://pz.) Where the power of the tidal wave 
 balances that of the rivers, no current exists, a condition which may 
 continue for hours. (Revy-8i : <?p, jo.) Here at from 10 to 20 
 miles above the mouth of the estuary, the material held in sus- 
 pension is dropped, as a result of which submerged banks are form- 
 ing, which eventually grow into islands. The current during both 
 flood and ebb tide is swifter in the deep channels than in shallow 
 portions of the estuary, hence deposits made during flood tide will 
 be more copious over the shallows than in the deeper channels, 
 
662 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 which latter are also more subject to scour during the ebb tide. 
 The shallows thus become tide flats, which later are raised rush- 
 grown islands, thus restricting the water within narrow channels. 
 The original length of the La Plata was 325 miles, but about two- 
 thirds of this has been filled up in the manner described. Where 
 material of different sizes is brought by the rivers into the estuary 
 the coarser will be dropped when the current is first checked by the 
 rising tide, the finer following when the checking is complete. 
 During the scouring of the bottom at ebb tide much of the fine 
 material may be carried away again. (Willis-iO5 : 492.) 
 
 The floor of the Hudson has in many places been built up by 
 mud deposits to such an extent that extensive mud flats are laid 
 
 FIG. 132. Diagram illustrating the relationship between subsidence and the 
 growth of estuarine deposits. A, bar and lagoon (barachois) on 
 a young coast; B, estuarine deposits covered by transgressing 
 sea on subsiding coast. The bar and lagoon rest on terrestrial 
 deposits and not on the old crystalline base. (After Barrell.) 
 
 bare at low tide, a hundred or more miles above its mouth, while 
 the channel over much of this distance is comparatively shallow. 
 The rock bottom of the Hudson, on the other hand, is, in places, as 
 in the Highlands, more than 600 feet below tide level. It is proper 
 to note, however, that a part of the filling of this channel is proba- 
 bly glacial, only the upper hundred feet on the average being river 
 silt. 
 
 The estuary of the Severn (Sollas-89) may serve as another 
 example. The tidal channel of this river is notorious for its mud. 
 "At high tide it is filled with a sea of turbid water, thick and 
 opaque with tawny-colored sediment; as the tide ebbs a broad ex- 
 panse of shining mud flats is revealed fringing the coast; but so 
 like is the water to the mud that, seen from a distance, it is often 
 hard to tell where the sea ends and the shore begins. It is the 
 same with its tributaries, the Wye, the Usk, Ely and Rhymney on 
 
ESTUARINE DEPOSITS 663 
 
 the Welsh side, the Avon, Yeo, Parrot and others on the English 
 coast." (Sollas-Sgid//.) 
 
 The origin of this mud has been a subject of much dispute. In 
 part no doubt it is supplied by the rivers which have a catchment 
 basin of 9,193 square miles (English), but much is also produced 
 by the Waves washing the shores of the estuary. The water in the 
 tidal portion of the Severn Channel flows up and down twice daily 
 at the rate of from 6 to 12 miles an hour, a velocity much greater 
 than that required to move along large boulders of rocks. As a 
 result scouring of the channel occurs in many places. The devel- 
 opment of the currents has been described by Mr. W. R. Browne 
 (13) : "In ordinary tidal channels such as the Avon below Bristol, 
 the course of events during an ebb seems to be as follows. At first 
 the slope of the surface is exceedingly small (in the Avon it was 
 about ij/2 feet in 7*4 miles), and, while the velocity at the surface 
 is considerable, it diminishes rapidly from thence downward, and 
 at some distance from the bottom becomes nil. This continues for 
 about two-thirds of the ebb, the surface velocity increasing up to a 
 certain point, and then becoming nearly constant. During all this 
 time not only is no scour going on at the bottom, but, if the waters 
 be muddy, an actual deposition of silt, is taking place. At this time, 
 after about two-thirds of the ebb, the water has fallen about three- 
 quarters of its total height, the slope of its surface has considera- 
 bly increased, and the conditions approximate to those of an ordi- 
 nary river. The bottom layers of the water then spring suddenly 
 into motion, the surface velocity diminishes steadily as the tidal 
 waters disappear, until it assumes the normal rate of the low-water 
 flow. During this period a scour of the bottom is of course going 
 on ; but, as this velocity is not much higher than in the subsequent 
 period of low- water flow, the rate of scour will not be much greater ; 
 and the actual scour will be insufficient to compensate for the 
 amount of deposit from the tidal waters which has taken place, not 
 only during the period of high water, but also during the first two- 
 thirds of the ebb. It must follow, therefore, that the scouring effect 
 of the tide is little or nothing, and the observed incapacity of tidal 
 flows to sweep away the silt they have deposited is amply and satis- 
 factorily explained." 
 
 Sollas thinks that eventually much of the silt will find its way 
 t)ut to sea, owing to the constant outward pressure of the normal 
 river current. As a part of the material is carried seaward from 
 the. constant mass moved back and forth, new material is supplied by 
 the rivers. 
 
 The material of this estuarine mud consists of "a variable qnan- 
 
664 PRINCIPLES OF STRATIGRAPHY 
 
 tity of fine, argillaceous granules, small, angular fragments of color- 
 less transparent quartz containing numerous minute included cavi- 
 ties, a few similar fragments of flint, siliceous fragments of a 
 glauconite green color, minute crystals of quartz of the ordinary 
 form, minute prisms of tourmaline highly dichroic and similar in 
 form to macroscopic prisms of schorl, and minute rhombohedra of 
 calcite." Materials of organic origin also occur, such as coccoliths 
 and rarely coccospheres, both of the ordinary cyatholith type so 
 common in adjacent seas and in the Atlantic ooze; further, For- 
 aminifera, including Miliola, Textularia, several species, Nonionina 
 crassula, Polystomella umbilicata, Rotalia sp., Spirillina sp., etc., 
 more rarely spicules of Alcyonaria, fragments of echinoderm skele- 
 tons and minute spines; and triradiate spicules of calcisponges, 
 probably Sycandra. "Most of the Foraminifera are quite empty, 
 glassy and transparent; but some contain a brownish, soft granu- 
 lar material; and in one instance a small Rotaline form was ob- 
 served partially replaced by pyrites." (90- 6*4-) The siliceous or- 
 ganic remains comprise chiefly sponge spicules, very rarely Radi- 
 laria, and a variable quantity of diatoms. The remains of other 
 organisms found in the mud are all of marine types, though they 
 occur on the banks of rivers at a great distance from a truly marine 
 area. 
 
 In the muds of the rivers above the limit of tidal influence, only 
 spicules of fresh-water sponges and diatoms were found (Spongilla 
 fluviatilis), foraminifera and other marine organisms being absent. 
 Nor were any of these organisms derived from the Mesozoic 
 strata through which these rivers flow. The organic remains of the 
 modern, as well as the older, muds of the Severn estuary were ap- 
 parently all derived from the Bristol Channel, which is the further 
 enlargement of the Severn estuary and along the shores of which 
 from 10 to 15 miles west of the Severn estuary marine life abounds. 
 The older alluvial deposits of the Severn estuary have a maximum 
 thickness of about 50 feet. These comprise in descending order : 
 
 a More sandy zone 5 to 7 feet 
 Zone i. Upper clay \ b More argillaceous zone, with disseminated 
 
 vegetable matter 7 to 8 feet 
 Upper peat, I to 2 feet 6 inches 
 
 Zone 2. Lower clay 
 
 Lower peat, i to 4 feet 
 
 Zone 3. Sands and mud 
 Gravel 
 Triassic sandstones 
 
ESTUARINE DEPOSITS 665 
 
 The gravel contains glacial pebbles and rolled boulders up to a 
 cubic foot in size. It is not always present. The mud is a marine 
 or tidal deposit like the blue clay which replaces it elsewhere, and 
 from which it differs chiefly in being nearly or quite free from 
 clay. There seems to be a gradual transition from coarse at the 
 bottom to fine at the top. Some of the sands contain fragments of 
 a bryozoan, and many chips of pelecypod shells, including a small 
 Avicula. Foraminifera, spines of echinoderms and sponge spicules 
 also occur. In a section through Caldicot Marsh near Portskewet, 
 fifty feet deep, a bed of marl was encountered 10 feet above the 
 base, which contained a mixture of fresh and brackish water shells, 
 such as Limnsea, Planorbis, Scrobicularia piperata and Cardium 
 edule. Diatoms are common in it, and also remains of Chara. 
 A similar bed occurs near Cardiff, about 19 miles farther south. It 
 occurs at the same depth. Altogether the beds of zone 3 repre- 
 sent a normal estuarine deposit, with a fauna and flora both brack- 
 ish and fresh. 
 
 The lower part of zone 2 has remains of forest trees associated 
 with it. It is covered by blue clay with Foraminifera and other 
 marine organic remains, indicating a subsidence. The upper Peat 
 bed, sometimes the only one, "consists of various plant remains, in- 
 cluding leaves and roots of yellow flags and spores and mycelia of 
 fungi, while its upper surface is strewn with trunks and branches of 
 trees, oak, fir, and birch being the chief. The fir still retains its 
 bark, and the heartwood, when cut, is often found to have pre- 
 served its original color. Some of the wood has been bored by 
 some kind of beetle." (go 1621.) The peat is very pure, though 
 containing occasional sand grains, Foraminifera or sponge spicules. 
 It often contains an abundance of spherules of iron pyrites, and 
 sometimes the vegetable cells are filled with it, these occupying the 
 place of the departed protoplasm within the resistant cell walls. 
 The origin of this pyrite is similar to that of coast marshes or 
 swamps in general. When the salt water comes in contact with the 
 decaying vegetable matter a series of reactions occurs, which will 
 end in the formation of iron pyrites. The upper clay contains 
 Foraminifera, sponge spicules and other marine organisms, besides 
 disseminated vegetal material. 
 
 2. The Marginal Lagoon or Barachois. These names are ap- 
 plied to the water bodies cut off from the main portion of the sea 
 by the formation of barrier beaches. So long as the lagoon is not 
 filled in by silt and organic deposits, it belongs to the neritic zone 
 of the littoral district. The process by which it is converted into 
 
666 PRINCIPLES OF STRATIGRAPHY 
 
 tidal flats and marshes has already been sketched. (See Chapter 
 XL) It need only be noted here that the deposits accumulating 
 in the lagoon are the finer sands and muds brought by the tidal 
 currents, and the sands blown across from the beach. Though 
 stratification may be well marked in these lagoon deposits, the evi- 
 dence of agitation by waves or currents is slight. Cross-bedding 
 structure is not characteristic of such deposits, but ripple marks, 
 of the oscillation type, i. e., symmetrical, sharp crests with broad, 
 rounded troughs, may be formed. A characteristic feature of these 
 deposits is the presence of the eel grass leaves which penetrate the 
 strata in a vertical direction, having been instrumental in the pre- 
 cipitation around them of the suspended material, through a check- 
 ing of the velocity of the current. In the last-formed deposits of 
 the lagoons organic matter will predominate and peat beds the 
 coal of the future mark the transition through the shore zone to 
 terrestrial conditions. Of older deposits of this type the Low- 
 ville limestone has already been cited. This is a formation of fine 
 lime mud deposited around vertical stems or branches of a marine 
 organism, probably not a plant, however. Thus the resulting calci- 
 lutyte is penetrated by numerous vertical tubules, now largely oc- 
 cupied by crystalline calcite, and producing on the bedding planes 
 the so-called bird's-eye structure which gave the formation its orig- 
 inal name. 
 
 3. Epicontinental Seas and Mediterraneans. Tho'se portions of 
 the littoral district which extend into the land as arms or partly 
 enclosed embayments of no great depth, without being estuaries of 
 great rivers, are of considerable importance to the stratigrapher, 
 since epicontinental seas of this type were very characteristic of 
 many geologic epochs. Their chief significance is, however, a faunal 
 one, since sedimentation, except in special cases, does not differ 
 much from that upon the continental shelf. Nearly landlocked epi- 
 continental seas within pluvial districts, such as Hudson Bay or the 
 Baltic Sea, do not differ appreciably from the littoral belt of the 
 open ocean, but where such enclosed seas occur in arid climates the 
 greater density and increased salinity of their waters will influence 
 perceptibly not only the fauna and flora, but also the deposits. If 
 the intracontinental sea of the arid or semiarid climate is a med- 
 iterranean, i. e., if its center extends to depths much greater than 
 its outlet, the peculiarities of the deposits will be emphasized. The 
 Black Sea forms an instructive example of the conditions found in 
 an almost completely enclosed water body of great depth in a semi- 
 arid region. According to Andrussow (5; 2i:?oo), the superficial 
 
MARINE LITTORAL 667 
 
 water layer, of about 125 fathoms, has a less salinity and density 
 than the deeper water, being largely renewed by the fresh water 
 of the drainage. The heavier lower water is derived from the 
 Mediterranean by way of the richly saline Marmora and yEgean 
 seas, requiring about 1,700 years for its renewal. Vertical cur- 
 rents are slight on account of the greater density of the deeper 
 water, and hence* these lower waters have not sufficient oxygen to 
 support animal life. Sulphuretted hydrogen is separated out, prob- 
 ably through the agency of sulphobacteria, in the deeper water ; be- 
 ginning at 100 fathoms, with 33 c.c. of H 2 S per 100 liters of water 
 until, at 500 fathoms, 570 c.c. of H 2 S per 100 liters of the water are 
 separated. Below this the increase is less^rapid. As the H 2 S in- 
 creases, the sulphates of the water decrease, and carbonates and 
 FeS are separated out. 
 
 The sediments of the Black Sea comprise sandy detritus to a 
 depth of 20 fathoms, below which occurs gray, blue, sticky mud 
 rich in Modiola phaseolina to the loo-fathom line. In the great 
 depths occurs a very fine, sticky, black mud with rich separation of 
 FeS, abundant remains of planktonic diatoms, and shells of young 
 pelecypods, which have descended to this depth on completion of 
 their early pelagic existence (mero-planktonic stage). Besides the 
 black is a dark-blue mud with less FeS, but a richer separation of 
 CaCO 3 in minute grains, this lime often constituting thin banks, 
 while pelagic diatoms are likewise abundant. Clarke (21 : 201} has 
 suggested the possible origin of some of the Upper Devonic black 
 shales of New York (Portage) under similar conditions, but this is 
 a much mooted question. Pompeckj (71 : 43 et seq) has interpreted 
 the black Posidonia bronni shales of the Jurassic of Regens- 
 burg, Bavaria, as deposits of this type. It is, however, difficult to 
 understand how such a region can furnish conditions for the per- 
 fect preservation of the saurians of that period, so that in some 
 cases even the skin of the animals is intact. 
 
 4. The Ocean Littoral, or the Neritic Zone. This is the most 
 widely distributed littoral belt at the present time. Its deposits vary 
 considerably, according to distance from shore, depth of water and 
 relation to currents. In general a seaward gradation in the texture 
 of the material from coarse to fine is observable, sands being found 
 near shore (though often extending out for great distances), while 
 muds are formed further offshore and in specially protected places. 
 In the Arabian Sea muds are carried from 700 to 800 miles from 
 land, owing to the nature of the ocean currents. Calcareous accu- 
 mulations are typical of this region, especially those formed around 
 coral reefs. These have been fully described above. 
 
668 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 DEPOSITS OF THE BATHYAL DISTRICT. 
 
 < 
 
 On the whole the deposits of this region, which nominally lie be- 
 tween 200 and 900 meters or between 100 and 500 fathoms, are con- 
 tinuous with those of the neritic zone on the one hand, and with 
 those of the abyssal on the other. The following deposits seem to 
 be most characteristic of this district, though extending into both of 
 the adjoining ones: 
 
 Table Showing Kinds and Distribution of Bathyal Deposits. 
 
 
 Clastic deposits 
 
 Mean depth 
 
 Area covered 
 in square miles 
 
 in fathoms 
 
 in meters 
 
 I 
 
 2 
 
 3 
 
 4 
 5 
 6 
 
 7 
 8 
 
 Blue mud 
 
 1,411 
 623 
 513 
 449 
 i,033 
 243 
 740 
 176 
 
 2,397 
 1,140 
 920 
 
 821 
 1,889 
 444 
 i,353 
 322 
 
 
 14,500,000 
 
 100,000 
 
 850,000 
 600,000 
 
 2,556,800 
 
 Red mud 
 
 Green mud 
 
 Green sand 
 
 Volcanic mud. . 
 
 Volcanic sand 
 
 Coral mud 
 
 Coral sand 
 
 
 The table on page 669, taken from Clarke's Data of Geochemistry 
 (2ob:^6 5 p), gives the analysis of the terrigenous and volcanic muds 
 and the green sands: i, Blue mud dried at 110 (Brazier); 2, 
 red mud dried at 100 (Hornung) ; 3, green mud dried at 110 
 (Brazier) ; 4, green sand dried at 110 (Brazier) ; 5, volcanic mud 
 dried at 110 (Brazier). 
 
 Three types of land-derived muds are found in the modern sea 
 away from the shore. These are the blue, the red and green muds. 
 
 The Blue or Slate-Colored Mud. This is the most widely dis- 
 tributed, extending, according to Murray and Renard, over an area 
 of 14,500,000 square miles. It covers the floors of the shallow sea 
 to the edge of the continental shelf, as well as the floor of the entire 
 polar sea. The greatest depth at which it was observed by the 
 Challenger was 5,120 meters. In the Gulf of Naples it begins at 
 a depth of 15 meters, where in contact with the sea water it gen- 
 
BATHYAL DEPOSITS 
 
 669 
 
 TABLE OF ANALYSES OF MUDS OF TERRIGENOUS AND VOLCANIC 
 
 ORIGIN. 
 
 
 (i) 
 Blue mud 
 
 (2) 
 
 Red mud 
 
 (3) 
 Green mud 
 
 (4) 
 Green sand 
 
 (5) . 
 Volcanic 
 mud 
 
 Ignition 
 SiO 2 
 
 5.60 
 64.20 
 
 6. 02 
 31 66 
 
 3-30 
 
 ^I 27 
 
 9.10 
 
 2Q 7O 
 
 6.22 
 \A 12 
 
 A1 2 O 3 
 
 IV 55 
 
 9.21 
 
 4.08 
 
 TI 2S 
 
 Q 22 
 
 Fe 2 O 3 
 
 8 *8 
 
 452 
 
 12 72 
 
 5O5 
 
 I ^ A6 
 
 MnO 2 
 
 
 
 
 
 trace 
 
 CaO 
 
 2. . SI 
 
 25.68 
 
 O. 1O 
 
 O 22 
 
 I 44 
 
 MgO 
 
 O 2S 
 
 2 O7 
 
 O 12 
 
 O IT. 
 
 O 22 
 
 Na 2 O .. 
 
 
 I 6^ 
 
 
 
 
 K 2 O 
 
 
 I . V* 
 
 
 
 
 CaCO 3 
 
 2.94 
 
 
 46. 16 
 
 4Q 46 
 
 12 22 
 
 Ca 3 P 2 O 8 
 CaSO 4 
 
 i-39 
 
 O 42 
 
 
 
 0.70 
 
 o s8 
 
 trace 
 i 07 
 
 trace 
 o 27 
 
 MgCO 3 
 
 ., o 76 
 
 
 O S7 
 
 2 O2 
 
 o 8^ 
 
 SO 3 . 
 
 
 O 27 
 
 
 
 
 CO 2 
 
 
 17 11 
 
 
 
 
 Cl 
 
 
 2.46 
 
 
 
 
 
 
 
 
 
 
 Total 
 
 IOO OO 
 
 IOI 98 
 
 IOO OO 
 
 IOO OO 
 
 IOO OO 
 
 LessO = Cl 
 
 
 0.87 
 IOI. II 
 
 
 
 
 erally has a red or brown color, due to iron oxide or hydrate, and 
 when dried its color is gray or brown from the oxidation of its con- 
 tained iron sulphides. Pure clay often constitutes only a small pro- 
 portion of this mud (though ranging from 16 to 97 per cent.), and 
 the lime content may be as high as 35 per cent. Quartz is a char- 
 acteristic constituent. This is the type of mud which has in the past 
 given rise to most of the marine shales and slates. 
 
 The Red Mud. This is much more restricted -in its distribution 
 than either the blue or green. It is found opposite the mouths of 
 tropical rivers, such as the Amazon and the Yang-tze-Kiang, and is 
 derived from the red laterite or residual soil of the tropical coun- 
 tries. Its percentage of pure clay varies from 28 to 68, and its 
 lime content varies from 6 to 60 per cent. ; glauconite is absent, but 
 quartz is characteristic. The red mud closely resembles the red mud 
 of the deep sea, which has, however, a different origin, being proba- 
 bly in large part the product of decay of volcanic material which 
 has settled to this depth. Muds of this kind may easily preserve an 
 
670 PRINCIPLES OF STRATIGRAPHY 
 
 abundance of shells and other remains of marine organisms. Since 
 they are formed opposite the mouths of great rivers, which may 
 sweep terrestrial organisms into the sea, such remains may also be 
 expected in these deposits. 
 
 The Green Mud. This ranges in depth from 180 to 2,300 meters 
 (99 to 1,250 -|- fathoms), and may contain as much as 56 per cent, 
 of lime. In shallower depths this green mud passes into greensands. 
 The percentage of clay in the green mud varies from 24 to 48. 
 Glauconite is one of the chief constituents of both the greensands 
 and green muds. 
 
 Greensand. This is essentially the mineral glauconite, an impure 
 hydrous silicate of iron and potassium. Clarke states that, "accord- 
 ing to the best analyses, glauconite probably has when pure the 
 composition represented by the formula Fe"' KSi,O,.--aq., in which 
 some iron is replaced by aluminum, and other bases partly replace 
 K." This is forming in the present ocean near the "mud line" 
 around continental shores. It is never pure, but contaminated by 
 alteration products and other substances, and hence its composition 
 varies widely. In the present ocean it is chiefly formed on the in- 
 terior of foraminiferal shells, and it is believed that the decompos- 
 ing organic matter in these shells is responsible for its formation. 
 According to Murray and Renard (62:3.83), the shell is partly 
 filled with fine silt or mud, and upon this the organic matter will 
 act. "Through intervention of the sulphates contained in the sea 
 water, the iron of the mud is converted into sulphide, which oxi- 
 dizes later to ferric hydroxide. At the same time alumina is re- 
 moved from the sediments by solution, and colloidal silica is lib- 
 erated. The latter reacts upon the ferric hydroxide in presence of 
 potassium salts extracted from adjacent minerals, and so glauconite 
 is produced." (Clarke-2ob -.402.) The constant association of the 
 glauconite shells with the debris of rocks in which potassium-bear- 
 ing minerals such as orthoclase and muscovite occur seems to sus- 
 tain this view of Murray and Renard of the origin of glauconite. 
 
 Glauconite may, however, form under other conditions than 
 those now obtaining in the glauconite region of the present oceans. 
 L. Cayeux (15) has shown that in certain instances glauconite has 
 formed subsequent to the consolidation of the rocks in which it 
 occurs. Cayeux shows that this mineral can also form without the 
 intervention of organisms. 
 
 While glauconite of the present sea and in the sedimentary rocks 
 is crystalline (monoclinic, La Croix), having a definite cleavage, 
 though not crystal form, the mineral caladonite of nearly identical 
 composition is earthy in texture and never granular. This is a de- 
 
GREENSANDS 671 
 
 composition product of augite in various basaltic rocks, and may be 
 identical with glauconite (Clarke). Another mineral of similar 
 appearance is greenalite, found in the iron-bearing rocks of the 
 Mesabi range of Minnesota. It is free from potassium, the iron 
 being practically all in the ferrous state (Leith-56: 240), while in 
 glauconite, where potassium is an essential constituent, the iron is 
 mainly in the ferric state. Cayeux has also observed that glau- 
 conite is frequently present in arable soils, in all conditions from 
 perfect freshness to complete alteration into limonite, to which 
 Clarke remarks that the formation of the species is perhaps "one 
 of the modes by which potassium is withdrawn from its solution in 
 the ground water." (20^:494.) "Probably, in all their occur- 
 rences," says Clarke, "the final reaction is the same, namely, the 
 absorption of potassium and soluble silica by colloidal ferric hy- 
 droxide. In the ocean these materials are prepared by the action of 
 decaying animal matter upon ferruginous clays and fragments of 
 potassium-bearing silicates. In the sedimentary rocks, where glau- 
 conite appears as a late product, the action of percolating waters 
 upon the hydroxide would account for its formation. In igneous 
 rocks the hydroxide is derived from augite, or perhaps from olivine, 
 and percolating waters again come into play. Thus the various pro- 
 ductions of glauconite and caladonite become the results of a single 
 process, which is exactly equivalent to that in which .potassium com- 
 pounds are taken up by clays." (20^:4^4.) 
 
 Greensands are found in nearly all formations from the Cambric 
 to the present, and often constitute a predominant element of the 
 formation, as in the Cretacic Greensands of England and America. 
 Analyses of the mineral from different horizons show on the whole 
 a close correspondence in composition, there being, however, a stead- 
 ily decreasing percentage of potash from the older to the more re- 
 cent. In the table on page 672, the average composition of various 
 glauconites is given : (a) from the Lower Ordovicic of Minnesota, 
 
 (b) from the Cretacic .Greensands of Wooburn, Antrim, Ireland, 
 
 (c) from the Cretacic Greensand marls of Hanover County, Vir- 
 ginia, (d) modern oceanic glauconite, mean of four analyses from 
 Challenger dredgings (analyses b, c, d quoted from Clarke-2ob : 
 
 494)- 
 
 The mechanical composition of typical greensand marls (Nave- 
 sink) of the Cretacic of New Jersey has been determined by 
 Prather (73: 162 ; 74) to be as follows: 
 
 Fine clay (settling out of suspension in water in the course of 
 from i to 24 hours), 14.41 per cent. ; sand, almost wholly composed 
 of pure glauconite, pyrite, shell fragments and Foraminifera (set- 
 
6 7 2 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Table of Analyses of Glauconite from Various Horizons. 
 
 
 (a) 
 Ordovi- 
 cic 
 
 (b) 
 Cretacic 
 Ireland 
 
 (c) ; 
 Cretacic 
 Virginia 
 
 (d) 
 Modern 
 oceanic 
 
 SiO 2 
 
 48. 18 
 
 40.00 
 
 51 .56 
 
 53.61 
 
 A1 2 O 3 
 
 6.97 
 
 13.00 
 
 6.62 
 
 9.56 
 
 Fe9CK 
 
 
 16.81 
 
 15. 16 
 
 21 .46 
 
 FeO 
 
 27.08 
 
 10. 17 
 
 8.33 
 
 1.58 
 
 MnO 
 
 
 
 
 trace 
 
 MgO 
 
 
 i .97 
 
 0.95 
 
 2.87 
 
 CaO 
 
 
 I 07 
 
 o 62 
 
 I IQ 
 
 Na 2 O 
 
 i .25 
 
 2.16 
 
 1.84 
 
 0.42 
 
 K 2 O 
 
 7.40 
 
 8.21 
 
 4. 15 
 
 3-49 
 
 H 2 O 
 
 8 75 
 
 6 IQ 
 
 IO. \2 
 
 5.96 
 
 
 
 
 
 
 Total 
 
 OQ 6^ 
 
 100 48 
 
 OQ ct; 
 
 IOO. ^4 
 
 
 
 
 
 
 tling out of suspension in water in five minutes or less), 85.59 per 
 cent. A sample from a lower bed of the same formation (Nave- 
 sink) gave clay as above 8.18 per cent.; sand, composed about 
 equally of pure glauconite and of rounded grains of quartz, with 
 some mica, 91.82 per cent. 
 
 Many grains of glauconite represent internal molds of forami- 
 niferal shells, though frequently further enlargement of these molds, 
 after the solution of the shell, produces irregular glauconite nodules. 
 W. B. Clark (17: 238 '; 18) believes that the New Jersey glauconites 
 were formed in much the same manner as the modern glauconites 
 of the ocean, but Prather (74:509) points out some objections to 
 this interpretation, and cites evidence of shallow-water conditions 
 during the accumulation of these glauconite sands. He finds that 
 the casts of Foraminifera are the exception. The greensand grains 
 of the Lower Ordovicic dolomites of Minnesota are regarded by 
 Hall and Sardeson (42 : 186} as having their origin "in the chem- 
 ical conditions of the mingled mineral matters of the including 
 rocks. . . ." and not in the chemical changes within foraminiferal 
 shells. (See Hunt-49 : joj ; 50 : 196, 309 551: 257.) Though mod- 
 ern glauconite deposits are chiefly confined to depths at or for some 
 distance below the 100- fathom line, the frequent association of this 
 mineral with typical littoral deposits, and in formations containing 
 a littoral fauna, indicates that in the past it may have formed in 
 
BATHYAL DEPOSITS 673 
 
 shallower water sufficiently removed from the shore to prevent ex- 
 cessive detrital deposition. 
 
 The secondary origin, through erosion of older greensand de- 
 posits and redeposition of the material in shallow water, must also 
 be considered. Such deposits are forming at the present time by 
 the erosion of the Cretacic greensands of the Atlantic coastal plain. 
 Andree (3 '.381) holds that this may have been the origin of green- 
 sand lenses in the Neocomien sandstones of northwest Germany 
 (Teutoburger Wald, especially the Oswing). The lower Cenoma- 
 nien deposits of greensands (Essener Greensand) of northwestern 
 Germany are other examples of such deposits formed near shore, 
 passing laterally near Mons into a shore conglomerate with rich 
 fauna. 
 
 Greensand is to-day found sporadically on the shallow ocean 
 floor under the Gulf Stream in depths of only a few hundred 
 meters. ( Pourtales-72 : jp/. ) 
 
 The decomposition of glauconite produces, according to L. 
 Cayeux, ferric hydroxide and pyrite, but other alteration products 
 may also result. Thus the bright-red "Redbank" sands of the New 
 Jersey Cretacic seem to owe their color to the decomposition of the 
 glauconite mingled with the quartz grains of the deposit. This de- 
 composition may be due to the more porous character of these sands, 
 but that it was not produced under present climatic conditions is 
 shown by the bright-red tints which indicate a prolonged period of 
 subjection to dehydrating agencies. 
 
 Deposits on Lee Banks and on the Edge of the Continental Shelf. 
 
 Where ocean currents carrying fine silt pass from shoals to deep 
 water, the checking of the current resulting causes a deposition of 
 more or less of the silt. (Willis-io5 : 497.) Thus on the lee of a 
 submerged ridge a bank of silt will form, the structure of which is 
 probably that of the delta, the successive additions being at a com- 
 paratively steep angle. The Gulf Stream crosses several shoals or 
 submerged terraces, and deposits of the type mentioned are formed 
 in the lee of these. "The steepest slope of the Gulf of Mexico from 
 the looth to the 2,oooth- fathom line is in the position of a lee-bank 
 northwest of the Yucatan plateau. . . . The Blake plateau, over 
 which the Gulf Stream sweeps north of the Bahamas, is clean, hard 
 limestone, but a lee-bank of mud and ooze is forming on its short, 
 steep slope into deep water." (105 : 497-) 
 
 A similar type of deposit is forming on the edge of the conti- 
 
674 PRINCIPLES OF STRATIGRAPHY 
 
 nental plateau off the Atlantic coast of North America. The pla- 
 teau or shelf itself is covered with shore-derived arenaceous de- 
 posits. Dredgings from these were examined by Bailey Willis, who 
 states that they "are indeed finer near the eastern edge, yet are dis- 
 tinctly granular and incoherent." 
 
 The black muds of the Ordovicic with their world-wide distri- 
 bution of graptolites seem to offer an older illustration of this type 
 of sedimentation. The graptolites are often arranged so as to in- 
 dicate current action, and it appears that these muds (Deep Kill, 
 Norman's Kill, Utica) were distributed by these currents and de- 
 posited on the ocean floor under their pathway. 
 
 ABYSSAL DEPOSITS. 
 
 In the abyssal district of the ocean, beyond the one thousand- 
 meter line, current-borne detrital material is relatively unimpor- 
 tant. Terrestrial material borne by currents is not unknown, how- 
 ever, as in the case of the deep-sea vegetal deposits already referred 
 to. Even rock waste is carried by currents to realms of greater 
 depths where these are not far from shore, while terrestrial material 
 carried by floating icebergs or rocks held by the roots of floating 
 trees or sea weeds may come to be deposited at any depth. Among 
 other deposits of the littoral district which pass over into the abys- 
 sal, greensand has already been noted, as extending to a depth of 
 700 fathoms. The characteristic deposits of this district, exclusive 
 of the marine derelicts, may be divided, according to their origin, 
 into the pelagic and the terrigenous. To these must be added the 
 meteoric or extra-terrestrial materials, and the subcrustal or vol- 
 canic. 
 
 Abyssal Deposits of Pelagic Origin. 
 
 Pelagic deposits are those which have descended to the bottom 
 from the pelagic district of the ocean, i. e., the upper hundred- 
 fathom layer of water of the open ocean. They comprise chiefly 
 the shells and skeletal parts of pelagic animals and plants, such as 
 Foraminifera, radiolaria, pteropods, ostracods and diatoms, the 
 shells and other hard parts of pelagic molluscs, and the skeletal 
 parts of fish, especially the teeth of selachians, and, further, the 
 ear bones of whales, and other hard parts of this as well as other 
 pelagic vertebrates. The young stages of organisms, such as mol- 
 luscs, brachiopods and echinoderms, may also be included in these 
 
ABYSSAL DEPOSITS 675 
 
 deposits. The former group may be termed the holopelagic group, 
 since it comprises organisms permanently at home in the pelagic 
 district, while the latter may be termed the meropelagic group, com- 
 prising types at home in the pelagic district during part of their 
 lives only. 
 
 Foraminifera, ostracods and pteropod shells are calcareous, and 
 these form the chief source of the lime deposits of the deep sea. 
 Foraminiferal oozes of the modern sea generally abound in the 
 shells of Globigerina, hence the term Globigerina ooze is ap- 
 plied to them. It should be emphasized, however, that the For- 
 aminifera of this ooze are pelagic species, i. e., types which float in 
 the pelagic district of the open ocean. This point is often over- 
 looked in interpreting former foraminiferal oozes as deep-sea de- 
 posits. Thus it has been shown repeatedly that the Foraminifera 
 of the chalk are largely of littoral types with only such pelagic ad- 
 ditions as might be expected from the fact that the pelagic district 
 really overlaps the littoral. Nevertheless the chalk is commonly 
 compared with the modern Globigerina ooze, and referred to abys- 
 sal deposits, whereas the Foraminifera composing it point rather to 
 a littoral origin. 
 
 The great purity of deep-sea oozes of pelagic origin is due to 
 the fact that the amount of terrigenous material settling here is 
 relatively slight. Thus in tropical seas, in depths of 600 fathoms 
 or less, pelagic shells of carbonate of lime often constitute 80 
 per cent, to 90 per cent, of the deposit. With increasing depth, 
 however, the percentage of carbonate of lime decreases, though the 
 surface conditions are the same. Thus at 2,000 fathoms the lime 
 is less than 60 per cent., at 2,400 fathoms 30 per cent, and at 2,600 
 fathoms 10 per cent. (Chamberlin and Salisbury-i6: 382), while 
 below this lime is generally absent. The most rapid falling off of 
 the percentage of lime carbonate is below 2,200 fathoms, while be- 
 tween 2,400 and 2,600 fathoms the floor of the ocean is covered 
 with red clay. The explanation generally given for this decrease 
 in the percentage of carbonate of lime is the greater power of solu- 
 tion of the deeper waters, owing either to the great pressure under 
 which it exists or to the abundance of CO 2 in it derived from emana- 
 tions from the sea floor, or to both causes. (For other factors in- 
 fluencing this, see Philippi-69.) The red clay of the deeps has 
 been regarded as the insoluble residue left on solution of these 
 shells, a not unlikely source for at least a part of this deposit. 
 
 Radiolaria and diatom shells are siliceous, and often constitute 
 extensive deposits in the modern oceans. Diatoms are, however, 
 not confined to salt water, but occur in fresh water as well. Ex- 
 
676 PRINCIPLES OF STRATIGRAPHY 
 
 tensive beds of diatoms are known in various older deposits both 
 marine and lacustrine. Characteristic examples are found in the 
 coastal plain strata of eastern North America, where a single bed 
 underlying the city of Richmond, Virginia, has a thickness of 18 
 feet. Beds of fossil Radiolaria of considerable thickness are also 
 known from older deposits, the most famous being the "Barba- 
 does earth" and the "Tripolite," though this name is often applied 
 to diatomaceous or other siliceous earths. 
 
 Abyssal Deposits of Terrigenous Origin. 
 
 Among these may first be noted the terrigenous matter carried 
 to great distances by the currents, especially opposite the mouths of 
 great rivers. Thus terrigenous deposits are carried out for a thou- 
 sand miles opposite the mouth of the Amazon. The fine coral mud, 
 found around oceanic coral islands, often making the water milky 
 for miles, may settle to the more moderate depths of the abyssal 
 region around these islands. Characteristic deep-sea deposits of 
 continental origin are the blue, green and red clays already referred 
 to, the greensand in the upper portion and the deposits of drift logs 
 and leaves, such as were dredged by the Blake and the Albatross in 
 the Caribbean and off the west coast of America. The most abun- 
 dant deep-sea deposits of terrestrial origin are volcanic ejecta- 
 menta, especially the finer volcanic ashes which are spread far and 
 wide by wind currents and eventually settle on sea and land alike. 
 Even fragments of pumice, dropped on the surface of the ocean 
 and floated until they become waterlogged, are characteristic of 
 deep-sea deposits. Volcanic glass and lapilli are likewise found in 
 the deep-sea deposits, some of these probably originating from sub- 
 marine volcanoes. It is believed that much of the red clay which 
 covers the deeper ocean floor is a result of the decomposition of 
 such volcanic material. This floating volcanic debris is often classed 
 as pelagic, but it is evident that it has nothing in common with the 
 true pelagic material. It may for convenience be classed as pseudo- 
 pelagic, in which class also may be included the leaves, tree trunks, 
 etc., which have 'floated out from the land (pseudoplankton) and 
 come to rest on the bottom of the deep sea. All of these are strictly 
 terrestrial, only the holopelagic and meropelagic types being truly 
 marine. 
 
 The Red Clay. 
 
 The red clay of the deep sea is distributed over an area aggre- 
 gating 51,500,000 square miles, and occurs in depths below 2,400 to 
 
ABYSSAL DEPOSITS 
 
 677 
 
 2,600 fathoms. It contains much volcanic debris, besides the bones 
 of mammals, zeolitic crystals and spherules of extra-terrestrial ori- 
 gin. As already noted, the solution of the pelagic shells in deeper 
 water liberates a minute quantity of such red clay, but a consid- 
 erable part also appears to be derived by decomposition of volcanic 
 dust. The clay is generally rich in Radiolaria; indeed these have 
 been regarded as forming merely a phase of the red clay deposit of 
 the deep sea, they seldom if ever occurring quite pure. 
 
 Analyses of Deep-Sea Deposits. 
 
 The following analyses quoted from Clarke (2oa 436) give (a) 
 the composition of the red clay from 23 analyses. Others have 
 given a carbonate of lime content as high as 60 per cent. Added to 
 this are analyses of (b) radiolarian ooze, (c) diatom ooze, (d) 
 Globigerina ooze, average of 21 analyses, (e) Globigerina ooze very 
 high in carbonate, and (f) pteropod ooze. All samples dried at 
 110. Soluble and insoluble portions in analyses a, b and d are not 
 separated in the table. 
 
 Table of Analyses of Deep-Sea Deposits. 
 
 
 a 
 
 b 
 
 c 
 
 d 
 
 e 
 
 f 
 
 
 Red clay 
 
 Radio- 
 larian 
 
 Diatom 
 ooze 
 
 Globi- 
 gerina 
 
 Globi- 
 gerina 
 
 Ptero- 
 pod 
 
 
 
 ooze 
 
 
 ooze 
 
 ooze 
 
 ooze 
 
 Ignition 
 
 4 5O 
 
 7 41 
 
 5 ^O 
 
 7 QO 
 
 i 40 
 
 2 OO 
 
 SiO 2 
 
 62 10 
 
 56.02 
 
 67.92 
 
 U .71 
 
 1.36 
 
 3 65 
 
 A1 2 O 3 
 
 16.06 
 
 10.52 
 
 o. 55 
 
 II . IO 
 
 0.65 
 
 0.80 
 
 Fe 2 O 3 
 
 ii 81 
 
 14. OQ 
 
 o ^o 
 
 7 O"* 
 
 o 60 
 
 1 06 
 
 MnO 2 
 
 o 55 
 
 1 2T, 
 
 
 trace 
 
 
 
 CaO 
 
 0.28 
 
 O. ^9 
 
 
 0.41 
 
 
 
 MgO . 
 
 o 50 
 
 O 25 
 
 
 O 12 
 
 
 
 CaCO 3 
 
 0.92 
 
 3.89 
 
 19.29 
 
 37-51 
 
 92.54 
 
 82.66 
 
 Ca 3 P 2 O 8 
 
 0.19 
 
 1-39 
 
 0.41 
 
 2.80 
 
 0.90 
 
 2.44 
 
 CaSO 4 
 
 0.37 
 
 0.41 
 
 0.29 
 
 0.29 
 
 0.19 
 
 o-73 
 
 MgCO 3 
 
 2 7O 
 
 i 50 
 
 I n 
 
 i i^ 
 
 0.87 
 
 0.76 
 
 Insoluble*. . . . 
 
 
 
 4.72 
 
 
 1.49 
 
 3-90 
 
 
 IOO.OO 
 
 IOO.OO 
 
 100.00 
 
 100.00 
 
 IOO.OO 
 
 IOO.OO 
 
 * Contains silica, alumina, and ferric oxide not separated. 
 
678 PRINCIPLES OF STRATIGRAPHY 
 
 Older Deposits That Have Been Considered of Deep-sea Origin. 
 
 The question, Are there any deep-sea deposits among the sedi- 
 ments in the older geological series, has been variously answered 
 in the past. Sir John Murray held that abyssal sediments were not 
 represented among the known sediments, except perhaps in such 
 instances as the radiolarian ooze of Barbados. Chalk has in the 
 past frequently been cited as an example of a deep-sea deposit of 
 Cretacic time, and this opinion is still defended by some. (Supan- 
 91: #55.) There seems to be, however, a growing recognition of 
 the fact that this formation is of comparatively shallow-water ori- 
 gin, the organisms composing it being benthonic rather than pelagic. 
 
 Many older radiolarian cherts or radiolarites have been referred 
 to deep-sea origin. Their almost constant interpolation between 
 beds of shallow-water origin has, however, thrown doubt upon this 
 interpretation. Of comparatively deep-water origin are believed to 
 have been the massive limestones of the Trias of the eastern Alps 
 and of some of the Jurassic deposits of the Alpine region. This 
 applies especially to the Aptychus beds of the Upper Jurassic, some 
 of which seem to have no other remains than the operctila of am- 
 monite shells, the so-called Aptychi. These opercula are believed 
 to have sunk to the bottom on the death and decay of the pelagic 
 ammonite, while the shell continued to float and eventually was de- 
 posited in other sediments of generally shallower water origin. 
 
 Whether these deposits will eventually prove to have such an 
 origin, or whether they, too, may not be of shallow-water origin, 
 must for the present remain undecided. 
 
 In North America the black muds of the Upper Devonic have 
 been regarded as of deep-water origin (Clarke-2i), but formed 
 under conditions similar to those obtaining in the Black Sea. The 
 same origin has been suggested by Pompeckj (71) for the dark 
 Liassic shales with saurian remains found in Wiirttemberg and in 
 England. In both cases, however, the deposits may with equal if 
 not greater certainty be classed as of shallow-water origin. 
 
 Concretions of the Deep Sea. 
 
 Concretions are a characteristic feature of the deep sea. Though 
 not clastic, they may be noted here for the sake of completeness. 
 Foremost among these are manganese concretions, which are widely 
 distributed on the abyssal ocean floor. Sometimes they occur in 
 
ABYSSAL DEPOSITS 679 
 
 heaps of small grains or lumps. They range in depth to over 8,000 
 meters, being especially abundant in the Pacific. They are, how- 
 ever, also found in shallow water, as in the case of the deposits 
 formed in Loch Fyne in Scotland. (Buchanan.) The mineral is 
 generally the hydrous oxide, and, according to Murray, is a product 
 of disintegration of the volcanic rocks found so abundantly in these 
 deeper waters. The manganese and iron derived from the vol- 
 canics are at first in the form of carbonate, after which they become 
 altered to the oxide. The concretions commonly contain fragments 
 of pumice or lapilli or a bone or other organic structure as a nucleus. 
 (See also Chapter IX.) Besides the manganese concretions there 
 are concretions of other minerals, of which barium is one. 
 
 Cosmic Deposits in the Deep Sea. 
 
 Fine particles with a metallic interior often magnetic are found 
 in the deeper water deposits. These have been interpreted as cosmic 
 dust, the product of meteoric showers. Chamberlin and Salisbury 
 ( 16 : 381-2) state that the number of meteorites which enter the 
 atmosphere daily has been estimated at from 1 5,000,000 to 20,- 
 000,000, and that if on the average each weighs 10 grains (a high 
 estimate), the total amount of extra-terrestrial matter reaching the 
 earth yearly would be 5,000 to 7,000 tons, of which about three- 
 fourths on the average would fall into the sea. At this rate it would 
 take some fifty billion years to cover the sea bottom with a layer 
 one foot in thickness. 
 
 Submarine Volcanic Deposits. 
 
 Deposits formed on the floor of the ocean by submarine volcanic 
 eruptions probably constitute an important part of the deep-sea 
 deposits. Not all of the widely distributed volcanic material, how- 
 ever, found in the deep sea is the product of submarine volcanic 
 eruptions ; a large part of the pumice, lapilli and volcanic glass and 
 dust is derived from terrestrial volcanoes, and is carried to the deep 
 sea by flotation on the surface of the ocean, or as wind-borne 
 dust, or as both. The Hawaiian Islands represent the result of 
 prolonged submarine volcanic eruptions, and the accumulation of 
 the material in the vicinity, until they rose to the present height of 
 the sea-level. For the general subject of submarine eruptions, see 
 Thoulet (94). (See also Chapter XXII.) 
 
68o PRINCIPLES OF STRATIGRAPHY 
 
 INTERRUPTIONS OF MARINE SEDIMENTATION. 
 
 It is generally assumed that deposition in the deep sea is rela- 
 tively constant and not subject to interruptions of any but acci- 
 dental character. Under this latter may be classed the appearance 
 of submarine volcanoes, which will act in a twofold manner by dis- 
 turbing the waters of the bottom of the sea and creating currents 
 which will stir up and sweep away sediment previously accumu- 
 lated, and, second, by forming a new series of deposits, as well as 
 creating new slopes and regions of deposition. Seismic disturbances 
 likewise cause interruptions of sedimentation and rearrangement of 
 sediments. 
 
 In the lesser depths of the ocean, however, the currents of the 
 surface will to a certain extent also affect the bottom sediment. 
 This is partly due to their ability to sweep away loose material 
 even in considerable depths and partly to their influence in pre- 
 venting sedimentation. As already noted in Chapter V in narrow 
 passages, the currents may be effective at considerable depths. 
 Agassiz states "that the bottom of the Gulf Stream along the Blake 
 plateau is swept clean of slime and ooze, and is nearly barren of 
 animal life." (i : <?5p.) This effect is felt to a depth of 1,281 me- 
 ters. According to Verrill, the floor of the ocean beneath the Gulf 
 Stream in depths of 150 to 600 meters, and at a distance of 100 to 
 200 km. from land, is covered with fine sand, mostly quartz, some 
 feldspar, mica and magnetite, fragments of shells, etc., coral and 
 rhizopods. Fine mud is absent and is even scarce in depths of 
 1,000 meters, having apparently been carried away by the Gulf 
 Stream. A current of more than 7 mm. per second at the bottom 
 can stir up and move shell particles of 0.12 mm. or less in diameter 
 and be quite effective in transporting mud particles. Currents of 
 3 mm. per second can carry along Globigerina ooze. Measure- 
 ments on the Gulf Stream have shown a velocity of about 31 mm. 
 per second at a depth of 910 m. west of the Bermudas. In 1,100 
 m. depth, however, no measurable velocity was shown. 
 
 As already noted (Chapter V), the passages between the several 
 islands of the Canary group have their bottoms kept clean by the 
 tidal currents rushing through them. These currents are effective 
 to a depth of 2,000 meters. On the submarine banks in the neigh- 
 borhood of these islands the denuding effect of the tidal currents is 
 felt to considerable depths. On the Seine bank only hard rock bot- 
 tom was found in depths of less than 200 meters. In greater depths, 
 down to 964 meters, only coarse sand was found. Only in the 
 
INTERRUPTIONS OF MARINE SEDIMENTATION 681 
 
 depths exceeding 1,500 and 2,000 meters is an accumulation of the 
 fine Globigerina ooze possible. 
 
 In the passes between the islands of the Indian Archipelago, the 
 Siboga expedition found mostly "hard bottom," the sounding in- 
 struments bringing up only broken-off rock fragments, or impres- 
 sions of a rock bottom. In exceptional cases coarse sand was 
 found. Since these depths extend to 1,500 meters, it is probable that 
 we have here a prevention of sedimentation by the removal of the 
 particles before they reach the bottom, rather than any effect of 
 eroding work of the current at such depth. (Weber-ioi : 187.} 
 Compensatory currents, such as those formed in the Roman Med- 
 iterranean by greater evaporation, also affect sedimentation. In the 
 case mentioned the Gibraltar current flows in at the surface, while a 
 deeper current passes out beneath, affecting the lower 30 meters of 
 the water in the pass. Currents due to melting ice also affect sedi- 
 mentation. The diatoms of the Antarctic region settle only north 
 of the region of drift ice (Philippi). In addition to the oceanic 
 and the tidal currents, the upward currents, which bring the colder 
 water of the depths to the surface, are effective agents in modifying 
 deposition. All such currents are further effective in determining 
 the facies of the sediment, and abrupt changes from one to another 
 type of sediment may often be due to them. 
 
 It thus appears that sedimentation on the sea bottom is unequal 
 in extent and that the surface of more elevated ridges, or areas 
 subject to current scour, may remain free from sediment, while this 
 is accumulating all around. Cases of interruption of the continuity 
 of sediments referable to such causes are not unknown from the 
 older rocks. A good example is found in the Upper Siluric beds 
 of the Helderberg Mountains in eastern New York. Near the city 
 of Kingston a submarine ridge of folded and eroded sandstones of 
 Mid-Ordovicic age projected above the general bottom of the late 
 Siluric sea, and was kept free from the deposits accumulating all 
 around it. Thus the Rosendale waterlimes and the Wilbur lime- 
 stone are wanting over the Kingston ridge, but present all around 
 at a distance of a few miles. Only the upper part of the Cob- 
 bleskill limestone is deposited upon the ridge, which became buried 
 in the deposits accumulating around it, to which, however, the 
 ridge itself did not contribute any material. These deposits, how- 
 ever, accumulated in shallow water, as lime muds derived by the 
 erosion of a not too distant limestone shore. The shallow water is 
 indicated by the abundance of mud cracks at several levels. The ab- 
 sence of the Credneria beds and of the carinata-quader (sand- 
 stone) in the vicinity of Dresden (Plauenscher Grund) has also 
 
682 PRINCIPLES OF STRATIGRAPHY 
 
 been referred to the existence of elevated ridges and cliffs in the 
 Cretacic sea in that vicinity, on which coarse boulders formed the 
 only loose material, while around were accumulating finer sedi- 
 ments. ( Petrascheck-65 : 26 et seq., Fig. 45.) 
 
 It further appears that interruption of sedimentation and even 
 contemporaneous erosion are processes which may be active in the 
 moderate depths of the ocean, especially between depths of 200 and 
 900 meters, i. e., in the bathyal zone of the sea. Such an interrup- 
 tion may give rise to a distinct hiatus, as well as a variation in thick- 
 ness of sediments. It is not improbable that some of the breaks in 
 the geological series referred to subaerial erosions and the forma- 
 tion of disconformities may be due to the processes outlined above. 
 That such is frequently the case may perhaps be questioned, though 
 much emphasis is laid upon it by some stratigraphers and students 
 of Pakeogeography. (Bailey Willis-io6; 107.) 
 
 The numerous breaks in the Alpine Jurassic limestone series 
 have been regarded by Neumayr and others as examples of dis- 
 continuous deposition without the occurrence of periods of dry land 
 and erosion. Currents are believed to have been the disturbing 
 agent. From the Rhsetic upward irregularities in the distribution 
 of the sediment are of increasing frequency and extent ; these are 
 partly due to variations in the sea-level, partly to tectonic move- 
 ments of the suboceanic floor, and partly to the periodic want of 
 material for sedimentation (Diener). In part these breaks may 
 also be due to oceanic or tidal currents. (Andree-3.) 
 
 Stratigraphic gaps are numerous in the geological formations of 
 North America, but it remains still to be determined which of these, 
 if any, are due to contemporaneous erosion, or to prevention of 
 deposition by currents, etc. Some of the gaps in the Ordovicic 
 limestones of the Appalachians may be explained in this manner. 
 When the great limestone series of the Palaeozoic of western 
 North America are more fully investigated, evidences of such intra- 
 formational gaps may be found. 
 
 PERSISTENCE AND VARIATION IN THICKNESS OF MARINE STRATA. 
 
 One of the familiar phenomena confronting the field geologist 
 is the enormous variation in the thickness of strata when traced 
 from point to point. For this variation several explanations are 
 available. In the first place, it often happens that a given series of 
 great thickness is in other regions represented by only a fraction 
 of the formation, this being due to the occurrence of a constantly 
 
VARIATIONS OF MARINE SEDIMENTS 683 
 
 widening hiatus between the adjacent formations. Thus it appears 
 that the Lower Ordovicic series of eastern North Ameriea is repre- 
 sented by some 2,500 feet of limestones in central Pennsylvania, 
 while only about 400 feet are found in the Mohawk Valley of New 
 York. This diminished series, however, represents only the lowest 
 part of the Pennsylvania deposits, the entire middle and upper part 
 being absent. Upon these beds rests a series of limestone 2,500 
 feet thick and representing the Middle Ordovicic, but this again is 
 represented by less than 100 feet in the Mohawk Valley. This 
 time, however, it is the upper part of the Middle Ordovicic which 
 is present. Thus the gap in the Mohawk Valley cuts out all 
 but the lowest of the Lower Ordovicic and all but the highest of 
 the Middle Ordovicic. Southward the gap becomes less by the ap- 
 pearance of higher members of the subjacent and lower members 
 of the superjacent series. This is perhaps the most frequently ap- 
 plicable explanation of the differences in thickness of marine 
 formations of similar lithologic character. In the next place, there 
 is variation in thickness due to variation in character of the sedi- 
 ment. Formations of different lithic composition may show great 
 variation in thickness due to original difference in deposition. Thus 
 a sandy series is likely to be much thicker than a shale series into 
 which it passes and which was formed during the same period. 
 Again, sediments of two kinds from separate sources may over- 
 lap, and so one may thin away as the other thickens. This is espe- 
 cially the case where continental sediments overlap a marine series 
 of the same age or vice versa. The Catskill and Chemung series of 
 the Upper Devonic of the eastern United States is a case in point. 
 The Catskill continental beds are thick in the east, but die away 
 westward, while beneath the thinning cover of this series the marine 
 Chemung increases progressively from nothing in the east until it 
 alone fills the interval in western New York. But even the marine 
 series may overlap in this manner. Thus the Black shales of Port- 
 age time are thickest in Ohio, and wedge out eastward in New York 
 and Pennsylvania. Their place is taken by the sandy Portage beds 
 which have their source in the east and grow thinner toward the 
 west. 
 
 The third cause of differences in thickness is local variation 
 in the regions of sedimentation. A relatively shallow and stationary 
 area of the sea bottom may experience little sedimentation, while a 
 slowly subsiding area may receive a great supply of sediment of es- 
 sentially similar character. The Moscow shale of the Middle De- 
 vonic of western New York is a good example of this. In the 
 Genesee Valley region its thickness is about 250 feet, while on Lake 
 
684 PRINCIPLES OF STRATIGRAPHY 
 
 Erie it is only 17 feet. Still further west in Canada the thickness in- 
 creases again to over a hundred feet. The 17 feet of shales in the 
 Lake Erie section apparently represent the 250 feet of the eastern 
 section, but owing to lack of accumulation, probably because the wa- 
 ter remained shallow and currents were active, the amount of de- 
 posit was slight. That this shallow area seems to have formed a 
 barrier between the eastern and western faunas is indicated by their 
 diversity. 
 
 In contradistinction to this marked variation is the persistence 
 in thickness of the underlying Encrinal or Morse Creek * limestone. 
 This bed is only about 2 feet thick, but it has been traced almost con- 
 tinuously from western Ontario (Thedford) to the Genesee Valley, 
 a distance of over 200 miles, and throughout the extent it retains its 
 lithic character, thickness and uniformity of organic content. (Gra- 
 bau-39.) 
 
 COMPREHENSIVE FORMATIONS. 
 
 
 
 Under this title may be grouped deposits which apparently 
 without break continued over long periods of time. That 
 such exist has frequently been observed, though many appar- 
 ent lithic units have been found to consist of several members 
 separated by disconformities. The Hunton limestone of Okla- 
 homa was formerly believed to be a unit, extending without break 
 from the Niagaran to the Oriskanian. It is now known to consist 
 of at least four distinct and disconformable members separated by 
 great time gaps (Reed-8o). The Durness limestone of northern 
 Scotland, believed to range from Lpwer Cambric to Ordovicic, is 
 now known to consist of a basal member of Lower Cambric age, 
 separated by a hiatus and disconformity from the Lower Ordovicic, 
 the Middle and Upper Cambric being wanting. (Grabau~4O.) That 
 such comprehensive formations occur, nevertheless, is shown by the 
 deposits on the floor of the modern deep sea, where teeth of Ter- 
 tiary sharks (Carcharodon) occur side by side with remains of or- 
 ganisms now living. Here sedimentation is so slow that the time 
 interval since the Tertiary, when these sharks died, has not been 
 sufficient to completely bury their teeth. 
 
 So far, however, no such comprehensive sediments are known 
 from the older geological formations, though a commingling of or- 
 ganisms of various geological horizons is not uncommon. This 
 
 * The "Encrinal Limestone" of western New York is not the same as the 
 Tichenor of central New York. 
 
COMPREHENSIVE FORMATIONS 685 
 
 may be due to a weathering out of the fossils of an older forma- 
 tion and their incorporation in the deposits of a later one, as in the 
 case of the Ordovicic fossils included in the base of the overlying 
 Mississippic black shale in Tennessee, or again fossils of an older 
 formation may be washed out along the shore and incorporated in 
 the new deposit. Thus Miocenic oyster shells on the Atlantic coast 
 serve as a basis for attachment of modern oysters, and are buried 
 with these in the modern deposits. 
 
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 Neues Jahrbuch fur Mineralogie, u. s. w., pp. 1-38, taf. III. 
 
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 37. GEBBING, J. 1909- Chemische Untersuchungen von Meeresboden-, 
 
BIBLIOGRAPHY XV 687 
 
 Meerwasser- und Luftproben der Deutschen Sudpolarexpedition. 
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 40. GRABAU, A. W. 1910. Ueber die Einteilung des Nordamerikanischen 
 
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 pp. 971-995- 
 
 41. GUMBEL, C. W. VON. 1888. Die Mineralogisch-Geologische Beschaf- 
 
 fenheit der auf der Forschungsreise S. M. S. Gazelle gesammelten 
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 43. HAUG, EMILE. 1907. Traite de Geologie, Tome I. 
 
 44. HAZEN, ALLEN. 1904. On Sedimentation. Transactions of the Ameri-i/ 
 
 can Society of Civil Engineers, Vol. LXIII, pp. 45-88. 
 
 45. HEIM, ALBERT; CULM ANN; GRANICHER, G.; HELLWAG, W.; 
 
 LANG, FR., MOSER, R. 1876. Bericht und Expertengutachen ueber 
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 46. HEIM, ALBERT; MOSER, R.; BURKLI; ZIEGLER, and others, 
 
 1888. Die Katastrophe von Zug, 5 Juli, 1887 (mit 5 Tafeln). Gutach- 
 ten der Experten, herausgegeben auf Veranlassung der Behorden von 
 Zug. Verlag von Hofer und Burger, Zurich, 1888. 
 
 47. HEIM, ARNOLD. 1908. Ueber Rezente und Fossile Subaquatische 
 
 Rutschungen und deren Lithologische Bedeutung. Neues Jahrbuch fur 
 Mineralogie, etc., 1908, II, pp. 136-157, 2 figs., pi. 13. 
 
 48. HEIM, F. 1911. In W. Brennecke. Ozeanographische Arbeiten der 
 
 deutschen Antarktischen Expeditionen. Annalen der Hydrographie, 
 etc., Vol. XXXIX, pp. 350-353, 464-471, taf. 25, pp. 642-647. 
 
 49. HUNT, T. STERRY. 1878. Chemical and Geological Essays. 
 
 50. HUNT, T. S. 1891. Mineral Physiology and Physiography. 
 
 51. HUNT, T. S. 1892. Systematic Mineralogy. 
 
 52. JOLY, J. 1900. The Inner Mechanism of Sedimentation. Report oft/ 
 
 the British Association for the Advancement of Science, p. 732. 
 
 53. JOLY, J. 1902. Ibid. Proc. R. Dublin Soc., N. S., Vol. IX, pp. 325-332. 
 
 54. KINDLE, E. M. 1911. Cross-bedding and Absence of Fossils Considered ^ 
 
 as Criteria of Continental Deposits. American Journal of Science, Vol. 
 XXXII, pp. 225-230. 
 
 55. KRUMMEL, OTTO. 1907. Handbuch der Ozeanographie, Bd. I, 2nd ed. 
 
 56. LEITH, C. K. 1903. The Mesabi Iron-bearing District of Minnesota. 
 
 Monograph U. S. Geological Survey, XLIII, 316 pp., 33 plates. 
 
 57. McGEE, W. J. 1896. The Formation of Arkose. Science, N. S., Vol. IV, S 
 
 pp. 962-963. 
 
 58. MURRAY, JOHN. 1900. Description of Marine Deposits on the Cable 
 
 Route between Bermuda, Turk's Island and Jamaica. Proceedings of 
 the Royal Society of Edinburgh, Vol. XXII, pp. 409-429. 
 
688 PRINCIPLES OF STRATIGRAPHY 
 
 59. MURRAY, JOHN. 1909. On the Depth and Marine Deposits of the 
 
 Indian Ocean, with Descriptions of the Deposit-Samples, Collected by 
 J. Stanley Gardiner in 1905. (The Percy Sladen Trust Expedition to 
 the Indian Ocean in 1905.) Transactions of the Linnaean Society, Vol. 
 XIII, 3, pp. 355-396, pis. 22-24. London. 
 
 60. MURRAY, JOHN, and LEE, G. V. 1909. The Depth and Marine De- 
 
 posits of the Pacific. Memoirs of the Museum of Comparative Zoology 
 at Harvard College, Vol. XXXVIII, 169 pp. 
 
 61. MURRAY, JOHN, and PHILIPPI, E. 1908. Die Grundproben der 
 
 "Deutschen Tief see-Expedition, " Bd. X der Wissenschaftlichen Ergeb- 
 nisseder "Deutschen Tief see-Expedition 1898-1899" auf dem Dampfer 
 Valdivia, pp. 67-206, taf. XVI-XXII, 2 maps. Jena. 
 
 62. MURRAY, JOHN and RENARD, A. F. 1891. Deep Sea Deposits. 
 
 In "Report on the Scientific Results of the Voyage of H. M. S. Chal- 
 lenger during the years 1873-1876. " London. (Reviewed in extenso by 
 K. Futterer in Neues Jahrbuch fur Mineralogie, u. s. w., 1893, Bd. II, pp. 
 281-320.) 
 
 63. ORTMANN, ARNOLD E. 1894. Anmerkung iiber Littoral Jenaische 
 
 Denkschrift, Vol. VIII, p. 5. Anmerkung. 
 
 / 64. OWENS, J. S. 1911. Experiments on the Settlement of Solids in Water. 
 Geographical Journal, Vol. XXVII, pp. 59-79. 
 
 65. PETRASHECK. 1894. Studien iiber Facienbildung im Gebiete der 
 
 sachsischen Kreideformation. Leipziger Inaugural Dissertation. 
 
 66. PHILIPPI, E. 1908. Ueber das Problem der Schichtung und ueber 
 
 Schichtbildung am Boden der heutigen Meere. Zeitschrift der deutschen 
 geologischen Gesellschaft, Vol. LXI, pp. 346-377. 
 
 67. PHILIPPI, E. 1908. Zwei Proben vom antarktischen Eisrand. Cen- 
 
 tralblatt fur Mineralogie, pp. 356-357. 
 
 68. PHILIPPI, E. 1909. Ueber Schichtbildung am Boden der heutigen und 
 
 vorweltlichen Meere. Internationale Revue der gesammten Hydrobi- 
 ologie und Hydrographie, Vol. II, p. 9. 
 
 69. PHILIPPI, E. 1910. Die Grundproben der deutschen Siidpolar-Expedi- 
 
 tion 1901-1903. "Deutsche Siidpolar Expedition," Vol. II, Heft 6, 
 pp. 411-416. 
 
 70. PHILIPPI, E. 1910. Ueber Sandablagerungen am Boden, der kiisten- 
 
 fernen Tiefsee. Compte Rendu, 9 me Congres International de Geo- 
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 71. POMPECKJ, JOSEF F. 1901. Die Jura Ablagerungen zwischen Regens- 
 
 burg und Regenstauf. Geognostische Jahreshefte, Bd. XIV, pp. 43 
 et seq. 
 
 72. POURTAL^S, L. F. VON. 1870. Der Boden des Golfstroms und der 
 
 atlantischen Kuste Nordamerikas. Petermann's Geographische Mit- \ 
 theilungen, Bd. XVI, pp. 393-398. 
 
 73. PRATHER, JOHN K. 1905. The Atlantic Highlands Section of the 
 
 New Jersey Cretacic. American Geologist, Vol. XXXVI, pp. 162-178, 
 3 pis. 
 
 74. PRATHER, J. K. 1905. Glauconite. Journal of Geology, Vol. XIII, 
 
 PP. 509-513- 
 
 75. PUMPELLY, R. 1891. The Relation of Secular Rock Disintegration 
 
 to Certain Transitional Crystalline Schists. Bulletin of the Geological : 
 Society of America, Vol. II, pp. 209-224. 
 
 \/ 76. QUINCKE, G. 1901. The Clearing of Turbid Solutions. Report of the 
 British Association for the Advancement of Science. Glasgow. 
 
BIBLIOGRAPHY XV 689 
 
 77. QUINCKE, G. 1904. Ueber die Klarung truber Losungen. Verhand- 
 
 lungen des Naturhistorisch-Medizinischen Vereins. Heidelberg, N. F., 
 Bd. VII, pp. 97-I04- 
 
 78. RAMANN, E. 1906. Einteilung und Benennung der Schlammablager- 
 
 ungen. Zeitschrift der deutschen geologischen Gesellschaft, Bd. LVIII, 
 Monatsberichte, pp. 174-183. 
 
 79. RAMSAY, W. 1876. On the Influence of Various Substances in Accelerat- , 
 
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 of the Geological Society of London, Vol. XXXII, pp. 129-133. 
 
 80. REED, CHESTER A. 1911. The Hunton Formation of Oklahoma. 
 
 American Journal of Science, 4th series, Vol. XXXII, pp. 250-268. 
 
 81. REVY, J. J. Hydraulics of Great Rivers. 
 
 82. ROBERTSON, D. 1874. Note on the Precipitation of Clay in Fresh and 
 
 Salt Water. Transactions of the Glasgow Geological Society, Vol. IV, 
 pp. 257-259. 
 
 83. ROBSON, H. 1904. Abysmal Deposits. Nature, Vol. LXIX, p. 297. u^ 
 
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 86. SCHARDT, H. 1893. L'effondrement du Quai du Trait de Baye a 
 
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 87. SCHUCHT, F. 1904. Das Wasser und seine Sedimente im Flutgebiete 
 
 der Elbe. Jahrbuch der koniglich-preussischen geologischen Landes- 
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 88. SHALER, NATHANIEL S. 1895. Beaches and Tidal Marshes of the 
 
 Atlantic Coast, National Geographic Monographs, No. 5, pp. 137-168. 
 Ameri'can Book Company. 
 
 89. SOLLAS, W. J. 1883. The Estuaries of the Severn and Its Tributaries; 
 
 an Inquiry into the Nature and Origin of Their Tidal Sediment and 
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 XXXIX, pp. 611-626. 
 
 Sga. SORBY, HENRY C. 1908. On the Application of Quantitative 
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 terly Journal of the Geological Society of London, Vol. LXIV, pp. 171- 
 233, pis. xiv-xviii. 
 
 90. SPRING, W. 1900. La Floculation des Mileux Trouble's. Recueil des 
 
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 91. SUPAN, ALEXANDER. 1911. Grundziige der physischen Erdkunde. 
 
 5te Auflage, Leipzig, Veit & Co. 
 
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 93. THOULET, J. 1900. Fixation des argiles en suspension dans 1'eau par 
 
 les corps poreux. Comptes Rendus, des Stances de 1'Acad^mie des 
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 94. THOULET, J. 1903. Les volcans sous-marins. Revue des Deux 
 
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690 PRINCIPLES OF STRATIGRAPHY 
 
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 96. THOULET, J. 1908. Etude comparee des fonds marins anciens et 
 
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 97. THOULET, J. 1910. Instructions pratiques pour 1'etablissement d'une 
 
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 98. TORNQUIST, AL. 1909. Ueber die Wanderung von Blocken und Sand 
 
 am ost-preussischen Ostseestrand. Schriften der physisch-okonomischen 
 Gesellschaft, pp. 79-88, taf. I, II. 
 
 99. UDDEN, J. A. 1894. Erosion, Transportation and Sedimentation Per- 
 
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 the Action of Seawater in Accelerating the Deposit of River-silt and the 
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 101. WEBER, M. 1900. Die niederlandische "Siboga" Expedition zur 
 
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 Petermann's Geographische Mittheilungen, Vol. XLVI, p. 187. 
 
 102. WEULE, K. 1896. Zum Problem der Sedimentbildung. Annalen der 
 
 Hydrographie, Bd. XXIV, pp. 402-413. 
 
 103. WHEELER, W. H.- 1902. The Sea Coast. New York, Longmans, 
 
 Green & Co. 
 
 104. WHITNEY, MILTON. 1892. Some Physical Properties of Soils. 
 
 United States Department of Agriculture, Bulletin No. 4. 
 
 105. WILLIS, BAILEY. 1893. Conditions of Sedimentary Deposition. 
 
 Journal of Geology, Vol. I, pp. 476-520. 
 
 1 06. WILLIS, B. 1910. Principles of Palaeogeography. Science N. S., Vol. 
 
 XXXIII, Feb. 18, 1910, pp. 246-251. 
 
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 from the Eddystone to Start Point, near the Thirty-fathom Line. Trans- 
 actions of the Devonshire Association for the Advancement of Science, 
 Vol. XXXI, pp. 356-375. 
 
CHAPTER XVI. 
 CHARACTERS AND LITHOGENESIS OF THE BIOCLASTIC ROCKS. 
 
 Bioclastic rocks consist of fragments of older rocks which have 
 been broken by the mechanical activities of organisms. Among 
 these man is the most active, and he is undoubtedly the greatest 
 producer of bioclastic rocks. To distinguish this type the name of 
 artificial elastics is applied to it, and as examples concrete and other 
 artificial stone may be mentioned. These need not be more fully dis- 
 cussed, though their variety is great and their characters manifold. 
 
 There are also other organisms which in a more or less effec- 
 tive way render rocks clastic and so furnish the material from 
 which new rocks may be formed. Chief among these are the great 
 herds of vertebrates of the plains and steppes and the even larger 
 animals of former geological periods. 
 
 Pechuel-Loesche (7:^5) describes the destruction of the land 
 surface through the immense herds of cattle which he had wit-- 
 nessed in Herero land, German Southwest Africa. He says in ef- 
 fect: "In extensive manner these animals aid in the leveling of 
 many land areas. As the dryness increases, the herds of grazing 
 cattle become more numerous around the last of the sparsely dis- 
 tributed water bodies. Thousands and tens of thousands of the 
 large and the small animals overrun for miles the surrounding 
 country for days, weeks and months. Through countless hoof- 
 beats the ground is loosened, and so furnishes enormous masses of 
 dust, while at the same time all inequalities are trampled down and 
 destroyed. The inclined surfaces would be furrowed by numerous 
 rain-water gullies, if these were not constantly destroyed by the 
 hoofs of the roaming animals, and if it were not for the fact that 
 the rain water is constantly guided along the paths formed by the 
 animals going to and from the water in long lines ranged one be- 
 hind the other. Furthermore, the cover of dust prevents to an as- 
 tonishing degree the penetration of the short, heavy downpour of 
 rain into the deeper strata." 
 
 Where herds abound, the surface of the country is a compara- 
 
 691 
 
692 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 tively level plain, but where herds are absent, as in the regions be- 
 tween Karibib, the Otyipatura and the Erongo, infested by the Hot- 
 tentot robber hordes, the country is much dissected by rain-water 
 streams. 
 
 Passarge thinks that it is not too much to attribute to the de- 
 structive force of the great herds of vertebrates in semiarid regions 
 the principal role in the lowering of great regions and the produc- 
 tion of gently inclined plains free from river furrows, with rem- 
 nants of higher monadnocks such as the Inselberge of the Kalahari 
 (Passarge^: 730-131). 
 
 What is true of the modern herds of vertebrates must have been 
 equally true of the great herds of mammals of Tertiary time, and 
 
 sfc 
 
 FIG. 133. White ants' nests of earth in Matto Grosso, on the plains of the 
 upper Paraguay. (After Branner.) 
 
 perhaps to an even greater extent of the gigantic saurians of the 
 Mesozoic. Certain it is that by their activities these creatures have 
 furnished an immense supply of material to the winds, which would 
 carry it to other regions and deposit it as new sediment. Burrow- 
 ing mammals such as the prairie dog, rabbit, mole, badger, wood- 
 chuck, gopher and ground squirrel are also very active in tunneling 
 the upper layers of the soil and in transferring material from below 
 to the surface. The beaver may also be mentioned in this connec- 
 tion as a destructive as well as a constructive agent. 
 
 The manner in which fish, feeding on corals and nullipores, pro- 
 duce fine coral sand and mud has already been noted. In like 
 manner Crustacea are known to be active in breaking up the skele- 
 tons of echinoderms and other organisms, thus producing lime sand. 
 Sponges and algae riddle shells and even rocks, forming winding 
 passageways, which render these masses more liable to destruction 
 by waves and other agencies. Similarly certain mollusca, Pholas, 
 
LITHOGENESIS OF THE BIOCLASTIC ROCKS 693 
 
 Saxicava, etc., bore into solid rocks or into heavy shells, thus aid- 
 ing in the destruction of the mass. To a certain extent this is also 
 true of some echini. 
 
 Earthworms are active agents in loosening and rearranging the 
 soil particles, and to a certain extent in destroying the rock masses. 
 According to Darwin, in many places over 50,000 earthworms are 
 at work in a single acre of soil. The amount of material which 
 they transport to the surface each year was estimated by Darwin to 
 be over 18 tons per acre. (4.) The lugworms or lobworms, 
 crawling through the sands along the shore, are similarly active in 
 
 FIG. 134. Mound of white ants in the laterite region of Africa. (After 
 Branner.) 
 
 working over the soil. They leave behind casts of sand, and the 
 amount of soil they work over has been estimated to be sometimes 
 as much as 3,147 tons per acre. (Davison-5 : 491.) Ants and 
 termites are also important agents in the rearrangement of the soils, 
 especially in tropical regions, where, according to Branner, they 
 "are vastly more important as geologic agents than the earthworms 
 of temperate regions." (i : i^2\ 253.) In Brazil the ants excavate 
 chambers and galleries, which radiate and anastomose in every di- 
 rection, and into these they carry great quantities of leaves. The 
 mounds resulting from these excavations are often from 15 to 30 
 meters long, from 3 to 6 meters across and from one-third to over 
 one meter high, and contain tons of earth. In the forests the 
 
694 PRINCIPLES OF STRATIGRAPHY 
 
 mounds are sometimes 14 feet high (4^ meters), and from 10 to 
 30 feet (3 to 9 meters) in basal diameter. They are often so close 
 together that their bases touch each other. Branner has estimated 
 (3:^9) that in an area of 10,000 square meters on which 53 
 mounds occurred the amount of earth brought up by ants and built 
 into mounds would cover the area with a layer 22.25 centimeters in 
 thickness. 
 
 The termites' nests rise to 3^ meters in height, and may be 3 
 meters in basal diameter. They, too, are often closely set, those 
 along the upper Paraguay being not over 3 meters apart. (Fig. 
 
 I33-) 
 
 A comparison of the work of earthworms and ants gave the 
 following result (Branner-3 : 495). Total weight of earth brought 
 to the surface in 100 years over I hectare (10,000 square meters) : 
 
 By worms in England (Darwin-4), 2,598,500 kilograms. 
 
 By ants in Brazil (Branner-3), 3,226,250 kilograms. 
 
 The work of ants on the soil and subsoil is summarized by 
 Branner as follows (3:494) : 
 
 Directly : 
 
 1. "By their habits of making underground excavations that 
 radiate from a central nucleus and often aggregate several miles 
 in length. 
 
 2. "By opening the soil to the atmospheric air and gases. 
 
 3. "By bringing to the surface large quantities of soil and sub- 
 soil. 
 
 4. "By introducing into their subterranean excavations large 
 quantities of organic matter, which must yield acids that affect the 
 soil and the subjacent rocks. 
 
 5. "By using these excavations for habitations and the pro- 
 duction of gases that attack the soil and its contained minerals." 
 
 Indirectly. 
 
 6. "By the periodic passage and circulation of meteoric waters 
 through their extensive tunnels. 
 
 7. "By affecting the availability of the soil for agricultural 
 purposes. 
 
 8. "By affecting the habitability of the land by man. 
 
 9. "By the destruction of crops. 
 
 10. "By the consumption (by the termites) of dead plants and 
 of timbers and lumber used in houses and for the manufacture of 
 furniture, machinery, etc." 
 
 In temperate regions ants are less active, though, according to 
 Shaler, they transfer annually half a centimeter of material from 
 the subsoil to the surface, in certain fields in Massachusetts. (8.) 
 
LITHOGENESIS OF THE BIOCLASTIC ROCKS 695 
 
 Plants also are destroyers of rocks, though their work is nor- 
 mally very slow. Lichens growing on smooth rock surfaces will 
 eventually roughen them by appropriating some of the material. 
 Roots of higher plants often penetrate into the rock, especially 
 limestones, to an astonishing extent. In sandstones they have been 
 found to penetrate several meters. Growing saplings in fissures 
 tend to disrupt the rock masses. Finally bacteria abound in the 
 upper soil layers (2 l / 2 millions have been estimated in a cubic cen- 
 timeter of soil in the surface layers), and these are active agents 
 in modifying the soil. 
 
 It thus appears that the work of organisms is by no means a 
 negligible factor, and will in the course of time produce important 
 results. Of these organisms man is of course the most important, 
 and it is not going too far to say that on the whole he is the most 
 powerful geological agent at work in modifying the surface of the 
 land. 
 
 BIBLIOGRAPHY XVI. 
 
 1. BRANNER, JOHN C. 1896. Decomposition of Rocks in Brazil. Bulletin 
 
 of the Geological Society of America, Vol. VII, pp. 255-314. 
 
 2. BRANNER, J. C. 1900. Ants as Geological Agents in the Tropics. 
 
 Journal of Geology, Vol. VIII, pp. 151-153. 
 
 3. BRANNER, J. C. 1910. Geologic Work of Ants in Tropical America. 
 
 Bulletin of the Geological Society of America, Vol. XXI, pp. 449-496. 
 
 4. DARWIN, CHARLES. 1883. The Formation of Vegetable Mould. 
 
 D. Appleton & Co., New York, pp. 1-313. 
 
 5. DAVISON, CHARLES. 1891. Work Done by Lobworms. Geological 
 
 Magazine, 3d Ser., Vol. VIII., pp. 489-493. 
 
 6. PASSARGE, SIEGFRIED. 1911. Die pfannenformigen Hohlformer der 
 
 sudafrikanischen Steppen. Petermann's Mittheilungen LVII, pt. ii, pp. 
 130-135- 
 
 7. PECHUEL-LOESCHE. 1884. Das Ausland. 
 
 8. SHALER, NATHANIEL S. 1892. Effects of Animals and Plants on Soils. 
 
 In "The Origin and Nature of Soils, " U. S. Geological Survey, I2th Annual 
 Report, pt. I, pp. 219-345 (268-287). 
 
CHAPTER XVII. 
 SUMMARY OF ORIGINAL FEATURES OF CLASTIC ROCKS. 
 
 We may now summarize the various structural features of clas- 
 tic rocks which were formed at the time these rocks were deposited 
 and which therefore serve as guides in the determination of the 
 mode of origin of the rocks possessing them. In dealing with each 
 feature separately it will be possible to indicate the extent to which 
 it is characteristic of one or the other of the types of clastic rocks 
 so far discussed. 
 
 We may treat these characters under the following headings : 
 
 1. Stratification. 
 
 2. Cross-bedding. 
 
 3. Beach cusps. 
 
 4. Wave marks. 
 
 5. Rill marks. 
 
 6. Mud cracks (sun cracks or desiccation fissui'es). 
 
 7. Clay galls. 
 
 8. Clay boulders and pebbles. 
 
 9. Rain prints. 
 
 10. Ripple marks. 
 
 11. Impressions made by animals in transit. 
 
 12. Application of these structures in determining position of 
 
 strata. 
 
 13. Rounding and sorting of sand grains, and wearing of pebbles. 
 "14. Characteristics of inclusions in sand grains, 
 
 15. Organic remains. 
 
 16. Concretions (partly secondary). 
 
 17. Secretions (secondary). 
 
 Nearly all of these structural characters have been generally con- 
 sidered as preeminently if not exclusively characteristic of marine 
 or lacustrine hydroclastics. From the foregoing discussion, how- 
 ever, it will appear that many of them are far from being the ex- 
 clusive features of these types of deposits. In fact, it may be said 
 
 696 
 
STRATIFICATION 697 
 
 that, with the exception of the beach cusps, the wave marks and 
 the clay pebbles, they are characteristic of subaerial deposits, while 
 some of them, such as cross-bedding, desiccation fissures, rain prints 
 and footprints, are almost exclusively confined to the formations 
 other than marine or lacustrine. The most pronounced of the char- 
 acters enumerated, stratification, is also of frequent occurrence in 
 the endogenetic formations. 
 
 Concretions are only occasionally original structures, being for 
 the most part secondary. Secretions are always of secondary char- 
 acter, but they are included here for the sake .of comparison with 
 concretions which belong here in part. 
 
 i. STRATIFICATION. In its broadest sense ( Walther-23 \6so 
 et seq.) stratification is the arrangement of rock masses in layers 
 or strata, each one of which was at one time the latest deposit, and 
 the top of each stratum was successively the top of the lithosphere 
 at that point. Stratification thus defined occurs in all rocks, which 
 are deposited in successive layers. Thus a series of lava-flows will 
 show stratification, each flow representing a distinct stratum. These 
 volcanic strata are often steeply inclined, as is also the case in 
 clastic strata along the margins of coral reefs or in the alluvial fan 
 or talus heap. 
 
 Among the pyrogenic rocks stratification is produced where 
 lava streams of different composition succeed each other, or where 
 streams of the same composition are separated by an interval, dur- 
 ing which the surface of the earlier one either hardened or became 
 altered to some extent, or again was covered by a layer of clastic 
 material, before the second flow occurred. Atmogenic snow ice or 
 glacial ice becomes stratified when the succeeding deposits of snow 
 are separated by intervals during which the older layer solidified or 
 was covered by a thin layer of dust or by other clastic material. 
 False stratification is often produced in this rock by the formation 
 of shearing planes, along which some of the subglacial detritus is 
 carried up into the ice. Hydrogenic and biogenic rocks may also 
 be stratified, this being brought about by cessation of deposition, 
 by change in the material, through interposition of elastics, or by 
 alternation in deposition of different classes of endogenetic ma- 
 terials. Examples of this are shown in the alternation of layers of 
 gypsum and salt, or in the intercalation of layers of potash and 
 other salts between the beds of ordinary rock salt. The numerous 
 intercalated silt layers of the salt deposits of the Bitter Lakes of 
 Suez further serve as an illustration. While stratification is thus 
 not confined to the clastic rocks, it finds its most typical expression 
 in this group. All clastic deposits may be stratified, this stratifi- 
 
698 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 cation being due to change in material, to change from one type of 
 clastic to another, or to alternation of clastic with endogenetic de- 
 posits. The most typical development of stratification is in the 
 water-laid elastics (hydroclastics), and especially in those laid down 
 in standing water. Before considering the various kinds of stratifi- 
 cation, however, we must first have a clear conception of the mean- 
 ing of the term stratum. 
 
 Definition of Stratum. The current definitions of the term 
 stratum vary greatly, as will be seen from the following quotations : 
 (a) "A layer of rock; a portion of a rock mass which has so much 
 homogeneity and is so separated from the rock that lies over and 
 under it that it has a character of its own." (Century Diction- 
 ary.) (b) "The term stratum is sometimes applied to one layer 
 and sometimes to all the consecutive layers of the same sort of 
 
 FIG. 135. A mass of stratified rocks 
 bounded by joint faces and iso- 
 lated by erosion. The strata are 
 inclined but appear horizontal in 
 one section. 
 
 FIG. 136. Stratified chalk penetrated 
 by pipes of sand and gravel. 
 Kent, England. (Prestwich.) 
 
 rock." (Chamberlin and Salisbury, Geology-i : 464.) (c) "Strata 
 or Beds are layers of rock varying from an inch or less up to many 
 feet in thickness. A stratum may be made up of numerous laminae, 
 if the nature of the sediment and the mode of deposit have favored 
 the production of this structure . . . [it] . . . may be one of a 
 series of similar beds in the same mass of rock, as where a thick 
 sandstone includes many individual strata, varying considerably in 
 their respective thicknesses; or it may be complete and distinct in 
 itself, as where a band of limestone or iron stone runs through the 
 heart of a series of shales." 
 
 "The smallest subdivisions of the Geological Record are lam- 
 inae, a number of which may make a stratum, seam or bed. As a 
 rule, a stratum is distinguishable by lithological rather than palae- 
 ontological features." (Geikie-Textbook, 4th ed.-i:<5j5; 2:860.) 
 
 (d) "In the description of a formation the term stratum (from 
 
STRATIFICATION 699 
 
 the Latin for bed, strata in the plural) is used for each section of 
 the formation that consists throughout of approximately the same 
 kind of rock material. Thus, if shale, sandstone and limestone suc- 
 ceed one another in thick masses, each is an independent stratum. 
 A stratum may consist of an indefinite number of beds, and a bed 
 of numberless layers. But the distinction of layer and bed is not 
 always obvious." (Dana-Manual, 5th ed.-p/.) 
 
 (e) Schichten nennt man plattenformige Lagen welche "... 
 durch parallele Flachen begranzt werden, bei weiter Ausdehnung 
 in der Regel, nur geringe Dicke besitzen, und das Product successiver 
 Ubereinanderlagerung bilden." (Credner-Elemente, 8th ed.,-^5.) 
 
 (f) "The material between two planes of stratification forms 
 a stratum or bed, though if the deposit be very thin it is known as 
 a lamina, and the planes are spoken of as planes of lamination (no 
 hard and fast line can be drawn between strata and laminae; sev- 
 eral of the latter usually occur in the space of an inch)." (Marr- 
 Principles of Stratigraphical Geology-^/.) 
 
 From the foregoing definitions it will be seen that there is a 
 considerable diversity of opinion regarding the value of the term 
 stratum. We may gain a clearer concept if we consider it in the 
 light of its origin. Continuous deposition under the same condi- 
 tions will produce a deposit nearly uniform throughout, and of a 
 thickness commensurate with the rate of deposition, the length of 
 time and the coarseness of the material. A sudden change in con- 
 ditions will bring about an abrupt change in the character of the 
 material deposited. It may be coarser, or it may be finer in grain, or 
 it may be of a wholly different composition. Variation in grain, 
 or texture, unless an abrupt change occurs, is indicative of only 
 minor changes in physical condition of the region. But variation in 
 the composition of the material denotes a change of some magni- 
 tude. This being the case, a decided change in the composition of 
 the material ought to be considered a change in strata, while a 
 change in texture, unless it be a great one, should be considered as 
 of minor value, and therefore should constitute a subdivision of the 
 stratum into layers. The great changes in texture which may con- 
 veniently be regarded as of stratum value are those from one to 
 the other of the three primary textural divisions of the clastic rocks, 
 namely, lutaceous, arenaceous and rudaceous. Thus a rudyte fol- 
 lowing an arenyte may well be considered a distinct stratum. But 
 the change from a fine arenyte to a coarse one or vice versa is bet- 
 ter regarded as a change in layers. Where deposition is continu- 
 ous, while increase in the force of the currents and increase in the 
 coarseness of the deposit are progressive, an arenyte may gradually 
 
700 PRINCIPLES OF STRATIGRAPHY 
 
 pass upward into a rudyte, whereupon the distinction of strata is 
 a matter of judgment. In such cases the stratum of arenyte ter- 
 minates with a layer of rudaceous arenyte where the arenaceous 
 material still predominates, while the stratum of rudyte begins with 
 a layer of arenaceous rudyte, in which the rudaceous material has 
 become most prominent. 
 
 A change in composition is not always of sufficient magnitude 
 to warrant separation into a new stratum. Thus a stratum of 
 silicarenyte or pure quartz sandstone may have interbedded layers 
 of ferruginous, argillaceous, calcareous or glauconite material, 
 where this material is only of sufficient quantity to produce a variety 
 of the sandstone. Where, however, a calcarenyte or a clay rock 
 (argillutyte) succeeds to a silicarenyte, a new stratum is produced. 
 Where deposition is continuous, but the supplied material changes 
 in composition, a gradation from a pure silicarenyte to a pure cal- 
 carenyte may occur, without break of continuity. In this case, as 
 in the case of the gradation in texture, the line of division between 
 the two strata must be drawn on the relative preponderance of ma- 
 terials. The stratum of silicarenyte will terminate with a layer of 
 calcareous silicarenyte, while the stratum of calcarenyte will begin 
 with a layer of siliceous calcarenyte. 
 
 While gradations as here discussed are not of uncommon occur- 
 rence, in the more familiar type of stratification the strata abruptly 
 succeed each other. Thus a stratum of limestone, clastic, organic or 
 chemical and frequently composed of only one layer, may be inter- 
 calated between strata of shales. Again strata of limestones are 
 separated by strata of carbonaceous clay or by sandstones, the sep- 
 arating strata in many cases being mere films. In such cases the 
 stratum of clayey material is represented by only one lamina. Not 
 infrequently strata of clastic limestones (calcarenytes) are sepa- 
 rated by a thin stratum of organic limestone in a single layer, and 
 generally containing an admixture of clayey matter. A decided 
 change in color may readily serve as a basis for division into strata, 
 since such change generally indicates a marked change in physical 
 conditions during deposition. Thus a black shale succeeding a gray 
 or bluish one marks a change in conditions of deposition. A change 
 from a gray to a red sandstone likewise indicates physical changes 
 from conditions preventing to those permitting extensive oxidation, 
 as elsewhere discussed. Finally the occurrence or indications of de- 
 cided physical breaks, such as erosion surfaces and disconformities, 
 serves to separate distinct strata. 
 
 Types of Stratification. Walther (23:631) recognizes two 
 kinds of stratification, direct and indirect. The former is produced 
 
STRATIFICATION CROSS-BEDDING 701 
 
 when the changes in sedimentation produce differences in the strata, 
 as when, for example, volcanic ashes are deposited upon a lava 
 flow, or when fine clay deposits are succeeded by deposits of sands 
 from a rising flood, or when in the deep sea, after continuous 
 deposition of Globigerina ooze, a bionomic change brings about a 
 deposition of diatomaceous oozes. Here each stratum corresponds 
 to the physical change which brought about the change in deposi- 
 tion. When, however, a rearrangement of the sediment of the 
 shallow sea occurs, owing to the agitation of this sediment by the 
 waves, a secondary separation of materials results, which was not 
 dependent on original changes in sedimentation. Thus a mixed 
 sand may be assorted into layers, according to grain, or a pebbly 
 deposit, charged originally with sand, may be separated into a 
 stratum of conglomerate and one of sand. Again, a deposit of 
 mixed foraminiferal and pteropodan shells may be separated into 
 two strata, one of Foraminifera, tfre other of pteropods, on account 
 of the difference in their specific gravities. The cases just cited 
 constitute what Walther has termed indirect stratification. Some- 
 times it finds expression in layers, sometimes in strata. The re- 
 markable alternation of pure limestone and calcareous clays in the 
 Cincinnati series of the Ordovicic of Ohio, etc., has been explained 
 in this manner as indirect stratification. The sharp assortment of 
 the material, the abruptness of contact and freedom from grada- 
 tions would seem to indicate that this interpretation is correct. 
 (Perry-i8.) 
 
 Stratification is often indicated only by the arrangement of 
 pebbles, mica scales, or of fossils in interrupted horizontal lines, 
 within a single stratum or even a single bed. The arrangement of 
 the flints in the chalk suggests the stratification of this deposit, a 
 single stratum appearing often of exceeding thickness, while the 
 material is of uniform texture, thus exhibiting no lamination. The 
 same thing is true of the Losspuppchen or concretions of the loess, 
 but in this case it is not always the stratification which is indicated 
 by them, but lines of permeability, which have no direct relation to 
 stratification. This may possibly be the case also in some flint layers 
 of the chalk, as already suggested. 
 
 2. CROSS-BEDDING. This is most readily seen in elastics of an 
 arenaceous texture, though rudytes sometimes show it on a large 
 scale. It consists of an- arrangement of the grains in diagonal lay- 
 ers with reference to the plains bounding the strata. Originally 
 these laminae may have been deposited at a considerable angle from 
 the horizontal. Above and below, these oblique layers are bounded 
 by the planes of stratification, and they are commonly truncated on 
 
702 PRINCIPLES OF STRATIGRAPHY 
 
 their upper surfaces. Successive beds may have their oblique lam- 
 inae inclined at different angles or in different directions, and hori- 
 zontal layers may rest upon the truncated edges of inclined layers, 
 thus simulating unconformity. This oblique lamination may range 
 in magnitude from beds a millimeter or less in thickness to strata 
 having a thickness of a hundred feet or more. In such a case the 
 deposit was generally formed as a delta in a standing body of water, 
 with strong currents flowing in and depositing the sands or pebbles 
 on the growing delta front. Oblique beds formed in this manner 
 are known as "fore-sets," and are generally truncated at the top by 
 the currents, which deposit horizontal beds or "top-sets," generally 
 of coarser material, upon the truncated upper edges. Basally the 
 fore-set beds will either rest upon or directly merge into the bot- 
 tom-set beds, which are made of finer material, mostly clay and silt. 
 The angle of the fore-set beds generally decreases outward, the 
 last fore-sets of a large delta being fine and less steeply inclined 
 than the older ones (see ante, p. 610). Small deltas were formed 
 in numerous localities toward the end of the last glacial epoch in 
 standing bodies of water along the ice front. Their structure can 
 readily be examined in many sand pits. Several types of cross- 
 bedding may be distinguished. 
 
 a. Delta Type. This type of cross-bedding, already noted, con- 
 sists essentially of a single bed of diagonal layers bounded below 
 and above by nearly horizontal beds. It appears to be characteristic 
 of deltas deposited in a standing body of water. Whether or not 
 this type is also characteristic of deltas formed on the sea coast 
 depends on the strength and magnitude of the tides. It is evident 
 that only one series of fore-set beds will be formed in any given 
 delta, and that relatively stationary conditions alone permit the 
 formation of the delta. If, after the building of a delta in a lake, 
 a rise in the water level should occur, a new delta might be built up 
 over the old one, and thus the resulting formation would show two 
 sets of diagonal beds, separated by horizontal beds, the top sets of 
 the first and the bottom beds of the second. Such a superimposition 
 of two deltas is, however, difficult to conceive of on a subsiding sea 
 coast where subsidence is accompanied by transgression, and con- 
 sequent transference of the zone of delta building. 
 
 b. Cross-bedding of Torrential Deposits. Superimposition of 
 obliquely bedded strata is, however, eminently characteristic of tor- 
 rential deposits. Each succeeding deposit will be characterized by 
 fore-set and top-set beds, and the number of such superimposed 
 strata is chiefly dependent on the frequency of recurrence of the 
 torrents. The length of the fore-set bed formed by a river on dry 
 
CROSS-BEDDING 703 
 
 land is of course much less than that of a delta fore-set. Most 
 likely a greater length than six feet is rare, while probably by far 
 the greater number fall below a foot in length. The angle which 
 the fore-set beds make with the horizontal varies proportionately 
 to the coarseness of the material, but in any given case it is ap- 
 proximately uniform. Moreover, the angle of the fore-sets of suc- 
 cessive strata is as a rule similar and in the same direction, while the 
 dividing top-set beds are parallel in the successive strata. Thus a 
 section of a torrential deposit will show a succession of obliquely 
 bedded strata, separated and bounded above and below by strata, 
 which make a high angle with them, are parallel to each other, and 
 originally represented the surface slope of the deposit. The inclina- 
 tions of the laminae of the successive cross-bedded strata are uni- 
 form, and the laminae all slope in the same direction. This is the 
 type of cross-bedding found in many ancient sandstones, and it 
 seems to be highly improbable that any such structure could be 
 produced by agents working on the sea coast. (Fig. 123.) 
 
 c. Cross-bedding of Eolian Deposits. Such regularity of cross- i/ 
 bedding as is found in both lacustrine and torrential deposits is, 
 however, not characteristic of eolian deposits. In these the laminae 
 when oblique show no uniformity of slope or direction within either 
 the same stratum or successive strata. Nor are the dividing laminae 
 parallel to each other. Cross-bedding of eolian deposits is brought 
 about in the following manner : A sand dune in its structure shows 
 a series of concentric shells of sand consisting of alternating coarse 
 and fine layers. This is a feature characteristic, according to 
 Forchhammer (9:7), of every dune of the Jutland coast, and in- 
 ferentially of the majority if not of all sand dunes. Toward the 
 side of the. wind the dune layers have an angle of 5, while on the 
 lee side the angle is as high as 30. The stratification is shown 
 chiefly by the varying coarseness of the grains composing succes- 
 sive layers, this being determined by the variable strength of the 
 winds, to which the dune owes its origin. If through a change of 
 the conditions which built up the dune, i. e., change in the force or 
 the direction of the wind or in the amount of the sand supplied, 
 or through other causes, the dune begins to migrate, a part of 
 its basal portion may remain behind, as the truncated base of the 
 dune, while upon this truncated surface a new dune may accumu- 
 late, which in turn will meet with the same fate, leaving its basal 
 portion behind. Successive portions of this kind will eventually 
 produce a bed of sand in which the cross-bedding is of extreme 
 irregularity and inconstancy. (Fig. 137.) (Walther-22: 7/5 
 [519].) Huntington (15) has shown that a characteristic feature" 
 
704 PRINCIPLES OF STRATIGRAPHY 
 
 of such cross-bedding is the tangency of the layers at the base, while 
 at the top erosion has sharply truncated them. 
 
 This type of cross-bedding is not infrequently met with in 
 arenytes among the strata of all ages. The Medina sandstone 
 (Siluric) of western New York affords some excellent examples 
 of this type, and it is highly probable that the beds showing this 
 structure were originally wind-laid deposits. Other excellent 
 examples of such cross-bedding are shown in the Sylvania sand- 
 stone (Upper Siluric) of Ohio, Michigan and Canada (Figs. 
 119, 120) and in the White Cliff sandstones (Jurassic) of the Kanab 
 Plateau and in the La Platte sandstone (Jurassic) of Utah. Cal- 
 carenytes, too, sometimes show this structure, as noted above, for 
 the Junagarh limestone of India and for other modern deposits 
 recognized as wind-laid. The cross-bedding of the Somersetshire 
 oolite (Forest marble), referred to above (Fig. 121), appears also 
 to be indicative of the eolian origin of this rock. Excellent exam- 
 
 FIG. 137. Eolian cross-bedding as found in desert sands. (After Walther.) 
 
 pies of this type of bedding in a heavy-bedded, non-siliceous lime- 
 stone (calarenyte) have been observed by the author in the cut 
 through the. Warsaw (Mississippic) limestone on the Missouri Pa- 
 cific Railroad, south o St. Louis, Missouri. This is reproduced in 
 Figs. I22a and b, on page 577. Compare, also, Figs. 13,8, 139. 
 
 Comparison of Types. A comparison of the three types of 
 cross-bedding, i. e., the delta, the torrential and the eolian, will show 
 the distinctive character of each, namely : uniformly sloping fore- 
 set beds in one series and generally on a large scale, for delta de- 
 posits; uniform fore-set beds of small size and in successive but 
 similar series separated by horizontal deposits, for torrential de- 
 posits ; and oblique beds, variable in angle and slope within the same 
 and successive series commonly without horizontal dividing beds, 
 for eolian deposits. While these types grade into each other where 
 the deposits meet or overlap, it is not known that any one type of 
 cross-bedding is produced by another agent. Thus the torrential 
 type of cross-bedding cannot be readily conceived of as formed in 
 w the sea, and the same may be said of the eolian type. The bedding 
 of a sand bar may perhaps show something analogous to the wind- 
 
CROSS-BEDDING 
 
 705 
 
 formed cross-bedding, but conditions for the preservation of such 
 are perhaps seldom realized. Gilbert has described the mode of 
 formation of cross-bedding through the shifting of ripples on the 
 
 FIG. 138. Crosfc-bedding of the Eolian type (Orange sand or La Fayette 
 Formation), Mississippi Central Railroad, Oxford, Miss. (After 
 Hilgard.) 
 
 sea floor, due to a current accompanying oscillatory movements. He 
 considers "that sediment may be added to a rippled surface without 
 any disturbance of the pattern, but that there is usually a coinci- 
 dent gradual bodily shifting of the pattern in some direction." 
 
 FIG. 139. Ledges of sandstone near Colorado Springs, showing Eolian cross- 
 bedding. 
 
 "The shifting of the ripple profile during the accumulation of the 
 sediment makes the accumulation unequal on the two sides of the 
 trough (figure 3), and, if the ratio of shifting to deposition exceeds 
 a certain amount, there is deposition on only one side of the trough 
 and erosion on the other." (Gilbert-i2 : ijp, Figs. 3-4-} In this 
 case two sets of oblique planes are produced, one due to deposi- 
 tion, the other to erosion, the latter representing the progress of the 
 
7 o6 ' PRINCIPLES OF STRATIGRAPHY 
 
 profile of the troughs along certain tangents. The tangent planes 
 are often nearly horizontal, in which case the cross-bedding would 
 approach in appearance the torrential type. The absence of divid- 
 ing strata would, however, readily distinguish it. Cross-bedding of 
 this type has been observed by Gilbert in the Medina sandstone of 
 western New York, and referred to wave work. 
 
 "When the waves from a new direction act on a surface already 
 rippled, they. produce a new pattern, which at first combines with 
 the old one, but eventually obliterates it. The troughs of the new 
 pattern are formed in part by excavation from ridges of the old, and 
 the lamination associated with the old ridges is truncated, so that 
 the new lamination is unconformable." (12:140, Fig. 5.) Sev- 
 eral such unconformities may succeed each other, and Gilbert 
 holds that the irregular cross-bedding of the Medina sandstone, 
 referred to above as perhaps of eolian origin, was produced in this 
 manner. It may be doubted, however, if ripples of a sufficient mag- 
 nitude to produce such a structure are ever produced under water, 
 and still more if when produced they are accompanied by such 
 rapid deposition as the case would seem to require. For, as Gil- 
 bert has pointed out, the formation of large ripples requires great 
 waves, and therefore broad and deep water bodies, and in such 
 deposition of sands is not extensive. On the whole, the structure de- 
 scribed conforms much more nearly to the observed structure of 
 anemoclastic deposits. It may also be questioned if the ripple cross- 
 bedding on a small scale may not with equal or perhaps greater 
 facility be produced by the wind alone. It would seem that shift- 
 ing wind ripples, which are sand dunes on a small scale, would pro- 
 duce the same structure that shifting sand dunes produce on a 
 larger scale. 
 
 Strata which show the irregular type of cross-bedding must be 
 carefully scrutinized for other evidence of eolian activity as well 
 as for evidence of marine or fluviatile origin. The occurrence in 
 the rock of scattered marine organisms is no conclusive evidence 
 of the marine origin of the formation, unless it can be shown that 
 the organisms in question lived where found or at least were car- 
 ried there by currents of water and not by wind. 
 
 3. BEACH CUSPS. (Johnson-i6.) Beach cusps are triangular 
 ridges extending across the beach generally at right angles to the 
 shore front. When most typically developed the beach cusp has the 
 form of an isosceles triangle with its base parallel to the beach, but 
 at its upper edge, and its apex near the water. The cusp may be 
 broad, approaching in form an equilateral triangle, but more gen- 
 erally it is long, narrow and extremely acute, the sides sometimes 
 
BEACH CUSPS 707 
 
 appearing almost parallel. 'The cusps may constitute the serrate 
 seaward side of a prominent beach ridge, or may occur as isolated 
 gravel hillocks separated by fairly uniform spaces of smooth, sandy 
 beach. They may be sharply differentiated from the rest of the 
 beach, or may occur as gentle undulations of the same material as 
 the beach proper, and so be scarcely discernible as independent 
 features." "A cusp may rise from an inch or less to several feet 
 above the general level of the beach. Many are relatively low and 
 flat, others high and steep-sided. Sometimes the highest part is 
 comparatively near the apex; at other times the highest part is far 
 back, and from it a long, sloping ridge trails forward toward the 
 water. As a rule,, the cusps appear to point straight out toward 
 the water that is, the axis of the cusp is at right angles to the 
 shore line and neither side of a cusp is steeper than the other, ex- 
 cept where oblique, wind-made waves have eroded one side only." 
 (Johnson 16: 605-606.) The material of the cusp varies from the 
 finest sand to the coarsest cobblestone, there being no necessary 
 relationship between the size of the cusp and the size of the material 
 composing it. Gravel cusps are often found on sandy beaches, the 
 cusps being always built of the coarser material of the beach. In 
 size cusps vary from a length of 8 or 12 inches to 30 feet or more. 
 The distance between cusps, measured from crest to crest, ranges 
 on small ponds from less than a foot to two feet or more. On sea 
 beaches they may be less than 10 feet apart, while those built by 
 large storm waves may be 100 feet apart The spacing is fairly 
 regular, though in some cases there seems to be irregularity in 
 spacing, as shown by Jefferson. (Johnson-i6.) Compound cusps 
 are also occasionally formed. 
 
 Various theories have been propounded to explain the origin 
 of beach cusps ; for a review of these the reader is referred to the 
 paper by Johnson, where a reference to the bibliography is also 
 found. Johnson's theory, and the one best supported by the facts, 
 is, concisely stated, ''that selective erosion by the swash develops 
 from initial, irregular depressions in the beach, shallow troughs of 
 approximately uniform breadth, whose ultimate size is proportional 
 to the size of the waves, and determines the relative uniform spac- 
 ing of the cusps, which develop on the intertrough elevations." 
 (16:620.) 
 
 Fossil Beach Cusps. Beach cusps on old shore lines are known 
 especially from the Medina sandstone of western New York. They 
 were described by Gilbert (12) as giant ripples, but, as suggested 
 by Branner (3) and by Fairchild (7), they are undoubted examples 
 of ancient beach cusps. The spacing of these cusps varies from 
 
708 PRINCIPLES OF STRATIGRAPHY 
 
 10 to 30 feet, and their height from 6 inches to 3 feet. Fairchild 
 has found crests 80 feet apart, but it is not certain that all such 
 structures are referable to cusps. 
 
 4. WAVE MARKS. On shallow coasts the advancing waves slide 
 up onto the shore after breaking, forming the "swash." After the 
 retreat of the wave, its furthermost advance is found to be marked 
 by a fine, wavy line, corresponding in outline to that of the water's 
 edge, and composed of fine particles of mica, fragments of seaweed, 
 fine sand grains and other matter light enough to be carried along 
 by the water. Numerous wave lines of this character may generally 
 be seen on a shore of the type noted. In exceptional cases, as in 
 the Medina sandstone of New York, these are finely preserved after 
 the consolidation of the rock, appearing often as perfect as on the 
 unconsolidated beach. (Fairchild-7.) 
 
 5. RILL MARKS. The water running off after each swash, or on 
 the retreat of the tide, frequently cuts rills into the surface of the 
 beach. These rills represent a river system in miniature, and gen- 
 erally consist of a number of small, quickly widening channels, 
 which join a trunk channel at a very oblique angle, and which are 
 in turn joined by other branches at an oblique angle. 
 
 A different type of rill marks is found where small streams de- 
 bouch upon a flat, sandy or clayey plain. Here the waters of the 
 stream will divide into innumerable fingers and fingerlets, the re- 
 verse of the river-system type. Thus before the water sinks into 
 the ground or runs off, a series of channels, branching more and 
 more in their lower courses, have been produced. These channels 
 are reproductions on a small scale of the large channels spreading 
 over the subaerial deltas at the debouchure of desert streams. 
 
 After the dying out of the streamlets which produced the rills, 
 the conditions are generally favorable for the preservation of these 
 in the hardening mud, and through covering by wind-drifted sand or 
 flood deposits. On the shore conditions for the preservation of rill 
 marks are less favorable, since the succeeding wave will generally 
 destroy the marks left by the run-off preceding. Occasionally, how- 
 ever, such a preservation may occur. In either case, the filling mud 
 or sand will on hardening show the relief of the original rill, re- 
 producing the minutest channel as a raised ridge. These relief 
 structures greatly resemble branching stems of plants and have 
 sometimes been described as such.. (Rogers, Lesquereux, New- 
 berry.) 
 
 Water flowing down the beach is often checked locally by peb- 
 bles or shells lying partly buried on the beach. In such cases the 
 water flowing down on either side of the obstruction will excavate 
 
RILL-MARKS; MUD CRACKS 709 
 
 characteristic depressions, or the water falling over the obstruction 
 will gully the surface for a short distance below. Examples of 
 these are found in the Medina sandstone. 
 
 6. MUD-CRACKS, SUN-CRACKS OR DESICCATION FISSURES. 
 When lutaceous deposits are exposed by the retreat of the tide, or 
 by the shrinking or disappearance of a playa lake or a pond, or by 
 the uncovering of the flood-plain of a river, the drying which they 
 undergo will result in the formation of polygonally arranged cracks, 
 and a gentle concaving of the upper surfaces of the polygons thus 
 bounded. When the desiccated layers of mud are thin, they will 
 often curl up like wood shavings, and may be blown away by the 
 wind. When on reflooding of the surface or by the deposition of 
 wind-blown material, these cracks are filled in by deposits of the 
 same or different material, the polygons will remain more or less 
 perfectly outlined. This desiccation fissure, sun-crack, mud-crack, 
 prismatic, or paving block structure, as it is variously called, is 
 found not only in clayey rocks, but also in fine calcilutytes, like 
 those of the Helderberg mountains (Rondout waterlimes), the 
 Solnhofen beds (Marsh), the Cincinnati limestones (Perry-i8), and 
 in many other lutaceous deposits. They testify to the exposure 
 of these deposits before they were solidified. (For a full dis- 
 cussion of this subject see Barrell-i.) 
 
 Playa Surface. Taking the areas of mud-crack formation in 
 the order of their magnitude, the playa surface would probably 
 stand first. Here the entire surface for hundreds of square miles 
 becomes mud-cracked, often to considerable depth, on the complete 
 drying up of the temporary playa lake. Here, too, the conditions 
 for the preservation are most favorable. Not only is the exposure 
 a long one, often the greater part of the year, or for many years, 
 and for much of the time to intense heat, but the chances of proper 
 burial are much greater. Wandering sand dunes may thus preserve 
 the record, dust deposits may fill the fissures, or, at the next flood, 
 sands or mud may be swept into them. In fact, the playa or takyr 
 seems to be the ideal surface for mud-crack record, and one is 
 tempted to refer most mud-cracked strata to such an origin. Cer- 
 tainly where fossil mud-cracks penetrate a formation to the depth 
 of ten feet, as is the case in the upper Shinarump (Jura-Triassic) 
 shales of Utah (Gilbert-n : p), it is difficult to believe that they 
 could be formed under other conditions than those permitting pro- 
 longed exposure such as is found only in the playas of the desert, 
 where ten years or more may elapse between rainfalls. 
 
 Permanent Lake Surface. Much less extensive, and of minor 
 significance, are the sun-cracked areas which come into existence 
 
710 PRINCIPLES OF STRATIGRAPHY 
 
 around permanent lake bodies as the result of periodic shrinking 
 of the lake after a flooding of the adjacent lands. Such mud- 
 cracked areas will be exposed for long periods of time and so re- 
 semble the flood plains of rivers. They at best, however, form but 
 a narrow marginal belt around the lake and the beds characterized 
 by them would grade laterally into fresh water lake beds in which 
 remains of fresh water organisms are found. The mud cracks of 
 the Tertiary lake beds of Florissant may be of this type. 
 
 River Flood Plains. Next in importance to the playa, and 
 perhaps even rivaling it in extent, is the river flood plain. "Here 
 after a great flood extensive areas may be laid bare and be sub- 
 jected to desiccation and cracking during the long period of expo- 
 sure before the next flood. Since, in the lower reaches of rivers, 
 the material spread out by the flood is of the nature of a fine silt, 
 the conditions for the formation of the mud-cracks are fully satis- 
 fied. Here, too, preserval of the mud-crack record is readily ac- 
 complished by the filling of the fissures by the sediment of the next 
 flood. 
 
 The mud-cracked flood plain deposit would differ from the playa 
 deposit in the more frequent presence of carbonaceous material, since 
 vegetation is an accompaniment of river courses, but, as a rule, 
 absent from the playa, or found only around the margin. Aquatic 
 animals, too, should be more characteristic of the flood-plain than 
 of the desert deposit, and would especially characterize the old 
 stream channels dissecting the flood plain, and recognizable in the 
 fossil state by the lines of coarser sediment the filling of these 
 channels which traverse the finer deposits. 
 
 The Shore Zone. The shore zone between high and low water 
 also may furnish conditions favorable for the formation of mud- 
 cracks. This is especially the case where, as in the Bay of Fundy, 
 the tide recedes very far, and where large tracts remain exposed 
 during the fortnightly interval between high spring tides. Along 
 the margins of estuaries broad mud-flats are often exposed, and 
 here shrinkage cracks may form between tides. The time of expo- 
 sure of all but the highest parts of the shore zone, is, however, too 
 short to allow of a sufficient hardening of the mud-cracked area 
 to enable it to resist the softening and destroying effects of the 
 returning tide. Moreover, in modern mud flats of this type, or- 
 ganisms exist in great numbers, so that we would expect to find 
 mud-cracked rocks which are formed on the shore to be more or 
 less fossiliferous. 
 
 On the whole, mud-cracks are much more characteristic of con- 
 tinental deposits, especially of the playa and flood plain, than of 
 
CLAY GALLS; CLAY BOULDERS 711 
 
 the seashore. Only under exceptional conditions can we expect 
 the preservation of extensive mud-cracked surfaces of the sea- 
 shore. Moreover, the formation of great littoral deposits must 
 be accompanied by a subsidence of the sea-floor, and a consequent 
 landward transgression of the seashore with its .attendant phe- 
 nomena. The migration of the shore zone would thus bring about 
 a transference of the zone of mud-crack formation, so that we 
 could hardly expect to find a thick marine formation with repeated 
 horizons of mud-cracked layers unless we assumed that the subsi- 
 dence was so gradual a one that deposition kept pace with it. 
 
 7. CLAY GALLS (THON-GALLEN). When the mu.d layers on 
 the playa surface or on the river flood plain are very thin, drying 
 will cause them to curl up into masses resembling shavings. Such / 
 curly mud shavings occur on river flood plains exposed to a hot sun, 
 and they may also under favorable conditions be formed on the 
 seashore, as in the case of the coast of the Red Sea (Walther- 
 
 23 '-847) , When thoroughly dry these shavings may be blown by 
 the wind into neighboring sand dunes in which they become buried. 
 Subsequent softening of the clay when the sand dune is saturated 
 with water, as in the rainy seasons, will bring about a compression 
 of the clay-shaving into a thin, flat pellet of clay which will lie 
 embedded in the sand parallel to the stratification. Such clay pel- 
 lets, called Thon-gallen, or clay galls, are common in sandstones 
 of subaerial origin, especially in red sandstones. They may/ indeed, 
 be regarded as practically positive evidence of a subaerial origin 
 of the rock containing them, though these rocks may be seashore 
 dunes or formed far inland. . 
 
 8. CLAY BOULDERS. Clay boulders formed of plastic clay 
 rolled about by the waves are not uncommon occurrences on the sea- 
 shore. They have been recorded by Walther (23:847) and by 
 O. Fraas (10:^77) from the coast of the Red Sea. On the coasts 
 mentioned they represent the clay deposited during the previous 
 high tide, which on exposure at low tide dries and breaks up into 
 fragments. These are rolled into balls by the returning tide and 
 incorporated in the later sediment, where they have the appearance 
 
 of concretions. Examples of such structures seem to occur in the J 
 Dev9nic calcilutytes of Michigan, where rounded balls of a darker 
 color are included in lighter bedded deposits of similar character. 
 The author has observed the formation of clay boulders on the 
 coast of Scotland. Here fragments of glacial clays broken from 
 the cliffs are rolled about by the waves and fashioned into pebbles 
 and boulders of elongate but well-rounded outline. Where these 
 are rolled over a pebble beach, the hard pebbles are pressed 
 
712 PRINCIPLES OF STRATIGRAPHY 
 
 into the clay ball which then assumes the appearance of a worn 
 conglomerate fragment. As such it may be. embedded in the suc- 
 ceeding formation. Frass (10) records such boulders with shell 
 fragments for pebbles, from the Jurassic of Spitzbergen. 
 
 9. RAIN PRINTS. Partly dried clay surfaces and to some ex- 
 tent those of other lutaceous deposits, when exposed to a short, 
 sharp rain, will receive the impressions made by the striking rain 
 drops. When the rain drops strike obliquely a low rim around part 
 of the impression shows where the mud was displaced more 
 strongly, and therefore the side away from that from which the 
 rain slanted. Thus the more pronounced marking is always on the 
 obtuse side of the intersection of the surface and the path of the 
 rain drop. A replica in relief of this impression is found on the 
 under side of the layer of mud spread next above. This feature is 
 eminently characteristic of continental mud deposits, its preserva- 
 tion on the sea coast being a matter of doubtful probability. Im- 
 pressions apparently of this character have, however, been re- 
 
 FIG. 140. Plan of Eolian rip- FIG. 141. Diagram showing direction of 
 pie-marks in fine sand. currents and vortices in the formation 
 
 (After Walther.) of ripple-marks. (After Darwin.) 
 
 ported from the marine (shallow water) limestones of the Cin- 
 cinnati region. (Perry-i8: j^p, Fig. i.) 
 
 10. RIPPLE MARKS. These, are rhythmic undulations or waves 
 of the sand due either to the motion of the air or of the water. 
 Two types of ripples are recognized: i. Current ripples, formed 
 by the wind on the surface of sand dunes, etc., or by currents of 
 water in shallow basins; and 2. Oscillation ripples, formed by the 
 vortices of water in the sands at the bottoms of shallow stationary 
 water bodies. 
 
 "A current of water flowing over a bed of sand reacts on any 
 prominence of the bed. An eddy or vortex is created in the lee of 
 the prominence, and the return current of this vortex checks travel- 
 ing particles, causing a growth of the prominence on its down- 
 stream side. At the same time the upstream side is eroded, and the 
 prominence thus travels downstream. It is a subaqueous dune. Its 
 upstream slope is long and gentle ; its downstream slope is short and 
 steep." ( Gilbert-i 2 :IJ7.) The natural mold of this type of ripple 
 
RIPPLEMARKS 713 
 
 will be difficult to distinguish from the original ripple, though the 
 directions of the slopes will be reversed. A careful examination, 
 however, will show that, whereas the surfaces of the normal cur- 
 rent ripple are gently convex, those of the mold will be gently 
 concave. 
 
 Oscillation ripples are produced . . . "by the to-and-fro 
 motion of the water, occasioned by the passage of wind waves. 
 During the passage of a wave each particle of water near the 
 surface rises, moves forward, descends, and moves back, describing 
 an orbit which is approximately circular. The orbital motion is 
 communicated downward, with gradually diminishing amplitude. 
 Unless the water is deep the orbits below the surface are ellipses, 
 the longer axes being horizontal, and close to the bottom the ellipses 
 are nearly flat, so that the water merely swings forward and back. 
 It is in this oscillating current, periodically reversed, that the 
 sand-ripples are formed. A prominence occasions vortices alternat- 
 ing on its two sides, and is thereby developed in a systematic way, 
 with equal slopes and a sharp apex. There is a strong tendency to 
 produce the mole laterally into a ridge, the space between ridges is 
 definitely limited by the interference of vortices, and in time there 
 results a regular pattern of parallel ridges equally spaced." (Gil- 
 bert-12.) In the center of the oscillation ripple a low sharp ridge 
 is frequently found which bn the mold is represented by a groove. 
 (Van Hise-2i : 720.) See, further, the discussion by Darwin (6) of 
 the movements and vortices involved in ripple formation (Fig. 141). 
 
 The amplitude of the water oscillations and their frequency con- 
 trol the size of the resulting ripples, as has been shown by experi- 
 ment. The depth of the water has a direct bearing upon the ampli- 
 tude of the wave and therefore upon the size of the ripple. No 
 definite law has, however, been worked out as yet. 
 
 According to Siau, who studied the ripple-marks of the haven 
 of St. Giles, on the English Channel, their crests are distant from 
 30-45 cm. at a depth of 20 meters, while their troughs are from 
 8-10 cm. below their crests, and contain heavier basaltic gravel. 
 At greater depths their size diminishes. The greatest depth at 
 which they were observed was 188 meters. (Hunt-i4.) 
 
 In cross-section the oscillation ripple presents regular concavi- 
 ties divided by sharp ridges, and a faint central ridge in many cases. 
 This type is distinguished from the mold of the current ripple 
 chiefly by the asymmetry of the concavity of the latter, one side 
 being shorter and steeper than the other in the mold of the cur- 
 rent ripple. The central ridge when present is likewise a charac- 
 teristic feature. A mold of the oscillation ripple would show 
 
PRINCIPLES OF STRATIGRAPHY 
 
 gently rounded or convex ridges often with a groove on top, and 
 separated by sharp depressions. This mold is distinguished from 
 the normal current ripple mainly by its symmetry. In the desert, 
 wind ripples of all dimensions and of great variety of form occur. 
 They vary in width from 2 'cm. or less to a meter or more. Some- 
 times they are sharp angled, at others round. They generally 
 occur in long parallel series, often branching repeatedly, the 
 branch running parallel to the main stem. (Walther-22 : 5^5 [179] .) 
 (Figs. 140, 142.) 
 
 The width and height of the ripple-mark are dependent on the 
 size of the grain of sand and the strength of the wind. Uniform 
 currents will produce an elongation of the ripple which always 
 extends at right angles to the direction of the wind. (Hunt-i4.) 
 In many respects the arrangement of wind ripples and of sand 
 
 FIG. 142. Plan of Eolian ripple-marks in coarse desert sand. (After Wal- 
 ther.) (Compare with Fig. 140.) 
 
 dunes in. deserts is very similar, the former being reduced replicas 
 of the latter. 
 
 In the distribution of the material of the wind ripple, there 
 appears also to be a distinctive character, in that the coarser mate- 
 rial is found on the crest of the ripple, instead of in the trough, as 
 in subaqueous ripples. 
 
 ii. IMPRESSIONS OF ANIMALS AND PLANTS IN TRANSIT. Ani- 
 mals walking or crawling over a surface of mud or sand commonly 
 leave characteristic impressions. Plants rafted along by the wind 
 or waves, and medusae floating and dragging their tentacles, also 
 make characteristic markings, though these are not always readily 
 determinable. All such markings are depressions, and they will 
 be reproduced in relief on the under side of the next overlying 
 stratum. Occasionally the burrows of certain animals will be 
 marked by elevations or knobs. These structures will be dis- 
 cussed in their biological relations in the chapter on fossils, and 
 they are mentioned here only to complete the survey of minor 
 original features of sediments. 
 
ROUNDING AND SORTING OF SAND GRAINS 715 
 
 As to their occurrence, it may be repeated that footprints of 
 terrestrial animals are best preserved in the clays of the desert 
 playas, and the flood-plains of rivers, while those formed on the 
 seashore are commonly obliterated again by the action of the re- 
 turning tide and the waves. Tracks and burrows of worms, and 
 trails of molluscs and Crustacea, on the other hand, point more gen- 
 erally to a seashore or the borders of interior tideless seas, or, again, 
 more rarely to river flood-plains. 
 
 12. APPLICATION OF THESE STRUCTURES IN DETERMINING 
 POSITION OF STRATA. The importance of discriminating between 
 the original structure as here described and its reproduction in 
 reverse, in the overlying stratum, will be appreciated when it is 
 considered that strata often stand vertical, and are even overturned. 
 The determination of the upper and lower surfaces of the strata 
 may be the only means for recognizing the superposition of the 
 strata of a region. In all cases, the surface on which the structure 
 (ripple-mark, impression, etc.) was originally made is the upper 
 surface of the stratum, while the surface having a reverse repro- 
 duction of the structure (raised footprint, mold of ripple-mark, 
 etc.) is the lower surface of that stratum. 
 
 13. ROUNDING AND SORTING OF SAND GRAINS AND WEARING 
 OF PEBBLES. This subject has already been discussed in previous 
 sections, but may be briefly summarized here. Sand grains under 
 o.i mm. in diameter will not be rounded by wave action upon the 
 coast, for they are held in suspension, and, moreover, capillarity 
 provides the adjacent grains with a separating cushion of water 
 which prevents mutual attrition. Larger grains may under favor- 
 able conditions be rounded by the waves. They are even better 
 situated in this respect in river beds. The most efficient agent of 
 all in the rounding of grains is the wind, as it it is also the most 
 efficient sorting agent. 
 
 Pebbles are rounded largely by the action of running water 
 and by waves. That the wind is able to do work in this direction 
 is shown by the rounded pebbles of the Hamada or stony desert, 
 where water activity is absent. It has been repeatedly asserted that 
 there is a decided difference in form between pebbles of river bot- 
 toms and those of the shore. The former are said to be typically 
 flat, from the fact that they are shoved along on the bottom of 
 the stream, while the latter are rounded because they are rolled about 
 by the waves. The reverse has also been held. Until more detailed 
 observations on modern shores and river bottoms are made, no 
 such general criterion can be accepted. As a matter of fact, flat 
 pebbles abound on many shores where the material from which 
 
7i6 PRINCIPLES OF STRATIGRAPHY 
 
 they are derived is a thin-bedded rock or tends to split into thin 
 layers. Here the pebbles are shoved up the beach and dragged 
 back, rolling being seldom seen. Pebbles formed from angular 
 fragments, on the other hand, are rolled about on the beach. 
 Thus it appears that the original form of the material is of more 
 significance than the agent active in the rounding. 
 
 14. CHARACTERISTICS OF INCLUSIONS IN SAND GRAINS. In 
 tracing the source of the quartz grains in sands and sandstones 
 Mackie (17) has advocated the use of inclusions found in the 
 quartz or their absence. He divides the inclusions into: 
 
 (1) Regular inclusions^ of quartz, chlorite, muscovite, bio- 
 
 tite, rutile, apatite, zircon, garnet, magnetite, titanifer- 
 ous iron, etc. Characteristic of the quartz of schists. 
 
 (2) Acicular, or fine needle-like inclusions of doubtful min- 
 
 eral, capable of being subdivided according to arrange- 
 ment of the needles. Characteristic of granites. 
 
 (3) Irregular inclusions, mostly fluid lacunae with or with- 
 
 out gas bubbles. Characteristic of granites, but more 
 readily subject to disruption by changes in tempera- 
 ture or to crushing than the others, and, hence, di- 
 minishing in proportion with the age of the forma- 
 tion, and the repeated reworkings of the grains. 
 
 The absence of inclusions in quartz suggests vein quartz as the 
 source, or the quartz of schists. After a determination of the in- 
 clusions in the quartz grains of the crystallines which might have 
 furnished the sands of the Rothes Burn, and the determination of 
 the percentage of feldspar, garnet, staurolite, mica, hornblende, 
 chlorite and magnetite in the sands of this stream, together with 
 the inclusions in the quartz grains, Mackie concludes that 23% of 
 the sand was derived from granite, 57% from schist, and 20% 
 from diorite. The matrix of the Lower Old Red conglomerate of 
 Gollachy Mill^ was in like manner determined as derived 20% 
 from granite, 77% from schist, and 3% from diorite and volcanics. 
 In these analyses the feldspar was divided between the granite 
 schist and diorite, the garnet, staurolite, mica, chlorite and the 
 quartz with regular inclusions and without inclusions were referred 
 to schists, while the hornblende and magnetite were referred to 
 diorite. Analyses of the sand grains of successive members of 
 both the lower and upper Old Red Sandstone showed that, during 
 the* process of erosion of the lands supplying the material of this 
 formation in northern Scotland, different sand-supplying forma- 
 
 
INCLUSIONS; ORGANIC REMAINS 717 
 
 tions were uncovered, the first or highest of which supplying mate- 
 rial for the oldest beds was non-granitic. 
 
 From the nature of the inclusions Berkey has been enabled 
 to determine that the quartz grains of the St. Peter sandstone were 
 derived from the gneisses and granites of the Canadian Old Land, 
 and that the Sylvania sands were most probably derived from the 
 older St. Peter sands, with which they agree in all respects. 
 
 15. ORGANIC REMAINS. Abundant remains of marine organ- 
 isms are generally a good criterion for the marine origin of the 
 strata containing them. There are, however, important exceptions 
 to this. Thus the foraminiferal limestones of India and South 
 Africa are formed as eolian deposits upon dry land, and often at a 
 distance from the shore, though the remains themselves are all 
 of marine types. Marine types may also be included in a terrestrial 
 deposit as a result of derivation from older marine strata by 
 weathering or erosion. Again shells of marine organisms may be 
 carried inland by birds and other animals (including man) and 
 become embedded in later deposits. Man-made shell heaps are 
 generally recognizable by the presence in them of human imple- 
 ments as well as evidence of fire, but shells carried inland by birds 
 are not readily recognizable as such. The occurrence of organisms 
 of marine types in relict seas distant from the coast must be con- 
 sidered. This subject will be more fully discussed in a subsequent 
 chapter. 
 
 Occasional intercalation of marine layers in delta formations 
 otherwise of non-marine origin must also be noted here. Such 
 intercalations have been used to prove the marine origin of an en- 
 tire formation, the bulk of which is most probably of terrestrial 
 origin. 
 
 Fresh water and terrestrial organisms when exclusively found 
 in a formation indicate a continental origin. But such remains 
 may be as characteristic of fluviatile as of lacustrine deposits and 
 often more so. Thus the remains of land vertebrates and of plants 
 in a formation indicate more commonly river, flood-plain, swamp, 
 or, in the case of the vertebrates, steppe deposits, the remains being 
 embedded in the river muds or covered by blown sands. Abundant 
 remains of fresh water molluscs, Crustacea, etc., of Chara and other 
 fresh water plants, indicate a lacustrine or paludal origin of the 
 formation containing them. 
 
 Terrestrial organisms, especially plants, may also be carried out 
 to sea and so become embedded in marine formations. The same 
 thing is true of river-inhabiting fish, Crustacea, and Mollusca. The 
 extent of such transportation is generally determinable, as shown 
 
;i8 PRINCIPLES OF STRATIGRAPHY 
 
 by David White (24), by the degree of injury suffered by the 
 perishable parts, such as bark, leaves, etc. Seeds and spores of river 
 plants, such as the water ferns or rhizocarps. may also be carried 
 out to sea and buried in normal marine sediments. Their occur- 
 rence, however, 'always suggests a river-borne origin for the mud 
 in which they are found, as in the case of the Genesee and Portage 
 muds of the Devonic in which occur the spore cases of the water 
 fern Protosalvinia, mingled with marine organisms. 
 
 16. CONCRETIONS. Concretions are segregations of mineral 
 matter which grow in size by addition externally, internally or in- 
 terstitially. From the point of view of their origin and relation- 
 ship to the enclosing rocks, two types .may be distinguished : ( i ) 
 those forming as contemporaneous accumulations, afterward buried 
 by clastic or other strata, and (2) those forming within the strata 
 after their deposition. This second group clearly belongs to the 
 secondary structures of rocks. 
 
 Concretions of calcium carbonate, of barite, of manganese, and 
 concretions composed of fragmental material cemented by phos- 
 phate of lime are among the first group, forming at the present 
 time. The phosphate concretions are most characteristic of the 
 shore zone, while the manganese concretions are common in the 
 deep sea. The latter (Walther-23 : 701) are most abundant in the 
 Pacific between 767 and 8,183 meters, and in the Indian and 
 Antarctic Oceans between 2,926 and 4,754 meters depth. In the 
 Atlantic Ocean they are found between 767 and 5,211 meters depth, 
 chiefly in the neighborhood of volcanic islands. 
 
 These concretions commonly constitute the uppermost layer of 
 the lithosphere in the deep sea, and they are gradually buried by 
 the accumulation of fine muds. Not infrequently they constitute 
 the foundation on which corals or other sedentary benthonic organ- 
 isms gain a foothold, and such a concretion in moderately deep 
 water may serve as the nucleus about which a coral reef is built up. 
 Chemically formed oolites and pisolites should be mentioned under 
 contemporaneous concretions. These have been fully discussed 
 in a preceding chapter. 
 
 The secondarily formed concretions, or those growing within 
 the strata, and therefore of later age, are represented by clay-stone 
 concretions, so characteristic of shale and clay beds, and readily 
 recognized as belonging to this secondary type by the fact that the 
 stratification lines are seen to pass through them. Large examples 
 of these are found in Devonic and later lutaceous deposits. They 
 have not infrequently grown about fossils. Many of these also 
 show the septarium structure as described below. The Losspiippchen 
 
CONCRETIONS 719 
 
 and "Lossmannchen," of the German loess, the "Marlekor" and 
 "Nakkebrod" of similar Swedish deposits, the "Kankar" of India, 
 and the clay iron stones of the British Carbonic shales are other 
 examples of concretions of this type. 
 
 According to their method of growth concretions have been 
 divided by Todd into four types (20) : 
 
 1. Accretions. 
 
 2. Intercretions. 
 
 3. Excretions. 
 
 4. Incretions. 
 
 Accretions grow regularly and steadily from the center out- 
 ward by successive additions of materials. This type' of concre- 
 
 FIG. 143. Concretion (accretion) of clay stone, Connecticut Valley. (After 
 Gratacap.) 
 
 tion will be solid from the center and if of subsequent growth will 
 include or enmesh particles of the rock in which it forms without 
 any considerable disturbance of it. The stratified structure may 
 also be preserved in accretions, unless by crystallization a radiate 
 structure is produced. Examples of this type are the remarkable 
 concretions of the postglacial clays of the Connecticut Valley. 
 (Sheldon-i9.) (Fig. 143.) 
 
 The radial structure due to crystallization is well developed in 
 the large spherical concretions of the Devonic black shales of Kettle 
 Point,* Ontario, and of Michigan. From their fibrous structure 
 they are not infrequently mistaken for petrified wood. (Daly-5.) 
 
 Intercretions grow by accretion on the exterior and by inter- 
 stitial addition, causing a circumferential expansion and resultant 
 cracking and wedging apart of the interior of the concretion. The 
 cracks widen toward the center and are commonly filled by mineral 
 
 * So named from the resemblance of partly exposed concretions to inverted 
 kettles. 
 
720 PRINCIPLES OF STRATIGRAPHY 
 
 matter, chiefly calcite, the accumulation of which helps to widen 
 and extend these internal fissures. Concretions of this type are 
 familiarly known as septaria. from the fact that when they have 
 been worn on the surface the veins sometimes weather in relief, 
 and thus produce a septate structure. Often, however, the veins are 
 depressed. These concretions are sometimes thought to be petri- 
 fied turtles, and in many localities are known by the name of 
 "turtle stones." They are abundant in the Devonic shales of 
 eastern North America and in the Cretacic beds of the interior, 
 while the Jurassic of western Europe is famous for its remarkably 
 beautiful* examples. 
 
 Excretions are centripetal concretions "consolidation progress- 
 ing inward from the exterior." (Dana-Mawwa/, 4th ed. p#.) 
 They are represented by nodular shells of sand cemented by iron 
 oxide, and generally filled by more or less unconsolidated sand or 
 contain other shells of cemented sand. Todd holds that normal ac- 
 cretions or intercretions of ferrous carbonate, on coming in contact 
 with waters charged with carbon dioxide and oxygen, will begin to 
 dissolve and a shell of ferric -hydroxide will form on its surface by 
 precipitation. The iron carbonate of the portion of the concretion 
 within this shell will similarly be dissolved and reprecipitated as 
 ferric hydrate, a second shell thus being added on the interior of the 
 first. The impurities of sand or clay in the original concretion re- 
 main behind, in a loose condition. Thus while the actual thickening 
 of the shell is on the inside, and the growth, therefore, from without 
 inward, the molecular movement of the iron salts is froim within 
 outward, i. e., from the core of the original concretion to the inner 
 wall of the shell. When the process is completed a loose mass of 
 sand or other impurities alone remains behind, or, if the original con- 
 cretion was free from impurities or nearly so, the resultant excre- 
 tion may be hollow. Excretions formed within ferruginous sand- 
 stones are of ten 'the cause of puzzling hollow cavities. 
 
 Incretions. These are cylindrical concretions with a hollow 
 core. Todd infers that these originate where the walls of a cavity, 
 like the cylindrical tube left by a decayed root in the sand or clay, 
 serve as the nucleus for deposition. The iron is drawn from the 
 surrounding material and moves inward to the center, where it 
 is added to the central cylinder, which grows in thickness outward 
 by the addition of successive shells on the exterior, until the sur- 
 rounding matrix is depleted. 
 
 Minute concretions of this type are common in the loess. They 
 consist of carbonate of lime, and resemble clay pipe stems in size 
 and form. 
 
SECRETIONS 721 
 
 17. SECRETIONS. Secretions are deposits formed on the walls 
 of cavities in rocks, the first layer being the outer one of the secre- 
 tion. A constant supply of material may bring about the filling 
 of the cavity, as in veins and agate geodes, while the cutting off of 
 the supply results in the production of hollow geodes, lined with 
 crystals. 
 
 All secretions are secondary rock structures, and they are men- 
 tioned in this chapter merely for convenience in comparison with 
 concretions. Of the latter, incretions and excretions are secondary 
 structures, and the same is true largely if not wholly of intercre- 
 tions. Accretions are, however, extensively represented by con- 
 temporary concretions, though many kinds of true accretions are 
 also formed secondarily in strata of various kinds. 
 
 BIBLIOGRAPHY XVII. 
 
 1. BARRELL, JOSEPH. 1906. Relative Geological Importance of Con- 
 
 tinental, Littoral and Marine Sedimentation, Part III. Journal of 
 Geology, Vol. XIV, pp. 524-568. 
 
 2. BERKEY, CHARLES P. 1906. Paleogeography of Saint Peter Time. 
 
 Geological Society of America, Bulletin, Vol. XVII, pp. 229-250. 
 
 3. BRANNER, JOHN C. 1901. Origin of Ripple Marks. Journal of 
 
 Geology, Vol. IX, pp. 535~53 6 - 
 
 4. CANDOLLE, CASIMIR DE. 1883. Rides formus a la surface du 
 
 sable depose" au fond de 1'eau et autres phenomenes analogues. Archives 
 des Sciences Physiques et Naturelle, Geneve. No. 3, Tome IX, pp. 
 241-278. 
 
 5. DALY, REGINALD A. 1900. The Calcareous Concretions of Kettle 
 
 Point, Lambton County, Ontario. Journal of Geology, Vol. VIII, pp. 
 135-150. 
 
 6. DARWIN, GEORGE H. 1883. On the Formation of Ripple Mark/ 
 
 in Sand. Proceedings of the Royal Society of London, Vol. XXXVI, pp. 
 18-43. 
 
 7. FAIRCHILD, HERMAN L. 1901. Beach Structure in the Medina/ 
 
 Sandstone. American Geologist, Vol. XXVIII, pp. 9-13, pis. II-IV. 
 
 8. FLEMING, J. A. 1902. Waves and Ripples in Water, Air and ^Ether. 
 
 London. ' 
 
 9. FORCHHAMMER, G. 1841. Geognostische Studien, am Meeresufer. 
 
 Neues Jahrbuch fur Mineralogie, etc., pp. 1-38, t. III. 
 
 9a. FOREL, F. A. 1883. Les Rides de Fond e"tudius dans le lac Le"man. 
 Archives des Sciences Physiques et Naturelles, Geneve, (3.) Tome X, 
 pp. 39-72. 
 
 10. FRAAS, O. 1872. Heuglin's geologische Untersuchungen in Ost Spitz- 
 
 bergen. Petermanns geographische Mittheilungen, Bd. XVIII, pp. 275- 
 277. 
 
 11. GILBERT, G. K. 1877. Report on the Geology of the Henry Mountains. 
 
 United States Geographical and Geological Surveys of the Rocky Moun- 
 tain Region. 
 
722' PRINCIPLES OF STRATIGRAPHY 
 
 12. GILBERT, G. K. 1899. Ripple Marks and Cross-bedding. Bulletin, 
 
 of the Geological Society of America, Vol. X, pp. 135-139, pi. XIII 
 5 %s. 
 
 13. GRABAU, AMADEUS W. 1907. Types of Cross-bedding and Their 
 
 Stratigraphic Significance. Science, N. S.~, Vol. XXV, pp. 295-296. 
 
 J 14. HUNT, A. R. 1882. On the Formation of Ripple Mark. Proceedings 
 
 of the Royal Society of London, Vol. XXXIV, pp. 1-18. 
 
 15. HUNTINGTON, ELLSWORTH. 1907. Some Characteristics of the 
 Glacial Period in Non-Glaciated Regions. Geological Society of America, 
 Bulletin, Vol. XVIII, pp. 35i~388, 9 pis., 16 figs. 
 
 ] 16. JOHNSON, DOUGLAS W. 1910. Beach Cusps. Geological Society of 
 America Bulletin, Vol. XXI, pp. 599-624 (with review of previous litera- 
 ture on Beach Cusps). 
 
 17. MACKIE, WILLIAM. 189^. The Sands and Sandstones -of Eastern 
 
 Moray. Edinburgh Geological Society Proceedings, Vol. VII, pp. 148- 
 172. 
 
 18. PERRY, NELSON W. 1889. The Cincinnati Rocks. What was their 
 
 Geological History? American Geologist, Vol. IV, pp. 326-336, 2 pis. 
 xj 19. SHELDON, J. M. ARMS. 1900. Concretions from the Champlain 
 
 Clays of the Connecticut Valley. Boston, 1900. 
 x\ 20. TODD, J. E. 1903. Concretions and Their Geological Effects. Bulletin 
 
 of the Geological Society of America, Vol. XIV, pp. 353-360. 
 
 21. VAN HISE, CHARLES R. 1896. Principles of North American Pre- 
 
 Cambrian Geology. U. S. Geological Survey,' i6th Annual Report, Pt. I, 
 pp. 581-872, pis. CVIII-CXVII. 
 
 22. WALTHER, JOHANNES. 1891. Die Denudation in der Wuste. Ab- 
 
 handlungen der koniglich-kaiserlichen Gesellschaft der Wissenschaften. 
 Mathematische-Physische Klasse, Bd. XVI, pp. 345-570 (1-225). 
 
 23. WALTHER, J. 1894. Die Auflagerungsflachen und die Entstehung der 
 
 Schichtung, pp. 620-641, and other chapters in Einleitung in die Geologic 
 
 Jals Historische Wissenschaft, 3 Teil. Lithogenesjs der Gegenwart. 
 24. WHITE, DAVID. 1911. Value of Floral Evidence in Marine Strata as 
 Indicative of Nearness to Shores. Geological Society of America Bulle- 
 tin, Vol. XXII, pp. 221-227. 
 
CHAPTER XVIII. 
 OVERLAP RELATIONS OF SEDIMENTARY FORMATIONS. 
 
 Overlap, or the extension of one formation beyond the other, 
 is a structural feature of the greatest significance in stratigraphy. 
 Two kinds of overlap may be recognized, the irregular and the 
 regular or progressive. The irregular overlap of strata, resulting 
 from sudden changes of physical conditions, is more of the nature 
 of an accidental feature, and belongs rather to the general subject 
 of unconformity of formations. While its recognition is of great 
 importance in establishing the progress of events, it has not the 
 stratigraphic significance of the other type. 
 
 PROGRESSIVE OVERLAP. 
 
 Under this term we include the regular overlapping of suc- 
 cessive formations due either to a normal transgressive movement 
 or to a regular regressive movement. According as we deal with 
 marine or non-marine sediments we have (Grabau-3) : (A) The 
 marine progressive or (B) the non-marine progressive overlaps. 
 The former are the more varied in type and will be discussed first. 
 
 A. MARINE PROGRESSIVE OVERLAP. We may dis- 
 tinguish two types of marine progressive overlap: i. Normal 
 transgressive overlap, due to a progressively encroaching sea ; and, 
 2. Regressive or retreatal overlap, due to a progressively retreating 
 sea. Generally a regressive movement is both preceded and fol- 
 lowed by a transgressive movement, so that as a result of this 
 compound progressive overlap a complex type of structure comes 
 into existence. 
 
 The progress of deposition of the clastic sediments on a normal 
 shelving seashore is controlled by two factors : namely, the rate of 
 supply of material, and the rate and direction of change in the rela- 
 tive position of sea-bottom and sea-level. According to the varia- 
 tion of one or both, sedimentation will vary. 
 
 723 
 
724 PRINCIPLES OF STRATIGRAPHY 
 
 Three relations of land and sea may be recognized : 
 
 1. Subsiding land block or rising sea-level. 
 
 2. Stationary sea-level. 
 
 3. Rising land block or falling sea-level. 
 
 Each of these conditions is further complicated by variation in 
 the rate of subsidence, or elevation, and the rate of supply of detri- 
 tal material. In general, rising sea-level produces transgressive 
 movements, except where the supply of detritus is excessive, when 
 stationary or regressive movements are produced. Stationary and 
 falling sea-level produce regressive movements. 
 
 I. RISING SEA-LEVEL OR POSITIVE DIASTROPHIC MOVEMENT. 
 
 A subsiding land block or rising sea-level may be either of local 
 or of world-wide effect. Its cause may be diastrophic movements, or 
 the gentle displacement of the water by the accumulation of sedi- 
 ment on the ocean floor. Such rising of the sea-level produces a con- 
 tinuous transgression of the sea upon the land, i. e., a landward mi- 
 gration of the shore-line. The rate of migration, other things being 
 equal, varies inversely as the steepness of the slope of the coast. 
 Thus a slight depression of a very gentle shore will cause a great 
 transgression of the sea, while even a considerable depression of a 
 steep or vertical coast may produce little or no transgression. In the 
 following discussions, the slope of the land surface affected by the 
 transgression will be considered as a gentle one, such as is pro- 
 duced by a period of prolonged erosion of an old land surface. 
 
 Wilson (9:776*; Rutot-7) has tabulated the possible relationship 
 between the rate of depression of the land (rise of the sea-level) 
 and the rate of supply of detritus, as follows : 
 
 Rate of /-_.-> Rate of 
 
 Depression Uniform *r~ j^f -7^ Uniform supply of 
 
 detritus 
 
 Variable ^ ^Variable 
 
 The simplest conditions are those in which the rate of depression 
 and the rate of supply are both uniform. These alone will be con- 
 sidered; the variable conditions of either one, or of both factors, 
 will produce corresponding variations of the norm to an almost 
 unlimited degree. 
 
TRANSGRESSIVE OVERLAP 725 
 
 With uniform rates of both subsidence and supply, three cases 
 may be considered : 
 
 a. Rate of depression is equal to the rate of supply of 
 
 detritus. 
 
 b. Rate of depression exceeds rate of supply. 
 
 c. Rate of depression is exceeded by rate of supply. 
 
 The first case would result in the production of relatively stationary 
 conditions, if the shore-line were bounded by a vertical face, when 
 a uniform regular amount of detritus equaling the amount of sub- 
 sidence would produce a constant depth of water. With a shelving 
 shore, on the other hand, a uniform regular transgressive move- 
 ment would occur, with a regular and uniform change in the char- 
 acter of the deposit at any given point. The second case will pro- 
 duce a rapid transgressional movement with a less normal suc- 
 cession of formations, while the third will produce either stationary 
 or retreating coast-line, coupled with an increasing amount of 
 subaerial deposition. 
 
 i. Transgressive Movements. 
 
 a. Rate of Depression Equals Rate of Supply. Under these 
 conditions a uniform and progressive overlapping of each later 
 layer over all the preceding ones takes place. Each layer has a 
 rudaceous or coarsely arenaceous texture at the shore, and grades 
 seaward into finer arenaceous and ultimately lutaceous material. 
 If the shore is composed of old crystalline rocks, the rudytes and 
 arenyte,s resulting from their destruction will be largely , siliceous, 
 while the lutytes will be argillaceous and more or less micaceous. 
 The coarse shoreward ends of the beds, when viewed in their 
 ensemble, will appear as a single coarse bed resting upon the old 
 land. From the consideration of its origin, however, it will be 
 seen that no two portions of the bed along a line transverse to 
 the seashore will be of the same age, each seaward portion will 
 be younger than that lying next to it nearer the land. Thus the 
 formation line, limiting the basal conglomerate or sandstone, will 
 run diagonally upward through the planes of synchronous deposi- 
 tion. The basal bed is not generally a conglomerate, for where 
 the sea transgresses upon an old land which has long been subject 
 to subaerial disintegration a basal sandstone will be produced, since 
 there is not coarse material enough to form pebbles. When de- 
 composition has gone on for a long time prior to the transgression 
 of the sea, and when the decomposed material is subjected to a 
 
726 PRINCIPLES OF STRATIGRAPHY 
 
 thorough sorting by the encroaching waters, a nearly pure -silicar- 
 enyte may come to rest directly upon the eroded surface of the 
 crystalline old land. This is finely shown in the basal Palaeozoic 
 contact in portions of the Front Range of the Rocky Mountains, 
 where a nearly pure quartz sandstone rests on an almost perfectly 
 even erosion surface of granite. (Crosby-2.) Where atmospheric 
 agencies have been sufficiently active to disintegrate a granite 
 surface, without, however, reducing the feldspar to clay, the basal 
 sandstone will be a feldspathic arenyte or arkose. Again examples 
 are known where decomposition has affected the underlying crystal- 
 line old land to a considerable extent, but where little sorting of 
 material was accomplished by the transgressing sea, so that the 
 basal bed is a highly argillaceous arenyte. The contact of this with 
 the underlying crystalline basement rock will in consequence not 
 be a sharp one, the crystalline rock grading through a decomposed 
 zone into the overlying sandstone. An example of this indefinite 
 type of contact is seen on Presque Isle near Marquette, Michigan, 
 where the Lake Superior sandstone passes downward into a rock 
 produced by the consolidation of the undisturbed disintegrated sur- 
 face of the basal peridotite. 
 
 A consideration of the progressive landward migration of the 
 coarser deposits under uniform conditions will lead to the recogni- 
 tion that the changes in any given bed, from the shore seaward, 
 will be exactly duplicated by the changes in a given vertical sec- 
 tion from the base upward.* For it will be seen -that the coarse 
 bed deposited directly upon the old sea-floor of crystalline rock is 
 succeeded upward by a somewhat finer bed, since the zone of dep- 
 osition of the coarse material has, by the continuous subsidence, 
 migrated further landward. Thus, as shown in the annexed figure 
 (Fig. 144), the lowest coarse deposits of bed (a) which form the 
 shore zone of that bed are succeeded vertically by the finer deposits 
 of bed (b) made at a somewhat greater distance from the new 
 shore. At this new shore (of bed b) coarse deposits are accumu- 
 lating, but they are beyond the belt'of the former deposition of 
 coarse material. Again a"n advance of the shore to c transfers 
 the shore belt of coarse (rudaceous) deposition in the same direc- 
 tion and by the same amount. Consequently the belt of arenaceous 
 deposits of bed c is likewise transferred shoreward and comes to 
 
 * The variation in texture of deposits due to storms and the corresponding 
 change in the power of waves and currents discussed in a preceding chapter, 
 are here left out of consideration, since they will at best produce only minor 
 variations in the strata. The present discussion deals with formations on a large 
 scale. 
 
TRANSGRESSIVE OVERLAP 
 
 727 
 
 rest on the belt of rudaceous deposits of bed b, just as the arenace- 
 ous deposits of that bed come to rest on the rudaceous deposits of 
 bed a. In like manner the lutaceous deposits of bed c come to 
 rest on the arenaceous deposits of bed b, just as the lutaceous 
 deposits of bed b come to rest on the arenaceous belt of bed a. 
 Two sections, then, made at I and II, will show precisely the same 
 succession in coarseness and kind of material from the bottom up, 
 the only difference being that in section II the lutaceous bed is much 
 thicker than in section I. Erosion, however, may remove so much 
 of the lutaceous beds of section II as to equalize the amount in 
 the two sections. It would, of course, be incorrect to consider each 
 lithic unit in section I to be of the same age as the corresponding 
 lithic unit in section II, for, although there is a similar lithic suc- 
 cession, bed a, and the lower portion of bed b are unrepresented in 
 
 Section I. Section II. 
 
 FIG. 144. Diagram showing regular marine progressive overlap on an old 
 land surface. A basal sandstone occurs everywhere, this grading 
 upward and seaward into lutaceous deposits. At section I the 
 series comprises beds b and c only, but at section II beds a-c are 
 present. 
 
 section I. In general, it is safe to assume that in a case of this 
 kind, where continuous transgression on a uniformly shelving shore 
 has taken place, the basal bed of the section farther up the old shore 
 is of later age than the corresponding lithic bed of the section 
 farther seaward. There are many cases where relationships of this 
 type must be considered in the correlation of strata. 
 
 We have so far considered only, siliceous detrital material de- 
 rived from an old land composed of crystalline or other siliceous 
 rocks. We must now consider, in addition to these, the organic 
 rocks and their clastic derivations, which play so important a role 
 in the sedimentary series accumulating on the sea bottom. As 
 noted in an earlier chapter, purely biogenic stratified deposits are 
 formed by the accumulation of the various organic oozes on the 
 sea-floor, such as foramini feral, radiolarian, diatomaceous or ptero- 
 podan. Where clastic sediments are accumulating very slowly, 
 as at a distance from shore, these organic oozes may constitute 
 an important part, if not most, of the sediment. In such cases, the 
 ooze being a calcareous one, the clay and other lutaceous beds 
 
728 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 forming in quieter water will shade off into calcareous sediments, 
 and may even be entirely replaced by limestones of this type. 
 Where coral reefs or shell heaps are forming off shore, the clastic 
 derivations of these will become commingled with, and shade off 
 into, the terrigenous sediments near shore. As explained in 
 Chapter X, the coarsest fragments will remain near the reef, the 
 calcarenytes coming next, and shading off into the finest calcilutytes. 
 These calcilutytes may be gradually replaced shoreward by siliceous 
 or argillaceous lutytes, or they or the calcarenytes may grade di- 
 rectly into the silicarenytes. Where this latter occurs, we have a 
 seaward change from pure quartz sand (silicarenyte), through cal- 
 ciferous sandstone (calcareous silicarenyte) and siliceous calca- 
 renytes to pure calcarenytes. This change is probably more 
 often observed in the Palaeozoic series than the change from siliceous 
 to argillaceous sediments. (Fig. 145.) 
 
 FIG. 145. Diagram showing regular marine progressive overlap; a basal 
 sandstone is present, but this grades upward and seaward into 
 calcareous deposits. The differences between sections A and C 
 are readily seen. 
 
 Older examples. The type of overlap here described seems to 
 have been by far the most general as recorded in both Palaeozoic 
 and Mesozoic deposits. An illustration is seen in the basal Ordo- 
 vicic sandstone of Ontario, which on Lake Huron lies at the base 
 of the Chazy series, but farther northeast is basal Trenton. The 
 basal Cambric sandstone of Sweden also varies in age from Lower 
 to Upper Cambric, though there is probably a series of unre- 
 corded intervals during which retreat and erosion took place with- 
 out the deposition of a basal sandstone by the readvancing sea. 
 From the evidence of the dreikanter and other structural features 
 it is known that this basal bed represents an old residual sandy 
 covering of terrestrial origin, subsequently encroached upon by the 
 sea. It is not improbable that wherever basal sandstones occur, 
 extending upward through such a long series, as the entire Cam- 
 bric in which there are, moreover, stratigraphic breaks, these sand- 
 
EXAMPLES OF TRANSGRESSIVE OVERLAP 729 
 
 stones are older continental deposits slightly reworked by an ad- 
 vancing sea. This appears also to be the case in the Cambric of 
 North America. The basal Cambric sandstones and conglomerates 
 of the southern Appalachian region underlie the Olenellus-bearing 
 shales and limestones, while those of the Oklahoma and Ozark 
 regions underlie beds generally referred to the Middle Cambric. 
 Finally, in the upper Mississippi Valley the St. Croix sandstone 
 series actually contains in its upper portion the Cambro-Ordovicic 
 transition fauna. In many cases this northern "Potsdam" sand- 
 stone shows evidence of continental origin in pre-ma"rine time by 
 the occurrence of well-marked torrential cross-bedding in parts 
 which apparently have not been reworked. In the North American 
 Cambric there are numerous distinct breaks, the magnitude of 
 which is not yet fully ascertained, except that it is now generally 
 recognized that above the Middle Cambric there is a hiatus corre- 
 sponding to nearly the whole of the Upper Cambric of the Atlantic 
 coast. These breaks are, as a rule, not marked by retreatal inter- 
 calated sandstones. Further examples of overlap involving large 
 portions of a system are shown in the North American Palaeozoic 
 by the entire absence of the Lower Cambric at St. John, New 
 Brunswick, where the basal marine elastics belong to the Middle 
 Cambric, while only 30 miles northeastward, at Hanford Brook, 
 the Lower Cambric (Etcheminian) has a thickness of 1,200 feet. 
 In Cape Breton this thickness measures several thousand feet. The 
 well-known fact that the Cambric of Bohemia begins with the 
 Paradoxides beds of Middle Cambric age, while Lower Cambric 
 beds occur in western Europe, shows a pronounced eastward trans- 
 gression of the Cambric sea in Europe with corresponding overlap 
 of formations. 
 
 The 'basal Mesozoic sandstone of the Texas and Mexico re- 
 gions furnishes another typical example of a rising basal bed in a 
 transgressive series. In central Mexico this basal .sandstone lies 
 beneath Upper Jurassic limestones ; on the Tropic of Cancer it 
 has risen into the base of the Comanchic; on the Texas-Oklahoma 
 line it has risen through the Lower Comanchic (Trinity) and lies 
 at the base of the Fredericksburg or Middle Comanchic; and, 
 finally, in central Kansas it has passed up to near the base of the 
 Upper Comanchic or Washita series. There are, however, one pro- 
 nounced (Paluxy) and several smaller sandstone members inter- 
 calated in the limestone series, and these mark either shoaling or 
 an actual emergence of the sea-bottom. 
 
 In this case, as in the Cambric, the basal sands are most prob- 
 ably of continental origin reworked by the transgressing Coman- 
 
730 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 chic sea. These basal sands indicate by their purity a distant source 
 and long transportation, and the time interval during the Triassic 
 and early Jurassic periods was ample to make possible an extended 
 accumulation of widespread river and eolian sands derived in large 
 part from the crystallines of the Canadian and western uplands, 
 added to no doubt by contributions from uncovered Palaeozoic and 
 older sediments. A striking case of change in lithic character with 
 progress of transgression is seen in the Cretacic series of south- 
 east England and in that of northeast Ireland and the west of 
 Scotland (Mull and Morvern). (Fig. 146.) In both cases the series 
 begins with basal conglomerates, followed by sands, clays, and 
 
 FIG. 146. Diagram showing overlap and change in lithic character of the 
 Cretacic formations of England and Ireland, from southeast to 
 northwest. 
 
 greensands. This is followed by (2) Glauconite sands and marls, 
 then by (3) marls and Greensand chalk, passing into glauconitic 
 and argillaceous chalk, and, finally, by (4) pure white chalk. In 
 England the basal series (i) rests on the Weald clays, and is of 
 Aptien age, while in Ireland it rests on Lias and is of Cenomanien 
 age. In Scotland it also is of Cenomanien age. The next lithic 
 series (No. 2) is of Albien (Gault) age in England, but of Turonien 
 age in Ireland. The succeeding marls and Greensand chalk (No. 3) 
 are of Cenomanien age- in England, but of lower Senonien age in 
 Ireland. Finally, the white chalk of England begins in the Turo- 
 nien, but in Ireland and Scotland it occurs only in the upper Seno- 
 nien. This illustrates not only the progressive overlap of the forma- 
 
OVERLAP ON PENEPLAIN 731 
 
 tions, but also the progressive overlap of facies in the same direc- 
 tion. 
 
 b. Rate of Depression Exceeds Rate of Supply. Under these 
 conditions there will be a rapid transgression of the sea, and the 
 meager supply of detritus will be spread thinly over the sea-floor, 
 or, if the depression is a rapid one, in many places deeper water 
 deposits may accumulate upon the original old land surface. Such 
 cases are known and are probably less infrequent than one is led 
 to suppose from the scattered observations available in the litera- 
 ture. Wilson (8 '.148) cites the case of a calcareous conglomerate 
 of Black River age, carrying angular quartz fragments, molds of a 
 Cameroceras and fragments of crinoid stems, which rests directly 
 upon the Archaean red granite near Kingston Mills, Ontario. From 
 the basin of the Moose River, Devonic corals have been reported, 
 with their bases attached to an Archaean abyssolith. (Parks-6 -.188.) 
 As under normal conditions of transgression, with an equivalent 
 supply of detritus, the change in lithic character is a gradual one 
 from coarse at the base to fine at the top, so, in any rapid or sudden 
 transgression, we would expect to find an abrupt change from 
 coarse material to fine, or from near-shore to off-shore deposits. 
 Conversely, where we find a sudden change from coarse beds be- 
 low to fine beds above, we may postulate a sudden relative change, 
 either a sudden transgression or a sudden diminution in the supply 
 of material. Sometimes a sudden transgression will transfer the 
 shore zone, from which much of the detrital material is supplied, 
 from one lithic formation to another, when the character of the 
 deposit will change. Thus an abrupt change of sea-level may 
 transfer the shore from a broad outcropping belt of quartz sand- 
 stones to a parallel belt of limestones, the sandstones being covered 
 by the encroaching sea. As a result, the deposition of quartz sands 
 may cease, and fine calcareous muds derived from the erosion of 
 limestones may be deposited upon the coarse quartz sands without 
 transition. Such a change appears to have taken place in eastern 
 North America in late Siluric time, effecting a change from the 
 Salina silicarenytes (Binnewater sandstones) to the fossiliferous 
 limestones and water-limes (Rosendale cement) which overly them. 
 
 Where transgression takes place over an old peneplain surface, 
 on which residual soil has accumulated during the long period of 
 exposure, this ancient soil may be incorporated, without much 
 change, as a basal bed. Where the soil is lutaceous, especially 
 where it is a residual clay containing much carbonized vegetable 
 material, as in the case of an old swamp-covered surface, a black 
 carbonaceous mud will constitute the basal layer, which is sue- 
 
732 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 ceeded upward by other beds of fine-grained terrigenous material 
 or by limestones derived from organic sources. Such a black 
 basal shale may also result from the washing of the residual black 
 soil from the surface of the plain into the shallow encroaching 
 sea. In any case, the basal black shale will rise diagonally across 
 the planes of synchroneity, and, although it will constitute a lithic 
 unit, it is not a stratigraphic unit, but made up of the shale ends 
 of a successive series of deeper water formations. This relation- 
 ship is shown in the following diagram. (Fig. 147.) An example 
 of this type of basal bed is found in the Eureka (Noel) black shale 
 of the Mississippi Valley. This formation rests generally upon 
 eroded Ordovicic strata, the contact being a disconformable one. 
 Upward it passes into limestones, which in southwestern Missouri 
 
 /~ **/ 7( B l ,L /^wJLSJbJ 
 
 FIG. 147. Diagram of overlap of marine strata on basal black shale in south- 
 western Missouri and northern Arkansas. 
 
 are of Chouteau age, the shale itself carrying Kinderhook fossils, 
 while in northern Arkansas it is succeeded by limestone carrying 
 Burlington fossils. The same relationship exists in the southern 
 Appalachian region, where the black shale has risen into the base 
 of the Keokuk, if not higher. (Grabau~3.) 
 
 T2. Regressive Movements. 
 
 c. Rate of Depression Is Exceeded by Rate of Supply. In this 
 case accumulation will go on so fast as to fill in the shallow shore 
 zone, when the coarse material begins to extend seaward, progres- 
 sively overlapping the off-shore deposits in a seaward direction. 
 We will thus have a gradual change in the character of the sedi- 
 ment from the lutaceous material at the bottom to arenaceous and 
 sometimes coarser terrigenous material. This material will all be 
 land-derived, and, as it is deposited rapidly, not a very thorough 
 sorting can generally be expected. As the shore migrates seaward, 
 subaerial deposits may accumulate above it. (Wilson-p: 
 
REGRESSIVE MOVEMENTS 733 
 
 Local temporary increase in the rate of supply may be due to 
 causes not readily determinable, but widespread and persistent 
 changes must be regarded as indicative of climatic change. Be- 
 fore we accept such a climatic change, however, as the cause of a 
 seaward migration of terrigenous deposits we must satisfy our- 
 selves, if possible, that the migration in question is not due to a 
 change in the rate of subsidence, the climatic conditions and, there- 
 fore, the rate of supply of detritus remaining the same. For it is 
 evident that a gradual diminution of the rate of subsidence would 
 produce practically the same results as a corresponding increase 
 in supply. 
 
 II. STATIONARY SEA-LEVEL. 
 
 When the supply of detritus continues uniformly, while the 
 sea-level remains stationary, a regression of the seashore will take 
 place, but at a faster rate than would be the case if subsidence 
 still continued, though at a diminished rate. The shore zone would 
 creep out over the deeper water deposits, the transition from the 
 one to the other being rather more abrupt than in the case of a 
 slowly subsiding sea-floor. On the whole, however, stationary 
 conditions produce a change of sediment differing in degree only 
 from that incident upon a diminution in the rate of subsidence. 
 
 III. FALLING SEA-LEVEL. 
 
 The falling sea-level or rising land block is accompanied by a 
 continuous regression of the seashore, and a consequent seaward 
 migration of the shore zone with its attendant deposits. If the 
 emergence is not too fast the waves will be able to remove much 
 of the formerly deposited shore detritus and carry it seaward into 
 the shoaling off-shore districts. Thus a bed of sand or conglom- 
 erate will advance seaward over the finer off-shore deposits, com- 
 ing to rest upon these often without transition beds. Further- 
 more, the continuous movement of the clastic shore derivatives 
 will tend, in the coarser material, to a perfect rounding off of the 
 pebbles, and in general to a destruction of all but the most resistant 
 materials. Thus a much washed-over sandstone or conglomerate 
 may come to consist entirely of quartz, constituting a pure silica- 
 renyte or silicirudyte. It is probably not saying too much that all 
 pure quartz elastics, derived from a complex crystalline old land, 
 and resting abruptly upon a clayey or calcareous off-shore deposit, 
 
734 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 represent the seaward spreading shore zone of a rising sea-floor, 
 unless they are referable to continental deposits. 
 
 Characteristics of Regressive Deposits. 
 
 As the retreat of the sea from the land may under normal condi- 
 tions be considered a process occupying a greater or less amount 
 of time, it is evident that deposition at a distance from shore need 
 not be interrupted. Thus, while within the zone of retreat for any 
 given time period, no sedimentation will occur, such sedimentation 
 may, nevertheless, go on at a regular rate beyond this zone. In 
 other words, a certain thickness of off-shore deposits must be 
 considered the depositional equivalent of a given time period, 
 which in the shore zone is represented by a given amount ot re- 
 
 FIG. 148. Diagram illustrating regressive overlap (off-lap) and the forma- 
 tion of a sandstone of emergence Or-v) into which the shore- 
 ends of the successive members of the retreatal series (a-d) 
 grade. 
 
 treat. Thus it is brought about that each successive formation of 
 the retreatal series extends shoreward to a less extent than the 
 preceding one. As each formation or bed passes shoreward into 
 a coarser clastic it is evident that the shore ends of all the forma- 
 tions deposited during the retreat will together constitute a stratum 
 of sandstone or conglomerate which in age rises seaward, since in 
 that direction it is progressively composed of the ends of higher 
 and higher formations. These relationships are shown in Fig. 148, 
 where it will be noted that the diagonal rise of the shore-formed 
 stratum is from the shore seaward, whereas in transgressive move- 
 ments the shore-formed stratum or basal bed rises diagonally land- 
 ward. In the series shown in the diagram, the beds a-d were suc- 
 cessively laid down during the retreat of the sea from A to B. 
 Each later formed bed comes to an end before it has reached the 
 shoreward end of the preceding one, and each formation grades 
 from a clayey or calcareous character landward into silicoarena- 
 ceous character. Thus b reaches landward to a less extent than a, 
 the shore end of which, composed of quartz sands, remains ex- 
 
REGRESSIVE DEPOSITS 735 
 
 posed. The shore end of b is also composed of quartz sands, since 
 during the formation of b the shore has migrated seaward. In like 
 manner c does not entirely cover b, and d does not wholly cover 
 c, each ending .in a sand facies. Thus the sand ends of all the beds 
 will be exposed at or just above sea-level, and constitute a continu- 
 ous sand formation, which, however, is not of the same age at 
 any two points along a line transverse to the direction of the shore. 
 Such a sand formation will, however, be mapped as a unit, and re- 
 ceive a formational name. If the basal portion of such a sand for- 
 mation is fossiliferous, it will contain in a seaward direction the 
 fossils of successively higher formations. Thus the portion of the 
 sandstone formation x, y in Fig. 148 will at x contain the fossils 
 of formation a, and at 3; the fossils of formation d, while -between 
 these points it will contain the fossils of b and c, where it forms 
 the end of these respective formations. When the land is suffi- 
 ciently elevated during the retreat of the sea, stream erosion will 
 set in and the material left by the retreating sea may be removed 
 by the streams. Furthermore, if elevation of the land is responsible 
 for the retreat of the sea, the streams coming from this higher 
 land will bring more detritus, and hence, where erosion is not 
 going on, deposition by rivers will further elevate the surface of 
 the emerging coastal plain. The same thing is true also if the 
 regressive movement is due to an increase in the supply of detrital 
 material. In either case, pebbles and sands derived through the 
 erosion of the old land or of old conglomerates and sandstones 
 may be carried out for great distances over this emerging surface, 
 while wind-assorted sands, with their grains rounded and pitted 
 from attrition, may also accumulate over this surface. The peculiar 
 structures of both torrential and eolian sands, i. e., cross-bedding, 
 ripples, etc., may thus be incorporated in this retreatal sandstone. 
 Remains of land-plants and of land and fresh water animals may 
 readily be entombed in the deposits thus accumulating upon the 
 flat plain of retreat, and even coal beds may form and become em- 
 bedded in sandstones the bases of which vary in age from place 
 to place. 
 
 Burial of Retreatal Sandstones by Subsequent Transgressive 
 
 Movements. 
 
 When the regressive movement of the shore has come to an 
 end, and transgressive changes recommence, the upper portions of 
 these migratory shore deposits may be worked over once more, and 
 now partake of the character of a basal sandstone or conglomerate. 
 
PRINCIPLES OF STRATIGRAPHY 
 
 As the shore zone advances landward, finer deposits will be laid 
 down over the coarser basal bed and thus the transgressive portion 
 of such a sandstone or conglomerate will pass diagonally across the 
 planes of synchroneity. The deposit resulting by the time the 
 shore zone has returned to its former position will therefore be 
 a composite formation including within it a hiatus, which may rep- 
 resent a considerable time interval, but is not recognizable by any 
 structural character. The encroaching sea will work over the sand 
 dune deposits and thus water-laid sandstone beds, composed of 
 rounded translucent quartz grains and well stratified, will result. 
 In the upper part of these worked-over sandstones marine shells 
 and other remains may be included, the age o<f which changes 
 shoreward, since the transgressive portion of this sandstone repre- 
 sents successively the ends of higher and higher formations, after 
 the manner of a true basal sandstone of a transgressive series. 
 
 FIG. 149. Diagram showing the relationship of the strata in five successive 
 sections, in a compound regressive-transgressive series. The 
 intercalated sandstone x y encloses the hiatus. (See Fig. 150.) 
 
 The recognition of an intercalated shore formation of great 
 areal extent between off-shore sediments as the product of combined 
 regressive and transgressive movement must be based on a com- 
 parison of sections taken at intervals over the entire area covered 
 by the formation in question. Such sections will show the inter- 
 calated shore formation (sandstone or conglomerate) to be in 
 more or less intimate association with the lower beds of the under- 
 lying formation and the higher beds of the overlying formation at 
 their shoreward ends, but, away from the shore, higher members of 
 the lower formation and lower members of the higher formation 
 will progressively appear until near the line of farthest retreat 
 both lower and upper formation will be complete, while beyond that 
 the intercalated bed will gradually lose its shore character and 
 merge with the enclosing formations. This character of the sec- 
 tions is shown in the preceding diagram (Fig. 149). Formation 
 A, consisting of divisions J to 4, and formation B, consisting of 
 
COMPOUND OVERLAP 
 
 737 
 
 divisions a to d, are both complete in section 5, which marks the 
 farthest limit of retreat of the sea. Bed x, the intercalated shore 
 formation, fades away in this section. In section 4 all the members 
 of both formations -are represented, but divisions 4 and a are not. 
 complete, while the intercalated bed x is prominent. In section 3, 
 divisions 4 and a are wanting, and in section 2, divisions j and b are 
 likewise wanting. In section I, finally, all except the lowest divi- 
 sion (/) of formation A, and the highest (d) of formation B, are 
 missing. It would be obviously wrong to correlate division / of sec- 
 tion I w r ith the whole of formation A as exposed in section 5, or 
 division d of section I with the whole of formation B of section 5. 
 Yet such correlations have not infrequently been made in the past. 
 In each of the above sections the intercalated sandstone or con- 
 glomerate may be intimately related to both overlying and underly- 
 ing formations, and contain tjieir fossils. Such a relation would 
 
 FIG. 150. Diagram of a compound regressive-transgressive series, showing the 
 seaward decrease of the hiatus between the upper and lower 
 part of the series. (See Fig. 149.) 
 
 show that the actual hiatus is represented by the middle part of the 
 intercalated bed, which middle part may not infrequently be repre- 
 sented by continental deposits. Yet so intimate are the physical re- 
 lationships between the bottom, middle and top of the intercalated 
 formation that a separation into more than one formation is im- 
 possible. Thus in section I the intercalated formation x may have 
 all the characters of a formational unit or a single stratum, and may 
 grade upward into division d and downward into division I, so that 
 to all appearance continuous deposition obtained in this locality. If 
 the respective ages of divisions d and / are recognized, formation x 
 will be likely to be considered the depositional equivalent of divi- 
 sions 2 to 4 and a to c of section 5. Such is indeed the fact, except 
 that the central portion of x, the terrestrial portion, whether repre- 
 sented by continental deposits or an unrecognizable erosion plane, 
 represents all but the upper fraction of division c, and the lower of 
 division 2. The hiatus or stratigraphic break thus represented in 
 
738 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 the middle portion of the intercalated formation is a constantly de- 
 creasing one from section I to section 5. In each section it covers 
 the interval of time between the emergence of the sea bottom at that 
 point during the regressive movement and its resubmergence during 
 the succeeding transgressive movement. This relationship may be 
 expressed in the preceding diagram. (Fig. 150.) The following 
 diagrammatic sections (Fig. 151) show the relation of a series of 
 strata recording a transgressive movement followed by a regressive 
 and again by a transgressive movement, x-z is the basal sandstone 
 bed of the transgressive series, x-y the intercalated sandstone of the 
 
 FIG. 
 
 151. Diagram showing the relationships of the strata In a transgressive- 
 regressive-transgressive series. Basal sandstone x and inter- 
 calated sandstone x y are both present. 
 
 regressive-transgressive series. Beds i to 3 are the first series of 
 transgressive formations, beds 4 to 7 the regressive formations, and 
 beds 8 to 12 the second series of transgressive formations. 
 
 EXAMPLES OF INTERCALATED SANDSTONES FROM THE PALAEOZOIC 
 AND MESOZOIC FORMATIONS OF NORTH AMERICA. 
 
 The Saint Peter Sandstone. This is an exceedingly pure quartz 
 sandstone of rounded, well-worn and pitted grains of nearly uni- 
 form size in any given region. It is widely distributed in central 
 North America, lying generally between a member of the Chazyan 
 and one of the Beekmantownian formations of the Ordovicic. In 
 Minnesota it lies beneath the upper beds of the Stones River (Up- 
 per Chazyan), grading upward into and containing some of its 
 characteristic fossils in the upper layers. Its base rests upon lower 
 Beekmantown (Shakopee), into which it also grades in many sec- 
 tions, though in others it forms a sharp contact or even rests on an 
 
INTERCALATED SANDSTONES 
 
 739 
 
 erosion plane of the dolomite. Where conformable it may contain 
 lower Beekmantown fossils. Sometimes the lower beds are slightly 
 disturbed, while the upper ones do not partake of such disturbance. 
 This indicates an interval of time after the deposition of the lower 
 beds, during which they were disturbed, and after which the higher 
 strata were deposited upon them. Southward, higher members of 
 the Beekmantown series come in beneath the Saint Peter sandstone 
 and lower members of the Chazyan above it. In the Arbuckle 
 Mountains the upper bed (here known as the Simpson formation) 
 is about 2,000 feet thick, while the Beekmantown below the Saint 
 Peter is of similar thickness. This sandstone thus has all the char- 
 acteristics of a regressive-transgressive sandstone intercalated be- 
 tween limestones, and may be regarded as a typical example. (Gra- 
 bau-3; 4.) (Fig. 152.) 
 
 FIG. 152. Diagram representing the Cambric, Lower Ordovicic (Beekman- 
 town), and Middle Ordovicic (Chazyan) formations, and the 
 compound transgressive-regressive-transgressive overlaps between 
 Oklahoma and Minnesota. The intercalated sandstone is the 
 Saint Peter. 
 
 The Dakota Sandstone. This sandstone of Mid-Cretacic age has 
 essentially the same relation to the enclosing calcareous strata as has 
 the Saint Peter. It contains, besides, an abundant flora of terres- 
 trial plants, so that its value as a record of complete emergence be- 
 comes even greater. In southern Kansas this sandstone lies at the 
 top of the Fredericksburg division of the Comanchic, while in Texas 
 it lies on top of the Washita or LTpper Comanchic. In either case 
 there is commonly a gradation from the limestones and shales to 
 the sandstones. The top of this sandstone passes upward into the 
 marine Eagle Ford formation in Texas, while further north, in 
 Colorado and the Dakotas, it grades into the much later Benton 
 beds. 
 
 B. NONMARINE PROGRESSIVE OVERLAP. This term 
 is applied to the large structure normally produced during the 
 formation of a great fan or subaerial delta, from the wash carried 
 by the streams from the mountains and deposited upon the plains 
 adjoining. Such a subaerial fan will of course grow in extent year 
 
74 o 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 by year, and in so growing the latest deposits, whether derived from 
 the mountain or whether obtained through the reworking of the 
 previously deposited portion, will as a rule extend further out into 
 the plain than did those of previous periods of deposition. In other 
 words, each later formation will overlap the previous ones by a 
 margin commensurate with the increase in the size of the fan, and 
 beyond the margin of the previously formed bed it will come to rest 
 directly upon the floor of the plain. This overlapping of later 
 formed over earlier ones will of course be a progressive one if .the 
 growth is continuous. The essential point of difference between this 
 type of overlap and that formed in a transgressing sea is that in 
 the subaerial fan the formations will primarily overlap one another 
 away from the source of supply of the material, while in the ma- 
 rine progressive overlap the overlap is toward the source of supply 
 of the material. The following diagrams will illustrate this differ- 
 
 FIG. 153. Diagrams illustrating the relationship of the strata in nonmarine 
 progressive overlap (a) and marine progressive overlap (b). 
 The source of the material in each case is on the left. 
 
 ence, the source of supply in each case being on the left. (Figs. 
 153, a, b.) It should, however, be noted here (Barrell i) that at 
 the head of the delta an overlap toward the source of supply may 
 occur, since with the aggradation of the delta plain and the conse- 
 quent lowering of the river grade deposition may commence farther 
 upstream. Such effects are seen in interior basins, where the upper 
 beds extend farther toward the mountains from which the material 
 has been derived. It appears to be shown also in the case of the 
 Newark formation, where the upper beds extend farther north, 
 overlapping the lower ones. (Kummel-5 '.48.) It may, however, 
 be questioned whether headward overlapping of the formations is 
 ever of marked character, since it is necessarily confined to the 
 stream channels supplying the detritus and probably does not spread 
 greatly in a lateral direction. In any case it cannot be compared in 
 extent and importance with the overlap on the margin of the fan, 
 which is always away from the source of supply. 
 
 The coarsest material of the subaerial fan will of course be de- 
 posited near the head of the delta. Finer material may be carried 
 
NONMARINE TRANSGRESSIVE OVERLAP 741 
 
 out for hundreds of miles across such a delta, as is abundantly 
 shown by the delta plains of the Indus and Ganges and of the 
 Huang-ho River. Occasionally pebbles well rounded may be car- 
 ried out to great distances, and this is especially true of the well- 
 rounded pebbles derived from older conglomerates. When the sur- 
 face of the delta has become very flat, drainage obstructions may 
 take place, in which case swamps and the deposit of carbonized 
 plant remains will form. Thus a fossil delta of this type may in- 
 clude coal seams, the tops of which may again be eroded, or covered 
 with a moderately coarse river deposit. 
 
 An essential feature of this type of overlap in purely nonmarine 
 sediments is the relation which the beds have to the surface on 
 which the overlapping edges rest. If this is an old land surface, 
 
 N.VM 
 
 FIG. 154. Diagram showing the westward overlap of the various members of 
 the Pottsville series of eastern North America, upon the old 
 erosion surface of pre-Pottsville age; the surface of supply is in 
 the southeast. 
 
 *. e., without contemporaneous sediments of .a marine origin, the 
 evidence of the nonmarine origin of this overlapping series is com- 
 plete. For it is manifestly inconceivable that clastic sediment will 
 be carried across a body of water and be deposited upon the oppo- 
 site shore in such a relationship as to suggest marine transgressive 
 overlap. 
 
 THE POTTSVILLE SERIES, A TYPICAL EXAMPLE OF NONMARINE 
 PROGRESSIVE OVERLAP. (Fig. 154.) 
 
 This is a deposit of quartzose elastics, consisting for the most 
 part of rounded quartz pebbles embedded in a matrix of sand. In 
 the eastern area the conglomerate is coarsest, the pebbles often 
 reaching a diameter of several inches. They consist also of a 
 greater variety of material, but westward, where the pebbles are 
 smaller, scarcely any but those of quartz remain. Several distinct 
 coal beds with associated shales occur, making identification of 
 
742 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 horizons possible. The formation is thickest in the eastern Appa- 
 lachians and thins away westward by failure of the lower beds and 
 overlap of the higher. The lowest beds are found in two localities in 
 the eastern area, near Pottsville, Pennsylvania, and in the Poca- 
 hontas region of West Virginia and Virginia. From these two cen- 
 ters the deposits spread northward, westward and southwestward, 
 each later division overlapping the preceding ones, until in western 
 
 FIG. 155. Diagram showing replacing overlap of a nonmarine series over a 
 marine one. 
 
 Pennsylvania and Ohio only the highest members of the series are 
 present. Since the source of these beds can only be in the eastern 
 Appalachians, where alone rocks capable of furnishing such ma- 
 terial exist, the overlap becomes one away from the source of sup- 
 ply. Such an overlap might perhaps be produced under water if 
 the overlapping marine sediments belonged to a spreading sub- 
 marine delta. In this case the beds would become increasingly finer 
 around the periphery of the submerged delta, and they would merge 
 
 
 FIG. 156. Diagram showing the relationship of the nonmarine Catskill and 
 the marine' Chemung in eastern North America. A Devonic ex- 
 ample of replacing overlap. 
 
 into deposits of purely marine origin. Nor would the delta be of a 
 size comparable to that of the Pottsville, which by its character, its 
 coal beds and its overlap relations is shown to be of subaerial ori- 
 gin. There are to be sure one or more reported horizons of marine 
 faunas, a brachiopod fauna having been found in the middle Potts- 
 ville (Horsepen) as far north as Sewell, on New River. If these 
 organisms really indicate marine conditions and not secondary in- 
 clusions, this can only mean a momentary invasion of the delta 
 area from a neighboring arm of the sea. Naiadites and "Spirorbis" 
 have been found in the Lower Lykens division of the anthracite 
 
REPLACING OVERLAP 
 
 743 
 
 region of Pennsylvania, but these organisms do not necessarily in- 
 dicate marine conditions. 
 
 REPLACING OVERLAP. This type of overlap occurs 
 
 c. 
 
 when a series of clastic sediments of terrestrial origin replaces a 
 typical oceanic or thalassic series, or where continental elastics re- 
 
 
 FIG. 157. Diagram showing the westward replacing overlap of the Utica 
 shale on the Trenton limestone, both being marine formations, 
 but one (the Utica) terrigenous and the other thalassigenous. 
 
 place those formed in the sea (Fig. 155). The latter is associated 
 only with a retreating seashore, and the overlapping of the nonma- 
 rine beds does not take place on the old land surface, but upon previ- 
 ously deposited and all but contemporaneous marine beds. Along 
 the border line the two will blend, and it will appear as if the non- 
 
 Appalaehlan Reffln 
 
 interior Region 
 
 Continental Srl 
 
 FIG. 158. Diagram showing replacing overlap of terrigenous marine, fol- 
 lowed by continental sediments on the east over marine lime- 
 stones, etc., on the west. 
 
 marine series overlay the marine series, though in reality it is a case 
 of replacement of the one by the other. A typical example of such 
 a progressive replacement is seen in the Catskill sandstone, which 
 as a nonmarine formation spread westward from its centers of ori- 
 gin, of which it appears there were at least two. The correspond- 
 
744 PRINCIPLES OF STRATIGRAPHY 
 
 ing marine beds are the Chemung sandstones and shales, which may 
 be regarded as the submerged continuations of the Catskill beds. 
 Oscillatory conditions are indicated by occasional intercalations of 
 the marine between the nonmarine layers. In the eastern area the 
 series is represented wholly by the nonmarine Catskill; in the 
 western it is represented wholly by the marine Chemung. Between 
 these extremes marine Chemung is always overlain by nonmarine 
 Catskill. These relationships are shown in the diagram on page 
 742. (Fig. 156.) 
 
 This type of overlap, though away from the source of supply, 
 is not, however, limited to nonmarine deposits. It may likewise be 
 shown by a spreading clastic shore deposit, which gradually re- 
 places a limestone of neritic origin without actual emergence of the 
 zone of shore deposits occurring. Or a current-borne type of ter- 
 rigenous sediment may progressively replace a limestone of neritic 
 origin. Examples of such replacement .are found in the changing 
 facies of the Trenton limestones, which (Grabau-4) are gradually 
 replaced westward by the spreading Utica * type of deposit, which 
 is of near-shore and probably shallow-water origin. This is illus- 
 trated in the diagram on page 743 (Fig. 157). A combination of 
 this type and the replacing by sediments of continental origin is 
 shown in Figure 158 on page 743, involving the Upper Ordovicic 
 and Lower Siluric deposits of eastern North America. 
 
 BIBLIOGRAPHY XVIII. 
 
 1. BARRELL, JOSEPH. 1912. Criteria for the Recognition of Ancient 
 
 Delta Deposits. Geological Society of America Bulletin, Vol. XXIII, 
 PP. 377-446. 
 
 2. CROSB Y, WILLIAM O. 1899. Archaean-Cambrian Contact near Manitou, 
 
 Colorado. Bulletin of the Geological Society of America, Vol. X, pp. 
 141-164. 
 
 3. GRABAU, AMADEUS W. 1906. Types of Sedimentary Overlap. Bulle- 
 
 tin of the Geological Society of America, Vol. XVII, pp. 567-636. 
 
 4. GRABAU, A. W. 1910. Physical and Faunal Evolution of North America 
 
 During Ordovicic, Siluric and Early Devonic Time. In "Outlines of 
 Geological History," etc., Chapter IV. t 
 
 5. KUMMEL, HENRY B. 1898. .Annual Report of the State Geologist 
 
 of New Jersey for 1898. New Jersey Geological Survey. 
 
 6. PARKS, WILLIAM ARTHUR. 1899. The Nipissing-Algoma Boundary 
 
 (Ontario). Ontario Bureau of Mines, Vol. VIII, pp. 175-196. 
 
 * Using this term in its broader sense, in which it is practically equivalent 
 to the whole of the Trenton. 
 
BIBLIOGRAPHY XVIII 745 
 
 7. RUTOT, A. 1883. Les Phenomenes de la Sedimentation Marine. Etudies 
 
 dans leur Rapports avec la Stratigraphie regionale. Bulletin du Muse"e 
 Royal d'histoire naturelle de Belgique, Tome II, pp. 41-83. 
 
 8. WILSON, A. W. G. 1901. Physical Geology of Central Ontario, Canadian 
 
 Institute Transactions, Vol. VII, pp. 139-186. 
 
 9. WILSON, A. W. G. 1903. The Theory of the Formation of Sedimentary 
 
 Deposits. Canadian Record of Science, Vol. IX, pp. 112-132. 
 
CHAPTER XIX. 
 METAMORPHISM OF ROCKS/ 
 
 GENERAL DEFINITIONS. The term metamorphism, from the 
 Greek /utera, interchange, and fiop<?7 form (+ism), has been 
 applied to the process of alteration of rock masses in any manner 
 whatsoever. The product of such metamorphism is metamorphic 
 rock, often an entirely new substance so far as form and other 
 physical characters are concerned. It is true that the term is sel- 
 dom used in the comprehensive sense, metamorphism being gener- 
 ally considered as brought about by the agencies of heat and pres- 
 sure, due to contact with heated bodies, or from being subject to 
 dynamic disturbances. There can be no question, however, that 
 these are only special phases of metamorphism, and that they can- 
 not be separated genetically from the more quiet processes of altera- 
 tion to which rocks are subject under ordinary physical conditions. 
 As such, the weathering of rocks must be included. Metamorphism 
 may bring about a change in one or more of the following charac- 
 ters : composition, texture, structure. The change in composition 
 may be chemical alteration or mineralogical change, new minerals 
 appearing in a rock as a result of metamorphism, and old minerals 
 may disappear. Texture may be changed completely, as from compact 
 limestone to crystalline marble, or special textures, characteristic of 
 metamorphic rocks, may be produced, such as cataclastic , parallel 
 orientation, etc. Original structures, such as flow structure, stratifi- 
 cation, etc., may be obliterated and new ones produced, such as 
 cleavage, fissility, joints, slatiness, schistosity and gneissosity (Van 
 Hise-34). 
 
 THE FORCES PRODUCING METAMORPHISM. The forces at work 
 in the production of metamorphism are given by Van Hise (34:45) 
 as: I, chemical energy; 2, gravity; 3, heat and light; while the 
 agents through which these work upon the rocks are: (a) gases, 
 (b) liquids, and (c) organic compounds. Organic compounds are 
 mainly active in the surface belt where weathering of rocks takes 
 
 746 
 
METAMORPHISM 747 
 
 place, but gaseous and liquid solutions * are agents everywhere 
 present and active, within the known crust of the earth. 
 
 THE REGIONS OF METAMORPHISM. The regions where meta- 
 morphism of various kinds takes place are classified by Van Hise 
 (34:4^), according to depth, as follows: 
 
 I. The zone of katamorphism, or that zone in which simple 
 compounds are produced from more complex ones, comprising (a) 
 the belt of weathering, extending from the surface to the level of 
 ground water, and (b) the belt of cementation, extending from the 
 ground-water level to the next zone. 
 
 II. The zone of anamorphism, or that zone in which complex 
 compounds are produced from simple ones. 
 
 Characteristics of the Zones of Mefamorphism. The belt of 
 weathering is the region of rock destruction; the belt of cementation 
 is the region of rock construction and the zone of anamorphism the 
 region of rock reconstruction. The zone of katamorphism is also the 
 zone of fracture of rocks, where openings may exist. Van Hise has 
 calculated that the maximum depth of this zone cannot be greater 
 than 12,000 meters, and in most cases is probably much less. The 
 zone of anamorphism also corresponds to the zone of rock flowage, 
 where the pressure is greater than the strength of the rocks, and 
 deformation will take place without fracture, but with rock flowage, 
 which will not permit the existence of empty pore spaces. 
 
 Recent experiments on rock flowage made by Professors F. D. 
 Adams (2) and L. V. King (21) at McGill University, Montreal, 
 have shown that cavities can exist at much greater depths than 
 10,000 meters. They placed cylinders of granite, with holes bored 
 through them, in a testing machine, and subjected them for seventy 
 hours to a pressure of 96,000 pounds per square inch at a temper- 
 ature of 550 C. After the experiment it was found that the hole 
 was unchanged. The pressure obtained corresponded to that occur- 
 ring at a depth of .about 15 miles, but the temperature was that esti- 
 mated to prevail in the earth's crust at a depth of only eleven miles. 
 
 * Solutions have been defined as "homogeneous mixtures which cannot be 
 separated into their constituent parts by mechanical means" (Ostwald). They 
 may consist of gases mingled with other gases, with liquids or with solids, of 
 liquids mingled with liquids or with solids, and of solids mingled with solids. 
 "The solutions resulting from these various combinations may be gases, liquids, 
 or solids or partly two or all." (Van Hise~34:5p). The gases important in 
 rock alteration are oxygen (O 2 ) sulphur (S s to S 2 ) water vapor (H 2 O), ammonia 
 (NH 3 ), carbon dioxide (CO 2 ), sulphurous oxide (SO 2 ), boric acid (H 3 BO 3 ), hydro- 
 chloric acid (HC1) and hydrofluoric acid (HF). The liquid solutions are all 
 water solutions. 
 
748 PRINCIPLES OF STRATIGRAPHY 
 
 KINDS OF METAMORPHISM. 
 
 Metamorphism is always a complex problem, but according to 
 the dominant forces three distinct types have generally been recog- 
 nized, viz., static, contactic (contagic), and dynamic. Static meta- 
 morphism is that process of alteration which goes on without the 
 interference from without of forces producing deformation, or the 
 invasion of heat from contact with a molten mass. It is essentially 
 an endogenetic process, being concerned only with those forces uni- 
 versally active within the mass. These include chemical energy, 
 gravitative rearrangement within the rock mass and the pressure 
 due to its own mass, as well as the pressure resulting from the 
 crystallization of the mass. Further, the influence of heat caused 
 by these changes within the mass but not invading heat (or cold) 
 from without and the influence of the omnipresent water and gases 
 within the rock mass. This complex activity is essentially metaso- 
 matic and includes in reality two quite distinct processes : the de- 
 struction of rock masses by the atmosphere and water and the 
 construction and reconstruction of rocks by the processes going on 
 within the mass. 
 
 The process of weathering has been dealt with at length in 
 earlier chapters; there remain for present consideration only the 
 constructive and reconstructive processes of metamorphism. To 
 the static phases of these processes of alteration the name diagenesis 
 has been applied by Johannes Walther, the name itself having been 
 used first by Gumbel in 1868 in his "Geognostische Beschreibung 
 des ostbayerischen Grenzgebirges" for the more general processes 
 of metamorphism. Andree has proposed to restrict the term to those 
 molecular and chemical transformations which the sediment under- 
 goes under the influence of the medium in which it was deposited, 
 and to which it is still subject after separation from this medium, 
 through the ordinary circulating or vadose waters, in so far as these 
 do not contain any foreign substances in solution, i. e., such sub- 
 stances as are derived from outside of the sediment. He would 
 include as chief of these changes: recrystallization, formation of 
 concretions, lithification and desalinification. In so far as this 
 restriction excludes changes due to percolating thermal waters or 
 waters bearing mineral solutions, changes which may affect locally 
 parts of various rock formations, this restriction seems .warranted. 
 Such changes are to be classed under the heading of contact meta- 
 morphism and are to be placed either with thermic metamorphism 
 or are to be considered separately as hydrometamorphism. The 
 
KINDS OF METAMORPHISM 749 
 
 name contact metamorphism is applied here to the reconstruction of 
 rocks due to contact with ( I ) heated masses such as igneous bosses, 
 dikes, sills, etc. (thermic metamorphism or pyrometamorphism) ; (2) 
 mineralizing waters, or the alteration produced in the rock walls by 
 the rising of heated or acidulated waters through fissures (hydro- 
 metamorphism). Since such fissures are generally closed shortly 
 after by the formation of veins, no pronounced or extended altera- 
 tion is produced in the wall rock. Finally, (3) vapors bearing or 
 acting as mineralizers in passing through rock masses also produce 
 profound local changes which would come under the same general 
 heading of contact metamorphism (atmometamorphism). If the 
 rock undergoes any change in character, when in contact with a 
 glacier or ice cover, this too is to be classed as thermometamor- 
 phism, while contact with a heated meteoric body would also belong 
 here. In all cases this is, therefore, to be regarded as a contact 
 metamorphism. Grabau (16) has suggested for this process the 
 name cethobalUsm, from aW6s, fire, and /?oAAo>, to strike, which 
 though emphasizing the heat element may, nevertheless, be expanded 
 to cover all contact cases. Rocks altered in this manner would be 
 designated aethoballic rocks. The essential of such changes is that 
 they are local. 
 
 Dynamic metamorphism is a term restricted to the reconstruction 
 processes initiated by tectonic movements, such as faulting, thrust- 
 ing, gliding or folding of rocks. Since it generally affects extensive 
 regions, it is also called regional metamorphism, as contrasted with 
 the local contact metamorphism. The essential causes here are the 
 pressure due to the tectonic movements, and the motion accompany- 
 ing them, the result being a crushing, shearing and rearrangement 
 of the component particles of rock, and often a recrystallization. A 
 secondary factor is the heat developed during this movement. The 
 alterations duevto impact with meteoric bodies, whether hot or cold, 
 must also be classed here, and it is not improbable that in the past 
 they have played a considerable role. Finally, it must be consid- 
 ered whether the normal changes supposed to go on in the zone of 
 flowage, under the immense pressure of the superincumbent rocks, 
 do not in reality belong under the division of dynamic metamor- 
 phism. Grabau (16) has proposed the term symphrattism from 
 o-v/A<paTTo>, to press together, for this type of metamorphism, and 
 for the rocks of this type he suggests the term symphrattic rocks. 
 
 As has been repeatedly emphasized, especially by Johannes Wal- 
 ther, metamorphic rocks of all kinds are naturally classed with the 
 rocks from which they are derived, and not as a separate class. 
 
750 PRINCIPLES OF STRATIGRAPHY 
 
 STATIC METAMORPHISM OR DIAGENISM. 
 
 Of the diagenetic processes affecting rocks the following may be 
 especially considered : (I) lithification, (II) recrystallization, (III) 
 dolomitization, (IV) replacement of limestone by silica, etc., (V) 
 desalinification, (VI) formation of concretions, (VII) hydratioo 
 and dehydration. 
 
 I. LITHIFICATION OR INDURATION. 
 
 The lithification of a rock is not restricted to diagenetic proc- 
 esses, but may be greatly aided if not altogether caused by the 
 other processes of metamorphism, especially the dynamic ones. Nor 
 is lithification a natural result of aging, for time has little or no 
 influence as a primary factor, though it may become important 
 when lithification is primarily due to some other factors. As ex- 
 amples may be cited the still unconsolidated early Palaeozoic sands 
 and clays of the undisturbed plains of Russia, and the much meta- 
 morphosed Eocenic rocks of the Alps, or of the Coast Range of 
 California. In the last two cases cited, the alteration of the rocks 
 is of course due to the dynamic disturbances which have affected 
 them, but consolidation by purely diagenetic processes of recent 
 sediments is not unknown. Thus the consolidation of the coral 
 sand of Bermuda furnishes a good example of a lithified rock of 
 modern origin, .while the Nagelfluh of Salzburg, Austria, and other 
 districts illustrates the solidification of a clastic deposit of Pleisto- 
 cenic origin. (See Chapter XIV, p. 601.) 
 
 Lithification takes place with varying rapidity in rocks of dif- 
 ferent origin. Thus pyrogenic rocks, lavas or intruded masses 
 solidify comparatively rapidly through cooling. This results either 
 in congelation into an amorphous mass or in crystallization wholly 
 or in part. Water solidifies with extreme rapidity by crystalliza- 
 tion when subjected to the proper reduction of temperature. Snow 
 crystals (atmogenic rocks) solidify somewhat more slowly from 
 granular neve into glacier ice, a typical process of diagenetic meta- 
 morphism, though involving to a certain extent recrystallization. 
 The same method of solidification probably affects most hydrogenic 
 rocks. Organic rocks are solidified at the time of their formation, 
 except organic oozes and granular organic rocks (pulverites, granu- 
 lites, etc.), which may be combined into masses much as clastic 
 rocks are. The lithification of clastic rocks is due to pressure- 
 cohesion, to cementation, or to recrystallization. 
 
DIAGENESIS; LITHIFICATION 751 
 
 The methods of lithification, not confined to diagenetic processes, 
 however, may thus be tabulated : 
 
 1. Congelation in amorphous bodies. 
 
 2. Crystallization chiefly in pyrogenic rocks. 
 
 3. Recrystallization chiefly in atmogenic and hydrogenic 
 
 rocks. 
 
 4. Welding or pressure cohesion chiefly in clastic rocks. 
 
 5. Cementation chiefly in clastic and organic rocks. 
 
 Igneous rocks solidify by congelation into an amorphous glass 
 (obsidian, etc.) or by crystallization. Atmogenic snow crystals con- 
 solidate into firn and glacier ice by a process of recrystallization, 
 when the smaller crystals are destroyed to the gain of the larger 
 ones. This is also true of granular hydrogenic rocks such as rock 
 salt and gypsum. Hydrogenic rocks are also solidified through 
 cementation by precipitated material of the same kind. Biogenic 
 rocks are usually consolidated by the precipitation of calcium car- 
 bonate under the influence of decaying organic matter and the for- 
 mation of ammonium carbonate. 
 
 Sphserites, granulites and pulverites, of whatever origin, are gen- 
 erally consolidated by the same agents which consolidate the clastic 
 strata. 
 
 LITHIFICATION OR INDURATION OF CLASTIC ROCKS. Under this 
 heading will also be included the granular or pulverulent endoge- 
 netic substances. The two chief methods are : ( I ) Pressure-cohe- 
 sion, or welding, and (2) cementation. Recrystallization, especially 
 through secondary enlargement, also consolidates loose material, but 
 is more common in rocks already lithified. Though distinct proc- 
 esses, they seldom if ever, occur wholly alone, both welding and 
 cementation generally taking place at the same time, though in 
 unequal amount. Recrystallization may accompany these processes. 
 
 i. Welding. (Van Hise-34: 595-597, 670-671.) This is a proc- 
 ess of mechanical consolidation caused either by the pressure of 
 superincumbent rocks or by tectonic movements. This pressure re- 
 sults in bringing closely together the particles of which the rocks 
 are composed. If water is present, this is squeezed out, while the 
 mineral particles are mechanically readjusted with reference to one 
 another. The particles will cohere, because they are brought so 
 close together by the pressure that they are within the limit of 
 molecular attraction of one another. This takes place especially in 
 the zone of anamorphism, where the pressures in all directions are 
 greater than the crushing strength of the rocks, and hence sufficient 
 to bring the particles within the sphere of molecular attraction. 
 
752 PRINCIPLES OF STRATIGRAPHY 
 
 The depth at which this occurs varies with the rock substances, 
 being comparatively moderate for plastic substances like coal and 
 clay, and much greater for refractory rocks like quartzites, etc. 
 (Van Hise-34: 671.} 
 
 While universal within the zone of anamorphism, welding is not 
 unknown in the belt of cementation of the zone of katamorphism. 
 Here especially the lutaceous sediments are affected, the arenaceous 
 and coarser -elastics, especially when the particles are of uniform 
 size, having too few points of contact for welding to occur. Thus 
 quartz sandstone of nearly uniform grain may become slightly co- 
 herent by incomplete welding, with cementation weak or absent, and 
 so constitute a "free-stone," so called on account of the ease with 
 which it is quarried and cut. Many of the British cathedrals and 
 abbeys, and some Continental ones as well, are built of rocks of 
 this type, rocks which from their uniformity of grain and ready 
 response to the gravers' tools made possible the elaborate carvings 
 which adorn these structures. In not a few cases this rock seems 
 to have been formed by the induration of former wind-blown sands. 
 The slight cohesion of the round and uniform-grained Sylvania 
 sandstone (Siluric) of Michigan, Ohio and Canada, and of the 
 scarcely more coherent Saint Peter sandstone of the United States 
 furnishes examples of cases where induration has scarcely been 
 effected, though what there is may probably be referred to welding 
 processes. This is seen in the fact that these sandstones are almost 
 absolutely free from foreign matter, which might act as a cement, 
 while, except in rare cases, secondary silica has not been deposited. 
 
 Cohesion may occur in lutaceous sediments without complete 
 exclusion of water. Thus Becker (7:157) has shown that, "when 
 the films of water between the particles become very thin, they may 
 become an important factor in the coherence of the rocks. The 
 molecular attraction of the water films and the adjacent particles, 
 or their adhesion, and the cohesion of the molecules of the films 
 may be sufficient to give the rocks a certain amount of strength." 
 (Van Hise-34 : 506. ) Thus muds and silts welded in this manner 
 may have a marked coherence. 
 
 The squeezing out of the water, in whole or in part, the rear- 
 rangement of particles, and the partial compression of the particles 
 themselves result in a reduction of volume. Thus a considerable 
 reduction in the thickness of a formation may occur. Fossil shells 
 or other organisms in such a formation may be pressed flat or 
 crushed unless previously altered so as to be resistant. The gener- 
 ally flattened or crushed character of brachiopods and other shells in 
 Palaeozoic shales are good illustrations. If, however, a resistant 
 
DIAGENESIS : LITHIFICATION 753 
 
 structure, such as a calcareous or other concretion, exists in the 
 rock, this will resist compression more than the enclosing mud, and 
 so the layers of the latter may assume an upward or downward 
 curving attitude arching over or under the concretion, or, if the 
 latter is large, end abruptly against it, sometimes with the occur- 
 rence of slickensided surfaces on the exterior of the concretion. 
 Stylolites also belong in this category of pressure structures. They 
 will be more fully discussed beyond. 
 
 That rocks are ordinarily under great strain from lateral and 
 vertical pressure has been shown by the fact that when the pressure 
 is relieved, as in quarrying, expansion takes place, while upward 
 bucklings of the quarry floor are also frequently observed. (Niles 
 24; 25 ; Johnston-2o; Cramer-o,; 10.) 
 
 The further phenomena resulting from pressure will be more 
 fully discussed under symphrattism or dynamo-metamorphism. 
 
 2. Cementation. This is accomplished by the deposition, in the 
 pores of the rock mass and between the particles, of a substance 
 which will bind them together. The material is brought in solution 
 by the percolating rain or ground water, and may be derived from 
 a distance, from immediately adjoining formations, or from the 
 formation in question itself. Thus the calcareous sands of the 
 dunes on Bermuda are cemented by the rain water which percolates 
 through them and which dissolves some of the lime only to redeposit 
 it elsewhere in the same formation. The oolite grains of Gran 
 Canaria in the Canary Islands are cemented by lime deposited by 
 the sea water which is instrumental in forming these oolite grains. 
 This, as in the similar cementation of organic lime accumulations, 
 on coral reefs, etc., is brought about by the separation from the 
 water of additional lime, through the decay of the organic matter 
 and the formation of ammonium carbonates in the warm waters, 
 this chemical reacting with the lime salts in solution in the sea 
 water. Pleistocenic gravels are often cemented by the lime derived 
 from a partial solution of the limestone pebbles which they contain 
 or which are found in an overlying gravel or sand. Examples of 
 this are not uncommon in limestone regions. The great Pleisto- 
 cenic Nagefluh deposit of the Salzburg region is an example of the 
 cementation of a deposit in this manner never buried under younger 
 formations. The pebbles and grains of the rock are so firmly 
 cemented that the galleries and crypts, cut into the formation and 
 dating back to the third century, are still perfectly preserved. 
 Pleistocenic delta deposits exposed near Lewiston, New York, and 
 formed when the ice front rested near the Niagara escarpment, and 
 before Lake Iroquois came into existence, have become consolidated 
 
754 PRINCIPLES OF STRATIGRAPHY 
 
 by lime cementation so as to form a fairly cohesive rock, showing 
 well the oblique bedding of the fore-set beds. 
 
 The porosity of the rock is an important factor in aiding cemen- 
 tation. Other things being equal, the more porous rocks will have a 
 better chance of cementation. Thus the Columbian gravels (Pleis- 
 tocenic) of the Raritan Bay region in New Jersey are frequently 
 cemented into a hard pebbly rock, the yellowish well-worn quartz 
 pebbles being embedded in a deep brown sandstone cemented by 
 iron oxide, the whole resembling a giant peanut brittle. The under- 
 lying Cretacic strata, on the other hand, are unconsolidated except 
 where locally some of the sands are bound together by iron oxide. 
 Certain layers in the Monument Creek Tertiary sandstone of Colo- 
 rado Springs are strongly cemented by iron oxide, while the re- 
 mainder of the sandstone mass is free from such cement. As a 
 result, monuments are carved by the wind out of these rocks, the 
 iron-cemented layers forming the capping stones of these monu- 
 ments. In the Miocenic deposits of Baden, near Vienna, the shell- 
 bearing pebble beds are often cemented by lime into a fairly re- 
 sistant rock, while the clays are entirely unconsolidated. 
 
 The principal minerals deposited between the particles of a rock 
 to form a cement are lime, iron and silica. Silica may be in the 
 form of a colloidal cement, but in quartz sandstone it is far more 
 often deposited in such a way as to have optical and crystallographic 
 continuity with the silica of the grain it surrounds. This secondary 
 enlargement of a quartz grain, forming more or less perfect crystals 
 which interlock closely, is not an uncommon thing and may result 
 in the formation of a hard and strongly indurated rock. Neverthe- 
 less, such close cohesion of new grown crystals does not always take 
 place, and the mass will fall to pieces at the blow of a hammer, 
 leaving a mass of angular quartz crystals which only under the 
 microscope show that they represent the secondary development by 
 addition of the originally more or less well-rounded quartz grains. 
 This is not an uncommon source of angular quartz grains. 
 
 Van Hise mentions as the most important cementing substances : 
 silica, iron oxide and aluminum oxide, among the oxides; calcite, 
 dolomite and siderite among the carbonates, both hydrous and 
 anhydrous silicates,* and marcasite and pyrite among the sulphides. 
 (Van Hise-34: 621-622.) 
 
 The Keweenawan sandstone of Lake Superior may be cited as a 
 case in which the cementation is largely due to the deposition of 
 
 . * Among the hydrous silicates are: (i) zeolites and prehnite; (2) chlorites; 
 (3) epidotes; (4) serpentine and talc. Among the anhydrous silicates are feld- 
 spars, hornblende and mica. 
 
DIAGENESIS : RECRYSTALLIZATION 755 
 
 feldspar upon worn grains of that mineral, the old and new mineral 
 being in optical continuity. (Van Hise-32.) The sandstone con- 
 tains both orthoclases and plagioclases, and both are enlarged by 
 deposition of new material in optical continuity with the old. Horn- 
 blende has also been found to be secondarily enlarged in old volcanic 
 tuffs. 
 
 Quart zites and Novaculites. 
 
 When quartz sandstones are so completely cemented by second- 
 ary silica, whether deposited independently or in optical continuity 
 with the original quartz grains, that the rock will break across the 
 original grains rather than between them, the rock is called a 
 quartzite. If the original grain of the quartz rock was a luta- 
 ceous one, the result 01 this excessive induration is a novaculite. 
 
 Lithification of Clastics Largely a Supramarine Process. 
 
 Since lithification of elastics by cementation and recrystallization 
 requires the active circulation of ground water, it is apparent that 
 it is chiefly effective after the deposits in question have been lifted 
 above sea-level, if they originally were marine. This is not entirely 
 true for processes of recrystallization, which may go on even be- 
 neath sea-level. 
 
 II. RECRYSTALLIZATION. 
 
 Recrystallization of the mineral constituents may affect all rocks, 
 and occur under static, dynamic or contactic conditions. As a proc- 
 ess of diagenism it often produces marked results, though these 
 are never carried to the extremes which are attained when it acts 
 as a process of symphrattism. When it takes place in unconsoli- 
 dated material it may become a method of lithification, but it is 
 more commonly found in rocks already consolidated by one or the 
 other method. As a method of change from a less stable to a more 
 stable form of mineral it is of the greatest importance. Thus the 
 original less stable forms of CaCO 3 , aragonite, ktypeit, found in 
 marine oolites and organic deposits, are changed to the more stable 
 form calcite. (See Chapter IX.) In the case of organic remains so 
 altered, the finer structural features are commonly lost. 
 
 Recrystallization is especially effective in the more soluble rocks, 
 
756 PRINCIPLES OF STRATIGRAPHY 
 
 such as limestones, gypsum and salt, though the secondary enlarge- 
 ment of quartz crystals in reality also belongs here. Gypsum, anhy- 
 drite, rock salt and granular snow are other substances easily sub- 
 ject to recrystallization. In this process the smaller particles are 
 commonly dissolved and their material added to the larger ones. 
 In the zone of katamorphism, solution and redeposition are going 
 on throughout the limestone with the result that the entire mass is 
 gradually recrystallized. This may affect both loose aggregates of 
 calcite grains which thereby become consolidated, and it may affect 
 indurated limestones which are then gradually altered toward the 
 condition of marble. True marble is probably formed only under 
 the influence of dynamic forces, but many recrystallizations come 
 close to approaching this state. 
 
 It is often assumed that recrystallization has affected most of 
 the older Palaeozoic limestones, because of their lack of organic 
 remains, which, it is argued, are destroyed by recrystallization. It 
 may be questioned whether organic remains are ever destroyed by 
 ordinary recrystallization, though there is no doubt of this when 
 recrystallization under dynamic influences goes on. In the case of 
 many of the older Palaeozoic limestones, however, the absence of 
 organic remains is a primary character. Many of these limestones 
 were deposited as lime muds and silts derived from the erosion of 
 still older limestones, and without the direct participation in their 
 formation of lime-secreting organisms. 
 
 Rock salt deposits on recrystallization tend to become coarser, 
 as in the case of the Polish deposits. The same is true for gypsum, 
 which sometimes crystallizes out into masses of large dimensions. 
 The largest found up to date in Utah measured in some cases 150 
 cm. in greatest dimension. When deeply buried, gypsum loses its 
 water under the influence of pressure and recrystallizes into anhy- 
 drite. This brings with it a decrease of volume of 38%. 
 
 An important point for consideration lies in the fact that recrys- 
 tallization is favored by pressure. The greater the pressure, the 
 more likely is the deformation to be accomplished by recrystal- 
 lization. 
 
 Pressure Phenomena Due to Recrystallization. 
 
 In rocks of homogeneous character and fine grain, recrystalliza- 
 tion may have a deformative effect on the original structure lines 
 and not infrequently upon the enclosing strata. This is especially 
 well seen in the salt deposits of undisturbed regions, such as the 
 Zechstein salt of north Germany and the Salina salt of New York. 
 
DIAGENESIS: ENTEROLITHIC STRUCTURE 757 
 
 In the former, where the enclosing rocks are undisturbed, the 
 layers of brightly colored bittern salts and of gypsum often show 
 a remarkable flexuous, sinuous or disrupted character not unlike a 
 structure produced by strong compressive strains during tectonic 
 deformation. That such deformation is not tectonic can often be 
 shown by the undisturbed character of the enclosing sandstones and 
 shales. Thus, in the Salina deposit of central New York, some of 
 the alternating salt and gypsum layers occasionally show a pro- 
 nounced flexing and overfolding, while others are wholly undis- 
 turbed. This is well shown in the following illustration reproduced 
 from Everding (Fig. 159) and representing the endolithic deforma- 
 
 FIG. 159. Section of the potash layers of the Berlepsch shaft near Stassfurt. 
 Scale i :35. The vertically lined beds are carnallite ; the beds 
 with horizontal dashes are rock salt; the deformed layers (white) 
 are kieserite. (After Everding.) 
 
 tion of the potash layers in the Berlepsch salt shaft near Stassfurt. 
 Here the rock salt and the carnallite are apparently undisturbed, 
 while the kieserite bands within the carnallite layers show most 
 pronounced distortions in different directions. "The forces," says 
 Arrhenius in this connection, "which have brought about this pecu- 
 liar deformation, are evidently of very local character, and con- 
 fined to the respective. carnallite layers." Arrhenius concludes that 
 tectonic forces cannot be the cause which produced these deforma- 
 tions. (Arrhenius-4.) 
 
 From the resemblance of the distorted layers to the convolutions 
 of an intestine, this structure has come to be known in German 
 scientific literature as "Gekrose" structure, a name first applied by 
 Koken in 1900. (22.) The English equivalent of this term, pro- 
 
758 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 posed by me some time ago, and first used in print by Harm (18), 
 is enterolithic structure. 
 
 What is believed by many to represent extreme cases of defor- 
 mation due to endogenetic causes is found in the remarkable salt 
 domes of Louisiana and eastern Texas, and of North Germany, es- 
 pecially in middle and northern Hanover and Brunswick, extending 
 as far as the Elbe. Similar occurrences are reported from Tran- 
 sylvania, on both sides of the Pyrenees, and from southern Algeria 
 (Fig. 160). 
 
 These "salt domes'' are elliptical in section, with folded, often 
 much distorted layers of salt, gypsum, and in some sections potash 
 salts, which rise through the enclosing strata, deforming them, and 
 maintaining a plug-like relation to them. It is true that some writers 
 
 FIG. 160. Section and ground plan of a salt dome in the Moros Valley, 
 Hungary. (After Lamprecht in Fiirer's Salzbergbau.) 
 
 (Stille, papers cited by Hahn-i?) have explained these relation- 
 ships as due to repeated foldings, but the consensus of opinion 
 (Hahn-i7) seems to be that, while some folding has undoubtedly 
 occurred in certain places, the main force was the endogenetic one 
 due to the crystallizing force of the salts and to metasomatic proc- 
 'esses. (Arrhenius-4.) 
 
 Enterolithic structure is also a frequent occurrence in fine- 
 grained limestones or dolomites. A remarkably fine example is 
 seen in the basal "hydraulic" limestones of the Lockport series of 
 Siluric age, in a section opened by the canyon of Niagara. The 
 strata are finely shown along the railroad bed on the right bank of 
 the canyon. This structure is equally well developed (Fig. 161) in 
 the Upper Muschelkalk of the Neckar Valley, in Wiirttemberg, Ger- 
 many (Koken-22), and will probably be recognized in other forma- 
 tions. The essential feature is here, as pointed out by Hahn, that 
 the deformation is in all directions,* not in certain ones, as would 
 
 * The multi- gyro- and a-polar deformations of Lachmann. 
 
DIAGENESIS: ENTEROLITHIC STRUCTURE 759 
 
 be the case in tectonic or in gliding deformations. Thus deforma- 
 tion is shown in whichever direction the section of the formation is 
 cut, nor is there any evidence of slickensiding, such as is to be 
 expected if the deformation is tectonic. 
 
 Koken, who described the disturbed layers of the Upper Mus- 
 chelkalk of the Neckar Valley in detail, and originated the name 
 Gekrosekalk for them, held that the folding and wrinkling were due 
 to vertical pressure of overlying rocks upon the still plastic layers. 
 He notes, however, that the folds are notably sharp and their limbs 
 are thickened as is the case in deformations formed by swelling 
 
 Myophoria Gpl_dfussi 
 
 FIG. 161. Enterolithic structure in the Upper Muschelkalk (Gekrosekalk) of 
 the Neckar Valley in Wiirttemberg, Germany. (After Koken.) 
 
 masses, such as gypsum, but not through horizontal pressure. While 
 it is not difficult to conceive that mere vertical pressure on still 
 plastic layers can produce deformation of these layers, it is not 
 quite clear what should cause the retention of plasticity in some 
 layers and not in others. The deformed Muschelkalk layers are 
 bluish, argillaceous calcilutytes, much like the similarly deformed 
 layers of the Niagara section. In both cases internal pressure due 
 to crystallization seems to have been an active agent in the deforma- 
 tion of the rock. 
 
 III. DOLOMITIZATION OF LIMESTONES. 
 
 The change of limestones into dolomites, or dolomitization, has 
 occurred in all geologic ages and is in progress to-day. (Pfaff-26.) 
 
760 PRINCIPLES OF STRATIGRAPHY 
 
 True, not all dolomites are of secondary origin, some being no doubt 
 deposited as dolomite rock in the beginning. Among dolomites of 
 secondary origin we may distinguish those derived by the clastation 
 and redeposition of older dolomites and those due to the replace- 
 ment of limestones. Only the latter class belongs here, but the 
 dolomites of clastic origin deserve brief attention. Here belong 
 the many well-bedded, fine and uniformly grained rocks with few 
 or no fossils which abound in many Palaeozoic and later forma- 
 tions. As a typical example may be mentioned the Monroe (Upper 
 Siluric) dolomites of Michigan, Ohio and Ontario, which have 
 most probably been derived by the destruction of the older Niagaran 
 dolomites and deposited as dolomitic sand and mud. This is prob- 
 ably the origin of most of the fine-grained, well-bedded dolomites 
 which, from the fact that they contain scattered fossils, are seen 
 not to be the product of alteration of limestone. 
 
 When limestones and dolomites are found interstratified, the 
 successive beds being sharply differentiated from one another, this 
 seems to be most satisfactorily explained as a primary difference in 
 the materials deposited. Suess (31, 11:262) regards this altera- 
 tion in the Plattenkalke as due to alternate chemical precipitation 
 of dolomites and limestones, but in practically all rocks of this 
 type a clastic origin of the deposit must be postulated. In other 
 words, the beds are calcilutytes, some of them pure, others mag- 
 nesian, the mud being derived alternately from calcareous and mag- 
 nesian sources. Or, again, the limestones may be of organic origin, 
 while the enclosed dolomites are of terrigenous origin, being derived 
 from the erosion of dolomites forming a portion of the land, and 
 such alternation would have no more significance than alternations 
 of limestones (of thalassigenous origin) and shales (of terrigenous 
 origin). The possibility of secondary separation of a mixture of 
 lime and dolomite grains by agitation of the water and the unequal 
 settling according to specific gravity must not be overlooked. 
 
 Secondary dolomites due to diagenetic alteration processes may 
 originate either before or after the original limestones are raised 
 above the sea-level. ( Steidtmann-3o. ) Such alteration may be 
 primarily a process of leaching, either under the sea by sea water 
 or by the ground water circulating through the upper zones of the 
 earth's surface. By leaching out of the lime the proportion of the 
 original magnesian content is greatly increased. Such differential 
 leaching is due to the fact that calcium carbonate is several times 
 as soluble as magnesium carbonate as first shown by Bischoff. When 
 it occurs, one result is the rendering porous of the altered rock, 
 which, if under pressure, may actually collapse. The process of 
 
DIAGENESIS : DOLOMITIZATION 761 
 
 alteration may on the other hand be one of secondary replacement 
 of calcium by magnesium. Such replacement in the sea had appar- 
 ently taken place in the case of coral rock reported by Dana (12: 
 jpj) from the elevated reefs of Makatea Island in the Pacific; this 
 rock contained 38.7% f magnesium carbonate, whereas such rock 
 usually contains less than i%. Similar alterations have been re- 
 ported by others, thus Branner (8:26 4) found 6.95% of magnesia, 
 equivalent to 14.5% MgCO 3 , in reef rock of Porta do Mangue, 
 Brazil; the corals of the reef containing only from 0.2 to 0.99% 
 of MgO. Similarly Skeats (28) reports analyses of modern coral 
 rock from the Pacific with 43.3% of MgCO 3 . Such alterations 
 have also been reported from Funafuti, the deep boring on which 
 showed 16.4% MgCO 3 at a depth of 500 feet, 16% MgCO 3 at 640 
 feet, with much smaller but variable percentages above and below. 
 A boring at Key West showed the highest percentage of MgO 
 (6.7%) at a depth of 775 feet, the percentage of CaO at that depth 
 being 46.53%. At a depth of 25 feet and 1,400 feet the two minima 
 occurred (0.29% and 0.30% respectively). 
 
 Metasomatic replacement through the agency of ground water 
 is also an active means by which dolomites are produced. In some 
 cases it is less effective than submarine replacement, principally 
 because sea water carries more magnesium than is found in such 
 underground circulation. Where such magnesia is supplied, how- 
 ever, as in regions of decomposing magnesium-bearing rocks, this 
 ground water replacement may be very effective. The magnesia 
 is of course obtained from the belt of weathering where it occurs 
 as carbonate in older dolomites, etc., or as silicate in crystalline 
 rocks and minerals (garnet, staurolite, tourmaline, chondrodite, 
 chlorite and the zeolites, etc.). The silicates are subject to carbona- 
 tion (see ante, pp. 35, 178), and the carbonate then passes into solu- 
 tion and is carried downward to the belt of cementation, when, on 
 coming in contact with limestones poor in magnesia, replacement 
 takes place. 
 
 Local dolomitizations also occur, as for example at Aspen, Colo- 
 rado, where hot magnesian spring waters rising through the lime- 
 stone locally alter it to dolomite. These are, however, not dia- 
 genetic, but belong to the division of contact metamorphisms. In 
 general limestones which have suffered orogenic disturbances are 
 more commonly altered to dolomites than those not so disturbed. 
 Thus (Van Hise-34:#o/) the Tertiary limestones of the Coast 
 Range of California and of the Alps are more strongly magnesian 
 than the undisturbed limestones of the same age. This is due to 
 the fact that disturbed and shattered strata of mountain regions 
 
762 PRINCIPLES OF STRATIGRAPHY 
 
 offer better access to waters bearing magnesium, through the agency 
 of which the replacement is brought about. - 
 
 The replacement of calcite by dolomite involves a contraction of 
 12.30%. Dolomites due to alteration will thus show a high degree 
 of porosity unless they have been subjected to compression during 
 orogenesis. Such porosity is shown in the early Palaeozoic dolo- 
 mites of the Mississippi Valley, and also in the Siluric and the 
 Devonic dolomites of Michigan, Ohio and Canada. When the rock 
 is under pressure, as in the zone of anamorphism, mashings and 
 recrystallizations close the openings. It is also highly probable that 
 pressure promotes dolomitization, since this means a decreasing 
 volume, a result favored by pressure. 
 
 IV. REPLACEMENT OF LIMESTONES BY SILICA, IRON OXIDE, ETC. 
 
 Metasomatic replacement of limestone by silica is a familiar 
 phenomenon. In* most cases the replacement affects chiefly certain 
 parts of the limestones which by their structure seem best suited to 
 such replacement. Such are the shells, corals and other organic 
 remains embedded in Palaeozoic or younger limestones where the 
 enclosing matrix generally remains unaffected, though the fossil 
 may be completely replaced. Oolitic limestones also suffer replace- 
 ment by silica and in them often the steps of replacement are shown 
 by the decrease in lime and the increase in silica. A mass of such 
 siliceous oolite occurs in the lower Palaeozoic rocks of central 
 Pennsylvania, where it covers an area of about 40 square miles, 
 with scattered extensions over a much wider area. Locally the 
 oolite passes into chert. These siliceous oolites have bee'n regarded 
 as originating in rising hot springs containing silica in solution 
 (Wieland-36:<?<fe), but others (Moore-23; Brown)' hold that 
 they represent replacements of originally calcareous oolites. This 
 explanation is fully borne out by the analysis, and the incomplete- 
 ness of the replacement in many cases. (See 'also Ziegler-37.) 
 
 Replacement of limestone by iron oxide is also a frequent occur- 
 rence. In the basal Siluric beds of Wisconsin, oolites, which from 
 their character and appearance were most probably calcareous -in 
 the first place, have been changed to iron oxide (hematite). The 
 so-called Clinton iron ore seems to be an example of metasomatic 
 replacement of limestones, for here the organic fragments (brachi- 
 opod shells, Bryozoa, etc.) are replaced by iron oxide. In the Gen- 
 esee gorge at Rochester the steps in replacement could formerly be 
 observed, these being shown by the progressive increase in iron 
 
DESALINIFICATION ; CONCRETIONS 763 
 
 oxide and a corresponding decrease in calcium carbonate. It is 
 true that these deposits have been regarded as formed directly in 
 lagoons and cut-offs (Smyth-29) along the sea coast of the time, 
 the iron being brought by the wash from the crystalline old land. 
 This theory has, however, been discarded by some recent students of 
 the subject in favor of the older replacement theory. 
 
 The replacement of calcareous bodies of organic origin by iron 
 pyrites and other mineral substances will be more fully discussed 
 in a later chapter. 
 
 V. DESALINIFICATION. 
 
 Among other diagenetic processes of importance may be men- 
 tioned the desalinification of old marine sediments. As already 
 noted, the amount of salt absorbed by marine sediments varies 
 greatly, chiefly in proportion to their pore space. (Gerbing-i5 : 85, 
 118.) After these sediments are raised into the zone of circulating 
 ground water, a slow removal of these salts takes place. Under 
 arid climatic conditions, as already noted, this may go on more 
 rapidly, and the leached salt may be redeposited in salinas and 
 desert salt basins. 
 
 VI. FORMATION OF CONCRETIONS. 
 
 This has already been discussed at some length in a previous 
 chapter (see pp. 718-720) and need be dwelt on only briefly here. 
 Percolating waters carrying lime, silica or other substances in solu- 
 tion will deposit these in the strata at favorable localities, forming 
 concretions of lime, of clay-iron-stones, or of silica. The first are 
 common in calcareous shales, often growing to large size, with a 
 corresponding deformation of the enclosing layers, through the 
 pressure of the growing concretion. Not infrequently the concre- 
 tions become confluent, forming a concretionary limestone bed. 
 The nucleus of the concretion is very often some organic fragment 
 or a shell. In the Champlain clays of Cumberland, Ontario, entire 
 specimens of fish are common. Fish remains are found in similar 
 concretions of the glacial and post-glacial clays of Norway, 16 
 species having been recognized so far. 
 
 The common types of concretion in the Mesozoic and rakeozoic 
 shales are the septaria already described. These are often of great 
 size, examples 10 feet in diameter occurring in the Devonic of New 
 York. They not infrequently contain a fish bone as a nucleus, 
 
764 PRINCIPLES OF STRATIGRAPHY 
 
 while the smaller ones commonly have a goniatite shell at the center. 
 Frequently the stratification of the enclosing beds on either side 
 appears to be continuous through the concretion, while the beds 
 above and below are arched, owing to the pressure caused by the 
 growing septarium. Some of this arching may be due to the com- 
 pression of the shale around the resistant septarium. 
 
 Calcareous clay stones are also common in the loess, where they 
 are known as Losspuppen or Lossmannchen, by the Germans, as 
 Fairy stones by the Scots, and as Imatra stones by the Finlanders. 
 They form in parallel lines, giving the deposit the appearance of 
 stratification, though the original bedding may have been 4 quite 
 diverse. The lines of concretions mark rather the successive levels 
 of ground water than any structural features of the rock itself. 
 
 Claystone concretions of very regular form are found in the 
 Champlain clays of the Connecticut Valley, while clay-iron-stones 
 enclosing ferns, insects, crustacean and other remains, occur in the 
 Carbonic shales of Grundy County, Illinois, the fossil-bearing con- 
 cretions of Mazon Creek having become famous on account of their 
 well-preserved organic remains. 
 
 A special form of calcareous concretion is known from the black 
 Devonic shales of Michigan and Ontario, being especially abundant 
 at Kettle Point, Lake Huron. These are spherical, or nearly so, 
 and are composed of radiating crystals of calcium carbonate, which, 
 growing outward, crowd the enclosing strata until they curve about 
 the concretion. The structure resembles that of a fibrous wood, 
 and fragments are not infrequently mistaken for "petrified" wood. 
 Their manner of occurrence, growth and significance is fully dis- 
 cussed by Daly (n). 
 
 Concretions of iron pyrite and ef marcasite are forming in many 
 strata. Sometimes these are globular masses composed of crystals 
 of pyrite, at other times they have a radial structure. Generally 
 some object of organic origin forms the nucleus around which the 
 concretion grows. In the Cretacic clays of New Jersey pyrite con- 
 cretions are forming around fragments of lignite, all stages of in- 
 crustation and replacement being observable. 
 
 Siliceous concretions are common in calcareous formations. 
 Thus flints characterize chalk, and chert layers abound in many 
 limestones. Flints may occur in continuous layers in massive chalk 
 beds in which their arrangement alone indicates stratification. As 
 in the case of the concretions in the loess, these lines of flints need 
 not have a necessary relation to the original stratification. 
 
 In many cases, however, the flints formed around a siliceous 
 sponge oV some other organism which acted as a nucleus to attract 
 
CONTACT METAMORPHISM 765 
 
 the silica in solution. Here the flints mark the original distribution 
 of the organic remains in the strata. The source of the silica is to be 
 found in the organic structures of silica scattered through the mass 
 of the chalk. These are dissolved by the circulating waters and 
 redeposited around the organic nucleus. 
 
 Chert concretions occupy the same relation to limestone that 
 flints do to chalk. They too. are derived from the organic silica 
 enclosed in the deposit, and redeposited in favorable places. Con- 
 fluent concretions of chert produce a more or less continuous chert 
 bed such as is common in the Devonic limestones of eastern North 
 America. Chert concretions may enclose organic remains, but they 
 do not necessarily form around a visible nucleus. Van Hise holds 
 that the heavier chert bands are formed first by the original segre- 
 gation of siliceous organisms and the subsequent enrichment by 
 silica-bearing ground waters of these siliceous strata. 
 
 VII. HYDRATION AND DEHYDRATION. 
 
 Hydration, or the union with water of originally anhydrous de- 
 posits, may produce profound results. Thus anhydrite is changed 
 to gypsum with a corresponding swelling of the entire mass (see 
 ante, p. 177) and the production of deformative structures. Dehy- 
 dration of gypsum, on the other hand, produces a corresponding 
 shrinking of the entire mass. 
 
 CONTACT METAMORPHISM OR ^THOBALLISM. 
 
 I. Pyrometamorphism. When rocks come in contact with 
 heated igneous masses, as a result of subterranean intrusions, or of 
 surface flows, they are more or less altered, especially along the 
 contact, this alteration gradually decreasing in intensity away from 
 the igneous mass, until its effect has been entirely lost. Such a 
 phase of the contact metamorphism may be called igneo- or pyro- 
 metamorphism. It is especially manifested in the formation of 
 new minerals along the contact zone and in the introduction of 
 mineral substances from the igneous mass. A zonal arrangement 
 is commonly formed, different alteration products arising at dif- 
 ferent distances from the igneous mass. Effects are felt by both 
 the intruded and the intruding (or overflowing) rock; the former 
 is exomorphic, the second endomorphic. The exomorphic effect 
 from contact with dry heat is first of all a raising of the temper- 
 
766 PRINCIPLES OF STRATIGRAPHY 
 
 ature of the country rock adjacent to the igneous mass, such rise 
 in temperature reaching even fusion point. Three stages of influ- 
 encing the country rock are recognized : baking, fritting, and vitri- 
 fication. As a result of baking, induration of unconsolidated ma- 
 terial will occur without fusion. Hydrous minerals are dehydrated 
 with a corresponding change, such as limonite to hematite, gypsum 
 to anhydrite, etc. From carbonates the CO., is given off, changing 
 limestone and dolomites to lime and magnesium oxides, respectively, 
 which have a caustic reaction. Volatile gases are driven off, as in 
 the case of coal which is changed to coke. 
 
 Fritting is partial fusion, carried to the point where the silica 
 begins to act on the bases, forming an imperfectly melted or fritted 
 mass. Vitrification results from complete fusion, the mass being 
 transformed into a glass. 
 
 The effects of pyrometamorphism on clastic rocks are various. 
 "Sandstones are decolorized and often fritted to a glistening enamel, 
 like a porcelainic mass; where the cement is of a calcareo-argilla- 
 ceous nature, this is melted into a glass ; clay and mud are con- 
 verted into porcelainite or brick, with marked change of color in 
 many cases ; tuffs and phonolites are so far vitrified as to acquire a 
 character resembling that of obsidian; brown coal is altered into 
 seam coal or anthracite, and these in other cases into a substance 
 more resembling graphite, while in others (probably under less 
 pressure) the coal is converted into coke; a prismatic structure is 
 developed not only in clays and marls, but even in sandstones, in 
 brown coal, in seam coal and in dolomite; limestones are altered 
 into crystalline marble, often with complete effacement of their 
 stratification and even of all traces of their fossils ; the finer varieties 
 of grauwacke and its associated shales are converted into horn- 
 stone, as in the classical region of the Brocken." (Irving-iQ: /<5.) 
 The effects of dry heat are very limited in extent, usually penetrat- 
 ing the rocks only for a short distance. Where hydro- and gaseo- 
 (atmo-) metamorphism are also active, as is almost universally the 
 case in pyrometamorphism, the alterations will be more extensive 
 and widespread. The endomorphic effects, or those on the igneous 
 mass itself, are largely confined to a more rapid solidification and 
 hence the production of finer crystallization along the contact, owing 
 to the chilling effect of the cool wall rock. The presence of water 
 in the latter, of course, contributes to a much modified result, as 
 already indicated in an earlier chapter (p. 312). 
 
 2. Hydrometamorphism. Contact with rising waters, whether 
 hot or cold, carrying mineralizers, produces the second type of con- 
 tact metamorphism to which the term hydrometamorphism may be 
 
HYDRO- AND ATMOMETAMORPHISM 767 
 
 applied. As already noted, waters carrying magnesium locally alter 
 limestone into dolomites. Sulphuretted springs on the Sinai Penin- 
 sula and at several points along the west coast of the Red Sea alter 
 coral limestones to gypsum, and silica-bearing waters locally alter 
 many reef limestones into siliceous rocks, as in the Upper Devonic 
 coral reef limestones of Grund in Harz and elsewhere. 
 
 The greatest amount of alteration is, however, produced by the 
 highly heated waters, given off by the igneous rock, or accompany- 
 ing the intrusion. Here must be classed all the phenomena of 
 secondary enrichment of the wall rocks of fissures, by the rising 
 waters, though the actual deposits in the fissures themselves are to 
 be classed as hydrogem'c rocks. The subject is too special to be 
 pursued here at greater length. The student is referred to the cur- 
 rent works on ore deposits and to Van Hise's Treatise on Meta- 
 morphism. The work of geysers and hot springs not directly asso- 
 ciated with volcanic intrusions, in so far as it affects the wall rock, 
 must also be classed here'. The deposits formed by these agencies, 
 however, are hydrogenic deposits. 
 
 3. Atmometamorphism. Contact with rising vapors and gases, 
 as in solfataras, fumaroles, etc., constitutes a third type of contact 
 metamorphism, to which the term gaseo- or atmometamorphism may 
 be applied. In its broadest sense the weathering of rocks in con- 
 tact with the great gas envelope of the earth, the atmosphere, also 
 belongs here, having the same relation to the intrusion of gases as 
 the surface flow has to the intruded igneous masses. Practically, 
 however, we may confine gaseous metamorphism to the work of hot 
 vapors and gases emitted in connection with volcanic activity and 
 always accompanying pyrometamorphism. Such effects are visible 
 to-day in solfataras and fumaroles where the alteration of the wall 
 rock is proceeding at a rapid rate. 
 
 The high temperature of the vapors and their high -content of 
 active chemical agents make their work of alteration much more 
 effective than the work of water solution would be. The work of 
 the gases at very high temperature is called fumarolic, while the 
 work of the gases at lower temperature is solfataric. 
 
 The most important gases active in the fissures of the rock are : 
 water vapor, sulphurous oxide (SO 2 ), chlorine (CL), hydrochloric 
 acid (HC1), hydrofluoric acid (HF1), hydrosulphuric acid (H 2 S), 
 sulphuric acid gas (SO 3 ), carbon dioxide (CCX), oxygen (O 2 ) and 
 hydrogen (H 2 ). Nitrogen is of course an abundant but essentially 
 useless gas, and boric acid (H 3 BO 3 ) is sometimes plentiful. Among 
 the processes going on in atmometamorphism are the common ones 
 of oxidation, hydration and carbonation. The last produces sodium 
 
;68 PRINCIPLES OF STRATIGRAPHY 
 
 carbonate, which is abundant at times. Chlorinization results in the 
 formation of NaCl, KC1, NH 4 C1, Fed,, CuCL, MnCL and other 
 chlorides. By the action of sulphuric acid alums are formed, of 
 which the potash and soda alums are the most abundant. Gypsum 
 is formed by the action of the calcium-bearing compounds and sul- 
 phuric acid, this latter also forming Glauber's salts, sodium sul- 
 phate and potassium sulphate. The hydrosulphuric acid acting upon 
 various compounds forms sulphides, and so in turn each acid acting 
 upon the rocks forms compounds of various kinds. 
 
 These activities are of course not always sharply isolated. In- 
 deed, solfataric and fumarolic actions are a common accompaniment 
 of igneous activity and thus the alteration of the rocks is a com- 
 plex of pyro-, hydro- and atmometamorphism. 
 
 4. Biometamorphism. A change in the rock due to contact with 
 organisms, or biometamorphism, is of little effect, when we remem- 
 ber that the change must be produced by the physiological activities 
 of the organism. Thus the changing of clay into bricks by baking 
 is not primarily an organic process, though directed by man. It is 
 a case of pyrometamorphism, even though the heat is artificially 
 supplied. Disintegration of rocks by growing organisms is perhaps 
 their only significant metamorphic activity. 
 
 DYNAMIC OR PRESSURE METAMORPHISM, OR 
 SYMPHRATTISM. 
 
 When rocks are subjected to erogenic disturbances, their internal 
 structure will be affected by the movement and pressure, and to 
 some extent by the heat developed by these processes. The effect 
 in slight deformations is often confined to the planes of gliding 
 along which deformation has taken place. Here smooth gliding sur- 
 faces or slickensides are formed, often with the development of a 
 thin layer of mineral matter, and marked by striations and flutings 
 which indicate the direction of motion. Extreme polishing some- 
 times results from such movements. Here belong the glacial stria- 
 tions and groovings which are slickensides on a large scale. 
 
 The development of a mineral coating on the polished surface 
 of the gliding plain may be the direct result of the energy liber- 
 ated by the gliding process, or it may be the secondary deposit in 
 the fissure, when the surface of the mineral will take on the cast 
 of the striated surface. Hematite, chlorite, calcite, pyrite and other 
 minerals have been active in such wise. In some cases, however, 
 the mineral may have been deposited in the fissure before slipping 
 
DYNAMIC METAMORPHISM 769 
 
 took place. In such a case, the effect of movement is seen on the 
 mineral. 
 
 In general, when extensive dynamic disturbances take place, 
 resulting in crushing and mashing of the rocks, new minerals and 
 new structures are developed. The former are numerous ; among 
 the latter are cleavage, fissility, and schistosity. 
 
 Different types of rocks suffer different alterations under the 
 influence of the mass-mechanical motion characteristic of symphrat- 
 tism. A few of these alteration products may be mentioned, but 
 the student is referred to special treatises on the subject for more 
 detailed information. 
 
 When coarse, clastic rocks, or rudytes, are subjected to dynamic 
 metamorphism, there will generally result a recrystallization and 
 granulation, and the development of schistose structure. This is 
 especially the case in the matrix in which, owing to its great range 
 in composition, a large variety of minerals may be developed. A 
 schist conglomerate or conglomerate schist is produced, generally 
 with the pebbles flattened and elongated and more or less granulated 
 and recrystallized. With extreme movement, the pebbles may be 
 flattened into laminae or changed into a variety of minerals accord- 
 ing to their original composition. A quartz pebble may thus be 
 drawn out into a lamina of granulated quartz, often only as thin as 
 cardboard or even as paper. Granite pebbles may be transformed 
 into a micaceous lamina with quartz and feldspar grains. The ma- 
 terial of the original pebble may become more or less commingled 
 with the matrix so that the outline of the pebble disappears and 
 finally all trace of the conglomeratic character is lost, the mass 
 being a schist with laminae of varying composition interspersed. 
 The matrix may become progressively slate, schist and foliated 
 schist, the particles at first winding in and out among the pebbles, 
 but becoming more parallel as the pebbles disappear. 
 
 Impure arenytes and lutytes may suffer changes similar to those 
 of the matrix of rudytes. Clastic gneisses and schists are thus 
 produced, or exogneisses and exoschists, since they are derived from 
 exogenetic rocks. They are distinguished from endogneisses and 
 endoschists, or those produced from endogenetic (chiefly pyrogenic) 
 rocks, by the parallel orientation of their mineral particles, which 
 gives cleavage to the rock. This structure is almost if not quite 
 universal with the schists and gneisses derived by the metamorphism 
 of sedimentary rocks, but is commonly lacking in schists and 
 gneisses produced from igneous rocks. 
 
 The alteration of other sedimentary rocks by dynamic meta- 
 morphism may be briefly reviewed. Thus quartz sandstone changes 
 
770 PRINCIPLES OF STRATIGRAPHY 
 
 to quartzite and then to quartzite schist ; arkoses into arkose schists, 
 and arkose gneisses ; grits into graywackes, graywacke slates, gray- 
 wacke schists and graywacke gneisses, and shales or lutytes into 
 lutyte schists and lutyte gneisses (pelite schists and pelite gneisses). 
 Limestones are changed to marble and soft coals to anthracites and 
 graphites. In general, pure sediments are the least altered, while 
 mixed sediments are likely to produce the greatest variety of new 
 minerals under metamorphism. 
 
 . The Terms Slate, Schist and Gneiss. 
 
 The term slate, though generally used as a lithological term, 
 is strictly applied only as a structural one. A slate is a metamor- 
 phic rock of a lutaceous texture and homogeneous character, split- 
 ting into parallel leaves, and whose mineral particles are for the 
 most part so small as to be invisible to the naked eye. ( See, further, 
 Chapter XX.) A schist has been defined as "a rock possessing a 
 crystalline arrangement into separate folia." (Geikie-i4: 178.) A 
 typical schist has its cleavable minerals arranged in the same way 
 and like one another and large enough to be for the most part 
 visible to the naked eye. Mica is the most important cleavage- 
 making mineral, and the most typical schist is one composed of 
 quartz and mica scales, a quartz mica schist, more commonly spoken 
 of as a mica schist. 
 
 Van Hise has urged the use of the term schist in a purely 
 structural sense, much as the terms shales and slate should be used. 
 This is in strict accord with the definition by Geikie given above. 
 In mineral composition and in origin schists may vary greatly. 
 Thus we may have the ordinary quartz mica schist, which contains 
 quartz and mica in about equal proportions. Hornblende schists 
 are schists containing hornblende and some other minerals, generally 
 feldspar. Thus we may have a hornblende plagioclase schist. If 
 the origin of the schist is known this may be indicated in the 
 name, as arkose schist, silicirudyte schist, or if derived from an 
 igneous rock such as gabbro it becomes a gabbro schist. Both com- 
 position and origin may be indicated, as in the name mica-quartz- 
 feldspar-arkose-schist. 
 
 In certain petrographic circles, especially the German ones, the 
 term schist was applied to rocks not^only having a schistose struc- 
 ture, but also a definite composition. Thus quartz was considered 
 essential in the formation of a schist and was assumed to be pres- 
 ent. We thus had mica schists, hornblende schists, chlorite schists, 
 
SLATE; SCHIST; GNEISS , 771 
 
 etc., in which the other mineral was supposed to be quartz. If 
 feldspar was present, the rock was called a gneiss. (Rosenbusch- 
 27.) The structural use of the term seems, however, to be the 
 preferable one. 
 
 Gneiss was originally defined as a banded or foliated rock hav- 
 ing essentially the composition of granite, i. e., quartz, feldspar and 
 mica or hornblende. The quartz and feldspar were taken as dis- 
 tinctive minerals and the others added as qualifying prefixes. Thus, 
 mica gneiss meant a schistose or foliated rock, consisting of quartz, 
 feldspar and mica; and hornblende gneiss, the same combination 
 with hornblende added or replacing the mica. Such gneisses were 
 supposed to be metamorphic derivatives of granites. Since, how- 
 ever, many rocks, to which the name gneiss has been commonly 
 applied, prove not to have the composition above given, the petro- 
 graphic use of the name must be abandoned in favor of the struc- 
 tural use, or the use of the term gneiss as well as schist must be 
 very much restricted. Van Hise's proposition to use the term as 
 a purely structural one seems to be the most satisfactory solution, 
 and accordingly we may define gneiss as a banded metamorphic 
 rock in which crystalline structure has been developed and in which 
 the bands are petrographically unlike one another and consist of 
 interlocking mineral particles. The bands in different gneisses are 
 of variable thickness, ranging from a fraction of a centimeter to 
 many centimeters (Van Hise). There may also be a similar varia- 
 tion and range in thickness of the different bands of the same gneiss. 
 Thus the fundamental distinction between gneiss and schist is the 
 banded character of the former as compared with the homogeneous 
 character of the latter. This homogeneous character is still more 
 strongly expressed in the slates in which the cleavable mineral par- 
 ticles are not visible as they are in the schists. 
 
 Gneiss may be derived either from igneous or from sedimentary 
 rocks. When derived from igneous rocks the parallel arrangement 
 of the mineral particles which results in cleavage is more often 
 lacking. 
 
 General Terms for Metamorphic Rocks. 
 
 Two terms have come into use for general designation of meta- 
 morphism in rocks. These are meta and apo. Meta is used as a 
 prefix to any rock name and designates that the rock has been 
 altered without stating how or to what degree. Thus we may say 
 meta-arenyte, meta-shale, meta-granite, meta-diofite, etc. Rocks 
 already metamorphosed to a certain degree may undergo a second 
 
772 PRINCIPLES OF STRATIGRAPHY 
 
 set of changes producing meta-graywackes, meta-quartzite, etc. 
 Here the rock was first metamorphosed to a graywacke or a quartz- 
 ite, after which a second set of alterations occurred. 
 
 Apo is used as a prefix for rocks in which metasomatic changes 
 have taken place without entire loss of original texture or structure. 
 Thus a devitrified rhyolite is an apo-rhyolite. (Bascom-5.) This 
 name applies especially to rocks which have undergone diagenetic 
 alterations without loss of structure, though the chemical and min- 
 eral composition may differ greatly from those of the original rock. 
 The term is useful to call attention to the original rock from which 
 the new rock is derived. Thus quartzite is an apo-arenyte, gray- 
 wacke an apo-grit, etc. When new structures are produced we 
 obtain slates, schists or gneisses. 
 
 Variation in Metamorphism of Strata. 
 
 In a given series of metamorphosed strata a change may often 
 be noted in the intensity of the metamorphism as one passes from 
 point to point. This change may be along the strike of the strata 
 or across it. In the first case, it is generally gradual, the pro- 
 foundly metamorphosed strata of one region passing gradually into 
 the slightly metamorphosed equivalent of another. Thus the three 
 unconformable series of strata, the Archaean, the Lower Huronian 
 and the Upper Huronian, are so closely mashed and altered in the 
 western part of the Marquette district of Michigan as to appear 
 completely conformable and suggest an inseparable series. In trac- 
 ing the formations to the less metamorphosed central and eastern 
 parts of the district, the three unconformable series are readily 
 recognizable as well as the original character of the formations. 
 
 The change in the degree of metamorphism across the strike is 
 generally more abrupt. "Thus the rocks at the crown of an arch 
 or at the bottom of a trough may be only partly metamorphosed, 
 while the same formations on the limbs of the folds may be pro- 
 foundly metamorphosed, this being due to the difference in the 
 amount of shearing in different parts of the folds, or to the dying 
 out or change in character of orogenic movements across the 
 strike." (Van Hise-33 : 598-600.} This change is well illustrated 
 in the Hudson River series, which in the Hudson Valley is prac- 
 tically unaltered, but eastward across the strike in the Taconic 
 range becomes schists and gneisses, while in Vermont and parts of 
 eastern New York the series changes to roofing slates. 
 
METAMORPHISM 773 
 
 Age of Metamorphic Rocks. 
 
 Rocks of all ages may become metamorphosed, but it may be 
 stated for a restricted region that the metamorphosed rocks of that 
 region are generally older than the non-metamorphosed rocks. 
 Strictly considered, this should apply only to symphrattic rocks, 
 since later rocks may be affected by an intrusive sheet or laccolith, 
 the effect dying out upward and downward and thus not being 
 noticeable in older and younger strata. Or a set of folded strata 
 may be locally affected by intrusions which are visible in the newer 
 and not in the older strata. Again different strata are differently 
 affected by the heat of a dike which cuts all of them, and some in 
 the middle of the series may be much altered, while lower strata 
 may be less readily altered. Even symphrattic rocks are not equally 
 altered throughout, some very resistant strata being scarcely af- 
 fected by the agents which strongly metamorphose others. 
 
 While metamorphism is undoubtedly most marked in pre-Cam- 
 bric and in early Palaeozoic rocks, it is also known in rocks of later 
 age, as shown by the metamorphic gold-bearing slates of Jurassic age 
 in the Sierra Nevada and in Sonora, and the Eocenic marble of the 
 Himalayas. See further, Correlation by Regional Metamorphism, 
 Chapter XXXII. 
 
 BIBLIOGRAPHY XIX. 
 
 1. ADAMS, FRANK D. 1912. An Experimental Contribution to the 
 
 Question of the Depth of the Zone of Flow in the Earth's Crust. Journal 
 of Geology, Vol. XX, pp. 97-118. (See also King-2i.) 
 
 2. ADAMS, F. D., and COKER, ERNEST G. 1906. An Investigation into 
 
 the Elastic Constants of Rocks, more Especially with Reference to Cubic 
 Compressibility. Carnegie Institute of Washington, Publication No. 46. 
 Ibid. American Journal of Sciences, 4th series, Vol. XXII, pp. 95-123. 
 
 3. ANDREE, KARL. 1911. Die Diagenese der Sedimente, ihre Bezieh- 
 
 ungen zur Sedimentbildung und Sediment Petrographie. Geologische 
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 3a. ANDREE, K. 1912. Die geologische Bedeutung des Wachstunsdruchs 
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 4. ARRHENIUS, SVANTE. 1912. Zur Physik der Salzlagerstatten. Medde- 
 
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 7-25- 
 
 5. BASCOM, FLORENCE. 1897. Aporhyolite of South Mountain, Penn- 
 
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 393-396. 
 
 6. BASCOM, F. 1900. Volcanics of Neponset Valley, Massachusetts. 
 
 Bulletin of the Geological Society of America, , Vol. XI, pp. 115-126. 
 
i 
 
 774 PRINCIPLES OF STRATIGRAPHY 
 
 7. BECKER, GEORGE F. 1895. The Torsional Theory of Joints. Trans- 
 
 actions of the American Institute of Mining Engineers, Vol. XXIV, pp. 
 130-138; 865-867. 
 
 8. BRANNER, J. C. 1904. The Stone Reefs of Brazil, Their Geological and 
 
 Geographical Relations, with a Chapter on the Coral Reefs. Bulletin 
 of the Museum of Comparative Zoology, Vol. XLIV, 285 pp., 95 plates. 
 Ibid. 1905. Geological Society of America. Bulletin, Vol. XVI, pp. 
 
 I-I2, pis. I-II. 
 
 9. CRAMER, FRANK. 1890. On a Recent Rock Flexure. American Journal 
 
 of Sciences, 3rd series, Vol. XXXIX, pp. 220-225. 
 
 10 CRAMER, F. 1891. On the Rock Fracture at the Combined Locks 
 Mill, Appleton, Wisconsin. Ibid., 3rd series, Vol. XLI, pp. 432-434. 
 
 11. DALY, REGINALD A. 1900. The Calcareous Concretions of Kettle 
 
 Point, Lambton County, Ontario. Journal of Geology, Vol VIII, pp. 
 135-150. 
 
 12. DANA, JAMES D. 1890. Corals and Coral Islands, 3rd edition. 
 
 13. EVERDING, H. 1907. Deutschlands Kalibergbau. Festschrift zum 
 
 loten Allgemeinen deutschen Bergmannstage zu Eisenach, Vol. I, pp. 
 25-133 (especially pp. 50, 83, 88). 
 
 14. GEIKIE, A. 1893. A Textbook of Geology, 3rd edition. 
 
 15. GERBING, J. 1909. Chemische Untersuchungen von Meeresboden- 
 
 Meereswasser- und Luft-Proben der deutschen siidpolar Expedition. 
 1901-1903, Bd. VII. Berlin. 
 
 1 6. GRABAU, A. W. 1904. On the Classification of Sedimentary Rocks. 
 
 American Geologist, Vol. XXXIII, pp. 228-247. 
 
 17. HAHN, F. FELIX. 1912. The Form of Salt Deposits. Economic Geology, 
 
 Vol. VII, pp. 120-135 (and papers cited there). 
 
 18. HAHN, F. F. 1912. Untermeerische Gleitungen bei Trenton Falls 
 
 (Nord Amerika) und ihr Verhaltniss zu ahnlichen Storungsbildern. 
 Neues Jahrbuch fur Mineralogie, u. s. w., Beilage Bd. XXXVI, pp. 1-41, 
 taf. I-III. 
 
 19. IRVING, A. 1889. Chemical and Physical Studies in the Metamorphism 
 
 of Rocks. Longmans, Grfeen & Co., London. 
 
 20. JOHNSTON, JOHN. 1854. Notice of some spontaneous movements 
 
 occasionally observed in the sandstone strata in one of the quarries at 
 Portland, Connecticut. Proceedings of the American Association for 
 the Advancement of Science, 8th meeting, 1854, pp. 283-286. 
 
 21. KING, L. V. 1912. On the limiting strength of rocks under conditions 
 
 of stress existing in the Earth's interior. Journal of Geology, Vol. XX, 
 pp. 119-138. 
 
 22. KOKEN, ERNEST. 1902. Ueber Gekrosekalke des ob'ersten Muschel- 
 
 kalkes am unteren Neckar. Zentralblatt fur Mineralogie, etc., 1902, No. 3. 
 
 23. MOORE, ELWOOD S. 1912. Siliceous- oolites and other concretionary 
 
 structures in the vicinity of State College, Pennsylvania. Journal of 
 Geology, Vol. XX, No. 3, pp. 259-269. 
 
 24. NILES, WILLIAM H. 1876. The Geological Agency of Lateral Pressure 
 
 in Quarrying. Proceedings of the Boston Society of Natural History, 
 Vol. XIV, pp. 1-8. 
 
 25.- NILES, W. H. 1876. The Geological Agency of Lateral Pressure Ex- 
 hibited by Certain Movements of Rocks. Ibid., Vol. XVIII, pp. 272-284. 
 
 26. PFAFF, F. W. 1895. Beitrage zur Erklarung iiber die Entstehung des 
 Magnesits und Dolomits. Neues Jahrbuch fur Mineralogie, u. s. w., 
 Beilage Bd. IX, pp. 485-507. 
 
BIBLIOGRAPHY XIX 775 
 
 27. ROSENBUSCH, II. 1898. Elemcnte tier Gesteinslehre. Stuttgart. 
 
 28. SKEATvS, E. W. 1903. The chemical composition of limestones from 
 
 upraised coral islands, with notes on their microscopical structure. Bul- 
 letin of the Museum of Comparative Zoology, Vol. XLII, pp. 53-126. 
 
 29. SMYTH, C. H., JR. 1892. On the Clinton Iron Ore. American Journal 
 
 of Sciences, 3rd series, Vol XLIII, pp. 487-496. 
 
 30. STEIDTMANN, EDWARD. 1911. The Evolution of Limestones and 
 
 Dolomite. Journal of Geology, Vol. XIX, pp. 323-345; 392-428. 
 
 31. SUESS, EDUARD. 1910. The Face of the Earth, Vol. II (English 
 
 translation by Sollas and Sollas). 
 
 32. VAN HISE, CHARLES R. 1884. Enlargement of Feldspar Fragments 
 
 in Certain Keweenawan Sandstones. Bulletin of the United States 
 Geological Survey, No. 8, pt. I, pp. 44-47. 
 
 33. VAN HISE, C. R. 1896. Principles of North American Pre-Cambrian 
 
 Geology. i6th Annual Report of the United States Geological Survey, 
 pt. I. 
 
 34. VAN HISE, C. R. 1904. A Treatise on Metamorphism. United States 
 
 Geological Survey, Monograph XLVII. 
 
 35. WALTHER, JOHANNES. 1894. Einleitung in die Geologic, Litho- 
 
 genesis der Gegenwart. 
 
 36. WIELAND, G. R. 1897. Eopalaeozoic Hot Springs and the Origin of J 
 
 the Pennsylvania Siliceous Oolites. American Journal of Science, 4th 
 series, Vol. IV, pp. 262 et seq. 
 
 37. ZIEGLER, VICTOR. 1912. The Silicious Oolites of Central Pennsylvania. 
 
 American Journal of Science, 4th series, Vol. XXXIV, pp. 1 13-127. 
 
CHAPTER XX. 
 DEFORMATION OF ROCK MASSES. 
 
 Having in the preceding chapters dealt at length with the subject 
 of rock formation, or Litho gene sis, we must next turn our attention 
 to the subject of rock deformation or Orogenesis, i. e., the making 
 of mountain structures. 
 
 As the result of rock deformation a number of distinct struc- 
 tural features come into existence, some of which have already 
 been noted in the preceding chapters. Deformation may be classed 
 as endogenetic or exogenetic, i. e., produced by internal or external 
 causes, respectively. Internal causes are diagenetic, such as chemi- 
 cal change, recrystallization, etc., while external causes include 
 pressure and motion due to gravity, to tectonic disturbances, etc. 
 The following types of deformation may be considered : 
 
 I. Endogenetic. 
 
 1. Endolithic brecciation. 
 
 2. Enterolithic structure. 
 
 3. Contractive joints (prismatic) (basaltic). 
 
 II. Exogenetic. 
 
 A. Gravitational Deformations. 
 
 a. Structures Due to Movement. 
 
 4. Intraformational brecciation. 
 
 5. Gliding deformations. 
 
 6. Surface deformation through creep. 
 
 b. Structures Due to Compression. 
 
 7. Squeezed-out strata. 
 
 8. Shaliness. 
 
 9. Slatiness. 
 
 c. Of Complex Origin. 
 
 10. Pressure sutures and stylolites. 
 
 11. Cone-in-cone structure. 
 
 776 
 
TYPES OF DEFORMATION 777 
 
 B. Tectonic or Orogenic Deformation. 
 
 12. Tectonic joints. 
 
 13. Earthquake fissures. 
 
 14. Slaty cleavage. 
 
 15. Fissility. 
 
 16. Schistosity. 
 
 17. Gneissoid structure. 
 
 1 8. Folding Anticlines, synclines, isoclines, fan folds, mono- 
 
 clines, etc. 
 
 19. Domes and basins. 
 
 20. Faulting. 
 
 C. Contact Deformations. 
 
 21. Prismatic structure. 
 
 22. Insolation joints. 
 
 D. Complex Structures Partly Due to Deformation. 
 
 23. Metamorphism. 
 
 24. Disconformity and unconformity. 
 
 ENDOGENETIC DEFORMATIONS. 
 
 i. Endolithic Brecciation. This term is applied to brecciation 
 of strata caused by forces acting from within the mass, such as 
 crystallization and especially swelling or hydration, as in the case 
 of gypsum, etc. In this last case it is only the extreme of entero- 
 lithic structure. Similar structures are produced by contraction of 
 the rock mass on drying and the disruption into blocks or cakes 
 which are subsequently enclosed by later deposits and form an endo- 
 static rudyte. Examples of such have recently been described by 
 Hyde (11:400-408) from the Coal Measures of Ohio. Beds of 
 fresh-water limestone intercalated in the series and deposited in a 
 playa lake were subject to periodic drying, as a result of which the 
 surface for several acres was broken up into polygonal blocks of 
 various sizes, the surfaces of which were frequently covered by 
 the shells of the animals killed in the drying of the lake. The 
 fragments seem to have been exposed for a while to weathering 
 and were then covered by a second flooding. Where the covering 
 deposits were muds, the limestone fragments form a striking series 
 of pebbles in a lutaceous matrix and often weather out in relief. 
 Many intraformational conglomerates may have such an origin. 
 Such breccias are of course closely similar to intraformational brec- 
 cias due to gliding movements as described under Section 4. 
 
PRINCIPLES OF STRATIGRAPHY 
 
 2. Enterolithic Structure. This has already been discussed in 
 the preceding chapter. In so far as it can be shown that this struc- 
 ture is a purely diagenetic one, brought about by the swelling of 
 the mass either through crystallization or hydration, it properly 
 belongs to endogenetic deformations. If, on the other hand, it 
 should be proven that enterolithic structure in some rocks is pro- 
 duced by the pressure of the overlying mass and the consequent 
 creep and rearrangement of the particles under pressure, such de- 
 formation must be classed under the gravitational section of the 
 exogenetic class. 
 
 The important distinction between enterolithic and other de- 
 formations, such as folding under lateral pressure, or gliding in a 
 given direction, lies in the fact that the enterolithic structure folds 
 in all directions is apolar or multipolar instead of unipolar. 
 
 FIG. 162. Diagram illustrating the formation of contraction joints and of 
 desiccation fissures. The normal form is hexagonal, but, as 
 shown in the left-hand member, an irregular pentagonal form is 
 developed when one side is suppressed. 
 
 3. Contraction Joints Basaltic Jointing. This is seen in the 
 formation of mud cracks in lutaceous sediments such as clay or 
 argillo-calcareous mud and in the development of prismatic jointing 
 in cooling basalt and other igneous rocks. In the latter case the 
 prisms always form at right angles to the enclosing surface, such 
 as the upper and lower surface of a sill or laccolith, when the prisms 
 will be vertical or curved, or the lateral walls of a dike, when the 
 prisms will be horizontal. The prevalence of six-sided forms in 
 these prisms suggests that the crystallizing force centers about 
 equidistant points in the magma, each of which will draw an equal 
 amount of the surrounding matrix toward it from all sides. This 
 results in other equally spaced points between these around which 
 the tension in all directions is greatest. Since the points around 
 which attraction takes place are all equally distant from one an- 
 
ENDOGENETIC DEFORMATION 779 
 
 other, they form the apices of a series of equilateral triangles and 
 the points around which the greatest tension is focused will be the 
 centers of these triangles. The smallest number of cracks about 
 these central points which will relieve the tension in all directions is 
 three. If these cracks are symmetrically arranged about the point, 
 the angle between any two of them is 120, which is the angle 
 between the two sides of a hexagonal prism. As shown in the 
 diagram (Fig. 162), this uniform contraction about equidistant 
 points will result in the formation of a set of uniform hexagonal 
 prisms. Unequal development or failure of the cracks to develop 
 about one of the points may lead to five-sided or other irregular 
 prisms. 
 
 Drying mud will in like manner cause a development of a series 
 of prisms which typically are hexagonal, but from lack of homo- 
 geneity of the material through unequal drying, or from some other 
 cause, are frequently irregular polygons. The prisms are seldom 
 very high, though in exceptional cases the cracks may penetrate to 
 a depth of ten feet. In general a fraction of an inch is the usual 
 height of the dried mud prisms, the sides of which are slightly 
 raised, giving a concave surface. (See ante, Chapter XVII.) 
 
 Prismatic jointing is also sometimes found in undisturbed hydro- 
 genie rocks. Examples of these occur in some gypsum beds of the 
 Paris Basin. It is quite probable that this structure is due to 
 pressure exerted by hydration of anhydrite and so belongs to the 
 diagenetic processes. 
 
 DEFORMATIONS DUE TO EXTRANEOUS CAUSES 
 EXOGENETIC DEFORMATIONS. 
 
 This type may be divided into (A) Gravitational, (B) Orogenic, 
 and (C) Contactic. 
 
 A. GRAVITATIONAL DEFORMATIONS. 
 a. Structures Due to Movements. 
 
 4. Intraformational Brecciation. This has already been dis- 
 cussed in the chapter on Autoclastic rocks, but is again mentioned 
 here as a structural feature. It is probably in all cases an extreme 
 of the next type, and so may be considered in connection with that 
 subject. Here belong the edgewise conglomerates of many lime- 
 stone formations. 
 
780 PRINCIPLES OF STRATIGRAPHY 
 
 5. Subaquatic, Gliding-deformation. Offshore deposits of sedi- 
 ments on a gently sloping sea or lake bottom may suffer from time 
 to time deformation of the surface layers through gliding or slip- 
 ping down the gently inclined sea floor. Such deformation has 
 been repeatedly observed in modern deposits. The best known 
 modern examples are those which affected the village of Horgen 
 on the lake of Zurich in 1875, and the village of Zug in 1887. Both 
 of these have already been described in Chapter XV, p. 658. The 
 most remarkable fact about the gliding in Zug was that it took place 
 on an average grade of 6% (3 26'), while the larger and more 
 
 FIG. 163. Folding accompanying subaquatic gliding in Miocenic marl of 
 Oeningen natural size. (After Heim.) 
 
 pronounced movement occurred on a grade as low as 4.4% (a 
 trifle over 2 31'). The material which thus slid into the lake 
 was brecciated and folded with overfolds, overthrusts, reversals of 
 layers, excessive strata, etc., and furnishes an excellent guide to 
 the interpretation of similar movement in the past. Among the 
 chief points in which these folds differ from those produced diage- 
 netically by swelling of gypsum, or by pressure of overlying masses, 
 is that they are of the nature of normal folds due to lateral com- 
 pression and so show movement in one direction only, whereas in 
 the case of the other deformations movements in several directions 
 are shown. Furthermore, the axes of the folds are thickened in 
 the gliding as in normal tectonic folds, instead of the limbs, as is 
 the case in folds due to swelling. 
 
GLIDING DEFORMATIONS 781 
 
 Examples of fossil subaqueous soliftuction. 
 
 A. Miocenic sublacustrine glidings of Oeningen. The Miocenic 
 marls of Oeningen, noted for their wonderful remains of insects, 
 etc., show in the midst of these beds a strongly folded layer,, lying 
 between horizontal beds of the same character. These foldings are 
 so pronounced that they inevitably suggest lateral compression as 
 the cause of their production, yet the entirely undisturbed charac- 
 
 FIG. 164. Folding accompanying subaquatic gliding in Miocenic marl of 
 Oeningen. One-half natural size. (After Heim.) 
 
 ter of the enclosing strata forbids such an assumption. Another 
 feature which indicates gliding is the independence of the folded 
 beds from the basal beds, against which the limbs commonly abut 
 directly. The axes of the folds are notably thickened, while the 
 limbs are thinned by compression exactly as in tectonic folding. 
 (Figs. 163, 164.) 
 
 B. Jurassic deformations of this type are known from the 
 Solnhofen Plattenkalke, where the so-called distorted layer (krumme 
 Lage) furnishes a good example. The zone has a thickness 
 of i to 1.5 meters, and in it are found all the phenomena of 
 folding, including folds 5 meters in length. Here the glidings took 
 place in the periodically submerged lagoons within the reefs and the 
 
782 PRINCIPLES OF STRATIGRAPHY 
 
 calcareous nature of the material probably insured a partial cemen- 
 tation before the gliding took place. (See Fig. 95, p. 440.) 
 
 C. Triassic examples are known from the Muschelkalk of Ger- 
 many, especially the Main region, but not all of the disturbances 
 found in this formation and so fully described by Reis (20) belong 
 
 FIG. 165. Deformation due to subaqueous gliding, Muschelkalk, Franken 
 (Germany) 1 150. (After Reis.) 
 
 here. The enterolithic structure described by Koken (13) from the 
 Neckar Valley must certainly be removed from this category of 
 deformation due to submarine glidings. 
 
 D. Devonic examples of this class have been figured by Sir 
 Wm. Logan from the Cape Bon Ami limestones of Lower Devonic 
 age from Gaspe (Logan-i5 : jp^) where in division 4 and less 
 
 FIG. 166. Deformation due to subaqueous gliding, Muschelkalk, Franken 
 (Germany) 1 150. (After Reis.) ^ 
 
 than 400 feet above the base of the entire series is a bed seven 
 feet thick made up of several thin layers of limestone and limestone 
 shale and presenting a series of wrinkles or contortions from which 
 the overlying and underlying beds are free. ', The series now dips 
 at an angle of 24 southwest. The folding in some cases has been 
 so intense as to cause a brecciation of the limestone beds. (Fig. 167.) 
 
GLIDING DEFORMATIONS 
 
 783 
 
 E. Ordovicic examples of this type are beautifully exposed in 
 the walls of the gorge of East Canada Creek at Trenton Falls, 
 N. Y. Here there are at least three such disturbed zones, one well 
 
 FIG. 167. Corrugated limestone beds, showing the effects of subaqueous 
 gliding. Gaspe limestone, Canada. Scale about i :20O. (After 
 Logan.) 
 
 shown below the Lower or Sherman Falls, one just below the High 
 Falls (now replaced by a high dam), and a third higher up. All of 
 these show a wonderful series of folds and overthrusts, the zones 
 varying in thickness up to 4 meters, and, as is to be expected, dying 
 
 FIG. 168. Deformation due to sub- FIG. 169. Deformation due to sub- 
 aqueous gliding, Trenton lime- aqueous gliding, Trenton lime- 
 stone, Trenton Falls, N. Y. 1 175. stone, Trenton Falls, N. Y. i :ioo. 
 (After Hahn.) (After Miller.) 
 
 out after a while, though traceable for some considerable distance. 
 The upper and lower layers are not disturbed, but absolutely nor- 
 mal, not even showing evidence of excessive compression. The 
 layers involved in the folding are not always the same, sometimes 
 they are granular limestones with abundant organic remains, but 
 
784 PRINCIPLES OF STRATIGRAPHY 
 
 more often they are calcilutytes. The fossils are often broken, but 
 no recrystallization occurs; the appearance is such as would be 
 expected from the result of gliding of a mass of imperfectly lithi- 
 fied lime mud. The overlying layers have all the characters of 
 normal deposits on the deformed layers, there being thus a struc- 
 tural unconformity, though without a hiatus. (Figs. 168, 169.) 
 These disturbances at Trenton Falls have been variously explained, 
 the general conclusions of geologists being either : ( i) that they were 
 truly tectonic lateral pressure having resulted in the folding of 
 certain strata while others took up the thrust without deformation, 
 or (2) that they were due to squeezing out of certain layers under 
 the weight of the overlying rock masses. Both explanations are 
 unsupported by the detailed characteristics of the folds and their 
 
 FIG. 170. Edgewise conglomerate, Beek- FIG. 171. Section across the 
 mantown limestones, Center county, two interlocking stylolites, 
 
 Pennsylvania. (After Hahn.) shown in Fig. 172, much 
 
 reduced. (After Wagner.) 
 
 relationship to the enclosing layers. The recognition of these layers 
 as gliding surfaces, analogous to the Horgen-Zug occurrences, and 
 comparable to the Oeningen folds, is to the credit of Dr. F. Felix 
 Hahn, at that time curator in Palaeontology in Columbia Univer- 
 sity. (Hahn-/.) 
 
 F. A Cambric or earlier example of such movements seems to 
 be indicated by the folded layers of the Biri limestone of Mjosen, 
 Norway, described by Rothpletz (21). This limestone contains 
 certain layers "which are deformed in a singular manner without 
 the enclosing layers partaking of such deformation. It appears as 
 if, during the tilting, these layers had not enough stability, and 
 collapsed within themselves, so that between the more stable layers 
 there occurred a movement in which the enclosing strata had no 
 part." (Rothpletz-2i : 28.) The characters of these foldings seem 
 in every way analogous to those of the younger formations de- 
 scribed. 
 
INTRAFORMATIONAL CONGLOMERATES 785 
 
 Finally, it should be mentioned that in the unconsolidated deposit 
 of the Pleistocenic such deformations occur, though some of them, 
 no doubt, are due to glacial thrust. The deformation of the Ter- 
 tiary beds of Martha's Vineyard may possibly belong to this cate- 
 gory. 
 
 Deformation through gliding may result in complete brecciation 
 of the deformed layers. The fragments may lie in all positions, as 
 in the case of ordinary "intraformational conglomerates," or they 
 may consist of thin cakes, many of which in the gliding process have 
 assumed a vertical position in the mass. This forms the so-called 
 "edgewise conglomerate" common in the Ordovicic limestones of 
 the Appalachian region. The characteristics of all these forma- 
 tions seem to point to rather shallow water as the place of deposi- 
 tion of these strata, and the possible periodic exposure and partial 
 hardening of the surface layers. A different explanation has, how- 
 ever, been given for these by Seely and amplified by Brown (i). 
 
 6. Surface Deformation Due to Creep. As already noted (p. 
 543), vertical strata, especially of a shaly or slaty character, are 
 subject to deformation in portions of their exposed ends by the 
 creep of the surface soil down a sloping hillside composed of thin 
 strata. A bending in the direction of movement is generally found 
 to occur after a while. Such deformation is of slight importance, 
 and is probably never preserved in the older rocks. 
 
 b. Deformations Due to Vertical Pressure of Overlying Rock 
 
 Masses. 
 
 7. Squeezing Out of Layers. This may occur in cases where 
 certain beds are especially susceptible to such deformation. Fine- 
 grained, homogeneous strata seem to be most readily affected in this 
 way. An enterolithic structure similar to that produced by swelling 
 masses (gypsum, salt) is thus produced, the effect being similar 
 whether the pressure originated from the swelling of the mass itself 
 or from the weight of the overlying rock. Koken believes that the 
 enterolithic structure in the Muschelkalk of the Neckar Valley 
 (Gckrosekalke) is due to vertical pressure and squeezing out of 
 these layers. (Ante, Fig. 161.) 
 
 8. Shaliness is the property of lutaceous rocks, rich in clay, to 
 split with concave or "shelly" surfaces in a general way parallel to 
 the bedding planes. The structure is a secondarily derived one, due 
 to vertical pressure and the character of the rock. It seems to be 
 best developed in calcareous shales. That it is a secondary struc- 
 ture is shown by the fact that the splitting will sometimes pass 
 
786 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 across a fossil, a part of which remains with either portion of the 
 split mass. 
 
 9. Slatiness. This term is applied to the structure developed by 
 many siliceous and carbonaceous argillutytes of splitting into thin 
 layers or plates parallel to the bedding and with essential regularity 
 of surfaces similar to true slaty cleavage. The Genesee and Black 
 Portage shales of New York, the Black Shale of Ohio and Michigan 
 and others of their kind show this feature well. It is shown in the 
 undisturbed Jurassic lutytes of Wtirttemberg, which are split into 
 slate blocks to all appearance comparable to slates from disturbed 
 
 
 FIG. 1.72. Stylolite from Trigonodus limestone (Muschelkalk) of Frauenthal. 
 Three-quarters natural size. (After Wagner.) (See Fig. 171.) 
 
 regions. Finally a certain slatiness is observed in the Plattenkalke 
 of the Upper Jura in the Solnhofen region, where layers are split 
 thin enough for roofing slate purposes. 
 
 In all these cases the region is undisturbed, and the slaty struc- 
 ture is parallel to the bedding. It is apparently developed as the re- 
 sult of pressure of the overlying rock masses, and, when exposed 
 to erosion, it is developed by the weather in the same way that 
 slaty cleavage is developed by the weather. 
 
 c. Of Complex Origin. 
 
 10. Pressure Sutures and Stylolites* In massive limestones 
 are not infrequently found irregular sutures or seams, which pene- 
 
 * For a recent comprehensive survey of the subject together with discussion 
 of all the theories of origin advanced, and reference to literature, see Wagner-24. 
 
PRESSURE SUTURES AND STYLOLITES 787 
 
 trate the rock usually in a direction parallel to the bedding planes. 
 These sutures (Drucksuturen of the Germans) range from a 
 scarcely visible size to projections an inch or more in 7 length. They 
 interlock on opposite sides in a most complicated manner, which 
 has led to their comparison with the sutures of a skull (Vanuxem). 
 Such sutures have been found in limestones of widely varying geo- 
 logical ages and in different parts of the world. They seem to pass 
 by gradation into the true stylolite structures which generally occur 
 in the same or in similar limestone beds. Stylolites generally occur 
 along a horizontal plane of separation^ and consist of flutes and 
 slickensided columns of limestone, varying in length up to 4 inches 
 or more, and in diameter up to two or more inches and projecting al- 
 ternately from the upper and from the lower layer at right angles. 
 At the end of each column is usually a cap of clay, which weathers 
 out in the cliff, leaving hollow cavities. That these structures are 
 due to pressure is suggested by the fact that the fracture line often 
 passes across recognizable organic remains, the two parts of which 
 are displaced in opposite sides of the fracture plane. The structure 
 thus resembles minute faulting, the flutings on the sides of the col- 
 umn being analogous to the slickensides formed at the fault planes. 
 Stylolites are often mistaken for corals or other organic remains. 
 Not infrequently a shell or other fossil remains caps the stylolite, 
 and determines the outline of the fluted column. 
 
 Ordinary pressure work has, however, not taken place here, 
 for nowhere is there any evidence of deformation of the beds by 
 crowding or compression above the columns, which project from 
 one face of the suture into the hollows of the other. In other 
 words, if the interlocking of the notch-like projections were due to 
 simple compression before or after solidification, then wherever a 
 hollow occurs there should be evidence above and around that hol- 
 low of compression and movement to crowd away the material so as 
 to produce that hollow. 
 
 That the structure was produced after the solidification of the 
 rock is shown by the fact that the surfaces of separation are sharp, 
 that the sides are striated and that all evidence of massive deforma- 
 tion or squeezing is wanting. The most satisfactory theory yet ad- 
 vanced to explain these remarkable structures is that they are the 
 result of unequal solution along sutures or fracture planes. If solu- 
 tion takes place on the concave surfaces of both the upper and lower 
 face of the fracture, the result must be the production of a series of 
 tooth-like projections from both sides of the fissures, which, owing 
 to the pressure of the overlying rock, interpenetrate more and more 
 as room is macje by solution. In other words, the rock opposite the 
 
788 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 end of each tooth-like projection is dissolved away the hollows are 
 deepened, and thus the teeth, by gliding under pressure, penetrate 
 deeper and deeper into the opposite bed, while at the same time 
 they become longer by the deepening of the hollows which surround 
 and isolate them. The residual clay, left on solution, comes to rest 
 as a cap on the top of the stylolite, protecting this top from solu- 
 tion. 
 
 It is not necessary that the suture or dividing plane should be 
 irregular to begin with. Unequal solution on opposite sides of the 
 plane is sure to occur, since rocks are seldom so homogeneous that 
 all parts are equally soluble. Such irregularity once produced, it 
 will continue to be augmented, for the greatest amount of pressure 
 
 FIG. 173. Sketch of a portion of a limestone face of white Jura j8 in Tal- 
 heim, showing stylolites. (After Wagner.) The spaces result- 
 ing (black) are filled with calcite. (After Wagner.) (Much 
 reduced.) 
 
 will occur where the rocks on opposite sides come in contact. The 
 projecting mass, especially if it is crowned by a fossil which is less 
 readily soluble than the enclosing rock, generally suffers the least 
 solution, while the hollow opposite into which it presses suffers 
 the largest amount of solution. The protecting cap of clay also 
 helps this process. The sides of the growing teeth are free from 
 pressure, so solution is absent here, and deposition even may oc- 
 cur. (Figs. 171-173.) 
 
 The length of the individual stylolite tooth serves as a fair meas- 
 ure of the amount of material removed by solution from both sides 
 of the fracture plane. 
 
 ii. Cone in Cone. This is a structure sometimes found in 
 lutaceous rocks, particularly in calcareous or ferruginous argil- 
 lutytes. It consists of a number of crenulated or corrugated conical 
 
TECTONIC DEFORMATION 789 
 
 layers one within the other. In the beds they are seen to consist of 
 two sets interlocking from opposite sides, the top and bottom of the 
 beds affected being formed by the bases of the two sets of cones. 
 
 Professor Marsh (16) has suggested that this structure is the 
 result of concretions forming under pressure. It has also been 
 held that crystallization of the calcium carbonate in the bed is re- 
 sponsible for the formation of this structure. 
 
 B. TECTONIC OR OROGENIC DEFORMATIONS. 
 
 Of late the term tectonic has come to be more specially applied 
 in geology to larger rock structures, due to disturbances such as ac- 
 company and bring about the formation of mountains. In other 
 words, orogenic disturbances have come to be considered the chief 
 causes in the production of tectonic features. Lateral pressure 
 seems to be the chief active agent responsible for such deformation, 
 but it is by no means certain that the products of such lateral com- 
 pression are always distinguishable from those of vertical compres- 
 sion by the superincumbent strata. 
 
 The various types of tectonic deformation will be considered, be- 
 ginning with tectonic jointing. 
 
 d. Deformation Resulting in Fractures and Related Structures. 
 
 12. Joints. Rocks separated into more or less regular blocks by 
 natural fissures are said to be jointed. Joints may be due to shrink- 
 age on cooling, or on desiccation, forming shrinkage joints, already 
 discussed, or they may be caused by folding or other tensile stresses, 
 giving tension joints, or finally they may be due to compression on- 
 folding, forming compression joints. Both tension and compression 
 joints frequently occur together. In tension joints the surfaces will 
 be rough if the rock is arenaceous or rudaceous and the grains 
 weakly held. If the rock is lutaceous or otherwise a strong, tolera- 
 bly homogeneous rock, the fracture will be smooth and sharply cut. 
 Faulting and slickensiding may develop along such joints when sub- 
 jected to pressure, and deposit of mineral matter will take place 
 along the joint surfaces. 
 
 Daubree (3) has shown by experiments with glass plates that, 
 if a brittle stratum is subjected to torsion, when the limit of elas- 
 ticity is reached it will break, with two sets of parallel fractures 
 forming nearly a right angle with each other (Figs. 174, 175). 
 
790 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Crosby (2) has shown that, if a shock were sent through the strata 
 before this limit was reached, the fracture would be produced in a 
 similar manner. The shock may be produced by the giving way 
 of the first portion of the bed, in which torsion has been carried 
 beyond the resisting strength of the bed, or it may have extraneous 
 causes. 
 
 The slight amount of torsion required in a brittle bed is easily 
 accounted for by differential uplift of the bed. It may be illus- 
 
 FIG. 174. Illustration of Daubree's 
 method of breaking a sheet of 
 glass by torsion to produce inter- 
 secting joints. 
 
 FIG. 175. Arrangement of fractures 
 in glass plate broken by torsion. 
 (Daubree.) 
 
 trated by the torsion produced in a large sheet of stiff cardboard 
 lifted slightly by one corner. 
 
 Compression joints are produced in the folding of rocks. Simply 
 folded rocks will have joints in two planes at right angles to each 
 other. Joints of this kind are closely related to fissility, which is 
 distinguishable only by the greater number and closer approxima- 
 tion of the shearing planes. 'The same compression might produce 
 fissility along one set of shearing planes and joints along another." 
 (Van Hise-23 : 671.) 
 
 Minor characteristics of joint faces. 
 
 Feather fracture. This, as shown by Woodworth (26), is char- 
 acteristic of the joint surfaces of certain fine-grained phyllites or 
 
 
JOINTS 791 
 
 siliceous lutytes. It consists of a "delicate tracery of feathery lines 
 diverging from a roughly outlined axis, which traverses the face of 
 the joint block in a plane parallel with the stratification. When the 
 axis of the feather fracture departs from this plane it becomes sinu- 
 ous." (Woodworth-26.) 
 
 Dendritic markings. These are formed on the joint planes of 
 fine-grained rocks, and are due to the arborescent deposit of earthy 
 oxide of manganese or of iron. They may be compared to the 
 plumose frost traceries on window panes. In the so-called land- 
 scape marble, this deposit has penetrated the entire rock, and is seen 
 on all polished sections. Dendrites of iron pyrites and other min- 
 erals are also known. Not infrequently they are mistaken for 
 vegetable impressions. 
 
 Widening of joints. 
 
 Joints of tectonic origin may be widened by separation of the 
 blocks, by solution or erosion of their sides, and in other ways. The 
 Olean conglomerate on the hills of southwestern New York fur- 
 nishes a good illustration of widening of joints by separation of the 
 blocks. Here huge masses 40 feet in height and of similar basal 
 dimensions have been formed in the coarse conglomerate, and the 
 blocks have in many cases slid far enough apart to open passage- 
 ways between them. These street-like passageways between the 
 blocks have given the region the name of Rock City. The gliding of 
 the masses is favored by the soft, clayey strata underlying and by 
 the constant erosion which is going on on the hillsides. 
 
 Joints in limestones are commonly widened by solution of the 
 wall rock, which when continued long enough will produce cavern- 
 like passages and eventually caves. The peculiar character of the 
 Karst regions of the world is accounted for by such solution. 
 (See ante, p. 133.) Not infrequently partly widened fissures are 
 filled with clay, sand, gravel or other substances from above, con- 
 stituting a clastic "dike." Sandstone dikes are especially common, 
 though not always originating in solution fissures (see beyond). 
 Fissures thus filled are common in most modern limestone masses, 
 covered by drift deposits. A remarkable example of a Devonic fis- 
 sure in Niagaran limestone, filled with fossiliferous Upper Devonic 
 shales, has been described by Weller from Illinois (25). 
 
 Widening of joint fissures by erosion is of common occurrence. 
 The most active agent is often the wind, which cuts away at the 
 sides of the prism produced by the joints, and narrows it until only 
 a pillar, isolated from its neighbor, remains behind. All stages of 
 
792 PRINCIPLES OF STRATIGRAPHY 
 
 such erosion along joint cracks may be seen in the Tertiary sand- 
 stone of Monument Park, Colorado, where in the ledges the begin- 
 nings of this erosion work are seen, while scattered through the park 
 are numerous isolated stone pillars, generally capped by a fer- 
 ruginous block of greater resistance, the last remnants of an ex- 
 tensive formation which formerly covered the entire region. 
 
 13. Earthquake Fissures. A well-known phenomenon accom- 
 panying more or less violent seismic disturbances is the opening of 
 fissures in the rock by the tearing asunder of the mass. Such fis- 
 sures may remain open or be filled subsequently by the washing into 
 them of surface material, or they may be filled at the time of forma- 
 tion by material violently injected into them from above. Recent 
 fissures have been described by Whimper and others. (See Chapter 
 XXIII.) Examples of such fissures are sometimes found in the 
 fossil state. Thus the Upper Siluric limestones and dolomites of 
 western New York and Ontario are traversed by vertical fissures, 
 which show evidence of violent disruption, and into these fissures 
 sands representing the Oriskany period were injected. These sands 
 apparently rested on the old erosion surface of the Siluric limestone 
 before the shock came. The shock was a pre-Middle Devonic one, 
 for Middle Devonic (Onondaga) strata rest upon this mass without 
 showing any evidence of being affected by the shock. One of the 
 best examples of this group has been described from the cement 
 quarries of North Buffalo. 
 
 "The total depth of the fissure as now exposed with its filling 
 of sandstone is in the neighborhood of 10 feet. The dike is squarely 
 cut off at the top, where the Onondaga limestone rests on its trun- 
 cated end and on the limestones flanking it. The Onondaga lime- 
 stone is entirely unaffected by the dike, being evidently deposited 
 after the formation and truncation of this remarkable mass of sand- 
 stone. The width of the fissure is scarcely anywhere over 2 feet, 
 but lateral offshoots extend for many feet into the walls of Bull- 
 head [and Bertie] limestone. These offshoots or rootlets of the 
 dike are irregular, commonly narrow, and often appear as isolated 
 quartz masses in the Bullhead or Waterlimes, the connection with 
 the main dike not being always observable. Such masses of sand- 
 stone have been noted at a distance of 20 or 30 feet from the main 
 dike. They are always small. The dike itself has been traced for 
 more than 30 feet in an east and west direction in the sloping walls 
 of the quarry. The walls of this ancient fissure are very irregular, 
 angular masses of the limestone projecting into the quartz rock, 
 while narrow tongues of sandstone everywhere enter the limestone. 
 Extensive brecciation of the limestone has occurred along the mar- 
 
SLATY CLEAVAGE 793 
 
 gin, and the sandstone there is filled with angular fragments of the 
 limestone, which show no traces of solution, or wear by running 
 water. These limestone fragments are themselves frequently in- 
 jected with tongues of the quartz sand. The nature of the contact 
 between the quartz and the limestone, the trituration of the latter, 
 and the inclusion of individual grains of quartz sand in a triturated 
 mass of limestone, the presence of cavities along the contact filled 
 with recrystallized calcite, the presence of elongated limestone 
 "streamers" in the quartz mass near the contact, all "point to a 
 cataclysmic origin of the fissure . . . and a more or less violent in- 
 jection of the sand. ... It seems also certain that the fissure was 
 formed after the deposition of a considerable mass of sand over 
 the . . . limestone, and that the formation of the fissure and the in- 
 jection of sand from above occurred simultaneously. In no other 
 way can we account for the inclusion of horses of the wall rock, 
 often of considerable size, and the injection of the sand into all the 
 fissures and crevices; nor can we readily explain on any other hy- 
 pothesis the trituration of the limestone along the borders, which 
 clearly indicates a violent contact between the sand and the already 
 consolidated limestone. The supposition that the fissure is due to a 
 violent disruption of the wall ... is further borne out by the nu- 
 merous minute faults which occur in the Waterlimes in the vicinity 
 of the fissure and elsewhere." (Grabau-5 : 360-361.) 
 
 14. Slaty Cleavage. Slaty cleavage (Leith-i4) is the property 
 of strata to split or "cleave" along certain planes which as a rule 
 have no relation to the planes of stratification. This property is 
 especially well developed in argillutytes, resulting in the formation 
 of "slates," from which the term slaty cleavage has been derived. 
 Slate is therefore a structural term, and has no lithic significance, 
 except in so far as the structure is best developed in the clastic 
 rocks of lutaceous texture, and generally in part at least of argil- 
 laceous composition. This rock structure has been explained as 
 "due to the arrangement of the mineral particles with their longer 
 diameters or radial cleavage, or both, in a common direction, and 
 that this arrangement is caused, first and most important, by paral- 
 lel development of new minerals; second, by the flattening and 
 parallel rotation of old and new mineral particles, and, third, 
 and of least importance, by the rotation into approximately paral- 
 lel positions of random original particles." (Van Hise-23 : 635.) 
 (See also page 770.) 
 
 The original cause of these changes is the lateral compression of 
 the rocks due to orogenic disturbances. Cleavage may be considered 
 as separation of the laminae, potentially developed in the rock. The 
 
794 PRINCIPLES OF STRATIGRAPHY 
 
 actual cleavage or splitting is subsequently developed by the frost, 
 or other atmospheric agent, or by the hand of man. 
 
 Coarse-grained rocks are seldom affected by cleavage. Lime- 
 stones likewise offer great resistance to compression, and are not 
 generally cleaved. Thus cleavage may often be developed in a 
 stratum of argillaceous lutytes, while adjoining arenytes or calcare- 
 ous beds will be unaffected. This sometimes gives rise to the ap- 
 pearance of an unconformity. 
 
 Cleaved strata commonly have their original bedding structure 
 obliterated. Only in exceptional cases are the bedding planes pre- 
 served, when the strata are differently colored or when a change 
 in texture occurs. In such cases ribbon slates or banded slates are 
 produced. In cleaved fossiliferous strata the fossils may sometimes 
 be detected on the weathered surfaces of the bedding plane, the 
 position of which they indicate. A very general distortion of the 
 fossils accompanies the formation of cleavage, so that in many cases 
 the remains are no longer recognizable. 
 
 Unless the relation of cleavage to the bedding is detected, an er- 
 roneous conception of the structure of a country is obtained. Strata 
 which are strongly cleaved generally appear to be vastly thicker 
 than they really are, and unconformities are sometimes considered 
 to exist between strata where in reality the bedding planes are per- 
 fectly concordant. If, however, a formation with slaty cleavage is 
 overlain by one without such structure, although of a composition 
 which would permit its development as readily as would the under- 
 lying rock, a discordance of relation is indicated, though in the ab- 
 sence of other evidence this is not fully demonstrated. (Van Hise- 
 23:7**.) 
 
 15. Fissility is the structure found in some rocks, "by virtue of 
 which they are already separated into parallel laminae in a state of 
 nature." It thus differs from cleavage, where this separation is 
 only potential. Fissility belongs in the zone of fracture, while 
 cleavage belongs in that of flowage. Both occur and grade into 
 each other in the zone of combined fracture and flowage. 
 
 16. Schistosity. This structure is the result of intense meta- 
 morphism under pressure, and is characterized by the development 
 of planes of cleavage due to the presence of large, cleavable par- 
 ticles. It is essentially comparable to slaty cleavage, except that 
 metamorphism has gone farther and the rock has become crystal- 
 line. Schistosity may be developed in rocks of many kinds, both 
 clastic and igneous. Foliation is another term applied to these 
 rocks. 
 
 The structure is essentially due to recrystallization of the rock 
 
DEFORMATION BY FOLDING 795 
 
 on mashing. It is often not apparent in fresh rocks, but, as in the 
 case of slaty cleavage, is developed on exposure to the atmosphere. 
 17. Gneissoid Structure. This structure, like schistosity, re- 
 sults from intense mashing and recrystallization of rocks subjected 
 to symphrattic metamorphism. Gneissoid structure is essentially 
 characterized by banding, the bands being of unlike composition. 
 The mineral particles also interlock so that the cleavage is much less 
 perfect than in schists. Usually it is parallel to the banding, but 
 this is not always the case. Gneissoid structure may be developed 
 in igneous and in clastic rocks. In the former case we have granite- 
 gneisses, diortite-gneisses, etc., in the lattc arenyte or sandstone 
 gneisses, rudyte gneisses or conglomerate gneisses, etc. 
 
 e. Deformations Due to Folding, and to Folding and Erosion. 
 
 1 8. Folding. Rock folds are among the most conspicuous and 
 easily recognized tectonic features. They vary greatly in magni- 
 tude, from the minute wrinkles formed in the axes of larger folds, 
 to those whose limbs are many miles apart. In regions of erosion 
 generally only a part of the fold is found, the folded strata having 
 been truncated and cut down until only portions of the limbs re- 
 main. In this way the appearance of tilted strata is produced, these 
 tilted strata being, however, only the remnants of great folds. 
 
 The form of folds is very variable, but it has been possible to 
 select a number of distinct types, of which the others are variants. 
 These distinct types are (a) anticline, (b) synclines, (c) isoclines, 
 (d) fan folds, and (e) monoclines. Compound anticlines are 
 anticlinoria and compound synclines are synclinoria. 
 
 (a) Anticlines. In this type the sides or limbs of the fold 
 typically slope away, from the plane of the axis on either side. The 
 sloping portions are known as the limbs of the anticline, and the 
 amount of slope as compared with the horizontal is the angle of dip. 
 All folds are wrinkles in the earth's crust, and if followed far 
 enough along the axis they will die out. The amount of inclination 
 of the axis of the fold, also measured from the horizontal, is called 
 the pitch. Every anticlinal axis pitches in two directions, i. e., to- 
 ward the two ends of the folds. A short anticline in which the two 
 axes are of approximately equal length is a dome. 
 
 (b) Synclines. When the limbs of the fold dip toward the axis 
 a trough fold or syncline is produced, : the axis of which pitches to- 
 ward the center of the fold. A short syncline, in which the two 
 axes are of nearly equal length, is a basin. 
 
79 6 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Anticlines and synclines may be either symmetrical or asym- 
 metrical, according as the limbs are equal in length and inclination, 
 or unequal. Anticlines may be erect or recumbent. In the latter 
 case one limb of the anticline is overfolded, and the strata compos- 
 ing it are overturned. 
 
 FIG. 176. Anticlinal fold near St 
 Abbs Head, Scotland. (Geikie.) 
 
 FIG. 177. Two anticlines enclosing a 
 s y n c 1 i n e truncated above. 
 (Geikie.) 
 
 (c) Isoclines. When the limbs of a fold are parallel an isocline 
 is produced. The limbs of such a fold may stand vertically or they 
 may be inclined. In the latter case some portion of the strata in- 
 volved will always be overturned, i. e., their original surface now 
 
 FIG. 178. Synclinal fold near Banff, Scotland. (After Geikie.) 
 
 lies below. Nearly horizontal isoclines are produced by overfolds 
 and underfolds. 
 
 In a region of isoclinal folds, the most important problem con- 
 fronting the stratigrapher is the recognition of the repetition of 
 strata and the proper relationship between them. It is evident that 
 a succession of strata, such as is shown in Fig. 179, a, may be inter- 
 
ISOCLINAL FOLDS 
 
 797 
 
 preted as all belonging to one limb of a fold, and therefore repre- 
 senting a continuous series, or as representing one or more isoclinal 
 folds. According to the first interpretation, the sediments have 
 great thickness, and there is a recurrence of similar beds, while, 
 according to the second interpretation, the series is much thinner 
 and the recurrence of beds is only apparent, there being an actual 
 repetition of the same beds. The problem is often a difficult one to 
 solve, and depends upon the identification of the similar beds as 
 parts of the same bed. A knowledge of the degree of folding char- 
 acteristic of the region in question and a knowledge of the charac- 
 ters and thicknesses of the formations involved in other and undis- 
 
 123 4 4 321 123443 
 
 FIG. 179. Isoclinal strata, showing repetition of strata (a) and two methods 
 of reconstructing them (b, c). 
 
 turbed regions will often serve to settle the question. If more than 
 two kinds of beds are involved, the order of repetition will often 
 give a clue to the original condition. Thus in a closely folded dis- 
 trict, the strata within the same fold will be repeated in inverse 
 order, as shown in Fig. 179, a. 
 
 This generally is conclusive evidence of repetition by folding. If 
 this point is settled, the next question is: Which bed is the upper 
 and which is the lower of the series? If the character of the folds 
 can be determined by inspection, the proper relation will at once 
 appear, for if, when beds 4 and 4 come in juxtaposition, they pre- 
 sent the upper ends of the fold, i. e., they are parts of an anticline, 
 bed 4 is the oldest and originally the lowest of the series (Fig. 
 179, &). 
 
 If, however, the two limbs of the folded bed 4 join below the 
 
798 PRINCIPLES OF STRATIGRAPHY 
 
 surface in a concave or synclinal fold, bed 4 is the youngest of the 
 series, and formerly overlay all the others. When the actual type 
 of folding cannot be observed, an examination of the beds them- 
 selves will often reveal their relationships. Thus, if bed 3 shows 
 normal ripple marks, footprints or other markings (see Chapter 
 XVII) on the surface of any layer facing bed 2, it is evident that 
 the surface of 3 next to bed 2 was the upper surface of that bed, 
 and that the strata are related, as in Fig. 179, b, bed 3 being older 
 than bed 2. If, however, bed 3 shows on the side of its layers 
 facing bed 2 the natural molds or reverse impressions of the mark- 
 ings named, it is evident that that is the lower side of the bed, and 
 that 3 therefore overlies 2 and is younger, as shown in Fig. 179, c. 
 (d) Fan folds. In regions of sharp folding a fan type of fold 
 
 FIG. 180. Generalized section of the fan fold of the central massif of the 
 Alps. (After Heim.) 
 
 may be produced, in which the limbs of the arch dip toward each 
 other for a certain distance. Here the lower or concave portions of 
 the fold are pressed inward with the result that the beds at the cen- 
 ter of the fold are squeezed out or pinched. This type of fold is 
 characteristic of the Alps and other strongly folded districts (Fig. 
 180). 
 
 (e) Monoclines. Typically a monocline is a part of an anti- 
 cline, cut off by faulting or erosion. Simple monoclines are those 
 in which the strata have no further continuation. Thus the Front 
 Range of the Rocky Mountains is flanked by a series of simple 
 monoclines, all of which face, with their erosion slopes, the crys- 
 talline axis of these mountains. In many cases the continuation of 
 these folds is, however, on the opposite side of the crystalline axis. 
 The Blue Ridge extending from New Jersey for the entire length 
 of the Appalachians is a variable series of eastward facing mono- 
 clines. The Appalachians themselves are for the most part com- 
 posed of complementary monoclines, these representing the oppo- 
 site limbs of 'anticlines with the axis opened by erosion. Simple 
 
ANTICLINORIA ; SYNCLINORIA; GEOSYNCLINES 799 
 
 flexures of strata are sometimes spoken of as monoclines, but these 
 are in reality strongly asymmetrical anticlines. They may be spoken 
 of as monoclinal flexures, but should not be spoken of as monoclines. 
 (Figs. 181-183.) 
 
 FIG. 181. A, recumbent isoclinal fold, with over- and underfolds. B, mono- 
 cline due to faulting. C, corresponding monoclines, due to ero- 
 sion of an anticline. 
 
 Anticlinoria and synclinoria. When a succession of anticlines 
 has such a relationship as to make a large anticline, it is called an 
 anticlinorium. The central massif of the Alps may be taken as an 
 illustration. In like manner a large synclinal fold composed of a 
 succession of minor folds is a synclinorium. Such a condition exists 
 
 FIG. 182. A simple monoclinal 
 flexure. 
 
 FIG. 183. The same passing into a 
 fault. 
 
 in the Mount 'Grey lock massif of western Massachusetts. (Figs. 
 184, 185.) 
 
 Geosyncline and foredeep. The term "geosyncline" was pro- 
 posed by Dana for the long trough which formed to the east of the 
 Appalachian old land during Palaeozoic time. In this trough some 
 
8oo PRINCIPLES OF STRATIGRAPHY 
 
 40,000 feet of strata, partly of marine and partly of continental 
 origin, were deposited. It is evident that there must have been a 
 gradual downbending of the old land to permit this extensive series 
 of deposits to accumulate. This depression should not, however, be 
 regarded as primarily of tectonic origin. It is much more likely 
 that it represented the slow sinking of the crust under loading and 
 that its formation was due to the progressive reestablishment of 
 isostatic equilibrium. The foredecps, which are situated off the 
 continental margins, are probably of a different character. Here 
 we have in general downward-bending troughs, next to the land 
 mass, where, however, there is no great amount of deposition. Such 
 down-war-ping of a part of the ocean bed may well be regarded as 
 
 FIG. 184. Anticlinorium. Generalized section in the Alps. (After Heim.) 
 
 of tectonic origin, serving to relieve the accumulating stresses in 
 the earth's crust. An examination of the ocean bottom charts will 
 locate the existing foredeeps. (See further, Chapter XXIII.) 
 
 Relation of dip, strike and outcrop. 
 
 Dip has already been defined as the inclination of the strata from 
 the horizontal. Strike may be defined as the compass-bearing of the 
 line of intersection which the stratum in question makes with a hori- 
 zontal plane. It may also be spoken of as the compass-bearing of 
 the edge of the inclined bed when cut off by a horizontal plane. 
 The direction of strike is determined by compass, with reference to 
 the true north and south line, i. e., the meridian. A wrong direc- 
 tion is often furnished by the outcrop of the stratum on a 
 sloping surface. If the slope of the surface and the dip of 
 the strata are in the same direction, varying only in amount, or if 
 the slope and dip are in exactly opposite directions, no difference 
 will be observed between outcrop and strike. (Fig. i86a.) Again, 
 if the strata stand vertically, no difference will be observed between 
 
RELATIONS OF DIP, STRIKE AND OUTCROP 801 
 
 outcrop and strike (Fig. i86b), no matter what the surface slope. 
 In all other cases, however, the outcrop on a sloping surface will 
 differ in direction from the true strike of the strata, and is apt to 
 mislead unless this fact is borne in mind. In general, it may be 
 said that the lines made by the intersection of inclined strata with 
 a sloping surface have their down-slope end deflected in the direc- 
 tion of the dip of the strata. (Fig. i86c.) If the dip is vertical, 
 this deflection will not alter the direction. If the lines of inter- 
 
 FIG. 185. Synclinorium. Mt. Greylock, Mass. (After Dale.) 
 
 section run at right angles to the slope of the surface, there is no 
 down-slope end, and hence no deflection. (Fig. i86a.) Again, it 
 should be stated that the true strike and the true dip are always at 
 right angles to each other, and any slope whose intersection with the 
 inclined stratum makes a line at right angles to the line of dip must 
 show the true strike in the outcrops in its surface. (Fig. i86a.) 
 
 In the diagram, Fig. i86c, the inclined plane, A B C C' A' has its 
 outcrop and strike coinciding where cut by the horizontal surface 
 
 FIG. i86a. 
 
 K C* W 
 
 FIG. i86b. 
 
 FIG. i86c. 
 
 E F G H, but where cut by the inclined surface D E H I the out- 
 crop is deflected toward the down-dip side. It is evident from com- 
 parison with Fig. i86b that any vertical plane, as A B X Y Z, whose 
 intersection with the horizontal surface coincides with that of the in- 
 clined plane A B C C' A', will intersect the inclined surface along a 
 line B X continuous with the line A B and having the same com- 
 pass direction. This is evidently the true strike, and the angle 
 X B C marks the angle of deflection from this direction of the in- 
 tersection of the inclined plane on the sloping surface, i. e., the 
 
802 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 angle of deflection of the strike. Its projection on a horizontal 
 plane is the angle Y' X' Y. 
 
 The amount of deflection of the strike, by a sloping surface, may 
 be seen by the following consideration: Given a stratum dipping 
 due west, at an agle of 45 degrees, a horizontal surface intersecting 
 this will show the true strike due north and south. Given a second 
 surface, whose intersection with the horizontal surface is at right 
 angles to the strike, i. e., due east and west in the given case*, and 
 which also intersects the inclined plane. If this surface is tilted to 
 the vertical, i. e., if the beds are seen in vertical section at right 
 angles to the strike of the inclined bed, the outcrop or intersection 
 of this stratum with the surface will coincide with the dip, i. e., the 
 
 B 
 
 FIG. 187. 
 
 line of outcrop as marked by compass direction has been deflected 
 90 by a tilting of the surface to the extent of 90. If the surface 
 is tilted 45, the line of intersection as marked by compass direc- 
 tion will evidently lie halfway between the two or N. 45 E. by S. 
 45. (Fig. 187.) Thus in the model the shaded bed A C 
 H F is inclined at 45 from the horizontal, while the surface A B 
 C D is also inclined 45 from the horizontal, but in a direction at 
 right angles to that of the bed A C H F, i. e., its intersection with 
 the horizontal surface is at right angles to the strike of the bed. 
 Thus, by construction, X Y = X C ' = X D, hence A X, being the 
 diagonal of the square A D X Y, makes an angle of 45 with 
 D X E and with the direction of C H. It is evident that the line of 
 intersection C H between the inclined bed and the horizontal surface 
 B C H G is the true strike. It is also the strike of the vertical bed 
 C H E D. The line C D, the intersection of this vertical plane with 
 
RELATION OF DIP, STRIKE AND OUTCROP 803 
 
 the sloping surface A B C D, has the same compass direction as 
 C H, and hence represents the true strike. The line A C, however, 
 the intersection between the surface A B C D and the plane A C 
 H F, is deflected 45 from that direction, since its direction corre- 
 sponds to that of the line A X, the diagonal of the square A D X Y. 
 
 With a constant surface, as given, and sloping at 45, the out- 
 crop of a vertical stratum will have no deflection from the line of 
 strike. As the stratum becomes inclined from the vertical the down- 
 slope end will be deflected in the direction of dip, a degree for every 
 degree of departure of the dip from 90. When 45 of dip are 
 reached the deflection will be 45. With decreasing dip, i. e., its 
 approach to o, the deflection will approach 90, which is reached 
 when the strata are horizontal. When the slope of the postulated 
 surface is other than 45 the deflection of the strata must be calcu- 
 lated. Designating the dip of the stratum by 6, the angle of inclina- 
 tion of the sloping surface from the horizontal by < and the deflec- 
 tion of the outcrop by i^, we have tan $ = cot tan <j> or ^ = 
 tan-i (cot tan <). 
 
 It sometimes happens that only the outcrop of inclined strata is 
 visible on the surface of a region, the angle of dip not being ascer- 
 tainable. In such a case the angle of deflection ( ^ ) can often 
 be measured directly by taking a reading of the true strike on a 
 horizontal portion of the surface and another of the apparent strike 
 on a sloping surface, where the intersection with the horizontal is 
 at right angles with the strike. The angle of slope of this surface 
 (<f>) must also be read by the clinometer. Thus with the values of 
 two terms of the equation ascertained the third or angle of dip 
 (0) may be readily found by the formula tan 6 = tan < cot ^ or 
 = tan- ! (tan < cot ^). 
 
 An example may further illustrate this : Given an inclined 
 stratum of which the true strike as shown by the intersection with a 
 horizontal surface is N. 10 E., while the apparent strike on an in- 
 clined surface of the postulated direction of slope is N. 30 W., the 
 angle of deflection of outcrops between horizontal and inclined sur- 
 face, i. e., \J/, is therefore 40. The angle of slope of the inclined 
 surface may be assumed as 30. Thus the dip is: tan - - tan 
 30 cot 40 or 0.6882608; /. about 34 32'. The direction of 
 dip is to the east, since the deflection was to the west.* 
 
 The above formulas apply only to the case where the inclined 
 surface intersects the horizontal along a line at right angles to the 
 true strike, i. e., when the directions of slope of the inclined strata 
 and surface are at right angles to each other. When the direction 
 of slope of surface varies from this, the amount of deflection will 
 
804 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 increase or decrease according as the direction varies toward or 
 away from that of the inclined strata. Thus the more nearly the 
 direction of slope of the inclined surface approaches that of the 
 inclined strata, the more nearly will the amount of deflection ap- 
 proach 90 degrees, while the more the direction of slope approaches 
 the opposite of that of the strata the more nearly will the true strike 
 be approached. The following formulas will serve in such a case. 
 In Fig 188. 
 
 Let A D represent the outcrop of a stratum along a sloping hill- 
 side. 
 
 D B represent the dip of the stratum. 
 
 a =outcrop dip, or the angle CAD made by the line of out- 
 crop A D with a horizontal plane obtained by placing the 
 clinometer on the line of outcrop A D. 
 
 j8 = the angle of dip of the stratum, B D K or C B D in 
 diagram. 
 
 y = the angle by which the outcrop is shifted by the slope of the 
 hill (ACE). 
 
 mi. tan a 
 
 Then sm y = 5 or y 
 
 and tan ft = 
 
 tari/8 
 tana 
 sin y 
 
 sn 
 
 or = tan 
 
 / tan a' 
 
 ! / tan a 
 
 sin 
 
 an a\ 
 iny/ 
 
 * It should be noted that, as viewed from above, the deflection is in the 
 direction of the dip, but, as viewed from below, looking up the plane, the 
 deflection is in the opposite direction. This must be borne rn mind when 
 the compass direction is read; that on a northward sloping plane will be 
 read from above, that on a southward sloping plane from below. 
 
RELATION OF DIP, STRIKE AND OUTCROP 805 
 
 The following method is given by Keilhack (12:65, 6<5) f r the 
 determination of the true dip and strike when observations are pos- 
 sible only on vertical cliffs or quarry walls (Fig. 189) : 
 
 Given two dip observations on vertical quarry walls, one of 65, 
 on a wall, the compass alignment of which is N. 45 W., and one 
 of 45 on a wall, the alignment of which is N. 65 E. Draw two 
 lines at a b and a c, the former at an angle of N. 45 W., and the 
 latter N. 65 E., so that they intersect in the point a. At the point a 
 erect perpendiculars to a b and a c. Lay off equal distances on these 
 from a, locating the points e and d, respectively. At d lay off the 
 
 FIG. 189. 
 
 complement of the angle observed on the wall represented by a c, 
 that is, the complement of 45, which is 45. At e lay off the com- 
 plement of the angle observed on the wall represented by the line 
 a b, that is, the complement of 65, which is 25. Complete the 
 right angle triangles by continuing the hypothenuses until they meet 
 the lines a c and a b, at f and g, respectively. Join f g by a line 
 which represents the true strike of the strata, which if a c and a b 
 are properly oriented can be readily measured. Drop a perpendicu- 
 lar a h from a to f g. This is the direction of dip toward either 
 a or h, as the case may be. Erect a perpendicular to a h at a, and 
 lay off the length a d (=a e), on it, locating point i. Connect i and 
 h, then the angle i h a is the angle of true dip. This will be readily 
 understood if the three shaded triangles are bent at right angles to 
 
806 PRINCIPLES OF STRATIGRAPHY 
 
 the plane of the paper, either up or down, until the three sides a d, 
 a e and a i coincide with the apices of all three (d e i), meeting in a 
 common point. The triangles a d f and a e g would then represent 
 the walls of which the original dip measurements were made, the 
 angles in each case being represented by the angles a f d and a g e, 
 respectively. A plane resting on the three hypothenuses would rep- 
 resent the inclined stratum. 
 
 Strike as affected by pitching axis of folds,. 
 
 As long as the axis of an anticline or syncline continues hori- 
 zontal, the outcrops of the -beds exposed by planing off the summit 
 of the fold in a horizontal surface will be in the form of parallel 
 bands, the lowest appearing at the center and the repetition of the 
 
 a b .: 
 
 FIG. 190. a, Eroded anticline with horizontal axis, b, Eroded anticline with 
 pitching axis, showing resulting outcrops of strata. 
 
 beds being in the same order, from the center outward in both direc- 
 tions. (Fig. 190, a.) 
 
 When the axis of the fold is inclined the strike of the strata on 
 opposite sides of the axial plane will converge and finally meet.' 
 (Fig. 190, b.) In an anticlinal fold the inner strata are the older; 
 in a synclinal fold the inner strata are the younger. 
 
 Folding as indication of unconformity. 
 
 In a complexly folded region an unconformity may sometimes 
 be detected between two formations not actually seen in contact by 
 the fact that the lower formation is folded much more strongly 
 than the upper one. In this case it is apparent that the lower forma- 
 tion was folded and truncated before the upper one was deposited, 
 after which both were again folded. (See Fig. 191.) 
 
THE APPALACHIAN FOLDS 807 
 
 The trend of the Appalachian folds. 
 
 The Appalachians furnish a good example of an extended line bf 
 folding formed at approximately the same time, i. e., the end of 
 the Palaeozoic. They show a remarkable series of curves of varying 
 size, which; with reference to the land, may be called convex or 
 land lobes, when they bulge seaward, and concave or sea lobes, 
 when they extend back into the land. (See the map, Fig. 192.) 
 Beginning in the southwest, we have the following: 
 
 FIG. 191. Diagrams showing the steps by which complexly folded strata are 
 produced. A C, deposition, folding and truncation of first series ; 
 D F, deposition, folding and erosion of second series, the fold- 
 ing and erosion also affecting the first series. 
 
 1. Louisiana sea lobe, extending from Texas to central Mis- 
 sissippi with the apex near Little Rock, Arkansas, and with proba- 
 bly a subordinate .land lobe at McAlester in Oklahoma. 
 
 I a. Mississippi land lobe, extending through northern Missis- 
 sippi and "northwestern Alabama. 
 
 2. Birmingham sea lobe, a small lobe in central Alabama. 
 2a. Rome land lobe with a moderate curve. 
 
 3. Knoxville sea lobe, with its apex looping around the Knox- 
 jville area. 
 
 3a. Alleghany land lobe along the main line of the Alleghany 
 Mountains of Virginia. ' 
 
 4. Pennsylvania sea lobe, a marked lobe with the apex in cen- 
 tral Pennsylvania, the trend changing to nearly east. 
 
 4a. New York land lobe, the apex being near New York City. 
 
 5. Champlain sea lobe, east of the Adirondacks. 
 
8o8 PRINCIPLES OF STRATIGRAPHY 
 
 5a. Maine land lobe, along the northwesern boundary of Maine 
 
 6. Gaspe sea lobe, a pronounced lobe, the trend actually chang- 
 ing to southeast (40). 
 
 6a. Cape Breton land lobe, the change of trend being near Syd- 
 ney, Cape Breton, the trend again turning northeastward and con- 
 tinuing thus through Newfoundland. 
 
 19. Domes and Basins. Domes are shortened anticlinal struc- 
 tures with the dip of the strata away from the center in all direc- 
 tions or quaquaversal. These dips may vary greatly in different 
 domes. In some cases they are so low as to be scarcely or not at 
 all perceptible (Cincinnati dome) ; in others they may be 45 or 
 over (Black Hills dome). Many of the low-dipping domes are 
 perceptible as such only by the erosion which has removed their 
 central portion, often leaving a topographic depression. Such low 
 domes have also been called parmas, after one of the low east and 
 west ranges which project from the western side -of the .Urals 
 (which have a north-south trend), and which are formed by gently 
 folded strata, the folds dying out in the plains. 
 
 Basins are the reverse of domes, the strata all dipping toward 
 the center. As a rule, basins are composed of gently dipping strata 
 only so that-their basin character is recognized only by the rimming 
 outcrops of the lower strata after erosion (Michigan basin, Paris 
 basin, etc.). Between two basins lies generally a more sharply 
 marked anticline, while between two domes a pronounced syncline 
 often occurs. Sometimes the basin structure is ascertained by the 
 location by borings all over the area of the summit (or bottom) of 
 a certain formation, such as a coal bed or a marked sandstone. 
 Thus the basin structure of Iowa is beautifully brought out by the 
 series of contours connecting areas of equal depression beneath the 
 surface of the summit of the St. Peter sandstone. (Iowa Geol. 
 Survey, Vol. VI, p. 316, map.) 
 
 Eastern North America is marked by a number of distinct basins 
 and domes, many of which are indicated by the outcrops, while 
 others are recognized only from their general relationship and the 
 occurrence of separating anticlines or synclines. All of these basins 
 and domes owe their final character to the Appalachian folding, but 
 "some of them apparently existed during much of Palaeozoic time. 
 The accompanying map (Fig. 192) shows the location of these 
 domes and basins. It will be observed that the outermost basins 
 are generally embraced by convex lobes of the Appalachian system, 
 while the concavities of that system are opposite domes or opposite 
 anticlines separating basis. (See also Ruedemann-22 ; Willis-3O.) 
 
 The principal basins so far determined are in the northeast, the 
 
FIG. 192. Map of North America, showing the sinuous trend of the Ap- 
 palachian folds (see text) and the domes and basis. A=Alle- 
 ghany basin ; AM =: Alabama-Mississipf>i basin ; I=/ott'a basin ; 
 I]=Illinois basin; J = Jamcs Bay basin; IJ=St. Lawrence basin 
 (Montreal, etc.); M=Michigan basin; N=New York basin; 
 O=0klahoma basin; o=Ottawa basin; Q=Quebcc basin. The 
 line or lines between basins represent anticlines. The domes 
 are: The Adirondack; west of this the Ontario; north of this the 
 North Ontario; southwest of this the Wisconsin dome. In the 
 southern area are: the Cincinnati, the Nashville, and the Ozark 
 domes. 
 
8io PRINCIPLES OF STRATIGRAPHY 
 
 St. Lawrence, the Quebec, the Ottawa, and the New York. 
 The Frontenac axis separates the last two basins, and joins 
 the Adirondack dome to the Ontario dome. Northwest of the lat- 
 ter is the North Ontario dome, the Temiscaming syncline separat- 
 ing the two. To the north of this is the James Bay Basin. Next 
 southward of this series is the Alleghany basin, embraced by the 
 Alleghany land lobe of the Appalachians on the east. Northwest of 
 this is the Michigan basin, these two being separated by the Toledo 
 anticlinals. Northwest of the Michigan basin is the Wisconsin 
 dome, which is separated from the North Ontario dome by the deep 
 Superior synclinals. Southwest of the Wisconsin dome is the Iowa 
 basin, and southeast of this the Illinois basin, with the Keokuk anti- 
 cline between. The Illinois and Michigan basins are separated by 
 the Kokomo anticline. The Cincinnati dome is enclosed by the Illi- 
 nois, Michigan and Alleghany basins, and south of it is the smaller 
 Nashville dome, with small basins on either side. The southern 
 tier is formed by the Alabama-Mississippi basin in the embrace of 
 the Mississippi land lobe, the Ozark dome, and the Oklahoma basin. 
 
 f. Deformations Due to Dislocation of Strata. Faulting. 
 
 20. Faults. "A fault is a fracture in the rock of the earth's 
 crust accompanied by a displacement of one side with respect to 
 the other in a direction parallel with the fracture." (Reid, etc.-i8; 
 
 19.) 
 
 <C A closed fault is one in which the two walls of a fault are in 
 contact." 
 
 "An open fault is one in which the two walls of a fault are sep- 
 arated. The same fault may be closed in one part and open in 
 another." 
 
 "A fault surface is the surface of fracture. It is rarely plane, 
 but where it is without notable curvature over any area it may be 
 called a fault plane for that area. 
 
 "A fault line is the intersection of a fault surface with the 
 earth's surface." 
 
 "The shear zone: When a fault is made up of a number of 
 slips on closely spaced surfaces, the section of the earth's crust con- 
 taining these minor faults is called 'shear zone.' This name would 
 also apply to the brecciated zone, which characterizes some faults." 
 
 "A horse is a mass of rock broken from one wall and caught be- 
 tween the walls of the fault. (Fig. 1933.) 
 
FAULTS 
 
 811 
 
 "The fault strike is the direction of the intersection of the fault 
 surface, or the shear zone, with a horizontal plane." The same pre- 
 cautions apply here as in the case of the strike of the strata on a 
 sloping hillside. (See p. 800.) The term "trend" would be bet- 
 ter and would avoid confusion. 
 
 "The fault dip is the inclination of the fault surface, or shear 
 zone, measured from a horizontal plane. It is never greater than 
 90." 
 
 <( The hade is the inclination of the fault surface or shear zone, 
 measured from the vertical ; it is the complement of the dip." Hade 
 is to be preferred to dip to avoid confusion with dip of strata. (See 
 beyond.) 
 
 "The hanging wall is the upper wall of the fault." It generally 
 overhangs the vertical. 
 
 "The foot wall is the lower wall of the fault." It generally pro- 
 jects footwise at the base. 
 
 FIG. 1933. A horse. 
 
 In stratified rocks faults may be parallel in strike to the strike of 
 the strata, when they are called strike faults, or the strike may be 
 approximately at right angles to the strike of the strata, when they 
 are called dip-faults. The bedding fault is a special type of strike 
 fault, in which the fault plane and bedding plane coincide. Be- 
 tween the strike faults and the dip faults are many directions giving 
 oblique faults. When the general structure of a region is consid- 
 ered, the faults may be called longitudinal, when their strike (or 
 trend) is parallel to this structure, or transverse, when it is across 
 the structure. 
 
 The slip of a fault is the displacement on the fault surface. The 
 net slip is the actual amount of movement between points on the 
 opposite walls originally in contact. The strike * slip (trend-slip) 
 
 * Strike and dip here refer to the strike and dip of the fault, not of the strata. 
 Trend and hade would be better. 
 
812 PRINCIPLES OF STRATIGRAPHY 
 
 is the component of the slip parallel with the strike, and the dip- 
 slip (hade slip) the component parallel with the dip. Thus (in 
 Fig. 193!)) a b is the net slip, a c the strike-slip and b c the dip- 
 slip. 
 
 The shift is the relative displacement of the rock masses outside 
 of the zone of displacement, and is used when there are many minor 
 slips making up the shear zone or when the strata in the neighbor- 
 hood of the fault are bent. It is the relative displacement which 
 would exist had there been only one slip of the same magnitude as 
 the combined minor slips. 
 
 Features shown in section of faults. 
 
 Throw is the vertical displacement of the strata, as seen in sec- 
 tions, even if the slip is inclined, d e in the figures (No. 194, A B) 
 
 A B 
 
 FIG. 194. Sections of faults: A, with dip of fault plane across strata; B, 
 with dip of fault plane in same direction as dip of strata. 
 
 Heave or horizontal throw is the horizontal displacement of 
 srrata seen in section, as e g in the figures (No. 194, A B). 
 
 Stratigraphic throw. This is the distance between the two parts 
 of a disrupted stratum measured at right angles to the plane of the 
 stratum, (a b, Fig. 194, A B.) 
 
 The Stratigraphic heave, or dip throw, is the displacement of 
 the strata in section in .the direction parallel to the strata, as c b in 
 Fig. 194, A B. In Fig. A it signifies shortening and overlapping of 
 the strata, in Fig. B, lengthening by separation of the strata. 
 
SURFACE APPEARANCE OF FAULTS 
 
 Features shown in surface appearance of faults, i. e., map features 
 
 of faults. 
 
 These features are seen in strike and oblique faults. In the 
 former the apparent horizontal displacement or offset is measured 
 along the fault line, and is the same as the actual horizontal dis- 
 tance between the ends of the corresponding strata (a b). (Fig. 
 195 A.) This is the same as the trend-slip, but is probably never or 
 but seldom the actual or net slip. In oblique faults the offset is 
 
 A. Map of StriKe Fault 
 
 gap 
 
 Plan or Map of 
 oblla/ue Fault 
 
 offset 
 
 D. Plan or Map of 
 oblique Fault 
 
 FIG. 195. Map or surface views of faults. 
 
 measured at right angles between the two ends of the disrupted 
 strata, as (a b) in Figs. 195 B and C, where the trend-slip is 
 marked by a c. In Fig. B, the strata are disrupted and pulled apart ; 
 the distance thus separated is the gap. In Fig. C the ends are 
 pushed past each other, making an overlap, c b. 
 
 Classification of faults. 
 
 Faults have been classified with reference to direction, as strike 
 (and bedding), dip and oblique faults. With reference to their 
 movements, they may be classified into normal and reverse faults, 
 
8i4 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 and with reference to the force producing them they may be 
 classified as gravity and thrust faults. 
 
 With reference to direction. The classification with reference to 
 direction has already been in part explained. It includes strike 
 faults, dip faults %nd oblique faults, with reference to the strata. 
 With reference to each other, they may be parallel, intersecting or 
 radial, the last when radiating roughly from a point. With refer- 
 ence to a geological region whether raised or depressed (geologi- 
 cally, but not necessarily topographically), they may be peripheral, 
 when running along the periphery of the geological formation, or 
 cross-faults when they cut across it. 
 
 With reference to movement. Movement is relative. If the 
 stratum of the hanging wall in any given section is lower, it is 
 designated a normal fault. If the stratum of the hanging wall is 
 higher, it is a reverse fault. 
 
 FIG. 196. 
 
 With reference to cause. In most cases normal faults probably 
 mean a tension and a down-sinking of the hanging wall, accom- 
 panied by an elongation of that part of the crust. In this case the 
 normal fault would also be a gravity fault. In like manner the re- 
 verse fault generally implies an upward movement of the hanging 
 wall with consequent foreshortening of the crust by overlapping 
 under pressure. In such a case the reverse fault is also a thrust 
 fault. Under certain conditions, however, a gravity fault may in 
 section show the conditions of a reverse fault (Figs. 196, A B), for, 
 though the hanging wall has slipped down, owing to the oblique 
 character of the displacement and the dip of the strata, the beds 
 seem actually to have slipped up over each other. 
 
 In like manner a thrust fault may in section show the charac- 
 ters of a normal fault, the ends of the strata on the hanging >vall 
 being actually lower than on the foot wall. This is shown in Figs. 
 197, A B. 
 
FAULTED STRUCTURES 
 
 Terms applied to rock masses formed by or bounded by faults but 
 not topographically distinguishable from surrounding masses. 
 
 1. A horst is a mass geologically elevated relatively to the sur- 
 rounding region and separated from it by faults. 
 
 2. A fault basin is a region geologically depressed relatively to 
 the surrounding region from which it is separated by faults. 
 
 3. A fault block is a mass bounded on at least two opposite 
 sides by faults. It may be geologically elevated or depressed rela- 
 tively to the adjoining region, or it may be geologically elevated 
 
 relatively to the region on one side and depressed relatively to that 
 on the other. 
 
 4. A fault ridge is a relatively elongated fault block lying be- 
 tween two faults with roughly parallel trends. 
 
 5. A fault trough is a relatively depressed (geologically) fault 
 block lying between two faults with roughly parallel trends. 
 
 Terms applied to the topographic expression of faults. 
 
 1. Fault scarp a scarp or cliff presenting the original surface 
 form of the displacement. 
 
 2. Graben, or fault scarp valley a long, narrow topographic 
 depression, the surface expression of a new fault trough. Ex. 
 Rhine Graben ; Purgatory Chasm, near Sutton, Mass. It is bounded 
 on both sides by fault scarps facing inward. 
 
8i6 PRINCIPLES OF STRATIGRAPHY 
 
 3. Fault scarp ridge a topographic ridge bounded by two 
 roughly parallel fault scarps which face outward or toward the sur- 
 rounding low country. 
 
 4. Fault scarp block a topographic block bounded on all sides 
 by outward facing fault scarps. 
 
 5. A tilted block a topographic block bounded on all but one 
 side by fault scarps facing outward. The excepted side may be 
 faced by the fault scarp of another tilted block. 
 
 6. A fault scarp basin a topographic basin bounded on all 
 sides by fault scarps facing inward. 
 
 7. A complex scarp basin a topographic basin bounded on 
 
 FIG. 198. A fault-line valley. 
 
 most of its sides by fault scarps facing inward, but bounded by 
 warpings or in other ways on one or more sides. 
 
 Secondary features due to erosion. 
 
 1. Fault-line scarp. (Davis-4.) This is the fault scarp resur- 
 rected in the second cycle of erosion, after the obliteration of the 
 original fault scarps. This may face either way and may be 
 greater or less than the original fault scarp. If it faces in the same 
 direction as the original fault scarp it is resequent; if in the opposite 
 direction it is obsequent. 
 
 2. Fault-line valley a valley cut out along an old fault-line 
 after the obliteration of the original fault scarp. (Fig. 198.) 
 
 3. The graben and fault scarp basin, the fault scarp ridges, 
 fault scarp block and tilted block may all be destroyed by erosion 
 and then resurrected in the second cycle of erosion. Such cases 
 may be designated by prefixing the word erosion an erosion 
 graben, erosion fault scarp basin, erosion fault scarp ridge, etc. 
 See, further, Davis (4) and Hobbs (Qa) ; also Chapter XXI. 
 
REPETITION AND ELIMINATION OF STRATA 817 
 
 Stratigraphic significance of faults. 
 
 From the Stratigraphic viewpoint, strike faults are of the great- 
 est importance, for they often lead to a duplication of strata or to 
 the elimination of certain beds. Many mistakes in stratigraphy have 
 been made because of the nonrecognition of such faults. The Og- 
 den quartzite, for example, regarded as a distinct formation in the 
 western Ordovicic, has been shown to be a repetition of a lower 
 formation due to overthrust. In the Helderberg region of New 
 York, near Kingston, duplication by overthrust has led to the con- 
 fusion of the stratigraphy. The overthrust New Scotland beds 
 were originally described as the Upper Shaly (Port Ewen), and the 
 higher formation was held^to have the same fossils as the lower one. 
 
 In discussing the effects of strike faulting on the apparent suc- 
 cession of strata, eight principal cases may be considered : 
 
 A. Gravity faults. (Figs. 199, A-G.) 
 
 1. Dip of fault plane with dip of strata, but at greater angle. 
 (Fig. A.) In this case elimination of beds will take 
 place. 
 
 2. At smaller angle. In this case repetition of beds will 
 take place. (Fig. B.) 
 
 3. Dip of fault planes against dip of strata. In this case 
 repetition of beds will result. (Figs. C-E.) 
 
 4. Dip of fault plane vertical (hade o). The "down dip" 
 portion descends. In this case elimination of beds results. 
 (Fig. F.) 
 
 5. The "up dip" portion descends. In this case repetition 
 results. (Fig. G.) 
 
 B. Thrust faults. (Figs. 199, H-J.) 
 
 6. Dip of fault plane with dip of strata, but at greater 
 angle, repetition results. (Fig. H.) 
 
 7. Dip at smaller angle elimination results. (Fig. I.) 
 
 8. Dip of fault plane against dip of strata. In this case 
 elimination of strata results. (Fig. J.) 
 
 A consideration of the diagram, Figs. A to J, will show that 
 the plane of faulting cuts the inclined strata so as to leave a portion 
 which is limited below by the fault-plane, but may extend indefi- 
 nitely upward except as limited by the earth's surface. This por- 
 tion may be called the "tip-dip" end of the strata (see the fig- 
 ures). The other part is limited above by the fault plane, and may 
 extend indefinitely downward. This is the "down-dip" end (d) of 
 
8i8 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 the strata. When the fault plane cuts the obtuse angle between the 
 strata and the surface, i. e., when its dip is greater than that of the 
 strata, the "up-dip" end lies on that side (to the right of the plane 
 in the figures). When it cuts the acute angle, i. e., dips at a less 
 angle than the strata, the up-dip end lies on the acute side (left side 
 of the fault plane in the figures). With the part thus oriented, the 
 
 21 23456 12 1 2 3456 
 
 
 FIG. 199. Sections showing the effects of strike faults in eliminating beds 
 (A, F, I and J) and in repeating beds (B, C, E, G, and H). 
 
 general law may be stated that, if the "up-dip" end moves down, we 
 have repetition of strata, while, if the up-dip end moves up, elimi- 
 nation of strata results. Conversely, when strata are repeated or 
 eliminated, the up-dip end must be assumed as having moved either 
 down or up. If the angle of the fault plane is ascertained, the fault 
 will appear to be either thrust or gravity, according to the greater 
 or less angle of inclination of the fault plane, as compared with the 
 
RELATIONSHIPS OF ROCK STRUCTURES 819 
 
 strata, and the repetition or elimination of the strata. The general 
 rule can be easily ascertained at any time by a consideration of the 
 simple case shown in Figs. F-G. There it will be readily seen that, 
 when the tip-dip end is moved up, elimination results, and when 
 it is moved down repetition occurs, or, to put it the other way, when 
 the down-dip end moves up repetition occurs, but when the down- 
 dip end moves down elimination occurs.* 
 
 Faults as indications of unconformity. 
 
 If in two superposed formations of similar character and sus- 
 ceptibility to faulting the lower is more complexly faulted than the 
 upper, the indications are that the lower was faulted before the 
 upper was deposited upon it, and that then the two formations are 
 unconformably related. 
 
 Relation of folds, faults, cleavage, fissility and joints. 
 
 Van Hise has emphasized the close relationships existing be- 
 tween these structures, which may in general be considered as dif- 
 ferent manifestations of the same forces thrust and gravity act- 
 ing upon heterogeneous rocks under varying conditions. When rocks 
 are under less weight than their ultimate strength, while being rap- 
 idly deformed, they will break, with the formation of crevices, of 
 joints, faults, brecciations or fissility, as a result of extensive frac- 
 turing. Such rocks are then regarded as being in the zone of -frac- 
 ture. When rocks are buried to such a depth that the weight of the 
 superincumbent strata exceeds their ultimate strength, they will 
 flow as plastic material under deforming strains and folding with- 
 out fracture results. The depth at which this takes place marks 
 the position of the zone of plasticity and flowage. The depth at 
 which flowage occurs varies with the character of the rock. For 
 soft shales, Van Hise estimates that probably 500 meters or less of 
 overlying strata will prevent the formation of crevices and fractures 
 to any considerable extent, while for the strongest rocks a depth 
 of perhaps 10,000 meters is required to reach this condition. Cleav- 
 age normally belongs in this zone. Between these two is the zone 
 of combined fracture and plasticity. In this zone all the structures 
 occur together in complex relationship. Folds may pass into faults 
 and faults into folds. Fissility and cleavage occur side by side. 
 
 * This may be condensed into the slogan cfown, down, out. 
 
820 PRINCIPLES OF STRATIGRAPHY 
 
 Downward probably most faults pass into flexuresj these flexures 
 dying out at still greater depth. Van Hise thinks that 5,000 meters 
 is a possible depth, at which important faults disappear, though 
 some may extend to the depth of a number of miles. Others, how- 
 ever, regard the necessary depth as very much less. 
 
 C. CONTACT DEFORMATIONS. 
 
 Under this heading may be placed changes in the rock mass as 
 a whole, produced by contact with a deforming agent. The deform- 
 ing force is heat or cold, and the agents conveying the former are 
 igneous masses (intruded or extruded), hot waters or gases, and 
 the direct rays of the sun. Heating rock masses by any of these 
 agents results in expansion of the rock. The agents conveying cold 
 are glaciers and the cold atmosphere. Their action on the rocks 
 results in contraction. The chief structures produced by these 
 agents singly or in conjunction are prismatic jointing and insola- 
 tion joints. 
 
 21. Prismatic Jointing Due to Contact with Igneous Masses. 
 When igneous masses come in contact with sedimentary rocks a 
 prismatic structure is not infrequently developed. This has been 
 noted in clays, marls, sandstones, brown coal, seam coal and even 
 in dolomites. Beautiful examples of this structure are found in the 
 coal seams of Ayrshire. 
 
 In all cases of prismatic jointing thus produced, the columns 
 diverge perpendicularly from the surface of the igneous mass which 
 caused the alteration. When the latter is vertical, the columns are 
 horizontal ; when it undulates, the columns follow its curvation. It 
 is most probable that this structure is developed as the result of 
 expansion of the heated rocks. That such structure can develop 
 under pressure due to expansion is shown by an experiment in 
 which prismatic structure is formed in a box of powdered starch, 
 stored for some time in a moist region. The swelling of the starch 
 exerts a pressure in all directions against the sides of the enclosing 
 box, and after a time a series of prismatic columns is developed 
 which radiate from the center outward, being at right angles in 
 most cases to the enclosing walls. Prismatic structure produced by 
 swelling seems also to have occurred in nature, as is shown in the 
 gypsum beds of the Paris Basin (probably originally deposited in 
 part at least as anhydrite), where, as observed by Jukes, some beds 
 are divided from top to bottom by vertical hexagonal prisms. If 
 this structure is due to swelling on hydration, as in the case of the 
 
DISCONFORMITY UNCONFORMITY 821 
 
 starch cited, it belongs properly under the subject of diagenetic al- 
 terations. Thus there are at least three ways in which prismatic 
 structure is produced: 
 
 1. Contraction and shrinking, on cooling or drying. 
 
 2. Expansion and pressure by heating from without. 
 
 3. Expansion and pressure by swellings from hydration. 
 
 22. Insolation Joints. ' These are joints produced in massive 
 rocks, such as granite, etc., by the alternate expansion and contrac- 
 tion to which they were subjected under the diurnal heating and 
 cooling. Such joints are parallel to the surface subjected to change 
 in temperature, and are close together in the outer portion of the 
 mass, but farther apart at a depth. They serve an excellent pur- 
 pose in quarrying operations, which in such rocks would be more 
 difficult otherwise. 
 
 D. STRUCTURES IN PART DUE TO DEFORMATION AND IN PART TO 
 
 EROSION. 
 
 23. Disconformity and Unconformity. Strata separated by an 
 unrepresented time interval are generally spoken of as unconforma- 
 bly related. Two types of such unconformable relation may be rec- 
 ognized, the stratic where the stratification of the formation on both 
 sides of the plane of nonconformity is parallel or nearly so, and 
 the structural, where the two sets of strata are inclined at a greater 
 or less angle with reference to each other. 
 
 For the first type, in which no folding of the older set of strata 
 is involved, the term dis conformity has been proposed (Grabau 6: 
 534)) with the corresponding limitation of the term unconformity to 
 the second type, or that in which folding plus erosion of the first set 
 of strata precedes the formation of the second set. 
 
 Crosby (2a) has called attention to the unsatisfactory character 
 of the prefix dis, since it means divergence rather than parallelism. 
 He prefers to divide unconformity into para-unconformity (parun- 
 conformity) the disconformity of Grabau, and clino-unconformity 
 (clinunconformity) for the angular type with discordant strata. 
 Heim (9) had previously proposed the term paenaccordanz for 
 approximate conformity with the strata nearly parallel. This, as 
 Crosby says, is not quite the equivalent of the parunconformity, 
 which implies crustal oscillation, rather than deformation, whereas 
 Heim's term suggests rather gradation between true conformity or 
 accordan2 f and unconformity or discordant. 
 
822 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Disconformity (Par unconformity, Paenaccordanz). When strata 
 are elevated without folding or other disturbances, and subjected 
 to a prolonged period of erosion, after which their truncated edges 
 are covered by other strata, either marine or nonmarine, a stratic 
 unconformity or disconformity (parunconformity, paenaccordanz) 
 is produced. Here a hiatus, measured by the length of time during 
 which the lower strata were exposed to erosion, plus the amount 
 worn away during this exposure, separates the two series. While 
 this hiatus measures the unrepresented strata it must be borne in 
 mind, however, that it does not represent the length of time dur- 
 ing which deposition was interrupted in the region in question. 
 The amount of nondeposition can be determined only when the 
 
 E 
 
 
 b 
 
 a 
 
 
 a 
 
 A 
 
 I 
 
 B 
 
 FIG. 200. Diagrams illustrating the development of disconformities. 
 
 amount of erosion during the elevation of the region is known. 
 We may assume two locations A-B, where elevation may occur or 
 some other changes by which deposition continued uninterruptedly 
 at B, while erosion replaced it at A. (Fig. 200, I-IV.) Under as- 
 sumed conditions a formation c, equal in thickness to formation a, 
 may be deposited at B, while b is eroded at A. If later deposition 
 becomes uniform again in both localities, d will rest conformably on 
 c at locality B, but disconformably on a at A. The hiatus at locality 
 A comprises formations b and c, but the actual time interval is meas- 
 ured only by the deposition of formation c at locality B. In this 
 case the erosion at A was assumed to equal the amount of deposi- 
 tion at B, and hence the hiatus at A represents twice the amount of 
 the time interval involved, as developed at B. 
 
 If erosion at A exceeds deposition at B, then the hiatus at A 
 representing a definite time interval will be greater than twice the 
 depositional equivalent of that time interval at B, by an amount pro- 
 portional to the excess of erosion over deposition. If erosion at A 
 
DISCONFORMITY 823 
 
 is exceeded by deposition at B, then the hiatus at A will be smaller 
 than twice the depositional equivalent by a corresponding amount. 
 When the amount of erosion is zero at A, the hiatus will be repre- 
 sented by the deposit at B above, when formation d will rest discon- 
 formably on b at A, instead of resting on a. (Fig. 200, IV.) 
 
 The disconformity at A may be scarcely indicated in the strata, 
 and, if it were not for the fact that formations elsewhere found 
 intercalated between the two strata (as at B) are missing here, the 
 disconformity would not be recognized at all. Very many such dis- 
 conformities exist in our formations, but few of them are readily 
 recognized on account of the parallelism of the strata. Sometimes 
 an erosion interval and the subsequent encroachment of the sea are 
 indicated by the existence of a basal conglomerate in the later 
 formation, which includes fragments of the earlier one. In some 
 cases, where a rapid transgression of the sea took place, or where 
 fine, residual soil on the old surface is but slightly reworked, such 
 basal rudytes may be wanting; and the two formations follow ap- 
 parently with perfect conformity upon each other. This is the 
 case with the black Chattanooga shale, where it rests upon the 
 Rockwood clays in the Appalachians. The hiatus here comprises 
 the whole of the Devonic and part of the Siluric as well, yet the 
 contact, though abrupt, appears like a conformable one. Careful 
 examination should, however, reveal in such cases a more or less im- 
 perfect upper surface of the lower bed, where some traces of ero- 
 sion are still visible. When this upper surface is an undoubted 
 deposition surface, i. e., when it shows no traces of erosion what- 
 ever, and when furthermore the succeeding beds show no evidence 
 of derivation from the underlying bed, the existence of a discon- 
 formity may be doubted. 
 
 Examples of contacts where disconformities have been assumed, 
 but are not supported by evidence of erosion, are the contact be- 
 tween the pyritiferous Brayman shale and basal Siluric sandstone 
 (Binnewater) in the Schoharie region, and the Oriskany-Esopus 
 contact in the Helderbergs of eastern New York. In the former 
 case the Brayman shales are known to be of Salina age, while the 
 sandstones on which they rested were regarded as of Lorraine age. 
 There is, however, no evidence of a hiatus comprising most of the 
 Siluric between these two formations, the basal arenyte being too 
 intimately related to the shale and of the same age. The hiatus, 
 known to exist in this region, occurs at a lower level, unless, in- 
 deed, as has recently been suggested by Ruedemann and others, the 
 Brayman shale is Upper Ordovicic. The Oriskany-Esopus contact 
 of the Helderbergs also has the aspect of a conformable one. This 
 
82 4 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 conformity if fully established has even a more far-reaching signifi- 
 cance. Where a marine formation is abruptly succeeded by a con- 
 tinental formation, the existence of a possible hiatus between the 
 two must be taken into consideration. Recently the tendency has 
 manifested itself in certain quarters to greatly multiply the number 
 
 FIG. 201. Basal Palaeozoic sandstone resting unconformably upon gneisstiid 
 granite, Williams Canyon, Colorado. (After Hayden.) 
 
 of disconformities. (Ulrich-22a.) In many cases the apparent 
 absence of a formation between two others is merely due to a 
 change in facies so that the formation is actually present, but in a 
 different lithic or faunal facies or both. 
 
 Unconformity (Clinunconformity, Discordanz). (Figs. 201-202.) 
 
 FIG. 202. 
 
 Unconformity at Siccar Point, Scotland, a a, Ordovicic strata, 
 d, d, d, Old Red Sandstone. (After Lyell.) 
 
 The structural unconformity is readily recognized and the one 
 generally detected wherever it occurs. This type of uncon- 
 formity involves the folding of the older strata, and the subsequent 
 erosion of the folds followed by the deposition of the later strata 
 upon the eroded edges of the older beds. This type of unconformity 
 
UNCONFORMITY 
 
 825 
 
 may often become complicated by further folding and erosion, when 
 the complex relationship shown in Fig. 191 is produced. 
 
 In all cases of structural unconformity a considerable time in- 
 
 FIG. 203. Cross-section of the Aletschhorn, showing inverted unconformity 
 of schists upon the laccolithic crystallines. (After Baltzer.) 
 
 terval remains unrecorded. This is measured by the amount of 
 folding and erosion which the strata have undergone. In this cir- 
 cumstance it is often the case that the last deposited strata prior to 
 the time that folding and erosion commenced were folded down to 
 
 it j^ , ;. .-... 
 
 Griinschiefer 
 
 Gran it 
 
 FIG. 204. Detail of the peak of the Aletschhorn. i, dragging of greenslate 
 at granite contact; 2, infolding of greenslate into the granite. 
 
 such an extent that they were preserved from complete removal by 
 erosion. Especially is this the case when the folding has been so 
 intensive as to place the strata in parallel positions, i. e., isoclinal 
 folding. In this case the actual time interval, during which no 
 deposition went on in the region in question, may be determined by 
 a comparison of the ages of the youngest stratum in the folded 
 
J 
 
 826 PRINCIPLES OF STRATIGRAPHY 
 
 series with that of the first stratum unconformably overlying the 
 series. 
 
 Unconformities and disconformities are often suggested by the 
 occurrence of dikes of igneous material in the lower rocks, which 
 do not penetrate the upper beds. Stronger folding or faulting in the 
 lower than in the upper series also suggests an unconformity, as 
 shown below. As a unique example of an indicated disconformity 
 may be cited the sandstone dikes rilling fissures in the Siluric lime- 
 stones of western New York and Canada, the overlying beds being 
 wholly unaffected by these fissures and dikes because a later de- 
 posit. Faulting affecting a lower set of strata, but not a higher one, 
 also indicates a disconformable relationship, and a hiatus represent- 
 ing a sufficient time interval to allow for the removal of the fault 
 scarps of the lower series. 
 
 The appearance of an inverted unconformity, where the later 
 strata end abruptly against the older ones, may be produced by in- 
 tense folding of the rocks of a complex region, as shown in the 
 figures of the structure of the Aletschhorn on page 825. (Figs. 203- 
 204.) 
 
 Conformable or accordant strata may also show a variety of as- 
 pects. Crosby has shown that on the Atlantic coastal plain of North 
 America, the strata wedge out landward.* This wedging conformity, 
 where the formations are thinner in one locality than in the other, 
 though fully represented, Crosby has called spheno conformity, and 
 its correlative, where the strata are of uniform thickness, he calls 
 piano conformity. If contemporaneous faulting of the older series 
 goes on with the deposition of the newer, fractoconformity is pro- 
 duced. 
 
 BIBLIOGRAPHY XX. 
 
 1. BROWN, THOMAS C. 1913. Notes on the Origin of Certain Paleozoic 
 
 Sediments, Illustrated by the Cambrian and Ordovician Rocks of Center 
 County, Pennsylvania. Journal of Geology, Vol. XXI, pp. 232-250. 
 
 2. CROSBY, WILLIAM O. 1893. The Origin of Parallel and Intersecting 
 
 Joints, American Geologist, Vol. XII, pp. 368-375. 
 
 2a. CROSBY, W. O. 1912. Dynamic relation and terminology of strati- 
 graphic conformity and unconformity. Journal of Geology, Vol. XX, 
 No. 4, 1912, pp. 289-299. 
 
 3. DAUBREE, AUGUSTE. 1879. Etudes synthetiques de Geologic Ex- 
 
 perimentale, pp. 300-374. 
 
 4. DAVIS, WILLIAM M. 1913. Nomenclature of Surface Forms on Faulted 
 
 Structures. Bulletin of the Geological Society of America, Vol. XXIV, 
 pp. 187-216. 
 
 * A part of this is no doubt due to actual breaks in the series, which disappear 
 seaward. 
 
BIBLIOGRAPHY XX 827 
 
 5. GRABAU, AMADEUS W. 1900. Siluro-Devonic Contact in Erie 
 
 County, New York. Bulletin of the Geological Society of America, 
 Vol. XI, pp. 347-376. 
 
 6. GRABAU, A. W. 1905. Physical Characters and History of Some New 
 
 York Formations. Science, N. S., Vol. XXII, pp. 528-535. 
 
 7. HAHN, F. FELIX. 1912. Untermeerische Gleitung bei Trenton' Falls 
 
 (Nord Amerika) und ihr Verhaltniss zu Ahnlichen Storungsbildern. 
 Neues Jahrbuch fur Mineralogie, etc. Beilage Band XXXVI, pp. 1-41, 
 Taf. I-III, 1912. 
 
 8. HEIM, ARNOLD. 1908. Ueber rezente und Fossile Subaquatische 
 
 Rutschungen und deren Lithologische Bedeutung. Neues Jahrbuch fur 
 Mineralogie, etc., 1908, pt. II, pp. 136-157. 
 
 9. HEIM, ARNOLD. 1908. Die Nummuliten- und Flysch-bildungen der 
 
 schweizer Alpen (discusses Accordanz, Discordanz, Paen-accordanz). 
 Abhandlungen der schweizerischen Palaeontologischen Gesellschaft, 
 XXXV, 1908, p. 173. 
 
 9a. HOBBS, WILLIAM H. 1911. Repeating Patterns in the Relief and in y 
 the Structure of the Land. Bulletin of the Geological Society of 
 America, Vol. XXII, pp. 123-176, pis. 7-13. 
 
 10. HOW, JOHN ALLEN. 1913. Joints. Encyclopedia Britannica, nth>/ 
 
 edition, Vol. XV, pp. 490-491. 
 
 11. HYDE, J. E. 1908. Desiccation conglomerates in the Coal Measures-^/ 
 
 limestone of Ohio. American Journal of Science, Vol. XXV, pp. 400408. 
 
 12. KEILHACK, KONRAD. 1908. Lehrbuch der Praktischen Geologic, 
 
 2te auflage, Stuttgart. 
 
 13. KOKEN, E. 1902. Ueber die Gekrosekalke des Obersten Muschelkalkes 
 
 am Unteren Neckar. Centralblatt fur Mineralogie, etc., 1902, pp. 74 
 et seq. 
 
 14. LEITH, C. R. 1905. Rock Cleavage. Bulletin of the U. S. Geological 
 
 Survey, no. 239. 
 
 15. LOGAN, SIR W. 1863. Geology of Canada, 1863, pp. 391 et seq. 
 
 16. MARSH, OTHNIEL C. 1868. On the origin of the so-called lignites 
 
 or epsomites. Proceedings of the American Association for the Advance- 
 ment of Science, Vol. XVI, pp. 135-143. 
 
 17. MILLER, W. J. 1909. Geology of the Remsen Quadrangle. New York 
 
 State Museum Bulletin 126, 1909. 
 
 18. REID, H. F.; DAVIS, W. M.; LAWSON, A. C.; and RANSOME, F. L. 
 
 1912. Proposed Nomenclature of Faults. Advance Publication, Geo- 
 logical Society of America, Bulletin 24. 
 
 19. REID, H. F.; DAVIS, W. M.; LAWSON, A. C., and RANSOME, F. L. 
 
 1913. Report of the Committee on the Nomenclature of Faults. Geo- 
 logical Society of America Bulletin, Vol. XXIV, pp. 163-186. 
 
 20. REIS, OTTO M. 1909. Beobachtungen ueber Schichten-folge und 
 
 Gesteins-ausbildungen in der fnmkischen Unteren und Mittleren Trias. 
 I. Muschelkalk und Untere Lettenkohle. Geognostische Jahreshefte, 
 Bd. XXII, 1909 (1910), pp. 1-285, plates I-XI. 
 
 21. ROTHPLETZ, A. 1910. Meine Beobachtungen ueber den Sparagmit 
 
 und Birikalk am Mjosen in Norwegen-Sitzungsbericht. K. bayrischen 
 Akademie der Wissenschaften, Mathematisch-Naturwissenschaftliche 
 Klasse, Bd. XV, 1910, 65 pages and maps. 
 
 22. RUEDEMANN, RUDOLF. 1910. On the Systematic Arrangement in 
 
 the elements of the Palaeozoic platform of North America. New York 
 State Museum of Natural History, Bulletin 140, pp. 141-149. 
 
1 
 
 828 PRINCIPLES OF STRATIGRAPHY 
 
 22a. ULRICH, E. O. Revision of the Palaeozoic Systems. Bulletin of the 
 Geological Society of America, Vol. XXII, pp. 281-680. 
 
 23. VAN HISE, CHARLES R. 1904. A Treatise on Metamorphism. United 
 
 States Geological Survey, Monograph XL VI I. 
 
 24. WAGNER, GEORG. 1913. Stylolithen und Druck-suturen. Geolog- 
 
 ische und Palaeontologische Abhandlungen (Koken), N. P., Band XI 
 (XV), Heft 2, pp. 101-127, taf. X-XII. (With literature.) 
 
 25. WELLER, STUART. 1899. A Peculiar Devonian Deposit in North- 
 
 eastern Illinois. Journal of Geology, Vol. VII, pp. 483-488. 
 
 26. WOOD WORTH, J. B. 1896. On the fracture system of joints, with 
 
 remarks on certain great fractures. Boston Society of Natural History 
 Proceedings, Vol. XXVII, pp. 163-183, pis. 1-5. 
 
 Supplementary . 
 
 27. BOHM, A. (Edler von Bohmersheim) 1910. Abplattung und Gebirgs- 
 
 bildung. Leipzig und Wien; p. 83. 
 
 28. POKELS, F. 1911. Aenderungen der Rotationsgeschwindigkeit der Erde 
 
 als geologischer Faktor. Geologische Rundschau, Band II, pp. 141- 
 144. 
 
 29. TAYLOR, F. B. 1885. On the Crumpling of the Earth's Crust. American 
 
 Journal of Science. 3rd ser., Vol. XXX, pp. 259-277. 
 
 30. WILLIS, BAILEY. 1907. A Theory of Continental Structure Applied 
 
 to North America. Geological Society of America. Bulletin Vol. 
 XVIII, pp. 388-412. 
 
CHAPTER XXI. 
 
 THE PRINCIPLES OF GLYPTOGENESIS, OR THE SCULPTURING 
 OF THE EARTH'S SURFACE. 
 
 During every geological period the complementary processes of 
 erosion and deposition were in evidence, sometimes the one pre- 
 dominating and sometimes the other. Deposition added material 
 to the crust locally, erosion removed it elsewhere. The results of 
 erosion in terms of form are the relief features, and the process 
 viewed from this angle is a process of sculpturing. The genesis of 
 land forms is thus in large part a genesis by sculpturing or glypto- 
 genesis* 
 
 At all times, wherever land existed, erosion produced its charac- 
 teristic forms, controlled to a large degree by the character of the 
 material on which the forces of erosion were at work. Many of 
 the old erosion forms were buried beneath accumulations of new 
 rock material, and were thus preserved in a fossil form. Where 
 much deformation and alteration of the rocks has since occurred, 
 those older land forms may have become unrecognizable. Never- 
 theless, in many cases they are still in part preserved, and from a 
 study of modern types we may gain a sufficient insight into the order 
 of the development to enable us to reconstruct ancient examples 
 from partly preserved remains. 
 
 THE CYCLE OF EROSION. It is needful at the outset* for us to 
 have a clear conception of the entire cycle of erosion as expressed 
 in land forms. Beginning with the young or newly formed land, 
 which may be a recently emerged coastal plain, a dome, anticline, 
 fault block, etc., the development of a drainage system as outlined 
 in Chapter III brings with it a progressive sculpturing and the pro- 
 duction of a series of topographic features, which carries the land- 
 scape through all stages of youthfulness to maturity and on toward 
 old age. With the completion of the cycle in a moist climate the 
 condition of a peneplain is reached, when the region is worn down 
 to essential uniformity, with but little elevation above sea-level. 
 
 * From 7Xu7rr6s, carved, and ytvKuru, origin 
 
 829 
 
830 PRINCIPLES OF STRATIGRAPHY 
 
 The encroaching sea may finish this surface into an almost abso- 
 lutely level plane of marine planation. In an arid climate a more or 
 less sloping plane (chonoplain) or a series of planes will be formed 
 in the old age of the landscape, these depending for their character, 
 slope, and elevation on the forces controlling the local base level 
 of erosion. 
 
 After the cycle has thus been completed, a new one may be inau- 
 gurated by an uplift of the land or lowering of the sea-level or other 
 base-level of erosion or by a climatic change, etc. Thus a second 
 cycle of erosion will be inaugurated which, if left undisturbed, will 
 continue to its end, and a second peneplain or chonoplain is pro- 
 duced. The cycle may at any time, however, be interrupted by a 
 premature rejuvenation, the earlier cycle remaining thus incomplete. 
 
 Considering the principal land forms resulting from land sculp- 
 ture, we may first note the characteristics of immature stages, and 
 later on those of the completed cycle. Strata unaffected by orogenic 
 disturbances will be considered first, and later on those which have 
 suffered deformation. The types to be discussed include the forms 
 resulting from the normal sculpturing of i. the coastal plain, 2. the 
 monoclinal strata, 3. the dome, 4. the anticline, 5. the basin, and 6. 
 the syncline. Faulted structure (7) will be briefly noted, and after 
 this the peneplain (8) will be considered more at length. 
 
 A. EROSION FEATURES IN UNDISTURBED STRATA, 
 i. THE COASTAL PLAIN. 
 
 The submerged deposits on the continental or island margin, of 
 which the sub-coastal plain is composed, represent most typically a 
 series of clastic sediments, in part land-derived and in part thalas- 
 sigenous or derived from organic or biogenic, rarely chemical, de- 
 posits formed in the sea. Stratification is well developed, and the 
 phenomenon of progressive overlap is generally well marked. Re- 
 gressive phenomena, accompanied by landward erosion and seaward 
 retreat of shore features, and transgressive phenomena accompanied 
 by overlap of the upper beds of later formations on the eroded 
 surfaces of earlier ones, are all commonly represented in the struc- 
 ture of the sub-coastal plain. When this is elevated into a coastal 
 plain by epeirogenic movements, or into a mountain by orogenic 
 disturbances, these structures will to a greater or less extent influ- 
 ence the erosion topography induced upon these surfaces. 
 
 The coastal plain has normally a gentle dip seaward, while, close 
 
THE COASTAL PLAIN 
 
 831 
 
 to the margin of the old land, the upper thin edges of the last de- 
 posited layer, provided continuous subsidence precedes the elevation 
 of the coastal plain, lap over the earlier layers and rest directly 
 upon the old land. These overlapping edges of the strata are gen- 
 erally the first to be removed again, and in their place will appear a 
 shallow valley running parallel to the upper edge of the coastal plain, 
 the inner lowland of the normal coastal plain erosion topography. 
 Dissection of the Coastal Plain. Streams originating upon the 
 coastal plain as the "run-off" of the rain and snow-fall, continue 
 down the slope of the surface to the sea in more or less parallel 
 lines, and with more or less directness, according to the angle of 
 slope. These consequent streams, together with the extended conse- 
 quents, i. e., the old streams of the old land, now extended across 
 the coastal plain to the new sea margin, will incise more or less 
 
 fcor 
 
 FIG. 205. The emerged coastal plain with the youthful consequent streams 
 bearing a few simple insequents. 
 
 parallel channels across the coastal plain. When these channels are 
 cut down to the level of the "ground water," they will be supplied 
 by springs with a permanent stream, whereupon down-cutting may 
 proceed at an accelerated pace. Along the margin of the main 
 streams, lateral tributaries will begin, and, cutting headward, will 
 soon diversify the original channel of the streams. These lateral 
 branches are the "insequent" streams of the physiographer, since 
 they are not consequent upon a constructional slope. Insequent 
 streams, furthermore, cut their channels backward from the edge of 
 a stream, and only deepen their channels as the channels of the con- 
 sequents to which they are tributary are deepened. Consequent 
 streams, on the other hand, cut their channels downward, headward 
 extension being generally a secondary mode of growth. Near the 
 old land the insequents will remove the feather edges of the coastal 
 plain strata, as indicated above, and here will come into existence a 
 stripped belt, expressed topographically in a broad, shallow valley, 
 the inner lowland, containing the enlarged insequents, now more 
 
832 PRINCIPLES OF STRATIGRAPHY 
 
 generally spoken of as the subsequents. This inner lowland is 
 bounded on one side by the stripped slope of the old land and on 
 the other by the cut edges of the coastal plain strata. If these latter 
 contain resistant members of limestone or sandstone, they will pre- 
 sent an escarpment or cliff of some steepness. As the inner lowland 
 is widened and deepened the cliff increases in height because lower 
 and lower members of the coastal plain series are discovered by 
 the removal of the overlapping higher members. This will con- 
 tinue until the consequent has reached a condition of grade, and so 
 will arrest further deepening of the channels of its tributaries. 
 Beyond this point the cliff will be gradually lowered, through con- 
 tinued backward pushing, until the plane of erosion and the sloping 
 
 FIG. 206. The same coastal plain as shown in Fig. 205. After dissection 
 and the formation of the cuesta; the broad inner lowland is 
 occupied by the subsequents. 
 
 surface of the coastal plain intersect near the seashore, when the 
 condition of peneplanation is reached. 
 
 The topographic element produced by the dissection of the 
 coastal plain is known as the cuesta. Its main elements are the 
 "inface" or cliff facing the old land, and the gentle outward slope 
 conforming to the slight inclination of the coastal plain strata, and 
 formed by its top member. Between the cuesta and the old land is 
 the stripped belt or inner lowland, occupied by the subsequent 
 stream. This is tributary to the consequent stream, which dissects 
 the cuesta transversely. (Figs. 205, 206.) 
 
 Deposition in dissected coastal plain. A moderately dissected 
 coastal plain in which transverse consequent and longitudinal sub- 
 sequent valleys are formed may be affected by partial subsidence, 
 in which case erosive activity not only comes to a standstill, but 
 deposition will actually take place in the valleys, if subsidence has 
 been sufficient to result in the entrance of the sea into the valleys, 
 and the consequent drowning of the same. Examples of drowned 
 consequent valleys are seen to-day in Chesapeake and Delaware 
 
DISSECTION OF THE COASTAL PLAIN 833 
 
 bays which dissect the Atlantic coastal plain of North America. A 
 drowned subsequent valley or inner lowland is seen in Long Island 
 Sound, the northern edge of Long Island forming the more or less 
 ice-disturbed and moraine-covered escarpment, the inface of a 
 normal cuesta, now largely submerged. Deposits of the present 
 geologic epoch are being formed within these valleys, which were 
 cut in the partly consolidated Tertiary and Cretacic clays and sands, 
 the stratification of which is almost horizontal. The result of such 
 deposition will be that horizontally stratified modern deposits come 
 to rest upon the Cretacic or later strata of similar position which 
 form the bottoms of these eroded valleys, and that laterally they 
 will become continuous with or merge into the horizontal beds of 
 Cretacic or Tertiary age, of the valley sides and of the rewashed 
 material of which these modern strata will in part at least be com- 
 posed. Since these old drowned valleys have in places a width of 
 a score of miles or more, and since it is not at all unlikely that 
 conditions like the present one may have existed at different stages 
 in the formation of the Atlantic coastal plain, of North America 
 not to mention earlier coastal plains of this and other countries 
 the significance of these facts becomes apparent. The commingling 
 of the older and newer organic remains is another feature charac- 
 terizing such deposits. Thus, in Chesapeake Bay, modern oyster 
 shells are found attached to oyster shells of Miocenic age. 
 
 Effect of dissection and peneplanation of coastal plain strata on 
 outcrop. Where normal deposition with continuous subsidence and 
 progressive overlapping of strata occurs the undissected coastal plain 
 will show on elevation the highest stratum only, which then rests 
 directly by overlap against the old land. The formation of the 
 inner lowland results in the exposure of a belt of lower strata next 
 to the old land, while the edge of the higher stratum is farther and 
 farther removed from the old land. As the inner lowland is wid- 
 ened and deepened, lower strata appear by erosion of the over- 
 lapping ones, and the map of a strongly dissected coastal plain 
 region will show several belts of strata next to the old land, the 
 lowest exposed one being nearest it. These belts of strata will also 
 appear on the banks of the consequent streams, but will progres- 
 sively disappear below the valley bottoms in a seaward direction 
 and from the lowest to the highest. When the coastal plain has 
 been reduced to a peneplain, the various strata composing it will 
 outcrop in a series of more or less parallel bands from the lowest 
 next to the old land to the highest of the series. This last will ap- 
 pear as a belt near the point where the coastal plain passed beneath 
 the sea-level at the time the peneplanation was completed. Thus a 
 
834 PRINCIPLES OF STRATIGRAPHY 
 
 glance at the geologic map of New York State shows a series of 
 color bands representing the various strata of an ancient (Palaeo- 
 zoic) coastal plain, the lowest appearing around the Adirondack old 
 land and along the border of the crystallines north of Lake On- 
 tario, while each later one is further and further .removed south- 
 ward, until the latest, the Carbonic strata, scarcely extend into New 
 York State at all. Now, most if not all of these strata once ex- 
 tended far toward, if not entirely to, the Adirondacks, and to the 
 Laurentian old land in Canada. Their present distant outcrop is 
 in large measure due to peneplanation across gently inclined strata. 
 Subsequent erosion has, of course, pushed the edges of many of 
 these strata further south than where they were left at the end of 
 the period of peneplanation, but the amount of this later removal 
 was small as compared with the greater separation of outcrops 
 effected by peneplanation. It was formerly thought that the out- 
 crop of the edges of strata along the margin of the old crystalline 
 land marked their former extent. Since the strata of eastern North 
 America crop out in a series of belts margining the old-land, each 
 later formation falling short of the preceding one, it was believed 
 that North America rose by a series of steps, the sea, at the end of 
 each period, retreating to the region near which the next later for- 
 mation now comes to an end. From the characters of the forma- 
 tions, however, it appears that they accumulated in a subsiding sea, 
 and that each formation in turn overlapped the preceding ones, with 
 few exceptions. 
 
 The present appearance of the outcrops is due wholly to erosion, 
 the higher formations having suffered most. Many of the later 
 Palaeozoic strata of the eastern United States derived their clastic 
 material from the Appalachian region on the southeast, and their 
 northwestward limit in some cases was far beyond the border lines 
 of the present Canadian old land, a great portion of which may in 
 fact have been entirely submerged during a part of the Palaeozoic. 
 That the erosion of the strata continued until peneplain conditions 
 were reached is shown, not only by the fact that the remnants of 
 this old surface in the eastern United States form parts of a some- 
 what warped plain rising southward, but also and more especially 
 by the fact that this surface is not formed by a single hard stratum, 
 but by various hard beds which have been beveled across. Thus the 
 Alleghany plateau of western New York, which is a characteristic 
 part of this old peneplain, is composed of the beveled edges of suc- 
 cessively higher southwestward dipping strata as shown in the 
 following diagram. (Fig. 207.) 
 
 This beveling of the strata can be interpreted only as the result 
 
BEVELING OF STRATA 
 
 835 
 
 of peneplanation, in other words, when the level of erosion was 
 reached, erosion could go no further because this surface stood so 
 close to sea-level that the streams could not cut lower. Subsequent 
 elevation would permit of the cutting of lowlands on the softer 
 strata (5, 9 and 12), leaving the harder ones in relief. 
 
 That this beveling of the strata is due to erosion and not to a 
 
 L.ONTARIO- -pj 
 
 U JO 9 8 7 6 5 " 4 32 
 
 FIG. 207. Section across New York State, from Ontario to the Pennsyl- 
 vania line, showing the peneplanation of the strata along the 
 dotted line, and the subsequent carving of valleys on the softer 
 strata, i, Archaean ; 2, Potsdam or Beekmantown ; 3 and 4, Black 
 River-Trenton ; 5, Utica-Lorraine ; 6, Queenston ; 7, Medina- 
 Clinton-Rochester ; 8, Lockport-Guelph ; g, Salina ; 10, Bertie- 
 Cobleskill; n, Onondaga; 12, Marcellus; 13, Hamilton; 14, 
 Genesee-Portage-Chemung. 2-6, Ordovicic; 7-10, Siluric; 11-14, 
 Devonic. 
 
 shoreward thinning is shown by the fact that the material of the 
 strata does not change toward the beveled portion as it would if that 
 part had marked a progressively retreating shore accumulation, 
 while the fact that the lowest portion of the beds extends farther 
 than the higher portions shows that the thinning cannot represent 
 an overlapping transgressive series. The following diagrams illus- 
 trate the thinning of the strata by overlap and by beveling. (Figs. 
 208, A B.) 
 
 A B 
 
 FIG. 208. Diagram* illustrating the thinning of strata : A, by overlap ; B, by 
 beveling through erosion. 
 
 Ancient Coastal Plains Showing Cuesta Topography. 
 
 Looking over the geological maps of the world, many examples 
 of ancient coastal plain strata, in which a cuesta topography has 
 been revived after peneplanation, are found. The Palaeozoic strata 
 of New York and Canada furnish excellent examples, though part 
 of the topography is drowned, or obliterated by subsequent de- 
 posits. (Figs. 209, 210.) 
 
836 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 A nearly continuous cuesta in face may be traced along the south 
 shore of Lake Ontario from Rochester to Niagara, and thence 
 northwestward through Canada, the Indian Peninsula between 
 Georgian Bay and Lake Huron, and across the Manitoulin Islands. 
 Turning westward on these islands, it passes through the Northern 
 Peninsula of Michigan, and then turns southward, forming the 
 peninsula between Lake Michigan and Green Bay, beyond which it 
 continues southward through eastern Wisconsin. 
 
 ;v 
 
 FIG. 209. Map showing the probable drainage and topography in eastern 
 North America during Tertiary time, when a revived cuesta- 
 topography was produced. 
 
 The cuesta is cut out of the Lower Siluric formations which 
 here consist of the capping hard Niagaran (Lockport) limestones 
 and dolomites, underlain by softer shales and sandstones, into which 
 the inner lowland has been cut. In New York the softer strata 
 are thickest while the overlying hard beds thin eastward. Here the 
 inner lowland is very deep, approaching in places a thousand feet 
 below the top of the cuesta. Most of it is submerged by the waters 
 of Lake Ontario. Eastward from Rochester the cuesta becomes 
 less defined, owing to the failure of the hard capping stratum, and 
 it finally unites with the next higher cuesta to the south, to form 
 
ANCIENT CUESTAS 
 
 837 
 
 the Helderberg escarpment. Westward the limestone thickens, and 
 hence the escarpment becomes bold, but the inner lowland suffers. 
 In Western Ontario this inner lowland is largely obliterated by 
 drift deposits, but it appears again in the basin of Georgian Bay. 
 The basin of Green Bay likewise occupies a part of the inner low- 
 land in its western extension, south of which the deposits of drift 
 somewhat obscure it. There is, however, a chain of small lakes 
 (Winnebago, etc.) which shows its continuation. Lake Winnipeg 
 
 o. 
 
 'V, 
 
 FIG. 210. A later stage, showing probable river adjustment by capture, etc., 
 as deduced from the present topography. The partial blocking 
 of the valleys by glacial drift, the glacial over-deepening of 
 others, and the subsidence of the land on the northeast, produced 
 the present topography and drainage. 
 
 in Canada lies in a similar inner lowland faced on the west by a 
 cuesta inface of the Niagaran formation. In a few places the 
 cuesta is broken by ancient or by modern stream channels. The 
 most pronounced of the former is at the western end of Lake 
 Ontario (Dundas Valley) and in the channel connecting Georgian 
 Bay with Lake Huron, and continued in Saginaw Bay (Saginaw 
 River Valley). (Grabau-i6 : 37-54.) The most pronounced of the 
 modern stream channels are those of the Genesee and the Niagara. 
 North and west of this cuesta series, i. e., nearer to the old land, 
 
838 PRINCIPLES OF STRATIGRAPHY 
 
 are several smaller cuestas, less continuous, but still in places quite 
 pronounced. These are carved out of the Ordovicic limestones, 
 where they rest on softer shales or sandstones. (Wilson-3i.) 
 South of the Niagara cuesta are several others cut into the De- 
 vonic strata. The most pronounced is that of the Onondaga lime- 
 stone crossing the Niagara River at North Buffalo and extending 
 east across the State until it culminates in the Helderberg edge 
 northwest of Albany. This extends northwestward from Buffalo, 
 and crosses Lake Huron as a submerged ridge, finally reappearing 
 in Mackinac Island, beyond which it merges with the cuesta formed 
 by the Hamilton strata, which continues southward along the east- 
 ern border of Lake Michigan. 
 
 Throughout western New York and Canada this cuesta is buried 
 under drift, but in Lake Huron, though submerged, it forms a 
 cliff 400 feet high. (Fig. 211.) A still higher but generally less 
 
 FIG. 211. Cross-section of Lake Huron, from Point au Sable (a) across nine- 
 fathom ledge (b) to Cape Hurd (c), showing the submerged 
 cuesta 'and inner lowland. 
 
 pronounced cuesta extends eastward across central and southern 
 New York, formed by the sandy Upper Devonic strata. Eastward 
 this, too, merges into the Helderberg escarpment. 
 
 The Palaeozoic outcrops of northern Europe also fall into line as 
 parts of a series of discontinuous cuestas. Thus the drowned region 
 of the Baltic shows an Ordovicic cuesta series, partly submerged in 
 the islands of Oland, Dago and the coast of Esthonia, the infaces 
 of which faced the old land of Sweden and Finland. The drowned 
 inner lowland includes the Kalmar Sund.in Sweden and the Gulf of 
 Finland in Russia. A second discontinuous cuesta formed of Silu- 
 ric rocks runs in a general way parallel to the first and farther to 
 the south and east. This comprises the islands of Gotland and Osel, 
 and continues in the Baltic provinces of Russia. Central Europe 
 has its main Mesozoic cuestas in the Swabian Alp which extends 
 across southern Germany as a bold escarpment of horizontal Juras- 
 sic limestones from Wiirttemberg to the borders of the Bohemian 
 forest. 
 
 England, too, has its Palaeozoic cuesta in the westward facing 
 Wenlock Edge of Siluric strata. It has two distinct Mesozoic 
 cuestas :- one in the range of oolite cliffs which extends from Dorset 
 
MESOZOIC CUESTAS 839 
 
 to the Yorkshire coast and forms the Cotswold hills of middle 
 England with the Worcester lowland in front of it, and the other 
 in the chalk cliffs which extend in like manner from the Channel to 
 Flamborough Head, and forms the Chiltern hills of middle Eng- 
 land, the Oxford lowland lying to the west of them. (Fig. 212.) 
 All of these topographic features are revived, being probably in 
 the second if not later cycle of erosion. The coastal plain of Ala- 
 bama, on the other hand, furnishes an example of a cuesta appar- 
 ently in the first cycle. The cuesta itself is formed by the Tertiary 
 strata of the coastal plain, the inface rising rather abruptly 200 feet 
 above the lowland and being locally known as Chunnenugga ridge. 
 On the broad upland dissected by short streams running down the 
 
 FIG. 212. Stereogram of the Mesozoic coastal plain of central England : A, 
 old land of Palaeozoics (Wales) ; B, Worcester lowland on Trias- 
 sic sandstone; C, Cotswold hills or Oolite cuesta; D, Oxford 
 lowland on Upper Jurassic and Lower Cretacic clays, etc.; E, 
 Chiltern hills or -chalk cuesta; F, Tertiary coastal plain. (After 
 Davis.) 
 
 inface (obsequent streams) lie the "hill prairies," the surface being 
 formed by a resistant limestone bed. This slopes south to the coast 
 and supports the "coastal prairies." Extensive pine forests also 
 grow on this surface. The inner lowland, which lies between the 
 inface and the old land formed by the rocks of the Appalachians, 
 is so level that rainfall drains slowly and roads are impassable in 
 wet weather. "It is called the 'Black Prairie' from the dark color 
 of its rich soil, weathered from the weak underlying limestone. 
 This belt includes the best cotton district of the state." (Davis- 
 
 5 : 135 : ) 
 
 Minor Erosion Forms of Horizontal Strata. Among these is 
 the mesa or flat-topped table mountain, the surface of which is 
 formed by a resistant capping stratum. It is limited on all sides 
 by erosion cliffs, and it may constitute one of the last remnants of 
 a once widespread series of formations. The name "mesa" is also 
 
840 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 sometimes applied to a tableland cut out of a peneplaned region, 
 where the strata are disturbed or where the material is crystalline 
 rock. Its restriction to an erosion remnant of horizontal strata is 
 desirable. When the mesa has been reduced to small dimensions 
 so that it has no longer an extended flat top the name butte ap- 
 plies, though here again the designation is not always uniform, for 
 the name is applied to hills of varying origin, even to volcanic cones. 
 Restriction here would serve the cause of accuracy and precision. 
 A tepee-butte is a conical erosion hill, so named from its resem- 
 blance to the Indian wigwam or tepee. Tepee-buttes abound in the 
 region east of the Front Range in Colorado, where they are formed 
 by the resistance to erosion of a core of organic limestone which is 
 surrounded by soft, easily eroded shale. These have been described 
 and figured in Chapter X and the student is referred to the paper 
 by Gilbert and Gulliver there cited. 
 
 B. EROSION FEATURES IN DISTURBED STRATA. 
 2. THE MONOCLINE. 
 
 When the old land, together with the edge of the coastal plain 
 lapping onto it, suffers an uplifting which does not affect the coastal 
 plain strata at a distance from the old land, a monoclinal structure 
 
 d 
 
 FIG. 213. Diagrams illustrating the formation of a simple hog-back (a, b), 
 
 and of complementary hog-backs (c, d). 
 
 
 is given to the edge of these coastal plain strata. On these up- 
 bending ends of the strata erosion will proceed in much the same 
 manner as in the normal coastal plain, and a topography com- 
 parable to the cuesta and differing from it only in the greater inclin- 
 
EROSION OF DISTURBED STRATA 841 
 
 ation of the component strata will be produced. The resistant 
 stratum will produce a ridge, one side of which is composed of the 
 steeply dipping surface of the resistant stratum and comparable to 
 the gentle outward slope of the cuesta surface, while the other is 
 formed of the eroded edges of the strata composing the ridge, and 
 is comparable to the inface of the cuesta. (Fig. 213, a b.)- Topo- 
 graphic elements of this type are common on the flanks of the 
 Rocky Mountain Front Range where they are familiarly known as 
 "hog-backs." In some cases these hog-backs may, however, be parts 
 of normal anticlines of which the crystalline mountain mass was the 
 original core. The outcropping edges of the component strata will 
 not appear different on the map from those of the normal cuesta, 
 and the phenomenon of overlap is perhaps as frequently preserved 
 in this case as in that of the dissected normal coastal plain. 
 
 3. EROSION FEATURES OF THE STRUCTURAL DOME. 
 
 Wherever strata are locally uplifted into the form of a broad, 
 flat dome, as in the case of the Black Hills, a radial arrangement 
 of consequent streams will come into existence, and a series of radial 
 consequent valleys will be incised in the surface of the dome. The 
 birth of numerous insequent streams at the summit of the dome 
 will cause a gradual opening up of a series of summit valleys. If 
 the surface stratum is a resistant one, while the stratum next below 
 is readily eroded, a compound summit valley, drained by tributaries 
 of the various consequent streams, will come into existence on the 
 soft stratum, while the eroded edge of the hard stratum will sur- 
 round this valley as a series of ramparts broken at intervals by the 
 breaches through which the drainage is carried out. The character 
 of the enclosing rampart will be that of a breached circular hog- 
 back with an erosion inface and a steeply inclined outward slope. 
 Continued erosion by the tributary (subsequent) streams will widen 
 the circumference of the rampart by pushing it down slope, and 
 thus increasing the size of the summit valley. If a second resistant 
 layer is discovered beneath the soft layer on which the valley was 
 opened, it may be breached in a manner similar to the first, and a 
 second inner set of encircling hog-back ridges may come into exist- 
 ence surrounding an inner valley opened up on a second soft layer. 
 Several sets of such encircling hog-backs may thus be produced, 
 two sets always being separated by a circular valley which drains 
 through one or more branches in the outer hog-back ring. If the 
 level to which erosion is carried, i. e., base-level, is reached while 
 
842 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 the center is still composed of a soft stratum, a central lowland will 
 remain as in the case of the Weald of southeastern England. If, 
 however, erosion goes on until the underlying crystallines are ex- 
 posed a central mountainous area will remain as in the case of the 
 Black Hills. (Fig. 214.) 
 
 In outcrop, an eroded dome will show the strata in a series of 
 concentric rings, the oldest at the center and the youngest outer- 
 
 FIG. 214. Stereogram of the Black Hills dome, showing the mountainous 
 center formed by the resistant crystallines, and the rimming 
 hog-backs and valleys. (After Davis.) 
 
 most. As in the case of the cuesta and the monocline, the ultimate 
 result of erosion of such a dome is the obliteration of the ridges, 
 and the reduction of the dome as a whole to peneplain condition. 
 When that has occurred all the strata involved will be beveled off 
 toward the center of the dome, their lower edges projecting farthest 
 up onto the dome. (Fig. 215, A.) A structure of this kind is not 
 infrequently mistaken for a marginal thinning of strata on the shore 
 
 A 
 
 FIG. 215. Diagrams illustrating the thinning of strata under cover toward the 
 center of a dome: A, by erosion; B, by overlap. 
 
 of an island. In this case, however, the strata should overlap each 
 other, and the higher portions reach farthest onto the dome. ( Fig. 
 215, B.) The thin overlapping edges, moreover, should be of a clas- 
 tic character, and composed in part of material derived from the 
 shore of the island, while, in the case of the eroded dome, the strata 
 on both sides, being part of a formerly continuous whole, should be 
 of the same character, and show no shore features on the thin 
 edge. Furthermore, strata deposited in this area, subsequently to 
 
EROSION OF DISTURBED STRATA 843 
 
 the erosion of the dome (Fig. 215, A, b d e) would progressively 
 come to rest upon the beveled edges of older and older strata, in the 
 direction of the center of the dome, the relation being an uncon- 
 formable one. This same type of structure might, of course, be 
 produced by a gradually retreating sea from a rising island, so that 
 each succeeding stratum reaches to a less distance than the pre- 
 ceding. In that case, however, the ends of the successive strata 
 would show shore characteristics, and fragments of the lower might 
 be enclosed in the higher formations. 
 
 The Cincinnati and Nashville domes are typical examples of low 
 domes with very gently inclined strata formed and eroded during 
 Palaeozoic time. As pointed out repeatedly by Dr. Foerste (15) and 
 others, the lower Siluric (Niagaran) strata found on the flanks of 
 the dome conform in character to the first of the two cases cited, 
 all the evidence pointing to the fact that the Niagaran strata for- 
 merly extended across the domes, which therefore formed in late 
 Siluric or early Devonic time. As the eroded edges of the strata 
 are disconformably overlain by Mid-Devonic limestones, or by 
 Upper Devonic or younger black shales, it is evident that the ero- 
 sion of the dome preceded Mid-Devonic time. This probably oc- 
 curred during the Helderberg period, while the greater part of 
 North America was above sea-level. 
 
 Subsequently to the deposition of the higher Palaeozoic over this 
 pre-Devonic truncated dome, one or more additional domings took 
 place, followed by erosion which again exposed the lowest central 
 strata. 
 
 4. EROSION FEATURES ON THE ANTICLINE. 
 
 The anticline differs from the dome chiefly in the fact that the 
 longitudinal axis is many times longer than the transverse. Since 
 the anticline must come to an end in either direction by a downward 
 pitching of the axis, the characteristics of the simple anticline may 
 be considered those of an excessively elongated dome. While domes, 
 however, generally occur singly, anticlines occur most commonly in 
 series, a number of parallel anticlines being separated by synclines. 
 The erosion structure of such anticlines is in general similar in 
 each anticline to that of the dome, except that the subsequent val- 
 leys and the hog-back ridges are parallel, instead of circumferential, 
 and the transverse consequent gorges in the ridges are parallel in- 
 stead of radial. The most important difference lies in the duplica- 
 tion of the structure in each anticline and its complication by the 
 
8 4 4 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 intervening synclines. The resultant outcrops have been discussed 
 in the preceding chapter. 
 
 When anticlines are partly eroded a series of monoclines or 
 hog-backs results, similar in character to that formed by the uplifted 
 upper end of the coastal plain as above described. Monoclines 
 formed by breached anticlines usually occur in pairs opposing each 
 other as in the Appalachians of to-day, but monoclines without a 
 corresponding opposite occur which in reality represent one limb 
 of an anticline of which the other limb has been entirely removed. 
 (Fig. 216.) Thus the monocline which forms the Front Range 
 of the Appalachians in New Jersey, Pennsylvania and southward 
 
 cofictfon across tfie QreotVodUy dt^arnsliit.ry. 
 Jo illustrate Chap XXII oftfincUtfeport, 1X31 
 
 'tteyliniKlone . 
 l( Trias) york. 
 
 W&ry pastlUy 
 great faults should le 
 ^ placed alony lints AB,CD. 
 
 y/tu AecTio* AAaivJ iturety tht great depth of the 
 Cort Synclinal , but not Its exact thape under 
 ground., ft indicates the e lose plications alsoof-lhe 
 Alate and limestone belts ; and tke vast Jjenal Zrosion 
 
 FIG. 216. Section of the Appalachian folds near Harrisburg, to show the 
 removal of the eastern part of the folds by erosion. 
 
 represents merely the western limb of an anticline, the eastward 
 continuation of which has been entirely removed by erosion. This 
 was accomplished by peneplanation which cut below the axes of the 
 synclines into the underlying more intensely folded rocks in which 
 the Appalachian folds are not recognizable. The same is in part 
 true of the monoclines facing the Front Range of the Rocky Moun- 
 tains. The Triassic and Cretacic strata most probably once ex- 
 tended across what is now the front range axis, and this was per- 
 haps true of much of the Palaeozoic series as well. From the fact 
 that the axis of the long Front Range anticline was a granite one, 
 erosion, which removed the formerly continuous sediments, left it 
 in relief, so that it holds the same relation to the flanking mono- 
 clines on either side that the central crystalline mass of the Black 
 Hills holds to its encircling hog-backs. (Fig. 213, c, d, p. 840.) The 
 completion of the cycle of erosion in a region of monoclinal flexures 
 
EROSION OF ANTICLINES 
 
 845 
 
 results in the formation of a peneplain across which rivers wander 
 with little or no regard to the underlying structure. As already 
 outlined, the mapping of the outcrops of the strata on such a sur- 
 face would form a series of color bands parallel for a long dis- 
 tance, but uniting when the pitch of the anticline carried the strata 
 below the erosion surface. The central color band of the eroded 
 anticline would, of course, represent the oldest formation, while on 
 either side of this would be bands corresponding on opposite sides 
 and representing the successively younger formations from the cen- 
 ter outward (Fig. 190, a, b, p. 806; see also Figs. 217, 218.) 
 
 Elevation of the peneplain and renewal of the erosive processes 
 will result in the revival of the topography, since the harder layers 
 
 .217. Anticlinal fold with pitch- 
 ing axis, truncated across the 
 top. The harder beds form 
 monoclinal ridges; the valleys 
 were cut on soft strata. (After 
 Willis.) 
 
 FIG. 218. Synclinal fold with pitch- 
 ing axis eroded. The harder 
 beds form monoclinal ridges. 
 (After Willis.) 
 
 will again be carved into relief by the concentration of the erosive 
 processes on the" softer layers. The Appalachians furnish an in- 
 structive example of such a revived topography they are at pres- 
 ent in the second if not in a later cycle of erosion.* This fact is 
 well brought out by the numerous entrenched transverse streams 
 which cross the monoclines more or less at right angles. These 
 streams, of which the Susquehanna is a good example, came into 
 existence on the tilted peneplain, and their constant downward cut- 
 ting made possible the openings of the longitudinal valleys on the 
 softer strata, by the tributary streams. 
 
 * This is graphically expressed by the formula n th + I cycle suggested by 
 Davis for such cases, where it is known that the region is not in the first cycle 
 of erosion, but where it is impossible to say how many cycles have been completed. 
 Thus n may stand for one or for more than one. 
 
846 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 5. THE BASIN. 
 
 The basin is the complement of the dome, representing the down- 
 ward arching of the strata. As in the dome, the basin may be 
 gentle, with strata so slightly inclined as to seem horizontal or it 
 may be a pronounced one with highly inclined sides. The former 
 is represented by the Paris Basin and the Michigan Basin and is 
 in many respects the most significant type to the stratigrapher, being 
 often difficult to detect. The Paris Basin represents a case in which 
 the successive strata have been breached by radial consequent 
 streams running from the surrounding higher old-land to the lower 
 center, while their tributaries carved out circumferential valleys 
 bounded by outward facing cliffs of the "inface type." The dis- 
 sected basin at this stage differs from the dissected dome in having 
 its oldest formations on the outside, the circumferential valleys 
 
 FIG. 219. Strata of a basin, trun- FIG. 220. The same series after a 
 cated and covered by horizontal second folding and truncation, 
 
 strata. 
 
 being cut out of higher and higher strata toward the center, while 
 in the dome the youngest formations are on the outside, and the 
 successive circumferential valleys are cut on lower and lower strata 
 toward the center. In the basin the infaces or escarpments face 
 outward; in the dome they face inward. The Paris Basin is most 
 probably to be regarded as a region in the second cycle of erosion, 
 having been peneplained once, after which the topography has been 
 revived by a resumption of stream activity. 
 
 The Michigan basin forms an interesting example of a com- 
 pound type. At the beginning of Devonic time, the basin was 
 formed, after which erosion beveled off the margins, leaving the 
 successive formations superimposed after the manner of a nest of 
 plates, the highest being the smallest, while the edges of the suc- 
 cessively lower ones project beyond the higher. Across this series 
 were deposited the Devonic and later strata, after which a second 
 downward arching took place, followed by beveling of the edges of 
 this later formed basin. Thus the highest formations occupy the 
 center of the area and are surrounded by the rims of successively 
 
THE PENEPLAIN 847 
 
 lower formations. (See Figs. 219 and 220.) The dome and basin 
 have generally a definite relation to each other. Thus in Europe 
 the Weald dome lies north of and immediately adjacent to the 
 Paris Basin, while in North America the Michigan Basin is sur- 
 rounded by domes. As already outlined in the preceding chapter 
 (see map, Fig. 192), these domes and basins suffered simultaneous 
 deformations at at least two distinct periods, but some of the 
 domes and perhaps some of the basins may have suffered repeated 
 deformations throughout Palaeozoic time. 
 
 6. THE SYNCLINE. 
 
 This corresponds to a much elongated basin, and the charac- 
 teristics it exhibits will be essentially those of the basin except that, 
 instead of radiality or concentric arrangement, many of the features 
 will be characterized by parallelism of arrangement. The charac- 
 teristics of synclines as of anticlines are best exhibited in the Appa- 
 lachian region of North America and the Jura Mountains of 
 Europe. 
 
 7. EROSION FEATURES IN FAULTED STRATA. 
 
 These have already been discussed, to some extent in Chapter 
 XX. Some special features are shown in Figs. 221 and 222. 
 
 8. THE COMPLETION OF THE CYCLE. 
 
 THE PENEPLAIN. When the surface of a country is worn to so 
 low a relief that the streams have practically ceased eroding and 
 are throughout in a graded condition, the surface of the region may 
 be considered as in the peneplain state. This is by no means a per- 
 fectly level surface, but rather one of a rolling or undulating topog- 
 raphy, and not infrequently erosion remnants or monadnocks rise 
 considerably above the general level of the peneplain. Since streams 
 erode their beds until every portion is graded, the stream bed repre- 
 sents a continuous gentle slope to sea-level. As long as the rela- 
 tive position of land and sea remains stable, reduction of the relief 
 will progress, and the surface of the land will approach closer and 
 closer to the level of the sea. If that could be reached, the region 
 would be reduced to base-level. It is obvious, however, that as the 
 relief is reduced more and more, the rate of reduction rapidly de- 
 
848 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 creases, so that the process of base-leveling goes on at a progres- 
 sively diminishing rate. 
 
 While the harder or more resistant strata of any region are the 
 last to be reduced to the level of the peneplain, they eventually also 
 succumb, and the surface of the peneplain thus shows a lack of 
 conformity to the structure of the country. This lack of conform- 
 ity to structure is one of the most characteristic features of a pene- 
 plain, and the one by which it is most readily recognized. When 
 the peneplain is gradually submerged beneath a transgressing sea, 
 the final inequalities may be smoothed off by marine planation. In 
 this manner erosion surfaces of remarkably level character may be 
 produced, such as are seen on the Archaean granites of the Manitou 
 
 FIG. 221. Section on San Juan River, Colorado, showing erosion escarp- 
 ments in horizontal and tilted strata. 
 FIG. 222. The same section interpreted by the assumption of a fault. 
 
 region in Colorado, where the early Palaeozoic sandstones rest upon 
 a surface almost as level as a table top. (Crosby-i.) (Fig. 52, p. 
 310.) Where transgression of the sea is gradual and uniform on a 
 peneplain surface, a basal conglomerate or sandstone is formed 
 which everywhere rests directly upon the old peneplaned surface. 
 The age of this sandstone or conglomerate will, however, vary as 
 pointed out in Chapter XVIII, being younger shoreward and older 
 seaward. Where monadnocks rise above the level of the submerged 
 peneplain, these will be gradually buried under the accumulating 
 coastal plain strata, which along their contact with the monadnock 
 will be of a more or less coarsely fragmental character. A typical 
 example of a monadnock buried in coastal plain strata, and now 
 partly resurrected by erosion, is found in the Baraboo ridges of 
 southern Wisconsin. An example of a monadnock being partly 
 buried by marine sediment is found in the island of Monhegan, off 
 
THE PENEPLAIN 
 
 849 
 
 the coast of Maine, which is still partly above the level of the sea, 
 though the peneplain from which it rises is here completely sub- 
 merged. 
 
 In an old region, where peneplanation has long been in progress, 
 the surface is formed by a layer of atmoclastic material of greater 
 or less depth: With this are mingled peat and other phytogenic 
 material, while here and there may occur a deposit of wind-blown 
 matter. On this surface the rivers will assume a meandering course 
 which has no regard to the underlying structure. When such 
 
 Section across a branching fault. 
 
 Fault and Monocline. 
 
 Fault with thrown beds flexed upward a dragged Fault with thrown beds flexed downward. 
 fault. 
 
 FIG. 223. Erosion scarps formed in horizontal and in flexed strata, com- 
 pared with erosion and fault scarps in faulted strata. 
 
 material is exposed to the activities of a slowly encroaching sea, it 
 will be pretty thoroughly sorted and the finer material carried sea- 
 ward to settle in quieter water. But if transgression is rapid, other 
 sediments may be deposited over the ancient soil, which will remain 
 relatively undisturbed. Such ancient buried soils are sometimes met 
 with in the geological series marking former periods of extended 
 peneplanation. 
 
 The Relation of the Peneplain to Sedimentation. A region of 
 low relief will furnish only the finest material for its rivers to 
 carry, and hence the sea bordering- a peneplained country will 
 receive only the finest lutaceous sediment which is washed from 
 the lands by the rains and swollen streams. Thus lutaceous sedi- 
 ments, often heavily charged with decaying organic matter, may 
 accumulate in the form of extensive mud flats or deltas. The pres- 
 
850 PRINCIPLES OF STRATIGRAPHY 
 
 ent Mississippi and Nile deltas are examples, being composed only 
 of the finest mud. The Black Devonic shale of Michigan and Ohio 
 also appears to represent a deposit of this type, as already outlined 
 in a previous chapter. 
 
 When the continent has been worn so low that little or no sedi- 
 ment is carried into the sea, organic deposits may accumulate close 
 to the shore. Since rivers, even in low countries, are probably 
 never without their modicum of silt, it follows that pure organic 
 accumulations can be formed near shore only where large rivers do 
 not discharge. A consideration of the chalk beds of England and 
 Ireland shows them to be part of a series of coastal deposits in a 
 slowly westward transgressing sea. This is partly shown by the 
 westward overlapping of the successive members on an eroded pre- 
 Cretacic peneplain. Thus while the basal conglomerates, sands and 
 greensands of southeastern England are of Aptien age and rest dis- 
 conformably upon the Wealden, the basal Cretacic conglomerates, 
 sandstones and greensands of northeast Ireland and of Mull and 
 Morvern in Scotland are of Cenomanien age. Here the Aptien and 
 the Gault have been overlapped, while the Cenomanien of the north- 
 west has the characteristics held by the Aptien in the southeast. 
 The Cenomanien in the southeast is a glauconitic chalk, and is suc- 
 ceeded by the pure chalk which begins with the Turonien. In the 
 northwest the Turonien is still a glauconite sand to be succeeded by 
 lower Senonien glauconitic chalk and only toward the last by pure 
 chalk. (See Fig. 146 in Chapter XVIII, page 730.) 
 
 It is thus seen that the great mass of organic material which 
 forms the chalk was deposited in comparatively shallow water not 
 very remote from the coast, and this suggests that the land of that 
 time must have been in a state of peneplanation. The micro- 
 organisms of the chalk bear out this interpretation, for shallow 
 water benthonic forms predominate. The possibility of eolian 
 deposition of some chalk beds, mentioned in an earlier chapter, must 
 not be overlooked. 
 
 Dissection of the Peneplain. If a peneplain is elevated, with or 
 without tilting, a new cycle of erosion commences; all the streams 
 will be revived, and they will incise their valleys, thus dissecting 
 the peneplain. At first the stream valleys are relatively insignificant 
 as compared with the broad, gently rolling upland of the elevated 
 peneplain. But as the valleys are widened, the interstream por- 
 tions are reduced and the upland dwindles into a series of ridges 
 and peaks which eventually become lowered, so that a new peneplain 
 is produced. Thus the second cycle of erosion is completed. While 
 the upland portion of the elevated peneplain is still broad, the char- 
 
THE PENEPLAIN 851 
 
 acter of the old peneplain surface is easily seen. As the valleys 
 become widened and the interstream portions reduced, the old 
 peneplain level is less and less readily recognized, the uniform 
 agreement in height of the interstream ridges being the most con- 
 spicuous feature. It can, however, be shown that uniform height 
 of interstream ridges may also be brought about in a country where 
 the original surface was very diverse, if the streams are uniformly 
 spaced. (Shaler-27.) This is especially true if the streams are of 
 approximately equal power, and the rate of erosion is thus more 
 or less uniform. 
 
 Age of the Peneplain. It is evident that the peneplain is of 
 later age than that of any of the strata affected by the erosion in 
 the formation of the peneplain. In the case of folded strata which 
 have become peneplaned the commencement of peneplanation may 
 be regarded as simultaneous with the folding, and since in a strongly 
 folded region even the latest strata deposited may be involved in 
 the folds and so protected from complete erosion, we may not be 
 . far wrong in considering that folding and peneplanation begin 
 shortly after the deposition of the youngest stratum involved. It 
 must, however, be borne in mind that folding of strata without 
 fracture takes place at some distance below the surface (see Chap- 
 ters XIX and XX), and that therefore a series of perfect folds in 
 any given series of strata suggests that these strata were at con- 
 siderable depth below the surface at the time of the formation 
 of the folds. Under such conditions, when perfectly folded strata 
 are found near the surface of a peneplain, it is not likely that the 
 later strata, deposited before the commencement of folding, are 
 included within the folds. Thus within some of the strongly folded 
 strata of the Hudson River group in Albany County, N. Y., only 
 middle and earlier Ordovicic strata are involved so far as known, 
 though there is every reason for believing that the folding did not 
 take place until late Ordovicic, if not early Siluric time. 
 
 In the case of horizontal strata which have been peneplained, 
 the latest preserved stratum is not to be regarded as the last one 
 deposited before elevation and erosion, for this would allow no 
 removal of strata by erosion during the peneplanation. In general 
 we may consider that the amount of rock removed from a given 
 region during a stated period of elevation and erosion is propor- 
 tional to the distance of that region from the point where erosion 
 was replaced by deposition, i. e., from the seashore or piedmont 
 plain of the period. Exceptions to this must, however, be recog- 
 nized where local conditions limited or accentuated erosion, as in the 
 case of a warped surface where some portions of a given formation 
 
852 PRINCIPLES OF STRATIGRAPHY 
 
 were raised excessively and so became subject to pronounced ero- 
 sion, or where other portions were proportionally more depressed 
 and so escaped great erosion, or where other causes were active. 
 
 The end of the period of peneplanation is commonly marked by 
 the age of the strata overlying the peneplain surface. Here, how- 
 ever, it must be borne in mind that slow subsidence of a peneplain 
 surface produces a gradual deposition of formations which suc- 
 cessively overlap each other, each later one in turn coming to rest 
 upon the old peneplain surface beyond the edge of the preceding 
 one. Thus, the pre-Cambric peneplain of North America is over- 
 lain by Lower or Middle Cambric strata in the southern United 
 States, by Upper Cambric strata in the Upper Mississippi Valley 
 and northeastern New York, by Lower or Middle Ordovicic in 
 northwestern New York, by Middle, and later Ordovicic, in por- 
 tions of Canada, and by later formations in other parts. In each 
 case the age of the peneplain terminates with the age of the over- 
 lying bed, while the part still above water continues to be subject to 
 erosion. Thus these higher portions continued to be peneplained, 
 though at an exceedingly slow rate, long after the southern end 
 of the peneplain was buried under thousands of feet of strata. 
 
 HIGH-LEVEL PLAINS OF ARID REGIONS. In arid regions, where 
 the rainfall is insufficient, and where a large part of the erosive 
 work is done by wind, high-level plains of erosion comparable to 
 peneplains, but having no definite relation to sea-level, may come 
 into existence. Under the influence of arid erosive forces, the 
 initial relief of even a rugged region will gradually become extinct, 
 partly by erosion and partly by filling of the desert basins with 
 waste. The process has been fully described by Davis (12) and 
 enlarged upon by others. A few quotations from Davis will serve 
 to point the essentials of the process and its results: Under the 
 conditions cited "the most perfect maturity would be reached when 
 the drainage of all the arid region becomes integrated with respect 
 to a single aggraded basin-base-level, so that the slopes should 
 lead from all parts of the surface to a single area for the deposition 
 of the waste. The lowest basin area which thus comes to have a 
 monopoly of deposition may receive so heavy a body of waste that 
 some of its ridges may be nearly or quite buried. Strong relief 
 might still remain in certain peripheral districts, but large plain 
 areas would by this time necessarily have been developed. In so 
 far as the plains are rock-floored, they would truncate the rocks 
 without regard to their structure." (12: J#p.) 
 
 "As the dissected highlands of maturity are worn down, the 
 rainfall decreases, and the running streams are weakened and ex- 
 
PLAINS OF ARID REGIONS 853 
 
 tinguished ; thus . . . the winds in time would appear to gain the 
 upper hand as agents of erosion and transportation. If such were 
 the case, it would seem that great inequalities of level might be 
 produced by the excavation of wide and deep hollows in areas of 
 weak rocks. As long as the exportation of wind-swept sand and 
 of wind-borne dust continued, no easily denned limit would be 
 found for the depth of the hollows that might thus be developed in 
 the surface, for the sweeping and lifting action of the wind is not 
 controlled by any. general baselevel. In an absolutely rainless re- 
 gion there appears to be no reason for doubting that these abnormal 
 inequalities of surface might eventually produce a strong relief in 
 a still-standing land of unchanging climate ; but in the actual deserts 
 of the world there appears to be no absolutely rainless region ; and 
 even small and occasional rainfalls will suffice, especially when 
 they occur suddenly and cause floods, as is habitual in deserts, to 
 introduce an altogether different regime in the development of sur- 
 face forms from the rock hills and hollows which would prevail 
 under the control of the winds alone. The prevailing absence of 
 such hill-and-hollow forms, and the general presence of graded 
 wadies and of drainage slopes in desert regions, confirm this state- 
 ment." 
 
 "As soon as a shallow wind-blown hollow is formed, that part 
 of the integrated drainage system which leads to the hollow will 
 supply waste to it whenever rain falls there ; the finer waste will be 
 blown away, the coarser waste will accumulate, and thus the ten- 
 dency of the winds to overdeepen local hollows will be sponta- 
 neously and effectively counteracted. As incipient hollows are 
 formed in advancing old age, and the maturely integrated drainage 
 system disintegrates into many small and variable systems, each 
 system will check the deepening of a hollow by wind action ; hence 
 no deep hollow can be formed anywhere, so long as occasional rain 
 falls." (12-391-59,?.) 
 
 With the continuance of the processes and the further disin- 
 tegration of the drainage, the surface is slowly lowered, leaving 
 only those rock masses projecting as monadnocks or "Inselberge" 
 which most effectually resist dry weathering. The production of 
 the Inselberg landscape chiefly by eolian agencies has already been 
 considered in an early chapter. 
 
 "At last, as the waste is more completely exported, the desert 
 plain may be reduced to a lower level than that of the deepest 
 initial basin" which originally was a temporary recipient of the 
 waste, "and then a rock-floor, thinly veneered with waste, unre- 
 lated to normal baselevel, will prevail throughout except where 
 
854 PRINCIPLES OF STRATIGRAPHY 
 
 monadnocks still survive." (i2:jpj.) This condition of wide- 
 spread desert-leveling has actually been reached in the Kalahari 
 region of South Africa, as described by Passarge and these ex- 
 amples of the final stage, Davis holds, justify the assumption that 
 the various stages, through which they must have passed to reach 
 this last stage, and the characters of which can easily be deduced 
 theoretically, may actually find representation in the arid regions 
 of the world. Furthermore, fossil examples of such desert-leveled 
 plains, as well as examples of stages which precede the final stage, 
 ought to be looked for in the sections of the earth's crust, and we 
 can no longer assume that any level plain, recent or fossil, is a 
 normal peneplain ; the possibility that it may be a high-level desert 
 plain must not be overlooked. 
 
 Some criteria for distinguishing modern peneplains from desert 
 plains are given by Davis. 
 
 "A plain of erosion lying close to sea-level in a region of normal 
 climate, and therefore traversed by rivers that reach the sea, but 
 
 FIG. 224. Erosion-buttes (Zeugenberge) near Guelb-el-Zerzour. The erosion 
 is mainly eolian. (After Walther.) 
 
 that do not trench the plain, might conceivably be a depressed desert 
 plain standing long enough in a changed climate to have become 
 cloaked with local soils; but it is extremely unlikely that the de- 
 pression of a desert plain could place it so that it should slope 
 gently to the seashore, and that its new-made rivers should not 
 dissect it, and that there should be no drifted sands and loess 
 sheets on adjoining areas, and no signs of submergence on neigh- 
 boring coasts. An untrenched plain of erosion in such an attitude 
 would be properly interpreted as the result of normal processes, long 
 and successfully acting with respect to normal baselevel." (12: 
 397-398.} 
 
 "In the same way a high-standing plain of erosion in a desert 
 region might be possibly explained as an evenly uplifted peneplain 
 whose climate had in some way been changed from humid to arid, 
 whose deep weathered soils had been removed and replaced by 
 thin sheets of stony, sandy, or saline waste, and whose residual 
 reliefs had been modified to the point of producing shallow basins. 
 But in this case there should be some indications of recent uplift 
 around the margin of the area, either in the form of uplifted marine 
 
PLAINS OF ARID REGIONS 855 
 
 formations whose deposition was contemporaneous with the ero- 
 sion of the peneplain, or in the form of fault-escarpments separat- 
 ing the uplifted from the non-uplifted areas. Moreover, it is ex- 
 tremely unlikely that the uplift of an extensive peneplain could 
 place it in so level a position that it should not suffer dissection 
 even by desert agencies; hence a high-standing desert plain is best 
 accounted for by supposing that it has been leveled in the position 
 that it now occupies." (12: 398.) 
 
 "It should not, however, be overlooked that there is some danger 
 of misreading the history of a depressed desert plain which has 
 been by a moderate amount of normal weathering and erosion 
 transformed into a normal peneplain; and of an uplifted peneplain 
 which has been by a moderate amount of arid weathering and 
 erosion transformed into a typical desert plain; the danger of error 
 here is similar to that Ly which a peneplain, wave-swept and scoured 
 during submergence', might be mistaken for a normal plain of 
 marine abrasion." ( 12 : 300.) 
 
 "If an old rock-floored desert plain be gently warped or tilted, 
 marine submergence is not likely to follow immediately, but the 
 regular continuation of general degradation will be interrupted. 
 The patches and veneers of waste will be washed from the higher 
 to the lower parts of the warped surface; the higher parts, having 
 an increased slope, might be somewhat dissected, and would cer- 
 tainly be exposed to more active degradation than before, until 
 they were worn down to a nearly level plain again. The lower 
 parts would receive the waste from the higher parts, and the con- 
 tinuance of this process of concentration would in time cause the 
 accumulation of extensive and heavy deposits in the lower areas. 
 Such deposits will be, as a rule, barren of fossils ; the composition, 
 texture and arrangement of their materials will indicate the arid 
 conditions under which they have been weathered, transported, and 
 laid down ; their structures will seldom exhibit the regularity of 
 marine strata, and they may reach the extreme irregularity of sand- 
 dune deposits. If warping continues, the desert deposits may gain 
 great thickness; their original floor may be depressed below sea- 
 level, while their surface is still hundreds or thousands of feet 
 above sea-level." ( 12 : 400-401.) 
 
 Examples which serve to illustrate such deposits have been 
 described from South Africa (Passarge) and West Australia, where 
 barren sandstones of continental origin surround the monadnocks 
 ("Inselberge"). Ancient examples seem to occur in the great 
 deposits of barren Uinta sandstones 12,000 to 14,000 feet thick in 
 some localities which lie at the base of the Palaeozoic series in the 
 
8 5 6 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 region of the present Wasatch Mountains. The basal Palaeozoic 
 sandstones of eastern North America, from a few feet to over a 
 thousand feet thick ("Potsdam" sandstone), also have many char- 
 acters pointing to such an origin. In this case, of course, the trans- 
 gressing Paleozoic sea modified the deposits to a certain degree and 
 redeposited a part of them as fossiliferous marine sands and clays. 
 
 "If a change from an arid toward a moister climate causes a 
 drainage discharge to the sea, a dissection of the plain will ensue. 
 The valleys thus eroded cannot expectably exhibit any great de- 
 gree of adjustment to the structures, because the stream courses will 
 result from the irregular patching together of the preexisting 
 irregularly disintegrated drainage. This peculiar characteristic, 
 taken together with the absence of neighboring uplifted marine de- 
 posits, will probably suffice in most cases to distinguish desert plains, 
 dissected by a change to a moister climate, from peneplains dissected 
 in consequence of uplift; but there still might be confusion with 
 peneplains dissected by superposed streams." (12:401.) 
 
 Locally, around individual mountains in an arid climate, a sur- 
 face sloping outward in all directions partly due to erosion and 
 partly to deposition is produced by the forces operative under such 
 conditions. Such a plane, though never very perfect, will have the 
 appearance of a broad-based cone the center of which is the un- 
 dissected mountain remnant. Dr. Ogilvie (21) has described these 
 as forming around the laccoliths of the Ortiz Mountains in New 
 Mexico and has named them "conoplains." They are essentially 
 elements in the stages of desert planation. 
 
 C. MINOR EROSION FEATURES. 
 
 Many of these have already been noted in previous chapters. 
 We may recall the grooves formed by eolian corrasion in the Libyan 
 limestone plateau and the erosion needles capped by Operculina 
 in the Libyan desert (p. 52) ; the Yardangs of central Asia and 
 
 FIG. 225. Erosion features (Schichtenkopfe) in inclined Cretacic limestones. 
 Chiefly eolian. Abu Roasch. (After Walther.) 
 
MINOR EROSION FEATURES 
 
 857 
 
 the erosion monuments of Monument Park, Colorado (p. 53) ; the 
 facetted pebbles (p. 54) ; erosion forms produced by solution (pp. 
 174-176), by waves (pp. 221-226), by rivers (pp. 246-257), and by 
 ice (pp. 263-265). A striking example of eolian erosion is further 
 shown in Fig. 225, where alternating hard and soft limestone strata 
 
 FIG. 226. Solution fissures in chalk, forming organ-pipe structure. The hol- 
 lows are filled with sand and clay from above. (After Lyell.) 
 
 inclined at a considerable angle were carved into fantastic forms by 
 wind. Another example, illustrating the effect of solution on lime- 
 stone, is given in Fig. 226, which shows the solution fissures in chalk 
 and other limestone regions where cylindrical depressions often 
 occur in great numbers, and close together, forming geological 
 "organ pipes" (Geologische Orgeln) (Fig. 136, p. 698). Broad 
 kettle-like hollows or dolinas are also produced by solutions on 
 joint-cracks. These may be up to i km. in diameter and 30 meters 
 in depth. 
 
 BIBLIOGRAPHY XXI. 
 
 i. 
 
 CROSBY, WILLIAM O, 1899. Archaean Cambrian Contact near / 
 Manitou, Colorado. Geological Society of America Bulletin, Vol. X, * 
 pp. 141-164. 
 
 2. DAVIS, WILLIAM MORRIS. 1896. Plains of Marine and Subaerial J 
 
 Denudation. Geological Society of America Bulletin, Vol. VII, pp. 
 378-398. 
 
 3. DAVIS, W. M. 1899. The Peneplain. American Geologist, Vol. XXIII, V 
 
 pp. 207-239. 
 
 4. DAVIS, W. M. 1899. The Geographic Cycle. Geographical Journal J 
 
 (London), Vol. XIV, pp. 481-584. 
 
 5. DAVIS, W. M. 1899. Physical Geography. Ginn & Co. 
 
 6. DAVIS, W. M. 1899. The Drainage of Cuestas. London Geologists' 
 
 Association Proceedings, Vol. XVI, pp. 75-93, 16 figures. 
 DAVIS, W. M. 1900. The Physical Geography of the Lands. Popular 
 Science Monthly, Vol. LVII, pp. 157-170. 
 
 7- 
 
858 PRINCIPLES OF STRATIGRAPHY 
 
 8. DAVIS. W. M. 1901. Peneplains of Central France and Brittany. 
 
 Geological Society of America Bulletin, Vol. XII, pp. 480-487. 
 
 9. DAVIS, W. M. 1901. The Geographical Cycle. Verhandlung des 7ten 
 
 Internationalen Geographischen Kongresses, pt. II, pp. 221-231. 
 
 10. DAVIS, W. M. 1902. Base-level Grade and Peneplain. Journal of 
 
 Geology, Vol. X, pp. 77~ IO 9- 
 
 11. DAVIS, W. M. 1905. Leveling without Base Leveling. Science, N. S., 
 
 Vol. XXI, pp. 825-828. 
 
 12. DAVIS, W. M. 1905. The Geographic Cycle in an Arid Climate. Journal 
 
 of Geology, Vol. XIII, No. 5, pp. 381-407. 
 
 (13. DAVIS, W. M. 1905. The Bearing of Physiography on Suess' Theories. 
 American Journal of Sciences, Vol. XIX, pp. 265-273. 
 
 14. DAVIS, W. M. 1905. The Complication o' the Geographical Cycle. 
 
 Compte Rendu, 8th International Geographical Congress, pp. 150-163. 
 
 15. FOERSTE, A. E. 1902. The Cincinnati Anticline in Southern Kentucky. 
 
 American Geologist, Vol. XXX, pp. 359-369. 
 
 16. GRABAU, A. W. 1901. Geology and Palaeontology of Niagara Falls 
 
 and Vicinity. N. Y. State Museum Bulletin No. 45. 
 
 17. GRABAU, A. W. 1908. Pre-Glacial drainage in Central Western New 
 
 York. Science, N. S., Vol. XXVIII, pp. 527-534- 
 
 18. JOHNSON, DOUGLAS W. 1903. Geology of the Cerillos Hills. (Lac- 
 
 colith and Dome Mountain Dissection.) School of Mines Quarterly, 
 Vol. XXIV, pp. 173-246; 456-600. 
 
 19. JOHNSON, D. W. 1905. Youth, Maturity and Old Age of Topographic 
 
 Forms. American Geographical Society Bulletin, XXXVII, pp. 648-653. 
 
 20. KEYES, C. R. 1903. Geological Structure of New Mexican Bolson 
 
 Plains. American Journal of Science, Vol. XV, pp. 207-210. 
 
 21. OGILVIE, IDA H. 1905. The High Altitude Conoplain: A topographic 
 
 form illustrated in the Ortiz Mountains. American Geologist, XXXVI, 
 pp. 27-34. 
 
 22. PASSARGE, SIEGFRIED. 1904. Die Kalahari. Berlin. 
 
 23. PASSARGE, S. 1904. Rumpfflache und Inselberge. Zeitschrift der 
 
 deutschen geologischen Gesellschaft, Bd. LVI, pp. 193-209. 
 
 24. PASSARGE, S. 1904. Die Inselbergelandschaft im tropischen Africa. 
 
 Naturwissenschaftliche Wochenschrift. N. F., Bd. Ill, pp. 657-665. 
 '25. PENCK, A. 1883. Einfluss des Klimas auf die Gestalt der Erdoberflache. 
 Verhandlungen des 3ten deutschen Geographentages, pp. 78-92. 
 
 26. PENCK, A. 1905. Climatic Features in the Land Surface. American 
 
 Journal of Science, Vol. XIX, pp. 165-174. 
 
 27. SHALER, N. S. 1899. Spacing of Rivers with Reference to the Hypothesis 
 
 of Base-Leveling. Geological Society of America Bulletin, Vol. X, pp. 
 263-276. 
 
 28. WALTHER, JOHANNES. 1891. Denudation in der Wuste. (See 
 
 Bibliography II.) 
 
 29. WALTHER, JOHANNES. 1900. Das Gesetz der Wiistenbildung (2nd 
 
 ed., 1912). 
 
 30. WILSON, ALFRED W. G. 1903. The Laurentian Peneplain. Journal 
 
 of Geology, Vol. XI, pp. 615-669. 
 
 31. WILSON, A. W. G. 1904. Trent River System and St. Lawrence Outlet. 
 
 Geological Society of America Bulletin, Vol. XV, pp. 211-242. 
 
 32. WILSON, A. W. G. 1905. Physiography of the Archaean Areas of 
 
 Canada. International Geographical Congress, 8th report, pp. 116-135. 
 
D. THE PYROSPHERE. 
 CHAPTER XXII. 
 
 GENERAL SUMMARY OF PYROSPHERIC ACTIVITIES. 
 
 The activities of the pyrosphere are judged by their surface 
 manifestations, and by the observations on results of igneous ac- 
 tivities .in the past. So far as the pyrosphere itself is concerned 
 direct observation is, of course, out of the question, nevertheless 
 much may be learned regarding its probable character by experi- 
 mentation and the study of igneous activities in the laboratory, as 
 well as in the field, while much more may be inferred from a logical 
 interpretation of past igneous work in portions of the earth's crust 
 exposed as a result of dislocations, or of prolonged erosion, or of 
 both. No attempt is made to discuss volcanic activities in anything 
 more than a summary manner, though the subject is of vast geologi- 
 cal importance. The science of pyrology or vulcanology has already 
 developed a literature which only a specialist may hope to master. 
 The list given at the end of this chapter is an extremely fragmentary 
 one, but it contains a sufficient number of general works in which 
 the subject is treated from a comprehensive viewpoint, and which 
 will open for the student the gateways to the special fields of re- 
 search in which ground has been broken. 
 
 VOLCANIC ACTIVITIES. 
 
 TYPES OF VOLCANIC ACTIVITIES. These may be purely 
 explosive or purely extravasative or, what is more frequent, a 
 combination of both in varying proportions. According as the one 
 or the other prevails, the form of the resulting deposit will vary 
 from simply conical in the first to flat and plain-like in the second 
 case. 
 
 SUBDIVISION WITH REFERENCE TO LOCATION. Volcanic mani- 
 festations may take place either on the surface of the lithosphere 
 (effusive) or within the earth's crust (plutonic, intrusive). In 
 
 859 
 
86o PRINCIPLES OF STRATIGRAPHY 
 
 the latter case direct observation of such manifestations is im- 
 possible, but their characters may be inferred from the results of 
 past intrusive and plutonic manifestations as indicated by the char- 
 acteristics of intrusive and deep-seated (plutonic) igneous masses. 
 (See ante, Chapter VII.) 
 
 Extrusive manifestations may further be divided into the ter- 
 restrial and the submarine, the latter again being withdrawn from 
 direct observation, except when their results appear above the 
 surface of the sea, after prolonged existence. Indirect observation 
 on the results of submarine eruptions is likewise scanty, mainly 
 because, in the case of older volcanics, it is at present difficult to 
 distinguish with certainty between submarine and subaerial erup- 
 tions, and many so-called submarine lava flows must probably be 
 relegated to the subaerial type. 
 
 In discussing the types of eruptions, the primary division into 
 explosive and extravasative will be kept in mind, and under each 
 of these will be noted the subaerial or terrestrial and the submarine 
 types. 
 
 Explosive Eruptions. 
 
 Terrestrial Type. Volcanoes of purely explosive type are prob- 
 ably very rare, though the "maare" craters may be classed here. In 
 the typical examples of the Eifeler Maare, no volcanic cone exists ; 
 instead, there is merely a more or less circular opening, the result 
 of the explosion, and this has subsequently been filled with water. 
 Lapilli, bomblets, and even large bombs often abound in the neigh- 
 borhood of the maare craters, but lava flows are typically absent. 
 The coarse and fine lapilli of the maare region in the Eifel and 
 Rhein districts form stratified deposits which have all the appear- 
 ance of stratified sands of clastic origin. As outlined in Chapter 
 VI, the lapilli are not to be regarded as pyroclastic in the true sense 
 of the word, but rather as granular pyrogenics, being primarily of 
 endogenetic origin, and classifiable as pyrogranulites rather than 
 as pyrarenytes. True pyroclastics are, of course, also associated 
 with the deposits of lapilli and bombs, these resulting from 
 the clastation, by eruptive explosion, of already consolidated 
 rock masses, either of igneous or of "sedimentary" origin. The 
 vicinity of the Laacher See, the largest and most picturesque of 
 the explosive craters of Germany, is characterized by deposits of 
 volcanic bombs and tuffs, of trachyte, mingled with clastic frag- 
 ments of granite and various metamorphic rocks, brought up by 
 the explosion from great depths below the cover of Devonic strata. 
 
EXPLOSIVE ERUPTIONS 861 
 
 Some of the bombs consist of a remarkable mixture of crystals, 
 characteristically developed at great depth within the earth's crust, 
 such as sanidine, olivine, hornblende, garnet, etc. (Walther-4i : 
 170-777.) 
 
 A modern case of such an explosion without lava extrusion 
 occurred in Japan in 1888, the explosion being a sudden and violent 
 one, and tearing away the side of a volcano which had not been 
 active for at least a thousand years. The air was filled with ashes 
 and debris as in a typical volcanic eruption, and a large tract of 
 the adjacent region was devastated and many lives lost. 
 
 Coon Butte, in Arizona, has also been regarded by Gilbert 
 (u:7#7) as a possible example of such an explosive eruption 
 though he also suggests the possibility that it was formed by the 
 impact of a meteorite. Both theories have had their advocates, the 
 former origin being favored by Chamberlin and Salisbury (4:596), 
 while the latter is especially defended by Fairchild (8). 
 
 The cinder cone. While the explosion-craters seen in the Maare 
 represent probably a single eruption, or one which, with slight 
 intervening pauses, lasted only for a comparatively short time, the 
 more general examples of explosive volcanoes last sufficiently long 
 to build up a cinder cone. Such eruptions may be of comparatively 
 limited duration, and may occur at short intervals, as in the volcano 
 Stromboli in the ^Eolian Islands north of Sicily (Strombolian type), 
 where the interval of explosion is from i to 20 minutes, as shown 
 by the "flash" of this "Lighthouse of the Mediterranean"; or it 
 may be of a more violent character and occur at great intervals 
 with dormant or "strombolian" periods intervening. Such is the 
 case in Vulcano of the same group of islands, and in other violent 
 volcanoes (Vulcanian type) which have an interval of decades 
 (moderate phase), or of centuries (grander phase). 
 
 Material of the cinder cone. This includes the bombs, the 
 lapilli, and the volcanic sand, ash, and dust which fall in the im- 
 mediate vicinity of the crater. Not all the ejected material falls 
 here much being carried to a distance, this distance increasing 
 with increasing fineness of material. Even large bombs may be 
 hurled beyond the actual radius of the cinder cone, one such, fully 
 three feet in diameter, being hurled to a distance of a mile and a 
 half during the eruption of Vulcano in 1888 (Hobbs-i5 :77o). A 
 remarkable example of the propulsion of volcanic ejecta has been 
 described by Hovey (17:560) in the eruption of Mont Pelee in 
 1902. Frequent explosions of dust and lava-laden clouds have 
 brought material enough from the crater to fill the gorge of the 
 Riviere Blanche. "The lower portion of the gorge has been entirely 
 
862 PRINCIPLES OF STRATIGRAPHY 
 
 obliterated and the adjoining plateau elevated, while the upper and 
 deeper portion near the center has been almost filled by ejecta. 
 The dust-flows are the material left behind by the dust-laden clouds 
 of steam. The exploding clouds of steam were so overloaded with 
 dust and larger fragments of comminuted lava, that' they flowed 
 down the slope of the mountain and the gorge, like a fluid propelled 
 at a high velocity by the horizontal or partly downward component 
 of the force of the explosion. Many large fragments of solidified 
 lava were carried down the gorge by these clouds. Such blocks 
 10 to 15 feet in diameter were not uncommon" (17:560). 
 
 Lapilli vary in size from that of a walnut to dust. The term 
 is somewhat loosely used, and should be restricted to pyrogenic 
 material in a state of division, i. e., pyrogranulytes and the smaller 
 pyrosphaerytes (more rarely pyro-pulverytes) which by their ap- 
 pearance show that they were unconsolidated or at least in a plastic 
 state on eruption. (See ante, Chapters VI and XII.) The sand 
 and dust are, for the most part, true pyroclastic material character- 
 ized by angularity of outline and density of material. 
 
 The forms of cinder cones. Cinder cones are essentially local 
 accumulations of unconsolidated materials, and so their form is 
 determined by the general laws which govern the accumulation of 
 such material, modified, of course, by the special influences char- 
 acteristic of the mode of accumulation. The form will also vary 
 in accordance with the prevailing size and character of the material, 
 being steeper for coarse and gentler for fine material, and gentler 
 also for rounded material (lapilli) than for angular. There will 
 be further variation induced by the abundance or scarcity of water 
 vapor, condensed into rain in the vicinity of the eruption, the 
 variation being analogous to that found in the slopes of alluvial 
 cones and dry "cones of dejection," or between that of alluvial 
 cones of dry and pluvial regions. "Speaking broadly, the diameter 
 of the crater is a measure of the violence of the explosion within 
 the chimney. A single series of short explosive eruptions builds a 
 low and broad cinder cone. A long-continued succession of moder- 
 ately violent explosions, on the other hand, builds a high cone with 
 crater diameter small if compared with the mountain's altitude, and 
 the profile afforded is a remarkably beautiful sweeping curve." 
 (Hobbs-i5 :/^j.) Owing to the fact- that material near the summit 
 lies at the maximum angle of repose, while that lower down gener- 
 ally has a lower angle the product of change wrought by time 
 and by the addition of material fallen from the sky upon the 
 surface of the original slope the form of the lateral curve of the 
 cinder-cone will be a faintly concave one, whereas that of a lava 
 
THE CINDER CONE 
 
 863 
 
 cone is more typically convex. This is shown in the following 
 sketch of a cinder cone (Fig. 227) and appears further in Fig. 232. 
 
 Monte Nuovo, in the Bay of Baie, near Naples, is an example of 
 a cone composed almost entirely of loose cinders. This volcano 
 had its birth within historic time, arising on the borders of the 
 ancient Lake Lucrinus on September 20, 1538, and attaining a 
 height of 440 feet. Other volcanoes largely composed of cinders 
 have arisen within the knowledge of man. Among them are Jorullo 
 (Mexico), 1759; Pochutla (Mexico), 1870; Camiguin (Philippine 
 Islands), 1871; a new mountain of the Ajusco Mountain group 
 (Mexico), 1881 ; and the new mountain of Japan formed on Sep- 
 tember 9, 1910, and rising to a height of 690 feet. 
 
 Both Jorullo and the new Camiguin volcano started from fissures 
 in level plains. The former arose in the night of September 28, 
 1759, 35 miles distant from any then existing volcano, and its sum- 
 
 FIG. 227. Campo Bianco, in the 
 Island of Lipari. A pumice-cone, 
 breached by the outflow of an 
 obsidian lava stream. 
 
 FIG. 228. Experimental illustration 
 of the mode of formation of vol- 
 canic cones composed of frag- 
 mental materials. (After Judd.) 
 
 mit has since reached an elevation of 4,265 feet above sea-level. 
 The Camiguin volcano had a growth period of four years during 
 which it reached a height of about 1,800 feet. 
 
 Consolidation of cinder cones. Unless extravasations of lava 
 should punctuate the eruptions of cinders, the cinder-cone is not 
 likely to be thoroughly consolidated, but remains rather in the con- 
 dition of an ash or sand heap. Diagenetic processes will, of course, 
 go on throughout the mass and thus consolidation may be brought 
 about, aided by the metamorphosing effect of the steam and hot 
 vapors accompanying each eruption, and penetrating more or less 
 through the mass of accumulated material (atmo-metamorphism). 
 
 Submarine Explosive Eruptions, Explosive eruptions are prob- 
 ably as common in the littoral belts of the sea as they are on land, 
 and, indeed, near the margins of the lands they, in common with the 
 extravasative eruptions, may be more frequent than elsewhere, as 
 discussed beyond. There is no reason for doubting that explosive 
 eruptions also occur on the floor of the deeper sea though exam- 
 
864 PRINCIPLES OF STRATIGRAPHY 
 
 pies of such cinder-cones rising from the abyssal sea-bottom are 
 unknown. 
 
 The Mediterranean has been the region best known for sub- 
 marine volcanic eruptions. Of these a number have been of the 
 explosive type, though more generally the compound (explosive 
 and extravasative) type prevailed. The most noted of the recorded 
 submarine eruptions "occurred in the year 1831, when a new vol- 
 canic island (Graham's Island, lie Julia) was thrown up, with 
 abundant discharge of steam and showers of scoriae, between 
 Sicily and the coast of Africa. It reached an extreme height of 
 200 feet or more above sea-level (800 feet above sea-bottom) with 
 a circumference of 3 miles, but, on the cessation of the eruption, 
 was attacked by the waves and soon demolished, leaving only a 
 shoal to mark its site." (Geikie-o, 1^50.) "The upper part of this 
 volcanic cone, above the sea at least, seemed to have been solely 
 composed of ashes, cinders, and fragments of stone, commonly 
 small. Among these fragments of limestone and dolomite, with 
 one several pounds in weight, of sandstone, were observed. (De 
 la Beche-6:p5.) These fragments were broken off from the rocks 
 through which the eruption passed on its upward way. "During 
 the time that this volcanic mass was accumulating, a large amount 
 of ashes and cinders must have been mingled with the adjacent sea 
 before it reached its surface, and no slight amount would be dis- 
 tributed around, when ashes and cinders could be vomited into the 
 air. Add to this the quantity caught up in mechanical suspension 
 by the breakers and there would be no small amount to be accumu- 
 lated over any deposits forming, or formed, on the bottom around 
 this locality . . ." (De la Beche-6 :p5, pd). These deposits in- 
 cluded, of course, abundant remains of organisms, killed by the ex- 
 plosive eruption. Another example of a volcano formed in the his- 
 toric period is Sabrina Island in the Azores, off the coast of St. 
 Michaels. Here a submarine eruption built a cone of loose cinders 
 to a height of about 300 feet, and a circumference of about a mile. 
 This, too, soon disappeared under the subsequent attack of the 
 waves. 
 
 "The formation of this island was observed and recorded. It 
 was first discovered rising above the sea on the thirteenth of June, 
 1811, and on the seventeenth was observed by Captain Tillard, 
 . . . from the nearest cliff of St. Michael's. The volcanic bursts 
 were described as resembling a mixed discharge of cannon and 
 musketry; and were accompanied by a great abundance of light- 
 ning." (De la Beche-6 :/PJ.) A sketch made at that time is here 
 reproduced (Fig. 229). A similar occurrence is recorded from 
 
SUBMARINE ERUPTIONS 
 
 865 
 
 the west coast of Iceland, where, in the early summer of 1783, 
 arose an island of volcanic nature about thirty miles from Cape 
 Reykjanaes. In less than a year, however, it had again been washed 
 away by the waves, leaving only a submerged reef or shoal from 
 five to thirty fathoms below sea-level. 
 
 Numerous submarine eruptions which never reach the surface 
 no doubt occur over many portions of the ocean floor. In these 
 both cinders and lava enter, sometimes one and sometimes the other 
 
 FIG. 229. Sketch of the submarine volcanic eruption which, in June, 1811, 
 formed Sabrina Island, off St. Michaels in the Azores. (After 
 De la Beche.) 
 
 predominating. On the floor of some parts of the deep sea volcanic 
 ejectamenta are abundant, and these are in part at least due to 
 submarine explosive eruptions. 
 
 Extravasative Eruptions. 
 
 Terrestrial Type Fissure Eruption. The fundamental charac- 
 teristics of this type are best developed in the great fissure erup- 
 tions which have resulted in the formation of extensive lava fields, 
 and in the broad flat lava domes of the Hawaiian group. The 
 fissures from which the great lava extravasations take place are 
 generally ranged parallel with and near to the coast and seem to 
 be especially prevalent where the edge of the land drops off rapidly 
 
866 PRINCIPLES OF STRATIGRAPHY 
 
 to deep sea. The most stupendous modern examples of fissure 
 eruptions are those of eastern Iceland. In this island occur a 
 number of distinct and parallel clefts arranged in two dominant 
 series, one extending northeast and southwest, the other north and 
 south. "Many such fissures are traceable at the surface as deep 
 and nearly straight clefts or gjas, usually a few yards in width but 
 extending for many miles. The Eldgja has a length of more than 
 1 8 English miles and a depth varying from 400 to 600 feet." 
 (Hobbs-i5:pp.) 
 
 According to Thoroddsen, the lava wells out quietly from the 
 whole length of some of these fissures, overflowing on both sides 
 without the formation of cones. These fissures, therefore, consti- 
 tute connecting dikes, such as are known to occur under the older 
 lava flows of this type. At three of the wider portions of the great 
 Eld cleft of Iceland the lava has welled out quietly without the 
 formation of cones, flooding an area of 270 square miles. Upon 
 the southern narrower prolongation of the fissure, however, a 
 row of low slag cones appeared, and this is a feature characteristic 
 of other fissures in Iceland, as well as the great. Skaptar fissure 
 reopened in 1783, emitting great volumes of lava. Subsequently the 
 eruptive processes became concentrated at the wider portions of 
 the fissure and a row of small cones was left over the line of the 
 fissure. Upon this fissure, too, stands the large volcano of Laki. 
 The great eruptions and the larger volcanoes are generally found 
 at the intersection of two fissures, as in the case of the great 
 eruption of Askja in 1875, and of the volcanoes of Java. On a 
 small scale, the formation of volcanoes along fissures is shown in 
 the frozen surface of the lava lake in the caldron of Kilauea, where 
 miniature volcanoes form whenever the crust which hardens in the 
 lava-lake becomes fissured. 
 
 The connection of volcanic activities with fissuring of the earth's 
 surface is further shown in the great rift-valley of eastern Africa, 
 where extensive outpourings of lava have covered portions of the 
 valley floor, while volcanoes of great height and comparatively 
 recent origin have arisen within the valley, as in the case of the 
 Mfumbiro Mountains, already referred to, which block the rift- 
 valley north of Lake Kivu and which rise to great altitudes, the 
 crater rim of the still active volcano Kirungo-cha-Gongo rising to 
 11,350 feet above the sea-level, while Karisimbi reaches an altitude 
 approaching 14,000 feet. (Fig. 21, p. 125.) The valley floor 
 on which these volcanoes arose was considerably less than 4,000 
 feet above sea-level ; indeed, this same valley floor in the region of 
 Lake Tanganyika to the south actually descends below sea-level. 
 
FISSURE ERUPTIONS 867 
 
 The most gigantic outpouring of lavas from fissures occurred in 
 late Tertiary or early Quaternary time in western North America. 
 There lava floods formed the great plains of the Snake River region 
 in southern Idaho, and the vast basaltic plateau of Washington, 
 Oregon, and northern California. This lava field has more or less 
 interrupted extensions through Nevada, Arizona, New Mexico, 
 and the western half of Mexico south into Central America and 
 northward through British Columbia to the Alaskan Peninsula and 
 the Aleutian Islands. (See the Geological Map of North America.) 
 The main lines of fissures were probably parallel to the Pacific coast, 
 but of this nothing is visible, except the general trend of the lava 
 sheets from north to south. The area covered by the lava outpour- 
 ings aggregates 200,000 square miles, while the thickness of the 
 sheet averages 2,000 feet and reaches in some places 3,700 feet. 
 The comparatively recent origin and the location of the lava plateau 
 have precluded much destructive work by the surface agents, al- 
 though the Snake River has cut a series of picturesque gorges 
 through it. The cones now rising from this surface indicate 
 localization of eruption subsequent to the outpouring of the lava 
 floods. Prismatic structure is well developed in parts of these 
 lava sheets. Intercalated river sediments often separate successive 
 flows. 
 
 Remnants of early Tertiary basaltic lavas are now found in 
 numerous places in northeast Ireland, western Scotland, the lower 
 Hebrides, the Faroe islands, and faraway Iceland. These, famous 
 for their columnar partings (Giants' Causeway, Fingal's Cave, etc.), 
 were probably part of a once continuous lava field, now dismem- 
 bered by the agents of erosion, not the least of which is the sea. 
 Numerous dikes of similar material occur in regions from which 
 this lava has apparently been eroded, and these dikes probably 
 mark the fissures through which this welling-up of the lava took 
 place. 
 
 These dikes are extremely abundant in the northwest of Scot- 
 land (Peach and Horn 6-28) and range eastward across Scotland 
 and the north of England and Ireland. They have been traced 
 from the Orkney Islands southward to Yorkshire and across Britain 
 from sea to sea over a total area of probably not less than 100,000 
 square miles. This may indicate the former wide extent of this 
 basaltic lava field which then rivaled the younger one of western 
 America. When erosion has been carried far enough in the great 
 lava plateau of western North America, to remove a considerable 
 portion of the lava sheet, there will no doubt appear an equally 
 
868 PRINCIPLES OF STRATIGRAPHY 
 
 vast number of dikes, which represent the filling of the fissures 
 through which the lava reached the surface. 
 
 A Cretacic example of such outpouring of basic lava, rivaling 
 in extent that of the northwestern United States, is seen in the great 
 bed of Deccan trap which forms the surface of the Deccan Plateau 
 in India. Here the depth of the lava is from 4,000 to 6,000 feet. 
 Where the basement rocks on which this trap sheet rest are exposed 
 by erosion along the margin of the plateau dikes of basalt are seen 
 penetrating them, representing in part the fissures through which 
 
 FIG. 230. End of the lava flow of 1881 near Hilo, Hawaiian Islands. The 
 lava surface is a typical pahoehoe surface. (After Button.) 
 
 the lava reached the surface. No cones or definite vents have been 
 found. 
 
 What appears to be a pre-Pakeozoic example of such eruptions 
 is seen in the great Keweenawan lava sheets which represent a pro- 
 longed succession of outpourings in the Lake Superior region, 
 a gg re g atm g an enormous amount variously estimated as reaching 
 the great thickness of 15,000 or 25,000 feet. Here, too, there is 
 little evidence of explosive or other concentrated volcanic activity. 
 
 The lava dome. Where eruptions are concentrated about a 
 single opening a mountain of lava will be built up which rises in 
 proportion to the frequency of the eruption and the volume of lava 
 poured out. Where fragmental material is absent, as in the Ha- 
 waiian volcanoes, the slope is a very gentle one, though the actual 
 
LAVA DOMES 
 
 869 
 
 height is great. Though now rising to nearly 14,000 feet above sea- 
 level these volcanoes began as submarine eruptions, starting on the 
 floor of the deep sea and having a total height of 20,000 or 30,000 
 feet. The visible portion is less than a hundred miles in diameter, 
 but the actual base is probably much more than twice that. The two 
 active volcanoes are Mauna Loa, the rim of which is 13,675 feet 
 above sea-level ; and Kilauea, which is less than 4,000 feet high and 
 appears to rest on the flanks of the larger volcano. The craters, 
 or caldera, have each a circumference exceeding seven miles, being 
 irregularly elliptical in outline with the sides descending in a series 
 of steps to the central pit, which is formed by the "frozen" surface 
 of the lava. The floor of the pit of Kilauea is a "movable plat- 
 form" of frozen lava which rises and falls with the variation in 
 
 FIG. 231. View of Kilauea caldera from the Volcano House. (After But- 
 ton.) 
 
 the pressure of the lava beneath. The difference in height between 
 1823 and 1884 was estimated by Button (7 112?) to be nearly 400 
 feet. 
 
 "Beneath the floor of the caldera," says Button, "we may con- 
 jecture the existence of a lake of far greater proportions than those 
 which now expose a fiery surface to the sky. The visible lakes 
 might be compared to the air-holes in the surface of a frozen pond." 
 The proof for this is found in the fact that new eruptions are not 
 overflows of the open pools of lava, but break out anywhere in 
 the floor of the caldera. (Fig. 231.) 
 
 Acid lava domes. Lavas of the acid type are, as a rule, too 
 viscous to form mountains of gentle slope, occurring more often as 
 steep-sided domes, especially if the lava is only semi-fluid. This 
 is well shown in Figure 232, where, in the Auvergne district of 
 France, a trachyte cone of highly viscid lava was extruded between 
 cinder cones. The domed character of the extravasated pustular 
 
8;o 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 cone contrasts strongly with the concave surfaces of the cinder 
 cones. The results of experiments recorded in Figures 228 and 
 233 show the fundamental differences between fragmental cones 
 and domes of pustular lava. 
 
 The spine of Pelce. What is regarded by many as a most 
 stupendous example of the extravasation of a viscous mass of 
 andesitic lava which cooled as it was extravasated is found in 
 the remarkable spine of Mont Pelee which formed after the great 
 eruption of 1902. According to Hovey (16; 17; 18), this spine 
 was a lava mass pushed up vertically without spreading, the mass 
 cooling either in the upper part of the conduit or upon its appear- 
 ance at the surface, so that no extended flow was possible. The 
 spine grew at an average of forty-one feet per day during a period 
 
 FIG. 232. The Grand Puy of Sarconi, 
 in the Auvergne, composed of 
 trachyte, rising between two 
 breached scoria-cones. A typical 
 example of a pustular cone 
 formed of highly viscid* lava. 
 
 FIG. 233. Experimental illustration 
 of the mode of formation of vol- 
 canic cones composed of viscid 
 lavas. 
 
 of eighteen days out of the new cone, which itself had attained a 
 height of 1,600 feet during the last ten days of May, and was of 
 the same character as the spine. As the spine rose 1,100 feet above 
 this new cone in October it appears that the total elevation of this 
 mass above the top of the cone as it existed prior to the eruption 
 of May, 1902, was 2,700 feet. (See, further, Heilprin-i2; Hill- 
 I2a; Jaggar-2o and Russell-34a.) 
 
 Composite Lava and Cinder Cones. 
 
 Volcanic cones built by a combination or an alternation of the 
 explosive and extravasative activities are by far the most common. 
 They generally have pronounced slopes and are more resistant than 
 cones built wholly of cinders, because the lava binds together the 
 loose material into a complex mass. This is sometimes accomplished 
 by the formation of radial dikes, as in the case of ^Etna. These 
 represent lateral fissuring of the cone and the filling of these fissures 
 
COMPOSITE CONES 
 
 871 
 
 by lava (Figs. 234, 235). The lava sometimes extended through 
 these fissures, building up secondary cones or monticules on the flank 
 of the main cone, as in the case just cited. Fissuring of the cone is 
 of common occurrence in volcanoes, the lava of many of them rarely 
 or never overflowing the crater, but finding an outlet at a lower 
 level through the side of the volcano. If parasitic cones (monti- 
 cules) are built up over such a fissure these may remain the site of 
 eruption for a long period, but sooner or later they are likely to 
 become extinct, and then they may be buried by later flows and 
 ejectamenta. Cinder cones, which are relatively weak structures, 
 will be breached if a subsequent lava stream is poured out, and this 
 
 FIG. 235. Basaltic dikes projecting 
 from stratified scoria or tuff in 
 the walls of the Val del Bove, 
 
 FIG. 234. Diagram illustrating the 
 formation of parasitic cones 
 (monticules) along lines of fis- 
 sures formed in the flanks of a 
 great volcano. (After Judd.) 
 
 will issue from their sides. (Fig. 227.) Large composite cones 
 may be breached by explosive eruptions and the shifting of the 
 center of the eruption. A new cone may be built up within the 
 breached outer rim of an original large caldera, as in the case of 
 Vesuvius, which was built within the breached rim of the extinct 
 Monte Somma. The displacement of the eruptive point may be 
 a gradual one, when a series of adjoining cones will result, all but 
 the youngest being breached on the side toward the direction of 
 migration of the cones. Examples of such consecutively breached 
 cones are found in the volcanic region of central France (Mont 
 Dore Province), and elsewhere. Many variations and combinations 
 occur, and the student is referred for the details of these phenom- 
 ena to the numerous general treatises, some of which are listed at 
 the end of the chapter. 
 
 Compound volcanoes, such as Vesuvius, have alternating periods 
 of light (or Strombolian) and violent (or Vulcanian) activity. Dur- 
 
872 PRINCIPLES OF STRATIGRAPHY 
 
 ing the former cinder cones are built up which are destroyed again, 
 in part or entirely during the violent periods, when crater formation 
 is the marked characteristic. It is during this period of activity 
 that the extravasative eruptions are in the ascendency, and at this 
 time also fissuring of the volcano takes place, with all the varied 
 activities which accompany such a state. 
 
 Submarine Cones. Submarine cones of pure extravasation are 
 apparently illustrated by the Hawaiian Islands, though the early 
 history of many of these volcanoes is shrouded in obscurity. Sub- 
 marine cones of the composite type are well known, however. 
 Probably many of the volcanoes of the Mediterranean began as 
 submarine volcanoes and subsequently reached the surface. Vol- 
 canoes of this type are also known from the Aleutian island group 
 (Jaggar-2i), while volcanoes apparently rising from the abyssal 
 portions of the sea abound in the western Pacific. A singular ex- 
 ample of a volcanic peak projecting from mid-ocean is seen in the 
 little island of St. Paul, which rises from the Indian Ocean mid- 
 way between the southern end of Africa and the west of Australia 
 and more than 2,000 miles distant from Madagascar, the nearest 
 mass of dry land. This little island, scarcely 2 l / 2 geographical 
 miles long and about i l /2 miles broad, is the mere summit of a 
 volcano. The crater has been breached by the waves and is now 
 occupied by the sea, the break in the rim being nearly dry at low 
 tide. (Figs. 236, 237.) 
 
 Mud Volcanoes. Of an origin fundamentally the same as that 
 for lava volcanoes are the mud volcanoes found in various regions 
 of the world, but not associated with igneous eruptions. They 
 occur in Sicily, the Apennines, Caucasus, and on the peninsulas of 
 Kertch and Taman bordering the Black Sea, as well as in India. 
 They find their chief activity in the escape of various gases, which 
 play much the same part as does the escaping steam in igneous 
 volcanoes. Hydrocarbons, carbon dioxide, nitrogen, and naphtha 
 are some of the gases emitted. The mud volcanoes of Sicily have 
 been explained as due to the slow combustion of sulphur beneath 
 the surface. Whatever the causes, these volcanoes are manifested 
 on the surface in mounds or hillocks of mud. They generally 
 occur in groups and range in elevation up to several hundred feet, 
 while during periods of explosion they throw mud and stones up 
 into the air to much greater heights. They are built up by succes- 
 sive outpourings of mud, which harden and form a foundation for 
 later mud flows. "In the region of the Lower Indus, where they 
 are abundantly distributed over an area of 1,000 square miles, some 
 of them attain a height of 400 feet, with craters 30. yards across." 
 
COMPOSITE CONES 
 
 873 
 
 ( Geikie-9 1245. ) These are not to be confused with the mud flows 
 which form on the sides of volcanoes from the saturation of dust 
 
 FIG. 236. View of the Island of St. Paul in the southern Indian Ocean, show- 
 ing the breach in the rim of the extinct volcano and the crater 
 flooded by the sea. (From a sketch by Charles Velain in Haug.) 
 
 and cinders by rain. Such flows always occur in regions of igneous 
 extrusion on the sides of igneous volcanoes, while mud volcanoes 
 may occur in any region where gases accumulate beneath the sur- 
 
 FIG. 237. Map of the Island of St. Paul in the southern Indian Ocean. A 
 breached volcano. (After Charles Velain in Haug.) 
 
 face in large enough quantities to be forced out. Neither should 
 these mud volcanoes be confused with mud mounds, cones, or 
 craterlets which form along earthquake fissures where the release 
 
874 PRINCIPLES OF STRATIGRAPHY 
 
 of pressure sends forth a stream of water carrying sand and mud 
 with it. (See farther in Chapter XXIII, on Seismology.) 
 
 Dissection of Volcanoes. When volcanoes have become 
 extinct the ordinary forces of erosion set in and progressive 
 destruction goes on. The rapidity with which this takes place 
 varies, of course, with the nature of the material, the prevailing 
 strength of the erosive forces, and with other factors. Many of 
 the Tertiary volcanoes of the Eifel in Germany and of the Auvergne 
 district in France are still almost perfect, while others of earlier 
 date show all stages of dissection. Of interest in this connection 
 is the Kammerbuhl near Franzensbad in northern Bohemia, which 
 
 FIG. 239. Section of the Kammer- 
 buhl, showing the probable 
 former outline of the volcano : 
 a, metamorphic rock ; b, basaltic 
 scoriae ; c, plug or neck of basalt ; 
 FIG. 238. The Kammerbuhl, an old d, stream of basalt; e, alluvial 
 
 volcanic hill in Bohemia. beds. 
 
 Goethe pronounced an extinct volcano, though Werner had explained 
 its character as originating, in common with those of others of 
 similar aspect, through the combustion of a bed of coal. Goethe 
 predicted the finding of a core of volcanic rock in the center of 
 this hill were a tunnel driven into it horizontally. The excavating 
 of this tunnel in 1837 verified this prediction, while more recent 
 excavations have revealed the entire structure, showing that the 
 small lava stream on the side of the hill was connected with the 
 central plug or neck and rested on basaltic scoria. The above 
 figures show the appearance of this hill and the structure ascer- 
 tained by these excavations. (Figs. 238, 239.) 
 
 In extensively dissected volcanoes often only the central neck 
 or plug remains, as in the case of the volcanic necks of the Mount 
 Taylor Region in New Mexico (Johnson-22 '.303-324), the Leucite 
 Hills of Wyoming (Kemp-25), and many others of this type. 
 Dikes dissecting the tufa beds of old volcanoes often stand out 
 in bold relief owing to the steady removal of the easily eroded tufa 
 enclosing them. Examples of such are known from many locali- 
 ties. The geological map of the Spanish Peaks region in Colorado 
 shows excellently the numerous radiating dikes which center in the 
 old volcanic necks of that region. 
 
DESTRUCTION OF VOLCANOES 875 
 
 Where extinct volcanoes have been subject to the attack of 
 the waves of the sea sections are often cut which reveal their struc- 
 ture. This is the case in the island of St. Paul, already noted, and 
 in Vulcanello on the shores of the Island of Vulcano in the Mediter- 
 ranean. Some of the outlying islands of the Sandwich or Hawaiian 
 group likewise represent partly dissected extinct volcanic cones 
 whose sides, moreover, are deeply gullied into a series of parallel 
 valleys so sharply divided one from the other as to effectively 
 isolate certain of the organisms inhabiting them. (See Chapter 
 XXIX.) 
 
 Finally, the destruction of volcanoes by their own explosive ac- 
 tivity may be noted. Examples are furnished by the Vesuvian 
 eruption of A. D. 79, which shattered the cone of Monte Somma; 
 by the Japanese volcano Bandai-san, of which a considerable portion 
 was blown out in 1888; and by the Javanese volcano Krakatoa, 
 which was practically blown to pieces on August 26 and 27, 1883, 
 furnishing the most stupendous example of volcanic activity in 
 modern times. "After a series of convulsions, the greater portion 
 of the island was blown out with a succession of terrific detonations 
 which were heard more than 150 miles away. A mass of matter 
 estimated at about \V% cubic miles in bulk was hurled into the air 
 in the form of lapilli, ashes, and the finest volcanic dust. . . . 
 The sea in the neighborhood was thrown into waves, one of which 
 was computed to have risen more than 100 feet above tide-level, 
 destroying towns, villages, and 36,380 people." (Geikie-p:^/^.) 
 The oscillations of the wave were noted at Port Elizabeth, South 
 Africa, 5,450 miles away, having traveled with a maximum velocity 
 of 467 statute miles per hour. The air waves generated traveled 
 from east to west and are supposed to have passed three and a 
 quarter times around the earth (82,200 miles) before they died 
 away. The barometric disturbances, passing round the globe in 
 opposite directions from the volcano, proceeded at the rate of almost 
 700 miles per hour. 
 
 Special Erosion Features. An interesting type of erosion has 
 been observed on some steep-sided volcanoes, such as those of the 
 islands of St. Vincent and Martinique. Vast amounts of dust were 
 deposited during the eruption of May, 1902, and these formed a 
 bed varying from a few inches to many feet in thickness, and 
 extending over an area of 50 square miles on each island. The 
 heavy rains that followed the eruption turned this dust into a 
 cement-like mud which was firm enough to remain in place and 
 which, during the eruptions of September and October of the same 
 year, was covered by a new layer of coarser ejectamenta. In the 
 
876 PRINCIPLES OF STRATIGRAPHY 
 
 valleys the permanent and periodical rivers were loaded with the 
 new ash to such an extent as to form viscous streams, which, how- 
 ever, had great powers of erosion, on account of the steep slope of 
 the declivities down which they flowed. The bottoms and sides of 
 the gorges were deeply grooved by the sand carried down in this 
 manner by the flowing water. 
 
 ''During the great eruptions the ejected material was drifted into 
 large beds in the gorges extending radially down the Soufriere 
 [on St. Vincent Island]. The massing of material was most im- 
 portant in the gorge of the Wallibou River on the west, and in 
 that of the Rabaka River on the east, side of the island. In these 
 gorges the bed of new material reached a thickness of from 60 
 to 100 feet. This enormous amount of material was almost entirely 
 washed out of the gorges during the first rainy season following 
 the eruptions of 1902. Not less than 150,000,000 cubic feet of 
 ashes have been washed out of the Wallibou gorge itself, without 
 taking into account the thousands of cubic yards of fresh ash re- 
 moved from the watershed of the river during the, same period. 
 All this material was, of course, transported directly to the ocean." 
 (Hovey-i8:5<5o.) 
 
 FORMATION OF THE LAVA. 
 
 Since it is very unlikely that at any point within the earth's crust 
 the temperature is sufficiently high to melt rocks (see Chapter I) 
 at the increased fusing point caused by the increase in pressure 
 downward, it follows that some other factors must be taken into 
 consideration in explaining the liquefaction of rock. We must, 
 therefore, seek either for causes producing an increase of tempera- 
 ture, or for such producing a decrease of pressure. The former 
 may be found in the energy liberated by radio-active substances, 
 such as are found in practically all the rocks of the earth's crust, as 
 well as in the water and the air. Since, says Chamberlin (3:679), 
 "radio-activity increases as we go from air to water, from water 
 to sediment, and from sediment to igneous rock, it might be inferred 
 . . . that radio-activity would be found to reach its maximum 
 concentration in the heart of the earth, and certainly that the deeper 
 parts would be as rich as the superficial ones." This, however, 
 would imply a more rapid increase in temperature than observation 
 indicates. Strutt (quoted by Chamberlin) has computed that, if 
 the quantity of radio-active substances known to exist in surface 
 rocks is also found throughout the rocks of the upper 45 miles 
 
FORMATION OF LAVA 877 
 
 of the earth's crust, the rise in temperature equal to that observed 
 in deep wells and mines would be produced by this cause alone, 
 irrespective of any other source of heat. Whether this distribution 
 is equal, or whether it increases or decreases downward, can not, 
 at present, be determined; but it is seen that if we start with an 
 original increase in temperature downward the amount added to 
 it by radio-activity might serve, locally, to overcome the opposing 
 effects of pressure in raising the fusing point, whereupon reser- 
 voirs of molten rock would be formed which would become the 
 source of volcanic activity. 
 
 If excessive temperature increase is not to be accepted as the 
 cause of rock fusion at a depth, we must turn to a local decrease 
 of pressure to permit the lowering of the fusing point of the rocks. 
 This would be effected by the formation, locally, of rock arches 
 within the crust capable of maintaining the weight of the superin- 
 cumbent portion of the crust. Such arches, or domes, by relieving 
 the pressure, would permit the liquefaction of the rock mass for 
 some distance beneath them, provided the temperature is sufficiently 
 high, and so furnish the requisite conditions for volcanic activities. 
 
 Arches of this type might be expected to form along the margins 
 of the continent where the down-warping of the continental edges 
 takes place. Now, it is precisely along these lines, where the con- 
 tinental margin drops off steeply to the deep sea, that the great 
 volcanic phenomena of the past have been located, while the dis- 
 tribution of most of the modern volcanoes of the earth is essentially 
 in harmony with this idea. Thus by far the largest number of 
 still active or but recently extinct volcanoes are ranged in belts or 
 lines parallel to the margins of the continents or within the oceanic 
 areas. The most important belt of volcanic activity surrounds 
 the Pacific Ocean, the deepest and perhaps the oldest of the oceans 
 of the earth, and the one which has experienced the least change. 
 This belt includes the volcanic mountains of the west coasts of 
 South and Central America, of Mexico, and of the western United 
 States and Canada to Alaska and the Aleutian Island chain. It is 
 continued along the eastern coast of Eurasia, and through the 
 Malaysian islands to New Zealand, the belt being finally closed by 
 the volcanoes of Victoria Land, King Edward Island, and West 
 Antarctica. It is significant that the belt for the most part is 
 paralleled by an inner one of exceptional depressions the great 
 fore-deeps of the marginal Pacific. That these are produced by 
 downwarping or faulting seems certain, and this would imply an 
 arching or unwarping of the adjoining continental margins. 
 
878 PRINCIPLES OF STRATIGRAPHY 
 
 BIBLIOGRAPHY XXII. 
 
 J I. ANDERSON, TEMPEST. 1903. Volcanic Studies in Many Lands. 
 John Murray, London. 
 
 2. BONNEY, T. G. 1899. Volcanoes, Their Structure and Significance. 
 
 John Murray, London. 
 
 3. CHAMBERLIN, THOMAS C. 1911. The Bearing of Radioactivity on 
 v Geology. Journal of Geology, Vol. XIX, pp. 673-695. 
 
 4. CHAMBERLIN, T. C., and SALISBURY, ROLLIN D. 1906. Geology, 
 
 Vol. I. Henry Holt & Co., New York. 
 
 I 5. DANA, JAMES D. 1890. Characteristics of Volcanoes, with contribu- 
 tions of Facts and Principles from the Hawaiian Islands. Dodd, Mead 
 and Company, New York. 
 
 6. DE LA BECHE, HENRY T. 1851. The Geological Observer, Phil- 
 adelphia. 
 
 j 7. DUTTON, CLARENCE E. 1884. Hawaiian Volcanoes. Fourth An- 
 nual Report of the United States Geological Survey, 1882-83, pp. 81-219. 
 j 8. FAIRCHILD, HERMAN L. 1907. Origin of Meteor Crater (Coon 
 Butte), Arizona. Bulletin of the Geological Society of America, Vol. 
 XVIII, pp. 493-504, pis., 54-56. 
 9. GEIKIE, ARCHIBALD. 1893. Text-book of Geology, 3rd edition. 
 
 Macmillan & Co. 
 
 10. GEIKIE, A. 1897. The Ancient Volcanoes of Great Britain, 2 vols. Mac- 
 millan & Co. 
 
 1 II. GILBERT, G. K. 1893. Report on Coon Butte, Arizona. Fourteenth 
 Annual Report of the United States Geological Survey, pt. I, p. 187. 
 
 12. HEILPRIN, A. 1904. The Tower of Pelee. Philadelphia. 
 
 I2a. HILL, R. T. 1905. Pelee and the Evolution of the Windward Archi- 
 pelago. Bulletin of the Geological Society of America. Vol. XVI, pp. 
 243-288, 5 pis. 
 
 13. HITCHCOCK, C. H. 1909. Hawaii and Its Volcanoes. Honolulu. 
 
 14. HOBBS, WILLIAM H. 1906. The Grand Eruption of Vesuvius in 1906. 
 
 Journal of Geology, Vol. XIV, pp. 636-655. 
 
 15. HOBBS, W. H. 1912. Earth Features and Their Meaning, an Introduc- 
 
 tion to Geology. Macmillan Company, New York. 
 \ 16. HOVEY, E. O. 1903. The New Cone of Mont Pelee and the Gorge of the 
 
 Riviere Blanche, Martinique. American Journal of Science, Vol. XVI, 
 
 pp. 269-281. 
 ,117. HOVEY, E.G. 1904. New Cone and Obelisk of Mont Pelee. Bulletin of 
 
 the Geological Society of America, Vol. XV, pp. 558-560. 
 4i8. HOVEY, E. O. 1904. Some Erosion Phenomena Observed on the Islands 
 
 of Saint Vincent and Martinique in 1902 and 1903. Ibid., pp. 560-561, 
 
 pis. 57-58. 
 ^19. HOVEY, E. O. 1905. Present Conditions of Mont Pelee. Bulletin of the 
 
 Geological Society of America, Vol. XVI, pp. 566-569, pi. 92. 
 -, 20. JAGGAR, THOMAS A. 1904. The Initial Stages of the Spine on Pelee. 
 
 American Journal of Science, 4th series, Vol. XVII, pp. 39 et seq. 
 21. JAGGAR, T. A. 1908. The Evolution of the Bogoslof Volcano. Bulletin 
 
 of the American Geographical Society, Vol. XLV, pp. 385-400, 8 figs. 
 \ 22. JOHNSON, DOUGLAS W. 1907. Volcanic Necks of the Mount Taylor 
 
 Region, New Mexico. Bulletin of the Geological Society of America, 
 
 Vol. XVIII, pp. 303-324, pis. 25-30. 
 
BIBLIOGRAPHY XXII 879 
 
 23. JOHNSTON-LAVIS, H. J- 1891. The South Italian Volcanoes. 
 
 Naples. 342 pp. 
 
 24. JOHNSTON-LAVIS, H. J. 1909. The Eruption of Vesuvius in April, 
 
 1906. Transactions of the Royal Dublin Society, Vol. IX, pt. VIII, V 
 pp. 139-200. 
 
 25. KEMP, JAMES F., and KNIGHT, W. C. 1903. Leucite Hills of Wyo- 
 
 ming. Bulletin of the Geological Society of America, Vol. XIV, pp. 
 305-336, pis. 37-46. 
 
 26. MOORE, J. E. S. 1903. The Tanganyika Problem. Hurst and Blackett, 
 
 London. 
 
 27. OMORI, F. 1911. The Usu-san Eruption and Earthquake and Elevation 
 
 Phenomena. Bulletin of the Earthquake Investigation Committee, 
 Japan. Vol. V, pp. 1-37. 
 
 28. PEACH, BENJAMIN, and HORNE, JOHN. 1907. The Geological 
 
 Structure of the North-west Highlands of Scotland. 
 
 29. RATH, G. VON. 1872. Der Aetna. Bonn. 
 
 30. RECLUS, JEAN JACQUES fiLISEE. 1906-1910. Les Volcans de la 
 
 Terre. Belgian Society of Astronomy, Meteorology and Physics of the 
 Globe. 
 
 31. ROYAL SOCIETY OF LONDON. 1888. The Eruption of Krakatoa 
 
 and Subsequent Phenomena. Report of Special Committee. London. 
 
 494 PP- 
 
 32. RUDOLPH, E. 1887. Ueber Submarine Erdbeben und Eruptionen. 
 
 Gerlands Beitrage zur Geophysik, pp. 133-365; ibid., 1895, pp. 537-666; 
 ibid., 1898, pp. 273-336. 
 
 33. RUSSELL, I. C. 1897. Volcanoes of North America. Macmillan, New 
 
 York. 
 
 34. RUSSELL, I. C. 1902. Geology of Snake River Plains, Idaho. Bulletin 
 
 United States Geological Survey, No. 199. (Abstract: Bulletin of the 
 Geological Society of America, Vol. XIII, 1902, p. 527; and Science, Vol. 
 XV, 1902, pp. 85-86.) 
 
 34a. RUSSELL, I C. 1905. The Pelee Obelisk. Science N. S. Vol. XVIII, 
 pp. 792-795- 
 
 35. SCROPE, PAULET. 1858. The Geology of the Extinct Volcanoes of 
 
 Central France. John Murray, London. 
 
 36. THORODDSEN, TH. 1905. Die Bruchlinien und ihre Beziehungen zu den 
 
 Vulkanen. Petermann's Mittheilungen, Bd. LI, pp. 1-573. 
 
 37. THORODDSEN, TH. 1906. Island, IV. Vulkane. Petermann's Mit- 
 
 theilungen, Erganzungsheft 153, pp. 108-111. 
 
 38. THOULET, J. 1903. Les Volcans sousmarins. Revue des Deux 
 
 Mondes. 73^6 ann( e) 5 ieme periode, T. XIII, pp. 611-624. 
 
 39. VERBECK, R. D. M. 1885. Krakatau. Batavia. 557 pp., 25 pis. 
 
 40. WALTERSHAUSEN, SARTORIUS VON. 1880. Der Aetna. Leip- 
 
 zig. 2 Vols. 
 
 41. WALTHER, JOHANNES. 1910. Lehrbuch der Geologic von Deutsch- 
 
 land. Quelle und Meyer. Leipzig. 
 
E. THE CENTROSPHERE OR BARYSPHERE. 
 
 CHAPTER XXIII. 
 
 DIASTROPHISM, OR THE MOVEMENTS TAKING PLACE WITHIN 
 THE EARTH'S CRUST AND THEIR CAUSES., 
 
 In discussing the subject of diastrophism under the heading 
 of the Centrosphere, it is intended to emphasize the fact that 
 the great mass of such movements is directly or indirectly induced 
 by gravity, i. e., the terrestrial phenomenon of weight or downward 
 acceleration,* which has for its two components the gravitation or 
 attracting force between bodies and the centrifugal force due to 
 the rotation of the earth on its axis. 
 
 Other forces which induce earth movements have their origin 
 in the interior heat of the earth ; in chemical combination ; in molec- 
 ular attraction and repulsion; in radio-activity; in electrical and 
 vital energy; in the centrifugal energy due to the rotating of the 
 earth on its axis and its revolution around the sun ; in the attraction 
 of the moon and sun ; and in the radiant energy of the sun. Im- 
 pact with heavenly bodies may be further mentioned as a source 
 of possible energy. But 'all of these, except perhaps the last, 
 are of minor significance as compared with gravity as the great 
 source of energy influencing earth movements. The displacement 
 of the earth's center of gravity through any cause, and the conse- 
 quent displacement of the earth's axis, would also be a direct cause 
 of the setting free of a vast amount of available energy. 
 
 CLASSIFICATION OF EARTH MOVEMENTS. 
 
 Earth movements may be classified either as local disturbances 
 or as widespread or regional ones. The movements are manifested 
 
 * The amount of downward acceleration is about 385.1 inches (978 centi- 
 meters) per second at sea-level at the equator, and 387.1 inches at sea-level' at 
 the poles, diminishing slightly on mountain tops. The centrifugal force at the 
 
 equator is of gravity. 
 
 880 
 
CLASSIFICATION OF EARTHQUAKES 881 
 
 as seismic disturbances, of which earthquakes and sea-quakes are 
 the recognized effects, while the products of the disturbances are 
 tectonic structures* 
 
 Not all tectonic structures are accompanied in their formation 
 by seismic disturbances, for some deformations may go on so 
 gradually, and at such a uniform rate, that no surface manifesta- 
 tions are felt. In this class fall especially the large or epeirogenic 
 earth movements, and the bradyseisms noted below. 
 
 CLASSIFICATION OF SEISMIC DISTURBANCES. 
 
 Not all seismic disturbances are due to earth movements, as 
 the term is here used, for volcanic activities, especially of the ex- 
 plosive type, may generate such disturbances, these being sometimes 
 of considerable magnitude, as in the case of the explosive eruption 
 of Krakatoa in 1883. As there illustrated, the three inorganic 
 spheres the litho, hydro, and atmosphere, not to mention the bio- 
 sphere were disturbed by this explosion, and earthquakes, sea- 
 quakes, and air-quakes f resulted. The air-waves which charac- 
 terized the last passed around the earth several times, while the 
 sea disturbances or tsunamis J generated were noticeable more 
 than five hundred miles away. 
 
 Recognizing the different modes of production of earthquakes, 
 seismologists have divided them according to origin into: (Suess- 
 
 38.) 
 
 1. Dislocation or fault earthquakes. 
 
 2. Volcanic, or explosive earthquakes. 
 
 * The term tectonic, originally applied to all structures, has come of late to be 
 more especially applied to structures due to earth movements, or deformation 
 structures. These include faults, folds, torsion joints, etc., but not stratification, 
 unconformity, overlap, flow-structure, or any other original structures, nor such 
 secondary structures as concretions, enterolithic deformation, or any other 
 structures due to diagenetic or contactic metamorphism. 
 
 t If we consider that the term seisma refers to the trembling or shaking of the 
 geos, or earth as a whole (geoseism), and not merely to the tremblings of the land, 
 we may extend the meaning of the term seismology so as to cover the shaking or 
 trembling of any portion of the earth as the result of such disturbances. We 
 could thus distinguish: lithoseisma, or earthquakes proper (land-quakes); hydro- 
 or thalassoseisma or sea-quakes and atmoseisma, or air-quakes. The bioseisma arc, 
 of course, a universal accompaniment of all these disturbances. 
 
 t The Japanese term for the "tidal wave," or "sea- wave" of sea-quakes. 
 Suggested for general adoption by Hobbs (17). 
 
382 PRINCIPLES OF STRATIGRAPHY 
 
 The first type of seismic disturbance may be spoken of as bary- 
 seismic* and the second as pyroseismic. "f these terms indicating 
 the relationship of the disturbances to the respective spheres. 
 Hoernes (19) has designated as a third type the results of incaving 
 of the roofs of fissures (Einstursbeben) which characterize the 
 Karst region of the Dalmatian coast. This, however, is to be classed 
 as a special phase of the dislocation (baryseismic) type, since such 
 cavings-in of cavern roofs are merely special phases of faulting. 
 In the same way, we must class under the volcanic or explosive 
 (pyroseismic) type the tremors resulting from explosions of g m- 
 powder or dynamite, and of gases, in mines and elsewhere, which 
 may not be sufficient to affect the seismograph, but are certainly 
 noticeable as sea-quakes (submarine explosions) and as air-quakes. 
 These, as well as the disturbances due to incaving, may be dis- 
 missed without further notice. 
 
 The Volcanic or Pyroseismic Type of Earthquake. This is, of 
 course, an accompaniment of volcanic activities ; but such dis- 
 turbances are not necessarily always felt, for, even if they occur, 
 they may be so slight as to escape notice. 
 
 The Tectonic or Dislocation (Baryseismic) Earthquake. This 
 is a jar occasioned by the breaking of rock under strain. "The 
 strain may be caused by the rising of lava in a volcano or by the 
 forces that make mountain ranges and continents." The rupture 
 of the rock mass "may be a mere pulling apart of the rocks, so as 
 to make a crack, but examples of that simple type are compara- 
 tively rare. The great majority of ruptures include not only the 
 making of a crack but the relative movement or sliding of the rock 
 masses on the two sides of the crack; that is to say, instead of 
 a mere fracture, there is a geologic fault." (Gilbert-i3 \2.) 
 
 The walls of the fault plane may eventually become cemented 
 together, but they will remain as a plane of weakness for a long 
 time, so that repeated slipping may take place, making the region 
 one of frequent earthquakes. This has been the case in the repeated 
 California earthquakes, of which the San Francisco quake of 1906 
 is the most recent. The fault-line there extends for several hun- 
 dred miles northwest and southeast and nearly parallel to the 
 coast. The "Fossa Magna" crosses Japan from north to south, 
 while the southern border lands of Afghanistan have such an 
 habitual earthquake-producing fault-line extending for 120 miles. 
 
 The faulting or slipping which produces the earthquake may 
 
 * From the Greek fiapfa = heavy, -f a-eifffj-a earthquake; signifying that 
 weight or gravity is the dominant factor in their production. 
 t From the Greek irfy = fire, -f- <rd<rfw. = earthquake. 
 
BARYSEISMIC DISTURBANCES 883 
 
 be deepseated or may reach the surface. The depth to which the 
 dislocation penetrates may be very great it may pass from the 
 zone of fracture into that of flowage; but the origin of the shock 
 is probably never deeper than 30 geographical miles, and usually 
 does not exceed 5 to 15 miles. (Hovey-2i '.244.) The point or 
 locus of origination of the earthquake is variously called the 
 seismic center, centrum, hypocenter, origin, or focus. This, though 
 conveniently regarded as a point, is really a space of three dimen- 
 sions which in different cases varies much in size and shape and 
 may be of great magnitude. The part of the earth's surface which 
 is vertically above the center is the epicenter or epicentral or epi- 
 focal tract. 
 
 SURFACE MANIFESTATIONS OF BARYSEISMIC DISTURBANCES. 
 
 The surface manifestations of an earthquake-producing fault 
 or other tectonic movement may, so far as the lithosphere is con- 
 cerned, be classed as rifting, as slipping, and as disruption. The 
 first is mere separation, the second involves displacement. It is to 
 the latter movement that the term faulting is commonly applied. 
 
 Rifting. 
 
 As a result of rifting, fissures will open in the earth (Fig. 240) 
 and these may remain open or be filled by injected material. So 
 far as arrangement is concerned these fissures may be in parallel 
 series, as in the case of the fissures formed by the earthquake of 
 Sinj, Austria, in 1898, in which slipping also occurred along each 
 rift. Or, again, these fissures may radiate from a center, branch- 
 ing repeatedly. Such fissures were formed during the Calabrian 
 earthquake of 1783. Finally, fissures formed during earthquakes 
 may be irregularly intersecting, forming a network. This type has 
 been observed at Aigon in the Balkans after the earthquake of 
 December 26, 1861 ; in Owens Valley, California, after the earth- 
 quake of 1872 (Whitney) ; and in Ecuador, where it is a very 
 characteristic feature of the Andes region. Whimper (43) says of 
 these: "In no other part of Ecuador is there anything equaling 
 this extraordinary assemblage of fissures, intersecting one another 
 irregularly and forming a perfect maze of impassable clefts . . . 
 the cracks are all V-shaped and, though seldom of great breadth, 
 are often very profound, . . . Several, at least, have been 
 formed within the memory of man, while others are centuries old." 
 
884 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 These intersecting fissures are locally known as earthquake "que- 
 bradas." 
 
 Fissures often open and close repeatedly, even during the same 
 
 FIG. 240. Small earthquake fissure and fault in the Arizona desert. 
 (After Branner.) 
 
 disturbance ; sometimes in closing, the walls are pressed violently 
 together, while shattering of the adjoining rock masses occurs, with 
 the formation of autoclastic material or fault-breccias. This gen- 
 
 \\ ' ) IU . 
 
 FIG. 241. Section of one of the sandstone pipes in limestone on the eastern 
 coast of Anglesey in Wales. (After Greenly, from Hobbs.) <*, 
 cherty limestone; p, sandstone pipe; 7, cherty limestone. 
 
 erally falls into the fissure, more or less filling it, or it marks the* 
 sides of the fissure for some distance outward. 
 
 Filling of the Fissures. Sandstone Dikes. Fissures formed by 
 earthquakes may remain open for a longer or shorter period of 
 
SANDSTONE DIKES; CRATERLETS 885 
 
 time, becoming gradually filled up by debris which falls in from 
 above, or is washed into them. Such is the case in several vertical 
 fault fissures at Meriden, Connecticut, which have been filled by 
 infiltration of trap fragments and sandstone from above. (Davis, 
 in Diller-8:^^.) 
 
 Davis says : "These fractures traverse a sheet of lava and 
 are chiefly filled with angular trap-fragments, but the interstices are 
 occupied with sandstone, not in fragments as if it had fallen in 
 with the pieces of trap, but in a close-fitting mass, as if it had 
 settled down in the form of separate particles derived from the 
 sandstone originally overlying the trap sheet, thus, in a general way, 
 taking a structure conformable to the blocks of trap that it sur- 
 rounds, but showing also a tendency to a transverse or horizontal 
 stratification. It seems probable that these fissures were filled 
 gradually by infiltration from above . . ." 
 
 In some cases, however, such fissures are filled at the time of 
 their formation by sand violently injected into them either from 
 below or above. Cases of mud and sand welling up from volcanic 
 fissures have been frequently observed, and seem to be a general 
 accompaniment of such fissures near the surface. In some cases, 
 as in the earthquake of Chemakha, Turkestan (Feb. 12, 1902), "salty 
 plastic mud exuded from the open faults and built up high hillocks 
 of the pasty material, which were surmounted by craters" (Hobbs- 
 18:134). Subsequent movement along the plane caused a dis- 
 placement in these "mud volcanoes" to the extent of 1.5 meters 
 in some cases. Sand and mud injections of this type are known 
 from older geological formations, where they form sandstone dikes. 
 Thus Newsom ($$'.233} describes a sandstone dike 2}/ 2 to 5 feet 
 wide from California, in which the upward bending of the shales 
 on either side is regarded as proving its injection from below. 
 Others from the same general region are also described. Violent 
 injection into an earthquake fissure of loose sand, which covered the 
 surface of the rock, seems to have taken place in the case of the 
 Lower Devonic sandstone dike (injected into Upper Siluric strata) 
 at Buffalo, as described in a preceding chapter. For a general 
 summary of sandstone dikes with references to the literature, the 
 student is referred to Newsom's article (33). 
 
 Craterlets. Analogous to the injected sandstone dikes are the 
 craterlets formed by sand and mud ejected with water from earth- 
 quake fissures. One such has already been noted in connection 
 with the Chemakha earthquake. Others were noted in the Charles- 
 ton earthquake of 1886. Some of these which were aligned along 
 fissures measured 20 feet in diameter, while the water and sand 
 
886 PRINCIPLES OF STRATIGRAPHY 
 
 ejected from them shot in some cases 20 feet into the air. Many of 
 the craterlets, especially those formed during the Calabrian earth- 
 quake, are merely funnel-shaped holes in the ground, and so re- 
 semble the volcanic explosion craters. (Fig. 242.) Such craterlets 
 formed in the Mississippi Valley during the earthquake of 1811. 
 They were commonly surrounded by a ring of sand and carbonized 
 wood, sometimes as much as 7 feet in height. They have a diam- 
 eter ranging from 20 to 100 feet, and some were sounded to a depth 
 of 20 feet or over. 
 
 Much sand and water is ejected from these and is spread 
 over the surrounding country, which may thus be blanketed by a 
 
 FIG. 242. Funnel-shaped holes formed during the Calabrian earthquake of 
 1783. (C. Vogt.) 
 
 layer of sand brought from below, the analogue of a lava 
 flow. Sulphuretted hydrogen frequently accompanies these erup- 
 tions. 
 
 Fossil examples. Ancient craterlets of the type above described 
 have been noted in some cases. Thus, on the coast of East Angle- 
 sey, in Wales, sandstone pipes have been observed, penetrating the 
 Ordovicic limestones, and having a general funnel form comparable 
 to the funnels formed by the Calabrian earthquake. They are 
 continuous above with a spreading- blanket of sandstone, which 
 may be the ejected layer of sand. The entire series is again cov- 
 ered by the Ordovicic limestones of the region. A section of this, 
 copied from Hobbs, is shown in Fig. 241. Care must, however, be 
 exercised to distinguish these fissures from the solution fissures 
 subsequently filled by sand and forming the organ-pipe structure 
 described in a preceding chapter. 
 
DISLOCATIONS 887 
 
 Slipping. 
 
 When differential movements of the two sides of a fracture 
 occur a fault results. This movement may be horizontal, diagonal, 
 or vertical. The displacement may be profound or very slight. It 
 may be sudden or by a series of progressive slips, or it may be 
 the resultant of a series of slips in various (even opposite) direc- 
 tions, and of varying amounts. The California earthquake of 1906 
 and the Japanese earthquake of 1811 were caused by slips of large 
 amplitude along well-defined seismotectonic lines. The frequent 
 New England quakes are due to a relatively large number of slight 
 adjustments along joint planes. These minor slippings may be 
 so slow as to produce no perceptible seismic disturbances, though 
 they may find a surface expression in minute faults. Here, prob- 
 ably, belong the numerous minute post-glacial faults of New Eng- 
 land and eastern New York. (Woodworth-45.) 
 
 The local rise and fall of the land in response to adjustment 
 to stresses, but without violent shocks, or abrupt ruptures, may 
 be considered as forming one end of the series of earthquake- 
 producing disturbances. To these the name bradyseisms has been 
 given, and they are well illustrated by the changes of level re- 
 corded in the ruins of the Temple of Jupiter Serapis in the Bay 
 of Naples, already referred to in an earlier chapter. 
 
 On the surface the fault is expressed by the dislocation of 
 structures, such as fences, roadways, and parts of buildings, bridges, 
 railroad tracks, or of natural objects, such as trees, etc., while if 
 the slipping has a vertical component, a fault scarp will result. 
 These phenomena, and the types of faults and their effects, have 
 been discussed in Chapter XXI. When successive shocks from 
 various directions are experienced, a vortical movement of objects 
 may result, as in the case of statues turned on their pedestals. 
 The various effects of such shocks on buildings and other structures 
 are fully illustrated in the reports on the recent Californian and 
 other earthquakes. 
 
 Block Movement. The faulting may be manifested as a block 
 movement, strips of land dropping or rising and forming rift 
 valleys (Graben) or fault blocks. On a large scale, these form 
 fault-block mountains. Such faulting occurred in connection with 
 the Owens Valley earthquake of 1872, the resulting scarps reaching 
 in some cases a height of ten feet or more. At Big Pine, Califor- 
 nia, a tract of land 200 to 300 feet wide sank, some portions being 
 depressed 20 feet or more, leaving vertical walls on either side. 
 
888 PRINCIPLES OF STRATIGRAPHY 
 
 (Johnson-23.) During the earthquake of Yakutat Bay, Alaska, in 
 1899, great sections of the country moved as individual masses, 
 some blocks being elevated, some depressed, the extent of the dif- 
 ferential movement reaching 30 to 47 feet. Portions of the sea- 
 shore were elevated ; beaches only recently abandoned being now at 
 a considerable height above the sea, while many of the depressed 
 areas became submerged. Similar block movements occurred dur- 
 ing the great Icelandic earthquake of 1896. 
 
 Disruptive Effects of Earthquakes. 
 
 The more pronounced earthquake shocks often have a very de- 
 structive effect on the rocks of the earth's surface. Land slips of 
 great extent may be set in motion by them. A piece of land one 
 mile long fell from the cliff at Scilla during the Messina earth- 
 quake. 
 
 Darwin describes the overwhelming forces of the earthquake 
 of February 20, 1835, in Chile. He particularly notes the effects 
 on the islands in Concepcion Harbor, where upward of a hundred 
 villages were destroyed and where rocks from beneath the sea 
 were broken off and cast high up on the shore. "One of these 
 was six feet long, three broad, and two thick." Darwin describes 
 the destruction on Quinquina Island as follows : "The ground in 
 many parts was fissured in north and south lines, perhaps caused 
 by the yielding of the parallel and steep sides of this narrow 
 island. Some of the fissures near the cliffs were a yard wide. 
 Many enormous masses had already fallen on the beach, and the 
 inhabitants thought that when the rains commenced far greater 
 slips would happen. The effect of the vibration on the hard 
 / primary slate, which composes the foundation of the island, was 
 still more curious: the superficial parts of some narrow ridges 
 were as completely shivered as if they had been blasted by gun- 
 powder." This effect, which was rendered conspicuous by the fresh 
 fractures and displaced soil, must be confined to near the surface, 
 for otherwise there would not exist a block of solid rock throughout 
 Chile ... I believe this convulsion has been more effectual 
 in lessening the size of the island of Quinquina than the ordinary 
 wear-and-tear of the sea and weather during the course of a whole 
 century." (Darwin-6, Chap. XIV.) 
 
 Effects of Earthquakes on Topography. 
 
 Many minor changes in topography in regions of frequent seis- 
 mic disturbances may have their origin in the earth tremors. 
 
SEA-QUAKES 889 
 
 Changes due to displacement are not to be classed in this category, 
 as they are due to the same cause which is responsible for the 
 earthquake, namely, the faulting. But topographic changes caused 
 by the shaking of the earth are properly classed here. Such are 
 the formation and sudden drainage of lakes ; the blocking of rivers 
 by land slips; the shifting of river channels in level delta regions, 
 and other changes. After the Indian earthquake of 1897 no ^ ess 
 than 30 earthquake lakes were produced. The earthquakes of 
 1811-12 caused the appearance of many new lakes along the lower 
 Mississippi, owing, probably, to the local settling of the river sedi- 
 ment. One of these is Reelfoot Lake, in Obion county, Tennessee, 
 which has a length of more than 20 miles and a width of seven 
 miles; the water in places covering the tops of submerged cypress 
 trees. Near Little* Prairie a lake, many miles in length but only 
 from 3 to 4 feet in depth, came into existence. Upon its disap- 
 pearance it left behind a stratum of sand. On the other hand, Lake 
 Eulalie, 300 yards long and 100 yards wide, was suddenly drained 
 through parallel fissures which opened in its bottom. Many other 
 examples of this kind might be cited. 
 
 This same earthquake was responsible for a local and temporary 
 reversal of the current of the Mississippi. Similar phenomena 
 have been observed in other rivers. 
 
 SUBMARINE EARTHQUAKES AND SEA-QUAKES. 
 
 As might be expected, seismic disturbances are common along 
 the borders of the Pacific, where, as before noted, we have the 
 regions of down-warping, and, therefore, the region of stresses 
 and of readjustments to these stresses. From their proximity to the 
 sea the latter is, of course, strongly affected by the shocks, and sea- 
 quake waves, or tsunamis, are the result. These, on account of their 
 height and velocity, are exceedingly destructive. Perhaps the most 
 memorable one is that which destroyed Lisbon in 1775. The sea- 
 quake originated on the ocean floor fifty or more miles off the 
 coast of Lisbon, and the vibrations were transmitted along the 
 surface of the water in a series of monstrous waves. The greatest 
 of these was sixty feet high, and was followed by others of decreas- 
 ing height. Spending their strength on the coast of Spain the 
 waves passed on with diminished amplitude, but were felt even 
 on the shores of the West Indies, across the whole expanse of 
 the Atlantic. 
 
890 PRINCIPLES OF STRATIGRAPHY 
 
 Even greater distances have been traveled by tsunamis, as, for 
 instance, those originating in an earthquake at Concepcion, Chile, 
 which "set in motion a wave that traversed the ocean to the Society 
 and Navigator Islands, 3,000 and 4,000 miles distant, and to the 
 Hawaiian Islands, 6,000 miles." (Dana~5 :^/j.) 
 
 The velocity of these mighty waves has been ascertained, and 
 is seen to be far greater than that of ordinary sea-waves, though 
 it does not equal that of earthquakes proper. "The waves of the 
 Japan earthquake crossed the Pacific to San Francisco, a distance of 
 4,525 miles, in a little more than twelve hours, and, therefore, at a 
 rate of 370 miles per hour, or over six miles per minute. The 
 waves of the South American earthquake of 1868 ran to the 
 Hawaiian Islands at a rate of 454 miles per hour." (Le Conte- 
 26:137.) 
 
 Seismic disturbances are not confined to the shore, however, 
 but also occur under the sea. Both pyroseismic and baryseismic 
 disturbances are likely td affect the water and produce pronounced 
 disturbances. That faulting occurs on the bottom of the deep sea 
 is shown by soundings and studies of cable routes. The frequent 
 breaking of the cables, accompanied by thrusting and fraying, fur- 
 nishes visible evidence of such disturbances. Precipices from 3,000 
 to 5,000 feet in height have been detected by soundings in the 
 Mediterranean, a difference in depth of 2,000 feet having been 
 noticed between the bow and the stern of the cable repair ship. 
 The earthquake of October 26, 1873, caused the cable to break 7 
 miles from the cable office at Zante, Greece, by the formation of a 
 submarine fault scarp 600 feet in height, the change in depth being 
 from 1,400 to 2,000 feet. Similar breaks, with the formation of 
 submarine fault scarps more than a thousand feet in height, have 
 been reported from the same region. Submarine earthquakes 
 ought to be distinguished from sea-quakes proper. The latter 
 always accompany the former and may even accompany earth- 
 quakes originating in the land near the sea. On the other hand, 
 true sea-quakes, or thalassoseisma, may be formed by causes which 
 will not produce earthquakes, as, for example, submarine explosions. 
 The latter represent a submarine pyroseismic disturbance (whether 
 of a submarine volcano or a submarine mine), and this is the only 
 kind of directly induced sea-quake or thalassoseisma possible. Sec- 
 ondarily induced or communicated thalassoseisma are, however, the 
 most frequent type, and here belong, besides the effects of many 
 volcanic explosions on the sea coast (e. g., Krakatoa), the great 
 series of baryseismic disturbances or tectonic faultings. 
 
DISPLACEMENT OF THE POLES 891 
 
 AIR-QUAKES. 
 
 What is true of the sea is in an even greater measure true of 
 the atmosphere. This, like the water, is too mobile to permit the 
 setting up of strains within its mass, and so baryseismic disturb- 
 ances cannot originate in the atmosphere any more than they can 
 in the hydrosphere. Such disturbances may, however, be com- 
 municated from the baryseismic disturbances of the land. Origin- 
 ally induced pyroseismic disturbances are, however, as readily pro- 
 duced in the air as in the water, and they are more readily trans- 
 mitted, owing to the greater mobility of the atmosphere over that 
 of the water. 
 
 PERIODICITY OF EARTHQUAKES. 
 
 Periods of strong seismic disturbances (macroseisms) are 
 known to alternate with periods of relative quiescence, or only 
 minor disturbances (microseisms). In Japan the seismic periods 
 recur about once in thirteen years, though observations at Kioto in- 
 dicate a period as short as six and one- fourth years. Too little 
 is yet known to warrant predictions of recurrences of earthquakes. 
 
 MOVEMENTS DUE TO DISPLACEMENT OR MIGRATION OF THE POLES. 
 
 The theory of pole migration, or the shifting of the earth's axis 
 of rotation with reference to the earth itself, together with the 
 accompanying changes in the form of the earth, in distribution 
 of land and sea and in climatic belts, has ever proved attractive 
 to speculative geologists who sought for means of accounting for 
 the ascertained variations in the surface characters of the earth in 
 the past. Thus, evidence is accumulating which points to a widely 
 different position of the earth's axis during Palaeozoic time from 
 that which it held during the Mesozoic and subsequent periods. 
 This evidence is furnished in part by the occurrence of mild cli- 
 mate, and even of tropical vegetation, in regions having an arctic 
 climate at present, and in part by the presence of glacial deposits 
 where tropical conditions prevail to-day. It is further found in 
 the occurrence of sediments which indicate the existence during 
 Palaeozoic time of easterly winds where now the westerlies prevail. 
 (See ante, Chapters II and XIV, also Fig. 128, page 636.) 
 
 A wealth of biological evidence has been accumulated which 
 
892 PRINCIPLES OF STRATIGRAPHY 
 
 also seems to point to the phenomenon of polar migration. (Sim- 
 roth-37.) The signs further point to the existence, in the border 
 regions of the present Atlantic, of large continental masses which 
 became submerged with the close of the Palaeozoic. Thus Appa- 
 lachia, the source of clastic sediments in eastern North America 
 during the whole of Palaeozoic time, disappeared at the end of that 
 period; the disappearance being coincident with, or closely related 
 to, the formation of the Appalachian folds. Similar conditions have 
 been ascertained for western Europe. As demonstrated in an ear- 
 lier chapter, the clastic sediments of North America indicate that 
 in Palaeozoic time this continent came under the influence of the 
 trade winds, at least so far as the eastern portion is concerned, 
 while in Mesozoic and later time it had passed into the region of 
 the westerlies. This suggests that the end of Palaeozoic sedimenta- 
 tion was brought about by a profound change in physical geography 
 which affected not only North America, but also the earth as a 
 whole. A comparatively rapid shifting of the position of the earth's 
 axis would be sufficient explanation of the profound changes which 
 brought about the all but universal extinction of life, so that only 
 the pelagic and deep-sea types of the oceans (especially of the 
 Pacific), and the terrestrial types in the interior of the continents, 
 remained unaffected. These probably formed a source from which 
 the earth was repopulated after the widespread extermination 
 of life on the margins of the continents and in shallow water. 
 That migrations of the poles occurred before and after this great 
 cataclismic shifting is indicated by the nature of the sediments, 
 the changes in climate and life during the successive periods, and, 
 especially, by the occurrence of glacial conditions in Pleistocenic 
 times in regions not now subject to such conditions. (See ante, 
 Chapters II and VIIL) The map (Fig. 245), copied from Walther, 
 shows the location of the Pleistocenic ice sheets, and the suggested 
 position of the pole, to account for its occurrence. All such wan- 
 derings of the poles, however, if they occurred, are insignificant 
 in comparison with the catastrophic change which brought to an 
 end the period of Palaeozoic sedimentation and biologic develop- 
 ment. 
 
 THE PENDULATION THEORY. Though frequently suggested as 
 a possible cause of changes in the geologic development of the 
 earth, the theory of polar migration seems to have been first def- 
 initely formulated by Paul Reibisch in .1901. Reibisch developed 
 the theory of polar pendulation, or swinging, i. e., a back and forth 
 migration of the poles along certain well-defined paths. Dr. Hein- 
 rich Simroth, of the University of Leipzig, developed this theory 
 
THE PENDULATION THEORY 
 
 893 
 
 more fully in his book, "Die Pendtilations Theorie," fortifying it 
 by a wealth of illustrations furnished by the distribution of animals 
 and plants in both the present and past geologic periods. Simul- 
 taneously with Reibisch, the theory of polar migrations was formu- 
 lated by Dr. D. Kreichgauer (25), who approached the subject 
 from a purely geological point of view. He endeavored to explain 
 the changes of climate in past geological periods by a change in 
 the position of the earth's equator and therefore a shifting of the 
 north pole, which he thought had migrated 180 since Cambric 
 
 FIG. 243. Map showing the hypothetical wanderings of the earth's North 
 Pole during the successive periods of its history. (After Kreich- 
 gauer.) 
 
 time, having been at the beginning of that period where the south 
 pole is now. Kreichgauer's map, showing the migration of the 
 poles, is here reproduced. (Fig. 243.) As Simroth points out, how- 
 ever, Kreichgauer did not consider the phenomenon of polar pen- 
 dulation. 
 
 The theory of polar pendulation, as formulated by Reibisch 
 (34) and developed by Simroth (37), postulates the existence of 
 two "oscillation poles" (Schwingpole) in addition to the two ro- 
 tation poles. These oscillation poles lie in the region of modern 
 Equador, on the one hand, and of Sumatra, on the other. The 
 
8 9 4 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 meridian which passes through the rotation and oscillation poles 
 forms the culmination circle (Kulminatiomkreis) , and it divides 
 the earth into a Pacific and an Atlantic-Indian hemisphere. (Fig. 
 244.) Each hemisphere is again divided by the equator into a north- 
 ern and a southern quadrant. The meridian of 10 E. longitude 
 from Greenwich, which bisects each hemisphere, is called the 
 oscillation circle, because it is upon it that the poles swing back 
 and forth. The culmination circle is so called because each point 
 reaches its closest approximation to the poles when it crosses this 
 circle. 
 
 FIG. 244. Map of the earth, divided by the oscillation circle (near the 
 meridians of 10 E. and 170 W. of Greenwich) into two hemi- 
 spheres, according to the theory of P. Reibisch. The oscillation 
 poles form the centers of the hemispheres. The vertical meridian 
 is the culmination circle (80 on the left, 100 on the right). 
 The concentric rings around the oscillation axis mark the paths 
 along which the points cut by them move during the pendulation. 
 (After Simroth.) 
 
 The form of the geoid, i. e., the difference in length of the axis 
 of rotation and the equatorial diameter, amounting to more than 40 
 kilometers (43 km., or nearly 27 miles; see ante, Chapter I), is re- 
 sponsible for the transgressions and regressions of the sea; and the 
 elevation and subsidence of the land. The sea, the mobile element, 
 assumes the flattened geoid form with every position of the axis 
 of rotation, but the land, owing to its greater rigidity, does not so 
 readily assume this form. Hence, as every point approaches the 
 pole during the pendulation, the waters recede from it, while at 
 the same time they rise over the points approaching the equator. 
 The differences between rise and fall of the water are greatest on 
 the oscillation circle and decrease progressively to the oscillation 
 
THE PENDULATION THEORY 895 
 
 poles, where they are zero. A point on the oscillation circle, which 
 lies 10,000 meters below sea-level when under the equator, would, 
 by the time that it has come to lie at the pole (after a rotation of 
 90), lie 10,000 meters above sea-level. It must be remembered 
 that every point on the globe is nearest to the pole as it crosses 
 the culmination circle, which, together with the ends of the axis 
 of rotation, may be regarded as having a fixed position in space. 
 At the moment of crossing, therefore, the point has its greatest 
 elevation above sea-level, while, as it passes away from the culmina- 
 tion circle, the sea-level will rise, where previously, during the ap- 
 proach, the sea-level fell. This seems to be illustrated by Florida, 
 which at present lies under the culmination circle. The eastern 
 half has a rising sea-level and would, therefore, be passing away 
 from it, while the western half has a falling sea-level, i. e., the land y 
 emerges, and this section would, therefore, be approaching the 
 culmination circle. All this would indicate that the earth is swing- 
 ing in such a way that the north pole is migrating toward Behring 
 Sea, which thus becomes a region of emergence, and away from 
 the Greenland-Iceland region, where, it has been supposed, the pole 
 had its location in Pleistocenic time. (Fig. 245.) (See ante, Chap- 
 ter II.) 
 
 Owing to the proximity of Florida to the oscillation poles 
 (where emergence and submergence are zero), the total amount 
 of oscillation of the sea was never great, and hence old coral 
 reefs which grew near the surface go only to the depth of 50 / 
 feet. In Funafuti, on the other hand, which lies not far from the 
 oscillation circle (under which the greatest variation of sea-level 
 occurs), the reef corals grew to a depth of more than 600 feet. 
 (See ante, Chapter X.) The coral islands of the North Pacific lie 
 in the quadrant approaching the pole and the culmination circle, 
 and hence they show at the present time a retreating sea-level; as 
 in the case of the Hawaiian Islands. The islands of the South 
 Pacific, on the other hand, are moving toward the equator, and 
 hence, in this case, submergence is taking place. In the Indian 
 Ocean, again, the region north of the present equator is one of 
 rising sea-level (submergence of reefs and islands), while that 
 south of the equator is one of falling sea-level (emerging reefs). 
 This would explain why the Maldives, north of the equator, are 
 apparently being submerged, while the Cocos Islands to the south 
 are rising out of the water. 
 
 The regions around the oscillation poles were always tropical 
 regions, as compared with the regions near the oscillation circle. 
 In the former, therefore, life conditions changed little and slowly, 
 
8 9 6 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 and so they are the regions where ancient types persisted, while the 
 region near the oscillation circle (northern North America, north- 
 ern Eurasia, western Europe, Africa, and Antarctica), on the con- 
 trary, showed the greatest oscillation in climate and in life during 
 the successive periods of the earth's history. 
 
 When we next consider what effects the shifting of the poles 
 would have on the form of the lithosphere we realize that, while 
 it would be more gradual than the effect on the hydrosphere, it 
 
 
 FIG. 245. Map of the Pleistocenic Tee Period, showing the distribution of the 
 ice and the hypothetical North Pole. (After Walther.) The 
 black dots in western Europe indicate the localities where re- 
 mains of early man have been found. 
 
 must still result in a series of important changes, if the hypothesis 
 of pendulation is correct. The influence of the centrifugal force 
 on the equatorial region is manifested by an expansion or stretch- 
 ing of the equatorial zone, and this will result in the formation of 
 depressions, through the sinking of fault blocks. Depressions in 
 the present surface of the lithosphere are most marked in the 
 quadrant now approaching the equator, near which lie all the large 
 terrestrial or submarine trenches and deeps. Thus the great sub- 
 marine depressions of the present day, the Tonga and Kermadec 
 deeps, lie in the South Pacific quadrant, whereas similar depressions 
 
THE PENDULATION THEORY 897 
 
 in the land, such as the Caspian and the Dead Sea, etc., lie in the 
 North Atlantic quadrant, which also approaches the equator. It 
 should be noted, however, that the Marian depression with the 
 deepest submarine pit, the Nero deep, lies mostly north of the 
 equator and therefore in the opponent quadrant. However, its 
 proximity to the equator (less than 20 N.) is evident, and it may 
 be regarded as still retaining the characters acquired as it passed 
 under the equator. In like manner, the greater part of the African 
 rift valley lies in the south Atlantic-Indian quadrant, though again 
 within 20 degrees of the equator. 
 
 Conversely, regions approaching the poles are regions of 
 shrinking land, and hence regions where mountain-making through 
 folding is marked. 
 
 Ingenious and suggestive as this theory is, and much as it seems 
 to throw light on many geological as well as biological phenomena, 
 it is still too new and too little tested to receive more than re- 
 spectful attention. As a working hypothesis in the attempt to in- 
 terpret the history of the earth, it is likely to be of much value. 
 (See the application of this theory by Yokoyama to the interpreta- 
 tion of the Pleistocenic problem, .given in Chapter II.) 
 
 In this connection may also be mentioned the recent studies by 
 Eugenio Jacobitti (22), who, attacking the problem as a study in 
 geology, finds the wanderings of the poles to be of a more irregular 
 character, through the various geological periods, as illustrated in 
 the subjoined figures reproduced from his paper. (Figs. 246, 247.) 
 He also reconstructs a series of charts showing the position of 
 the equator in the successive periods. All such reconstructions are, 
 of course, premature, and must be taken as suggestions rather than 
 as demonstrations. What is probably the most complete attempt at 
 restoration of the earth's surface during a period of different polar 
 location is that made by Koken (233.) for the Permic. His map 
 not only locates the poles but also the lands and seas of the period, 
 as well as the ocean currents, etc. See ante, page 536. 
 
 It may again be remarked here, as was stated in Chapter II, that 
 astronomers have generally looked with disfavor on such specula- 
 tions, though George Darwin concedes the possibility of the pole 
 having wandered some 10 or 15 degrees from its original position, 4 
 provided the degree of rigidity of the earth is not so great as to 
 be inconsistent with a periodic readjustment to a new form of 
 equilibrium. Sir William Thompson (Lord Kelvin), for ^one, 
 readily entertained the idea of such changes. He says: "We 
 may not merely admit, but assert as highly probable, that the axis 
 of maximum inertia and axis of rotation, always very near one an- 
 
PRINCIPLES OF STRATIGRAPHY 
 
 other, may have been in ancient time? very far from their present 
 geographical position, and may have gradually shifted through 10, 
 
 FIG. 246. Map of the hemispheres, showing the hypothetical migration of 
 the North Pole during the successive geologic periods. 
 (Jacobitti.) 
 
 20, 30, 40, or more degrees, without there being at any time any 
 perceptible sudden disturbance of either land or water." (42:11.) 
 
 FIG. 247. Map of the hemispheres, showing the hypothetical migrations of 
 the South Pole during the successive geologic periods. (Jacobitti.) 
 
 Various theories have been advanced to account for and ex- 
 plain such wanderings of the poles, but at present the whole sub- 
 ject is too little investigated to make their discussion profitable. 
 Geologists must first gather a larger body of facts, which will tend 
 
ACTUAL MIGRATIONS OF THE POLES 
 
 899 
 
 either to prove or disprove these theories, before the discussion of 
 causes need be undertaken. 
 
 Determined Migrations of the Poles. 
 
 That the poles, i. e., the points of intersection between the 
 earth's axis of rotation and the surface of the earth, are not 
 actually fixed, but wander about within small limits, was first 
 recognized toward the end of the nineteenth century. From thou- 
 sands of careful observations on latitude made in recent years .in 
 
 +0*30 
 
 +Oi/O O'.OO -O*/0 ~O*2O -O~3Q 
 
 -nfeo +o~/o 0*00 -o'so - -c&o -o'.So 
 
 FIG. 24& Map showing the ascertained migration of the North Pole from 
 1892 to 1894 (after Milne) ; the figures indicate the number of 
 large earthquakes in each period. 
 
 Europe and America this wandering has been determined to lie 
 within a circle 40 or 50 feet in diameter. It has a curiously ir- 
 regular, but somewhat spiral path, and completes its erratic circuit 
 in about 428 days. The path described by the North Pole between 
 the years 1892 and 1894 is shown in the above map by Milne, 
 in which each year is divided into ten parts. (Fig. 248.) The 
 figures show the number of earthquakes which occurred in each 
 period, the largest of them, as John Milne has pointed out, coin- 
 ciding with the sharpest curvature in the path of the pole. As 
 Milne suggests, both the abrupt curvature and the sharp earthquake 
 
900 PRINCIPLES OF STRATIGRAPHY 
 
 may be the result of sudden readjustments, due to the redistribution 
 of material on the earth's surface by currents and by meteorological 
 agents. 
 
 Accompanying the changes of position of the poles, is, of course, 
 a change in the position of the equator, the plane of which is always 
 at right angles to the axis of rotation of the earth. A further re- 
 sult of such changes is a variability of terrestrial latitudes gen- 
 erally. 
 
 It is now commonly admitted that the movement of large bodies 
 of water, or of air, over the 'surface of the globe, and, more es- 
 pecially, an accumulation of vast masses of snow and ice in differ- 
 ent regions, may all be causes effecting slight displacements of the 
 earth's axis. More pronounced effects might follow from wide- 
 spread upheavals or depressions of the surface of the lithosphere. 
 
 If the earth's center of gravity should be sensibly displaced, 
 momentous rearrangements, accompanied by pronounced wander- 
 ings of the pole, would result. It has long been known that the 
 center of gravity does not coincide with the center of figure of 
 the earth, but lies to the south of it. This is due to the greater 
 aggregation of dense material in the southern hemisphere, but 
 whether this is a result of original distribution of matter, or is 
 due to later readjustments, cannot be said. Simroth has even 
 suggested that the in-falling of a satellite, or second moon, into the 
 earth in the African region may have been a possible cause of the 
 displacement of the center of gravity, and that the pendulations of 
 the earth's axis were the result of a gradual readjustment. That 
 meteoric or extra-telluric bodies reaching the earth in great numbers 
 may sensibly affect the center of gravity, and hence the position 
 of the earth's axis, cannot be doubted. 
 
 EARTH MOVEMENTS AND GEOSYNCLINES. 
 
 As already noted in Chapter XX, the term geosyncline was ap- 
 plied by Dana (in 1873) to the great earth troughs, whether simple 
 or compound, which are formed in regions of excessive deposition, 
 the Appalachian region being taken as the type of such troughs. 
 The idea of great downward bowings under heavy load was de- 
 veloped much earlier by James Hall, who held that this downward- 
 bending was in direct response to the load added by the sediment, 
 and thus, in effect, constituted an isostatic readjustment. Dana, 
 on the other hand, regarded the downward bending as primary, 
 and of the nature of a fold due to compressive strains, and the 
 
GEOSYNCLINES 
 
 901 
 
 filling by sediment as a secondary consequence. Among subsequent 
 authors, Haug (14, 15) has greatly extended this idea, and has in- 
 cluded under this title all great submarine depressions parallel to 
 land areas, such as the great depressions of the Pacific coast. (See 
 Chapter III and Figures 16 and 17, pages 101 and 105.) These "fore 
 deeps" (Vortiefen) are undoubtedly the direct result of deforma- 
 tion under strain, but they are not areas of excessive deposition. 
 Indeed, sedimentation here goes on with extreme slowness, and is 
 confined to materials normal to the deep sea. Haug has identified 
 among many of the deposits bathyal sediments (see Chapter XV), 
 which he regards as accumulations in geosynclines, and he holds 
 that the great thickness of these deposits indicates a progressive 
 deformation of the region of deposition. He finds that many 
 bathyal sediments pass laterally into neritic or shallow-water de- 
 posits, though other deposits in the geosynclines are throughout of 
 
 FIG. 249. Diagrammatic section of a geosyncline according to Haug. The 
 numbers i-io indicate the successive strata, which are complete 
 in the center of the geosyncline but incomplete on its margins, 
 where thinning away of beds and overlap of others is characteris- 
 tic. (After Haug.) 
 
 neritic origin. Haug does not, apparently, recognize the presence 
 of continental sediments in the geosynclines, -though he finds these 
 on the margins. This type of sediment is, however, eminently 
 characteristic of the Appalachian region throughout, and is included 
 in the main mass of the sediment itself. 
 
 The bathyal origin of many of the sediments in the geosyn- 
 clines of the Alpine region and elsewhere is by no means wholly 
 established, and it may be questioned whether, on the whole, sedi- 
 ments of that class are abundant or widespread. The frequent 
 marginal disconformities in the sediments of most geosynclines 
 lead one to the supposition that, after all, many of the so-called 
 bathyal deposits may be of littoral (neritic) origin, and that, fur- 
 thermore, repeated laying bare of the margins of the geosyncline 
 permitted erosion of the already deposited sediments. 
 
 Haug recognizes the shading away of the sediments by overlap 
 and by thinning toward both sides of the geosyncline (Fig. 249) 
 
902 PRINCIPLES OF STRATIGRAPHY 
 
 and he explains this by the supposition that the geosyncline was 
 located between two continental masses and not, as held by Ameri- 
 can students, on the borders of the continent. He holds that the 
 geosynclines are zones of weakness and mobility between two rela- 
 tively stable masses. 
 
 The Himalayas are chosen by Haug as an illustration of a great 
 geosyncline (in pre-mountain time) formed, not on the border of 
 a sea, but between two continental masses, the stable Indian land 
 mass on the south and a similar land mass on the north. In spite 
 of this location, he holds that Palaeozoic and Mesozoic sediments in 
 this geosyncline are none of them of a littoral (neritic) character. 
 The chains of central Europe are in like manner regarded by Haug 
 as occupying the sites of former geosynclines. If the expanded 
 Mediterranean basin of Mesozoic time is to be considered in the 
 light of a geosyncline, the bathyal nature of some of the sediments 
 therein, or at any rate their thalassogenic character, may be readily 
 conceded. It may be questioned, however, if the use of the term 
 geosyncline for an intracontinental sea with abyssal regions (i. e., 
 a mediterranean) is permissible. Certainly such a condition did 
 not prevail in the Palaeozoic of the Appalachian region. Here an 
 accumulation of 40,000 feet of sediment was accompanied by a 
 downward bowing of the sea-floor bordering the old Appalachian 
 continent. But this was probably never of great depth, nor was 
 there, as a rule, a land mass to the west of the region of sedimenta- 
 tion. Indeed, as has already been pointed out, and, as has elsewhere 
 been discussed by the author in great detail, the prevailing sedi- 
 ments were of shallow water and terrestrial type. As stated in 
 Chapter XX, it seems best to restrict the name geosyncline to such 
 regions of deposition, and use the name fore-deep for regions 
 known to have descended to bathyal or abyssal depths. That these 
 fore-deeps are due to tectonic movements is freely conceded, but 
 the geosyncline of the Appalachian type is most probably due to 
 isostatic readjustments incident upon the loading of the earth's 
 surface along the line of subsidence. This does not imply, how- 
 ever, that the subsequent folding of these strata is due to any 
 other cause than that of yielding under compressive strain. Such 
 an origin alone seems to be possible, in view of the many features 
 which can be explained only as originating under compressive 
 stresses. 
 
 GEOSYNCLINES THE SITES OF OROGENIC DISTURBANCES. As long 
 ago pointed out by Hall and Dana, and as emphasized by Haug, 
 the geosynclines are the sites of subsequent foldings of the strata, 
 or, conversely, the regions of folded mountains are the sites of 
 
FOLDING OF THE APPALACHIANS 903 
 
 former geosynclines. Bailey Willis (44) has pointed out that 
 the gradual downward sinking of the strata in the geosyncline gives 
 them an individual steepness along the margin of the depression, 
 and that this initial dip forms the beginning of the deformation, 
 and determines the subsequent folding under the influence of lateral 
 pressure. The folds of the Appalachians are asymmetrical anti- 
 clines, with the steeply inclined, vertical, or even overturned limb 
 on the northwest or away from the present ocean. It must, how- 
 ever, be remembered that the present Atlantic coast is near the 
 western border of the old Appalachian land, and that hence if the 
 folds occurred before this land mass disappeared by subsidence, 
 the thrusting, which was from the east or southeast, was performed 
 or transmitted by this ancient land mass. In this westward thrust- 
 ing many folds were not only overturned, but thrust-faults of con- 
 siderable magnitude were developed. Thus the crystalline range 
 of the Hudson Highland was thrust northwestward over the Palaeo- 
 zoic strata (Berkey) and numerous other overthrusts were devel- 
 oped in the Palaeozoic and older strata along the entire Appalachian 
 range. 
 
 FORESHORTENING OF THE CRUST. During the folding of the 
 Appalachians there was, of course, a considerable amount of fore- 
 shortening of the earth's crust. Lesley long ago estimated the 
 movement to have extended over a distance of forty miles, while 
 Claypole, considering the major folds, arrived at the approximate 
 conclusion that a section of the earth's surface measuring origin- 
 ally one hundred and fifty-three miles had been compressed into 
 sixty-five miles. (4.) 
 
 Recently R. T. Chamberlin (2) has published the results of 
 some careful measurements of the Appalachian folds in the district 
 between Harrisburg and Tyrone, Pennsylvania, and these have fur- 
 nished more exact data for the estimation of the amount of crustal 
 foreshortening, and have likewise thrown some light on the form 
 and thickness of the crust involved in the folding. He concludes 
 that, so far as his measurements warranted, and postulating the 
 correctness of the assumed basis of investigation, the region west 
 of Harrisburg showed 81 miles of strata compressed into 66 miles. 
 The uncertainties of this result lie in the difficulty of eliminating 
 the amount of loss due to thickening and thinning of strata in 
 various parts of the fold; the variation in closeness of folding; or 
 the subsequent relaxation of the strata under the influence of 
 gravity, with resultant gliding on the limb of the fold. These un- 
 certainties can make such estimates only approximate. 
 
 HEIGHT OF THE FOLDS. Assuming that, when the folding of 
 
9 o 4 PRINCIPLES OF STRATIGRAPHY 
 
 the Appalachians commenced, the strata were practically horizon- 
 tal and the upper surface of the youngest beds essentially at sea- 
 level, and assuming, furthermore, that the higher Carbonic and 
 Permic beds of the region (above the Pottsville) was 1,100 
 feet thick, Chamberlin concludes that 3 miles represents the average 
 height of the top of the restored Pottsville conglomerate over the 
 area from Tyrone to Harrisburg, i: e., the vertical deformation was 
 of that amount. 
 
 There are here several assumptions which need careful consid- 
 eration before we can regard this as anything more than a very 
 general estimate. In the first place, if we regard the late Palaeozoic 
 sediments as terrestrial in type rather than marine, as their nature 
 seems to indicate, we can not assume an initial horizontality with 
 the upper strata at sea-level throughout. Even on the basis of the 
 gentle gradient of the present delta-fan of the Huang-ho the eleva- 
 tion at the heads of the delta plains would be some 500 feet or 
 more above sea-level, and from the coarseness of the material in 
 the deposits it is likely that this elevation was a thousand feet, if 
 not more. 
 
 In the second place, it appears that the estimate of the original 
 thickness of the post-Pottsville Palaeozoic is much too low. A 
 comparison of the thickness of the Pottsville and Kanawha forma- 
 tions between the eastern and western portions of their outcrops 
 shows the thickness of these two formations in the western region 
 to be only one-fifth or one-sixth that of the part preserved in the 
 eastern Appalachians. Since the sediment of the later formations 
 was also derived from the Appalachian old land, and since the 
 nature of the deposit suggests a similar origin of the later strata, 
 it does not seem amiss to consider that a similar eastward increase 
 in thickness originally obtained in the case of these higher strata as 
 well. This would make the Allegheny alone some 1,500 or more 
 feet in thickness in the Appalachian region, while the remaining 
 formations, if increased at the same rate, would aggregate 11,000 
 or 12,060 feet, making a total above the Pottsville in round num- 
 bers of about 13,000 feet of strata. This is not an improbable 
 thickness when we consider the 15,000 feet of late Tertiary delta 
 deposits of the Siwalik formation of India (see ante, Chapter 
 XIV). 
 
 CHARACTER AND THICKNESS OF THE DEFORMED MASS. On the 
 assumed elevation of about 3 miles for the entire area, Chamberlin 
 figures out the thickness of the part of the crust involved in the 
 folding. Since different sections have been differently affected, 
 he considers each independently with the following results : 
 
THICKNESS OF DEFORMED SECTIONS 
 
 905 
 
 Section Number 
 
 i 
 
 2 
 
 3 
 
 4 
 
 5a 
 
 5b 
 
 Original length of tract, in 
 miles (a) 
 
 17.8 
 
 16.3 
 
 13.56 
 
 14.44 
 
 9.6 
 
 5 
 
 Length after folding, in 
 miles (6) 
 
 14.0 
 
 15.2 
 
 12 . I 
 
 12. IO 
 
 7. VI 
 
 4 75 
 
 Mean elevation through fold- 
 ing in miles (c) 
 
 V4S 
 
 2. V] 
 
 2.88 
 
 2.71 
 
 2.16 
 
 c ye 
 
 Deduced thickness of crustal 
 block, in miles (x) 
 
 17.7 
 
 32.7 
 
 23-8 
 
 14.00 
 
 7.8 
 
 5-7i 
 
 be 
 The formula for ascertaining (x) is x = -~- f 
 
 The following diagram, copied from Chamberlin, shows the 
 location of the sections, the extent of the folding and the cal- 
 
 FlG. 250. Plot of the Tyrone-Harrisburg folded section, representing the 
 thickness of the deformed shell beneath each of the six blocks as 
 developed by Chamberlin's method of measurement. The lines 
 A-B and B-C are drawn through the middle points of the 
 bottom lines of each of these blocks, except section 2, the apex 
 block. The triangle G, B, F is drawn equal in area to the sum 
 of the triangles G, H, I and D, E, F. The whole deformed mass 
 appears, subject to the necessary limitations, to be the triangular 
 block A, B, C. (After R. D. Chamberlin.) 
 
 culated thickness of the block affected. (Fig. 250.) It shows 
 strikingly the fact that, where the crust is folded intensely, the 
 thickness of the crust involved is least ; where folding is slight, it is 
 
906 PRINCIPLES OF STRATIGRAPHY 
 
 greatest. In any case, folding is shown to be a superficial phenome- 
 non, a conclusion which must have an important bearing on the 
 mechanics of folding. As shown by the section, the eastern portion 
 suffered most, the western portion was the next most affected, while 
 the intermediate ones suffered the least. The form of the entire 
 block affected is that of a triangular prism, the lower bounding 
 planes being shear-zones. This is the form which such a block 
 should assume theoretically, two sets of planes of greatest tangen- 
 tial stress developing at right angles to each other, and approxi- 
 mately at an angle of 45 degrees to the direction of greatest pres- 
 sure, though varying with the nature of the material and other 
 factors. (Becker-i 150; Hoskins-2O '.865 ; Leith-27 -.121.) Experi- 
 ments by Daubree have shown this to be the type of fracture de- 
 veloped in compressed blocks where a triangular prism is developed 
 with faces approximately at 45 degrees to the direction of pressure. 
 In the experiment the prism was lifted without folding, the other 
 parts being thrust under it on both sides (Fig. 251). The exten- 
 sive development of over (or under) thrusts along the western 
 margin of the folded Appalachian region is quite in harmony with 
 this principle. It should, however, be mentioned here that there 
 is some evidence that the folds of the Appalachians were not purely 
 asymmetrical anticlines, modified by overthrust, but that the Ap- 
 palachians had originally a fanfold structure. 
 
 CHANGES DUE TO EXTRA-TELLURIC INFLUENCES. 
 
 The impact of a mass of meteoric matter upon the surface of 
 the earth would form an effective source of energy, which would 
 set into motion geological agents of vast magnitude. If the mass is 
 sufficiently large, as in the case of a satellite, a great displace- 
 ment of the earth's center of gravity would result, with the 
 attendant phenomena already outlined. If the earth were bom- 
 barded by a vast number of meteoric bodies, if, in other words, 
 a swarm of meteors should descend upon the earth, changes affect- 
 ing the entire earth might take place. Among these might be the all 
 but universal extermination of life, as well as the modification 
 of the lithosphere and hydrosphere, and perhaps the atmosphere 
 as well. The heat of impact might result in nearly universal nieta- 
 morphism of the rock masses of the earth, with the accompanying 
 destruction of the record of life in these rocks. It might be 
 asked if some such catastrophe may not have altered the surface 
 of the earth in pre-Carhbric time, inaugurating the forces which 
 
EXTRA-TERRESTRIAL CAUSES 907 
 
 produced the widespread metamorphism and exterminating most 
 of the organisms which had reached a high state of development 
 prior to the opening of Palaeozoic time. Such catastrophic occur- 
 rences are within the range of possibility, and, indeed, the rising 
 school of astro-geologists regards the origin of the earth itself as 
 due to accretion of planetary matter, rather than to the development 
 by condensation from an original nebular condition. If the accre- 
 
 FIG. 251. Prism of wax, deformed under pressure, between two iron plates 
 (B, B) and exerted in the direction shown by the arrows. Two 
 main sets of fissures are formed nearly at right angles to each 
 other (FF, f) leaving a triangular prism between them. RR, 
 plexus of fine fissures at right angles to one another. Scale 1 175. 
 (After Daubree from Haug.) 
 
 tion theory of earth-building, whether from planetesimals or from 
 meteorites, should become established, the recurrence of such an 
 event the repetition of the celestial bombardment to which the 
 earth owed its origin is brought within the range of probability, 
 and thus the stupendous problem of the origin of the great differ- 
 ence everywhere observed between the Cambric and the undoubted 
 pre-Cambric * rocks may be brought a step nearer solution. 
 
 * Some of the undisturbed clastic rocks now referred to the pre-Cambric 
 have not yet been proven to be such. The occurrence of disconformities between 
 Middle Cambric or late Lower Cambric and underlying unaltered sediments is 
 not conclusive evidence of the pre-Cambric age of these sediments, especially if 
 they are of continental origin. 
 
908 PRINCIPLES OF STRATIGRAPHY 
 
 BIBLIOGRAPHY XXIII. 
 
 (See also Bibliography xx, pp. 826-828.) 
 
 i. BECKER, G. F. 1893. Finite Homogeneous Strain, Flow and Rupture 
 of Rocks. Bulletin of the Geological Society of America, Vol. IV, pp. 13-90. 
 v/ 2. CHAMBERLIN, ROLLIN T. 1910. Appalachian Folds of Central Penn- 
 sylvania. Journal of Geology, Vol. XVIII, No. 3, pp. 228-251. 
 
 3. CHAMBERLIN, THOMAS C., and SALISBURY, ROLLIN D. 1906. 
 
 Geology, Vol. I. 
 
 4. CLAYPOLE, E. W. 1885. Pennsylvania Before and After the Elevation 
 
 of the Appalachian Mountains. American Naturalist, Vol. XIX, pp. 
 257-268. 
 
 5. DANA, JAMES D. 1895. Manual of Geology, 4th edition. American 
 
 Book Co. 
 ,/6. DARWIN, CHARLES. 1841. The Voyage of the Beagle. 
 
 7. DAVISON, CHARLES. 1905.^ A Study of Recent Earthquakes. Con- 
 
 temporary Science Series, London. 
 
 8. DILLER, J. S. 1889. Sandstone Dikes. Bulletin of the Geological 
 
 Society of America, Vol. I, pp. 411-442, pis. 6-8; with discussion by 
 Davis. 
 
 9. DUTTON, CLARENCE E. 1904. Earthquakes in the Light of the New 
 
 Seismology. New York and London. 
 
 10. FALB, R. 1871. Grundziige einer Theorie der Erdbeben und Vulcanen- 
 
 ausbriicke. Graz. 
 
 11. FALB, R. 1874. Gedanken und Studien uber den Vulkanismus, etc. 
 ,12. GILBERT, GROVE KARL. 1893. Continental Problems. Bulletin of 
 
 the Geological Society of America, Vol. IV, pp. 179-190. 
 
 13. GILBERT, G. K.; HUMPHREY, RICHARD; SEWELL, JOHN S., 
 
 and SOULfi, FRANK. The San Francisco Earthquake and Fire of 
 April 1 8, 1906, and their Effects on Structures and Structural Material. 
 United States Geological Survey Bulletin 324. 
 
 14. HAUG, EMILE. 1900. Les geosynclinaux et les aires continentales. Con- 
 
 tribution a 1' etude des transgressions et des regressions marines. Bulletin 
 de la societe geologique de France, 3rd series, Vol. XXVIII, pp. 617- 
 71 1, 3 figs. 
 
 15. HAUG, E. 1907. Traite de Geologic. T. I. 
 
 Vi6. HAY, ROBERT. 1892. Sandstone Dikes in Northwestern Nebraska. 
 
 Bulletin of the Geological Society of America, Vol. Ill, pp. 50-55. 
 VI 7. HOBBS, WILLIAM H. 1907. Origin of the Ocean Basins in the Light of 
 
 the New Seismology. Bulletin of the Geological Society of America, 
 
 Vol. XVIII, pp. 233-250, pi. 5. 
 
 1 8. HOBBS, W. H. 1907. Earthquakes. D. Appleton and Company, New 
 
 York. 
 
 19. HOERNES, RUDOLPH. 1893. Erdbebenkunde. Die Erscheinungen und 
 Ursachen der Erdbeben, die Methoden ihrer Beobachtung. Leipzig. 
 
 20. HOSKINS, L. M. 1896. Flow and Fracture of Rocks as Related to 
 
 Structure. Sixteenth Annual Report of the United States Geological 
 Survey, 1894-95, Pt. I, pp. 845-872, figs. 163-169. 
 
 21. HOVEY, E. O. 1909. Earthquakes: Their Causes and Effects. Pro- 
 
 ceedings of the American Philosophical Society, Vol. XLVIII, No. 192, 
 pp. 235-258. 
 
 22. JACOBITTI, EUGENIO. Mobilita dell 'Asse Terrestre. Studio Geologico. 
 
 Torino. 
 
BIBLIOGRAPHY XXIII 
 
 909 
 
 23. JOHNSON, WILLARD D., and HOBBS, W. H. 1908. The Earthquake 
 
 of 1872 in Owens Valley, California. Abstract: Science, N. S., Vol ^ 
 XXVII, p. 723- 
 
 23a. KOKEN, E. 1907. Indisches Perm und die permische Eiszeit. Neues 
 Jahrbuch fur Mineralogie, etc., Festband, pp. 446545, Map. 
 
 24. KOTO, B. 1893. On the Cause of the Great Earthquake in Central 
 
 Japan, 1891. Journal of the College of Science, Imperial University,'" 
 Tokyo, Vol. V, pp. 295-353, pis. XXVIII-XXXV. 
 
 25. KREICHGAUER, D. 1902. Die Aequatorfrage in der Geologic. Steyl. 
 
 26. LE CONTE, JOSEPH. 1902. Elements of Geology, 4th edition. D. 
 
 Appleton. 
 
 27. LEITH, C. K. 1905. Rock Cleavage. United States Geological Survey 
 
 Bulletin 239. 
 
 28. MARTIN, LAWRENCE. 1910. Alaskan Earthquakes of 1899. Bulle- 
 
 tin of the Geological Society of America, Vol. XXI, pp. 339-406, pis. 29-30. 
 
 29. MALLET. 1862. The Great Neapolitan Earthquake of 1857. 2 vols. 
 
 30. McGEE, W. J. 1893. A Fossil Earthquake. Bulletin of the Geological ^ 
 
 Society of America, Vol. IV, pp. 411-414. 
 
 31. MILNE, J. 1898. Earthquakes and Other Earth Movements. 4th 
 
 edition. 
 
 32. MONTESSUS DE BALLORE, F. DE. 1906. Les Tremblements de 
 
 Terre. Paris. 
 
 33. NEWSOM, JOHN F. 1903. Clastic Dikes. Bulletin of the Geological ^ 
 
 Society of America, Vol. XIV, pp. 227-268, pis. 21-31. 
 
 34. REIBISCH, PAUL. 1901. Ein Gestaltungsprincip der Erde. 27ter 
 
 Jahresbericht des Vereins fiir Erdkunde zu Dresden, 1901, pp. 105-124; 
 II, ibid., 1905, pp. 39-53- 
 
 35. ROSSI, M. S. DE. 1879 and 1882. La Meteorologia Endogena. 2 vols. 
 
 36. RUDOLPH, E. 1887-1898. Ueber submarine Erdbeben und Eruptionen. 
 
 Beitrage zur Geophysik. Vol. I, 1887, pp. 133-365, pis. IV-VII; Vol. II, 
 1895, PP. 537-666; Vol. Ill, 1898, pp. 273-336. 
 
 36a. SIEBERG, AUGUST. 1904. Handbuch der Erdbebenkunde. Braun- 
 schweig. 
 
 37. SIMROTH, HEINRICH. 1907. Die Pendulations-theorie. Leipzig. 
 
 38. SUESS, EUARD. 1875. Die Entstehung der Alpen. Vienna. 
 
 39. SUESS, E. 1886. Ueber unterbrochene Gebirgsfaltung. Sitzungsbe- 
 
 richte der koniglichen Akademie der Wissenschaften zu Wien. Bd. 
 XCIV, Abth. i, pp. 111-117. 
 
 40. SUESS, E. 1898. Ueber die Asymetrie der nordlichen Halbkugel. Ibid., 
 
 Bd. CVII, Abth. i, pp. 89-102. 
 
 41. TAYLOR, FRANK BURSLEY. 1903. The Planetary System. Pub- 
 
 lished by the author, Fort Wayne, Indiana. 
 
 42. THOMPSON, SIR WILLIAM. 1876. Report of the British Association. 
 
 Report of Section 81. 
 
 42a. VAN HISE, C. R. 1898. Earth Movements. Wisconsin Academy of 
 Arts, Sciences and Letters, Transactions, Vol. xi, pp. 465-516. 
 
 43. WHIMPER, EDWARD. 1892. Travels Among the Great Andes of the 
 
 Equator. 2nd edition. 
 
 44. WILLIS, BAILEY. 1893. Mechanics of Appalachian Structure. Thir- 
 
 teenth Annual Report of the United States Geological Survey, Pt. II, 
 pp. 211-281. (See also reference 30, on page 828.) 
 
 45. WOODWORTH, J. B. 1907. Postglacial Faults of Eastern New York, y 
 
 New York State Museum Bulletin 107, pp. 5-28, 5 pis. 
 
F. THE BIOSPHERE. 
 
 CHAPTER XXIV. 
 
 SUBDIVISION OF THE BIOSPHERE. CLASSIFICATION AND GEN- 
 ERAL MORPHOLOGICAL CHARACTERS OF ORGANISMS. 
 
 The organic world or biosphere falls naturally into two great 
 subdivisions or kingdoms, the phytosphere, or plant kingdom, 
 and the zoosphere, or animal kingdom, though organisms occur or 
 have occurred which are not readily placed in either division. 
 The detailed study of organisms has developed the sciences of 
 phytology (botany) and zoology, with its many subordinate sciences. 
 As ordinarily understood, these sciences deal with the plants and 
 animals of the present, or Holocenic, geological epoch, while those 
 of the many epochs of the earth's history anterior to the present 
 are reserved for the palaeontologist. Such a division, however, is 
 illogical, for the life of the earth has been continuous and its de- 
 velopment has been progressive from the earliest time to the 
 present day. The scientific palaeontologist can not neglect the study 
 of the existing organisms, nor can the scientific zoologist and botan- 
 ist, or student of the present living world, neglect the organisms of 
 the past. Palaeozoology cannot be divorced from zoology, nor 
 palaeobotany from botany. From the nature of the organic remains 
 of former periods it follows, however, that the palaeontologist lays 
 most stress upon the hard parts of organisms, or those capable 
 of preservation, in former as well as the present geological periods, 
 while the botanist and zoologist in the study of the modern floras 
 and faunas tend to lay more stress upon the soft tissues which 
 perish readily and so are not, or only rarely, preserved in the case of 
 ancient forms of life. 
 
 There are, however, good reasons for believing that the hard 
 parts of organisms form in some respects a more reliable index 
 to their relationship than do the soft parts. This is especially the 
 case in animals which build external hard parts which increase by 
 serial addition, without change of the older parts deposited. In 
 
 910 
 
THE ORGANIC WORLD 911 
 
 such cases we are certain to get a complete record of the individual 
 development of the animal from the youngest stages in which such 
 structures are formed to the adult or even old age stage. Thus, in 
 the case of the molluscan shell, for example, we have a complete 
 record of the individual development or ontogeny, all the changes 
 being indicated in the successive whorls or areas of the shell, from 
 the initial shell-plate to the adult. Moreover, such shells will 
 preserve the detailed features assumed necessarily hy the mantle 
 of the animal in conformity with development and increase of in- 
 ternal organs, features which are evanescent in the soft parts and 
 can in many cases not even be observed. 
 
 What has just been stated is true mainly of animals whose 
 hard parts are external structures, retained throughout life and 
 increased by addition in one region only. Such additions are recog- 
 nizable by the formation of growth lines, and they are typically 
 shown in the shells of the Mollusca, as already noted. Brachiopoda 
 also show such changes in external form but there are, in addition, 
 changes in interior structures, for the study of the development 
 of which a complete series of individuals, representing all the 
 stages, is needed. Corals likewise show their growth lines, and 
 sections made across the older part in most cases show the prog- 
 ress of development of the individual. Other invertebrates are less 
 satisfactory. While the serial development of parts can.be made 
 out in the plates of an adult echinoderm, yet the fact that each 
 plate changes with the progress of development interposes certain 
 difficulties 'in the study of the life history, and for its complete 
 determination individuals of various age stages are needed. This 
 is also true of the vertebrated animals where the internal skeleton or 
 external armor changes with the growth and development of the 
 individual, and where, therefore, skeletons of the young as well 
 as the adult are needed to determine the entire life history. 
 
 PLANTS AND ANIMALS AS INDICATORS OF THE AGE OF THE PERIOD 
 IN WHICH THEY OCCUR. 
 
 Since we have realized, by a prolonged study of modern as 
 well as ancient organisms, that animals and plants have gradually 
 increased in complexity of structure and diversity of form, from 
 the earliest times to the present, it has become possible to use the 
 remains of organisms embedded in the strata as indices of the 
 chronology of the earth's history, and by extensive collection of 
 facts from all geological levels, and over wide areas, to build up an 
 
9 i2 PRINCIPLES OF STRATIGRAPHY 
 
 organic succession which parallels the stratigraphic succession in 
 the development of the earth's crust. It has been found that cer- 
 tain groups of organisms did not extend beyond a certain time 
 period in the earth's history, and so their occurrence in the strata 
 indicates the upper age limit of these strata. Thus, trilobites are 
 known only from Palaeozoic formations hence the finding of one 
 of these extinct organisms stamps the strata in which it occurs 
 as of Palaeozoic age. More restricted occurrences of special forms 
 have made it possible to recognize the geological levels with greater 
 precision, thus the trilobite Paradoxides characterizes only the 
 Middle Cambric rocks of the earth's crust in certain regions, while 
 the trilobite Holmia characterizes the lower Cambric strata in the 
 same regions. Again, the Hydrozoan Dictyonema flabellifornie is 
 of world-wide distribution in the basal Ordovicic strata. Organisms 
 used in this manner become indices of geological horizons and, since 
 all but those of the present geological period occur only in fossil 
 form, the term ''index fossiF' is properly applied to them. This 
 subject will be considered further in a subsequent chapter. 
 
 CLASSIFICATION OF PLANTS AND ANIMALS. 
 
 The classification of plants and animals is a process of assort- 
 ment into natural groups, or groups of related types, and the ar- 
 rangement of these groups in a natural order, according to their 
 genetic relationship. Groups of various denominations are rec- 
 ognized, the smallest of those in general use being the spe- 
 cies. Smaller groups, known as varieties or as mutations, are, 
 however, included within the species. Species are grouped into 
 genera, each genus comprising one or more species. The generic 
 and specific name of an organism are always used together in 
 speaking of any particular species, since the same specific name 
 may be used for a species of another genus. Thus, the fossil brach- 
 iopod genus Productus includes among its many species Productus 
 muricatus. Likewise the fossil pelecypod genus Actinopteria has 
 among its species Actinopteria rnuricata, while another brachiopod 
 g-enus, Strophalosia, also has a species Strophalosia muricata. 
 These three species, though they have the same specific name, are 
 not at all related to each other, belonging to distinct genera, one 
 of which belongs to a different division or phylum of the animal 
 kingdom from that to which the other two belong. 
 
 Naming of genera and species. (18.) The generic name is 
 always a noun, and is commonly derived from the Greek, though 
 
PRINCIPLES OF TAXONOMY 
 
 913 
 
 generic names derived from the Latin are not uncommon. Names 
 compounded from the two languages are undesirable. The name 
 should always express some prominent character of the genus, as 
 Orthoceras, from the Greek opOos (orthos), meaning straight, and 
 Kfpas (ceras), meaning horn, the essential form of the genus 
 being that of a straight horn. Names are, however, not always 
 chosen with such direct meaning, while not infrequently the deriva- 
 tion of the name is obscure or fanciful. Proper names are fre- 
 quently chosen for generic names, as Hyattella for a genus of 
 brachiopods, the name being given in honor of the great American 
 palaeontologist, the late Alpheus Hyatt. In the formation of such 
 names the original name is reduced to the genitive case, and the 
 termination is in a (a, ia, iia, oia, cca, ella, etc.). When the original 
 name ends in y this letter is treated as a consonant and the termina- 
 tion is added. Example : from Gray we may derive Grayia, Gray- 
 ella, Graysia, etc. In all cases the form of the word must be the 
 Latin form, the Latin equivalent of the original Greek being used. 
 The gender of the generic name is the same as in the language 
 from which it is derived. If the generic name is a compound of 
 two or more words, the terminal word determines the gender. 
 Thus, in Orthoceras, the terminal ceras is neuter in the Greek, and 
 hence all names ending in this manner are neuter. The same is 
 true of the words nema (thread), stoma (mouth}, and desma 
 (band), often employed as endings. Special uniform endings are 
 often employed in the naming of genera within certain classes, such 
 endings having reference to the class. Thus pora and phyllum are 
 the common terminations for corals, the former being used in the 
 poriferous corals, as Aulopora, Syringopora, Tubipora, etc., and 
 the latter in the septate corals, especially the Tetraseptata ; example : 
 Cyatho phyllum, Heterophyllum, etc. In graptolites the termination 
 graptus is common. In Cystoidea, Blastoidea, Crinoidea and Echi- 
 noidea the common terminations of the generic names are cystites, 
 blastus, crlnus, and echinus, respectively, though these are by no 
 means exclusively employed. Examples are : Pleurocystitcs, Crypto- 
 blastus, Encrinus, Eucalyptocrinus, etc., and Rhocchinus. In 
 Bryozoa trypa and pora are frequent endings ; example : Callotrypa, 
 Bythopora. In Cephalopoda ceras is the prevailing termination, as 
 in Orthoceras, Gephyroceras, Phylloceras, Lytoceras, etc., though 
 in some orders of ammonites (e. g., Discocampyli) the termination 
 ites is the prevailing one ; example : Ceratites, Stephanites, etc. 
 Among Reptilia saurus is a common termination ; example : Mosa- 
 saurus, Stegosaurus, etc., and names of fossil birds not infrequently 
 
9 i4 PRINCIPLES OF STRATIGRAPHY 
 
 have the termination pteryx (wing); example: Archa>optcry.\-, 
 Megalopteryx, etc. 
 
 The generic name is always written with an initial capital. 
 Specific names, on the other hand, have the value of adjectives and 
 should always be written with a small initial letter, even though 
 they are derived from proper names. It should be noted, however, 
 that this rule is not universally accepted. 
 
 The gender of the specific name, as expressed in its termination, 
 should agree with that of the generic name. Thus, the specific name 
 in the above examples is miiricatus in Productus, which is mascu- 
 line, and nmricata in the other two genera, which are feminine. 
 In general, the specific name is derived from the Latin, while all 
 other words are rendered in the Latin form. Names of persons 
 are frequently used for the formation of specific names, an appro- 
 priate termination being added. Geographical names likewise are 
 commonly used for the formation of specific names. The more 
 common terminations of specific names thus derived are : anus, a, inn 
 (pertaining to), as americanus, linnccanus; further, ensis, is, e (be- 
 longing to a locality), as cincinnatiensis, canadcnsis, chicagoensis, 
 kentuckiensis (final a or e when occurring in the original word is 
 dropped and terminal y changed to i) ; and, finally, i as halli, 
 knighti, etc., a common termination for names derived from per- 
 sons. Common terminations for names derived from other words 
 are : atus, a, uwi, as costatus, lobatus, galeatus; formis, is, e, as 
 tubiformis, filiciformis, etc. ; inns, a, urn, - ex : rugatinus; oides 
 (added only to words derived from the Greek), as discoides, etc., 
 and others. 
 
 Priority and Synonymy (13; 14; 15). Since there is such a 
 vast number of specific names in natural history, and since it often 
 happens that the same species receives distinct names by different 
 authors, owing to ignorance or ignor'ance of each other's works, it 
 is necessary to have a fixed standard by which the name which is 
 to survive is invariably chosen. The standard is priority the name 
 used in the first description of the species being adopted, even if a 
 later proposed name is more suitable. All later names become 
 synonyms. In certain cases, however, exceptions to this rule are 
 allowed. Thus, if the original description is too poor, so that 
 the true characters of the genus and species cannot be ascertained, 
 a later name, proposed with a better description or illustration, is 
 often accepted. Where a name has long been in general use the 
 discovery of a prior name ought not to overthrow the established 
 usage, especially if the older name has itself come into use for 
 another species. Thus Spirifer mucronatus has become the widely 
 
PRIORITY AND SYNONYMY 
 
 915 
 
 accepted name for the species described by Conrad as Delthyris 
 miicronata in 1841. One of the numerous varieties of this species 
 had, however, been described by Atwater in 1820 as Terebratula 
 pennata, and it has hence been argued that Spirifer pennatus and 
 not Spirifer mucronatus should be the name of the species. Spirifer 
 pennatus has, however, come into use for another species, described 
 under that name by Owen in 1852. The adoption of Atwater's 
 name requires not only the discarding of a well-known and appro- 
 priate name, but also requires the substitution of another name 
 for Owen's Spirifer pennatus. This strict adherence to the rule of 
 priority in this case would lead to so much confusion that it is much 
 better to make an exception and retain the names which have been 
 so extensively used in the literature. 
 
 In the example cited, the name pennatus has been given to two 
 species of Spirifer by different authors. That we may know which 
 species is meant, it is necessary to write the name of the author 
 after the specific name. Thus, in the case cited, the names should 
 be written : Spirifer pennatus (Atwater) and Spirifer pennatus 
 Owen. This custom of adding the author's name is a general one, 
 and should always be observed in all but the most general dis- 
 cussions. When the author of the species has placed it in the 
 wrong genus, or if the species is subsequently referred to a new 
 genus, the author's name after the species is placed in parentheses, 
 and frequently the name of the person who first placed the species 
 in the correct genus is added. Thus, in the examples cited above, 
 Conrad described his species under the generic name Delthyris, but 
 it belongs to the genus Spirifer ; hence the name is written Spirifer 
 mucronatus (Conrad). Since Billings was the first to place the 
 species in the genus Spirifer, his name may be added, viz., Spirifer 
 mucronatus (Conrad) Billings; but this method is not always 
 adopted. Sometimes the form Spirifer mucronatus Conrad sp. is 
 used. 
 
 Synonymy. 
 
 No genus can have two species of the same name. If two 
 authors describe, under the same name, two different species of the 
 same genus, the one to which the name was first applied retains it, 
 the name becoming a synonym so far as the other species is con- 
 cerned; for this later-described species a new name must be pro- 
 posed. When reference to the first-described species is made, it is 
 often desirable to note the fact that the name has been applied to 
 another species to avoid possible confusion. Thus Dunker in 1869 
 
916 PRINCIPLES OF STRATIGRAPHY 
 
 described and named Fusus meyeri, a modern species, and Aldrich 
 in 1886 described a Tertiary species as Fusus meyeri. Reference to 
 the former would thus be made as follows : Fusus meyeri Dunker 
 1869 (non Aldrich 1886). Since Aldrich considered his species a 
 true Fusus he was forced to change its name on discovering that 
 the name had been preoccupied for that genus. So in 1897 he pro- 
 posed the name Fusus ottonis for this species. It appeared, how- 
 ever, that Aldrich's species is not a true Fusus, but belongs to a 
 series of distinct origin. The name Falsifusus (Grabau) was, 
 therefore, proposed for it, with the present species as the type, 
 and, since this genus has no other species by the name of meyeri, 
 it became proper to retore that specific name to its original rank. 
 Thus we now have the synonymy of this species as follows (omit- 
 ting references to authors which did not change the name) : 
 
 FALSIFUSUS MEYERI (Aldrich) Grabau. 
 
 1886 Fusus meyeri Aldrich * 
 
 not Fusus meyeri Dunker, 1869 
 
 1897 Fusus ottonis Aldrich 
 
 1904 Falsifusus meyeri Grabau 
 
 In this case the specific name ottonis not only becomes a syno- 
 nym, but, so far as Fusus is concerned, it is dead and cannot be 
 used again, even for a new species of Fusus. Unless this rule is 
 observed much confusion is likely to arise. Should the generic 
 name Falsifusus be found invalid, however, the type species Falsi- 
 fusus meyeri being proved a true Fusus after all, the specific name 
 ottonis will have to be restored to its original rank, the species in 
 question being then Fusus ottonis. The general rule is that no spe- 
 cific name which has become a synonym in a genus can ever be 
 used again for another species of that genus, though it may be 
 used for species of other genera. If an old comprehensive species 
 is divided into a number of species the original name is retained 
 for that subdivision to which it was originally applied, or to which 
 the diagnosis corresponds most closely. For the other subdivisions 
 new names must be proposed. If two authors describe the same 
 species under different names, the name given in the earlier de- 
 scription is retained, the other one becoming a synonym. If a spe- 
 cies is transferred from one genus to another, in which there is 
 already a species of that name, that one of the two species to which 
 the specific name in question was first applied retains it, while the 
 
 * The dotted lines take the place of the reference to the literature where 
 this name was used. 
 
NOMINA NUDA 917 
 
 other species takes the oldest tenable synonym applied to it, if such 
 exists, otherwise it receives a new name.* 
 
 Manuscript Names, List Names (Nomina Nuda). Sometimes 
 authors propose names in manuscript, or in lists with the intention 
 of giving descriptions later, but the manuscripts are not published 
 or the descriptions not written. Such a nomcn nudum has no 
 standing, unless a subsequent describer chooses to adopt it and 
 give the original proposer credit for the name. Thus U. P. James 
 in 1871 listed Ambonychia costata in his catalogue of Lower Silu- 
 rian (Ordovicic) Fossils of the Cincinnati group, proposing the 
 name without description. Meek in 1873 described the fossils for 
 which James had proposed the above name, which Meek adopted, 
 and credited to James. In this case the description was based on 
 the material originally named by James, so that there could be no 
 question regarding the applicability of the name. Even so, many 
 subsequent writers have credited the name costata to Meek, refus- 
 ing to recognize James' claim to priority. In general, manuscript 
 names and list names are best discarded. 
 
 Generic Names as Synonyms, As a general rule, a generic name 
 can be used but once in natural history, even if the genus to be 
 named belongs to a wholly distinct phylum of the animal or plant 
 kingdom. Thus in 1835 Swainson proposed the generic name 
 Clavella for an Eocenic gastropod shell, but this name had been 
 preoccupied in 1815 by Oken for a crustacean^ The name Clavi- 
 lithes was therefore proposed by Swainson in 1840 for his shell. 
 Many authors, however, consider that preoccupation of a name 
 disqualifies it for subsequent use only if both cases are within the 
 same phylum, and in the case cited Clavella is retained by some 
 for the gastropod as well as for the crustacean. The stricter rule, 
 however, which allows one name to be used once only is the better, 
 since it avoids all ambiguity. f When species described under differ- 
 ent generic names are found to belong to one genus, the oldest of 
 the generic names applied to them is retained, the others becoming 
 synonyms. Such synonyms ought not to be used again, but rele- 
 gated to the limbo of invalid terms. If, however, the supposed 
 generic identity of the species is shown to be untenable, the original 
 name or names must be restored to rank. Thus naturalists have 
 commonly regarded the generic name Cyrtulus, proposed by Hinds 
 
 *For further extensive discussion of this question see recent numbers of 
 Science. 
 
 t For the generic names used in zoology up to 1879, see Scudder (25). For 
 those used subsequently see the annual lists published by the Zoological Society 
 of London in the Zoological Record (complete index every ten years, 1865-1906), 
 continued in tehe International Catalogue of Scientific Literature since 1907. 
 
918 PRINCIPLES OF STRATIGRAPHY 
 
 in 1843 for a modern gastropod, as a synonym of Clavilithes, pro- 
 posed by Swainson in '1840 for a Tertiary one, and relegated the 
 name Cyrtulus to the limbo of dead terms. As the types of these 
 genera are, however, widely distinct, the name Cyrtulus must be 
 restored to its original significance. 
 
 When a genus includes several distinct groups of species, each 
 of which is subsequently raised to the rank of an independent genus, 
 the original name should be retained for the group considered 
 most typical by the original author, or corresponding best to his 
 diagnosis. New names must be given to the other groups. Thus 
 the name Clavilithes has been restricted to that group to which 
 the generic characters, as described by Swainson, best correspond 
 (C. parisiensis, etc.), while another group included by Swainson 
 under the same generic name has been separated under the term 
 Rhopalithes (R. noa, etc.). 
 
 TYPES. 
 
 A type in natural history is the material used in describing, 
 defining, and illustrating a species or genus, etc. Two kinds of 
 types are recognized Primary or Proterotypes and Secondary or 
 Supplementary types or Hypotypes (Apotypes). Typical specimens 
 (Icotypes) not used in the literature, but serving a purpose in 
 identification, are further recognized. 
 
 Terms Used for* Specific Types. The following terms have 
 been proposed and have come into more or less general use (24) 
 for types of species: 
 
 I. Primary types (Proterotypes). 
 
 a. Holotypes. 
 
 b. Cotypes (Syntypes). 
 
 c. Paratypes. 
 
 d. Lectotypes, 
 
 II. Supplementary types (Hypotypes or Apotypes). 
 
 e. Autotypes (Heauto types). 
 
 f. Plesiotypes. 
 
 g. Neotypes. 
 
 III. Typical specimens (Icotypes). 
 h. Topotypes. 
 i. Metatypes. 
 j. Idiotypes. 
 k. Homoeotypes. 
 1. Chirotypes. 
 IV. Casts of Types (Plastotypes). 
 
CLASSIFICATION OF TYPES 919 
 
 I. Among the primary types a holotype is the original speci- 
 men selected as the type, and from which the original description 
 (protolog), or the original illustration (protograph), is made. 
 A cotype (syntype) is a specimen of the original series when there 
 is no holotype, the describer having' used a number of specimens 
 as of equal value. 
 
 A paratype is a specimen of the original series when there is a 
 holotype. When the original describer selected one specimen out 
 of the number used to be the type par excellence, i. c., the holotype, 
 the remainder of the specimens used in the original description con- 
 stitute the paratypes. 
 
 A lectotype is a specimen chosen from the cotypes subsequently 
 to the original description to represent the holotype. 
 
 II. Among the supplementary types : 
 
 An autotype (heautotype} is a specimen not belonging to the 
 primary or proterotype material and identified with an already 
 described and named species and selected by the nomenclator him- 
 self for the purpose of further illustrating his species. 
 
 A plesiotype is a similar specimen but selected by some one 
 else than the original describer of the species. 
 
 A neotype is a specimen identified with an already described 
 and named species, and selected to represent the holotype in case 
 the original material (all the proterotypes ) is lost or too imperfect 
 for determination. A neotype must be from the same locality and 
 horizon as the holotype or lectotype which it represents. 
 
 III. Among typical specimens or Icotypes: 
 
 A topotype is a specimen (hot used in the literature) from the 
 same locality and horizon as the holotype or lectotype. 
 
 A metatype is a topotype identified by the nomenclator himself. 
 
 An idiotype is a specimen (not used in the literature) identified 
 by the nomenclator himself, but not from the original locality or 
 horizon of the holotype or lectotype with which it is identified, i. e., 
 not a topotype. 
 
 A homotype (homocotype) is a specimen (not used in the litera- 
 ture) identified by a specialist, after comparing with the holotype 
 or lectotype. 
 
 A chirotype is a specimen upon which a chironym or manuscript 
 name (a name never published) is based. 
 
 IV. Casts of type material (plastotypes) may be used or not 
 in descriptions or illustrations. They are accordingly holoplasto- 
 type or any other protoplastotype. Hypoplastotypes and icoplasto- 
 types also may be made, but are generally of comparatively little 
 value. 
 
920 PRINCIPLES OF STRATIGRAPHY 
 
 GENERIC TYPES. Species upon which genera are based are 
 genotypes* Three kinds of genotypes may be recognized : 
 
 Genoholotype the original species on which the genus is 
 founded, or the species selected by the author from those originally 
 described as the type of the genus. 
 
 Genosyntype one of a series of species upon which a genus is 
 founded when there is no genoholotype. 
 
 Genolectotype a species subsequently selected from the geno- 
 syntypes to represent the genoholotype. 
 
 Selection of the Genotype or Type Species of a Genus. 
 
 Many genera are monotypic, i. e., had only one species when 
 founded, though others may subsequently have been referred to 
 them. The original species upon which the genus is founded in 
 such a case is the true genotype or genoholotype. When a genus 
 is founded on a group of species (heteiotypic) the originator of 
 the genus should select one species as the genoholotype. This has 
 not always been done, especially in the case of the older genera, 
 the genus being founded on a group of species or genosyntypes de- 
 scribed at the same time. It then becomes the duty of the first re- 
 viser of the genus to select the type species (genolectotype) from 
 the original species (or genosyntypes). Two principal methods 
 are used by naturalists in such cases the first species method and 
 the elimination method. The first of these methods appears to be 
 the simplest one, since the species first described by the author of 
 the genus is taken as the type. It sometimes happens, however, 
 that the first species is not the most typical of the genus as defined 
 by the author, or it may have been subsequently separated from the 
 other species and perhaps placed in a genus by itself, the diagnosis 
 of which differs from the original one, or is more circumscribed 
 than it. In such a case it is the practice to choose the genolectotype 
 from the remaining species of the original group. Often several 
 sections have been separated from the original group and placed in 
 distinct genera. By this process of elimination the genotype thus 
 becomes restricted to the remaining species (genosyntypes), one of 
 which must be selected. This selection is to be done by the first 
 reviser of the old genus and his designation of the genolectotype 
 will stand. Occasionally it may happen that all the original species 
 have been removed to new genera, in which case the last one so 
 
 * This name has recently been employed by zoologists and botanists in a very 
 different sense (see Osborn-i9), 
 
HIGHER GROUPS THAN GENERA 921 
 
 removed is to be taken as the type of the restricted genus, the new 
 name applied to it becoming a synonym. 
 
 The application of the first species rule to the determination 
 of the type of the genus may lead to a great many unnecessary and 
 undesirable changes, but where possible it is best applied, as being 
 the most readily carried out. Where, however, this would lead to 
 confusion in the nomenclature, the elimination rule is best followed. 
 (For illustration and discussion see Stone-26; Allen-i2 and sub- 
 sequent articles in Science.) 
 
 Union of Genera into Groups of Higher Taxonomic Value. 
 
 Sub-families, Families, Super-families. Genera are united in- 
 to families, the name of the family being generally derived from its 
 principal genus or the one longest known. The termination of 
 families in zoology is generally idee (short i), as Terebratulidce 
 from Terebratula. Families are often divided into sub-families, 
 the names of which terminate in incc (long i), as Terebratulincc. In 
 Botany the family generally ends in acece, as Rosacecc, but there are 
 a number of exceptions to this rule. Sub-families in botany end 
 in ea or inece, the name in each case being derived from the prin- 
 cipal genus. Super-families in which a small group of related 
 families are united, are sometimes made use of. The names of 
 these end in acea, the name being derived from the principal family. 
 Ex. : Terebratulacea. 
 
 Sub-orders, Orders. The important division of next higher 
 rank is the order, which often comprises a number of sub-orders. 
 The names of these divisions have no uniform ending in zoology, 
 though the terminal letter is commonly a, the termination ata being 
 most common. Other terminations are : ia, oida or oidea, acea, era, 
 etc. In botanical nomenclature the orders end in ales. 
 
 Groups of Higher Rank. Above the orders we have in ascend- 
 ing rank: (super-orders}, (sub-classes) classes, (sub-types) phyla 
 (or types), sub-kingdom, kingdom. When a taxonomic division 
 of higher rank takes its name frojn a genus the name of which is 
 afterward found to have been preoccupied, and so has to be 
 changed, the name of the higher division must also be changed. 
 
 The law of priority is not strictly applied to names of divisions 
 of higher rank than genera, since newly discovered facts often 
 make a change in the classification necessary when the substitution 
 of a new for an old term becomes desirable. A uniform termina- 
 tion for the names of divisions higher than families is much to be 
 desired. 
 
922 PRINCIPLES OF STRATIGRAPHY 
 
 Faunas and Floras. An association of all the animals in a given 
 locality constitutes the fauna of that locality, while a similar associa- 
 tion of the plants produces the flora. In the study of past geologic 
 epochs it is often necessary to speak of the totality of animal or 
 plant life in any given formation. This constitutes the fauna and 
 flora, respectively, of that formation. It matters not whether the 
 formation is great or small whichever is considered all the animal 
 remains found in that formation together make up the fauna of 
 that formation, and all the plant remains constitute its flora. To 
 designate the fauna and flora of a time period we may conveniently 
 employ the terms chronofauna and chronoflora, or chronobios for 
 both. Each chronofauna or flora comprises numerous geographic 
 faunas or floras, and these may be designated the loco fauna and 
 locoftora, or, in its entirety, the locobios. We must, of course, 
 realize that the terms fauna and flora refer to the assemblage of 
 animal and plant life as a whole, in the time-period of the forma- 
 tion, and at the locality where the formation now occurs, and that 
 therefore the fossil remains of a given bed do not adequately 
 represent the fauna or flora of that time, since many types have 
 not been preserved. Hence the term fossil faunas is useful as in- 
 dicating that only a certain portion of the original fauna, i. e., that 
 preserved as fossils, is spoken of. Thus we may speak of the fossil 
 fauna of the Hamilton period of western New York, by which 
 we would mean that portion of the western New York loco fauna of 
 the Hamilton chronofauna which has been preserved. 
 
 TABLE I. SUBDIVISIONS OF THE PLANT KINGDOM. 
 
 Phanerogamous plants. 
 PHYLUM V. SPERMATOPHYTA or seed plants. 
 
 Class 2. Angiosperma (covered seed-plants). 
 Sub-class 2. Dicotyledoneae (seed-leaves 2). 
 Sub-class i. Monocotyledonese (seed-leaves i). 
 Class i. Gymnospermce (naked-seeded plants). 
 Order V. Ginkgoales 
 Order IV. Gnetales (joint firs). 
 Order III. Coniferales. 
 Family 2. Pinaceae. 
 Family i. Taxaceae. 
 
 Order II. Cycadales (cycads, sago palms). 
 Order I. Cordai tales (Cordaites). 
 
 Cryptogamous plants. 
 
 PHYLUM IV. PTERIDOPHYTA or Fern Plants (Vascular Cryptogams). 
 Class 6. Felicince. 
 
 Order IV. Marattiales (Ringless Ferns). 
 Order III. Feliciales (True Ferns). 
 

 CLASSIFICATION OF PLANTS 923 
 
 Order II. Cycadofiliciales. 
 
 Order I. Hydropteridiales. 
 Family 2. Salviniacese. 
 Family I. Marsiliaceae. 
 Class 5. Ophioglos since. 
 
 Order I. Ophioglossales. 
 Class 4. Lycopodince. 
 
 Order IV. Isoetalcs. 
 
 Order III. Lepidodendrales. 
 Family 2. Sigillariaceae. 
 Family I. Lepidodendraceas. 
 
 Order II. Selaginellales. 
 
 Order I. Lycopodiales (Club-mosses). 
 Class 3. Psilotina. 
 
 Order I. Psilotales. 
 Class 2. Sphenophyllincz. 
 
 Order II. Cheirostrobales. 
 
 Order I. Sphenophy Hales. 
 Class i. EquisetincB 
 
 Order II. Equisetales (Horsetails)-. 
 
 Order I. Calamariales (Calamites). 
 
 PHYLUM III. BRYOPHYTA or Moss-plants. 
 Class 2. Musci (Mosses). 
 Order IV. Bryales. 
 Order III. Phascales. 
 Order II. Andreacales. 
 Order I. Sphagnales (Peat-moss). 
 Class i. Hepatic (Liverworts). 
 
 PHYLUM II. THALLOPHYTA or Thallus plants. 
 C, LICHENS. 
 
 Class 2. Basidiolichenes. 
 Class i. Ascolichenes. 
 
 Sub-class 2. Discholichenes. 
 
 Sub-class i. Pyrenolichenes. 
 B. FUNGI. 
 
 Class 2. Mycomycetes (True Fungi). 
 
 Order III. Basidiales (Mushrooms, etc.). 
 
 Order II. Ascomycetes (Mildews). 
 
 Order I. Ustilaginales. (^cidiomycetes, rusts). 
 Class i. Phyco-mycetes (Algo-fungi). 
 
 Order II. Zygomycetes. 
 
 Order I. Oomycetes. 
 A. ALG/E. 
 
 Class 3. Rhodophycea (Red algae). 
 Class 2. Pk&ophycecs (Brown algae). 
 
 Order IV. Euphseophyceae. 
 
 Order III. Cryptomonadaceas. 
 
 Order II. Diatomaceae. 
 
 Order I. Peridiniaceae. 
 
924 PRINCIPLES OF STRATIGRAPHY 
 
 Class i. Chlorophyceoe. (Green algae). 
 Order III. Characeae. 
 Order II. Euchlorophyceae. 
 Order I. Conjugataceae. 
 PHYLUM I. PROTOPHYTA. 
 
 Class 3. Myxomycetes (Slime-molds), sometimes regarded as Protozoa 
 
 (Mycetozoa). 
 
 Class 2. Flagellata (more generally regarded as Protozoa). 
 Class i. Schizophyta. 
 
 Order II. Cyanophyceae (Blue-green algae). 
 Order I. Schizomycetes (Bacteria). 
 
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THE BIOSPHERE 933 
 
 BRIEF SUMMARY OF THE MORPHOLOGICAL CHAR- 
 ACTERS OF THE PHYLA OF PLANTS 
 AND ANIMALS. 
 
 A. PLANTS. 
 
 PHYLUM I PROTOPHYTA. This division is not often employed, 
 the members here classed under it being referred either to the algse 
 or to the fungi. It is, however, a convenient division for those 
 simple plants which have not the true characters of either of the 
 other two groups. In this group are placed organisms which com- 
 bine characteristics of both plants and animals. Such are the 
 Flagellata, which more generally are placed among the Protozoa, 
 and the Myxomycetes, which are also regarded by some zoologists 
 as Protozoa under the name Mycetozoa. The Flagellata are aquatic, 
 and so named from the fact that their dominant phase is a "flagel- 
 lula" or cell-body provided with one, few, or, rarely, many, long, 
 actively vibratile processes. They are attached or free and some of 
 them (Volvocacece, etc.) develop chlorophyll, and in this, and in 
 the mode of multiplication, they have the characters of undoubted 
 unicellular plants. Some types placed here (Coccolithophoridcc} 
 (Fig. 104) have their bodies invested in a spherical test strength- 
 ehed by calcareous elements or tangential circular plates which are 
 variously named coccoliths, discoliths, cyatholiths, or rods called 
 rhabdoliths. These are often found in the Foramini feral ooze 
 and in chalk. 
 
 Flagellates are frequently considered as forming the starting 
 point for unicellular plants on the one hand and Protozoa on the 
 other. That they have given rise to both groups is held by good 
 authorities. The largest species range up to 130^ in length, ex- 
 clusive of the flagellum, though a large number of them rarely 
 exceed 2O/x in length. 
 
 The Myxomycetes (Mycetozoa), or slime molds, are sometimes 
 classed with the Fungi and also with the Protozoa. They are ter- 
 restrial and devoid of chlorophyll and reproduce by spores, which 
 are scattered by the air, as in Fungi. The spore hatches out as a 
 mass of naked protoplasm, which assumes a free-swimming flagel- 
 late form, multiplies by division, and then passes into an amoeboid 
 stage. By fusion of many amceboids the plasmodhun is formed, 
 which is a mass of undifferentiated protoplasm without envelope and 
 endowed with the power of active locomotion. It penetrates de- 
 caying vegetable matter or spreads over the surface of living fungi, 
 
934 PRINCIPLES OF STRATIGRAPHY 
 
 and may reach an expanse of several feet, though generally small. 
 
 The Schizophyta form a group distinct from the preceding and 
 unconnected with them or higher types. Bacteria are minute uni- 
 cellular plants, devoid of chlorophyll, and multiplying by repeated 
 division. In form they are spherical, oblong, or cylindrical, often 
 forming filamentous or other aggregates of cells. The absence 
 of an ordinary nucleus, of the ordinary sexual method of repro- 
 duction, and the manner of division, unite them with the Cyano- 
 phycece, or blue-green algae. Some forms (Sarcina) show relation- 
 ship to, or analogies with, green algae (Palnicllacea), while others 
 suggest relationship to myxomycetes. Again, certain features sug- 
 gest some flagellates and many forms exhibit a power of indepen- 
 dent movement when suspended in a fluid. The group is no doubt a 
 heterogeneous one, including at present primitive forms of many 
 types of plants. Their size is commonly i/w.* in diameter and 
 from two to five times that length, though smaller and larger forms 
 are known. They occur fossil since Devonic and probably earlier 
 time. 
 
 The Cyanophycece are unicellular or multicellular and contain, 
 besides chlorophyll, a blue-green coloring matter, hence their name, 
 though the actual color of some ranges from yellows to browns, 
 reds, purples, or violets of all shades. Generally the single cells 
 are held together in a common jelly. Some members of this division 
 secrete lime (Gloeocapsa, Gloeothece) and serve to build up con- 
 siderable deposits (see organic oolites, Chapter XI). Nearly a 
 thousand species of Cyanophycese are known. No fossil representa- 
 tives are known, though they must have existed in earlier ages. 
 
 PHYLUM II THALLOPHYTA. The vegetative portion of these 
 plants consists of one or many cells forming a thallus, often 
 branched. There is no differentiation of the body into a root, 
 stem, or leaf, while the internal structure is comparatively simple. 
 Both sexual and asexual reproduction take place. In many classi- 
 fications the Bacteria, the Cyanophycecc, and the Myxomycetes are 
 also classed here, and, besides them, the following classes are made : 
 i. Peridinecu, 2. Conjugate, 3. Diatomacece (Diatoms), 4. Hetero- 
 contecu, 5. Chlorophycecc (Green algae), 6. Characea? (Stoneworts), 
 7. Rhodophycecc (Red algae), 8. Eumycetes (Fungi), 9. Phycoin\- 
 cetes (Algal fungi), 10. Phccophycecc (Brown algae). The older di- 
 vision into the three classes of a, Alga, bearing Chlorophyll ; b, 
 Fungi, without Chlorophyll ; and c, Lichens, symbiotic colonies of 
 algae and fungi, is the most familiar and will be used here. 
 
 * One micromillimeter or o.ooi mm. 
 
PLANTS. THALLOPHYTA 935 
 
 a. Alga. 
 
 Algae, or seaweeds, are thallophytes characterized by the pres- 
 ence of Chlorophyll, or leaf-green, though the color is by no means 
 always green. They are largely aquatic in habitat, most of the more 
 striking forms occurring in the sea. According to the prevailing 
 color, three divisions are made the Green Algae, or Chlorophycccc; 
 the Brown Algae, or Phaophycece; and the Red Algae, or Rhodo- 
 phycea. The Cyanophycece, or blue-green algae, are also frequently 
 included under the algae. 
 
 The Chlorophycecc include three forms in which the chlorophyll 
 is not accompanied by other coloring matter. With the typical 
 green algae (Euchlorophycece) are generally included the divisions 
 Conjugatacece and Characea, which have a separate phyletic stand- 
 ing. The common green sea-lettuce, Ulva, is a good example of an 
 expanded form, but in many of the green algae (especially the Con- 
 fervales), the thallus consists of filaments, branched or unbranched, 
 attached at one extremity and growing almost wholly at the free 
 end. Some forms (Halimeda, Acetabularia, etc.) are encrusted 
 with lime and are important on "coral" reefs. The Pond-scums, 
 or Conjugates (so named from their method of reproduction) in- 
 clude the Desmids, which have the power of independent move- 
 ment. 
 
 Quite distinct from the others are the Characece, the most highly 
 differentiated of the green algae. Of these the common stonewort, 
 Chara, growing in fresh water lakes, is. the typical form. This is 
 attached to the bottom of pools by rhizoids and grows upward by 
 means of an apical cell forming a pointed axis, which gives off 
 whorled appendages at regular intervals. Long branches occur in 
 each whorl, and these give off secondary whorls of jointed ap- 
 pendages. The distance between the nodes from which the ap- 
 pendages arise may be several centimeters. All are encrusted with 
 lime. The reproductive organs are also highly differentiated. 
 Antheridia and oogonia are formed at the nodes of the appendages. 
 The egg cells, or oogonia, when ripe are surrounded by five spirally 
 twisted cells, and crowned by a circle of smaller ones, which after- 
 ward separate to allow fertilization. The outer cells become very 
 hard and calcareous and are extensively preserved, in some cases 
 contributing to the formation of limestones. 
 
 Over i, 600 species of true green algae are known. The Pond 
 Scums, or Conjugate, add nearly 1,300 species more, while the 
 stoneworts, or Characeae, are represented by only about 180 species, 
 making a total of over 3,000 species. 
 
936 PRINCIPLES OF STRATIGRAPHY 
 
 The Phceophycece, or brown algae, are distinguished by the pos- 
 session of a brown coloring matter in addition to the chlorophyll. 
 The Peridiniacece and Diatomacea are included here, together with 
 the Cryptomonadacea, all of them unicellular plants with little ex- 
 cept color in common with the true brown algae (Eupluzophycece), 
 which are multicellular. Familiar examples of the last class are 
 Fucus, Laminaria, and Sargassum. The kelps (Laminar ia) de- 
 velop large round "stems" which branch root-like at the base and 
 have an oar-like expansion at the top. The rock-weeds (Fucus) de- 
 velop air-bladders which serve for purposes of flotation. They 
 are attached to the rock by means of a disc or root-like expansion ; 
 have a stem of rough leathery texture which forks regularly; and 
 are expanded in a leaf-like manner with thick mid-ribs. The Gulf- 
 weeds (Sargassum) have distinct stems, leaves, and stalked air- 
 bladders, and strikingly resemble land plants. 
 
 The diatoms are microscopic unicellular plants of a yellow or 
 reddish-brown color, and not closely related to the other algae except 
 perhaps to the desmids. The cell wall is impregnated with silica, 
 so that its shape is preserved after the death of the plant. The 
 "shell" consists of two parts, one overlapping the other like a pill- 
 box and cover. These show great variety of form and have the 
 power of locomotion. 
 
 Of the true brown algae there are only about 620 species. The 
 Peridiniacece and Cryptomonadacecc comprise only about 220 spe- 
 cies, but the diatoms, recent and fossil, include about 5,000 species. 
 
 The Rhodophycece, or red algae, also called Floridecc, are "so 
 named from the presence of a red color besides the chlorophyll. 
 Species growing near high-water mark are generally of a dark hue 
 and may be mistaken for brown algae. The Irish moss, Chondrus, 
 is a good example. Those growing near low-water, or in the shade 
 of other algae, are bright colored. They are all multicellular and 
 mostly microscopic in size, but some large species occur. Lime- 
 secreting forms are common, the branching Corallina, the encrust- 
 ing Melobesia and Lithothamnion abounding both in recent and 
 fossil state. The total number of species of red algae is about 1,400; 
 this, together with the brown algae, 840 species, the diatoms, 5,000 
 species, and the 3,000 species of green algae, makes a total of over 
 10,200 species of algae. 
 
 Fucoids. This is a general term applied to impressions on 
 rocks, suposed to represent sea-weeds. In some cases land plants 
 and even traces of inorganic structures have been included here. 
 Ex. : Fucoides verticalis of the Portage, probably a land plant ; 
 
THALLOPHYTA; BRYOPHYTA 937 
 
 Arthrophycus harlani of the Medina, probably a trail; Dendrophy- 
 cus triassicus of the Newark sandstone, a rill-mark impression. 
 
 b. Fungi. 
 
 Fungi or mushroom-plants are thallophytes devoid of chloro- 
 phyll, and growing often in the dark. They arise from spores, 
 and the thallus is either unicellular or composed of tubes or cell- 
 filaments (hyphse), which may be branched, and have an apical 
 growth, or, again, they are composed of sheets or tissue-like masses 
 of such filaments, forming a mycelium. True tissue may develop 
 in some cases by cell-division in the larger forms. Two classes are 
 recognized : Phycomycetes, which are alga-like, with unicellular 
 thallus and well-marked sexual organs, and Mlcomycetes, or higher 
 fungi, with segmental thallus and sexual reproduction. Some of 
 them (Polyporus, Dsedelia) form resistant, more or less woody, 
 structures growing on dead trees. 
 
 The number of species of Fungi is probably around 20,000, 
 though some have placed it as high as 50,000 or even 150,000. 
 Fossil forms extend back at least to the Carbonic, where they occur 
 as hyphse in fossil wood. Good specimens are also found in amber 
 of Tertiary age. 
 
 c. Lichens. 
 
 The lichens are terrestrial thallophytes, composed of algae and 
 fungi living together symbiotically. The fungi are generally Asco- 
 mycetes, the higher class of Basidomycetes seldom taking part, 
 while the algae are either the blue-green algae, Cyanophycea or the 
 green algae, Chlorophycccc. The same alga can combine with dif- 
 ferent fungi to form different lichens. The fungal portion always 
 forms the reproductive organs, though the algre may do so when 
 separated from the association, and growing free. Reproduction 
 is also carried on by fragmentation, i. c., the breaking off of parts 
 capable of starting new plants. There are some thousands of 
 existing species, but fossil forms have not been recognized except 
 from very recent formations. It is not unlikely, however, that 
 lichenous plants formed a chief element of the ancient land vegeta- 
 tion. 
 
 PHYLUM III BRYOPHYTA. The Bryophyta include the mosses 
 and liverworts, both terrestrial plants. In the former, and in some 
 of the latter as well, the plant consists of a stem bearing small 
 leaves, though in many liverworts this distinction is not present, 
 
938 PRINCIPLES OF STRATIGRAPHY 
 
 but a thallus is formed closely applied to the substratum. The at- 
 tachment of the bryophytes is by rhizoids, true roots being ab- 
 sent. These rhizoids resemble the root-hairs of higher plants. 
 The reproductive organs are antheridia and archegonia, serving 
 for sexual reproduction. The former are stalked and develop the 
 spermatozoids, while the archegonia are flask-shaped, with long 
 neck, the egg-cell lying at the bottom. From the fertilized ovum a 
 capsule arises, generally borne on a stalk, and within this the 
 spores are developed. There is thus an alternation of generation 
 the sexual stage, or gametophyte, developing from the spore, and 
 the asexual, or spore stage (sporogonium or sporophyte), develop- 
 ing from the fertilized egg of the gametophyte, and, in turn, pro- 
 ducing the spores. The spore-bearing generation is throughout life 
 dependent on the gametophyte, whereas in pteridophytes it becomes 
 an independent plant. The order Sphagnales contains the single 
 genus, Sphagnum, with numerous species known as bog-mosses. 
 The order Andreaales also contains a single genus, Andreaea, for 
 the most part an Alpine and Arctic plant, growing on bare rocks. 
 The order Phascales includes a few small species, chiefly of the 
 genus Phascum. The order Bryales, on the other hand, contains a 
 very large number of genera and species. 
 
 Fossil mosses, especially of the genus Hypnum, have been ob- 
 tained from the Miocenic and Quaternary deposits of Europe and 
 the Arctic region, and also from western America (Green River 
 beds). They are doubtfully represented in Mesozoic and earlier 
 deposits. 
 
 PHYLUM IV PTERIDOPHYTA. The pteridophytes, or vascular 
 cryptogams, form the highest division of the flowerless plants. 
 Their internal vascular structure allies them with the higher plants. 
 In them alternation of generation has been carried farthest, in 
 that the first stage to develop from the germinating spore is the 
 gametophyte, known as the pro thallus. This is a small, flat, green 
 plant-organism which carries on its under side the archegonia and 
 antheridia, together with the rootlets or rhizoids. This sexual 
 plant is independent of the sporophyte or asexual generation, 
 while the latter at first draws nourishment from the prothallus but 
 becomes physiologically independent when its roots develop. This 
 independence of the two generations is the distinctive feature of 
 the pteridophytes, whereas in bryophytes the sporophyte is through- 
 out its life attached to the gametophyte, while in the spermaphytes 
 the more or less reduced gametophyte remains enclosed within the 
 tissues of the sporophyte. 
 
 The Equisetales, including the single living genus, Equiset"m, 
 
PTERYDOPHYTA 939 
 
 with about 25 species, and the extinct Calamites, represent a range 
 in height from a few inches in the modern forms to from 30 to 60 
 meters in the extinct Calamites. Equisetum arises from a subter- 
 ranean rhizome, which may be a meter in length, and is jointed; 
 the aerial shoot consists of hollow internodes, with whorls of 
 leaves near the top of each, the leaves cohering, except near their 
 tips. In section the aerial stem shows a hollow central cylinder, 
 around which is arranged a circle of fibrovascular bundles, triangu- 
 lar in section, with the point inward. The inner end is occupied by 
 a large air space, and outside of this again is a circle of long air 
 tubes alternating with the fibrovascular bundles. These latter 
 extend into the leaves, equaling in number the leaf teeth. 
 
 The stem of the extinct Calamites had essentially the same 
 structure, but with secondary growth in thickness. In all large 
 specimens a broad zone of wood is added, with a structure compar- 
 able in the true Calamites to that of the simplest conifers. The 
 vascular bundles project into the pith as in Equisetum, and from 
 their more resistant character they will remain when the pith 
 breaks down. A rock-filling of the hollow cylinder thus made will 
 be marked by longitudinal grooves, representing the projecting 
 vascular bundles. In Calamites proper these grooves alternate at 
 the nodes, while in Archseocalamites they are continuous. This 
 shows that in the latter the leaves were superposed, while in Cala- 
 mites they were alternating. In modern Equisetum both fertile 
 and sterile branches arise from the rhizomes. The sterile are more 
 slender than the spore-bearing ones, and bear numerous whorls of 
 branches, which form a bushy plant, from which the name "horse- 
 tail" originated. The fertile branches bear a terminal u strobilus," 
 or cone of sporangiophores, each of which consists of a hexagonal 
 disk, attached by a stem to the axis and supporting on its under 
 side six to nine large spore-cases or sporangia. The outer surfaces 
 of the hexagonal plates form the solid outer surface of the cone, 
 the sporangia extending inward toward the axis. They are not 
 visible until the cone separates into its component parts. Some 
 Calamites (Archaeocalamites) agree closely with this mode of 
 organization, but in others the structure of the cones was more 
 complicated, this being brought about chiefly by the insertion of 
 whorls of sterile bracts between those of the sporangiophores. 
 
 The Sphenophyllina, known only from the Palaeozoic, and rep- 
 resented by the genus Sphenophyllum, had some characters of the 
 Equisetales. The slender, little-branched, and probably clinging 
 stem had from six to eighteen wedge-shaped or linear leaves at 
 the swollen nodes, the leaves of successive whorls not alternating. 
 
940 PRINCIPLES OF STRATIGRAPHY 
 
 The structure of the stem is, however, more like that of lycopods, 
 but the cone again suggests affinities with the Equisetales. The 
 sporangiophores, however, spring from the bracts instead of the 
 axis. The class combines the characters of ferns, lycopods, and 
 Equisetales. Their nearest living relatives are probably the Psilo- 
 tales (Psilotum and Tmesipteris) formerly classed with the Lyco- 
 podiales. 
 
 The Lycopodina are represented by three living and one extinct 
 orders. The Lycopodiales are represented by two genera Phyllo- 
 glossum with one species, and Lycopodium with nearly a hundred. 
 Selaginella with between 300 and 400 species and Isoetes with 
 about 50, mostly aquatic, species are each the sole representatives 
 of their respective orders. The modern genera are small forms, 
 but the extinct orders contained some of the largest Palaeozoic 
 trees, reaching 100 feet or more in height. A general external 
 characteristic of these plants is the simple form of the leaves, 
 which are generally of small size, while the sporangia are situated 
 on the upper surface of the sporophylls. In structure the stem is 
 a single cylinder (monostelic) with a centripetal development of 
 woody tissue (xylem). The earliest, or protoxylem, is at the periph- 
 ery of the stele. In Selaginellales the stem contains one, two, 
 or several stele, while the Lepidodendrales are monostelic, as in 
 Lycopodium. A section of a Lepidodendron stem shows the central 
 pith, often destroyed, surrounded by a zone of primary wood, and 
 outside of this, in most cases, a zone of secondary wood, sharply 
 defined from the inner zone by the layer of protoxylem. In some 
 of the smaller species the wood was solid, without central pith. 
 The cortex or bark surrounds this and is bounded externally by the 
 persistent leaf scars. In Sigillaria the ring of primary wood is 
 narrower. The leaf scars are arranged spirally in Lepidodendron, 
 but in vertical rows in Sigillaria. Both were attached to large 
 creeping root-stocks or stigmaria, which were provided with 
 numerous cylindrical "roots" which penetrated the soil on all 
 sides. 
 
 The spores of lycopods are formed in sporangia of considerable 
 size, which are situated on the upper surface and near the 
 base of the sporophylls. These are arranged in definite terminal 
 cones, or they may resemble the foliage leaves and occur in alter- 
 nate zones with them. In Selaginella the sporophylls are arranged 
 radially in the cones, these terminating the branches. A single 
 sporangium is borne on the axis just above the insertion of each 
 sporophyll. Large and small spores (mega- and micro-spores) 
 occur in this genus, but in Lycopodium they are all of one kind. 
 
PTERYDOPHYTA; SPERMATOPHYTA 941 
 
 In the Lepidodendrales they were heterosporous, at least in some 
 cases. The cones of Lepidodendron and allied forms (Lepidostro- 
 bus) vary from an inch to a foot in length, according to species, 
 and are borne on ordinary or on special branches. The sporophylls 
 are arranged spirally upon the axis and each carries a single 
 large sporangium on its upper surface, which in turn carries either 
 an enormous number of minute or a small number of large spores. 
 The upturned and overlapping laminae from the sporophyllae form 
 the exterior of the cone. The Lepidodendraceae range from the 
 Devonic to the Permic, while the Sigillariaceae range through the 
 upper Palaeozoic above the Devonic. 
 
 The Ferns are among the most varied of existing pteridophytes 
 and exhibit a wide range in size, from the little epiphytic Hymeno- 
 phyllacea, whose fronds are hardly a centimeter in length, to gigan- 
 tic tree-ferns, 80 feet or more in height. The leaves or fronds 
 vary from simple to highly compound, each pinna or pinnule being 
 characterized by a mid-vein, and by forking lateral veins. The 
 sporangia are borne on the under side of the frond, or on separate 
 fronds. In the Ophioglossales a separate spike is produced. In 
 some of the Palaeozoic Cycadofilices ( comprising most of the ferns 
 of that period *) actual seeds instead of spores were produced, the 
 forms also being intermediate in structure of the stems, etc., be- 
 tween ferns and cycads. The water-ferns or Rhizocarps (Hydro- 
 pteridiales) produce both mega- and micro-spores. The former 
 produce female, the latter male, prothallia. The common pepper- 
 wort, Marsilea, looking like a small four-leaved clover, is a good 
 example. 
 
 PHYLUM V SPERMATOPHYTA. The true flowering plants 
 (Phanerogams), or seed-plants (Spermatophyta), comprise the 
 gymnosperms and the angiosperms. Conifers are the most abundant 
 representatives of the gymnosperms in the northern regions, while 
 the palm-like cycads occur in tropical districts. They are, however, 
 abundant in the Jurassic and other Mesozoic deposits of America 
 and Europe. The late Palaeozoic Cordaitales were large trees with- 
 wood of a coniferous type (Daxoxylen wood) and long strap-shaped 
 leaves. 
 
 The angiosperms, including all the true flowering plants, are 
 divided into the Monocotyledons, which include the grasses, palms, 
 lilies, etc., with parallel-veined leaves, and the Dicotyledons with 
 net-veined leaves. The latter make their first appearance in Co- 
 manchic time. 
 
 * Also classed as a separate order Pteridosperma under the gymnosperms. 
 
942 PRINCIPLES OF STRATIGRAPHY 
 
 ANIMALS. 
 
 PHYLUM I PROTOZOA. The Protozoa are unicellular animals 
 either naked or enclosed in a cell membrane. In addition, many 
 rhizopods secrete calcareous or siliceous structures, or, by cementa- 
 tion, form a covering of foreign substances. One or more nuclei 
 are generally present, and reproduction is by fission. The Rhizo- 
 poda include the Foraminifera, which secrete shells of carbonate 
 of lime, or build them by cementing sand grains, etc. The shells 
 have one or more chambers (unilocular or multilocular). If many, 
 they increase in size successively, and are arranged in various ways, 
 including nautilian and spiral coiling. In many forms the surface 
 is pierced by fine pores the foramina through which protoplasm 
 is extruded in fine streamers forming the pseudopodia. In size the 
 Foraminifera shells vary from minute shells to those an inch or 
 more in diameter (Nummulites). They range from the Cambric to 
 the present with several thousand species. 
 
 . The Radiolaria secrete horny or siliceous internal structures, 
 which form a much perforated latticework, ornamented by spines, 
 bosses, etc. They also range from the Cambric to the present. 
 
 PHYLUM II PORIFERA (SPONGES). The sponges are aquatic 
 multicellular animals in which the body is penetrated by a complex 
 set of canals, into which water enters, through pores in the outer 
 wall. From the canals are given off, at intervals, digestive sacs, and 
 these finally converge into one or more main canals, with large exter- 
 nal excurrent openings or oscula. Modern sponges generally secrete 
 a skeleton of horny substance (chitin) and, in addition, many secrete 
 siliceous or calcareous rods or needles (spicules) which are often 
 compound in form. In many older and some modern forms, these 
 unite into solid structures so that the form of the sponge is pre- 
 served. They abound in all marine formations, from the Cambric 
 to the present. The number of extinct and living species is very 
 great. 
 
 PHYLUM III CCELENTERATA. The coelenterates have a body 
 composed of two cellular layers, the ectoderm and endoderm, the 
 latter enclosing the ccclomic cavity into which the mouth opens. 
 An intermediate non-cellular or imperfectly cellular layer is often 
 present but no true body cavity occurs. The animals (polyps) have 
 a simple body in the Hydrozoa the mouth generally at the end 
 of a proboscis-like elevation, and surrounded by tentacles. Gen- 
 erally they are compound, many polyps being united by hollow 
 tubes. Special polyps for reproduction (gonopolyps) are com- 
 monly developed, and these often give rise to medusae, or jelly-fish 
 
CCELENTERATA ; MOLLUSCOIDEA 943 
 
 a free-swimming sexual generation, which, however, sometimes 
 remains attached to the parent. Many Hydrozoa secrete a horny 
 or chitinous envelope, which ends in many cases in cups or hydro- 
 thecce. In the fossil graptolites these horny structures alone are 
 preserved, as compressed carbonaceous films. In other cases 
 (Hydrocorallines) a calcareous structure is secreted, which may be 
 important as a reef- former (Millepora). The stromatoporoids of 
 the Palaeozoic are believed to belong to this group. They repre- 
 sent enormous accumulations of lime taken by minute organisms 
 from the sea-water and built into their structures. These are often 
 heads of great size, some attaining a diameter of ten feet. 
 
 The coral or anthozoan polyp is more complicated, there being, 
 in addition to the parts found in the hydroid polyp, an enteric sac, 
 or stomodaum, formed by invagination of the mouth area, and a 
 series of fleshy septa or mesenteries, dividing the body radially. 
 Many anthozoan polyps secrete a calcareous structure (coral) 
 which typically is characterized by a series of radially placed calcar- 
 eous plates or septa, variously united by transverse structures and 
 surrounded by one or more calcareous walls. In Palaeozoic time 
 these were built mostly on the plan of four and grew into isolated 
 horn-shaped structures on the broad septate end of which the 
 polyp rested (Tetraseptata) . In later times to the present the plan 
 of six (Hexaseptata) or eight (Octoseptata) became the dominant 
 one, and the forms became compound, so that in some modern 
 coral heads thousands of individual polyps participate. A fourth 
 group in which the septa were absent or represented by spines only, 
 while the walls were provided with pores (Aseptata), was chiefly 
 confined to the Palaeozoic. The reproduction of the Anthozoa is 
 carried on by fission and by ova. 
 
 PHYLUM IV MOLLUSCOIDEA. The Molluscoidea comprise two 
 classes which are widely different in their external adult charac- 
 ters but closely similar in their early life history. The Bryozoa 
 are commonly compound aquatic forms, either encrusting other ob- 
 jects or forming solid masses not unlike in form to some early 
 corals, with which they have sometimes been united. The colony, or 
 zoarium, consists of cells (zo&cia) generally of lime and loosely or 
 closely aggregated, in the latter case often becoming prismatic. 
 They are hollow or divided by transverse calcareous partitions or 
 dissepiments and have various other structures. Smaller tubes 
 (mesopores) are present in some cases. Colonially the Bryozoa 
 may constitute a solid mass or head, a flat expansion, a network, 
 in which large open spaces are left between series of zooecia (as in 
 Fenestella, etc.), or a great variety of other forms. In Palaeozoic 
 
944 PRINCIPLES OF STRATIGRAPHY 
 
 time, when the number of specimens was considerably over a thou- 
 sand, they often acted as important reef-formers. Mesozoic and 
 Cenozoic Bryozoa (close to a thousand species) also contributed 
 largely to calcareous reefs. (See Chapter X.) The animal differs 
 from the coral polyp by the possession of a well-marked body cavity 
 and a definite alimentary system. 
 
 The Brachiopoda are simple animals encased in a shell with 
 dorsal ventral and sometimes accessory valves. In general, the 
 ventral valve is larger and some provision is afforded for the 
 emission through a foramen or otherwise of the fixing organ, or 
 pedicle. It is, hence, called pedicle valve. The other valve carries 
 supports (crura brachidia), from which the soft internal respira- 
 tory organs, the brachia, or arms, are suspended ; hence the 
 name brachial valve is applied. The accessory pieces are either 
 a third shell plate (pedicle plate, deltidial plate} secreted by the 
 pedicle, or a double set of plates (deltidial plates} meeting in the 
 center below the foramen. These accessory plates are commonly 
 very small and situated below the beak of the pedicle valve. Open- 
 ing and closing of the valves is effected by muscular systems. Sur- 
 ficially the shells are either smooth or variously plicated, and 
 sometimes spines are developed. There are about 140 living and 
 over 6,000 fossil species. 
 
 PHYLUM V MOLLUSCA. The molluscs are soft-bodied animals 
 generally enclosed in a calcareous shell. The headless molluscs, or 
 Pelecypoda, have a shell of two, generally symmetrical valves placed 
 right and left and united dorsally by a hinge, which generally in- 
 cludes a series of interlocking hinge-teeth and sockets. The valves 
 are opened either by an external ligamental structure variously ar- 
 ranged or by an internal compressible resilium which often has 
 special supports or resilifers developed. The shell is closed by the 
 adductor muscles, of which there are typically an anterior and a 
 posterior one (dimyarian), or only one, situated subcentrally 
 (monomyarian) . Externally the shell is smooth, showing only 
 growth lines, or it may be ornamented by radiating plications or 
 striations, or by marked concentric ribs parallel to the growth-lines. 
 A horny outer covering, or periostracum, is generally present. The 
 animal is provided with an anterior hatchet-shaped foot, and with 
 gills which hang in pairs on opposite sides -of the abdomen, and 
 with a mantle, the attachment of which to the shell is marked 
 by the pallial line, and the outer portion of which secretes the shell. 
 The remainder of the mantle secretes the inner shell layer (nacre- 
 ous layer), which is often iridescent. A pair of siphons (excurrent 
 and incurrent) is frequently formed, their presence being generally 
 
MOLLUSCA 945 
 
 indicated by a pronounced reentrant in the pallial line below the 
 posterior adductor impression (pallial sinus). 
 
 The cephalophorous mollusca build a shell of only one part, 
 though extra horny or shelly pieces, not secreted by the mantle, may 
 occur. Such are the opercula of certain gastropods and the aptychi 
 of ammonite cephalopods. In the gastropods the animal is pro- 
 vided with a lingual ribbon, or radula, beset with teeth and having a 
 rasping function. In the cephalopods horny jaws are developed. 
 In Gastropoda the shell is normally a spiral one, though in some 
 cases the coiling is in a single plane, as is typical of coiled cephalo- 
 pods. Both right- and left-handed coils occur, the former being 
 more common, while the left-handed coils are variations in some 
 cases, but fixed types in others. The apex of the shell is formed 
 by the protoconch, generally somewhat differentiated from the 
 conch. The latter may be smooth (except for growth lines) but 
 is more generally ornamented by plications (spirals) and by ribs 
 which extend across the whorl from suture to suture. The ribs 
 may become concentrated into spiral rows of nodes, or spines (hol- 
 low emarginations of the shell-lip) may result. Temporary resting 
 stages in shell growth are often marked by varices consisting of 
 abrupt deflections of the lip, or by rows of spines (Murex). The 
 mouth of the shell is in many cases drawn out into an anterior 
 notch or a long canal. The inner or columellar lip of specialized 
 types is marked by oblique plications. Old age or phylogerontic 
 forms often have the last whorl loose-coiled or straight. The shell 
 of primitive cephalopods is a straight cone (Orthoceras) divided 
 regularly by transverse septa, which are pierced by the siphuncle. 
 All the resulting chambers are empty, representing cut-off space 
 as the shell became too small for the growing animal, which finally 
 occupied only the large outer or living chamber. When the cham- 
 bers are all filled with hardened mud and the shell is broken away, 
 the edges of the septa are seen, forming the suture. In Nautiloidea 
 this suture is generally simple, but in Ammonoidea it is often much 
 fluted so as to produce a complicated pattern. The siphuncle of 
 nautiloids is generally at or near the center, while that of the am- 
 monoids is external. Curved forms (Cyrtoceras), loose-coiled 
 (Gyroceras), and close-coiled (Nautilus and Ammonites) shells are 
 progressively developed. Old age individuals, or phylogerontic 
 groups, generally lose the power of coiling in the last whorl, which 
 may be loose-coiled or even straight. 
 
 Baculites, one of the last survivors of the ammonoids, was 
 straight except for the very earliest portion, which was coiled. 
 The ammonoids are all extinct, ending with the Cretacic. Nautil- 
 
946 PRINCIPLES OF STRATIGRAPHY 
 
 oids are represented by the living Nautilus. These two groups 
 are classed as Tetrabranchiata. The Dibranchiata are represented 
 by the living Argonauta, the Octopus, Squid, Cuttlefish, and 
 Spirula. The last is an internal loose-coiled shell with septa and 
 siphuncle. A straight-coiled ancestor, the Jurassic and Cretacic 
 Belemnites, had its shell, which was straight, protected by a heavy 
 calcareous outer guard, often cigar-shaped, and when perfect 
 showing the hollow at one end occupied by the shell. A modified 
 portion of the guard alone remains in the cuttlefish, the so-called 
 cuttlefish bone, which is embedded in the fleshy mantle of the 
 animal. 
 
 The Pteropoda have thin transparent shells of various shapes, 
 but rarely coiled. The "foot" of the animal is divided into two wing- 
 like appendages by which these ''Butterflies of the sea" keep them- 
 selves afloat on the water. The shell of the Conulariida and Hyo- 
 lithida was coarser and generally rectangular in section in the 
 former and variously shaped in the latter. The Scaphopoda (Den- 
 talium, etc.) have conical, often curved, shells, open at both ends, 
 which begin as a saddle-shaped structure growing into a ring and 
 increasing in length. In the Polyplacophora (Chiton, etc.) the shell 
 is composed of several pieces arranged serially. 
 
 Pelecypoda are rare in the Cambric but become abundant in 
 the succeeding horizons. There are about 10,000 fossil species and 
 about 5,000 recent ones. The Gastropoda are likewise sparsely 
 represented in the Cambric. They appear to be at their acme of 
 development at the present time, there being some 15,000 living 
 species, as compared with about half that number or less of fossil 
 ones. Only one cephalopod is known from the Cambric. They 
 abound in the Ordovicic, at the end of which period many races 
 died out, while new ones arose. The Ammonoidea begin in the 
 Devonic, reach their acme in the Jurassic and die out in the Cretacic. 
 The Nautiloidea and Dibranchiata (the latter appearing first in the 
 Trias) have modern representatives. 
 
 PHYLUM VI PLATYHELMINTHA, AND VII VERMES. The pla- 
 tyhelminths, or flat-worms, are soft-bodied, worm-like animals with- 
 out body cavity or ccelom. They have no hard parts, and nothing is 
 known of their geological history. The great mass of animals 
 classed together as Vermes is in reality a heterogeneous assemblage, 
 many of the groups having no direct relationship with others placed 
 here. Typical worms (chaetopods) have a distinct body cavity from 
 which the enteric and digestive tracts are separated. The body is 
 divided into many similar segments, each of which, except the oral 
 one, carries on each side two bundles of bristles or setae, a dorsal 
 
VERMES; ARTHROPODA 947 
 
 and a ventral one, placed typically on elevations or parapodia. The 
 head segment carries appendages varying in the different sub- 
 classes. Aquatic worms possess gills for breathing, but these be- 
 come more or less modified or even entirely lost in the mud- and 
 earth-worms. The alimentary system consists of an anterior mouth, 
 an intestinal canal, divisible into fore-gut, mid-gut and hind-gut, and 
 ending in the posterior anus. In some parasitic forms, this system 
 is much degenerated. In some chaetopods a series of horny cesoph- 
 ageal teeth is developed, and these are often preserved in great per- 
 fection. The conodonts may be of this order. 
 
 Many worms build tubes of agglutinated sand, either free, or 
 in the sand, while others secrete calcareous tubes. These are often 
 well preserved and show the presence of these organisms in Cam- 
 bric times. Trails left by errant worms on mud and the peculiar 
 form of the string of sand, which has passed through the annelid 
 body, all serve as evidence of the existence of the worms in former 
 periods. 
 
 PHYLUM VIII ARTHROPODA. The arthropods, or jointed- 
 legged invertebrates, comprise a number of distinct assemblages of 
 organisms, as indicated by the several classes included. The crus- 
 taceans are in many respects the most characteristic, but even they 
 comprise a number of subclasses of very diverse characters. The 
 Myriopoda and Peripatus are worm-like. The former occur first 
 in the Old Red Sandstone (Devonic) and are common in the Car- 
 bonic. The oldest, and in some respects the most generalized, of 
 the Crustacea are the Trilobites, which are already highly developed 
 and very numerous in the Cambric. They do not extend beyond 
 the Palaeozoic. The organism is covered by a chitinous exoskeleton 
 in which a head or cephalon, a thorax and an abdomen or pygidimn 
 are distinguishable. Each division consists of a median axis and 
 lateral lobes and hence shows a trilobate division. The axis of 
 the head constitutes the glabella and the lateral portions are com- 
 monly divided into fixed and free cheeks, the latter generally carry- 
 ing the compound eyes. The thorax is divided into a number of 
 movable rings, but the pygidium is a single though grooved piece. 
 The mouth is ventral and the head is provided with antennas. 
 Jointed thoracic legs were also present. The Entomostraca are 
 modified crustaceans with a shell-like carapace. They are repre- 
 sented in all geological horizons. The Ostracoda, with a bivalve 
 shell, were especially abundant in the Palaeozoic. The barnacles 
 also had representatives in the Palaeozoic but are more typical in 
 later horizons. The animal is degenerate, attached either directly 
 or by a fleshy stalk. In the former case a circle of shell-plates is 
 
948 PRINCIPLES OF STRATIGRAPHY 
 
 developed, forming the corona. The Phyllocarlda were of great 
 importance in the Palaeozoic. They generally had head and thorax 
 enclosed in a carapace consisting mainly of two valves, with acces- 
 sory pieces. The ringed abdomen and the tailpiece or telson (often 
 triple) projected beyond the carapace. 
 
 The Decapoda have head and thorax united into a cephalo- 
 thorax, and covered by a single carapace, or with one segment 
 free. Each of the thirteen cephalothoracic segments has a pair of 
 jointed appendages, some of which are modified into antennae or 
 mouth-parts. The abdomen consists of seven segments, the terminal 
 one being a telson. In the Macrura (lobsters, crayfish, etc.) these 
 segments are all visible, but in the Brachiura (crabs) they are gen- 
 erally turned under the carapace. Locomotor appendages (perelo- 
 poda) are in five pairs, and with few exceptions each consists 
 of seven joints. Some of the final joints are claw-like, others 
 paddle-like, and others again merely pointed for walking pur- 
 poses. Six pairs of abdominal legs occur. The claws are often 
 found fossilized separately. Decapods first appear in the Triassic. 
 The remaining orders show various modifications of the decapod 
 type. They are mostly rare as fossils. 
 
 Among the Acerata the Merostomata are in many respects of 
 greatest interest. Some Eurypterida in the Devonic reached a length 
 of six feet, but were smaller in other horizons. The Limulava are 
 known only from the Middle Cambric. They combined trilobite 
 with eurypterid characters. The eurypterids had a short cephalo- 
 thorax, a ringed abdomen and a telson, the body, as in Crustacea, 
 being covered with a chitinous exoskeleton, which was repeatedly 
 shed. A pair of compound eyes and a pair of median simple eyes 
 or ocelli formed the chief dorsal features of the carapace. Ventrally 
 this bore six pairs of jointed appendages, the first preoral and che- 
 late, the others non-chelate, the last usually forming a large paddle. 
 The first six segments of the abdomen bore broad, leaf-like append- 
 ages, referable to "gills." The posterior segment and telson were 
 without appendages. The number of known species is over 150. 
 The Synxiphosura (Cambric to Siluric, few species) had a trilo- 
 biti-form abdomen, which, in the adult Xiphosura, of which Limu- 
 lus, the horseshoe crab, is the only living example, was fused into a 
 single piece, though still indicating the segments and trilobation. 
 The fossil species (few in number) have been obtained from the 
 Upper Devonic, the Carbonic, and (genus Limulus, only) from 
 the Mesozoic and Tertiary of Europe. 
 
 The scorpions and spiders are more complex Acerata adapted 
 
INSECTA; ECHINODERMATA 949 
 
 to a terrestrial life. The former are known from the Siluric 
 (Upper), the latter from the Coal Measures on. 
 
 Altogether more than 300 fossil species of arachnids and 
 several thousand modern species are known. 
 
 Insects are known from the Ordovicic graptolite slates of 
 Sweden and from the Siluric of France. They are especially well 
 preserved in the Carbonic and later terrestrial formations. The 
 Palaeozoic forms constitute a distinct group with 14 orders, all ex- 
 tinct. Two other orders were, however, also represented in the late 
 Palaeozoic, the cockroaches (Blattoidea) being especially well repre- 
 sented on account of the hard coriaceous character of the front 
 wings or teginina. The number of known Palaeozoic insects is close 
 to 1,000 species while the Tertiary and Quaternary have furnished 
 over 5,800 species. There are over 384,000 living species (Hand- 
 lirsch). 
 
 PHYLUM IX ECHINODERMATA. The echinoderms or spiny- 
 skined animals are characterized generally by an apparently radial 
 form, by the possession of calcareous plates or sclerites in the in- 
 tegument, and by an elaborate internal structure, the most marked 
 portion of which is the highly developed water-vascular system. 
 The oldest known forms are the Cystoidea (Cambric to Car- 
 bonic) in which the body was enclosed in a calyx of irregular 
 plates, closely united by sutures and generally supported on a 
 stem. Arms were rudimentary and the respiratory and water- 
 vascular system were not pronounced. The Blastoidea (Ordovicic 
 to Carbonic) were more regular in the arrangement of plates and 
 were armless. The calyx was, however, provided with five petaloid 
 ambulacral areas radiating from the mouth. The Crinoidea (Ordo- 
 vicic to Recent) were mostly stemmed, though some had the power 
 of separation in the adult. The calyx is composed of regular plates 
 generally arranged in five series and terminated by branching or 
 simple arms often of great length. The mouth of many Palaeozoic 
 forms (Camerata) was under a vaulted arch or tegmen, and the 
 anus was often placed at the end of a tube or proboscis. The 
 brittle-stars and starfish have the body cleft into five or more 
 movable rays, which are supplied with branches from the water- 
 vascular system and diverticula from the other body organs. The 
 branch begins in the Ordovicic, but has few fossil representatives. 
 The sea-urchins or Echini, on the other hand, are abundantly repre- 
 sented in the Mesozoic and later strata. Palaeozoic forms occur as 
 early as the Ordovicic (Bothriocidaris). In them the body is gen- 
 erally covered by a large number of plates, which, however, fall 
 into ten zones, five anibulacral, with plates pierced for the tubed 
 
950 PRINCIPLES OF STRATIGRAPHY 
 
 feet or ambulacra, and five inter ambulacral. The whole forms a 
 more or less solid corona. In the post- Palaeozoic types each zone is 
 generally composed of two columns of plates, so that there are in 
 all 20 columns, forming 5 ambulacral and 5 interambulacral zones. 
 The mouth and anus are generally opposite each other in the 
 Palccechinoidea, and in the Cidaroidea and Diadematoidea. In the 
 others the anus migrates toward the mouth. The Clypeosteroidea 
 and Spatangoidea show an elongation of form, with a pronounced 
 bilateral symmetry. In most of the Spatangoidea the mouth passes 
 forward, so as to lie no longer in the median axis. In the IIolo- 
 thuroidea the plates of the integument are not united, the body 
 thus being soft and changeable in form by inflation. The separate 
 plates are found fossil as early as the Carbonic. 
 
 PHYLUM X PROTOCHORDA. These are soft-bodied animals, 
 some of them, as the Tunicates, degenerate, but showing affinities 
 with the vertebrates, in the possession of a notochord, branchial 
 slits, and a central nervous system. The Cephalochorda (Am- 
 phioxus) are fish-like and readily mistaken for a vertebrate, while 
 the Enter opneusta (Balanoglossus) are worm-like. While some of 
 these have been considered ancestral to vertebrates, it is not at all 
 impossible that the suggestive characters are independently de- 
 veloped. Vertebrates arose in the Palaeozoic, and no modern form 
 is likely to preserve intact all the primitive characters of a class. 
 
 PHYLUM XI VERTEBRATA. This, the most highly specialized 
 phylum of the animal kingdom, has its most primitive representa- 
 tive in the Ostracoderma of the early Palaeozoic (Cephalaspis, 
 Pterichthys, Bothriolepis, etc.). Known definitely from the De- 
 vonic and Siluric, there are fragments indicating their existence 
 in the Upper Ordovicic of America. They retain many characters 
 of invertebrates and seem to unite the fish with the eurypterids, a 
 group of Merostomes, which flourished at the same time. (See 
 Patten-2i ; 22.) Their most striking characteristic was a well- 
 developed armor, or exoskeleton of bony plates, which covered the 
 head and anterior portion of the body. The endoskeleton was not 
 calcified and the mouth without hard parts. Hence all we know 
 of them is from the external plates and scales. The Devonic 
 Arthrodira have also been regarded as an independent class, differ- 
 ing from fishes in that their jaw elements are merely dermal ossifi- 
 cations and are not articulated with the skull (Dean). The head 
 and trunk are covered by symmetric bony plates, the head-shield 
 is movably articulated with the body-shield. The endoskeleton is 
 superficially calcified, and paired fins are rudimentary or absent. 
 The Devonic Coccosteus, Dinichthys and Titanichthys are examples. 
 
VERTEBRATA: PISCES 951 
 
 Pisces. 
 
 The Cyclostomata (Agnatha) represented to-day by the lam- 
 preys, appear to have had some representatives in the remarkable 
 Palaeospondylus of the Old Red Sandstone. The Conodonts have 
 been regarded as teeth of myxinoids. The elasmobranchs, or 
 sharks, were well represented in the Devonic and later beds, the 
 first three orders being wholly confined to the Palaeozoic. The 
 endoskeleton is more or less cartilaginous, the exoskeleton and 
 teeth structurally identical (placoid scales). Generally only 
 teeth, calcified vertebrae and dermal spines are preserved. The 
 true sharks and rays (Plagiostomi) are mostly Mesozoic and later, 
 but examples from the Carbonic and even the Mississipic are 
 known. The chimaeras, however (Holocephali), had representa- 
 tives from the Devonic on. 
 
 The ganoids are remarkable in that their trunk and tail are 
 usually covered with scales, consisting of a thick bony inner layer, 
 and an outer layer of enamel, the scales being in some groups articu- 
 lated by a peg-and-socket arrangement, and in others overlapping. 
 The skull is covered with dermal bones, or completely ossified. 
 The vertebral column is cartilaginous or shows various degrees of 
 ossification. Most of the Palaeozoic ganoids belong to the order 
 Crossopterygii or fringe-finned ganoids. Such are the Devonic 
 genera Holoptychius and Osteolepis and numerous Mississippi 
 to Permic genera. Other crossopterygians occur in the Mesozoic, 
 and two genera (Polypterus and Calamoichthys) are still living in 
 the rivers of tropical Africa. The cartilaginous ganoids (Chon- 
 drostei) range from the Mesozoic to the present time, a number of 
 genera being still extant, such as the sturgeons and paddle-fish. 
 
 A considerable number of Palaeozoic forms also belong to the 
 Heterocerci, an order ranging from the Devonic (Cheirolepis) to 
 the Upper Jurassic (Coccolepis of the Lithographic beds). Many 
 Carbonic and Permic species (including Palaeoniscus, Platysomus, 
 etc., the common forms of the Kupferschiefer of Thuringia, etc.), 
 belong to this order, as well as the Triassic Catopterus of North 
 America. The Lepidostei include the "bony pikes" (Lepidosteus) 
 of the North American rivers, and many Cenozoic and Mesozoic 
 genera, but only one genus (Acentrophorus) has Permic representa- 
 tives. Here belong the widely distributed Triassic Semionotus and 
 the many common Jurassic genera (Dapedius, Lepidotus, Eugna- 
 jthus, Caturus, etc.), the order being at its height at that time. 
 The Amioidei also have a surviving genus (Amia) in the rivers of 
 
952 PRINCIPLES OF STRATIGRAPHY 
 
 the southern United States and Central America, while other mem- 
 bers extend as far back as the Lias. 
 
 The Dipnoi, or Lung-Fishes, range from the Devonic to the 
 present time. Their skeleton is chiefly cartilaginous, but the upper 
 and lower vertebral arches, the ribs and fin-supports exhibit a ten- 
 dency toward ossification. They have paddle-shaped, paired fins 
 and a highly specialized air-bladder which serves as a lung. Dental 
 plates are common in the Devonic (Dipterus) and Carbonic (Cte- 
 nodus), while many perfect specimens also occur in these deposits. 
 
 These fish may be considered as approaching Amphibians in 
 many respects. The Teleosts, or bony fishes, appear first in the 
 Triassic deposits, and increase in prominence until they are the 
 leading type to-day. 
 
 Amphibia. 
 
 The Amphibia are cold-blooded terrestrial vertebrates, with 
 partly branchial respiration, in early stages, while in some forms 
 gills remain functional throughout life. The limbs are never fins 
 and are rarely absent. The Stegocephalia (Carbonic to Upper 
 Trias) comprise the largest known Amphibians, and were pro- 
 tected by a dermal armor of bony scales or scutes. The teeth were 
 sharply conical, with a large pulp-cavity, and the walls were some- 
 times highly complicated by infolding of the dentine (Labyrintho- 
 donts). The Gymnophiona or ccecilians are vermiform amphibia, 
 covered with scales and without limbs. They are restricted to the 
 South American and Indo- African tropics. The Urodeles are 
 naked bodied, usually with two pairs of short limbs and persistent 
 tail. Gills often remain throughout life. The vertebrae are usually 
 completely ossified. This group appears first in the Upper Jurassic 
 (Wealden), and has living representatives in the newts and sala- 
 manders. The Anura (frogs, toads) are tailless and develop by 
 metamorphosis. The oldest fossil forms are from the Eocenic. 
 
 Reptilia. 
 
 Reptilia are cold-blooded, naked, scaly or armored vertebrates 
 of terrestrial or aquatic habit, and breathing exclusively by lungs. 
 There is no metamorphosis during development. The Rhyncho- 
 cephalia date from the Permic, but were most extensively repre- 
 sented in the Trias. A single living genus (Hatteria or Spheno- 
 don) occurs in New Zealand. ' The body was lizard-like, long- 
 
VERTEBRATA; REPTILIA 953 
 
 tailed and sometimes scaly. The Squamata comprise the lizards 
 and snakes and two extinct groups of aquatic reptiles from the 
 Cretacic (Mosasaurus, etc.). The lizards (Lacertilia) have 1,925 
 living species but few fossil ones are known, the oldest being from 
 the late Jurassic. Of the snakes (Ophid-ia) nearly 1,800 recent 
 species but only about 35 fossil ones are known, chiefly from the 
 Tertiary, though some Cretacic forms are probably referable to 
 snakes. The Ichthyosauria are entirely extinct reptiles which in- 
 habited the Triassic, Jurassic, and Cretacic seas. Their body was 
 in general whale- or fish-like and the jaws were furnished with nu- 
 merous conical teeth. 
 
 The Sauropterygia, also restricted to the Mesozoic, were mostly 
 marine, lizard-like reptiles, with long necks and well-developed 
 limbs, with five normal digits (N othosauridce Triassic) or paddle- 
 shaped, the digits elongated by supernumerary phalanges (Plesio- 
 saurida, Trias to Cretacic). The Theromorpha were primitive land 
 reptiles with many mammalian characters and often of grotesque 
 forms and proportions (Pareiasaurus, Dicynodon, etc.). They 
 lived in the Permic and the Triassic of North America, Europe, 
 and South Africa. 
 
 The Chelonians or turtles are characterized by the possession 
 of a more or less complete bony shell, partly composed of modified 
 neural spines of the dorsal vertebrae and partly of dermal ossifica- 
 tions more or less intimately united with the former. The limbs, 
 tail, and generally the neck and head can be withdrawn into this 
 shell. In general a dorsal shield, or carapace, and a ventral one, 
 or plastron, composes this shell and both are, as a rule, superficially 
 covered by a horny or leathery epidermal layer divided by grooves 
 or sutures into a few large scutes or shields. Their arrangement 
 is independent of the underlying osseous plates. Turtles first ap- 
 peared in the Upper Triassic (Keuper) of Europe. 
 
 The Crocodilia are lizard-like reptiles with the highest internal 
 organization of the class. Their skeletal structure differs widely 
 from that of lizards, and their respiratory organs resemble those 
 of birds. The entire body is covered with horny scales. The most 
 primitive groups (Parasuchia), resembling the Rhynchocephalia, 
 occur in the Trias of America (Belodon or Phytosaurus, and Epis- 
 coposaurus) ; of Scotland (Stagonolepis) ; and the Gondwana 
 formation of India (Parasuchus). There are also more specialized 
 Triassic forms, such as the little Aetosaurus (of which 24 complete 
 individuals occur on a single block of Stuben-sandstone [Upper 
 Keuper] in the Stuttgart Museum), and others from the Trias of 
 Elgin, Scotland. 
 
954 PRINCIPLES OF STRATIGRAPHY 
 
 Typical marine Crocodiles occur in the Jurassic and Comanchic 
 (Mesosuchia), while in the Cretacic-Tertiary and modern times 
 these crocodiles (Eusuchia) again lived chiefly in fresh water and 
 on the land. They include both long-snouted (longirostral) and 
 broad-snouted (brevirostral) forms, the latter comprising the alli- 
 gators. 
 
 The Dinosauria were long-necked and long-tailed reptiles with 
 limbs adapted for support of the body. The earliest species were 
 Triassic, the latest Cretacic. A bony exoskeleton was developed in 
 some forms, consisting of isolated bony plates or spines, or of 
 interlocking scutes forming a continuous shield. Most dinosaurs, 
 however, were naked or covered by scales. The skull of most forms 
 was extremely small in proportion to the body, while the legs in 
 many cases were exceedingly massive. 
 
 The Pterosauria, or winged lizards, ranged from the Trias to the 
 Cretacic, and their whole organization was adapted to an aerial ex- 
 istence. They ranged from the size of a sparrow to forms which had 
 a spread of wing of nearly six meters. The skull was bird-like and 
 generally fitted with sharp, conical teeth, mostly long and sharply 
 pointed in front (Pteranodon, Nyctodactylus, Ramphorhynchus), 
 but sometimes blunt (Dimorphoden). The neck and tail were gen- 
 erally long. The fifth digit of the hand consisted of four enor- 
 mously elongated phalanges, which were turned backward to 
 support the wing membrane. Three families are known : Rham- 
 phorhynchidce (Jurassic), Pterodactylida (Upper Jurassic and 
 Cretacic), and Ornithocheirida (Pteranodon, etc.) Cretacic. 
 
 Aves. 
 
 The birds form a homogeneous and circumscribed class derived 
 from the reptiles and partaking of their character in the Jurassic 
 and Cretacic, where teeth and a vertebrated tail still existed. The 
 exoskeleton consists of feathers, horny coverings for the beak, 
 claws, etc. The endoskeleton is compact but light, the bones being 
 permeated by air-cavities with thin but dense-textured walls, rich in 
 calcium phosphate. The vertebrae have peculiar saddle-shaped ar- 
 ticulations which allow great freedom of movement. The bones of 
 the forearm are modified into wings. The oldest bird, Archseop- 
 teryx of the Jurassic, had its jaws provided with conical teeth like 
 those of reptiles, and its vertebral column had about 20 caudal verte- 
 brae. The Odontolcse (with Hesperornis) and Odontonncz (with 
 Ichthyornis) also had toothed jaws, but other birds were free from 
 
AVES; MAMMALIA 955 
 
 them. The Struthiones, or ostriches, rheas, cassowaries and emus 
 are all large, flightless birds with small wings, a keelless sternum, 
 and well-developed walking legs. They also include the extinct 
 ^Epyornis and the equally extinct moas (Dinornithida) , without or 
 with extremely rudimentary wings and pectoral arch and with 
 massive legs. The Struthiones appear first in the Tertiary. The 
 New Zealand Apteryx, a small flightless bird, represents the order 
 Apteryges and the living tinamous the order Crypturi. Both have 
 only fragmentary fossil representatives. The super-order Euorni- 
 thes, with 13 orders, includes most of the existing birds. A few 
 representatives (cormorants, etc.) occur in the Cretacic, but the 
 great majority of types are not known before the Eocenic and 
 many not until later. 
 
 Mammalia. 
 
 The mammals are warm-blooded animals with the body typically 
 covered by hair, and in nearly all cases they bring forth their 
 young alive, the monotremes alone laying eggs. All, however, 
 suckle their young. The marsupials (opossum, kangaroo, etc.) 
 bear their young in an immature state, and these are then placed in a 
 pouch or marsupium. The placental mammals bear perfect young. 
 The Insectivora go back to the Eocenic ; they comprise the moles, 
 shrews, hedgehogs, etc. The Chiroptera, or bats, also go back 
 to the Eocenic. The Dermoptera are characterized by a cutaneous 
 expansion, extending from the wrists to the ankles and forming a 
 parachute. They are generally called flying lemurs and are un- 
 known in a fossil form. The Edentata, chiefly restricted to South 
 America, are nearly or quite toothless and include the living ant- 
 eaters and sloths, the armadillos, with jointed armor, and the ex- 
 tinct Glyptodon with solid armor. Here also belong the giant 
 sloths, the Megatherium, the Mylodon, and Grypotherium all of 
 them but recently extinct. 
 
 The Rodentia comprise the gnawing types with long, sharp 
 curved incisors. They go back to the Eocenic. The Tillodontia 
 are extinct forms from the North American Eocenic. They are 
 related to the rodents. The Carnivora, or flesh-eaters, comprise a 
 large number of living and extinct types, such as the Creodontia, 
 of the Tertiary; the Fissipedia, including Canidcc (dogs), Ursidce 
 (bears), Viverrida, Mustelidcc (otters, etc.), Hyanidcc (Hyaenas) 
 and Felidcc (cats, tigers, lions, panthers, etc.) ; and the Pinnipedia, 
 or marine carnivores, such as seals, sealions, etc. Many of these 1 
 have representatives in the Tertiary. The Cctacca, ar whales, dol- 
 
956 PRINCIPLES OF STRATIGRAPHY 
 
 phins, etc., are aquatic (mostly marine) mammals, and occur as far 
 back as the Miocenic. Squalodon and Zeuglodon are fossil repre- 
 sentatives. The Sirenia are herbivorous aquatic mammals repre- 
 sented by the living manatee and dugongs, and the recently extinct 
 sea-cow (Rhytina), etc. The Ungulates, or hoofed mammals, com- 
 prise: (i) the Eocenic Amblypoda (Coryphodon, Tinoceras, etc.), 
 large, heavy creatures; (2) the Proboscidea, or elephants (Dino- 
 therium, Mastodon, Stegodon, Elephas, etc.) ; (3) the Condilarthra 
 (Phenacodus) ; (4) the Perissodactyla, or unevenly-toed ungulates 
 (Tapir, Rhinoceros, Titanothere, and the horse family) ; (5) the 
 Artiodactyla, or even-toed ungulates, divided into the Bunodontia 
 (pigs, hippopotamus, Anthracotherium, etc.) ; and Selenodontia, 
 (Oreodon [Tertiary], camels, deer, etc.; giraffes, antelopes, goats, 
 sheep, cattle, etc.) ; (6) Toxodontia Tertiary forms, including 
 Toxodon, Typotherium, etc. 
 
 The final order of the mammals is that of the primates, which 
 includes Quadrumana (apes, monkeys, etc.), and the Bimana, or 
 man. 
 
 BIBLIOGRAPHY XXIV. 
 
 (Text-books of Palaeontology, etc.) 
 
 1. BERNARD, FfiLIX. 1895. Elements de Paleontologie. Bailliere et 
 
 Fils, Paris. 
 
 2. GRABAU, A. W., and SHIMER, H. W. 1909-1910. North American 
 
 Index Fossils. 2 vols. A. G. Seiler and Company, New York. 
 
 3. GURICH, GEORG. 1908-09. Leitfossilien. 2 parts. Gebruder Born- 
 
 traeger, Berlin. 
 
 4. KOKEN, ERNEST. 1896. Die Leitfossilien. Hermann Tauchnitz, 
 
 Leipzig. 
 
 5. NICHOLSON, ALLEYNE, and LYDEKKER, RICHARD. 1889. A 
 
 Manual of Palaeontology. 2 vols. W. Blackwood and Sons, Edinburgh 
 and London. 
 
 6. OSBORN, HENRY F. 1910. The Age of Mammals. Macmillan Com- 
 
 pany, New York. 
 
 7. STEINMANN, GUSTAV. 1903. Einfiihrung in die Palaeontologie. 
 
 Wilhelm Engelmann, Leipzig. 2nd edition, 1907. 
 
 8. STROMER, ERNST. 1909,1912. Lehrbuch der Palaeozoologie. 2 parts. 
 
 9. ZITTEL, KARL A. VON. 1881-85. Handbuch der Pateontologie. French 
 
 translation, Traite de Paleontologie, by Charles Barrois, Paris. 
 
 10. ZITTEL, K. A. VON. 1895. Grundziige der Palaeontologie. 2nd Edi- 
 
 tion, 1910-11. 2 vols. Munich. 
 
 11. ZITTEL, K. A., VON. 1900. Text-book of Palaeontology. Translated by 
 
 Charles R. Eastman with collaboration by many specialists. 2 vols. 
 Macmillan Company, New York. 
 
 (Classification, etc.) 
 
 12. ALLEN, J. A. 1906. The "Elimination" and "First Species" Methods of 
 
 Fixing the Types of Genera. Science, N. S., Vol. XXIV, pp. 773-779. 
 
BIBLIOGRAPHY XXIV 957 
 
 13. AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCI- 
 
 ENCE. 1877. Report of the Committee on Zoological Nomenclature. 
 Nashville Meeting. 
 
 14. BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 
 
 1842. Report of the Manchester Meeting. 
 
 15. BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 
 
 1865. Report of the Birmingham Meeting. 
 
 16. BUCKMAN, S. S. 1909. Yorkshire Type Ammonites, Part I. 
 
 17. ENCYCLOPAEDIA BRITANNICA. Eleventh edition. Articles on Zool- 
 
 ogy and various Phyla, Classes and Orders. Also Palaeontology and 
 Palaeobotany. 
 
 1 8. MILLER, S. A. 1889. North American Geology and Palaeontology. 
 
 19. OSBORN, HENRY F. 1912. First Use of the Word "Genotype." Sci- 
 
 ence, N-. S., Vol. XXXV, No. 896, pp. 340-341. 
 
 20. PAL^EONTOLOGIA UNIVERSALIS. 1904. Edited by D. P. Oehlers. 
 
 21. PATTEN, W. 1912. The Evolution of the Vertebrates and Their Kin. 
 
 P. Blakiston & Co., Philadelphia. 
 
 22. PATTEN, W. 1913. A Problem in Evolution. Popular Science Month- 
 
 ly, Vol. LXXXII, pp. 417-435. 
 
 23. SCHUCHERT, CHARLES. On Type Specimens in Natural History. 
 
 Catalogue, etc., of Fossils, Minerals, etc., in U. S. National Museum, 
 Pt. I, pp. 7-18, with bibliography of literature on type terms. 
 
 24. SCHUCHERT, CHARLES, and BUCKMANN, S. S. 1905. The Nom- 
 
 enclature of Types in Natural History. Science, N. S., Vol. XXI, pp. 
 899-901. 
 
 25. SCUDDER, SAMUEL. 1882. Nomenclator Zoologicus. Bulletin of the 
 
 United States National Museum, No. 19. 
 
 26. STONE, WITMER. 1906. The Relative Merits of the "Elimination" and 
 
 ' 'First Species" Method in Fixing the Types of Genera, with special refer- 
 ence to Ornithology. Science, N. S., Vol. XXIV, pp. 560-565. 
 
CHAPTER XXV. 
 
 BIOGENETIC RELATIONS OF PLANTS AND ANIMALS.* 
 THE CONCEPTION OF SPECIES. 
 
 A species is commonly held to comprise a group of individuals 
 which differ from one another only in a minor degree. The degree 
 of individual difference admissible within the species is commonly 
 a matter of personal opinion and probably no two systematists al- 
 ways agree as to the precise taxonomic value of a character in dif- 
 ferent cases. In pre-modern days the idea of permanence and im- 
 mutability of the species, or, in pre-Linnaean days, of the genus, 
 dominated the minds of naturalists generally, though there were 
 not wanting, at nearly all times, observers to whom the fixity of 
 specific characters appeared as a dogma unsupported by facts. 
 That variation existed within the specific limits was admitted, but 
 the believers in the special creation and immutability of species 
 would not admit that this variation could exceed certain limits, 
 though what these limits were was a matter of diverse and, more- 
 over, of constantly changing opinion. No matter how different 
 the end members of a perfectly graded series of individuals were, 
 if that gradation was established all those members were placed 
 within the limits of the species. Even if some of the members of 
 the series were originally described as distinct species or placed 
 in distinct genera the discovery of intermediate forms, or "con- 
 necting links," caused them all to be referred to one species. The 
 differences originally deemed amply sufficient for specific or even 
 generic distinction at once dwindled in taxonomic value to the rank 
 of varietal characters of a very variable species. A classic case 
 in point is that of the Tertiary species of Paludina (Vivipara) from 
 Slavonia. (Neumayr and Paul-29). (Fig. 252.) In the lowest 
 members of the Paludina beds P. neumayri (Fig. a), a smooth, 
 
 * The principles here outlined will be more fully discussed in "The Principles 
 of Palaeontology" by Henry F. Osborn and Amadeus W. Grabau, to be published 
 shortly. 
 
 958 
 
THE CONCEPTION OF SPECIES 
 
 959 
 
 round-whorled species, is the characteristic form, while the highest 
 beds are characterized by P. hoernesi (Fig. &), an angular- whorled, 
 strongly bicarinate type, which had been separated under the dis- 
 tinct generic name of Tulotoma. Certainly these end-forms are 
 widely separated, yet from the intermediate beds individuals con- 
 stituting a complete gradational series from one to the other have 
 been obtained. This discovery led many to reconsider the classifica- 
 tion of these forms and to group them all as varieties under one 
 species. 
 
 The belief in the mutability of species was gradually accepted 
 
 FIG. 252. Series of Paludinas (Vivipara) from the Lower Pliocenic deposits 
 of Slavonia. (After Neumayr.) a. Paludina neumayri, k. P. 
 {Tulotoma} hoernesi from the highest beds, b-i, intermediate 
 forms, showing gradation, from the intermediate beds. 
 
 by naturalists after the publication of "The Origin of Species" in 
 1859. To-day there is scarcely a naturalist of prominence who does 
 not unhesitatingly affirm his belief in the mutability of species. 
 Nevertheless, we may ask, with Farlow: "... is our belief 
 in evolution merely dogmatic, like some of the theological doctrines 
 which we believe thoroughly but which we do not allow to inter- 
 fere with our daily life, or, ... has our belief modified the 
 manner in which we treat what we call species?" (10) When we 
 note how unwilling systematists are to-day to recognize more than 
 one species in a series whose end forms differ widely, when a suf- 
 ficient number of members are known to bridge over all the more 
 striking gaps, we are forcibly impressed with the fact that, uncon- 
 sciously though it may be, the majority of systematists are still 
 
960 PRINCIPLES OF STRATIGRAPHY 
 
 influenced by the old inherited ideas of the fixity of specific limits. 
 Palaeontologists are, as a rule, no freer from the shackles of in- 
 herited ideas than are the workers in the morphology and taxonomy 
 of living plants and animals. This may in large measure be ac- 
 counted for by the fact that the very recognition of such a thing 
 as a species carries with it the impression of an entity, and the 
 recognition of certain characters as belonging to a species, in a 
 measure carries with it the conception .that, if those characters are 
 modified or supplanted by others, the organism in question no 
 longer belongs to that species. 
 
 That the Linnaean species is a fragment or group of fragments 
 of one or more evolutional series separated from other fragments, 
 in space or time, by the extermination of the connecting links, is 
 pretty generally recognized by naturalists of a philosophical turn of 
 mind. Among such the belief in the nonexistence of species is, 
 theoretically at least, widely held. In other words, naturalists have 
 come to the conclusion that what we call species are merely "snap- 
 shots at the procession of nature as it passes along before us, and 
 that the views we get represent but a temporary phase, and in a 
 short time will no longer be a faithful picture of what really lies 
 before us." "For the procession is moving constantly onward." 
 (Farlow-io.) 
 
 THE MUTATION OF WAAGEN. 
 
 Waagen in 1868 (44) recognized two kinds of variation within 
 the species geographic and chronologic. To the former, which 
 comprises the variable members appearing together in the same 
 rime period, though they may be geographically separated, he re- 
 stricted the term variation or variety, while for those occurring in 
 chronological succession he proposed the term "mutation," A mu- 
 tation may then be defined as a slightly modified form of the species 
 appearing in a later time-period, and in this sense it has been 
 commonly used by palaeontologists. As an example of a number of 
 mutations appearing in successively higher horizons, the Tertiary 
 series of Paludinas (Vivipara), already referred to, may be cited. 
 
 Palaeontologists, whose business it is to study large series of 
 forms from each successive horizon, have since recognized that 
 what Waagen called varieties, in the belief that they had no very 
 definite relationship to each other, are really secondary mutations 
 or sub-mutations (Grabau-i7). Thus each developing series has, 
 on reaching a higher horizon, become modified in a certain definite 
 
MUTATION OF WAAGEN 
 
 961 
 
 way and within this horizon the derivatives of this species will 
 become modified in certain definite directions. 
 
 As an illustration may be chosen the Linnsean species of brachi- 
 opod Spirifer mucronatus of the Middle Devonic of eastern North 
 America (Fig. 253). This is represented by at least five distinct 
 mutations in successive horizons, or in distinct basins. Each of 
 these five mutations differs from the others in certain more or less 
 constant characters, which, however, are the result of definite 
 modifications of the preceding more primitive types, chiefly by the 
 appearance of new characters.* Thus these mutations are readily 
 
 FIG. 253. Spirifer mucronatus, a. primitive mutation b.-d. mutation thed- 
 fordense. b. Long-winged retarded submutation, shell index 
 1.7. c. The most accelerated submutation (shell index 0.73). d. 
 The same drawn with curvature eliminated so as to show full 
 length. The more transverse character (higher shell index) of 
 the younger stages is shown in each. 
 
 recognizable and separable from one another with comparative 
 ease. Within each mutation, however, there is a long series of vari- 
 ants, which are modified by a progressive change in the relative 
 proportion of width and height a modification or change of quan- 
 titative rather than qualitative character a type of change to which 
 Osborn has applied the term allometric, while the resulting char- 
 acters are allometrons. The change in proportion in each of these 
 successive mutations is from broad-winged to short-winged types, 
 or allometrons. Expressed in shell indices, derived by dividing the 
 entire width along the hinge-line by the height measured on the 
 curvature, the change is from a high shell index to a lower one. 
 In each mutation the change is in the same direction, and in each 
 a dominant type can be designated which, as a sub-mutation,^ repre- 
 sents, for the mutation to which it belongs, that index to which the 
 * Termed, by Osborn, Rectigradations. (See beyond.) 
 
962 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 majority of individuals of that fauna approximate. The dominant 
 sub-mutation of a higher mutation will be found to have a smaller 
 index than the dominant sub-mutation of a lower mutation. In 
 the same way, the most primitive sub-mutation of the higher muta- 
 tion, i. e., the one with the largest shell index, has a smaller index 
 than the most primitive sub-mutation of the lower mutation. In 
 like manner the most specialized sub-mutation of the higher (geo- 
 logic) mutation will have a smaller index than the most specialized 
 sub-mutation of the lower mutation. In other words, not only has 
 the dominant sub-mutation of the higher mutation advanced beyond 
 
 75% 
 
 5,0 To - 
 
 
 2.1 2J9 
 
 1.1 1.0 0.85 0.73 
 
 FIG. 254. Curves representing the range in shell index of two mutations of 
 Spirifer mucronatus. 
 
 that of the lower mutation in the same direction of modification of 
 proportions, but also the most primitive and the most specialized 
 sub-mutation and all the intermediate sub-mutations of the later 
 mutations are ahead of the earlier one. This may be expressed in 
 the accompanying diagram (Fig. 254), where the height of the 
 curve represents the percentage of individuals and the base the 
 decline in shell index from 3.0 to 0.5. 
 
 MUTATION THEORY OF DE VRIES. 
 
 In 1901 Professor Hugo De Vries published his epoch-making 
 book "Die Mutations-theorie" (6) in which he recognized that the 
 Linnaean "species" was in reality a compound of innumerable 
 groups of more restricted relationship. These minor groups, which 
 have generally been classed together as a "species," are really enti- 
 ties composed of very definite associations of minute characters, 
 and to them the name elementary species applies. Of these ele- 
 mentary species there may be very many in a Linnaean species. 
 These elementary species De Vries thinks arose suddenly by a new 
 combination of the elements of which the characters of organisms 
 are made up. These elements (Einheiten) are sharply separated 
 
MUTATION; ORTHOGENESIS 963 
 
 from one another and the resulting- combinations or elementary 
 species are likewise distinct and definite and without transitional 
 connecting forms. They are constant and transmit their characters 
 truly. The sudden appearance of these new forms is a process 
 which De Vries calls "mutation," thus using Waagen's term for a 
 process instead of a result, as originally proposed. The "elementary 
 species" as defined by De Vries is, in a measure, identical with the 
 mutation of Waagen, in that the variation is a slight and definite 
 one; but in so far as De Vries believes in the stability and immuta- 
 bility of the elementary species, they do not correspond to the muta- 
 tion and sub-mutation (allometrons) as used by most palaeontolo- 
 gists to-day. 
 
 ORTHOGENESIS AND THE CONCEPT OF SPECIES. 
 
 The doctrine of definite directed variation, or Orthogenesis, 
 which finds many adherents, especially among palaeontologists, has 
 led to a very logical conception of the method by which species 
 become differentiated. Though independently formulated with 
 more or less precision by many naturalists this doctrine was most 
 consistently and vigorously championed by the late Professor Theo- 
 dor Eimer of Tubingen. . Eimer's illustrations were chiefly drawn 
 from the color patterns of recent animals, especially lizards and 
 butterflies (9). He found that the color patterns of organisms may 
 be reduced to four types, which always appear in the individual 
 development in a definite succession, viz. : ( i ) Longitudinal stages, 
 (2) spots, (3) cross stripes, and (4) uniform coloration. Each 
 succeeding type is developed out of the preceding one and replaces 
 it to a greater or less extent. When in a large number of indi- 
 viduals all developing in the same direction (orthogenetically) a 
 complete cessation of development occurs in different groups at indi- 
 vidual stages, the individuals thereafter only increasing in size, but 
 not changing, a large number of distinct species will originate which 
 differ from one another to the extent by which one group continued 
 to develop beyond the other. If a number of characters develop, 
 each in a given direction, and at a given rate in a large group of 
 individuals, all starting from the same point, cessation of develop- 
 ment of different characters at different times will soon result in 
 the formation of a great number of species varying in one or 
 more characters. 
 
 We may assume, by way of illustration, a case in which there 
 are three structural characters, which we may designate characters 
 (a), (b), and (c), in a given group of individuals, each changing 
 
964 PRINCIPLES OF STRATIGRAPHY 
 
 in a definite order and at a uniform rate. A certain percentage 
 of these individuals may, after a while, cease to develop character 
 (a) while characters (b) and (c) continue to develop. Later in 
 some of these, character (b) may cease to develop further and (c) 
 continue alone, while in others (c) ceases to develop and (b) 
 continues. In another portion of the original group character (b) 
 may cease to develop first and (a) and (c) continue, after which 
 character (a) may stop in some and (c) in others the other char- 
 acter continuing. The combinations possible by this method will be 
 readily recognized and the number of different types mutations, 
 varieties, or species, according to the rank to which they are ad- 
 mitted will be readily seen. The possibilities of differentiation 
 will be further recognized when it is considered that the length 
 of time during which each character develops may also vary greatly. 
 Complete cessation of development of characters has been termed 
 genepistasis by Eimer, and the differential cessation heterepistasis. 
 
 ACCELERATION AND RETARDATION IN DEVELOPMENT (TACHYGENE- 
 sis AND BRADYGENESIS). 
 
 Another principle which is of great importance in this connec- 
 tion, and which was first clearly recognized by Hyatt and by Cope, 
 is acceleration or tachygenesis.* Instead of a uniform rate of de- 
 velopment some organisms may .develop more rapidly and so are 
 able to reach a higher stage in development. Differential accelera- 
 tion may obtain between the different characters. Again, retarda- 
 tion (bradygenesis *), first recognized by Cope, may progressively 
 diminish the rate of development, so that certain individuals in 
 some or all of their characters may fall more and more behind the 
 normal rate of progress. 
 
 Illustrations of Orthogenetic Development. Some of the most 
 satisfactory series, showing development in definite directions, have 
 been brought to light by the labors of palaeontologists. Such series 
 are especially well known among the ammonoids, a class of cephalo- 
 podous Mollusca which began its existence in the Devonic, culmi- 
 nated in the Jura, and had its last representatives in late Cretacic 
 time. 
 
 Some of the earliest studies of the developmental changes of 
 this group were carried on by Alcide d'Orbigny (8), who recognized 
 a distinct succession in the form and ornamentation of the shell 
 
 * From raxfo = fast and ppadfa = slow, ytvceu = birth. The term bradyge- 
 nesis was used by Grabau in 1910 (16) as a complement of the term tachygenesis. 
 
ACCELERATION AND RETARDATION 965 
 
 from rounded and smooth in youth; through ribbed, and tubercled, 
 with angular and, later, keeled whorls; to old age, which was 
 marked by a complete loss of all ornamentation. The late Pro- 
 fessor Alpheus Hyatt was, however, the first to recognize the sig- 
 nificance of these changes and to point out that they recapitulated 
 the adult characteristics of successive ancestors. The number of 
 recognizable characters of which the development may be studied 
 is exceptionally large in the Ammonite shell. Thus there is the 
 degree of coiling or involution, which varies from the condition in 
 which the whorls do not even touch each other through whorls in 
 contact and whorls impressed on each other to complete involution, 
 in which the last whorl covers all the preceding ones. Then there 
 is the form of the cross-section of the shell and the character of 
 the outer or ventral surface of the shell, which varies from rounded 
 through angulated to various degrees of channeled and keeled. 
 Again the surface ornamentation varies from smooth to ribbed, 
 noded, or even spinous, and, finally, and in many respects most 
 significantly, there is the progressive change in the complexity of 
 the septal sutures, from simple in the young to often highly complex 
 in the adult. In addition to these, the form and position of the 
 siphuncle often show a definite variation, which may be of consider- 
 able importance. To give a concrete example of the changes in 
 the individual development of the shell and the correlation of the 
 various stages with the adult stages of ancestral forms, we may 
 select a closely related series of ammonites of the family Placenti- 
 ceratida, all of which are characteristic of the Cretacic formations 
 of North America. The changes here are chiefly in the form of the 
 cross-sections and the characters of the surface ornamentations. 
 The most advanced form of the series is Stantonoceras pseudo- 
 costatum Johnson, a large, robust ammonite with a broad, rounded 
 venter and rather ill-defined, coarse, rib-like elevations on the lat- 
 eral surfaces of the whorls. When this form is broken down it is 
 found that the next inner whorl has a flattened ventral band bor- 
 dered by a row of faint elongated nodes on either side and a large 
 row of tubercles on the ventro-lateral angles. At this stage the 
 species has the characters of the adult Stantonoceras guadalupce 
 (Roemer), which may be regarded as an immediate ancestor. A 
 still earlier whorl shows a very narrow flattened venter, with a 
 strong row of elongated nodes on either side of the flattening, the 
 surface being otherwise smooth. This corresponds to more primi- 
 tive species, Placenticeras intermedium Johnson, and P. planum 
 Hyatt, one or the other of which was probably in the direct line 
 of ancestry. At a still earlier stage in these shells the venter is 
 
966 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 hollowed and bordered by smooth ridges, while the surface is 
 smooth features characteristic of the adults of certain species of 
 the genus Protengonoceras of the Lower Cretacic. In all these 
 types the sutures show close relationship and increasing complexity 
 with the progressive changes of the form of the shell. At a still 
 earlier stage the venter is flattened without channel, the section of 
 the whorl being helmet^shaped, while the earliest marked stage 
 shows a rounded venter. The sutures of this early stage are very 
 simple, corresponding in general to the adult suture of Devonic or 
 Carbonic Goniatites, which the form of the shell also recalls. As 
 
 FIG. 255. a. Cross-section of 'the three outer whorls of Stantonoceras 
 pseudocostatum reduced. (After Johnson.) b. Cross-section of 
 the inner whorls of Stantonoceras guadalupa, enlarged. (After 
 Hyatt.) 
 
 the form changes the complexity of the sutures increases until the 
 complex adult suture is developed. The cross-sections of the vari- 
 ous stages are shown in Fig. 255. The early "Goniatite" stages of 
 Schloenbachia aff. chicoensis Trask, a highly developed ammonite 
 of the Lower Cretacic of Oregon, are, according to J. P. Smith, as 
 follows (43:5^1): The first suture (immediately succeeding the 
 protoconch) has narrow lateral lobes and saddles * and a broad 
 ventral saddle. The second suture has a small lobe in the center 
 of the broad ventral saddle, which is thus divided. This corre- 
 sponds to the adult suture of the Devonic genus Anacestes, a 
 simple form of "goniatite" which Hyatt considers the immediate 
 radicle of the ammonoid stock. The third and fourth sutures show 
 
 * Lobes are the backward loops of the suture and saddles the forward loops, 
 i. e., those convex toward the mouth of the shell. The ventral border is the 
 outer border of the shell ; the space between the inner margins of the whorl is the 
 umbilicus, in which can be seen the earlier coils. 
 
ILLUSTRATIONS OF ORTHOGENESIS 967 
 
 accentuation of the lobes and saddles, and recapitulate the adult 
 sutures of such later Devonic types as Tornoceras and Prionoceras. 
 The fifth suture is transitional to the sixth, which is characterized 
 by a divided ventral lobe, one lateral lobe on each side, and another 
 on each side of the umbilical border. Here, then, the lobe which 
 complicated the original ventral saddle is itself divided by a second 
 low ventral saddle. The shell at -this stage has a low, broad, in- 
 volute whorl, and in this and the character of the suture recalls the 
 adult of the older species of Glyphioceras. The typical Glyphio- 
 ceras condition is represented by a somewhat later suture, and still 
 later, with the appearance of a second lateral lobe next to the 
 umbilicus, the shell begins to resemble the late Carbonic goniatite 
 Gastrioceras, and at a still later stage, when the diameter of the 
 shell is 2.25 mm., a third lateral lobe appears next to the umbilicus 
 which subsequently widens, while the whorls become higher and 
 narrower. In this stage it recalls the genus Paralegoceras. The 
 next stage ushers in true ammonitic ornamentation in the form of a 
 ventral keel (2.7 mm. diam.), while the suture still remains goni- 
 atite-like. But when the shell has reached a diameter of 3.2 mm. the 
 first lateral saddle becomes indented, a true ammonoid suture thus 
 coming into existence. The future development is along the line 
 of increasing complexity of suture. 
 
 A consideration of the possible mutations which may come into 
 existence by the operation of the law of heterepistasis, or differ- 
 ential arrestation in development, and by the operation of the laws 
 of differential acceleration and retardation of characteristics, will 
 convince one that all the known types of ammonites, as well as 
 many yet unknown types, may be accounted for in this manner. 
 Not only all .so-called species, but every individual variation will 
 fall into its proper determinate place in the series when the method 
 of analysis of individual characters has become sufficiently de- 
 tailed. 
 
 Another example, taken from the gastropods, may serve to 
 further illustrate the principles here discussed (Fig. 256). The 
 modern Fulgur caricum, a large gastropod occurring on the Atlantic 
 coast between Cape Cod and the Gulf of Mexico, begins its embry- 
 onic existence with a smooth shell drawn out anteriorly into a canal 
 and not unlike in form to some smooth Fasciolarian shells (Fig. 
 256, b, c). At a very early age the shell is furnished with ribs and 
 then an angulation appears in the outer whorl. On this angulation 
 the ribs are soon reduced to rounded tubercles. This condition 
 recalls the adult characters of Lower Miocenic species of this genus, 
 which never pass beyond the tubercled stage. This stage in the 
 
968 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 modern species is succeeded by one in which strong spines occur, 
 caused by periodic notchings or emarginations of the shell margin 
 along the line of the angulation. The tubercles and spines pass the 
 one into the other by what appears to be a process of enlargement 
 of the tubercles. 
 
 When we come to consider the series of forms which lead up 
 from the tubercled (Tertiary) species (F. fusiformis, F. tuber cn- 
 latum) to the modern form, we find that certain intermediate 
 characteristics have been omitted. As shown by the specimen of 
 
 FIG. 256. Development of the gastropod shell (Fulgur and Sycotypus). a. 
 Protoconch of _ Sycotypus canaliculatus. b, c. The same before 
 hatching, showing smooth shell; animal with velum. (The early 
 stages of Fulgur caricum are identical with these.) d. Fulgur 
 fusiformis. e. F. rapum (representing F. maximum), f. F. 
 tritonis. 
 
 F. fusiformis figured (Fig. 256, d), the last part of the last whorl 
 has already lost the tubercles and has become smooth and rounded 
 in outline. This is prophetic of the form next to be noted, F. maxi- 
 mum (Fig. 256, e). In this shell the tubercled stage is passed through 
 quickly a case of acceleration in development and the smooth, 
 rounded whorl stage makes up the greater part of the shell. Thus 
 the normal characters of F. fusiformis have become condensed to 
 a few whorls, in this manner making room for the smooth whorl 
 which characterizes the shell. It is in certain advanced accelerated 
 individuals of this type that the emarginate spines so characteristic 
 
DEVELOPMENT OF A GASTROPOD 969 
 
 of the modern F. caricum first make their appearance. In a more 
 advanced type, F. tritonis (Fig. 256, /), the characteristic round 
 "maximum" type of whorl has become restricted to a few earlier 
 whorls, the adult whorl being marked by the spinous "caricum" type 
 of whorl. Different individuals show progressive encroachment of 
 the "caricum" type on the "maximum" type, until the latter has 
 been completely superseded, the spines then following immediately 
 upon the tubercles; and, in still more advanced forms, becoming 
 telescoped with them. This is the character of the modern type, 
 where the tubercles pass imperceptibly into the earliest spines. 
 It is thus only by the consideration of the intermediate Tertiary 
 
 A I 
 
 1 1 2 
 
 I 
 1 
 
 6 
 
 n 1 
 
 n |_ 
 
 1 1 2 1 3 
 
 L)l 
 
 r \ 
 
 I 1 
 
 1 i 2 i 3 i 4 
 
 L 1 
 
 n i 
 
 1 i 2 i 3 i 4 i 5 
 
 U 1 
 
 Ei 
 
 III 1 
 12345 6 
 
 1 
 
 i 
 P i 
 
 1 1 1 1 1 
 
 1.23456 7 
 
 r i 
 r i 
 
 II 1 1 II 
 
 1.2.3.4.5. 7 
 
 FIG. 257. Diagram illustrating the development of the Fulgur series. 
 
 Stage r is the protoconch which persists throughout. 
 
 Stage 2 is the smooth shell stage which in the primitive species A forms 
 the adult, but in B is shortened. 
 
 Stage 3 is the ribbed stage, which is wanting in A, but in a somewhat more 
 advanced species B is well developed in the adult. 
 
 Stage 4 is characterized by an angular whorl, the ribs still continuing. It is 
 the adult character of species C, in which stages 2 and 3 are condensed. 
 
 Stage 5 is the tubercled stage characteristic of the adult of F. fusiformis. 
 
 Stage 6 is the smooth round-shelled stage found in the old age of species D 
 and the adult of E. 
 
 Stage 7 (F. maximum) shows the caricum spines well developed in species 
 F while in species G the modern F. caricum, Stage 6, has been eliminated and 
 Stage 7 follows directly upon the tubercles (Stage 5). 
 
 types that the true history of the development of the Fulgurs is 
 learned, the individual life history of the modern F. caricum being 
 an abbreviated and incomplete recapitulation of the history of its 
 race. Here acceleration has been so pronounced as actually to 
 eliminate certain stages in the sequence of development. The pre- 
 
970 PRINCIPLES OF STRATIGRAPHY 
 
 ceding diagram (Fig. 257) will summarize this method and also 
 give a graphic illustration of the law of acceleration. 
 
 Origin and Development of Characters the Important Question: 
 Rectigradations and Allometrons. As pointed out by Osborn, the 
 origin and development of individual characters or parts is the 
 important subject for investigation, the species question being of 
 minor significance. It has been shown in the preceding sections 
 that characters develop more or less independently of each other, 
 and also that they develop in recognizable directions, or ortho- 
 genetically. Such definitely developing characters when arising as 
 new characters are termed by Osborn rectigradations ; whereas, if 
 they are due to a change in proportion of such characters, they are 
 termed by him Allometrons (30:32). 
 
 NOMENCLATURE OF STAGES IN DEVELOPMENT. 
 
 Ontogenetic Stages and Morphie Stages. In the preceding ex- 
 amples it will be noted that the stages dealt with are form stages 
 or morphic stages only, and that they have no constant relation to 
 the actual stages in successive ontogenetic development. Thus, 
 one and the same morphic stage, i. e., stage characterized by certain 
 morphological characters, as, for example, ribs, tubercles, or spines, 
 etc., may be characteristic of the adult of one individual, and, of a 
 more youthful stage, of another. In dealing with changes in form 
 it is desirable to refer each morphic stage to the corresponding adult 
 stage of an ancestor, and to designate it by the name of that ances- 
 tor. Thus the tubercled stage of Fulgur tritonis (Fig. 256, /) is des- 
 ignated the F. fusiformis stage, since the feature in question charac- 
 terizes the adult of that species. In like manner, the smooth 
 morphic stage of F. tritonis is designated the maximum stage, and 
 the spinose stage the F. caricum stage, from the species in which 
 these characters belong to the adult. The development of each in- 
 dividual (ontogeny) comprises a series of stages which develops 
 from birth to old age. These ontogenetic stages, or onto-stages, 
 are similar in time-duration for related organisms and are further 
 characterized, in a general way, by a correspondence in the pro- 
 portional rate of growth in closely related types. They are, how- 
 ever, independent of the morphic characters, for, as already shown, 
 a certain morphic character may appear in one individual in the 
 adult stage and in another more accelerated individual in a more 
 youthful stage. (Grabau-na.) 
 
 Simple Organisms. Hyatt and others have given us a set of 
 
NOMENCLATURE OF STAGES IN ONTOGENY 971 
 
 terms which are applicable to the ontogenetic stages of development 
 of all non-colonial organisms, and hence deserve to be widely and 
 generally used. The ontogenetic cycle, 'or cycle of individual de- 
 velopment (Hyatt-2o), is divided into the Embryonic and the 
 Ep-embryonic periods, and each is further subdivided into onto- 
 stages and sub-stages, as follows : 
 
 EMBRYONIC. 
 
 EP-EMBRYONIC. < 
 
 Onto-stage. 
 Prot-embryonic 
 Mes-embryonic 
 Met-embryonic 
 Neo-embryonic 
 Typ-embryonic 
 Phyl-embryonic 
 
 Nepionic 
 Neanic 
 Ephebic 
 Gerontic 
 
 Onto Sub-stage. 
 
 A na-prot-embryonic 
 
 Meta-prot-embryonic 
 
 Para-prot-embryonic 
 
 A na-mes-embryonic 
 
 Meta-mes-embryonic 
 
 Para-mes-embryonic 
 
 A na-met- embryonic 
 
 { Mela-met- embryonic 
 Para-met- embryonic 
 A na-neo-embryonic 
 Meta-neo-embryonic 
 Para-neo-embryonic 
 A na-typ-embryonic 
 Meta-typ-embryonic 
 Para-typ- embryonic 
 
 [ Ana-phyl-embryonic 
 M eta- phyl- embryonic 
 Para-phyl-embryonic 
 
 Ana-nepionic 
 
 Meta-nepionic 
 
 Para-nepionic 
 
 Ana-neanic 
 
 Meta-neanic 
 
 Para-neanic 
 
 A na-ephebic 
 
 Meta-ephebic 
 
 Para-epnebic 
 
 Ana-gerontic 
 
 Meta-gerontic 
 
 Para-gerontic 
 
 The sub-stages ana, meta, and para, or the early, intermediate, 
 and later sub-stages, are useful for more detailed subdivision 
 than is possible with the stages alone. The phyl-embryonic is the 
 only em?3ryonic stage with which the palaeontologist has to deal. It 
 is the first stage in which hard parts capable of preservation are 
 generally formed. The phyl-embryonic stages of the following 
 classes of invertebrates have been definitely recognized and named : 
 
972 PRINCIPLES. OF STRATIGRAPHY 
 
 Simple corals proto-corallum. 
 
 Brachiopoda protegulum (Beecher). 
 
 Pelecypoda prodissoconch (Jackson). 
 
 Gastropoda protoconch (protorteconch) (Hyatt and Grabau). 
 
 Scaphopoda periconch (Hyatt). 
 
 Cephalopoda protoconch (Owen). 
 
 Trilobites protaspis (Beecher). 
 
 Echinoidea protechinus (Jackson). 
 
 The Nepionic Stage is the babyhood stage of ep-embryonic ex- 
 istence. Its exact limitation cannot be denned in general terms, 
 as it is different in different classes of organisms. In general, it 
 may be said that, for ammonites, it covers most, if not all, of the 
 morphic stages in which the suture is of the goniatite type. In the 
 case of Schloenbachia, cited above, the morphic stages, up to the 
 point where the young ammonite resembles in its sutures the genus 
 Paralegoceras, are considered by Smith to belong in the nepionic 
 stage. Here the neanic stage begins shortly before the suture has 
 lost its goniatite character, but an ammonite character has made its 
 appearance in the form of a keel. In Fulgur caricum and other 
 advanced species of this group of gastropods the nepionic stage 
 may be regarded as completed with the end of the tubercled condi- 
 tion (F. fusiformis, morphic stage). 
 
 The neanic is the youthful or adolescent stage, which comprises 
 the interval during which the organism acquires all the characteris- 
 tics of maturity. When this condition is reached the organism 
 enters on the ephebic, or adult, stage. Long-lived individuals often 
 show old age or senile characteristics, which consist especially in the 
 loss of ornamentation and a degenerate change in the manner of 
 growth. This is the gerontic stage in the ontogenic cycle, and it is 
 followed by death. 
 
 Gerontic characteristics may appear early in the life of indi- 
 viduals of a specialized race. Thus the loss of characters and the 
 degenerate change in growth may occur while the individual is still 
 in the adult (ephebic) stage or even earlier. Such races are said 
 to be phylogerontic and are approaching extinction. Thus the late 
 Cretacic cephalopods, which lost the power of coiling either partly 
 (Heteroceras, etc.) or wholly in the adult (Baculites), represent 
 the phylogerontic terminals of the degenerating race of ammonoids. 
 
 It must, however, be clearly borne in mind that the existence of 
 phylogerontic lines or races at any time does not indicate that the 
 phylum or class as a whole is gerontic. Even within the same 
 genus there may be found species showing a gerontic tendency. 
 The phylogerontism here applies only to the particular branch in 
 question, while the rest of the evolutional tree of this phylum may 
 
CHARACTERS OF COLONIAL FORMS 973 
 
 be perfectly sound. Many early Ordovicic nautiloids show a loss 
 of the power to coil, and so indicate the existence of degenerating 
 or phylogerontic branches at a time when the class of cephalopods 
 as a whole had not yet permanently acquired the power of coiling. 
 Gastropods with the last whorl not coiled are found throughout 
 the geologic series, even in Lower Cambric time, where coiling had 
 but just begun. Such senile branches are, of course, to be expected 
 in any developing series where wrong or too hasty experiments may 
 be made by individual genetic lines. (See illustrations in North 
 American Index Fossils.) 
 
 Colonial Forms. These require a specially modified nomencla- 
 ture since we deal not with individuals, but with groups of indi- 
 viduals. In these we must keep separate the individual life history 
 or ontogeny and the life history of the colony, i. e., colonial on- 
 togeny (astogeny or autogenesis). The first form considered in such 
 cases is nepionic so far as the colony is concerned. To express this 
 fact Cumings (5) has coined the terms nepiastic, neanastic, ephe- 
 bastic and gerontastic* which express for the colony what the 
 Hyattian terms express for the individual. The first completed 
 individual of a colony may be dignified by a distinctive term, though 
 it cannot be considered homologous with the phyl-embryonic stage 
 of the individual. In Hydrozoa and in compound corals the first 
 completed individual is the prototheca (the sicula of graptolites, the 
 initial pipe-like corallite of the Favositid corals), and in Bryozoa it 
 is the protoccium. (Cumings-5.) 
 
 INTRACOLONIAL ACCELERATION AND RETARDATION. 
 
 Colonial organisms may suffer differential acceleration or re- 
 tardation when certain groups of individuals develop either more 
 rapidly or more slowly than others. This leads to the formation, 
 within the same colony, of two or more types of structure, normally 
 characteristic of distinct species. In this manner we can ex- 
 plain such phenomena as the occurrence of different types of leaves 
 upon the same plant, and different groups of individuals in the same 
 colony of animals where some individuals retain ancestral charac- 
 ters, while others develop further. Among plants the tulip tree 
 (Lyriodendron tulipifera) may be taken as an illustration. The 
 two and four-lobed types of leaf are characteristic of ancestral 
 -Cretacic species. Modern trees, with normally 6-lobed leaves, also 
 
 * From &<rrv (asty), a group of dwellings. 
 
974 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 contain adult leaves and sometimes entire branches in which the 
 leaves never pass beyond the four-lobed or even two-lobed type. 
 By retardation the ancestral characters are retained side by side 
 with the normal characters of the modern species. Eight-, 10-, 12- 
 and sometimes 14-lobed leaves also occur, evidencing local intra 
 colonial acceleration. 
 
 An example among colonial animals will further make this 
 clear. Favosites canadensis of the Ononclaga limestone is charac- 
 terized by small corallites with polygonal openings, while among 
 these are scattered at regular intervals larger ones with nearly cir- 
 cular openings. Favosites placenta of the middle Hamilton of 
 
 FIG. 258. Portions of the surfaces of two colonies of Favosites, somewhat 
 enlarged, to show intracolonial acceleration, a. F. canadcusis, 
 showing the regular distribution of the large cylindrical corallites 
 among the smaller prismatic ones. b. F. placenta, showing the 
 F. canad-ensis condition on the left, and the large prismatic 
 corallites on the right. 
 
 Canada when young (nepiastic) has the characteristics of adult 
 F. canadensis, but when colonially adult it has retained the F. cana- 
 densis type in certain portions of the colony only, other portions 
 having developed a uniform series of large corallites with polygonal 
 apertures. Here, then, certain portions of the colony have been 
 retarded in their development, retaining ancestral characters, while 
 others have continued to develop. In the upper Hamilton a species 
 of the F. placenta type (F. placentoides) occurs with all the coral- 
 lites uniform, large and angular in aperture (Fig. 258). 
 
 Acceleration in certain portions and retardation in others when 
 occurring in more or less regular manner result in the formation of 
 colonial ornamentation, such as is so characteristic of Bryozoa. 
 
 Atavism or Reversion. Not infrequently among a large number 
 of individuals of a species characterizing a certain horizon a few 
 will be found in which ancestral characters occur in the adult, thus 
 recalling species of a lower geologic horizon. This atavism or 
 
ATAVISM OR REVERSION 975 
 
 reversion of the species to ancestral characters may often be seen 
 to be nothing more than an arrestation of development at an imma- 
 ture morphic stage, when the characters of the young are like those 
 of the adult ancestor of earlier geologic horizons. This arrestation 
 of development or genepistasis is only a step removed from pro- 
 gressive retardation in development of which it forms the distal 
 limit. In either case, whether complete or partial arrestation (heter- 
 epistasis) occurs, or whether development is retarded altogether 
 or along certain lines, the resultant form will seem out of place 
 in the horizon characterized by the more advanced species, and may 
 sometimes lead to mistaken classification of the strata containing 
 them. 
 
 As an example of atavistic individuals occurring in a horizon 
 above their normal may be cited the case of the Devonic brachiopod 
 Spirifer mucronatus and its derivatives already mentioned. This 
 species, so far as known, is represented by the elongated, strongly 
 mucronate type in the lower Hamilton beds of eastern North 
 America. In the Upper Hamilton of Ontario occurs the mutation 
 S. thedfordense, which in its younger stages has all the features of 
 the typical lower Hamilton form, but in the adult it is proportionally 
 much less extended, without mucronate points, without the charac- 
 teristic plication in the median sinus of the pedicle and groove in 
 the median fold of the brachial valve, and with strongly marked, 
 regular lines of growth. With this species occur a number of 
 individuals which have been retarded in their development and 
 which, hence, recall the ancestral type in some of their characters 
 notably the strong mucronate lateral extensions. In the New York 
 province of the Middle Devonic the chief developmental changes 
 acquired by S. mucronatus consist in the relative shortening of the 
 mucronate angles as the shell approaches the adult stage, until 
 from a width several times its height it had changed to a form in 
 which the width was more nearly equal to the height, and in which 
 the mucronations were wholly obliterated. In other respects 
 the changes were very slight. With this mutation occurs not infre- 
 quently a form showing arrestation of development (genepistasis) 
 at an early stage, and hence it retains into the adult its youthful 
 mucronate character, which recapitulates the ancestral condition. 
 These arrested individuals thus recall in practically all respects 
 the primitive mucronate type from which they are derived. 
 
 An example of a retarded individual from the Karnic lime- 
 stone of the California Trias is cited by J. P. Smith. This was 
 an immature specimen of the ammonoid genus Trachyceras which 
 had persisted unusually long in the ancestral Tirolites stage, thus 
 
976 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 resembling the adult of that genus which belonged in a lower hori- 
 zon. This occurrence threatened to cause difficulty in correlation. 
 
 PARALLELISM AND CONVERGENCE IN DEVELOPMENT. 
 
 Homer agenesis. One of the most important of the many facts 
 brought to light by the researches of palaeontologists is that many 
 groups of organisms develop independently in similar directions, 
 
 FIG. 259. Illustration of parallelism. A series of Eocenic Fusoid shells, be- 
 longing to different genera, but readily mistaken for members of 
 the same genus Fusus under which they were originally de- 
 scribed, a. Falsifusus mey'eri; b. Fulgurofusus rugatus. c. 
 Fusus asper X i^. d. Early whorls of same, enlarged X 10. 
 
 and that hence in disconnected series species with similar adult 
 characteristics may develop. These, morphological equivalents, as 
 Hyatt has termed them (or Homoeomorphs of Buckman), are often 
 so much alike that they have been united under the same generic 
 or even specific name. The Eocenic fusoid shell Falsifusus, from 
 the Gulf Coast of the southern United States, is an example of 
 this, the adult form having all the characteristics of the genus 
 Fusus, though, as shown by the young stages, the American form 
 
PARALLELISM AND CONVERGENCE 
 
 977 
 
 is probably derived from a Pleurotoma-like ancestor, and not a 
 true Fusus at all.* (Fig. 252.) 
 
 The Eocenic genus Clavilithes furnishes a number of striking 
 examples of this similar development or homceogenesis, as Eimer 
 has termed it.f (Fig. 260.) 
 
 The typical species of this genus, C. parisiensis, from the Cal- 
 caire Grossier of the Paris Basin, finds its almost exact equivalent 
 in the modern Cyrtulus serotinus, Hinds, of the Marquesas region 
 in the South Pacific. Clavilithes became extinct in the Eocenic, 
 while Cyrtulus is a derivative from the modern stock of Fusus. 
 But by far the most interesting type of this complex series is 
 
 FIG. 260. Clavilithoid shells showing "convergence." a, b. Cyrtulus sero- 
 tinus. A modern clavilithoid, being the phylogerontic terminal of 
 the Fusus series (slightly reduced), c. The protoconch and 
 early conch stages of Clavilithes parisiensis, an Old World 
 Eocenic clavilithoid (enlarged), d. Clavilithes (f) kennedy- 
 anus, a New World Eocenic clavilithoid of independent origin 
 (slightly reduced). 
 
 Clavilithes scalar is (Lamarck), from the Sables Moyens of France. 
 This species is characterized by a projecting rim or flange on 
 the shoulder of the adult whorl. This same feature is reproduced 
 in Clavilithes longcevus (Solander) of the Barton Beds of England, 
 which is of wholly independent origin. Again, Clavilithes f cham- 
 berlaini, Johnson and Grabau, from the Lower Claibornian of 
 Texas, shows the same type of structure, and here, too it is inde- 
 pendently derived. Finally, Rhopalithes japeti (Tournouer) repre- 
 sents this same feature in a genus entirely distinct from Clavilithes 
 
 * The distinction is not accepted by all. (Grabau-i4.) 
 
 f The controversy regarding this and the other species mentioned here is 
 dealt with by Grabau (13:622 et seq.) in the Studies of Gastropoda III. 
 
978 PRINCIPLES OF STRATIGRAPHY 
 
 Examples of such equivalents could be multiplied indefinitely. In 
 the majority of cases, where classification has taken account only 
 of the adult characters, such homceogenetic types have been classed 
 together as of the same genus or species, and sometimes even as 
 varieties of the same species. 
 
 It is hardly going too far to say that the majority of classifica- 
 tions of invertebrates now in vogue may be likened to a more or 
 less warped plane passed through the crown of a tree; all the 
 points of intersection of the branches and the plane are considered 
 as species, while all the neighboring and some distant ones are 
 grouped together in a genus, or family. The illogical nature 
 of this method, which is the natural result of a consideration of 
 adult characters only, must be apparent. 
 
 Morphologic equivalents have been recognized most frequently 
 among ammonoids. Formerly all types in which the suture was 
 composed of simple lobes and saddles were classed as Goniatites. 
 All those in which the lobes were crenulated as Ceratites, and all 
 those in which both lobes and saddles had become compound were 
 placed in the genus Ammonites. It is now known that many and 
 diverse genetic series started with genera of the goniatite type, 
 branched out in diverse genera with ceratite sutures and that from 
 these latter were derived the genera in which the suture was am- 
 monitic. Again, similar types of ornamentation and similar de- 
 grees of coiling or involution appeared independently in distinct 
 genetic series, thus producing species which often closely re- 
 sembled each other in the adult type, but which had a wholly dis- 
 tinct ancestry. 
 
 Among vertebrates many cases of similar independent morpho- 
 logical equivalents have been discovered, especially in the class of 
 mammals, and in that of reptiles. It sometimes happens that it is 
 impossible or impracticable to separate such heterogenetic homceo- 
 morphs into their respective genera. In such cases a generic name 
 is retained for this polyphyletic group, but it must not be considered 
 a genus. The name Circulus (Bather) has come into use for such 
 groups of homoeomorphs. Platyceras is an example of a circulus 
 among gastropods ; it is commonly given the value of a genus, but 
 its species are phylogerontic terminals of a number of genetic 
 series. Many of the generic names applied to graptolites, such as 
 Tetragraptus, Dichograptus, etc., are really circuli, for they repre- 
 sent similar stages in development in different genetic series. Since 
 they occur at the same geologic horizon they have also been called 
 ''Geologic genera" (Ruedemann-39). 
 
 A distinction has commonly been maintained between cases in 
 
PARALLELISM AND CONVERGENCE 979 
 
 which related animals or plants have developed in a similar man- 
 ner but independently and those in which unrelated animals or 
 plants have developed similar characteristics which apparently 
 bring them more closely together. To the former the term parallel- 
 ism has generally been restricted, while the term convergence has 
 been applied to the latter case. Of course, it is understood that 
 the use of this term does not imply that the organisms in question 
 actually converge in their relationship, as seems to have been as- 
 sumed by some, but merely that the convergence is only a morpho- 
 logic one and may lead to mistaken ideas of relationship. The 
 similar independent development of the projecting flange in the 
 species of Clavilithes, cited above, may be considered a case of 
 pure parallelism, while its development in Rhopalithes may be con- 
 sidered a case of convergence. A similar case of convergence is 
 seen in the American Eocenic Falsifusus and the British Eocenic 
 Fusus, already cited, both of which have adult characteristics which 
 have led to their being classed in the same genus. That they are of 
 independent ancestry, however, seems to be established.* 
 
 BIBLIOGRAPHY XXV. 
 
 1. BEECHER, CHARLES E. 1901. Studies in Evolution. Charles Scrib- 
 
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 2. BUCKMANN, S. S. 1909. Yorkshire Type Ammonites. 
 
 3. CLARK, WILLIAM B. 1910. Contributions to Morphology from Pale- 
 
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 5. CUMINGS, E. R. 1904. Development of Some Palaeozoic Bryozoa. 
 
 Ibid., Vol. XVII, pp. 49-78. 
 
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 * See the controversy above referred to. 
 
980 PRINCIPLES OF STRATIGRAPHY 
 
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 Vol. xxxvi, pp. 917-945. 
 
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 Seventh International Zoological Congress, Proceedings, Boston, 1907. 
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 tures in Determining Phylogeny. Paleontologic Record, pp. 51-53. 
 Reprinted from Popular Science Monthly. 
 
 27. LULL, RICHARD S. 1910. Relation of Embryology and Vertebrate 
 
 Palaeontology. Ibid., pp. 47-50. 
 
 28. MORGAN, THOMAS HUNT. 1903. Evolution and Adaptation. Mac 
 
 millan Company, New York. 
 
 29. NEUMAYR, MELCHIOR, and PAUL, C. M. 1875. Congerien und 
 
 Paludinen-schichten Slavoniens. Abhandlungen der koniglich-kaiser- 
 lichen geologischen Reichsanstalt. Bd. VII, Heft 3. 
 
 30. OSBORN, HENRY F. 1907. Evolution as It Appears to the Paleontolo- 
 
 gist. Seventh International Zoological Congress Proceedings. Boston 
 
BIBLIOGRAPHY XXV 981 
 
 Meeting, 1907. Advance sheets, 1910. Also Science N. S., Vol. XXVI, 
 No. 674, pp. 744-749, Nov., 1907. 
 
 31. OSBORN, H. F. 1908. The Four Inseparable Factors of Evolution. 
 
 Science N. S., Vol. XXVII, No. 682. Jan., 1908, pp. 148-150. 
 
 32. OSBORN, H. F. 1908. Coincident Evolution through Rectigradations. 
 
 Ibid., Vol. XXVII, No. 697, pp. 749-752. 
 
 33. OSBORN, H. F. 1910. Paleontologic Evidences of Adaptive Radiation. 
 
 The Paleontologic Record, pp. 34-38. Reprinted from Popular Science 
 Monthly. 
 
 34. OSBORN, H. F. 1911. Biological Conclusions drawn from the Study of 
 
 the Titanotheres. Science N. S., Vol. XXXIII, pp. 825-828. 
 
 35. OSBORN, H.F. 1912. The Continuous Origin of Certain Unit Characters 
 
 as Observed by a Palaeontologist. American Naturalist, Vol. XLVI, pp. 
 185-206, 249-278. 
 
 36. OSBORN, H. F. 1912. First Use of Word "Genotype." Science N. S., 
 
 Vol. XXXV, pp. 340-341. 
 
 37. OSBORN, H. F. 1912. Tetraplasy, the Law of the Four Inseparable 
 
 Factors of Evolution. Journal of the Academy of Natural Sciences, 
 Philadelphia. Vol. XV, second series, pp. 273-309. 
 
 37a. OSBORN, H. F. Assisted by Grabau, A. W. 1911. Article on Palae- 
 ontology. Encyclopaedia Britannica, nth Edition, Vol. xx, pp. 579591. 
 
 38. PENHALLOW, D. P. 1910. The Relation of Paleobotany to Phytogeny. 
 
 The Paleontologic Record, pp. 67-72. Reprinted from Popular Science 
 Monthly. 
 
 39. RUEDEMANN, RUDOLF. 1904. Grapholites of New York. Memoir 
 
 VI of the New York State Museum, Part I, Vol. I. 
 
 40. RUEDEMANN, R. 1910. Anatomy and Physiology in Invertebrate Ex- 
 
 tinct Organisms. Paleontologic Record, pp. 39-42. 
 
 41. SHIMER, H. W. 1906. Old Age in Brachiopoda. American Naturalist, 
 
 Vol. XL, pp. 95-121. 
 
 42. SHIMER, H. W. 1908. Dwarf Faunas. Ibid., Vol. XLII, pp. 472-490. 
 
 43. SMITH, JAMES PERRIN. 1897. Development of Schloenbachia. 
 
 Journal of Geology, Vol. V, pp. 521 et seq. 
 
 44. WAAGEN, W. 1868. Die Formenreihe des Ammonites subradiatus. 
 
 Beneckes Geognostisch-Palaeontologische Beitrage, Bd. II, pp. 179- 
 256 (185-6). 
 
CHAPTER XXVI. 
 
 PHYSICAL CHARACTERISTICS OF THE INHABITABLE EARTH. 
 BIONOMIC CHARACTERS OF THE ENVIRONMENT.* 
 
 A comprehensive survey of the inhabitable world shows its 
 divisibility into three great bionomic realms, each of which has its 
 peculiar characteristics and its specially adapted forms of animal 
 and plant life. The essential character of each is determined by the 
 nature of the medium in which the organisms live, i. e., whether salt 
 water, fresh water, or air. We have, accordingly: 
 
 1. The Marine, or Halo-biotic realm. 
 
 2. The Fresh Water, or Limno-biotic realm. 
 
 3. The Terrestrial, or Atmo-biotic (also called Geo-biotic) 
 
 realm. 
 
 While each of these is distinct from the others, they also grade 
 into one another to a greater or less extent along their lines of in- 
 tersection. Thus the marine and fresh-water realms intergrade 
 in the estuaries of rivers, where the water is brackish. The marine 
 and terrestrial realms intergrade at the shore, where organisms 
 are periodically exposed between tides first to the one and then 
 to the other medium. Again, the terrestrial and fresh-water flu- 
 vial, lacustrine, etc., realms intergrade along the margins of streams 
 and the shores of lakes. 
 
 Each one of the bionomic realms may be further subdivided 
 into a light, or photic region, and a dark, or aphotic region. Be- 
 tween these two may frequently be determined a dusk, or dysphotic 
 region. Schimper (6) has defined these regions in the marine 
 realm on the basis of plant life as follows : 
 
 The photic region extends over such depths wherein the in- 
 tensity of sunlight is sufficient for the normal development of 
 macrophytes. The dysphotic region is insufficiently lighted for the 
 
 * This and the succeeding two chapters are in part a reprint, with additions 
 and emendations, of a paper published by the author in 1899 under the title 
 Relation of Marine Bionomy to Stratigraphy. Bulletin of Buffalo Society Natural 
 Sciences, Vol. VI, pp. 319-365. 
 
 982 
 
i 
 
 CLASSIFICATION OF LIFE DISTRICTS 983 
 
 normal development of macrophytes, which exist there but scantily 
 or not at all, while certain moderately assimilating microphytes, 
 especially diatoms, still exist. The aphotic region comprises that 
 part of the sea where only the non-assimilating vegetable organisms 
 can. exist. The depth at which these regions pass into one another 
 varies with the locality and the purity of the water. In the open 
 sea the dark region begins at a depth of about 200 fathoms. In 
 the fresh water realm the aphotic region is not often found, though 
 deep lakes, like Lake Superior and Lake Geneva, extend to depths 
 not penetrated by sunlight. Such cases are, however, comparatively 
 uncommon. A limno-aphotic region is further found in the streams 
 and lakes of caves where the sunlight is shut out by the roof 
 of the cavern. Caverns, too (natural and artificial), constitute the 
 only aphotic region of the terrestrial realm, and they are often 
 peopled with a well-adapted fauna and flora. 
 
 The final division into life districts depends on the absence or 
 presence of a substratum, and this division can be equally well 
 carried out in the marine, fresh water, and terrestrial realms. The 
 absence of a substratum compels the organism to float or swim in 
 the medium, and for this purpose special organs and a specially 
 modified body- form commonly exist. The substratum may be 
 visited for food or other purposes, but the organism is perfectly 
 at home in the medium. 
 
 Each realm may, then, be divided into the following life-districts, 
 the medium being salt water, fresh water, or air, according as the 
 marine, fluvio-lacustrine, or terrestrial realms are considered : 
 
 1. Littoral district: Light; substratum present. 
 
 2. Pelagic district: Light; substratum absent. 
 
 3. Abyssal district: Dark; substratum present. 
 
 4. Abysso-pelagic district: Dark; substratum absent. 
 
 I. THE LITTORAL DISTRICTS. 
 
 A. Marine. The marine littoral district extends from the 
 shore at high-water mark to the edge of the continental shelf, 
 where it quickly merges into the abyssal district. The depth to 
 which the littoral district extends is approximately 200 meters, 
 though the hundred-fathom line is commonly taken as the seaward 
 boundary of this district. Around oceanic islands and young con- 
 tinents the littoral district is very narrow, the ocean 'floor soon 
 falling off to deep water. The origin of this district is to be 
 sought in the activities of various geologic agencies, chief among 
 
984 PRINCIPLES OF STRATIGRAPHY 
 
 which are the inland cutting of waves and currents, thus extend- 
 ing the sea landward ; and the deposition of the land-derived detri- 
 tus on the edge of the continental shelf, thus pushing this ed^e 
 seaward and widening the submarine platform. Subsidence of 
 the land permits the advance of the sea over the low country, and 
 broad epicontinental seas are formed, which fall entirely within 
 the littoral life district. In mediterraneans, too, the littoral belt is 
 generally a broad one, only the central portion descending to abyssal 
 depth. (See further, Chapter III.) 
 
 The conditions become more favorable for the development of 
 littoral life as the continent grows older, provided, of course, that 
 no important oscillatory movements occur. As time progresses the 
 breadth of the submerged continental shelf increases, both by land- 
 ward cutting and by seaward building, and the surface of the land 
 becomes more and more reduced, thus causing a decrease in the 
 amount of detrital material which can be carried into the sea, and 
 a concomitant increase in the purity of the water. When peneplana- 
 tion, or the reduction of the land to base-level, has been accom- 
 plished, the amount of detritus carried into the sea is practically 
 nil; and any organisms, like corals, adapted only to pure water, 
 can flourish close to the continental shore, and deposits of a purely 
 organic nature, such as extensive deposits of pteropod or foramini- 
 feral shells, may form in comparatively shallow water. 
 
 The epicontinental sea and the littoral belt of the mediterraneans 
 are especially adapted for the development of local or provincial 
 faunas. Such provincializing of faunas is most marked if, by some 
 oscillatory movement of the land or some other physical change, 
 the basins of these intracontinental seas become separated from the 
 littoral district of the ocean sufficiently to prevent intercommunica- 
 tion between the organisms of the two provinces. A barrier is thus 
 formed, which need not necessarily.be a land barrier, and a great 
 diversity of faiinas may result. A rather marked diversity of fauna 
 existed in early Tertiary time between the Mississippi embayment 
 and the Atlantic coast, and in Palaeozoic time between the Bay of 
 New York and the central interior sea. Recent provincial faunas 
 are frequently met with. It requires only a comparatively slight 
 elevation of the sea-floor, or a moderate deepening of the abyssal 
 oceanic basins, to draw off the water from the shallower regions 
 and lay dry large portions of the littoral district. Such a change 
 would, of course, result in an almost complete extinction of the 
 littoral flora and fauna thus exposed and force the survivors to ac- 
 commodate themselves to a narrower field. Revival of stream ac- 
 tivities, consequent upon elevation of the land, would result in 
 
THE LITTORAL DISTRICT 985 
 
 carrying a large amount of debris into the sea and thus produce 
 conditions unfavorable to the existence of many organisms. 
 
 Landward the littoral district interlocks with the corre- 
 sponding districts of the terrestrial and fluvial realms, the faunas 
 and floras of all more or less intermingling. It is in this portion 
 of the littoral district that an important subdivision must be con- 
 sidered; namely, the shore. The shore, as already noted (ante, 
 Chapter XV), is that part of the littoral district which lies between 
 the highest water mark (often considered as including even the 
 highest point of the wave mark) and the lowest line drawn during 
 the lowest ebb. In the greater part of this division of the littoral dis- 
 trict there is a change of medium twice every twenty-four hours, 
 and a change of the consequent physical conditions attendant upon 
 the character of the medium. Organisms living in this portion of 
 the littoral zone must be capable of withstanding the effects of 
 the partial or complete removal of their normal medium for a 
 greater or less time. It is here that the interlocking of the terres- 
 trial and marine floras and faunas becomes most marked, and an 
 intermingling and a migration from one district into the other 
 occur. Migration from the land to the sea is exemplified by the 
 whales, seals, and other aquatic mammals, which have become 
 marine in so far as their mode of locomotion is concerned. Owing 
 however, to the inability of air-breathing animals to adapt them- 
 selves to a water-breathing habit, all terrestrial animals passing 
 into the sea must assume a pelagic life, where they can retain their 
 normal method of respiration. 
 
 Among other animals which have exchanged their normal ter- 
 restrial habit for a prevailingly marine one may be mentioned 
 several birds, such as the Penguins and the Albatross; certain 
 snakes, turtles, and crocodiles, and a number of insects. The birds 
 and insects here considered represent a passage from the aerial to 
 the marine pelagic district; while the reptiles, like the mammals, 
 illustrate a passage from the land to the pelagic district of the sea. 
 
 While thus the land fauna, in advancing into the sea, naturally 
 takes to a pelagic life, the land flora can adapt itself to the condi- 
 tions of the littoral district. This is well shown by the eight spe- 
 cies of phanerogams, which have acquired a wholly marine habit, 
 and are now known as eel grasses or sea grasses. In the case of 
 these plants the adaptation is so complete that they can no longer 
 live out of their adopted habitat. The mangrove plants, on the 
 other hand, are only partially accommodated to the conditions of 
 the marine littoral district, for it is necessary that their crowns of 
 leaves should be above water. 
 
986 PRINCIPLES OF STRATIGRAPHY 
 
 Marine animals and plants, likewise, attempt migrating from the 
 sea to the land. In their adaptation to the new habitat the animals 
 are the more successful, just as the plants are the 'more successful 
 in migrating the other way. Thus two genera of fish, Periophthal- 
 mus and Boleophthalmus, are able to pass the greater part of their 
 lives out of water. They "skip along close to water-line on the 
 seashore, where they hunt for molluscs (Onchidium) and insects." 
 (Semper-7 :/#p.) The large branchial cavity of these fishes is not 
 completely filled by the gills, but serves in part as an air cavity or 
 primitive lung. In a number of fishes, such as Anabas scandens of 
 the Philippines, this gill-cavity is further modified into a "laby- 
 rinthine organ," or much prolonged cavity, the mucous membrane 
 of which is thrown into complicated folds, thus greatly increasing 
 the surface. These fish can exist for days out of water and are 
 able to make long overland excursions. Semper holds that these 
 fish may be regarded "as Amphibians with quite as much reason as 
 toads and frogs, or even better, since they are capable of changing 
 the nature of their respiration of air, that is, or of water at will, 
 and suddenly without any interruption." Several of our littoral 
 gastropods, e. g., Littorina, Ilyanassa, etc., are capable of existing 
 out of water for a considerable time. In Brazil Littorina climbs 
 the trees of the mangrove high above water and oysters and other 
 bivalves are attached to the roots of these trees and are laid bare 
 at low tide. Ampullaria forms a connecting link between sea 
 and land snails, for it not only breathes by means of a gill but also 
 has a pulmonary sac like that of the land snails into which air is 
 carried by means of a long breathing-siphon. 
 
 The possibility that related species of marine gastropod Mollusca 
 may leave the sea in different parts of the world and give rise to 
 terrestrial forms, which, though differing from their marine an- 
 cestors, may be very similar to each other, deserves attention. 
 In this way some of the puzzling problems of distribution of ter- 
 restrial gastropods on widely distant oceanic islands may be ac- 
 counted for. 
 
 Among the Crustacea there are several species of crabs (e. g., 
 Birgus latro, etc.) which live in damp woods far from all water 
 and whose respiration is carried on chiefly without the intermedia- 
 tion of their normal medium. 
 
 The advent of marine vegetation on the land has occurred only 
 up to the limit of the salt spray on exposed shores, and here the 
 number of species is small. But at, or just below, high-tide limit 
 a number of algae find a congenial abode, and grow there in luxuri- 
 ant masses. Chief of these in our northern latitudes are the Fuci, 
 
THE LITTORAL DISTRICT 987 
 
 with Fucus vesiculosus and Ascophyllum nodosum predominating. 
 At low-tide these hang like a wet fringe over the exposed rocks 
 and give shelter to numerous species of the smaller littoral animals, 
 as well as other algae. 
 
 The littoral districts of the marine and fluvial realms also inter- 
 lock along the shores where streams mouth into the sea or expand 
 into broad estuaries. Here marine animals will venture up into the 
 fresh water littoral district, while, similarly, fresh water animals 
 pass into the littoral district of the marine realms. The common 
 meeting-ground of the two approaching floras and faunas is in 
 the estuarine or brackish water facies of the littoral districts. 
 
 The neritic zone, "Flachsee," or thalassic zone, is that portion 
 of the littoral district which is never uncovered. It is separated 
 as a distinct district by Walther, Haug, and others, who restrict 
 the term littoral to the shore zone. It is, however, so intimately 
 connected with the shore zone in all its physical and bionomic 
 characteristics that a separation is not natural. The bottom of 
 the neritic zone of the littoral district is less diversified than that 
 of the shore zone. In its upper portion and in its shoals it may 
 partake of the character of the shore zone, but in its deeper por- 
 tions the character of the bottom is usually more uniform, being 
 either rocky or, what is more common, composed of fine detrital 
 material mingled with organic matter in various stages of dissolu- 
 tion. According to the character of the bottom, plant life will vary 
 and with it, to a greater or less extent, animal life. 
 
 Taken as a whole, the littoral district is the most important 
 portion of the sea, both from a bionomic point of view and from its 
 bearing on palaeontology. "The littoral region," says Loven (4:86), 
 ''comprises the favored zones of the sea, where light and shade, a 
 genial temperature, currents changeable in power and direction, 
 a rich vegetation spread over extensive areas, abundance of food, of 
 prey to allure, of enemies to withstand or evade, represent an in- 
 finitude of agents competent to call into play the tendencies to vary 
 which are embodied in each species, and always ready, by modify- 
 ing its parts, to respond to the influences of external conditions." 
 This district may perhaps be regarded as the cradle of organic 
 life, from which were peopled the abyssal and pelagic districts, on 
 the one hand, and the terrestrial and fluvial realms and their vari- 
 ous districts, on the other. 
 
 B. Fresh Water. The littoral district of the fresh water realm 
 is almost coextensive in area with that of the streams and fresh 
 water lakes and ponds of the world. The only exception to this is 
 found in those portions of very deep lakes where sunlight does not 
 
988 PRINCIPLES OF STRATIGRAPHY 
 
 penetrate to the bottom and in the subterranean streams and lakes. 
 The fauna of the limno-littoral district is much less diverse than 
 that of the corresponding district in the sea. Whole classes of ani- 
 mals, like those of the Echinodermata, the Anthozoa, the Brachio- 
 poda, Cephalopoda, Pteropoda, Scaphopoda, etc., are normally ab- 
 sent from fresh water, while most of the remaining ones are poorly 
 represented by genera and species, though often prolific in indi- 
 viduals. Plant life, on the contrary, is abundantly represented, not 
 only by desmids, diatoms, and fresh-water algae, but also by the 
 large number of swamp plants which grow partly submerged and 
 represent the transition zone between the terrestrial and limno- 
 littoral districts. 
 
 C. Terrestrial. The terrestrio-littoral district is coextensive 
 with the surface of the land. No other life district comprises such 
 a range of physical characteristics, and no other district is inhabi- 
 ted by such a variety of highly specialized types of animal and 
 plant life. Here we pass from the cold of the arctic snow-fields 
 to the burning sands of the tropics, from the land of nearly continu- 
 ous rains to the rainless desert regions, parched by the continued 
 drought of years, and from the region of plentiful food supply to 
 the stony, arid wastes, where the nature of the soil is hostile to 
 practically all forms of plant life. It is to be expected that under 
 such widely varying conditions a fauna and flora should develop 
 which in its variety outruns that of any other life district, and which 
 in its own extremes reflects the range of its environment. 
 
 II. THE PELAGIC DISTRICTS. 
 
 A. Marine. The marine pelagic, or halo-pelagic district, is 
 the common meeting-ground of most of the life districts. It 
 touches all shores and communicates with the corresponding dis- 
 tricts of both the terrestrial and fluvial realms. It has direct com- 
 munication with the littoral district, many inhabitants of which 
 leave the bottom at times to lead a temporary existence in the pela- 
 gic district; while many pelagic animals, in turn, visit the bottom 
 or shores for 'food. Occasionally inhabitants of the pelagic dis- 
 trict enter for a time the corresponding district of the terrestrial 
 realms, i. e. } the aerial; as, for example, the so-called flying-fish; 
 and, in turn, as already noted, many aerial animals spend a part 
 of their lives in the marine pelagic district, or at least show a de- 
 cided preference for a pelagic life. The passage of land animals 
 to the halo-pelagic district has already been noted. Similar in- 
 
THE PELAGIC DISTRICTS 989 
 
 termingling of fresh water, or limno-pelagic, and salt water pelagic 
 types occurs in the estuaries and stream mouths, and it is notorious 
 that halo-pelagic fish will enter the limno-pelagic district in breed- 
 ing time. It is quite probable, as Sir William Flower suggests, that 
 the Cetacea, in their transition from a terrestrial to a marine life, 
 passed through a stage in which they lived in fresh water. A sim- 
 ilar transition for the sea-grasses is not improbable, though they can 
 no longer live in fresh water. Intercommunication between the 
 abysso-pelagic and pelagic districts also occurs, as well as between 
 the abysso-pelagic and abyssal. 
 
 B. Fresh Water. The pelagic life of ponds, lakes, and rivers 
 is much less varied than that of the sea, though, as will be seen 
 later, the number of individuals of a given species may often be very 
 great. In ponds and lakes no very distinctive characteristics not 
 found in shallow seas exist, aside, of course, from the distinctions 
 due to the difference in degree and kind of salinity. In rivers, on 
 the other hand, we must consider the importance of currents, which 
 vary greatly in strength, but are essentially constant in direction. 
 It is this constancy which, as Chamberlin has pointed out, favors 
 the development of a special body form, the resistance of which to 
 the current is at a minimum. Such a body form is found in fish 
 and in the ancient Eurypterida, and it is a possibility not to be 
 lightly set aside that both fish and eurypterids originated in the 
 rivers of the Palaeozoic and earlier lands. Indeed, this is all but 
 definitely proven for the Eurypterida (O'Connell-5) and seems to 
 be indicated for the fish as well. Significant in this connection is 
 the fact that the early remains of fish as of eurypterids are not 
 found in normal marine deposits, but in those which are at least 
 open to the suspicion that they are formed by rivers or at least at 
 the mouths -of rivers, while the best preserved remains, and the 
 most abundantly represented in the Palaeozoic, are found in river 
 flood-plain deposits and in deltas. This subject will be more fully 
 discussed in the next chapter (Grabau-3). 
 
 C. Terrestrial. The pelagic life of fresh water is, as we have 
 seen, much less abundant than that of the sea, and, again, the aerial 
 life, or that of the pelagic district of the land, is much less prom- 
 inent than that of the streams and lakes. This gradation is in direct 
 correspondence with that observed in the gradation in the density 
 of the medium. Moreover, in the terrestrial realm the pelagic dis- 
 trict is only temporarily inhabited, few, if any, terrestrial animals 
 or plants spending their entire existence suspended in the air. The 
 most familiar examples of animals spending a part of their lives 
 at least in the atmo-pelagic district are : insects among invertebrates, 
 
990 PRINCIPLES OF STRATIGRAPHY 
 
 pterosaurs among reptiles, the birds, and, among mammals, the 
 bats. 
 
 III. THE ABYSSAL LIFE DISTRICT. 
 
 A. Marine. The marine abyssal districts comprise the lightless 
 depths, or generally those depths exceeding two hundred fathoms. 
 (Chapter III.) As assimilating plant life is absent in these dis- 
 tricts the food supply of the organisms existing in them must 
 be wholly derived from the districts in which such assimilating 
 vegetation exists. A large proportion of the food of the abyssal 
 animals is contained in the organic oozes and sediments which con- 
 stantly settle down in a more or less decomposed state from the 
 lighted districts. The abysso-pelagic district is frequently invaded 
 by organisms from the pelagic district, which descend into the dark 
 regions during the day. 
 
 B. Fresh Water and C. Terrestrial. In the non-marine realms 
 the lightless districts are sparingly represented. Lakes of great 
 depth, whose bottom is in perpetual darkness, do exist, but the life 
 of these dark regions is mostly unknown. Cave life, on the other 
 hand, both fluvio-lacustrine and terrestrial, has been made the sub- 
 ject of much study, and its characteristics are known to harmonize 
 with the peculiar conditions which give these districts their especial 
 stamp. 
 
 BIBLIOGRAPHY XXVI. 
 
 1. CHAMEERLIN, THOMAS C. 1900. The Habitat of the Early Verte- 
 
 brates. Journal of Geology, Vol. VIII, pp. 400-412. 
 
 2. GRABAU, A. W. 1899. The Relation of Marine Bionomy to Stratigraphy. 
 
 Chapter III in the Geology and Palaeontology of Eighteen-mile Creek. 
 Bulletin of the Buffalo Society of Natural Sciences, Vol. VI, pp. 319-365. 
 
 3. GRABAU, A. W. 1913. Ancient Delta Deposits of North America. Bul- 
 
 letin of the Geological Society of North America, Vol. XXIV pp. 498-526. 
 
 4. LOVEN, SVEN. 1883. On Pourtalasia, a Genus of Echinoidea. Stock- 
 
 holm. 
 
 5. O'CONNELL, MARJORIE. 1912. The Habitat of the Eurypterida. 
 
 Paper presented before the New York Academy of Sciences. Also in 
 Grabau (2), pp. 499-515- 
 
 6. SCHIMPER, A. F. W. 1898. Pflanzengeographie auf physiologischer 
 
 Grundlage. Jena. English translation by W. R. Fisher. Plant Geog- 
 raphy, Oxford, 1903. 
 
 7. SEMPER, KARL. 1881. Animal Life as Affected by the Natural Condi- 
 
 tions of Existence. Appleton International Scientific Series, Vol. XXX. 
 
CHAPTER XXVII. 
 BIONOMIC CLASSIFICATION OF PLANTS AND ANIMALS. 
 
 A bionomic classification, or one based on the relationship of 
 the organism to its environment, cannot agree with one based en- 
 tirely on anatomic characteristics. It is a more primitive classifica- 
 tion, but a very useful one from many points of view. 
 
 SUBDIVISIONS. 
 
 Primary Divisions. The primary divisions of the organisms 
 agree with 'the primary divisions of the life districts, i. e., the 
 marine, fresh water, and atmospheric or terrestrial. We have, ac- 
 cordingly, halo-bios, limno-bios, and atmo-bios (geo-bios), each of 
 these including the plants and animals of the respective realms. 
 
 Secondary Divisions. The next division is based on the rela- 
 tion of the organism to the substratum, where we have floating 
 types or plankton, swimming types or nekton, and bottom types 
 or benthos. The first two belong to the pelagic and abysso-pelagic 
 districts, the third to the littoral and abyssal. Their further sub- 
 divisions and relationships are as follows : 
 
 1. Holoplankton: organisms spending all their 
 
 lives as plankton (ex., jelly fish). 
 
 2. Meroplankton: organisms leading a plank- 
 
 tonic life during larval stages only (ex., 
 Crustacea, echinoderms, ccelenterates). 
 
 3. Pseudo plankton: organisms normally at- 
 
 tached but floating through accident, as 
 the Sargassum, leaves and trunks of trees, 
 or parts of 'dead organisms, such as shells of 
 molluscs, etc. 
 
 4. Epiplankton: organisms living upon or at- 
 
 tached to floating objects (ex., Crustacea 
 and hydroids of the pseudoplanktonic Sar- 
 gassum ; Lepas attached to floating logs, etc. 
 
 1. Holonekton. 
 
 2. Meronekton. 
 
 3. Epinekton: organisms parasitically or other- 
 
 wise attached to swimming or flying ani- 
 mals. 
 
 991 
 
 A. Plankton (floating or- 
 ganisms) 
 
 B. Nekton (swimming or 
 flying organisms) .... 
 
992 PRINCIPLES OF STRATIGRAPHY 
 
 C. Benthos (bottom or- ( I. Vagrant: with power to walk, crawl, or 1 Littoral 
 
 ganisms) < creep over the bottom. > and 
 
 [ 2. Sedentary: Attached to the bottom. j Abyssal. 
 
 According to the realm in which the organism lives we have, 
 therefore : 
 
 I. Marine or Halobios, including 
 
 A. Haloplankton 
 
 B. Halonekton 
 
 C. Halobenthos 
 
 II. Freshwater or Limnobios, including 
 
 D. Limnoplankton 
 
 E. Limnonekton 
 
 F. Limnobenthos 
 
 III. Terrestrial or Atmobios (Geobios), including 
 
 G. Atmoplankton 
 H. Atmonekton 
 I. Atmobenthos 
 
 With reference to depth, we may further subdivide marine 
 plankton, etc., into anoplankton (from av<o, upward*) or that 
 occurring above the 100 fathom-line; this may be divided into 
 anoholoplankton, anomeroplankton, anopseudoplankton and anoepi- 
 plankton. Below 100 fathoms we have the mesoplankton (from 
 /w,ros, middle), and again, just above the abyssal depths may 
 occur the hypoplankton (from VTTO, under), anonekton, mesonek- 
 ton and hyponekton, as well as anobenthos (littoral district), meso- 
 benthos (bathyal district) and hypobenthos (abyssal district) may 
 also be recognized. 
 
 Each of these divisions may now be considered in detail. 
 
 A. Haloplankton. 
 
 i. Holoplankton. The term plankton was introduced by Vic- 
 tor Hensen in 1887. It is derived from the Greek TrXayK-ros, which 
 means wandering or drifting about aimlessly. The true plankton, 
 or holoplankton, is most typically developed in the sea. It com- 
 prises those organisms which spend their lives in the sea drifting 
 about from place to place, without power to direct their own 
 
 *The term epiplankton was proposed for this by George H. Fowler in 1911 
 (Encyclopedia Britannica, nth ed., vol. xxi, p. 721), but was preoccupied by 
 Grabau in 1909 as above defined (3). Hence the names- anoplankton and ano- 
 benthos are here proposed. The names mesoplankton, mesobenthos, hypo- 
 plankton and hypobenthos, also proposed by Fowler, are, however, acceptable. 
 
HOLOPLANKTON ; MEROPLANKTON 993 
 
 course. These organisms range in size from creatures of micro- 
 scopic dimensions to medusae 50 cm. in diameter. While some of 
 the larger animals of this group have power to propel themselves 
 through the water, they nevertheless are subject to the force of 
 strong waves or currents, which render them helpless. Holoplank- 
 tonic organisms are wholly pelagic, and are characterized by a more 
 or less transparent body and by the absence of opaque skeletal struc- 
 tures, only a few forms retaining delicate calcareous shells, inherited 
 from their benthonic ancestors. In its horizontal distribution the 
 holoplankton of the sea is dependent chiefly upon the marine cur- 
 rents, as the organisms composing it are practically unable to carry 
 on independent migrations, though many of them can dart about 
 in quiet water. Hence they fall an easy prey to actively predaceous 
 animals/ The occurrence of holoplanktonic animals in swarms is 
 also accounted for by their lack of independent locomotion, for the 
 eggs, liberated by the floating parent, commonly develop without 
 separating far from the parent, with which they are carried along 
 by the currents of the sea. These animals have, however, the 
 power to rise and descend in the water, and during the day many 
 of them live at a depth of from fifty to one hundred and fifty 
 fathoms, coming to the surface only on quiet nights. The animals 
 of this class also occur in the abyssopelagic district. 
 
 2. Meroplankton. This term (from /xepos, a part) was intro- 
 duced by Haeckel in 1890 (4) and is applicable to the larvae of ben- 
 thonic animals which lead, during the larval stages, a truly plank- 
 tonic existence and which occur with and suffer the same vicissi- 
 tudes as the true or holoplankton. The upper levels of the ocean 
 are usually crowded with such meroplanktonic organisms, and to 
 them is due the horizontal distribution of benthonic species. Float- 
 ing about in the sea in perfect clouds or swarms these mero- 
 planktonic organisms pass their short existence a sport of the waves 
 and currents. Sooner or later, however, they sink to the bottom, 
 a veritable rain of seedling organisms ; and, if they fall on a fertile 
 soil, if they reach the proper facies of the substratum, they develop 
 into the benthonic adult ; but, if they fall upon an unfavorable bot- 
 tom, or if the food supply is scarce, they perish. Thus, other things 
 being favorable, wherever the facies of sea-bottom normal to a 
 particular species of benthonic organism exists, the bottom may be 
 peopled with that species by the larvae which reach it from the 
 upper waters, where they were carried by waves and currents 
 during their meroplanktonic wanderings. As Walther says, should 
 unfavorable circumstances temporarily destroy a whole fauna, its 
 depopulated home would at once be surrounded by swarms of 
 
994 PRINCIPLES OF STRATIGRAPHY 
 
 delicate larvae, and, as soon as the old conditions are reestablished, 
 this fauna will again appear with countless individuals. This ex- 
 plains the sudden reappearance in later strata of the fauna of an 
 earlier bed, even though it was absent from the intervening strata. 
 From a stratigraphic point of view the meroplankton is of vast 
 importance, for to it is due the wide dispersal of the benthonic 
 organisms, which of all marine life forms are the best indices 
 of the physical conditions of the sea bottom. It is during the larval 
 period that benthonic marine invertebrates spread in all directions 
 from their center of occupancy, and that they have an opportunity 
 to enter and occupy distant regions. 
 
 3. Pseudoplankton. This term was introduced by Schiitt (8) 
 for such organisms which, like the Sargassum, are normally or in 
 early life benthonic, but continue their later existence as plankton. 
 Walther has extended the meaning of the term so as to include 
 those organisms which are carried about by floating objects, to 
 which they are either attached as sedentary benthos or which serve 
 them as a substratum on which they lead a vagrant benthonic 
 existence. This group, however, is distinct, and is separated here 
 under the name of epiplankton. 
 
 Under pseudoplankton may, however, be included those ben- 
 thonic or nektonic organisms which become planktonic only after 
 death ; i. e., that portion of the plankton which consists of the float- 
 ing parts of dead organisms, such as the leaves and trunks of 
 trees, dead insects and carcasses of vertebrates, and, above all, 
 the shells of molluscs, which, on the death of the animal, are dis- 
 tributed more or less widely, according to the nature of the shell. 
 Thus the shell of Spirula is widely distributed and embedded in 
 contemporaneous sediments where the organism never lived, and 
 leaves of terrestrial plants are found in sediments far from land. 
 Tree trunks from tropical America are carried to the northeast 
 coast of Iceland, where they become embedded in contemporaneous 
 sediments. 
 
 4. Epiplankton. This term (from 7Tt, upon) was proposed 
 (Grabau-3) for those organisms which live upon a floating sub- 
 stratum, to which they are either attached or upon which they lead 
 a vagrant existence. The substratum may be holoplanktonic or 
 pseudoplanktonic, the latter being the most frequent. Examples of 
 epiplankton are the algae, hydroids, and bryozoans attached to the 
 floating Sargassum and other algae; and the Crustacea, molluscs, 
 and other animals living among their branches ; and the organisms 
 attached to floating tree trunks and other pseudoplankton. 
 
 A large number of algae, especially the shallow- water forms, 
 
EPIPLANKTON 995 
 
 have attached to them sedentary animals as well as other species 
 of algae. Among the animals, hydroids and bryozoans are the most 
 common, though other sedentary animals, such as Spirorbis, are 
 frequently abundant. Animals belonging to the vagrant type of 
 the benthos are by no means rare. The large fronds of the Lami- 
 naria cast up on our northern shores during every storm are fre- 
 quently veritable menageries of invertebrate life, which, under 
 favorable conditions, may float about for days. These fronds, for 
 example, are commonly covered with a dense growth of the delicate 
 littoral hydroids Obelia and Campanularia, while Bugula and other 
 Bryozoa and Spirorbis are usually common. The hollow stem is 
 commonly surrounded by an extensive growth of Membranipora, 
 while not infrequently tubularian and other hydroids find this a 
 suitable resting place. The root-like base of the stem often em- 
 braces the shell of Modiola or Cyprina, which in turn is over- 
 grown with coralline algae. Sponges are also found among the 
 "roots" of the Laminaria, and Acmaea, Chiton, Crepidula, Anomia, 
 and other molluscs are attached to the shell, or to the stone which 
 frequently takes its place. Finally, worms and crustaceans are not 
 rare inhabitants of the sheltering space between the branches of 
 the "roots" ; and sea anemones, small star-fish, brittle-stars, and 
 sea urchins also occur, both on the basal portion of the stem and 
 on the frond itself. Such floating menageries may be carried far 
 out to sea or, what is perhaps more frequent, may be driven ashore. 
 Not infrequently they are carried far up into the estuaries and, 
 becoming stranded, are buried in the mud ; or else they are cast up 
 on mud flats behind some sheltering bar or ledge. 
 
 While these cases illustrate an epiplanktonic existence due to 
 accident, the cirriped Lepas illustrates a habitually epiplanktonic 
 existence ; this barnacle rarely occurring except attached to floating 
 objects. Many of the animals found on the Sargassum seem to 
 be characteristic of it in its floating condition, not occurring on it in 
 its native haunts. (Ortmann-7.) Walther has adduced evidence 
 which goes to show conclusively that many of the larger fossil 
 Pentacrini, and perhaps other crinoids, occurred with their stems 
 wound around floating timbers, and he explains the occurrence of 
 these marine animals in fresh water coal strata as due to stranding 
 in estuaries of species leading an epiplanktonic existence. 
 
 The marine or haloplankton forms one of the chief sources of 
 food for many marine animals and is everywhere devoured in 
 vast quantities. Dead organisms which sink to the sea-floor in an 
 incomplete state of decomposition form the chief element of the 
 organic oozes which furnish food to many littoral as well as abyssal 
 
996 PRINCIPLES OF STRATIGRAPHY 
 
 animals. The skeletal portions of the dead plankton often accumu- 
 late in vast quantities on the bottom, and, in the greater depths 
 where terrigenous sediments are absent, they usually form diatoma- 
 ceous, radiolarian, globigerina, pteropod, and other oozes. The 
 purity of such oozes, i. e., their freedom from clastic sediment, is 
 usually an index of the purity of the water in which they were 
 deposited, but from this we cannot always decide that such oozes, 
 when found in fossil state, indicate deep sea. The absence of 
 clastic sediment may be due to the low relief of the land, which 
 may have been worn down to base-level, thus allowing water of 
 moderate depth near shore to be free from detrital material. 
 
 B. Halonekton. 
 
 The term nekton, derived from the Greek WJKTOS, which means 
 swimming, was introduced by Haeckel in 1890 (4), for those ani- 
 mals which lead an actively swimming life. The group is typified by 
 the class of fishes. A torpedo-like form, terminating anteriorly 
 in a head, and perfect bilateral symmetry are the chief character- 
 istics of these animals. A strong musculature for propulsion is 
 usually situated in the posterior portion of the body, while ap- 
 pendages for balancing and steering are also usually present. The 
 body is non-transparent and a calcareous supporting skeleton is 
 ordinarily developed. Typical nektonic animals of the modern sea 
 are: the squids, the fish, and the degenerate 'mammals whales, 
 porpoises, etc. Besides holonektonic forms there are in the sea 
 epinektonic ones, i. e., sessile forms more or less pemanently at- 
 tached to a swimming host! The whale barnacle, attached to the 
 under side of whales, and the ship's barnacles are examples among 
 invertebrates, while the Pilot-fish attached by suckers to sharks 
 represent this type among vertebrates. 
 
 C. Halobenthos. 
 
 The term benthos, from /?<n/0os, the depths of the sea, was like- 
 wise introduced by Haeckel in 1890 (4). It covers those organisms 
 which inhabit the sea-bottom. We may divide the benthos into 
 sedentary and vagrant (vagile) benthos, the former attached to 
 the bottom, the latter moving over it. Living in such intimate rela- 
 tion with the sea-bottom, halobenthonic organisms are to a high 
 degree dependent upon its facies, and their remains are generally 
 entombed in the region where they have lived, instead of being 
 
 
 
HALOBENTHOS LIMNOPLANKTON 997 
 
 deposited anywhere else, as in the case with planktonic and nektonic 
 organisms. The sedentary benthos is, to a large degree, dependent 
 for food on those organisms which are swept within its reach 
 by the currents, while the vagrant benthos is more actively en- 
 gaged in seeking out its food. Large numbers of sedentary ben- 
 thonic animals have assumed a radial structure, especially well 
 typified in corals and crinoids, and also shown in the corona of 
 the barnacle; while others, such as brachiopods, have a bilateral 
 symmetry of high degree. Some of the lower vagrant benthonic 
 animals, e. g., the Echinoidea, are also built on the radial plan, but 
 the majority of the free benthonic animals are bilaterally symmetri- 
 cal. Among the vagrant benthos the struggle for existence is most 
 intense, and, as a result, the variety of adaptations and the wealth 
 of form and color are almost unlimited. Transitions from the 
 vagrant benthos to the nekton are numerous, and it sometimes 
 becomes difficult to decide if an animal belongs to the vagrant 
 benthonic or to the nektonic type. The gradation is just as com- 
 plete as between nekton and plankton. In general, a radial form 
 may be said to be characteristic of the sedentary benthos, while a 
 bilaterally symmetrical form is as characteristic of the vagrant 
 benthos. Examples of change of form with change of habit occur 
 in many classes. Both plants and animals, themselves belonging to 
 the sedentary benthos, may lead, secondarily, a vagrant life by 
 being attached to vagrant benthonic forms. These may be regarded 
 as vagrant epibenthos. Among plants, algae are the most familiar 
 examples, while among animals hydrozoa (Hydractinia on shells 
 inhabited by hermit crabs), actinians, and bryozoans furnish the 
 most characteristic examples. 
 
 D. Limno plankton. 
 
 Fresh water plankton is met with in all fresh water lakes, 
 ponds, and streams. It not infrequently occurs in surprising 
 amounts. Thus studies of the Illinois River and its tributaries 
 have shown that it averages 2.7 parts per million of the water in 
 the stream, and that the total average moving down stream past 
 any given point aggregates 75,000 tons per annum, or about 8.5 tons 
 per hour (6). The holoplankton here is largely composed of 
 minute plants, while the meroplankton, consisting both of larval 
 plants and animals, constitutes a very large percentage of the 
 mass. Finally, the pseudoplankton makes up a not inconsiderable 
 portion of this mass. The term limnoplankton has been restricted 
 
998 PRINCIPLES OF STRATIGRAPHY 
 
 to the plankton of the larger fresh water seas by a number of 
 writers, notably O. Zacharias, who uses the term hdco plankton for 
 the plankton of shallow ponds and potamo plankton for that of 
 rivers. 
 
 E. Limnonekton (Heleonekton, Potatnonekton). 
 
 The nekton of fresh water, like that of the sea, is typically 
 represented by the fish, though other classes of animals, such as 
 the aquatic mammal, are also represented. The merostomes of the 
 Palaeozoic also appear to belong here. An interesting example of 
 a meronektonic life is evidenced by the tadpole, while an epinektonic 
 condition exists in the larval fresh water mussel (Unio) which 
 attaches itself to the gills of fishes. 
 
 F. Limnobenthos (Heleobenthos, Potamobenthos). 
 
 Both sedentary and vagrant benthos occur in fresh water; the 
 former is chiefly represented by plants, but a number of inverte- 
 brates also belong here. Such are the sedentary infusoria, rotifers, 
 and bryozoa, and the fresh water sponges and hydrozoa, though 
 the principal members of the latter class are only temporarily at- 
 tached and may move about at will. The vagrant benthos, on the 
 other hand, is well represented by molluscs, worms, and Crustacea, 
 though the crawfish also leads at times a benthonic life. 
 
 G. Atmoplankton. H. Atmonekton. I. Atmobenthos. 
 
 Among the air-breathers permanent planktonic and nektonic 
 types are unknown, though many unicellular plants, especially bac- 
 teria, live in the atmosphere for a considerable period of time, and 
 must during that period be classed as atmoholoplankton. The 
 meroplankton, however, is well represented, chiefly by the spores and 
 seeds of plants, which are wafted about by the winds, and so be- 
 come widely dispersed. Terrestrial nekton is represented by in- 
 sects, birds, flying reptiles, and bats. None of these lead a per- 
 manently nektonic life in the air, for all return, more or less fre- 
 quently, to the substratum. Nevertheless, during their period of 
 flight, which often is very long, they must be considered as nekton 
 of the air. The benthos of the earth's surface is pretty sharply 
 divided into sedentary benthos, or plants, and vagrant benthos, or 
 
ATMOPLANKTON ATMOBENTHOS 999 
 
 animals, though some exceptions occur among 1 the lowest plants, 
 while some animals lead a temporary or permanent (parasitic) at- 
 tached existence. 
 
 BIBLIOGRAPHY XXVII. 
 (See also Bibliographies XXVI and XXVIII.) 
 
 1. CHUN, CARL. 1890. Die pelagische Thierwelt in Grossen Tiefen. Ver- 
 
 handlungen der Gesellschaft deutscher Naturforscher und Aerzte. Bremen. 
 
 2. GRABAU, A. W. 1899. The Relation of Marine Bionomy to Stratigraphy. 
 
 Chapter III in Geology and Palaeontology of Eighteen-mile Creek. Bulle- 
 tin of the Buffalo Society of Natural Sciences, Vol. VI, pp.- 319-365. 
 
 3. GRABAU, A. W. 1909. Some New or Little Known Geological Terms 
 
 and Their Application in Stratigraphic Writing. Abstract: Science, N. S., 
 Vol. XXIX, p. 750. 
 
 4. H^ECKEL, ERNST. 1890. Planktonstudien. Vergleichende Unter- 
 
 suchungen iiber die Bedeutung und Zusammensetzung der pelagischen 
 Fauna und Flora. Jena. 
 
 5. HENSON, VICTOR. 1887. Ueber die Bestimmung des Planktons, oder 
 
 des im Meere treibenden Materials an Pflanzen und Thieren. (V. Bericht 
 der Commission zur Wissenschaftlichen Untersuchungen der deutschen 
 Meere.) 
 
 6. ILLINOIS STATE LABORATORY OF NATURAL HISTORY. Bulletin, 
 
 Vol. VI, Art. II. 
 
 7. ORTMANN, ARNOLD. 1895. Grundziige der marinen Thier-geographie. 
 
 Jena. 
 
 8L SCHUTT, F. 1893. Das Pflanzenleben der Hochsee. Plankton Expedi- 
 tion, Vol. I. Leipzig. 
 
 9. WALTHER, JOHANNES. 1894. Einleitung in die Geologic als histor- 
 ische Wissenschaft. I. Bionomie des Meeres. II. Die Lebensweise der 
 Meerestiere. Jena. Gustav Fischer. 
 
CHAPTER XXVIII. 
 BIONOMIC CHARACTERISTICS OF PLANTS AND ANIMALS. 
 
 A bionomic consideration of the different classes of modern 
 plants and animals is of the utmost importance to the stratigrapher, 
 since it is from such studies that he is enabled to interpret the 
 conditions of the past, in so far as they are indicated by organisms. 
 The present chapter will, therefore, deal somewhat at length with 
 the bionomic characters of the various classes, special stress being 
 laid on those types which are capable of fossilization. 
 
 BIONOMIC CHARACTERS OF PLANTS (Schimper-25). 
 
 PROTOPHYTA. 
 
 The majority of these primitive plants are not adapted for 
 preservation, and hence are unknown in the fossil state. The slime 
 molds, or Myxomycetes, occur on decaying logs, in damp wood, on 
 rotting leaves, etc. The Schizophytes or bacteria are every- 
 where present. They are abundant in the plankton of the shallower 
 portions of the sea, but rare in the open sea. In fresh water, in 
 the air, and in the soil, as well as in all decaying substances, they 
 occur, themselves forming the principal agents of decay. Their 
 work in the formation of iron ore deposits has elsewhere been re- 
 ferred to. The Cyanophycese occur in the sea, in fresh water, on 
 moist earth, on damp rocks, and on the bark of trees. They enter 
 the intercellular spaces of higher plants, and may enter into the 
 structure of the lichen thallus. Some species flourish in hot springs 
 with a temperature as high as 85 C. Volvox and other flagellates, 
 most of which are generally regarded as animals, are especially 
 at home in stagnant water, and amidst putrefying organic matter in 
 the sea or in fresh water. Many flagellates are also parasitic and 
 the spores of some may survive a temperature of 250 to 300 F. 
 for ten minutes, though the adults are killed at 180. 
 
 1000 
 
BIONOMIC CHARACTERS OF PLANTS 1001 
 
 THALLOPHYTA. 
 
 ALG.E. The lowest of the green algae (Protococcaceae) consti- 
 tute, with the diatoms, the Cyanophyceae, and the bacteria the 
 chief holoplanktonic plants, though many of them also have a 
 benthonic habit, being attached chiefly to other plants, or encrust- 
 ing stones, as in the case of some fresh water Cyanophyceae. They 
 are mainly inhabitants of fresh water, though diatoms are also 
 abundant in the sea. Protococcus itself is terrestrial. The Charo- 
 phycea, often classed with the green, algae, secrete lime. This is 
 especially true of Chara, which occurs in fresh water lakes from 
 two meters down, and which is probably an important factor in the 
 formation of fresh water limestones. (See ante, page 471.) The 
 majority of the green algae belong to the benthos, being equally 
 abundant in the marine and fresh water realms. The red algae 
 are benthonic and chiefly marine, though some species occur in 
 fresh water. Lime- secreting types also occur in this class, consti- 
 tuting the nullipores or coralline seaweeds which inhabit the littoral 
 district of the sea, chiefly in tropical regions but to some extent 
 also in temperate climates. They occur as jointed fronds of a red 
 color (Corallina), as crusts on other algae (Melobesia), or as ex- 
 tensive pink incrustations on stones or shells (Lithothamnion). 
 They are especially characteristic of depths between 15 and 35 (or 
 50) fathoms, where they constitute the "coralline zone" of the lit- 
 toral district. The brown algae are mainly marine benthonic types, 
 usually attached to a rocky substratum. The common brown algae 
 of the northern coasts (Fucus, Ascophyllum) have already been 
 referred to as clothing the rocky ledges and forming a substratum 
 for Hydrozoa, Bryozoa, sponges, etc., as well as other algae. Though 
 typically attached, some forms, like the Sargassum, will continue 
 to grow and multiply, even after they have been torn from their 
 anchorage and carried into mid-ocean. The Sargassum is thus 
 typically pseudoplanktonic, as are also all the other algae attached 
 to it. Many of the brown seaweeds grow to great size. A familiar 
 example is the common kelp (Laminaria) of the Atlantic coast, 
 which generally grows to ten or more feet in length, while the 
 giant kelp of the Pacific (Macrocystis) is said sometimes to reach 
 a length of three hundred meters. The Laminarians are typical 
 of the littoral district down to fifteen fathoms, this interval being 
 known as the zone of Laminarians. The large species all grow in 
 the deeper portions of this zone, where they are anchored by 
 their "roots" to stones, shells, or other objects of support. They 
 
ioo2 PRINCIPLES OF STRATIGRAPHY 
 
 often hold on to objects small enough to be carried away with 
 the seaweed during a violent storm ; and since the stipe and frond 
 of the seaweed are commonly covered with sedentary benthonic ani- 
 mals, this seaweed forms a ready agent for the wider dispersal of 
 such organisms. 
 
 In general the larger algae are attached to a rocky or other 
 hard substratum or to other algae (epiphytic). On muddy or 
 sandy bottoms algae are rare, though stranded algae may be buried 
 in numbers in mudflats. The large algae (macrophytes) are mostly 
 restricted to the photic region, where they are distributed in the 
 two belts, the perpetually submerged (i. e., below low tide) and the 
 periodically emerging belt (between tides). Marine algae are found 
 to the height of the salt spray on the shore, while terrestrial algae 
 are known from the tropics, where they live as epiphytes on leaves, 
 especially in the rainy districts. In the temperate regions they are 
 associated symbiotically with fungi to form lichens, which increase 
 in numbers and importance as the climate becomes cooler. They and 
 the mosses constitute the chief epiphytes and epiliths in the tem- 
 perate and cooler climates. Lichens sometimes form structures 
 which under favorable conditions may be preserved. In the arctic 
 regions microscopic red and brown algae (Sphaerella, etc.) often 
 color the snow and ice and, together with many other microphytes, 
 form a characteristic element of the vegetation of these regions. 
 
 Diatoms are important rock-builders, since their siliceous skele- 
 tons or frustules are readily preserved. They occur both in fresh 
 and salt water, no ditch, pond, or pool being without them, and they 
 form a characteristic member of the marine plankton.' A great 
 many types, however, are benthonic, forming yellowish-brown 
 films on the mud in shallow pools, or growing attached by slender 
 stalks to other plants. They commonly possess the power of mo- 
 tion found also in desmids and other unicellular plants. Fossil 
 diatoms are abundant in the Tertiary of many localities, often form- 
 ing extensive beds of nearly pure frustules, generally of fresh 
 water origin. Underlying the city of Richmond, Virginia, is a 
 bed of these organisms eighteen feet thick, while other extensive 
 deposits occur in the coastal plain of Maryland and New Jersey, 
 as well as in many other parts of the world. In Mesozoic deposits 
 they are less abundant, and they are not known positively from 
 Palaeozoic deposits, probably owing to alteration of the frustule. 
 Diatomaceous deposits are often erroneously spoken of as infusorial 
 earth. 
 
 FUNGI. The members of this group are destitute of chlorophyll 
 and, consequently, are dependent upon organic matter for food, be- 
 
BIONOMIC CHARACTERS OF PLANTS 1003 
 
 ing either parasites (growing upon living organisms) or saprophy- 
 tes (growing upon dead organic matter) or both parasitic and 
 saprophytic. Fungi can thus grow in the dark regions of the 
 earth, sunlight not being essential. They are mostly terrestrial 
 (when not living within their host), though some marine repre- 
 sentatives are known, and certain of the molds (phycomycetes) 
 form on decaying animals in fresh water or sometimes on living 
 fish or Crustacea. The large terrestrial fungi are most characteristic 
 of the temperate zones, the tropical species being mostly small. 
 
 LICHENS. Lichens are terrestrial plants growing chiefly upon 
 the bark of trees, rocks, the ground, mosses, and, more rarely, upon 
 perennial leaves. In large forests they hang as a dense growth 
 from the trees (Usnea), but in other cases they encrust the rough 
 bark of the trees. They may also occur on the smooth bark of 
 young trees or shrubs, and sometimes on decayed or decaying 
 wood. All of these are classed as corticolous lichens. Saxicolous 
 lichens grow on rocks and stones, which they disintegrate. They 
 comprise the calcicolous forms, growing on limestones, or other cal- 
 careous rocks, on the mortar of walls, ets., and calcifugous forms 
 which grow on rocks of non-calcareous character. Terrestrial 
 lichens grow on all kinds of soil, some preferring peaty, some cal- 
 careous, some sandy, and some granitic soil, but none grow on 
 cultivated soil. 
 
 Muscle olous lichens grow on decaying moss, such as the dead 
 peat mosses, while epiphyllous species grow on perennial leaves, 
 whose vitality they do not affect. The distribution of lichens is 
 greater than that of any other class of plant, occurring from the 
 poles to the equator, practically wherever land exists. Lichens 
 may be dried so thoroughly that they can easily be reduced to 
 powder, yet their vitality is only suspended, and moisture will 
 restore them to renewed activity. Their growth is extremely slow, 
 and the life of the plant seems to be very long, in some cases many 
 hundreds of years. 
 
 BRYOPHYTA AND PTERIDOPHYTA. 
 
 These are wholly absent from the sea, but in fresh water a 
 few bryophytes are known. The peat-moss (Sphagnum) grows 
 abundantly in wet woods or in bogs. The growing ends increase 
 while the old portion dies off. Among the pteridophytes the class 
 of Filicinse has an aquatic group in the rhizocarps, or water ferns 
 (Hydropteridese), which grow partly submerged or floating. The 
 spores of these plants are widely distributed by flotation and 
 
1004 PRINCIPLES OF STRATIGRAPHY 
 
 may become enclosed in the finer lutaceous sediments. Spores 
 referred to rhizocarps (Protosalvinia) are found in abundance in 
 the black Devonic shales of North America, and it lias been held 
 that the black color and petroliferous character of these shales 
 are wholly due to the spores of these plants. If the spores are, 
 indeed, those of rhizocarps, they would be an indication of the 
 formation of the black shales in the estuaries of rivers, since 
 these plants are found only in fresh water. 
 
 Ferns are most abundant in the tropics, where they develop 
 an extraordinary wealth of form, and vary in their dimensions 
 from small moss-like plants to trees. They are especially character- 
 istic of humid forests. 
 
 Equisetina, or horse-tails, are represented by the living Equise- 
 tum and by the extinct Calamites, which latter often grew into 
 large trees. Equisetum to-day grows in low moist ground and in 
 the sand and gravel of railroad embankments, and along road sides. 
 Much silica is present in the epidermis of the plants, giving to it a 
 rough, harsh feel. 
 
 Lycopodiacecc, or club-mosses. These are to-day represented 
 by small prostrate plants found mainly in the deeper woods. In 
 late Palaeozoic time, however, they were represented by forest trees 
 (Lepidodendron, Sigillaria, etc.) A few aquatic lycopods exist 
 (quill-worts, Isoetae). These plants grow either partly or com- 
 pletely submerged, and in general resemble the smaller club-mosses. 
 
 Both Equisetae and Lycopodiaceae are characteristic of the tropic 
 and temperate zones, the Lycopodiaceae being more prominent in 
 the tropics. 
 
 SPERMATOPHYTA. 
 
 By far the greater mass of spermatophytes or phanerogamous 
 plants are terrestrial in habitat, though a not inconsiderable number 
 live in fresh water. Certain members of the pondweed family 
 (Potamogetonaceae) and the frog's-bit family (Hydrocharitaceae), 
 comprising about twenty-five species in all, have become wholly 
 adapted to a marine benthonic habit and are known as sea-grasses. 
 The pondweed family is represented on the Atlantic coast by the 
 eel-grass (Zostera marina L.) and the ditch-grass (Ruppia nmri- 
 tima L.), both of which are extremely common, and both of which 
 are concerned in the gradual choking of the marshes. A number 
 of species are partly marine, as the marsh-grass (Spartina) growing 
 within the limit of tide-water. The mangrove, as already noted, 
 is partly adapted to a marine habitat, all of it but the leaves being 
 periodically submerged. 
 
BIONOMIC CHARACTERS OF PLANTS 1005 
 
 All degrees of freshwater phanerogams are found, from those 
 having only their roots in the water, as many of the larger swamp 
 plants, to those nearly or entirely submerged. Parasitic, saprophytic, 
 and epiphytic phanerogams are further characteristic types adapted 
 to peculiar habitats. In short, the variety and adaptability of the 
 spermatophytes are as multitudinous as the variation in the character 
 of the terrestrial realm. 
 
 The coniferous gymnosperms are almost wholly confined to 
 temperate climates, especially the colder belts, but cycads are most 
 characteristically tropical plants. Both monocotyledons and dicoty- 
 ledons are more commonly represented by trees in the tropical than 
 in the temperate zone, the number of trees diminishing- toward the 
 colder belts, where the conifers increase in number. 
 
 Arboreal vegetation is characteristically unknown in regions 
 where the sub-soil is permanently frozen, i. e., where the mean sum- 
 mer temperature is below 10 C. Such is the character of the tree- 
 less plains of northern Canada, the coldest part of the North Ameri- 
 can continent, where the mean annual temperature is below 8 C. 
 and the mean summer temperature below 10 C. Here sedges, 
 grasses, and lichens predominate, while trees and sphagnum-bogs 
 are conspicuously absent. 
 
 The present northern extent of the forest regions of Canada 
 is limited by the mean summer temperatures of io-i5 C. Here 
 the poplar (Populus tremuloides and P. balsatnifera) , the birch 
 (Betula alba), spruce (Picea alba and P. nigra), pine (Pimts bank- 
 siana), and larch (Lariv americana) occur, while beneath them 
 the ground is often an extensive sphagnum swamp. "Poplar, birch, 
 and pine extend northward as far as the heavy forest extends, 
 while larch and the true species of spruce extend northward to 
 the northern limit of trees, becoming small and dwarfed before 
 they finally disappear." (Tyrrell-28:j#p-pi.) 
 
 South and west of the forested area are the grassy plains, which, 
 because of their dryness, do not support trees or sphagnum bogs. 
 As these plains were in the condition of the frozen tundra after 
 the retreat of the ice, and with the amelioration of the climate 
 became dry, no trees or sphagnum bogs ever developed there. 
 
 Ecology and Ecological Adaptations of Sphermatophytes. 
 
 Modern spermatophytes, as a whole, are divisible into a number 
 of habitudinal types, among which the following are the most 
 important : 
 
ioo6 PRINCIPLES OF STRATIGRAPHY 
 
 1. Hydrophytes and Hemihydrophytes. Aquatic plants are 
 marine, or brackish, or fresh water. The marine types comprise 
 the grass-wracks or eel-grasses' (Zoster a marina, and Z. nana). A 
 few plants are confined to a brackish-water habitat (Ruppia niari- 
 tima, etc.), while others are adapted to both fresh and brackish 
 water. The aquatic vegetation of ponds and lakes may be divided 
 into types with: (a) submerged leaves, (b) submerged and float- 
 ing leaves, (c) floating leaves, (d) submerged leaves and erect 
 leaves or stems, (e) erect leaves or stems, and lastly (f) marsh 
 plants. 
 
 2. Xerophytes. This group includes the plants which have 
 devices for procuring or for storing water, or for limiting trans- 
 piration, adaptations related to dry habitats. They have frequently 
 long tap roots which, in some cases, reach down to a subterranean 
 water supply. There is also often a superficial root system. Xero- 
 phytes of the deserts often have succulent stems, like the cacti of 
 southern and central America. In other deserts, such as the 
 Sahara, succulents are not prominent. A spiny character also 
 characterizes many Xerophytes. 
 
 3. Bog Xerophytes. These are plants living in the peaty soil 
 of fens and moors, which, though physically wet, are physiologically 
 dry. Such plants can survive a partial or complete drying up of 
 the bog. 
 
 4. Tropophytes. These are plants with a xerophytic character 
 during the unfavorable season. Thus deciduous trees are xerophytic 
 during the leafless period of winter while other plants survive the 
 unfavorable period by means of their bulbs, rhizomes, or other 
 special structures. 
 
 5. Hygrophytes. These are intermediate between Xerophytes 
 and hydrophytes and are sometimes called Mesophytes. Assimila- 
 tion goes on throughout the whole year, except during periods of 
 frost or when buried by snow. 
 
 6. Sciophytes. These are plants growing in the shade of 
 forests. They may be hygrophytes or they may be herbaceous 
 tropophytes. 
 
 7. Halophytes. These are plants growing in saline soils, and 
 they are characterized by xerophytic adaptations. Many of them 
 are succulent, their leaves and, to some extent, their stems having 
 much water-storing tissue. 
 
 8. Calcicole and Calcifuge Plants. Plants invariably inhabiting 
 calcareous soils are said to be calcicoles, while calcifuge species are 
 rarely or never found in calcareous soil. They are sometimes 
 termed silicicoles. 
 
THE BIOSPHERE 1007 
 
 BIONOMIC CHARACTERISTICS OF ANIMALS.* 
 I. PROTOZOA. 
 
 FORAMINIFERA. The Foraminifera are typically marine organ- 
 isms, though a considerable number of species has become adapted 
 to brackish water, living in estuaries and near the mouths of 
 streams, while many species, commonly placed in this class, 'live 
 entirely in fresh water. Their distribution is so great that scarcely 
 any marine sediments are wholly free from the shells of these ani- 
 mals. Most Foraminifera belong to the vagrant benthos, though 
 sedentary benthonic forms also occur. Only something over twenty 
 living planktonic species are known, these belonging chiefly to the 
 genera Globigerina, Orbulina, and Pulvinulina (Figs. 101-103), the 
 first predominating. The small number of species is, however, 
 counterbalanced by the enormous number of individuals. The ben- 
 thonic Foraminifera are confined chiefly to the littoral district, where 
 the character of the bottom and the temperature of the water exert 
 important influences on the distribution of these organisms. A 
 muddy facies of the sea-bottom seems to be conducive to the ex- 
 istence of a large number of species, but the rocky bottoms are not 
 without their types ; while algae and sea-grasses commonly form the 
 home of vast numbers of these organisms. The coarse, sandy and 
 gravelly bottoms are not generally inhabited by these animals, 
 though their dead shells are not uncommon in the sands along our 
 beaches ; while along some shores, they are so abundant as to con- 
 stitute the greater portion, if not the whole, of the deposit. Dana (9) 
 states that in the Great Barrier-reef region of Australia the shells 
 of Orbitolites are so abundant that . . . ''they seemed in some 
 places to make up the whole sand of the beaches, both of the 
 coral islets and of the neighboring Australian shore." 
 
 The vertical range of the benthonic Foraminifera is very great, 
 species sometimes passing through a range of several thousand 
 fathoms. In such cases there is often a change in the size or 
 thickness of the shell with the change in depth. Although the 
 planktonic Foraminifera comprise so few species, the number of 
 their individuals is enormous. From their shells the Globigerina 
 oozes form in deep water, where no sediment is carried; but it is 
 evident that, in a region where the land is reduced to near base- 
 level, so that little or no sediment is carried into the sea, pure 
 accumulations of such shells will occur near shore, thus, forming a 
 
 * Only those represented by fossils are taken into account here. 
 
ioo8 PRINCIPLES OF STRATIGRAPHY 
 
 foraminiferal ooze in shallow water. But not only planktonic shells 
 but the benthonic species as well may form a pure accumulation 
 of foraminiferal shells, as has been the case in the chalk, in which 
 the planktonic species are practically wanting. ( Walther-29 :<?/5. ) 
 Reproduction of the Foraminifera is carried on by fission, budding, 
 and spore formation. In the first two cases, the resulting part and 
 the buds have the characteristics of the parent, except its size, and 
 there are no special structures which serve for the greater distribu- 
 tion of the species. When spores are formed, these may be pro- 
 vided with a flagellum, whereupon the organisms pass through a 
 mero-planktonic stage. 
 
 While the geographical distribution of the benthonic species is 
 very restricted, and influenced by the facies of the sea bottom, 
 the geographical distribution of the pelagic species is prevented 
 from being world-wide only by the changes in the temperature of 
 the water and by the ocean currents. The pelagic species are ex- 
 tremely abundant in tropical regions, and their shells form vast 
 accumulations on the sea-bottoms over which they live. In the 
 great depths these shells are absent, for they may be completely dis- 
 solved while they sink to the bottom, or shortly after reaching it. 
 
 RADIOLARIA. The Radiolaria are marine planktonic Protozoa. 
 They inhabit principally, the open sea, where they occur at the 
 surface or at various depths below it. In regions of terrigenous 
 sedimentation, or where an influx of fresh water occurs, these 
 animals are seldom met with. Hence their siliceous shells occur 
 in abundance only in the deposits found at a distance from shore, 
 and in deep water, where they may constitute as high as seventy 
 per cent, of the mass. The greatest abundance of radiolarian skele- 
 tons was found by the Challenger expedition at a depth between 
 2,000 and 4,475 fathoms the greatest depth sounded. In many 
 places in the Pacific the bottom ooze is almost entirely composed 
 of radiolarian shells with some intermixture of sponge spicules. 
 The celebrated Barbados earth, a Tertiary deposit, is likewise com- 
 posed of radiolarian remains, to the exclusion of almost every other 
 organism. 
 
 Fission, budding, and spore formation constitute the methods 
 of reproduction in Radiolaria. The spores may be provided with 
 flagella, constituting "swarm spores," which, like their progenitors,' 
 lead a planktonic existence. 
 
 II. PORIFERA. 
 
 The sponges are marine or fresh-water animals, of a sedentary 
 benthonic habit. In general only such species as secrete a calcare- 
 
BIONOMIC CHARACTERS OF PORIFERA 1009 
 
 ous or siliceous skeleton either continuous or consisting of separate 
 spicules are capable of preservation in a fossil state. The vertical 
 distribution of marine species ranges from the shore zone down 
 to the greater depths of the sea. Not infrequently species are found 
 which regularly undergo an exposure of several hours between 
 tides, though most littoral species occur below low-water mark, or in 
 tide pools from which the water is never drained. Sponges will 
 grow wherever a suitable surface for attachment is found, the most 
 usual substratum chosen being cliffs, boulders, shells, or the stems 
 and "roots" of the larger algae. In deeper and quieter water, 
 the sandy and gravelly bottoms are inhabited by sponges, and in 
 the great depths they occur on the oozes and other soft deposits. 
 A pseudovagrant (epi-vagrant) benthonic habit is assumed by a 
 number of species, which attach themselves to the carapaces of 
 Crustacea. Certain sponges bore into shells and other calcareous 
 substances, forming extensive galleries and commonly destroying 
 the shell. Clione sulphurea, common on our Atlantic coast, com- 
 pletely riddles shells, and then forms large irregularly rounded 
 masses of a sulphur yellow color, often entirely enveloping the 
 shell. 
 
 The reproduction of the sponges is either asexual or sexual. 
 In the former case, buds are formed, which, growing larger, with- 
 out detaching themselves, put out buds of their own, thus forming 
 a colonial aggregation. Sponges torn into several pieces will fre- 
 quently form as many new individuals, and sponges which were 
 placed in close juxtaposition by Bowerbank in a relatively short 
 time united into one. A method of internal gemmation occurs, in 
 which groups of cells, or gemmulse, become detached and after a 
 time develop into complete, sponges. Sexual reproduction, from 
 either hermaphrodite or sexually distinct parents, leads to a free 
 swimming blastula. This develops into a gastrula, which attaches 
 itself and develops into the adult. Thus a mero-planktonic stage 
 occurs in sponges, which serves as a means of extensive distribu- 
 tion. 
 
 III. CCELENTERATA. 
 
 . . 
 
 HYDROZOA. The Hydrozoa are typically marine Coelenterates, 
 though a few species occur in fresh water, e. g., Hydra viridis and 
 H. fusca, Cordilophora lacustris and the fresh water medusa of 
 Lake Tanganyika : Limnocnida tanganyika. Some Scyphomedusse 
 (Aurelia, Cyanea), according to Moseley, seem to prefer to float 
 near the mouths of fresh water streams ; while in New South Wales 
 
lOio PRINCIPLES OF STRATIGRAPHY 
 
 these medusae were observed floating in shoals where the water 
 was pure enough to be drinkable. The majority of species have a 
 sedentary benthonic stage, the hydriform stage, which is generally 
 colonial, the compound polyp stock being attached to rocks, algae, 
 shells, timbers, or other objects of support, by means of a thread- 
 like branching root-stock or hydrorhyza, which spreads out over 
 the object of support and from which the individual polyparia arise, 
 each with a distinct stem or hydrocaulus. A few forms, like Hydrac- 
 tinia polyclina and some Podocoryne, are pseudo-vagrant benthos, 
 being attached to the shells of gastropods carried about by hermit 
 crabs. Some species, like Bougainvillia fruticosa, prefer an epi- 
 planktonic habit, becoming attached to floating timbers, a similar 
 habit being assumed by those hydroids which live attached to the 
 floating Sargassum. An epi-nektonic manner of life may perhaps 
 be considered the habit of Hydrichthys, which lives parasitically 
 upon a fish. Corymorpha pendula, though not attached, lives partly 
 buried in the mud of the shallow sea ; while Hydra leads, at times 
 at least, a kind of vagrant benthonic life, though its journeyings 
 are probably never very great. 
 
 Many, if not most Hydrozoa have a distinct medusiform person 
 which, when perfect, is perhaps the best type of a holo-planktonic 
 organism. In a few Hydrozoa Hydra Sertularidae the medusi- 
 form stage is wanting, in others it is degenerate, never becoming 
 free (Clava) ; but in a large number of species it is a free individual. 
 Again, in the Narco- and Trachymedusae, as well as in some others, 
 only the medusa occurs, the hydroid being suppressed. Compound 
 medusae occur as well as compound hydroids. The former are 
 the Siphonophora in which, by budding from the parent medusa, a 
 compound colony is formed which leads a holo-planktonic existence. 
 Lucernaria is an example of a medusa attached to foreign objects. 
 The medusae, whether free or attached, produce the sexual products 
 which give rise to new hydroid colonies or directly to new medusae. 
 The egg develops into a ciliated planula which leads a mero-plank- 
 tonic existence before it settles down to become a benthonic 
 hydroid, or before it develops into the medusa. A number of hy- 
 droids grow attached to rocks and sea-weeds, or to bridge piles, in 
 such a position as to become regularly exposed for several hours 
 each day during ebb tide. Even the delicate and unprotected Clava 
 of our northern shores delights to live under such conditions, and 
 is rarely found in deeper water or in tide pools. Most hydroids, 
 however, can not withstand such exposure, and hence they are 
 found only in the deeper waters or the deeper tide pools. 
 
 The majority of hydroids are inhabitants of the littoral district, 
 
BIONOMIC CHARACTERS OF CCELENTERATA ion 
 
 and they usually occur in the more moderate depths. The tubularian 
 hydroids probably never extend to any considerable depths, the 
 deep-water forms belonging chiefly to the Plumularidae. (Agassiz- 
 i, ii:j5-) One of the abyssal Plumularians was obtained by the 
 Blake at a depth of 1,240 fathoms, which exceeded by more than 
 300 fathoms that at which Plumularians were obtained by the Chal- 
 lenger. (Agassiz-i.) 
 
 The Palaeozoic class of graptolites or Graptozoa is the most im- 
 portant group of the Coelenterata from a stratigrapher's point of 
 view, for it constitutes one of the most important classes of index 
 fossils known. 
 
 Lapworth (Walther-29) holds that the majority of dendroid 
 graptolites (Dendroidea) undoubtedly grew attached to sea- weeds, 
 rocks, or other supports, in the manner of most modern hydroids, 
 but some were attached to floating algae, leading an epi-planktonic 
 existence. Cases of such attachment have been observed among 
 these fossils. 
 
 Lapworth argues that, if the sicula was attached by means of 
 the slender basal thread, the nema, to floating objects of support, 
 whether disc or sea-weed, the second and succeeding hydrothecae, 
 growing in the same direction as the sicula, would open downward. 
 This suggests that the earlier graptolites were not planktonic, but 
 grew attached to sea-weeds and rocks after the manner of modern 
 hydroids. This view is taken by Hahn (16) with reference to 
 Dictyonema. In later genera of graptolites, however, which may 
 have been attached to floating objects (epi-plankton), the branches 
 either bent backward, so as to cause the later hydrothecae to open 
 in an opposite direction from the sicula and early hydrothecae; or 
 the direction of growth was reversed, the second and succeeding 
 hydrothecae growing backward along the nema, which became the 
 supporting rod or virgula. 
 
 Some of the graptolites appear to have led a holoplanktonic ex- 
 istence, the nema being attached to a central organ or disc, which 
 probably served as a float. This was long ago demonstrated in a 
 number of species by Professor Hall, and lately has been shown in 
 great detail in Diplograptus by Ruedemann. This observer holds 
 that this mode of attachment was characteristic of the virgulate 
 graptolites (Axonophora) as a whole, while the Axonolipa he 
 thinks were attached to seaweeds. (Ruedemann-25 15/5.) Whether 
 holo-planktonic or epi-planktonic, either method of life accounts 
 for the wide distribution of the graptolites. The fact that they are 
 almost universally found in carbonaceous shales suggests that float- 
 ing algae may have been the principal carriers of these organisms, 
 
ioi2 PRINCIPLES OF STRATIGRAPHY 
 
 the decaying vegetable matter furnishing the carbon for coloring 
 the muds in which the organisms were buried. On the other hand, 
 it is not improbable that much of the carbonaceous material was 
 derived from the graptolites themselves. The general slight thick- 
 ness of these beds, and the fact that in successive beds the species 
 change, indicate a slow accumulation of the deposits in relatively 
 quiet water. 
 
 According to Ruedemann's observations (23), the young Diplo- 
 graptus, on leaving the gonophore, has already advanced into the 
 sicula stage, so that a free-swimming planula stage appears not to 
 exist. It is probable that this is true of most, if not all, graptolites, 
 and that hence the distribution of these animals is such as will be 
 accounted for by the vicissitudes which they met with as a floating 
 colony. 
 
 ANTHOZOA. The Anthozoa are typically marine sedentary ben- 
 thonic animals, inhabiting the warmer waters of the oceans. A 
 large number are without hard supporting parts, and consequently 
 leave no remains, while others, probably the majority of Anthozoa, 
 secrete a calcareous or horny corall'um, which is capable of preserva- 
 tion. Among the Actinaria, or fleshy polyps, a certain amount of 
 locomotion of a creeping or gliding nature is often observable 
 (Metridium, etc.), the individuals possessing this ability thus passing 
 from a normal sedentary to a vagrant benthonic life. A few forms 
 are also met with among the plankton. Occasionally epi-planktonic 
 individuals are met with, attached to floating algae or timbers; and 
 epi-vagrant benthonic individuals attached to moving crustaceans 
 are not unknown. The Madreporaria, or stone corals, are normally 
 sedentary forms, though they are not necessarily attached, but 
 may rest upon the sands. (Fungia, some Porites.) 
 
 Though the normal medium of the Anthozoa is salt water, a 
 few are known in brackish and even in tolerably fresh water. Cili- 
 cia rubeola is reported by the Challenger (Vol. XVI, pt. II; 36) in 
 the river Thames in New Zealand; and Dana (9:1^0) states that 
 
 . . . upon the reefs enclosing the harbor of Rewa (Viti 
 Lebu), where a large river, three hundred yards wide, empties, 
 which during freshets enables vessels at anchor two and a half 
 miles off its mouth to dip up fresh water alongside, there is a single 
 porous species of Madrepora (M. cribripora), growing here and 
 there in patches over a surface of dead coral rock or sand. In sim- 
 ilar places about other regions species of Porites are most common." 
 Several species of corals grow at the mouth of the Rio de la 
 Plata. 
 
 Porites limosa flourishes in muddy water, and Astrea bower- 
 
BIONOMIC CHARACTERS OF ANTHOZOA 1013 
 
 banki does not seem to mind mud or sediment, or even muddy 
 brackish water, growing on, and encrusting the stones at the mouth 
 of the Mangrove Creek, Australia, these stones being covered with 
 mud and slime, and being washed over twice in the twenty-four 
 hours by muddy, brackish water. (Tenison- Woods.) A common 
 Red Sea coral, Stylophora pistillata, is recorded by Milne-Edwards 
 and Haime from the intensely salt and dense waters of the Dead 
 Sea. 
 
 The simple corals (Caryophyllia, etc.) are chiefly found on 
 muddy bottoms, often attached to a shell or other object resting on 
 the mud. The bathymetric distribution varies from shallow water 
 to a thousand fathoms or more. This method of life corresponds 
 well with what is known of the Palaeozoic Tetraseptata, which com- 
 monly lived on a muddy bottom, with their bases not infrequently 
 showing signs of attachment to shells or other foreign objects. The 
 compound corals build heads or stocks often of great size and 
 weight. They are generally attached to stones, shells, or to the 
 rock bottom and, through rapid increase by budding or division, 
 masses of great size may be formed over a small object of support. 
 Even on muddy bottoms a small object of support may serve as 
 the nucleus around which a coral mass will grow, which, as it in- 
 creases in size and weight, will sink to a greater or less depth into 
 the mud on which it rests. 
 
 The typical compound or reef corals are very restricted in their 
 bathymetric distribution. They do not normally occur below fifty 
 fathoms, and the majority live in less than twenty fathoms of 
 water. Very many, indeed, live so close to the surface as to be 
 exposed at the lowest tides. A minimum annual temperature of 
 twenty degrees centigrade marks the regions in which most reef- 
 building corals occur, though in a few cases colder regions are 
 known to be inhabited by true reef-builders. In all seas, however, 
 which are subject to freezing, or are regularly invaded by floating 
 ice, reef-building corals cannot thrive, and hence the occurrence of 
 modern or ancient coral reefs is a reliable indication of a minimum 
 winter temperature above freezing. 
 
 The reproduction of the Anthozoa is both asexual and sexual. 
 The asexual method is carried on by fission and budding, the new- 
 formed corallites usually remaining united with their parents, thus 
 producing colonial forms. In some cases, however, the buds become 
 free and begin an independent life (Eungia, Balanophyllia, etc.). 
 New colonies, however, are mostly begun by sexually generated 
 individuals. From the fertilized egg develops a meroplanktonic 
 ciliated embryo, in appearance not unlike the planula of the hydro- 
 
ioi4 PRINCIPLES OF STRATIGRAPHY 
 
 zoa. After attachment this develops into the polyp, which early 
 begins to secrete its horny or calcareous corallum. 
 
 IV. MOLLUSCOIDEA. 
 
 BRYOZOA. The Bryozoa or Polyzoa are marine or fresh water, 
 chiefly colonial, benthonic animals. A few occur parasitic on a liv- 
 ing substratum, but the majority of species are epiphytically attached 
 to algae, to hydroids, etc. (epizoon), or to inorganic objects (epilith), 
 either basally or in an encrusting manner. The majority of species 
 are marine; and their bathymetric distribution ranges from the 
 shore zone, where they are exposed at low tide, to the abyssal 
 depths, a species of Bifaxia having been obtained below 3,000 
 fathoms. The majority of species, however, live in moderate 
 depths. While the Bryozoa normally lead a strictly sedentary ben- 
 thonic life, a few species may drift about with the sea-weed to which 
 they are attached, thus assuming an epi-planktonic habit. Holo- 
 planktonic forms are, however, unknown. 
 
 Many of the Palaeozoic species resembled and had a habitat 
 similar to that of certain corals, often forming extensive beds or 
 even reefs composed of few species but of an enormous number of 
 individuals. 
 
 The egg of the bryozoan develops into a meroplanktonic cili- 
 ated larva, which later on settles down, becomes attached, and 
 develops into a full-grown individual which, by budding, produces 
 the colony. 
 
 BRACHIOPODA. The brachiopods are marine benthonic organ- 
 isms, of exceptional stratigraphic importance, since they are to a 
 high degree dependent on the facies of the sea bottom. Some 
 species of Terebratula and Lingula can withstand a considerable 
 exposure, the former having been noted out of water for hours 
 together at low tide. Lingula is buried, by means of its long 
 fleshy peduncle, in the sand near shore ; Crania is attached to rocks 
 and shells by one of its valves; but the majority of brachiopods are 
 attached by their fleshy pedicles to rocks, shells, corals, or to one 
 another. They seldom live on muddy or sandy bottoms, but are 
 readily embedded in these, by becoming detached, after death, 
 from the rocks or other objects to which they adhered. 
 
 The bathymetric distribution of the Brachiopoda ranges from 
 shallow water to 2,900 fathoms (in one case) ; the majority of 
 species occurring, however, above the hundred-fathom line, while 
 a goodly number have been, obtained in depths of ten fathoms or 
 
BIONOMIC CHARACTERS OF MOLLUSCA 1015 
 
 less. A number of species have an individual range of several 
 hundred fathoms, this range in one of two cases being nearly 
 800 fathoms. 
 
 The mero-planktonic larva of brachiopods is known as the 
 cephalula, and consists of a ciliated umbrella-like anterior end, car- 
 rying four eyes ; a middle portion carrying the mantle lobes ; and a 
 posterior portion. When the larva becomes attached by the posterior 
 end, which develops into the pedicle of the adult, the anterior end 
 becomes enveloped by the forward-turning mantle lobes and de- 
 velops into the body of the brachiopod. 
 
 V. MOLLUSCA. 
 
 PELECYPODA. The pelecypods are marine or fresh-water ben- 
 thonic molluscs, which lead either a sedentary or a vagrant life. 
 The majority of species live in the sea, but of these some can adapt 
 themselves to brackish or even fresh water. Thus species of Car- 
 dium, Solen, Mya, and other marine pelecypods have been obtained 
 in fresh, or nearly fresh, water ; while Unio, on the other hand, has 
 been found in the Brisbane river within reach of the flood tide. 
 In the neighborhood of Rio Janeiro, Solen, and Mytilus, were 
 found living with fresh-water Ampullaria in brackish water (Dar- 
 win-io). 
 
 A number of pelecypods inhabit the shore zone, but the majority 
 of these live buried in the sands and muds, and so are protected 
 from desiccation at low tide. Mytilus edulis, however, is a good 
 example of a shore pelecypod, for it habitually grows in positions 
 where it will periodically be exposed at low tide ; while Modiola 
 plicatula is especially common in salt marshes, where it is covered 
 only for a short period at high water. The closely related Modiola 
 modiola, which occurs on our northern shores, is, however, seldom 
 exposed, growing either in deep water or in tide pools which are 
 never drained. 
 
 Ostrea arborea is another striking shore mollusc, growing in 
 vast quantities on the free roots of the mangrove, and withstanding 
 a periodic exposure under a tropical sun. Ostrea borealis, on the 
 other hand, is at home only in water of several fathoms' depth. 
 The bathymetric range of the pelecypods is very great, and even 
 a single species may have a range of considerable magnitude. 
 Thus, while Mytilus edulis does not occur below fifty fathoms, 
 another species, M. phaseolinus, ranges from the shore to a depth 
 of 3,000 fathoms. In the greater depths, the pelecypods are com- 
 
ioi6 PRINCIPLES OF STRATIGRAPHY 
 
 monly characterized by exceeding delicacy of shell and sculpture, 
 the shell being often quite transparent. Some deep-water species 
 show bright colors, but the majority are pale. Altogether there 
 are to be found among these deep-water species "innumerable illus- 
 trations of beauty, adaptation, or unusual characteristics . . ." 
 (Agassiz). In the littoral district, on the other hand, the thick- 
 shelled pelecypods predominate, and this is especially true of the 
 shore zone. 
 
 Pelecypods, like brachiopods, are excellent facies indicators, 
 for, though they live on all kinds of sea bottom, the species, or 
 at least the faunal combinations, are dependent on, and character- 
 istic of, the particular facies on which they live. The majority 
 of pelecypods are free animals, a few, such as the oyster, mussel, 
 and the like, being attached to foreign objects either by direct 
 cementation or by a byssus. The free pelecypods often have the 
 power of locomotion, Unio, Mactra, and others traveling occasion- 
 ally for considerable distances. Generally, however, these molluscs 
 lie buried wholly or partially in the sand, and never change their 
 location except when disturbed by storm waves. Some few pele- 
 cypods (Pecten, Lima) have the power of swimming short dis- 
 tances by the opening and closing, in rapid succession, of their 
 valves, and the forcible ejection of water. Even Solen, though 
 normally a burrowing animal, will swim for some distance in search 
 of the proper bottom, and it may often be seen circling around in 
 an aquarium, by a series of jerks, due to the periodic ejection of 
 the water from the siphons. A number of pelecypods bore into 
 wood or stone (Teredo, Lithodomus, Saxicava, etc.), leading a 
 sedentary life within the habitation thus formed. 
 
 The bivalve molluscs have many enemies which prey upon them. 
 Not the least of these are the carnivorous gastropods, whose depre- 
 dations are usually marked by the vast number of shells with 
 round holes bored into them, scattered along our beaches. Boring 
 sponges will riddle the shells of littoral species, and corallines, 
 Bryozoa, worms, and hydroids will attach themselves to the shells. 
 There is abundant evidence in the riddled and punctured shells 
 that even the Palaeozoic molluscs were subject to similar attacks 
 of boring sponges and carnivorous gastropods. When the animals 
 die, their valves usually fall apart; and from their position, and 
 the character and direction of the waves and currents, one valve 
 may be carried shoreward, the other, seaward. This explains the 
 frequent predominance, along the shore and in certain local por- 
 tions, of fossiliferous beds of one valve, the other being entirely 
 absent or at least very rare. 
 
BIONOMIC CHARACTERS OF MOLLUSCA 1017 
 
 The marine pelecypod normally passes through a mero-plank- 
 tonic larval stage the trochophore in which the young is pro- 
 vided with a velum, furnished with vibratory ciliae (veliger stage). 
 At certain seasons of the year these ciliated embryos swarm in th^ 
 pelagic district, especially in the neighborhood of the shores, where 
 they become the sport of the currents, which distribute them far 
 and wide. When they finally settle down upon the sea bottom, on 
 the loss of the velum, they develop further if they reach the proper 
 substratum, other conditions being favorable. Vast numbers of 
 the larvae are destroyed before they reach the bottom, serving as 
 food for all kinds of animals, or succumbing to unfavorable condi- 
 tions ; and vast numbers of others die from falling on an unfav- 
 orable bottom. That most species nevertheless develop to the 
 fullest extent is due to the enormous fecundity of most pelecypods. 
 As an extreme example may perhaps be mentioned our common 
 northern oyster, Ostrea virginiana, which, according to Brooks 
 (2:xxviii), produces nine millions of eggs. In fresh-water pelecy- 
 pods the mero-planktonic veliger larva exists in one species only 
 (Dreissensia polymorpha), which is believed to have migrated from 
 salt to fresh water in recent geologic times. (Lang- 19.) In the 
 other freshwater pelecypods the development proceeds in a different 
 manner, special adaptations to special modes of life being met with. 
 In some cases (Pisidium, Cyclas) the eggs develop in special brood- 
 capsules in the gills of the mother, which they leave with shell 
 fully formed, as young bivalves. In these genera the velum re- 
 mains rudimentary, the animal passing through the trochophore 
 stage within the gills of the mother. In the Unionidae the embryo 
 passes through its several stages in the gill of the mother, leaving 
 it with a bivalve shell, which is, however, furnished with a trian- 
 gular process on the ventral border of each valve, by means of 
 which the embryo attaches itself to the fins (Anodonta) or gills 
 (Unio) of fishes. In this manner the animal leads an epinektonic 
 existence, becoming enclosed by the rapid growth of the epithelium 
 of the part where the embryo is attached, and leading then a truly 
 endo-parasitic life. After several weeks the embryo has become 
 transformed into a young mussel, which, breaking through the 
 enclosing tissue of its nest, falls to the bottom of the water, there 
 to develop into the adult. 
 
 SCAPHOPODA AND AMPHINEURA. The first of these classes is 
 represented by the Dentalidae; the second by the Chitonidae, which 
 alone are important palaeontologically. Both are marine, being of 
 a sedentary benthonic habit, though not permanently attached. 
 Dentalium lies buried in the mud and sands usually at great depths, 
 
ioi8 PRINCIPLES OF STRATIGRAPHY 
 
 while Chiton and its allies cling to stones, shells, etc., and are 
 rare in deep water, where only their more archaic representatives 
 occur. A few species of Dentalium occur in moderately shallow 
 water, but most of them live below the hundred fathom line, some 
 reaching a depth of 2,000 fathoms or more. Chiton seldom ex- 
 tends below 500 fathoms. In both groups a mero-planktonic larva 
 occurs. 
 
 GASTROPODA. The gastropods are typical benthonic animals, 
 inhabiting the sea, fresh water, and the land. They almost invari- 
 ably belong to the vagrant benthos, though the degree of locomotion 
 varies greatly among the different species. Among the exceptions 
 to the general vagrant habit are Vermetus and some other genera, 
 which lead a truly sedentary benthonic life, being attached to rocks 
 or shells. Some genera, like Capulus, adhere continually to shells 
 and the tests of echinoderms and Crustacea ; while the limpets, 
 though adhering powerfully to rocks and shells by the muscular 
 foot, are, nevertheless, in the habit of crawling about in search of 
 food. Swimming and floating gastropods are also known, the 
 latter (Janthina, Glaucus, etc.) belonging to the true plankton. 
 
 The number of species living on land and in fresh water is 
 relatively small, though the individuals often occur in great num- 
 bers. The sea is the home of most gastropods, though some marine 
 forms can live in fresh water, while conversely fresh-water forms 
 have been found in water temporarily salt. Thus Limnsea was 
 found by Darwin (10) in Brazil, in a fresh-water lake to which 
 the sea had access at least once a year. 
 
 Among the normally fresh-water gastropods several occur which 
 have become adapted to a marine life. Thus Planorbis glaber was 
 found at a depth of 1,415 fathoms at Cape Teneriffe, and two 
 species of Nerita have been found in the sea. Limnaea and Neri- 
 tina live in the Baltic, where the water contains from 10 to 15 per- 
 mille of salt. 
 
 The variety of form and coloration is exceedingly great among 
 the gastropods, a fact which can easily be correlated with their high 
 degree of cephalization and actively vagrant life. They occupy all 
 parts of the sea, being much less dependent on the facies of the 
 sea bottom than the pelecypods are. The division into carnivorous 
 and herbivorous forms is also much more strongly emphasized than 
 in the pelecypods, which live largely upon the plankton. 
 
 The shore zone is occupied by a number of species, which can 
 withstand periodic exposure. Many of them require this exposure 
 and will invariably crawl to the surface if kept in confinement, 
 even if the water is kept cool and well aerated. Other species, 
 
BIONOMIC CHARACTERS OF MOLLUSCA 1019 
 
 again, live in shallow water, even if stagnant, and will not stand 
 a long exposure. 
 
 Various species of Neritina (N. dubia, N. ziczac, etc.) live 
 habitually high up on the trees of the mangrove swamps, deposit- 
 ing their eggs, however, on the surface of the water. Others occur 
 on the dry land, far from any water. (Semper-26.) 
 
 Nassa obsoleta covers the gentle muddy beaches at low tide, 
 where dead organisms remain for it to feed upon, and it also 
 abounds on every exposed mud flat on our northern coast. Littorina 
 rudis and L. palliata are commonly found on the New England 
 shore clinging to rocks or to the stems of the marsh-grass (Spar- 
 tina), high up, where they are exposed to the air for half the day. 
 The lack of a siphon forces these animals to live above the mud 
 (12:168). On the marshes of Cold Spring Harbor, these species 
 of Littorina occur in places where they are "submerged for only 
 a short time at high tide, and then under water that is nearly fresh." 
 (Davenport-i2:/dp.) In the Mississippi sound Davenport found 
 nearly all of the individuals of Littorina irrorata "living on the 
 stems of the short marsh-grass twenty to thirty centimeters above 
 the water level and exposed to the sunlight." Littorina rudis lives 
 prevailingly where it is much exposed. On the English Channel it 
 has been found two meters above the other marine animals, where 
 it is moistened only by the highest tides (Fisher-i3 :i&?) ; and on 
 the New England coast it is sometimes found in similar positions. 
 Species of Littorina are reported as passing the winter out of water, 
 with their gill chambers full of air. (Simroth-27:^.) 
 
 The majority of gastropods are shallow-water forms, though a 
 number of them range to depths of between 1,000 and 2,000 
 fathoms. The deep-sea gastropods are characterized by faint col- 
 ors, though often this is counterbalanced by the brilliancy and 
 beauty of the iridescence, and even the non-iridescent abyssal spe- 
 cies give out "a sort of sheen which is wanting in their shallow- 
 water allies." (Agassiz-i, ii:<5j.) The coarse ornamentation by 
 knobs, spines, etc., so common in shallow-water species, does not 
 occur in the deep-sea forms, where the ornamentation is more 
 delicate, and often of exquisite richness and beauty. Gastropods 
 feeding on vegetable matter are wanting in the deep sea, where no 
 vegetable matter occurs, except what is brought down as sediment. 
 The food of deep-sea molluscs is largely confined to soft-tissued 
 animals, since thick shells and other hard armors are generally ab- 
 sent in these depths. Agassiz states that the Pleurotomidae out- 
 number any other group of molluscs in the abyssal fauna. These 
 gastropods are characterized by a notch in the outer lip near the 
 
1020 PRINCIPLES OF STRATIGRAPHY 
 
 suture, which serves for the discharge of the refuse, thus pre- 
 venting fouling of the water used for respiration. Some of these 
 molluscs are provided with hollow barbed teeth and poison fangs, 
 which they use to kill their prey. This apparatus "is even more 
 fully and generally developed in the related group of the Conidae, 
 few of which reach any great depth." ( Agassiz-i, ii :66.) 
 
 A few gastropods are viviparous (Paludina vivipara, Littorina 
 rudis), producing their young in advanced state of development. 
 
 In nearly all the marine gastropods a veliger larva occurs, the 
 velum being generally large, wing-like, and fringed with cilia. This 
 velum may be retained until the shell is long past the protoconch 
 stage. While in most marine gastropods the veliger larva leads, a 
 mero-planktonic existence, some marine forms (Fulgur, Sycoty- 
 pus), and the^ oviparous, land, and fresh-water gastropods pass 
 through their veliger stage within the egg capsule, losing the velum 
 and other larval organs before passing from the capsule, which they 
 leave as young gastropods with well-developed shells. 
 
 In the case of the marine forms cited, the velum, though of 
 no use to the animal as a locomotor organ, is very large, and is 
 lost only just before the embryo leaves the egg capsule. In terres- 
 trial and fresh-water forms, on the other hand, the velum is re- 
 duced to a single ring of cilia or to two lateral ciliated streaks. 
 (Lang-ip, ii:^5/), while in some terrestrial species it is wanting 
 entirely. It is obvious that the distribution of species thus de- 
 prived of a temporary 'pelagic life must be more restricted, other 
 things being equal, than that of species having a free veliger stage 
 of greater or less duration. 
 
 Land snails generally require a considerable amount of moisture 
 in the atmosphere in order to be able to live an active life. Hence 
 they are found most abundantly near streams and in damp woods 
 and ravines, where they live on the ground or on the vegetation. 
 Nevertheless they can withstand a considerable amount of desicca- 
 tion by burying themselves in the soil or closely clinging to rocks 
 or trees. Even the deserts have their species, which obtain their 
 required moisture chiefly from the dew, and from the succulent 
 plants on which they feed. Hence the presence of snail shells in 
 loess deposits is not necessarily indicative of deposition by water. 
 Some remarkable cases are recorded by Woodward (31 '.14), of the 
 suspension of vitality in snails and their subsequent revivification. 
 Thus a specimen of a desert snail which had been affixed to a card 
 in the British Museum for a period of four years (1846-1850), 
 again came to life upon being immersed in tepid water. 
 
 PTEROPODA. The pteropods are marine planktonic molluscs 
 
BIONOMIC CHARACTERS OF MOLLUSCA 1021 
 
 which live in vast numbers in the pelagic district, usually some 
 distance from shore. While able to swim about in the water, they 
 are, nevertheless, at the mercy of the waves and currents. Their 
 food consists of pelagic organisms, and not uncommonly one species 
 of pteropod will prey upon another. They shun the light, descend- 
 ing during the day to the regions of perpetual twilight or even 
 darkness, some descending as far as 700 fathoms. Nearly all the 
 shelled pteropods of the present time are confined to warmer 
 waters, and are especially abundant in the warm ocean currents. 
 Their shells often accumulate in vast numbers on the ocean bottom. 
 A veliger larva, similar to that of the gastropods, occurs. 
 
 CEPHALOPODA. The cephalopods are marine nektonic or ben- 
 thonic molluscs inhabiting water of moderate depths. Swimming is 
 accomplished by the forcible ejection of water from the hyponome, 
 and probably also by the use of the arms. Among the dibranchiata 
 the majority of Sepioidea (Squids, Calamaries) are active swim- 
 mers, usually inhabiting the open sea, but appearing periodically on 
 the coasts in great shoals. They live mostly on small fish. The 
 Octopoda are less adapted to active swimming, 'lying usually in 
 wait for their prey on the sea-bottom or in crevices and hollows. 
 The Argonauta is, however, a partial exception to this, for, though 
 it crawls about on the sea-bottom like other octopods, it is often 
 met with swimming at or near the surface, by the ejection of the 
 water from its hyponome. Argonauta is, therefore, like other 
 cephalopods, at times a vagrant benthos, at others a nekton, in- 
 clining perhaps more to the latter, as do the decapods ; while 
 other octopods are commonly benthonic. Among the less active 
 decapods, Sepia may be mentioned as more normally a vagrant 
 benthonic form, crawling about on the sea-bottom, though able 
 to swim as well. A sedentary benthonic cephalopod is also known. 
 This is Spirula, which attaches itself to rocks like an actinia 
 (Agassiz, Walther), or lies partly buried in the mud, with its 
 beautiful coiled and chambered shell wholly concealed by the 
 fleshy parts. A perfect specimen was dredged off Grenada in the 
 Caribbean by the Blake, from a depth of 950 fathoms. (Agassiz-i, 
 ii:<5/.) 
 
 Spirula would seem to be a widely distributed form, judging 
 from the occurrence of its shell in almost all parts of the tropical 
 and temperate seas. The animal is very rare, however; only one 
 specimen with soft tissues preserved having been obtained by the 
 Challenger expedition. This was taken close to the island of 
 Banda in 360 fathoms (Challenger Narrative). Altogether perhaps 
 only half a dozen animals with the soft parts preserved have been 
 
1022 PRINCIPLES OF STRATIGRAPHY 
 
 obtained. The wide distribution of the shell of Spirula is due to 
 the fact that after the death of the animal the shell ascends to the 
 surface, owing to the air-filled chambers, and then becomes a part 
 of the plankton. It is carried hither and thither by the currents 
 and waves, and finally may reach the sea-bottom in regions remote 
 from its original home, and be buried in sediments of every descrip- 
 tion, and under conditions in which the animal never existed. 
 Thus the shell of Spirula becomes an excellent index fossil, being 
 widely distributed and buried in all kinds of sediment. 
 
 To a more restricted degree this method of pseudo-planktonic 
 distribution of the shell, after the death of the animal, occurs also 
 in Nautilus, the only modern representative of the tetrabranchiate 
 cephalopods. The animal belongs to the benthos, living in shallow 
 water in the tropics. Occasionally it swims near the surface, but 
 before long it returns to the bottom, where it crawls about with its 
 shell uppermost, feeding on Crustacea and other animals. On the 
 death of the animal the shell may float for a considerable time on 
 the surface, buoyed up by the air in the chambers, and thus it may 
 be carried for a greater or less distance before it settles to the 
 bottom, where it will be buried in all kinds of sediment (Walther). 
 The verity of such statements has, however, been questioned by 
 Ortmann and others, who believe that the Nautilus shell is seldom 
 carried far from the region inhabited by the living animal. 
 
 What is true of the shells of Nautilus and Spirula is true of 
 the shell of Sepia, and was undoubtedly true of the shells of Am- 
 monites as well. (Walther-29:5op; 30:^56* et seq.) In fact, we 
 may even believe that the shells of the Ammonites were better 
 floaters than either those of Spirula .or Nautilus, for these two 
 genera are retrosiphonate, the siphonal funnels passing backward 
 and thus giving more ready access to the water; while the shells of 
 the Ammonites were prosiphonate, their siphonal funnels bending 
 forward like the neck of a bottle, and thus making the entrance 
 of water more difficult. This conception of the planktonic wan- 
 derings of the shells of cephalopods after the death of the animal 
 furnishes a satisfactory explanation of many anomalies observed 
 in the occurrence of these animals in the geologic series. It ac- 
 counts, especially, for the sudden appearance and disappearance of 
 the same species in widely separated localities, irrespective of the 
 character of the rock, and of its normal faunal contents. This 
 widespread distribution of these shells makes them excellent index- 
 fossils, so that even small formations may readily be correlated by 
 their species of Ammonites, even though widely separated. 
 
 It does not follow, of course, that ammonoid shells must always 
 
BIONOMIC CHARACTERS OF VERMES 1023 
 
 be regarded as strangers which have drifted to their present posi- 
 tion ; in fact, it is often easy to see that such has not been the case 
 in any particular locality, from an examination of the shells them- 
 selves, as well as from the extraneous evidence. Thus, according 
 to Clarke (5:155, et seq.), the ammonoids of the Naples beds of 
 western New York "... bear sufficient demonstration in 
 themselves that they have lived and died in these sediments." 
 Many of the most delicate shells retain their apertures unbroken, 
 and their suface ornamentation uninjured, a fact which is not con- 
 sistent with transportation by waves and currents. The presence 
 of the young in all stages of development further argues for an 
 indigenous occurrence. "On the other hand," says Clarke, "there 
 are excellent reasons for regarding the prenuncial Intumescens 
 fauna, that of the Styliola [Styliolina] limestone, as due to trans- 
 portation from some adjoining province not yet known to us." 
 The Goniatites of this fauna are associated with the millions of 
 holo-planktonic Styliolina, with floated logs, and probably other 
 pelagic organisms, and the sediment in which they were embedded 
 was such as probably was not conducive to the well-being of such 
 animals, so that their occurrence is best explained by the hypothesis 
 of flotation. 
 
 Of the embryology of Nautilus, and hence of the whole group of 
 Tetrabranchiata, nothing is known. The Dibranchiata develop di- 
 rectly within the egg capsule, no veliger stage occurring. 
 
 VI. PLATYLELMINTHA. VII. VERMES. 
 
 These worms are marine, fresh-water, or terrestrial animals. 
 They belong chiefly to the benthos, though some marine forms lead a 
 partially nektonic existence, while others are typically planktonic. 
 Several oligochsetous annelids have become adapted to a marine 
 life, though the group is normally fresh-water or terrestrial. Among 
 the benthonic species all grades of a sedentary life are observable, 
 from the tube-building orders, which live permanently in attached 
 tubes, to those which only temporarily occupy a given area. Tubi- 
 colous worms, which, like Spirorbis, attach their tubes chiefly to 
 algse, may often lead an epi-planktonic existence when the algae are 
 torn from their anchorage and washed away by currents. 
 
 A muddy bottom seems to be the favorite haunt of the littoral 
 species, except such forms as build attached tubes (e. g., Serpulidae, 
 etc.), which occupy stony and shelly bottoms. These latter often 
 build extensive reefs of interwoven calcareous tubes. 
 
1024 PRINCIPLES OF STRATIGRAPHY 
 
 Besides calcareous tubes, many worms build tubes of aggluti- 
 nated sand grains or shell particles, and worms living in the shells 
 of dead molluscs are frequently met with. These agglutinated sand 
 tubes are often very resistant, sometimes, with the castings, covering 
 the mud flats and beaches in great numbers, and not infrequently 
 being heaped together in windrows. The dredge brings large 
 numbers of these tubes, together with numerous castings, from the 
 deeper water. The bathymetric distribution of the worms is varied. 
 The majority are undoubtedly littoral species, but deep-sea forms 
 are also common. Beyond the hundred-fathom line the tubicolar 
 annelids are the most characteristic, specimens having been ob- 
 tained from a depth of 4,000 fathoms off Teneriffe (Challenger). 
 Other worms also occur. Even species of the same genus have a 
 widely varying distribution in depth. Thus the tubicoloid genus 
 Spirorbis has its littoral species growing within the shore zone ; 
 while another species, S. nautiloides, has been dredged at a depth 
 of 700 fathoms. Similarly, the Sipunculid Phascolosoma is repre- 
 sented along our northern shores by a species living in mud and 
 sand above low tide, while the Blake brought up a species in a- Den- 
 talium shell from a depth of 1,568 fathoms. (Agassiz-i, ii:5J.) 
 The Myzostomidse are parasitic on living Comatula, and also have 
 been found on the column segments of Jurassic crinoids (Graff). 
 
 Among the annelids, the family Eunicidse is of particular in- 
 terest, in that its several members are characteristic of different 
 bathymetric zones, thus furnishing, in a measure, an index to the 
 bathymetric position of the fauna which they characterize. This 
 family is well represented in the lithographic shales of Bavaria. 
 (Ehlers.) 
 
 Among the worms regeneration of lost parts and generation of 
 new individuals from fragments of old ones are not uncommon. 
 Thus, in one of our common halo-pelagic worms, Autolytus, swim- 
 ming buds carrying the sexual products are periodically constricted 
 off, each regenerating a new head, with highly developed eyes at 
 the anterior end. The oligochaete Lumbriculus in autumn falls 
 into pieces, all of which are able to regenerate into complete ani- 
 mals. (Lang-iQ; ii^d/.) 
 
 A mero-planktonic ciliated larva, the trochophore, is character- 
 istic of worms, this being the product of a sexual mode of repro- 
 duction. These larvae are often obtained in vast numbers in the 
 tow-net, together with other mero-planktonic and many holo-plank- 
 tonic forms. 
 
 The oesophageal teeth of annelids are abundantly represented 
 in many bituminous shales, from the Palaeozoic on. Some of these 
 
BIONOMIC CHARACTERS OF CRUSTACEA 1025 
 
 objects, known as conodonts, were formerly regarded as the teeth 
 of mixinoid fishes or as radulae of gastropods. 
 
 VIII. ARTHROPODA. 
 Crustacea. 
 
 Trilobita. The trilobites are extinct Palaeozoic Crustacea of an 
 undoubted marine habitat, probably able to swim as well as crawl, 
 and so belonging at one time to the nekton, at another to the vagrant 
 benthos. Whether or not a mero-planktonic larva existed is not 
 known, but it might be assumed from the wide distribution of some 
 species. Since trilobites cast off their exoskeletons, as does Limulus, 
 some of these may have floated a considerable distance, coming to 
 lodge where trilobites never lived. It is certain that from the 
 number of fossil trilobites we cannot judge the number of individ- 
 uals existing at a given place, since a number of specimens may rep- 
 resent the cast-off exoskeletons of one individual. Trilobites, like 
 many modern Crustacea, probably turned on their backs while sink- 
 ing to the sea-floor, this accounting for the frequent overturned 
 position in which their remains are found. 
 
 Phyllopoda; Copepoda. These belong largely to the plankton, 
 the phyllopods occurring mostly in fresh water, the copepods having 
 fresh water (Cyclops) and marine representatives. The copepods 
 further comprise commensal forms, which live in the branchial 
 cavity of Ascidians (Notodelphus) or on the carp (Argulus) ; and 
 a large number of parasitic types. Some of them, however, are 
 only occasionally or temporarily parasitic. Some phyllopods have 
 a bivalve shell (Estheria, etc.), which is frequently preserved in 
 the finer fresh water sediments of continental formations. A plank- 
 tonic nauplius larva occurs. The eggs of some phyllopods have 
 the power to withstand desiccation for years. In fact, the eggs 
 of Apus do not develop unless they have been subjected to desicca- 
 tion for some time (Semper). This accounts for the periodic 
 reappearance of these organisms in the temporary water bodies 
 of desert regions. The occurrence of such types (Estheria) in 
 otherwise unfossiliferous deposits thus indicates that these deposits 
 may be of desert origin. 
 
 Ostracoda. The ostracods are marine or fresh-water, planktonic 
 or vagrant benthonic Crustacea whose imperfectly segmented body 
 is enclosed in a bivalve shell. The majority of the marine forms 
 are holo-planktonic, living in shallow 7 water or in moderate depths, 
 
1026 PRINCIPLES OF STRATIGRAPHY 
 
 though a few species were found by the Challenger at depths ex- 
 ceeding 2,000 fathoms. Some species are cosmopolitan and the 
 order is represented in nearly all waters, their shells occurring in 
 nearly all the bottom deposits. The animals are also abundant on 
 alga?, over which they crawl slowly. The fresh-water Cypris 
 swims about, subject, however, to the influences by which other 
 members of the plankton are affected ; or it crawls about on the 
 vegetation. Cypris is also represented in brackish and salt water. 
 Its eggs have the power to withstand desiccation for a long time, 
 and hence the species can continue in water bodies which become 
 periodically dried up, as in desert regions. The larva of the ostra- 
 cods is a pelagic nauplius. 
 
 Cirripedia. The cirripeds, or barnacles, are marine sedentary 
 benthonic Crustacea which have degenerated much from the true 
 type of crustacean, owing, no doubt, to their attached mode of life. 
 The body is covered with calcareous plates variously arranged, 
 which fall apart after the death of the animal; after which, from 
 single pieces, it is quite impossible to determine the species, owing 
 to the great variation of the skeletal parts. (Darwin.) Balanus 
 and its congeners are sessile, being attached to the rocks and other 
 solid supports along the shore, seldom venturing into water of 
 great depth. Some species are periodically exposed for many 
 hours at low tide, some, in fact, never being covered more than one 
 or two hours at flood tide, so high up on the shore do they attach 
 themselves. Balanus has been found at a depth of 500 fathoms, 
 but it usually lives in lesser depths. Balanus improvises occurs also 
 in brackish water, and some species of this barnacle have been re- 
 ported from fresh water (Tscherniansky). Coronula diadema 
 leads an epi-nektonic life, attaching itself to the body of whales. 
 Verruca incerta, a common West Indian type, occurs in the Glo- 
 bigerina ooze. Lepas and its congeners are pedunculate, attach- 
 ing themselves by a fleshy peduncle, which represents the elongated 
 head end. The majority of the Lepadidae are pelagic, leading an 
 epi-planktonic existence, attached to floating logs, pumice, or other 
 objects. Three species of Lepas were found by the Challenger 
 attached to the Sargassum. Some members of this family descend 
 into deep water, Scalpelluni regiuni having been dredged by the 
 Challenger from nearly 3,000 fathoms. These abyssal cirripeds are 
 usually attached to nodules, dead or living shells, corals, large 
 Crustacea, to spines of sea urchins and other objects. (Agassiz- 
 i, 11:50.) The cirripeds, upon hatching from the egg, pass through 
 several larval stages, the first of which is the nauplius stage. In 
 this the body is unsegmented, with median frontal eyes, dorsal 
 
BIONOMIC CHARACTERS OF CRUSTACEA 1027 
 
 shield, frontal sensory organs and three pairs of limbs. After 
 a series of moults the Cypris stage is reached, in which the larva 
 is enclosed in a bivalve shell, like that of the Ostracoda. During 
 these stages the larva belongs to the mero-plankton. When it 
 settles down and becomes attached it passes through a pupa stage, 
 during which' the transformation of the larva into the cirriped 
 takes place. 
 
 PJiyllocarida. These are mostly extinct forms, represented in 
 all the divisions of the Palaeozoic. Several living genera (Nebalia, 
 etc.) are regarded as belonging %ere, and these are marine. They 
 are swimmers, and their development is direct, without metamor- 
 phosis. Some of the Palaeozoic forms referred to this class were 
 undoubtedly marine (Stenotheca, Ribeiria), but the majority seem 
 to have been fresh water forms living in the rivers of the Palaeozoic 
 lands. This is inferred from their peculiar occurrence in sediments 
 which could only have been formed at the mouths of streams and 
 in playa-like basins. At any rate, they did not seem to be normal 
 inhabitants of the open sea, but, if marine at all, lived near the 
 mouths of great streams. 
 
 Schlzopoda, Stomatopoda, Sympoda. These are marine Crus- 
 tacea, capable of swimming about by the use of their abdominal 
 legs and caudal fin. Larval stages are often wanting. 
 
 Decapoda. The decapods belong chiefly to the benthos, inhab- 
 iting either fresh or salt water, rarely the land. Pelagic species also 
 occur, some of which are good swimmers; while a few belong to 
 the plankton and others to the epi-plankton, living on the Sargas- 
 sum. They commonly feed on living or dead animal matter. The 
 bathymetric distribution varies greatly, though the majority of 
 species are confined to comparatively shallow water, generally not 
 exceeding fifty fathoms. A considerable number, nevertheless, are 
 abyssal. The range of individual species is often great; Alpheus 
 avarus, for example, is said to range on the Australian coast from 
 less than ten to about 2,500 fathoms (Challenger}, though this is 
 questioned by Ortmann (21:75). Among the hermit crabs occur 
 some forms which have left their native element and have taken 
 to the land. The Challenger found some of them in the mountains 
 of the Antilles, up to 300 meters. They sometimes inhabit the 
 shells of land snails and have been seen climbing trees. Among 
 the true crabs, or Brachyura, shallow-water species predominate, 
 comparatively few occurring below 400 fathoms. A number of 
 species live in fresh water or on land. The majority of decapods 
 leave the egg in the zoe'a stage, in which the abdominal region is 
 perfectly segmented, though still without appendages, except per- 
 
1028 PRINCIPLES OF STRATIGRAPHY 
 
 haps the rudiments of the sixth pair. The compound eyes are 
 stalked. Other larval stages follow until the adult is reached. 
 These larvae often occur in vast quantities in the plankton. 
 
 Arthrostraca. This super-order includes mostly marine forms, 
 though the order Isopoda comprises marine, fresh water, and ter- 
 restrial types. The latter occur in damp woods, under moss, stones, 
 or logs, and are also abundant in the crevices of rocky cliffs. The 
 marine Isopods are common in shallow water, on algae, or swim- 
 ming about in tide pools. Chiridotea cocca lives on sandy shores, 
 moving about just below the surface of the sand, and leaving a 
 meshwork of curious trails in its wake. Some of the lower sand 
 flats are often found covered with these markings. The animal 
 is usually found at the end of the trail, its whereabouts being in- 
 dicated by a little lump of sand. Limnoria lignorum eats its way 
 into driftwood or bridge piles, often completely riddling and de- 
 stroying the wood. Caprella clings to hydroids and slender sea- 
 weeds. Though chiefly found in the littoral district, some abyssal 
 species are known, several having been obtained at a depth of over 
 3,600 meters. Sometimes different species of the same genus range 
 from shallow water to great depths. Blind species are common 
 in the Mammoth and other caverns. A number of types are 
 parasitic on fishes. The Amphipods are chiefly marine, though 
 fresh and brackish water species also occur in marine genera 
 (Gammarus). Cyamus is parasitic on the skin of whales. Several 
 species live on the beach just above the reach of the ordinary tide, 
 where they hide under the dead seaweed or burrow in the sand 
 (Orchestia). They generally move about by leaps and hence are 
 commonly known as beach fleas. Talorchestia lives in a similar 
 manner just a little below high- water mark and the beach at low 
 tide is often completely riddled by its burrows. A number of 
 Orchestidae can live wholly out of the water in damp woods or in 
 the dry stream beds. 
 
 Acerata. 
 
 Merostomata. The Xiphosurans are represented by the single 
 living genus Limulus, which is a marine vagrant benthonic animal, 
 though often swimming on its back when young. The usual habitat 
 of this animal is in shallow water, where it is often partly buried in 
 the mud or sand. Portions of the coast are often strewn with the 
 cast-off exoskeletons of Limulus, which usually lie on their backs, 
 a position which these structures will naturally take on sinking to 
 the bottom. 
 
BIONOMIC CHARACTERS OF MEROSTOMES 1029 
 
 The young Limulus on hatching is a trilobitiform, free-swim- 
 ming, commonly meroplanktonic organism without caudal spine 
 (J. S. Kingsley). 
 
 Modern Limulus is restricted to the eastern shores of America 
 and Asia. A Tertiary species (L. decheni} is known from the 
 Oligocenic brown coal of Teuchern, near Merseburg, in Saxony, 
 an occurrence scarcely suggestive of marine habitat. A marine 
 species (L. walchi) is abundant in the lithographic slates of Ba- 
 varia, associated with land forms, however. A small species occurs- 
 in the Bunter Sandstein of the Vosges, a formation chiefly of ter- 
 restrial (river) origin, and suggesting that Limulus in the Trias 
 was still a river animal. This was most probably true also of 
 Protolimulus, which occurs in the Chemung delta deposits of 
 Pennsylvania. The Carbonic Xiphosurans, Prestwichia, and Beli- 
 nurus were undoubtedly fresh-water (river) organisms, occurring 
 in the non-marine coal deposits. Cyclus, on the other hand, is 
 found in the interbedded limestone of the Coal Measures, as well 
 as in the Coal Measures themselves. The habitat may have been 
 marine, but not necessarily so, since these carapaces could easily 
 have been washed from the land. 
 
 Altogether it seems as if the early Xiphosurans were river-living 
 animals, venturing perhaps occasionally into the sea (euryhaline) 
 and assuming their marine habitat in the Mesozoic and modern 
 times. 
 
 The Synxiphosurans may have been partly marine and partly 
 fresh water, The Upper Cambric Aglaspis suggests their derivation 
 from the trilobites. This occurs in the St. Croix sandstone of 
 Wisconsin, a terrestrial deposit reworked by the sea. The Siluric 
 genera Neolimulus, Bunodes, Hemiaspis, and Bunodella occur in 
 deposits which are partly marine and partly of delta type. It is 
 not improbable that most of them were derived from the land- 
 waters and buried in the sea margin deltaic deposits. The possi- 
 bility of a marine character for some can, however, not be denied. 
 Pseudoniscus, on the contrary, in America occurs in the Pittsford 
 black shale deposits, which are most suggestive of influx of fresh 
 water, and hence a non-marine habitat is indicated. The European 
 species are from Oesel and their real habitat is doubtful. (O'Con- 
 nell-2o.) 
 
 The Eurypterida have generally been considered marine, but 
 the elaborate study of the habitat of these organisms made by Miss 
 O'Connell (20) points unmistakably to a non-marine habitat of 
 these merostomes since pre-Cambric time. The majority of forms 
 occur in rocks not explainable as normal marine sediments, but as 
 
1030 PRINCIPLES OF STRATIGRAPHY 
 
 delta or as playa-lake deposits without direct connection with the 
 sea. Individuals are occasionally found in marine deposits which 
 cannot be interpreted as deltas, but in such cases the remains are 
 of single individuals or are fragments. Since all known specimens 
 of this kind represent merely the exoskeleton (Clarke and Ruede- 
 mann 6), it is easy to see that they may have reached their resting 
 place as pseudoplankton. A characteristic mode of occurrence 
 of these organisms* is in the black muds intercalated in torrential 
 conglomerates and sandstones. The geographic distribution, too, 
 is of such a character as to indicate a river rather than a marine 
 habitat. For further discussion of this problem see page 1043 anc ^ 
 the references there cited. 
 
 The Limulava are known only from the Cambric, where they 
 are found in a remarkable state of preservation in black bituminous 
 shales (sapropellutytes), together with trilobites, worms and other 
 animals suggesting a marine habitat. 
 
 Arachnida; Pantapoda. The spiders and scorpions are typically 
 terrestrial animals, breathing by means of trachea. The Panta- 
 poda (Pycnogonida), or sea-spiders, however, constitute a class 
 of marine organisms, resembling in many characters the Arach- 
 nida, of which class they are often considered relatives. There is 
 also a true spider, Argyroneta aquatica, which leads an aquatic 
 life in fresh water. Scorpions first appear in the Siluric, where 
 they are associated with eurypterids, from which they may have 
 been derived. Spiders are known from the Coal Measures, but 
 insects date from the Ordovicic graptolite slates of Sweden (Pro- 
 tocimex). 
 
 Myriopoda and Insecta. 
 
 These are also terrestrial tracheates, but with marine representa- 
 tives. 
 
 Larvae of insects also live in the sea, and a number of adult 
 insects are marine in habit, though continuing to breathe air. Many 
 insects and spiders have been met with in the open sea, far from 
 land, swimming in great numbers on the surface, while others have 
 been found creeping between rocks under water by the shore. The 
 bug Halobates comprises some fourteen species living on the sur- 
 face of the sea, running about like the fresh-water bug Hydro- 
 metra, often hundreds of miles from land. In the Upper Siluric 
 of France a primitive cockroach, Pal&oblattina, has been obtained. 
 Myriopods have been found in the Devonic, but more abundantly in 
 the Carbonic. The Palaeozoic myriopods, like the Palaeozoic insects. 
 
BIONOMIC CHARACTERS OF ECHINODERMS 1031 
 
 were distinct from the Mesozoic and recent forms. The modern 
 Chilopoda date from the Tertiary ; the Diplopoda from the Cretacic. 
 
 ECHINODERMATA. 
 
 CYSTOIDEA AND BLASTOIDEA. These classes are entirely extinct, 
 being confined to the Palaeozoic. They were undoubtedly marine 
 organisms like all the echinoderms. 
 
 CRINOIDEA. The crinoids are without exception marine organ- 
 isms, though Ante don rosacea has been taken in water containing 
 only 25 permille of salts, or nearly a third less than in normal sea- 
 water. The majority of crinoids belong to the sedentary benthos, 
 being anchored or attached to the sea-bottom either by a stem or 
 by the base of the calyx. Antedon must be classed with the vagrant 
 benthos for, although it ordinarily rests on the sea-bottom or other 
 stationary objects of support, it is able to walk about on the bottom 
 by means of its arms ; and also to swim with graceful movements 
 through the water. Planktonic crinoids appear to have existed in 
 the Mesozoic seas (Saccocoma, Uintacrinus), and, as already noted, 
 Walther has furnished evidence which indicates that some of the 
 stemmed Pentacrini of the Lias led an epiplanktonic life, grow- 
 ing attached to floating timbers with which they were carried about, 
 calyx downward. 
 
 Kirk (18) has recently brought forward evidence to show that 
 many Palaeozoic as well as later crinoids separated from their stems 
 late in life and assumed secondarily a planktonic existence, the 
 crowns floating away, while the dead stems remained behind to 
 separate into their component ossicles .and form a bed of crinoidal 
 limestone. 
 
 The bathymetrical distribution of the modern crinoids ranges 
 from shallow water to 2,000 fathoms, rarely more. One species of 
 Antedon (A. abyssicola, Carp.) has been obtained at a depth of 
 2,900 fathoms, but most of the species of this genus live in shal- 
 low water, A. lovcni, occurring in three to four fathoms. This 
 genus is perhaps the most cosmopolitan of the modern crinoids, its 
 geographic range being between eighty degrees northern and fifty- 
 two degrees southern latitude. The following modern stalked cri- 
 noids have been obtained in less than ninety fathoms of water 
 ( Walther-2(j 1298-300) : 
 
 Eudiocrinus indivisus Semp., 30 fathoms (54 meters). 
 Metacrmus rotundus Carp., 70 fathoms (128 meters). 
 
1032 PRINCIPLES OF STRATIGRAPHY 
 
 Pentacrinus asterius L., 80 fathoms (range 80-320 fathoms 
 
 equals 146-584 meters). 
 P. decorus Wy. Th., 84 fathoms (range 84-667 fathoms equals 
 
 153 to 1,219 meters). 
 P. miilleri Oerst, 84 fathoms (range 84-531 fathoms equals 153 
 
 to 970 meters). 
 Promachocrinus kerguelensis Carp., 28 fathoms (range 28-120 
 
 fathoms equals 51-218 meters). 
 
 Rhizocrinus lofotensis Sars, 80 fathoms (range 80-1,900? fath- 
 oms equals 146-3,474 meters). 
 
 R. rawsoni Pourt., 73 fathoms (range 73-1,280 fathoms equals 
 
 133-2,340 meters). 
 
 The egg of Antedon develops into an egg-shaped mero-plank- 
 tonic larva, which has a tuft of long flagella on the anterior end 
 and five ciliated rings surrounding it ; no mouth or anus is present. 
 This embryo swims about for a period of time, varying from a few 
 hours to several days, and, on settling down to a benthonic life, 
 attaches itself at a point on the ventral side between the first and 
 second ciliated rings. The whole anterior part, as far as the third 
 ciliated ring, becomes the stalk, the posterior part developing into 
 the calyx. In Antedon the stem is retained only during the early 
 stages of development, the adult animal being free. 
 
 ASTEROIDEA ; OpHiuROiDEA. These belong to the marine vagrant 
 benthos, living mainly in shallow water or in moderate depths, 
 though some species descend to depths of 2,000 fathoms or over. 
 Some littoral starfish can undergo an exposure for several hours 
 in regions laid bare by the tide. A muddy or sandy bottom seems 
 to be the most characteristic facies for these animals, and from 
 such bottoms hundreds are often brought up in a single haul of 
 the dredge. Their relative scarcity in beds in which they are known 
 to occur is probably due to the fact that, after the death of the ani- 
 mal, the skeleton quickly falls apart into its component plates, which 
 become separately embedded in the sediments. In the majority of 
 the Asterozoa meroplanktonic, bilaterally symmetric, ciliated larvae 
 occur, which in the Asteroidea are known as bipinnaria and brach- 
 iolaria, and in the Ophiuroidea as pluteus. These are often found 
 in great numbers in the pelagic fauna. 
 
 ECHINOIDEA. The Echinoids, or Sea Urchins, are without ex- 
 ception marine vagrant benthonic animals, living usually in large 
 numbers in moderate depths. A few species descend to depths 
 between 2,000 and 3,000 fathoms, but the majority prefer the 
 shallow portions of the littoral districts. On the coast of Maine 
 
BIONOMIC CHARACTERS OF VERTEBRATES 1033 
 
 thousands of Strongylocentrotus drobachiensis are exposed at very 
 low tides, lying among stones and covered with fragments of shells 
 and small pebbles. The Echinoidea delight in a sandy bottom, from 
 which they are brought up in vast numbers at each haul of the 
 dredge. Some species prefer fine mud, in which they are often 
 buried to some extent. When living on rocks they commonly ex- 
 cavate holes for themselves, and even the solid granite has been 
 known to be thus attacked by the animal. If corners and crannies 
 are available, these are often occupied by the animal in preference 
 to the drilled hole. 
 
 The larva of echinoids is known as a pluteus, and is a mero- 
 planktonic, bilaterally symmetrical, usually more or less ciliated 
 organism, with a number of processes or arms. It is often carried 
 by marine currents to great distances, remaining in some cases 
 afloat for several weeks before settling down. 
 
 HOLOTHUROIDEA. The holothurians, like the echinoids, are ma- 
 rine benthonic organisms, but their habit of life is often more 
 sedentary than vagrant, the animals being buried in the sand and 
 mud, though never attached. Their bathymetric range is from the 
 shore zone, where they may be dug out of the sand at low tide, to 
 the depths of the abyssal district. Sandy or muddy bottom is usu- 
 ally preferred by these animals, though many live among coarse 
 blocks, and vast numbers occur among the coral masses of every 
 coral reef. The ciliated larva, or auricularia, of the holothurians is 
 a mero-planktonic organism with definite mouth and anal opening. 
 
 From the fact that only isolated plates occur in the skin of 
 the holothurians, they do not constitute any important part of 
 marine deposits. 
 
 X. PROTOCHORDATA. 
 
 These animals are all marine and unknown in the fossil state. 
 XL VERTEBRATA. 
 
 OSTRACODERMA. These extinct fish-like animals appear to have 
 led primarily a fluviatile and lacustrine existence, if we may judge 
 by the strata in which they occur. The earliest remains are frag- 
 ments from an Upper Ordovicic sandstone (Harding sandstone) of 
 Colorado, which was probably deposited as a terrestrial sediment 
 and subsequently in part reworked by the advancing sea. The late 
 Siluric transition beds of Great Britain and eastern North America, 
 
1034 PRINCIPLES OF STRATIGRAPHY 
 
 and the beds of the Old Red Sandstone type of the same countries, 
 show the best preserved representatives, these beds being strictly 
 non-marine deposits. Some of the best preserved specimens of 
 Bothryolepis are from the fresh water (river, flood-plain and delta) 
 deposits, which constitute the Gaspe sandstone of eastern Canada. 
 
 The Upper Siluric bone-bed (Ludlow) of England also fur- 
 nishes these remains, and this deposit may have been formed in 
 an estuary, or an enclosed basin near the sea. A few fragmentary 
 remains have been obtained from marine Siluric and Devonic strata, 
 but these, like the similar occurrences of eurypterids, are not satis- 
 factory evidence of the marine character of these fishes. In Penn- 
 sylvania, remains occur in sandstone beds, most probably of river 
 origin, belonging in the Upper Siluric (Monroan) horizon. 
 
 PISCES. The earliest true fish appear in the Siluric, but are 
 more typical of the Devonic. Here the Arthrodires were espe- 
 cially abundant, many of them still inhabiting the rivers of the 
 continent. They began to migrate into the sea, however, judging 
 from the more numerous remains found in open sea deposits, such 
 as the Onondaga limestone. The abundant fish fauna of the Upper 
 Devonic shales of Ohio is associated with tree trunks, spores of 
 land plants, etc., in sediments suggesting a river delta rather than 
 open sea. These Upper Devonic fish did, however, live in the seas 
 of that time as well, for their remains are also found in undoubted 
 marine strata. The Cyclostomi (or Lampreys) seem to be first 
 represented by' the remarkable Palaeospondylus of the Old Red 
 Sandstone of Caithness, Scotland. The Elasmobranchs, or sharks, 
 also lived in the rivers of Old Red Sandstone time, and their re- 
 mains are found in the semi-terrestrial deposits of the Upper Siluric 
 in Europe and America. These fish, however, entered the sea in 
 Devonic, if not in Siluric, time, and thereafter became chiefly ma- 
 rine organisms, continuing so down to the present time. 
 
 The living ganoids either inhabit fresh water rivers exclusively, 
 or, as in the case of the sturgeons, enter the rivers from the sea. 
 In Palaeozoic and Mesozoic time they were marine and fluviatile. 
 The living Dipnoi inhabit the tropical swamps of South America 
 (Lepidosiren) and of Africa (Protopterus) and also the rivers of 
 Queensland (Ceratodus). Ceratodus also occurs in the Bunter 
 Sandstein of Wiirttemberg, the Keuper of Austria, the Stonesfield 
 slates of England, and the fresh water Jurassic of Colorado. It 
 also occurs in the Kota-Maleri beds of India and in the Karoo 
 formation of South Africa. All of these formations represent river 
 deposits. With few exceptions the other Dipnoans (Ctenodipterini) 
 also occur in fresh water (chiefly river) deposits, such as the Old 
 
BIONOMIC CHARACTERS OF AMPHIBIA 1035 
 
 Red Sandstone, the Devonic sandstones of Canada, the Coal Mea- 
 sures and the continental Permic deposits. The living Protopterus 
 of Africa regularly spends the dry season of several months in its 
 crust of dried mud, leading a latent existence or summer sleep until 
 the rains again soften the crust and release the fish. 
 
 The various species of mud-fish are examples of fishes leading 
 an amphibious life, for these have been transported in their "nest" 
 of dried mud halfway round the world without suffering. Dean 
 believes that the vitality of these fish becomes exhausted by being 
 kept in water all the time, which deprives them of their periodic 
 summer rest. Many fresh-water fish regularly swallow air and 
 will die if prevented from doing so, even more quickly than frogs 
 which have been similarly placed, although the latter are provided 
 with true lungs. 
 
 A few other types of fish are able to live in the air for a certain 
 length of time, as, for example, the tropical fish (Periophthalmus 
 and Boleophthalmus), referred to in the preceding chapter, which 
 spend a good part of their existence on the beach, and Anabas 
 scandens of the Philippines is able to exist for days out of water. 
 
 Many fresh-water fish periodically visit the sea, while marine 
 fishes as frequently ascend fresh-water streams. 
 
 AMPHIBIA. The amphibians are cold-blooded, aquatic or ter- 
 restrial vertebrates, usually without dermal covering, which, how- 
 ever, is present in some forms as a corneous or osseous structure. 
 These animals breathe by gills and by lungs, the former remain- 
 ing functional throughout life in some species. True limbs are 
 generally present in the Amphibia, and are used for swimming or 
 walking. 
 
 The Carbonic and Triassic Stegocephalia were mostly ar- 
 mored, especially on the ventral side. They lived on land or 
 possibly in fresh water. The larger forms were predatory and 
 probably fed on other amphibians, fishes, and Crustacea. The 
 Coecilians (Gymnophiona) are worm-like, legless amphibians con- 
 fined to the tropics. They are unknown in the fossil state. The 
 Urodeles are naked-bodied types with generally two pairs of limbs 
 and persistent tail. They inhabit fresh water (newts), where the 
 gills remain permanent; or ^amp, shady places on the land (sala- 
 manders), where they lose their gills. They subsist on worms, 
 gastropods, small aquatic animals, and fish spawn. Permanent 
 larval forms (Axoldtl) of the land form, Amblystoma, inhabit 
 the lakes and ponds of Mexico and other countries. These have 
 the form of large tadpoles about to be transformed, with legs and 
 external gills. They reproduce in this state, some of them never 
 
1036 PRINCIPLES OF STRATIGRAPHY 
 
 reaching the Amblystoma stage. The Urodeles began in the Cre- 
 tacic and continue to the present. 
 
 The Anura (frogs and toads) pass through a tadpole stage, 
 during which they breathe by means of gills and lead an aquatic 
 life. On transformation they lose the gills and the tail and become 
 air-breathers, though frogs can remain under water for a very 
 long period of time, absorbing oxygen through the skin. The 
 Anura are wholly post-Mesozoic in age. No marine amphibians 
 are known. 
 
 REPTILIA. The Rhynchocephalia comprised terrestrial and aqua- 
 tic forms, often of great size. The Squamata include two Cretacic 
 groups of marine reptiles, some of which, like the mosasaurs, were 
 of large size. The lizards (Lacertilia) and snakes (Ophidia) are 
 chiefly terrestrial reptiles, though some of the latter (Hydrophidce) 
 live in the water. Some Pleistocenic species attained a length of 
 10 meters, but modern forms are all small. The lizards are 
 mostly provided with legs, while the snakes are legless. At the 
 present time, lizards are chiefly restricted to the warmer regions 
 of the earth's surface. Comparatively few forms pass beyond the 
 fortieth parallel, while above the sixtieth parallel lizards are prac- 
 tically absent ; though Lacerta vivipara, a species ranging over 
 nearly the whole of Europe, extends northward to the seventieth 
 parallel in Norway, and, together with the blind-worm (Angius 
 fragilis) occurs in Lapland but is absent from the New World. Both 
 groups probably appeared in the Cretacic. The fish-lizards (Ich- 
 thyosauria and Sauropterygia) were wholly nektonic in habit, liv- 
 ing in the sea, but breathing by means of lungs. They were, there- 
 fore, neither true holo-nekton nor atmo-nekton, but a transitional 
 type between the two, as are other vertebrates which lead a per- 
 manently nektonic life (e. g., whales, etc.). Some species inhabited 
 fresh or brackish water. 
 
 The Theromorphs were habitually walking animals. It is be- 
 lieved by many that the mammals have arisen from these reptiles. 
 
 The Chelonia or turtles are terrestrial or aquatic in habit, but, 
 like all other reptiles, are air-breathers. A few types are exclusively 
 marine, but the larger number live in fresh-water lakes or rivers. 
 It has been supposed that the ancestral species were aquatic, living 
 in swamps and shallow water, like modern crocodiles ; and that 
 from these descended the fluviatile types, from which in turn were 
 derived the early marine types, on the one hand, and the terrestrial, 
 on the other. 
 
 The modern crocodiles are aquatic reptiles living in fresh water, 
 swamps and streams. The oldest Triassic crocodiles (Parasuchia 
 
BIONOMIC CHARACTERS OF REPTILIA 1037 
 
 and Pseudosuchia) are all found in terrestrial partly fluviatile and 
 partly eolian deposits, such as the Newark beds of eastern North 
 America, the Stuben Sandstein of Germany, the Elgin sandstone 
 of Scotland, and the Gondwana beds of India. They appear to have 
 been land and river forms. The Mesosuchia in Jurassic and Co- 
 manchic time had taken to a marine life, but in the Cretacic and 
 later periods, the crocodiles were chiefly fluviatile or terrestrial. 
 In the Pliocenic alligators and crocodiles became extinct in Eu- 
 rope, but in America they continued in the tropical and sub-tropical 
 districts. The crocodiles inhabit, further, nearly all the larger 
 streams and many lakes of Africa, India, and the north coast of 
 Australia (Heilprin). The Dinosaurs are wholly confined to the 
 Mesozoic, where they were represented by a wealth of types. They 
 comprise three groups: 1st, carnivorous land forms (Theropoda) , 
 varying in size from that of a cat (Compsognathus) to that of an 
 elephant (Megalosaurus, Trias to Cretacic), and mostly very gro- 
 tesque in appearance. They walked upon their hind limbs, the 
 shorter fore limbs being lifted from the ground and the body being 
 further balanced and supported by a huge tail. Some leaping or 
 kangaroo-like forms likewise occurred (Trias to Cretacic). 2d. 
 Massive herbivorous quadrupedal forms without dermal armor 
 (Sauropoda, Middle and Upper Jurassic and Lower and Upper 
 Cretacic), and comprising some of the most prodigious land animals 
 known; Brontosaurus having a length upward of 18 meters, and 
 Diplodocus upward of 20 meters. 3d. (Predentata) . Large herbiv- 
 orous unarmored bipedal (Iguanodonts), and armored quadru- 
 pedal forms with small skulls (Stegosauridfu) , or with large horned 
 skulls (Ceratopsidcc) . The carnivorous dinosaurs were frequenters 
 of the estuaries and deltas of rivers, and roamed about the low, 
 flat, and muddy flood plains of rivers, as shown by the countless 
 footprints preserved in the rocks of the Newark system, the Bunter 
 Sandstein, and other non-marine deposits of early Mesozoic age. 
 The Pterosauria or Ornithosaurs (Jurassic and Cretacic) were a 
 remarkable group of bird-like lizards, with hollow bones and fore 
 limbs adapted for flight, after the manner of bats ; some forms be- 
 ing strong and others weak flyers. 
 
 AVES. Birds are essentially aerial nekton. A number of living 
 and extinct forms (Drom&ognathce, with the Struthiones, the New 
 Zealand Apteryx and the South American Tinamous), are either 
 nearly wingless or have wholly or to a considerable extent lost 
 the power of flight, even though possessing small wings. To com- 
 pensate for this loss the legs are generally powerfully developed, 
 especially in the Struthious birds (ostriches, rheas, cassowaries, 
 
1038 PRINCIPLES OF STRATIGRAPHY 
 
 emus, and the extinct ^Epyornys and the Moas). The majority of 
 birds have the power of flight to a greater or less extent, some forms 
 being able to remain in the air for a long time (gulls, petrels), 
 though flightless forms exist in several orders of the Euornithes. 
 Some are especially adapted to a natatory existence (penguins, 
 ducks, etc.), while others spend much of their life wading in streams 
 and ponds (herons, storks, ibises, cranes, snipes, etc.). 
 
 MAMMALIA. This, the highest class of vertebrates, is primarily 
 adapted to a terrestrial life, though volatorial or atmonektonic 
 types (Chiroptera, or bats) and natatorial or halo- and limnonek- 
 tonic (hydronektonic) types (Cetacca, or whales, and Sircnia, or 
 sea-cows) are also known. Among the terrestrial mammals, climb- 
 ing or arboreal types, running and walking or cursorial types, leap- 
 ing or saltatorial types, and burrowing or fossorial types are dis- 
 tinguishable. 
 
 BIBLIOGRAPHY XXVIII. 
 
 1. AGASSIZ, ALEXANDER. 1888. Three Cruises of the Blake. 2 vols. 
 
 Bulletin of the Museum of Comparative Zoology, Vols. XIV, XV. 
 
 2. BROOKS, W. K. 1881. Developpement de 1'huitre Americaine. Archives 
 
 de Zoologie Experimentale et Generate, T. IX. Notes et Revue, pp. 
 xxviii xxix. 
 
 3. CHAMBERLIN, THOMAS C. 1898. A Systematic Source of Evolution 
 
 of Provincial Faunas. Journal of Geology, Vol. VI, pp. 597 et seq. 
 
 4. CHUN, CARL. 1888. Die pelagische Thierwelt in grosseren Meerestief en 
 
 und ihre Beziehungen zu der Oberflachen Fauna. Bibliothoca Zoologica, 
 Heft. i. 
 
 5. CLARKE, JOHN M. The Naples Fauna, Pt. I. Fifteenth Annual Report 
 
 of the New York State Geologist. . \ 
 
 6. CLARKE, J. M., and RUEDEMANN, RUDOLF. 1912. The Eurypte- 
 
 rida. Monograph of the New York State Museum, No. XIV, and plates.. 
 
 7. CONN, H. W. 1885. Marine Larvae and Their Relation to Adults. 
 
 Studies of the Biological Laboratory of Johns Hopkins University, Vol. 
 Ill, pp. 165-192, pis. VIII, IX. 
 
 8. DALL, WILLIAM H. 1890. Deep Sea Molluscs and the Conditions 
 
 Under Which They Live. Presidential Address. Biological Society, 
 Washington. Proceedings, Vol. V, pp. 1-27. 
 
 9. DANA, JAMES D. 1872. Corals and Coral Islands. 
 
 10. DARWIN, CHARLES. 1841. Voyage of the Beagle. 
 
 11. DAVIDSON, TH. 1886. A Monograph of the Recent Brachiopoda. 
 
 Transactions of the Linnaean Society of London. Zoology, IV. 
 
 12. DAVENPORT, C. B. 1903. Animal Ecology of the Cold Spring Sand 
 
 Spit. University of Chicago, Decennial Publication, X. 
 
 13. FISCHER, PAUL. 1887. Manuel de Conchyliologie. Paris. 
 
 14. FUCHS, TH. 1882. Ueber die pelagische Flora und Fauna. Ver- 
 
 handlungen der koniglich-kaiserlichen geologischen Reichsanstalt in 
 Wien, pp. 49-55. 
 
BIBLIOGRAPHY XXVIII 1039 
 
 15 H^ECKEL, ERNST. 1893. Planktonic Studies. Translated from the 
 German by George W. Field. Report of United States Fish Commission, 
 1889-1891, pp. 565-641. 
 
 16. HAHN, F. FELIX. 1912. Dictyonema Fauna of Navy Island, New 
 
 Brunswick. New York Academy of Science, Annals, Vol. XXII, pp. 
 135-160, pis. xx-xxii. 
 
 17. HENSEN, VICTOR. 1890. Einige Ergebnisse der Plankton Expedition 
 
 der Humboldt Stiftung. Sitzungsbcrichte der Berliner Akademie der 
 Wissenschaften, von 13 ten. Marz, 1890, pp. 243-253. 
 
 18. KIRK, EDWIN. 1911. Some Eleutherozoic Pelmatozoa. United States 
 
 National Museum Proceedings, Vol. XLI, pp. 1-137. Contributions 
 from the Geological Department of Columbia University, Vol. XXI, 
 No. 6. 
 
 19. LANG, ARNOLD. 1891-1896. Text Book of Comparative Anatomy. 
 
 Translated by H. M. and M. Bernard, Vols. I, II. London, Macmillan. 
 
 20. O'CONNELL, MARJORIE. 1912. The Habitat of the Eurypterida. 
 
 Paper presented before the New Academy of Sciences, November meeting. 
 
 21. ORTMANN, ARNOLD E. 1896. Grundziige der Marinen Tiergeo- 
 
 graphie. Jena, Gustav Fischer. 
 
 22. ORTMANN, ARNOLD E. 1896. An Examination of the Arguments 
 
 Given by Neumayr for the Existence of Climatic Zones in Jurassic 
 Times. American Journal of Science, 4th series, Vol. I, p. 257. 
 
 23. RUEDEMANN, RUDOLF. 1895. Development and Mode of Growth 
 
 of Diplograptus. McCoy. Fourteenth Annual Report New York State 
 Geologist, pp. 219-249, pis. 1-5. 
 
 24. RUEDEMANN, R. 1904. Graptolites of New York, Part I. New York 
 
 State Museum Memoirs, Vol. VII. 
 
 25. SCHIMPER, A. F. W. 1898. Pflanzengeographie auf Physiologischer 
 
 Grundlage. Jena, G. Fischer. English Translation (Plant Geogra- 
 phy) by W. R. Fischer, Oxford, 1903. 
 
 26. SEMPER, KARL. 1881. Animal Life as Affected by the Natural Con- 
 
 ditions of Existence. International Scientific Series, Vol. XXX. 
 
 27. SIMROTH, HEINRICH. 1891. Die Entstehung der Landtiere. (See 
 
 also Die Pendulations-theorie, 1907.) 
 
 28. TYRRELL, J. B. 1910. Changes of Climate in Northwestern Canada 
 
 Since the Glacial Period. In Veranderung des Klimas, etc. Stockholm, 
 
 PP- 389-39 1- 
 
 29. WALTHER, JOHANNES. 1897. Ueber die Lebensweise fossiler Meeres- 
 
 thiere. Zeitschrift der deutschen geologischen Gesellschaft. Band 
 XLIV, Heft II, pp. 209-273. 
 
 30. WALTHER, J. 1894. Einleitung in die Geologie als historische Wissen- 
 
 schaft. I. Bionomie des Meeres. II. Die Lebensweise der Meeresthiere. 
 
 31. WOODWARD, S. P. 1880. Manual of the Mollusca. 
 
CHAPTER XXIX. 
 
 CHOROLOGY, OR THE PRINCIPLES OF THE GEOGRAPHICAL DIS 
 TRIBUTION OF ANIMALS AND PLANTS. 
 
 Having briefly considered the life districts of the habitable 
 earth, and the bionomic characters of plants and animals, we may 
 now enquire into the laws which govern the geographical distribu- 
 tion of organisms. It is clear that, whatever the present distribution 
 of plant and animal life, it has not always been so. Even the most 
 cosmopolitan species had its circumscribed center of origin, for 
 it is extremely unlikely that the same species originated in more 
 than one locality.* From this locality, its center of dispersion, it 
 spread to occupy whatever territory was available. Occupancy of 
 new territory, however, is possible only if this territory corresponds 
 in facies to that from which the species is derived, in the degree 
 in which the species is dependent upon the facies. Hence the exo- 
 dists from their land of birth are not always able to find a suitable 
 place of settlement, and, though their numbers may be vast, a 
 large proportion is sure to perish. 
 
 The factor of greatest importance in determining whether or 
 not an area is to be permanently occupied by the members of a 
 newly arrived species is the organic factor, or the question of food 
 supply and protection from enemies. If the food supply is insuf- 
 ficient, or if contending species hold the ground, the new arrivals 
 may be prevented from occupying the territory, even though the 
 facies is otherwise adapted to their needs. 
 
 * Strictly speaking, of course, a species is monophyletic and can arise only 
 in one locality. But types so similar that they may easily be mistaken for the 
 same species may arise in different localities. Thus, what appears to be the same 
 species of Fusus (F. closter) occurs in the West Indies and in the Red Sea, but 
 they are most probably of independent origin. Organisms of such similar 
 characteristics that they are commonly mistaken for members of the same genus 
 are frequently met with in widely separated localities, where they have arisen 
 independently. The independent origin of horses in America and in the Old 
 World was advocated by Cope but rejected by others. Some widely separated 
 pulmonate gastropods, placed in the same genus, may have arisen independently 
 from marine ancestors. 
 
 1040 
 
GEOGRAPHICAL DISTRIBUTION 1041 
 
 DISPERSAL AND MIGRATION. 
 
 It will help us to realize the dependence of organisms on their 
 environment if we distinguish two modes of distribution, the in- 
 voluntary and the voluntary. The former may be called dispersal; 
 the latter, migration./ 
 
 Dispersal is the distribution of animals and plants by causes not 
 primarily involving the activities of these organisms, as the carrying 
 of the seeds of plants by the wind, the carrying of marine or fresh 
 water planktonic or meroplanktonic organisms by currents and the 
 like. Migration, on the contrary, is accomplished by active move- 
 ments in search of food, or to escape from enemies, and is confined 
 chiefly to animals, though stolonal propagation of plants may also be 
 classed as a species of migration. Migrants are composed of the) 
 nekton and the vagrant benthos, while dispersants comprise the holo-/ 
 plankton, the epiplankton, and the meroplankton. Sedentary 
 benthonic organisms cannot migrate, but they may be carried by 
 a floating sub-stratum, and their mero-planktonic young may be 
 dispersed and thus settle in other districts. Migrating organisms 
 require a continuity of the conditions of existence in space, such 
 as continuous shores for the marine vagrant littoral benthos, or a 
 more or less uniform medium for pelagic migrants. The involun- 
 tary dispersal of organisms, on the other hand, may often go on in 
 spite of barriers which migrants could not surmount. Thus, as 
 already pointed out, the meroplanktonic young of the vagrant 
 benthos may have a much wider distribution than could ever be 
 brought about by the migration of the adults, who are often re- 
 stricted by barriers not present in the pelagic district. Fresh-water 
 molluscs, for example, are dispersed widely in streams, lakes, and 
 ponds which are discontinuous, and to which the adults could not 
 migrate. Again, plants may, by the dispersal of their seeds, sur- 
 mount streams or other barriers, which root or stolonal migration 
 could never bring about. The wide dispersal of cocoanut palms, 
 by flotation of the nut, is a good example. 
 
 Littorina littorea may be instanced as a type which has mi- 
 grated down the Atlantic coast within the space of a few years. 
 Originally introduced from England, it characterized Halifax har- 
 bor in 1852 and slowly made its way southward and northward. 
 In 1855 it was noted at Bathurst, Bay of Chaleur; in 1868 on the 
 coast of Maine, appearing at Portland in 1870. At Salem, Massa- 
 chusetts, it was first noted in 1872, and at Barnstable, Cape Cod, 
 in 1875. It was rare at Woods Hole in 1875, common in 1876, and 
 
1042 PRINCIPLES OF STRATI! IRAI'HY 
 
 appeared at New Haven, Connecticut, in 1880 (Morse-jj). In 1898 
 Littorina rudis and L. palliata were still the predominant types on 
 the Long Island coast, but by 1901 L. littorea had gained a marked 
 predominance (Balch-3), and it is still rapidly advancing. (Daven- 
 port-n :i68.) Since the opening of the Suez Canal in 1869 many 
 Mollusca of the Mediterranean have migrated into the Red Sea. 
 
 BARRIERS TO MIGRATION AND DISPERSAL. Under barriers to 
 migration and dispersal we may place topographical barriers first, 
 such as northward and southward stretching continents for marine 
 organisms, desert tracts for fresh water organisms, and great bodies 
 , of water for terrestrial organisms. But topographical barriers are 
 not the only ones, nor in many cases the most important. Differ- 
 ences in temperature, character, and direction of winds and ocean 
 currents, improper facies of the substratum, and insufficient food 
 supply, as well as hostile species, constitute some of the chief bar- 
 riers to distribution. If by some means or other a barrier is sur- 
 mounted, and a new colony is established,, the new colony may 
 become more or less isolated, the barrier proving too effective for 
 all but a few individuals. "Migration," says Ortmann (38:186),. 
 "is often slow or only possible under peculiar circumstances, often 
 it is accidental, and only a few individuals can transgress the 
 original limits on rare occasions; then even migration acts as a 
 means of separation. The few individuals occupying a new local- 
 ity are afterward practically separated from the original stock 
 remaining in their native country, and thus they may develop sep- 
 arately into a different species, even in the case that immigration 
 from the original stock is not altogether impossible, since any rare 
 individuals of the latter reaching the new colony from time to time 
 are soon absorbed by the new form and their characters disappear 
 by the continuous crossing with the modified individuals and by the 
 transforming power of the external conditions." 
 * Where barriers are numerous, the number of species of a given 
 group of animals or plants is, as a rule, much greater than where 
 barriers are few. Thus in the eastern United States, where impor- 
 tant barriers are wanting, only one true species of chipmunk occurs ; 
 while in California, where barriers are numerous, a dozen or more 
 species and sub-species are found (Jordan 25). On the other hand, 
 the fauna and flora of a region with few barriers are likely to show 
 a greater variety of organisms of types which do not interbreed 
 than is found in a region with many barriers, since immigration 
 of many different types is possible into an open region, but pre- 
 vented by the barriers of a closed region. Where separation by 
 barriers has brought about the formation of distinct species, nearly 
 
BARRIERS TO MIGRATION 1043 
 
 related species are normally found in adjoining districts, and not 
 generally in the same or in widely separated districts. It is uni- 
 versally true that in such cases the species of a genetic series 
 within the same chronofauna, or fauna of the same geological time 
 division, differ more widely the further they are removed in space, 
 and are closely related in immediately adjoining loco faunas. This 
 is beautifully illustrated by the mutations of the Hawaiian Acha- 
 tinellidae, a group of brilliantly colored tree snails, different species 
 of which inhabit the different rugged valleys incised in the margins 
 of the extinct volcanic craters of these islands. The most nearly 
 related mutations of these snails live in adjoining valleys, where, 
 nevertheless, they are almost wholly isolated from the inhabitants 
 of the neighboring valleys. Here the amount of divergence in 
 characters between the occupants of two valleys can, as Gulick 
 says, be roughly estimated by measuring the number of miles be- 
 tween the valleys. Recently Gulick has formulated this in the fol- 
 lowing law : "Forms that are most nearly related, and are, there- 
 fore, the least subject to sexual and impregnational isolation, are 
 distributed in such a manner that their divergence is directly pro- 
 portional to their distance from each other, which is also the mea- 
 sure of the time and degree of their geographical isolation ; while 
 those most manifestly held apart by sexual instincts and impregna- 
 tional incompatibilities do not follow this law." (Gulick-i 9:^7.) 
 The trout of the modern (Holocenic) chronofauna furnishes a 
 good illustration of this law. Thus Salmo clarki, the cut-throat 
 trout of the Columbia and Missouri rivers which interlace at their 
 headwaters has its nearest relatives in the basin of Utah (S. vir- 
 ginalis) and in the Platte ( S. stomias). "Next to the latter is 
 Salmo spilurus of the Rio Grande, and then Salmo pleuriticus of 
 the Colorado. The latter in turn may be the parent of the Twin 
 Lakes trout, Sahno mdcdonaldi. Always the form next away from 
 the parent is onward in space across the barrier." ( Jordan-25 : 
 547.) The distribution of the fossil eurypterids of the American 
 Siluric in such a manner as to parallel the distribution of the trout 
 above mentioned has been cited as a proof of the river habitat of 
 these organisms. (Grabau-i8.) It should be emphasized, how- 
 ever, that isolation cannot always be determined to be a factor in 
 the production of species, and, indeed, if variation is orthogenetic, 
 the development of new mutations in a progressive series can very 
 well go on within one area. Thus many of the pronounced muta- 
 tions of Planorbis in the Steinheim strata occurred within the same 
 Tertiary locofauna. In the Eocenic locofauna of the Paris basin 
 a large number of successive mutations in each of a number of 
 
1044 PRINCIPLES OF STRATIGRAPHY 
 
 genetic series of molluscs occurred side by side, and the same is 
 also true to some extent of the corresponding molluscan fauna of 
 the Gulf States of America. 
 
 FAUNAL GROUPS. The fauna of any area may be considered 
 as belonging to one or more of the following groups : endemic spe- 
 cies, immigrants and erratics, and relicts. Endemic species are 
 those which originated in the locality in which they are found. 
 Immigrants have invaded the region, and erratics have been car- 
 ried there accidentally, and both have established themselves in the 
 new region. Relicts are remnants, in favored places, of a once 
 widely distributed fauna, which, by the breaking up of the area 
 which they occupied, became resolved into a number of local rem- 
 nants, which remain separated. 
 
 FACTORS GOVERNING DISPERSAL AND MIGRATION. In all cases 
 when considering the laws which govern the distribution of or- 
 ganisms it is necessary to consider two phases of the subject : 
 first, the chemical, physical, and organic characters of the localities ; 
 and, second, the nature and habits of the organisms their bionomic 
 characteristics. If the two are harmonious in a given case, it 
 is evident that the locality considered can be inhabited by the or- 
 ganism in question. Under chemical characters we must consider 
 the composition of the medium and its variation ; and under physi- 
 cal characters we comprise climate and topography of the sub- 
 stratum ; while under organic characteristics we include the presence 
 of suitable food in sufficient quantity, and absence or paucity of 
 competing organisms. 
 
 Inorganic Factors. The Medium. 
 
 Composition of Medium. Under this heading we include the 
 salinity of the sea ; the inclusion of air and other gases in the 
 water, and of water and carbon dioxide in the air. The salinity of 
 the sea is its most characteristic bionomic feature. On the whole, 
 salinity is a pretty constant factor, varying but slightly in surface ex- 
 tent or in depth in the open sea. Along the continental margins, 
 however, in the bays and marginal seas, a great variation is observa- 
 ble. The question of variation has already been discussed at length 
 (Chapter IV), but a few salient points may here be repeated. 
 Thus in the Red Sea, where the supply of water is scanty, and the 
 evaporation great, the salt constituent is 4.3 per cent, or 43 permille ; 
 while in the Baltic, where the supply of fresh water is abundant and 
 evaporation is small, the surface-salinity is very low, averaging 7 
 permille. The decrease in salinity eastward is very striking; thus it 
 
FACTORS GOVERNING DISTRIBUTION 1045 
 
 is 34 permille in the Skagerak, 22 permille in the Kattegat, 6 per- 
 mille at Riga and 3 permille at the northern end of the Gulf of 
 Bothnia (Uleaborg). The vertical range is also greater than in the 
 open sea, the salinity in the ''Great Belt" of the Baltic increasing 
 downward from 10 permille on the surface to 30 permille at the bot- 
 tom (66 meters). 
 
 Stenohalinity and euryhalinity. Many animals cannot live in 
 water with less than 30 or 35 permille of salts; i. e., that of the 
 normal open sea. These stenohalic * types will die when the sal- 
 inity is lowered or raised. Euryhalic f types, on the other hand, can 
 suffer a considerable freshening of the water, and will live as long 
 as any salt remains. Brackish-water organisms are adapted to a 
 small amount of salt and will suffer if the amount is increased. The 
 brackish state of water has never been definitely delimited, but prob- 
 ably a salinity of 2 or 3 permille (.2 to .3 per cent.) would be the up- 
 per limit. Of other mineral matter besides the normal salts iron in 
 the form of ferrous carbonate (FeCO 3 ) may sometimes be present 
 in considerable quantity, especially in more or less land-locked 
 portions. Such excess of iron or of other minerals in solution 
 appears to have a distinct effect on the growth of the fauna living 
 in the water, resulting in its dwarfing, as has been repeatedly found 
 by experiments. As an example may be mentioned the fauna of 
 the Clinton iron ore layer of Rochester, which consists of individuals 
 having "an average of about one-third the diameter of the same 
 species in the beds just above and below" (Loomis-28 : #95). The 
 fauna of the Tully pyrite layer of western New York, consisting of 
 upward of forty-five species, is composed of individuals "on an 
 average only one-fifteenth the size of the same species in the normal 
 and preceding Hamilton fauna." (Loomis-28 :p^o.) In this case 
 the dwarfing was undoubtedly in part effected by the H 2 S liberated 
 by sulpho-bacteria from decaying organic matter. The reaction of 
 this upon the iron carbonate produced the pyrite which enclosed 
 the fauna. (FeCO 3 +2H 2 S+O=FeS 2 +CO,+2H,O.) 
 
 Quantity of Air. The quantity of air in the water, both salt 
 and fresh, depends upon the depth and the amount of agitation. 
 Deeper strata of water have necessarily less air than those nearer 
 the surface, while agitated water will include more air than still 
 water. It is upon the oxygen of this included air that all animals 
 are dependent, and when it is present in insufficient quantity the 
 animals generally perish, though some will come to the surface for 
 more air. In partially enclosed bodies of water where the density 
 
 * From <rTQi/6s = narrow and AXs = the sea, (salt)* 
 f From ftpts = broad. 
 
io 4 6 PRINCIPLES OF STRATIGRAPHY 
 
 of the bottom layers is greater than that of the surface, vertical 
 currents are slight, and hence the lower strata are poor in oxygen 
 and unable to support animal life. Thus in the Black Sea animal 
 life is practically absent below a depth of 125 fathoms, though 
 dead planktonic organisms sink to the bottom, where they are 
 decomposed by anaerobic bacteria. The great depths of the Black 
 Sea are covered by a layer of black mud, from which H 2 S is 
 abundantly separated and which is rich in pelagic diatoms and frag- 
 ments of very young pelecypods from the meroplankton. The 
 presence of abundant H 2 S in these depths is characteristic. It is 
 separated by the sulphobacteria from the dead organic matter and 
 the sulphates of the sea water. Accompanying it is the formation 
 of iron sulphide and the separation of carbonates, especially CaCO 3 . 
 Pure atmospheric air contains almost 21 per cent, of oxygen and 
 about 79 per cent, of nitrogen (see ante, Chapter II). There is 
 always, however, some carbon-dioxide and water vapor present, 
 the quantity varying with the temperature and the movements of 
 the air, besides being very variable in different localities. 
 
 Carbon-dioxide, while necessary to plant life, is injurious to 
 the higher types of animals, if the proportion is above I to 2,000 
 of volume. A somewhat larger quantity, however, has no serious 
 effect on some lower forms of terrestrial animals, and in some 
 cases it may even be beneficial to them. The moisture in the 
 air is necessary to the existence of most terrestrial organisms, many, 
 indeed, being unable to exist in a region where the percentage of 
 water vapor in * the air is low. Nevertheless, some animals are 
 found in extremely dry regions, and these are not infrequently types 
 which belong normally to moist climates. Land snails, for ex- 
 ample, generally require much moisture, and large numbers of 
 such animals perish during the dry summers, or survive only by 
 burying themselves in the earth or in crevices of rocks, and closing 
 the mouth of the shell with a membranous operculum. In deserts 
 these snails can obtain moisture only during the night or early 
 morning from the heavy dews which result through excessive radia- 
 tion, and it is only during these times that they lead an active life. 
 
 In the saturated atmosphere of the tropical forests are found 
 many types of animals which are normally aquatic. Thus a type 
 of leach, allied to the medicinal leach of the fresh water ponds, 
 lives on trees in the moist forests of India and the Indian islands ; 
 and a number of species of land planarians are known, mostly from 
 the tropics. Many amphipod Crustacea of the family Orchestidae, 
 or beach fleas, live exclusively on land, though they have the gills 
 of the true water species. These require a very moist atmosphere. 
 
CLIMATE AND TEMPERATURE 1047 
 
 Numerous other types of normally aquatic animals can live on land 
 in a moist atmosphere. Some of these animals which have become 
 adapted to a terrestrial life can be drowned by being kept under 
 water; and this is true even of a number of fish, which habitually 
 come to the surface to swallow air. 
 
 Volume of Water, The volume of water has in many cases a 
 direct effect upon the size of the animals living in it, the controlling 
 factor being the amount of water allotted to each individual. Thus 
 in experiments on the common fresh water snail, Limncca stagnalis, 
 Semper found that if a large number of individuals developed in a 
 given quantity of water, the size of their shell will be smaller than 
 that of a smaller number occupying the same amount of water. 
 Again, a number of individuals developing in a limited amount of 
 water will have smaller shells than the same number of individuals 
 developing in a larger amount of water. This would be noticeable 
 in a gradually filling lake basin, where the shells in the lower strata 
 would be larger than those of the upper strata. Here the diminish- 
 ing food supply, which may be supposed to characterize a shoaling 
 lake, would be another factor contributing to the same result. In 
 Semper 's experiment it was found "that the favorable effect of 
 an increase of volume of water is highest between 100 and 500 
 cubic centimeters for each individual, and that it then gradually 
 decreases, till, at 5,000 cubic centimeters, it would seem to cease 
 entirely; i. e., an increase of volume above this maximum has, as 
 it appears, no further effect whatever upon the rapidity of growth." 
 Fouling of a limited quantity of water by the excretions of the 
 animals also causes dwarfing. The number of eggs produced under 
 unfavorable conditions is also smaller. 
 
 Climate. 
 
 Climate and Temperature. The climate of the sea is much more 
 uniform than that of the land. It is true that, in the very shallow 
 parts of the sea, the water is often heated to such a degree as to 
 make these regions uninhabitable for most animals. Ordinarily, 
 however, the continual change of water, due to tidal and other 
 currents, is sufficient to keep the temperature at a moderately low, 
 and more or less uniform, degree. The daily range of temperature 
 in the sea is of less importance to organisms than the total amount 
 of heat received ; for daily changes affect chiefly the upper strata 
 of the water, which are directly influenced by the heat of the sun. 
 At a moderate depth below the surface, the stratum of mean 
 
1048 PRINCIPLES OF STRATIGRAPHY 
 
 temperature is reached ; this, where not affected by oceanic currents, 
 varying mainly with the change in latitude. It is to this region 
 of unvarying temperature that many of our littoral vagrant benthos 
 descend on the approach of winter; so that, as every collector 
 knows, many tide pools and sandy bottoms of moderate depth be- 
 come deserted during the colder months. Many marine organisms 
 are eurythermal, i. e., able to bear a considerable range of tempera- 
 ture. Others, again, are stenothermal, a comparatively slight devia- 
 tion from the normal temperature of their medium being fatal to 
 them. The larvae or eggs of stenothermal animals are often able 
 to resist very great changes of temperature which would destroy 
 the adult animal. Thus the winter eggs of some of the lower Crus- 
 tacea, the germs of Bryozoa and of fresh water sponges, resist any 
 degree of cold, while the full-grown individuals perish in the au- 
 tumn. Many insects cannot survive the winter, though the eggs 
 and the embryo within the eggs commonly withstand the severest 
 cold. On the other hand, the young may be more susceptible to 
 changes in temperature than the adult. Brooks found that, in the 
 case of the oyster, the difference of 2 or 3 F. in the temperature 
 of the water was sufficient to kill the whole larval brood. Thus, 
 as Dall says, "By inhibiting natural increase ... a species 
 may be as sharply limited in its permanent range as if material 
 barriers interposed." (Dall-9 :?/#.) 
 
 Cold-blooded animals can usually withstand a lowering of tem- 
 perature better than warm-blooded animals. Thus frogs and toads 
 can be frozen into the ice and survive, and so can certain fishes 
 (e. g. } Salmon, etc.). 
 
 In all cases a rapid change of temperature is more fatal to or- 
 ganisms than is a gradual one; for many normally stenothermal 
 types can by degrees adapt themselves to a higher or lower tem- 
 perature. When once acclimatized it is the change from the normal 
 temperature of the new habitat which affects the organism. Thus 
 members of a species acclimatized to more tropical regions will be 
 affected by a fall of temperature to a point where members of the 
 same species in more northern regions are wholly unaffected. 
 
 Currents. One of the marked features of the media characteriz- 
 ing the three organic realms is the frequent presence of currents 
 within them. These may be temporary or fixed, and, according to 
 this characteristic and their strength, they become powerful factors 
 in the influence which they exert upon the distribution of organisms 
 in the realms in question. In the air, currents are most numerous 
 and also more variable, though certain air currents, as the "trade 
 winds/' have a great constancy within certain limits. Irregular 
 
CURRENTS AND DISTRIBUTION 1049 
 
 and variable air currents often greatly influence the migration of 
 aerial organisms, even the strongest flyers being carried away by 
 them. But the greatest influence exerted by air currents on organ- 
 isms is in the dispersal of seeds of plants, which thus may become 
 widely scattered. Air currents are the chief cause of the persistent 
 ocean currents, which are of such importance in the distribution of 
 life. In fresh water lakes temporary currents may be set up by the 
 winds, but these are of minor significance. The important currents 
 in fresh waters are those due to gravity, as exemplified in every 
 stream and river. That river currents are of great importance 
 in the distribution of fluvial life, as well as in the transportation of 
 terrestrial animal and plant life, is a matter of common knowledge. 
 
 By far the most important currents affecting the life districts 
 of the earth are the ocean currents, for they not only aid in the dis- 
 tribution of organisms, but they are also instrumental in imparting 
 to sea and land characters which they would not otherwise possess. 
 
 The characteristics of the ocean currents of the present geologic 
 period (Holocenic) may be taken as an illustration, especially since 
 it is highly probable that similar conditions prevailed throughout 
 most of Tertiary time. The depth of the moving bodies of water 
 constituting the oceanic currents is from 50 to 100 fathoms ; and 
 the direction of motion corresponds to that of the prevailing winds. 
 As already discussed at length in Chapter V, each of the great 
 oceans has its own eddy-like current, moving slowly around it and 
 leaving the central portion in a relative state of quiescence. In 
 the northern hemisphere the currents move in the direction of the 
 hands of a clock, i. e., clockwise ; in the southern hemisphere, coun- 
 ter-clockwise. As a result, the motion of the waters is westward 
 at the equator, both north and south of it, and eastward in the 
 polar ends of the north and south oceans, respectively. Hence 
 dispersals of organisms dependent on ocean currents would be 
 from east to west in the equatorial regions, as from the west coast 
 of Central America to the east coast of Asia, and from the west 
 coast of South America to Polynesia and Australia. It is true 
 that the equatorial counter-current sets eastward between the 
 north and south equatorial currents, but this is a relatively weak 
 current. The comparatively warm drift across the north Pacific 
 (Kuroshiwo drift) is an aid to eastward migration and dispersal 
 across the north Pacific, and this would probably be much more 
 effective if the cold water from the Arctic were shut off by the 
 closure of Behring strait. Such conditions existed during part of 
 Tertiary time, and thus may have greatly aided migration of ma- 
 rine organisms in this direction. The cold west-wind drift or 
 
1050 PRINCIPLES OF STRATIGRAPHY 
 
 Antarctic stream of the South Pacific, together with the cold Peru- 
 vian current of the west coast of South America, acts as a barrier 
 to migration of warm water animals and plants from Australia to 
 South America, and probably did so throughout Tertiary time. 
 
 In the Atlantic the peculiar conformation of Africa and South 
 America results in the splitting of the South Equatorial current into 
 the Brazilian current, flowing southward along the east coast of South 
 America, while the main current crosses the equator into the Carib- 
 bean Sea and the Gulf of Mexico. Here again the cold west-wind 
 drift and the cold Benguela current on the west coast of South 
 Africa prevent dispersion between the southern portions of these 
 continents of all warm water types. The presence, however, in 
 the modern fauna of gastropods on the east coast of South America, 
 which appear to be derived from species inhabiting Indo-Pacitic 
 waters, suggests that migration of tropical animals up the west 
 coast of Africa is possible under certain conditions, in spite of the 
 cold Benguela current. In the North Atlantic, the Gulf Stream, 
 with its northeastward drift, favors dispersal of species from the 
 east American to the west European coast ; while the return Canary 
 and North Equatorial currents may well be effective in carrying 
 planktonic organisms from the northeast African coast and the 
 Mediterranean to the West Indian waters of tropical America. 
 
 A factor which must be taken into consideration is the varying 
 rapidity of flow of the currents. Thus the Gulf Stream, as it issues 
 from the Florida straits, has an average velocity of 80 or 90 miles 
 a day,* while the drifts, like that crossing the middle North Atlantic, 
 may have a velocity of only from ten to fifteen miles per day. If 
 the meroplanktonic stage of a normally benthonic animal is passed 
 through very quickly it is evident that before the creature can be 
 carried very far it will end its pelagic existence and sink to the 
 bottom. In the case of such larvae carried by the transoceanic 
 currents, the depths to which they will settle after having been 
 carried for a few days is likely to be such as to prove destructive 
 to the organism. Thus organisms taken up by the Gulf Stream as 
 it leaves the Florida coast would, even if the stream retained its 
 maximum velocity, have to travel considerably over a month be- 
 fore they could reach the European coast, while with the actually 
 diminishing velocity of the drift in the North Atlantic the time 
 required will be many months. Before that time most meroplank- 
 tonic organisms will have completed their metamorphosis and have 
 perished on an uncongenial bottom. Holoplanktonic types, how- 
 ever, and even nektonic animals are widely dispersed by these cur- 
 
 * It varies from 1.5 to 2.5 meters per second. 
 
CURRENTS; TOPOGRAPHY 1051 
 
 rents. Thus even Middle and South Atlantic fish are carried by 
 the Gulf Stream to the Norwegian coast, though these do not gen- 
 erally propagate themselves in these northern waters. 
 
 One mode of dispersal that must not be overlooked is that ef- 
 fected by the epiplanktpn. The transportation of the Crustacea, 
 Hydrozoa and other organisms, with the Sargassum, from the 
 Bahamas to the middle North Atlantic, is an example. Trunks of 
 trees from the forests of the Mississippi and the Orinoco are car- 
 ried northward by the Gulf Stream, past the coast of Norway, as 
 far as Spitzbergen, whence they are again carried southward and 
 cast ashore on the northeast coast of Iceland. Sea-weeds, molluscs 
 and other organisms are frequently found attached to these trees, 
 having made the long journey on their floating substratum. Seeds 
 of land plants commpnly accompany these woods. 
 
 The warm ocean currents also have an important influence on 
 the relative abundance of the benthonic life in the regions traversed 
 by them. Being rich in plankton, and thus supplying an abundance 
 of food to the animal life inhabiting the sea-bottom below it, it is 
 not surprising to find that here the bottom life is developed in the 
 greatest luxuriance, and that vast accumulations of organic lime- 
 stones occur in the littoral regions thus affected. This is true, how- 
 ever, only of those portions of the littoral district which lie at a 
 sufficient depth below the surface to escape the motion of the 
 streaming water, which might otherwise prevent the attachment 
 of the benthos as it settles down. Thus, off Charleston, South 
 Carolina, in depths from 100 to 350 fathoms, the sea-floor is 
 but sparsely settled beneath the Gulf Stream. 
 
 Topography. Next to the climate of the sea the topography 
 of the sea-bottom, and that-of the adjacent land, are the most pow- 
 erful factors in determining the distribution of marine organisms. 
 The facies of the ocean floor, or the material of which it is com- 
 posed, is perhaps the most significant part of sea-bottom topog- 
 raphy, though submarine ridges and barriers are of great im- 
 portance, especially when such barriers cut off marginal bodies of 
 water, the inhabitants of which may be prevented from interming- 
 ling. The separation thus produced may lead to the development 
 of local faunas and floras. The importance of the greater inequali- 
 ties of the sea-bottom and the submarine continental shelves and 
 deep oceanic basins that result from them, as well as the conforma- 
 tion of the coast-line, with its varying facies, has already been con- 
 sidered. (See Chapter III.) 
 
 Of all topographical features which influence the distribution of 
 marine organisms, northward and southward stretching bodies of 
 
1052 PRINCIPLES' OF STRATIGRAPHY 
 
 land, like the continents of North and South America, are perhaps 
 the most important. For since they form a continuous barrier 
 across the warmer portions of the ocean, extending into the cold 
 regions, the migration of the warmer-water species from one side 
 to the other is prevented. Thus the marine faunas on the opposite 
 sides of North or South America differ widely. 
 
 By the application of this principle to the Cambric faunas of 
 North America and Europe, it has become apparent that a more 
 -or less continuous land mass, sufficient to prevent intermingling 
 of faunas, separated the Atlantic and Pacific oceans in Cambric 
 time. This land barrier must have extended from New England 
 northeastward, joining this land-mass to the Scottish highlands, 
 and southward, forming the Appalachian old-land, which was 
 joined with the continent of South America. On opposite sides of 
 this land-mass different faunas flourished; in the lower Cambric 
 the Olenellus fauna on the west and the Holmia fauna in the At- 
 lantic; in Middle Cambric time the Olenoides and Paradoxides 
 faunas flourished in these respective basins (see the maps in 
 Grabau-i7). (See also Figs. 264a-c.) 
 
 The only topographic element of importance in lakes and other 
 bodies of standing fresh water is the enclosing land mass, which 
 prevents direct migration from one lake into another. In rivers 
 the presence of rapids and falls may become a barrier to all but the 
 most agile of swimmers. Here, however, the barrier is most ef- 
 fective against upstream migration. The banks likewise constitute 
 barriers. 
 
 Terrestrial animals and plants are often prevented from migrat- 
 ing or becoming dispersed by the existence of topographic barriers 
 in the form of mountains of great height and consequent range in 
 climate; by large bodies of water, deep river gorges and impass- 
 able streams ; and by extensive desert tracts ; the last being produced 
 by a combination of the topographic and climatic factors. For ani- 
 mals of a more limited range of habitat, minor topographical bar- 
 riers become restrictive, as shown by the distribution of the Hawai- 
 ian tree snails (Achatinellidce) , already referred to, for which the 
 exposed ridges separating adjoining ravines form almost impass- 
 able barriers. 
 
 The Organic Factors. 
 
 The organic conditions of the three realms likewise exert an 
 important influence on the distribution of animal and plant life. 
 
THE ORGANIC FACTOR 1053 
 
 By organic conditions is meant the nature and abundance of food 
 supply and the relative importance of competing organisms. Since 
 plants primarily furnish the food supply of animals, those regions 
 rich in plant life are, in general, well adapted for the existence of 
 animal life. Yet even in regions where plant life is wholly absent, 
 as in the deep sea, an abundant fauna exists, the food supply of 
 which, however, is derived from the illuminated regions where 
 plants grow. 
 
 Closely related to the food supply is the struggle for a living 
 among species and individuals. It is a well-known fact that most 
 of the lower animals have such an enormous offspring that, sup- 
 posing none were destroyed, in a short time all the space in a given 
 region would be occupied by the progeny of a single pair; and the 
 number would be such as to exceed enormously that permitted by 
 the food supply. Migration to new regions is therefore a necessity, 
 and emigrants are continually sent out in all directions from the 
 mother country. If no other occupants were in the region, an 
 intraspecific struggle for existence would be witnessed in every 
 locality settled by these migrants members of the same species 
 fighting among themselves for a living. Such a struggle would, 
 of course, result in the destruction of vast numbers and in the 
 emigration of others. But, when the newly opened area is entered 
 simultaneously by several species, or if the area is already occu- 
 pied by other species, an interspecific struggle occurs, the outcome 
 of which depends on the relative ability of the contending species 
 to hold their own. The resident species may be driven out by the 
 newcomer, or it may hold its own and prevent the intruder from 
 settling; or, again, what is perhaps more common, the two species 
 may accommodate themselves side by side and jointly occupy the 
 disputed area. 
 
 An example of a struggle between resident and invading spe- 
 cies is found in the faunas of the Portage beds of New York State. 
 The resident fauna was the Ithaca fauna, derived by modification 
 from the preceding Hamilton fauna. The invading fauna came 
 from Eurasia, invading the New York area from the northwest. 
 The interspecific, or interfaunal, struggle continued throughout 
 Portage time, the invading species gradually acquiring the mastery. 
 
 BlOGEOGRAPHICAL PROVINCES. 
 
 At each period of the earth's history, zoogeographic and phyto- 
 geographic provinces existed which were more or less distinctly sep- 
 
1054 PRINCIPLES OK STRATIGRAPHY 
 
 arable from one another and which varied from period to period. 
 Even within the same period the geographic provinces are not 
 constant for all animals or plants, because some groups of animals 
 and plants are not affected by barriers which are restrictive to 
 others. Nevertheless a general division of the earth's surface into 
 biotic provinces is possible, up to a certain extent ; at least within 
 the marine and terrestrial realms. Within these two realms the 
 distribution of organisms is the resultant of migration and dis- 
 persal, not only of the organisms themselves, but also of their 
 ancestors in preceding geologic periods. Thus the problem of 
 geographic distribution of a given group of organisms resolves itself 
 into a study of the migrations and dispersions of the ancestral types 
 of these organisms from the point of their origin in past time. 
 From the point of origin or center of distribution a process of 
 adaptive radiation has carried the organism outward and onward in 
 space and time. Barriers arising across the path of distribution break 
 the continuity of the range ; and from these separated remnants, or 
 relicts, arise new diversified types, along a number of distinct lines 
 radiating from the central stock, the resultants being in general 
 well adapted each to a particular phase of the environment. In 
 other distinct provinces similar lines of evolution may give rise 
 to parallel series of modifications ; so that, in provinces widely sep- 
 arated, similar lines may arise independently, the closeness of the 
 resemblance seemingly indicating a close geographic connection 
 between the provinces. The species of the gastropod genus Clavi- 
 lithes are an excellent example of this phenomenon. This genus 
 is represented by a number of very marked species in the Eocenic 
 strata of the Paris Basin. A parallel series occurs in the London- 
 Hampshire Eocenic basin, but there are scarcely any identical spe- 
 cies. Another parallel series occurs in the Gulf Eocenic of the 
 United States, a province entirely distinct from, and without com- 
 munication with, the European provinces, which .themselves were 
 closely circumscribed. Nevertheless, the American series has the 
 same specific types as the Paris series, corresponding species of 
 the two generic stocks being scarcely distinguishable, so far as the 
 specific characters are concerned ; though it is an easy matter to 
 separate them generically that is, to place each species in its 
 proper genetic series. If, as seems highly probable, these two 
 groups of Clavilithids had a common ancestor, in early Eocenic, 
 Palaeocenic, or late Cretacic time, they became entirely separated 
 in mid-Eocenic time, and the parallel specific types arose indepen- 
 dently. 
 
BIOGEOGRAPHICAL PROVINCES 1055 
 
 Marine Provinces. 
 
 The following 1 are the marine zoogeographical regions of the 
 present geologic epoch, as given by Ortmann (38: 66) : 
 
 I. Littoral life-district 
 
 1. Arctic region 
 
 2. Indo-Pacific region 
 
 3. West American region 
 
 4. East American region 
 
 5. West African region 
 
 6. Antarctic region 
 
 II. Pelagic life-district 
 
 1. Arctic region 
 
 2. Indo-Pacific region 
 
 3. Atlantic region 
 
 4. Antarctic region 
 III, Abyssal life-district 
 
 No regions distinguishable. 
 
 Marine geographical provinces have been distinguished for sev- 
 eral classes of organisms by different authors. Among these the 
 following may be mentioned : 
 
 I. Corals. Dana recognized three principal regions: (i) Red 
 Sea and Indian Ocean; (2) the whole of the Pacific Islands and the 
 adjacent coasts of Australia; (3) the West Indies. The last region 
 is the most isolated and it contains the largest proportion of peculiar 
 forms. 
 
 II. Higher Crustacea. Prof. J. D. Dana also proposed to divide 
 the oceans into the three main areas, based on the distribution of 
 the Crustacea. These are: (i) the Occidental; (2) the Africo- 
 European, comprising the western shores of the Atlantic, both 
 African and European; and (3) the Oriental, which includes the 
 vast area from the east coast of Africa to the Central Pacific. Each 
 region is subdivided into local and climatic provinces. 
 
 III. Barnacles. Darwin, considering the distribution of the spe- 
 cies of barnacles, divided the oceans into the following regions : 
 (i) The North Atlantic, comprising North America and Europe 
 down to N. lat. 30; (2) the West American, from Behring Strait 
 to Tierra del Fuego ; (3) the Malayan, from India to New Guinea; 
 (4) the Australian, comprising Australia and New Zealand. The 
 third and fourth regions are the richest in species. 
 
 IV. Mollusca. S. P. Woodward (61) divided the oceans into 
 three main divisions or regions: (i) The Atlantic; (2) the Indo- 
 Pacific, corresponding to Dana's Oriental region for Crustacea ; 
 and (3) the West American. The following is the modified system 
 of Woodward (Lydekker-29:/o/<5) : 
 
1056 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Molluscan Regions. 
 
 A. Atlantic and Circumpolar regions, 
 
 B. Indo-Pacific regions 
 
 C. Australian regions. 
 
 D. American regions. 
 
 1. Arctic sub-region 
 
 2. Boreal " 
 
 3. Celtic " 
 
 4. Lusitanian sub-region 
 
 5. West African " " 
 
 6. South African" 
 
 1. Indo-Pacific sub-region. 
 
 2. Japanese sub-region 
 
 1. Australian sub-region 
 
 2. Neozealandian sub-region 
 
 1. Aleutian sub-region 
 
 2. Calif ornian 
 
 3. Panamic 
 
 4. Peruvian 
 5.. Magellanic 
 
 6. Argentinian 
 
 7. Caribbean 
 
 8. Trans- Atlantic ' 
 
 V. Fishes. Gunther (20) recognized the following marine zoo- 
 logical regions based on the distribution of shore-haunting fishes : 
 
 i. Arctic ocean. 2. Northern temperate zone divided into: (a) the temperate 
 North Atlantic and (b) the temperate North Pacific with further subdivisions 
 of each. 3. Equatorial zone, divided into: (a) Tropical Atlantic, (b) Tropical 
 Indo-Pacific, and (c) Pacific coast of tropical America with further subdivisions. 
 4. Southern temperate zone with several subdivisions, and 5. Antarctic ocean. 
 
 VI. Marine Mammals. The following marine geographic 
 regions based on the distribution of seals, sea-cows, and cetaceans 
 have been recognized by Sclater (43) : 
 
 1. Arctatlantica (seals of the sub -family Phocinae). 
 
 2. Mesatlantica (monk seal and manatis). 
 
 3. Philopelagica (Indian ocean, etc.), characterized by the presence of 
 dugongs and absence of seals. 
 
 4. Arctirenia (North Pacific) with Phoca, and sea-bears and sea-lions, for- 
 merly the northern sea-cows (Rhytina) now also the gray whale (Rhachianectes). v 
 
 5. Mesirenia (Mid-Pacific) without sea-cows, but with the elephant-seal 
 (Macrorhinus). 
 
 6. Notopelagica (Southern ocean) with four peculiar genera of seals, numerous 
 sea-bears and sea-lions, and two peculiar whales, the pigmy whale and Arnoux's 
 beaked whale. 
 
BIOGEOGRAPHICAL PROVINCES 1057 
 
 Former Marine Geographic Provinces. 
 
 The most elaborate attempt to divide the world into marine 
 zoogeographical provinces for one of the past geological periods of 
 the earth's history is that of the late Victor Uhlig of Vienna, in 
 his "Die marinen Reiche des Jura und der Untern Kreide" (52). 
 He recognizes at least four large faunal districts, based mainly on 
 the distribution of fossil cephalopods, namely : 
 
 1. The boreal. 
 
 2. The Mediterranean Caucasian. 
 
 3. The Himamalayian. 
 
 4. The Japan Province. 
 
 5. The South Andine realm. 
 
 The boreal realm of the Jurassic time originally defined by 
 Neumayr was circumpolar in the arctic region with extensions into 
 the heart and the northern region of Russia to the east of the Urals 
 and westward to Greenland, including the Urals and Scandinavia 
 as probable islands. A narrow southward extension included the 
 region of the Lena River and the lower Amur. The Pacific ex- 
 tension of this realm comprises Alaska and the western coast of 
 America (California, Nevada, etc.) to the head of the Gulf of Cali- 
 fornia and with an epicontinental lobe extending into Montana, 
 Wyoming, Idaho and eastward to the Black Hills (Logan Sea). 
 This region has been separately named the North Andine Province. 
 On the whole, the boreal was a shallow sea, with a peculiar and 
 uniform fauna. Coral reefs were conspicuously absent. 
 
 The Mediterranean-Caucasian realm comprised the expanded 
 Mediterranean area, which extended eastward to the borders of 
 India and northward to the Caucasus Mountains. It included the 
 Jurassic formations of the Alps. Between it and the Boreal realm 
 of Russia lay the mid-European province of Neumayr, which, by 
 Haug, Uhlig, and others, is regarded as a neritic border zone of 
 the deeper Mediterranean sea. The characteristic genera of am- 
 monites of the Mediterranean realm (Phylloceras, Lytoceras) are 
 regarded by Haug as stenothermic and able to live only in the 
 deeper waters where temperature changes are slight; while the 
 other genera were eurythermic and so had a wider distribution. 
 
 The Himamalayian realm comprised northern India and the 
 Himalayan region, and extended thence to the Malay archipelago. 
 In it are recognizable an argillo-arenaceous and a calcareous facies, 
 a part of the latter being often considered as abyssal. Two related 
 
1058 PRINCIPLES OF STRATIGRAPHY 
 
 provinces are recognized: (a) the Ethiopian, comprising the east 
 coast of Africa and part of Madagascar; and (b) the Maorian, 
 in Oceanica. The Japan Province is a small one limited to the 
 Japanese archipelago and Korea. It is characterized by a comming- 
 ling of boreal and Malayian features, though less markedly related 
 to the latter. The South Andine realm comprised Central America 
 and the whole west coast and the southern end of South America, 
 and appears to be likewise represented in the southern coast of 
 Africa. 
 
 Considering these realms as a whole it appears that the faunas 
 of the last four are more closely related to each other than they are 
 to the boreal. Haug has united the Mediterranean-Caucasian, the 
 Himamalayian, and the North Andine realms into a single broad 
 equatorial faunal arid climatic belt which is sharply contrasted with 
 the Holarctic-Boreal belt. Such a broad zonal division is favored 
 by Uhlig. 
 
 On the whole, it appears, as Koken (27:550) pointed out, that 
 the distribution of marine faunas is less dependent on climatic 
 differences than on the distribution and development of coast lines. 
 
 Present and Former Biogeographic Provinces of the Land. 
 
 The terrestrial provinces of the present time are generally com- 
 prised within three great divisions or sub-realms, as first proposed 
 by Blanford, and under these are included a number of distinct 
 regions. As commonly accepted, these are : 
 
 I. Arctogaea, or northern sub-realm, with 
 
 1. Arctic, or circumpolar region. 
 
 2. Ethiopian, or African region (south of the Sahara). 
 
 3. Indo-Malayan, or Oriental region (including southern 
 
 Asia and the Malayan islands). 
 
 4. Malagasian, or Madagascar region. 
 
 5. Nearctic, or North American region. 
 
 6. Palaearctic, or Eurasiatic region. 
 
 II. Notogaea, with four regions : 
 
 1. Austro-Malayan. 
 
 2. Australian. 
 
 3. Polynesian. 
 
 4. Hawaiian. 
 
 III. Neogaea, comprising South America, with one region: 
 
 i. Neotropical. 
 
BIOGEOGRAPHICAL PROVINCES 1059 
 
 To these may be added the Antarctic continent, or Antarctogaa, the 
 former existence of which, connecting most of the other regions, 
 seems to be demonstrated by a number of independent lines of evi- 
 dence, as developed in the study of the distribution of a great 
 variety of types of organisms. 
 
 Fresh Water Bio tic Provinces. 
 
 Simpson (47) has proposed the following regions as subdivisions 
 of the fresh water realm, based on the distribution of the fresh 
 water mussels or Unios in the present chronofauna. 
 
 1. Palsearctic. 5. Neotropic. 
 
 2. Ethiopic. 6. Central American. 
 
 3. Oriental. 7. Mississippian. 
 
 4. Australian. 8. Atlantic. 
 
 The Pal(carctic region comprises Europe, North Asia, and 
 western North America; the Oriental includes the Malaysian Is- 
 lands to New Guinea. Simpson holds that the mussels originated in 
 North America in the Triassic, whence they migrated or dispersed 
 into South America, from which region they passed by an old 
 Antarctic land bridge to New Zealand and Australia, thence to 
 southern East Asia, whence they entered the remaining part 
 of Asia, Europe and Africa. In early Tertiary time they migrated 
 across northeast Asia to northwest America. 
 
 It should be noted in this connection that the active migration 
 of the adult is a comparatively slow process, and is, of course, con- 
 fined to streams. The young are attached to the gills of fishes and 
 so are much more rapidly distributed. Here, too, of course, con- 
 tinuous water bodies are required. But there are other methods 
 of dispersal by means of which these shells can transgress land 
 barriers often of considerable extent. Notable among these are 
 the dispersal of the eggs and young shells by water birds, to whose 
 feet they become attached, and by large water beetles and other 
 insects. Thus, while large bodies of sea water cannot be traversed 
 in this way, narrow straits could easily be covered. 
 
 Perhaps a better index to the former land connections is found 
 in the distribution of the fresh water crayfish. Their migrations 
 were traced to a certain extent by Huxley (24), later by Faxon, 
 and most recently by Ortmann (39). 
 
 The distribution of the family Potamobiidce Huxl., compris- 
 ing two genera, Cambarus and Potamobius, may be briefly con- 
 
io6o PRINCIPLES OF STRATIGRAPHY 
 
 sidered. The first of these genera includes 67 species, and is 
 found only in the eastern parts of North America, Mexico, and 
 Cuba. The genus is divisible into five groups, the smallest of 
 which contains three species and the largest twenty-six. The first 
 group of sixteen species is restricted chiefly to the southern parts 
 of the United States and Mexico. The most primitive species belong 
 chiefly to the southwest ; and in fact this is also true of the primitive 
 species of the second and fifth groups. This fact points to an origin 
 of the genus in the southwest, its starting point being apparently in 
 Mexico. The second genetic group, with eight species, shows a 
 striking discontinuity of distribution, isolated representatives being 
 found in Mexico, the Gulf States, the southern Atlantic States, 
 and Cuba; all of them separated from the members of the group 
 found in the southwestern and central States. This indicates that, 
 after the migration of the species of this group from Mexico into 
 the United States, unfavorable physical conditions at intermediate 
 points broke up the former continuous range. The third group, 
 with thirteen species, has a continuous distribution in the Alle- 
 ghany mountains and in the east ; a single species reaching north to 
 the Gulf of St. Lawrence region. It also extends northward in 
 the Mississippi region, but is less prominent, and is represented at 
 only one station in the southwest, and there by a single species. 
 The fourth group, with twenty-six species, is also scarce in the 
 south and southwest, but is abundant in the Upper Mississippi- 
 Missouri-Ohio basin. Eastward it extends up the Ohio into Penn- 
 sylvania, Virginia, Maryland, New Jersey, and New York, its 
 northeastern limit being near Montreal. In the central region it 
 extends northward to Lake Winnipeg and the Saskatchewan River, 
 the most northerly locality known for this genus. Westward it 
 extends to Wyoming. The fifth group consists of three species, one 
 occurring near New Orleans, the other two in Mexico. On the 
 whole, the most primitive species are in the Mexican region, the 
 probable birthplace of the genus, as has already been suggested. 
 Here also has remained a rather primitive side branch, group 5- 
 The other groups advanced northward and northeastward, the 
 most specialized becoming discontinuous on account of adaptation 
 to a changed environment. 
 
 Cambarus appears to be derived directly from a less specialized 
 fresh water crayfish, Potamobius, which has a strikingly discon- 
 tinuous distribution, one group of seven species occupying a con- 
 tinuous area in Europe and western Asia, and another in western 
 North America. A third group, separated as the subgenus Cam- 
 baroides, occurs in northeastern Asia ; this group, according to 
 
BIOGEOGRAPHICAL PROVINCES 1061 
 
 Ortmann, forming a morphologic equivalent (homceomorph) of 
 Cambarus, though not closely related to it. Ortmann believes that 
 the three groups originated from a common ancestor whose home 
 was in eastern Asia. A branch was sent out westward, which finally 
 reached Europe ; while another branch migrated eastward, reaching 
 western America by means of a land area connecting Asia and 
 America. Of these migrants a single species has remained behind 
 in Unalaska. When finally, by geographical changes, the European 
 and American branches became separated from the Asiatic one, 
 each developed independently, the result being three distinct groups, 
 as above stated. From members of the American group, which had 
 reached Mexico, the genus Cambarus developed, in a remote period, 
 becoming differentiated into five groups, through processes of geo- 
 graphical isolation. 
 
 From the distribution of these and other -fresh water decapods 
 Ortmann concludes that the following land connections must have 
 existed in the near past. 
 
 1. Northeast Asia with Northwest America across the Behring 
 
 Sea. 
 
 2. East Asia with Australia. 
 
 3. South Asia with Madagascar and Africa. 
 
 4. New Zealand with Australia. 
 
 5. Australia with South America. 
 
 6. West Indies with Central and South America. 
 
 7. South America with Africa. 
 
 Ortmann holds that the above connections were necessary; for, 
 while a few species of fresh water crayfish or crabs have been 
 found in brackish or even salt water, this occurrence is very excep- 
 tional, the animals being preeminently dwellers in fresh water, so 
 that a migration across oceans or parts of oceans is practically pre- 
 cluded. Furthermore, since these animals cannot live out of 
 water for any great length of time, deserts or waterless tracts form 
 absolute barriers for them. The eggs of these creatures are carried 
 under the abdomen of the female, and the young hatch in a state 
 similar to the parents. While water fowl or other agents may oc- 
 casionally effect a passive transport, such cases are rare and have 
 never been observed. "The whole character of the distribution of 
 the different species is against the assumption of exceptional means 
 of dispersal." (Ortmann-39.) The connection of Asia and north- 
 west America by way of Behring Sea is also indicated by the dis- 
 tribution of mammals and other land animals. The connection con- 
 tinued probably through the whole of Tertiary time. The connec- 
 
1062 PRINCIPLES OF STRATIGRAPHY 
 
 tion between eastern Asia and Australia is also indicated by the 
 distribution of the snails (Helix). This bridge appears to have 
 existed before the Upper Cretacic. The connection between Africa 
 and India demanded by the distribution of the fresh water decapods 
 seems to have been in mid-Cretacic time or earlier. Other facts 
 show that this union continued through Eocenic time. The con- 
 nection between New Zealand and Australia is believed to have 
 been by way of New Caledonia and New Guinea, and belongs to 
 pre-Eocenic time; while that between Australia, New Zealand and 
 South America, generally assumed by students of zoogeography, is 
 believed by Ortmann to have been across the Pole, and to have con- 
 tinued to the end of Mesozoic time. There are indications that 
 the West Indies, Central America,, and the northern margin of 
 South America formed the "Antillean continent" during Jurassic 
 and Cretacic time, a remnant of and successor to Appalachia ; after 
 this was broken up, the northern remnant, consisting of the Greater 
 Antilles and parts of present Central America, probably remained 
 a unit up to the Eocenic, after which it was dismembered, to be 
 once more established in Pleistocenic time, and finally destroyed 
 in the present. Finally, the connection between South America and 
 Africa is believed to have existed in Jurassic and early Cretacic 
 time, but was severed in subsequent periods. 
 
 Terrestrial animals, especially mammals, are even better indices 
 of former land connections than the fresh water animals cited, 
 inasmuch as even moderate dividing straits form absolute barriers 
 to the majority of types. For an extensive account of this subject 
 the student is referred to Lydekker's "Geographical Distribution 
 of Mammals." 
 
 RELICTS. 
 
 RELICT FAUNAS AND LAKES. The occurrence of halo-limnic 
 organisms or animals or plants normally of marine type in conti- 
 nental seas or lakes has been a matter of great scientific interest 
 ever since Loven, in 1860, announced the presence of Crustacea 
 closely related to marine types in the great fresh water lakes of 
 Sweden, and showed by the geological structure of the region that 
 these organisms entered the lakes at a time when they were con- 
 nected with the sea. They, therefore, constituted the relics of a 
 former marine fauna, which had mostly become extinct by the grad- 
 ual freshening of the waters of the lakes after the connection with 
 the sea was broken. Similar left-over marine faunas or relicts 
 were discovered in many other continental seas, both fresh and 
 
RELICT FAUNAS AND LAKES 1063 
 
 salt; some of these occurrences, like that of the sea-dog, or harbor 
 seal, Phoca, in the Caspian and other seas, had been known pre- 
 viously, and used by Pallas and V. Humboldt to demonstrate the 
 former connection of these lakes with the oceans. Oscar Peschel 
 (41) in 1875 applied the name relict seas (Reliktenseen) to these 
 bodies of water, which he regarded as derived from the sea by 
 the growth of enclosing land. He and most authors since his 
 time regarded all continental seas containing marine organisms as 
 relicts, even though some of these seas are far inland. Credner 
 (8), however, strongly opposed this view, evidently believing, with 
 Penck, that a distinction should be made between a relict fauna 
 and a relict sea. The former may enter the lake by a process of 
 migration, as is believed to be the case in many instances where 
 the seals (Phoca) are found in fresh water lakes the geologic 
 surroundings of which show that they never were a part of the 
 ocean; or where a marine fauna has entered a lake basin of inde- 
 pendent origin through a temporary connection with the sea. Such 
 is the case with the Great Lakes of North America, some of which 
 are known to have been temporarily invaded by the sea by way of 
 the Hudson-Champlain depression during early Pleistocenic time, 
 but the origin of which was wholly independent of the sea (16). 
 Thus Lake Ontario was a fresh water lake before it became tempo- 
 rarily connected with the sea. Credner classes as true relict seas 
 all those which at one time were a part of and connected with the 
 oceans. He makes the following divisions : 
 
 I. Relict seas due to damming and isolation of parts of the sea, 
 through a growth to above the sea-level of enclosing rock 
 masses. 
 
 II. Relict seas due to isolation of basin-like depressions in the 
 sea-floor, owing to a negative change in the sea-level. 
 Emersion lakes. 
 III. Relict seas due to shrinking of former mediterraneans. 
 
 The first division includes (a) coastal lakes due to damming 
 of bays and inlets, by growth of deltas (Lake Akiz), or by the 
 enclosure of bodies of water between the growing delta and the 
 open coast (Lake Pontchartrain and others in the Mississippi 
 delta) ; (b) coastal lakes or lagoons (barachois) due to the growth 
 of sand-bars (Kurische Haff) and barrier reefs; (c) atoll seas or 
 coral island lagoons, and others. 
 
 Under the second division are comprised the marginal lakes 
 of the fjord type, as on the coast of Norway, Scotland (Loch 
 Lomond), Iceland (Lagarfljotj, and others. Credner classes Lake 
 
1064 PRINCIPLES OF STRATIGRAPHY 
 
 Champlain in this group, but this basin can hardly be said to have 
 been a part of the sea in the sense that the marginal fjord lakes 
 are. It is an ancient erosion basin of truly continental origin, as is 
 the case with most of the Great Lakes. The Champlain valley was 
 temporarily invaded by the sea, as was Lake Ontario, both being 
 primarily continental basins due to erosion and damming. For this 
 group a separate division that of relict seas due to invasion 
 might be erected. In this category may belong Lake Venern and 
 Lake Vettern of Sweden, both of which are old erosion basins 
 and may have been lakes before the marine invasion. This group 
 of relict seas is more nearly related to the true lakes which contain 
 a relict fauna. 
 
 Among other lakes containing a pronounced relict fauna, Lake 
 Baikal of central Asia and Lake Tanganyika of central Africa 
 are perhaps the best known. The relict nature of the former basin 
 has been much questioned (Credner-8, ii:^5), but the relict nature 
 of a part of the fauna is commonly conceded (Hoernes-22). Be- 
 sides the seal Phoca baikalensis, B. Dyb., and a number of fish, 
 among them Salmo migratorius Pallas, planarians, and sponges are 
 represented by types more closely related to marine than to fresh 
 water forms. One of the sponges especially (Lubomirskia baika- 
 lensis, W. Dyb.) is a truly marine type, occurring in Behring Sea. 
 The molluscan fauna of Lake Baikal is especially peculiar. Of the 
 twenty-five described species of gastropods only three are found 
 elsewhere, but none outside of Siberia (Dybowski, W.-I3). There 
 is a marked resemblance, however, between this fauna and that of 
 the Tertiary fresh water lakes of eastern Europe, which most 
 probably were the. source whence the Baikal fauna migrated. 
 
 The relict fauna of Lake Tanganyika is a most interesting and 
 remarkable one (Moore 32). It includes the fresh water medusa 
 Limnocnida tanganyica, the first and almost the only jelly-fish found 
 outside of the sea ; and a number of molluscs which can be traced 
 back to ancestors .probably in the Jurassic seas of that region. 
 Some of these would unhesitatingly be classed as marine types if 
 found in a fossil condition, which is particularly true of the Fulgur- 
 like genus Holacantha, of which four species inhabit this lake ; and 
 of the trochoid genus Limnotrochus, also represented by four spe- 
 cies (Bourguignat-4). This association, with Planorbis, Physa, 
 Vivipara, and other normal fresh water forms, would, if found 
 embedded in the strata, lead to some interesting speculations re- 
 garding the conditions of deposition. 
 
 The relict fauna of the Scandinavian and Finnish lakes, of 
 which there are no less than thirty-one, comprises seven Crustacea, 
 
MARINE RELICTS; BIPOLAR FAUNAS 1065 
 
 three fish, and one seal (Phoca annellata Nilss). The Crustacea 
 are especially interesting. Mysis oculata Fabr. var. relicta is the 
 most widely distributed type. It is a variety of a true marine 
 form which occurs in the northern seas on the coast of Labrador 
 and Greenland. The same variety occurs in lakes Superior, Michi- 
 gan, and Ontario, in the Gulf of Bothnia, and in the Caspian Sea. 
 The other marine Crustacea of the Scandinavian-Finnish seas are 
 three amphipods ; one isopod, one phyllopod, and one lophyropod. 
 
 Relict seas derived from the shrinking of former mediterraneans 
 are found in the Caspian and Aral seas, which are still shrinking. 
 These seas are fragments of a once extensive southeast European- 
 Asiatic mediterranean of later Tertiary time (Sarmatien). The 
 relict fauna of the Caspian includes, besides the seal (Phoca cas- 
 pica), sixteen species of molluscs, including Cardium, Adacna, 
 Venus, etc. ; two Crustacea, four sponges, and a number of fish. 
 These seas are further characterized by having salty or brackish, 
 instead of fresh, water. 
 
 MARINE RELICTS BIPOLAR FAUNAS. "Bipolarity .in the strict 
 sense," says Ortmann, "i. e., the presence of an identical species at 
 the North and South Poles, while it is absent in the intermediate 
 regions, is extremely rare, and there are hardly any well-established 
 cases. Bipolarity in a wider sense presence of closely allied spe- 
 cies at the poles, while in the intermediate regions allied forms 
 are absent is a well-established fact." The known cases are chiefly 
 of pelagic animals. Ortmann thinks that, in some cases, as medu- 
 sae, pteropods, and tunicates, the ancestors lived in the tropical 
 seas of Tertiary time, and their descendants migrated both north 
 and south, the tropical forms subsequently becoming extinct. The 
 difference between the north and south polar types in other cases 
 is explained by Ortmann as due to different sources of the migrants, 
 the Arctic faunas being derived from the old Mesozoic Mediter- 
 ranean waters, and the Antarctic from Pacific waters. Other ex- 
 amples of marine relicts, or the occurrence of faunas in basins of 
 the sea, while they have become extinct in the neighboring region, 
 is shown by the fauna of Quahog Bay near Portland, Maine ; and 
 in the southern parts of the Gulf of St. Lawrence, as about Prince 
 Edward's Island, and the opposite coast of Nova Scotia, where the 
 water is shallow and much warmer than on most parts of the 
 Maine coast. Here Venus mercenaria is found' in some abundance, 
 associated with oysters and other southern species which are absent 
 from the New England coast. They constitute "a genuine southern 
 colony, surrounded on all sides, both north and south, by the 
 boreal fauna." (Verrill and Smith-54 :j<5o.) 
 
io66 PRINCIPLES OF STRATIGRAPHY 
 
 TERRESTRIAL RELICTS. These are faunas and floras which have 
 migrated into certain regions during a period of different climatic 
 conditions, and then became stranded in certain spots where the 
 environment remained uniform, while the surrounding area 
 changed. The Arctic plants and butterflies of Mount Washington 
 in New Hampshire are examples. These occupied the region dur- 
 ing the general refrigeration of the climate in the last glacial pe- 
 riod, and on the retreat of the ice were left stranded on the higher 
 points where these conditions were more nearly normal for them. 
 According to Professor Asa Gray, 37 northern species of plants 
 still remain and thrive on the summits of the White Mountains of 
 New Hampshire, and part of them also on the Adirondack and 
 Green Mountains. A number of these species were found on 
 a Greenland nunatak by the Jensen expedition of 1878. 
 
 DWARF FAUNAS AND MICRO-FAUNAS. 
 
 These are faunas in which all the individuals are of much 
 smaller size than their norm, and which therefore clearly lived 
 under conditions preventing the organisms from reaching- their 
 full size. That such conditions are primarily environmental is 
 indicated by the fact that all the organisms are affected, whereas, 
 if individuals only were dwarfed, or only members of one species, 
 this might be considered as more likely an individual response. 
 Micro'-faunas are associations of small species determined by the 
 peculiarity of physical conditions and not due to dwarfing of 
 normally large species. While dwarfed forms of known larger spe- 
 cies are readily enough recognized, it is not always easy to say 
 whether a given fauna not known elsewhere is dwarfed or is a 
 micro-fauna due to selection. 
 
 Shimer (45) has listed the chief agencies of dwarfing noted 
 in recent and fossil marine invertebrate faunas, as follows: 
 
 1. A change in the normal chemical content of the sea water. 
 
 (a) Due to freshening of the sea water. 
 
 (b) Due to a concentration of the salt, iron, etc. 
 
 (c) Due to an increase in H 2 S and other gases. 
 
 2. Presence of sand and other mechanical impurities in the 
 
 water. 
 
 3. A floating habitat. 
 
 4. Variation in temperature. 
 
 5. Extremes in depth of water and variation in amount of 
 
 water per individual. 
 
DWARF FAUNAS AND MICROFAUNAS 1067 
 
 As an illustration of the dwarfing due to the freshening of sea 
 water Shimer cites the organisms of the Black and Caspian Seas, 
 which are freshened by the influx of stream water (see tables of 
 salinity, pp. 146, 154). As shown by Forbes (14), the species of 
 molluscs in the Black Sea are all smaller than those same species 
 in the British seas. Cardium edule, the common cockle of the 
 British coast, is dwarfed when it lives in the brackish water of 
 the estuaries. The shell is not only reduced in size, but becomes 
 thin and has its external character less strongly marked. The 
 cockles of the Caspian Sea are small, thin, and smooth, with lateral 
 or central teeth or both suppressed. The cockle of the Green- 
 land estuaries is likewise thin, smooth and almost edentulous, the 
 rudiments of hinge-teeth occurring in the young but disappearing 
 in the adult. This species is abundant in the Pliocenic Crag de- 
 posits of Suffolk and Norfolk, especially in the fluvio-marine por- 
 tion. Among other species dwarfed by brackish water are M ya 
 arenaria and Littorina littorea. 
 
 Shimer described a diminutive Pleistocenic? fauna from the 
 estuarine clays of the Hudson bottom opposite Storm King, 40 
 feet below the bed of the river. This fauna consisted mainly of 
 large numbers of Mulinia lateralis (Say) and a lower development 
 of Trivia trivittata Say. These species live at present off the New 
 England and New Jersey coasts in normal marine or but slightly 
 freshened water, where their size is almost twice that of the Hud- 
 son estuary specimens. 
 
 Dwarfing due to concentration of salt, i. e., increase in salinity, 
 is shown to some extent in the Mediterranean, which, with a salinity 
 of 39 permille, has many of its species smaller than their repre- 
 sentatives in the open water of the British and Spanish coasts. 
 The dwarfed faunas of the European Permic have in part been 
 ascribed to such concentration of the water. The possibility of 
 dwarfing of faunas through an excess of iron salts has been shown 
 by experiments upon fishes and tadpoles, which in eight months 
 were retarded in growth from 3 to 5 mm. Fossil examples are 
 found in the Pyrite layer, which in the Genesee Valley and west- 1 
 ward in New York replaces the Tully limestone of the Upper 
 Devonic. In this the fauna of 45 species was found by Loomis 
 (28) to be on the average only one-fifteenth the size of the normal 
 form. The dwarfing was apparently due to presence of much iron 
 in solution, in the form of ferrous carbonate, and this was precipi- 
 tated as pyrite by sulphuretted hydrogen derived from the decay- 
 ing organic matter (FeOCO 2 +H a S=FeS+CO 2 +H 2 O). The 
 
io68 PRINCIPLES OF STRATIGRAPHY 
 
 Clinton iron ore also contains a somewhat dwarfed fauna which 
 may have been due to the presence of much iron in the sea water. 
 
 Dwarfing effects due to an abundance of H.,S in the water are 
 shown in the Black Sea, where, owing to the slight vertical cur- 
 rents, much stagnation occurs, and much H 2 S is separated out 
 (see ante, Chapter IV). Here life below a certain depth is prac- 
 tically absent, while the bottom deposits are strewn with young 
 shells from the plankton. The dwarf faunas of the Palaeozoic 
 Black shales have been considered as produced by conditions such 
 as now exist in the Black Sea, but the depth during the formation 
 of most of them was probably slight, thbugh stagnation was no 
 doubt marked. 
 
 The presence of mud or other mechanical impurities likewise 
 exerts a dwarfing effect on many organisms. This is illustrated 
 by the fauna of the eastern part of the Mediterranean, where a 
 large quantity of fine mud brought in by the Nile is held in suspen- 
 sion. (De Lapparent-i2:/j^.) Shimer thinks that the dwarfed 
 faunas of the late Siluric rocks of eastern New York (Rosendale, 
 Cobleskill, Rondout, Manlius) are due to the presence of an abun- 
 dance of lime-mud, of the same kind of which the strata are com- 
 posed. This is a general characteristic of Palaeozoic calcilutytes. 
 
 Dwarfing of organisms due to a floating habitat is seen in the 
 case of a California coast Pecten (P. latiauritus), which when 
 growing near the coast is large and more strongly sculptured than 
 when fastened to floating kelp far from the coast (var. fucicolus). 
 The molluscs, living on and among the sea-weed which crowds the 
 eastern shallower part of the harbor of Messina, are throughout of 
 smaller forms, but are present in enormous number of individuals. 
 (Fuchs-i5:<?cxf) Walther (56) remarks upon this that the physi- 
 cal conditions of a special type of plant life here cause indirectly 
 the origin of the micro-fauna. The micro-fauna here is not so 
 much a dwarf fauna as one due to selection of small species by the 
 peculiar characteristics of the habitat. 
 
 The influence of variation in temperature on the size of the 
 individuals is illustrated by the experiment of Semper (44) on 
 Linmcca stagnalis, in which he found that growth began at a 
 temperature of 12 C, but that a lower temperature retarded or 
 completely arrested growth, though not affecting the life of the 
 animal. "If," says Semper "a Limnaea came to be placed in a 
 pool or stream where for only two months of the year the tempera- 
 ture is higher than the minimum (12 C.), growth will be checked 
 throughout the greater part of the year, and a diminutive race 
 result, since sexual maturity cannot be reached with a lower tern- 
 
CAUSES OF DWARFING 1069 
 
 perature." Excessive temperature also causes dwarfing, for polar 
 species entering waters the temperature of which is higher than 
 their optimum will remain smaller than normal. Thus northern 
 species of Pecten never reach the same size in warmer southern 
 waters. The same rule holds for mammals and birds. The dwarfing 
 of the faunas of the Black and Caspian seas may be in part caused 
 by the extremes of temperature in these waters. 
 
 Variation in the amount of water supplied likewise affects 
 the size of aquatic animals. Thus Semper found, in experiment- 
 ing with Limncca stagnalis, that "the smaller the volume of water 
 which fell to the share of each animal the shorter the shell re- 
 mained." (Semper-/j4:/d7.) With the same number of whorls, 
 the average length of shell for a given number of animals in 100 c.c. 
 of water was J4 inch, while the same number of animals in 2,000 
 c.c. of water had an average shell length of ^4 inch. 
 
 Deep-water individuals are also, as a rule, smaller than the 
 shallow-water forms, various factors, such as difference in tempera- 
 ture, density and salinity of water, of food supply, etc., being op- 
 erative here. 
 
 The dwarf faunas of the Windsor limestone ( Mississippi of 
 Nova Scotia) and of the Magnesian limestone or Zechstein of 
 Europe, is probably due to several causes, notably the decrease 
 in volume of water and the accompanying increase in salinity of 
 the water, these deposits being intercalated between continental 
 sediments. Similar dwarfed faunas are obtained from the Cretacic 
 of New Mexico and southern Colorado. (Stanton-49; Shimer and 
 Blodgett-46:6>.) 
 
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1070 PRINCIPLES OF STRATIGRAPHY 
 
 I 
 
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BIBLIOGRAPHY XXIX 1071 
 
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CHAPTER XXX. 
 
 FOSSILS, THEIR CHARACTER AND MODE OF PRESERVATION. 
 DEFINITION AND LIMITATION OF THE TERM FOSSIL. 
 
 Fossils are the remains of animals and plants, or the direct evi- 
 dence of their former existence, which have been preserved in 
 the rocks of the earth's crust. By direct evidence is meant the im- 
 pressions left by animals in transition, the structures built by them, 
 etc. Beds of iron one and deposits of apatite or of crystalline 
 limestone must be considered indirect and not always reliable evi- 
 dence of the former existence of organisms, since, in these cases, 
 organisms were only the agents active in their formation. Under 
 remains preserved in the earth's crust must be included those 
 formed in the northern ice fields, for we have seen that these ice 
 masses are to be regarded as a portion of the rocky crust of the 
 earth, though in most respects the least permanent one. 
 
 It has been a common custom to limit the term fossil to those 
 remains which were buried prior to the present geologic period. 
 This will be seen from the common text-book definitions of this 
 term. A few of them may be quoted. Fossils: "All remains or 
 traces of plants and animals which have lived before the beginning 
 of the present geological period, and have become preserved in 
 the rocks." (Zittel, Eastman's translation.) "Remains of animals 
 and plants which have existed on the earth in epochs anterior to 
 the present, and which are buried in the crust of the earth, are 
 called fossils." (Bernard's Elements, adapted from the English 
 translation.) "All the natural objects which come to be studied 
 by the palaeontologists are termed 'fossils' . . . Remains of 
 organisms . . . found ... in those portions of the earth's 
 crust which we can show by other evidence to have been formed 
 prior to the establishment of the existing terrestrial order . . ." 
 (Nicholson and Lydekker, Manual of Palsentology.) "Of those 
 animals and plants which have inhabited the earth in former times, 
 certain parts, decomposable with difficulty, or not at all, have been 
 
 1073 
 
1074 PRINCIPLES OF STRATIGRAPHY 
 
 preserved in the strata of the earth, and these we call fossils, or 
 petref actions." (Steinmann, Einfiihrung in die Palaontologie, 
 translated.) This definition in terms of past geologic time is an 
 arbitrary one, and is not based on any distinction in character 
 between the remains which were buried before and those which 
 were buried during the present geologic epoch. Thus the marine 
 shells in the post-glacial elevated clays of northern New England 
 and Canada (Leda, Saxicava, etc.) differ in no wise from those 
 of the same species buried in the modern deposits off the present 
 coast. "In the former case the strata have been elevated several 
 hundred feet ; while in the latter case they still retain their original 
 position, or, at least, have experienced no appreciable disturbance. 
 In like manner many of the Miocenic and Pliocenic shells are not 
 only of the same species as those recently buried on neighboring 
 shores, but the changes which they have undergone since burial are 
 frequently not greater than those experienced by shells buried in 
 modern accumulations. The difference in the alteration is merely 
 one of degree, and with proper discrimination specimens can be 
 selected which show all grades of change, from the unaltered state 
 of shells in modern mud-flats to the crystalline condition of an 
 ancient limestone fossil, in which the original structure has been 
 completely lost." (Grabau-i3 :o/, p#.) It is thus seen that it is 
 far more logical to extend the term "fossil" so as to include all 
 remains of animals and plants preserved from the time of the 
 earliest fossiliferous strata to the present. This is the position 
 taken by Lyell, who defines a fossil as : "Any body or the traces 
 of the existence of any body, whether animal or vegetable, which 
 has been buried in the earth by natural causes." In this definition 
 made by the geologist the time element is entirely omitted and in 
 this respect it contrasts markedly with the definitions quoted above 
 from palaeontologists. Of the latter, however, D'Orbigny forms 
 an exception, for he considers the term "fossil" to comprise "all 
 bodies or vestiges of bodies of organisms buried naturally in the 
 rocks of the earth and found to-day, except when actually in the 
 living state." (Cours lementaire de Paleontologie, Vol. I, p. 13.) 
 Geikie, too, neglects the time element in his definition of a fossil. 
 He says : "The idea of antiquity or relative date is not necessarily 
 involved in this conception of the term. Thus, the bones of a sheep 
 buried under gravel and silt by a modern flood and the obscure 
 crystalline traces of a coral in ancient masses of limestone are 
 equally fossils." (Text-book of Geology, 3d ed., p. 645.) This 
 general definition of a fossil is the one insisted upon by Grabau 
 and Shimer in "North American Index Fossils" (Volume I, page i.) 
 
 
PRESERVATION OF FOSSILS 1075 
 
 FOSSILIZATION. 
 
 "Geologic time is continuous, and the development of life is 
 progressive. No break divides the present from the past, and the 
 geologic phenomena of the present epoch are controlled by the same 
 laws which governed those of past time. Fossilization is a mere 
 accident by which some animals and plants are preserved, and it 
 resolves itself into a process of inhumation, neither the nature 
 of the organism nor the time or mode of burial being of primary 
 significance. These are of first importance in determining the 
 degree of preservation which the fossil is to experience, and, conse- 
 quently, the nature of the record which is to remain ; but they do 
 not affect the process of fossilization, which is merely the burial 
 of the dead organism. Thus the idea of change is not necessarily 
 involved in the concept of a fossil, although it is true that few 
 organisms long remain buried without undergoing some chemical 
 change. Examples of the preservation of organisms in an almost 
 unchanged condition are nevertheless known, the most conspicuous 
 being the mammoths frozen into the mud and ice of Siberia, and 
 retaining hair, skin, and flesh intact ; and the insects and other ani- 
 mals included in the amber of the Baltic, where they have remained 
 unchanged since early Tertiary time. Ordinarily, however, the 
 flesh of the buried animal soon decays, and, consequently, no rec- 
 ord of the soft parts is retained. In plants the decay is less rapid, 
 and the buried vegetable remains may be indefinitely preserved in 
 the form of carbonaceous films. 
 
 'The hard parts of animals are best preserved as fossils. Such 
 are the shells and other external skeletal structures secreted by a 
 variety of animals, as crustaceans, molluscs, echinoderms, corals, 
 and so forth ; and the bones, teeth, and other hard structures of 
 the vertebrates. Besides the actual remains of animals and plants, 
 any evidence of their existence, which is preserved, is commonly 
 included under the name of fossil. Thus impressions made by 
 living animals and plants in the unconsolidated rock material, and 
 structures built by animals from inorganic material, are fossils if 
 properly buried. Examples of the first are the footprints of verte- 
 brates ; the tracks and trails of jelly-fish, worms, molluscs, or 
 Crustacea; the burrows of worms, borings of animals in stones or 
 shells, and the impression made by sea-weeds in motion. Among 
 the second class are worm tubes built of sand grains ; foraminiferal 
 shells, built of foreign particles ; flint implements and other utensils 
 of primitive man ; and the relics of the Swiss Lake dwellers . . . 
 
1076 PRINCIPLES OF STRATIGRAPHY 
 
 (Grabau-i3:p#, pp.) Here belong, further, ancient buried cities, 
 like Pompeii; the Roman coins, weapons, etc., buried in the peat 
 bogs of Flanders and the north of France ; and, in fact, all artificial 
 productions of early man or other animals which have been pre- 
 served. Finally, coprolites, or the characteristic excrementa of 
 animals, have frequently been preserved, and these constitute a 
 class by themselves. Thus four distinct types or classes of fossils 
 may be recognized, viz.: (Grabau and Shimer-14 :j.) 
 
 1. Actual remains and their impressions. 
 
 2. Tracks, trails, and burrows of organisms. 
 
 3. Artificial structures. 
 
 4. Coprolites. 
 
 These may now be discussed more fully. 
 
 TYPES OF FOSSILS. 
 I. Actual Remains. 
 
 Preservation of Soft Tissues. As has already been noted, a 
 number of cases are known where the fleshy portions of animals 
 have been preserved. The mammoth (Elephas primigenius) , and 
 the rhinoceroses frozen into the mud and ice of Siberia are classi- 
 cal examples. Insects, spiders, and myriopods have been preserved 
 in great perfection in the Oligocenic amber of the Baltic provinces. 
 This fossil resin was produced by a species of pine (Finns succiui- 
 fer) and its quantity was so great that the deposits, though they 
 have been worked since very ancient times, have not yet been 
 exhausted. 
 
 Remains of man and other animals have been found perfectly 
 preserved in peat-bogs where they had been entombed for hun- 
 dreds of years. Mummification, or the preservation of the flesh 
 in dried condition, must also be noted in this connection, for in 
 this manner many remains of the human period have been pre- 
 served. Natural mummies have been found in saline soil at Arica 
 in Chili (South America), and they have also been found occa- 
 sionally in dry caverns and in crypts, notably in Bordeaux, France. 
 In the desert region west of the Peruvian Cordillera in South 
 America climatic and other conditions have proved particularly 
 favorable to the natural preservation of human remains. "The 
 tombs and graves [of the Incas] are usually found on elevated 
 places outside of the valleys where the extreme dryness of the air 
 
PRESERVATION OF SOFT TISSUE 1077 
 
 combines with the nitrous character of the sand, into which mois- 
 ture has seldom found its way, to desiccate and preserve the bodies 
 of the dead, thus mummifying them naturally. The same factors 
 have caused the clothing and objects placed with the dead to be 
 preserved for many centuries." (Mead-i^ :#.) Bodies of animals 
 have been similarly mummified, particularly those of household 
 pets, such as dogs and parrots ; and foods, such as corn and beans, 
 have been perfectly preserved. In the Atacama desert in Chile, in 
 the Chuquicamata copper mining district, was found the body of a 
 miner who had been caught, while at work, by a cave-in of the roof 
 of a mine in a side hill. "The stone and earth surrounding the 
 mummy were impregnated with anhydrous sulphate of copper 
 (brochantite), and sulphate of copper (blue vitriol). This mineral 
 prevented the organic matter from decomposition." "The skin 
 has not collapsed on the bones, as in the mummies found usually 
 in the region, but the body and limbs preserve nearly their natural 
 form and proportions, except for the crushing . . ." which 
 took place on the caving-in of the mine. The age of the mummy 
 is unknown, but it is probably several hundred years old, as indi- 
 cated by the primitive character of the implements embedded with 
 the body. 
 
 Preservation of animal tissue by impregnation with mineral 
 matter also occurs. As an example may be mentioned the well- 
 preserved body of a negro woman which had been buried for fifty- 
 seven years and was found near Tuskegee, Macon county, Alabama, 
 in 1894. The body lay in a sandy soil where the water from a near- 
 by spring kept it continually wet. In this water, silica, lime, and 
 magnesia were held in solution, and silica, lime, and oxide of iron 
 in suspension. About 50 per cent, of the substance of the body 
 had been replaced by mineral matter. Lead was also found present 
 in the body and might have been active in its preservation. (Sted- 
 man-23.) All told, however, the complete preservation of the ani- 
 mal body is of rare occurrence, and probably never dates back 
 very far in geologic history. A remarkable exception to this rule 
 is found in the muscle fibers of Devonic and later fish, and in 
 Mesozoic reptiles, which have been so perfectly preserved by a 
 process of replacement that their structure can readily be de- 
 termined under the microscope. These will be noted again in 
 the discussion of modes of preservation. 
 
 Impressions of the soft parts in rocks, or even a carbonaceous 
 film representing them, are found under favorable conditions. The 
 most familiar examples of this kind are ferns and other plant re- 
 mains, but those of animals are not unknown. In the fine litho- 
 
1078 PRINCIPLES OF STRATIGRAPHY 
 
 graphic lutytes of the Solnhofen district in Bavaria have been 
 found the impressions of medusae and of naked cephalopods with 
 the inkbag still containing the sepfa in a solidified state, while the 
 beautiful impressions of insect wings and the membranous wings 
 of pterosauria are among the most noted preservations obtained 
 from this rock. 
 
 Even more perfect examples of the preservation of soft parts 
 have recently been obtained by Walcott from the Stephen shale 
 (Cambric) of western Canada (26). Here worms, holothurians, 
 and other soft-bodied animals occur in a wonderful state of preser- 
 vation, so that, in many cases, even the internal anatomy can be 
 ascertained. The appendages of trilobites and other organisms are 
 also well preserved. The rock in which these fossils occur is an 
 exceedingly fine-grained sapropellutyte. Other remarkable pres- 
 ervations of soft tissues in rock of this type are known from the 
 Lias of Wurttemberg, where, at Holzmaden, the impression of the 
 skin of the Ichthyosaurians has been obtained. 
 
 Preservation of Hard Structures and of Petrified Remains. 
 The hard parts of animals are best adapted for preservation. This 
 is particularly the case where these parts are either calcareous 
 or siliceous. Such are the shells of Protozoa; the spicules of 
 sponges ; the coral of the coral-polyps ; the test of the echinoderm ; 
 the shell of brachiopod or mollusc; the calcareous structure of 
 Bryozoa ; the exoskeleton of Crustacea ; and the bones and teeth 
 of fishes, amphibians, reptiles, birds, and mammals. But hard 
 parts of a purely organic origin are also commonly preserved. 
 These are the structures composed of chitin and conchiolin. Chit in, 
 or entomolin, as it is also called, is the substance of which the elytra 
 and integuments of beetles and other insects are composed, and 
 which, commonly with an admixture of calcium carbonate or 
 phosphate, forms the carpace and other exoskeletal parts of Crusta- 
 cea, etc. Its composition is probably expressed by the formula 
 C 15 H 26 N 2 O 10 . Chitinous structures of other animals are the peri- 
 sarc of Hydrozoa and the similar network of horny fibers in the 
 Ceratospongise. Conchiolin is the organic matter of shells which, 
 on solution of the lime by acids, remains as a soft mass. The 
 young shells, particularly the protoconch, consist wholly of this 
 material. It is generally strengthened by subsequent deposition of 
 calcium carbonate, but in some cases, as in the nautiloids, it seems 
 to remain in the original chitinous condition, and is occasionally 
 preserved. 
 
 These structures, whether of chitin or conchiolin, are preserved 
 either as impressions, or, more generally, as carbonaceous films. 
 
PRESERVATION OF HARD STRUCTURES 1079 
 
 Sometimes various minerals, as pyrite, or chlorite, or even talc, 
 replace them. The same thing may be said of the cellulose com- 
 posing the tissues of plants, where decomposition is a slower process 
 than in the fleshy tissues of animals. The cell structure of plants 
 may thus be conserved for a long period, and this is especially the 
 case where there is a nearly complete exclusion of air, as in fine 
 sediments or in peat bogs. 
 
 The first requisite in fossilization is the burial or inhumation 
 of the remains. Even the hard parts of animals will be destroyed 
 if exposed too long to the atmosphere. Thus the bones of the 
 American bison, which, during the process of extinction that this 
 animal was undergoing on the western plains, were abundantly 
 scattered about, are fast disappearing by decay, so that shortly 
 no traces of them will remain except where they have been buried. * 
 This fact must be borne in mind in considering the remains of 
 earlier mammals. Those found can constitute but a small portion 
 of the skeletons once scattered about but which disintegrated before 
 the slow process of burial by continental waste or by dust saved 
 them. The soft tissues of animals and the tissues of plants decay, 
 of course, rapidly, and even inhumation, except in the cases noted 
 above, will not check the process of decay. Immersion in water 
 likewise results in the decay of organic matter, for bacteria here 
 become an active agent in the dissolution of tissues. Hard struc- 
 tures, such as shells or bones, will also suffer destruction by solu- 
 tion, especially if the waters are rich in carbon dioxide. Thus, as 
 already noted in an earlier chapter, the shells of many Protozoa 
 are dissolved after the death of the animal before they settle down 
 to the abyssal portions of the sea, and hence deposits of these shells 
 are generally absent from the greater deeps, though abundant in 
 regions of lesser depth. Solution may continue even after burial 
 if the beds are raised above the sea-level, and if they are per- 
 meable. 
 
 The buried hard parts of animals generally undergo a process 
 of petrifaction, which most commonly is either calcification or 
 silicifi cation, or sometimes the first followed by the second, i. e., 
 a replacement of the lime by silica, or, more rarely, the reverse. 
 Pyritization, or the replacement of the remains by iron pyrites 
 (or, more frequently, by marcasite) and replacement by iron oxide, 
 sphalerite, barite, vivianite, glauconite, or other minerals, also 
 occurs. The process of replacement differs in different groups 
 of organisms. 
 
 *A certain percentage of these bones, however, has been picked up and 
 burned for commercial and other purposes. 
 
io8o PRINCIPLES OF STRATIGRAPHY 
 
 Petrifaction of non-mineral substances. 
 
 (a) Replacement of soft animal tissue. As stated above, the 
 muscle tissues of a number of groups of vertebrates have been 
 known to be preserved in a most remarkable manner. In the upper 
 Devonic shales (Cleveland shales) of Ohio the muscular tissue 
 of cladodont sharks has been mineralized in such a perfect manner 
 that in places "they suggest in color, distinctness, and texture the 
 mummified tissue of recent fish." (Dean-io:^/,/.) Similarly, well- 
 preserved muscular tissue has been found in fishes of the litho- 
 graphic stone (Reis-2o, pi. II), and in other deposits both finer 
 and coarser. The muscular mass thus preserved is pure mineral, 
 composed of about So%-\- of calcium phosphate. Reis holds that the 
 muscular tissue was in a semi-decomposed condition, that minerali- 
 zation took place quickly, and that the remains must have been so 
 effectively enclosed that decomposition was checked. The phos- 
 phate, he thinks, is derived from the body of the animal and precipi- 
 tated on contact of the decomposing material with the calcium car- 
 bonate of the surrounding sediment. Dean, on the other hand, 
 favors the view that the phosphate was deposited from solution 
 within the undecomposed tissue of the shark, which thus became 
 mineralized before it had time to decompose. The partial replace- 
 ment of human bodies mentioned above is analogous to the more 
 ancient case here cited. 
 
 (b) Petrification of plants. ( Roth-22 -.605. ) Aside from the 
 unicellular diatoms, in which the cell walls of the living plant are 
 impregnated with amorphous silica, and the unicellular to multi- 
 cellular lime-secreting algae, the tissues of plants may in general 
 be regarded as free from mineral matter. But plants immersed in 
 mineral waters, or buried where such waters have free access, are 
 saturated and completely impregnated with the mineral matter. 
 Colloidal silica is most favorable for the preservation of the delicate 
 cell structures, while calcite or other minerals of high crystallizing 
 power will cause deformation if not disruption and complete de- 
 struction of the cell walls. 
 
 A mass of wood completely penetrated by and saturated with 
 silica still shows its original form and structure, even to the orna- 
 mentation of the cell walls, which, in a properly prepared slide, will 
 not appear very different from the fresh or dried tissues. Even 
 in appearance the impregnated wood resembles the unaltered wood, 
 being- fibrous and splintery, and the change is often noticeable only 
 from the difference in weight and hardness. The silica of wood 
 
PETRIFACTION OF PLANTS 1081 
 
 thus saturated may be dissolved in concentrated hydrofluoric acid, 
 when the woody tissue will be left behind unattacked. This shows, 
 according to Goppert, a cellular structure which in most cases 
 is sufficient for the generic determination of the wood. 
 
 Replacement of the cell walls themselves generally follows 
 impregnation, and thus the wood becomes wholly changed to silica. 
 Under these circumstances the finer structure is often destroyed 
 and the mass becomes uniform and breaks with a conchoidal frac- 
 ture. Illustrations of this are found in the brilliantly colored, 
 agatized woods of Arizona, fragments of which are hardly dis- 
 tinguishable from agates of wholly inorganic origin. 
 
 Opalized woods are not uncommon. Here, as in the case of 
 woods replaced by quartz, the structure of the wood is generally 
 retained, and in some cases the interior has been found to be but 
 slightly impregnated with the opal, or even to be unaltered wood, 
 thus showing the progress of opalization from without inward. 
 (Blum-4:/p7.) 
 
 Calcified woods are not uncommon, occurring in all formations, 
 from the Devonic up. They have been found in limestones, sand- 
 stones, shales, basaltic conglomerates, volcanic ashes and tuffs, and 
 other deposits. Daubree found at Bourbonne-les-Bains, in the de- 
 partment of Haute-Marne, France, piles of red beechwood, in 
 places so completely impregnated with transparent calcium car- 
 bonate that on solution in hydrochloric acid only 3.1 per cent, of 
 insoluble matter, showing plant structure, remained. The piles 
 supported an ancient Roman canal, and when found were buried 
 about 8 meters below the surface. 
 
 Aragonite is also known to have replaced wood. Even gypsum 
 has been found replacing wood in some Tertiary beds, and phosphate, 
 as well as fluorite of lime, is likewise known in this connection. 
 Barite also has replaced wood in some limestones of the Lias, and 
 a talc-like, complex silicate, probably pyrophyllite, has been found 
 replacing fronds of Neuropteris and Pecopteris and the leaves of 
 Annularia in Carbonic rocks in the Piedmont district. Chlorite has 
 been found occurring in a similar manner. So delicate is the replace- 
 ment that the venation is easily recognizable, although no part of the 
 original organic matter remains. Wood largely replaced by sulphur 
 and devoid of structure has been found in Cesena, Italy, and 
 plant remains replaced by sulphur have also been obtained from 
 the Tertiary beds of Aragon. (Blum-7 ://o.) 
 
 In the Carbonic and later coal-bearing horizons wood replaced 
 by siderite, often with considerable iron oxide, or wholly by limonite 
 or hematite, is not uncommon in various parts of the earth; while 
 
io82 PRINCIPLES OF STRATIGRAPHY 
 
 sphalerite, galenite, and marcasite are also known. Galenite has 
 been reported as replacing the fronds of ferns in some Coal Meas- 
 ures of Saxony. Malachite, azurite, and chalcocite are found in 
 carboniferous marls, probably of Jurassic age, in the district of An- 
 gola, West Africa, in the Urals, and in other regions. Even mod- 
 ern cedar wood has been found coated with and, in some cases, 
 largely replaced by malachite, as reported by Dr. A. F. Rogers 
 from Brigham, Utah (21). From a tuff bed enclosed between 
 basaltic flows below the Limburg (Germany) wood of Primus 
 nadus (?) replaced by a kaolin-like substance has been obtained in 
 abundance. This still retains the structure and occasionally car- 
 bonaceous remnants of the wood occur. 
 
 Where the actual plant remains have been removed by decay an 
 impression or mold often remains, in which a cast of the plant may 
 be formed by infiltrating foreign material. Such casts are common 
 in the Carbonic sandstones of the Joggins region of Nova Scotia, 
 in western Scotland and elsewhere. Trunks of Calamites, Sigillaria 
 and Lepidodendra, together with their rootstalks, Stigmaria, are 
 abundant in these strata as sandstone casts, resulting from the filling 
 of the cavities left by the decaying wood. 
 
 Decaying wood or other delicate parts of plants may leave a 
 record behind in the rocks in the form of a film of colored mineral 
 matter, precipitated by the decaying organic matter, or by the re- 
 moval of the coloring matter of that portion of the rock covered 
 by the decaying plant. This process of self-inscription upon the 
 rock by the plant has been termed autophytography (White-28), 
 the first mode producing a positive picture, and the second a nega- 
 tive one. 
 
 Petrifaction of mineral structures. 
 
 (a) Protozoa. The shell of the Foraminifera is typically com- 
 posed of carbonate of lime, either in the form of calcite (vitreous 
 species) or of aragonite (porcellaneous species). The skeletal 
 structures of Radiolaria are mainly of silica, though horny types (of 
 acanthin) also occur. Both types of Protozoa are well adapted for 
 preservation and extensive deposits of them are known, such as the 
 Radiolarian beds of Barbados (Miocenic) and the chalk of west- 
 ern Europe (Cretacic). 
 
 (b) Sponges and hydrozoans. These organisms are generally 
 capable of preservation on account of the chitinous material which 
 composes the network of many sponges and forms the perisarc of 
 the Hydrozoa. They are most commonly preserved as carbonaceous 
 
PETRIFACTION OF INVERTEBRATES 1083 
 
 films, but cases of pyritization among the graptolites are not un- 
 common. Such pyritized specimens stand out in relief and afford 
 good material for sectioning. (Wiman-27.) Pyrophyllite also 
 has been found replacing these organisms, which thus became out- 
 lined in white on the dark shales in which they occurred. (Blum-5 : 
 
 In a considerable number of sponges siliceous or calcareous 
 spicules occur, frequently uniting into a solid network, and then 
 preserving the form of the sponge. The siliceous spicules of 
 sponges are sometimes replaced by calcite in the process of fossili- 
 zation. 
 
 (c) Silicification of corals. Most corals are composed of cal- 
 cium carbonate in the form of aragonite, with the exception of 
 the Alcyonaria, which are calcite. Often a small percentage of 
 magnesium carbonate is present. The structure of the corals is 
 frequently very porous, but it is most probable that these pores 
 are first filled by calcium carbonate, and that silicification is a proc- 
 ess of replacement pure and simple. While silicified corals pre- 
 serve the form well, the finer structure is commonly destroyed. 
 The ringed structure, known as Beekite rings and more fully de- 
 scribed under the section on molluscan shells, occurs rarely in 
 corals; the rings seldom occur so abundantly or of such size as in 
 molluscs or brachiopods. Corals are occasionally replaced by other 
 minerals, sphalerite having been most frequently observed. 
 
 (d) The brachiopod shell. In a number of inarticulate brachio- 
 pods the shell consists chiefly of chitin, and here the preservation is 
 similar to that of other chitinous structures. In Lingula, alter- 
 nating layers of chitinous and calcareous matter make up the shell, 
 but in the majority of species the shell is wholly composed of cal- 
 cium carbonate. This is present in the form of calcite. The 
 greater portion of the shell is composed of a layer of fibers or 
 prisms of calcic carbonate which constitutes the inner layer of the 
 shell. Outside of this is a thin lamellar layer of calcic carbonate, 
 covered in turn by the periostracum. or outer corneous film. In 
 a large number of species the shell is traversed by vertical canals 
 or tubules which expand upward and terminate in the lamellar 
 layer, not piercing the periostracum. 
 
 Calcification and silicification occur in the brachiopods as in 
 the mollusc shells, the tubules, when present, forming additional 
 spaces for the infiltration of lime or silica. Details will be men- 
 tioned in the description of molluscs. Nearly all the minerals men- 
 tioned under molluscs have been found replacing brachiopod shells ; 
 i. e., pyrite, galenite, sphalerite, the various iron oxides, barite, etc. 
 
1084 PRINCIPLES OF STRATIGRAPHY 
 
 (e) Shells of molluscs. These are composed of calcareous salts, 
 either carbonate of lime or. mixed carbonate and phosphate of 
 lime, penetrated and bound together by an organic network of con- 
 chiolin. In the Pelecypoda the shell consists of three layers : ( i ) 
 the outer or periostracum, a horny integument without lime; (2) 
 the middle prismatic or porcelaneous layer, consisting of slender 
 prisms perpendicular to the surface and closely crowded; and (3) 
 the inner or nacreous layer, which has a finely lamellate structure 
 parallel to the shell surface. Many pelecypod shells consist en- 
 tirely of aragonite. In Ostrea and Pecten the whole shell is cal- 
 cite, while in some others (Pinna, Mytilus, Spondylus, etc.) the 
 nacreous layer is aragonite, while the prismatic layer is calcite. 
 In the gastropod and cephalopod shell the inner or nacreous layer is 
 often wanting, while the periostracum is generally present. The 
 structure of the middle layer differs much from that of the pele- 
 cypods. The shells are mostly aragonite, except those of a few 
 gastropods (Scalaria and some species of Fusus) and a few 
 cephalopods (e. g., the guard of Belemnites), which are of calcite. 
 
 The first process of alteration in the shells is the removal by 
 decay of the horny periostracum covering the shell and of the 
 conchiolin which penetrates the calcareous mass. As a result the 
 shell is rendered porous, which can be proved by applying it to the 
 tongue, when it will be found to be adhesive. This porous condition 
 may be observed in many Miocenic and later shells. The aspect 
 of a shell which has thus undergone the first change is more or less 
 chalky, instead of firm and often shiny, as in the fresh shell. Fre- 
 quently shells composed of aragonite are entirely destroyed, while 
 in those in which both calcite and aragonite occur the latter is dis- 
 solved away while the calcite remains unimpaired. Water carrying 
 salts in solution will enter the pores and there deposit its mineral 
 matter, until the pores are filled. If the matter in solution is car- 
 bonate of lime, this process of infiltration will result in the complete 
 calcification of the shell, whereby the finest structural details will 
 be fully preserved. Those portions of the shell which originally 
 were aragonite may be changed to calcite. In some cases, however, 
 the whole shell is converted into crystalline calcite, and then the 
 finer structure is destroyed. At other times granular limestone re- 
 places the shells. If, however, the infiltrating substance is silica, 
 the process of fossilization does not stop with the filling of the 
 pores, but from the greater insolubility of the silica it becomes the 
 dominating substance and gradually replaces the more soluble lime. 
 This process is frequently most active around certain centers, and 
 is then indicated by the formation of concentric rings of silica 
 
PETRIFACTION OF MOLLUSC SHELL 1085 
 
 (Kieselringchen), which have been named beekite rings, after Dr. 
 Bee'k, sometime Dean of Bristol, who first called attention to them. 
 These rings often form a regular ornamentation of the surface of 
 shells and have been mistaken for original features. According to 
 T. M. McKenny Hughes (15:^5 ct scq.}, these rings form in a 
 layer */$ to j4-inch thick, just beneath the outside film of lime. 
 Blum (4:190) records cases where the calcium carbonate of the 
 shell is still largely retained, while at many places single tubercles 
 of silica project, surrounded each by one or two rings, but seldom 
 more. This was especially noted in brachiopods. In some cases 
 the shell was changed to chert with only scattered rings. A shell of 
 Or this rectangular is from the Carbonic limestone was wholly silici- 
 fied, the silica appearing in the form of small spheres which are 
 arranged in place of the former radial striations of the shell. A 
 shell of Gryphsea contained several layers of silica in. the form of 
 beekite rings. A Plicatula armata had its inner surface preserved 
 in compact yellowish-brown chert; while its outer surface, with 
 all its original roughnesses, was composed of beekite rings. Pecten 
 vagans showed the reverse, with a layer of stalactitic quartz be- 
 tween the two layers. Area had both outer and inner surfaces made 
 up of beekite rings, while between these layers appeared a porous 
 mass of chert. A specimen of Exogyra reniforniis from the Oxford 
 Oolite was replaced by beekite rings, while Trigonia costata, to 
 which it adhered, was replaced by chert only. Belemnite guards 
 had their surfaces covered with beekite rings, while the interior 
 was still fibrous calcite. Others had been changed entirely to 
 beekite. The rings here had become concentric cylinders, the axes 
 of which coincided with the original calcite fibers. In other cases 
 the guard was composed of a number of concentric layers or fun- 
 nels, each of which was composed of beekite rings. 
 
 So far as present observation goes, there seems to be no in- 
 herent character within the organism or the formation within which 
 it is embedded which determines whether silicification is to be ac- 
 companied by the formation of beekite rings or not. Both cases 
 have been found within the same formation at the same locality and 
 within the same genus. 
 
 Silicified shells are among the most acceptable fossils, for they 
 will readily weather out in relief or even become entirely free, or 
 they may also be easily separated from the enclosing matrix by 
 the use of weak acid. 
 
 A great variety of minerals besides silica replaces the calcium 
 salts of mollusc shells. The chambers of ammonites often con- 
 tain ankerite (Quenstedt), others again are chiefly filled by stron- 
 
io86 PRINCIPLES OF STRATIGRAPHY 
 
 tianite (Sandberger). In the Zechstein of Altenburg shells of 
 Schizodus have been found replaced by malachite, which fills the 
 space between external and internal mold. Gypsum has also oc- 
 casionally served as replacing substance of pelecypods and gastro- 
 pods. Barite is not an uncommon replacing agent of molluscan as 
 well as brachiopod shells and other hard structures. In the Lias 
 of Whitby, England, the ammonites are commonly replaced by 
 barite, colored brownish by bituminous matter. Celestite or angle- 
 site more rarely takes the place of barite. Vivianite not uncom- 
 monly replaces the guards of Belemnites in the New Jersey Creta- 
 cic, as well as shells of other molluscs. Even wulfenite has been re- 
 corded as replacing the shell of an Isocardia. Iron pyrite or marca- 
 site is a common replacing agent of mollusc shells, especially those of 
 ammonites. This substance often becomes altered to limonite, and 
 not infrequently disintegrates altogether, where not protected from 
 the air; and thus beautiful fossils are destroyed. Blum records the 
 case of an Avicula in which the outer surface was pyrites and 
 the inner calcite. Sphalerite, and, rarely, smithsonite, galenite, and 
 other metallic salts, replace the shells of pelecypods and gastropods 
 and, more rarely, of cephalopods. In the Cote-d'Or, a Liassic 
 pelecypod has been found completely replaced by specular hema- 
 tite, while ordinary red hematite is not infrequently found replacing 
 mollusc shells. Chlorite has been found replacing shells in several 
 cases. In the Tertiary beds of Aragon, Spain, Planorbis has been 
 found replaced by native sulphur (Blum-?:///, if 6) ; and Tertiary 
 Helix from near Madrid has been reported replaced by meerschaum 
 or sepiolite. 
 
 (f) Crustaceans, Merostomes, Insects, etc. As has been noted 
 above, the exoskeleton of Crustacea is composed of chitin impreg- 
 nated with calcium carbonate and phosphate. Sometimes the chitin 
 carbonizes and a black mass of carbon mixed with lime remains, 
 which is susceptible of a high polish. Again, the organic matter may 
 be entirely removed and replaced by calcium carbonate or other min- 
 erals. Thus trilobite tests are sometimes changed entirely to 
 crystalline calcite. Pyrite not infrequently replaces the tests of tri- 
 lobites, as in the famous specimens of Triarthrus becki from near 
 Rome, New York, discovered by Valient, in which Matthew and 
 Beecher have found the antennae and legs beautifully preserved, the 
 whole test having become pyritized. The exoskeletons of mero- 
 stomes correspond closely to those of Crustaceans. The insect body 
 is rarely preserved, except the wings and the elytra of beetles, owing 
 to the absence of mineral matter. 
 
 (g) Echinoderms. This class of animals is characterized by the 
 
PETRIFACTION OF ECHINODERMS 1087 
 
 possession of calcareous dermal plates wholly composed of calcite, 
 which in many groups form a solid test or enclosure for the main 
 mass of viscera within. The plates are not firmly united with each 
 other, but they have the power to grow and change form during 
 the life of the individual. A characteristic feature of all the skele- 
 tal parts is their extreme porosity. This is true of the test and 
 the spines of the sea-urchin as well as of the calyx, arms, and 
 stem of the.crinoids. The porosity shows in section, and it is also 
 indicated by the fact that the specific gravity of a recent Cidaris 
 spine, with its pores unfilled by water, is only 1.46, while the com- 
 pletely calcified spine has a specific gravity of 2.7. The hollow 
 spaces constitute about 43 per cent, of the spine. (Haidinger, 
 Blum-4:/di.) During the life of the animal the pores in the cal- 
 careous tissue are occupied by organic matter (chitin), which is 
 removed by decay after death. Furthermore (Haidinger), each 
 skeletal element of the echinoderm test is composed of an individual 
 crystal, the crystalline axis of which is coincident with the organic 
 axis; and the new lime which fills the pores crystallizes in con- 
 tinuity with the calcite of the original structures. As a result, per- 
 fect cleavage is obtained in the skeletal parts, each plate or spine 
 having virtually become a perfectly cleaving calcite fragment. The 
 axis of the crystal coincides with the organic axis of the part. 
 (Hessel, Blum.) In crinoid stems the cleavage often shows a rota- 
 tion of axis in the successive joints, so that corresponding cleavage 
 planes make an angle with each other. (Blum-4:/<5i.) Accord- 
 ing to investigations carried on by Dr. A. F. Rogers (21) the 
 twisting is sometimes such as to place the crystals composing the 
 successive joints into a twinning position. At other times it is ir- 
 regular, and again in some species there is no twisting at all. 
 
 Silicification of echinoderms occurs more rarely. When it does 
 occur, beekite rings, while present, are often less pronounced and 
 abundant than in molluscs or brachiopods. (Blum-4:/p^.) 
 
 Pyrites occasionally replaces echinoderm structures. Thus pyr- 
 itized crinoid stems are not uncommon in some formations. Pyri- 
 tized spines of Cidaris have been recorded from the Oolite of Helgo- 
 land. (Blum-4:^o^.) 
 
 Entire specimens of Liassic Pentacrinites are found in the sa- 
 propellutytes of Holzmaden, Wiirttemberg, replaced by iron di- 
 sulphide. 
 
 Cerussite (lead carbonate) has been found as a frequent re- 
 placing agent of crinoid remains in the lead-bearing formations of 
 the department of Kielce, southwestern Russia. These replaced 
 remains commonly have the aspect of crystals of this mineral, with 
 
io88 PRINCIPLES OF STRATIGRAPHY 
 
 which they occur loose in the gange of the ore-beds. (Blum- 
 4:209.) 
 
 (h) Vertebrates. The bones of vertebrates contain much cal- 
 cium phosphate with the calcium carbonate, the whole being bound 
 together by the organic ossein, or bone-cartilage. According to 
 Berzelius, the bones of mammals consist of: bone cartilage 32.17 
 per cent. ; ducts 1.13 per cent. ; basic phosphate of lime with a trace 
 of fluoride of calcium, 54.04 per cent. : carbonate of lime, 11.30 per 
 cent.; phosphate of magnesia, 1.16 per cent.; and carbonate of 
 sodium with a trace of the chloride, 1.20 per cent. The organic 
 substance is replaced by the mineralizer, which is commonly calcium 
 carbonate. Sometimes complete crystallization takes place. Among 
 the bones found in the gypsum beds of the Paris basin and other 
 regions many had been more or less impregnated with gypsum. 
 
 Pyritized skeletons of Ichthyosaurs, Plesiosaurs and other rep- 
 tiles, as well as higher types, are common. Where marcasite is the 
 replacing agent decomposition readily sets in and, if the matrix 
 is a clay slate (argillutyte), alum efflorescence marks the progress 
 of this decay. 
 
 Chalcopyrite is common as a coating of fish remains in Thur- 
 ingia and Hessia, though seldom wholly replacing them. Bornite 
 occasionally performs the same office. Native copper sometimes 
 results from the alteration of these coatings. Cinnabar sometimes 
 occurs in the same manner as the copper ores, seldom completely 
 replacing the fish remains. 
 
 The teeth of mammals are rich in phosphate of lime, 60 per 
 cent, or more of this salt being present. To the large proportion 
 of this substance the durability of the teeth is attributable, they 
 being among the most frequently preserved parts of mammals. The 
 enamel of the teeth contains a somewhat larger percentage of phos- 
 phate of lime than the dentine, a difference which is expressed in 
 the diverse degrees of preservation of these parts. (D'Orbigny- 
 
 n:57.) 
 
 Eggs of vertebrates have not infrequently been found well 
 preserved. Examples are: the eggs of the Moas of New Zealand, 
 Chelonian eggs from the Tertiary of Auvergne, France, in which 
 the shell was filled with mud which subsequently hardened ; the 
 Miocenic egg from South Dakota described by Farrington (12), 
 which was completely silicified, and the fossil egg of Quaternary 
 age from Arizona, described by Morgan and Tallmon (18), in 
 which the shell is perfectly preserved, showing the same structure 
 found in modern hen's eggs, the shell agreeing in composition 
 with that of the egg of the wild goose. The interior with the 
 
SPECIAL MODES OF PRESERVATION 1089 
 
 exception of a small space near the periphery was rilled solidly 
 with a beautiful crystalline mass of the mineral colemanite. "In 
 several places next the shell a semi-fluid layer of bitumen occurs, 
 which probably represents the original organic matter within the 
 shell." 
 
 Excessive silicification. 
 
 In some cases, notably in the Carbonic strata of the Mississippi 
 Valley region, it has happened that silica has been deposited to 
 excess in crinoids, shells or corals, with the result that the original 
 form has been wholly destroyed, the fossil at the same time swell- 
 ing out enormously. This excessive deposition goes on more par- 
 ticularly along lines of fracture, or, as in the crinoid calices, 
 between the component plates. These become more and more 
 separated as the deposition of silica goes on, and they also become 
 sunken below the level of the network of silica. Eventually they 
 are probably buried in the accumulation of silica which closes over 
 them. Thus from a small fossil in which all the plates are discerni- 
 ble, a large mass of structureless silica is formed, which seldom 
 gives a clue to its origin. (Bassler-i.) 
 
 Molds and Casts. Whenever organisms are buried in material of 
 sufficient plasticity to adapt itself to the contours of the buried 
 bodies, molds of the exteriors of these bodies will be made. Such 
 molds may be temporary or they may be persistent ones. Lutace- 
 ous material generally furnishes the most perfect molds. Even soft 
 tissues, when encased in a matrix which solidifies rapidly enough, 
 may leave a mold behind after decay. Thus the bodies of human 
 beings buried in the volcanic mud which overwhelmed Herculaneum 
 and Pompeii left behind a perfect mold of their exterior. Again, 
 the calcareous tufa, forming constantly in many portions of the 
 earth, encloses leaves, mosses, or even fish and other animals and 
 covers them with a crust of lime. On the subsequent decay of 
 the enclosed body a perfect mold of its exterior is commonly pre- 
 served from which an artificial cast could be made. Viscous lava 
 also may flow around and enclose a foreign body, which, if it is 
 able to withstand the heat of the molten mass, may leave a distinct 
 mold or impression. Impressions of medusae are known from the 
 Cambric of the southeastern United States (Walcott-25). When 
 two valves of a bivalve mollusc become buried in juxtaposition, the 
 space between them is filled with mud and thus an internal mold 
 is produced. The same occurs in gastropods, in cephalopods and 
 in other shelled animals, and may also be found in trilobites and 
 
1090 PRINCIPLES OF STRATIGRAPHY 
 
 other Crustacea. This mold of the interior is commonly spoken 
 of as a "cast," which is wholly erroneous, since the cast reproduces 
 the original in a new substance, whereas the mold is a reverse 
 copy. Between the external and internal mold a cast may be formed 
 by infiltration of mineral matter or by artificial means. Not un- 
 commonly the removal of the shell by solution is followed by a 
 closing of the cavity between the external and internal mold, owing 
 to the pressure to which the enclosing rocks are constantly subjected. 
 In such cases, the more strongly marked surface features will be 
 impressed upon the smoother surface, or, in general, the features 
 of the exterior will be impressed on the mold of the interior, which 
 thus shows the normal external features, though weakened, to- 
 gether with a reversed impression of the interior. This, as shown 
 by J. B. Woodworth, is illustrated by many Palaeozoic mussels, 
 which are represented by internal molds (Steinkerne). These show 
 the lines of growth and other features of the exterior of the shell, 
 and, on the same specimen, may be seen the mold of the scars mark- 
 ing the former attachment of the mussel. 
 
 In the Tampa beds of Florida natural casts of corals occur. 
 The original corals have been removed by solution, but have left 
 behind hollow molds in which afterward geodes of chalcedony were 
 formed, the exterior of which accurately reproduces in silica 
 the form of the corals. On the whole, while natural molds both 
 external and internal are common, and characteristic of nearly 
 all porous rocks, natural casts are correspondingly rare. It should, 
 however, be noted that pseudomorphs are closely akin to casts as 
 here defined, since in them the replacement is pari passu with the 
 removal of the original substance of the shell or other hard struc- 
 ture, while in normal casts complete removal of the original sub- 
 stance precedes deposition of the new material. 
 
 2. Tracks, Trails and Burrows of Animals. 
 
 Tracks. These are made by vertebrates walking or hopping 
 along the soft sand or mud, which will register their footprints. 
 If the mud is very soft the footprint will be closed again by the 
 flowage of the mud, but, if it is viscous, or so nearly dry as to 
 remain permanent, the footprints may readily be preserved. Nu- 
 merous reptilian footprints are known from the Newark sandstones 
 of the Connecticut Valley and the related district of New Jersey. 
 Lull (16) believes that these may have been partially hardened by 
 the heat of an underlying lava sheet, which was only recently 
 
TRACKS, TRAILS AND BURROWS 1091 
 
 covered by sediments and had not yet cooled completely. This is 
 not necessary, however, since, as shown in an earlier chapter, foot- 
 prints may be preserved for a long period by mere drying of the 
 mud. Even the delicate impressions of the web membranes of 
 the foot were frequently preserved, which seems to indicate that 
 the arenaceous mud must have been fairly hard and resistant 
 before the next layer of sand was spread over it. This later layer 
 on its under side furnishes accurate impressions in relief of the 
 footprint, which, though rudely reproducing the form of the foot 
 which made the impression, reproduces the impression in reverse. 
 Since the original fossil is the impression (of which there may be 
 many made by one individual) and not the animal's foot, the relief 
 impression of it must be considered a mold and not a cast. 
 
 Trails. These are made by animals crawling over the mud and 
 dragging their bodies along. Jelly-fish floating in shallow water 
 may have their tentacles dragging along over the bottom, thus 
 leaving distinct impressions. Plants are not infrequently dragged 
 along over the shallow sea-bottom, with the result that a certain 
 type of trail is made on the mud which may be indistinguishable 
 from similar trails made by floating animals. Even attached plants, 
 like the beach grass on the sand-dunes, may have a very charac- 
 teristic semi-circular trail when swung about by the wind. Sea- 
 weeds partly buried on an uncovered mud flat may be moved by 
 the wind and so 'produce similar markings. These may, in some 
 instances, be preserved, as appears to have been the case in the 
 structures described as Spirophyton from the Palaeozoic rocks of 
 North America and elsewhere. 
 
 Burrows. While tracks and trails are made by animals in 
 transit, burrows are the temporary or permanent abodes of animals. 
 At the end of many trails of molluscs or Crustacea a mound is 
 found which marks the place where the creature has temporarily 
 buried itself in the sand. This type of burrow is not generally 
 well preserved, though under favorable conditions it may be found. 
 At the end of a peculiar trail on the Potsdam sandstone of New 
 York, known as Climactichnites, Woodworth (29) has discovered 
 an oval impression which he considers to have been made by 
 the animal in resting. This may possibly represent the collapsed 
 burrow. 
 
 The remarkable structures known as Daemonelix which occur 
 in the Miocenic deposits of the Nebraska region and which were 
 first described as sponges and have often been considered as plants, 
 are probably the burrows of some species of burrowing mammal. 
 The strata in which they occur are of the continental type of de- 
 
1092 PRINCIPLES OF STRATIGRAPHY 
 
 posit and the skeletons of rodents have been found in the expansion 
 at the base of the erect spiral. The material which has filled the 
 burrow has solidified and now forms a solid core or mold of the 
 original burrow. It should, however, be said that sections of the 
 core disclose what appears to be a cellular structure, which has led 
 to the supposition that the Dsemonelix is not a burrow but a plant, 
 which grew around the skeleton and has been preserved in the atti- 
 tude of growth. 
 
 The borings of sponges in shells (Clione) and the excavations 
 made by molluscs and echinoderms in wood and stone represent 
 
 FIG. 261. Two views of a typical example of Dccmonclix circumaxilis, from 
 the Miocenic beds of Nebraska. (After Barbour.) 
 
 permanent lodgments of the organisms, and are more nearly of 
 the grade of artificial structures than is the case with the burrows 
 before mentioned, which are more transient, and more nearly re- 
 lated to trails made in transit. For illustration of the burrows of 
 echinoids of limestone in Brazil, see Branner (8). 
 
 Burrows like the Devil's Corkscrew, above described, if, indeed, 
 they are burrows, and like the borings of aquatic animals, are pre- 
 served by reason of the character of the material in which they 
 were excavated. Worm-tubes, on the other hand, so characteristic 
 of the sandy and muddy beaches, are maintained by a lining or 
 cement of mucus, secreted by the animal. These, therefore, 
 carry us a step further into the class of undoubtedly "artificial 
 structures." 
 
ARTIFICIAL STRUCTURES; COPROLITES 1093 
 
 3. Artificial Structures. 
 
 Beginning with the worm-tubes already mentioned, or even with 
 the excavations made by some animals, we have this type of fossil 
 increasing in importance as we rise in the scale of organic being. 
 Even as far down as the group of rhizopods we find many types 
 building shells by cementing foreign particles with the aid of a 
 secretion. This type of habitation is analogous to the worm-tube 
 already mentioned. Though represented in most classes of animals, 
 it is not until we reach man that these artificial structures assume 
 any great importance. 
 
 Thus the implements of stone, shell, bone or metal, the pottery 
 and the copper, bronze and iron vessels; the beads and other orna- 
 ments ; the coins and the habitations of man from the rude exca.va- 
 tion in the rock to the buried cities of historic time, with all their ac- 
 cessories, belong to this type of fossils. This group, therefore, falls 
 largely in the province of Anthropology, or the science which is 
 concerned with man in all his relations, including his palaeontology. 
 
 4. Coprolites. 
 
 The excrements of certain animals have a definite and recogniz- 
 able form, and so become valuable indices to the former presence 
 of such animals. Most important among these are the coprolites 
 of fishes and reptiles, the latter constituting important fossils in 
 the Mesozoic rocks. Very much concerning the food of the ani- 
 mal can often be learned from the remains found within the copro- 
 lite. The excrements or "castings" of worms also belong here. 
 They generally consist of cord-like masses of molded sand which 
 have passed through the intestine of the worm and from which 
 the nutrient organic matter has been abstracted. They cover some 
 modern beaches in great quantities, and are not infrequently pre- 
 served. Certain echinoderms, particularly holothurians, have rec- 
 ognizable excrements. Rothplotz has found an abundance of 
 calcareous rods in the bottom deposits of Great Salt Lake, which 
 he regards as excrements of Artemia, an abundantly represented 
 crustacean in this body of water. They closely resemble known 
 excrements of Artemia, but are calcareous, since the species of the 
 Salt Lake are supposed to feed on calcareous algae. 
 
1094 PRINCIPLES OF STRATIGRAPHY 
 
 MECHANICAL DEFORMATION OF FOSSILS. 
 
 Wherever rocks containing fossils have been under pressure, 
 or have, through other means, suffered mechanical disturbances, 
 the fossils commonly show a more or less pronounced deformation. 
 Two types of deformation may be considered: (i) that due to 
 the normal desiccation and consequent shrinking of the rocks in 
 otherwise undisturbed regions, and (2) that due to erogenic dis- 
 turbances. The first type is especially marked in shales, and is due 
 to the vertical pressure exerted by the overlying rock and the verti- 
 cal shrinking of the shales upon the loss of water. Shells of 
 brachiopods and pelecypods are commonly flattened out, while gas- 
 tropods, cephalopods and trilobites are most frequently distorted by 
 this vertical pressure. The amount of compression can sometimes be 
 estimated by noting the sagging of the strata on either side of a con- 
 cretion enclosed by them. Again, it may be estimated from a com- 
 parison of the compressed shell with uncompressed examples from 
 the same formation, but preserved in limestone bands or lenses. The 
 latter have suffered little or no vertical compression on account of 
 the fact that the component grains of the rock were already as firmly 
 packed when the rock solidified as they were ever likely to be. 
 
 The second group begins with the deformations due to horizon- 
 tal slipping within a stratum, owing to the pressure of a superin- 
 cumbent mass. Under such circumstances slickensides are fre- 
 quently produced within a given formation, and fossils may readily 
 be affected by such movements. Lateral compression of the strata, 
 either slight or sufficient to produce foldings, will distort the fossils 
 embedded in them arid not infrequently alter their form so that 
 they are no longer recognizable. A brachiopod, for example, by 
 compression may assume the outline of a pelecypod, and may readily 
 be mistaken for one. When, through strong compression, cleavage 
 is induced in a given stratum, the fossils of that bed may become 
 largely or entirely destroyed. The same is true if metamorphism 
 affects the strata, though occasionally, as in the Palaeozoic of Scan- 
 dinavia, fossils are found in schists and other metamorphic rocks. 
 
 INDEX FOSSILS. 
 
 Fossils which serve to indicate definite geological horizons are 
 called Index Fossils (German, Leitfossilien). The best index 
 fossils for marine formations are furnished by invertebrates, though 
 
INDEX FOSSILS 1095 
 
 marine vertebrates, when well preserved, are also good horizon 
 markers. The very detailed knowledge of vertebrate anatomy 
 required, however, to determine the genera and species makes verte- 
 brate remains available only to the trained specialist. Plants fur- 
 nish good and reliable index fossils for terrestrial or delta forma- 
 tions, although their distribution is much more subject to limita- 
 tions, owing to climatic influence. The same may be said to be 
 true of land vertebrates. The subject is further discussed under 
 correlation, in .Chapter XXXIL 
 
 BIBLIOGRAPHY XXX. 
 
 1. BASSLER, R. S. 1908. The Formation of Geodes with remarks on the 
 
 Silicification of Fossils. Proceedings of the United States National 
 Museum, Vol. XXXV, pp. 133-154. 
 
 2. BASSLER, R. S. 1910. Adequacy of the Paleontologic Record. The 
 
 Paleontologic Record, pp. 6-9, reprinted from Popular Science Monthly. 
 
 3. BERNARD, FELIX. 1895. Elements de Paleontologie. 
 
 4. BLUM, J. REINHARD. 1843. Die Pseudomorphosen der Mineralogie, 
 
 and First Appendix (Erster Nachtrag) 1847. Stuttgart. 
 
 5. BLUM, J, R. 1852. Pseudomorphosen, Second Appendix. 
 
 6. BLUM, J. R. 1863. Pseudomorphosen, Third Appendix. 
 
 7. BLUM, J, R. 1879. Pseudomorphosen, Fourth Appendix. 
 
 8. BRANNER, JOHN C. 1905. Stone Reefs on the Northeast Coast of 
 
 Brazil. Bulletin of the Geological Society of America, Vol. XVI, pp. 
 
 I-I2, pis. I-II. 
 
 9. CALVIN, SAMUEL. 1910. Adequacy of the Paleontologic Record. The 
 
 Paleontologic Record, pp. 2-6. Reprinted from Popular Science Monthly. 
 
 10. DEAN, BASHFORD. 1902. The Preservation of Muscle Fibers in 
 
 Sharks of the Cleveland Shale. American Geologist, Vol. XXX, pp. 
 273-278, pis. VIII and IX. 
 
 11. D'ORBIGNY, ALCIDE. 1849. Cours Elementaire de Paleontologie et 
 
 de Geologic Stratigraphiques. 3 vols. Victor Masson, Paris. 
 
 12. FARRINGTON, OLIVER C. 1899. A Fossil Egg from South Dakota. 
 
 Field Columbian Museum. Publication 35, Vol. I, No. 5, Geol. Series 
 pp. 192-200, pis. XX-XXI, figs. 1-2. 
 
 13. GRABAU, A. W. 1899. Palaeontology of Eighteen Mile Creek. Bulle- 
 
 tin of the Buffalo Society of Natural Sciences, Vol. VI. 
 
 14. GRABAU, A. W. and SHIMER, H. W. 1909. North American Index 
 
 Fossils, Invertebrates. Vol. I. 
 
 15. HUGHES, T. McKENNY. 1889. On the Manner of Occurrence of 
 
 Beekite and Its Bearing upon the Origin of Siliceous beds of Palaeozoic 
 Age. Mineralogical Magazine, Vol. Ill, No. 40, pp. 265-271. 
 
 16. LULL, RICHARD S. 1904. Fossil Footprints of the Jura-Trias of 
 
 North America. Memoirs of the Boston Society of Natural History, 
 Vol. V, 97 pp., i pi. 
 
 17. MEAD, CHARLES W. 1907. Peruvian Mummies. American Museum 
 
 of Natural History. Guide Leaflet No. 24. 
 
1096 PRINCIPLES OF STRATIGRAPHY 
 
 18. MORGAN, WILLIAM C., and TALLMON, MARION C. 1904. A 
 
 Fossil Egg from Arizona. California University, Department of Geology, 
 Bulletin, Vol. Ill, pp. 403-410, 2 pis. 
 
 19. NICHOLSON, H. ALLEYNE, and LYDEKKER, RICHARD. 1889. 
 
 Manual of Palaeontology. 2 vols. Third edition. 
 
 20. REIS, OTTO M. Die Coelacanthinen, mit besonderer Beriicksichtigung 
 
 der im weissen Jura, Bayerns Vorkommenden Arten. Palaeontographica 
 XXXV, pp. 1-96, pis. I-V. 
 
 21. ROGERS, AUSTIN F. Private Communication. 
 
 22. ROTH, I. 1879. Allgemeine und chemische Geologic, Vol. I. Especially 
 
 literature on fossilization of plants. 
 
 23. STEDMANN, J. M., and ANDERSON, J. T. 1895. Observations on a 
 
 so-called petrified man, with a report on chemical analysis by J. T. 
 Anderson. American Naturalist, Vol. XXIX, pp. 326-335. 
 
 24. STEINMANN, GUSTAV. 1903. Einfuhrung in die Palaeontologie. 
 
 Wilhelm Engelmann, Leipzig. 
 
 25. WALCOTT, CHARLES D. 1898. Fossil Medusae. Monograph of the 
 
 United States Geological Survey. XXX. 
 
 26. WALCOTT, C. D. 1911. Cambrian Geology and Palaeontology. Smith- 
 
 sonian Institution Collections, Vol. 57. 
 
 27. WIMAN, C. 1895. Ueber die Graptolithen. Geol. Inst. Upsala, Bull., 
 
 Vol. II, No. 2. 
 
 28. WHITE, C. H. 1905. Autophytography : a Process of Plant Fossilization. 
 
 American Journal of Science, 4th series, Vol. XIX, pp. 231-236. 
 
 29. WOOD WORTH, JAY B. 1903. On the Sedentary Impression of the 
 
 Animal whose trail is known as Climactichnites. New York State 
 Museum Bulletin 69, pp. 959-966, 2 pis,, 3 figs. 
 
G. PRINCIPLES OF CLASSIFICATION AND COR- 
 RELATION OF GEOLOGICAL FORMATIONS. 
 
 CHAPTER XXXI. 
 
 NOMENCLATURE AND CLASSIFICATION OF GEOLOGIC 
 FORMATIONS. 
 
 DEVELOPMENT OF CLASSIFICATIONS. 
 
 The history of the earth is written in the strata of the earth's 
 crust. Like all histories, it is a continuous succession of events, but 
 the record of these events is never complete and seldom even un- 
 broken in any given region. It is of the first importance to the 
 chroriographer of earth history that he should find a continuous 
 record, in order that he may have a measure by which to judge 
 the partial records of -any given region and to discover the breaks 
 and imperfections in the local records thus presented. (Grabau-5.) 
 The question then arises : under what conditions may we expect to 
 obtain a continuous record and how are we to guard against the 
 introduction of errors? 
 
 We have, in the first place, to deal with the time element in the 
 history of the earth. In human history the time element is a mea- 
 surable factor, its duration being recorded in years and centuries. 
 No such precise measurements are possible in earth history, al- 
 though several attempts have been made to reduce geologic time to 
 units of human chronology. (For methods and results, see beyond.) 
 But while we cannot now, and probably may never, hope to divide 
 geologic time into centuries and millenniums, we can divide it into 
 periods, each of which has its own special significance in the his- 
 tory of the earth. The basis for such subdivision was long ago 
 found in the succession of organic types from relatively simple to 
 highly complex forms. As long as the doctrine of special creation 
 of organic types was held, and with it the belief in successive acts 
 of creation, and more or less complete extinction of the faunas and 
 
 1097 
 
1098 PRINCIPLES OF STRATIGRAPHY 
 
 floras preceding, it was a comparatively simple matter to divide 
 the earth's history into periods or eras characterized by these suc- 
 cessive changes in the ancient inhabitants of the earth. That there 
 was much apparent justification for this belief in the characters of 
 the faunas and floras found in the strata of the earth cannot be 
 questioned. Thus, trilobites are even to-day unknown from strata 
 later than Palaeozoic, nor until recently have strata containing am- 
 monites been recognized as older than the Mesozoic. That sudden 
 disappearances of whole organic assemblages, and the equally sud- 
 den appearance of others of a different type occur repeatedly are 
 matters of common observation ; but it was not always recognized 
 that such sudden changes are seldom universal in extent, though 
 generally traceable over wide areas. While abrupt changes in or- 
 ganic content of the strata have come to be generally regarded as 
 marking the lines between the greater divisions in the earth's history, 
 they are correlated with, and, in fact, dependent on, widespread 
 physical breaks in the continuity of the strata which compose the 
 earth's crust. Such physical breaks were, indeed, taken as the planes 
 of division by the pioneers in stratigraphy, who considered strati- 
 graphic succession rather than geologic chronology. Thus, about 
 the middle of the i8th Century Lehman, a German miner (u) 
 proposed a threefold division of the rocks of the earth's crust into 
 (i) "Primitive" (Primitiv) or "Urgebirge," including all the igne- 
 ous and metamorphic rocks in which there was no sign of life and 
 which showed no evidence of having been derived from the ruins of 
 preexisting rocks, and, therefore, of chemical origin, antedating the 
 creation of life; (2) Secondary, comprising the fossili-ferous strata, 
 and largely composed of mechanical deposits, produced after the 
 planet had become the habitation of animals and plants; and (3) 
 Alluvial deposits, due to local floods, and the deluge of Noah. 
 Fiichsel, a contemporary of Lehmann, recognized that certain groups 
 of strata belonged together and constituted a geologic formation. 
 He held that each formation represented an epoch in the history of 
 the earth, and thus he brought into consideration the time element 
 in the earth's history. Half a century later Werner introduced his 
 "transition formations" between the primitive and secondary rocks, 
 comprising a series of strata, first found in northern Germany, which 
 were intermediate in mineral character between the crystallines and 
 sedimentaries and partook in some degree of the characters of both. 
 This Uebergangsgebirge, or transition formation, consisted princi- 
 pally of clay slates, argillaceous sandstones or graywackes and cal- 
 careous beds, which, in the region studied by Werner, were highly 
 inclined and unconformably overlain by the horizontal Secondary 
 
DEVELOPMENT OF CLASSIFICATION 1099 
 
 strata. The latter, including formations up to the top of the chalk, 
 were called by Werner the Plotsgebirge formation, on account of 
 their horizontally, and because they were the stratified rocks par ex- 
 cellence. The term Plots signifies "a level floor," and had been 
 generally used since the time of Agricola for stratified rocks. With 
 the Flotz were included the trap rocks of the Secondary strata, as 
 subordinate members, these being held by Werner and his followers 
 to be the result of aqueous precipitation. All deposits above the 
 chalk were referred by Werner to alluvial deposits under the desig- 
 nation Angeschwemmtgebirge. Werner's followers later on 
 distinguished a series of strata between the chalk and the alluvium, 
 and applied to this the term Newer Plots (Neues Flotsgebirge). 
 These are the rocks subsequently named "Tertiary" by Cuvier and 
 Brongniart. In the Wernerian terminology, the characters of the 
 strata themselves rather than their time relations were considered, 
 and Fuchsel's term "formation" was applied by Werner and his 
 followers to groups of strata of similar lithic composition. Thus 
 he spoke of limestone formation, sandstone formation, slate forma- 
 tion, etc. The term "transition" strata soon began to take on chron- 
 "ologic meaning, and it was widely applied to rocks older than those 
 designated as Secondary. It was still retained even after it was 
 shown that these strata are not always transitional in mineral char- 
 acter and that strata belonging to the Secondary or even later series 
 had sometimes the mineralogical character of the original Transition 
 rocks. 
 
 At the time of Lyell, the strata of the earth's crust were gen- 
 erally divided into Primary, Transition, Secondary, Tertiary and 
 post-Tertiary. It had become recognized that crystalline and 
 metamorphic rocks were not all of one age, but that some were even 
 newer than the Secondary formation. As a chronologic term, Pri- 
 mary had come to be applied by some to the fossiliferous rocks older 
 than the Secondary, while it had become a matter of some question 
 whether any of the crystalline rocks really antedated the oldest 
 fossiliferous deposits. Lyell, to avoid confusion, used the term 
 Primary Fbssiliferous formation "because the word primary has 
 hitherto been most generally connected with the idea of a nonfos- 
 siliferous rock." About this time the terms "Paleozoic" * "Meso- 
 zoic^ f an d "Cccnozoic' f were introduced to replace the terms 
 Primary Fossiliferous (the former Transition), Secondary and 
 
 * Proposed by Sedgwick, 1838. From ira\cu6s, palaios, ancient, and fwij, 
 zoe, life. 
 
 f Proposed by Philips, 1841, from /?<H>S, mesos, middle; icaivfa, new, recent. 
 The latter was also written Kainozoic. 
 
i ioo PRINCIPLES OF STRATIGRAPHY 
 
 Tertiary, but they met at first with little favor. Palaeozoic was the 
 first to be adopted, while Secondary and Tertiary were still re- 
 tained. Later Mesozoic gradually replaced Secondary, but Tertiary 
 has still retained its hold in geologic literature to the present day. 
 To it the Quaternary * has been added, which comprises the forma- 
 tions designated by Lyell as Post-Pliocene, together with his Later 
 Pliocene or Pleistocene. These have frequently been included with 
 the Tertiary under the term Caenozoic (=Kainozoic), but they have 
 also been separated under the term Psychozoic, introduced by Le 
 Conte, but limited by him to the most recent formations, which in- 
 include abundant remains of man. 
 
 It is thus seen that the classification at first proposed as a rock 
 classification became a chronologic one, as geologists began to 
 perceive that all kinds of rock may be formed during each period 
 of the earth's history. When the fossils of each of these four divi- 
 sions became better known, it was found that each was character- 
 ized by its peculiar assemblage of organisms. It was further 
 found that in most regions the strata of each of these larger sub- 
 divisions were separated from those above or below by a marked 
 unconformity, so that records of disturbances of widespread occur- 
 rence were looked upon as generally marking the dividing lines 
 between the greater subdivisions of the earth's history. The use 
 of unconformities in defining limits of geologic formations was also 
 extended to the further subdivision of the larger units, and, in 
 fact, such breaks have frequently been advocated as the best avail- 
 able criterion. But geologists have pretty generally recognized 
 the fact that a classification based on unconformities is an incom- 
 plete one, and that a complete record of geologic time can be ex- 
 pected only in a series resulting from continuous deposition. Such 
 a series is, however, nowhere obtainable, since in no known region 
 of the earth has there been continuous and uniform deposition. 
 Stratigraphers are thus compelled to construct their typical section 
 from fragments of overlapping sections from all parts of the world. 
 Each fragment thus used in the building up of the typical scale 
 must be complete in itself, and its relationship to the next adjoining 
 fragments of the scale must be determined. 
 
 Selection of the Type Section. 
 
 What, then, are the criteria which must guide us in the selection 
 of our typical section? First and foremost, the section must show 
 
 * Proposed by Morlot in 1854. 
 
CHARACTERISTICS OF TYPE SECTIONS noi 
 
 continuous deposition. No sharp break either lithic or, faunal should 
 occur between the members, but all should be transitional. The 
 character and origin of the strata composing the section must be 
 carefully considered, since all rocks are not of equal value as in- 
 dices of continuous deposition. 
 
 Hydroclastic rocks are by far the most reliable indices of depo- 
 sition, since none other are formed under so uniform an environ- 
 ment. Marine sediments, further, are more reliable than those of 
 fresh water lakes, since the latter are only temporary features of 
 the earth's surface and are preceded and succeeded by conditions 
 which will of necessity destroy the continuity of formation of strata. 
 Thus marine formations alone will serve for the erection of a 
 standard scale, all formations of a continental type, whether of 
 fresh water or of atmo-, anemo-, or pyroclastic origin, must be ruled 
 out of the standard scale. Hence the Old Red Sandstone of Brit- 
 ain, the non-marine Carbonic formations, the Newark, Potomac, 
 Dakota and Laramie formations of North America, are all to be 
 discarded in the making of a true geologic formation scale. Even 
 among marine strata, there are some which must be ruled out, as 
 not furnishing a reliable account of the progress of rock deposi- 
 tion. Thus sandstones and conglomerates, either as basal members 
 or intercalated between a series of clay or lime rocks, are almost 
 sure to introduce an element of uncertainty, if not error, into the 
 section, even if the gradation above and below is a perfect one. 
 As has been pointed out in an earlier chapter, shore-derived silice- 
 ous elastics of coarse grain, when not forming a basal sandstone or 
 conglomerate, can become widespread only by an oscillatory move- 
 ment of the land, which results in a temporary retreat and re- 
 advance of the sea. Such a change involves almost certainly a time 
 interval unrecorded in the section, but represented rather by an 
 unrecognizable break within the terrigenous member itself. An 
 example of such a formation is found in the St. Peter Sandstone 
 of central United States, a formation which in itself represents a 
 disconformity, constantly increasing in magnitude toward the north, 
 where it includes an unrecorded interval elsewhere represented by 
 from 2,000-3,000 feet of limestones. Shore deposits of all kinds 
 should be ruled out in the establishment of a typical section, for 
 they represent local conditions and, therefore, cannot furnish re- 
 liable evidence of the general progress of development. 
 
 Deposits formed in an enclosed basin, whether marine or con- 
 tinental, are likewise unsatisfactory for purposes of establishing 
 a general scale. Such deposits at present included in the standard 
 scale of North American strata are : the Medina and Salina forma- 
 
1 102 PRINCIPLES OF STRATIGRAPHY 
 
 tions of New York, which were formed under local and in part 
 continental conditions, and cannot, therefore, represent a standard 
 by which the more widespread marine conditions existing elsewhere 
 can be measured. Wherever possible, such local formations should 
 be taken out of the standard scale of strata and replaced by forma- 
 tions of purely marine origin. These may, of course, not exist 
 within the limits of the territory for which the scale is made, in 
 which case the old terms, perforce, have to be retained. 
 
 The best example of a truly representative classification of the 
 divisions of a larger formation, which has yet been devised, is that 
 of the Triassic system. In no one region of the world is there a 
 complete representation of marine Triassic strata; in fact, the best 
 known divisions of this system are to a large extent non-marine. 
 But, by a careful study of all the widely dissociated marine mem- 
 bers and their relation to each other, a standard classification, more 
 nearly perfect than that of most other similar formations, has been 
 devised. By its use the various dissociated marine members of 
 each region, as well as the non-marine members, may be measured 
 and the time relation of each to the others and to all may be 
 ascertained. 
 
 Time Scale and Formation Scale. 
 
 While the time scale is thus of primary importance as a stand- 
 ard of comparison, a formation scale is also needed. A formation 
 is a stratigraphic unit, composed in general of similar or closely 
 related strata and characterized by a particular assemblage of organ- 
 isms (fauna or flora). Sometimes a formation may consist of a 
 single stratum more frequently it comprises many strata. The 
 rules recently promulgated by the United States Geological Survey 
 for the government geologists in the preparation of the geologic 
 folios of the United States (18:^5) make the formation the carto- 
 graphic unit, and define it among sedimentary rocks as follows : 
 "Each formation shall contain between its upper and lower limits 
 either rocks of uniform character or rocks more or less uniformly 
 varied in character, as, for example, a rapid alternation of shale 
 and limestone." It is further suggested that, "As uniform con- 
 ditions of deposition were local as well as temporary, it is to be 
 assumed that each formation is limited in horizontal extent. The 
 formation should be recognized and should be called by the same 
 name as far as it can be traced and identified by means of its lith- 
 ologic character, its stratigraphic association, and its contained 
 fossils." 
 
TIME AND FORMATION SCALE 
 
 1103 
 
 Subdivisions of Time and Formation Scales. 
 
 The primary divisions of the geologic time scale are, as we have 
 seen, based on the changes in life, with the result that fossils alone 
 determine whether a formation belongs to one or the other of 
 these great divisions. The primary divisions now generally recog- 
 nized are as follows : 
 
 
 
 C\\A 
 
 Corresponding 
 
 Present name. 
 
 Definition. 
 
 vJlQ 
 
 Equivalent. 
 
 formation as 
 generally used. 
 
 Psychozoic 
 
 Mind-life 
 
 Quaternary* 
 
 Quaternary 
 
 Cenozoic 
 
 Recent-life 
 
 Tertiary 
 
 Tertiary 
 
 Mesozoic 
 
 Mediaeval-life 
 
 Secondary 
 
 Mesozoic 
 
 Palaeozoic 
 
 Ancient-life 
 
 Transition or Pri- 
 
 Palaeozoic 
 
 
 
 mary Fossilifer- 
 
 
 
 
 ous 
 
 . 
 
 Eozoic (or Proterozoic) 
 
 Dawn of life (or ^ 
 
 
 ( Algonkianf 
 
 
 First life) \ 
 
 Primary 
 
 \ 
 
 Azoic 
 
 Without Life J 
 
 
 v. Archaean J 
 
 Corresponding to each time division we have a formational divi- 
 sion, which represents the rock material accumulated during the 
 continuance of that time. As will be seen from the above table, 
 the formation scale now generally in use is made up partly of the 
 old names in vogue during Lyell's time, partly of the newer names, 
 and in part of distinct names applied to the rocks of these divisions 
 by American geologists and adopted by workers in other countries 
 as well. 
 
 A number of terms have been proposed by which the subdivi- 
 sions of the time and formation scale are to be known, but at 
 present there is no unanimity in the usage of these terms. The 
 following are the most important of the proposals made, the num- 
 bering being in the order of magnitude of the categories : 
 
 * In many text-books the Quaternary is included with the Tertiary under 
 Cenozoic, which is not the historic sense of the term. Post-Tertiary time is 
 essentially characterized by the presence of man and may be separated as 
 Psychozoic. 
 
 f Walcott, 1889. From a tribe of North American Indians. 
 
 t Proposed by Dana. 
 
1 104 PRINCIPLES OF STRATIGRAPHY 
 
 1. International Geological Congress. At the first meeting 
 of the Congress in Paris in 1878 a commission was appointed to 
 frame a plan of procedure for the unification of geologic classifi- 
 cation and naming. The recommendations of this Commission, 
 adopted at the Bologna Congress in 1881, as far as they affect 
 the point in question, are as follows. (i) Era Group; (2) 
 Period System; (3) Epoch Series; (4) Age Stage; '(5) 
 
 . . . Assize. No time equivalent for (5) (Assize) was 
 designated. 
 
 During succeeding Congresses proposed modifications of this 
 scheme were discussed until in 1900 the 8th Congress, convened 
 in Paris, accepted the following scheme: 
 
 Chronologic. Stratigraphic. 
 
 i. Era (Eres). i. (No stratigraphic term). 
 
 2. Period (Pe"riode). 2. System (Systeme). 
 
 3. Epoch (fipoque). 3. Series (Series).* 
 
 4. Age (Age). 4. Stage (Etage).f 
 
 5. Phase (Phase). 5. Zone (Zone). 
 
 Periods, and the corresponding systems, have a worldwide value, 
 and are characterized by the development of the organisms during 
 the period, and their entombment in the strata of the system. Pe- 
 lagic faunas, where available, are especially characteristic, owing 
 to their wide distribution and independence of local environments. 
 The termination of the names of periods and systems adopted is ic, 
 ique (French) ; isch (German) ; ico (Spanish, Italian, Portuguese, 
 Roumanian) ; Ex. Cambric (Cambrique, Kambrisch, Cambrico) ; 
 Devonic (Devonique, Devonisch, Devonico) ; also Carbonic (Car- 
 bonique, Karbonisch, Carbonico) ; Cretacic (Cretacique, Kretacisch, 
 Kreide Formation), etc. 
 
 Periods are generally divisible into three epochs each, which are 
 designated by the prefixes Palceo-, Meso-, and Neo-. For Palcco- 
 the term Eo may be used, wherever the name is long and the name 
 itself further abbreviated. (Williams-ig.) Thus, while Palaeocam- 
 bric, Mesocambric and Neocambric are used, Eodevon, Mesodevon 
 and Neodevon, or, Eocret, Mesocret and Neocret, may be used for 
 these longer terms. Locally, series are commonly given names de- 
 rived from typical localities, these ending in ian (ien, Fr., etc.), as 
 the following example will show : 
 
 * German, Abtheilung. f German, Stufe; Italian, piano; Spanish, piso. 
 
STRATIGRAPHIC AND TIME SCALES 1105 
 
 Epoch Local name of series. 
 
 Eastern United States. Western Europe. 
 
 Neodevonic . . . . / Chautauquan 1 f Famennien 
 
 { Senecan / \ Frasnien 
 
 Mesodevonic 
 
 f Erian } f Givetien 
 
 \ Ulsterian J 1 Eifelien 
 
 / Oriskanian 1 f Coblentzien 
 
 Eodevomc 1 Helderbergian Taunusien 
 
 ( Gedmien 
 
 The values of these local series are not always uniform nor 
 equivalent. In practice it is often more convenient to speak of 
 Lower, Middle and Upper Siluric, Devonic, etc., series (German: 
 Unterdevon, Mitteldevon, Oberdevon, etc. ; French Devonien in- 
 fcrieur, Devonien moyen, Devonien superieur, etc.). These terms 
 are commonly employed in a general discussion of the strata of a 
 series. 
 
 Ages and their corresponding stages receive local names. 
 Stages are relatively restricted in areal distribution and dif- 
 ferent countries have different stages corresponding to the same 
 age. 
 
 Stages end in ian (ien, Fr. ; ian, Germ.* ; iano, Spanish, Italian, 
 Portuguese, Roumanian). Thus we have Bartonian, Bartonien, etc. ; 
 Portlandian, Portlandien, etc., stages. 
 
 The stratigraphic division of the fifth order, the zone, is often 
 needed, and this division is named wherever possible after a par- 
 ticular species of organism which characterizes it. Thus we have 
 in the Lias of England the following 17 zones characterized by 
 particular species of ammonites. (Geikie-4:ujj.) 
 
 Ii 7 zone of Lytoceras jurense 
 1 6 zone of Dactylioceras commune 
 15 zone of Harpoceras serpentinus, etc. 
 14 zone of Dactylioceras annulatum 
 
 A/r-jji T- T- f 1 1 zone of Paltopleuroceras spinatum 
 
 Middle Lias or Liassian , A 7 \ , .. , 
 
 | 12 zone of Amaltheus margantatus 
 
 * The German terms are often contracted, instead of Astian Stufe, Astistufe 
 is used. 
 
iio6 PRINCIPLES OF STRATIGRAPHY 
 
 1 1 zone of Liparoceras henleyi, etc. 
 
 10 zone of Phylloceres ibex 
 9 zone of ^Egoceras jamesoni 
 8 zone of Deroceras armatum 
 7 zone of Caloceras raricostatum 
 
 Lower Lias or Sinemurian^ 
 
 6 zone of Oxynoticeras oxynotum 
 5 zone of Arietites obtusus, etc. 
 4 zone of Arietites turneri, etc. 
 3 zone of Arietites bucklandi 
 2 zone of Schlotheimia angulata 
 I zone of Psiloceras planorbe 
 
 In the Trias, too, a number of distinct zones marked by species 
 of ammonites or other fossils are recognized. 
 
 II. Dana's System. In the last edition of his Manual (3:40*5), 
 Professor James D. Dana gives the following classification: 
 
 Chronologic. Stratigraphic. 
 
 I. Aeon (Ex.: Palaeozoic).* I. Series (Ex: Palaeozoic). 
 2. Era (Ex.: Siluric). 2. System (Ex.: Siluric). 
 
 3. Period (Ex.: Palaeo-Siluric). 3. Group (Ex.: Niagaran). 
 
 4. Epoch (Ex.: Clinton). 4. Stage (Ex.: Clinton). 
 
 III. United States Geological Survey. The United States Geo- 
 logical Survey in its ruling of 1903 makes the period the unit of the 
 time scale and correlates with it the system of the formation scale, 
 thus following the usage of the International Congress. The sys- 
 tems recognized are : "Quaternary, Tertiary, Cretaceous, Jurassic, 
 Triassic, Carboniferous, Devonian, Silurian, Ordovician, Cambrian, 
 Algonkian, and Archaean." No complete scheme is formulated, only 
 the following terms being used: 
 
 Chronologic. Stratigraphic. 
 
 I I 
 
 2. Period. 2. System. 
 
 3 3. Series. 
 
 4 4. Group. 
 
 As far as this scheme was developed it is thus seen to correspond 
 to the one promulgated by the International Congress, with the 
 exception that group is used for the division of the fourth order 
 
 * Examples added by the author. 
 
STRATIGRAPHIC TERMINOLOGY 1107 
 
 instead of stage. The terminations of the names of the systems 
 are not altered to correspond to that adopted by the Congress. 
 
 Unification of Terminology. 
 
 In the development of the classification of the geologic forma- 
 tions, the systems were gradually introduced either by intercalation 
 of a previously unknown system between two well-established ones, 
 as the Devonian between the Silurian and Carboniferous; or by 
 the separation of the new system from an older one with which it 
 was formerly included, as Ordovician from Silurian. No uniform 
 method of derivation of these names was followed, though the 
 majority of names had a geographic origin. Neither was uni- 
 formity of termination considered, though among the later-formed 
 names ian was generally selected. This heterogeneous terminology 
 has become so firmly embodied in the framework of stratigraphic 
 classification that it probably will be a long time before we can 
 hope to replace it by a more homogeneous one. Such terms as 
 Carboniferous are wholly out of harmony with the majority of 
 other terms and ought to be discarded. But the adoption of a 
 uniform termination of these names, as suggested by the Congress, 
 and as is widely practiced, particularly in Europe, will do away 
 with the most objectionable part of this terminology and bring it 
 into harmony with the remaining portion of the scheme. In the 
 table on p. 1108 the systems used in this work are given with the 
 termination used by the International Congress, and with it the 
 old heterogeneous termination. The author and derivation of each 
 term is given. (See also table on page 22.) 
 
 A tendency toward splitting up some of the larger systems and 
 uniting others has been shown by many stratigraphers. The 
 Palseocenic has been introduced in the Cenozoic and united with the 
 Eocenic and Oligocenic as Pabeogenic; Miocenic and Pliocenic have 
 been united as Neogenic; and Pleistocenic and Holocenic as Ceno- 
 genic. The Liassic has also been separated as a distinct system by 
 some European stratigraphers. Recently this method of subdi- 
 vision has been carried to great extremes in the works of Schuchert 
 and Ulrich, to which the student is referred (14; 17). The sub- 
 divisons advocated by Ulrich are more extreme than the facts seem 
 to warrant, and they have not generally been adopted. 
 
 Local Stages arid Substages. Generally, detailed study of a 
 given region will show the occurrence of numerous local forma- 
 
iio8 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 ERAS. 
 
 SYSTEMS 
 Chiefly accord- 
 ing to recom- 
 mendation of 
 International 
 Congress. 
 
 SYSTEMS 
 Old usage. 
 
 FOUNDER. 
 
 ORIGIN OR DERIVATION 
 
 OF NAME. 
 
 Psychozoic or j 
 Quaternary "i 
 
 Holocenic 
 Pleistocenic 
 
 Recent 
 Pleistocene 
 
 Portuguese Com- 
 mitted. C. (1885) 
 Lyell (1839) 
 
 Wholly recent.* 
 Most recent.* 
 
 f 
 
 Pliocenic 
 
 Pliocene 
 
 Lyell (1833) 
 
 More recent.* 
 
 Cenozoic 
 
 Miocenic 
 
 Miocene 
 
 Lyell (1833) 
 
 Less or intermediate re- 
 
 or 
 
 
 
 
 cent.* 
 
 Tertiary 
 
 Oligocenic 
 Eocenic 
 
 Dligocene 
 Eocene 
 
 Bey rich (1854) 
 Lyell (1833) 
 
 Few recent.* 
 Dawn of recent.* 
 
 
 Cretacic 
 
 Cretaceous 
 
 Omalius d'H alloy 
 
 Greta chalk (chalk bear- 
 
 
 
 
 (1822) 
 
 ing) 
 
 
 Comanchic 
 Jurassic 
 
 3omanchean 
 Jurassic 
 
 R. T. Hill (1893) 
 Alexander von 
 Humboldt (i?95) 
 
 Comanche Indians 
 Jura Mountains 
 
 
 Triassic 
 
 Triassic 
 
 F. von Alberti, 
 
 Original three-fold divi- 
 
 
 
 
 (1834) 
 
 sion 
 
 
 Permic 
 
 Permian 
 
 Murchison (1841) 
 
 Government of Perm , 
 
 
 
 
 
 Russia 
 
 
 Carbonic 
 
 Carboniferous 
 (Pennsylvanian) 
 
 Conybear (1822) 
 H. S. Williams 
 
 Coal-bearing 
 Pennsylvania 
 
 
 
 
 (1891) 
 
 
 
 Mississippic 
 
 Sub-Carbonifer- 
 
 D.D.Owen (1852) 
 
 Below the coal-bearing 
 
 
 
 ous (Mississip- 
 
 
 strata 
 
 Palaeozoic or 
 Primary 
 Fossiliferous 
 
 Devonic 
 Siluric 
 
 pian) 
 Devonian 
 
 Silurian (Upper 
 
 A. Winchell (1870) 
 Sedgwickand Mur- 
 chison (1839) 
 Murchison (1835) 
 
 Mississippi valley 
 Devonshire, England 
 
 Ancient tribe of Silures 
 
 
 
 Silurian) 
 
 
 inhabitingSouth Wales, 
 
 
 
 
 
 etc. 
 
 
 Ordovicic 
 
 Ordovician 
 
 Lapworth (1879) 
 
 Ancient tribe of western 
 
 
 
 (Lower Silurian) 
 
 Murchison (1835) 
 
 England 
 
 
 
 (Up'r Cambr'n) 
 
 Sedgwick (1835) 
 
 
 
 Cambric 
 
 Cambrian 
 
 Sedgwick (1835) 
 
 Old Roman Province of 
 
 
 
 
 
 Cambria, N. Wales 
 
 Thus names were derived, in part, from the age of the formation, in part, from their lithic 
 character and contents, in part from typical localities, and in part from former inhabitants of 
 typical localities. 
 
 tions of the value of stages or substages, as in the following case: 
 
 Hiatus and disconformity 
 
 {Lucas dolomite 
 Amherstburg limestone 
 Anderdon limestone 
 Flat Rock dolomite 
 
 Upper Siluric or Monroan.^ 
 (Neosiluric) 
 
 Hiatus and disconformity 
 
 Sylvania sandstone 
 
 Hiatus and disconformity 
 
 f Raisin River series 
 Bass Island I Put-in-Bay series 
 Series 1 Tymochtee shale 
 
 I Greenfield dolomite 
 
 Hiatus disconformity 
 * Referring to the percentage of modern organisms present. 
 
STRATIGRAPHIC NOMENCLATURE 
 
 1109 
 
 Where fully developed most formations include several zones. 
 Thus, in Maryland and West Virginia, the Oriskany formation, 
 which belongs to the Oriskany stage of the Lower Devonic series 
 of eastern North America, contains at least two zones, the upper, or 
 Hipparionyx proximus, zone, 258 feet thick, and the lower, 90 
 feet thick with Anoplotheca flabellites and other fossils. In some 
 cases, however, what has been considered a single formation may 
 represent an aggregation of apparently uniform lithic character, 
 of such great stratigraphic range as not only to transgress the limit 
 of a series, but even that of a system. An example of this is found 
 in the Arbuckle and Wichita sections of Indian Territory and Okla- 
 homa, where the following pre-Mississippic formations were for- 
 merly recognized : (Ulrich-i6.) 
 
 [Upper* 
 
 Devonic Middle 
 I Lower 
 
 ( Upper 
 
 Siluric j Middle 
 I Lower { 
 
 f Upper { 
 
 Ordovicicj Middle 
 I Lower 
 
 Woodford chert (Woodford formation) probably Post- 
 
 Devonic 
 Absent 
 
 Hunton limestone (Himton formation) 
 
 Sylvan shale (Sylvan formation) 
 
 Viola limestone (Viola formation) 
 Simpson formation 
 
 {Upper 1 Arbuckle limestone (Arbuckle formation) 
 Middle) * Reagan sandstone 
 Lower Absent 
 
 It has since been found that the Hunton formation is not a 
 unit, but represents fragments of several distinct formations sep- 
 arated by large breaks and unrepresented time intervals (13). 
 
 PRINCIPLES GOVERNING THE NAMING OF FORMATIONS. 
 
 A formation may. retain its name only so far as its essential 
 unity is retained, though change in lithic character does not neces- 
 sarily require a change of name. Thus, when a shaly formation 
 in one locality can be traced into, and can be shown to be the ex- 
 act depositional equivalent of, a limestone formation in another 
 
 *The classification is by tjie author, and is made in harmony with the 
 present classification of the formations supposed to be included in the divisions 
 given. 
 
I IIO 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 locality, both should be called by the same name. Such exact 
 equivalency, however, seldom obtains. The following figures 
 copied from Willis' paper (20) show the case mentioned and 
 the far more common cases in which such depositional equiva- 
 lency is not complete. In Diagram II the m (shale) formation 
 grades into the n (limestone) formation, but with a prolonged over- 
 lap. In this case neither formation is the exact equivalent of the 
 other, and both may occur together. Hence, each should receive 
 a different name. An example of this kind is furnished by the 
 
 Lmesttitc or formation. '^ 
 
 m ttiau r nmalun. 
 
 FIG. 262. Diagrams showing horizontal variation in sediments. (After 
 Willis.) 
 
 Catskill and Chemung formations, which grade into each other by 
 overlap, the Catskill alone being present in eastern New York and 
 the Chemung alone in western New York, while between these 
 points parts of both are present. In the diagram cited, the near 
 shore overlapping the offshore deposits, the overlap is regressional 
 and a replacing one and due to shoaling of the water. In the Cat- 
 skill-Chemung case, a continental formation overlaps a marine one. 
 Diagram III represents three formations on the right equivalent 
 to the shale formation (m) on the left. This shale formation (m) 
 is represented on the right by its middle portion, while the lower is 
 replaced by a sandstone formation and the upper by a limestone 
 formation. Each of the two new formations receives a distinct 
 name, as p sandstone formation and s limestone formation. If the 
 name "m shale" is retained for the middle member, a new name 
 (#) for the entire group p m s must be given, the x group being 
 then equivalent to the m shale of the left hand locality, but in- 
 cluding the m shale at the right hand locality. A better method, 
 however, is to give the shale on the right hand a new name (k) 
 and call the group p k s the m group, this being equivalent to the 
 
STRATIGRAPHIC NOMENCLATURE mi 
 
 m shale. While a difference of opinion exists as to whether or not 
 the name m should be applied in the above case to the middle mem- 
 ber, it is generally agreed that, when the shale formation m 
 breaks up into a number of units, as in diagram IV, none of which 
 can absolutely be identified with the original mass m, each of the 
 smaller members should receive a distinct name, while collectively 
 they may be called the m group, being the exact equivalent of the 
 m. shale. If lenses of sandstone or conglomerate of importance 
 are present in a formation these should receive distinct names, as 
 n and p lenses in m shale. (Diagram VI.) If only one lens is 
 present, however, this may be known by the same name as the 
 enclosing formation, though it may be better to give even a single 
 lens a distinct name. Thus, in the Cattaraugus formation of south- 
 western New York and adjacent areas in Pennsylvania, three con- 
 glomerate lentils occur, the Wolf Creek, near the base, the Sala- 
 manca higher up, and the Kilbuck still higher up. In some locali- 
 ties only one of the upper two lentils is present: in others both are 
 absent. The desirability of distinct names, even where only one of 
 these lentils occurs, is apparent. 
 
 Where the main mass is of uniform character, but contains 
 thin beds of another character, the whole may be classed as one 
 formation (m), while the minor strata are spoken of as distinct 
 members. (Diagram VII.) Thus the Waldon sandstone forma- 
 tion of the southern Appalachians contains the Sewanee coal mem- 
 ber besides shale and other coal members and conglomerate lenses. 
 
 Names of sedimentary formations are derived from localities 
 where the formation is best developed or where it was first studied. 
 "The most desirable names are binomial, the first part being geo- 
 graphic and the other lithologic (e. g., Dakota sandstone, Trenton 
 limestone, etc.) The geographic term should be the name of a 
 river, town, or other natural or artificial feature at or near which 
 the formation is typically developed. Names consisting of two 
 words should be avoided. Names taken from natural features are 
 generally preferable, because less changeable than those of towns or 
 political divisions. When the formation consists of beds differing 
 in character, so that no single lithologic term is applicable, the 
 word "formation" should be substituted for the lithologic term 
 (e. g., Rockwood formation)" (18:^.) 
 
 SELECTION OF NAMES FOR SYSTEMS, SERIES AND STAGES 
 (GROUPS). These divisions, as already noted, are of much wider 
 distribution than formations. The names of systems are mostly 
 uniform throughout the world, as Devonic, Triassic, Cretacic, etc. 
 American terms have in some cases been proposed where the origi- 
 
1 1 12 PRINCIPLES OF STRATIGRAPHY 
 
 nal European names seemed less desirable. Thus, Taconic has 
 been used for Cambric, Champlainic for Ordovicic, Ontario for 
 Siluric, Guadaloupic for Permic. Where names proposed origin- 
 ally for series became those of systems, on the raising of the 
 original series to the rank of a system, they naturally differed in 
 different countries. Thus the original Subcarboniferous is known 
 as the Mississippic in America and is now regarded as a separate 
 system, while in eastern Europe it is the Donjetic and in western 
 Europe the Dinantic. The old Lower Cretacic or Infra-Cretacee * is 
 the Neocomic of Europe, in its broader sense, and the Comanchic 
 of America. The names of series generally differ in different coun- 
 tries, and those of stages in the different sections of the same coun- 
 try. The name in either division is derived from a typical locality 
 and the appropriate ending (ian, ien) is affixed. When the name 
 itself is not adaptable in its original form, the practice generally has 
 been to substitute the Latin form (Turonien from Touraine, Cam- 
 panien from Champagne and Carentonien from the Charent). 
 Sometimes the name is derived from the original name of the 
 locality, as Cambrian from Cambria, the old Roman name for 
 North Wales, and Cenomanien from Coenomanum, the old Latin 
 name of the town of Mans in the Department of Sarthe and Roth- 
 omagien from Rothomagus, the Roman name of Rouen. 
 
 MAPPING. 
 
 The question is often asked : Should geologic maps express 
 primarily formations or geologic horizons ? In other words, should 
 the mapping be based on lithic formations or on time units? The 
 decision generally has been in favor of the mapping of lithic units 
 or formations. Generally the units have been small enough to 
 allow a grouping into systems, and these have then been referred 
 to their proper time period. This method is apparently the most 
 satisfactory, since all mappable features, such as the outcrops 
 themselves, as well as the topography of the region, are the direct 
 consequence of the lithic formations, and have no regard whatever 
 to time relations. The present outcrops show only the present ex- 
 tent of the formations, and give no clue to the former extent of the 
 strata deposited during a given time interval, except in so far as 
 the lithic character of the formation indicates this. 
 
 Mapping on Formational Basis. The United States Geological 
 Survey has adopted the formation as its cartographic unit, mapping 
 
 * In recent classifications this term is discarded. See Haug Traite", p. 1170. 
 
GEOLOGICAL MAPPING 1113 
 
 being hence conducted on a lithic basis. "As uniform conditions 
 of deposition were local as well as temporary it is to be assumed 
 that each formation is limited in horizontal extent. The forma- 
 tion should be recognized and should be called by the same name 
 as far as it can be traced and identified by means of its lithologic 
 character, its stratigraphic association and its contained fossils." 
 (18:75.) I* 1 mapping it is often impossible to draw a sharp line 
 when two contiguous formations grade into each other. In such 
 cases the boundary has to be more or less arbitrarily established. 
 An example of this is the Siluro-Devonic boundary of the Helder- 
 bergs. Here in some places the Manlius or uppermost Siluric 
 member is found to grade up into the Coeymans or lower Devonic 
 member both lithically and faunally.* 
 
 Mapping on Faunal Basis. When two formations of the same 
 lithic character are separable by their faunal content only it is 
 often found practicable to map them separately on a purely faunal 
 basis. In such a case it is frequently necessary to represent the 
 transition portion by a commingling of colors of the two series. 
 Sometimes the faunal change is a horizontal one, where two distinct 
 faunas occupied different portions of the province at the same time, 
 there being no change in lithic character. An example of this is 
 seen in the two Portage faunas of New York, the Ithaca and the 
 Naples, which existed side by side throughout Portage time. This 
 is expressed on the map by two colors, or two shades of the same 
 color, which horizontally pass into each other or overlap along the 
 line of interlocking of the faunas. (Clarke-2.) 
 
 Mapping of Discontinuous Formations. It is a matter of com- 
 mon experience that formations change in passing away from the 
 shore line, certain more terrigenous ones (as sandstones, etc.) 
 coming to an end and others of more truly marine origin (such as 
 limestones) appearing. As a result, detailed maps of adjoining 
 areas, not parallel to the old shore line, may exhibit considerable 
 diversity of formations, and it may even happen that quadrangles 
 not so far removed from each other may exhibit scarcely any for- 
 mations of the same name. Thus the Columbia quadrangle of 
 Central Tennessee (Hayes and Ulrich-9) and the McMinnville 
 quadrangle of eastern Tennessee (Hayes-8) have no formations 
 in common, though they are separated by an interval f of only 
 
 * This is not always the case, however, and this close relationship has been 
 .denied by Ulrich. But there can be no question of this gradation in the Schoharie 
 region of New York (see Grabau-6). 
 
 f The Chattanooga formation which appears on both maps is not of the 
 same age, being younger in the more eastern quadrangle. 
 
IH4 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 two quadrangles. This distinctness is partly due to the fact that 
 formations represented in one are wanting in the other, owing to 
 discontinuity of sequence (represented by either unconformities or 
 disconformities). It would, however, be just as true if the forma- 
 tions were complete in both. The greater number of subdivisions 
 found in the more western nearer shore phase of the lower 
 
 is 
 
 (Ordovicic) system, while the Siluric and Mississippi systems have 
 their nearer shore phase in the eastern sections. The following dia- 
 
 FIG. 263. A. Section showing variation of strata from shore seaward. B. 
 The same section after folding and erosion. C, D. Maps of 
 the same region, representing the two end quadrangles which 
 have scarcely any formations in common. 
 
 grams (Fig. 263) illustrate the change in formations away from 
 shore, and the resultant differences in the cartographic units of two 
 quadrangles separated by an interval of one quadrangle only. In 
 the eastern portion of the section only sands were deposited, con- 
 stituting but one formation. Owing to repeated oscillation during 
 the deposition of these sands, a series of intercalations of the more 
 off-shore clays and the still more distant limestones occurred. 
 Two anticlinal folds were formed which subsequently suffered 
 erosion and exposed the succession of beds. The strike of the eroded 
 strata is northeasterly, though the section is due east and west at 
 
CHARACTER AND KINDS OF GEOLOGIC MAPS 1115 
 
 right angles to the original shoreline. The two quadrangles mapped 
 have only formations b, c, and d (called b 1 , c l , d 1 ) in common. 
 Formation b 1 of the western quadrangle is, however, more nearly 
 equivalent to the upper part of c, as it appears in the eastern quad- 
 rangle. The bed c 1 of the western quadrangle is only a part the 
 lower of bed c as it appears in the eastern quadrangle, while d 1 
 and d are almost exact equivalents. In the eastern quadrangle occur 
 the formations a and e, which are not found in the western 
 one, while the latter shows formations /, g, h, i, m and y, not found 
 in the eastern quadrangle. In the eastern quadrangle, furthermore, 
 the formations differ on opposite sides of the valley, b being tHin 
 on fhe eastern and thick on the western side, while c and d of the 
 western side are represented by e on the eastern side. 
 
 Types of Geological Maps. 
 
 Formation and System Maps. Two kinds of geological maps 
 are in vogue in most countries. These are the formation map and 
 the system map. The first takes account of the geological forma- 
 tions, and is illustrated by the folio sheets of the Geological Atlas 
 of the United States, already referred to. In these each formation 
 is given a distinct color, or pattern, all the formations of a system 
 generally being grouped together under a similar tint, such as pink, 
 brown, etc. For the production of such maps, large scale base- 
 maps are needed, those used by the United States Geological Sur- 
 vey being mostly on the scale of I to 62,500, or approximately i 
 inch to a mile. As the scale of the map is increased, smaller units 
 can be mapped, and structural details not representable on the 
 smaller scale map may be introduced. The system map aims to 
 represent in distinctive colors only the geologic systems, each of 
 which receives a distinct color pattern. The new geological map 
 of North America, issued by the United States Geological Survey, 
 may be taken as an example of this type. Here eighteen distinct 
 color shades are used to represent the systems from the Cambric 
 to the Quaternary, though for convenience the boundary in a few 
 cases is not drawn precisely at the dividing line between the 
 systems. 
 
 The International Geological Map of Europe is also a system 
 map, though the attempt has there been made to differentiate by 
 distinctive shades the lower, middle and upper portions of some of 
 the systems (e. g., Triassic, Jurassic, etc.). 
 
 Intermediate Maps. Maps intermediate between the system and 
 
in6 PRINCIPLES OF STRATIGRAPHY 
 
 formation map are also known. The best examples are the com- 
 plete maps of New York State, on the scale of 5 miles to I inch, 
 while the map issued with the summary final report of the Second 
 Geological Survey of Pennsylvania may serve as another example. 
 These maps represent series rather than formations, though in 
 many cases the series consist practically of one formation only, such 
 as the Onondaga limestone. In other cases the unit mapped in- 
 cludes what, on a map of larger scale, would be represented as 
 several distinct formations. Such, for example, is the Clinton series 
 which on the New York State map is shown by one color only, 
 while on the map of the Rochester quadrangle it is shown as five 
 distinct formations. The Portage group, represented as a single 
 unit on the State map, is divided into eleven formations on the 
 Canandaigua-Naples map (1/62,500), exclusive of the Genesee 
 shale and the Tully limestone. 
 
 Notation of Formations on Map. In addition to the color and 
 pattern used in the representation of the formations or larger 
 units, a conventional sign, which may be a letter, or combination 
 of letters, or a number is used. This insures greater ease in identi- 
 fying the formation on the map. The United States Survey, 
 in its folios, has adopted a group of letters as the symbol, the 
 first letter representing the horizon, the other the name of the 
 formation. Thus, on the Hancock quadrangle, where the 
 Siluric is represented by five formations some of the symbols 
 are: Sc, Clinton shale; Smk, McKenzie formation; Stw, Tonolo- 
 way limestone. The S in each case signifies Siluric (Silurian). 
 In the Geological Map of North America, above referred to, 
 numbers are used to further differentiate^ the systems from one 
 another. 
 
 Legend. In order that the proper superposition of the forma- 
 tion may be ascertained, a legend is added consisting of small 
 rectangles colored to correspond to the color pattern which it repre- 
 sents on the map, and furnished, moreover, with the corresponding 
 symbol and the name of the formation. These rectangles are ar- 
 ranged in the order of superposition or sequence. As a rule, the 
 oldest formation is put at the bottom and the youngest on top. 
 The New York State Survey has, however, adopted in some of its 
 larger maps the reverse arrangement, the oldest being on the top. 
 This is done, apparently, to bring the color pattern of the legend 
 into harmony with that of the map ; in which the successive older 
 formations crop out in belts of decreasing age from the north 
 southward. 
 
GEOLOGICAL SECTIONS 1117 
 
 Continuous and Discontinuous Mapping. 
 
 Since rock outcrops are, as a rule, scattered over a consider- 
 able area with intervening portions in which the rock is covered 
 by glacial or other loose soil deposits, two modes of mapping on 
 the same scale have come into usage. The first is the mapping of 
 outcrops only, forming what may be called outcrop maps. The 
 intervening covered spaces may be left blank or may be colored 
 for the superficial deposits. The result will be a map very difficult 
 to read and to follow, while the structure of the region is not 
 readily ascertainable from such a map. The practice of printing 
 the pattern, representing the superficial unconsolidated deposit, 
 over the color pattern of the formation is adopted in some quarters, 
 as in the case of the International Geological Map of Europe. 
 American maps, as a rule, represent rock formations only, with- 
 out the overtint for superficial unconsolidated deposits. These de- 
 posits are either entirely omitted or represented on a separate map. 
 It is, of course, understood that in such cases the map does not 
 represent an accurate picture of the surface features of the litho- 
 sphere, but is hypothetical so far as the covered portions are con- 
 cerned. In a region of simple structure no appreciable errors are 
 likely to arise from such a mapping, but in a complicated region this 
 may readily be the case. 
 
 SECTIONS. 
 
 Types of Sections. Geological sections are of three kinds : ( I ) 
 the natural cross-section, (2) the columnar section, and (3) the 
 ideal section. The natural cross-section represents structure (in 
 so far as it is ascertainable) and surface features, and is the one most 
 generally employed in connection with geological representation. 
 It gives the third dimension of the land form, the other two being 
 furnished by the map. Cross-sections should, whenever the scale 
 permits it, be drawn to the natural scale, i. e., vertical and horizontal 
 scales should be alike. In some instances this is not possible, owing 
 to the smallness of the scale and the large number of structural 
 features to be represented. In such cases an exaggeration of the 
 vertical over the horizontal scale, is necessary, but this should not 
 be over five times, or, in rare cases, ten times, the horizontal. It 
 must be borne in mind that vertical exaggeration of the scale always 
 involves an increase in the steepness of dip of the strata and a cor- 
 responding distortion of other characters. 
 
ni8 PRINCIPLES OF STRATIGRAPHY 
 
 Columnar sections are designed to show the superposition and 
 relative thickness of the strata of the region which they- represent, 
 provided they are drawn to scale. They serve their main purpose 
 in giving a quick and comprehensive view of the stratigraphy of a 
 region and in making comparison with other regions possible. If a 
 uniform set of scales, each a multiple of the others, could be adopted, 
 ready comparisons of published sections for different regions would 
 be possible, and would greatly facilitate the work of correlation. 
 
 Ideal sections are attempts to restore the conditions as they were 
 before deformation or erosion has taken place. The term is also 
 sometimes used for generalized cross-sections, but this is better 
 avoided. In so far as structure is eliminated, the columnar section 
 is an ideal section, but sections to which the term is best applicable 
 should show a wider relationship than is possible in a columnar 
 section. Fig. 152, page 739 and Figs. 157 and 158, page 743, are 
 examples of ideal cross-sections. 
 
 THE LENGTH OF GEOLOGICAL TIME. 
 
 Various estimates of the actual length of geologic time have been 
 attempted, the basis of most of such estimates being the rate of 
 deposition, ascertainable in modern river systems, or the rate of 
 erosion of river canyons, such as the Niagara, the Yellowstone, 
 Colorado, etc., and the rate of retreat of the Falls of St. Anthony. 
 (See Williams- 1 9.) If it can be ascertained that the beginnings 
 of erosion have a definite relation to some other event which itself is 
 of definite value in geochronology, a basis for a rational estimate of 
 the actual time duration is furnished. Such a relationship seems to 
 have existed between the beginnings of the Falls of Niagara and of 
 St. Anthony, and the end of the Pleistocenic glacial period. So 
 many questionable factors, however, enter into the problem, that 
 it is scarcely worth while, with our present incomplete knowledge, 
 to attempt much more than the most general estimate. Thus 
 Cambric, Ordovicic and Siluric time has been estimated at 10,000,- 
 ooo years ; Devonic time at 2,000,000 years ; Mississippic to Permic 
 time at 5,000,000 years, making a total of 17,000,000 years for the 
 Palaeozoic. Mesozoic time has been estimated at 7,000,000 years, 
 Caenozoic at 3,000,000 years and Psychozoic at 50,000, marking a 
 total of 27,050,000 years since the beginning of Cambric time. This 
 estimate is conservative, others having made a much larger one. Thus 
 Dana's estimate of the age the earth was at least 48,000,000 years. 
 Geikie's estimate ranges from 100,000,000 to 680,000,000 years, 
 
LENGTH OF GEOLOGIC TIME 1119 
 
 while McGee has suggested a possible age of 7,000,000,000 years 
 for our earth. Since we have not as yet ascertained the actual 
 thickness of the stratified rocks of the earth, and since we know so 
 little about the rate of erosion, we must conclude that all such esti- 
 mates are premature and almost valueless, and that even the esti- 
 mates of the proportional length of duration of the various divi- 
 sions are extremely hypothetical. Geological time was long, very 
 long, as measured in terms of human chronology long enough to 
 permit the development of the multifarious forms of life upon the 
 earth. Only a part of this time is recorded in the known rocks of 
 the earth's crust for there are probably many lost intervals, the 
 duration of which we cannot even estimate. 
 
 BIBLIOGRAPHY XXXI. 
 
 1. CLARKE, JOHN M. 1896. The Stratigraphic and Faunal Relations of 
 
 the Oneonta Sandstone and Shales, the Ithaca and Portage Groups in 
 Central New York. New York Geological Survey, Fifteenth Annual 
 Report, pp. 27-82, map. 
 
 2. CLARKE, J. M. 1903. The Naples Fauna in Western New York. New 
 
 York State Museum, Memoir 6, pp. 199-454, 26 pl s -> J 6 figs. 
 
 3. DANA, JAMES D. 1895. Manual of Geology. Fourth Edition. 
 
 American Book Company, New York. 
 
 4. GEIKIE, ARCHIBALD. 1903. Text-book of Geology. Fourth edition. 
 
 Macmillan and Co., London. 
 
 5. GRABAU, A. W. 1905. Physical Characters and History of Some New 
 
 York Formations. Science, N. S., Vol. XXII, pp. 528-535. 
 
 6. GRABAU, A. W. 1906. Guide to the Geology and Paleontology of the 
 
 Schoharie Valley in Eastern New York. New York State Museum 
 Bulletin 92 (58th Annual Report, Vol. Ill), pp. 77-386, 24 pis., 216 figs. 
 
 7. GRABAU, A. W., and SHIMER, H. W. 1910. Summary of North 
 
 American Stratigraphy. North American Index Fossils, Vol. II, pp. 
 604-663. A. G. Seiler & Co. New York. 
 
 8. HAYES, C. WILLARD. 1895. McMinnville Folio, Tennessee. United 
 
 States Geological Survey, Geological Atlas of the United States, Folio 22. 
 
 9. HAYES, CHARLES W., and ULRICH, EDWARD O. 1903. Columbia 
 
 Folio, Tennessee. Geological Atlas of the United States, Folio No. 95. 
 United States Geological Survey. 
 
 10. LE CONTE, JOSEPH. 1902. Elements of Geology. D. Appleton and 
 
 Co., New York. 
 
 11. LEHMANN, JOHANN G. 1736. Versuch einer Geschichte von Flotz- 
 
 gebirgen. - 
 
 12. LYELL, CHARLES. 1856. A Manual of Elementary Geology. Sixth 
 
 Edition. 
 
 13. REEDS, CHESTER A. 1911. The Hunton Formation of Oklahoma. 
 
 American Journal ot Science, 4th series, Vol. XXXII, pp. 256-268. 
 
 14. SCHUCHERT, CHARLES. 1910. Paleogeography of North America. 
 
 Geological Society of America Bulletin, Vol. XX, pp. 427-606, 56 pis. 
 
1 120 PRINCIPLES OF STRATIGRAPHY 
 
 15. SINCLAIR, W. J. 1910. Interdependence of Stratigraphy and Paleon- 
 
 tology. The Paleontologic Record, pp. 9-11. Reprinted from Popular 
 Science Monthly. 
 
 1 6. ULRICH, EDWARD O. 1904. In Tail's Preliminary Report on the 
 
 Geology of the Arbuckle and Wichita Mountains in Indian Territory and 
 Oklahoma. United States Geological Survey, Professional Paper No. 31, 
 pp. 11-81. 
 
 17. ULRICH, E. O. 1911. Revision of the Paleozoic System. Bulletin of 
 
 the Geological Society of America, Vol. XXII, pp. 281-680, pis. 25-29. 
 
 1 8. UNITED STATES GEOLOGICAL SURVEY. 1903. Nomenclature 
 
 and Classification for the Geologic Atlas of the United States. 24th 
 Annual Report. 
 
 19. WILLIAMS, HENRY S. 1895. Geological Biology. An Introduction 
 
 to the Geological History of Organisms. New York. Henry Holt & Co. 
 I9a. WILLIAMS, HENRY S. 1893. The Elements of the Geological Time 
 Scale. Journal of Geology, Vol. I, pp. 283-295. 
 
 20. WILLIS, BAILEY. 1901. Individuals of Stratigraphic Classification. 
 
 Journal of Geology, Vol. IX, pp. 557-569- 
 
CHAPTER XXXII. 
 
 CORRELATION: ITS CRITERIA AND PRINCIPLES 
 PAL^OGEOGRAPHY. 
 
 CORRELATION. 
 
 "The fundamental data of geologic history are: (i) local se- 
 quences of formations; and (2) the chronologic equivalences of 
 formations in different provinces. Through correlation all forma- 
 tions are referred to a general time scale, of which the units are 
 periods. The formations made during a period are collectively des- 
 ignated a system!' (Rule 14, Nomenclature and Classification for 
 the Geologic Atlas of the United States.) 
 
 History of Development of Methods of Correlation. 
 
 Correlation of strata, or the establishment of an orderly relation- 
 ship between the formations of separate regions, has been one of 
 the chief aims of stratigraphers ever since the days of Werner and 
 William Smith. Werner's correlations were based on the lithic 
 character of the strata, but William Smith in England and Cuvier 
 and Brogniart in France made their identifications of strata by 
 means of the organic remains included in them. Each of these 
 workers based his investigation upon the ascertained succession 
 of strata in the region selected by him as typical, and thus the 
 three fundamental criteria of correlative geology : lithic similarity, 
 likeness of fossil content and superposition of strata, were made 
 use of by the pioneers in stratigraphy. 
 
 The efforts of these founders of stratigraphy were directed 
 chiefly toward establishing the identity or correspondence of strata 
 between different localities ; and, when it was recognized that strata 
 were formed at different periods in the earth's history, the effort 
 was further directed toward establishing the time-equivalency or 
 synchroneity of strata. Before fossils were extensively studied, 
 
 II2I 
 
1 122 PRINCIPLES OF STRATIGRAPHY 
 
 similarity of superposition and lithic identity were taken as the 
 guides to synchroneity, a proceeding which naturally led to many 
 erroneous correlations. Thus McClure and Eaton in their early 
 studies of the rocks of the United States were entirely guided by 
 superposition and lithic and structural character of the rocks, their 
 classification being modeled upon that of Werner. Both McClure 
 and Eaton identified the undisturbed Palaeozoic formations of east- 
 ern United States with the Secondary or Mesozoic formations of 
 England, being thus influenced in their correlation by another cri- 
 terion, namely, the relative position of the strata. Lithic similarity 
 caused Eaton to identify the Rochester shale of New York (Lower 
 Siluric) with the Lias of England (Lower Jurassic). Lithic sim- 
 ilarity and similarity of superposition led many of the early geolo- 
 gists to identify the Potsdam sandstone and the quartzose sand 
 rock of Vermont as of the same age, though one is Upper and 
 the other Lower Cambric. In the same manner lithic similarity 
 led some of the earlier geologists to identify the Upper Cambric 
 or early Ordovicic, Lake Superior sandstone with the Triassic sand- 
 stone of New Jersey and the Connecticut Valley, while the ribbon 
 limestones of Pennsylvania and New Jersey, of Cambric and Lower 
 Ordovicic age, and the Waterlimes of the Hudson River region of 
 Upper Siluric age were not so long ago thought to be stratigraphic 
 equivalents, on account of their great similarity in lithic characters. 
 Superposition, sometimes erroneously inferred, similarity of lithic 
 character, and superficial comparison of fossils led Bigsby in 1824 
 to identify the Rideau sandstone of Kingston, Ontario (Lower 
 Ordovicic), with the Medina of the Niagara and Genesee gorges 
 (Lower Siluric), and both with the Old Red Sandstone of Eng- 
 land, on account of lithic resemblance of the two formations, and 
 the apparent similarity of fossils in the limestones overlying them. 
 In his later investigations Eaton, like Bigsby, made use of fossils 
 in correlation, but the comparisons made by both were of the 
 crudest, being chiefly by classes of organisms. Thus the Ordovicic 
 conglomerates opposite Quebec were correlated by Bigsby with the 
 "Carboniferous limestone" of England, because both contain re- 
 mains of trilobites, "encrinites," "corallites" and other fossils. An- 
 other of the early correlations of formations by lithic characters was 
 made in 1821 by Dr. Edwin James. He considered that the sand- 
 stone of Sault Ste. Marie (Cambric or early Ordovicic) the Trias- 
 sic sandstone of the eastern foothills of the Rocky Mountains, the 
 Catskill, Medina and Potsdam sandstones of New York and the 
 Newark sandstone of New Jersey were of the same relative geologic 
 
HISTORY OF CORRELATIVE GEOLOGY 1123 
 
 age and occupied a place similar to that assigned to the "Old Red 
 Sandstone" by Werner. Geologists, however, were not long in find- 
 ing out that beds of the same lithic character are not all of the 
 same age, but it has taken them much longer to realize that beds of 
 the same age are not always of the same or even similar lithic char- 
 acter. 
 
 With the detailed study of the New York strata by the five 
 geologists and palaeontologists on the survey (Mather, Emmons, 
 Vanuxem, Conrad and Hall), correlation by fossils became recog- 
 nized as the most reliable known method. At first American species 
 were directly identified with European types, and such identification 
 was in many cases not far wrong. Extensive collections of fossils, 
 however, soon showed that the rocks of this country contained an 
 assemblage of organisms largely peculiar to themselves and specifi- 
 cally, if not generically, distinct from that of Europe. Correlation by 
 similarity of faunas was then substituted for correlation by species 
 and so the general correspondence of the strata in the two continents 
 was established. The need of an American standard of comparison 
 was soon felt, and such a need was supplied by the development 
 of the "New York series" of geological formations. The succes- 
 sion of New York strata and the organic remains characterizing 
 them was so thoroughly worked out that "it is and has been for 
 decades a standard of reference for all students of the older rocks 
 throughout the world." (Clarke-n.) Professor James Hall was 
 one of the first in America to recognize the importance of naming 
 formations from localities in which they were best exposed. In 
 his report to the New York State legislature in 1839 he urges that 
 neither lithic character nor characteristic fossils is a satisfactory 
 source from which to derive the name of the formation, for the 
 first may change while the second is not always ascertainable and 
 may even be absent. He holds that it "becomes a desideratum to 
 distinguish rocks by names which cannot be traduced, and which, 
 when the attendant circumstances are fully understood, will never 
 prove fallacious." Such names can be derived only from localities. 
 It is most fortunate that this principle was recognized before the 
 New York series of formations was fully promulgated in the final 
 reports of the survey. As a result, the majority of formations were 
 named from typical localities, only a relatively small number re- 
 taining the lithic or palaeontologic names given them by the earlier 
 investigators. More recently these, too, have been replaced by 
 names derived from typical localities, of which the following is a 
 partial list: 
 
1 12 4 PRINCIPLES OF STRATIGRAPHY 
 
 Calcif erous i replaced by Beekmantown. 
 
 Birdseye replaced by Lowville. 
 
 Waterlime (of Buffalo) replaced by Bertie. 
 
 Coralline replaced by Cobleskill. 
 
 Waterlimes (of the Hudson) replaced by Rondout & Rosendale 
 
 Tentaculite limestone replaced by Manlius. 
 
 Lower Pentamerus replaced by Coeymans. 
 
 Delthyris shaly replaced by New Scotland. 
 
 Upper Pentamerus replaced by Becraf t. 
 
 Upper Shaly replaced by Port Eweh. 
 
 Cauda-Galli replaced by Esopus. 
 
 Corniferous replaced by Onondaga 
 
 As the Palaeozoic formations of other districts of North America 
 were studied, it was found that the correspondence between them 
 and the New York formations was not as close as could have been 
 hoped. Not only did the lithic character of the strata change 
 when traced away from the type locality, but the superposition did 
 not, in many cases, correspond, some formations being absent alto- 
 gether while others were found to be united in a single unit, often 
 of slight thickness. Even the fossils, which had gradually come to 
 be looked upon as the surest indicators of position in the geologic 
 scale, appeared in horizons not known to contain them in New York. 
 Thus the chain-coral Halysites was universally thought to be char- 
 acteristic of the Lower Siluric (Niagaran) age, until it was dis- 
 covered that this coral also occurred in the Ordovicic, in some of 
 the localities west of New York, and in the Anticosti region, while 
 in eastern New York it was found in an Upper Siluric horizon, the 
 Cobleskill, which is stratigraphically many hundred feet above the 
 Niagaran beds. In like manner Tropidoleptus carinatus and some 
 of its associates, believed formerly to be restricted to the Hamilton 
 (Mid-Devonic) formation, were found in south central New York 
 to occur in the Ithaca (Portage) beds and, again, in the Chemung 
 (Upper Devonic). 
 
 Recurrent faunas have also been described from the Mississipic. 
 Weller (53) found Devonic elements in the Kinderhook fauna, and 
 Williams and others have described such recurrence of Devonic 
 elements in the Spergen and other Mississippi beds of central 
 North America. Ulrich (49 -.296) has noted the occurrence of the 
 trilobite Triarthrus becki in the Fulton shale, and in the Southgate 
 beds 156 feet above it. 
 
 Chronological Equivalency, Contemporaneous and Homotaxial 
 Formations. Chronological equivalency as one of the fundamental 
 data of geologic history has repeatedly been assailed by eminent 
 scientists. Huxley, indeed, went so far as to question the possi- 
 
CONTEMPORANEOUS AND HOMOTAXIAL 1125 
 
 bility of determining in any case the existence of contemporaneous 
 strata, and he coined the term homotaxis, signifying similarity of 
 order, to express the correspondence in succession rather than exact 
 time equivalence. Geikie also held that "strict contemporaneity 
 cannot be asserted of any strata merely on the ground of similarity 
 or identity of fossils" (14:608), and H. S. Williams, among 
 American authors, has most strenuously insisted on the impossibility 
 of recognizing strict contemporaneity among strata of widely sepa- 
 rated regions. Williams would refer formations not to a general 
 time scale, but to a stratigraphic scale, of which not "periods" but 
 systems are units. He advocates the revision of Rule 14 of the 
 U. S. Geological Survey quoted at the beginning of this chapter 
 so as to read (56:73$) : 
 
 "The -fundamental data of geologic history are: (i) the local 
 sequence of formations and (2) the similarity of the fossil faunas 
 of the formation of different provinces. Through correlation all 
 formations are referred to a standard stratigraphic scale, of which 
 the units are systems." 
 
 Contrary to the views of Huxley and other writers, some of 
 whom like Edward Forbes went so far as to assert that similarity 
 of organic content of distant formations is prima facie evidence, not 
 of their similarity, but of their difference of age, most modern 
 stratigraphers have come to believe in the possibility of essential 
 chronological equivalency of formations characterized by the same 
 faunas, recognizing at the same time the fact that such equivalency 
 is not necessarily indicated by the similarity of faunas, and that a 
 given fauna may appear earlier and continue longer in some sections 
 than in others. The rapidity of migration shown by modern faunas 
 indicates that, if the path is open and no barriers exist, widespread 
 migration or dispersal may occur within such short time limits as 
 to be considered almost homochronic. 
 
 Contemporaneity of Faunas. That several distinct faunas may 
 exist side by side in not too widely separated districts is a well 
 known fact. The difference of faunas north and south of Cape 
 Cod on the Atlantic Coast may be mentioned as a modern ex- 
 ample; also the difference between the Red Sea fauna and that of 
 the Mediterranean, and, finally, the distinct faunas on opposite sides 
 of the Isthmus of Panama. In all of these cases a partial or com- 
 plete land barrier separated the faunas. In the case of Cape Cod, 
 this barrier is incomplete and, although aided by cold currents from 
 the north, it has not entirely prevented the migration around it of 
 the faunas. The other two barriers were complete, and separated 
 faunas of different provinces, but the transsection in 1869 f tne 
 
1 126 PRINCIPLES OF STRATIGRAPHY 
 
 Suez barrier by the canal has permitted a certain commingling of 
 faunas, a phenomenon predictable for the faunas on opposite sides 
 of the Isthmus of Panama on the completion of the canal. 
 
 Contemporaneous faunas existed in North America at various 
 times in its geologic history. The most noted case is that of the 
 Upper Devonic. An indigenous fauna, the Ithaca fauna, derived 
 largely by development from the earlier Hamilton fauna, occupied 
 the eastern area in New York and Pennsylvania, while an immigrant 
 fauna, the Naples fauna, occupied the region to the west of this. 
 At first the two faunas were separated by a land barrier, but this 
 was subsequently submerged. Nevertheless, the two faunas con- 
 tinued in their essential integrity through Portage time, though the 
 area of occupancy of each varied from time to time, but within 
 comparatively narrow limits. 
 
 Prenuncial Faunas, Colonies. Prenuncial faunas are the ad- 
 vance invaders of a new territory of members of a foreign host, 
 which subsequently occupies the territory. Such have been noted 
 in some cases, especially in that of the Styliolina limestone of the 
 Upper Devonic of New York, which marks the first invasion of 
 the Naples fauna into this Upper Devonic province. 
 
 The term "Colonies" was employed by Barrande to designate 
 the appearance of a fauna normal to a later geological horizon, 
 during a period when an earlier fauna still flourished. Though the 
 examples cited by Barrande have proved to be mostly inadequate 
 to establish his theory, the fact remains that faunas in their en- 
 semble suggestive of a much later period may appear in deposits 
 otherwise marked by the normal fauna of that period. Thus, during 
 the Upper Siluric (Upper Monroan) time, a fauna in large measure 
 suggestive of Middle Devonic time flourished in Michigan, Ohio, 
 and Ontario (Anderdon fauna). In this fauna something over 
 twenty species have exact specific, or closely similar, representatives 
 in the Onondaga or Schoharie formation. This similarity is largely 
 found in the coral, brachiopod, pelecypod, and trilobite elements of 
 the fauna, while the cephalopods and gastropods are of typical 
 Siluric species. The whole fauna is succeeded by a normal Siluric 
 fauna, and is separated by an extensive hiatus from the overlying 
 limestones of Middle Devonic age. The explanation of this com- 
 mingling of faunas is found in the fact that two faunas, with dis- 
 tinctive characters, existed simultaneously, one of which furnished 
 the faunal elements with Devonic affinities, but did not make much 
 headway against the resident normal Siluric fauna. Continuing to 
 modify in its own center of distribution, the more specialized fauna 
 finally evolved into the normal Middle Devonic fauna of that region, 
 
STANDARD SECTIONS 1127 
 
 some parts of which spread widely over the earth, and, with ele- 
 ments derived from other sources, constituted the local Middle De- 
 vonic faunas of eastern North America. (Grabau and Sherzer-2oa.) 
 
 Standard or Type Sections. In general the first section studied 
 is taken as the type section for the country. Often it is not the 
 most complete nor the most perfect section, as in the case of the 
 Devonic section of southern England (Devonshire), which is less 
 perfect than that of the Rhine region; or the Cretacic section of 
 Colorado and Montana, which is less complete than that of Texas 
 and Mexico. In such cases it not infrequently happens that, by a 
 process of natural selection, the poorer section is gradually re- 
 placed by the better, as in the case of the Rhenish Devonic, which 
 is now more frequently used for comparison, or the Cambric of 
 Scandinavia, which is more satisfactory than that of Wales. In 
 America the type section for the Palaeozoic formations is found in 
 the State of New York. This not only was the first section thor- 
 oughly studied in this country, but, what is more significant, it 
 turned out to be in many respects the most complete and most rep- 
 resentative of all American Palaeozoic sections. So truly repre- 
 sentative is this section that, " . . . while other classifications 
 proposed for these rocks, contemporaneously or subsequently, have 
 fallen to the ground, it has withstood all the attacks of time." 
 (Clarke-n.) 
 
 Not a little did the detailed palaeontologic work carried on by 
 the State Survey of New York contribute to this prominence of the 
 New York Section. No other American region has had the organic 
 remains of its formations so fully investigated and descriptions and 
 illustrations of them published in such a complete manner. This 
 thoroughness, for which in a large measure James Hall was re- 
 sponsible, has forever made the New York column the foundation 
 on which all other work on Palaeozoic Stratigraphy of America 
 must be based. 
 
 In spite of this fact, however, the relationships between the 
 various local sections of the State of New York have not yet been 
 fully ascertained, and each year facts are discovered which de- 
 mand a modification, in details, of these standard sections. 
 
 Nor is the New York column as a whole complete and without 
 flaws. Undoubted Middle Cambric appears to be but slightly de- 
 veloped in the state, while the Lower and Upper Cambric also are 
 not fully represented, so far as the sections have been studied. 
 Hence the American type sections for these formations are ob- 
 tained from other regions : that for the Lower Cambric from north- 
 western Vermont and that for the Middle Cambric in the Acadian 
 
1 128 PRINCIPLES OF STRATIGRAPHY 
 
 provinces of Canada. In the latter region is likewise found a more 
 complete representation of the Upper Cambric formations than 
 has yet been ascertained to exist in the State of New York. 
 It is on this account that the East Canadian names Bretonian, 
 Acadian and Etcheminian (cf. Georgian) have been used for the 
 Upper, Middle and Lower Cambric, respectively. (Grabau-i/.) 
 
 Again, a hiatus exists in New York between the Ordovicic and 
 Siluric, the upper part of the Ordovicic not being represented, at 
 least not by fossiliferous formations. The lower Siluric, too, is 
 less satisfactorily represented in New York than elsewhere, for, 
 as currently understood, it begins with a sandstone formation, the 
 Medina, which is a shore formation, where not of non-marine origin. 
 For the Upper Ordovicic and Lower Siluric, then, the New York 
 column has to be piecejl out by formations developed elsewhere, 
 the standard selected being the Cincinnati group of the south-cen- 
 tral states for the one, and the lower Mississippi region for the 
 other.* Even within the lower Ordovicic there is an incomplete 
 representation of the top of the Beekmantown and of the Chazy for- 
 mation, this incompleteness being measurable by thousands of feet of 
 limestone in the Mohawk Valley, but by very much less in the Lake 
 Champlain region. The Salina of New York, of Mid-Siluric age, 
 also forms an unsatisfactory member of the standard series, as al- 
 ready pointed out, since it represents abnormal conditions of sedi- 
 mentation. Aside from these, however, the New York column 
 represents an eminently satisfactory standard of the Palaeozoic 
 formation below the Mississippic. 
 
 The standard American series for the Mississippic is that of the 
 Mississippi Valley, though that is not itself a complete section. 
 The standard marine sections for the Carbonic and Permic have not 
 yet been fully worked out for this country. The former is found 
 in Kansas, Missouri and Arkansas ; the latter in Texas. No Ameri- 
 can Triassic or Jurassic standards are recognized, the fragmentary 
 development of these formations being referred to foreign stand- 
 ards. The Comanchic and Cretacic, on the other hand, are well 
 represented by formations in Mexico, Texas and the Great Plains 
 region, which localities have furnished the standard section's. The 
 Comanchic is well represented in the southern areas, but the sections 
 of the typical Cretacic in the standard region (Colorado and Mon- 
 tana) are incomplete at the bottom and at the top, where they 
 include non-marine formations, . e., the Dakota sandstone, and the 
 
 * The Anticosti section promises to be one of the most perfect North American 
 Lower Siluric (Niagaran) sections, but it is not as yet certain in how far this 
 section belonged to a distinct geographic province. (See Schuchert~39:5J2.) 
 
METHODS OF CORRELATION 1129 
 
 Laramie formation. The standards of the North American marine 
 Eocenic and Oligocenic are found in the Gulf States, while those 
 of the Miocenic and Pliocenic are found on "the Atlantic coast of 
 Maryland and Virginia, the Carolinas and Florida. All these locali- 
 ties together, however, furnish only a partial standard of the 
 American marine Tertiary. 
 
 A Double Standard. In some cases it has been found most 
 practicable to have a double standard of formations: one marine, 
 the other non-marine. This has been most fully worked out for the 
 American Tertiary, where the continental deposits of the Great 
 Plains region serve as a standard of comparison for similar de- 
 posits of other American regions, while the Gulf and Atlantic 
 Coast deposits serve as our standard of marine formations. In 
 western Europe the Carbonic is represented by the non-marine 
 Westphalian and Stephanian, while the corresponding marine forma- 
 tions of eastern Europe are the Moscovian and Uralian. In 
 America the Pocono-Mauch Chunk formations are the non-marine 
 equivalents of the Mississippic, and the Pennsylvanic (Pottsville- 
 Monongahela) is the non-marine standard of the Carbonic, the 
 marine standard being still undetermined, though in part represented 
 in the Kansas section. The Laramie, Belly River, Bear River, and 
 Dakota formations form a nearly complete non-marine standard for 
 the American Cretacic, and the Kootanie for the Comanchic. 
 
 Methods of Correlation. 
 
 The means by which formations of different localities are cor- 
 related may be summarized as follows : 
 
 1. Superposition. 
 
 2. Stratigraphic continuity. 
 
 3. Lithic characters. 
 
 4. Organic conteiits. 
 
 5. Unconformities or disconformities. 
 
 6. Regional metamorphism. 
 
 7. Diastrophism. 
 
 i. Superposition. 
 
 The basis of all stratigraphic work is the ascertainment of the 
 order of superposition of the strata. No correlation of the strata 
 in any two localities is possible until the exact superposition in 
 
1 130 PRINCIPLES OF STRATIGRAPHY 
 
 each has been ascertained. The general law of superposition is : 
 that, of any two strata of sedimentary rocks, the one zvhich was 
 originally the lower is also the older. This does not, of course, 
 apply to intruded igneous rock, for a much later sheet of intrusive 
 material may find its way between strata very much older and 
 so be followed by strata older than itself. In exceptional cases, 
 too, sedimentary rocks may not follow this rule, as in the case of 
 deposits in caverns cut out of older rocks. Here strata may 
 actually form beneath the surface of the lithosphere and hence 
 below an older stratum. 
 
 Of course, in regions of faulting and strong folding, the order 
 of the strata may be reversed, so that it becomes necessary, first 
 of all, to demonstrate the original position of the formations. 
 
 In the ascertainment of the superposition of strata of a given 
 region great care must be taken to note the existence of strati- 
 graphic breaks. Disconformities of strata are often difficult to 
 recognize, but unless ascertained are sure to introduce an element of 
 error into the geologic columns of the region. Abrupt changes 
 in sedimentation are a useful guide in the location of such discon- 
 formities and, in fact, where such sudden changes occur it may 
 be taken as an indication of the possibility of the existence of such 
 a hiatus, though this alone is not sufficient proof of its existence. 
 A good example of a great hiatus indicated only by an abrupt 
 change in the character of the rock is found in the case of the con- 
 tact of the Black Chattanooga shale with the gray Rockwood clays 
 in eastern Tennessee. Here there seems to be, at times, no other 
 indication, than this sudden change in character, of the absence, 
 between these two formations, of more than the entire Devonic 
 system of strata. Indication of erosion surfaces, and the inclusion 
 of the fragments of the lower in the upper beds, commonly charac- 
 terize the disconformity, but give no clue as to the magnitude of 
 the hiatus. The change from one lithic unit to another may be 
 abrupt, without necessarily indicating a disconformity. In such 
 cases, generally, there is some alternation of beds of the two series 
 before the complete disappearance of the lower series.. Thus the 
 Black Shale at the top becomes intercalated with thin bands of 
 the overlying formation, and itself occurs at intervals in the form of 
 thin layers for some time after the extensive development of the 
 overlying series. 
 
 Correlation by superposition, however, is a method fraught 
 with grave dangers. Thus a succession of formations from sand- 
 stones to shales and limestones in one part of a province is not 
 necessarily the same as a similar series in another part of the same 
 
METHODS OF CORRELATION 1131 
 
 province, and most probably not the same as a similar series in 
 another geologic province. Indeed, from a consideration of the 
 phenomena accompanying marine progressive overlap, it becomes 
 apparent that even within the same province the two series are dif- 
 ferent, unless they are situated along a line parallel to the old 
 shore of the time when the strata accumulated. 
 
 2. Stratigraphic continuity. 
 
 When a formation can be traced, with but slight interruptions, 
 over a wide area, the general assumption is, that it is synchro- 
 nous in all its outcrops. This is true enough where the tracing 
 of the formation is parallel to the old shore line, or source of sup- 
 ply, but not always true when at an angle with that line. This is 
 especially the case when the formation in question is of terrigenous 
 origin, formed either as a marine or as a fluviatile deposit. A 
 basal sandstone or conglomerate, formed in a transgressing sea, 
 rises in the scale shoreward ; in a regressing sea it rises seaward 
 (see Chapter XVIII). The Mahoning sandstone of the Lower Con- 
 emaugh of northwestern Pennsylvania had been traced almost con- 
 tinuously around the bituminous coal field and united with the 
 Charleston sandstone of the Kanawha district of West Virginia. 
 It has since been shown, however, that these sandstones are part 
 of a series rising and overlapping northwestward, and that, where- 
 as the Charleston end of the series lies in the Lower Allegheny, the 
 Mahoning sandstone proper forms the westernmost part of the 
 series, lying at the base of the Conemaugh. (Campbell.) 
 
 Limestones are, however, much more continuous, and, if traced 
 for moderate distances, are apt to hold their own pretty well. 
 This is especially the case with limestone beds of slight thickness 
 interbedded with shales. Thus the Encrinal limestone has been 
 recognized in all its outcrops, from Thedford, Ontario, to the 
 Genesee Valley, a distance of over 200 miles, holding its own 
 throughout in lithic character as well as fossil content, though 
 there are other strata which have been mistaken for it farther 
 east. It forms a prominent plane of 'correlation of the strata, for 
 it seems pretty certain that this limestone in all of its occurrences 
 represents simultaneous, or nearly simultaneous, accumulation as 
 the result of widespread uniformity of conditions. (Shimer and 
 Grabau-43.) 
 
 The Agoniatite limestone of the New York Marcellus has been 
 traced from Buffalo to Schoharie, and southward to Maryland. 
 
n 3 2 PRINCIPLES OF STRATIGRAPHY 
 
 This limestone, intercalated between black shales, indicates a pe- 
 riod of widespread uniform conditions, followed by a resumption 
 of the Black Mud sedimentation. It therefore serves as an excel- 
 lent horizon marker, by which the rocks above and below can be 
 correlated. Still another example is the Cobleskill of New York, 
 which has been traced across the State, chiefly by its fauna, and 
 serves as a datum-plane for the strata above and below it. 
 
 3. Lit hie characters. 
 
 Correlation by lithic characters is possible only in very limited 
 areas, and where it can be used in connection with stratigraphic 
 continuity and order of superposition. Under certain conditions, 
 however, the lithic character becomes an important guide in cor- 
 relation. An example is the St. Peter sandstone, a pure silicarenyte, 
 which has been widely recognized by its lithic character, and its 
 enclosure within pure limestone or dolomytes. The uniformity of 
 grain and composition over thousands of square miles of area 
 is its most remarkable feature. As already outlined, however 
 (Chapter XVIII), the St. Peter, though occupying a definite posi- 
 tion in the scale, encloses within itself a hiatus, which constantly 
 widens northward, so that the top of the sandstone is higher in 
 the scale and the bottom is lower in the northern region, as com- 
 pared with its more southern occurrence. Moreover, there are 
 formations, such as the Sylvania sandstone of Ohio (Upper Sil- 
 uric), which are lithically identical with the St. Peter, and might 
 be mistaken for it, if lithic character alone were considered. 
 
 An intercalated shore-derived formation between offshore 
 formations can generally be recognized in its various outcrops by 
 its lithic character. Such a formation represents an oscillation of 
 the land during sedimentation, either a shoaling or a total retreat 
 of the sea, followed by a re-advance or a deepening. Lithic charac- 
 ter then, when taken in conjunction with superposition, may be 
 a valuable guide in correlation. Intercalated off-shore beds among 
 terrigenous formations may likewise serve a good purpose in cor- 
 relation. Thus the Ames or Crinoidal limestone, a marine bed, has 
 been widely recognized as an intercalated bed in the non-marine 
 Conemaugh formation of the bituminous coal field. In this case 
 the correlation is confirmed by the contained fauna. 
 
 Another way in which lithic character serves a useful purpose 
 in correlation is by the occurrence of what may be called sympa- 
 thetic changes in sedimentation. Thus two regions, one more dis- 
 
METHODS OF CORRELATION 1133 
 
 tant from the shore than the other, may experience a sympathetic 
 change in sedimentation, when simultaneously affected by an oscilla- 
 tory movement. Thus, when in the near-shore region muds change 
 upward into sands, and still higher into muds again, the corre- 
 sponding change in the more distant region may be from lime- 
 stones to terrigenous muds and higher still to limestones again. 
 Such sympathetic changes seem to have taken place between the 
 New York and Michigan Hamilton deposits. 
 
 4. Organic contents. 
 
 Correlation by organic contents, or Pakeontologic correlation, 
 has been found to be the most reliable method, far surpassing in 
 importance any other single method. Nevertheless, there are many 
 pitfalls which must be guarded against, and the sources of error 
 must be recognized and taken into account. 
 
 (a) Index 1 fossils. Index fossils have already been defined 
 as species characteristic of definite geologic horizons, and typically 
 occurring only in beds of that horizon (page 1094). Index fossils 
 in order to be efficacious must be of limited vertical but wide hori- 
 zontal distribution. Thus the brachiopod Hypothyris cuboides 
 characterizes a certain zone in the Upper Devonic of America, 
 Europe and Asia, while the Goniatite Manticoceras intumescens 
 likewise characterizes late Devonic rocks throughout much of the 
 northern hemisphere. Similarly, Spirifer disjunctus has a limited 
 vertical range, combined with a wide horizontal one, being char- 
 acteristic of the Upper Devonic of many countries. Locally, the 
 type may transgress the normal vertical range, as in the case of 
 the last-mentioned species, which passes up into Lower Mississippic 
 beds in eastern North America, or, as in the case of Tropidoleptus 
 carinatus, a widespread index fossil of the Mid-Devonic, but which 
 locally passes into the Upper Devonic. The best index fossils are 
 those which are capable of wide distribution, and remains of which 1 
 will occur in regions where the organisms may never have lived, 
 and in sediments which may differ widely from those forming the 
 normal facies of sea bottom for the type in question. As pointed 
 out in an earlier chapter, epiplanktonic and pseudoplanktonic forms 
 are most likely to produce such index fossils. The shell of Spirula, 
 a dibranchiate cephalopod of the modern fauna, illustrates the wide 
 distribution possible by flotation, though the animal has been found 
 to occur only in a few localities in deep water. Epiplanktonic Hy- 
 drozoa and Bryozoa likewise suffer a wide distribution through 
 the flotation of their host. 
 
1 134 PRINCIPLES OF STRATIGRAPHY 
 
 Among the pseudoplankton the shells of Ammonites should 
 be especially noted as being included, at least to some extent, in sedi- 
 ments of varied character over wide areas. * The genera and spe- 
 cies of ammonites as a rule were short-lived cephalopods, different 
 species characterizing different zones. Besides having their shells 
 widely distributed after death, by flotation, living ammonites also 
 seem to have spread rapidly and widely, probably during a mero- 
 planktonic stage. 
 
 Holoplanktonic organisms may also suffer a wide distribution 
 and, if they contain parts capable of preservation, these may be 
 entombed in sediments of widely different character. Such cases 
 are seen in the pteropod oozes of various geologic horizons. 
 
 The wide distribution of the Ordovicic graptolites was probably 
 due to epiplanktonic as well as holoplanktonic dispersion. Grapto- 
 lite species were short-lived, hence successive zones are characterized 
 by distinct types over a wide area. Plants whose seeds are widely 
 distributed by winds or other agents produce good index fossils 
 for continental deposits. Here, however, the climatic factor exer- 
 cises a limiting influence, since plants will only grow where climatic 
 conditions are favorable. 
 
 (b) Grade of index fossil. The grade of the index fossil com- 
 monly has a very direct relation to the magnitude of the strati- 
 graphic divisions to be correlated. Thus, while the class of trilo- 
 bites as a whole may serve for the recognition of Palaeozoic rocks 
 the world over none having as yet been found outside of the 
 Palaeozoic smaller subdivisions must be used for the correlation 
 of more restricted stratigraphic divisions. Thus the family Cono- 
 coryphidce among the trilobites is characteristic of the Cambric, 
 and any member of that family will serve to determine the Cambric 
 age of the strata in which it occurs. The family Olenidce is princi- 
 pally restricted to the CJambric, though some members occur in 
 the Ordovicic. The most 'characteristic types, nevertheless, serve to 
 correlate the Cambric formations in all their occurrences-. While any 
 of the more characteristic genera of this family (Olenidae) will 
 thus serve in correlating Cambric formations as a whole, certain 
 genera of this family serve as indices of the three principal sub- 
 
 * The pseudoplanktonic dispersal of the shells of Ammonites is strongly 
 advocated by Walther, but questioned by Ortmann (34), Tornquist (46), J. P. 
 Smith and others. Tornquist has urged against such interpretation the observa- 
 tion that in the Jurassic and Cretacic the Ammonites are distributed according 
 to climatic zones. Examples of dispersal by flotation are, however, known, for 
 as shown by Clarke (Naples fauna) the Goniatite fauna of the Styliolina or Ge- 
 nundewah limestone of western New York ("prenuncial intumescens fauna") 
 must be regarded as derived in this manner. (See also Chapter XXIX.) 
 
METHODS OF CORRELATION 1135 
 
 divisions. Thus Olenellus and Holmia characterize the Lower Cam- 
 bric, Paradoxides the Middle Cambric, and Olenus and Dikelloceph- 
 alus the Upper Cambric.* Again, the Middle Cambric may be 
 subdivided into a number of zones, each characterized by a species 
 of Paradoxides. These species are either identical or representative 
 in the corresponding zones of the East American and West Euro- 
 pean Middle Cambric. 
 
 The dendroid graptolite Dictyonema may serve as an example 
 of a genus of more extended range, some of whose species are, 
 nevertheless, good index fossils. The genus itself begins in the 
 transition beds from the Upper Cambric to the Lower Ordovicic, 
 where D. ftabelliforme is a characteristic index fossil and is 
 of almost worldwide distribution. Other species characterize the 
 Siluric and still others the Devonic. 
 
 (c) Correlation by equivalent stages in development. Among 
 organisms characterized by community of descent corresponding 
 stages in development are sometimes reached in different lines of 
 evolution at about the same time period. Such homceomorphic 
 representatives (morphological equivalents, see Chapter XXV) 
 may thus serve as indices of a given horizon even where inter- 
 communication has not occurred. Thus Goniatites the world over 
 characterize the upper Palaeozoic, but Goniatites are derived along 
 different lines of descent.f The simpler types along the various 
 lines of descent characterize the Devonic, while those with more 
 complicated sutures.4 greater involution, or marked ornamentation 
 are mostly characteristic of the Mississippic and Carbonic. The 
 Ceratite type, in which the lobes of the sutures are further modi- 
 fied by secondary indentations, while the saddles are entire, are 
 typically developed along the various lines of evolution, in the 
 Trias. Finally, the Ammonite type, in which both lobes and saddles 
 are modified by additional indentations, appears chiefly in the Juras- 
 sic, in the various evolutional lines, and continues into the Cretacic. 
 Owing to these facts the orginal idea prevailed that Goniatites con- 
 stituted one genus, characteristic of the formations from the Devonic 
 to the Carbonic; Ceratites formed another genus characteristic of 
 the Trias ; while Ammonites was regarded as a genus characterizing 
 the time from the Jurassic to the Cretacic inclusive. 
 
 It is now known, however, that many exceptions to this general 
 rule exist. Genetic series, in which acceleration of development 
 prevailed, reached the Ceratite or even the Ammonite stage in pre- 
 Triassic time. Thus the genus Prodomltes from the Lower Missis- 
 
 * For illustrations see Grabau and Shimer, North American Index Fossils 
 Vol. II. f See Chapter XXV, p. 978. } See Chapter XXIV, p. 945- 
 
u 3 6 PRINCIPLES OF STRATIGRAPHY 
 
 sippic (Chouteauan) has advanced into the Ceratite stage, while 
 Waagenoceras of the Permic has already true Ammonite (phylli- 
 form) sutures. Sometimes, by retardation, a type remains in a 
 more primitive evolutional stage, one which normally characterizes a 
 lower horizon. The case of the Triassic ammonite Trachyceras, 
 cited by J. P. Smith (45), from the Karnic limestone of California, 
 and referred to in Chapter XXV, belongs here. This had persisted 
 in the more primitive Tirolites stage and so suggested correlation 
 of the beds with those of a lower horizon. The "Pseudoceratites" 
 of the Cretacic (Hyatt-23) form another instructive example. In 
 these types (Protengonoceras, Engonoceras,* etc.) arrestation in 
 development affects the later stages (the earlier stages being ac- 
 celerated with reference to the corresponding stages of their Juras- 
 sic ancestors), so that the adult sutures remain in the ceratite or 
 even goniatite stage. This is a case of heterepistasis, the cessation 
 in development affecting only the sutures. What appears to be a 
 good example of corresponding stages in development in distinct 
 provinces at about the same time period, thus serving for inter- 
 regional correlation, is seen in the case of Clavilithes of the Parisian 
 Eocenic, and the corresponding morphologic equivalents of the 
 Eocenic of the Gulf States of North America. The American 
 series of species parallels the Parisian to such an extent that they 
 have been regarded as varieties of the Parisian species. There is 
 every reason for believing, however, that they represent an in- 
 dependent development. (Grabau-i5.) 
 
 The graptolites present other examples of corresponding stages 
 in development reached in distinct genetic series at approximately 
 the same time. Thus, Dichograptus, Tetragraptus, Didymograptus, 
 etc., represent stages in development rather than monophyletic 
 genera, but, since these stages appear simultaneously in the various 
 lines of descent, they may be used as geologic genera, eminently 
 adapted for correlative purposes. (Ruedemann-38.) 
 
 (d) Correlation by faunas and floras. Representative species. 
 When the index species themselves are not represented, correlation 
 by means of the sum total of associated organisms must be made. 
 Thus Paradoxides is absent from the Middle Cambric of the Ap- 
 palachian and Pacific provinces of North America, nor are any 
 of the associated species of the other genera present in these faunas. 
 Representative species, however, occur and the sum total of the 
 Middle Cambric faunas of the various provinces has similarity 
 of expression, which is almost as good as absolute identity. The 
 lower Middle Cambric of the Atlantic Coast and of western Europe 
 
 * For illustrations see North American Index Fossils, Vol. II. 
 
 
METHODS OF CORRELATION 1137 
 
 has different species of Paradoxides in the different provinces, but 
 these species are representative, so that they serve to correlate even 
 the zones. The zones with their representative or identical spe- 
 cies are as follows : 
 
 Eastern North America. Western Europe. 
 
 Paradoxides forchhammeri P. forchhammeri 
 
 P. davidis P. davidis 
 
 P. abenacus P. tessini 
 
 P. eteminicus P. rugulosus 
 
 P. lamella tus P. celandicus 
 
 Even between provinces as close as New Brunswick and east- 
 ern Massachusetts the species are representative rather than iden- 
 tical. Thus Paradoxides harlani, the large Middle Cambric trilo- 
 bite of eastern Massachusetts, is representative of P. eteminicus of 
 New Brunswick, while Acrothele gamagii of the Massachusetts 
 Middle Cambric is the representative of A. matthewi of New Bruns- 
 wick. The Meekoceras beds of the Lower Trias of the Himalayas, 
 Siberia, California, Idaho and Utah are readily correlated, though 
 no species common to these regions are known. The genera, how- 
 ever, which characterize them are sufficiently short-lived and the 
 species of the different provinces are closely representative. 
 (Smith-45.) 
 
 5. Correlation bv unconformities and dis conformities. 
 
 Correlation by unconformities has in the past been extensively 
 employed, and some stratigraphers have advocated the use of un- 
 conformities as a primary basis for correlation. A little reflec- 
 tion, however, will show that such a method, when used indis- 
 criminately, is sure to lead to confusion and false correlation, for 
 it is a well-ascertained fact that folding of formations was not 
 simultaneous in different parts of a region, nor in different regions, 
 but may be earlier in some and later in others. Thus, while there 
 was a rather widespread period of folding in later Palaeozoic time, 
 both in Europe and North America, this folding began in the De- 
 vonic in some sections, and not until the Permic in others. More- 
 over, the formation next succeeding the unconformity is by no 
 means always the same one, and grave mistakes have been made 
 by assuming this to be the case. Thus in some cases the Triassic 
 beds rest directly upon the folded Palaeozoics, while in other cases 
 beds of much later age, even Cretacic or Tertiary, succeed them. 
 
1 138 PRINCIPLES OF STRATIGRAPHY 
 
 In the same way the beds resting upon the truncated Ordovicic 
 folds in New York and Pennsylvania vary considerably in age. 
 The conglomerates succeeding the unconformity were originally all 
 classed as basal Siluric. In reality some are of Lower and some 
 are of Middle Siluric age, while in still other cases beds of upper 
 Siluric or even younger age rest directly upon the truncated roots 
 of the old folds. 
 
 Nevertheless, with due circumspection it is possible to use 
 great and widespread unconformities for broad correlation of 
 formations. Since there were two periods of widespread, if not uni- 
 versal, disturbance of the earth's crust, besides many minor ones, 
 these at least have a considerable value in correlation. One of 
 these occurred before the. beginning of Palaeozoic time, and the 
 other came to an end before the beginning of Mesozoic time. Thus 
 everywhere, the world over, the Archaean rocks are separated from 
 the Palaeozoic formations by great unconformities. This does not 
 apparently hold for all pre-Cambric rocks, however, since some of 
 the formations commonly referred to the Algonkian are separated 
 from the Cambric only by a disconformity. It may, however, be 
 true, as already pointed out, that the unaltered or but slightly 
 altered rocks, like the Belt terrane, the Uinta sandstone, and others, 
 are not necessarily pre-Palaeozoic. They are known to be pre- 
 Cambric, or better, in most cases only pre-Middle Cambric, and, 
 since they are largely, 'if not entirely, of non-marine origin, they 
 may, in part at least, represent the continental equivalents of the 
 marine Lower Cambric beds. The unconformity between the Palae- 
 ozoic and Mesozoic, though widespread, is nevertheless much more 
 restricted than the earlier one mentioned. Moreover, it is of suffi- 
 cient constancy to make possible this broad correlation, though, as 
 before remarked, there is no guarantee that the beds next succeed- 
 ing are everywhere of the same age. 
 
 - Disconformities are, to a certain extent, better criteria for cor- 
 relation, especially the larger and more extensive ones, which can 
 be interpreted as due to eustatic movements of the sea. Withdraw- 
 als or transgressions of the sea, due to change in sea-level, will 
 affect all continents more or less in the same manner, and thus 
 serve as a primary basis for subdivision. The danger with this 
 method lies in the difficulty of distinguishing between the local and 
 the widespread character of the disconformity and the tendency 
 which it induces to multiply the number of breaks in the geologic 
 column by assuming that the minor breaks of one locality are 
 necessarily reproduced elsewhere. 
 
 That there are widespread breaks in the geological column, 
 
METHODS OF CORRELATION 1139 
 
 which are undoubtedly due to eustatic movements of the sea, be- 
 comes more and more apparent. The widespread mid-Jurassic 
 transgression of the sea over Europe is well known and the discon- 
 formity (and occasional unconformity) produced by this trans- 
 gression has been used for widespread correlation. The great 
 Mid-Ordovicic hiatus first observed in North America/ (Grabau- 
 16; 18), and the similarly widespread hiatus in the tipper Ordo- 
 vicic (Weller-52), are now known to be marked in North Europe 
 as well (Bassler-5). In like manner the Mid-Siluric hiatus and 
 disconformity so widespread in North America appear also to be 
 present in the Baltic region of Russia and Sweden and in the 
 Bohemian Palaeozoic district. The probabilities are that in Mid- 
 Siluric time the sea left a large part of the present land area dry. 
 Similar widespread disconformities are recognized in the Mesozoic. 
 
 6. Correlation by regional metamorphism. 
 
 Regional metamorphism has already been defined as an altera- 
 tion or metamorphism, which affects extensive regions and which is 
 primarily due to tectonic disturbances. Such metamorphism may, 
 of course, occur at any time in the history of the earth, but when- 
 ever it does occur it will affect all the formations of the region in 
 which it takes place, though, obviously, some formations may be 
 more strongly affected than others. This being the case, it follows 
 that, wherever unaltered rocks overlie the metamorphosed ones, 
 the age of the former cannot date back of the period of meta- 
 morphism, and that, hence, the lower limit of their age is fixed 
 by this period of metamorphism. Evidently there is no guarantee 
 here, however, that the strata of the overlying series are all of 
 the same age, though within moderate limits this is probably true. 
 One^general rule may, perhaps, be formulated, and within certain 
 limits applied, namely, that, of two formations in contact, the more 
 strongly metamorphosed one is the older. Here, however, the same 
 caution is necessary that is required in applying the rule of greater 
 deformation to two deformed formations in contact. Some forma- 
 tions are more subject to metamorphism than others, just as some 
 formations are more subject to deformation. 
 
 The method of correlation by metamorphism is, perhaps, the 
 most applicable to the determination of the boundary line between 
 the pre-Palaeozoic and later formations, though even here it seems 
 not always to be reliable. This would appear from the fact that 
 extensive sedimentary formations, such as the Belt series of Mon- 
 
1 140 PRINCIPLES OF STRATIGRAPHY 
 
 tana, and its continuation into Canada, with a thickness of over 
 12,000 feet, and similar formations in Utah (Uinta quartzite) 
 and in the Grand Canyon district (Unkar and Chuar series*) 
 have suffered no appreciable metamorphism, though from their 
 relationship to the overlying Cambric formations they are believed 
 to be of pre-Cambric age. The Torridon sandstone of Scotland is 
 another example of a formation underlying the Olenellus-bearing 
 sandstones (Lower Cambric), the two being separated by a slight 
 unconformity, while the American formations are generally sep- 
 arated from the Cambric only by a disconformity, or at least by an 
 unconformity in which the deformation of the lower beds has 
 been so slight as to appear non-existent. If these formations are 
 really pre-Cambric, and not basal Cambric, they may well represent 
 an earlier system, which, however, still belongs in the Palaeozoic; 
 or they may represent a pre-Palaeozoic, but still post-Algonkic sys- 
 tem, one, the formation of which succeeded the apparently world- 
 wide metamorphism which has affected the Algonkic and earlier 
 formations. 
 
 Finally, it must be noted that extensive metamorphism has af- 
 fected rocks of Palaeozoic and even of much later age. The schists 
 and marbles of the New York City area are believed by many to 
 be the altered Cambro-Ordovicics, which, north of the Highlands, 
 appear unmetamorphosed. Berkey, however, holds that they be- 
 long to the pre-Cambric (6), a view strongly advocated by Crosby. 
 A similar difference of opinion exists with reference to the meta- 
 morphic rocks of New Jersey, especially those in the region about 
 Franklin Furnace. 
 
 On the whole, it will be seen that correlation by metamorphism, 
 while serviceable and often very reliable within certain limits, is, 
 nevertheless, a method likely to mislead. We need but recall that 
 the early stratigraphers classed all metamorphic rocks as Pri- 
 mary, and that this included the metamorphosed Palaeozoic forma- 
 tions of western Europe, as well as the metamorphosed Mesozoic 
 and later formations of the Alps. Or we may compare the older 
 and newer maps of New England and of the Appalachians, where 
 we shall find that many of the formations formerly classed as pre- 
 Cambric are now placed into the Palaeozoic. The international 
 map of Europe also shows many areas of pre-Cambric rock, where 
 more recent study has led the observers to place the metamorphic 
 formations high in the geological column. 
 
 * In the Chuar group fossils of Palaeozoic character have been found, 
 which suggests that these formations form a pre-Cambric Palaeozoic system if 
 they are not actually a part of the Lower Cambric, 
 
METHODS OF CORRELATION 1141 
 
 7. Correlation by diastrophism. 
 
 The recognition of the widespread character of hiatuses or gaps 
 in the sedimentary series, noted in preceding sections, suggests 
 that the causes of these breaks are of more or less universal extent. 
 These causes are diastrophic, or deformative of the earth's crust, 
 for every hiatus signifies a retreat of the sea, followed by a read- 
 vance, indicating, thus, a relative rise of the land-mass, which re- 
 sults in the emergence of large tracts, followed by a relative de- 
 pression, resulting in submergence. If these movements affect in- 
 dividual land blocks only, the regression and transgression are 
 chiefly confined to this block, while, at the same time, as has been 
 shown in Chapter I, a reverse change in relative level of sea and 
 land may be noted on the stationary blocks, this being brought about 
 by the readjustment of the entire sea-level, necessitated by the 
 partial displacement of it in one region. Thus, if one land block 
 rises independently of the others, its shores will suffer a negative 
 or retreatal movement, and its margins will emerge. As a result 
 of this, however, there will be a partial elevation of the sea-level 
 as a whole, due to the displaced water, and this will affect all 
 blocks, including the emerging one. In the latter it will tend 
 merely to reduce somewhat the total amount of sea-retreat which 
 the elevation of the block would bring about, but in the stationary 
 blocks there would be a universal advance of the sea over their 
 margins. Thus retreatal movements in one continent would be 
 correlated with transgressive movements in the other, and, since 
 emergence is followed by erosion, and submergence by deposition, 
 base-leveling of one continent would go on, with deposition beyond 
 its margins, at the same time that deposition over the submerged 
 margins of the other continents and a reduction in the erosive ac- 
 tivities over the unsubmerged portions of those continents would 
 occur. 
 
 If the movement affects the suboceanic crustal block, however, 
 a universal sinking or rising of the sea-level will result, in con- 
 formity with the lowering or elevation of this block. This will be 
 manifested in a universal retreat and readvance of the sea along all 
 continental margins, with the production of a widespread hiatus 
 in the succession of formations. If the interval between the two 
 movements is a large one, with comparative stability of the land, the 
 base-leveling processes will tend to wear the country down to a 
 nearly uniform level, while the resultant marginal deposits will terfd 
 further to raise the sea-level, and thus set the gravitative movement 
 
1 142 PRINCIPLES OF STRATIGRAPHY 
 
 going. The shrinking of the land from invading lower temperatures 
 will likewise tend to reduce the level of the land, and so permit 
 the sea to transgress across it anew. 
 
 If erosion is not uniform in amount, owing to variable hardness 
 of formations, or to other causes, the resulting hiatus will vary 
 in magnitude from point to point. For, though the time interval 
 between the retreat and readvance of the sea in two localities might 
 be the same, it is obvious that the missing formations will be more 
 extensive than can be accounted for by non-deposition, since, dur- 
 ing the interval of exposure, erosion removes a part of the earlier 
 deposited sediments. The amount thus removed in different sections 
 may vary greatly, and, hence, the gap in the series will vary from 
 place to place. 
 
 Chamberlin (9:504) has considered four stages, which must be 
 taken cognizance of in correlation by general diastrophic move- 
 ments: (i) "the stages of climacteric base-leveling and sea trans- 
 gression; (2) the stages of retreat, which are the first stages of 
 diastrophic movement after the quiescent period; (3) the stages 
 of climacteric diastrophism and of greatest sea-retreat; and, (4) 
 the stages of early quiescence, progressive degradation, and sea- 
 advance/' 
 
 (i) The stage where base-leveling and sea transgression have 
 successively reached their climax is especially characterized by 
 diminution in land, a reduction in the amount of solution, oxidation 
 and carbonation of. rocks, and, hence, in the abstraction of carbon 
 dioxide from the "atmosphere, coupled with the greatest extension 
 of lime deposition and hence the setting free of carbon dioxide. 
 Thus there will be a tendency toward the amelioration of the cli- 
 matic conditions, and this will aid the great expansional evolution 
 of marine life favored by the broad expansion of the littoral belt 
 and the- formation of numerous epicontinental seas. New marine 
 faunas and floras, often of a provincial type, will come into exis- 
 tence, which are likely to arise through parallel evolution from 
 closely related ancestors in the various provinces. Thus a wide- 
 spread basis for faunal correlation will be inaugurated, such faunas 
 comprising not identical, but rather closely representative, species. 
 Pathways for extensive migration along the littoral belts of the 
 oceans also result, and these tend to produce widespread uniformity 
 of the littoral fauna of the oceans. Such periods of extensive trans- 
 gression of the sea and corresponding expansional evolution are 
 seen in the late Cambric and early Ordovicic, in the Middle, and 
 early Upper Ordovicic, in the early Siluric, Middle Devonic, early 
 
METHODS OF CORRELATION 1143 
 
 Mississippic and in the Middle and early Upper Jurassic (Callovian 
 to Oxfordian), as well as in the early part of the Cretacic. 
 
 (2) The stages of initial diastrophism and sea-retreat are 
 marked by the increase in deposition of the material resulting from 
 the deep decomposition of the rock, during the period of base- 
 leveling; the increasing deposition of terrigenous elastics, and the 
 consequent change in the character of the fauna, a turbid water 
 fauna taking the place of the one previously flourishing in the 
 purer waters. The littoral belt is narrowed, the epicontinental seas 
 disappear, and the evolution of shallow-water life and the migration 
 of organisms are restricted. 
 
 (3) When the climax of the regression is reached the restric- 
 tion in the evolution of the shallow water organisms is at its maxi- 
 mum. Clastic deposits predominate and they even encroach upon 
 the continents. Climatic changes are toward a colder period, ow- 
 ing to the locking up of the carbon dioxide in land-vegetation, by 
 solution of limestones, and by carbonation of silicates. Such refrig- 
 eration may go so far as to result in glaciation, at least locally, the 
 evidences of such glaciation furnishing an additional basis for cor- 
 relation. Broad land expansions would in general favor wide dis- 
 tribution of animals and plants, unless the severity of the climate 
 should enter in as a deterrent factor. Should climatic factors be less 
 in evidence, however, the wide expansion of the land might favor 
 a wide distribution of land life. As a result, the struggle for ex- 
 istence would be less intense and modifications would be slower, 
 and more of the nature of adaptations to slowly changing environ- 
 ment. The littoral region of the sea being, however, much reduced, 
 the survivors of the once widespread marine littoral fauna would 
 be forced into a more restricted area and hence a fierce struggle 
 for existence would be sure to result. This would lead to the rapid 
 extinction of numerous types and to the comparatively rapid modi- 
 fication of the survivors, and would thus produce a comparatively 
 sudden change in the character of the fauna. 
 
 (4) The early stages of quiescence and base- leveling which fol- 
 low and which initiate anew the slow transgressive movement 
 of the sea, will again favor migration of marine faunas. Owing to 
 the effect of the previous restrictions, however, the aspect of the 
 fauna will have been changed to a marked degree, so that the ex- 
 panding fauna will have a distinct aspect of its own. The great 
 expansion which followed the retreat of the sea in the late Middle 
 or early Upper Cambric time in North America brought with ^it 
 the spread of a fauna widely different from that which preceded it. 
 The Middle and early Upper Ordovicic expansional faunas (Chazy- 
 
1 144 PRINCIPLES OF STRATIGRAPHY 
 
 Trenton) differed, likewise, in a marked degree from the preced- 
 ing Beekmantown faunas. The Siluric fauna of North America, 
 also an expansional fauna, differed radically from that of the preced- 
 ing Upper Ordovicic (Weller-52), which was largely exterminated 
 by the late Ordovicic or early Siluric retreat of the sea. The com- 
 parative uniformity of expansional faunas, over wide areas, such 
 as that of the Mid-Ordovicic, the early Siluric, the Mid-Devonic, 
 and the later Jurassic and Cretacic, shows that such periods are 
 eminently fitted to furnish a basis for practically worldwide cor- 
 relation. 
 
 Finally, it may here be noted that, if the theory of polar pendu- 
 lations, as outlined in Chapter XXIII, should prove to have a 
 sound basis in fact, we must modify our conception of movements 
 of the water body, to the extent of recognizing the coincident ris- 
 ing of the sea-level in the region approaching the Equator, and the 
 fall of the sea-level in the regions approaching the poles. Thus 
 movements of the water body would not be uniform over the earth, 
 but compensatory, rising in the equatorial and falling in the polar 
 regions. For an attempt at correlation on such a basis the student 
 is referred to Simroth's book "Die Pendulations-theorie." (44.) 
 
 PALuEOGEOGRAPHY AND PAI^EOGEOGRAPHIC MAPS. 
 
 "Palaeogeography," says Dacque, "may be compared to a fire 
 which has smoldered long under cover, but which has at last broken 
 forth with all-consuming energy" (12). Attempts to restore the 
 outlines of continents and seas during former geological periods 
 were essayed by geologists and palaeontologists before the middle of 
 the nineteenth century. Since then the subject has smoldered 
 under cover of the detailed investigations carried on in other fields 
 by the students of the earth sciences, until, in recent years, it has 
 burst forth with almost volcanic violence, and palaeogeographic maps 
 and palaeogeographic discussions have become the order of the day. 
 
 The term Palao geography is credited to Robert Etheridge, and 
 its birth is given as in the year 1881 (Schuchert-39),* but palaeo- 
 geographic maps were made much earlier. Schuchert regards those 
 given by Dana in the first edition of his manual (1863) as the earli- 
 est; but earlier maps, though less definite in character, had been 
 published, as, for example, those by Goodwin Austen for England 
 
 *Dacque" mentions A. Bou6, who in 1875 used the terms palaogeologische Geo- 
 graphic and geologische Paldo-Geographie. (Sitzungsberichte K. K. Akad. Wiss. 
 Wien. Math. Nat. Kl. Bd. 71, i te Abt., s. 305-405.) 
 
PAL^OGEOGRAPHIC MAPS 1145 
 
 in 1856, by B. Crivelli for Italy in 1853 and by Gemmellaro for 
 Sicily in 1834. (Dacque-i2:/p^.) The most elaborate recent at- 
 tempt to map the conditions of land and water at different geologic 
 periods is that of Schuchert, who, in his instructive monograph on 
 the Palseogeography of North America, has published fifty separate 
 maps showing the changes in outlines of North America from 
 Cambric to Pliocenic time. 
 
 TYPES OF PALyEOGEOGRApmc MAPS. Palseogeographic maps may 
 be simple or complex, special or generalized. The simple map aims 
 to show the distribution of geographic features, of a particular pe- 
 riod in the earth's history, over the surface of the earth, much as a 
 modern geographic map shows this distribution for the present time ; 
 a complex map, on the other hand, attempts to show more than this. 
 The simple map need not be confined to the depiction of the hypo- 
 thetical coastline, but, if the facts available allow it, should repre- 
 sent the ocean currents, the mountains, the rivers, etc. As examples 
 of maps of this type, though very incomplete, especially in so far as 
 the land features are concerned, may be mentioned the Ordovicic 
 map by Ruedemann (38) and those for the same time-period by 
 Grabau (18); the older Devonic maps of Schuchert, and many 
 others. The excellent maps by De Lapparent (31) may also be 
 classed here, though on them the areas of continental as well as 
 marine sedimentation are shown. The complex maps may show, 
 in addition to the deduced geographic conditions, some of the data 
 on which this deduction is based, especially the distribution of the 
 geological formation in question, or of its outcrops. Such a map^ 
 is in reality a combination of a palseogeographic and a geologic 
 map, and this may prove highly useful, for the degree of detail de- 
 picted upon the map, and the extent to which the map is hypotheti- 
 cal, are at once apparent. Such are the maps issued by Schuchert 
 for North America. A somewhat more complicated type is repre- 
 sented by the Palseogeographic maps issued by Chamberlin and 
 Salisbury ( 10) where the attempt is made to represent not only the 
 outcrop, but also the parts believed to exist beneath cover, and 
 the areas from which the formations are believed to be removed 
 by erosion. 
 
 The most complex and detailed maps of this type published in 
 America are those issued by Bailey Willis (57; 59). In them the 
 attempt is made to represent the oceanic basins, the littoral and the 
 epicontinental waters, the areas which may have been either sea 
 or land separating those which were more likely sea and those 
 which were more likely land the lands of the time, the indetermi- 
 nate areas, and the ocean currents, both polar and equatorial. 
 
1146 
 
 PRINCIPLES OF STRATIGRAPHY 
 
 Maps of this kind are more easily read when colors instead of 
 symbols are used. Another type of complex map is that which at- 
 tempts to show changes in outline of the lands and seas during the 
 period represented. Such are the maps of Freeh (13), in which 
 transgressions and regressions of the sea are represented by differ- 
 ences in color. Haug, too (21), indicates the areas of trans- 
 gression upon his maps, . and, furthermore, outlines the limits 
 of the geosynclines. And, in addition, his maps are facies 
 maps. 
 
 Special maps aim to show the outlines of lands and seas at a 
 definite time period, as at the end of the Lower, Middle or Upper 
 Cambric (Fig. 264 a-c), or at the beginning of a time period. 
 Such maps may be either simple or complex. Examples of the 
 
 FIG. 264. Maps showing the probable distribution of land and sea around 
 the Atlantic basin in Cambric time. a. At end of Lower Cam- 
 bric, b. At end of Middle Cambric, c. At end of Dictyonema 
 ftabelliforme time. (A. W. Grabau.) 
 
 former are the maps published by Grabau (19) for the Cambric 
 (Fig. 264), and for the various stages of the Ordovicic (18). The 
 maps published by Schuchert, Chamberlin and Salisbury, Willis, 
 Haug, De Lapparent, and, indeed, by most authors are general 
 maps to cover a whole time period, though in some cases this period 
 may be very small. 
 
 CONSTRUCTION OF PAL^EOGEOGRAPHIC MAPS. In the construction 
 of palseogeographic maps it is first of all necessary to bear in mind 
 that modern geographic maps can at least serve only as a distorted 
 base for such depiction. Thus the Appalachian region of North 
 America, and the region of the Alps in southern Europe are areas 
 where the earth's crust has been greatly foreshortened, and where, 
 hence, localities far apart at an earlier time were brought close 
 together. It is, of course, impossible to allow for such foreshorten- 
 ing, if the localities where certain formations crop out to-day are 
 
METHODS OF PAL^OGEOGRAPHY 1147 
 
 to be brought into the seas in which they were deposited. Thus, 
 as will be seen on the maps for the Lower Cambric (Fig. 2643.), the 
 New England land barrier between the Atlantic and the Pacific ex- 
 tension in the Appalachian or Cumberland trough is much too nar- 
 row, while the width of that trough is also too small. The same 
 is true for the land-barrier in North Britain, between the Atlantic 
 and Arctic oceans. Since, however, the rocks carrying the faunas 
 of these two seas are found so much nearer together .to-day than 
 was the case at the time of the deposition, such faulty construction 
 seems to be unavoidable. 
 
 The overlap relations of marine strata are especially significant 
 as aids in determining old shore-lines, for such overlap of a later 
 over an earlier formation indicates, as a rule, that the point of 
 overlap is also a point on the shore-line of the earlier formation. 
 Due attention must here be given to the type of overlap (see Chap- 
 ter XVIII), and the fact must be borne in mind that minor over- 
 laps may also be developed upon an irregular sea-bottom, where 
 wave activity or current scour is active. 
 
 Important factors that must not be overlooked in the construc- 
 tion of palaeogeographic maps are the nature of the sediment and its 
 source. Where coarse clastic sediments abound in the formation, 
 a land of sufficient size must have existed to furnish this sediment. 
 This is especially the case when the sediment consists of well-as- 
 sorted material, such as quartz-sand or pebbles, when it must be 
 remembered that such assorted material may represent only a part, 
 perhaps less than one-fourth, of the original rock which was its 
 source. In general, it may be said that much closer discrimination 
 between marine and non-marine sediments than has generally been 
 the case is necessary; and the conditions of deposition must be 
 borne in mind, as well as the factors of marine and non-marine bion- 
 omy, and the effects of topography on currents and of both on 
 deposition, so that we may not again fall into the error of recon- 
 structing the area of former coral-rock formation as an arm of the 
 sea, one-half or one-quarter of a mile in width, and less than ten 
 fathoms in depth. 
 
 When the science of Stratigraphy has developed so that its basis 
 is no longer purely or chiefly pabeontological, and when the sciences 
 of Lithogenesis, of Orogenesis and of Glyptogenesis, as well as of 
 Biogenesis, are given their due share in the comprehensive investi- 
 gation of the history of our earth, then we may hope that Pabeo- 
 geography, the youthful daughter science of Stratigraphy, will have 
 attained unto that stature which will make it the crowning attract- 
 ion to the student of earth history. 
 
1 148 PRINCIPLES OF STRATIGRAPHY 
 
 BIBLIOGRAPHY XXXII. 
 
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INDEX 
 
 (Consult also the table of contents. Names of genera and species are, with few 
 
 exceptions, omitted.) 
 
 Aar, delta of, 610 
 
 Aarmassive, 308 
 
 Abbe, C., cited, 56 
 
 Abbotsham, 223 
 
 Ablation, 17, 263 
 
 Abrasion, 18 
 
 Abrolhos Islands, 416 
 
 Abu Roasch, 856 
 
 Abu Sir, 355 
 
 Abyssal district, 983 
 
 Abyssinia, 355 
 
 Abyssinian Mountains, rainfall in, 68 
 
 Abyssolith, 310, 731 
 
 Abysso-pelagic district, 983 
 
 Acadian, 1128 
 
 Acanthin, 457 
 
 Acaustobioliths, 384 
 
 Acaustophytoliths, 280, 467 
 
 Acceleration, differential, 964 
 
 , illustration of law of, 969, 970 
 
 Accordanz, 821 
 
 Accretions, 719 
 
 Achatinellidse, mutations of, 1043, 1052 
 
 Acid, crenic, 37 
 
 , humic, 37 
 
 , ulmic, 37 
 
 Actinic (chemical) rays, 28 
 
 Adams, F. D., cited, 92, 747, 773 
 
 Adams, F. D., and Coker, E. G., cited, 773 
 
 Adaptive radiation, " 1054 
 
 Adirondacks, 834 
 
 Adour River, 223, 558 
 
 Adriatic Sea, 108, 240 
 
 , Po delta in, 584 
 
 , surface salinity of, 153 
 n Sea, 240, 334 
 
 , temperatures of, 189 
 JQolian Islands, volcanoes of, 861 
 ^Ethoballism, 749, 765 
 Mtna, radial dikes of; 870, 871 
 Afghanistan, habitual fault lines of, 882 
 Africa, coast of, 235 
 African deserts, salinas of, 359 
 Agarica, 406 
 Agassiz, A., cited, 102, 125, 219, 387, 406, 
 
 408, 414, 416, 461, 462, 469, 470, 471, 
 
 519, 520, 685, ion, 1021, 1024, 1026, 
 1038, 1069 
 
 , quoted, 519, 680, 1016, 1019, 1020 
 
 Agassiz, L., cited, 143, 462 
 
 Agger, 224 
 
 Agoniatite limestone, 425, 1131, 1132 
 
 Agra, 26 
 
 Agulhas banks, 218 
 
 Agulhas shelf, 103 
 
 Aidin, 54 
 
 Aigon, earthquake fissures in 1861 at, 883 
 
 Air frost, 63 
 
 Airy, G. B., cited, 265 
 
 Ajusco Mountain group, new mountain 
 formed in 1881 in, 863 
 
 Alabama, coastal plain of, 839 
 
 Aland Islands, 241 
 
 Alands deep, temperatures in, 190 
 
 Alaska, 263 
 
 , dredging off coast of, 641, 642 
 
 , glaciers of, 324 
 
 , stone glaciers from, 544 
 
 , tundra of, 507 
 
 Albatross, dredgings by, 519, 676 
 
 Albatross, marine habitat of, 985 
 
 Alberta, pre-Cambric reefs of, 418 
 
 Albert Edward Nyanza Lake, 124, 359 
 
 Albert Lake, 118, 119 
 
 , composition of, 157, 158, 159, 160 
 
 , salinity of, 155 
 
 , soda deposits of, 361 
 
 Albert Nyanza Lake, 124 
 
 Albien, 730 
 
 Albuquerque, dune sands from, 553 
 
 Alcyonaria, 385, 392, 1083 
 
 Aldborough, church at, 225 
 
 Alden, W. C., cited, 92 
 
 Aldrich, T. H., cited, 916 
 
 Aletschhorn, 308 
 
 , unconformity in, 825, 826 
 
 Aleutian Islands, basaltic lava field in, 867 
 
 , submarine volcanoes of, 872 
 
 Algae, 935 
 
 , encrustation by silica, 477 
 
 Algal Lake, peat of, 498 
 
 Algeria, onyx deposits of, 345 
 
 , salt dome of, 379, 758 
 
 Algiers, 221, 240 
 
 Alhambra formation, 591 
 
 , torrential deposits from, 30 
 
 Allahabad (Persia), 26 
 
 Allan, Dr., cited, 413 
 
 Allegheny formation, thickness in Appala- 
 chians of, 904 
 
 Allegheny River, gravel terraces of, 136 
 
 Allen, H. S., cited, 685 
 
 Allen, T. A., cited, 921, 956 
 
 Allochthonous, 298, 467, 478 
 
 Allolebod, 355 
 
 Allometrons, 961, 970 
 
 Allotriomorphic dolomite crystals, 445 
 
 Alpena, reefs at, 427, 428 
 
 Alps, alluvial deposits of, 584 
 
 , igneous intrusions in, 308 
 
 Altenburg, 1086 
 
 Amazon River, 248 
 
 , red mud opposite mouth of, 669 
 
 Amber, 1075 
 
 Amboina Island, 519 
 
 Ambulacral areas, 949 
 
 H5I 
 
1152 
 
 INDEX 
 
 Ames limestone, 1132 
 
 Amfila Bay, 355 
 
 Amherstburg, 422 
 
 Ammonites, 945, 978 
 
 , minerals in chambers of, 1085 
 
 , naming of, 913 
 
 , wide distribution of shells of, 1022 
 
 Ammonoidea, 945 
 
 Ammonoids, range of, 945, 946 
 Amu-darja (Amudaria), see Oxus 
 
 Amundsen, R., cited, 327 
 
 Amygdaloidal structure, 277 
 
 Amygdules, 313 
 
 Anam, 242 
 
 Anamorphism, zone of, 747 
 
 Andaman Islands, 109 
 
 Andaman Sea, 109, 393 
 
 Anderdon fauna, 1126 
 
 Anderdon limestone, 52, 422 
 
 Anderdon, Ontario, 423 
 
 Anderson, J. G., cited, 543, 578 
 
 Anderson, T., cited, 878 
 
 Anderson, W. S., cited, 380 
 
 Andersson, G., cited, 85 
 
 Andersson, J. G., cited, 92 
 
 Andes, earthquake fissures in, 883 
 
 , rainfall on, 67 
 
 , snow-line of, 322 
 
 Andesites, depth of formation of, 15 
 
 Andree, K., cited, 367, 380, 644, 673, 682, 
 685, 748, 773, 1069 
 
 Andresen C. C., cited, 223, 265 
 
 Andrussow, N., cited, 338, 351, 354, 380, 
 443, 444, 462, 609, 637, 666, 685 
 
 , quoted, 354 
 
 Anegada Straits, 108 
 
 Anemoclasts, 285 
 
 Angara River, 116 
 
 ,Anglesey, craterlets of, 885 
 
 , sandstone pipes of, 884 
 
 Anhydrite, changed to gypsum, 537 
 
 Animikie, 385 
 
 , Archaeocyathidae of, 417 
 
 Anschutz quarry, 420 
 
 Antarctic block, 9 
 
 Antarctic glacial clay, salt content of, 367 
 
 Antarctic Ocean, manganese concretions in, 
 718 
 
 Antedon, development of, 1032 
 
 Anthracite coal, 510, 511 
 
 Anthracolithic period, 511 
 
 Anticosti, 418 
 
 , peat beds of, 508, 509, 514 
 
 Anticyclones, 46 
 
 Antigua Salines, onyx marble of, 344 
 
 Antilles, decapods in mountains of, 1027 
 
 Antilles, Lesser, 233 
 
 , pteropod ooze outside of, 456 
 
 Apennines, mud volcanoes in, 872 
 
 Aphotic region, 982, 983 
 
 Apo, 77? 
 
 Apocremc acid, 173 
 
 Apophyses, 304 
 
 Appalachian region, basal Cambric sand- 
 stones in, 729 
 
 , overlap of marine strata in, 732 
 
 Appalachians, disconformities in, 823 
 
 , folding of, 903 
 
 , foreshortening of, 903 
 
 , revived topography of, 845 
 
 , source of Pottsville conglomerate in, 
 
 742 
 
 , spring line in, 261 
 
 Aptien, 730, 850 
 
 , overlapping of, 850 
 
 Aptychus beds, age of, 459 
 
 , origin of, 677 
 
 Aquileja, 153 
 
 Aquitanien, 454 
 Arabia, dune area of, 562 
 Arabian Gulf, temperature in, 187 
 Arabian Sea, 240 
 
 , miliolitic limestone of, 574 
 
 , oolite dunes of, 472 
 
 , temperature of, 187, 190 
 
 Arago, cited, 72 
 
 Aragon, Planorbis of, 1086 
 
 Aragon, woods replaced by sulphur at, 1081 
 
 Aragonite, oolites of, 473 
 
 , oolites changed to, 469 
 
 , recrystallization of, 755 
 
 Aral Sea, composition of, 157 
 
 , dunes of, 561 
 
 , salinity of, 155 
 
 Arbuckle Mountains, Saint Peter standstone 
 
 in, 739 
 
 Area, in Bermudaite, 573 
 Arctic climatic period, 506 
 Arctic Ocean, Lithothamnion in, 470 
 
 , mean temperature of, 193 
 
 Arenaceous texture, 285 
 
 Arenig, 315 
 
 Arenytes, 285 
 
 Argentina, 367 
 
 Argentine basin, 105 
 
 Argon, 25 
 
 Arizona, onyx marble of, 343 
 
 , pre-Cambric "reefs" of, 418 
 Arizona desert, earthquake fissure in, 884 
 Arkansas, caverns of, 346 
 
 , hot springs of, 201 
 
 , overlap of marine strata in, 732 
 
 Arkansas River, 245 
 
 Arkose, 33 
 
 Arldt, T., cited, 1148 
 
 Armenia, alkaline lakes of, 361 
 
 Armorican Mountains, 71, 373, 375 
 
 , elevations of, 374 
 
 Arrhenius, S., cited, 22, 29, 92, 757, 758, 
 
 Arsis, climatic, 82, 83 
 Artemia, excrements of, 1093 
 Arundel formation, 632 
 Ascutney Mountain, 302 
 Ascension Island, 105, 215 
 
 , oolites of, 336 
 
 , pteropod ooze near, 456 
 
 Aseptata, 943 
 
 Ashkabad, unbedded eolian deposits at, 554 
 
 , well-boring near, 592 
 
 Ashokan formation, origin of, 635 
 
 Asia, connection with America by Behring 
 
 Sea, 1 06 1 
 
 Asia Minor, 240, 334 
 Askja, eruption of, 866 
 
 Aspen, dolomitization of limestone at, 761 
 Astogeny, defined, 973 
 Astrakhan, rainfall at, 65 
 Astrakhan desert, salt lakes of, 357, 358 
 Atacama desert, 32, 364, 365 
 
 , dunes in, 563 
 
 , natural mummies in, 1077 
 
 , soda niter deposits in, 364 
 
 Atlantic climatic period, 506 
 
 Atlantic Ocean, manganese concretions in, 
 
 718 
 
 , mean temperature of, 193 
 
 , surface temperature of, 182 
 
 , temperatures in, 185, 187 
 
 Atlantosaurus beds, see Como beds 
 Atmobips, 991, 992 
 Atmo-biotic realm, 982 
 Atmoliths, 279 
 Atmology, 20 
 
 Atmometamorphism, 749, 767 
 Atmoseisma, 88 1 
 
INDEX 
 
 H53 
 
 Atmosphere, chemical work of, 34 
 - circulation of, 42 
 
 composition of, i, 24 
 
 electrical phenomena of, 72 
 
 impurities of, 24, 27 
 
 mechanical work of, 5 1 
 
 optical characters of, 28 
 
 temperature of, 29 
 
 Atmospheric pressure, 2 
 Attawapishkat River, reefs of, 430 
 Atwater, cited, 915 
 
 Aube, pebble "rain" of, 56 
 Austen, G., cited, 1144 
 Australia, 390 
 
 , barrier reefs of, 387 
 
 , Cambric tillites of, 534, 535 
 
 , Muree glacial formation of, 536 
 
 Autochthonous, 298, 467 
 Autoclasts, 285 
 Autophytography, 1082 
 Autotype, 919 
 Autun, cannel coal of, 481 
 Auvergne, acid lavas of, 869 
 
 mineral springs of, 179 
 
 petrified chelonian eggs from, To88 
 
 pustular lava cones in, 870 
 
 volcanic lake basins of, 120 
 
 volcanoes of, 874 
 
 Aves, 954 
 
 Avon River, 663 
 
 Ayin Musa Springs, entomostracan ooze of, 
 
 456 
 Ayrshire, prismatic jointing in coal seams 
 
 of, 820 
 Azores, 152, 205, 218 
 
 , pteropod ooze near, 456 
 
 , transported rocks off the, 452 
 
 , volcanic cone in the, 864, 865. 
 
 Bacteria, anaerobic, 338 
 Baden, Miocenic deposits of, 754 
 Bader, H., cited, 352, 380 
 Bad land topography, 53 
 Baffin Bay, 108, 109, 237 
 Baffin Land, 418 
 Bahama Banks, 233 
 Bahama Islands, 398, 411 
 
 , foraminiferal sands of, 455 
 
 Bahia, 341 
 
 Bahia Blanca, 360 
 
 Baie, Bay of, volcano in, 863 
 
 Bain, F., cited, 82, 93 
 
 Bakalsk, rock streams at, 547 
 
 Bakewell Buxton, warm springs of, 201 
 
 Bala-ischem, 54 
 
 Balbi lagoon, 401 
 
 Balch, F. N., cited, 1042, 1069 
 
 Balchash Sea, elevation of, 115 
 
 Bald Eagle conglomerate, 636 
 
 Ballingtang channel, 237 
 
 Baltic, amber of, 1075 
 
 Baltic Provinces, cuesta of, 838 
 
 Baltic Sea, 109, no 
 
 , osmotic pressure in, 180 
 
 , salinity of, 1044, 1045 
 
 , temperatures of, 190 
 
 Baltic stream, 241 
 
 Baltzer, A., cited, 307, 308, 320, 825 
 Baluchistan, desert areas of, 562 
 Banda, Island of, Spirula dredged near, 
 
 1021 * 
 
 Banda Sea, 107, 186, 242 
 Rinff, synclinal fold near, 796 
 Ranks, 104 
 Baraboo ridge, 848 
 
 Barbados, dust falls at, 60 , 
 
 , radiolarian ooze of, 458, 678 
 
 Barbados earth, 458, 1008, 1082 
 Barbour, E. H,, cited, 1092 
 Barca, 153, 240 
 Barchans, 556, 563 
 Bardarson, G., cited, 92 
 Baren, G. van, cited, 92 
 Barent shelf, 103 
 Barent Straits, 236 
 Barents Sea, 112, 236 
 Barnstable, 1041 
 Barnstable Bay, waves in, 222 
 Barrande, J., cited, 1126 
 Barrell, J., cited, 93, 541, 578, 619, 633, 
 634. 635, 637, 662, 709, 721, 740, 744 
 
 , quoted, 604, 621 
 
 Barren lands, 133 
 
 Barrows, W. L., cited, 72, 73, 93 
 
 Barus, C., cited, 15, 22, 685 
 
 Barysphere, i. 
 
 Basal bed, formation of, 731 
 
 Basalts, depth of formation or, 15 
 
 Bascom, F., cited, 772, 773 
 
 Basel, 251 
 
 Basin, Alabama-Mississippi, 810 
 
 Allegheny, 810 
 
 Brazilian, 105 
 
 Illinois, 810 
 
 Iowa, 810 
 
 James Bay, 810 
 
 Michigan, 810, 846 
 
 New York, 810 
 
 North African, 105 
 
 North Atlantic, 105 
 
 Oklahoma, 810 
 
 Ottawa, 8 10 
 
 Paris, 846 
 
 Quebec, 810 
 
 St. Lawrence, 810 
 
 Wisconsin, 810 
 Baskunchak Lake, 357 
 
 Bassler, R. S., cited, 1089, 1095, 1139, 1148 
 Bastei, 53 
 Batavia, 26 
 
 Bath, hot springs of, 201 
 Bather, F. A., cited, 93 
 Batholith, 303 
 Bauer, M., cited, 93, 537 
 Bauermann, cited, 469 
 Bavaria, Jurassic reefs of, 437 
 Bay of Bengal, 240 
 
 , temperature of, 187 
 
 Bay of Biscay, 112, 219 
 
 , dune areas of, 557 
 
 , salinity range of, 152 
 
 Bay of Cadiz, temperatures of, 189 
 Bay of Danzig, salinity of, 151 
 
 , delta in, 614 
 
 Bay of Fundy, 112, 649 
 
 , tides of, 226 
 
 Bay of Morlaix, peat of, 514 
 
 Bay of Naples, mud of, 334 
 
 Bay of New York, in Tertiary, 984 
 
 Bayou la Fourche, 245 
 
 Beach cusps, 706 
 
 Beardmore, cited, 248, 265 
 
 Bear Island, solifluction on, 543, 544 
 
 Bear Island stream, 236 
 
 Bear River, calcium carbonate in, 468 
 
 Beaumont, Elie de, cited, 203 
 
 Beche, see de la Beche 
 
 Bechilite, 364 
 
 Becker, G. F., cited, 752, 774, 906, 908 
 
 Beecher, C. E., cited, 979, 1086 
 
 Beede, J. W., cited, 624, 637 
 
 Beekite rings, formation of, 1083, 1085 
 
 Behrens, J. H., cited, 685 
 
1 154 
 
 INDEX 
 
 Behring Sea, 108, 242 
 
 Behring Sea, pole migrating toward, 895 
 
 , surface freezing of, 181 
 
 Behring shelf, 104 
 
 Behring Straits, 242 
 
 Belfast, South Africa, glacial deposit at, 
 
 Belgica, 185, 187 
 Belgium, dunes of, 558 
 
 , Permic climate of, 375 
 
 , reefs of, 423 
 
 Bell, R., cited, 430, 462 
 
 Belle Isle, Cambric limestone of, 417 
 
 Belt of cementation, 17 
 
 Belt of weathering, 17 
 
 Belt terrane, 334 
 
 , age of, 1138, 1139, 1140 
 
 , Cryptozoan of, 417 
 Belvedere gravels, 595 
 Bengal Gulf, temperature in, 187 
 Ben Nevis, 32 
 
 , wind-blown pebble on, 56 
 
 Benthos, denned, 991, 996 
 
 , sedentary, 996 
 
 , vagrant, 996 
 
 Benton clay, 261 
 
 Berckhemer, F., cited, 438 
 
 Berendt, G., cited, 126, 133, 557 
 
 Bergschrund, 264 
 
 Berkey, C. P., cited, 206, 223, 265, 637, 
 
 717, 721, 903, 1140, 1148 
 Berkey, C. P., and Hyde, J. E., cited, 200 
 Berlepsch salt shaft, 757 
 Bermuda, 390, 397, 411 
 
 calcareous dunes of, 573 
 
 calcareous sand of, 651 
 
 cementation of sands of, 753 
 
 consolidation of sand of, 750 
 
 eolian rocks of, 293, 439 
 
 lime-sand dunes of, 343 
 
 Lithothamnion at, 471 
 
 peat in, 509 
 
 reefs, 416 
 Bermudaite, 573 
 Bernard, F., cited, 956, 1095 
 
 quoted, 1073 
 
 Bert e waterlime, 376 
 Bertin, cited, 217 
 
 Bertrand, C. E., cited, 481, 482, 520 
 Bessarabia, 443 
 Bessel, cited, 7 
 Beyrich, E., cited, 1108 
 Biarritz, 103, 558 
 Bigelow, H. B., cited, 520, 685 
 Biggs, Oregon, 53 
 
 Bighorn Basin, Eocenic and Oligocenic de- 
 posits of, 627 
 
 Big Pine, block movement of, 88/ 
 Bigsby, J., cited, 1122 
 Big Soda Lake, analysis of, 361 
 Billings, E., cited, 915 
 Bilma oasis, 359 
 Bimana, 956 
 Bingerloch, 245 
 Binnewater sandstone, 731, 823 
 
 , Lorraine age of, 823 
 
 Bioclasts, 285 
 
 Biogenesis, importance of, 1147 
 
 Bioliths, 384 
 
 Bionomic realms, 982 
 
 Biometamorphism, 768 
 
 Bioseisma, 88 1 
 
 Biosphere, i, 16 
 
 Bird s Eye limestone (see Lowville), 488, 
 
 1124 
 
 Birma shelf, 103 
 Birsig River, 251 
 Bischof, G., cited, 163, 350, 614, 637, 760 
 
 Bitter Lakes of Suez, 366 
 
 , deposits of, 352 
 
 , intercalated silt layers of, 697 
 
 Bitter Spring Laa, sulphate waters of, 168 
 Bituminous coal, 510, 511 
 Black Hills, 308 
 
 , dome of, 841, 842, 843 
 
 Black Hills dome, dips in, 808 
 
 Black Hills, flanking monoclines of, 844 
 
 Black Lake, salinity of, 154 
 
 Black Prairies, 839 
 
 Black Rock Desert, playa lake in, 603 
 
 Black Sea, 107, 115, 230, 240 
 
 , black mud at bottom of, 1046 
 
 , dwarf fauna of, 1067 
 
 evaporation from, 27 
 
 faunal conditions in, 666, 667 
 
 muds in, 479 
 
 optics of, 204 
 
 salinity of, 153 
 
 , salt and gypsum deposits on borders 
 
 of, 348 
 
 , surface freezing of, 181 
 
 Black shale, 261 
 
 , Devonic, origin of, 636, 637, 850 
 
 Blackwell, T. E., cited, 248, 249, 265 
 
 Bladderworts, 495 
 
 Blake, abyssal deposits dredged by, 676 
 
 , dredging of Spirula by the, 1021 
 
 , dredgings of, off West Indies, 519 
 
 Blake, T. F., cited, 685 
 Blake, W. P., cited, 637 
 Blake Plateau, 673 
 Blanck, E., cited, 578 
 Blanckenhorn, M., cited, 92 
 Blastoidea, 949 
 
 , naming of, 913 
 
 Blattermollasse, 630 
 
 Bludenz, weather at, 48 
 
 Blue Lick Springs, Upper, composition of, 
 
 1 68 
 
 Blue Ridge, monoclines of, 798 
 Blum, J. R., cited, 1081, 1083, 1085, 1086, 
 
 1087, 1088, 1095 
 Blytt, A., cited, 506 
 Bodlander, G., cited, 657, 658 
 Bogdo Lake, salinity of, 154 
 Bohemia, 336 
 
 , Devonic reefs of, 423 
 
 , overlap relations of Cambric of, 729 
 
 Bohemian Mass, 373 
 
 Bokkeveld series, Devonic fossils in, 536 
 
 Bolivia, 365, 369 
 
 Bolson plains, 341 
 
 Bolsons, 58 
 
 Bon Ami, Cape, gliding in limestones of, 
 
 782, 783 
 Bonney, T. C., cited, 462, 878 
 
 , quoted, 400 
 
 Bombay shelf, 103 
 Boracite, 372 
 Borax Lake, 363 
 
 , composition of, 158 
 
 , salinity of, 154 
 
 Bordeaux, natural mummies from, 1076 
 
 Boreal climatic period, 506 
 
 Bornemann, J. G., cited, 284, 417, 455, 520 
 
 Borneo, 242 
 
 Borneo-Java shelf, 104 
 
 Bornhardt, W., cited, 58, 93 
 
 Bornholm, 191 
 
 Borocalcite, 364 
 
 Bosnia, 284 
 
 Bosphorus, 240 
 
 Boss, 303 
 
 Boston, sea-breeze at, 44 
 
 Boston Basin, drumlins in, 532 
 
 Boston Harbor, drumlins of, 265 
 
INDEX 
 
 H55 
 
 Bosworth, T. O., cited, 93 
 
 Botany, 20 
 
 Bothnian Gulf, 109, no, in, 241 
 
 , salinity of, 1045 
 
 Boue, A., cited, 1144 
 
 Bound skerries, 222 
 
 Bourbonne-les-Bains, petrified wood of, 1081 
 
 Bourguignat, J. R., cited, 1064, 1069 
 
 Bourne, G. C., cited, 392, 462 
 
 , quoted, 392 
 
 Bournemouth, 215 
 
 Boussingault and Lewy, cited, 38 
 
 Boussingaultite, 364 
 
 Bowland shales, 432 
 
 Bowling Green, Ohio, 167 
 
 Brachiopoda, 944 
 
 , bathymetric distribution of, 1014 
 
 , importance of growth lines of, 911 
 
 Bradygenesis, defined, 964 
 Bradyseisms, 887 
 Brahmaputra delta, 607, 608 
 
 , thickness of, 609 
 
 Brahmaputra River, alluvial plain of, 585 
 Branner, J. C., cited, 32, 34, 38, 93, 341, 
 
 380, 692, 693, 695, 707, 721, 761, 774, 
 
 884, 1092, 1095 
 
 , quoted, 33, 342, 693, 694 
 
 Brauhauser, cited, 634 
 Brayman shale, 261, 823 
 
 Salina age of, 823 
 
 Upper Ordovicic age of, 823 
 
 Braz 1, 341 
 
 disintegration of rocks in, 33 
 
 fringing reefs of, 390 
 
 hydration of rocks of, 38 
 
 lime sands of, 416 
 
 rainfall of, 67 
 
 range of temperature in, 32 
 Brazilian basin, 105 
 Breccia, limestone, 432, 433 
 
 , limestone tuff of Tyrol, 437 
 
 Breccias, endolithic, 536 
 
 , intra-formational, 529, 779 
 
 , fault, 528 
 
 Breckenridge, cannel coal of, 481 
 
 Breisbach, 250 
 
 Bretonian, 1128 
 
 Brewer, W. H., cited, 656, 685 
 
 Bridger beds, volcanic dust in, 572 
 
 , tuff of, 526 
 
 Brighton, force of waves at, 222 
 
 Brisbane River, Unio in, 1015 
 
 British coast, force of waves on, 221 
 
 British Columbia, 305 
 
 , pre-Cambric reefs of, 418 
 
 British Isles, mild temperatures of, 234 
 
 British shelf, 103 
 
 Brock, R. W., cited, 92 
 
 Brocken, hornstone of, 766 
 
 Brockmann-Jerosch, H., cited, 92 
 
 Brogger, W. C., cited, 302 
 
 Brongniart, A., cited, 1099 
 
 Brooks, W. K., cited, 1017, 1038 
 
 Brown, T. C., cited, 530, 537, 762, 785, 826 
 
 Brown coal, 510, 511 
 
 Browne, W. R., cited, 685 
 
 , quoted, 663 
 
 Bruckner, E., cited, 71, 92, 93 
 Bruckner cycle, 71 
 Brunswick, salt domes of, 758 
 Bryozoa, 385 
 
 , bathymetric range of, 1014 
 
 , growing on corals, 428 
 
 Buchanan, J. Y., cited, 215, 265, 679, 685 
 Buchenstein, 435 
 Buchensteiner formation, 434 
 Buckley, E. R., quoted, 140 
 Buckmann, S. S., cited, 957, 976, 979 
 
 Buenos Ayres, droughts in, 593 
 Buffalo, fossil earthquake fissure of, 792 
 
 , sandstone dike at, 885 
 
 Bugula, growing on Laminaria, 995 
 Bunsen, R. W., cited, 164 
 
 , quoted, 169 
 Bunter sandstein, 71, 225, 436 
 
 , Ceratodus in, 1034 
 
 , Limulus in, 1029 
 
 , origin of, 634 
 
 , Rogensteine of, 472, 473 
 
 , tracks in, 605 
 
 , transgression on Zechstein, 565 
 
 , windkanter of, 55 
 
 Burlington formation, fossils in, 732 
 
 Burma Mountains, rainfall in, 69 
 
 Burma Sea, 109 
 
 Butte, tepee, 840 
 
 Buttes, 57 
 
 Bysmalith, 303, 304 
 
 Byssus, attachment of Lucina by, 448 
 
 Cabot Straits, 113, 235 
 
 Cader Idris, lavas of, 315 
 
 Caithness, 219 
 
 Caithness flags, 651 
 
 Caithness Old Red sandstone, Palseospon- 
 
 dylus in, 1034 
 Calabria, earthquake in, 883 
 
 , earthquake craterlets in, 886 
 
 , Pliocenic foraminiferal deposits of, 
 
 454 
 
 , torrential deposits in, 591 
 
 Calamites, 375, 512, 939, 1004, 1082 
 
 Calcaire de Givet, 431 
 
 Calcaire de Waulsort, 432 
 
 Calcaire Grossier, 977 
 
 Calciferous, 1124 
 
 Calciferous series of Scotland, oil shales 
 
 in, 479 
 
 Calcification, 1079 
 Calcutta, borings in alluvial deposits at, 
 
 586 
 
 Caliche, 365 
 California, basaltic plateau of, 867 
 
 borax lakes of, 363 
 
 earthquakes of, 882, 887 
 
 lava of, 315 
 
 onyx marble of, 344 
 
 sandstone dike of, 885 
 
 valley of, alluvial fans in, 584 
 
 Call, R. E., cited, 578 
 
 Callao, tripolite near, 460 
 I Callunetum, 503 
 Calms, equatorial, 43, 67 
 Calumet and Hecla mine, 14 
 Calvin, S., cited, 1095 
 Cambrian, origin of name, 1112 
 Cambric, breaks in, 729 
 Cambric salt deposits, 371 
 Camiguin volcano, 863 
 Camillus shales, 376, 378 
 Campanularia, growing on Laminaria, 995 
 Campbell, M. R., cited, 363, 380, 1131, 1148 
 Campeche bank, 104, 335 
 Campeche shelf, 103 
 Campo Bianco pumice-cone, 863 
 Campos, 68 
 Canada, old land of, 834 
 
 , unconformity in Siluric of, 826 
 
 Canadian shield, 311 
 Canary Islands, 244, 335, 336 
 Canary Islands, dust falls of, 60 
 
 , passages between, 680 
 
 , pteropod ooze west of the, 456 
 
1156 
 
 INDEX 
 
 Candolle, C. de, cited, 721 
 
 Caney shale, 262 
 
 Cannel coal, analyses of, 481 
 
 , ash of, 480 
 
 , Carbonic, 479 
 
 , organic remains in, 481 
 
 , origin of, 482 
 
 Canu, F., cited, 1148 
 
 Cape Ann, boulders on, 226 
 
 Bojador, dunes on, 558 
 
 Breton, Etcheminian at, 729 
 
 Canaveral, 234 
 
 Cod, 234 
 
 apron plains of, 54, 598 
 difference of faunas on north and 
 
 south side of, 1125 
 dunes of, 551, 559 
 lignite in dunes of, 565 
 moraine of, 265 
 old marshes on, 491 
 sand plains of, 600 
 strand dunes on, 557 
 wave work on, 223 
 wind kanter from, 573 
 
 Colony, 238 
 
 tillite of, 535 
 
 Comorin, 456 
 
 Farewell, 234 
 
 Finisterre, 187 
 
 Gata, 152 
 
 Hatteras, 226, 652 
 
 Hurd, 838 
 
 Leeuwin, 239 
 
 of Good Hope, 214, 238 
 
 Palmas, 235 
 
 Pedaran, 242 
 
 Reykyanaes, 865 
 
 St. Roque, 233 
 
 Skagen, 103 
 
 Teneriffe, 1018 
 
 , dredging off, 1024 
 
 trough, temperatures in, 187 
 
 Verde, dunes on, 558 
 
 Islands, 152, 235 
 
 York, 387 
 
 Capps, S. R., cited, 544, 578 
 Carbonatipn, 17, 30, 38 
 Carbon dioxide, 24, 29 
 
 , climate affected by, 30 
 
 , sources of, 25 
 
 Carbonization, 25 
 Carcharadon, teeth of, 684 
 Caribbean Sea, 107, 239 
 
 , Spirula from, 1021 
 
 Carinata-quader sandstone, absent near Dres- 
 den, 681 
 Carlsbad Sprudel, 203 
 
 , composition of waters of, 168 
 
 , origin of algous limestone of, 476 
 
 , pisoliths of, 284, 336 
 
 , travertine deposits of, 475 
 
 Carnallite, 368, 371, 372 
 
 Carney, F., cited, 265 
 
 Caroline Archipelago, 389, 390, 401 
 
 Carpentaria, 394 
 
 Carse lands, peat of, 514 
 
 Carson River, tufa in, 340 
 
 Carter T. H., cited, 575, 579 
 
 Casa Colorado, 57 
 
 Cascq Bay, relict fauna of, 89 
 
 Caspian Sea, 108, 356, 365, 897 
 
 , composition of, 157, 159 
 
 , dwarf fauna of, 1067 
 
 , elevation of, 115 
 
 , salinity of, 155, 159 
 Cassian formation, 434, 435, 437 
 Cataclastic, 746 
 Catinga limestone, 341 
 
 Catskill formation, 635 
 
 , alternation in colors of beds in, 623 
 
 624 
 
 , overlap relations of, 742 
 
 , progressive replacement in, 743 
 
 , red beds of, 636 
 
 , variation in thickness of, 683 
 
 Caucasus, mud volcanoes in, 872 
 Cauda-galli, 1124 
 Caustobioliths, 280, 384 
 
 , classification of, 486, 487 
 
 Caustophytoliths, 280, 467, 478 
 
 Cave Creek, onyx marble of, 344 
 
 Caverns, aphotic region of, 983 
 
 Cavonne River, delta of, 608 
 
 Cayeux, L., cited, 336, 380, 514, 670, 671, 
 
 673, 685 
 
 Cedarburg, fossil reefs of, 419 
 Celebes, 392 
 
 Sea, 107 
 
 , temperature of, 189 
 
 Cementation, 751, 753 
 
 , belt of, 747 
 
 , substances causing, 754 
 
 Cenomanien, 730, 1112 
 
 Center of the earth, density of, 15 
 
 , fusion of rocks at, 15 
 
 Centrosphere, i, 13 
 
 Centrum, 883 
 
 Cephalochorda, 950 
 
 Cephalonia, Sea Mills of, 257 
 
 Cephalopoda, naming of, 913 
 
 Ceratopyge limestone, 53 
 
 Cesena, wood replaced by sulphur at, 1081 
 
 Cette, 348 
 
 Cevennes, 133 
 
 , winds from, 50 
 
 Ceylon, 390 
 
 Chagos group, 388, 389, 39O, 392, 393, 399 
 
 , nullipores of, 471 
 
 Chaleur, Bay of, 1041 
 
 Chalk, chemical precipitation of, 336 
 
 , Radiolaria of, 1082 
 
 Challenger Bank, nullipores on, 471 
 
 Challenger, the, 334, 410 
 
 , annelids dredged by the, 1024 
 
 Anthozoa dredged by the, 1012 
 
 blue mud dredged by the, 668 
 
 Cirripedia dredged by the, 1026 
 
 glauconite dredged by the, 671, 672 
 
 Ostracods dredged by the, 1026 
 
 Plumularians obtained by the, ion 
 
 Radiolaria dredged by the, 1008 
 
 Spirula dredged by the, 1021 
 
 Challenger Expedition, 147, 184, 451, 452, 
 
 Challenger Exploration, in Marian deep, 
 
 Challenger narrative, cited, 469 
 
 Chama, in Bermudaite, 573 
 
 Chamaeliths, 281 
 
 Chamberlin, R. T., cited, 903, 904, 905, 908 
 
 Chamberlin, T. C., cited, 29, 93, 107, 265, 
 327, 418, 420, 462, 990, 1038, 1148 
 
 , quoted 876, 1142 
 
 Chamberlin, T. C., and Salisbury, R. D., 
 cited, 2, 4, 22, 59, 93, 148, 206, 263, 
 265, 278, 294, 297, 298, 325, 326, 327, 
 579, 634, 637, 675, 679, 861, 878, 908, 
 1145, 1146, 1148 
 
 , ^quoted, 698 
 
 Chamisso, A. von, cited, 399, 410 
 
 Champlain clays, concretions in, 763 
 
 Chapeiros, 396 
 
 Chapman, F., cited, 575 
 
 Chara, 426, 471, 475, 495, 935, 1001 
 
 , analyses of, 471 
 
 marls, 494 
 
INDEX 
 
 Charleston, 234 
 
 , earthquake craterlets at, 885 
 
 sandstone, 1131 
 
 Charybdis, maelstrom at, 230 
 Chatard, cited, 362 
 Chattanooga shale, 823 
 
 , complex nature of, 549 
 
 , hiatus indicated in, 1130 
 
 , origin of, 479, 514 
 
 Cheirotherium, tracks in Bunter Sandstein, 
 
 605 
 
 Chelonians, 953 
 Chelsea, England, 28 
 Chemakha, earthquake at, 885 
 Chemical (actinic) rays, 28 
 Chemnitzia, 436 
 Chemung, overlap relations of, 742 
 
 , progressive overlap of, 744 
 
 , Protolimulus in, 1029 
 
 , variation in thickness of, 683 
 
 Cherbourg, 221 
 
 Cherry county, Nebraska, dune-enclosed 
 
 lakes in, 562 
 
 Chesil Bank, force of waves on, 222 
 Chile, 369 
 
 , dunes in, 563 
 
 , earthquake in, 888 
 
 , natural mummies from, 1076 
 
 , nitrate deposits of, 364 
 
 , origin of nitrates of, 370 
 
 Chiltern Hills, chalk cuesta of, 839 
 China, loess of, 565 
 
 Sea, 237, 240, 242, 392 
 
 . , atolls and fringing reefs of, 390 
 
 Chin-kiang, dust storm at, 59 
 Chirotype, defined, 919 
 Chitin, composition of, 1078 
 Chlorides, 177 
 Chlorinization, 768 
 Cholnoky, E. de, cited, 92 
 Chonolith, 304, 305, 307, 309 
 Chonos Archipelago, peat in, 509 
 Chotila Hill, miliolite limestone on, 575 
 Chouteau limestone, 732 
 Christmas Island, 393 
 
 , radiolarian ooze around, 458 
 
 Chronobios, 922 
 
 Chronofauna, 922, 1043 
 
 Chuar series, age of, 1140 
 
 Chun, C, cited, 460, 999, 1038, 1069 
 
 Chunnenugga Ridge, 839 
 
 Chuquicamata, natural mummy at, 1077 
 
 Cidaroidea, 950 
 
 Cincinnati, artesian well at, 168 
 
 Cincinnati dome, 808 
 
 Circulus, 978 
 
 Civitavecchia, 221 
 
 Clamshell cave, basaltic jointing of, 318 
 
 Clapp, F. C., cited, 143, 600 
 
 Clark, W. B., cited, 672, 686, 979 
 
 Clarke, F. W., cited, 39, 93, 157, 168, 206, 
 
 348, 362, 363, 364, 365, 369, 380, 468, 
 
 570, 579, 614, 637, 657, 671, 678 
 , quoted, 154, 156, 161, 162, 163, 166, 
 
 169, 173, 468, 668, 670, 671, 677 
 Clarke, J. M., cited, 456, 462, 479, 520, 667, 
 
 686, 1038, 1069, 1070, 1113, 1119, 1134, 
 
 1148 
 
 , quoted, 1023, 1123, 1127 
 
 Clarke, J. M., and Ruedemann, R., cited, 
 
 1030, 1038 
 Clarke Range, 334 
 Clastation, 17 
 Clay-galls, 564, 711 
 Clay iron stones, 719 
 Claypole, E. W., cited, 903, 908 
 Cleavage, 769 
 Clement, J. M., cited, 317, 320 
 
 Cleveland shales, tissue of sharks in, 1080 
 Climate, desert, 77 
 
 , interior, 76 
 
 , littoral, 75 
 
 , mountain, 77 
 
 , oceanic, 75 
 
 , physical, 74, 75 
 
 , solar, 74 
 
 Climatic belts, 74 
 
 provinces, 77 
 
 types, 78 
 
 zones, Mesozoic, 80 
 
 , Neumayr's Jurassic, 79 
 
 , past, 78 
 Clino-unconformity, 821 
 Clinton formation, ballstone reefs of, 446 
 iron ore, dwarf fauna of, 1045, 1068 
 
 , origin of, 762 
 
 Clinunconformity, 821, 824 
 Clione, borings of, 1092 
 
 Clitheroe district, carbonic limestones of, 
 449 
 
 , limestone, 432 
 Closs, H., cited, 93 
 Clouds, cirrus, 63 
 , cumulus, 63 
 
 , nimbus, 63 
 
 - , stratus, 63 
 
 Coal, oxidation of, 37 
 
 Coal measure limestones, intraformational 
 
 breccia in, 530 
 Coastal plain, 830 
 
 , New York Palaeozoic, 834 
 Cobalt, Huronian tillite from, 534 
 Cobequid Bay, tides in, 227 
 Coblenz, 245 
 
 Cobleskill limestone, continuity of, 1132 
 Coccoliths, 453, 454, 456, 933 
 
 , in Severn muds, 664 
 
 Cochabamba, 365 
 
 Cochin China, 242 
 
 Cocos Islands, gradual emergence of, 895 
 
 , radiolarian ooze around, 458 
 Cocos-Keeling atoll, 388, 389, 390 
 Codden Hill beds, 459 
 Cohn, F., cited, 476, 520 
 Coire Bog, peat in, 505 
 Cole, G. A. J., and Crook, T., cited, 686 
 Cole, G. A. J., and Gregory, J. W., cited, 
 
 315, 316, 320 
 
 Coleman, A. P., cited, 81, 92, 93, 534, 537 
 Colemanite, 364 
 Colima, dust from, 60 
 Collet, L. W., cited, 686 
 Collet, L. W., and Lee, G. W., cited, 686 
 Colob formation, dune origin of, 571 
 Cologne, brown-coal north of, 513 
 Colorado, 291 
 
 , Cretacic dwarf fauna of, 1069 
 
 , Palaeozoic sandstones of, 310 
 
 delta, deposits of lime in, 616 
 
 desert, 70 
 
 desert, dunes of, 562 
 
 River, delta, 619 
 
 Springs, eolian cross-bedding near, 
 
 705 
 
 Columbia River, dune area of, 561 
 
 Columbian gravels, cementation of, 754 
 
 Columbus limestone, 424 
 
 Commentry basin, coal deposits of, 518 
 
 Como beds, colors of, 624 
 
 Comoro Isles, 388 
 
 Concepcion, earthquake waves from, 890 
 
 Harbor, earthquake in, 888 
 
 Conchiolin, 1078 
 Concretions, 718, 763 
 Condore Islands, 242 
 Conduction, 30 
 
1158 
 
 INDEX 
 
 Coney Island, sea-breeze at, 45 
 
 Confervales, 935 
 
 Conformable strata, 826 
 
 Congelation, 31, 751 
 
 Conglomerate, edgewise, 530, 784, 785 
 
 Congo River, 235, 248 
 
 Congress Spring, chloride waters of, 168 
 
 Conidae, poison fangs of, 1020 
 
 Conifers, 375 
 
 Conn, H. W., cited, 1038 
 
 Conneautsvillej well at, 168 
 
 Connecticut River, 131 
 
 1 Valley, concretions in post-glacial 
 
 , clays of, 719 
 
 , trap of, 313 
 
 Conocoryphidae, as index fossil, 1134 
 Conodonts, 947, 951 
 Conoplains, 830, 856 
 Conrad, T., cited, 915, 1123 
 Constantinople, 240 
 Contacts, fault, 309 
 
 , igneous, 309 
 
 -, sedimentary, 309 
 
 Continental block, 7, 100 
 
 deposits, 70, 71, 734 
 
 , red color of, 84 
 
 platform, 8 
 
 slope, 7 
 
 Convection currents, 30, 31 
 Convergence 979 
 Conybeare, W., cited, 1108 
 Coode, Sir J., cited, 222, 266 
 Cook Inlet, in 
 
 Coon Butte, 86 1 
 
 Cooper Creek, dry delta of, 584 
 
 Copal, 518 
 
 Cope, E. D., 964, 1040 
 
 Coquina, 260 
 
 Coral basin, temperature in, 187 
 
 Coralline Crag, faunas of, 89 
 
 Corallines, 476 
 
 Coral Sea, 108 
 
 Corals, growth lines on, 911 
 
 , naming of, 913 
 
 Cordonan, lighthouse of, 223 
 
 Corndon, 307 
 
 Corniferous limestone (see Onondaga), 424, 
 1124' 
 
 Cornish, V., cited, 215, 265, 286 
 
 Corrasion, eolian, 18 
 
 , glacial, 1 8 
 
 , river, 18 
 
 , wind, 51, 52 
 
 Corrosion, 18 
 
 Corsica, 275 
 
 Coseguina, volcanic ash from, 60 
 
 Cotentin, peat at, 514 
 
 Cotidal lines, 228 
 
 Cotopaxi dust from, 60 
 
 Cotswold Hills, oolite cuesta of, 839 
 
 Cotype, defined, 919 
 
 Couvin, Devonic reef near, 431 
 
 Covesea, 256 
 
 Crabs, production of alkalinity by, 331 
 
 Cragin, F. W., cited, 521 
 
 , quoted, 469 
 
 Craigellachie, 255 
 
 Cramer, F., cited, 753, 774 
 
 Crammer, H., cited, 601, 602, 637 
 
 Crater Lake, 120 
 
 , depth of, 116 
 
 Craven district, 432 
 
 Credner, G. R., cited, 609, 613, 618, 637 
 
 Credner, H., cited, 317, 320, 537 
 
 , quoted, 699 
 
 Credner, R., cited, 1063, 1064, 1070 
 
 Credneiia beds, absent in vicinity of Dres- 
 den, 681 
 
 Creep, 541 
 
 "Creeping Joe" dune, 560 
 
 Crenic acid, 173 
 
 Creodontia, 955 
 
 Cretacic clays, pyrite concretions in, 764 
 
 Crete, 240, 334 
 
 Crinoidea, 421, 949 
 
 , naming of, 913 
 
 Crivelli, B., cited, 1145 
 
 Croatia, lakes of, 125 
 
 Crocodiles, marine habitat of, 985 
 
 Cromdale, 252 
 
 Crosby, W. O., cited, 4, 13, 15, 16, 22, 38, 
 
 93, 143, 264, 265, 266, 287, 288, 298, 
 
 310, 315, 320, 412, 462, 533, 537. 600, 
 
 638, 726, 744, 790, 821, 826, 848, 857 
 
 , quoted, 36, 532, 621 
 
 Crosby, W. O., and Ballard, H., cited, 265, 
 
 266 
 Crosby, W. O., and Crosby, F., cited, 257, 
 
 266 
 Cross, W., cited, 58, 82, 93, 638 
 
 , quoted, 627 
 
 Cross, W., iddings, J. P., Pirsson, L. V., 
 
 and Washington, H. S., cited, 273, 277, 
 
 298 
 Cross-bedding, delta type, 701 
 
 , eolian, 702, 703 
 
 , in Devonic limestone of Michigan, 
 
 429 
 
 , torrential, 701 
 
 Cross Fell, peat covering, 504 
 
 Croton reservoir, salinity of, 155 
 
 Crozet Islands, 40 
 
 Crustacea, destruction of limestone by, 415 
 
 Crustal block, lowering and elevation of, 
 
 1141 
 
 , thickness of, 905 
 
 Crustal blocks, 4 
 
 Cruzy, sulphate waters of, 168 
 
 Cryohydrate, 194 
 
 Cuba, 233 
 
 Cuesta, 832, 836 
 
 Cuestas, Devonic, 838 
 
 , , 
 
 , Mesozoic, 838 
 
 , Palaeozoic, 838 
 
 Culbin, dunes of, 256 
 Cullis, G., cited, 445, 462 
 Culm, cherts from, 459 
 Culmination circle, 894 
 Cumings, E. R., cited, 973, 979 
 Current ripples, 712 
 Currents, Agulhas Stream, 238 
 
 , Benguelan, 235, 1050 
 
 , Brazil, 233, 235, 1050 
 
 , Cabot, 235 
 
 , California, 237, 239 
 
 , Canary, 235, 1050 
 
 , Cape Horn, 235 
 
 , East Australian, 237 
 
 , East Greenland, 234 
 
 , Equatorial counter, 235, 237, 238 
 
 , Falkland, 235 
 
 , Florida, 235 
 
 , Guiana, 233 
 
 , Guinea, 235 
 
 , Irminger, 234 
 
 , Kuroshiwo drift, 237, 242, 1049 
 
 , Labrador, 234, 237 
 
 , Mozambique, 238 
 
 , North Cape, 236 
 
 , North Equatorial, 233, 235, 237, 1050 
 
 , North Pacific west-wind drift, 237 
 
 , Peruvian, 238, 460, 1050 
 
 , South equatorial, 233, 237, 238, 1050 
 
 , South Pacific west-wind drift, 238 
 
 , West Australian, 239 
 
 , West Greenland, 237 
 
INDEX 
 
 H59 
 
 Cutch, Miliolite of, 575 
 
 Cuttle-fish, 946 
 
 Cuvier, G., cited, 1099 
 
 Cuxhaven, 229 
 
 Cvijic, J., cited, 133, 143 
 
 Cyatholiths, 457, 933 
 
 Cycle of erosion, 137, 829, 849 
 
 Cyclones, 46 
 
 Cypress, 513 
 
 Cypns, in playa lakes, 603 
 
 Cyprus Island, 153 
 
 Cystoidea, 949 
 
 , naming of, 913 
 
 Dacque, E., cited, 1145, 1148 
 
 , quoted, 1144 
 
 Dadoxylon wood, 941 
 Daemonelix, 1091, 1092 
 Dago Island, cuesta of, 838 
 Dakota sandstone, 71, 260, 642 
 
 , compound overlap of, 739 
 
 , dune origin of parts of, 570 
 
 , non-marine, 1101 
 
 Dale, T. N., cited, 80 1 
 
 Dall, W. H., cited, 92, 1038, 1070 
 
 , quoted, 1048 
 
 Dallas, dunes at, 561 
 
 Dalmatia, 240 
 
 Dalmatian coast, Karst region of, 882 
 
 Daly, R. A., cited, 302, 303, 304, 305, 307, 
 
 309, 320, 331, 333, 334, 338, 380, 719, 
 
 721, 764, 774 
 
 , quoted, 333, 334 
 
 Dana, J. D., cited, 16, 38, 143, 314, 320, 
 
 336, 380, 391, 406, 408, 409, 462, 520, 
 
 537, 76i, 774, 799, 878, 900, 902, 908, 
 
 1038, 1055, 1103, 1106, 1119, 1144 
 , quoted, 315, 396, 409, 414, 481, 699, 
 
 720, 890, 1007, 1012 
 Danish coast, dunes of, 558 
 Danube, 248, 251, 587 
 
 delta, 608 
 
 , rate of growth of, 609 
 
 , velocity of, 245 
 
 Danzig Bay, temperatures in, 190 
 
 Daphnia, in playa lakes, 603 
 
 Darcy, cited, 257 
 
 Dardanelles, 240 
 
 Darwin, C., cited, 335, 336, 380, 386, 397, 
 
 398, 404, 408, 413, 462, 509, 520, 544, 
 
 579, 638, 693, 694, 695, 908, 1015, 
 
 1018, 1026, 1038, 1055, 1070 
 , quoted, 360, 398, 399, 415, 416, 593, 
 
 594, 888 
 Darwin, G. H., cited, 91, 92, 94, 579, 712, 
 
 713, 721, 897 
 Darya, salinas of, 358 
 Daubree, A., cited, 226, 266, 294, 295, 298, 
 
 686, 789, 790, 826, 906, 907, 1081 
 Davenport, C. B., cited, 1038, 1042, 1070 
 
 , quoted, 1019 
 
 David, T. W. E., cited, 81, 94, 393, 462, 
 
 535, 538 
 
 David Island, 397 
 Davidson, T., cited, 1038 
 Davis, C. A., cited, 471, 491, 495, 496, 498, 
 
 500, 502, 516 
 
 , quoted, 490, 491, 492 
 
 Davis, W. M., cited, 22, 40, 43, 54, 94, 
 
 116, 120, 121, 124, 126, 128, 133, 134, 
 
 137, 143, 212, 217, 2l8, 220, 228, 266, 
 
 356, 409, 410, 462, 487, 520, 535, 538, 
 573, 579, 626, 638, 816, 826, 839, 842, 
 845, 852, 854, 857, 858 
 
 Davis, W. M., quoted, 90, 215, 229, 410, 
 535, 536, 566, 584, 585, 588, 589, 839, 
 852, 853, 854, 885 
 
 Davison, C., cited, 693, 695, 908 
 
 Davis Straits, 186, 234, 237 
 
 Dawson, Sir W., cited, 515, 520, 621, 638 
 
 , quoted, 515, 516, 622 
 
 Daylight, diffusion of, 28 
 
 Dead Sea, 897 
 
 composition of, 157, 159 
 
 coral from, 1013 
 
 elevation of, 115 
 
 leached salt of, 367 
 
 salinity of, 154, 159 
 
 Deadwood Gulch, 308 
 Dean, B., cited, 950, 1095 
 
 -, quoted, 1080 
 
 th Valley, Cal., 27 
 
 Deatl ... , . 
 
 , soda niter deposits of, 364 
 
 desert, 364 
 
 De Candolle, A., cited, 56 
 
 Decapods, range of, 948 
 
 Decarbonation, 39 
 
 Deccan Plateau, Cretacic trap forming, 868 
 
 Decewville beds, 424 
 
 Decomposition, 17 
 
 Deep, Nero, 106 
 
 , Tuscarora, 106 
 
 Deep sea platform, 8 
 Deflation, 17, 51, 52, 55 
 Deformation, endogenetic, 776, 777 
 
 , endolithic, 757 
 
 , exogenetic, 776 
 
 De Groot, H., cited, 363, 380 
 
 Dehna Desert, dune area of, 562 
 
 Dehydration, 38 
 
 De la Beche, Sir Henry T., cited, 269, 299, 
 
 576, 577, 578, 865, 878 
 
 , quoted, 864 
 
 De Lapparent, A., cited, 203, 1068, 1070, 
 
 1145, 1146, 1149 
 
 -. quoted, 6 
 
 De Laumy, cited, 203 
 Delaware Bay, drowned, 832 
 
 River, tides in, 227 
 
 Delesse, A., cited, 219, 266, 686 
 Delta beds, 612 
 
 Deltas, coal in fossil, 741 
 Delthyris shale, 1124 
 Demorphism, belt of, 34 
 Dendrites, 791 
 
 Denmark, Chara in lakes of, 471 
 S coastal erosion of, 224 
 
 Straits, 109 
 
 , ridge, 188, 192 
 
 Density of the earth, 12, 15 
 Denudation, 17 
 Deposition, 17, 19 
 Depressed oceanic region, 8 
 Depth of compensation, 10 
 Derby, O. A., cited, 38 
 Desalinification, 748, 763 
 
 De Saussure, H. B., cited, 72 
 Desert, Hamada, 57 
 
 ' of Gobi, material brought from, 566 
 
 varnish, 27, 57 
 
 Deserts, eolian ripple marks in, 714 
 
 Desmids, 935 
 
 Deuterogenous, 260 
 
 De Vries, H., cited, 962, 963, 979 
 
 Dew, 26, 62 
 
 point, 62 
 
 D'Halloy, O., cited, 1108 
 Diabase, defined, 278 
 Diadematoidea, 950 
 Diagenesis, 748 
 Diagenetic processes, 750 
 
n6o 
 
 INDEX 
 
 Diagenism of cinder cones, 863 
 
 Diastrophism, 12, 16 
 
 Diatomaceous ooze, salt content of, 367 
 
 Diatom ooze, analysis of, 677 
 
 Diatoms, 983 
 
 Dicotyledons, 941 
 
 Diego Garcia, 388, 392, 393 
 
 Diener, C., cited, 682 
 
 Diener, C, and Arthaber, G., cited, 435, 
 
 462 
 
 Dietrich, cited, 397 
 Dikes, clay, 564 
 
 , composite, 304 
 
 , multiple, 304 
 
 , sandstone, 791 
 
 Diller, J. S., cited, 72, 299, 885, 908 
 
 Dinosauria, 954, 1037 
 
 Dippersdorf, 246 
 
 Disceras limestone, 438 
 
 Discolith, 457, 933 
 
 Disconformity, 821, 822, 823, 826 
 
 Discordanz, 821, 824 
 
 Disintegration, 17 
 
 Disko Island, post-glacial deposits of, 87 
 
 Dismal Swamp, 120, 500 
 
 Distillery quarry, 419 
 
 Dittmar, W., cited, 147, 148, 194 
 
 Dixon, E. E. L., and Vaughan, A., cited, 
 
 459, 460, 462 
 
 Dnieper River, dunes along, 560 
 Dodge, R. E., cited, 131, 143 
 Dogger Bank, 104, 191, 218, 230 
 
 ?er, 459 
 
 Dog's Bay, Foraminifera in, 576 
 Doldrums, 67 
 Dolerite, 278 
 
 of Bombay, 39 
 
 . of South Staffordshire, 39 
 
 Dolgeville, 243 
 Dolinas, 857 
 Dolomitization, 761 
 Domes: 
 
 Adirondack, 810 
 
 Black Hills, 841, 842, 843 
 
 Cincinnati, 810, 843 
 
 Nashville, 810, 843 
 
 North Ontario, 810 
 
 Ontario, 810 
 
 Ozark, 810 
 
 Wisconsin, 810 
 
 Donetz Valley, dunes in, 561 
 
 Donney Lake, 361 
 
 D'Ooust, Virlet, cited, 336 
 
 D'Orbigny, A., cited, 964, 979, 1088, 1095 
 
 , quoted, 1074 
 
 Dorpat, 27 
 Dorset, 838 
 Dover, 228 
 
 Straits, 234 
 
 , tidal interference in, 229 
 
 Drasche, R. von, cited, 462 
 Dreikanter, 54 
 
 , in basal Cambric of Sweden, 728 
 
 Dresden, 651 
 
 Dresser, J. A., cited, 92 
 
 Drift, englacial, 265 
 
 , subglacial, 265 
 
 , superglacial, 265 
 
 Drigg, fulgurites of, 73 
 
 Drumlins, material of Boston, 532 
 
 Drummond Island, corals of, 420 
 
 Ducie Island, 390 
 
 Dufour, L. cited, 196, 206 
 
 Dundee limestone, 424, 648 
 
 Dundelbach, delta of the, 610, 613 
 
 Dune deposits, reworked by encroaching 
 
 Dune Park, height of dunes in, 559 
 
 Dunes, slopes of, 563, 703 
 
 Dunker, G., cited, 915, 916 
 
 Dunnet Head, Lighthouse of, 219 
 
 Dupont, E., cited, 431, 462, 463 
 
 Durance, Mont Genevre, 316 
 
 Durham, Magnesian limestone series of, 341 
 
 Durham, W., cited, 686 
 
 Durness limestone, gaps in, 684 
 
 Dust falls, volume of, 60 
 
 Dust fogs, 6 1 
 
 storms, 28 
 
 Dutton, C. E., cited, 314, 320, 868, 869, 
 878, 908 
 
 , quoted, 869 
 
 Dwyka conglomerate, 82, 535, 536 
 Dybowski, W., cited, 1064, 1070 
 Dysodil, 479 
 Dysphotic region, 982 
 
 Earawalla, Isthmus of, foraminiferal de- 
 posit of, 576 
 
 Earth glacier, 34 
 
 Earth's axis, displacement of, 90 
 
 Earth's crust, characters of, 12 
 
 , denned, 10 
 
 , deformation of, 12 
 
 , materials of, 12 
 
 , specific gravity, 12 
 
 , thickness of, 10, n, 12 
 
 Earth's interior, condition of, 16 
 
 , temperature of, 13, 14, 15 
 
 East Abyssinian mountains, 355 
 
 East China Sea, 107 
 
 Easter Ross, peat of, 505 
 
 East Greenland, post-glacial fauna of, 88 
 
 Mediterranean, salinity of, 151 
 
 sea, 109 
 
 stream, temperature of, 192 
 
 Eastham, sand plains of, 600 
 
 East Islet, 392 
 
 Eaton, Amos, cited, 1122 
 
 Ebro River, delta of, 608 
 
 Ecca formation, coals of, 536 
 
 Eccles, J., cited, 72 
 
 Echinodermata, 949 
 
 Echinoderms, destruction of limestone by, 
 4*5 
 
 Echinoidea, naming of, 913 
 
 Echinoids, burrows in limestone made by, 
 1092 
 
 Ecuador, earthquake fissures in, 883 
 
 , position of oscillation poles in, 893 
 
 Edentata, 955 
 
 Eel grasses, 985 
 
 Egleston, T., cited, 54, 94 
 
 Egmont Island, 399 
 
 Egypt, 369 
 
 , alkaline lakes of, 361 
 
 , Foraminifera in eastern desert of, 576 
 
 , soda lakes of, 362 
 
 Ehlers, cited, 1024 
 
 Ehrenberg, C. G., cited, 384, 455, 686 
 
 Eifel, crinoidal limestone of the, 431 
 
 , Maare region of the, 860 
 
 , reefs of the, 423, 430, 431 
 
 , Tertiary volcanoes of the, 874 
 
 Eimer, T., cited, 963, 964, 977, 979 
 
 Einkanter, 54 
 
 Eisenach, 434 
 
 Ekman, F. L., cited, 191 
 
 Elbe River, 225, 229 
 
 , dune areas of, 557 
 
 Elbruz Lake, 120 
 
 Eld cleft, lava from, 866 
 
INDEX 
 
 1161 
 
 Eldgja, length of, 866 
 
 Elgin, Triassic reptiles from, 953 
 
 Elgin sandstone, dune origin of, 571 
 
 Ellis Island group, 388, 389, 393, 394, 401 
 
 El Late Mountains, 308 
 
 Elm, Switzerland, rock fall at, 546, 66 1 
 
 Elton Lake, 357 
 
 , composition of, 157 
 
 , salinity of, 154, 156 
 
 Ely River, 662 
 Embryonic periods, 971 
 Emerson, B. K., cited, 313, 320 
 Emmons, E., cited, 1123 
 Ems delta, 607 
 
 Encrinal limestone, continuity of, 684, 1131 
 Encyclopaedia Britannica, cited, 24, 348 
 Endell, K., cited, 463 
 . Endolithic brecciation, 777 
 Endosmosis, 180 
 England, Carbonic oolites of, 472 
 
 , Jurassic oolites of, 472 
 
 , origin of chalk of, 850 
 
 , transgressing Cretacic of, 730 
 
 English Channel, 112, 218, 219, 234 
 
 , tides in, 228 
 
 Enterolithic structure, 527, 758, 778 
 
 Eolation, 51 
 
 Eolian cross-bedding, tangency of layers in, 
 
 704 
 
 Eolian deposits, size of grains of, 56, 553 
 Eophyton sandstone, windkanter from, 573 
 Epeirogenic movements, 12 
 Epembryonic periods, 971 
 
 stages, 971 
 
 Ephebastic, 973 
 
 Ephebic stage, 972 
 
 Epicenter, 883 
 
 Epicontinental sea, provincial fauna of, 984 
 
 Epidote, 177 
 
 Epiphytes, 1-002 
 
 Epiplankton, 994 
 
 Equatorial currents, 390 
 
 Erdmann, E., cited, 372, 373, 380 
 
 Erongo, 692 
 
 Erosion, 17 
 
 Erosion cycle, 137, 829, 849 
 
 Eruptions, explosive, 860 
 
 , extravasative, 860, 865 
 
 Erzgebirge, 375 
 
 Escambia, 295 
 
 Eschscholtz Bay, tundra at, 508 
 
 Eskers, 133, 257 
 
 Esmeralda county, Nev., 363 
 
 Esopus grit, 635 
 
 Estheria, in playa lakes, 603 
 
 Esthonia, 838 
 
 Etcheminian, 1128 
 
 , thickness of, 729 
 
 Etheridge, R., cited, 1 144 
 Etna, volcanic gases from, 203 
 Eureka black shale, 732 
 Euryhalinity, 1045 
 Eurypterida, 377, 425, 948, 950 
 
 , habitat of, 989, 1029, 1030 
 
 Eurythermal organisms, 80 
 Eustatic movements, negative, 3, 4 
 
 , positive, 4 
 
 Eutraphent, 498 
 
 Evans, J. W., cited, 574, 577, 579 
 
 Evaporation, 27 
 
 Everding, H., cited, 757, 774 
 
 Everglades, 126, 404, 406, 407 
 
 Ewing, A. L., cited, 94, 175, 206 
 
 Exaration, 17, 263 
 
 Excretions, 719, 720 
 
 Exfoliation, concentric, 33 
 
 Exomorphic, 765 
 
 Exosmosis, 180 
 
 Faira Island, 218 
 
 Fairchild, H. L., cited, 126, 127, 137, 143, 
 
 264, 266, 297, 299, 652, 686, 707, 708, 
 
 721, 861, 878 
 Falb, R., cited, 908 
 Falkland Islands, glacial deposits of, 82 
 
 , peat in, 509 
 
 , "stone rivers" of, 544 
 
 Falls of the Ohio, corals of, 420 
 
 , reefs of, 426 
 
 Farafrah, chalk from, 454 
 Farlow, W. G., cited, 979 
 
 , quoted, 959, 960 
 
 Faroe-Iceland ridge, no, 188 
 Faroe Islands, 192, 218, 234 
 
 , Tertiary basaltic flows in, 867 
 
 Farrington, O. C., cited, 1088, 1095 
 
 Fault breccias, 291 
 
 Fault scarps, submarine, 890 
 
 Favosites, worn heads of, 428 
 
 Faxon, W., cited, 1059 
 
 Fedden, F., cited, 574, 579 
 
 Feldspar, clouding of, 33 
 
 Fenneman, N. M., cited, 686 
 
 Fenner, C. N., cited, 312, 320 
 
 Fermor, L., cited, 94 
 
 Ferns, 375, 941 
 
 Ferrara, height of channel of Po in, 617 
 
 Fetlar, 72 
 
 Fife, lava flows of, 313 
 
 Fiji basin, temperature in, 187 
 
 Islands, 388, 411 
 
 , nullipores on, 471 
 
 , pteropod ooze around, 456 
 
 , raised reefs of, 436 
 
 , reefs of, 393 
 
 Fillmore, gypsum deposit at, 359 
 Finckh, A. E., cited, 394, 463, 471, 520 
 Fingal's Cave, columnar structure of, 318 
 
 , Tertiary basaltic flows forming, 867 
 
 Finger Lakes, 123, 127 
 Fimstere, peat deposits of, 514 
 Finland, eskers in, 599 
 
 , undecomposed granite of, 40 
 
 Finlay, G. L, cited, 300 
 
 Finnish Gulf, 109, no, in 
 
 Fire clay, 517 
 
 Firn, 279 
 
 Fischer, P., cited, 603, 1019, 1038 
 
 Fissility, 769, 794 
 
 Fissures, gases active in, 767 
 
 Fissures, solution, 857 
 
 Flachsee, 987 
 
 Flamborough head, 224 
 
 Flammarion, C., cited, 28 
 
 Flanders, dunes of, 557 
 
 Fleming, J. A., cited, 721 
 
 Flints, 764 
 
 Flocculation, 654, 655, 656 
 
 Flores Sea, 186, 242 
 
 Florida, 233, 405, 411 
 
 , cypress swamps of, 500 
 
 , deposits in lagoons of, 424 
 
 , fringing reefs of, 386, 390 
 
 , muds in lagoons of, 479 
 
 , peat in cypress swamps of, 509 
 
 , ripple marks off coast of, 219 
 
 , sands of, 226, 295 
 
 Straits, 233, 244 
 
 Florida-Texas shelf, 103 
 Florissant Lake, beds of, 291 
 
 , mud cracks in, 710 
 
 , volcanic ashes of, 524 
 
 , volcanic dust in, 572 
 
 Flower, Sir William, cited, 989 
 Flying fish, 988 
 
Il62 
 
 INDEX 
 
 Focus, earthquake, 883 
 
 Foehn, explanation of, 49 
 
 Foerste, A. E., cited, 843, 858 
 
 Fogs, 63 
 
 Fol and Sarasm, cited, 205 
 
 Folds section of Appalachian, 844 
 
 Foraminifera, 942, 1007 
 
 Forbes, E., cited, 248, 266, 686, 1070, 1125 
 
 Forchhammer, G., cited, 147, 194, 206, 559, 
 
 579, 686, 703, 721 
 Foredeep, defined, 800 
 Forel, F. A., cited, 170, 196, 197, 198, 204, 
 
 205, 206, 244, 266, 721 
 Fore-set beds, 702 
 Forestian, Lower, 506 
 
 , Upper, 506 
 
 Forest marble, cross-bedding in, 704 
 
 Formaldehyde, 24 
 
 Forres, 413 
 
 Fort Jefferson, 391 
 
 Fossa Magna, 882 
 
 Fosters Flats, 246 
 
 Foureau, F., cited, 604, 638 
 
 Fowey Rocks, 406 
 
 Fowler, G. H., cited, 992 
 
 Fox, H., and Teall, J. J., cited, 316, 320 
 
 Fraas, E., cited, 442, 634, 635, 638 
 
 Fraas, O., cited, 456, 463, 711, 721 
 
 Fractoconformity, 826 
 
 Fracture, zone of, 819 
 
 From, ijj i 
 
 Frank, Canada, rock fall in, 546 
 
 Franken, Solnhofen reefs at, 438 
 
 , subaquatic gliding at, 782 
 
 dolomite, 438, 440 
 
 Frankenwald, 375 
 
 Frantzen, T., cited, 455, 521 
 
 Franzensbad, volcanic hill near, 874 
 
 Franz Josef fjord, post-glacial fauna of, 88 
 
 Franz Josef Land, 236 
 
 , post-glacial fauna of, 88 
 
 Frasnien reef, 43 1 
 
 Frauenthal, stylolites at, 786 
 
 Freeh, F., cited, 94, 431, 463, 1146, 1148 
 
 Fredericksburg formation, Dakota sand- 
 stone on, 739 
 
 Free, E. E, cited, 55, 56, 57, 60, 94, 579 
 
 , quoted, 59, 60 
 
 Freeman, W. B., and Bolster, R. H., cited, 
 356, 380 
 
 Free-stone, 752 
 
 Fresenius, K., cited, 346 
 
 Friendly Islands, 386 
 
 Friesian Islands, dunes of, 557 
 
 Frische Haff, 126 
 
 , strand dunes of, 557 
 
 Nehrung, dunes of, 559 
 
 Fritsch, K. von, cited, 60, 94, 537 
 Fritting, 766 
 
 Frontenac axis, 810 
 
 Front Range, Appalachian, 844 
 
 , Rocky Mountain, 260 
 
 , basal Palaeozoic contact 
 
 in, 726 
 
 > , hog-backs of, 841 
 
 , monoclines facing, 798, 
 
 844 
 , torrential deposits of, 
 
 59 1 
 Frost, 26, 62, 63 
 
 work, 31, 34 
 
 Fuchs, T., cited, 463, 684, 1038, 1068, 1070 
 
 Fiichsel, cited, 1099 
 
 Fucoids, 936 
 
 Fulgurites, 72 
 
 Fuller, M. L., cited, 5, 22, 142, 143, 257, 
 
 266 
 Fumarolic action, 768 
 
 Funafuti, 388, 426 
 
 - atoll, 389, 393, 394, 49, 4*2, 4*3, 
 
 4i5 
 -- , d 
 
 epth of lagoon of, 393 
 -- , diagenism in, 761 
 -- , nullipores on, 471 
 Fungi, 933, 937, 1002, 1003 
 Fusulina limestone, 453 
 
 Fusulina limestones, asphaltic material in, 
 485 
 
 Gagas River, jet deposits of, 483 
 Gagatite, 482 
 
 Gaisa series, glacial deposits on, 534 
 Galapagos Islands, 237, 239 
 
 , tripolite near, 460 
 
 Galicia, 443 
 
 , Oligocenic shales of, 485 
 
 Galveston, range of tide at, 230 
 
 Ganges, 127, 248 
 
 , alluvial plain of, 585 
 
 delta, 607 
 
 , lignitized wood in, 614 
 
 , overlap in. 741 
 
 , remains of river animals in, 615 
 
 , thickness of, 609 
 
 flood plain, 589 
 
 system, hydrographic basin of, 247 
 
 , sediment of, 247 
 
 Ganoids, 951, 1034 
 Gardiner, J. S., cited, 463, 471, 520 
 Garden River, dunes in valley of, $( 
 Garonne River, 223, 558 
 
 , alluvial fan of, 584 
 
 Gaspe limestones, enterolithic structure in, 
 782 
 
 sandstone, Bothryolepis from, 1034 
 
 , dry delta deposit, 635 
 
 Gaub, F., cited, 521 
 
 Gault, 730 
 
 -, overlapping of the, 850 
 
 560 
 
 Gciuss, 185 
 
 Gautier, A., cited, 24, 206 
 
 , quoted, 203 
 
 Gaylussite, 362 
 
 Gaysum Island, calcareous eolian deposits 
 
 on, 577 
 
 Gazelle, observations on the, 204 
 Gebbing, J., cited, 687 
 Geer, G. de, cited, 92 
 Geic acid, 173 
 Geikie, A., cited, 175, 206, 266, 304, 318, 
 
 320, 537, 774, 796, 873, 875, 878, 1119, 
 
 1148 
 , quoted, 219, 315, 698, 770, 864, 872, 
 
 1074, 1105, 1106, 1125 
 Geikie, J., cited, 505, 506 
 Gekrose, 757 
 Gekrosekalk, 759, 785 
 Gemmellaro, G., cited, 1145 
 Genepistasis, 964 
 Generation, alternation of, 938 
 Genesee glacial lakes, 126 
 
 River, 137, 837 
 
 shale, origin of, 479 
 
 , Protosalvinia in, 718 
 
 Valley, Portage sandstone in, 569 
 
 Geneva, foehn of, 47 
 Genoholotype, 920 
 
 Genolectotype, 920 
 Genosyntype, 920 
 Genotype, selection of, 920 
 
 , , elimination method, 920, 921 
 
 , , first species method, 920, 921 
 
 Geo-biotic realm, 982 
 
INDEX 
 
 1163 
 
 Geologic genera, 978 
 Geological time scale, 22 
 Geology, defined, 19 
 
 , subdivided, 20 
 
 Georgia Straits, iti 
 Georgian Bay, 836, 837 
 Geosyncline, 799 
 
 , proposed by Dana, 900 
 
 Gephyrean worms, destruction of corals by, 
 
 415 
 
 Gerbing, J., cited, 763, 774 
 Germersheim, 251 ^ 
 
 Gerontastic, 973 
 Gerontic stage, defined, 972 
 Ghadames, 26 
 Giants' Causeway, columnar structure of, 
 
 3i8 
 
 , Tertiary basalt of, 867 
 
 Gibbsite, 177 
 
 Gibraltar, limestone breccias of, 547 
 
 , Straits of, 240 
 
 Gilbert, G. K., cited, 119, 143, 380, 705, 
 
 706, 707, 709, 721, 861, 878, 908 
 
 , quoted, 705, 706, 712, 713, 882 
 
 , and Gulliver, F. B., cited, 447, 448, 
 
 463, 840 
 , and others, cited, 908 
 
 Islands, 389 
 
 Gironde River, 223 ? 231 
 Girvan district, oolites of, 471 
 Girvanella, 283, 474 
 Givetien, 431 
 
 Gjas, 866 
 Glabella, 947 
 Glacial grooves, 264 
 
 periods, 30 
 
 Glaciation, Cambric, 81 
 
 , Lower Huronian, 81 
 
 , Permo-Carbonic, 82 
 
 , Pleistocenic, 80, 81 
 
 , pre-Cambric, 81 
 
 Glaciers, ablation of, 642 
 
 alpine, 324 
 
 cliff, 324 
 
 continental, 325 
 
 piedmont, 324 
 
 plateau, 325 
 
 ravine, 324 
 
 , valley, 324 
 
 Glauberite, 363 
 
 Glauconite, 330, 451 
 
 Glen Roy, "Parallel Roads" of, 125 
 
 Glinka, K., cited, 687 
 
 Globigerina ooze, 450-453, 675 
 
 , analysis of, 677 
 
 , salt content of, 367 
 
 Glossopteris, 481, 967 
 Glyptogenesis, 16, 829, 1147 
 Glyptoliths, 572 
 Gneiss, 279, 771 
 
 , restriction of term, 770 
 
 Gneissoid structure, defined, 795 
 
 Goat Island, fossiliferous gravels of, 89 
 
 Gobi desert, strength of wind in, 56 
 
 Goebel, quoted, 357 
 
 Goethe, cited, 874 
 
 Goldspie, 650 
 
 Golfe di Taranto, 113, 608 
 
 Golfe du Lion, 113 
 
 Gollachy Mill, Old Red conglomerate of, 
 
 716 
 Gondwana formation, reptiles of, 953 
 
 land, 82 
 
 Goniatites, 978 
 
 Goodchild, J. G., cited, 253, 266 
 Goodenough Lake, composition of, 157, 158 
 
 , salinity of, 154 
 
 Goppert, cited, 1081 
 
 Gorjanovic-Kramberger, K., cited, 92 
 
 Gorteen Bay, 576 
 
 Gossendorf, 246 
 
 Gotan, S., cited, 79, 94 
 
 Gotland, 420, 421, 838 
 
 , reefs of, 418, 427 
 
 , Siluric oolites of, 472 
 
 Gotthard road, 368 
 
 Gotzinger, G., cited, 543, 579 
 
 (Jour, 53 
 
 Gower, limestones of, 459 
 
 Grabau, A. W., cited, 124, 126, 127, 143, 
 243, 257, 266, 271, 283, 288, 299, 355, 
 366, 377, 380, 381, 418, 419, 424, 425, 
 427, 446, 463, 547, 579, 599, 600, 635, 
 636, 637, 638, 684, 687, 719, 721, 723, 
 732, 739, 744, 749, 758, 774, 821, 827, 
 837, 858, 916, 960, 964, 970, 977, 979, 
 980, 981, 989, 990, 992, 994, 999, 1043, 
 1052, 1066, 1070, 1095, 1097, 1113, 
 1119, 1136, 1139, 1145, 1146, 1148 
 
 , quoted, 273, 282, 792, 793, 1074, 
 
 1075, 1076 
 , and Reed, M., cited, 980 
 
 , and Sherzer, W. H., cited, 52, 94, 
 
 537, 538, 1127, 1148 
 
 , and Shimer, H. W., cited, 956, 1095, 
 
 n 19 
 
 ; , quoted, 1074, 1076 
 
 Graff, cited, 1024 
 
 Grafton, 420 
 
 Graham's Island, 864 
 
 Grampians, Carex peat of, 505 
 
 Gran Canada, 244, 336 
 
 , oolite grains of, 753 
 
 Grand Banks, 234 
 
 Grand Canyon, lava flows of, 313 
 
 Grand Cayman Island, 108 
 
 Grand Puy of Sarconi, lava cone of, 870 
 
 Granite, disintegration of, 32 
 
 Granite, graphic, 194 
 
 Granulites, consolidation of, 751 
 
 Graphite, 510, 511 
 
 Graptolites, 243 
 
 , wide distribution of, 1134 
 
 Gravenzande, destruction of dunes at, 224 
 
 Graz, 246 
 
 Great Bahama Banks, 104 
 
 Great Banks, red algae on, 470 
 
 Great Barrier Reef, 387, 389, 390, 391, 402, 
 403, 411, 413, 417 
 
 , pterppod ooze near, 456 
 
 , Orbitolites on, 1007 
 
 Great Basin, diatomaceous earth of, 461 
 
 , rainfall in, 69 
 
 Great Fisher Bank, 191 
 
 Great Geyser, siliceous waters of, 168 
 
 Great Lakes, American, wave erosion on, 
 606 
 
 Great Oolite, worn grains of, 577 
 
 Great Pamir Mountains, sands brought 
 from, 561 
 
 Great Plains, 260 
 
 Great Salt Lake, 70, 338, 360 
 
 , absence of calcium carbon- 
 ate in, 476 
 
 , calcium carbonate in tribu- 
 taries of, 468 
 
 , change in salinity of, 155, 
 
 156 . 
 
 , composition of, 159 
 
 , dune-forming oolites of, 550 
 
 , elevation of, 115 
 
 , excrements of Artemia in, 
 
 1093 
 
 , oolite dunes of, 472, 574 
 
 , oolites of, 467, 468, 473 
 
 , salinity of, 154, 159 
 
1164 
 
 INDEX 
 
 Great Salt Lake, soda deposits of, 361 
 
 Great Syrt, dunes on, 559 
 
 Grebenau, cited, 251 
 
 Greece, 257 
 
 Greenalite, 671 
 
 Greenfield, Triassic extrusives of, 317 
 
 Greenland, 236 
 
 , Eocenic climate of, 29 
 
 , glaciers of, 263 
 
 , ice cap of, 325 
 
 , snow-line in, 322 
 
 Greenland-Iceland region, migration of pole 
 
 from, 895 
 
 Sea, temperatures in, 192 
 
 Greenly, cited, 884 
 
 Green River Beds, fossil mosses from, 938 
 
 Gregory, J. W., cited, 22, 81, 94 
 
 Grenada, 1021 
 
 Greylock, Mount, 799, 80 1 
 
 Griquatown series, tillite of, 535 
 
 Ground water, 4, 139 
 
 , depth of, 4, 5, 142 
 
 Grund, alteration of limestones of, 767 
 Grundy county. 111., concretions in carbonic 
 
 shales of, 764 
 
 Guadalquiver River, dunes on bank of, 560 
 Guam, island of, 2 
 Guano, 370, 461 
 Guayaquil, 60 
 
 Guelb-el-Zerzour, erosion-buttes near, 854 
 Guelph . dolomite, 376, 377 
 Guiana shelf, 103 
 Guinea current, 187 
 Gulf of Aden, 113 
 
 , temperatures of, 190, 192 
 
 Akabah, 113 
 
 Cadiz, 113 
 
 , salinity of, 153 
 
 , temperature of, 187, 192 
 
 California, 1 12, 356, 652 
 
 Finland, 241, 838 
 
 Guinea, 113, 195, 235 
 
 :msa, 576 
 ion, 113 
 
 Mexico, 107, 230, 233, 239, 247 
 
 Naples, 470 
 
 , blue mud in, 668 
 
 Obi, in 
 
 Oman, 113 
 
 Panama, 113 
 
 Riga, dunes of, 557 
 
 St. Lawrence, 113 
 
 Sidra, 240 
 
 Suez, 113 
 
 Taranto, delta in, 608 
 
 Tartary, 242 
 Gulf Stream, 192, 215, 233, 234, 236, 239, 
 
 335, 390, 405, 406, 407 
 
 , greensand under, 673 
 
 , velocity of, 680, 1050 
 
 Gulick, J. T., cited, 1070 
 
 , quoted, 1043 
 
 Giimbel, C. W. von, cited, 73, 298, 482, 
 
 687, 748 
 
 Gunnison River, 131 
 Giinther, A. C. L. G., cited, 1056, 1070 
 Gunther, S., cited, 13, 22, 23 
 Guppy, H. B., cited, 59, 94, 248, 411, 463 
 Giirich, G., cited, 956 
 Gypsum, dehydration of, 765 
 , recrystallization of, 756 
 
 H 
 
 Haeckel, E., cited, 993, 996, 999, 1039 
 Haecker, V., cited, 463 
 Hagg, R., cited, 92 
 
 gro 
 
 Ish 
 
 Hague, A. cited, 143, 201, 203, 206 
 Hahn, F. F., cited, 380, 381, 459, 463, 530, 
 
 . 538, 758, 774, 783, 784, 827, 1039 
 Haidinger, cited, 1087 
 Hail, 62, 63 
 Halimeda, 388, 394, 474, 476, 935 
 
 , chemical analysis of, 469, 470 
 
 Hall, C. W., and Sardeson, F. W., cited, 
 687 
 
 , quoted, 672 
 
 Hall, J., cited, 900, 902, ion, 1123, 1127 
 Halle, J., cited, 82, 94 
 Halligan, G. *H., cited, 463 
 Hallock, W., cited, 73 
 Halobips, 991, 992 
 Halo-biotic realm, 982 
 Halo-pelagic district, 988 
 Hamburg, cited, 194 
 Hamilton fauna, 1053 
 jroup, 426 
 land, 397 
 -, locofauna of, 922 
 
 sandstone, 636 
 
 Hanamann, J., cited, 166, 206 
 Handlirsch, A., cited, 949 
 
 Hanford Brook, thickness of Etcheminian 
 
 at, 729 
 
 Hankow, dust storm at, 59 
 Hanksite, 363 
 Hann, J., cited, 26, 28, 47, 76, 94, 323, 
 
 328 
 
 , quoted, 48, 50 
 
 Hanover, salt domes of, 758 
 
 county, Va., Greensand marls of, 671, 
 
 672 
 
 Hansen, H., and Nansen, F., cited, 236, 
 
 266 
 
 Hansen, H. J., quoted, 181 
 Harder, P., cited, 92 
 Harding sandstone, ostracoderms from, 
 
 1033 
 
 Hard war, 127 
 Harker, A., cited, 277, 299, 306, 307, 308, 
 
 320 
 
 Harper, R. M., cited, 521 
 Harris, G. D., cited, 380, 381 
 
 , G. F., cited, 275, 299 
 
 Harrisburg, Appalachian folds at, 844, 903, 
 
 904 
 Harrison, J. B., and Jukes-Browne, cited, 
 
 463 
 
 , and Williams, J., cited, 206 
 
 Harrison beds, loess-like origin of, 568 
 
 Hartland Point, 222 
 
 Hartsalz, 371 
 
 Hartt, C. F., cited, 463 
 
 , quoted, 396 
 
 Harz, 375 
 
 , Zechstein reefs of, 433 
 
 Hatcher, J. B., cited, 538 
 
 Haug, E., cited, 23, 79, 94, 101, no, 270, 
 
 299, 643, 687, 873, 901, 902, 907, 908, 
 
 987, 1057, 1146, 1148 
 Hawaiian Islands, lava of, 314 
 
 , marine erosion of, 875 
 
 , origin of, 679 
 
 , pteropod ooze around, 456 
 
 , rainfall of, 67 
 
 , submarine cones of, 872 
 
 Hay, O. P., cited, 90, 92, 95 
 
 , R., cited, 908 
 
 Hayden, F. V., cited, 36, 202, 342, 824 
 
 Hayek, A. von, cited, 92 
 
 Hayes, C. W., cited, 95, 176, 206, 1113, 
 
 1119 
 
 , and Ulrich, E. O., cited, 1113, 1119 
 
 Hayford, J. F., cited, 10, 11, 23 
 Hazen, A., cited, 258, 266, 687 
 
INDEX 
 
 1165 
 
 Heautotype, 919 
 
 Heawandoo Pholo, 399 
 
 Hebrides, 234 
 
 Hecker, O., cited, 58, 95 
 
 Hedin, S., cited, 53, 92, 95 
 
 Hedstrom, H., cited, 420, 463 
 
 Heidelberg Schloss, erosion of, 58 
 
 Heiderich, quoted, 6 
 
 Heilprin, A., cited, 870, 878, 1037, 1070 
 
 Heim, Albert, cited, 176, 546, 579, 657, 
 
 687, 798, 800 
 , Arnold, cited, 657, 660, 661, 687, 780, 
 
 821, 827 
 
 , F., cited, 687 
 
 Helderberg escarpment, 837, 838 
 
 mountains, 261, 709 
 
 Heleoplankton, 998 
 
 Helgoland, Island of, 225 
 
 Helium, 25 
 
 Hellbrun, Nagelfluh of, 602 
 
 Hell Gate, narrows at, 229 
 
 Hellmann, J. G. G., and Meinardus, W., 
 
 cited, 95 
 
 Helman, C. H., cited, 556, 579 
 Helmert, F. R., cited, 15, 23 
 Helmsdale, 651 
 Heluan, 594 
 Hematite, 35 
 
 Henning, K. L., cited, 633, 638 
 Henry Mountains, 308 
 Hensen, V., cited, 992, 999, 1039 
 Herculaneum, human bodies preserved at, 
 
 525 
 
 , molds of bodies buried at, 1089 
 
 Herero Land, destruction of surface by 
 
 herds in, 691 
 
 Hermansville, peat deposit near, 502 
 Hernpsand, no 
 Heroppolite Gulf, 352 
 Herrick, C. L., cited, 578, 579 
 Heterepistasis, 964 
 
 , illustration of, 1136 
 
 Heterocerci, 951 
 
 Heteroconteae, 934 
 
 Hexaseptata, 943 
 
 Hibbert-Ware, S., cited, 72, 95 
 
 Hieber, V., cited, 443, 463 
 
 Hilgard, E. W., cited, 140, 369, 381, 611, 
 
 638, 70S 
 Hill, R. T., cited, 58, 95, 575, 579, 870, 
 
 878, 1108 
 
 , and Vaughan, T. W., "cited, 587, 638 
 
 Hill, W., and Jukes-Browne, A. J., cited, 
 
 463 
 
 Hilo, lava flow near, 868 
 Himalayas, a geosyncline, 902 
 
 , Eocenic marble of, 773 
 
 , Meekoceras beds of, 1137 
 
 , rainfall in, 69 
 
 , rock fall in, 546 
 
 Hinde and Fox, cited, 459 
 Hinds, R. B., cited, 917 
 Hindu Rush Mountains, sands brought 
 
 from, 561 
 
 Hippopus, in Arabian eolian limestone, 575 
 Hitchcock, C. H., cited, 314, 317, 320, 878 
 Hjort, J., cited, 205, 206 
 Hobbs, W. H., cited, 328, 547, 590, 629, 
 
 630, 638, 816, 827, 861, 886, 878, 881, 
 
 908 
 
 , quoted, 862, 866, 885 
 
 Hoburgen, reefs of, 421 
 
 Hochenburger, cited, 246, 256 
 
 Hochstetter, F. V., cited, 336, 381 
 
 Hoernes, R., cited, 595, 638, 882, 1064, 1070 
 
 Hog-backs, 840, 841 
 
 Hogoleu, 402 
 
 Holland, subsidence of coast of, 224 . . . 
 
 Hollick, A., cited, 1070 
 
 Holmboe, J., cited, 86, 92 
 
 Holmia, index fossil of Lower Cambric, 912 
 
 fauna, 1052 
 
 Holocenic, 910 
 Holocephali, 951 
 Holoplankton, 992 
 Holoplastotype, 919 
 Holothuroidea, 950 
 Holotype, 919 
 Holyoke, trap of, 313 
 
 Holy Well, composition of water of, 168 
 Holzmaden, jet from, 483 
 
 , Lias of, 1078 
 
 , petrifaction of Pentacrinites at, 1087 
 
 Homceomorph, 976, 978, 1061 
 
 Homoeotype, 919 
 
 Homozooidal belts, 78 
 
 Horgen, subaqueous gliding at, 657, 780, 
 
 784 
 
 Hornblendite, 278 
 
 Horsepen, brachiopod fauna of, 742 
 Hoskins, L. M., cited, 906, 908 
 Hot Lake, composition of water of, 168 
 Hot Spring, borate waters of, 168 
 Housatonic River, 131 
 Houtin, sea advance at, 558 
 Hove, force of waves at, 222 
 Hovey, E. O., cited, 86 1, 870, 878, 883, 
 
 908 
 
 , quoted, 862, 876 
 
 How, j. A., cited, 827 
 
 Howchin, W., cited, 81, 535, 538 
 
 Howe, M. A., cited, 385, 463, 471, 521, 
 
 545, 579 
 
 Huang-hai (Yellow) Sea, m 
 Huang-ho, 248 
 , alluvial fan of, 584 
 
 delta, extent of, 252 
 
 , overlap in, 741 
 
 , rate of growth of, 609 
 
 , slope of, 904 
 
 flood plain, 589 
 
 Hubbard, L. L., cited, 381 
 Hudson Bay, 109, 241 
 
 , mean temperature of, 193 
 
 , temperatures in, 191 
 
 furrow, 104 
 
 Highland, northwest thrusting of, 903 
 
 River, depth of channel of, 662 
 
 beds, 261 
 
 , drowning of, 136 
 
 group, folding of, 851 
 
 series, metamorphism of, 772 
 
 , tides in, 227 
 
 Hughes, T. McK., cited, 1085, 1095 
 
 Hugh River, tidal bore of, 227 
 
 Hull, cited, 1149 
 
 Humber River, 224, 225 
 
 Humboldt, A. von, cited, 72, 322, 1108 
 
 Lake, composition of, i$7> *58 
 
 , salinity of, 155 
 
 Hume, W. F., cited, 92 
 
 Humic acid, 173, 174 
 
 Humidity, absolute and relative, 26 
 
 Humphreys, A. G., and Abbott, H. L., 
 
 cited, 247, 267 
 Humulith, 281 
 Humus, 281 
 Hungary, alkaline lakes of, 361 
 
 , dune area of, 562 
 
 Hunt, A. R., cited, 713, 721 
 
 Hunt, T. S., cited, 206, 347, 369, 381, 672, 
 
 687 
 
 , quoted, 174 
 
 Huntington, E., cited, 82, 83, 84, 95, 381, 
 
 555, 579, 623, 638, 703, 722 
 , quoted, 358, 359 
 
ii66 
 
 INDEX 
 
 Hunton limestone, 684 
 
 Huronian, Lower, tillite from, 534 
 
 Hurst castle, 222 
 
 Hussakof, L., cited, 980 
 
 Huxley, T., cited, 1059, 1070, 1125 
 
 Hyatt, A., cited, 913, 964, 965, 9 66 97, 
 
 971, 976, 980, 1136, 1149 
 Hyde, T. E., cited, 530, 538, 777. 827 
 Hydration, 17, 37, 765 
 Hydrargillite, 39 
 Hydroclasts, 285 
 Hydrocorallines, 385, 418, 943 
 Hydrogen sulphide, 24 
 
 , in peat beds, 493 
 
 Hydrology, 20 
 
 Hydrometamorphism, 748, 749, 766 
 Hydromicas, 177 
 Hydroseisma, 88 1 
 Hydrosphere, i 
 
 , subdivisions of, 99 
 
 Hydrothecae, 943 
 Hydrozoa, 942 
 
 reefs, 439 
 
 Hyolithidae, 946 
 Hyphae, 937 
 
 Hypnetum, 486, 487, 500 
 Hypocenter, 883 
 Hypoplastotype, 919 
 Hypsometric niveau, 444 
 
 Ice, glacier, 279 
 
 , snow, 279 
 
 caps Cordilleran, 326 
 
 Keewatin, 326 
 Labradoran, 326 
 Newfoundland, 326 
 Pleistocenic, 325, 326 
 
 floes, 198 
 
 Iceland, 234 
 
 , earthquake in, 888 
 
 , hot springs and geysers of, 201 
 
 , sinter deposits of7 475 
 
 , Tertiary basaltic flows in, 867 
 
 , volcanic fissures of, 866 
 
 Iceland-Faroe shelf, 103 
 
 Icoplastotype, 919 
 
 Idaho, Archaean d9lomites of, 334 
 
 Iddings, J. P., cited, 277, 299, 303, 304, 
 313, 319, 320 
 
 Idiotype, 919 
 
 Ihering, H. von, cited, 1149 
 
 He Julia, 864 
 
 Illinois River, plankton in, 997 
 
 Illye's Lake, salinity of, 154 
 
 Imatra stones, 764 
 
 Inclusions, acicular, 716 
 
 , irregular, 716 
 
 , regular, 716 
 
 Incretions, 719, 720 
 
 Indevsk Lake, salinity of, 154 
 
 India, earthquake lakes of, 889 
 
 , isobars of, 45, 46 
 
 , regur of, 514 . , 
 
 , winds of, 45, 46 . . 
 
 Indian Ocean, 240 . < ... 
 
 atolls of, 388 
 
 evaporation from, 182, 183 .. . 
 fringing reefs in, 386,. 390 
 manganese concretions in, 718 
 mean temperature of, 193 
 Permic position of North Pole 
 in, 536 
 
 , surface temperature of, 182, 183 
 
 , temperatures of, 185, 187 
 
 Peninsula, 836 
 
 Indo-Gangetic delta plain, 584 
 
 flood plain, 585 
 
 Indus, 248 
 
 , delta, 607, 608 
 
 , deposits or lime in, 616 
 
 , overlap in, 741 
 
 River, alluvial plain of, 585 
 
 , mud volcanoes along, 872 
 
 Inner Lowland, 83 1 
 
 Innsbruck, fohn days of, 47 
 Insectivora, 955 
 Insects, marine habitat of, 985 
 Inselberge, 58, 853 
 
 , Kalahari, 692 
 
 , South Africa, 854, 855 
 
 , West Australia, 855 
 
 Insolation, 31, 41 
 Intercontinental seas, 9 
 Interactions, 719 
 Interformational sheets, 304, 305 
 Interlaken delta at, 127 
 Interstrophe, climatic, 82, 83 
 Intervale, flood plain in, 588, 596 
 Intracontinental seas, 9 
 Intumescens fauna, 1023 
 Inyo county, Cal., 362 
 
 , soda niter deposits in, 364 
 
 Ionian Sea, 230, 240 
 Iquique, guano of, 461 
 Iran, desert areas of, 562 
 Ireland, 374 
 
 , greensands of northeast, 850 
 
 , mild temperatures of, 234 
 
 , origin of chalk of, 850 
 
 , transgressing Cretacic of, 730 
 
 Irish Sea, 112 
 
 -, tidal interference in, 229 
 
 "Irish Stream," 234 
 
 Irondequoit limestone, ballstone reefs of, 
 
 Iron Gate, gorge of, cut by Danube, 587 
 Irvine, R., cited, 194 
 
 , and Woodhead, G. S., cited, 331, 
 
 381, 464 
 
 , and Young, G., cited, 381 
 
 Irving, A., cited, 774 
 , quoted, 766 
 
 Island of Gran Canaria, 244, 336 
 Island of Rhodes, 153 
 
 , Skye, 306, 308 
 
 , Staffa, 318 
 
 Isle of Man, 229 
 
 of Wight, ercsion of chalk cliffs of, 
 
 225 
 
 Isobars, 4 1 
 Isostacy, 9 
 
 , Penck's illustration of, 9 
 
 Isostatic equilibrium, 10 
 
 readjustment, 900 
 
 Issyk Kul, composition of, 157 
 
 , salinity of, 155 
 
 Isthmus of Suez, Bitter lakes of, 352 
 Italy, 221 
 
 , cavern deposits of, 346 
 
 , travertine of, 343 
 
 Ithaca, salt well at, 376 
 
 fauna, 1053 
 
 abor, lagoon at, 441 
 
 ackson, K. T., cited, 980 
 
 acobitti, E.. cited, 897, 898, 908 
 
 aggar, T. A:, cited, 870-, 872, 878 
 
 ahn, J., cited, 464 
 
 aluit, lagoon at, 441 
 
 amaica, foramini feral limestone of, 455 
 
INDEX 
 
 1167 
 
 James, E., cited, 1122 
 James, U. P., cited, 917 
 James Bay, 430 
 Japan, earthquake in, 887 
 
 , explosive eruption in, 86 1 
 
 , New Mountain formed in, 863 
 
 , Pliocenic climate of, 89 
 
 , seismic periods observed in, 891 
 
 Sea, 108, 242 
 
 , mean temperature of, 193 
 
 Jatulian formation, anthracite in, 478 
 Java, 390 
 
 Sea, 242 
 
 Jaxartes delta, 608 
 
 , rate of growth of, 609 
 
 River, dunes along, 561 
 
 Jefferson, M. W., cited, 707 
 Jeffersonville limestone, 426 
 Jeffrey, E. C., cited, 482, 521 
 , quoted, 482 
 Jena, 252 
 
 , Muschelkalk of, 335 
 
 Jensen, A. S., cited, 92 
 
 , and Harder, P., cited, 87 
 
 Jensen expedition, 1066 
 
 Jentzsch, A., and Michael, R., cited, 95 
 
 Jet, 482, 483 
 
 , analysis of, 483 
 Jhelam River, 587 
 Joggins, South, section at, 515 
 Johnson, D. W., cited, 135, 143, 228, 267, 
 706, 722, 858, 874, 878, 966, 980 
 
 , quoted, 707 
 
 , Willard D., cited, 888, 909 
 
 , and Hobbs, W. H., cited, 909 
 
 Sohnston, J., cited, 753, 774 
 ohnston-Layis. H. j., cited, 879 
 ointing, prismatic, in coal, 820 
 oints, compression, 789 
 
 , tension, 789 
 
 , widening of, 791 
 
 Joly, J., cited, 687 
 
 Jordan, D. S., cited, 1042, 1070 
 
 , quoted, 1043 
 
 Jordan River, Utah, calcium carbonate in, 
 
 468 
 
 orullo, cinder cone formed in, 863 
 osephine bank, 335 
 udith Mountains, 306 
 uglans, 630 
 
 ukes-Browne, A. J., cited, 104, 387, 464 
 ulien, A. A., cited, 73, 95, 166, 173, 174, 
 
 206 
 Jumna River, vertebrate remains in clays 
 
 of, 586 
 Junagarh limestone, 455, 574 
 
 , eolian cross-bedding in, 704 
 
 Tuniata shales, 636 
 
 Jupiter Serapis, temple of, 3, 887 
 
 Jura, formation, 367 
 
 , origin of oolites of, 455 
 
 , White, of Swabia, 442 
 
 Mountains, anticlines and synclines 
 
 of, 847 
 
 Jurassic limestone, Alpine, breaks in, 682 
 Jutland, dunes of, 557 
 , structure of dunes of, 703 
 
 Kainite, 371, 372 
 
 Kalahari, Inselberge of, 692 
 
 desert, 123, 124 
 
 , erosion in, 58, 70 
 
 , leveling of, 854 
 
 , oolites of lakes in, 469, 473 
 
 , rainfall of, 63, 64 
 
 Kalahari desert, salinas of, 359 
 
 Kalala oasis, 359 
 
 Kalkowsky, E., cited, 469, 472, 473, 521 
 
 Kalmar Sund, 838 
 
 Kammerbuhl, volcanic hill, 874 
 
 Kampar River, 509, 510 
 
 Kamtchatka, 186 
 
 Kanab formation, dune origin of, 571 
 
 Kankar, 586, 719 
 
 Kaolin, 37, 177 
 
 Kaolinite, 39, 292, 540, 548 
 
 Kaolinization, 37 
 
 Kapstadt, 452 
 
 Karabugas Gulf, 366 
 
 , composition of, 157 
 
 density of, 180 
 
 deposits of, 354 
 
 freezing of, 181 
 
 map of, 353 
 
 salinity of, 154, 351 
 
 sulphate of soda deposits in, 360 
 
 Kara Kum, dunes of, 551, 561, 565 
 Kara Sea, in, 241 
 
 Straits, 236 
 
 Karibib, 692 
 
 Karisimbi Mountain, 125 
 
 , height of crater rim of, 866 
 
 Karnic Alps, Devonic reefs of, 431 
 Karnic limestone, ammonoid from, 975 
 
 , Trachyceras from, 1136 
 
 Karoo formation, Ceratodus in, 1034 
 
 , glacial deposits in, 535 
 
 Karpinsky, A., cited, 82, 1149 
 Karst landscape, 133 
 
 region, 125, 791, 882 
 
 Kashmir, Vale of, 587 
 Katamorphism, zone of, 747 
 
 , , depth of, 747 
 
 Kathiawar peninsula, foraminiferal (Juna- 
 garh) limestone of, 455, 574 
 
 Kattegat, 241, 1045 
 
 Katwee Lake, 359 
 
 Katwijk, 224 
 
 Kauar, oasis of, 26 
 
 Kayser, E., cited, 247, 267, 434, 442 
 
 , and Holzapfel, E., cited, 423, 464 
 
 Kazan district, dunes in, 561 
 Keeling atoll, 397, 398, 399, 416 
 Keewatin, 311 
 
 , Devonic reefs of, 430 
 
 Keilhack, K., cited, 252, 267, 287, 299, 805, 
 
 828 
 
 Kelheim, 440 
 , Solnhofen reefs, 438 
 
 limestone. 438 
 
 Kelley's Island, glacial grooves of, 264 
 Kelvin, see Thompson 
 
 Kemp, J. F., cited, 23, 138, 142, 144, 206, 
 277, 279, 299, 874 
 
 , quoted, 4 
 
 , and Knight, W. C., cited, 879 
 
 Kengott, cited, 368 
 
 Kenny, Captain, cited, 224 
 
 Kent, pipes of sand in chalk at, 698 
 
 Kentucky, fossil reefs of, 420 
 
 Keokuk anticline, 810 
 
 Kerguelen Islands, 40 
 
 Kermadec deep, 3, 896 
 
 , temperatures in, 187 
 
 Islands, pteropod ooze around, 456 
 
 Kerr, W. C., cited, 34, 95 
 Kertch, peninsula of, 443 
 
 , and Taman, mud volcanoes in, 872 
 
 Kettle Point, concretions of, 719, 764 
 
 River, 305 
 
 Keuper, Ceratodus in, 1034 
 
 marls, loess-like origin of, 568 
 
 , organic remains of, 635 
 
n68 
 
 INDEX 
 
 Keuper sandstone, origin of, 634 
 
 , transgression on Muschelkalk, 565 
 
 Kew, 28 
 
 Keweenawan, lava sheets of, 868 
 
 sandstone, cementation of, 754 
 
 Keyes, C. R., cited, 58, 95, 579, 858 
 "Keys," 404, 406, 407 
 Key West, 404 
 
 , diagenism of limestone of, 761 
 
 Khanat Desert, sand ripples in, 556 
 
 Khasi Hills, rainfall in, 68 
 
 Kielce, petrifaction of crinoids at, 1087 
 
 Kieserite, 368, 372, 757 
 
 Kiev, rainfall at, 65 
 
 Ki Island, 519 
 
 Kilauea, 138 
 
 , elevation of rim of, 869 
 
 , frozen lava surface of, 866, 869 
 
 Kilnsea, church at, 225 
 
 Kinderhook fauna, 732, 1124 
 
 Kindle, E. M., cited, 641, 687 
 
 King, C., cited. 15, 23, 626, 638 
 
 King, F. H., cited, 258, 267 
 
 King, L. V., cited, 747, 774 
 
 King Charles Land, Jurassic temperature 
 
 of, 79 
 
 , post-glacial fauna of, 88 
 
 King Edward Island, volcanoes of, 877 
 King River, alluvial fan of, 126 
 Kingsley, J. S., cited, 1029 
 Kingston, repetition by faulting near, 817 
 'Kiota, seismic periods observed at, 891 
 Kirchoff, A., cited, 1070 
 Kirk, E., cited, 449, 464, 1031, 1039 
 Kizil Kum, dunes of, 551, 561 
 Klintar of Gotland, 420, 430 
 Knight, C. W., cited, 534, 538 
 Knop, A., cited, 381 
 Knorria, 518 
 
 Knowlton, F. H., cited, 92, 1149 
 Knudsen, cited, 179, 180 
 Kochbrunnen, composition of the, 168 
 Koken, E., cited, 513, 536, 538, 757, 758, 
 
 759, 774, 784, 785, 827, 897, 909, 956, 
 
 1058, 1070, 1149 
 
 Koko-Nor Lake, salinity of, 159 
 Kola, peninsula of, 86 
 Konjepruss, 423 
 
 limestones, 431 
 
 Koppen, cited, 45, 46 
 
 Korea, 242 
 
 Kormos, T., cited, '92 
 
 Kossmat, F., cited, 1149 
 
 Kostritz, 433 
 
 Kota-Maleri beds, Ceratodus in, 1034 
 
 Koto, B., cited, 909 
 
 Kotzebue Sound, 508 
 
 Krakatoa, 28 
 
 , ashes from, 60 
 
 , dust from, 59, 550, 572 
 
 , explosive eruption of, 875, 881 
 
 , secondary thalassoseisma from, 890 
 
 Kraus, E. H., cited, 537, 538 
 Kreichgauer, D., cited, 893, 909 
 Kriimmel, O., cited, 2, 3, 6, 8, 23, 99, 105, 
 
 106, 107, 144, 145, 147, 149, 150, 151, 
 
 153, 165, 170, 179, 180, 183, 184, 193, 
 
 206, 231, 232, 234, 236, 239, 245, 267, 
 
 453, 458, 464, 644, 657, 687 
 , quoted, 103, 171, 181, 182, 194, 212, 
 
 213, 214, 216 
 Krypton, 25 
 Ktypeit, 336 
 
 , oolites changed to, 469 
 
 , recrystallization of, 755 
 
 Kufra, oasis of, 26 
 
 Kiimmel, H. B., cited, 634, 740, 744 
 
 Kupferschiefer, 372, 375, 434 
 
 Kupferschiefer, fishes of, 951 
 
 , origin of, 479 
 
 Kurische Haff, 126, 1063 
 
 , strand dunes of, 557 
 
 Nehrung, migrating dunes on, 559 
 
 Kurland, dunes on coast of, 557 
 Kuroshiwo, see currents 
 Kymoclastic, 295 
 
 Laacher Sea, 122, 860 
 
 , salinity of, 155 
 
 Labadie-Cockburn bank, 104 
 Labrador, 234 
 
 , Archaeocyathidae of, 417 
 
 , lakes of, 199 
 
 Labyrinthodonts, 633 
 
 Laccadive Islands, 389, 390 
 
 Laccoliths, 306, 308 
 
 Lac de Brenets, 125 
 
 Lacertilia, 953 
 
 Lachmann, cited, 758 
 
 Ladakh, 364 
 
 Ladinian, 435 
 
 Ladrone (Marian) Islands, 2 
 
 Lady Elliott Island, 387 
 
 La Fayette formation, eolian cross-bedding 
 
 in, 705 
 
 Lagarfljot, 1063 
 Laggo Maggiore, 116, 124 
 Lagonite, 364 
 Lahore, 26 
 Lake Agassiz, 126 
 
 Agnano, 120 
 
 Akiz, 1 063 
 
 Altai Beisk, soda deposits of, 361 
 
 Averno, 120 
 
 Baikal, 118 
 
 , composition of, 161 
 
 , depth of, 116 
 
 . , drainage of, 116 
 
 , elevation of, 116 
 
 , salinity of, 155 
 
 Balaton, 122 
 
 Biljo, composition of, 157, 158 
 
 , salinity of, 155 
 
 Bonneville 70, 121 
 
 , alluvial fans in, 83 
 
 , calcareous deposits of, 338 
 
 , ^former extent of, 119 
 
 Bouve, 126 
 
 , sand plains in, 600 
 
 Brienz, 127, 610 
 
 Champlain, composition of, 161 
 
 , fulgurites of, 73 
 
 , salinity of, 155 
 
 Charles, 126 
 
 Chichen-Kanab, composition of, 157 
 
 , gypsum in, 359 
 
 , salinity of, 155 
 
 Como, depth of, 116 
 
 Constance, 622 
 
 , composition of silt in, 616 
 
 , optics of, 205 
 
 , rock slide at, 546 
 
 , shells in, 631 
 
 Domoshakovo, composition of, 157 
 
 , salinity of, 154 
 
 , soda deposits of, 361 
 
 Drummond, 120 
 
 , peat of, 500 
 
 Erie, 245, 264 
 
 , composition of, 161 
 
 , nature of pebbles on shores of, 
 
 595 
 
INDEX 
 
 1169 
 
 Lake Erie, salinity of, 15 
 
 ic, salinity ot, 155 
 
 , shale pebbles of, 650 
 
 Eulalie, drainage of, 889' 
 Florissant, 125 
 Geneva, 196, 197, 198 
 
 , aphotic region of, 983 
 
 , Characeae in, 204 
 
 , subaquatic glidings in, 659 
 
 Hachinchama, 363 
 
 Huron, composition of, 161 
 
 , cross-section of, 838 
 
 , elevation of, 116 
 
 , salinity of, 155 
 
 Illye's, 122, 154 
 Iroquois, glacial lake, 753 
 Kisil-Kull, soda deposits of, 361 
 Kivu, 124, 125 
 
 , rift-valley of, 866 
 
 Koko-Nor, composition of, 157, 158, 159 
 
 , salinity of, 155 
 
 Ladoga, 85 
 
 Lahontan, calcareous deposits of, 338 
 
 , successors of, 121 
 
 , tufa deposits of, 340, 341, 347 
 
 Lucerne, 124 
 
 Lucrinus, 863 
 
 Lugern, delta in, 610, 613 
 
 Maggiore, depth of, 116 
 
 Michigan, composition of, 161 
 
 , dunes on, 559 
 
 , elevation of, 116 
 
 , glacial sands of, 553 
 
 , limestone pebbles of, 650 
 
 , nature of pebbles on shores of, 
 
 595 
 
 , salinity of, 155 
 
 , shore dunes of, 557 
 
 , storm terraces on, 606 
 
 , tides of, 231 
 
 Nashua, 126 
 Nemi, 120 
 Nicaragua, 1 18 
 Nyassa, 118 
 
 , drainage of, 116 
 
 Onega, 478 
 
 Ontario, 118, 124, 218 
 
 , crystallines of, 834 
 
 , elevation of, 116 
 
 Pangkong, 126 
 Passaic, 126 
 Pontchartrain, 121, 1063 
 
 , cypress swamps in, 500 
 
 Rukwa, figured, 119 
 
 St. Laurent, 127 
 
 Schunett, soda deposits of, 361 
 
 Seyistan, deposits in, 84 
 
 Shaler, 126 
 
 Superior, 118 
 
 , aphotic region of, 983 
 
 , composition of, 16 1 
 
 , depth of, 116 
 
 , salinity of, 155 
 
 region, Keweenawan lava sheets 
 
 in, 868 
 
 sandstone, 648 
 
 , basal arkose of, 548 
 
 Tahoe, depth of, 116 
 Tanganyika, 118, 119, 125 
 
 , elevation of, 116, 867 
 
 , medusa of, 1009 
 
 , relict fauna of, io64 
 
 Thaxter, 23 
 Thun, 127 
 Tinetz, 351 
 
 , salinity of, 154 
 
 Venern, 1064 
 Vettern, 1064 
 Winnipeg, 837 
 
 Lake Winnipegasie, 199 
 
 Zurich, optics of, 205 
 Laki, volcano of, 866 
 Laminaria, 470, 936, 995, 1001 
 
 - , organisms growing on, 995 
 Lamination, planes of, 699 
 Lamplugh, G. W., cited, 92 
 Lamprecht, cited, 758 
 Lampreys, 951, 1034 
 
 Land, area of, 6 
 
 - , elevation of surface of, 6 
 
 - breezes, 45 
 
 Lander, red beds from, 633 
 Landes, 223 
 
 - , dunes of, 558 
 
 Land lobe, Alleghany, 807, 809 
 -- Cape Breton, 808, 809 
 -- Maine, 808, 809 
 -- Mississippi, 807, 809 
 -- New York, 807, 809 
 -- Rome, 807, 809 
 Landscha, 246 
 Lane, A. C., cited, 138, 139, 144, 167, 326, 
 
 376, 381, 635, 1017, 1020, 1024 
 Lang, A., cited, 1039 
 Langenbeck, R., cited, 464 
 Languedoc, dunes in, 560 
 Lapilli, 860, 862 
 Lapland, snow-line in, 322 
 La Plata, mountains, 308 
 
 - , River and Estuary, 248, 66 1, 662 
 
 La Platte sandstone, eolian cross-bedding in, 
 
 704 
 
 Lapparent, A. de, see De Lapparent 
 Lapworth, C., cited, ion, 1108 
 
 - , and Watts, cited, 307, 308, 321 
 Laramie formation, non-marine, 1101 
 La Soufriere, dust from, 60 
 
 Las Palmas, 336 
 
 Laterite, 39, 292, 540, 548 
 
 Laterization, 39 
 
 Laufer, E., cited, 287, 288 
 
 - , and Wahnschaffe, F., cited, 299 
 Laurentian, 311 
 
 Lava, pillowy (pahoehoe), 313, 314, 868 
 
 - , ropy 3/3 
 
 - , rough (aa), 313, 316 
 Le Chenaillet Ridge, 316 
 
 Le Conte, J., cited, 247, 267, 386, 387, 388, 
 405, 407, 464, 617, 639, 909, 1119 
 
 - , quoted, 890 
 Lecoq cited, 179 
 Lectotype, 919 
 Leda, 88 
 
 clays, 1074 
 
 Lehmann, T. G., cited, 1098, 1119 
 
 Leitersdorf, 246 
 
 Leith, C. R., cited, 671, 687, 793, 827, 906, 
 
 909 
 
 Lena delta, 607, 608 
 Lendenfeld, R. v., cited, ,92 
 Lepidodendraceae, geologic range of, 941 
 Lepidodendrales, 940 
 Lepidodendron, 512, 940, 1004, 1082 
 Lepidophytes, 512 
 Lesley, J. P., cited, 903 
 Lesquereux, cited, 708 
 Leucite Hills, volcanic necks of, 874 
 Leverett, F., cited, 579 
 Lewiston, Pleistocenic delta near, 60 1, 616, 
 
 Lewistown limestone, 418, 422, 423 
 
 Leythakalk, 474 
 
 Lias of Ireland, 730 
 
 Liburnau, J. L. von, cited, 595, 639 
 
 Libyan desert, chalk from, 454 
 
 -- , erosion needles in, 856 
 
 -- , fossils in, 642 
 
1170 
 
 INDEX 
 
 Libyan desert, fulgurites in, 73 
 
 rounding of grains in, 553 
 
 sorting of sands in, 552 
 
 source of sands of, 62 
 
 , transgressing dunes of, 565 
 
 wind erosion in, 52 
 
 windkanter of, 54 
 
 dunes, origin of sands of, 551 
 
 Lichens, 937, 1003 
 
 calcicolous, 1003 
 
 calciferous, 1003 
 
 corticolous, 1003 
 
 destruction of rocks by, 695 
 
 epiphyllous, 1003 
 
 muscicolous, 1003 
 
 wind blown, 56 
 Liebenstein, 434 
 Life districts, 983 
 Light, 28 
 Lightning, 72 
 Lignite, 510 
 Ligurian Sea, 240 
 Lil, lagoon of, 441 
 Lille, France, 24 
 Lima, 438, 1016 
 Limnaaa, 630, 665, 1018, 1047, 1067 
 
 , in Baltic, 1018 
 
 Limno-aphotic region, 983 
 
 Limnobios, 991, 992 
 
 Limno-biotic realm, 982 
 
 Limnogenic deposits, 329 
 
 Limnography, 21 
 
 Limno-littoral district, fauna of, 988 
 
 , flora of, 988 
 
 Limnology, 20 
 
 Limonite, 35, 177 
 
 Limulava, 948, 1030 
 
 Linck, G., cited, 332, 337, 381, 464, 469, 
 
 Lincoln, F. C., cited, 144, 203, 207 
 
 Lincoln, New Zealand, rain at, 166 
 
 Lindberg, H., cited, 92 
 
 Linnaean species, 960, 962 
 
 Linth, foehn of, 47 
 
 Linton, organic remains in cannel coal of, 
 
 481 
 
 Lipari group, 317, 863 
 Liptobiolith, 281 
 
 Lisbon, tidal wave of, 889, 890 
 Lithification, 748, 750 
 Lithodomus, 1016 
 Lithogenesis, 16, 1147 
 Lithographic beds, fish from, 951 
 Lithology, 20 
 Lithophysae, 277 
 Lithoseisma, 88 1 
 Lithosphere, i 
 Lithothamnion, 394, 406, 415, 470, 471, 474, 
 
 476, 649, 936 
 Little Ararat, fulgurites of, 72 
 
 Prairie, earthquake lake near, 888 
 
 Rocky Mountains, igneous intrusion 
 
 in, 308 
 
 Soda Lake, analysis of, 361 
 Littoral belt, 100 
 
 belts, explosive eruptions on, 863 
 
 district, 646, 647, 983, 987, 988 
 
 districts, estuarine facies of, 987 
 
 zone, 646, 647 
 
 Littorina, on mangrove trees, Brazil, 986 
 
 Livingston, David, cited; 32 
 
 Livonia, 378 
 
 salt shaft, 376 
 
 Lizard, greenstone of the, 316 
 
 Lizards, Fimer's observations on, 963 
 
 Llanos, 68 
 
 Lobes, defined, 966 
 
 Lob (Lake) Nor, waste-filled basin of, 588 
 
 Loch Fyne, concretions in, 679 
 Loch Lomond, 1063 
 Lockport, New York, 420 
 , ballstone reefs of, 44"6 
 
 dolomite, 261 
 
 series, enterolithic structure in, 758 
 
 Locobios, 922 
 
 Locofauna, 922, 1043 
 Locoflora, 922 
 Loczy, L. de, cited, 92 
 Loess, 565 
 
 coloring agent of, 622 
 
 concretions in, 701 
 
 Mississippi Valley, origin of, 566 
 
 Prairie, origin of, 566 
 
 vertical tubes in, 566 
 
 Loesskindel, 568 
 
 Loessmannchen, 568, 578, 719, 764 
 Loesspiippchen 568, 701, 718, 764 
 Lofoten Islands, whirlpools of, 230 
 Logan, Sir W., cited, 782, 783, 827 
 Loire, the, 251 
 
 Lomas, J., cited, 569, 579 
 
 Long Island, apron plains of, 598 
 
 coast marshes of, 493 
 
 destruction of coast of, 649 
 
 dunes on, 557, 559 
 
 old marshes of, 491 
 
 wave work on, 223 
 
 Sound, 229 
 
 , drowned, 833 
 
 Reef, 406 
 
 Longwood shales, 377, 636 
 
 Loo Choo group, fringing reefs of, 390 
 Looking Glass Rock, 57 
 
 Loomis, F. B., cited, 568, 580, 980, 1067, 
 1070 
 
 , quoted, 1045 
 
 Lop, Great Salt Plain of, 358 
 Lossie River, 252, 256 
 Loueche, spring at, 175 
 
 Lough Neagh, 173 
 Louisiana, de 
 
 , eformed salt domes of, 758 
 Louisville, fossil reefs of, 420 
 
 limestone, 418 
 
 Loup River, 259 
 
 Loven, S., cited, 990, 1062 
 
 , quoted, 987 
 
 Low Archipelago, 388, 389, 390, 399, 456 
 
 Lowville limestone, origin of, 488 
 
 Lucknow, depth of alluvial deposits at, 582 
 
 Ludlow, bone bed, 1034 
 
 Luksch, J., cited, 189 
 
 Lull, R. S., cited, 980, 1090, 1095, 1149 
 
 Lumfjord, the, 224 
 
 Lutaceous texture, 285 
 
 Lu-Tschu Islands, 108 
 
 Lutytes defined, 285 
 
 Luzon, dredgings off coast of, 519 
 
 Lycia, jet of, 483 
 
 Lycopods, 940 
 
 Lydekker, R., cited, 1055, 1062, 1070 
 
 Lyell, Sir C., cited, 3, 23, 343, 381, 475. 
 
 521, 611, 615, 824, 857, 1099, iioo. 
 
 1108, 1119 
 
 , quoted, 1074 
 
 Lykens, Lower, Naiadites and "Spirorbis" 
 
 in, 742 
 Lyme Regis, black shale of, 483 
 
 M 
 
 Maare, 122, 860 
 Macclesfield bank, 391 
 Mackenzie delta, 607, 608 
 , driftwood in, 614 
 
INDEX 
 
 1171 
 
 Mackie, W., cited, 252, 253, 254, 255, 256, 
 267, 293, 294, 299, 716, 722 
 
 .quoted, 254, 255, 256 
 
 Mackinac, breccias of, 547, 548 
 
 Maclear, Captain, cited, 399, 400 
 
 Macrophytes, 983 
 
 Madagascar, 195, 386, 390, 413 
 
 Madeira, 235 
 
 Madras, fish falls at, 56 
 
 Maelstrom, 230 
 
 Magdeburg-Halberstadt region, 371 
 
 Magnesian limestone of England, 571 
 
 , dwarf fauna of, 1069 
 
 Magnet Cove, composition of spring near, 
 1 68 
 
 Magnetite, oxidation of, 35 
 
 Magnolias, in brown-coal, 513 
 
 Mahoning sandstone, continuity of, 1131 
 
 Maine coast, sea urchins on, 103;:, 1033 
 
 Makaroff, cited, 240 
 
 Makatea Island, diagenism in reefs of, 761 
 
 Malaspina Glacier, 324 
 
 Malaysian Islands, volcanic belt in, 877 
 
 Maldive Islands, 186, 388, 389, 390, 399 
 
 , gradual submergence of, 895 
 
 Mallet, P., cited, 909 
 
 Malm, 459 
 
 Malta, 153, 240, 454 
 
 Mammoth Cave, organisms in, 1028 
 
 Mangrove, 494 
 
 , floating islands of, 235 
 
 , partial marine habitat of, 985 
 
 Creek, Anthozoa in, 1013 
 
 Manitou, 310 
 
 , pre-Cambric, peneplain of, 848 
 Manitoulin Islands, 836 
 Manlius, Stromatopora reefs of, 445 
 
 limestone, 423, 456 
 
 Mannheim, 245 
 Manouai, 402 
 Manson, M., cited, 95 
 Maranhao, 416 
 Marcellus muds, 407, 424 
 
 shale, origin of, 479, 484 
 
 Marcou, J., cited, 78 
 Marian depression, 2, 897 
 
 Islands, diatomes near, 460 
 
 , (Ladrone), 2 
 
 trench, 105 
 
 Mariana Islands, 386 
 
 Marin county, 315 
 
 Marine elastics, negative characters of, 642 
 
 littoral district, depth of, 983 
 
 , life of, 984 
 
 ; , origin of, 983 
 
 Marlekor, 719 
 
 Marquesas, 406, 441 
 
 Marquette, basal sandstone at, 726 
 
 , buried peat at, 516 
 
 , Lake Superior sandstone of, 310 
 
 district, metamorphism in, 772 
 
 Marr, J. E., cited, 432, 433, 464, 1070 
 
 , quoted, 432, 699 
 
 Marsh, O. C., cited, 709, 789, 827 
 
 Marshall group, 388, 389, 399 
 
 Martha's Vineyard, apron plains of, 598 
 
 , deformation of Tertiary beds of, 
 
 785 
 
 Martin, L., cited, 909 
 
 Martinique, Island of, erosion on, 875, 876 
 Martonne, E. de, cited, 52, 96 
 Marzelle, cited, 149 
 Masmarhu, 399, 400, 401 
 Massachusetts, 392 
 
 , peat deposits of coast of, 514 
 
 , sea-breeze of, 44 
 
 Mastodon, 956 
 
 Mather, W. W., cited, 1123 
 
 Matilda atoll, 399 
 
 Matthew, G. F., cited, 92, 1086 
 
 , W. D., cited, 568, 580 
 
 Matto Grosso, ants' nests in, 692 
 Mauch Chunk, 635, 636 
 
 shales, carnotite in, 365 
 
 Mauna Loa, 314 
 
 , elevation of rim of, 869 
 
 Mauritius, 386, 390, 399, 402 
 
 Maurua, 402 
 
 Maury, M. F., cited, 96 
 
 , quoted, 44 
 
 Mauth-Eichdorf, 246 
 
 Mazon Creek, concretions of, 764 
 
 McClure, W., cited, 1122 
 
 McConnell, R. G., cited, 92, 580 
 
 McGee, W. J., cited, 245, 267, 580, 652, 
 
 687, 909, 1119 
 Mead, C. W., cited, 1095 
 
 , quoted, 1076, 1077 
 
 Mean sphere level, 6, 7 
 
 Mecklenburgian period, 506 
 
 Medina sandstone, beach cusps in, 707 
 
 beach features of, 652 
 
 eolian cross-bedding in, 704, 706 
 fucoid in, 937 
 rill marks in, 709 
 wave marks in, 708 
 Mediterraneans, 8, 99, 107, 108, 109, 115, 
 
 219, 240, 344, 355 
 
 , provincial fauna of, 984 
 
 , temperatures of, 189 
 
 Mediterranean Sea, evaporation from, 27 
 
 , height of waves of, 210 
 
 , salinity of, 152 
 
 , submarine volcanic eruptions of, 
 
 864 
 Medlicott, H. B., and Blanford, W. T., 
 
 cited, 639 
 
 , quoted, 592 
 Medve Lake, 122 
 Meek, F. B., cited, 917 
 Meigen, W., cited, 39, 96 
 Melville Sound, in 
 Menilite shales, 485 
 Mentawie Islands, 456 
 Merced River, alluvial fan of, 584 
 Mer-de-Glace, glacial sand of the, 532 
 Meriden, earthquake fissures at, 885 
 Merionthshire, 315 
 Merjelen See, 125 
 Meroplankton, defined, 993 
 Merostomata, 948, 950 
 Merriam, J. C., cited, 1071 
 Merrill, G. P., cited, 38, 96, 286, 287, 299, 
 
 344, 38i 
 
 , quoted, 344, 345 
 
 Merseburg, 1029 
 
 Mesa, 839 
 
 Mesabi Range, greenalite in, 671 
 
 Mesotraphent, 498 
 
 Messina, earthquake at, 888 
 
 , Straits of, 230 
 
 Metamorphism, 746 
 
 , contactic, 748 
 
 , dynamic, 748 
 
 , regional, 749 
 
 , static, 748 
 
 Metatype, 919 
 
 Meunier, S., cited, 56, 96 
 
 Meuse delta, 607 
 
 River, 224 
 
 , capture of, 134, 136 
 Mexican lagoons, oolites of, 336 
 
 Sea, temperature of, 190 
 
 Mexico, 341 
 
 , cinder cones of, 863 
 
 , onyx marble of, 344 
 
1172 
 
 INDEX 
 
 Mfumbiro Mountains, 124, 125 
 
 , volcanic origin of, 866 
 
 Michael Sars, the, 205 
 
 Michalski, cited, 443, 464 
 
 Michigan, Devonic clay boulders of, 711 
 
 , reefs in Southern Peninsula of, 427 
 , salt deposits of, 376 
 
 City, dune sands from, 553 
 
 Microphytes, 983 
 Microspherulites, 277 
 Mid-Atlantic rise, 105 
 
 Milan, weather at, 48 
 Miliola, in Severn muds, 664 
 Miliolitic formation, 574 
 Mill, H. R., cited, 7, 23 
 Miller, S. A., cited, 957 
 
 , W. J., cited, 569, 580, 621, 639, 783, 
 
 827 
 
 Millstone grit, composition of, 596 
 Milne, J., cited, 899, 909 
 Milne-Edwards and Haime, cited, 1013 
 Milwaukee, 419 
 Mindanao, 519 
 
 Minnesota, glauconite of, 671, 672 
 Mississippi delta, 608, 611 
 
 fine muds of, 850 
 
 mud lumps of, 615 
 
 passes of, 610 
 
 thickness of, 609 
 embayment, 984 
 River, 248 
 
 back swamp of, 497, 589 
 
 load of, 247 
 
 mud at mouth of, 655 
 
 reversal of current of, 889 
 
 tree trunks carried by, 1051 
 
 velocity of, 245 
 
 system, discharge of sediment of, 247 
 , hydrographic basin of, 247 
 
 Valley, black shale in, 732 
 
 Mississippi black shale, Ordovicic fossils 
 
 in, 685 
 Missouri, caverns of, 345 
 
 , overlap of marine strata in, 732 
 
 River, Great Falls of, 137 
 Mittagong, chalybeate waters of, 168 
 Mjodoboren hills, 443 
 Mjosen, Biri limestone of, 784 
 Moas, 1038 
 
 , petrified eggs of, 1088 
 
 Moencopie beds, 84 
 
 , alternation of colors in, 623 
 
 Mohave Desert, 70, 364 
 
 , dunes of, 562 
 
 Mohn, PL, cited, 96 
 
 , quoted, 51 
 
 Mojsisovics, E. von, cited, 435, 464, 474, 
 
 521 
 
 Mollasse, 591 
 , subaqueous gliding of the, 658 
 
 torrential deposits, 630 
 
 Mollusca, importance of shells of, 911 
 Molucca Straits, 237 
 
 Mombas, 404 
 
 Monadnock, 847, 848, 849 
 
 Mona passage, 108 
 
 Monchsberg, Nagelfluh of the, 602 
 
 Monhegan, Island of, 848 
 
 Mono Lake, salinity of, 155 , 
 
 , soda deposits of, 361 
 
 Valley, extinct lake of, 340 
 
 Monongahela River, gravel terraces of, 136 
 Monroe limestone, 261, 422 
 
 , endolithic brecciation in, 537 
 
 , oolites of, 472 
 
 Mons, greensands near, 673 
 
 Monsoons, 45, 75 
 
 Mont Blanc, fulgurites of, 72 
 
 Mont Dore Province, breached lava cones 
 
 of, 871 
 
 Mont Genevre, 315 
 Mont Pelee, dust from, 60 
 , eruption of, 86 1 
 
 - , spine of, 870 
 
 Montana, Belt terrane of, 334, 417 
 Monte Nuovo, cinder cone of, 863 
 Monte Somma, 871, 875 
 Monte Viso, fulgurites of, 72 
 Montessus de Ballore, F. de, cited, 909 
 Montgomery county, O., peat bed in, 515 
 Monticules, formation of, 871 
 Montreux-Veytaux, subaquatic glidings of, 
 
 659 
 
 Montrose county, Col., carnotite of, 365 
 Monument Creek beds, cementation of, 754 
 
 , dune origin of, 570 
 
 , joints in, 792 
 
 Park, 53 
 
 , erosion features of, 857 
 
 Moor, Captain, 227 
 
 Moore, J. E. S., cited, 119, 125, 144, 761, 
 774, 879, 1064, 1071 
 
 Moraines, lateral, 265 
 
 , medial, 265 
 
 Moray, rivers of Eastern, 252 
 
 , sands on eastern shores of, 226 
 
 , Firth, 256, 650 
 
 , temperatures of, 191 
 
 Morgan, T. H., cited, 980 
 , W. C, and Tallmon, M. C., cited, 
 1088, 1096 
 , quoted, 1089 
 
 Morlot, cited, uoo 
 
 Moros Valley, salt dome in, 758 
 
 Morphological equivalents, 976, 1135 
 
 Morrisville, 377 
 
 Morse, E. S., cited, 1042, 1071 
 
 Morse Creek limestone, 684 
 
 Morvern, Cenomanien greensands of, 850 
 
 Moscow shale, variation in thickness of, 
 683 
 
 Moselle River, 134 
 , meanders of, 137 
 
 Mosely, H. N., cited, 1009, 1071 
 
 Mosken, 230 
 
 Mosquito bank, 335 
 
 Mottez, Admiral, cited, 215 
 
 Mt. Adams, 32 
 
 Mt. Everest, 5 
 
 Mt. Hillers, 308 
 
 Mt. Holmes, 308 
 
 Mt. Mar^ellina, 308 
 
 Mt. Mica, composition of spring near, 168 
 
 Mt. Monadnock, 32 
 
 Mt. Shasta, fulgurites of, 72 
 
 Mt. Sinai, 33 
 
 Mt. Starr-King, 32 
 
 Mt. Taylor region, volcanic necks of, 874 
 
 Mt. Thielson, fulgurites of, 72 
 
 Mt. Washington, Arctic plants and butter- 
 flies on, 1066 
 
 Mountain Home, hot springs of, 201 
 , limestone reefs in, 432 
 
 Mozambique, 386 
 
 channel, 388 
 
 Mud cracks, 530 
 
 lumps, 611, 615 
 
 Muir glacier, 263 
 Mulder, cited, 173 
 
 Mull, Cenomanien greensands of, 850 
 
 and Morvern, transgressing Cretacic 
 
 of, 730 
 
 Mullion Island, greenstone of, 316 
 Mummies, Chile, 1076, 1077 
 Munthe, H., cited, 420, 464 
 Mur River, 252 
 
INDEX 
 
 Murchison, Sir R., cited, 222, 1108 
 
 Muree glacial formation, 53$ 
 
 Murgoci, G., cited, 92 
 
 Murray, Sir J., cited, 7, 23, 63, 65, 96, 165, 
 194, 207, 387, 391, 408, 410, 451, 452, 
 466, 678, 679, 687, 688, 1071 
 
 , quoted, 6, 66, 164 
 
 and Hjort, J., cited, 205, 207 
 
 and Lee, G. V., cited, 688 
 
 and Philippi, E., cited, 688 
 
 and Renard, A. F., cited, 451, 453, 
 
 455, 643, 644, 668, 670, 688 
 
 and Renard, M. A., cited, 56, 96 
 
 Muschelkalk, 225, 436 
 
 , cementation of, 335 
 
 , origin of oolites of, 455 
 
 , subaquatic gliding in, 782 
 
 Sea, 376 
 
 Muskegon, dune near, 559 
 Mutation of De Vries, 963 
 
 , of Waagen, 912, 960 
 
 Mycelium, 937 
 Myxinoids, 951 
 
 N 
 
 Nagasaki, 59 
 Nagelfluh, 601, 602, 750 
 , cementation of, 753 
 
 delta, 616 
 
 Naiadites, in Lower Lykens, 742 
 
 Nairn River, 252 
 
 Nakkehrod, 719 
 
 Namak, 358 . 
 
 Nansen, F., cited, no, 267 
 
 Nantasket, Carbonic lavas of, 315 
 
 , drumlins of, 532 
 
 Nantucket Island, apron plains on, 598 
 
 , old marshes on, 491 
 
 Naples, Bay of, bradyseisms in, 887 
 
 , Gulf of, 3 
 
 Napoleonite, 275 
 
 Narni, travertine deposits of, 343 
 Natissa River, salt water in, 153 
 Natron, 362 
 
 Lake, salinity of, 155 
 
 Natterer, cited, 332 
 Nattheim, reefs near, 439 
 Natuna Islands, 242 
 
 Naumann, C. F., cited, 269, 270, 299, 537 
 Nautiloidea, 945, 946 
 Nautilus, 945, 946, 1022 
 Nauset Lights, 223 
 
 ; peat under sand dunes at, 564 
 
 Navahoe Lake, 125 
 Navigator Islands, 386 
 Neanastic stage, 973 
 Neanic stage, 972 
 Nebraska, 259 
 
 , lakes in sandhill region of, 562, 564 
 Nebraska dunes, 122, 572 
 
 , lignite in, 565 
 
 , origin of sands of, 
 
 Nebular hypothesis, 92 
 Neckar, velocity of, 245 
 
 Valley, enterolithic structure in, 758, 
 
 759, 785 
 
 Nefud desert, 37 
 
 , red sands of, 562 
 
 Nekton, 991, 996 
 
 Neocomien, greensand lenses in, 673 
 
 Neon, 25 
 
 Neotype, 919 
 
 Nepiastic, 973 
 
 Nepionic stage, 972 
 
 Neritic zone, 643, 987 
 
 Nero deep, 2, 105, 897 
 
 551 
 
 Netherlands, dunes of, 557 
 Neumayr, M., cited, 78, 80, 133, 144, 682, 
 1057, 1149 
 
 , quoted, 79 
 
 , and Paul, C. M., cited, 958, 959, 9o 
 
 Neutral level, u 
 
 Nevada, borax lakes of, 363 
 
 ; , playa lakes in, 603 
 
 Neve, 279 
 
 Newark sandstone, arkose character of, 84 
 
 , footprints in, 1090 
 
 , fucoid in, 937 
 
 , non-marine, noi 
 
 , origin of, 633 
 
 , overlap relations in, 740 
 
 , red color of, 625 
 
 Newark trap sheets, 312 
 Newberry, J. S., cited, 708 
 New Caledonia, 388 
 New England, color of till of, 532 
 
 , destruction of coast of, 649 
 
 , eskers in, 599 
 
 Newfoundland, 215, 234 
 
 , Archaeocyathidae of, 417 
 
 , frost work in, 34 
 
 , peat beds of, 508 
 
 banks, 104, 218, 234, 262 
 
 shelf, 103 
 
 New Guinea, 334 
 New Haven, 1042 
 
 New Hebrides Islands, 386 
 
 New Jersey coast, dunes on, 557, 559 
 
 , marshes of, 493 
 
 New Mexico, Cretacic dwarf fauna of, 1069 
 
 , dune of gypsum in, 578 
 
 New Red sandstone, origin of, 569 
 
 New Scotland beds, overthrust of, 817 
 
 Newson, J. F., cited, 885, 909 
 
 New South Wales, medusae of, 1009, 1010 
 
 New World block, 9 
 
 New York, beveling of Palaeozoic strata in 
 
 835 
 , Lower Cambric limestones of, 335 
 
 , thickness of salt beds of Central, 378 
 
 , type section for the Palaeozoic, 1127 
 
 , Western, disconformity in Siluric of. 
 
 826 
 
 City, age of schists and marbles of, 
 
 1140 
 
 , Aqueduct Commission of, 286 
 
 New Zealand, 239 
 
 , sinter deposits of, 475 
 
 Niagara Falls, amount of water per min- 
 ute, 246 
 , height of, 246 
 
 escarpment, 261 
 
 gorge, 261 
 
 River, 133 
 
 , changes in bed of, 245, 246 
 
 , consolidated plains along, 601 
 
 , old shore lines of, 654 
 
 Niagaran, former extent of the, 379 
 , reefs of the, 431 
 
 Sea, evaporation of, 377 
 
 Nicaragua, 335 
 
 , colors of soil of, 36, 620 
 
 Nicholson, H. A., cited, 455 
 
 and Etheridge, R., cited, 472 
 
 , and Lydekker, R., cited, 956, 1096 
 
 , quoted, 1073 
 
 Nicobar Islands, 109, 386, 390, 456 
 Niger delta, 608 
 Nikitinsky, quoted, 357 
 Nile delta, 252, 607, 608 
 
 , deposits of lime in, 616 
 
 , iron content of, 622 
 
 , nature of deposits of, 614 
 
 , rate of growth of, 609 
 
1 174 
 
 INDEX 
 
 Nile delta, salines of, 355 
 
 , saline deposits on, 617 
 
 , thickness of, 609 
 
 River, 248 
 
 , flood plain of, 589 
 
 , overflow of, 68 
 
 Nile Valley, angular sands along, 553 
 
 , caverns in Eocenic limestones 
 
 of, 346 
 
 Niles, W. H., cited, 753, 774 
 Nitrogen, 24, 25 
 Nittany Valley, 175 
 Nodes, 945 
 
 Noel black shale, 732 
 Nontronite, 39 
 Nordmann, V., cited, 92 
 Normandy, dunes of, 557 
 North Cape, 236 
 
 Germany, Permic climate of, 375 
 
 Pole, ascertained migration of, 899 
 
 , hypothetical migration of, 898 
 
 Sea, 112, 218, 234, 236, 239 
 
 , height of waves of, 210 
 
 , submarine forests of, 224 
 
 , subsidence of coast of, 223 
 
 , temperatures in, 191 
 
 Siberian shelf, 103 
 
 Northwest Australian shelf, 103 
 
 Norway, Cambric glacial deposits from, 534 
 
 , concretions m clays of, 763 
 
 , dolomites of, 334 
 
 , recent corals of, 392 
 
 Norwegian shelf, 103 
 
 Novaculite, 755 
 
 Nova Scotia, erosion stacks of, 225 
 
 , peat bog of, 515 
 
 , red Mississippic beds of, 622 
 
 Nova Zembla, 236 
 
 , red algae at, 470 
 
 Novorssiisk, winds from, 49 
 Nubian sandstone, 61, 565 
 
 , dune origin of, 570 
 
 , Libyan sands derived from, 553 
 
 Nullipore, 385, 470 
 
 Nummulite limestone, 453 
 
 Nummulites, 942 
 
 Nunatack, 326 
 
 Nunda sandstone, see Portage 
 
 Nyssetum, 487, 500 
 
 O 
 
 Oatka, 377 
 
 Oaxaca, volcanic ash deposit of, 60 
 
 Obrutschew, cited, 604 
 
 Ocean, composition of, 158, 159 
 
 , mean depth of, 6 
 
 Oceanography, 20, 21 
 
 Oceanology, 20 
 
 Oceans, areas of, 100 
 
 Ochsenius, C., cited, 267, 350, 353, 359, 
 
 366, 369, 370, 381, 382 
 
 O'Connell, M., cited, 989, 990, 1029, 1039 
 Octapoda, 1021 
 Octoseptata, 943 
 
 Odessa, subaquatic glidings at, 659 
 Oeningen, deformations at, 784 
 
 , folding in Miocenic marl of, 780, 781 
 
 , Miocenic shell deposits of, 631 
 
 Oesel, Island of, cuesta of, 838 
 
 , Synxiphosurans from, 1029 
 
 Ogden quartzite, 817 
 
 River, calcium carbonate in, 468 
 
 Ogilvie, I. H., cited, 856, 858 
 Ogilvie-Gorden, M., cited, 435, 464 
 Ohio, Devonic limestones of, 471 
 , origin of black shale of, 484 
 
 River, 245 
 
 Oisan Mountains, 127 
 Ojen, P. A., cited, 92 
 Okefenoke Swamp, 500 
 Oken, L V cited, 917 
 Okhotsk-Sachalin shelf, 104 
 
 Sea, 1 08 
 
 Oklahoma, 262 
 
 n , basal Cambric sandstones in, 729 
 
 Oland, Island of, cuesta, 838 
 
 Old Faithful Geyser, siliceous waters of, 
 
 168 
 Oldham, R. D., cited, 585, 639 
 
 , quoted, 586 
 
 Old Red sandstone, analyses of sand grains 
 of, 716 
 
 , cliffs of, 225 
 
 , deltaic origin of, 636 
 
 , dune origin of parts of, 571 
 
 , fishes in, 951 
 
 , Myriopoda in, 947 
 
 , non-marine, 1101 
 
 , unconformity below, 824 
 
 Old World Block, 9 
 Olean conglomerate, 252 
 Olenellus fauna, 1052 
 Olenidae, as index fossils. 1134 
 Olenoides fauna, 1052 
 Olenus limestones, 53 
 Oligocenic, pyroclastics of, 526 
 Oligochaete, 1024 
 Oligotraphent, 498 
 Olkusz, fulgurites in, 73 
 Omori, F., cited, 879 
 Onchidium, 986 
 Oneonta, see Portage 
 
 sandstone, 636 
 
 Onondaga limestone, 261, 407, 423, 424, 
 
 425, 426 
 Onto-stages, 971 
 Onto sub-stages, 971 
 Oolite, Great, 472 
 
 -, Inferior, 472 
 
 , Superior, 472 
 Oolites, size of phytogenic, 468 
 Oolitic sands, 422 
 Oozes, formation of, 996 
 Opercula, 945 
 Operculina limestone, 52 
 Oran, province of, 345 
 Orange Spring, composition of, 168 
 Orbitoidal limestone, 453 
 Ordovicic, black shale resting on, 732 
 
 , insects from graptolite shales of, 949 
 
 -, origin of black shales of, 674 
 
 , Upper, replacing overlap of, 744 
 
 sandstone, marine progressive overlap 
 
 of, 728 
 
 Oregon, basaltic plateau of, 867 
 Ore Sound, 241 
 Organ Pipe Reef, 404 
 Orinoco delta, 608 
 
 River, tree trunks carried by, 1051 
 
 Oriskany-Esopus, contact in Heldeijaergs, 
 
 823 
 Orkney Islands, 112, 218, 230, 234 
 
 , Tertiary dikes in, 867 
 
 Orogenesis, 16, 776, 1147 
 
 Orogenic movements, 12 
 
 Orpiksuit fjord, 87 
 
 Orth, cited, 287, 299 
 
 Orthoboric acid, 364 
 
 Orthogenesis, 963 
 
 Ortiz Mountains, conoplains of, 856 
 
 Ortmann, A. E., cited, 80, 96, 647, 688, 
 
 995 999. 1022, 1027, 1039, 1059, 1061, 
 
 1062, 1071, 1134, "49 
 
 , quoted, 1042, 1055, 1061, 1065 
 
 Orton, 252 
 
INDEX 
 
 H75 
 
 Osage River, boulders in loess on, 567 
 Osborn, H. F., cited, 920, 956, 957, 961, 
 970, 980, 981, 1149 
 
 and Grabau, A. W., cited, 958 
 
 Oscillation, circle, 894 
 
 ripples, 712, 713 
 
 Ostrea, in Arabian eolian limestone, 575 
 Ostwald, quoted, 747 
 Oswing, Neocomien of, 673 
 Ottawa River, 334 
 
 , drainage of, 166 
 
 Otyipatura River, 692 
 Owen, D. D., cited, 915, 1108 
 Owens, J. S., cited, 688 
 Owens Lake, 362, 369 
 
 , change in salinity of, 155 
 
 , composition of, 157, 158 
 
 , salinity of, 154, 155 
 
 , soda deposits of, 361 
 
 Valley, earthquake fissures in, 883 
 
 , earthquake of, 887 
 
 Oxford lowland, 839 
 
 Oxidation, 17, 25, 35 
 
 , of organic compounds, 37 
 
 Oxus River, 23 
 
 , delta of, 608 
 
 , dunes along, 561 
 
 Oxygen, 24 
 
 sources of, 25 
 
 Oysters, attached to roots of mangroves, 
 
 986 
 Ozark region, basal Cambric sandstones in, 
 
 729 
 Ozone, 72 
 
 Pacific Ocean, manganese concretions of, 
 330, 718 
 
 , mean temperature of, 193 
 
 , surface temperature of, 182, 183 
 
 , temperatures of, 185, 187 
 
 Paenaccordanz, 821, 822 
 Pahoehoe, Hawaiian Islands, 868 
 Palseechinoidea, 950 
 Palaeobotany, 20, gio 
 Palseo-Cordillerans, 70 
 Palaeohypsometric, 444 
 Palaeozoic, diversity of fauna of, 984 
 
 rocks, desert varnish of, 57 
 
 Palaeozoology, 20, 910 
 
 Palawan Island, 242 
 
 Palgrave, W. G., cited, 562, 580 
 
 Palic Lake, C9mposition of, 157, 158 
 
 , salinity of, 155 
 
 Palisades trap, 320 
 
 Pallas, cited, 443 
 
 Pallas and Humboldt, V., cited, 1063 
 
 Paludina, 631 
 
 , in loess, 568 
 
 series, 960 
 
 Paluxy sandstone, 729 
 Pantelleria, 153 
 
 Paradoxides, index fossil of Middle Cam- 
 bric, 912 
 
 , fauna, 1052 
 
 Parallelism, 979 
 
 , illustration of, 976, 977 
 
 Parallelkanter, 54 
 
 Parana, carcasses of animals in, 593 
 
 , tributary of La Plata, 66 1 
 
 Paratype, 919 
 
 Para-unconformity, 821 
 
 Paris, Lieutenant, cited, 214 
 
 Paris Basin, Eocenic locofauna of, 1043 
 
 , Eocenic shales of, 485 
 
 i 1 prismatic structure in gypsum 
 
 beds of, 779. 820 
 
 Parks, W. A., cited, 731, 744 
 
 Parmas, 808 
 
 Parrot fish, destruction of corals by, 415 
 
 . River, 663 
 
 Parry Archipelago, 237 
 Parsons, A. L., cited, 485, 521 
 
 , quoted, 486 
 
 Partiot, cited, 231, 267 
 Parunconformity, 821, 822 
 Paruschowitz well, 14 
 Pas-de-Calais, dune areas of, 557 
 
 , peat of, 514 
 
 Pass a 1'Outre, form of, 610 
 
 , rate of growth of, 609 
 
 Passarge, S., cited, 58, 196, 359, 382, 580, 
 
 692, 695, 854, 855, 858 
 Patagonia, 239 
 
 coast of, 235 
 
 salinas of, 360 
 
 salitrales, 329, 360 
 
 shelf, 103 
 
 Tertiary volcanic dust deposits of, 
 
 572 
 
 Patapsco formation, 632 
 
 Paterson, trap of, 312 
 
 Patten, W., cited, 950, 957 
 
 Patuxent formation, 632 
 
 Paumota Archipelago, see Low, 456 
 
 Peach, B. N., and Home, J., cited, 315, 
 
 321, 867, 879 
 
 Peat bog, succession of strata in, 499, 506 
 Pebbles, facetted, 54 
 Pechuel-Loesche, E., cited, 32, 695 
 
 , quoted, 691 
 
 Pedro bank, 108 
 
 Pei-ho, 248 
 
 Pelagic district, 101, 983, 988 
 
 organisms, quantity of, 451 
 
 Pelew Islands, 388 
 
 Pelytes, 285 
 
 Penck, A., cited, 2, 3, 5, 6, 7, 8, 9, 23, 100, 
 125, 144, 165, 248, 250, 251, 257, 267, 
 541, 580, 595, 602, 639, 858, 1063 
 
 , quoted, 162, 163, 213, 246, 248, 584 
 
 and Bruckner, E., cited, 328, 639 
 
 and Supan, A., cited, 23 
 
 Pendleside limestone, 432 
 Peneplain, defined, 847 
 
 , transgression over, 731 
 
 Penhallow, D. P., cited, 981 
 
 Pennines, peat of, 504 
 
 Penrose, R. A. F., Jr., cited, 370, 382 
 
 Pensauken gravels, fulgurite in, 73 
 
 Pentland fjord, 230 
 
 Permic, position of North Pole in, 897 
 
 Permille, defined, 147 
 
 Perry, N. W., cited, 701, 709, 712, 722 
 
 Persia, onyx deposits of, 345 
 
 Persian Gulf, in, 242, 390 
 
 , temperature of, 193, 373 
 
 Peru, natural mummies from, 1076, 1077 
 Peschel, O., cited, 1063, 1071 
 Pestalozzi, cited, 251, 267 
 Peterhead, force of waves at, 221 
 Petermann, A., cited, 584, 639 
 Petersen, C. G. J., 92 
 Petit Codiac River, tidal bore of, 227 
 Petoskey, reefs of, 429 
 Petrascheck, cited, 682, 688 
 Petro-Alexandrovsk, rainfall at, 65 
 Petten, height of dunes near, 558 
 Pettersson, S. O., cited, 193, 207 
 Pfaff, F. W., cited, 96, 175, 759, 774 
 Phacoliths, 307 
 Phanerogams, 941 
 
 , acquired marine habitat of, 985 
 
 Philippi, E., cited, 82, 92, 96, 332, 334, 335, 
 382, 635, 639, 644, 675, 681, 688 
 
1176 
 
 INDEX 
 
 Philippine Islands, 204, 237, 242 
 
 , diatoms near, 460 
 
 Philippine Sea, 195 
 
 Phillips, J., cited, 224, 267, 1099 
 
 , J. A., cited, 37, 96, 294, 299, 639 
 
 Phillipsite, 330 
 
 Phoca, in fresh water, 1063 
 
 Photic region, 982 
 
 Phragmitetum, 486, 487, 500 
 
 Phyllocarida, 377, 948 
 
 Phylogerontic stages, 973 
 
 Phylum, 912 
 
 Physa, in Florissant Lake Basin, 525 
 
 Phytogenic deposits, 384 
 
 Phytolitharia, marine, in Mississippi mud, 
 
 615 
 
 Phytoliths, 280 
 Phytology, 20 
 Phytosphere, 16, 910 
 Piedmont region, 226 
 Pierre shales, 447 
 Pike's Peak, 32, 33, 310 
 Pilgrim, G. E., cited, 92 
 Pilot, fish, 996 
 Pine Creek Valley spring, composition of, 
 
 168 
 
 Pittsford shales, 376, 377, 1029 
 Planetesimal hypothesis, 92, 297 
 Planetesimals, 907 
 Plankton, denned, 991, 992 
 Planoconformity, 826 
 Planorbis, 1064 
 
 in Florissant Lake basin, 525 
 
 in loess, 568 
 
 in Severn deposits, 665 
 
 mutations of, 1043 
 
 shell replaced by sulphur, 1086 
 
 Plants, chlorophyll-forming, 25 
 Plasmodium, 933 
 
 Plasticity, zone of, 819 
 Plastotype, 919 
 Plattenkalke, 438 
 Playa lake, 77, 123, 602 
 Playa surface, 709 
 Pleistocenic, beaches of, 654 
 
 , location of pole in, 895, 896 
 
 Pleistocenic ice sheet, 344 
 
 Plesiotype, 919 
 
 Plitvicer seas, 125 
 
 Plucking, 1 8 
 
 Plum Island, map of, 491 
 
 Plymouth, force of waves at, 221 
 
 Po, 248 
 
 delta, 607, 642 
 
 , lignitized wood in, 614 
 
 , thickness of, 609 
 
 River, alluvial plain built by, 584 
 
 , flood plain of, 589 
 
 , natural levees of, 617 
 
 Pocahontas, Pottsville conglomerate at, 742 
 Pochutla, cinder cone of, 863 
 
 Pocono conglomerate, 636 
 
 sandstone, 635 
 
 Podolia, 443 
 
 Point au Sable, 838 
 
 Point Bonita, basic lava of, 315 
 
 Polar Sea, temperatures of, 193 
 
 Pole, migration of, 891, 892 
 
 Pole, shifting of, 536 
 
 Poles, wanderings of, 91, 92 
 
 Polyhalite, 371, 372, 374 
 
 Pomerania, brackish ponds of, 126 
 
 Pompeckj, J. F., cited, 479, 521, 667, 678, 
 
 688 
 Pompeii, human bodies in volcanic mud at, 
 
 525, 1089 
 Pool, R. J., cited, 563, 580 
 
 Porta do Mangue, diagenism of reefs of, 
 
 761 
 
 Portage beds, faunas of, 1053 
 Portage sandstone, 554, 635, 936 
 -- , loess-like origin of, 569 
 
 - shales, origin of, 479 
 -- , Protosalvinia in, 718 
 Portageyille, 127 
 
 Port Elizabeth, sea wave at, 875 
 
 Port Hudson clays, 611 
 
 Port Jefferson, wave cutting at, 223 
 
 Portugal, recent corals of, 392 
 
 Posidonia shale, jet from, 483 
 
 -- , organic remains in, 483, 484 
 
 -- , origin of, 479 
 
 Possneck, 433 
 
 Potamoclastic, 295 
 
 Potamogenic deposits, 329 
 
 Potamology, 20 
 
 Potamoplankton, 998 
 
 Potomac formation, colors of beds of, 624 
 
 -- , delta and flood plain deposits of, 
 
 631 
 
 -- , non-marine, not 
 Potonie, H., cited, 280, 330, 382, 480, 482, 
 
 510, 517, 521, 578 
 Potsdam sandstone, 642, 729, 856 
 -- , trails in, 1091 
 Pottsville conglomerate, 635, 742 
 -- , extent of, 252, 594 
 -- , pebbles from,. 596 
 -- , thickness of, 904 
 
 - series, westward overlap of members 
 of, 741 
 
 Poughkeepsie, 227 
 
 Pouillon-Boblage, cited, 267 
 
 Pourtales, L. F. von, cited, 406, 464, 673, 
 
 688 
 
 Pourtales Plateau, 106, 244, 335, 407, 414 
 Pozzuoli, 3 
 
 - , solfatara at, 168 
 
 Prather, J. K., cited, 671, 672, 688 
 Pre-Cambric ocean, lime of, 331 
 Precipitation, effect of latitude on, 71 
 Presque Isle, Lake Superior sandstone of, 
 
 726 
 Pressure, areas of high and low, 41 
 
 - , belts of, 43 
 
 - , normal atmospheric, 40 
 Prestwich, J., cited, 698 
 Primates, 956 
 
 Prince Edward Island, glacial conglomerate 
 
 of, 82 
 
 Progressive overlap, marine, 740 
 Prothallus, 938 
 Protcecium, 973 
 Protogenous, 269 
 Protograph, 919 
 Protolimulus, 1,029 
 Protolog, 919 
 Protoplastotype, 919 
 Protosalvinia, 718, 1004 
 Prouyot, cited, 188 
 Provincetown, dunes of, 557, 559 
 Provincial faunas, 984 
 Przhevalsky, N. M., cited, 56, 562, 580 
 Psammytes, 285 
 Psephytes, 285 
 Pseudoplankton, 994 
 Psilotales, 940 
 Pteropod ooze, 455, 456 
 -- , analysis of, 677 
 Pteropoda, 946 
 Pueblo, 27 
 
 Pugha. lake plain of, 364 
 Pulverites, consolidation o, 751 
 Pumpelly, R. W., cited, 56, 96, 580, 655, 
 
INDEX 
 
 1177 
 
 Punjab district, 26 
 
 , salt range of, 592 
 
 Punta Robanal, 218 
 Pupa, in delta beds, 613 
 
 , in loess, 568 
 
 Purgatory chasm, graben of, 815 
 
 Put, the, 355 
 
 Pyramid Lake, 160, 340 
 
 , composition of, 157, 158 
 
 , salinity of, 155 
 
 Pyrenees Mountains, fulgurites of, 72 
 Pyroclasts, 285 
 Pyrogeology, 20 
 Pyrometamorphism, 749, 765 
 Pyrosphere, i 
 
 , limits of, 12 
 
 , manifestations of, 13 
 
 juadrumana, 956 
 
 iuahog Bay, 1065 
 
 Juaquaversal dip, 808 
 
 Juartz, secondary enlargement of grains, 
 
 754 
 
 . jartzite, 755 
 
 Juebradas, earthquake, 884 
 Jueensland shelf, 104 
 jueneau, A. L., cited, 319, 321 
 'uenstedt, A., cited, 438, 1085 
 uiriquina Island, earthquake destruction 
 
 of, 888 
 
 Rabaka River, volcanic mud in, 876 
 Radiation, 30, 31 
 Radioactivity, 876 
 Radiolarian ooze, 457 
 
 , analysis of, 677 
 
 Ragaz, 251 
 Ragged Keys, 406 
 Ragged Top Mt., 308 
 Ragtown, 361 
 Raibler beds, 437 
 Rain, 26, 62, 63 
 Rainberg, Nagelfluh of, 602 
 Rainfall, amount of, 63, 64 
 
 , influence of winds on, 66, 67 
 
 , influence of topography on, 66, 67 
 
 , equatorial type of, 68 
 
 , tropical type of, 68 
 
 , periodicity of, 71 
 
 Rain-prints, 712 
 
 Ramann, E., cited, 499, 503, 521, 689 
 
 , quoted, 486 
 
 Ramsay, W., cited, 175, 689 
 Rann, the, Miliolite of, 575 
 Rann of Cutch, in, 348 
 
 , salt deposits in, 617 
 
 , salt pans of, 354, 355 
 
 Ransome, F. L., cited, 315, 321 
 
 Rantum, 223 
 
 Rantum, advance of dunes in, 558 
 
 Rapakiwi, 275 
 
 Raritan Bay, Pleistocenic gravels, 754 
 
 Raritan clays, 632 
 
 Raritan formation, dune origin of, 570 
 
 , lignitic sands of, 365 
 
 Raritan sands, fulgurites in, . 73 
 Rath, G. von, cited, 879 
 Rauchwacke, 434 
 Ravenser, 225 
 Ravenserodd, 225 
 Raymond, P. E., cited, 72 
 
 Reade, T. M., cited, 175, 244, 248, 267, 
 
 6 34 639 
 
 Recklinghausen, coal at, 482 
 Reclus, J. J. E., cited, 127, 144, 175, 879 
 Recrystallization, 748, 755 
 Rectigradations, 961, 970 
 Redbank sands, origin of color of, 671 
 Red beds, 70 
 Red River, lakes along, 127 
 
 , rafts of, 127 
 
 Red Sea, 107, 109, 334, 352, 393 
 
 barrier reefs of, 388 
 
 clay boulders from, 711 
 clay galls from, 711 
 fringing reefs in, 386, 390 
 mean temperature of, 193 
 oolites on shores of, 468 
 osmotic pressure in, 180 
 salinas on borders of, 355 
 salinity of, 154, 190, 1044 
 
 , salt and gypsum on borders of, 348 
 
 -, temperature, of, 189, 190, 373 
 Reed, F. R. C., cited, 1071 
 Reede of Suez, oolites of, 336 
 Reeds, C. A., cited, 684, 689, 1119 
 Reef knolls, 449 
 Reefs, atoll, 386 
 , barrier, 386 
 
 bedded, 417 
 
 epicontinental, 389 
 
 fringing, 386 
 
 inter-fringing of, 422 
 
 neritic, 389 
 
 oceanic, 389 
 
 Reelfoot Lake, origin of, 889 
 Regensburg, Jurassic of, 667 
 Regnard, P., cited, 181, 207 
 Regressions, 3 
 Regressive deposits, 734 
 Regressive movements, 1141 
 Regressive-transgressive series, 736, 737 
 Reibisch, P., cited, 892, 909 
 
 Reid, H. F., cited, 263, 267, 328, 810, 8n 
 
 and others, cited on faults, 827 
 
 Reis, O. M., cited, 782, 827, 1080, 1096 
 Relicts, 1044, 1054 
 
 Renault, cited, 482 
 
 Renevier, cited, 643 
 
 Replacement, metasomatic, 761 
 
 Reptilia, naming of, 913 
 
 Retreatal sandstone, 735, 736 
 
 Reusch, H., cited, 81, 267 
 
 Reuss, foehn of, 47 
 
 Revy, J. J., cited, 661, 689 
 
 Rewa, Anthozoa in harbor of, 1012 
 
 Reyer, cited, 203 
 
 Rhabdoliths, 456, 933 
 
 Rhaetic sandstone, destruction of, 247 
 
 Rhang-el-Melah, 379 
 
 Rhine, foehn of, 47 
 
 , Maare region of, 860 
 
 Rhine delta, 607, 642 
 
 , composition of silt in, 616 
 
 , lime content of, 622 
 
 , thickness of, 609 
 
 Rhine graben, 815 
 
 Rhine River, 137, 248, 250, 251 
 
 , velocity of, 245 
 
 Rhine Valley, loess of, 565 
 
 Rhizocarps, 941 
 
 Rhizopoda, 942 
 
 Rhodes' Marsh, 363 
 
 Rhombenporphyry, 305 
 
 Rhone, foehn of, 47 
 
 Rhone delta, cementation of deposits in, 616 
 
 , inclination of strata in, 610 
 
 , rate of growth of, 609 
 
 , thickness of, 609, 610 
 
INDEX 
 
 Rhymney River, 662 
 
 Richmond, Va., diatoms beneath, 461, 676, 
 
 1002 
 
 Richmond formation, reefs of, 418 
 Richthofen, F. von, cited, 40, 96, 435, 465, 
 
 565, 58o 
 
 Richthofen reef, 434 
 Ridge, Wyville-Thompon, see Wyville-Thom- 
 
 son ridge 
 
 Faroe-Iceland, 106 
 
 Ries, H., cited, 533, 538, 622, 639 
 
 Riga, salinity of Baltic at, 1045 
 
 Rill marks, 708 
 
 Ringer, cited, 194 
 
 Rio de la Plata, corals at mouth of, 1012 
 
 , estuary of, 113 
 
 , temperatures of, 195 
 
 Rio de los Papagayos, 367 
 
 Rio Grande rise, 105 
 
 Rio Janeiro, 1015 
 
 Riparia, dunes at, 561 
 
 Ripple marks, 219, 712 
 
 , greatest depth of formation of, 713 
 
 in Devonic limestone of Michigan, 
 
 429 
 
 Rise, Easter Island, 106 
 
 , Kerguelen, 106 
 
 River Bar, 136 
 
 Findhorn, 252 
 
 Jordan, salinity of, 156 
 
 Mur, 246 
 
 Saale, 252 
 
 Spey, 252, 255 
 Rivers, annual rainfall in, 66 
 
 , solids in, 163, 164 
 
 Riviere Blanche, filling of, 86 1 
 Roba-el-Khali desert, dune area of, 562 
 Robertson, cited, 689 
 Robson, H., cited, 689 
 Roches moutonnees, 264, 265 
 Rochester shales, 261 
 Rock city, joints in, 791 
 Rock fracture, zone of, 142 
 Rockwood clays, 823 
 Rogensteine, 283, 336, 472, 473 
 
 , structure of, 472, 473 
 
 Rogers, A. F., cited, 1082, 1087, 1096 
 
 , A. W., cited. 81, 92, 96, 538 
 
 , A. W., and Schwartz, E. H. L., 
 
 cited, 576, 580 
 
 , H. D., cited, 708 
 
 Rohlfs, cited, 56 
 
 Rolland, quoted, 167 
 
 Romanche deep, 188 
 
 Romieux, A., cited, 7, 23 
 
 Romney shale, 424 
 
 Rondout waterlimes, mud-cracks in, 709 
 
 Roost, the, 230 
 
 Rosalind bank, 108 
 
 Rosenbusch, H., cited, 270, 271, 299, 302, 
 
 771, 775 
 Rosendale cement, 731 
 
 waterlimes, absent at Kingston, 68 1 
 
 Rossi, M. S. de, cited, 909 
 
 Rotalia, in Severn muds, 664 
 Roth, J., cited, 164, 537, 1080, 1096 
 Rothes Burn, origin of sand of the, 716 
 Rothliegende, windkanter of, 55 
 Rothliegende desert, 375 
 Rothpletz, A., cited, 337, 338, 465, 468, 
 469, 472, 474, 476, 521, 1093 
 
 quoted, 468, 784, 827 
 
 Royal gorge, 587 
 Rudaceous texture, 285 
 Rudolph, E., cited, 879, 909 
 Rudytes, 285 
 
 Ruedemann, R., cited, 243, 268, 474, 521, 
 
 808, 823, 827, 928, 981, ion, 1012, 
 
 1039, 1136, 1145, ii 49 
 Kuedemann, K., quoted, 243, 244 
 Ruetschi, G., cited, 580 
 Rust, cited, 458, 465 
 Russell, I. C., cited, 36, 38, 40, 96, 119, 
 
 i2i, 144, 159, 161, 163, 164, 200, 201, 
 
 207, 268, 324, 338, 339, 340, 341, 359, 
 
 382, 517, 625, 634, 639, 870, 879 
 , quoted, 154, 159, 160, 162, 163, 199, 
 
 507, 5o8 
 
 Russell, W. J., cited, 28, 96 
 Russia, unconsolidated Palaeozoic sands of 
 
 750 
 
 , tchernpzom of, 514 
 
 Rutot, A,, cited, 92, 689, 724, 745 
 
 Saalfeld, 434 
 
 Sabrina Island, 864, 865 
 
 Saco, flood plain of, 588, 596 
 
 Saddle Mt., 313 
 
 Saddles, defined, 966 
 
 Saginaw Bay, 837 
 
 Sahara, 359 
 
 , dune area of, 562 
 
 , migration of dunes from, 558 
 
 , preservation of tracks in, 604 
 
 , rainfall of, 63, 77 
 
 , spring water of, 167 
 
 , strength of wind in, 56 
 
 St. Anthony, falls of, m8 
 St. Augustine, 406 
 St. Croix, dalles, 23, 648 
 , formation, 648 
 
 sandstone, 729 
 
 sandstone, Aglaspis in, 1029 
 
 St. Giles, ripple marks of, 713 
 St. Gotthard Pass, weather in, 48 
 St. Helena, Island, 105 
 
 , harbor of, 215 
 
 St. Ignace, brecciated limestone of, 547 
 St. Jean-de-Luz, encroachments of sea at, 
 
 558 
 . John, absence of Lower Cambric at, 
 
 72 
 . John's River, tides in, 227 
 
 St 
 
 St 
 
 St. Lawrence, furrow, 104 
 
 , gulf of, 235, 241 
 
 river, 133 
 
 , drowning of, 136 
 
 spring, 175 
 
 St. Louis limestone, cross-bedding of, 577 
 St. Michaels, 864, 865 
 
 , humus layer at, 507 
 
 St. Paul, Island of, 872, 873, 875 
 St. Peter sandstone, 642 
 
 disconformity represented by, 1101 
 
 dune origin of parts of, 571 
 
 hiatus in, 1132 
 
 inclusions in, 717 
 
 intercalated, 738-, 739 
 
 loess-like origin of portions of, 569 
 
 slight cohesion of, 752 
 
 . transgression of, 565, 738 
 
 St. Vincent, erosion on Island of, 875, 876 
 
 Salem, 1041 
 
 Salina, endolithic brecciation in, 537 
 
 Salina group, 376 
 
 Salina salt, 366, 731, 756 
 
 Salinas, 603 
 
 Salinity, defined, 145 
 
 , types of, 150 
 
 Salisbury, R. D., cited, 25, 42, 43, 45, 46, 
 59, 96, 116, 125, 144, 200, 207, 247, 
 268 
 
INDEX 
 
 1179 
 
 Salitrales, 329 
 
 Salitre, 341 
 
 Salt, efflorescence of, 124 
 
 , Miocenic deposits of, 351 
 
 Salt domes, 758 
 
 Saltenfjord, 230 
 
 Salton Sink, 355, 356 
 
 Saltstrom, 230 
 
 Salversen, Captain, cited, 224 
 
 Salzburg, foehn of, 47 
 
 Nagelfluh of, 601, 616, 750, 753 
 
 Samoan islands, 40 
 Samuelson, G., cited, 521 
 
 , quoted, 504, 505 
 
 San Bernardino, alluvial fans of, 83 
 
 , borax lakes in county of, 363, 364 
 
 , pass, 53 
 
 , soda niter deposits of, 364 
 
 Sandberger, F., cited, 1086 
 Sand grains, dimming of, 61 
 
 , effective size of, 258 
 
 , rounding and sorting of, 61, 715 
 
 Sands, coating of, 37 
 
 , desert type of, 37 
 
 Sandwich Islands, 386 
 
 , marine erosion of, 875 
 
 San Filippo, travertine of, 343 
 San Francisco, Bay of, 1 1 1 
 
 , earthquake at, 882 
 
 San Joaquin River, 126 
 
 San Juan Mts., rock streams in, 545 
 
 San Juan River, section on, 848 
 
 Sankaty Head, 599 
 
 Santa Anna Island, 411 
 
 Santa Fe, 27 
 
 Santa Maria, dust from, 60 
 
 San Vignone, baths of, 343 
 
 Sapping, 18 
 
 Saprocollyte, 480 
 
 Saprodillyte, 480 
 
 Sapropel, 281 
 
 Sapropelite, 281, 480 
 
 Sapropeliths, 478, 479, 480 
 
 Sardinia, Archaeocyathidae of, 417 
 
 Sargasso Sea, 187, 236 
 
 , temperature of, 187 
 
 Sarle, C. J., cited, 465 
 
 , quoted, 446 
 
 Sarmatian reefs, 443 
 
 Sassolite, 364 
 
 Sault Ste. Marie, 1122 
 
 Sava de Malha group, 389, 390 
 
 Saville-Kent, W., cited, 391, 400, 401, 465 
 
 Savu-Savu, chloride waters of, 168 
 
 Scandinavia, eskers in, .599 
 
 Scania, Cretacic boulder bed of, 651 
 
 Schala, The, 603 
 
 Schardt, H., cited, 659, 689 
 
 Schiaparelli, G. V., cited, 96 
 
 Schiefergebirge, rheinische, 375 
 
 Schimper, A. F. W., cited, 982, 990, 1000, 
 
 1039 
 
 Schire River, 116 
 Schist, 279, 770 
 
 , restriction of term, 770 
 
 Schistosity, 769, 794 
 Schladebach bore hole, 14 
 Schlern dolomite, 435 
 Schleswig-Holstein, 223 
 
 , coastal dunes of, 557. 558 
 
 Schmelck, cited, 194 
 Schnaitheim, quarries of, 439 
 Schneider, K., cited, 203, 207 
 Schoenite, 37*, 372 
 Schoharie grit, 424 
 
 Schoharie region, disconformities in, 823 
 Schott, G., cited, 149, 150, 207 
 Schott-Mel-Rir, The, 359 
 
 Schramberg, Bunter Sandstein of, 634 
 
 Schuchert, C., cited, 957, 1107, 1119, 1144, 
 1145, 1146, 1149 
 
 Schuchert, C., and Buckmann, S. S., cited, 
 957 
 
 Schucht, F., cited, 689 
 
 Schutt, F., cited, 994, 999 
 
 Schwartz, E. H. F., cited, 535, 538 
 
 Scilla, land slip at, 888 
 
 , maelstrom at, 230 
 
 Sclater, P. L., and W. L., cited, 1056, 1071 
 
 Scotland, 219, 293 
 
 clay boulders on coast of, 711 
 fundamental gneiss of, 252 
 Ordovicic rocks of, 315 
 recent corals of, 392 
 section of peat moor of, 504 
 waves on coast of, 221 
 
 Scorpions, 948, 949 
 
 Screes, 33 
 
 Scrope, P., cited, 879 
 
 Scudder, S. H., cited, 
 
 , 525, 538, 917, 957 
 sculpturing processes, 16 
 Sea, bathymetric zones of, 100 
 
 , regional subdivisions of, 99 
 
 , salinity of, 145 
 
 Sea-breezes, 44 
 
 Sea-lobes of Appalachians, 807, 809 
 
 Sea of Aral, elevation of, 115 
 
 Azov, 240 
 
 , salinity of, 153 
 
 Marmora, 240 
 
 , salinity of, 153 
 
 , temperature of, 189 
 
 Okhotsk, 242 
 
 Searles's Marsh, 363 
 
 , soda niter of, 364 
 
 Seas, dependent, 99, 107 
 
 epicontinental, 109 
 
 funnel, 112 
 
 independent, 99, 106 
 
 intercontinental, 99, 100 
 
 intracontinental, 99, 106 
 
 marginal, 99 
 Sebcha, the, 603 
 Secca di Benda Palumno, 470 
 Secca di Gajola, 470 
 Secretions, 721 
 
 Sedgwick, A., cited, 1099, 1108 
 Sedgwick, A., and Murchison, R., cited, 
 
 1108 
 
 Sedimentation, eolian, 51 
 Seeley, A., cited, 530, 538, 785 
 Seiches, 209, 231 
 Seidlitz, N. von, cited, 382 
 Seine bank, no sediments on, 680 
 Seine-Dacia bank, 335 
 Seine River, meanders of, 137 
 
 , tidal bore of, 227 
 
 Seismic center, 883 
 
 Seismic disturbances, baryseismic, 882 
 
 , pyroseismic, 882 
 
 Semper, K., cited, 465, 990, 1019, 1025, 
 1039, 1047, 1071 
 
 , quoted, 986, 1047, 1068, 1069 
 
 Semper, M., cited, 1149, 1150 
 Senomien, 730 _ 
 
 , glauconitic chalk of, 850 
 
 Sentis Mts., 176 
 
 Sepia, wide distribution of shells of, 1022 
 
 Septaria, 763 
 
 Sernander, R,, cited, 92 
 
 Serpentine, 177, 279 
 
 Sett Sass, reef of, 434 
 
 Severn, corals on wreck of, 412 
 
 Severn, estuary of, 662 
 
 , tidal bore of, 227 
 
 Sevier lake, composition of, 157 
 
n8o 
 
 INDEX 
 
 Sevier lake, salinity of, 154 
 
 , soda deposits of, 361 
 
 Sewell, middle Pottsville at, 742 
 
 Seychelles Island, 386, 390 
 
 Seyistan, alternation of beds in Lake of, 
 
 623 
 Shaler, N. S., cited, 32, 82, 96, 226, 268, 
 
 448, 473, 485, 487, 489, 491, 494, 52i, 
 
 522, 652, 689, 694, 695, 851, 858 
 
 , quoted, 488, 652 
 
 Shaliness, 785 
 
 Shan-Tung Mts., 585 
 
 Sharon conglomerate, 252 
 
 Shaw, E. W., cited, 136, 144 
 
 Shawangunk conglomerate, 377, 596, 636 
 
 Sheboygan, 167 
 
 Sheik Zayed, 355 
 
 Shelden, J. M. A., cited, 719, 722 
 
 Shelf, Florida-Carolina, 106 
 
 Sheppard limestone, 334 
 
 Sherlock, R. L., cited, 465 
 
 Sherzer, W. H., and Grabau, A. W., cited, 
 
 422, 465, 553, 570, 571, 580 
 Shetland Islands, 219, 236 
 
 , force of waves on, 222 
 
 Shimek, B., cited^ 566, 580 
 
 Shimer, H. W., cited, 981, 1067, 1068, 1071 
 
 , quoted, 1066 
 
 , and Blodgett, M. E., cited, 1069, 1071 
 
 , and Grabau, A. W., cited, 1131, 1150 
 
 Shinarump, playa surface in, 709 
 
 Shoonmaker quarry, 419 
 
 Shore formations, intercalated, 736 
 
 Shropshire, 307, 447 
 
 Shunett Lake, 360 
 
 Siau, cited, 713 
 
 Siberia, Archaeocyathidae of, 417 
 
 , mammoths of, 1075 
 
 Siboga expedition, 68 1 
 
 Siccar Point, unconformity at, 824 
 
 Sicily, 240, 343 
 
 , mud volcanoes in, 872 
 
 , Pliocenic foraminifera of, 454 
 
 Sickenberger, cited, 369 
 
 Sieberg, A., cited, 909 
 
 Sierra Nevada, gold-bearing slates of, 773 
 
 , rivers from, 584 
 
 Silicification, 1079 
 
 Sills, 304, 305 
 
 Siluric, abrupt change in sea-level in, 731 
 
 , hiatus in Appalachians, 823 
 
 , replacing overlap of, 744 
 
 Silver Pit, furrow, 104 
 Simpson, C. T., cited, 1071 
 
 , quoted, 1059 
 
 Simpson formation, 739 
 
 Simroth, H., cited, 91, 97, 892, 894, 900, 
 
 909, 1019, 1039, 1144, 1150 
 Sinai desert, quartz in, 552 
 
 peninsula, hydrometamorphism on, 767 
 
 , oolites on, 336, 468 
 
 Sinclair, W. J., cited, 538, 539, 572, 580, 
 
 1119 
 
 , and Granger, W., cited, 639 
 
 , quoted, 624, 625, 627, 628 
 
 Singapore, nsh falls at, 56 
 Sinj, earthquakes of, 883 
 Sink holes, 176 
 Sirmur group, 591 
 Siwalik formation, 904 
 
 , alternation of colors in, 623 
 
 , thickness of, 591 
 
 , torrential origin of, 630 
 
 Siwalik Hills, 591 
 
 Siyeh limestone, 334 
 
 Skagerak, 224, 1045 
 
 Skaptar fissure, lava from, 866 
 
 Skeat.c, E. W., cited, 331, 382, 436, 445, 
 
 465, 761, 775 
 skerries, 651 
 Skerryvore, 221 
 Skottsberg, C., cited, 92 
 Slate, restriction of term, 770 
 Slatiness, 786 
 Slaty cleavage, 793 
 Slavonia, Paludina beds of, 958, 959 
 Slichter, C. S., cited, 4, 23, 140, 141, 142, 
 
 144, 258, 259, 260, 268 
 Shckensides formation of, 768 
 Smith, J. P., cited, 966, 972, 975, 981, 
 
 c 'u 71 /- Vr 34 ' T II36 J II3 ?' IJ 5 6 
 Smyth, C. H., Jr., cited, 763, 775 
 Snake River, dune area of, 561 
 
 , lava plains of, 867 
 
 Snakes, in marine habitat, 985 
 
 Snow, 26, 62, 63 
 
 Snow line, 322 
 
 Society Archipelago, 401, 402 
 
 Society Islands, barrier reefs of, 388 
 
 Soda Lake, 120, 361 
 
 , composition of, 157, 158 
 
 , salinity of, 154, 156 
 Soil, colors of, 36, 621 
 
 Sokolow, N. A., cited, 97, 552, 555, 556, 
 557, 58o 
 
 , quoted, 56 
 
 Sokotora, 456 
 
 Soldier Key, 406 
 
 Solent, 222 
 
 Solfataric action, 768 
 
 Sollas, W. J., cited, 662, 689 
 
 , quoted, 662, 663 
 
 Solnhofen, calcilutytes of, 336 
 
 deformation at, 531, 781 
 
 impressions in rock of, 1078 
 
 insects in limestone of, 440 
 
 , mud cracks in beds of, 709 
 
 reefs of, 437 
 
 remains in limestone of, 439 
 
 roofing slates of, 786 
 
 solution of limestone of, 175 
 
 Solomon Islands, 386, 411 
 Sombrero, 108 
 
 Somerville, drumlins of, 532 
 Somersetshire oolite, crosa-bedding in, 704 
 Sonora, gold-bearing slates in, 773 
 Sorby, H. C., cited, 250, 268, 455, 474 
 Soudan, rainfall of, 68 
 South African trough, 105 
 
 , temperature in, 187 
 
 South Australian shelf, 103 
 
 South Brazil shelf, 103 
 
 South China Sea, 107 
 
 South Dakota, artesian basin of, 260 
 
 South Pole, migration of, 898 
 
 South Tunis, 359 
 
 Southern Appalachians, caves in, 346 
 
 Spain, monsoons of, 46 
 
 , torrential deposits in, 629, 630 
 
 Spanish Peaks, radiating dikes in, 874 
 
 Species, 912, 962 
 
 Speremberg, bore hole, 13 
 
 Sphaerites, consolidation of, 751 
 
 Sphenoconformity, 826 
 
 Spirula, wide distribution of shell of, 102? 
 
 Spitzbergen, 192, 236 
 
 , postglacial fauna of, 88 
 
 red algae at, 470 
 
 _ . -, cited, 664, 665, 689 
 Squid, 946, 1021 
 Stalactites, 346 
 Stalagmites, 346 
 Stamm, K., cited, 580 
 Stanton, T. W., cited, 1069, 1071 
 
INDEX 
 
 1181 
 
 Stapff, F. M., cited, 23 
 Stassfurt, 371 
 
 salts, 350, 372, 374 
 
 , period of deposition of, 373 
 
 - , "ngs of, 355, 376 
 
 Stedman, J. M., cited, 1077 
 
 and Anderson, J. T., cited, 1096 
 
 Steidtmann, E., cited, 760, 775 
 Steinheim, Planorbis of, 1043 
 
 , shells in beds at, 631 
 
 Steinmann, G., cited, 332, 382, 522, 956, 
 
 1074, 1096 
 
 Stemme, H., cited, 522 
 Stenohalinity, 1045 
 Stenothermal organisms, 80 
 Stephen shale, preservation of organisms in, 
 
 1078 
 Stevenson, J. J., cited, 500, 522 
 
 , quoted, 509, 514, 515, 517, 518 
 
 Stevenson, T., cited, 213, 218, 221, 222, 268 
 
 , quoted, 221 
 
 Stille, cited, 758 
 
 Stinkkalk, 485 
 
 Stinkstein, 434 
 
 Stirling Island, 411 
 
 Stolle, J., cited, 522 
 
 Stone, W., cited, 921, 957 
 
 Stonesfield slate, 577, 1034 
 
 Stoneworts, 471, 934 
 
 Storm King, 1067 
 
 Strahan, A., cited, 81, 97, 534, 539 
 
 Straits of Bab-el-Mandeb, 190, 241 
 
 Gibraltar, 230, 244 
 
 , salinity of, 152 
 
 Kertch, 240 
 
 , salinity of, 154 
 
 Korea, 242 
 Strand, 647 
 Stratification, 700, 701 
 Stratified Rocks, 269 
 Stratigraphy i 
 
 Stratum, denned, 698, 699, 700 
 Stringocephalus beds, 430 
 Stromatoliths, 473 
 Stromatopora ; 421, 422, 430, 431 
 
 , asphaltic material in, 485 
 
 , worn heads of, 428 
 
 Stromatopora reefs, 423 
 
 Stromatoporoids, 385, 418 
 
 Stromboli, volcano of, 86 1, 871 
 
 Stromer, cited, 956 
 
 Strophe, climatic, 82, 83 
 
 Strutt, cited, 876 
 
 Stuben sandstein, origin of, 635 
 
 , reptiles in, 953 
 
 Stuttgart, weather at, 48 
 
 Styliolina limestone, 456, 1023 
 
 Stylolites, 786, 787, 788 
 
 Subaerial fans, overlaps of, 740 
 
 Subatlantic climatic period, 506 
 
 Subarctic climatic period, 506 
 
 Sub-mutation, 961, 962 
 
 Suchier, cited, 250, 268 
 
 Suess, E., cited, 3, 138, 201, 202, 203, 207, 
 
 595, 639, 760, 775, 881, 909 
 Suez, Bitter Lakes of, 697 
 
 , Quaternary oolite near, 469 
 
 Suez Canal, date of cutting, 352 
 
 , migration through, 1042 
 
 Sugar Loaf Mountain (Brazil), 32 
 Sumatra, 390 
 
 , oscillation poles in, 893 
 
 , peat swamp on, 509, 510, 512 
 
 Summer Lake, 118 
 
 Sunda Islands, 242 
 
 Sunderland, coast of, 225 
 
 Supan, A., cited, 74, 77, 78, 97, 101, 105, 
 
 106, 144, 678, 689 
 
 Surface features of earth, Compared, 13 
 Susquehanna River, 845 
 Sussex, chalk from, 454 
 Sutherland, conglomerate of, 651 
 Sutton, Mass., graben at, 815 
 Swabian Alp, 442 
 
 , cuestas of, 838 
 
 , Jurassic reefs of, 438 
 
 Swainson, T., cited, 917, 918 
 Sweden, Cambric windkanter of, 573 
 
 , coast of, 241 
 
 , Cretacic boulder beds of, 651 
 
 , overlap of basal Cambric of, 728 
 
 Swell, Crozet, 106 
 
 Swells, 209 
 
 Sylt, Island of, 223 
 
 , dunes of, 557, 558 
 
 Sylvania sandstone, 642 
 
 , cross-bedding in, 570, 571, 704 
 
 , dune origin of, 571 
 
 , hiatus in, 1132 
 
 , inclusions in, 717 
 
 , slight cohesion of, 752 
 
 , trangression of, 565 
 
 Sylvinite, 371, 372 
 Sylvite, 372 
 Symphrattism, 749 
 
 Synchroneity, black shale across planes of, 
 732 
 
 , sandstone crossing planes of, 736 
 
 Syntype, 919 
 
 Syracuse salt, 376 
 
 Syr-darja (Syrdaria), 561, 608 
 
 Syria, 240 
 
 , coast of, 218 
 
 , desert areas of, 562 
 
 Szovata, 122 
 
 Tabasco, volcanic ash deposit of, 60 
 
 Tachygenesis, 964 
 
 Tahiti, 388, 401, 402, 410 
 
 Takyr, 603, 709 
 
 Talbot formation, 87 
 
 Talc, 177 
 
 Talcot, Captain, cited, 609 
 
 Talheim, stylolites of, 788 
 
 TaltaJ, 365 
 
 Talus, 32 
 
 Taman, peninsula of, 443 
 
 Tamaracks, 498 
 
 , filling of swamps by, 496 
 
 Tampa beds, casts of corals in, 1090 
 
 Tanfiljef, G. L, cited, 92 
 
 Tapachula, volcanic ash deposit of, 60 
 
 Tapir, 956 
 
 Taramelli, T., cited, 92 
 
 Tarapaca desert, 365 
 
 , guano of, 461 
 
 , soda niter deposits in, 364 
 
 Tarawera, eruption of, 60 
 Tarim River, 588 
 Tarr, R. S., cited, 642, 689 
 Tasmania shelf, 104 
 Tasmanian Sea, 1 12 
 Taurida, Russia, dunes of, 560 
 Taylor, F. B., cited, 909 
 Tay River, peat of, 514 
 Tectonic, restriction of term, 88 1 
 Teisseyre, L., cited, 443, 465 
 Teleosts, 352 
 
 Temiscammg syncline, 810 
 Temperature arrangement, dichothermal, 
 183 
 
 , heterothermal, 183 
 
 . , homothermal, 183 
 
1182 
 
 INDEX 
 
 Temperature arrangement, katothermal, 183 
 
 , mesothermal, 183 
 
 Teneriffe, 244 
 
 Peak, trade winds of, 44 
 
 Tenison- Woods, cited, 1013 
 
 Tennessee, Lower Cambric limestone of, 335 
 
 Tentaculite limestone, 456, 1124 
 
 Tepee buttes, 447, 448 
 
 Tepetate, 341, 586 
 
 Teredo, 632, 1016 
 
 Terek delta, rate of growth of, 609 
 
 Termites, height of nests of, 694 
 
 Terra rossa, 40 
 
 Terreild, cited, 156 
 
 Tetrabranchiata, 946 
 
 Tetragraptus, 978 
 
 Tetraseptata, 913, 943, 1013 
 
 Teuchern, Limulus in brown coal of, 1029 
 
 Teutoburger Wald, 673 
 
 Texas, deformed salt domes of, 758 
 
 Textularia, in Severn muds, 664 
 
 Thalassic zone, 987 
 
 Fhalassogenic deposits, 329 
 
 Thalassoseisma, 88 1 
 
 Thallophytes, 935 
 
 Thalweg, 258 
 
 Thames River, 248 
 
 , currents in, 229 
 
 Thenardite, 363 
 
 Theobold, cited, 56, 97 
 
 Thermonatrite, 362 
 
 Thesis, climatic, 82, 83 
 
 Thetis Sea, 375 
 
 Thompson, Sir W., cited, 897, 909 
 
 , quoted, 897, 898 
 
 Thomson, W., cited, 456, 1071 
 Thon-gallen, 711 
 Thoroddsen, T., cited, 879 
 Thorpe, parish of, 225 
 Thorshaven (Faroe Islands), 31 
 Thoulet, J., cited, 34, 97, 268, 288, 299, 
 452, 679, 689, 879 
 
 , quoted, 55 
 
 Thuringia, Kupferschiefer of, 479 
 
 , Zechstein reefs in, 433 
 
 Thiiringer Wald, 252 
 
 Thurr, the, 355 
 
 Thursday Island, 404 
 
 Tian-Shan Mountains, sands brought from, 
 
 561 
 
 Tiber, cuspate delta of, 608 
 Tibet, borax deposits of, 364 
 Tichenor limestone, 684 
 Tidal bore, 227 
 Tidal race, 229 
 
 Tiddeman, R. H., cited, 432, 449, 465 
 - : '-, quoted, 433 
 Tides, 227 
 
 Tile fish, destruction of, 195 
 Tillard, Captain, 864 
 Tillers Ferry, fish falls of, 56 
 Tillite, 534 
 Timor, 242 
 Tirolites stage, preserved in a Trachyceras, 
 
 975 
 
 Titanothere, 956 
 Tizard bank, 391 
 Todd, J. E., cited, 719, 722 
 Toledo anticlinals, 810 
 Tolman, C. F., cited, 97, 197, 207 
 
 , quoted, 147, 148 
 
 Toltry, 443 
 
 Tomboro, dust from, 60 
 
 Tonga deep, 3, 896 
 
 , temperatures in, 187 
 
 Tonkin-Hong-Kong shelf, 104 
 Topography, karren, 176 
 , lapiaz, 176 
 
 Topotype, 919 
 
 Top-set beds, 702 
 
 Torell, O., cited, 236 
 
 Tornquist, A., cited, 690, 1134, 1150 
 
 Torres Strait, 387 
 
 Torridon sandstone, 33, 293 
 
 , arkose character of, 84 
 
 , windkanter of, 54, 573 
 
 Tortugas, 391 
 
 , dry, 406 
 
 Toula, F., cited, 1150 
 Tournasien, reefs of the, 432 
 Toxodontia, 956 
 Trachyceras, retarded, 975 
 Trachytes, depths of formation, 15 
 Transcaspian Desert, see Kara Kum 
 
 , dunes in, 563, 564 
 
 Transgressions, 3, 725, 738, 1141 
 Transportation, 17, 18 
 
 , distance of eolian, 58, 59 
 Transylvania, salt domes of, 758 
 Trap, 278 
 Traverse Bay, reefs of, 429 
 
 group, 423, 426 
 
 , Stromatopora reefs of, 444 
 
 Travertine, 343 
 Treasury Island, 411 
 Treitz,. P., cited, 92 
 Trench, Japan, 106 
 
 , Marian, 106 
 
 Trenton Falls, deformation in limestones 
 of, 783, 784 
 
 limestone, distortion of, 530 
 
 , overlapped by Utitica shales, 743, 
 
 744 
 
 Triassic time, climatic conditions of, 70 
 Tricyrtida, 458 
 
 Trigonodus limestone, stylolite from, 786 
 Trilobites, 912, 947 
 Trinity formation, 729 
 Tripoli, diatomaceous earth of, 461 
 Tripolite, 460, 461, 676 
 Tristan da Cunha, 105, 452 
 
 , pteropod ooze near, 456 
 
 Triumph reef, 406 
 Trona, 362, 363 
 Truckee River, 160 
 Truro, sands from, 559 
 
 , sand plains of, 600 
 
 Tschermak, cited, 203 
 
 Tschudi, cited, 461 
 
 Tsien-Tang River, tidal bore of, 227 
 
 Tsunamis, 88 1, 889 
 
 Tufa, calcareous, 342 
 
 -, dendritic, 340, 341 
 
 , lithoid, 339 
 
 , thinolithic, 339 
 
 Tulare Lake, 126 
 
 Tule Arroyo, onyx marble of, 344 
 
 Tully, pyrite layer, fauna of, 1045, 1065 
 
 Tultenango, Permic position of North Pole 
 
 at, 536 
 
 Tumlirz, O., cited, 23 
 Tundra, frozen soil of, 200 
 
 , lakes of, 121 
 
 Tung hai Sea, 107 
 
 shelf, 104 
 
 Tunis, 240 
 Turbarian, 506 
 Turkestan, 358 
 
 , earthquake in, 885 
 
 "Turks' Heads," 403 
 
 Turks' Island, 412 
 
 Turonien, 730, 850 
 
 Turtle Mountain, rock fall on, 546 
 
 stones, 720 
 
 Tuscany, 343 
 
 , borate deposits of, 364 
 
INDEX 
 
 1183 
 
 Tuscany, fumaroles of, 370 
 
 Tuscarora Sour Spring, composition of 
 
 water of, 168 
 
 Tuskegee, mineralized body near, 1077 
 Twenhofel, W. H., cited, 509, 522 
 
 , quoted, 508 
 Tyrol, dolomites of, 444 
 
 reefs of, 434, 435 
 
 Tyrone, 423 
 
 , Appalachian folds at, 903, 904 
 
 Tyrrhenian Sea, 230, 240 
 
 U 
 
 Udden, J. A., cited, 58, 59, 97, 552, ,581, 
 
 653, 654, 690 
 
 , quoted, 56, 59, 552 
 
 Ued Kir, the, 359 
 
 Ugi Island, 411 
 
 Uhlig, V., cited, 1057, 1058, 1072, 1150 
 
 Uinta sandstone, 855 
 
 , age of, 1138, 1140 
 
 Ulexite, 364 
 
 Ulmic acid, 173 
 
 Ulrich, E. O., cited, 824, 828, 1107, 1109, 
 
 1113, 1120, 1124, 1150 
 
 and Schuchert, C., cited, 1150 
 
 Unconformity, 821, 824, 826 
 
 , inverted, 826 
 
 Unkar series, age of, 1 140 
 
 Unst, lighthouse of, 219 
 
 Unter-Mauthdorf, 246 
 
 Unterschwarza, 246 
 
 Upham, W., cited, 126, 144, 373 
 
 Ural Mountains, undecomposed granite of, 
 
 40 
 
 Urao, 362 
 
 Urmiah Lake, salinity of, 154 
 Uruguay River, solids in, 174 
 
 - tributary of La Plata, 66 1 
 Usiglio, J., cited, 348, 350, 382 
 Usk River, 662 
 Utah, hot springs, 168 
 
 , onyx deposits of, 344 
 
 Utica shales, 243 
 
 , origin of, 479 
 
 , overlap on Trenton limestone, 
 
 743 
 
 , replacement of Trenton lime- 
 stone by, 744 
 
 Vaal River, glacial deposit at, 535 
 
 Vaccinium, 503 
 
 Val del Bove, basaltic dikes in walls of the, 
 
 871 
 
 Valdivia, 185 
 
 Valiant, W. S., cited, 1086 
 Valparaiso, sea-breeze of, 44 
 Valves, brachial, 944 
 
 , pedicle, 944 
 Van Hise, C. R., cited, 4, 23, 37, 38, 97, 
 
 138, 139, 140, 141, M4, 174. 175, 177. 
 
 178, 207, 293, 299, 528, 539, 713, 751, 
 
 752, 754, 755, 76i, 765, 767, 770, 77i, 
 
 775, 794, 819, 820, 828 
 , quoted, 528, 529, 747, 752, 772, 790, 
 
 793 
 
 Van Lake, salinity of, 155 
 Vanikoro, 401 
 
 Van't Hoff and Weigert, F., cited, 373, 382 
 Vanuxem, L., cited, 787, 1123 
 Varanger fjord, Cambric glacial deposits in 
 
 .81, 534^ 
 Variation, 960 
 
 Varieties, 912 
 
 Variplitic, 277 
 
 Varo, 230 
 
 Vater, cited, 373 
 
 Vaughan, T. W., cited, 391, 418, 465, 1072 
 
 Veatch, A. C., cited, 127, 144 
 
 Vegetation, tundra type of, 85 
 
 Veins, eruptive, 304 
 
 Velain, C., cited, 873 
 
 Venezuela, alkaline lakes of, 361 
 
 Vera Cruz, volcanic ash deposit of, 60 
 
 Verawal, miliolite limestone of, 574 
 
 Verbeck, R. D. M., cited, 879 
 
 Verdun, 231 
 
 Vermilion iron-bearing district, 316 
 
 Vermillion Creek beds, 626 
 
 Vernon-Harcourt, L. F., cited, 690 
 
 Vernon shales, 376, 377 
 
 , iron in, 621 
 
 , loess-like origin of, 569 
 
 , origin of red color of, 569, 622 
 
 Verrill, A. E., cited, 412, 465, 680 
 
 and Smith, S. J., cited, 1065, 1072 
 
 Vertebraria, in cannel coal, 481, 484 
 Vesuvius, dust from, 60 
 
 , eruption of, 875 
 
 , lavas of, 317 
 
 , periodic activity of, 871 
 
 , tuffs of, 290 
 
 , volcanic mud from, 525 
 
 Veta Park, rock streams in, 545 
 Victoria Land, volcanoes of, 877 
 Vienna, 245, 251 
 
 Basin, fossil nullipores of, 471 
 
 , Miocenic boulder beds of, 651 
 
 Ville, M., cited, 379 
 Vindelician Mountains, 373 
 , sediments from, 634 
 
 period, old shore of, 440 
 
 Virgin Islands, 108 
 
 Virginia, Lower Cambric limestone of, 335 
 
 Viry, phosphate waters of, 168 
 
 Visby, Siluric reefs near, 427 
 
 Viseen, reefs of the, 432 
 
 Vistula, velocity of, 245 
 
 Vistula delta, organic matter in, 614 
 
 Vitrification, 766 
 
 Vogt, C., cited, 886 
 
 Vogt, J. H. L., cited, 382 
 
 Voigt, F. S., cited, 605, 639 
 
 Volcanoes, distribution of, 877 
 
 , heights of, 863 
 
 , mud, 885 
 
 Volga delta, 608 
 
 , deposits of lime in, 616 
 
 River, 357 
 
 , dunes on shores of, 561 
 
 Volhynia, 443 
 
 von Baer, K. E., cited, 200 
 
 von Buch, L., cited, 336 
 
 von Kotzebu, cited, 204 
 
 von Kvassay, E., cited, 369 
 
 von Richthofen, see Richthofen. 
 
 von Seidlitz, cited, 353 
 
 von Tillo, cited, 39, 183, 566 
 
 Vosges, 1029 
 
 Vulcanello, erosion of, 875 
 
 Vulcanian periods, 861, 871 
 
 Vulcano, Island of, 875 
 
 , eruption of, 86 1 
 
 , lava flows of, 317 
 
 Vulcanology, 20 
 
 W 
 
 Waagen, W., cited, 960, 963, 981 
 Wade, A., cited, 54, 97, 594, 6 39 
 
1184 
 
 INDEX 
 
 Wadi Deheese, oolites of, 336 
 
 Wadsworth Lake, 340 
 
 Wagner, G., cited, 784, 786, 788, 828 
 
 , H., cited, 23, 100 
 
 , R., cited, 335, 382 
 
 Wagon-bed Spring, pyroclastic mud at, 526 
 
 Wahnschaffe, F., cited, 92, 287, 288, 300 
 
 Walcott, C. D., cited, 335, 382, 417, 418, 
 465, 530, 539. 1078, 1089, 1096, 1103 
 
 Walker Lake, salinity of, 155 
 
 Wallace, A. R., cited, 1072 
 
 Waltershausen, S. von, cited, 879 
 
 Walther, Johannes, cited, 23, 32, 34, 37, 52, 
 54, 56, 57, 6p, 61, 97, 120, 138, 140, 
 144, 167, 176, 207, 208, 225, 263, 271, 
 300, 336, 354, 355, 357, 362, 368, 372, 
 373, 382, 383, 397, 40i, 437, 439, 44<>, 
 441, 458, 461, 466, 470, 522, 541, 542, 
 552, 554, 56i, 573, 58i, 592, 603, 604, 
 605, 626, 634, 639, 697, 700, 701, 703, 
 704, 711, 712, 714, 718, 722, 748, 749, 
 775, 854, 856, 858, 861, 879, 892, 896, 
 987, 993, 995, 999, 1008, ion, 1021, 
 1022, 1031, 1039, 1068, 1072, 1134, 1150 
 
 , quoted, 371 
 
 Walther, J., and Schirlitz, R., cited, 334, 
 383 
 
 Warsaw limestone, cross-bedding of, 704 
 
 Wasatch formation, 629, 855, 856 
 
 River, analyses of clays of, 624 
 
 Washington, basaltic plateau of, 867 
 Washita formation, 729, 739 
 Waste-lake, Arkansas, 587 
 Waste-stream, 541 
 
 Water, density of, 179 
 
 , heat capacity of, 182 
 
 , heat conductivity of, 182 
 
 , potable, 161 
 
 Waterlime, 1124 
 Water plane, 141 
 Water vapor, 24, 25, 29 
 
 , amount of, 26 
 
 , source of, 27 
 
 Watson, T. L., cited, 23 
 
 Wauwatosa (Wis.), fossil reefs at, 419 
 
 Wave activity, depth of, 647 
 
 Wave marks, 708 
 
 Weald, dome of, 847 
 
 Wealden, the, 850 
 
 Weathering, belt of, 17, 34, 39, 139, 747 
 
 Weber, C. A., cited, 522 
 
 , M., cited, 68 1, 690 
 
 Weber River, calcium carbonate in, 468 
 Weed, W. H., cited, 346, 347, 383, 476, 
 
 477, 522 
 
 , quoted, 346, 476, 477 
 
 Weed, W. H., and Pirsson, L. V., cited, 
 
 306 
 Weissliegende, 375 
 
 , dune origin of, 571 
 
 Welding, 751 
 
 Weller, S., cited, 791, 823, 1072, 1124, 
 
 1139, 1144, 1150 
 Wellfleet, sands from, 559 
 
 , sand plains of, 600 
 
 Wengen formation, 434, 435 
 Wenlock, ballstone reefs of, 446 
 
 Edge, 446, 838 
 
 , reefs of, 418 
 
 Werner, A. G., cited, 874, 1098, 1099, 1122, 
 
 1123 
 
 Wernsee, 246 
 Werthausen. 245 
 
 Wesenberg-Lund, C., cited, 471, 522 
 West African trough, 105 
 West Atlantic, reefs in, 411 
 West Elk Mts., 308 
 
 West Indies, 386, 412 
 
 , dust falls at, 60 
 
 , fringing reefs in, 390 
 
 West Palm Beach, 226, 293 
 Wethered, E., cited, 472, 522 
 Wetterstein Kalk, 471 
 Weule, K., cited, 690 
 Whale rise (ridge), 105 
 
 , temperatures on, 188 
 
 Wheeler, W. H., cited, 225, 268, 656, 690 
 
 , quoted, 219, 221-225, 231 
 
 Wherry, E. T., cited, 365, 383 
 Whimper, E., cited, 792, 883, 909 
 Whirlwinds, 47 
 Whitby, ammonites of, 1086 
 
 , jet from, 483 
 
 White, C. H., cited, 718, 1082, 1096 
 White, David, cited, 519, 523, 535, 539, 722, 
 
 1 150 
 White Cliff sandstone, dune origin of, 571 
 
 , eolian cross-bedding in, 704 
 
 White Mountains, ice crystals on, 62 
 
 , pebbles in streams of, 596 
 
 , relicts in, 1066 
 
 White River beds, cross-bedding of, 84 
 
 , loess-like origin of, 568 
 
 White Sea, in 
 
 , temperature of, 193 
 
 Whitney, M., cited, 657, 690, 883 
 Whitsunday Island, 388 
 Wick, harbor of, 222 
 Wieland, G. R., cited, 761, 775 
 Wieliczka, 351 
 Wilbur limestone, 68 1 
 Wilckens, O. t cited, 459, 466 
 Wilckes, cited, 204 
 Wildon, 246 
 
 Williams, H. S., cited, 1072, 1108, 1118, 
 1 1 20, 1124, 1150 
 
 , quoted, 1125 
 
 Williams canyon, 310 
 
 , unconformity in, 824 
 
 Williamsville, 425, 426 
 
 Willis, B., cited, 81, 97, 534, 539, 654, 661, 
 662, 673, 682, 845, 903, 909, 1 1 10, 
 1120, 1145, 1146, 1150 
 
 , quoted, 653, 673, 674, 690 
 
 , and Salisbury, R. D., cited, 1150 
 
 Williston, S. W., cited, 1072 
 
 , and Case, E. C., cited, 633, 640 
 
 Wills. L. J., cited, 98 
 Wilmington, soda beds at, 361 
 Wilson, A. W. G., cited, 724, 731, 732, 745, 
 838, 858 
 
 , J. H., cited, 126, 144, 326, 599, 600, 
 
 640 
 
 Wiman, C., cited, 420, 421, 466, 1083, 1096 
 Winchell, A., cited, 1108 
 Wind, carrying power of, 55 
 
 , influence of mountains on, 47 
 
 , rounding of sand grains by, 61 
 
 , sorting power of, 61 
 
 , velocities of, 50, 56 
 
 Windkanter, 54 
 
 Wind River, analyses of clays of, 624 
 Wind River Basin, Eocenic and Oligocenic 
 of, 627 
 
 , tuff bed of, 525 
 
 Winds, easterlies, 43 
 
 mountain and valley, 50 
 
 Permic westerlies, 374 
 
 i planitary, 44 
 
 prevailing, 44 
 
 special types, 49, 50 
 
 trade, 43, 67 
 
 westerlies, 43, 69, 356, 652 
 
 Windsor limestone fauna, 1069 
 Winnebago Lake, 837 
 
INDEX 
 
 1185 
 
 Winnemucca Lake, salinity of, 155 
 
 Winter Park, fish falls of, 56 
 
 Wisconsin, oolitic iron ore of, 283, 473, 762 
 
 , reefs of, 419, 420 
 
 Withered, cited, 455 
 
 Witteberg series, 536 
 
 Wittecliff, 225 
 
 Witwatersrand Mines, 14, 15 
 
 Wollny, E., cited, 287 
 
 Wooburn, greensands of, 671, 672 
 
 Woods Hole, 392, 1041 
 
 Woodward, R. S., cited, 23, 200, 208 
 , S. P., cited, 1020, 1039, 1055, 1072 * 
 
 Woodworth, J. B., cited, 262, 268, 571, 
 581, 599, 640, 790, 828, 887, 909, 1090, 
 1091, 1096 
 
 , quoted, 791 
 
 Worcester lowland, 839 
 
 Worth, R. H., cited, 690 
 
 Wrangell and Spindler, cited, 153 
 
 Wright, G. F., cited, 566. 581 
 
 Wiirttemberg, Bunter Sandstein of, 1034 
 enterolithic structure in, 758, 759 
 Ichthyosaurians in Lias of, 1078 
 jet from Lias of, 483 
 Jurassic escarpment of, 838 
 Jurassic lutytes of, 786 
 origin of Liassic black shales of, 678 
 
 Wye River, 227, 662 
 
 Wynne, A. B., cited, 640 
 
 , quoted, 592 
 
 Wyoming, soda lakes of, 361 
 
 Wyoming county, New York, 378 
 
 Wyville-Thomson ridge, 106, no, 188, 192, 
 218 
 
 Yakutat Bay, 324 
 
 , earthquake of, 888 
 
 Yakutsk (Siberia), 31 
 
 , frozen soil at, 200 
 
 Yang-tse-Kiang, 248, 585 
 
 , Cambric glacial deposits of, 81, 534 
 
 , red mud of, 669 
 
 Yardangs, 53, 53, 856 
 
 Yavapai county, Ariz., onyx marble of, 344 
 
 Yellow River, dissection of loess by, 566 
 
 Yellowstone Park, 304 
 
 , columnar structure in, 319 
 
 Yellowstone Park, hot springs of, 201, 202, 
 343. 475 
 
 , rhyolite flows of, 313 
 Yeniseisk (Siberia), 27 
 Yeo River, 663 
 Yokoyama, M., cited, 89, 98, 897 
 
 , quoted, 91 
 Yorkshire, 839 
 
 , erosion of chalk cliffs of, 225 
 
 , marine erosion in, 224 
 
 Yucatan, 335, 357 
 
 basin, 108 
 
 Sea, temperature of, 190 
 
 Yukon, humus on delta of, 508 
 Yuma (Arizona), 27 
 
 Zacharius, Q., cited, 998 
 Zagazig, boring at, 594 
 Zambesi delta, 615 
 
 River, 116 
 
 shelf, 103 
 
 Zandt, quarries of, 439 
 
 Zante, earthquake scarp near, 890 
 Zechstein, bryozoan reefs of, 375, 433 
 
 , erosion cliff of, 225 
 
 , salt in, 756 
 
 Sea, 120, 373, 376 
 
 Zeolites, 177 
 
 Zepce, pisoliths of, 284 
 
 Ziegler, V., cited, 254, 268, 473, 523, 762, 
 
 775 
 
 Zirkel, F. von, cited, 270, 300, 336, 383 
 Zittel, K. A. von, cited, 98, 454, 552, 562, 
 
 581, 956 
 
 , quoted, 1073 
 
 Zoarium, 943 
 Zooecia, 943 
 Zoogenic deposits, 384 
 Zooliths, 280 
 Zoology, 20 
 Zoosphere, 16, 910 
 Zug, 784 
 
 , subaqueous gliding at, 657, 780 
 
 Zug spitze, massif of, 436 
 Zuidersee, 223 
 
 , deepening of, 558 
 
 Zurich, Lake of, subaqueous gliding in, 657, 
 
 780 
 
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