LIBRARY 
 
 UNIVERSITY OF 
 CALIFORNIA 
 
 EARTH 
 
 SCIENCES 
 LIBRARY 
 
THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 MRS. PRUDENCE W. KOFOID 
 
REVISED 
 
 TEXT-BOOK OF GEOLOGY 
 
 BY 
 
 JAMES D. DANA, LL.D. 
 
 LATE PROFESSOR OF GEOLOGY AND MINERALOGY IN YALE UNIVERSITY, 
 
 AUTHOR OF "GEOLOGICAL STORY BRIEFLY TOLD," "MANUAL OF GEOLOGY,' 
 
 "SYSTEM OF MINERALOGY," "CHARACTERISTICS OF VOLCANOES," 
 
 "CORALS AND CORAL ISLANDS," EEPORTS OF WILKES' 
 
 EXPLORING EXPEDITION, ON GEOLOGY, ZOO'PHYTES, 
 
 AND CRUSTACEA, ETC. 
 
 FIFTH EDITION, REVISED AND ENLARGED 
 
 EDITED BY 
 
 WILLIAM NORTH RICE, PH.D., LL.D. 
 
 PROFESSOR OF GEOLOGY IN WESLEYAN UNIVEESITT 
 
 NEW YORK : CINCINNATI : CHICAGO 
 
 AMERICAN BOOK COMPANY 
 
 JU. 
 
COPYRIGHT, 1897, BY 
 AMEKICAN BOOK COMPANY 
 
 REV. T. B. GEOL. 
 W. P. 8 
 
EARTH 
 
 SCIENCES 
 LIBRARY 
 
 PREFACE. 
 
 THE late Professor Dana had begun a revision of this 
 work a short time before his death. The request of his 
 family that I should complete the work of my revered 
 teacher, was responded to with something like a feeling 
 of filial obligation. 
 
 It was proposed in the plan of revision that the distinc- 
 tive characteristics of the book should be preserved so far 
 as possible. It was to be brought down to the present 
 time as regards its facts, but it was still to express the 
 well-known opinions of its author. The general plan of 
 arrangement was to be kept unchanged, and the size of 
 the book to be increased as little as possible. 
 
 In the progress of the work it became manifest that the 
 usefulness of the book would be increased by certain 
 changes more radical than had been at first contemplated. 
 The zoological and botanical classifications used in the 
 former edition were judged to be obsolete. The endeavor 
 has been made to substitute for them, as nearly as practi- 
 cable, the classifications which are followed in the major- 
 ity of recent manuals on zoology and botany, whether 
 precisely accordant with my own views or not. It was 
 decided that the theory of evolution required fuller recog- 
 
 iii 
 
iy PEEFACB. 
 
 nition than it had received in the previous edition of this 
 work or the last edition of the Manual. It was a proof 
 of Professor Dana's remarkable hospitality to new ideas, 
 that he adopted a belief in evolution at an age when most 
 men are incapable of important changes of opinion. But 
 the idea of evolution never influenced his thinking in 
 general as it doubtless would have done had he embraced 
 it earlier. In the present edition, the bearing of various 
 events in geological history upon the theory of evolution 
 is pointed out in the appropriate places; and, in the 
 closing chapter, which has been entirely rewritten, the 
 general bearing of paleontology upon evolution is dis- 
 cussed. The treatment of metamorphism also was be- 
 lieved to require considerable modification, especially 
 with reference to dynamic metamorphism and the de- 
 velopment of a foliated structure in igneous rocks. 
 
 With these exceptions, the book presents substantially 
 the views of the science which were held by the author in 
 his later years, and which are embodied in that monumen- 
 tal work, the fourth edition of the Manual. I have been 
 the more willing to follow this course, since in the main 
 my own opinions are in harmony with those of my teacher ; 
 although on a few points, if the responsibility for the 
 book had been solely my own, the views expressed would 
 have been somewhat different, as, for instance, in regard 
 to the geographic and climatic oscillations of the Quater- 
 nary era. It is a delicate task, in revising the work of 
 another, to discriminate between errors which should be 
 corrected, and statements at variance with the editor's 
 opinions, which, in deference to the author, should be left 
 
PREFACE. V 
 
 unchanged. I cannot flatter myself that questions of this 
 sort have always been decided aright. I have doubtless 
 sometimes changed too much, and sometimes too little. 
 
 The only important change in the arrangement of the 
 book, the insertion of the chapter on Zoological and Botan- 
 ical Classification before the chapter on Dynamical Geol- 
 ogy, was indicated in the notes left by the author. The 
 practice followed by Professor Dana, in previous editions 
 of this book, and in his other works, of writing the names 
 of zoological and botanical groups with anglicized termi- 
 nations, has been followed, in general, in this edition. 
 The full Latin form of names of groups above the grade 
 of family has been used only in cases where no anglicized 
 form is sanctioned by general usage. Professor Dana's 
 plan of terminating names of rocks in yte, in distinction 
 from the names of minerals which terminate in ite, it has 
 been deemed best to abandon, as that innovation in nomen- 
 clature has not been adopted by other writers. 
 
 The appendix to the former edition, giving localities of 
 fossils, has been omitted. It is believed that such a list 
 is not of much value unless given in more detail than the 
 space at disposal would permit. Teachers who desire 
 such a list are referred to Schuchert's Directions for Col- 
 lecting and Preparing Fossils, published as Part K of Bul- 
 letin No. 39 of the United States National Museum. 
 
 I take this opportunity for grateful acknowledgments 
 to Professor E. S. Dana, Ph.D., for his appreciative sym- 
 pathy in the perplexities of my work ; to the publishers, 
 for their earnest cooperation in the endeavor to make the 
 book as good as possible ; to G. K. Gilbert, A.M., of the 
 
VI PREFACE. 
 
 United States Geological Survey, for valuable criticisms 
 on the manuscript ; and to my son, Professor E. L. Rice, 
 Ph.D., for assistance in the correction of the proof. It is 
 hoped that the book in its revised form will prove itself 
 adapted to the use of students in our schools and colleges, 
 and that it will keep before their minds the name and the 
 scientific work of one of the greatest of geologists and one 
 of the noblest of men. 
 
 WILLIAM NORTH RICE. 
 
CONTENTS. 
 
 PAGE 
 
 INTRODUCTION. AIM, SUBJECTS, AND DIVISIONS OF GEOLOGY . 1 
 
 PART I. PHYSIOGRAPHIC GEOLOGY. 
 
 I. GENERAL FEATURES OF THE EARTH'S SURFACE ... 7 
 II. SYSTEM IN THE EARTH'S FEATURES ...... 14 
 
 PART II. STRUCTURAL GEOLOGY. 
 
 I. CONSTITUTION OF ROCKS . 18 
 
 Minerals ,~ 18 
 
 Kinds of Rocks - . 28 
 
 II. ROCK MASSES, OR TERRANES 41 
 
 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 CLASSIFICATION ........... 58 
 
 The Animal Kingdom . . ... . . .59 
 
 The Vegetable Kingdom .... . '. . 86 
 
 GEOGRAPHICAL DISTRIBUTION OF MARINE LIFE . . , . 91 
 
 PART III. DYNAMICAL GEOLOGY. 
 
 I. LIFE . . . ( . . .... . . . . . .97 
 
 1. Formative Work . . . . . 98 
 
 2. Protective and Destructive Effects 109 
 
vili CONTENTS. 
 
 PAGE 
 
 II. CHEMICAL ACTION OF THE AIR AND WATERS .... Ill 
 
 1. Destructive Effects Ill 
 
 2. Formative Effects 116 
 
 III. MECHANICAL EFFECTS OF THE ATMOSPHERE .... 118 
 
 1. Denudation, Transportation, Deposition .... 118 
 
 2. Winds as Transporters of Moisture . . . . . 123 
 
 IV. MECHANICAL EFFECTS OF WATER 124 
 
 1. Fresh Waters . 124 
 
 2. The Ocean 146 
 
 3. Freezing and Frozen Waters . . . . . .157 
 
 Summary. Formation of Sedimentary Strata . . . 165 
 
 V. HEAT . . . . .... . . .167 
 
 1. Sources of Heat 167 
 
 2. Effects of Heat . . . 172 
 
 1. Expansion and Contraction 172 
 
 2. Eruptions of Igneous Rock, and Associated Phe- 
 
 nomena . . . . . . . . . 174 
 
 3. Metamorphism 190 
 
 4. Formation of Veins . . . . . . .196 
 
 VI. CRUSTAL MOVEMENTS ; EVOLUTION OF CONTINENTS AND 
 
 MOUNTAINS ...... ... 203 
 
 Evolution of the Earth's Fundamental Features . . . 206 
 
 Structure of Mountain Ranges 210 
 
 Process of Formation of Mountain Ranges .... 216 
 
 PART IV. HISTORICAL GEOLOGY. 
 
 INTRODUCTION . 223 
 
 I. ARCHAEAN TIME 236 
 
 II. PALEOZOIC TIME 242 
 
 I. Eopaleozoic Section 244 
 
 I. Cambrian Era 244 
 
 II. Lower Silurian Era 252 
 
 Disturbances at the Close of the Lower Silurian Era . 260 
 
CONTENTS. ix 
 
 PAGE 
 
 II. Neopaleozoic Section 263 
 
 I. Upper Silurian Era 263 
 
 II. Devonian Era . . . . . . 275 
 
 III. Carboniferous Era . . . . . . 290 
 
 General Observations on Paleozoic Time .... 316 
 
 Disturbances at the Close of Paleozoic Time . . . 325 
 
 III. MESOZOIC TIME , . . 330 
 
 I. Triassic and Jurassic Eras ...... 332 
 
 Disturbances at the Close of the Jurassic Era . . ' . 362 
 
 II. Cretaceous Era . . 362 
 
 General Observations on Mesozoic Time .... 379 
 
 Disturbances at the Close of Mesozoic Time . . . 383 
 
 IV. CENOZOIC TIME 385 
 
 I. Tertiary Era 386 
 
 II. Quaternary Era 405 
 
 1. Glacial Period . . . . . ... 406 
 
 2. Champlain Period 420 
 
 3. Recent Period 425 
 
 Life of the Quaternary - . 429 
 
 General Observations on Cenozoic Time .... 442 
 
 GENERAL OBSERVATIONS ON GEOLOGICAL HISTORY . . . . 444 
 
 Length of Geological Time 444 
 
 Geographical Progress in North America . .... 445 
 
 Progress of Life 450 
 
 Conclusion 464 
 
GEOLOGY. 
 
 ITS AIM, SUBJECTS, AND DIVISIONS. 
 
 Aim of Geology. Beneath the soil and waters of the 
 earth's surface there is everywhere a basement of rocks. 
 The rocky bluffs forming the sides of many valleys, the 
 ledges about the tops of hills and mountains, and the 
 cliffs along seashores, are portions of this basement ex- 
 posed to view. Geology is the science that studies these 
 rocks, not merely to learn about ore beds, coal, and build- 
 ing materials, but primarily to gather from them facts 
 about the earth's history the history of its rocks, fea- 
 tures, and life. It is an outdoor science, and out of doors 
 are found the best places of instruction for pupils and 
 teacher. 
 
 Subjects of Study. 1. Making of Beds of EocJc. In 
 most of the rocky bluffs and ledges over the country, the 
 rocks lie in successive beds. The beds differ in thickness 
 and in other ways. They may be all sandstone, and show 
 the grains of sand distinctly under a pocket lens. One 
 or more of the beds may contain smoothly worn pebbles, 
 with sand the same material that constitutes a gravel 
 bed ; another may be a shale, so soft and fine-grained that, 
 if ground up and mixed with water, it will make mud 
 suggesting that it might have been formed out of mud. 
 
 The questions arise : How were the pebbles rounded ? 
 How were the mud, sand, and gravel distributed in beds ? 
 Whence the sand, pebbles, and mud? 
 
 1 
 
2 INTRODUCTION. 
 
 At the foot of such a bluff there commonly lie heaps of 
 loose sand and stones derived from the bluff. The rains, 
 frost, and other causes keep wearing its surface, dropping 
 grains, and tumbling down fragments ; and thus the 
 debris is formed. If a stream runs by the base of such a 
 bluff, the water when in rapid flow will wear away and 
 carry off the material, grinding and rounding the fallen 
 fragments. If the bluff stands on a seashore, the waves 
 beating against its exposed front will aid in the work of 
 reducing it to sand, stones, and mud, for distribution by 
 the waters off the shore and upon the beach. 
 
 All over the world the exposed rocks of hills, mountains, 
 and plains are undergoing wear and decay, and becoming 
 reduced to earth and coarser loose material. And, if the 
 whole world is thus engaged, and has always been at this 
 work since rocks were first exposed to the action of the 
 air and waters, there ought to have been produced at 
 all times, through period after period, not only loose 
 material enough for making soil, but also for the forma- 
 tion of vast accumulations of sand beds, gravel beds, mud 
 beds. 
 
 Along the bottom of a broad river valley, either side of 
 the stream, there are beds of loose sand, gravel, and clay, 
 lying in many alternations parallel with the surface. Up 
 or down the valley, evidence may usually be found that 
 the flowing waters are always at work, but especially in 
 flood times, wearing stones to earth, and carrying down 
 stream the ground-up material for deposition over the flats 
 either side ; evidence, therefore, that the rivers have made 
 the beds which border them. 
 
 So again, along seashores, there are great deposits which 
 the waters have made from the sand and pebbles supplied 
 by the battered bluffs and from the sediment which the 
 rivers carry to the ocean. They form wide sand flats off 
 the shores, which are left bare by the retreating tides, and 
 extensive mud beds and sand beds in the deeper waters, 
 and beach deposits above tide level. 
 
INTRODUCTION. 3 
 
 These river-made and sea-made beds are now unhard- 
 ened; but the evidence gathered has made it certain that 
 most of the hard rocks are similar deposits consolidated ; 
 that they were spread out in beds in the same ways in 
 which beds are now formed along or off seashores, in river 
 valleys, and in lakes. Nine tenths of the rocks studied 
 by the geologist are water-made rocks. Nearly all the 
 older water-made rocks are of marine origin, because, in 
 early time, the ocean spread over the continents, leaving 
 only islands to mark their sites. The continental seas 
 were then the great workers; the little lands had only 
 little rivers. 
 
 Again, rocky bluffs often consist in part or wholly of 
 beds of limestone. Limestones are now being made where 
 the seas abound in shells and corals. The process may be 
 studied about the shores of Florida, at the Bahamas, and 
 at Bermuda, as well as about many islands of the Pacific 
 and the East Indies. The process is now going on, as in 
 ancient time. 
 
 In many beds there are alternating ridges and furrows, 
 like the so-called ripple-marks now often formed by the 
 currents in shallow water ; or cracks though now tilled 
 that were opened by the drying sun in an exposed 
 mud flat ; or impressions that were produced by the drops 
 of a fall of rain. Such markings are records as to the 
 origin of the rocks the ripple-marks telling of their for- 
 mation in shallow waters, or as sand flats ; the mud-cracks 
 showing that the rock, when soft mud, was exposed at 
 times to the drying sun above the water's surface ; the 
 raindrop impressions teaching that it rained in ages long 
 past, and that the bed so marked was a mud flat or a bed 
 of fine wet sand, lying, during the storm, uncovered by the 
 water. Thus, among the geological records, there are 
 facts as to the depth of the waters, and meteorological 
 records. 
 
 2. Excavating Work of Waters. Over the earth's sur- 
 face rivers work, not merely at transporting and making 
 
4 INTRODUCTION. 
 
 deposits of sediment, but also at excavating channels over 
 the land. And so they have worked in the past; and to 
 them, in large part, the earth owes its valleys, great and 
 small, the shapes of its ridges, and the manifold details of 
 mountain scenery. Moreover, while doing this excavating 
 work, the waters of the land have gathered much of their 
 material for the making of rocks. 
 
 Part of the work of water, especially in later geologi- 
 cal time, in both transportation and excavation, has been 
 carried on by water in the state of ice, forming glaciers 
 and icebergs. 
 
 3. Fossils; Life. The beds, whether of sand, mud, 
 or gravel, or of limestone, often contain shells, corals, 
 bones, or remains of plants fossils, as they are called, 
 from the Latin word fossilis, signifying dug up. The 
 shells or bones could not have got into the beds, except 
 when the layer containing them was forming. They are 
 like the shells in the mud or sand of existing sea bottoms 
 or sand beaches, and bear evidence of the existence of 
 life, and make known what species were living in the seas 
 when the bed was made. The fossils of the lower and 
 upper beds in the same bluff often differ, showing that, 
 when the later beds were in progress, the old species had 
 gone and new kinds had come in. Through the whole 
 series of the earth's rocks new kinds continue to appear, 
 and the old to disappear, on passing up from one level to 
 another. Thus a history of the life of the globe, from 
 the simplest species of the early rocks to man, has already 
 been deciphered, and each year of further study is adding 
 to its completeness. The history of the earth's life is the 
 grandest subject of geological study. 
 
 But the fossils teach other lessons. As the species of 
 successive periods differed, the kinds found in any rock 
 are evidence as to its age. Again, they are evidence 
 whether rocks are of marine origin or not ; and thus they 
 contribute facts as to the earth's early geography. They 
 are often evidence, also, as to temperature or climate ; for, 
 
INTRODUCTION. 5 
 
 as now, some species have required a warm, and others a 
 cool temperature. 
 
 4. Mountain-making. Rocks over large areas in 
 many regions are now upturned and lifted into moun- 
 tain ranges hundreds or thousands of miles long. The 
 rocks show by their position that, in the mountain-making, 
 they were pushed out of their original positions by some 
 subterranean agency. The origin of mountains and the 
 times of such upturnings are subjects for geological 
 study. 
 
 The upturned rocks have sometimes become crystallized, 
 or converted into marble, granite, mica schist, and the 
 like ; and such transformations furnish another subject of 
 study. 
 
 5. Fractures; Veins; Volcanoes; Geysers. Again, 
 in many regions the earth's crust has been deeply frac- 
 tured. Sometimes mineral veins have formed in the fis- 
 sures. Often melted rock, from unknown depths, has 
 come to the surface and spread widely over it, thus adding 
 fire-made, or igneous, rocks to those which are water-made. 
 Occasionally volcanoes have formed over the larger fis- 
 sures ; and in a few places geyser regions, like that of the 
 Yellowstone Park, have been left as residual effects of 
 volcanic action. 
 
 From the above explanations it is obvious that several 
 great subjects are treated under Geology. 
 
 (1) The characteristics of the rocks of the globe. 
 
 (2) The historical succession in the formation of the 
 rocks. 
 
 (3) The origin of the rocks. 
 
 (4) The origin of rivers, lakes, and seas. 
 
 (5) The origin of mountains, igneous eruptions, vol- 
 canoes, and of fractures in the earth's crust and changes 
 of level. 
 
 (6) The history of continent-making, and the origin of 
 the system in the arrangement of the earth's coast lines, 
 its mountain chains, and its island ranges. 
 
6 INTRODUCTION. 
 
 (7) The history of the earth's climates. 
 
 (8) The history of life. 
 
 In the study of these subjects, Geology assumes with 
 good reason that the physical forces now in action have 
 been the same, and under the same laws, through all past 
 time. Whether those of the waters, the winds, heat, co- 
 hesion, or of whatever kind, these forces have produced 
 results through the ages like those observed about us, 
 with little difference except that some forces must have 
 acted with greater, and others with less, intensity in early 
 geological time. Existing nature, therefore, affords the 
 means of interpreting the geological records. 
 
 Divisions of the Science. The divisions of the science 
 here adopted are .the following : 
 
 1. Physiographic Geology. Treating of the earth's 
 physical features ; that is, of the system in the exterior 
 features of the earth. This department properly includes 
 also the system of movements in the water and atmos- 
 phere, and the system in the earth's climates, and in the 
 other physical agencies or conditions of the sphere. 
 
 2. Structural Geology. Treating of the rocks of the 
 globe, their kinds, structure, and arrangement in beds or 
 otherwise. 
 
 3. Dynamical Geology. Treating of the causes, or the 
 methods, by which all the earth's changes were brought 
 about, including the making of continents, of ocean 
 basins, of rocks, of mountains, of valleys ; the causes of 
 all variations in climate, and of all changes in the earth's 
 features, and of the system in the progress of life. The 
 word dynamical is from the Greek Svvafus, power or force. 
 
 4. Historical Geology. Treating of the successive 
 events in the history of the rocks, and of the continents, 
 oceans, mountains, valleys, coast lines, climates, and life. 
 
PAET L PHYSIOGRAPHIC GEOLOGY. 
 
 I. GENERAL FEATURES OF THE EARTH'S 
 SURFACE. 
 
 Size and Form. The earth has a circumference of 
 about 25,000 (24,899) miles. Its form is that of a sphere 
 flattened at the poles, the equatorial diameter (7926 miles) 
 being about 26J miles greater than the polar diameter. 
 
 Regions of Depression and Elevation. About eight 
 elevenths of the earth's surface, or 144,000,000 square 
 miles, is depressed below the rest, and occupied by salt 
 water. This sunken part of the crust is called the oceanic 
 basin, and the large areas of land are called the continents 
 or continental plateaus. The area of the continents and 
 islands is about 52,745,000 square miles. 
 
 Arrangement of Oceans and Continents. Nearly three 
 fourths of the area of the continental plateaus is situ- 
 ated in the northern hemisphere, and very nearly three 
 fifths of the oceanic basin in the southern hemisphere. 
 The dry land, as shown in the map, Fig. 1, may be 
 said to be grouped about the North Pole, and to stretch 
 southward in two masses, an Oriental, including Eu- 
 rope, Asia, Africa, and Australasia, and an Occidental, 
 including North and South America. The ocean is 
 gathered in a similar manner about the South Pole, and 
 extends northward in two broad areas separating the 
 Occident and Orient, namely, the Atlantic and Pacific 
 Oceans, and also in a third, the Indian Ocean, separating 
 
 7 
 
8 
 
 PHYSIOGRAPHIC GEOLOGY. 
 
 the southern prolongations of the Orient, namely, Africa 
 and Australasia. The Orient is made, by this arrange- 
 ment, to have two southern prolongations, while the Occi- 
 dent, or America, has but one. This double feature of 
 the Orient accords with its great breadth ; for it averages 
 6000 miles from east to west, which is far more than 
 twice the mean breadth of the Occident (2200 miles). 
 The inequality of the two continental masses has its 
 parallel in the inequality of the Pacific and Atlantic 
 oceans ; for the former (6000 miles broad) is more than 
 double the average breadth of the latter (2800 miles). 
 
 FIG. 1. 
 
 Land hemisphere and water hemisphere. 
 
 The northern portion of the Orient, or Europe and Asia 
 combined, makes one continental area, Eurasia; its gen- 
 eral course is east and west. The northern portion of the 
 Occident, North America, is elongated from north to south. 
 
 Depth of Oceans and Height of Continents. The mean 
 depth of the oceanic depression is about 14,000 feet ; 
 and the mean height of the land (according to Murray) 
 2252 feet. The greatest depth reached by soundings 
 (south of the Friendly Islands) is 30,930 feet ; the great- 
 est height on the land (Mt. Everest of the Himalayas) is 
 29,000 feet ; hence the interval between the extremes of 
 
THE EARTH'S FEATURES. 9 
 
 altitude and depression is over eleven miles. If the con- 
 tinental plateaus and the floor of the ocean were graded 
 to a common level, the ocean would still have a depth of 
 about 10,000 feet. The mean height of Europe is (accord- 
 ing to Murray) 939 feet ; Asia, 3189 feet ; Africa, 2021 
 feet ; Australia, 805 feet ; North America, 1888 feet ; 
 South America, 2078 feet. The mean depths of the great 
 oceans are : of the North Atlantic, 15,000 feet ; North 
 Pacific, 16,000 feet; South Atlantic and South Pacific 
 (and probably the Indian Ocean), about 13,000 feet. 
 
 The Form of the Ocean* s Bed. Fig. 2 shows the gen- 
 eral form of the ocean's bed beneath the larger oceans. 
 From north to south, along the middle of the Atlantic, 
 there is a wide zigzag ridge or plateau, conforming nearly 
 in trend to the American coast. It lies at a depth of 6000 
 to 12,000 feet, while on either side the bottom slopes away 
 to depths mostly between 15,000 and 20,000 feet. In the 
 area of 4000 fathoms and over, situated north of the 
 island of Puerto Rico, the United States Coast Survey 
 steamer Blake found, in 1883, a depth of 27,366 feet. 
 This greatest depth, and large areas of deep water, exist 
 in the western part of the ocean. In the Pacific Ocean, a 
 shallow area extends, with little interruption, from the 
 Malay Archipelago southeastward beyond the Paumotu 
 Islands, and thence northeastward to the Isthmus of 
 Panama, southeastward to Patagonia, and southward to 
 the Antarctic. The deepest parts of this ocean also are 
 in its western half. One deep area is east of Japan; another, 
 south of the Ladrones ; others, near the Friendly Islands. 
 Northward in the northern hemisphere the ocean shallows 
 rapidly. The depth in Bering Strait is not over 150 feet ; 
 and between Great Britain and Iceland it does not exceed 
 6000 feet, and is mostly under 3000 feet. 
 
 The ocean's bottom has no steep ridges like those of 
 ordinary mountain scenery. But broad elevations exist 
 in some parts, as found in the soundings of the Tuscarora 
 between the Hawaiian Islands and Japan. Besides these, 
 
Fi 
 
 160 
 
 190 
 
 Longitude 120 East 160 
 
 120 West 
 
 0-100 fathoms 
 
 100-2000 fathoms JJ 2000- 
 
 BATHYMETKLC CHJ? 
 
fathoms | 3000-4000 fathoms |H 4000 fathoms and over 
 
 ,T OF THE OCEANS 
 
12 PHYSIOGKAPHIC GEOLOGY. 
 
 there are many mountain ranges rising somewhat abruptly 
 from the depths, having the islands of the ocean as their 
 summits, which rival in length those of the continents. 
 The Hawaiian range, if the coral islands in the line 
 of the volcanic islands are included (see Fig. 2), has a 
 length of 2000 miles ; and it rises steeply from depths of 
 15,000 to 18,000 feet. The mountains of Hawaii have a 
 height above the ocean of nearly 14,000 feet, and a depth 
 of 17,000 feet was found but 50 miles south of the island, 
 thus making the whole height nearly 31,000 feet. The 
 islands of the tropical Pacific make together an island 
 chain about 5000 miles long ; and they are the tops of a 
 mountain chain of this great length. 
 
 True Outline of the Oceanic Depression. Along the 
 oceanic borders, the sea is often, for a long distance out, 
 quite shallow, because the continents continue on under 
 water with a nearly level surface ; then comes, usually 
 at a depth of about 100 fathoms, or 600 feet, a rather 
 sudden slope to the deep bed of the ocean. This is the 
 case off the eastern coast of the United States, east and 
 south of New England. Off New Jersey, as is shown by 
 Fig. 3, the deep water begins along a line about 80 miles 
 from the shore ; off Virginia this line is 50 to 60 miles 
 at sea ; and thus it gradually approaches the coast to the 
 southward: while to the northward it continues 80 to 100 
 miles off from the New England coast, and passes far out- 
 side of Nova Scotia and Newfoundland (see Fig. 2). The 
 slope of the bottom, for the 80 miles off New Jersey, is 
 only 1 foot in 700 feet. The true boundary between 
 the continental plateau and the oceanic depression is the 
 commencement of the abrupt slope. The same abrupt 
 slope near the 100-fathom line exists in the Gulf of 
 Mexico. The British Islands are situated on a submerged 
 portion of the European continent, and are essentially a 
 part of that continent, the limit of the oceanic basin 
 the 100-fathom line being 50 to 100 miles outside of 
 Scotland and Ireland, and extending south around the 
 
THE EARTH S FEATURES. 
 
 13 
 
 Bay of Biscay. West of the English Channel the depth 
 increases, in a distance of only ten miles, from 100 fathoms 
 to 2000. New Guinea is in a similar way proved to be a 
 part of Australia. Such facts occur on most coasts ; and 
 they teach that the oceanic depression is generally separated 
 from the continental plateaus by a well-defined outline. 
 
 FIG. 3. 
 
 Bathymetric chart of region south of Long Island. 
 
 Surfaces of the Continents. The surface of a conti- 
 nent comprises (1) plains or lowlands, (2) plateaus or 
 table-lands, and (3) mountain ridges. The mountain ridges 
 may rise either from the lowlands or the plateaus. The 
 plateaus are large areas of approximately level surface at 
 an altitude of a thousand feet or more above the sea. 
 They are often parts of the great mountain chains, lying 
 
14 PHYSIOGRAPHIC GEOLOGY. 
 
 between the ridges, or forming the mountain mass out 
 of which the ridges rise. For example, the regions of 
 northern and southern New York are plateaus (the 
 former averaging 1500 feet in height, the latter 2000 feet) 
 situated on the western borders of the Appalachian chain; 
 and the same is true of the Cumberland table-land in 
 Tennessee. Between the Sierra Nevada and the Wasatch, 
 there is a plateau of vast extent, called the Great Basin, 
 having the Great Salt Lake in its northeastern portion ; 
 its height above the sea averages 4000 feet; the Hum- 
 boldt Mountains and other high ranges rise out of it. It 
 continues northward into British America and southward 
 into Mexico. The eastern part of New Mexico, with the 
 western part of Texas, is a plateau of about the same ele- 
 vation, called the Llano Estacado. The Desert of Gobi, 
 between the Altai and the Kuen-Lun range, is a desert 
 plateau about 4000 feet high, while the plateau of Tibet, 
 between the Kuen-Lun range and the Himalayas, is 
 11,500 to 13,000 feet above the sea. Persia and Armenia 
 constitute another plateau. These examples are sufficient 
 to explain the use of the term. 
 
 II. SYSTEM IN THE EARTH'S FEATURES. 
 
 General Relief of the Continents. The continents are 
 constructed on a common model : they have high bor- 
 ders and a low center, and are, accordingly, basin-shaped. 
 North America has the Appalachians on the eastern border, 
 the Cordillera on the west, and between these the low 
 Mississippi basin. Fig. 4 illustrates this form of the con- 
 tinent. In the section, b represents the Rocky Mountain 
 chain on the west, with its lines of ridges at summit ; a, 
 the Sierra chain (including the Sierra Nevada and Cascade 
 Range), near the Pacific coast ; <?, the Mississippi basin ; 
 c?, the Appalachian chain on the east. 
 
 South America, in a similar manner, has the Andes on 
 the west, the Brazilian Mountains on the, east, and other 
 
THE EARTH'S FEATURES. 
 
 15 
 
 heights along the north, with the low region of the Ama- 
 zon and La Plata making up the larger part of the great 
 interior. Fig. 5 is a transverse section from west to 
 east, showing the Andes at a, and the Brazilian Moun- 
 tains at b. In these sections the height as compared with 
 the breadth is necessarily much exaggerated. 
 
 In the Orient there are mountains on the Pacific side, 
 others on the Atlantic ; and, again, the Himalayas, on the 
 south, face the Indian Ocean, and the Altai Mountains 
 
 FIG. 4. 
 
 Profile of North America. 
 
 face the Arctic seas. Between the Himalayas (or rather 
 the Kuen-Lun Mountains, which are just north) and the 
 Altai, lies the plateau of Gobi, which is low compared with 
 the inclosing mountains ; and farther west there are the 
 lowlands of the Caspian and Aral, the Caspian lying even 
 below the level of the ocean. The Urals divide the 6000 
 miles of breadth into two parts, and so give Europe some 
 
 FIG. 5. 
 
 Profile of South America. 
 
 title to its designation as a separate continent. West 
 of their meridian there are again extensive lowlands over 
 middle and southern European Russia. In Africa there 
 are mountains on the eastern border, and on the western 
 border south of Guinea ; there are also the Atlas Moun- 
 tains along the Mediterranean, and the Kong Mountains 
 along the Guinea coast ; and the interior is relatively low, 
 although mostly 1000 to 2000 feet in elevation. In Aus- 
 tralia, also, there are highlands on the eastern and western 
 borders, and the interior is low. All the continents are, 
 therefore, constructed on the basin-like model. 
 
16 PHYSIOGRAPHIC GEOLOGY. 
 
 The Greater Mountains border the Greater Ocean. 
 There is a second great truth with regard to the conti- 
 nental reliefs : the highest border faces the largest ocean. 
 Each of the continents sustains the truth announced. 
 North America has its great mountains, the Cordillera, on 
 the side of the great ocean, the Pacific ; and its small 
 mountains, the Appalachians, on the side of the small 
 ocean. South America, also, has its highest border on the 
 west. The Orient has high ranges of mountains on the east, 
 or the Pacific side, and lower ranges, as those of Norway 
 and other parts of Europe, on the west ; and the Hima- 
 layas face the great Indian Ocean, while the smaller Altai 
 range faces the small Northern Ocean. In Africa, the 
 mountains on the side of the Indian Ocean are higher 
 than those on that of the Atlantic. In Australia the 
 highest border is on the Pacific side ; for the South Pacific 
 fronting east Australia, is greater than the Indian Ocean 
 fronting west Australia. Hence the basin-like shape be- 
 fore illustrated is that of a basin with one border much 
 higher than the other ; and with the highest border on 
 the side of the largest ocean. 
 
 The features described have a vast influence in adapting 
 the continents for man. America has its highest border 
 in the far west, with all its great plains and great rivers 
 inclined toward the Atlantic; for, through the Gulf of 
 Mexico, the whole interior, as well as the eastern border, 
 has its natural outlet eastward. The Orient, instead of 
 rising into Himalayas on the Atlantic border, has its great 
 heights in the remote east ; and its vast plains, even those 
 of Central Asia, have their natural outlet westward, over 
 Europe and through the Mediterranean, or toward the 
 same Atlantic Ocean. Thus, as Professor Guyot has said, 
 the vast regions of the world, which are best fitted for 
 man, by their climate and productions, are combined into 
 one great arena for the progress of civilization. 
 
PART II. STRUCTURAL GEOLOGY. 
 
 THE term rock, in geology, is applied to all natural 
 formations of mineral material, whether consolidated, like 
 sandstones and slates, or unconsolidated, like sand and 
 gravel. All sandstones were once beds of loose sand ; 
 and there is every shade of gradation, from the hardest 
 sandstone to the softest sand bed ; so that it is impossible 
 to draw a line between the consolidated and the unconsoli- 
 dated. Geology does not attempt to draw the line, re- 
 garding consolidation as an accident in the history of the 
 earth's beds or deposits an accident that probably hap- 
 pened to only a small part of the sand beds and mud 
 beds that have existed, and yet to enough of them in 
 each period for the preservation of the wonderfully varied 
 records that are the materials of geological science. 
 
 Rocks may be studied simply as rocks, that is, with 
 reference to their composition, and collections may be 
 made containing specimens of their various kinds. Again, 
 they may be studied as rock masses spread out over the 
 earth and forming the earth's crust ; and, with this in 
 view, the condition, structure, and arrangement of the 
 great rock masses, called terranes, would come up for con- 
 sideration. The two subjects under Structural Geology 
 are, therefore : 
 
 1. THE CONSTITUTION OF ROCKS. 
 
 2. THE CONDITION, STRUCTURE, AND ARRANGEMENT 
 
 OF ROCK MASSES, OR TERRANES. 
 
 17 
 
18 STRUCTURAL GEOLOGY. 
 
 I. CONSTITUTION OF ROCKS. 
 Minerals. 
 
 Rocks are generally heterogeneous, being composed of 
 grains or particles of different materials. The separate 
 grains or particles, which are homogeneous or nearly 
 so, having a definite chemical constitution, are called 
 minerals. The minerals which constitute the principal 
 ingredients of the common rocks are included in three 
 groups : 
 
 1. SILICA, or silicon dioxide. 
 
 2. SILICATES, or compounds of silicon and oxygen with 
 other elements. 
 
 3. CARBONATES, or compounds of carbon and oxygen 
 with other elements. 
 
 Besides these, three other groups of minerals should 
 here be mentioned, as sometimes constituting rock masses, 
 and including materials of special importance : 
 
 4. CARBON AND ITS COMPOUNDS (other than carbo- 
 nates). 
 
 5. CHLORIDES. 
 
 6. IRON ORES. 
 
 1. SILICA. 
 
 Silica, or silicon dioxide (SiO 2 ), in its most common 
 molecular arrangement, constitutes the mineral quartz, 
 which far exceeds all other minerals in 
 abundance. It is one of the hardest of 
 i\ common minerals ; does not melt before 
 the blowpipe, and does not dissolve in 
 water, or in the ordinary acids. 
 
 It is often seen in crystals like Figs. 
 6, 7, though generally occurring in mas- 
 sive forms, or in grains or pebbles. It is distinguished 
 ordinarily by its glassy aspect, whitish or grayish color, 
 
CONSTITUTION OF ROCKS. 19 
 
 and an absence of all tendency to break with a bright even 
 surface of fracture (a quality possessed by many crystals, 
 called cleavage). Although usually nearly colorless or 
 white, it is often reddish, yellowish, brownish (especially 
 smoky brown), and even black; and the luster is some- 
 times very dull, as in chalcedony, flint, and jasper. The 
 sands and pebbles of the seashores and gravel beds are 
 mostly quartz ; because quartz resists the wearing action 
 of waters better than any other common mineral. For 
 the same reason, most sandstones and conglomerates con- 
 sist mainly of quartz. 
 
 The hardness (on account of which it scratches glass 
 easily), infusibility, insolubility in acids, and absence of 
 cleavage, are the characters that serve to distinguish 
 quartz from the other ingredients of rocks. 
 
 But, though quartz is so refractory, it easily fuses into 
 glass when mixed with potash, soda, lime, or an oxide of 
 iron. Ordinary glass is made by mixing powdered quartz 
 with soda and sometimes lime, and subjecting the mixture 
 to a high heat. 
 
 Silica exists also in a different molecular state, in which 
 it is called opal. Opal, a beautiful gem in some of its 
 varieties, does not occur crystallized, has a little less hard- 
 ness than quartz, and is more easily soluble in a heated 
 alkaline solution. The silica secreted by some minute 
 plants, as Diatoms, and by Sponges and Radiolarians 
 among animals, is opal ; and in many places large beds of 
 the minute shells and spicules are formed by the growth 
 and death of the above-mentioned organisms (see page 
 106). 
 
 2. SILICATES. 
 
 Most of the common rock-making minerals are silicates ; 
 that is, combinations of silicon and oxygen with certain 
 basic elements, as aluminium, magnesium, calcium, potas- 
 sium, sodium, iron, and a few otliers. 
 
 The silicates which contain no metal except aluminium 
 
20 STRUCTURAL GEOLOGY. 
 
 are infusible as well as very hard. But those which con- 
 tain one or more of the other metals mentioned are with 
 few exceptions fusible. 
 
 The following are the most common of these silicates : 
 
 1. Feldspar. The feldspars are silicates of aluminium 
 with one or more of the metals potassium, sodium, and 
 calcium. They are hard enough to scratch glass, but less 
 hard than quartz. They break easily, or have cleavage, in 
 two directions, and the two lustrous cleavage surfaces meet 
 nearly or quite at a right angle. The color is usually 
 white or flesh-red, rarely dark brown or greenish. The 
 specific gravity is 2.4 to 2.7. 
 
 The most common kind is a potash feldspar, affording 
 on analysis silica, alumina, and potash, and is called ortho- 
 clase ; another, named albite, from its usual white color, is 
 a soda feldspar ; others, as oligoclase, andesine, and labra- 
 dorite, are soda-lime feldspars. 
 
 2. Mica. Mica is a silicate of aluminium and potas- 
 sium, but some kinds of mica contain also magnesium and 
 iron. Mica cleaves easily into tough leaves, thinner than 
 the thinnest paper, and somewhat elastic ; it fuses with 
 great difficulty; hence its common use in lanterns and doors 
 of stoves. Its most common colors are whitish, brownish, 
 and black. The most common kind of mica has a light 
 color, and is called muscovite, from its old name, Muscovy 
 glass ; another, usually black in color, is called biotite. 
 Some micas are hydrous ; that is, they contain water ; and 
 these hydromicas, as they are called, are pearly in luster, 
 feel a little soapy, and are sometimes mistaken for talc. 
 
 The minerals, quartz, feldspar, and mica, are the con- 
 stituents of granite ; and they may be distinguished in it 
 as follows : the grains of quartz, by their glassy luster, 
 gray color, and want of cleavage ; the grains of feldspar, 
 by their shining cleavage, as is well seen when a surface 
 of fracture is held up to the sunlight ; the grains of mica, 
 by their very easy cleavage by means of the point of a 
 knife blade into thin elastic leaves. 
 
CONSTITUTION OF KOCKS. 21 
 
 3. Hornblende and Pyroxene. Hornblende and pyrox- 
 ene are silicates of magnesium, calcium, and iron, alumin- 
 ium not being an essential constituent, and, when present, 
 always in small amount. The most common variety of each 
 of these minerals, occurring as a principal constituent of 
 rocks, is black, or greenish black, and 2.9 to 3.5 in specific 
 gravity ; but white and light green varieties also are com- 
 mon. They are somewhat inferior to feldspar in hard- 
 ness; unlike mica, they are brittle. The crystals or 
 crystalline grains have two equally lustrous cleavages. 
 In hornblende, the angle between the two is about 124 ; 
 in pyroxene, about 87. Hornblende is often in long, 
 slender crystallizations, and asbestus is a very fine fibrous 
 variety of it, sometimes like wool. Both hornblende and 
 pyroxene make hard and tough rocks. Pyroxene is a 
 constituent of some of the most common igneous rocks. 
 
 4. Chrysolite. A silicate of magnesium with some 
 iron. It is generally of an olive-green color, and occurs 
 in many igneous rocks in disseminated grains or crystals, 
 looking much like bits of green bottle glass. 
 
 5. Chlorite. A silicate of magnesium, aluminium, and 
 iron, containing generally 12 per cent or more of water. 
 It resembles black mica in its crystallization and cleavage ; 
 but its folia are not elastic, its color is usually dark green, 
 and it feels a little greasy. It is often finely granular. 
 
 6. Talc ; Serpentine. Talc and serpentine are hydrous 
 silicates of magnesium ; that is, silicates containing water. 
 They both have a greasy feel especially talc. Talc is 
 very soft, so soft that it does not feel gritty to the teeth. 
 It is often in foliated plates or masses like mica ; but the 
 folia, or leaves, though separating rather easily, and flex- 
 ible, are not elastic. The usual color is pale green. 
 Soapstone, or steatite, is a massive variety of talc, of 
 whitish, grayish, or greenish color. 
 
 Serpentine contains much water (about 14 per cent). 
 It is usually a dark green massive mineral or rock, of 
 smooth fracture, and soft enough to be cut with a knife. 
 
STRUCTURAL GEOLOGY. 
 
 FIG. 8. 
 
 7. The following minerals occur distributed in crystals 
 through many crystalline rocks, though rarely forming 
 the principal constituents of rocks : 
 
 Garnet. The most common varieties are silicates of 
 aluminium, with iron, calcium, or magnesium. They occur 
 often in dark red, brownish, or black crystals of 12 or 24 
 sides (dodecahedrons or trapezohedrons). The first of 
 
 these forms is represented in Fig. 
 8, showing garnets distributed 
 through a mica schist. 
 
 Tourmaline contains, besides sili- 
 con and oxygen, aluminium, mag- 
 nesium, iron, boron, and fluorine. 
 It occurs generally (Fig. 9) in 
 crystals which are prisms of 3, 6, 
 9, or 12 sides ; the most common color is black, but it is 
 sometimes blue-black, brown, green, or red. 
 
 Andalusite is simply an aluminium silicate, and hence is 
 infusible. It is found in imbedded crystals in clay slate, 
 and sometimes in mica schist ; the form is nearly a square 
 prism. The interior of the crystals is very frequently 
 
 Garnet. 
 
 FIG. 9. 
 
 FIG. 10. 
 
 Tourmaline. 
 
 Andalusite. 
 
 black or grayish black at the center and angles (Fig. 10), 
 while the rest is nearly white ; and this variety is called 
 macle, or chiastolite. 
 
 Cyanite has the same composition as the preceding, and 
 like it is infusible. It usually occurs in mica schist or 
 gneiss, in thin, bladelike, pale blue crystals. 
 
CONSTITUTION OF HOCKS. 
 
 23 
 
 Staurolite. Related to the last two minerals, and in- 
 fusible ; but it contains some iron. Its crystals are stout 
 prisms of about 129, of brown or brownish black color ; 
 they often have the form of a cross, whence the name, from 
 o-ray/xfr, a cross. 
 
 3. CARBONATES. 
 
 1. Calcite, or Calcium carbonate (CaCO 3 ). The ma- 
 terial of limestone and marble. It crystallizes in many 
 forms, a few of which are represented in Figs. 11 and 12. 
 It cleaves easily in three directions with bright surfaces, 
 as may be seen on examining even the grains of a fine 
 white marble. Its colors are various. It is so soft as 
 to be easily scratched with a knife ; dissolves in diluted 
 
 Calcite. 
 
 Calcite. 
 
 acid (hydrochloric) with effervescence, that is, with an 
 escape of carbonic acid gas (CO 2 ); and, when heated (as 
 in a limekiln or before the blowpipe), it burns to quick- 
 lime without melting. By its effervescence with acids it 
 differs from all the minerals before mentioned. 
 
 2. Dolomite, Calcium-magnesium carbonate (CaMgC 2 O 6 ), 
 differs from calcite in containing magnesium in place of 
 part of the calcium. Very much of limestone is magnesian 
 limestone. It closely resembles ordinary limestone, but 
 may be distinguished by its effervescing scarcely at all 
 with acid unless heat be applied. 
 
 For iron carbonate (siderite) see page 27. 
 
24 STRUCTURAL GEOLOGY. 
 
 4. CARBON AND ITS COMPOUNDS (OTHER THAN CARBONATES). 
 
 Carbon occurs pure among minerals only in diamond 
 and graphite. It is the chief element in mineral coal, but 
 is combined in it with more or less of hydrogen and 
 oxygen, and also some nitrogen. Charcoal, the carlo of 
 the Romans, is nearly all carbon. 
 
 Carbon occurs in the atmosphere in the form of carbon 
 dioxide, or carbonic acid (CO 2 ). This gas constitutes 
 about 3 out of 10,000 parts of the atmosphere, and is 
 carried from tha atmosphere to the earth by the rains. It 
 is formed in the combustion of wood, -the combustion con- 
 sisting in the combination of oxj^gen with the constituents 
 of the wood. It is also given out in the respiration of 
 animals, the processes of life in animals being carried for- 
 ward through a sort of combustion, or a similar combina- 
 tion of oxygen with the materials of the tissues. 
 
 Aside from its occurrence in the carbonates, the chief 
 form in which carbon occurs as a rock material is that of 
 mineral coal. 
 
 1. Diamond and Graphite. These are both pure carbon, 
 but in different molecular states ; the former, the hardest 
 of minerals, crystallizing in octahedral and related forms ; 
 the latter, one of the softest, crystallizing in hexagonal 
 plates, with nearly the easy cleavage of mica, and with 
 metallic luster. Graphite is also called plumbago and 
 black lead, and is the material of the misnamed lead 
 pencils. It occurs in crystalline rocks in scales and 
 masses, and is ground up and subjected to pressure to 
 prepare it for making pencils. 
 
 2. Mineral Coal. Mineral coal is not a true mineral, 
 being not a definite chemical compound, but a mixture of 
 various compounds of carbon with hydrogen and oxygen. 
 It constitutes beds in various rock formations, and has 
 been formed from wood or some kind of vegetable mate- 
 rial. There are three prominent kinds, differing in the 
 amount of oxygen and hydrogen that is present with the 
 
CONSTITUTION OF ROCKS. 25 
 
 chief ingredient carbon, and consequently in the amount 
 of inflammable gas given out in burning. This gas con- 
 sists chiefly of carbon and hydrogen, and is essentially the 
 same as the gas used in illumination. 
 
 1. Anthracite contains generally over 85 per cent of 
 carbon. It yields little that is volatile, and burns with a 
 feeble blue flame. 
 
 2. Bituminous coal has less hardness and luster than 
 anthracite, contains usually 65 to 85 per cent of carbon, 
 and gives out on heating 20 to 50 per cent of volatile 
 matter. It therefore burns with a bright yellow flame. 
 When heated, it will yield illuminating gas, and also 
 mineral oil. Cannel coal is a compact bituminous coal 
 having a feeble luster ; it often yields 40 to 50 per cent 
 of volatile matter, and is an available source of mineral 
 oil. Bituminous coal is called caking coal when it softens 
 in the fire and cakes at the surface, so that a fire made of 
 it requires poking to make it burn freely ; non-caking 
 kinds have not this quality, and hence are preferable for 
 fuel. 
 
 3. Brown coal differs from bituminous coal in yield- 
 ing a brownish black powder, and in containing much 
 more oxygen (20 to 30 per cent or more). The min- 
 eral coal from rocks more recent than the Carboniferous 
 formation is often improperly called brown coal, even 
 when it is good bituminous coal, without a brownish 
 color to the powder. The name lignite is sometimes also 
 applied to it ; but true lignite is coal that retains the 
 fibrous texture of the original wood. 
 
 3. Mineral Oil. This consists of liquid hydrocarbons, 
 and is chemically related to illuminating gas. It was 
 formed out of animal or vegetable materials. Illuminat- 
 ing gas is often given off in great quantities from the 
 wells or sources yielding mineral oil, and in some villages, 
 in oil regions, the houses are heated and lighted by it. 
 Many black shales yield mineral oil when heated. They 
 do not contain the oil, but contain other hydrocarbons 
 
26 STRUCTURAL GEOLOGY. 
 
 (not yet satisfactorily investigated) which yield the oil 
 on heating. Mineral oil, on long exposure to the air, 
 combines with oxygen, and may ultimately become a 
 black fusible bitumen, or a coal-like substance having 
 little or no fusibility. 
 
 5. CHLORIDES. 
 
 The only chloride forming rock masses is 
 Common Salt, or Rock Salt. It is sodium chloride 
 (NaCl). It is easily distinguished by its taste. It 
 constitutes beds, more or less impure, in strata of various 
 ages from the Silurian to recent time ; which is accounted 
 for by the fact that the universal ocean is an abundant 
 source of salt, and only evaporation is required to deposit 
 it. Silurian rock salt occurs in western New York, and 
 Upper Canada ; and a great deposit, probably of Creta- 
 ceous age, nearly 40 feet thick and remarkably pure, 
 occurs at Petit Anse, Louisiana, near the Gulf of Mexico. 
 The saline constituents of the ocean's waters constitute 
 about 3.53 parts in 100; of which about three fourths is 
 common salt, the rest being chiefly magnesium chloride, 
 magnesium sulphate, calcium sulphate, or gypsum, potas- 
 sium sulphate, magnesium bromide, and calcium carbo- 
 nate, with traces also of other ingredients. 
 
 6. IRON ORES. 
 
 Iron ores are widely distributed in the rocks, and some 
 of them form thick beds. Unlike the minerals mentioned 
 above, they have a specific gravity above 3.5. The most 
 important are three oxides, three sulphides, and a car- 
 bonate. 
 
 The sulphides, however, are never used in the manu- 
 facture of iron, since no process is known by which iron 
 can be economically separated from sulphur. 
 
 1. Hematite, or ferric oxide (Fe 2 O 3 ). It yields a 
 red powder, whence its name, given it by the old Greeks, 
 from aljjia, blood. Its crystals have usually an iron-black 
 
CONSTITUTION OF ROCKS. 27 
 
 color, and high luster ; but it is deep red when earthy or 
 impure. It is the source of the color in red sandstones 
 and some other red rocks. 
 
 2. Limonite, or hydrous ferric oxide, includes two equiv- 
 alents of Fe 2 O 3 united with three equivalents of water. 
 It varies in color from black to brown and yellow, but 
 yields always a brownish yellow powder. While red ocher 
 of painters is impure hematite, yellow ocher is impure 
 limonite. Limonite is the coloring ingredient in a large 
 part of brown and brownish yellow rocks and clays. The 
 water present goes off on heating, and hence the mineral, 
 and all rocks colored by it, when heated, turn red. It 
 is formed from the oxidation and hydration of various 
 iron-bearing minerals (page 111), and often makes de- 
 posits in marshes (page 116). 
 
 3. Magnetite. Magnetite has an iron -black color, like 
 hematite ; but, unlike that ore, it is attracted strongly by 
 a magnet, and yields a black powder. It consists of three 
 atoms of iron and four of oxygen (Fe 3 O 4 ). It is common 
 in grains in many rocks (not in limestones), and among 
 the sands of seashores and soils ; and, like hematite, con- 
 stitutes great beds among the older rocks. 
 
 Ferrous oxide (FeO) never occurs as a mineral. 
 
 4. Pyrite ; Marcasite ; Pyrrhotite. Pyrite is an iron 
 sulphide (FeS 2 ), of a brass-yellow color, and nearly as 
 hard as quartz. It will strike fire with steel, and was 
 named by the Greeks from TTU/J, fire. It is common in 
 rocks, in massive forms, crystals (often cubes), and grains. 
 Marcasite has the same composition as pyrite, but a dif- 
 ferent crystalline form. Pyrrhotite is the name of another 
 common iron sulphide, containing proportionally less sul- 
 phur (Fe n S 12 ), having the color of bronze, so soft as to 
 be easily scratched with the point of a knife, and somewhat 
 strongly attracted by a magnet. 
 
 5. Siderite. This mineral, called also iron carbonate 
 (FeCO 3 ), and spathic iron, has, when crystallized, approxi- 
 mately the cleavage and form of calcite. The color is 
 
28 STRUCTUKAL GEOLOGY. 
 
 light gray, but changes readily to brown on exposure 
 (by alteration of more or less of the material to limonite). 
 It is much heavier than calcite, its specific gravity being 
 3.7 to 3.9. It effervesces, like dolomite, in heated dilute 
 hydrochloric acid. 
 
 The ironstone, or clay ironstone, of coal regions, used 
 as an ore of iron, is generally siderite ; that of other than 
 coal regions is commonly hematite or Ihnonite. 
 
 Kinds of Rocks. 
 
 PRELIMINARY DEFINITIONS. 
 
 Fragmental and Crystalline Rocks. The minerals of 
 which a rock consists may be either (1) in broken or worn 
 grains or pebbles, like those of sand or mud or a bed 
 of gravel ; or (2) in crystalline grains, in which case they 
 were formed where they now are at the time of the 
 crystallization of the rock. Such crystalline grains are 
 angular, as may be seen on a surface of fracture, and, in 
 the case of most minerals excepting quartz, show surfaces 
 of cleavage. Common white marble and granite are good 
 examples of rocks having a crystalline texture ; and, 
 among products of art, such a texture is shown in loaf 
 sugar and steel. 
 
 The rocks of the first kind, consisting of fragments of 
 other rocks, are called fragmental rocks ; and those of the 
 latter kind, crystalline rocks. Fragmental rocks are also 
 called clastic rocks, from the Greek /e\ao>, to break. 
 
 Besides rocks that are obviously fragmental and those 
 obviously crystalline there are others, of flinty compact- 
 ness, which show no distinct grains, and are therefore not 
 easily referred to either division. To determine the 
 division to which such rocks belong, they must be studied 
 in relation to the rocks associated with them. If these 
 associated rocks are fragmental, then the compact beds are 
 probably so also ; but, if these are crystalline, then the 
 compact beds are probably crystalline. The examination 
 
CONSTITUTION OF BOCKS. 29 
 
 of thin transparent slices with the microscope is often the 
 only means of distinguishing the two kinds.. 
 
 Fragmental Rocks. These are the most common of 
 rocks, constituting by far the largest part of the strata 
 accessible to geological study. The wear and decomposi- 
 tion of the oldest rocks produced fragmental material for 
 those of the next period, and so on through geological 
 time ; and the rocks made of such material, as, for ex- 
 ample, sandstones, shales, and conglomerates, are frag- 
 mental rocks. They are stratified rocks also, because they 
 are in beds. They are also called sedimentary rocks, 
 because the material was in most cases deposited as a 
 sediment from waters ; and detrital rocks, because com- 
 posed of the worn-out material (detritus) of older rocks. 
 
 While the great majority of fragmental rocks were 
 formed as sediments from water, others have been formed 
 of material transported by glaciers (see page 162) or by 
 wind (see page 120). Still other fragmental rocks have 
 resulted from the accumulation of the broken rocks, cin- 
 ders, and ashes discharged in the explosive phase of 
 volcanic eruptions. 
 
 Crystalline Rocks are either igneous or metamorphic 
 (with the exception of comparatively small accumulations 
 in veins and elsewhere, formed by deposit from solution). 
 
 Igneous Rocks include those which have come up 
 melted through volcanic vents, or through fissures opened 
 to some seat of melted rock within the earth's crust. 
 Besides those which have solidified at or near the surface, 
 other igneous rocks have solidified at considerable depth 
 below the surface. Such rocks must of course underlie 
 all superficial rocks. Igneous rocks solidified at great 
 depth may subsequently be laid bare by extensive erosion. 
 Igneous rocks include lavas, most porphyry and granite, 
 and other rocks described later (pages 36-39). 
 
 The igneous rocks which have solidified at or near 
 the surface are called volcanic rocks; those which have 
 solidified at great depth, plutonic rocks. In their more 
 
30 STRUCTURAL GEOLOGY. 
 
 typical forms, the two groups are strongly distinguished 
 from' each other, though indefinite gradations exist be- 
 tween them. Plutonic rocks have cooled slowly ; and 
 the molecules have therefore had time to arrange them- 
 selves into crystalline grains of comparatively large size. 
 Such rocks are therefore somewhat coarsely crystalline. 
 Volcanic rocks have cooled rapidly, and the process of 
 molecular arrangement was therefore interrupted by 
 solidification before large crystals could be formed. Such 
 rocks are therefore fine-grained, and more or less of the 
 material (sometimes nearly the whole) is amorphous or 
 glassy. Plutonic rocks have cooled under great pres- 
 sure. Thin sections examined under the microscope show 
 innumerable minute cavities, filled most commonly with 
 water, more rarely with carbon dioxide or some other 
 material, partly in liquid condition, but with a bubble of 
 the same material in gaseous form floating in the liquid. 
 Volcanic rocks have cooled under little more than atmos- 
 pheric pressure. In such rocks fluid cavities are want- 
 ing, since volatile materials enveloped in the mass have 
 been able to escape. 
 
 The name lava is applied to volcanic rocks in general, 
 especially to those which have come from recent volca- 
 noes, and to those which show a vesicular or scoriaceous 
 structure (page 175). 
 
 Metamorphic Rocks have assumed their present structure 
 under the action of heat and other subterranean agencies 
 without fusion. The rocks so changed were probably in 
 most cases ordinary fragmental rocks and limestones. The 
 alteration, when most perfect, has consisted in a complete 
 crystallization of the rock, and, when least so, in its con- 
 solidation ; between which extremes all gradations exist. 
 Examples of metamorphic rocks are marble, mica schist, 
 gneiss, and (probably) some granite. 
 
 While metamorphic rocks have probably been derived 
 for the most part from the alteration of sedimentary 
 rocks, it appears certain that in some cases rocks generally 
 
CONSTITUTION OF BOOKS. 31 
 
 included under this category have been formed t by a re- 
 arrangement of the materials of igneous rocks. 
 
 Massive Rocks. Rocks are termed massive when there 
 is no tendency to part along parallel planes, so as to 
 form slabs or plates. This is the case in general with the 
 coarser fragmental rocks, as sandstones and conglomer- 
 ates, with most igneous rocks, and with many limestones. 
 
 Laminated, Shaly, Slaty, Schistose Rocks. All these 
 terms express a tendency of the rock to part along parallel 
 planes, so as to form slabs or plates. 
 
 In laminated and shaly rocks, the planes of division are 
 those of deposition of the material. These structures 
 belong, accordingly, to sedimentary rocks, and are char- 
 acteristic of the fine-grained sediments. The shaly struc- 
 ture differs from the laminated in that the plates in the 
 former are thinner and more fragile. 
 
 In slaty rocks, the planes of division, or cleavage, are 
 independent of the planes of deposition, and may cross 
 the latter at any angle. The slaty structure is the result 
 of pressure subsequent to the deposition and consolidation 
 of the rock. 
 
 In schistose (or foliated) rocks, the planes of division 
 are determined by the parallel arrangement of crystalline 
 grains of some cleavable mineral, as mica, hornblende, 
 talc, or chlorite. This structure is characteristic of most 
 of the metamorphic rocks. In many cases, it is undoubt- 
 edly the result of the original stratified arrangement of 
 the material in a sedimentary rock. But in other cases 
 such a parallel arrangement appears to be due to pressure 
 or shearing, causing a rearrangement of the materials of 
 the rock. A schistose structure may, accordingly, be 
 developed in rocks of igneous origin or in vein deposits. 
 
 The rocks exhibiting most typically the laminated, 
 shaly, slaty, and schistose structures are called respec- 
 tively flagstones or flags, shales, slates, and schists. 
 
 Porphyritic Rocks. A porphyritic rock is one hav- 
 ing distinct crystals (usually of feldspar) disseminated 
 
32 STRUCTURAL GEOLOGY. 
 
 through a fine-grained or compact mass, so that, when 
 polished, the surface shows angular spots of a light-colored 
 mineral, usually between an eighth of an inch and two 
 inches in length. These disseminated crystals are called 
 phenocrysts. The red porphyry of Egypt, and the green 
 porphyry of the eastern borders of Greece, much used for 
 ornamental purposes by the ancients, are typical examples. 
 This structure is very frequent in felsite, but occurs also in 
 granite and many other rocks. It is especially character- 
 istic of igneous rocks. The phenocrysts formed slowly, 
 while the remainder of the material was still fluid. Later, 
 under other conditions, the remainder of the rock solidified 
 more rapidly, forming the fine-grained or compact mass. 
 
 Calcareous Rocks. Calcareous rocks, so named from 
 the Latin calx, lime, are the limestones. To a great extent 
 they are of organic origin ; that is, they have been formed 
 from broken or pulverized animal relics, such as shells and 
 corals ; and in this case they are properly fragmental beds, 
 although often so finely compact that this might not be 
 suspected from their texture. 
 
 Some limestones have been made from the accumula- 
 tion and consolidation of minute shells, called Rhizopods. 
 These shells, which are generally no larger than grains 
 of sand, are sometimes entire, but generally more or less 
 broken. Chalk is an example of a rock made of Rhizopod 
 shells. 
 
 Limestones made from fragments of earlier limestones 
 occur, but are not very common. Limestone conglomer- 
 ates are of this kind. 
 
 Other calcareous rocks have been deposited from waters 
 holding the material in solution, and are, therefore, of chem- 
 ical origin. Of this kind is the travertine of Tivoli near 
 Rome in Italy, and of Gardiners River in the geyser 
 region of the Yellowstone Park, and similar beds in many 
 regions of mineral springs. 
 
 Siliceous Rocks. Siliceous rocks are those that con^ 
 sist largely of silica in the form of quartz or (more rarely) 
 
CONSTITUTION OF ROCKS. 33 
 
 opal. The name is from the Latin silex, signifying flint, 
 a variety of quartz. Siliceous material, like the calca- 
 reous, is, as stated on page 19, of both mineral and organic 
 origin ; but the mineral is vastly the more abundant. It 
 sometimes occurs as a chemical product, as in the siliceous 
 depositions about geysers (page 187). The silica of 
 chemical, as well as that of organic origin, is often 
 in the state of opal. Opal, by solution and consolida- 
 tion, may become converted into true quartz, as in flint, 
 which has, for the most part, been made from the silica 
 of Sponges. 
 
 The principal kinds of rocks are here described under 
 the three heads : 
 
 1, FRAG MENTAL ROCKS, not calcareous ; 2, CRYSTAL- 
 LINE ROCKS, not calcareous ; 3, CALCAREOUS ROCKS. 
 
 1. FRAGMENT AL ROCKS, NOT CALCAREOUS. 
 
 The fragmental material which the wear and decompo- 
 sition of rocks ordinarily produces is either : (1) gravel 
 or shingle ; (2) sand ; (3) mud, earth, or clay. 
 
 1. Gravel. The pebbles in a gravel are often so coarse 
 as to be readily recognizable as fragments of various rocks. 
 Each pebble may accordingly contain two or more min- 
 erals. When the disintegration of rocks proceeds to the 
 point of pulverization, each grain is apt to consist entirely 
 of a single mineral. 
 
 2. Sand. Most sand consists chiefly of quartz ; but 
 in some sands many of the grains are of feldspar and mica. 
 Some contain much clay, or are argillaceous (so named 
 from argilla, clay) ; some are red or brownish yellow, 
 owing to the presence of iron oxide, and are called ferru- 
 ginous ; some will effervesce slightly with acid, owing to 
 the presence of some calcareous material. Beach sands 
 often contain red grains of garnet ; and commonly black 
 grains of magnetite, which- a magnet easily attracts. 
 
34 STRUCTURAL GEOLOGY. 
 
 3. Mud, Earth, Clay. Mud and earth contain, be- 
 sides grains of quartz, some pulverized feldspar, or else 
 clay, with more or less of other minerals. The terms 
 argillaceous, ferruginous, calcareous, are here applied as 
 above ; the calcareous grains are usually derived from 
 the grinding up of shells. When black, the color is due 
 to carbonaceous material derived from vegetable or animal 
 decomposition. The name soil is applied especially to 
 earth containing considerable quantities of such products 
 of organic decomposition, whence its fertility is largely 
 derived. 
 
 Common clay is a mixture of pure clay with grains of 
 quartz, feldspar, and usually traces of hydrous iron oxide 
 (limonite), or else iron carbonate. Owing to the iron, it 
 burns red, making red brick heat changing the iron 
 mineral present to hematite (page 27). Occasionally, 
 as in certain Milwaukee clays, the iron is in an iron sili- 
 cate, so that the heat cannot oxidize it ; and consequently 
 the bricks it makes are not red. Clays free from iron are 
 required for white pottery ; and clays free from grains of 
 feldspar, for making fire-brick, because the feldspar is 
 fusible. 
 
 Pure clay, or kaolin, is white, and feels greasy. It is 
 an aluminium silicate containing 14 per cent of water. It 
 results from the decomposition of feldspar (pages 113, 116). 
 It is used in making fine pottery and porcelain, and also 
 in giving body to paper. 
 
 Rock flour is finely pulverized rock of any kind. 
 
 The consolidation of gravel, sand, and mud or clay, pro- 
 duces, respectively, conglomerate, sandstone, and shale. 
 
 4. Conglomerate. Consolidated gravel. If the stones 
 are rounded, the rock is often called a pudding-stone ; if 
 in the form of angular fragments, a breccia ; if the peb- 
 bles are of quartz, a siliceous conglomerate, or, when very 
 firmly consolidated, a grit ; if of limestone, a calcareous 
 conglomerate. The stones may be a foot or more in 
 diameter, though usually much smaller. 
 
CONSTITUTION OF ROCKS. 35 
 
 5. Sandstone. A rock made of sand. Common colors 
 are red, gray, brown, white. If composed of quartz sand, 
 it is a quartzose or siliceous sandstone ; if of granite 
 sand, a granitic sandstone ; if fine, earthy or clayey, an 
 argillaceous sandstone ; if containing some calcium car- 
 bonate, a calcareous sandstone. It makes a durable build- 
 ing stone when firm, if not much absorbent of water when 
 immersed in it, and if free from pyrite so as not to rust 
 on exposure. The brownish red sandstone is often called 
 freestone. The sandstone used for grindstones is even- 
 grained and more or less friable. 
 
 6. Shale. A rock resulting from the consolidation of 
 clay or clayey earth or fine mud, and splitting readily into 
 rather thin laminae parallel to the planes of stratification 
 (page 31). The colors are of all dull shades from gray 
 to red and black. Carbonaceous shale is a blackish kind, 
 yielding mineral oil. Alum shale is a shale which has 
 become impregnated with alum through the decomposition 
 of the pyrite it contains. 
 
 7. Tufa. A volcanic sandstone, composed of volcanic 
 sand or ashes (see page 175). The color is usually brown- 
 ish, grayish, or reddish. 
 
 2. CRYSTALLINE ROCKS, NOT CALCAREOUS. 
 
 The most important of these rocks may be arranged 
 conveniently in four groups according to their miner- 
 alogical composition. 
 
 1. KOCKS CONSISTING CHIEFLY OF QuARTZ (OB OPAL). 
 
 1. Quartzite. A metamorphosed quartzose sandstone. 
 It is usually a very hard rock. It may be distinguished 
 from the accumulations of quartz in veins by its granular 
 structure (as seen under a lens, or in thin sections under 
 the microscope). Itacolumite, or flexible sandstone, is a 
 laminated, porous quartzite containing minute scales of a 
 hydrous mica, which render the rock somewhat flexible. 
 
36 STRUCTURAL GEOLOGY. 
 
 2. Chert. An impure flint or hornstone occurring in 
 beds or nodules in some stratified rocks. 
 
 3. Siliceous Sinter. Deposits of silica from solution 
 in water, most commonly formed by hot springs. The 
 silica is usually opal, more rarely quartz. The sinter 
 deposited by geysers (page 187) is often called gey- 
 serite. 
 
 2. ROCKS CONSISTING OF POTASH FELDSPAR, WITH OR WITH- 
 OUT QUARTZ, AND USUALLY WITH MICA OR HORNBLENDE. 
 
 1. Granite. A rock consisting of quartz, feldspar, and 
 mica, generally so coarsely crystalline that its ingredients 
 are conspicuous to the naked eye. Color, usually light or 
 dark gray, or flesh-red, the latter shade derived from a 
 flesh-colored feldspar; the quartz, uncleavable and usually 
 light grayish or smoky in color; the feldspar, white to 
 flesh-red, and yielding smooth, shining surfaces by cleav- 
 age ; the mica, white to black, and affording thin, flexible 
 leaves by cleavage. Most granite is igneous, and exhibits 
 most typically the characters of the plutonic rocks. Some 
 granite appears to be metarnorphic. Some granite appears 
 to constitute true veins (page 198). 
 
 2. Gneiss. Like granite in constitution, but having a 
 schistose structure, owing to the arrangement of the min- 
 erals, the mica, especially, being in parallel planes ; it has, 
 therefore, a banded appearance on a surface of transverse 
 fracture. If the color of the gneiss is dark gray, it is 
 banded usually with black lines consisting largely of black 
 mica. Along the micaceous planes it breaks rather easily 
 into slabs, which are sometimes used for flagging. Gneiss, 
 has probably been formed in most cases by the metamor- 
 phism of argillaceous sandstones. But other gneisses have 
 been formed from granites by pressure or shearing, by 
 which the ingredients have been forced into a parallel 
 arrangement. 
 
 3. Mica Schist. Related to gneiss, but consisting more 
 largely of mica, with usually less quartz and very much 
 
CONSTITUTION OF HOCKS. 7 
 
 less feldspar, and, in consequence of the mica, breaking 
 into thin slabs. The slabs have a glistening surface. In 
 regions of mica schist the dust of the roads is often full of 
 shining particles of mica. Mica schist is generally a meta- 
 morphic rock, and the same is probably true of most of the 
 schists. 
 
 4. Hydromica Schist. A slaty, fine-grained mica schist, 
 feeling somewhat greasy to the fingers. It used to be 
 called talcose slate ; but it contains a hydrous mica instead 
 of talc. 
 
 5. Slate, Argillite, Phyllite. The rocks included under 
 these names form a transition between the shales and the 
 hydromica schists, and may with about equal propriety be 
 placed in either position in the classification, being the 
 result of a very feeble metamorphism. The texture ap- 
 pears to the naked eye hardly crystalline. They are fine- 
 grained rocks ; and the kinds valued as roofing slates and 
 drawing slates are hard, smooth, and not absorbent of 
 water. The color is usually dark gray, passing into 
 bluish, greenish, and reddish shades. In these rocks the 
 slaty structure is most perfectly displayed. As already 
 explained (page 31), the planes of slaty cleavage are inde- 
 pendent of the planes of stratification, and are due to 
 pressure (page 219). 
 
 Perfectly gradual transitions may be traced from granite 
 to gneiss, from gneiss to mica schist, from mica schist to 
 hydromica schist, from hydromica schist to slate, and from 
 slate to shale. 
 
 6. Hornblende Granite, Quartz Syenite. A rock resem- 
 bling granite, but containing hornblende instead of mica. 
 Intermediate kinds occur, in which both mica and horn- 
 blende are present. Generally plutonic, like true granite. 
 
 7. Syenite. Like the preceding, but with little or no 
 quartz. Plutonic. 
 
 8. Syenite Gneiss, Hornblende Gneiss. Related to 
 hornblende granite precisely as gneiss is related to 
 granite. 
 
38 STRUCTURAL GEOLOGY. 
 
 9. Hornblende Schist. Related to the preceding as 
 mica schist is related to gneiss, the micaceous and horn- 
 blendic series showing a close parallelism. Generally a 
 metamorphic rock. Sometimes formed by alteration of 
 diorite or some such igneous rock. 
 
 10. Felsite. A fine-grained, often porphyritic rock, 
 consisting chiefly of orthoclase, containing no glass. 
 When quartz is present in considerable quantity, it is 
 called quartz felsite. Much of the so-called porphyry 
 belongs here. The colors are various, grayish and red- 
 dish shades being common. An igneous rock. 
 
 11. Rhyolite. Similar in composition to a quartz fel- 
 site, but showing under the microscope the presence of 
 glass, indicating rapid cooling. It is one of the common 
 kinds of lava. 
 
 12. Trachyte. Consists, like felsite, chiefly of ortho- 
 clase, but differs from felsite in containing some glass. 
 The feldspar is partly of a variety occurring in crystals of 
 glassy luster, called sanidin. One of the most common 
 lavas. 
 
 13. Obsidian. A lava having substantially the chemi- 
 cal composition of a rhyolite or trachyte, but cooled so 
 rapidly as to be almost entirely glassy. 
 
 3. BOCKS CONSISTING OF A SODA-LIME FELDSPAR, WITH 
 HORNBLENDE OR PYROXENE. 
 
 1. Diorite. Differs from syenite in containing a soda- 
 lime feldspar (generally oligoclase) instead of orthoclase. 
 Coarsely or finely crystalline, containing no glass. It is 
 sometimes porphyritic, and the classical red porphyry of 
 Egypt (rosso antico) is here included. Rather dark gray- 
 ish and greenish colors predominate. It is generally an 
 igneous rock, though it may be sometimes metamorphic. 
 
 2. Andesite. Similar in composition to diorite, but 
 partly glassy. A common kind of lava. 
 
 3. Gabbro. A coarsely crystalline rock, consisting 
 chiefly of* a soda-lime' feldspar (generally labradorite) and 
 
CONSTITUTION OF KOCKS. 39 
 
 pyroxene, often containing magnetite and chrysolite as 
 accessory ingredients. In its coarseness of crystallization 
 it resembles granite ; and, like granite, is generally a 
 plutonic rock. 
 
 4. Dolerite, Diabase. Similar in composition to gab- 
 bro, but not so coarsely crystalline. Often porphyritic. 
 Colors dark black, shading into gray, greenish, or brown- 
 ish colors. An igneous rock, very often occurring in 
 dikes. This and other dark heavy igneous rocks are 
 often called trap. 
 
 5. Basalt. Similar in composition to gabbro and dole- 
 rite, but showing the typical volcanic character of contain- 
 ing glass. The rock (or the ground mass, when the rock 
 is porphyritic) is so fine-grained as to appear compact to 
 the naked eye. Color black, or nearly so. One of the 
 most common kinds of lava. 
 
 6. Tachylite. A lava substantially similar to basalt in 
 chemical composition, but cooled so rapidly as to be almost 
 entirely glassy. 
 
 4. BOCKS CONSISTING CHIEFLY OF HYDROUS MAGNESIAN 
 SILICATES. 
 
 1. Chlorite Schist. A schistose rock of dark green 
 color, consisting chiefly of chlorite. It is connected by 
 intermediate gradations with hydromica schist. 
 
 2. Talc Schist. A schistose rock of grayish or green- 
 ish color and greasy feel, consisting chiefly of talc. A 
 comparatively rare rock, most of the rocks to which the 
 name has been applied being hydromica schist. 
 
 3. Steatite, Soapstone. Like talc schist, except in the 
 lack of the schistose structure. The finer-grained varieties 
 are used for slate pencils and for various other purposes. 
 
 4. Serpentine. A rock consisting chiefly of the min- 
 eral serpentine. In most cases it results from the hydra- 
 tion of rocks consisting wholly or largely of anhydrous 
 magnesian silicates. Rocks containing chrysolite are 
 especially liable to undergo this alteration. 
 
40 STRUCTURAL GEOLOGY. 
 
 3. CALCAREOUS ROCKS. 
 1. NON-METAMORPHIC. 
 
 1. Common Limestone. A compact rock of grayish and 
 other dull shades of color to black, consisting either of 
 calcite or dolomite, but often impure from the presence of 
 clayey or earthy material. It breaks with little or no 
 luster. If containing fossils, it is called fossiliferous lime- 
 stone ; if the fossils are Corals, coral limestone ; if remains 
 of Crinoids, crinoidal limestone. When impure, and there- 
 fore good for making hydraulic lime (quicklime that will 
 make a cement which sets under water), it is called hydrau- 
 lic limestone. Chalk is a variety of limestone soft enough 
 to be used for marking, and consisting chiefly of shells of 
 Rhizopods. 
 
 Many varieties of common limestone are polished and 
 used as marbles ; they have black, reddish, yellow, gray, 
 and other colors ; kinds containing fossil shells are called 
 shell marbles. 
 
 2. Oolite. A limestone consisting of concretions as 
 small as the eggs in the roe of fish, or smaller whence the 
 name, from the Greek o>oV, egg. Oolitic limestone occurs 
 in all the geological formations, and is forming in modern 
 seas about the Florida Keys and in other coral-reef regions. 
 
 3. Stalactite, Stalagmite, Travertine. Stalactites are ac- 
 cumulations of limestone hanging from the roofs of caverns; 
 and stalagmite is the same material covering the floors; both 
 are formed from the calcareous waters that come through 
 the roof, and are sometimes called dripstone. A similar 
 deposit from streams or ponds is called travertine ; it is 
 sometimes used for a building stone. 
 
 4. Marl. Clay containing much calcium carbonate, and 
 hence used as a fertilizer. The term is used popularly for 
 any rock material that can be so used. Shell marl consists 
 largely of shells. Greensand marl is sand consisting largely 
 of grains of a green silicate of iron and potash called 
 glauconite. 
 
ROCK MASSES, OR TERRANES. 41 
 
 2. METAMORPHIC. 
 
 Crystalline Limestone; Architectural and Statuary Mar- 
 ble. Limestone having a crystalline texture, and, conse- 
 quently, glistening on a surface of fracture. A pure, white 
 kind, of fine grain, is used for statuary, and both this 
 and coarser varieties for marble buildings. Many of the 
 clouded marbles are here included. 
 
 II. ROCK MASSES, OR TERRANES. 
 
 The rocks above described are the material of which the 
 great rock masses, or terranes, of the globe consist. These 
 rock masses are either stratified or unstratified. 
 
 The Stratified Condition. Stratified rocks are those 
 which lie in beds or strata. The word stratum (the 
 singular of strata) is from the Latin, and signifies that 
 which is spread out. 
 
 In geology, a stratum includes all the beds of one kind 
 of rock (as of limestone, or of sandstone, or of any other 
 kind) that lie in one continuous series. 
 
 The earth's rocky strata are spread out in beds of vast 
 extent, many of them thousands of square miles in area 
 and thousands of feet in thickness. 
 
 The stratified rocks exposed to view over the earth far 
 exceed in area the unstratified. They are the rocks of 
 nearly the whole of the United States and of almost all 
 of North America, and not less of the other continents. 
 Throughout central and western New York, and the states 
 south and west, the rocks, wherever exposed, are seen to 
 be made up of a series of beds. And, if the rocks are less 
 distinctly stratified over most of New England, it is, in 
 general, only because the structure has been partly obscured 
 by the upturning and crystallization they have undergone 
 since they were formed. 
 
 Fig. 13 represents a section of the rocks along the 
 river below Niagara Falls. It gives some idea of the 
 
42 STRUCTURAL GEOLOGY. 
 
 alternations which occur in the strata. In a total height 
 of 250 feet (165 feet at the falls, at F, on the right) 
 there are, on the left, six different strata in view, and 
 parts of two others, the upper and lower, making eight in 
 all. Number 1 is shale ; 2, sandstone ; 3, shale ; 4, sand- 
 stone ; 5, shale ; 6, limestone ; 7, shale ; 8, limestone. 
 Only two of these strata, 7 and 8, are in sight at the Falls 
 (at F). The alternations are thus numerous and various in 
 most regions of stratified rocks. Along the canon of the 
 Colorado, there are in some places more than 8000 feet of 
 consecutive stratified beds, showing their edges in lofty 
 precipices, and in the mountains towering above the adjoin- 
 ing plains. Fig. 14 represents one of the scenes along 
 the canon. 
 
 FIG. 13. 
 
 w F 
 
 Section along the Niagara River. 
 
 It must not be inferred that the earth is covered by a 
 regular series of coats, the same in all countries ; for this 
 is far from the truth. Many strata occur in New York 
 that are not found in Ohio and the states west, and many 
 in southern New York that are not found in the northern 
 part. Moreover, a stratum of limestone may change in 
 the course of a few miles to one of sandstone or shale. 
 
 A layer is one of the subdivisions of a stratum. A 
 stratum may consist of an indefinite number of layers. 
 
 In many stratified rocks, as in most limestones, con- 
 glomerates, and the coarser sandstones, the strata or 
 layers are thick, and the structure of the rock is massive 
 (page 31). But argillaceous sandstones and shales gen- 
 erally split into thin layers, showing thus a laminated or 
 shaly structure. Sometimes the rock shows on cross frac- 
 
BOOK MASSES, OR TERRANES. 
 
 43 
 
 ture a minutely banded appearance, due to variation in 
 the color or texture of the deposit, even though the thin 
 layers may not be separable. Such minutely banded 
 rocks are said to be straticulate, whether the layers are 
 separable or not. 
 
 Fio. 14. 
 
 Wall of Colorado Cafton. 
 
 A system includes all the various kinds of strata that 
 were formed in one age or era, as the Carboniferous sys- 
 tem, or that of the Coal. The term series is used like 
 system, but with most writers it denotes a less extensive 
 division. Subdivisions of a system or series are called 
 groups ; a subdivision of a group, a stage. 1 
 
 1 There is no uniformity of usage among geologists, in regard to the 
 order of the terms defined in this paragraph. 
 
44 STRUCTURAL GEOLOGY. 
 
 The term formation is often used instead of system or 
 series. But it is also employed to designate all the rocks 
 of a kind making a continuous mass in a region, as a 
 limestone formation, a coral formation, a granite formation. 
 
 Origin of Stratification. The stratified structure is 
 due to changes, at longer or shorter intervals, in the 
 formations in progress over a region. For a long time 
 limestones may have been forming. Then, through some 
 change in the conditions it may be a change of level, or 
 of marine currents, sandstones were formed over the 
 limestone stratum. After another change, deposits of 
 mud, or clay, or pebbles, succeeded. Such alternations 
 have been going on in one part or another of the seas over 
 the continental areas, through all geological time. 
 
 Changes, also, in kinds of species populating the seas 
 have helped to mark the distinction in successive strata; 
 though generally in connection with some physical or 
 geographical change, as change of currents, or of tem- 
 perature in the waters, or of their purity, or of level, 
 increasing or diminishing the depth. According as such 
 changes occur at long or short intervals, the beds conse- 
 quently produced are of greater or less thickness. 
 
 In all cases, the subdivisions are due to changes of 
 conditions ; and, for the very thin layers of the straticu- 
 late structure, those changes may be the daily alterna- 
 tions or ebb and flow of the tides ; or the changes of 
 velocity in the blasts of wind over a region of sand ; or 
 the successive throws of the breakers over a beach ; or 
 simply wavelike vibrations in any body of water. For a 
 wave has its time of maximum and minimum movement, 
 and therefore its times of unequal force in the process of 
 deposition, and waters of breakers descending a beach 
 have their time of action succeeded by a time of rest. 
 
 In volcanic work, also, there are alternations. Out- 
 flows of lava are separated from one another by intervals 
 of rest, or by times when only steam, other gases, and 
 volcanic ashes are ejected. 
 
ROCK MASSES, OR TERRANES. 45 
 
 Thus strata, beds, layers, from the coarsest stratification 
 to the finest straticulation, have one general cause ; and 
 bedding is absent from deposits only when alternations 
 did not occur during the deposition, or when the mate- 
 rials, as those of many conglomerates, are too coarse to 
 admit of the finer bedding. 
 
 Unstratified Condition. Unstratified rocks are those 
 which do not lie in beds or strata. Mountain masses of 
 granite are usually without any appearance of stratifica- 
 tion. The rock of the Palisades, on the Hudson, stands 
 up with a bold columnar front, and has no division into 
 layers. Most volcanic formations exhibit a sort of strati- 
 fication, due to the alternations mentioned above ; though 
 the name stratification is not usually applied technically 
 to volcanic rocks. But in some volcanic regions the rocks 
 rise into lofty summits without stratification. Veins 
 (page 196), dikes (page 188), and other special modes of 
 occurrence of Unstratified rock will be described hereafter. 
 
 Relation of Stratified and Unstratified Rocks in the 
 Earth's Crust. The relations of the stratified and un- 
 stratified rocks in the earth's crust will be understood 
 after considering the origin of the crust. 
 
 The Unstratified rocks which once formed the surface of 
 the globe were made by the solidification of the molten mass. 
 
 After the solidifying of the sphere at surface, the ocean 
 commenced at once to make fragmented stratified rocks 
 over the exterior through the wear of those primitive 
 Unstratified rocks, and the stratifying of the sand or mud 
 thus made. The ocean thus worked over and covered up 
 with strata nearly all, if not all, the original Unstratified 
 crystalline rocks. Hence the areas of the Unstratified 
 rocks that were made in the first solidification of the 
 globe, are of very small extent over the continents, if 
 visible anywhere. 
 
 Geology has, for its study, chiefly stratified rocks. 
 Much the larger part of all the facts in geological history 
 are derived from rocks of this kind, and therefore the 
 
46 
 
 STRUCTURAL GEOLOGY. 
 
 FIG. 15. 
 
 various details with regard to their structure and arrange- 
 ment are of the highest importance. 
 
 Concretions. Rocks often contain, and sometimes con- 
 sist of, small spheres or disks of mineral 
 matter, which are called concretions. Con- 
 cretions result from a tendency in matter to 
 concrete or solidify around centers. Some are 
 no larger than grains of sand, or the eggs in 
 the roe of fish, as in oolitic limestone (page 
 40). Others are as large as peas or bullets, 
 and others a foot or more in diameter. 
 Fig. 15 represents a spherical concretion ; Fig. 16, a 
 rock made up of rounded concretions, having a concentric 
 
 A spherical concre- 
 tion. 
 
 FIG. 16. 
 
 FIG. IT. 
 
 Concretions with concentric structure. 
 
 Disk-shaped concretions. 
 
 FIG. 18. 
 
 structure; frig. 17, one with flattened or disk-shaped 
 concretions. 
 
 Concretions are made by the deposit of calcium car- 
 bonate or some other material held in 
 solution or suspension by waters per- 
 colating through the rock. They are 
 usually spherical in massive sandstones, 
 because solutions in such rocks spread 
 equally in all directions ; but lenticular 
 in laminated rocks, and flattened disks 
 in argillaceous rocks or shales, because 
 in these rocks waters spread laterally 
 more easily than vertically. All these kinds are shown 
 in Fig. 18, 
 
 Strata containing con- 
 cretions. 
 
BOCK MASSES, OR TERKANES. 
 
 47 
 
 The balls are sometimes hollow, and the disks mere 
 rings. Frequently the concretions have a shell or other 
 organic object at center (Fig. 19). They are often cracked 
 through the interior (Fig. 20) from drying (some soft 
 clayey muds contracting to a tenth of their bulk) ; the 
 outside in such a case solidified while the inside was still 
 
 FIG. 19. 
 
 FIG. 20. 
 
 FIG. 21. 
 
 Concretion with a fossil 
 at its center. 
 
 Concretion with 
 shrinkage cracks. 
 
 Geode. 
 
 moist. The cracks may afterward become filled with other 
 minerals. Sometimes they contain a loose ball within 
 a concretion within a concretion. A cavity lined with 
 crystals (Fig. 21) is called a geode ; but the hollow balls 
 so lined within are not generally concretions. 
 
 Joints. The rocks of a region are often divided very 
 regularly by numerous planes of fracture, the most of them 
 
 FIG. 22. 
 
 Jointed structure, shore of Cayuga Lake. 
 
 parallel to one another, and cutting through the strata, 
 perpendicularly, or at various angles, to great depths, 
 but with the walls of the fissures generally in contact or 
 but slightly separated. Such deep unopened fractures 
 may characterize the rocks over areas hundreds of miles 
 in extent. They are called joints ; and a rock thus divided 
 is said to present a jointed structure. In many cases .there 
 
48 
 
 STRUCTURAL GEOLOGY. 
 
 are two systems of joints or divisional planes in the same 
 region, crossing one another ; and the undermining of a 
 bluff of jointed beds and tumbling down of masses lead 
 to the production of forms like those of fortifications or 
 broken walls, as shown in Fig. 22, representing a view 
 on the shores of Cayuga Lake. The directions of such 
 joints are facts which the geologist notes down with care. 
 Slaty Cleavage. The peculiar structure of slates and 
 allied rocks (cleavage) has been referred to on page 81 ; 
 and it has been -stated that the planes of cleavage are 
 usually not parallel to the bedding ; that is, they cross the 
 layers of stratification more or less obliquely, instead of 
 conforming to the layers of bedding like the divisional 
 planes in the shaly structure. Slaty cleavage is in this 
 respect like the jointed structure ; but it has the divisional 
 planes so numerous that the rock divides into slates in- 
 
 FIG. 28. 
 
 Fir,. 24. 
 
 Slaty cleavage. 
 
 stead of blocks ; and the two differ in mode of origin. 
 Slaty cleavage is confined to fine-grained rocks. In Fig. 
 23, the lines of bedding or stratification are shown at a, 5, 
 <?, d, while the transverse lines correspond to the direction 
 of the cleavage. The same is shown in Fig. 24, with the 
 addition of a slight irregularity in the slates along the 
 junction of two layers. 
 
 POSITIONS OP STRATA. 
 
 1. Original Position of Strata. Horizontal Position. 
 Ordinary stratified rocks were once beds of sand or earth, 
 or of other rock material, spread out by the currents and 
 waves of the ocean, or the waters of lakes or rivers, or 
 by the winds. 
 
ROCK MASSES, OR TERRANES. 49 
 
 When the larger portion of the beds over the North 
 American continent were formed, the continent lay to a 
 great extent beneath the ocean, as the bottom of a great, 
 though mostly shallow, continental sea. The principal 
 mountain chains the Rocky Mountains and the Appa- 
 lachians had not been made, and the surface of the 
 submerged land was nearly flat. That those beds were 
 really marine, is proved by their containing, in most cases, 
 marine shells, crinoids, or corals, the relics of marine life ; 
 and that the continental seas had great extent, is proved 
 by the fact that the beds cover surfaces tens of thousands 
 of square miles in area, some of them reaching from the 
 Atlantic border westward beyond the Mississippi. In 
 those large continental seas, the deposits made by means 
 of the currents and waves were nearly or quite horizontal. 
 Wherever they reached the surface, like the sand flats off 
 many modern seashores, the sweep of the waters over 
 them during the incoming tide would tend to plane off and 
 keep level the upper surface of the beds, whether accumu- 
 lations of sand or earth, or of shells or corals. If the bottom 
 over the region were very slowly sinking, the accumulations 
 might go on thickening, and the beds continue to have 
 the same level or horizontal position. Strata formed along 
 the borders of rivers and lakes are nearly horizontal, and 
 so are those on the borders of the ocean ; and for a like 
 reason, that the water works with reference to its surface, 
 which is horizontal. Moreover, the bottom of the border 
 of the Atlantic, south of Long Island, for 80 miles from 
 the coast line (see Fig. 3, page 13), deepens only 1 foot for 
 every 600 to 700 ; and, if the area were above the ocean, 
 no eye would detect that it was not a perfect level. 
 
 The view of the rocky wall of the Colorado Canon, on 
 page 43, illustrates well the approximate horizontally of 
 the original bedding, and shows that it was continued 
 through many long periods ; for the series of rocks, more 
 than 5000 feet thick, represents a long succession of geo- 
 logical formations. 
 
50 
 
 STRUCTURAL GEOLOGY. 
 
 Some beds were originally vast marshes, like the marshes 
 of the present day, only larger. Such was the condition 
 of the beds that are now coal in the Coal formation. 
 Many coal beds contain stumps of trees rising out of the 
 coal (Fig. 25); and they always stand perpendicularly 
 to the bed, however much the latter may be displaced, 
 showing that the bed was horizontal when it was formed, 
 or when the trees were growing. 
 
 Exceptions to a Horizontal Position. When a river 
 empties into a lake or sea, the bottom of which, near its 
 FIG. 25. mouth, is more or less inclined, the 
 
 deposits of detritus made by the river 
 will for a while conform to the slope 
 of the bottom, as in Fig. 26. When 
 a river falls down a precipice, it makes 
 a steep bank of earth at the foot, whose 
 coai beds with fossil stumps. i ayers? if aiiy are ma d e , have the slope 
 
 of the bank. In beach-made deposits the layers have the 
 slope of the beach (page 154). But these and similar cases 
 of exceptions to a horizontal position are of small extent. 
 
 2. Dislocations of Strata. Most of the strata of the 
 globe have lost their original horizontal position so as 
 to be more or 
 less inclined; and 
 some are even ver- 
 tical. They are 
 occasionally bent 
 or folded, as a 
 quire of paper might be folded, only the folds are miles, 
 or scores of miles, in sweep. 
 
 They have often also been fractured, and the separated 
 parts have been pushed, or else have fallen, out of their 
 former connections, so that the portion of a stratum on 
 one side of a fracture is often inches, feet, or even miles, 
 above that on the other side. 
 
 The maximum thickness of stratified rocks is said 
 to be over 25 miles, though only a part of this thick- 
 
 Fifi. 26. 
 
 Inclined strata deposited on a steep slope. 
 
ROCK MASSES, OR TERRANES. 
 
 51 
 
 FIG. 2T. 
 
 ness exists in any one region (pages 42, 224). If the strata 
 were all in their original horizontal position, it is evident 
 that no such thickness of strata could be within the reach 
 of observation. The maximum thickness of strata ob- 
 servable under such conditions would be limited by the 
 height of cliffs formed by erosion, or by the depth of arti- 
 ficial borings. But the up- 
 turning which the earth's 
 crust has undergone has 
 brought the edges of strata 
 to the surface, and there is 
 hence no such limit : how- 
 ever deep stratified beds 
 may extend, there is no outcrop, 
 
 reason why the whole 
 
 should not be brought up so as to be exposed to view in 
 some parts of the earth's surface. 
 
 The following are explanations of the terms used in 
 describing the positions of strata: 
 
 Outcrop. The portions or ledges of strata projecting 
 out of the ground, or in view at the surface (Fig. 27). 
 
 Dip. The slope of inclined or tilted strata. In 
 Figs. 27, 28, dp is the direction of the dip. Both the 
 
 angle of slope (i.e., 
 the angle between 
 the plane of stratifi- 
 cation and a horizon- 
 tal plane), and the 
 direction with refer- 
 ence to points of com- 
 pass, are noted by the 
 geologist: thus, it may 
 be said of beds, the 
 dip is 50 to the south, or 5 to the northwest, etc. 
 
 When only the edges of layers are exposed to view, it 
 is not safe to take the slope of the edges as the slope of 
 the layers ; for, in Fig. 28, the edges on the faces 1, 2, 3, 4 
 
 Sections showing true and false dips. 
 
52 
 
 STRUCTURAL GEOLOGY. 
 
 FIG. 29. 
 
 are all edges of the same beds, and only those of the face 
 1 would give the right dip. 
 
 The dip is measured by means of instruments called 
 clinometers. In Fig. 29, abed represents a square block 
 of wood, having a graduated arc be, and a plummet hung 
 below a. Placed on the sloping surface AB, the position of 
 the plummet gives the angle of dip. This kind of clinom- 
 eter is often made in the form of a watch, and combined 
 with a compass. It is most convenient for use when it 
 has a square base. One like that figured is easily made 
 
 out of a piece of 
 board ; it may be 3 
 to 4 inches on a side, 
 and about half an 
 inch thick. To avoid 
 errors from the un- 
 evenness of a rock, a 
 board mav be laid 
 
 Measurement of dip, by clinometer. 
 
 down first, and the 
 
 measurement be made on its surface. But, if the instru- 
 ment has a square base, it is often best to measure the dip 
 by holding it between the eye and the rock, with one 
 edge of the base in the direction of the dipping layers. 
 Strike. The horizontal direction at right angles with 
 the dip. In Fig. 27, the dotted line st represents the 
 direction of the strike. It is measured by means of a 
 small compass, which usually forms part of the clinometer. 
 Such a compass may be set in a clinometer made like the 
 one shown in Fig. 29. It need not be central in the 
 square, but should have the meridian line parallel to one 
 of the four sides. If the edges of the layers in view over 
 a ledge are in any part quite horizontal, the direction of 
 those edges will give the true strike ; but, if they are at 
 all inclined, the direction of a horizontal line must be de- 
 termined on the surface of one of the layers. The cli- 
 nometer may be used also for measuring the dip of rocks 
 that are rods distant, and the slopes of distant mountains. 
 
ROCK MASSES, OR TERRANES. 
 
 53 
 
 Faults. In the making of faults (aa, bb, Fig. 30), 
 there is a fracturing, and a shoving up or down of the 
 beds on one side of the fracture; FIG. so. 
 
 that is, a downthrow on one side 
 .or an upthrow on the other. The 
 amount of displacement is the 
 amount of fault ; it may be a 
 foot or less, or 10,000 feet or 
 more. The friction attending 
 the movement may cause a bend- 
 ing of the layers in contact, as along the line bb, in Fig. 30. 
 The deepest fractures and faults have been produced in 
 connection with the making of mountains. 
 
 Folds or Flexures. Folds or flexures in strata are rep- 
 resented in Fig. 31, A, B ; and in the natural sections 
 
 Anticlines and synclines. 
 
 Figs. 206-209, pages 212, 213, from the Appalachian Moun- 
 tains, a region of numerous flexures on a grand scale, as 
 well as of many faults ; some flexures having a span of 
 several miles, and others of only a few feet or inches. 
 
 In Fig. 31, A, ax represents the axial plane of the fold, 
 and the intersection of the surface of the strata by that 
 plane is the axis of the fold. 
 
 The flexure very often has one 
 side steeper than the other, as illus- 
 trated above. In some regions, the 
 overturned folds. Ph by which it was made was 
 
 continued until the strata became 
 
 vertical ; and, further still, until the top was pressed over 
 beyond the vertical, and fold of this kind followed fold, as 
 illustrated in Fig. 32. In more extreme cases, the push 
 
 FIG. 32. 
 
54 
 
 STRUCTURAL GEOLOGY. 
 
 was continued until there was produced a complete inver- 
 sion of the beds, as is represented in Fig. 33, a section 
 of the Dent de Morcles, near Martigny in Switzer- 
 land, by Golliez. The length of the section is about 
 five miles; and the horizontal and the vertical scale of 
 the figure are equal. The horizontal line at the base of 
 the figure represents the level of the sea. The stratum 9, 
 which before the folding was the uppermost stratum, is 
 folded back on itself ; and 8, 7, and 6, which were origi- 
 nally underlying strata, now overlie it, upside down. It 
 is seen that the strata 6 and 7 are present only in the 
 overturned part of the fold; these beds must have ex- 
 
 FIG. 33. 
 
 N.W. 
 
 S.E. 
 
 Section of the Dent de Morcles. 1, Metamorphic rocks ; 2, Carboniferous ; 3, Triassic ; 
 4, Lower Jurassic (Lias and Dogger) ; 5, Upper Jurassic (Malm) ; 6, Lower Cretaceous 
 (Neocomian); 7, Upper Cretaceous; 8, Lower Eocene (Numinulitic) ; 9, Upper Eocene. 
 
 tended northwestward between 5 and 8, but they have 
 been pinched out in the lower limb of the fold by the tre- 
 mendous pressure to which the rocks have been subjected. 
 At the extreme left of the figure, stratum 6 is seen in its 
 normal position overlying 5. 
 
 Flexures often have fractures somewhere along the 
 bend ; and the fractures are often lines of fault. 
 
 Anticline. An upward arching of the strata, which 
 slope away from the axial plane in opposite directions, 
 as the layers either side of ax in Fig. 31, A : the axis is 
 here called an anticlinal axis. The word anticline is 
 
ROCK MASSES, OB TERRANES. 55 
 
 from the Greek air/, iu opposite directions, and K\LVO), to 
 incline. 
 
 Syncline. A downward bend, the strata sloping toward 
 the axial plane. In Fig. 31, B, the axes corresponding 
 to ax, ax, are anticlinal axes, that corresponding to a'x', 
 between the others, a synclinal axis. The word syncline 
 is from the Greek avv, together, and K\LVCO. 
 
 Monocline. A form of flexure in which the strata slope 
 in only one direction, as when a series of strata is elevated 
 (relatively) in one area and depressed in an adjacent area 
 without fracture. Such monoclinal flexures pass by fine 
 gradations into faults. A series of strata having an 
 apparently monoclinal attitude may be only a part of 
 an anticline or syncline of which the other side is con- 
 cealed. The word monocline is from the Greek /-to'z/os, 
 one, and K\IVCO. 
 
 Geanticline, Greosyncline. Bendings of the earth's crust, 
 geanticline an upward bend, and geosyncline a downward 
 bend. These words are from the Greek yrj, earth, and the 
 words anticline and syncline. 
 
 In ordinary synclines and anticlines, the flexures involve 
 a varying thickness of strata, the arches have a span of 
 a few miles at most, and the height of the arches bears 
 generally a large ratio to the width. In geanticlines and 
 geosynclines, the earth's crust is affected to a much 
 greater depth (extending much below the stratified por- 
 tion, or supercrust), the arches have a span of scores or 
 hundreds of miles, and the height of the arches is very 
 small in comparison with their width. Within the limits 
 of a single geanticline or geosyncline, there may be a 
 number of alternating anticlines and synclines. 
 
 The subject of flexures and faults is best studied by 
 making models out of sheets of moist clay (or better of 
 paraffin containing a little beeswax), using lampblack 
 and red and yellow ocher for coloring the different beds, 
 and then making cross sections. 
 
 Effects of Denudation on Flexed or Upturned Hocks; 
 
56 
 
 STRUCTURAL GEOLOGY. 
 
 FIG. 34. 
 
 Fio. 35. 
 
 123 32 
 
 Decapitated Folds. If the top of the fold in Fig. 34 were 
 cut off at ab, there would remain the part represented in 
 Fig. 35, in which there is no appearance of any fold, and 
 
 only a uniform series of dips ; 
 and, although 1', 2', 3', appear to 
 be the lower strata of the series, 
 they are actually parts of 1, 2, 
 3. A long series of such folds 
 
 seaums showing effect'of decked pressed together, and then decap- 
 folds - itated, would make a series of uni- 
 
 form dips (an apparently monoclinal structure) over a wide 
 extent of country (see Fig. 32). 
 
 The true succession has been further obscured by the 
 removal of the beds over great areas and the filling up of 
 intermediate depressions by soil ; so that the rocks are 
 visible only at long intervals (as in Fig. 36). Many of the 
 difficulties in the study of rocks arise from this cause. 
 
 Fro. 36. 
 
 Section showing discontinuity of outcrops. 
 
 Unconformable Strata. When strata have been ele- 
 vated (usually with more or less tilting or folding), and, 
 after more or less erosion, have been again depressed 
 below the water level, and, subsequently, horizontal beds 
 have been laid down over them, the two sets are said to 
 be unconformable. Thus, in Fig. 37, the beds ef are un- 
 conformable both with the tilted beds cd and with the 
 folded beds ab ; so also the tilted beds cd are uncomforin- 
 able with those beneath. 
 
 It is plain that the folded rocks ab are the oldest, and 
 that the folding took place before the overlying beds were 
 deposited. Again, it is evident that the beds cd are older 
 than the beds ef, and also that they were tilted and faulted 
 before the latter were formed. Supposing the uppermost 
 of the folded rocks ab were of Carboniferous age, and the 
 tilted beds cd were Triassic, the geologist would conclude 
 
HOCK MASSES, OR TERRANES. 
 
 57 
 
 that the upturning and folding of the earlier rocks occurred 
 after the deposit of the Carboniferous strata and before 
 that of the Triassic. In like manner, if the horizontal 
 strata ef were Cretaceous, the time of the tilting and 
 faulting of the beds cd would be shown to be between 
 the Triassic and the Cretaceous. 
 
 The special significance of unconformability in the inter- 
 pretation of the geological record, is that it always marks 
 an interval of time during which (in the region in ques- 
 tion) no rocks were formed. The two sets of strata may 
 
 FIG. 37. 
 
 o 
 
 Unconformable strata. 
 
 be richly fossiliferous, and so bear testimony in regard to 
 the history of life in their respective periods. But, for the 
 interval, long or short, in which the older series of strata 
 was above the water level, and was undergoing erosion, 
 there is, at least locally, a gap in the record. 
 
 Overlap is the name given to the condition which exists 
 when the sea, after depositing a series of strata, has spread 
 more widely over the land, and has deposited another 
 series of beds with these new limits. These changes of 
 sea level were going forward during the progress of mosi. 
 formations, and, consequently, overlap should be common, 
 though not always easily distinguished. 
 
THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 SINCE life has been an important agent, dynamically, in 
 Geology, and its history constitutes a chief part of the 
 historical branch of the science, some knowledge of the 
 various kinds of animals and plants is of the highest im- 
 portance to the student. A brief review of the classifica- 
 tion of the animal and vegetable kingdoms, and of the 
 distribution of life over the globe, is here introduced. 
 
 CLASSIFICATION. 
 
 Distinctions between an Animal and a Plant. A typical 
 animal (1) is sustained by nutriment taken into its inte- 
 rior for digestion and assimilation. (2) It is capable of 
 perceiving the existence of other objects, through one or 
 more senses. (3) It has (except in some of the lower 
 species) a head, in which are the principal nerve centers 
 controlling voluntary motion, and the mouth. (4) It is 
 fundamentally a fore-and-aft structure, the head being 
 the anterior extremity ; and it is typically forward- 
 moving. (5) With its growth from the germ, there is 
 an increase in mechanical power until the adult size is 
 reached. (6) In the process of respiration, it uses oxy- 
 gen and gives out carbonic acid. (7) It finds nutriment 
 only in organic materials, or tissues of plants or animals ; 
 never in mineral material. 
 
 A plant (1) is sustained by nutriment taken into the 
 tissues by absorption at the surface. (2) It is incapable 
 of perception, having no senses. (3) It has no head, no 
 
 68 
 
CLASSIFICATION. 59 
 
 power of voluntary motion, no mouth. (4) It is funda- 
 mentally an up-and-down, structure, and, with few excep- 
 tions, fixed. (5) In its growth from the germ or seed, 
 there is no increase of mechanical power. (6) In the 
 process of nutrition, ordinary plants use carbonic acid, 
 and give out oxygen with only an extremely small amount 
 proportionally of carbonic acid. The Fungi, and some 
 other plants that are not green, are an exception, using 
 oxygen, and giving out much carbonic acid. (7) A plant 
 finds nutriment in mineral material, from which it makes 
 organic tissues. 
 
 The Animal Kingdom. 
 
 The nature of an animal requires, for a full exhibition 
 of its powers, the following parts : 
 
 1. A stomach and its appendages, to turn the food into 
 blood, with an arrangement for carrying off refuse mate- 
 rial. 
 
 2. A system of vessels for carrying this blood through- 
 out the body, so as to promote growth and a renewal of 
 the structure. 
 
 3. A heart, or forcing pump, to send the blood through 
 the vessels. 
 
 4. A means of respiration, or of taking oxygen into 
 the system (as by lungs or gills), since the energy of the 
 body is derived from the combination of oxygen with the 
 elements contained in the food. 
 
 5. Muscles, or contractile fibers, to put the parts or 
 members in motion by their contraction. 
 
 6. A brain, or head mass of nervous matter, to serve 
 as a seat of sensation and volition, and a system of nerves 
 to convey sensory impressions to the brain and motor 
 impulses to the muscles. 
 
 In the lowest forms of animal life, as some microscopic 
 Protozoans, the stomach is not a permanent cavity, but 
 is formed in the mass of the tissue whenever and wherever 
 a particle of food comes in contact with the body. In 
 
60 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 other words, a stomach is extemporized as it is needed. 
 Animals of a little higher grade, as Anthozoans, have a 
 mouth and a stomach, muscles, an imperfect nervous sys- 
 tem, and a means of respiration through the general 
 surface of the body ; but there is no heart, and the animal 
 is ordinarily fixed to a support. 
 
 The subkingdoms, or primary divisions of the animal 
 kingdom, most commonly recognized at present by zoolo- 
 gists, are the following : 
 
 1, PROTOZOANS ; 2, SPONGES ; 3, CCELENTERATES ; 4, 
 ECHINODERMS ; 5, MOLLUSCOIDS ; 6, MOLLUSKS ; 7, VER- 
 MES, or WORMS ; 8, ARTHROPODS ; 9, TUNIC ATES ; 10, 
 
 VERTEBRATES. 1 
 
 1. PROTOZOANS. 
 
 The name Protozoans is derived from Greek TT/JWTO?, 
 first, and ftwoz/, animal, and accordingly signifies the 
 simplest and lowest of animals. According to the mod- 
 ern doctrine of evolution, some representatives of this 
 group must have been the first of animals in time, and 
 the ancestors of all more complex forms. The Protozoans 
 are characterized by their extreme simplicity, the minute 
 body consisting strictly of a single cell. The Protozoans 
 that form communities by continuous budding or fission, 
 and thus come to form masses of some size, constitute 
 only an apparent exception to the above statement. 
 
 1 This classification is provisionally adopted as a matter of convenience, 
 since it is believed to be used more generally than any other in recent 
 manuals of zoology, though it does not precisely express the views of the 
 editor. In former editions of this work, the Sponges were included 
 among the Protozoans ; the Coelenterates and Echinoderms were united 
 under the name Radiates; the Molluscoids, Mollusks, and Tunicates 
 were united under the name Mollusks ; and the Vermes and Arthropods 
 were united under the name Articulates. In the latest edition of the 
 Manual, the Ccelenterates and Echinoderms are united under the name 
 Radiates ; the Molluscoids, Mollusks, and (doubtfully) a part of the 
 Vermes are united under the name Non-Articulates ; and the remainder 
 of the Vermes and the Arthropods are united under the name Articu- 
 lates. 
 
CLASSIFICATION. 
 
 61 
 
 There is in these creatures nothing like the development 
 of the higher animals, in which the egg (originally a 
 
 FIGS. 38-51. 
 
 FORAMINIFERS : Fig. 38, Orbuliiia universa ; 39, Globigerina rubra ; 40, Textularia globu- 
 losa; 41, Rotalia globulosa; 41 a, side view of Kotalia Boucana; 42, Grammostomum 
 phyllodes ; 43, a, Frondicularia annularis ; 44, Triloculina Josephina ; 45, Nodosaria vul- 
 garis ; 46, Lituola nautiloides ; 47, a, Flabellina rugdsa ; 48, Chrysalidina gradata ; 49, , 
 Cuneolina pavonia ; 50, Nummulites nummularia ; 51 a, &, Fusulina cylindrica. 
 
 single cell, like a Protozoan) comes to be divided into 
 numerous cells, of which the various tissues of the body 
 
 FIG. 52. 
 
 FORAMINIFER : Globigerina bulloides. 
 
 are formed. Some of these minute creatures form cal- 
 careous or siliceous skeletons, and are therefore capable 
 of preservation as fossils. 
 
62 
 
 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 FIG. 53. 
 
 FORAMINIFER : Eotalia, with pseu- 
 dopods protruded. 
 
 Of the classes of Protozoans, only one is of any impor- 
 tance in Geology, the Rhizopods. 
 
 Rhizopods. The name is derived from the Greek 
 pi^a, root, and TTOU?, foot, and re- 
 fers to the power which the ani- 
 mal possesses of protruding the 
 jelly-like protoplasm of which the 
 body is composed, into temporary 
 processes, often slender and branch- 
 ing like little roots. These tem- 
 porary extensions of the body, 
 called pseudopods (Greek i/reuS^, 
 false, and TTOU?, foot), envelop 
 particles of food, and serve as 
 extemporaneous stomachs for its 
 digestion. The power of extending the protoplasm of 
 the body in various directions enables the creature to 
 move with a sort of flowing movement. 
 
 Two groups of Rhizopods are especially important in 
 Geology, the Foraminifers and 
 the Radiolarians. The Foramini- 
 fers (Latin foramen, in allusion 
 to the minute pores in the shell 
 through which the pseudopods 
 are protruded) have generally 
 calcareous shells. A number of 
 the shells are represented in 
 Figs. 38-51. Figs. 50, 51 are 
 of natural size, and a few Fora- 
 minifers have shells even larger 
 than these. The others are mag- 
 nified, most of the shells being no larger than grains of 
 sand. Fig. 52 represents (much enlarged) the common 
 species of Grlobigerina, which lives at the surface of the 
 ocean over wide areas, and whose dead shells accumulate 
 in the ooze at the bottom. As shown in the figure, the 
 shell, when alive or unbroken, is covered with radiating 
 
 FIG. 54. 
 
 KADIOLARIAN : Xipbacantha, x 50. 
 
CLASSIFICATION. 
 
 63 
 
 57 
 
 FIGS. 58-72. 
 
 spines. Fig. 53 represents another living species (also 
 much enlarged), showing the pseudopods extended. 
 
 The Radiolarians (Latin radius, in allusion to the 
 
 radiated arrangement 
 of the pseudopods) are 
 somewhat more highly 
 organized than the For- 
 aminifers, the proto- 
 plasm of their bodies 
 showing more indica- 
 
 RADIOLAKIANS : Fig. 55, Lychnocanium ; 56, Eu- tion of differentiation 
 cyrtidium : 57. Halicalyptra. , rp\i i 
 
 into parts. They have 
 
 siliceous skeletons, which are often exquisitely beautiful. 
 Some of them are rep- 
 resented, considerably 
 magnified, in Figs. 
 54-57. 
 
 2. SPONGES. 
 
 The Sponges show 
 a higher grade of or- 
 ganization than the 
 Protozoans, since 
 they produce true 
 eggs, which di- 
 vide into numerous 
 cells in the process of 
 development. They 
 attain, however, no 
 such degree of differ- 
 
 Pntiatinn of ti<i<mp<j anrl SPONGE SPICULES: Figs. 58-61, Geodia or allied genera; 
 
 62, globostellate spicule, related to Geodia ; 63, Stel- 
 letta ; 64, Carterella ; 65, 66, Tetractinellid spicules ; 
 67, Ventriculites ; 68, Eagadinia annulata; 69, Tisi- 
 phonia ; 70, the same ; 71, Kacodiscula ; 72, Plintho- 
 sella squamosa. Figs. 62, 65, 66, x 10; 68, x 68; 
 others, x 34. Hinde. 
 
 organs as is shown in 
 the higher animals. 
 The gelatinous body 
 of a sponge is trav- 
 ersed by a system of canals, to which the sea water is 
 
64 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 admitted by numerous minute pores, and from which it 
 is discharged through a smaller number of larger orifices. 
 In most Sponges the gelatinous body is supported by a 
 network of horny fibers, generally associated with minute 
 spicules of silica. The sponges used in bathing are the 
 horny skeletons of species which are destitute of siliceous 
 spicules. In some Sponges the skeleton is entirely com- 
 posed of siliceous spicules, and still others have a cal- 
 careous skeleton. The spicules of Sponges have various 
 forms, as shown in Figs. 58-72. 
 
 3. CCELENTERATES. 
 
 The name is derived from #04X09, hollow, and evrepov, 
 intestine, and refers to the fact that in these animals the 
 only cavity is the digestive cavity, there being no body- 
 cavity, or peri visceral cavity, such as is found in the 
 higher animals. By the possession of a distinct mouth 
 and digestive cavity, the Coelenterates show a higher 
 grade than the preceding groups. Rudiments also of a 
 nervous system appear. The mouth is generally sur- 
 rounded by a wreath of radiating tentacles, and in most 
 species all the organs are repeated in radial order. 
 
 Two of the classes of Coelenterates are important in 
 geology, 1, Hydrozoans ; 2, AntTiozoans. 
 
 1. Hydrozoans. The name (from Greek, v$pa, hydra, and 
 ftwoy, animal) denotes animals resembling the little fresh- 
 water hydra. In that little creature (Fig. 73) the body 
 is little more than a tube, with the opening of the mouth 
 at one end, surrounded by a wreath of tentacles. Fig. 74 
 represents a somewhat similar marine form. In many 
 cases communities are formed by budding, the succes- 
 sively formed individuals (zooids) remaining permanently 
 attached to each other. These communities are often 
 branching, and look like delicate seaweeds. They are 
 often inclosed in a delicate horny investment. Two of 
 these horny skeletons are shown in Figs. 75, 76. A few 
 
CLASSIFICATION. 
 
 65 
 
 (as Millepore) form a calcareous skeleton or coral. Other 
 Hydrozoans, called Jellyfishes, or Medusae, have the 
 gelatinous body disk-shaped or hemispherical, and swim 
 freely with the mouth downward. A Medusa is shown in 
 Fig. 77. In many species, Medusae are produced by bud- 
 ding from a colony of hydra-like zooids. In this case the 
 Medusa produces eggs, from which the Hydroid com- 
 munity is developed. This alternation of generations is 
 very common among Hydrozoans, and occurs in some 
 other classes of animals. 
 
 HYDROZOANS : Fig. 73, Hydra, x 8 ; 74, Syncoryne ; 75, Sertularia abietina ; a, same, 
 magnified ; 76, Sertularia rosacea ; a, same, magnified ; 77, Tiaropsis. 
 
 2. Anthozoans. The name (from Greek aV0o?, flower, 
 and fwoz/, animal) refers to the beautiful flower-like aspect 
 given to many of these. creatures by their tentacles, which 
 radiate like the petals of a flower (Figs. 78, 79, 81), and 
 which are often brightly colored. Anthozoans are dis- 
 tinguished from Hydrozoans by having an involution of 
 the body wall at the mouth, forming a short esophagus 
 leading into the main cavity or stomach ; and by hav- 
 ing the latter cavity partly divided into radiating cham- 
 bers by partitions extending inward from the body wall. 
 Most of the Anthozoans form communities, branching 
 (Fig. 79), incrusting, or massive (Fig. 80), by budding or 
 
66 
 
 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 fission. Some Anthozoans, as the Sea Anemone (Fig. 78), 
 have no hard parts. Most of them, however, form corals 
 by the deposit of calcareous material in some part of the 
 body wall, and in radiating plates (septa) extending into 
 the radiating chambers. These radiating plates cause a 
 coral to be marked by stars (one corresponding to each 
 zooid in the community), as shown in Fig. 80, which rep- 
 resents a piece of fossil coral. Most of the coral animals 
 belong to the group of Zoantharians, in which the ten- 
 tacles and other radiating parts are indefinite in number 
 
 ANTHOZOANS : Fig. 78, Actinia ; 79, Dendrophyllia ; 80, Isastraea oblonga ; 81, Gorgonia. 
 
 (Figs. 78, 79), and usually in multiples of six. In the 
 remarkable fossil group of CyathophyUoids, the parts were 
 in multiples of four. The Precious Coral and the Sea 
 Fans ( Grorgonians), with their peculiar horny skeletons, be- 
 long to the Alcyoniarians, in which the tentacles (Fig. 81) 
 are uniformly eight in number and pinnate in form. 
 
 4. ECHINODERMS. 
 
 The name is derived from Greek e^vo?, hedgehog, and 
 SejOyLta, skin, and refers to the armor of spines with which 
 many of the species are covered (Fig. 8.7). The Echino- 
 derms differ from the Coelenterates in having a distinct 
 body-cavity, or perivisceral cavity, within which the ali- 
 mentary canal is contained. They show also a nervous 
 
CLASSIFICATION. 
 
 67 
 
 system much more highly developed, consisting of a 
 nervous ring around the mouth and radiating nerves 
 passing to the several segments of the body. As in the 
 Coelenterates, the organs of the body in general are 
 radially repeated. The number of radial segments is gen- 
 erally five. In some Echinoderms, the radial segments 
 are very unequally developed, and the radial symmetry 
 gives place in large degree to a bilateral symmetry. 
 
 Four of the classes of Echinoderms have considerably 
 developed external skeletons, and are important in Geol- 
 ogy : 1, Crinoids ; 2, Ophiuroids ; 3, Asterioids ; 4, JSchi- 
 noids. 
 
 FIGS. 82-84. 
 
 CRINOIDS : Fig. 82, Callocystites Jewettii ; 83, Pentremites pyriformis ; 84, Encrinus lilii- 
 
 formis. 
 
 1. Crinoids. The name is from Greek Kplvov, lily, and 
 many of the species have been commonly called Stone-lilies. 
 The species shown in Fig. 84 is named the Lily Encrinite. 
 Unlike all other Echinoderms, they are (with perhaps a 
 few exceptions) attached, at least temporarily, by a stem 
 of greater or less length growing out from the pole of 
 the body opposite the mouth. The Crinoids are a class 
 almost extinct. One of the few living species is repre- 
 sented in Fig. 85. Two of the three orders of the class 
 (Cystoids and Blastoids) are entirely extinct. 
 
 The Cystoids have the plates of the shell not regularly 
 radial in arrangement, and the arms either altogether 
 
68 
 
 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 wanting or feebly developed, and not regularly radiating. 
 One species is represented in Fig. 82. 
 
 The Blastoids (Greek /SXacrro?, bud) have an aspect of 
 which the name is beautifully descriptive. The plates of 
 the shell are arranged in regularly radial order. The 
 arms are wanting, but are represented by five areas radiat- 
 ing from the oral pole of the shell, and bearing pinnules 
 like those which are borne on the arms in the Brachiates. 
 Fig. 83 represents a Blastoid. 
 
 FIGS. 85-87. 
 
 CRINOIDS : Fig 1 . 85, Pentacrinus capnt-medusse ; ffl, ft, c, d, sections of stems of different 
 species of Pentacrinus. ASTERIOID : Fig. 86, Palseaster Niagarensis. ECHINOID : Fig. 
 . 87, Echinus, x J. 
 
 The Brachiates (Latin brachium, arm) have the plates 
 of the shell and the well-developed arms arranged in 
 regularly radial order. The arms are typically five in 
 number, but generally fork almost at the base, and often 
 branch repeatedly, so as to seem very numerous. Two 
 species are shown in Figs. 84, 85. 
 
 2. Ophiuroids. The name (Greek 6'<^?, snake, and 
 ovpd, tail) refers to the slenderness and flexibility of the 
 rays which radiate from the small central disk. Brittle 
 Stars and Serpent Stars are common names of these 
 
CLASSIFICATION. 69 
 
 animals. The viscera do not extend into the slen- 
 der rays. 
 
 3. Asterioids. The scientific name (Greek do-rijp, 
 star) is descriptive of the form of the body, like the com- 
 mon name Starfish. A fossil species is shown in Fig. 86. 
 The .rays, or arms, blend with the central disk, instead of 
 being sharply distinguished from it, as in the Ophiuroids ; 
 and the appendages of the alimentary canal and the other 
 viscera extend into the rays. 
 
 4. Echinoids. The name (from Greek e'%m>9, hedgehog) 
 refers to the spines, which in some species are large and 
 conspicuous. In Fig. 87 they are shown on the left side, 
 having been removed from the other side to show the 
 arrangement of the plates of which the shell is composed. 
 In most of the Echinoids, the plates are immovably articu- 
 lated with each other, so as to form a rigid shell. In this 
 they differ from the preceding classes, in which the plates 
 (at least in the rays) are movably articulated. The Echi- 
 noids are usually spheroidal or discoidal in form. They 
 are commonly called Sea Urchins. 
 
 5. MOLLUSCOIDS. 
 
 The name implies a resemblance to the Mollusks, with 
 which the Molluscoids were formerly confounded. The 
 two groups agree in the absence of the radial repetition 
 of homologous parts, which is characteristic of the two 
 preceding subkingdoms, and in the absence of the longi- 
 tudinal repetition of homologous parts, which is char- 
 acteristic of many Vermes and of the Arthropods and 
 Vertebrates. The Molluscoids differ from the Mollusks 
 in having a much less strongly developed nervous system; 
 in not having particular parts of the body specialized for 
 locomotive and sensory functions (foot and head), as is 
 the case in most of the Mollusks ; and in being generally 
 attached, while the Mollusks are generally locomotive. 
 Eminently characteristic of the Molluscoids is a sort of 
 collar about the mouth (lophophore) , sometimes nearly 
 
70 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 circular, sometimes horseshoe-shaped, sometimes produced 
 into a pair of long arms, bearing a fringe of tentacles or 
 cirri. 
 
 The Molluscoids include two classes, both of which are 
 important in geology : 1, Bryozoans ; 2, Brachiopods. 
 
 1. Bryozoans. The name (Greek ftpvov, moss, and fcSo^, 
 animal) is prettily descriptive of the delicate mosslike 
 tufts which are formed by many of the communities of 
 these little creatures. They multiply by budding (as well 
 as by producing eggs), and the communities thus formed 
 often greatly resemble those .of Hydrozoans. The ani- 
 mals, however, are much higher in their grade of or- 
 ganization, possessing an alimentary 
 
 1*1 1* * i * 
 
 canal inclosed in a perivisceral cavity, 
 an( ^ a we ll-developed nervous gang- 
 lion. The lophophore (well shown 
 in Figs. 88, 89) is circular or horse- 
 shoe-shaped, bears a wreath of rela- 
 tively long tentacles, and is never 
 produced into a pair of long arms. 
 The Bryozoan communities are some- 
 time * Destitute of any hard parts, 
 
 removed from its cell, more j^ generally secrete a horny or 
 
 enlarged. J _ . , * 
 
 calcareous covering, which incloses 
 
 each zooid in a little cell. When the skeleton is calca- 
 reous, it forms a delicate sort of coral. 
 
 2. Brachiopods. The name (from Greek fipaxfov, arm, 
 and Trow, foot) refers to the peculiar development of the 
 lophophore, which in these animals is produced into a pair 
 of long fringed arms, which are spirally coiled within the 
 shell. 'In Fig. 90, one of the arms is extended beyond the 
 margin of the shell. Unlike the Bryozoans, the Brachio- 
 pods never multiply by budding. The skin is produced 
 into two folds, one on the dorsal, and one on the ventral 
 side of the body, which secrete the two pieces of a bivalve 
 shell. Brachiopods were formerly confounded with the 
 Lamellibranchs among the Mollusks (Clams, Mussels, etc.), 
 
CLASSIFICATION. 
 
 FIG. 90. 
 
 since these animals also have bivalve shells. The valves 
 in the Lamellibranchs are right and left, and are therefore 
 entirely different from those of Brachio- 
 pods in their relation to the body of the 
 animal. This difference of position is 
 correlated with characteristic differences 
 in the form of the shell. In Brachiopods 
 the two valves are never alike, while in 
 Lamellibranchs (with a few exceptions, 
 as the Oyster) they are nearly or exactly 
 alike. On the other hand, each valve is 
 almost always symmetrical in the Brachi- 
 opods, never in Lamellibranchs. The 
 shells of a number of Brachiopods are 
 shown in Figs. 91-98. In many Brachiopods, processes 
 are developed from the interior of the dorsal valve, to 
 
 FIGS. 91-98. 
 
 BRACHIOPOD : Ehyn- 
 chonella psittacea. 
 
 BRACHIOPODS: Fig. 91, Waldheimia flavescens, interior view; 92, loop of Terebratula 
 vitrea ; 93, loop of Terebratulina caput-serpentis ; 94, Spirifer striatus ; 95, same, interior 
 of dorsal valve; 96, Athyris concentrica; 97, Atrypa reticularis ; 98, same, interior of 
 ventral valve. 
 
 support the arms of the lophophore. These arm-supports 
 may be looplike (Figs. 91-93) or spiral (Figs. 95, 98). 
 The Brachiopods are generally attached by a fleshy stem 
 
72 
 
 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 FIGS. 99-101. 
 
 passing out between the valves, or (more commonly) 
 through an aperture in the beak of the ventral valve 
 (shown at a in Fig. 96). In one recent species of Lin- 
 gula, the pedicel has been observed to serve as an organ 
 of locomotion. The Brachiopods are represented by but 
 few living species, but were immensely abundant in early 
 geological periods. 
 
 6. MOLLUSKS. 
 
 Mollusks agree with the Molluscoids in the absence of 
 segmentation, either radial or longitudinal. They show, 
 however, a much higher grade of organization. Almost 
 always there is a foot, or specialized loco- 
 motive portion of the body; and gener- 
 ally a head, or specialized oral and sensory 
 portion. The nervous system is well 
 developed. Special respiratory organs are 
 generally present, most commonly in the 
 form of gills. Budding is entirely un- 
 known, reproduction being solely by 
 means of eggs. The integument is gener- 
 ally produced into a fold, or a pair of 
 folds, called the mantle, which secretes a 
 calcareous shell. The shell is generally 
 large enough to form a covering for the 
 body; but is sometimes small arid con- 
 cealed.in the mantle, and sometimes rudi- 
 99, cyprina; ioo, Tel- meiitary or wanting. 
 
 lina; 101, Ostrea. ^ ,t -, * *r n i ,1 
 
 Or the classes of Mollusks, three are 
 important in Geology: 1, Lamellibranchs ; 2, Gastro- 
 pods; 3, Cephalopods. 
 
 1. Lamellibranchs. The name (from Latin lamella and 
 branchia) refers to the form of the gills, which in most 
 species are developed as two lamellar folds on each side of 
 the body. The Lamellibranchs differ from the other classes 
 to be described, in the lack of a distinct head, and in the 
 lack of any masticatory apparatus connected with the 
 
CLASSIFICATION. 73 
 
 mouth. The mantle is always developed in two lobes 
 (right and left), and the shell accordingly is always bi- 
 valve. The distinctions between the shells of the Lamelli- 
 branchs and those of the Brachiopods have been given on 
 page 71. The interior of the shell in Lamellibranchs bears 
 markings which give much information in regard to the 
 soft parts of the body. The shell is generally closed by 
 two powerful muscles, the anterior and the posterior ad- 
 ductor. These make deep impressions where they are 
 inserted into the shell (1, 2, in Figs. 99, 100). Sometimes 
 (as in the Oyster) the anterior adductor is wanting, and 
 then only one impression is shown in the shell (2, in Fig. 
 101). In most shells a somewhat distinct line extends 
 from one adductor to the other (jt?jt?, in Figs. 99, 100), 
 formed where the muscular border of the mantle adheres 
 to the shell. In some species, the mantle lobes are entirely 
 separate along the ventral margin, admitting the water 
 freely to the gill chamber. In others, the mantle lobes 
 are united along the ventral margin, and their posterior 
 border is produced into two tubes (siphons) by which, re- 
 spectively, water is admitted and expelled. These siphons 
 are generally more or less perfectly retractile ; and the 
 mantle impression shows a notch, or sinus (s, in Fig. 100), 
 marking the area into which the siphons are withdrawn. 
 These markings are often clearly shown in fossil shells. 
 
 2. Gastropods. The name (from yao-Trjp, belly, and 
 TTOW, foot) refers to the fact that these animals generally 
 crawl on the ventral surface of the flattened foot, as well 
 shown in Fig. 102, representing a land Snail. The head 
 is supplied typically with two pairs of sensory tentacles, 
 one of which bears a pair of eyes. In the Snail (Fig. 102) 
 the eyes are borne on the larger posterior tentacles. The 
 two pairs of tentacles may be more or less perfectly fused 
 into a single pair. Respiration is generally effected by 
 means of gills ; but in the land Snails there is an air sack, 
 or simple lung ; and some Gastropods have no special 
 organs of respiration. The great majoritv of the Gatro- 
 
74 
 
 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 FIG 
 
 pods have shells in the form of a turreted spiral, large 
 enough to cover the animal completely. A number of 
 
 fossil species are shown in 
 Figs. 103-108. Others have 
 shells flattened, conical, or of 
 other forms. The shell may 
 be small and concealed in the 
 mantle, or may be entirely 
 wanting. 
 
 In the Pteropods (Greek 
 
 oV, wing, and TTOU?, foot), regarded by most zoologists 
 as an aberrant group of Gastropods, though perhaps 
 deserving to be considered as a distinct class, a pair of 
 
 GASTROPOD : Helix. 
 
 FIGS. 103-108. 
 
 108 
 
 GASTROPODS : FIG. 103, Pyrifusus Newberryi ; 104, 105, Bulla speciosa ; 106, Anchura 
 (Drepanocheilus) Americana ; 107, Fasciolaria buccinoides ; 108, Margarita Nebrascensis. 
 
 lateral appendages to the foot are developed as fins (shown 
 in Fig. 109). Unlike most Mollusks, these little crea- 
 tures are adapted for a free-swimming, pelagic FlG . 10 g. 
 life. At present, the Pteropods include only 
 a small number of species, all of which are of 
 very small size. In early geological times much 
 larger species existed. 
 
 3. Cephalopods. The name is from Greek 
 #e(aX?7, head, and TTOU?, foot. In these most 
 highly organized of Mollusks, the head is armed with a 
 
 Cleodora - 
 
CLASSIFICATION. 
 
 75 
 
 FIG. 110. 
 
 circle of prehensile tentacles, and bears two large eyes 
 of remarkably elaborate structure. Respiration is always 
 by means of gills. The water taken into the gill chamber 
 is expelled through a funnel (shown at i in Fig. 111). 
 The reaction of the water, 
 when forcibly ejected, propels 
 the body in the opposite di- 
 rection, affording one of the 
 means of locomotion possessed 
 by these active creatures. The 
 Cephalopods are divided into 
 two orders, both of which have 
 played an important role in 
 geological history. 
 
 The Tetrabranchs (Greek 
 rerpa, four, and /3pdy%i,a, gills) have four gills. Their 
 tentacles are numerous, but not armed with suckers or 
 hooks. They have no ink-bag. They are defended by 
 
 FIG. ill. 
 
 TETKABKANCH : Nautilus. 
 
 DIBRANCH: Loligo vulgaris, x |; i, funnel; p, pen. 
 
 an external shell :r, the form of a tube, which may 'be 
 straight or coiled, but which is always divided into 
 chambers by transverse partitions (septa), which are per- 
 forated by a smaller tube (siphuncle). Fig. 110 shows 
 in section the coiled and chambered shell of Nautilus, the 
 only living genus of the order. 
 
 The Dibranchs (Greek &, twice, and ffpdyxia, gills) have 
 two gills. Their tentacles are eight or ten in number, and 
 bear suckers or hooks, making them very powerful weapons. 
 
76 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 They secrete an inky fluid, which is discharged through 
 the funnel when they seek to escape from pursuers. With 
 an apparent exception in a single genus, they have no 
 external shell. They generally, however, have some 
 sort of a shell concealed in the mantle. This may 
 be the horny pen of the Squid (j?, in Fig. Ill), the 
 so-called bone of the Cuttlefish, or a chambered shell 
 resembling the shells of the Tetrabranchs. 
 
 7. VERMES, OR WORMS. 
 
 The animals commonly included under this name are 
 a heterogeneous group. Some of them have the body 
 divided into a longitudinal series of segments, and the 
 nervous system constructed on the same plan as that of 
 the Arthropods, with which the Segmented Worms are 
 probably closely related. Others (including the numerous 
 parasitic Worms) are not segmented. The only skeletal 
 structures possessed by any Worms are minute jaws, which 
 are occasionally preserved as fossils. Otherwise, they are 
 indicated in the rocks only by trails left on the mud and 
 by remains of the tubes and burrows in which they have 
 lived. The whole subkingdom is unimportant to the 
 geologist. 
 
 8. ARTHROPODS. 
 
 The name is derived from the Greek apOpov, joint, and 
 TTOU?, foot, and refers to the jointed appendages, or limbs, 
 which are so conspicuous in the Lobster and in most 
 Insects. The body is composed of a longitudinal series of 
 joints or segments, well shown in the posterior part of 
 a Lobster. The segmented structure is often obscured 
 (especially in the anterior part of the body) by a number 
 of the segments being fused together, as in the anterior 
 part of a Lobster. Typically, each segment of the body 
 bears a pair of jointed appendages, which may be antennae 
 (or feelers), jaws, accessory mouth organs, legs for walk- 
 
CLASSIFICATION. 
 
 77 
 
 ing or swimming, etc. The nervous system consists typi- 
 cally of a pair of ganglions in each segment, connected 
 by a double nervous cord along the ventral side of the 
 body, though in many cases the ganglions of several seg- 
 ments come to be united. 
 
 Four of the classes of Arthropods are important in Ge- 
 ology : 1, Crustaceans; 2, Merostomes ; 3, Arachnoids ; 
 4, Insects. 
 
 1. Crustaceans. The name (from Latin crusta, crust 
 or shell) refers to the fact that the integument is gener- 
 ally hardened by a deposit of calcium carbonate, so as to 
 
 FIGS. 112-120. 
 
 ENTOMOSTRACANS: Fig. 112, Anatifa; 113, Cythere Americana; 114, Sapphirina iris, female ; 
 115, same, male, x6; 116, Calymene Blumenbachii. MALACOSTRACANS: Fig. 117, Por- 
 cellio; 118, Serolis, x ; 119, Orchestia; 120, Cancer. 
 
 form a sort of shell. The Crustaceans are aquatic Arthro- 
 pods, breathing by means of gills (or through the integu- 
 ment, without special organs of respiration), and having 
 typically the two anterior pairs of appendages developed 
 as antennae. 
 
 The Crustaceans are divided into two subclasses, the 
 Entomostracans and the Malacostracans. In the former, 
 the number of segments of the body varies widely, and 
 very rarely more than three pairs of appendages serve as 
 jaws or other mouth organs. In the latter subclass the 
 number of segments of the body never varies far from the 
 
78 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 typical number (19) 1 , and almost always four to six pairs 
 of appendages function as mouth organs. 
 
 Among the Entomostracans, the Trilobites, named from 
 Greek rpla, three, and Xo/3o?, lobe, in allusion to the 
 division of the body longitudinally into three lobes, as 
 shown in Fig. 116, are an order now extinct, but im- 
 mensely abundant in earlier geological periods. The 
 Trilobites appear to represent a very primitive type of 
 Crustacea, and they perhaps deserve to rank as a distinct 
 subclass. In the Ostracoids (Fig. 113), the integument is 
 produced into a pair of folds, right and left, forming a 
 bivalve carapace, which reminds one of the bivalve shell of 
 a Larnellibranch. The name is from the Greek oarpaKov, 
 shell. The Cirripeds, or Barnacles (Fig. 112), attach 
 themselves by means of modified antennae, and become 
 covered by a hard shell of several pieces, looking some- 
 what like the shell of a Mollusk. 
 
 Among the Malacostracans is included the curious group 
 of the Leptostracans, which are in many respects inter- 
 mediate between the typical Malacostracans and the En- 
 tomostracans. The Leptostracans are now nearly extinct, 
 though they seem to have been represented in earlier times 
 by numerous species, some of them being of large size. 
 One of them is shown in Fig. 233, on page 249. The 
 Arthrostracans, or Tetradecapods (Greek Terpa, four, Sexa, 
 ten, 7TOU9, foot), have four pairs of appendages developed 
 as mouth organs, and seven pairs as legs. Here belong 
 the Sow-bugs and Sand-fleas* Three species are shown 
 in Figs. 117-119. The highest order of the Malacostra- 
 cans is that of Decapods (Greek Se'/ca, ten, and TTOI;?, foot), 
 in whicB six pairs of appendages are developed as mouth 
 organs, and only five pairs as legs. Here belong the Lob- 
 ster and the Crab (Fig. 120), the former representing the 
 suborder of Macrurans (Greek yLtatf/oo?, long, and ovpd, tail), 
 
 1 Exclusive of the telson, at the posterior extremity of the body, which, 
 though it never bears appendages, is considered by many zoologists a true 
 segment. 
 
CLASSIFICATION. 79 
 
 the latter representing the suborder of Brachyurans (Greek 
 w, short, and ovpd, tail). 
 
 2. Merostomes. The name is derived from the Greek 
 , thigh, and o-ro/ia, mouth, and refers to the fact that 
 
 some of the appendages have their basal joints developed 
 as jaws and their terminal portions developed as legs. 
 The Merostomes differ from the Crustaceans in the absence 
 of antennae. The Limulus, or Horseshoe Crab, is the only 
 living genus of this class. In early geological times the 
 class was represented by the Eurypterids, one of which is 
 shown in Fig. 278, page 271. 
 
 3. Arachnoids. The name is from the Greek apd%vr), 
 spider, and the Spiders and Scorpions are typical members 
 of the class. They are terrestrial Arthropods, breathing 
 by means of air sacks (lungs) or ramifying air tubes (tra- 
 cheae). They have no antennae, two pairs of mouth organs, 
 and four pairs of legs. The absence of antennae, as well 
 as certain other characters, has been held by many zoolo- 
 gists to indicate a close relationship to the Merostomes. 
 
 4. Insects. Terrestrial Arthropods, breathing by 
 means of tracheae. They have one pair of antennae, three 
 pairs of mouth organs, and (in the typical subclass) three 
 pairs of legs. The Insects are divided into two subclasses, 
 Myriopods and Hexapods. The Myriopods (Greek 
 fjivpios, countless, and TTOW, foot) have numerous legs, the 
 series of legs extending to the posterior extremity of the 
 body. They have no wings. The Hexapods (Greek ef, 
 six, and Trow, foot) have three pairs of legs, borne on the 
 three segments of the body (thorax) next behind the head. 
 Most of them have two pairs of wings ; but the Flies and 
 their allies (Dipters) have only one pair, and some Hexa- 
 pods are entirely wingless. 
 
 9. TUNICATES. 
 
 The Tunicates have no skeletons, and are unknown 
 in fossil condition. They appear to be a degenerate 
 branch of the Vertebrate stem. In adapting themselves 
 
80 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 to a sedentary life, they have lost most of the charac- 
 teristics of Vertebrates, though their relation to that 
 group is indicated by their embryology. 
 
 10. VERTEBRATES. 
 
 The Vertebrates, or vertebrated animals, take their name 
 from the backbone, or vertebral column. The distinctive 
 character of the Vertebrates is the division of the body 
 into a dorsal cavity containing the central organs of 
 the nervous system, and a ventral cavity containing the 
 nutritive viscera, separated from each other by an axial 
 skeleton. In the lowest Vertebrates, as in the embryos 
 of the higher forms, this axial skeleton appears as an 
 unsegmented chord (notochord). But, in all except the 
 lowest Vertebrates, cartilaginous or bony rings are devel- 
 oped in the sheath of the notochord, which encroach upon 
 it, often to its entire obliteration, forming the bodies of 
 the vertebrae. Cartilaginous or bony arches connected 
 with the vertebral bodies come to inclose more or less 
 completely the nervous cord on the dorsal side of the axis 
 and the viscera on the ventral side of the axis. The axial 
 skeleton and the nervous cord both undergo remarkable 
 modifications at the anterior extremity of the body, form- 
 ing the skull and brain. 
 
 Vertebrates are divided into the following classes : 1, 
 Leptocardians ; 2, Marsipolranchs ; 3, Fishes; ^Amphibi- 
 ans; 5, Reptiles; 6, Birds; 7, Mammals. 
 
 1. Leptocardians. The name (Greek Xe-Trnfc, thin, and 
 /capSia, heart) refers to the absence of a massive, muscular 
 heart, the blood being propelled only by the action of 
 muscular tissue diffused through various parts of the 
 arterial system. The notochord shows itself in very 
 primitive condition. There are no bones, scales, teeth, 
 limbs, skull, nor brain. Having no hard parts, these 
 animals have never been preserved as fossils. They are, 
 however, profoundly interesting, since they represent, 
 more nearly than any other animals, what must have been 
 
CLASSIFICATION. 81 
 
 the primitive type of Vertebrates. The class is repre- 
 sented only by the Amphioxus, or Lancelet. 
 
 2. Marsipobranchs. The name (Greek pdpo-iTros, pouch, 
 and Ppdyxia, gills) refers to the form of the gills, which 
 are a series of pouches on each side, communicating with 
 the pharynx. The Marsipobranchs show a persistent noto- 
 chord, with no vertebral bodies. They have no limbs, and 
 the mouth is not provided with jaws. The Lampreys 
 are familiar examples of this class. Their only hard 
 parts are little teeth inserted in the mucous membrane 
 of the mouth. Such teeth might be preserved as fossils, 
 but have not yet been recognized. 
 
 3. Fishes. These differ from the preceding classes in 
 the development of cartilaginous or bony vertebral bodies, 
 and in the possession of jaws and (generally) two pairs of 
 limbs. They differ from the remaining classes in that the 
 limbs are developed as fins, the respiration is by gills, and 
 the heart consists (except in one subclass) of one auricle 
 and one ventricle. The teeth, fin spines, scales, and bones 
 of Fishes are among the important fossils in many forma- 
 tions. 
 
 Fishes are divided into five subclasses : 1, Selachians; 
 2, Placoderms ; 3, Granoids; 4, Teleosts ; 5, Dipnoans. 
 
 The Selachians (Greek 0-eXa^?;, cartilaginous fishes) have 
 skeletons but slightly ossified. The vertebral column 
 extends to the extremity of the tail fin, generally bending 
 up into the upper lobe, which is then commonly much 
 longer than the lower, as shown in Figs. 121, 123. Such 
 tails are called heterocercal (Greek ere/oo?, other, and /cep/eo?, 
 tail). In some Selachians, however, the vertebral column 
 extends in a straight line to the extremity of a symmetri- 
 cal tail fin. This form of tail, called diphycercal, is 
 believed to be the primitive type. 
 
 Many Selachians have strong spines at the margin of 
 some of the fins (Figs. 121-123). They all have a skin 
 roughened by minute toothlike points (shagreen). Some 
 of them have sharp cutting teeth, as shown in Figs. 124- 
 
82 
 
 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 126; others have flat pavement teeth, adapted to crush 
 the shells of Mollusks and Crustaceans (Figs. 129-131). 
 Figs. 127, 128, represent a somewhat intermediate type. 
 The gills of Selachians are developed as a series of 
 pouches through which the water passes from the pharynx 
 
 FIGS. 121-131. 
 
 SELACHIANS : Fig. 121, Spinax Blainvillii, x J ; 122, spine of anterior dorsal fin, natural 
 size ; 123, Cestracion Philippi, x ; 124, tooth of Lamna elegans ; 125, Carcharodon 
 angustidens ; 126, Notidanus primigenius ; 127, Hybodus minor ; 128, Hybodus plica- 
 tilis ; 129, lower jaw of Cestracion, showing pavement teeth ; 130, tooth of Acrodus 
 minimus ; 131, Acrodus nobilis. 
 
 to escape by holes in the sides of the neck. The arrange- 
 ment resembles that in the Marsipobranchs. In most 
 Fishes the gills are developed as fringes projecting freely 
 from the branchial arches of the skull. Most of the 
 Selachians are commonly known as Sharks and Rays. 
 The Placoderms (Greek vrXa'f, plate, 8e^a, skin) have 
 
CLASSIFICATION. 83 
 
 the body, or at least its anterior part, covered with an 
 armor of large, bony plates. Some of them are repre- 
 sented in Figs. 297-300, on page 285. As these creatures 
 are known only as fossils, their true nature is somewhat 
 doubtful. Some of them (Figs. 297, 298) appear to have 
 no lower jaw, or at least none capable of preservation in 
 a fossil state ; and it is doubtful whether they are truly 
 Fishes. Others (Figs. 299, 300) have a well-developed 
 lower jaw, and are believed by many paleontologists to be 
 an aberrant group of Dipnoans. 
 
 The Ganoids (Greek 7^1/09, luster) are generally covered 
 by hard, lustrous, enameled scales, most commonly of 
 
 FIG. 132. 
 
 GANOID : Palaeoniscus Freieslebeni, x J. 
 
 rhombic form (Figs. 132-136). Some Ganoids, however, 
 are clothed with cycloid scales (Fig. 141) like those of 
 many Teleosts, from which they differ only in certain 
 anatomical details relating to the optic nerves, the heart, 
 and the intestine. The skeleton in the Ganoids varies 
 greatly in the degree of ossification, sometimes becoming 
 as perfectly ossified as in the Teleosts. The tail is some- 
 times heterocercal (Fig. 132) or diphycercal. In other 
 Ganoids the vertebral column stops at or near the base 
 of the tail fin, whose lobes then appear nearly symmetri- 
 cal (Fig. 133). Such tails are called homocercal (Greek 
 6/409, the same, and /cepfcos, tail) . The Ganoids are a group 
 now nearly extinct, though very abundant in early geo- 
 logical times. 
 
 Teleosts (Greek re'Xeo?, perfect, and Qcrreov, bone) are so 
 
84 
 
 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 named on account of the high degree of ossification of 
 their skeletons. With few exceptions, they are clothed 
 with thin, membranous scales, which are called cycloid 
 (Greek KVK\O<;, circle) when the posterior margin is 
 smoothly rounded (Fig. 141), and ctenoid (Greek terek, 
 comb) when the margin is beset with teeth (Fig. 142). 
 Teleosts, with very few exceptions, have homocercal tails. 
 The great mass of familiar Fishes belong to this subclass. 
 Dipnoans resemble the Ganoids in many respects, but 
 have the air bladder developed into a functional lung, the 
 auricle of the heart divided into two, and a distinct pul- 
 
 138 
 
 GANOIDS: Fig. 133, tail of Aspidorhynchus ; 134, scales of Cheirolepis Traillii, x 12; 135, 
 Palaeoniscus lepidurus, x 6 ; 136, inner surface of same ; 137, pavement teeth of Gyrodus 
 umbilicus ; 138, tooth of Cricodus ; 139, Lepidosteus osseus ; 140, section of same, 
 enlarged. TELEOSTS : 141, cycloid scale ; 142, ctenoid scale. 
 
 monary circulation. In these characters they show a 
 transition to the Amphibians. They also differ from 
 most Fishes, and agree with the higher classes of Verte- 
 brates, in the mode of articulation of the jaws with the 
 skull. The name is from the Greek S&, twice, and wen, 
 to breathe, in allusion to their possessing both gills and 
 lungs. 
 
 4. Amphibians. The name (Greek a/^t, on both sides, 
 /Sib?, life) refers to the fact that most of these animals are 
 partly aquatic and partly terrestrial in habit. Most .of 
 them undergo a strongly marked metamorphosis. In 
 
CLASSIFICATION. 85 
 
 their early stage, they breathe by means of gills, have a 
 heart with a single auricle, and are aquatic ; in adult life, 
 they breathe by means of lungs, have two auricles and a 
 distinct pulmonary circulation, and are more or less com- 
 pletely terrestrial. Their limbs (rarely wanting) are 
 developed not as fins, but as legs. Toads, Frogs, and 
 Salamanders are well-known examples of this class. The 
 remarkable extinct group of the Stegocephala, or Laby- 
 rinthodonts, is illustrated on pages 308, 352. 
 
 5. Reptiles. These resemble adult Amphibians in 
 having a heart with two auricles and one ventricle (the 
 Crocodiles being exceptional among recent Reptiles in 
 having the ventricle divided), and in breathing by means 
 of lungs. No gills are developed at any stage of life. 
 Turtles, Lizards, Snakes, and Crocodiles are the principal 
 groups of living Reptiles. The remarkable order Rhyn- 
 chocephala is referred to and illustrated on pages 308, 309. 
 That order is nearly extinct, being represented by a single 
 genus in New Zealand. Numerous orders of Reptiles are 
 entirely extinct, the present representatives of the class 
 being only a remnant. Some of these fossil groups are 
 described on pages 340, 352, 372. 
 
 6. Birds. These differ from Reptiles in having a 
 covering of feathers, and also in having two ventricles 
 and a perfect double circulation. The more vigorous 
 circulation and respiration cause Birds (like Mammals) to 
 have a temperature often considerably above that of the 
 surrounding medium. Birds and Mammals are accord- 
 ingly said to be warm-blooded, while the preceding classes 
 are said to be cold-blooded. The class of Birds is at 
 present remarkably distinct and homogeneous ; but some 
 of the fossil birds (pages 356, 374) show characters which 
 ally them very closely with Reptiles. 
 
 7. Mammals. The name (from Latin mamma, breast) 
 refers to the habit of suckling the young, by which these 
 animals are characterized. 
 
 The subclass Monotremes are the lowest and most rep- 
 
8b" THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 tilian of Mammals. Like most Reptiles, they are ovipa- 
 rous ; and in many points of their anatomy they greatly 
 resemble Reptiles. They are now represented only by 
 the Duckbill (Ornithorhynchus) and the Spiny Ant-eater 
 (Echidna), both of which live in Australasia. 
 
 In the subclass Marsupials (Latin marsupium, pouch), 
 the young are produced viviparously ; but, in the absence 
 of a placenta, the development is not far advanced before 
 birth. The young are accordingly, in most species, carried 
 by the mother for a time in a pouch formed by folds of 
 skin, within which the teats are situated. With the 
 exception of the Opossums, which live in America, the 
 Marsupials are now confined to Australasia, where they 
 are represented by Kangaroos, Phalangers, Wombats, etc. 
 Formerly they existed in all regions of the globe. 
 
 In the Placentals, or typical Mammals, provision is 
 made for the nutrition of the embryo before birth, by 
 means of the structure called the placenta ; and the young 
 are accordingly bom in a more advanced stage of devel- 
 opment. In this subclass are included all the familiar 
 Mammals (with the exceptions above indicated), as well 
 as Man himself. 
 
 The Vegetable Kingdom. 
 
 Plants are commonly divided into the two groups, 
 Cryptogams and Phanerogams. 
 
 1. CRYPTOGAMS.l 
 
 The name (from Greek fcpvTrrds, secret, and 7^0?, 
 marriage) was given to these plants by Linnseus, in 
 allusion to the fact that the reproductive organs appeared 
 
 1 The group of Cryptogams is retained simply as a matter of conven- 
 ience. It is a heterogeneous assemblage, like the assemblage of Inverte- 
 brates among animals. But the lower plants play so unimportant a r61e 
 in Geology, that it is not worth while to trouble the beginner in Geology 
 with the technicalities of the modern classification. 
 
CLASSIFICATION. 87 
 
 in general less conspicuous than in the Phanerogams, and 
 that in many of them the reproductive processes were in 
 his time altogether unknown. Here are included all 
 plants which do not bear flowers and produce seeds. The 
 reproductive bodies are single cells, and are called spores. 
 
 1. Thallophytes. 1 This name is given to an assemblage 
 of the lower Cryptogams, most of which agree in the 
 negative character of showing no definite axis of upward 
 growth, and no distinction of root, stem, and leaf. They 
 all consist entirely of cellular tissue, being destitute of 
 wood. These plants arid the Bryophytes are sometimes 
 called Cellular Cryptogams, in distinction from the Pteri- 
 dophytes, which are called Vascular Cryptogams. The 
 lowest Thallophytes are unicellular organisms. Some of 
 the higher Thallophytes are large and complex plants. 
 
 Disregarding the differences of structure of which a 
 truly natural classification must take note, we may con- 
 veniently, for present purposes, divide the Thallophytes 
 into two groups, on the basis of a single physiological 
 character. Some of them contain chlorophyll, and are 
 therefore capable of decomposing carbon dioxide and 
 nourishing themselves upon inorganic materials. These 
 are called Algce. Most of these are aquatic, and many 
 of them are popularly called Seaweeds. Other Thallo- 
 phytes are destitute of chlorophyll, and must feed on 
 organic materials. Some of them live as parasites upon 
 other plants or upon animals ; others live upon decaying 
 organic matters. These are called Fungi. Mushrooms, 
 Toadstools, Molds, Bacteria, etc., are here included. 
 The Lichens, which often appear as grayish crusts on 
 rocks and trees (often mistakenly called Mosses), appear 
 to be composite organisms, consisting of an Alga and a 
 Fungus. 
 
 Of these soft, woodless plants, only the aquatic Algae 
 attain any importance as fossils. 
 
 1 This group, like that of Cryptogams, is heterogeneous, and is here 
 adopted simply as a matter of convenience. 
 
THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 FIGS. 143-148. 
 
 DIATOMS, highly magnified : Fig. 143, 
 Pinnularia peregrina ; 144, Pleuro- 
 eigma angulatum ; 145, Actinop- 
 tychus senarius ; 146, a, Melosira 
 sulcata ; 147, Grammatophora 
 marina ; 148, Bacillaria paradoxa. 
 
 Diatoms are unicellular Algae which secrete siliceous 
 skeletons. They abound in both salt and fresh water, 
 and their remains often accumulate so as to form deposits 
 
 of considerable thickness. Sev- 
 eral species are represented in 
 Figs. 143-148. An interesting 
 group of fossil Diatoms is shown 
 in Fig. 440, on page 392. 
 
 Desmids are unicellular Algse, 
 somewhat resembling Diatoms, 
 but destitute of any siliceous 
 skeleton. They are sometimes 
 found fossil in flint and chert. 
 
 Corallines and Nullipores are 
 Algae which contain in their tis- 
 sues a large amount of calcium 
 carbonate. 
 
 The Fucoids include many large species of Algse whose 
 fronds have a leathery consistency. Casts of these are 
 found fossil in many strata. 
 
 2. Bryophytes. The name is from Greek fipvov, moss, 
 and (J>VTOV, plant. The plants here included are the Liver- 
 worts and Mosses. In the Mosses, the habit of growth 
 resembles that of the higher plants in the development 
 of an axis of upward growth, forming a leafy stem. The 
 Bryophytes, however, agree with the Thallophytes in 
 being destitute of wood. A woodless terrestrial plant 
 has little chance of preservation in fossil condition, and 
 the .Bryophytes are unimportant to the geologist. 
 
 3. Pteridophytes, or Acrogens. The former name is 
 from Greek Trrepis, fern, and (pvrov, plant; and the plants 
 here included are the Ferns, Equiseta, and Lycopods. In 
 these plants, as in the Phanerogams, the stems are strength- 
 ened by bundles of woody fiber. Such plants are much 
 less perishable than the cellular plants, and accordingly 
 are much more important in Geology. In the Ferns of 
 temperate climates the stems are mostly underground, so 
 
CLASSIFICATION. 89 
 
 , 
 
 that the fronds spring from the ground ; but in some 
 tropical Tree Ferns the fronds spring from the summit of 
 a trunk fifty feet or more in height. The Equiseta of the 
 present time (often called Horsetails, or Scouring Rushes) 
 are slender plants with hollow, jointed stems. The 
 Lycopods are often called Club Mosses, or Ground Pines. 
 
 A11 living species of Equiseta and Lycopods are small 
 plants, rising only a few inches above the ground. In 
 former geological times, both groups were represented by 
 large trees. 
 
 2. PHANEROGAMS, OR PREJNOGAMS. 
 
 Both names (one from Greek (fravepos, manifest, and 
 , marriage; the other from <atVo>, to appear, and 
 refer to the fact that the reproductive organs are 
 conspicuous, and the reproductive processes have long 
 been well known. The essential reproductive organs are 
 the stamens and pistils ; and these, with the floral enve- 
 lopes, which are generally present and often conspicuously 
 colored, constitute the flowers. The pistils bear the 
 ovules, which develop into seeds. A seed contains an 
 embryo plant already formed. In most Phanerogams, as 
 in the higher Cryptogams, there is a definite axis of up- 
 ward growth, and a distinct differentiation of root, stem, 
 and leaves ; and in all Phanerogams, as in the Pterido- 
 phytes, more or less of wood is developed. In the 
 arrangement of the wood cells and ducts (fibrovascular 
 bundles) Phanerogams exhibit two distinct types. In 
 exogenous stems (Greek ef&>, outward, yei>o>, to grow), the 
 fibrovascular bundles are arranged in a hollow cylinder 
 around a central pith. If the stem continues to grow for 
 successive years, each season of growth adds a layer of 
 wood between the outermost of the previous layers and 
 the bark. A transverse section of such a stem (Fig. 149) 
 shows a series of rings corresponding to the successive 
 seasons of growth. In endogenous stems (Greek ev&ov, 
 within, and 7eV&>), the fibrovascular bundles are dis- 
 
90 
 
 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 FIGS. 149-152. 
 
 tributed through the stem without any definite arrange- 
 ment in concentric zones (see Fig. 150). 
 
 Phanerogams are divided into two classes, G-ymno- 
 sperms and Angiosperms. 1 
 
 1. Gymnosperms. The name (from Greek yvfjivds, 
 naked, and (nrepua, seed) refers to the fact that the seeds 
 are not enveloped in a closed case, or ovary. In the Pines 
 and other Conifers, the pistil is simply a scale upon whose 
 surface the ovules are borne. The dense clusters of very 
 
 simple flowers form the 
 so-called cones in these 
 plants. The mode of 
 growth of the Gymno- 
 sperms is exogenous. 
 The wood consists al- 
 most exclusively of a 
 single kind of cells, 
 showing under the mi- 
 croscope peculiar mark- 
 ings (disks), which are 
 really pits in the wall 
 of the cell (see Figs. 
 151, 152). This structure may be recognized even in 
 petrified wood of Gymnosperms. In one group of the 
 Conifers, , the Araucarice, the disks are arranged alter- 
 nately (Fig. 152), arid fossils of that group have been 
 recognized by that character. 
 
 The two principal orders of Gymnosperms are the Coni- 
 fers (Pines, Spruces, Cedars, etc.) and the Cycads (often 
 mistakenly called Sago Palms). 
 
 2. Angiosperms. The name (from Greek ayyeiov, 
 vessel, and oW/ofta, seed) refers to the fact that the pistil 
 forms a closed case, or ovary, in which the ovules and 
 
 1 In the Manual of Geology, and in the previous editions of this work, 
 the Phanerogams are divided into Exogens and Endogens. Exogens are 
 equivalent to Gymnosperms and Dicotyledons, and Endogens to Mono- 
 cotyledons, of the present classification. 
 
 Fig. 149, section of exogenous stem ; 150, same of 
 endogenous; 151, wood cells of the Conifer, 
 Pinus strobus, showing disks magnified 300 
 times ; 152, same of Araucaria Cunninghami. 
 
GEOGBAPHICAL DISTRIBUTION OF MARINE LIFE. 91 
 
 seeds are developed. The wood is more complex in its 
 structure than in the Gymnosperms, consisting in part of 
 very slender, thick- walled cells (the ordinary wood cells), 
 and in part of cells of somewhat larger diameter (ducts), 
 with a variety of microscopic markings due to the thick- 
 ening of parts of the cell wall. 
 
 The Angiosperms are divided into two subclasses, 
 Monocotyledons and Dicotyledons. 
 
 In Monocotyledons, the embryo in the seed bears only a 
 single leaf (cotyledon), and the growth is endogenous. 1 
 The leaves are generally parallel-veined. Palms, Grasses, 
 Lilies, and Orchids are examples of this subclass. 
 
 In Dicotyledons, the embryo in the seed bears a pair of 
 opposite leaves (cotyledons), and the growth is exogenous. 
 The leaves are generally net-veined. To this group 
 belong the great majority of the trees and shrubs of our 
 forests and of the herbs of our fields and gardens. 
 
 GEOGRAPHICAL DISTRIBUTION OF MARINE 
 
 LIFE. 
 
 Range of Life in Depth. Recent investigations have 
 shown that living species not only inhabit the border 
 regions of the oceans, but also extend widely and abun- 
 dantly over a large part of the ocean's depths. Fishes, 
 Crabs and other Crustaceans, Worms, Echini, Starfishes, 
 Crinoids, Corals, are abundant to depths of 10,000 to 
 13,000 feet, and some of them to 18,000 feet. Crusta- 
 ceans of large size, allied to Shrimps, many of them with 
 good eyes, have been found at all depths to 2900 fath- 
 oms ; and large Crabs, with perfect eyes, at 1700 fathoms. 
 Some species have a very wide range in depth ; one Coral 
 
 1 The correlation of monocotyledonous embryos with endogenous stems, 
 and of dicotyledonous embryos with exogenous stems, holds good in 
 general, yet in some members of each group there are instances of stems 
 which fail more or less completely to show the typical character. 
 
92 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 (a disk-shaped kind, Bathyactis symmetrica) occurs (states 
 Moseley) at depths from 30 to 2900 fathoms. 
 
 Character of the Sea Bottom. The material most widely 
 diffused over the ocean's bottom is a fine red or gray 
 mud or clay. But over vast regions less than 15,000 feet 
 in depth occurs the Globigerina ooze. At these and 
 greater depths occur areas of Diatom ooze, especially in 
 the Antarctic seas, in a zone between 50 and 70 south 
 latitude ; and areas of Radiolarian ooze, especially in 
 tropical and warm-temperate regions. 
 
 The character of the bottom shows that sediments from 
 the rivers of the continents are not carried far out to sea. 
 Stones of a pound weight, and larger, occur 100 miles 
 southeast of Long Island ; but these are supposed by 
 Verrill to have been carried out by shore ice. Clay, 
 with some fine quartz sand and particles of mica, makes 
 up the gray mud ; and the winds may be a principal 
 source of the sand and mica. Pumice and fine materials 
 of volcanic origin are also widely distributed, indicating 
 that the driftings by the wind from volcanic islands have 
 been to great distances and over very large areas. The 
 reddish color of much of the oceanic clay is attributed to 
 the oxidation of the iron in volcanic cinders. Grains and 
 nodules of oxide of manganese are very common over the 
 ocean's bottom. 
 
 The bottom is the receiving place of all the dead remains 
 of the ocean's life, both plant and animal, exclusive of the 
 very large part that does not have a chance to reach the 
 bottom, because of the eaters. In the Challenger expe- 
 dition, in the South Pacific, the trawl brought up, at one 
 haul, more than 1500 Sharks' teeth and fragments (not 
 counting very small fragments) and about 50 ear bones of 
 Cetaceans. Among the Sharks' teeth found in that re- 
 gion, many are believed to be of Eocene age ; and their 
 being buried not more than a foot, although lying there 
 since the early Tertiary, is regarded as evidence of the 
 very small amount of detritus that falls over the bottom. 
 
GEOGRAPHICAL DISTRIBUTION OF MARINE LIFE. 93 
 
 Causes limiting Distribution. The two prominent phys- 
 ical causes limiting distribution are the amount of (1) 
 heat, and (2) light. 
 
 1. Temperature. The temperature of the water varies 
 (1) with the zones, from 90 F. in the tropics, to 32 F., 
 and even 28 F., in the polar seas ; (2) with the distribu- 
 tion of marine currents, the warm currents from the equa- 
 torial regions, and the cold from high latitudes ; (3) with 
 the depth, the temperature diminishing downward to 35 
 F. as a general thing, but in some places to 28 in the 
 polar regions and polar currents. There is even in the 
 tropics a temperature of 45, and often of 40, within 300 
 fathoms of the surface, and almost everywhere of 40 or 
 less, below 1000 fathoms ; so that, from 1000 fathoms to 
 the greatest depths, the variation is only from 40 to 32 
 F., or in extreme cases to 28 F. 
 
 The influence of marine currents on the temperature is 
 great. The Gulf Stream, a deep Atlantic current, carries 
 heat from the tropical to the polar seas. The portion of 
 the broad current which passes through the Florida Strait 
 is as deep as the strait (400 fathoms), and 83 to 44 F. 
 in temperature, and has a maximum velocity of 5 miles an 
 hour. It washes the deep-water border of the Atlantic 
 basin at depths between 60 and 300 fathoms off South Caro- 
 lina, and between 60 and 150 fathoms (Verrill) southeast 
 of New England ; crosses the ocean northeastward to the 
 British seas, and has a temperature of 45 off the Faroe 
 Islands at a depth of 600 to 800 fathoms ; and thence con- 
 tinues on poleward. From the polar regions the waters, 
 chilled down to 39 to 28 F., flow back, as the Labrador 
 Current along the east coast of America, and also south- 
 ward beneath the warmer current over the ocean's depths 
 to the equator and beyond. Comparatively little goes 
 out through Bering Strait, because the depth is only 150 
 feet. 
 
 In the Pacific, there is a warm or tropical current on the 
 west side, answering to the Gulf Stream of the Atlantic. 
 
94 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 Again, on the east side of the South Pacific, a reverse flow 
 exists : a cold-water current from the southwest strikes the 
 submarine slopes of southern South America, and carries 
 cold to the equator, and thus narrows the region of tropi- 
 cal waters. 
 
 The range of temperature favorable to any marine 
 species is small generally not over 20 F., and often 
 less than 15 F. Within the favorable temperature the 
 species thrives ; approaching the limit, the size usually 
 diminishes ; and beyond it, growth and egg-development 
 cease. A current too cold for species within its reach is 
 destructive, even more so than one of too much warmth. 
 
 2. Light. Light is the chief limiting cause as to depth 
 (Fuchs). If it were temperature, multitudes of species 
 might grow hundreds of feet below their present level. 
 Light has been found by experiment to penetrate down- 
 ward in the ocean a little more than 200 fathoms ; but 
 the light becomes very feeble long before this limit is 
 reached. The species of shallow waters differ to a large 
 extent from the deep-sea species ; they are (as stated by 
 Fuchs) the species of the light, the latter the species of 
 the darkness. The two groups of species, the ocean-border 
 species (or those of the light) and the deep-sea species (or 
 those of the darkness) are mingled somewhat between 
 depths of 30 and 90 fathoms, and some shore species ex- 
 tend down to a much greater depth. 
 
 The eyes of animals of the dark sea depths are often 
 rudimentary, or else unusually large. The blindness is 
 evidence of darkness ; and the large eyes, of adaptation 
 to the very feeble light of the regions. But this feeble 
 light may be, as Dr. Carpenter, Wyville Thomson, and 
 others have supposed, that of phosphorescence, since 
 many Crustaceans, Alcyoniarians, Starfishes, and other 
 animals are brightly phosphorescent. 1 
 
 1 The following are enumerated as the most characteristic types of the 
 dark sea depths : of Corals, Oculinidse, Cryptohelia, and various solitary 
 species ; the Vitreous Sponges ; Crinoids (Pentacrinus, Rhizocrinus, Hyo- 
 
GEOGRAPHICAL DISTRIBUTION OF MARINE LIFE. 95 
 
 The Border Region. Over the ocean's border region 
 not only is the diversity of temperature between the 
 equator and the poles felt in full force, but also that 
 produced by the warm and cold currents. Off eastern 
 North America down to Cape Hatteras, the cold Labrador 
 current cools the waters over the border region between 
 the Gulf Stream and the shore line ; while south of this 
 cape the Gulf Stream has possession. 
 
 The other causes limiting distribution in the border 
 regions of the ocean are : (1) the condition of the water, 
 whether pure, or impure from sediments and fresh waters 
 received from the land ; (2) the character of the bottom, 
 whether of mud, sand, or rock, and whether firm, or easily 
 stirred by waves or currents. 
 
 Reef-forming Corals grow only in the sea-border regions 
 of tropical seas, and at shallow depths. They extend from 
 the equator to about latitude 28, on the average, where the 
 sea temperature of the coldest month is not below 68 F. 
 Owing to the warm Gulf Stream, they occur in the Atlan- 
 tic in 32 north latitude, Bermuda being of coral formation ; 
 and, owing to the cold waters off western South America, 
 they are excluded from that coast south of Guayaquil. In 
 depth the limit is 20 to 25 fathoms. A vast variety of 
 tropical animals live and find shelter among coral reefs. . 
 
 Seaweeds, like most other plants, are species of the 
 light ; they grow mostly within 10 fathoms of the sur- 
 face, and rarely beyond 30. 
 
 The Sea Depths. In this region, the range of tempera- 
 ture is for the most part small 55 to 30. Only two 
 well-marked divisions exist : that of the cold depths, the 
 temperature below 45 F. ; and that within the range of 
 the tropical currents (as the Gulf Stream in the North 
 Atlantic), the temperature mostly 45 to 55 F. 
 
 crinus, Bathycrinus); of Echinoids, Echinothurise, Pourtalesise, Ananchy- 
 tidse ; of Asterioids, Urisinga; Holothurians of suborder Elasmopodia ; and 
 Fishes, ribbonlike in form, of the families Lepidopidse, Trachypteridse, 
 Macruridse, and O;ihidiidse. 
 
96 THE ANIMAL AND VEGETABLE KINGDOMS. 
 
 The border of the Atlantic basin where swept by the 
 Gulf Stream (page 93), both on its west side and in the 
 British seas, is crowded with life species of Crustaceans, 
 Echinoderms, Polyps, Mollusks, Worms, Fishes ; and some 
 kinds are larger than any of the same groups found in 
 shallower waters. Wyville Thomson mentions his bring- 
 ing up 20,000 specimens of one species of Sea Urchin at 
 one haul ; and Verrill and Agassiz state parallel facts from 
 the American seas. 
 
 The life from the cold and warmer regions differs to a 
 great extent in species ; but the more comprehensive 
 groups represented in the two are largely the same. The 
 colder depths are much less profuse in life, fail of some 
 prominent groups, and contain many species of very 
 peculiar character. 
 
 The cold and warm currents are in places in abrupt con- 
 tact. The pushing of the former, along the eastern sub- 
 merged border of North America, over the narrow warmer 
 area, in consequence of a severe storm, was probably the 
 cause of the destruction of Fishes, Crustaceans, etc., that 
 took place during the winter of 1881-82 (A. E. Verrill). 
 
 
PAET III. DYNAMICAL GEOLOGY. 
 
 DYNAMICAL GEOLOGY treats of the causes or origin of 
 events in geological history that is, of the origin of 
 rocks, of disturbances of the earth's strata and the ac- 
 companying effects, of valleys, of mountains, of conti- 
 nents, and of all changes iii the earth's features, climates, 
 and living species. The agencies of most importance, 
 next to the universal powers of Gravitation and Cohesive 
 and Chemical Attraction, are Life, the Atmosphere, Water, 
 and Heat. 
 
 The following are the subdivisions of the subject here 
 adopted: 
 
 1, LIFE; 2, THE CHEMICAL ACTION OF THE ATMOS- 
 PHERE AND WATERS; 3, MECHANICAL EFFECTS OF THE 
 ATMOSPHERE ; 4, MECHANICAL EFFECTS OF WATER ; 
 5, ACTION OF HEAT ; 6, MOVEMENTS IN THE EARTH'S 
 CRUST, including the folding and uplifting of strata, and 
 the origin of mountains and of the earth's general features. 
 
 I. LIFE. 
 
 Life has done much geological work, by contributing 
 material for the making of rocks. Nearly all the lime- 
 stones of the globe, all the coal, and some siliceous beds, 
 besides portions of rocks of other kinds, have been formed 
 out of the remains of living organisms. Both animals and 
 plants have been sources of the material. The skeletons, 
 or stony secretions, of animals, after fulfilling the pur- 
 
 97 
 
98 DYNAMICAL GEOLOGY. 
 
 poses of life, have been turned over to the mineral king- 
 dom, to be made into minerals and rocks. Similarly, 
 from vegetable structures have come beds of stone, as 
 well as beds of coal. Moreover, fossils, or relics reveal- 
 ing the form or structure of once living creatures, are 
 common in the rocks. This is the formative work of life. 
 Life has done geological work also through its protective 
 and its destructive effects. 
 
 1. Formative Work. 
 
 Aquatic Species the Principal Rock-makers. The kinds 
 of life which have contributed most material to the earth's 
 rock formations, and which are most common as fossils, 
 are the aquatic, and particularly the marine. This is so 
 for several reasons. 
 
 (1) The accumulation of material for beds of rock has 
 been done mostly by the sea. 
 
 (2) The species which have the most stony matter in 
 their structures, viz., Corals, Crinoids, Mollusks, and 
 Molluscoids, are, with inconsiderable exceptions, aquatic, 
 and the great majority are marine. 
 
 (3) The animal remains which are covered by the 
 water itself, or by the sediments deposited therein, are 
 protected from the chemical action of the atmosphere, 
 and from various other destructive agencies. Coal has 
 been made only where the plants grew in or near marshes 
 or shallow lakes, or were drifted into bays or lakes ; for 
 the leaves that fall in the dry woods undergo complete 
 decomposition, and pass away in gaseous combinations. 
 The bones of animals dropped over the land disappear by 
 becoming the food of other animals, as well as by decay. 
 But those of Mammals, Birds, and Reptiles living about 
 the shores of lakes, have often become buried in lacustrine 
 deposits of sand or mud, and thus have been preserved. 
 Mastodons have been mired in marshes, and their skeletons 
 preserved whole, while the thousands that died over the 
 

 LIFE. 99 
 
 dry land left no relics. The wings and other parts of 
 Insects have been kept perfect, and in great numbers, in 
 the muds of some ancient ponds. 
 
 Shells, bones, corals, etc., after fossilization, have rarely 
 their original composition. They have in almost all cases 
 lost at least the animal matter they contained, and thus 
 become friable. But frequently they are petrified ; that 
 is, the original material is replaced by quartz, calcite, or 
 (less commonly) pyrite, oxide of iron, an ore of copper, or 
 a silicate of some kind. Wood is often thus changed to 
 quartz, or to calcite, making what is called petrified wood. 
 
 Besides water, the resins that have exuded from conif- 
 erous and other trees have been good at catching and 
 preserving Insects, Spiders, and Myriopods the smaller 
 flying and crawling things of a forest. The resin has 
 usually undergone a change to amber or some similar 
 substance. 
 
 The preceding review of the kingdoms of life brings 
 out prominently the fact that only animals of rather low 
 grade consist largely of stony secretions. Rhizopods, Cor- 
 als, Crinoids, Brachiopods, and Mollusks, among animals, 
 and Nullipores, Corallines, and some other Algae, among 
 plants, are the chief workers at rock-making, for the rea- 
 son that they may consist one half or more of stone, and 
 yet carry on the processes of life. 
 
 CALCAREOUS FORMATIONS; LIMESTONES. 
 
 The method of forming limestones is, in general, the 
 same, whether the source of the calcium carbonate be 
 shells of Mollusks or Brachiopods, or tubes of Worms, 
 or Crinoids, or Anthozoan corals, or Hydrozoan corals, or 
 Bryozoan corals, or vegetable corals, as Nullipores and 
 Corallines. If shells are in great profusion, there will 
 pretty certainly be also some of the various species of 
 corals, if the temperature of the seas favor; and over coral 
 reefs, where Anthozoan corals are the prominent growth, 
 
100 DYNAMICAL GEOLOGY. 
 
 shells of many species also abound, with more or less of 
 Millepores and Nullipores. Whatever the species, the 
 process is the same. An account of the formation of 
 limestone from coral reefs will therefore serve as a gen- 
 eral illustration of the subject. 
 
 CORAL REEFS AND ISLANDS. 
 
 In tropical regions, corals grow in vast plantations 
 about most oceanic islands and along the shores of conti- 
 nents, with a profusion of other marine life. In the 
 shallow waters the patches or groves of coral are usually 
 distributed among larger areas of coral sand, like small 
 groves of trees or shrubbery in some sandy plains. 
 
 The coral plantations are swept by the waves, and with 
 great force when the seas are driven by storms. The 
 corals are thus frequently broken, and the fragments 
 washed about until they are either worn to sand by the 
 friction of piece upon piece, or become buried in the holes 
 among the growing corals, or are washed up on the beach. 
 Corals are not injured by mere breaking, any more than 
 is vegetation by the clipping of a branch ; and those that 
 are not torn up from the very base and reduced to frag- 
 ments continue to grow. 
 
 The fragments and sand made by the waves, and by 
 the same means strewn over the bottom, along with the 
 shells of Mollusks and other calcareous relics, are spread 
 out in a bed in the shallow water like any sedimentary 
 material. The bed consolidates as accumulation goes on, 
 and thus becomes a bed of limestone. 
 
 As the corals continue growing over this bed, fragments 
 and sand are constantly forming, and the bed of limestone 
 thus increases in thickness until it reaches the level of low 
 tide. Beyond this it rises but little, because corals can- 
 not grow where they are liable to be left for hours wholly 
 out of water ; and the waves have too great force at this 
 level to allow of their holding their places, if they were 
 
LIFE. 101 
 
 able to stand 'the hot and drying sun. A bed of lime- 
 stone is thus produced, which is the coral reef. 
 
 The coral reef at or just above low-tide level is often 
 covered with a thick growth of Nullipores. Millepores 
 and Corallines sometimes grow in large patches among 
 the other corals of the plantation. Occasionally, as has 
 been observed at Bermuda and Florida, the tubes of 
 Worms (Serpulce) furnish important contributions of 
 material. 
 
 The limestone beds made from corals and shells are not 
 a result of growth alone, as in the case of the deposits formed 
 from microscopic organisms, but of growth in connection 
 with the breaking and wearing action of the ocean's waves 
 and currents. Corals and shells, unaided, could make 
 only an open mass full of large holes, and not a compact 
 rock. There must be sand or fine fragments at hand, 
 such as the waters can and do constantly make in such 
 regions, in order to fill up the spaces or interstices be- 
 tween the corals or shells. If there is clayey or ordinary 
 siliceous sand at hand, this will suffice, but it will not 
 make a pure limestone ; in order to have the rock a pure 
 limestone, the shells and corals must be the source of the 
 sand or fine fragments, for these alone yield the needed 
 calcareous material or cement. The limestone made in 
 this way by the help of the waves may be, and often is, of 
 impalpable fineness of grain, having been formed, in such 
 a case, of the finest coral sand or mud. In other cases, it 
 contains some imbedded fragments in the solid bed ; in 
 others, it is a coral conglomerate ; and, over still other 
 large sheltered areas, it is a mass of standing corals with 
 the interstices filled in solid with the sand and fragments. 
 
 Along the shores, above low tide, the sands are aggluti- 
 nated into a beach sand-rock, and the beds have the slope 
 of the beach, or 5 to 15. The waters contain calcium 
 bicarbonate in solution ; and, as the sands, wet at high 
 tide, dry again when the tide is out, the calcareous cement 
 is deposited between the grains as calcium carbonate, and 
 
102 
 
 DYNAMICAL GEOLOGY. 
 
 so consolidation goes forward. The cement coats each 
 grain with calcium carbonate, and in this way the rock 
 sometimes takes the character of an oolite. 
 
 The calcareous sands left dry on the upper part of the 
 beach may be blown inland by the winds, and piled in 
 dunes, consolidating into a wind-drift rock, or seolian 
 rock. This has occurred on a large scale at Bermuda and 
 the Bahamas (page 121). 
 
 FIG. 153. 
 
 \ lew of a high island, bordered by coral reelo. 
 
 The coral formations of the Pacific are sometimes broad 
 reefs around hilly or mountainous islands, as shown in 
 Fig. 153. To the left, in the figure, there is an inner reef 
 and an outer reef, separated by a channel of water, the 
 inner (/) called a fringing reef, and the outer (6) a barrier 
 reef. They are united in one beneath the water. At 
 intervals there are usually openings through the barrier 
 
 FIG. 154. 
 
 Coral island, or atoll. 
 
 reef, as at A, A, which are entrances to harbors. The 
 channels are sometimes deep enough for ships to pass from 
 harbor to harbor. Some islands are surrounded only by 
 a fringing reef, close to the shore ; others only by a bar- 
 rier reef, separated from the shore by a channel several 
 miles in width. 
 
 Many coral reefs stand alone in the ocean, far from any 
 other lands. A view of one of these coral islands, or atolls, 
 
LIFE. 103 
 
 is shown in Fig. 154, and a map in Fig. 155. An atoll 
 consists of a. reef encircling a salt-water lake, called the 
 lagoon. On the windward side the reef first rises above 
 the surface, and becomes covered with vegetation. Very 
 often, as in Fig. 155, the leeward part of 
 the belt is dry only at low tide, or wooded 
 only in spots, so as to be a string of green 
 islets. There are sometimes deep open- 
 ings through the reef on the leeward side, 
 as at (0) in Fig. 155, so that ships can 
 enter the lagoon and find good anchorage. 
 Fig. 155 is a map of one of the atolls of 
 the Gilbert (or Kingsmill) Islands in the A P ia > of the Gilbert 
 Pacific. sroup ' Padflc - 
 
 The Paumotu Archipelago, east-northeast of the Society 
 Islands, contains between 70 and 80 atolls ; the Carolines, 
 with the Radack, Ralick, and Gilbert groups, on the east 
 and southeast, as many more ; and others are scattered 
 over the intervening ocean. Most of the high islands 
 between the parallels of 28 north and south of the equator 
 (where the seas are sufficiently warm, page 95) have a 
 fringe or barrier of coral reefs. 
 
 The extent of some of the modern reefs matches nearly 
 that of the largest Paleozoic reefs. On the north of the 
 Fiji Islands the reef grounds are 5 to 15 miles in width. 
 The barrier reef of New Caledonia extends 150 miles north 
 of the island and 50 miles south. Along northeastern 
 Australia the reefs extend, although with many interrup- 
 tions, for 1000 miles. 
 
 Since the reef-forming corals grow only where the 
 depth is not more than about 150 feet, the thickness of 
 the reef cannot much exceed that amount, if the sea 
 bottom remains at a constant level. But in the vicinity 
 of many barrier reefs, and of atolls in general, soundings 
 show a depth of hundreds or thousands of feet, apparently 
 indicating for the reefs a thickness vastly exceeding the 
 depth which is the limit of coral growth. Darwin ex* 
 
104 DYNAMICAL GEOLOGY. 
 
 plained the facts by the theory of a subsidence of the 
 ocean bottom in the region of these barrier reefs and 
 atolls. The author's own observations upon numerous 
 coral formations in the Pacific led him to adopt the same 
 
 view. If a fringing reef 
 FIG - 156 - had formed about a vol- 
 
 canic island, a subsidence 
 of the bottom at a rate 
 not faster than the rate 
 of upward growth of the 
 
 Diagram illustrating origin of atolls. TGef, WOllld Certainly COn- 
 
 vert the fringing reef into 
 
 a barrier reef, and (if the subsidence continued until the 
 original island was submerged) into an atoll. The theory 
 is illustrated diagrammatically in Fig. 156, the dotted 
 lines showing the successive levels of the water, and the 
 letters F, B, and A marking the successive stages of the 
 reef, fringing reef, barrier reef, and atoll. 1 
 
 DEEP-SEA CALCAREOUS FORMATIONS. 
 
 In the deep ocean the Globigerina ooze is limestone 
 material ; and the shells of Globigerinae are so small that 
 they do not need pulverizing for the making of a rock. 
 The beds contain also molluscan shells and other relics 
 from the pelagic species of the ocean and those of its 
 
 1 Darwin's theoiy explains completely the observed facts with regard 
 to coral formation. But it assumes the fact of a great oceanic subsidence, 
 which, though not a priori improbable (see page 221), has not been inde- 
 pendently proved. Moreover, it has been shown by Murray, Agassiz, 
 and others, that, under certain conditions, both barrier reefs and atolls 
 may have been formed without subsidence. A coral formation growing 
 on a shoal of small area would assume the form of an atoll by reason of 
 the more luxuriant growth of corals at the margin of the shoal, where 
 the water would be purest. Murray has suggested that such a shoal may 
 bave been produced by the erosion of a volcanic peak which once rose 
 above the sea level ; and that, in other cases, shells of Khizopods and 
 the stony secretions of other forms of marine life may have built up por- 
 tions of the sea bottom to within 100 or 150 feet of the surface the 
 
LIFE. 105 
 
 depths ; and among them those of Pteropods, pelagic 
 species, are common in some places. 
 
 FRESH-WATER SHELL LIMESTONE. 
 
 Fresh-water shells, especially those of the genera Sphce- 
 rium, LimnceuS) Pliysa, Planorbis, and Paludina, make 
 white, often chalky, beds on the bottoms of small ponds ; 
 which, as the pond shallows, become overlain by a growth 
 of peat. In such accumulations, the shells are sometimes 
 but little broken, and they then make shell limestone. 
 The large shells of the Unio group, the Fresh-water Mus- 
 sels of rivers, occasionally make beds, but seldom of much 
 extent. 
 
 PHOSPHATIC FORMATIONS. 
 
 Vertebrate animals have contributed very little material 
 to the rocks, compared with inferior tribes of animals. 
 But they have been an important source of calcium phos- 
 phate, and the deposits are often worked, because the 
 material is valuable as a fertilizer. Bones, scales, and 
 various tissues of both Vertebrates and Invertebrates con- 
 tain phosphatic material. The mineral apatite, common 
 in many crystalline limestones, is a calcium phosphate, 
 and is sometimes of organic origin. Guano, which owes 
 its value largely to its phosphates, has been made chiefly 
 
 depth at which reef corals can grow, and that only the upper 150 feet 
 consists of coral rock. The great depth of the lagoons in many of the 
 larger atolls is not very satisfactorily explained on Murray's theory ; and 
 many facts in regard to coral formations as, for instance, the succession 
 of small atolls, large atolls, barrier reefs, and fringing reefs, in passing 
 outward from the central area of the Pacific, which is destitute of islands 
 are better explained on the theory of subsidence. A few borings in a 
 coral island to a depth of 500 or 1000 feet, with a drill large enough to 
 give a core six inches in diameter for examination, would settle the ques- 
 tion as to whether the rock below is of coral-reef origin or not. The 
 notion formerly entertained, that atolls have been formed upon the 
 rims of submarine craters, involves so many improbabilities that it has 
 been universally abandoned. 
 
106 DYNAMICAL GEOLOGY. 
 
 from the excrements of Birds in dry regions where the 
 Birds long had undisturbed possession ; as on some small 
 coral islands in the central Pacific, islands off the Peruvian 
 coast, the coast of equatorial Africa, and in the Caribbean 
 Sea. Over the coast regions of South Carolina, Georgia, 
 and Florida, there are large phosphatic deposits of great 
 commercial value. 
 
 Coprolites, or isolated excrements of Reptiles and Fishes, 
 and sometimes of other animals, occur in many rocks. 
 
 The shells of certain Brachiopods Lingula and some 
 related genera are largely phosphatic. These shells 
 and the shells of Crustaceans, when fossilized, are usually 
 black, because of the large amount of animal matter they 
 contain, this portion becoming carbonized. 
 
 Vegetable tissues also afford phosphates, the ashes of 
 ordinary meadow grass affording 8 parts of phosphoric 
 acid in 100 ; of rye straw, 4 parts ; of clover, 18 parts ; 
 of seaweeds, 1 to 5 parts. 
 
 SILICEOUS FORMATIONS. 
 
 Siliceous beds of organic origin are made chiefly from 
 the accumulation of the shells of Diatoms, and, in the 
 tropical ocean more especially, from those of Kadiolarians. 
 Diatom deposits are common in marshes beneath the peat 
 of the marsh. They were made while the marsh was in 
 the state of a pond. The deposit looks like chalk, but 
 shows under the microscope that it consists chiefly of the 
 shells of Diatoms. Moreover, the material does not effer- 
 vesce with acids like chalk or limestone. It is used as a 
 polishing powder, also in making giant powder or dyna- 
 mite preparations, also for making "soluble silica." 
 
 Some Algae living in the geysers of the Yellowstone 
 Park secrete silica, and thus make siliceous growths and 
 accumulations, as first observed by W. H. Weed. 
 
 Such deposits of organic silica often become solidified 
 by infiltrating waters, and so converted into opal or chal- 
 cedony. 
 
LIFE. 107 
 
 Organic silica has been largely distributed through 
 limestones while they were in the process of formation, 
 because Diatoms, Sponges, and Radiolarians were living 
 in the same waters that supplied the shells, corals, and 
 other materials of the limestones. Through the tendency 
 of particles of the same kind of matter diffused through a 
 rock to collect and concrete together, being carried by 
 percolating waters in a state of solution* or suspension, the 
 limestones are now filled with siliceous concretions. The 
 flint which constitutes concretions of irregular form in 
 some beds of the English chalk, and the chert, or horn- 
 stone, of many limestones, have been thus derived. More- 
 over, in the petrifaction of the fossils of a limestone or 
 other rock by silica, the silica has often come from this 
 organic source. 
 
 CARBONACEOUS FORMATIONS; PEAT, COAL, ETC. 
 
 The most abundant contributions from the vegetable 
 kingdom to rocks are those constituting beds of mineral 
 coal, coal being made from woody tissues as the result of 
 a more advanced stage of the same process by which peat 
 is formed (as explained below). Mineral oil has in part 
 the same source, but is chiefly of animal origin. Graphite, 
 which is pure carbon, is often also of vegetable origin, 
 coal sometimes occurring changed to graphite when it has 
 been subjected to high heat under pressure. Carbonaceous 
 matter, of vegetable or animal origin, gives the black color 
 to black limestones and shales, as it does to soils. This is 
 proved by the fact that, when such rocks are burnt, they 
 become white, owing to the combustion of the carbonaceous 
 part. 
 
 PEAT FORMATIONS. 
 
 Peat is an accumulation of half-decomposed vegetable 
 matter formed in wet or swampy places. In temperate 
 climates it is due mainly to the growth of mosses of the 
 genus Sphagnum. These mosses form a loose, spongy 
 
108 DYNAMICAL GEOLOGY. 
 
 turf ; and, as they have the property of dying at the 
 extremities of the roots while increasing above, they may 
 gradually form a bed of great thickness. The roots and 
 leaves of other plants, or their branches and stumps, and 
 any other vegetation present, may contribute to the accumu- 
 lating bed. The small Crustaceans, Worms, and various 
 other organisms living in the waters, including often fresh- 
 water Sponges, add to the material ; the siliceous spicules 
 of the Sponges may generally be found in the ashes of the 
 peat. The carcasses and excrements of large animals at 
 times become included. Dust may also be blown over the 
 marsh by the winds. 
 
 In wet parts of Alpine regions there are various flower- 
 ing plants which grow in the form of a close turf, and give 
 rise to beds of peat, like the moss. In Tierra del Fuego, 
 although not south of the parallel of 56, there are large 
 marshes of such Alpine plants, the cool summers which 
 prevail in that latitude in the southern hemisphere giving 
 the vegetation an Alpine character even at low altitudes. 
 
 The dead and wet vegetable mass slowly undergoes 
 a change, becoming an imperfect coal, of a brownish black 
 color, loose in texture, and often friable, although com- 
 monly penetrated with rootlets. In the change the woody 
 fiber loses a part of its oxygen and hydrogen ; but, unlike 
 the typical varieties of coal, it still contains usually 25 to 
 33 per cent of oxygen. Occasionally it is nearly a true 
 coal. 
 
 Peat beds cover large surfaces of some countries, and 
 occasionally have a thickness of forty feet. One tenth of 
 Ireland is covered by them ; and one of the " mosses " of 
 the Shannon is stated to be fifty miles long and two or 
 three miles broad. A marsh near the mouth of the Loire 
 is described by Blavier as more than fifty leagues in cir- 
 cumference. Over many parts of New England and other 
 portions of North America there are extensive beds. The 
 amount of peat in Massachusetts alone has been estimated 
 to exceed 120,000,000 cords. Many of the marshes were 
 
LIFE. 109 
 
 originally ponds or shallow lakes, and gradually became 
 swamps as the water, from some cause, diminished in 
 depth. 
 
 Peat is often underlain by a bed of whitish shell marl, 
 consisting of fresh- water shells mostly species of Lim- 
 nceus, Physa, and Planorbis which were living in the 
 lake. Beds of white chalky material consisting of the sili- 
 ceous shells of Diatoms, referred to on page 106, are often 
 found beneath peat. 
 
 Peat is used for fuel, and also as a fertilizer. Muck 
 is another name of peat, and is used especially when the 
 material is employed as a manure ; but it includes all 
 impure varieties not fit for burning, being applied to 
 any black swamp earth consisting largely of decomposed 
 vegetable matter. 
 
 Peat beds sometimes contain standing trees, and entire 
 skeletons of animals that had sunk in the swamp. The 
 peat waters have an antiseptic power, and flesh is some- 
 times changed by the burial into adipocere. 
 
 2. Protective and Destructive Effects. 
 
 Slopes are protected from erosion by a covering of turf ; 
 sand hills, from the winds, by tufts of grass and other 
 vegetation ; shores, from the surf in many places, by a 
 growth of long seaweeds ; and the outer margins of coral 
 reefs, by a growth of Nullipores over the exposed surface. 
 
 Further, forests keep a vast amount of moisture in the 
 wet ground beneath them, which is gradually supplied to 
 the streams as from a reservoir, making them serviceable 
 for mills and other purposes through the year ; whereas, 
 if the forests are cut away, the rains fill suddenly the 
 river channels, producing disastrous floods, and the long 
 droughts which intervene are seasons of dwindled and 
 useless waters. And, besides, the floods carry away the 
 soil from the steep hillsides, and may reduce a productive 
 region to one of rocky ledges. These evils are already a 
 
110 DYNAMICAL GEOLOGY. 
 
 reality in portions of North America, and are on the 
 increase. 
 
 The common Earthworm, as Darwin has shown (1881), 
 moves a great amount of earth or soil in the pellets it 
 discharges at the surface. He found that the weight 
 per acre in a year in four cases was 7.56, 14.58, 16.1, 
 and 18.12 tons. Lobworms, on seashores, are even 
 greater workers, according to C. Davison, who reports 
 that the amount of sand carried up each year on the shores 
 of Holy Island, Northumberland, was equivalent to 1911 
 tons per acre (1891). Marmots (Spermatophilus Evers- 
 mani), in the Caspian steppes, bring great quantities of 
 earth to the surface. In a few years after their introduc- 
 tion they had brought up 75,000 cubic meters of earth to 
 the square mile (Muschketoff, 1887). The loosening of 
 the soil by such means allows it to be more easily washed 
 away by rains. 
 
 Rocks, where jointed or fissured or laminated, are often 
 torn asunder or upturned by the growth of a seed in a 
 crevice, and the subsequent enlargement of the root and 
 stem trunks sometimes growing to a diameter of sev- 
 eral feet, and gradually opening the crevice, and thus dis- 
 placing great masses. The same agency opens crevices 
 to moisture, and so promotes decomposition ; and it pre- 
 pares for the action of freezing in winter (page 157). 
 
 Boring animals cause destruction in various ways. The 
 Mole, Mouse, and some other animals tunnel embank- 
 ments, and open channels which the exit of the confined 
 waters rapidly enlarges ; and sometimes a vast amount of 
 erosion is occasioned by the waters thus discharged. The 
 levees of the Mississippi are thus tunneled by Crawfish, 
 occasioning great floods and devastations. Boring shells, 
 as the Saxic&va, weaken the parts of rocks exposed to the 
 surf. 
 
 The decay of vegetable and animal matters in the soil 
 produces organic acids as well as carbonic acid, which 
 corrode rocks and promote their decomposition. 
 
CHEMICAL ACTION OF THE AIR AND WATERS. Ill 
 
 II. CHEMICAL ACTION OF THE AIR AND ' 
 WATERS. 
 
 Geological work of a destructive kind is carried forward 
 in a quiet way through the chemical action of the con- 
 stituents of the earth's atmosphere and waters, preparing 
 thus for the rougher mechanical work of these agents ; 
 and the same processes have their formative effects. 
 
 1. Destructive Effects. 
 
 Oxygen is a constituent both of air and water, it being 
 mixed (in the proportion of 23.1 per cent by weight) 
 with nitrogen to form air, and combined (in the propor- 
 tion of 88.89 per cent) with hydrogen to form water 
 (H 2 O). Many substances in minerals or rocks have an 
 intense affinity for oxygen. 
 
 Iron rusts because of its tendency to combine with 
 oxygen ; and iron in the protoxide state, or ferrous oxide 
 (FeO), will take more oxygen, and so pass to the sesqui- 
 oxide state, or ferric oxide (Fe 2 O 3 ). Consequently, a 
 mineral containing iron in the former state, as pyroxene, 
 hornblende, or black mica, often goes to destruction 
 through this affinity ; and hence rocks containing these 
 minerals, like trap, usually suffer easy decomposition ; for 
 disturbing one constituent is, like taking a stone from an 
 arch, destruction to the whole. The other ingredients of 
 the iron-bearing mineral are set free to make earth, and 
 commonly the associated minerals participate in the decay 
 and add to the earth. The ferric oxide may make a red 
 earth (red ocher), which is one form of the species hema- 
 tite. But it generally combines with water, and becomes 
 a brownish yellow earth, which is yellow ocher, or the 
 mineral called limonite. The hematite or limonite may 
 be pure, but it is usually mixed with the other materials 
 of the rock, or makes ocherous stains over the surfaces of 
 fissures or joints. 
 
112 DYNAMICAL GEOLOGY. 
 
 In this process of oxidation, moisture as well as air 
 must be present ; the oxygen taken up is usually derived 
 from the moisture. 
 
 Again, iron when combined with sulphur, constituting 
 a sulphide of iron, like pyrite or marcasite (FeS 2 ), or 
 pyrrhotite (Fe u S 12 ), oxidizes readily (unless in the firmest 
 crystals), and passes to the same state of yellow ocher, 
 or linionite. The sulphur also oxidizes, and becomes 
 sulphuric acid, which is a destructive agent, owing to its 
 tendency to take into combination many of the ingredients 
 of minerals, as lime, magnesia, soda, potash, alumina, and 
 iron oxides, making sulphates ; and it hence aids much 
 in the work of destruction. This acid may combine with 
 the iron, and so make green vitriol ; but, as its affinity for 
 the other substances above enumerated is stronger than 
 for iron, the iron is usually left in the ocherous state. 
 
 Now iron sulphide, in the form of pyrite or marcasite, 
 is disseminated more or less abundantly through nearly 
 all the rocks of the globe. Hence, rocks in all lands are 
 undergoing destruction through this agency. Many a 
 fair-looking stone is worthless for building on account of it. 
 It is the most universal of rock destroyers. When the 
 minute grains of pyrite in a granite or sandstone oxidize, 
 the other mineral particles of the rock are set loose, and 
 become discolored with the ocher that is made ; and the 
 sulphuric acid, formed at the same time, eats into some 
 of them to cause their decomposition. Thus the granite 
 either (1) disintegrates into a loose granitic sand, or (2) 
 becomes decomposed to earth or clay. Blocks of trap have 
 a thin decomposed crust, which is incessantly receiving 
 additions inside while losing outside. 
 
 The decomposition of iron sulphide in shales or clays 
 often forms alum, and makes alum clays, because of the 
 combination of the sulphuric acid that is formed with the 
 alumina of the rock, and usually with some other element 
 in the protoxide state, as potash, soda, magnesia, etc. 
 
 When iron carbonate (siderite) is left exposed to the 
 
CHEMICAL ACTION OF THE AIR AND WATERS. 113 
 
 air and moisture, the iron oxidizes, and the surface color 
 changes from grayish white to brown, yellowish, or black, 
 owing to the formation of limonite. An exposure to the 
 weather for a year is sufficient to cause a superficial change; 
 and by continued exposure the whole mass becomes limon- 
 ite. Crystalline limestone, when pure calcite (CaCO 3 ) 
 or pure dolomite (CaMgC 2 O 6 ), is a durable rock. Col- 
 umns, statues, and pinnacles, as in the marvelous Milan 
 cathedral, will stand exposure to the weather almost in- 
 definitely. But, if the limestone contains one per cent of 
 iron combined with the calcium, the iron will soon show 
 itself over the exposed surface by giving it an iron-rust 
 color, and the destruction of structures made of it is sure 
 to follow. If manganese is present instead of the iron, the 
 destruction of the rock is equally certain, but the stains 
 produced are black. To prevent evil to marble buildings, 
 blocks of such limestone are sometimes smeared with tar 
 over all their surfaces, except those exposed to view. 
 
 Carbon Dioxide and Organic Acids. Carbon dioxide 
 is present in the atmosphere, about 3 parts in 10,000 
 consisting of this gas. It is present in all rain water, 
 the rain water deriving it from the atmosphere. It is 
 present in the soil, being produced wherever the mate- 
 rial of plants and animals is undergoing decomposition; 
 and thence it is given to the waters percolating through 
 soils. By all the methods mentioned, and also through 
 animal respiration, the sea derives carbonic acid. More- 
 over, in the earlier ages of the globe, the amount of car- 
 bonic acid in the atmosphere and waters was far greater 
 than at present. Organic acids result from the decompo- 
 sition of vegetable and animal materials in the soil ; and, 
 like carbonic acid, are carried by the waters of the soil 
 downward through the porous rocks. 
 
 Carbonic acid tends strongly to form combinations with 
 magnesia, lime, potash, soda, and with iron in the protoxide 
 state. Hence a feldspar, since it contains potash, soda, or 
 lime, is liable to have its alkali carried off by percolating 
 
114 DYNAMICAL GEOLOGY. 
 
 waters ; and, with such a loss, the mineral changes to a 
 hydrous clayey mineral called kaolin the material used 
 in making porcelain. Common feldspar yields on analysis 
 17 per cent of potash, 18.5 of alumina, and 64.5 of silica ; 
 and kaolin yields no potash, 14 per cent of water, 40 of 
 alumina, and 46 of silica. Granite and other rocks are 
 often eaten into by this process, so as to be fragile to the 
 depth of a foot or more, and sometimes to a depth of 50 
 or 100 feet. Like results are produced by organic acids 
 in percolating waters. 
 
 The depth of decomposition is determined by the depth 
 to which moisture is absorbed ; so that the architectural 
 
 value of a stone is in- 
 
 FIG - 157 - FlG - 158 - versely as its absorb- 
 
 ent quality. All 
 cracks or joints by 
 which water enters 
 may have a discol- 
 ored border (Fig. 
 
 Decomposition of rocks along cracks. 157); aild the 
 
 cess goes on by this 
 
 means, in some granite, trap, and other rocks, until the 
 mass becomes reduced to what looks like a pile of large 
 spheroidal concretions (Fig. 158) ; and ends finally in 
 making earth, or loose sand, of the whole. 
 
 The decomposition of iron-bearing minerals is promoted 
 by the action of carbonic acid, or of organic acids con- 
 tained in the soil waters. These acids extract the iron 
 protoxide and make with it a soluble salt of iron, and thus, 
 by the aid of streamlets, may carry the iron away. The 
 salt of iron generally becomes oxidized in the low places 
 or marshes to which it may be carried, and forms there a 
 yellow or brown or brownish black deposit of limonite or 
 a related ore. 
 
 In regions of dry climate, like |i large part of the Rocky 
 Mountain region, the waters percolating through porous 
 rocks, as sandstones, bring to the surface of the rock the 
 
CHEMICAL ACTION OF THE AIR AND WATERS. 115 
 
 soluble iron compounds produced within it by decomposi- 
 tion ; and, by the deposit of the iron in the form of ferric 
 oxide, give to the lofty walls and bluffs of canons and 
 plateaus brilliant colors of buff, yellow, orange, vermilion, 
 and other shades ; and often the tints are in vertical bands 
 or stripes, owing to the descent of the solution along the 
 vertical surfaces. These colors prevail through Colorado, 
 Utah, Montana, Wyoming, and other states north and 
 south. They gave the name of Yellowstone to the large 
 lake and river so called, and to the Yellowstone Park in 
 northwestern Wyoming. Were rains abundant, the iron- 
 made tints would be washed out by the descending waters, 
 and only the commonplace grays and dull reds remain. 
 
 The organic material of the soils, owing to its using oxy- 
 gen when decomposing, will take it from any Fe 2 O 3 pres- 
 ent, and may thus change it to FeO, and this FeO may then 
 combine with the organic acid or carbonic acid at hand. 
 Many red beds of rocks have lost the red color in spots 
 or seams or along cracks, by this method of deoxidation. 
 
 When calcareous grains or fossils are distributed through 
 beds of porous siliceous sandstone, percolating waters will 
 carry off the grains and fossils. But, if the rocks are .not 
 porous, such fossils remain for indefinite time. Moisture 
 usually penetrates a compact rock to a very small distance 
 generally less than an eighth of an inch, and only to 
 this depth does change go forward. The frequent preser- 
 vation of calcareous fossils, and the unaltered state of the 
 minerals of much granite and trap, show that infiltration 
 and change have ordinarily very narrow limits. 
 
 Waters containing carbonic acid readily erode limestone. 
 The limestone is converted into calcium bicarbonate, 
 which is soluble. On exposure to the air, the bicarbonate 
 loses its excess of carbonic acid, and the limestone taken 
 up is again deposited. Thus limestone strata are eroded, 
 and caverns made ; and, by the depositions, the caverns 
 are hung with stalactites and floored with stalagmite. 
 (See pages 40, 144.) 
 
116 
 
 DYNAMICAL GEOLOGY. 
 
 FIG. 159. 
 
 2. Formative Effects. 
 
 Deposits Formed. 1. By the decomposition of iron- 
 bearing limestone or iron carbonate, as explained in the 
 preceding section, great beds of limonite, of the purest 
 quality, have been made, sometimes over 100 feet deep, 
 and they often lie in place ; that is, they occupy the place 
 of the rocks from whose decomposition they were derived. 
 Those of Richmond and West Stockbridge in Massachu- 
 setts, of Salisbury in Connecticut, of Millerton and other 
 places in eastern New York, and of many localities south 
 of New York in Pennsylvania and Virginia are of 
 this kind. 
 
 Fig. 159 represents the decomposition here described, 
 
 as it is now going on at 
 the Amenia ore pit in 
 Dutchess County, east- 
 ern New York. 
 
 Again, the iron salts 
 carried for long periods 
 to marshes the pockets 
 of a region have often 
 made large beds of bog 
 ore, a variety of limonite. Such ore is likely to contain 
 sulphur and phosphorus (from the decomposing organic 
 materials present in a marsh), and hence the iron afforded 
 is generally of inferior quality. 
 
 2. From the decomposition of feldspar have come large 
 beds of kaolin, or porcelain clay. Some of the best 
 and largest have been made from quartzites containing 
 disseminated feldspar, as on the southern margin of New 
 Marlboro, Massachusetts, the kaolin being removed by per- 
 colating waters, and deposited in the valleys of streams. 
 Other beds of kaolin have resulted from the decomposition 
 of the feldspar in granite and allied rocks. 
 
 3. Carbonated waters, besides forming stalactites and 
 stalagmites, have made large beds of limestone, like the 
 
 Impure limestone, decaying to limonite ; Arnenia 
 ore pit, New York. 
 
CHEMICAL ACTION OF THE AIR AND WATERS. 117 
 
 travertine of Tivoli, near Rome, and the deposits of 
 Gardiners River, Yellowstone Park. Such deposits are 
 formed in many rivers that flow through limestone coun- 
 tries, and in lakes into which such rivers flow. 
 
 4. In dry countries, lakes without outlets often occur, 
 the inflow of water being balanced by evaporation, so that 
 the water in the lake is unable to rise to a level at which 
 it can find an outlet. In such lakes the soluble materials 
 present in river waters may accumulate to supersatura- 
 tion, and be deposited. In regions where marine sedi- 
 ments are the prevailing rocks, the soluble ingredients 
 taken up by the rivers will be largely the same that exist 
 in sea water, as common salt (sodium chloride) and gypsum 
 (calcium sulphate). In regions of volcanic rocks, alkaline 
 carbonates, derived from the decomposition of the feld- 
 spars and allied minerals, will be more abundant than 
 chlorides. Salt lakes may also be formed by the isolation 
 of portions of the sea by elevation of portions of the 
 earth's crust. In the progressive concentration of salt 
 lakes, gypsum is first deposited, being comparatively little 
 soluble, and afterwards the salt. Deposits of salt and 
 gypsum may be formed also in salt marshes and lagoons 
 along seashores. 
 
 Consolidation of Rocks. Carbonated waters, besides 
 serving in the consolidation of limestones (page 101), 
 often also consolidate sand beds, gravel beds, and clay 
 beds, when grains of limestone are even sparingly present, 
 through alternate wetting and drying. Very commonly 
 the solidification in beds of clay and sand takes place 
 around centers (some grain, or it may be fossil, serving 
 as the. nucleus), making concretions (page 46) in the bed. 
 The making of concretions may end in complete consolida- 
 tion. Again, consolidation takes place to some extent 
 through the deposition of limonite over the surfaces of 
 pebbles in gravel. But the most common method of 
 solidifying such fragmental deposits is through siliceous 
 waters (page 194). 
 
118 DYNAMICAL GEOLOGY. 
 
 III. MECHANICAL EFFECTS OF THE 
 ATMOSPHERE. 
 
 The Atmosphere does mechanical work in denudation, 
 transportation, and deposition of rock material. It also 
 accomplishes, indirectly, important geological work by 
 the transportation of moisture. Its work is called ^Eolian 
 work, from the classical name for the god of the winds. 
 
 1. Denudation, Transportation, Deposition. 
 
 The force of the wind in its movements against objects 
 varies as the square of the velocity. Supposing the air 
 to be of mean density at 60 F. near the ocean's level, the 
 pressure it exerts on a square foot at a velocity of 5 miles 
 an hour is equal to about 2 ounces ; at a velocity of 10 
 miles, or that of a light breeze, 8 ounces ; of 20 miles, a 
 good steady breeze, 2 pounds ; of 40 miles, a strong gale, 
 8 pounds; of 60 miles, 18 pounds; of 100 miles, 50 
 pounds. 
 
 But the density diminishes with increasing temperature, 
 and with increase of height above the sea level. The 
 diminution is one half at a height of 3|- miles. 
 
 Denudation. The work of denudation is carried on 
 by the winds, by (1) the direct impact of the air, and 
 (2) abrasion by means of transported sand and pebbles. 
 
 Great effects from impact require that broad surfaces 
 of unstable structures (as the side of a house) should be 
 exposed to the moving air, and the effect is greater where 
 the surfaces struck are concave. Broad tracks of pros- 
 trate trees across a forest are examples of such work. 
 Moreover, loose stones may be dislodged from natural 
 walls by the same means, besides the sand and fragments 
 made by slow decomposition or weathering over their 
 surfaces. 
 
 Abrasion by transported material is another important 
 
MECHANICAL EFFECTS OF THE ATMOSPHERE. 119 
 
 means of denudation. The sands carried by the winds 
 over the surfaces of rocks sometimes wear them smooth, 
 or cover them with scratches and furrows, as early observed 
 by W. P. Blake on granite rocks at the Pass of San Ber- 
 nardino, in California. The different minerals in the 
 granite were found to stand out more or less prominently 
 over the rock, according to hardness. 
 
 In the more arid regions of the Rocky Mountains, and 
 in deserts elsewhere, mountain ledges have been deeply 
 worn, and bold bluffs shaped, so as to present the features 
 usually derived from denudation by water. The following 
 sketch (Fig. 160) gives a good idea of the power of the 
 winds at rock sculpture, and affords also a suggestion as 
 
 FIG. 160. 
 
 ' 
 
 * ~" 
 
 ^Eolian denudation in the Egyptian desert. 
 
 to the great diversity of scenery that seolian work may 
 produce. It represents a scene in the Egyptian desert. 
 The softer layers or strata are worn most deeply, and 
 the harder left to cap the hills and form cornices and lines 
 of molding. 
 
 Glass in the windows of houses on Cape Cod some- 
 times has holes worn through it by the same means. 
 The hint from nature has led to the use of sand driven 
 by a blast for cutting and engraving glass, and even for 
 cutting and carving granite and other hard rocks. 
 
 The transported sands also rub against and wear one 
 another. This mutual attrition makes the sand grains 
 smaller, and produces also the finest of dust, the lightest 
 of the wind-drift materials. 
 
120 
 
 DYNAMICAL GEOLOGY. 
 
 Transportation and Deposition. The streets of most 
 cities, as well as the roads of the country, often afford 
 examples of the drifting power of the winds ; and the 
 burial of ancient Rome and of Egyptian monuments is 
 among its effects. The moving sands of seashores and 
 deserts afford the best opportunity for the study of its 
 methods of work. 
 
 The transporting power of air is small compared with 
 that of water, because of its lightness and want of co- 
 hesion. Ordinary stony material, such as common sand, 
 is 2100 times heavier than dry air, while only 2.5 to 2.7 
 times heavier than water. A strong breeze is therefore 
 required to raise the dust of a road for transportation, and 
 a still stronger breeze to raise quartz sand; while large 
 pebbles are seldom lifted from the ground. 
 
 The winds, moreover, are extremely irregular in their 
 movements and action. The trades, over the ocean, have 
 a degree of uniformity. But they have a velocity gener- 
 ally of only 10 to 20 miles an hour. The winds that do 
 the chief part of seolian geological work are those of 
 storms, whose velocity per hour is from 40 to more than 
 100 miles. Such winds are very unsteady in action, blow- 
 ing in blasts or gusts, in which there is a sudden increase 
 to a maximum and a slower decline to a minimum. There 
 is no constancy in force even for an hour, and no uni- 
 formity over large areas. 
 
 In these and other ways, air manifests its unsteady 
 character as a geological agent, and contrasts strongly 
 with water. As a consequence, the transporting power of 
 the strong winds undergoes rapid variations. The wind 
 that carries and drops pebbles, a few minutes later carries 
 only sand for deposition, and finer sand follows coarser. 
 
 As a consequence, seolian deposits are generally straticu- 
 late, finer and coarser laminae succeeding each other in 
 indefinite alternations. But there is not the evenness of 
 layer characterizing aqueous deposits, even when made 
 over level surfaces. To make beds without straticulation 
 
MECHANICAL EFFECTS OF THE ATMOSPHERE. 121 
 
 would require winds without these irregularities, little 
 varying, and long continuing, such as few regions have, 
 except those that have winds of too moderate velocity to 
 carry any but the finest particles. The gusty winds tend, 
 by their denuding as well as transporting work, to make 
 wavy rather than plane upper surfaces. Moreover, any 
 barrier, as a projecting rock or ledge, or a stump, or 
 group of trees, causes a heaping of the sands around the 
 obstacle, and makes curving surfaces in the heaps, owing 
 to the eddies that are made in the air. 
 
 On seashores the loose sands of the beach are driven 
 inland by the winds, and thereby often form parallel ridges 
 called dunes. They are grouped somewhat irregularly, 
 owing to the course of the wind among them, and also to 
 little inequalities of compactness, or to protection from 
 vegetation. They form especially (1) where the sand is 
 almost purely siliceous, and therefore only slightly adhesive 
 even when wet, and not good for giving root to grasses ; 
 and (2) on windward coasts. 
 
 The stratification in such drift hills is of the kind rep- 
 resented in Fig. 161. Successive layers dip in various 
 directions, and are abruptly cat 
 
 T i - ,-, .,! . FIG. 161. 
 
 short, showing that the growing 
 hill was often partly cut down by 
 storms, and was again and again 
 completed after such disasters. 
 
 On the southern shore of Long Irregular Iamina tion m drifted sand. 
 Island, series of such sand hills, 
 
 10 to 40 feet high, extend along for 100 miles. They are 
 partially anchored by straggling tufts of grass. The 
 coast southward to the Chesapeake is similarly fronted 
 by sand hills. They occur also on the east coast of Lake 
 Michigan, where some are 100 to 200 feet in height. In 
 Norfolk, England, between Hunstanton and Weybourne, 
 the sand hills are 50 to 60 feet high. In desert regions, the 
 drifting of sand takes place on a far more extensive scale. 
 
 Drift hills of calcareous sand, from the disintegration of 
 
122 DYNAMICAL GEOLOGY. 
 
 shells and corals, in Bermuda, have a height of 100 to 250 
 feet. Similar drift hills occur at the Bahamas. Such 
 hills of calcareous sands consolidate through alternations 
 of wet and dry, and thus exhibit well in sections the 
 irregular dip of the layers. 
 
 The drifting of sand is a means of recovering lands 
 from the sea. The appearance of a bank at the water's 
 surface off an estuary at the mouth of a stream is followed 
 by the formation of a beach, and then the raising of hills 
 of sand by the winds, which enlarge till they sometimes 
 close up the estuary, exclude the tides, and thus aid in the 
 recovery of the land by the deposition of river detritus. 
 Lyell observes that at Yarmouth, England, thousands of 
 acres of cultivated land have thus been gained from a 
 former estuary. In all such results the action of the 
 waves in first forming the beach is a very important part. 
 
 Drift sands sometimes overwhelm and destroy forests 
 and cultivated lands. East of Lake Michigan the sand 
 hills extend to a height of 100 to 200 feet above the lake ; 
 and even 215 feet at Grand Haven, where, according to 
 A. Winchell, the forest has been buried so as to leave 
 only the " withered tree-tops projecting a few feet above 
 the waste of sands." In Norfolk, England, between 
 Hunstanton and Weybourne, the sands have traveled 
 inland with great destructive effects, burying farms and 
 houses. They reach, however, but a few miles from the 
 coast line ; and, were it not that the seashore itself is being 
 undermined by the waves, and is thus moving landward, 
 the effects would soon reach their limit. 
 
 Dust is carried by storm winds, sometimes hundreds of 
 miles. Dust from Africa has fallen on ships more than 
 1000 miles from the coast, and at points 1600 miles apart 
 in a north and south direction (Darwin). Volcanic dust 
 was carried in 1835 from Guatemala to Jamaica, 800 miles. 
 In one dust shower, about Lyons in France, 720,000 pounds 
 of dust fell; and of this 90,000 consisted of Diatoms and 
 other organic relics (Ehrenberg). 
 
MECHANICAL EFFECTS OF THE ATMOSPHERE. 123 
 
 2. Winds as Transporters of Moisture. 
 
 The atmosphere takes moisture from the ocean and 
 land, proportionally to its temperature, and transports it. 
 If the air increases in temperature as it passes over a 
 continent, it keeps taking up moisture, and so dries up 
 the land ; if, on the contrary, it loses in temperature, its 
 capacity for moisture is lessened, and it drops it, making 
 rain and mists over the land. If the warm wind strikes 
 the cold side or summit of a mountain, the moisture is 
 largely dropped, so that little remains for the region on 
 the opposite side of the mountain, which therefore experi- 
 ences drought. 
 
 The trade winds are movements of the air within the 
 tropics, westward, against the east side of the continents ; 
 they are warm winds, well charged with moisture. Con- 
 sequently, in those latitudes the eastern portions of con- 
 tinents are regions of much rain ; and the farther back 
 from the east coast the higher mountains are set, the larger 
 the surface benefited by the rains. The position of the 
 Andes, on the extreme western margin of South America, 
 accordingly gives to nearly all the tropical portion of that 
 continent an abundant rainfall, making it the greatest 
 forest region of the globe. 
 
 The prevailing winds in middle latitudes, on the other 
 hand, move eastward, being southwest winds in the north- 
 ern hemisphere, and northwest winds in the southern 
 hemisphere. The great warm- water area of the Gulf 
 of Mexico is thus of immense service to eastern North 
 America, furnishing to the southwest winds the abundant 
 water supply which makes the eastern half of the conti- 
 nent a region of moist climate and abundant forests. 
 
 The arid climate of the Great Basin and much of the 
 eastern slope of the Rocky Mountains, and that of the coast 
 of Peru and the plains of southern Argentina, illustrate 
 the other side of the working of the same laws. 
 
 Thus the winds are largely the distributors of fertility, 
 
124 DYNAMICAL GEOLOGY. 
 
 the locators of great forest regions and deserts, and the 
 limiters of distribution for the living species of the land ; 
 and they have done their work essentially in the same way 
 through all past time, and, in general, with like geo- 
 graphical effects over the same regions from one age to 
 another. 
 
 IV. MECHANICAL EFFECTS OF WATER. 
 
 Water does mechanical work in the conditions of 
 
 1. FRESH WATER, or that of Rivers ; 
 
 2. THE OCEAN ; 
 
 3. FROZEN WATERS, or Glaciers and Icebergs. 
 
 1. Fresh Waters. 
 
 Sources of Rivers. The water of rivers descends in 
 the form of rain and snow from the clouds ; and the clouds 
 derive it, by evaporation, from the surface of the land, 
 its soil, lakes, rivers, and foliage, and more abundantly 
 from the ocean. The water rises in vapor into the upper 
 regions of the atmosphere, and, becoming condensed into 
 raindrops or snowflakes, falls over the hills and plains. 
 The drops gather first into rills ; these, as they descend, 
 unite into rivulets; these, again, if the region is elevated 
 or mountainous, into torrents ; torrents, flowing down the 
 different mountain valleys, combine with other torrents 
 to form rivers ; and rivers from one mountain chain some- 
 times join the rivers from another, and make a common 
 stream of great magnitude and great drainage area, like 
 the Mississippi or the Amazon. 
 
 The Mississippi has its tributaries among all the eastern 
 heights of the great Rocky Mountain chain, throughout 
 a distance of 1000 miles, or between the parallels of 35 N. 
 and 50 N. ; and another set of tributaries gather waters 
 from the Appalachian chain, between western New York 
 and Alabama. Rills, rivulets, torrents, and rivers com- 
 
MECHANICAL EFFECTS OF WATER. 125 
 
 bine, over an area of 1,244,000 square miles, to make 
 the great central southward-flowing stream of the North 
 American continent. 
 
 The amount of water poured each year into the ocean by 
 the Mississippi averages 19 trillions (19,500,000,000,000) 
 of cubic feet, varying from 11 trillions in dry years to 27 
 trillions in wet years. This amount is about 25 per cent 
 of that furnished by the rains, the rest being lost mostly 
 by evaporation. The pitch of the river from Memphis 
 down its last 885 miles is 4.82 inches per mile at low 
 water. 
 
 The Amazon extends its arms north of the equator to 
 the parallel of 3, and south to that of 20, and has a 
 drainage area of 2,500,000 square miles, equal to a third 
 of all South America. Starting within sixty miles of the 
 Pacific, it flows as a mountain torrent through the gorges 
 of the eastern range of the Andes, and then the navigable 
 part of the river commences, the length of which to the 
 Atlantic is over 3300 miles. It discharges into the ocean 
 five times as much water as the Mississippi, because of 
 the large precipitation (50 inches) over much of the area. 
 For 3000 miles, the mean pitch of the stream is less than 
 an inch a mile, the descent in this distance being only 
 210 feet. 
 
 Snowy mountains deal out water gradually, under the 
 control of the sun and winds, day and night and summer 
 and winter making alternations in the supply to the 
 streams. Forest regions, also, are like reservoirs in hold- 
 ing long, and yielding up gradually, the waters supplied 
 to them. Lakes are literally reservoirs, storing water for 
 slow discharge. 
 
 THE MECHANICAL WORK OF RIVERS. 
 
 Working Power. The working power of a river 
 depends primarily on (1) the volume of flowing water, 
 and (2) the amount of fall in the descent to sea level, 01 
 to the final outlet. According to the mathematical law 
 
126 DYNAMICAL GEOLOGY. 
 
 respecting falling bodies, the energy should vary as the 
 product of volume and height of fall. This working 
 power is expended in friction, between the water and the 
 bed of the water way, between the water and the atmos- 
 phere, and between the molecules of the water itself; 
 and in transportation of rock material (which must mean- 
 while be supported in opposition to gravitation). In 
 these ways, the energy of a stream is generally so far 
 used up that it has very little velocity as it approaches 
 its outlet. 
 
 Kinds of Work. The kinds of work done by streams 
 are the following : 
 
 1. Transportation of earth and stones, and often also 
 of logs and leaves, for deposition down stream. 
 
 2. Excavation of a waterway, by the impact of the mov- 
 ing water, and by that of the transported stones and earth. 
 
 3. Mutual abrasion of the transported stones and 
 earthy particles, reducing them in size, and rendering 
 them thereby easier to transport. 
 
 The action of running waters in wearing down the 
 elevated portions of the earth's surface toward sea level 
 is called denudation, or degradation. 
 
 Nearly all valleys of the world owe their formation 
 in large degree to excavation by running water. Even 
 valleys which had their origin in differential elevation 
 of the earth's crust, have been considerably modified by 
 river erosion. 
 
 DENUDATION. 
 
 Causes and Conditions influencing Denudation. Denu- 
 dation is carried on chiefly by the process of abrasion. 
 Direct blows of the water are efficient in rapid, plung- 
 ing streams, especially where the rocks are much jointed, 
 fissile, or fragile, and .where cavities or recesses exist 
 to receive the blows ; but over firm rocks of flat or 
 convex surface they have little effect. Blows of solid 
 material, as grains of sand or stones, are more effective 
 
MECHANICAL EFFECTS OF WATER. 127 
 
 than those of water. Hence, up to a certain limit, abra- 
 sion is increased by the load of sediment which the stream 
 is carrying. ' Beyond that limit, however, the load of sedi- 
 ment so far diminishes the velocity of the stream as to 
 diminish or entirely abolish its power of erosion. 
 
 Moreover, the decomposing and dissolving action of 
 water and other agencies gives important aid in the work 
 of denudation. Decomposition and disintegration (pages 
 111-115) are going on over almost all exposed surfaces of 
 rocks, thus making softened material for the abrading and 
 transporting rills and rivers. Solution also has consid- 
 erable effect, especially in limestone regions; it helps 
 much in the excavation of valleys, and finds in the joints 
 of the rocks a chance to begin the work (page 144). 
 
 The rounded stones, gravel, and earth of fields, and 
 also the material of most geological formations, have been 
 made to a large degree by the wearing action of waters 
 either those of streams over the land, or those of the 
 ocean. But this action is, and ever has been, greatly 
 aided by the processes of decomposition and disaggrega- 
 tion due to the elements causes that are sufficient alone 
 to turn angular blocks of most rocks into rounded masses. 
 
 Rivers do the chief part of their work in times of floods. 
 Many a torrent is a quiet brook at other seasons, or per- 
 haps only a string of pools. At low water the pitch of 
 the stream, or that of its upper surf ace,* is at its minimum, 
 while the ratio of friction to the amount of water is at a 
 maximum, so that the water often lies almost still between 
 its banks. But at flood height the pitch is increased, and 
 the friction relatively decreased ; and hence comes the flood 
 velocity. The Connecticut, from Hartford to the Sound, 
 36 miles (in an air line), is a tidal stream, zero in working 
 force, at low tide and low water ; but, in its highest flood 
 (30 feet at Hartford), it has a mean pitch of 10 inches a 
 mile, and flows off with great rapidity. On mountain 
 streams the transition is often from almost or quite zero 
 to a succession of cataracts of vast working force. 
 
128 
 
 DYNAMICAL GEOLOGY. 
 
 FIG. 162. 
 
 Rain prints. 
 
 Work of Denudation. Denudation commences with the 
 raindrop; for a shower of rain consists of an infinitude 
 of little waterfalls, each having power to denude by strip- 
 ping off grains from the surface of soft or weathered rocks, 
 and to excavate where it falls on a 
 mud flat or sand flat recently laid 
 bare (as by the ebb of the tide), and 
 make the raindrop impression. The 
 quick succession of drops ordinarily 
 obliterates the special work of each; 
 but, in a shower of large drops and 
 short duration, they remain, so that 
 rain prints (Fig. 162) are not un- 
 common markings on the surface of 
 strata. 
 
 The next sweep of the waters 
 over the surface may fill the cavi- 
 ties with fine mud or sand, and so 
 they may become buried records. 
 
 A wind may give the drops greater efficiency in abra- 
 sion. At the same time it may register its direction in 
 the elliptical form of the rain prints. 
 
 When the drops strike a gravel bed, stones in the gravel 
 may protect the material directly be- 
 neath, while the surrounding material 
 is eroded. Thus slender columns are 
 left, each capped with a pebble or 
 bowlder. 
 
 Fig. 163 shows a miniature exam- 
 ple of this phenomenon. It was ob- 
 served by the author in 1887, near the 
 path which leads down to the bottom of 
 the crater of Kilauea, on the Island of Hawaii. The drops 
 had fallen from shrubbery, wet by the heavy mist con- 
 densed from the steam of the volcano. In other localities, 
 columns scores of feet in height have been carved by rain- 
 drops in glacial drift and similar materials. 
 
 FIG. 163. 
 
 Drop-made columns, natu- 
 ral size. 
 
MECHANICAL EFFECTS OF WATER. 
 
 129 
 
 The raindrops make rills and rivulets ; and these, as 
 they hurry on their way, carry off light earth or sand, 
 and so make channels and deepen their beds. This may 
 be well seen along many a roadside, or over sand banks 
 during and after a shower. 
 
 Torrents, from combined rivulets, work with greater 
 power, tearing up rocks and trees as they plunge along, 
 
 FIG. 164. 
 
 Eastern part of the Island of Maui, Hawaiian Islands. 
 
 and, in the course of time, making deep gorges or valleys 
 in the mountain slopes ; and rivers, when in full action, 
 work with vast power, making wide valleys over the 
 breadth of the continent. The slopes of a lofty mountain, 
 exposed through ages to the action described, finally 
 become reduced to a series of valleys and ridges, with 
 towering peaks and crested heights all these effects 
 originating in the fall of raindrops or snowflakes. 
 
130 
 
 DYNAMICAL GEOLOGY. 
 
 The successive steps in the degradation of mountains 
 are well illustrated among the volcanic cones of the 
 Pacific. The surface of such mountains is kept free from 
 river channeling as long as the volcano is active, because 
 of the successive outflows of lava. This is illustrated in 
 
 FIG. 165. 
 
 Northwest peninsula of Tahiti, the coral reefs excluded (the lower side is the northern). 
 
 Mauna Loa, on the Island of Hawaii (see map, Fig. 198, 
 page 179). Denudation has its chance only after the vol- 
 canic activity has begun to decline. The waters of the 
 rains (which are always most copious about the summits 
 of high mountains), beginning in rivulets down the slopes, 
 
MECHANICAL EFFECTS OF WATEB. 131 
 
 first gather sufficient strength for effective denudation to- 
 ward the base of the mountain. 
 
 In the eastern volcanic cone of Maui (see map, Fig. 164), 
 the process of valley-making has commenced. The chan- 
 nels of the rivers of the north side, as the map indicates, 
 extend only halfway up the mountain; on the northeast, 
 or the most rainy side, they extend up to a level just be- 
 low the summit ; while on the west side, they are merely 
 narrow trenches, and are dry through nearly all the year. 
 The last eruption of the volcano took place, according to 
 tradition, about 250 years since. 
 
 Fig. 165 represents the topography of the northwest 
 peninsula of Tahiti, one of the Society Islands. The 
 volcano has been long extinct long enough for the 
 extension of the river channels to the summit, and for 
 the continued excavation of these channels until they 
 have become valleys 1000 to 3000 feet deep, with spacious 
 amphitheaters, or cirques, at their head, reducing the island 
 to a group of knife-edge ridges and steep-sided gorges. 
 The highest peaks (a and b on the map) are parts of the 
 narrow ridges thinned down to a breadth at top of one to 
 ten feet, while 8000 and 7000 feet in altitude. They face 
 with a nearly vertical front, at one point at least 4000 feet 
 high, two of the grandest of the amphitheaters. The 
 amphitheaters, or cirques, are made by water alone, in a 
 tropical region, and show that the help of glaciers is not 
 required, as sometimes supposed, for such results. 
 
 Forms of Valleys ; Channels and Flood Grounds of Riv- 
 ers. The valleys excavated by mountain streams have 
 a V-shaped cross section. But, when the river flows into 
 a region of gentle declivities or plains, the waters lose 
 in velocity, and may even deposit sediment over the bed, 
 instead of deepening it by excavation. At the same time, 
 the waters, no longer able to deepen their channel, begin 
 to erode laterally, undermining their banks, and making a 
 flood plain, over which the waters spread in their annual 
 or occasional freshets. 
 
DYNAMICAL GEOLOGY. 
 
 Nearly all streams over the plains and lower slopes of 
 the land have narrow channels for dry times, and flood 
 grounds which they cover in times of great rains or melt- 
 ing snows. The alluvial plains of rivers are, in part, these 
 plains formed by lateral erosion, but covered by deposits 
 left by the flooded stream ; in part, areas reclaimed from 
 sea or lake, as in the formation of deltas (pages 138-140). 
 
 Marble Caflon, Colorado River. 
 
 Cascades. Cascades are often formed where, in the 
 course of a rapid stream, there are alternations of hard and 
 soft rocks. The hard rocks resist wear, while the soft ones 
 easily yield ; and thus a plunge begins, which increases in 
 force as it increases in extent. Rills and rivulets made by 
 a shower of rain along roadsides or sand banks often illus- 
 trate this feature of great mountain streams. 
 
MECHANICAL EFFECTS OF WATER. 133 
 
 Canons. When a region has been recently elevated to 
 a high altitude, giving the streams power for rapid erosion, 
 especially if the rocks are nearly horizontal, the valleys cut 
 by the rivers have usually bold rocky sides. In many 
 parts of the Rocky Mountains, the streams have worked 
 their way down through the rocks for hundreds, and in 
 some places even thousands, of feet. Such a valley is 
 called a canon. 
 
 These canons have great depth and magnitude on the 
 Colorado River, over the west slope of the Rocky Moun- 
 tains, between longitude 111 W. and 115 W. For more 
 than 300 miles there is a nearly continuous canon, 3000 
 to 6000 feet deep. The preceding sketch, from one of 
 the excellent photographs of the region by the artist of 
 Powell's Expedition, represents a portion of it, called the 
 Marble Canon. The rocks stand in nearly vertical preci- 
 pices on either side of the stream, and the height above 
 the water to the top of the bluff seen in the distance is 
 5000 feet. The deep gorge is the result of erosion by the 
 stream. 
 
 Fig. 167 presents a view of another part of the canon, 
 and shows better the details of the stratification in its 
 lofty walls. 
 
 In many places, the wall of the canon is carved into 
 alcoves and buttresses in infinite variety. Some of the 
 larger projecting masses imitate on a colossal scale the 
 forms of oriental temples. All these picturesque features 
 are the work of the sculpturing waters since the time 
 of the early Tertiary. Moreover, over the country to the 
 northward, rise plateaus and mountains, in which the 
 strata are piled up to an additional altitude of 5000 to 
 7000 feet, and these are portions of great formations that 
 once spread across the whole region. 
 
 Sculpture of Mountain Forms ; Mountains of Circum- 
 denudation . Given a great elevated plateau in a region 
 of rains, and mountain sculpturing will go on about it, 
 continue until all is ridge and valley, not a square 
 
134 
 
 DYNAMICAL GEOLOGY. 
 
 mile of the original plateau retaining its flat surface ; and 
 the resulting crested ridges may rise thousands of feet 
 above the bottoms of the valleys, if the plateau was one 
 of sufficient height. The Catskill Mountains, New York, 
 are an example of mountains of circumdenudation. 
 
 FIG. 16T. 
 
 Wall of Colorado Caflon. 
 
 The following figures, by Lesley, illustrate some of the 
 results of sculpturing by water, in both horizontal and 
 upturned or flexed strata. In the production of such 
 erosion forms, the ocean has sometimes taken part during 
 the submergence of a continent ; but the final results are, 
 in almost all cases, due to the chiselings of fresh waters. 
 The figures here given are small, but the elevations they 
 
MECHANICAL EFFECTS OF WATER. 
 
 135 
 
 represent, as illustrated in the Appalachians, Jura, and 
 many other mountain regions, are often thousands of feet 
 in height. 
 
 When the beds are horizontal, or nearly so, but of unequal 
 hardness, the softer strata are easily worn away, and by 
 this means the harder strata become undermined. Table- 
 
 FIG. 168. 
 
 Fm. 169. 
 
 Erosion forms in nearly horizontal strata. 
 
 shaped mountains are often thus formed, having a top of 
 the harder rock, and the declivities banded with projecting 
 shelves and intervening slopes. Figs. 168, 169 represent 
 the common character of such hills. Such flat-topped 
 elevations in the Colorado region have been called mesas, 
 from the Spanish for table. 
 
 When the beds are inclined between 5 and 30, there 
 is a tendency to make hills with a long back slope and 
 bold front; but, with a much larger dip, the ridges are 
 more nearly symmetrical. 
 
 When the dipping strata are of unequal hardness, and 
 
 170 
 
 FIGS. 1TO-175. 
 
 173 
 
 Erosion forms in synclinal strata. 
 
 lie in folds, there is a wide diversity in the results on the 
 features of the landscape. 
 
 Figs. 170-175 represent the effects from the erosion 
 of a synclinal region consisting of alternations of hard 
 and soft rocks. The protection of the softer beds by 
 the harder is well shown. 
 
136 DYNAMICAL GEOLOGY. 
 
 Anticlinal strata give rise to another series of forms, 
 in part the reverse of the preceding, and equally varied. 
 Figs. 176-179 represent some of the simpler cases. When 
 the back of an anticlinal mountain is divided (as in Figs. 
 176-178), the mountain apparently loses the anticlinal 
 
 FIGS. 176-179. 
 
 Erosion forms in anticlinal strata. 
 
 character, and the parts are, in aspect, simply monoclinal 
 ridges. In Fig. 179 the anticlinal character is distinct in 
 the central portion, while lost in the parts on either side. 
 In Fig. 179, to the right, the protection afforded to softer 
 strata by even a vertical stratum of hard rock is illus- 
 trated : the vertical stratum forms the axis of a low 
 ridge. 
 
 TRANSPORTATION AND DEPOSITION. 
 
 Fact of Transportation. It has been stated that the 
 massive mountains have been eroded into ridges and val- 
 leys by running water. The material worn out has been 
 transported somewhere by the same waters. 
 
 Part of the transported material in all such operations 
 goes to form the great alluvial plains that occupy the 
 river valleys, especially in the lower part of their course. 
 Part is carried to the sea into which the river empties, 
 where it meets the counteracting waves and currents, and 
 is distributed for the most part along the shores, filling 
 estuaries or bays, or making deltas, and extending the 
 bounds of the lands ; or to lakes, with or without outlets. 
 
 The mountains of a continent are ever on the move 
 seaward, and thus contribute to the enlargement of the 
 seashore plains. The continent is losing annually in mean 
 height, but gaining in width, or extent of dry land. 
 
MECHANICAL EFFECTS OF WATER. 137 
 
 Transporting Power of Water. The transporting power 
 of running water is very great when the flow is rapid. 
 Large stones and masses of rock are torn up and moved 
 onward by the mountain torrent. A current of four 
 miles an hour will carry stones 2 J inches in diameter ; 
 of two miles, pebbles of 0.6 inch ; of two thirds of a mile, 
 fine sand, about .064 inch in diameter; of one third of a 
 mile, fine earth or clay, the particles .016 inch in diame- 
 ter ; the mean diameter of the largest transportable parti- 
 cles varying as the square of the velocity, supposing them 
 of like density. 
 
 Hence, as a stream loses in velocity, it leaves behind 
 the coarser material, and carries only the finer; if the 
 rate becomes very slow, it drops the gravel or the sand, 
 and bears on only the finest earth or clay. Consequently, 
 where the current is swift, the bottom (if not consisting 
 of rocky ledges) is stony or pebbly ; and where the water 
 is still, or nearly so, the bottom is muddy. Slow rivers 
 and small lakes have commonly muddy borders. 
 
 Amount of Material Transported. The amount of trans- 
 ported material varies with the size and current of the 
 rivers and the kind of country they flow through. The 
 Mississippi carries annually to the Gulf of Mexico, accord- 
 ing to Humphreys and Abbot, on an average, 812,500,- 
 000,000 pounds of silt equal to a mass one square mile 
 in area and 241 feet deep, and its bottom waters push 
 on enough more to make the 241 feet 268 feet. The proc- 
 ess slowly lowers the drainage area of the river, and the 
 mean amount of lowering indicated by the facts stated is 
 one foot in 4920 years. The total annual discharge of 
 silt by the Ganges has been estimated at 6,368,000,000 
 cubic feet. 
 
 Besides the silt, rivers carry what the waters take into 
 solution. The amount is generally between a third and 
 a half of that mechanically transported ; but sometimes 
 nearly an equal weight. If one half, in the case of the 
 Mississippi, the period of 4920 years would be reduced to 
 
138 DYNAMICAL GEOLOGY. 
 
 3280. The salts held in solution are often about one half 
 calcium carbonate, and the rest calcium sulphate, sodium 
 chloride (common salt), sodium carbonate, and inagnesian 
 and potash salts, with traces of silica and other ingredi- 
 ents. In some cases the rivers carry the salts to inland 
 seas or lakes, which have no drainage toward the ocean, 
 and which therefore are saline (page 117). Moreover, arid 
 plains become saline because of the capillary action which 
 brings moisture from below to the surface, as evaporation 
 goes on above, depositing the contained saline ingredients, 
 such as the sodium chloride, sodium carbonate, and mag- 
 nesian salts of such places. 
 
 Alluvial or Fluvial Formations. The deposits made 
 by the transported material, which now constitute the 
 alluvial plains of the river valleys, cover a large part of 
 a continent, since rivers or smaller streams are almost 
 everywhere at work. They are made up of layers of 
 pebbles or gravel, and of earth, silt, or clay, especially 
 of these finer materials. Logs, leaves, shells, and bones 
 occur in them : but these are rare ; for whatever floats 
 down stream is widely scattered by the waters, and to a 
 great extent destroyed by wear and decay. The level of 
 the alluvial plain is ordinarily about that of the level of 
 the higher floods. The spreading waters, by here losing 
 their velocity, owing to friction, build up the deposits. 
 The river margin is often a little above flood level, owing 
 to the shrubbery growing along it, and to the abundant 
 deposit of sediment where the water flowing outward from 
 the channel onto the flood plain, receives the first check to 
 its velocity. 
 
 Terraces. River valley or fluvial formations often 
 have the form of terraces. Terraces are in general rem- 
 nants of old flood plains, the rivers having deepened 
 their channels on account of elevation of the land ; and 
 seashore flats and beaches, and horizontal lines of wave 
 erosion on cliffs, have often been left high in the same 
 movements. 
 
MECHANICAL EFFECTS OF WATER. 
 
 139 
 
 Estuary and Delta Formations. The detritus discharged 
 by the river at its mouth tends to fill up the bay into 
 which it empties, and make wide flats on its borders, and 
 thus contract it to the breadth merely of the river current. 
 
 Where the tides are feeble and the river large, the de- 
 posits about the mouth of the stream gradually encroach 
 on the ocean, and make great plains and marshy flats, 
 which are intersected by the many mouths of the river 
 
140 DYNAMICAL GEOLOGY. 
 
 and a network of cross channels. Such a formation is 
 called a delta. Fig. 180 represents the delta of the 
 Mississippi, the white lines being the water channels, and 
 the black areas the great alluvial plains. The delta prop- 
 erly commences below the mouth of Red River, where the 
 Atchafalaya Bayou, or side channel of the river, begins. 
 The whole area is about 12,300 square miles ; about one 
 third is a sea marsh, only two thirds lying above the level 
 of the gulf. 
 
 The deltas of the Nile and the Ganges are similar in 
 general features to the delta of the Mississippi. 
 
 The detritus poured into the ocean where the tides or 
 currents are strong, and a considerable part of that where 
 the tides are feeble, goes to form seashore flats and sand 
 banks and offshore deposits. In their formation the 
 ocean takes part through its waves and currents, and hence 
 they are more conveniently described in connection with 
 the remarks on the work of the ocean. 
 
 HISTORY OF RIVERS. 
 
 Youth and Old Age of Rivers. The work of excava- 
 tion tends toward the lowering of the bed of a stream to 
 the sea level. The process involves the wearing away of 
 waterfalls and rapids ; the draining of the lakes along 
 the river course, as far as these have their beds above sea 
 level ; and the filling up of lake basins, even those that 
 descend below that level. Reducing the slope of the bed 
 deprives the waters of working power, and finally the 
 stage is reached when abrasion and deposition over the 
 bed balance each other. Thus rivers pass from youth to 
 old age. 
 
 The condition of balance between erosion and deposi- 
 tion has been called by Powell the condition of base level; 
 and he has formulated the important general law that a 
 river always works toward its base level, eroding its bed 
 when it is too high, and filling it up when it is too low. 
 

 MECHANICAL EFFECTS OF WATER. 141 
 
 When the river ends in a lake without outlet, the 
 process terminates at the lake, but is otherwise the same 
 as above described. 
 
 The history of a river is often modified by continental 
 changes of level. An elevation may rejuvenate streams 
 that are approaching old age, or a subsidence may bring 
 the streams to a premature old age. 
 
 In a region which has undergone subsidence, the lower 
 part of a river's course may be below base level. In that 
 case, deposition will be in excess, and the level of the bed 
 will be annually raised. Consequently, during floods, the 
 waters along the region of the shallowed channel will 
 spread more and more widely, as the years pass, over the 
 country either side, with disastrous encroachments on 
 forests and whatever is in their way. Man, to protect his 
 buildings and cultivated fields, raises the banks, or builds 
 dikes or levees along them ; but the waters cannot be 
 crowded, and at intervals they sweep away the confining 
 levees, to the confusion of the dwellers on the " recovered " 
 lands. 
 
 Again, the extraordinary floods of a Glacial period have 
 given temporary increase of vigor to enfeebled rivers. 
 
 Moreover, changes of level have sometimes joined the 
 head of one stream to the trunk of another; or made 
 a northward-flowing stream of one that had previously 
 flowed southward ; or converted a region of once active 
 rivers into a vast lake. Rivers were few and small when 
 lands were small ; and multiplied and extended and finally 
 became combined into great drainage systems, with the 
 growth and completion of the continents. 
 
 The effect of the long work of the waters over the land 
 is the gradual degradation of the hills and mountains, 
 reducing great regions to approximately level plains 
 peneplains (from the Latin pene, almost, and planum, 
 plain), as they have been called by W. M. Davis; and 
 finally, in theory at least, the reduction of the whole 
 continent to the condition of a base-level plain. 
 
142 DYNAMICAL GEOLOGY. 
 
 Cause of Direction of Flow. The simple explanation of 
 the direction of flow in a river is that it was determined 
 by the slope of the land. But in many cases the course is 
 due not to the present slopes and conditions, but to others 
 that existed at some earlier time. The working waters 
 have sometimes started on their way to the sea, Avhen the 
 topography was very different from the present ; and they 
 have kept their old course in spite of such obstacles as 
 folds or faults developed transversely to their course. 
 Such drainage has been called by Powell antecedent 
 drainage ; and that which is a consequence of existing 
 conditions, consequent drainage. When a stream has cut 
 through the entire thickness of the formation upon which 
 it commenced, and is flowing now in unconformably un- 
 derlying rocks, without regard to their structure, the 
 drainage is said to be superimposed. 
 
 SUBTERRANEAN WATERS. 
 
 Origin and Course of Subterranean Waters. A part 
 of the water that falls on the earth's surface on its 
 mountains as well as its plains sinks through the ground 
 and into the rocks beneath, wherever there are openings 
 or crevices, or looseness of texture, and thus becomes 
 subterranean. The waters usually pass easily through 
 sandstones ; but over a clayey or other compact stratum 
 they accumulate, and often make wet, springy soil above ; 
 or, if the stratum is inclined, they may descend to great 
 depths, or come to light again wherever it outcrops at a 
 lower level. The descending waters sometimes gather 
 into subterranean streams, which have powers of abrasion. 
 Over large areas in some limestone regions, and in many 
 volcanic regions, surface streams are wanting, because of 
 the cavernous recesses ; the waters carry on an under- 
 ground system of drainage. Thus come springs, subter- 
 ranean streams large and small, and copious outflows 
 beneath the sea level along coasts. 
 
MECHANICAL EFFECTS OP WATER. 
 
 143 
 
 A region of horizontal limestone abounds in sink-holes, 
 as well as caverns ; and sometimes rivers plunge down 
 the openings into the recesses below, and are lost, or 
 emerge again in fuller flow a mile or more away. 
 
 FIG. 181. 
 
 MAP OF THE 
 MAMMOTH CAVE 
 
 From "The Mammoth Cave Illustrated" 
 ByH.C.HOVEY AND R.E.CALL 
 
 SCALE OF FEET 
 
 2000 
 
144 DYNAMICAL GEOLOGY. 
 
 Ordinary waters easily erode limestone, because they 
 contain carbonic acid (page 115). Through the joints or 
 fissures the waters find a way downward, and the erosion 
 they produce widens the joints, often forming funnel- 
 shaped sink-holes. At the bottom of the sink-hole the 
 waters work laterally, eroding channels and chambers, in 
 long series and varying directions ; and if, later, they 
 succeed in penetrating to a still lower level, another tier 
 of chambers is begun. Undermining also goes on, causing 
 falls of rock, which are sometimes large enough to make 
 feeble earthquakes. Occasionally some part of the roof 
 caves in, and the cavern, with the river inclosed, becomes 
 open to the light, and thus affords an example of one 
 method of making limestone gorges. 
 
 The preceding map (modified from Hovey's " Celebrated 
 American Caverns," with additions by R. E. Call) shows 
 the passages and chambers of Mammoth Cave, Kentucky. 
 This cave occupies an area of several square miles in the 
 Subcarboniferous limestone. The length of the caverns 
 in this limestone in Kentucky (a rock 200 to 1000 feet 
 thick) is estimated by Professor Shaler at 100,000 miles. 
 Luray Cavern, in Luray Valley, Virginia, is comparatively 
 small; but, as described by Mr. Hovey, it is one of the most 
 remarkable in the world, for the beauty of its stalactitic 
 hangings and the grandeur of its subterranean chambers. 
 
 In many caverns, bones of the animals that have in- 
 habited them, including sometimes those of Man, with his 
 implements of stone or shell or other material, are found 
 buried beneath or within the stalagmite that covers the 
 floor the perpetual dripping keeping up its constant 
 deposition (pages 40, 115). 
 
 Caves exist in the elevated coral reefs of the Pacific, 
 which are certainly of comparatively recent origin. One, 
 on the island of Atiu, near Tahiti, has "interminable 
 windings" and many chambers, "with fretwork ceilings 
 of stalactite" (J. Williams). There are others on Oahu, 
 which give a passage to streams. 
 
MECHANICAL EFFECTS OF WATER. 
 
 145 
 
 The erosion may be helped forward (1) by the oxida- 
 tion of pyrite (page 112) where it is present, the result- 
 ing sulphuric acid turning limestone into gypsum ; and 
 also (2) by the formation of nitric acid (probably from 
 the nitrogen of the air, by means of micro-organisms), 
 which corrodes the limestone, making calcium nitrate. 
 The caves of Kentucky and Indiana have afforded a large 
 amount of this nitrate for the making of niter. 
 
 Subterranean waters often become mineral waters. 
 They are made calcareous by limestones along their course; 
 saline, by the saline ingredients of rocks ; sulphurous, by 
 decomposing iron sulphides ; carbonated, by any acid, as 
 sulphuric, attacking a limestone and setting carbonic acid 
 free ; chalybeate, by the reduction of ferric oxide in pres- 
 ence of organic matters, and the formation of ferrous 
 bicarbonate ; magnesian, by the decomposition of minerals 
 containing magnesium. They may become warm waters 
 through subterranean heat, and may receive vapors and 
 various mineral materials from the depths below. 
 
 Artesian Wells. When strata are inclined, and water 
 descends along one of the layers between others that are 
 sufficiently impervious to confine it, the pressure increases 
 with the depth ; so that the water will rise through a bor- 
 ing made down to it, 
 and sometimes in a 
 high jet. The princi- 
 ple is illustrated in 
 Fig. 182, in which ab 
 is the water-bearing 
 stratum, be the boring, 
 and eb the amount of 
 descent. The height of 
 the jet falls much short of be, chiefly on account of the 
 underground friction. 
 
 Such wells are called Artesian wells or borings, from the 
 district of Artois in France, where they were early made. 
 The Artesian well of Grenelle in Paris is 1798 feet deep, 
 
 Fir,. 182. 
 
 Section illustrating Artesian wells. 
 
146 DYNAMICAL GEOLOGY. 
 
 and when it was first made the water darted out to a 
 height of 112 feet. One at St. Louis has a depth of 3843 J 
 feet, but without getting water, because the region for 
 many miles around is one of horizontal rocks. A boring at 
 Wheeling, West Virginia, has been carried to the depth of 
 4500 feet without finding water. A well at Schladenbach 
 near Leipzig is 5736 feet in depth. Such wells are made 
 for agricultural and manufacturing purposes in many dry 
 regions, and they have proved successful even in Sahara. 
 Landslides. Landslides are of different kinds: 
 
 1. The sliding of the surface earth, or gravel, of a hill 
 down to the plain below. This effect may be caused by 
 the waters of a severe storm wetting the material deeply 
 and giving it greatly increased weight, besides loosening 
 its attachment to the more solid mass below. 
 
 2. The sliding down a declivity to the plain below of 
 the upper layer of a rock formation. This may happen 
 when this upper layer rests on a clayey or sandy layer, 
 and the latter becomes very wet and greatly softened by the 
 waters ; the upper layer slides down on the softened bed. 
 
 3. The settling of the ground over a large area. This 
 may take place when a layer of clay or loose sand becomes 
 wet and softened by percolating waters, and then is pressed 
 out laterally by the weight of the superincumbent layers. 
 But such a result is not possible unless there is a chance 
 for the wet layer to move or escape laterally. Sometimes 
 part of a wet clayey layer, pressed to one side in this way, 
 is left very much folded, while the associated sandy layers 
 have their usual regular bedding. 
 
 2. The Ocean. 
 
 The ocean is vast in extent and vast in the power which 
 it may exert. But its mechanical work in Geology is 
 mostly confined to its coasts and to soundings, where alone 
 material exists in quantity within reach of the waves or 
 currents. 
 
MECHANICAL EFFECTS OF WATER. 
 
 147 
 
 The saltness of the ocean gives it a density of 1.0240 to 
 1.0278, that of pure fresh water being 1. It is slightly 
 the greatest in the tropics, because of the evaporation. 
 A cubic foot weighs about 64 pounds. There are three 
 consequences of the saltness: (1) slightly greater trans- 
 porting power than fresh water, on account of its density ; 
 (2) much quicker deposition of the finest sediment, the salt 
 causing a flocculation and rapid precipitation of minute 
 clayey particles, which in pure water remain in suspension 
 for an indefinite period ; (3) a supply of common salt and 
 magnesian salts, etc., for making deposits of salts, and for 
 use in chemical changes attending the making of rocks 
 and minerals, the ocean being, so to speak, the largest of 
 mineral springs. 
 
 The mechanical effects of the ocean are produced by its 
 waves and currents. 
 
 EROSION AND TRANSPORTATION. 
 
 1. Waves. Greneral Action. The force in oceanic 
 waves is a constant force. Night and day, year in and 
 year out, with hardly an intermission, they break against 
 the beaches and rocks of the coast ; sometimes gently, 
 sometimes in heavy plunges that have the force of a 
 Niagara of almost unlimited breadth. The gentlest 
 movements have some grinding action among the sands, 
 while the heaviest may dislodge and move along, up the 
 shores, rocks many tons in weight. Niagara wastes its 
 power by falling into an abyss of waters ; but in the case 
 of the waves the rocks are bared anew for each successive 
 plunge. The waters are often loaded with gravel and 
 sand when they strike, and thus carry on abrasion. Cliffs 
 are undermined, rocks are worn to pebbles and sand, and, 
 through mutual friction, sand is ground to the finest pow- 
 der. Rocky headlands on windward coasts are especially 
 exposed to wear, since they are open to the battering force 
 Prom different directions. 
 
148 DYNAMICAL GEOLOGY. 
 
 Level of Greatest Eroding Action. The eroding action 
 is greatest for a short distance above the height of 
 half tide, and, except in violent storms, it is almost null 
 below low-tide level. Fig. 183 represents in profile a 
 cliff, having its lower layers, near the level of low tide, ex- 
 tending out as a platform a 
 FlG - 183 - hundred yards wide. As the 
 
 tide commences to move in, 
 the waters, while still quiet, 
 swell over and cover this 
 platform, and so give it their 
 
 f, New south Wales. protection ; and the force of 
 
 wave action, which is great- 
 est above half tide, is mainly expended near the base of 
 the cliff, just above the level of the platform. But to give 
 opportunity for much battering effect a coast should be 
 shelving, so that the waters may advance up the slope. If 
 the water is deep alongside of a cliff, there is simply a 
 rise and fall, with little abrasion. 
 
 Action Landward. Waves on shallow soundings have 
 some transporting power ; and, as they always move 
 toward the land, their action is landward. They thus 
 beat back, little by little, any detritus in the waters, pre- 
 venting that loss to continents or islands which would 
 take place if it were carried out to sea. 
 
 Effect on the Outline of Coasts; No Excavation of Nar- 
 row Valleys. As the action of waves on a coast tends to 
 wear away headlands, and at the same time to fill up bays 
 with detritus, it usually results in making the outline more 
 regular or even. There is nowhere a tendency to exca- 
 vate narrow valleys into a coast, like those occupied by 
 rivers. Such valleys are made by the waters of the land. 
 If a continent were sinking slowly in the ocean, or rising 
 slowly from it, wave action would still be attended by the 
 same results ; for each part of the surface would be suc- 
 cessively a coast line, and over each there would be the 
 same wearing away of headlands, and filling of bays, in- 
 
MECHANICAL EFFECTS OF WATER. 149 
 
 stead of the excavation of valleys. The chasms, or " pur- 
 gatories," sometimes made on a rocky coast, where a dike 
 of trap, or a thin slice of rock included between parallel 
 joints, yields to the disintegrating action of the waves, are 
 of course readily distinguished from true valleys. 
 
 2. Tidal Currents. Tidal currents often have great 
 strength when the tide moves through channels or among 
 islands, and then they are a means of erosion and trans- 
 portation daily in action, wherever there is rock, mud, or 
 sand within their reach. 
 
 The outflowing current from bays, or that connected 
 with the ebbing tide, is deeper in its action, and has, 
 therefore, more excavating and more transporting power 
 than the inflowing, or that of the incoming tide. The 
 latter moves on as a great swelling wave, and fills the 
 bays much above their natural level ; but the outflowing 
 current begins along the bottom before the tide is wholly 
 in, owing to the accumulation of waters ; and, when the 
 tide changes, it adds to the strong current movement 
 already in progress. 
 
 The piling up of the waters in a bay by the tides, or by 
 storms, produces, especially if the entrance is not very 
 broad, a strong outflowing current at bottom, which tends 
 to keep the channel deep and clear of obstructions. 
 
 The inflowing tide, sweeping along a coast, checks partly 
 or wholly the outflow of the rivers. This causes the depo- 
 sition of more or less of the detritus which the rivers 
 transport, near or against the shores or flats just beyond 
 the river channel ; and thus it often makes great sand 
 flats, which encroach on the entrance. If a long point 
 projects on the side of the mouth first reached by the in- 
 flowing tide, the tidal flow may carry the detritus far 
 beyond the river's mouth ; but, if no such point exists, 
 and the opposite cape is the longer, the detritus will be 
 thrown into the throat of the stream, and the entrance 
 become more or less choked. The river mouths of the 
 Connecticut shore, on the north side of Long Island 
 
150 DYNAMICAL GEOLOGY. 
 
 Sound, along which the inflowing tide moves westward, 
 well illustrate these facts. The two largest of the rivers, 
 the Connecticut and Housatonic, are of the unfortunate 
 kind, as they have no eastern cape ; while the harbor of 
 New Haven, although it receives only very small streams, 
 is much better off, as regards depth of water for entrance, 
 because of a projecting eastern cape. 
 
 The bore, or eager, of some great rivers is a kind of tidal 
 flow up a stream. It is produced when the regular rise 
 of the tide in the bay at the mouth of the river is ob- 
 structed by the form of the entrance and its sand banks, 
 together with the outflow of the river, so that the waters 
 are for a while prevented from entering, until, finally, all 
 those of one tide rush in at once, or in a few great waves. 
 The eagers of the Amazon, the Hoogly in India (one of 
 the mouths of the Ganges), and the Tsien-tang in China, 
 are among the most remarkable. In the case of the Tsien- 
 tang, the water moves up stream in one great wave, plung- 
 ing like an advancing cataract, four or five miles broad 
 and 30 feet high, at a rate of 25 miles an hour. The 
 boats in the Middle of the stream simply rise and fall with 
 the passage of the wave, being pushed forward only a 
 short distance ; but along the shores there is often great 
 devastation, the banks being worn away, and animals 
 sometimes surprised and destroyed. 
 
 3. Currents made by Winds. The great currents of the 
 ocean, such as the Gulf Stream, are attributed by most 
 physicists to this source. But, besides these, there are 
 local currents along many coasts produced by winds, espe- 
 cially when there are long and violent storms, or winds 
 blowing for months in one direction. Such currents, 
 sweeping by a coast, transport from one place to another 
 in their course more or less of the sand of the shores, 
 often making long sand flats or spits off the shores to lee- 
 ward, as on the south coast of Long Island and along the 
 more southern parts of the Atlantic border. The action 
 is aided by the tidal currents. In some cases the drifted 
 
MECHANICAL EFFECTS OF WATER. 151 
 
 sand may be in part carried back again when the season 
 changes to that in which the wind blows from the 
 opposite direction. Other portions of detritus may be 
 carried away from the land and distributed in the deeper 
 waters. 
 
 The great currents of the ocean are for the most part so 
 distant from the borders of the continents that little de- 
 tritus comes within their reach. As these currents have 
 great depth often a thousand feet or more, their 
 course is determined partly by the deep-water slopes of 
 the submerged border of a continent, so that, when the 
 border is shallow for a long distance out (as off New 
 Jersey and Virginia, where this distance is even 50 
 to 80 miles), the main body of the current is equally 
 remote. Wherever it actually sweeps close along a coast, 
 it may bear away some detritus, to drop it over the bot- 
 tom in the neighboring waters. The flow of the Gulf 
 Stream against the submerged slope of the oceanic basin 
 (at the rate of a mile or more per- hour) is sufficient to 
 keep the bottom free from loose detritus. Verrill has 
 suggested that the burrowing of fishes for food aids the 
 erosive action of currents, by loosening the material. 
 
 The oceanic currents flowing from polar seas produce 
 important effects by means of the icebergs which they bear 
 into warmer latitudes. These icebergs are sometimes 
 freighted with earth and rocks ; and, wherever they melt, 
 they drop all to the ocean's bottom. The sea about the 
 Newfoundland banks is one of the regions of melting 
 icebergs ; and there is no doubt that vast submarine ac- 
 cumulations of such material have been made there by 
 this means. 
 
 DISTRIBUTION OF MATERIAL, AND FORMATION OF MARINE 
 AND FLUVIO-MARINE DEPOSITS. 
 
 Origin of Material. The material used by the waves 
 and currents is either (1) the stones, gravel, sand, clay, 
 or earth produced by the wear of coasts ; or (2) the. detri- 
 
152 DYNAMICAL GEOLOGY. 
 
 tus brought down by rivers and poured into the ocean, as 
 explained on pages 136-140. 
 
 The latter, in the present age, is by far the more im- 
 portant. But in the earlier geological ages, when the dry 
 land was of small extent, rivers were small and were but 
 a feeble agency. 
 
 The decomposition or disintegration of exposed rocks 
 through the agency of air and moisture must have aided 
 in degradation formerly more than now, since, in Paleozoic 
 time and earlier, carbonic acid, the chief agent of destruc- 
 tion, was much more abundant in the atmosphere than it 
 is now. This agent is carried to the earth's surface by 
 the rains, and it is still effective in the decomposition of 
 granite, gneiss, and many other rocks. The higher tem- 
 perature of the atmosphere in early geological times was 
 also favorable to rapid chemical action. 
 
 Forces in Action. In the distribution of the materiaj, 
 the waves and marine currents have either worked alone, 
 in the manner explained on the preceding pages, or in 
 conjunction with river currents wherever these existed. 
 
 Marine Formations. The marine formations are of the 
 following kinds : 
 
 1. Beach Accumulations. Beaches are made of the ma- 
 terial borne up the shores by the waves and tides and left 
 above low-tide level. This material consists of stones or 
 pebbles, sand, mud, earth, or clay. It is coarse where the 
 waves break heavily, because, although trituration to pow- 
 der is going on at all times, the powerful wave action and 
 the undercurrent carry off the finer material into the off- 
 shore shallow waters, where it settles over the bottom or 
 is distributed by currents. It is fine where the waves are 
 gentle in movement, as in sheltered bays, or estuaries, the 
 triturated material remaining in such places near where it 
 is made, and often being the finest of mud. 
 
 2. Sand Banks, or Reefs; Shallow-water Accumulations. 
 Shallow-water accumulations may be produced in bays, 
 estuaries, or the inner channels of a coast, and over the 
 
MECHANICAL EFFECTS OF WATER. 
 
 153 
 
 FIG. 184. 
 
 bottom outside. They consist usually of coarse or fine 
 sand and earthy detritus, but may include pebbles or 
 stones when the currents are strong. The material consti- 
 tuting them is derived from the land through the wearing 
 and transporting action either of the waves and currents 
 or of rivers. The accumulations may increase under wave 
 action in shallow water, until they approach or rise above 
 low-tide level, and then they form sand banks. Such sand 
 banks keep their place in the face of the waves, for the 
 same reason as the platform of rock mentioned on page 148 
 and illustrated in Fig. 183. 
 
 3. Fluvio-marine Formations. Most of the accumula- 
 tions in progress on existing shores, whether sand banks, 
 or estuarine, or off-shore deposits, especially about well- 
 watered continents, contain more or less of river detritus, 
 and are modified in their forms by 
 the action of river currents. Along 
 the whole eastern coast of the 
 United States south of New Eng- 
 land, and on all the borders of the 
 Gulf of Mexico, the formations in 
 progress are mainly fluvio-marine that is, the combined 
 result of rivers and the ocean. The coast region of the 
 continent is now slowly widening through this means, 
 and has been widening for an indefinite period. This 
 coast region is low, flat, often marshy, full of channels or 
 sounds ; and facing the ocean there is a barrier of sand. 
 
 The rivers pour out their detritus especially during their 
 floods, and the ocean's waves and currents meet it as the 
 tide sets in, with a counter action, or one from the sea 
 landward ; between the two, the waters, as they lose their 
 velocity, drop the detritus over the bottom. Where the 
 river is very large and the tides feeble, the banks and reefs 
 extend far out to sea. The Mississippi thus stretches its 
 many-branched mouth (Fig. 180) fifty miles into the Gulf. 
 Where the tide is strong, sand bars are formed ; and the 
 stronger the tides, the closer are the sand bars to the coast. 
 
 Beach structure. 
 
154 DYNAMICAL GEOLOGY. 
 
 Where the stream is small, the ocean may throw a sand- 
 bank quite across its mouth, so that there may be no egress 
 to the river waters except by percolation through the sand; 
 or, if a channel is left open, it may be only a shallow one. 
 
 STRUCTURE OP THE FORMATIONS. 
 
 Beach Formations are very irregular in stratification in 
 their upper portions, where they are made by the toss of 
 the waves combined with drifting by the winds. The 
 layers as shown in Fig. 184 have but little lateral ex- 
 tent, and change in character every few feet. But the 
 
 sloping part swept by the 
 
 FIG. 185. "Y 1 u- iT a.- i 
 
 waves below high-tide 
 level is very evenly strati- 
 fied parallel to the sur- 
 face ; and, since this sur- 
 face dips usually at an 
 angle of 5 to 15, the 
 beach-made beds have the 
 same dip. The coarsest 
 beaches have the steepest 
 slopes. 
 
 The sand banks and 
 reefs made in shallow 
 waters along a coast have 
 
 Eipple-marks. 
 
 a more regular and more 
 
 nearly horizontal stratification, and are mostly composed 
 of sand with some beds of pebbles. They often vary 
 much every mile or every few miles. The extent and 
 regularity of level of the submerged area off a coast will 
 determine in a great degree the extent to which the uni- 
 formity of stratification may extend ; and, in this respect, 
 the conditions were much more favorable for the deposit 
 of uniformly stratified sediments over wide areas in for- 
 mer geological ages than at present, since large areas of 
 the continents were formerly submerged at shallow depths. 
 
MECHANICAL EFFECTS OF WATER. 
 
 155 
 
 FIG. 186. 
 
 I 
 
 Ripple-marks (Fig. 185) are alternate ridges and fur- 
 rows made by the wash of the waters over a sand flat 
 or beach, or over the bottom within soundings. They 
 may also be made by the action of wind on fields of sand. 
 The width of the furrows may 
 be a fraction of an inch, or 
 several inches. Rill-marks (Fig. 
 186) are produced when the 
 return waters of a tide, or of 
 a wave that has broken on a 
 beach, flow by an obstacle, as 
 a shell or pebble, and are piled 
 up a little by it, so as to be made 
 to plunge over it, and so erode 
 the sands for a short distance 
 below the obstacle. The figure 
 shows such markings in con- 
 nection with shells (Lingula) 
 in a Silurian sandstone. 
 
 The cross-bedded structure (Fig. 187) is characterized 
 by lamination or straticulation in a plane oblique to that 
 of the stratification. It results from the pushing along of 
 the sand or earth by currents, causing at first a little ele- 
 vation, and then the deposition 
 of successive layers over the 
 front, or down-stream, slope of 
 the elevation. If the currents 
 are transient, alternating with 
 conditions of still water, the 
 obliquely laminated beds will 
 alternate with others horizon- 
 tally laminated. Such alternations may be due to changes 
 of tide, or to the periodical or occasional fluctuations in the 
 volume of rivers. When there are plunging waves accom- 
 panying the rapid flow of a current, the obliquely laminated 
 layer is broken up into short, wavelike parts, as in the 
 flow-and-plunge structure (Fig. 188). 
 
 Eill-marks. 
 
 FIG. 187. 
 
 Cross-bedded structure. 
 
156 
 
 DYNAMICAL GEOLOGY. 
 
 Mud-cracks, Earth-cracks. When a mud flat is ex- 
 posed to the air or sun to dry, as by the ebbing of a tide 
 or the subsiding of a freshet, it becomes cracked to a few 
 inches or feet in depth. Fig. 189 represents mud-cracks 
 in argillaceous sandstone. Such cracks may subsequently 
 
 FIG. 188. 
 
 Flow-and-plunge structure. 
 
 become filled with stony material, either sediment or 
 material in solution ; and, as such fillings are often harder 
 than the rock itself, they may stand as prominent ridges 
 above a weathered surface of the rock. It is actually a 
 
 FIG. 189. 
 
 Mud-cracks. 
 
 network of veins, but of very shallow veins that were 
 filled from above. In regions of long droughts, the earth- 
 cracks over prairies and alluvial flats are sometimes many 
 and deep, and over a foot wide. 
 
 The imbedded shells and other animal relics in a beach 
 are commonly broken ; those in the bays or offshore 
 
MECHANICAL EFFECTS OF WATER. 157 
 
 waters out of the reach of the waves may be unbroken, 
 or may lie as they did when living ; but, if the waters 
 are so shallow that the shells or corals are exposed to 
 wave action, they may be broken or worn to powder, and 
 enter in this state into the formation in progress. (See 
 pages 99-105 for further discussion of the formation of 
 limestone from shells or corals.) 
 
 Deposits of broken shells under water are sometimes 
 made by Fishes that have taken the animals for food. 
 Such beds made by Fishes answer to the shell heaps of 
 human origin. 
 
 In the sands of beaches near low-tide level, borings 
 of Worms, Mollusks, or Crustaceans, may exist ; and, if 
 sand or mud is left above the water level, as by the re- 
 ceding tide, it may be marked by tracks of various land 
 animals. 
 
 3. Freezing and Frozen Waters. 
 
 Freezing Water. As water in the act of freezing ex- 
 pands after reaching 39.2 F. (4 C.), freezing in the 
 seams of rock opens the seams and tears masses asunder. 
 The expansion on reaching 32 F. is -^ lineally, and the 
 density is diminished to 0.92. The results of expansion 
 are most marked in rocks that are much fissured, or 
 intersected by joints, or that have a slaty or laminated 
 structure. As the action continues through successive 
 years and centuries, it often results in great accumula- 
 tions of broken stone. The slope, or talus, of fragments 
 at the foot of a cliff of trap or basalt is often more than 
 half as high as the cliff itself. In tropical countries, 
 cliffs have no such masses of ruins at their base. 
 
 Granular rocks, whether crystalline or not, when they 
 readily absorb water, lose their surface grains by the same 
 freezing process. Granite, as well as porous sandstones, 
 may thus be imperceptibly turning to dust, earth, or 
 gravel. In Alpine regions this action may be incessant. 
 
 Alternate freezing and thawing produces (as explained 
 
158 DYNAMICAL GEOLOGY. 
 
 by Kerr) a downward movement of earth and gravel on 
 slopes, with rearrangement of the materials. 
 
 Frozen Water. The effects of ice and snow are con- 
 veniently considered under three heads : 1, The Ice of 
 Lakes and Rivers ; 2, Glaciers ; 3, Icebergs. 
 
 1. ICE OF LAKES AND RIVERS. 
 
 The ice of lakes and rivers often forms about stones 
 along their shores, and sometimes over those of the bot- 
 tom (then called anchor ice), making them part of the 
 mass ; and other stones sometimes fall on shore ice from 
 overhanging bluffs. The ice serves as a float to the 
 stones ; and in times of high water, or floods, it may 
 carry its burdens high up the shores, or over the flooded 
 flats, to leave them there as it melts. Large accumula- 
 tions of bowlders are sometimes made, by this means, on 
 shores far above the ordinary level of the waters. 
 
 2. GLACIERS. 
 
 Glaciers are Ice Streams, or rivers in which the moving 
 material is frozen instead of liquid water. 
 
 Like large rivers, they ordinarily have their sources 
 in high mountains, and descend along the valleys ; but 
 (1) the mountains must be high enough to receive snow 
 from the clouds instead of rain ; and (2) they must be 
 extensive enough to receive annually a large supply of 
 snow, so that it may accumulate to a great depth ; and 
 (3) the region must be one of sufficient precipitation. 
 
 As in the case of rivers, many tributary streams coming 
 from the different valleys may unite to make the great 
 stream. 
 
 As with rivers, their movement is dependent on gravity, 
 or the weight of the material ; but the average rate of 
 motion, instead of being several miles an hour, is generally 
 in summer but 10 to 18 inches a day, or a mile in 18 to 
 20 years. Twelve inches a day corresponds " to a mile 
 
MECHANICAL EFFECTS OF WATEE. 159 
 
 in 141 years. The rate in winter is about half of that in 
 summer. 
 
 As with rivers, the central portions move most rapidly, 
 the sides and bottom being retarded by friction. 
 
 The snow of the mountain tops, called nv, or firn, 
 which is perhaps hundreds of feet deep, becomes com- 
 pacted and converted into ice mainly by its own weight, 
 with the aid of water penetrating it, derived from partial 
 melting ; and thus the glacier begins. Through alternate 
 melting and freezing, the change to ice is made more 
 complete. As the glacier starts on its course, the clouds 
 furnish new snows to keep up the supply and help press 
 on the moving mass. 
 
 Descent below the Snow Line. The height, in the 
 Alps, of the snow-line, or that below which the snow 
 annually precipitated melts during the year, is about 8400 
 feet on the north side of the Alps, and about 8800 feet on 
 the south side ; and the glacier may descend below this 
 line 5000 feet or more. The ice resists the melting heat 
 of summer because of its mass, like the ice in an ice-house. 
 Though starting where all is white and barren, it passes 
 by regions of Alpine flowers, and often continues down to 
 a country of gardens and human dwellings before its course 
 is ended. Thus, the Grlacier des Bois, an upper portion of 
 which is called the Mer de Grlace, rises in Mont Blanc and 
 other neighboring peaks, and terminates, like several other 
 glaciers, in the vale of Chamouni. In a similar manner, 
 two great glaciers descend from the heights of the Bernese 
 Alps to the Grindelwald valley just south of Interlaken. 
 
 Fig. 191 represents one of the ice streams of the Monte 
 Rosa region in the Alps, from a view in Professor 
 Agassiz's work on Glaciers. It shows the lofty regions 
 of perpetual snow in the distance ; the bare rocky slopes 
 that border it, later on its course ; and the many crevasses 
 that intersect the surface of the ice stream. 
 
 Fractures attending the Movement ; Crevasses. Every 
 valley has its ridgy sides, its sharp turns, its abrupt nar- 
 
160 DYNAMICAL GEOLOGY. 
 
 rowings and widenings, its irregular bottom ; and the stiff 
 ice, compelled to accommodate itself to these irregularities, 
 forms by its rupture profound crevasses, besides multi- 
 tudes of cracks that are not visible at the surface. There 
 are crevasses on the convex side of every bend in the 
 glacier ; transverse crevasses, crossing even its whole 
 breadth, where the ice plunges down a steep place in an 
 ice cascade ; and longitudinal crevasses, where the ice, 
 escaping from a narrow gorge, spreads laterally over a 
 broad valley or plain. Independently of any local irregu- 
 larities, the more rapid motion of the central part of a 
 glacier causes a diagonal strain (theoretically in a direc- 
 tion at an angle of 45 with the axis of the 
 
 FIG. 190. . . & . 
 
 glacier}, which produces a series or marginal 
 crevasses, having the direction indicated by 
 Fig. 190. 
 
 Again, crevasses once formed may close up 
 again, when the form of the valley is such 
 that a portion of the ice is subjected to 
 pressure in a direction in which it has formerly 
 Diagram niustrat- been subjected to tension, 
 mg marginal Glacier Torrent. The melting of the gla- 
 
 crevasses. . 
 
 cier, especially during the warm season, gives 
 rise to streams of Water flowing beneath it, which finally 
 unite in a torrent of considerable size, emerging to the 
 light from beneath the bluff of ice in which the glacier 
 terminates. Thence it continues on its rocky course down 
 the valley. 
 
 Method of Movement. The capability of motion in a 
 glacier is dependent (1) partly on a degree of plasticity 
 in ice. Ice may be made, through pressure, to copy a 
 seal, or may be drawn out into cylinders ; or, if a slab is 
 supported only at the sides, it will become bent downward, 
 through gravity. The apparent plasticity of glacier ice is, 
 however, in great part due to the processes referred to in 
 the next two paragraphs. 
 
 (2) The movement depends in great part upon the facil- 
 
MECHANICAL EFFECTS OF WATER. 
 
 161 
 
 ity with which ice breaks, and afterwards reunites into a 
 solid mass when the broken surfaces are brought into con- 
 tact. This property of regelation was first noticed by 
 Faraday. It is easily shown by breaking a lump of ice 
 and bringing the surfaces again jnto contact: if moist, as 
 they are at the ordinary temperature, they at once become 
 firmly united. A glacier moves on and accommodates 
 
 FIG. 191. 
 
 Glacier of Zermatt, or Gorner Glacier. 
 
 itself to its uneven bed by breaking ; and, however frac- 
 tured it may be, it becomes, when the parts are pressed 
 together, as solid as before. 
 
 (3) The movement of the ice is facilitated by alter- 
 nate melting and freezing in the interior of the glacier. 
 The crystalline grains of which the glacier is composed, 
 are found to increase from the almost microscopic size of 
 
162 DYNAMICAL GEOLOGY. 
 
 the crystals of the snowflakes on the mountain summits 
 to a diameter of several inches near the end of a glacier; 
 and this indicates a great amount of melting and freezing. 
 This process goes on most rapidly when the greatest 
 amount of heat is communicated to the glacier. Hence 
 the motion is more rapid in summer than in winter. 
 
 (4) A glacier may, here and there, at times, slide along 
 its bed, yet only portions at a time. 
 
 Transportation by Glaciers ; Moraines. Glaciers be- 
 come laden with stones and earth falling from the heights 
 above, or coming down in avalanches of snow and stones. 
 The stones and earth make a band along either border of 
 a glacier, and such a band is called a moraine. When two 
 glaciers unite, they carry forward their bands of stones 
 with them ; but those on the uniting sides combine to 
 make one moraine, which is called a medial moraine, in 
 distinction 'from the lateral moraines on the margins of 
 the glacier. A large glacier, like that in Fig. 191, may 
 have many moraines one more than the number of trib- 
 utaries by whose union the trunk glacier has been formed. 
 
 In the lower part of a glacier the several moraines gen- 
 erally lose their distinctness, through the melting of the 
 ice, and also by reason of the fact that the glacier is gen- 
 erally compressed in its lower part to a width very much 
 less than the aggregate width of its tributaries. The sur- 
 face of the glacier, accordingly, often becomes covered 
 with earth and stones for the greater part of its breadth. 
 The bluff of ice which forms the foot of a glacier is often 
 a dirty mass, scarcely revealing superficially its real nature. 
 
 Some of the masses of rock on glaciers are of immense 
 size. One is mentioned containing over 200,000 cubic feet 
 which is equivalent in cubic contents to a building 100 
 feet long, 50 feet wide, and 40 feet high. 
 
 Besides the superficial moraines, a glacier also gathers 
 rock material from the bottom over which it moves. The 
 disintegrated and decomposed rock is mostly scraped from 
 the surface, masses of rock are torn off from jointed ledges, 
 
MECHANICAL EFFECTS OF WATER. 
 
 163 
 
 and soft rocks in the path of the glacier are deeply abraded. 
 The materials thus gathered from the bed of the glacier, 
 with additions from stones which have fallen into the 
 crevasses from above, form the ground moraine, or moraine 
 profonde. 
 
 The final melting leaves all the earth and stones in un- 
 stratified heaps or deposits, which may be further trans- 
 ported, abraded, and deposited, by the stream that flows 
 
 FIG. 192. 
 
 View on Koche-moutoimee Creek, Colorado. 
 
 from the glacier. The mass of such deposits dropped at 
 the foot of a glacier is called the terminal moraine. 
 
 Erosion by Glaciers. A glacier laden with stones 
 will have stones in its lower surface and sides, as well as 
 in its mass. As it moves down the valley, it consequently 
 abrades the exposed rocks over which it passes, smoothing 
 and polishing some surfaces, covering others closely with 
 parallel scratches, and often plowing out broad and deep 
 
164 DYNAMICAL GEOLOGY. 
 
 channels, besides having its abrading bowlders scratched 
 or polished. 
 
 Deep plowing is accomplished chiefly (1) where the rock 
 beneath is soft or fragile, or (2) where it is jointed, rifted, 
 or laminated. In the latter case the action is rending, 
 rather than abrading, and by this means the larger part of 
 the direct excavation by glaciers has been done. 
 
 The rocky ledges over which the ice has moved are 
 often reduced to rounded prominences ; they then look, in 
 the distance, like groups of crouching sheep, and hence 
 have been called, in French, roches moutonnges. They are 
 exhibited on a grand scale in some of the valleys of the 
 high ranges along the summit of the Rocky Mountains, 
 where were formerly extensive glaciers ; and Fig. 192 
 represents such a scene, in the region of the Mountain 
 of the Holy Cross (the remote summit near the center 
 of the view), as photographed by the photographer of the 
 expedition under Dr. Hayden. Further, the stones in 
 the ever-shifting ice are worn, and become rounded at the 
 angles ; and the very fine rock flour derived in part from 
 the transported stones and in part from the bed rock, is 
 carried down by the glacier torrent, to make beds of clay 
 or earth, and give a milky hue to the rivers flowing from 
 a glacier region. 
 
 Glaciers deepen and widen the valleys in which they 
 move. But in this work they are aided by frosts, ava- 
 lanches, and especially by the torrents beneath the glacier. 
 
 Glacier Regions. The best known of Glacier regions 
 are those of the Alps, in one of which Mont Blanc stands, 
 with its summit 15,760 feet above the sea. There are 
 glaciers also in the Pyrenees, the mountains of Norway, 
 Spitzbergen, Greenland, Alaska, and other Arctic regions, 
 in the Caucasus and Himalaya, in the southern Andes, in 
 the Cascade Range, and in the Rocky Mountains of British 
 America. Greenland is a great glacier-covered land, send- 
 ing many large streams of ice through the fiords of the 
 border region to the polar seas. 
 
MECHANICAL EFFECTS OF WATER. 165 
 
 3. ICEBERGS. 
 
 When glaciers, like those of Greenland, terminate in 
 the sea, the icy foot becomes broken off from time to time ; 
 and these fragments of glaciers, floated away by the sea, 
 are icebergs. The geological effects of icebergs have been 
 stated on page 151. Seashore ice sometimes carries stones 
 and gravel far out to sea. 
 
 Summary. Formation of Sedimentary Strata. 
 
 The following is a brief recapitulation of the explana- 
 tions of the origin of deposits given in the preceding 
 pages. Igneous and other crystalline rocks are not here 
 included. 
 
 1. Sources of Material. The greater part of the ma- 
 terial of sedimentary rocks has come from the degradation 
 of preexisting rocks. But another part (as limestone 
 and infusorial earth) has been taken up from a state of 
 solution in the ocean or in fresh waters, through the 
 agency of life ; yet the waters have received the ingredi- 
 ents from the rocks, either when the ocean first began to 
 exist, or subsequently through the dissolving action of 
 streams on exposed rocks (page 137). 
 
 2. Means of Degradation. The principal means of 
 degradation are the following : (1) Erosion by moving 
 waters, either those of the sea or land (pages 126, 147); 
 (2) Erosion by ice, chiefly in the condition of glaciers (page 
 163); (3) Pressure of the water descending into fissures; 
 (4) Formation of substances, for example oxide of iron, in 
 cracks, tending to open and deepen the cracks ; (5) Growth 
 of rootlets, roots, and trunks of trees, in crevices, result- 
 ing in opening and tearing apart rocks, and often produc- 
 ing extensive destruction of rocks, especially when they 
 are jointed ; (6) Freezing of water in fissures (page 157); 
 (7) Chemical decomposition of one or more of the ingre- 
 dients of a rock, in the course of which process the rock 
 
166 DYNAMICAL GEOLOGY. 
 
 becomes crumbled or reduced to earth ; (8) Removal by 
 solution, as of limestones by carbonated waters ; (9) Un- 
 dermining of rocks by any method ; (10) Expansion and 
 contraction by heat (page 172). 
 
 3. Formation of Deposits. The principal methods by 
 which deposits have been formed are the following : 
 
 1. By the Waters of the Sea. (1) Through the sweep 
 of the ocean over the submerged portions of the continents 
 (pages 12, 154) : making sandy or pebbly deposits near or 
 at the surface where the waves strike, or at very shallow 
 depths where swept by a strong current ; argillaceous or 
 shaly deposits near or at the surface, where sheltered from 
 the waves, and also at considerable depths, out of material 
 washed off the land by the waves or currents ; but not 
 making coarse sandy or pebbly deposits over the deep bed 
 of the ocean, as even great rivers carry only silt to the 
 ocean; and not making even argillaceous deposits over the 
 ocean's bed except along the borders of the land, unless 
 by the aid of a very great river like the Amazon, though 
 even in that case the greater part of the detritus is thrown 
 back on the .coast by the waves and currents. In former 
 geological periods, the submerged borders of the conti- 
 nents, on which sedimentation mainly takes place, were 
 much more extensive than at present. 
 
 (2) Through living species, and mainly Mollusks, Mol- 
 luscoids, Crinoids, Corals, and Rhizopods, affording cal- 
 careous material for strata; and Diatoms, Radiolarians, 
 and Sponges, affording siliceous material. Most rocks 
 made of Corals and the shells of Mollusks have required 
 the help of the waves, at least to fill up the interstices. 
 
 2. By the Waters of Lakes. Lacustrine deposits are 
 essentially like those of the ocean in mode of origin, unless 
 the lakes are small, when they are like those of rivers. 
 
 3. By the Running Waters of the Land. (1) Filling 
 the valleys with alluvial deposits, and moving the earth 
 from the hills over the plains (page 138). (2) Carrying 
 detritus to the sea or to lakes, to make, in conjunction 
 
HEAT. 167 
 
 with the action of the waters of sea or lake, deltas and 
 other shore accumulations (pages 138, 153). 
 
 4. By Frozen Waters. (1) Acting in the condition of 
 glaciers ; and thus spreading the rocks and earth of the 
 higher lands over the lower, in definite lines of moraine, 
 or in sheets of drift, bearing onward in the process, blocks 
 of great size, as well as finer material* (page 162). 
 (2) Acting as icebergs ; and, in this condition, transport- 
 ing stones and earth to distant parts of the ocean, as 
 from the Arctic regions to the Newfoundland Banks, and 
 so contributing to sedimentary accumulations in deep or 
 shallow water, distinguished by their containing huge 
 blocks of stone, besides pebbles and earth. 
 
 V. HEAT. 
 1. Sources of Heat. 
 
 The crust of the earth derives heat from three sources : 
 > 1, The Sun, an external source ; 2, The Earth's Heated 
 Interior ; 3, Chemical and Mechanical Action. 
 
 1. The Sun. This agency is peculiar in being regu- 
 larly variable, through the alternations in day and night, 
 in the seasons, in the time of aphelion and perihelion, and 
 in the eccentricity of the earth's orbit. The amount of 
 heat imparted to the earth and retained by it, varies also 
 with changes in the atmosphere ; since the atmosphere 
 absorbs a part of the heat radiated to the earth from the 
 sun and stars, and absorbs in greater proportion the heat 
 rays of extremely great wave length radiated from the 
 earth. The following are some of the causes to which 
 change in climate has been attributed : 
 
 1. A gradual diminution in the heat of the sun through 
 the geological ages. Such a change must have taken 
 place ; and it is believed by Lord Kelvin and others that 
 it has been adequate to produce a very considerable 
 change in the earth's climate since the beginning of Paleo- 
 zoic time. 
 
168 DYNAMICAL GEOLOGY. 
 
 2. Variations in the condition of the surface of the sun, 
 causing periodical alterations in the amount of heat radi- 
 ated, and thus producing alternating cold and warm eras. 
 Such changes are possible, though their occurrence has 
 not been proved. 
 
 3. Variations in. the level of the earth's surface. In 
 any latitude the highlands are colder than the lowlands, so 
 that very appreciable changes of climate must have been 
 produced by the great mountain elevations of the Tertiary 
 era, and by the extensive changes of continental levels in 
 the Quaternary. But even more important may be the 
 indirect effects of crustal movements, when a change in 
 the level of the land or sea bottom diverts the oceanic 
 currents from one course to another. Elevating the sea 
 bottom between Europe and Greenland, would shut out 
 the warm Gulf Stream from the Arctic region, and in- 
 crease its cold. For, according to Croll's calculations, 
 this stream contributes to the North Atlantic Ocean 77,- 
 479,650,000,000,000,000 foot-pounds of energy, in the form 
 of heat, per day. Such a change might, therefore, make 
 a glacial climate for large areas in the northern hemi- 
 sphere. On the contrary, a subsidence opening Bering 
 Strait for the free passage of the tropical current of the 
 Pacific would ameliorate the Arctic climate. 
 
 4. Variations in the constitution of the earth's atmos- 
 phere. As already stated, the atmosphere absorbs a part 
 of the heat radiated from the sun to the earth, but absorbs 
 in greater proportion the heat rays of very great wave 
 length emitted from the earth. The effect of the atmos- 
 phere is to make the temperature of the surface of the 
 earth more uniform, and on the average higher, than it 
 would otherwise be. This absorptive action is chiefly due 
 to the carbon dioxide and water vapor in the atmosphere. 
 It has been inferred that the effect of a larger amount of 
 these constituents (which must have existed in early 
 geological time) would have been to make the earth 
 warmer than at present. The researches of Langley, 
 
HEAT. 1169 
 
 however, have shown that the law of selective absorption 
 of heat rays by the atmosphere is more complex than was 
 formerly supposed ; and the inference as to the climatic 
 effect of the greater amount of water vapor and carbon 
 dioxide in former times, is somewhat doubtful. 
 
 5. Variations in the eccentricity of the earth's orbit. 
 The earth, through all such variations, receives the same 
 amount of heat annually from the sun, but not the same 
 for the winter as for the summer. The maxima of eccen- 
 tricity are unequal, and are passed at variable periods 
 ranging from about 100,000 to somewhat more than 
 200,000 years. The earth is at present near a minimum, 
 and the distance from the sun is about 93.9 millions of 
 miles in aphelion (which comes now in summer), and 
 nearly 90.9 millions in perihelion the difference, about 
 3 millions. About 100,000 years since, a maximum oc- 
 curred, with the aphelion and perihelion distances 96.65 
 and 88.15 millions of miles the difference, 8J millions; 
 and 850,000 years since, an extreme maximum, with these 
 distances 99.3 and 85.5 millions the difference, 13.8 
 millions of miles. When the aphelion comes in the winter 
 of the northern hemisphere, the cold of the winters in that 
 hemisphere is increased, the amount of heat received being 
 inversely as the square of the distance (which ratio gives 
 for the heat in winter, during the extreme maximum re- 
 ferred to, about five sixths of that now received in that 
 season). Moreover, the winter part of the year (from 
 the autumnal to the vernal equinox) is, at the extreme 
 maximum, 36 days longer than the summer part (from 
 the vernal to the autumnal equinox) ; whereas at present 
 the latter is 8 days the longer. At the same time, the 
 summers are hotter, but shorter. In the southern hemi- 
 sphere the reverse, in each respect, is true. The cold 
 of a Glacial period has been thus accounted for, and also 
 the warmth of warm eras, by Croll; but others reject 
 the theory. The theory requires several Glacial epochs in 
 each hemisphere during one prolonged time of maximum 
 
170 DYNAMICAL GEOLOGY. 
 
 eccentricity, since the effect of precession and revolution 
 of the apsides is to reverse the relation of the seasons of 
 each hemisphere to aphelion and perihelion twice in a 
 cycle of about 21,000 years. In an age of maximum 
 eccentricity, Glacial epochs should accordingly occur alter- 
 nately in the northern and the southern hemisphere, cul- 
 minating at intervals of 10,500 years. 
 
 6. A change in the earth's axis has been suggested as 
 a possible cause of variation in climate. But calculations 
 by G. H. Darwin, Haughton, and others, have shown that 
 no such change can have taken place sufficient for any 
 marked result. 
 
 2. Internal Heat. The fact of a high temperature in 
 the earth's interior is established in various ways. 
 
 1. The form of the earth is a spheroid, and a spheroid 
 of just the shape that would have resulted from the earth's 
 revolution on its axis, provided it had passed through a 
 state of fusion, and had slowly cooled over its exterior. 
 Hence is drawn the inference that it has passed through 
 such a state of fusion, which is strengthened by the other 
 evidence here given. Another conclusion also follows ; 
 namely, that the earth's axis had the same position (or, at 
 least, very nearly the same) when cooling began as now. 
 There is no evidence that there has been at any time any 
 considerable change. 
 
 2. In deep borings for water, and in shafts sunk in 
 mining, it has been found that the temperature of the 
 earth's crust increases, on an average, one degree Fahren- 
 heit for 55 to 60 feet of descent. Such a rate, in the 
 latitude of New York, would give heat enough to boil 
 water at a depth of less than two miles ; and at a depth 
 of 35 miles the temperature would be 3000 F., or that of 
 the fusing point of iron. Since, however, the fusing tem- 
 perature of nearly all substances increases with the pres- 
 sure, a zone of universal fusion in the earth, if such a zone 
 exists at all, must be at a much greater depth than would 
 be suggested by the figures given above. 
 
HEAT. 171 
 
 3. The great Pacific Ocean has nearly a complete girdle 
 of volcanoes, extinct or active ; and all of its many islands 
 that are not coral islands, are volcanic, excepting New 
 Zealand and a few others of large size in its southwest 
 part. Volcanoes occur along many parts of the Andes 
 from Tierra del Fuego to the Isthmus of Darien ; in Cen- 
 tral America, in Mexico, California, Oregon, and beyond ; 
 in the Aleutian Islands on the north ; in Kamchatka, 
 Japan, the Philippines, New Guinea, New Hebrides, and 
 New Zealand on the west ; and in Antarctic lands south 
 of New Zealand and South America. The volcanic region 
 thus bounded is almost a hemisphere ; and, besides, there 
 are volcanoes in many parts of the other hemisphere. 
 Outlets of molten matter so extensively distributed seem 
 to indicate that there is some world- wide region of heat 
 beneath. 
 
 4. The flexures which the earth's crust and its strata 
 have undergone over regions of continental extent, and 
 even as late as the Cenozoic, have been held by some 
 to prove that there have been, up to the middle Cenozoic, 
 if not later, great regions of liquid rock beneath the 
 earth's crust; though most physicists and geologists be- 
 lieve those movements to be compatible with a condition 
 of substantial solidity of the globe. 
 
 3. Chemical and Mechanical Action. In the upturning 
 and flexure of rocks attending mountain-making, there 
 have been movements on a grand scale ; and, through the 
 transformation of this motion into heat, the rocks have 
 received in some cases a high temperature, sufficient to 
 promote, through the moisture present, the consolidation 
 of rocks, and even their crystallization, or metamorphism ; 
 and also, in the view of Mallet, their fusion on a scale 
 grand enough to originate volcanoes. This is probably 
 one chief source of the heat through which the metamor- 
 phism and consolidation of rocks have been produced, the 
 other chief source being the internal heat. 
 
 Heat is produced by condensation, as when vapors 
 
172 DYNAMICAL GEOLOGY. 
 
 become liquid or solid, or when liquids (as water) become 
 solid. It is also produced in many chemical changes, 
 as in the oxidation of pyrite and other substances. 
 
 2. Effects of Heat. 
 
 The following are the effects of heat here considered: 
 1, Expansion and Contraction; 2, Eruptions of Igneous Rock, 
 and associated phenomena ; 3, Metamorphism ; 4, Forma- 
 tion of Veins. 
 
 The subject of movements of the earth's crust, and 
 the evolution of continents and mountain ranges, might 
 be included here, since these movements probably result 
 from the reaction of the earth's heated interior upon its 
 surface ; but the subject is so comprehensive that it has 
 been deemed best to give it a distinct chapter (page 203). 
 
 1. EXPANSION AND CONTRACTION. 
 
 (1) Heat from any subterranean source penetrating 
 upward may cause wide changes of level. Lyell has cal- 
 culated that a mass of sandstone a mile thick, raised 
 in temperature to 1000 F., would have its upper surface 
 elevated 50 feet. Fractures and displacements would be 
 likely to attend such movements. (2) The diurnal varia- 
 tion of temperature, which in some countries amounts to 
 80 F. or more, and also the annual variation, is a force 
 always at work. The expansion and contraction may 
 gradually move blocks of rock from their places. It will 
 move the heated side of the block outward ; and, if this 
 outer part so moved cannot, because of wedging or fric- 
 tion, return with the succeeding contraction, the mass 
 will move to it or have its edges fractured. Blocks lying 
 on a slope will tend to crawl downward, since gravitation 
 will make the downward movement slightly exceed the 
 upward, in both expansion and contraction. The Bunker 
 Hill obelisk at Charlestown in Massachusetts has been 
 proved to swing back and forth with the passage of the 
 sun over it. (3) The alternating action of expansion and 
 
HEAT. 
 
 173 
 
 FIG. 198. 
 
 contraction peels off the grains or outer surface of rocks, 
 and is, especially in dry climates, an important means of 
 rock disintegration. 
 
 Shrinkage Cracks. (1) In the cooling of liquid rocks 
 shrinkage cracks are produced, 
 and thence comes the columnar 
 structure of trap, basalt, etc. 
 (Fig.. 193). The columns show 
 a tendency to the form of hex- 
 agonal prisms, since less expen- 
 diture of force in the rupture 
 of cohesion is required to pro- 
 duce a hexagonal network of 
 cracks than one of any other 
 form. The cracks tend to be propagated in a direction 
 perpendicular to the cooling surface ; and the position 
 of the columns is thereby determined. Fingal's Cave 
 
 Columnar structure. 
 
 FIG. 194. 
 
 Basaltic columns, Illawarra, New South Wales. 
 
 and the Giant's Causeway are familiar examples of co- 
 lumnar structure in great perfection. Fig. 194 (from 
 a sketch by the author in 1840) illustrates the same 
 phenomenon at Illawarra on the coast of New South 
 Wales. (2) Similar columnar forms are sometimes pro- 
 duced in sandstone after heating, though in general only 
 irregular cracks result. (3) Heat penetrates rocks over 
 
174 DYNAMICAL GEOLOGY. 
 
 wide regions wherever metamorphism is in progress ; and 
 the subsequent cooling and contraction may leave multi- 
 tudes of fractures, in long lines or in reticulations, the 
 subsequent filling of which may make veins. 
 
 Drying is another source of shrinkage cracks. It makes 
 the shallow mud-cracks (page 156), and the soil-cracks, 
 sometimes yards in depth, in countries of fertile prairies 
 that have a long hot and dry season ; and may produce 
 far deeper jointlike cracks in mud-made rocks (shales 
 and argillaceous sandstones), as they become slowly dried 
 by the action of subterranean heat. Further, the drying 
 of beds produces a sinking of the surface. A soft mud 
 may contract to a tenth of its bulk. All mud beds will 
 suffer a large diminution in thickness on drying ; but the 
 pressure of overlying strata may prevent shrinkage cracks 
 from forming. 
 
 2. ERUPTIONS OF IGNEOUS ROCK, AND ASSOCIATED PHENOMENA. 
 GENERAL NATURE OF VOLCANOES AND THEIR PRODUCTS. 
 
 Volcanoes are mountain elevations of a somewhat coni- 
 cal form, which have a crater at the summit, and eject, 
 from time to time, vapors and melted rock. If the ejec- 
 tions have long since ceased, the volcano is said to be 
 extinct. 
 
 The cavity or pit in the top of a volcanic mountain, 
 called the crater, where the lavas may often be seen in 
 fusion, is sometimes thousands of feet deep, but may be 
 quite shallow ; and in extinct volcanoes it is often wholly 
 wanting, owing to its having been left filled when the 
 action ceased. 
 
 The liquid rock issuing from a crater, and the same 
 after becoming cold and solid, is called lava. 
 
 An active crater, even in its most quiet state, emits 
 vapors. These vapors are mostly steam, or aqueous vapor; 
 but in addition there are usually sulphur gases, and some- 
 
HEAT. 175 
 
 times carbonic acid, hydrochloric acid, and more rarely 
 other gases. 
 
 In a time of special activity fiery jets are sometimes 
 thrown up to a great height, which are made of red-hot 
 fragments the fragments of great bubbles of lava pro- 
 duced by the escaping vapors. The fragments cool as 
 they descend about the sides of the crater, and are then 
 called cinders or ashes, according as they are coarse or fine. 
 
 When a shower of rain (which often results from the 
 condensation of the escaping steam) accompanies the fall 
 of the ashes, the result is a mudlike mass, which becomes, 
 on drying, a brownish or yellowish brown rock called tufa. 
 Tufa is often much like a soft sandstone, except that the 
 materials are of volcanic origin. 
 
 The materials produced by the volcano are, then : 
 1, Lavas ; 2, Cinders and ashes; 3, Tufas; 4, Vapors or 
 gases. 
 
 The lavas are of various kinds. They are often more 
 or less cellular sometimes light cellular, like the scoria 
 of a furnace, but more commonly heavy rocks, with some 
 scattered ragged cellules or cavities through the mass. A 
 stream of lava of this more solid kind has often a few 
 inches of scoria at top, as a running stream of sirup may 
 have its scum or froth. The most of the scoria has this 
 scum-like origin. Pumice is a very light grayish scoria, 
 full of long and slender parallel air cells. 
 
 When lava cools rapidly, it solidifies as a glass ob- 
 sidian or tachylite (pages 38, 39). When it cools slowly, 
 it forms a truly crystalline rock. Between the extremes 
 are various gradations. 
 
 The stony, or crystalline, lavas may be divided into 
 three groups, according to their chemical and mineralogi- 
 cal constitution, of which basalt, andesite, and trachyte 
 may be considered types. The lavas of the first group 
 consist chiefly of pyroxene and labradorite. They contain 
 a relatively small amount of silica, are dark and heavy 
 rocks (specific gravity above 2.8), and have an average 
 
176 
 
 DYNAMICAL GEOLOGY. 
 
 fusion point of about 2250 F. Those of the second group 
 consist chiefly of hornblende (or pyroxene) and oligoclase 
 or andesine. In percentage of silica, specific gravity, and 
 fusibility, they hold an intermediate position. Their aver- 
 age fusion point is about 2520 F. Those of the third 
 group consist chiefly of orthoclase, and sometimes contain 
 some quartz. They have a high percentage of silica, and 
 a specific gravity below 2.7. They are often light-colored. 
 Their fusion point is about 2700 F., and some of them are 
 considerably viscid even at a temperature of 3100 F. 
 
 FIG. 195. 
 
 Mount Vesuvius: from a sketch by the author in June, 1834. a, the main cone; &, 
 summit cinder cone ; c, Monte Somma, part of former outline of crater ; d, Hermitage 
 (now Observatory) ; e,f t Portici and Kesina, covering the site of Herculaneum ; g, Torre 
 del Greco. 
 
 A volcanic mountain is made out of the ejected mate- 
 rials : either (1) of lavas alone; (2) of cinders alone; 
 (3) of tufas alone ; or (4) of alternations of two or more 
 of these materials. As the ejections flow off or fall more 
 or less symmetrically around the vent, the form of a vol- 
 canic peak necessarily tends to become conical. 
 
 The angle of slope of a lava cone is from 3 to 10 ; of a 
 tufa cone, 15 to 30; of a cinder cone, 30 to 42; of mixed 
 cones, intermediate inclinations according to their consti- 
 tution. 
 
HEAT. 
 
 177 
 
 The cone of Vesuvius, shown in Fig. 195, consists 
 mostly of cinders, and is accordingly pretty steep. Etna, 
 about 10,000 feet high, and Mauna Loa in Hawaii, nearly 
 14,000 feet, consisting mainly of lava streams, have an 
 average slope of less than 10. The form of a cone with 
 a slope of 7 which is the average for the Hawaiian 
 volcanoes is shown in Figs. 196, 197. Fig. 196 has a 
 pointed top like Mauna Kea, and Fig. 197 a rounded out- 
 
 FIG. 196. 
 
 Mauna Kea. 
 
 line like Mauna Loa, whose form is that of a very low 
 dome. 
 
 The highest of volcanic mountains on the globe are the 
 Aconcagua peak in Chile, 23,000 feet, and Sorata and 
 Illimani in Bolivia, each over 24,000 feet. . The former 
 appears to be still emitting vapors. The mountains 
 
 FIG. 197. 
 
 Mauna Loa. 
 
 Shasta, Hood, St. Helen's, and others in California and 
 Oregon, are isolated volcanic cones 11,000 to 14,400 feet 
 high, the latter being the height of Mount Shasta. The 
 average slope of the upper half of Mount Shasta is about 
 27. The slopes of most of the lofty volcanoes of the 
 Andes are between 25 and 34. 
 
 VOLCANIC ERUPTIONS. 
 
 The process of eruption, though the same in general 
 method in all volcanoes, varies much in its phenomena. 
 The fundamental principles are well shown at the great 
 craters of Hawaii, the southeasternmost of the Hawaiian 
 (or Sandwich) Islands. 
 
178 DYNAMICAL GEOLOGY. 
 
 General Description of Hawaii. Hawaii is made up 
 mainly of three volcanic mountains two, Mauna Kea 
 and Mauna Loa (Figs. 196, 197, page 177), nearly 14,000 
 feet high ; and one (the western), Mauna Hualalai, about 
 10,000 feet. Mauna Kea is alone in being extinct. 
 
 Mauna Loa has a great crater at its summit, and 
 another independent one 4000 feet above the level of 
 the sea. The latter is the famous Kilauea, called also 
 Lua PSle, or Pele's pit, Pele being, in the mythology of 
 the Hawaiians, the goddess of the volcano. 
 
 The accompanying map of Hawaii (Fig. 198) shows 
 the positions of Mauna Loa and Mauna Kea, and of the 
 crater of Kilauea. , 
 
 Kilauea. The crater of Kilauea is literally a pit. It 
 is three miles in greatest length, and nearly two in great- 
 est breadth, and about seven and a half miles in circuit. 
 The pit has nearly vertical sides of solid rock (made 
 of lavas piled up in successive layers), and has been 
 1000 feet in depth after several of its eruptions, and 400 
 to 600 feet previous to its eruptions. The bottom is a 
 great area of solid lava, with one or more lakes or pools 
 of liquid lava, or crater-like openings, from which vapors 
 rise. The largest lake, in 1840, was 1000 feet in diameter. 
 The interior may be surveyed from the brink of the pit, 
 even when in most violent action, as calmly and safely as 
 if the landscape were one of houses and gardens. 
 
 Action in Kilauea. The ordinary action, in the inter- 
 vals between the great eruptions, is simply this. The 
 lavas in the active pools are in a state of ebullition, jets 
 rising and falling as in a pot of boiling water with this 
 difference, that the jets are 30 to 100 feet high. Such jets, 
 in lava as well as water, arise from the effort of vapors to 
 escape ; in water the vapor is steam derived from the water 
 itself ; in lavas it is chiefly steam from waters that have 
 gained access to the lavas, but also gases and vapors de- 
 rived from materials in the lavas, or from depths below. 
 
 The lavas of the pools or lakes overflow at times and 
 
HEAT. 
 
 179 
 
 spread in streams across the great plain that forms the 
 bottom of the crater. In times of great activity the pools 
 and lakes are numerous, the ebullition incessant, the jets 
 
 FIG. 193. 
 
 HAWAII 
 
 F.ROM THE 
 
 GOVERNMENT MAP 
 
 SCALE OF MILES 
 
 higher, and the overflowings follow one another in quick 
 succession. 
 
 Cause of Eruption. In part as the result of these over- 
 flows, but in part (and sometimes chiefly) as the result of 
 the bodily uplifting of the crater floor by lavas ascending 
 beneath it, the pit slowly fills. In the intervals between 
 
180 DYNAMICAL GEOLOGY. 
 
 1823 and 1832, and between 1832 and 1840, the bottom 
 was raised 400 feet or more above the lowest level, so that 
 the depth was reduced from 1000 feet to 600 feet or less. 
 The addition of 400 feet to the height of the column of 
 liquid lava in the crater caused a corresponding increase 
 of pressure against the sides of the mountain. The amount 
 of this pressure is at least two and a half times as great 
 as that which a column of water of equal height would 
 produce. The mountain must be strong to bear it. The 
 lavas at such times may be in a state of violent activity, 
 and a large addition to the pressure against the sides of 
 the mountain comes from the force of the imprisoned 
 vapors. 
 
 The consequence of this increase of pressure, both from 
 the lavas and the vapors, may be, and has several times 
 been, a breaking of the sides of the mountain. One or 
 more fractures result, and out flows the lava through the 
 openings. Thus simple have been the eruptions. 
 
 In the eruption of 1840 the lavas first appeared at the 
 surface a few miles below Kilauea, and then again at other 
 points somewhat more remote ; finally a stream (repre- 
 sented on the map, Fig. 198) began at a point about 15 
 miles east of the great crater, and extended to the shores 
 at Nanawale. Here, on encountering the waters, the great 
 flood of lava was shivered into fragments, and the whole 
 heavens were thick with an illuminated cloud of vapors 
 and cinders, the light coming from the fiery stream below. 
 The lavas which escaped at this relatively small eruption 
 amounted to at least 15,400,000,000 cubic feet. 
 
 This eruption of Kilauea took place, it will be observed, 
 not over the sides of the crater, but through breaks in the 
 mountain's sides below ; and the pressure of the column 
 of lava within, and that of the escaping vapors, appear to 
 have caused the break. 
 
 Summit Crater of Mauna Loa. Eruptions have also 
 taken place from the summit crater of the same mountain 
 (Mauna Loa), which is nearly 14,000 feet above the sea ; 
 
HEAT. 181 
 
 and in each case there has been, not an overflow from the 
 crater, but an outflow through breaks in the sides of the 
 mountain. In 1852 there was first a small issue of lavas 
 near the summit, and then another of great magnitude 
 about 10,000 feet above the sea level. At this second 
 outbreak the lava was thrown up in a fountain, or mass of 
 jets, two or three hundred feet high ; and thus it continued 
 in action for several days. The forms of the fountain of 
 liquid fire were compared by Rev. T. Coaii to the clustered 
 spires of a Gothic cathedral. Similar lava fountains have 
 been observed also at other eruptions of the volcano. 
 
 The pressure producing the jet in the case above men- 
 tioned, so far as it was hydrostatic, was that of the column 
 of lava between the point of outbreak and the level of the 
 lavas in the summit crater, 3000 to 4000 feet above. The 
 same pressure in connection with confined vapors must 
 have caused the breaking of the mountain in which the 
 eruption began. 
 
 Usually, no great earthquakes accompany the Hawaiian 
 eruptions, sometimes not even slight ones, the first an- 
 nouncement being merely "a light on the mountain." 
 But the eruptions of 1868 and 1887, from the summit 
 crater of Mauna Loa, were preceded by earthquakes of 
 considerable violence. When the summit crater is in 
 action, Kilauea, though 10,000 feet lower on the same 
 mountain, and even a larger pit crater, commonly shows 
 no agitation, no signs whatever of sympathy. 
 
 At some of the eruptions of Mauna Loa the lava has 
 continued down the mountain to a distance of 50 or 60 
 miles. 
 
 The shaded bands descending from near the summit, on 
 the map (Fig. 198), show the courses of several great out- 
 flows of lava. 
 
 Conclusions. These cases of eruption indicate (1) 
 that the lavas go on gradually increasing the pressure 
 in the interior by their accumulation, while augmented 
 activity in the production of vapors still further increases 
 
182 DYNAMICAL GEOLOGY. 
 
 the pressure ; and that finally the mountain, when it can 
 no longer resist the forces within, somewhere breaks and 
 lets the heavy liquid out. They show (2) that, while 
 earthquakes may attend volcanic action, they are no neces- 
 sary part of it. They show (3) that lavas may be so very 
 liquid that no cinders are formed during a great erup- 
 tion ; for, in the ebullition of the lava in the boiling lakes 
 of Kilauea, the jets (made by the confined vapors) are 
 usually thrown only to a height of 30 to 100 feet ; and, on 
 falling back, the material is still hot ; it either falls back 
 into the pool or lake, or becomes plastered to its sides. 
 The liquidity of the lavas is shown by the jetting out 
 sometimes, from small holes, of drops but a fourth of an 
 inch thick, which fall back on one another, adhere, and so 
 make a model of a fountain. 
 
 Vesuvius. Vesuvius is an example of another type 
 of volcano. The characteristic of the Hawaiian type of 
 volcanoes is the comparatively perfect liquidity of the 
 lavas. The lavas are of the most fusible (basaltic) type ; 
 and the temperature is so high that they are completely 
 fused. In the case of less fusible lavas, the temperature 
 is generally insufficient for perfect liquefaction, sufficing 
 only to bring them to a viscid, semifused condition. In 
 Vesuvius, the lavas are so viscid that jets cannot rise 
 freely over the surface : the vapors are therefore kept 
 confined until they form a bubble of great dimensions ; 
 and, when such a bubble, or a collection of them, bursts, 
 the fragments are sometimes thrown to a height of thou- 
 sands of feet. The crater, at a time of eruption, is a 
 scene of violent activity, and cannot be approached. 
 Destructive earthquakes often attend the eruptions. 
 
 In many of the eruptions of Vesuvius, there has been 
 no outflow of lava streams, the lava emitted being all pro- 
 jected into the air by the violence of the explosions, and 
 falling as cinders, ashes, or tufa. This appears to have 
 been the case in the famous eruption in the year 79, in 
 which Pompeii and Herculaneum were overwhelmed. 
 
HEAT. 183 
 
 Before that catastrophe, there was a large circular crater, 
 the northern half of whose inclosing rampart remains as 
 the ridge of Monte Somma (<?, Fig. 195). In the explo- 
 sions of that eruption, the southern half of the old ram- 
 part disappeared. 
 
 In the minor activity of the mountain, during the inter- 
 vals between the great eruptions, the same explosive char- 
 acter shows itself. Instead of quiet outflows from lakes 
 of lava, as in Kilauea, there are generally explosive dis- 
 charges of cinders, building up small cones. Such a cone 
 is shown at b in Fig. 195. 
 
 The lavas at Vesuvius may flow directly from the top 
 of the crater ; but they generally escape partly, if not 
 entirely, through fissures in the sides of the mountain. 
 
 Some volcanoes, as those of Java, are characterized even 
 more strongly than Vesuvius by the predominance of the 
 explosive type of eruption. The eruption of Krakatoa in 
 1883 was a remarkable example of this type. The ashes, 
 according to Verbeek, ascended to a height of more than 
 150,000 feet, and are supposed to have been carried around 
 the world, and to have caused the red sunset glows of the 
 autumn following. Even Kilauea is known to have had 
 one violently explosive eruption, probably about 1789. 
 
 Besides the difference in the composition of the lavas, 
 other circumstances, as the size of the conduit, the tem- 
 perature of the subterranean reservoir, etc., affect the 
 character of the eruption. Such extremely violent explo- 
 sions as that of Krakatoa are probably due to the sudden 
 access of a large amount of water to the molten mass. 
 
 Of the two causes of eruption hydrostatic pressure, 
 and elastic force of confined vapors, the latter appears 
 to be the most effective in Vesuvius, while the former may 
 be in Hawaii. The vapors in Mauna Loa appear to be 
 supplied mainly by the fresh waters (rains) which fall 
 over the mountain and descend through the rocks ; while 
 Vesuvius is, in part at least, supplied by salt waters from 
 the Mediterranean, as is proved by the presence of hydro- 
 
184 DYNAMICAL GEOLOGY. 
 
 chloric acid in its vapors, and of chlorides among its saline 
 incrustations. 
 
 Trachytic Domes. Trachytic lavas are less common 
 in modern volcanoes than the basaltic. They have in 
 some cases preceded basalt in the history of a volcanic 
 cone. In some cases these trachytic lavas (which, owing 
 to the predominance of orthoclase in their constitution, are 
 much less fusible than the basaltic) have come up through 
 fissures in so pasty a state that they have swelled up into 
 steep domes and cooled in this form. Domes of this kind 
 occur in Auvergne ; also in the Black Hills of South 
 Dakota (Newton and Jenny). 
 
 Lateral Cones of Volcanoes. In eruptions through fis- 
 sures the lavas may continue issuing for some days or 
 weeks through the widest or most freely open part of the 
 fissure, and consequently form at this point a cone of cin- 
 ders or lava. Thus have originated innumerable cones 
 on the slopes of Etna and other volcanic mountains. 
 
 Submarine Eruptions. Eruptions may sometimes take 
 place from the submarine slopes of the mountain when 
 it is situated near the sea, as has happened with Etna and 
 Mauna Loa; and in such cases accumulations of tufa or 
 of solid lava may form under water about the opened vent. 
 The numerous volcanic islands of the ocean of course 
 commenced with submarine eruptions. Fishes and other 
 marine animals are usually destroyed in great numbers by 
 such submarine eruptions. 
 
 Subsidence of Volcanic Regions ; Overwhelming of Cities. 
 Among the attendant effects of volcanoes are the sink- 
 ing of regions in their vicinity that have been under- 
 mined by the outflow of 'the lavas; the tumbling in of 
 the summit of a mountain ; and earthquakes, or vibra- 
 tions of the rocks, in consequence of fractures. Another 
 is the burial, not only of fields and forests, but even of 
 cities and their inhabitants, by the outflowing streams, or 
 by the falling cinders and accumulating tufas. Pompeii 
 and Herculaneum are two of the cities that have been 
 
HEAT. 185 
 
 buried by Vesuvius ; and every few years we hear of 
 some new devastation of habitations or farms by this 
 uneasy volcano. Pompeii is covered only by the tufas of 
 the eruption in which it was destroyed ; Herculaneum is 
 covered also by tufas and lava streams of several later 
 eruptions. 
 
 SUBORDINATE VOLCANIC PHENOMENA. 
 
 1. Solfataras. In the vicinity of volcanoes, and some- 
 times in regions in which no active volcanoes exist, there 
 are areas where steam, sulphur vapors, and perhaps car- 
 bonic acid and other gases, are constantly escaping. Such 
 areas are called solfataras (from the Italian, solfo, sulphur, 
 and terra, earth). The sulphur gases deposit sulphur in 
 crystals or incrustations about the fumaroles (as the steam 
 holes are called) ; and alum and gypsum often form from 
 the action of sulphuric acid (derived from the oxidation 
 of the sulphur gases) on the rocks. 
 
 2. Hot Springs ; Geysers. Fountains or springs of hot 
 water are common in volcanic regions, and are often so 
 abundant as to be used for baths. Such springs occur 
 also in many other parts of the world, especially in regions 
 of upturned or of eruptive rocks. In some cases the heat 
 is produced by chemical changes in progress beneath, or 
 by friction and crushing of rocks in the upheavals which 
 have taken place ; but often the source is the residual heat 
 of great masses of lava. 
 
 When the heated waters are thrown out in intermittent 
 jets, they are called geysers. The Yellowstone Park in the 
 Rocky Mountains (between the parallels of 44 and 45 N., 
 and the meridians of 110 and 111 W.) is the most 
 remarkable region of geysers in the world, far exceeding 
 that of Iceland. One of the geysers the Beehive 
 is represented in action in Fig. 199. The Beehive jet 
 is 200 feet high. Its eruptions occur at somewhat irreg- 
 ular intervals, but generally two or three times in a day. 
 The periods of other geysers vary from less than a minute 
 
 
186 
 
 DYNAMICAL GEOLOGY. 
 
 to several weeks. The eruptions of some are very regu- 
 larly periodical, while others are very irregular. 
 
 The action of geysers is due to the condition that sub- 
 terranean waters have access to hot rocks (as the interior 
 
 FIG. 199. 
 
 Beehive Ge,y 
 
HEAT. 187 
 
 of great lava sheets, retaining a high temperature on 
 account of the poor conductivity of the material), and' 
 that the conduit communicating with the surface is so 
 narrow that convection currents cannot be freely estab- 
 lished. The heat accordingly increases in the deeper part 
 of the column of water, until steam is formed, by whose 
 expansion the cooler waters above are explosively ejected. 
 After an eruption, the water flows back into the under- 
 ground passages, and gradually becomes heated up for 
 another explosion. 
 
 Heated waters act on the rocks with which they are in 
 contact, and decompose them ; and, as most rocks espe- 
 cially volcanic rocks contain some kind of feldspar, the 
 waters become slightly alkaline through the alkali of the 
 feldspar, and so are enabled to take up silica and make 
 siliceous solutions. The silica taken into solution is de- 
 posited again around the geyser in many beautiful forms, 
 and makes the bowl or crater from which the waters are 
 thrown out. 
 
 When the material in the vicinity of a boiling pool con- 
 sists of earth or mud, mud cones are formed, as in some 
 parts of the Yellowstone Park, and also at Geyser Canon, 
 north of San Francisco, California. 
 
 Besides hot springs that deposit silica, there are others 
 that deposit calcium carbonate, making thus the kind of 
 porous limestone called travertine, as on Gardiners River, 
 Yellowstone Park. 
 
 In some cases, the action of the heated waters on the 
 rocks exposed to them gives origin to deposits of quartz 
 crystals, agate, opal, and different silicates and other 
 minerals. 
 
 IGNEOUS ERUPTIONS NOT VOLCANIC. 
 
 It has been stated that eruptions of volcanoes generally 
 take place through fissures. Fissure eruptions have oc- 
 curred also in regions remote from volcanoes ; and they 
 have been the source of ejections over the western slope of 
 
188 DYNAMICAL GEOLOGY. 
 
 the Rocky Mountains vastly greater than any from volcanic 
 centers. The narrow mass of igneous rock that tills 
 such fissures is called a dike. The liquid rock has some- 
 times merely filled the fissure, without overflowing ; but 
 in other cases it has spread widely over the surface, making 
 sheets of great extent and thickness. The outflow of liquid 
 rock has often been followed by sedimentary deposits, and 
 then another outflow has taken place ; thus making alter- 
 nations of fire-made and water-made strata. In that case, 
 the sheets of igneous rock are said to be contemporaneous, 
 or extrusive. Beds of tufa, or "ash beds," may also be 
 included in the series. In other cases, the strata have 
 been parted along a plane of stratification, and molten 
 rock has forced itself in. Such sheets are called intrusive. 
 In the case of intrusive sheets, both the overlying and 
 the underlying strata are affected by the heat of the igne- 
 ous rock (local metamorphism, page 190); in the case of 
 contemporaneous sheets, only the underlying strata. 
 
 The rocks most commonly occurring in dikes are felsite, 
 diorite, and dolerite (pages 38, 39). The igneous rock is 
 very often without cellules or air cavities ; and, if any are 
 present, they are in general neatly formed, instead of 
 being ragged like those of lavas. If the cavities in such 
 a rock are filled by the deposit of minerals (as quartz, cal- 
 cite, zeolites, etc.), it is called amygdaloid. The rock of 
 an amygdaloid is usually hydrous (and chloritic) through- 
 out (owing, it is supposed, to subterranean waters gaining 
 access in some way while the eruption was in progress); 
 and the cavities were formed in the outer or upper part, 
 where the diminished pressure allowed of the water's pass- 
 ing to the state of vapor. 
 
 Dikes are common on all the continents, especially in 
 the regions between the summits of the border mountains 
 and the ocean, which are usually between 300 and 800 
 milss in breadth ; as, for example, between the Appalach- 
 ians and the Atlantic, and between the Rocky Mountains 
 and the Pacific. 
 

 HEAT. 189 
 
 The Pacific slope of the Rocky Mountains (500 to 800 
 miles wide) is remarkable for its lava floods. Some of 
 them are around volcanoes, or volcanic vents, but many 
 were from fissure eruptions remote from any volcano. 
 The largest continuous area extends from the Yellowstone 
 Park in Wyoming, westward along the Snake River 
 through southern Idaho, and then spreads northward over 
 most of Oregon and a large part of Washington, and 
 southward into northern California. Its boundaries have 
 not been exactly determined, but its area is estimated to 
 be between 100,000 and 150,000 square miles. On the 
 western margin are the lofty volcanoes of the Cascade 
 Range, and a number of smaller volcanoes are dotted over 
 various parts of the region ; but it is evident that these 
 were not the source of the widespread lavas. The Colum- 
 bia River is bordered for long distances by walls 1000 to 
 2000 feet high, made of ranges of basaltic columns ; and, 
 in the vicinity of Mount Hood, the thickness is 3500 feet. 
 Again, in northern California, south of the combined vol- 
 canic area of Mount Shasta and Lassens Peak, on the west 
 slope of the Sierra, the lavas were so copious as to obliter- 
 ate the deep valleys of an old system of drainage, and 
 force the streams to make new channels. The erosion 
 then begun has since cut out valleys 1000 to 3000 feet 
 deep, partly along new routes, leaving the remnants of the 
 lava field as caps of "Table Mountains." The miners 
 have tunneled beneath the lava cap for gold-bearing 
 gravels, and found rich deposits in the beds of the old 
 streams (J. D. Whitney). Nevada, southern Utah, Colo- 
 rado, New Mexico, and Arizona have other wide lava fields. 
 
 Still more wonderful are the fissure eruptions of the 
 Deccan, in India, where a railway out of Bombay runs for 
 519 miles continuously over a lava field ; its area is not 
 less than 200,000 square miles. 
 
 In eastern North America, outflows through fissures 
 made the Palisades on the Hudson ; long narrow ranges 
 through the Connecticut valley, including among the sum- 
 
 
190 DYNAMICAL GEOLOGY. 
 
 mits, Mount Tom and Mount Holyoke ; ridges in Nova 
 Scotia ; others similar, at intervals, from New Jersey to 
 North Carolina; and others, in the vicinity of Lake 
 Superior. In Europe, examples are seen in the rocks of 
 Salisbury Crags near Edinburgh, and of the Giant's Cause- 
 way and FingaTs Cave. 
 
 The intrusion of igneous rock has at times lifted the 
 overlying strata high enough to make subterranean dome- 
 shaped masses 1000 to 4000 feet high (named laccoliths, 
 from the Greek Xa/c/eo?, cistern, and Xt'0o9, stone) ; as in the 
 Henry Mountains, in southern Utah, where denudation 
 has exposed to view some of the laccoliths (G. K. Gilbert). 
 Ten thousand feet of strata are said to have been thus 
 lifted evidence of the vastness of the erupting force. 
 
 3. METAMORPHISM. 
 
 The term metamorphism signifies change or alteration; 
 and, in Geology, specifically, a change in rocks, under 
 the action of heat and other subterranean agencies (but 
 without fusion), generally in the direction of greater 
 induration or more highly crystalline structure. The 
 rocks which have suffered such a change are probably for 
 the most part ordinary stratified rocks, mechanical and 
 organic. But lavas and other igneous rocks, tufa beds, 
 and chemical deposits, have also in many cases undergone 
 alteration to a condition in which they are undistinguish- 
 able from metamorphosed sediments. Such changes may 
 be either local or regional. 
 
 Local Metamorphism. Local metamorphism has often 
 taken place in the walls of dikes of igneous rocks, or 
 in the adjoining parts of the strata over or between 
 which they have flowed, in consequence of the heat from 
 the melted and cooling rock. Near dikes of trap, the 
 rock is sometimes made cellular by escaping steam, and 
 filled with shrinkage fissures made on cooling or drying ; 
 and, besides these effects, various minerals have been 
 often formed, as epidote, chlorite, hematite, tourmaline, 
 
HEAT. 191 
 
 garnet, out of the ingredients present in the adjoining 
 stratified rock, or the trap, or both. The waters of hot 
 mineral springs have often produced metamorphic effects 
 in the rocks, and many mineral species have been formed 
 by this means. 
 
 Regional Metamorphism. In regional metamorphism, 
 the regions undergoing change have often been thou- 
 sands of square miles in area, and the depth to which 
 the alteration has extended has sometimes exceeded 
 30,000 feet. The rocks were originally, in great part, 
 uncrystalline limestones, shales, sandstones, conglomer- 
 ates. They are changed to crystalline limestone or marble, 
 quartzite, gneiss, mica schist, and the like. They were 
 originally in horizontal strata ; they are now upturned 
 or folded, and are often intersected by veins. 
 
 New England is mostly covered by metamorphic rocks ; 
 and they spread over the eastern border of New York, to 
 Manhattan Island. They occur in the Adirondacks, and 
 over a large area in Canada ; in the Highlands of New 
 Jersey and Putnam County, New York; in the Blue Ridge 
 and the Black Mountains, and the Piedmont region east of 
 those mountains ; in a large area south of Lake Superior ; 
 in high ranges along the summit of the Rocky Mountains ; 
 and in the Sierra Nevada in California. They occur also 
 in Scotland, Wales, Cornwall, Scandinavia, and various 
 other regions. 
 
 In some cases, conclusive proof that such crystalline 
 rocks are metamorphosed stratified rocks is afforded 
 by the occurrence of unobliterated fossils, in some por- 
 tions of a metamorphic stratum, where the change is least 
 complete: as in part of the marble of West Rutland and 
 other places in Vermont ; in the limestone and schists near 
 Poughkeepsie and elsewhere in Dutchess County, New 
 York, and near Bernardston, Massachusetts ; in the Sierra 
 Nevada ; in Norway ; in the Alps ; and in several other 
 localities in Europe. 
 
 In other cases, a sedimentary origin has been inferred 
 
192 DYNAMICAL GEOLOGY. 
 
 from the bedded structure, which has been supposed to 
 correspond to the original stratification. But an appear- 
 ance of bedding is by no means conclusive proof of the 
 sedimentary origin of a rock. Gneisses and allied rocks 
 are undoubtedly derived in some cases from granites and 
 other plutonic rocks, a schistose structure being devel- 
 oped by pressure or shearing. When the planes of appar- 
 ent bedding in gneisses and schists are parallel to the 
 planes of contact of these rocks with quartzites or crystal- 
 line limestones, the probability that the structure represents 
 a true stratification is strengthened. While the presence 
 of a schistose structure is not always proof of origin from 
 sediments, the absence of such structure is not always 
 proof of igneous origin. Granite and other massive rocks 
 may be in some cases only the extreme term of metamor- 
 phism of sediments. It is not always possible to decide 
 with certainty whether a mass of crystalline rock is of 
 igneous or of sedimentary origin. 
 
 Effects. The effects of metamorphism include: 
 
 1. Simple compacting and solidification ; as in making 
 quartzite from quartzose sandstone, or a rock looking like 
 granite from granitic sandstone. 
 
 2. A change of color; as the gray and black of common 
 limestone to the white color, or the clouded shadings, 
 of marble ; and the brown and yellowish brown of some 
 sandstones colored by iron, to red, making red sandstone 
 and jasper rock. 
 
 3. In most cases, a partial or complete expulsion of 
 water. 
 
 4. An evolving and expulsion of mineral oil or gas; as 
 when bituminous coal is changed to anthracite or graphite. 
 
 5. An obliteration of all fossils; or of nearly all, if the 
 metamorphism is partial. The obliteration is usually pre- 
 ceded by the compression and distortion of the fossils. 
 
 6. Often a change in crystallization, with little or 
 none in chemical constitution ; as when a limestone is 
 turned to white statuary marble ; and a sandstone or 
 
HEAT. 193 
 
 argillaceous rock, made from the disintegration of granite, 
 gneiss, and related rocks, is changed to granite or gneiss 
 again. Grains of pyroxene may be changed into horn- 
 blende, the two minerals being substantially identical in 
 chemical composition, though differing in crystalline form. 
 
 7. In many cases, a change of constitution ; for the 
 ingredients subjected to the metamorphic process often 
 enter into new combinations ; as when a limestone, with 
 its impurities of clay, sand, phosphates, and fluorides, 
 gives rise, under the action of heat, not merely to white 
 granular limestone, but to various crystalline minerals 
 disseminated through it, such as mica, feldspar, scapolite, 
 pyroxene, apatite, chondrodite, etc. 
 
 It is thus seen that metamorphism may fill a rock with 
 crystals of various minerals. Even gems are often among 
 its results. What is of more value, it makes out of rude 
 sandstones and limestones crystalline rocks, as granite and 
 marble, for architectural and other uses. Man's imita- 
 tions of nature are seen in his little red bricks. 
 
 Process. The principal agencies in metamorphism are 
 heat, water, and mechanical action. 
 
 Heat is important : (1) in order to produce that weak- 
 ening of cohesion among the particles of a rock which is 
 the preparatory step toward a recrystallization ; and (2) 
 in order to bring about the chemical changes that are 
 required, nearly all demanding a higher than the ordinary 
 temperature, though less than that of complete fusion. 
 
 Water is important because : (1) dry rocks (as illus- 
 trated in a fire-brick) are bad conductors of heat ; (2) it 
 helps greatly in the weakening of cohesion ; (3) it takes 
 up silica and alkali from all rocks containing feldspar 
 (page 187), if heated (and little heat is necessary), and 
 thus becomes a siliceous solution, which, on cooling, may 
 deposit the silica as a cement among the grains of the 
 rock, and so promote its solidification as in altering 
 sandstone to quartzite, and may also deposit quartz in 
 cavities or fissures ; (4) at higher temperatures, in the 
 
194 DYNAMICAL GEOLOGY. 
 
 state of steam of high pressure, it decomposes readily 
 many of the silicates, or the ordinary minerals of rocks, 
 and so prepares for the formation of new minerals thus 
 making sometimes feldspar, mica, hornblende, etc. The 
 quartz grains of a sandstone have often been converted 
 into minute crystals of quartz by the deposition of silica 
 over the exterior. 
 
 The water is for the most part that contained in the rocks 
 themselves ; for beds of sandstone, limestone, etc., con- 
 tain, before alteration, on an average at least 2 per cent of 
 water (independently of any in spaces between the beds), 
 which means 2 pints of water to 100 pounds of the rock. 
 
 The heat is (1) partly the result of mechanical action ; 
 for metamorphism has generally taken place where the 
 rocks have undergone shoving, folding, and faulting, and 
 sometimes crushing (see page 218) : and (2) partly also, the 
 heat of the earth's interior conducted upward into the beds 
 (page 217) ; for metamorphism has generally taken place 
 where the strata have accumulated to very great depth. 
 
 These are some of the various ways in which heat and 
 water have operated in metamorphic changes. Direct 
 experiments have shown that crystallization does result 
 from the action of heat and water. Quartz crystals, feld- 
 spar, mica, and other minerals have been artificially made 
 by the subjection of the ingredients to highly heated 
 moisture. 
 
 Alkaline waters dissolve silica even at very moderate 
 temperatures ; and, wherever such solutions exist, they 
 may work at consolidating, altering, and dissolving min- 
 erals, and making geodes and veins of quartz. Large 
 corals in Florida have been hollowed out by this means, 
 and the cavities lined with quartz crystals or agate. 
 The fossils of a limestone have been silicified and flint 
 nodules made even in cold waters. The ordinary decom- 
 position of a feldspar or mica, of hornblende or pyroxene 
 one or more of which silicates occur as constituents of 
 granite, syenite, trap, porphyry, trachyte, and tufa, sets 
 

 HEAT. 195 
 
 free silica to make opal or quartz ; and, in some tufas of 
 California and Colorado, the clustered tree trunks of 'a 
 former forest, as well as scattered logs and stumps, have 
 been petrified by silica from such, a source. 
 
 Pressure is requisite for most metamorphic changes. 
 Limestone heated without pressure loses its carbonic acid 
 and becomes quicklime ; but, under pressure, as has been 
 proved by experiment, the carbonic acid is not driven off. 
 The needed pressure may be that of an ocean above ; it 
 may be that of the superincumbent rocks, and a few hun- 
 dred feet would suffice. 
 
 Crustal movements have operated in metamorphism, 
 partly by producing heat through the crushing of rocks, 
 but also by producing rearrangement of the materials of 
 rocks. The schistose structure, which is so characteristic 
 of metamorphic rocks, is doubtless often produced in this 
 way (dynamic metamorphism). Sometimes the crystalline 
 plates of mica and other minerals are forced by pressure 
 into a position at right angles to the direction of pressure ; 
 sometimes the rock has been sheared, and the crystalline 
 plates drawn out along the planes of shearing. 
 
 The similarity of an argillaceous sandstone to gneiss or 
 granite is often much greater than appears to the eye. 
 When a sandstone has been made out of a gneiss, it may 
 have the quartz, feldspar, and mica of the gneiss, merely 
 pulverized, with little or no chemical alteration ; so that 
 the change produced in it by metamorphism may be mainly 
 a change in state of crystallization. By simply heating a 
 bar of steel, arid cooling it slowly or rapidly, it may be 
 made coarse or fine steel, the process causing the molecules 
 of the small grains to unite into larger grains in the coarser 
 kind, and the reverse for the finer. There is something 
 analogous in the change, above described, of an argilla- 
 ceous sandstone to gneiss or granite. It cannot be as- 
 serted, however, that the feldspar grains in the sandstone 
 will always remain feldspar ; they may contribute to the 
 making of mica or some other mineral. 
 
196 DYNAMICAL GEOLOGY. 
 
 Often, however, the material derived from the wear of 
 gneiss and granite and other rocks is not only pulverized, 
 but also more or less decomposed. The feldspar, for exam- 
 ple, may have lost its alkalies, or the mica its oxide of 
 iron and alkalies ; and in such a case the process of meta- 
 morphism cannot, of course, restore the original rock. 
 The new rock made can contain no feldspar or mica, if 
 the alkalies have been wholly removed, but it may turn 
 out an argillite or slate ; or, if much oxide of iron and 
 magnesia are present, a hornblende rock, or a chlorite 
 rock, or some other kind from which the alkalies, potash 
 and soda, are absent. 
 
 4. FORMATION OP VEINS. 
 
 Nature and Origin of Spaces occupied by Veins. > 
 Veins, like dikes, are fillings of spaces in the rocks ; but 
 they differ from dikes in the manner in which the filling 
 has taken place. Dikes, as explained on page 188, are fis- 
 sures filled with igneous rock injected in a state of fusion. 
 The mode of formation of veins will be explained later. 
 
 The spaces filled by veins are usually cracks or fissures 
 made (1) by uplifting or disturbing forces ; (2) by the 
 expansion or pressure of vapors ; (3) by shrinkage from 
 cooling or drying ; they may be (4) openings between 
 the layers or laminse of a rock produced in the flexing of 
 the beds, like those between the leaves of a quire of paper 
 when folded over ; or (5) open spaces made in rocks by 
 solution, as caverns are made. 
 
 The uplifting and flexing of rocks which have resulted 
 in fissures and openings, are often accompaniments of 
 metamorphic change, and the fissures may have become 
 filled before the era of metamorphism had passed. The 
 heat concerned in such a case may be, as explained above, 
 that derived from the movements in the strata, in connec- 
 tion with that of the earth's depths. 
 
 Veins are large or small, deep or shallow, single or like 
 a complex network, according to the character of the 
 
HEAT. 
 
 197 
 
 fractures in which they were formed. They may be as 
 thin as paper, or they may be rods in thickness. Figs. 
 200-203 represent some of the forms. In Fig. 200, 
 
 FIGS. 200-205. 
 
 201 
 
 202 
 
 203 
 
 204 
 
 65 4321 2 4 5b 
 
 N 
 
 
 i 
 
 1 1 * 
 
 1 '1 
 
 1! 
 
 !< 
 
 ',i 
 
 I ! 
 
 ';" 
 
 
 V 
 t\ 
 
 ; 
 
 1 1 
 
 
 1 r 
 
 
 i 
 
 1 
 
 ',U i 
 
 'ft 
 
 , ! 
 
 .; 
 
 i 
 i 
 
 1 
 
 
 fill 
 
 
 
 , i 
 
 
 
 '1 
 
 : 
 
 
 ^ i 
 
 
 Fi 
 
 
 ' 'l', 
 
 
 v 
 
 1 1 
 
 W 
 
 1 III 
 
 111 
 
 rj 
 
 I 
 
 1 
 
 III* 
 
 !v 
 
 205 
 
 Veins. 
 
 there are two veins, a and ; in Fig. 201, a network of 
 thin veins ; in Fig. 202, two veins, a, a', of very irregular 
 form a kind not uncommon, and another, 5, intersect- 
 ing one of these ; in Fig. 203, two large veins, of still 
 more irregular character, crossing one another. 
 
198 DYNAMICAL GEOLOGY. 
 
 Materials of Veins. Quartz is the most common, be- 
 cause siliceous solutions are easily made, requiring little 
 heat. Granitic material, requiring higher heat, is also 
 common, but especially in veins intersecting the more 
 crystalline rocks; and vein granite is usually much coarser 
 in crystallization than ordinary granite. Other materials 
 of frequent occurrence are calcite, barite (barium sul- 
 phate) and fluorite (calcium fluoride); but, where these 
 occur, quartz may also be present. Along with the earthy 
 minerals may occur gold, or various ores of copper, lead, 
 silver, and other metals, besides pyrite (iron sulphide), 
 which is almost universally present in ore-bearing veins, 
 or lodes. The earthy minerals are called the gangue of 
 the ore. 
 
 Many veins have a banded structure, like Figs. 204 and 
 205. Metallic veins, especially, are often thus banded, 
 and have the ores lying in one or more bands alternating 
 with other bands consisting of different minerals or rock 
 material. 
 
 In Fig. 204, representing a vein at Valparaiso, the 
 bands numbered 1, 3, and 6 are quartz ; the others are 
 granite. In Fig. 205, representing a vein at Godolphin 
 Bridge, Cornwall, a is a band of quartz, , b are bands of 
 agate, c is crystallized quartz, d is chalcopyrite mixed with 
 quartz. 
 
 Origin of Vein Deposits. The material of veins has 
 been deposited from solutions or vapors. The solutions 
 or vapors are generally hot. This is always the case in 
 large veins, or in veins extending down to any consider- 
 able depth. Such veins may be divided into two classes, 
 according to the source of the heat. 
 
 1. Where the Heat is not Derived from Eruptions of 
 Igneous Hock. Such veins are apt to occur in regions 
 of metamorphic rock ; and the heat, like that in regional 
 metamorphism, is the result of movements in the earth's 
 crust, or is the general heat of the interior of the globe. 
 In this class are included nearly all veins of quartz and 
 
HEAT. 199 
 
 granite, whether containing metallic ores or not, and 
 most banded mineral veins. The fissures or openings are 
 a result of profound disturbances, such as give rise also to 
 metamorphism. The material of the vein is brought into 
 the opening either from the rocks directly adjoining, or 
 from those of depths below. The fissured rocks being 
 heated, as above stated, all water or vapor present tends 
 to decompose the rock material near the fissure ; it takes 
 alkalies from the feldspars, and so becomes siliceous, and 
 few minerals will withstand its action. The water or 
 vapor presses into the fissures or openings, carrying the 
 mineral material it can dissolve, and depositing it ; and it 
 keeps on supplying material until the fissure is filled or 
 the supply of material is exhausted. It is natural that 
 veins in gneiss and mica schist filled in this way should 
 often be granitic veins, for these rocks contain the quartz, 
 feldspar, and mica of granite ; and that they should often 
 be quartz veins simply, which they are likely to be if the 
 temperature is not high enough to make or dissolve feld- 
 spar and mica. The veins of extremely coarse granite, or 
 pegmatite, appear to be in origin somewhat intermediate 
 between ordinary veins and dikes. Under the joint action 
 of heat and water, the material was probably in a condi- 
 tion somewhat intermediate between fusion and solution. 
 The various phases of aqtieo-igneous fusion form, in fact, a 
 complete series of gradations between fusion and solution. 
 
 Under the action, whatever metallic ores or constituents 
 of gems the fissured rock contains, are carried into the 
 fissure with the other mineral material; and additions may 
 be received largely through solutions or vapors rising 
 from its deeper parts. 
 
 By such means veins have been supplied with their gems 
 and ores. The quartz veins in the slate rocks of a gold 
 region have in this way become gold-bearing veins, the 
 gold and quartz having been brought in by the same 
 moisture, and both having been gathered from the adjoin- 
 ing or underlying rocks. These openings, in the case of 
 
200 DYNAMICAL GEOLOGY. 
 
 auriferous quartz veins, were often openings between layers 
 of the slate made in the folding or upturning. Quartz 
 veins are the usual original sources of gold; and the gold- 
 bearing gravels, which afford the metal by simple washing, 
 and have yielded the larger part of the gold in use, are 
 the detritus made out of the gold-bearing rocks. The 
 same gravels often afford platinum, iridium, and diamonds. 
 
 While fissures filled by this lateral inflow of material, in 
 connection with emanations from the depths below, may 
 be uniform in material across, as in many quartz veins, 
 they may also consist of bands of different minerals, as in 
 many metallic veins (Figs. 204, 205). In the formation 
 of banded veins, the process has brought in for a while 
 one kind of mineral, as quartz, and deposited it over the 
 walls of the fissure ; then, through some change, some 
 other mineral or ore, as an ore of lead, or one of zinc, or 
 one of copper ; then quartz again, or fluorite, or calcite ; 
 and so on until the fissure was filled. In a normal banded 
 vein the succession of bands from each side to the middle 
 is identical or nearly so, as illustrated in Fig. 204. In the 
 case shown in Fig. 205, the fissure appears to have been 
 opened and filled at two different times, the band d being 
 virtually a separate vein from the adjoining bands 6, e, b. 
 
 The above is one of the methods by which the earth's 
 precious metals have been gathered out of the rocks, in 
 which they were sparingly disseminated, into generous 
 veins, and thereby placed within reach of the miner. 
 
 2. Where the Heat is Derived from Eruptions of Igneous 
 Rock. (a) Dikes of porphyry, dolerite, and related rocks 
 sometimes determine the courses of veins of metallic ores. 
 The veins are generally situated near the walls of the -dike, 
 and either in the igneous rock or in the rock adjoining. 
 
 The veins (1) may have been made when the dike was 
 made ; or (2) they may occupy fissures made subsequently, 
 but during the same epoch of disturbance ; or (3) they 
 may have been formed later, the old plane of fracture 
 being a plane of weakness liable to be opened anew. The 
 
HEAT. 201 
 
 metallic materials of the vein have been brought up as 
 solutions or vapors, either from the depths that afforded 
 the igneous rock itself, or, more probably, from the walls 
 of a deep part of the fissure. 
 
 The veins of native copper at Keweenaw Point, those 
 containing ores of the same metal in the red sandstone 
 (Triassic) of the Connecticut Valley, New Jersey, and 
 Pennsylvania, those of silver ores in Nevada and other 
 localities along the Rocky Mountains and Andes, thus 
 originated that is, in connection with igneous ejections; 
 the ores not coming up as a constituent part of the 
 igneous rock, but through the agency of vapors and sub- 
 terranean waters. 
 
 (6) Frequently, in regions of igneous ejections, fissures 
 have been made that have received not igneous rock, but 
 only vapors or mineral solutions from below, and thus 
 have become metallic veins. Each of the regions just 
 mentioned contains examples of such veins. 
 
 The filling may continue in progress long after the 
 igneous rock is cooled, or as long as hot water or vapor 
 continues to rise through the fissure. Shrinkage cracks 
 and other openings in the rock adjoining the fissure 
 may spread the mineral depositions widely on either side. 
 The vent may continue as a source of heat to surface 
 waters, making hot mineral springs and steaming pools 
 or basins, about or from which deposits may take place 
 of a veinlike character, as is going on now in Nevada and 
 California. 
 
 Superficial Veins. Besides the veins thus far con- 
 sidered, which occupy fissures extending to some consid- 
 erable depth, and whose formation involves the action of 
 heat in considerable degree, there are numerous small 
 superficial veins which may have been formed without 
 any considerable elevation of temperature. Shrinkage 
 cracks and other small cracks in rocks have been filled 
 with calcite or other minerals brought in by infiltrating 
 waters from the immediate vicinity. 
 
202 DYNAMICAL GEOLOGY. 
 
 Depositions of galenite, or lead ore (sometimes with 
 zinc ores), have taken place in cavities or caverns in lime- 
 stones, as in Wisconsin, Illinois, and Missouri. In these 
 deposits, the source of the ore is somewhat uncertain; but it 
 is apparently derived from the concentration of ores which 
 had been diffused through the sedimentary strata, since 
 the cavities do not have the character of fissures extending 
 to great depths. Such deposits often have great extent, 
 and are a valuable source of ore, as in the localities men- 
 tioned. During the deposition of the ores, the limestone 
 underwent much corrosion from acid solutions concerned 
 in or resulting from the process. 
 
 Many cases of extensive bodies of ore in cavities in 
 limestone appear not to be of the above-mentioned kind, 
 but to be vein deposits of the ordinary sort. They may 
 in some cases have originated in fissures which produced 
 ore deposits only where they intersected limestones, be- 
 cause only limestones were easily rendered cavernous by 
 the corroding waters or vapors, so as to afford spaces for 
 the ores. 
 
 So-called Veins that are not True Veins. In the 
 course of the earth's rock-making, metallic ores have 
 often been deposited along with the detritus when a 
 sedimentary bed was in progress of formation ; they 
 have been brought into marshes, or spread over confined 
 sea margins and mud flats, by running waters which took 
 up the metal (in some soluble state of combination) from 
 the decomposing rocks of the region around. Deposits of 
 iron ores are thus made at the present time (page 116), and 
 ores of zinc, cobalt, nickel, and copper were so deposited 
 in early geological ages. When strata containing such 
 metalliferous layers have undergone uplifts and crystalli- 
 zation, the nearly vertical beds look like veins. Many 
 of the great deposits of hematite and magnetite in the 
 Archaean terranes are probably beds, not veins nor dikes. 
 
 Wide cracks opening to the surface have sometimes been 
 filled with sand or earth. Such deposits have sometimes 
 
CEUSTAL MOVEMENTS. 203 
 
 been called false veins. They have the character of neither 
 veins nor dikes, though both these names have been applied 
 to them. 
 
 VI. CRUSTAL MOVEMENTS; EVOLUTION OF 
 CONTINENTS AND MOUNTAINS. 
 
 Explanations already given. In the preceding chapters 
 the origin of many geological phenomena, and of some 
 of the earth's features, have been briefly explained. 
 
 1. Changes of level have been described as caused (1) by 
 change of temperature, this cause producing the expan- 
 sion and contraction of rocks (page 172) ; (2) by under- 
 mining due to subterranean water (page 144); (3) by 
 undermining due to volcanic outflows (page 184). 
 
 2. Mountain forms have been described as often a result 
 )f the sculpturing of elevated plateaus of nearly horizontal 
 
 >ck by streams, as exemplified among some of the most 
 lajestic mountains of the globe (page 133). 
 
 3. Folding of beds has been shown to have been caused, 
 rhen they are clayey, soft, and wet, by a lateral move- 
 lent produced through the pressure of superincumbent 
 taterial (page 146). 
 
 4. Fractures and faultings of strata have been at- 
 tributed (1) to undermining by different methods (pages 
 144, 184); (2) to contraction or expansion by change of 
 temperature ; (3) to shrinkage on drying, producing deep 
 or shallow fractures (page 174); (4) to the expansive 
 force of vapors (page 182); (5) to the hydrostatic pres- 
 sure of a column of lava (page 180) ; and to other 
 causes. 
 
 5. MetamorpMsm has been described as produced on a 
 small scale, (1) in the vicinity of dikes of igneous rock, 
 through the heat of the rock when it was cooling from 
 fusion, if vapors or moisture were present to aid (page 190) ; 
 and (2) in the neighborhood of hot springs (page 191). 
 Metamorphism on a large scale (regional rnetamorphism) 
 
204 DYNAMICAL GEOLOGY. 
 
 has been said to occur in connection with great crustal 
 movements (p. 195); but no explanation has been given of 
 the cause of those movements. 
 
 6. Earthquakes have been stated to result from frac- 
 tures of rocks in subterranean regions, consequent (1) on 
 undermining by the solvent action of water (page 144), 
 or by the extrusion of lava (page 184); or (2) on the 
 explosions attending volcanic action (page 182). 
 
 But none of the causes that have been considered explain 
 the great changes of level involving large parts of conti- 
 nents or of oceanic areas ; or the phenomena attending the 
 making and uplifting of mountain ranges ; or the earth- 
 quakes that have shaken a hemisphere. 
 
 Relation in Size between the Earth and its Surface 
 Features. On a globe twelve feet in diameter, the height 
 of the earth's loftiest mountains would be represented by 
 an elevation of about one tenth of an inch ; the whole 
 difference of level between the deepest part of the oceanic 
 basin and the highest point of the land, by twice this 
 amount ; and the mean depth of the ocean, by a depression 
 of one nineteenth of an inch. The deformation of the 
 sphere produced in the making of the continents and 
 mountains was, therefore, very small. 
 
 Probable Condition of the Earth's Interior. It is almost 
 certain that the central portions of the earth are now 
 solid. The enormous pressure in those central portions 
 would raise the melting point far above any tempera- 
 ture which can be supposed to exist there. Indeed, it is 
 probable that when the material of the globe first aggre- 
 gated itself together, the central portions were already 
 solid from the effect of pressure, so that the earth has 
 never been completely liquid. Whether there is now, as 
 presumably there once was, a liquid stratum between the 
 solid nucleus and the solid crust, is a question on which 
 there is much difference of opinion. 
 
 It is urged by many physicists, though not by all, that 
 the earth has become solid throughout, as solid as steel; 
 
CRUSTAL MOVEMENTS. 205 
 
 the conclusion being based on the ground that, if the 
 earth were liquid within, the crust would yield in con- 
 siderable degree to the tide-producing force of the moon 
 and sun, and hence the tides of the ocean would be dif- 
 ferent in amount from what they actually are. 
 
 It is claimed, on the other hand, that geological facts 
 cannot be explained on the basis of absolute solidity. 
 Great subsidences, like that of 30,000 feet or more, which 
 was a prelude to the making of the Appalachians, cer- 
 tainly suggest the idea that plastic rock exists beneath, to 
 be pushed aside so as to render subsidence possible. 
 Many have urged that there must have been in past time 
 a plastic layer between the crust and a solid nucleus, or at 
 least the remains of such a plastic layer, wherever the 
 great movements have taken place. This argument, how- 
 ever, is weakened by the consideration that solid metal 
 and rock, when under pressure, yield through molecular 
 movement, as first illustrated by Tresca. When holes are 
 punched in plates of cold iron, the cores punched out may 
 be less than half the thickness of the plates, and not in- 
 creased in density, showing that there has been a flow of 
 the metal outward from the punch. In this way the 
 apparent plasticity of the subcrustal regions may proba- 
 bly be explained. 
 
 Moreover, it is claimed that, if a plastic layer exists, and 
 the crust above it is thin say twenty-five miles, the 
 crust would rest on the mobile sea underneath it like a 
 floating mass, and hence it would be pressed down by any 
 local addition to its weight, however slight ; that it could 
 not sustain mountain elevations, unless the loAver part of 
 the crust beneath the mountain were flexed downward 
 as the upper part was flexed upward. It seems to be 
 evident that, with a crust so mobile as above described, 
 the lateral pressure generated within it could have pro- 
 duced no long range of mountains under one common 
 method of action ; nothing of that uniformity of results 
 exhibited in many great regions from Archaean time 
 
206 DYNAMICAL GEOLOGY. 
 
 onward ; no mountain borders for the continents ; no 
 general system of feature lines for the globe. 
 
 The facts would appear, therefore, to prove that, if a 
 liquid or plastic subcrustal layer exists, the crust must 
 be thick enough to possess some considerable degree of 
 rigidity. And, probably, whatever the condition of the 
 plastic layer underneath the crust may have been in past 
 time, only mere remnants of it now exist, the greater 
 part of it (if not the whole) having become solid. 
 
 On the supposition that the liquid subcrustal layer 
 which once existed has mostly solidified, there must still 
 remain, at no great depth, a zone where the temperature is 
 just below the melting point, and where fusion would be 
 produced by any local diminution of pressure or increment 
 of heat, such as might result from movements of the crust. 
 Such regions of liquefaction may furnish the supplies for 
 volcanoes and other forms of igneous eruption. 
 
 Evolution of the Earth's Fundamental Features. 
 
 Whether its interior be substantially solid, or exten- 
 sively liquid, the earth is believed to be capable of adjust- 
 ment to gravitational pressure through molecular flow, 
 and to owe its shape primarily to the principle of gravita- 
 tional equilibrium. The condition of equilibrium to which 
 gravitation tends to reduce the earth has been called by 
 Button isostasy. 
 
 Origin of Continent and Ocean. The greatest ine- 
 qualities of the earth's surface continental plateaus and 
 oceanic basins are probably dependent on the principle 
 of isostasy. Observations on the force of gravity in dif- 
 ferent localities appear to show that the materials under- 
 lying the oceans are denser than those underlying the 
 continents. The downward pressure on the oceanic radii 
 may thus equal that on the continental radii, the denser 
 material compensating for the inferior height of the 
 column. 
 
 On this view, the distinction between the continental 
 
CBUSTAL MOVEMENTS. 207 
 
 plateaus and the oceanic basins must have been deter- 
 mined by the original distribution of material in the mass 
 of the earth. Hence continents and oceans must have 
 been substantially permanent. Though the continental 
 plateaus have been extensively covered by shallow seas, 
 they have probably always been for the most part ele- 
 vated regions as compared with the real oceans. 
 
 Origin of Mountain Ranges. It is here assumed that 
 the cause of the movements in mountain-making is the 
 contraction of the cooling globe. Although that theory 
 is not without difficulties, and is not universally accepted, 
 it gives a far more satisfactory explanation of the facts 
 than any other theory which has been proposed. 
 
 That contraction must be going on within the earth, 
 follows from the high temperature which has been shown 
 to exist there. Heat must escape to the surface by con- 
 duction, and there appears to be no internal source of 
 heat which can make good the loss. Hence the earth's 
 skin, like that of a drying and shriveling apple, comes to 
 be continually too large for the shrinking interior. 
 
 Location of Mountain Chains. The compressive force 
 is universal in the superficial zone of the earth. Never- 
 theless, the wrinkles which result from it have in general 
 a direct reference to continental lines. 
 
 The oceanic area, besides being much depressed below 
 the continental, has rather abrupt sides, as explained on 
 page 12. The change of curvature of the surface along 
 the borders between continents and oceans must have 
 made those borders lines of weakness in the crust. The 
 lateral pressure in the crust being universal over the 
 sphere, but greatest in the oceanic basins, since these have 
 always been the regions of greatest subsidence, the force 
 in the oceanic crust must have acted obliquely upward 
 against the crust of the continental border. The action 
 was that of a shove or thrust from the direction of the 
 ocean, and in each oceanic area was somewhat proportional 
 to its extent ; consequently, bendings, uplifts, fractures, 
 
208 DYNAMICAL GEOLOGY. 
 
 foldings of strata, earthquakes, mountain-making, became 
 eminently features of the continental borders, and most 
 prominently so of the borders which face the largest 
 oceans. 
 
 Continental Evolution, as illustrated in North Amer- 
 ica. The two systems of forces engaged in the progress 
 of North America were those from the direction of the 
 Atlantic and the Pacific basin the latter the greater. 
 Under their action the V-shaped Archaean area (see map, 
 page 237) was first defined, one branch stretching north- 
 eastward to Labrador and the other northwestward to the 
 Arctic seas, and thus facing respectively the Atlantic and 
 Pacific areas, while linear areas of Archaean rock extend, 
 in a series approximately parallel with the eastern arm of 
 the V, from Newfoundland to Georgia, and, in another 
 series approximately parallel with the western arm of the 
 V, along the course of the western Cordillera. It follows 
 from the courses of the arms of the V, and of the other 
 Archaean areas, that the Atlantic force acted mainly from 
 the southeastward, and the Pacific from the southwest- 
 ward, and the two, therefore, nearly at right angles to 
 one another. It is also apparent that the Pacific force 
 even then was the greater, and hence the Pacific Ocean 
 the larger ; for the northwestward brancn of the V is far 
 the longer. 
 
 Thus the Archaean nucleus was outlined, and the posi- 
 tion of Hudson Bay determined within the arms of the V. 
 From this nucleal dry land progress went forward south- 
 eastward, or toward the Atlantic, and southwestward, 
 or toward the Pacific, successive formations being added, 
 and the dry land gradually extending (though with many 
 oscillations) under changes of level caused mainly by the 
 same forces. 
 
 Then, when the Lower Silurian closed, appeared the 
 mountains of the Taconic system ; and, when Paleozoic 
 time was closing, appeared the Appalachian system, 
 parallel to the eastern branch of the Archaean heights. 
 
CRUSTAL MOVEMENTS. 209 
 
 Again, on the Pacific side, other ranges were made, 
 parallel to the course of the Rocky Mountain chain ; 
 among them after the Jurassic era, the Sierra Nevada ; 
 after the Cretaceous era, the ranges of the Laramide 
 system ; and, still later, Tertiary ranges toward the coast, 
 each epoch adding new parallels to the western branch of 
 the Archaean nucleus. Finally, in the course of the Ter- 
 tiary era, occurred the vast geanticlinal movement in 
 which the mass of the Rocky Mountains rose to its full 
 height above the ocean. 
 
 Each added range, as is seen, proves that the mountain- 
 making forces continued to act to a large degree from the 
 same directions as in Archaean time. 
 
 Thus the continent made progress, adding layer after 
 layer to the rocks over its surface, and range after range 
 in parallel lines to its heights, until finally the continental 
 area reached its limit, and the great interior basin had its 
 mountain borders completed : on the side of the Atlantic, 
 the low Appalachians ; on the side of the Pacific, the 
 massive and lofty Cordillera. 
 
 On this view, the evolution of the features of the sur- 
 face went forward through one system of forces originat- 
 ing in one single cause the earth's contraction from 
 cooling. North America, which is here appealed to for 
 explanations, affords the truest and clearest illustration of 
 the principles involved in the system of evolution, because 
 it lies alone between the two oceans. The progress on 
 this account went forward with great regularity, each age 
 repeating the preceding in the direction of all oscillations 
 or uplifts. It was a single isolated individual making 
 systematic progress throughout until its final completion, 
 and exhibits truly the system in the earth's development, 
 whatever the true theory of that development. Europe, 
 in contrast, has Africa on the south and Asia on the east ; 
 it is, therefore, full of complexities in its feature lines, and 
 in the succession of events that make up its geological 
 history. 
 
210 DYNAMICAL GEOLOGY. 
 
 Structure of Mountain Ranges. 
 
 It has already been stated that mountain-making move- 
 ments result from the compressive force exerted upon the 
 crust of the globe by reason of the cooling and consequent 
 contraction of the hot material beneath ; and that in gen- 
 eral that force manifests itself most conspicuously near 
 the continental borders as a thrust from the direction 
 of the oceans. Before giving more detailed explanation of 
 the process of mountain-making, it is necessary to give 
 some account of the characteristic structure of mountain 
 ranges. 
 
 Range, System, Chain, Cordillera. A mountain range 
 includes all the ridges resulting from a single orogenic 
 movement that is, in general, as will be explained here- 
 after (page 216), the structure resulting from the crushing 
 and upfolding of a single geosyncline. Ranges are the 
 individuals or units in mountain structure. 
 
 A mountain system includes all ranges in any one region 
 made in different, more or less independent, geosynclines, 
 at the same epoch. Thus the Appalachian range, the 
 Acadian range in Newfoundland and Nova Scotia, and 
 the Ouachita range in Arkansas and the Indian Territory, 
 form together the Appalachian system. 
 
 A mountain chain is a combination of approximately 
 parallel ranges or mountain systems of different epochs. 
 Thus the Appalachian chain is the whole mountain border 
 of the Atlantic side of North America including high- 
 lands of Archaean age, the Taconic system of mid-Paleo- 
 zoic age, and the Appalachian system of post-Paleozoic 
 age. 
 
 A combination of two or more mountain chains consti.- 
 tutes a cordillera. The complex mass which includes the 
 chain of the Rocky Mountains on the east, and the Sierra 
 Nevada and the Coast ranges on the west, is an example 
 of a cordillera. 
 
 
CRUSTAL MOVEMENTS. 211 
 
 The study of the structure and history of a mountain 
 range gives, then, an understanding of the whole subject, 
 since systems, chains, and Cordilleras involve only repeti- 
 tion of ranges. The subject will be illustrated chiefly 
 from the Appalachian range, extending (under various 
 names) from New York to Alabama a typical and classi- 
 cal example of mountain structure. 
 
 Thickness of Strata. A marked characteristic of moun- 
 tain structure is the immense thickness of the strata. 
 The Paleozoic strata of which the Appalachians are built 
 have a thickness of 30,000 to 40,000 feet, while the strata 
 of the same age in parts of the Mississippi Valley do not 
 exceed one tenth of that thickness. Moreover, these strata 
 were all formed in water of no great depth, showing that 
 during their deposition occurred a progressive subsidence 
 to a depth more than twice the mean depth of the ocean. 
 
 Disturbed Condition of the Strata. The following 
 are among the characteristic features of the Appalachian 
 region : 
 
 1. Strata have been upraised and flexed into great folds, 
 some of the folds a score or more of miles in span. 
 
 2. Deep fissures of the earth's crust have been opened, 
 and faults innumerable have been produced, some of them 
 of 10,000 to 20,000 feet. 
 
 3. Rocks have been consolidated ; and, in the region of 
 the Green Mountains, sandstones and shales have been 
 crystallized into gneiss, mica schist, and other related 
 rocks, and limestone into architectural and statuary 
 marble. 
 
 4. Bituminous coal has been turned into anthracite. 
 Figs. 206-210 illustrate the folds and faults in the strata 
 
 of the Appalachian range. 
 
 Figs. 206-208 represent sections in the coal regions of 
 Pennsylvania. In Fig. 207, the Carboniferous beds are 
 the uppermost beds at the left, numbered 14 ; the rest 
 are beds of underlying Paleozoic formations, as explained 
 under the figure. 
 
212 
 
 DYNAMICAL GEOLOGY. 
 
 Fig. 208 represents a section of the anthracite region 
 between Nesquehoning Valley (on the west, left in section) 
 
 FIG. 206. 
 
 Section at Trevorton Gap, Pennsylvania, the dark bands representing coal beds. 
 
 and Mauch Chunk (from the Report of C. A. Ashburner, 
 of the Geological Survey of Pennsylvania under Profes- 
 sor Lesley). The length is about 3600 feet (the scale 
 
 FIG. 20T. 
 
 Section on the Schuylkill, Pennsylvania : P., Pottsville ; 2, Cambrian ; 3, 4, Lower Silurian ; 
 5, Niagara; 7, Lower Helderberg; 8, Oriskany ; 10, Hamilton ; 11, 12, Upper Devonian; 
 13, Subcarboniferous ; 14, Carboniferous. 
 
 of the figure being 1000 feet to the inch). The flexures 
 to the west have their summits pushed westward 40 be- 
 yond the vertical. The folded rocks consist of beds of 
 
 FIG. 208. 
 
 Section of the Panther Creek Anthracite basin at Nesquehoning tunnel. 
 
 anthracite and intervening strata of shale and sandstone ; 
 and the anthracite beds include the great " Mammoth 
 bed" (lettered at its outcrop E, E 1 , E 2 ) which is 13 to 27 
 feet thick, and the bed F (outcropping also at F 1 . F 2 , F 3 , 
 
CRUSTAL MOVEMENTS. 
 
 213 
 
 F 4 , F 5 ), 11 to 20 feet thick, besides one of 8 to 9 feet. 
 The " Mammoth bed " is doubled on itself at E 1 . 
 
 Fig. 209 was taken from the vicinity of Bore Springs, in 
 Virginia, and includes Silurian and Devonian beds. 
 
 Fig. 210 represents one of the great faults in south- 
 ern Virginia (between Walkers Mountain and Peak 
 Hills) ; the break is at F, and the rocks on the left were 
 
 vin 
 
 v vi v vi v iv in 11 
 
 S.E. 
 
 H.W. vi v iv m ii m i 
 
 Section from the Great North to the Little North Mountain through Bore Springs, Virginia: 
 t, t, position of thermal springs; II.-IV., Lower Silurian; V., VI., Upper Silurian; 
 VII., Devonian. 
 
 shoved up along the sloping fracture until a Lower Silurian 
 limestone (a) was on a level with the Subcarboniferous 
 formation (c) a fault of about 8000 feet. 
 
 Such examples are found in great numbers throughout 
 the Appalachians. In many of the transverse valleys the 
 curves of alternating anticlines and synclines may bf 
 traced for scores of miles. 
 
 FIG. 210. 
 
 Section of the Paleozoic formations of the Appalachians in southern Virginia, betweo-i 
 Walkers Mt. and the Peak Hills (near Peak Creek Valley): F, fault; a, Lower Silurian 
 limestone ; ft, Upper Silurian ; c, Devonian ; d, Subcarboniferous, with coal beds. 
 
 As shown in the above sections (Figs. 206-209), tLo 
 anticlines, instead of remaining in regular rounded ridges 
 with synclinal valleys between, such as the flexing of the 
 strata might make, have been to a great extent worn away, 
 or modeled into new ridges and valleys, by the action of 
 waters during subsequent time ; and often what was the 
 top of a fold is now the bottom of a valley. The figures 
 on pages 135, 136 illustrate still further the condition of 
 folded strata after denudation. Some of the Appalachian 
 
214 DYNAMICAL GEOLOGY. 
 
 folds were probably 20,000 feet in height above the 
 level of the ocean, or would have had this height if 
 they had remained unbroken, while in fact the loftiest 
 summits now are less than 5000 feet, and few exceed 
 3000 feet. 
 
 The following are some of the general truths connected 
 with the uplifts and metamorphisin in the Appalachian 
 region : 
 
 1. The strike of the strata, and the courses of the great 
 flexures and faults, are approximately northeast, or parallel 
 to the Atlantic border. 
 
 2. The anticlines generally have their steepest slope 
 toward the northwest, or away from the ocean. This is 
 shown in Fig. 209 ; and in Fig. 208 the western anticline 
 is actually overthrown, so that its western limb is carried 
 beyond the perpendicular. 
 
 3. The flexures are most numerous and most abrupt 
 on that side of the Appalachian region which is toward 
 the ocean, and the folding diminishes in intensity west- 
 ward. There is seldom, however, a gradual dying out 
 westward, the region of disturbance being often bounded 
 on the west by one or more of the great fractures and 
 faults, as in eastern Tennessee. 
 
 4. The consolidation and metamorphism of the strata 
 are more extensive and complete to the eastward (or 
 toward the ocean) than to the westward. 
 
 5. The change of bituminous coal to anthracite, by 
 the expulsion of volatile ingredients, was most complete 
 where the disturbances were greatest ; that is, in the 
 more eastern portions of the coal areas. The anthracite 
 region of Pennsylvania (see map, page 292) owes its broken 
 character partly to the uplifts and partly to denudation. 
 To the westward the coal is first semi-bituminous, and 
 then, as at Pittsburg, bituminous. In Rhode Island, 
 where the associated rocks are partly true metamorphic or 
 crystalline rocks, and the disturbances are very great, the 
 coal is an extremely hard anthracite, and in some places 
 

 CRUSTAL MOVEMENTS. 
 
 215 
 
 is altered to graphite an effect which may be produced 
 in ordinary coal by the heat of a furnace. 
 
 These facts lead to the following conclusions : 
 
 1. The movement producing these vast results was due 
 to lateral pressure, the folding having taken place just as 
 it might in paper or cloth under a lateral or pushing 
 movement. 
 
 2. The pressure was exerted at right angles to the 
 courses of the folds, as is the case when paper is folded 
 in the manner mentioned. 
 
 3. The pressure was exerted from the ocean side of the 
 Appalachians ; for the results in foldings and metamor- 
 phism are most marked toward the ocean. 
 
 FIG. 211. 
 
 trpturned strata of the west slope of the Elk Mountains, Colorado. The light-shaded stratum, 
 Jura-Trias ; that to the right of it, Carboniferous ; that to the left, Cretaceous. 
 
 4. The force was vast in amount. 
 
 5. The force was slow in action and long continued 
 not abrupt or paroxysmal, as when a wave or series of 
 waves is thrown up by an earthquake shock on the sur- 
 face of an ocean. For the strata were not reduced by it 
 to a state of chaos, but retain their stratification, and show 
 comparatively little confusion, even in the regions of 
 greatest disturbance and alteration. 
 
 6. The action of the force was attended by the produc- 
 tion of heat. For, without some heat above the ordinary 
 temperature, it is not possible to account for the consoli- 
 dation and crystallization of the rocks. 
 
 The characteristic features of mountain structure which 
 
216 DYNAMICAL GEOLOGY. 
 
 have thus been illustrated from the Appalachian region, 
 are repeated, with variations in detail, in most mountain 
 regions. Mountain ranges in general consist of masses of 
 strata of enormous thickness, folded and faulted often 
 with great complexity, and often showing intense meta- 
 morphism. Fig. 33, on page 54, illustrates a very com- 
 plex fold in the Alps. Fig. 211 is an illustration of 
 folded and overturned strata in the Rocky Mountain 
 region. 
 
 Moreover, the unsymmetrical character which has been 
 pointed out in the descriptions of Appalachian structure, 
 is generally more or less strongly marked in other moun- 
 tain ranges. The flexures are in general more numerous 
 and steeper, and metamorphism and igneous eruptions 
 more extensive on one side than on the other ; and the 
 flexures themselves are very commonly inequilateral. 
 
 Process of Formation of Mountain Ranges. 
 
 A Geosyncline, or Downward Bend of the Crust, the 
 First Step in Ordinary Mountain-making. In the making 
 of the Appalachians, there was first a slowly progressing 
 subsidence ; it began in, or before, the Cambrian era, and 
 continued in progress until the Carboniferous era closed. 
 As the trough deepened, deposits of sediment, and some- 
 times of limestone, were made, that kept the surface of 
 the region near the water level ; and, when the trough 
 reached its maximum, there were 30,000 to 40,000 feet in 
 thickness of stratified rock in it (page 317), and this, 
 therefore, was the depth of the trough. The Taconic 
 Mountains began in a similar subsidence, and at the same 
 time ; and the trough was kept full with deposits as it 
 progressed ; but it reached its maximum, or the era of 
 catastrophe, at the close of the Lower Silurian. The his- 
 tory of most other mountain ranges is similar to these. 
 
 The subsidence in such a geosyncline has been attrib- 
 uted by some geologists to the weight of the accumulating 
 
CRUSTAL MOVEMENTS. 217 
 
 sediments, in accordance with the principle of isostasy ; 
 but the gradual downward bending of the crust may be 
 better explained as a result of the same lateral pressure to 
 which the final catastrophe is due. 
 
 The Bottom of % the Geosyncline weakened by the Heat 
 rising into it from below. As planes of equal temperature 
 within the earth are approximately parallel to the sur- 
 face, the accumulation of sedimentary beds in a sinking 
 trough would occasion, as Herschel long since urged, the 
 corresponding rising of heat from below, so that, with 
 30,000 feet of such accumulations, a given isothermal 
 plane would be raised 30,000 feet. Under such an ac- 
 cession of heat, the rocks at the bottom of the trough 
 would be greatly weakened. If the lower surface of the 
 crust dipped down six or eight miles into a zone of plas- 
 tic material beneath it, it would be actually melted off. 
 Even on the supposition that the earth is completely 
 solid, and no subcrustal plastic layer exists, the weak- 
 ening of the geosyncline by the rise of the isothermal 
 planes would be no less real. For, in the formation 
 of the geosyncline, a great thickness of anhydrous, crys- 
 talline, refractory rock would be replaced by water- 
 loaded sediments capable of suffering aqueo-igneous 
 fusion (or at least pastiness) at a comparatively low tem- 
 perature. The lateral pressure, acting against a trough 
 thus weakened, would end in causing a collapse that is, 
 a catastrophic crushing of the trough, and a folding of the 
 stratified beds within it. And with this the shaping of 
 the mountain range would begin. 
 
 Character of the Mountain thus made. Under such cir- 
 cumstances, the stratified rocks lying in the geosyncline 
 or trough would be folded, profoundly broken, shoved 
 along fractures, and pressed into a narrower space than 
 they occupied before. The flexures were flexures in the 
 strata that filled the geosyncline, not in the subjacent mass. 
 They were simply anticlines and synclines, as distinguished 
 from geanticlines and geosyiiclines (page 55). They be- 
 
218 DYNAMICAL GEOLOGY. 
 
 came unequal-sided, as represented on pages 212, 213, and 
 the mountain range itself inequilateral (pages 214, 216), 
 because there was a pushing side in the mountain-making, 
 the force coming mainly from one direction (the oceanic, in 
 the case of the Appalachians). Such a mountain range, 
 begun in a geosyncline, and ending in a catastrophe of dis- 
 placement and upturning, has been named a synclinorium. 
 (The word is from the Greek words from which syncline 
 is derived, and o/jo?, mountain.) 
 
 On the side away from the chief source of movement, 
 and beyond the profoundest faults, the elevations that 
 have taken place have commonly made vast plateaus of 
 nearly horizontal beds, like the Cumberland Mountain 
 region of Tennessee and its continuation through western 
 and northern Pennsylvania to the Catskill Mountain 
 plateau of southern New York, on the outskirts of the 
 Appalachian range. In such elevated areas, several thou- 
 sands of feet above the sea level, and of wide extent, 
 running waters have had their opportunity for sculptur- 
 ing, and have thus made some of the most majestic 
 mountain groups of ridges and peaks in the world. In 
 Tennessee, the region of great folds and faults directly 
 east of the Cumberland plateau was at first, beyond doubt, 
 of far greater height than the plateau; but, owing to the 
 vast amount of fracturing, as well as the less resistant 
 character of the rocks, denudation has finally made it 
 lower, and it is now the " Valley of East Tennessee," 
 while the plateau is " Cumberland Mountain." Not less 
 was the denudation in front of the Catskill plateau. 
 
 Metamorphism and other Attendant Effects. The heat 
 developed through the transformation of motion, added 
 to that rising into the strata from below, would pro- 
 duce all the consolidation and crystallization that is, 
 all the metamorphism which has been in any case 
 observed, and on a scale as vast as that of the mountain 
 range so developed. It gives a full explanation, there- 
 fore, of the origin of regional metamorphism. 
 

 CBTJSTAL MOVEMENTS. 219 
 
 The heat might be sufficient in some parts to reduce a 
 rock to a plastic state, and so obliterate all its original 
 bedding. One result of this would be tg make a massive 
 rock, like granite, in place of gneiss or other schistose 
 kind; and another result, if the overlying rocks were 
 fractured, and so fissures opened down to the plastic rock, 
 would be to fill the fissures with the plastic rock, making 
 dikes of granite, or of other material, according to the 
 kind of rock so fused. It might possibly give a long core, 
 or central mass, of granite to a mountain range a con- 
 dition of the Sierra Nevada which has been attributed by 
 some to this cause. 
 
 Slaty Cleavage ; Jointed Structure. Slaty cleavage has 
 been proved by experiments to result whenever fine- 
 grained material is subjected to pressure ; and to be due 
 to the flattening of all compressible particles, and the 
 arranging of all flat grains in planes at right angles to 
 the pressure. Since it occurs in fine-grained rocks that 
 have been upturned or flexed, and since it is parallel to 
 the axes of the folds, the pressure producing the upturn- 
 ing or flexure and the concomitant mountain-making, has 
 been generally the cause. The cleavage conforms to the 
 bedding whenever the bedding is, as a consequence of the 
 upturning, at right angles, or nearly so, to the pressure. 
 
 A jointed structure, on the large scale observed in many 
 regions, has been another result of the slow uplifting or 
 flexing action from lateral pressure. Sometimes a region 
 thus disturbed is traversed by a single series of nearly 
 parallel joints ; in other cases two such series of joints 
 are produced nearly at right angles to each other (a 
 structure which, as shown by Daubree, may be due to 
 torsion of the strata). Sometimes joints are produced in 
 various directions, no system being traceable. 
 
 Geanticlines in Mountain-making. In the movements 
 of the earth's crust there would necessarily be upward 
 as well as downward flexures, that is, geanticlines as 
 well as geosynclines. During the progress of the Appa- 
 
220 DYNAMICAL GEOLOGY. 
 
 lachian geosyncline, geanticlines were in progress both 
 east and west of the subsiding area. In the eastern 
 geanticline, the Atlantic border from New York south- 
 westward beyond Virginia emerged, and continued appar- 
 ently to be dry land until the middle of the Cretaceous. 
 The western geanticline the Cincinnati uplift made 
 two large islands in the mediterranean sea which then 
 covered much of the continent, one in the region of 
 Cincinnati, the other in Tennessee. The present altitude 
 of the Appalachians, in spite of the enormous denudation 
 they have suffered, is probably due in part to a geanticlinal 
 movement which lifted the eastern border of the continent 
 in the Tertiary era. 
 
 The Rocky Mountains, in the Cretaceous era, within the 
 area of the United States, were 10,000 feet below their 
 present level, the sea covering large areas over what is now 
 the summit region (page 376). They were raised as a 
 whole during the Tertiary, and it must have been through 
 a broad and gentle geanticline. While the Tertiary moun- 
 tain ranges were in progress, the part of the force not ex- 
 pended in producing them appears to have carried forward 
 an upward bend, or geanticline, of the vast Rocky Moun- 
 tain region as a whole. 
 
 As a mountain range resulting from the crushing of a 
 geosyncline is called a synclinorium (page 218), a region 
 raised to a high altitude by a geanticlinal movement may 
 be called an anticlinorium. The same region inay expe- 
 rience both kinds of movement in the course of its history. 
 The Rocky Mountain region as a whole is an anticlino- 
 rium. Many of its component parts are typical syncli- 
 noria. 
 
 The movements over the continents in Cenozoic time 
 were characterized in general by the vast areas of the re- 
 gions affected. Great geanticlinal movements in the Ter- 
 tiary gave to some of the great mountain chains a large 
 part of their altitude. Areas of continental extent were 
 involved in the oscillations of level which characterized 
 
CRUSTAL MOVEMENTS. 221 
 
 the Quaternary. If Darwin's view of the formation of 
 atolls is true (see page 103), the coral island subsidence 
 affecting an area in the Pacific over 5000 miles in its 
 longer diameter may well have been the counterpart of 
 the vast geanticlmal movements over the continents in the 
 later Tertiary and early Quaternary. 
 
 Eruptions of Igneous Rock. The great fractures as- 
 sociated with mountain-making movements have often 
 extended down to regions of molten rock, and given pas- 
 sage for eruptions. This seems to have been especially 
 true in connection with the great geanticlinal movements 
 of later geological time. The greatest lava floods of which 
 we have evidence, as those of the Deccan and of the north- 
 western United States (page 189), belong to late Meso- 
 zoic or to Ceriozoic time. 
 
 Such are the general steps of progress, and their expla- 
 nations, according to that theory of mountain-making 
 which attributes the movement to a lateral thrust in the 
 earth's crust as a result of contraction in cooling. The 
 universality of system in the features of continents and 
 the characters of mountains has as yet no other probable 
 explanation. 
 
 To obtain an adequate idea of the slow progress of the 
 earth in the making of its mountains, it is necessary to re- 
 member that orogenic disturbances have taken place only 
 after immensely long periods of quiet and gentle oscilla- 
 tions. After the beginning of the Cambrian, the first pe- 
 riod of disturbance in North America of special note was 
 that at the close of the Lower Silurian, in which the 
 Taconic Mountains were finished ; and, if time, from the 
 beginning of the Cambrian to the present, included only 
 48 millions of years (page 444), the interval between the 
 beginning of the Cambrian and the uplift and metamor- 
 phism of the Taconic Mountains was at least 20 millions 
 of years. Another epoch of disturbance was that at the 
 close of the Carboniferous era, in which the rocks of the 
 
222 
 
 DYNAMICAL GEOLOGY. 
 
 Appalachian range were folded up ; on the above estimate 
 of the length of time, it occurred about 36 millions of 
 years after the commencement of the Cambrian ; so that 
 the Appalachians were at least 36 millions of years in mak- 
 ing, the preparatory subsidence having begun as early as 
 the beginning of the Cambrian. Thus, whatever the 
 mountain-making force, an exceedingly long time was re- 
 quired in order to accumulate a sufficient amount to pro- 
 duce a general yielding and plication or displacement of 
 the beds, and start a new range of prominent elevations 
 over the earth's crust. 
 
PAKT IV. HISTOEICAL GEOLOGY. 
 
 HISTORICAL GEOLOGY treats of the order of succession 
 in the strata of the earth's crust, and of the changes that 
 were going on during the formation of each bed or stratum 
 that is, of the changes in the oceans and the land ; of 
 the changes in the atmosphere and climate ; of the changes 
 in the plants and animals. In other words, it is an his- 
 torical view of the events that took place during the 
 earth's progress, derived from the study of the successive 
 rocks. It is sometimes called stratigraphical geology; but 
 this term properly denotes only a description of the nature 
 and arrangement of the earth's strata. 
 
 It has already been explained that the rocks of the 
 earth's crust are historical records as to the past condi- 
 tions of the earth's surface. In order that the records 
 may afford an intelligible history, there must be some way 
 of arranging them in their proper order; that is, in the 
 order of time. The determination of this order is one of 
 the first things before the geologist in his examination of 
 a country. 
 
 Many difficulties are encountered. 
 
 1. The strata of the same period called equivalent 
 strata, because approximately equivalent in age differ, 
 even on the same continent. Sandstones and shales were 
 often forming along the Appalachians in Pennsylvania and 
 Virginia, when limestones were in progress over the Missis- 
 sippi Valley. The Cretaceous formation in England con- 
 
 223 
 
224 
 
 HISTORICAL GEOLOGY. 
 
 tains thick strata of chalk; but in eastern North America 
 the same formation exists without any chalk. 
 
 2. When rocks have been forming in one region, there 
 have been none in progress in many others. Hence the 
 series of strata serving as records of geological events is 
 nowhere perfect. In one country one part may be very 
 complete ; in another, another part ; and all have their 
 long blanks that is, large parts of the series entirely 
 wanting. In New York and the states west to the Missis- 
 sippi, there is only part of the lower half of the series. 
 In New Jersey there is part of the lower half and part of 
 the upper half, with wide breaks between. Over a large 
 part of northern New York there exist only the very 
 earliest of rocks. 
 
 3. The rocks of a country are to a great extent cov- 
 ered with earth or soil, so that they can be examined only 
 at distant points. 
 
 4. The strata, in many regions, have been displaced, 
 folded, fractured, faulted, and even crystallized exten- 
 sively, adding greatly to the difficulties in the way of the 
 geological explorer. 
 
 The following are the methods to be used in determin- 
 ing the true order of arrangement : 
 
 (1) In sections of the rocks exposed to view in the sides 
 of valleys or ridges, the order of superposition should be 
 directly studied, and each stratum traced, as far as possi- 
 ble, through all the exposed sections. 
 
 When, through large intervals, a covering of soil or 
 water prevents the tracing of the beds, other means must 
 be used. 
 
 The order of superposition, when not directly observ- 
 able, may often be inferred by observation of strikes and 
 dips at the various accessible outcrops. For instance, a 
 stratum dipping east must underlie another stratum with 
 the same dip whose outcrop is farther east (unless the 
 strata have been disturbed by faults or overturned folds). 
 
 The validity of the criterion of superposition is self- 
 
HISTORICAL GEOLOGY. 225 
 
 evident. The overlying stratum must be newer than the 
 underlying. But it is obvious that this criterion is only 
 applicable within a single district. For the comparison 
 of the age of rocks in different regions, some other means 
 are necessary. 
 
 (2) The aspect or composition of the rock may help to 
 determine which strata are identical. But this method 
 should be used with great caution, for the reason already 
 stated namely, that rocks made at the very same time may 
 be widely different; and, conversely, those made in very 
 different periods may look precisely alike in color and 
 texture. Within a small area, the resemblance of the 
 rocks at two or more outcrops may often be satisfactory 
 proof that they are really parts of the same stratum. 
 But the value of this test diminishes rapidly as the dis- 
 tance increases. In one class of cases, the character of a 
 rock affords unquestionable evidence in regard to its age. 
 A rock including fragments of some other rock is neces- 
 sarily later than that other rock. 
 
 (3) Fossils afford the most generally applicable means 
 of determining the age of rocks. This is so because of the 
 fact, already mentioned, that the fossils of an epoch are 
 'very similar in genera if not also in species the world 
 over ; and those of different epochs are different. The 
 geologist, by studying the fossils of the several beds at any 
 locality, learns what kinds are characteristic of each bed, 
 and the order of succession. Then, by comparing the beds 
 of different localities, he ascertains whether any are essen- 
 tially alike in species, and therefore of like age or period ; 
 and from this determination he continues further his study 
 of the order of succession. By pursuing this course, for all 
 accessible localities in different countries, geologists have 
 ascertained the characteristic kinds of fossils for the suc- 
 cessive strata through the long series of formations ; and 
 the lists which have been thus made serve for the identifi- 
 cation of strata in widely distant regions. By a comparison 
 of fossils it was proved that the Cretaceous formation exists 
 
226 HISTORICAL GEOLOGY. 
 
 in eastern North America, although there is no chalk to be 
 found there. In the same manner, the equivalents in 
 America of the principal subdivisions of the rock series 
 of Great Britain and Europe, Asia, and even Australia, are 
 approximately ascertained; for this means of determination 
 is a universal one, applying to the equivalency of rocks 
 in different hemispheres as well as those on the same 
 continent. 
 
 This method has its uncertainties. One continent may 
 have received part of its species by immigration from 
 another long after their first appearance in that other ; and 
 species may have survived in one continent long after they 
 have become extinct in another. Moreover, especially in 
 the later geological periods, the progress of evolution 
 seems to have been more rapid in some regions than in 
 others. The mammalian fauna of Australia at present 
 consists almost exclusively of Marsupials and Monotremes. 
 In a former geological period, the same was true of Europe 
 and North America. Other continents have apparently 
 outstripped Australia in the march of evolution. Again, 
 there are doubts arising from the fact that, in any period, 
 the life of one locality, even of marine animals, is very 
 different from that of another, on account of differences* 
 in depth or purity of waters, muddy or rocky bottom, and 
 temperature ; and the range of terrestrial and fresh-water 
 species is generally more local, and their value as criteria 
 of age accordingly less, than that of marine species. The 
 removal of all doubts, and the determination of the exact 
 parallelism of the minor subdivisions of the geological 
 series in different continents or distant parts of the same 
 continent, are not to be looked for. Yet, by proceeding 
 with care, and using not isolated facts, but the whole 
 range of evidence afforded by the fossils, animal as well 
 as vegetable, the general chronological order may be deter- 
 mined with a satisfactory degree of approximation. 
 
 The chronological order of events recorded in the 
 various strata being determined by the methods already 
 
HISTORICAL GEOLOGY. 227 
 
 explained, it becomes possible to divide geological time 
 into a series of ages, each of which is characterized by 
 a particular stage in the earth's progress, and particularly 
 in the evolution of life. The progress of the earth's his- 
 tory, like that of human history, has been continuous, the 
 idea characteristic of one age being always foreshadowed 
 in the previous age. The boundaries of the various aeons, 
 eras, periods, and epochs recognized in geological history 
 are therefore necessarily in some degree arbitrary. In 
 many cases a great and relatively rapid geographical 
 change, as the elevation of a range of mountains, serves 
 as a time boundary ; and such changes are generally indi- 
 cated, at least in the more disturbed areas, by unconf orma- 
 bility in the strata. 
 
 Geological time is thus divided into four aeons : 
 
 1. In the rocks of the earliest aeon, only doubtful traces 
 of life are found. For a long time after the formation of 
 the earth's crust, the high temperature must have ren- 
 dered the existence of life impossible. Before the close 
 of the aeon, some low forms of vegetable and animal life 
 doubtless appeared. But the rocks are in general more 
 or less strongly metamorphic; and whatever fossils they 
 may once have contained, have been entirely destroyed, or 
 left in condition doubtfully recognizable. This aeon is 
 called Archcean time, from the Greek ap%tj, beginning. It 
 may be considered the earth's prehistoric age. 
 
 2. The rocks of the next aeon reveal the fossil remains 
 of an abundant fauna and flora. In the early part of the 
 aeon, the animals were exclusively marine Invertebrates. 
 Before the close of the time, however, Insects, Fishes, and 
 Amphibians became abundant, and a few Reptiles made 
 their appearance in the closing period. At first, the plants 
 were only Seaweeds ; but plants of higher grade appeared 
 later, and the closing era was characterized by a luxuriant 
 development of Acrogens and Gymnosperms. Birds, 
 Mammals, and Angiosperms were entirely wanting. This 
 aeon is called Paleozoic time, from the Greek T 
 
228 
 
 HISTORICAL GEOLOGY. 
 
 ancient, and &>?;, life. It represents the earth's ancient 
 history. 
 
 3. The next aeon is characterized by the immense de- 
 velopment of reptilian life, the class of Reptiles showing 
 a greater number of species and of ordinal types, greater 
 size, and higher grade of organization, than ever before or 
 after. Birds and Mammals made their first appearance, 
 but attained only a feeble development. Among plants, 
 Gymnosperms were predominant in the early part of the 
 aeon, but Angiosperms became abundant in its closing era. 
 This aeon is called Mesozoic time, from the Greek /-te'o-o?, 
 middle, and 0)77, life. It represents the earth's mediaeval 
 history. It may fitly be called the Age of Reptiles. 
 
 4. The last *eon is characterized by the great develop- 
 ment of Mammals among animals and of Angiosperms 
 among plants. In the latter of the two eras into which 
 it is divided, Man himself appeared as the crown of the 
 animate creation. With the beginning of this aeon, we 
 find species introduced which have continued to the 
 present time, whereas the species of the former aeons are 
 all (or nearly all) extinct. This aeon is called Cenozoic 
 time, from the Greek KCUVOS, recent, and far), life. It 
 represents the earth's modern history. 
 
 Extensive upturnings of rocks in various regions mark 
 the close of the three earlier aeons, so that, in many locali- 
 ties, strongly marked unconformabilities separate the rocks 
 of successive aeons from one another. In North America, 
 the elevation of the Appalachian mountain system marks 
 the close of Paleozoic time, and the elevation of the 
 Laramide mountain system, the close of Mesozoic time. 
 
 Paleozoic time is divided into five eras, Mesozoic time 
 into three, and Cenozoic time into two. 
 
 The eras of Paleozoic time are the following : 
 
 1. Cambrian. In this era, the animals were exclusively 
 marine Invertebrates, and the plants were exclusively Sea- 
 weeds. 
 
 2. Lower Silurian, or Ordovician, In this era appeared 
 
HISTORICAL GEOLOGY. 229 
 
 a few Fishes, Insects, and terrestrial plants a sort of 
 prophecy of the life of succeeding eras. But the land 
 areas were as yet small, and the development of terrestrial 
 life insignificant. The Cambrian and Lower Silurian eras 
 may be called the Age of Invertebrates. 
 
 3. Upper Silurian. In this era, Fishes, Insects, and 
 land plants became more abundant. 
 
 4. Devonian. In this era, Fishes showed a further 
 increase in number of species and diversity of type. 
 Amphibians seem to have made their first appearance. 
 The land areas became more extensive, and were clothed 
 in part with a forest vegetation consisting chiefly of Aero- 
 gens, but with a few Gymnosperms. The Upper Silurian 
 and Devonian eras may be called the Age of Fishes. 
 
 5. Carboniferous. A luxuriant forest and swamp 
 vegetation of Acrogens and Gymnosperms furnished the 
 material for most of the great coal beds of eastern North 
 America and of Europe. Amphibians became abundant, 
 and a few Reptiles appeared in the closing period of the 
 era. The Carboniferous era may be called the Age of 
 Acrogens, or the Age of Amphibians. 
 
 Paleozoic time may be divided into two sections, the 
 Eopaleozoic and the Neopaleozoic, the former including the 
 first two eras, and the latter the last three. They are 
 characterized, respectively, by the almost complete absence 
 of terrestrial life in the former, and its considerable de- 
 velopment in the latter. Extensive upturnings of rocks, 
 and consequent unconformability in many regions, mark 
 the transition. In eastern North America, the elevation 
 of the Taconic mountain system forms a well-defined time 
 boundary between the two sections of Paleozoic time. 
 
 The eras of Mesozoic time are the following : 
 
 1. Triassic. In this era, Reptiles first became abun- 
 dant, and the earliest Mammals (probably Monotremes) 
 made their appearance. 
 
 2. Jurassic. In this era, Reptiles became still more 
 abundant, and presented a greater diversity of type. The 
 
230 
 
 HISTORICAL GEOLOGY. 
 
 -<EONS. ERAS. 
 
 FIG. 212. 
 
 AMERICAN PERIODS. FOREIGN EQUIVALENTS. 
 
HISTORICAL GEOLOGY. 
 
 231 
 
 ERAS. 
 
 FIG. 212 (continued). 
 
 AMERICAN PERIODS. FOREIGN EQUIVALENTS. 
 
 Keuper and Ehaetic 
 
 Muschelkalk 
 Bunter Sandstein 
 
 class culminated at the end of this era, or at the beginning 
 of the next. Birds made their first appearance. Gymno- 
 sperms were the dominant type of vegetation. 
 
 3. Cretaceous. The appearance of Angiosperms gave 
 to the vegetation a modern aspect. Fishes of modern 
 type (Teleosts) became abundant. 
 
 The eras of Cenozoic time are the following : 
 1. Tertiary. In this era there is still no evidence of 
 the existence of Man. The Invertebrates were in large 
 part of species which still exist, but the Vertebrates were 
 all of extinct species. The Tertiary era may be called the 
 Age of Mammals. 
 
232 HISTORICAL GEOLOGY. 
 
 2. Quaternary. Man himself, and other existing spe- 
 cies of Vertebrates, made their appearance. The era may 
 be called the Age of Man. 
 
 The successive strata in the formations of an era are very 
 diversified in character, limestones being overlain abruptly 
 by sandstones, conglomerates, or shales, or either of these 
 last by limestones ; and each may be very different from 
 the following in its fossils. These abrupt transitions in 
 the strata are proofs that there were great changes at times 
 in the conditions of the region where the strata were 
 formed, and the transitions in the kinds of fossils are evi- 
 dence of great destruction at intervals in the life of the 
 seas. Such transitions, therefore, naturally divide the 
 eras into smaller portions of time, or periods, as they are 
 called. By transitions similar in kind, but not so great, 
 periods may generally be subdivided into still smaller 
 parts, or epochs ; and even the epochs often admit of still 
 more minute subdivision. 
 
 The preceding summary of the life of the successive 
 seons and eras will suggest to the student two important 
 generalizations. 
 
 1. There has been a continuous approximation to the 
 life of the present day, as shown, through all geological 
 time by the increasing number of classes and other com- 
 prehensive groups identical with those now existing, and, 
 finally, in Cenozoic time, by the gradual introduction of 
 species that still survive. 
 
 2. There has been, on the whole, a progress from lower 
 to higher forms of life. 
 
 These facts will be recognized as strikingly in harmony 
 with that theory of the origin of species by evolution, or 
 descent with modification, which is generally adopted by 
 the naturalists of the present time. The subject will be 
 discussed more fully when the student is in possession of 
 the facts in some degree of detail. 
 
 The aeons, eras, and periods recognized in American 
 geology are exhibited in the following table : 
 
HISTORICAL GEOLOGY. 
 I. ARCH JEAN TIME. 
 
 233 
 
 2, 
 
 2. 
 
 H. PALEOZOIC TIME. 
 
 i. Eopaleozoic Section. 
 Cambrian Era. 
 
 1. Lower Cambrian, or Georgian, Period. 
 
 2. Middle Cambrian, or Acadian, Period. 
 
 3. Upper Cambrian, or Potsdam, Period. 
 
 Lower Silurian Era. 
 
 1. Canadian Period. 
 
 2. Trenton Period. 
 
 2. Neopaleozoic Section. 
 
 Upper Silurian Era. 
 
 1. Niagara Period. 
 
 2. Onondaga Period. 
 
 3. Lower Helderberg Period. 
 
 Devonian Era. 
 
 1. Oriskany Period. 
 
 2. Corniferous Period. 
 
 3. Middle Devonian, or Hamilton, Period. 
 
 4. Upper Devonian, or Chemung, Period. 
 
 3. Carboniferous Era. 
 
 1. Subcarboniferous Period. 
 
 2. Carboniferous Period. 
 
 3. Permian Period. 
 
 III. MESOZOIC TIME. 
 
 1. Triassic Era. 
 
 2. Jurassic Era. 
 
 3. Cretaceous Era. 
 
 1. Tertiary Era. 
 
 1. Eocene Period. 
 
 2. Miocene Period. 
 
 3. Pliocene Period. 
 
 2. Quaternary Era. 
 
 1. Glacial Period. 
 
 2. Champlain Period. 
 
 3. Recent Period. 
 
 IV. CENOZOIC TIME. 
 
 AGE OF 
 INVERTEBRATES. 
 
 AGE OF FISHES. 
 
 AGE OF ACRO- 
 GENS, OR AGE 
 OF AMPHIBIANS. 
 
 AGE OF REPTILES. 
 
 AGE OF MAMMALS. 
 
 AGE OF MAN. 
 
234 HISTORICAL GEOLOGY. 
 
 The ideal section on pages 230, 231, will further illus- 
 trate the succession of eras and periods, and will also in- 
 dicate to some extent the European (especially British) 
 equivalents for the divisions recognized in this country. 
 
 The names of the periods in the first part of the section 
 (those of the Paleozoic) are mostly derived from the 
 names of American rocks or localities. The names in 
 the other part are mostly European, as the series of rocks 
 it includes (those of Mesozoic and Cenozoic time) is more 
 complete in Europe than in America. 
 
 It will be observed that the same names are in use on 
 both continents for the eras, and to some extent for the 
 periods, since approximate correlations have been estab- 
 lished for the larger divisions of geological time all over 
 the world. It is, however, impossible to establish such 
 correlations in regard to the smaller subdivisions. Hence, 
 the names of periods to some extent, and of epochs and 
 minuter subdivisions universally, differ in different coun- 
 tries and even in different parts of the same country. 
 The names of several of the eras are derived from localities 
 in Great Britain a region in which the series of forma- 
 tions is displayed with remarkable completeness, and in 
 which the study of stratigraphical geology was first devel- 
 oped. In somewhat analogous fashion, the American 
 names of periods and epochs in the Paleozoic are in 
 great part derived from localities in the State of New 
 York the series of Silurian and Devonian rocks in that 
 state being remarkably complete, and having been thor- 
 oughly studied in the beginning of geological work in 
 this country. 
 
 The map on page 235 represents the distribution of 
 the rocks of the different ages, as surface rocks, over 
 part of the United States and Canada. The areas indi- 
 cated by the different kinds of shading are stated on the 
 map. The areas left white are of unascertained or doubt- 
 ful age. 
 
 Silurian strata may underlie the Devonian, and both 
 
235 
 
236 HISTORICAL GEOLOGY. 
 
 Silurian and Devonian may underlie the Carboniferous. 
 The black areas of the Carboniferous period do not, there- 
 fore, indicate the absence of Devonian and Silurian, but 
 only that the Carboniferous strata are the surface strata 
 over the region. ' 
 
 I. ARCHAEAN TIME. 
 
 Archaean time, in geology, commences with the earth 
 already a solid globe, or at least having a solid crust ; for 
 the conditions of only such a globe are within reach of 
 geological investigation. There must have been an earlier 
 time in which the earth was superficially liquid, and 
 astronomy leads us back to the still more ancient time 
 when the earth formed a part of the nebula of which the 
 sun is the central residue. 
 
 When the earth's crust was first formed, its temperature 
 must have exceeded 2500 F. The atmosphere must then 
 have contained all the water of the globe, all the carbon 
 (in the form of carbon dioxide) now stored in solid form 
 as coal and other hydrocarbon compounds and as car- 
 bonates, and various other materials which have since 
 formed solid compounds. When the ocean was first 
 formed by condensation from the atmosphere, its tem- 
 perature may have been as high as 500 F., the atmos- 
 pheric pressure being still perhaps 30 times as great as at 
 present. The chemical action of the ocean in rock de- 
 struction and rock formation must then have been very 
 much more important than in later times. Long ages 
 must have elapsed before the earth was cool enough to 
 permit the existence of the lowest organisms. Archaean 
 time must have been immensely long. 
 
 ROCKS: KINDS AND DISTRIBUTION. 
 
 1. Distribution. Since the Archaean era commenced 
 with the origin of the earth's crust, Archaean rocks must 
 extend around the globe, underlying all rocks of sub- 
 
ARCHAEAN TIME. 
 
 237 
 
 sequent ages, and furnishing the material out of which 
 most of these later rocks have been made. Over by far 
 the larger part of the surface of the globe, they are 
 concealed from view by subsequent formations. In North 
 America they are surface rocks over a large area north of 
 the Great Lakes, shaped like the letter V, the longer branch 
 
 FIG. 214. 
 
 Map showing areas of Archaean rocks in North America. 
 
 of which runs northwest to the Arctic Ocean, and the 
 shorter northeast to Labrador. The large white area on 
 the preceding map, in what is now British America, is the 
 portion of the continent here referred to. Archaean rocks 
 also appear in linear areas along the course of the moun- 
 tain chains which form the borders of the continent. The 
 longest of these areas in the east extends (though not 
 
238 HISTORICAL GEOLOGY. 
 
 > 
 
 without interruptions) from near the St. Lawrence to 
 Georgia, appearing in the Green Mountains of Vermont 
 and Massachusetts, the Highlands of New York and New 
 Jersey, and the "Piedmont belt" of the South Atlantic 
 states. Another may be traced from Newfoundland 
 through Nova Scotia (with a submerged interval) to 
 southeastern Massachusetts. In the west the most exten- 
 sive area is that which forms the "backbone" of the 
 Rocky Mountains. An isolated area appears in the 
 Adirondacks, and another south of Lake Superior. 
 
 In Europe, Archaean rocks are in view in the great 
 iron regions of Sweden and Norway, in Bohemia, and in 
 Scotland. 
 
 2. Kinds of Rocks. The rocks are mostly crystalline 
 rocks, such as granite, quartz syenite, gabbro, gneiss, 
 syenite gneiss, mica schist, hornblende schist, chlorite 
 schist, and granular limestone. But besides these there 
 are some hard conglomerates, quartzites, or gritty sand- 
 stones, and slates. The beautiful iridescent feldspar called 
 labradorite (page 20) is a common constituent of some of 
 the coarse crystalline rocks. 
 
 An abundance of iron is one characteristic of the beds. 
 
 The rocks very often contain hornblende, an iron-bearing 
 mineral, or black mica, also iron-bear- 
 ing. There are in some regions im- 
 mense beds of iron ore (z, i, i, in Fig. 
 215). In northern New York the beds 
 are 100 to 200 feet thick. Similar 
 
 iron ore b^s, Essex County, j r on ore deposits occur in New Jersey, 
 in Michigan, south of Lake Superior, 
 
 and in Missouri. Graphite is common in some places, and 
 
 constitutes 2 to 30 per cent of some beds, especially of the 
 
 limestones. 
 
 3. Disturbance and Crystallization of the Rocks. The 
 layers of gneiss and other schistose rocks, with the in- 
 cluded limestones, are nowhere horizontal ; but, instead of 
 this, they dip at all angles, and are often flexed or folded 
 
AKCILEAN TIME. 
 
 239 
 
 in a most complex manner. Fig. 216 represents the folded 
 character of the Archaean rocks of Canada. The folded 
 rocks in this figure are overlain by beds that are nearly hori- 
 zontal, which belong to the Cambrian and Lower Silurian. 
 
 Owing to the dislocations and uplifts which the rocks 
 have undergone, giving the strata often a nearly vertical 
 position, the iron ore beds look like veins (Fig. 215); and 
 even the strata of crystalline limestone have often a similar 
 veinlike appearance. 
 
 4. Origin of the Rocks. The indurated sandstones, 
 quartzites, and slates are of course ordinary sediments which 
 have undergone more or less of metamorphism. 1 The same 
 is doubtless true of some of the gneisses and schists. But 
 a considerable part of the gneisses are undoubtedly derived 
 
 FIG. 216. 
 
 
 From the south side of the St. Lawrence in Canada, between Cascade Point and St. Louis 
 Rapids : 1, Archaean gneiss ; 2, Cambrian ; 3, Canadian ; 4 a, 6, Trenton. 
 
 from igneous rocks (see pages 30, 192). Even in the 
 case of those schistose rocks which have been derived from 
 stratified rocks, it is often impossible to determine whether 
 the foliation corresponds to the original stratification, or 
 is a structure superinduced by dynamic metamorphism 
 (page 195). The materials which have crystallized into 
 the Archaean rocks must have included not only mechani- 
 cal sediments, but also chemical deposits (which, as re- 
 marked on page 236, must have been more important then 
 than in later times), lava flows, and tufa beds. Some, at 
 least, of the iron ore beds are doubtless metamorphosed 
 chemical deposits (page 116). 
 
 1 The limestones, quartzites, slates, and other rocks whose sedimentary 
 origin is pretty certain, together with the associated igneous rocks, con- 
 stitute the Aljronkian system of the United States Geological Survey. 
 In many localities, such rocks overlie unconformabiy the more highly 
 crystalline granites and gneisses. 
 
240 HISTORICAL GEOLOGY. 
 
 The granites, gabbros, and other massive rocks are prob- 
 ably for the most part plutonic, but such rocks may be in 
 some cases only the extreme term of metamorphism. 
 
 The earliest rocks formed in Archaean time must have 
 resulted from the solidification of the molten material of 
 the globe. But it is unlikely that any of those primitive 
 rocks are anywhere accessible to observation. Most of 
 the visible Archaean rocks bear evidence of a derivative 
 origin. 
 
 It is probable that, in the course of Archaean time, there 
 were a number of epochs of extensive crustal movements 
 accompanied by metamorphism, for instances of uncon- 
 formability between one Archaean rock and another are 
 frequent. Since a strongly marked unconformability 
 everywhere separates the Archaean from later formations, 
 it is inferred that the age closed with an epoch of very 
 general disturbance. 
 
 Archaean rocks in general are more highly crystalline 
 than those of later formations ; yet there seems to be no 
 definite lithological criterion which will distinguish rocks 
 of that age from metamorphic and plutonic rocks of later 
 times. 
 
 LIFE. 
 
 The graphite, abundant in some beds in Canada, is 
 probable evidence of the existence of plants, since it is 
 known that in later times graphite has been formed out 
 of vegetable remains. The limestone beds suggest the 
 idea that there was present either vegetable or animal 
 life ; for almost all limestones (see page 99) are of organic 
 origin. But the inference in both cases is doubtful, since 
 both graphite and limestone may have been formed by 
 purely chemical processes. 
 
 No distinct fossil plants have been found, though gen- 
 eral considerations render it probable that plants com- 
 menced before the close of Archaean time. The earliest 
 plants were doubtless Seaweeds. No vegetable remains 
 
ARCHAEAN TIME. 
 
 241 
 
 but those of Seaweeds are found. in the overlying Cam- 
 brian strata. 
 
 Fig. 217 represents what has been regarded as a fossil 
 animal, and named Eozoon Canadense. It is supposed to 
 have been a coral-like mass made 
 by Protozoans of the class of 
 Rhizopods, the simplest of all 
 kinds of animal life. The dark 
 layers in the mass are supposed 
 to mark the position of the soft 
 part of the animals, while the 
 white layers are supposed to be 
 derived from their calcareous 
 skeleton. The supposed animal 
 nature of Eozoon is, however, 
 probably a mistake. Structures 
 of very similar appearance have 
 been produced, where the sup- 
 position of organic origin is out 
 of the question. Still, it is alto- 
 gether probable that Rhizopods existed in the waters 
 before the close of the Archaean era, and that they 
 furnished material for beds of limestone. In some of the 
 less strongly metamorphic rocks, supposed to belong to 
 the later part of Archaean times, obscure and doubtful 
 traces of animal fossils have been reported. 
 
 GENERAL OBSERVATIONS. 
 
 The large area of Archaean rocks shown on the map, 
 page 237, represents the main portion of the dry land of 
 North America at the close of the Archaean age ; for it 
 consists of rocks made during the age, and is bordered on 
 its different sides by the earliest rocks of the next age. 
 It shows the outline, approximately, of North America 
 as it appeared when the Cambrian era opened. It was 
 the nucleus around which in the course of time the 
 continent grew. The smaller Archaean areas appear to 
 
 Eozoon Canadense. 
 
242 HISTORICAL GEOLOGY. 
 
 have been mountain ridges and islands in the great con- 
 tinental seas. There may have been other areas of dry 
 land at the close of Archaean time, which were subse- 
 quently submerged and covered by later formations. 
 
 Since the Archaean rocks are mainly metamorphosed sedi- 
 ments, they were presumably derived in large degree from 
 the waste of lands already emerged, and subject to ocean 
 waves and other denuding agencies ; but of the situation 
 and boundaries of those earliest lands we have no definite 
 knowledge. 
 
 Europe had its Archaean lands at the same time in Scan- 
 dinavia, Scotland, Bohemia, and some other regions ; and 
 probably each of the other continents was then repre- 
 sented by larger or smaller areas of dry land. 
 
 The facts to be presented in the discussion of Paleozoic 
 time teach that the great but yet unmade continents, 
 although small in the amount of dry land, were not cov- 
 ered by the deep ocean, but only by comparatively shallow 
 seas. They were already outlined, though mostly under 
 water. Portions may have been at times a few thousands 
 of feet under water, but in general the depth was small 
 compared with that of the ocean. 
 
 We thus gather some hints with regard to the geography 
 of America in the period of its first beginnings. 
 
 The outlines of the northern Archaean area on the map, 
 page 237, the embryo of the continent, and the direc- 
 tions of the other Archaean lands, are very nearly parallel 
 to the coast lines of the present continent. The Archaean 
 lands, both in North America and Europe, are largest in 
 the more northern latitudes. 
 
 II. PALEOZOIC TIME. 
 
 Paleozoic time is divided as follows : 
 I. EOPALEOZOIC SECTION. 
 
 1. Cambrian Era. 
 
 2. Lower Silurian Era. 
 
PALEOZOIC TIME. 243 
 
 II. NEOPALEOZOIC SECTION. 
 
 1. Upper Silurian Era. 
 
 2. Devonian Era. 
 
 3. Carboniferous Era. 
 
 The prefixes used in forming the names of the two sec- 
 tions are derived, respectively, from 770)5, dawn, and veo?, 
 new. The boundary of the two sections is defined, in 
 eastern North America and western Europe, by an epoch 
 of mountain-making, and consequently by extensive un- 
 conformability in the strata. The Eopaleozoic section, or 
 Age of Invertebrates, was marked by a rich and varied 
 display of marine invertebrate life, but only the scantiest 
 beginnings of Vertebrates and of terrestrial animals and 
 plants. In the Neopaleozoic, the dry lands increased in 
 extent, and terrestrial plants and animals became abun- 
 dant. Vertebrates increased greatly in number and 
 variety, Amphibians making their appearance in the 
 Devonian, and Reptiles in the Carboniferous era, in 
 addition to the earlier class of Fishes. The Upper Silu- 
 rian and Devonian are called the Age of Fishes, and the 
 Carboniferous the Age of Amphibians, or the Age of 
 Acrogens. 
 
 As has been already stated, and as will appear more 
 clearly in the sequel, the American continent was essenti- 
 ally a unit in its evolution through all geological time. 
 The areas of rock-making and geographical progress in 
 the Paleozoic were accordingly defined by the conditions 
 of Archaean geography. The map of North America at 
 the close of the Archaean (Fig. 214) shows the shallow 
 continental sea divided into three parts by the two great 
 Archaean chains of islands or island ridges, following 
 respectively the general course of the Appalachian and 
 the Rocky Mountain chains. Those three regions the 
 Interior Continental Sea, the Atlantic Border, and the 
 Pacific Border require separate consideration in tracing 
 the history of continental growth. The Atlantic Bor- 
 
244 HISTORICAL GEOLOGY. 
 
 der and the Pacific Border regions are to some extent 
 subdivided by the shorter Archaean ridges indicated on 
 the map. 
 
 I. EOPALEOZOIC SECTION. 
 
 I. CAMBRIAN ERA. 
 
 SUBDIVISIONS. 
 
 The name Cambrian is derived from an ancient name 
 of Wales a region in which the rocks of this era were 
 studied by Sedgwick and Murchison. 
 
 It includes three periods : 1, LOWER CAMBRIAN, or 
 GEORGIAN; 2, MIDDLE CAMBRIAN, or ACADIAN; 3, UPPER 
 CAMBRIAN, or POTSDAM. 
 
 ROCKS: KINDS AND DISTRIBUTION. 
 
 The Cambrian rocks usually appear along the borders 
 of the Archaean areas. In eastern North America they 
 border the Archaean nucleus of the continent, and the 
 adjacent Adirondack island ; they appear at intervals 
 along both sides of the Appalachian Archaean area; and 
 they occur in parts of the troughs between the more 
 eastern Archaean ridges. In the west they border in 
 various places the Rocky Mountain Archaean area and 
 various Archaean islands ; they are laid bare in the 
 Colorado Canon by the deep erosion which has removed 
 the overlying strata. 
 
 The rocks include sandstones, shales, conglomerates, 
 and limestones, and, in some localities, quartzites, slates, 
 schists, and marbles, resulting from the metamorphism of 
 ordinary stratified rocks. Many of the beds bear evidence 
 of origin in very shallow water, and none of them bear 
 positive evidence of deep-sea origin. 
 
 The Potsdam Sandstone a characteristic rock in the 
 vicinity of the Adirondacks belongs to the Upper 
 Cambrian. 
 
CAMBRIAN ERA. 245 
 
 The beds contain, in many places, ripple-marks (Fig. 185, 
 page 154); mud-cracks (Fig. 189); layers showing the 
 wind-drift, and the ebb-and-flow, structure (Figs. 161, 
 187); worm burrows (Fig. 230); and occasionally the 
 tracks of some of the animals of the period. 
 
 In the Taconic Mountains of Vermont and Massa- 
 chusetts, the Cambrian is represented by a great quartzite 
 formation, with intercalations of mica and hydromica 
 schist. 
 
 In southeastern Pennsylvania, the Lower Cambrian in- 
 cludes a great thickness of quartzite with overlying shales, 
 or slates, and limestone ; and besides these rocks there 
 are, in South Mountain, large flows of basaltic and rhyo- 
 litic rocks. 
 
 The Keweenaw formation, south of Lake Superior, 
 consisting of many thousands of feet of sandstone strata, 
 with numerous intercalations of dolerite, felsite, and other 
 igneous rocks, and bearing the remarkable deposits of 
 native copper for which the region is famous (page 201), 
 is very probably Cambrian, though it contains no fossils, 
 and is considered by some geologists to be older. 
 
 In Great Britain the Cambrian rocks are hard sand- 
 stones and slates. The Lingula Flags are included in the 
 Upper Cambrian. They are most extensively in view in 
 North and South Wales and in Shropshire. 
 
 In Lapland, Norway, Sweden, and Bohemia, Cambrian 
 strata have been observed. If the strata of later date 
 could be removed from the continents, we should probably 
 find the Cambrian beds extensively distributed over all 
 the continents. 
 
 LIFE. 
 
 These most ancient of fossiliferous rocks contain no 
 remains of terrestrial life. The plants of the period that 
 left traces in the rocks were all Seaweeds. Among ani- 
 mals, all the Invertebrate subkingdoms except the Tuni- 
 cates (which are destitute of skeletons) were represented 
 
246 
 
 HISTORICAL GEOLOGY. 
 
 by aquatic species, and by these only ; there is no evi- 
 dence that there were any Vertebrates. 
 
 It is remarkable that all of these subkingdoms were 
 represented already in the Lower Cambrian. Moreover, 
 among the Mollusks, both Lamellibranchs and Gastropods 
 had already appeared. In the Middle and Upper Cam- 
 brian the species are mostly different from those of the 
 
 218 
 
 FIGS. 218-221. 
 219 
 
 SPONGE: Fig. 218, Leptomitus Zittelli. ANTIIOZOANS: Fig. 219, Archseocyathus pro- 
 fundus ; 220, 221, Spirocyathus Atlanticus. 
 
 Lower Cambrian, but they belong in general to the same 
 groups. The most important step of progress during the 
 Cambrian is the introduction of the class of Cephalopods 
 the highest class of Mollusks in the Upper Cambrian. 
 Sponges; Coelenterates ; Echinoderms. Fig. 218 repre- 
 sents one of the Sponges, and Figs. 219-221 represent 
 two of the Corals of the Lower Cambrian. The Echino- 
 
CAMBRIAN ERA. 
 
 247 
 
 derms were represented chiefly by Cystoid Crinoids. 
 Fragments of Crinoidal stems are not uncommon. 
 
 Molluscoids. Remains of Brachiopods are abundant. 
 The Potsdam sandstone abounds in many places in a 
 shell smaller, in general, than a finger nail, related to the 
 modern Lingula (Fig. 222). Shells of genera related to 
 
 FIGS. 222-225. 
 
 FIGS. 226-229. 
 
 226 
 
 BRACHIOPODS: Fig. 222, Lingulella prima; 223, a, Acrotreta gemma, x4; 224, Orthis 
 Highlanders ; 225, Orthisina (Billingsella) festinata. 
 
 Lingula are so characteristic of certain strata of the Cam- 
 brian as to have suggested the name Lingula Flags, or 
 Lingula Sandstone. 
 
 Mollusks. Figs. 226-229 represent some of the Mol- 
 lusks of the Lower Cam- 
 brian. Especially note- 
 worthy were the forms 
 referred (though not 
 without somewhat of 
 doubt) to the Ptero- 
 pods. The species of 
 that group at present 
 are few and small. In 
 Cambrian times it was 
 probably represented by 
 numerous species, some 
 of which were of con- 
 siderable size. Some 
 of the Cambrian Ptero- 
 pods were peculiar in 
 having the shell pro- 
 vided with a lid, or operculum. The Cephalopods of the 
 Upper Cambrian include both forms with straight shells 
 
 LAMELLIBRANCH : Fig. 226, Fordilla Troyensis, 
 x 5. GASTROPODS : Fig. 227, Stenotbeca ru- 
 gosa ; 228, Platyceras primaevum, x 4 ; 229, 
 Hyolithes Americanus, x 2 ; 229 a, operculum 
 of same, x 2. 
 
248 
 
 HISTORICAL GEOLOGY. 
 
 FIG. 230. 
 
 WORM: burrows of Scoli- 
 thus linearis. 
 
 (Orthoceras) and forms with curved shells (Cyrtoceras)-, 
 
 but not those with spiral shells, as Nautilus. 
 
 Worms. The existence of marine Worms among the 
 
 earliest animals of the globe is proved by the great num- 
 bers of worm holes or burrows in the 
 sandstones, now filled with hard sand- 
 stone like that of the rock. They are 
 very similar to the holes made by such 
 worms in the sands of seashores at the 
 present time. One species has been 
 called Scolithus linearis (Fig. 230). 
 These worm holes are common in the 
 European as well as the American Cam- 
 brian sand- FIG. 23i. 
 stones. The 
 minute tooth- 
 like bodies 
 
 called Conodonts, found in 
 
 the Cambrian, as well as in 
 
 later formations, are probably 
 
 jaws of Worms. 
 
 Arthropods. One of the 
 
 most characteristic groups of 
 
 the Cambrian fauna was that 
 
 of Trilobites, belonging to 
 
 the class of Crustaceans. One 
 
 of the largest of them, and a 
 
 kind characteristic of the Aca- 
 dian, or Middle Cambrian, is 
 
 represented in Fig. 231, one 
 
 third of the natural size. Its 
 
 total length when living must 
 
 have been about ten inches. 
 
 The specimen figured was 
 
 found at Braintree, south of 
 
 Boston. Fig. 232 represents (natural size) a species 
 
 characteristic of the Georgian, or Lower Cambrian. 
 
 TEILOBITE : Paradoxides Harlani, x 
 
CAMBRIAN EKA. 
 
 249 
 
 shown in the figures, both of these species had large eyes 
 situated on the head shield. 
 
 Most specimens of Trilobites, as illustrated in these 
 figures, fail to show antennae, legs, or other appendages. 
 
 FIG. 232. 
 
 FIG. 283. 
 
 LEPTOSTBACAN : Protocaris 
 Marshi. 
 
 A recent discovery of speci- 
 mens of Trilobites in the 
 Lower Silurian showing 
 these parts (page 258, Fig. 
 253) has added much to our 
 knowledge of the group. 
 
 Fig. 233 illustrates an- 
 other group of Crustaceans 
 (the Leptostracans) which 
 was (like the Trilobites) 
 eminently characteristic of 
 the Paleozoic. 
 
 Brachiopods and Trilo- 
 bites among animals, and Seaweeds among plants, make 
 up the bulk of the living species thus far discovered. 
 There is as yet no evidence that the hills bore a Moss or 
 Lycopod, or harbored the meanest Insect, or that the 
 oceans contained a single Fish. 
 
 TRILOBITE : Olenellus Vermontanus. 
 
250 HISTORICAL GEOLOGY. 
 
 GENERAL OBSERVATIONS. 
 
 The ripple-marks, mud-cracks, and tracks of animals 
 preserved in these most ancient of Paleozoic rocks are 
 records left by the waves, the sun, and the life of the 
 period, as to the extent and condition of the continent 
 in that early era. These markings teach that, when the 
 beds were in progress, a large part of the continent lay 
 at shallow depths in the sea, so shallow that the little 
 currents made by the waves could ripple its sands ; that 
 over other portions the surface was a sand flat exposed 
 at low tide ; or a sea beach, the burrowing place of 
 worms ; or a mud flat, that could be dried and cracked 
 under the heat of the sun, or in a drying atmosphere. 
 
 With such evidences of shallow water or emerged flats 
 in a formation extending widely over the continent, it is 
 a safe conclusion that the North American continent was 
 at the time in actual existence, and probably not far from 
 its present extent ; and, although mostly below the sea 
 level, and in some places somewhat deeply so, it was 
 generally covered only by shallow waters, and probably 
 nowhere submerged to truly oceanic depth. The same 
 was probably true of the other continents. There is, 
 in fact, evidence of other kinds which, taken in con- 
 nection with the above, leaves little doubt that the ex- 
 isting places of the deep ocean and of the continents 
 were determined even in the first formation of the earth's 
 crust in early Archaean time, and that, in all the move- 
 ments that have since occurred, the oceans and continents 
 have never changed places. 
 
 This preservation of markings, seemingly so perishable, 
 on the early shifting sands, is a very instructive fact. 
 They illustrate part of the means by whidh the earth has 
 been recording its own history. The track of a Trilobite, 
 or the furrow left by the sweep of the wave over the 
 sand, is a mold, in sand or earth, into which other 
 sands are cast both to copy and preserve it; for, if the 
 
CAMBRIAN EEA. 251 
 
 waves or currents that succeed are light, they simply 
 spread new sands over the indented surface, without 
 obliterating the mold ; and so the addition of successive 
 layers only buries the markings more deeply, and thus 
 protects them against destruction. When, finally, con- 
 solidation takes place, the track or ripple-mark is made 
 as enduring as the rock itself. 
 
 The appearance in the Lower Cambrian of so many dif- 
 ferent groups of pretty highly organized animals, without 
 any clear evidence of series of lower and more embryonic 
 forms preceding them, is one of the most remarkable facts 
 in geological history. It has been regarded by many as 
 affording a strong objection to the theory of evolution. 
 But it must be considered that the apparently abrupt 
 introduction of the Cambrian fauna may be due to the 
 imperfection of the record. Both animal and vegetable 
 life was probably in existence during the latter part of the 
 Archaean (page 240), though the general metamorphism 
 of the rocks has destroyed or rendered unrecognizable 
 whatever fossils may have been formed. The general 
 unconformability between the Archaean and the Cambrian 
 indicates an interval of time whose record is entirely lost 
 (page 57). As it was a time of great geographical change, 
 it may be supposed that it was a time in which evolution- 
 ary changes in fauna and flora were unusually rapid. 
 
 That most of the subkingdoms of animals should appear 
 very early and almost simultaneously, is just what would 
 be expected on evolutionary grounds. For it is not to be 
 supposed that the subkingdoms were successively evolved 
 in an ascending series, but most of them must have been 
 independently evolved from ancestral forms almost as 
 simple as Protozoans. Moreover, the fact that almost all 
 groups of marine Invertebrates have larval forms which 
 are minute, free swimming, and destitute of heavy skele- 
 tons, indicates that probably the ancestral forms from 
 which they were derived were likewise minute, free swim- 
 ming, and destitute of skeletons. Such forms would be 
 
 
252 HISTORICAL GEOLOGY. 
 
 altogether unlikely to be preserved as fossils. This is 
 probably the principal reason for the absence of any 
 record of the ancestors of the Cambrian fauna. 
 
 II. LOWER SILURIAN ERA. 
 
 SUBDIVISIONS. 
 
 The name Silurian (from SUures, the name of an 
 ancient Welsh tribe) was given by Murchison, whose 
 studies in Wales and the adjacent parts of England first 
 led to the definite recognition of the Silurian system. 
 The division of the Silurian of Murchison into two eras 
 has been required by later researches. 
 
 The Lower Silurian era is divided into two periods : 
 1, CANADIAN, and 2, TRENTON. 
 
 The Canadian period is so named from Canada, where 
 the rocks are well displayed and have been most thoroughly 
 studied; and the Trenton period, from Trenton Falls, just 
 north of U tica, the river at the Falls running between 
 high bluffs of Trenton Limestone. 
 
 In Great Britain the first of these periods is represented 
 by the Arenig group ; and the latter by the Llandeilo 
 Flags, and the Bala, or Caradoc. 
 
 ROCKS: KINDS AND DISTRIBUTION. 
 
 In the Upper Cambrian, or Potsdam, period, the rock 
 deposits formed over the North American continent were 
 mainly of sand or mud, making sandstones aiid shales ; 
 and but little limestone was formed. The Canadian period 
 is one of transition to the Trenton, in which limestones 
 were in progress over nearly the whole breadth of the 
 continent, the Appalachian and Arctic regions, as well as 
 the Interior Continental. 
 
 The rocks of the Canadian period along the borders of 
 the Archaean of northern New York and Canada are: 
 (1) A limestone, often arenaceous and siliceous, usually 
 
LOWER SILURIAN ERA. 253 
 
 magnesian, called the Calciferous Sand Rock; (2) a purer 
 limestone formation, mostlj' magnesian, called the Chazy 
 Limestone, from a place of that name in northern New 
 York. In the Interior basin the rock of the period is 
 mainly limestone in Iowa and Wisconsin the Lower 
 Magnesian Limestone, excepting to the north, where 
 the upper part is sandstone (St. Peter's Sandstone). 
 
 The Trenton period opens with the Trenton epoch, 
 which is remarkable for its extensive limestone formation. 
 The limestone occurs in Canada; in New York (the beds 
 at Trenton Falls giving it its name); along the Appa- 
 lachian range; in Ohio and other states of the Ohio and 
 Mississippi basin; from Wisconsin, northwestward along 
 the -west side of the Archaean area ; and in the Arctic 
 regions. It is in most places full of fossils. The Bird's- 
 eye and Black River Limestones are part of the Trenton 
 formation. The rocks of the later part of the Trenton 
 period (called the Utica and Hudson epochs), in New 
 York and the Appalachians, are shale and sandstone; and 
 even in the Interior basin the limestones are often, as 
 about Cincinnati, quite clayey or impure. 
 
 The crystalline limestone (marble) of Vermont and 
 western Massachusetts and Connecticut, with the associ- 
 ated mica schist, hydromica schist, clay slate, and quartz- 
 ite, is partly Cambrian, and partly Lower Silurian ; it 
 contains, at several localities, Canadian and Trenton fos- 
 sils. Since the rocks over most of the region are strongly 
 metamorphic, and consequently destitute of fossils, the 
 limits of the different formations cannot be precisely 
 determined. 
 
 The thickness of the rocks of the Canadian and Tren- 
 ton periods in Pennsylvania is over 7500 feet ; while in 
 Illinois it is but 750 feet, and in Missouri about 2000 feet. 
 
 The rocks of this era in Great Britain are chiefly 
 shales and flags, with but little limestone. The Arenig 
 group at the base of the formation corresponds approxi- 
 mately with the Canadian. The rocks of this group are 
 
254 
 
 HISTORICAL GEOLOGY. 
 
 FIG. 234. 
 
 overlain by the Llandeilo Flags. Above them there are 
 the Caradoc Sandstone of Shropshire, and the Bala for- 
 mation, the latter sandy slates and sandstone, with thin 
 beds of limestone, in Wales. In Scandinavia the rocks 
 are mostly shales, with some limestone, especially in the 
 upper part of the formation. 
 
 LIFE. 
 
 The life of this era, like that of the Cambrian, was 
 chiefly marine; but the era is remarkable as showing the 
 first vestiges of terrestrial life, both vegetable and animal. 
 
 The plants found 
 fossil are mostly Sea- 
 weeds ; but the Skid- 
 daw Slates (included 
 in the Arenig group) 
 of Great Britain have 
 afforded remains of a 
 plant (Fig. 234) which 
 has been referred to the 
 Marsileacese, a group 
 of the higher Crypto- 
 gams (Acrogens) al- 
 lied to the Ferns and 
 Lycopods. 
 
 All the subking- 
 doms of animals were 
 represented (except 
 the Tunicates), the 
 earliest of Vertebrates 
 belonging to this era. 
 Moreover, Arthropods 
 were represented not 
 only by the aquatic Crustaceans, but also by the earliest 
 Insects. 
 
 Ccelenterates. The Lower Silurian beds, especially 
 the finer shales and slates, are remarkable for the great 
 
 ACROGEN: Protannularia Ilarknessi. 
 
LOWER SILURIAN ERA. 
 
 255 
 
 abundance of very delicate plumelike fossils, called Grap- 
 tolites, from the Greek ypdcjxo, to write. 
 
 A few species from the Canadian are represented in 
 Figs. 235, 236, 238-240, and one species from the Utica 
 epoch of the Trenton period, in Fig. 237. In the living 
 state there were cells along the notched margin, one for 
 each notch, from which little animals protruded them- 
 selves. They belong to the Hydroids, among the Hydro- 
 zoans. The Graptolites are especially characteristic of 
 the Lower Silurian, though represented also in the Cam- 
 brian and the Upper Silurian. 
 
 FIGS. 235-240. 
 
 GRAPTOLITES : Fig. 235, Loganograptus Logani, the central portion of a radiating group of 
 stems, with parts of the stems; 236, same, portion of one of the stems, enlarged; 236 a, 
 part of stem, more enlarged ; 237, Diplograptus pristis ; 238, 239, Phyllograptus typus ; 
 240, the young of a Graptolite. 
 
 Fig. 241 represents one of the Cyathophylloid Corals 
 of the Trenton. Its shape is that of a curved cone, a 
 little like a short horn, the small end being the lower. 
 At top, when perfect, the cavity of the coral is divided 
 off by plates radiating from the center. The name, Cya- 
 thophylloid, from the Greek /eua#o?, cup, and <j>v\\ov, leaf, 
 alludes to the cup full of radiating leaves or plates. These 
 Cyathophylloid Corals, which were eminently character- 
 istic of Paleozoic time, have the radiating partitions and 
 other structures which are radially repeated in the body, 
 in multiples of four, while in most modern Corals they 
 are in multiples of six. 
 
 Echinoderms. Fig. 242 shows the form of one of the 
 
256 
 
 HISTORICAL GEOLOGY. 
 
 Crinoids, though the stem on which it stood is mostly 
 wanting, and the arms are not entire. There were also 
 true Starfishes in the seas. 
 
 FIGS. 241-252. 
 
 ANTHOZOAN: Fiff. 241, Streptelasma corniculnm. CKTNOTD : Fijr. 242, Taxocrinus elepans. 
 HKYO/.OANS: Fig. 243, Stictopora acnta; 244, Prasopora lycoperdon ; 245, section of 
 same. BRACHIOPODS : Fip. 246, Orthis testudinaria; 247, Orthis occidentalis : 248, 
 Leptaena sericea. MOLUTSKS: Fig. 249, Ambonychia bellistriata; 250, Hbapbistoma 
 lenticulare ; 251, Orthoceras junceuin. TRILUBITE : Fig. 252, Asapbus platycepha- 
 lus, x |. 
 
 Molluscoids. Among Molluscoids, Bryozoans were very 
 common. The fossils are small cellular corals : one is 
 shown in Fig. 243. 
 
 
LOWER SILURIAN ERA. 257 
 
 A group of corals, mostly of small size, appearing in 
 hemispherical (Fig. 244) or incrusting or branching forms, 
 and consisting of minute columnar cells closely packed 
 together (Fig. 245), were very abundant in the Lower 
 Silurian. They were probably Bryozoans, though re- 
 garded by some paleontologists as true Anthozoan corals. 
 One species is represented in Figs. 244, 245. Other im- 
 portant genera of the group are Monticulipora, Chcetetes, 
 etc. 
 
 Brachiopods were still more characteristic of the era, 
 and occur in vast numbers. Three species are repre- 
 sented in Figs. 246-248. 
 
 Mollusks. All the principal classes of Mollusks were 
 represented. A Lamellibranch is shown in Fig. 249, and 
 a Gastropod in Fig. 250. Shells of Cephalopods were 
 especially common, under the form of a straight or curved 
 horn with transverse partitions. Fig. 251 represents a 
 small species. One species had a shell 12 or 15 feet long, 
 and nearly a foot in diameter. The word Orthoceras is 
 from the Greek o/?0o?, straight, and fcepas, horn. There 
 were some species also of the genus Nautilus, a genus 
 which has survived to the present time. While Trilobites 
 appear to have been the largest and most powerful animals 
 of the Cambrian seas, Cephalopods, of the Orthoceras 
 family, far exceeded Trilobites in both respects in the 
 Trenton. The larger kinds must have been powerful 
 animals to have borne and wielded a shell 12 or 15 feet 
 long. Although clumsy compared with the Fishes of a 
 later age, they emulated the largest of Fishes in size, and 
 no doubt also in their voracious habits. 
 
 Arthropods. Fig. 252 represents one of the large 
 Trilobites of the Trenton rocks, the Asaphus platycepha- 
 lus, a species sometimes found eight inches or more 
 in length. Another genus of Trilobites, very common in 
 the Lower Silurian, and represented also in the Upper 
 Silurian, is Calymene, a species of which is shown in 
 Fig. 116, page 77. The rocks of the Utica epoch, in a 
 
258 
 
 HISTORICAL GEOLOGY. 
 
 locality near Rome, New York, have lately yielded a mul- 
 titude of specimens of the Trilobite Triarthrus Beckii, in 
 which the legs and other appendages are beautifully pre- 
 served. The species is shown, twice the natural size, in 
 Fig. 253 ; and a more enlarged view of two of the two- 
 branched legs is given in Fig. 254. 
 
 An Insect allied to the Cockroaches (Palceoblattina) 
 has been found in Normandy, in a sandstone probably 
 of the age of the Caradoc or Hudson. More recently 
 
 FIG. 253. 
 
 TRILOBITE: Triarthrus 
 Beckii. 
 
 Second and third thoracic leg of Triarthrus 
 Beckii, x 12. In II. the fringe of setae 
 has been removed, to show more plainly 
 the joints : en, the main stem of the leg 
 (endopodite) ; ex, the natatory branch 
 (exopodite). 
 
 has been reported the discovery of an Insect in Sweden 
 in strata of about the same age. These are the earliest 
 land animals thus far discovered. 
 
 Vertebrates. The earliest traces of Vertebrates thus 
 far discovered are remains of Fishes found abundantly 
 in a sandstone near Canon City, Colorado, believed to 
 belong to the Trenton period. The remains are bony 
 plates of Placoderms and scales of Ganoids, and struc- 
 tures supposed to be the ossified sheaths of notochords 
 (a rudimentary form of vertebral column) of Selachians. 
 
 
LOWER SILURIAN ERA. 259 
 
 GENERAL OBSERVATIONS. 
 
 Geography. The wide continental region covered by 
 the Trenton limestone formation, stretching over the 
 Appalachian region on the east, and widely through the 
 Interior basin, must have been throughout a clear sea, 
 densely populated over its bottom with Brachiopods, 
 Corals, Crinoids, Trilobites, and the other life of the 
 era. It may, however, have been a shallow sea ; for the 
 corals and beautiful shells of coral reefs live mostly within 
 100 feet of the surface. 
 
 During the later part of the period, the Utica and 
 Hudson epochs, the same seas, especially on the north, 
 became more open to sediment, through some change 
 of level or of coast barriers, and consequently much of 
 the former life disappeared, and other kinds, adapted to 
 impure waters or to muddy bottoms, supplied its place. 
 
 Life. The appearance of the earliest land plants 
 (Acrogens), the earliest Insects, and the earliest Fishes, 
 marks the progress in life during the Lower Silurian. 
 
 Among the genera of the Lower Silurian, probably only 
 seven have living species. These are Saccammina among 
 Rhizopocls, Lingula, Discina, Rhynchonella, and Crania 
 among Brachiopods, Avicula among Lamellibranchs, and 
 Nautilus among Cephalopocls. Discina probably goes back 
 even to the Cambrian, and perhaps Lingula also, though some 
 systematists refer all the supposed Cambrian species to other 
 genera. These genera of long lineage thus reach through 
 all time from the Lower Silurian onward. All other genera 
 disappear some at the close of an era, others at the close 
 of a period, epoch, or other subdivision of an era. 
 
 The extinction of species took place at intervals through 
 the periods, as well as at their close ; though the exter- 
 minations at the close of the periods were more general. 
 With the changes from one stratum to another, there were 
 disappearances of some species; and, with the changes 
 from one formation to another, still larger numbers of 
 
260 HISTORICAL GEOLOGY. 
 
 species became extinct. Scarcely any Cambrian species 
 are known to occur in the Canadian period ; very few 
 of the species of the Canadian period survive into the 
 Trenton ; and very many of those of the early part of 
 the Trenton did not exist in the later part. Thus life and 
 death were in progress together, species being removed, 
 and other species appearing, as time moved on. 
 
 Economic Products. The Galena Limestone (Trenton 
 period) of Wisconsin and the adjoining states derives its 
 name from the deposits of lead ore which it contains. 
 The ore occurs in cavities in the limestone, and its origin 
 was probably much later than that of the rock. 
 
 A large amount of mineral oil and gas is afforded in 
 some regions by the Trenton formation and chiefly the 
 limestone. At Findlay, and some other places in Ohio, 
 borings are made to a depth of several hundred feet, 
 through the overlying rocks, and then for 10 to 50 feet 
 into the limestone ; the gas comes up with a rush, and 
 continues to escape for years. From one boring over 
 a million cubic feet of gas have been obtained per day. 
 The gas is used both for illumination and for fuel. In 
 other cases oil is obtained, which, when purified, becomes 
 kerosene. The gas consists chiefly of marsh gas (CH 4 ), 
 the principal ingredient of ordinary illuminating gas ; 
 and the oil consists of mixtures of other hydrocarbons. 
 They were produced by the decomposition of the animal 
 or vegetable substances in the rock, afforded by the life 
 of the seas. 
 
 DISTURBANCES AT THE CLOSE OF THE LOWEB, 
 SILUftlAK 
 
 Archaean time closed, as has been already remarked 
 (page 240), with an epoch of general upturning and meta- 
 morphism, so that the Cambrian rocks are everywhere 
 unconformable with the Archaean. But, from that time 
 until the close of the Lower Silurian, no extensive dis- 
 
TACONIC REVOLUTION. 261 
 
 turbances occurred either in eastern North America or in 
 Europe. The alternations of limestones with shales and 
 sandstones during the Eopaleozoic are evidence, indeed, 
 that changes of level, by gentle movements or oscillations 
 of the earth's crust, were going on. But the close of 
 Eopaleozoic time was signalized by geographical changes 
 of a much more striking character. 
 
 1. The Taconic Range. This mountain range, 500 
 miles long, extending along the western and northwestern 
 border of New England, from Canada to northwestern Con- 
 necticut and Putnam County in eastern New York, was 
 made at the close of the Lower Silurian. That the region 
 was not dry land before, is shown by the presence of 
 Chazy and Trenton Limestones, for these are of marine 
 origin : and that the region was above the water from and 
 after this time, is indicated by the fact that the formations 
 of the Trenton period were the latest there formed ; and 
 by the still more important observation that, near Hudson, 
 in the Hudson River valley, and at other localities, near 
 the border of the Taconic region, there are Upper Silurian 
 rocks overlying unconformably the upturned older rocks, 
 the uplift being shown thereby to have preceded the 
 deposit of the Upper Silurian rocks. 
 
 During the progress of the Lower Silurian era a great 
 thickness of rock had been made over the region of the 
 Taconic Mountains, probably 15,000 or 20,000 feet. 
 These beds were laid down, not in a sea 15,000 or 20,000 
 feet deep until it was full, but in shallow waters over a 
 bottom that was gradually sinking so gradually that the 
 rock material accumulating over it kept it shallow. Then, 
 when the slowly forming trough had reached this depth, 
 the epoch of catastrophe, that is, of mountain-making, 
 began, when the beds were displaced and folded, and 
 consolidated or crystallized. Quartzose sandstones were 
 changed to hard quartzite the rock of high ridges in 
 Berkshire and Vermont ; earthy sandstones were made 
 into mica schist and gneiss ; and common limestones came 
 
262 HISTORICAL GEOLOGY. 
 
 out white or clouded marbles, now extensively quarried 
 for architectural purposes at Canaan, Connecticut, in 
 Berkshire County, Massachusetts, and at Rutland and 
 elsewhere in Vermont. 
 
 The history of the Taconic range thus exemplifies the 
 same stages already described with reference to the Appa- 
 lachian range, which has been taken as a type of mountain 
 structure : a slowly progressing geosyncline, in which a 
 vast thickness of strata is accumulated; the weakening 
 of the mass as the bottom of the trough becomes heated 
 in its descent ; and finally the crushing of the weakened 
 strata to form the complex folds characteristic of a syncli- 
 norium. The Taconic range differs, however, from the 
 Appalachian range, in that the rocks of the former have 
 suffered a much more intense degree of metamorphism. 
 
 2. The Taconic System. It is probable, also, that an- 
 other mountain range was formed at the same time, com- 
 mencing in the eastern part of Canaan, Connecticut, and 
 continuing southward through Westchester County, New 
 York, to Manhattan Island ; and still another, if not a 
 continuation of the last, extending from the vicinity of 
 Philadelphia to Buckingham County, Virginia (where the 
 crystalline rocks have afforded fossils), and beyond this 
 southwestward. These ranges extending southward and 
 southwestward beyond the Taconic range proper have 
 suffered so much denudation as no longer to constitute 
 strongly marked geographical features, though the oro- 
 genic movements are indicated by the disturbed and meta- 
 morphosed rocks. The Taconic revolution, in this view, 
 left its marks in mountains and in crystalline rocks along 
 the whole Atlantic Border, and the two or three mountain 
 ranges dating from that time constitute together a long 
 Taconic mountain system. 
 
 3. Emergence of the Atlantic Border Region. Simul- 
 taneously with the formation of the Taconic system, a 
 large part of the Appalachian Border region was raised 
 above the sea level. This is proved by the fact that, along 
 
UPPER SILURIAN ERA. 263 
 
 this border south of New York, no marine deposits are 
 known, of the Upper Silurian or of any later formation 
 until the Cretaceous. It is probable that the geanticlinal 
 movement of the Atlantic Border region continued through 
 the remainder of the Paleozoic, contemporaneously with 
 the progress of the Appalachian geosyncline. 
 
 4. The Cincinnati Uplift. Another geanticlinal move- 
 ment west of the Appalachian region caused the emer- 
 gence of two large islands from the Interior Continental 
 sea, one in the region of Cincinnati, the other farther 
 south in Tennessee. The axis of the geanticline trends 
 in general northeast and southwest, parallel with the trend 
 of the Appalachians. This line of shallow waters and 
 emerged lands made thenceforth a partial division between 
 the main body of the Interior Continental sea (Central 
 Interior sea) and a narrow Eastern Interior sea. 
 
 5. Disturbances in Europe. In the interior of Europe, 
 as in the Continental Interior region of North America, 
 the Lower Silurian rocks are generally overlain conforma- 
 bly by the Upper Silurian. But in Wales and western 
 England, where the Cambrian and Lower Silurian rocks 
 are of great thickness, they are disturbed and metamor- 
 phosed, and separated from the Upper Silurian by well- 
 marked unconformability. 
 
 II. NEOPALEOZOIC SECTION. 
 I. UPPER SILURIAN ERA. 
 
 The Eopaleozoic had been characterized by the small 
 area of dry land in all the continents, and the almost ex- 
 clusively marine flora and fauna. The Neopaleozoic was 
 characterized by a gradual increase in the land areas, and a 
 progressive development of terrestrial life, reaching a climax 
 in the great forests of Acrogens and Gymnosperms which 
 characterized the Carboniferous era, and the' varied terres- 
 trial fauna, including Snails, Insects and Arachnoids, Am- 
 phibians and Reptiles, which tenanted the widening lands. 
 
264 
 
 HISTORICAL GEOLOGY. 
 
 GEOGRAPHICAL CONDITIONS AT THE OPENING OF THE ERA. 
 
 The accompanying map shows approximately the areas 
 where Archaean and Eopaleozoic rocks are surface rocks, 
 and which were therefore probably, for the most part, 
 dry land at the beginning of the Upper Silurian. There 
 may have been, however, other areas which were dry 
 land at that time, but which have been subsequently 
 
 FIG. 255. 
 
 North America at the opening of the Upper Silurian. 
 
 covered by newer formations. The portion of those areas 
 where Archaean rocks are surface rocks is indicated by 
 a shading composed of Vs, except that, in the Atlantic 
 Border region, the Archgean rocks have not been fully 
 distinguished from metamorphic rocks of later date, and 
 no attempt is therefore made to indicate their boundaries 
 on the map. 
 
 A comparison of this map with that on page 237 will 
 
 
UPPER SILURIAN ERA. 265 
 
 show that the area of dry land was not greatly increased 
 during the Eopaleozoic. The Atlantic Border region, 
 south of New York, had become dry land, and was no 
 longer receiving deposits. The marine connection which 
 had existed between the Interior Continental sea and the 
 Atlantic, through the St. Lawrence channel, was closed 
 by the elevation of land in the region of Lake Champlain. 
 It is, however, probable that communication between the 
 Interior Continental sea and the Gulf of St. Lawrence 
 was temporarily reopened in the closing period of the 
 Upper Silurian. The Gulf of St. Lawrence extended 
 southward in long bays in the troughs between the eastern 
 ridges of Archaean rocks, and in these bays Upper Silurian 
 rocks were deposited. The separation between the Inte- 
 rior Continental sea and the Gulf of St. Lawrence, and 
 the free opening of the former into the Pacific, had a 
 marked effect on the marine faunas of the different regions. 
 The fossils of Canada and New England show the influ- 
 ence of migration from western Europe ; while the Interior 
 Continental sea was open to immigration from the old 
 world chiefly by way of the Pacific. An Eastern Interior 
 sea or bay was imperfectly separated from the main body 
 of the Interior Continental sea by the line of islands and 
 shallows formed by the Cincinnati uplift ; and it was in 
 the eastern part of this bay that the vast subsidence of 
 the Appalachian geosyncline was in progress. 
 
 SUBDIVISIONS. 
 
 The Upper Silurian era in North America includes three 
 periods: 1, NIAGARA; 2, ONONDAGA; 3, LOWER HEL- 
 
 DERBERG. 
 
 The name of the first is from the Niagara River, along 
 which the rocks are displayed ; that of the second, from 
 the name of a town and county in central New York ; 
 that of the third, from the Helderberg Mountains, south 
 of Albany, where the lower rocks are of this period. 
 
266 HISTORICAL GEOLOGY. 
 
 ROCKS: KINDS AND DISTRIBUTION. 
 
 1. Niagara Period. The rocks of the Niagara period, 
 in the eastern part of the Interior Continental region oi 
 North America, are : (1) A conglomerate and grit rock 
 called the Oneida Conglomerate, which extends from 
 central New York southward along the Appalachian 
 region, having a thickness of 700 feet in some parts 
 of Pennsylvania ; which, together with the Medina 
 Sandstone, spreading westward from central New York 
 through Michigan, and also southward along the Ap- 
 palachian region, being 1500 feet thick in Pennsylvania, 
 is included in the Medina epoch ; (2) Hard sandstones, 
 or flags and shales, with some limestones (particularly 
 westward) and some beds of iron ore, belonging to 
 the Clinton epoch, having nearly the same distribution 
 as the Medina formation, though a little more widely 
 spread in the west, and about 2000 feet thick in Pennsyl- 
 vania ; (3) The formations of the Niagara epoch, occur- 
 ring in New York from the Hudson to the Niagara, and 
 extending widely over the Interior Continental region; 
 they consist, at Niagara, of shale below and thick lime- 
 stone above, but mainly of limestone in the Interior region. 
 The Niagara is one of the great limestone formations of 
 the continent, existing also in the Arctic regions. 
 
 Ripple-marks and mud-cracks are very common in the 
 Medina formation. The example of rill-marks figured on 
 page 155 is from its strata in western New York. 
 
 The section, Fig. 256, represents the rocks on the Niagara 
 River at and below the Falls. The Falls are at F ; the 
 Whirlpool, three miles below, at W; and the Lewiston 
 Heights, which front Lake Ontario, at L. Nos. 1, 2, 3, 4 
 are different sandstone and shale strata of the Medina 
 epoch ; 5, shale, and 6, limestone, of the Clinton epoch ; 
 7, shale, and 8, limestone, of the Niagara epoch. 
 
 2. Onondaga Period. The rocks of the Onondaga 
 period include the Salina beds and the Water-lime group. 
 
UPPER SILURIAN ERA. 267 
 
 The Salina beds are fragile, clayey sandstones and shales, 
 usually reddish in color, and including a little limestone. 
 They occur in New York, in western Ontario, and in the 
 vicinity of Cleveland, Ohio. 
 
 The salt of Salina and Syracuse, in central New York, 
 is obtained from wells of salt water 150 feet and upward 
 in depth, which are borings into these saliferous rocks. 
 From 35 to 45 gallons of the water afford a bushel of salt, 
 while of sea water it takes 350 gallons for the same amount. 
 No solid salt is there found ; but farther south and west 
 one or more beds of rock salt occur over an area measur- 
 ing 150 miles from east to west and probably not less 
 than 60 miles from north to south. The aggregate thick- 
 ness of these salt beds varies widely, being, in the vicinity 
 of Ithaca, about 250 feet, though much less than that in 
 most places. At Ithaca, the total thickness of the Salina 
 formation is 1230 feet, and it is covered by 1900 feet of 
 later strata. Beds of rock salt are also found at Gode- 
 rich, Ontario, and near Cleveland. 
 
 The rocks of the Water-lime group are impure mag- 
 nesian limestones. Owing to these impurities, the quick- 
 lime made from the rock will set under water, and is 
 accordingly used in the manufacture of hydraulic cement. 
 The name of the group refers to that fact. 
 
 Both the Salina and the Water-lime beds contain gypsum, 
 sometimes in layers, sometimes in imbedded masses. In 
 some cases it may have been formed directly, like the salt, 
 by the evaporation of sea water. But much of it has 
 resulted from the decomposition of the limestone by the 
 action of sulphuric acid derived from the oxidation of the 
 sulphuretted hydrogen dissolved in subterranean waters. 
 Sulphur springs are common in the region. 
 
 3. Lower Helderberg Period. The Lower Helderberg 
 group consists mainly of limestones, and is the second 
 limestone formation of the Upper Silurian. The forma- 
 tion is well developed in the State of New York and 
 along the Appalachian region to the south. It also 
 
268 HISTORICAL GEOLOGY. 
 
 occurs in Tennessee and probably in southern Illinois; 
 but the beds are thin or wanting over most of the Central 
 Interior region. The formation is also found in Canada 
 in the line of the Connecticut Valley, in northern Maine, 
 and in New Brunswick and Nova Scotia. 
 
 Upper Silurian Rocks in Europe. In Great Britain 
 the base of the Upper Silurian rocks is formed by con- 
 glomerates, sandstones, and shales, called, where occurring 
 in South Wales, the Llandovery group, and corresponding 
 
 FIG. 256. 
 
 
 L W 
 
 Section along the Niagara, from the Falls to Lewiston Heights. 
 
 to the Medina and Clinton groups. Above these there is 
 the Wenlock group, consisting of limestone and some 
 shale (including, in the upper portion, the Dudley Lime- 
 stone), and corresponding to the Niagara group. These 
 rocks occur as surface rocks near the borders of Wales 
 and England. Next comes the Ludlow group, of the age 
 of the Onondaga and Lower Helderberg beds. 
 
 LIFE. 
 
 The limestone strata and most of the other beds of the 
 Niagara group are full of fossils; and so also are the rocks 
 of the Lower Helderberg period, and of the Wenlock and 
 Ludlow formations in Great Britain. Fossils are well-nigh 
 wanting in the Salina beds, and not abundant in the Water- 
 lime. 
 
 The life of the era was the same in general features as 
 that of the latter part of the Lower Silurian, though mostly 
 different in species. 
 
 The most of the vegetable remains are those of Sea- 
 weeds ; but the Lower Helderberg rocks of this country 
 
UPPER SILURIAN ERA. 
 
 FIGS. 257-269. 
 
 269 
 
 257 
 
 ANTHOZOANS : Fig. 257, Zaphrentis bilateralis, Clinton group ; 258, Favosites Niagarensis, 
 Niagara group; 259, Halysites catenulatus, ibid. CYSTOID : Fig. 260, Caryocrinus 
 ornatus, Niagara group. BRACIIIOPODS : Fig. 261, Pentamerus oblongus, Clinton and 
 Niagara groups, also Llandovery and Wenlock ; 262, Orthis varica, x 2, Niagara group 
 and Dudley Limestone ; 263, Lepta-na transversalis, ibid. ; 264, Strophomena rhom- 
 boidalis, ibid. ; 265, Rhynchotreta cuneata, ibid. LAMELMBRANCH : Fig. 266, Avicula 
 emacerata. Niagara group. GASTROPODS : Fig. 267, Cyclonema cancellatum, Clinton 
 group ; '268, Platyceras angulatum, Niagara group. TRILOBITB : Fig. 269, Homalonotus 
 delphinocephalus, x J, Niagara group. 
 
270 HISTORICAL GEOLOGY. 
 
 have afforded a few remains of Acrogens, representing 
 apparently both the Equiseta and the Lycopods. 
 
 Among animals, the Coelenterates were represented 
 chiefly by Anthozoan corals, the Echinoderms by Crinoids, 
 and the Molluscoids by Brachiopods. The last are espe- 
 cially abundant, their shells outnumbering all other fossils. 
 All the principal classes of Mollusks were represented, 
 Cephalopods of the Orthoceras group being most charac- 
 teristic. Arthropods were represented by Trilobites, Os- 
 tracoids, and Leptostracans, among Crustaceans, also by 
 Merostomes, Arachnoids, and Insects. The only Verte- 
 brates were Fishes. 
 
 Coelenterates. Fig. 257 is a coral of the Cyathophyl- 
 loid group, showing the radiating plates of the interior ; 
 Fig. 258, a species of Favosites, a genus in which the cells 
 have a columnar form (somewhat honeycomb-like, whence 
 the name, from Latin favus, honeycomb), and are divided 
 by transverse partitions; Fig. 259, a Chain Coral, Haly sites 
 (Greek aXim?, chain), the cells appearing, in a transverse 
 section, like links of a chain. 
 
 Echinoderms. Fig. 260 is a Cystoid with the arms 
 broken off. Another Cystoid of the Niagara group is 
 shown in Fig. 82, on page 67. A Starfish, also of the 
 Niagara, is shown in Fig. 86, on page 68. 
 
 Molluscoids. Figs. 261-265 are Brachiopods of the 
 Niagara period ; Figs. 270-274, Brachiopods of the Lower 
 Helderberg. 
 
 Mollusks. Fig. 266 is a Lamellibranch, and Figs. 
 267, 268, Gastropods, of the Niagara period. 
 
 Fig. 275 represents small, slender, tubular cones, called 
 Tentaculites, which almost make up the mass of some layers 
 in the Water-lime group ; the form of one enlarged is shown 
 in Fig. 276 ; they are regarded as shells of Pteropods. 
 The same genus is abundant also in the Lower Helderberg. 
 
 Arthropods. Fig. 269 is a reduced figure of a common 
 Trilobite of the Niagara group. The species is often 8 
 or 10 inches in length. 
 
UPPER SILURIAN ERA. 
 
 271 
 
 Fig. 277 is an Ostracoid Crustacean, Leperditia alta, 
 of unusually large size for that group, modern Ostracoids 
 seldom exceeding a twelfth of an inch in length. 
 
 Fig. 278 is a Eurypterus, a representative of the class 
 of Merostomes, of which the Limulus, or Horseshoe Crab, 
 is now the sole surviving genus. The Eurypterus group 
 makes its first appearance in the Utica Shale, but is more 
 characteristic of Neopaleozoic time, attaining its greatest 
 
 FIGS. 270-278. 
 
 270 
 
 271 
 
 BEACHIOPODS : Figs. 270, 271, Pentamerus galeatus ; 272, 273, Ehynchonella ventricosa ; 
 274, Spirifer macropleurus. PTEROPOD : Fig. 275, Tentaculites gyracanthus ; 276, 
 same, enlarged. OSTRACOID : Fig. 277, Leperditia alta. MEROSTOME : Fig. 278, Euryp- 
 terus reinipes, a small specimen. Figs. 270-274 are species from the Lower Helderberg ; 
 Figs. 275-278, from the Water-lime. 
 
 development in the Upper Silurian. The species figured 
 is from the Water-lime, and is sometimes nearly a foot long. 
 Species of the same order occur in Great Britain in the 
 Wenlock and Ludlow beds, and one of them is supposed, 
 from the fragments found, to have been 6 or 8 feet long, 
 far surpassing any Arthropod now living. The Upper 
 Silurian of Great Britain has also afforded forms still 
 more closely related to the modern Limulus, 
 
272 HISTORICAL GEOLOGY. 
 
 Arachnoids are represented by Scorpions, which have 
 been found in the Water-lime group in New York, and 
 also in the Upper Silurian of Scotland and Sweden. 
 
 Vertebrates. Remains of Fishes have been found in 
 the Clinton and the Water-lime of this country, and in 
 the Ludlow beds of Great Britain. They include plates 
 of Placoderms, and probably fin spines of Selachians. 
 
 GENERAL OBSERVATIONS. 
 
 On the map, page 235, the areas over which the Cam- 
 brian and Silurian formations are surface rocks are distin- 
 guished by being horizontally lined. It is observed that 
 they spread southward from the northern Archaean area, 
 and indicate an extension of the growing continent in that 
 direction. . 
 
 South of the Silurian area commences the Devonian, 
 which is vertically lined; and the limit between them shows 
 approximately the course of the seashore at the close of 
 the Upper Silurian era. It is seen that more than half of 
 New York, and nearly all of Canada and Wisconsin, had 
 by that time become part of the dry land ; but a broad 
 bay covered the Michigan region to the northern point of 
 Lake Michigan, for here Devonian rocks, and to some 
 extent Carboniferous, were afterward formed. The Ar- 
 chaean dry land, the nucleus of the continent, had also 
 received additions in a similar manner on its eastern and 
 western sides, through British America. And there may 
 have been other areas of dry land which were subse- 
 quently submerged and covered by more recent strata. 
 
 But, with all the increase, the amount of dry land in 
 North America was still small. Europe is proved by 
 similar evidence to have had much submerged land. The 
 surface of the earth was a surface of great waters, with 
 the continents only in embryo one large area and some 
 islands representing that of North America, and an archi- 
 pelago that of Europe. The emerged land, moreover, 
 was most extensive in the higher latitudes. The rivers 
 
UPPER SILURIAN ERA. 273 
 
 of a world whose lands were so small must also have been 
 small. The lands, too, according to present evidence, had 
 no greensward over the rocks, until the latter part of the 
 Silurian age. 
 
 The succession of Upper Silurian formations is as 
 follows : (1) The Medina Sandstone, having at its base 
 the coarse grit called Oneida Conglomerate, occurring in 
 great thickness along the Appalachian region, and reach- 
 ing north to central New York, and spreading west- 
 ward beyond the limits of that state ; (2) The Clinton 
 group of flags and shales, with some limestone (especially 
 westward), having the same Appalachian extension and 
 great thickness, but spreading on the north much farther 
 westward, even to the Mississippi; (3) The Niagara group, 
 represented in New York by shales and limestones, and 
 spreading as a great limestone formation through the 
 larger part of the Interior region ; (4) The Salina salt- 
 bearing shales of New York, extending west through 
 Canada, and over part of the Appalachian region south- 
 west ; (5) Another limestone, but mostly impure, spread- 
 ing over New York State and the Appalachian region, 
 and also some of the states west, and occurring in the 
 northward extension of the Connecticut Valley, and over 
 Maine to the Gulf of St. Lawrence. 
 
 These facts teach that geographical changes took place 
 from time to time, in the course of the era, corresponding 
 to these several changes in the formations. The clear con- 
 tinental seas of the Trenton period were succeeded by 
 conditions fitted to produce the several arenaceous and 
 argillaceous formations, of varying limits, which followed ; 
 but clear waters returned again at the epoch of the 
 Niagara group, when corals, crinoids, and shells covered 
 the bottom of the continental sea, and made the Niagara 
 limestone formation. But these seas in the Niagara 
 epoch were less extended than those of the Trenton, not 
 covering the Appalachian region. The Niagara epoch 
 of limestone-making was followed by the Onondaga or 
 
274 HISTORICAL GEOLOGY. 
 
 Saliferous period. Since the beds (1) are clays and 
 clayey sands, (2) are almost wholly without fossils, and 
 (3) afford salt, it may be inferred that central New York 
 was at the time a great salt marsh, mostly shut off from 
 the sea. Over such an area the waters would at times 
 become too salt to support life, owing to partial evapora- 
 tion under the hot sun, and, possibly, too fresh at other 
 times from the rains. Moreover, muddy deposits would 
 be formed ; for such deposits are now commonly formed 
 in salt marshes. The salt water would deposit salt by 
 evaporation in dry seasons, and from time to time, by an 
 occasional ingress of the sea, salt water would be resup- 
 plied for further evaporation. 
 
 There is direct testimony as to the condition of the land 
 and shallowness of the waters in the regions where many 
 of the rocks were in progress ; for ripple-marks and mud- 
 cracks are common in some layers, and are positive evi- 
 dence that the sands and earth that are now the solid 
 rock were then the loose sands of beaches, sand flats, or 
 sea bottoms, or the mud of a salt marsh. Such little 
 markings, therefore, remove all doubt as to the condition 
 of central New York during the deposition of the Salina 
 beds. 
 
 Similar markings indicate, also, the precise condition of 
 the region of the Medina Sandstone, showing that there 
 were sand flats, sea beaches, and muddy bottoms open 
 to the inflowing sea. Where the rill-marks were made 
 (Fig. 186, page 155), the sands were those of a gently 
 sloping flat or beach ; the waters swept lightly over the 
 sands, dropping here and there a stray shell (as the Lingula 
 cuneata shown in the figure) or a pebble, which became 
 partly buried ; and then, as they retreated, they made a 
 tiny .plunge over the little obstacle, and furrowed out the 
 loose sand below it. The fineness of the sand, lightness 
 of the shells, and small-ness of the furrows are proof that 
 the movements were light. 
 
 The great thickness of most of the formations of the 
 
DEVONIAN ERA. 275 
 
 Upper Silurian along the Appalachian region leads to 
 many interesting conclusions. The Appalachian region 
 was in strong contrast with the Central Interior region, 
 where the series of contemporaneous beds is hardly one 
 tenth as thick. Taking this into connection with another 
 fact, that very many of the strata among the thousands of 
 feet of Upper Silurian formations in the Appalachian re- 
 gion contain those evidences of shallow-water and mud-flat 
 or sand-flat origin above explained, there is full proof that, 
 in the Upper Silurian era, the region was for the most part 
 a shallow sea border receiving the debris from the Atlantic 
 Border region, which had emerged as a land area at the 
 close of the Lower Silurian. The great thickness of the 
 strata was rendered possible by the progressive subsi- 
 dence which was preparing the Appalachian region 
 for the mountain-making epoch at the close of Paleo- 
 zoic time. 
 
 During the Cambrian and Lower Silurian eras a similar 
 gradual subsidence had permitted the accumulation of the 
 thick series of strata which were upturned and metamor- 
 phosed in the making of the Taconic Mountains. The 
 subsiding area during the Upper Silurian era extended 
 from Pennsylvania northward into New York, and not 
 along the Taconic region; the rocks in the state of New 
 York have great thickness for some distance beyond the 
 Pennsylvania border. 
 
 II. DEVONIAN ERA. 
 
 SUBDIVISIONS. 
 
 The Devonian formation was so named by Sedgwick 
 
 and Murchison, from Devonshire, England, where it occurs. 
 
 The era may be divided into four periods : 1, OBIS- 
 
 KANY ; 2, CORNIFEROUS ; 3, HAMILTON ; 4, CHEMUNG. 
 
 The Oriskany and Corniferous periods are often called 
 Lower Devonian; the Hamilton, Middle Devonian; and 
 the Chemung, Upper Devonian. 
 
276 
 
 HISTORICAL GEOLOGY. 
 
 ROCKS: KINDS AND DISTRIBUTION. 
 
 1. Oriskany Period. The Oriskany beds are mostly 
 rough calcareous sandstones. The formation extends from 
 Oriskany, New York, southward along the Appalachian 
 region through Pennsylvania, Maryland, and Virginia, 
 where it is several hundred feet thick. It occurs also in 
 northern Maine, and at Gaspe on the Gulf of St. Lawrence, 
 where the rock is partly limestone. 
 
 2. Corniferous Period. The lowest rocks of this period 
 are fragmental beds, called the Cauda-Cralli Grit and the 
 Schoharie Grrit, having their distribution along the Appa- 
 lachian region, commencing in central and eastern New 
 York, and extending southwestward into Pennsylvania. 
 
 Next follows the great Corniferous Limestone, the lower 
 part of which is sometimes called the Onondaga Limestone, 
 and the whole of which is often called the Upper Helder- 
 berg group. It stretches from eastern New York westward 
 to the states beyond the Mississippi. 
 
 The name Corniferous (derived from the Latin cornu, 
 horn) was given it by Eaton, from its frequently contain- 
 ing a variety of quartz called hornstone. This hornstone 
 differs from true flint in being less tough, or more splin- 
 tery in fracture, though it is like it in hardness and in 
 consisting of silica. 
 
 The limestone is in many places literally an ancient 
 coral reef. It contains corals in vast numbers and of 
 great variety; and in some places, as at the Falls of the 
 Ohio, near Louisville, Kentucky, the resemblance to a 
 modern reef is perfect. Some of the coral masses at that 
 place are 5 or 6 feet in diameter; and single polyps of 
 the Cyathophylloid corals had in some species a diameter 
 of 2 or 3 inches, and in one species a diameter of 6 or 7 
 inches. 
 
 The same reef rock occurs near Lake Memphremagog 
 on the borders of Vermont and Canada, and also at Little- 
 
DEVONIAN ERA. 277 
 
 ton, New Hampshire ; but the corals have in these places 
 been partly obliterated by metamorphism. 
 
 The Corniferous Limestone in some places abounds in 
 mineral oil. The oil wells of Enniskillen, Ontario, are 
 from this rock. 
 
 3. Hamilton Period. The Hamilton formation consists 
 in New York of sandstones and shales, with a few thin 
 layers of limestone. It consists of two parts correspond- 
 ing to two epochs : the lower part is called the Marcellus 
 Shale; the upper, the Hamilton beds. It has its greatest 
 thickness along the Appalachians. From New York it 
 spreads westward, where it is in part calcareous. The 
 formation occurs also in New Brunswick, and at Gaspe, 
 on the Gulf of St. Lawrence. 
 
 The Hamilton beds afford an excellent flagging stone 
 in central New York, and on the Hudson River, near 
 Kingston, Saugerties, Coxsackie, and elsewhere, which is 
 extensively quarried and exported to other states. 
 
 4. Chemung Period. The Chemung period includes 
 two epochs, the Portage, and the Chemung proper. The 
 Portage beds are mainly shales and shaly sandstones ; the 
 Chemung beds mainly sandstones, or shaly sandstones, 
 with some conglomerate. The base of the Portage is 
 formed by a stratum of black bituminous shale called the 
 Genesee Shale. The beds of the Chemung period spread 
 over a large part of southern and western New York, 
 attaining a thickness of between 2000 and 3000 feet. 
 
 In the following section, taken on a iiorth-and-south 
 line south of Lake Ontario, No. 6 represents the beds of the 
 Onondaga period ; 7, the Lower Helderberg Limestone ; 
 9, the Corniferous, or Upper Helderberg, Limestone ; 10 a, 
 6, the Hamilton beds ; 11 a, the Genesee Shale ; and 11 6, 
 the overlying beds of the Chemung group. 
 
 In the Catskill Mountains, the Portage and Chemung 
 epochs are not distinguished from each other, being jointly 
 represented by a mass of sandstones, varying into con- 
 glomerates and shales, predominantly red, called the Cats- 
 
278 
 
 HISTORICAL GEOLOGY. 
 
 kill group. The rocks in the Catskills have a thickness of 
 3000 feet. The same formation extends southwestward 
 along the Appalachians into Pennsylvania, attaining near 
 Mauch Chunk a thickness of more than 7500 feet. 
 
 The Upper Devonian, like most of the Paleozoic forma- 
 tions, is much thinner in the Central Interior region than 
 along the Appalachians. It is chiefly represented in 
 the Central Interior by a bituminous shale resembling the 
 
 FIG. 279. 
 
 6 7 y 
 
 Section of Upper Silurian and Devonian formations south of Lake Ontario. 
 
 Genesee Shale of New York, and commonly called the 
 "Black Shale." In Ohio, the Upper Devonian is repre- 
 sented by the Huron, Erie, and Cleveland Shales. 
 
 The Upper Devonian is the great " oil horizon " of 
 Pennsylvania. 
 
 Devonian Rocks in Europe. In Great Britain the 
 Devonian rocks include the Old Red Sandstone, the 
 prevailing rock of the age in Wales and Scotland; and 
 slates and limestones in Devon and Cornwall. The thick- 
 ness of the Old Red Sandstone in some places in Scotland 
 is said to be 10,000 to 16,000 feet. The Devon beds are 
 estimated to be 10,000 to 12,000 feet in thickness. The 
 distribution in Great Britain is shown on the map, page 
 295. In Germany, in the Rhenish provinces, there is a 
 coral limestone very similar to that of North America. 
 
 LIFE. 
 GENERAL CHARACTERISTICS. 
 
 The Devonian was characterized by forests and an 
 abundance of Insects over the land, and by Fishes of 
 many kinds in the waters. The earliest Amphibians 
 probably appeared in this era. 
 
DEVONIAN ERA. 
 
 279 
 
 PLANTS. 
 
 Cryptogams. The hornstone of the Cornif erous and 
 other limestones develops, under the microscope, the fact 
 that it was probably made from the siliceous remains of 
 plants and animals, shells of Diatoms, spicules of 
 Sponges, and other organic relics having been detected 
 in it. 
 
 Figs. 280-282 represent portions of some of the land 
 plants. Fig. 282 is a fragment of a Fern, and Figs. 280, 
 
 FIGS 
 
 
 I 
 
 ACROGKNS : Fig. 280, Lepidodendron primaevum, from the Hamilton group ; 281, Sigillaria 
 Hallii, ibid. ; 282, Archseopteris Halliana, from the Chemung group. 
 
 281, are portions of Lycopodiaceous trees. The scars or 
 prominences over the surface are the points of attachment 
 of the fallen leaves; a dried branch of a Norway Spruce, 
 stripped of its leaves, looks somewhat like Fig. 281. By 
 referring to page 88, it will there be seen that among 
 the Flowerless Plants or Cryptogams there is one group, 
 the highest, that of Acrogens, in which the plants have 
 upward growth like ordinary trees, and the tissues are 
 partly vascular: it is the one containing the Ferns, Lyco- 
 pods, and Equiseta or Horsetails. The most of the land 
 
280 HISTORICAL GEOLOGY. 
 
 plants of the Devonian belong to the three orders just 
 mentioned. 
 
 A somewhat fuller description of these groups is here 
 appropriate, since in the Devonian era, for the first time, 
 they attained such development as to clothe the land with 
 forests. 
 
 1. Ferns. The species have a general resemblance to 
 the Ferns or Brakes of the present time. 
 
 2. Lycopods. These are plants related to the Ground 
 Pine. The existing plants of this tribe are slender species, 
 seldom more than a few inches in height, though the creep- 
 ing stems of some species may be many feet in length. 
 Some of the ancient species were of the size of forest 
 trees. These ancient species belong mostly to two groups, 
 of which the genera Lepidodendron and Sigillaria, respec- 
 tively, are the types. In the former, the scars are con- 
 tiguous, and are arranged in quincunx order, that is, 
 alternate in adjoining rows, as shown in Fig. 280. The 
 name Lepidodendron is from the Greek XeTrt?, scale, and 
 ev$pov, tree, and alludes to the scar-covered trunk, which 
 looks somewhat like a scale-covered reptile. The Sigil- 
 larids include trees of moderate height, with stout, spar- 
 ingly branched trunks, bearing long, linear leaves much 
 like those of the Lepidodendrids ; but the scars on the 
 exterior are in parallel vertical lines, as in Fig. 281, and 
 Fig. 308, page 300. The name is from the Latin sigillum, 
 seal, in allusion to the scars. 
 
 3. Equiseta, or Horsetails. The Equiseta of modern 
 wet woods are slender, hollow, jointed rushes, called some- 
 times Scouring Rushes. They often have a circle of slender 
 leaflike appendages at each joint. The Calamites or Tree 
 Rushes, which are referred to this group, are peculiar to 
 the ancient world, none having existed since the Paleozoic. 
 They had jointed stems like the Equiseta, and otherwise 
 resembled them. But they were often a score of feet or 
 more in height, and over 6 inches in diameter. Fig. 
 311, page 300, represents a portion of one o these plants. 
 
DEVONIAN ERA. 281 
 
 Phanerogams. Others of the land plants belong to the 
 lowest class of Flowering Plants or Phanerogams, called 
 Gymnosperms (see page 90). 
 
 Both of the principal orders of Gymnosperms the 
 Conifers and the Cycads seem to be represented in the 
 Devonian. Some of the Paleozoic genera appear to be in 
 some respects intermediate between the two orders, and 
 there is some doubt to which they should be referred. 
 The fossils are impressions of leaves and portions of the 
 trunk or branches. 
 
 ANIMALS. 
 
 The early Devonian was the coral period of the ancient 
 world. In no age before or since have coral reefs of 
 greater extent been formed. 
 
 The Molluscoid Brachiopods still predominated over 
 the Mollusks, though Lamellibranchs and Gastropods were 
 more abundant than in the Silurian. A new type of Ceph- 
 alopods commenced in the Lower Devonian. Hitherto, 
 the partitions or septa in the shells, straight or coiled, were 
 flat or simply concave ; but in the new genus Gf-oniatites 
 the margin of the septum is crumpled into one or more 
 deep flexures. The name is from the Greek <ycovLa, angle. 
 Fig. 293 (page 283) represents one of the species, and 
 Fig. 293 a shows some of the flexures along the margin of 
 the shell. 
 
 Trilobites continued to be the dominant group of Crus- 
 taceans, though less abundant than in the Silurian. The 
 earliest of the order of Decapods (the order now repre- 
 sented by Lobsters, Crabs, etc.) appeared in the Devonian 
 era. The earliest species were Macrurans, the higher 
 group of Brachyurans (Crabs) appearing much later. 
 Land Arthropods were represented by Insects and Myrio- 
 pods ; the wings of some species of Insects having been 
 reported from the Devonian of New Brunswick, and two 
 species of Myriopods having been described from the Old 
 Red Sandstone of Scotland. 
 
282 
 
 HISTORICAL GEOLOGY. 
 
 The increase of Fishes in number of species and diversity 
 of types forms the most marked characteristic of the era 
 The appearance of Amphibians is an important step o 
 progress. 
 
 Coelenterates. Figs. 283, 284, are two species of Cya 
 thophylloid corals from the Corniferous. Both are found 
 at the Falls of the Ohio, where the latter species, Cya 
 thophyllum rugosum, forms very large masses. Fig. 285 
 is a species of Favosites from the same locality, occurring 
 also in Europe. Figs. 286, 287, are small corals, probably 
 belonging to the group of Alcyoniarians. 
 
 FIGS. 283-287. 
 
 280 
 
 ANTHOZOANS: Fig. 288, Zaphrentis Raflnesquii; 284, 284 a, Cyathophyllum rugosum 
 285, Favosites Goldfussi; 286, Syringopora Maclurii ; 28T, Komingeria cornuta. Al 
 from the Corniferous period. 
 
 Molluscoids. Figs. 288-290 are Brachiopods of the 
 Hamilton period. 
 
 Mollusks. Figs. 291, 292, are Hamilton Lamellibranchs. 
 Fig. 293 is a Cephalopod, a species of Groniatites, from the 
 same formation. Fig. 293 a is a view of a part of the mar- 
 howing- the crumpled edges of the septa. 
 
 gin of the shell, showing 
 
 Arthropods. Fig. 294 is one of the most common spe- 
 cies of Trilobites of the Hamilton. Remains of Insects 
 have been found in beds supposed to be of the Hamilton 
 period, at St. John, New Brunswick. A wing of a 
 gigantic species of May-fly is represented in Fig. 295. 
 
 
 
DEVONIAN ERA. 
 
 283 
 
 The earliest Myriopods thus far discovered are from the 
 Old Red Sandstone of Scotland. 
 
 PIGS. 288-294. 
 
 BRACHIOPODS: Fig. 288, Atrypa aspera; 289, Spirifer pennatus; 290, Chonetes setigerus. 
 LAMELLIBRANOHS : Fig. 291, Grammysia bisulcata ; 292, Microdon bellistriatus. 
 CEPHALOPOD: Figs. 293, 293 a, Goniatites Vanuxemi. TRILOBITE : Fig. 294, Phacops 
 rana. All from Hamilton group. 
 
 Vertebrates. The Fishes of the Devonian belong to 
 four subclasses : 1, Selachians ; 2, Placoderms ; 3, Gran- 
 
284 
 
 HISTORICAL GEOLOGY. 
 
 These groups have been defined on 
 
 FIG. 295. 
 
 oids; 4, Dipnoans. 
 pages 81-84. 
 
 The Selachians, or Sharks, belong, for the most part, to 
 the family of Cestracionts, in which the mouth has a pave- 
 ment of broad, flat-crowned teeth for grinding, as shown 
 in Figs. 129-131, on paga 82. There were species as 
 
 large as the largest of modern 
 time. Fig. 296 represents a 
 fin spine of a shark, two thirds 
 its actual size, from the Cor- 
 niferous beds of New York. 
 
 The Placoderms are an ex- 
 tremely aberrant group, known 
 exclusively as Silurian and De- 
 vonian fossils. Some of them 
 are represented in Figs. 297-300. Figs. 297-299 are 
 Fishes from the Old Red Sandstone of Great Britain. 
 Fig. 300 is a gigantic Placoderm from Ohio, named by 
 
 FIG. 296. 
 
 INSECT : wing of Platephemera antiqua. 
 
 SELACHIAN : fin spine of Mackseracanthus sulcatus, x . 
 
 Newberry DinichtJiys (Greek Se^o'?, terrible, t'x#tfc, fish), 
 which had a head four feet wide. 
 
 As the Placoderms are known only in fossil condition, 
 their true nature is somewhat problematical. Some of 
 them, as CepTialaspis and Pterichthys (Figs. 297, 298), 
 appear to have had no lower jaw (at least, none capable 
 of fossilization). It is doubtful whether they were truly 
 Fishes. Others, as Coccosteus and the gigantic Dinich- 
 tJiys (Figs. 299, 300), had well-developed jaws, and are 
 believed by many paleontologists to have been an aberrant 
 group of Dipnoans. 
 
 One of the G-anoids is shown in Fig. 301. The Ganoids 
 
DEVONIAN ERA. 
 
 285 
 
 PLACODERMS : Fig. 29T, Cephalaspis Lyelll, x|; 29T a, 6, scales of same; 298, Pterichthys 
 Milled, x | ; 299, Coccosteus decipiens, x $ ; 300, Dinichthys Hertzeri. front view of 
 jaws, x &. 
 
286 
 
 HISTORICAL GEOLOGY. 
 
 are now represented by only a few species, among which 
 is the Gar Pike of North American lakes and rivers. 
 
 The Dipnoans are in many respects similar to the 
 Ganoids, but they show a close relation to the Am- 
 phibians in the structure of the heart and of the skull. 
 They are at present even less numerous than the Ganoids. 
 One of the Devonian Dipnoans is represented in Fig. 302. 
 The figure shows the vertebrated (heterocercal) tail. 
 A vertebrated tail (heterocercal or diphy cereal) was 
 
 FIGS. 301, 302. 
 
 801a 
 
 GANOID : Fig. 301, Holoptychius, x f ; 301 a-, scale of same. DIPNOAN : Fig. 302, Dipterus 
 macrolepidotus, x ; 302 a, scale of same. 
 
 generally characteristic of Paleozoic Fishes, whether 
 Selachians, Ganoids, or Dipnoans. The vertebrated 
 character of the tail has been retained by Selachians and 
 Dipnoans to the present time ; but most of the Ganoids 
 after the Paleozoic have the tail homocercal. 
 
 An impression supposed to be the track of an Amphibian 
 was found in 1896, in the Upper Devonian rocks of western 
 Pennsylvania. This is the most ancient representative yet 
 discovered of the classes of Vertebrates above Fishes. 
 
 
DEVONIAN ERA. 
 
 28T 
 
 GENERAL OBSERVATIONS. 
 
 Geography. During the Silurian, there had been a 
 gradual gain of dry land, extending the Archaean con- 
 tinent southward (page 272). This gain continued 
 through the Devonian, so that the formations of the next 
 era, the Carboniferous, extend only a short distance north 
 
 FIG. 303. 
 
 Map of part of North America at the commencement of the Carboniferous era. 
 
 of the southern boundary of New York. The seashore 
 was thus being set farther and farther southward with the 
 successive periods. The Cincinnati Island became con- 
 nected with the mainland, becoming the extremity of a 
 peninsula extending southeastward from northern Illi- 
 nois. The Eastern Interior sea thus acquired more dis- 
 
288 HISTORICAL GEOLOGY. 
 
 tinctly the character of a bay. The Tennessee Island be- 
 came submerged. The map, Fig. 303, illustrates the geo- 
 graphical progress during the Devonian. 
 
 The formations have their greatest thickness along the 
 Appalachian region, in the Devonian era, as in the Silu- 
 rian. And both this fact and the succession of different 
 kinds of strata lead to the general conclusions stated on 
 page 275. The Devonian age passed quietly for the 
 larger part of the North American continent, without any 
 tilting of the rocks ; yet not without wide, though small, 
 changes of level, varying the limits and depth of the 
 Interior sea, such changes of level and of limits being 
 indicated by the varying limits of the rocks, all of which 
 are of marine origin. This quiet was not interrupted 
 between the Devonian and Carboniferous eras, so far as 
 yet discovered, except to the northeast in the region of 
 New Brunswick, Nova Scotia, and northeastern Maine. 
 There an upturning and flexing of the beds occurred, and, 
 as a result, some mountain-making. 
 
 In Europe, also, the Devonian and Carboniferous strata 
 are conformable, with only slight local exceptions. 
 
 Life. The great features of the Devonian age are 
 the occurrence of forests of Acrogens and Gymnosperms ; 
 the increasing number of Insects and the first appearance 
 of Myriopods, among terrestrial Arthropods; and the 
 great abundance and variety of Fishes, and the first ap- 
 pearance of Amphibians. 
 
 That Acrogens should have appeared in the Silurian 
 and Devonian, while no traces have been found of the 
 more lowly organized terrestrial plants, which, according 
 to the theory of evolution, might have been expected to 
 precede the Acrogens, will not appear strange when it is 
 remembered that the Acrogens are the lowest plants 
 which contain wood in their tissues. A Seaweed, in spite 
 of the perishable nature of its tissues, may readily be pre- 
 served as a fossil, since the station in which it lives affords 
 the opportunity for it to be buried before it has time to 
 
 
DEVONIAN BRA. 289 
 
 decompose. But a woodless terrestrial plant can be pre- 
 served as a fossil only by a very exceptional combination 
 of circumstances. 
 
 That Gymnosperms should have been the earliest of 
 Phanerogams is of course precisely what would be ex- 
 pected. The step of progress from Acrogens to Gymno- 
 sperms is a short one. 
 
 The fact that Vertebrates should have commenced in 
 the Silurian and Devonian with somewhat highly organ- 
 ized forms, is a case somewhat analogous with that of the 
 Acrogens. According to the theory of evolution, the 
 primitive Vertebrates should have been creatures allied to 
 the Leptocardians. But Leptocardians (as represented by 
 Ampliioxus) have neither bones, teeth, scales, nor fin spines 
 nothing, in fact, capable, under any ordinary conditions, 
 of being preserved in fossil condition. The class of 
 Marsipobranchs seems not much better fitted for fossiliza- 
 tion, though the living members of the class do have little 
 teeth implanted in the mucous membrane of the mouth, 
 which might be preserved in scattered condition. When 
 a Vertebrate has acquired sufficient skeletal development 
 to have a good chance of preservation, it is already a Fish. 
 The Selachians, though showing some noteworthy features 
 of high grade, are the Fishes which most resemble the Mar- 
 sipobranchs, and which would be expected to be the earliest 
 of true Fishes. The Teleosts, now the most abundant of 
 Fishes, are wanting in Paleozoic and early Mesozoic time. 
 As the most specialized of Fishes, it would naturally be 
 expected that they would be a late development. 
 
 Economic Products ; Mineral Oil and Gas. The oil 
 wells of Enniskillen, Canada, as already stated, are in 
 the Corniferous; but the "oil horizon" of Pennsylvania, 
 the most important in North America, belongs to the 
 Upper Devonian. The oil region forms a belt about 40 
 miles wide, extending across western Pennsylvania, from 
 Monongalia County, West Virginia, to Allegany County, 
 New York. This belt contains many productive areas, and 
 
290 HISTORICAL GEOLOGY. 
 
 hundreds of oil wells. In 1891 the wells near Bradford, in 
 McKean County, yielded nearly 5J millions of barrels of 
 oil ; those of Allegheny County, in which Pittsburg is 
 situated, yielded over 10J millions ; and all western Penn- 
 sylvania nearly 32 millions. All the other oil regions of 
 the United States yielded in 1891 about 22 millions, and 
 of this 17J millions were from Ohio. A barrel holds 
 42 gallons. The rock to which the Pennsylvania wells 
 descend is usually a coarse and very porous sandstone ; 
 the oil is in its pores. It is supposed by most writers on 
 the subject that the oil in the "oil sands "was derived 
 from subjacent black or carbonaceous shales, like the 
 Genesee or Marcellus, by means of a gentle heating of 
 the rocks during a period of upturning, and that it 
 became condensed in the pores or cavities of the rocks 
 above. Such shales, like coal, do not contain the oil, at 
 least not in large quantity ; but they contain hydrocar- 
 bon compounds which yield oil when heated. But others 
 have thought that the " oil sands " originally contained 
 the vegetable or animal debris from which the contained 
 oil was made by decomposition. A third view is that the 
 oil has ascended into the porous sandstones by hydrostatic 
 pressure from underlying shales in which it was formed. 
 On any view, the oil is derived directly or indirectly 
 from the decomposition of organic materials. The gas 
 comes from the same regions as the oil. But it appears 
 to be mostly obtained from anticlinal belts, since it rises 
 above the heavier oil and water contained in the porous 
 strata to the highest parts of those strata. 
 
 III. CARBONIFEROUS ERA. 
 
 GENERAL CHARACTERISTICS: SUBDIVISIONS. 
 
 The Carboniferous era was remarkable, in general, for: 
 1. A low elevation of large areas of the continents 
 above the sea level, alternating with shallow submer- 
 gences of the same. 
 
CARBONIFEROUS ERA. 291 
 
 2. Extensive marshy or fresh-water areas over large 
 portions of these low continents. 
 
 3. Luxuriant vegetation, covering the land with forests 
 and jungles. 
 
 4. A great increase in terrestrial animal life Snails, 
 Scorpions, Spiders, Centipedes, Insects, over the land, and 
 Amphibians in the marshes. In the closing period of the 
 era, true Reptiles appeared. 
 
 But, while having these as its main characteristics, it 
 was not an age of continuous verdure. There was, first, a 
 long period the jSubcarboniferous in which the land 
 was largely beneath the sea; for limestone, full of marine 
 fossils, is the prevailing rock, and there are but few, and 
 mostly thin, coal beds intercalated among the sandstones 
 and shales. This period was followed by the Carbonifer- 
 ous, or that of the true Coal Measures. Yet, even in this 
 middle period of the era, there were alternations of sub- 
 merged with emerged continents, long times of dry and 
 marshy lands luxuriantly overgrown with shrubbery and 
 forest trees, intervening between other long times of great 
 continental seas. Then there was a closing period the 
 Permian, in which the ocean prevailed again, though 
 with narrower limits than in the Subcarboniferous ; for 
 the rocks are mainly of marine origin. 
 
 The Carboniferous era and period were so named from 
 the fact that most of the great coal beds of the world 
 originated during their progress. The term Permian was 
 given to the rocks of the third period by Murchison, De 
 Verneuil, and Keyserling, from a region of Permian rocks 
 in Russia, the ancient country of Permia, a part of which 
 now constitutes the government of Perm. 
 
 DISTRIBUTION OF CARBONIFEROUS ROCKS. 
 
 The Carboniferous areas on the map of the United 
 States (page 235) are the dark areas ; the heavily cross- 
 lined areas being the Subcarboniferous; the pure black, 
 the Carboniferous and Permian. 
 
292 
 
 HISTORICAL GEOLOGY. 
 
 The following are the positions of the several great coal 
 areas in North America : 
 
 1. Atlantic Border Region. 1. The Nova Scotia and 
 New Brunswick area. 
 
 2. The Rhode Island area, extending from Newport in 
 Rhode Island northward into Massachusetts. 
 
 2. Appalachian and Interior Region. 1. The great 
 Appalachian area, extending from the southern border of 
 New York southwestward to Alabama, covering the larger 
 part of Pennsylvania, half of Ohio, part of Kentucky and 
 
CARBONIFEROUS ERA. 293 
 
 Tennessee, and a portion of Alabama. To the northeast 
 in Pennsylvania this coaf held is much broken into 
 patches, as shown in the accompanying map of a part 
 of the state, the black areas being those of the coal 
 district. 
 
 2. The Michigan area, covering the central part of the 
 state of Michigan. 
 
 3. The Illinois-Indiana area, covering much of Illinois, 
 and part of Indiana and Kentucky. 
 
 4. The Iowa-Texas area, covering part of Iowa, Nebraska, 
 Missouri, Kansas, Arkansas, and northern Texas. 
 
 3. Arctic Region. On Melville Island, and other 
 islands between Grinnell Land and Banks Land, mostly 
 north of latitude 70. 
 
 Besides these, there is a small barren Carboniferous area 
 about Worcester, Massachusetts, and much more extensive 
 barren regions about the slopes and summits of the Rocky 
 Mountains, around the Great Salt Lake in Utah, and in 
 California the workable coal beds of the Rocky Moun- 
 tain region and Pacific slope being Cretaceous or Ter- 
 tiary. 
 
 The areas of the Coal Measures in North America have 
 been estimated as follows : 
 
 1. Nova Scotia and New Brunswick . 18,000 square miles. 
 
 2. Rhode Island . . . . . 500 " " 
 
 3. Appalachian 65,000 
 
 4. Michigan . . ". . . . 7,000 " " 
 
 5. Illinois-Indiana . v , '.'"* 48,000 " " 
 
 6. Iowa-Texas ..... . . 98,000 " " 
 
 But of these the workable portion probably does not 
 exceed 120,000 square miles. 
 
 Carboniferous strata occur also in Great Britain and 
 various parts of Europe*. The beds in England (as shown 
 in map, Fig. 305) are distributed over an area between 
 South Wales on the west and the Newcastle 'basin on the 
 northeast coast. The most important for coal are the 
 South Wales region ; the Lancashire district, bordering on 
 
294 HISTORICAL GEOLOGY. 
 
 Manchester and Liverpool , the Yorkshire, about Leeda 
 and Sheffield ; and the Newcastle. In South Wales the 
 thickness of the Coal Measures is 7000 to 12,000 feet, with 
 more than 100 coal beds, 70 of which are worked. 
 
 Scotland has some small areas between the Grampian 
 range on the north and the Lammermuirs on the south ; 
 and Ireland, several coal regions of large extent. 
 
 The coal fields of the continent of Europe that are 
 most worked are the Belgian, bordering on and passing 
 into France. Germany contains small coal-bearing areas 
 in Rhenish Prussia, Westphalia, and Silesia. Russia in 
 Europe affords very little coal, although rocks of the 
 Carboniferous era cover large portions of the surface. 
 
 The area of the Coal Measures in Great Britain and 
 Ireland is about 12,000 square miles ; in Spain, 4000 ; in 
 France, 2000 ; Germany, 1800 ; Belgium, 518. 
 
 Coal beds of Carboniferous age occur also in China and 
 in Spitzbergen. Valuable coal beds of Permian age occur 
 in India (in the Lower Gondwana series) and in Australia. 
 
 Valuable coal beds are not found in any rocks older 
 than those of the Carboniferous era, although black car- 
 bonaceous shales are not uncommon even in the Lower 
 Silurian. They occur, however, in various Mesozoic for- 
 mations, and also in the Cenozoic, but not on so extensive 
 a scale as in the Carboniferous formations. 
 
 KINDS OP ROCKS. 
 
 1. Subcarboniferous Period. The Subcarboniferous 
 strata in the Central Interior region are mainly limestone ; 
 and, as the limestone abounds in many places in Crinoidal 
 remains, the rock is often called the Crinoidal Limestone. 
 In the Appalachian region, in southwestern Virginia, Ten- 
 nessee, and Alabama, the rock is also in large part lime- 
 stone, and has great thickness ; but farther north, in West 
 Virginia and Pennsylvania, it is mostly a sandstone or con- 
 glomerate (Pocono group), overlain by shaly sandstones and 
 shales of reddish and other colors CMauch Chunk group) 
 
CARBONIFEROUS ERA. 
 
 295 
 
 the whole having a maximum thickness of 4000 to 
 5000 feet. In the Atlantic Border region, in Nova Scotia, 
 the rocks are mostly reddish sandstone and shale, with 
 
 FIG. 305. 
 
 Geological map of England and southern Scotland. The small white areas are those of 
 igneous rocks. The areas numbered 1 are Cambrian and Silurian ; 2, Devonian ; 8, Sub- 
 carboniferous and Millstone Grit; 4, Coal Measures; 5, Permian; 6, Triassic ; 7, Lias; 
 8, Oolite ; 9, Wealden ; 10, Cretaceous (exclusive of Wealden) ; 11, Tertiary. A is London ; 
 B, Liverpool ; C, Manchester : D, Newcastle : E, Gla<row 
 
296 HISTORICAL GEOLOGY. 
 
 some limestone the estimated thickness 6000 feet. In 
 Michigan and Ohio the Subcarboniferous rocks yield brines, 
 which are used for the manufacture of salt. 
 
 The prevailing rock in Great Britain and Europe is a 
 limestone, called the Mountain Limestone. In Northum- 
 berland and Scotland, the Subcarboniferous consists chiefly 
 of sandstones, and contains productive coal beds. 
 
 2. Carboniferous Period. The base of the series of 
 Carboniferous rocks is generally formed by a hard, gritty 
 sandstone or conglomerate, called in England the Millstone 
 Grit from its frequent use for millstones. A similar rock 
 in Pennsylvania is called the Pottsville Conglomerate. In 
 the center of the Anthracite region it attains a thickness 
 of 800 to 1700 feet, but thins out westward. In parts of 
 Pennsylvania the Pottsville Conglomerate contains beds 
 of coal. In Nova Scotia, the Millstone Grit is 5000 to 
 6000 -feet thick. 
 
 This conglomerate is overlain by the Coal Measures 
 proper. The rocks of the Coal Measures are sandstones, 
 shales, conglomerates, and occasionally limestones ; and 
 they are so similar to the rocks of the Devonian and 
 Silurian ages that they cannot be distinguished except by 
 the fossils. They occur in various alternations, with an 
 occasional bed of coal between them. The coal beds, taken 
 together, generally make up not more than one fiftieth of 
 the whole thickness ; that is, there are i-n general 50 feet 
 or more of barren rock to 1 foot of coal. The maximum 
 thickness in Pennsylvania is nearly 3000 feet; in Nova 
 Scotia, about 5000 feet. 
 
 Although coal beds may occur in any part of the Coal 
 Measures, they are often very unequally distributed through 
 the series. In Pennsylvania three divisions of the series 
 are recognized: (1) the Lower Productive Measures, (2) 
 the Lower Barren Measures, (8) the Upper Productive 
 Measures. The second of these divisions contains only 
 thin and insignificant coal beds. The Upper Barren 
 Measures, overlying the Upper Productive Measures, be- 
 
 

 CARBONIFEROUS EKA. 
 
 297 
 
 long to the Permian. In the coal field of South Wales, 
 the Coal Measures are similarly divided into two parts 
 by a great thickness of barren sandstone. 
 
 The limestone strata are more numerous and extensive 
 in the Central Interior region than in the Appalachian; 
 west of the states of Missouri and Kansas, limestone is the 
 prevailing rock. In Kansas and in West Virginia the 
 rocks afford brines. 
 
 Beds of argillaceous iron ore or clay ironstone are very 
 common in coal districts, so that the same region affords 
 ore and the coal for smelting it. Some of the largest iron 
 works in the world, on both sides of the Atlantic, occur 
 
 FIG. 806. 
 
 Section of a portion of the Coal Measures at the Joggins, Nova Scotia, having erect stump . 
 and also roots in the underclays. 
 
 in coal di3tricts. The ore is usually siderite, or iron car- 
 bonate (more rarely, limonite), impure from mixture with 
 some earth or clay. 
 
 The coal beds often rest on a bed of grajdsh or bluish 
 clay, called the underclay, which is filled with the roots or 
 underground stems of plants. When this underclay is 
 absent, the rock below is usually a sandstone or a shale. 
 Above the coal bed the rock may be sandstone, shale, con- 
 glomerate, or even limestone; often the layer next above, 
 especially if shaly, is filled with fossil leaves and stems. 
 In some cases, trunks of old trees rise from the coal and 
 extend up through overlying beds, as shown in Fig. 306, 
 by Dawson, from the Nova Scotia Coal Measures. Occa- 
 
298 HISTORICAL GEOLOGY. 
 
 sionally, as in Ohio and Pennsylvania, logs 50 to 60 feet 
 long lie scattered through the sandstone beds, looking as 
 if a forest had been swept off from the land into the sea. 
 
 The coal beds vary in thickness from a fraction of an 
 inch to scores of feet, but seldom exceed 8 feet, and are 
 generally much thinner. Eight to 10 feet is the thick- 
 ness of the principal bed at Pittsburg, Pennsylvania; 50 
 feet or more, the thickness (in some places) of the "Mam- 
 moth" bed of the Anthracite region of Pennsylvania; 38 
 feet, that of one of the two great beds at Pictou in Nova 
 Scotia. In these thick beds, and often also in the thin 
 ones, there are some intervening beds of shale, or of very 
 impure coal, so that only a part is fit for burning. 
 
 The coal varies in kind, as explained on page 25 ; that 
 yielding only about 5 per cent of volatile hydrocarbons, 
 and burning with little flame, being called anthracite ; and 
 that yielding 20 to 50 per cent of volatile hydrocarbons, 
 and burning with a bright yellow flame, bituminous coal. 
 Varieties intermediate between the typical anthracite and 
 bituminous coal are often called semi-bituminous coal. The 
 coal of the Pottsville, Lehigh, and Wilkesbarre regions in 
 Pennsylvania is anthracite; that of Pittsburg and the West, 
 bituminous coal; and that of part of the intermediate dis- 
 trict, semi-bituminous, as designated on the map, page 292. 
 
 The coal also varies as to the impurities present. All of 
 it contains more or less of earthy material, and this con- 
 stitutes the ashes and slag of a coal fire. Ordinary good 
 anthracite contains 4 to 8 pounds of impurities in a 
 hundred pounds of coal, and the best bituminous coals 
 1 to 6. In some coal beds there is much iron sulphide, or 
 pyrite, and the coal is then unfit for use. It is seldom 
 that the sulphide is altogether absent; it is the chief source 
 of the sulphur gases that are perceived in the smoke or gas 
 from a coal fire. 
 
 Mineral coal, although it seldom breaks into plates unless 
 quite impure, still consists of thin layers. Even the hardest 
 anthracite is delicately banded, as seen on a surface of f rac- 
 

 CARBONIFEROUS ERA. 299 
 
 ture when it is held up to the light. This structure is absent 
 in the variety called cannel coal, which is a bituminous coal, 
 very compact in texture, feeble in luster, and smooth in 
 fracture. 
 
 3. Permian Period. The upper part of the Carbonifer- 
 ous formation (Upper Barren Measures) of Pennsylvania 
 and Virginia has been shown by its fossil plants, and that 
 of Illinois, Kansas, and Texas, by its Reptiles and Mol- 
 lusks, to be Permian. The uppermost strata in the Aca- 
 dian Coal area also are Permian. Permian strata occur 
 also in the Rocky Mountain region. The rocks are mostly 
 reddish and gray sandstones and shales, with some impure 
 limestone. The Permian strata of Texas have been in- 
 cluded with the Triassic, under the name Red Beds. In 
 Kansas the rocks include a large amount of limestone. 
 Similar red and gray sandstones and shales occur in Great 
 Britain, in the vicinity of several of the Coal regions, and 
 also in Germany and Russia. The Permian rocks of 
 Great Britain were formerly included with the Triassic 
 under the name New Red Sandstone. 
 
 In India and in Australia, the Permian formation con- 
 tains valuable beds of coal. 
 
 In England, India, Australia, South Africa, and south- 
 ern Brazil, the Permian includes a conglomerate with 
 bowlders of great size, some of which show subangular 
 forms and smoothed and striated surfaces, like those of 
 glaciated bowlders (pages 164, 408). While some geolo- 
 gists have not hesitated to infer the existence of a glacial 
 climate in those regions, others believe that a conclusion 
 so startling requires confirmation. 
 
 LIFE. 
 PLANTS. 
 
 The plants of the forests, jungles, and floating islands 
 of the Carboniferous age, thus far made known, number 
 nearly 2000 species. Among the fossils there are none 
 
300 
 
 HISTORICAL GEOLOGY. 
 
 that afford satisfactory evidence of the presence of Angio- 
 sperms. There were no Oaks, nor Maples, nor Palms in 
 the forests, and the plains were without grass. At the 
 
 FIGS. 307-312. 
 
 309 
 
 ACROGENS : Fig. 307, Lepidodendron aculeatum ; 308, Sigillaria oculata ; 309, Stigmaria 
 ficoides ; 310, Sphenopteris Gravenhorstii ; 311, Calamites cannaeforinis. GYMNOSPERM : 
 Fig. 312, Trigonocarpus. 
 
 present day, Angiosperms, along with Conifers, make up 
 the great bulk of our shrubs and trees ; Palms abound 
 in all tropical countries; and grass covers all exposed 
 slopes where the climate is not too arid. 
 
CARBONIFEROUS ERA. 301 
 
 Cryptogams. The Carboniferous species, like their 
 predecessors in the Devonian age, belonged mostly to 
 the following groups : 
 
 1. Ferns. Ferns were very abundant, a large part of 
 the fossils of a coal region being their delicate fronds, or 
 leaves. A portion of a fossil Fern is represented in Fig. 
 310. Besides small species, like the common kinds of the 
 present day, there were (as is now the case in the tropics) 
 Tree Ferns species that had a trunk, perhaps 20 or 30 
 feet high, which bore at top a radiating tuft of very large 
 fronds. Tree Ferns, however, were not very common in 
 the Carboniferous forests. The scars in fossil or recent 
 Tree Ferns are many times larger than those of Lepidoden- 
 drids, and the fossils may be thus distinguished. 
 
 2. Lycopods. The Lepidodendrids appear to have been 
 among the most abundant of Carboniferous forest trees, 
 especially in the earlier half of the era, or to the middle 
 of the Coal Measures. They probably covered both the 
 marshes and the drier plains and hills. Some of the old 
 logs now preserved in the strata are 50 to 60 feet in length, 
 strikingly contrasting with the little Ground Pines of mod- 
 ern times; and the pinelike leaves were occasionally a foot 
 or more long. Fig: 307 shows the surface markings of 
 one of the species, natural size. 
 
 The SigiUaricB were a very marked feature of the great 
 jungles and deep forests of the Coal period. They grew 
 to a height sometimes of 30 to 60 feet ; but the trunks 
 were seldom branched, and must have had a stiff, clumsy 
 aspect, although covered above with long, slender, rush-, 
 like leaves. Fig. 308 represents a common species, ex- 
 hibiting the usual arrangement of the scars in vertical 
 lines, and also indicating, by the difference between the 
 scars of the right row and the others, their difference of 
 form on the outer surface of* the tree and beneath the rind. 
 
 The fossil Stigmarice are stout stemlike bodies, generally 
 2 to 3 or more inches thick, having over the surface distinct 
 rounded depressions, or scars. Fig. 309 is a portion of 
 
302 HISTORICAL GEOLOGY. 
 
 the extremity of a stem, showing the rounded depressions, 
 and also the appendages (rootlets) whose position, when 
 they have decayed or fallen off, is marked by the scars, 
 and which are occasionally observed in place. The stems 
 are a little irregular in form, and sparingly branched. 
 They have been found spreading, like roots, from the base 
 of the trunk of a Sigillaria, and sometimes also from that 
 of a Lepidodendron ; arid they are hence regarded as the 
 roots or rootstocks of these trees. They are an exceed- 
 ingly common fossil, especially in the underclays of the 
 Coal Measures (page 297). 
 
 3. Equiseta. Fig. 311 represents a portion of one of 
 the Tree Rushes, or Calamites, of the Equisetum, or Horse- 
 tail group. These plants were very abundant in the 
 great marshes, through the whole of the era. Some of 
 them were 20 feet or more in height, and 10 or 12 inches 
 in diameter. 
 
 Besides these Acrogens, a few remains of Fungi have 
 been found, but, as yet, no remains of Mosses. A Moss, 
 however, could only be preserved as a fossil under very 
 exceptional conditions; and in such a case the negative 
 evidence is of little value. 
 
 Phanerogams. As in the Devonian era, both Conifers 
 and Cycads were probably present. Some of the genera 
 seem to show characters intermediate between these two 
 types. - 
 
 Trunks of trees, Coniferous in character, are not uncom- 
 mon. 
 
 There are also various nutlike fruits found in the Car- 
 boniferous strata. One is represented in Fig. 312 (page 
 300), the figure to the left being that of the shell, and the 
 other that of the nut which it contained. Some of them 
 are two inches in length. Thejnost of them were probably 
 the fruit of Conifers, but possibly of Cycads. 
 
 It is seen from the above that 
 
 1. The vegetation of the Carboniferous era consisted 
 very largely of Cryptogams, or flowerless plants. 
 
CARBONIFEROUS ERA. 303 
 
 2. The flowering plants, or Phanerogams, associated 
 with the flowerless vegetation, were of the class of Gym- 
 nosperms, whose flowers are simple and inconspicuous. 
 
 . 3. While, therefore, there was abundant and beautiful 
 foliage (for no foliage exceeds in beauty that of Ferns), 
 the vegetation was nearly flowerless. 
 
 4. The characteristic Cryptogams were not only of the 
 highest group of that division of plants, but many of them 
 exceeded in size and in complexity of organization the 
 species of the present day. 
 
 ANIMALS. 
 
 Coelenterates. Fig. 313 presents a view of the upper 
 surface of a very common Coral of the Subcarboniferous 
 period : it has a columnar appearance in a side view. 
 
 Echinoderms. Crinoids were especially numerous in 
 the Subcarboniferous period. Figs. 314-316 represent 
 some of the species. Figs. 314, 315, are Brachiate 
 Crinoids. In the former, the arms are perfect; in the 
 latter, they have been broken off. Fig. 316 is a repre- 
 sentative of the Blastoids, a group which commenced in 
 the Upper Silurian, attained its maximum development 
 in the Subcarboniferous, and became extinct at the close 
 of the Carboniferous period. 
 
 Molluscoids. The class of Bryozoans included the 
 singular screw-shaped (or auger-shaped) Coral shown in 
 Fig. 317, and named Archimedes (referring to Archimedes' 
 screw). The upper, or inner, surface of the spiral lamina 
 shows the orifices of the cells, each of which, when alive, 
 contained a minute individual of the colony (page 70). 
 These fossils are common in some of the Subcarboniferous 
 limestone strata. 
 
 Brachiopods were very abundant through the Carbon- 
 iferous age, and especially species of the genera Spirifer 
 and Productus. Figs. 318-321 are of species from the 
 American Coal Measures. 
 
304 
 
 HISTORICAL GEOLOGY. 
 
 Mollusks. Fig. 322 represents one of the marine Gas- 
 tropods of the Coal Measures. Fig. 323 is a Pupa, the earli- 
 
 FIGS. 313-323. 
 
 ANTHOZOAN : Fig. 313, Lithbstrotion Canadense. CRINOIDS : Fig. 314, Woodocrinus elegans; 
 315, Actinocrinus proboscidialis ; 316, Pentremites pyrifonnis. BRYOZOAN : Fig. 317, 
 Archimedes Wortheni. BRACHIOPODS: 318, Chonetes mesolobus ; 319, Productus Ne- 
 brascensis; 320, Athyris subtilita; 321, Spirifer cameratus. GASTROPODS : 322, Pleu- 
 rotomaria tabulata ; 323, Pupa vetusta. 
 
 est yet found of Land Snails : it is from the Coal Measures 
 of Nova Scotia ; others have been found in Illinois. The 
 class of Cephalopods was represented by few and small 
 
CARBONIFEROUS ERA. 
 
 305 
 
 FIG. 324. 
 
 species of the old group of Orthocerata, but by many of 
 the Ammonite-like Goniatites. 
 
 Arthropods. Trilobites, which 
 had been in earlier times the domi- 
 nant group of Crustaceans, were 
 rare in the Carboniferous era, and 
 entirely disappeared at its close. 
 The Macruran Decapods, which 
 had commenced in the Devonian, 
 became more abundant. One of 
 them is represented in Fig. 324. 
 
 Arachnoids were represented 
 by Scorpions (Fig. 325) and Spi- 
 ders (Fig. 326), the latter group 
 making their first appearance in 
 this era. Insects were represented 
 by. Myriopods (Fig. 327) and 
 Hexapods. Among the Hexapods, the Orthopters were 
 abundantly represented by Cockroaches (Fig. 328) and 
 
 FIG. 325. 
 
 DECAPOD : Anthracopalaemon 
 gracilis. 
 
 L 
 
 ARACHNOID : Eoscorpius carbonarius. 
 
 Locusts, and the Pseudoneuropters by May-flies. Fig. 
 329 represents an Insect which is either a Pseudoneuropter 
 
306 
 
 HISTORICAL GEOLOGY. 
 
 or a Neuropter, those two orders being often undistinguish- 
 able in fossil condition. The earliest remains of Hemipters 
 occur in the Permian. Remains of Beetles (Coleopters) 
 have been doubtfully reported from the Subcarboniferous 
 of Silesia. With doubtful exceptions, the higher orders 
 of Insects, characterised by passing through an inactive 
 pupa stage (complete metamorphosis), are wanting in the 
 Paleozoic. 
 
 Vertebrates. Fishes were numerous, including Selach- 
 ians, Ganoids, and Dipnoans. Many of the Selachians 
 
 FIGS. 326-329. 
 
 ARACHNOID : Fig. 326, Arthrolycosa antiqua. MYRIOPOD: FIG. 327, Xylobius sigillarise. 
 HEXAPODS: Fig. 328, wing of Etoblattina venusta; 329, Miamia Bronsoni. 
 
 were of great size, as shown by the fin spines. Fig. 331 
 represents a small portion of one of these spines, natural 
 size, from the Subcarboniferous beds of Europe. One of 
 the largest specimens of a spine of the same species, when 
 entire, must have been 18 inches long. Nearly all the 
 Ganoids had vertebrated tails, as shown in Fig. 330, 
 which represents a common Permian species. 
 
 Amphibians occur throughout the era. They all belong 
 to an order which became extinct at the close of the 
 Triassic or during the Jurassic. Unlike the Frogs and 
 
CARBONIFEROUS ERA. 
 
 307 
 
 Salamanders, their skulls had a complete bony roof (Fig. 
 384, page 352), which has suggested the name Stego- 
 cephala, from oreyo>, to cover, and /ce^aXt;, head. Many 
 of the species show a complicated structure of the teeth, 
 the cementum forming a series of folds which penetrate 
 to a greater or less depth into the dentine. These laby- 
 rinthine teeth have suggested the name Labyrinthodonts. 
 This peculiarity they share with many Ganoid Fishes. It 
 
 FISHES: Fig. 330, Pala-oniscus Freieslebeni, x J ; 331, part of a spine of Ctenacanthus major. 
 
 is shown in a comparatively simple form in the recent 
 Lepidosteus (Fig. 140, page 84). It becomes much more 
 complex in some of the Triassic Labyrinthodonts. The 
 earliest traces of Amphibians known (until the recent 
 discovery of Devonian tracks, mentioned on page 286) 
 are tracks found in the Subcarboniferous beds at Potts- 
 ville, Pennsylvania (Fig. 332) ; they are about four inches 
 broad, those of the fore feet, as described by Dr. Lea, 
 5-toed, and those of the hind feet 4-toed. Fig. 333 repre- 
 sents a skeleton of another species from the Ohio Coal 
 Measures. Some of the related Amphibians from Ohio 
 are long and destitute of limbs, like Snakes. 
 
308 
 
 HISTORICAL GEOLOGY, 
 
 Reptiles made their first appearance in the Permian. 
 Two orders of Reptiles were represented : (1) the Rhyn- 
 chocephala, a group represented by numerous Permian and 
 
 FIGS. 832, 833. 
 
 AMPHIBIANS : Fig. 332, tracks of Sauropus primsevus, x f ; 383, Pelion Lyellii. 
 
 Mesozoic species, but now nearly extinct, a single genus 
 surviving in New Zealand ; (2) the Theromorphs, a group 
 confined to the Permian and Triassic, remarkable for 
 certain striking resemblances to Mammals, particularly in 
 the skull. Fig. 334 shows the skull of one of the Rhyn- 
 chocephala, from the Permian of Saxony. 
 
CARBONIFEROUS ERA. 
 
 309 
 
 FIG. 834. 
 
 GENERAL OBSERVATIONS. 
 
 Mode of Formation of the Coal Measures. Origin of the 
 Coal. The vegetable origin of coal is proved by the 
 following facts: 
 
 1. Trunks of 
 trees, still retain- 
 ing the original 
 form and part of 
 the structure of the 
 wood, have been 
 found changed to 
 mineral coal, both 
 in the Carbonifer- 
 ous strata and in 
 more modern for- 
 mations, showing 
 that the change 
 may and does take 
 place. 
 
 2. Beds of peat, 
 
 a result of vegetable growth and accumulation, exist in 
 modern marshes ; and in some cases they are altered be- 
 low to an imperfect coal. (See page 107, on the formation 
 of peat.) 
 
 3. Remains of plants leaves, branches, and stems or 
 trunks abound in the Coal Measures ; trunks sometimes 
 extend upward from a coal bed into and through some of 
 the overlying beds of rock ; roots or stems abound in the 
 underclays. 
 
 4. The hardest anthracite contains throughout its mass 
 vegetable tissues. Professor Bailey examined with a high 
 magnifying power several pieces of anthracite burnt at 
 one end, like Fig. 335, taking fragments from the junc- 
 tion of the white and the black portion, and readily de- 
 tected the tissues. Fig. 336 represents the ducts, as they 
 
 REPTILE : Palaeohatteria longicaudata. 
 
310 
 
 HISTORICAL GEOLOGY. 
 
 appeared in one case under his microscope ; and Fig. 337, 
 part of the same, more magnified. Fig. 338 shows the 
 appearance of the spores of Lycopods (Lepidodendrids) 
 much magnified ; they are common in coal. 
 
 FIGS. 335-33T. 
 
 FIG. 338. 
 
 Vegetable tissues in anthracite. 
 
 Decomposition of Vegetable Material. The mineral coal 
 of the Coal Measures consists (impurities excluded) of 
 65 to 93 per cent of carbon, along with 2 to 9 of hydro- 
 gen, and 2 to 17 of oxygen ; 
 and woody material, whether 
 of Conifers, Ferns, Lycopods, 
 or Equiseta, consists of about 
 45 per cent of carbon, 6 of 
 hydrogen, and 49 of oxygen. 
 To change the vegetable ma- 
 terial to coal, it is necessary 
 to get rid of part of the oxy- 
 gen and hydrogen. Vegetable 
 matter decomposing in the 
 open air like wood burnt 
 
 Spores and part of a sporangium of Lepido- j n an open fire is COmplete- 
 
 dendron in bituminous coal of Ohio, x TO. . , . , , 
 
 ly oxidized, and passes on as 
 
 water vapor and carbon dioxide. Both the oxygen of the 
 air and that of the wood take part in the combustion or 
 decomposition. But, if the former is more or less excluded 
 by a covering of earth or of water (as in a swamp), the 
 
CARBONIFEROUS ERA. 311 
 
 combustion is incomplete, and coal may result, consisting 
 of the unconsumed carbon combined with some hydrogen 
 and oxygen. 
 
 The actual loss, by weight, in conversion into bitumi- 
 nous coal, is at least three fifths of the wood, and, in con- 
 version into anthracite, three fourths. Adding to this loss 
 that from compression, by which the material is brought 
 to the density of mineral coal, the whole reduction in bulk 
 is not less than four fifths for the former, and seven eighths 
 for the latter. In other words, it would take 5 cubic feet 
 of vegetable matter to make 1 of bituminous coal, and 8 
 feet to make 1 of anthracite. 
 
 Impurities in Coal. The coal thus formed derived some 
 silica and other earthy ingredients from the wood itself, 
 including probably, in the case of the Lepidodendrids, 
 some alumina, since this earth exists in the ash of modern 
 Lycopods. From this source the best coal received some 
 earthy impurities, while the poorer coals contain, in addi- 
 tion, clay or earthy material carried over the marshes by 
 the waters or winds. Sulphur is a common impurity; it 
 usually occurs combined with iron, forming pyrite, or sul- 
 phide of iron. 
 
 Accumulation and Formation of Coal Beds. The ori- 
 gin of coal beds was, then, as follows : The plants of the 
 great marshes and shallow lakes of the Carboniferous 
 period, the latter with their floating islands of vegetation, 
 continued growing for a long period, dropping annually 
 their leaves, and from time to time decaying stems or 
 branches, until a thick accumulation of vegetable remains 
 was formed probably 5 feet in thickness for a one-foot 
 bed of bituminous coal. The bed of material thus pre- 
 pared over the vast wet areas of the continent early com- 
 menced to undergo at bottom that slow decomposition the 
 final result of which is mineral ccal. But the alternation 
 of the coal beds with sandstones, shales, conglomerates, 
 and. limestones, shows that the long period of verdure was 
 followed by a period of overflowing waters, which dis- 
 
312 HISTORICAL GEOLOGY. 
 
 tributed sands, pebbles, earth, or the remains of the skele- 
 tons of aquatic organisms, over the old marsh", till scores 
 or hundreds of feet in depth of such deposits had been 
 made. In the Central Interior region of North America, 
 the overflowing waters were generally marine, as is proved 
 by marine fossils in the strata. Thus the bed of vegetable 
 material was buried ; and under this condition the process 
 of decomposition and change to mineral coal went forward 
 to its completion ; it had the smothering influence of the 
 burial, as well as the presence of water, to favor the process. 
 
 Climate of the Age. The wide distribution of the 
 coal regions over the globe, from the tropics to remote 
 Arctic lands, and the general similarity of the vegetable 
 remains in the coal beds of these distant zones, prove that 
 there was a general uniformity of climate over the globe 
 in the Carboniferous period, or at least that the climate 
 was nowhere colder than warm-temperate. Besides, corals 
 and shells existed during the Subcarboniferous period 
 in Europe, the United States, and the Arctic regions 
 within 20 of the North Pole, and so profusely as to form 
 thick limestones out of their accumulations ; and some 
 Arctic species are identical with those of Europe and 
 America. The ocean's waters, even in the far north, 
 were, therefore, warm compared with those of the modern 
 temperate zone, and probably quite as warm as the coral- 
 reef seas of the present age, which lie mostly between the 
 parallels of 28 either side of the equator. This uniform 
 warm climate appears to have characterized the whole 
 of the Paleozoic, no clearly defined climatic zones being 
 indicated until a later period. Whether the bowlder 
 beds of the Permian (page 299) will require modification 
 of current opinions regarding Paleozoic climate, is at 
 present matter of doubt. 
 
 Atmosphere. The atmosphere contained a larger amount 
 than now of carbon dioxide the gas from which plants 
 derive their carbon. The mineral coal of the world 
 is approximately a measure of the amount of carbon 
 
CARBONIFEROUS ERA. 313 
 
 dioxide permanently withdrawn from the atmosphere by 
 the coal plants. The growth of the flora of that age 
 was a means of purifying the atmosphere, so as to fit 
 it for the higher terrestrial life that was afterward to 
 possess the world. The amount of carbon dioxide lost 
 by the atmosphere in the formation of carbonate of lime 
 and other carbonates, in the course of geological time, 
 is even greater than the loss by means of vegetation. 
 (See page 236.) 
 
 Again, the atmosphere was more moist than now. This 
 follows from the greater warmth of the climate, and the 
 greater extent and higher temperature of the oceans. 
 The land areas, although large, during the times of ver- 
 dure, compared with the land areas of the Devonian 
 or Silurian, were still small, and the land low. It must, 
 therefore, have been an era of prevailing clouds and mists 
 and abundant rains. But then, as now, there must have 
 been inequalities in the distribution of rain. America 
 is now the moist forest continent of the globe ; and the 
 great extent of the coal fields of its northern half suggests 
 that it may have borne the same character in the Carbo- 
 niferous age. 
 
 Geography. Appalachian and Rocky Mountains not yet 
 made. On page 290 it is stated that the continents 
 in this age were low, with few mountains. The non- 
 existence of the Appalachians of Pennsylvania and Vir- 
 ginia is proved by the fact that Carboniferous rocks 
 make up a part of the mass of these mountains partly 
 marine rocks, indicating that the sea then spread over 
 the region; partly coal beds, each bed evidence that a 
 great fresh-water marsh, flat as all marshes are, for a 
 long while occupied the region of the present mountains. 
 
 There is the same evidence that the mass of the Rocky 
 Mountains had not been lifted ; for marine Carboniferous 
 rocks constitute a large part of these mountains, many 
 beds containing remains of the life of the Carboniferous 
 seas that covered that part of North America. Only 
 
314 HISTORICAL GEOLOGY. 
 
 islands, or archipelagoes, made by Arahseah, and perhaps 
 also Paleozoic, ridges, existed in the midst of the wide- 
 spread western waters. 
 
 Condition in the Subcarloniferous Period. Through 
 the first period of this era, the Subcarboniferous, the 
 continent was almost as extensively beneath the sea as in 
 the Devonian. This is shown by the nature and extent 
 of the Subcarboniferous rocks the great Crinoidal Lime- 
 stones. 
 
 Transition to the Carboniferous Period. Finally, the 
 Subcarboniferous period closed, and the Carboniferous 
 opened. But, in the transition from the period of sub- 
 mergence to that of emergence, required to bring into 
 existence the great marshes, a widespread bed of pebbles, 
 gravel, and sand was accumulated by the waves dashing 
 rudely over the surface of the rising continent ; and these 
 pebble beds make the Pottsville Conglomerate, or Millstone 
 Grit, that marks the commencement of the Carboniferous 
 period in a large part of eastern North America, especially 
 along the Appalachian region, and also in Europe. 
 
 Coal-plant Areas in the Carboniferous Period. The 
 positions of the great Coal areas of North America (see 
 map, page 235) are the positions, beyond question, of 
 the great marshes and shallow fresh-water lakes of the 
 period. But it is probable that the number of these 
 marshes was less than that of the coal areas. The Appa- 
 lachian, Illinois-Indiana, and Iowa-Texas fields may have 
 made one vast Interior Continental marsh region, and those 
 of Rhode Island, Nova Scotia, and New Brunswick an 
 Atlantic Border marsh region, connected over Massachu- 
 setts Bay and the Bay of Fundy. It may be, however, 
 that a low area of dry land extending from the region of 
 Cincinnati southward across Kentucky nearly or quite sepa- 
 rated the Eastern Interior, from the Central Interior, marsh. 
 
 The Michigan marsh region appears also to have had its 
 dry margins, instead of coalescing with the Illinois-Indiana 
 or the Appalachian area. 
 
CARBONIFEROUS ERA. 315 
 
 It is not to be inferred that the marshes alone were cov- 
 ered with verdure. The vegetation probably spread over 
 all the dry land, though making thick deposits of vege- 
 table remains only where there were marshes under dense 
 jungles and shallow lakes with their floating islands. 
 
 Alternations of Condition; Changes of Level. It has 
 been remarked that the many alternations of the coal beds 
 with sandstones, shales, conglomerates, and limestones 
 (page 311), are evidence of as many alternations of level, 
 or at least alternations of condition, during the era. After 
 the great marshes of the Continental Interior had been 
 long under verdure, the salt waters began again to en- 
 croach upon them in consequence of a sinking of the land, 
 and finally swept over the whole surface, destroying the 
 terrestrial and fresh-water life of the area, but distrib- 
 uting at the same time the new life of the salt waters. 
 Then, after another long period, one perhaps of many 
 oscillations in the water level, in which sedimentary beds 
 in many alternations were formed, the continent again rose 
 to aerial life, and the marshes and shallow lakes were lux- 
 uriant anew with the Carboniferous vegetation. Thus the 
 sea prevailed at intervals intervals of long duration 
 through the era even of the Coal Measures ; for the asso- 
 ciated sedimentary beds, as has been stated, are in most 
 localities at least fifty times as thick as the coal beds. In 
 the Nova Scotia Coal area, the waters which came in over 
 the coal beds were the brackish or fresh waters of a great 
 estuary that at the mouth of the St. Lawrence River of 
 the Carboniferous period. 
 
 These oscillations continued until nearly 3000 feet of 
 strata were formed in some parts of Pennsylvania, and 
 about 5000 in Nova Scotia. 
 
 The Carboniferous period was, therefore, ever varying 
 in its geography. A map of its condition when the great 
 coal beds were accumulating would have its eastern coast 
 line,' from the Carolinas northward, even outside of the 
 present. The southern coast line would pass through 
 
316 HISTORICAL GEOLOGY. 
 
 South Carolina, Georgia, Alabama, and northern Missis- 
 sippi, then turn northward around the bay which occupied 
 the lower Mississippi Valley, then southward around the 
 southern end of the Carboniferous area in Texas ; thence 
 the coast line would stretch northward, bounding a sea 
 covering a large part of the Rocky Mountain region, for 
 the Coal period was, in that part of the continent, mainly 
 a time of limestone-making. On the contrary, in a map 
 representing the continent during the succeeding times of 
 submergence, the coast line would be nearly as laid down 
 in the map, Fig. 303, page 287. Through these condi- 
 tions, as the extremes, the continent may have passed 
 several times in the course of the Carboniferous period. 
 Many of the oscillations, however, may have affected only 
 parts of the continent, some parts of the Carboniferous 
 area being submerged while other parts were clothed with 
 vegetation. 
 
 Condition in the Permian Period. Finally, in the 
 Permian period, the continent seems in some degree to 
 have reverted to a condition of submergence like that 
 of the Subcarboniferous, the coal beds being insignificant. 
 
 GENERAL OBSERVATIONS ON THE PALEOZOIC. 
 
 Rocks. 1. Maximum Thickness. The maximum 
 thickness of the rocks of the various Paleozoic eras in 
 North America is approximately estimated as follows : 
 Cambrian, 20,000 feet ; Lower Silurian, 18,000 ; Upper 
 Silurian, 7000 ; Devonian, 14,000 ; Carboniferous, 16,000. 
 
 2. Diversities of the Different Continental Regions as to 
 Kinds of Hocks. The Paleozoic rocks of the Appalachian 
 region are mainly sandstones, shales, and conglomerates ; 
 only about one fourth of the whole thickness consists of 
 limestone. The rocks of the Central Interior are mostly 
 limestone, fully two thirds being of this nature. 
 
 In the Central Interior, the Cambrian rocks are largely 
 limestones ; those of the Lower Silurian, even those of 
 
PALEOZOIC TIME. 317 
 
 the Hudson epoch, are mostly limestones ; the Upper 
 Silurian and Devonian are represented by an almost con- 
 tinuous series of limestones, excepting the Upper Devo- 
 nian, which is represented by the " Black Shale " ; the 
 Subcarboniferous consists mostly of limestone ; and the 
 Coal Measures include a much larger proportion of lime- 
 stone than in the Appalachian region. 
 
 3. Diversities of the Appalachian and Central Interior 
 Regions as to the Thickness of the Rocks. In the Appala- 
 chian region the maximum thickness of the Paleozoic rocks 
 is more than 40,000 feet. But this thickness is not observed 
 at any one locality, being obtained by adding together the 
 greatest thicknesses of the several formations wherever 
 observed. The greatest actual thickness in Pennsylvania 
 is about 30,000 feet, or nearly six miles. 
 
 In the central portions of the Interior region the thick- 
 ness varies from 3000 to 6000 feet ; and it is, therefore, 
 from one sixth to one tenth that in the Appalachian region. 
 
 Time Ratios. Judging from the maximum thick- 
 ness of the rocks of the several Paleozoic ages in North 
 America, and assuming that five feet of fragmental rocks 
 may accumulate in the time required for one foot of lime- 
 stone, the relative lengths of the Eopaleozoic, Upper 
 Silurian, Devonian, and Carboniferous ages were not far 
 from 6:1:2:2. 
 
 The method of computation is, however, essentially 
 uncertain, since thickness of sediment must depend on 
 amount of subsidence. In a locality which was not sub- 
 siding, thick sediments could not accumulate, even in 
 infinite time. But the estimates are so far reliable as 
 to show clearly that time moved on slowly in the earth's 
 first beginnings. 
 
 Geography. Close of Archcean Time. The map on page 
 237 shows approximately the outline of the dry land of 
 North America at the close of the Archsean. The only 
 mountains were Archaean mountains, among the chief of 
 which were the Laureutian Mountains of Canada, the Adi- 
 
318 HISTORICAL GEOLOGY. 
 
 rondacks of northern New York, the Highlands of south- 
 eastern New York and New Jersey, the long Archaean 
 range whose degraded remnant is seen in the " Pied- 
 mont belt" of the South Atlantic states, and the still 
 longer range which forms the " backbone " of the Rocky 
 Mountains. We cannot judge of the height of these moun- 
 tains then from what we now see, after all the ages of 
 Geology have passed over them, for the atmosphere and 
 water have never ceased action since the time of their 
 uplift, and the amount of loss by degradation must have 
 been very great ; while, on the other hand, the altitude of 
 Archaean ranges in the Appalachian and Rocky Mountain 
 regions may have been increased by orogenic movements 
 of those regions in later time. 
 
 General Progress through Paleozoic Time. The in- 
 crease of dry land during the Paleozoic has been shown 
 (pages 272, 287) to have taken place mainly along the 
 borders of the Archaean, so that the original area was thus 
 gradually extending. This increase is well marked from 
 north to south across New York. At the close of the Lower 
 Silurian the shore line was not far from the present position 
 of the Mohawk, indicating but a slight extension of the dry 
 land in the course of this very long era ; when the Upper 
 Silurian ended, the shore line was probably about a score 
 of miles south of the Mohawk. When the Devonian 
 ended and the Carboniferous age was about opening, 
 the coast line was just north of the Pennsylvania boun- 
 dary. The progress southward went on in like manner 
 in Wisconsin, where there is an isolated Archaean region 
 like that of northern New York. By the close of the 
 Lower Silurian, the great Cincinnati island had emerged ; 
 and, by the close of the Devonian, that island had become 
 a peninsula connecting with the mainland in the region 
 of northern Illinois. (See map, Fig. 303, page 287.) 
 The region of the southern peninsula of Michigan con- 
 tinued through the Subcarboniferous and the times of 
 submergence in the Carboniferous to be the head of the 
 
PALEOZOIC TIME. 319 
 
 great Eastern Interior bay of the Continental sea. In 
 the times of emergence, the Michigan bay became a marsh 
 or fresh-water lake, filled with Coal-measure vegetation ; 
 and, at the same times, as explained on page 315, the 
 continent east of the western meridian of Missouri had 
 nearly its present extent, though not its mountains nor its 
 rivers. 
 
 Regions of Rock-making and their Differences. During 
 most of Paleozoic time, the greater part of the conti- 
 nent was submerged beneath marine waters, and that part 
 was the scene of nearly all the rock-making. Areas of 
 fresh water, however, existed at times, especially in the 
 Devonian and Carboniferous, as is proved by the coal 
 beds, and by occasional fresh- water shells in shales and 
 sandstones. 
 
 After the emergence of the Cincinnati and Tennessee 
 islands, at the close of the Lower Silurian, the Interior 
 Continental sea (as explained on page 263) was divided 
 into a Central Interior sea and an Eastern Interior sea or 
 bay. The eastern part of the latter occupied the region 
 of the Appalachian geosyncline. 
 
 The Central Interior region afforded the conditions fitted 
 for the growth of Corals and Crinoids and other clear- 
 water species, and hence for the making of limestones out 
 of their remains; for limestones are the principal rocks of 
 the interior. Yet there were oscillations in the level; for 
 there are abrupt transitions in the limestones, and some 
 sandstones and shales alternate with them. But these 
 oscillations were not great, the whole thickness of the 
 rocks, as stated on page 317, being small. 
 
 The Appalachian region, on the contrary, presented the 
 conditions required for fragmental deposits. It was ap- 
 parently a region of immense sand reefs and mud flats, 
 with bays, estuaries, and extensive submerged offshore 
 plateaus. Here the change of level was very great; for 
 within this region occur nearly six miles of Paleozoic 
 formations (page 317). This vast thickness indicates that, 
 
320 HISTORICAL GEOLOGY. 
 
 while there were various upward and downward move- 
 ments over this Appalachian region through Paleozoic 
 time, the downward movements exceeded the upward even 
 by the amount just stated. 
 
 Mountains of Paleozoic Origin. The formation of the 
 Taconic system of mountains (page 261), and the emer- 
 gence of the Atlantic Border region from southern New 
 England to Georgia (page 262), are the most marked 
 geographical changes Avhich occurred during Paleozoic 
 time. The Taconic range itself extends along the north- 
 western and western boundary of New England, from 
 Canada to northwestern Connecticut. But it was ap- 
 parently only one of a system of approximately parallel 
 contemporaneous ranges extending southwestward to Vir- 
 ginia and perhaps still farther. As in the case of the 
 still earlier Archaean ranges, the original altitude of these 
 ranges of the Taconic system is matter for mere conjec- 
 ture. They have suffered ages of erosion, but they may 
 have been re-elevated in later orogenic movements. The 
 region of western New England and eastern New York 
 was not so much elevated at the time of the Taconic 
 movements, as to prevent the deposit of marine strata in 
 part of the Hudson Valley in the Upper Silurian, and in 
 the Connecticut Valley even in the Devonian. 
 
 Near Gaspe in eastern Canada, and in Maine, New 
 Brunswick, and Nova Scotia, the unconformability be- 
 tween the Devonian and the Carboniferous indicates some 
 mountain-making movements at the close of the Devonian. 
 
 Rivers ; Lakes. The depression between the New 
 York and the Canada Archaean, dating from Archaean 
 time, was the first indication of a future St. Lawrence 
 channel. It continued to be an arm of the sea, or deep 
 bay, through the Lower Silurian, and underwent a great 
 amount of subsidence as it received the thick formations 
 of that era. After the Lower Silurian era, marine strata 
 ceased to form, indicating thereby that the sea had retired ; 
 and fresh waters, derived from the Archaean heights of 
 
PALEOZOIC TIME. 321 
 
 Canada and New York, probably began their flow along 
 its upper portion, and emptied into the St. Lawrence Gulf 
 of the time not far below Montreal. 
 
 The Hudson-Champlain Valley apparently dates from 
 Archtean time, and was a salt-water channel in the Lower 
 Silurian. At the close of the Lower Silurian the channel 
 was closed by the elevation of the region, but it was 
 probably temporarily reopened in the Lower Helderberg 
 period. The Hudson River must have commenced at the 
 close of the Lower Silurian, as an insignificant stream, 
 draining a part of the Adirondacks, and emptying into 
 the Eastern Interior sea near Albany. 
 
 An embryo Mississippi River probably began early in 
 Paleozoic time to drain the Archsean regions of Wisconsin 
 and Minnesota. But the main part of the Mississippi 
 and its tributaries, east and west, was not in existence in 
 the Paleozoic ages. In the times of Carboniferous ver- 
 dure, when the continent was in large part above the sea 
 level, the Ohio and Mississippi basins were regions of 
 great marshes, lakes, and bayous, and not of great rivers; 
 for great rivers could not exist without high land to sup- 
 ply water and give it a flow. 
 
 Climate. No evidence has been found through the 
 Paleozoic records of any marked difference of temperature 
 between the zones. In the Carboniferous era the Arctic 
 seas had their Corals and Brachiopods, and the Arctic 
 lands their forests and marshes under dense foliage, no 
 less than those of America and Europe. The facts bear- 
 ing on this subject are stated on page 312. 
 
 Life. Appearance and Disappearance of Species. 
 With the beginning of each formation in the series, 
 new species appeared, and the old ones more or less com- 
 pletely disappeared. Local changes in the life occurred in 
 connection even with the minor transitions in the rock 
 formations, as in the transition from a bed of shale to 
 sandstone or to limestone, and the reverse. Thus, through 
 the ages, life and death were in concurrent progress, 
 
322 
 
 HISTORICAL GEOLOGY. 
 
 Beginning and Ending of G-enera, Families, and Higher 
 Groups. The following table of the range of genera 
 of Trilobites illustrates the progress which took place in 
 this group, and exemplifies the general fact with regard 
 to other groups : 
 
 Trilobites 
 Olenellus 
 
 Paradoxides. 
 Agnostus. . 
 
 Cambrian 
 
 Lower 
 Silurian 
 
 Upper 
 Silurian 
 
 Devonia.n 
 
 Carbon- 
 iferous 
 
 L. 
 
 M. 
 
 U. 
 
 C. 
 
 T. 
 
 jr. 
 
 
 
 I..H. 
 
 L. 
 
 M. 
 
 U. 
 
 B. 
 
 C. 
 
 P. 
 
 
 
 
 ll 
 
 4| 
 
 I 
 
 i 
 
 - 
 '- 
 
 1 
 
 > 
 
 ^ 
 
 J~~^ 
 
 ~-: 
 
 
 -^ 
 
 ?->-..'-- 
 
 
 2^^ 
 
 
 
 * 
 
 ^^ 
 
 
 
 Bathyurus 
 Asaphus 
 
 
 
 
 ^^^ 
 
 B 
 
 Illcenus 
 
 Co^77ie?ie._._.._.___. 
 Lichas. 
 Homalonotus 
 Phillipsia . 
 
 ^^ 
 
 ^^ 
 
 _...) 
 
 ^ 
 
 ^^ 
 
 n 
 
 
 \/ttr>r 
 
 *7*s;j77. 
 
 ^ 
 
 ~ 
 
 ^ 
 
 
 
 
 
 
 
 
 Griffithides. 
 
 
 
 
 c~ 
 
 ^^^= 
 
 
 
 
 In the above table, the vertical columns correspond 
 to the eras and periods. The shaded area opposite the 
 name Trilobites shows that the group commenced in the 
 beginning of the Cambrian, attained its chief development 
 in the Lower Silurian, then gradually declined, but con- 
 tinued till the Permian. Some genera are seen to have 
 a very limited range in time, as Olenellus and Paradox- 
 ides, confined respectively to the Lower and Middle 
 Cambrian ; while Agnostus extends through the Cam- 
 
PALEOZOIC TIME. 323 
 
 brian and Lower Silurian, and Homalonotus through the 
 Silurian and a large part of the Devonian. 
 
 In a similar manner the genera and families of Braohio- 
 pods began at different periods or epochs, and continued 
 on for a time, to become, in general, extinct. Many 
 genera ended in the course of the Paleozoic or at its 
 close ; only a few continued into later periods. The 
 history of other groups illustrates the same law. 
 
 Special Peculiarities of Paleozoic Life. The following 
 facts show in what respects the life of the Paleozoic 
 ages was peculiarly ancient: 
 
 1. Not only are the species all extinct (with the pos- 
 sible exception of a few Diatoms of the Carboniferous, said 
 to be identical with living species), but also the great 
 majority of the genera. 
 
 2. Among Coelenterates, the Anthozoans were largely 
 of the tribe of Cyathophylloid corals, which is almost 
 exclusively ancient or Paleozoic. 
 
 3. The Echinoderms were mostly Crinoids, and these 
 were in great profusion. Crinoids were far less abundant, 
 and of different genera, in the Mesozoic; and now very 
 few species exist. 
 
 4. Among Molluscoids, Brachiopods were exceedingly 
 abundant : their fossil shells far outweigh the fossils of 
 any other group. But in the Mesozoic they were much 
 less numerous ; and at the present time the group is 
 nearly extinct. 
 
 5. Among Mollusks, the Cephalopods were represented 
 very largely by Orthocerata, but few species of which 
 existed in the early Mesozoic, and none afterward. 
 
 6. Among Arthropods, Trilobites were the most com- 
 mon Crustaceans a group exclusively Paleozoic. 
 
 7. Among Vertebrates, the Paleozoic Fishes were 
 either Selachians, Placoderms, Ganoids, or Dipnoans. Of 
 the Selachians, a large proportion were Cestracionts a 
 tribe common in the Mesozoic, but now nearly extinct. 
 Nearly all the Ganoids had vertebra ted tails. Compara- 
 
324 HISTORICAL GEOLOGY. 
 
 lively few Ganoids with vertebrated tails lived after the 
 Paleozoic, and the whole subclass is now nearly extinct. 
 Of the Dipnoans, only four species now survive. The 
 Amphibians all belonged to the order of Stegocephala 
 a group which became extinct early in the Mesozoic. 
 
 8. Among terrestrial Plants, there were Lepidoden- 
 drids, Sigillarids, Calamites in great profusion, making, 
 with Conifers and Ferns, the forests and jungles of the 
 Carboniferous and later Devonian : no species of Lepido- 
 dendron or Calamites is known after the Paleozoic, and 
 only a single Triassic species of Sigillaria. 
 
 Thus, the Paleozoic or ancient aspect of the animal 
 life was produced through the great predominance of 
 Brachiopods, Crinoids, Cyathophylloid Corals, Orthocerata, 
 Trilobites, Placoderms, vertebrate-tailed Ganoids, and Ste- 
 gocephala; and that of the plants, through the Lepidoden- 
 drids, Sigillarids, and Calamites. In addition to this 
 should be mentioned the absence of Angiosperms among 
 Plants; the absence of Dibranchs among Cephalopods, 
 Brachyurans among Crustaceans, the higher orders (those 
 with complete metamorphosis) among Insects, 1 Teleost 
 Fishes, all modern orders of Amphibia, all orders of Rep- 
 tiles now existing except the nearly extinct Rhynchoce- 
 phala, and the entire classes of Birds and Mammals. 
 
 Mesozoic and Modern Types begun in Paleozoic Time. 
 The principal Mesozoic type which began in the Paleo- 
 zoic was the Reptilian. But besides these Reptiles there 
 were the first of the Decapod Crustaceans ; the first of 
 the great group of Ammonites, the Goniatites being of 
 this group; the first of Scorpions, Spiders, Centipeds, 
 and Hexapod Insects. The type of Insects belongs emi- 
 nently to modern time ; for it probably has now its fullest 
 display. 
 
 Thus, while the Paleozoic ages were progressing, and 
 the types peculiar to them were passing through their 
 
 1 With the exception of some Insects which were probably Neuropters, 
 and possibly a few Beetles (Coleopters), 
 
APPALACHIAN REVOLUTION. 825 
 
 time of greatest expansion in numbers and complexity 
 of structure, there were other types introduced which 
 were to have their culmination in a future age. 
 
 DISTURBANCES CLOSING PALEOZOIC TIME. 
 
 General Quiet of the Paleozoic Ages. The long ages 
 of the Paleozoic passed with few considerable disturbances 
 of the strata of eastern North America. There was, 
 indeed, the elevation of the Taconic system of mountains 
 at the close of the Lower Silurian, accompanied by the 
 emergence of much of the Atlantic Border region ; and 
 again, at the close of the Devonian, there were minor 
 disturbances and upturnings in eastern New Brunswick, 
 part of Nova Scotia, and eastern Canada. Besides these 
 changes, there was, through the ages, a gradual increase 
 in the amount of dry land ; and, through all the periods, 
 over a large part of the continent, slow oscillations were 
 in progress, varying the water level, and thus occasioning 
 alternations in the kinds and extent of the deposits. 
 But these movements of the earth's crust were exceed- 
 ingly slow probably less than a foot a century. There . 
 may have been many occasional quakings of the earth 
 perhaps even exceeding the heaviest of modern earth- 
 quakes. There may have been at times sudden risings or 
 sinkings of portions of the continental crust. But the 
 condition of the strata of the interior of the continent, 
 and of the Appalachian region south of the Green Moun- 
 tains, indicates that general quiet prevailed through the 
 long Paleozoic ages. In Europe there are more frequent 
 unconformabilities in the series of Paleozoic rocks, indi- 
 cating that the progressive development of that continent 
 was less simple and uniform than that of North America. 
 But even in Europe the changes in the course of Paleozoic 
 time were much less considerable than those near its close. 
 
 The Appalachian the Region of Greatest Change of Level. 
 The region of greatest movement during these ages 
 
326 HISTORICAL GEOLOGY. 
 
 was the Appalachian. For it has been shown that the 
 oscillations which there took place resulted in subsidences 
 of one or more thousand feet with nearly every period 
 of the Paleozoic. In Pennsylvania and Virginia the sub- 
 sidence continued through a large part of the Carbonifer- 
 ous age, until it amounted to about 30,000 feet. But this 
 sinking was quiet in its progress, as is proved by the regu- 
 larity in the series of strata. 
 
 The thickness of the coal beds indicates that the coal- 
 plant marshes were long undisturbed, and therefore that 
 long periods passed without appreciable movement. 
 
 The Post-Paleozoic, or Appalachian, Revolution. This 
 long time of comparative quiet was brought to a close by 
 one of the most strongly marked periods of comparatively 
 rapid change in the course of geological time. Mountains 
 were made in various parts of the world, other great geo- 
 graphical changes took place, and the changes in the life, 
 of the globe were as strongly marked as those in geogra- 
 phy. It was the close of one of the great seons in the 
 world's history, and the beginning of another. Such an 
 event is properly styled a revolution. 
 
 . The Appalachian Range. The most striking geographi- 
 cal change in eastern North America was the elevation 
 of the Appalachian range. As that range has been taken 
 as a type in the exposition of the theory of mountain- 
 making (page 211), it is unnecessary here to give any 
 detailed discussion. Attention has already been called to 
 the progressive subsidence of the geosyncline, the accumu- 
 lation of an enormous thickness of strata, the weakening 
 of the deeply buried sediments by the internal heat of the 
 earth, the final yielding to the accumulating strain, the 
 formation of a series of approximately parallel, more or 
 less unsymmetrical, folds, varied in parts of the range by 
 faults of thousands of feet. The Appalachian range 
 proper a single orogenic individual extends over a 
 distance of 1000 miles, from New York to Alabama. 
 
 The Appalachian System. The Appalachian range 
 
APPALACHIAN REVOLUTION. 327 
 
 is only one of the ranges made at this time in eastern 
 North America. There was another to the east, the 
 Acadian range, extending from Newfoundland probably 
 to Narragansett Bay in Rhode Island a distance exceed- 
 ing 800 miles (now partly submerged). In the metamor- 
 phic processes connected with the elevation of this range, 
 much of the coal of Rhode Island actually passed beyond 
 the anthracite stage, and was converted into graphite. A 
 third range belonging to the Appalachian system is the 
 Ouachita range in Arkansas and the Indian Territory. 
 There is also evidence of post-Carboniferous disturbance 
 in the beds of the Paleozoic trough extending from Gaspe, 
 Canada, to Worcester, Massachusetts. The upturning 
 and metamorphism of the Devonian rocks in the Connec- 
 ticut Valley may belong to the same date. In western 
 North America, some orogenic movements in the Great 
 Basin are believed to date from this time. 
 
 Disturbances in Foreign Countries. In the north of 
 England, and also in the region of the South Wales Coal 
 field, extensive disturbances took place between the Car- 
 boniferous and the Permian period. Murchison states 
 that the close of the Carboniferous period was specially 
 marked by disturbances and uplifts ; that it was then 
 "that the coal strata and their antecedent formations were 
 very generally broken up, and thrown, by grand upheavals, 
 into separate basins, which were fractured by numberless 
 powerful dislocations." 
 
 It is noteworthy that these disturbances in England 
 were not precisely contemporaneous with the Appalachian 
 revolution in eastern North America, the latter occurring 
 after the Permian. Devonian and Carboniferous rocks 
 were subject to pre-Permian dislocations also over a large 
 region of western Europe from Brittany to Bohemia, and 
 from Ardennes to the Vosges and the Black Forest. Car- 
 boniferous rocks are folded in the Urals, giving evidence 
 of orogenic movements of post- Carboniferous date, though 
 the backbone of the Urals is Archaean. Some disturb- 
 
328 
 
 HISTORICAL GEOLOGY. 
 
 ance also took place in the Alps about the close of Paleo- 
 zoic time, though the elevation of the Alps is chiefly due 
 to movements of much later date. 
 
 North American Geography after the Appalachian Revo- 
 lution. The accompanying map shows approximately the 
 condition of North America after the Appalachian revolu- 
 tion. Substantially the whole eastern half of the continent 
 
 FIG. 339. 
 
 Map of North America after the Appalachian Revolution. 
 
 had become dry land, the shore of the Continental sea cor- 
 responding roughly with the meridian of 97 W. Since 
 no marine strata of early Mesozoic age are known any- 
 where along the Atlantic or the Gulf border, it is probable 
 that the shore line was then even outside of its present 
 position. In the map, the shore line is drawn where the 
 100-fathom curve lies at present. It is possible, however, 
 that borings through the Tertiary and Cretaceous forma- 
 tions of the Atlantic and Gulf border may reveal the 
 existence of early Mesozoic strata of which no evidence 
 
APPALACHIAN REVOLUTION. 329 
 
 has yet been discovered. West of the meridian of 97, 
 the American continent was represented only by islands 
 whose shore lines cannot be as yet exactly located. 
 
 Geographical Changes in the Region of the Indian Ocean. 
 The Permian flora of South Africa, India, and Australia 
 is so nearly identical as to require the assumption of land 
 connection between those regions. The hypothesis has 
 been generally adopted, that a land area of which Mada- 
 gascar, the Mascarene, Seychelle, and other islands in the 
 Indian Ocean are remnants, connected South Africa with 
 India. This hypothetical area Suess has named G-ond- 
 wdiia-land, from the local name of a series of Permian and 
 Triassic strata in India. Some eminent geologists suppose 
 this land area to have extended across the Indian Ocean 
 to Australia ; but that extension is rendered improbable by 
 the great depth of the Indian Ocean. Whatever connec- 
 tion existed between Africa and Australia is better ex- 
 plained by the hypothesis of a northward extension of the 
 Antarctic continent. Such an extension of Antarctic 
 land may possibly account for the glacial conditions indi- 
 cated by some of the Permian conglomerates in those 
 regions (page 299). Gondwana-land, in the more re- 
 stricted sense of a land area between Africa and India, is 
 supposed to have persisted until the Tertiary era, when it 
 subsided, leaving the islands in the western part of the 
 Indian Ocean as its monuments. Recent discoveries indi- 
 cate the occurrence of substantially the same Permian 
 flora in South America, in southern Brazil, and in Argen- 
 tina. This fact also may find explanation in the hypoth- 
 esis of northward extensions of the Antarctic Continent. 
 
 Change of Fauna and Flora. With perhaps the ex- 
 ception of a few Diatoms, no Paleozoic species is known to 
 have survived into Mesozoic and later times. Many species 
 doubtless were exterminated. Others underwent variation 
 and adaptation, so that the remains of their modified descen- 
 dants, when recognized in later strata, are classified as dis- 
 tinct species. It cannot be affirmed that the extermination 
 
330 HISTORICAL GEOLOGY. 
 
 (or even the change in species) was universal ; for the 
 strata accessible to study, as they are confined to portions 
 of the continental seas, testify only as to changes and 
 destructions in those seas, and not respecting the life exist- 
 ing elsewhere. The causes of so great a change in fauna 
 and flora are only imperfectly understood. The gradual 
 cooling of the sun, the progressive removal of water and 
 carbon dioxide from the atmosphere, and the climatic 
 changes resulting directly and indirectly from geographi- 
 cal changes, must have profoundly affected the conditions 
 of life. Changes of land into sea or of sea into land must 
 have wrought great changes in the life of extensive 
 regions. Earthquake waves and other local catastrophes 
 may have wrought widespread devastation. (See page 458 
 for fuller discussion of causes of change in fauna and flora.) 
 And it must be remembered that unconformability always 
 means the loss, for the particular area, of the record of an 
 interval in which migrations and other biological changes 
 may have been in progress. 
 
 III. MESOZOIC TIME. 
 
 Mesozoic, or mediaeval, time, in Geological history, is 
 appropriately called the REPTILIAN AGE. In the course 
 of it the class of Reptiles passed its culmination that is, 
 its species increased in numbers, size, and diversity of 
 forms, until they vastly exceeded in each of these respects 
 the Reptiles of either earlier or later time. While the 
 culmination of Reptiles is the most characteristic feature 
 of the seon, it is also noteworthy as the time of culmina- 
 tion and incipient decline of Amphibians, Cephalopods, 
 and Cycads ; and of the commencement of Mammals, 
 Birds, Teleost Fishes, and Angiosperms. 
 
 Area of Progress in Rock-making. The area of rock- 
 making in North America, during Mesozoic time, was 
 somewhat different from what it was in Paleozoic. In 
 early Paleozoic time, nearly the whole continent, outside 
 
MESOZOIC TIME. 331 
 
 of the northern Archgean area, was receiving its successive 
 formations. By the close of Paleozoic time, substantially 
 the whole continent east of the meridian of 97 had become 
 dry land, as is shown by the absence of marine strata of 
 later date. (See map, Fig. 339.) The areas of progress 
 in Mesozoic time were (1) the Atlantic Border, (2) the 
 G-ulf Border, (3) the Western Interior, (4) the Pacific 
 Border, and (5) the Arctic Area. In the early Mesozoic, 
 only estuarine or fresh-water deposits were formed along 
 the Atlantic Border, and no deposits now accessible along 
 the Gulf Border ; but in later Mesozoic time a subsidence 
 of these border regions made them once more regions of 
 marine sedimentation. 
 
 In Europe no analogous change can be distinguished; 
 for the continent was, from the first, an archipelago, and it 
 continued to bear this geographical character, though with 
 an increasing prevalence of dry land, until the middle of 
 Cenozoic time. At the beginning of Mesozoic time, west- 
 ern England stood as three or four islands above the sea 
 (occupying approximately the area marked as covered by 
 Paleozoic rocks on the map, page 295) ; and the area of 
 future rock-making was mainly confined to the intervals 
 between these islands and to the submerged area on the 
 east and southeast. It is probable that this area and a 
 portion of northeastern France were, geologically, part of 
 a large North Sea basin. 
 
 Mesozoic time includes three eras. 
 
 1. Tr lassie : named from the Latin tria, three, in allu- 
 sion to the fact that the rocks of the era in some parts of 
 Germany consist of three separate groups of strata. This 
 is a local subdivision, not characterizing the rocks in 
 Great Britain or in most other parts of Europe. 
 
 2. Jurassic : named from the Jura Mountains, where 
 rocks of the era occur. 
 
 3. Cretaceous : named from the Latin creta, chalk, the 
 chalk beds of Great Britain and other regions in Europe 
 and America .being included in the Cretaceous formation. 
 
332 HISTORICAL GEOLOGY. 
 
 I. TRIASSIC AND JURASSIC ERAS. 
 
 ROCKS : KINDS AND DISTRIBUTION. 
 
 In American Geology, it is convenient to treat these 
 two eras together, since in several regions of the country 
 it is impossible with certainty to distinguish the respective 
 rock formations from each other. 
 
 In the Atlantic Border region these rocks occupy narrow 
 troughs or basins parallel with the Appalachian chain, fol- 
 lowing its varying courses. The most northerly of these 
 areas extends along the western border of Nova Scotia. 
 A second occupies the valley of the Connecticut from 
 northern Massachusetts to Middletown, Connecticut, and 
 extends thence southwestward to New Haven on Long 
 Island Sound, having a trend nearly parallel with the 
 Green Mountains ; it has a length of about 110 miles. 
 Another the longest commences at the north extrem- 
 ity of the Palisades, on the west bank of the Hudson 
 River, stretches southwestward through New Jersey and 
 Pennsylvania (here bending much to the westward, like 
 the Appalachians of the state), and reaches far into the 
 State of Virginia. Another stretches almost in the 
 line of the last across the southern boundary of Virginia 
 into North Carolina, and another is comprised entirely 
 within the limits of the latter state. The presence of 
 the Triassic beneath the later formations has been detected 
 in a boring for a well in one locality in South Carolina. 
 The Triassic areas are indicated on the map on page 235 
 by an oblique lining in which the lines run from the left 
 above to the right below. 
 
 The rocks are mainly sandstones and conglomerates, but 
 include some considerable beds of shale, and in a few places 
 impure limestone. The sandstones are generally red or 
 brownish red. The freestone, or browristone, of Portland, 
 near Middletown in Connecticut, and of the vicinity of 
 
TRIASSIC AND JURASSIC ERAS. 333 
 
 Newark in New Jersey, is from this formation. The 
 pebbles and sand of the beds were derived mainly from 
 metamorphic rocks alongside of the regions in which they 
 lie; and from some of the coarser layers large bowlders 
 of granite, gneiss, and mica schist may be taken. The 
 strata overlie directly, but unconformably, these meta- 
 morphic rocks. Some of the beds of shale are black and 
 bituminous; and near Richmond, Virginia, and in North 
 Carolina, there are valuable beds of bituminous coal. 
 
 The several ranges of this sandstone formation are re- 
 markable for the great number of dikes and sheets of trap 
 intersecting them. As the trap (diabase) is considerably 
 harder than the stratified rocks, the dikes and sheets have 
 generally formed more or less prominent ridges (hills of 
 circumdenudation, page 133). Mount Holyoke in Massa- 
 chusetts, East and West Rocks near New Haven in Con- 
 necticut, and the Palisades on the Hudson are a few 
 examples of these trap ridges. Trap is an igneous rock 
 one that was ejected in a melted state from a deep- 
 seated source, through fissures made by a fracturing of 
 the earth's crust. The proofs that the trap came up 
 through the fissures in a melted state are abundant; for 
 the adjacent sandstones are often baked so as to be very 
 hard, and sometimes filled with crystallizations, as of epi- 
 dote, tourmaline, garnet, hematite, etc., evidently due to 
 the heat. 
 
 Owing to the absence of marine fossils, it has been 
 somewhat uncertain to what part of the Triassic or Juras- 
 sic era this formation along the Atlantic Border belongs. 
 It is sometimes called the Jura-Trias, and sometimes the 
 Newark formation. The character of the fossil plants and 
 Vertebrates indicates that it is most probably Upper Tri- 
 assic, corresponding to the Keuper and Rhsetic of Europe. 
 
 The Jurassic is perhaps represented on the Atlan- 
 tic Border by the lower part of the Potomac formation 
 (page 364). 
 
 In the Western Interior region there is a sandstone 
 
334 HISTORICAL GEOLOGY. 
 
 formation in northern Texas, extending northeastward to 
 the boundary of Kansas, and westward into New Mexico, 
 containing much gypsum (and hence called the Gypsif erous 
 formation), but barren of fossils, except an occasional frag- 
 ment or trunk of fossil wood, which is regarded as Triassic. 
 Triassic beds occupy extensive areas along the Colorado 
 River and its tributaries, in Arizona, Utah, and Colorado. 
 Triassic beds also occur in the Black Hills of Dakota, the 
 Wasatch Mountains and the Sierra Nevada, and in the 
 western ranges of the Great Basin. In a large part of 
 the beds referred -to the Triassic, fossils are scanty or 
 wanting. 
 
 Jurassic rocks occur near the Black Hills of Dakota, at 
 many localities along the summit region of the Rocky 
 Mountains, and in the Sierra Nevada. Much of the 
 Jurassic rock is calcareous, and in many localities fossilif- 
 erous. The Upper Jurassic of Colorado, Wyoming, and 
 Montana includes the Baptanodon beds and the overlying 
 Atlantosaurus beds. The former have afforded fossils of 
 marine Invertebrates and aquatic Reptiles; the latter are 
 fresh-water deposits, and have yielded rich remains of 
 Reptiles and Mammals. The Atlantosaurus beds may 
 possibly be of Lower Cretaceous age, representing the 
 Weald en formation of England. The Jurassic rocks of 
 the Sierra Nevada have been to a large extent metamor- 
 phosed into crystalline schists, whose quartz veins are the 
 repositories of the gold. 
 
 In Europe, the Triassic rocks of eastern France and 
 Germany, east and west of the Rhine, consist of (1) a 
 thick sandstone, predominantly reddish, but very variable 
 in color, and often mottled (Eunter Sandsteiri)-, (2) a 
 fossilif erous limestone (Muschelkalk) ; (3) a formation 
 consisting chiefly of reddish and mottled shale and sand- 
 stone (Keuper). The uppermost beds of the Triassic con- 
 stitute the Rhcetic formation, consisting of limestone and 
 shale, and containing in places remains of a flora some- 
 what transitional between the Triassic and the Jurassic. 
 
TRIASSIC AND JURASSIC ERAS. 335 
 
 The Rhsetic is considered by some geologists the lowest 
 member of the Jurassic. In England, the Triassic forma- 
 tion (No. 6 on map, page 295) consists of reddish sand- 
 stone and shale; it is mostly confined to a region just east 
 of the Paleozoic areas of Wales and northern England, and 
 to an extension of this region westward to Liverpool Bay 
 (or over the interval between those two Paleozoic areas) 
 and up the west coast. 
 
 This formation, in Europe, contains in many places beds 
 of salt, and is -hence often called the Saliferous group. At 
 North wich in Cheshire, England, there are two beds of 
 rock salt, 90 to 100 feet thick; and there are similar beds 
 at Vic and Dieuze in Lorraine, and in Wiirtemberg. 
 
 In the eastern Alps, the Triassic shows a very different 
 lithological character from that which it bears in other 
 regions, the Upper, as well as the Middle, Triassic being 
 represented chiefly by great deposits of limestone. 
 
 The Jurassic rocks of Great Britain are divided into 
 two principal groups : 
 
 1. The Lias (No. 7 on map of England, page 295), 
 consisting of grayish compact limestone strata. 
 
 2. The Oolite (No. 8 on map, page 295), consisting 
 mostly of whitish and grayish limestones, part of them 
 oolitic (page 40). One stratum, near the middle of the 
 series, is a coral-reef limestone, much like the reef rock 
 of existing coral seas, though different in species of coral. 
 Near the top of the series there are some local beds of 
 fresh-water or terrestrial origin, in what is called the Pur- 
 beck group, and one of them on the island of Portland is 
 named, significantly, the Portland Dirt Bed. 
 
 On the continent of Europe, the Jurassic rocks are 
 generally divided into three parts commonly called in 
 Germany, respectively, Lias, Dogger, and Malm. 
 
 The Solenhofen lithographic limestone is a very fine- 
 grained rock (thereby adapted for lithography), belong- 
 ing near the top of the Upper Jurassic (Malm), occurring 
 in the vicinity of Solenhofen and Eichstadt in Bavaria. 
 
336 
 
 HISTOBICAX, GEOLOGY. 
 
 LIFE. 
 PLANTS. 
 
 The vegetation of the Triassic and Jurassic periods 
 included numerous kinds of Ferns, both large and small, 
 Equiseta, and Conifers, and so far resembled that of the 
 Carboniferous age. But there were no forests or jungles of 
 Lepidodendrids and Sigillarids. Instead of these Carbo- 
 
 FIGS. 340, 341. 
 340 
 
 CTCADS : Fig. 340, Cycas circinalis, x 
 
 niferous types, a group of trees and shrubs sparingly 
 represented in the Carboniferous, that of the Cycads, was 
 eminently characteristic of the Mesozoic world. This 
 group has now but few living species, Cycas and Zamia 
 being the best-known genera. The plants have the aspect 
 of Palms ; and there was, therefore, in the Mesozoic for- 
 
TRIASSIC AND JURASSIC ERAS. 
 
 387 
 
 FIG. 842. 
 
 ests a mingling of palmlike foliage with that of Conifers 
 
 (Spruce, Cypress, and the like). But the Cjcads are not 
 
 Palms. They are Gymnosperms, 
 
 resembling the Conifers both in 
 
 the structure of the wood and 
 
 in that of the extremely simple 
 
 flowers. The resemblance to 
 
 Palms is mainly in the cluster of 
 
 great leaves at the summit, and 
 
 the appearance of the exterior of 
 
 the trunk. Fig. 340 represents, 
 
 much reduced, a modern Cycas, 
 
 and Fig. 341 the leaf Of a living CYOAD : Stump of MantelUa megalo- 
 
 Zamia, one twentieth the actual 
 
 length. The fossil remains of Cycads are either their 
 
 FIGS. 843-34T. 
 
 i: Fig. 343, Clathropteris rectiuscula; 344, Oligocarpia robustior (in fruit); 845, 
 Acrostichites linnseaefolius. CYOADS : Fig. 346, Podozamites Emmonsi; 84T, Ptero- 
 phyllum Eiegeri. 
 
338 HISTORICAL GEOLOGY. 
 
 trunks or leaves. A fossil species from the Portland Dirt 
 Bed is represented in Fig. 342. The trunks of some 
 Cycads have a height of 15 or 20 feet. In one respect 
 some Cycads resemble the Ferns, that is, in the un- 
 folding of the young leaf, the leaf being at first rolled 
 up into a coil, and gradually unrolling as it expands. 
 
 Fossil plants are common in the coal regions of Rich- 
 mond, Virginia, and North Carolina, and occur also in 
 other localities. Figs. 343 to 345 represent a few of the 
 Ferns : Fig. 343, a Clathropteris, from Easthampton, Mas- 
 sachusetts; Fig. 344, an Oligocarpia, from Richmond, Vir- 
 ginia, and the Trias of Europe ; Fig. 345, an Acrostichites, 
 from Richmond, Virginia. Figs. 346 and 347 are parts of 
 leaves of two species of Cycad, from North Carolina. 
 Large cones of Conifers have also been found. Several of 
 the American plants are identical in species with those 
 of the European Triassic, and a few are akin to European 
 Jurassic forms. 
 
 ANIMALS AMERICAN. 
 
 The American beds of the Atlantic Border region are 
 remarkable for the absence of marine life : all the species 
 appear to be either those of brackish water, or of fresh 
 water, or of the land. 
 
 Invertebrates. In the beds of the Atlantic Border, 
 Sponges, Coelenterates, Echinoderms, and Molluscoids are 
 unknown ; and the remains of Mollusks are of doubtful 
 character. The Jurassic beds of the West contain many 
 species of marine Invertebrates, and the Triassic a few. 
 
 The shells of Ostracoid Crustaceans are common in New 
 Jersey, Pennsylvania, Virginia, and North Carolina, but 
 have not yet been found in New England. Fig. 348 
 represents one of the little shells of these bivalve species, 
 called Estheria. It was long supposed to be Molluscan. 
 The Estherise are brackish-water species. 
 
 A few remains of Insects have been found, and probably, 
 what is more remarkable, the tracks of several species. 
 
TRIASSIC AND JURASSIC ERAS. 339 
 
 These tracks were made on the soft mud, probably by the 
 larvae of the Insects, for many Insects pass their larval 
 state in the water. Fig. 349 represents one 
 of these larvae found in shale at Turners Falls, 
 Massachusetts; it resembles, according to Dr. 
 Le Conte, the larva of a modern Ephemera, 
 or May-fly. Figs. 350 and 351 are the tracks 
 of Insects. Professor Hitchcock named nearly 30 species 
 of tracks supposed to be those of Insects and Crustaceans. 
 
 Vertebrate . There are evi- 
 
 FIGS. 849-351. 
 
 350 JT\ 351 dences of the existence of 
 
 \ "\ Fishes, Amphibians, Reptiles, 
 
 M /\ I Birds, and Mammals. With 
 
 1 I * the appearance of the last two 
 
 )l ^ f\ i* types, the subkingdom of Ver- 
 
 I x X tebrates was finally represented 
 
 v> ' A r\ I \ in all its classes. 
 
 v v >- '\ 1. Fishes. The Fishes 
 INSECTS : Fig. 849, Mormoiucoides articu- found in the American rocks 
 
 latus ; 350, 351, tracks of Insects. , , i /-^ i j 
 
 include only Ganoids and a 
 
 few Dipnoans, although Selachian remains are common 
 in Europe. Fig. 352 represents one of the Ganoids, 
 reduced one half. In this, as in most Mesozoic and 
 
 FIG. 352. 
 
 <yv 
 
 I 
 
 GANOID : Catopterus gracills, x } ; a, scale of same, natural size. 
 
 modern Ganoids, the tail is but slightly vertebrated, being 
 nearly homocercal. 
 
 2. Amphibians, of the order of Stegocephala, or Laby- 
 rinthodonts (page 307), appear to have reached their 
 
340 
 
 HISTORICAL GEOLOGY. 
 
 greatest size and numbers in the Triassic era. A foreign 
 species is mentioned on page 351. Footprints in the 
 Connecticut Valley beds appear to indicate the existence 
 of American species. Figs. 353, 353 a, and 354, 354 #, 
 represent tracks of two of these. It is not, however, pos- 
 sible in all cases to distinguish the tracks of Amphibians 
 from those of Reptiles. 
 
 3. Reptiles. The most important Reptilian remains 
 in the American Triassic and Jurassic belong to the 
 orders of Crocodilians and Dinosaurs, though most of the 
 
 353 
 
 FIGS. 858-356. 
 
 *, 355a 
 
 356 a 
 
 AMPHIBIANS : FIGS. 853, 353 a, tracks of Anisichnus Deweyanus, x ; 354, 354 a, Anisich- 
 nus gracilis, x . REPTILES : FIGS. 355, 355 a, Otozoum Moodii, x ^ ; 356, 356 a, 
 Anomcepus scainbus. In each case the tracks of the hind foot are marked a. 
 
 other orders known from European specimens were also 
 more or less abundantly represented in the American 
 rocks. The Dinosaurs were so named from the Greek 
 Seiko's, terrible, and craO/so?, lizard, some species being of 
 gigantic size (though others were small animals, even 
 less than two feet in length). In eastern North America, 
 they are known by the thousands of footprints left by 
 them in the Connecticut Valley and New Jersey, and a 
 few portions of skeletons from Connecticut, Pennsylvania, 
 and North Carolina ; and in the West, by the huge skele- 
 
TBIASSIC AND JUKASSIC ERAS. 
 
 341 
 
 tons found in the Rocky Mountain region. Of the tracks 
 in the American Triassic, referred more or less probably 
 to Dinosaurs, some belonged to animals completely bipedal 
 in locomotion, others to animals more or less quadrupedal; 
 in some cases the animals appear to have rested the fore 
 feet on the ground occasionally, but not at every step. 
 Figs. 355, 355 a, and 356, 356 #, represent respectively 
 the fore and hind feet of two of the species. In the 
 case of the former species, tracks of the small fore feet 
 
 FIGS. 857, 858. 
 
 Fig. 857, track of Brontozoum giganteum, x J ; 358, slab of sandstone with tracks of Kep- 
 tiles and Amphibians, x fa. 
 
 are but rarely found. Fig. 357 represents one of the 
 completely bipedal species, no tracks of the fore feet 
 of that species being ever found. The track represented 
 in Fig. 357 is actually eighteen inches long, and that 
 of Fig. 355 a, nineteen inches ; and probably each of these 
 Dinosaurs was over twenty feet in height when standing 
 on his hind legs. Although some of the bipedal 3-toed 
 tracks are remarkably like those of birds, it is probable 
 that they were all those of Dinosaurs. The biped march 
 
342 HISTORICAL GEOLOGY. 
 
 of many of the Dinosaurs is a birdlike characteristic, 
 and it is connected with a more or less birdlike pelvis, 
 and (in many species) with hollow limb bones. 
 
 Fig. 359 represents the skeleton of one of the Dino- 
 saurs of the Connecticut Valley. 
 
 FIG. 359. 
 
 DINOSAUR : Anchisaurus colurus, x -fa. 
 
 The Jurassic beds of Colorado and Wyoming have 
 yielded a richer harvest of Dinosaurian remains than 
 any other localities in the world. Some of these Jurassic 
 Dinosaurs are shown by their teeth to have been herbivo- 
 rous, others carnivorous. In one group of the herbivorous 
 species (Sauropods), the jaws were toothed to the extrem- 
 ity, the anterior limbs were nearly as long as the posterior, 
 the hind feet were 5-toed, and the locomotion was com- 
 
TKIASSIC AND JUEASSIC ERAS. 
 
 343 
 
 pletely quadrupedal. Fig. 360 shows a species of this 
 group. To this group belong the most colossal land 
 animals that have ever existed. One species (Atlanto- 
 
 FIG. 360. 
 
 DINOSAUR : Brontosaurus excelsus, x 
 
 saurus immanis) was probably 70 or 80 feet in length. 
 The other group of herbivorous Dinosaurs (the Preden- 
 tata) had the anterior part of the jaws toothless, and 
 
 FIG. 861. 
 
 DINOSAUR : Camptosaurus dispar, x 
 
 probably covered by a horny bill. The pelvis was in 
 several respects strikingly birdlike. The hind limbs 
 were much longer than the fore limbs, and in many 
 
344 
 
 HISTORICAL GEOLOGY. 
 
 species the locomotion was completely bipedal. The 
 inner and the outer toe of the hind foot were apt to 
 be small or even wanting, so that the foot was often func- 
 tionally 3-toed. These birdlike characters were most 
 perfectly exhibited in the Ornithopods (from o/m?, bird, 
 and Trow?, foot). One of this group is represented in 
 Fig. 361. Another division of the Predentata, the Stego- 
 saurs, resembled the Ornithopods in many respects, but 
 
 FIG. 862. 
 
 DINOSAUR : Stegosaurus ungulatus, x 
 
 differed from them by the presence of bony armor, which 
 in some species was developed in a most extraordinary 
 degree. The name, from Greek (Treya, to cover, <ravpos, 
 lizard, refers to this character. One of these armored 
 species is shown in Fig. 362. Beside these groups of 
 herbivorous Dinosaurs, the carnivorous Dinosaurs (Thero- 
 pods), which had been the only Dinosaurs in the Triassic, 
 were abundant also in the Jurassic. Their limbs were 
 in general similar to those of the Ornithopods (though 
 
TRIASSIC AND JURASSIC ERAS. 345 
 
 with important differences in the pelvis), but their jaws 
 were toothed to the extremity. Fig. 359 represents one 
 of the Triassic Theropods. 
 
 4. Birds. A portion of a skull supposed to be that of a 
 Bird has been found in the Atlantosaurus beds of Wyoming. 
 
 5. Mammals. In the North Carolina Triassic have been 
 found two jawbones (one of which is represented in Fig. 
 363), representing two small species of Mammals, perhaps 
 Marsupials, but more prob- 
 ably Monotremes. The for- 
 
 mer of these groups is now 
 represented by the Opossums 
 in America and the Kanga- 
 
 , ,\ f MAMMAL : iawofDromatheriurn sylvestre, x 2. 
 
 roos and many other forms in 
 
 Australia. The Monotremes (now represented b} r only 
 two genera in Australia and the adjacent islands) are the 
 lowest of all Mammals, being oviparous, and resembling 
 Reptiles in many features of their anatomy. Several other 
 Mammals, probably all Marsupials and Monotremes, have 
 been described by Marsh from Jurassic beds in Wyoming 
 and Colorado. 
 
 The facts prove that the land population of Mesozoic 
 America included Insects, Amphibians, Reptiles, Birds, 
 and Mammals ; and that the forests which covered the 
 hills were mainly composed of Conifers and Cycads. 
 
 ANIMALS FOREIGN. 
 
 The European rocks of these periods, especially of the 
 Jurassic, abound in marine fossils, and afford a good idea 
 of the Mesozoic life of the ocean. The remains of terres- 
 trial life are also of great interest, Mammals and an im- 
 mense variety of Reptiles occurring in both the Triassic 
 and the Jurassic beds, and Birds in the Jurassic. 
 
 Coelenterates. Corals are common in some Jurassic 
 strata ; they are related to the modern types of corals, 
 and not to the ancient. Fig. 364 represents one of the 
 Oolitic species. 
 
346 
 
 HISTORICAL GEOLOGY. 
 
 Echinoderms. Crinoids are of many kinds; yet their 
 number, as compared with other fossils, is far less than in 
 the preceding ages ; and they are accompanied by various 
 new forms of Starfishes and Echinoids (page 69). Fig. 
 365 represents one of the Triassic Crinoids, the Lily 
 Encrinite, or Encrinus liliiformis ; Fig. 366, an Echinoid, 
 from the Oolite, stripped of its spines ; and Fig. 367, one 
 of the spines. 
 
 FIGS. 364-367. 
 
 365 
 
 ANTHOZOAN : Fig. 364, Isastrsea oblonga. CRINOID : Fig. 365, Encrinus liliiformis. 
 ECHINOID : Fig. 366, Cidaris Blumenbachii (with spines removed) ; 367, spine of same. 
 
 Molluscoids. Brachiopods are few compared with their 
 number in the Paleozoic. The last species of the Pale- 
 ozoic families Spiriferidce and Strophomenidoe lived in the 
 early part of the Jurassic period. Fig. 368 represents 
 one of these last of the Spirifer group. 
 
 Mollusks. Lamellibranchs and Gastropods abound 
 in species, and under various new, and many of them 
 modern, genera. Species of the genus G-ryphcea were 
 common in the Lias and later Mesozoic rocks ; they are 
 related to the Oyster, but have the beak incurved. Fig. 
 369 represents a Liassic species. Trigonia (Fig. 370) is 
 a characteristic genus of the Mesozoic ; the name alludes 
 
TRIASSIC AKD JUEASSIC ERAS. 
 
 347 
 
 to the triangular form of the shell : the species figured is 
 from the Oolite. The genus commenced in the Lias, and 
 still survives in the Australian seas. 
 
 FIGS. 368-370. 
 
 370 
 
 BRACHIOPOD : Fig. 368, Spiriferina Walcotti. LAMELLIBRANCHS : Fig. 369, Gryphsea in- 
 curva ; 370, Trigonia clavellata. 
 
 But the most remarkable and characteristic of all 
 Mesozoic Mollusks were the Cephalopods. This class 
 passed its maximum as to number and size in the Meso- 
 zoic, and hundreds of species existed. The last of the 
 
 FIGS. 371, 372. 
 
 371 
 
 CEPHALOPODS : Fig. 371, Stephanoceras Humphriesianum ; 372, Cosmoceras Jason. 
 
348 HISTORICAL GEOLOGY. 
 
 Paleozoic type of Orthocerata lived in the Triassic era. 
 In the same era, species of Ammonites, one of the most 
 characteristic of Mesozoic groups, became common ; and 
 the new order of Dibranchs made its first appearance, 
 being represented by genera of the Belemnite family, 
 though the genus Belemnites did not appear until the 
 Lias. 
 
 The Ammonites belonged to the order of Tetrabranchs, 
 and had external chambered shells like the Orthocerata, 
 Nautili (Fig. 110, page 75), and Goniatites. Two Oolitic 
 species are represented in Figs. 371, 372. One of them 
 (Fig. 372) has the side of the aperture very much pro- 
 373 longed ; but the outer margin of the shell, 
 
 whether prolonged or not, is seldom well 
 preserved. The partitions (or septa) with- 
 in the shells of Ammonites are bent back in 
 many folds (and much plaited within each 
 fold) at their junction with the shell, so as 
 to make deep plaited pockets. A front 
 view of the outer septum, with the entrances 
 to its side pockets, is shown in Fig. 373. 
 Fig. 416 6, page 371, illustrates the complex 
 ciadis- form of the junction of the edge of the 
 septum with the shell (suture) in some 
 species of Ammonites. The suture is also shown in Fig. 
 419. The Paleozoic Goniatites belonged to the Ammonite 
 group, but the pockets were much more simple than in the 
 typical Ammonites, the flexures of the margins of the 
 partitions being without plications. 
 
 The fossil Belemnite is an internal shell, analogous to 
 the pen or bone (osselet) of a Sepia, or Cuttlefish (see 
 Fig. 378). The part of the shell most commonly pre- 
 served is a conical or club-shaped body, shown in Figs. 
 375, 376, solid, except at its upper (anterior) end, which 
 incloses a conical cavity. This cavity is occupied by 
 a structure much resembling the chambered shell of 
 an Orthoceras, whose upper (anterior) extremity is ex- 
 
TRIASSIC AND JURASSIC ERAS. 
 
 340 
 
 panded on the dorsal side into a thin plate shown in Fig. 
 374. This plate is so fragile that in general it is pre- 
 served only in fragments or not at all. The animal had 
 
 OEPHALOPODS : Fig. 374, complete osselet of a Belemnite, restored ; 375, Belemnites 
 clavatus ; 376, Belemnites paxillosus ; 376 a, outline of section of same near extrem- 
 ity ; 377, fossil ink bag of a Cephalopod ; 378, Belemnoteuthis antiqua, x |. 
 
 an ink bag like the modern Sepia. In some allied genera 
 the ink bag was larger ; and the dried ink of these fossil 
 Cephalopods has been used in sketching pictures of them. 
 Fig. 377 represents the ink bag of a Jurassic Cephalopod. 
 Fig. 378 is another related Cephalopod, showing some- 
 
350 
 
 HISTORICAL GEOLOGY. 
 
 thing of the form of the animal, and also the ink bag in 
 place. 
 
 Arthropods. The Crustaceans were represented by 
 species of rather modern aspect. Trilobites were entirely 
 extinct. Tetradecapods were represented by species like 
 the modern Sow-bugs (Fig. 379). Decapods included 
 Macrurans, represented by numerous species of Shrimps 
 and Crawfishes (Fig. 380 shows a Triassic species) ; and 
 (in the Jurassic) Brachyurans, or Crabs. The presence of 
 this highest suborder is a noteworthy step of progress. 
 
 FIGS. 379-382. 
 
 CEUSTACBANS : Fig. 879, Archfeoniscus Brodiei ; 880, Pemphix Sueurii. INSECTS : Fig. 881, 
 Libellula ; 382, wing cover of Buprestis. 
 
 All but one of the important orders of Hexapod Insects 
 were abundant in the Jurassic. Even the highest order, 
 the Hymenopters (Bees, Ants, etc.), was well represented. 
 Of the Lepidopters (Butterflies, Moths, etc.), only scanty 
 remains have been discovered, whose reference to the order 
 in question is more or less doubtful. Fig. 381 is a Dragon- 
 fly from Solenhofen; and Fig. 382, the wing cover of a 
 Beetle, from the Stonesfield Oolite. 
 
 Vertebrates. The Fishes were chiefly Selachians, 
 Ganoids, and Dipnoans. Among the Selachians, the 
 ancient group of Cestracionts, characterized by a pavement 
 
TRIASSIC AND JURASSIC ERAS. 
 
 351 
 
 FIG. 383. 
 
 of grinding teeth (Figs. 129-131, page 82), still continued, 
 and was represented by numerous species. There were 
 also, in the Jurassic, Sharks with sharp-edged teeth, like 
 most of those inhabiting modern seas. Most of the 
 Ganoids were of modern type in having the tail nearly 
 or quite homocercal, as shown in Fig. 383. One genus of 
 Dipnoans, Ceratodus, occurring in both the Triassic and 
 the Jurassic, is still represented by two living species 
 in Australia. The discovery and dissection of the 
 living Ceratodus in Australia first revealed the Dip- 
 noan nature of the remarkable teeth which had long been 
 known as Triassic fossils. It thus became known that 
 Dipnoans were abun- 
 dant in both Meso- 
 zoic and later Pale- 
 ozoic time. Beside 
 the ancient groups 
 of Selachians, Ga- 
 noids, and Dipnoans, 
 there were probably 
 in the Jurassic, and 
 even in the Triassic, 
 representatives of 
 the modern Bony 
 Fishes, or Teleosts. These, however, did not become 
 abundant until the Cretaceous. 
 
 Amphibians were common in the European Trias, as in 
 the American, and some were of gigantic size. They all 
 belonged to the order of Stegocephala, or Labyrinthodonts 
 an order which passed its culmination in the Triassic, 
 and probably became extinct at the close of that era, 
 though a single species has been doubtfully reported from 
 the Jurassic. 
 
 One of these Triassic Labyrinthodonts had a skull over 
 two feet long, of a form shown in Fig. 384 ; its mouth was 
 set round with teeth three inches long (Fig. 385). The 
 specimen here figured was found in Wiirtemberg. It is 
 
 GANOID : Fig. 883, Dapedius (restored), from the Lias, 
 x J ; 383 a, scales of same. 
 
352 
 
 HISTORICAL GEOLOGY. 
 
 probable that some of the animals whose tracks are so 
 common in the Connecticut Valley were of this type. 
 Fig. 386 is a reduced view of handlike tracks, supposed 
 to have been made by a Labyrinthodont. The Am- 
 phibians of the present day are feeble and diminutive 
 compared with their Triassic predecessors. 
 
 The Triassic, and, in even greater degree, the Jurassic, 
 were characterized by the immense development of Rep- 
 tiles. To the two orders which had appeared in the Per- 
 mian Rhynchocephala and Theromorphs were added 
 in the Triassic, Ichthyosaurs, Plesiosaurs, Turtles, Croco- 
 
 :!S4 
 
 AMPHIBIANS : Fig. 384, skull of Mastodonsaurus giganteus, x & ; 385, tooth of same ; 
 386, footprints of Chirotherium, x &. 
 
 diles, Dinosaurs, and Pterosaurs; and before the close of 
 the Jurassic the earliest Lizards (Lacertilians) appeared. 
 The Theromorphs became extinct at the close of the 
 Triassic, but all the other orders survived till the close 
 of the Cretaceous or later. 
 
 The Reptiles included species for each of the elements 
 the water, the earth, the air. 
 
 The Swimming Reptiles have been called Enaliosaurs 
 from the Greek emXto?, marine, and o-avpos, lizard. They 
 include the two orders of Ichthyosaurs and Plesiosaurs. 
 
 The Ichthyosaurs (Fig. 387) had a short neck, a long 
 
TRIASSIC AND JURASSIC ERAS. 
 
 353 
 
 and large head, enormous eyes, and thin, doubly concave, 
 and therefore fishlike, vertebrae. Their paddles were 
 somewhat like the flippers of a Whale ; but their great, 
 vertically expanded, caudal fin, and the large dorsal 
 fin, gave them an aspect more fishlike than that of 
 Whales or of any other air-breathing Vertebrates. The 
 name is from the Greek &%0u9, fish, and a-avpo^ lizard. 
 
 FIGS. 387-392. 
 
 REPTILES : Fig. 38T, Ichthyosaurus quadriscissus ; 388, head of Ichthyosaurus communis, 
 x & ; 389, tooth of same, natural size ; 390 a, 6, view and section of vertebra of same ; 
 391, Plesiosaurus dolichodeirus, x &s 5 392 a, &, view and section of vertebra of same. 
 
 Fig. 388 represents the head of an Ichthyosaur, one 
 thirtieth the natural size, showing the large eye and the 
 numerous teeth. Fig. 390 a is one of the vertebrse, 
 reduced, and Fig. 390 6, a transverse section of the same, 
 exhibiting the fact that both surfaces are deeply concave, 
 nearly as in fishes ; Fig. 389 is one of the teeth, natural 
 size. Some of the Ichthyosaurs were 30 or 40 feet long. 
 
354 HISTORICAL GEOLOGY. 
 
 The Plesiosaurs, one of which is represented, very much 
 reduced, in Fig. 391, had generally a long, snakelike neck, 
 a comparatively short body, and a small head. Fig. 392 a 
 represents one of the vertebrae, and 392 b a section of the 
 same ; it is doubly concave, but less so, and much longer, 
 than in the Ichthyosaurs. Their limbs were paddles, but 
 departed in general much less from the ordinary structure 
 of a Reptilian foot than those of the Ichthyosaurs. Indeed, 
 in some of the earlier and less specialized members of the 
 order, the limbs still retained some adaptation for walking. 
 Some species of Plesiosaur were 25 to 30 feet long. The 
 Pliosaurs, which are included in the order of Plesiosaurs, 
 though differing from the typical genus Plesiosaurus in 
 having a larger head and a shorter neck, were 30 to 40 
 feet long. Remains of more than 70 species of Enaliosaurs 
 have been found in the Jurassic rocks. 
 
 Besides these swimming Reptiles, there were numerous 
 Crocodiles lO to 50 feet long, and Dinosaurs, the bulkiest 
 and highest in rank of all the class, 25 to 60 feet long. 
 
 The Dinosaurs, in Europe, as in America, included the 
 herbivorous Sauropods, Ornithopods, and Stegosaurs, and 
 the carnivorous Theropods. Among the Sauropods, a 
 species of Cetiosaurus was 40 to 50 feet long. One of the 
 best-known of the Theropods was the Megalosaurus ; it 
 was a terrestrial carnivorous Reptile about 30 feet in 
 length. Strongly contrasted in size with the huge Megalo- 
 saurus, though belonging likewise to the Theropods, was 
 the graceful, bird-like Compsognathus, not over two feet 
 in length, from the lithographic limestone of Kelheim, 
 Bavaria. 
 
 The Reptiles adapted for the air that is, for flying 
 constitute the order Pterosaurs, so named from the Greek 
 Trre/ooV, wing, and cravpos. The most common genus is 
 called Pterodactylus. The general form of a Pterodactyl 
 is shown in Fig. 393. The bones of one of the fingers 
 are greatly elongated, for the purpose of supporting a fold 
 of skin, so as to make it serve (like an analogous arrange- 
 
TRIASSIC AND JURASSIC ERAS. 
 
 355 
 
 ment in Bats) for flying. The name Pterodactylus is from 
 the Greek Trrepdv, wing, and Sa/crfXo?, finger. The Juras- 
 sic Pterodactyls were mostly small, and probably had the 
 habits of Bats ; the largest was about the size of ah Eagle. 
 
 FIG. 393. 
 
 PTEROSATTE : Pterodactylus spectabilis, natural size. 
 
 Other genera of Pterosaurs differed from Pterodactylus in 
 having long tails. A restoration of one of these, showing 
 the wing membranes and the rudder-like expansion of the 
 tail, is given in Fig. 394. As Bats are flying Mammals, 
 so the Pterosaurs are simply flying Reptiles, and have 
 
356 HISTORICAL GEOLOGY. 
 
 little resemblance to Birds in structure, except that their 
 bones are hollow, and adapted in form for the birdlike 
 characteristic of flying. 
 
 Besides the kinds of Reptiles already mentioned, there 
 were Turtles in both the Triassic and the Jurassic, and 
 Lizards in the Jurassic ; but, according to present know- 
 ledge, the world contained no Snakes. 
 
 Coprolites (or fossil excrements) of both Reptiles and 
 Fishes are common in the bone beds. When cut and 
 polished, they have a degree of beauty sufficient to give 
 them some value in jewelry. 
 
 FIG. 394. 
 
 PTEROSAUR : Ehamphorhynchus phyllurus, x \ . 
 
 Remains of Birds have been found in the quarries of 
 Solenhofen (page 335). They have revealed the fact 
 that some of the Mesozoic Birds were reptilian in certain 
 characters. The skeletons found (Fig. 395) show that 
 these Birds had long reptile-like tails consisting of many 
 vertebra?, and claws on the digits of the fore limb or 
 wing, like those of the Pterodactyl and Bat, fitting them 
 evidently for clinging. Moreover, the metacarpal bones 
 were free, as in Reptiles, while in modern Birds they are 
 immovably united. The mouth was provided with teeth. 
 But, while thus reptilian in some points of structure, they 
 were actually Birds, being feathered animals, and having 
 the expanse of the wing made, not by an expanded mem- 
 brane as in the Pterodactyl, but by long quill feathers. 
 
TRIASSIC AND JURASSIC ERAS. 
 
 357 
 
 The tail quills were arranged in a row either side of the 
 long tail. 
 
 Remains of Mammals occur in the Rhsetic beds of Ger- 
 many and England, in the Lower Oolite at Stonesfield, 
 England, and in the Middle Purbeck beds of the Upper 
 
 FIG. 395. 
 
 f 
 
 BIRD : Archaeopteryx macrura, x 
 
358 
 
 HISTORICAL GEOLOGY. 
 
 Oolite (page 335). About thirty species have been made 
 out, more than twenty of them from relics in the Middle 
 Purbeck. The larger part, if not all, are Marsupials and 
 Monotremes. Figs. 396, 397 represent the jaws of two 
 species from Stonesfield, twice the natural size. 
 
 The remarkable transitional forms between Reptiles and 
 Birds, as illustrated by the Ornithopod Dinosaurs on the 
 one hand and Archceopteryx on the other, are of course what 
 
 FIGS. 896, 39T. 
 
 R97 
 
 MAMMALS : Fig. 396, Amphilestes Broderipi, x 2 ; 39T, Phascolotherium Bucklandi, x 2. 
 
 would be expected in accordance with the theory of evolu- 
 tion. Probably all the Triassic Mammals are Monotremes, 
 and all the Jurassic Mammals Monotremes and Marsupials. 
 The theory of evolution would require the class of Mam- 
 mals to commence with reptile-like forms, such as Mono- 
 tremes. The remarkable mammal-like peculiarities of the 
 skulls of the Permian and Triassic Theromorph Reptiles 
 are very suggestive as to the ancestry of the Triassic 
 Mammals. 
 
 GENERAL OBSERVATIONS. 
 
 American Geography. The Triassic sandstones and 
 shales of the Atlantic Border region are sedimentary 
 beds ; consequently, the long, narrow tracts of country 
 in which they were formed were occupied, at the time, 
 more or less completely by water. 
 
 The absence of marine fossils has been remarked upon 
 as proving that this water was either brackish or fresh ^ 
 
TRIASSIC AND JURASSIC ERAS. 359 
 
 and hence the areas were estuaries or deep bays running 
 far into the land. 
 
 There was probably an abundance of marine life in the 
 ocean, if we may judge from its diversity 011 the other 
 side of the Atlantic; but the seacoast of the era must 
 have been farther east than at present, so that any marine 
 deposits that were made are now submerged. The present 
 sea border is shallow for a distance of 80 miles from the 
 New Jersey coast, the depth of water at this distance 
 being but 600 feet. (See map, page 18.) 
 
 The deposits contain, on many of the layers, footprints, 
 ripple-marks, raindrop impressions, and other evidences 
 that they were formed partly in shallow waters, and 
 partly as sand flats, or emerging marshes and shores, over 
 which Reptiles might have walked or waded. If, then, 
 they are several thousands of feet thick, there must have 
 been a progressive subsidence of the valleys in which the 
 deposits were formed. It is hence apparent that oscilla- 
 tions of level, like those that characterized the Appalachian 
 region before and during the Appalachian revolution, were 
 in progress. Two effects of this subsidence occurred : 
 (1) The sandstone beds were more or less faulted and 
 tilted, those of the Connecticut Valley receiving a dip to 
 the east or southeast, those of New Jersey and Penn- 
 sylvania to the northwest. (2) In the sinking of the 
 valley, an increasing strain was produced in the earth's 
 crystalline crust beneath, which finally became so great 
 that the crust broke, fissures opened, and liquid rock 
 came up. 1 The dikes and sheets of trap are this liquid 
 rock solidified by cooling. The earth's crust along the 
 
 1 In the opinion of the editor, most of the trap sheets of the Connecti- 
 cut Valley and New Jersey were poured out as contemporaneous sheets 
 (page 188) over the underlying strata, and subsequently covered by later 
 deposits. According to this view, the' eruption of the trap took place 
 before the tilting and faulting which occurred at the close of the depo- 
 sition. The trap masses of East and West Rock, near New Haven, and 
 the great Palisade sheet of New Jersey, are certainly intrusive, but they 
 probably date from about the same time as the contemporaneous sheets. 
 
360 HISTORICAL GEOLOGY. 
 
 Connecticut Valley for more than 100 miles was thus a 
 scene of igneous operations. All the Triassic areas from 
 Nova Scotia to southern North Carolina, a distance of 
 1000 miles, were similarly broken through and invaded 
 by trap ejections. 
 
 The Rocky Mountain region had been mostly submerged 
 during the Carboniferous era, as shown by the fact that 
 limestones were forming there in the period of the Coal 
 Measures, and fossiliferous sandstones in the Permian. 
 The Triassic sandstone there proves, by its nature, its 
 gypsum in many places, and the paucity of its fossils, that, 
 by some change, the region had become mostly an interior 
 shallow salt sea, shut off to a great extent from the ocean. 
 Such a sea would be liable at times to become too salt for 
 almost any life. Hence the scarcity or absence of fossils 
 in many of the beds. The salt waters by evaporation 
 would have furnished gypsum and salt to the beds, as 
 happens now sometimes from sea water. It follows, then, 
 from the beds of the Atlantic Border as well as those 
 of the Rocky Mountain region, that the continent during 
 the era of these Mesozoic beds was submerged to a less 
 extent than in the greater part of the Paleozoic ages and 
 the following portion of the Mesozoic. The fossiliferous 
 Jurassic beds overlying the western Triassic show that, 
 before the Jurassic period had closed, the sea had again 
 free access over large areas, and oceanic life was abundant. 
 
 Foreign Geography. The nature of the Triassic beds 
 in Great Britain and the continent of Europe shows that 
 there were large shallow interior seas also on that side of 
 the Atlantic. The salt deposits, the paucity of fossils in 
 most of the strata, and the general character of the rocks, 
 indicate conditions such as existed in New York during 
 the formation of the Onondaga beds of the Upper Silurian 
 (see page 274), and in the Rocky Mountain region during 
 the deposition of the Gypsiferous formation. The lime- 
 stone that intervened, along the Rhine, between the two 
 formations of sandstone and shale, shows an interval of 
 
TKIASSIC AND JURASSIC ERAS. 361 
 
 more open sea ; yet the impurity of the limestone suggests 
 that the ocean had not full sweep over the region. The 
 great limestone deposits of the eastern Alps bear witness 
 to a submergence of that region beneath a clearer sea. 
 
 The beds of the Jurassic era mostly afford evidence, both 
 from their constitution and from their abundant marine 
 life, that the ocean again had free sway over large portions 
 of the continental area. Its limits in Great Britain, how- 
 ever, became more contracted as the period passed ; and 
 toward its close fresh-water beds were forming in some 
 places that had earlier in the period been under salt water. 
 
 Climate. The Jurassic coral reefs of Great Britain indi- 
 cate that England then lay within the subtropical oceanic 
 zone. This zone now has, in general, as its outer limit the 
 parallel of 27 or 28 ; and, consequently, its Jurassic 
 limit, if including England, reached twice as far toward 
 the pole as now. It is possible, however, that the line 
 would have run along the British Channel, were it not for 
 the Gulf Stream of the era, which carried the subtropical 
 temperature northeastward through the British seas, as it 
 now does to Bermuda, in latitude 32. 
 
 The following are other facts of similar import. In 
 Arctic America, species of shells allied to those of Europe 
 and tropical South America occur in latitudes 60 to 77 
 16' ; and one species of Belemnite and one of Ammonite 
 are said to be identical with species occurring in these two 
 remote and now widely different regions. If not absolutely 
 identical, the evidence from them as to oceanic temper- 
 ature is nearly the same. Moreover, on Exmouth Island, 
 in 77 16' N., remains of an Ichthyosaur have been found, 
 and in 76 22' N., on Bathurst Island, bones of other large 
 Jurassic Reptiles (Teleosaurs). It is probable, therefore, 
 that a warm-temperate oceanic zone covered the Arctic to 
 the parallel of 78, if not beyond. No large living reptiles 
 exist outside of the torrid and warm-temperate zones. 
 
 It was believed, however, by Neumayr, that certain dif- 
 ferences between the Upper Jurassic 1'auna of the Medi- 
 
862 HISTORICAL GEOLOGY. 
 
 terranean region and that of northern Russia indicate that 
 an appreciable difference of climate had already become 
 established between northern and southern Europe. The 
 evidence is not altogether conclusive. 
 
 DISTUEBANCES CLOSING THE JUEASSIC EEA. 
 
 After the Jurassic era, or near its close, the lofty range 
 of the Sierra Nevada on the eastern boundary of California 
 was made. To the same system belong apparently the 
 Cascade Range and the Blue Mountains of Oregon. Some 
 disturbances took place also in the region of the Coast 
 Range of California and Oregon, though that region ex- 
 perienced a later movement of elevation at the close of the 
 Miocene. The close of the Jurassic is probably also the 
 time of making of the West Humbolt Range and some 
 other ranges over the dry plateau between the Sierra 
 Nevada and the Wasatch Range. Triassic and Jurassic 
 fossils have been found in the rocks of the Sierra Nevada, 
 while Cretaceous fossiliferous beds lie unconformably over 
 the upturned strata of the mountains : the former fact 
 proves that the mountain-making occurred after the Ju- 
 rassic era; and the latter, that it took place before the 
 Cretaceous. 
 
 II. CRETACEOUS EEA. 
 
 GENERAL CHARACTERISTICS. 
 
 The Cretaceous, the closing era of Mesozoic time, was 
 also, in some respects, a transition era between the Meso- 
 zoic and Cenozoic. During its progress, as is explained 
 beyond, occurred the decline, and, at its close, the extinc- 
 tion, of a large number of the tribes of the mediaeval world; 
 while, at the same time, there appeared in its course other 
 tribes eminently characteristic of the modern world. 
 Among the modernizing features, the most prominent are 
 the Angiosperms among plants, and the Teleosts among 
 Fishes. Of the Teleosts, indeed, some representatives 
 
CRETACEOUS ERA. 863 
 
 probably appeared in the earlier Mesozoic ; but it is not 
 certain that the supposed Triassic and Jurassic Teleosts 
 were not Ganoids. The Teleosts certainly first attained a 
 considerable development in the Cretaceous. 
 
 The Angiosperms include nearly all the fruit trees of 
 the world, and constitute by far the larger part of modern 
 forests. The Conifers and Cycads, wherever they now 
 occur near groves of Angiosperms, exhibit the contrast be- 
 tween the mediseval foliage and that of the present age. 
 The Teleosts (page 83) embrace nearly all modern Fishes 
 excepting those of the subclass of Selachians, or Sharks. 
 Their prevalence was as great a change for the waters as 
 the new tribes of plants for the land. 
 
 AMERICAN GEOGRAPHY : AREAS OF ROCK-MAKING. 
 
 The accompanying map, Fig. 398, shows the areas in 
 North America which were submerged beneath salt water 
 during the Cretaceous. The vertical lining indicates the 
 parts that were submerged during the Lower Cretaceous ; 
 the horizontal lining, those that were submerged during 
 the Upper Cretaceous ; and the cross lining, the areas 
 under water through the whole period. The scale of the 
 map is too small for the indication of the fresh-water 
 Cretaceous areas. 
 
 As shown by the map, rock-making was going on along 
 the Atlantic Border, the Gulf Border, and the Pacific 
 Border, as well as over the Western Interior (including 
 the summit region of the Rocky Mountains). The Gulf 
 Border may be considered as constituting two areas of 
 rock-making an eastern and a western, since the 
 deposits east of the Mississippi differ considerably from 
 those of Texas and Mexico. 
 
 ROCKS : KINDS AND DISTRIBUTION. 
 
 Both in America and in Europe the Cretaceous forma- 
 tion is divided into two periods, the LOWER CRETA 
 CEOUS and the UPPER CRETACEOUS. 
 
364 HISTORICAL GEOLOGY. 
 
 A comparison of the map on this page with that on page 
 387 will show that the Cretaceous deposits along the 
 Atlantic and Gulf Borders are to a very large extent con- 
 cealed beneath the overlying Tertiary strata. In the 
 Western Interior and along the Pacific Border, they con- 
 stitute the surface rocks over large areas. 
 
 FIG. 898. 
 
 North America in the Cretaceous era. 
 
 The Lower Cretaceous is represented on the Atlantic 
 Border by the fresh-water Potomac formation, including 
 sandstones and shales and unconsolidated sands and clays, 
 not exceeding 1200 feet in thickness, and exposed in a 
 narrow and interrupted belt from Nantucket to South 
 Carolina. 1 The presence of a few rare marine shells in 
 
 1 It is possible that the lowest part of the Potomac formation (James 
 River and Rappahannock stages) belongs to the Jurassic (see page 333), 
 and that the uppermost part (Albirupian, or Raritan, stage) belongs to 
 the Upper Cretaceous. 
 
CRETACEOUS ERA. 365 
 
 this fresh-water formation shows that the coast line could 
 not have been far off. In the western Gulf Border the 
 Lower Cretaceous formation (Comanche series) is mainly 
 marine, and consists largely of limestone, a part of which 
 is chalk. On the Rio Grande the formation attains a 
 thickness of 5000 feet, though it is much less over most 
 of the "region. Fresh-water beds of the Lower Cretaceous, 
 consisting of sandstones and shales, and containing some 
 coal, appear in some parts of the Rocky Mountain region. 
 
 The Upper Cretaceous appears on the Atlantic Border, 
 between the Tertiary of the coast and the older rocks of 
 the interior, in a continuous area extending from New 
 Jersey into Virginia, and in isolated patches farther north 
 and south. The rocks are marine deposits about 500 feet in 
 thickness, consisting of greensand alternating with beds of 
 sand and clay. The greensand (locally called marl) consists 
 of common sand mixed with blackish or olive-green grains 
 of glauconite (a hydrous silicate of iron, alumina, and 
 potash) formed by chemical changes at the bottom of 
 the sea within the shells of Rhizopods. Along the Gulf 
 Border marine Upper Cretaceous deposits were formed, 
 consisting largely of limestone, especially in the western 
 area, where much of the formation is chalk. 
 
 The Upper Cretaceous is immensely developed in the 
 Western Interior region, the aggregate maximum thick- 
 ness of the beds of the different epochs being over 15,000 
 feet. Four divisions are recognized, corresponding to 
 the Dakota, Colorado, Montana, and Laramie epochs. Of 
 these, the first and the last are fresh-water formations, 
 the others marine. The rocks of the Colorado epoch are 
 largely limestones, including much chalk. The deposits 
 of the other epochs are mainly fragmental materials, 
 including sandstones, shales, and conglomerates, with 
 unconsolidated sands and clays. The Upper Cretaceous 
 is the great coal formation of western North America, 
 coal beds occurring at various horizons, but especially 
 in the Laramie. The coal fields in Colorado alone have an 
 
366 HISTORICAL GEOLOGY. 
 
 area of about 18,000 square miles. Coal has been worked 
 also in Utah, Wyoming, Montana, and New Mexico, and 
 at various localities in British America. One bed at 
 Evanston, Wyoming, is said to be 26 feet thick. 
 
 The Laramie beds represent the latest epoch of the 
 Cretaceous, and show in their fossil flora a transition 
 to the Tertiary. This epoch is not represented On the 
 Pacific and the Eastern Gulf Border, and probably not 
 on the Atlantic Border, the latest Cretaceous beds of 
 those regions apparently belonging to the Montana epoch. 
 
 In Europe, as in North America, the Cretaceous forma- 
 tion constitutes the surface rocks in areas which form 
 more or less interrupted borders of the Tertiary regions, 
 or insular areas within those regions, indicating that the 
 Cretaceous seas covered in general the areas now occupied 
 by both Cretaceous and Tertiary rocks. 
 
 In England, the Cretaceous formation occupies most 
 of the southeastern part of the country (9 and 10, on map, 
 page 295). The Lower Cretaceous includes, as its basal 
 member, the Wealden formation (9, on map), which is 
 subdivided into the Hastings Sand and the Weald Clay. 
 This is a fresh- water formation deposited in a great delta 
 20,000 square miles in area. The remainder of the Lower 
 Cretaceous and the whole Upper Cretaceous consist of 
 marine deposits, mostly greensand and chalk. Some of 
 the chalk beds abound in concretions of flint, which 
 consist largely of Diatoms, Sponge spicules, and other 
 siliceous organisms. The Cretaceous formations of north- 
 ern France, Belgium, western Germany, and Denmark 
 much resemble those of England. Chalk appears also 
 farther east, in southern Russia. In Saxony and Bohe- 
 mia the Cretaceous rocks are mainly sandstones. In 
 the Mediterranean region, where there is a great de- 
 velopment of the Cretaceous, the rocks are mostly 
 limestones, but do not include the chalk and green- 
 sand which are so characteristic of the northern Cre- 
 taceous region. 
 
CRETACEOUS ERA. 
 
 367 
 
 LIFE. 
 
 PLANTS. 
 
 The first of Angiosperms, both Monocotyledons and 
 Dicotyledons, as already stated, date from the Cretaceous 
 period. Leaves of a few American species of Dicoty- 
 ledons are represented in Figs. 399-402; Fig. 401, a 
 species of Sassafras; Figs. 899, 400, species of Lirioden- 
 
 FIGS. 399-402. 
 
 ANGIOSPERMS : Fig. 399, Liriodendron primaevum ; 400, Liriodendron Meekii ; 401, Sassafras 
 cretaceum ; 402, Salix Meekii. 
 
 dron; Fig. 402, a Willow ; and with these occur leaves 
 of Oak, Dogwood, Beech, Poplar, etc. Among the Mono- 
 cotyledons are the earliest of the great family of the 
 Palms. 
 
 Beside these highest of plants, there were also Con- 
 ifers, Ferns, and Seaweeds, as in former time, with some 
 
368 
 
 HISTORICAL GEOLOGY, 
 
 Cycads. The microscopic Algae called Diatoms (page 
 88), which make siliceous shells, and others called Des- 
 mids, which consist of simple green cells without any 
 skeleton, were very abundant. Both occur fossil in flint; 
 and the Diatoms are believed to have contributed part of 
 the silica of which the flint is formed. 
 
 ANIMALS. 
 
 Protozoans. The simplest of animals, Foraminifers, 
 were of great geological importance in the Cretaceous 
 period ; for the Chalk is supposed to be made mostly of 
 their minute calcareous shells. The powdered chalk is 
 often found to contain large numbers of these shells, the 
 great majority of which do not exceed a pin's head in 
 size. A few of the forms are represented in Figs. 403- 
 407, all very much enlarged, except Fig. 407, which is 
 natural size. A very common kind resembles Fig. 50 
 
 404 
 
 FIGS. 403-407. 
 405 406 
 
 FORAMINIFEBS : Fig. 403, Lituola nautiloidea; 404, Flabellina rugosa; 405, Chrysalidina 
 gradata ; 406, Cuneolina pavonia ; 40T, Patellina Texana. 
 
 (page 61), and is named Rotalia. Fig. 407 represents a 
 large disk-shaped species from Texas. 
 
 Sponges. Sponges were also very abundant, and 
 their siliceous spicules (page 63) were another important 
 source of the silica of the flints. The skeletons of some 
 of the Sponges, both of the Cretaceous era and of modern 
 time, in the deeper seas, consist wholly of silica. Fig. 408 
 represents a species whose skeleton was probably siliceous. 
 
 Coelenterates. Corals of modern type are not uncom- 
 mon fossils. 
 
CRETACEOUS ERA. 
 
 369 
 
 FIG. 408. 
 
 Echinoderms. Echinoids are abundant ; and many of 
 the Echinoids are of the highest division of the class, 
 in which the radial arrangement of parts becomes largely 
 subordinated to a bilateral sym- 
 metry. This group commenced 
 in the previous era, but became 
 more abundant in the Qretaceous. 
 
 Mollusks. Figs. 409-412 rep- 
 resent some of the most charac- 
 teristic species of Lamellibranchs 
 from the American Cretaceous. 
 All these are of genera now ex- 
 tinct ; but many genera both of 
 Lamellibranchs and Gastropods 
 that still survive were already in existence. 
 
 Fig. 413 represents one of the Rudista, a remarkable 
 group of Lamellibranchs, peculiar to the Cretaceous, in 
 
 FIGS. 409-412. 
 
 SPONGE : Siphonia lobata. 
 
 410 N 
 
 LAMELLIBRANCHS: Fig 
 
 J. Exogyra costata ; 410, Gryphaea vesicularis ; 411, Gryphsea 
 Pitcher! ; 412, Inoceramus labiatus. 
 
 which the two valves of the shell are extremely unequal, 
 the small left valve appearing as a sort of cover to the 
 deep conical right valve, 
 
370 
 
 HISTORICAL GEOLOGY. 
 
 Fio. 413. 
 
 Figs. 414, 415, represent two American species of Gas- 
 tropods. 
 
 But the Cephalopods, in this era as in the preceding, 
 were the most characteristic class of Mollusks. The 
 Tetrabranchs were represented by numerous species of 
 the Ammonite group, and the Dibranehs by Belemnites. 
 Figs. 416-420 are Cephalopods, all American species ex- 
 cept Fig. 418. Fig. 416 is a front view 
 of a species of the Ammonite group, 
 showing the pockets formed by the 
 crumpling of the edge of the outer sep- 
 tum. Fig. 416 b shows the extremely 
 complicated form of the suture in this 
 species. Some of the Jurassic and Cre- 
 taceous Ammonites are 3 or 4 feet in 
 diameter. Especially characteristic of 
 the Cretaceous, though not unknown in 
 previous eras, were genera of the Ammo- 
 nite group in which the shell departed 
 from the form of a closely coiled discoidal 
 spiral (Fig. 371, page 347) which was 
 typical in the group. Three of these 
 aberrant forms are shown in Figs. 417 
 419. Fig. 417 is the loosely coiled 
 Scaphites ; Fig. 418, coiled in a turreted 
 spiral, is a Turrilites (Latin turris, 
 Hip- tower) ; Fig. 419 is the straight Bacu- 
 
 7 . r . , 7 , 
 
 htes (Latin oaculum, staff). 
 
 Fig. 420 represents a species of Belemnite common in 
 the Cretaceous beds of New Jersey. 
 
 Vertebrates. There were great numbers of Teleosts, or 
 Osseous Fishes, allied to the Herring, Salmon, Mackerel, 
 etc. They occur along with numerous Sharks of both 
 ancient and modern types, and also many Ganoids. Thus 
 the ancient and modern forms of Fishes were associated 
 in the population of the Cretaceous seas, the latter, how- 
 ever, greatly predominating, especially in the latter part 
 
 purites Toucasianus. 
 
CRETACEOUS ERA. 
 FIGS. 414-420. 
 
 371 
 
 416 a 
 
 
 4166 
 
 417 
 
 GASTROPODS : Fig. 414, Fasciolaria buccinoides ; 415, Pyrifusus Newberryi. CEPHALOPODS : 
 Fig. 416, Placenticeras placenta ; 416 <?-, same, in profile, reduced ; 416 6, diagram show- 
 ing form of suture in same ; 417, Scaphites larvaeformis ; 418, Turrilites cateuatus 419 
 Baculites ovatus ; 420, Belemnitella Americana, 
 
372 
 
 HISTORICAL GEOLOGY. 
 
 of the era. Fig. 421 represents one of these Teleost Fishes, 
 related to the Salmon and Smelt. 
 
 Reptiles included species of all the orders occurring in 
 the Jurassic. The Plesiosaurs were represented by the 
 
 PIG. 421. 
 
 TELEOST : Osmeroides Lewesiensis, x J. 
 
 genera Cimoliosaurus, Elasmosaurus, etc., some species of 
 which were 50 feet in length. The Dinosaurs included 
 species of all the groups represented in the Jurassic, though 
 the Sauropods appear to have become extinct before the 
 close of the Cretaceous. Lcelaps is a well-known example 
 
 FIG. 422. 
 
 DINOSAUR : Triceratops prorsus, x 
 
 of the Theropods, and Iguanodon and Hadrosaurus of the 
 Ornithopods. Besides Ornithopods and Stegosaurs, the 
 Predentata were represented by the remarkable Horned 
 Dinosaurs, or Oeratopsidce (Greek /ce/oa?, horn, cn/rt?, aspect), 
 peculiar to the Laramie beds (Fig. 422). These resem- 
 
CKETACEOUS ERA. 
 
 373 
 
 bled in many respects the Stegosaurs, but were strongly 
 characterized by the great horn cores shown in the figure, 
 which doubtless supported epidermic horns like those of 
 cattle. Among the Pterosaurs, Pteranodon differed from 
 the Jurassic genera (and from other Cretaceous genera) 
 in being destitute of teeth. Two species from Kansas had 
 a spread of wings of 20 to 25 feet. 
 
 There was also an order of Reptiles peculiar to the Cre- 
 taceous, that of the Mosasaurs, or Pythonomorphs : great 
 
 FiGS. 428, 424. 
 
 MOSASATJRS : Fig. 423, Mosasaurus Camperi, x 
 dispar, x . 
 
 ; 424, lower jaw of Edestosaurus 
 
 snakelike Reptiles, 15 to 75 feet long, swimming by 
 means of four paddles literally the Sea Serpents of the 
 era. The remains of the head of one, from the banks of 
 the river Meuse in Holland (whence the name), are repre- 
 sented in Fig. 423. The American rocks have afforded 
 nearly fifty species of these Mosasaurs. The head of the 
 largest was four feet long, and the mouth was of enormous 
 size. Moreover, these Reptiles had a movable joint in the 
 lower jaw, on either side, in place of the usual suture (at a, 
 
374 
 
 HISTOEICAL GEOLOGY. 
 
 FIG. 425. 
 
 in Fig. 424), which enabled the two rami of a jaw (since 
 the rami were not united at their extremities) to act like 
 a pair of arms, in working down the immense throat any 
 large animal they might undertake to swallow whole. A 
 tooth of one of the Mosasaurs, half the natural size, is 
 shown in Fig. 425. 
 
 Among the orders of Reptiles now living, there were 
 numerous species of Crocodiles and Turtles ; one of the 
 latter, from Kansas, measuring 15 feet, according to Cope, 
 between the tips of the extended flippers. There were 
 also a few Lizards, and the earliest of Snakes. 
 
 The Birds of the Cretaceous were all apparently free 
 from the reptilian characters of long tail and free meta- 
 carpals, possessed by the Jurassic Archce- 
 opteryx ; but some of them, as first 
 made known by Marsh, still retained 
 teeth. 
 
 Fig. 426, from Marsh, represents the 
 skeleton of Hesperornis regalis, one eighth 
 the natural size a large Bird with rudi- 
 mentary wings, flat sternum (as in the 
 Ostriches), and teeth inserted in a groove. 
 It resembled the Loons, or Divers, in 
 several features of the skeleton, and was 
 probably aquatic in habit. Fig. 432 
 represents a very different Bird, Ichthy- 
 ornis victor a Bird of moderate size, 
 with well-developed wings, keeled ster- 
 num, teeth inserted in sockets, but with 
 the very remarkable character "of bi- 
 concave vertebrae. Both these Birds are 
 from Kansas, but a Bird apparently allied 
 to Ichthyornis has been found in the 
 Greensarid of England. Apparently there were other Cre- 
 taceous Birds which were toothless, and related to the 
 modern Cormorants and Waders. 
 
 Mammals are represented by numerous teeth and frag- 
 
 Tooth of Mosasaurus 
 princeps, x . 
 
CRETACEOUS ERA. 
 
 FIGS. 426-481. 
 
 375 
 
 TOOTHED BIRD : Fig. 426, Hesperornis regalis, skeleton, x 
 x 4 ; 429, 430, vertebrae, x J ; 481, pelvis, side view, x * 
 a, acetabulum. 
 
 P 
 
 \ ; 427, lower jaw, x ; 428, tooth, 
 ; il, ilium ; is, ischium ; p, pubis ; 
 
376 HISTORICAL GEOLOGY. 
 
 ments of jaws, and a few fragments of other bones, from 
 the Laramie beds of North America, and by a single tooth 
 from the Wealden in England. They are probably all 
 Monotremes and Marsupials. 
 
 GENERAL OBSERVATIONS. 
 
 Geography. The Cretaceous, both in North America 
 and in Europe, as compared with the earlier periods of the 
 Mesozoic, was eminently a period of submergence. This 
 is indicated by the large areas occupied by marine forma- 
 tions ; and especially by the large areas of chalk and other 
 limestones. The deposits of chalk must have been formed, 
 not in shallow waters adjacent to the shores, but in open 
 seas. It is not probable, however, that the seas in which 
 the chalk was deposited were of oceanic depth. Forami- 
 nifers are animals, not of the abyssal depths, but of the 
 surface, the shells sinking to the bottom only after the 
 death of the animals ; and a f oraminiferal deposit is there- 
 fore evidence of an open sea comparatively free from 
 detritus, but not necessarily of great depth. The other 
 fossils of the chalk belong apparently not to the abyssal 
 fauna, but to that of comparatively shallow water. 
 
 As shown for North America by the map on page 364, 
 the submergence did not attain its maximum until the 
 earlier part of the Upper Cretaceous. The deposits of the 
 Lower Cretaceous were largely of fresh-water origin, on 
 both sides of the Atlantic. 
 
 On the Atlantic Border of North America, the strata of 
 the Upper Cretaceous are the first marine deposits known 
 since the Lower Silurian. The geanticlinal elevation 
 formed at the time of the Taconic Revolution seems at 
 last to have subsided. At the time of the greatest sub- 
 mergence, Chesapeake and Delaware bays were in the 
 ocean ; Florida was under water ; the region of the Mis- 
 souri River was a salt-water region ; the Rocky Mountain 
 region was largely submerged. This mountain region was 
 
CRETACEOUS ERA. 
 
 377 
 
 in some parts at least 10,000 feet lower than now, the Cre- 
 taceous beds having this elevation upon it. The Mexican 
 
 FIG. 432. 
 
 TOOTHED BIRD : Ichthyornis victor, x . 
 
 Gulf spread over the Gulf States from Florida to Texas, 
 and extended northward to the mouth of the Ohio ; while 
 a vast mediterranean sea stretched from the western part 
 
378 HISTORICAL GEOLOGY. 
 
 of the Gulf of Mexico, northward over the great plains 
 and the summit region of the Rocky Mountains, probably 
 even to the Arctic Ocean a distance of 3000 miles. 
 About the middle of the Upper Cretaceous, there was a 
 shallowing of the sea and an emergence of the land far 
 north in British America, so that the great western medi- 
 terranean was cut off from the Arctic Ocean, and became 
 a part of the Gulf of Mexico, though still having a length 
 of 2000 miles or more. Gradually the area of this great 
 western gulf contracted along its eastern border, and the 
 depth diminished; until at last, in the Laramie epoch, 
 brackish and fresh waters took the place of the seas in 
 which chalk and other limestones had been deposited. 
 
 The Upper Cretaceous (and especially the Laramie 
 epoch) was the great coal period of western North Amer- 
 ica, as the Carboniferous period was the coal period of 
 eastern -North America and western Europe. In each 
 case, a large area which had been submerged beneath the 
 sea was passing through an epoch of transition to terres- 
 trial conditions. For a long time the area was balancing 
 near the sea level, now emerging and clothing itself with 
 luxuriant vegetation, now submerged and receiving sedi- 
 mentary deposits. The kinds of plants which made the 
 Cretaceous forests were, however, widely different from 
 those of the Carboniferous. 
 
 Climate. Although there is clearer indication of dif- 
 ferentiation of zones of climate in the Cretaceous than in 
 any earlier period, a warm climate still prevailed even 
 in high northern latitudes. The Cycads of the Lower 
 Cretaceous in Greenland indicate, according to Heer, a 
 mean temperature not below 70 F. There appear to have 
 been no true coral reefs in the British seas, though such 
 reefs were certainly present in the Mediterranean basin. 
 The isotherm of 68 for the coldest winter month appar- 
 ently passed south, but not far south, of Great Britain. 
 The plants of the upper Missouri region indicate a warm- 
 temperate climate over that territory. 
 
MESOZOIC TIME. 379 
 
 GENERAL OBSERVATIONS ON THE MESOZOIC. 
 
 Time Ratios. The ratios between the Eopaleozoic, 
 Upper Silurian, Devonian, and Carboniferous ages, as to 
 the length of time that elapsed during their progress, or 
 their time ratios, are stated on page 317 as probably not far 
 from 6:1:2:2. By the same method, it follows that 
 the ratio for the time of the Paleozoic and Mesozoic was 
 nearly 4:1. That is, Mesozoic time was about one fourth 
 as long as the Paleozoic ; and the three eras of the Mesozoic 
 were not far from equal, the Cretaceous being probably 
 somewhat the longest. 
 
 American Geography. On page 331 it is remarked 
 that the Mesozoic formations were confined to the Atlantic, 
 Pacific, and Gulf Border regions, the Arctic region, and 
 an Interior region west of the Mississippi covering much 
 of the Rocky Mountain area ; and that the portion of the 
 continent between that Interior region and the Atlantic 
 Border had probably become part of the dry land. The 
 facts which have been presented in the preceding pages 
 have sustained this statement. The Triassic beds, as has 
 been shown, lie in long, narrow strips between the Appala- 
 chians and the coast, and spread widely over the Rocky 
 Mountain region and west nearly to the Pacific. The 
 Jurassic beds have a similar wide distribution in the West, 
 though probably wanting in the East. The Cretaceous 
 beds cover the Atlantic and Gulf Borders, and a very large 
 area over the slopes of the Rocky Mountains and the adja- 
 cent plains, and the Pacific Border west of the Sierra 
 Nevada. The eastern half of the continent during the 
 Mesozoic was, therefore, receiving rock formations only 
 along its borders, while the western half had marine de- 
 posits in progress over its great interior and on the 
 ocean's border. 
 
 The American Mesozoic deposits do not bear evidence 
 that they were formed in a deep ocean. The Triassic and 
 
380 HISTORICAL GEOLOGY. 
 
 Jurassic strata appear to have accumulated mainly along 
 coasts, or in shallow waters off coasts, or in shallow estuaries 
 or inland seas ; some of the Cretaceous deposits indicate a 
 clear and open sea, but not necessarily one of great depth. 
 
 The Appalachians the eastern mountains of the conti- 
 nent had been elevated before the early Mesozoic beds 
 commenced to form (page 326). But the region of the 
 Rocky Mountains the western chain was to a great 
 extent still a shallow sea even during the Cretaceous 
 era, or when Mesozoic time was drawing to its close 
 (page 376). 
 
 One strongly marked epoch of mountain-making, in 
 western North America, occurred at the close of the 
 Jurassic, the Sierra Nevada and other high ranges dating 
 from that time. 
 
 European Geography. Europe has its Mesozoic rocks 
 distributed in patches, or in several independent or nearly 
 independent areas, which show that it retained its con- 
 dition of an archipelago throughout Mesozoic time. The 
 oscillations of level, as indicated by the variations in the 
 rocks, variations both as to the nature of the beds and 
 their distribution, were more numerous and irregular 
 than in North America. The mountain elevations formed, 
 however, were few and small compared with those that 
 followed either the Paleozoic or the Mesozoic. One series 
 of disturbances is referred to the close of the Triassic, and 
 another to that of the Jurassic. 
 
 Among the Mesozoic formations of the European conti- 
 nent there are deposits of all kinds those of seashores ; 
 of offshore shallow waters ; of moderately deep, clear, and 
 open seas ; of inland seas ; and of marshy, or dry and 
 forest-covered, land. 
 
 Both in America and Europe there were some coal beds 
 made, though all of them were comparatively insignificant, 
 except those of western North America in the Upper 
 Cretaceous ; even these are inferior in extent to those of 
 the Carboniferous. 
 
MESOZOIC TIME. 381 
 
 Life. The Mesozoic age witnessed (1) the decline 
 of some ancient or Paleozoic types of both plants and ani- 
 mals, (2) the increase and culmination of mediaeval or 
 Mesozoic types, and (3) the beginning of some of the 
 most important of modern or Cenozoic types. 
 
 1. Disappearance of Ancient or Paleozoic Features. 
 Among the ancient tribes of plants, several genera of 
 Ferns disappear in the Jurassic. Among the old Brachio- 
 pod tribes, the Spirifer and Stropliomena families end in 
 the Lias ; among Mollusks, the Silurian type of Orthoceras 
 has its last species in the Triassic ; in the same era, the 
 Ganoid Fishes mostly lose the vertebrated feature of their 
 tails, characterizing them in the Paleozoic, and thus bear 
 evidence of progress. 
 
 2. Progress in Mesozoic Features. The Cycads, among 
 plants, were those most characteristic of the Mesozoic : 
 they afterward yielded to other kinds, and now are a 
 nearly extinct group. The Cephalopods, among Mollusks, 
 existed in vast numbers, both those with external shells 
 (Tetrabranchs), as the Ammonites, and those without (Di- 
 branchs), as the Belemnites. The whole number of species 
 of the Ammonite group thus far described is almost 5000 ; 
 and the vast majority of these belong to the Mesozoic, the 
 Paleozoic genera of the group including comparatively few 
 species. No Ammonite now exists, and the only Tetra- 
 branch Cephalopods now living are six species of the 
 genus Nautilus. The whole number of species of Cepha- 
 lopods living in the course of Mesozoic time must have 
 been many thousand, since only a part would have been pre- 
 served as fossils. The subkingdom of Mollusks, therefore, 
 culminated in Mesozoic time ; for its highest class, that of 
 the Cephalopods, was then at its maximum. 
 
 The Stegocephala, or Labyrinthodonts, culminated in 
 the Triassic, and became extinct at the close of that era 
 (or possibly during the Jurassic). 
 
 The type of Reptiles was another that expanded and 
 reached its culmination that is, its maximum in number, 
 
382 HISTORICAL GEOLOGY. 
 
 variety, size, and rank of species, and commenced its 
 decline in Mesozoic time. 
 
 There were huge swimming Reptiles, fishlike Ichthyo- 
 saurs, and snakelike Mosasaurs, some of the latter 75 or 
 80 feet long, in the place of Whales in the sea ; batlike 
 Reptiles, or Pterodactyls, flying through the air; four- 
 footed Reptiles, both grazing and carnivorous, many of 
 them 25 to 50 feet long, occupying the marshes and 
 estuaries 5 and great biped Reptiles, or Dinosaurs, over 
 the land. 
 
 The Wealden formation of England has afforded remains 
 of 30 or more species of Dinosaurs, Crocodiles, and Enalio- 
 saurs, most of which were 10 to 50 feet long, besides Ptero- 
 dactyls and Turtles ; and many more than this must have 
 lived, since not all that lived would have left their remains 
 in the deposits. It is, however, not certain that all the 
 species of the Wealden were contemporaneous. To appre- 
 ciate this peculiarity of Mesozoic time, it should be con- 
 sidered that in the present age Great Britain has no large 
 Reptiles. In the whole torrid zone (to which large Rep- 
 tiles are now mostly restricted) there are not much more 
 than a dozen species over 15 feet in length (Crocodiles, 
 and Snakes of the Python and Boa families), and probably 
 no species reaching a length of 30 feet. North America, 
 during the Jurassic and Cretaceous, appears to have ex- 
 ceeded all the world besides, in the number and size of its 
 Reptiles. Mesozoic time is well named the Age of Reptiles. 
 
 The Birds of the age, or at least some of them, partook 
 of the reptilian features of the time; some of them having 
 long tails like the associated Reptiles (though feathered 
 tails), and free metacarpals ; and several different groups 
 of Birds having reptile-like teeth. The Reptilian Birds 
 and Pterodactyls were the flying creatures of the age ; 
 the Ichthyosaurs and Plesiosaurs and the like, the "great 
 whales" ; the Crocodiles and Dinosaurs, the dominant life 
 of the estuaries and of the land. Even the Mammals bore 
 a reptilian character, being mostly, and probably exclu- 
 
LARAMIDE REVOLUTION. 383 
 
 sively, Monotremes and Marsupials. The Monotremes 
 resemble Reptiles in being oviparous, and in numerous 
 anatomical characters. And the Marsupials, though vivipa- 
 rous, have not attained to the typical mammalian character 
 of placental nutrition of the embryo (page 86). 
 
 3. Introduction of Cenozoic Features. Among plants 
 the first of Angiosperms are found in the Cretaceous. 
 These become the characteristic plants of Cenozoic time. 
 
 Among Vertebrates there was a great expansion of the 
 group of Teleosts, or Osseous Fishes, the species charac- 
 teristic of earlier time having been either Selachians, Placo- 
 derms, Ganoids, or Dipnoans (page 283). The earliest 
 species of the modern genus Crocodilus occur in the Creta- 
 ceous ; the first of Birds in the Jurassic Reptilian Birds; 
 the first of Mammals in the Triassic probably Mono- 
 tremes. 
 
 Of the classes of Vertebrates, Fishes commenced in the 
 early Paleozoic, Amphibia and Reptiles in the later Paleo- 
 zoic, Mammals in the early Mesozoic, and Birds in the 
 middle Mesozoic. 
 
 DISTURBANCES CLOSING MESOZOIC TIME. 
 
 The Post-Mesozoic, or Laramide, Revolution. The close 
 of Mesozoic time was marked by the making of the 
 greatest of American mountain systems. The Laramide 
 mountain system extends along the whole line of the sum- 
 mit region of the Rocky Mountains from near the Arctic 
 Ocean to central Mexico a distance exceeding 4000 
 miles. In the middle latitudes of the United States, it 
 includes the Wasatch Range of Utah and other ranges to 
 the east as far as the Front Range of Colorado. 
 
 In the Laramide system, as in the earlier Taconic and 
 Appalachian systems, there had been an accumulation of 
 many thousands of feet of strata in a geosyncline, which 
 was in progress through Paleozoic and Mesozoic time; and 
 the final orogenic catastrophe was of the same general nature. 
 
884 HISTORICAL GEOLOGY. 
 
 It is also probable that in South America, at this same 
 time, another system of ranges of as great a length was 
 made along the Andes, and that consequently the moun- 
 tain-making movements of America at the close of the 
 Cretaceous extended through nearly one third of the 
 earth's circumference. 
 
 The mountain-making of this time was accompanied 
 by extensive igneous outflows. Trachyte eruptions took 
 place in the Wasatch Mountains. 
 
 The eruption of the trap of the Deccan in India (page 
 189), the most colossal outflow of igneous rock of which 
 we have evidence, took place at or near the close of the 
 Cretaceous. 
 
 Change of Fauna and Flora. The disappearance of 
 life at this crisis was so extensive that no species of the 
 Cretaceous era, except some Foraminifers and land plants, 
 have yet been identified with certainty in any rock of the 
 following era. This is another great feature in which 
 the Post-Mesozoic revolution was like the Post-Paleozoic. 
 Not only species, but also many of the families and orders 
 characteristic of the Mesozoic disappeared. Here ended 
 the reign of Reptiles, all the characteristic Mesozoic kinds 
 the Dinosaurs, Enaliosaurs, Pterosaurs, and others 
 becoming extinct. ' The Ammonites also, and the Belem- 
 nites, with many of the genera of other classes of Mollusks, 
 disappeared. Among plants, the Cycads, which were a 
 prominent feature of the early Cretaceous forests, even 
 in Arctic lands, later retreated southward, and became 
 confined to the warm-temperate and tropical zones, where 
 the few species now existing are to be found. 
 
 As in other such exterminations, the extinction of life 
 was not universal. The survival of the genera and fami- 
 lies proves that there was no cataclysmic break in the 
 succession of life ; and some regions may have suffered 
 little extermination. All that can be affirmed is, that the 
 fossils of the Tertiary era, the next after the Cretaceous, 
 include, so far as yet discovered, no marine Cretaceous 
 
CENOZOIC TIME. 385 
 
 species, except a few species of Foraminifers, and no Cre- 
 taceous species of terrestrial Vertebrates. 
 
 As to the causes of so remarkable a change in the life 
 of the globe, the remarks made on page 330 in reference 
 to the Appalachian revolution are applicable here. Prob- 
 ably the extinction of species at the close of the Mesozoic 
 was in great degree due to climatic changes. The emer- 
 gence from the ocean of one third of North America, and 
 probably of as large a part of South America, and of large 
 portions of other continents, with the resultant changes 
 in the 1 paths of ocean currents, and the formation of lofty 
 mountain ranges, must have produced very appreciable 
 changes of climate. This may account for much extinc- 
 tion of species even in regions where the Cretaceous strata 
 and the overlying Tertiary are perfectly conformable. 
 
 IV. CENOZOIC TIME. 
 
 CENOZOIC TIME includes two eras : 1, THE TERTIARY 
 ERA, or AGE OF MAMMALS; and 2, THE QUATERNARY, 
 or AGE OF MAN. 
 
 General Characteristics. In the transition to this aeon 
 the life of the world takes on a new aspect. Trees of 
 modern types Oaks, Maples, Beeches, etc., and Palms 
 unite with Conifers to make the forests ; Mammals of 
 great variety and size Ungulates, Carnivores, and others, 
 successors to the small oviparous and semi-oviparous Mam- 
 mals of the Mesozoic tenant the land, in place of Rep- 
 tiles; typical Birds and Bats possess the air, in place of 
 Reptilian Birds and Pterodactyls ; Whales, and Teleosts, 
 with Sharks mainly of modern type, occupy the waters, in 
 place of Enaliosaurs, and almost to the exclusion of the 
 ancient tribes of Cestraciont Sharks and Ganoids. Finally 
 Man appears, when Mammals are passing their maximum 
 in grade and magnitude, and becomes the dominant species 
 of the finished world. 
 
386 HISTORICAL GEOLOGY. 
 
 I. TERTIARY ERA. 
 
 GENERAL CHARACTERISTICS. 
 
 The Mammals of this age are all extinct species, and 
 the animals of other classes largely so ; the number of liv- 
 ing species of Invertebrates varies from perhaps one per 
 cent in the early part of the age to 90 at its close. 
 
 SUBDIVISIONS. 
 
 The Tertiary strata have been divided by Lyell into 
 three groups, based upon the ratios between the extinct 
 species and those still living, among the Invertebrate fos- 
 sils of the respective beds : 
 
 1. Eocene (from the Greek 77069, dawn, and /eatw, recent) : 
 species nearly all extinct. 
 
 2. Miocene (from /-tetW, less, and /eatwfc) : less than half 
 the species living. 
 
 3. Pliocene (from TrXetW, more, and /caivo^ : more than 
 half the species living. 
 
 Some geologists recognize a period called Oligocene be- 
 tween Eocene and Miocene ; but the Oligocene strata are 
 here included in the Eocene. 
 
 The name Neocene is sometimes applied to the Miocene 
 and Pliocene taken together. 
 
 AMERICAN GEOGRAPHY: AREAS OF ROCK-MAKING. 
 
 The changes of level during the Laramie epoch and at 
 its close involved the emergence of the great Interior 
 region of the continent. Of the great mediterranean sea 
 which had characterized the Cretaceous period, the only 
 remnants were a large bay on the Arctic shores, an exten- 
 sion of the Gulf of Mexico at the south, and some large 
 fresh-water lakes distributed over the interior. Marine 
 Tertiary deposits (exclusive of those in the Arctic regions) 
 were accordingly confined to the Atlantic and Gulf Border 
 
TERTIARY ERA. 
 
 387 
 
 (which formed a single continuous area), and the Pacific 
 Border. Fresh-water deposits of great extent and im- 
 portance were made in the lakes of the Interior. The 
 map (Fig. 433) shows the areas of submergence and of 
 rock-making in the early and later Tertiary respectively. 
 The areas vertically lined were under water (salt or fresh) 
 in the Eocene ; those horizontally lined were under water 
 in one or both of the later periods of the Tertiary ; those 
 
 FIG. 483. 
 
 North America in the Tertiary era. 
 
 cross-lined were submerged in both early and later Ter- 
 tiary time. As shown in the map, the northward exten- 
 sion of the Gulf of Mexico in the region of the Mississippi 
 was about the same in the Eocene as in the Cretaceous, 
 but the shore line moved far southward in the later Ter- 
 tiary. The great lakes of the Eocene were in what is 
 now the summit region of the Rocky Mountains. One 
 of them (U, on the map) lies south of the Uinta Moun- 
 
388 HISTORICAL GEOLOGY. 
 
 tains, between the Wasatch and the Front Ranges of Colo- 
 rado ; another, still larger (W, on the map), lies north of 
 the Uinta Mountains. In the later Tertiary, the lakes of 
 the summit region were drained, and great lakes were 
 formed west, and especially- east, of that region. The 
 situation of these lakes indicates that the Rocky Mountain 
 region in general was much less elevated at the beginning 
 of the Tertiary than at present. 
 
 ROCKS: KINDS AND DISTRIBUTION. 
 
 The marine and lacustrine formations are independent 
 in their fossils, and are nowhere interstratified. More- 
 over, as geographical diversity of faunas has increased 
 through all geological time, the fossils of the Atlantic and 
 Pacific Borders are almost wholly of different species. It 
 is therefore impossible to make any exact correlation of 
 the formations of the different regions. 
 
 The most northerly outcrop of the Eocene on the Atlantic 
 Border is in New Jersey. The formation appears in that 
 state as a narrow and interrupted belt. It is wider in 
 Maryland and Virginia, and still wider in South Carolina. 
 But it is best displayed on the Gulf Border. 
 
 The Miocene appears on Marthas Vineyard, and dredg- 
 ings on Georges Bank and the Grand Bank of New- 
 foundland indicate that the deposit continues under the 
 shallow sea east of New England. It extends continu- 
 ously from New Jersey to North Carolina, is represented 
 by isolated patches in South Carolina, is well developed 
 in Florida, and extends along the Gulf Border to Texas 
 and beyond, though partly covered by later deposits. 
 
 Patches of marine Pliocene appear at various points 
 along the Atlantic Border, but the formation attains its 
 most extensive development in Florida ( Florid ian forma- 
 tion). Along the Gulf Border lacustrine deposits of late 
 Tertiary age occur in various places. 
 
 The Tertiary rocks are generally but little consolidated ; 
 they consist mostly of compacted sand, pebbles, clay, earth, 
 
TERTIARY ERA. 389 
 
 that was once the mud of the sea bottom or of estuaries 
 or lakes, mixed often with shells. They are, indeed, 
 such deposits as are now forming along seashores, and 
 in shallow bays, estuaries, and lakes, or in shallow waters 
 off a coast. There are also limestones made of shells, and 
 others of corals, resembling the reef rock of coral seas. 
 The latter are found mainly in the states bordering on 
 the Mexican Gulf. Another variety of rock is buhrstone, 
 a siliceous rock, cellular by reason of the removal of fossil 
 shells by solution, used, on account of its being so hard 
 and at the same time full of irregular cavities, for making 
 millstones. It occurs in the Eocene of South Carolina, 
 Georgia, and Alabama. Beds of greensand and of lignite 
 or coal occur in some of the deposits. Beds of Diatoms 
 and Radiolarians are sometimes of considerable thickness. 
 In general, the Tertiary rocks differ from those of earlier 
 periods in that the character of the beds of the same hori- 
 zon is apt to vary from mile to mile, instead of persisting 
 over large areas. There are, however, some exceptional 
 cases of Tertiary beds whose character is nearly uniform 
 over considerable areas. The lacustrine beds of the Inte- 
 rior are remarkable for the treasures of fossil Mammals 
 which they have yielded. Local lignitic beds of lacus- 
 trine origin are scattered over various parts of the coun- 
 try. One at Brandon, Vermont, supposed to be of Eocene 
 age, is famous for the fossils it has yielded. 
 
 The Tertiary of Great Britain (11, on map, page 295) 
 occurs mostly in the southeastern part of England, in the 
 London basin, and on the southern and eastern borders of 
 the island, adjoining the Cretaceous. The large areas are 
 mostly Eocene (including Oligocene) ; a narrow strip along 
 the coast of Norfolk and Suffolk is Pliocene. 
 
 On the continent of Europe, the Paris basin is noted 
 for its Eocene strata and their fossil Mammals. Other 
 Tertiary areas are those of the Pyrenean and Mediterra- 
 nean regions, those of Switzerland, of Austria, etc. Some 
 of the marine Eocene beds contain Rhizopods (p. 62) 
 
390 HISTORICAL GEOLOGY. 
 
 having the shape of a coin, called Nummulites (from the 
 Latin nummus, a coin). One is here figured, natural 
 size ; the exterior of one half has been removed to show 
 the cells within. Occasionally the beds are so far made 
 up of these Nummulites that the rock is called Nummulitic 
 Limestone. 
 
 These marine Eocene strata spread very widely over 
 Europe, northern Africa, and Asia occurring in the 
 Pyrenees, forming some of their summits ; 
 in the Alps to a height of more than 10,000 
 feet ; in the Carpathians ; in Algeria ; in 
 Egypt, where the most noted pyramids 
 were made of Nummulitic Limestone; in 
 Persia; in the Himalayas, to a height of 
 
 more than 20 > 000 feet > in Japan and the 
 East Indies. The later Tertiary formations 
 are much more limited in distribution, and many are of 
 terrestrial or fresh-water origin. 
 
 The rocks are similar to those of North America, but 
 include more of hard sandstone and limestone. The sand- 
 stone is a very common building stone in different parts 
 of Europe, being soft enough to be worked with facility, 
 yet generally hardening on exposure, owing to the fact 
 that it contains calcareous particles (triturated shells), 
 which render the percolating waters or rain calcareous, so 
 that on evaporating they produce a calcareous deposit, as 
 a cement, among the grains of sand. 
 
 LIFE. 
 
 PLANTS. 
 
 The great feature of the Tertiary vegetation is the 
 prevalence of Angiosperms, a class of plants which, thus 
 far, is unknown before the Cretaceous. Leaves of Oak, 
 Poplar, Maple, Hickory, Dogwood, Mulberry, Magnolia, 
 Cinnamon, Fig, Sycamore, Willow, and many others, rep- 
 resent the Dicotyledons, while the Monocotyledons are rep- 
 
TERTIARY ERA. 
 
 391 
 
 resented by numerous Palms. There are also remains of 
 Conifers. Nuts are common in some beds as at Bran- 
 don, Vermont. Fig. 435 is the leaf of an Oak ; Fig. 436, 
 of a species of Cinnamon ; Fig. 439, of a Palm ; Fig. 437, 
 the nut of a Beech, much like that of the common Beech; 
 Fig. 438, another nut, from Brandon, of unknown rela- 
 tions. 
 
 FIGS. 435-439. 
 
 DICOTYLEDONS: Fig. 435, Quercus myrtifolia; 436, Cinnamomum Mississippiense ; 
 437, Fagus ferruginea ; 438, Carpolithes irregularis. MONOCOTYLEDON : Fig. 439, Ca- 
 lamopsis Danae. 
 
 The Eocene Plants of Great Britain included Palms, 
 and among those of central and southern Europe there 
 were many species related to the trees of Australia ; while 
 the Miocene and Pliocene floras of Europe (especially the 
 former) had much similarity to the flora of America. 
 
 The microscopic plants which form siliceous shells, 
 called Diatoms (Figs. 143-148, page 88), make extensive 
 deposits in some places. One stratum near Richmond, Vir- 
 
392 
 
 HISTORICAL GEOLOGY. 
 
 ginia, is 30 feet thick, and is many miles in extent ; another, 
 near Monterey, California, is 50 feet thick, and the mate- 
 rial is as white and fine as chalk, which it resembles in ap- 
 pearance ; another, near Bilin in Bohemia, is 14 feet thick. 
 
 DIATOMS (and other organisms) from Richmond diatomaceous bed : a, Pinnularia peregrina ; 
 b, c, Odontidium pinmilatum ; d, Grammatophora marina; e, Spongiolithis appendic- 
 ulata ; /, Melosira sulcata ; g, same, transverse section ; h, Actinocyclus Ehrenbergii ; 
 i, Coscinodiscus apiculatus ; j, Triceratium obtusum ; k, Actinoptychus undulatus; 
 Z, Dictyocha crux ; m, Dictyocha; n, fragment of Actinoptychus senarius; o, Navicula; 
 p, fragment of Coscinodiscus gigas. 
 
 The material from the latter place was used as a polish- 
 ing powder (and called Tripoli, or polishing slate) long 
 before it was known that its fine grit was owing to the 
 remains of microscopic life. Ehrenberg has calculated 
 that a cubic inch of the fine earthy rock contains about 
 
TERTIARY ERA. 393 
 
 forty-one thousand millions of organisms. Such accumu- 
 lations of Diatoms are made both in fresh waters and 
 salt, and in those of the ocean at all depths. A group of 
 Diatoms from the Richmond bed is shown in Fig. 440. 
 
 ANIMALS. 
 
 The most prominent fact with regard to the Tertiary 
 Invertebrates is their general resemblance to modern spe- 
 cies. Although a number of the genera are extinct, and 
 nearly every Eocene species, there is still a modern look 
 in the remains, and the specimens have often the fresh- 
 ness of shells from a modern beach. Only a special stu- 
 dent of the Mollusca can distinguish the Tertiary species 
 from those now living. After the Eocene, species of the 
 present time begin to be abundant. The common Oyster 
 and Clam have been found fossil in deposits believed to 
 be of Miocene age. 
 
 Remains of Insects are more abundant and varied than 
 in any previous era. All the important orders are repre- 
 sented, including the Lepidopters (Moths and Butterflies), 
 which probably do not occur in any earlier formation. 
 More than 2000 species of Insects, in wonderfully perfect 
 state of preservation, have been obtained from the Amber 
 of the Baltic shores. The Amber is a fossil resin, derived 
 from Coniferous trees of the Upper Eocene (Oligocene) 
 period ; and the Insects were caught in .the resin while 
 it was still liquid, and thus effectually embalmed. Flo- 
 rissant, Colorado, is a famous locality for Eocene Insects ; 
 and Oeningen in Switzerland, and Radoboj in Croatia, are 
 among the richest Miocene localities. 
 
 With regard to Vertebrates, the points of special inter- 
 est are the following : 
 
 1. In the class of Fishes : (1) Teleosts, or Fishes allied 
 to the Perch a-nd Salmon, are, as already stated, the preva- 
 lent group ; (2) sharp-toothed Sharks are abundant, some 
 of them having teeth 6 inches long and nearly 5 inches 
 broad. The teeth of Sharks are the most durable part of 
 
394 
 
 HISTORICAL GEOLOGY. 
 
 442 
 
 FIGS. 441, 442. 
 
 441 
 
 the skeleton ; they are very abundant in both Eocene and 
 Miocene beds. Fig. 441 represents a tooth of Carcharodon 
 angmtidens. The larger teeth above alluded to belong to 
 Carcharodon megalodon, and are found at different places 
 on the Atlantic Border from Marthas Vineyard southward. 
 Fig. 442 represents the tooth of another common kind of 
 Shark, a species of Lamna, from the Eocene. 
 
 2. In the class of Amphibians: Only the modern groups 
 of Salamanders and Toads and 
 Frogs are represented. 
 
 8. In the class of Reptiles : 
 Crocodiles and Turtles are nu- 
 merous. The shell of one of the 
 Pliocene turtles, found fossil in 
 India, had a length of 12 feet, 
 and the animal is supposed to 
 have been 20 feet long. 
 
 4. In the class of Birds : The 
 species found are not long-tailed, 
 or in any respect reptilian, but 
 resemble modern Birds ; they are 
 related to the Geese, Pelicans, 
 Petrels, Herons, Rails, Pheasants, 
 Eagles, Owls, Doves, Parrots, 
 Woodpeckers, Sparrows, and 
 other kinds. 
 
 5. In the class of Mammals : 
 The typical (Placental) Mam- 
 mals attain a remarkable develop- 
 ment. In the Mesozoic, probably all the Mammalian re- 
 mains are those of Marsupials and Monotremes. But the 
 very earliest Eocene deposits contain remains of a number 
 of orders of Placental Mammals. Before the close of the 
 Eocene, most of the principal orders now in existence had 
 already appeared, in addition to some orders now extinct. 
 There were already, in the Eocene, Insectivores, Bats, Car- 
 nivores, Lemurs, Rodents, Ungulates, and Whales. Before 
 
 SELACHIANS: FIG. 441, tooth of Car 
 charodon angustidens ; 442, Lam 
 na elegans. 
 
TERTIARY ERA. 
 
 395 
 
 the close of the Miocene, Edentates and Monkeys were 
 added to the list. 
 
 Many of the Eocene Mammals exhibit remarkably gen- 
 eralized, or primitive, characters. They have the typical 
 number of teeth (44), and have the molars of simple form 
 with crowns showing three tubercles. Their feet are 
 five-toed, and plantigrade (i.e., the entire foot, even to 
 the wrist or heel, rests upon the ground) ; and the bones 
 
 FIG. 448. 
 
 UNGULATE: Phenacodus primaevus, Xj'g, a, fore foot; 6, hind foot. 
 
 of the wrist and ankle are in parallel series. The two 
 bones of the forearm (radius and ulna), and the corre- 
 sponding bones of the leg, are distinct from each other. 
 In later times, some of the Ungulates have departed most 
 widely from these primitive characters, as may be seen in 
 the Horse, with its smaller number of teeth, complicated 
 enamel folds in its molars, fingers and toes reduced to 
 one, only the finger nails and toe nails (hoofs) reaching 
 the ground, bones of wrist and ankle interlocking, bones 
 of the forearm united (the ulna becoming little more than 
 
396 HISTORICAL GEOLOGY. 
 
 a rudiment), and the leg showing a like modification. The 
 number of teeth has suffered reduction in almost all the 
 later Mammals ; but others of the primitive characteristics 
 which have been mentioned are retained in many groups 
 of modern Mammals (some of them in Man himself). 
 
 In the earliest Eocene, some of the representatives of the 
 Ungulate series exhibited all the primitive characters 
 just enumerated. Such a primitive Ungulate as is shown 
 in Fig. 443 differs but little from the types of Carnivores 
 (Creodonts) that existed in the same early Eocene strata. 
 The various orders had not then become as strongly differ- 
 entiated as they were destined to become in later times. 
 Before the close of the Eocene, Ungulates and Carnivores 
 had diverged much further from each other, and presented 
 themselves in much more characteristic forms. There 
 is perhaps no finer illustration of the theory of evolution 
 than that which is presented in the progress of the Ungu- 
 lates from the extremely generalized forms of the earliest 
 Eocene to such specialized forms as the Horses and 
 Ruminants of to-day. 
 
 Another noteworthy general fact in regard to the Mam- 
 mals of the early Tertiary is the small size of their brains, 
 as compared with later species, as illustrated in Figs. 
 444-446. 
 
 Cuvier first made known to science the existence of 
 Tertiary Mammals of extinct species. The remains from 
 the earthy beds about Paris had been long known, and were 
 thought to be those of modern beasts. But, by careful study 
 and comparison with living animals, Cuvier was enabled 
 to bring the scattered bones together into skeletons, as- 
 certain the orders to which they belonged, and determine 
 the food and mode of life of the extinct species. Cuvier 
 acquired his skill in the interpretation of fossils by 
 observing the mutual dependence which subsists between 
 all parts of a skeleton, and, in fact, all parts of an animal. 
 A sharp claw is evidence that the animal has trenchant 
 or cutting molar teeth, and is a flesh-eater ; a hoof, that 
 
TERTIARY ERA. 
 
 397 
 
 he has broad molars, and is a grazing species ; and, fur- 
 ther, almost every bone has some modification showing 
 the group of species to which it belongs, and may thus be 
 an indication, in the hands of one well versed in the sub- 
 ject, of the special type of the animal, and of its structure, 
 even to its stomach within and its hide without. In thus 
 applying comparative anatomy to the interpretation of 
 fossils, Cuvier laid the foundation of a new department 
 of science paleontology. 
 
 444 
 
 FIGS. 444-446. 
 445 
 
 Illustrations of relative sizes of brains: Fig. 444, Dinoceras (Eocene); 445, Titanotherium 
 (Miocene) ; 446, Equus (Recent). 
 
 One genus of these Paris beasts from the middle Eocene 
 beds is named Paloeotherium, from the Greek TraXato?, 
 ancient, and Oripiov, wild beast. It is related to the modern 
 Tapirs, though it had a longer neck and a more slender 
 and graceful form. It was in some respects intermediate 
 between the Tapir and the Horse. The largest species 
 of the genus was of the size of a Horse. Palceotlierium 
 was a representative of the Perissodactyls Ungulates 
 having an odd number of toes (at least in the hind feet), 
 
398 
 
 HISTORICAL GEOLOGY. 
 
 and the middle toe the largest. Anoplotherium, Xiphodon, 
 and others of the Paris fossils, were representatives of 
 the Artiodactyls, having the number of toes even, and the 
 third and fourth toes about equally developed, as in the 
 Hog, Deer, Ox, etc. It is noteworthy that these two 
 principal suborders of modern Ungulates had become dif- 
 ferentiated before the close of the Eocene. The fauna of 
 the Paris Eocene included also some Carnivores, a Bat, 
 and an Opossum. 
 
 FIG. 447. 
 
 UNGULATE : Dinoceras mirabile, x |. 
 
 The marine Eocene deposits of the Gulf States have 
 afforded remains of a species of Whale of great length, 
 called Zeuglodon, from evy\r), yoke, and oSou?, tooth, in 
 allusion to the fact that some of the teeth have two long 
 fangs which give them a yokelike shape. The bones occur 
 in many places in the Gulf States, and in Alabama the ver- 
 tebrae were formerly so abundant as to have been built 
 up into stone walls, or burned to rid the fields of them. 
 The living animal was probably 70 feet in length. One 
 
TERTIARY ERA. 
 
 399 
 
 of the larger vertebrae measures a foot and a half in length 
 and a foot in diameter. 
 
 The lacustrine deposits of the Rocky Mountain region 
 have yielded a wonderfully rich harvest of Mammalian 
 remains. The remarkably primitive Ungulate, Phenaco- 
 dus, shown in Fig. 443, is from the lower Eocene (Wasatch) 
 beds of Wyoming. From the Middle Eocene (Bridger 
 group) of the Green River basin, north of the Uinta 
 Mountains, a large number of species have been obtained. 
 The skull of one kind, of elephantine size, having six 
 horn cores, and called by Marsh Dinoceras, in allusion to 
 
 FIGS. 448-451. 
 
 449 
 
 EQUID*:: Fig. 448, fore foot of Orohippus (Eocene); 449, Anchitherium (Miocene); 450, 
 Hipparion (Pliocene); 451, Equus (Recent). 
 
 its horns, is represented in Fig. 447. There was also one 
 of the earliest genera of the Horse tribe, called Orohippus ; 
 and it is remarkable that these Eocene Horses had four 
 usable toes in the fore feet (Fig. 448), and three in the 
 hind feet, instead of the single toe of the modern Horse. 
 The relation of the foot of the latter to different kinds 
 of Tertiary Horses is illustrated in Figs. 448-451. 
 
 In Fig. 451 it is shown that the modern Horse has one 
 usable toe, the third, and rudiments of two others, the 
 second and fourth, in what are called the splint bones. 
 In Hipparion, of the Pliocene (Fig. 450), the second and 
 fourth have hoofs, but they are so short as not ordinarily 
 
400 HISTORICAL GEOLOGY. 
 
 to reach the ground. In Anchitherium, of the Miocene 
 (Fig. 449), the second and fourth toes come to the ground, 
 and are therefore usable. In Orohippus (Fig. 448), which 
 was not larger than a Fox, there are four toes, and all are 
 usable. 
 
 Other Wyoming species are related to the Tapir and 
 Hog, some approaching in characters the Paris Palceo- 
 therium. There were also Lemurs, Creodonts (animals re- 
 lated to Carnivores in form and habit, but retaining some 
 of the primitive characteristics of Insectivores), Bats, 
 Moles, and other Insectivores, Rodents, and Marsupials. 
 
 The Lower Miocene beds of the " Bad Lands," on the 
 White River (regarded by W. B. Scott as Oligocene), 
 
 FIG. 452. 
 
 UNGULATE: tooth of Titanotherfum Prouti, x . 
 
 have afforded remains of other Mammals. Among them 
 are several Carnivores related somewhat to the Hyena, 
 Dog, and Panther ; many Ungulates, including several 
 species of Rhinoceros, and forms approaching the Tapir, 
 Peccary, Deer, Camel, Horse ; also several genera of 
 Rodents. Fig. 452 represents a tooth of Titanotherium, 
 an animal related to the Tapir and Palceotherium, but of 
 elephantine size, standing probably 7 or 8 feet high. The 
 skull in this genus shows a pair of large horn cores on 
 the boundary between the frontal and the nasal bones 
 a structure not found in any Perissodactyl now living. 
 Horns in pairs are at present confined to the Artiodactyls. 
 Fig. 453 represents the skull of another Miocene Mam- 
 mal, called Oreodon* which is intermediate between the 
 
TERTIARY ERA. 
 
 401 
 
 Deer, Camel, and Hog. Remains of a Camel and Rhi- 
 noceros, and of some tapir-like beasts, have been found 
 in the Miocene of the Atlantic Border. 
 
 FIG. 453. 
 
 Fro. 454. 
 
 UNGULATE : Oreodon gracilis. 
 
 In the Upper Miocene beds (Loup Fork group) of 
 Nebraska and other localities (considered Pliocene by 
 some geologists), still other 
 species occur, including Camels, 
 a Rhinoceros, a Mastodon, 
 Horses, Deer, a Wolf, a Tiger, 
 Weasels a range of species 
 quite Oriental in character. 
 
 Among Mammals of the Eu- 
 ropean Miocene there were 
 Horses, Rhinoceroses, Deer, and 
 other Ungulates, including two 
 genera (^Dinotherium and Masto- 
 don) of the remarkable suborder 
 of Proboscideans. In the genus 
 Dinotherium, the tusks were in 
 the lower jaw, as shown in Fig. 454. The Elephant, now 
 the only surviving genus of Proboscideans, did not appear 
 
 PROBOSCIDEAN : Dinotherium gigan- 
 teum x 1 . 
 
402 HISTORICAL GEOLOGY. 
 
 until the Pliocene. The earliest Oxen occur in the Plio- 
 cene of Europe and India. 
 
 There were also in the European Miocene and Pliocene 
 many Carnivores, besides Monkeys, Aard-varks, etc. 
 
 GENERAL OBSERVATIONS. 
 
 Geography : Mountain-making. The Tertiary era was 
 characterized, both in the Old World and the New, (1) 
 by the approximate completion of the work of rock-mak- 
 ing on the borders of the continents, so that the land 
 areas gained nearly the outlines which they have at pres- 
 ent; (2) by great erogenic movements, in which most of 
 the loftiest mountain ranges of the globe acquired at least 
 a considerable part of their present elevation. 
 
 In North America, by the close of the Tertiary, the con- 
 tinent had reached substantially its present extent, along 
 the Atlantic, Gulf, and Pacific Borders, and the great lakes 
 of the Rocky Mountain region had been drained. 
 
 At the close of the Miocene, the Coast Range of Oregon 
 and California experienced a second uplift (see page 362), 
 Cretaceous, Eocene, and Miocene strata being tilted and 
 more or less folded. 
 
 But the most remarkable geographical change in North 
 America was a great geanticlinal movement affecting the 
 whole Rocky Mountain region. The long persistence of 
 lakes in the Rocky Mountain region indicates that the 
 elevation was not great in the Eocene and Miocene, and 
 that a large part of the movement took place in Pliocene 
 time. The Cretaceous beds (which must have been origi- 
 nally at or near sea level) have an altitude (in spite of 
 great denudation) of 13,000 feet in parts of the United 
 States, 10,000 feet in central Mexico, and 4000 feet in 
 British America near the Arctic Ocean. This elevation is 
 partly due to the post-Mesozoic orogenic movement (Lara- 
 mide revolution) described on page 383, and partly to the 
 Tertiary geanticlinal movement. But nearly horizontal 
 Tertiary strata are found in Wyoming, north of the Uinta 
 
TERTIARY ERA. 403 
 
 Mountains, at an elevation of more than 9000 feet, and in 
 the High Plateaus of Utah at an elevation of more than 
 10,000 feet. 
 
 The Sierra Nevada (as explained on page 362) was 
 formed by the crushing of a geosyncline at the close of 
 the Jurassic. But much of the height then gained was 
 doubtless lost by erosion. Le Conte has shown by a study 
 of the river valleys that a large part of the present altitude 
 of that range is due to its participation in the great Rocky 
 Mountain geanticlinal movement. The old river valleys 
 of the region have been filled up and obliterated by basaltic 
 eruptions whose date was not far from the close of the 
 Tertiary. The fact that the new valleys have been carved 
 to a far greater depth than the old ones indicates that the 
 region has been greatly elevated. 
 
 The formation of the great geanticline was accompanied 
 by the development of numerous faults, some of them hav- 
 ing a throw of thousands of feet, having in general a trend 
 approximately parallel with the axis of the mountain chain, 
 and distributed over the whole breadth of the Great Basin, 
 from the Sierra Nevada to the Wasatch, and southward 
 over the High Plateaus of Utah. The steep eastern front 
 of the Sierra is determined by one of these great faults. 
 
 In the Orient, the Eocene era was one of very extensive 
 submergence of the land, as shown by the distribution of 
 the Nummulitic beds over Europe, Asia, and northern 
 Africa, as stated on page 390. Before the close of the 
 Eocene, the greater part of these continental seas became 
 dry land, and in general continued so afterwards; for the 
 marine Miocene and Pliocene are, comparatively, of limited 
 extent. Many of the principal mountain ranges of Europe 
 and Asia, as the Pyrenees, Alps, Carpathians, Himalayas, 
 etc., received in Tertiary time a large part of their eleva- 
 tion. The Pyrenees were elevated at the close of the 
 Eocene. The region of the Alps had experienced a num- 
 ber of orogenic disturbances in former times, one of these 
 epochs of disturbance being at the close of the Paleozoic; 
 
404 HISTORICAL GEOLOGY. 
 
 but the great movement which formed the Alps of to-day 
 dates from the close of the Miocene. The Jura and the 
 Carpathians belong to the same period of disturbance which 
 produced the Alps. The Apennines give evidence of one 
 erogenic movement at the close of the Eocene and another 
 at the close of the Miocene. The Himalayas have Num- 
 mulitic (Eocene) beds, at a height of more than 20,000 
 feet; so that this great chain, although it shows in the 
 region of the Indus evidence of some disturbance before 
 the Eocene, was not completed till after the deposition of 
 the Nummulitic Limestones. Whether the principal move- 
 ment of elevation was at the close of the Eocene, or at the 
 close of the Miocene, has not been certainly shown. Some 
 elevation occurred even after the deposit of the Pliocene 
 beds of the Siwalik Hills. 
 
 Thus, when the Tertiary era closed, the globe had ac- 
 quired substantially its present features. 
 
 The great geanticlinal movements affecting large areas 
 of the continents probably had their counterpart in a sub- 
 sidence of great parts of the ocean bottom the Coral 
 Island subsidence (see page 104). 
 
 Gondwana-land, connecting India with southern Africa 
 in late Paleozoic time and throughout Mesozoic time, ac- 
 cording to Oldham, sank below the sea in the Tertiary. 
 
 Igneous Eruptions. A great period of igneous erup- 
 tions in western North America commenced at the close of 
 the Cretaceous (Laramide revolution), culminated in the 
 Miocene, and may be said to have continued with diminish- 
 ing intensity to the present time, some of the volcanic 
 cones being not yet extinct. The Tertiary eruptions were 
 in large part fissure eruptions (page 189), though great 
 volcanic cones were also formed. The area in the north- 
 western United States covered by sheets of eruptive rock 
 is only surpassed by that of the somewhat earlier (Cre- 
 taceous) outflows in the Deccan. 
 
 Climate. During the Eocene, Palms abounded in Great 
 Britain evidence of a subtropical or warm-temperate 
 
QUATERNARY BRA. 405 
 
 climate in that latitude; and the Arctic regions had forests 
 consisting of Beech, Plantain, Willow, Oak, Poplar, Wal- 
 nut, Magnolia, Redwood, showing a mean temperature of 
 at least 48 F. (Heer). In the Miocene, southern Europe 
 had a subtropical climate, but England had lost its Palms 
 and was cooler. 
 
 In North America, in the early Tertiary, a warm-tem- 
 perate climate must have extended to the northern boundary 
 of the United States, as shown by the fossil plants at 
 Brandon, Vermont, and in other localities. 
 
 The Camels, Rhinoceroses, and other animals of the 
 upper Miocene of Nebraska, seem to prove that a warm- 
 temperate climate prevailed there in that period. 
 
 It is therefore plain that the earth had not as great a 
 diversity of zones of climate in the early Tertiary as now; 
 and that Europe was not very much colder in the Eocene 
 period than in the Jurassic era. 
 
 * 
 II. QUATERNARY ERA. 
 
 General Characteristics. The Quaternary age was re- 
 markable (1) for oscillations of level and climatic changes 
 in high latitudes both north and south of the equator ; 
 (2) for the culmination of the type of brute Mammals ; 
 and (3) for the appearance of Man on the globe. 
 
 Periods. The periods are three : 
 
 1. The GLACIAL, or the period when, over the higher 
 latitudes, large areas of the continents stood at an alti- 
 tude considerably greater than at present, and experienced 
 a colder climate, with immense development of glaciers. 
 
 2. The CHAMPLAIN, when the ice disappeared, and the 
 same high-latitude portions of the continent, and to a less 
 extent other regions, were below their present level, and 
 became covered by extensive fluvial and lacustrine forma- 
 tions, and along seacoasts by marine formations. 
 
 3. The RECENT period, begun by a rising of the land 
 nearly or quite to its present level. 
 
406 HISTORICAL GEOLOGY. 
 
 The Glacial and the Champlain periods taken together 
 are often called the Pleistocene. They are in general not 
 clearly differentiated from each other except in the high- 
 latitude regions which experienced the remarkable changes 
 of level and climate above mentioned. 
 
 Physical History of the Quaternary. 
 
 1. GLACIAL PERIOD. 
 
 The Drift. The most characteristic phenomenon con- 
 nected with the Glacial period is a peculiar and wide- 
 spread deposit over the continents, which gives evidence in 
 general of transportation from the higher latitudes to the 
 lower. 
 
 The transported material consists of earth, gravel, stones, 
 and bowlders ; and includes, in America, nearly all the 
 earth, as well as stones, of the surface in the latitude of 
 New, England and farther north. It extends over hills and 
 valleys, and varies in depth from a few feet to hundreds. 
 A large part of the material is in an unstratified condition, 
 large stones and small, pebbles and sand, being mingled 
 pellmell. Part, especially that in the valleys or depres- 
 sions of the surface, is stratified, and thus bears evidence 
 of deposition by flowing waters, like fluvial and lacustrine 
 formations. But the greater part of the stratified drift 
 belongs to the Champlain period. 
 
 The transported material is called Drift, and the unstrati- 
 fied part of it till (a word of uncertain origin first applied 
 to this deposit in Scotland). The till, especially its lower 
 part, is often a clayey earth, or a clayey mixture of earth 
 and stones with frequent bowlders, called the bowlder clay ; 
 it is in general firmly compacted. 
 
 The traveled stones are of all dimensions, from that of 
 a small pebble to masses as large as a moderate-sized 
 house. One in Nottingham, New Hampshire, is 62, 40, 
 and 40 feet in its diameters, and is estimated to weigh 
 about 6000 tons. A still larger one in Madison, New 
 
QUATERNARY BRA. 
 
 407 
 
 Hampshire, is estimated to weigh 7650 tons. One lying 
 on a naked ledge in Whitingham, Vermont, measures 43 
 feet in length and 80 in height and width, or 39,000 cubic 
 feet in bulk, and was probably transported across Deer- 
 field valley, the bottom of which is 500 feet below the spot 
 where it lies. Many on Cape Cod are 20 feet in diameter. 
 There are many great bowlders of trap from 50 to 1250 
 tons in weight along the western border of the Triassic area 
 in Connecticut, the line reaching to Long Island Sound, 
 just west of New Haven ; and others of great magnitude 
 occur farther south on Long Island. A bowlder in Ohio, 
 
 FIG. 455. 
 
 Drift groovings and scratches. 
 
 16 feet in thickness, is said to cover three fourths of an 
 acre. 
 
 The directions of travel, as learned by tracing the 
 stones in numerous cases to the ledges whence they were 
 derived, are, in general, between southwestward and south- 
 eastward. The distance to which the stones were trans- 
 ported in North America is mostly from 10 miles or less 
 to 40 miles, though in some cases as much as 500 miles. 
 The material was carried southward across the depres- 
 sions now occupied by the Great Lakes and Long Island 
 Sound the land to the south, in each case, being covered 
 with stones from the land to the north. 
 
408 HISTORICAL GEOLOGY. 
 
 Scratches. The rocky ledges over which the drift was 
 borne are often scratched, in closely crowded parallel 
 lines, as in the preceding figure (Fig. 455), and planed off 
 besides. Besides fine scratches, there are sometimes deep 
 and broad grooves at times a yard or more deep and 
 several feet wide, as if made by a tool of great size as well 
 as great power. The scratches occur wherever the drift 
 occurs, provided the underlying rocks are sufficiently 
 durable to have preserved them, and they are usually 
 approximately uniform in direction in any given region. 
 In some places two or more directions may be observed on 
 the same surface. They are found in the valleys, and on 
 the slopes of mountains, to a height, on the Green Moun- 
 tains, of 4400 feet, and, on the White Mountains, of 5500 
 feet. They have nearly a common course over the higher 
 lands of a region, and cross slopes and sometimes even the 
 smaller valleys, without following the direction of the 
 slope or valley ; but, in the great valleys of the land, and 
 sometimes even in the smaller ones, their direction con- 
 forms to the trend of the valley. In the Hudson River 
 valley, between the Catskills and the Green Mountains, 
 the scratches have mostly the course of the valley ; and 
 also in the valleys of the Connecticut, the Merrimac, and 
 other large rivers. 
 
 The stones, or bowlders, of the till are often scratched, 
 as well as the underlying rocks, and in this respect they 
 differ from those of stratified drift ; the latter have gen- 
 erally lost all scratches by river abrasion. 
 
 Origin of the Drift. The earliest theory of the Drift 
 attributed its transportation to the tumultuous waves of 
 a deluge sweeping over the land ; and the formation was 
 formerly called Diluvium, in allusion to this theory. Later 
 it came to be generally admitted that nothing but moving 
 ice could have transported the Drift with its immense 
 bowlders. 
 
 When the inadequacy of water alone for the work was 
 recognized, the agency first thought of was that of float- 
 
QUATERNARY ERA. 409 
 
 ing ice in the form of icebergs. Icebergs transport earth 
 and stones, as in the Arctic seas ; and great numbers are 
 annually floated south to the Newfoundland Banks, through 
 the action of the Arctic, or Labrador, current, where they 
 melt and drop their great bowlders and burden of gravel 
 and earth to make deposits over the sea bottom. But ice- 
 bergs could not have covered great surfaces so regularly 
 with scratches. Again, there are no marine relics in the 
 unstratified Drift, to prove that the continent was under 
 the sea in the Glacial period. 
 
 These difficulties ultimately led to the well-nigh uni- 
 versal abandonment of the theory of icebergs, and the 
 adoption of the glacier theory first proposed by Louis 
 Agassiz. Glaciers, in the Alps and elsewhere, are now 
 doing precisely such work of transportation as is shown 
 by the Drift ; and stones of as great size as are contained 
 in the Drift have in former times been borne by a slowly 
 moving glacier from the vicinity of Mont Blanc, across the 
 lowlands of Switzerland, to the slopes of the Jura Moun- 
 tains, and left there at a height of over 2000 feet above the 
 level of the Lake of Geneva. Moreover, there are in many 
 places deposits of bowlder clay, made of the earth formed 
 by trituration of stones against stones during the moving 
 of the glacier. Further, there are scratches and grooves, 
 of precisely the same character as those observed in Drift 
 regions, on the granitic and limestone rocks of the ridges ; 
 and besides, the transported material is left unstratified 
 over the land, wherever it is not acted upon and dis- 
 tributed by Alpine torrents. 
 
 There is a seeming difficulty in the glacier theory, from 
 the supposed want of a sufficient slope in the surface to 
 produce movement. But a slope in the under surface is 
 not needed, any more than for the flowing of pitch. 
 Pitch, deposited in continuous supply on any part of a 
 horizontal plane, would spread in all directions around ; 
 and this it would do even if, instead of being horizontal, 
 the surface beneath had an ascending slope. The slope 
 
410 HISTORICAL GEOLOGY. 
 
 of the upper surface of a plastic or fluid substance deter- 
 mines the direction and rate of flow, not that of the under 
 surface. Hence, if ice were accumulated over a region so 
 that the upper surface had the requisite slope, there would 
 be motion in the mass in the direction of this slope, what- 
 ever the bottom slope might be. At the same time, the 
 slope of the land at bottom, or the courses of the valleys, 
 would determine to some extent the movement at bottom ; 
 just as oblique grooves in a sloping board, down which 
 pitch was moving, would determine more or less completely 
 the direction of the movement in the grooves. 
 
 The condition of the Drift regions in the Glacial period 
 finds its best illustration, not in the narrow and compara- 
 tively shallow glaciers of the Alpine valleys, but in the 
 great ice sheets of Greenland and the Antarctic. Green- 
 land is at the present time a glaciated continent, as the 
 region of Canada and the northeastern part of the United 
 States was in the Glacial period. The ice in Greenland 
 moves where the slope of the surface is less than half a 
 degree. 
 
 The phenomena connected with the northern Drift are 
 in general fully explained by reference to a great northern 
 semi-continental glacier as the cause ; and those relating 
 to local Drift about high mountains, south of Drift lati- 
 tudes, by referring them to local glaciers. But floating ice 
 doubtless had some share in the work. Icebergs drifted 
 down the coast, and smaller ones descended rivers, drop- 
 ping their stones by the way. On the Mississippi, the 
 floating ice may have reached the Gulf of Mexico, and the 
 chilled waters may have destroyed much tropical life. 
 
 The occurrence of bowlders near the summit of Mount 
 Washington in the White Mountains proves that the alti- 
 tude of the upper surface of the ice in that region was 
 6000 or 6500 feet ; and hence that the ice was not less 
 than 5000 feet thick over that part of northern New 
 England. Facts also show that the surface height in 
 southwestern Massachusetts was at least 2800 feet ; in 
 
QUATERNARY ERA. 411 
 
 southern Connecticut, 1000 feet or more ; in the Catskills, 
 3000 feet (Smock). 
 
 Since the slopes of the upper surface of a glacier deter- 
 mine the general direction of movement, and therefore of 
 transportation and abrasion, the lines of scratches or of 
 drift are an indication as to the position of the ice summit. 
 The prevailing direction over the higher lands of New 
 England, New York, and eastern Canada is southeastward, 
 and that over western Ohio and northwestward to the 
 Saskatchewan, is south westward. (See map on pages 
 412, 413.) The lines consequently converge northward, 
 toward the part of the Canada watershed northwest from 
 Montreal, and a region extending thence northeastward 
 and northwestward, encompassing the southern part of 
 Hudson Bay ; and hence along this course there must 
 have been the summit of a great ice range. 
 
 The stones and earth transported by the continental 
 glacier were gathered up mostly by its lower part, from 
 the surface of hills or ridges that projected into it, and 
 even from the plains beneath it. In New England, where 
 there were no peaks rising above the upper surface to be a 
 source of avalanches, as in the Alps, many of the masses 
 thus taken aboard exceed 1000 tons in weight. The mass 
 of decomposed and disintegrated rock which had been 
 accumulating for ages, was extensively scraped up and 
 shoved along. Even the underlying unaltered rock was 
 more or less attacked. 
 
 With a thickness of even 2000 feet, the glacier would 
 have had great excavating power. Soft rocks would have 
 been deeply plowed up by it, and all jointed and fissile 
 rocks, soft or hard, would have been torn to fragments, 
 and the loosened masses borne off. ,By this means, and 
 perhaps most of all by the erosive action of subglacial 
 streams, valleys were deepened and widened. 
 
 Area of the Drift in North America. As already stated, 
 the ice sheet which formed the Drift of Canada and 
 the northeastern United States, had its center over the 
 
Fio. 456. 
 
 412 
 
FIG. 456. 
 
 MAP OF 
 
 AMERICA 
 
 ILLUSTRATING THE PHENOMENA 
 
 OF THE 
 
 GLACIAL AND CHAMPLAIN 
 PERIODS 
 
 Limit of ice sheet - 
 
 Moraines * 
 
 n direction of Glacial \\\\ 
 
 scratches 
 
 Former shore line of lakes 
 
 75 70 
 
414 HISTORICAL GEOLOGY. 
 
 highlands which form the watershed between the St. 
 Lawrence basin and Hudson Bay. The extent of the 
 Drift area (and consequently the maximum extension of 
 the ice sheet) is indicated by the heavy line on the map, 
 Fig. 456. South and southeast of New England the line 
 lies outside of the present coast line. It may be traced by 
 the accumulations forming the terminal moraine, through 
 the islands of Nantucket and Marthas Vineyard, and near 
 the south shore of Long Island. It extends westward 
 and northwestward across New Jersey and Pennsylvania, 
 crosses the boundary of New York in a great northern 
 bend, follows a general southwesterly course through 
 western Pennsylvania, Ohio (crossing once into Ken- 
 tucky), Indiana, and reaches in southern Illinois the 
 lowest latitude which it anywhere attains (below 38). 
 Thence it extends nearly westward through Missouri into 
 eastern Kansas, where it bends sharply northward. Near 
 the western boundary of North Dakota it passes above the 
 parallel of 47. Thence the line continues nearly west- 
 ward across Montana till it reaches the independent area 
 of Drift formed by the ice sheet of the northern Rocky 
 Mountains. The contrasted meteorological conditions of 
 eastern and western North America explain in the main 
 the form of the southern boundary of the Drift. In the 
 east, where the precipitation is great, the boundary lies 
 near the parallel of 40. In the arid west, the boundary 
 recedes far to the north. Various local conditions, chiefly 
 topographical, serve to explain the minor curves of the 
 boundary, as also the occurrence of two isolated driftless 
 areas within the drift region, one of which (much the 
 larger of the two), lying mostly within the state of Wis- 
 consin, is represented on the map. 
 
 Besides the great area of the northeastern (Laurentide) 
 ice sheet, glacial areas were developed in various parts of 
 the Rocky Mountain region. In the extreme northwest 
 of the United States and in British Columbia, a large 
 area of the northern Rockies was covered with a great ice 
 
QUATERNARY EKA. 415 
 
 sheet, whose eastern edge met the western edge of the 
 Laurentide ice sheet. The boundary between the two is 
 represented by a dotted line on the map. The ice sheet 
 of the Rocky Mountains in British Columbia had a 
 northern, as well as a southern, limit, since, although the 
 cold increased northward, precipitation decreased. The 
 extreme northwest of British America, and Alaska (with 
 the exception of its high mountain areas), were left un- 
 covered by ice. 
 
 Farther south, local areas of glaciation were developed 
 in some of the higher parts of the Rocky Mountain region, 
 as in the Yellowstone Park and the mountain ranges sur- 
 rounding it, in the Front Range of Colorado, and in the 
 high Sierra of California. 
 
 It thus appears that the glaciation of North America 
 was not due, as has been sometimes imagined, to a great 
 polar ice cap investing all the region of high latitude. 
 The centers of glaciation were in the Laurentide high- 
 lands (whose altitude was probably considerably greater 
 than now) and in the Rocky Mountains. The general 
 laws of the relation of accumulation of perpetual snow to 
 climate and topography were the same as now. A study 
 of glaciation in the Old World sustains the same general 
 conclusions. 
 
 Subdivisions of the Glacial Period. The study of 
 every glacier region reveals the fact of oscillation in the 
 extent of the glaciers, dependent upon meteorological fluc- 
 tuations from year to year. There were on a larger scale 
 oscillations in the extent of the great ice sheets of the 
 Glacial period, though the causes of these oscillations are 
 by no means fully understood. 
 
 The Glacial period in North America may be conven- 
 iently divided into three epochs, (1) the Early Glacial 
 epoch, or that of the advance and maximum extension of 
 the ice ; (2) the Middle Grlacial epoch, or that of the first 
 retreat of the ice ; (3) the Later G-lacial epoch, or that of 
 the final retreat. 
 
416 HISTORICAL GEOLOGY. 
 
 The map (Fig. 456) shows a well-defined line of ter- 
 minal moraine (BBB), which .can be traced in substan- 
 tial continuity from Cape Cod to the Saskatchewan River. 
 In the east, from Cape Cod to central Ohio, that moraine 
 lies only a few miles north of the extreme boundary of the 
 Drift. Farther west, the line of the moraine diverges 
 from the southern boundary of the Drift, and in Wiscon- 
 sin and Minnesota it sweeps around the driftless area, so 
 as to be more than 500 miles north of the Drift boundary. 
 In British America, in the valley of the Saskatchewan, 
 the line of the moraine lies 300 miles east of the boundary 
 between the Laurentide Drift and the Rocky Mountain 
 Drift. 
 
 The line of moraine (BBB) marks the limit of the 
 ice sheet in Middle Glacial time, and the distance between 
 the moraine and the southern boundary of the Drift meas- 
 ures the extent of the first retreat of the ice. It is, 
 indeed, possible that the ice may have receded beyond the 
 line of the moraine for a greater or less distance, and then 
 readvanced to the line of the moraine. It is held by 
 Chamberlin and others that the ice had receded so far to 
 the north as to lay bare the greater part of the territory 
 it had previously covered, thus characterizing an Inter- 
 glacial epoch between an earlier and a later Glacial epoch. 
 But it is more probable that the various terminal moraines 
 mark halts in the retreat, or oscillations, more or less ex- 
 tensive, in the position of the ice front, than that the 
 glacial conditions were completely interrupted by one or 
 more than one Interglacial epoch. 
 
 During the rapid melting of the ice which characterized 
 the first retreat of the glacier, the Mississippi must have 
 been greatly swollen, and must have carried some floating 
 ice. To this epoch may perhaps be referred the coarse, 
 gravelly deposits of the lower Mississippi valley, with 
 flow-and-plunge structure and other indications of torren- 
 tial conditions, and occasionally containing stones weigh- 
 ing 100 pounds or more, described by Hilgard under the 
 
QUATERNARY ERA. 417 
 
 name of Orange Sand, and now included in the Lafayette 
 formation of McGee and others. By some geologists, 
 however, the Lafayette formation is believed to be of 
 Pliocene age. 
 
 After a long halt at the line BBB, the glacier con- 
 tinued its retreat. Numerous terminal moraines mark 
 halts in the retreat or temporary readvances. Some of 
 these moraines are indicated on the map. 
 
 By the retreat of the glacier, the surface of the country 
 was left covered with Drift, and diversified by kettle holes, 
 drumlins, eskers, and kames. 
 
 Kettle holes are bowl-shaped depressions, often 30 to 50 
 feet in depth, and 100 to 500 feet in diameter, sometimes 
 even considerably exceeding these dimensions. Each 
 kettle hole was the resting place and often the burial 
 place of a block of ice that became detached from the 
 glacier during the melting, and the final melting of the 
 ice block left a hole in the mass of the Drift deposits. 
 Kettle holes are often occupied by ponds. 
 
 Drumlins are elliptical domes, consisting wholly or in 
 part of till. 
 
 Eskers and kames are ridges and hummocks of coarsely 
 stratified Drift, and are attributed to the action of waters 
 flowing in or under the wasting ice. 
 
 By the deposit of Drift over the region forsaken by the 
 ice, river valleys were often obstructed, and the streams 
 compelled to seek new channels. Many lakes wer3 formed 
 in valleys obstructed by dams of Drift, or in depressions 
 left in the irregular distribution of Drift over the country. 
 Some small lakes, moreover, were formed in rock basins 
 excavated by the glacier. The glaciated regions in general 
 are regions abounding in lakes. 
 
 The Glacial Period in Other Countries. The main 
 facts in regard to the Glacial period are the same in 
 northern Europe as in North America. The till presents 
 the same characteristics, and the bed rocks show the same 
 polished and striated surfaces. 
 
418 HISTORICAL GEOLOGY. 
 
 The center of glaciation for northern Europe was in 
 the Scandinavian Mountains. At its period of greatest 
 extension, the ice sheet covered Ireland, Great Britain 
 (with the exception of a little strip in the extreme south 
 of England), Holland, Denmark, northern Germany, and 
 western Russia (extending southward almost to the Car- 
 pathians). In the extreme northeast, the Scandinavian 
 ice sheet became confluent with the ice of the Timan 
 Mountains and of the northern part of the Urals, as in 
 British Columbia the Laurentide ice sheet blended with 
 that of the Rocky Mountains. The fact that the southern 
 limit of the Drift in Europe is about 10 north of that in 
 North America suggests that there was probably in the 
 Glacial period about the same northward bending of the 
 isotherms in crossing the Atlantic eastward as at present. 
 In the retreat of the Scandinavian ice sheet, as in that 
 of the Laurentide, halts or temporary readvances were 
 marked by successive terminal moraines. In the opinion 
 of many geologists, some of the oscillations were so exten- 
 sive as to characterize Interglacial epochs. 
 
 Glaciers were developed on a large scale in mountain 
 regions beyond the limits of the Scandinavian ice sheet. 
 After that had retired from Great Britain, local glaciers 
 were extensively developed in the Highlands of Scotland. 
 The Alps formed the center of an ice sheet, which extended 
 westward to Lyons and northward to the vicinity of 
 Munich. Bowlders from the Alps are found in abundance 
 on the Jura. The glaciers of the Pyrenees, the Caucasus, 
 and the Himalayas also extended far beyond their present 
 limits. 
 
 In South America, a great ice mass extended in the region 
 of the Andes northward from Tierra del Fuego to the par- 
 allel of 37, and glaciers were formed about some of the 
 higher summits, even near the equator. There is evidence 
 also of a Glacial period in Australia and New Zealand. 
 
 Cause of the Glacial Climate. No perfectly satisfactory 
 explanation of the Glacial climate has been given. The 
 
QUATERNARY ERA. 419 
 
 upward movements of the continents which characterized 
 the latter part of the Tertiary, continued in some regions 
 into the Quaternary ; and in early Quaternary time large 
 areas in high latitudes stood at a much higher level than 
 now. This elevation of high-latitude regions would tend 
 to bring on a cold climate, partly by the direct effect of 
 elevation of land, and partly by the exclusion of warm 
 oceanic currents from the northern seas (see page 168). 
 This is an obvious and perhaps a sufficient explanation of 
 the Glacial climate. The fact that the oscillations of level 
 and those of climate seem not to have been strictly simul- 
 taneous, is perhaps sufficiently explained by the suggestion 
 of Le Conte that the accumulation and the removal of the 
 ice sheet were gradual processes, and that the maximum 
 effect might well be considerably later than the maximum 
 intensity of the cause. 
 
 The former elevation of the glaciated regions is shown 
 by the fact that their coasts are everywhere indented by 
 fiords deep, narrow bays penetrating far into the interior. 
 These fiords are unquestionably drowned valleys, and they 
 could have been excavated only when the land stood at a 
 higher level than at present. They are shown by any 
 map on a tolerably large scale along the coasts of Maine, 
 Labrador, Newfoundland, Greenland, British Columbia 
 and Alaska, Scotland and Scandinavia, Patagonia, and 
 South Australia. Some of the fiords of the Atlantic coast 
 of North America have been shown by soundings to have 
 depths of 2000 to 3670 feet, and the Sogne Fiord in 
 Norway is 4020 feet deep. These fiords are accordingly 
 proof that some parts of the land were once thousands of 
 feet above their present level. 
 
 Valleys filled with drift, deeper than the present river 
 valleys in the same regions, and often extending far below 
 the level of the sea, afford other evidence of the former 
 high level of the land. 
 
 The Glacial climate has been attributed by Croll and 
 many other geologists to the extreme cold of aphelion 
 
420 HISTORICAL GEOLOGY. 
 
 winters in an epoch of maximum eccentricity of the 
 earth's orbit. The theory has been briefly explained on 
 page 169. It is very doubtful whether the astronomical 
 conditions assumed by Croll would tend to produce 'a 
 Glacial period. The great heat of perihelion summers 
 would certainly tend to melt the snow. Moreover, the last 
 period of great eccentricity ended about 70,000 years ago, 
 whereas geological evidence indicates that the close of the 
 Glacial period was much more recent. A corollary of Croll's 
 theory would be the occurrence of glacial and interglacial 
 epochs in the northern hemisphere, alternately with corre- 
 sponding epochs in the southern hemisphere, during a period 
 of great eccentricity. There is no proof of such alternate 
 glaciation of the two hemispheres, though it is not im- 
 possible. 
 
 2. CHAMPLAIN PERIOD. 
 
 This period is so named from the marine deposits around 
 the shores of Lake Champlain. 
 
 The Champlain period is characterized by (1) the con- 
 tinuance of the subsidence which had probably begun in 
 the latter part of the Glacial period, the land in northern 
 latitudes becoming depressed considerably below the pres- 
 ent level ; (2) a diminution in the slope of southward-flow- 
 ing rivers, so that they ceased for the most part from the 
 work of erosion, and formed extensive stratified deposits ; 
 (3) a climate probably warmer than at present doubtless, 
 at least in part, the result of the subsidence ; (4) the com- 
 plete disappearance of the great ice sheets. 
 
 The deposits of the Champlain period are (1) marine, 
 (2) fluviatile, (3) lacustrine. In general, it is only the 
 marine deposits which afford positive evidence and definite 
 measures of the subsidence ; since fluviatile and lacustrine 
 deposits may be formed at various altitudes above the sea 
 level, the height of the water being modified by dams of 
 drift or of ice, and by variations in the ratio of precipita- 
 tion and evaporation, as well as by changes in the level of 
 the land. 
 
QUATERNARY ERA. 421 
 
 1. Marine Deposits; Sea Beaches. Marine deposits oc- 
 cur as sea beaches, now forming terraces above the present 
 shore lines, or as offshore deposits the Leda Clays. 
 
 Along the coast of southern New England, there are 
 apparently no marine Champlain deposits more than 15 or 
 20 feet above the sea level. The fossiliferous deposits of 
 Sankaty Head, Nantucket, reaching an altitude of about 
 50 feet, and those at a still higher elevation at Gay Head, 
 Marthas Vineyard, are apparently earlier than the true 
 Champlain deposits. They probably belong to some time 
 of oscillation when the ice front had receded to a greater 
 or less distance from the limit to which it subsequently 
 readvanced (page 416). Marine deposits of Champlain 
 age along the coast of Maine occur at altitudes of 150 to 
 300 feet. In the basin of the Bay of Chaleurs, the alti- 
 tude is 200 feet. Along the St. Lawrence valley, the 
 height is 375 feet near the mouth of the Saguenay, 520 
 feet at Montreal, and 600 feet not far from Lake Ontario, 
 so that the St. Lawrence River was then a vast St. 
 Lawrence Gulf, 500 to 600 feet deep. Even Lake Cham- 
 plain was an arm of this St. Lawrence Gulf ; for beaches 
 containing sea shells occur on its borders to a height of 
 370 feet at its southern, and about 500 feet at its northern, 
 end ; and in one locality remains of a Whale have been 
 found. The Champlain bay had then the great depth of 
 from 700 to 800 feet. At Nachvak, in Labrador, a beach 
 supposed to be of Champlain age is reported at an altitude 
 of 1500 feet. In the region south and west of James Bay, 
 beds with marine shells occur at altitudes of 300 to 500 feet. 
 
 The maximum subsidence in eastern North America 
 seems to have been in the region between the St. Law- 
 rence and Hudson Bay the region probably of maximum 
 elevation in the Glacial period. 
 
 On the Pacific coast, marine beaches are reported at 
 altitudes exceeding 1000 feet, but it is not known whether 
 they belong to the same date as the Champlain beds of 
 eastern North America or not. 
 
422 HISTORICAL GEOLOGY. 
 
 While there is much uncertainty in regard to the num- 
 ber and extent of climatic and geographical oscillations in 
 Europe, it appears certain that extensive subsidence took 
 place subsequently to the period of maximum glaciation. 
 The subsidence carried parts of Great Britain 500 feet 
 below the present level. In Sweden the depression varied 
 from 200 feet in the southern part to more than 600 in 
 the northern part. At the time of deepest submergence, 
 the Baltic is believed to have been connected with the 
 North Sea by the region of lakes extending westward 
 from Stockholm to the Skager Rack, and with the Arctic 
 Ocean by a channel extending over Finland to the White 
 Sea. 
 
 2. Fluvial Deposits. The subsidence of the land north- 
 ward diminished the slope of all southward-flowing rivers, 
 and consequently diminished their powers of erosion. 
 Moreover, the enormous mass of debris which had been 
 transported by the glaciers, and was set free by their 
 melting, overloaded the rivers. The effect of these causes 
 combined, was the deposit of enormous masses of sediment, 
 filling up the river valleys of the glaciated region to a 
 height now indicated by the highest terraces. The rivers 
 meandered over these great alluvial plains (sometimes 
 many miles in width), and in time of floods spread widely 
 over their surface. These alluvial plains were in fact the 
 flood plains of the Champlain rivers. 
 
 The structure of the deposits presents great variations. 
 Some parts consist of fine clays, with regular lamination, 
 indicating deposit in quiet waters, as of lakes. Others 
 consist of coarse sands, gravels, or cobble stones, and show 
 the flow-and-plunge structure and other forms of irreg- 
 ular lamination, indicative of strong currents. In places 
 the northward subsidence must have reduced the slope of 
 streams to zero, so that they would spread out in broad 
 lakes. In other places lacustrine conditions must have 
 been produced by dams of drift or ice. Coarse materials 
 would often be brought into the larger streams by tribu- 
 
QUATERNARY ERA. 423 
 
 taries whose slope and velocity were greater than those 
 of the larger streams, and would be piled up as deltas near 
 the mouths of those tributaries. Rapid melting of the 
 ice during part of the time may have increased the vol- 
 ume of water, and so increased the velocity of the streams. 
 
 3. Lakes of the Pleistocene. Lake basins in various 
 parts of the country are plainly marked by shore lines 
 formed in Pleistocene time. In some cases the basins are 
 still occupied by smaller lakes, and the old beaches appear 
 as terraces far above the present shore lines. In other 
 cases, the lakes have been drained, so that no considerable 
 remnants now exist. Climatic changes, and dams of drift 
 or of ice, as well as movements of subsidence and elevation, 
 may have been concerned in determining the existence 
 and the boundaries of these lakes. The correlation of 
 the history of the lakes with the history of general con- 
 tinental movements indicated by fiords and by sea beaches, 
 is matter of much question. 
 
 Ancient beaches have been observed in many places 
 around the Great Lakes of the Canadian frontier. Some 
 of those which have been most thoroughly studied are 
 shown by dotted lines on the map, Fig. 456. The highest 
 shore line around Lake Superior has an altitude of 500 
 to 600 feet above the present level of the lake, or of 
 1100 to 1200 feet above the level of the sea. At the 
 south end of Lake Michigan, the highest shore line is 
 only 45 feet above the present level of the lake. This 
 beach is supposed to be contemporaneous with one around 
 parts of Lake Superior about 400 feet above the lake. 
 A very strongly marked shore line has been traced around 
 the greater part of Lake Ontario, and has been named 
 the Iroquois beach. It has a height above the present 
 water level varying from 116 feet near the western end 
 of the lake to 483 feet at Watertown, New York. The 
 great difference between the altitudes of beaches around 
 the various lakes which have been supposed to be con- 
 temporaneous, and especially the great difference between 
 
424 HISTORICAL GEOLOGY. 
 
 the altitudes of different parts of the same continuous 
 beach (as in the case of the Iroquois beach), is evidence 
 of great changes of relative level in different parts of 
 the lake region. 
 
 There seems good reason to believe that at one time 
 the four upper lakes were confluent into one lake, more 
 than 100,000 square miles in area, which has been named 
 Lake Warren (in honor of General Warren, the discov- 
 erer of Lake Agassiz). 
 
 The high^ level of the water in these Pleistocene lakes 
 has been attributed by many geologists to the presence 
 of the remnant of the continental ice sheet in the St. Law- 
 rence valley, damming up the outlet in that direction, 
 and compelling the waters to seek outlets southward at 
 higher levels. Others hold that, at the time of the exist- 
 ence of these lakes, the ice had already receded from the 
 St. Lawrence valley, and that the great extension of the 
 lakes was due to the Champlain subsidence. At the time 
 of maximum Champlain depression, the Iroquois beach 
 must have been very nearly at the sea level; but the 
 absence of marine fossils shows that Lake Ontario did 
 not (like Lake Champlain) have so free communication 
 with the sea as to become salt. It is supposed by many 
 geologists that, at the time of the Iroquois beach, Lake 
 Ontario communicated with the sea by a channel leading 
 from Rome, New York, to the Mohawk valley, and thence 
 by way of the Hudson; but this is not certain. 
 
 The region of Lake Winnipeg was occupied at some 
 time in the Pleistocene by a lake even larger than Lake 
 Warren, which has been named Lake Agassiz (see map, 
 Fig. 456). General G. K. Warren, who first made known 
 the fact of the former drainage of the Winnipeg region 
 into the Mississippi by way of the Minnesota, attributed 
 the southward drainage to that high elevation of the 
 northern part of the continent, which existed at the 
 beginning of the Quaternary. According to this view, 
 the beginning of the Champlain subsidence depressed 
 
QUATERNARY EKA. 425 
 
 the Winnipeg region so greatly as to form Lake Agas- 
 siz. The further progress of subsidence depressed the 
 region to the north so far that Lake Agassiz found an 
 outlet through Nelson River into Hudson Bay, and the 
 Red River of the North began to flow northward instead 
 of southward. According to Upham and others, the 
 southward drainage of the Winnipeg region was due 
 to the presence of the ice sheet, damming up the Nelson 
 River outlet. In the case of Lake Agassiz, as in that 
 of Lake Warren and the other lakes of the Canadian 
 frontier, there is evidence of considerable oscillations of 
 level in the very different altitudes of different parts of 
 the same beach. 
 
 Lake Bonneville is the name of a Pleistocene lake 
 occupying a large part of Utah, and Lake Lahontan the 
 name of one occupying a large part of western Nevada 
 (see map, Fig. 456). The Great Salt Lake is the dimin- 
 ished representative of the former, while the latter is 
 now represented by still smaller remnants. At one time 
 Lake Bonneville rose so high as to find an outlet through 
 the Snake River and the Columbia, and thus became fresh; 
 but Lake Lahontan never had an outlet. The high level 
 of the water in these lakes is attributed to the cold 
 climate of the Glacial period, which must have diminished 
 evaporation. According to Gilbert, King, and Russell, 
 there is evidence of two high-water stages in each of 
 these lakes, with an intervening epoch in which the lakes 
 were nearly or quite desiccated. It is still uncertain 
 what phases in the Pleistocene history of eastern North 
 America are to be correlated with the alternations of 
 high and low water in these lakes of the Great Basin. 
 
 3. RECENT PERIOD. 
 
 The Champlain period was brought to a close by a 
 moderate elevation of the land over the higher latitudes, 
 bringing the continent up to its present level. This ele- 
 vation placed the old sea beaches of the Champlain period 
 
426 
 
 HISTORICAL GEOLOGY. 
 
 at their present level, high above the sea ; that is, over 
 500 feet near Montreal, 150 to 300 feet on the coast 
 of Maine, and so on, the height of the beaches being 
 a measure of the amount of elevation. River valleys, 
 after the rise, had a steeper slope than in the Champlain 
 period, and hence their flow was increased in velocity. 
 They consequently went on cutting down their beds 
 through the Champlain deposits of the valley to a lower 
 level ; and at the time of their annual floods they wore 
 
 FIG. 457. 
 
 Terraces on the Connecticut Kiver, south of Hanover, New Hampshire. 
 
 away the deposits on either side of the channel, making 
 thereby an alluvial flat or flood ground ; for a river has, 
 in general, a flood ground which it covers in its times of 
 flood, as well as a channel for dry times. 
 
 This sinking of the river beds left remnants of the 
 old flood grounds as terraces far above the level of the 
 stream. In the course of the elevation, a series of ter- 
 races was often made along the valleys, as illustrated in 
 Fig. 457. A section of a valley thus terraced is repre- 
 sented in Fig. 458. The formation terraced is, as is 
 
QUATERNARY ERA. 427 
 
 shown, the Champlain (sometimes in part Glacial Drift) ; 
 in the Champlain period it filled, in general, the valley 
 across (from / to /'), excepting a narrow channel for the 
 stream, the whole breadth having been the flood ground 
 of the Champlain river. But, after the elevation began 
 which closed the Champlain period, the river commenced 
 to cut down through the formation, making one or more 
 terraces in it, on either side of the stream. In general, 
 each terrace below the uppermost one indicates a pause 
 in the movement of elevation, being really a remnant of 
 a flood plain formed while the river was nearly at base 
 level (pages 131, 138). In Fig. 458, R is the position of 
 the river channel after the terracing ; and on either side 
 of it there are terraces at the levels ff, dr, bb f , and also 
 
 FIG. 458. 
 
 d , 
 
 Section of a valley with terraces. 
 
 another on the right side, at rd f . These terrace plains 
 are usually the sites of villages. They add greatly to the 
 beauty of the scenery along water courses. The terraces 
 usually fail where the valley is narrow and rocky: 
 
 In Europe, the close of the period of subsidence (Cham- 
 plain) seems to have been marked by a recurrence of 
 Glacial conditions, the northern portions of that continent 
 being again covered with ice, and glaciers extending once 
 more from the Alps over part of lower Switzerland. 
 Proofs of the occurrence of such an epoch are found in 
 the remains of the Reindeer and other sub-arctic animals, 
 in southern France (page 437), in deposits that are sub- 
 sequent in date to true Champlain deposits. 
 
 MODERN CHANGES OF LEVEL. 
 
 The sea, the rivers, the winds, and all mechanical and 
 chemical forces are still working as they have always 
 
428 HISTORICAL GEOLOGY. 
 
 worked ; and the earth is undergoing changes of level, 
 also, over wide areas, although it has beyond question 
 reached an era of comparative repose. 
 
 These changes of level are either paroxysmal that is, 
 they take place through a sudden movement of the earth's 
 crust, as sometimes happens in connection with an earth- 
 quake ; or they are secular that is, they are the effect 
 of a gradual movement prolonged through many years or 
 centuries. The following are some examples: 
 
 1. Paroxysmal Movements. In 1822, the coast of Chile 
 for 1200 miles was shaken by an earthquake, and it has 
 been estimated that the coast near Valparaiso was raised 
 at the time 3 or 4 feet. In 1835, during another earth- 
 quake in the same region, there was an elevation, it is 
 stated, of 4 or 5 feet at Talcahuano, which was reduced 
 after a few months to 2 or 3 feet. In 1819, there was an 
 earthquake about the Delta of the Indus, and simul- 
 taneously an area of 2000 square miles,' in which the fort 
 and village of Sindree were situated, sunk so as to become 
 an inland sea, with the tops of the houses just out of 
 water ; and another region parallel with the sunken area, 
 50 miles long and in some parts 10 miles broad, was raised 
 10 feet above the delta. These few examples all happened 
 within an interval of sixteen years. They show that the 
 earth is still far from absolute quiet, even in this its 
 finished state. 
 
 2. Secular Movements. Along the coasts of Sweden 
 and Finland, on the Baltic, there is evidence that a gradual 
 rising of the land is in slow progress. Marks placed 
 along the rocks many years since show that the change 
 is slight at Stockholm, but increases northward. Evi- 
 dence of elevation has been obtained from the west coast 
 as well as from the east coast, showing that the apparent 
 elevation is not due to oscillations in the water level of 
 the Baltic. At Udde valla the rate of elevation is equiva- 
 lent to 3 or 4 feet in a century. 
 
 In Greenland, for 600- miles, from Disco Bay, near 
 
QUATERNARY ERA. 429 
 
 69 N., to the frith of Igaliko, 60 43' N., a slow sinking 
 has been going on for at least four centuries. Islands 
 along the coast, and old buildings, have been submerged. 
 The Moravian settlers have had to put down new poles 
 for their boats, and the old ones stand "as silent witnesses 
 of the change." 
 
 It is believed also that a sinking is in progress along 
 the coast of New Jersey, Long Island, and Marthas Vine- 
 yard, and a rising in different parts of the coast region 
 between Labrador and the Bay of Fundy. There are 
 deeply buried stumps of forest trees along the seashore 
 plains of New Jersey, and other evidences of a change of 
 level (G. H. Cook). 
 
 This fact is to be noted, that these secular movements 
 of modern time over the continents are, for the most part, 
 so far as observed, high-latitude oscillations, just as they 
 were in the earlier part of the Quaternary. 
 
 Life of the Quaternary. 
 
 The history of Quaternary life is remarkable for the 
 extensive migrations occasioned by the great geographical 
 and climatic changes of the era. With the increasing cold 
 of the Glacial period, the range of various species of plants 
 and animals was contracted on the north and extended to 
 the south. With the coming on of the mild climate of the 
 Champlain, there was a corresponding northward shifting 
 of the range of various species. In the northward migra- 
 tion, colonies of northern plants and animals were left in 
 regions of high mountains, far south of their normal range, 
 finding on those summits a congenial climate, and freedom 
 from competition with the southern flora and fauna of the 
 low grounds. Plants and Insects of Labrador and the far 
 north occur on the summits of the White Mountains, the 
 Green Mountains, and the Adirondacks. Analogous facts 
 are reported from the Alps and other mountain regions 
 of Europe. The distribution of the flora and fauna was 
 
430 HISTORICAL GEOLOGY. 
 
 affected by all the minor oscillations of climate, the more 
 hardy plants and animals crowding upon the edge of the 
 ice sheet, and moving northward with every recession of 
 the front of the ice. While many species only migrated 
 southward and northward with the advance and recession 
 of the ice, other species were -exterminated by the climatic 
 changes. 
 
 The elevation of land in part of Quaternary time estab- 
 lished land connection between the eastern and the western 
 continent by way of the region of Bering Strait, perhaps 
 also by way of the Faroe Islands, Iceland, and Greenland. 
 The British Islands were connected with the continent of 
 Europe, and Europe was connected with Africa across the 
 Mediterranean. More or less of migration took place in 
 all these cases between the areas thus connected. 
 
 The Invertebrate animals of the Quaternary, and proba- 
 bly also the plants, were very nearly if not quite all identi- 
 cal with existing species. The shells and other Invertebrate 
 remains found in the beds on the St. Lawrence, Lake Cham- 
 plain, and the coast of Maine, are similar to those now 
 found on the coast of Maine or Labrador, or farther north. 
 
 The life of the Quaternary of greatest interest is the Mam- 
 malian, which type, as regards brutes, culminated in the 
 Champlain period. This culmination was manifested in 
 (1) the number of species, (2) the magnitude of the 
 animals the Mammalian life of the period exceeding in 
 each of these particulars that of the present time. 
 
 Along with the brute Mammals of the Quaternary ap- 
 peared also Man. 
 
 BRUTE MAMMALS. 
 
 Europe and Asia. The bones of Mammals are found 
 in caves that were their old haunts ; in stratified deposits 
 along rivers and lakes ; in sea-border deposits ; in marshes, 
 where the animals were mired; in ice, where they have 
 been preserved from decay by the intense cold. 
 
 The caves on the continent of Europe were the resort 
 
QUATERNARY ERA. 431 
 
 especially of the Cave Bear (Ursus spelceus), and those of 
 Great Britain of the Cave Hyena (Jlycena spelcea). Into 
 their dens they dragged the carcasses or bones of other 
 animals for food, so that relics of a large number of species 
 are now mingled together in the earth or stalagmite which 
 forms the floor of the cavern. In a cave at Kirkdale, 
 England, portions of a very large number of Hyenas have 
 been made out, besides remains of an Elephant, Lion, Bear, 
 Wolf, Fox, Hare, Weasel, Rhinoceros, Horse, Hippopota- 
 mus, Ox, Deer v and other species, all then inhabitants of 
 that country. A cave at Gaylenreuth is said to have 
 afforded fragments of at least 800 individuals of the Cave 
 Bear. The Cave Hyena is regarded as a large variety of 
 the HycBna crocuta of South Africa, and the Cave Lion, a 
 variety of Felis leo, the Lion of Africa. But many of the 
 Quaternary species are now extinct. 
 
 The fact that the number of species in the Quaternary 
 was greater than now, may be inferred from a comparison 
 of the fauna of Quaternary Great Britain with that of 
 any region of equal area in the present age. The species 
 included gigantic Elephants, two species of Rhinoceros, a 
 Hippopotamus, three species of Oxen, two of them of 
 colossal size, several species of Deer, including the colossal 
 Irish Deer (Cervus euryceros), whose height to the sum- 
 mit of its antlers was 10 to 11 feet, and the span of whose 
 antlers was in some cases 12 feet, the Horse, Ass, Wild 
 Boar, Wildcat, Lynx, Leopard, Lion, the huge Saber- 
 toothed Tiger (Machcerodus), with canines sometimes 
 eight inches long, the Cave Hyena, and Cave Bear, 
 besides various smaller species. 
 
 The Mammoth (Elephas primigenius) was nearly a 
 third taller than the largest modern species of Elephant. 
 It roamed over Great Britain, middle and northern Europe, 
 northern Asia, even to its Arctic shores, and North 
 America. Great quantities of tusks have been exported 
 from the borders of the Arctic Sea for ivory. These tusks 
 sometimes have a length of 12|- feet. Near the beginning 
 
432 HISTORICAL GEOLOGY. 
 
 of the century one of these Elephants was found frozen in 
 ice at the mouth of the Lena ; and it was so well pre- 
 served that wolves and bears ate of the ancient flesh. Its 
 length to the extremity of the tail was 16J feet, and its 
 height 9J feet. It had a coat of long hair. But no 
 amount of hair would enable an Elephant now to live in 
 those barren, icy regions, where the mean temperature 
 
 FIG. 459. 
 
 PROBOSCIDEAN : Mastodon giganteus. 
 
 in winter is 40 F. below zero. Siberia had also a hairy 
 Rhinoceros. 
 
 Although there were many Ungulates among the Qua- 
 ternary species of the Orient, the most characteristic 
 animals were the great Carnivores. 
 
 North America. - In the Champlain period, there were 
 great Elephants and Mastodons, Oxen, Horses, Stags, 
 Beavers, and some Edentates, in North America, unsur- 
 passed in magnitude by any in other parts of the world. 
 
QUATERNARY ERA. "433 
 
 Ungulates were the characteristic type. Of Carnivores 
 there were comparatively few species ; no true cavern 
 species have been discovered. Fig. 459 (from Owen) 
 represents the specimen of the American Mastodon now 
 in the British Museum. The skeleton set up by Dr. 
 Warren in Boston has a height of 11 feet, and a length, 
 to the base of the tail, of 17 feet. It was found in a 
 marsh near Newburgh, New York. The Mammoth (Ele- 
 phas primigenius} was the most common and wide-ranging 
 species of Elephant in North America, as in Europe and 
 Asia. 
 
 . 460. 
 
 EDENTATE: Megatherium Cuvieri (x ^). 
 
 South America. South America had, at the same 
 time, its Carnivores and Ungulates ; but it was most 
 remarkable for its Edentates, or animals related to the 
 Sloths and Armadillos. 
 
 Fig. 460 shows the form and skeleton of one of these 
 animals the Megatherium. It exceeded in size the largest 
 Rhinoceros : a skeleton in the British Museum is 18 feet 
 long. It was a clumsy, slothlike beast, but exceeded 
 immensely the modern Sloths in size. Another group of 
 Edentates, related to the modern Armadillos, had an 
 armor of bony plates developed in the skin, giving them 
 a superficial resemblance to Turtles. One genus named 
 
434 HISTORICAL GEOLOGY. 
 
 G-lyptodon is represented in Fig. 461, though it has been 
 recently discovered that the tail shown in the figure 
 belongs to another genus. Many of the animals of this 
 group also were gigantic, the Glyptodon here figured 
 having had a shell or carapace five or six feet in length. 
 
 South America was eminently the continent of Eden- 
 tates. 
 
 Australia. The Mammals of Australia, in the Cham- 
 plain period, were almost exclusively Marsupials, as is 
 the case in modern Australia ; but these partook of the 
 gigantic size so characteristic of the Mammalian life of 
 the period. The genus Diprotodon was as large as a 
 Hippopotamus, and Nototherium was as large as an Ox. 
 
 FIG. 461. 
 
 EDENTATE: Glyptodon clavipes (x 
 
 Conclusions. The facts sustain the following con- 
 clusions : 
 
 1. The Champlain period of the Quaternary was the 
 time of culmination of Mammals, both as to numbers and 
 as to magnitude. 
 
 2. The Mammalian faunas of the various continents 
 showed the same ordinal types by which they are now 
 characterized, but many of the species were much larger 
 than now exist. Thus, the Orient had its gigantic 
 Carnivores ; South America its gigantic Edentates ; Aus- 
 tralia its gigantic Marsupials. 
 
 3. The climate of Great Britain and the continent 
 
QUATERNARY ERA. 435 
 
 of Europe, where were the haunts of Lions, Tigers, 
 Hippopotamuses, etc., must have been warmer than now, 
 and probably not colder than warm-temperate. The 
 climate of Arctic Siberia was such that shrubs could 
 have grown there to feed the herds of Elephants, and 
 hence could not have been below sub-frigid, for which 
 degree of cold it is possible the animals might have 
 been adapted by their hairy covering. 
 
 4. The Champlain period, the meridian time of the 
 Quaternary Mammals, was, accordingly, as before stated, 
 one of warmer climate over the northern continents than 
 the present, and much warmer than that of the Glacial 
 period. The species may have begun to exist before the 
 Glacial period ended ; but they belonged preeminently 
 to the Champlain period. 
 
 5. The larger part of the great Mammals of the 
 Quaternary disappeared with the close of the Champlain 
 period or in the early part of the Recent period, while 
 others found refuge in the tropics. They were animals 
 of a warmer climate than now belongs to the regions 
 which they then inhabited; and the change to a some- 
 what colder climate at the close of the Champlain period 
 probably brought about the extermination and forced 
 migration. 
 
 Although there is no evidence in North America of a 
 recurrence of Glacial conditions after the Champlain 
 period, it is probable that there may have been oscilla- 
 tions of climate analogous to those of Europe, the climate 
 just at the close of the Champlain period being somewhat 
 colder than at present. Such an oscillation of climate 
 is perhaps indicated by remains of Reindeer which have 
 been found in southern New York, and near New Haven 
 in Connecticut. 
 
 Among the Mammals of Europe which existed before 
 the close of the Champlain period, some are now living ; 
 as the Reindeer, Marmot, Ibex, Chamois, Elk, Wild Boar, 
 Goat, Stag, Aurochs, Wolf, Brown Bear, and others. 
 
436 HISTORICAL GEOLOGY. 
 
 MAN. 
 
 Prehistoric Relics of Man in Europe. The earliest 
 relics of Man in Europe the region whose prehistoric 
 archaeology has been most thoroughly explored are rude 
 flint implements, as arrowheads, chisels, etc. ; flint chip- 
 pings, or the chips thrown off in making the implements ; 
 rude carvings ; human bones and skeletons ; the bones 
 of the animals used for food, split lengthwise, this being 
 done to get at the marrow ; charcoal, and other remains 
 of fires. They occur associated with the remains of the 
 Cave Bear, Cave Hyena, Cave Lion, Mammoth, and other 
 species which have either become extinct or migrated to 
 other regions. They date from the Champlain period, 
 and perhaps, in part, from the Glacial period. 
 
 1. The Paleolithic Epoch. As the only implements 
 of early Man in Europe were of stone or bone, the era in 
 human history has been called the Stone Age, in distinction 
 from the Bronze Age and the Iron Age, in which Man had 
 acquired the use of metals. These three stages of civili- 
 zation (and, for Europe, chronological periods) had been 
 long recognized by students of European archaeology. 
 But later studies made it manifest that the Stone Age in 
 Europe not only included a vastly greater lapse of time 
 than the two later ages together, but included widely 
 different types of culture. It became necessary, there- 
 fore, to subdivide the Stone Age. The earliest part of 
 that age has been designated the Paleolithic epoch, from 
 the Greek TraXcwo?, ancient, and \i6os, stone. Geologi- 
 cally, it may be correlated with the Champlain epoch, and 
 perhaps with the latter part of the Glacial epoch. The 
 Paleolithic implements are never polished, and are of 
 ruder make than those of the later part of the Stone Age. 
 Portions of skeletons referred to this era have been found 
 in various countries of Europe. In many cases, how- 
 ever, the evidence of age is more or less dubious. Some 
 
QUATERNARY ERA. 437 
 
 of the skulls and other bones present features which are 
 somewhat simian ; but this is not true of all the supposed 
 Paleolithic remains. The skull found at Engis in Belgium 
 is pronounced by Huxley "a fair average human skull" ; 
 and the same authority declares that " the most pithecoid 
 of human crania yet discovered " (the skull found at 
 Neanderthal in the Rhine valley) can in no sense "be 
 regarded as the remains of a being intermediate between 
 Men and .Apes." The antiquity of neither of these 
 famous relics is free from doubt. 
 
 2. The Reindeer Epoch. The second section of the 
 European Age of Stone has been called the Reindeer, 
 or Mewlithic, epoch. By many archaeologists it is con- 
 sidered only a subdivision of the Paleolithic epoch. It 
 was probably the time of transition from the Cham- 
 plain to the Recent epoch, which in Europe was marked 
 by a recurrence of Glacial conditions (page 427); and 
 the deposits, which are found in the caves of southern 
 France and elsewhere, are distinguished by the occur- 
 rence of large numbers of the bones of the Reindeer, 
 along with the human relics. The flint implements of 
 this epoch are well made, but are still exclusively made 
 by chipping, the men of the Reindeer epoch not hav- 
 ing developed the art of grinding and polishing stone ; 
 and among the relics there are implements of bone, ivory, 
 and horn, and drawings of animals upon these materials. 
 One of these drawings from southern France, made on 
 ivory, is copied in Fig. 462. It represents the hairy 
 Elephant, or Mammoth ; and shows that the men of that 
 epoch were familiar with the Mammoth as a living animal. 
 Remains of the Elephant, Cave Bear, Cave Hyena, Cave 
 Lion, occur in the same deposits, and also others of exist- 
 ing species, as the Elk, Ibex, Aurochs, etc. Perfect skel- 
 etons of Man have been found in some of the caverns. 
 Those of southern France are in part of tall stature, 
 5 feet 9 inches to 6 feet, having well-shaped heads, and 
 a large facial angle (85). One supposed to belong to 
 
438 HISTORICAL GEOLOGY. 
 
 this epoch, from a cave at Mentone (on the Mediterranean, 
 near the borders of France and Italy), was of a man fully 
 6 feet in height; and it lay buried in the stalagmite of the 
 cave, with flint implements and shell ornaments around, 
 and a chaplet of stag's teeth across its head. 
 
 3. The Neolithic Epoch. A third epoch is named the 
 Neolithic (from z/e'o?, new, and Xitfo?). The relics include 
 stone implements which are ground and polished, as well 
 as those which are chipped ; also broken pottery, and 
 bones of the Dog and (except in the earliest part of the 
 epoch) other domestic animals. The Neolithic men were, 
 therefore, in a much more advanced stage of culture 
 
 FIG. 462. 
 
 Picture of Elephas primigenius, engraved on ivory, x |. 
 
 than those of the preceding epochs. Remains of extinct 
 Champlain Mammals (except the Irish Deer) and of ani- 
 mals which have ceased to exist in central and southern 
 Europe, though surviving in some other region (as the 
 Reindeer), are absent. Neolithic man belongs unques- 
 tionably to the Recent period of geological time. The 
 earth and its fauna and flora had acquired substantially 
 their present condition. 
 
 The Neolithic race of men in Denmark resembled the 
 Laplanders. Their remains are found in shell heaps (the 
 so-called kjokkenmodingr, or kitchen middens) along the 
 shores of the Baltic. These shell heaps are relics of feasts, 
 
QUATERNARY ERA. 439 
 
 in which Oysters, Mussels, and other Mollusks apparently 
 formed a considerable part of the food. 
 
 To a later time in this epoch belong the earlier lake 
 dwellings of Switzerland structures built on piles in the 
 lakes, in which the only implements are of stone and 
 other non-metallic materials. But in the later lake dwell- 
 ings, about the western Swiss lakes, there are bronze imple- 
 ments, and these are of the Bronze Age. A few of the lake 
 dwellings belong even to the Iron Age. The Neolithic men 
 of the lake dwellings were no longer merely hunters and 
 fishers, but agriculturists, raising wheat .and barley. 
 
 Prehistoric Relics of Man in Other Countries. In 
 America, the Indians, at the time of the discovery of the 
 continent by Europeans, were mainly in a Neolithic stage 
 of culture. Rude stone implements have been found in 
 various localities, which have been considered to belong 
 to an earlier Paleolithic race ; but the evidence of such 
 an early race is less satisfactory than in Europe, since in 
 some cases the age of the deposit is in dispute, and the 
 localities have not in general been verified by a succession 
 of discoveries. The human skull reported from an ancient 
 gravel in Calaveras County, California, is probably an 
 authentic relic, and is associated with extinct species of 
 Mammals. It is, however, similar to that of a modern 
 Indian, and the implements in the gravels are of Neolithic 
 type. In that locality, some of the Pliocene and Pleisto- 
 cene Mammalia may have survived to a later date than 
 in most other regions. 
 
 In 1894, Dr. Dubois announced the discovery, in Java, 
 of a portion of a skull, two teeth, and a femur, which he 
 considered to belong to a manlike Ape, and which he 
 named Pithecanthropus erectus. The remains appear to 
 be human, but the skull shows simian characters even 
 more strongly marked than those of the Neanderthal 
 skull and others which have been found in Europe. It 
 is uncertain whether the formation in which the relics 
 were found is Pleistocene or Pliocene. 
 
440 
 
 HISTORICAL GEOLOGY. 
 
 The evidence seems to render it probable that the ear- 
 liest of prehistoric races, ranging from the East Indies to 
 western Europe, possessed features more simian than are 
 characteristic of any race of men now in existence. 
 
 Modern Human Relics. In modern deposits, buried 
 coins, statues, temples, cities, are found among the earth's 
 fossils, contrasting strangely with the remains of the species 
 
 FIGS. 463, 464. 
 
 Human skeleton from Guadeloupe. 
 
 Conglomerate containing coins. 
 
 with which the history of the world's life began. Fig. 
 464 represents a coin conglomerate, containing coins of 
 silver, of the reign of Edward I., found at a depth of ten 
 feet below the bed of the river Dove in England; and 
 Fig. 463, a portion of a human skeleton firmly imbedded 
 in a modern shell limestone of Guadeloupe, the former 
 owner of which was, less than three centuries ago, a 
 fighting Carib. 
 
 Man at the Head of the System of Life. With the 
 creation of Man a new era opens in geological history. In 
 earliest time only matter existed dead matter. Then 
 appeared life unconscious life in the plant, conscious 
 
QUATERNARY ERA. 441 
 
 and intelligent life in the animal. Ages rolled by, with 
 varied exhibitions of animal and vegetable life. Finally 
 Man appeared, a being made of matter and endowed with 
 life, but, more than this, partaking of a spiritual nature. 
 The systems of life belong essentially to time ; but Man, 
 through his spirit, belongs to the infinite future. Thus 
 gifted, man is the only being capable of reaching toward 
 a knowledge of himself, of nature, or of God. He is, 
 therefore, the only being capable of conscious obedience 
 or disobedience to moral law, the only being subject to 
 degradation through excesses of appetite and violation of 
 moral law, the only being with the will and power to 
 make nature's forces his means of progress. 
 
 Man shows his exalted nature in his material structure. 
 His fore limbs are not made for locomotion, as in all quad- 
 rupeds ; they are removed from the locomotive to the 
 cephalic series, being fitted to serve the head, and espe- 
 cially the intellect and soul. Man stands erect, his body 
 placed wholly under the brain, to which it is subservient. 
 His whole outer being, in these and other ways, shows 
 forth the divine nature of the inner being. 
 
 EXTINCTION OF SPECIES IN MODERN TIMES. 
 
 Species are becoming extinct in the present epoch, 
 as in the past. Man is now a prominent means of this 
 destruction. The Dodo, a large bird looking like an 
 overgrown chicken in its plumage and wings, was abun- 
 dant in the island of Mauritius until late in the seventeenth 
 century. In New Zealand have been found remains of 
 almost twenty species of Ostrich-like Birds, known collec- 
 tively under the native name Moa, and referred to the 
 genera .Dinornis, Meionornis, Palapteryx, etc. The largest 
 species was 10 or 12 feet in height, and the tibia ("drum- 
 stick ") 30 to 32 inches long. Some species at least of the 
 Moas may have survived until within a century or two. 
 In Madagascar remains of a still larger bird, but of similar 
 character, occur, called JEpyornis ; its egg is over a foot 
 
442 HISTORICAL GEOLOGY. 
 
 (13J- inches) long. The Great Auk, a bird of northern 
 seas, has become extinct within the present century ; the 
 last was seen in 1844. These are a few examples of the 
 modern extinction of species. 
 
 The progress of civilization tends to restrict forests and 
 forest life to narrower and narrower limits. The Buffalo 
 once roamed over North America to the Atlantic, but is 
 now practically extinct, except where it is under human 
 protection. The Beaver, Wolf, Bear, and Wild Boar 
 were .formerly common in Great Britain, but are now 
 wholly exterminated. 
 
 GENERAL OBSERVATIONS ON CENOZOIC TIME. 
 
 Contrast between the Tertiary and Quaternary Eras in 
 Geographical Progress. The study of Cenozoic time has 
 brought out the contrast in the geological work of the 
 Tertiary and Quaternary ages. 
 
 The Tertiary in North America carried forward the work 
 of rock-making, and of extending the limits of the dry land 
 southward, southeastward, and southwestward, which had 
 been in progress ever since Archsean time. 
 
 The Quaternary transferred the scene of operations to 
 the broad surface of the continent, and especially to its 
 middle and higher latitudes. 
 
 Through the Tertiary, the higher mountains of the 
 globe had been rising, and the continents extending ; and 
 hence the great rivers with their numerous tributaries 
 which are the offspring of great mountains on great con- 
 tinents channeled out the mountains and made valleys 
 and crested heights. In the Glacial epoch this work went 
 forward with special energy. The exposed rocks yielded 
 before the moving glacier, and the fragments torn from 
 the ledges, with the disintegrated material which had 
 accumulated in pre-Glacial time, were carried along to be 
 distributed over the continental surface. Torrents, fed 
 by the melting ice, were also at work, with perhaps even 
 
CENOZOIC TIME. 443 
 
 greater abrading power than the ice. Thus the excava- 
 tion of valleys and the shaping of hills and mountains 
 were everywhere in progress. In the Champlain period, 
 the low level at which the land lay, and the melting of the 
 ice, with the dropping of its earth and stones, enabled the 
 flooded streams to fill the great valleys deep with allu- 
 vium. In the Recent period, which followed, the upward 
 movements of the land led to a terracing of the Champlaiu 
 deposits along the seashores and about the lakes and rivers. 
 
 Thus, under the rending, eroding, and transporting 
 power of fresh water, frozen and unfrozen, eminently 
 the great Quaternary agent, in connection, probably, 
 with high-latitude oscillations of the earth's crust, the 
 making of the earth was finally completed. 
 
 Life. In Cenozoic time, as in the preceding seons, species 
 were disappearing and others took their places. The Mam- 
 mals of the early Eocene are different in species from those 
 of the later; and these from the Miocene, the Miocene from 
 the Pliocene, and the Pliocene from the Quaternary. 
 
 According to the present state of discovery, Mammals 
 commenced in Mesozoic time, late in the Triassic era, 
 and the Mesozoic species were probably all Monotremes 
 and Marsupials. They were the precursor species, pro- 
 phetic of that expansion of the new type which was to 
 take place after the Age of Reptiles had closed. In the 
 early Eocene, at the opening of the Age of Mammals, 
 appeared Ungulates and Creodonts of large size. The 
 earliest Ungulates (such as Phenacodm, Fig. 443, page 
 395) were scarcely distinguishable from the earliest repre- 
 sentatives of the Carnivores (Creodonts); but more typical 
 representatives of both groups appeared before the close 
 of the Eocene. In the early Tertiary there were Perisso- 
 dactyls allied to the Tapir and Rhinoceros, and Artiodac- 
 tyls allied to the Hog. Proboscideans commenced in the 
 Miocene, though the Elephant proper appeared first in the 
 Pliocene. Deer and Antelopes commenced in the Miocene, 
 Oxen in the Pliocene. 
 
444 HISTOKICAL GEOLOGY. 
 
 GENERAL OBSERVATIONS ON GEOLOGIC 
 GAL HISTORY. 
 
 LENGTH OF GEOLOGICAL TIME. 
 
 By employing as data the relative thickness of the forma- 
 tions of the geological ages, estimates have been made of 
 the time ratios of those ages, or their relative lengths 
 (pages 317, 379). These estimated time ratios for the 
 Paleozoic, Mesozoic, and Cenozoic, are 12 : 3 : 1. But the 
 numbers may be much altered when the facts on which 
 they are based are more correctly ascertained. It is quite 
 certain that the Eopaleozoic (Cambrian and Lower 
 Silurian) was, at the least, three times as long as either 
 the Devonian or Carboniferous, and longer than the 
 entire Neopaleozoic ; and probable that Mesozoic time 
 was not less than three times as long as Cenozoic. 
 
 Hence comes the striking conclusion that the longest age 
 of the world since life began was the earliest when the 
 earth's population (with the exception of a few Insects 
 and Fishes, in the latter part of the time) included only 
 marine Invertebrates. And the time of the earth's begin- 
 nings before the introduction of life must have exceeded 
 in length all subsequent time. 
 
 The actual lengths of these ages it is not possible to de- 
 termine even approximately. All that Geology can claim 
 to do is to prove the general proposition that Time is 
 long. If time from the commencement of the Cambrian 
 included 48 millions of years, which most geologists would 
 pronounce too low an estimate, the Paleozoic part, ac- 
 cording to the above ratio, would comprise 36 millions, 
 the Mesozoic 9 millions, and the Cenozoic 3 millions. 
 
 One of the means of estimating the length of past time 
 is that afforded by the rate of recession of the Falls of 
 Niagara. The river below the Falls flows northward in 
 a deep gorge, with high rocky walls, for seven miles, 
 toward Lake Ontario. It is reasonably assumed that the 
 
GEOGRAPHICAL PROGRESS. 445 
 
 gorge has been cut out by the river, for the river is 
 now accomplishing work of this very kind. By certain 
 fossiliferous Quaternary beds over the country bordering 
 the present walls, and by other evidence, it is proved that 
 at least about six miles of the present gorge, and probably 
 the whole seven miles, was made after the retreat of the 
 ice sheet of the Glacial period from that part of the coun- 
 try. A comparison of surveys made respectively in 1842 
 and 1886 shows that the recession of the apex of the Horse- 
 shoe Fall during that time has been at the rate of about 
 four feet per year. On the basis of that determination, 
 the time occupied in the erosion of the entire gorge has 
 been estimated at from 6000 to 10,000 years. It is, how- 
 ever, believed by many geologists that, during a part of 
 the time, the water of the Upper Lakes (Superior, Michi- 
 gan, Huron) was diverted into another channel. On that 
 supposition, the estimate of the time required for the cut- 
 ting must be considerably increased perhaps to about 
 30,000 years. In any case, when it is considered that the 
 work has been done in a small fraction of the latest and 
 shortest of the geological eras, the calculation may be 
 regarded as establishing, at least, the proposition that 
 Time is long, although it affords no satisfactory numbers. 
 
 Besides the estimates of geological time based on proc- 
 esses of erosion and sedimentation, other estimates have 
 been made by physicists based on the conditions of cooling 
 of the earth and the sun. 
 
 While neither the geological nor the physical modes of 
 calculation can yield any certain results in the present 
 state of our knowledge, it may be considered probable 
 that geological time from the beginning of the Cambrian 
 is measured by tens of millions, rather than by millions, 
 or by hundreds of millions, of years. 
 
 GEOGRAPHICAL PROGRESS IN NORTH AMERICA. 
 
 The principal steps of progress in the continent of North 
 America are here recapitulated: 
 
446 HISTORICAL GEOLOGY. 
 
 1. The continent at the close of the Archsean lay spread 
 out mostly beneath the ocean (map, page 237). Although 
 thus submerged, its outline was nearly the same as now. 
 The dry land lay mostly to the north, as shown on the 
 map. The form of the main mass approximated to that 
 of the letter V, and the arms of the V were nearly parallel 
 to the present coast lines. 
 
 2. Through the Paleozoic ages, as the successive periods 
 passed, the dry land gradually extended itself southward, 
 owing to a gradual emergence; that is, the sea border at 
 the close of the Lower Silurian was probably as far south 
 as the Mohawk valley in New York ; at the close of the 
 Upper Silurian it extended along not far from the north 
 end of Cayuga Lake and Lake Erie; and by the close of 
 the Devonian era the state was a portion of the dry land 
 nearly to its southern boundary. This southward prog- 
 ress of the sea border in New York may be taken as an 
 example of what occurred along the borders of the 
 Archasan farther west. In other words, there was 
 through the Cambrian, Silurian, and Devonian ages a 
 gradual extension of the dry part of the continent south- 
 eastward and southwestward. 
 
 By the close of the Carboniferous era, or before the open- 
 ing of Mesozoic time, the dry portion appears to have so 
 far extended southwardly as to include nearly all the area 
 east of the Mississippi, at least north of the Gulf States, 
 along with a part of that west of the Mississippi, as far as 
 the middle of Kansas. 
 
 3. During the Paleozoic ages, rock formations were in 
 progress over large parts of the submerged portions of the 
 continent ; and some vast accumulations of sand were 
 made as drifts or dunes over the flat shores and reefs. 
 These rock formations had in general ten times the thick- 
 ness along the Appalachian region which they had over the 
 interior of the continent ; and they were mostly f ragmental 
 deposits in the former region, while mostly limestones in 
 the latter. Hence two important conclusions follow : 
 
GEOGRAPHICAL PROGRESS. 447 
 
 First. The Appalachian region was through much of 
 the time a sea-border region, receiving the debris from 
 the land. There was a strip of emerged land along the 
 Appalachian region at the close of Archaean time, and 
 Cambrian and Lower Silurian deposits were formed on 
 both sides of the emerged land. At the close of the Lower 
 Silurian, a considerable region emerged, adjoining the 
 Archaean area on the east. Along the western shore of 
 this broad area of dry land, the debris accumulated to 
 form the later Paleozoic deposits. At the same time the 
 Interior region was a mediterranean sea, whose pure waters 
 over large areas, mostly free from mechanical sediments, 
 afforded the conditions for a luxuriant growth of the 
 marine life whose skeletons are the material for the mak- 
 ing of limestone. 
 
 Secondly. The Appalachian region was undergoing 
 great changes of level, the deposits having been made in 
 shallow waters ; the region was slowly sinking, not faster 
 than the rate of deposition, and the amount of subsidence 
 exceeded by ten times that in the Interior Continental 
 region. 
 
 4. In this Appalachian region, the Taconic range (and 
 probably a system of contemporaneous ranges farther 
 south) was upturned, rendered metamorphic, and elevated 
 above the ocean's level, at the close of the Lower Silurian ; 
 and at the same time the valley of Lake Champlain and 
 Hudson River was formed, if not earlier begun. At the 
 same time, also, the Atlantic Border region south of New 
 York emerged by an extensive geanticlinal movement, 
 forming a land mass of unknown breadth, whose denuda- 
 tion in later Paleozoic time furnished material for the 
 thick sediments of the Appalachian range proper. 
 
 5. As Paleozoic time closed, an epoch of revolution 
 occurred, in which the rocks of the Appalachian region 
 south of New York arid west of the Piedmont region of 
 ancient crystalline rocks underwent (1) extensive flex- 
 ures or foldings; (2) immense faultings in some parts; 
 
448 HISTORICAL GEOLOGY. 
 
 (3) consolidation, and, in some eastern portions, some 
 degree of metamorphism, with the conversion of bitumi- 
 nous coal into anthracite. These changes affected the 
 region from New York to Alabama. The effects of heat 
 and uplift were more decided toward the Atlantic than 
 toward the Interior, showing that the force producing the 
 great results was exerted in a direction from the Atlantic, 
 or from the southeast toward the northwest. The Appa- 
 lachian Mountains proper were then made ; and they 
 were, consequently, in existence when the Mesozoic era 
 opened. 
 
 These mountains are parallel to the eastern outline of 
 the original Archaean continent. 
 
 Some disturbances probably took place at the same time 
 in the Great Basin ; but no general revolution on the 
 Pacific side comparable to that on the Atlantic. 
 
 In Europe, also, this epoch of revolution was a time of 
 mountain-making. 
 
 6. In early Mesozoic time (the continent being largely 
 dry land, as stated in the latter part of 2), long depres- 
 sions in the surface of the continent, made in the course 
 of the Appalachian revolution, and situated between the 
 Appalachians and the sea border, were brackish-water 
 estuaries, or were occupied by fresh-water marshes and 
 streams ; and Mesozoic sandstones, shales, and coal beds 
 were formed in them. The Connecticut Valley region of 
 Mesozoic rocks (page 332) is one example. At the same 
 time there were formations in progress over the Rocky 
 Mountain region, a vast area from which the sea was not 
 excluded, or only in part. At the close of the Jurassic 
 period, the Sierra Nevada and some other great ranges 
 on the western side of the continent were made. 
 
 7. In the later Mesozoic, or the Cretaceous era, the 
 Atlantic and Gulf Borders of the continent were under 
 water (the Atlantic geanticline formed at the close of the 
 Lower Silurian having become submerged), and received 
 a deposit of Cretaceous rocks. The Western Interior 
 
GEOGRAPHICAL PROGRESS. 449 
 
 sea, opening south into the Gulf of Mexico, still existed, 
 and was probably for the most part a deeper and clearer 
 sea than in the earlier Mesozoic. Deposits were made in 
 it over a very large part of the great region reaching 
 from Iowa on the east to the Colorado on the west, and 
 northward probably to the Arctic Ocean. The Pacific 
 Border was also receiving an extension like the Atlantic. 
 
 8. Mesozoic, like Paleozoic, time closed with a revolu- 
 tionary epoch of mountain-making; but the theater of 
 this Laramide, or post-Mesozoic, revolution was on the 
 western side of the continent. The elevation extended 
 along the whole line of the summit region of the Rocky 
 Mountains from near the Arctic Ocean to central Mexico ; 
 and in all probability the long line of the Andes shared 
 in the movement. The Rocky Mountain and Sierra 
 ranges are parallel to the western arm of the Archaean V, 
 as the Taconic and Appalachian ranges are parallel to its 
 eastern arm. 
 
 9. In the Dearly Cenozoic, or the Tertiary era, the ex- 
 tension of the Atlantic and Pacific Borders was still con- 
 tinued. With its close the progress of the continent in 
 rock-making southeastward and southwestward was very 
 nearly completed. 
 
 The Interior sea, after the Laramide revolution, became 
 dry land, except remnants left as great fresh-water lakes, 
 a transition from marine to terrestrial conditions being 
 shown by the coal-bearing strata of the Laramie epoch. 
 During the Eocene Tertiary, the Ohio and Mississippi 
 emptied into a bay of the Gulf of Mexico, just where they 
 now join their waters; at the close of the Eocene the Ohio 
 had taken a secondary place as a tributary of the Missis- 
 sippi. The great Missouri River, now the main trunk of 
 the Interior river system, began its existence after the 
 Cretaceous period, and reached its full size only toward 
 the close of the Tertiary, when the Rocky Mountains 
 finally attained their full height. 
 
 10. The continent being thus far completed, as the Qua- 
 
450 HISTORICAL GEOLOGY. 
 
 . 
 
 ternary Age was drawing on, operations changed from 
 those causing southern extension, to those producing 
 movements of ice and fresh waters over the land, especially 
 in the higher latitudes; and thereby the surface of the 
 continent acquired its present character. 
 
 PROGRESS OF LIFE. 
 
 In the summary of the characteristics of the successive 
 aeons and eras of geological time given on page 233, the 
 student's attention was called to two generalizations : first, 
 that in the progress of time there has been an increasing 
 approximation to the flora and fauna of the present age ; 
 second, that there has been a rise in the grade of plants 
 and animals represented. It was then remarked that these 
 generalizations were strikingly in accord with the theory 
 of evolution, now almost universally adopted. The student 
 is now prepared to take a fuller survey of the general laws 
 of progress in the history of life, and to recognize the 
 significance of those laws in relation to evolution. 
 
 It would be inappropriate in this place to discuss the 
 evidences of evolution outside of the sphere of geology and 
 paleontology those, for instance, which are afforded by 
 the homologies of structure maintained in spite of wide 
 diversity of function, by rudimentary organs, by the laws 
 of embryology, by the facts of geographical distribution, 
 and by the difficulties and uncertainties of zoological and 
 botanical classification. Only the bearings of the geologi- 
 cal history of plants and animals can be here presented. 
 
 The concurrence of evidence from many different sources 
 has brought about a substantially unanimous opinion 
 among naturalists, that the existing species of plants and 
 animals have originated by descent with modification, from 
 species that preceded them in geological time, and these, 
 in turn, from still earlier species, and so on to the simplest 
 living forms with which life is supposed to have com- 
 menced. There is, however, much uncertainty and much 
 difference of opinion in regard to the method of evolution 
 
PROGRESS OF LIFE. 451 
 
 and the forces which have operated in the production of 
 the result. It is generally believed that the changes from 
 generation to generation, which have resulted in the evo- 
 lution of new species, are mainly due, directly or indirectly, 
 to the influence of environment. Some naturalists attrib- 
 ute very much to the direct influence of environment, 
 assuming that the effects of use or disuse of organs, and 
 other effects produced in the lifetime of individuals by the 
 environment, will be inherited in greater or less degree 
 by their offspring, and may, therefore, be accumulated 
 from generation to generation. Others believe that com- 
 paratively little is due to the direct influence of environ- 
 ment. All agree that a most potent influence in evolution 
 is the indirect influence of environment, as formulated 
 in Darwin's principle of natural selection. According to 
 this principle, those individuals in each generation whose 
 peculiarities of organization are most thoroughly adapted 
 to the environment will have the greatest chance of sur- 
 viving to maturity and leaving offspring. In this manner, 
 whatever may be the causes of variation, all variations 
 which place the individual more in harmony with its en- 
 vironment will tend to be preserved and accumulated from 
 generation to generation. Some naturalists have imagined 
 innate tendencies to progress in the organization of species, 
 and other occult or transcendental forces tending to evo- 
 lution. There may be causes of evolutionary change 
 as yet entirely unknown. In so far as evolution depends, 
 either directly or indirectly, upon the influence of environ- 
 ment, it is obvious that evolutionary changes in flora and 
 fauna must have gone on rapidly only when rapid changes 
 have taken place in the environment. The geological 
 record seems to indicate that, in every region of the globe, 
 there have been long periods of comparative stability in 
 geographical conditions, alternating with epochs of com- 
 paratively rapid change. Evolution cannot, therefore, 
 have progressed at uniform rate through geological time, 
 but periods of comparatively rapid evolution must have 
 
452 HISTORICAL GEOLOGY. 
 
 alternated with long ages of approximately stationary con- 
 ditions. It is uncertain to what extent the evolution of 
 new species has taken place by the accumulation of minute 
 variations from generation to generation, and to what 
 extent occasional abrupt variations have contributed to 
 that result. On the latter supposition, it is obvious that 
 the series of intermediate forms, which must have existed 
 between an ancestral species and a species derived from it, 
 would have shown much less fine, gradations than on the 
 former. 
 
 The General Fact of Progress in Life. In the survey 
 of geological history which the student has now completed, 
 he will have been impressed continually with the general 
 fact of progress. In the Cambrian, the only plants were 
 Seaweeds. Acrogens made their first appearance in the 
 Lower Silurian, and became abundant in the Devonian 
 and Carboniferous. Gymnosperms first appeared in the 
 Devonian, and culminated in the Mesozoic. Angiosperms 
 began in the Cretaceous, and attain their greatest develop- 
 ment at the present time. The Echinoderms of the Cam- 
 brian were Crinoids, the lowest class of the subkingdom. 
 The Echinoids, the highest of the classes possessed of 
 well-developed skeletons, in that subkingdom, appeared 
 as early as the Lower Silurian ; but the highest group of 
 this class, the Irregular Echinoids, did not appear till the 
 Jurassic. The class of Gastropods commenced, indeed, in 
 the Cambrian, but the higher families of that class, char- 
 acterized by the most specialized types of dentition, did 
 not appear until the Mesozoic. Of the Cephalopods, the 
 lower order, the Tetrabranchs, appeared in the Cambrian^ 
 but the higher order, the Dibranchs, not till the Triassic. 
 The most of the Crustaceans of early time belonged to 
 the lower subclass, the Entomostracans. The higher sub- 
 class of Malacostracans was, indeed, represented in the 
 Cambrian, but onl} 7 by its lowest order, the Leptostracans, 
 an order somewhat intermediate in character between 
 the two subclasses. The higher orders of Crustaceans 
 
PROGRESS OF LIFE. 453 
 
 appeared much later. The Macrurans made their first 
 appearance in the Devonian, and Brachyurans not till the 
 Jurassic. With the exception of some Neuropters and 
 possibly a few Beetles, the Hexapod Insects in the Pale- 
 ozoic all belonged to the orders with incomplete meta- 
 morphosis. The higher orders of Insects, exhibiting dis- 
 tinctly in their development the three stages of larva, pupa, 
 and imago (complete metamorphosis), belong to Mesozoic 
 and Cenozoic time. The highest of the subkingcloms, 
 the Vertebrates, did not appear at all in the Cambrian. 
 Fishes first appeared in the Lower Silurian, Amphibians 
 in the Devonian, Reptiles in the Permian, Birds and 
 Mammals not till the Mesozoic. The Reptiles of the 
 Permian belonged mostly to the comparatively low order 
 of Rhynchocephala. The more highly organized Dino- 
 saurs and Pterosaurs did not come in till Mesozoic time. 
 The Birds of the Jurassic, arid some of those of the Cre- 
 taceous, still retained characteristics allying them to 
 Reptiles. The Mammals of the Triassic were probably 
 all Monotremes, and those of the Jurassic and the Creta- 
 ceous probably all Monotremes and Marsupials. The 
 higher subclass of Placentals probably made its first 
 appearance in the Eocene, and Man himself marks the 
 culmination of living nature in the Quaternary. 
 
 Cephalization. The progress of animal life in gen- 
 eral, and the progress within each group of the animal 
 kingdom, involves a manifestation in increasing intensity 
 of the fore-and-aft structure, which has been stated (page 
 58) to be characteristic of animal life. Bilateral symme- 
 try takes the place of radial symmetry, as shown by the 
 contrast between the Regular Echinoids, which appeared 
 even in the Paleozoic, and the Irregular Echinoids, which 
 were unknown till the Jurassic. The posterior portion 
 of the body tends to become abbreviated, and power and 
 function to be concentrated in the organs and appendages 
 of the anterior portion of the body, as is seen in compar- 
 ing the Macrurans, which appeared in the Devonian, 
 
454 HISTORICAL GEOLOGY. 
 
 with the Brachyurans, which first appeared in the Juras- 
 sic. The cephalic nerve mass, or brain, acquires increas- 
 ing size with the increasing activity and intelligence of 
 the animal. See, for illustration, the figures of casts of 
 Mammals' brains on page 397. 
 
 Parallelism of Paleontology and Embryology. Ag- 
 assiz long ago called attention to the fact that, in their 
 development, many animals pass through embryonic or 
 larval forms more or less closely resembling animals of 
 lower grade, which appeared in earlier geological periods. 
 The Crabs, through all of their earlier stages of develop- 
 ment, have a long tail-like abdomen, such as is permanent 
 in the Shrimps and other Macrurans. The embryo Spider 
 has the abdomen segmented, as in the adult of the more 
 ancient group of Scorpions. Indeed, some of the earliest 
 Spiders, in the Carboniferous period, show traces of this 
 segmentation in the adult. The modern Ganoids and 
 Teleosts pass through an embryonic stage, in which they 
 have heterocercal tails like the Ganoids of the Paleozoic. 
 The embryos of Reptiles, Birds, and Mammals have on each 
 side of the neck a row of gill slits like those of Sharks. 
 
 Progress from Generalized to Specialized Forms. It 
 was remarked on page 396 that the representatives respec- 
 tively of the Ungulates and the Carnivores in the earli- 
 est Eocene are scarcely distinguishable from each other ; 
 whereas, in the progress of time, the divergent evolution 
 has led to a stronger accentuation of the characters of the 
 respective groups, as is seen when we contrast the limbs 
 or the dentition of the Horse and the Cat. This case of 
 the Tertiary Mammals well illustrates a general law. As 
 we go back in geological time, the lines of descent appear 
 to converge, indicating that forms now widely separated 
 may have been derived by divergent modification from 
 a common ancestry. The Ganoids, whose scales are pre- 
 served in Lower Silurian rocks, appear thus to have formed 
 the starting point of two divergent lines of evolution. In 
 one direction the accentuation of piscine characters resulted 
 
PROGRESS OF LIFE. 455 
 
 in the Homocercal Ganoids and Teleosts, while the other 
 line ascended through the Dipnoans to the Amphibians 
 and thence to the higher classes of Vertebrates. It was 
 long ago pointed out by Agassiz that the earliest repre- 
 sentatives of a group of animals often possessed character- 
 istics which appeared to connect them with some other 
 group. Such forms were called by him synthetic types. 
 By others they have been named comprehensive types. 
 Numerous examples of such comprehensive types occur 
 in geological history, and it is noteworthy that they have, 
 in general, become extinct or nearly so. The Dipnoans, 
 blending with the characters of the Fishes the pulmonary 
 respiration and mode of articulation of the lower jaw 
 characteristic of the higher Vertebrates ; the Labyrinth- 
 odonts, retaining fishlike structures in their skeletons; the 
 Dinosaurs, with their birdlike limbs and pelvic girdles ; 
 the Reptilian Birds, with their teeth, and long tails, and 
 free metacarpals ; the Monotremes, with their reptilian 
 characters in skeleton and reproductive organs ; are 
 striking examples of such comprehensive types. 
 
 Progress in Diversification of Type. It is a note- 
 worthy fact that no classes (in the classification of animals 
 adopted in this work), and very few orders, have ever 
 become extinct, while in the progress of geological time 
 several classes and a much larger number of orders un- 
 known in the Cambrian have been introduced. The 
 result has been an increasing diversification. The intro- 
 duction of higher classes and orders has not involved the 
 extinction of lower types. In some cases evolution has 
 involved a degradation, so that relatively low forms have 
 appeared later than allied forms of higher grade. The 
 Ichthyosaurs, Reptiles degraded to fishlike form and habit, 
 did not appear till the Triassic, although Reptiles of more 
 normal structure were already in existence in the Permian. 
 And, while the true Lizards appeared in the Jurassic, the 
 Snakes, which are essentially Lizards that have suffered 
 degradation in the loss of limbs, did not appear until 
 
456 HISTORICAL GEOLOGY. 
 
 late in the Cretaceous. So, among Mammals, although a 
 number of the comparatively normal orders of Placentals 
 were represented in the earliest Eocene, the Whales did 
 not appear till later in the Eocene ; and the Edentates, 
 whose degraded character is shown in the imperfection of 
 their teeth, did not appear till the Miocene. 
 
 Progress from Marine to Terrestrial Life. So far 
 -as our present knowledge goes, the life of the Cambrian, 
 both vegetable and animal, was exclusively marine. The 
 earliest forms of life were probably creatures floating on the 
 surface of the sea ; and animals developed heavy skeletons, 
 and took to crawling upon the bottom or attaching them- 
 selves thereto, only in a later stage of evolution (see page 
 251). In the Lower Silurian we get the earliest traces 
 of terrestrial life, in Acrogens and Insects ; but it is not 
 until ths Carboniferous that terrestrial life attains a very 
 great development ; and Phanerogams among plants, and 
 Insects, Birds, and Mammals among animals, the forms 
 of terrestrial life now dominant, belong chiefly or exclu- 
 sively to Mesozoic and Cenozoic time. 
 
 Increasing Approximation to the Present Flora and 
 Fauna. The dominant groups of Paleozoic life are, with- 
 out exception, groups which are now comparatively rare 
 or entirely extinct. The gigantic Sigillarids, Lepidoden- 
 drids, and Calamites that characterized the Carboniferous 
 forests, are now represented by insignificant forms which 
 make no conspicuous feature in the vegetation. Cya- 
 thophylloid Corals have only doubtful representatives 
 after the Paleozoic. Crinoids decrease in abundance 
 after the Paleozoic, and the class is now but very scan- 
 tily represented. The groups of Cystoids and Blastoids 
 are exclusively Paleozoic. The class of Brachiopods, 
 whose remains in the early Paleozoic outweigh all other 
 fossils put together, is now reduced to an insignificant 
 remnant. Of Tetrabranch Cephalopods, the genus Nau- 
 tilus is now the sole survivor. The Trilobites and the 
 Placoderms are unknown since the Paleozoic. 
 
PROGRESS OF LIFE. 45 T 
 
 The life of the Mesozoic shows a greater resemblance to 
 ths life of modern times. The forests of Acrogens are suc- 
 ceeded in the early Mesozoic by forests of Gymnosperms, 
 and in the Cretaceous Angiosperms appear. Brachio- 
 pods gradually decline, and Lamellibranchs gradually 
 increase. The order of Tetrabranchs is represented by a 
 vast multitude of Ammonites, but associated with them 
 are Belemnites and other representatives of the Dibranchs. 
 Insects appear in increasing numbers, and most of the 
 higher orders are represented. Reptiles attain their cul- 
 mination ; and, before the close of the Mesozoic, the 
 modern groups of Teleost Fishes, Birds, and Mammals 
 appear. 
 
 The Cambrian fauna includes not a single species now 
 surviving, and only two genera represented by living spe- 
 cies, Lingula and Discina. It is doubtful even whether 
 ths Cambrian Brachiopods referred to those two genera 
 really belong to them. Before the close of the Paleozoic, 
 a considerable number of genera appear which are still 
 represented by living species ; but no Paleozoic species, 
 either of plant or animal, has survived to the present 
 time, with the doubtful exception of a few species of 
 Carboniferous Diatoms. It is doubtful whether any Meso- 
 zoic species of animal, except a few species of Foraminifers, 
 has survived to the present day, although the number of 
 genera represented by living species becomes considerable. 
 With the beginning of the Tertiary, existing species of 
 Invertebrates make their appearance ; and, by the close of 
 the Tertiary, the Plants and Invertebrates are mainly 
 of species which still survive. During the Quaternary, 
 existing species of Vertebrates are gradually introduced. 
 
 Gradual Change in Genera and Species. As we pass 
 from one stratum to another within the limits of a forma- 
 tion, it may generally be observed that some species dis- 
 appear, and others take their place. At the close of an 
 epoch or a period, a greater proportion of the life is 
 changed. The diagram on page 322, showing the range 
 
458 HISTORICAL GEOLOGY. 
 
 of some of the principal genera of Trilobites, illustrates 
 well the history of most groups of organisms. Each class 
 or order generally appears first in comparatively small num- 
 bers of species, and increases to a culmination, after which 
 it may gradually decline ; and during the lifetime of a 
 class or order there is a constant appearance and disap- 
 pearance of genera and species. It is not certain that any 
 species represented in the Paleozoic appears in the Meso- 
 zoic, and scarcely any Mesozoic species appear in the Cen- 
 ozoic ; but, at the present day, all geologists would explain 
 this condition, not by the supposition of universal exter- 
 minations, but by reference to the imperfection of the 
 geological record (page 461). 
 
 The cause of the extinction of species must be supposed 
 to be, in general, an unfavorable environment. When 
 the environment changes so that a species is no longer in 
 harmony with it, the species may undergo modification, 
 if the change of environment is not too rapid, or may 
 migrate, if areas are open to it in which the environment 
 is more favorable. Otherwise it must become extinct. 
 Changes of climate have probably been, on a large scale, 
 the most important influence in determining such evolu- 
 tionary changes. The amount of heat received from the 
 sun has appreciably declined through geological time. 
 The water vapor, with which the atmosphere of earlier 
 ages was loaded, has been gradually condensed ; and the 
 carbon dioxide has been gradually removed from the 
 atmosphere, and its carbon stored in various forms in 
 the crust of the globe. The earth's atmosphere has 
 thereby become less absorptive of heat, and opposes less 
 resistance to the radiation of heat from the earth. Oscil- 
 lations of level of the earth's crust have directly affected 
 the temperature of the areas of elevation or subsidence, 
 and have indirectly affected the temperature of other 
 regions by changing the courses of ocean currents. While 
 changes of climate have often operated simultaneously 
 over a large part or the whole of the surface of the globe, 
 
PKOGEESS OF LIFE. 459 
 
 every movement of elevation or subsidence, however slight, 
 has made local changes in the conditions of life. Land 
 has been converted into sea, and sea into land ; salt water 
 has given place to fresh, and vice versa; muddy shoals, 
 receiving detritus from the shore, have given place to 
 clear seas in whose pure waters corals could grow luxu- 
 riantly; and, again, the debris of the coral gardens has 
 been covered with mud or gravel. Exterminations of 
 more local character have been produced by various catas- 
 trophes, as earthquake waves deluging the areas of land, 
 volcanic eruptions heating the waters, or emanations of 
 gas rendering the waters poisonous. And the conditions 
 of life of every species have been affected not only by the 
 direct influence of geographical or climatic changes, but 
 indirectly by the changes in the forms of life with which 
 it has been associated. Migration brings a species into 
 relation with a different set of other species, which may 
 furnish it with food, or become its rivals or enemies. 
 
 Lost Groups do not reappear. As a general rule, a 
 species, or a more comprehensive group, which has once 
 become extinct, does not reappear. To this proposition 
 there are some curious apparent exceptions. A few land 
 Snails are found in the Carboniferous, but no land Snails 
 have been recognized from the Permian, Triassic, or Ju- 
 rassic formations. In the Cretaceous they reappear, and 
 from that time the series is substantially continuous. A 
 few Scorpions are found in the Upper Silurian ; none 
 have been recognized from the Devonian ; but in the 
 Carboniferous both Scorpions and Spiders occur. Both 
 these groups appear to be missing from the Permian and 
 from the whole series of Mesozoic strata. They reappear 
 in the Tertiary. Amphibians of the order Labyrintho- 
 donts appear in the Subcarboniferous (or, probably, in 
 the Devonian), and continue through the Triassic, possi- 
 bly into the beginning of the Jurassic. The class of 
 Amphibians then remains unrepresented until a Salaman- 
 der appears in the Lower Cretaceous. Such exceptions, 
 
460 HISTORICAL GEOLOGY. 
 
 however, are readily explained as due to the imperfec- 
 tion of the record. They are not sufficient to throw any 
 doubt upon the general principle. 
 
 Persistence of Character of Faunas. In the early periods 
 of the earth's history there appears to have been little 
 differentiation between the faunas and floras of various 
 continents. After the development of such differentia- 
 tion, and the acquisition of distinct faunal characteristics 
 by the various continents, there is a noteworthy tendency 
 for these characteristics to persist from one geological 
 period to another. That principle is strikingly illustrated 
 in the comparison of the Mammalian faunas of the Quater- 
 nary with the existing faunas. In the early Quaternary, 
 Australia was distinctively the land of Marsupials, and, 
 in somewhat less striking degree, South America was the 
 land of Edentates. The present Mammalian faunas of 
 those regions are characterized by the predominance of 
 the same types. 
 
 Missing Links. The general laws of succession of 
 organic life, as above formulated, are all obviously in 
 accord with the theory of evolution. Yet there are pale- 
 ontological facts whose bearing appears, prima facie, 
 adverse to that doctrine. According to the theory of 
 evolution, existing species ought, in most cases, to be well 
 denned, since, in general, a species now existing must be 
 supposed to have been derived, not from some other exist- 
 ing species, but from a species now extinct. Between the 
 ancestral and the derived species there must have been 
 sometime a series of more or less finely gradational forms. 
 How fine those gradations must have been, depends some- 
 what upon the method of evolution. If evolution was by 
 the accumulation of minute and imperceptible variations, 
 the series must have presented very fine gradations. If, 
 as is probable, occasional abrupt variations have played 
 a considerable r61e, the gradations would have been less 
 fine. On that supposition, the missing links may be miss- 
 ing because they never existed. Certain it is that in most 
 
PROGRESS OF LIFE. 461 
 
 cases fine gradations between fossil species are no more to 
 be found than between living species. In the great majority 
 of cases, fossil species are well denned. Moreover, more 
 comprehensive groups often appear in geological history 
 where no preexistent forms are known as probable ances- 
 tors for them ; and the order of introduction of related 
 groups is often different from that which would be pre- 
 dicted, a priori, on the basis of the theory of evolution. 
 The highly diversified fauna of the Cambrian includes 
 many groups of by no means very low grade, which appear 
 without any apparent ancestry. Hexapod Insects appear 
 in the Lower Silurian, while the Myriopods, which are 
 more generalized, and would seem to be a more primitive 
 group, are unknown until the Devonian. No fossil forms 
 have been discovered which can be imagined to be the 
 immediate ancestors of the Placoderms, Selachians, and 
 Ganoids of the Lower Silurian. No intermediate forms 
 have been discovered bridging the gap between Seaweeds 
 and Acrogens. The sudden appearance of numerous 
 orders of Placental Mammals in the very earliest Eocene 
 is at least startling. The interrupted chronological range 
 of several groups, as in the cases of Snails, Arachnoids, 
 and Amphibians, above mentioned, would be a fatal objec- 
 tion to the theory of evolution, if the interruptions were 
 believed to be other than merely apparent. So long as 
 the complete change in the life of the globe at the close 
 of the Paleozoic, and again at the close of the Mesozoic, 
 was believed to be due to universal extermination, the 
 theory of evolution could have no standing ground. 
 
 The Imperfection of the Geological Record. This 
 phrase, now become classical, expresses the substance of 
 the answer given by Darwin, and by all evolutionists, to 
 such difficulties as have just been cited. The bearing of 
 the principle on some special cases has already been dis- 
 cussed (pages 251, 288, 289). But the subject of the 
 imperfection of the geological record may well receive 
 some further comment. 
 
462 HISTOKICAL GEOLOGY. 
 
 1. Geological Conditions of Imperfection of the Record. 
 Fossiliferous strata of considerable thickness can be formed 
 only during a progressive subsidence ; but, in general, 
 relative elevation must have predominated over subsidence 
 in the history of the continents ; and, moreover, Darwin is 
 probably correct in maintaining that periods of elevation 
 have been more fruitful in evolutionary changes than 
 periods of subsidence. After fossiliferous strata" have 
 been formed, their record has often been obliterated by 
 nietamorpliism. Fossiliferous strata not of great thick- 
 ness may^ often be entirely removed by erosion. The vast 
 areas occupied by plutonic and metamorphic rocks afford 
 striking proof of the enormous denudation which has taken 
 place, since these rocks must have assumed their present 
 crystalline character under the pressure of hundreds or 
 thousands of feet of superincumbent rock. In no region 
 of the globe have we any continuous series of fossiliferous 
 strata, and in many districts only mere fragments of the 
 series are present. The most abrupt changes in the fossil 
 contents of strata usually occur where the strata are un- 
 conformable ; and unconformability, as explained on page 
 57, is always the sign of a lost interval in the record. It 
 must, moreover, be considered that the period whose record 
 is lost by unconformability is necessarily a period of geo- 
 graphical change for the region in question. The area 
 which had been receiving sediment has been elevated so 
 as to become dry land, and, after a longer or shorter 
 period of erosion, has been again depressed below the 
 water level. These times of geographical, and conse- 
 quently of climatic, change, are the times in which evolu- 
 tionary changes in the fauna and flora are necessarily most 
 rapid. The geological record is therefore defective by 
 the loss of those chapters which, if present, would afford 
 the history of the most critical periods. The great changes 
 in fauna and flora at the close of the Paleozoic and the 
 Mesozoic are thus naturally correlated with the great 
 geographical revolutions which occurred at those times. 
 
PKOGHESS OF LIFE. 463 
 
 2. Biological Conditions of Imperfection of the Record. 
 The vast majority of living beings die under such circum- 
 stances that there is no chance of their fossilization. In 
 order that we may have a fossil for study, it is necessary 
 that the entire organism, or some recognizable part of it, 
 should be buried, before it can be decomposed or dissolved 
 (or at least an impression of the organism made), in some 
 deposit which is subsequently preserved without too much 
 alteration, and brought into an accessible position. Only 
 under an exceptional combination of circumstances can 
 this be the fate of an individual plant or animal. The 
 chance of such preservation is greater in the case of 
 aquatic, than in that of terrestrial, animals and plants. 
 It would naturally be expected, therefore, that the record of 
 terrestrial life would be extremely ragged. Moreover, in 
 general, only somewhat indurated structures, or skeletons, 
 can be expected to be preserved. Terrestrial plants whose 
 tissues contain no woody fiber, and animals that are 
 destitute of skeleton, have but an infinitesimal chance of 
 leaving any record. This latter principle probably affords 
 the chief explanation of the mystery of the Cambrian 
 fauna (page 251), although it must also be remembered 
 that the Archaean rocks have suffered so extensive meta- 
 morphism that whatever fossils they may have contained 
 are likely to have been obliterated, and that the universal 
 unconformability between the Archaean and the^ Cambrian 
 shows a lost interval in the record during which evolu- 
 tionary changes may have been in progress. 
 
 That the geological record is extremely imperfect, is 
 illustrated by the well-known fact that multitudes of 
 fossil species are known as yet only by a single specimen. 
 In many cases a family, an order, or a class, in some 
 particular formation, may be represented by only one or 
 two specimens. In the Jurassic formation of Europe, 
 the class of Birds is represented by two somewhat im- 
 perfect skeletons and a single odd feather. In the 
 Jurassic of North America, the same class is represented 
 
464 HISTORICAL GEOLOGY. 
 
 by a single doubtful fragment of a skull (page 345). In the 
 Triassic of North America, the class of Mammals is repre- 
 sented by two lower jaws. There can be no reasonable doubt 
 that the imperfection of the geological record affords a 
 sufficient answer to all arguments against evolution based 
 upon the gaps that exist in the series of fossils. Negative 
 evidence in paleontology must be considered of very little 
 value. 
 
 CONCLUSION. 
 
 In spite of all difficulties and uncertainties, geology is 
 able thus to give in outline the history of the evolution 
 of Man himself and of his dwelling place. It shows 
 how the featureless simplicity of the molten globe has 
 given place to continent and ocean, mountain and valley, 
 plain and plateau, river and lake, cataract and glacier ; 
 how ores have been stored in veins, and coal accumu- 
 lated in strata, and rock material crystallized into granite 
 strength and gemlike beauty. It shows how the earth 
 has come to be a fit dwelling place for a creature of 
 such physical and spiritual needs and capacities as those 
 of Man ; and how, in the progress of life, those plants 
 and animals have been evolved which could minister 
 to Man's physical or mental life. It shows how the 
 upward progress, from Protozoan simplicity, through Fish 
 and Amphibian and Reptile and Mammal, has culminated 
 at last in Man himself, the crown of creation, sharing 
 with the animal kingdom a place in nature, but asserting 
 by his intellectual and spiritual endowments a place above 
 nature. While it is the work of science to trace the 
 method of this twofold evolution, science, as such, knows 
 nothing of efficient cause or of purpose ; but it leaves 
 full scope for faith that the Power, whose modes of work- 
 ing science may in part reveal, is intelligent and personal, 
 and that the whole process of the evolution of Man and 
 his dwelling place has been guided by infinite Wisdom to 
 the fulfillment of a purpose of infinite Love. 
 
INDEX. 
 
 NOTE. The asterisk after the number of a page indicates that the subject referred to 
 is illustrated by a figure. 
 
 Abyssal deposits, 92. 
 
 Acadian period, 244. 
 
 Acadian range, 327. 
 
 Acids, organic, geological effect of, 113. 
 
 Aconcagua, 177. 
 
 Acrodus, 82*. 
 
 Acrogens, 88. 
 
 Age of, 229, 290. 
 
 Carboniferous, 300*, 301. 
 
 Cretaceous, 367. 
 
 Devonian, 279*. 
 
 Jurassic. 336. 
 
 Lower Silurian, 254*. 
 
 relation of, to evolution, 288. 
 
 Triassic. 336, 337*, 338. 
 
 Upper Silurian, 270. 
 Acrostichites, 337*, 388. 
 Acrotreta, 247*. 
 Actinia, 66*. 
 Actinocrinus, 304*. 
 Actinocyclus, 392*. 
 Actlnoptychus, 8S*, 392*. 
 ^olian denudation, 118, 119*. 
 ^Eolian deposits, 120, 121*. 
 .iEons, geological, 227. 
 ^Epyornis, extinction of, 441. 
 Agassiz, Lake, 424. 
 Age of strata, how determined, 228. 
 Ages, geological, 227. 
 Agnostus, 322. 
 Albirupian stage, 864. 
 Albite, 20. 
 Alcyoniarians, 66*. 
 Alga-, 87, 88*. 
 
 Cambrian, 245. 
 
 Cretaceous, 367. 
 
 Devonian, 279. 
 Lower Silurian, 254. 
 siliceous deposits made by, 106. 
 Upper Silurian, 268. 
 Alkaline lakes, 117. 
 Alluvial deposits, 188. 
 
 Alps, elevation of; 403. 
 
 glaciers in, 159, 161*, 164. 
 Altitude, effect of, on temperature, 168. 
 Alum clays, 112. 
 Alum shale, 35. 
 Amazon Kiver, 125, 150. 
 Amber, 99. 
 
 Insects in, 393. 
 Ambonychia, 256*. 
 America. See North America, South 
 
 America. 
 
 Ammonites, 347*, 348*, 370, 371*. 
 Amphibians, 84. 
 
 Age of, 229, 290. 
 
 Carboniferous, 306, 308*. 
 
 Devonian, 286. 
 
 interrupted range of, in time, 459. 
 
 Jurassic, 351. 
 
 Tertiary, 394. 
 
 Triassic, 339, 340*, 341*, 351, 352*. 
 Amphilestes, 358*. 
 Amphioxus, 81. 
 Amygdaloid, 188. 
 Anatifa, 77*. 
 Anchisaurus, 342*. 
 Anchitherium, 399*, 400. 
 Anchura, 74*. 
 Andalusite, 22*. 
 Andesine, 20. 
 Andesite, 38, 175. 
 Angiosperms, 90*. 
 
 Cretaceous, 367*. 
 
 Tertiary, 390, 391*. 
 
 Animal and plant, distinctions between, 68. 
 Animal kingdom, 59. 
 Anisichnns, 340*. 
 Anomoepus, 340*. 
 Anoplotherium, 398. 
 Antecedent drainage, 142. 
 Anthozoans, 65, 66*. 
 
 Cambrian, 246*. 
 
 Carboniferous, 303, 804*. 
 
 465 
 
466 
 
 EffDEX. 
 
 Cretaceous, 868. 
 
 Devonian, 282*. 
 
 Jurassic, 345, 846*. 
 
 Lower Silurian, 255, 256*. 
 
 Upper Silurian, 269*, 270. 
 Anthracite, 25, 214, 298. 
 
 origin of, 192, 214. 
 
 vegetable tissues in, 309, 810*. 
 Anthracite region of Pennsylvania, 214, 292*. 
 Anthracopalaemon, 805*. 
 Anticlinal axis, 53*, 54. 
 Anticline, 53*, 54. 
 Anticlines, erosion of, 136*, 218. 
 Anticlinoriuin, 220. 
 Apatite, 105. 
 
 Appalachian range, 211, 826. 
 Appalachian region, folds in, 211, 212*, 213*. 
 
 thickness of strata in, 211, 317, 825. 
 Appalachian revolution, 325. 
 Appalachian system, 326. 
 Aquatic organisms, the principal rock- 
 makers, 98. 
 Arachnoids, 79. 
 
 Carboniferous, 805*, 306*. 
 
 interrupted range of, in time, 459. 
 
 Upper Silurian, 272. 
 Araucaria, 90*. 
 Archaean rocks, origin of, 289. 
 Archaean time, 227, 236. 
 Archaean V, 237, 446. 
 Archaeocyathus, 246*. 
 Archaeoniscus, 350*. 
 Archseopteris, 279*. 
 Archaeopteryx, 356, 857*. 
 Archimedes, 303, 304*. 
 Arctic coal areas, 293. 
 Arenicola. See Lobworm. 
 Arenig group, 252, 253. 
 Argillite. See Slate. 
 Artesian wells, 145*. 
 Arthrolycosa, 306*. 
 Arthropods, 76, 77*. 
 
 Cambrian, 248*, 249*. 
 
 Carboniferous, 805*, 806*. 
 
 Devonian, 281, 282, 283*. 
 
 Jurassic. 350*. 
 
 Lower Silurian, 256*, 257, 258*. 
 
 Tertiary, 893. 
 
 Triassic, 338, 339*, 850*. 
 
 Upper Silurian, 269*, 270, 271*. 
 Arthrostracans, 77*, 78. 
 Articulates, 60. 
 Asaphus, 256*. 257, 822. 
 Asbestus, 21. 
 
 Ascidians. See Tunicates. 
 Ashes, volcanic, 175. 
 Aspidorhynchus, 84*. 
 Asterioids, 68*, 69. 
 
 Jurassic, 346. 
 
 Lower Silurian, 256. 
 
 Triassic, 346. 
 
 Upper Silurian, 68*, 270. 
 Athyris, 71*, 304*. 
 
 Atlantic Border geanticline, 262, 876. 
 Atlantic coast of North America, changes of 
 
 level in, 429. 
 Atlantosaurus, 343. 
 Atlantosaurus beds, 334. 
 Atmosphere, chemical action of, 111. 
 
 mechanical action of, 118. 
 Atmospheric absorption, effect of, on tem- 
 perature, 168. 
 Atolls, 102*, 103*, 104*. 
 Atrypa, 71*, 283*. 
 Auk, great, extinction of, 442. 
 Australia, Marsupials of, in Quaternary, 
 
 434. 
 Avicula, 269*. 
 
 range of, in time, 259. 
 Axial plane of fold, 53*. 
 Axis, anticlinal, 53*, 54. 
 
 synclinal, 53*, 55. 
 Azoic. See Archaean. 
 
 Bacillaria, 88*. 
 Baculites, 370, 371*. 
 Bala formation, 252, 254. 
 Baptanodon beds, 884. 
 Barite, 198. 
 Barnacles, 77*, 78. 
 Barrier reefs, 102*. 
 
 theory of, 103, 104*. 
 Basalt, 39, 175. 
 Base level, 140. 
 Bathyactis, 92. 
 
 Bathymetric map of oceans, 10*, 11*. 
 Bathyurus, 322. 
 Bats, Tertiary, 394, 398, 400. 
 Beach formations, 152, 153*, 154. 
 Bear, cave, 431. 
 Beehive Geyser, 185, 186*. 
 Beetles, Carboniferous, 306. 
 Belemnitella, 371*. 
 Belemnites, 348, 849*, 870, 871*. 
 Belemnoteuthis, 349*. 
 Bilin, diatomaceous deposit of, 392. 
 Biotite, 20. 
 Bird tracks, so-called, of Connecticut Valley, 
 
 341*. 
 Birds, 85. 
 
 Cretaceous, 874, 375*, 877*. 
 
 Jurassic, 345, 356, 357*. 
 
 Tertiary, 394. 
 Bird's-eye Limestone, 253. 
 Bituminous coal, 25, 298. 
 Black Hills of Dakota, 184, 834. 
 Black River Limestone, 253. 
 Black Shale, Devonian, 278. 
 
INDEX. 
 
 467 
 
 Blastoids, 67*, 68. 
 
 Carboniferous, 303, 304*. 
 Bog iron ore, 116. 
 Bonneville, Lake, 425. 
 Bore, 150. 
 Bowlder clay, 406. 
 
 Bowlders, glacial, large size of, 162, 406. 
 Brachiate Crinoids, 67*, 68*. 
 Brachiopods, 70, 71*. 
 
 Cambrian, 247*. 
 
 Carboniferous, 303, 304*. 
 
 Devonian, 281, 282, 283*. 
 
 Jurassic, 346, 347*. 
 
 Lower Silurian, 256*, 257. 
 
 Triassic, 346. 
 
 Upper Silurian, 269*, 270, 271*. 
 Brachyurans, 77*, 79. 
 Brains of Tertiary Mammals, 396, 397*. 
 Brandon, fossil fruits of, 389, 391*. 
 Breccia, 34. 
 Brontosaurus, 343*. 
 Brontozoum, 341*. 
 Bronze Age, 436. 
 Brown coal, 25. 
 Bryophytes, 88. 
 Bryozoans, 70*. 
 
 Carboniferous, 803, 804*. 
 
 Lower Silurian, 256*. 
 Buffalo, extinction of, 442. 
 Buhrstone, 389. 
 Bulla, 74*. 
 
 Bunter Sandstein, 334. 
 Buprestis, 350*. 
 
 Caerfai group, 230. 
 
 Calamites, 280, 300*, 302. 
 
 Calamopsis, 391*. 
 
 Calaveras skull, 439. 
 
 Calcareous rocks. 32, 40, 99. 
 
 Calciferous Sandrock, 253. 
 
 Calcite, 23*, 198. 
 
 Calcium bicarbonate, 115. 
 
 Calcium carbonate. See Calcite. 
 
 California, lava sheets of, 189. 
 
 Callocystites, 67*. 
 
 Cambrian era, 228, 244. 
 
 Cambrian fauna, relation of, to evolution, 251 
 
 463. 
 
 Camptosaurus, 343*. 
 Canada, geological map of, 235*. 
 Canadian period, 252. 
 Cancer, 77*. 
 Cannel coal, 25. 
 Canons, 133. 
 Caradoc group, 252, 254. 
 Carbon and its compounds, 18, 24. 
 Carbon dioxide, geological action of, 118. 
 Carbonaceous formations, 107. 
 Carbonic acid. See Carbon dioxide. 
 
 Carboniferous era, 229, 290. 
 
 Carboniferous period, 291, 296, 814. 
 
 Carcharodon, 82*, 394*. 
 
 Carnivores, Tertiary, 394, 396, 398, 400, 402. 
 
 Carpathians, elevation of, 403, 404. 
 
 Carpolithes, 391*. 
 
 Jarterella, 63*. 
 
 Oaryocrinus, 269*. 
 
 Cascade Range, 362. 
 
 Cascades, 182. 
 
 Catopterus, 339*. 
 
 Catskill formation, 277. 
 
 Catskill Mountains, 218. 
 
 Cauda-galli Grit, 276. 
 
 Cave animals of Quaternary, 480. 
 
 Caverns, 143*. 
 
 Cenozoic time, 228, 385. 
 
 Cephalaspis, 284, 285*. 
 
 Cephalization, progress in, 458. 
 
 Cephalopods, 74, 75*. 
 
 Cambrian, 247. 
 
 Carboniferous, 304. 
 
 Cretaceous, 370, 371*. 
 
 Devonian, 281, 282, 283*. 
 
 Jurassic, 347*, 349*. 
 
 Lower Silurian, 256*, 257. 
 
 Triassic, 347, 348*. 
 Ceratodus, 351. 
 Ceratopsidae, 372*. 
 Cervus euryceros, 481. 
 Cestracion, 82*. 
 
 Cestracionts, 82*, 284, 828, 850. 
 Cetiosaurus, 854. 
 Chaetetes, 257. 
 Chain coral. See Halysites. 
 Chalcedony, 19. 
 Chalk, 32, 40, 365, 366. 
 Chainplain, Lake, condition of, in Quaternary, 
 
 421, 424. 
 Chatnplain period, 405, 420. 
 
 marine deposits of, 421. 
 
 river deposits of, 422. 
 Changes of level, modern, 427. 
 Chazy Limestone, 253. 
 Cheirolepis, 84*. 
 
 Chemical action, as a source of heat, 171. 
 Chemical action of atmosphere, 111. 
 Chemical action of water, 111, 187, 193, 198, 
 
 236. 
 
 Cheinung epoch, 277. 
 Chemung period, 277. 
 Chert, 36, 107. 
 Chiastolite, 22. 
 
 Chile, recent changes of level in, 428. 
 Chirotherium, 852*. 
 Chlorides, 26. 
 Chlorite, 21. 
 Chlorite schist, 89. 
 Chonetes, 283*, 804*, 
 
468 
 
 INDEX. 
 
 Chrysalidina, 61*, 368*. 
 
 Chrysolite, 21. 
 
 Cidari S , 346*. 
 
 Cimoliosaurus, 372. 
 
 Cincinnati Island, 263, 287. 
 
 Cincinnati uplift, 220, 263. 
 
 Cinders, volcanic, 175. 
 
 Cinnamomura, 891*. 
 
 Circumdenndation, mountains of, 138. 
 
 Cirques, 131. 
 
 Cirripeds, 77*, 78. 
 
 Cladiscites, 848*. 
 
 Clam, fossil, in Miocene, 898. 
 
 Clathropteris, 837*, 888. 
 
 Clay, 34. 
 
 alum, 112. 
 
 Bowlder, 406. 
 
 of ocean bottom, 92. 
 
 Weald, 366. 
 
 Clay ironstone, 28, 297. 
 Clay slate. See Slate. 
 Cleavage, crystalline, 19. 
 
 slaty, 81. 48*, 219. 
 Cleodora, 74*. 
 Cleveland Shale, 278. 
 Climate, causes of changes in, 167. 
 
 Carboniferous, 312. 
 
 Champlain, 434. 
 
 Cretaceous, 878. 
 
 Glacial, cause of, 418. 
 
 Jurassic, 361. 
 
 Paleozoic, 821. 
 
 Tertiary, 404. 
 Clinometer, 52*. 
 Clinton epoch, 266, 273. 
 Club mosses. See Lycopods. 
 Coal, 24. 
 
 bituminous, 25. 
 
 brown, 25. 
 
 cannel, 25. 
 
 Carboniferous, 292, 296, 298. 
 
 Cretaceous, 365. 
 
 impurities in, 311. 
 
 lamination of, 298. 
 
 origin of, 309. 
 
 Tertiary, 389. 
 
 Triassic, 333. 
 
 vegetable tissues in, 809, 310*. 
 Coal areas of Europe, 293, 295*. 
 Coal areas of North America, 292*. 
 Coal areas of Pennsylvania, map of, 292*. 
 Coal Measures, 296. 
 Coccosteus, 284, 285*. 
 Cockroaches, Lower Silurian, 258. 
 Ccelenterates, 64, 65*, 66*. 
 
 Cambrian, 246*. 
 
 Carboniferous, 303, 304*. 
 
 Cretaceous, 368. 
 
 Devonian, 282*. 
 
 Jurassic, 345, 846*. 
 
 Lower Silurian, 254, 255*, 256*. 
 
 Upper Silurian, 269*, 270. 
 Coin conglomerate, 440*. 
 Colorado epoch, 365. 
 Colorado River, canon of, 42, 43*, 132*, 188, 
 
 134*. 
 
 Columbia River, lava sheet of, 189. 
 Columnar structure, 173*. 
 Comanche series, 365. 
 Comprehensive types, 455. 
 Compsognathus, 354. 
 Concretions, 46*, 47*. 
 Conformable strata, 56. 
 Conglomerate, 34. 
 
 Oneida, 266, 273. 
 
 Pottsville, 296. 
 Conifers, 90*. 
 
 Carboniferous, 302. 
 
 Cretaceous, 367. 
 
 Devonian, 281. 
 
 Jurassic, 336. 
 
 Triassic, 336, 338. 
 Connecticut River, deposits at mouth of, 150. 
 
 terraces of, 426*. 
 Connecticut Valley, sandstones of, 332, 859. 
 
 trap rocks of, 189, 359. 
 Conodonts, 248. 
 Consequent drainage, 142. 
 Contemporaneous sheets of igneous rock, 
 
 188. 
 
 Continent and ocean, boundary of, 12. 
 Continental plateaus, 7. 
 Continents, general relief of, 14. 
 
 height of, 8. 
 
 origin of, 206. 
 Contraction and expansion of rocks, by 
 
 changes of temperature, 172. 
 Contraction theory of mountain-making, 
 
 207. 
 
 Coprolites, 106, 356. 
 Coral animals. See Anthozoans, Bryozoans, 
 
 Hydrozoans. 
 
 Coral islands, 102*, 103*, 104* 
 Coral reefs, 100, 102*, 104*. 
 Corallines, 88. 
 
 Corals, reef-forming, range of, 95. 
 Cordilleras, 210. 
 2orniferous period, 275, 276. 
 Coscinodiscus, 392*. 
 Cosmoceras, 347*. 
 
 rabs, 77*, 78. 
 
 Crania, range of, in time, 259. 
 iraters, 174. 
 Creodonts, 396, 400. 
 retaceous era, 231, 331, 362. 
 
 map of North America in, 364*. 
 Crevasses, 159, 160*. 
 >inoidal Limestone, 294. 
 
INDEX. 
 
 469 
 
 Crinoids, 67*, 68*. 
 
 Cambrian, 246. 
 
 Carboniferous, 303, 304*. 
 
 Jurassic, 346. 
 
 Lower Silurian, 256*. 
 
 Triassic, 346*. 
 
 Upper Silurian, 269*, 270. 
 Crocodiles, 85. 
 
 Cretaceous, 374, 388. 
 
 Jurassic, 340, 354. 
 
 Triassic, 340, 354. 
 Crocodilus, 388. 
 Cross-bedded structure, 155*. 
 Crustaceans, 77*. 
 
 Cambrian, 248*, 249*. 
 
 Carboniferous, 305*. 
 
 Devonian, 281, 282, 283*. 
 
 Jurassic, 350*. 
 
 Lower Silurian, 257, 258*. 
 
 Triassic, 338, 339*, 350*. 
 
 Upper Silurian, 269*, 270, 271*. 
 Cryptogams, 86, 88*. 
 
 Crystalline rocks, 28, 29, 35, 41, 175, 188, 191. 
 Ctenacanthus, 307*. 
 Ctenoid scales, 84*. 
 Cumberland Mountains, 218. 
 Cuneolina, 61*, 368*. 
 Currents, oceanic, 150. 
 
 tidal, 149. 
 
 wind-made, 150. 
 Cuttlefish, 76. 
 Cyanite, 22. 
 Cyathophylloids, 66. 
 
 Devonian, 282*. 
 
 Lower Silurian, 255, 256*. 
 
 Upper Silurian, 269*, 270. 
 Cyathophyllum, 282*. 
 Cycads, 90, 336*. 
 
 Carboniferous, 302. 
 
 Cretaceous, 368. 
 
 Devonian, 281. 
 
 Jurassic, 336, 337*. 
 
 Triassic, 336, 337*. 
 Cycas, 336*. 
 Cycloid scales, 84*. 
 Cyclonema, 269*. 
 Cyprina, 72*. 
 Cyrtoceras, 248. 
 Cystoids, 67*, 269*, 270. 
 Cythere, 77*. 
 
 Dakota epoch, 365. 
 Dapedius, 351*. 
 Decapitated folds, 56*. 
 Decapods, 77*, 78. 
 
 Carboniferous, 305*. 
 
 Devonian, 281. 
 
 Jurassic, 850. 
 
 Triassic, 350*. 
 
 Deccan, lava sheet of, 189. 
 
 Deep-sea life, characteristic types of, 94. 
 
 Deer, Irish, 431. 
 
 Degradation, means of, 165. 
 
 Deltas, 139*. 
 
 Dendrophyllia, 66*. 
 
 Dent de Morcles, 54*. 
 
 Denudation. See Erosion. 
 
 Deposits, ajolian, 120, 121*. 
 
 estuarine, 139. 
 
 fluvial, 138, 166. 
 
 fluvio-marine, 153. 
 
 glacial, 163, 167, 406. 
 
 marine, 152, 166. 
 Depth/range of life in, 91. 
 Desmids, 88, 368. 
 Devonian era, 229, 275. 
 Diabase. See Dolerite. 
 Diamond, 24. 
 
 Diatomaceous deposits, 106, 109, 891, 892*. 
 Diatomaceous ooze, 92. 
 Diatoms, 88*. 
 
 Carboniferous, supposed to be identical 
 with living species, 328. 
 
 Cretaceous, 368. 
 
 Devonian, 279. 
 
 Tertiary, 391, 392*. 
 Dibranchs, 75*. 
 
 Cretaceous, 370, 871*. 
 
 Jurassic, 348, 349*. 
 
 Triassic, 348. 
 Dicotyledons, 90*, 91. 
 Dictyocha, 392*. 
 Dikes, 188, 196. 
 Dinichthys, 284, 285*. 
 Dinoceras, 397*, 398*, 399. 
 Dinornis, extinction of, 441. 
 Dinosaurs, Cretaceous, 372*. 
 
 Jurassic. 340, 342, 343*, 344*, 854. 
 
 Triassic, 340*, 341*, 842*, 854. 
 Diuotherium, 401*. 
 Diorite, 38, 188. 
 Dip, 51*. 
 
 Diphycercal tails, 81. 
 Diplograptus, 255*. 
 Dipnoans, 84. 
 
 Carboniferous, 306. 
 
 Devonian, 284, 286*. 
 
 Jurassic, 339, 350, 851. 
 
 Triassic, 339, 350, 351. 
 Diprotodon, 434. 
 Dipters, 79. 
 Dipterus, 286*. 
 
 Discina, range of, in time, 259. 
 Dislocations of strata, 50. 
 Distribution of marine life, causes limiting, 
 
 93. 
 
 Diversification of type, progress in, 455. 
 Dodo, extinction of, 441. 
 
470 
 
 INDEX. 
 
 Dolerite, 39, 188. 
 Dolomite, 23. 
 Domes, trachytic, 184. 
 Drainage, antecedent, consequent, and super- 
 imposed, 142. 
 Drift, 406. 
 
 area of, 411. 
 
 direction of movement of, 411. 
 
 origin of, 408. 
 Dripstone, 40. 
 Dromatherium, 345*. 
 Druinlins, 417. 
 Duckbill, 86. 
 Dudley Limestone, 268. 
 Dunes, 121*. 
 
 Dust, transportation of, by wind, 122. 
 Dykes. See Dikes. 
 Dynamic metamorphism, 195. 
 Dynamical geology, 6, 97. 
 
 Eager, 150. 
 
 Earth, interior of, solid or liquid, 204. 
 
 internal heat of, 170. 
 
 size and form of, 7. 
 
 system in features of, 14. 
 Earthquakes, 204. 
 
 in connection with volcanoes, 181, 182, 184. 
 Earthworms, geological action of, 110. 
 East Rock, 333. 
 East Tennessee, valley of, 218. 
 Eccentricity of earth's orbit, 169. 
 Echidna, 86. 
 Echinoderms, 66, 67*, 68*. 
 
 Cambrian, 246. 
 
 Carboniferous, 303, 304*. 
 
 Cretaceous, 369. 
 
 Jurassic, 346*. 
 
 Lower Silurian, 255, 256*. 
 
 Triassic, 846*. 
 
 Upper Silurian, 269*, 270. 
 Echinoids, 68*, 69. 
 
 Cretaceous, 369. 
 
 Jurassic, 846*. 
 
 Triassic, 346. 
 Echinus, 68*. 
 Edentates. Quaternary, 432, 433*, 434*. 
 
 Tertiary, 395, 402. 
 Edestosaurus, 373*. 
 Elasmobranchs. See Selachians. 
 Elasmosaurus, 372. 
 Elephants, Quaternary, 431. 
 
 Tertiary, 401. 
 
 Elephas priinigenius. See Mammoth. 
 Elevation, effect of, on temperature, 168. 
 Embryology and paleontology, parallelism 
 
 of, 454. 
 
 Enaliosaurs. 352, 358*. 
 Encrinus, 67*. 
 Endogenous stems, 89, 90*. 
 
 Engis skull, 437. 
 
 England, geological map of, 295*. 
 
 Entomostracans, 77*, 78. 
 
 Eocene period, 386. 
 
 Eopaleozoic section, 229, 243, 244. 
 
 Eoscorpius, 305*. 
 
 Eozoon, 241*. 
 
 Epochs, geological, 232. 
 
 Equiseta, 89. 
 
 Carboniferous, 300*, 302. 
 
 Devonian, 280. 
 
 Jurassic, 336. 
 
 Triassic, 336. 
 Equus, 397*, 399*. 
 Eras, geological, 228. 
 Erie Shale, 278. 
 Erosion, by glaciers, 168. 
 
 by ocean waves, 147, 148*. 
 
 by rain, 128. 
 
 by rivers, 126. 
 
 by wind, 118, 119*. 
 
 effect of, on folded rocks, 55, 56*. 
 
 topographical forms resulting from, 135*, 
 
 136*. 
 Eruptions, Cambrian, 245. 
 
 Cretaceous, 189, 384. 
 
 from fissures, 187. 
 
 in Connecticut Valley, 333, 359. 
 
 in connection with mountain-making, 221. 
 
 in Deccan, 189, 384. 
 
 in Lake Superior region, 245. 
 
 in northwestern United States, 189, 404. 
 
 submarine, 184. 
 
 Tertiary, 189, 404. 
 
 Triassic, 333, 359. 
 
 volcanic, 174. 
 Eschara, 70*. 
 Eskers, 417. 
 Estheria, 338, 839*. 
 Estuary formations, 189. 
 Etna, 177, 184. 
 Etoblattina, 306*. 
 Eucyrtidium, 68*. 
 Eurypterids, 79, 271*. 
 Eurypterus, 271*. 
 Evolution, 232, 251, 288, 858, 450. 
 Exogenous steins, 89, 90*. 
 Expansion and contraction of rocks, by 
 
 changes of temperature, 172. 
 Extinct groups do not reappear, 459. 
 Extinction of species, causes of, 330, 385, 
 458. 
 
 in modern times, 441. 
 Extrusive sheets of igneous rock, 188. 
 Eyes of deep-sea animals, 94. 
 
 Fagus, 391*. 
 False veins, 203. 
 Fasciolaria, 371*. 
 
INDEX. 
 
 471 
 
 Faults, 53*, 211, 213*. 
 Favosites, 269*, 270, 282*. 
 Feldspar, 20. 
 
 decomposition of, 118. 
 Felsite, 38, 188. 
 Ferns, 88. 
 
 Carboniferous, 300*, 301. 
 
 Cretaceous, 367. 
 
 Devonian, 279*, 280. 
 
 Jurassic, 336. 
 
 Triassic, 336, 337*, 338. 
 Fingal's Cave, 173, 190. 
 Fiords, 419. 
 Firn, 159. 
 Fishes, 81, 82*, 83*, 84*. 
 
 Age of, 229, 263. 
 
 Carboniferous, 306, 307*. 
 
 Cretaceous, 370, 372*. 
 
 Devonian, 283, 284*, 285*, 286*. 
 
 Jurassic, 339, 350, 851*. 
 
 Lower Silurian, 258. 
 
 relation of, to evolution, 289. 
 
 Tertiary, 393, 394*. 
 
 Triassic, 339*, 350. 
 
 Upper Silurian, 272. 
 Fissure eruptions, 187. 
 Flabellina, 61*, 368*. 
 Flags, 31. 
 Flagstone, 31. 
 Flies, 79. 
 Flint, 19, 107, 366. 
 
 implements of, 436. 
 Flood plains, 131. 
 Floridian formation, 388. 
 Flow-and-plunge structure, 155, 156*. 
 Flowering plants. See Phanerogams. 
 Flowerless plants. See Cryptogams. 
 Fluorite, 198. 
 
 Fluvio-inarine formations, 153. 
 Fold, axial plane of, 53*. 
 
 axis of, 53*. 
 Folded rocks, 53*, 54*, 211, 212*, 213*, 215*. 
 
 effect of denudation upon, 55, 56*. 
 Folds, decapitated, 56*. 
 Foliated rocks, 31. 
 Foraminifers, 61*, 62*. 
 Fordilla, 247*. 
 
 Forests, geological effect of, 109. 
 Formation, definition of, 44. 
 Fossilization, 99. 
 Fossils, 4, 98. 
 
 use of, in determining age of strata, 225. 
 Fragmental rocks, 28, 29, 33. 
 Freestone, 35. 
 
 Freezing water, action of, 157. 
 Fresh water, action of, 124. 
 Fresh-water limestone, 105. 
 Fringing reefs, 102*. 
 Frogs, 85. 
 
 Frondicularia, 61*. 
 
 Fruits, Carboniferous, 300*, 802. 
 
 Tertiary, 391*. 
 Fucoids, 88. 
 Fumaroles, 185. 
 Fungi, 59, S7. 
 
 Carboniferous, 802. 
 Fusulina, 61*. 
 
 Gabbro, 38. 
 
 Galena Limestone, 260. 
 
 Galenite, 202. 
 
 Ganges, detritus carried by, 187. 
 
 Gangue, 198. 
 
 Ganoids, 83*, 84*. 
 
 Carboniferous, 306, 307*. 
 
 Cretaceous, 370. 
 
 Devonian, 284, 286*. 
 
 Jurassic, 339, 350, 351*. 
 
 Lower Silurian, 258. 
 
 Triassic, 339*, 350, 851. 
 Garnet, 22*. 
 
 Gas, natural, 25, 260, 289. 
 Gastropods, 73, 74*. 
 
 Cambrian, 247*. 
 
 Carboniferous, 304*. 
 
 Cretaceous, 369, 870, 371*. 
 
 Devonian, 281. 
 
 Jurassic, 346. 
 
 Lower Silurian, 256*, 257. 
 
 Triassic, 346. 
 
 Upper Silurian, 269*, 270. 
 Gaylenreuth Cave, 481. 
 Geanticline, 55. 
 Geanticlines in connection with mountain- 
 
 makiug, 219. 
 Genera, long-lived, 259. 
 Generalized forms precede specialized, 454. 
 Genesee Shale, 277. 
 Geode, 47*. 
 Geodia, 63*. 
 Geographical progress in North America, 
 
 445. 
 
 Geography, North American, in Archaean, 
 241. 
 
 in Carboniferous, 313. 
 
 in Cenozoic, 442. 
 
 in Champlain period, 420. 
 
 in Cretaceous, 363, 364*, 376. 
 
 in Devonian, 287. 
 
 in Glacial period, 419. 
 
 in Jurassic, 360. 
 
 in Lower Silurian, 259. 
 
 in Mesozoic, 379. 
 
 in Paleozoic, 317. 
 
 in Tertiary, 386, 387*, 402. 
 
 in Triassic, 358. 
 
 in Upper Silurian, 272. 
 Geological map of England, 295*. 
 
472 
 
 INDEX. 
 
 Geological map of United States, 235*. 
 Geological record, imperfection of, 461. 
 Geological time, length of, 444. 
 Geology, aim and subject of, 1. 
 
 divisions of, 6. 
 
 dynamical, 6, 9T. 
 
 historical, 6, 223. 
 
 physiographic, 6, 7. 
 
 Btratigraphical, 228. 
 
 structural, 6, 17. 
 Georgian period, 244. 
 Geosyncline, 55. 
 
 Geosyncliues in connection with mountain- 
 making, 216. 
 Geyser Canon, 187. 
 Geyserite, 36. 
 Geysers, 185, 186*. 
 Giant's Causeway, 173, 190. 
 Glacial climate, cause of, 169, 418. 
 Glacial period, 405, 406. 
 
 in Europe, 417. 
 
 subdivisions of, 415. 
 Glacial scratches, 163, 407*, 408. 
 Glaciated bowlders, Permian, 299. 
 Glacier theory of the Drift, 409. 
 Glacier torrent, 160. 
 Glaciers, 158. 
 
 descent of, below the snow line, 159. 
 
 erosion by, 163. 
 
 method of movement of, 160. 
 
 transportation by, 162. 
 Glauconite, 40, 365. 
 Globigerina, 61*. 
 Globigerina ooze, 92, 104. 
 Glyptodon, 434*. 
 Gneiss, 86, 192, 195. 
 Gold-bearing veins, 199. 
 Gondwana-land, 329, 404. 
 Goniatites, 281, 282, 283*, 305. 
 Gorgonians, 66*. 
 Gorner Glacier, 161*. 
 Grammatophora, 88*, 892*. 
 Grammostomum, 61*. 
 Grammysia, 283*. 
 Granite, 20, 86, 195, 198, 199. 
 Graphite, 24, 107, 240. 
 Graptolites, 255*. 
 Gravel, 88. 
 
 Great Lakes, Quaternary history of, 423. 
 Green Mountains, Archaean rocks in, 238. 
 
 glacial scratches on, 408. 
 Greenland, as illustrating Glacial period, 410. 
 
 recent changes of level in, 428. 
 Greensand, 40, 365, 866, 889. 
 Grifflthides, 822. 
 Grit, 84. 
 
 Cauda-galli, 276. 
 
 Millstone, 296. 
 
 Schoharie, 276. 
 
 Ground moraine, 163. 
 Ground pines. See Lycopods. 
 Group, definition of, 43. 
 Grypha-a, 346, 347*, 369*. 
 Guadeloupe, human skeleton of, 440*. 
 Guano, 105. 
 
 Gulf Stream, 93, 151, 168. 
 Gymnosperms, 90*. 
 
 Carboniferous, 300*, 302. 
 
 Cretaceous, 367. 
 
 Devonian, 281. 
 
 Jurassic, 336, 337*. 
 
 Triassic, 336, 337*. 
 Gypsiferous formation, 384. 
 Gypsum, 117, 267. 
 Gyrodus, 84*. 
 
 Hadrosaurus, 372. 
 Halicalyptra, 63*. 
 Halysites, 269*, 270. 
 Hamilton epoch, 277. 
 Hamilton period, 277. 
 Hastings Sand, 366. 
 Hawaii, map of, 179*. 
 
 volcanoes of, 177*, 178, 179*. 
 Heat, 167. 
 
 derived from chemical and mechanical 
 action, 171. 
 
 effects of, 172. 
 
 internal, evidences of, 170. 
 
 sources of, 167. 
 Helderberg. See Lower Helderberg, Upper 
 
 Helderberg. 
 Helix, 74*. 
 
 Hematite, 26, 111, 202. 
 Henry Mountains, 190. 
 Herculaneum, 184. 
 Hesperornis, 374, 375*. 
 Heterocercal tails, 81, 82*, 88*. 
 Hexapods, 79. 
 Highlands of New Tork and New Jersey, 
 
 238. 
 
 Himalayas, elevation of, 403, 404. 
 Hipparion, 399*. 
 Hippurites, 870*. 
 Historical geology, 6, 223. 
 Holoptychius, 286*. 
 Holyoke, Mount, 333. 
 Homalonotus, 269*, 322, 328. 
 Homocercal tails, 83, 84*. 
 Hood, Mount, 177. 
 Hornblende, 21. 
 Hornblende gneiss, 37. 
 Hornblende granite, 37. 
 Hornblende schist, 38. 
 Horn stone, 107. 
 Horse, genealogy of, 399*. 
 Hot springs, 185. 
 Hualalai, Mauna, 178. 
 
INDEX. 
 
 473 
 
 Hudson epoch, 253. 
 Hudson-Champlain Valley, 821. 
 Huron Shale, 278. 
 Hyaena spelsea, 431. 
 Hybodus, 82*. 
 Hydra, 64, 65*. 
 Hydraulic limestone, 40. 
 Hydromica, 20. 
 Hydromica schist, 87. 
 Hydrozoans, 64, 65*. 
 
 Lower Silurian, 255*. 
 Hyena, cave, 431. 
 Hyolithes, 247*. 
 
 Ice, action of, 158. 
 Icebergs, 151, 165. 
 Iceland, geysers of, 185. 
 Ichthyornis, 374, 377*. 
 Ichthyosaurs, 3o2, 353*. 
 Idaho lava sheet, 189. 
 Igneous eruptions. See Eruptions. 
 Igneous rocks, 29, 86, 37, 88, 89, 175, 188. 
 Iguanodon, 872. 
 Illaenus, 322. 
 Illimsni, 177. 
 
 Imperfection of geological record, 461. 
 Infusorial deposits. See Diatomaceous de- 
 posits. 
 
 Ink bags of fossil Cephalopods, 349*. 
 Inoceramus, 369*. 
 Insectivores, Tertiary, 394, 400. 
 Insects, 79. 
 
 Carboniferous, 305, 306*. 
 
 Devonian, 281, 282, 284*. 
 
 Jurassic, 350*. 
 
 Lower Silurian, 258. 
 
 Tertiary, 393. 
 
 Triassic, 338, 339*. 
 Interglacial epochs, 416. 
 Interior of earth, heat of, 170. 
 
 solid or liquid, 204. 
 Intrusive sheets of igneous rock, 188. 
 Invertebrates, Age of, 229, 244. 
 Irish deer, 431. 
 Iron, deoxidation of, 115. 
 
 oxidation of, 111. 
 Iron Age, 436. 
 
 Iron carbonate. See Siderlte. 
 Iron ores, 26, 202. 
 
 Archaean, 238*. 
 
 Carboniferous, 297. 
 Iron oxides, 26. 
 Iron sulphides, 27. 
 Ironstone, 28. 
 Iroquois beach, 423, 424. 
 Isastrea, 66*. 
 Isostasy, 206. 
 Itacolumite, 35. 
 
 James Elver stage, 864. 
 
 Jasper, 19. 
 
 Java, fossil man in, 489. 
 
 volcanoes of, 188. 
 Jelly fishes, 65*. 
 Joints, 47*, 219. 
 Jura, Alpine bowlders on, 409. 
 
 elevation of, 404. 
 Jurassic era, 229, 831, 882. 
 
 Kames, 417. 
 
 Kangaroo, 88. 
 
 Kaolin, 34, 114, 116. 
 
 Kea, Mauna, 177*, 178. 
 
 Kettle holes, 417. 
 
 Keuper, 334. 
 
 Keweenaw formation, 245. 
 
 Keweenaw Point, copper veins of, 201, 
 
 Kilauea, 178. 
 
 Kirkdale Cavern, 431. 
 
 Kitchen middens, 488. 
 
 Kjokkenmodingr, 488. 
 
 Krakatoa, 183. 
 
 Labrador Current, 93. 
 
 Labradorite, 20. 
 
 Labyrinthodonts. See Stegocephala. 
 
 Laccoliths, 190. 
 
 Laelaps, 372. 
 
 Lafayette formation, 417. 
 
 Lahontan, Lake, 425. 
 
 Lake Champlain, etc. See Champlain, etc. 
 
 Lake dwellings, 439. 
 
 Lakes, saline, 117. 
 
 Lamellibranchs, 72*. 
 
 Cambrian, 247*. 
 
 Cretaceous, 369*, 370*. 
 
 Devonian, 281, 282, 283*. 
 
 Jurassic, 346, 847*. 
 
 Lower Silurian, 256*, 257. 
 
 Tertiary, 893. 
 
 Triassic, 346. 
 
 , Upper Silurian, 269*, 270. 
 Lamination, 31. 
 Lamna, 82*, 394*. 
 Lampreys, 81. 
 Lancelet, 81. 
 Landslides, 146. 
 Laramide revolution, 888. 
 Laramie epoch, 365, 866. 
 Lava, 30, 38, 39, 175. 
 Layer, 42. 
 Lead ores, 202. 
 Lemurs, Tertiary, 394, 400. 
 Leperditia, 271*. 
 
 Lepidodendron, 279*, 280, 800*, 801, 810*. 
 Lepidosteus, 84*. 
 Leptsena, 256*, 269*. 
 
474 
 
 INDEX. 
 
 Leptocardians, 80. 
 Leptomitus, 246*. 
 Leptostracaus, 78. 
 
 Cambrian, 249*. 
 
 Level, changes of, in Quaternary, 419, 420, 
 424, 425. 
 
 causes of change of, 203. 
 Lias, 335. 
 Libellula, 350*. 
 Lichas, 822. 
 Lichens, 87. 
 Life, agency of, In rock-making, 98. 
 
 Archaean, 240. 
 
 Cambrian, 245. 
 
 Carboniferous, 299. 
 
 change of, at close of Mesozoic, 384. 
 
 change of, at close of Paleozoic, 329. 
 
 Cretaceous, 867. 
 
 Devonian, 278. 
 
 general laws of progress of, 232, 450. 
 
 Jurassic, 336. 
 
 Lower Silurian, 254, 259. 
 
 marine, distribution of, 91. 
 
 marine, earlier than terrestrial, 456. 
 
 Mesozoic, 381. 
 
 Paleozoic, 321. 
 
 protective and destructive effects of, 109. 
 
 Quaternary, 429. 
 
 Tertiary, 390. 
 
 Triassic, 336. 
 
 Upper Silurian, 268. 
 Light, as limiting distribution of life in 
 
 depth, 94. 
 Lignite, 25. 
 Lily encrinite, 67*. 
 Limestone, 32, 40, 99. 
 
 Bird's-eye, 253. 
 
 Black River, 253. 
 
 Chazy, 253. 
 
 Corniferous, 276. 
 
 Crinoidal. 294. 
 
 Dudley, 268. 
 
 fresh-water, 105. 
 
 Galena, 260. 
 
 hydraulic, 40. 
 
 lithographic, 335. 
 
 Lower Helderberg, 267. 
 
 magnesian. 23, 253. 
 
 metamorphic, 41. 
 
 Mountain, 296. 
 
 Niagara, 266, 273. 
 
 Nummulitic, 390. 
 
 Onondaga, 276. 
 
 oolitic, 40, 46, 102, 835. 
 
 Trenton, 253. 
 
 Upper Helderberg, 276. 
 
 Wenlock, 268. 
 
 Limonite, 27, 111, 113, 116* V 297. 
 Limulus, 79. 
 
 Lingula, 106, 155*, 247. 
 
 range of, in time, 259. 
 Lingula Flags, 245, 247. 
 Lingulella, 247*. 
 Links, missing, 460. 
 Lion, cave, 431. 
 Liriodendron, 367*. 
 Lithographic limestone, 835. 
 Lithologic characters, as criterion of age of 
 
 rocks, 225. 
 Lithostrotion, 304*. 
 Lituola, 61*, 368*. 
 Liverworts, 88. 
 Lizards, 85. 
 
 Cretaceous, 874. 
 
 Jurassic, 356. 
 Llandeilo Flags, 252, 254. 
 Llandovery beds, 268. 
 Loa, Mauna, 177*, 178, 180, 183, 184. 
 Lobster, 76, 78. 
 
 Lobworm, geological action of, 110. 
 Loganograptus, 255*. 
 Loligo, 75*. 
 Lophophore, 70*, 71*. 
 Lower Helderberg period, 265, 267, 278. 
 Lower Silurian era, 228, 252. 
 Lowlands. See Plains. 
 Ludlow group, 268. 
 Lychnocanium, 63*. 
 Lycopods, 89. 
 
 Carboniferous, 300*, 301. 
 
 Devonian, 279*, 280. 
 
 Machaeracanthus, 284*. 
 Machaerodus, 431. 
 Made, 22. 
 Macrurans, 78. 
 
 Magnesian limestone, 23, 253. 
 Magnetite, 27, 202. 
 Malacostracans, 77*, 78. 
 Malm, 335. 
 Mammals, 85. 
 
 Age of, 231, 386. 
 
 Cretaceous, 374. 
 
 Eocene, primitive character of, 895. 
 
 Jurassic, 345, 357, 358*. 
 
 Quaternary, 430, 432*, 433*, 434*. 
 
 Tertiary, 394, 395*, 397*, 398*, 399*, 400*, 
 401*. 
 
 Triassic, 345*, 357. 
 Mammoth, 431, 433. 
 
 picture of, by men of Reindeer epoch, 
 
 437, 438*. 
 
 Mammoth Cave, 143*, 144. 
 Mammoth coal bed, 298. 
 Man, Ape of. 232. 405. 
 
 fossil remains of, 436. 
 
 modern relics of, 440*. 
 Mantellia, 337*. 
 
INDEX. 
 
 475 
 
 Map of England and southern Scotland, 
 
 geological, 295*. 
 Map of Hawaii, 179*. 
 
 Map of land hemisphere and water hemi- 
 sphere, 8*. 
 
 Map of Mammoth Cave, 143*. 
 Map of Maui, 129*. 
 
 Map of North America, after Appalachian 
 revolution, 328*. 
 
 at. close of Archaean, 287*. 
 
 Carboniferous, 287*. 
 
 Cretaceous, 364*. 
 
 Tertiary, 387*. 
 
 Upper Silurian, 264*. 
 Map of ocean, bathymetric, 10*, 11*. 
 Map of Pennsylvania coal areas, 292*. 
 Map of region south of Long Island, bathy- 
 metric, 13*. 
 Map of Tahiti, 130*. 
 
 Map of United States and Canada, geological, 
 235*. 
 
 Quaternary, 412*, 413*. 
 Marble, 41. 
 Marcasite, 27, 112. 
 Marcellus Shale, 277. 
 Margarita, 74*. 
 Marine formations, 152. 
 Marine life, distribution of, 91. 
 
 earlier than terrestrial, 456. 
 Marl, 40. 
 
 Marsipobranchs, 81. 
 Marsupials, 86. 
 
 Cretaceous, 376. 
 
 Jurassic, 345, 357, 358*. 
 
 Quaternary, 434. 
 
 Tertiary, 398, 400. 
 
 Triassic, 345, 357. 
 Massive rocks, 81. 
 Mastodon, Quaternary, 482*. 
 
 Tertiary, 401. 
 Mastodonsaurus, 352*. 
 Mauch Chunk Shale, 294. 
 Maui, map of, 129*. 
 
 valleys in, 129*, 181. 
 Manna Hualalai, etc. See Hualalai, etc. 
 Mechanical action, as source of heat, 171. 
 Medina epoch, 266, 273. 
 Medus*, 65*. 
 
 Megaceros Hibernicus. See Cervus euryceros. 
 Megalosaurus, 354. 
 Megatherium, 433*. 
 Meionornis, 441. 
 Melosira, 88*, 392*. 
 Menevian group, 230. 
 Mentone skeleton, 488. 
 Mer de Glace, 159. 
 Merostomes, 79. 
 Mesolithic epoch, 487. 
 Mesozoic life, characteristics of, 381. 
 
 Mesozoic time, 228, 229, 330. 
 
 change of life at close of, 884. 
 
 disturbances at close of, 388. 
 Metamorphic rocks, 80, 85, 86, 87, 88, 89, 41, 
 
 191, 238. 
 Metamorphism, 190. 
 
 agencies concerned in, 198. 
 
 dynamic, 195. 
 
 effects of, 192. 
 
 in connection with mountain-making, 218. 
 
 local, 190. 
 
 regional, 191. 
 Miamia, 306*. 
 Mica, 20. 
 Mica schist, 36. 
 Michigan, coal area of, 293. 
 Microdon, 283*. 
 
 Migrations in the Quaternary, 429. 
 Millepore, 65. 
 Mineral coal. See Coal. 
 Mineral oil. See Oil. 
 Mineral waters, 145. 
 Minerals, 18. 
 Miocene period, 886. 
 Missing links, 460. 
 Mississippi River, 124, 187. 
 
 delta of, 139*, 140. 
 Moas, extinction of, 441. 
 Molluscoids, 69, 70*, 71*. 
 
 Cambrian, 247*. 
 
 Carboniferous, 303, 304*. 
 
 Devonian, 281, 282, 283*. 
 
 Jurassic, 346, 347*. 
 
 Lower Silurian, 256*. 
 
 Triassic, 346. 
 
 Upper Silurian, 269*, 270, 271*. 
 Mollusks, 72*, 74*, 75*. 
 
 Cambrian, 247*. 
 
 Carboniferous, 304*. 
 
 Cretaceous, 369*, 370*, 371*. 
 
 Devonian, 281,282,283*. 
 
 Jurassic. 346, 347*. 349*. 
 
 Lower Silurian, 256*, 257. 
 
 Tertiary, 393. 
 
 Triassic, 346, 348*. 
 
 Upper Silurian, 269*, 270, 271*. 
 Monkeys, Tertiary, 395, 402. 
 Monocline, 55. 
 Monocotyledons, 90*, 91. 
 Monotremes, 85. 
 
 Cretaceous, 376. 
 
 Jurassic, 345, 357. 
 
 Triassic, 345*, 357. 
 Montana epoch, 365. 
 Monte Somma, 176*, 188. 
 Monticulipora, 257. 
 Moraine profonde, 163. 
 Moraines. 162. 
 
 of Glacial period, 416. 
 
476 
 
 INDEX. 
 
 Morcles, Dent de, 54*. 
 Monnolucoides, 339*. 
 Mosasaurs, 878*, 374*. 
 Mosses, 88. 
 
 Mount Etna, etc. See Etna, etc. 
 Mountain chains, 210. 
 
 height of, in relation to size of oceans, 16. 
 Mountain Limestone, 296. 
 Mountain ranges, location of, 207. 
 
 origin of, 207. 
 
 process of formation of, 216. 
 
 structure of, 210. 
 
 unsymmetrical, 914, 216. 
 Mountain systems, 210. 
 Mountain-making, at close of Archaean, 240. 
 
 at close of Jurassic, 862. 
 
 at close of Lower Silurian, 261, 320. 
 
 at close of Mesozoic, 383. 
 
 at close of Paleozoic, 211, 212*, 213*, 326. 
 
 in Tertiary, 402. 
 
 slowness of, 221. 
 Mountains, height of, 8, 204. 
 Mountains of circumdenudation, 183. 
 Muck, 109. 
 Mud, 34. 
 Mud cones, 187. 
 Mud-cracks, 156*, 174. 
 Muschelkalk, 334. 
 Muscovite, 20. 
 Myriopods, 79. 
 
 Carboniferous, 805, 806*. 
 
 Devonian, 281, 283. 
 
 Natural selection, 451. 
 Nautilus, 75*, 257. 
 
 range of, in time, 259. 
 Navicula, 392*. 
 Neanderthal skull, 437. 
 Neocene, 386. 
 Neocomian, 231. 
 Neolithic epoch, 438. 
 Neopaleozoic section, 229, 243, 268. 
 Neve, 159. 
 
 New Brunswick, coal area of, 292. 
 New Caledonia, coral reefs of, 103. 
 New Jersey, buried forest in, 429. 
 New Red Sandstone, 299, 385. 
 Niagara epoch, 266, 273. 
 Niagara Gorge, 41, 42*. 
 
 geological time measured by excavation 
 
 of, 444. 
 
 Niagara period, 265, 266. 
 Nitric acid, geological action of, 145. 
 Nodosaria, 61*. 
 Non-articulates, 60. 
 North America, geographical evolution In, 
 
 208, 445. 
 map of, after Appalachian revolution, 828*. 
 
 at close of Archaean, 237*. 
 
 Carboniferous, 287*. 
 
 Cretaceous, 364*. 
 
 Tertiary, 387*. 
 
 Upper Silurian, 264*. 
 Paleolithic Man in, 439. 
 profile of, 15*. 
 Notidanus, 82*. 
 Notochord, 80. 
 Nototherium, 434. 
 Nova Scotia, coal area of, 292. 
 Nullipores, 88. 
 Nummulites, 61*, 390*. 
 Nummulitic Limestone, 390. 
 
 Obsidian, 38, 175. 
 
 Ocean, bathymetric map of, 10*, 11*. 
 
 chemical action of, 236. 
 
 depth of, 8, 204. 
 
 mechanical action of, 146. 
 Ocean and continent, boundary of, 12. 
 Ocean basin, origin of, 206. 
 Ocean currents, 150. 
 Oceans, 7. 
 
 depth of, 8. 
 Ocher, 111. 
 Odontidium, 892*. 
 Oil, mineral, 25, 260, 277, 278, 289. 
 Old Red Sandstone, 278. 
 Olenellus, 249*, 322. 
 Oligocarpia, 337*, 338. 
 Oligocene, 386. 
 Oligoclase, 20. 
 Olivine. See Chrysolite. 
 Oneida Conglomerate, 266, 273. 
 Onondaga Limestone, 276. 
 Onondaga period, 265, 266. 
 Oolite, 40, 46, 102, 335. 
 Oolitic period, 835. 
 Ooze of ocean bottom, 92. 
 Opal, 19. 
 Ophiuroids, 68. 
 Opossum, 86. 
 Orange Sand, 417. 
 Orbit of earth, eccentricity of, 169. 
 Orbulina, 61*. 
 Orchestia, 77*. 
 Ordovician era, 228, 252. 
 Oregon, lava sheet of, 189. 
 Oreodon, 400, 401*. 
 Organic acids, geological effect of, 118. 
 Organic matter, reducing action of, 115. 
 Origin of species. See Evolution. 
 Oriskany period, 276. 
 Ornithopods, Cretaceous, 372. 
 
 Jurassic, 843*, 344, 354. 
 Ornithorhynchus, 86. 
 Orogenic movements. See Mountain-ranges, 
 
 Mountain-making. 
 Orohippus, 399*, 400. 
 
INDEX. 
 
 477 
 
 Orthts, 247*, 256*, 269*. 
 Orthisina, 247*. 
 Orthoceras, 248, 256*, 257, 805. 
 Orthoclase, 20. 
 Orthoclase rocks, 86. 
 Osmeroides, 372*. 
 Ostracoids, 77*, 78. 
 
 Triassic, 338, 889*. 
 
 Upper Silurian, 271*. 
 Ostrea, 72*, 393. 
 Otozoum, 340*. 
 Ouachita range, 827. 
 Outcrop, 51*. 
 Overlap, 57. 
 Oxen, Tertiary, 402. 
 Oxygen, geological action of, 111. 
 Oysters, Tertiary, 893. 
 
 Palseaster, 68*. 
 
 Palseoblattina, 258. 
 
 Palaeohatteria, 309*. 
 
 Palseoniscus, 83*, 84*, 307*. 
 
 Palaeotherium, 897. 
 
 Palapteryx, 441. 
 
 Paleolithic epoch, 436. 
 
 Paleontology and embryology, parallelism 
 
 of, 454. 
 
 Paleozoic life, characteristics of, 323. 
 Paleozoic time, 227, 228, 242. 
 
 change of life at close of, 329. 
 
 disturbances at close of, 325. 
 Palisades, 189, 832, 333. 
 Palms, Cretaceous, 367. 
 
 Tertiary, 391*. 
 Paradoxides, 248*, 322. 
 Paris basin, Tertiary animals of, 396. 
 Patellina, 368*. 
 Paumotu Archipelago, 108. 
 Peat, 107. 
 
 Pegmatite, 198, 199. 
 Pelion, 308*. 
 Pemphix, 350*. 
 Peneplains, 141. 
 Pennsylvania, map of coal areas of, 292*. 
 
 oil region of, 289. 
 Pentacrinus, 68*. 
 Pentamerus, 269*, 271*. 
 Pentremites, 67*, 304*. 
 Periods, geological, 232. 
 Permian glaciated bowlders, 299. 
 Permian period, 291, 299. 
 Petit Anse, salt deposit of, 26. 
 Petrifaction, 99. 
 Petroleum. See Oil. 
 Phacops, 283*. 
 
 Phaenogams. See Phanerogams. 
 Phalanger, 86. 
 Phanerogams, 89, 90*. 
 
 Carboniferous, 802. 
 
 Cretaceous, 867*. 
 
 Devonian, 281. 
 
 Jurassic, 336, 337*. 
 
 Tertiary, 390, 391*. 
 
 Triassic, 336, 337*. 
 Phascolotherium, 358*. 
 Phenacodus, 395*, 399. 
 Phenocryst, 32. 
 Phillipsia, 322. 
 Phosphatic formations, 105. 
 Phyllite. See Slate. 
 Phyllograptus, 255*. 
 Physiographic geology, 6, 7. 
 Piedmont belt, 238. 
 Pinnularia, 88*, 392*. 
 Pinus, 90*. 
 
 Pithecanthropus erectus, 489. 
 Placental Mammals, 86. 
 Placenticeras, 371*. 
 Placoderms, 82. 
 
 Devonian, 283, 284, 285*. 
 
 Lower Silurian, 258. 
 
 Upper Silurian, 272. 
 Plagioclase rocks, 38. 
 Plains, 13. 
 Plant and animal, distinctions between, 
 
 58. 
 
 Plateaus, 18. 
 Platephemera, 284*. 
 Platyceras, 247*, 269*. 
 Pleistocene, 406. 
 Plesiosaurs, Cretaceous, 372. 
 
 Jurassic, 352, 353*, 854. 
 
 Triassic, 852, 354. 
 Pleurosigma, 88*. 
 Pleurotomaria, 304*. 
 Plinthosella, 63*. 
 Pliocene period, 386. 
 Pliosaurus, 354. 
 Plumbago. See Graphite. 
 Plutonic rocks, 20, 36, 37, 88. 
 Pocono group, 294. 
 Podozamites, 837*. 
 Polycystines. See Radiolarians. 
 Polyps. See Anthozoans. 
 Polythalamia. See Foraminifers. 
 Pompeii, 184. 
 Porcellio, 77*. 
 Porphyritic rocks, 81. 
 Porphyry, 82, 38. 
 Portage epoch, 277. 
 
 Portland (Connecticut) sandstone, 882. 
 Portland (England) Dirt Bed, 885. 
 Potomac formation, 333, 364. 
 Potsdam period, 244. 
 Pottsville Conglomerate, 296. 
 Prasopora, 256*. 
 Predentata, Cretaceous, 372*. 
 Jurassic, 343*, 344*, 354. 
 
478 
 
 INDEX. 
 
 Present flora and fauna, progressive approxi- 
 mation to, 456. 
 Proboscideans, Quaternary, 481, 482*. 
 
 Tertiary, 401*. 
 Productus, 303, 804*. 
 Protannularia, 254*. 
 Protocaris, 249*. 
 Protozoans, 60, 61*, 62*, 68*. 
 
 Cretaceous, 368*. 
 
 Tertiary, 389, 890*. 
 Pseudopods, 62*. 
 Pteranodon, 378. 
 Pterichthys, 284, 285*. 
 Pteridophytes. See Acrogens. 
 Pterodactylus, 354, 355*. 
 Pterophylluin, 337*. 
 Pteropods, 74*. 
 
 Cambrian, 247*. 
 
 Upper Silurian, 270, 271*. 
 Pterosaurs, Cretaceous, 878. 
 
 Jurassic, 352, 354, 355*, 856*. 
 
 Triassic, 352, 854. 
 Pudding-stone, 84. 
 Pumice, 175. 
 Pupa vetusta, 304*. 
 Purbeck group, 335. 
 Pyrenees, elevation of, 408. 
 Pyrifusus, 74*, 371*. 
 Pyrite, 27. 
 
 oxidation of, 112, 145. 
 Pyroxene, 21. 
 Pyrrhotite, 27, 112. 
 Pythonomorphs, 873*, 874*. 
 
 Quartz, 18*, 198. 
 Quartz syenite, 87. 
 Quartzite, 85. 
 Quaternary era, 232, 405. 
 Quercus, Tertiary, 891*. 
 
 Eacodiscula, 63*. 
 Radiates, 60. 
 Eadiolarian ooze, 92. 
 Eadiolarians, 62*, 68*. 
 
 deposits of, 106. 
 Eagadinia, 63*. 
 Rain, distribution of, 128. 
 
 erosion by, 128. 
 Raindrop impressions, 128*. 
 Rappahannock stage, 364. 
 Raritan stage, 364. 
 Rays, 82. 
 
 Recent period, 405, 425. 
 Red Beds, 299. 
 
 Red clay of ocean bottom. 92. 
 Reefs, coral, 100, 102*, 104*. 
 Regelation, 161. 
 Reindeer epoch, 487. 
 
 Reptiles, 85. 
 
 Age of, 228, 330. 
 
 Cretaceous, 372*, 878*, 374*. 
 
 Jurassic, 340, 348*, 844*, 852, 858*. 855*. 
 856*. 
 
 Permian, 308, 809*. 
 
 Tertiary, 894. 
 
 Triassic, 340*, 341*, 342*, 352. 
 Resins, fossils preserved in, 99. 
 Revolution, Appalachian, 825. 
 
 Laramide, 383. 
 
 post-Mesozoic, 388. 
 
 post-Paleozoic, 325. 
 
 Taconic, 260. 
 Rhfetic formation, 334. 
 Rhamphorhynchus, 856*. 
 Rhaphistoma, 256*. 
 Rhinoceros, Quaternary, 481, 482. 
 
 Tertiary, 400, 401. 
 Rhizopods, 61*, 62*, 68*. 
 
 Cretaceous, 868*. 
 
 Tertiary, 389, 390*. 
 Rhode Island, coal area of, 292. 
 Rhynchocephala, 85. 
 
 Permian, 308, 309*. 
 Rhynchonella, 71*, 271*. 
 
 range of, in time. 259. 
 Rhynchotreta, 269*. 
 Rhyolite, 88. 
 
 Richmond, diatomaceous deposit of, 391, 892*. 
 Rill-marks, 155*. 
 Ripple-marks, 154*, 155. 
 River terraces, 138, 422, 426*, 427*. 
 River valleys, form of, 131. 
 
 making of, 129. 
 Rivers, energy of, 125. 
 
 geological action of, 124. 
 
 Paleozoic, 320. 
 
 youth and age of, 140. 
 Roches moutonnees, 163*, 164. 
 Rock, definition of, 17. 
 Rock salt. See Salt. 
 Rocks, Archaean, 236. 
 
 calcareous, 32, 40, 99. 
 
 Cambrian, 244. 
 
 carbonaceous, 107. 
 
 Carboniferous, 291. 
 
 clastic, 28, 29. 
 
 consolidation of, 117. 
 
 constituents of, 18. 
 
 Cretaceous, 363. 
 
 crystalline. 28, 29, 35, 41, 175, 188, 191. 
 
 Devonian, 276. 
 
 foliated, 81, 191, 195. 
 
 fragmental, 28, 29, 33. 
 
 hydrous magnesian, 39. 
 
 igneous, 29, 86, 37, 38, 39, 175, 188. 
 
 Jurassic, 333, 834, 335. 
 
 kinds of, 28. 
 
INDEX. 
 
 479 
 
 laminated, 81. 
 
 Lower Silurian, 252. 
 
 massive, 31. 
 
 metamorphic, 30. 35, 86, 37, 38, 39, 41, 191. 
 
 orthoclase, 36. 
 
 Paleozoic, thickness of, in North America, 
 211, 316. 
 
 phosphatic, 105. 
 
 plagioclase, 38. 
 
 plutonic, 29, 86, 37, 38. 
 
 porphyritic, 31. 
 
 schistose, 31, 191, 195. 
 
 sedimentary, 29. 
 mode of formation of, 165. 
 
 shaly, 31. 
 
 siliceous, 32, 35, 106. 
 
 slaty, 81, 
 
 stratified, 41. 
 
 Tertiary, 388. 
 
 Triassic, 832, 834. 
 
 unstratified, 45. 
 
 Upper Silurian, 266. 
 
 volcanic, 29, 38, 39, 175. 
 Rocky Mountains, glaciated areas in, 414. 
 
 geanticlinal elevation of, 402. 
 Rodents, Tertiary, 394, 400. 
 Romingeria, 282*. 
 Rotalia, 61*, 62*, 368. 
 Rudista, 369, 370*. 
 
 Saccammina, range of, in time, 259. 
 
 Saint Helen's, Mount, 177. 
 
 Saint Lawrence River in the Quaternary, 421. 
 
 Saint Peter's Sandstone, 253. 
 
 Salamanders, 85. 
 
 Saliferous group, 885. 
 
 Salina beds, 266, 273. 
 
 Salina salt wells, 267. 
 
 Salisbury Crags, 190. 
 
 Salix, Tertiary, 867*. 
 
 Salt, 26, 117. 
 
 Cretaceous, 26. 
 
 Subcarboniferous, 296. 
 
 Triassic, 335. 
 
 Upper Silurian, 267. 
 Salt lakes, 117. 
 Sand, 33. 
 
 Sand scratches, 119. 
 Sand-flea, 77*, 78. 
 Sandstone, 35. 
 
 Caradoc, 254. 
 
 Catskill, 277. 
 
 Medina, 266, 278. 
 
 New Bed, 299, 885. 
 
 Old Red, 278. 
 
 Oriskany, 276. 
 
 Potsdam, 244. 
 
 Saint Peter's, 258. 
 Sanidin, 88. 
 
 Sapphirina, 77*. 
 Sassafras, Cretaceous, 867*. 
 Sauropods, Cretaceous, 872. 
 
 Jurassic, 342, 343*, 854. 
 Sauropus, 808*. 
 Scaphites, 370, 371*. 
 { Schist, 31, 192, 195. 
 Schistose structure, 31, 192, 195. 
 Schoharie Grit, 276. 
 Scolithus, 248*. 
 Scoria, 175. 
 Scorpions, 79. 
 
 Carboniferous, 305*. 
 
 interrupted range of, in time, 459. 
 
 Upper Silurian, 272. 
 Scratches, glacial, 163, 407*, 408. 
 
 made by wind-drifted sand, 119. 
 Sea anemone, 66*. 
 Sea beaches, elevated, 421. 
 Sea fans, 66*. 
 
 Sea urchins. See Echinoids. 
 Seaweeds. See Algae. 
 Sedimentary formations, marine, 152. 
 Sedimentary material, origin of, 151, 165. 
 Sedimentary strata, formation oi, 165. 
 Selachians, 81, 82*. 
 
 Carboniferous, 806, 307*. 
 
 Cretaceous, 370. 
 
 Devonian, 283, 284*. 
 
 Jurassic, 850. 
 
 Lower Silurian, 258. 
 
 Tertiary, 393, 894*. 
 
 Triassic, 850. 
 
 Upper Silurian, 272. 
 Semi-bituminous coal, 298. 
 Series, definition of, 48. 
 Serolis, 77*. 
 Serpentine, 21, 89. 
 Serpula, 101. 
 Sertularia, 65*. 
 Shale, 81, 85. 
 
 alum, 85. 
 
 Black, 278. 
 
 Cleveland, 278. 
 
 Erie, 278. 
 
 Genesee, 277. 
 
 Hudson River, 258. 
 
 Huron, 278. 
 
 Marcellus, 277. 
 
 Mauch Chunk, 294. 
 
 Utica, 253. 
 
 Sharks. See Selachians. 
 Shasta, Mount, 177. 
 Shrinkage cracks, 156*, 173*. 
 Siderite, 27, 297. 
 
 alteration of, 112. 
 Sierra Nevada, crystalline rocks of, 219. 
 
 post-Jurassic elevation of, 862. 
 
 Tertiary elevation of, 403. 
 
480 
 
 INDEX. 
 
 Sigillaria, 279*, 280, 800*, 801. 
 
 Silica, 18. 
 
 Silicates, 19. 
 
 Siliceous rocks, 82, 35, 106. 
 
 Siliceous sinter, 86. 
 
 Silicon dioxide. See Silica. 
 
 Silurian. See Lower Silurian, Upper Silurian. 
 
 Sinter, 36. 
 
 Sipbonia, 369*. 
 
 Skiddaw Slates, 254. 
 
 Slate, 31, 37. 
 
 Slaty cleavage, 81, 48*, 219. 
 
 Sloths, Quaternary, 433*. 
 
 Snails, 73, 74*. 
 
 interrupted range of, in time, 459. 
 Snake River, lava sheets of, 189. 
 Snakes, 85. 
 
 Cretaceous, 374. 
 Snow line, 159. 
 Soapstone, 21, 89. 
 Sodium chloride. See Salt. 
 Soil, 34. 
 
 Solenhofen, lithographic limestone of, 835. 
 Solfataras, 185. 
 Solids, flowing of, 205. 
 Solva group, 230. 
 Somma, Monte, 176*, 183. 
 Sorata, 177. 
 
 South America, recent changes of level in, 
 428. 
 
 profile of, 15*. 
 Sow-bug, 77*. 78. 
 Spathic iron. See Siderite. 
 Specialized forms of life, later than gener- 
 alized, 454. 
 
 Species, origin of. See Evolution. 
 Sphagnum, 107. 
 Sphenopteris, 300*. 
 Spicules of Sponges, 63*, 64. 
 Spiders, 79. 
 
 Carboniferous, 305, 306*. 
 
 interrupted range of, in time, 459. 
 Spinax, 82*. 
 Spiny ant-eater, 86. 
 Spirifer, 71*, 271*, 283* 303, 304*. 
 Spiriferidse, last of, 346, 347*. 
 Spiriferina, 347*. 
 Spirocyathus, 246*. 
 Sponges, 63*. 
 
 Cambrian, 246*. 
 
 Cretaceous, 368, 369*. 
 Spongiolithis, 392*. 
 Spores of Lycopods in coal, 810*. 
 Springs, hot, 185. 
 Squids, 75*, 76. 
 Stage, definition of, 43. 
 Stalactite, 40, 144. 
 Stalagmite, 40, 144. 
 Starfishes. See Asterioids. 
 
 Statuary marble, 41. 
 Staurolite, 23. 
 Steatite, 21, 39. 
 Stegocephala, 85. 
 
 Carboniferous, 807, 308*. 
 
 Jurassic, 381. 
 
 Triassic, 339, 340*, 351, 352*. 
 Stegosaurs, Cretaceous, 372. 
 
 Jurassic, 344*, 354. 
 Stelletta, 63*. 
 Stenotheca, 247*. 
 Stephanoceras, 347*. 
 Stictopora, 256*. 
 Stigmaria, 300*, 301. 
 Stone Age, 436. 
 Strata, age of, how determined, 223. 
 
 conformable and unconformable, 56, 57*. 
 
 dislocations of, 50. 
 
 folded, 211, 212*, 213*, 215*. 
 
 maximum thickness of, 50. 
 
 original position of, 48, 50*. 
 Straticulate structure, 48. 
 Stratification, origin of, 44. 
 Stratified rocks, 41. 
 Stratigraphical geology, 223. 
 Stratum, definition of, 41. 
 Streptelasma, 256*. 
 Strife. See Scratches. 
 Strike, 51*, 52. 
 Strophomena, 269*. 
 Strophomenidse, last of, 346. 
 Structural geology, 6, 17. 
 Subcarboniferous period, 291, 294. 
 Submarine eruptions, 184. 
 Subsidence, coral island, 104*, 404. 
 
 effect of, on temperature, 168. 
 Subsidence of Atlantic coast of United States, 
 
 429. 
 
 Subsidence of Greenland, 428. 
 Subsidence of volcanic regions, 184. 
 Subterranean waters, 142. 
 Sulphur, volcanic deposits of, 185. 
 Sun, heat received from, 167. 
 Superimposed drainage, 142. 
 Superior, Lake, copper deposits of, 201. 
 Superposition, criterion of age of strata, 
 
 224. 
 
 Sweden, changes of level in, 428. 
 Switzerland, lake dwellings of, 489. 
 Syenite, 37. 
 Syenite, gneiss, 87. 
 Synclinal axis, 53*, 55. 
 Syncline, 53*, 55. 
 Synclinorium, 218. 
 Syncoryne, 65*. 
 Synthetic types, 455. 
 Syracuse, salt wells of, 267. 
 Syringopora, 282*. 
 System, definition of, 43. 
 
INDEX. 
 
 481 
 
 Table lands. See Plateaus. 
 
 Table mountains, 189. 
 
 Tachylite, 39, 175. 
 
 Taconic mountain system, 262. 
 
 Taconic range, Cambrian rocks of, 245. 
 
 elevation of, 201, 320. 
 Taconic revolution, 260. 
 Tahiti, erosion in, 130*, 181. 
 
 map of, 130*. 
 Talc, 21. 
 Talc schist, 39. 
 Taxocrinus. 256*. 
 Teleosts, 83, 84*. 
 
 Cretaceous, 370, 372*. 
 ' Jurassic, 351. 
 
 Tertiary, 393. 
 
 Triassic, 351. 
 Tellina, 72*. 
 Temperature, as limiting distribution 
 
 marine life, 93. 
 
 Tennessee, East, valley of, 218. 
 Tennessee Island, 263, 288. 
 Tentaculites, 270, 271*. 
 Terebratula, 71*. 
 Terebratulina, 71*. 
 Terraces, river, 138, 422, 426*, 427*. 
 Terranes, 17, 41. 
 
 Terrestrial life, later than marine, 456. 
 Tertiary era, 231, 386. 
 Tetrabranchs, 75*. 
 
 Cambrian, 247. 
 
 Carboniferous, 304. 
 
 Cretaceous, 370, 371* 
 
 Devonian, 282, 283*. 
 
 Jurassic, 347*. 
 
 Lower Silurian, 256*, 257. 
 
 Triassic, 347, 348*. 
 Tetractinellid spicules, 63*. 
 Tetradecapods, 77*, 78. 
 
 Jurassic, 350*. 
 Textularia, 61*. 
 Thallophytes, 8T, 88*. 
 Theromorphs, ;308. 
 Theropods, Cretaceous, 872. 
 
 Jurass'c, 344, 354. 
 
 Triassic, 340*, 341*, 342*, 354. 
 Tiaropsis, 65*. 
 Tidal currents, 149. 
 Till, 406. 
 
 Time, geological, length of, 444. 
 Time ratios, 317, 379, 444. 
 Tisiphonia, 63*. 
 Titanotherium, 397*, 400*. 
 Toads, 85. 
 Tourmaline, 22*. 
 Trachyte, 38, 175. 
 Trachytic domes, 184. 
 Tracks of animals, 250, 286, 307, 308*, 3 
 339*, 340*, 341* 352*. 
 
 of 
 
 Transportation, by glaciers, 162. 
 
 by rivers, 136. 
 
 Transporting power of water, 137. 
 Trap, 39. 
 
 Travertine, 40, 116, 187. 
 Tree ferns, 89. 
 
 Carboniferous, 301. 
 Tremadoc Slates, 230. 
 Trenton epoch, 253. 
 Trenton period, 252, 253. 
 Tresca, experiments of, on flowing of solids, 
 
 205. 
 
 Triarthrus, 258*. 
 Triassic era, 229, 331, 332. 
 Triceratium, 392*. 
 Triceratops, 372*. 
 Trigonia, 346, 347*. 
 Trigonocarpus, 300*. 
 Trilobites, 77*, 78. 
 
 Cambrian, 248*, 249*. 
 
 Carboniferous, 305. 
 
 Devonian, 281, 282, 283*. 
 
 Lower Silurian, 256*, 257, 258*. 
 
 range of genera of, in time, 322. 
 
 Upper Silurian, 269*, 270. 
 Triloculina, 61*. 
 Tripoli, 392. 
 Tufa, 35, 175. 
 
 calcareous. See Travertine. 
 Tuuicates, 79. 
 Turrilites, 370, 371*. 
 Turtles, 85. 
 
 Cretaceous, 374. 
 
 Jurassic, 356. 
 
 Tertiary, 394. 
 
 Triassic, 356. 
 
 Unconformable strata, 56, 57*. 
 
 Underclay, 297. 
 
 Ungulates, Tertiary, 394, 395*, 896, 897*, 
 
 398*, 399*, 400*, 401*. 
 United States, geological map of, 235*. 
 Unstratified rocks, 45. 
 Upper Helderberg Limestone, 276. 
 Upper Silurian era, 229, 243, 263. 
 Ursus speltcus, 431. 
 Utica epoch, 253. 
 
 V, Archaean, 237, 446. 
 
 Valleys, formation of, 129, 148. 
 
 Vegetable kingdom, 86. 
 
 Vegetable material, decomposition of, 810. 
 
 Veins, 196, 197*. 
 
 false, 203. 
 
 material of, 198. 
 
 origin of, 198. 
 
 superficial, 201. 
 Ventriculites, 63*. 
 
482 
 
 INDEX. 
 
 Vermes, 7fl. 
 
 Cambrian, 248*. 
 Vertebrates, 80, 82*, 83*, 84*. 
 
 Carboniferous, 806, 807*, 808*, 809*. 
 
 Cretaceous, 870, 872*, 878*, 874*, 875*, 
 377*. 
 
 Devonian, 283, 284*, 285*, 286*. 
 
 Jurassic, 339, 340, 842, 343*, 344*, 350, 
 851*, 353*, 355*, 356*, 357*, 858*. 
 
 Lower Silurian, 258. 
 
 Quaternary, 430, 432*, 483*, 434*. 
 
 Tertiary, 393, 394*, 395*, 897*, 898*, 899*, 
 400*, 401*. 
 
 Triassic, 339*, 340*, 841*, 842*, 845*, 850, 
 852*, 357. 
 
 Upper Silurian, 272. 
 Vesuvius, 176*, 177, 182, 186. 
 Volcanic eruptions, 177. 
 Volcanic rocks, 29, 88, 39, 175. 
 Volcanoes, 174. 
 
 distribution of, 171. 
 
 Waldheimia, 71*. 
 Warren, Lake, 424. 
 
 Washington, Mount, bowlders on, 410. 
 Water, action of, when freezing and frozen, 
 157. 
 
 chemical action of, 111, 187, 198, 198, 236. 
 
 mechanical action of, 124. 
 
 subterranean, 142. 
 
 transporting power of, 187. 
 Water-lime group, 267. 
 Waves, action of, 147. 
 Weald Clay, 866. 
 Wealden formation, 866. 
 Wenlock Limestone, 268. 
 West Rock, 333. 
 Whales, Tertiary, 394, 398. 
 White Mountains, glacial scratches on, 408. 
 Wind, geological action of, 118. 
 
 transportation of moisture by, 128. 
 Wind-drift structure, 121*. 
 Wombat, 86. 
 Woodocrinus, 804*. 
 Worms. See Vermes. 
 
 Xiphacantha, 62*. 
 Xiphodon, 398. 
 Xylobius, 306*. 
 
 Yellowstone Park, 117, 185, 187, 189. 
 Yellowstone River, 115. 
 
 Zamia, 836*. 
 Zaphrentis, 269*. 
 Zeuglodon, 398. 
 Zoantharians, 60*. 
 
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