LIBRARY
UNIVERSITY OF CALIFORNIA
RIVERSIDE
. ^ '.v v
BIED'S-EYE VIEW or MARBLE CxSoN FBOM THE VERMILION CLIFFS, NEAR THE MOUTII OF THE PABIA.
In the distance the Colorado River is seen to turn to the west, where its gorge divides the Twin
Plateaus. On the right are seen the Eastern Karbab Displacements appearing as folds, and farther
in the distance as faults.
ELEMENTS
GEOLOGY
A TEXT-BOOK
FOE
COLLEGES AND FOR THE GENERAL READER.
BY
JOSEPH LE CONTE,
'/'
MirnoE OF "BELIGIOX AND SCIENCE," ETC., AXD PBOFESSP* OF GEOLOGY ASD NATTOEAL
IN TUB UXIVEBSITY OF CAilFOESIA.
NEW YORK :
D. APPLETON AND COMPANY,
549 AND 551 BROADWAY.
1878.
COPYRIGHT BY
D. APPLETON AND COMPANY,
1877.
P E E F A O E .
IN preparing the following work I have not attempted to make an
exhaustive manual to be thumbed by the special student ; for, even if
I felt able to write such a work, Prof. Dana's is already in the field,
and is all that can be desired in this respect. I have endeavored only to
present clearly to the thoroughly cultured and intelligent student and
reader whatever is best and most interesting in Geological Science.
I have attempted to realize what I conceive to be comprised in the
word elements, as contradistinguished from manual. I have attempted
to give a really scientific presentation of all the departments of the
wide field of geology, at the same time avoiding too great multiplica-
tion of detail. I have desired to make a work which shall be both
interesting and profitable to the intelligent general reader, and at the
same time a suitable text-book for the higher classes of our colleges.
In the selection of material and mode of presentation I have been
guided by long experience, as to what it is possible to make interest-
ing to a class of young men, somewhat advanced in general culture
and eager for knowledge, but not expecting to become special geolo-
gists. In a word, I have tried to give such knowledge as every thor-
oughly cultured man ought to have, and at the same time is a suitable
foundation for the further prosecution of the subject to those who so
desire. The work is the substance of a course of lectures to a senior
class, organized, compacted, and disencumbered of too much detail, by
re-presentation for many successive years, and now for the first time
reduced to writing.
Most text-books now in use in this country are, in my opinion,
either too elementary on the one hand, or else adapted as manuals for
the specialists on the other. I wish to fill this gap to supply a want
iv PREFACE.
felt by many intelligent students and general readers, who desire a
really scientific general knowledge of geology. Lyell's " Elements "
comes nearest to supplying this want ; but there are two objections to
this admirable work : 1. The principles (dynamical geology) are sepa-
rated from the elements (structural and historical geology), and treated
in a different work ; 2. Its treatment of American geology is of course
meagre.
I have treated several subjects in dynamical and structural geology
e. g., rivers, glaciers, volcanoes, geysers, earthquakes, coral-reefs,
slaty cleavage, metamorphism, mineral veins, mountain-chains, etc.
more fully than is common. I feel hopeful that many geologists and
physicists will thank me for so doing. I am confident that I give
somewhat fairly the present condition of science on these subjects.
In the historical part I have found much more difficulty in being
scientific without being tiresome, and in being interesting without
being superficial and wordy. I have attempted to accomplish this diffi-
cult task by making evolution the central idea, about which many of
the facts are grouped. I have tried to keep this idea in view, as a
thread running through the whole history, often very slender some-
times, indeed, invisible but reappearing from time to time to give
consistency and meaning to the history.
If this work have any advantage over others already before the
public, it is chiefly in the two points mentioned above, viz., in a fuller
presentation of some subjects in dynamical and structural geology, and
in the attempt to keep evolution in view, and to make it the central
idea of the history. Another advantage, I believe, is, that it does not
seek to compete with the best works now before the public, but occu-
pies a distinct field and supplies a distinct want.
I have confined myself mostly, though not entirely, to American
geology, especially in giving the distribution of the rocks and the
physical geographv of the different periods. In only one case have I
made American geology subordinate, viz., in the Jura-Trias period, and
that only because of the meagreness of the record of this period in this
country.
In a science so comprehensive and many-sided as geology, it is
simply impossible, as every teacher knows, to avoid anticipations in
one part of what strictly belongs to a subsequent part. It is for this
reason that the order of presentation of the different departments, and
PREFACE. v
of the various subjects under each department, is so different in the
hands of different writers. The order which I have adopted I know is
not free from objection on this score, but it seemed to me, on the
whole, the best.
In preparing the work I have, of course, drawn largely from many
sources, both text-books and works of original research ; for whatever
of merit there be in a work of this kind must consist not so much in
the novelty of the matter as in the selecting, grouping, and presenta-
tion. Such obligations are acknowledged in the pages of the work.
I cannot forbear, however, making here a special acknowledgment of
my indebtedness, in the historical part, to the invaluable manual of
Prof. Dana. I must also acknowledge especial indebtedness to Profs.
Marsh and Newberry, and the geologists and paleontologists of the
United States Surveys, in charge of Prof. Hayden and Lieutenant
Wheeler, not only for valuable materials, but also for much personal
aid.
CONTENTS.
INTRODUCTORY.
PAGE
DEFINITION OF GEOLOGY, AND OF ITS DEPAKTNENTS 1-2
GEOLOGY, 1 ; Principal Departments, 2 ; Order of Treatment, 2.
PART I.
DYNAMICAL GEOLOGY.
CHAPTER I.
ATMOSPHERIC AGENCIES 3-8
Soils, 4 ; General Explanation, 6 ; Granite, Gneiss, Volcanic Rocks, etc., 7 ; Lime-
stone, 1 ; Sandstones, 7 ; Slate, 7. MECHANICAL AGENCIES OF THE ATMOSPHERE.
Frost, 8 ; Winds, 8.
CHAPTER II.
AQUEOUS AGENCIES 9-V6
SECTION 1. EIVERS, 9. Erosion of Rain and Rivers, 9 ; Hydrographical Basin, 10 ;
Kate of Erosion of Continents, 10 ; Law of Variation of Erosive Power, 11. Ex-
amples of Great Erosion now going on : Waterfalls, 12 ; Niagara, General
Description, 12 ; Recession of the Falls, 12 ; Other Falls, 13 ; Time necessary
to excavate Niagara Gorge, 14 ; Ravines, Gorges Canons, 15 ; Time, 17. Trans-
portation and Distribution of Sediments, 18 ; Experiments, 18 ; Law of Vari-
ation, 18. 1. Stratification, 20. 2. Winding Course of Rivers, 21. 3. Flood-
Plain Deposits, 22 ; River-Swamp, 22 ; Natural Levies, 23 ; Artificial Levees,
23. 4. Deltas, 24 ; Process of Formation, 26 ; Rate of Growth, 27 ; Age of River-
Deposits, 27. 5. Estuaries, 29 ; Mode of Formation, 29 ; Deposits in Estuaries,
30. 6. Bars, 30.
SECTION 2. OCEAN. Waves and Tides. Waves, 31 ; Tides, 32 ; Examples of the
Action of Waves and Tides, 33 ; Transporting Power, 36 ; Deposits, 36.
Oceanic Currents, 37 ; Theory of Oceanic Currents, 37 ; Application, 38 ; Geo-
logical Agency of Oceanic Currents, 39 ; Submarine Banks, 40 ; Land formed
by Ocean Agencies, 42.
SECTION 3. ICE, 43. Glaciers. Definition, 43 ; Necessary Conditions, 43 ; Rami-
fications of Glaciers, 44 ; Motion of Glaciers, 44 ; Graphic Illustration, 46 ; Line
of the Lower Limit of Glaciers, 46 ; General Description, 47 ; Earth and Stones,
etc., 49. Moraines, 50. Glaciers as a Geological Agent, 51 ; Erosion, 51 ; Trans-
portation, 52 ; Deposit Balanced Stones, 52 ; Material of the Terminal Moraine,
i CONTENTS.
PAG!
53 ; Evidences of Former Extension of Glaciers, 53 ; Glacial Lakes, 54. Mo-
tion of Glaciers and its Laws. Evidences of Motion, 54; Laws of Glacier-
Motion, 55. Theories of Glacier-Motion, 57. Viscosity Theory of Forbes.
Statement of the Theory, 57 ; Argument, 57. Regelation Theory of Tyndall,
58 ; Eegelation, 59 ; Application to Glaciers, 59 ; Comparison of the Two
Theories, 60 ; Conclusion, 60. Structure of Glaciers, 60 ; Veined Structure,
60 ; Fissures, 61. Theories of Structure. Fissures, 62 ; Veined Structure, 62 ;
Physical Theory of Veins, 63. Floating Ice Icebergs, 64 ; General Descrip-
tion, 65 ; Icebergs as a Geological Agent Erosion, 66 ; Deposits, 66. Shore-
Ice, 67. Comparison of the Different Forms of the Mechanical Agencies of
Water, 67.
SECTION 4. CHEMICAL AGENCIES OF WATER. Subterranean Waters, Springs, etc.,
68 ; Springs, 68 ; Artesian Wells, 69 ; Chemical Effects of Subterranean Waters,
70 ; Limestone Caves, 70. Chemical Deposits in Springs. Deposits of Carbon-
ate of Lime, 71 ; Explanation, 71 ; Kinds of Materials, 71 ; Deposits of Iron, 72 ;
Deposits of Silica, 72 : Deposits of Sulphur and Gypsum, 73. Chemical De-
posits in Lakes. Salt Lakes and Alkaline Lakes, 73 ; Conditions of Salt-Lake
Formation, 74 ; Deposits in Salt Lakes, 75. Chemical Deposits in Seas, 76.
CHAPTER III.
IGNEOUS AGENCIES 76-132
SECTION 1. INTERIOR HEAT OF THE EAETH. Stratum of Invariable Temperature,
76 ; Increasing Temperature of the Interior of the Earth, 77 ; Constitution of
the Earth's Interior, 78 ; 1. Rate of Increase not uniform, 78 ; 2. Fusing-Point
not the same for all Depths, 79 ; Astronomical Reasons, 80.
SECTION 2. VOLCANOES. Definition, 81 ; Size, Number, and Distribution, 81 ; Phe-
nomena of an Eruption, 82 ; Monticules, 83 ; Materials erupted, 83 ; Stones, 83 ;
Lava, 83 ; Liquid Lava, 84 ; Hardened Lava, 85 ; Gas, Smoke, and Flame, 85 ;
Kinds of Volcanic Cones, 86 ; Mode of Formation of a Volcanic Cone, 86 ;
Comparison between a Volcanic Cone and an Exogenous Tree, 89 ; Estimate of
the Age of Volcanoes, 89. Thtory of Volcanoes, 90 ; Force, 90 ; The Heat,
91 ; Internal Fluidity Theory, 91 ; Objections, 91 ; Chemical Theory, 92 ; Re-
cent Theories, 92. Subordinate Volcanic Phenomena, 94 ; General Explanation,
94. Geysers, 94 ; Description, 94 ; Phenomena of an Eruption, 94; Yellowstone
Geysers, 96 ; Theories of Geyser-Eruption, 99 ; Mackenzie's Theory, 99 ; Bun-
sen's Investigations, 100 ; Theory of Geyser-EruptionPrinciples, 101 ; Appli-
cation to Geysers, 101 ; Bunsen's Theory of Geyser-Formation, 103.
SECTION 3. EARTHQUAKES, 104 ; Frequency, 104 ; Connection with other Forms of
Igneous Agency, 104 ; Ultimate Cause of Earthquakes, 106 ; Proximate Cause,
106 ; Waves their Kinds and Properties, 106 ; Definition of Terms, 107 ; Ap-
plication to Earthquakes, 109 ; Experimental Determination of the Velocity of
the Spherical Wave, 111 ; Explanation of Earth quake- Phenomena, 111 ; Vorti-
cose Earthquakes, 114 ; Explanation, 114. Earthquakes originating beneath the
Ocean, 119 ; Great Sea-Wave, 119 ; Examples of the Sea-Wave, 120. Depth of
Earthquake- Focus, 122; Seismometers, 122; The Determination of the Epi-
centrum, 124 ; Determination of the Focus, 124 ; Effect of the Moon on Earth-
quake-Occurrence, 126 ; Relation of Earthquake-Occurrence to Seasons and At-
mospheric Conditions, 126.
SECTION 4. GRADUAL ELEVATION AND DEPRESSION OF THE EARTH'S CRUST, 127 ;
Elevation or Depression during Earthquakes, 127 ; Movements not connected
with Earthquakes South America, 127 ; Italy, 127 ; Scandinavia, 129 ; Green-
land, 129 ; Deltas of Large Rivers, 129 ; Southern Atlantic States, 130 ; Pacific
Ocean, 130. Theories of Elevation and Depression, 131 ; Babbage's Theory,
131 ; Herschel's Theory, 132 ; General Theory, 132.
CONTEXTS. i x
CHAPTER IV.
PAGE
ORGANIC AGENCIES 133-163
SECTION 1. VEGETABLE ACCUMULATIONS. Peat-Bogs and Peat-Swamps. Descrip-
tion, 133 ; Composition and Properties of Peat, 133 ; Mode of Growth, 134 ;
Rate of Growth, 135 ; Conditions of Growth, 135 ; Alternation of Peat with
Sediments, 136. Drift- Timber, 136.
SECTION 2. BOG-!RON ORE, 136.
SECTION 3. LIME ACCUMULATIONS. Coral Reefs and Islands. Interest and Im-
portance, 138 ; Coral Polyp, 138 ; Compound Coral, or Corallum, 138 ; Coral
Forests, 138 ; Coral Eeef, 139 ; Coral Islands, 139 ; Conditions of Coral-Growth,
140 ; Pacific Eeefs, 140 ; Fringing Eeefs, 140 ; Barrier Eeefs, 141 ; Circular
Reefs, or Atolls, 142 ; Small Atolls and Lagoonless Islands, 143. Theories of
Barrier and Circular Reefs, 143 ; Crater Theory, 143 ; Objections, 144 ; Sub-
sidence Theory, 144 ; Proofs, 145 ; Area of Land lost, 146 ; Amount of Vertical
Subsidence, 146 ; Eate of Subsidence, 147 ; Time involved, 148 ; Geological Ap-
plication, 148. Rtefs of Florida, 149 ; Description of Florida, 149 ; General
Process of Formation, 150 ; History of Changes, 150 ; Mangrove Islands, 151 ;
Florida Eeefs compared with other Eeefs, 152 ; Probable Agency of the Gulf
Stream, 152. Shell-Deposits, 153 ; Molluscous Shells, 153 ; Microscopic Shells,
154.
SECTION 4. GEOGRAPHICAL DISTRIBUTION OF ORGANISMS. Fauna and Flora, 155 ;
Kinds of Distribution, 155 ; Vertical Botanical Temperature-Eegions, 156 ; Bo-
tanical Temperature-Regions in Latitude, 156 ; Further Definition of Eegions,
157 ; Zoological Temperature-Eegions, 153 ; Continental Fauna and Flora, 159 ;
Subdivisions, 160 ; Special Cases, 161 ; Marine Fauna Distribution in Lati-
tude, 162 ; Distribution in Longitude, 162 ; Depth and Bottom, 162 ; Special
Cases, 162.
PART II.
STRUCTURAL GEOLOGY.
CHAPTER I.
GENERAL FORM AND STRUCTURE OF THE EARTH .... 164-170
1. Form of the Earth, 164. 2. Density of the Earth, 165. 3. The Crust of the
Earth, 166 ; Means of Geological Observation, 166. 4. General Surface Con-
figuration of the Earth, 167 ; Cause of Land-Surfaces and Sea-Bottoms, 167 ;
Laws of Continental Form, 168. Rocks, 169 ; CLsses of Eocks, 170.
CHAPTER II.
STRATIFIED OR SEDIMENTARY ROCKS 170-202
SECTION 1. STRUCTURE AND POSITION. Stratification, 170 ; Extent and Thickness,
170 ; Kinds of Stratified Eocks, 171 ; I. Stratified Eocks are more or less Con-
solidated Sediments, 171 ; Cause of Consolidation, 172 ; II. Stratified Eocks
have been gradually deposited, 172 ; III. Stratified Eocks were originally nearly
horizontal, 173 ; Elevated, Inclined, and Folded Strata, 174 ; Dip and Strike,
175 ; Anticlines and Synclines, 177 ; Monoclinal Axes, 178 ; Unconformity, 178 ;
Formation, 179. Cleavage Structure, 179 ; Sharpe's Mechanical Theory, 181 ;
Physical Theory, 185 ; Sorby's Theory, 185 ; Tyndall's Theory, 186 ; Geolog-
ical Application, 187. Nodular or Concretionary Structure, 188 ; Cause, 188 ;
Forms of Nodules, 189 ; Kinds of Nodules found in Different Strata, 189. Fos-
sils : their Origin and Distribution, 190 ; The Degrees of Preservation are very
various, 191 ; Theory of Petrifaction, 192. Distribution of Fossils in the Strata,
x CONTENTS.
PAGE
195 ; 1. Kind of Eock, 195. 2. The Country where found, 195 ; 3. The Age,
196.
SECTION 2. CLASSIFICATION OF STRATIFIED BOCKS, 197 ; 1. Order of Superposition,
198 ; 2. Lithological Character, 198 ; 3. Comparison of Fossils, 199 ; Manner
of constructing a Geological Chronology, 200.
CHAPTER III.
UNSTRATIFIED OR IGNEOUS ROCKS 202-212
Characteristics, 202 ; Origin, 202 ; Mode of Occurrence, 202 ; Extent on the Sur-
face, 203 ; Classification of Igneous Rocks, 203. 1. GRANITIC ROCKS, 203 ; Chem-
ical Composition and Kinds, 204 ; Mode of Occurrence, 204. 2. TRAPPEAN OR
FISSURE-ERUPTION ROCKS, 205 ; General Characteristics, 205 ; Varieties, 205 ;
Mode of Occurrence, 206 ; Effect of Dikes on the Intersected Strata, 207 ; Age
how determined, 208. 3. VOLCANIC ROCKS. Characteristics, 208 ; Varieties,
208. Of Certain Structures found in many Eruptive Rocks. Columnar Struct-
ure, 209 ; Direction of the Columns, 210 ; Cause of Columnar Structure, 210 ;
Volcanic Conglomerate and Breccia, 210; Amygdaloid, 211. Other Nodes of
Classification of Igneous Bocks, 211.
CHAPTER IV.
METAMORPHIC ROCKS 213-219
Origin, 213 ; Position, 213 ; Extent on the Earth-Surface, 213 ; Principal Kinds,
214. Theory of Metamorphism, 215 ; Water, 215 ; Alkali, 216 ; Pressure, 216 ;
Application, 216 ; Crushing, 216 ; Explanation of Associated Phenomena, 217.
Origin of Granite, 217.
CHAPTER V.
STRUCTURE COMMON TO ALL ROCKS 220-260
SECTION 1. JOINTS AND FISSURES. Joints, 220. Fissures, or Fractures, 221 ; Cause,
221 ; Faults, 222 ; Law of Slip, 224.
SECTION 2. MINERAL VEINS. Kinds, 225 ; Characteristics, 226 ; Irregularities, 226 ;
Metalliferous Veins, 227 ; Contents, 227 ; Ribboned Structure, 228 ; Age, 229 ;
Surface-Changes, 230 ; Cupriferous Veins, 230 ; Plumbiferous Veins, 231 ; Au-
riferous Quartz-Veins, 231 ; Placer-Mines, 232. Some Important Lazes affecting
the. Occurrence and the Richness of Metalliferous Veins, 232. Theory of Metal-
liferous Veins, 234 ; Outline of the most Probable Theory, 235 ; Vein-Stuffs, 235 ;
Metallic Ores, 236 ; Auriferous Veins of California, 237 ; Nuggets, 239 ; Illustra-
tions of the Law of Circulation, 239.
SECTION 3. MOUNTAIN-CHAINS: THEIR STRUCTURE AND ORIGIN, 240. Mountain-
Origin, 240. General Form, and how produced, 240. Mountain-Structure, 241 ;
Rate of Mountain-Formation, 244; Thickness of Mountain-Sediments, 244;
Foldings and Metamorphism, 245. Mountain-Sculpture, 245 ; Resulting Forms,
246 ; The Age of Mountain-Chains, 251. Theory of the Origin of Mountain-
Chains, 252 ; 1. Thick Sediments of Mountain-Chains, 254 ; Appalachian Chain,
254 ; Sierras, 256 ; Coast Range, 256 ; Alps, 256 ; 2. Position of Mountain-
Chains along the Borders of Continents, 256 ; 3. Parallel Ranges, 257 ; 4. Meta-
morphism of Mountain-Chains, 257 ; 5. Fissures and Slips, and Earthquakes,
258 ; 6. Fissure-Eruptions, 258 ; 7. Volcanoes, 258.
CHAPTER VI.
DENUDATION, OR GENERAL EROSION 260-265
Agents of Denudation, 260 ; Amount of Denudation, 261 ; Average Erosion, 263 ;
Estimate of Geological Times, 264.
CONTENTS. x i
PART III.
HISTORICAL GEOLOGY; OR, THE HISTORY OF THE EVOLUTION OF
EARTH-STRUCTURE AND OF THE ORGANIC KINGDOM.
CHAPTER I.
PAGE
GENERAL PKINCIPLES 266-271
Great Divisions and Subdivisions of Time-Eras, 268 ; Ages, 269 ; Subdivisions,
270 ; Order of Discussion, 270 ; Prehistoric Eras, 271.
CHAPTER II.
LAUREXTIAX SYSTEM OF ROCKS AND AECH^AX ERA .... 272-276
Rocks, 273 ; Area in North America, 274 ; Physical Geography of Archaean Times,
274 ; Time represented, 274 ; Evidences of Life, 274.
CHAPTER III.
PRIMARY OR PALEOZOIC SYSTEM OF ROCKS AND PALEOZOIC ERA . . 276-404
General Description, 276 ; Eocks Thickness, etc., 276; Area in the United States,
277 ; Physical Geography of the American Continent, 279 ; Subdivisions, 280 ;
The Interval, 230.
SECTION 1. SILURIAN SYSTEM : AGE OF INVERTEBRATES. The Eock System, 282 ;
Subdivisions, 282 ; Character of the Eocks, 282 ; Area in America, 282 ; Phys-
ical Geography, 283 ; Primordial Beach and its Fossils, 283 ; General Eemarks
on First Distinct Fauna, 287. General Life-System of the Silurian Age, 288.
Plants, 290. Animals. Protozoans, 290 ; Eadiates, Corals, 290 ; Hydrozoa, 293 ;
Polyzoa, 296 ; Echinoderms, 296 ; Mollusks, 801 ; General Description of a
Brachiopod, 301 ; Lamellibranchs, 304 ; Gasteropods, 305 ; Cephalopods, 305 ;
Articulates, 308 ; Crustacea, 309 ; General Description, 309 ; Affinities of Trilo-
bites, 312 ; Eurypterids, 313 ; Anticipations of the Next Age, 314.
SECTION 2. DEVONIAN SYSTEM AND AGE OF FISHES, 314 ; Area in United States, 315 ;
Physical Geography, 315 ; Subdivision into Periods, 315. Life-System of De-
vonian Age Plants, 315; General Eemarks on Devonian Land-Plants, 316.
Animals, 319 ; Eadiates, 319 ; Brachiopods, 320 ; Cephalopods, 320 ; Crustacea,
322 ; Insects, 322 ; Fishes, 322 ; Affinities of Devonian Fishes, 327 ; General
Characteristics of Devonian Fishes, 328 ; Bank of Devonian Fishes, 331 ; Bear-
ing of these Facts on the Question of Evolutiori, 332 ; Suddenness of Appear-
ance, 332.
SECTION 3. CARBONIFEROUS SYSTEM : AGE OF ACROGENS AND AMPHIBIANS. Eetro-
spect, 333 ; Subdivisions of the Carboniferous System and Age, 334. Car-
boniferous Proper Rock-System or Coal-Measures. The Name, 334 ; Thickness
of Strata, 335 ; Mode of Occurrence of Coal, 335 ; Plication and Denudation,
336 ; Faults, 337 ; Thickness of Seams, 338 ; Number and Aggregate Thickness,
338 ; Coal Areas of the United States, 338 ; Extra-Carboniferous Coal, 339 ;
Coal, Areas of Different Countries compared, 339 ; Eelative Production of Coal,
340. Origin of Coal and of its Varieties, 340 ; Varieties of Coal, 341 ; Varieties
depending upon Purity, 341 ; Varieties of Coal depending on the Degree of Bitu-
minization, 342 ; Varieties depending upon the Proportion of Fixed and Vola-
tile Matter, 342 ; Origin of these Varieties, 343 ; In Contact with Air, 344 ; Out
of Contact with Air, 344 ; Metamorphic Coal, 345. Plants of the Coal their
Structure and Affinities, 346 ; Where found, 347 ; Principal Orders, 347 ; 1. Con-
ifers, 347 ; Affinities of Carboniferous Conifers, 349 ; 2. Ferns, 349 ; 3. Lepido-
dendrids, 355 ; 4. Sigillarids, 358 ; 5. Calamites, 361 ; General Conclusion, 362.
xii CONTENTS.
PAGE
Theory of the Accumulation of Coal, 363 ; Presence of Water, 363 ; Application
of the Theory to the American Coal-Fields : a. Appalachian Coal-Field, 366 ; b.
Western Coal-Fields, 367 ; Appalachian Revolution, 367. Estimate of Time,
367 ; 1. From Aggregate Amount of Coal, 367 ; 2. From Amount of Sediment,
368. Physical Geography and Climate of the Coal Period. Physical Geog-
raphy, 369 ; Climate, 369 ; Cause of the Climate, 370. Iron- Ore of the Coal-
Measures, 373 ; Mode of Occurrence, 373 ; Kinds of Ore, 373 ; Theory of the Ac-
cumulation of the Iron-Ore of the Coal-Measures, 374. Bitumen and Petro-
leum, 376 ; Geological Eolations, 376 ; Oil-Formations, 377 ; Principal Oil-
Horizons of the United States, 377 ; Laws of Interior Distribution, 377 ; Kinds
of Rocks which bear Petroleum, 378. Origin of Petroleum and Bitumen, 379 ;
Origin of Varieties, 380 ; Area of Oil-bearing Strata in the Eastern United
States, 380. Fauna of the Carboniferous Age, 381 ; Vertebrates (Fishes), 388 ;
Reptiles Amphibians, 390; 1. Reptilian Footprints, 390; 2. Dendrerpeton,
391 ; 3. Archegosaurus, 393 ; 4. Eosaurus, 393 ; Some General Observations
on the Earliest Reptiles, 395. Some General Observations on the Whole Palaeo-
zoic, 396 ; Physical Changes, 396 ; Chemical Changes, 396 ; Progressive Change
in Organisms, 397 ; General Comparison of the Fauna of Paleozoic with that
of Neozoic Times, 397. General Picture of Palceozoic Times, 398. Transmis-
sion from the Palceozoic to the Mesozoic Permian Period. The Permian a Tran-
sition Period, 400.
CHAPTER IV.
MESOZOIO ERA AGE OF EEPTII.ES 404-475
General Characteristics, 404 ; Subdivisions, 404.
SECTION 1. TEIASSIC PERIOD, 405 ; Subdivisions, 405 ; Animals, 406 ; Fishes, 407 ;
Reptiles, 409 ; Birds, 411 ; Mammals, 411. Origin of Rock-Salt, 412 ; Age of
Rock-Salt, 412 ; Mode of Occurrence, 412 ; Theory of Accumulation, 413.
SECTION 2. JURASSIC PERIOD, 414 ; Origin of Oolitic Limestones, 415 ; Jurassic Coal-
Measures, 415 ; Dirt-BedsFossil Forest-Grounds, 415. Plants, 417. Animals,
419; Corals, 419 ; Brachiopods, 419 ; Lamellibranchs, 419 ; Cephalopods, 419';
Ammonites, 421 ; Belemnites, 423 ; Crustacea, 425 ; Insects, 425 ; Fishes, 425 ;
Reptiles, 428 ; Birds, 436 ; Mammals, 438 ; Affinities of the First Mammals, 438.
SECTION 3. JURA-TRIAS IN AMERICA, 439 ; Distribution of Strata, 439. Life-System,
440 ; Connecticut River Valley Sandstone the Strata, 440 ; The Record, 441 ;
Reptilian Tracks, 442 ; Bird-Tracks, 443 ; Richmond and North Carolina Coal-
Fields, 445 ; Other Patches, 447 ; Interior Plains and Pacific Slope, 447 ; Phys-
ical Geography of the American Continent during the Jura-Trias Period, 449 ;
Disturbances which closed the Period, 450.
SECTION 4. CRETACEOUS PERIOD, 450 ; Rock-SystemArea in America, 451 ; Phys-
ical Geography in America, 451 ; Rocks, 452 ; Chalk, 452 ; Origin of Chalk,
453 ; Extent of Chalk Seas of Cretaceous Times in Europe, 454 ; Cretaceous
Coal, 455 ; Subdivisions of the Cretaceous, 456. Life-System : Plants, 456.
Animals. Protozoa, 459 ; Echinoderms, 460 ; Mollusks, 461 ; Vertebrates
Fishes, 465 ; Reptiles, 467 ; Birds, 470 ; Mammals, 472. Continuity of the
Chalk, 473. General Observations on the Mesozoic, 474. Disturbance which
closed the Mesozoic, 475.
CHAPTER V.
CENOZOIO ERA AGE OF MAMMALS 475-557
General Characteristics of the Cenozoic Era, 476 ; Divisions, 476.
SECTION 1. TERTIARY PERIOD. Subdivisions, 477 ; Rock-SystemArea in the United
States, 477 ; Physical Geography, 478 ; Character of the Rocks, 480 ; Coal, 480 ;
Life-System. General Remarks, 480. Plants, 481 ; Diatoms, 483 ; Origin of In-
fusorial Earths, 483. Animals, 485 ; Insects, 488 ; Fishes, 490 ; Reptiles, 492 ;
CONTENTS. x iii
PAGE
Birds, 494 ; Mammals General Remarks, 495 ; 1. Eocene Basin of Paris, 496 ;
2. Siwalik Hills, India Miocene, 498 ; American Localities 3. Marine Eocene
of Alabama, 500 ; 4. Green-River Basin "Wahsatch Beds Lower Eocene, 501 ;
5. Green-River Basin Bridger Beds Middle Eocene, 502 ; 6. Mauvaises Terres
of Nebraska White River Basin Miocene, 505 ; 7. Mauvaises Terres Nio-
brara Basin Pliocene, 506 ; Some General Observations on the Tertiary Mam-
malian Fauna, 506 ; Genesis of the Horse, 509. General Observations on the
Tertiary Period, 511.
SECTION 2. QUATERNARY PERIOD. Characteristics, 513 ; Subdivisions, 513. Qua-
ternary Period in Eastern North America I. Glacial Epoch. The Materials
Drift, 514 ; The Bowlders, 515 ; Surface-Rock underlying Drift, 516 ; Extent,
516; Marine Deposits, 517. Theory of the Origin of the Drift, 517; State-
ment of the most Probable View, 518 ; Objections answered, 518 ; Probable
Condition during Glacial Times in America, 519. //. Champlain Epoch, 520 ;
Evidences of Subsidence, 521 ; Sea-Margins, 521 ; Flooded Lakes, 521 ; River
Terraces and Old Flood-Plain Deposits, 522. ///. Terrace Epoch, 524 ; Evi-
dencesSea, 524 ; Lakes, 524 ; Rivers, 524 ; History of the Mississippi River,
525. Quaternary Period on the Western Side of the Continent, 526 ; Glaciers,
526 ; Lake-Margins, 527 ; Rivers, 529 ; Seas, 530. The Quaternary Period in Eu-
rope, 530 ; 1. Epoch of Elevation First Glacial Epoch, 531 ; 2. Epoch of Sub-
mergence Champlain, 532 ; 3. Epoch of Reelevation Second Glacial Epoch
Terrace Epoch, 534 ; 4. Modern Epoch, 534. Home General Results of Glacial
Erosion. 1. Fiords, 534; 2. Glacial Lakes, 535. Life of the Quaternary Period.
Plants and Invertebrates, 535 ; Mammals, 536; 1. Bone-Caverns, 536; Origin
of Cave Bone-Rubbish, 538 ; Origin of Bone-Caverns, 539 ; 2. Beaches and Ter-
races, 539 ; 3. Marshes and Bogs, 539 ; 4. Frozen Soils and Ice Cliffs, 539 ; Qua-
ternary Mammalian Fauna of England, 541. Mammalian fauna in North
America, 542 ; Bone-Caves, 542 ; Marshes and Bogs, 542 ; River-Gravels, 544 ;
Quaternary in South America, 544 ; Australia, 547 ; Geographical Fauna of
Quaternary Times, 547. Some General Observations on the Whole Quaternary.
1. Cause of the Climate, 548 ; 2. Time involved in the Quaternary Period,
650 ; 3. The Quaternary a Period of Revolution a Transition between the Ceno-
zoic and the Modem Eras, 550 ; 4. Drift in Relation to Gold, 554 ; Age of the
River-Gravels, 556.
CHAPTER VI.
PsTcnozoic EBA AGE OF MAX RECENT EPOCH .... 557-570
Characteristics, 557 ; Distinctness of this Era, 557 ; The Change still in Progress
Examples of Recently-Extinct Species, 558. I. ANTIQUITY OF MAN, 560. Pri-
meval Man in Europe. Supposed Miocene Man Evidence unreliable, 561 ;
Supposed Pliocene Man, 562 ; Quaternary Man Mammoth Age, 562 ; a. In
River-Terraces, 562; b. Bone-Caves Engis Skull, 563; Neanderthal Skull,
563 ; Mentone Skeleton, 564 ; Reindeer Age or Later Palaeolithic, 564 ; Auri-
gnac Cave, 5b5 ; Perigord Caves, 565 ; Conclusions, 566. Neolithic Man Refuse-
Heaps Shell- Mounds Kitchen-Middens, 506 ; Transition to the Bronze Age
Lake Dwellings, 566. Primeval Man in America, 567 ; Supposed Pliocene Man,
567 ; Quaternary Man, 567 ; Quaternary Man in Other Countries, 568 ; Time
since Man appeared, 569. II. CHAEACTER OF PBIMEVAL MAN, 570.
INTKODUCTOKY.
DEFINITION OF GEOLOGY, AND OF ITS DEPARTMENTS.
GEOLOGY is the physical history of the earth and its inhabitants,
as recorded in its structure. It includes an account of the changes
through which they have passed, the laws of these changes, and their
causes. In a word, it is the history of the evolution of the earth and
its inhabitants.
The fundamental idea of geology, as well as its principal sub-
divisions and its objects, may be most clearly brought out by compar-
ing it with organic science. We may study an organism from three
distinct points of view : 1. We may study its general form, the parts
of which it is composed, and its minute internal structure. This is
anatomy. It is best studied in the dead body. 2. We may study the
living body in action, the function of each organ, the circulation of the
fluids, and the manner in which all contribute to the complex phenom-
ena of life. This is physiology. 3. We may study the living and
growing body, by watching the process of development from the egg
to the adult state, and striving to determine its laws. This is embry-
ology.
So, looking upon the earth as an organic unit, we may study its
form, the rocks and minerals of which it is composed, and the manner
in which these are arranged ; in other words, its external form and in-
ternal structure. This is the anatomy of the earth, and is called struct-
ural geology. Or, we may study the earth under the action of physical
and chemical forces, the action and reaction of land and water, of earth
and air, and the effects of these upon the form and structure. This is
the physiology of the earth, and is called dynamical geology. Finally,
we may study the earth in the progress of its development, from the
earliest chaotic condition to its present condition, as the abode of man,
and attempt to determine the laws of this development. This is the
embryology of the earth, or historical geology.
1
2 INTRODUCTORY.
Principal Departments. The science of geology, therefore, nat-
urally divides itself into three parts, viz.: 1. Structural geology, or
geognosy. 2. Dynamical geology, or physical and chemical geology.
3. Historical geology, or the history of the earth.
But there are two important points of difference between geology
and organic science. The central department of organic science is
physiology, and both anatomy and embryology are chiefly studied to
throw light on this. But the central department of geology, to which
the others are subservient, is history. Again : in case of organisms
especiallv animal organisms the nature of the changes producing
development is such that the record of each previous condition is suc-
cessively and entirely obliterated ; so that the science of embryology is
possible only by direct observation of each successive stage. If this
were true also of the earth, a history of the earth would, of course, be
impossible. But, fortunately, we find that each previous condition of
the earth has left its record indelibly impressed on its structure.
Order of Treatment. The prime object of geology is to determine
the history of the earth, and of the organisms which have successively
inhabited its surface. The structure and constitution of the earth are
the materials of this history, and the physical and chemical changes
now going on around us are the means of interpreting this structure
and constitution. Evidently, therefore, the only logical order of pre-
senting the facts of geology is to study, first, the causes, physical and
chemical, now in operation and producing structure ; then the structure
and constitution of the earth which, from the beginning, have been
produced by similar causes; and, lastly, from the two preceding to un-
fold the history of the earth.
Geology may be defined, therefore, as the history of the earth and
its inhabitants, as revealed in its structure, and as interpreted by
causes still in operation.
There is no other science which requires for its full comprehension
a general knowledge of so many other departments of science. A
knowledge of mathematics, physics, and chemistry, is required to under-
stand dynamical geology ; a knowledge of mineralogy and lithology is
required to understand structural geology ; and a knowledge of zoology
and botany is required to understand the affinities of the animals and
plants which have successively inhabited the earth, and the laws which
have controlled their distribution in time.
PAET I.
DYNAMICAL GEOLOGY.
THE agencies now in operation, modifying the structure of the sur-
face of the earth, may be classed under four heads, viz., atmospheric
agencies, aqueous agencies, igneous agencies, and organic agencies.
These agencies have operated from the beginning, and are still in
operation. We study their operation now, in order that we may un-
derstand their effects in previous epochs of the earth's history i. e., the
structure of the earth.
While all geologists agree that the nature of the agencies which
have operated in modifying the earth's surface has remained the same
from the beginning, they differ in their views as to the energy of their
operation in different periods. Some believe that their energy has been
much the same throughout the whole history of the earth, while others
believe that many facts in the structure of the earth require much
greater operative energy than now exists. We will attempt to show
hereafter that neither of these extreme opinions is probably true, but
that some of these agencies have been decreasing, while others have
been increasing, with the progress of time. It is the constant change
of balance between these which determines the development of the
earth.
CHAPTER I.
ATMOSPHERIC AGENCIES.
THE general effect of atmospheric agencies is the disintegration of
rocks and the formation of soils. The atmosphere is composed of nitro-
gen and oxygen, with small quantities of watery vapor and of carbonic
acid There are but few rocks which are not gradually disintegrated
4 ATMOSPHERIC AGENCIES.
under the constant chemical action of the atmosphere. The chemical
agents of these changes are oxygen, carbonic acid, and watery vapor,
the nitrogen being inert. To these must be added, where vegeta-
tion is present, the products of vegetable decomposition, especially
ammonia.
Atmospheric agencies graduate so insensibly into aqueous agencies
that it is difficult to define their limits. Water, holding in solution
carbonic acid and oxygen, may exist as invisible vapor; or, partially
condensed, as fogs ; or, completely condensed, as rain falling upon and
percolating the earth. In all these forms its chemical action is the
same, and, therefore, cannot be separated and treated under different
classes : and yet the same rain runs off from and erodes the surface of
the earth, comes out from the strata and forms springs, rivers, etc., all
of which naturally fall under aqueous agencies. We shall, therefore,
treat of the chemical effects of atmospheric water in the disintegration
of rocks, and the formation of soils, under the head of atmospheric
agencies ; and the mechanical effects of the same, in eroding the surface
and carrying away the soil thus formed, under the head of aqueous
agencies. In moist climates vegetation clothes and protects soil from
erosion, but favors decomposition of rocks and formation of soil.
Atmospheric agencies are obscure in their operation, and, therefore,
imperfectly understood. Yet these are not less important than aqueous
agencies, since they are the necessary condition of the operation of the
latter. Unless rocks were first disintegrated into soils by the action
of the atmosphere, they would not be carried away and deposited as
sediments by the agency of water. These two agencies are, therefore,
of equal power and importance in geology, but they differ very much in
the conspicuousness of their effects. Atmospheric agencies act almost
equally at all times and at all places, and their effects, at any one place
or time, are almost imperceptible. Aqueous agencies, on the contra-
ry, in their operation are occasional, and to a great extent local, and
their effects are, therefore, more striking and easily studied. Never-
theless, the aggregate effects of the former are equal to those of the
latter.
Soils. All soils (with the trifling exception of the thin stratum of
vegetable mould which covers the ground in certain localities) are
formed from the disintegration of rocks. Sometimes the soil is formed
in situ, and, therefore, rests on its parent rock. Sometimes it is re-
moved as fast as formed, and deposited at a distance more or less remote
from the parent rock. The evidence of this origin of soils is clearest
when the soil is formed in situ. In such cases it is often easy to trace
every stage of gradation between perfect rock and perfect soil. This
is well seen in railroad cuttings, and in wells in the gneissic or so-called
primary region of our southern Atlantic slope. On examining such a
ATMOSPHERIC AGENCIES.
section, we find near the surface perfect soil, generally red clay ; beneath
this we find the same material, but lighter colored, coarser, and more
distinctly stratified; beneath this, but shading into it by imperceptible
gradations, we have what seems to be stratified rock, but it crumbles
into coarse dust in the hand ; this passes by imperceptible gradations
into rotten rock, and finally into perfect rock. There can be no doubt
that these are all different stages of a gradual decomposition. But closer
observation will make the proof still clearer. In gneissic and other
metamorphic regions it is not uncommon to find the rock traversed, in
various directions, by veins of quartz OT flint. Now, in sections such as
those mentioned above, it is common to find such a flint-vein running
through the rock and upward through the superincumbent soil, until it
emerges on the surface. In the slow decomposition of the rock into
soil, the flint-vein has remained unchanged, because flint is not affected
by atmospheric agencies. Chemical analysis, also, always shows an
evident relation between the soil and the subjacent or country rock,
except in cases in which the soil has been brought from a considerable
distance.
The depth to which soil will thus accumulate depends partly on the
nature of the rock and the rapidity of decomposition, partly on the slope
of the ground, and partly
on climate. When the
slope is considerable, as
at d (Fig. 1), the rocks are
bare, not because no soil
is formed, but because it is
removed as fast as formed,
while at a the soil is deep,
being formed partly by de-
composition of rock in situ, and partly of soil brought down from d.
Wherever perfect soil is found resting on sound rock, the soil has
been shifted.
If rocks were solid and impervious to water, this process would be
almost inconceivably slow ; but we find that all rocks, for reasons to be
discussed hereafter, are broken by fissures into irregular prismatic blocks,
so that a perpendicular cliff of rock usually presents the appearance of
rude gigantic masonry. These fissures, or joints, increase immensely
the surface exposed to the action of atmospheric water. Again, on
closer inspection, we find even the most solid parts of rocks, i. e., the
blocks themselves, penetrated with capillary fissures which allow water
to reach every part. Thus the rock is decomposed, or becomes rotten,
to a great depth below the surface. But, while the rock is gradually
changed into soil, the soil is also slowly carried away by agencies to be
hereafter considered; and these changes, taking place more rapidly in
FIG. 1. Ideal Section, showing Eock passing into Soil.
Q ATMOSPHERIC AGENCIES.
some places than in others, give rise to a great variety of forms, some
of which are represented in the accompanying figure (Fig. 2).
In the process of disintegration the original blocks lose their pris-
matic form, and become more or
less rounded, and are then called tt
bowlders of disintegration. These
may lie on the. surface (Fig. 2),
or may be buried in the soil (Fig.
3). When of great size and very
solid, so as to resist decomposition
to a greater extent than the surrounding rocks, they often form huge
rocMng-stones (Fig. 4). These
must not be confounded with
true bowlders and rocking-
stones which are brought from
FIG. 8.
a distance, by agencies which
we will discuss hereafter, and
which are, therefore, entirely
different from the subjacent or country rock.
General Explanation. The process of rock-disintegration may be
explained, in a general way, as follows : Almost all rocks are composed
partly of insoluble materials, and partly of materials which are slowly
dissolved by atmospheric water. In the process of time, therefore,
these latter are dissolved out, and the rock crumbles into an insoluble
dust, more or less saturated with water holding in solution the soluble
ingredients. To illustrate : common hardened mortar may be regarded
as artificial stone ; it consists of carbonate of lime and sand ; the car-
bonate of lime is soluble in water containing carbonic acid (atmospheric
water), while the sand is quite insoluble. If, therefore, such mortar be
exposed to the air, it eventually crumbles into sand, moistened with
water containing lime in solution. Again, to take a case which often
occurs in Nature, it is not uncommon to find rock through which iron
pyrites, FeS 2 , is abundantly disseminated. This mineral is insoluble ;
but under the influence of water containing oxygen (atmospheric water)
it is slowly oxidized and changed into sulphate of iron, or copperas,
which, being soluble, is washed out, and the rock crumbles into an
insoluble dust or soil, saturated with a solution of the iron salt. We
ATMOSPHERIC AGENCIES. 7
have given these only as illustrative examples. We now proceed to
give examples of the principal kinds of rocks, and of the soils formed
by their disintegration.
Granite, Gneiss, Volcanic Rocks, etc. Granite and gneiss are
mainly composed of three minerals, quartz, feldspar, and mica, aggre-
gated together into a coherent mass. Quartz is unchangeable and in-
soluble in atmospheric water. Mica is also very slowly affected. Feld-
spar is, therefore, the decomposable ingredient. But feldspar is, itself,
a complex substance, partly soluble and partly insoluble. It is essen-
tially a silicate of alumina, united with a silicate of potash or soda,
although it often contains also small quantities of iron and lime. Now,
while the silicate of alumina is perfectly insoluble, the other silicates
are slowly dissolved by atmospheric water, with the formation of car-
bonates, and the silicate of alumina is left as kaolin or clay. But, since
we may regard the original rock as made up of quartz and mica, bound
together by a cement of feldspar, the disintegration of the latter causes
the whole rock to lose its coherence, and the final result of the process
is a mass of clay containing grains of sand and scales of mica, and
moistened with water containing a potash salt. If there be any iron
in the feldspar, or if there be other decomposable ingredients in the
rock containing iron, such, for example, as hornblende, the clay will be
red. This is precisely the nature of the soil in all our primary regions.
Volcanic rocks decompose into clay soils often, though not always,
deeply colored with iron.
Limestone. Pure limestone may be regarded as composed of gran-
ules of carbonate of lime, cohering by a cement of the same. The dis-
solving of the cement by atmospheric water forms a lime-soil, moistened
with a solution of carbonate of lime (hard water). Impure limestone
is a carbonate of lime, more or less mixed with sand or clay ; by disin-
tegration it forms, therefore, a marly soil.
Sandstones. Sandstones consist of grains of sand cemented togeth-
er by carbonate of lime or peroxide of iron. % Where peroxide of iron is
the cementing substance, the rock is almost indestructible, since this
substance is not changed by atmospheric water: hence the great value
of red sandstone as a building-material. But when carbonate of lime
is the cementing material, this substance, being soluble in atmospheric
water, is easily washed out, and the rock rapidly disintegrates into a
sandy soil.
Slate. In a similar manner slate-rocks disintegrate into a pure
clay soil by the solution of their cementing material, which is often a
small quantity of carbonate of lime.
There can be no doubt that all soils are formed in the manner above
indicated. We have given examples of soils formed in situ, but, as
soils are often shifted, they are usually composed of a mixture formed
8 ATMOSPHERIC AGENCIES.
by the disintegration of several kinds of rock. In some cases the
soil has been formed in situ during the present geological epoch, and
the process is still going on before our eyes. Such are the soils of the
hills of the up-country or yrimary region of our Southern Atlantic
States. 1 Sometimes the soil formed in the same way has been shifted
to a greater or less distance. Such are the soils of our valleys and
river-bottoms. In still other cases the soil has been formed by the pro-
cess already described, and transported during some previous geologi-
cal epoch and not reconsolidated. Such are many of the soils of the
Southern low-country or tertiary region.
MECHANICAL AGENCIES OF THE ATMOSPHERE.
Frost. Water, penetrating rocks and freezing, breaks off huge frag-
ments : these by a similar process are again broken and rebroken until
the rock is reduced to dust. These effects are most conspicuous in cold
climates and in mountain-regions.
In cold climates huge piles of bowl-
ders and earth are always seen at the
* base of steep cliffs (Fig. 5). Such
of the
cliff above, is called a talus. In
mountainous regions frost is a pow-
erful agent in disintegrating the
rocks, and in determining the out-
lines of mountain - peaks. This is
well seen in the Alps and in the Sierras.
Winds. The effect of winds is seen in the phenomenon of shifting
sands. At Cape Cod, for instance, the sands thrown ashore by the sea
are driven by the winds inland, and thus advance upon the cultivated
lands, burying them and destroying their fertility. The sands from
the beach on the Pacific coast near San Francisco are driven inland
in a similar manner, and are now regularly encroaching upon the better
soil. Large areas of the fertile alluvial soil of Egypt, together with
their cities and monuments, have been buried by the encroachments of
the Sahara Desert. In Brittany and in other parts of France villages
which existed during the middle ages have been overwhelmed by drift-
ing sands. The same phenomena are observed on various parts of the
coast of Holland and England. The rate of advance has been measured
in some instances. Thus on the coast of Suffolk it is said to advance
at the rate of about five miles a century; at Cape Finisterre, according
; to Ansted, at the rate of thirty-two miles per century, or 560 yards per
annum. The Downs of England and Scotland are such barrens of drifting
sand. Hills may be formed in this manner thirty to forty feet in height.
1 In the Northern States, in the region of the Drift, nearly all the soil has been shifted.
EROSION OF KAIN AND RIVERS.
CHAPTER IL
AQUEOUS AGENCIES.
THE agencies of water are either mechanical or chemical. The
mechanical agencies of water may be treated under the threefold aspect
of erosion, transportation, and sedimentary deposit. We will consider
them under the heads of Rivers, Oceans, and Ice. Under chemical
agencies we will consider the phenomena of chemical deposits in
Springs and Lakes.
Aqueous Agencies.
Mechanical.
I Chemical.
Rivers Erosion, Transportation,
Ocean
Ice " "
Springs Deposit in.
Lakes... " "
SECTION 1. RIVEKS.
Under the head of river agencies we include all the effects of" cir-
culating meteoric water from the time it falls as rain until it reaches
the ocean : i. e., all the effects of Rain and Rivers.
Water, in the form of vapor, fogs, or rain, percolating through the
earth, slowly disintegrates the hardest rocks. Much of these percolat-
ing waters, after accomplishing the work of soil-making, already treated
in the preceding chapter, reappears on the surface in the form of springs,
and gives rise to streamlets. A large portion of rain-water, however,
never soaks into the earth, but runs off the surface, forming rills, which
by erosion produce furrows. The uniting rills form rivulets, which exca-
vate gullies. The rivulets, uniting with one another and with the
streamlets issuing from springs, form torrents, which in their course
excavate ravines, gorges, and canons. The vmiting torrents, finally issu-
ing from their mountain-home upon the plains, form great rivers, which
deposit their freight partly in their course and partly in the sea. Such
is a condensed history of rain-water on its way to the ocean whence it
came. Our object is to study this history in more detail.
Erosion of Rain and Rivers.
The whole amount of water falling on any land-surface may be
divided into three parts : 1. That which rushes immediately off the
surface, and causes the floods of the rivers, especially the smaller
streams; 2. That which sinks into the earth, and, after doing its
chemical work of soil-making, reappears as springs, and forms the regu-
10 AQUEOUS AGENCIES.
lar supply of streams and rivers ; and, 3. That which reaches the sea
wholly by subterranean channels. Of these, the first two are the grand
erosive agents, and these only concern us at present. Of these, the for-
mer predominate in proportion as the land-surface is bare ; the latter in
proportion as it is covered with vegetation.
Hydrographical Basin. An hydrographical basin of a river, lake,
or gulf, is the whole area of land the rainfall of which drains into that
river, lake, or gulf. Thus the hydrographical basin of the Mississippi
River is the whole area drained by that river. It is bounded on the
east and west by the Alleghany and Rocky Mountains, and on the
north by a low ridge running from Lake Superior westward. The
whole area of continents, with the exception of rainless deserts, may be
'regarded as made up of hydrographical basins. The ridge which sepa-
rates contiguous basins is called a water-shed. It is evident that every
portion of the land, with the exception of the rainless tracts already
mentioned, is subject to the erosive agency of water, and is being worn
away and carried into the sea. There have been various attempts to
estimate the rate of this general erosion.
Rate of Erosion of Continents. This is usually estimated as follows :
Some great river, such as the Mississippi, is taken as the subject of
experiment. By accurate measurement during every portion of the
year, the average amount of water discharged into the sea per second,
per hour, per day, per year, is determined. This is a matter of no small
difficulty, as it involves the previous determination of the average cross-
section of the river and the average velocity of the current. The aver-
age cross-section X average velocity = the average discharge per sec-
ond : from which may be easily obtained the annual discharge. Next,
by experiment during every month of the year, the average quantity of
mud contained in a given quantity of water is also determined. By an
easy calculation this gives us the annual discharge of mud, or the whole
quantity of insoluble matter removed from the hydrographical basin in
one year. This amount, divided by the area of the river-basin, will give
the average thickness of the layer of insoluble matter removed from the
basin in one year. To this must be added the soluble matters, which
are about $ as much as the insoluble.
Estimates of this kind have been made for two great rivers, viz.,
the Ganges and the Mississippi. The whole amount of sediment
annually carried to the sea by the Ganges has been estimated as
6,368,000,000 cubic feet. This amount, spread over the whole basin of
the Ganges (400,000 square miles), would make a layer T - 7 1 - gT of a foot
thick. The Ganges, therefore, erodes its basin one foot in 1,751 years. 1
The area of the Mississippi Basin is 1,244,000 square miles. The
annual discharge of sediment, according to the recent and accurate
1 Philosophical Magazine, vol. v., p. 261.
EROSION OF RAIN AND RIVERS. u
experiments of Humphrey and Abbot, is 7,471,411,200 cubic feet, a
mass sufficient to cover an area of one square mile, 268 feet deep. 1 This
spread over the whole basin would cover it 4-5^5- of a foot. Therefore,
this river removes from its basin a thickness of one foot in 4,640 years.
The cause of the great difference in favor of the Ganges is, that this
river is situated in a country subject to very great annual fall of water,
the whole of which falls during a rainy season of six months. The rains
are therefore very heavy, and the floods and consequent erosion pro-
portionately great. The erosive power of this river is still further in-
creased by the great slope of the basin, as it takes its rise in the Him-
alaya, the highest mountains in the world.
Now, since continents may be regarded as made up of hydrographi-
cal basins, the average rate of their erosion may be determined either by
making similar experiments on all the rivers of the world, or, since this
is impracticable, by taking some river as an average. We believe the
Mississippi is much nearer an average river than the Ganges. It can
hardly be less than the average, for a considerable portion of the earth
as rainless deserts is not subject to any erosion. It is probable,
therefore, that the whole surface of continents is eroded at a rate not
exceeding one foot in 4,640 years. For convenience, we will call it one
foot in 5,000 years. We will use this estimate when we come to speak
of the actual erosion which has occurred in geological times.
Law of Variation of Erosive Power. The erosive power of water, or
itspoicer of overcoming cohesion, varies as the square of the velocity
of the current (p a v 2 ). The velocity depends upon the slope of the
bed, the depth of the water, and many other circumstances, so numerous
and complicated that it has been found impossible to reduce it to any
simple law. The angle of slope, however, is evidently the most im-
portant circumstance which controls velocity, and therefore erosive
power. In the upper portions of great rivers, like the Mississippi, the
erosion is very great ; while in the plains near the mouth there may be
no erosion, but, on the contrary, sedimentary deposit. The high lands
therefore, especially mountain-chains, are the great theatres of erosion.
The general effect of erosion is leveling. If unopposed, the final effect
would be to cut down all lands to the level of the sea, at an average
rate of about one foot in 5,000 years. But the immediate local
effect is to increase the inequalities of land-surface, deepening the fur-
rows, gullies, and gorges, and increasing the intervening ridges and
peaks. The effect, therefore, is like that of a graver's tool, constantly
cutting at every elevation, but making trenches at every stroke.
" Thus land-surfaces everywhere, especially in mountain-regions, are
cut away by a process of sculpturing, and the debris carried to the low-
lands and to the sea. The smaller lines and more delicate touches are
1 Humphrey and Abbot, "Report on Mississippi Riyer," pp. 148-150.
12 AQUEOUS AGENCIES.
due to rain, the deeper trenches or heavier chiselings to rivers proper.
The effects of the former are more universal and far greater in the
aggregate, but the effects of the latter are far more conspicuous. It is
only under certain conditions that rain-sculpture becomes conspicuous.
These conditions seem to be a bare soil and absence of frost. Beautiful
examples are found in the arid regions of Southern Utah.
We now proceed to discuss the more conspicuous effects of water
concentrated in river-channels.
EXAMPLES OF GREAT EROSION NOW GOING ON : WATERFALLS.
The erosive power of water is most easily studied in ravines, gorges,
canons, and especially in great waterfalls. One of the most interesting
of these is Niagara.
Niagara : General Description. The plateau on which stands
Lake Erie (P JV, Fig. 6) is elevated about 300 feet above that of
L.ERIE.
FIG- 6. Ideal Longitudinal Section through Niagara Elver from Lake Erie to Lake Ontario.
Lake Ontario, and is terminated abruptly by an escarpment about
300 feet high (P)- From this point a narrow gorge with nearly
perpendicular sides, and 200 to 300 feet deep, runs backward through
the higher or Erie plateau as far as the falls (^V). The Niagara
River runs out of Lake Erie and upon the Erie plateau as far as
the falls, then pitches 167 feet perpendicularly, and then runs in the
gorge for seven miles to Queenstown ( Q), where it emerges on the On-
tario plateau. Long observation has proved that the position of the
fall is not stationary, but slowly recedes at a rate which has been vari-
ously estimated from one to three feet per annum. The process of re-
cession has been carefully observed, and the reason why it maintains its
perpendicularity is very elear. The surface-rock of Erie plateau is a (
firm limestone (). Beneath this is a softer shale (5). This softer rock
is rapidly eroded by the force of the falling water, and leaves the harder
limestone projecting as table-rocks. From time to time these project-
ing tables are loosened and fall into the chasm below. This process is
facilitated by the joint structure spoken of on page 5.
Recession of the Falls. Now, there is every reason to believe that
the fall was originally situated at Queenstown, the river falling over
the escarpment at that place, and that it has worked its way backward
seven miles to its present position by the process we have just described.
These reasons are as follows: 1. The general configuration of the country
EROSION OF RAIN AND RIVERS. 13
as already described forcibly suggests such an explanation to the most
casual observer. 2. A closer examination confirms it by showing that the
gorge is truly a valley of erosion, since the strata on the two sides cor-
respond accurately (see Fig. 7). 3. As already seen, the falls have
receded in historic times at a rate, according to Mr. Lyell, of about one
foot a year. The portion of the gorge thus formed under our eyes does
not differ in any essential respect from other portions farther down the
stream. The evidence thus far is not perfectly conclusive that the gorge
was formed by the present river during the present geologic epoch, since
the gorge may have been eroded during a previous epoch, and the pres-
ent river found it, appropriated it as its channel, and continued to ex-
tend it. But (4.) certain stratified deposits have been found by Mr.
Lyell and others on the upper margin of the ravine, containing shells,
all of which are identical with the shells now living in Niagara River.
On the margins of all rivers we find stratified deposits of mud and sand
containing dead shell. The stratified deposits found by Mr. Lyell were
such mud-banks of the Niagara River before the falls had receded so
far, and therefore when the river still ran on the Erie plateau at this
point. This is well seen in the subjoined figure, representing an ideal
F IG . 7. Ideal Section across Chasm below the Falls.
cross-section of the gorge below the falls. The dotted lines represent
the former bed and level of the river ; a a represent the banks of strati-
fied mud left on the margin of the gorge, as the river eroded its bed
down to its present level.
Other Falls. The evidence is completed by examination of other
great falls. In almost all perpendicular falls we find a similar arrange-
ment of strata followed by similar results. The Falls of St. Anthony,
in the Mississippi River, are a very beautiful illustration. Here we find
a configuration of surface very similar to that in the neighborhood of
Niagara. Above the falls the Mississippi River runs on a plateau which
terminates abruptly at the mouth of Minnesota River by an escarpment
some fifty feet high. From this escarpment, backward through the
upper plateau, runs a gorge with perpendicular sides fifty feet high for
14; AQUEOUS AGENCIES.
ten miles to the foot of the falls. The river above the falls runs on a
hard, silurian limestone rock, only a few feet in thickness. Beneath
this is a white sandstone, so soft that it can be easily excavated with
the fingers. This sandstone forms the walls of the gorge as far as the
escarpment. The recession of the falls by the undermining and falling
of the limestone is even more evident than at Niagara. Tributaries
running into the Mississippi just below the falls are, of course, precipi-
tated over the margin of the gorge. Here, therefore, the same condi-
tions are repeated, and hence are formed subordinate gorges, headed by
perpendicular falls. Such are the falls and gorge of Little River (Min-
nehaha), which runs into the Mississippi about three miles above the
mouth of the Minnesota River.
Another admirable illustration of the conditions under which per-
pendicular falls recede is found in the falls of the numerous tributaries
of Columbia River where the great river breaks through the Cascade
Range. The Columbia River gorge is 2,500 to 3,000 feet deep. The
walls consist of columnar basalt underlaid near the water-level by a
softer conglomerate. Every tributary at this point emerges from a deep
gorge, headed two or three miles back by a perpendicular wall, over which
is precipitated the water of the tributary as a fall 200 to 300 feet high.
The falling water erodes the softer conglomerate, undermines the ver-
tical-columned basalt, which tumbles into the stream and is carried
away; and thus the fall has worked back in each case about two or three
miles to its present position. 1 All of this has taken place during the
present geological epoch. 3
The wonderful falls of the Yosemite Valley, of which there are six
in a radius of five miles, one of them 1,600 feet, three 600 to 700 feet,
and two over 400 feet high, seem to be an exception to the law given
above. Their perpendicularity seems to be the result of the compara-
tive recency of the evacuation of the valley by an ancient glacier, and
therefore the shortness of the time during which the rivers have been
falling, combined with the hardness of the granite rocks. The Yo-
semite gorge was not made by the present rivers.
Time necessary to excavate Niagara Gorge. All attempts to esti-
mate accurately the time consumed in excavating Niagara gorge must
be unreliable, since we do not yet know the circumstances which con-
trolled the rate of recession at different stages of its progress. Among
these circumstances, the most important are the volume of water, and
especially the hardness of the rocks, and the manner in which hard and
1 Gilbert has shown (American Journal, August, 1876) that comparative freedom
from detritus is another condition of the formation of perpendicular waterfalls. In mud-
dy rivers commencing inequalities are filled up by sediment, and waterfalls cannot be
formed.
a American Journal of Science and Art, 1874, vol. vii., pp. 167, 259.
EROSION OF RAIN AND RIVERS. 15
soft are superposed. The present position of the falls is apparently
favorable for rapid recession. Mr. Lyell thinks, from personal observa-
tion, that the average rate could not have been more than one foot per
annum, and probably much less. At this rate, it would require about
36,000 years. But, whether more or less than this amount, this period
must not be confounded with the age of the earth. In this part of
geology we are studying causes now in operation. The work of exca-
vating the Niagara chasm belongs to the present epoch, and the time
is absolutely insignificant in comparison with' the inconceivable ages of
which we will speak in the subsequent parts of this work.
Ravines, Gorges, Canons. We have already seen (page 11) that
ravines, gorges, etc., are everywhere produced in mountain- regions by
the regular operation of erosive agents. Nowhere are examples more
abundant or more conspicuous than in our own country, and especially
in the Western portion. On the Pacific slope, the most remarkable are
the gorges of the Fraser and of the Columbia Rivers, fifty miles long
and several thousand feet deep ; those of the North and South Forks of
the American River, 2,000 to 3,000 feet deep in solid slate ; the canon
of the Tuolumne River with its Hetchhetchy Valley ; the still grander
canon of the Merced, with its Yosemite Valley, with nearly vertical
granite cliffs, 3,000 to nearly 5,000 feet high ; and, deepest of all,
the grand canon of King's River, 3,000 to 7,000 feet deep, in hard
granite.
Some of these great canons have been forming ever since the forma-
tion of the Sierra Range i. e., since the Jurassic period. It is possible,
also, that in some of them the erosive agents have been assisted by
antecedent igneous agencies, producing fissures, which have been en-
larged and deepened by water and by ice. But there are some, at least,
which may be proved to have been produced wholly by erosion, and
that during the present or at least during very recent geological times.
We refer especially to those which have been cut through lava-streams.
In Middle and Northern California are.Tound lava-streams which
have flowed from the crest of the Sierra. By means of the strata on
which they lie, these streams are known to have flowed after the end of
FIG. 8. Lava-Stream cut through by Rivers : a a, Basalt ; b b. Volcanic Ashes ; c c, Tertiary ; d d,
Cretaceous Kocks. (From Whitney.)
the Tertiary period. Yet the present rivers have since that time cut
great canons through the lava and into the underlying rock, in some
cases at least 2,000 feet deep. Such facts impress us with the immen-
16
AQUEOUS AGENCIES.
Sity of geological times. This important point is discussed more fully
in a subsequent part of this work.
FIG. 9. Bnttes of the Cross (Powell).
But nowhere in this country, or in the world, are the phenomena of
canons exhibited on so grand a scale, and nowhere are they so obviously
FIG. 10. Canon of the Colorado and its Tributaries (from a Drawing by Newberry).
EROSION OF RAIN AND RIVERS.
17
the result of pure erosion, as in the region of the Grand Plateau of Utah,
Arizona, New Mexico, and Colorado. This plateau is elevated 7,000
to 8,000 feet above the sea, and composed entirely of nearly horizontal
strata, comprising nearly the whole geological series from the Tertiary
downward. Through this series all the streams have cut their way
downward, forming narrow canons with almost perpendicular walls sev-
eral thousand feet deep, so that in many parts we have the singular
phenomenon of a whole river-system running almost hidden far below
the surface of the country, and rendering the country entirely impass-
able in certain directions (see Frontispiece). Nor is the erosion confined
to canons ; for the rain-erosion has been so thorough and general that
much of the upper portion of the plateau has been wholly carried away,
leaving only isolated turrets (buttes) or isolated level tables with cliff-
like walls (mesas) to indicate their original height. All these facts are
well shown in Fig. 10. The explanation of these deep and narrow
canons is probably to be found in the predominance of stream-erosion
over general disintegration and rain-erosion, which is characteristic of
an arid climate (Gilbert).
Chief among these canons is the Grand
Canon of the Colorado, 300 miles long
and 3,000 to 6,200 feet deep, forming the
grandest natural geological section known.
Into this the tributaries enter by side-ca-
nons of nearly equal depth, and often of
extreme narrowness. Fig. 11 represents
the natural proportions of such a canon.
Time. These remarkable canons have
evidently been cut wholly by the streams
which now occupy them, and which are
still continuing the work. The work, prob-
ably commenced in the early Tertiary with
the emergence of this portion of the con-
tinent, became more rapid in the latter
portion of the Tertiary with the great ele-
vation of the plateau, and has continued
to the present time. Thus, causes now in
operation are identified with geological
agencies.
In the Appalachian chain gorges and
valleys of erosion are abundant, but the
evidences of present action are less ob-
vious, and therefore we defer their treat-
ment to Part II., for we are now discuss-
ing agencies still in operation. Among
2
FIG. 11 Section of the Virgen River
(after Gilbert).
18 AQUEOUS AGENCIES.
the more remarkable narrow gorges in this region, we may mention,
in passing, the Tallulah River gorge, several miles long and nearly
1,000 feet deep, in Rabun Count}-, Georgia, and the gorge of the French
Broad in North Carolina. The general effects of erosion will be more
fully treated under " Mountain Sculpture."
Transportation and Distribution of Sediments.
The specific gravity of most rocks is about 2.5. Immersed in water,
they, therefore, lose nearly half their weight. This fact greatly in-
creases the transporting power of water. The actual transporting
power of water is determined partly by experiment and partly by reason-
ing on the general laws of force. By experiment we determine the
transporting power under a given set of circumstances : by general rea-
soning we determine its law of variation, and apply the data given by
experiment to every possible case.
Experiments. It has been found by experiment that a current,
moving at the rate of three inches per second, will take up and carry
along fine clay ; moving six inches per second, will carry fine sand ;
eight inches per second, coarse sand, the siza of linseed ; twelve inches,
gravel ; twenty-four inches, pebbles ; three feet, angular stones of the
size of a hen's-egg. 1 It will be readily seen from the above that the
carrying-power increases much more rapidly than the velocity. For
instance, a current of twelve inches per second carries gravel, while a
current of three feet per second, only three times greater velocity,
carries stones many hundred times as large as grains of gravel. Let us
investigate the law.
Law of Variation. If the surface of the obstacle is constant, the
force of running water varies as the velocity squared: f oc if (1). This
may be easily proved. Suppose we have an obstacle like the pier of a
bridge, standing in water running with any given velocity. Now,
if from any cause the velocity of the current be doubled, since mo-
.mentum or force is equal to quantity of matter multiplied by velocity
(M ' = Q X V), the force of the current will be quadrupled, for there
will be double the quantity of water strike the pier in a given time with
double the velocity. If the velocity of the current be trebled, there
will be three times the quantity of matter striking with three times the
velocity, and the force will be increased nine times. If the velocity be
quadrupled, the force is increased sixteen times, and so on.
Next, if the velocity of the current remains constant, while the size
of the opposing obstacle varies, then evidently the force of the current
will vary as the opposing surface : if the opposing surface is doubled,
the force is doubled ; if trebled, the force is trebled, etc. But in similar
figures, surfaces vary as the square of the diameter. Therefore, in this
case, force varies as diameter squared: f l <xd* (2). Therefore, when
1 Page's " Geology," p. 28 Rankiue.
TRANSPORTATION AND DISTRIBUTION OF SEDIMENTS.
10
/ l d? (2)
F oc a 2 x d* (3)
TFcc d s
d 3 a 2 x d?
d cc v 2
both the velocity of the current and the size of the stone or other
obstacle vary, then the force varies as the square of the velocity
of the current multiplied by the square of the diameter of the stone :
F a u 2 x d* (3).
This last equation gives the law of variation of the moving force.
But the resistance to be overcome, or the weight of the stone, varies
as the cube of the diameters : W cc d 3 . We have, therefore, both the
law of the moving force and the law of the resistance: ]
' W <x. d .
Now the case we wish to consider is that in which the current is just
able to move the stone, or when F a W. In this case d* oc v* X d*,
or d on v 2 . Substituting, in the third equation, for d its value,
F<x v* X v* = v e . We place these equations together, so that they
may be better understood :
When surface = constant . . . f oc 2 (1)
When velocity = constant .
When both vary ....
But
And when W cc F, then .
Dividing by d? ....
Substituting in 3 .
Or F oc * 6
That is, the transporting power of a current varies as the sixth power
of the velocity. This seems so extraordinary a result that, before ac-
cepting it, we will try to make it still clearer by an example.
Let a (Fig. 12) represent a cubic inch of stone, which a current of
a certain velocity will just move. Now, the
proposition is that, if the velocity of the cur-
rent be doubled, it will move the stone b,
sixty-four times as large. That it would do 6
so is evident from the fact that the oppos-
ing surface of b is sixteen times as great as
that of a, and the moving force would be
increased sixteen times from this cause. But
the velocity being double, as we have already
seen, the force against every square inch of
b will be four times that against a, and,
therefore, the whole force from these two
causes would be 16 X 4 = 64 times as great. But the weight is also
sixty-four times as great ; therefore, the current would be just able to
move it. We may accept it, therefore, as a law, that the transporting
power varies as the sixth power of the velocity. If the velocity, there-
fore, be increased ten times, the transporting power is increased 1,000,-
000 times.
20 AQUEOUS AGENCIES.
"We have seen that a current running three feet per second, or about
two miles per hour, will move fragments of stone of the size of a hen's-
egg, or about three ounces' weight. It follows from the above law that
a current of ten miles an hour will bear fragments of one and a half
ton, and a torrent of twenty miles an hour will carry fragments of 100
tons' weight. "We can thus easily understand the destructive effects of
mountain-torrents when swollen by floods.
The transporting power of water must not be confounded with its
erosive power. The resistance to be overcome in the one case is weight,
in the other cohesion ; the latter varies as the square, the former as the
sixth power of the velocity. In many cases of removal of slightly coher-
ing material the resistance is a mixture of these two resistances, and the
power of removing material will vary at some rate between v* and v*.
There are certain corollaries which follow from the above law:
A. If a current bearing sediment have its velocity checked by any
cause, even in a slight degree, a comparatively large portion of the sedi-
ment is immediately deposited. But if, on the other hand, the velocity
of a current be increased by any cause, in never so small a degree, it
will again take up and carry on materials which it had deposited ; in
other words, it will erode its bed and banks ; and these effects are sur-
prisingly large on account of the great change in erosive and transport-
ing power, with even slight changes of velocity.
B. Water, whether still or running, has a wonderful power of sorting
materials. If heterogeneous material, such as ordinary earth, consisting
of grains of all sizes, from pebbles to the finest clay, be thrown into
still water, the coarse material sinks first to the bottom, and then the next
finer, and the next, and so on, until the finest clay, falling last, covers
the whole. In running water the same sorting takes place even more
perfectly, only the different kinds of materials are not dropped upon one
another, but successively farther and farther down the stream in the
order of their fineness. This property we will call the sorting power of
water. Advantage is often taken of this property in the arts to separate
materials of different sizes or specific gravities. By this means grains
of gold are separated from the gravel with which it is mingled, and
emery or other powders are separated into various degrees of fineness.
We will now apply the foregoing simple principles in the explana-
tion of all the phenomena of currents.
I. Stratification.
We have seen that heterogeneous material thrown into still water
is completely sorted. This is not stratification, since the various degrees
of fineness graduate insensibly into one another. But if we repeat the
experiment, the coarsest material will fall upon the finest of the previ-
ous experiment, and then graduate similarly upward. If we examine the
WINDING COURSE OF RIVERS. 21
deposit thus made, we observe a distinct line of junction between the
first and the second deposit. This is stratification, or lamination. For
every repetition of the experiment a distinct lamina is formed. It is
evident, therefore, that to produce stratification two conditions are
necessary, namely : 1. An heterogeneous material ; and, 2. An inter-
mittently-acting cause. Now, these two conditions are always present
in Nature where sediments are depositing. Into every body of still
water, as a lake or sea, rivers bring heterogeneous material torn from the
land ; but this process is not equable, being increased in the case of
small streams by every rain, and in large rivers by the annual floods.
Therefore, sedimentary deposits in still water are always stratified.
In running water the case is somewhat different. If the stream runs
with a velocity at all times the same, then with every repetition of the
foregoing experiment the same kind of material falls on the same
spot gravel on gravel, sand on sand, and mud on mud and there will
be no stratification. In running water, therefore, another condition is
necessary, namely, a variable current. For, when the velocity increases,
coarser material will be carried and deposited where finer was previ-
ously deposited; when the velocity decreases, finer will be deposited on
coarser, and very perfect stratification is the result. Now, these three
conditions are always present in every natural current. The velocity
of every river-current varies not only very greatly in different portions
of the year, as in seasons of low water and seasons of flood, but also
(from the constant shifting of the subordinate currents of the stream)
from day to day, from hour to hour, and even from moment to moment.
It follows, therefore, that deposits in running water are also always
stratified. Sometimes extreme beauty and distinctness of stratification in
the deposits of large rivers are due to the fact that the different branches
flood at different seasons, and bring down differently-colored sediments.
We may, therefore, announce it as a law, that all sedimentary de-
posits are stratified ; and, conversely, that all stratified masses in which
the stratification is the result of sorted material are sedimentary in
their origin. Upon this law is founded almost all geological reasoning.
2. Winding Course of Eivers
The winding course of rivers is due partly to erosion, and partly to
sedimentary deposit. It is most conspicuous and most easily studied
in rivers which run through extensive alluvial deposit. If the channel
of such a river be made perfectly straight by artificial means, very soon
some portion of the bank a little softer than the rest will be excavated ;
this will reflect the current obliquelv across to the other side, which
will become similarly excavated. Thus the current is reflected from
side to side, increasing the excavations. In the mean time, while ero-
sion is progressing on the outer side of the curves, because the current
AQUEOUS AGENCIES.
is swiftest there, deposit is taking place on the inner side, because there
the current is slowest ; thus, while the outer curve extends by erosion,
the inner curve extends, paripassu, by deposit (Fig.
13), and the winding continues to increase, until,
under favorable circumstances, contiguous curves
on the same side run into each other, as at a b,
and the curve c on the other side is thrown out
and silted up. Thus are formed the crescentic
lakes, or lagoons (I I), so common in the swamps
of great rivers. They are abundant in the swamps
of all the Gulf rivers, especially the Mississippi.
They are old beds of the river, thrown out and
silted up in the manner indicated above.
3. Flood-Plain Deposits.
All great rivers annually flood portions of level
land near their mouths, and cover them with sedi-
mentary deposits. The whole area thus flooded
is called the flood-plain. These flood-plains are
very extensive, and the deposits very large, in the
case of rivers rising in lofty mountains and flow-
ing in the lower portion of their course through
extensive tracts of flat country. In the lofty
mountains the current runs with great velocity,
and gathers abundant sediment ; on reaching the
flat country the velocity is checked, the river over-
flows, and the sediment is deposited. The flood-
^^ f the Mississi PP i River is 30,000 Square
Meandering miles. The flood-plain of the Nile is the whole
land of Egypt.
The flood-plain of a river may be divided into two parts, viz., the
river-swamp and the delta. The river-swamp is that part which was
originally land-surface ; the delta that part which has been reclaimed
from the sea or lake by the river. We will take up these in succession.
River-Swamp. We have already seen that, with every recurrence
of the rainy season or of the melting of snows, the flooding and the
deposition of sediment are repeated. Thus the river-swamp deposit
increases in thickness, and the level of the whole flood-plain rises con-
tinually. Fig. 14 is an ideal section showing the manner in which the
flood-plain is successively built up ; a a a is the supposed original con-
figuration of the surface, b b the successive levels of deposit, e the level
of the river at low water, and i i the level of flood- water.
The extent of such river-swamp deposits is sometimes very great.
The river-swamp of the Nile constitutes the whole fertile land of Egypt
FLOOD-PLAIN DEPOSITS. 23
above the delta. The river-swamp of the Mississippi River, or its
flood-plain exclusive of the delta, extends from fifty miles above the
mouth of the Ohio to the head of the delta, a distance of about 700
miles ; its width is ten to fifty miles, and it includes an area of 16,000
FIG. 14. Ideal Section of a River subject to Floods.
square miles. It is bounded on either side by high bluffs belonging to
a previous geological period. The depth of this deposit at the head
of the delta is assumed by Lyell to be 264 feet. 1 But Hilgard has
shown that but a small portion of this is actually river deposit.
Natural Levies. It is seen by the cross-section (Fig. 14) that the
level of the river-swamp slopes gently from the river outward, so that
the river is bounded on each side by a higher ridge, d d. The material
of this ridge is coarser than that of the swamp farther back. Such
natural levees are found along all rivers subject to regular overflows.
They are formed as follows : In times of flood the whcle flood-plain is
covered with water moving slowly seaward. Through the midst of this
wide expanse of water runs the rapid current of the river. Now, on
either side, just where the rapid current of the river comes in contact
with the comparatively still water of the flood-plain, and is checked by
it, a line of abundant sediment is determined, which forms the natural
levee. Except in very high freshets, these natural ridges are not en-
tirely covered, so that the river in ordinary floods is often divided into
three streams, viz., the river proper and the river-swamp water on
either side. They cannot, however, confine the river within its bank
and prevent overflows, since the river-bed is also constantly rising by
deposit. Thus the river-bed, the natural levee, and the river-swamp,
all rise together, maintaining a certain constant relation to one another.
Artificial Levies, This constant relation is interfered with by the
construction of artificial levees. These are constructed for the purpose
of confining the river within its banks, and thus reclaiming the fertile
lands of the river-swamp. As the bed of the river continues to rise
by deposit, the levees must be constantly elevated in proportion ; but
the river-swamp, being deprived of its share of deposit, does not rise.
Thus, under the combined effect of human and river agencies contend-
ing for mastery, an ever-increasing embankment is formed, until finally
the river runs in an aqueduct elevated far above the surrounding plain.
1 Lyell, " Principles of Geology," vol. i., p. 462.
AQUEOUS AGENCIES.
This is very remarkably the case with the river Po, which is said to run
in a channel that has been thus elevated above the tops of the houses
in the town of Ferrara. Fig. 15 is an ideal cross-section of a river and
flood-plain, left at first to the action of natural causes for a time, but
afterward interfered with by the construction of artificial levees. The
dotted strata show the work of Nature, and the undotted the work of
man. It is easy to see that the destructive effects of overflow from acci-
dental crevasses become greater and greater with the elevation. The
Po has thus several times broken through its levees and deserted its
bed, destroying several villages. The best examples of rivers success-
fully levied are those of Italy and Holland. The Mississippi has never
been successfully levied ; but if it should be, it would commence to
build up a similar aqueduct, until the whole bed of the liver would
finally rise above the level of the river-swamp. 1
4. Deltas.
Deltas are portions of land situated at the mouths of rivers, and
reclaimed from the sea by their agency. Over the fiat surface of the
delta the river runs by inverse ramification, and empties by many
mouths. They are usually of irregular triangular form, the apex of the
triangle pointing up the stream. The delta of the Nile (Fig. 16) is
perhaps the best example of the typical form. As seen in the figure,
at the head of the delta the river divides into branches, and communi-
cates with the sea by many mouths. The area of land thus made va-
ries with the size of the river, the proportion of sediment in its waters,
and the time it has been making sedimentary accumulations. The
delta of the Nile is 100 miles long and 200 miles wide at its base ; that
of the Ganges and Brahmapootra is 220 miles long and 200 miles wide
at its base, comprising an area of 20,000 square miles. The delta of
the Mississippi (Fig. 17) is very irregular in form, and is an admirable
illustration of the manner in which each mouth pushes its way into
the sea. Its area is estimated at 12,300 square miles. The materials
1 It is probable that the effect of levees in raising the river-bed has been greatly ex-
aggerated. Recent observations on the Po seem to show that the elevation is confined to
the upper reaches of the flood-plain region, being prevented in the lower course by the
increased velocity of the current produced by levees.
DELTAS.
25
FIG. 16. Delta of the Nile.
of which deltas are composed are usually the finest sands and clays, all
the coarser materials having been deposited higher up the stream.
Deltas are formed only in lakes and tideless or nearly tideless seas.
FIG. 17. Delta of the Mississippi.
26
AQUEOUS AGENCIES.
In tidal seas, the sediments brought down by the rivers are swept
away and carried to sea by the retreating tide ; and instead of the land
encroaching upon the domain of the sea by the formation of deltas,
the sea encroaches upon the land by the erosive action of the tides, and
forms bays or estuaries. Thus in tideless seas or lakes the rivers empty
by many slender mouths, while in tidal seas they empty by wide bays ;
thus, for example, all the rivers emptying into the great Canadian
lakes, and all the rivers emptying into the Gulf of Mexico, form deltas,
while all the rivers emptying into the Atlantic in both North and
South America form estuaries. In Europe all the rivers emptying into
the Black, the Caspian, the Mediterranean, and the Baltic, form deltas,
while those emptying into the Atlantic form estuaries.
Process of Formation. The process of formation of a delta may be
best studied by observing it on a small scale, in the case of streamlets
running into ponds. In such cases we observe always a sand or mud
flat at the mouth of the streamlet, evidently formed by the sand and
clay brought down by the current. As soon as the current strikes the
still water of the pond,
its velocity is checked,
and its burden of secli-
ment is deposited.
Through the sand-flat
thus formed the stream-
let ramifies, as seen in
Fig. 18. The ramification seems to be the result of the choking of
the stream by its own deposit, which forces it to seek new chan-
nels. The sand-flat is gradually extended farther and farther into the
pond by successive deposits, as shown in Fig. 18. Fig. 19 shows
the irregular stratified appearance of the deposit as seen on cross-sec-
tion. In all such cases of streams flowing into ponds or lakes, the
stream flows in at a muddy, but flows out at b perfectly clear, having
deposited all its sediment in the pond or lake. Evidently if this pro-
cess continues without interruption, the pond will eventually be filled
up, after which, of course, the sediment will be carried farther down
the stream. In this manner small mountain-lakes are often entirely
filled up. The Rhone flows into Lake Geneva a turbid stream, but
flows out beautifully transparent. The whole of its sediment is de-
TRANSPORTATION AND DISTRIBUTION OF SEDIMENTS. 2Y
posited where it enters the lake, and it has there formed a delta six
miles long. We may confidently look forward to the time, though
many thousand years distant, when this lake will be entirely filled up.
After leaving the lake the Rhone again gathers sediment from tribu-
taries flowing in below the lake, and forms another delta where it emp-
ties into the Mediterranean. Many examples of lakelets partially filled,
or entirely filled and converted into meadows, are found among the
Sierra Mountains.
In the section view (Fig. 19), we have represented the strata as
irregular and highly inclined. This is called oblique lamination. This
can only occur when a rapid stream, bearing abundant coarse material,
rushes into still water. But in the case of large rivers flowing long
distances and bearing only the finest sediment, the stratification is
much more regular and nearly horizontal.
Rate of Growth. There have been several attempts to estimate the
rate of growth of deltas, in order to base thereon an estimate of their
age. The delta of the Rhdne in Lake Geneva has advanced at least
one and a half mile since the occupation of that country by the Romans ;
for the ancient town Porta Valesia (now Port Valais), which stood then
on the margin of the lake, is now one and a half mile inland. The
delta of the same river at its mouth in the Mediterranean is said to
have advanced twenty-six kilometres, or sixteen miles, since 400 B. c.,
or thirteen miles during the Christian era. 1 The delta of the Po has
advanced twenty miles since the time of Augustus ; for the town Adria,
a seaport at that time, is now twenty miles inland. But the most elab-
orate observations have been made on the Mississippi. This river, as
seen in Fig. 17, has pushed its way into the Gulf in a most extra-
ordinary manner. According to Thomassy, 2 and also Humphrey and
Abbot, the rate of advance is about one mile in sixteen years. The
rate of progress in the deltas mentioned has, however, probably not
been uniform. There are special reasons for their more rapid advance
at the present time. In the case of the Po, the successful leveling of
this river has transferred to the sea the whole of the sediment which
would otherwise have been spread over the flood-plain. In the case of
the Mississippi, for many centuries the principal portion of the deposit
has been confined to a narrow strip but a few miles wide, and the ad-
vance has been proportionately rapid. For this reason the river has
run out to sea for more than fifty miles, confined only by narrow strips
of land, the continuation of the natural levees. These marginal ridges
are continued as submarine banks even much beyond the present mouths
of the river. The rate of advance of the Nile delta seems to be much
slower.
Age of River-Deposits. The age of river-swamp deposits may be
1 "Archives des Sciences," vol. li., p. 157. 2 "Geologie pratique de la Louisiana"
28
AQUEOUS AGENCIES.
estimated by determining their absolute thickness and their rate of
increase. The river Nile is peculiarly adapted for estimates of this
kind, because we have on its alluvial deposits the seat of the oldest
civilization and the oldest known monuments of human art. These
monuments, the ages of which are approximately known, are many
of them more or less buried in the river-deposit. At Memphis, the
FIG. 20. Ideal Section of Delta and Submarine Bank.
foundation of the colossal statue of Rameses II., over 3,000 years
old, was found in 1854 buried about nine feet in river-deposit. 1 This
makes the rate of increase of the deposit three and a half inches per
century. Experiments at Heliopolis bring out nearly the same result.
The whole depth of the alluvial deposit at Memphis was found to be
about forty feet, which, at the above rate, would make the age of the
deposit at this point about 13,500 years. The alluvial deposit of the
Nile is much thicker at some points than forty feet ; but, on the other
hand, the rate of increase for different places is probably variable.
The age of a delta is usually estimated by determining the annual
mud-discharge, and dividing it into the cubic contents of the delta. The
cubic contents of the delta are
estimated by multiplying the
superficial area by the mean
depth. The mean depth of the
Mississippi Delta, as determined
by borings, is taken by Mr.
Lyell as 528 feet, the superficial
area at 13,600 square miles, and
the annual mud-discharge at
7,400,000,000 cubic feet. Upon
these data he makes the prob-
able age of the delta 33,500
years. To this he adds half as
much for the age of the. river-
swamp, making in all 50,000
years.
It is evident, however, that
this estimate cannot be relied on as even approximately accurate. For
there is no reason why the time of river-swamp deposit should be added
to that of the delta, for they were both probably formed at the same
1 Philosophical Magazine, vol. xvi., p. 225.
FIG. 21. Delta and Submarine Bank.
TRANSPORTATION AND DISTRIBUTION OF SEDIMENTS. 29
time one by deposits higher up the river, the other by deposits at the
mouth. Again, on the other hand, the estimate takes no account of
the submarine extension of the delta, in area certainly, and in cubic
contents probably, much greater than the subaerial delta. Figs. 20
and 21 are an ideal section and a map of a delta, in which a is the
aerial and b the submarine portion. This would greatly increase the
time.
It is evident, therefore, that although the problem is one of great
interest, we are not yet in possession of data to make a reliable esti-
mate. Every estimate, however, indicates a very great lapse of time.
But it must not be imagined, as all estimators seem to do, that this
time, be it greater or less than Mr. Lyell's estimate, belongs all to the
present geological epoch. Prof. Hilgard has shown that the true allu-
vial deposit of the Mississippi is only forty or fifty feet thick. Beneath
this the deposit belongs to the Quaternary or preceding geological epoch.
5. Estuaries.
We have already seen that rivers which empty into tideless seas
communicate with the sea by numerous branches traversing an alluvial
flat, formed by the deposits of the river ; while rivers emptying into
tidal seas communicate by wide mouths or bays, formed by the erosive
action of the flowing and ebbing tide. Such bays are called estuaries.
We have fine examples of estuaries in the Amazon and La Plata Rivers,
in the Delaware and Chesapeake Bays, in the friths of Scotland and
the fiords of Norway : in fact, at the mouths of all the rivers emptying
into the Atlantic on our own coast as well as on the European coast.
The mouth of the Columbia River is a good example on the Pacific
coast. The phenomena of a delta and an estuary are sometimes com-
bined in the same river. This is the case to some extent in the Ganges.
Mode of Formation. Estuaries are evidently formed by the erosive
action of the inflowing and outflowing tide. Their shape, narrow above
and widening toward the sea, gives great force to the tidal currents,
which, entering below and concentrated in the ever-narrowing channel,
rushes along with prodigious velocity and rises to an immense height.
In the Bay of Fundy the tide rises seventy feet, and at Bristol, England,
it rises forty feet, in Puget Sound twenty-five feet. Sometimes, from ob-
structions at the mouth of the river, the tide enters as one or more im-
mense waves, rushing along like an advancing cataract. This is called
an eagre or bore. The finest examples are perhaps in the Amazon and
Tsien-tang Rivers. In the eagre of the Amazon " the tide passes up in
the form of five or six waves following one another in rapid succession,
and each twelve to fifteen feet high." In the Tsien-tang, a single wave
plunges along at the rate of twenty-five miles an hour, 1 with perpen-
1 American Journal of Science and Arts, 1855, vol. xx., p. 305.
30 AQUEOUS AGENCIES.
dicular front, like an advancing cataract, four or five miles wide and
thirty feet high. In the river Severn also we have a remarkable exam-
ple of an eagre. According to the laws already developed (p. 19), the
erosive and transporting power of such currents must be immense.
Deposits in Estuaries. The larger portion of the materials thus
eroded is carried out to sea by the retreating tide, and will be again
spoken of under " Sea-deposits." A portion of these materials, however,
is always deposited in the estuary in sheltered coves and bays (Fig. 22,
a and b), and often, when the outflowing tide is obstructed by sand-
spits and islands at the mouth, over every portion of the estuary. In
addition to this, especially in rivers subject to great freshets, there are
deposits of silt from the river. Thus many estuaries are occupied alter-
nately, during the wet and dry seasons, by fresh and brackish or salt
water, and the deposits in them are therefore alternately fresh-water
and salt-water deposits, containing fresh-water and salt or brackish
water shells. These alternations are highly characteristic of estuary-
deposits in all geological periods ; in fact, of all deposits at the mouths
of rivers where river and ocean agencies meet.
6. Bars.
Bars are invariably formed in accordance with the law already-
enunciated as that controlling all current-deposits, viz., if the velocity
of a current bearing sediment be checked, the sediment is deposited.
There are two positions in which bars are formed : 1. At the mouths
of rivers ; and, 2. At the head of the estuaries. In the first position
ft
FIG. 22. An Estuary.
(Fig. 22, d d} the bar is formed by the contact of the river-current
with the still water of the ocean. It is most marked in the case of
estuaries. The outfiWing tide scours out the estuary, carrying with it
sediment partly brought down by the river, and partly the debris of
land eroded by the inflowing tide. The larger portion of this is dropped
as soon as the tidal current comes in contact with the open sea and is
checked by it. They are usually irregularly crescentic in form. Such
are the bars at the mouths of all harbors. In the second position they
WAVES AND TIDES. 31
are found just where the upward current of the inflowing tide meets the
downward current of the river, and makes still water. At this point
we have not only a bar, but usually also an extensive marsh caused by
the daily overflow of the river. Through this marsh the river winds
in a very devious course, as is common in all rivers whose banks are
alluvial.
Thus, then, in rivers like the Mississippi, emptying into tideless seas
and forming deltas, there is but one bar, viz., that at the mouth ; while
in rivers forming estuaries there are two bars, an outer and an inner.
This inner bar may be many miles up the river. In the Hudson River
the inner bar is 140 miles up the river, and only a few miles below
Albany. This is really the head of the estuary, or of tide-water, in this
river.
It is evident that bars, being produced by natural and constantly-
acting causes, cannot usually be permanently removed, though they may
be sometimes greatly improved. If they are scraped away by dredg-
ing-machines, they are speedily reformed on the same spot. If we cause
the river itself to remove them, as has sometimes been done by narrow-
ing the channel and thus increasing the erosive power, we indeed
remove the bar, but it is reformed farther down the stream at a new
point of equilibrium.
We have thus traced river agencies from their source to the sea.
This brings us naturally to ocean agencies.
SECTION 2. OCEAN.
Waves and Tides.
Waves. "Waves produce no current, and therefore no geological
effect in deep water. The erosive effect of this agent is almost en-
tirely confined to the coast-line, but at this point is incessant and
powerful. The average force of waves on the west coast of Scotland
for the summer months is estimated by Stevenson at 611 pounds per
square foot, and for the winter months at 2,086 pounds per square
foot. 1 In violent storms the force is estimated at 6,000 pounds
per square foot, 5 and fragments of rock of many hundred tons' weight
are often hurled to a considerable distance on the land. These frag-
ments hurled against the shore are the principal agent of wave-erosion.
The rapidity of the erosion of a coast-line by the action of waves is
determined partly by the softness and partly by the inclination of the
strata. If the strata turn their faces to the waves, particularly if in-
clined at a small angle, the effect of the waves is comparatively slight
(Fig. 23) ; but if the edges of the strata are exposed to the waves, the
1 Dana's " Manual," p. 654. 2 Herschel's " Physical Geography," p. 75.
32
AQUEOUS AGENCIES.
erosion is much greater. For instance, if the strata be horizontal, as
in Fig. 24, then the strata are undermined and form overhanging table-
rocks, which from time to time fall into the sea ; if the strata are verti-
cal or highly inclined
and their edges
turned to the sea,
then an exceedingly
irregular coast-line is
formed and the ero-
sion is very rapid, as
the force of the
waves is concen-
trated upon the reen-
tering angles. Fig.
25 is a map view of a
coast, in which from a to b the waves strike the edges, while from a to
c they strike the faces of the same rocky strata. The difference in the
form of the coast-line is seen at a glance.
Waves cutting ever at the shore-line only, act like an horizontal saw.
The receding shore-cliff, therefore, leaves behind it an ever-increasing
subaqueous platform which marks the amount of recession. This is
"3
.
>T 1
FIG. 24.-Section of an Exposed Cliff.
shown in the section (Fig. 26), in which s is the present shore-line, I the
water-level, a b the platform, s' the original shore-line, and s' b c the
original slope of bottom. The recession of the shore-line and the
formation of the shore platform have been accurately observed in Lake
Michigan (Andrews).
Level platforms termi-
nated by cliffs, there-
fore, when found in-
| land, sometimes indi-
FlG 26 - cate the position of old
shore-lines.
Tides. The tide is a wave of immense base, and three or four feet
in height in the open ocean, produced by the attractive force of the moon
WAVES AND TIDES. 33
and sun on the waters of the ocean. The velocity of this wave is very
great, since it travels around the earth in twenty-four hours. In the
open ocean it produces very little current, only a slow transfer of the
water back and forth, too slow to produce any geological effect ; * but in
shallow water, where the progress of the wave is impeded, it piles up
in some cases forty to fifty feet in height, and gives rise to currents of
great velocity and immense erosive power. By this means bays and
harbors are formed, and straits and channels are scoured out and
deepened. Tides also act an important part in assisting the action of
waves upon the whole coast-line. The action of waves on exposed
cliffs quickly forms accumulations of d&bris at their base, composed of
sand, mud, shingle, or rocky fragments (Fig 24), which receive first and
greatly diminish the shock of the waves upon the cliff. The inces-
sant beating of the waves upon this debris reduces it to a finer and
finer condition, and the retreating waves bear much of it seaward;
so that, even without the assistance of any other agent, the protection
is incomplete, and the erosion therefore progresses. But if strong tidal
currents run along the coast, these effectually remove such debris and
leave the cliff exposed to the direct action of the waves.
Examples of the Action of Waves and Tides. The coasts of the
United States show many examples of the erosive action of waves and
tides. The form of the whole New England coast is largely determined
by this cause. The softer parts are worn away into harbors by the
waves and scoured out by the tides, while the harder parts reach out
like rocky arms far into the sea. Sometimes only small rocky islands,
stripped of every vestige of earth, mark the position of the former coast-
line. Boston Harbor and the rocky points and islands in its vicinity
are good examples. The process is still going on, and its progress
may be marked from year to year.
On the Southern coast examples of a similar process are not want-
ing. At Cape May, for instance, the coast is wearing away at a rate
of about nine feet per annum. The more exposed portions about
Charleston Harbor, such as Sullivan's Island, are said to be wearing
away even more rapidly. As a general fact, however, the low, sandy or
muddy shores of the Southern coasts are receiving accessions more
rapidly than they are wearing ; while, on the contrary, the New Eng-
land coast, as proved by its rocky character, is losing much more than
it gains. The shores of Lake Superior (Fig. 27) furnish many beauti-
ful examples of the action of waves, in this case, of course, unassisted
by tides. The general form of the lake along its south shore is deter-
mined by the vary ing hard ness of the rock ; the two projecting promon-
tories La Pointe (a) and Keweenaw Point (c) being composed of hard,
igneous rocks, while the intervening bays b and d are softer sandstone.
1 Herschel's " Physical Geography," p. 64.
3
34. AQUEOUS AGENCIES.
On the south shore, about e t between La Pointe and Fond du Lac (/), the
conditions of rapid erosion are beautifully seen. The shores are sand-
stone cliffs, with nearly horizontal strata. These have been eroded
beneath by the waves, in some places for hundreds of feet, forming
FIG. 27. Lake Superior.
immense overhanging table-rocks, supported by huge sandstone pillars
of every conceivable shape. Among these huge pillars, and along these
low arches and gloomy corridors, the waves dash with a sound like thun-
der. From time to time these overhanging table-rocks, with their load
of earth and primeval forests, fall into the lake.
The coasts of Europe furnish examples en a more magnificent scale,
and have been more carefully studied. The cliffs of Norfolk are carried
away at a rate of three feet, and those of Yorkshire six feet, annually.
The church of Reculver, on the coast of Kent, near the mouth of the
Thames, stood, in the time of Henry VIII., one mile inland. Since that
time the sea has steadily advanced until, in 1804, a portion of the church-
yard fell in, and the church was abandoned as a place of worship. The
church itself, ere this, would have been undermined and fallen in, had
it not been protected by artificial means. There are many instances in
the German Ocean of islands which have been entirely washed away
during the historic period.
The tidal currents through the British and Irish Channels, along the
western coasts of Ireland and Scotland, among the Orkneys and Heb-
rides, and especially along the coast of Norway, are very powerful.
Along this latter coast it forms the celebrated Maelstrom. The erosive
effects of the sea are, therefore, very conspicuous. On the south and
east coasts of England the erosion is now progressing rapidly. On the
west coasts of Ireland and Scotland the waste is not now so great, be-
cause the softer material is all removed, but the configuration of the
coast shows the waste which it has suffered. A glance at a good map
WAVES AND TIDES.
35
of Ireland shows a deeply-indented western coast, composed entirely
of alternating rocky promontories and deep bays. On the western coast
of Scotland, and especially on the Orkney, Shetland, and Hebrides Isl-
ands, the wasting effect of the sea has been still greater. Not only
have we here the same character of coast as already described (as seen
in the friths of Scotland), but many small islands have been eroded,
until only a nucleus of the hardest rock is left ; and even these have
been worn until they seem but the ghastly skeletons of once-fertile isl-
ands. Figs. 28 and 29 will give some idea of the appearance of these
spectral islands.
The coast of Norway consists entirely of deep fiords alternating
with jutting headlands of hardest rock several thousand feet high.
Along this intricately -dissected coast there runs a chain of high, rocky
islands, which in an accurate map is scarcely distinguishable from the
coast itself, being separated only by narrow, deep fiords. Toward the
36 AQUEOUS AGENCIES.
northern part of the coast the crest of the Scandinavian chain seems to
run directly along the jutting promontories of the coast-line, for these
headlands are the most elevated part of the country ; in fact, in some
parts, it would seem that the original crest was at one time still farther
west, along the line of coast-islands. If so, then the sea has not only
carried away the whole western slope, but has broken through the main
axis, leaving only these isolated rocky islands as monuments of its
former position, and is even now carrying its ravages far inland on the
eastern slope. In the case of Norway, however, and probably in case of
nearly all bold, rocky coasts, the intricacy of the coast-line is not due
wholly or even principally to the action of waves and tides, but also to
other causes to which we shall refer hereafter.
Transporting Power. The transporting power of waves is immense-
ly great, often taking up and hurling on shore masses of rock hundreds
of tons in weight ; but, being entirely confined to the coast-line, the dis-
tance to which they carry is necessarily very limited. There are some
instances, however, of materials carried to great distances by the inces-
sant action of waves. Thus, according to Prof. Bache, coast-sand
is carried slowly farther and farther south by the action of waves, and
siliceous sand is found at Cape Sable on the extreme southern point of
Florida, although the whole Florida coast as far as St. Augustine is
composed of coral limestone alone. He accounts for this by supposing
that the trend of the United States coast is such that waves coming
from the east strike the coast obliquely and fall off toward the south,
carrying each time a little sand with them. A similar phenomenon has
been observed on Lake Michigan : the sands are carried steadily toward
the south end, where they accumulate.
Deposits. The invariable effect of waves, chafing back and forth
upon coast debris, is to wear off their angles and thus to form rounded
fragments and granules. Thus pebbles, shingle, and round-grained
sand, though produced by all currents, are especially characteristic of
wave-action. Hippie-marks are also characteristic of current-action in
shallow water. They are, therefore, always formed on shore by the
action of waves and tides. By means of these characteristics of shore
deposit, many coast-lines of previous geological epochs have been deter-
mined.
We have seen that waves usually destroy land. In many cases,
however, they also make land. This is the case whenever other agen-
cies, such as river or tidal currents, drop sediment in shallow water, and
therefore within reach of wave-action. We shall again speak of these
under the head of Land formed by the Ocean Agencies.
OCEANIC CURRENTS. 3f
Oceanic Currents.
The ocean, like the atmosphere, is in constant motion, not only on
its surface, but throughout its whole mass. The general direction of the
currents in the two cases is also similar, but there are disturbing and
complicating causes peculiar to each, which interfere with the regularity
and simplicity of the phenomena. If the currents of the atmosphere are
more variable on account of the greater levity of the fluid, oceanic cur-
rents have also their peculiar disturbing causes in the existence of im-
passable barriers in the form of continents. In both atmosphere and
sea, currents may also be deflected by submarine banks, for mountain-
chains are the banks of the aerial ocean.
Theory of Oceanic Currents. By some distinguished physicists,
oceanic currents have been attributed entirely to the action of the trade-
winds. 1 There can be no doubt that this is a real cause; yet it seems
probable, nay, almost certain, that the great and controlling cause of
currents of the ocean, as of the air, is difference of temperature between
the equatorial and polar regions. 8 "We will, therefore, discuss the sub-
ject from this point of view, although the effect would be much the same,
whatever be our view of the theory. For the sake of clearness, we will
take first the simplest case, and then introduce disturbing influences
and show their effects.
Suppose, first, the earth covered with a universal ocean, continually
heated at the equator, and cooling at the poles : the difference of den-
sity of the equatorial and polar seas would cause exchange or circula-
tion between these regions by means of north and south currents in all
longitudes, the equatorial currents being superficial because warm, and
the polar currents deep-seated because cold. It is obviously impossible,
however, that the principal exchange should be with the pole itself,
since this is but a point, but with the northern regions. Observation
shows that it is between the equator and the polar circle. In the case
we are now considering, the exchange, being in all longitudes, would be
scarcely, if at all, perceptible.
Suppose, second, the earth be set a rotating: then the currents pass-
ing from either polar to the equatorial region would be deflected more
and more to the westward until, uniting at the equator, they would
there form a directly westward equatorial current running around the
earth. This westward-moving water would be constantly turning north-
ward and southward in all longitudes as a superficial current, and finally
eastward about the polar circle, to join again the deep-seated polar cur-
rent going to the equator ; thus forming a series of regular ellipses
lying over each other in strata, dipping eastward and outcropping
1 Herschel, " Physical Geography," p. 13 ; and Croll, " Climate and Time."
9 Guyot, " Earth and Man," p. 189.
AQUEOUS AGENCIES.
westward as represented in Fig. 30. As the north and south currents
a a' and b b' would take place in all longitudes, they would be scarcely,
if at all, perceptible ; but the east currents d d', and the westward
equatorial current c c, where all these unite, would be decided.
In the third place, introduce continents passing across the equator
from north to south, forming impassable barriers to the east and west
currents c c and d d. Then
many of the lines of current
aaa would be crowded
against the western shore
of the ocean, and of the
lines bbb against the east-
ern shore, forming in each
case by concentration very
decided currents, while in
mid-ocean these currents
would be still impercepti-
ble. Thus the perceptible
situated between continents would be repre-
FIG. 80. The strong lines aaa show superficial,
dotted lines b b b deep-seated currents.
currents of an ocean
sented by the figure (Fig. 31) taken from Dana.
Besides the main currents above mentioned there would be mi-
nor exchanges with the pole itself. 1
A portion of the eastward current
d and d ' would turn north and south-
ward, e e', and circling around would
return toward the equator as a deep-
seated current under , hugging the
shore on account of the westward ten-
dency of all currents moving toward the
equator.
The effect of the trade-winds would
be to conspire with the cause already
discussed in the formation of the equa-
torial current c c', and by the reflection
of this from continents, the other cur-
90"
60
30'
60
DO
FIG. 81. Ideal Diagram, showing General rents SDoken of
Course of Oceanic Currents.
Application. We will now apply
these principles in the explanation of the currents of the Atlantic
Ocean, for these are best known.
Currents coming from the north and south on the African coast, and
corresponding to b b' in the above diagram, unite to form an equatorial
current, c c', which stretches across the Atlantic until, striking (Fig. 32)
against the coast of South America, it turns north and south, a a'. The
1 Dana's " Manual," p. 88.
OCEANIC CURRENTS.
39
southern branch has not been accurately traced. It probably turns
gradually eastward, c?', and forming a grand circle in the southern
Atlantic joins again the South African current b'. The northern branch,
#, runs along the coast of South America, through the Caribbean Sea
and into the Gulf of Mexico, from which emerging it runs with great
velocity through the narrow straits of Florida and thence under the
name of the Gulf Stream along the coast of North America, turning
Strc
glot
FIG. 32. General Course of Currents of the Atlantic.
more and more eastward in obedience to the law already mentioned,
until it becomes an eastward current, <?, about 50 to 60 latitude ; and
then stretches across to the coast of Europe, and turns again southward
to join the equatorial current. A portion of it, however, in its east-
ward course turns northward, e, and returns as a cold polar current hug-
ging the shore of North America as a cold wall to the Gulf Stream,
and thus passes south.
Geological Agency of Oceanic Currents. The velocity of oceanic
currents is generally small, although, in the case of the Gulf Stream, at
the Florida Straits, it reaches almost the velocity of a torrent, viz.,
three and a half to five miles per hour. The volume of water carried
by them is almost inconceivably great ; it is estimated that the Gulf
Stream alone carries many times more water than all the rivers of the
globe. According to Croll, it is equal to a current fifty miles wide and
40 AQUEOUS AGENCIES.
one thousand feet deep, running at a rate of four miles per hour. The
geological agency of these powerful currents in modifying the bottom
of the sea by erosion may be, and by sedimentary deposit must be,
very important, though as yet comparatively little known.
One of the chief functions of oceanic currents is the transportation
and distribution over the open-sea bottom of sediments brought down
by the rivers. By far the larger part of the debris of the land is cer-
tainly dropped near the shore, and marginal sea-bottoms are everywhere
the great theatres of sedimentation ; but, without the agency of marine
currents, none would reach open sea, all would be dropped near shore.
By the agency of these, however, the finer portions are carried and
widely distributed over certain portions of deep-sea bottoms. We
have undoubted evidence of this in some cases. Thus the sediments
brought down by the Amazon are swept seaward by a strong tide, and
then taken by the oceanic current which sweeps along that coast, and
carried 300 miles and deposited much of it on the coast of Guiana.
According to Humboldt, the same stream carries sediment from the
Caribbean into the Gulf of Mexico. 1 There is little doubt, too, that
much of the sediments brought into the Gulf of Mexico by the Gulf
rivers is swept along by the Gulf Stream, and a part of it deposited on
Florida Point and the Bahama Banks. The surface transparency of
the Gulf Stream is no objection to this view, as a little reflection will
show. Ocean-currents differ from rivers, in the fact that the former
run in perfectly smooth beds of still water. There are, therefore, no
subordinate currents from side to side, or up and down, whereby in river-
currents the water is thoroughly mixed up, and the finer sediments
prevented from settling. In ocean-currents the conditions are as favor-
able for subsidence as in still water. It is evident, therefore, that sedi-
ments carried by ocean-currents must in a little time sink out of sight,
although from the great depth of these currents they mav still be car-
ried to considerable distances. Deep-sea deposits have until recently
received little attention, although they are acknowledged to be of the
greatest geological importance.
Submarine Banks. These are always accumulations of material
dropped by currents. They are formed under conditions similar to
those which determine the formation of bars; i. e., either by the meet-
ing of opposing sediment-laden currents or else bv such a current coming
in contact with still water. In fact, the outer bar is. a true submarine
bank. The currents may be either tidal or oceanic or river. Admira-
ble examples of both these modes of formation are found in the Ger-
man Ocean. The tidal wave from the Atlantic strikes the British Isles,
passes round in both directions, and enters this ocean from the north
around the north point of Scotland, and from the south through the
1 Lycll's " Principles of Geology."
TIDES AND CURRENTS.
41
British Channel and Straits of Dover (Fig. 33). These two currents
coming from opposite directions meet and make still water, and there-
fore deposit their sediment and form banks. Again, the tidal current
is concentrated in the British Channel, and runs with great velocity,
scouring out this channel, and in addition gathering abundant sediment
from the rivers emptying into the channel. Thus loaded with sedi-
FIG. 33. Tides of the German Ocean.
ment it rushes through the narrow Straits of Dover, and, coming in
contact with the still water of the German Sea, forms eddies on either
side, and deposits its sediments. Besides the banks thus formed, there
are, of course, bars formed at the mouths of the rivers emptying into
this shallow sea. By a combination of all these causes, we explain the
numerous banks which render the navigation of this sea so dangerous.
But great banks far away from shore are usually formed by oceanic
currents. Thus the Banks of Newfoundland are evidently formed by
the meeting of the polar current (e, Fig. 32), bearing icebergs loaded
with earth, and the warm current of the Gulf Stream, perhaps also bear-
ing its share of fine sediment. Again, the Gulf Stream, rushing at
42
AQUEOUS AGENCIES.
high velocity (four miles per hour) through the narrow Straits of Florida,
coming in contact with the still water of the Atlantic beyond and form-
ing eddies on each side, and depositing sediment, has certainly con-
tributed to form, if it has not wholly formed, the Bahama Banks on one
side, and the bank on which the Florida reefs are built on the other.
It is probable that many other peculiarities of the Atlantic bottom in
the course of the Gulf Stream may be similarly accounted for. 1
Land formed by Ocean Agencies. Upon submarine banks, however
these may be produced, are gradually formed islands. These islands
are always formed by the immediate agency of waves. As soon as the
submarine bank rises so near the surface that the waves touch bottom
and form breakers, these commence to throw up the sand or mud until an
island is formed, which continues to grow by the same agency, until it
becomes inhabited by plants and animals, and finally by man. The
height of such islands above the sea
will depend upon the height of the
tides and the force of the waves.
They are seldom more than fifteen
feet above high water. Thus, we
find that extensive banks are always
dotted over with islands. In this
manner are formed the low islands so
common about the mouths of har-
bors and estuaries, also the narrow
sand-spits all along our Southern
coast, separating the harbors and
sounds from the ocean. Fig. 34,
which is a map of the North Caro-
lina coast, will give a good idea of
these sand-spits. In the course of
time such sounds, being protected
in some measure by the sand-spits
from the scouring action of the
tides, are gradually filled up with
sediments brought down by the
rivers, leaving only narrow passages
for the flow of the tide. In this
manner were formed the sea-islands
all along our Southern coast, separated from the mainland only by
narrow tidal inlets. These tidal inlets may become filled up, and the
whole coast-line transferred farther seaward.
A large portion of the coasts of the world is thus bordered by wave-
FIG. 84. Coast of North Carolina.
1 See the author's views on this subject, American Journc
46, 1857.
of Science, vol. xxiii., p.
GLACIERS. 43
formed islands. We have already seen, however, that on some coasts,
e. g\, Norway, Scotland, etc., islands are formed by the destructive action
of waves. Bordering islands, so common along all coasts, are there-
fore of two classes, and formed by two opposite effects of waves the
one land-destroying, the other land-forming. The islands of one class
are high and rocky, of the other low and sandy or muddy ; the former
are the scattered remains of an old coast -line, the latter the commencing
points of a new coast-line.
SECTION 3. ICE.
The agency of ice will be considered under the heads of Glaciers and
Icebergs; the effects of frost in disintegrating rocks having been already
treated of under Atmospheric Agencies. It is only comparatively re-
cently that the great importance of ice as a geological agent has been
recognized. To Agassiz is due the credit of having first fully recognized
this importance.
Glaciers.
Definition. In many parts of the earth, where the mountains reach
into the region of perpetual snow, and other favoring conditions are
present, we find that the mountain-valleys are occupied by masses of
compact ice, connected with the snow-cap above, but extending far
below the snow-line into the region of cultivated fields, and moving
slowly but constantly down the slope of the valley. Such valtey-pro-
longations of the perpetual snow-caps are called glaciers. The exist-
ence of glaciers, and their motion, is necessitated by the great law of
circulation, so universal in Nature. For in those countries where gla-
ciers exist, the waste of perpetual snow by evaporation is small in com-
parison with the supply by the fall of snow. There would be no limit,
therefore, to the accumulation of snow on mountain-tops, if it did not
run off, down the slope, by these ice-streams, and thus return into the
general circulation of meteoric waters. Glaciers extend not only far
below the snow-line, but even far below the mean line of 32. In the
Alps the snow-line is about 9,000 * feet above the sea-level, while some
of the glaciers extend down to within 3,400 feet of the same level, i. e.,
more than 5,000 feet below the snow-line.
Necessary Conditions. The conditions necessary to the formation
of glaciers are : 1. The mountain must rise into the region of perpetual
snow, for the snow-cap is the fountain of glaciers. 2. There must be
considerable changes of temperature, and therefore alternate tha wings
and freezings. This condition seems necessary to the gradual compact-
ing of snow into glacier-ice. The want of this condition is apparently
the cause of the non-existence, or small . development, of glaciers in
1 Dana's " Manual of Geology."
44 AQUEOUS AGENCIES.
tropical regions. 3. A moist atmosphere is favorable to their produc-
tion, for the moister the climate the greater is the snow-fall, and the
smaller is the waste by evaporation, and therefore the greater the
excess which must run off by glaciers. This is an additional reason
why glaciers are not formed under the equator ; for the great capacity
for moisture of the air in this zone increases the waste while it decreases
the fall of snow. This is also the reason of the scanty formation of gla-
ciers in the Sierra Mountains, and their abundance and magnitude in
the Alps.
Ramifications of Glaciers. We have said glaciers are valley-prolon-
gations of the ice-cap. Now, mountain-valleys are of two kinds, viz.:
1. The deeper and larger longitudinal valleys, between parallel ranges;
and, 2. The transverse or radiating valleys, transverse in case of ridges,
and radiating in case of peaks. The longitudinal valleys may be formed
either by erosion or by igneous agencies folding the crust of the earth ;
but the transverse or radiating valleys are always formed by erosion.
It is these valleys of erosion which are occupied by glaciers. In coun-
tries where there are no glaciers they are occupied, of course, by
streams. We have already shown (p. 9) how these valleys commence
near the top of the mountain as furrows, which, uniting, form gullies,
and these, in their turn, forming ravines and gorges, thus becoming less
and less numerous, but larger as we approach the base of the mountain.
In the same manner, therefore, as streams ramify, so also do glaciers.
The only difference is the degree of ramification. Streams ramify
almost infinitely, while glaciers seldom have more than three or four
tributaries. Fig. 35 is a map of the Mont Blanc glacier-region. By
inspection of this map it will be seen that the Merde Glace, m, receives
four tributaries, marked ta, I, g, etc. On page 51 is an enlarged view
of the same glacier, with its tributaries.
Motion of Glaciers. Again, we have said in our definition that gla-
ciers are in constant motion. By the law of circulation, constant down-
ward motion is as necessary to the idea of a glacier as it is to that of a
river, since both the glacier and the river carry away the excess of sup-
ply over evaporation. But a glacier, though in constant motion, never
passes beyond a certain point, where the slow downward motion is^
exactly balanced by the melting of the ice by sun and air. This point
is called the lower limit of the glacier. As long as conditions remain
unchanged, the lower end of the glacier remains exactly at the same
point, although the substance of the glacier moves always downward.
But if external conditions change, the point of the glacier may move
upward or downward. Thus, during a succession of cool, damp years,
the melting being less rapid, the point of the glacier moves slowly down,
sometimes invading cultivated fields and overturning huts, until it finds
a new point of equilibrium. During a succession of warm and dry years,
GLACIERS.
46
AQUEOUS AGENCIES.
on the contrary, the melting being more rapid, the point retreats, to
find a new point of equilibrium higher up the mountain. But, whether
the point be stationary, or advance or recede, the substance of the gla-
cier is ever moving steadily onward. It may be compared to those
rivers, in dry, sandy countries, which run ever toward the sea, but never
reach beyond a certain point, being absorbed by the sand.
Graphic Illustration. These facts may be conveniently represented
as follows : Let a d (Fig. 36) equal the length of the mountain-slope,
and the line a b (= c d) the velocity of the
a. glacier-motion taken as uniform. This velocity
varies with the slope, as will be seen hereafter,
but is little affected by the elevation. It may
be taken, therefore, as the same in every part
of the slope, and therefore correctly repre-
sented by equal lines, i. e., by the ordinates of
the parallelogram abed. The melting power
of the sun and air, on the contrary, regularly
increases from the top, where it is almost noth-
ing, to the bottom of the mountain. We will,
therefore, represent it by the increasing ordi-
nates of the triangle a e d. At a?, therefore,
where the ordinates of the triangle and of the
parallelogram are equal to each other, will be
the lower limit of the glacier. During a suc-
cession of cool years the rate of melting will
be represented by the ordinates of the smaller
triangle a g d, and the point of the glacier will advance to z. During
a succession of warm, dry years, the rate of melting will be represented
by the larger triangle afd, and the point of the glacier will recede to y.
Line of the Lower Limit of Glaciers. We have said, again, that 'the
glacier reaches below the snow-line. There are three lines, or rather
spheroidal surfaces, running above the surface of the earth, which are
apt to be confounded with one another, and must, therefore, be now
defined. These are the line of perpetual snow, the mean line of 32,
and the line of the lower limit of glaciers. The line of perpetual snow,
at the equator, is about 16,000 to 17,000 feet above the sea-level. As
we approach the poles it gradually approaches the sea-level, until it
touches at or near the poles, forming thus a spheroid more oblate than
the earth itself (Fig. 37). Next follows the mean line of 32. This
commences at the equator, E, coincident with the snow-line (it may
be even above it Dana), but diverges as we pass toward the pole,
and finally touches the sea-level at about 66 north and south lati-
tude, at b b. Below this, again, is the line of lower limit of glaciers,
which, commencing again nearly coincident with the two preceding, at
u c
FIG. 86.
GLACIERS.
47
the equator, approaches and touches the sea-level at about 50 latitude,
or, under favorable circumstances, at even lower latitudes. The differ-
ence between these lines is often several thousand feet. In the Alps,
the line of 32 is 2,000 feet, and the line of lower limit of glaciers 5,000
feet, below the snow-
line. In some parts
of the arctic region,
the line of 32 is 3,500
feet below the snow-
line, and in Norway
the lower limit of gla-
ciers is 4,000 feet be-
low the line of 32
(Dana). For the sake
of simplicity we have
represented the sur-
faces, of which these
lines are the sections,
as regular spheroids ;
but, in fact, they are
very irregular, being
much influenced by
climate. Their inter-
section with the sea-
level will, therefore, not be along lines of latitude, but will be irregular,
like isotherms. As the line a c marks the lower limit of glaciers in
different latitudes, it is evident that at c glaciers will touch the sea, and
beyond this point will run far into the sea. It is in this manner, as we
will see hereafter, that icebergs are formed. In Chili, glaciers touch
the sea-level at 46 40' south latitude. 1
General Description. In glacial regions a mountain-valley is occu-
pied in its highest part by perpetual snow; below this, farther down
the valley, by neve a granular snow, intermediate between snow and
ice ; still farther down, by true glacier-ice ; and, finally, by a river
(Fig. 41). This river is formed partly by the melting of the whole
surface of the glacier, both above and below, and partly by the natural
drainage of the valley. The glacier, however, is the principal source.
From the point of every glacier, therefore, runs a river.
The size of glaciers varies very much. Alpine glaciers are some of
them fifteen miles long, and vary from half a mile to three miles in
breadth, and from one hundred to six hundred feet in thickness. In
the region about Mont Blanc and Finsteraarhorn alone there are about
four hundred glaciers. In the temperate regions of North America, gla-
1 D'Archiac, " Histoire de Geologic."
FIG. 3T.-General Relation of Limit of Glaciers to Snow-Line.
4$ AQUEOUS AGENCIES.
ciers are found only on the Pacific coast, in the Sierra and Cascade
Ranges. On Mount Shasta, and 'especially on Mount Rainier, glaciers
equal to those of the Alps have been recently found. In the Himalaya
Mountains they are developed upon a much more gigantic scale ; but it
is only in arctic regions that we can form any just conception of their
immense importance as geological agents. In Spitzbergen, a glacier
was seen eleven miles wide and four hundred feet thick at the point. 1
Of course, this thickness only represents the part above water. By far
the larger part, or six-sevenths, is below water-level. In Greenland the
great Humboldt Glacier enters the sea with a point forty-five miles wide
and three hundred feet thick (Kane). But even these examples give
an incomplete idea of the whole truth. Greenland is apparently en-
tirely covered with an immense sheet of 'ice , several thousand feet thick,
which moves slowly seaward, and enters the ocean through immense
fiords. 8 Judging from the immense barrier of icebergs found by Cap-
tain Wilkes (United States Exploring Expedition) on its coast, the an-
tarctic continent is probably even more thickly covered with ice than
Greenland.
We are apt to suppose that the surface of a glacier must be smooth.
This is, however, very far from being true. On the contrary, the ex-
treme roughness of the ice-surface renders the ascent along the glacier
extremely difficult. This inequality of surface is due partly to unequal
melting, and partly to crevasses, or fissures. The unequal melting is
produced as follows : A stone, lying on the surface of a glacier, pro-
tects the surface beneath from the rays of the sun. Meanwhile the
surrounding ice is melted, until finally the slab
of stone stands on a column of ice often several
feet in height (Fig. 38). A slab seen by Forbes
measured 23 feet long, 17 feet wide, and 3 feet
thick, and rested on a column 13 feet high. In such
/ \ cases the stone finally falls off, leaving a sharp
___-- < ^ pinnacle, and another column commences to form
FIG. 88. Mod^of^Formaaon under the stone. In this manner are formed what
are called needles. When we consider that there
are immense numbers of stones on the glacier-surface, we can easily see
that these needles will multiply indefinitely. If, on the other hand, a
thin stratum of earth stains the surface of the glacier in spots, these
spots will melt faster than the surrounding ice, because more absorb-
ent of heat, and thus form deep holes.
Again, fissures or crevasses, often of great size, ten to twenty feet
wide, one hundred feet deep, and sometimes running entirely across the
glacier, are very abundant. As the surface of the glacier is often cov-
ered with snow, and the fissures thus concealed, they form the most
1 Dana's " Manual." 2 Dr. Rink, " Archives des Sciences," vol. xxvii., p. 155.
GLACIERS. 49
dangerous feature connected with Alpine travel. The law which gov-
erns their formation will be discussed hereafter ; suffice it to say that
the great transverse fissures are formed by the glacier passing over an
angle formed by a sudden change in the slope of the bed. Streams,
produced by the melting of ice, running on the surface of the glacier,
plunge into these fissures with a thundering noise, and hollow out im-
mense wells, called moulins, and magnificent ice-caves. Although the
FIG. 39. Inequalities of the Surface of a Glacier (after Agassiz).
glacier moves, the great crevasses and the wells with their falls remain
stationary, precisely as the position of a rapid or breaker remains sta-
tionary, although the river runs onward ; and for the same reason, viz.,
that it is reformed alwaj^s on the same spot.
From all these causes the surface of a glacier is often studded over
with conical masses and projecting points of every conceivable shape.
This is well shown in the accompanying figure (Fig. 39).
Earth and Stones, etc. The surface of a glacier is, moreover,
largely covered with earth and stones gathered in its course from the
crumbling cliffs on either side. These are often so abundant as almost
to cover the surface. More usually, however, they are distributed in
two or more rows, called moraines. Fig. 40 is a view of a glacier, with
its moraines and lateral crevasses.
Such is a general description of the appearance of a glacier. There
are, however, several points which, by their importance and interest,
require special notice. These are : 1. Moraines ; 2. Glaciers as a geo-
logical agent ; 3. Glacier-motion ; and, 4. Glacier-structure.
50
AQUEOUS AGENCIES.
FIG. 40. Zermatt Glacier (Agassiz).
Moraines.
There are three kinds of moraines described by writers, viz., lateral
moraines, medial moraines, and terminal moraines. Lateral moraines
are continuous lines of earth and stones, arranged on either margin of
the glacier, and evidently formed from the ruins of the crumbling cliffs
of the inclosing valley. This debris does not fall from every part of
the valley-sides, but generally only from certain bold, projecting cliffs.
It is converted into a continuous line by the motion of the glacier, just
as light materials thrown constantly into a river at one poirit would
appear as a continuous line on the stream.
Medial moraines are similar lines of debris, occupying the central
portions of the glacier. Sometimes there is but one ; sometimes two, or
more ; sometimes the whole surface of the glacier is almost covered with
them. The true explanation was first pointed out by Agassiz. They
are formed by the coalescence of the interior lateral moraines of tribu-
tary glaciers, carried down the main trunk by the motion of the ice-
current. The accompanying map (Fig. 41) of the Mer de Glace and
its tributaries shows clearly the manner in which these moraines are
formed. Both lateral and medial moraines are generally situated on a
ridge of ice, sometimes fifty to eighty feet high, evidently formed by
the protection of the ice, in this part, from the melting-power of the
GLACIERS AS A GEOLOGICAL AGENT.
51
sun. The fragments of rock brought down by glaciers are often of
enormous size. One described by Forbes contained 244,000 cubic feet.
Everything which falls upon
the surface of the glacier is
slowly and silently carried down-
ward by this ice-stream, and
finally dropped at its point.
Much finely-triturated matter is
also pushed along beneath the
glacier, and finds its way to
the same point. In the course
of time an immense accumula-
tion is formed, of somewhat
crescentic shape, as seen in
Fig. 41.
This accumulation is called
the terminal moraine. It is the
delta of this ice-river. The ex-
istence of moraines is a con-
stant witness of the motion of
the glaciers.
Glaciers as a Geological Agent.
Glaciers, like rivers, erode the
surface over which they move,
carry the materials gathered in
their course often to great dis-
tances, and finally deposit them.
In all these respects, however, the effects of their action are perfectly
characteristic.
Erosion. When we consider the weight of a glaciers and their un-
yielding nature as compared with water, it is easy to see that their
erosive power must be very great. This is increased immensely by
fragments of stone of every conceivable size carried along between the
glacier and its bed. These partly fall in at the sides and become
jammed between the glacier and the confining rocks, partly fall into
crevasses and work their way to the bed, and partly are torn from the
rocky bed itself. The effects of glacier erosion differ entirely from
those of water : 1. Water, by virtue of its perfect fluidity, wears away
the softer spots of rock and leaves the harder standing in relief ; while
a glacier, like an unyielding rubber, grinds both hard and soft to one
level. This, however, is not so absolutely true of glaciers as might
be supposed. Glaciers, for reasons to be discussed hereafter, conform
to large and gentle inequalities of their beds, though not to small ones,
FIG. 41. Mer de Glace.
52 AQUEOUS AGENCIES.
acting thus like a very stiffly viscous body. Thus their beds are worn
into very remarkable and characteristic smooth and rounded depressions
and elevations called roches moutonnees (Fig. 42). Sometimes large
and deep hollows are swept out by a glacier at some point where the
FIG. 42. Eoches Moutonnees of an Ancient Glacier, Colorado (after Hayden).
rock is softer or where the slope of the bed changes suddenly from a
greater to a less angle. If the glacier should subsequently retire, water
accumulates in these excavations and forms lakelets. Such lakelets are
common in old glacial beds.
2. The lines produced by water-erosion, if detectible at all, are
always more or less irregular and meandering ; while those produced by
glaciers are straight and parallel (Fig. 43).
Thus, smooth, gently-billowy surfaces, marked with straight parallel
scratches, are very characteristic of glacial action. We will call such
surfaces glaciated, and the process glaciation.
Transportation. The transporting power of glaciers follows no law
similar to that pointed out under rivers in fact, it has no relation at all
to velocity. The reason is, that the stone rests on the surface as afloat-
ing body. There is, therefore, no limit to the transporting power.
Bowlders of 250,000 cubic feet are carried with the same ease and the
same velocity as the finest dust.
Deposit Balanced Stones. A water-current carrying stones bruises
and rounds their corners, and deposits them always in the most secure
positions ; but glaciers often deposit huge angular fragments of rock
GLACIERS AS A GEOLOGICAL AGENT. 53
in the most insecure positions so nicely balanced, sometimes, that a
touch of the hand will dislodge them. The reason is, they are set
down by the gradually melting ice with inconceivable gentleness. Thus
balanced stones, rocking-stones, etc., are common in glacial regions.
In using these as a sign of glacial action, however, we must recollect
FIG. 43. Glacial Scorings (after Agassiz).
that a bowlder dropped by any agent, or even a bowlder of disintegra-
tion (p. 6), may in time become a rocking-stone, by slow but irregular
disintegration changing the position of the centre of gravity. But angu-
lar erratics in insecure positions are very characteristic of glacial action.
Material of the Terminal Moraine. The material of the terminal
moraine is very characteristic : 1. It consists of fragments of every con-
ceivable size, from huge bowlders down to fine earth, mixed together
into an heterogeneous mass entirely different from the neatly-sorted de-
posits from water. It is, therefore, entirely unsorted and unstratified,
and without organic remains. 2. The mass consists of two parts, viz., that
which was carried on the top of the glacier, and that which was forced
out beneath (moraine profonde). The first consists of loose material
containing angular, unworn fragments ; the other of fine compact mate-
rial containing fragments worn and polished, and scratched with
straight parallel scratches, but in both cases entirely different from
water-worn pebbles. In all respects, therefore, the action of glaciers is
characteristic and cannot be confounded with that of water.
Evidences of Former Extension of Glaciers. It is by evidence of
this kind that the former great extension of glaciers in regions where
they now exist, and the former existence of glaciers in regions where
they no longer exist, have been proved. We have already stated that
during a succession of cool, damp seasons, a glacier may extend far
54
AQUEOUS AGENCIES.
FIG. 44. Section across Glacial Valley, showing
old Lateral Moraines.
beyond its previous limits. Similar changes take place also in the
depth of a glacier. In a word, glaciers are subject to floods like rivers ;
only these floods, instead of being annual, are secular. Now, as rivers
after floods leave floating material stranded on the banks, showing the
height of the flood-water, so, in
the decrease of a glacier, lines
of bowlders are left stranded,
often delicately balanced, on
ledges high up the sides of the
valley. These
lines of bowlders
mark the former
height of the gla-
cier. Some of these lines have been found in the Alps
2,000 feet above the present level. Fig. 44 is a cross-sec-
tion of a glacial valley. The dotted lines show the for-
mer level. In the same valleys we find old terminal mo-
raines (Fig. 45, ') miles beyond the present limit of the
glacier. The characteristic planing, polishing, and par-
allel scoring, have been found equally far above the
present level and beyond the present limit of Alpine
glaciers.
Glacial Lakes. When a glacier retreats, the water of
the river which flows from its point may accumulate in
great rock-basins scooped out by the glacier, or else be-
hind the old terminal moraines. In these two ways lakes
are often formed.
Motion of Glaciers and its Laws.
Evidences of Motion. That glaciers move slowly down their valleys
was long known to Alpine hunters. Rude experiments of the first scien-
tific explorers, confirmed this popular notion. Hugi in 1827 built a hut
upon the Aar glacier. This hut was visited from year to year by scien-
tific explorers and its change of position measured. In 1841 Agassiz
found that it had moved in all 1,428 metres in fourteen years, or about
100 metres (330 feet) per annum. Numerous other observations from
year to year by Agassiz and others, on the position of conspicuous bowl-
ders lying on the surface of glaciers, confirmed these results and placed
the fact of glacier-motion beyond doubt. But the most important obser-
vations determining both the rate and the laws of glacier-motion were
made in 1842 by Prof. Agassiz on the Aar glacier, and Prof. Forbes on
the Mer de Glace. By these experiments, carefully made by driving
stakes into the glacier, in a straight row from one side to the other, and
observing the change in the relative position of the stakes, it was deter-
<L' T, c rif
MOTION OF GLACIERS AND ITS LAWS. 55
mined that the centre of the glacier moved faster than the margins.
This differential motion is the capital discovery in relation to the motion
of glaciers. It is claimed by both Agassiz and Forbes. It had, how-
ever, been previously distinctly stated, though not proved, by Bishop
Rendu.
Laws Of Glacier-Motion. The term differential motion is a con-
densed expression for all the laws of glacier-motion. It asserts that
the different parts of a glacier do not move together as a solid, but
move among themselves in the manner of a fluid. A glacier moves
like a fluid, though a very stiff, viscous fluid ; its motion may there-
fore be rightly called viscoid. We will mention some of the most im-
portant laws of fluid motion, and show that glaciers conform to them.
1. The Velocity of the Central Parts is greater
than that of the Margins. This well-known law of
currents, the result of friction of the fluid against
the containing banks, was completely proved in the
case of glaciers by the experiments of Agassiz and ^*\^--ov-<>-'^''/
Forbes, and recently confirmed in the most perfect a/
manner by Tyndall. A line of stakes, a b c d efg,
placed in a straight row across a glacier, becomes
every day more and more curved, as seen in Fig.
46. The exact rate of motion for each stake
is easily measured by the theodolite. The rate
of the centre is often many times greater than that of the margins.
2. The Velocity of the Surface is greater than that of the Bottom.
This law of currents, which is the necessary result of friction on the
bed, is more difficult to prove in the case of glaciers, because it is dif-
ficult to get a vertical section. The necessary observation was, how-
ever, successfully accomplished by Prof. Tyndall in 1857. We have
already said (page 51) that glaciers
po' conform to large but not to small
; inequalities of their channels : a
glacier, therefore, passing by a nar-
row side-ravine will expose its whole
thickness on the side. Prof. Tyn-
dall, having found such a side ex-
posure more than 140 feet vertical,
placed three pegs in a vertical line, one near the top, one near the mid-
dle, and one at the bottom (Fig. 47, a b c). The vertical line became more
and more inclined daily. The daily motion at top was six inches, in the
middle 4.5 inches, and at the bottom 2.5 inches. Thus, glaciers, like
rivers, slide on their beds and banks, producing erosion ; but, also, the
several layers, both horizontal and vertical, slide on each other.
3. The Velocity increases with the Slope. Fig. 48 represents the
56
AQUEOUS AGENCIES.
surface-slope of the glacier Du Geant, G ; the Mer de Glace, M ; and
the glacier De J3ois, B ; and their daily motion. The increase of ve-
locity with the slope is evident.
4. The Velocity increases with the Fluidity. The daily motion of
glaciers is greater in summer, when the ice is rapidly melting, than in
winter ; and in mid-day than at night.
5. The Velocity increases with the Depth. In the Alps, where the
thickness is 200 to 300 feet, the mean daily motion is one to three
feet ; but in Greenland, where the thickness is 2,000 to 3,000 feet, the
daily motion, in spite of the much lower temperature, is in some cases
60 feet. 1
6. Fluid Currents conform to the Irregularities of their Channel
Glaciers, like water-currents, conform to the inequalities of the bot-
tom and sides of their channels. They
have their shallows and their deeps, their
narrows and their lakes,
their cascades, their rap-
ids, and their tranquil por-
tions. Fig. 49 shows a
glacier running through a
narrow gorge into a wide
lake of ice, and again
through another gorge.
There is this difference,
however, between a gla-
cier and a water-current, viz., that, while the latter
conforms to even the minutest and sharpest outlines,
the former conforms only to the larger or more gentle.
In this, a glacier acts like a stiff, viscous fluid.
7. The Line of Swiftest Motion is more sinuous
than the Channel. We have already seen that this is
true of rivers (page 21). The line of swiftest current
is reflected from side to side, increasing the curves by erosion. The
same has been recently proved by Tyndall to be the case with glaciers.
Fig. 50 represents a portion of a sinuous glacier, like the Mer de Glace :
the dotted line represents the line of swiftest motion.
1 Helland, Journal of Geological Society, vol. xxxiii., p. 142, et scq.
FIG. 50.
THEORIES OF GLACIER-MOTION. 57
Theories of Glacier- Motion.
There are few subjects connected with the physics of the earth
which have excited more interest than that of glacier-motion. The
subject is one of exceeding beauty, and not without geological im-
portance. Passing over several very ingenious theories which have
now been abandoned, the first theory which was conceived in the true
inductive spirit, and which explains the differential motion, is that of
Prof. James Forbes.
Viscosity Theory of Forbes.
Statement of the Theory. According to Forbes, ice, though ap-
parently so hard and solid, is really, to a slight extent, a viscous body.
In small masses this property is not noticeable, but in large masses and
under long-continued pressure it slowly yields, and will flow like a stiffly
viscous fluid. In large masses like a glacier, this steady, powerful press-
ure is furnished by the immense weight of the superincumbent ice.
Argument. It is evident that this theory completely accounts for
all the phenomena of glacier-motion, even in their minutest details. A
glacier, beyond all doubt, moves like a viscous body, but it is still a
question whether it does so by virtue of a property of viscosity. The
proposition that ice is a viscous substance seems at first palpably ab-
surd. It is necessary, therefore, to show that this proposition is not so
absurd as it seems.
The properties of solidity and liquidity, though perfectly distinct
and even incompatible in our minds, nevertheless, in Nature, shade into
one another in the most imperceptible manner. Malleability, plasticity,
and viscosity, are intermediate terms of a connecting series. The idea
which underlies all these expressions is that of capacity of motion of
the molecules among themselves without rupture : the difference among
them being the greater or less resistance to that motion. In the case
of malleable bodies, like the metals, great force is required to produce
motion ; in plastic bodies, like wax or clay, less force is required ; in
viscous bodies, like stiff tar, motion takes place spontaneously but
slowly ; while in liquids it takes place freely and with little or no resist-
ance. In all of these cases, if the pressure be sufficient, the body will
change its form without rupture in other words, will flow. Now, by
increasing the mass we may increase the pressure to any extent.
Therefore, all malleable, ductile, plastic, or viscous bodies, if in suffi-
ciently large masses, will flow like water. Thus, a mass of lead, suffi-
ciently thick, would certainly flow under the pressure of its own weight.
But solid bodies may be divided into two great classes, viz., bodies
which are malleable, plastic, or viscous, and bodies which are brittle y
the very idea of brittleness being that of total incapacity of motion
58 AQUEOUS AGENCIES.
among the particles without rupture. Now, ice belongs to the class of
brittle bodies. Forbes attempts to remove this difficulty by showing
that many apparently brittle bodies will also flow under their own
weight ; for instance, pitch, so hard and brittle that it flies to pieces
under a blow of the hammer, will, if the containing barrel be removed,
flow and spread itself in every direction. So, also, molasses-candy,
made quite hard and brittle, will still flow by standing. A remarkable
pitch-lake, about three miles in circumference, occurs in Trinidad. The
pitch is described as in constant, slow-boiling motion, coming up in
the centre, flowing over to the circumference, and again sinking down.
Yet this pitch, in small masses, would be called solid and brittle.
Struck with a hammer, it flies to pieces like glass. In fact, the essen-
tial peculiarity of a stiff, viscous body, in which it differs from mal-
leable or plastic bodies, is, that it yields only to slowly-applied force.
Forbes, therefore, thinks that glacier-ice is an exceedingly stiff, vis-
cous substance, which, though apparently brittle in small quantities and
to sudden force, yet, under the slow-acting but powerful pressure of
its own weight, flows down the slope of its bed, squeezing through
narrows and spreading out into lakes, conforming to all the larger and
gentler inequalities of bed and banks, but not to the sharper ones.
The velocity of motion is small in the same proportion as the viscous
mass is stiff. The descent of the Mer de Glace from the cascade of the
Glacier du Geant to the point of Glacier de Bois, a distance of ten miles,
is 4,000 feet. Water, under these circumstances, would rush with fear-
ful velocity. The glacier moves but two feet in twenty-four hours.
Regelation Theory of Tyndall.
If ice be indeed a viscous body, then there seems no reason why it
should not yield to pressure even in small masses, if the pressure be
sufficiently slowly graduated. In the hands of a skillful experiment-
alist it ought to exhibit this property. Prof. Tyndall tried the ex-
periment. Masses of ice of various forms were subjected to slowly-
graduated, hydrostatic pressure. In every case, however slowly grad-
uated the pressure, the ice broke ; but if the broken fragments were
pressed together, they reunited into new forms. In this manner, ice in
the hands of Prof. Tyndall proved as plastic as clay : spheres of ice
(a, Fig. 51) were flattened into lenses (>), hemispheres (c) were changed
into bowls (f), and bars (e) into semi-rings (./") He even asserts that
ice may be moulded into any desirable form ; e. g., into vases, statuettes,
rings, coils, knots, etc. Here, then, we have a power of being moulded
such as was not dreamed of before ; but this power was not depend-
ent on a property of viscosity, but upon another property long known,
but only recently investigated by Faraday, viz., the property of rege-
lation.
THEORIES OF GLACIER-MOTION.
59
Regelation. If two slabs of ice be laid one atop of the other, they
soon freeze into a solid mass. This will take place not only in cold
weather, but in midsummer, or even if boiling 1 water be thrown over
the slabs. If a mass of ice be broken to pieces, and the fragments be
pressed, or even brought in contact with one another, they will quickly
unite into a solid mass. Snow pressed in the warm hand, though con-
FIG. 51. A B C, moulds ; a c e, original forms of the ice ; 6 df, the forms into which they
were moulded.
stantly melting, gradually becomes compacted into solid ice. This very
remarkable but imperfectly understood property of ice completely ex-
plains the phenomena of moulding ice by experiment. By this property
the broken fragments reunite in a new form as solid as before. We
may possibly call this property of moulding under pressure plasticity
(although it is not true plasticity, since it does not mould without rupt-
ure, but by rupture and regelation} ; but it cannot in any sense be called
viscosity, for the true definition of viscosity is the property of yielding
under tension the property of stretching like molasses-candy, or
melted glass ; but ice in the experiments, according to Tyndall, did not
yield in the slightest degree to tension. In the experiment, if, instead
of placing the straight bar at once into the curved mould, it had been
placed successively in a thousand moulds, with gradually-increased
curvature, or, still better, if placed in a straight mould, and this mould,
while under pressure, curved slowly, then there would have been no
sudden visible ruptures, but an infinite number of small ruptures and
regelations going on all the time. The ice would have behaved pre-
cisely like a viscous body. Now, this is precisely what takes place in
a glacier.
Application to Glaciers. A glacier, on account of its immense mass,
is, in its lower parts, under the immense pressure of its own weight
tending to mould it to the inequalities of its own bed, and in every part
under a still more powerful pressure a pressure proportioned to the
height of the head of the glacier urging it down the slope of its bed.
Under the influence of this pressure the mass is continually yielding by
60 AQUEOUS AGENCIES.
fracture, but again uniting by regelation. By this constant process of
crushing, change of form, and reunion, the glacier behaves like a
plastic or viscous body; though of true plasticity or true viscosity there
is, according to Tyndall, none. In fact, we have in the phenomena of
glaciers the most delicate test of viscosity conceivable ; but we find the
glaciers will not stand the test. For instance, the slope of the Mer de
Glace at one point changes from 4 to 9 25' ' (Fig. 52), and yet the
glacier, although moving but two feet a day, cannot make this slight
bend without rupture ; for at this point there are always large trans-
verse fissures which heal up below by pressure and regelation. In an-
other place the glacier is similarly broken by passing an angle produced
by a change of slope of only 2. It seems almost impossible that a
body having the slightest viscositv should be fractured under these cir-
cumstances. Tyndall concludes, therefore, that the motion of glaciers
is viscoid, but the body is not viscous the viscoid motion being the
result, not of the property of viscosity, but of fracture and regelation.
Comparison Of the Two Theories. Forbes's theory supposes motion
among the ultimate particles without rupture. Tyndall's supposes
motion among discrete particles by rupture, change of position, and
regelation. The undoubted viscoid motion is equally explained by
both : by the one, by a property of viscosity ; by the other, by a prop-
erty of regelation.
Conclusion. It seems almost certain that both views are true, and
that both properties are concerned in glacial motion. Eecent observa-
tions and experiments have shown an undoubted viscosity in ice es-
pecially in ice containing much inclosed and dissolved air, as is the case
with glacier-ice. Ice boards supported at the two ends gradually bend
into an arc under their own weight. Cylinders of snow compacted into
'ice may be bent in the hand to a semicircle without rupture. 8
Structure of Glaciers.
There are two points connected with the structure of glaciers which
require notice, viz., the veined structure and the fissures.
Veined Structure. The ice of glaciers is not homogeneous, but con-
sists of white vesicular ice (white because vesicular), banded, often very
beautifully, with solid transparent blue ice (transparent blue because
solid), the banding sometimes so delicate that a hand-specimen looks
1 Tyndall, " Glaciers of the Alps."
8 Altkin, American Journal of Science, vol. v., p. 305, third series.
THEORIES OF GLACIER-MOTION. 61
like striped agate. These blue veins are not continuous planes, but
apparently very flat lenticular in shape, varying in thickness from a
line to several inches, and in length from a few inches to several feet.
Their direction being parallel to one another, they give a stratified or
cleavage structure to the glacier, and, in melting, the glacier often
splits or cleaves along these planes. According to Prof. Forbes, look-
ing upon the glacier as a whole, we may regard the strata as taking
the form represented by the subjoined figures. In a section parallel to
FIG. 53. Sections of a Gkcier.
FIG. 5t. Ideal Diagram, showing Struct-
ure of Glaciers (after Forbes).
the surface (Fig. 53, a), the strata outcrop in the form of loops. A
cross-section (Fig. 53, b) shows them lying in troughs, and a longi-
tudinal vertical section (Fig. 53, c) shows the manner in which they
dip. Fig. 54 is an ideal glacier cut in several directions, and combining
in one view the three sections given above. It is generally impossible
to trace the veins around from side to side. Sometimes they are most
distinct on the margins, and then are called marginal veins ; some-
times at the point of the loop transverse veins / sometimes tributaries
running together, as in the figure (Fig. 54) the interior branches of the
two loops coalesce, and are flattened against one another, and form
longitudinal veins.
Fissures. These are also marginal, transverse, and longitudinal.
The marginal fissures are shown in Fig. 40 ; they are always at right
angles to the marginal veins.
62 AQUEOUS AGENCIES.
Theories of Structure.
Fissures. There can be no doubt that the great fissures or crevasses
are produced by tension or stretching, and that their direction is always
at right angles to the line of greatest tension. Thus the transverse
fissures are produced by the stretching of the glacier in passing over a
salient angle. The marginal fissures are produced by the dragging or
pulling of the swifter central portions upon the slower marginal por-
tions. It has been proved by Hopkins, the English physicist and geolo-
gist, that the line of greatest tension from this cause would be inclined
45, with the course of the glacier as shown by the arrows (Fig. 55).
The fissures should be at right angles to these lines, and, therefore, also
inclined 45 with the margin, and running upward and inward. The
longitudinal fissures are best seen where a glacier runs through a nar-
row gorge out on an open plain. The lateral spreading of the glacier
causes it to crack longitudinally (Fig. 56). Fig. 57 is a longitudinal
vertical section of the same.
Veined Structure. Tyndall has shown conclusively that veins are
always at right angles to the line of greatest pressure, and that, there-
fore, they are produced by pressure. Thus fissures and veins, being
produced by opposite causes one by tension and the other by pressure
are found under opposite con-
ditions. Thus as transverse fis-
sures are produced by the longi-
tudinal stretching of a glacier
passing over a salient angle, so
transverse veins are formed by
the longitudinal compression of
a glacier passing over a re'enter-
ing angle. Fig. 57 is a section
of the Rh6ne glacier (Fig. 56),
showing the crevasses (c c c)
THEORIES OF STRUCTURE.
63
produced by the steep declivity, and the veined structure (s s s) pro-
duced by the compression consequent upon the change of angle on
coming out on the plain. The relation of crevasses and vein-structure
is still better shown in the ideal section (Fig. 58).
Again, as marginal fissures are produced by the pulling of the cen-
tral portions upon the lag-
ging margins behind, so /n c
the marginal veins are pro-
duced by the crowding or
pushing of the swifter cen-
tral parts upon the mar-
ginal parts in front (Fig.
59). The marginal veins
are. therefore, inclined to
the margin about 45, but pointing inward and downward, and, there-
fore, at right angles to the crevasses. The relation of these to one
another is shown in Fig. 60.
Finally, as longitudinal fissures are produced by lateral spreading
(Fig. 56), so longitudinal veins are produced by lateral compression.
This is best seen where two tributaries meet at high angle (Fig. 61)
for instance, where the Glacier du G6ant and the Glacier de Lechaud
form the Mer de Glace (Fig. 41). All these facts have been experi-
mentally illustrated by Tyndall.
Physical Theory of Veins. There is little doubt that veins are
formed by pressure at right angles to the direction of the veins ; but
how pressure produces this structure is very imperfectly understood.
Probably at least a partial explanation is contained in the following
proposition : 1. White vesicular ice by powerful pressure is crushed, the
air escapes, and the ice is refrozen into solid blue transparent ice. 2.
Ice being a substance which expands in freezing, and, therefore, con-
tracts in melting, its freezing and melting point is lowered by pressure.
Therefore, ice at or near 32 Fahr. is melted by pressure. Now, the
glacier is under powerful pressure of its own weight, and the stress of
64
AQUEOUS AGENCIES.
this pressure is ever changing from point to point by the changing
position of the particles produced by the motion. Thus the glacier in'
places is ever melting under pressure, and again refreezing by relief of
pressure. The melting discharges the air-bubbles, and, in refreezing,
the ice is blue. 3. No substance is perfectly homogeneous, and of
equal strength in all parts ; therefore, this crushing and melting, and
consequent conversion of white into blue ice, take place irregularly in
spots. 4. As ice of a glacier acts like a viscous substance, the final
effect of pressure would be to flatten these spots, both white and blue,
in the direction of greatest pressure, and extend them in a direction at
right angles to the pressure, and thus create bands in this direction. 5.
Differential motion would also tend to bring the veins into the direction
indicated by Forbes.
Floating Ice Icebergs.
We have already seen (page 47) that at a certain latitude, varying
from 46 in South America to about 65 in Norway, glaciers touch the
surface of the ocean. Beyond this latitude, they run out to sea often to
great distances. By the buoyant power of water, assisted by tides and
waves, these projecting floating masses are broken off, and accumulate
as immense ice-barriers in polar seas, or are drifted away by currents
toward the equator. Such floating fragments of glaciers are called ice-
FIG. 62. Formation of Icebergs.
bergs. Fig. 62 is an ideal section, through a glacial valley, in which
a g is the glacier, b the cliffs beyond, Ij the sea-level, and * an iceberg.
The principal source of the icelfergs of the north Atlantic is the
coast of Greenland. This country is an elevated table-land, sloping
in every direction to a coast deeply indented like Norway, with alter-
nate deep fiords and jutting headlands. The whole table-land is com-
pletely covered with an ice-sheet, probably several thousand feet thick,
moving slowly seaward, and discharging through the fiords as immense
FLOATING ICE ICEBERGS. 65
glaciers, 1 which, as already explained, form icebergs. In this remarkable
country no water falls from the atmosphere except in the form of
snow, and all the rivers are glaciers. The geological effects of such a
moving ice-sheet may be easily imagined. The whole surface of the
country rock must be polished and scored, the general direction of the
striae being parallel over large areas.
The antarctic continent is probably similarly, and even more thick-
ly, ice-sheeted, for the humid atmosphere of that region is very favorable
to the accumulation of snow and ice. Captain Wilkes found an impen-
etrable ice-barrier, in many places 150 to 200 .feet high, for 1,200
miles along that coast. From this ice-barrier, icebergs separate and
are drifted toward the equator.
The formation of icebergs in polar regions, and their drifting into
warmer latitudes, to be melted there, is evidently a necessary conse-
quence of the great law of circulation, for otherwise ice would accumu-
late without limit in these regions.
General Description. The number of icebergs accumulated about
polar coasts is almost inconceivable. Scoresby counted 500 at one
view. Kane counted 280 of the first magnitude at one view. They
are often 200 and sometimes even 300 feet high, and the mass above
water 66,000,000 cubic yards (Dr. Rink). As the specific gravity of
ice is 0.918, if these were solid ice, there would be but one-twelfth
above water; but as glacier-ice is somewhat vesicular, there is about
one-seventh above water. The thickness of some of these icebergs
must therefore be 2,000 to 3,000 feet, and their volume near 500,000,000
cubic yards, which is about equivalent to a mass one mile square, and
500 feet thick. Under the influence of the melting power of the sun un-
1 Dr. Rink, "Archives des Sciences," vol. xxvii., p. 155.
5
66 AQUEOUS AGENCIES.
equally affecting different parts, they assume various and often strange
forms. The accompanying figure (Fig. 63) gives the usual appearance
in the northern Atlantic. Those separated from the antarctic barrier
present, before they have been much acted upon by the sun, a much
more regularly prismatic appearance. Fig. 64 gives the appearance of
one of these prismatic blocks or tables, 180 feet high, seen by Sir James
Ross in the antarctic seas.
Icebergs as a Geological Agent Erosion. The polishing and scor-
ing effects of the ice-sheets and of their discharging glaciers must, of
course, extend over the sea-bottoms about polar coasts as far as the
glaciers touch bottom, which, considering their immense thickness,
must be for considerable distance (Fig. 62, j to g). This, however, is
glacier agency rather than iceberg agency. On being separated they
float away, and are carried by currents with their immense loads of
earth and bowlders, amounting often to 100,000 tons or more, as far as
40 or even 36 latitude, where, being gradually melted, they drop
their burden. If the water be not sufficiently deep, they ground, and
being swayed by waves and tides they chafe and score the bottom in a
somewhat irregular manner ; or, packing together in large fields, and
urged onward by powerful currents, they may possibly score the bot-
tom over considerable areas somewhat in the manner of glaciers. A
large iceberg will ground in water 2,000 and 2,500 feet deep ; they
have been found by James Ross actually aground in 1,560 feet of water
off Victoria Land. A true glaciated surface, however, cannot be pro-
duced by icebergs.
Deposits. The bottom of the sea about polar shores is found deep-
ly covered with materials brought down by glaciers and dropped by
icebergs (Fig. 52). Again, similar materials are carried by icebergs as
far as these are drifted by currents, and spread on the bottom of the
sea everywhere in the course of these currents. Where stranded ice-
bergs accumulate, as on the banks of Newfoundland, large quantities of
such materials are deposited. These banks are in fact supposed to
MECHANICAL AGENCIES OF WATER. 6f
have been formed in this way. Such deposits have not been sufficient-
ly examined ; they are probably somewhat similar to those of glaciers,
exhibiting, however, some signs of the sorting power of water. Bal-
anced stones or bowlders in insecure positions can hardly be left by
icebergs.
Shore-Ice.
In cold climates the freezing of the surface of the water forms
sheets of ice many inches or even feet thick, and of great extent,
about the shores of rivers, bays, and seas. They often inclose stones
and bowlders of considerable size, and when loosened in spring from
the shore they bear these away, and again drop them at considerable
distances from their parent rock. Also such sheets packed together in
large masses, and driven ashore by river and tidal currents, and chafed
back and forth by waves, produce effects on the shore-rocks somewhat
similar to the scoring, polishing, and even the roches moutonnees of
glacier-action. These effects are well seen on the shores of the St.
Lawrence River and Gulf.
The importance of the study of ice-agencies will be seen when we
come to explain the phenomena of the Drift or Glacial period, a remark-
able period in the history of the earth.
Comparison of the Different Forms of the Mechanical Agencies of
Water.
Rivers and glaciers are constantly cutting down all lands, bearing
away the materials thus gathered, and depositing them on the sea-
margins. Acting alone, therefore, their effect must be to diminish the
height and to extend the limits of the land. Ocean agencies, on the
other hand, by tides and currents bear away to the open sea the mate-
rials brought down from the land, and thus tend to prevent marginal
accumulations ; and by waves and tides constantly eat away the coast-
line, and thus strive to extend the domain of the sea. Thus, while river
and ocean agencies are in conflict with one another at the coast-line,
the one striving to extend the limits of the land, and the other of the
sea, yet they cooperate with each other in destroying the inequalities
of the earth's surface, and are therefore called leveling agencies. More-
over, it is evident that the erosion of the land and the filling up of the
seas are correlative, and one is an exact measure of the other. Now,
we have seen (page 11) that the probable rate at which all continents
are being cut down by rivers is about one foot in 4,500 to 5,000 years.
But since the ocean is about three times the extent of the land, this
spread evenly over the bottom of the sea would make a stratum about
four inches thick. Therefore, we conclude that, neglecting the destruc-
tive effects of waves and tides on the coast-line, which, according to
68 AQUEOUS AGENCIES.
Phillips, 1 are small in amount compared with general erosion of the
land-surface, we may say that stratified deposits are now forming, or
the ocean-bed filling up, at the rate of about four inches in 5,000 years.
SECTION 4. CHEMICAL AGENCIES OF WATER.
Subterranean Waters, Springs, etc.
As we have already seen (page 9), of the rain which falls on any hy-
drographical basin, a part runs from the surface, producing universal ero-
sion. A second part sinks into the earth, and, after a longer or shorter
subterranean course, comes up as springs, and unites with the surface-
water to form rivers ; while a third portion never comes up at all, but
continues by subterranean passages to the sea. This last portion is
removed from observation, and our knowledge concerning it is very
limited. But there are numerous facts which lead to the conviction
that it is often very considerable in amount. In many portions of the
sea near shore, springs, and even large rivers, of fresh water, are known
to well up. Thus, in the Mediterranean Sea, " a body of fresh water
fifty feet in diameter rises with such force as to cause a visible con-
vexity of the sea-surface." * Similar phenomena have been observed
in many other places in the same sea, and also in the Gulf of Mexico
near the coast of Florida, among the West India isles, and near the
Sandwich Islands. Besides the last mentioned, there is still another
portion of subterranean water existing permanently in every part of
the earth far beneath the sea-level, filling fissures and saturating sedi-
ments to great depths, and only brought to the surface by volcanic
forces. This, in contradistinction from the constantly-circulating me-
teoric water, may be called volcanic water.
Springs. The appearance of subterranean waters upon the surface
constitutes springs. They occur in two principal positions, viz. : 1.
FIG. 65. Hill-side Spring.
Upon hill-sides, just where porous, water-bearing strata such as sand
outcrop, underlaid by impervious strata like clay ; 2. On fissures, pene-
trating the country rock to great depth.
Most of the small springs occurring everywhere belong to the first
class. The figure (Fig. 65) represents a section of a hill composed mostly
1 Phillips, "Life on the Earth," p. 131. * Herschel's "Physical Geography."
SUBTERRANEAN WATERS, SPRINGS, ETC.
69
of porous strata, #, but underlaid by impervious clay stratum, c. Wa-
ter falling upon the surface sinks through b until it comes in contact
with c, and then by hydrostatic pressure moves laterally until it emerges
at a. Sometimes this is a geological agent of considerable importance,
modifying even the forms of mountains, and producing land-slips, etc.
Thus the Lookout and Raccoon Mountains, in Tennessee, are table-
mountains of nearly horizontal strata, separated by erosion-valleys.
These mountains are all of them capped by a sandstone stratum about
100 feet thick, underlaid by shale. The water which falls upon the
mountain emerges in numerous springs all around where the sandstone
cap comes in contact with the underlying shale. The sandstone is gradu-
ally undermined, and falls from time to time, and thus the cliff remains
always perpendicular (Fig. 66).
Large springs generally is-
sue from fissures. Water pass-
ing along the porous stratum
#, perhaps from great distance,
and prevented from rising by
the overlying impervious strat-
um c, coming in contact with a fissure, immediately rises through it to
the surface at a (Fig. 67).
Artesian Wells. If subterranean streams have their origin in an ele-
vated region, a d, composed of regular strata dipping under a lower flat
country, c, then the subter-
n. d
FIG. 67. Fissure-Spring.
Rc
;. Artesian Well.
ranean waters passing along
any porous stratum, as a
(Fig. 68), and confined by
two impermeable strata, b
and ?, will be under power-
ful hydrostatic pressure, and
will, therefore, rise to the
surface, perhaps with considerable force, if the stream be tapped by bor-
ing at c. Borings by which water is obtained in this manner are called
artesian wells, from the French province Artois, where they were first
successfully attempted. The source of the water may be 100 miles or
more distant from the well. Some of these wells are very deep. The
Greville artesian in Paris is 2,000 feet deep. At the moment of tapping
the stream, a powerful jet was thrown 112 feet high. One in West-
phalia, Germany, is 2,385 feet deep; one at St. Louis, 3,843 feet; one
at Louisville, Kentucky, 2,852. In parts of Alabama and California,
the principal supply of water for agricultural purposes is drawn from
these wells.
Thus there is on all coasts a constant flowing of water, both super-
ficial and subterranean, into the sea. Their relative amount it is impos-
70 AQUEOUS AGENCIES.
sible to determine. Much, no doubt, depends upon the configuration
of the country and the nature of the strata. The heavy hydrostatic
pressure to which subterranean water is subjected, especially in ele-
vated countries, brings by far the larger portion of it to the surface in
the form of springs. But, in limestone regions (this rock being affected
with frequent and large fissures, and open subterranean passages, as
will be hereafter explained), large subterranean rivers often exist, and
these, even after coming to the surface, are often reengulfed, and finally
reach the sea by subterranean passages. The largest springs, there-
fore, generally occur in limestone countries. From the Silver Spring,
in Florida, issues a stream navigable for small steamers up to the very
spring itself. The country for sixty miles around is entirely destitute
of superficial streams, the whole drainage of the country being subter-
ranean, and coming up in this spring.
Chemical Effects of Subterranean Waters. We have already seen
(page 6) how atmospheric water disintegrates rocks, dissolving out
their soluble parts, and reducing their unsoluble parts to soils. Springs,
therefore, always contain these soluble matters. In granite regions
they contain potash ; in limestone regions they contain lime, and are
called hard ; in other cases they contain salt, and are brackish ; when
the saline ingredients are unusual in quantity, or in kind, they are
called mineral waters.
Limestone Caves. In most rocks, the insoluble part left as soil is
far the largest, only a small percentage being dissolved ; but in the
case of limestone the whole rock is soluble. Therefore, in limestone
regions, percolating waters passing through fissures and between strata
dissolve the limestone and hollow out open passages, and form immense
caves. Water charged with limestone, dripping from the roofs and
falling on the floors of these caves, deposit their limestone by evapora-
tion, and form stalactites
b b, which, meet-
ing each other, form lime-
stone pMars, c c. The
great Mammoth Cave, in
Kentucky ; Wier's Cave,
i Q Virginia, and Nico-
J ac k Cave, m Tennessee,
are familiar examples.
FIG. eO.-Limestone Cave. " As mi g ht be expected,
subterranean rivers are
often found running through these caves. This is the case in the Mam-
.moth Cave, and in Nicojack Cave.
CHEMICAL DEPOSITS IN SPRINGS. 71
Chemical Deposits in Springs.
Deposits of Carbonate Of Lime. We have just seen that ordinary
subterranean waters in limestone districts, and, therefore, containing
small quantities of carbonate of lime, deposit this substance only very
slowly by drying, as stalactites and stalagmites ; but in carbonated
springs in limestone districts a very rapid deposit of lime carbonate
often occurs.
Explanation. In order to understand this, it is necessary to re-
member : 1. That lime carbonate is insoluble in pure water, but soluble
in water containing carbonic acid ; 2. That the amount of carbonate
dissolved is proportionate to the amount of carbonic acid contained ; 3.
That the amount of carbonic acid which may be taken in solution by
water is proportionate to the pressure.
Now, there are two sources of carbonic acid, viz., atmospheric and
subterranean. All water contains carbonic acid from the atmosphere,
and will, therefore, dissolve limestone, but this deposits only slowly by
drying, as already explained. But in many districts, especially in vol-
canic districts, there are abundant subterranean sources of carbonic
acid. If subterranean waters come in contact with such carbonic acid,
being under heavy pressure, they will take up a large quantity of this
gas ; and if such water comes to the surface, the pressure being re-
moved, the gas will escape in bubbles. This is a carbonated spring.
If, further, the subterranean waters, thus highly charged with carbonic
acid, come in contact with limestone rocks, or rocks of any kind con-
taining lime carbonate, they will dissolve a proportionably large amount
of this carbonate ; and when they come to the surface, the escape of
the carbonic acid causes the lime carbonate to deposit abundantly.
Thus around carbonated springs in limestone districts, and along the
course of the streams which issue from them, are generally found ex-
tensive deposits of this substance. Being found mostly in volcanic
regions, these springs are commonly hot.
Kinds of Materials. The material thus deposited is usually called
travertine, but is very diverse in appearance. If the deposit is quiet,
the material is dense ; if tumultuous, the material is spongy ; if no
iron is present, it is white like marble ; but if iron be present, its oxida-
tion colors it yellow, brown, or reddish. If the amount of iron be vari-
able, the stone is beautifully striped. If objects of any kind, branches,
twigs, leaves, are immersed in such waters, they are speedily incrusted,
often in the most beautiful manner.
Examples of such deposits are found in all countries. At the baths
of San Vignone, Italy, a carbonated spring issuing from the top of a
hill has covered the hill with a stratum of white, compact travertine 250
feet thick. In the conduit-pipe which leads the water to the baths, the
AQUEOUS AGENCIES.
deposit accumulates six inches thick every year. A similar deposit of
travertine occurs at the baths of San Filippo. At this latter place,
beautiful fac-similes of medallions, coins, etc., are formed by placing
these objects of art in the spray of an artificial cascade. In Virginia,
around the " Old Sweet " and the " Red Sweet " Springs, and in the
course of the stream which flows from them
for several miles, a brownish-yellow deposit
of travertine has accumulated to the depth
of at least thirty feet. The spray of Beaver
Dam Falls, about three miles below the
springs, incrusts every object in its reach
with this deposit.
In California, all about the shores of Lake
Mono, abundance of beautiful and strangely-
branched coralline forms are found,
which have evidently been formed in
a somewhat similar way. In the re-
gion of the Yellowstone Park, de-
posits of traver-
tine from waters
of hot springs run-
ning down a steep
incline, in a suc-
cession of cas-
cades, assume the
most beautiful
forms, as shown
in the accompany-
ing figure, taken
from Hayden.
Deposits of
Iron. Iron car-
bonate, like lime
carbonate, is to some extent soluble in water containing carbonic acid.
Subterranean waters, therefore, which always contain atmospheric car-
bonic acid, when they meet this carbonate, will take up a small quan-
tity in solution. Such waters are called chalybeate. On coming to
the surface the iron gives up its carbonic acid, is peroxidized, becomes
insoluble, and is deposited. As the presence of organic matter is usu-
ally necessary to bring the iron into a soluble condition, the full dis-
cussion of this very interesting subject is reserved until we take up
organic agencies.
Deposits of Silica. Silica is soluble in alkaline waters, especially if
the waters be hot. Such waters reaching the surface and cooling, de-
FIG. 70. Deposits from Carbonated Springs.
CHEMICAL DEPOSITS IN LAKES. 73
posit the silica in great abundance, often at first in a gelatinous con-
dition, but drying to a white porous material called siliceous sinter.
Examples of such deposits are found in all geysers, as in those of Ice-
land, and in the Steamboat Springs in Nevada, and especially in the
wonderful geysers of Yellowstone Park. Such deposits are confined
to volcanic regions, the volcanic rocks furnishing both the alkali and
the heat. We will discuss these again under Igneous Agencies.
Deposits of Sulphur and Gypsum. Springs containing sulphide of
hydrogen (H 2 S), usually called sulphur - springs, sometimes deposit
sulphur by oxidation of the hydrogen (H 2 S + O=H 2 O + S), and some-
times gypsum. This latter deposit is caused by the more complete oxi-
dation of the sulphide of hydrogen, forming sulphuric acid (H 2 S + 4O
=H 2 SO 4 ), and the reaction of this acid on lime carbonate held in solu-
tion in the same water.
Chemical Deposits in Lakes.
Salt Lakes and Alkaline Lakes. Salt lakes may be formed either
1. By the isolation of a portion of sea-water in the elevation of sea-
bottom into land ; or, 2. By indefinite concentration of river-water in
a lake without an outlet. Thus, the Dead Sea, Lake Elton, and the
brine-pools of the Russian steppes, are probably concentrated remains
of isolated portions of the sea, 1 for their waters are highly-concen-
trated mother-liquors of sea-water, having a composition very similar
to the mother-liquors of the salt-maker. The Caspian Sea, on the other
hand, although elevated lake-margins show that much of its waters
has dried away, is still much fresher than sea-water. This fact, to-
gether with the composition of its waters, is usually supposed to indi-
cate that it has been formed by the simple concentration of the waters
of a once fresh lake. 2 Yet there are some evidences, as we shall see
hereafter, of this sea having been once connected with the Black and
with the Arctic Ocean. The composition of the waters of the Great
Salt Lake of Utah would seem to indicate its origin in the isolation of
sea-water ; but there are also some evidences of its once having had an
outlet, in which case it must have been fresh, or at least brackish. 3
Alkaline lakes can only be formed by the second way-. Both salt
and alkaline lakes, therefore, may be formed by indefinite concentra-
tion of river-water in a lake without outlet. Whether the one or the
other is formed depends on the composition of the river-water. If al-
kaline chlorides predominate, a salt lake will be formed ; but if alka-
line carbonates, an alkaline lake. Such alkaline lakes are found in
Hungary, in Lower Egypt, and in Persia. In our own country, Lake
Mono, fifteen miles long and twelve miles wide, and Lake Owen, of at
1 Bischof, " Chemical and Physical Geology," vol. i., p. 396.
2 Ibid., p. 91. 3 Gilbert, " Wheeler Report for 1872," p. 49.
74: AQUEOUS AGENCIES.
least equal dimensions, are examples of alkaline lakes. The waters of
Lake Mono consist principally of a strong solution of carbonate of
soda, with a little carbonate of lime and borate of soda. 1
Conditions of Salt-Lake Formation. Spring and river waters always
contain a small quantity of saline matter derived from the rocks and
soils. Suppose, then, we have a lake supplied by rivers: 1. If the
supply of water by rivers is greater than the loss by evaporation from
the lake-surface, then the water will rise until, finding an outlet in the
rim of the lake-basin, it flows into the sea. In this case the lake will
remain fresh, or the quantity of saline matter will be inappreciable.
But if, on the other hand, the loss by evaporation is greater than the
supply by rivers, the lake will decrease in extent, and therefore in evap-
orating surface, until an equilibrium is established. Now all the saline
matters constantly leached from the earth accumulate in the lake with-
out limit ; the lake, therefore, must eventually become saturated with
saline matter, and afterward begin to deposit salt. It is evident, then,
that whether a lake is fresh or salt depends upon whether or not it has
an outlet, and this latter depends upon the relation of supply by rivers
to loss by evaporation. Lakes are mostly fresh, because much more
water falls on continents than evaporates from the same surface, the
excess running back to the sea by rivers. It is only in certain parts
of the continents, where the climate is very dry, that there is no such
excess. In these regions alone, therefore, can salt lakes exist. Such
regions occur in the interior of Asia, on the plateau of Mexico, in the
basin of Utah, and in several other places.
Even in case a salt lake is originally formed by the isolation of a
portion of sea-water, whether it remains a salt lake or gradually becomes
fresh will depend upon the conditions we have already mentioned.
For example : if the Mediterranean should be separated from the At-
lantic at the straits of Gibraltar, it would not only remain a salt lake,
but would diminish in area, and finally deposit salt. This we conclude,
because the water of the Mediterranean seems to be a little more salt
than that of the Atlantic. If, on the contrary, the Black Sea were sepa-
rated from the 'Mediterranean, or the Baltic from the Atlantic, or the
bay of San Francisco from the Pacific, the supply by rivers, in the case
of these inland seas being greater than their loss by evaporation, they
would rise until they found an outlet, and then would be gradually
rinsed out, and become fresh. Lake Champlain was, in very recent
geological time, an arm of the sea. When first isolated it was salt. It
has become fresh by this process.
1 The probability of Great Salt Lake having been produced by simple evaporation of
river-water is increased by the difference in the composition of the waters of lakes in
this general region. Where sedimentary rocks prevail, as in Utah, they are salt ; where
volcanic rocks prevail, as about Mono and Owen, they are alkaline.
CHEMICAL DEPOSITS IX LAKES. 75
Deposits in Salt Lakes. The nature of the chemical deposits in salt
lakes will depend upon the manner in which these lakes have been
formed. We will take the simplest case, viz., that of a lake formed
by the isolation of sea-water, and its concentration by evaporation. In
this case the substance first deposited would be gypsum ; for this siib-
stance is insoluble in a saturated brine, and therefore always deposits
first in the artificial evaporation of sea-water in salt-making. Upon the
gypsum would be deposited salt. Meanwhile, however, the rivers dur-
ing their flood-season would bring down sediments. During the flood-
season, the supply of water being greater than loss by evaporation, the
deposit of salt or gypsum would cease ; while during the dry season the
deposit of sediment would cease, and the evaporation being now in ex-
cess, the deposit of salt would recommence. Thus the deposits in the
bottom of salt lakes probably consist of alternations of salt and sedi-
ment, the whole underlaid by layers of gypsum. These views have
been confirmed by observation. During the dry season Lake Elton
deposits annually a considerable layer of salt. Wells dug near the
margin of this lake revealed 100 alternations of salt and mud, the salt-
beds being many of them eight or nine inches thick. 1 Most of the salt
has already deposited ; for the water of this lake is an almost pure bit-
tern. The great predominance of chloride of magnesium in Dead Sea
water shows that it is a mother-liquor, from which immense quantities
of common salt have already been deposited. Similar alternations,
therefore, no doubt exist in the bottom of this sea. 2 The Great Salt
Lake, in Utah, is also a saturated brine depositing salt, as is proved by
the incrustations of salt about its margin in dry seasons ; but the de-
posit has not progressed so far in this case as in the preceding. The
great extent to which the waters of this lake have dried away and be-
come concentrated is further shown by old lake-margins far beyond
the limits, and several hundred feet above the level, of the present shore-
line. Similar phenomena are observed about other salt lakes, especially
about the Caspian Sea (Murchison).
In the case of salt lakes, either formed entirely, or modified, by river-
water, the deposits are probably much more complex and various some-
times salt, sometimes carbonate of lime, and sometimes sulphate of lime.
This subject, however, has been but little investigated.
Deposits are also sometimes formed in lakes which are not salt. For
example : the Solfatara Lake, Italy, is formed by the accumulation of
the water from warm carbonated springs, similar to those of San Filippo
and San Vignone. In this lake, therefore, deposits of travertine are
forming. Although these deposits take place in a lake, they properly
belong to deposits from springs, since they do not take place by concen-
tration.
a Bischof, " Chemical and Physical Geology," vol. i., p. 405. 2 Ibid., p. 400.
76 IGNEOUS AGENCIES.
Chemical Deposits in Seas.
Concerning these little is known. It is certain, however, that all
rivers carry to the sea carbonate of lime in solution, and some of them
in considerable quantities. There is scarcely any river-water which
contains less carbonate of lime than sea-water ; many rivers contain
four times as much. 1 This carbonate of lime thus constantly carried
into the sea must eventually deposit in some form. Usually, however,
sea-water is kept below the saturating point for this substance, by its
constant withdrawal by shells and corals, as will be explained under Or-
ganic Agency. But in shallow bays nearly cut off from the sea, or in
salt lagoons on the sea-margin near the mouths of rivers in dry climates,
and subject to occasional overflows by the sea and floodings by rivers,
carbonate of lime and sulphate of lime may deposit by evaporation. At
the mouths of many rivers, whose waters contain much carbonate of
lime, as, for instance, the Rhine, the delta deposit is cemented into
hard rock by means of this substance. On shores of coral seas, as
upon the Keys of Florida, the coast of the West India Islands, and the
islands of the Pacific, shore-material is consolidated into hard rock by
the same means. On many shores in tropical regions, the waves, being
driven up on flat beaches far inland, leave sea-water inclosed in shallow
pools, which by evaporation give rise to calcareous deposits which are
increased by the frequent alternate influx and evaporation of sea-water.
Conglomerate rocks are thus forming at the present time in the Canaries
and many other places.
CHAPTER III.
IGNEOUS AGENCIES.
THE agencies thus far considered tend to reduce the inequalities of
the earth by cutting down the continents and filling up the seas. Their
final effect, if unopposed, would be to bring the whole surface to one
level, and thus to make the empire of the sea universal. This is pre-
vented by igneous agencies, which tend, by elevation of land and de-
pression of sea-bottoms, to increase the inequalities of the earth-surface,
and thus to increase the area and the height of the land. All the dif-
ferent forms of igneous agency are connected with the interior heat of
the earth. This must, therefore, be first considered.
SECTION 1. INTERIOR HEAT OF THE EARTH.
Stratum of Invariable Temperature. The mean surface temperature
of the earth varies from 80 at the equator to nearly at the poles.
1 Bischof, " Chemical and Physical Geology," vol. i., p. 179.
INTERIOR HEAT OF THE EARTH. 77
The rate of decrease in passing from the equator to the poles is not the
same in all longitudes ; the isotherms, or lines joining places of equal
mean temperatures, are therefore not parallel to the lines of latitude,
but quite irregular. The mean temperature of the whole earth-surface
is about 58. There is also in every locality a daily and an annual
variation of temperature. As we pass below the surface both the daily
and annual variations become less, until they cease altogether. The
stratum of no daily variation is but a foot or two beneath the surface;
but the stratum of no annual variation, or stratum of invariable temper-
ature in temperate climates, is about sixty to seventy feet deep. The
temperature of the invariable stratum is nearly the mean temperature
of the place. The depth of the invariable stratum depends upon the
amount of annual variation ; it is, therefore, least at the equator, and
increases toward the poles. At the equator it is only one or two feet
beneath the surface ; 1 in middle latitudes about sixty feet, and in high
latitudes probably more than 100 feet. It is, therefore, a spheroid more
oblate than the earth itself. The temperature of the earth everywhere
within this spheroid is unaffected by external changes.
Increasing Temperature of the Interior of the Earth. Beneath the
invariable stratum the temperature of the earth everywhere increases,
a. o
for all depths to which it has been penetrated, at an average rate of 1
for every 53 feet. This very important fact has been determined by
numerous observations on the temperature of mines and of artesian
wells in almost every part of the earth. All the facts thus far stated
are graphically illustrated in the accompanying figure (Fig. 71), in
which the line a b represents depth below the surface, and the diverging
1 Humboldt, "Cosmos," Sabine's edition, vol. i., p. 165.
78 IGNEOUS AGENCIES.
line c d the increasing heat ; m the invariable stratum ; n the line of no
daily variation ; the curves p e, c e, o e, the temperatures in summer,
autumn, and winter, respectively ; the space p e o the annual swing of
temperature; and the smaller curves meeting on the line n, the daily
variation or swing of temperature.
We have given the rate of increase as about 1 in 53 feet. It
varies, however, in different places, from 1 in 30 feet to 1 in 90 feet.
Except in the vicinity of volcanic action, this difference is probably
due to varying conductivity of the rocks. The lines, or rather surfaces,
which join places in the interior of the earth, having equal tempera-
tures, may be called isogeotherms. If the rate of increase were every-
where the same, the isogeotherms would be regularly concentric ; but,
as this is not the case, they are irregular surfaces (Fig. 72), rising
nearer the earth-surface, and closing upon one another where the con-
ductivity is poor, and sinking deeper and separating where the con-
ductivity is greater.
Constitution Of the Earth's Interior. From the facts given above
it is probable that the temperature of the interior of the earth is very
great. A rate of increase of 1 for every 53 feet would give us, at the
depth of twenty-five or thirty miles, a temperature sufficient to fuse most
rocks. Hence it has been confidently concluded by many, that the
earth, beneath a comparatively thin crust of thirty miles, must be liquid.
A crust of thirty miles on our globe is equivalent to a crust of less than
one-tenth of an inch in a globe two feet in diameter. There are, how-
ever, many objections to this conclusion. The question of the interior
constitution of the earth is one of extreme difficulty and complexity,
and science is not yet in a position to solve it completely. Neverthe-
less, it can be proved that the solid crust must be much thicker than is
usually supposed, if, indeed, there be any general interior fluid at all.
The argument for the interior fluidity of the earth, beneath a crust
of only thirty miles, proceeds upon two suppositions, viz. : 1. That the
interior temperature increases at the same rate for all depths and,
2. That the fusing -point of rocks is the same for all depths. Now,
neither of these can be true.
1. Rate of Increase not uniform. Although we have spoken of 1
for every 30 feet or 50 feet or 90 feet, yet it must not be supposed
that observation gives a uniform rate of increase at any place. On the
contrary, the rate is sometimes faster and sometimes slower, depending
on the conductivity of the rock penetrated, and on other causes little
understood. The rate given is always an average. In other words,
observation gives the fact of increase, but not the law. We are thus
thrown back on general reasoning.
If two bars, one a good conductor, like metal, and the other a bad
conductor, like charcoal, be heated red hot at one end, and the rate of
INTERIOR HEAT OF THE EARTH. 79
decreasing temperature fall of heat toward the other be observed, it
will be found that the rate is very rapid in the case of the charcoal ; so
that a temperature of 60 is reached at the distance of two or three
inches, while in the case of the metal the rate of decrease is much
slower, and 60 is only reached at a distance of several feet. Con-
versely, the rate of increase, or rise, in passing toward a source of
heat, is rapid in the case of the bad conductor, and slow in the case of
the good conductor. Now, the average density of materials at the sur-
face of the earth is about 2.5, but the average density of the whole
earth is more than 5.5 ; therefore the density of the central portions
must be much more than 5.5. It has been estimated at 16.27. 1 There
can be no doubt, therefore, that the density of the earth increases
toward the centre ; and as this increase is probably largely the result
of pressure, it is probably somewhat regular. Whatever be the cause,
the effect would be to increase the conductivity for heat, and there-
fore to diminish the rate of increasing temperature. Thus it follows
that, though in an homogeneous globe the melting-point of rocks
(3,000) would be reached at the depth of 30 miles, yet, in a globe
increasing in density toward the centre, we must seek this temperature
at a greater depth.
If Alt (Fig. 73), representing depth from the surface S S, be taken as
absciss, and heat be represented by ordi-
nates, then, in an homogeneous earth,
CD would represent uniform increase
of heat, and the heat ordinate of 3,000,
m m, would be reached at the depth of
A m = thirty miles. But in an earth in-
creasing in density, and, therefore, in
conductivity, the rate would not be uni-
form, but gradually decreasing. This
would be represented, not by a straight
line, C D, but by a curved line, C E ; D
and the ordinate of 3,000 would not
be reached at thirty miles, but at a
much greater depth say at m', of fifty
miles.
2. Fusing-Point not the same for all Depths. Nearly all substances
expand in the act of melting, and contract in the act of solidifying.
Only in a few substances, like ice, is the reverse true. Now, the fusing-
point of all substances which expand in the act of fusing must be
raised by pressure, since the expanding force of heat, in this case, must
overcome not only the cohesion, but also the pressure. That this is
1 " Cosmos," vol. iv., p. 33.
80 IGNEOUS AGENCIES.
true, has been proved experimentally for many substances by Hopkins. 1
But granite and other rocks have been proved to expand in fusing ;
therefore the fusing-point of rocks is raised by pressure, and must be
greatly raised by the inconceivable pressure to which they are sub-
jected in the interior of the earth. For this reason, therefore, we
must again go deeper to find the interior fluid. In the figure, m' is the
point where we last found the fusing-point of 3,000. But this is the
fusing-point on the surface, or under atmospheric pressure. The press-
ure of 'fifty miles of rock would certainlv greatly raise the fusing-
point. Suppose it is thus raised to 3,500 : to find this we must go
still deeper, to m", perhaps seventy-five miles in depth. But the in-
creased pressure would again raise the fusing-point ; and thus, in this
chase of the increasing heat after the flying fusing-point, where the
former would overtake the latter, or whether it would overtake it at all,
science is yet unable to answer.
From this line of reasoning, therefore, we conclude that the solid
crust of the earth must be much thicker than is usually supposed, and
there may be even no interior liquid at all.
Astronomical Reasons. There is another and an entirely different
line of reasoning which has led some of the best mathematicians and
physicists to the same result. According to the thin-crust theory, the
earth is still substantially a liquid globe, and therefore under the at-
tractive influence of the sun and moon it ought to behave like a yielding
liquid. Now, according to Hopkins, Thomson, and others, the earth in
all its astronomical relations behaves like a rigid solid a solid more
rigid than a solid globe of glass and the difference between the be-
havior of a liquid globe and a solid globe could easily be detected by
astronomical phenomena. 9 A complete exposition of the proof would
be unsuitable to an elementary work. Suffice it here to say that the
force of these arguments has led many of the most advanced geologists
to the conclusion that the earth, if not solid to the centre, must have a
crust so thick that for all purposes of the geologist it may be regarded
as substantially solid ; that volcanoes are openings into local masses
of liquid, not into a general interior liquid into subterranean fire-lakes,
not into a universal Jire-sea in a word, that all the theories of igneous
phenomena must be reconstructed on the basis of a solid earth. A few
geologists, however, find a compromise in the view that there exists a
semi-liquid stratum between the solid crust and a solid nucleus.
The interior heat of the earth manifests itself at the surface in three
principal forms, viz., volcanoes, earthquakes, and gradual oscillations
of the earth's crust.
1 American Journal of Science and Art, II., vol. xxxii., p. 367.
8 Thomson has recently reaffirmed these conclusions with still greater positiveness.
Nature, vol. xiv., p. 426 ; American Journal of Science and Art, vol. xii., p. 336, 1876.
VOLCANOES. 81
SECTION 2. VOLCANOES.
Definition. A volcano is usually a conical mountain, with a funnel-
shaped, or pit-shaped, or cup-shaped opening at the top, through which
are ejected materials of various kinds, always hot and often in a fused
condition. The activity of volcanoes is sometimes constant, as in the
case of Stromboli, in Italy, from which continuous lava-streams flow
(" Cosmos," vol. iv.), but more commonly intermittent, i. e., having pe-
riods of eruption alternating with periods of more or less complete re-
pose. Volcanoes which have not been known to erupt during historic
times are said to be extinct. It is impossible, however, to draw the
line of distinction between active and extinct volcanoes. Vesuvius,
until the great eruption which overthrew the ancient cities of Hercu-
laneum and Pompeii, was regarded as an extinct volcano. Since that
time it has been very active.
Size, Number, and Distribution. Some volcanoes are among the
loftiest mountains on our globe. Aconcagua, in Chili, is 23,000 feet,
Cotopaxi, in Peru, 19,660 feet in height. These volcanic cones, how-
ever, are situated on a high plateau ; their height, therefore, is not due to
volcanic eruptions entirely. But Mauna Loa, in Hawaii, nearly 14,000
feet, and Mount Etna, 11,000 feet high, seem to be due entirely, and
Mount Shasta, California, 14,440 feet, Rainier, Washington Territory,
14,444, almost entirely to this cause. The crater of Mauna Loa is two
and a half miles across ; that of Kilauea three miles across and 1,000
feet deep.
The number of known volcanoes, according to Humboldt, is 407,
and of these 225 are known to have been active in the last 160 years.
The actual number is, however, probably much greater. It has been
estimated that, in the archipelago about Borneo alone, there are 900 vol-
canoes. 1 The distribution of volcanoes is remarkable, (a.) They are
almost entirely confined to the vicinity of the sea. Two-thirds of them
are found on islands in the" midst of the sea, and the remainder, with
the exception of a few in the interior of Asia, are near the sea-coast.
Those on islands in the sea probably commenced, most of them, at the
bottom of the sea, the islands having been formed by their agency.
New islands have been suddenly formed under the eye of observers in
the Mediterranean. The basin of the Pacific is the great theatre of
volcanic activity, nearly seven-eighths of all known volcanoes being situ-
ated on its coasts, or on islands in its midst, (b.) Volcanoes are, more-
over, distributed in groups (as the Hawaiian volcanoes, the Mediter-
ranean volcanoes, the West Indian volcanoes, the volcanoes of Auvergne,
etc.), or along extensive lines as if connected with a great fissure
of the earth's crust. The most remarkable linear series of volcanoes
1 Herschel, " Physical Geology," p. 113.
82 IGNEOUS AGENCIES.
is that which belts the Pacific coast. Commencing with the Fuegian
volcanoes it runs along the whole extent of the Andes, then along the
Cordilleras of Mexico, the Rocky Mountains, then along the Aleutian
chain of .islands, Kamtchatka, the Kurile Islands, Japan Islands, Philip-
pines, New Guinea, New Zealand, to the antarctic volcanoes Mounts
Erebus and Terror, thence back by Deception Island to Fuegia again,
thus completely encircling the globe. (c.) Volcanoes are generally
formed in comparatively recent strata. This seems to be connected
with their relation to the sea ; for recent strata are abundant about the
sea-coast, and the most recent are now forming in the bed of the sea.
The extinct volcanoes of France and Germany are in tertiary regions.
Possibly the retiring of the sea has extinguished them. In the oldest
strata volcanic activity has apparently died out long ago.
Phenomena of an Eruption. The phenomena of an eruption are very
diverse. Sometimes there is a gradual melting of the floor of the crater,
and then a rising and boiling of the liquid contents until they quietly over-
flow and form immense streams of lava, extending fifty to sixty miles.
After the eruption, the melted lava again sinks and cools, and solidifies,
to form the floor of the crater until another eruption. This is the case
with the Hawaiian and many other volcanoes in the South Seas. In
other cases, as in the Mediterranean volcanoes, and especially in many
in the Indian Ocean, the eruption is fearfully explosive. In such cases the
eruption is usually preceded by premonitory earthquakes and sounds
of subterranean explosions ; then the bottom of the crater is blown out
with a violent explosion, throwing huge rocky fragments to great dis-
tances, often many miles ; then the melted lava rises and overflows in
streams running down the side of the mountain. The rise and overflow
of lava are accompanied with violent explosions of gas which throw up
immense quantities of ashes and cinders 6,000 and even 10,000 feet
above the crater. 1 In the great eruption of Tomboro, in the island of
Sumbawa near Java, in 1815, these explosions were heard in Sumatra,
970 miles distant. 2 The emission of gas usually continues after all other
ejections cease. Violent storms and heavy rain accompany the eruption,
and when the mountain reaches into the region of perpetual snow, as
in many of the South American volcanoes, the fearful deluges produced
by the sudden melting of the snows are often the most destructive
phenomenon connected with the eruption.
Volcanic eruptions, therefore, may be divided into two great types,
viz., the quiet and the explosive. In the one, lava-flows predominate ;
in the other, cinders and ashes, and steam and gas. The Hawaiian vol-
canoes are perhaps the best examples of the former, and the Javanese
volcanoes of the latter. The Mediterranean and most other volcanoes
. are .mixtures of these two types in varying proportions.
- 1 Dana's " Manual," p. 692. * Lyell, " Principles of Geology."
VOLCANOES. 33
The quantity of materials ejected during an eruption is sometimes
almost inconceivable. During the great eruption of Tomboro, already
mentioned, ashes and cinders were ejected sufficient to make three
Mont Blancs, or to cover the whole of Germany two feet deep. 1 The
lava which streamed from Skaptar Jokull, Iceland, in 1783, has been
computed to be equivalent to about twenty-one cubic miles, or to the
whole quantity of water poured by the Nile into the sea in one year!
These were, however, very extraordinary eruptions. In the greatest
eruptions of Vesuvius the quantity of lava poured out was not more
than 600,000,000 cubic feet = one square mile covered twenty-two feet
deep. The volume of lava poured out by Kilauea, in 1840, is estimated
by Dana as sufficient to cover one square mile of surface 800 feet deep.
Great destruction of life is often produced by volcanic eruptions.
The overthrow of Herculaneum and Pompeii by ejections from Vesu-
vius is well known. The great eruption of Skaptar Jokull destroyed
1,300 human lives and 150,000 domestic animals. The eruption of
Etna, in 1669, overwhelmed fourteen towns and villages. In the prov-
ince of Tomboro, out of a population of 12,000, only twenty-six persons
escaped the great eruption of 1815.'
Monticules. Eruptions occur not only from the summit-crater, but
also frequently from fissures in the side of the mountain. By the im-
mense upheaving force necessary to raise lava to the mouth of the
crater of a lofty volcano, the mountain is fissured by cracks radiating
from the crater in all directions. These cracks are filled with lava,
which on hardening form radiating dikes which intersect the successive
layers of ejections, and bind them into a stronger mass. Through these
fissures the principal streams of lava often pass. During an eruption
of Mauna Loa, in 1852, the immense pressure of the lava in the princi-
pal crater fissured the side of the mountain, and a fiery fountain of
liquid lava, 1,000 feet wide, was projected upward through the fissure
to the height of 700 feet, and continued to play for several days. Upon
these fissures subordinate craters, and finally cones, are formed. These
subordinate cones about the base, and upon the slopes of the principal
cone, are called monticules or hornitos. There are about 600 monticules
on Etna one of them over 700 feet high (Jukes).
Materials erupted. As we have already stated, the materials erupted
are stones, lava-streams, cinders, ashes, and gases.
Stones. In explosive eruptions the solid floor of the crater is often
blown out with violence, and rock-fragments, sometimes of great size,
are thrown to great distances.
Lava. The term lava is applied to the liquid matter poured from a
volcano during eruption, and also to the same when it has hardened
into rock.
1 Herschel, "Physical Geology," p. 111.
84 IGNEOUS AGENCIES.
Liquid Lava, At the time of eruption the liquidity of lava varies
very much, depending partly upon the heat, partly on the fusibility of
the material, and partly upon the kind of fusion. In the Hawaiian
volcanoes the lava is a melted' glass almost as thin as honey. In Ki-
lauea this lava is often thrown into the air by the bursting of gas-bubbles,
and drawn out into long threads like spun glass, which is carried by the
winds, and collects in places as a soft, brownish, towy mass, called
" Pele's hair." Completely fused lava, when cooled rapidly, forms vol-
canic slag or volcanic glass (obsidian) ; but if cooled slowly, so that
the several minerals of which it is composed have time to separate and
crystallize, forms stony lava. If it is full of gas-bubbles (rock-froth),
and hardens in this condition, it forms vesicular or scoriaceous lava.
If the quantity of gas and steam be very great, the whole liquid mass
may swell into a rock-froth, which rises to the lip of the crater, and
outpours much as porter or ale from a bottle when the cork is drawn.
Or the rock-froth may be thrown violently into the air, and, hardening
there, may fall again in cindery or scoriaceous masses ; or, thrown with
still greater violence, the rock-froth may be broken into fine rock-spray,
and fall as volcanic sand and ashes'. Ashes, when consolidated by time
and percolating water, form tufa. Thus, there are four physical condi-
tions in which we find lava viz., stony, glassy, scoria ceous, and tufaceous.
Again, the liquidity of lava and its character depend much on the
kind of fusion. Daubree has shown that all siliceous rocks and glass
mixtures, in the presence of superheated water even in small quanti-
ties, and under pressure, will become more or less liquid, at tempera-
tures far below that necessary to produce true fusion. At 400 Fahr.,
such rocks become pasty ; at 800, completely liquid. The same
change takes place at even lower temperatures if a little alkali be pres-
ent. To distinguish this liquidity from that of true igneous fusion,
which requires a temperature of 2,500 to 3,000, it has been called aqueo-
igneous fusion. Now, very much lava at the time of eruption is in this
condition. Such lava, when the pressure is suddenly removed by break-
ing up of the floor of the crater, and the contained water suddenly
changed into steam, is blown into the finest dust, which is then carried
to great height by the out-rushing steam, and falls again as volcanic
ashes, which may consolidate into tufa. If the heat be not sufficient
to produce complete aqueo-igneous fusion, the lava is outpoured as a
kind of rock-broth, consisting of unfused particles in a semifused mass,
which concretes into an earthy kind of rock. Or the material may pour
out only as hot mud, which concretes into a kind of tufa. In fact,
every variety of fusion and semifusion, depending on the degree of heat
and the quantity of water, may be traced, from perfect igneous fusion
through various grades of aqueo-igneous fusion, to the condition of hot
mud.
VOLCANOES. 85
It is evident that, of the two kinds of eruption mentioned above, the
quiet type is characterized by igneous fusion, the explosive type by
aqueo-igneous fusion. In the former the heat is great, but the amount
of water is small ; while in the latter the heat is less, but the amount
of water far greater.
The rapidity of the flow of a lava-stream depends on its fluidity. In
the Hawaiian volcanoes the lava, where it issues from the crater, has been
seen to flow with a velocity of fifteen miles an hour ; while Vesuvian lava
seldom flows at a rate of more than two or three miles an hour. Lava,
like glass, passes through various grades of viscous fluidity in cooling.
It gradually becomes so stiff that it may flow only a few feet per day.
The froth or scum which covers the surface of a lava-stream quickly
cools and hardens into a crust of vesicular lava, which may even be
walked upon while the interior is still flowing beneath. In this way
are often formed long galleries. Also the running together of the con-
tained gas-bubbles and steam-bubbles forms huge blisters in the viscous
mass, which, on hardening, form cavities often of great size.
Hardened Lava. Miner alogically, lava consists essentially of feld-
spar and augite, either intimately mixed, as in glassy lava, or aggre-
gated in more or less distinct particles or crystals, as in the stony varie-
ties. Now, feldspar is a light-colored mineral, having a specific gravity
of about 2.5, while augite is usually a very dark-colored mineral, having
a specific gravity of about 3.5. It is evident, therefore, that in propor-
tion as feldspar predominates the lava is lighter colored and of less spe-
cific gravity, and in proportion as augite predominates the rock is darker
and heavier. Chemically, feldspar is a silicate of alumina and alkali
(the latter being either potash or soda), with excess of silica (acid sili-
cate) ; while augite is a silicate of lime, magnesia, and iron, with excess
of base (basic silicate). Therefore, lavas may be divided into two
classes the feldspathic or acidic lavas and the augitic or basic lavas.
Further, it is seen that all lavas are multiple silicates, like glass : they
are, therefore, true glass-mixtures. Now, the feldspathic or acid lavas
are a more difficultly fusible, the augitic or basic lavas a more easily
fusible, glass-mixture. Either of these two kinds of lava may exist in
any of the conditions mentioned above viz., as stony, glassy, vesicular,
or tufaceous lava. Trachyte is an example of feldspathic lava, and
basalt or dolerite of augitic lava in a stony condition. Pumice is a
peculiar vesicular variety of feldspathic lava.
It is highly probable that the fusion and subsequent cooling of
granite, or gneiss, or even of the purer varieties of mixed sandstones
and clays, would make a feldspathic or trachytic lava ; while the fusion
and cooling of impure slates and shales and limestones would produce
an augitic or basaltic lava.
Gas, Smoke, and Flame. The gases emitted by volcanoes are princi-
86 IGNEOUS AGENCIES.
pally steam, sulphurous vapor (S and SOJ, hydrochloric acid, and car-
bonic acid. By far the most abundant of these is steam. In violent,
explosive eruptions, which eject principally cinders and ashes, it is prob-
able that water, mostly in the form of steam, is one of the most abun-
dant of all the ejected materials. In quiet lava-eruptions, like those of
the Hawaiian volcanoes, the quantity of steam arid gases is small. It
is worthy of notice, in connection with the position of volcanoes near
the sea, that the gases ejected are such as might be formed from sea-
water and from limestone. The so-called smoke and flame of volcanoes
have no connection with combustion. The condensed vapors and the
ashes suspended in the air, often in such quantities as to make midnight-
darkness at high noon, form the smoke ; and the red glare of the same,
reflecting the light from the incandescent lava beneath, forms the
apparent flame.
All volcanic ejections, except the gases, accumulate about the crater,
and continue to increase with every successive eruption, forming a sort
of stratified deposit. Sometimes the cone is made up of successive lay-
ers of lava, as in Hawaiian volcanoes ; sometimes it is made up of suc-
cessive layers of cinders or tufa ; sometimes of alternate layers of lava
and tufa. Stratified materials of this kind, however, cannot be con-
founded with those produced by the action of water. In the former case
the stratification is not the result of the sorting of the materials.
Kinds of Volcanic Cones. Volcanic cones and craters have been
divided into two kinds viz., cones of elevation and cones of eruption.
A cone of elevation is formed by interior forces lifting the crust of the
earth at a particular point until the latter breaks and forms a crater,
through which eruptions take place. It is an earth-bubble which swells
and breaks at the top. A cone of eruption, on the other hand, is
formed by the accumulation around a crater of its own ejections. There
has been much discussion among physical geologists as to whether
existing volcanic cones are formed mostly by the one method or the
other. We will not enter into this discussion. It seems probable,
however, that most cones are principally cones of eruption, although
their height and size have been increased somewhat also by elevating
forces.
Mode of Formation of a Volcanic Cone. A volcano commences 1.
As a simple opening in the earth's crust, in most cases with little or no
FIG. 74. Section across Hawaii.
VOLCANOES.
elevation. Through this opening or crater are ejected, from time to
time, lava, cinders, ashes, etc., which accumulate immediately about the
crater, and continue to increase, by successive layers, with every erup-
tion. Ejections of pure lava, particularly if the lava is very fluid,
form a cone of broad base and low inclination. This is the case with
the Pacific volcanoes. Fig. 74 is a section through Hawaii, show-
ing the slope of the pure lava-cones of Mauna Loa (Z), nearly 14,-
000 feet high, and of Mauna Kea (K). Tufa -cones and cinder-cones
(Fig. 75) take a much higher angle
of slope. 2. With every eruption the
powerful internal forces fissure the
mountain, in lines radiating from the
crater. These fissures are filled with
liquid lava, which, on hardening, forms
e ' FIG. 75. Section of Cinder-Cone.
radiating dikes, intersecting the lay-
ers of ejections, and binding them into a more solid mass. Fig. 76
shows how these dikes, rendered more visible by erosion, intersect the
at the Base of the Serra del Solflzio, Etna.
strata. 3. After a time, when the mountain has grown to considerable
height, the force necessary to raise liquid lava to the lip of the crater
becomes so great that it breaks in preference through the fissured sides
of the mountain. The secondary craters thus formed immediately com-
mence to make accumulations around themselves, and thus form second-
88
IGNEOUS AGENCIES.
ary cones (Fig. 77, c'), or monticules, about the base and on the sides
of the primary cone. If a secondary cone becomes extinct, it is finally
buried (Fig. 77, c") in the layers of the primary cone. 4. Finally, in
FIG. 77. Section of Volcano, showing Monticules.
volcanoes of the explosive type, during great eruptions the whole top
of the mountain is often blown off, and in volcanoes of the quieter type
is melted and falls in in either case forming an immense crater, within
which, by subsequent eruptions, another smaller cone of eruption is
FIG. 78. Section of Vesuvius atod Mount Somma.
built up, and in this latter often a still smaller cone is again built.
This cone-within-cone structure is well illustrated by the present condi-
tion, and still better by the history, of Vesuvius. Vesuvius is a double-
peaked mountain, with a deep, semicircular valley between the peaks.
FIG. 79. Mount Vesuvius in 1756 (after Scrope).
The present active cone of Vesuvius is encircled by a rampart, very high
on one side, and called Mount Somma, but traceable to some degree all
around, and having the same structure as Vesuvius itself. This rampart
VOLCANOES. 89
is the remains of a great crater, many miles in diameter. Fig. 78
is an ideal section through Mount Somma ($), and Vesuvius (V}.
S' is the almost obliterated remains of the old crater on the other
side. This is further and beautifully illustrated by the history of this
mountain, which records the repeated destruction and rebuilding of
these cones within cones. Fig. 79 is an outline of Vesuvius as it existed
in 1756 ; 1 S is Mount Somma.
Many other volcanoes are known which have similar circular ram-
parts made up of layers of volcanic ejections. One of the most remark-
able of these is Barren Island, in the bay of Bengal (Fig. 80). The
FIG. 80. Section of Barren Island.
difference between this and Vesuvius is, that the circle is more com-
plete, and the valley between it and the present cone is occupied by
the sea.
Comparison between a Volcanic Cone and an Exogenous Tree. It
is evident, then, that a cone of eruption grows by layers successively
applied on the outside. Both in structure and growth it may, there-
fore, be compared to an exogenous tree : 1. As the sap ascends
through the centre of the shoot and descends on the outside, forming
layers of wood, one outside of the other, increasing every year the
height and the diameter of the tree, so in a volcano lava ascends through
the centre and pours over the outside, forming also successive layers,
increasing both the diameter and the height. 2. As a cross-section of
a tree shows concentric rings around (Fig. 81) a central pith, and trav-
ersed by pith-rays, so a cross-section of a volcano
would show a central crater, with concentric layers,
traversed by radiating dikes. 3. As on the pith-rays,
where they emerge upon the surface, arise buds, which
grow in a manner similar to the trunk, so on the radi-
ating dikes are formed monticules, which grow like the
principal cone. If buds die, they are covered up in the Fl - si-
annual layers of the trunk ; so, in like manner, extinct monticules are
buried in the layers of the principal cone.
Estimate of the Age Of Volcanoes. The age of exogenous trees, as
is well known, may be estimated by counting the annual rings. The
age of volcanoes cannot be estimated accurately in a similar manner :
1. Because the overflows are not regularly periodical ; 2. Because
1 Scrope, Philosophical Magazine, vol. xiv., p. 139.
90 IGNEOUS AGENCIES.
in the case of lava-overflows it requires many overflows to make one
complete layer ; and, 3. Because it is impossible to make a complete
section of the mountain. Nevertheless, Nature gives us partial sec-
tions, which reveal an almost incalculable antiquity. Thus, the Val de
Bove, of Etna (a huge valley reaching from near the summit to the
foot, and probably formed bv an engulfment of a portion of the moun-
tain), gives a perpendicular section into the heart of the mountain
3,000 feet deep. Throughout the whole of this section the mountain
is composed entirely of layers of lava and cinders. It is almost cer-
tain, therefore, that the whole mountain to its very base, 11,000 feet,
is similarly composed. That the time necessary to accumulate this im-
mense pile, 11.000 feet high and ninety miles in circumference at the
base, was almost inconceivably great, is shown by the fact that Etna
had already attained very nearly its present size and shape 2,500 years
ago, when it was observed by the early Greek writers. The lava-stream
which stopped the Carthaginians in their march against Syracuse, 396
years before Christ, may still be seen at the surface, not yet covered by
subsequent eruptions. And yet Etna belongs to the most recent geo-
logical epoch, for it has broken through, and is built upon, the newer
tertiary strata.
Theory of Volcanoes.
In the theory of volcanoes there are two things to be accounted for,
viz. : 1. The force necessary to raise melted lava to the crater, and even
to project it with violence high into the air ; 2. The heat necessary to
fuse rocks and form lava.
Force. The specific gravity of lava being about 2.5 to 3, it would
require the pressure of one atmosphere, or fifteen pounds to the square
inch, for every eleven or twelve feet of vertical elevation of the liquid
mass. The following table gives the pressure in atmospheres for four
well-known volcanoes, assuming the point of hydrostatic equilibrium
to be at the sea level :
NAME.
Height.
Pressure in Atmospheres.
3 900 feet
325
Etna
11 000 "
920
13 800 "
1 150
Cotopaxi
19,660 "
1.638
The lava is often, however, in a frothy orVesicular condition. In such
cases the pressure necessary to produce overflow would be much less.
But, on the other hand, the force in most cases is not only sufficient to
lift lava to the top of the crater, but to project it thousands of feet in
the air. A rock -mass of over 2,700 cubic feet was projected from the
crater of Cotopaxi to a distance of nine miles (Lyell). The agent of
VOLCANOES. 91
this prodigious force is evidently gas and vapors, especially steam. The
great quantity of steam issuing from all volcanoes, but especially from
those of the explosive type, is sufficient proof. Thus far theorists
generally agree, but from this point opinions diverge into the most op-
posite directions.
The Heat. There are many and diverse opinions as to the source of
the heat associated with volcanic eruptions. Two prominent views,
however, may be said to divide geologists. According to the one, the
heat is the remains of the primal heat of the once universally incandes-
cent earth ; according to the other, the heat is produced by chemical
or mechanical action. According to the former, the heat is general, and
only the access of water is local ; according to the latter, both the heat
and the access of water are local. According to the former, volcanoes
are openings through the comparatively thin crust, revealing the uni-
versal interior fluid ; according to the latter, they are openings into
isolated interior lakes of molten matter. The former may be called the
" interior fluidity " theory ; the latter divides into two branches, which
may be called respectively the " chemical " and the " mechanical " the-
ory. In all, access of water to the hot interior furnishes the force.
Internal Fluidity Theory. This theory supposes that the earth, from
its original incandescent condition, slowly cooled and formed a surface-
crust ; that this surface-crust, though ever thickening by additions to
its interior surface, is still comparatively very thin, and beneath it is
still the universal incandescent liquid ; that by movements of the sur-
face the solid crust is fissured, and water from the sea or from other
sources finds its way to the incandescent liquid mass, and develops
elastic force sufficient to produce eruption.
By this view the focus of volcanoes is situated at the lower limit of
the solid crust. The theory seems clear and simple enough, but when
closely examined there are many difficulties in the way of its accept-
ance.
Objections. The objections to this view are : 1. That the crust, as
already shown, must be far thicker than this theory requires, probably
hundreds of miles thick, if, indeed, there be any general liquid interior
at all ; but volcanoes are evidently very superficial phenomena. Under
the pressure of this difficulty these theorists have been driven to the
acknowledgment of local thinnings of the solid crust in the region of
volcanoes.
2. Pressure on a general interior liquid from any cause at any place
would, by the law of hydrostatics, be transmitted equally to every part
of the crust, which would, therefore, yield at the weakest point, wher-
ever that may be, even though it be on the opposite side of the globe ;
but the force of volcanic eruption is evidently just beneath the volcano.
3. Volcanoes belonging to the same group, and therefore near to-
92 IGNEOUS AGENCIES.
gether, often erupt independently, as if each had its own reservoir of
liquid matter. The pressure of these two objections has driven many
to the admission of a sort of honey-combed remains of the interior
liquid inclosed in the solid crust, and now isolated both from the in-
terior liquid and from each other.
4. There is a limit to the descent of water into the interior of the
earth ; gravity urges it downward, but the interior heat drives it
back. The limit, therefore, will be where these two balance each
other, i. e., where the elastic force of steam is equal to the superincum-
bent columja of water. We will call this point the limit of volcanic
waters. It is evident that when water was first condensed on the cool-
ing earth, this limit was at the surface : water could not penetrate at
all. As the earth cooled, this limit became deeper and deeper ; and, if
the earth became perfectly cool to the centre, there is little doubt that
the whole of the water on the earth would be absorbed. This is per-
haps the case with the moon now.
Now, it seems probable that at the limit of volcanic water the in-
terior heat of the earth, increasing at the rate of 1 for every fifty feet,
would be far short of the temperature necessary for igneous fusion of
rocks. Again, the elastic force necessary to sustain the superincum-
bent water would by no means be sufficient to break up the crust of
the earth, or raise melted lava to the surface.
But we will not pursue this subject, as it is too complex to be yet
solved by science. We rely, therefore, on the first three objections.
Chemical Theory. Whether or not the earth consist of solid crust
covering an interior liquid, it almost certainly consists of an oxidized
crust covering an unoxidized interior. Now, the oxidizing agents are
water and air, and therefore the limit of the oxidized crust is the limit
of volcanic water. Therefore, the oxidizing agent and the unoxidized
material are in close proximity, and the former ever encroaching on the
latter, and therefore liable at any moment to set up chemical action,
the intensity of which would vary with the nature of the material. If
the action be intense, heat may be formed sufficient to fuse the rocks
and to develop elastic force necessary to produce eruption.
In this general form, the chemical theory seems plausible, but many
have attempted to give it more definiteness, and to explain the special
forms of oxidization which cause volcanoes. The most celebrated of
these definite forms is that of Sir Humphry Davy, who attributed it to
the contact of water with metallic potassium, sodium, calcium and
magnesium, in the interior of the earth. In such definite forms the
theory seems far too hypothetical.
Recent Theories. 1. Aqueo-igneous Theory. Accumulation of
sediment on sea-bottoms would necessarily produce corresponding rise
of isogeotherms, and thus the interior heat of the earth would invade
VOLCANOES. 93
the sediments with their contained waters. The lower portion of
sediments 10,000 feet thick would be raised to a temperature of about
260, and of 40,000 feet thick (sediments of this thickness and more are
known) to that of 860. This temperature, or even a less temperature
if alkali be present, would be sufficient in the presence of the contained
water of the sediments to produce complete aqueo-igneous fusion, and
probably to develop elastic force sufficient to produce eruption. This
view was first brought forward by John HerscheH Observe that this
temperature and the corresponding force would be gradually developed
as the accumulation progressed, until sufficient to produce these effects.
Observe, again, that in this case the water does not seek the heat by
descending, but the heat seeks the already imprisoned water by as-
cending.
It seems very probable that cases of eruption of hot mud and of
aqueo-igneously fused lavas may be accounted for in this way, but the
temperature would not be sufficient to account for true igneous fusion.
Some geologists go much further, and, supposing that the whole sur-
face of the earth consists of sedimentary rocks of great thickness, im-
agine that between the solid surface and a solid nucleus there exists a
continuous layer of aqueo-igneously fused matter which is the seat of
igneous activity.
2. Mechanical Theory. As we shall explain hereafter (p. 252),there
is much reason to believe that the interior of the earth is contracting
more rapidly than the exterior, and that the exterior is thus necessarily
thrust upon itself by irresistible horizontal pressure. According to Mr.
Mallet, the crushing of the rocky crust in places under this pressure
develops heat sufficient to fuse the rocks, and to produce eruption.
3. Issuing of Super-heated Gases. Very recently Rev. O. Fisher
has advanced a view which deserves attention. He thinks volcanoes
are vents through which issue from the earth's interior super-heated
steam and gases, melting the rocks in their course and ejecting them by
their pressure. According to this view, the water is not derived from
the surface, but is original and constituent. This view is independent
of the condition of the earth's interior, whether solid or liquid ; for a
temperature which would permit solidity at great depths would produce
fusion under less pressure near the surface. 1 The sun may be regarded
as a globe in an earlier and more active stage of vulcanism. From its
interior gases are seen to issue in great quantity, and almost constantly.
The complete development of these later theories cannot be under-
taken in this part of our treatise. We will take the subject up again
under the head of Mountain Formation (p. 240).
Cambridge Philosophical Society, 1875.
94 IGNEOUS AGENCIES.
Subordinate Volcanic Phenomena.
These are hot springs, carbonated springs, solfataras, fumaroles,
mud-volcanoes, and geysers. They are all secondary phenomena, i. e.,
formed by the percolation of meteoric water through hot volcanic ejec-
tions. Or perhaps in some cases the heat may be produced by slow
rock-crushing by horizontal pressure, as explained above.
General Explanation. Thick masses of lava outpoured from vol-
canoes remain hot in their interior for an incalculable time. Water
percolating through these acquires their heat, and comes up again as hot
springs ; or, if it contains carbonic acid, as carbonated springs ; or, if it
contains sulphurous acid and sulphureted hydrogen, as solfataras. If
condensable vapors issue in abundance so as to make an appearance of
smoke, they are called fumaroles. If the hot water brings up with it
mud which accumulates about the vent, then it is a mud-spring or a
mud-volcano. If the heat is very great, so that violent eruption of water
takes place periodically, then it becomes a geyser. This is the onty one
which need detain us.
Geysers.
A geyser may be defined as a periodically eruptive spring. They
are found only in Iceland, in the Yellowstone Park, United States, and in
New Zealand. The so-called geysers of California are rather fumaroles.
Those of Iceland have been long studied ; we will, therefore, describe
these first.
Iceland is an elevated plateau about two thousand feet high, with a
narrow marginal habitable region sloping gently to the sea. The ele-
vated plateau is the seat of every species of volcanic action, viz., lava-
eruptions, solfataras, mud-volcanoes, hot springs, and geysers. These
last exist in great numbers ; more than one hundred are found in a
circle of two miles diameter. One of these, the Great Geyser, has long
attracted attention.
Description. The Great Geyser is a basin or pool fifty-six feet in
diameter, on the top of a mound thirty feet high. From the bottom of
the basin descends a funnel-shaped pipe eighteen feet in diameter at
top, and seventy-eight feet deep. Both the basin and the tube are lined
with silica, evidently deposited from the water. The natural inference
is, that the mound is built up by deposit from the water, in somewhat
the same manner as a volcanic cone is built up by its own ejections.
In the intervals between the eruptions the basin is filled to the brim
with perfectly transparent water, having a temperature of about 170
to 180.
Phenomena Of an Eruption. 1. Immediately preceding the erup-
tion sounds like cannonading are heard beneath, and bubbles rise and
break on the surface of the water. 2. A bulging of the surface is then
GEYSERS.
95
seen, and the water overflows the basin. 3. Immediately thereafter
the whole of the water in the tube and basin is shot upward one hundred
feet high, forming a fountain of dazzling splendor. 4. The eruption of
water is immediately followed by the escape of steam with a roaring
noise. These last two phenomena are repeated several times, so that
the fountain continues to play for several minutes, until the water is
sufficiently cooled, and then all is again quiet until another eruption.
96
IGXEOUS AGENCIES.
The eruptions occur tolerably regularly every ninety minutes, and last
six or seven minutes. Throwing large stones into the tube has the
effect of bringing on the eruption more quickly.
Yellowstone Geysers. In magnificence of geyser displays, however,
Iceland is far surpassed by the geyser basin of Firehole River. This
wonderful geyser region is situated in the northwest corner of Wyo-
ming, on an elevated volcanic plateau near the head-waters of the Madi-
son River, a tributary of
the Missouri, and of the
Snake River, a tributary
of the Columbia. The
basin is only about three
miles wide. About it are
abundant evidences of pro-
digious volcanic activity
in former times, and, al-
though primary volcanic
activity has ceased, sec-
ondary volcanic phenom-
ena are developed on a
stupendous scale and of
every kind, viz.: hot
springs, carbonated springs, fumaroles, mud-volcanoes, and geysers.
In this vicinity there are more than 10,000 vents of all kinds. In
some places, as on Gardiner's River, the hot springs are mostly lime-
depositing (p. 71) ; in others, as on Firehole River, they are geysers
depositing silica.
In the upper geyser basin the valley is covered with a snowy de-
FIG. 83.-(After Hayden.)
FIG. 84. The Turban (after Hayden).
posit from the hot geyser-waters. The surface of the mound-like,
chimney-like, and hive-like elevations, immediately surrounding the
GEYSERS.
97
vents, is, in some cases, ornamented in the most exquisite manner by-
deposits of the same, in the form of scalloped embroidery set with
pearly tubercles ; in others, the siliceous deposits take the most fan-
Fio. 85. Giant Geyser (after Hay den).
tastic forms (Figs. 82, 83, 84). In some places the silica is deposited in
large quantities, three or four inches deep, in a gelatinous condition
like starch-paste. Trunks and branches of trees immersed in these wa-
ters are speedily petrified.
7
98
IGNEOUS AGENCIES.
We can only mention a few of the grandest of these geysers :
1. The " Grand Geyser," according to Hayden, throws up a column
of water six feet in diameter to the height of 200 feet, while the steam
ascends 1,000 feet or more. The eruption is repeated every thirty-
two hours, and lasts twenty minutes. In a state of quiescence the
temperature of the water at the surface is about 150.
FIG. 86. Bee-Hive Geyser (from a Drawing by Holmes).
2. The " Giantess " throws up a large column twenty feet in diame-
ter to a height of sixty feet, and through this great mass it shoots up
five or six lesser jets to a height of 250 feet. It erupts about once in
every eleven hours, and plays twenty minutes.
GEYSERS.
99
3. The " Giant " (Fig. 85) throws a column five feet in diameter
140 feet high, and plays continuously for three hours.
4. The " Bee-Hive " (Fig. 86), so called from the shape of its mound,
shoots up a splendid column two or three feet in diameter to the height
by measurement of 219 feet, and plays fifteen minutes.
5. " Old Faithful," so called from the frequency and regularity of its
eruptions, throws up a column six feet in diameter to the height of 100
to 150 feet regularly every hour, and plays each time fifteen minutes.
FIG. ST. Forms of Geyser-Craters (after Hayden).
Theories of Geyser-Eruption. The water of geysers is not volcanic
water, but simple spring-water. A geyser is not, therefore, a volcano
ejecting water, but a true spring. There has been much speculation
concerning the cause of their truly wonderful eruptions.
Mackenzie's Theory. According to Mackenzie, the eruptions of the
Great Geyser may be accounted for by supposing its pipe connected
by a narrow conduit with the lower part of a subterranean cave,
whose walls are heated by the near vicinity of volcanic fires. Fig.
88 represents a section through the basin, tube and supposed cave.
Now, if meteoric water should run into the cave through fissures more
rapidly than it can evaporate, it would accumulate until it rose above,
and therefore closed, the opening at a. The steam, now having no out-
let, would condense in the chamber b until its pressure raised the water
into the pipe, and caused it to overflow the basin. The pressure still
continuing, all the water would be driven out of the cave, and partly
up the pipe. Now, the pressure which sustained the whole column a d
100
IGNEOUS AGENCIES.
would not only sustain, but eject with violence, the column c d. The
steam would escape, the ejected water would cool, and a period of qui-
escence would follow. If there were but one geyser in Iceland, this
would be rightly considered a very ingenious and probable hypoth-
esis, for without doubt
we may conceive of a
cave and conduit so con-
structed as to account
for the phenomena. But
there are many eruptive
springs in Iceland, and
it is inconceivable that
all of them should have
caves and conduits so
peculiarly constructed.
This theory is therefore
entirely untenable.
FIG. 88. Mackenzie's Theory of Eruption.
Bunsen's Investigations. The investigations of Bunsen and his
theory of the eruption and the formation of geysers are among the
most beautiful illustrations of scientific induction which we have in
geology. We therefore give it, perhaps, more fully than its strict
geological importance warrants.
Bunsen examined all the phenomena of hot springs in Iceland. 1.
He ascertained that geyser-water is meteoric water, containing the
soluble matters of the igneous rocks in the vicinity. He formed iden-
tical water by digesting Iceland rocks in hot rain-water. 2. He ascer-
tained that there are two kinds of hot springs in Iceland, viz., acid
springs and alkaline-carbonate springs, and that only alkaline-car-
bonate springs contain any silica in solution. The reason is obvious :
alkaline waters, especially if hot, are the natural solvents of silica. 3.
He ascertained that only the silicated springs form geysers. Here is
one important step taken one condition of geyser-formation discov-
ered. Deposit of silica is necessary to the existence of geysers. The
tube of a geyser is not an accidental conduit, but is built up try its own
deposit. 4. Of silicated springs, only those with long tubes erupt
another condition. 5. Contrary to previous opinion, the silica in solu-
tion does not deposit on cooling, but only by drying. This would make
the building-up of a geyser-tube an inconceivably slow process, and the
time proportionally long. This, however, is not true, for the Yellow-
stone geyser-waters, which deposit abundantly by cooling, evidently
because they contain much more silica than those of Iceland. 6. The
temperature of the water in the basin was found to be usually 170 to
180, and that in the tube to increase rapidly, though not regularly,
with depth. Moreover, the temperature, both at the surface and at
GEYSERS.
101
Pressure In
Atmospheres.
Bofflng-Point.
1 Atmos.
2 "
3 "
4 "
212
250
275
293
all depths, increased regularly as the time of eruption approached.
Just before the eruption it was, at the depth of about forty-five feet,
very near the boiling-point for that depth.
Theory of Geyser-Eruption Principles. 1. It is well known that
the boiling-point of water rises as the pressure increases. This is
shown in the adjoining table. 2. It follows
from the above that if water be under strong
pressure, and at high temperature, though
below its boiling-point for that pressure, and
the pressure be diminished sufficiently, it will
immediately flash into steam. 3. Water
heated beneath, if the circulation be unim-
peded, is very nearly the same temperature throughout. That it is
never the same temperature precisely is shown by the circulation itself,
which is caused by difference of temperature, producing difference in
density. The phenomenon of simmering is also a well-known evidence
of this difference of temperature, since it is produced by the collapse of
steam-bubbles rising into the cooler water above. 4. But if the circula-
tion be impeded, as when the water is contained in long, narrow, irreg-
ular tubes, and heated with great rapidity, the temperature may be
greater below than above to any extent, and the boiling-point may be
reached in the lower part of the tube, while it is far from this point in
the upper part.
Application to Geysers. We will suppose a geyser to have a simple
but irregular tube, without a cave, heated below by volcanic fires, or
by still hot volcanic ejections. Now, we have already seen that the
temperature of the water in the tube increases rapidly with the depth,
but is, at every depth to which observation extends, short of the boil-
ing-point for that depth. Let absciss
a d (Fig. 89) represent depth in the ^ _ n| I I | 1 1 |
tube, and also pressures ; and the cor-
responding temperature be measured
on the ordinate a n. If, then, a #, b c,
c d, represent equal depths of thirty-
three or more feet, which is equal to
one atmospheric pressure, the curve
e f passing through 210, 250, 275,
and 293, at the horizontal lines, repre-
senting one atmosphere, two atmos-
pheres, three atmospheres, etc., would
correctly represent the increasing boil-
ing-points as we pass downward. We
shall call this line, e /, the curve of
boiling-point. The line a g commencing
/
/
/
/
'
/>
/
66.6 ft.
1
/
/
100 ft jg
at the surface at 180,
102
IGNEOUS AGENCIES.
and gradually approaching the boiling-point line, but everywhere
within it, would represent the actual temperature in a state of qui-
escence. Now, Bunsen found that, as the time of eruption approached,
the temperature at every depth approached the boiling-point for that
depth, i. e., the line a g moved toward the line ef. There is no doubt,
therefore, that, at the moment of eruption, at some point below the
reach of observation, the line a g actually touches the line ef the boiling-
point for that depth is actually reached. As soon as this occurs, a quan-
tity of water in the lower portion of the tube, or perhaps even in the sub-
terranean channels which lead to the tube, would be changed into steam,
and the expanding steam would lift the whole column of water in the
tube, and cause the water in the basin to bulge and overflow. As soon
as the water overflowed, the pressure would be diminished in every part
of the tube, and consequently a large quantity of water before very
near the boiling-point would flash into steam and instantly eject the
whole of the water in the pipe ; and the steam itself would rush out
immediately afterward. The premonitory cannonading beneath is evi-
dently produced by the collapse of large steam-bubbles rising through
the cooler water of the upper part of the tube ; in other words, it is
simmering on a huge scale. An eruption is more quickly brought on
by throwing stones into the throat of the geyser, because the circula-
tion is thus more effectually impeded.
The theory given above is substantially that of Bunsen for the erup-
tion of the Great Geyser, but modified to make it applicable to all gey-
sers. In the Great Geyser, as already stated, Bunsen found a point, forty-
five feet deep, where the temperature was nearer the boiling-point than
at any within reach of observation, though doubtless beyond the reach
of observation the temperature again approached and touched the boil-
ing-point. This point, forty-five feet deep, plays an important part in
Bunsen's theory. To illustrate : if e f (Fig. 90) represent again the
curve of boiling-point, then the
f a curve of actual temperature in
the Great Geyser tube would be
the irregular line a g h. At the
moment of eruption, this line
touched boiling-point at some
depth, h, beyond the reach of
observation. Then followed
the lifting of the column, the
overflow of the basin, the re-
lief of pressure by which the
point g was brought to the boil-
ing-point, the instantaneous
formation of steam at <?, and
4
e66ft
GEYSERS.
103
:
the phenomena of an eruption. But it is extremely unlikely that this
condition should exist in all geysers ; neither is it at all nee- _
essary in order to explain the phenomenon of an eruption. ,^'k
To prove beyond question the truth of his theory, Bun- jjjl*j\
sen constructed an artificial geyser. The apparatus (Fig. 91) /: :
consisted of a tube of tinned sheet-iron about ten feet long,
expanded into a dish above for catching the erupted water. '
It may or may not be expanded below for the convenience
of heating. It was heated, also, a little below the middle, by
an encircling charcoal chauffer, to represent the point of
nearest approach to the boiling-point in the geyser-tube.
When this apparatus was heated at the two points, as shown
in the figure, the phenomena of geyser-eruption were com-
pletely reproduced ; first, the violent explosive simmering,
then the overflow, then the eruption, and then the state of
quiescence.. In Bunsen's experiment, the eruptions oc-
curred about every thirty minutes.
Bunsen's Theory of Geyser - Formation. According to
Bunsen, a geyser does not find a cave, or even a perpen-
dicular tube, ready made, but, like volcanoes, makes its own
tube. Fig. 92 is an ideal section of a geyser-mound, show-
ing the manner in which, according to this view, it is formed.
The irregular line, b a <?, is the original surface, and a the
position of a hot spring. If the spring be not alkaline, it
will remain an ordinary hot spring; but, if it be alkaline,
it will hold silica in solution, and the silica will be deposited Fie. 91. Arti-
about the spring. Thus the mound and tube are gradually
built up. For a long time the spring will not be eruptive, for the cir-
culation will maintain a nearly equal temperature in every part of the
tube it may be a boiling,
but not an eruptive spring.
But, as the tube becomes
longer, and the circulation
more and more impeded, the
difference of temperature be-
tween the upper and lower
parts of the tube becomes
greater and greater, until,
finally, the boiling-point is
reached below, while the wa-
ter above is comparatively
cool. Then the eruption com-
mences. Finally, from the gradual failure of the subterranean heat, or
from the increasing length of the tube repressing the formation of
1
FIG. 92.-Ideal Section of a Geyser-Tube, according to
104 IGNEOUS AGENCIES.
steam, the eruptions gradually cease. Bunsen found geysers in every
stage of development some playful springs without tubes ; some with
short tubes, not yet eruptive ; some with long tubes, violently erup-
tive ; some becoming old and indisposed to erupt unless angered by
throwing stones down the throat.
It is evident, however, that Bunseii's theory of geyser-eruption is
independent of his theory of geyser-formation. A tube or fissure of
any kind, and formed in any way, if long enough, would give rise to
the same phenomena. The Yellowstone geysers have mounds or chim-
ney-like cones, but it is by no means certain that the whole length of
their eruptive tubes has been built up by siliceous deposit. Bunsen's
theory of eruption none the less, however, applies to these also. The
more chimney-like form of the craters in the case of the Yellowstone
geysers is probably due to the greater abundance of silica in solution.
SECTION 3. EARTHQUAKES.
Only very recently, and mainly through the labors of Mr. Mallet, of
England, our knowledge on the subject of earthquakes has commenced
to take on scientific form. This slowness of advance has arisen not
from any want of materials, but from the great complexity of the phe-
nomena, their origin deep within the bowels of the earth and there-
fore removed from observation, and, more than all, from the surprise
and alarm usually produced unfitting the mind for scientific observa-
tion. For these reasons, until fifteen or twenty years ago, the state of
knowledge on this subject was much the same as it was 2,000 years
ago. And yet now, we think, our knowledge of earthquakes is even
more advanced than that of volcanoes.
Frequency. Mallet, in his earthquake catalogue, has collected the
records of 6,830 earthquakes as occurring in 3,456 years previous to
1850 ; but, of that number, 3,240, or nearly one-half, occurred in the
last fifty years ; not because earthquakes were more numerous, but be-
cause the records were more perfect. If the records had been equally
complete throughout the whole time, the number would have been over
200,000. Taking the last four years of his record, the number was about
two a week. According to the more complete catalogue of Alexis
Perry, from 1843 to 1872, inclusive, there were 17,249, or 575 per an-
num. It seems probable, therefore, that, considering the fact that even
now the larger number of earthquakes are not recorded, occurring in
mid-ocean or in uncivilized regions, the earth is constantly quaking in
some portion of its surface.
Connection with other Forms of Igneous Agency. The close connec-
tion of earthquakes with volcanoes is undoubted : 1. Volcanic eruptions,
especially those of the explosive type, are always preceded and accom-
panied by earthquakes. 2. Earthquake-shocks which have continued to
EARTHQUAKES. 105
trouble a particular region for a long time, often suddenly cease when
an outburst takes place in a neighboring volcano, showing that the lat-
ter are safety-vents for the interior forces which produce earthquakes.
Also, the sudden cessation of accustomed volcanic activity will often
bring on earthquakes. Thus, when the wreath of smoke disappears
from Cotopaxi, the inhabitants of Quito expect earthquakes. During
the great Calabrian earthquake of 1783, Stromboli, for the first time in
the memory of man, ceased erupting. The great earthquake which de-
stroyed Riobamba in 1797, and in which 40,000 persons perished, took
place immediately after the stopping of activity in a neighboring vol-
cano. The earthquake-shocks which destroyed Caracas in 1812 ceased
as soon as St. Vincent, 500 miles distant, commenced erupting. 3. Ex-
amination of Prof. Mallet's earthquake-map shows that the distribution
of earthquake-centres is much the same as that of volcanoes already
given (page 81). It may be regarded as almost certain, therefore, that
the forces which generate earthquakes are closely allied, if not identical,
with those which produce volcanic eruptions.
Again, the connection of earthquakes with bodily movements of
great areas of the earth's crust, by elevation or depression, is equally
close. In 1835, after a great earthquake, which shook the coast of
South America over an area of 600,000 square miles, the whole coast-
line of Chili and Patagonia was found elevated from two to ten feet
above sea-level. Again, in 1822, after a similar earthquake in the same
region, the coast-line was found elevated from two to seven feet. Now,
in this very region, old beach-marks, 100 feet to 1,300 feet above the
sea-level, and extending 1,200 miles along the coast on each side of the
southern end of this continent, plainly show that, in very recent geo-
logical times, the whole southern end of South America has been bodily
raised out of the sea to that extent. It is impossible to doubt that the
force which produced this continental elevation was also the cause of
the accompanying earthquakes. Again, in 1819, after a severe earth-
quake, which shook the whole region about the mouth of the Indus, a
large tract of land of 2,000 square miles was sunk and became a salt
lagoon; while another area, fifty miles long and ten to sixteen miles
wide, was elevated ten feet. In commemoration of this wonderful
event, the raised portion was called Ullah Bund, or the Mound of God.
Again, in 1811, a severe earthquake shook the valley of the Missis-
sippi. In the region about the mouth of the Ohio, where it was se-
verest, large tracts of land were sunk bodily several feet below their for-
mer level, and have been covered with water ever since. It is now
called the " Sunk Country" In the two cases last mentioned there
was evidently formed & fault or dislocation, i. e., there was a fissure in
the earth's crust, and one side dropped down lower than the other.
Such fissures and faults are found intersecting the earth in all direc-
106 IGNEOUS AGENCIES.
tions. We see them, in these cases, formed under our eyes, and in
connection with earthquakes.
Ultimate Cause of Earthquakes. The connection of earthquakes
with the two other forms of igneous agency suggests each a possible
cause. Preceding and accompanying volcanic eruptions, especially of
the explosive type, occur subterranean explosions, which are often heard
hundreds of miles. Such eruptions are also accompanied with escape of
immense quantities of steam and gas. These facts, together with the
association of earthquakes with volcanoes, have suggested the idea that
the sudden formation or the sudden collapse of vapor is the cause of
earthquakes. According to this view, an earthquake is, on a grand
scale, a phenomenon similar to the jar produced by the explosion of a
keg of gunpowder buried in the earth.
But the association of earthquakes with bodily movements of large
areas of the earth's crust suggests another and a far more probable
cause. The earth's crust, as is well known, is in gradual movement by
elevation or depression almost everywhere. These movements, as we
shall show hereafter, are probably due to the greater interior contrac-
tion of the earth thrusting the crust upon itself, by horizontal pressure.
If the yielding is constant like the force, the movement will be grad-
ual; but if the crust resists, and the force still accumulates, the yielding
must take place suddenly by fissure or crushing. Such assuring or
crushing of the rocky crust would certainly produce a concussion or
jar, which, propagating itself, would finally reach the surface and
spread outward from the point of first emergence. Furthermore,
when we remember that these fissures often break through thousands
of feet and even miles in thickness of solid rock, we easily perceive
that the resulting concussion would be fully adequate to produce all
the dreadful effects of earthquakes.
Proximate Cause. But whatever be our view of the ultimate cause
of earthquakes, there can be no doubt that the proximate or immediate
cause of the observed effects is the arrival of an earth-jar the emer-
gence, on the earth-surface, of a succession of elastic earth-waves, pro-
duced by a violent concussion of some kind in the interior. Evidently,
therefore, the discussion of earthquake phenomena is nothing more
than the discussion of the laws of propagation and the effects of elastic
waves occurring under peculiar and very complex conditions. It is
impossible to understand the subject without some preliminary knowl-
edge of the nature and properties of waves. For the sake of greater
clearness we will state some principles which we will make use of in
this discussion.
Waves their Kinds and Properties. Waves may be classified in
several ways, according to the point of view from which we regard
them. Regarding only the force of propagation, they are divided into
EARTHQUAKES. 107
waves of gravity and waves of elasticity. Regarding the direction of
oscillation, they are divided into waves of transverse and waves of
longitudinal oscillation ; regarding the form, into circular and spheri-
cal waves.
( of elasticity _^_z^._longitudinal oscillation <^ K- spherical.
Waves -j ^^v
( of gravity - ^> -transverse oscillation <-.. -circular.
A wave of elasticity may have either longitudinal or transverse oscil-
lation, as shown in the diagram, but those of which we shall speak will
be principally the former. Waves of gravity are always of transverse
vibration. Spherical waves are of longitudinal vibration, and circular
waves are transverse.
If a stone be thrown into still water a series of waves run in every
direction from the point of disturbance, becoming lower and lower as
the distance increases, until the}' become insensible. These are circular
waves of transverse oscillation propagated by gravity alone. The direc-
tion of propagation is along the surface of the water in direction of the
radius of the circle ; the direction of oscillation is up and down, or trans-
verse to the direction of propagation. Water-waves are, therefore,
transverse waves of gravity, and, if propagated from a central point,
are circular. They move with uniform velocity ; their height decreases
as they pass outward. If, on the other hand, an impulse like an ex-
plosion originate in the interior of a medium, as, for example, in the
air or in the interior of the earth, the impulse acting in every direction
compresses a spherical shell of matter all around itself, while the point
of impulse itself passes into a state of rarefaction ; this compressed shell
in expanding by its elastic force compresses the next outer shell of mat-
ter, itself becoming rarefied in the act, and this last in its turn propa-
gates the impulse to the next, and so on. Thus, if only a single wave
were formed, there would run outward from the focal point an ever-
widening spherical shell of compressed matter, followed closely by a
similar shell of rarefied matter. But in every case of impulse or con-
cussion there is always a series of such alternate compressed and rare-
fied shells following one another. The alternate compression and
rarefaction causes each particle in succession to move forth and back.
This oscillatory motion is in the direction of propagation of the wave,
and therefore longitudinal. All waves propagated from a point within
a medium, such as sound-waves^ are elastic spherical waves of longi-
tudinal oscillation.
Definition Of Terms. In transverse waves, such as water-waves, the
distance from wave-crest to wave-crest, or from wave-trough to wave-
trough, is called the wave-length, and the perpendicular distance from
trough to crest is called the wave-height. Similar terms are used in
speaking of waves of longitudinal vibrations. The sense in which they
108 IGNEOUS AGENCIES.
are used and their propriety are shown in the accompanying figure (Fig.
93). Let the bar A B represent a prism cut from a vibrating sphere in
the direction of the radius, i. e., the direction of propagation of the
wave, and let the dark and light portions represent condensation and
rarefaction. Now, on the line a b, representing the natural state of the
bar, draw ordinates above, to represent the degrees of compression, and
below, to represent degrees of rarefaction ; then the undulating line
will correctly represent the state of the bar during the transmission of
elastic longitudinal waves. Thus longitudinal waves may be repre-
sented in the same way as transverse waves. The most compressed
portions are called crests, and the most rarefied troughs ; from crest to
crest is the length, and the amount of oscillation of the particles back
and forth in compression and rarefaction is the height of the wave.
We shall be compelled to use these terms in speaking of earthquake-
waves.
Thus, then, there are two very distinct kinds of waves, both of
which are common viz., circular waves of gravity, of which water-
waves are the type, and spherical elastic waves, of which sound-waves
are the type. We will have much to do with both of these in the ex-
planation of earthquake phenomena.
The velocity of water-waves depends wholly on the wave-length,
and not at all on the wave-height. Therefore, water-waves run with
uniform motion, since, although their height diminishes, their length
remains the same. But there is one important exception to this law,
and one which peculiarly concerns us in this discussion viz., when the
length of waves is great in proportion to the depth of the water, then
they drag bottom, and their velocity is a function of the depth of the
water as well as of the length of the wave.
The velocity of elastic waves, on the other hand, is not affected
either by the height or the length of the wave, but only by the elasticity
of the medium. Thus the harmony of a full band of music is perfect
even at a great distance ; but this would be impossible unless loud
sounds (high waves) and soft sounds (low waves), deep sounds (long
waves) and sharp sounds (short waves), all run with the same velocity.
But there is one exception here also which especially.concerns us in the
EARTHQUAKES. 109
discussion of earth-waves. It is this : When the medium is very im-
perfectly elastic, and the waves are high, then the medium is broken by
the passage of the waves at every step, its elasticity is diminished, and
the waves retarded.
In order to understand clearly what follows, it is necessary to bear
well in mind the distinction between velocity of oscillation and velocity
of transmission or transit. These bear no relation to one another.
Thus we may have a long, low water-wave moving with immense
velocity along the surface, and yet communicating only a slow oscillat-
ing motion up and down to a boat resting on its surface. In the case
of water-waves the velocity of transit depends on the length of the
wave only, the amount of vibration on the height of the wave only,
while the velocity of vibration depends on the relation of the height to
the length. In elastic longitudinal waves the velocity of transit de-
pends on the elasticity of the medium only; the amount of vibration, as
in the last case, on the height of the wave, and the velocity of vibration
upon the relation of height to length of wave.
Application to Earthquakes. Suppose, then, a concussion of any
kind to occur at a considerable depth (x, Fig. 94), say ten or twenty miles,
beneath the earth-surface, S S. A series of elastic spherical waves will
be generated, consisting of alternate compressed and rarefied shells, the
whole expanding with great rapidity in all directions until they reach
FIG. 94.
the surface at a. From this point of first emergence immediately above
the focus a, the still-enlarging spherical shells would outcrop in rapidly-
expanding circular waves similar in form to water-waves, but very dif-
ferent in character. This we will call the surface-wave. Fig. 94 is a
vertical section through the focus x and the point of first emergence
(epicentrum) a, showing the series of spherical waves outcropping at
a, J, c, d, etc. The circles here drawn would equally represent a series
of waves, or the same wave in successive degrees of enlargement.
This surface-wave would not be similar to any wave classified above.
It would not be a normal wave of any kind. It would be only the out-
cropping or emergence of the ever-widening spherical wave on the
earth-surface. Both its velocity of transit along the surface, and the
direction of its vibration in relation to the surface, will vary constantly
110 IGNEOUS AGENCIES.
according to a simple law. The direction of vibration, being along
the radii x a, x b, x c, etc., will be perpendicular to the surface at a,
and become more inclined until it finally becomes parallel with the
surface at an infinite distance. The velocity of its transit will be in-
finite at a, and then gradually decrease until, if we regard the surface
as a plane surface, at an infinite distance it reaches its limit, which is
the velocity of the spherical wave. Between these two extremes of
infinity at a, and the velocity of the spherical wave at infinite distance,
the velocity of the surface-wave varies inversely as the cosine of the
angle of emergence x b a, x c a, etc.
For, if a a, bb, cc, del, etc., be successive positions of the spherical
wave, then the radii x a, x b, x c, would be the direction both of propaga-
tion and of vibration. Now, when the wave-front is at b while the
spherical wave moves from b' to c, the surface-wave would move from b
to c ; when the spherical wave moves from c' to d, the surface-wave
moves from c to d, etc. If, therefore, be, cd, etc., be taken very small,
so that b b' c, c c' d, may be considered right-angled triangles, then in
every position the surface-wave moves along the hypothenuse, while
the spherical wave moves along the cosine of the angle of emergence
x ca,x da, etc. Letting v = velocity of the spherical wave, and v r
that of the surface-wave, and E the angle of emergence, we have the
proportion v' : v'.'.Rad. I cos. .Z?, and v' = =,, or if v is constant
cos. J?
v' oc j-. Therefore, at a, the point of first emergence, E being a
right angle, and the cos. E = 0, v' = = infinity. At an infinite
distance from a the angle E becomes 0, and the cosine = 1, and
v' = = v. That is, at the point of first emergence the velocity of the
surface-wave is infinite ; from this point it decreases as the cosine of the
angle of emergence increases, until finally at an infinite distance it be-
comes equal to the velocity of the spherical wave.
On a spherical surface (Fig. 95) it is evident that E never becomes
0, and therefore v' never reaches the limit v. If we conceived the
wave to pass through the whole earth (Fig. 96), then the velocity of
the surface-wave would decrease to a certain point where E is a mini-
EARTHQUAKES. HI
mum, say about c, and then would again in-
crease to infinity on the opposite side of the
earth,>, where E becomes again a right angle.
If x be near the surface, v' would become nearly
equal to v at some point of its course ; but
as x approaches the centre, (7, the limit of v'
would be greater and greater, until, if x is at
the centre, v' would become infinite every-
where : i. e., a shock at the centre of the
earth would reach the surface everywhere at
the same moment.
Experimental Determination of the Velocity of the Spherical Wave.
On the supposition that earthquakes are really produced by the emer-
gence on the surface of a series of elastic earth-waves, Mallet under-
took to determine experimentally the velocity of such waves. Two
stations were taken about a mile or more apart, and connected by tele-
graphic apparatus ; a keg of gunpowder was buried at one, and at the
other was placed an observatory, in which was a clock, a mercury mir-
ror, and a light, the image of which reflected from the mercury mirror
was thrown on a screen. The slightest tremor communicated to the
mercury surface of course caused the image to dance. The moment
of explosion was telegraphed ; the moment of arrival of the earth-
tremor was observed. The difference gave the time of transit ; the
distance, divided by the time, gave the velocity per second. In this
manner Mallet found the velocity in sand 825 feet per second, or nearly
nine and one-half miles per minute ; in slate, 1,225 feet per second, or
fourteen miles per minute ; and in granite 1,665 feet per second, or
nineteen miles per minute. As an earthquake-focus is always several
miles beneath the surface, and as rocks at that depth are probably as
hard as granite, nineteen miles per minute may be taken as the aver-
age velocity of earth-waves as determined by these experiments. It
agrees well with the observed velocity of many earthquakes.
This result was unexpected, considering the law that all elastic
waves in the same medium run with the same velocity, for the velocity
of sound in granite or slate is probably not less than 10,000 or 12,000
feet per second. The explanation is to be found in the very imperfect
coherence and elasticity of rocks. The medium is broken by the pas-
sage of large and high waves of the explosion, but carries successfully
the small waves of sound.
Explanation of Earthquake-Phenomena Earthquakes have been
divided into three kinds, viz., the explosive, the horizontally progres-
sive, and the vorticose. The first kind is described by Humboldt as
a violent motion directly upward, by which the earth-crust is broken
up, and bodies on the surface are thrown high in the air. The shock
112 IGNEOUS AGENCIES.
is extremely violent, but does not extend very far. In the second, the
shock spreads on the surface like the waves on water to a great dis-
tance. In the third there is a whirling motion of the earth entirely
different from ordinary wave-motion. These three kinds are sometimes
supposed to be essentially distinct, and possibly produced by different
causes ; but we will attempt to show that the difference is wholly due
to the different conditions under which the waves emerge on the sur-
face. The three kinds are, iu fact, often united in the same earth-
quake.
The most remarkable example of explosive earthquake is that which
destroyed Riobamba in 1797. In this dreadful earthquake the shock
came suddenly, like the explosion of a mine. Not only was the earth
broken up and rent in various places, but objects lying on the surface
of the earth were thrown violently upward ; bodies of men were hurled
several hundred feet in the air, and afterward were found across a
river and on the top of a hill. In earthquakes of this kind 1. The
impulse is very powerful and sudden, so as to make a high but not
a long wave, or, in other words, the velocity of vibration or of the
shock is very great ; and, 2. The focus is not deep, so that the
velocity of the shock (height of the wave) does not become small be-
fore it reaches the surface. At Riobamba the velocity of the shock
was still very great when the wave reached the surface. From the
distance bodies were thrown, Mallet supposes the velocity of the shock
could not have been less than eighty feet per second (Jukes).
The horizontally progressive kind may be regarded as the true
type of an earthquake ; it is in fact the spreading surface-wave al-
ready explained. If the elasticity of the earth, and therefore the
velocity of the waves, is the same in all directions, the surface-wave
will spread in concentric circles; but if the elasticity, and therefore
the velocity of the waves, be greater in one direction than in another,
as, for example, north and south than east and west, or the converse,
then the form of the outcrop will be elliptical. In some rare cases the
shock seems to run along a line. Thus progressive earthquakes have
been subdivided into circular, elliptical, and linear progressive. We
have already given the simple explanation of the first two ; the last
may be briefly explained as follows :
Let it be borne in mind : 1. That these linear earthquakes usually
run along mountain-chains ; 2. That most great mountain-chains consist
of a granite axis (appearing along the crest and evidently connected be-
neath with the great interior rocky mass of the earth), flanked on each
side with stratified rocks consisting of many different kinds ; 3. When
elastic waves pass from one medium to another of different elasticity,
in all cases a part of the waves passes through, but a part is always
reflected. For every such change for every layer a reflection oc-
EARTHQUAKES.
113
curs; and, therefore, if there are many such layers, the waves are
quickly quenched. If, now, Fig. 97 represent a transverse section
across such a mountain, and X the focus of an earthquake, it is evident
that portion of the enlarging spherical wave which emerged along the
axis a would reach the surface successfully; while those portions which
FIG. 97. Diagram illustrating Linear Earthquakes. FIG. 9a
struck against the strata of the flanks would be partially or wholly
quenched. The mode of outcrop on the surface is shown in the map-
view, Fig. 98, in which a is the epicentrum, b b the granite axis, and
c c the stratified flanks.
The velocity of the surface-waves, as observed in many cases of
severe earthquakes, is about twenty miles a minute. This accords
well with Mallet's experiments in granite. In some earthquakes the
velocity has been found to be twelve to fifteen miles (Mallet's results in
slate), and in some as high as thirty to thirty-five miles per minute. In
no great earthquake has the velocity been found higher than the last
mentioned. In some slight shocks, however, occurring recently in
New England, the velocity, as determined by telegraph, is estimated
as high as one hundred and forty miles per minute, or 12,000 feet per
second.
This amazing difference may be fully explained : It will be re-
membered that the velocity of the surface- wave is infinite at the epi-
centrum, and diminishes, according to a law already discussed, until it
reaches, or nearly reaches, the velocity of the spherical wave. Now, if
the earthquake-focus be comparatively shallow, the initial velocity of
the surface-wave very rapidly approaches its minimum, and therefore
the observed velocity of the surface-wave may be taken as nearly the
same as that of the spherical wave ; but, if the earthquake be very
deep, the diminution, even on a plane surface, is far less rapid ; and
when we take into consideration the curvature of the earth-surface, it
is evident that the velocity of the surface-wave is always and for all
distances much greater than that of the spherical wave. This would
well account for velocities of thirty to thirty-five miles, but not for one
8
114 IGNEOUS AGENCIES.
hundred and forty miles. This latter is accounted for by another
principle.
We have seen that these high velocities occur only in slight shocks.
Now, while heavy shocks (large and high waves) break the medium at
every step of their passage, and are therefore retarded, as already
explained, slight tremors (small and low. waves) are successfully trans-
mitted without rupture, and therefore run with the natural velocity
belonging to the medium, i. e., the velocity of sound. Now, the
velocity of sound in granite is probably about 12,000 feet per second,
or one hundred and forty miles per minute.
Vorticose Earthquakes. In these cases the ground is twisted or
whirled round and back, or sometimes ruptured and left in a twisted
condition. The most conspicuous examples of this kind of motion
occurred in the earthquake of Riobamba, and in the great Calabrian
earthquake of 1783. In this latter earthquake the blocks of stone
forming obelisks were twisted one on another ; the earth was broken
and twisted, so that straight rows of trees were left in interrupted zig-
zags. Phenomena similar to some of these were observed also in the
California earthquake of 1868. Chimney-tops were separated at their
junction with roofs, and twisted around without overthrow ; wardrobes
and bureaus turned about at right angles to the wall, or even with
their faces to the wall.
Explanation. Some of these effects such as twisting of obelisks
and chimney-tops, and turning about of bureaus, etc. may be ex-
plained, as Lyell has shown, without any twisting motion of the earth
at all or any other than the backward and forward motion common to
all earthquakes. Thus, if we place one brick on another, and shake
them back and forth, holding only the lower one, they are almost cer-
tain to be left twisted one on the other. The reason is, that the adhe-
sion is almost certain to be greater toward one end than the other the
centre of friction does not coincide with the centre of gravity. This
is the probable explanation of twisted obelisks and chimney -tops, etc.
Also, the simple back-and-forth shaking of a wardrobe in a diagonal
direction would almost certainly lift up one end and swing it around.
The vorticose motion in such cases is probably not real, but only
apparent.
But there are other cases of undoubtedly real vorticose motion ; as,
for example, straight rows of trees changed into interrupted zigzags by
fissures and displacement. All such cases of real twisting are prob-
ably explicable on the principle of concurrence and interference of
waves. If two systems of waves of any kind meet each other, there
will be points of concurrence where they reenforce each other, and
points of interference where they destroy each other. Suppose, for
instance, a system of water-waves, represented by the double lines i, i
EARTHQUAKES.
115
(Fig. 99), running in the direction b , strike against a wall, w w:
the waves would be reflected in the direction c c, and are represented
by the single lines r, r. Then, if the lines represent crests, and the inter-
vening space the troughs, at the places marked with crosses and dots
there would be concurrence, and therefore higher crests and deeper
FIG. 99. Diagram illustrating Reflection of Waves.
troughs, while at the points indicated by a dash there would be inter-
ference and mutual destruction, and therefore smooth water. The same
takes place in earth- waves. If two systems of earth-waves meet and
cross each other, we must have points of concurrence and interference
in close proximity. The ground, therefore, will be thrown into violent
agitation points in close proximity moving in opposite directions
(twisting). If the motion be sufficient to rupture the earth, restoration
is not made by counter-twisting, and the earth is left in a displaced
condition.
The causes of interference may be various sometimes difference
of velocity of waves, already explained, by which some overrun others,
concurring and interfering; more often it is the result of reflection
from surfaces of different elasticity. For example, it is well known
that the most violent effects of earthquakes, especially twisting of the
ground, usually occur near the junction of the softer strata of the
plains with the harder and more elastic strata of the mountains. Now,
suppose from a shock at X (Fig. 100) a system of earth-waves should
emerge at a, and run as a surface-wave toward the mountain m. The
116 IGNEOUS AGENCIES.
waves, striking the hard, elastic material m, would be partly trans-
mitted and partly reflected. The reflected waves, running in the direc-
tion of the arrow r,
would meet the ad-
vancing incident waves
moving in the direc-
tion of the arrow i, and
N / concurrence and inter-
'. ference would be in-
evitable.
Minor Phenomena.
kinds of earthquakes, but many of the minor phenomena, are explained
by the wave-theory.
1. Sounds. These are usually described as a hollow rumbling, roll-
ing, or grinding / sometimes as clashing, thundering, or cannonading.
They are probably produced by rupture of the earth at the origin, and
by the passage of the wave through the imperfectly elastic rocky
medium, breaking the medium and grinding the broken parts together.
But what is especially noteworthy is, that these sounds precede as well
as accompany the shocks. In every earthquake there are transmitted
waves of every variety of size. The great waves are sensible as shocks,
or jars, or tremors ; the very small waves, too small to be appreciated
as tremors, are heard as sounds. But, as already explained, these
last run with greater velocity in an imperfectly coherent and elastic
medium like the earth, and therefore arrive sooner than the great
waves, which constitute the shock. The same was observed in Mallet's
experiments.
2. Motion. As to direction, the observed motion is sometimes verti-
cally up and down, sometimes horizontally back and forth, and some-
times oblique to the horizon. Almost always a rocking motion, i. e., a
leaning of tall objects first in one direction and then in the other, is
observed. As to violence or velocity of motion, this is sometimes so
great that objects are thrown into the air, and whole cities are shaken
down as if they were a mere collection of card-houses, while in other
cases only a slow swinging, or heaving, or gentle rocking, is observed.
The difference in direction is wholly due to the position of the ob-
server. At the epicentrum it is of course vertical, and thence it be-
comes more and more oblique, until at great distances it is usually
horizontal. The violence of the shock or velocity of ground-motion de-
pends partly upon the violence of the original concussion, and partly on
the distance from the origin or focus. This velocity of the ground-
motion must not be confounded with the velocity of the wave already
discussed. The latter is the velocity of transit from place to place ; the
EARTHQUAKES.
117
former is the velocity of oscillation up and down, or back and forth.
The velocity of oscillation has no relation to the velocity of transit, but
depends only on the height of the wave, which constantly diminishes
and becomes finally very small, though the velocity of transit remains
the same, and always enormously great. The rocking motion is also
easily explained. A series of waves, somewhat similar in form to water-
waves (though differing in nature), actually passes beneath the observer.
Of course, when an object is on the front-slope, it will lean in the direc-
tion of transit ; and, when on the hind-slope, in the contrary direction.
3. Circle of Principal Destruction. In some earthquakes a certain
zone at considerable distance from the point of first emergence (epicen-
trum) has been observed, in which the destruction by overthrow is very
great, and beyond which it speedily diminishes. This has been called
the circle of principal destruction or overthrow. It is thus explained :
The overthrow of buildings depends not so much on the amount of oscil-
lation as upon the horizontal element of the oscillation. Now, the whole
amount of oscillation is greatest at the point of first emergence, and
decreases outward ; but
the horizontal element
is nothing at , and in-
creases as the cosine E.
Therefore, under the in-
fluence of these two con-
ditions, one decreasing
the whole oscillation, the
other increasing the hor-
izontal element of that
Oscillation, it is evident FlG ' 101 - Dia g ram illustrating Circle of Principal Disturbance.
that there will be a point on every side, or, in other words, a circle, where
a maximum. This is shown in Fig.
\
the horizontal element will be
101, in which a a', b ', c c', etc., are the decreasing oscilation, and
b b\ c c", are the horizontal element. This reaches a maximum at c. It
has been found by mathematical calculation, based upon the supposition
that the whole oscillation varies inversely as the square of the distance
from JT, that the horizontal element will be a maximum when the angle
of emergence is 54 44'. By determining by observation the circle of
principal disturbance, it is easy to calculate the depth a X of the focus,
for it will be the apex of a cone whose base is that circle, and whose
apical angle is 70 32'.
4. Shocks more severely felt in Mines. It has been sometimes ob-
served that shocks are distinctly felt in mines which are insensible at
the surface. This is probably explained as follows : Let 8 S (Fig. 102)
be the surface of the ground ; and let a b represent hard, elastic strata,
covered with loose, inelastic materials, c c. Now, if a series of waves
118
IGNEOUS AGENCIES.
come in the direction of the arrows d <#, and, passing through a b on
their way to the surface, strike upon the lower surface of c c, a portion
would reach the surface by refraction, but a portion would be reflected
and return into a 5, concurring and interfering with the advancing
waves, and producing great commotion in these strata.
5. Shocks less severe in Mines. This case is probably more common
than the last. It was notably the case in the earthquake of 1872 in
FIG. 102. Shocks in Mines.
Inyo County, California. While the surface was severely shaken, and
many houses destroyed, and large fissures formed in the earth, the
miners, several hundred feet below the surface in the hard rock, scarcely
felt it at all.
This fact has scarcely been noticed, and no attempt has been made
to explain it.
6. Bridges. In a somewhat similar manner are to be accounted for
the phenomena of bridges. In the earthquake-regions of South America
there are certain favored spots, often of small extent, which are partially
exempt from the shocks which infest the surrounding country. The
FIG. 108.
earthquake-wave seems to pass under them as under a bridge to reap-
pear again on the other side. The mere inspection of Fig. 103 will
explain the probable cause of this exemption, viz. : reflection from the
under surface of an isolated mass of soft, inelastic strata, c c.
7. Fissures. The ground-fissures, so commonly produced by earth-
quakes, are sometimes of the nature of the great fissures of the crust,
which are the probable cause of earthquakes. Such great fissures are
EARTHQUAKES ORIGINATING BENEATH THE OCEAN. H9
usually wholly beneath the surface at great depth, but sometimes may
break through and appear on the surface. This is certainly the case
when decided faults occur with elevation or depression of large tracts
of land. But the surface-fissures so frequently described, small in size,
very numerous, and running in all directions, have an entirely different
origin. They are evidently produced by the shattering of the softer,
more incoherent, and inelastic surface-soil, and by the passage of the
earth-wave. Even the more elastic underlying rock is broken by the
same cause, but to a much less extent.
Earthquakes originating beneath the Ocean.
We have thus far spoken of earthquakes originating beneath the
land-surface. But three-fourths of the earth-surface is covered by the
sea ; and we have already seen that other forms of igneous agency are
most abundant in and about the sea. As we might expect, therefore,
the greater number of earthquake-shocks occur beneath the sea-bed.
In such, the phenomena already described are complicated by the ad-
dition of the " Great Sea - Wave."
Suppose, then, an earthquake-shock to occur beneath the sea-bed :
the following waves will be formed : 1. As before, a series of elastic
spherical waves will spread from the focus, until they emerge on the
sea-bed. 2. As before, a series of circular surface-waves, the outcrop of
the spherical waves, will spread on the sea-bottom until they reach the
nearest shore, and perhaps produce destructive effects there. 3. On the
back of this submarine earth-wave is carried a corresponding sea-wave.
This is called the "forced sea-wave," since it is not a free wave, but a
forced accompaniment of the ground-wave beneath. It reaches the
shore at the same time as the earth-wave. It is of little importance.
4. In addition to all these is formed the great sea-wave or tidal wave.
Gfreat Sea- Wave. This common and often very destructive accom-
paniment of earthquakes is formed as follows : The sudden upheaval of
the sea-bad lifts the whole mass of superincumbent water to an equal
extent, forming a huge mound. The falling again of this water as far
beloio as it was before above its natural level generates a circular wave
of gravity, which spreads like other water-waves, maintaining its origi-
nal wave-length, but gradually diminishing its wave-height until it be-
comes insensible. Usually, a series of such waves is formed by the
motion of the sea-bottom up and down several times. These waves are
often 100 to 200 miles across their base (wave-length) and fifty to sixty
feet high at their origin. Their destructive effects may be inferred from
the enormous quantity of water they contain. In the open sea they
create no current, and are not even perceived, but, when they touch
bottom near shore, they rush forward as great breakers fifty or sixty
feet high, sweeping away everything in their course.
120 IGNEOUS AGENCIES.
Being waves of gravity, their velocity, though very great on account
of their size, is far less than that of the earth-waves, and they reach the
neighboring shore, therefore, some time later, and often complete the
destruction commenced by the earth-waves.
Examples of the Sea-Wave. In the great earthquake which de-
stroyed Lisbon in 1755, the epicentrum was on the sea-bed fifty or more
miles off the coast of Portugal. From this point the surface earth-
waves spread along the sea-bottom until they reached shore. It was
the arrival of these waves which destroyed Lisbon. About a half-hour
later, when all had become quiet, several great sea-waves, one of them
sixty feet high, came rushing in, deluging the whole coast and com-
pleting the destruction commenced by the earth-waves. This wave was
thirty feet high at Cadiz, eighteen feet at Madeira, and five feet on the
coast of Ireland. It was sensible on the coast of Norway, and even on
the coast of the West Indies, after having crossed the whole breadth
of the Atlantic.
In 1854 a great earthquake shook the coast of Japan. Its focus was
evidently beneath the sea-bed some distance off the coast, for, in about
a half-hour, a series of water-waves thirty feet high rushed upcn shore
and completely swept away the town of Simoda. From the same cen-
tre the waves, of course, spread in the contrary direction, traversed the
whole breadth of the Pacific, and in about twelve and a quarter hours
struck on the coast of California at San Francisco, and swept down the
coast to San Diego. These waves were thirty feet high at Simoda, fif-
teen feet high at Peel's Island, about 1,000 miles off the coast of Japan,
0.65 feet, or eight inches, high at San Francisco, and six inches at San
Diego. 1
On the 13th of August, 1868, a great earthquake desolated the coast
of Peru. Its focus was evidently but a little way off shore, for in less
than a half-hour a series of water-waves fifty or sixty feet high rushed
in and greatly increased the devastation commenced by the earth-waves.
These waves reached Coquiinbo, 800 miles distant, in three hours;
Honolulu, Sandwich Islands, 5,580 miles, in twelve hours ; the Japan
coast, over 10,000 miles, the next day. They were also observed on
the coast of California, Oregon, and Alaska, over 6,000 miles in one
direction, and on the Australian coast, nearly 8,000 miles in another
direction. This series of waves was distinctly sensible at a distance of
nearly half the circumference of the earth. Had it not been for the
barrier of the South American Continent, it would have encircled the
globe. 9
There are several points in the above description which we must
very briefly explain :
1. The velocity of these great sea-waves, though less than that of
1 " Report of Coast Survey for 1862." 2 " Report of Coast Survey for 1869."
EARTHQUAKES ORIGINATING BENEATH THE OCEAN. J21
the earth-waves, is still very great in comparison with ordinary sea-
waves. The waves of the Japan earthquake crossed the Pacific to San
Francisco, a distance of 4,525 miles, in a little more than twelve hours,
and therefore at a rate of 370 miles per hour, or over six miles per
minute. The waves of the South American earthquake of 1868 ran to
the Hawaiian Islands at a rate of 454 miles per hour. This amazing
velocity is the result of the great size of these waves.
2. The size of these great waves is determined by multiplying the
time of oscillation by the velocity, on the well-known principle that
every kind of wave runs its own length during the time of one com-
plete oscillation. The velocity is obtained by observing the time at
different points. The time of oscillation is determined by means of
tidal gauges. The tidal gauges established by the coast survey on the
Pacific coast showed that the time of oscillation of the larger waves of
the Japan earthquake was about thirty-three (thirty one to thirty-five)
minutes. This would give a wave-length of a little over 200 miles. It
is probable that the wave-length in the case of the South American
earthquake was at least equally great.
3. The distance to which the sea-waves run is far greater than that
of the earth-waves. The former is distinctly sensible for 10,000 miles ;
the latter very rarely more than a few hundreds. There are two rea-
sons for this : 1. All waves diminish in oscillation (wave-height) as they
spread from the origin, because the quantity of matter successively
involved in the oscillation constantly increases. But in the one case
the matter involved lies in the circumference of a fcircle ; in the other,
in the surface of a sphere ; therefore, the one increases as the distance,
the other as the square of the distance. Therefore, the decrease of os-
cillation (height of wave) is far less rapid for water-waves than for elas-
tic spherical waves. 2. A still more effective reason is this: Water-
waves run in a perfectly homogeneous medium, and therefore diminish
only according to the regular law just stated ; but the earth-waves run
in an heterogeneous, imperfectlv elastic, and imperfectly coherent me-
dium, and therefore they are rapidly quenched and dissipated by re-
peated refractions and reflections, and by repeated fractures of the
medium, and thus changed into other forms of force, as heat, electrici-
ty, etc. Were it not for this, the destructive effects of earthquakes
would be far more extensive.
4. We have said the wave-length remains unchanged. This length,
therefore, represents the diameter of the original water-mound, and
therefore of the original sea-bottom upheaval. In the Japan earth-
quake this was 200 miles across. This shows the grand scale upon
which earthquake-movements take place.
5. As already explained, earthquake sea-waves differ from all other
sea-waves in that their great size makes them drag bottom even in open
122 IGNEOUS AGENCIES.
deep sea. In their case, therefore, the velocity depends not only on
the wave-length, but also on the depth of the sea. Knowing the size
(wave-length) of these waves, and therefore what ought to be their
free velocity, and also knowing their actual velocity by observation,
the difference gives the retardation by dragging ; and by the retarda-
tion may be calculated the mean depth of the ocean traversed. In this
Avay it has been determined that the mean depth of the Pacific between
Japan and San Francisco is 12,000 feet, and between Peru and Hono-
lulu, Sandwich Islands, 18,500 feet. The great importance of such
results is obvious.
Depth of Earthquake-Focus.
The great obscurity which hangs about the subject of the interior
condition of the earth and the ultimate cause of igneous agencies ren-
ders any positive knowledge on these subjects of peculiar interest. There
can be little doubt that the phenomena of earthquake-waves, their form,
their velocity, their angle of emergence, etc., if once thoroughly under-
stood, would be a most delicate index of this condition, and a powerful
means of solving many problems which now seem beyond the reach of
science. Among problems of this kind none is more important, and at
the same time more capable of solution, than the depth of the origin of
earthquakes, and therefore presumably of volcanoes.
Seismometers. The most direct way of determining the depth of
an earthquake-focus is by means of well-constructed seismometers.
These are instruments for measuring and recording earthquake-phenom-
ena. They are of infinite variety of forms, depending partly upon the
facts desired to be recorded, and partly upon the mode of record. As
examples we will mention only two :
An excellent instrument for recording slight tremors is one invented
and used by Prof. Palmieri, of the Vesuvian Observatory. It consists
of a telegraphic apparatus with the usual paper-slip and stile. The
paper-slip, accurately divided into hours, minutes, and seconds, travels
at a uniform rate by means of clock-work. The battery-circuit is closed
and opened, and the recording stile worked by the shaking of a metallic
bob, hung by a delicate spiral spring above a mercury-cup ; the shak-
ing of the bob being determined by the tremor of the earth. Such an
instrument records the exact moment of occurrence of earthquake-shocks,
however slight ; also, the moment of passage of every wave and its time
of oscillation ; and if there be more than one such instrument, the mo-
ment of occurrence at different places gives the velocity of the surface-
wave v'. It records, however, rather than measures earthquake-phe-
nomena ; it is a seismograph rather than a seismometer.
The best form of seismometer which we have seen described that
which gives the most important information is that of Prof. Cavalleri,
of Monza. It consists essentially of two pendulums, one horizontally
DEPTH OF EARTHQUAKE-FOCUS.
123
and the other vertically oscillating (Figs. 104 and 105). The former
(Fig. 104) is an ordinary pendulum, with a heavy bob, b, armed with a
stile which touches a bed of sand, s s. The sharp point of the stile
rests loosely in a slight depression in a small flat cylinder or button, c,
resting lightly on the top of the firm column d. When the earthquake-
shock arrives, the whole building, and therefore the attachment a, above,
and the bed of sand, s s, on the floor, will move in the direction of the
shock. This direction will generally be partly horizontal and partly
vertical (x b,xc,x d, Fig. 94). We will consider now only the hori-
V
d FIGS. 104 and 105. Cavalleri's Seismometer.
zontal element. The pendulum, b, will tend to retain its position, and
the bed of sand will move beneath it, first in one direction and then in
the other, and the stile will thus mark the sand back and forth to a dis-
tance equal to the back-and-forth motion of the earth. The direction
from which the impulse came is determined by the side on which the
little cylinder falls. It is easy to connect the pendulum with a clock
set at twelve, in such wise that the motion of the former will in-
stantly set agoing the latter. The difference between this clock-time
and the real time will give the instant of transit. It is clear that this
pendulum does not give the whole amount of the vibration or motion
of the shock, but only the horizontal element. If a b (Fig. 106) repre-
sent the direction and amount of vibration, then
a c is the horizontal element measured by the
pendulum. This instrument, therefore, gives
the moment of transit, the direction of transit,
and the horizontal element of vibration.
The vertical element, b c, of the vibration is
FIG. 106.
124
IGNEOUS AGENCIES.
given bv a vertically oscillating pendulum (Fig. 105), the point of
which rests lightly on one arm, a, of a very easily-moved lever, the other
arm, b, of which acts as an index by means of a graduated quadrant.
When the shock moves the floor of the building upward, the heavy
weight of the pendulum retaining its position by stretching of the wire
spring, the arm a is pressed against the stile, and the arm b is elevated ;
when the floor descends again, b is retained in its elevated position by a
ratchet at <?, and thus records the amount of elevation of the floor. This
pendulum, therefore, gives the upward movement or one-half the whole
vertical element. Having now the horizontal and vertical element, i. e.,
the base and perpendicular of a right-angled triangle, the hypothenuse, or
whole oscillation, and the direction of oscillation, or angle of emergence
(a, Fig. 106), are gotten by simple calculation (a b \/ a c* + b c a ,
and a b : R :: be: sine a), or by accurate plotting.
The important facts recorded by this instrument are : 1. The in-
stant of transit ; 2. The direction of transit ; 3. The direction of os-
cillation, or angle of emergence ; 4. The amount of oscillation. From
these elements (if we have several seismometers scattered about the
country) may be calculated : 1. The velocity of transit ; 2. The posi-
tion of the focus ; 3. The form of the focus, whether point or fissure;
4. The force of the original concussion. The most important of these
are the position and depth of the focus.
The Determination of the Epicentnim. Cavalleri's seismometer
gives the direction of transit of the surface-wave. If, by the use of
many such seismometers, or even by rougher methods, we get a number
of these surface-lines of transit, by following these back we get the
epicentrum at their intersec-
tion. Or if, by means of many
seismographs giving time of
transit, or even by observa-
tories or stations of any kind
_ with accurate clocks, we get
several points of simultaneous
arrival of the wave, then by
drawing a curve through these
points we have a coseismal
curve. A perpendicular drawn
from the middle point of the
line joining any two of these
points will pass through the
epicentrum, and two such per-
pendiculars would determine its position. Fig. 107 represents coseismal
curves, and b, c, <7, three points on the curve ; a is the epicentrum.
Determination of the FOCUS. The spherical wave is a wave of longi-
Fio. 107. Coseismal Lines.
DEPTH OF EARTHQUAKE-FOCUS. 125
tudinal oscillation. The direction of oscillation, therefore, is the same
as the direction of transmission (wave-path), which is the radius of
the agitated sphere. If, therefore, the direction of the ground-motion
(the line a , Fig. 106) be followed into the earth, it carries us back
along the wave-path to its origin, the focus. Two such wave-paths
by their intersection would determine its position. Thus, in Fig. 108,
if c and b be the position of two seismometric observatories, the angles
of emergence, x c a and x b , being given by observation, and the dis-
tance, c b, being known, we have all the elements necessary to deter-
mine either by calculation or by accurate plotting the wave-paths c x
and b x, and their point of intersection x, and therefore of the depth a x.
Although seismometers, such as we have described, are necessary
for accurate results from few observations, yet by multiplying the ob-
servations, even by rough methods, approximative results may be ob-
tained. We will mention only two examples :
In 1857 a terrible earthquake shook the territory of Naples, de-
stroying many towns and villages, and killing about 10,000 people.
The scene of destruction was visited soon after by Mr. Mallet. By care-
ful examination of overthrown objects, many lines of transit of the sur-
face-wave were determined, which, protracted, carried him with consider-
able certainty to the epicentrum ; similarly many lines of emergence, or
paths of the spherical wave, protracted back, conducted to the focus.
This focus was determined to be not a point, but a fissure, nine miles
long and through three miles of solid rock. The centre of this rent
was about six miles beneath the surface.
In 1874 a not very severe earthquake shook Central Germany. It
has been thoroughly investigated by Seebach. The epicentrum was
determined with great precision by erecting perpendiculars to the bi-
sec,ted chords of the coseismal curves. The focus was determined as
a rent through four miles of rock, the centre of the rent being nine or
ten miles in depth.
The velocity of transit of the waves of the Naples earthquake was
860 feet per second, or between nine and ten miles per minute ; that
126 IGNEOUS AGENCIES.
of the earthquake of Middle Germany was about twenty-eight miles
per minute.
There have been many attempts to determine the depth of earth-
quakes by other methods, especially by using the relative velocities of
the spherical and the surface waves as a means of getting the angle of
emergence (cos. E = H ; but such a method is evidently valueless,
because the velocity of the spherical wave (v) is not constant.
Effect of the Moon on Earthquake - Occurrence. By an extensive
comparison of the times of occurrence of several thousand earthquakes
with the positions of the moon, Alexis Perry has made out with some
probability the following laws : 1. Earthquakes are a little more fre-
quent when the moon is on the meridian than when she is on the
horizon. 2. They are a little more frequent at new and full moon
(syzygies) than at half-moon (quadratures). 3. They are a little more
frequent when the moon is nearest the earth (perigee) than when she
is farthest off (apogee). Now, if these laws are really true, it would
seem that there is a slight tendency for earthquakes to follow the law
of tides : for the first law gives the time of flood-tide, and the sec-
ond and third the times of highest flood-tide. It would seem, there-
fore, that the attraction of the sun and moon has a perceptible effect
in determining the time of occurrence of earthquakes. Many geolo-
gists regard these laws, if established, as conclusive proof of the gen-
eral fluid condition of the earth beneath a comparatively thin crust.
This interior liquid they suppose to be influenced by the tide-generat-
ing forces of the sun and moon ; but, if this were true, the effect ought
to be far greater than we find it. Whatever be the interior condition
of the earth, the effect of the moon on the meridian would be to assist,
and on the horizon to repress, any force whatsoever tending to break
up the crust of the ea % rth and to produce an earthquake.
Relation of Earthquake-Occurrence to Seasons and Atmospheric Con-
ditions. By extensive comparison of earthquake-occurrence with the
seasons, it has been shown that they are a trifle more frequent in win-
ter than in summer. Constructing a curve representing the annual
variation of earthquake-intensity, this curve rises to its maximum in
January and sinks to its minimum in July. But the difference is small.
There has been no satisfactory explanation of this fact.
There is an almost universal popular belief in earthquake-regions
that the occurrence is preceded by a still, oppressive state of the air.
Although no scientific investigations have confirmed this impression,
yet it seems quite possible and even probable that diminished atmos-
pheric pressure, indicated by a slow state of the barometer, may act as
a determining cause of earthquake-occurrence, precisely as the position
of the moon on the meridian. In both cases, however, we must regard
ELEVATION AND DEPRESSION OF EARTH'S CRUST. 127
these not as true causes of earthquakes, but only as causes determin-
ing the moment of occurrence.
SECTION 4. GRADUAL ELEVATION AND DEPRESSION OF THE EARTH'S
CRUST.
Of all the effects of igneous agencies these are by far the most impor-
tant. Although not violent and destructive like volcanoes and earth-
quakes, although indeed so little conspicuous as to be generally unob-
servable except to the eye of science, yet, acting not paroxysmally but
constantly, not in isolated spots but over wide areas, and affecting
whole continents, their final result in modifying the crust of the earth
and making history is far greater than that of all other igneous agen-
cies put together. It is probable that the same causes which are now
at work gradually raising or depressing the earth's crust have during
geological times formed the continents and the seas.
Elevation or Depression during Earthquakes. We have already
spoken (page 105) of sudden elevations or depressions of very great
areas of country at the time of earthquake-occurrence in Hindostan, in
the valley of the Mississippi River, and especially of the southern part of
South America. It is not probable, however, that much is accomplished
in this paroxysmal way. These cases are referred to in order to show
the close connection of such sudden bodily movements, and therefore
presumably, also, of the slower movements about to be described, with
the causes and forces which produce earthquakes.
Movements not connected with Earthquakes South America. Be-
sides the sudden elevation of Chili and Patagonia by earthquakes, the
same countries show evidences of gradual elevation on a stupendous
scale. The evidences are old sea-beaches, full of shells of species now
living in the adjacent sea, far above the present water-level. These
" raised beaches " have been traced 1,180 miles on the eastern shore
and 2,075 miles on the western, and at different levels from 100 to 1,300
feet above the sea. More recently Alexander Agassiz has traced them
by means of corals still sticking to the rocks to the height of 3,000 feet.
It is not probable that all this movement took place during the present
geological epoch, but it is the more instructive on that very account,
since it shows the identity of geological causes with causes now in
operation.
Italy. The most carefully-observed instance of gradual depression
and elevation is that of the coast of Naples. Fig. 109 is a map
and Fig. 110 a section of the coast of the bay of Baiae, near Naples.
Between a a a, the present coast-line, and the cliff b b b, which marks
the position of the former coast-line, there is a nearly level plain called
the Starza. Now, there is perfect evidence that at one time the land
was depressed until the sea beat against the cliff b 5, and that both
128
IGNEOUS AGENCIES.
the depression and the reelevation to its present condition took place
since the period of Roman greatness. The evidence is as follows :
Sta,
1. There are certain shells abundant in the Mediterranean and in
many other seas, called lithodomus (/U0oc, a stone; domus, a house),
from their habit of boring for them-
selves holes in the rocks near the
water-line. Such borings, often
with the dead shells in them, are
found all along the base of the cliff
b b, twenty feet above the present
sea-level. 2. The level plain called
Starza is composed of strata containing shells cf the Mediterranean
and Roman works of art. 3. On this plain, near the present sea-
margin, are the ruins of a Roman temple dedicated to Jupiter Serapis.
The floor and three of the columns of this beautiful work are still almost
perfect (Fig. 110). When first discovered the floor and the lower part
of the columns were covered by the materials of the plain. Above the
part thus covered the columns were bored with lithodomi to a height
of twenty feet. This temple was, of course, above the sea-level during
the Roman, period. After that period it sank until the sea-level stood
at s' (Fig. 110), twenty feet above the base. Now, the floor of the
temple is again on a level with the sea. These changes were so gradual
that they were entirely insensible, and, in fact, unknown to the inhab-
itants. The upright position of the columns also shows that it could
not have been produced by convulsive action. 4. Italian historians
state that in 1530 the sea beat against the cliff b b. 5. Evidences of
similar changes, in some cases depression and in others elevation, are
seen in many places along the coast of Italy, Candia, and Greece.
ELEVATION AND DEPRESSION OF EARTH'S CRUST. 129
In all the cases thus far mentioned, but especially that of the tem-
ple of Serapis, the near vicinity of volcanoes (Fig. 109) suggests that
these effects were probably in some way connected with volcanic ac-
tion. But there are many instances in which no such connection can
be traced.
Scandinavia. The best-observed instance of this kind is that of the
coasts of Norway and Sweden. Careful observations on the coasts of
the Baltic and Polar Seas have proved that nearly the whole of Norway
and Sweden is rising slowly, and has been rising for thousands of years.
South of Stockholm there is no elevation, but, on the contrary, slight de-
pression; but north of Stockholm the whole coast is rising at a rate which
increases as we go north until it attains a maximum at the North
Cape of five to six feet per century. These observations were made
under the direction of the Swedish Government by means of permanent
marks made at the sea-level, and examined from year to year. That
similar changes have been in progress for thousands of years, and have
greatly increased both the height and the extent of these countries, is
proved by the fact that old sea-beaches, full of shells of species now
living in the neighboring seas, are found fifty to seventy miles inland,
and 100, 200, and even 600 feet above the present sea-level. In some
places, the country rock, when uncovered by removing superficial de-
posit of beach-shells, is found studded with barnacles like those which
mark the present shore-line (Jukes).
The rising area is about 1,000 miles long north and south, and of
unknown breadth. It may embrace a considerable portion of Russia.
Lyell estimates the average rate as not more than two and a half
feet per century. At this rate, to rise 600 feet would require 24,000
years. 1 Similar raised beaches are found in nearly all countries. We
give these as examples of an almost universal phenomenon, which will
be again more perfectly described in the chapter on the Quaternary.
Greenland. For obvious reasons, evidences of elevation are much
more conspicuous than evidences of depression. One of the best-ob-
served instances of the latter is that of the coast of Greenland. This
coast is now sinking along a space of 600 miles. Ancient buildings on
low rock-islands have been gradually submerged, and experience has
taught the native Greenlander never to build his hut near the water's
edge.
Deltas of Large Rivers. In the deltas of the Mississippi, the
Ganges, the Po, and many other large rivers, there are unmistakable
evidences of gradual depression. These evidences are fresh-water
shells, and planes of vegetation, or dirt-beds, far below the present level
of the sea. A section of the delta deposits of the Mississippi River re-
veals the fact that these deposits consist of river sands and clays, s, cl
1 Lyell'a " Antiquity of Man," p. 58.
9
130
IGNEOUS AGENCIES.
(Fig. Ill), containing fresh-water shells, with now and then an inter-
calated stratum of marine origin, I, containing marine shells, and at
uncertain intervals distinct lines of turf or vegetable soil, g', g", each
with the stumps and roots of cypress-trees as they originally grew.
Each one of these turf-lines is a submerged forest-ground, except the
uppermost, which is the pres-
ent forest-ground. Precisely
similar phenomena have been
observed in other large deltas.
The deltas of the Ganges and
the Po have been penetrated
more than 400 feet without
reaching bottom. In both
the deposit is made up ' of
fresh -water strata alternat-
ing with dirt-beds or forest-
grounds. These facts prove that these great deltas have been at
intervals during the whole period of their formation, as they are now,
fresh-water swamps, overgrown in parts with trees, etc. ; that they have
steadily subsided to a depth indicated by the thickness of the deposit
containing the old forest-levels; that the upbuilding by river-deposit
has gone on pari passu, so as to maintain nearly the same level all the
time ; but that from time to time the subsidence was more rapid, so
that the sea gained possession for a while until it was again reclaimed
by river-deposit, and again more slow, so that the area was again thor-
oughly covered with forests, and so on. These facts are of great im-
portance in geology, and will be frequently referred to in the following
pages.
Southern Atlantic States. Evidence of a similar kind proves that a
'large portion of the coasts of our Southern Atlantic States is slowly sub-
siding at the present time, though there are also evidences, in the form
of raised beaches, of elevation immediately preceding the present sub-
sidence. The evidences of subsidence are most conspicuous along the
coast of South Carolina and Georgia. They consist of cypress-stumps
in situ below the present tide-level.
These facts seem to point to the conclusion that subsidence is going
on in nearly all places where large deposits of sediment are accumu-
lating.
Pacific Ocean. But by far the grandest example of subsidence
known is that which has been going on for thousands, probably hundreds
of thousands, of years, and is still going on in the mid-Pacific Ocean.
The subsiding area is situated under the equator, and is about 6,000
miles long, by about 2,000 to 3,000 miles wide. The evidence of the
.subsidence and its rate is entirely derived from the study of coral-reefs
THEORIES OF ELEVATION AND DEPRESSION. 131
in this region. The further discussion of the subject will be deferred
until we take up coral-reefs.
Our examples, be it observed, are all taken from the vicinity of
coast-lines, the sea-level being used as term of comparison. In the
interior of continents, and in the midst, of the sea where there are no
islands, we have no such means of detecting changes, yet it is precisely
there, i. e., in the middle of the rising or subsiding area, that the
changes are probably the greatest.
Theories of Elevation and Depression,
It is evident that observation only determines changes of relative
position of sea and land. These changes may be the result of rise and
fall of sea, or rise and fall of land. The popular mind naturally at-
tributes them to the rise and fall of the sea, as the more unstable ele-
ment. But, by the principle of hydrostatic level, it is clearly impossi-
ble that the ocean should rise or fall permanently at one place without
being similarly affected everywhere. It is certain, therefore, that the
changes we have described above, being in different directions in dif-
ferent places, must be due to movements of the solid crust. Neverthe-
less, it is also true that any increase in the height and extent of the
whole amount of land on the globe must be attended with a correspond-
ing depression of the sea-bottoms, and therefore an actual subsidence
of the sea-level everywhere. Hence, if it be true, as is generally be-
lieved, that the continents have been, on the whole, increasing in ex-
tent and in height, in the course of geological history, then it is true
also that the seas have been subsiding, and that therefore the relative
changes are the sum of these two.
Admitting, however, that the actual increase of land at the present
time is imperceptible, or at least very small in comparison with the
oscillatory movements described above, we may look upon the sea-level
as fixed ; this statement being sufficiently correct when regarding the
subject from the physical point of view, though untenable when re-
garded from the geological point of view. Admitting, then, the fixed-
ness of the sea-level, what are the causes of the gradual movements of
the solid crust ?
Babbage's Theory. Babbage believed that, in the vicinity of volca-
noes, the rise and fall of ground were due to the expansion and contrac-
tion of rocks by heating and cooling. The reelevation of the temple
of Serapis occurred apparently soon after the eruption which formed
Monte Nuovo (Fig. 109). It is not improbable that this reelevation
was the result of the heating and vertical expansion of the rocks to
great depth, caused by the eruption of the interior heat at this point.
A very small elevation of temperature of rocks several miles thick
would be sufficient to produce a vertical expansion of twenty feet.
132 IGNEOUS AGENCIES.
Other cases, such as the rise of sea-margins at a distance from
volcanic action, Babbage explains as follows : Large accumulations of
sediments, such as occur generally on coasts, would cause a rise toward
the surface of all the subjacent isogeotherms. This increase of tem-
perature of the crust would cause a vertical elongation or swelling of
the crust at that point, and a consequent rise above the sea-level.
The great objection to this theory, as applied to these latter cases,
is, that the places where the greatest quantities of sediments are depos-
iting (as, for instance, the deltas of great rivers) are places of subsi-
dence, instead of elevation.
Herschel's Theory. Sir John Herschel assumes, as a general law
what has been proved in a great number of instances that areas of
great accumulation of sediment are areas of subsidence. He agrees
with Babbage, that accumulation of sediments must cause an upward
movement of the isogeotherms, but he differs from Babbage in believ-
ing that this invasion of sediments by the interior heat would produce
subsidence instead of elevation. For, according to Herschel, the inva-
sion of sediments by the interior heat would produce chemical changes,
and sometimes even aqueo-igneous fusion. These chemical changes,
whatever other effects they produce, would certainly change sediments
into crystalline rocks (metamorphism). The accumulating sediment
meanwhile would subside, by the pressure of its own weight, on the
liquid or semi-liquid thus formed.
General Theory. The theory of Babbage accounts with great prob-
ability for the rise of ground in the vicinity of volcanoes, and Herschel's
theory accounts, perhaps, for the subsidence of deltas and other places
where great accumulation of sediments occurs ; and this latter theory
has the additional advantage of accounting for metamorphism, and
perhaps, also, for volcanic phenomena. But it is evident that some
other and more general theory is necessary to account for those great
inequalities of the earth's crust which form land and sea-bottom. The
formation of these must be a phenomenon somewhat different from
those local oscillations which alone have been the subject of direct ob-
servation. Such general changes can only be the result of gradual un-
equal contraction of the whole earth consequent upon its secular cool-
ing. The full discussion of this theory, however, belongs properly to
the second part of this work.
PEAT-BOGS AND PEAT-SWAMPS. 133
CHAPTER IV.
ORGANIC AGENCIES.
As agents modifying the crust of the earth, organisms are, per-
haps, inferior to the agents already mentioned (although the immense
thickness and extent of limestone strata are a monument of their power
in this respect) ; nevertheless, they are peculiarly interesting to the
geologist as delicate indicators of climate, and recorders of the events
of the earth's history. We will take up the subject of their agency
under four heads, each having a separate application in interpreting the
structure and history of the earth, viz. : 1. Vegetable Accumulations, to
account for coal ; 2. Bog-iron Ore, to account for iron-ores inclosed in
the strata ; 3. Lime Accumulations, to account for limestones, etc. ; 4.
Geographical Distribution of Organisms, to explain their distribution
in former epochs.
SECTION 1. VEGETABLE ACCUMULATIONS.
Peat-Bogs and Peat- Swamps.
Description. In humid climates, in certain places, badly drained
and overgrown with moss and shrubs, a black carbonaceous mud accu-
mulates often to great depths. This substance is called peat or turf,
and such localities peat-bogs. The thick mass of vegetation which
covers their surface, with its interlaced roots, often forms a crust,
upon which a precarious footing may be found, but beneath this is a
tremulous, semi-fluid quagmire, sometimes twenty to forty feet deep, in
which men and animals, venturing in search of food, are often lost.
These bogs are most numerous in northern climates. One-tenth of the
whole surface of Ireland, and large portions of Scotland, England, and
France, are covered with peat. The bog of the Shannon River is fifty
miles long and three miles wide ; that of the Loire in France is 150
miles in circumference. Extensive bogs exist also in the northern por-
tions of our own country. The amount of peat in Massachusetts alone
has been estimated at more than 15,000,000,000 cubit feet (Dana). In.
California, an imperfect peat covers large areas about the mouth of the
San Joaquin River and elsewhere (tule-lands). In more southern cli-
mates, where the condition of humidity is present, immense accumula-
tions of peat also occur not, however, in bogs overgrown with moss
and shrubs, but in extensive swamps covered with large trees.
Composition and Properties of Peat. Peat is disintegrated and
134: ORGANIC AGENCIES.
partially decomposed vegetable matter. It is composed of carbon, with
small and variable quantities of hydrogen, oxygen, and nitrogen. It is,
therefore, vegetable matter which has lost a part of its gaseous con-
stituents, and in which, therefore, the carbon is greatly in excess. In
more recent peat, the vegetable nature and structure are plainly detect-
able by the eye, but in older peat only by the microscope. In all coun-
tries where it occurs, it is dried and used as a valuable domestic fuel.
By powerful pressure it may be converted into a substance scarcely
distinguishable from some varieties of coal, and, thus changed, is now
extensively used for all purposes for which coal is used, and has there-
fore become an important article of commerce.
Peat possesses a remarkable antiseptic property. This property is
probably due to the presence of humic acid and of hydrocarbons anal-
ogous to bitumen, which are formed only when vegetable matter is
decomposed in presence of excess of water. The bodies of men and
animals have been found in bogs in a good state of preservation, which
must have been buried many hundred years. In 1747, in an English
bog, the body of a woman was found, with skin, nails, and hair, almost
perfect, and with sandals on her feet. In Ireland, under eleven feet of
peat, the body of a man was found clothed in coarse hair-cloth. Several
other instances of bodies of men and animals, and innumerable instances
of skeletons of animals, preserved in bogs where they have perished,
might be mentioned. Large trunks of trees are often so perfectly pre-
served that they are used as timber, and stumps similarly preserved
are found with their roots firmly fixed in the under-soil of the bog as
if they had grown on the original soil on which the bog was accumu-
lated.
Mode of Growth. Plants take the greater portion of their food from
the air, and give it, by the annual fall of leaf and finally by their own
death, to the soil. Thus is formed the humus or vegetable mould found
in all forests. This substance would increase without limit, were it not
that its decay went onparipassu with its formation. But in peat bogs
and swamps the excess of water, and, still more, the antiseptic property
of the peat itself, prevent complete decay. Thus each generation takes
from the air and adds to the soil continually and without limit. The
soil which is made up entirely of this ancestral accumulation continues
to rise higher and higher, until the bog often becomes higher than the
surrounding country, and, when swollen by unusual rains, bursts and
floods the country with black mud. A bog is therefore composed of
the vegetable matter of thousands of generations of plants. It repre-
sents so much matter withdrawn from the atmosphere and added to
the soil. In some cases, besides the material deposited from the
growth of vegetation in situ, the accumulation may be partly also the
result of organic matter drifted from the surrounding surface-soil.
PEAT-BOGS AND PEAT-SWAMPS. 135
Rate of Growth. The rate of peat-growth must be very variable,
since it depends upon the vigor of the vegetation and upon the manner
of accumulation, whether entirely by growth of plants in situ, or partly
by driftage. Many of the European bogs are evidently the growth of not
more than eighteen hundred years, for they were forests in the time of
the Romans, or even later. The felling of these forests, as a military
measure to complete the subjugation of the country, and the consequent
impediments to drainage thus produced, have changed them into bogs.
At their bottoms, and covered with eight to ten feet of peat, are found
the trunks and the stumps of the original forests, the axe and coins of
the Roman soldiers, and the roads of the Roman army. The rate of
accumulation has been variously estimated, from one or two inches to
several feet per century. In all cases of simple growth in situ, however,
and therefore always in great peat-swamps, the increase is very slow.
Conditions of Growth. The conditions usually considered necessary
for the formation of peat are cold and moisture; and of these the
former is considered the more important, as without cold it is supposed
vegetable matter would be destroyed by decay. In proof of this it is
stated that peat-bogs are more numerous in cold climates. But it is
more probable that excess of moisture is the only important condition.
This condition may be rarer in warm climates on account of the greater
capacity of the air for moisture in these climates ; but when it is pres-
ent, immense accumulations of peat occur in extensive swamps. The
Great Dismal Swamp is a good illustration. This swamp, situated
partly in North Carolina and partly in Virginia, is forty miles long by
twenty-five miles wide. It is covered with a dense forest of cypress
and other swamp trees, by the annual fall of whose leaves the peat is
formed. These trees, by means of their long tap-roots and their wide-
spreading lateral roots, maintain a footing in the insecure soil, but are
FIG. 112.
often overthrown, and add their trunks and branches to the vegetable
accumulation. The original soil, upon which the accumulation was
formed, must have been lower in the centre, but the surface of the peat
rises very gently toward the centre, which is twelve feet higher than
the circumference (Fig. 112). Near the centre there is a lake of clear,
wine-colored water, seven miles across and fifteen feet deep, the banks
and bottom of which are composed of pure peat.
In the Mississippi River swamps there are also large areas where pure
peat has been accumulating for ages, and is still accumulating, by
growth of trees in situ, though subject to the annual floods of the river.
136 ORGANIC AGENCIES.
The pureness of the peat in these cases is due to the fact that the mud-
dy waters of the river are strained of all their sedimentary matter by
passing through the dense jungle-growth of cane and herbage which
surrounds these favored spots. Thus only pure water reaches them. 1
Similar peat-swamps are found at the mouths of the Ganges, the Niger,
and other great rivers.
Alternation Of Peat With Sediments. We have already stated (page
129) that a section of the delta-deposit of many great rivers, such as the
Mississippi, Ganges, and Po, reveals alternate layers of fresh-water and
marine sediments, with thin layers of vegetable mould containing
stumps. In some cases these layers of vegetable mould amount to con-
siderable thickness of turf or peat. Layers of peat two feet thick have
been found between layers of river-mud in the delta of the Ganges
(Lyell's "Principles of Geology"). Similar layers have been found in
the delta of the Po. They are evidently submerged peat-swamps.
These facts are of great importance in the explanation of the accumu-
lation of coal.
Drift-Timber.
Great rivers in wooded countries always bring down in large num-
bers the trunks of trees torn from the soil of their banks. These trunks
lodging near their mouths, where the current is less swift, and accumu-
lating from year to year, form rafts of great extent. The great raft of
the Atchafalaya, which was removed in 1835 by the State of Louisiana,
was a mass of timber ten miles long, seven hundred feet wide, and eight
feet thick. It had been accumulating for more than fifty years, and at the
time of its removal was covered with vegetation, and even with trees
sixty feet high. Similar accumulations of drift-wood are described as
occurring in the Red River, the Mackenzie River, and in Slave Lake.
Such rafts become finally imbedded in river-mud, and undergo a slow
change into lignite or imperfect coal. Beds of partially -formed lignite
are therefore found in sections of the delta-deposit of almost all great
rivers. "We will use these facts in speaking of the theories of the coal.
SECTION 2. BOG-!RON ORE.
At the bottom of peat-bogs is often found a " hard pan " of iron-
ore, sometimes one to two feet thick. The same material often collects
in low spots, even when there is no decided bog. The manner in which
this iron-ore accumulates is very interesting, and in a geological point
of view very important.
Peroxide of iron exists very generally diffused as the red coloring-
matter of soils and rocks. In this form, however, it is insoluble, and
therefore cannot be washed out by percolating waters. For this pur-
1 Lyell's "Elements of Geology," fifth edition, p. 385.
BOG-IRON ORE. 13f
pose the agency of decomposing organic matter, present in all percolat-
ing waters, is necessary. Decomposition of organic matter is a process
of oxidation. In contact with peroxide of iron (ferric oxide) it deoxi-
dizes, and reduces it to protoxide (ferrous oxide). The acids, especially
carbonic acid, produced by decomposition of the organic matter, then
unite with the protoxide, forming carbonate of iron. The carbonate,
being soluble in water containing excess of carbonic acid, is washed out,
leaving the soils or rocks decolorized, and the iron-charged waters come
up as chalybeate springs. But the ferrous carbonate rapidly oxidizes
again in the presence of air, by exchanging its carbonic acid for oxygen,
and returns to its former condition of ferric oxide, and is deposited.
Thus all about iron-springs, and in the course of the streams which
flow from them, and in low places where their waters accumulate, we
find reddish deposits of ferric oxide. This is the most common but not
the only form. For if the iron-waters accumulate, and the iron be de-
posited in the presence of excess of organic matter, as peat, then the
iron is not (for in the presence of this reducing agent it cannot be)
reoxidized, but remains in the form of ferrous carbonate.
Thus there are two forms in which iron leached out from the soils
and rocks may accumulate, viz., ferric oxide and ferrous carbonate : the
former is accumulated where the organic matter is in small quantities,
and consumes itself in doing the work of dissolving and carrying ; the
latter where the organic matter is in excess.
Many familiar phenomena may be explained by the principles given
above : 1. Clay containing both iron and organic matter is never red,
but always blue or slate-colored, because the iron is in the form of fer-
rous carbonate ; but the same clay will make good red brick, because
by burning the organic matter is destroyed and the iron peroxidized.
2. In red-clay soils, such as those of our primary regions, the surface-
soil, especially in forests, is always decolorized, the coloring of peroxide
of iron being washed out and carried deeper by water containing or-
ganic matter derived from the vegetable mould. 3. In sections of red
clay, as the sides of gullies or railroad-cuttings, along every fissure or
crevice through which superficial waters percolate, the clay is bleached.
The marbled appearance of red clays is also probably due, in a great
measure, to the irregular percolation of superficial waters containing or-
ganic matter. 4. The under clay or sand of peat-bogs is usually de-
colorized.
We will hereafter make use of these facts and principles in the ex-
planation of beds of iron-ore.
138 ORGANIC AGENCIES.
SECTION 3. LIME ACCUMULATIONS.
Coral Reefs and Islands.
Interest and Importance. The subject of corals and coral reefs is
one of much popular as well as scientific interest. The strange forms
and often splendid colors of the living animals ; the number and ex-
treme beauty of the coral islands which gem the surface of certain
seas ; the large amount of habitable land which owes its existence to
the agency of these minute animals ; the fact that a large area, prob-
ably several thousand square miles, has been thus added to our own
territory ; the great dangers connected with the navigation of coral seas,
strikingly displayed on our own coast by the fact that the considerable
town, of Key West is almost wholly dependent on the wrecking busi-
ness for its existence these and many other facts invest the subject
with popular interest, while the great importance of corals as a geo-
logical agent gives the subject a scientific interest no less strong.
Coral Polyp. The animal which secretes coralline stone is no insect,
as generally supposed, but belongs to one of the lowest divisions of
the animal kingdom, viz., the class of polyps. Like most of the lowest
animals, it is composed of soft, gelatinous, and almost transparent
tissue. The animal, however, has the power of extracting carbonate of
lime from sea-water, and depositing it within its own body. The lime
carbonate is deposited only in the lower portion of the animal, leaving
thus the upper part and the tentacles free to move. The radiated
structure of the polyp is perfectly reproduced in the coralline axis.
This is a purely vital function, having no more connection with voli-
tion than the secretion of the shell of an oyster or the bones of the
higher animals. The limestone thus deposited within the animal con-
stitutes 90 to 95 per cent, of its whole weight.
Compound Coral, or Corallum. A single coral polyp is very small,
but, like many of the lower animals, it has the power of multiplying
indefinitely by buds and branches. Thus are formed compound corals.
These may branch profusely, and then may be called coral-trees ; or may
grow in hemispherical masses, and are then called coral-heads. Coral-
trees are sometimes six or eight feet high, and coral-heads fifteen to
twenty feet in diameter. They consist of millions of individual coral
polyps. Only the upper and outer portions of a coral-tree, and outer
portion of a coral-head, are living ; the lower and interior portions con-
sist only of coralline limestone without life.
Coral Forests. Coral polyps, however, reproduce not only by bud-
ding, but also by eggs. These eggs have the power of locomotion.
As soon as they are extruded, they swim and float away, and, if they
fall on sea-bottom favorable for their growth, they soon form first a
CORAL REEFS AND ISLANDS. 139
coral polyp, and finally a coral-tree or coral-head. Thus from one coral-
tree other coral-trees spring up all around and form a coral forest, which
spreads in every direction where they find conditions favorable.
Coral Reef. Finally, the limestone accumulation of thousands and
millions of coral forests growing and dying on the same spot, to-
gether with the shells of mollusks and the bones of fishes which live in
swarms preying on the corals, the whole, of course, crowned with the
living forest of the present generation, constitute the coral reef. It is
evident, then, that a reef is formed somewhat after the manner of a
peat-bog. As a peat-bog represents so much matter taken from the
air, so a coral reef represents so much matter taken from the sea-water.
As each generation adds itself to the ancestral funeral-pile, the ground
upon which the corals grow steadily rises until it becomes elevated far
above the surrounding sea-bottom.
Coral Islands. These are due to the action of waves upon the
coral reefs. We have already seen how low islands are formed on sub-
marine banks by this agency. Now, reefs are also a kind of submarine
FIG. 113
bank. On these, therefore, islands are also formed by waves. Fig. 113
represents an ideal section across a reef, as it would be if no wave-
action interfered, II being the sea-level. But by the action of the
beating waves during storms large masses of reef-rock, often six or eight
feet in diameter, or great coral-heads, are broken off from the outer or
I
FIG. 114.
seaward side of the reef and rolled over to the leeward side. These
form a nucleus about which collect similar or smaller fragments, and
among these still smaller fragments, and these again are filled in and
made firm with coral-sand, and the whole cemented into solid lime-
stone rock (breccia) by the carbonate of lime in the sea-water.
Islands thus formed, like all wave-formed islands, are low (twelve to
fifteen feet high) and narrow (one-quarter to one-half mile wide), but
long in the direction of the reef. They are at first perfectly bare, but
140 ORGANIC AGENCIES.
become in time covered with vegetation, and even teeming with
population. They are celebrated for their gem-like beauty. The final
result is shown in ideal section in Fig. 114, in which the dotted portion
is reef-rock, the strong waving line the surface of the living reef, and
the shaded portion the island.
Conditions of Coral-Growth. Reef-building corals do not grow in
all seas, nor over the whole bottom of the sea indiscriminately, but are
confined to certain seas, and in these to certain spots and lines. The
conditions of their growth are :
1. A Winter-Temperature 0/68. This condition confines them al-
most entirely to the torrid zone. The most marked exception to this is
on the Florida coast and the Bahamas, where corals extend to 28 north
latitude, and in the Bermudas to 32 north latitude. This extension of
the usual limits of reef-building corals is due to the warm tropical
waters carried northward by the Gulf Stream.
2. A Depth of not more than One Hundred Feet. r Y\\\s, condition
confines them to submarine banks, and especially to the shores of con-
tinents and islands.
3. Clearness and Saltness of the Water. On account of this con-
dition corals will not grow on muddy shores, nor off the mouths of
rivers, being destroyed by the fresh and muddy water.
4. Free Exposure to Waves. Some species of corals grow in still
water, but the strongest reef-building species delight in the dash of the
surf. They will even flourish and build an almost perpendicular wall
in breakers which would wear away the hardest rock. The reason is,
that the immense profusion of life on a reef rapidly exhausts the water
of the oxygen necessary for respiration, and of the carbenate of lime
necessary for their stony structure, and therefore constant change of
water is necessary. t
All the conditions mentioned above apply only to reef-building
species. Some corals live in temperate regions, some in very deep
water, and some in sheltered places.
Pacific Reefs. The reefs of the Pacific Ocean are of three general
kinds, viz., fringing reefs, barrier reefs, and circular reefs or atolls.
We will describe these in the order mentioned.
Fringing Reefs. In the tropical Pacific every high island or previ-
ously-existing land of any kind is surrounded by a reef which attaches
itself to the shore-line, and extends outward on every side just beneath
the water-level, as far as the condition of depth will allow, thus forming
a submarine platform bordering the island or other land. At the outer
margin of this platform the bottom drops off very suddenly, forming
a slope of 50 to 60, and sometimes almost perpendicularly. The po-
sition and extent of the coral platform is indicated to the eye of the
observer by a white sheet of breakers which surrounds the island like
CORAL REEFS AND ISLANDS.
141
a snowy girdle, and extends some distance from the shore-line (Fig.
115.) The section Fig. 116 will give a clear idea of the contour of
land and sea bottom. In this and the following sections the dotted
parts represent coral formation. If the island is large, and considerable
rivers flow into the sea, breaks in the reef platform will occur opposite
the mouths of the rivers, the corals in these places being destroyed by
the fresh, muddy waters. In the case of fringing reefs no islands are
formed by the action of waves, but only a shore-addition to the orig-
inal island, as shown at a a in the section.
Barrier Reefs In many cases besides the fringing reef there is an-
other reef surrounding the island like a submarine rampart at the dis-
tance of from ten to fifty miles. As the reef rises nearly to the surface of
the sea, its position is indicated by a snowy girdle of breakers surround-
ing the island at a distance, and this snowy girdle is gemmed with wave-
formed green islets. Within this girdle, and between the rampart and
the island, there is a ship-channel twenty or thirty fathoms deep (Fig.
117). Through breaks in the coral rampart ships enter this channel
and find secure harbor in a stormy sea. The section Fig. 118 wih give
a clear idea of the conformation of bottom. On the landward side of the
142
ORGANIC AGENCIES.
coral rampart the slope of the bottom is gentle, but on the seaward side
it is very steep, so that it is almost unfathomable at a short distance
from the reef.
Circular Reefs, or Atolls. These are the most wonderful of the
reefs of the Pacific. In a circular reef there is no volcanic island or
other visible land to which the reef is attached. Imagine a circular
line of breakers like a snow-wreath on the sea, indicating a circular
FIG. 120.
submarine ridge (the coral reef) gemmed as before with wave-formed
FIG. 121. View of Whitsunday Island.
CORAL REEFS AND ISLANDS.
143
islets ; and within the circle a lagoon of placid water twenty or thirty
fathoms deep (Fig. 119). It is a submarine urn standing in unfath-
omable water, as seen in the section Fig. 120. Through breaks in the
reef ships enter the charmed circle and find safe harbor. By means of
sounding it is found that on the interior or lagoon side the slope of the
bottom is very gentle, but on the outer or seaward side is very steep,
often 50 to 60, and sometimes in places almost perpendicular to al-
most unfathomable depth. Fig. 121 gives a perspective view, and
Fig. 122, a, a map view, of an atoll, showing their regular circular form
of the reef and the little islands which gem its surface.
Small Atolls and LagOOnless Islands. Besides the atolls already de-
scribed, there are others, evi-
dently of similar origin, but
much smaller, in which the
land is continuous. Some-
times the continuous line
is open on one side (Fig.
122, b), and the lagoon is
still in connection with the
open sea. Sometimes the
circle of land is complete,
and the lagoon is isolated
from the sea (Fig. 122, c).
Sometimes the lagoon closes FIG 122
up, and a lagoonless isl-
and is the result (Fig. 122, (?). These different forms graduate into one
another and into the typical atoll.
Theories of JBarrier and Circular Reefs.
Fringing reefs require no theory. Corals attach themselves to the
shore-line because they find there the depth necessary for their growth,
and they extend outward until they are limited by the increasing depth.
But there is a real difficulty in explaining barriers, for they seem to rise
from water too deep for coral-growth; and the difficulty becomes still
greater in the case of circular reefs or atolls, for these seem to have no
connection with any preexisting land, but seem to grow up from an
unfathomable bottom. These latter, by their singularity and extreme
beauty, have always attracted the attention and excited the wonder of
Pacific travelers ; and to their explanation theories have been princi-
pally addressed.
Crater Theory. This theory supposes that an atoll is an extinct
submarine volcano, the lagoon being the crater and the reef the lip or
margin of the crater ; that corals, finding on this circular rim the con-
ditions of depth necessary for their growth, occupy and build upon it to
144 ORGANIC AGENCIES.
the surface of the water, after which, of course, waves finish the work
by beating up the islets. The incredible supposition that thousands of
these volcanoes should have come within 100 feet of the surface, and
yet none of them appear above the surface, is not necessary ; for we
may suppose that many of them were originally above the surface,
but, being composed of ashes and cinders, have been washed down by
the waves. In 1831 a volcano burst forth in the Mediterranean and
quickly formed an island of cinders and ashes, called Graham's Island.
In a few months this island was entirely washed away by the waves,
and only a circular submarine bank remained. If corals grew in the
Mediterranean, there seems no reason why a circular reef should not
have been formed.
Objections. Even in its most plausible form, however, this theory
is very improbable as a general explanation of atolls. 1. The great
size of some of these atolls thirty, sixty, and even ninety miles in
diameter ; and, 2. The high angle of the slope of these submarine moun-
tains 50 to 60 or more seem inconsistent with their volcanic origin.
3. This theory offers no explanation of the barrier reefs, and yet it is
possible to trace every stage of gradation between barriers and atolls,
showing that they are due to similar causes.
Subsidence Theory. There can be little doubt that this is the true
theory. It explains not only atolls, but also barriers, and connects both
in a satisfactory manner with fringing reefs. It supposes that the sea-
bottom, where atolls and barriers occur, has been for ages subsiding,
but at a rate not greater than the upward building of the coral-ground ;
that every reef commences as a fringing reef, but, in the progress of
subsidence, was converted first into a barrier and finally into an atoll.
For, as the volcanic island went down, the corals would build upward
on the same spot ; and as the island would become smaller and smaller,
and the corals would grow fastest on the outer side of the reef, where
they are exposed to the breakers, it is evident that the reef would be-
come separated from the island by a ship-channel, and thus become a
barrier. Finally, when the island disappears entirely, the reef, still
building upward, would become an atoll. These changes are represented
in the accompanying section (Fig. 123). As the changes are relative,
they may be represented either by the land sinking or the sea-level ris-
ing ; for the sake of convenience we use the latter. In the figure, I" I"
represents the sea-level when the reef was a. fringe, I' I' when it was a
barrier, and 1 1 the present sea-level, when it has become an atoll. The
ship-channel and the lagoon, though always lower, rise pari passu with
the reef proper. This is the result partly of the growth of placid-water
species of corals, and partly of the drifting of coral debris from the
reef, and detritus from the volcanic island. It is seen that the corals
do not build a vertical wall, and therefore that the atoll is always
THEORIES OF BARRIER AND CIRCULAR REEFS. 14.5
smaller than the coast-line of the original island. Consequently, if the
subsidence continues, a typical atoll is changed into a small closed
lagoon, and, finally, into a lagoonless island. These, therefore, indicate
the deepest subsidence.
Proofs. 1. This theory accounts for all the more obvious phenomena
of atolls, such as their irregular circular form, their size, the steepness
of their outer slopes, etc. 2. Every stage of gradation between the
fringing reef on the one hand, and the atoll on the other, has been
traced by Dana, showing that they are all different stages of develop-
ment of the same thing. We have in the Pacific some high islands,
which are surrounded by a pure fringing reef; others in which the reef
is a fringe on one side and a barrier on the other ; others in which the
barrier is one mile, two miles, five miles, ten miles, twenty, or thirty
miles distant ; others which are called atolls, but the point of the origi-
nal volcanic island is still visible in the middle of the lagoon ; others
which are perfect atolls, but, by sounding, the head of drowned volcanic
island is still detectible. The next step in the series is the perfect atoll,
then the small atoll, and, finally, the lagoonless coral island. These last
kinds show that the original island has gone down deeply. 3. By grap-
pling-hooks dead coral-trees have been broken off and brought up from
the ground where they once grew, now far below the limiting depth of
coral-growth. The evidence of subsidence in this case is of the same
kind arid force as that derived from submerged forest-ground (page
129). The corals have been carried below their depth and drowned.
4. The remarkable distribution of the various kinds of reefs brought to
light by Dana is satisfactorily explained by this theory, and therefore is
an argument in its favor. In the middle of the atoll region of the Pa-
cific there is a blank area, 2,000 miles long and 1,000 or more miles
wide, where there are no islands. Next about this is an area in which
small atolls predominate ; about this again the region of ordinary atolls;
beyond this the region mostly of barriers, and finally of fringes. Now,
by this theory this distribution is thus explained : The sea-bottom in
the blank area has gone down so fast that the corals have not been able
to keep pace, and have therefore been drowned, and left no monu-
10
146 ORGANIC AGENCIES.
ment of their existence. In the next region the corals have been able
to keep within living distance of the surface, but the original islands
have not only disappeared, but gone down to great depths. In the
next the original high islands have disappeared, but not gone down so
deep ; in the next they have sunk only to the middle. The fringing reefs
stand on the margin of the sinking area. Outside of this again there is
in some places even evidence of upheaval instead of subsidence. Raised
beaches in the form of fringing-reef rocks are found clinging to the
sides of high islands many feet above the present sea-level. 5. In some
places this subsidence seems to be still in progress. On certain coral
islands sacred structures of stone made by the natives are now stand-
ing in water, and the paths worn by the feet of devotees are now pas-
sages for canoes (Dana).
It may be regarded as certain, therefore, that every atoll marks the
site of a sunken volcanic island.
Area Of Land lost. Probably several hundred thousand square
miles of habitable high land has been lost by this subsidence. The
actual extent of atolls known is at least 50,000 square miles. But this
is far less than the loss of high land. For 1. It is certain that the
area of an atoll is always less than that of the original fringe or base of
the original high island, for the outer wall of an atoll is not perpendicu-
lar. The contraction continues as the subsidence progresses, until
small atolls or only lagoonless islands remain. 2. An immense lost
area is represented by the space between barriers and their high isl-
ands. The great Australian barrier extends along that coast 1,100
miles, at an average distance of thirty miles, with a ship-channel be-
tween of thirty to sixty fathoms deep. This single barrier, therefore,
represents a lost land-area of 33,000 square miles. 3. In the blank
area already spoken of, probably many islands went down, and left no
record behind.
The large amount of high land thus lost has been replaced only to a
small extent by the wave-formed coral islets on the reefs.
Amount of Vertical Subsidence. The amount of subsidence may be
estimated by the distance of barriers from their high islands, or by
soundings off the reefs, to ascertain the height of these coral mounds,
or by the average height of the high islands of the Pacific. 1. The
average slope of the high islands of the Pacific is about 8. Now, as-
suming this slope (Fig. 124), a barrier, d, at the distance of five miles
THEORIES OF BARRIER AND CIRCULAR REEFS. 14.7
would be 3,700 feet thick, and would represent a subsidence nearly to
that extent (Rad. : tan. 8 :: a d : d b); a distance of ten miles would
represent a vertical subsidence of 7,400 feet. Many barriers are at much
greater distance. 2. Off Keeling atoll 6,600 feet, a line of 7,200 feet
found no bottom (Darwin). Near other atolls a depth of 3,000 feet has
been found (Dana). 3. The average height of the high islands of the
Pacific cannot be less than 9,000 feet (Dana) ; some of them reach
nearly 14,000 feet. It is very improbable that among the hundreds
of atolls known, not one of their high islands should have reached
the average elevation of 9,000 feet. Yet these have entirely disap-
peared, and not only so, but the small atolls and lagoonless islands,
and more especially the blank area, would seem to indicate that they
have disappeared to great depths. For these reasons, it is almost cer-
tain that the extreme subsidence has been at least 9,000 feet. We will
take 10,000 feet as the most probable extreme subsidence.
Rate of Subsidence. The rate of subsidence may have been to any
degree less, but cannot have been greater, than the rate of coral ground-
rising^' for otherwise the corals would have been carried below their
depth and drowned. It is difficult to estimate the rate of coral ground-
rising, but the only basis of such estimate is the rate of coral-growth.
Of the observations on this point we select two, one of them on the
head-coral (meandrina), the other on the staghorn-coral (madrepore) :
1. On the walls of the fort at the Tortugas, Florida, meandrina com-
menced to grow, and in fourteen years the crust had become only one
inch thick. Agassiz takes one inch in eight years as a probable rate
under favorable circumstances. This would be one foot in a century.
As this is a head-coral, the coral-growth may be taken as the measure
of the reef ground-rising.
2. In examining the reefs about the Tortugas in the winter of 1851,
an extensive grove of madrepore was found in the comparatively still
water on the inside of the outer reef, in which the thick-set prongs had
grown, year after year, to the same level, and were successively killed.
The mean level of the water here is lower during the winter, by about
a foot, than during the summer. The falling of the water annually
clips this grove at the same level. Now all the prongs at this level
were dead for about three inches. Evidently, therefore, this is the an-
nual growth of madrepore-prongs. 1 But in branching corals the rate
of point-growth is very different from the rate of ground-rising. If all
the points of a madrepore be cut off three inches, then ground into
powder, and the powder strewed evenly over the ground shaded by
the coral-tree, the elevation thus produced would correctly represent
the annual rate of reef ground-rising for this species. A quarter of an
1 See full account of these observations in American Journal of Science and Arts, vol.
x., p. 34.
148 ORGANIC AGENCIES.
inch would probably be a full estimate. This would make two feet for
a century. One foot to two feet per century is, therefore, probably
about the rate at which coral ground rises. As already stated, the rate
of subsidence may be less, but cannot be greater, than this.
Time involved. At this rate 10,000 feet of vertical subsidence would
require 500,000 to 1,000,000 years. How much of this belongs to the
present geological epoch, it is impossible to say. Dead corals, identical
with those still living on the reefs, have been brought up from a depth
of 250 feet, but, as this is only 150 feet below the limit of coral-growth,
it would require only 75 to 150 centuries. The process probably com-
menced in previous geological epochs, and has continued to the present
time. This is, therefore, an admirable example of geological agencies
still at work.
Geological Application. The facts brought out in the preceding
pages are of great -importance in geology.
1. We have here the most magnificent example of subsidence still
in progress. The subsiding area has not been accurately defined, but
it probably covers nearly the whole of the intertropical Pacific. Ac-
cording to Dana, estimated by the atolls alone, it is 6,000 miles long
and 2,000 miles wide ; but if we take into account also barriers, which
are equally certain evidences of subsidence, it extends east and west
from the extreme of the Paumotu group on the one side to the Pelews
on the other, and north and south from the Hawaiian group to the Fee-
jees, making an area of not less than 20,000,000 square miles. Now, it is
evident that there must have been, as a correlative of this extensive and
permanent downward movement, an equally extensive permanent ele-
vation of the earth's crust somewhere else. Dana thinks its correlative
is found in the extensive elevations of the Glacial epoch, and there-
fore that the whole work was accomplished since the Tertiary.
But it is more probable that its correlative is found in the gradual
bodily upheaval of the whole western side of the continent, especially
in the Rocky Mountain region, which commenced after the Cretaceous.
2. We have here the formation of limestone rocks of various kinds
going on before our eyes over immense areas and several thousand feet
in thickness, and we learn thus that limestones are of organic origin.
3. The character of the rocks thus formed is very interesting to
the geologist. In some places, as we have already seen, it is a coarse
conglomerate, or breccia, composed of fragments of all sizes cemented
together ; in some places it is made up entirely of rounded granules of
coralline limestone (coral-sand}, cemented together, and forming a pe-
culiar oOlitic rock (wov kiOog, egg-stone). But the larger portion of
the reef ground is a fine compact limestone, made up of comminuted
coralline matter (coral mud), cemented together. This fine coral mud
is carried by waves and tides into the lagoon, and serves to raise its
REEFS OF FLORIDA.
149
bottom: it is also carried by currents and distributed widely over the
neighboring sea-bottoms. Soundings in coral seas bring up everywhere
this fine coral mud, showing that compact limestone is now forming over
wide areas in coral seas. The reef-rock, as already stated, has been
found clinging to the sides of high islands, having been elevated many
feet above sea-level; in other cases atolls have been elevated 250 feet
above the sea-level. The structure of the reef-rock has thus been ex-
posed to view. In some places it contains imbedded remains of corals
and shells, but in other parts it is entirely destitute of these remains.
Reefs of Florida.
The reefs of Florida deserve a brief separate notice, both because
they are different from those of the Pacific, having been formed under
different conditions, and because they are much more efficient agents in
land-making, and illustrate in a striking manner how different agencies
cooperate for this purpose. The process has been accurately observed.
Description of Florida. Fig. 125 is a map of Florida, with its
reefs and keys, and Fig. 126 is a section along the line p p. The
southern coast (a a) is ridge, elevated twelve to fifteen feet above the
FIG 125. Gulf Stream and the Eeefs and Keys of Florida.
150 OKGANIC AGENCIES.
sea-level, within which is the Everglades (e), an extensive fresh-water
swamp only two or three feet above sea-level, and dotted over with
small islands, called hummocks. Between the southern coast (a a) and
the line of keys (b b) the water (e') is very shallow, only navigable to
smallest fishing-craft, and dotted over with small low mangrove islands.
A considerable portion of this area, in fact, forms mud-flats at low tide.
Between the line of keys (b b) and the living reef (c c) there is a ship-
channel (e") five to six fathoms deep. Outside the reef (c c) the bot-
FIG. 126. In both figures a = Southern coast; 6, Keys c, Reef; e, Everglades ; e f , Shoal water ; e",
Ship-channel ; ff S S, Gulf Stream.
torn slopes rapidly into the almost unfathomable abyss of the Gulf Stream
(GSS).
General Process of Formation. Now, Agassiz has proved that not
only the living reef but the keys, the southern coast, and the peninsula,
certainly as far north as the north shore of the Everglades (d d), and
probably as far north as St. Augustine (c?'), have been formed by coral
agency. The evidence of this important conclusion is that the rock in
all these parts is identical with the reef-rock already described, and with
what is even now forming under our eyes on the living reef (c c). It is,
moreover, almost certain that the peninsula of Florida has been progres-
sively elongated by the formation of successive barrier reefs, one outside
of the other, from the north toward the south, and the successive filling
up of the intervening ship-channels, probably by coral d&bris from the
reef and sediments from the mainland.
History of Changes. The history of changes was as follows: There
was a time when the north shore of the Everglades (d d) was the south-
ern limit of the peninsula. At that time the ridge (a a) which now
forms the south shore was a reef. Upon this reef by the action of waves
was gradually formed a line of coral islands, which finally coalesced into
a continuous line of land, and by the filling up of the intervening ship-
channel was added to the peninsula, the ship-channel being converted
into the present Everglades. In the mean time another reef was formed
REEFS OF FLORIDA. 151
in the position of the present line of keys. This has already been con-
verted into a line of wave-formed islands, and its ship-channel into shoal
water and mud-flats. Eventually the peninsula will be extended to the
line of keys, and the shoal water (e r ) will become another Everglades
and the mangrove islands its hummocks. Already another reef has
been again formed outside the last, viz., the present living reef (c c),
and upon it the process of island-formation has commenced. This will
also be eventually converted into a line of keys, into a continuous line
of land, and be added in its turn to the peninsula. It is not probable
that another reef will be formed outside of this, for the bottom slopes
rapidly under the Gulf Stream, as seen in the section Fig. 126. In
this process each reef dies when another is formed beyond it, for the
water being protected by the outside reef becomes placid or lagoon
water, and the strong reef-building species no longer flourish.
North of the line d d the evidence is of the same kind, but less com-
plete. True reef-rock, similar to that now forming on the reef, has
been found at various points as far north as St. Augustine, on the east-
ern shore. The western shore is less known. Tuomey found the bluffs
at Tampa Bay to consist of tertiary. The line d' d', therefore, may indi-
cate the limit of the peninsula at the end of the Tertiary period. The
position of the successive reefs in this part has not been determined.
Mangrove Islands. Mangrove-trees cooperate in an interesting man-
ner with corals in the process of land-formation. These trees form
dense jungles on the low, muddy shores of tropical regions. They are
very abundant on the southern and western shores of Florida. They
have the remarkable power of throwing out aerial roots from their
trunks and branches, thus forming subordinate connections with the
ground or with the bottom of shallow water. From these may spring
other trunks, which throw out similar roots, etc. Thus an inextricable
entanglement of roots and branches continues to extend far beyond the
actual shore-line. These form a nidus for the detention of sediments,
and protect them from the action of waves ; and the shore-line thus
steadily advances.
The seeds of the mangrove have also the faculty of shooting out
long roots and stems, even while still attached to the parent tree. These
shoots, falling into the water, float away, and if their roots touch bottom
immediately fix themselves, grow into mangrove-trees, and commence
multiplying in the manner described. Thus in the shoal water (e r ) are
found mangrove islands in which there is no land, but only a mangrove
forest, standing above water by means of their interlaced roots. By
these, however, sediments are detained, and a true island is speedily
formed. It is in this way that the small mangrove islands in the shoal
water on the south and west of Florida are formed. They are en-
tirely different from the wave-formed coral islands or keys. The hum-
152 ORGANIC AGENCIES.
mocks in the Everglades have probably a similar origin, although some
of them may possibly be of coral origin.
Florida Reefs compared with other Reefs. In comparing the reefs
just described with other reefs, it will be seen that the former are en-
tirely unique. JVo other reefs continuously make land. In fringing reefs
there is a small accretion about the shore-line of the previously-existing
land, but this process is quickly limited. In barriers and atolls there
is always loss of land, only a small fraction of which is recovered by
coral and wave agency. But under these agencies Florida has steadily
advanced southward more than 200 miles, and the area thus added to
the continent is at least 20,000 square miles. It seems to us utterly
impossible to account for this, except by supposing some other agency
at work preparing the ground for the growth of successive reefs.
Probable Agency of the Gulf Stream. Since corals cannot grow in
water more than sixty to one hundred feet deep, it is evident that, unless
subsidence goes on pari passu with the growth of the corals, a coral
formation cannot be more than one hundred feet thick. But there is no
evidence of subsidence on the coast or keys of Florida. 1 On the contrary,
the height of these parts is precisely the usual height of icave-formed
islands, although no longer exposed to their action. It follows, there-
fore, that the corals must have built upon an extensive submarine bank,
produced by some other agency. Furthermore, since the reefs were
formed successively one beyond another, it is evident that there must
have been a progressive formation of this bank from the north toward
the south. Such a progressive extension of a bank can only be formed
by sedimentary deposit. It is impossible to conceive how such sedi-
mentary deposit could have been formed, except by the Gulf Stream.
It is to this agencv, therefore, that we attribute the formation and ex-
tension of the bank upon which the corals grew.
We have already (p. 40) given reasons for believing that the Gulf
Stream carries sediment in its deeper parts. Now, a current bearing
sediment and sweeping around a deep curve, like the Gulf Stream
around Florida (Fig. 125), must, as we have already shown (p. 22), con-
tinually deposit sediment on the interior of the curve, forming in the
case of a river a bank above water, but, in the case of an oceanic stream,
a submarine bank. This bank, in the case of the Gulf Stream, has been
extending southward for ages almost inconceivable. On every part, as
soon as it reached within 100 feet of the surface, corals built. Previous
positions of the southern limit of the bank and of the successive reefs
are shown in Fig. 126 in dotted outline.
1 Evidences of subsidence, in the form of drowned corals, have been recently found
by the Coast Survey in the course of the Gulf Stream oif the Florida reefs, but this sub-
sidence cannot have extended to the keys and peninsula, for this is inconsistent with the
continual extension of land.
SHELL-DEPOSITS. 153
It is probable, therefore, that the peninsula of Florida is due to the
cooperation of four or five different agencies, viz. : 1. The Gulf Stream
building up a submarine bank to the dotted line n w, Fig. 126, within
100 feet of the surface ; 2. Then corals building up to the surface ; 3.
Then waves raising it twelve to fifteen feet above the surface ; 4. And,
finally, debris from the peninsula on the one side, and the reef and keys
on the other, filling up the intervening channels, and afterward raising
the level of the swamps or Everglades thus formed. 5. In this last
process the mangrove-trees have assisted.
The reefs of Florida are barrier reefs;. Barriers are usually supposed
to indicate subsidence. This is certainly true of the Pacific barriers,
which commenced as fringes and became barriers by subsidence. But
in Florida there has been no subsidence. They did not commence as
fringes. The probable explanation is this : Corals will not grow in
muddy water. On a gently-sloping shore with mud bottom, such as
probably always existed on the southern shore of Florida, a fringing
reef could not form, because the bottom would be always chafed by the
waves and the water rendered turbid. But at a distance from shore,
where such a depth was attained that the waves no longer chafed the
bottom, a barrier would form, limited on the one side by the muddi-
ness, and on the other by the depth, of the water.
Shell-Deposits.
Rivers carry carbonate of lime in solution to the sea (p. 76). In
some bays, where large quantities of this material are carried by rivers
running through limestone countries, the excess may be deposited as a
chemical deposit. But in most cases sea-water contains less lime-car-
bonate than river-water. The reason is, that the lime-carbonate in sea-
water is continually being drafted upon by organisms and deposited on
their death as organic limestones. We have already shown how coral
limestone is thus formed. But there are many other limestone-forming
animals, and some species form other kinds of deposits besides lime-
stone.
Molluscous Shells. Shallow-water deposits of this kind are made
principally by mollusca which, living in immense numbers near shore
and on submarine banks, leave their dead shells generation after gener-
ation, and thus form sometimes pure shelly deposits, and sometimes
shells mingled with sediments due to other agencies. On quiet shores
the shells are quite perfect, whether imbedded in mud or forming shell-
banks like our oyster-banks ; but when exposed to the action of break-
ers, they are broken into coarse fragments, or even comminuted, worn
into rounded granules, and cemented into shell-rock or oo'litic rock.
Such shell-rock and oolitic rock are now being formed on the coast of the
Florida keys and of the West Indies. Similar rock is found in every
154:
ORGANIC AGENCIES.
part of the world in the interior of continents. They indicate the ex-
istence in these places of a shore-line or of shallow water in some pre-
vious geological epoch.
Microscopic Shells. Microscopic plants and animals are known to
multiply in numbers with almost incredible rapidity. Many of them
form no shell, and therefore are of no geological importance ; but many
species form shells of silica or of carbonate of lime, and these of course
accumulate generation after generation, until important deposits are
formed.
Fresh-water Deposits. In streams, ponds, lakes, and hot springs,
the beautiful siliceous shells of diatoms (uni-celled plants) accumulate
without limit. The ooze at the bottom of clear ponds or lakes, as, for
example, in the deepest parts of Lake Tahoe, consists often wholly of
FIG. 127. Shells of livinjr Fornminifera. a, Orbulina wniversa, in its perfect condition, showing the
tubular spines which radiate from the surface of the shell ; b. Qlobigerina l/ulloides, in its ordinary
condition, the thin hollow spines which are attached to the shell when perfect having heen broken
off; c, Tfytnlaria rariabilis; d, Peneroplis pfanatus; e, Kotalia concamerata ; f, Cristellaria
subarciuitula. >"ig. a is after Wyville Thomson ; the others are after Williamson. All the figures
are greatly enlarged (after Nicholson).
these shells. Diatoms live also in great numbers in the hot springs of
California and Nevada, and the deposits of such springs sometimes con-
sist wholly of these shells. Thick strata, belonging to earlier geological
times, are found wholly composed of diatoms. We are thus able to
explain the formation of these strata.
GEOGRAPHICAL DISTRIBUTION OF ORGANISMS. 155
Deep-sea Deposits. Over nearly all the bottom of deep seas, be-
yond the reach of sedimentary deposits, we find a white, sticky ooze,
composed of the carbonate-of-lime shells of microscopic animals (fora-
minifers) and microscopic plants (coccospheres), Fig. 127. Some of these
seem to be living, or recently dead ; some dead and empty, but still
perfect ; but most of them completely disintegrated. On account of the
great abundance of the shells of one form of foraminifera, this soft,
white mud is called globigerina ooze. Mingled in considerable numbers
among the calcareous shells are others of silica. These are also partly
animals (radiolaria) and partly plants (diatoms). The extraordinary
resemblance of this deep-sea ooze, both in chemical and microscopic
character, to chalk, leaves no room for doubt that chalk was formed in
this way.
SECTION 4. GEOGRAPHICAL DISTRIBUTION OF ORGANISMS.
Fauna and Flora. The animals and plants inhabiting any country
are called the fauna and flora of that country. In a more scientific
sense, however, a natural fauna or flora is a group of organisms in-
habiting one locality, differing conspicuously from other natural groups
inhabiting other localities. All the members of such a natural group
must bear certain harmonic relations to one another, and the whole
group to the external physical conditions. Moreover, each group is
circumscribed and separated from other neighboring groups by limiting
physical conditions.
Kinds of Distribution. Distribution of organisms is of two general
kinds, viz., distribution in space and distribution in time, or geographi-
cal distribution and geological distribution. There are, therefore, geo-
graphical faunae and floras and geological faunae and florae. A geographi-
cal fauna is the group of animals inhabiting any natural geographical
region. Thus the animals of Australia form a distinct fauna, differing
entirely from any other upon the earth's surface. A geological fauna
is the whole group of animals inhabiting the earth at one epoch, and
differing from that of other epochs. Thus the whole group of animals
inhabiting the earth during what geologists call the secondary period
form a distinct fauna, differing remarkably from all preceding or sub-
sequent faunae. The flora of the coal period is very distinct from all
others.
The organisms of every epoch, however, were distributed over the
earth's surface in separate faunas and florae. Every geological fauna
and flora is, therefore, divisible into more or less distinct geographical
faunae and florae. Geological faunae and florae will form the principal
subject of Part III. We propose now to study only geographical dis-
tribution of organisms at the present time, this portion of geology
being concerned only with " causes now in operation." We study the
156
ORGANIC AGENCIES.
laws of geographical distribution in the present epoch because it throws
light on the geographical distribution in previous epochs, and also on
the laws of geological distribution, or the history of organisms. It also,
as will be shown hereafter, furnishes a key to former changes in physical
geography and former migrations of species.
Among physical conditions limiting the distribution of organisms,
one of the most important is temperature. We will, therefore, first
speak of temperature-regions, confining ourselves, for the sake of greater
clearness, to plants. The principles thus established we will then ex-
tend and modify. And, further, since temperature-regions may be either
vertical or horizontal in latitude, we will commence with
Vertical Botanical Temperature-Regions. To explain vertical dis-
tribution we will take the case of a mountain, at or near the equator,
because all the vertical regions are there represented. If we pass from
base to summit of such a moun-
tain we will traverse, first, a
region of palms, so called be-
cause the vegetation is char-
acterized by the abundance of
palms and palm-like plants, such
as bananas, tree-ferns, etc. The
second region traversed is char-
l acterized by the prevalence of
FlG - m evergreens, such as myrtles, lau-
rels, etc., and ordinary deciduous trees, such as hickory, oaks, elms,
poplars, etc. ; and therefore may be called the region of ordinary forest
or hard-wood trees. The third region traversed is characterized by
the prevalence of pines and other conifers, and therefore called the
region of pines. The fourth region contains few or no trees, but only
shrubs and Alpine herbaceous plants, and therefore may be called the
Alpine or treeless region. The fifth, being the region of perpetual snoic,
is plantless, or nearly so.
Botanical Temperature-Regions in Latitude. As the regions above
spoken of are determined entirely by temperature, it is evident that
they must be reproduced in latitude in zones
where these limiting temperatures successively
reach the earth's surface. Thus, if a (Fig. 129)
represents an equatorial mountain, the temper-
atures which limit the botanical regions will
approach the earth as we go toward either pole,
as shown by the dotted lines, and successively
reach the sea-level, giving rise to similar zones
of temperature, and therefore to similar botan-
ical regions, extending all around the earth.
HARD WOOD TRESS
PALMS AND TREE -FEffAIS
GEOGRAPHICAL DISTRIBUTION OF ORGANISMS. 157
These zones, being temperature-zones, are not limited by parallels of
latitude as represented in the figure, but by isothermal lines. In pass-
ing from the equator to the poles, we traverse : 1. A region of palms, or
tropical zone ; 2. A region of ordinary forest or hard-wood trees, ever-
green and deciduous, or subtropical and temperate zone ; 3. A region
of pines and birch, or cold temperate and subarctic zone ; 4. A treeless
region, or arctic zone. The fifth or plantless region can hardly be said
to exist at the sea-level in any part of the earth.
Further Definition of Regions. 1. The regions we have given are
characterized by the prevalence of certain orders of plants ; but the same
law of limitation applies with still greater force to families, genera,
and species. These smaller classification-groups are still more limited
in range. Thus palms range over the whole of region No. 1 (Fig. 129) ;
but one genus of palms may occupy the warmer or equatorial part, and
another genus the higher or tropical parts. Thus, generally, the range
of families is more restricted than that of orders, the range of genera
than that of families, and the range of species than that of genera.
Thus, these regions may be divided into subordinate regions, and these
again into still more subordinate regions. What we further say will
have reference principally, though not entirely, to species. 2. We
have separated these regions by lines. It must not be supposed, how-
ever, that these limits are distinctly marked. On the contrary, they
shade insensjbly into each other. Some species of palms, etc., pass
into the region of hard- wood trees, and vice versa. Many species of
hard- wood trees pass into the region of pines, and vice versa. So, also,
the sub-regions of families, genera, and species, cannot be separated by
hard lines. They shade insensibly into, interpenetrate, or over-
lap one another at their margins. Thus if a a' and b b' (Fig.
130) be the range, either vertical or horizontal, of two species,
then in the zone b a' the two species coexist. 3. In any region
or sub-region the organic forms which characterize it are most
abundant in the middle portion, and become less and less
abundant toward the margin, whe.re they disappear. If the
line a a' (Fig. 130) represents the range of any species, then
the breadth of the elliptical area will represent the relative
abundance of individuals in different parts of the range. 4.
Although, therefore, species, so far as numbers of individuals
are concerned, come in gradually on the margin of their nat-
ural region, reach their greatest abundance in the middle por- v f
tion, and again gradually die out on the other margin, yet in ^
specific characters we see usually no such gradual transition.
In specific character they seem to come in suddenly, to remain sub-
stantially unchanged throughout their range, and pass out suddenly on
the other margin. Thus, to take a single instance : in passing from
158 ORGANIC AGENCIES.
the equator to the poles, at a certain latitude, the sweet-gum or liquid-
amber tree first appears, few in number; it increases in number in the
middle part of its range, and finally again diminishes in number and
gradually disappears. But throughout its whole range this species is
unmistakably the same it does not pass into any other species. It is
as if the species had originated somehow (we will not now discuss
how) in the area where we find it, and had extended its range as far
as physical conditions and the struggle for life with other species
would permit. 5. We have seen that the botanical zones in elevation
and in latitude are similar to one another in the great orders which
characterize them ; but they are by no means identical in genera and
species. This follows from what we have said under 4. The vertical
and horizontal zones No. 1 being in direct connection with one another,
the species are to a large extent identical. But between zones No. 2
communication is impossible, except through zone No. 1, but this is
forbidden by physical conditions ; and, therefore, although forest-trees
may exist in both, the species are all different. The same is true of
zones Nos. 3 and 4, and also of corresponding zones north and south of
the equator. It is as if the present species had originated in the areas
where we now find them, and had not been able to mingle on account
of temperature barriers intervening. 6. Although, when no physical
obstacle intervenes, regions or zones in latitude like those in elevation
shade insensibly into one another by interpenetration, as already ex-
plained, yet when physical barriers, such as an east-and-west mountain-
chain, occur, no such shading is possible ; but, on the contrary, there is
an abrupt change. Thus, north and south of the Himalaya Moun-
tains, or north and south of the Sahara Desert, the plants are entirely
different, apparently because interpenetration of contiguous flora? by
spreading is impossible in this case.
Zoological Temperature-Regions. We have spoken first of plants,
because, being fixed to the soil, they illustrate more clearly the natural
laws of distribution as determined by temperature. Animals, by their
power of locomotion and migration with the seasons, interfere seriously
with the simplicity of these laws. Although families, genera, and spe-
cies of animals, like plants, are limited in their range, particular form*
characterizing certain zones as monkeys, parrots, elephants the torrid
zone, and walruses and white bears the polar zone yet it is impossible
to divide the surface of the earth into zones characterized by particular
orders in the same broad, general way as in the case of plants. Never-
theless, all that we have said concerning the limitation of range of
families, genera, and species, and the manner in which contiguous
regions or sub-regions shade into one another, applies with equal force
to animals. The apparent fixity of animal species within certain nar-
row limits of variation is even more striking than in the case of plants.
GEOGRAPHICAL DISTRIBUTION OF ORGANISMS. 159
What we shall further say will apply to animals and plants without
distinction.
Continental Fauna and Flora. If no physical barriers intervened,
there seems to be no reason why the fauna and flora of each zone of
temperature should not be continuous all around the earth. But im-
passable barriers exist in the form of oceans separating continents, and
on the continents in the form of north-and-south ranges of mountains.
Consequently, on the supposition of the local origin of species, it fol-
lows that, although the orders and sometimes families of animals and
plants are similar on the two continents, the species and many of the
genera are entirely different. That this diversity is the result of impas-
sable barriers is sufficiently proved by the fact that most species of
animals or plants, introduced from one continent to the correspond-
ing zone of another, flourish well, and soon become permanent mem-
bers of the fauna or flora of their adopted country. We will now dis-
cuss the subject in more detail.
The accompanying figure (Fig. 131) is a view of the northern hemi-
sphere, the circumference being the equator and the centre the north-
pole, and the circular zones being the same as already described.
These, however, will not be regular circles as represented in the figure,
but will be isothermal zones. They really run farther north in Europe,
160 ORGANIC AGENCIES.
and farther south in North America, than represented in the figure.
Now, comparing the eastern and western continents with one an-
other, commencing with the arctic zone No. 4, we find that in this
zone the fauna and flora are nearly identical in the two continents,
the reason being, apparently, their close approximation to one an-
other in this zone, and their connection by means of solid ice. In the
next zone, No. 3, the species are already quite different ; and in No.
2, to which the United States and Europe mostly belong, nearly all
the species, and many of the genera, and even some families, are dif-
ferent. The few exceptions to the universal diversity of the fauna
and flora of this country, as compared with Europe and Asia, are prin-
cipally : 1. Introduced species ; 2. Species of wide range, either by
reason of great hardihood or by extensive migration, and which, there-
fore, belong to No. 4 as well as Nos. 3 and 2; and, 3. Alpine spe-
cies, which seem to have extended, during a former cold epoch (Glacial
epoch), from No. 4 to No. 3 in both continents, and with the return of
milder climate have retreated, some northward, and some up the sides
of the mountains of No. 3, to their appropriate zone of tempera-
ture. In No. 1 the difference between the two continents is still
greater, and continues without abatement into corresponding zones of
the southern hemisphere, since these do not approach each other tow-
ard the pole as they do at the north. Thus, we find the fauna and
flora of South America and Africa as different as possible. As an illus-
tration of this, we will only mention the prehensile-tailed monkeys,
sloths and armadillos, llamas and toucans, humming-birds, among ani-
mals, and the cacti among plants, as characteristic of South America ;
and the lions, tigers, elephants, rhinoceroses, hippopotamuses, giraffes,
and the tailless monkeys, of Africa.
Subdivisions. The continental faunae and florae are again subdi-
vided in longitude by north-and-south mountain-chains. Thus the fauna
and flora of the United States are divided by the Rocky Mountain and
Appalachian chains into three sub-faunae and sub-floras, viz., an Atlantic
slope, an interior continental, and a Pacific slope fauna and flora. The
difference between the Atlantic slope and the interior continental
region is not great, because the mountain-barrier is not so high but it
may be overpassed. The Rocky Mountains being a wider and higher
and therefore the more impassable barrier, the fauna and flora of the
Pacific slope are very distinct, almost all its species being peculiar to
that region. The exceptions are mostly strong-winged birds. In a
similar manner in South America the Andes chain separates faunae and
florae which are very distinct, and in the eastern continent the Ural
Mountains separate a European from an Asiatic fauna and flora. Sub-
divisions of this kind are more marked in the case of plants and of those
animals which are closely connected with plants, such as insects, than in
GEOGRAPHICAL DISTRIBUTION OF ORGANISMS. 101
the case of higher animals which have a greater power of locomotion,
and therefore of overcoming obstacles.
Special Cases. We might mention many special cases of remarkable
groups of animals and plants, especially on isolated islands. We will
only mention a few by way of illustration : 1. The fauna and flora of
Australia are perhaps the most remarkable in the world. Not only are
the species different, but the genera, families, and orders, are peculiar to
this continent. So remarkably and conspicuously is this the fact, that
even the unscientific traveler is at once struck with the strange ap-
pearance of the vegetation and the animals trees with narrow, rigid
leaves twisted on their leaf-stalk so as to turn their edges to the sky;
the mammals, about 200 species, nearly all belonging to the non-
placentals, including marsupials and monotremes, a great sub-class of
quadrupeds to which the kangaroos, the opossums, and the ornitho-
rhynchus belong, and which are confined to Australia, with the excep-
tion of several species of opossum found in America. The island of
Madagascar is another remarkable zoological province. All the ani-
mals on this island, with one single exception, are peculiar, being
found nowhere else. This exception is that of a small quadruped sup-
posed to have been introduced. On the Galapagos, a small group of
islands at a considerable distance from the west coast of South Amer-
ica and from all other islands, all the animals are entirely different
from those of any part of the world. Reptiles of peculiar species
abound, but no mammal, except one species of mouse, has yet been
found.
Thus we see that species are limited in one direction by tempera-
ture, and in all directions by physical barriers. If we now add to these
limitations also peculiar climates and soils (such, for example, as the
dry plains of Utah and Arizona), which limit vegetation, and there-
fore animals, we easily perceive that all these limiting causes produce
groups of species confined within certain areas differing from other
groups, sometimes overlapping them, sometimes trenchantly separated.
Taking all causes into consideration, the whole earth has been
divided into six principal faunal regions, viz. : 1. JVearctic, including
North America, exclusive of Central America ; 2. Neotropic, including
Central and South America ; 3. Palcearctic, including Europe, North
Africa, and Asia north of the Himalayas ; 4. African, including Africa
south of the Sahara ; 5. Indian or Oriental, including Asia south of
the Himalayas, and the adjacent islands ; 6. Australian, including Aus-
tralia, New Zealand, New Guinea, and South-Sea Islands, etc. These
primary regions are subdivided into provinces and sub-provinces accord-
ing to the principles already explained. For example, the neartic has
been subdivided into four provinces, viz., (a) the Alleghanian, (b) the
Rocky Mountain, (c) the Californian, and (d) the Canadian.
11
162 ORGANIC AGENCIES.
Marine Fauna. Distribution in Latitude. In passing along the
shores of Europe or of America, from south to north, we find that the
species of marine animals, such as molluscous shells and fishes, gradu-
ally change, one species being replaced by another in the manner al-
ready explained. If the change of temperature be gradual, the change
of fauna will also be gradual ; but if the change, from any cause, be
sudden, the change of species will be correspondingly sudden. Thus,
for example, on the coast of the United States, Cape Hatteras and Cape
Cod divide the littoral fauna into three quite distinct subdivisions,
changing somewhat suddenly at these points, viz., a Southern, a Middle
States, and a New England, fauna. The reason is that the Gulf Stream
hugs the shore as far as Hatteras, thus carrying the southern fauna
northward beyond its natural limit, and then turns away from the
coast. On the other hand, the arctic current hugs the New England
coast as far as Cape Cod, bringing with it an arctic fauna, and then
leaves the surface and goes downward.
Distribution in Longitude. Both land and deep sea are impassable
barriers to marine species. Hence we find that the marine species
on the east and west coasts of each continent, as well as those inhabit-
ing the east and west shores of the same ocean, are almost entirely dif-
ferent. Thus the marine species on our Atlantic shores are not only
different from those of our Pacific shores, but also from those on the
Atlantic shores of Europe and Africa. The same is true of the species
on the two shores of the Pacific, as compared with one another, or with
those of Europe. The exceptions to the general rule, that the marine
species of different shores are different, are principally arctic species of
wide range, such as whales, etc.
Depth and Bottom. It is found that marine species vary with the
depth, so that there are littoral species, and deep-water species, and pro-
found sea-bottom species. Also the species on sand-bottoms are differ-
ent from those on mud-bottoms.
Special Cases. The marine fauna of Australia, like its land fauna,
is very peculiar, differing from all others, not only in species, but in
genera and families. It is also a remarkable fact that some of its fishes
belong to families once abundant in the seas everywhere, but now ex-
tinct except in these waters. The marine shells of almost every isolated
island in the ocean are peculiar. This is still more true of land and
fresh-water shells of islands and even of different rivers of the same
continent. A remarkable illustration of this is found in the species of
the common river-mussels. Almost every large river in the United
States has some species of shell peculiar to it. Nearly all the shells of
the Altamaha River are peculiar, being found nowhere else on the face
of the earth.
Thus in all cases species in different localities are different in pro-
GEOGRAPHICAL DISTRIBUTION OF ORGANISMS. 163
portion to the height or depth and the width of the intervening barriers,
and (most important of all) also in proportion to the length of time
since these barriers were established. These facts are now so well at-
tested that they are used as a basis of reasoning. If two countries now
separated have species identical, we are sure that they have been only
very recently separated. The substantial identity of the species of Eng-
land and those of contiguous Europe shows that the British Isles have
been connected with the Continent at a period geologically very recent.
The general resemblance, though not identity, of some plants on the
Pacific coast and in Japan, produces a strong conviction that the two
continents have been formerly connected in the region of the Aleutian
Isles. The great distinctness of the fauna of Australia indicates a
long period of isolation from all other continents. It is as if there
had been a slow change of species in time, and after separation each
group had taken its own way, and thus become more and more different.
This subject, however, cannot be further discussed at present.
PAET II.
STRUCTURAL GEOLOGY.
CHAPTER I.
GENERAL FORM AND STRUCTURE OF THE EARTH.
I. Form of the Earth.
THE form of the earth is that of an oblate spheroid flattened at the
poles. The polar diameter is less than the equatorial diameter by
about twenty-six miles, or about -^ of the mean diameter. The
highest mountains, being only five miles high, do not interfere greatly
with the general form.
This form, being precisely that which a fluid body revolving freely
would assume, has been regarded by many of the most distinguished
physicists as conclusive evidence of the former fluid condition of the
earth. The argument may be stated as follows : 1. A fluid body stand-
ing still, under the influence only of its own molecular or gravitating
forces, would assume a perfectly spherical form ; but, if rotating, the
form which it would assume, as the only form of equilibrium, is that of
an oblate spheroid, with its shortest diameter coincident with the axis of
rotation. Now, this is precisely the form not only of the earth, but, as
far as known, of all the planetary bodies. 2. In an oblate spheroid of
rotation the oblateness increases with the rapidity of rotation. Now
Jupiter, which turns on its axis in ten hours, is much more oblate than
the earth. The flattening of the earth is only about -^ of its diameter,
while that of Jupiter is about -fa. 3. The forms of the earth and of
Jupiter have been calculated ; the data of calculation being the former
fluidity, the time of rotation, and an assumed rate of increasing density
from surface to centre ; and the calculated form comes out nearly the
same as the measured form.
FORM OF THE EARTH. 165
This argument, however, only proves that the forms of the planets
have been assumed under the influence of rotation, or that they are
spheroids of rotation, but not that they have ever been in a fluid condi-
tion. For since a rotating body, whatever be its form, always tends to
assume an oblate spheroid form, and since the materials on the surface
of the earth are in continual motion, being shifted hither and thither
under the influence of atmospheric and aqueous agencies, it is evident
that the final and total result of such motions must be in the course of
infinite ages to bring the earth to the only form of equilibrium of a ro-
tating body, viz., an oblate spheroid. If, for example, we have a solid
and perfectly spherical earth, standing still and covered, as it would be,
by a universal ocean, and then set it rotating, it is evident that the
waters would gather into an equatorial ocean, and the land be left as
polar continents. But this condition would not remain; for atmospheric
and aqueous agencies, if unopposed, would eventually cut down the
polar continents and deposit them as sediments into the equatorial seas,
and the solid earth would thus become an oblate spheroid. This final
effect of degrading agencies would not be opposed by igneous agencies,
as the action of these is irregular, and does not tend to any particular
form of the earth.
Therefore, although there are many reasons, drawn both from ge-
ology and from that cosmical theory (the nebular hypothesis) which ac-
counts for the formation of worlds, for believing that the earth was
once in an incandescent fluid condition, and that it then assumed an
oblate spheroid form in obedience to the laws of equilibrium of fluids,
yet the form of the earth alone is not only not conclusive proof of this
former condition, as has been generally believed, but adds nothing to
proofs derived from other sources, since this form is the necessary result
of the forces now in operation on the earth-surface, whatever may have
been its original form or condition. Further, since the earth from the
time of its first consolidation has continued to cool and contract, and
therefore to increase its rate of rotation, the degree of oblateness which
it now has is not that which it first assumed in its incandescent fluid
condition, but much greater.
2. Density of the Earth.
The mean density of the earth, as determined by several independent
methods, is about 5.6. The density of the materials of the earth-sur-
face, leaving out water, is only about 2 to 2.5. It is evident, therefore,
that the density of the central portions must be much more than 5.6.
This great interior density may be the result 1. Of a difference of ma-
terial. It is not improbable that the surface of the earth has become
oxidized by contact with the atmosphere, and that at great depths
the earth may consist largely of metallic masses. Or the great in-
166
GENERAL FORM AND STRUCTURE OF THE EARTH.
terior density may be the result 2. Of condensation by the immense
pressure of the superincumbent mass. In either case the tendency of
increasing heat would be to diminish the increas-
ing density. But how much of the greater den-
sity is due to difference of material and how
much to increasing pressure, and how much these
are counterbalanced by expansion due to increas-
ing heat, it is impossible to determine.
The increase of density has been somewhat
arbitrarily assumed to follow an arithmetical law.
Under this condition a density equal to the mean
density would be found at radius from the sur-
face, and taking the surface density at 2, and the
mean density at 5.5, the central density would
be 16. In the diagram (Fig. 132), if a c = radius, the ordinate a x =
surface density = 2, and b y = mean density = 5.5, then c z, the central
density, will be = 16.
It is needless to say that this result (Plana's) is unreliable.
. 3. The Crust of the Earth.
The surface of the earth undoubtedly differs greatly in many respects
from its interior, and therefore the exterior portion may very properly
be termed a crust. It is a cool crust, covering an incandescent interior ;
a stratified crust, covering an unstratified interior ; probably an oxi-
dized crust, covering an unoxidized interior; and many suppose a solid
crust, covering a liquid interior. This last idea, which, however, we
have shown (p. 79) to be very doubtful, has probably given rise to the
term crust. The term, however, is used by all geologists, without ref-
erence to any theory of interior condition, and only to express that por-
tion of the exterior which is subject to human observation. The thick-
ness which is exposed to inspection is about ten to twenty miles.
Means of Geological Observation. The means by which we are en-
abled to inspect the earth below its immediate surface are : 1. Artificial
sections, such as mines, artesian wells, etc. These, however, do not pen-
etrate below the insignificant depth of half a mile. 2. Natural sections,
such as cliffs, ravines, canons, etc. These, as we have already seen
(p. 17), sometimes penetrate 5,000 to 6,000 feet. 3. Tilting, and sub-
sequent erosion, of the rocks, by which strata from great depths have
their edges exposed. Thus, in passing along the surface from a to b
(Fig. 133), lower and lower rocks are successively brought under in-
spection. This is by far the most important means of observation;
without it the study of geology would be almost impossible. 4. Volca-
noes bring up to the surface materials from unknown but probably very
great depths.
GENERAL SURFACE CONFIGURATION OF THE EARTH.
167
Ten miles seem an insignificant fraction of the earth's radius, being,
in fact, equivalent to less than one-thirtieth of an inch in a globe two
feet in diameter. It may seem at first sight an insufficient basis for a
Fio. 133.
science of the earth. We must recollect, however, that only this crust
has been inhabited by animals and plants on this crust only have oper-
ated atmospheric, aqueous, and organic agencies and therefore on this
insignificant crust have been recorded all the most important events in
the history of the earth.
4. General Surface Configuration of the Earth.
The earth-surface is very irregular. The hollows are occupied by the
ocean, and the protuberances constitute the continents and islands.
Nearly three-quarters of the whole surface is covered by the ocean.
The mean heights of the continents are given by Humboldt * as follows :
Europe, 671 feet ; North America, 748 feet ; South America, 1,151
feet ; Asia, 1,132 feet. The mean height of all land is probably not
far from 1,000 feet.
The mean depth of the ocean is probably 12,000 to 15,000 feet
(Thomson). There is probably water enough in the ocean, if the ine-
qualities of the earth-surface were removed, to cover the earth to a
depth of at least 8,000 to 9,000 feet.
The extreme height of the land above the sea-level is five miles, and
the extreme depth of the ocean is at least as much. The extreme re-
lief of the solid earth is therefore not less than ten miles.
Cause of Land-Surfaces and Sea-Bottoms. The most usual idea
among geologists as to the general constitution of the earth is that the
earth is still essentially a liquid mass, covered by a solid shell of twen-
ty-five to thirty miles in thickness ; and that the great inequalities,
constituting land-surfaces and ocean-bottoms, are produced by the up-
bending and down-bending of this crust into convex and concave arches,
as shown in Fig. 134. The clear statement of this view is sufficient to
1 " Cosmos," Sabine's edition, vol. i., p. 293.
168 GENERAL FORM AND STRUCTURE OF THE EARTH.
refute it ; for, when it is remembered that the arches with which we are
here dealing have a span of nearly a semi-circumference of the earth, it
becomes evident that no such arch, either above or below the mean
level, could sustain itself for a moment. The only condition under
which such inequalities could sustain themselves on a supporting liquid
FIG. 135. Diagram illustrating the Conditions of Equilibrium of a Solid Crust on a Liquid Interior.
is the existence of inequalities on the under surface of the crust next
the liquid, similar to those on the upper surface, but in reverse, as
shown in Fig. 135. And these lower or under-surface inequalities
would have to be repeated not only for the largest inequalities, viz.,
continental surfaces and ocean-bottoms, but also for great mountain
plateaus. And thus the hypothesis breaks down w r ith its own weight.
Besides, we have already given good reasons (pages 79 and 80) for
believing that the earth is substantially solid. Upon the hypothesis of
a substantially solid earth, we explain the great inequalities constitut-
ing continental surfaces and ocean-bottoms by unequal radial contrac-
tion of the earth in its secular co.oling.
It is evident that, in such secular cooling and contraction, unless the
earth were perfectly homogeneous, some parts, being more conductive,
would cool and contract more rapidly in a radial direction than others.
Thus some radii would become shorter than others. The more conduc-
tive, rapidly-contracting portions, with the shorter radii, would become
sea-bottoms ; and the less conductive, less rapidly -contracting portions,
with the longer radii, land-surfaces. In other words, the solid earth
in contracting becomes slightly deformed, and the water collects in the
depressions.
It is only the greatest inequalities, viz., land-surfaces and sea-bot-
toms, which we account for in this way. Mountain-chains are certainly
formed by a different process, which we will discuss under that head
(p. 240) ; and it is even possible that the causes which operate to pro-
duce mountain-chains may also produce these greater inequalities.
The continuance of these causes would tend constantly to increase
the extent and height of the land, and to increase the depth, but dimin-
ish the extent of the sea. This, on the whole, seems to have been the
fact during the history of the earth, as will be shown in Part III.
Nevertheless, local causes, both aqueous and igneous, as already shown
in Part I., have greatly modified the general contour, both map and
profile, given by secular contraction.
Laws of Continental Form. That the general contour of conti-
ROCKS. 169
nents and sea-bottoms has been determined by some general cause,
such as secular contraction, affecting the whole earth, is further shown
by the laws of continental form. The most important of these are as
follows :
1. Continents consist of a great interior basin, bordered by elevated
coast-chain rims. This typical form is most conspicuously seen in North
and South America, Africa, and Australia. Europe- Asia is more irregu-
lar, and therefore the typical form is less distinct. We give in Fig. 136,
W
FIG. 136. A, Section across North America (after Guyot) ; S, Section across Australia (after Guyot).
A. and B, an east-and-west section of North America and of Australia,
as typical examples of continental structure.
The great rivers of the world, e. g., the Nile, Mississippi, Amazon,
La Plata, etc., drain these interior continental basins.
2. In each continent the greatest range of mountains faces the great-
est ocean. Thus in America the greatest range is on the west, facing
the Pacific ; while in Africa the greatest range is on the east, facing the
Indian Ocean. In Asia the Himalayas face the Indian Ocean, while
the Altai face the Polar Sea. In Australia the greatest range is to the
east, facing the Pacific.
3. The greatest ranges have been subjected to the greatest and
most complex foldings of the strata, and are the seats of the greatest
metamorphism (p. 213) and the greatest volcanic activity.
4. The outlines of the present continents have been sketched in the
earliest geological times, and have been gradually developed and per-
fected in the course of the history of the earth. In the case of the
North American Continent this will be shown in Part III.
The cause of some of these laws will be discussed under the head
of Mountain-Chains.
Rocks.
In geology the term rock is used to signify any material consti-
tuting a portion of the earth, whether hard or soft. Thus, a bed of
sand or clav is no less a rock than the hardest granite. In fact, it is
impossible to draw any scientific distinction between materials founded
170 STEATIFIED OR SEDIMENTARY ROCKS.
upon hardness alone. The same mass of limestone may be soft chalk
in one part and hard marble in another ; the same bed of clay may be
hard slate in one part and good brick-earth in another ; the same bed
of sandstone may be hard gritstone in one part and soft enough to be
spaded in another. The same volcanic material may be stony, glassy,
scoriaceous, or loose sand or ashes.
Classes Of Rocks. All rocks are divided into two great classes, viz.,
stratified rocks and unstratified rocks. Stratified rocks are more or
less consolidated sediments, and are usually, therefore, more or less
earthy in structure and of aqueous origin. Unstratified rocks have
been more or less completely fused, and therefore are crystalline in
structure and of igneous origin.
CHAPTER II.
STRATIFIED OR SEDIMENTARY ROCKS.
SECTION 1. STRUCTURE AND POSITION.
Stratification. Stratified rocks are characterized by the fact that
they are separated by parallel division-planes into larger sheet-like
masses called strata, and these into smaller layers or beds, and these
again into still smaller lamince. These terms are purely relative, and
are therefore somewhat loosely used. Usually, however, the term
stratum refers to the mineralogical character ; the term layer to sub-
divisions of a stratum distinguish-
able by difference of color or fine-
ness ; and the term lamina to those
smallest subdivisions, evidently pro-
duced by the sorting power of water.
For instance, in the annexed figure,
, b, and c, are three strata of sand-
stone, clay, and limestone, each di-
visible into two layers differing in
fineness or compactness of the ma-
terial, and all finely laminated by the sorting power of water. The
lamination, however, is not represented, except in the clay stratum, b.
Extent and Thickness. Probably nine-tenths of the surface of the
land, and, of course, the whole of the sea-bottom, are covered with strati-
fied rocks. This proves that every portion of the surface of the earth
has been at some time covered with water. The extreme thickness of
STRUCTURE AND POSITION. Jfl
stratified rocks is certainly not less than ten miles ; the average thick-
ness is probably several miles.
Kinds of Stratified Rocks, Stratified rocks are of three kinds, and
their mixtures, viz., arenaceous or sand rocks, argillaceous or clay
rocks, and calcareous or lime rocks. Arenaceous rocks, in their inco-
herent state, are sand, gravel, shingle, rubble, etc., and in their com-
pacted state are sandstones, gritstones, conglomerates, and breccias.
Conglomerates are composed of rounded pebbles, and breccias of angu-
lar fragments cemented together. Argillaceous rocks, in their inco-
herent state, are muds and clays; partially consolidated and finely
laminated they form shales, and thoroughly consolidated they form
slates. Calcareous rocks are chalk, limestone, and marble. They are
seldom in an incoherent state, except as chalk.
These different kinds of rocks graduate into each other through
intermediate shades. Thus we may have argillaceous sandstones, cal-
careous sandstones, and calcareous shales or marls.
The most important points connected with stratified rocks we will
now, for the sake of greater clearness, bring out in the form of distinct
propositions. On these propositions is based nearly the whole of
geological reasoning.
I. Stratified Rocks are more or less Consolidated Sediments. The
evidence of this fundamental proposition is abundant and conclusive.
1. Beds of mud, clay, or sand, as already stated, may often be trace'd
by insensible gradations into shales and sandstones. 2. In many places
the process of consolidation is now going on before our eyes. This is
most conspicuous in sediments deposited at the mouths of large rivers
whose waters contain abundance of carbonate of lime in solution, or on
the coasts of seas containing much carbonate of lime. Thus the sedi-
ments of the Rhine are now consolidating into hard stone (p. 76), and
on the coasts of Florida, Cuba, and on coral coasts generally, com-
minuted shells and corals are quickly cemented into solid rock (p. 148).
3. All kinds of lamination produced by the sorting power of water
which have been observed in sediments, have also been observed in
stratified rocks. 4. Stratified rocks contain the remains of animals and
plants, precisely as the stratified mud of our present rivers contains
river-shells, our present beaches sea-shells, or the mud of our swamps
the bones of our higher animals drifted from the high lands. 5. Im-
pressions of various kinds, such as ripple-marks, rain-prints, footprints,
etc., evidently formed when the rock was in the condition of soft mud,
complete the proof. It may be considered as absolutely certain that
stratified rocks are sediments. Arenaceous and argillaceous rocks are
the debris of eroded land, and are therefore called mechanical sedi-
ments or fragmental rocks. Limestones are either chemical deposits
in lakes and seas, or are the comminuted remains of organisms. They
172
STRATIFIED OR SEDIMENTARY ROCKS.
are therefore either chemical or organic sediments. Conglomerates,
grits, and sandstones, indicate violent action ; shales and clays quiet
action in sheltered^spots. Limestones are sometimes produced by vio-
lent action e. g., coral breccia sometimes very quiet action, as in
deep-sea deposits.
We have already seen (p. 4) that rocks under atmospheric agen-
cies are disintegrated into soils, and these soils are carried by rivers
and deposited as sediments in lakes and seas. Now we see that these
sediments are again in the course of time consolidated into rocks, to be
again raised by igneous agencies into land, and again disintegrated into
soils, and redeposited as sediments. Thus the same material has been
in some cases worked over many times in an ever-recurring cycle.
This is another illustration of the great law of circulation, so universal
in Nature.
Cause of Consolidation. The consolidation of sediments into rocks
in many cases is due to some cementing principle, such as carbonate of
lime, silica, or oxide of iron, present in percolating waters. In such
cases the consolidation often takes place rapidly. In other cases it is
due to long -continued heavy pressure, and in still others to long-con-
tinued, though not necessarily very great, elevation of temperature in
presence of water. In these cases the process is very slow, and there-
fore it has not progressed greatly in the more recent rocks.
II. Stratified Rocks have been gradually deposited. The following
facts show that in many cases rocks have been deposited with extreme
slowness : 1. Shales are often found the lamination of which is beau-
tifully distinct, and yet each lamina no thicker than cardboard. Now,
each lamina was separately formed by alternating conditions, such as
the rise and fall of tide, or the flood and fall of river. 2. Again, on the
interior of imbedded shells of mollusca, or on the outer surface of the
shells of sea-urchins deprived of their spines,
are often found attached other shells, as
shown in the following figures. Now, these
shells must have been dead, but not yet
covered with deposit during the whole time
the attached shell was growing. As a
general rule, in fragmental rocks the finest
FIG. 138 Serpula on Shell of an Echinoderm. FIG. 139. Serpulse on Interior of a Shell
STRUCTURE AND POSITION.
173
materials, such as clay and mud, have been deposited very slowly, while
coarse materials, such as sand, gravel, and pebbles, have been de-
posited rapidly. Limestones, being generally formed by the accumula-
tion of the calcareous remains of successive generations of organisms,
living and dying on the same spot, must have accumulated with extreme
slowness. The same is true of infusorial earths.
It is necessary, therefore, to bear in mind that all stratified rocks
were formed in previous epochs by the regular operation of agents
similar to those in operation at present, and not by irregular or cataclys-
mic action, as supposed by the older geologists. Thus, cceteris paribus,
the thickness of a rock may be taken as a rude measure of the time
consumed in its formation.
III. Stratified Rocks were originally nearly horizontal. The hori-
zontal position is naturally assumed by all sediments, in obedience to
the law of gravity. When, therefore, we find strata highly inclined or
folded, we conclude that their position has been subsequently changed.
It must not be supposed, however, that the planes which separate strata
were originally perfectly horizontal, or that the strata themselves were
of unvarying thickness, and laid atop of each other like the sheets of a
ream of paper. On the contrary, each stratum, when first deposited,
must be regarded as a widely expanded cake, thickest in the middle and
thinning out at the edges, and interlapping there with other similar
cakes. Fig. 140 is a diagram showing the mode of interlapping.
FIG. 140. Diagram showing Thinning out of Beds : a, sandstones and conglomerates ; 6, limestones.
The extent of these cakes depends upon the nature of the material. In
fine materials strata assume the form of extensive thin sheets, while
coarse materials thin out more rapidly, and are therefore more local.
The most important apparent exception to the law of original hori-
zontality is the phenomenon of oblique or cross lamination. This kind
of lamination is formed by rapid, shift-
ing currents, bearing abundance of
coarse materials, or by chafing of
waves on an exposed beach. Many
examples of similar lamination are
found in rocks of previous epochs.
Figs. 141 and 142 represent such ex- FIG. wi.-obiique Lamination,
amples. In some cases oblique lami-
nation may be mistaken for highly-inclined strata ; careful examination,
1Y4: STRATIFIED OR SEDIMENTARY ROCKS.
however, will show that the strata are not parallel with the laminae.
The strata were originally (and in the cases represented in the figures
are still) horizontal, while the laminae are oblique.
FIG. 142. Section on Mississippi Central Railroad at Oxford (after Hilgard) : Oblique Lamination.
Elevated, Inclined, and Folded Strata. We may assume, there-
fore, that strata were originally horizontal at the bottom of seas and
lakes ; and, therefore, when we find them in other places and positions,
they have been subsequently disturbed. Now, \ve actually do find
strata in every conceivable position and place ; sometimes they retain
their original horizontality, but are raised above their original level ;
sometimes they have been squeezed by lateral pressure, and thrown into
the most intricate contortions
(Figs. 143, 144, and 145);
sometimes whole groups of
strata many thousand feet
thick are thrown into huge
parallel folds or wrinkles,
forming parallel ranges of
mountains (Figs. 146 and
147) ; sometimes by these
movements the strata are
broken, and one side of the
fissure slips up, while the other
FIG. 148. Contorted Strata (after Hitchcock). side drops down, thus produ-
cing what is called a fault
(see page 222). But whether simply elevated, or also contorted, or
broken and slipped, in nearly all cases large portions of the original
FIG. 144. Contorted Strata (from Logan).
strata are carried away by erosion, and they are left in patches and
basins, or with their upturned edges exposed on the surface, as shown
STRUCTURE AND POSITION.
175
1 c
FIG. 146.-Section of Appalachian Chain.
FIG. 14T. Section of the Jura Mountains.
'
FIG. 148.
in Figs. 148, 149, and 150, in which the dotted lines show the part
removed. We are thus
enabled to examine strata ---I~x
which would otherwise
have remained forever hid
from us. The exposure
of the edges of strata on
1 / 1 -T 11*. -i- 1 *!?.
the surface by erosion is
called outcrop. There are certain terms in constant use by geologists
which must be explained in this connection.
Dip and Strike. The inclination of strata to an horizontal plane is
176 STRATIFIED OR SEDIMENTARY ROCKS.
called the dip. Thus, in Fig. 152, the strata dip 25 toward the south.
c \ d
\ \
FIG. 151. Upturned and Eroded Strata, Elk Mountains, Colorado (after Hayden).
The dip may vary from to 90, from horizontally to vertically. Fig-.
153 gives an example of vertical strata. When in strong foldings the
strata are pushed over be-
yond the perpendicular, as
in Fig. 150, we have what
is called an overturn dip.
When strata dipping regu-
larly are exposed on their
edges, as in Fig. 152, their
thickness may be easily
calculated. If we measure
the distance a b and the angle of dip c a b, then c b, the thickness of
the stfata, is equal to the sine of the angle of dip, multiplied by the dis-
tance a b (R = 1 : a b
: : sine cab : c b and c b
= a b X sine c a b).
The angle of dip is ob-
tained by means of an in-
strument called a clinome-
ter (Fig. 154). The most
convenient form is a pock-
et compass containing a
pendulum to indicate the
angle of dip.
T . FIG. 153. Vertical Strata.
It is rarely the case
that the geologist is able to get a complete natural section of an exten-
STRUCTURE AXD POSITION. 177
sive series of strata. He is usually, therefore, compelled to construct a
more or less ideal section from the examination of outcrops and partial
sections wherever he can find them.
FIG. 154. Clinometer.
The strike is the line of intersection of strata with an horizontal
plane, or the direction of the outcrop of strata on a level surface. It is
always at right angles to the dip. If the dip is toward the north or
south, the strike is east and west. If the strata are plane, the strike is
a straight line, but in folded strata the strike may become very sinu-
ous. The outcrop of strata upon the actual surface is often extremely
irregular, since this is affected not only by the foldings of the strata,
but by the inequalities of surface
produced by erosion. The intricate
outcrop of rocks, under these circum-
stances, can only be understood by
actual examination in the field or by
the use of models. 1 A comparatively
simple case of such outcrop is given
in Fig. 155, and the manner in which
the rocks are folded and eroded is
shown in the section Fig. 156.
Anticlines and Synclines. Fold-
ed strata, of course, usually dip al-
ternately in opposite directions, forming alternate ridges and hollows,
or saddles and troughs (Fig. 156). A line from which the strata dip in
opposite directions on the two
sides is called an anticlinal
axis, or simply an anticline /
a line toward which the strata
dip in opposite directions on
Fte. 156.-Section of Undulati'stra'ta. tllG tW SideS ' S C&lled * ^
clinal axis, or a syncline. The
strata, in the case of an anticline, always form a ridge, and in the case
of a syncline a trough ; but, in the actual surface, this is often entirely
1 Sopwith's Geological Models.
FIG. 155. Plan of Undulating Strata.
178 STRATIFIED OR SEDIMENTARY ROCKS.
reversed by erosion, so that the synclines become the ridges and the
anticlines the hollows or valleys. Fig. 149 represents a section in
which the anticlines or original ridges have become valleys, while the
synclines or original valleys have become mountain-ridges. Examples
of synclinal mountains and anticlinal valleys are by no means uncom-
mon. In both anticlines and synclines the strata are repeated on each
side of the axis.
Monoclinal Axes. Sometimes strata over large areas are lifted
bodily upward with little change of inclination, while over contiguous
areas they are dropped down, the two areas being connected by a sharp
bend of the strata instead of a fault. Such a bend is called a mono-
clinal fold or axis (Fig. 157). Monoclinal folds pass by insensible gra-
dations into faults, and are evidently produced in a similar manner
the degree of flexibility of the strata determining whether the one or
the other is formed. In the plateau of Colorado, where monoclinal
folds are common, they may be traced into faults. Fig. 157 is taken
from this region.
Unconformity. We have seen (page 175) that land-surfaces are
always composed of eroded, and usually of tilted, strata. We have
also seen (pages 127-130) that land-surfaces are now in some places
sinking and becoming sea-bottoms, while in others sea-bottoms are ris-
ing and becoming land-surfaces. The same thing has happened in every
geological epoch. Now, whenever an eroded land-surface sinks below the
water and receives sediments, these sediments will lie in horizontal layers
upon the upturned edges, and filling up the erosion hollows of the pre-
vious strata. If, now, the two series of strata be again elevated into
land-surface, and exposed to the inspection of the geologist, the relation
of the two series to one another will be represented by the following
sections (Figs. 158 and 159). When one series of strata rests thus on
CLEAVAGE STRUCTURE.
179
the eroded surface or edges of another series, the two series are said to
be unconformable. Of course, the whole series may be again elevated,
tilted, and eroded, making the phenomena far more complex than here
onformity.
represented. By far the most common case is that of Fig. 158, in which
the upper series rests on the upturned edges of the lower series, and
there is therefore a want of parallelism between the two series ; and
FIG. 159.-Unconformity.
the term unconformity is usually defined as a want of parallelism ; but
it should be applied also to cases like Fig. 159, where there is no want
of parallelism.
Conformable strata indicate a period of comparative repose, during
which sediments were quietly deposited. Unconformity indicates a pe-
riod of disturbance, during which the strata were elevated into a land-
surface, subjected to erosion, and again subsided to receive other sedi-
ments. A section like Fig. 158 or 159, one of the commonest in struct-
ural geology, indicates two periods of repose and one of disturbance.
The lapse of time in the periods of repose is represented by the strata ;
the lapse of time in the period of disturbance is represented by the ero-
sion. Every case of unconformity, therefore, indicates a gap in the
history of the earth a period unrecorded by strata at that place.
Formation. A group of conformable strata often constitutes what
geologists call a formation. Unconformable strata usually belong to
different formations. These divisions, however, are founded also upon
the character of the contained fossils. This subject will be more fully
explained hereafter.
Cleavage Structure*
We have thus far spoken only of the original and universal structure
of stratified rocks, together with the tiltings, foldings, and erosion, to
1 This structure is usually treated under metamorphic rocks, as a kind of metamor-
phism ; but it is found in rocks which have not undergone ordinary metamorphic changes,
and it is produced by an entirely different cause.
180 STRATIFIED OR SEDIMENTARY ROCKS.
which they have been subjected. There is, however, often found in
stratified rocks a superinduced structure which simulates, and is often
mistaken for, stratification. It is called cleavage structure, or (since it
is usually found in slates) slaty cleavage. This subject has recently
attracted much attention, and is an admirable example of the successful
application of physics to the solution of problems in geology.
Cleavage may be defined as the easy splitting of any substance in
planes parallel to each other. Such definite splitting may result, in
different cases, from entirely different causes. For example (a), under
the influence of the sorting power of water, sedimentary materials may
be so arranged as to give rise to easy splitting along the planes of lami-
nation. Many rocks may be thus split into large coarse slabs called flag-
stones, and are used for paving streets, or even sometimes as roofing-
slates. This may be called flag-stone cleavage, or lamination cleavage.
Again (5), the arrangement of the ultimate molecules of a mineral un-
der the influence of molecular or crystalline forces gives rise to an ex-
quisite splitting along the planes parallel to the fundamental faces of
the crystal. This is called crystalline cleavage. Again (c), the ar-
rangement of the wood-cells under the influence of vital forces gives rise
to easy splitting of wood in the direction of the silver-grain. This may
be called organic cleavage.
Now, in certain slates and some other rocks is found a very perfect
cleavage on a stupendous scale. Whole mountains of strata may be
cleft from top to bottom in thin slabs, along planes parallel to each
other. The planes of cleavage seem to have no relation to the strata,
but cut through them, maintaining their parallelism, however the strata
may vary in dip (Fig. 160). Usually the cleavage-planes are highly in-
clined, and often nearly perpendicular. It is from the cleaving of such
FIG. 160.-Cleavage-Planes cutting through Strata.
slates that roofing-slates, ciphering-slates, and blackboard-slates are
made. This remarkable structure has long. excited the interest of
geologists, and many theories have been proposed to explain it.
On cursory examination of such rocks, the first impression is, that the
cleavage is but a very perfect example of flag-stone or lamination cleav-
age that the cleavage-planes are in fact stratification-planes, and that
we have here an admirable example of finely laminated rocks which
have been highly tilted and then the edges exposed by erosion. Closer
examination, however, will generally show the falseness of this view.
CLEAVAGE STRUCTURE. 181
Fig. 161 represents a mass of slate in which three kinds of structure are
distinctly seen, viz., joint faces, A, J3, C, J, J ; stratification-planes,
FIG. 161. Strata, Cleavage-Planes, and Joints.
S S S, gently dipping to the right; and cleavage-planes, highly inclined,
D J), cutting through both. Cleavage-planes are therefore not stratifi-
cation-planes.
Again, it has been compared to crystalline cleavage, on a huge scale.
It has been supposed that electricity traversing the earth in certain di-
rections, while certain rocks were in a semi-fluid or plastic state through
heat, arranged the particles of such rocks in a definite way, giving rise
to easy splitting in definite directions. In support of this view it was
urged that cleaved slates are most common in metamorphic regions; and
metamorphism, as we shall see hereafter (p. 215, et seq.), indicates the
previous plastic state of rocks, which is a necessary condition of the
rearrangement of the particles by electricity. The great objections to
this theory are 1. That the cleavage is not like crystalline cleavage,
between ultimate molecules, and therefore perfectly smooth, but be-
tween discrete and quite visible granules ; and, 2. That although the
phenomenon is indeed most common in metamorphic rocks, yet meta-
morphism is by no means a necessary condition ; on the contrary, when
the real necessary conditions are present, the less the metamorphism
the more perfect the cleavage.
It is evident, therefore, that slaty cleavage is not due to any of the
causes spoken of above. It is not flag-stone cleavage, nor crystalline
cleavage, and of course cannot be organic cleavage.
Sharpe's Mechanical Theory. The first decided step in the right
direction was made by Sharpe. According to him, slaty cleavage is al-
ways due to powerful pressure at right angles to the planes of cleavage,
by which the pressed mass has been compressed in the direction of press-
ure and extended in the direction of cleavage. This theory may be
now regarded as completely established by the labors of Sharpe, Sorby,
Haughton, Tyndall, and others. We will give a few of the most impor-
tant observations which establish its truth.
(a.) Distorted Shells. Many cleaved slates are full of fossils. In
182
STRATIFIED OR SEDIMENTARY ROCKS.
such cases the fossils are always crushed and distorted as if by powerful
pressure, their diameters being shortened at right angles to the cleavage,
and greatly increased in the direction of the cleavage-planes. The fol-
lowing figures (Fig. 162) are examples of distortion by pressure. In
FIG. 162. -Distorted Fossils (after Sharpe).
Fig. 162, Z Z gives the direction of the planes of cleavage ; Figs. 1, 2, 3,
4, represent one species ; 5, 6, 7, 8, another. In Fig. 163 still another
species is represented in the natural and distorted forms.
Fio. 163. Cardium Hillanum : A, natural form ; B and C, deformed by pressure.
(J.) Association with Foldings. Cleavage is always associated with
strong foldings and contortions of the strata. The folding of the strata
FIG. 164. Cleavage-Planes intersecting Strata.
is produced by horizontal pressure ; the strike of the strata, or the
direction of the anticlinal and synclinal axes, being of course at right
CLEAVAGE STRUCTURE.
183
angles to the direction of pressure. Now, if cleavage is produced by
the same pressure which folded the strata, then in this case we ought
to find the cleavage-planes highly inclined, and their strike parallel
with the strike of the strata ; and such we find is usually the fact. In
Fig. 164 the heavy lines represent the strata and the light lines the
cleavage-planes, both outcropping on a nearly level surface, and parallel
to each other.
(c.) Association with Contorted Laminae. The last evidence was
taken from foldings on a grand scale of the crust of the earth ; but even
fine lines of lamination are often thrown into
intricate foldings by squeezing together in the
direction of the lamination-planes. In such case,
of course the cleavage ought by theory to be at
right angles to the original direction of the lami-
nation, and in such direction we actually find them.
Fig. 165 represents a block of rock in which three
lamination-lines are visible. The lower one, f d,
consists of coarse sand which could not mash, and
therefore has been thrown into folds. As the
specimen stands in the figure, the pressure has
been horizontal ; the perpendicular lines represent
the position of the cleavage-planes. Fig. 166 rep-
resents a beautiful specimen of laminated slate, in
which the lamination -planes have been thrown into
folds by pressure. The direction of the pressure is obvious. The planes
of cleavage are parallel to the
face, cp, and therefore at right
angles to the pressure.
(d.) Flattened Nodules.
In some finely-cleaved slates,
such as are used for writing-
slates, it is common to find
small light-greenish, elliptical
spots of finer material. In clay-
deposits of the present day
it is also common to find im-
bedded little round nodules of
finer material. It is probable
that the greenish nodules in
slates were also rounded nodules
of finer clay in the original clay-
deposit from which the slate
was formed by consolidation.
FIG. 166.-A Block of Cleayed Slate (after Jukes). But in cleaved slates these nod-
FIG. 165. Cleavage-Planes
(after Tyndall).
184
STRATIFIED OR SEDIMENTARY ROCKS.
ules are always very much flattened in the direction at right angles to
the cleavage-planes, and spread out in the direction of these planes.
(e.) Apparent Diamagnetism of Cleaved Slates .under Certain Con-
ditions. If a bar of iron be placed between the poles of a magnet,
it will immediately place itself in the line connecting the poles (axial
position) ; but if a bar of bismuth be similarly placed, it will assume
a position at right angles to the axial line (equatorial position). In
the former case the ends of the bar are attracted by the poles ; in the
other they are repelled. Bodies which, like iron, assume the axial posi-
tion, are called paramagnetic ; bodies which, like bismuth, assume the
equatorial position, are called diamagnetic. But Tyndall has shown *
that by strong compression a paramagnetic substance may be made to as-
FIG. 167. Illustrating Behavior of Cleaved Slates in the Magnetic Field.
sume an equatorial or diamagnetic position. If a cube of iron be -placed
between the poles JVand S of a magnet (Fig. 167, ^4), the cube will be in-
different as to position, since the attraction along any two lines, a #, c d,
at right angles to one another, will be equal. But if iron-filings be made
into a mass with gum, and then subjected to strong compression in one
direction, and from the pressed mass a cube be cut, this cube, placed in
the magnetic field, is no longer indifferent, but sets with its line of great-
est compression, a b (Fig. 167, -B), axial; the attraction along tliis line
being greater than along any other line, because the number and prox-
imity of the particles are greater along this line. And so much greater
is the magnetic attraction along this line than along any other, that this
diameter may be cut away to a considerable extent, so as to make a
short bar, and still the line a b will maintain its axial position (Fig. 167,
(7), and the bar will seem to be diamagnetic, i. e., its long diameter will
be equatorial ; not, however, because its ends are repelled, but because
the attraction along the shorter diameter a b is greater than along the
long diameter. If, therefore, the cutting-down of the diameter a b be
continued, finally the influence of length will prevail over that of com-
1 Philosophical Magazine, third scries, vol. xxxvii., p. 1, and fourth series, vol. ii.,
p. 165.
CLEAVAGE STRUCTURE.
185
pression, and the bar will assume its true axial position (Fig. 167, D).
Now, Tyndall, while experimenting upon the magnetic properties of
various bodies, 1 found that a short bar of cleaved slate, with its longer
diameter in the plane of cleavage, when placed in the magnetic field,
takes the equatorial position ; although, if the bar be slender, it at once
shows its paramagnetism by assuming the axial position. In other
words, cleaved slate behaves exactly as if it was a paramagnetic pow-
der pressed in the direction at right angles to the cleavage-planes.
(/.) Experimental Proof. Finally, experiments by Sorby and by
Tyndall show that clay (the basis of slates), when subjected to power-
ful pressure, exhibits always a cleavage, often a very perfect cleavage,
at right angles to the line of pressure.
Physical Theory. Cleavage is certainly produced by pressure, but
the question still remains : How does pressure produce planes of easy
splitting at right angles to its own direction ? What is the physical
explanation of cleavage ?
Sorby's Theory. 2 Mr. Sorby's view is that all cleaved rocks con-
sisted, at the time when this structure was impressed upon it, of a plastic
mass, with unequiaxed foreign particles disseminated through it; and
that by pressure the unequiaxed particles were turned so as to bring
their long diameters in a direction more or less nearly at right angles
to the line of pressure, and thus determined planes of easy fracture in
that direction. Usually, as in slates, the plastic material is clay, and the
unequiaxed particles are mica-scales. Let A, Fig. 168, repre-
sent a cube of clay with mica disseminated. If such a cube
be dried and broken, the fracture will take place principally
along the surfaces of the mica, which may therefore be seen
glistening on the uneven surface of the fracture ; but if the
cube, while still plastic, be pressed into a flattened disk,
then the scales are turned with their long diameters in the
direction of extension and at right angles
to the line of pressure, as in B, Fig. 168,
and the planes of easy fracture, being
still determined by these surfaces, will
be in that direction.
In proof of this view, Mr. Sorby mixed
clay with mica-scales or with oxide-of-iron
scales, and, upon subjecting the mass to
powerful compression and drying, he al-
ways found a perfect cleavage at right angles to the line of pressure.
Furthermore, by microscopic examination he found that both in the
pressed clay and in the cleaved slates the mica-scales lay in the direc-
tion of the cleavage-planes.
1 Philosophical Magazine, 4th series, vol. v., p. 303. 2 Ib., 2d series, vol. xi., p. 20.
FIG. 168. Illustrating Sorby's Theory
of Slaty Cleavage (after Sorby).
186
STRATIFIED OR SEDIMENTARY ROCKS.
FIG. 169. Illustrating Sorby's Theory
of Slaty Cleavage (after Sorby).
Although cleavage is most perfect in slates, yet other rocks are
sometimes affected with this structure. In a specimen of cleaved lime-
stone, Sorby found under the microscope unequiaxed fragments of
broken shells, corals, crinoid stems, etc. (organic particles), ^
in a homogeneous limestone-paste, lying with their long
diameters in the direction of cleavage. Originally the
limestone was a lime-mud with (he supposes) unequiaxed
organic particles disseminated. In some cases, however,
Sorby recognized the very important
fact that the organic fragments, which
were encrinal joints, had been flattened
by pressure had changed their form
instead of their position. A., Fig. 169,
gives a section of the mass in the sup-
posed original condition, and B the
condition after pressure. This obser-
vation contained the germ of the theory
proposed by Tyndall.
TyndalTs Theory. 1 Tyndall was led to reject Sorby's theory by the
observation that cleavage structure was not confined to masses contain-
ing unequiaxed particles of any kind, but, on the contrary, the cleavage is
more perfect in proportion as the mass is free from all such particles.
Clay, deprived of the last trace of foreign particles by the sorting power
of water, when pressed, cleaved in the most perfect manner. Common
beeswax, flattened by powerful pressure between two plates of glass
and then hardened by cold, exhibits a most beautiful cleavage structure.
Almost any substance curds, white-lead powder, plumbago subjected
to powerful pressure, exhibits to some extent a similar structure. Tyn-
dall explains these facts thus : Nearly all substances, except vitreous,
have a granular or a crystalline structure, i. e., consist entirely of dis-
crete granules or crystals, with surfaces of easy fracture between them.
When such substances are broken, the fracture takes place between the
crystals or granules, producing a rough crystalline or granular surface,
entirely different from the smooth surface of vitreous fracture. Marble,
cast-iron, earthenware, and clay, are good examples of crystalline and
granular structure. Now, if a mass thus composed yield to pressure,
every constituent granule is flattened into a scale, and the structure be-
comes scaly / and as the surfaces of easy fracture will still be between
the constituent scales, we have cleavage at right angles to the line of
pressure. A mass of iron, just taken from the puddling-furnace and
cooled, exhibits a granular structure ; but if drawn out into a bar, each
granule is extended into a thread, and the structure becomes fibrous ;
1 Philosophical Magazine, 2d series, vol. xii., p. 35.
CLEAVAGE STRUCTURE. 187
or if rolled into a sheet, each granule is flattened into a scale, and we
have a cleavage structure.
There can be little doubt that this is the true explanation of slaty
cleavage. The change of form which, as we have seen, has taken place
in the fossil-shells, encrinal joints, and rounded nodules, has affected
every constituent granule of the original earthy mass, so that the struct-
ure becomes essentially scaly instead of granular ; the cleavage being
between the constituent scales. Sorby, it is true, in his observations
on cleaved limestones, recognized the true cause of cleavage, viz., the
change of form of discrete particles ; but he regarded this as subordi-
nate to change of position. Besides, the particles of Sorby were for-
eign, which Tyndall has shown to be unnecessary ; while the particles
of Tyndall are constituent.
Geological Application. It may be considered, therefore, as certain
that cleaved slates have assumed their peculiar structure under the in-
fluence of powerful pressure at right angles to the cleavage-planes, by
which the whole squeezed mass is mashed together in one direction and
extended in another. Taking any ideal sphere in the original unsqueezed
mass : after mashing the diameter in the line of pressure has been short-
ened, the diameter in the line of cleavage-^//? has been correspondingly
extended, and the diameter in the line of cleavage-strike unaffected, since
extension of this diameter in any place must be compensated by short-
ening in a contiguous place right or left ; so that the original sphere has
been converted into a greatly-flattened ellipsoid of three unequal diame-
ters. The amount of compression and extension may be estimated in the
case a by the amount of distortion of shells of known form (Figs. 162
and 163) ; in the case c by a comparison of the transverse diameter with
the length of the folded line/V? (Fig. 165) ; in the case d by the relation
between the diameters of the elliptic spots. By these means, but prin-
cipally by the first, Haughton * has estimated that the original sphere has
been changed into an ellipsoid, whose greatest and shortest diameters
are to each other, in some cases, as 2 : 1, in others as 3 : 1,4: 1, 6 or
7 : 1,9:1, and in some even 11 : 1. The average in well-cleaved slates,
according to Sorby, is about 6 : 1. Now, since this ratio is the result
partly of compression and partly of extension, it is evident that either
the compression alone or the extension alone would be the square roots
of these ratios. Therefore, we may assume the average compression
as 2| : 1, and the average extension as 1 : 2|.
It is impossible to over-estimate the geological importance of these
facts. Whole mountains of strata, whole regions of the earth's crust,
are cleaved to great and unknown depths, showing that the crust has
been subjected to an almost inconceivable force, squeezing it together
in an horizontal direction and swelling it upward. This upward swell-
1 Philosophical Magazine, fourth series, vol. xii., p. 409.
188
STRATIFIED OR SEDIMENTARY ROCKS.
ing, or thickening of the strata by lateral squeezing, is a probable cause
of gradual elevation of the earth's crust, which has not been noticed by
geologists. We will speak again of this important subject in our dis-
cussion of mountain-formation.
There are reasons for believing that the squeezing did not take
place, and the structure was not formed, while the strata were in their
original condition of plastic sediment, but after they had been consoli-
dated into rock and the contained fossils had been completely petrified,
otherwise the shells must have been broken by the pressure. Yet, on
the other hand, some degree of plasticity seems absolutely necessary to
account for so great a compression in one direction and extension in
another without disintegration of the mass. It seems most probable
that at the time the structure was produced these rocks were deeply
buried beneath other rocks and in a somewhat plastic state, through
the influence of heat in the presence of water. Afterward, they were
exposed by erosion.
Nodular or Concretionary Structure.
In many stratified rocks are found nodules of various forms scattered
through the mass or in layers parallel to the planes of stratification.
Like slaty cleavage, this structure is the result of internal changes sub-
sequent to the sedimentation ; for the planes of stratification often pass
directly through the nodules (Figs. 170 and 171). The flint nodules of
FIG. 170. FIG. 171.
the chalk, and the clay iron-stone nodules of the coal strata and hy-
draulic lime-balls, common in many clays, are familiar illustrations of
this structure.
Cause. Nodular concretions seem to occur whenever any substance
is diffused in small quantities through a mass of entirely different mate-
rial. Thus, if strata of sandstone or clay have small quantities of car-
bonate of lime or carbonate of iron diffused through them, the diffused
particles of lime or iron will gradually, by a process little understood,
segregate themselves into more or less spherical or nodular masses, in
some cases almost pure, but generally inclosing a considerable quantity
of the material of the strata. In this manner lime-balls and iron-ore
balls and nodules, so common in sandstones and clays, are formed. In
like manner, the flint nodules of the chalk were formed by the segre-
gation of silica, originally diffused in small quantities through the chalk-
NODULAR OR CONCRETIONARY STRUCTURE.
189
sediment. Very often some foreign substance forms the nucleus about
which the segregation commences. On breaking a nodule open, a shell
or some other organism is often found
beautifully preserved. These nodules,
therefore, are a fruitful source of beau-
tiful fossils. In most cases, probably
in all cases, the segregating substance
must have been to some extent soluble
in water pervading, or suspensible in
water percolating, the stratum. Some-
times the nodules run together, form-
ing a more or less continuous stratum.
In such cases, the segregating material
is more impure.
Forms of Nodules. The typical and most common form is globular.
This is well seen in lime-balls and iron-balls. Sometimes these balls
are solid, sometimes they have irregular cracks in the centre (Fig. 172),
sometimes they have a radiated structure (Fig. 173), sometimes they
are hollow like a shell (this is common in iron-balls). They vary in size
from that of a pea to six and eight feet in diameter. Often, however,
instead of the spherical form, they take on various and strange and
FIG. 173. Dolomite containing Concretions, Sunderland (after Jukes).
fantastic shapes (Fig. 174), sometimes like a dumb-bell, sometimes a
flattened disk, sometimes a ring, sometimes a flattened ellipsoid, regu-
larly seamed on the surface like the shell of a turtle (turtle-stones).
They are often mistaken by unscientific observers for fossils.
Kinds of Nodules found in Different Strata. In sandstone strata the
nodules are commonly carbonate of lime or oxide of iron (lime or iron
balls). In clay strata they are carbonate of lime or carbonate of iron
(clay iron-stone of coal strata), or a mixture of these (Roman cement
nodules of the London clay).
190
STRATIFIED OR SEDIMENTARY ROCKS.
In limestone the nodules are always silica, and conversely silica
nodules are peculiar to limestone. The flint nodules of the chalk are
remarkable for being arranged in planes parallel to the planes of strati-
FIG. 174. Limestone Strata containing Concretions.
fioation (Fig. 175). Sometimes the siliceous matter segregates in con-
tinuous strata of siliceous limestone (Fig. 176).
In the cases thus far spoken of, the nodules are scattered through
the mass of the strata or arranged in planes parallel to planes of stra-
FIG. 175. Chalk-Cliffs with Flint Nodules.
tification. But in some cases the whole mass of the rock assumes a con-
cretionary or concentric structure (Fig. 177). The cause of this is still
more difficult to explain.
FOSSILS : THEIR ORIGIN AND DISTRIBUTION.
Stratified rocks, as we have already seen, are sediments accumulated
in ancient seas, lakes, deltas, etc., and consolidated by time. As now,
so then, dead shells were imbedded in shore-deposits ; leaves and logs of
FOSSILS: THEIR ORIGIN AND DISTRIBUTION.
191
high land-plants, and bones of land-animals, were drifted into swamps
and deltas and buried in mud ; and tracks were formed on flat, muddy
shores by animals walking
on them. These have been
preserved with more or less
change, and are even now
found in great numbers in-
closed in stratified rocks.
They are called fossils. A
fossil, therefore, is any evi-
dence of the former existence
of a living being. Fossils
are the remains of the fauna
and flora of previous geolog-
ical epochs. Their presence
is the most constant charac-
teristic of stratified rocks.
The Degrees of Preservation are very various. Sometimes only the
tracks of animals, or impressions of leaves of plants, are preserved.
More commonly the bones or shells, or other hard parts of animals, are
FIG. 176.-Chalk-Cliffs.
FIG. 177. Coal-measure Shale, weathering into Spheroids.
preserved with various degrees of change. Sometimes even the soft
and more perishable tissues are preserved. We will treat of these
degrees under three principal heads :
1. Decomposition prevented and the Organic Matter more or less
completely preserved. Cases of this kind are usually found in compar-
atively recent strata, and imbedded either in frozen soils, or in peat, or
in stiff clays ; although some cases of partial preservation of the or-
192 STRATIFIED OR SEDIMENTARY ROCKS.
ganic matter are found even in old rocks. Extinct elephants have been
found frozen in the river-bluffs of Siberia so perfectly preserved that
dogs and wolves ate their flesh. Skeletons of men and animals are
found in peat-bogs and stiff clays of a comparatively recent formation,
the organic matter of which is still preserved. In clays of the Tertiary
period the imbedded shells still retain the epidermis, and even in the
Lias (mesozoic) shells are found retaining the nacreous lustre. Coal is
vegetable matter changed but not destroyed. It is found in almost
every formation, even down to the oldest. Every degree of change may
be traced in different specimens of fossil wood, between perfect wood
and perfect coaL
2. Petrifaction: Organic Form and Structure preserved. In t : :e
last case the organic matter is more or less preserved. In the case
now to be described the organic matter is entirely gone ; but the or-
ganic form and the organic structure are preserved in mineral matter.
This is what is usually called petrifaction or mineralization. The best
example of this is petrified wood. In a good specimen of petrified
wood, not only the external form of the trunk, not only the general
structure of the stem viz., pith, wood, and bark not only the radiating
silver-grain and the concentric rings of growth, are discernible, but
even the microscopic cellular structure of the wood, and the exquisite
sculpturings of the cell-walls themselves, are perfectly preserved, so
that the kind of wood may often be determined by the microscope with
the utmost certainty. Yet not one particle of the organic matter of
the wood remains. It has been entirely replaced by mineral matter ;
usually by some form of silica. The same is true of shells and bones
of animals ; but as shells and bones consist naturally partly of organic
and partly of mineral matter, very often it is only the organic matter
which is replaced, although sometimes the original mineral matter is
also replaced by silica or other mineral substance. The radiating
structure of corals or the microscopic structure of teeth, bones, and
shells, is often beautifully preserved. This kind of preservation for
shells and corals is most common in limestones and clays ; for wood, in
gravels.
Theory of Petrifaction. If wood be soaked in a strong solution of
sulphate of iron (copperas) and dried, and the same process be re-
peated until the wood is highly charged with this salt, and then
burned, the structure of the wood will be preserved in the peroxide of
iron left. Also, it is well known that the smallest fissures and cavities
in rocks are speedily filled by infiltrating waters with mineral matters.
Now, wood buried in soil soaked with some petrifying material becomes
highly charged with the same, and the cells filled with infiltrated mat-
ter, and when the wood decays the petrifying material is left, retaining
the structure of the wood. But this is not all, for in Nature there is
FOSSILS: THEIR ORIGIN AND DISTRIBUTION. ^93
an additional process, not illustrated either by the experiment or by
the example of infiltrated fillings. As each particle of organic matter
passes away by decay, a particle of mineral matter takes its place, until
finally the whole of the organic matter is replaced. Petrifaction, there-
fore, is a process of substitution, as well as interstitial filling. Now,
it so happens, probably from the different nature of the process in the
two cases, that the interstitial filling always differs, either in chemical
composition or in color, from the substituting mate-
rial. Thus the structure is still visible, though the
mass is solid. If Fig. 178 represent a cross-section
of three petrified wood-cells, the matter filling the cells
(b) is always different from the matter forming the
cell-wall (a).
The most common petrifying materials are silica,
carbonate of lime, and sulphide of iron (pyrites). In the case of petri-
faction by pyrites the process is quite intelligible, but the structure is
usually very imperfectly preserved. If water containing sulphate of
iron (FeSOJ come in contact with decaying organic matter, the salt is
deoxidized by the organic matter, the latter passing off as carbonic
acid and water, and the former becomes insoluble sulphide (FeS), and
is deposited. Now, as each particle of organic matter passes away as
CO, and H 2 O, the molecule of iron sulphate which effected the change
is itself changed into insoluble sulphide, and takes its place.
The process of replacement by silica (silicification) is less clear, but
it is probably as follows : Silica is found in solution in many waters,
being held in this condition by small quantities of alkali present in the
waters. In contact with decomposing wood the alkali is neutralized
by the humic, ulmic, and other acids of decomposition, and the silica
therefore deposited.
3. Organic Form only preserved. In the third case organic mat-
ter and organic structure are both lost, and only organic form is pre-
served. This kind of fossilization is most commonly seen in shells. It
may be subdivided into four subordinate cases, represented in section
by , b, c, and d of Fig. 179. In this figure the horizontal lines represent
the original sediment which may or may not have consolidated into
rock ; the vertical lines represent a subsequent filling of different and
usually finer material. In a we have a mould of the external form of
13
194
STRATIFIED OR SEDIMENTARY ROCKS.
the shell preserved in sediment. The shell with the undecayed animal
was imbedded, and afterward entirely dissolved away, leaving only the
hollow mould. In b the same process has taken place, only the mould
has been subsequently filled by infiltration of slightly soluble matters.
In this case we have both the mould and the cast of the external form ;
the mould being formed of sediment, and the cast of infiltrated matter.
These are always of different materials, i. e., different either in chemical
composition or in state of aggregation. In c we have a mould of the
external form in sediment, and a cast of the internal form in the same
material, with an empty space between, having the exact form and
thickness of the shell. In this case, the already dead and empty shell
FIG. 180. o, Cast of interior; 6, natural form.
Fro. 181. a, Natural form ; &, cast
of interior and mould of exterior.
FIG. 182. Trigonia Longa, showing cast (a) of the
exterior and (6) of the interior of the shell.
was imbedded in sediment, which also filled its interior ; afterward the
shell was removed, leaving an empty space. In d this empty space
was subsequently filled by infiltration. In shore and river deposits of
the present day it is very common. to find shells imbedded in, and filled
with, sand or mud. In the more recent tertiary rocks shells are com-
monly found in the same condition precisely ; but in the older rocks
more commonly the original shell is removed, and the space either left
empty or filled by infiltration. Cases c and d are well represented by
Figs. 180, 181, and 182. Cases like a and c are most commonly found
in porous rocks like sandstone ; b and c?, especially the latter, are found
DISTRIBUTION OF FOSSILS IN THE STRATA. 195
in all kinds of rocks. By far the most common infiltration fillings are
carbonate of lime and silica.
Often we find impressions of the forms of small portions only of the
original organism, as of the leaves of trees, or the feet of animals walk-
ing on the soft mud of the flat shores of ancient bays. Such tracks
were afterward covered up with river or tidal deposit, and thus pre-
served. On cleaving the rock along the lamination-planes we have on
one side a mould and on the other the cast of the foot.
Between cases 1 and 2 every stage of gradation may be traced.
The amount of change, as a general fact, varies with the age of the
rock ; but is still more dependent on the kind of rock and the degree
of metamorphism (p. 213). In an impermeable rock, like clay, the
changes are much more slow than in a porous rock, like sandstone.
Distribution of Fossils in the Strata.
The nature of the fossil species found in rocks is determined partly
by the kind of rock, partly by the country where the rock is found, and
partly by the age of the rock.
1. Kind of Rock. It has been already stated (p. 162) that the
species of lower marine animals vary with the depth. They also vary
with the kind of bottom. Thus, along shore-lines and on sand-bottom
the species differ from those in deep water and on mud-bottom. Shells
are found mostly along shore-lines, corals in opener seas, and foramini-
fera in deep seas. The same was true in every previous epoch. We
might expect, therefore, and do find, that the lower marine fossils of
sandstones, shales, and limestones, differ even when these strata belong
to the same country and geological epoch. The higher marine animals,
such as fishes, cuttle-fish, etc., swimming freely in the sea, are more
independent of bottoms, and we find their skeletons and shells equally
in all kinds of strata. Land animals perish on land, and their skeletons
are drifted into bays, river-deltas, and lakes, and buried there mostly in
fresh-water or brackish-w.ater deposits of sand and clay. It is, there-
fore, in such strata that their remains are commonly found.
2. The Country where found. We have already seen (p. 155) that
the fauna and flora of different countries at the present time differ as
to species, and often as to genera and families ; the difference being
generally in proportion to the difference in .climate and the physical
barriers intervening. The same was true of the faunas and floras of
previous epochs, and therefore of the fossils of the same age in differ-
ent countries. The fossil species of the same epoch in America, and in
Europe and in Asia, are not usually identical, although there may be a
general resemblance. The geographical diversity, however, is small in
the lowest and oldest rocks, and becomes greater and greater as we
196 STRATIFIED OR SEDIMENTARY ROCKS.
pass upward into newer and newer rocks, and is greatest in the fauna
and flora of the present day.
3. The Age. This introduces the subject of the laws of distri-
bution of organisms in time, or of fossils vertically in the series of
stratified rocks. The subject will be more fully treated in Part III.,
of which it constitutes the principal portion. We now bring out only
so much as is necessary as a basis of classification of stratified rocks.
(a.) Geological Fauna and Flora. As we pass from the oldest
and lowest rocks upward to the newest and highest, we find that all the
species, most of the genera, and many of the families, change many times.
Now, all the species of animals and plants inhabiting the earth at one
time constitute the fauna and flora of that geological time. Geological
faunae, therefore, have changed many times. In a conformable series
of rocks the change from one fossil fauna or flora to another succeeding
is always gradual, the species of the later fauna or flora gradually
replacing those of the earlier. But between two series of unconform-
able strata the change is sudden and complete as if one fauna and
flora had been suddenly destroyed and another introduced. It must be
remembered, however, that unconformity always indicates a great
lapse of time unrepresented at the place of observation by strata or
fossils. It is therefore probable that the apparent suddenness of the
change is only the result of our ignorance of the fauna and flora of the
period unrepresented. Nevertheless, as unconformity always indi-
cates changes of physical geography, and therefore of climate, it is
probable that in the history of the earth there were periods of great
changes, marked by unconformity of strata, during which changes of
species were more rapid, separated by periods of comparative quiet,
marked by conformity, during which the species were either un-
changed, or changed slowly. Such a period is called a geological
period or geological epoch, and the rocks formed during a geological
period, or epoch, is called & formation.
There are, therefore, two tests of a formation and a corresponding
geological period, viz., 1. Conformity of the strata, or rock-system,
and, 2. General similarity of fossils, or life-system / and two modes
of separating formations and corresponding periods, viz., unconformity
of the rock-system, and great and sudden change of the life-system.
A geological formation, therefore, may be defined as a group of con-
formable rocks containing similar fossils, usually separated from other
similar groups containing different fossils by unconformity. A geo-
logical period may be defined as a period of comparative quiet, during
which the physical geography, climate, and fauna and flora, were sub-
stantially the same, usually separated from other similar periods by
changes of physical geography and climate, which resulted in changes
of fauna and flora. Of these two tests, however, the life-sj^stem is
CLASSIFICATION OF STRATIFIED ROCKS. 19^
usually considered the most important, and in case of disagreement
must control classification.
(b.) Geological Faunce and Florae differ more than Geographical
Faunae and Florae. If there were no geographical diversity, species
of the same age would be identical all over the earth, and therefore it
would be easy to determine strata of the same age (geological horizon).
On the other hand, if geographical diversity in any age were as great
as the diversity between two successive ages, then it would seem im-
possible to establish a geological horizon. But this law states that the
difference between two successive faunas is greater than between two
contiguous faunae. In other words, the species of successive periods,
or fossils of successive formations, differ from each other more than
species of the same period or fossils of the same formation in different
parts of the earth. There is a general similarity in the species of the
same period all over the surface of the earth. Kence by comparison of
fossils it is possible to determine what strata, in different portions of
the earth, belong to the same period (to synchronize strata). The strata
all over the earth, which were formed at the same time, are said to be-
long to the same geological horizon. Strata of the same horizon are
determinate by similarity of fossils with considerable certainty, until
we come up to the tertiary rocks. In all the newer rocks, however, the
geographical diversity is so great as to interfere seriously with the
ability to synchronize by means of comparison of fossils. Another
method, therefore, is used for these higher rocks.
(c.) By examining and comparing fossils from the lowest to the
highest rocks, it has been observed that there is a steady approach of
the fossil faunas and florae to the present faunae and florae, first in the
families, then in the genera, and finally in the species. The species of
fossil molluscous shells begin to be identical with molluscous species of
the present day only in the tertiary rocks, and the proportion of iden-
tical species steadily increases as we pass upward. Thus in the newer
rocks, just where the other method (comparison of fossil faunas with one
another) begins to fail, we mav svnchronize strata of different localities,
by comparing their shell fauna with the shell fauna of the present day,
in the same localities. Those are said to be of the same age which
contain the same percentage of shells identical with those of the present
day.
SECTION 2. CLASSIFICATION OF STRATIFIED ROCKS.
Geology is essentially a history. Stratified rocks are the leaves on
which this history is recorded. The fundamental idea of every clas-
sification is therefore relative age. The object to be attained in clas-
sification is, first, to arrange all rocks in chronological order, so that
the history may be read as it was written ; and then, second, to collect
198 STRATIFIED OR SEDIMENTARY ROCKS.
them into larger and smaller groups, called systems, series, formations,
corresponding to the great eras, periods, epochs, of the earth's history.
There are several different methods of determining the relative age of
rocks :
1. Order of Superposition. It is evident, from the manner in which
stratified rocks are formed viz., by sedimentation that their original
position indicates, with absolute certainty, their relative age, the lower
being older than the higher. If, therefore, the original position of any
series of strata be retained or not very greatly disturbed, and we have
a good section, the relative age of the strata which compose the series
may be easily determined. But the strata, as we have already seen,
have in many cases been crushed and contorted and folded in the most
intricate manner, sometimes even turned over ; have been broken and
slipped, and large masses carried away by erosion, and often so changed
by heat and other agents, that their stratification is nearly or quite
obliterated. For these reasons it is often very difficult to determine
the relative position, and thus to construct an ideal section of the
strata of a series of rocks, even in a single locality. Nevertheless, in
spite of all these difficulties, the method of superposition is conclusive,
and takes precedence of all others whenever it can be applied. In
spite of all these difficulties, if the whole geological series were present
in any one locality, it would be comparatively easy to construct the
geological chronology.
But a series of rocks in any one locality cannot give us the whole
history of the earth. Since sedimentation only takes place at the bot-
tom of water, those places which were land-surfaces during any geo-
logical epoch received no deposit, and therefore the strata representing
that epoch must be wanting there. Now, as there have been frequent
oscillations of land-surfaces and sea-bottoms in past times, similar to
those taking place at the present time, we find that in every known
local series of strata there exist many and great gaps, so many and so
great that the record may be regarded as only fragmentary. Such gaps
are usually indicated by unconformity. It is the task of the geolo-
gist, by extensive comparison of rocks in all countries, to fill up these
gaps, and make a continuous series. The leaves of the book of Time
are scattered hither and thither over the surface of the earth, and it is
the duty of the geologist to gather and arrange them according to their
paging. This is done by comparison of rocks of different localities,
partly by their lithological character, but principally by the fossils which
they contain.
2. Lithological Character. At the present time, in our seas and
lakes, deposits are forming composed of sand, clav, mud, and lime, of ev-
ery kind, in different localities. The same has taken place in previous
epochs. Sandstones, limestones, and slates, not differing greatly from
CLASSIFICATION OF STRATIFIED ROCKS. 199
those forming at the present time, except in degree of consolidation,
have been formed in every geological period. Lithological charac-
ter, therefore, is no test of age. In comparing rocks of widely-sepa-
rated localities, as, for example, the rocks of different continents, dif-
ference of lithological character is no evidence of difference of age, nor
similarity of lithological character of any value in determining a geo-
logical horizon. But, as deposits are now being formed of a similar char-
acter over considerable areas, so also we find strata (the deposits of pre-
vious epochs), continuous and unchanged in lithological character, over
large tracts of country. Therefore, in contiguous localities, similarity
of lithological character becomes a very valuable means of identifying
strata. If, in two localities not too widely separated, we find a similar
rock, e. g., a sandstone of similar grain and color, we conclude that
they probably belong to the same age, or are, in fact, the same stratum.
3. Comparison of Fossils. This is by far the best, and in widely-
separated localities the only, method of determining the age of rocks.
The principle of this method is that every geological epoch has its own
fauna and flora by which it may be identified everywhere in spite of
those slight differences which result from geographical diversity ; and,
therefore, similarity of fossils shows similarity of age. There are, how-
ever, certain limitations to the application of this method which must
be borne in mind :
(a.) The lower marine species are much affected by depths and bot-
toms, and therefore we should expect that sandstone fossils, limestone
fossils, and slate fossils, would differ in species even in the same epoch.
Again, in lake and delta deposits, the entombed species would prob-
ably be entirely different from those of marine deposits. We must be
careful, therefore, to compare fossils of rocks formed under similar con-
ditions.
(b.) We must also make due allowance for geographical diversity.
This, as we have already stated, becomes greater and greater as we
pass up the series of rocks. In the lower or older rocks the geographi-
cal diversity is small ; in strata of the same age in different countries
the fossils are quite similar, most of the genera and many of the species
being undistinguishable. It is therefore comparatively easy, by com-
parison of fossils, to synchronize the strata and determine the geological
horizon. In the middle rocks the geographical diversity is greater, but
the general similarity is still considerable the difference between or-
ganisms of consecutive epochs (geological faunae and florae) is still much
greater than the difference between organisms of the same epoch in dif-
ferent countries (geographical faunas and floras) ; and, therefore, it is
still quite possible, by comparison of fossils, to synchronize the strata.
In the higher or newer rocks the geographical diversity has become so
great that we are compelled to determine age and synchronize strata,
200
STRATIFIED OR SEDIMENTARY ROCKS.
no longer entirely by comparison of fossils of the different localities
with each other, but also by the comparison of the fossils of each local-
ity with the living species in the same locality. In these rocks we de-
termine relative age by relative percentage of living species, and simi-
larity of age (geological horizon) by similarity of this percentage.
Manner of constructing a Geological Chronology. The manner in
which a geological chronology has actually grown up, under the com-
bined labors of the geologists of all countries, may be briefly stated as
follows : First, the order of superposition, and therefore the relative
ages of the strata composing the rock-series of many different countries,
were determined independently ; next, by comparison of these, partly
by lithological character, if the localities are contiguous, and partly by
fossils, the geologist determines those which are synchronous and those
which are wanting in each locality. Thus, out of several local series,
by intercalation, he constructs a more complete ideal series. In case of
doubt, he strives to find places where the doubtful strata come together,
and observes their relative position. In Fig. 183, A and B represent
FIG. 183 Diagram illustrating the Mode of determining the Chronological Order of Strata.
two contiguous localities in which by independent study the relative po-
sitions and ages of 6 and 7 strata respectively have been determined.
By comparison, the rocks of the two series are found to consist of
eleven strata of different ages, some being wanting in the one and
some in the other locality. The figure represents the strata as con-
nected and traceable from one locality to the' other, but the intervening
portions between A and B may be removed by erosion, as shown by the
dotted line, or covered with water. In such case, the actual overlapping
cannot be observed, if it ever existed, but the comparison in other re-
spects is the same. In widely-separated localities of course the compar-
ison can only be made by means of fossils. Thus as the examination of
the earth's surface progresses, with every new country examined some
gaps are filled up, and the series becomes more perfect. Many gaps still
remain unfilled. The series will continue to be made more perfect, and
the chronology more complete, until the geological examination of the
earth-surface is complete.
CLASSIFICATION OF STRATIFIED ROCKS.
201
The second object to be attained by classification is the division and
subdivision of the whole series into larger and smaller groups, corre-
sponding to the eras, periods, and epochs of time.
The following is an outline of the classification of Dana, slightly
modified. Except in the uppermost part it is carried only as far as
periods :
EBAS.
AGES.
PERIODS.
EPOCHS.
5. Psychozoic.
7. Age of Man.
Human,
22 Recent.
4. Cenozoic.
6 The Age of Mam-
mals.
f Quaternary,
[ Tertiary,
! Terrace.
Champlain.
Glacial.
( Pliocene.
20 -J Miocene.
( Eocene.
3. Mesozoic.
5. The Age of Rep-
tiles.
( Cretaceous,
} Jurassic,
( Triassic,
19
18
17
2. Palaeozoic.
Carboniferous Age. "|
4. The Age of Aero- 1
gens and Am- f
phibians.
{Permian,
Carboniferous,
Sub-carboniferous,
16
15
14
Devonian.
3. The Age of Fishes.
fCatskill,
I Chemung,
"I Hamilton,
[Corniferous,
13
12
11
10
Sttunan. (>A
2. The Age of Inverte-
brates. /,
- ? . -'-^
'Oriskany, 9
i "Helderberg, 8
Salina, 7
> Niagara,-^ ^_U- 6
^Trenton, ^ 5
< .Canadian, 4
Primordial, /,,... 3
1. Archaean, or
Eozoic.
1. Archaean.
( Huronian,
| Laurentian,
2
1
As we have already stated, the gaps in the series are usually indi-
cated by unconformity. Now, since unconformity always indicates move-
ments of the crust, changes of the outlines of sea and land, changes of
climate, and consequent changes in the fauna and flora, these gaps mark
the times of great revolutions in the earth's history, and are therefore
the natural boundaries of the eras, periods, etc. The whole rock-series,
202 UNSTRATIFIED OR IGNEOUS ROCKS.
therefore, is divided, by means of unconformity and the character of the
fossils, into larger groups called systems, and these again into smaller
groups called series and formations. The largest groups are founded
upon universal, or almost universal, unconformity, and a consequent very
great difference in character of organisms; the smaller groups are
founded upon a less general unconformity and less difference in char-
acter of the organisms. Corresponding with the great divisions and
subdivisions of the rock-system are the eras, ages, periods, and epochs
of the history. The several terms expressing the divisions and sub-
divisions, both of the rocks and of the history, are unfortunately used in
a loose manner. We will try to use them in the manner indicated. It
will be observed that the divisions are founded upon (a) unconformity,
and (b) change in fossils. These generally accompany each other, since
they are produced by the same cause, viz., change of physical geography.
In some localities, however, they may be in discordance. In this case,
the change of fossils is considered the more important, and controls
classification.
CHAPTER III.
UNSTRATIFIED OR IGNEOUS ROCKS.
Characteristics. The unstratified are distinguished from the strati-
fied rocks a. By the absence of true stratification or lamination of
sorted materials ; b. By the absence of fossils ; c. Usually by a crystal-
line or else a glassy structure ; and, d. By their mode of occurrence,
explained below.
Origin. They have evidently been consolidated from a fused or
semi-fused condition, and are therefore called igneous rocks. This ori-
gin is clearly shown by their structure, by their occurrence in dikes
and tortuous veins, by the effect they often produce upon the stratified
rocks with which they come in contact, and by their resemblance to
ordinary lavas.
Mode of Occurrence. They occur a. Underlying the strata, and
forming the great mass of the interior of the earth ; b. Forming the
peaks and axes of many mountain-chains ; c. Filling fissures, often of
great extent, in the stratified rocks, or other igneous rocks ; d. Over-
lying strata, as if erupted through fissures and outpoured on the surface ;
and, e. Lying conformably between the strata, as if forced between
them in a melted condition, or else outpoured upon the bed of the sea,
and afterward covered with sediments. All these positions are illus-
trated in Fig. 184. In all these modes of occurrence, the observed rock
is connected with an underlying mass, of which it is-but the extension.
GRANITIC ROCKS.
FIG. 184. Diagram showing Mode of Occurrence of Igneous Rocks.
Extent on the Surface. The appearance of these rocks on the sur-
face is far less extensive than that of the stratified rocks. Certainly
not more than one-tenth of the surface of the earth is composed of
them. But beneath they are supposed to constitute the great mass of
the earth.
Classification of Igneous Rocks. Igneous rocks are best classified,
not by means of their relative age,. but partly by their lithological
character, and partly by their mode of occurrence. They are thus
divisible into three groups, viz., the granitic rocks, the trappean or
fissure-eruption rocks, and the volcanic or crater-eruption rocks. After
describing these, we will notice briefly attempts at classification on
other bases.
1. GRANITIC ROCKS.
The rocks of this group are characterized by a coarse-grained,
speckled or mottled appearance, arising from the fact that they are
formed by the aggregation of distinct crystals or masses of different
FIG. 185. -Graphic Granite: A, cross-section ; J3, longitudinal section.
colors. Granite, which is the type of this group, consists of quartz,
feldspar, and mica. Sometimes the mica is wanting, and the quartz is
in the form of curiously-bent laminae, which on cross-section resem-
ble Hebrew or Arabic characters, disseminated in a mass of feld-
spar. The rock is then called graphic granite (Fig. 185) ; when the
204
UNSTRATIFIED OR IGNEOUS ROCKS.
mica is replaced by hornblende, the rock is called syenite y 1 when, in
addition to the quartz and feldspar, both mica and hornblende occur, it
is called syenitic granite. Most of the granite in this country is syenitic.
The dark specks in granite are due to mica or to hornblende ; the opaque
white, or reddish, or greenish, with distinct cleavage, is feldspar, and
the grayish glassy is quartz.
Chemical Composition and Kinds. Quartz is pure silica or silicic
acid (SiO a ). Feldspar of this group is an acid silicate of alumina and
alkali, potash or soda (orthoclase). Hornblende is a basic silicate of
magnesia and lime, with also oxide of iron and alumina. Remembering
also that hornblende is a black mineral, while quartz and feldspar are
either colorless or very light-colored, it is evident that this group may
be divided into two sub-groups, the one more acid, and the other more
basic ; and in proportion as quartz and feldspar predominate, the rock is
lighter colored, less dense, and more acid ; in proportion as hornblende
predominates, it is darker, heavier, and more basic. Granite may be
taken as the type of the more acid sub-group, and the darker varieties
of syenite as the type of the more basic sub-group. These sub-groups
graduate insensibly into each other. Since a general characteristic of
the granitic group is the existence of free quartz in notable quantity,
this group, taken as a whole, is usually regarded as more acid than the
other two groups.
Mode Of Occurrence. Granitic rocks commonly occur forming the
axes and peaks of mountain-chains (Fig. 186, A), or as rounded masses,
of greater or less extent, coming up through stratified rocks of the older
series (Fig. 186, J3). They
also sometimes occur as tor-
tuous veins, running from
an underlying mass into the
stratified rocks above, as if
forced by heavy pressure,
while in a fused condition,
into small, irregular fissures
of the overlying strata (Fig.
187, A and _B), and some-
times, though rarely, as dikes filling great fissures, as in the elvans of
Cornwall; but it is doubtful whether these should be considered as
true granites. They are probably a quartz-porphyry.
We have no distinct evidence that granite is ever an eruptive rock,
i. e., that it has ever been forced upward through great fissures of the
earth's crust, and outpoured on the surface in the manner of lavas and
1 Some writers use the term syenite to designate a rock consisting of feldspar and
hornblende only. In this case syenite would differ from diorite only in the form of the
feldspar, which in the former is orthic (orthoclase), and in the latter clinic (plagioclase).
FIG. 1S6. Diagram illustrating Mode of Occurrence of
Granite.
TRAPPEAN OR FISSURE-ERUPTION ROCKS.
205
traps. Hence also ashes, cinders, tufas, or other evidences of contact
of a fused mass with the atmosphere, have never been found in connec-
tion with granites. Most geologists, therefore, believe that granite, al-
though it may be irruptive or intrusive by pressure, as explained above,
FIG. 187. Granite Veins.
is never an eruptive rock. Granitic rocks are most probably formed at
great depths, and remain where they are formed. Whenever, there-
fore, they appear on the surface, it is probable they have been exposed
by extensive denudation.
2. TRAPPEAN OR FISSURE-ERUPTION ROCKS.
Some geologists identify these with volcanic rocks, regarding their
lithological differences, especially their more crystalline structure, as the
result only of the fact that they have been subjected to erosion, which
has exposed their deeper parts, while of modern lavas we see only the
surface. But the distinctive character of these rocks consists not in
their age, but in their mode of occurrence, having come up through
fissures and spread out on the surface as extensive sheets, rather than
through craters, and run off in streams.
General Characteristics. Trappean rocks, differ from granitic in
being usually finer grained ; in usually, though not always, wanting
quartz and mica ; and in their mode of occurrence, explained below. In
general appearance they vary greatly. They are sometimes minutely
speckled with distinct crystals, sometimes compact or crypto-crystalline,
sometimes even glassy or scoriaceous or tufaceous, like modern lavas.
They consist usually of only two minerals, viz., feldspar (or other allied
mineral replacing) and hornblende or augite. These may be inti-
mately mixed or in distinct crystals.
Varieties. The varieties are so numerous and run by such insen-
sible gradations into each other, that it is useless to do more than
mention the principal types. Like granitic rocks, they are divided into
ACID 8EK1ES.
Porphyry,
Felstone,
Phonolite,
Trachyte,
Pumice,
Obsidian.
BASIC SERIES.
Diorite,
Dolerite,
Melaphyr,
Basalt,
Black obsidian.
206 UNSTRATIFIED OR IGXEOUS ROCKS.
two sub-groups a more acid and a more basic. In proportion as feld-
spar predominates, the rock is lighter colored and more acid ; in pro-
portion as hornblende or augite predominates, it is darker colored and
more basic. Felstone, phonolite, porphyry, trachyte, and the light-
colored obsidians, are types of the acid series ; diorite, dolerite, basalt,
and black obsidians, of the basic, as shown in the following table.
Phonolite is a grayish, crypto-crystalline rock, composed chiefly of
feldspar, which breaks or joints into thin slabs like slate, and rings under
the hammer. Felstone and petrosi-
lix have a composition similar to
phonolite. The term porphyry is
very loosely applied to a great va-
riety of rocks in which large crystals
are imbedded in a more compact
matrix. Felsite porphyry, which may
be considered the type, consists of a
grayish or reddish feldspathic mass, containing large crystals of lighter-
colored and purer feldspar. Quartz-porphyry contains distinct crystals
of quartz, etc. But any rock is called porphyritic which contains large
crystals, giving the mass a spotted appearance. Thus there may be a
porphyritic diorite, porphyritic diabase, or even porphyritic granite.
Trachyte is a light-colored, feldspathic rock, having a rough feel, from
the presence of small crystals of feldspar.
Diorite is a distinctly crystalline, and therefore a distinctly speckled,
dark-colored rock, consisting of feldspar and hornblende. Dolerite has
a similar general appearance, but finer grained, and a similar composi-
tion, except that augite replaces hornblende as the basic ingredient.
Melaphyr and diabase may be regarded as varieties of dolerite. Basalt
is a very dark, crypto-crystalline variety of dolerite. Many of these
more basic varieties of rock, when somewhat changed by weathering,
are called green-stones.
The glassy and scoriaceous varieties are found, but are not so com-
mon in the trappean as in the recent lavas.
These extreme varieties pass insensibly into each other by change
of proportion of their mineral ingredients, and into the granitic series
by the addition of quartz and mica. Some varieties of quartz-porphyry
thus pass into granite, and some varieties of diorite into syenite.
Mode of Occurrence. Trap-rocks usually occur in vertical sheets,
filling great fissures intersecting the strata, or in extensive horizontal
sheets outpoured on the surface. Sometimes similar sheets are found
between the strata as if outpoured on the sea-bottom, and afterward
covered with sediments. In some cases, however, such bedded traps
are metamorphic, and not truly eruptive. Trap-dikes (as the fillings
of fissures are called) vary in thickness from a few inches to fifty or
TRAPPEAN OR FISSURE-ERUPTION ROCKS.
207
Fio. 188,-Dikes.
even one hundred feet ; they are often fifty to one hundred miles long,
and extend downward to unknown depth. When there is no overflow-
ing portion observable, but the dike simply outcrops along the surface,
then it is probable either that the overflow has been subsequently removed
by erosion, or else that the liquid matter filled a fissure which originally
did not reach the surface (as at/, Fig. 184), and has subsequently been
exposed by erosion. In either case, such an outcropping dike is an
evidence of extensive denudation.
Sometimes the outcropping dike
has resisted the erosion more than
the country rock, and the dike is
left standing, like a low wall, run-
ning over the face of the country
(Fig. 188, a) ; at other times the
country rock has resisted more
than the dike, and the place of the dike is marked by a slight depression
like a ditch (Fig. 188, b). These appearances have given rise to the
term dike. They are represented in section in the figure.
Outpoured masses of fissure-eruption rocks are often of immense
thickness and extent, forming, in some cases, the chief bulk of whole
mountain-chains. There is also,
.mr.nmm _,
frequently, abundant evidence
of repeated outflows over the
same region, forming sheets,
piled one atop of another, as
shown in the figure. In such
cases, on account of the peculiar
columnar structure described on
page 209, the crumbling of the
rocks gives rise to somewhat regular terraces or benches. From this
circumstance has arisen the term trap, from the Swedish word trappa,
a stair.
The great lava-flood of the Northwest covers an area of 150,000 to
200,000 square miles, and is 3,000 to 4,000 feet thick in its thickest
part, where cut through by the Columbia River. In another place, at
least seventy miles distant, where cut into 2,500 feet deep by the Des-
chutes River, at least thirty successive sheets may be counted. Another
great lava-flood, according to Gilbert, covers 25,000 square miles of
Arizona, and is 3,000 feet thick in its thickest portions. 1
The scoriaceous and tufaceous conditions, though not so common as
in crater-eruption rocks, are also often found in connection with trap,
clearly indicating the contact of melted rock with the atmosphere.
Effect of Dikes on the Intersected Strata, The strata forming the
1 Wheeler's " Report Geology," 1874.
f---^^*-'""-'- ^ ^sU-ETT^ -7-J M^IJT _ - I~~
208 UNSTRATIFIED OR IGNEOUS ROCKS.
bounding walls of a dike are almost always greatly changed by the
intense heat of the fused matter. Limestones and chalk are changed
into crystalline marble ; clay is baked into porcelain jasper ; impure
sandstones are changed into a speckled rock resembling gneiss ; seams
of bituminous coal are changed into anthracite, or sometimes into coke.
In all cases the original stratification and the contained fossils are more
or less completely destroyed. These effects extend sometimes only a
few feet, sometimes many yards, from the dike itself.
Age how determined. "When two dikes intersect each other, then,
of course, the intersecting must be younger than the intersected dike.
In this manner the relative age of dikes intersecting the same region
may often be determined. The absolute age of igneous rocks can only
be determined by means of the strata with which they are associated.
If a dike is found either intersecting (c) or outpoured upon the sur-
face of strata of known age (t?, Fig. 184), the dike must be younger
than the strata. If a dike (c'), intersecting strata and outcropping on
the surface, is found overlaid by other strata through which it does not
break, then the igneous injection is younger than the former and older
than the latter. The series of events indicated is briefly as follows :
first, the older series of sediments has been formed ; then fissures
formed and filled by igneous injection ; then erosion has carried away
the upper portion of the strata and its included dike, so that the dike
outcrops along the eroded surface ; and, lastly, the whole has been
submerged and again covered with sediment.
3. VOLCANIC ROCKS.
Characteristics. Volcanic differ from trappean rocks, in being still
finer grained ; in being more frequently glassy, scoriaceous, and tufa-
ceous ; but especially in their mode of occurrence, having come up
through craters instead of fissures, running off as streams instead of
spreading as extensive sheets, and accumulating in the form of isolated
cones instead of covering great areas of country. Some believe, also,
that as a group they are more basic than either of the others.
Varieties. These have already been described under Volcanoes.
It is almost impossible to draw any clear lithologic distinction be-
.tween this and the last group. Many of the varieties described under
the last as, for example, trachyte and basalt, pumice and obsidian
belong equally here. The rocks of this group also are divisible into
two sub-groups : a feldspathic lighter-colored, more acid group ; and
an augitic darker-colored and more basic group. As already explained
under Volcanoes, both of these may exist under all the different physi-
cal conditions of stony, glassy, and scoriaceous lava, and also as sand
and ashes. Of the acid series, trachyte, the lighter-colored obsidians,
STRUCTURES FOUND IN ERUPTIVE ROCKS.
209
and pumice, are good types ; and of the basic series are basalt and the
black obsidian, and black scoriae.
Of Certain Structures found in many Eruptive Hocks.
Columnar Structure. Many kinds of eruptive rock, both trappean
and volcanic, exhibit sometimes a remarkable columnar structure.
This is most conspicuous in basalt, and is therefore often called basaltic
structure. Sheets and dikes of this rock are often found composed
wholly of regular prismatic jointed columns, closely fitting together,
FIG. 190. Columnar Basalt, New South Wales (Da
varying in size from a few inches to a foot or more, and in length from
several feet to fifty or one hundred feet. When these columns have
been well exposed on cliffs by the action of waves, or on river-banks by
the erosive action of currents, or even by atmospheric disintegration,
FIG. 191. Basaltic Columns on Se
2ntary Eock, Lake Superior (after Owen).
they produce a very striking scenic effect (Figs. 190, 191). In Europe
the Giant's Causeway, on the coast of Ireland, and Fingal's Cave, in
the island of Staffa, on the west coast of Scotland, are conspicuous ex-
amples. In the United States we have examples in Mount Holyoke,
14
210 UNSTRATIFIED OR IGNEOUS ROCKS.
on the Connecticut River ; in the Palisades of the Hudson River ; in
the traps on the shores of Lake Superior ; and especially in splendid
cliffs of the Columbia and Deschutes Rivers, in Oregon.
Direction Of the Columns. The direction of the columns is usually
at right angles to the cooling surface. In horizontal sheets, therefore,
the columns are vertical, but in dikes they are horizontal (Fig. 192).
A dike left standing above the general surface of country sometimes
FIG. 192. Columnar Dike, Lake Superior (after Owen).
presents the appearance of a long pile of cord-wood. In some cases
the columns are curved and twisted in a manner not easy to explain ;
sometimes, instead of columnar, a ball structure is observed.
Cause of Columnar Structure. There is little doubt that this
structure is produced by contraction in the act of cooling. Many sub-
stances break in a prismatic way in contracting. Masses of wet starch,
or very fine mud exposed to the sun, crack in this way. In basalt the
structure is more regular than in any other known substance. The
subject of the cause of jointed columnar structure has been very ably
discussed by Mr. Mallet. 1
Volcanic Conglomerate and Breccia. If a stream of fused rock,
whether from a crater or a fissure, run down a stream-bed, it gathers
up the pebbles in its course, and after solidification forms a conglom-
erate which differs from a true conglomerate (p. 171) in the fact that
the uniting paste is igneous instead of sedimentary. In a similar
manner volcanic breccias are formed by the flowing of a lava-stream over
a surface covered with rubble.
1 Philosophical Magazine, August and September, 1875.
OTHER MODES OF CLASSIFICATION OF IGNEOUS ROCKS. 211
Amygdaloid. Still another structure, very common in lavas and
traps, is the amygdaloidal. The rock called amygdaloid greatly resembles
volcanic conglomerate, being appar-
ently composed of almond-shaped peb-
bles in an igneous paste, but is formed
in a wholly different way. Outpoured
traps, and especially lava-streams, are
very often vesicular, i. e, filled with
vapor-blebs, usually of a flattened el-
lipsoidal form. In the course of time
these cavities are filled with silica,
carbonate of lime, or some other mate-
rial, by infiltrated water holding these
matters in solution. Sometimes the
filling has taken place very slowly by FlG " 193 -
successive additions of different-colored material. Thus are formed the
beautiful agate pebbles, or more properly amygdules, so common in trap.
The most common filling is silica, because water percolating through
igneous rocks is always alkaline, and holds silica in solution.
Other Modes of Classification of Igneous Hocks.
There is no subject connected with geology which is in a state of
greater confusion than the classification and nomenclature of igneous
rocks. It seems proper to mention some of the different views enter-
tained.
Many geologists think that the three groups mentioned above are
characteristic of different periods of the earth's history, and therefore
associated with strata of different ages. They think that granites are
associated only with the Archaean and Palaeozoic strata, traps with
Mesozoic, and volcanic rocks with Tertiary and modern strata, and that
therefore the earliest eruptions were granitic, then trappean, and last
volcanic.
Again, many think that erupted matters of different times have
become progressively more basic. They think that, although each group
may be divided into a more acid and a more basic sub-group, yet as a
whole the granitic group is the most acid, the volcanic most basic, and
the trappean intermediate, as shown in the diagram on page 212.
Again, these two views, usually held by the same persons, are by
them connected with a third view in regard to the original constitu-
tion of the earth's crust. On first cooling the outer layer is supposed
to have been highly oxidized and highly siliceous or acid, in other words
granitic; beneath was a less oxidized and less acid layer, and so on,
becoming less and less acid or more and more basic. The first erup-
tions were from the outer layer, and therefore granitic. Afterward,
212 UNSTRATIFIED OR IGNEOUS ROCKS.
as tlie solid crust grew thicker and thicker, the eruptions were from
deeper and deeper layers, and therefore more and more basic.
But as to age there can be no doubt that
. granite, though most commonly found in the
older rocks, is associated with strata of all
ages up to the Middle Tertiary ; and trappean
eruptions (if we use this term to mean fissure-
Acid. fcasic.
Granitic.
Granite. Syenite.
Trappean.
Porphyry. I Diorite.
, :
Volcanic.
Trachyte.
Basalt.
eruptions) have occurred until the later ter-
tiary. The granite of Mont Blanc was pushed
up about the end of the Eocene period (Lyell),
and the lava-flood of the Northwest was out-
poured from fissures in the Cascade Range at
the end of the Miocene. Also, as to compo-
sition^ trachyte has much the same compo-
sition as granite, except that more of the
silica is in combination and less of it free in
the former than in the latter. Similarly, the dark, very hornblendic
varieties of syenite have much the same chemical (though not miner-
alogical) composition as basalt.
Again, others, with great show of reason, think that much if not all
the difference between the three groups, in mineralogical character and
crystalline structure, is due to the different depths at which, and slow-
ness with which, the solidification took place ; for slowness of cooling
tends to produce a more complete separation and crystallization of
different minerals from the fused glassy magma ; they think, therefore,
that if trachyte could be traced down deep enough, it would be found
to pass into porphyry, and finally into granite, and similarly basalt
would become diorite, and finally dark syenites. 1 On this view, what
we cannot do, erosion has done for us ; and granite is most commonly
associated with the older rocks only because these have been most
eroded, and therefore their deeper parts exposed. Similarly, a less
erosion of the Mesozoic or Secondary rocks has exposed porphyries and
diorites. Of the modern lavas, only the upper parts are exposed. If
we take this view, then the only true distinction among igneous rocks
is founded on the mode of eruption, viz., fissure-eruption rocks and
crater-eruption rocks ; and each of these may assume the form of lava,
or trap, or granite, according to the depth of formation.
The confusion in the classification and nomenclature of igneous
rocks is still further increased by the undoubted fact that nearly all the
varieties of igneous rocks mentioned above are found also among meta-
morphic rocks, which have not been erupted at all. This subject is
further treated under the head of Metamorphism.
1 This gradual change has very recently been distinctly observed in Southeastern Eu-
rope by Judd. Geological Magazine, 1876, vol. xxxii., p. 292.
METAMORPHIC ROCKS. 213
CHAPTER IV.
METAMORPHIC ROCKS.
THERE is a third class of rocks, intermediate in character between
the ordinary sedimentary and the igneous rocks, and therefore put off
until these had been described. The rocks of this class are stratified,
like the sedimentary, but crystalline, and usually non-fossiliferous, like
the igneous rocks. They graduate insensibly on the one hand into the
true unchanged sediment, and on the other into true igneous rocks.
Origin. Their origin is evidently sedimentary, like other stratified
rocks, but they have been subsequently subjected to heat and other
agents which have changed their structure, sometimes entirely destroy-
ing their fossils and even their lamination structure, and inducing in-
stead a crystalline structure. The evidence of their sedimentary origin
is found in their gradation into unchanged fossiliferous strata ; the
evidence of their subsequent change by heat, in their gradation
into true igneous rocks. For this reason they are called metamorphic
rocks.
Position. All the lowest and oldest rocks are metamorphic. The
converse, however, viz., that metamorphic rocks are always among the
oldest, is by no means true. Metamorphism is not, therefore, a test of
age. Metamorphic rocks are found of all ages up to the Tertiary. The
Coast Range of California is much of it metamorphic, although the strata
belong to the Tertiary and Cretaceous periods. Metamorphism seems to
be universal in the Laurentian, is general in the Palaeozoic, frequent in
the Mesozoic, exceptional in the Tertiary, and entirely wanting in recent
sediments. It is therefore less and less common as we pass up the series
of rocks. The date of metamorphism is also different from that of
the origin of the strata. Metamorphism has taken place in all geologi-
cal periods, and is doubtless now progressing in deeply-buried strata.
Metamorphism is also generally associated with foldings, tiltings, in-
tersecting dikes, and other evidences of igneous agency, and is there-
fore chiefly found in mountainous regions. It is also usually found only
in very thick strata.
Extent on the Earth-Surface. These rocks exist, outcropping on
the surface, over wide regions. Nearly the whole of Canada and Labra-
dor, a large strip on the eastern slope of the Appalachians, and a large
portion of the mountainous regions of the western border of this con-
tinent, are composed of them. Beneath the surface they probably un-
derlie all other stratified rocks. Their thickness is also often immense.
214: METAMORPHIC ROCKS.
The Laurentian series of Canada is probably 40,000 feet thick, and
metamorphic throughout.
Principal Kinds. The principal kinds of metamorphic rocks are:
Gneiss, mica-schist, chlorite-schist, talcose-schist, hornblende-schist,
clay-slate, quartzite, marble, and serpentine.
Gneiss, the most universal and characteristic of these rocks, has the
general appearance and mineral composition of granite, except that it is
more or less distinctly stratified. Often, however, the stratification can
only be observed in large masses. Gneiss runs by insensible grada-
tions, on the one hand, into granite, and on the other, through the more
perfectly stratified schists, into sandy clays or clayey sands.
FIG. 194 Gneiss.
The schists are usually grayish fissile rocks, made up largely of scales
of mica, or chlorite, or talc. Hornblende-schist is similarly made up of
scales of hornblende, and is therefore a very dark rock. The fissile
structure of schists is due to the presence of these scales, and is therefore
wholly different from that of slates. It is called foliation-structure.
/Serpentine is a compact, greenish magnesian rock. The other varie-
ties need no description. Hornblende-schists run by insensible grada-
tions into clay-slates on the one hand, and into diorites and syenites on
the other.
All these kinds may be regarded as changed sands, limestones, and
clays, the infinite varieties being the result of the difference in the original
sediments and the degrees of metamorphism. Sands and limestones are
often found very pure ; such when metamorphosed produce quartzite and
marble. Clays, on the contrary, are almost always impure, containing
sand, lime, iron, magnesia, etc. Such impure clays, if sand is in excess,
produce by metamorphosis gneiss, mica-schist, and the like ; but if
lime and iron are in considerable quantities they produce hornblende-
schist or clay-slate ; if magnesia, talcose-schist. The origin of serpen-
tine is not well understood ; but it is evidently a changed magnesian
clay. All gradations between such clays and serpentine may be found
in the Tertiary and Cretaceous strata of the Coast Range of California.
THEORY OF METAMORPHISM. 215
Theory of Metamorphism.
There are few subjects more obscure than the cause of metamor-
phism, and the conditions under which it occurs. Some important light
has been thrown on it, however, recently. For the sake of clearness, it
will be better to divide metamorphism into two kinds, somewhat dif-
ferent in their causes, viz., local and general.
Local Metamorphism is that produced by direct contact with evident
sources of intense heat, as when dikes break through stratified rocks.
As already seen (p. 207), under these circumstances, impure sandstones
are changed into schists, or into gneiss ; clays, into slates, or into porce-
lain jasper; limestones, into marbles; and bituminous coal, into coke,
or into anthracite. In these cases it is evident that the cause of the
change is the intense heat of the incandescent, fused contents of the
dike at the moment of filling. In such cases of local metamorphism, the
effects usually extend but a few yards from the wall of the dike.
General Metamorphism. But in many cases we cannot trace the
change to any evident source of intense heat. Rocks, thousands of feet
in thickness, and covering hundreds of thousands of square miles, are
universally changed. The principal agents of this general metamorphism
seem to be heat, water, alkali, pressure.
That heat is a necessary agent is sufficiently evident from the gen-
eral similarity of the results to local metamorphism. But that the heat
was not intense, and therefore not sufficient of itself to produce the ef-
fects, is also quite certain. For (a.) metamorphic rocks are often found
interstratified with unchanged rocks. Intense heat would have affected
them all alike, or nearly alike. (#.) Many minerals are found in meta-
morphic rocks which will not stand intense heat. As an example, carbon
has been found in contact with magnetic iron-ore, although it is known
that this contact cannot exist, even at the temperature of red-heat, with-
out reduction of the iron-ore, (V.) The effect of simple dry heat, as
shown in cases of local metamorphism, does not extend many yards.
(d.} Water- cavities are found abundantly in metamorphic rocks. This
will be more fully explained farther on.
Water. Heat combined with water seems to be the true agent.
Recent experiments of Daubree, Senarmont, and others, prove that
water at 400 C. (= 752 Fahr.) reduces to a pasty condition nearly all
ordinary rocks ; moreover, that at this temperature crystals of quartz,
feldspar, mica, augite, etc., are formed. Such a pasty or aqueo-fused
mass slowly cooled would form a crystalline rock containing crystals of
quartz, feldspar, mica, etc. ; in other words, would be metamorphic. The
quantity of water necessary for these effects is shown by experiment
to be very small only five to ten per cent. In other words, the in-
cluded water of sediments is amply sufficient.
216 METAMORPHIC ROCKS.
Alkali. Alkaline carbonates, or alkaline silicates, so common in
natural waters, greatly promote the process, causing the aqueo-igneous
pastiness or aqueo-igneous fusion to take place at a much lower tem-
perature.
Pressure. Simple pressure is not itself a direct agent, but the
necessary condition for the action of the others, since it is impossible to
have high temperature in the presence of water without corresponding
pressure.
It is evident, therefore, that while metamorphism by dry heat would
require a temperature of 2,000 to 3,000, in the presence of water the
same result is produced at 300 or 400 C. ; or in the presence of alkali,
even in small amount, probably at 300 or 400 Fahr.
Application. All these agents are found associated in deeply-buried
sediments. Series of outcropping strata are often found 20,000 or even
40,000 feet thick. The lower strata of such a series, by the regular
increase of interior heat alone, must have been, before uptilting, at a
temperature of between 700 and 800 Fahr., a temperature sufficient,
with their included water, to produce complete aqueo-igneous pasti-
ness, and therefore, by cooling and crystallization, complete meta-
morphism.
Suppose, then, a b 5, Fig. 195, represent the contour of land and
sea-bottom at the beginning of any period, and the dotted line i i the
FIG. 195. Diagram illustrating the Invasion of Sediments by the Interior Heat.
isogeotherm of 800. If, now, sediments 40,000 to 50,000 feet thick
be deposited so that the sea-bottom is raised to V b', then the isotherm
of 800 will rise to i' i' and invade the lower portions of the sediments
with their included water. Such sediments would be completely
changed in their lower portions, and to a less extent higher up. It is
probable that even 300 to 400 Fahr. is sufficient to produce a consid-
erable degree of change ; or even 200, if alkali be present.
Crushing. Although simple gravitative pressure is only a condi-
tion, and not a cause, of heat, horizontal pressure with crushing of the
crust, by the conversion of mechanical energy into heat, becomes, as
Mallet has shown, 1 an active source of this agent. Now, in all cases
1 "Philosophical Transactions," 1873, p. 147.
ORIGIN OF GRANITE. 217
of metamorphism we find ample 'evidences of such horizontal crushing
in the associated foldings and cleavage of the strata.
Explanation Of Associated Phenomena. This theory readily ex-
plains 1. Why metamorphism is always associated with great thick-
ness of strata; 2. Why the oldest rocks are most commonly meta-
morphic, since these have usually had the newer rocks piled upon
them, and have been subsequently exposed by erosion. The newer
rocks are sometimes also metamorphic, but in these cases they are very
thick. 3. It also explains the interstratification of metamorphic with
unchanged rocks ; since some rocks are more easily affected by heated
water than others, and the composition of the included water may be
also different, some containing alkali and some not. 4. It also explains
its association with foldings of strata and with mountain-chains, as will
be more fully explained hereafter.
If metamorphism is only produced in deeply-buried sediments, then
the exposure of such rocks on the surface can only result from exten-
sive erosion.
Origin of Granite.
There is much reason to believe that most granites are npt the re-
sult of simple dry fusion, as is usually supposed ; but, on the contrary,
only the last term of metamorphism of highly-siliceous sediments. Ac-
cording to this view, incipient pastiness by heat and water makes
gneiss ; complete pastiness, completely destroying stratification, makes
granite. The principal arguments for this view may be briefly stated
as follows : 1
1. In many localities in mountain-regions, and nowhere better than
in the Sierras of California, every stage of gradation may be observed
between clayey sandstones and gneiss, and between gneiss and granite.
So perfect is this gradation, that it is impossible to draw sharply the
distinction. Even geologists who believe that granite is the primitive
rock have been compelled to admit that there is also a metamorphic
granite, scarcely distinguishable from primitive granite.
2. Not only gneiss, but even granite, is sometimes interstratified
with unchanged fossiliferous rock.
3. Chemists recognize two kinds of silica, viz., an amorphous va-
riety of specific gravity 2.2, and a crystallized variety, specific gravity
2.6. These two varieties differ from each other not only in density,
but also in chemical properties, the former being much more easily
attacked by alkalies than the latter. By solidification from fusion (dry
way) only the variety of specific gravity 2.2 can be formed, while the
variety 2.6 is formed only by slow deposit from solution (humid way).
1 Rose, Philosophical Magazine, xix., p. 32 ; Delesse, " Archives des Sciences," vol.
vii., p. 190; Hunt, American Journal of Science and Arts, new series, vol. i., pp. 82, 182.
218 METAMORPHIC ROCKS.
Now, the quartz of granite is always of the variety 2.6, and therefore
must have been formed in presence of water.
4. The several minerals of which granite is composed will not sep-
arate from a fused granitic magma on cooling; but, on the contrary,
fused granite solidifies into a highly-siliceous glass. The only answer
to this, as well as to the preceding, is that the behavior of the granitic
magma, when fused on a large scale and cooled slowly in the laboratory
of Nature, is possibly different from its behavior when melted in small
masses and cooled less slowly in our laboratories.
5. Crystals of quartz, feldspar, and mica, are frequently formed in
Nature by the humid process, as, for example, in, metamorphic rocks ;
and have also been artificially formed by the same process by Daubree,
Senarmont, and others, as already stated (p. 215) ; but they have never
been formed artificially by the dry way.
6. In nearly all rocks and minerals microscopic cavities are found
indicating the conditions under which crystallization or solidification
took place. If crystals are formed by sublimation, they contain vacu-
ous cavities. If they are formed by solidification from fusion (dry
way), and if gases are present, they may contain air-blebs ; but, if they
crystallize slowly from a glassy magma, they contain spots of glassy
matter or glass cavities, as in slags and lavas. If they are formed by
crystallization from solution, then they have fluid cavities. Now, not
only are these fluid cavities found in metamorphic rocks, but also in the
quartz and feldspar of granite. " A thousand millions of these micro-
scopic cavities in a cubic inch is not at all unusual ; and the inclosed
water often constitutes one to two per cent, of the volume of the
quartz." * Besides these fluid cavities, however, glass cavities are also
found in the quartz and feldspar of granite. These facts point plainly
to the agency of both heat and water in the formation of granite.
Even the temperature at which metamorphic rocks and granite
solidified has been approximately determined by Mr. Sorby. The prin--
ciple on which this is done is as follows : If crystallization from solution,
or solidification in the presence of water, take place at ordinary temper-
atures, then the fluid cavities will be full ; but if at high temperatures,
and the mass subsequently cools, then by the contraction of the con-
tained liquid a vacuous space will be formed which will be larger, in
proportion to the amount of contraction, and therefore to the tempera-
ture of solidification. Knowing, therefore, the relative sizes of the
vacuole and the contained water, and the coefficient of expansion of the
water and the rock, the temperature at which the cavity would fill
(which is the temperature of solidification) may be calculated. Some-
times this temperature may be gotten by actual experiment, i. e., by
heating until the cavity fills. By this method Mr. Sorby has calculated
1 Sorby, Quarterly Journal of the Geological Society, vol. xiv., pp. 3*29, 453.
ORIGIN OF GRANITE. 219
the temperature of solidification of certain metamorphic rocks of Corn-
wall as 392 Fahr., and of some granites as 482, and others only 212.
It seems almost certain, therefore, that most granites have not been
formed by dry, igneous fusion. Yet that this rock has been in a liquid or
pasty condition is perfectly certain from its occurrence in tortuous veins.
Therefore it has been rendered pasty by heat in the presence of water
under great pressures, such as always exist in deeply -buried strata. The
weight of the superincumbent strata, or else pressure by folding and
crushing of the strata, has forced it into cracks and great fissures.
What we have said of granite applies of course to the whole gra-
nitic group. Granitic rocks are often only the last term of the metamor-
phism cf sediments ; granite being produced from the more siliceous
sediments, and dark syenites from the mere basic impure clays. But
we cannot stop with this group. It is certain that many if not all the
rocks of the Trappean group also may be made by metamorphism of
sediments. Many bedded diorites, dolerites, and felsites, are undoubt-
edly formed in this way, for the gradations can be distinctly traced into
slates. Prof. Dana * has recently recognized this as so certain that he
proposes the addition of the prefix metct to these to indicate their
origin. Thus he recognizes a syenite and a metasyenite, a diorite and
a metadiorite, dolerite and metadolerite, felsite and metafelsite, etc.,
and we might add granite and metagranite.
Many geologists push these views so as to include also even the
true lavas. Deeply-buried sediments under gentle heat in the presence
of water and pressure undergo incipient change and form metamorphic
rocks ; under greater heat become pasty and form granite, metasyenites,
metadiorites, metafelsites, etc. ; under still greater heat, increased
probably, as Mallet suggests, by mechanical energy in crushed strata
being converted into heat, become completely fused, and are then out-
poured upon the surface either by the elastic force of the steam gener-
ated, or by the pressure and squeezing produced by the folding of the
crust of the earth, so common in mountainous regions. According to
this view, every portion of the earth's crust has been worked over and
over again, passing through the several conditions of soil, sediment,
stratified rock, metamorphic rock, and igneous rock, perhaps many
times in the course of the geological history of the earth, and we look
in vain for the primitive rock of the earth's crust.
1 American Journal of Science and Arts, vol. xi., p. 119, February, 1876.
220 STRUCTURE COMMON TO ALL ROCKS.
CHAPTER V.
STRUCTURE COMMON TO ALL ROCKS.
WE have thus far given a brief description of the three classes of
rocks, their structure and mode of occurrence. There are still, how-
ever, several important kinds of structure which are common to all
these classes of rocks, and require description. These are joints, fissures,
and veins. Mountain-chains, as involving all kinds of rocks and all
kinds of structure, must be taken up last.
SECTION 1. JOINTS AND FISSURES.
Joints.
All rocks, whether stratified or igneous, are divided, by cracks or
division-planes, in three directions, into separable irregularly prismatic
blocks of various sizes and shapes. These cracks are called joints. In
stratified rocks the planes between the bedding constitute one of these
division-planes, while the other two are nearly at right angles to this
and to each other, and are true joints. In igneous rocks all the
division-planes are of the nature of joints. In sandstone these blocks
are large and irregularly prismatic ; in slate, small, confusedly rhom-
Fio. 196. Regular Jointing of Limestone.
boidal ; in shale, long, parallel, straight ; in limestone, large, regular,
cubic; in basalt, regular, jointed, columnar ; in granite, large, irregularly
cubic or irregularly columnar. On this account a perpendicular rocky
FISSURES, OR FRACTURES.. 221
cliff usually presents the appearance of huge, irregular masonry, with-
out cement.
The cause of joints is probably the shrinkage of the rock in the act
of consolidation from sediments (lithification), as in stratified rocks, or
FIG. 197. Granitic Columns.
in cooling from a previous condition of high temperature, as in the
igneous and metamorphic rocks.
Fissures, or Fractures.
These must not be confounded with joints. Joints are cracks in
the individual strata or beds; fissures are fractures in the earth's
crust, passing through many strata, and even sometimes through many
formations. The former are produced by shrinkage ; the latter by
movements of the earth's crust. Fissures, therefore, are often fifty or
more miles in length, thirty to fifty feet in width, and pass downward
to unknown but certainly very great depths.
Cause. The cause of great fissures is evidently always movements,
and usually foldings or wrinkling of the earth's crust, produced probably
by contraction of the interior portions, as will be explained under Moun-
tain-Chains, page 240. The natural tendency of such foldings would be
to form a parallel system of fissures in the direction of the folds, and
therefore at right angles to the direction of the folding force. Fissures
are usually thus found in systems parallel among themselves, and to
the axes of mountain-chains. Through such fissures igneous rocks in a
fused condition are often forced, forming dikes and overflowing sheets.
Besides the principal fissures just explained, Hopkins has shown that,
in the case of the formation of mountains, there would be formed also
other smaller fissures at right angles to these.
Often the walls on the two sides of a fissure do not correspond with
each other, but one side has been pushed up higher or dropped down
lower than the other. Such a displacement is called a fault, a slip, or
dislocation. This may occur in fissures in any kind of rock, but is most
marked and most easily distinguished in stratified rocks. When the
222
STRUCTURE COMMON TO ALL ROCKS.
strata are sufficiently flexible to admit it, they are bent instead of brok-
en, and a monocline is formed instead of a fault (Fig. 198). When the
fissure is filled at the moment of its formation with fused matter from
beneath, it is called a dike. When it is not filled at the moment of its
formation with igneous injection, but slowly afterward with other mat-
ter, and by a different process, it is called a vein.
FIG. 19S. -Section of Nutria-Fold, New Mexico (after Gilbert).
Faults. In faults the extent of vertical displacement varies from a
few inches to hundreds or even thousands of feet. In the Appalachian
chain there occur faults in which the vertical dislocation is 5,000 to
20,000 feet. In Southwest Virginia, according to Rogers, there is a
line of fracture extending parallel to the Appalachian chain for eighty
miles, in which there is a vertical slip of 8,000 feet, 1 the Lower Silurian
being brought up on one side until it comes in conjunction with the
Lower Carboniferous on the other (Fig. 199). In Western Pennsylvania,
FIG. 199.-Fault in Southwest Virginia : a, Silurian ; d, Carboniferous (after Lesley).
according to Lesley, there is another fault extending for twenty miles,
in which the lowermost of the Lower Silurian is brought up on a level
with the uppermost of the Upper Silurian, the whole Silurian strata be-
ing at this place 20,000 feet thick, so that one may stand astride of the
fissure with one foot on the Trenton limestone (Lower Silurian), and
the other on the Hamilton shales (Devonian). 2 On the north side of
the Uintah Mountains there is a slip, according to Powell, of nearly
20,000 feet, 3 The Sevier Valley fault, Utah, may be traced partly as a
slip, partly as a monocline, for 225 miles (Gilbert).
1 Dana's " Manual," p. 399. 5 " Manual of Coal," p. 147.
3 " Exploration of Colorado River," p. 156.
FISSURES, OR FRACTURES.
223
If such slips were suddenly produced by violent convulsion, then, at
the time of formation, there must have been a steep (Fig. 200), or
sometimes even an overhanging, escarpment (Fig. 199), equal to the
displacement. In some cases there is such an escarpment or line of
steep mountain-slope corresponding to the line of slip. In the Colo-
rado Plateau region the north and south cliffs are produced by faults
(Powell). The Zandia Mountains, New Mexico, are produced by a
Fit;. 200.
drop of 11,000 feet on the western side, leaving an escarpment still
7,000 feet high (Gilbert). In the Basin Range region also many of
the ridges are formed by faults. But in most cases there is no such
escarpment, the two sides of the fault having been cut down to one
level by subsequent erosion, so that the unpractised eye detects nothing
unusual along the line of fracture and slip. In Fig. 200 the strong
I
FIG. 201. Strata repeated by Faults.
line a a shows the present surface, while the dotted line bbb shows the
surface after the displacement as it would be if unaffected by erosion.
In many cases, however, it seems more probable that there never
existed any such escarpment as represented in Fig. 200, but that the
displacement was produced by a slow, creeping motion, or else by a
succession of smaller sudden slips probably accompanied with earth-
224
STRUCTURE COMMON TO ALL ROCKS.
quakes (p. 106), and thus that the slipping and the denudation have
gone on together pari passu. In Fig. 243, on page 263, the upper
part shows the great Uintah fault restored, while the lower part shows
the actual condition of things produced by erosion.
FIG. 202. Section through Portion of Plateau Region of Utah, showir
(after Howell).
: a Succession of Faults
When faults occur in inclined outcropping strata, the same series
of strata may be repeated several times, as in Fig. 201. In such a
case, the observer walking over the surface of the cbuntry from A to B
FIG. 203.-Fault with Change of Dip: d, dike.
might suppose here a series of nine strata, whereas there are but three
strata, a, b, c, three times repeated. Fig. 202 is a natural section show-
ing this. Sometimes the dip of the
strata on the two sides of a fault are
not parallel, the change of inclination
being effected at the time of the dis-
placement, as shown in Fig. 203. Upon
the eroded surface of such dislocated
strata, by subsequent subsidence, other
strata may be unconformably depos-
ited (Fig. 204).
FIG. 204. Unconformity on Faulted Strata.
Law of Slip. In faults the plane of fracture is sometimes vertical,
but much more generally it is more or less inclined. In such cases, in
by far the larger number of great faults, the strata on the upper side
(hanging wall) of the fracture have dropped down, while the strata on
the lower side (foot-wall) have gone up, as in Figs. 205 and 206. This
would probably be the case if, after the fracture, the relation of parts
was adjusted by gravity alone. In some cases of strongly-folded strata,
however, the hanging wall seems to have been pushed and made to
slide upward over the foot-wall as if by powerful horizontal squeezing.
This is the case with the great slip in Southwestern Virginia, repre-
sented in Fig. 199. Examples of this kind, however, are exceptional.
In several hundred cases of great fissures, examined by Phillips, in
MINERAL VEINS.
225
England, nearly all followed the law given above. 1 Fig. 205 is a sec-
tion across Yarrow Colliery, in which all the slips follow this law. Of
FIG. 205. Section across Yarrow Colliery, showing the Law of Faults (after De la Beche).
the numerous slips figured by Powell, Gilbert, and Howell, as occurring
in the Plateau and Basin Range region, nearly all follow this law. Fig.
206 is a section illustrating this fact.
East *
FIG. 206. Section of Pahranagat Range, Nevada, showing the Law of Faults (after Gilbert).
SECTION 2. MINERAL VEINS.
All rocks, but especially metamorphic rocks in mountain-regions,
are seamed and scarred in every direction, as if broken and again
mended, as if wounded and again healed. All such seams and scars, of
whatever nature and by whatever process formed, are often called by
the general name of veins. It is better, however, that dikes and so-
called granite-veins, or all cases of fissures filled at the moment of
formation by igneous injection, should be separated from the category
of veins. True veins, then, are accumulations, mostly in fissures, of
certain mineral matters usually in a purer and more sparry form than
they exist in the rocks. The accumulation has in all cases taken place
Kinds. Thus limited, veins are of three kinds : Veins of segrega-
tion, veins of infiltration, and great fissure-veins. These three, how-
ever, graduate into each other in such wise that it is often difficult to
determine to which we must refer any particular case. Some writers
make many other kinds.
1. Veins of Segregation. In these the vein-matter does not differ
greatly from the inclosing rock. Such are the irregular lines of granite
in granite, the lines differing from the inclosing rock only in color or
texture ; also irregular veins of feldspar in granite or in gneiss. Under
the same head belong also the irregular streaks, clouds, and blotches, so
1 Phillips's " Geology," p. 35.
, 15
226 STRUCTURE COMMON TO ALL ROCKS.
common in marble. In these cases there seems to be no distinct line of
separation between the vein and the inclosing rock no distinct wall to
the vein. The reason is, these veins are not formed by the filling of a
previously-existing fissure, but by the segregation of certain materials,
in certain spots and along certain lines, from the general mass of the
rock, either when the latter was in plastic condition from heat and
water, or else by means of percolating water, somewhat as concretions
of lime, clay, iron-ore, and flint, are formed in the strata (p. 188).
2. Veins of Infiltration. Metamorphic rocks have, probably in all
cases, been subjected to powerful horizontal pressure. Besides the wide
folds into which such rocks are thus thrown and the great fissures thus
produced, the strata are often broken into small pieces by means of the
squeezing and crushing. The small fissures thus produced are often
filled by lateral secretion from the walls, or else by slowly-percolating
waters holding in solution the more soluble matters contained in the
rocks. The process is similar to the filling of cavities left by imbedded
organisms (p. 193), and still more to the filling of air-blebs in traps and
lavas, and the formation of agates and carnelian amygdules (p. 211).
In veins of this kind, therefore, a beautiful ribbon-structure is often
produced by the successive deposition of different-colored materials on
the walls of the fissure. Veins of this kind also, since they are the
filling of a previously-existing fissure, have distinct walls. The filling
consists most commonly of silica or of carbonate of lime.
3. Fissure - Veins. These are fillings of the great fissures produced
by movements of the earth's crust. When these fissures are filled at
the time of formation by igneous injection, they are called dikes ; but
if subsequently with mineral matter, by a different process, to be dis-
cussed hereafter, they are fissure-veins. These veins, therefore, like
dikes, outcrop over the surface of the country often for many miles,
fifty or more. Like dikes, also, they are often many yards in width,
and extend to unknown, but certainly very great, depths. Like dikes
and fissures, also, they occur in parallel systems.
Characteristics. The most obvious characteristics of the veins of
this class are their size, their continuity for great distances and to
great depths, and their occurrence in parallel systems. As the vein
is a filling of a previously-existing fissure, the distinction between the
vein and the wall-rock is usually quite marked. In many cases, in fact,
the vein-filling is separated from the wall-rock by a layer of earthy or
clayey matter called a selvage, as if the sides of the open fissure had
become foul by percolating waters carrying clay, before the fissure was
filled with mineral matter. The contents of fissure-veins are also far
more varied than those of other classes.
Irregularities. Although more regular than other kinds, yet fis-
sure-veins are also often quite irregular sometimes branching, some-
MINERAL VEINS.
227
times narrowing or pinching out in some parts and widening in others
(Fig. 207), sometimes dividing and again coming together, and thus
inclosing a portion of the wall-rock (Fig. 208). Such an inclosed mass
of country rock in the midst of a vein is called a " horse" Many of
these irregularities are probably the result of movements after the fis-
sure was formed, or even after it was filled. Thus, it abed (Fig. 207)
be one wall of an irregular vein, then it is probable that a' b' c d' was
the original position of this wall ; but, before it was filled, it slipped up
FIG. 20T. -Irregularities in Veins.
Fto. 208. Irregularities of Veins.
to its present position. Again, movements may reopen a fissure after
it is filled. In such cases, if the adhesion of the filling to the wall is
strong, portions of the wall- rock are torn away; and if a second filling
takes place, a " horse " is formed. Thus aaa and bbb (Fig. 208)
represent the two original walls of an irregular vein ; but subsequent
movement reopened the fissure to b' b' b' and tore away the horse H,
after which the vein was again filled.
Veins, of course, usually intersect the strata; but in some cases
where strata-planes, or else cleavage-planes, are highly inclined, the
opening is between these planes, and the veins are, therefore, conform-
able with them.
Metalliferous Veins. Some metals, particularly iron, occur prin-
cipally in great beds, being accumulated by a process already described
(p. 136). Others, especially lead, often accumulate in flat cavities be-
tween the strata, especially of limestone. But most metals occur in
veins. All the kinds of veins mentioned above may contain metals, but
the segregative veins are usually too irregular and uncertain, and the
infiltrative veins too small, to be profitable. True, profitable metal-
liferous veins are almost always great fissure-veins. We will speak,
therefore, only of these, and the further description of fissure-veins is
best undertaken under this head.
Contents. The contents of metalliferous veins are of two general
228 STRUCTURE COMMON TO ALL ROCKS.
kinds, viz., vein-stuffs and ores. The principal vein-stuffs are quartz,
carbonate of lime (calc-spar), carbonate of baryta, carbonate of iron,
sulphate of baryta (heavy spar), and fluoride of calcium (fluor-spar).
By far the most common of these is quartz, and next is calc-spar.
Often, however, the vein-stuff is an aggregate of minerals forming a true
rock. Nearly the whole of a vein consists usually of vein-stuff. The
ore exists in comparatively small quantities, sometimes forming a cen-
tral rib or sheet, as if deposited last (Fig. 209) ; sometimes in irregular
isolated masses called bunches or pockets, or in small strings, or grains,
irregularly scattered through the vein-stuff and extending often a little
way into the wall-rock.
The chemical forms in which metals occur are very various ; some-
times they occur as pure metal (as always in the case of gold and plat-
inum, and sometimes in the case of silver and copper), but more com-
monly in the form of metallic sulphides, metallic oxides, and metallic
carbonates. Of these the metallic sulphides are by far the most com-
mon. It is worthy of remark that all these forms are comparatively
very insoluble. The same is true of the vein-stuffs.
Ribboned Structure. The ribboned or banded structure, already
spoken of under Veins of Infiltration, is very commonly found in great
fissure-veins. This structure is as characteristic of veins as the colum-
nar structure is of dikes. The layers on the two sides usually corre-
spond to each other (Fig. 209) ; sometimes the successive layers are of
different color, giving rise to a beautiful, striped appearance. Some-
times the successive layers on both sides are of different materials, as
in Fig. 210, in which the central rib, <7, is galena, and a or, b b, c c, are
successive layers of quartz, fluor, and baryta. Sometimes, in cases of
quartz-filling, the layers are agate, except the centre, which is filled up
with a comb of interlocking crystals, as in Fig. 211. The same occurs
often in amygdules, the last filling being crystalline. Sometimes there
is evidence of successive openings and fillings, as in Fig. 212, where a
represents quartz crystals, interlocking in the centre and based on agate
layers, b b, while c represents quartz with disseminated copper pyrites.
MINERAL VEINS.
229
In this case it seems probable that 1 and 2 were the walls when the
agate and quartz filling took place, and that afterward the fissure was
I CL I
FIG. 211.
reopened along 2, so that the walls became 2 and 3, and the new fis-
sure thus formed was filled with cuprif-
erous quartz. The same is well shown
in Fig. 213, where a, #, c, <?, e,/", are
successive quartz-combs, separated by
2, 3, 4, 5, 6, which are clay selvages, and
therefore old walls.
Age. The relative age of veins in
the same region is determined in the
same way as that of dikes, viz., by the
manner in which they intersect each other; the intersecting vein being,
of course, younger than the intersected vein. Thus in Fig. 214, which
is a section of a hill-side in Cornwall, it is evident that the tin-vein, ,
is the oldest, since it is intersected and slipped by all the others. The
copper-vein, #, is older than the
clay-filled fissure, c. There is
a fourth fissure, d, younger than
, but its relation to b and c is
not shown in the section.
The absolute age of fissure-
veins, or the geological period
in which the fissure was formed,
can only be determined by the
stratified rocks through which
it breaks. The lead-veins of
Cornwall (b b, Fig. 216) break
through the Cretaceous. Their fissures were probably formed by the
changes or oscillations which closed the Cretaceous and inaugurated the
Tertiary period. The auriferous veins of California break through the
Jurassic ; and, as there are good reasons for believing that the Sierras
were formed at the end of the Jurassic, it is probable that these fissures
230 STRUCTURE COMMON TO ALL ROCKS.
were formed at that time, by the foldings of the strata consequent upon
the pushing up of this range. The filling, of course, was a slow, sub-
sequent operation, but commenced then.
Surface-Changes. Mineral veins seldom or never outcrop on the
surface in the condition we have described them. On the contrary,
there are certain changes which they undergo through the influence of
atmospheric agencies, which render their appearance along their out-
crop quite different from that of the same vein at some depth below.
A knowledge of these changes is, of course, of the greatest practical
importance. They are, however, extremely various, differing not only
according to the metallic contents, but also according to the nature of
the vein-stuffs, and therefore must be learned by observation in each
country. We will give three of the most constant as illustrations.
Cupriferous Veins. The original form in which copper seems to
exist in veins is copper pyrites, a double sulphide of copper and iron
(CuFe a S a ). Now, along the back or outcrop of copper-veins, to a depth
of thirty to sixty feet, the vein usually contains no copper at all, but
consists of vein-stuff (more or less changed, according to its nature),
among which are scattered masses of a dark reddish or brownish
hydrated peroxide of iron, in a light, spongy condition. This peculiar
form of peroxide of iron, so characteristic of the outcrop of copper-
veins, is called by the Cornish miners gossan, and by the German and
French miners iron hat (eiserner hut ; chapeau defer). Below the influ-
ence of atmospheric agencies the vein is in its original condition, i. e.,
consists of vein-stone containing disseminated masses of copper pyrites.
Just at the junction of the changed with the unchanged vein i. e., run-
ning along the back of the vein
at a depth varying from thirty
to sixty feet occur rich accu-
mulations of copper, as native
copper, red and black oxides of
co PP"'S reen and """ carbon-
ates of copper, etc. These facts
are illustrated by Fig. 215,
which * a section O f the D UC k-
town mines of Tennessee. The
irregular line, s s, is the outline
of a hill, along the crest of
FIG. 215.-Ducktown (Tennessee) Copper- Vein, showing which the Vein Outcrops ; the
Surface-Changes (after Safford). \ '
part b consists almost wholly of
gossan, with only small masses of quartz-vein stuff ; a is the rich accu-
mulation of copper-ore, here about two or three feet thick ; and c is
the unchanged vein, consisting of vein-stuff, inclosing arsenical pyrites,
and copper pyrites in very large quantities.
MINERAL VEINS. 231
These phenomena may be explained as follows : There can be no
doubt that the gossan represents copper pyrites, from which the copper
has been entirely washed out, leaving the iron in an oxidized condition.
Thus the whole of the copper from b (and probably from much more
than 5, for the process of denudation has gone on pari passu with the
process of leaching) has been leached out and accumulated at a. Fur-
ther, it is probable that the process was as follows : When copper
pyrites is exposed to moist air, the copper, iron, and sulphur, are
all oxidized, forming sulphate of copper and oxide of iron, thus :
2(CuFeS a ) + HO=2CuSO 4 + Fe 2 O 3 . The soluble sulphate is then washed
out and carried downward, while the insoluble iron peroxide is left
in a spongy condition. This much seems certain, but by what sub-
sequent process the copper takes all the forms actually found at a, is
little understood, although it is probable that the carbonate is produced
by the reaction on the sulphate of waters containing alkaline carbonate
or bicarbonate of lime. 1
PlumMferous Veins. The natural or original form in which lead
occurs in veins is sulphide of lead, or galena. But along the backs or
outcrops of lead-veins it is found more commonly as carbonate. The
explanation seems to be as follows : Lead occurs mostly in veins inter-
secting, or in sheets between, strata of limestones. It is probable that
the galena (PbS) is oxidized by meteoric agencies and becomes sulphate
(PbSOJ, and then the sulphate, by reaction with the carbonate of lime
derived from the wall-rock or from the calc-spar of the vein-stuff, be-
comes carbonate, thus: PbSO 4 +CaCO 3 =PbCO 3 + CaS0 4 . In proof
of this process it is stated 2 that galena, thrown out of the old mines of
Derbyshire among rubbish of limestone, has all, in the course of ages,
been changed into carbonate.
Auriferous Quartz- Veins. Gold is found either in quartz-veins in-
tersecting metamorphic slates (quartz-mines) or in gravel-drifts in the
vicinity of these (placer-mines). Originally it existed in the quartz-
veins usually associated with metallic sulphides, particularly the sul-
phide of iron (pyrites). If the pyrites be dissolved in nitric acid, the
gold is left as minute threads and crystals. Evidently, therefore, it exists
in minute threads and crystals scattered through the pyrites. Now,
when such a vein is exposed to meteoric agencies, the pyrites is oxi-
dized, partly as soluble sulphate, and carried away, and partly as insol-
uble reddish peroxide, which remains. 3 The quartz-vein stone is, there-
fore, left in a honey-comb condition by the removal of the pyrites, and
1 Bischof, " Chemical and Physical Geology." vol. iii., p. 509.
2 De la Beche, " Geological Observer," p. 794.
3 Probably the iron sulphide is oxidized to the condition of sulphate, then reduced to
carbonate by water containing alkaline carbonate or bicarbonate of lime, and lastly per-
oxidized by exchanging carbonic acid for oxygen (Bischof).
232 STRUCTURE COMMON TO ALL ROCKS.
more commonly stained of a rusty color by the peroxide. Among the
cells of this rusty j cellular quartz the gold is found in minute, sharp
grains, evidently left by the removal of the pyrites. Hence, in an
auriferous quartz-Vein, along the outcrop to a depth of thirty to sixty
feet (i. e., as far as meteoric agencies extend), gold is found free in
small grains among the cellular quartz ; but below the reach of these
agencies it is inclosed in the undecomposed pyrites.
Placer-Mines. If a mountain-slope, along which outcrop auriferous
quartz-veins, be subjected to powerful erosion by water-currents, then
in the stream-beds will be found gravel-drifts, composed partly of the
country rock and partly of the quartz vein-stone. Among the gravel
will be found particles of gold, washed out from the upper parts of the
veins. By the sorting power of water the heavy gold particles are apt
to accumulate mostly near the bed of the gravel-deposit (bed-rock).
These gravel-deposits are the placers. In these, the gold-particles, like
the stone-fragments, are always rounded and worn by attrition.
Some Important Laws affecting the Occurrence and the Richness of
Metalliferous Veins.
1. Metalliferous veins occur mostly in disturbed and highly-meta-
morphic regions, where the strata are tilted, and folded, and metamor-
phosed. The tilting and folding are necessary to the formation ot fis-
sures; and the conditions under which metamorphism takes place seem
necessary for the subsequent filling with mineral matter. Mineral veins,
therefore, occur mostly in mountain-regions, and in the vicinity of more
or less obvious evidences of igneous agency. Lead-veins seem to be an
exception to this rule. They are often found in undisturbed regions,
-where the rocks are entirely unchanged. The rich lead-mines of Illinois,
Iowa, and Missouri, are notable examples, the country rock being hori-
zontal, fossiliferous limestones of the Palaeozoic era.
2. Metalliferous veins occur mostly in the older rocks. In Great
Britain, for example, no profitable veins occur above the Trias. This
rule, which was regarded as of great importance by the older geologists,
is not so regarded now. There seems to be no close connection between
the occurrence of metalliferous veins and simple age alone ; the con-
nection is rather with metamorphism. Metamorphism, as we have seen,
(p. 213), is most common in the older rocks, and becomes more and
more exceptional as we pass upward. The occurrence of metalliferous
veins follows the same law. But when the newer rocks are metamor-
phic, they are as likely to contain veins as are rocks of the older series.
The metalliferous veins of California occur in Jurassic, Cretaceous, and
even Tertiary strata ; but these strata are there highly metamorphic, and
LAWS AFFECTING METALLIFEROUS VEINS. 233
strongly folded. In Bohemia, also, and elsewhere, metalliferous veins
occur in the higher series (Phillips, p. 549).
3. Parallel veins are apt to have similar metallic contents, while
veins running in different directions (unless at right angles) are apt to
contain different metallic contents. Thus, the nearly east-and-west
lodes of Cornwall, #, #, a (Fig. 216), contain tin and copper, while the
FIG. 216. Map of Cornwall : a, tin and copper ; 6, lead and iron.
north-and-south courses, b b, contain lead and iron. The auriferous
veins of California are parallel to each other and to the Sierras, except
a few smaller ones, which are at right angles to these. The reason of
this rule is, that parallel fissures belong to the same system, and were
therefore formed at the same time, broke through the same strata, and
were filled under similar conditions, and therefore with the same mate-
rials ; while fissures running in different directions (unless in some cases
at right angles, p. 221) were probably formed at different times, broke
through different strata, and were filled under different conditions.
Thus, the east-and-west veins of Cornwall break only through the
Trias, while the north-and-south veins break through the Cretaceous.
The auriferous veins of California all break through the Jurassic ; they,
or their fissures, were all produced at the same time, viz., at the time of
pushing up of the Sierras.
4. A change of country rock of an outcropping vein is apt to deter-
mine some change, either in the contents or in the richness of the vein.
Nevertheless, there is not that close connection between the nature of
the country rock and the vein-contents which obtains in infiltrative
veins. The reason is, that infiltrative veins derive their contents en-
tirely from the wall-rock on either side, while fissure-veins derive their
contents from all the strata through which they break, even to great
depths, and especially from the deeper strata. The nature of the sur-
234 STRUCTURE COMMON TO ALL ROCKS.
face or country rock is, therefore, only one factor, determining the vein-
contents.
5. Metallic veins are usually richer near their point of intersection
with granite or with an igneous dike, especially if the strata have
suffered metamorphism. This shows the influence of such heat as is
present in metaraorphism, in determining the metallic contents.
6. If two veins cross each other, especially if at small angle, one or
both are apt to be richer at the point of crossing. No sufficient reason
has been given for this law. It is probably due to the reaction of waters
bearing different materials circulating in the two fissures.
7. Since veins are the fillings of fissures, they are often slipped by
each other or by dikes or by simple unfilled fissures. If a metalliferous
vein is thus slipped, according to the law of slips already given (p. 224)
the foot-wall of the vein has usually gone upward, and the hanging wall
dropped downward. The great importance of this law in practical
mining is sufficiently obvious. All the slips of Fig. 214, except that
made by the fissure c, follow this law.
8. The sitrf ace-indications are to be learned by attentive observa-
tion in each case. We have already given these in the case of copper,
lead, and gold.
Theory of Metalliferous Veins.
Our knowledge of the conditions under which, and the chemical pro-
cess by which, fissures have been filled with mineral matter, is yet, un-
fortunately, very imperfect. Many vague and crude theories have been
proposed. Some have supposed that they have been filled in the man-
ner of dikes and granite veins, by igneous injection ; others, that these
fissures, opening below into the regions of incandescent heat, have been
filled by sublimation, i. e., by vaporization of certain materials and
their condensation in the fissures above. Some suppose that electric
currents, such as are known by observation to traverse certain veins,
have been the chief agents in the transference and accumulation of the
mineral matter. Still others have thought that great fissures have filled
in the same manner as the smaller fissures, and cavities of every kind
found in the rocks, viz., by infiltration of soluble matters from the fis-
sured rocks. There is certainly considerable analogy between small
in filtrative veins and great fissure-veins in their mode of formation; yet
there is a decided difference. The fillings of infiltrative veins are de-
rived, in each part, entirely from the bounding rock on either sid.e. The
fissure is filled by a lateral secretion from its walls ; the broken rocks
heal themselves " by first intention " by means of a plasma oozing from
the sides. But great fissure-veins derive their contents in each part
from all the strata to great depths, and especially from the deeper
strata. Hence the contents of these veins are far more varied.
THEORY OF METALLIFEROUS VEIXS. 235
Outline of the Most Probable Theory. The contents of mineral
veins seem to have been deposited from hot alkaline solutions coming
up through the fissures ; in other words, from hot alkaline springs. We
will attempt to show this first for the vein-stuffs, especially quartz, and
then for the metallic ores, especially the metallic sulphides.
Vein-Stuffs. 1. They were deposited from solutions, (a.) The
ribbon-structure and the interlocked crystals (Fig. 211) suggest at once
successive deposition from solution, especially as a similar structure
occurs in the fillings of cavities of all kinds, which could not have been
filled in any other way. (b.) Quartz is by far the most common of all
vein-stuffs. Now, as already explained (p. 217), there are two varieties
of quartz one having a specific gravity of 2.2, the other 2.6. The dry
way produces only quartz-glass, which has a specific gravity of 2.2,
while the variety of specific gravity 2.6 cannot be formed except by the
humid way. In fact, this variety, as far as we know, is always produced
by slow deposition from solution. Now, the quartz of veins is always
the variety 2.6, and therefore was produced by slow deposit from solu-
tion. The beautiful crystals so often found in veins could be produced
in no other way. (c.) We have already seen (p. 218) that fluid
cavities are a proof of formation by humid process. Now, such fluid
cavities are especially abundant in vein-stuffs generally. They are
best seen in quartz-vein stuffs, because of their transparency. (<?.) Not
only quartz, but many other minerals found among vein-stuffs are of
such nature that it is difficult or impossible to understand how they
could have been formed except by the humid way, as they will not
stand fusing temperature.
2. The solutions were hot. (a.) Fissures running deep into the
interior of the earth could hardly remain empty of water. But from
their great depth the contained waters must be hot. The solvent
power of water, when heated to high temperature under pressure, is
well known. Scarcely any substance wholly resists it. (b.) The fluid
cavities found in quartz and other vein-stuffs are not usually entirely
filled, but contain a small vacuous space. Such a vacuous space in-
dicates (p. 218) that the inclosed liquid was at high temperature at the
time of being inclosed, and has since contracted on cooling. By heat-
ing the mineral until the cavity fills and the vacuous space disappears,
we ascertain the temperature of deposit. Now, by this process the
temperature of deposit of vein-minerals has been ascertained to vary
from ordinary temperatures even up to 300 and 350. J (c.) The in-
variable association of metalliferous veins with metamorphism demon-
strates the agency of heat.
3. The solutions were alkaline. Alkaline carbonates and alkaline
1 Sorby, Philosophical Magazine, vol. xv., p. 152 ; Quarterly Journal of the Geological
Society, vol. xiv., p. 453, et seq.
236 STRUCTURE COMMON TO ALL ROCKS.
sulphides are the only natural solvents of quartz, the commonest of
vein-stuffs. Moreover, when these waters contain excess of carbonic
acid, as is almost always the case, they dissolve also the carbonates of
lime, baryta, iron, etc., the next most common forms of vein-stuffs. In
California and Nevada such alkaline carbonate and alkaline sulphide
springs abound, and are daily depositing silica (quartz) and carbonates
of lime and of iron, and even in some cases filling fissures.
Metallic Ores. There seems no reason to doubt, then, that, in most
cases at least, vein-stuffs have been deposited from hot alkaline solu-
tions. Now, it is evident, from their intimate association with the vein-
stuffs, that the metallic ores must have been deposited from the same
solution. The exact nature of the solvent and the chemical reaction
is still very doubtful. We may imagine many by either of which the
deposit might take place : 1. Metallic sulphides are by far the most
common form of ore, and even when other forms exist we may in many
cases trace them to sulphide as their original form (p. 230, et seq.). But
metallic sulphides are soluble in alkaline sulphides, and these latter are
often found associated with alkaline carbonates in hot springs, as in
California and elsewhere. Such waters would hold in solution silica,
carbonates of lime, etc., and metallic sulphides, and, coming up through
fissures, would deposit them by cooling in the fissures. Or, 2. Alka-
line carbonate waters holding in solution silica and lime carbonate for
vein-stone, and also containing alkaline sulphide, meeting and min-
gling in the same fissure with other waters containing metallic sul-
phates, by reaction would precipitate metallic sulphides ( NaS +
MSO 4 =NaS0 4 + MS). This seems to be the reaction by which the
inky waters of some of the hot springs of the California geysers are
formed. Or, 3. The alkaline carbonates still remaining for vein-
stone, metallic sulphates, in solution in the same waters with organic
matter (and all meteoric waters contain organic matter in solution),
would be reduced to the form of metallic sulphide, which, being insol-
uble, would be deposited. 1 For greater clearness we annex a table ex-
pressing these processes :
f Alk.S + MS in sol deposit MS by cooling.
Alk.CO 3 + HCO 3 + J Alk.S + MSO 4 meeting " MS " reaction.
{ MSO 4 + org mat r " MS " reduction.
There are many difficulties in the way of every attempt to place
these reactions in a clear and distinct form, but in spite of these diffi-
culties there seems little reason to doubt that great fissures have been
1 It might at first seem that there is a chemical difficulty in this last case that me-
tallic sulphate cannot coexist in solution with alkaline carbonate, but would be precipi-
tated as metallic carbonate. But it is evident that this reaction would not take place in
a weak metallic solution, in the presence of excess of carbonic acid, since in this case the
metallic carbonate is soluble.
THEORY OF METALLIFEROUS VEINS. 237
filled by deposit from hot alkaline waters holding various mineral sub-
stances in solution. The more insoluble substances are deposited in
the vein, while the more soluble substances reach the surface as mineral
springs.
This view is powerfully supported by the phenomena of hot alkaline
springs in California and Nevada. The Steamboat Springs, near Vir-
ginia City, Nevada (so called from the periodic eruption of hot water
and steam), come up through fissures in comparatively recent volcanic
rock. The waters are strongly alkaline, and deposit silica in abundance.
By this deposit the fissures are gradually filling up and forming veins.
Some fissures are now partially and some entirely filled. The ribbon-
structure in some cases is perfect. Moreover, sulphides of several of
the metals, viz., iron, lead, mercury, copper, and zinc, have been found
in the quartz vein-stuff. Here, then, we have true metalliferous veins
forming under our very eyes. 1
Thus, then, there seems no longer any room for doubt that metallif-
erous veins are actually deposited from hot alkaline solutions coming
up through fissures. It is only the exact chemical reaction which is yet
obscure. The work of the geologist is all but complete ; the problem
must now be turned over to the chemist. It may be interesting, how-
ever, before leaving this subject, to consider separately the auriferous
veins of California, and apply to them the principles set forth above.
Auriferous Veins of California. Gold is one of the most insoluble
of substances, and the occurrence of this metal in veins has always been
regarded as a difficulty in the way of the solution theory. The only
free solvent of gold is a solution of free chlorine ; but this does not
exist in Nature. Nevertheless, gold is known to be slightly soluble in
the salts, especially the persalts of iron. These salts, especially the
sulphate and persulphate of iron, are the probable solvents of gold.
There is also a silicate of gold, which, according to Bischof, is slightly
soluble under certain conditions.
There is abundant evidence that the auriferous quartz-veins of Cali-
fornia have been deposited from hot solutions. These veins exhibit in
many cases the characteristic ribbon-structure. They exhibit also the
water-cavities characteristic of deposits from solutions, and the vacuous
spaces, indicating that the solutions were hot. By actual experiment, 2
the temperatures at which the vacuous spaces disappear, and therefore
at which the deposit took place, has been ascertained being 180,
212, 350, and even more. 3 Again, there can be no doubt that the
associated metallic sulphides were deposited from the same solutions as
the vein-stuffs, for they are completely inclosed in the latter. But the
1 Arthur Phillips, American Journal of Science, vol. xlvii., p. 194 ; and Philosophical
Magazine, 1872, vol. xlil., p. 401.
2 Arthur Phillips, ibid. 3 n,^
238 STRUCTURE COMMON TO ALL ROCKS.
gold, as already stated (p. 231), exists as minute crystals and threads
of metal inclosed in the sulphide of iron, and must therefore have been
deposited from the same solution as the iron. It seems most probable
that the gold was dissolved in a solution of sulphate or persulphate of
iron, and that the sulphate was deoxidized, and became insoluble sul-
phide and precipitated ; and that the gold thus set free from solution
was entangled in the sulphide at the moment of the precipitation of
the latter.
There are some phenomena connected with the occurrence of gold
in the iron sulphides of the deep placers which seem to prove the truth
of this view. 1 The deep placers of California are gravel-drifts in ancient
river-beds, covered up by lava-flows 100 to 200 feet thick. These placers
N S
FIG. 217. Section across Table Mountain, Tuolumne County. California: Z, lava; G, gravel; S, slate;
, old river-bed ; R present river-bed.
are worked by running tunnels beneath the basaltic lava until the river-
gravel is reached. Now, the waters percolating through these lava-
flows and reaching the subjacent gravels are charged with alkali from
the lava. These alkaline waters are also charged with silica from the
same source. Hence, the drift-wood of these ancient rivers has all
been silicified by these siliceous waters. The gravels are also in many
places cemented by the same material. These percolating waters have
evidently also contained sulphate of iron ; for in contact with the sili-
cified wood is often found iron sulphide. Thus, while the wood decayed
it was partly replaced by silica and partly by iron sulphide produced
by deoxidation of the sulphate by organic matter (p. 192). The gravel
has also in some places been cemented by iron sulphide reduced from
solution in a similar way. Now, both in this petrifying and in this
cementing sulphide of iron is found (by solution in nitric acid) gold:
sometimes in rounded grains, and therefore simply inclosed drift-gold ;
but also sometimes in minute crystals and threads, exactly as in
the sulphide of the undecomposed quartz-vein. Evidently, this gold
has been deposited from a solution of sulphate of iron at the moment
of the reduction of the latter to a sulphide. The process was probably
as follows : Percolating water oxidized iron sulphide and took it into
solution as sulphate. This solution coming in contact with drift-gold
dissolved it, but, subsequently, coming in contact with decaying or-
J Arthur Phillips, ibid.
THEORY OF METALLIFEROUS VEINS. 239
ganic matter, was again deoxidized and deposited as sulphide ; and the
gold crystallizing at the same moment is inclosed. 1 If these waters
had circulated through a fissure, we would have had an auriferous
quartz-vein. In fact, this may be regarded as a sort of horizontal vein.
"We conclude, therefore, that metalliferous veins have been deposited
from hot alkaline waters, circulating through fissures, and that in the
case of auriferous veins the solvent of the gold was sulphate of iron,
and the sulphate was deoxidized by organic matter in the same solution,
the gold and the iron crystallizing at the same moment, one as metal,
the other as sulphide.
Gold is sometimes found in pure quartz without the sulphide of iron.
In these cases it may have been in solution in alkaline water as silicate
of gold, as suggested by Bischof. There is a silicate of gold which
may be made by artificial means. It is slightly soluble under certain
conditions."
Nuggets. It is well known that, although gold exists in the iron
sulphide of the unchanged vein only in minute, even microscopic,
crystals and threads, yet in the changed upper portions of the veirn it
exists in quite visible particles, and often in large nuggets weighing-
several ounces, or even rarely several pounds. This fact is additional
evidence that sulphate of iron is the natural solvent of gold. There
can be no doubt that these larger grains and nuggets result from the
coalescence of all the minute particles, contained in a mass of sulphide,
into one or more larger masses. By meteoric agencies, as already ex-
plained (p. 231), the sulphide is oxidized into sulphate, and the gold
redissolved. From this solution it crystallizes into one mass, as the
solution concentrates by losing its sulphuric acid and changing into
peroxide. In the case of large nuggets, the gold is probably in some
way deposited constantly at the same place from a similar solution
bringing gold for a long time.
Illustrations of the Law of Circulation. We have said that the
iron sulphate comes from oxidation of sulphide, but also the sulphide
from the deoxidation of the sulphate. This is only another example
of a perpetual cycle of changes. Again, the gold in the veins is leached
from the strata ; the strata doubtless received it from the sea, for small
quantities of gold have been detected in sea-water ; but, again, doubt-
less the sea received it from the rocks, and this brings us to another
perpetual cycle of changes.
But in the midst of all these changes there has evidently been an
increasing concentration and availability of gold and other metals. In
the strata the quantity is so small as to be undetectible ; it is thence
carried and concentrated in veins in a more available form ; it is next
set free along the backs of these veins in a still more available form;
1 Arthur Phillips, ibid. 2 " Chemical and Physical Geology," vol. iii., p. 535.
240 STRUCTURE COMMOX TO ALL ROCKS.
it is last carried down by currents along with other materials, neatly
sorted, and deposited in placers in a form the most available of all.
SECTION 3. MOUNTAIN-CHAINS : THEIR STRUCTURE AND ORIGIN.
Mountains are the glory of our earth, the culminating points of
scenic beauty and grandeur. They are so because they are also the
culminating points, the theatres of the greatest activity, of all geologi-
cal agencies. The study of mountain-chains, therefore, must ever be of
absorbing interest, not only to the painter and the poet, but also to the
geologist. A thorough knowledge of their structure, origin, and mode
of formation, would undoubtedly furnish a key to the solution of many
problems which now puzzle us ; but their structure is as yet little
known, and their origin still less so.
Mountain- Origin.
The general cause of mountain-chains (as in fact of all igneous phe-
nomena) is the ''reaction of the earth's hot interior upon its cooler
crust." Mountain-chains seem to be produced by the secular cooling,
and therefore contraction, of the earth, greater in the interior than the
exterior; in consequence of which, the face of the old earth is become
wrinkled. Or, to express it a little more fully, by the greater interior
contraction, the exterior crust is subjected to enormous lateral pressure,
which crushes it together, and swells it upward along certain lines, the
strata, by the pressure, being at the same time thrown into more or less
complex foldings. These lines of upswelled and folded strata are
mountain-chains. The first grand forms thus produced are afterward
chiseled down and sculptured to their present diversified condition by
means of aqueous agency. Thus much it was necessary to say of the
origin of chains, in order to make the account of their structure intelli-
gible. The theory of their origin will be given more fully hereafter.
General Form, and how produced.
A mountain-cAn consists of a great plateau or bulge of the earth's
surface, often hundreds of miles wide and thousands of miles long.
This plateau or bulge, which is the chain, is usually more or less dis-
tinctly divided by great longitudinal valleys into parallel ranges; and
these ranges are again often separated into ridges by smaller longitudi-
nal valleys; and these ridges, again, serrated along their crests, or di-
vided into peaks, by transverse valleys.
Thus, the Appalachian chain is a great plateau or bulge, 100 miles
wide, 1,000 miles long, and 3,000 feet high. It is divided into three
ranges, the Blue, the Alleghany, and the Cumberland, separated by great
valleys, such as the Valley of Virginia and the Valley of East Tennessee.
MOUNTAIN-STRUCTURE. 241
These ranges are again in some places quite distinctly divided into
parallel ridges, which are serrated into peaks. The American Cordil-
leras consist of an enormous bulge running continuously through the
whole of South and North America, nearly 10,000 miles long, and from
500 to 1,000 miles wide. This great chain is divided into parallel ranges.
In North America there are at least three of these very conspicuous, the
Rocky Mountain, the Sierra Nevada, and the Coast Range, separated by
the Great Salt Lake Valley and the Valley of Central California, respec-
tively. Each of these ranges is separated more or less perfectly into
ridges and peaks, as already explained. These terms, chain, range, and
ridge, are often used interchangeably. I have attempted to give a more
definite meaning.
Chains are evidently .always produced solely by the bulging of the
crust by lateral pressure. Ganges are usually produced in a similar
manner, i. e., by greater crushing together, and therefore greater bulging
along parallel lines, within the wider bulge ; this is the mode of forma-
tion of the ranges of the North American Cordilleras. In such cases,
they have been probably consecutively formed. The ranges of the Ap-
palachian chain, however, have been formed almost entirely by erosion.
The ridges and intervening ' longitudinal valleys are usually, and the
peaks, with their intervening transverse valleys, are always, produced
by erosion.
Such is the simplest ideal of the form of a mountain-chain ; but in
most cases this ideal is far from realized. In many cases the chain is a
great plateau, composed of an inextricable tangle of ridges and valleys
of erosion, running in all directions. In all cases, however, the erosion
has been immense. Mountain-chains are the great theatres of erosion,
as they are of igneous action. As a general fact, all that we see, when
we stand on a mountain-chain every peak and valley, every ridge and
canon, all that constitutes scenery is wholly due to erosion.
3fo untain- Structure.
The simplest idea of a mountain-range is that of a single fold of
thick strata. Such a simple range is shown in Fig. 218, which is a
generalized section of the Uintah Mountains, taken from Powell. But,
more commonly, mountains, even when they are composed wholly of
stratified rocks, consist of many folds, sometimes open, as in the Jura
Mountains (Fig. 219), but more often closely pressed together. This is
admirably illustrated in the following section of the Coast Range of
California (Fig. 220), and also in the section of the Appalachian, on
page 244 (Fig. 225). The manner in which mountains are formed is
very evident in such cases. Such mountains cannot be formed except
by a mashing together of the strata horizontally.
16
242
STRUCTURE COMMON TO ALL ROCKS.
FIG. 218. Ideal Section across the Uintah Mountains (after Powell).
FIG. 219. Section of the Jura Mountains.
FIG. 220. Section of Coast Range, showing Plication by Horizontal Pressure.
But most great mountain-ranges, as shown in Fig. 221, consist of a
granite axis, g, coming up from beneath and appearing at the surface
along the crest and forming the
peaks, flanked on either side by
tilted strata, a, a, usually of enor-
mous thickness, and correspond-
ing on the two sides. Sometimes
several series of unconformable strata on the flanks show that the range
has been formed by successive upheavals (Fig. 222). The succession
of events represented by this figure are : 1. The strata a, a, were de-
posited ; 2. a, a, were up-
tilted and the mountain
formed ; 3. The strata
b, b, were deposited hori-
zontally, and therefore
unconformably, on a, aj 4. The mountain-axis was pushed up higher,
MOUNTAIN-STRUCTURE.
243
FIG. 223. Ideal Section showing Exposure of
Granite by Erosion.
so as to tilt b, 5, also ; 5. c, c, were then deposited unconf ormably on 5, b ;
and, finally, 6. The whole was raised bodily, so as to expose c, c, but
without tilting them.
Now many geologists seem to regard these two kinds of mountains,
viz., those composed only of folded strata, and those with granite axis,
as essentially different, and formed in different ways. Mountains of
the latter class, they seem to think, were formed by a force acting ver-
tically, pushing the granite axis through the broken strata to its pres-
ent highest position along the crest. .--:::.";-..
But it is far more probable that the
stratified rocks and the subjacent
granite were all pushed up by hori-
zontal pressure into a fold, and the
strata were afterward removed by
erosion, leaving the harder granite as a crest. This is shown in the
ideal section, Fig. 223, in which dotted lines represent the part removed
by erosion. In many ranges, as, for example, in the Sierra, patches of
the flanking strata are still left on the summits.
Thus, then, mountain-ranges are all formed in the same general
way, viz., by horizontal crushing. Sometimes they consist of a single
fold, more often of many close folds ; sometimes the strata are little
changed, sometimes they are greatly metamorphosed ; sometimes they
are little eroded, sometimes very deeply eroded. The combination of
these various conditions gives rise to a great variety of kinds : 1. If it
consist of a single fold and the strata be unchanged, then we have the
simplest conceivable range, as in the Uintah Range, Fig. 218. 2. But if
the strata be greatly changed and deeply eroded, then the upper part
of the fold is removed, and the completely metamorphic granite is ex-
FIG. 224. Ideal Section of a Mountain-Range.
posed along the crest, and we have a case like Figs. 221 and 223.
3. If the range consist of many folds and the stratification be not de-
stroyed by metamorphism, then we have cases like the Jura (Fig. 219),
the Coast Range (Fig. 220), and the Appalachian (Fig. 225). 4. Lastly,
if ranges like the last be greatly metamorphosed and deeply eroded,
then we have the common case represented by Fig. 224. This may,
perhaps, be regarded as the best type of a great mountain-range. It
represents strata strongly folded and deeply denuded. But the most-
244 STRUCTURE COMMON TO ALL ROCKS.
folded and least-changed upper portions of the strata have been re-
moved, and the very metamorphic and less-folded deeper portions are
exposed along the axis. The axis in this case, also, is represented as
gneiss (i. e., a granite in which the original strata are still imperfectlv
visible), in order the better to bring out the real structure. But carry
the process of metamorphism one step further, and the foldings of this
part disappear, and we have a range of the type represented in Fig. 221.
In fact, it is probable that many mountains which consist only of gran-
ite axes and tilted strata corresponding on each side, and therefore
seem to be but one fold, were really originally of many close folds,
only these have been carried away by erosion.
In still other ranges the constituent strata are overlaid by immense
ejections of liquid matter, which conceal the true structure of the
mountain. The Cascade Range is perhaps the most remarkable ex-
ample of this.
As a general rule the degree of mashing, and therefore of folding,
is greatest near the axis, and gradually passes into gentler and gentler
undulations as we leave this line. This is strikingly seen in the Ap-
palachian. Fig. 225 is a simplified section of this chain, in which each
7
FIG. 225. Appalachian Chain.
fold is really composed of a number of subordinate folds. It is seen
that the folds are strong along the crest, but die away in gentle un-
dulations westward until the strata become horizontal.
Rate Of Mountain-Formation. The uprising of a mountain-range is
probably in all cases extremely slow, so much so that it may be going
on now without our observing it. Hence, though so deeply denuded,
it is not necessary to suppose they ever were higher than now. An
admirable proof of this slowness is pointed out by Powell in the case of
the Uintah Mountains. This range consists of a single great fold of
stratified rocks, which has risen right athwart the course of the Green
River. But so slow has been the uprising, that the river has not been
turned from its course, but has cut through the range to the bottom
(Fig. 218). The uprising has not been faster than the down-cutting of
the river.
Thickness of Mountain-Sediments. Mountain-chains seem always to
be composed of sedimentary rocks of enormous thickness. The strata
composing the Appalachian chain are 40,000 feet thick, while the same
strata on the Mississippi River are only 4,000 feet. According to
MOUNTAIN-SCULPTURE. 245
Clarence King, the Wahsatch Mountains are composed of 56,000 feet
of conformable strata. According to Powell, the strata exposed on
the flanks of the Uintah Range are 32,000 feet thick. According to
Whitney, the cretaceous strata alone of the Coast Range are 20,000
feet thick. "We have taken these examples from the United States,
but the same is true everywhere. It seems certain that the origin
of mountain-chains is in some way connected with thickness of sedi-
ments ; that mountain-chains are, in fact, formed by the crushing to-
gether and folding of lines of thick sediments.
Foldings and Metamorphism. In consequence of the foldings, we
find associated with mountains fissures, dikes, veins, etc. If any liquid
matters existed beneath, these would naturally be squeezed out through
the fissures, and hence we find outpourings of lava associated with
mountain-chains. In consequence of the thickness of the sediments,
and also from the heat developed by crushing, mountain-strata, espe-
cially those along the crest, which are the lowest, are usually meta-
morphic (p. 213). In fact, thickness, folding, and metamorphism,
not only go together, but seem to be 'proportional to each other. Thus,
as already stated, the Appalachian strata, which in the Appalachian
region are 40,000 feet thick, gradually thin out westward until they
become only 4,000 on the Mississippi River. Both the foldings and
the metamorphism diminish and pass away in the same direction.
Inspection of the figures given above (Figs. 221 and 224) shows
1. That mountain-chains are necessarily anticlinal. This, however, is
far from being true for ridges ; which, we will show hereafter, are often
synclinal. 2. It shows that the rocks of mountain-crests are usually
granitic or metamorphic. '3. That the rocks of the crest are usually
lower in the geologic series, i. e., older than the flanking strata, these
lower rocks of the crest having been exposed by enormous erosion.
Therefore mountain-regions have been the great theatres 1. Of sedi-
mentation before the mountain was formed; 2. Of upheaval in the
formation of the chain ; and, 3. Of erosion which determined the present
outline. Add to these the metamorphism, thefissures, slips, dikes, veins,
and volcanic outbursts, and it is seen that all geological agencies con-
centrate there.
Moun tain- Sc ulpture.
All mountain-chains have been formed in the same general way,
viz., by a bulging of the earth's crust along certain lines, produced by
interior contraction. But the original mountain-plateau thus formed
has been in all cases subsequently so enormously sculptured by aqueous
agencies as to obscure the origin of the chain and confuse the use of
the term mountain. This term is loosely used to express every con-
spicuous inequality of surface, whatever be its origin, from a great
chain, like the Andes or Himalayas, to isolated erosion hills of a few
26 STRUCTURE COMMON TO ALL ROCKS.
hundred feet altitude. But we should carefully distinguish mountain-
chains from hills, ridges, peaks, formed by erosion. The one belongs
to mountain-formation, the other to mountain-sculpture. The grand
forms, the chain always, the ranges usually, are produced by interior
or igneous agencies, and have only been modified by exterior or aque-
FIG. 226. Section across the Valley of East Tennessee (after Safford).
ous agencies ; but in some cases even what are called ranges, with their
wide intervening valleys, have been produced by erosion. The valley
of East Tennessee, fifty miles wide, separating the Cumberland from the
Blue Range, has been formed by this cause. Fig. 226 is a section across
a portion of the valley of East Tennessee, the length of the section
being about twenty miles. It is evident that it has been swept out by
erosion alone. On account of the immense work which has in all cases
been done by erosion, and the grand forms which have often resulted,
many writers divide mountains into two classes, viz., mountains of up-
heaval and mountains of denudation. It is better, however, to treat
the subject of mountains under two heads, viz., mountain-formation
and mountain-sculpture.
Resulting Forms. It is very interesting to trace the laws of form
resulting from erosion. These laws have been brought out chiefly by
Lesley. 1 We have added some from our own observations:
1. Horizontal Strata. Horizontal or very slightly undulating
strata give rise by erosion to flat-topped ridges or table-mountains.
Fig. 227 is an ideal section of such table-mountains. The outcrop of
harder strata on the slope will often determine benches. This table-
FiG. 22S. Table-Mountains.
form is especially conspicuous if the eroded table-land is capped by
hard sandstone, or by lava, as in Fig. 228. Examples of this kind of
1 "Manual of Coal."
MOUNTAIN-SCULPTURE.
247
erosion hills are found abundantly in Illinois, Iowa, Tennessee, and in
Arizona. We give in Fig. 229 an actual section across Cumberland
FIG. 229. Section across Cumberland Pltiteau and Lookout Mountain, Tennessee.
table ((7), Sequatchee Valley (S), Walden's Ridge ( TF), Tennessee
River (^'), Lookout Mountain Valley (J!/J 7 ~), and Lookout Mountain
(1,31), Tennessee, in which this structure is well seen.
On the other hand, if the strata be very soft, then erosion produces
steep, rounded hills, standing thickly together like potato-hills on a
FIG. 230. Bad Lands, north of Uintah Mountains (after Powell).
large scale, or, when somewhat firmer, like crowded pinnacles (Figs. 230
and 231). The singular aspect of the Bad Lands, or soft tertiary lake-
deposits of the Rocky Mountain region and of Oregon, is thus produced.
The forms represented by Figs. 228 and 229 graduate insensibly
into the next, viz. :
2. Gently-folded Strata. These by erosion usually produce syn-
clinal ridges and anticlinal valleys. This is beautifully shown in the
248 STRUCTURE COMMON TO ALL ROCKS.
subjoined section of the Appalachian coal-fields in Pennsylvania. By
restoring the strata as in the figure, it is seen that the original ridges
Fie. 231. Mauvaises Terres, Bad Lands (after Hayden).
have become hollows, and the original hollows have become ridges.
The reason of this seems to be that the bending of the strata in oppo-
site directions crushes together and hardens them in the synclinals,
and stretches them and perhaps breaks them along the anticlinals.
Thus the erosion has taken effect on the anticlinals more than the syn-
clinals.
3. Strongly-folded or Highly-inclined Outcropping Strata. In
these the ridges arid valleys are determined by the outcrop of harder and
S SK S J-fc $ *A, -S-
FIG. 233. Parallel Kidges.
softer strata respectively. In the ideal section Fig. 233 the ridges are
determined by the outcrop of a succession of hard sandstone strata
which resisted erosion more than the intervening soft shale, sh. Beau-
MOUNTAIN-SCULPTUKE.
249
tiful examples of ridges and valleys formed in this way are found in the
Appalachian chain, especially in Virginia. Standing on the top of
Warm Springs Mountain, a dozen or more parallel ridges may be
counted, each with a longer slope on one side, and a steeper slope on
the other, like billows ready to break. The crest of each ridge is deter-
mined by an outcropping sandstone, and the valleys by the softness
of the intervening shales. Fig. 226, on p. 246, shows the formation of
ridges in this way in Tennessee. A similar structure on a magnificent
scale is seen in the hog-backs of the Uintah Mountains described by
Powell. In Fig. 233 I have represented a single series of strata con-
taining several sandstones ; but sometimes by repeated foldings the
Fi. 234. Parallel Eidges, Infolded Strata.
same sandstone or other hard strata may form many ridges. This is
shown in Fig. 234.
In ridges determined by the outcrop of hard strata the relative
slope on the two sides is determined by the dip of the strata. If the
strata are perpendicular, the slopes on the two sides are equal (Fig. 235,
a) ; but if the strata are inclined, the longer slope is on the side toward
which the strata dip, and the difference of the slopes increases as the
angle of dip is less (Fig. 235, b and c). This case passes by insensible
gradations into the next, viz. :
4. Gently-inclined Outcropping Strata. These by erosion, perhaps
under peculiar climatic conditions, give rise to a' sucession of broad,
250 STRUCTURE COMMON TO ALL ROCKS.
nearly level tables, coincident with the face of a hard stratum, termi-
nated by parallel lines of cliffs. Fig. 236 is an ideal section of such
FIG 237. Bird's-eye View of the Terrace Caflon (after Powell).
strata. This form of sculpture is developed on a magnificent scale in
the region of Colorado Plateau. Fig. 237, taken from Powell, shows
MOUNTAIN-SCULPTURE. 251
three such tables, twenty to sixty miles wide, terminated by as many
cliffs, 1,200 to 2,000 feet high. It is evident that the drainage of the
region Avould be against the foot of the cliffs, and that, therefore, all
the cliffs recede by erosion.
5. Highly-metamorphic or Granitic Rocks. In granitic or highly-
metamorphic regions, where the stratification is indistinct or wanting,
the ridges and peaks can generally be traced to the relative hardness
of lines or spots, or else to some peculiar rock-structure. Thus the
domes and spires so conspicuous about Yosemite have evidently been de-
termined, the one by a concentric structure on a huge scale, the other by
a coarse, perpendicular cleavage. In all cases erosion inequalities, once
commenced, tend to increase by the concentration of erosion in the
valleys first formed.
The Age Of Mountain-Chains. The time of formation of a chain or a
range is determined by the age of the strata which enter into its struct-
ure, or which lie inclined on its flanks. Thus, the mountain represented
in Fig. 221 (p. 242) must be younger than the tilted strata (a) on its
flanks ; for the strata must have been first deposited in an horizontal
position, and afterward tilted, when the mountain was formed; but it
must be older than the horizontal strata (), for these are yet undis-
turbed. When mountain-chains have been gradually raised by successive
upheavals, this fact, and the date of the successive upheavals, are known
by the existence and the age of the several series of tilted or folded strata,
unconformable with each other. Thus, in Fig. 222 (p. 242), the chain
was raised first between the periods of deposition of a and b, and again
higher, between the periods of deposition of b and c. Thus, it is known
that the Appalachian was formed at the end of the Palaeozoic era ; for
all the Palaeozoic strata enter into its folded structure, while even the
oldest Mesozoic strata do not. By similar means, it is ascertained that
the Sierra Range was formed at the end of the Jurassic^ while the Coast
Range Avas not formed until the end of the Miocene.
It seems most generally true that the oldest chains are only of mod-
erate altitude, while the highest mountains are among the youngest.
The converse of these propositions, however, is by no means true, for '
there are many young mountains which are also of moderate altitude.
In the United States, the Laurentides are the oldest, then the Appa-
lachians, and then the Sierra Nevada. In South America, the Brazilian
mountains are older than the higher Andes. In Europe, the Ural Moun-
tains and the Scandinavian mountains are older than the loftier Alps.
The Himalayas, also, are among the youngest of mountains, at least in
their last development. This may be due in part to the enormous
erosion of the older chains, and in part to other causes, yet imperfectly
understood.
252 STRUCTURE COMMON TO ALL ROCKS.
Theory of the Origin of Mountain- Chains*
We have already (p. 78, et seq.) given reasons for believing that the
usual view that the earth is an incandescent liquid globe, covered by a
solid shell twenty-five to fifty miles thick, is untenable, and therefore
that geological theories must be reconstructed on the basis of a sub-
stantially solid earth. We have also shown (p. 168) how continents and
sea-bottoms are probably formed by the unequal radial contraction of a
solid earth. We wish now to show how mountain-chains also may be
formed on this supposition.
A cooling, solid earth may be regarded as composed of concentric
isothermal shells, each cooling by conduction to the next outer, and the
outermost by radiation into space. Furthermore, under these conditions,
at first and for a long time, the outermost shell would cool the fastest ;
but there would eventually come a time when, the surface having be-
come substantially cool, and moreover receiving heat from external
sources (sun and space) as well as internal, its temperature would be-
come nearly fixed, while the interior would still continue to cool by con-
duction. This has probably been the case during the whole recorded
history of the earth. The interior, now cooling faster, would also con-
tract faster, than the exterior. There is another cause which would con-
tribute to the same result : The amount of contraction for equal cooling,
or the coefficient of contraction, is greater at high than at low tempera-
tures; and therefore for equal, or even slightly less, loss of heat, the hot
interior would contract more than the cool exterior. Now, therefore,
the interior, for both of these reasons, contracting more rapidly than the
exterior, the latter, following down the shrinking interior, would be
subjected to powerful horizontal pressure, which continuing to increase
with the progressive interior contraction, the exterior must eventually
yield somewhere. Mountain-chains are the lines along which the
yielding of the surface to horizontal thrust has taken place. But, ob-
serve : According to our view, this yielding is not by upbending into
an arch, leaving a hollow space beneath, nor yet into such an arch, filled
and supported by an interior liquid, as usually supposed ; but by mash-
ing or crushing together horizontally, like dough or plastic clay, icith
foldings of the strata and an upswelling and thickening of the whole
squeezed mass.
The complex foldings so universal in mountain-chains cannot be
accounted for except by this crushing together bv horizontal pressure.
Simple inspection of the structure of such ranges as the Coast Range
and the Appalachian (Figs. 220 and 225, pp. 242, 244) is sufficient to
1 This subject is certainly best taken up here, but some very general knowledge of
Part III. is necessary to its full appreciation. Those who have not this general knowledge
had perhaps better put it off to the end of the course.
THEORY OF THE ORIGIN OF MOUNTAIN-CHAINS. 253
convince one of this. But there is another phenomenon which fur-
nishes demonstrative proof both of the crushing together and the up-
swelling of mountain-chains, viz., the phenomenon of slaty cleavage.
We have already seen (p. 181, et seq.) that slaty cleavage is cer-
tainly produced by powerful pressure perpendicular to the cleavage-
planes, by which the whole rock-mass in which it occurs has been
mashed together and shortened in that direction, and correspondingly
extended in the direction of these planes ; furthermore, as the planes
are nearly or quite vertical, that the rock-mass has been crushed to-
gether horizontally and swollen up vertically. As a necessary qonse-
quence of the crushing together, we find associated the most complex
foldings, not only of the strata, but also of the layers, and even of
the finest lines of lamination. Thus, plication is always associated
icith cleavage; and, vice versa, cleavage, when the rock-material is
suitable for developing this structure, is always associated with plica-
tion ; and both are associated with mountain-chains.
A mashing together horizontally and an extension vertically are
therefore certain in slaty cleavage, and therefore in mountain-chains
where slaty cleavage occurs. It only remains, therefore, to show
that the amount of upswelling absolutely proved in these cases is
fully adequate to account for the upheaval of the greatest moun-
tain-chains.
We have seen (p. 182) that, taking any ideal cube or sphere of the
original unsqueezed mass, in the process of mashing, the diameter at
right angles to cleavage (horizontal and in the direction of pressure) has
been diminished, that in the dip of the cleavage (vertical) has been in-
creased, while that in the strike of the cleavage is unaffected. Now, it
has been shown that in the case of the first two diameters mentioned, viz.,
the horizontal in the direction of pressure and the vertical, their original
equality has been changed into a ratio of 2 : 1, 4 : 1, 6 : 1, 9 : 1, and
in some cases even 11 : 1 ; the average being 5 or 6 : 1. It follows,
therefore, that the change of each diameter, either in the direction of
compression or of elongation, must be the square roots of the above
ratios. Thus, if a cube of three inches' diameter be crushed together
horizontally and allowed to extend only vertically, until these previous-
ly equal diameters become as 9:1, it is evident that the horizontal
diameter has been diminished and the vertical diameter increased, each
three times. Taking 6 : 1 as the ratio, in cleaved slates, of diameters
originally equal, we may assert that in cleaved rocks the whole mass has
been stootten up two and a half (2.45) times its original thickness. Sup-
pose, then, a mass of sediments 10,000 feet thick subjected to hori-
zontal pressure and crushing sufficient to develop well-marked cleavage-
structure: a breadth of two and a half miles has been crushed into one
mile, and the 10,000 feet thickness swollen to 25,000 feet, making an
254: STRUCTURE COMMON TO ALL ROCKS.
actual elevation of the surface of 15,000 feet. Now, we actually have
strata, not only 10,000, but 20,000, and even 40,000, feet thick.
We are justified, therefore, in asserting that the phenomena of pli-
cation and of slaty cleavage demonstrate a crushing together hori-
zontally and an upswelling of the whole mass of mountain-sediments;
and that the phenomenon of slaty cleavage demonstrates, in addition,
that the amount of upswelling produced by this cause alone is sufficient
to account for the elevation of the greatest mountain-chains. For it
must be remembered that an equal degree of crushing takes place in
mountains even when the proof derived from slaty structure is wanting.
No other theory of mountain-formation takes cognizance of slaty cleav-
age. Some take cognizance of the crushing and folding, but in all it is
a subordinate accompaniment, instead of a sufficient cause, of the ele-
vation.
Unquestionably, therefore, mountain-chains are produced by hori-
zontal pressure crushing together the whole rock-mass and swelling it
up vertically, the horizontal pressure being the necessary result of the
secular contraction of the interior of the earth. It is possible that even
continents may have been formed by a similar yielding to horizontal
thrust, and a similar crushing together and upswelling. If so, it is
necessary to suppose that the amount of horizontal crushing is much
less, but the depth affected much greater, than in the case of mountain-
chains. But, as we find no unmistakable relation between elevation
and amount of crushing, except in the case of mountain-chains, we have
preferred to attribute the formation of continents and sea-bottoms to
unequal radial contraction (p. 168).
Let us now apply this theory to the explanation of the most con-
spicuous phenomena associated with mountain-chains.
1. Thick Sediments of Mountain-Chains. It is now generally ac-
knowledged that mountain-chains consist either wholly or principally
of enormously thick sediments crumpled together. But where do such
great accumulations of sediments now take place ? Evidently off the
shores of continents and in inland seas. Nearly the whole debris of
eroded land is deposited near shore only a very small quantity of
very fine sediment reaching deep-sea bottom. Hence great accumula-
tions take place only along shore. Mountain-chains, therefore, are
evidently formed by the crushing together and upswelling of sea-bot-
toms where great accumulations of sediments have taken place ; and as
such accumulations usually occur off the shores of continents, mountain-
chains are formed by the up-pressing of marginal sea-bottoms. The
proof of this proposition is found in the history of the chains of the
North American Continent.
(a.) Appalachian Chain. The area now occupied by this chain was,
during the whole Silurian and Devonian ages, the eastern margin of
THEORY" OF THE ORIGIN OF MOUNTAIN-CHAINS. 355
the bed of the great interior Palaeozoic Sea, which then covered nearly
the whole basin now drained by the Mississippi River. During all this
time the whole of this interior sea, but especially its eastern margin,
received sediments from a continental mass northward (the Laurentian
area), and also especially from a continental mass to the eastward.
Besides the marks of shore-deposit, found abundantly in the Appala-
chian strata, other evidences are daily accumulating, that the area to
the east of the Appalachian chain the so-called primary or gneissic
region of the Atlantic slope is largely Laurentian, and therefore was
land during the Pakeozoic era. The size of this old eastern continen-
tal mass it is now impossible for us to know, since it has been partly
covered by later deposits, and is perhaps even partly covered now by
the sea ; but, judging by the enormous quantity of sediments, 30,000
feet thick, carried westward from it into the Palasozoic interior sea, and
deposited along the eastern margin of this sea, it must have been very
large.
At the end of the Devonian age much of the middle portion of the
interior Palasozoic Sea was upheaved and became land ; and the Appa-
lachian region became now alternately a coal-marsh, a lake, and an in-
land sea or estuary, emptying into the ocean southward (see map, page
278 the eastern black area). Into this estuary, or marsh, during the
Coal period, sediments were brought down from land north, east, and
west, until 10,000 feet more were deposited. / During the whole of this
immense time (Palaeozoic era), while the 40,000 feet of sediments were
depositing, this area whether sea-margin bottom, or estuary-bottom,
or coal-marsh slowly subsided, so as to maintain nearly the same
level. This is certain for the Coal period (for every coal-seam indi-
cates a marsh nearly at sea-level), and almost equally certain for the
previous periods, for marks of shallow-water shore-deposits are found
throughout. Besides, it seems to be a general law throughout the
whole history of the earth that areas of great sedimentation have been
areas of slow subsidence pari passu. The same seems to be true now.
Nearly all great river-deltas are slowly subsiding (p. 129). In fact, in
all shallow-water deposits, and therefore in all shore-deposits, the
accumulation would soon cease, and therefore would never become
thick, but for subsidence, which constantly renews the conditions of
deposit. The subsidence of the Appalachian area, therefore, must have
been 40,000 feet vertical.
Observe, then, that during the whole Coal period the Appalachian
region, so far from being a mountain-chain, was a northeast and south-
west trough, lower than the. land to the east and west of it. At the
end of the Coal period occurred the Appalachian revolution. The
great mass of sediments which had been accumulating for so many
ages, yielded to the horizontal pressure, was crushed together and
256 STRUCTURE COMMON TO ALL ROCKS.
folded, and swollen upward to a height proportioned to the horizontal
crushing. Thus was formed the Appalachian chain. The mode and
the date of its formation are both recorded in its structure. Subse-
quent sculpturing has made it what it now is. It is probable that in
the process of up-pushing of the Appalachian (or possibly at a later
time), the eastern continental mass was diminished both in height and
in extent on its eastern border, by subsidence.
(b.) Sierras. There can be no doubt that a considerable portion of
the area now occupied by the Rocky Mountains (the Basin Range re-
gion) was land during the Palaeozoic era. The extent and height of this
land we do not know. We shall say nothing of the mode of formation
of this the oldest portion of the North American Cordilleras, as the his-
tory of its formation is little known. We will commence with a con-
siderable body of land which certainly existed in this region at the
beginning of the Mesozoic era. Now, during the whole Triassic and
Jurassic periods, the region now occupied by the Sierra range was a
marginal sea-bottom receiving abundant sediments from a continental
mass to the east. At the end of the Jurassic this line of enormously
thick off-shore deposits, yielding to the horizontal thrust, was crushed
together and swollen up into the Sierra range. All. the ridges, peaks,
and caiions all that constitutes the grand scenery of these mountains
are the result of an almost inconceivable subsequent erosion.
(<?.) Coast Range. The up-squeezing of the Sierras, of course, trans-
ferred the coast-line farther westward, and the region now occupied by
the Coast Range became the marginal sea-bottom. This in its turn
received abundant sediments from the now greatly-enlarged continent,
until the end of the Miocene, and then it also yielded in a similar man-
ner, and formed the Coast Range.
(d.) Alps. Mr. Judd has recently shown that the region of the Alps,
during the whole Mesozoic and early Tertiary, was a marginal sea-bot-
tom (probably a mediterranean), receiving sediments until a thickness
was attained not less than that of the Appalachian strata. At the end
of the Eocene these enormously thick sediments were crushed together
with complicated foldings, and swollen upward to form these mountains,
and subsequently sculptured to their present forms. 1
Thus, then, it is quite certain that the places now occupied by
mountain-chains have been, previous to their formation, places of great
sedimentary deposit, and therefore most usually marginal sea-bottoms.
In some cases, however, perhaps in many cases, the deposits in interior
seas or mediterraneans may have yielded in a similar manner, giving
rise to more irregular chains or groups of mountains.
2, Position of Mountain-Chains along the Borders of Continents.
The view that mountain-chains are the up-squeezed sediments of mar-
1 Geological Magazine, 1876, vol. iii , p. 337.
THEORY OF THE ORIGIN OF MOUNTAIN-CHAINS. 257
ginal sea-bottoms completely explains the well-known law of conti-
nental form, viz., that continents consist of interior basins, with coast/-
chain rims. In fact, the theory necessitates this as a general form of
continents, but at the same time prepares us for exceptions in the case
of mountains formed from mediterranean sediments.
3. Parallel Ranges. Whitney has drawn attention ' to the fact that
" parallel ranges of the same system are formed successively" and we
would add, most usually formed successively coastward. An example
is found in the North American Cordilleras, the three parallel ranges of
which were successively formed first the Rocky Mountains, then the
Sierras, and last the Coast chain. The same is probably true of many
other mountains. Both the general parallelism and the successive
formation, and the successive formation coastward, are explained by the
theory.
4. Metamorpbism of Mountain-Chains. Admitting, then, as quite
certain, that mountains are formed by the squeezing together and the
upswelling of lines of off-shore sediments, the question still occurs,
" Why does the yielding to horizontal pressure take place along these
lines in preference to any others ? " The answer to this question is
found in the metamorphic changes and the aqueo-igneous softening of
deeply-juried sediments. Taking the increase of heat as we descend
into the interior of the earth to be 1 for every 50 feet, and adding the
mean surface temperature, 60, the lower portion of 10,000 feet of strata
must have a temperature of about 260, and of 40,000 feet of strata
860 Fahr. Even the former moderate temperature, long continued in
the presence of the included water of sediments, would probably pro-
duce incipient change, especially if the included waters be at all alka-
line. The latter temperature, we know from Daubree's experiments,
would certainly produce aqueo-igneous pastiness or even aqueo-igneous
fusion. Now, this aqueo-igneous softening would affect not only the
sediments, but also the crust beneath on which the sediments were de-
posited. Thus would be produced a line of weakness, and therefore a line
of yielding to the horizontal crushing. Thus we fully account for the
formation of the chain along the line of thick sediments, and at the
same time for the metamorphism of the strata, especially the lower
strata, involved in mountain-structure. By this view, of course, the ex-
posure of metamorphic rocks on the surface, as already stated (p. 217),
is the result of erosion. Even the granite axis, in most if not in all
cases, is but the lowermost, and therefore the most changed, portion of
the squeezed mass exposed by erosion ; although it is possible that in
some cases the granite may have been squeezed out as a pasty mass
through a rupture at the top of the swelling mass of strata.
Thus it will be seen that the thickness of mountain-strata, the nor-
1 Whitney on " Mountain-Building."
258 STRUCTURE COMMON TO ALL ROCKS.
mal position of chains on the borders of continents, the successive for-
mation coastward of parallel ranges, and the metamorphism of the
strata of great chains, are all accounted for, and shown to be neces-
sarily connected with each other.
5. Fissures and Slips, and Earthquakes. The enormous foldings
of strata which must always occur in the formation of a mountain-
chain by lateral thrust would of necessity often produce fractures at
right angles to the thrust, or parallel to the folds, i. e., to the range.
The walls of such fissures would often slip by readjustment by the force
of gravity, or else, in cases of great mashing together, might be pushed
one over the other by the sheer force of the horizontal thrust. The for-
mer case would give rise to those slips in which the hanging wall has
dropped down, which are by far the most common slips in gently -folded
strata (Figs. 204, 205, pp. 224, 225). The latter would give rise to
those cases often found in strongly-folded strata, as in the Appalachian
(Fig. 199, p. 222), in which the hanging wall has been pushed upward,
and slidden over the foot-wall. The sudden rupture of the earth's crust
under accumulating horizontal forces, or the sudden slipping of the
broken strata, sufficiently accounts for the phenomena of earthquakes.
6. Fissure-Eruptions. It will be observed that, according to our
view, beneath every thick mass of sediments there is a layer of aqueo-
igneously softened matter. This it is which determines the line of
yielding, and therefore the place of the mountain-chain. Perhaps this
aqueo-igneous softening may be sufficient to account for some cases of
semi-fused lavas and hot volcanic muds ; although the intense heat of
ordinary fused lavas cannot be thus accounted for. But as soon as the
yielding commences, mechanical energy, by means of the friction of
the crushed strata, is converted into heat. Mr. Mallet believes ' that the
heat thus produced is sufficient to fuse the rocks. Beneath every
chain, therefore, there must be, or has been, a mass of fused matter.
Now, in the progressive crushing together of the mountain-strata, it
follows inevitably that this fused matter is squeezed into fissures of the
folded strata, forming dikes, or squeezed out through such fissures, and
outpoured upon the surface as great sheets of lava. Thus the associa-
tion of these lava-floods with mountain-chains is also completely ac-
counted for ; and it is simply impossible to account for them in any
other way, unless, indeed, by Fisher's view of superheated steam issu-
ing from the fissures.
7. Volcanoes. No doubt the study of causes now in operation forms
the only true foundation of a scientific geology. Nevertheless, the
assimilation of agencies in previous geological epochs to those now in
operation may be carried too far. For instance, there is a strong ten-
dency among the best geologists to make volcanoes or crater-eruptions
1 " Philosophical Transactions " for 18"72.
THEORY OF THE ORIGIN OF MOUNTAIN-CHAINS. 259
(the only form of eruption now going on) the type of all igneous erup-
tions in all times. But the attentive study of the mode of occurrence
of eruptive rocks will show that by far the larger quantity have come
through fissures, as explained above, and not through craters. No one
who has examined the eruptive rocks of the Pacific coast can for a
moment believe that these immense floods of lava have issued from
craters. The lava-flood of the Sierra and Cascade ranges is certainly
among the most extraordinary in the world. Commencing in Middle
California as separate lava-streams (which, however, cannot be traced
in any case to craters), in Northern California it becomes an almost con-
tinuous sheet, several hundred feet thick; and in Oregon an overwhelm-
ing flood, at least 2,000 feet thick. In apparently un diminished thick-
ness it then stretches through Washington Territory to the borders of
British Columbia. An area 800 miles long and 100 miles wide is
apparently entirely covered with a universal lava-flood, which, in the
thickest part, where it is cut through by the Columbia River, is certainly
not less than 3.000 feet thick. Over this enormous area there are scat-
tered about a dozen extinct volcanoes mere pimples on its face. It is
incredible that all this flood should have issued from these craters.
There is no proportion between the cause and the effect. We therefore
unhesitatingly adopt the view of Richthofen, 1 that these immense
floods of lava, so often associated with mountain-chains, and often form-
ing, as in this case, the great mass of the chain itself, have issued, not
from craters, but from fissures / and that volcanoes or crater-eruptions
are secondary phenomena, arising from the access of water to the hot
interior portions of great fissure-eruptions. Thus, as monticules are
parasites on volcanoes, so are volcanoes parasites on fissure-eruptions,
and fissure-eruptions themselves parasites on an interior fluid mass.
This interior fluid mass, however, according to Richthofen, is the sup-
posed universal liquid interior / while, according to our view, it is the
sub-mountain reservoir, locally formed, as above explained.
By this theory it is necessary to suppose that there have been, in
the history of the earth, periods of comparative quiet, during which the
forces of change were gathering strength ; and periods of revolutionary
change periods of gradually-increasing horizontal pressure, and peri-
ods of 'yielding and consequent mountain-formation. These latter
would also be periods of great fissure-eruptions, and would be followed
during the period of comparative quiet by volcanoes gradually decreas-
ing in activity. The last of these great fissure-eruption periods in the
United States occurred in the later Tertiary. Since then we have been
in a crater-eruption period, which has been steadily decreasing in activ-
ity, until only geysers and hot springs remain to tell us of the still hot
interior masses of the great fissure-erupted lavas. The periods of
1 " Natural History of Volcanic Rocks," Memoirs of California Academy of Science.
260 DENUDATION, OR GENERAL EROSION.
revolution separate the great eras and ages of geological history, and
are marked by unconformity r , because the sea-margin sediments, upon
which the sediments of the next period are necessarily dep9sited,
are crumpled up y and also by change of species, because changes of
physical geography determine changes of climate, and therefore en-
forced migration of species.
The theory here presented accounts for all the principal facts asso-
ciated in mountain-chains. This is the true test of its general truth.
It explains satisfactorily the following facts : 1. The most usual position
of mountain-chains on the borders of continents. 2. When there are
several ranges belonging to one system, these have been formed suc-
cessively coastward. 3. Mountain-chains are masses of immensely
thick sediments. 4. The strata of which mountain-chains are composed,
are strongly folded, and, where the materials are suitable, are affected
with slaty cleavage ; both the folds and the cleavage being usually par-
allel to the chain. 5. The strata of mountain-chains are usually affected
with metamorphism, which is great in proportion to the height of the
chain and the complexity of the foldings. 6. Great fissure-eruptions and
volcanoes are usually associated with mountain-chains. 7. Many other
minor phenomena, such as fissures, slips, and earthquakes, it equally
accounts for.
Rev. O. Fisher and Captain Button 1 have objected to the above
view, that at the calculable rate at which the earth is now cooling, the
amount of contraction is wholly inadequate to produce the supposed
effect. But even if this be true, the objection does not touch the fact
of contraction, which is certain, but only the cause of contraction, viz.,
by cooling. Other causes of contraction are conceivable, for example,
loss of interior vapors and gases, according to Fisher's theory of volca-
noes (p. 93).
CHAPTER VI.
DENUDATION, OR GENERAL EROSION.
THE term denudation is used by geologists to express the general
erosion which the earth-surface has suffered in geological times. The
correlative of denudation is sedimentation, and the amount of denudation
is measured by the amount of stratified rocks.
Agents of Denudation. The agents of erosion, as we have already
seen in Part I., are : 1. Rivers, including under this head the whole
course of rainfall on its way back to the ocean whence it came ;
1 Fisher, " Cambridge Philosophical Transactions," vol. xii. ; Dutton, Pcnn Monthly^
May and June, 1876.
DENUDATION, OR GENERAL EROSION. 261
2. Glaciers, including under this head not only glaciers proper, but
moving ice-sheets, such as now exist in polar regions and in the Glacial
epoch extended far into now temperate regions, and also moving snow-
fields, for it is probable that all extensive snow-fields and snow-caps are
in motion ; 3. Waves and tides ; and, possibly, 4. Oceanic currents.
Oceanic currents usually run on a bed and between banks of still
water, and therefore produce no erosion. It is possible, however, that
a rising sea-bottom may be eroded by this agent ; but as we have no
knowledge of such effects, we are compelled to omit this from our esti-
mate of the probable rate of denudation. The action of waves and tides
is violent and conspicuous; yet these agents are so entirely confined to
the shore-line that their aggregate effect is but a small fraction of the
whole erosion. Prof. Phillips has shown * that, taking the coast-lines of
the world as 100,000 miles, and making the extravagant estimate that
the average erosion along this whole line is equal to that of the English
coast, or one foot per annum of a cliff one hundred feet high, still the
aggregate wave-erosion is far less than river-erosion, being equivalent
to a general land-surface erosion of only z ^ 00 of an inch per annum, or
-jJg- of that which is now going on over the hydrographical basin of the
Ganges, and ^ of that going on in the basin of the Mississippi. Glaciers
and rivers, therefore, are the great agents of erosion. The one takes the
place of the other, according as falling water takes the form of rain or
snow; both come under the general head of circulating meteoric water.
In a general estimate of the rate of denudation we may, therefore, with-
out sensible error, regard it as the work of circulating meteoric water.
Again, although it is probable that the erosive power of glaciers
is far greater than that of rivers, yet their action is so much more local,
both in time and space, that we believe we may take the average rate of
river-erosion as a fair representative of the average rate of denudation.
Amount of Denudation. A mere glance at the figures below will
show in a general way the manner in which geologists estimate the
amount of denudation in certain regions. In almost all countries, espe-
cially in mountain-regions, we find slips varying from a few feet to
many thousands of feet perpendicular (Fig. 238). There are slips in
the Appalachian chain which are estimated to be 8,000, and even one
20,000, feet perpendicular. And yet in most cases the escarpment,
which would otherwise exist, is completely
cut away, so that no surface-indication of
the slip exists. Evidently in such cases there
must have been erosion on the elevated side,
at least equal to the amount of slip, and
probably much greater. The dotted line
represents the probable original surface. FIG. 238.
1 "Life, its Origin and Succession," p. 130.
262
DENUDATION, OR GENERAL EROSION.
Sometimes the horizontal strata of isolated mountain-peaks corre-
sponding to each other (mountains of erosion) show that these are but
scattered fragments of a once high plateau, which has been removed by
FIG. 239. Denudation of Red Sandstone, Northwest Coast of Boss-shire, Scotland.
erosion, as shown in the annexed figure (Fig. 239), and in the sections
of the Appalachian, on pages 246, 247 (Figs. 226, 229). In such cases the
erosion must have been at least equal to the height of the peaks, and
FIG. 240. Section across Middle Tennessee. The dotted lines show the amount of matter removed.
may have been to any extent greater. The accompanying section across
Middle Tennessee shows a vertical erosion of 1,200 to 2,400 feet, over
the whole valley of Middle Tennessee, which is sixty miles across,
FIG. 241. Section through Portions of England.
and one hundred miles long. In most cases the removed matter is not
so easily estimated as in those mentioned. The strata in mountain-
chains are usually folded in a very complex way, and then denuded.
FIG. 242.-Section through Portions of England.
But the ideal restoration of these may be effected, and the amount of
erosion approximately estimated. Figs. 241 and 242 are sections across
the mountainous parts of England, as restored by Prof. Ramsay.
DENUDATION, OR GENERAL EROSION, 263
Average Erosion. By these methods Prof. Ramsay estimates the
denudation over many portions of England to be not less than 10,000
to 11,000 feet in thickness. 1 Over the whole Appalachian region the
denudation has probably been enormous, in some places 8,000 to 20,000
feet. Over the whole region of the high Sierra Range, as we have
shown, 2 erosion has removed the whole of the Jurassic and Triassic
slates, and bitten deep into the underlying granite. The thickness of
these slates is not known, but it must be many thousand feet. In
the TJintah Mountain region, according to Powell, over an area of
2,000 square miles, an average thickness of three and a half miles
}. 243. Uintah Mountains Upper Part restored, showing Fault; Lower Part showing the Present
Condition as produced by Erosion" (after Powell).
has been taken away (Fig. 243), the extreme thickness removed being
nearly five miles. Over the whole Colorado Plateau region the succes-
sion of cliffs, separated by broad tables (Fig. 237), shows enormous
erosion.
It seems impossible to avoid the conclusion, therefore, that the
average erosion over all present land-surfaces has been at least several
thousand feet.
There is another mode of estimating the average erosion, viz., by
the average thickness of stratified rocks. The debris of erosion is car-
ried down into seas and lakes, and forms strata, and the amount of strat-
ified rocks becomes thus the measure of the erosion ; the average thick-
ness of sediments, if they had been spread over an equal area, Avould
be an accurate measure of the average thickness removed by erosion.
Now, the stratified rocks are in some localities 10,000 feet, 20,000 feet,
and sometimes 40,000 and 50,000 feet thick. They are scarcely ever
found less than 2,000 or 3,000 feet. It is certain, therefore, that the
average thickness of strata over the whole known sui'face of the earth is
not less than several thousand feet. Let us take it at only 2,000 feet.
But the area of sedimentation, the sea-bottom, is now, and has proba-
1 Geological Observer, p. 819.
2 American Journal of Science and Arts, voL v., p. 325.
264 DENUDATION, OR GENERAL EROSION.
bly alwa3 T s been, at least three times the area of erosion, the land-surface.
Thus an average of 2,000 feet of strata would require an average erosion
of 6,000 feet.
Estimate of Geological Times. There are many facts connected
with geology, especially the facts of evolution, which cannot be under-
stood without the admission of inconceivable lapse of time. It is im-
portant, therefore, that the mind should become familiarized with this
idea. It will not be out of place, therefore, to make a rough estimate
of time based upon the amount of erosion.
We have already seen (p. 11) that, taking the Mississippi as an aver-
age river in erosive power (it is probably much more than an average),
the rate of continental erosion is now about one foot in 5,000 years.
At this rate, to remove an average thickness cf 6,000 feet would re-
quire 30,000,000 years.
Some may object to this estimate, on the ground that geological
agencies were once much more active than now. It is probable that
this is true of igneous agencies, since these are determined by the in-
terior heat of the earth, and this has evidently been decreasing. It is
probable also that this is true of the chemical agencies of water in dis-
integrating rocks and forming soils, since chemical effects are also usu-
ally increased by heat. But there is good reason to believe that the
mechanical agencies cf water, i. e., its erosive power y have been con-
stantly increasing with the course of time, and are greater now than
at any previous epoch except the Glacial epoch.
For observe : The erosive power of water is determined entirely by
the rapidity of circulation of air and water, and this is determined by
the diversity of temperature in different portions, and this in its turn by
the size of continents and the height of mountains. Continents and
seas are two poles of a circulating apparatus at one pole is condensa-
tion, at the other evaporation. In proportion to condensation are also
evaporation and circulation. Now, there is good reason to believe that,
amid many oscillations, there has been throughout all geological times a
constant increase in the size of continents and the height of mountains.
If so, then the circulation of air and water has been becoming swifter
and swifter ; the life-pulse of our earth has beaten quicker and quicker,
and therefore the waste and supply (erosion and sedimentation) have
been greater and greater.
We therefore return to our estimate of 30,000,000 years with
greater confidence that it is even far within limits of probability. For,
1. We have taken the average thickness of strata at 2,000 feet, while
it is probably much more. 2. We have taken the Mississippi as an
average river, and therefore the present rate of general erosion as one
foot in 5,000 years : it is probably much less. 3. We have taken the
rate of erosion in previous epochs as the same as now, while it is prob-
DENUDATION, OR GENERAL EROSION. 65
ably much less, for two reasons : 1. The land-surface to be eroded was
smaller ; and, 2. The erosive power of water was less. Taking all these
things into consideration, the time necessary to produce the structure
which we actually find, is enormously increased.
But even this gives us no adequate conception of the time involved
in the geological history of the earth. For rocks disintegrated into
soils, and deposited as sediments, are again reconsolidated into rocks,
lifted into land-surfaces to be again disintegrated into soils, transported
and deposited as sediments. And thus the same materials have been
worked over and over again, perhaps many times. Thus the history of
the earth, recorded in stratified rocks, stretches out in apparently end-
less vista. And still beyond this, beyond the recorded history, is the
infinite unknown abyss of the unrecorded. The domain of Geology is
nothing less than (to us) inconceivable or infinite time.
PAET III.
HISTORICAL GEOLOGY;
THE HISTORY OF THE EVOLUTION OF EARTH -STRUCTURE AND OF THE
ORGANIC KINGDOM.
CHAPTER I.
GENERAL PRINCIPLES.
THBEE are certain laws underlying all development certain general
principles common to all history, whether of the individual, the race, or
the earth. We wish to illustrate these general principles in the more
unfamiliar field of geology by running a parallel between the history
of the earth and other more familiar forms of history.
1. All history is divided into eras, ages, periods, epochs, separated
from each other more or less trenchantly by great events producing
great changes. In written history these are treated, according to their
importance, in separate volumes, or separate chapters, sections, etc.
So earth-history is similarly divided into geological eras, ages, periods,
etc. ; and these have been recorded by Nature in separate rock-systems,
rock-series, rock-formations, and rock-strata. In geology these terms,
both those referring to divisions of time and those referring to divisions
of record, are unfortunately loosely and interchangeably used. We
shall strive to use them as definitely as possible, the eras and the cor-
responding rock-systems being the primary divisions, and the others
subdivisions in the order mentioned.
2. In all history successive eras, ages, periods, etc., usually graduate
insensibly into each other, though sometimes the change is more rapid
and revolutionary. In individual history childhood usually graduates
into youth, and vouth into manhood ; yet sometimes a remarkable
GENERAL PRINCIPLES. 267"
event determines a more rapid change. In social and political life, too,
successive phases of civilization embodying' successive dominant prin-
ciples usually graduate into each other ; yet great events have some-
times determined exceptionally rapid changes in the direction or the
rate of movement. So also is it in geological history. The eras,
periods, etc., usually shade more or less insensibly into each other ; yet
there have been times of comparatively rapid or revolutionary change.
In all history there are periods of comparative quiet, during which
forces of change are gathering strength, separated by periods of more
rapid change, during which the accumulated forces produce conspicuous
effects.
3. Ages, periods, etc., in all history, whether individual, political,
or geological, are determined by the rise, culmination, and decline, of
certain dominant forces, principles, ideas, functions. Thus, in individual
development, we have the culmination, first, of the nutritive functions;
then of the reproductive and muscular functions ; and, last, of the cere-
bral functions. And in mental development, also, we have the culmina-
tion, first, of the perceptive faculties, and memory; then, the imaginative
and aesthetic faculties ; and, last, the reflective faculties ; the first gath-
ering and storing material, the second vivifying it, the third using it in
productive mason-work of science. In social history, too, the succes-
sive culminations of different phases of civilization have been the result
of the introduction and culmination of successive dominant principles
or ideas of successive social forces or functions. So has it been in
geological history. The great divisions of time, especially what are
called ages, are characterized by the introduction and culmination of
successive dominant classes of organisms, for these are the highest
expression of earth-life. Thus, in geology, we have an age of mollusks,
an age of fishes, an age of reptiles, in which these were successively
the dominant class.
But since (Law 2) successive ages graduate more or less into and
overlap each other, we might expect, and do indeed find, that the char-
acteristics of each age commence in the preceding age. Each age is
foreshadowed in the previous age. The same is true of all history.
4. In all history, at the close of an age, the characteristic dominant
principle or class declines, but does not perish. It only becomes sub-
ordinate to the succeeding dominant class or principle. Thus, to illus-
trate from individual history, in youth, the characteristic faculties of
childhood, viz., perception and memory, decline, and become subordinate
to the higher faculty of imagination, and this in turn becomes subordi-
nate to the still higher faculty of productive thought ; and thus the
whole organism becomes higher and more complex, each stage of devel-
opment including not only its own characteristic, but also, in a subordi-
nate degree, those of all preceding stages. The same is true of social
268 GENERAL PRINCIPLES.
history. Each stage of social development absorbs and includes the
social principles and forces characteristic of previous stages, but subor-
dinates them to the higher principles which form its own characteristic,
and thus the social organism becomes ever higher, more complex, and
varied.
So is it also in geologic history. When the dominance of any class de-
clines at the end of an age, the class does not disappear, but remains sub-
ordinate to the next succeeding and higher dominant class, and the organ-
ic kingdom, as a whole, becomes successively more and more complex and
varied. This is graphically represented by the accompanying, diagram,
FIG. 244. Diagram illustrating Successive Culminations of Classes.
in which 1, 2, 3, 4, represent four successive ages determined by the
culmination of successive dominant classes.
5. There are two modes of determining and limiting eras, ages, peri-
ods, etc., in geology, viz., unconformity of the rock-system and change
in the life-system. In written human history, the divisions of time are
recorded in separate volumes, chapters, sections, with boards or blanks
between. These divisions in the record ought to correspond to con-
spicuous changes in the character of the most important contents. So,
in the history of the earth, the rock-systems, rock-series, rock-forma-
tions, are volumes, chapters, sections, respectively, more or less com-
pletely separated from each other by unconformity, indicating blanks
in the known record; and the most important changes in the contents,
i. e., in the life-system, ought to, and usually do, correspond with the
unconformity of the rock-system. But if there should be (as there is in
some limited localities) a discordance between these two, we should fol-
low the life-system rather than the rock-system, the contents rather
than the artificial divisions of the record.
6. As in human history there is a general onward movement of the
race, and yet special modifications in character and rate in each coun-
try, so in geology there has been a general march of evolution of the
whole earth and the organic kingdom, and yet special modifications in
character and rale in each continent, and to a less extent in different
portions of the same continent. The great eras, ages, and periods, be-
long to the whole earth alike, and are the same in all countries, but the
epochs and the smaller divisions of time, though similar, are probably
not contemporaneous in different countries. This fact has probably
been too much overlooked by geologists.
Great Divisions and Subdivisions of Time. Eras. It is upon these
GENERAL PRINCIPLES. 269
principles that geologists have established the divisions of time and
the corresponding divisions of strata.
The whole history of the earth is divided into five eras, with corre-
sponding rock-systems. These are : 1. Archaean or Eozoic 1 era, em-
bodied in the Laurentian system ; 2. Palaeozoic a era, embodied in the
Paleozoic or Primary system ; 3. Mesozoic * era, recorded in the Sec-
ondary system ; 4. Cenozoic* recorded in the Tertiary and Quaternary
systems ; and, 5. The Psychozoic era, or era of Mind, recorded in the
recent system.
These grand divisions, with the exception of the last, are founded on
an almost universal unconformity of the rock-system, and a very great
and apparently sudden change in the life-system, a change affecting not
only species but also genera, families, and even orders. Between the
last and the preceding, it is true, neither the unconformity of the rock-
system nor the change in the life-system is so great as in the others ;
but the introduction of man upon the scene is deemed sufficient to make
this one of the grand divisions of time.
We have already seen (p. 179) that unconformity is the result of
deposit of strata on old eroded land-surfaces, and that it therefore always
indicates an oscillation of the crust, and an emergence and submergence
of land. In every such case, as already explained, a portion of the
record is lost, which may or may not be recovered elsewhere. It is
certain that if the lost leaves could be all recovered, and the record made
complete, the suddenness of the break in the life-system would disap-
pear. Nevertheless, it is also certain that these general unconformities
indicate times of great change in physical geography, and therefore of
climate, and therefore of rapid changes of organic forms ; and therefore,
also, they mark the natural boundaries of the great divisions of time.
Ages. Again, the whole history of the earth is otherwise divided
into seven ages, founded, with perhaps the exception of the first, on the
culmination of certain great classes of organisms. These are : 1. The
Archaean or Eozoic Age, represented by the Laurentian system of
rocks; 2. The Age of MollusJcs, represented by the Silurian series of
rocks ; 3. The Age of Fishes, represented by the Devonian rocks ;
4. The Age of Acrogens, or sometimes called the Age of Amphibians,
represented by the Carboniferous rocks ; 5. The Age of Reptiles, repre-
sented by the Secondary rocks ; 6. The Age of Mammals, by the Ter-
tiary and Quaternary; and, 7. The Age of Man, by the recent rocks.
In the accompanying diagram (Fig. 245), vertical height represents
time, the strong horizontal lines divide the whole into eras, while the
lighter lines, where necessary, separate the ages. The shaded spaces
represent the origin, the increase and decrease, in the course of time, of
the great dominant classes of animals and plants. To illustrate : The
1 Dawn of animal life. * Old life. 3 Middle life. * Recent life.
270
GENERAL PRINCIPLES.
class of reptiles commenced in the Carboniferous increased to a maxi-
mum in the Secondary, and again decreased to the present time. It
Age of Man .
Age of Mam-
Age of Rep-
tiles.
Age of Aero-
gens.
Age of Fishes
Age of Inver-
tebrates.
Archaean Age.
HIM! 11! I II I
III 14M-M1:
LI, I i'-l ^asSS "III
ii i >
IBONIFEROUS
DEVON lf\N
S I L U R JAN
LAUREN T I A N
SYSTEM
S YS T E M
Psychozoic.
Cenozoic.
Mesozoic.
Archaean, or
Eozoic.
Fio. 245.
will be seen that the ages correspond with the eras, except in the case
of the Palaeozoic era. This long and diversified era is clearly divisible
into three ages.
Subdivisions. The subdivisions of eras and ages into periods and
epochs are founded, as already explained (p. 201), on less general un-
conformity in the rock-system, and less conspicuous changes in the life-
system. The names of periods are often, and of epochs are nearly
always, local, and therefore different in different countries. We will,
of course, use those appropriate to American geology. The table on
page 201 represents, as far as periods, the classification used in this
country. We have added epochs only in the uppermost part, viz., in
the Tertiary and Quaternary.
We give, also (Fig. 246), an ideal diagram of the principal groups
of strata, which we shall notice in the order of their superposition, indi-
cating also the principal places of general unconformity.
Order of Discussion. Many geologists take up the several epochs
and periods of the history of the earth in the inverse order of their oc-
currence. Commencing with a thorough discussion of " causes now in
operation" i. e., geological history of the present time, as that which
is best known, they make this the basis for the study of the epoch
immediately preceding, and which, therefore, is most like it. Having
acquired a knowledge of this, the studsnt passes to the preceding, and
so on. This has the great advantage of passing ever from the better
known to the less known, which is the order of induction. Other
GENERAL PRINCIPLES.
2T1
geologists prefer to follow the natural order of events. This has the
great advantage of bringing out
the philosophy of the history
the law of evolution. The first EK '
method is the best method of in- ' sy
vestigation ; the second method
is the best method of presenta-
tion. In common with most 4 cenozoie.
geologists, I shall, therefore, fol-
low the order of history.
As in human history, so in the
geological history, the recorded
events of the earliest times are
very few and meagre, but become 3 ; M esozoic...,
more and more numerous and in-
teresting as we approach the
present time. Our account of
the Archaean era will, therefore,
be quite general, and will not en-
ter into any subdivisions, al-
though this era was very long.
In the next era we will go into
the description of the several
ages, in the next into the pe-
riods, and in the next even into 2. Palaeozoic.,
the epochs.
Prehistoric Eras. Previous
to even the dimmest and most
imperfect records of the history
of the earth there is, as already
said (p. 265), an infinite abyss of
the unrecorded. This, however,
hardly belongs strictly to geol-
ogy, but rather to cosmic philos-
ophy. We approach it not by i- Archrean...
written records, but by means of
more or less probable general
scientific reasoning. We pass on,
therefore, without pause to the
lowest system of rocks contain- FIG. 246. Ideal General Section of the Whole Series of
J Strata, showing the Principal Divisions and Subdi-
ing the record of the earliest era. visions.
Carboniferous.
Silurian.
272 LAURENTIAN SYSTEM OF ROCKS
CHAPTER II.
LAURENTIAN SYSTEM OF ROCKS AND ARCHAEAN ERA.
IT is one of the chief glories of American geology to have estab-
lished this as a distinct system of rocks and a distinct era.
It had been long known that beneath the lowest Palaeozoic rocks
there still existed strata of unknown thickness, highly metamorphic
and apparently destitute of fossils.' These had been usually regarded
as lowermost Palaeozoic as the earliest defaced leaves of the Palgeo-
zoic volume. But the study of the Canadian rocks, by Sir William
Logan, revealed the existence of an enormous thickness of highly-con-
torted, metamorphic strata, everywhere unconformable with the over-
lying Potsdam or lowest Silurian. More recent observations show this
relation not only in Canada, but also in New York, on Lake Superior,
in Nebraska, Montana, Idaho, Wyoming, Colorado, Utah, Nevada,
Texas, New Mexico, and Arizona. Nor is it confined to our own coun-
try, for the same unconformable relation has been found by Murchison
on the west coast of Scotland, between the lowest Silurian (Cambrian)
and an underlying gneiss, evidently corresponding to the Laurentian
of Canada. Similar rocks, and in similar unconformable relation, have
been found underlying the lowest Silurian in Bohemia, and also in Swe-
den and Bavaria. Such general unconformity shows great and wide-
spread changes of physical geography at this time. There seems no
longer any doubt, therefore, that it should be regarded as a distinct
system.
The following figures give the relation between the Palaeozoic and
the Laurentian in New Mexico, in Canada, and in Scotland.
FIG. 247. Section across Santarita Mountain, New Mexico: c. Carboniferous; S, Silurian; A, Archscan ;
m, metalliferous vein (after Gilbert).
These, then, are the oldest known rocks. They form the first vol-
ume of the recorded history of the earth. Yet they evidently are not
the absolute oldest ; evidently they do not constitute any part of the
primitive crust. For they are themselves stratified or fragmental
AND ARCILEAN ERA.
273
rocks, and therefore formed from the debris of other rocks still older
than themselves ; and these last possibly from still older rocks. Thus,
FIG. '248. Section showing Primordial unconformable on the Archaean : 1, Archaean or Laurentian ;
Primordial or Lowest Silurian (after Logan).
FIG. 249. Diagram Section, showing the Structure of the North
dial ; c, Lower Silurian (Jukes).
: a, Laurentian ; 6, Primor-
we search in vain for the so-called primary rocks of the original crust.
Thus is it with all history. No history is able to write its own beginning.
Rocks. There is nothing very characteristic in the rocks of the
Laurentian system. They do not differ very conspicuously from those
of other periods ; consisting, in fact, only of altered sandstones, lime-
stones, and clays. They are all, however, very much contorted and
very highly metamorphic. In Canada they consist mainly of the schist
series, passing on the one hand into gneiss and granite, and on the
other into hornblehdic gneiss, syenites, and diorites; of sandstones,
passing into qnartzites; and of limestones, passing into marbles, which
are sometimes even intrusive. These together, in Canada, form a
series of rocks at least 40,000 feet thick.
Interstratified with these are found immense beds of iron-ore 100 or
more feet thick, and great quantities of graphite, sometimes impreg-
nating the rocks, and sometimes in pure seams. In rocks of this age
occur the great iron-beds of Missouri, of New Jersey, of Lake Superior,
and of Sweden. The quantity of iron found in these strata is far
greater than in any other. It may be well called the Age of Iron.
The following figures show the contortion of the strata (Fig. 250),
and the mode of occurrence of the iron (Figs. 251, 252).
FiQ. 252.
74 LAURENTIAN SYSTEM OF ROCKS
Area in North America. 1. These strata cover the greater portion
of Labrador and Canada, and then, turning northwestward, extend to
an unknown distance, but probably to the Arctic Ocean. The area forms
a broad V, within the arms of which is inclosed Hudson's Bay. It may
be seen on map, p. 278. This is the only extensive area known on the
continent. 2. On the eastern slopes of the Appalachian chain un-
doubted patches are found as far south as Virginia, and a considerable
area in this region is referred with much probability to the same. This
is shown on map, p. 278, as the area left blank. Its further extension
southward along the chain is still doubtful, though probable. 3. In
the Rocky Mountain region extensive lines and areas of outcrop are
known, trending in the general direction of the chain, especially a large
area in the Basin region. 4. Several small patches are also found scat-
tered about in the basin of the Mississipi, apparently exposed by erosion.
Doubtless the Laurentian rocks are far more extended, but covered
and concealed by other and later rocks. The area mentioned is the
area of surface-exposure. It represents so much of Archaean sea-bot-
tom as was subsequently raised into land, and not afterward again
covered by sediments; or, if so covered, again exposed by erosion.
Physical Geography of Archaean Times. As these are the oldest
known rocks, we know nothing of the land from which they were
formed. But since, during the rest of the geological history, the con-
tinent has developed from the north toward the south, it seems most
probable that this earliest land lay still farther north, and disappeared
when the Laurentian area was elevated into land.
Time represented. The enormous thickness of these rocks (40,000
feet in Canada, and still greater in Bohemia and Bavaria) certainly in-
dicates a very great lapse of time. It is probable that the Archaean
era is longer than all the rest of the recorded history of the earth put
together ; and yet, precisely as in the beginnings of human history, the
record is almost a blank. The events are few, and imperfectly re-
corded.
Evidences of Life. We have already explained (p. 136) how iron-
ore is ^present accumulated. We have there shown that all accumu-
lations or this kind now going on are formed by the agency of organic
matter. It is almost certain that the same is true for all times, and
therefore that iron-ore accumulations are the sign of the existence of
organic matter, and quantity of the ore accumulated is a measure of the
amount of organic matter consumed in doing the work. The immense
beds of iron-ore found in the Laurentian rocks are, therefore, evidence
of the existence of organisms in great abundance. That these organ-
isms were chiefly vegetable, we have the further evidence derived from
the great beds of graphite ; for graphite, as we shall see hereafter is
only the extreme term of the metamorphism of coal.
AND ARCHAEAN ERA.
275
Of the existence of animal organisms the evidence is not yet com-
plete, although it is probable that the lowest forms of Protozoa, such as
Rhizopods, were abundant. We have seen that limestones are abun-
dant among the Laurentian rocks. Now, the limestones of subsequent
FIG. 253. Fragment of Eozoon, of the Natural Size, showing Alternate Lamince of Loganite and Dolomite
(after Dawson.)
geological epochs are almost wholly composed of the accumulated shelly
remains of lower organisms, especially nullipores and coccolites among
plants, and rhizopods among animals.
The existence of rhizopods is believed by many to have been demon-
strated. There have been found abundantly, in the Laurentian lime-
stones of Canada, of Bohemia, of Bavaria, and elsewhere, large, irreg-
ular, cellular masses, which are fwmur-/'-'-' ">
believed by the best authori- iglliii i ,...,,, (
ties to be the remains of a gi-
gantic foraminiferous rhizopod.
The supposed species has been
called Eozoon l Canadense.
Fig. 253 is a section of an
Eozoonal mass, natural size,
in which the white is the cal-
careous matter secreted by the
rhizopod, and the dark corre-
sponds to the animal matter of
,. , . ., Fro. 254,-Diagram of a Portion of Eozoon cut vertically:
the rhizopod itself ; and Flff. A, B, <?, three tiers of chambers communicating with
, 1C ,, ,. _ .. one another by slightly constricted apertures ; a, a,
/i04 a Small portion Ot the Same, the true shell-wall, perforated by numerous delicate
fl-j . i ,, tubes; b, b, the main calcareous skeleton ("interme-
magnineu SO as to SHOW the diate skeleton "); c, passage of communication ("sto-
a+m-in+ui.** ^f -(-V.^ 11 Ion-passage") from one tier of chambers to another :
Structure Ot the Cells. ^ ramifying tubes in the calcareous skeleton (after
There has been, and is still, Car P enter >-
much discussion as to the organic or mineral nature of these curious
structures. If these irregular masses be indeed of animal origin, as
1 Dawn animal.
276 PALAEOZOIC SYSTEM OF ROCKS.
seems most likely, it is evident that they belong to the lowest forms of
compound protozoa lower far than the symmetrically-formed forami-
nifera of later times. It is precisely in such almost amorphous masses
of protoplasmic matter that, according to the evolution hypothesis, the
animal kingdom might be expected to originate.
Some very obscure tracings, suggesting the possible existence of
marine worms, have been found both in Canada and in Bohemia ; but
as yet we have no reliable evidence of any animals higher than the pro-
tozoa. It is impossible to say that other animals of low form did not
exist ; yet the absence of any reliable trace in rocks not more metamor-
phic than some of the next era, which are crowded with fossils of many
kinds, seems to indicate a paucity, if not an entire absence, at this time,
of such animals.
CHAPTER III.
PRIMARY OR PALAEOZOIC SYSTEM OF ROCKS AND PALAEOZOIC
ERA.
General Description.
THIS is a distinct system of rocks, revealing a distinct time-world
a distinct rock-system, containing the record of a distinct life-system.
The rock-system is distinct, being everywhere unconformed to the
Laurentian below and the Secondary above a bound volume volume
second of the Book of Time. The life-system is also equally distinct,
being conspicuously different from that which precedes and that which
follows. Whatever of life existed before, its record is too imperfect to
give us a clear conception of its character. But in the Palaeozoic the
evidences of abundant and very varied life are clear ; about 20,000 spe-
cies having been described. It stands out the most distinct era in the
whole history of the earth. The Archaean must be regarded as the
mythical period. Here, with the Palaeozoic, commences the true dawn
of history.
Rocks Thickness, etc. The rocks of this system, although less
powerful than the preceding, are also of enormous thickness compared
with those of later geological times, being in the Appalachian region
about 40,000 feet. It is believed that we are safe in saying that the
time represented by them is equal to all subsequent time to the present.
There is nothing very characteristic in the rocks composing Palaeo-
zoic strata, though the practised eye may often distinguish them by
their lithological character. Though strongly folded and highly meta-
GENERAL DESCRIPTION. 277
morphic in some regions, these characters are not so universal as in the
Laurentian.
In the United States the rocks of the whole system are conformable.
In Europe, on the contrary, the principal divisions are usually uncon-
formable. In this country, therefore, the subdivisions are founded
almost wholly on change in the life-system ; while in Europe the same
subdivisions are founded on unconformity of the rock-system, as well as
change in the life-system. Further, in this country, in passing from
Pennsylvania, through New York, into Canada, we pass over the out-
cropping edges of the whole system, from the highest to the lowest ;
and finally into the Laurentian (Fig. 255). This, taken in connection
with the conformity of the rocks, shows that during the Palaeozoic the
continent in this part was successively developed, from the north toward
the south, by bodily upheaval of the Laurentian area and successive ex-
posure of contiguous sea-bottom. In Europe the oscillations seem to
have been more frequent and violent.
Fig. 255 is a section from Pennsylvania to Canada, showing the
JJS ' li S I A.
FIG. 255. Ideal Section north and south from Canada to Pennsylvania : A, Archsean ; L S and US,
Silurian ; Z>, Devonian ; C, Carboniferous.
relation of the subdivisions to each other, and the manner in which they
lie on the Archaean. This will be better understood if the map on page
284 be at the same time carefully examined.
Area in the United States. The area in the Eastern United States
in which the country rock belongs to this system is seen in the map given
on next page (Fig. 256). It may be stated roughly to embrace all that
part included between the Great Lakes on the north, the Blue Ridge of
the Appalachian chain on the east, the Prairies on the west, and Middle
Alabama and Southern Arkansas on the south. It includes the richest
portion of our country. Besides this great continuous area there are
also areas of imperfectly known size and shape in the Rocky Mountain
region, and on either side of the Sierra Nevada.
If we compare the Palaeozoic rocks of the Appalachian region
with the same in the central portion of the Mississippi basin, we ob-
serve the following changes as we go westward : (a.) The rocks in the
Appalachian region are highly metamorphic ; as we go westward, they
become less and less so, until in the region about the Mississippi River
they are wholly unchanged, (b.) In the Appalachian region they are
strongly and complexly folded; as we go west, these folds pass into
278
PALAEOZOIC SYSTEM OF ROCKS.
gentle undulations, which die away into horizontally (see section
on p. 244). (c.) In the Appalachian region they are about 40,000 feet
thick ; as we go west, they thin out until the whole series is only 4,000
feet at the Mississippi, (d.) In the Appalachian region grits and sand-
GENERAL DESCRIPTION. 279
stones and shales predominate greatly over limestones ; as we go west,
the proportion of limestone increases, until these are the predominating
rocks. These four changes are closely connected with each other, and
all with the formation of the Appalachian chain, as we have already
explained in the chapter on Mountain-Formation (p. 252, et seq.).
Physical Geography of the American Continent. At the beginning
of the Palaeozoic era the land was the Laurentian area, already described,
excepting Archaean areas exposed by erosion. From this nucleus, dur-
ing Palaeozoic times, the continent was developed southward, until,
at the end, it included also the Palceozoic area just described. The
accompanying map (Fig. 257) ' gives approximately the area of land at
FIG. 257. Existing Seas. Lakes, etc.. shaded black ; Portions of Continent then covered, lighter; Land of
that Time left white ; where Outline known, surrounded with Full Line ; when doubtful, by Dotted Line.
the beginning. The map of the physical geography of Cretaceous times
(p. 452) gives somewhat less approximately its area at the end. It
will be seen that the continent was already sketched out at the begin-
ning, and steadily developed throughout its continuance. There is
much reason to believe that a considerable body of land existed at this
1 A map similar to the above, but containing also small scattered patches of Archaean
exposures, is sometimes spoken of as an Archaean map of North America, or map of
Archaean land. It must be borne in mind, however, that it represents indeed land of
Archaean strata, but, for that very reason, not of Archaean time, but of Silurian time.
280 PALAEOZOIC SYSTEM OF ROCKS.
time to the east of the Appalachian region, much of which afterward
disappeared by subsidence. It is only thus that we can explain the
thick strata of this region.
Subdivisions. The Palaeozoic era is divided into three ages, which
are embodied in three distinct subordinate rock-systems. These ages
are each characterized by the dominance of a great class of organisms.
They are : 1. The Silurian System, or Age of Invertebrates, or some-
times called Age of Mollusks ; 2. The Devonian System, or Age of
Fishes; and, 3. The Carboniferous System, or Age of Acrogens and
Amphibians. These are three chapters in the Palaeozoic volume.
These three systems are generally conformable with each other in
the Palaeozoics of the United States, as we have already shown, but
elsewhere they are often unconformable. Before taking up the first in
the order of time, viz., the Silurian, it is necessary to say something of
the interval which in our record separates the Archaean from the Palaeo-
zoic era.
The Interval. We have already seen that the lowest Silurian lies
unconformably on the upturned and eroded edges of the crumpled strata
of the Lauren tian. We have also shown (p. 179) that unconform-
ability indicates always an oscillation of the earth's crust at the ob-
served place. More definitely it indicates an upheaval, by which the
lower series of rocks became land-surface, and were at the same time,
perhaps, crumpled ; then a long period unrecorded at that place, during
which the land was eroded and the edges of the crumpled rocks were ex-
posed; then a subsidence, and the deposit of the upper series of rocks on
these exposed edges. Now, oscillation necessitates increase and decrease
of land-surface. Evidently, therefore, such increase and decrease of land-
surface took place in the unrecorded interval between the Archaean and
Palaeozoic eras ; and the length of this unrecorded interval is measured
by the amount of erosion which the Laurentian underlying the lowest
Palaeozoic has suffered. We have stated that the land at the beginning
of the Silurian age was approximately the Laurentian area. The shore-
line of the earliest Palaeozoic sea was the line of junction between the
Silurian and Laurentian (see map, p. 278). But this was not the shore-
line at the end of the Archaean time. , Evidently this shore-line was
much farther south ; evidently the land-area was much greater at the
end of the Archaean than at the beginning of the Silurian. The Archae-
an era was closed by the upheaval into land-surface and the crumpling
of the strata of the whole Laurentian area, and much more. Then fol-
lowed an interval of which we know nothing, except that it was of long
duration, during which the crumpled Laurentian strata forming the then
land-surface were deeply eroded. Then, at the end of this interval came
a subsidence down to the shore-line already indicated as the Silurian
shore-line, and the Silurian age commenced, its first sediments being
GENERAL DESCRIPTION.
281
of course deposited on the exposed edges of the submerged Laurentian
rocks.
I have attempted to illustrate these facts by the following diagrams
(Fig. 258), in which c represents a section north and south through the
Laurentian and Palaeozoic rocks. The crumpled Laurentian strata, with
their outcropping eroded edges, are seen to underlie the lowest Silurian
to some distance. This is the actual condition of things. The manner
FIG. 258. Ideal Sections, showing how Unconformity is produced.
in which this condition was brought about is shown in a and b. In a
we have represented the supposed condition of things during the inter-
val, s I being the sea-level, and s the shore line ; in b the condition of
things at the end of the interval or beginning of the Silurian, when by
subsidence the shore-line had been shifted northward to s', and on the
exposed edges of the strata of the previous land-surface, from s to s',
Silurian sediments had begun to deposit.
We have spoken thus far only of the unconformity of the New
York rocks on the Canadian rocks. This phenomenon may be explained,
as we have seen, by local oscillations, with increase and decrease of land-
area during the lost interval. But, when we remember that the same
unconformity is found in the most widely-separated localities, over
the whole area of the United States, we are forced to the conclusion
that the lost interval, as compared with the Silurian, was probably a
continental period a period of widely-extended land composed of
282 PALAEOZOIC SYSTEM OF ROCKS.
Laurentian rocks. The whole of this land disappeared by submergence
at the beginning of the Silurian, except the Canadian area, and prob-
ably a considerable area in the Basin region, and perhaps a few islands
or larger areas in Silurian seas between.
In all speculations on the origin of the animal kingdom by evolu-
tion, it is very necessary to bear in mind this lost interval, for it was
evidently of great duration.
SECTION 1. SILURIAN SYSTEM : AGE OF INVERTEBRATES.
The Rock-System. The rocks of this age have been carefully studied
in England, by Sedgwick and Murchison ; in Russia and Sweden, by
Murchison ; in Bohemia, by Barrande ; and in New York, by Hall. The
divisions and subdivisions established by these geologists have become
the standard of comparison elsewhere. The system was first clearly
defined by Murchison in Wales. The name Silurian (from Silures, the
Roman name for the inhabitants of Wales) was given by him, and is
now universally adopted. But the most perfect examples are, perhaps,
those found in Bohemia and in New York. We have already given
(Fig. 255) a section of the Palaeozoics of New York, including, of Course,
the Silurian. Some geologists call the lower portion Cambrian a
name given bv Sedgwick.
Subdivisions. The following table gives the divisions and subdi-
visions of the Silurian system and the corresponding periods of this
age in this country :
rOriskany Period.
TT r,., . I Lower Helderbere
Upper Silurian. j Sa]ina
[Niagara
( Trenton
Lower Silurian. -I Canada
[Primordial
The larger divisions, viz., Lower and Upper Silurian, are generally
recognized ; also, the Primordial is generally recognized ; by some as a
subdivision of the Silurian, by others as more distinct than the other
periods and as synonymous with Cambrian. The subdivisions are,
with this exception, local, each country having its own ; but they are
synchronized, as far as possible, by comparison.
Character of the Rocks. The Silurian, like nearly all rocks, are
greatly disturbed and metamorphosed in mountain-regions, though less
so than the Laurentian ; but in Sweden and Russia, and in the valley
of the Mississippi, Silurian rocks are found in their original horizon-
tal position, and not greatly changed from their original sedimentary
condition.
Area in America. By turning to the map (p. 278) it will be seen :
1. That the Silurian is attached to the Laurentian nucleus as an irregu-
SILURIAN SYSTEM: AGE OF INVERTEBRATES. 283
lar border on the outer side of the V-shaped area ; 2. Again, the Ap-
palachian Laurentian region is also bordered on the west side by
Silurian ; 3. Also we observe large patches in the interior one about
Cincinnati, another occupying the southern portion of Missouri and
northeastern portion of Arkansas, and one in Middle Tennessee ; 4.
Also, large areas are known to occur in the Rocky Mountain region and
in the Basin region between the Wahsatch Mountain and the Sierra ;
but their outlines are yet too little known to describe them accurately.
Physical Geography. At the beginning of the Silurian, as already
said, the land was approximately the Laurentian area (Fig. 257). The
Silurian, which embraces the great V-shaped Laurentian area on the
southeast, south, and southwest, was then the sea-bottom border of the
coast of that Silurian continent. The Silurian bordering the Appalachian
Laurentian was also then a sea-bottom bordering the Silurian continent
in that region. It is probable, also, that the Silurian of the Rocky
Mountain region also borders Laurentian areas, and these areas repre-
sent Silurian continents, and the Silurian border the marginal sea-bot-
tom of that time. The other patches mentioned in the interior were
probably bottoms of open seas.
Now, the Silurian area represents so much of Silurian sea-bottoms
as were raised into land-surfaces during or at the end of Silurian times,
and not subsequently covered by sea. 1 Therefore, at the beginning of
Silurian times the land was the Laurentian area ; while at the end of
the Silurian times the land was increased by the addition of the Silurian
area. This addition was not all made at once, but very gradually. The
steps of this increase have been carefully studied in New York. The
following map (Fig. 259) shows the principal successive steps, as does
also the section (Fig. 255) with which it should be compared. Inspec-
tion of these figures shows not only the Silurian bordering the Laurentian,
but the rocks of the several periods bordering each other successively ;
so that in walking from Pennsylvania to Canada, or to the Adirondack
Mountains of New York, we successively walk over the Carboniferous,
the Devonian, the Silurian, and the Laurentian ; and in the Silurian
over rocks of the successive periods, from the highest to the lowest.
This plainly shows that during Silurian times the continent (Laurentian
area) was slowly upheaved, and contiguous sea-bottoms successively
added to the land, and the shore-line gradually pushed southward from
the Canadian region, and probably westward from the land-mass along
the Appalachian. Of course, therefore, the oldest Silurian shore-line
was the most northern and eastern. This is the primordial beach.
Primordial Beach and its Fossils. As already stated, the element-
ary character of this treatise renders it impossible to take the several
1 This is true as a broad, general fact ; but patches of Silurian may also be exposed
by removal of later deposits by erosion.
284
PALEOZOIC SYSTEM OF ROCKS.
periods of this age. We must confine ourselves to a general descrip-
tion of the age only. But there is so peculiar and special an interest
connected with the dawn of life on the earth, that, before taking up
the life-system of the whole age, it seems necessary to say something
of the earliest fauna.
We have seen that at the beginning of Silurian times a large V-
shaped mass of land occupied the region now embraced by Canada and
Labrador, and stretched northwestward to an unknown distance, the two
arms of the V being nearly parallel to the two present shores of the
American Continent ; further, that a land-mass of extent unknown
occupied the position of the eastern slope of the Appalachian chain ;
also, that land of unknown extent occupied the position of the Rocky
Mountains ; and the continent was thus early sketched out. Now,
southward of the first-mentioned land-area and betw r een the other two
FIG. 259. Oeolojrical Map of New York : o, Archaean ; PS, Primordial ; LS, Lower Silurian ;
US, Upper Silurian ; d, Devonian ; SC, Subcarboniferous ; C, Coal-measures.
there was a great interior sea, which we will call the Interior Palceozoic
Sea. The shores of that sea beat upon the continental masses north,
east, and west, and accumulated, on exposed places, a beach. Patches
of that earliest beach still remain. They are found, of course, closely
bordering the Laurentian rocks, Canadian and Appalachian, and lying un-
conformably upon them. They are the primordial sandstones and slates
of Canada, New York, Pennsylvania, Virginia, and probably Tennes-
SILURIAN SYSTEM: AGE OF INVERTEBRATES. 285
FIGS. 260-69. AMEBICAX PRIMORDIAL FOSSILS: 260. Plant: Scolithus linearis (after Hall). 261.
Brachiopod : a and 6, Linsrula acmninata (after Lo^an). 262. Lineula antiqua (after Hall). _ 263.
Gasteropod : Ophileta compacta. 264. Cephalopod : Orthoceras. 265. Pteropod : Hyahthis primor-
dialis (after White). 266. Tracks: Crustacean (after White). 267. Trail of Marine Worm (after
Logan). 263. Conocoryphe Kingii (after White). 269. Agnostus interstrictus (after White).
286
PALEOZOIC SYSTEM OF ROCKS.
see, and possibly Georgia. The fact that these are indeed remnants of
a beach is proved by the existence, in almost every part, of shore-marks
of all kinds such as ripple-marks, sun-cracks, worm-tracks, worm-bor-
ings, broken shells, etc.
This, then, is the old primordial beach. It is of the extremest inter-
est to the geologist because it marks the outline of the earliest Silurian
sea, and contains the remains of the earliest Silurian fauna. Indeed,
we may say it contains the remains of the earliest known fauna. It is
true, the lowest Rhizopods probably existed in Archaean times, but
these cannot be said to constitute a fauna. With the very commence-
ment of Silurian times, however, we find at once a considerable variety
of animal forms.
What, then, was the character of this earliest fauna and flora ? If
we could have walked along that beach when it was washed by pri-
mordial seas, what would we have found cast ashore ? We would have
found the representatives of all the great types of animals except the
vertebrata. The Protozoa were then represented by sponges and
Rhizopods ; the Radiates by Hydrozoa (graptolites) and Cystidean
Crinoids ; the mollusks by Brachiopods, Gasteropods (Pleurotomaria),
Pteropods, and even Cephalopoda (orthoceras) ; and the Articulates by
Crustaceans (trilobites, etc.) and Worms. Plants are represented by
Fucoids. These widely-distinct classes are already clearly differentiated
and somewhat highly organized. Nor is the fauna a meagre one in
number of species. In the United States and Canada alone about 200
species are already known, of which nearly 100 are trilobites. About
a dozen species of plants are also known. When we recollect the great
FIGS. 270-278FoRKiGN PRIMORDIAL FOSSILS: 270. Oldhamia antiqua. probably a plant. 271 Arenico-
272. Linpulclla ferrufrinea. 273. Theca Davidii. 274. Modiolopsis
lites didymus. Worm-tubes,
solvensis. 275. Orthis Hicksii.
Olenus macrurus.
270. Obolella sagittalis. 277. Hymenocaris vermicauda. 278.
SILURIAN SYSTEM: AGE OF INVERTEBRATES.
287
age of these rocks and their usual metamorphism, and the fragmentary
character of all fossil fauna, it seems certain that great abundance and
variety of life existed already in these early seas. Of this life the tri-
lobites, by their size, their abundance, their variety, and their high
organization, must be regarded as the dominant type. Among the
largest trilobites known at all are some from this period. The Para-
doxides, represented in Figs. 279 and 280, attained a length of twenty
FIG. 279. Paradoxides Bohemicus,
Foreign.
FIG. 280. Paradoxides Hsrlani,
x J (after Kogers), American.
inches. English beds of the same age furnish specimens of the same
genus two feet long.
We give in the above figures a few of the more remarkable primor-
dial forms taken from the rocks of this country, and of foreign coun-
tries. They are intended only to give a general idea of the fullness
and variety of the primordial life ; the affinities of these fossils will be
discussed hereafter.
General Remarks on First Distinct Fauna. There are several
points of great philosophic interest suggested by the nature of these
first organisms :
1. Plants in this, and in all other geological periods, are far less
numerously represented in a fossil state than animals. This cannot be
because animals were more abundant than plants, for since the animal
kingdom subsists on the vegetable kingdom, and since every animal
consumes many times its own weight of food, plants must have been
always more abundant than animals. The true reason of the greater
abundance of animal remains is to be found in the fact that the hard
parts of animals are far more indestructible than any portion of vege-
table tissue. .
2. At the end of the Archa3an times when the Archaean volume
288 PALAEOZOIC SYSTEM OF ROCKS.
closed we find only the lowest Protozoan life. But with the opening
of the next era, apparently with the first pages of the next volume, we
find already all the great types of structure except the vertebrata. And
these not the lowest of each type, as might have been expected, but al-
ready trilobites among Articulata, and Cephalopods among Mollusca
animals which can hardly be regarded as lower than the middle of the
animal scale.
We must not hastily conclude, however, that these widely-divergent
and highly-organized types originated together at once. We must re-
member that between the Archaean and Palaeozoic there is a lost interval
of enormous duration. Evidently, therefore, the Primordial fauna is not
the actual first fauna. Evidently we have not yet recovered the leaves
in which is recorded the gradual differentiation of these widely-distinct
types. All this must have taken place during the lost interval.
But if, on the other hand, we suppose, as many do, that evolution
proceeds always " with equal steps," then we are forced to the very im-
probable conclusion that the lost interval is equal to all geological times
which followed to the present ; for the differentiation of types which
occurred during that interval is equal in value to all that has taken
place since.
Therefore, we are compelled to admit that there have been in the
history of the earth periods of rapid change in physical geography, and
periods of comparative quiet in this respect ; that, corresponding with
these, there have been also periods of rapid evolution of the organic
kingdom, developing new forms, and periods in which forms are more
stationary. The periods of rapid change are marked by unconformity,
and are therefore unfortunately often lost.
As we proceed, we will probably find many examples of rapid change
which must be accounted for in a similar manner.
General Life- System of the Silurian Age.
There were evidently extraordinary abundance and variety of life in
the Silurian. These early seas literally swarmed with living beings.
The quantity and variety of life the number of individuals and of
species were probably not less than at the present time ; though orders,
classes, and departments, were less diversified. Over 10,000 species have
been described from the Silurian alone (Barrande) ; and these must be
regarded as only a small fragment of the actual fauna of the age. In cer-
tain favored localities, the number of species found in a given area of a
single stratum will compare favorably with the number now existing in
an equal area of our present sea-bottoms. Yet, in all this teeming life
there is not a single species similar to any found in any other geological
time. And not only are the species peculiar, but even the genera, the
families, and the orders, are different from those now existing.
GENERAL LIFE-SYSTEM OF THE SILURIAN AGE. 89
FIG. 2S4. r , G . 28 5.
FIGS. 281-286. SILURIAN PLANTS: 2S1. Sphenothallus an<nistifolius (after Hall). 2S2. Buthotrephis
succulens (aftor Hall). -.'S3. tt and b, Buthotrc-phis gracUis (after Hall). 2S1. Arthrophycus H?rlani
Cafter Hall). 2S5. Ouziana bilobata (after Hall)
290 PALEOZOIC SYSTEM OF ROCKS.
"We can give only a very brief sketch of this early life, touching only
the most salient points, especially such as throw light on the great
question of evolution.
Plants.
The only plants yet found are the lowest forms of cellular crypto-
gams, viz., marine algae, or sea-weeds. It is difficult, from the impres-
sions left by these, to determine genera, much more species, with any
degree of certainty. We shall, therefore, call them by the general some-
what indefinite name of Fucoids (Fucus, tangle or kelp), or Fucus-like
plants. As already stated, plants are far less abundantly and perfectly
preserved than animals, on account of their want of a skeleton.
"We give above some of the more characteristic Fucoids of the Silu-
rian age.
Animals.
Protozoans. The large, irregular masses which are called EozoOn
seem entirely characteristic of Archaean times. They are replaced in
the Silurian age by the more regular sponges. Of these, the most
characteristic Silurian genera are Stromatopora and Receptaculitis.
They seem to have formed large coralline masses, which are regarded
either as calcareous sponges, or as compound Rhizopods like EozoOn.
FIG. 286. Stromatopora rugosa.
Radiates, Corals. Corals were very abundant, forming often whole
rock-masses, as if they, while living, formed reefs. These, if they in-
ANIMALS.
291
dicate warm seas, show a great uniformity of temperature, since they
are found in all portions of the earth alike.
The corals of the Silurian age belong principally to three families,
Fia. 290.
FIGS. 2S7-290. SILURIAN PROTOZOANS: 28T. a, Stromatopora concentrica ; 5, section of same; c, view
from above (after Hall). 2SB. Keceptaculitis formosus (after Worthen). 2S9. Diagram showing
Strucure of Keceptaculitis (after Nicholson). 290. Brachiospongia Euemerana x i (after Marsh).
292 PALEOZOIC SYSTEM OF ROCKS.
viz., Cyathophylloids, or cup-corals ; Favositidce, or honey-combed
corals ; and Halysitidce, or chain-corals. They are remarkable in not
usually being profusely and widely branched like most modern corals,
but consisting mostly of masses of parallel or nearly parallel columns. In
Cyathopliylloids the corals are sometimes separate and of a horn-like
form, and sometimes aggregated in large, rough, columnar masses (Ru-
gosa). Their upper portions are cup-shaped, and the radiating laminae
are very distinct. In Favositids the hexagonal parallel columns are di-
vided somewhat minutely b} r horizontal plates (Tabulatse), giving a
cellular structure which may be finer or coarser. The Halysitids seem
to be made up of small, hollow, flattened columns with imperfect
septa, united to form inosculating plates which on section "have the
appearance of chains crossing in all directions. These are also minutely
tabulated. The Syringoporoids are similar to the Halysitids, except
that the hollow columns are cylindrical and connect with each other
only in places.
The following are some of the more characteristic species of these
families.
FIG. 292.
FIGS. 291-293. CTATHOPHTLLOrD CORALS : 291. Lonsdaiia floriformis (after Nicholson). 292. a and b,
Zaphrentis bilateralis (after Hall). 293. Stroinbodes pentagonus (after Hall).
ANIMALS.
293
FIGS. 294-290. FA VOSITID AND HALYSITID CORALS: 294. Columnaria alveolata: a, vertical; 5, cross-
section (after Hall). 295. Syringopora verticillata. 296. Halysites catenulata (after Hall).
There are many other forms than those mentioned above, but their
affinities are little understood, and many are not true corals, but Polyzoa
and sponges. Nearly all the corals of Silurian, in fact of Palaeo-
zoic times, fall under two orders Rugosa and Tabulata. The Cyatho-
phylloids are Rugosa, the other families mentioned are Tabulata. The
Rugosa are characteristic of the Palaeozoic ; the Tabulata are also near-
ly extinct : they have only one family living, viz., the millipores. The
Rugosa dift'er from modern star-corals in having their radiating septa
in multiples of four, while modern star-corals have theirs in multiples
of five or six. Hence 'star-corals have been divided into two types a
Palaeozoic and a Neozoic the one four-parted (quadripartita), the other
six-parted (sexpartita).
Hydrozoa The perfect forms of this class, viz., Medusae, or jelly-
fishes, are so soft and perishable that, with one or two exceptions in
the Mesozoic rocks, they are not found preserved at all in the strata of
294
PALAEOZOIC SYSTEM OF ROCKS.
any geological period. They may or may not have existed at this time ;
probably they did not. But the larval form of most, if not all, Medusre
is a compound polypoid animal, forming a minutely-branching, horny,
or coralline axis. These minutely-branching axes are strung on each
side with cells, in which are inclosed little polypoid animals. They
grow in still, quiet waters, and are. often mistaken by the unscientific
for sea-weed. These, by their composition, are well adapted for preser-
vation, and it is this larval form, therefore, only that we might expect
to find.
Fro. 298 a.
FIG. 298 b.
FIGS. 297-299. LIVING HYDROZOA : 297. Sertularia pinnata: a, natural size; &, enlarged. 298. and&,
Different Forms of Sertularia. 299. Pluinularia.
Now, in very fine shales of Silurian age, especially of Lower Silu-
rian, are found abundantly beautiful impressions of an organism which
is most probably a compound Hydrozoan allied to Sertularia of the
present day. They are called graptolites. Sometimes the cells are
arranged on one side of the axis, sometimes on both sides, sometimes
the axis is divided. Whatever be their affinities, they are of great
importance, inasmuch as they are entirely characteristic of the Silurian
ANIMALS.
295
age, and those with cells on both sides, of the Lower Silurian. The
twin graptolites (Fig. 302) are also wholly characteristic of Lower
Silurian.
FIG. 300.
FIG. 801.
FIG. 302.
FIG. 303. Fifl. 804.
FIGS. 300-304.-GRAPTOLITES: 300. Diplograptus pristis (after Nicholson). 301. Phyllograptus typus
(after Hall). 302. Didymograptus V-fractus (after Hall). 803. Graptolithus Logani (after Hall). 304.
Monograptus priodon : a, side-view ; Z>, back-view; c, front-view, showing opening (after Nicholson).
PALEOZOIC SYSTEM OF ROCKS.
FIGS. 305. 306. GBAPTOLITES : 305. Dendrograptus Ilallianus (after Hall). 306. Graptolites Clintonensis
(after Hall).
Polyzoa. There are many kinds of compound coralline animals,
probably allied to the Bryozoa (sea-mats) of our present seas, found in
the Silurian. The doubtful affinities of these Palseozoic forms, and the
difficulty of separating them sharply from certain forms of true corals on
ffl
FIG. 807. Living Polyzoa : Flustra truncata : a, natural size ; &, enlarged to show the cells.
the one hand, and from certain forms of graptolites on the other, seem
to require their notice in this connection, although their affinities are
probably molluscoid. Two of the Silurian forms are represented on
page 297, Figs. 308 and 309.
EcMnoderms. During Silurian times the class of Echinoderms was
represented principally by Crinoids, A Crinoid is a stemmed Echino-
derm, usually with branching arms. The animal consists of a long
jointed stalk, rooted to the sea-bottom, and bearing atop a rounded or
ANIMALS.
297
pear-shaped body, covered with calcareous plates (calyx), from the mar-
gin of which spring the arms, which may be long and profusely branched,
FIGS. 80S and 309. SIIXRIAN POLYZOA : 308. Fenestella elegans (after Hall). 809. Alecto auloporoides
(after Hall).
or short and simple, or absent altogether. In the middle of the calyx,
between the bases of the arms, is placed the mouth. Their general
structure and appearance will be better understood by examination
of the following figures of living Crinoids.
FIG. 810. FIG. 811.
FIGS. 310 and 311. LIVING CRIXOIDS: 310. Rhizocrimis Lofotensis (after Thompson). 811. Pentacrinus
Caput-Medus.i?.
. At present, leaving out the Holothurians, or sea-cucumbers, which,
having no shell, are little apt to be preserved as fossils, the class of
298 PALEOZOIC SYSTEM OF ROCKS.
Echinoderms may be conveniently divided into three orders, viz. : the
Echinoids, or sea-urchins ; the Asteroids, or starfishes ; and the Cri-
noids. The members of the first and second orders are free moving,
while those of the third are stemmed. Of these orders the Crinoids are
the lowest, as proved not only by their simpler organization, but also
by the fact that a living Crinoid, the Comatula, is attached when
young, but free when mature.
FIG. 812. A Living Free Crinoid Comatula rosacea. the Feather-Star : , free adult ; b, fixed young
(after Forbes).
Now, in Silurian times, the stemmed Echinoderms are very abun-
dant, while the free are very rare : at the present time, on the contrary,
the reverse is the case. Thus, in the course of time, the former de-
creased until they are now almost extinct, while the latter increased
until they are now very abundant. If we take the abundance of Echino-
derms during geological times as constant, and represent the course of
FIG. 813. Diagram showing the General Distribution in Time of Stemmed and Free Echinoderms.
time by the absciss A B (Fig. 313), and the abundance by distance
from A JB to C D, then the parallelogram would represent this fact.
If, now, we draw the diagonal, C J3, then the shaded triangle would
ANIMALS.
299
represent the stemmed, and the unshaded the free, and the diagonal the
line of decrease of the one and increase of the other; and the whole
figure the general relations of the two sub-classes throughout time.
In the Palaeozoic the stemmed predominate ; in the Mesozoic the two
are equally represented ; in modern times the free predominate.
FIG. 318 a.
FIG. 319.
FIGS. 314-819. SILURIAN CRINOIDS: 314. Caryocrinus ornatus. 315. Pleurocystitis squamosus. 816.
Pseudocrinus bifasciatus. 317. Lepadocrinus Gebhardii. 318. Glyptocrinus deeadactylus (after
Hall) : a, specimen with arms ; 6, larger specimens without the arms. 319. Ichtbyocrinus sublaevis
(after Hall).
Stemmed Echinoderms, or Crinoids, may be divided into three fami-
lies, viz.: 1. Crinids ; 2. Cystids ; 3. Blastids. Crinids are the typi-
cal Crinoids, with branching arms, already illustrated from living exam-
300
PALAEOZOIC SYSTEM OF ROCKS.
FIGS. 320-824 SiLtmrAN CRINOFDS ANT> ASTEROIDS: 820. Mnriacrinus noWlissiaius (after Hall). 321.
Ilomocrimis sroparius (after Hall). 322. Heterocrinus simplex (after Meek). 323. Protaster Scdg-
wickii. S24. 1'aliuaster Sba'fferi (after Hall).
ANIMALS.
301
pies (Figs. 310-312). Cystids are of a bladder-like form (hence the
name), and are either without arms, or else have few, short, simple
arms springing from near the centre of the upper part of the body, the
mouth being probably on one side. The radiated structure in these is
imperfect. Blastids (Gr. 0/la<7TOC, a bud} had a bud-shaped body, with
five petalloid spaces (ambulacra) radiating from the top and reaching
half-way down the body (see Figs. 510-513, p. 382). If Crinids are com-
parable to inverted Starfishes with many arms and set upon a stalk, the
Cystids and Blastids may be compared to Sea-urchins similarly set.
All these families are found in the Silurian. The Cystids pass away
with the Silurian, and are therefore characteristic of that age. The
Blastids pass away before the end of the Carboniferous age, and are
therefore characteristic of the Palaeozoic era. The Crinids continue,
though in diminished numbers, to the present day. Figures of Blastids
are given under the Carboniferous, where they were far more abundant.
Mollusks AcepTials or Bivalves. Bivalves may be divided into
two great sub-classes, viz., Lamellibranchs (leaf-gills)
and Brachiopods (arm-feet). The valves of Lamelli-
branchs are right and left ; those of Brachiopods are
upper and lower, or dorsal and ventral. Brachiopods
'are much less highly organized than the other sub-class,
and differ so essentially in their organization that some
of the best naturalists remove them not only from the
class of Acephals, but from the department of Mollusca,
and ally them rather with the Worms. Their general
resemblance in external form to bivalves makes it more
convenient to treat them under that head, until the
question of their affinity is more definitely settled.
General Description of a Brachiopod. A Brachiopod
shell consists of two valves, a dorsal and a ventral. The
ventral is the larger, and usually projects beyond the
dorsal, at the hinge, as a prominent beak. This pro-
jecting portion is often perforated to give passage to a
muscular peduncle, by which the shell is attached in the
living animal. The following figures (Figs. 325, 326) of
Brachiopods, living and extinct, will make these points
clear.
The viscera of a Brachiopod fill but a small space
in the shell, this cavity being occupied principally by
two long spiral arms (hence the name), which probably subserve the
functions of respiration and alimentation. These arms are attached
to a curious bony apparatus, sometimes itself spiral in form. Figs.
327-329 show the internal structure described above.
In the present seas the Lamellibranchs are extremely abundant,
anatina, showing
the muscular ped-
uncle bv which the
shell is attached.
302
PALAEOZOIC SYSTEM OF ROCKS.
FIG. 326. Rhynchonella sulcata: side-view, dorsal view, and showing suture
FIG. 329.
FIGS. 827-329. SHOWING THE STBrcrrRE OF BKACHTOPODS : 827. Spirifer striatus (Carboniferous) : a,
dorsal surface ; b, interior, showing the bony spirals. 828. Tercbratula llavrsrcns diving species):
. exterior surface ; 6, showing bony structure for attachment of spiral arms. 329. Spirifer hysterica
(Carboniferous) : a, exterior; 6, showing bony spires.
while the Brachiopods are nearly extinct, being represented by very
few species. In Silurian times, on the contrary, the very reverse is the
case, bivalve shells being represented mostly by Brachiopods. Taking
the number of bivalve species throughout geological times as constant,
then the general relation of these two sub-classes to each in time may
be roughly represented by the following diagram, in which the lower
ANIMALS.
303
triangle represents Brachiopods, the upper Lamellibranchs, and the com-
mon diagonal the line of decrease of one and increase of the other.
FIG. 330. Diagram showing the General Alteration of Brachiopods to Lamellibranchs.
The abundance of individuals and the number of species of this
order in Silurian times are almost incredible. The following figures
represent some of the common and characteristic forms.
FIGS. 331-334.-Sii.cRiAX BRACIUOPODS : 331. Orthis Davidsonii. 332. Orthis porcata. 833. Spirifer
Cumberlandiaa: a, ventral valve; 6, dorsal valve; c, suture. 334. Pentamerus Knightii.
It is very difficult to give any general distinctive mark of Silurian
Brachiopods, although, of course, the species and even the genera are
peculiar, and may be recognized by the paleontologist. It may be said,
however, that the straight-hinged or square-shouldered Brachiopods,
including the Spirifer family, the Strophomena or Leptena family, and
304
PALAEOZOIC SYSTEM OF ROCKS.
the Productus family, are characteristic of the Palaeozoic, though not of
the Silurian.
Lamellibranchs. We have said that Lamellibranchs are also found
in the Silurian, but not so abundantly as the Brachiopods. Lamelli-
branchs are divided into Siphonates and Asiphonates, i. e., those with
FIG. 336.
FIG. 337. FIG. 338. FIG. 389.
FIGS. 335-339. SILURIAN LAMELLIBRANCHS: 335. Orthonota parallela. 336. Cardiola interrupta (after
Hall). 837. Avicula Trentonensis (after Ilall). 338. Ambonychia belli striatus (after Hall). 3S9.
Tellenomya curta (after Hall).
and those without breathing-siphons behind. The Siphonates are the
higher. At present the Siphonates are the more abundant in Palaso-
zoic times the Asiphonates. We give seme figures above.
FIG. 340.
FIG. 841. FIG. 342.
FIGS 340-342 SILURIAN GASTEROPODS: 840. Pleurotomaria dryope. 341. Pleurotoiuaria agave. 842.
Murchisoni gracilis.
ANIMALS.
305
Gasteropods Univalves. Land and fresh-water Gasteropods have
not been found in the Silurian. If we divide marine Gasteropods or
univalves into those having beaked shells and those having smooth-
mouthed or beakless shells, the former being carnivorous and the latter
herbivorous, then only the smooth-mouthed or beakless shells have
FIG. 345.
FIG. 344.
FIG. 346.
FIGS. 343-346. SILURIAN GASTEROPODS AND PTEROPODS : 843 Cyrtolites compressus (after Hall). 844.
Cyrtolites Trentonensis (.after Hall). 345. Cyrtolites Dyeri (after Meek). 346. Conularia Trentonensis
(after Hall), a Pteropod.
been found in the Silurian. The beaked-shelled are usually regarded
as the more highly-organized class. The affinities of Conularia (Fig.
346) and Tentaculites are little understood. They are usually placed
among Pteropods.
Cephalopods Chambered Shells. These are by far the most high-
ly organized of Mollusks, and the most powerful among Invertebrates.
They are represented in the present seas
by the Nautilus, the Squids, and the Cut-
tle-fishes. If we divide all known Cepha-
lopods into Dibranchs (two-gilled) and f ...
Tetrabranchs (four-gilled), the former be-
ing naked and the latter shelled, then, at
the present time, the Dibranchs, or naked,
vastly predominate, there being only a
single genus of shelled or Tetrabranchs
known, viz., the Nautilus, and of this
genus only three or four species. In the
Silurian age, and. for many ages after-
ward, only the shelled existed. The naked or Dibranchs are decidedly
the higher in organization.
20
FIG. 347. P
pilius) : c
c, hood ;
nel.
arly Nautilus (Nautilus pom-
mantle ; b, its dorsal fold ;
9, eye ; t, tentacles ; /, fun-
306
PALAEOZOIC SYSTEM OF ROCKS.
Again, if we divide chambered shells into those having simple
septa and central or subcentral tube or siphon (Nautilus tribe], and
those having septa plaited at their junction with the shell (plaited
suture) and dorsal tube (ammonite tribe), then in the Silurian age the
former only were represented.
Again, if we divide the Nautilus tribe into straight-shelled and
coiled-shelled, then the straight-chambered shells greatly predominated.
Straight-chambered shells are called Orthoceratites (opflo^, straight ;
wepaf, horn). The Orthoceratites, therefore, are a very striking feat-
ure of the Silurian age. They may be defined as straight-chambered
a, Onnoceras.
b, Actinoceras.
c, Huronto. d, Section of Siphuncle of Huronia.
FIG. 848. , ft, c, d, Showing Structure of Orthoceratite.
shells, with simple partitions and a central or subcentral siphon-tube
(siphuncle). The siphuncle of the family was large in proportion to
the shell, and had often a beaded structure (Fig. 348, a, , c, d). The
genera are founded largely on the form of this part.
They existed in great numbers, and attained very great size. Speci-
mens have been found fifteen feet long, and eight to ten inches in diam-
eter. They were, without doubt, the most powerful animals of that
ANIMALS.
307
time, the tyrants and scavengers of these early seas. We give, in Fig.
357, a restoration of the creature. They are entirely characteristic of
FIG. 850.
FIG. 851.
'
JK^niignM i^MMnBHBMBMHBBHMWfflSflffl^Bffil
FIG. 853.
FIGS. 849-353. SILTJRIAN CEPIIALOPODS : $49. Orthoceras medullare (after Meekl. 850. Ormoeeras
tenufilum, showing chambers and siphimele (after Hall). 351. Orthoceras vertebrale (after Hall).
852. Orthoceras multicarneratum (after Hall). 353. Orthoceras Duseri (after Hall).
308
PALAEOZOIC SYSTEM OF ROCKS.
the Palaeozoic ; commencing in the Primordial, extending through into
the Carboniferous, and passing out there. They attained their maxi-
mum of development in size and number in the Silurian.
Although straight-chambered shells (Orthoceratites) are most abun-
dant and characteristic, coiled shells of the same tribe are also found,
and some of them of considerable size. Some of these are close-coiled
FIG. 354.
FIG. 855. FIG. 856.
FIGS. 854-856. SILURIAN CKMIALOPODS : 854. Trocholites Ammonias (after Hall): a, exterior;/;, cast,
showing septa, 855. Lituites Graftonensis (Meek and Worthen). 356. Lituites cornu-anetis.
shells, true Nautilus family ; others open-coiled, and more nearly allied
to the straight. Barrande gives 1,622 species of Cephalopods in the
Silurian.
Articulates Worms. These are fleshy animals without skeletons,
and are therefore not preserved. They are known only by their tracks,
their borings, and their tubes. Nevertheless, some 185 species, accord-
ing to Barrande, have been described from the Silurian of different
ANIMALS.
309
countries. Fig. 358 represents worm-tubes, and Fig. 359 worm-tracks,
from Upper Silurian.
Crustacea Trilobites. The principal representatives of the articu-
late department in Silurian times were Crustaceans, but mostly of a
very characteristic order of that class, now long extinct, viz., Trilobites.
General Description. The carapace or shell of these curious creat-
ures was convex and usually smooth above, and flat or concave below,
and divided transversely, like most Crustacea, into a number of movable
FIG. 3n7. Restoration of Orthoeeras, the
shell bein<r supposed to be divided ver-
tically, and only its upper part being
shown : a, arms ; /; muscular tube
("funnel") by which water is expelled
from the mantle-chamber; c, air-cham-
bers, s, siphuncle (after Nicholson).
PIG. 359.
FIGS. 353, 359. SILURIAN ANNELIDS : 358. Cor-
nulitis serpentarius (Worm - Tube). 359.
Trail of an Annelid (after Hall).
joints. Several of the front joints are always consolidated to form a
head-shield or Buckler, and sometimes a number of the posterior joints
are similarly consolidated to form a tail-shield or Pygidium. The whole
shell or carapace is divided longitudinally, more or less distinctly, into
three lobes (hence the name) a middle, a right, and a left. Well-or-
ganized compound eyes are distinctly seen in well-preserved specimens
310
PALJ30ZOIC SYSTEM OF ROCKS.
on the lateral lobes of the head-shields (cheeks) (Fig. 360). The under
side of the animal has never been distinctly seen, and therefore the
character of the locomotive organs is not certainly known. But it is
believed that, like some of the lower Crustaceans of the present day
(Phyllopods), their limbs were thin, flat, soft, leaf-like swimmers. On
this view it is easy to see why the under side is never exposed ; for the
mud, in which they were entombed, would become entangled among
these leaf-like swimmers, and in breaking the rock this would determine
FIG. 360. Structure of the Eye of Trilobites: o, Dalmania pleuroptoryx ; b, eye slightly magnified;
c, eye more highly magnified ; d, small portion still more highly magnified (after Hall).
the line of fracture over the smooth back, and leave the creature firmly
attached by its ventral surface to the lower piece. Not uncommonly
Trilobites are found folded up on their ventral surface, so as to bring
head and tail together and form a kind of ball. This was probably a
position of defense. In such cases the Trilobite may be gotten out of
the rocky matrix complete ; but none the less are the feet completely
hidden (Fig. 361 b).
The great number of genera into which this large order is divided is
founded principally on the form and sculpturing of the Buckler, the size
and form of the Pygidium, the number of the movable segments, etc.
The figures below will give an idea of some of these forms.
It is very interesting to observe that a complex mechanism, the
compound eye like that of crustaceans and insects of the present day,
an exquisite instrument for the formation of an image on the retina,
was already developed even in the earliest Primordial times.
Trilobites commenced, as already stated, in the earliest Primordial,
continued through the whole Palaeozoic, and then became extinct for-
ever. They are therefore entirely characteristic of the Palaeozoic. They
reached their maximum of development, in size, number, and variety, in
the Silurian. Barrande gives the number of species described in the Silu-
rian alone as 1,579. They reached in some cases a size equal to any crus-
taceans now living. The Asaphus (Isotelus) gigas, from the Lower
ANIMALS.
311
FIGS. 361305. SILCTITAN TRILOBITES : 361. Calymene Blumenbachii : b, same In folded condition.
362. Trinucleus Ponsrerardi. 3i>3. Lichas Boltoni (alter Hall). 364. Acidaspis crosotus (after Meek).
805. Isotelus gigar, reduced (after Hall) ; 365 a, same, side-view.
Silurian (Fig. 365), was sometimes twenty inches in length and thir-
teen wide. Paradoxides (Fig. 280, p. 287), of the earliest Primordial,
312
PALAEOZOIC SYSTEM OF ROCKS.
attained a length of twenty-two inches. On account of their great
abundance and fine preservation, their embryonic development has been
carefully studied by Barrande, who has described and figured thirty
steps in the development of some species. According to Agassiz, we
know more of the development of trilobites than of any living crustacean.
FIG. 3G6. Dalmania limulurns.
FIG. 31'tf. </, Larva of a Trilobite ;
ft, Larva of a King-Crab.
3.-Limulus before hatching, Trilobite Stage : a, Bide view. Limulns beYore hatching, Trilobite
Stage : ft, dorsal view.
Affinities Of Trilobites. The affinities of this very distinct order are
imperfectly understood. Crustaceans are divided into two sub-classes, a
higher, Malacostraca (mollusk-shelled or calcareous-shelled), and a lower,
JE/ntomostraca (insect-shelled). Now, Trilobites, though belonging to the
ANIMALS.
313
lower division, or Entomostraca, occupy a position near the confines of
the two divisions. More definitely, they probably stand between the
Isopocls (tetradecapod Malacostracans), on the one hand, and the Phyl-
lopods and Limuloids (Entomostracans), on the other. In general ap-
pearance they certainly approach Limuloids (horseshoe-crabs or king-
crabs), and these seem to have replaced them in the process of evolution.
They are by no means very low in the scale of crustaceans ; their position
being near the middle. The larvag of Crustaceans, especially of Limu-
loids, greatly resemble some forms of Trilobites, and especially the larva?
of Trilobites. From the generalized forms represented by Figs. 367 and
368 have been probably differentiated, in one direction the more per-
fect Trilobites, and, in the other, the Limuloids.
FIG. 369.
FIGS. 869-371.-- SILUKIAN EURTPTEBTDS : 369. Pterygotus Anxious, viewed from the under side, re-
duced in size, and restored : c o, the feelers (antennae), terminating in nippintr-claws ; o o. eyes: m m,
three pairs of jointed limbs, with pointed extremities ; n n, swimming-paddles, the bases of which
are spiny and act as jaws Upper Silurian, Lanarkshire (after Henrv Woodward). 870. Eurypterus
remipes, greatly reduced. 871. Same restored: a, dorsal view; b, ventral view (after Hall).
FIG.
Eurypterids. In the Upper Silurian was introduced and continued
to exist along with Trilobites during the rest of the Palaeozoic, another
314: PALAEOZOIC SYSTEM OF ROCKS.
family of huge entomostracans probably in advance of Trilobites in
organization, viz., Eurypterids. The family includes the two genera
Eurypterus (broad wing) and Pterygotus (winged ear). Some of the
latter are the largest crustaceans known. The huge Inachus Koemp-
feri (Japan crab), with carapace sixteen inches in diameter, and legs
four feet long, and the Moluccas king-crab (Limulus Moluccanus),
three feet long and eighteen inches across the carapace, are the largest
crustaceans now living. But the Eurypterids were some of them far
greater. The Pterygotus Anglicus (Fig. 369) was six feet long and
one foot wide, and the Pterygotus Gigas, seven feet long and propor-
tionately wide. The above figures represent some species of these two
genera from the American and English rocks.
Anticipations of the Next Age. Higher animals and plants than
those already mentioned do not strictly belong to this age. Neverthe-
less, in the uppermost beds of the Upper Silurian, or passage-beds into
the Devonian, are found several anticipations of the next age. Land-
plants are there introduced in the form of a few small club-mosses
(Psilophyton) and vertebrates in the form of fishes. The latter have
not yet been found in this country. Such anticipations are in accord-
ance with the law already mentioned (p. 267), that the characteristics
of an age often commence in the preceding age. It is better, however,
to treat of these classes in connection with the age in which they cul-
minate, or at least become a striking feature.
The Silurian was, therefore, essentially an age of Invertebrates. In
number, size, and variety, these have scarcely been surpassed in any
subsequent period. The most characteristic orders were : Among plants,
Fucoids ; among animals, Cyathophylloid and Tabulate corals, Grapto-
lites, Cystidean crinoids, Square-shouldered brachiopods, Beakless gaster-
opods, Orthoceratites, and Trilobites. Orthoceratites and trilobites were
the highest animals of the age, and the former were the rulers and scav-
engers of these early seas. We give below a table showing, according
to Barrande, the number of Silurian species described up to 1872 :
Sponges and other Protozoans.. . 153
Corals 718
Echinoderms 588
Worms 185
Trilobites 1,679
Brachiopods 1,567
Lamellibranchs 1,086
Heteropods ) OQA
Pteropods \ 89
Gasteropods 1,306
Other Crustaceans 348 Cephalopods 1,622
Bryozoans 478 Irishes 40
"Which, with four of uncertain relatives, make 10,074 species.
SECTION 2. DEVONIAN SYSTEM AND AGE OF FISHES.
The name Devonian was given to these rocks by Murchison and
Sedgwick, because in Devonshire the system occurs well developed,
LIFE-SYSTEM OF DEVONIAN AGE PLANTS. 3^5
and abounds in fossils. In England the system is usually uneonform-
able with the underlying Silurian, and sometimes with the overlying
Carboniferous, as in Fig. 372. But in the Eastern United States, as
already stated, the Palaeozoics are conformable throughout (Fig. 255).
d
FIG. 872.*, Silurian ; d, Devonian ; c, Carboniferous (after Phillips).
Area in United States. The area over which the Devonian appears
as a country rock is shown in map, page 278. It borders generally
the Silurian on the south and southwest, extending with it far south-
ward in the middle region, viz., in Indiana, Western Ohio and Ken-
tucky. In the Basin Range region, especially about White Pine,
Nevada, Devonian is known to exist, but the limits of these areas are
too imperfectly known to be described.
Physical Geography. In the eastern portion of the United States
the land of the Devonian age was approximately that of the Silurian
age already described, increased by the addition of the Silurian area,
which Silurian was of course so much marginal sea-bottom exposed by
upheaval during and at the end of Silurian times. At the end of De-
vonian times the Devonian area was added to the existing land, and
the continental mass thus further increased.
Subdivision into Periods. In the United States the following four
periods are recognized by Dana:
4. Catskill period.
3. Chemung period.
2. Hamilton period.
1. Corniferous period.
We shall, however, neglect these subdivisions in our general de-
scription of the life of the age.
^Life-System of Devonian Age Plants.
It will be remembered that during the Silurian age, except in the
very last part where a few small club-mosses were introduced, the only
plants found were Fucoids. These, of course, continued in Devonian
times. But, in addition to these, were now introduced land-plants in
considerable numbers and variety, and decided complexity of organiza-
tion. They included all the orders of vascular cryptogams, viz., ferns,
Lycopods, and JSquisetce ; and also Conifers among gymnospermous
Pha3nogams ; and by their great size and numbers probably formed for
the first time in the history of the earth a true forest vegetation.
The Ferns were represented by several genera, such as Cyclopteris
and Neuropteris ; the Lycopods (club-mosses) not only by the Psilophy-
316
PALAEOZOIC SYSTEM OF ROCKS.
ton, which had been already introduced in the uppermost Silurian, but
also now by gigantic Lepidodendrids and Sigillarids, and the Equi-
setas by Calamites and Asterophyllites. The Conifers were represented
FIG. 373. Microscopic Section of the Silicifled
Wood of a Conifer (Sequoia}, cut in the long
direction of the fibres. Post-tertiary? Colorado.
(After Nicholson.)
FIG. 874. Microscopic Section of the Wood of the
Common Larch (Abies larix). cut in the long
direction of the fibres. In both the fresh and
the fossil wood (Fig. 867) are seen the disks
characteristic of coniferous wood. (After
Nicholson.)
by the genus Protaxites, allied to the yew (Taxus). They are known
to be conifers by their concentric rings of growth and gymnospermous
tissue, i. e., the elliptic disk-like markings on the walls of the wood-
cells on longitudinal section (Figs. 373 and 374),
and the entire absence on cross-section of the
visible pores so characteristic of dycolytedonous
Exogens (Fig. 375). Some of these conifers have
f T*f f' [frf 1 been found by Dawson eighteen inches, and one
FIG. 375. Pine-Wood, Cross- three feet, in diameter. There have been fifty
species of land-plants of these various orders found
by Dawson in the Devonian of Nova Scotia alone. On pages 317 and
318 we give the most characteristic Devonian land-plants.
General Remarks on Devonian Land-Plants. We will not at present
discuss the affinities of these plants, and their relations to evolution,
because they are similar to those found in the coal, where they exist
in far greater variety and abundance, and the subject will be discussed
under that head. There are, however, some thoughts suggested by
the first appearance of highly-organized plants which ought not to be
omitted :
1; The ringed structure of Devonian conifers shows that, at that
time, there was a growing season and a season of rest, and therefore,
probably, a warm and a cold season. In one trunk the number of rings
counted was 150, indicating a considerable age.
2. What were the precursors of this highly-organized forest vegeta-
tion ? That there were precursors, from which these were derived, there
LIFE-SYSTEM OF DEVONIAN AGE PLANTS.
317
can be little doubt, and we shall probably some day find them in the
Upper Silurian ; but that the steps of evolution were just at this point
somewhat rapid, seems also certain. It is impossible to account for
this comparatively sudden appearance of .so highly-organized a vege-
FIG. 379.
Fio. 8SO.
FIGS. 376-380. DEVONIAN PLANTS (after Dawson) : 37C. Psilophyton princeps, restored. 377. a, Lopido-
dendron Gaspianum; ft, same enlarged. 37S. a, Asterophillites latifolia; b, fruit of same. 379. Cy-
clopteris obtusa, a fern. 3SO. Neuropteris polymorpha,- a fern.
tation bj' evolution, unless we admit that there have been periods of
rapid evolution, as explained on page 288. When all the conditions
are favorable for a great advance, the advance takes place at once, i. e.,
with great comparative rapidity.
3. We have seen that the coal vegetation is to a large extent an-
ticipated in the Devonian. So, also, to some extent, were the condi-
tions necessary to the preservation of this vegetation and the formation
318
PALEOZOIC SYSTEM OF ROCKS.
of coal. In the Devonian, for the first time, we find dark bands between
the strata, impregnated with carbonaceous matter. We find, also, thin
seams of coal, with under-clajs filled with ramifying rootlets, such as \ve
shall find in the coal ; in other words, we find ancient dirt-beds, sub-
Fia. 884.
FIG. 886.
FIGS. 881-386. DEVONIAN PLANTS (after Dawson) : 881. Cyclopteris Jacksoni, a Fern. 882. Dadoxylon
Quangondianum, a Conifer: a, Pith; ft, Pith-Sheath; c. Wood. 883. Sections of same; a;, Longi-
tudinal ; y. Transverse, enlarged z, greatly magnified, showing disk-like markings. 884. Cardio-
carpum Baileyi, a Fruit. 885. Anthophyllitis Devonicus. 886. Uordaites Kobbii, a Group of Leaves.
merged forest-grounds, and peat-bogs. All the phenomena of the coal-
measures, therefore, are here found, though imperfectly developed, and
the coal not workable. The Carboniferous day is already dawning.
ANIMALS.
Animals.
319
In accordance with our prescribed plan, all we can do in describing
Devonian animals is to touch prominent points to notice what is going
out, what is coming in, and to dwell only on what bears on evolution.
FIGS. 3S7-300. DEVONIAN CORALS: 3ST. Acervularia Davidsoni (after Hall). 388. Favosites hemi-
spherica. 339. Crepidopkyllum Archiaci. 390. Zaphrentis Wortheni (after Meek).
Radiates. Among corals, the chain-corals (Halysitids) have disap-
peared ; the other orders continue under different species. Among
hydrozoa, the Graptolites are gone ; among Crinoids, the Cystids are
gone, but in their place the Blastids (bud-like), those curious armless
crinoids, with petalloid markings already spoken of as rare in the Silu-
rian, become more abundant. The Crinids, or plumose-armed crinoids,
320
PALEOZOIC SYSTEM OF ROCKS.
continue undiminished. The Blastids, however, are far more character-
istic of the Carboniferous. We therefore defer their illustration to that
period.
BracMopods. Brachiopods are still very abundant, and still many
of them of the characteristic Palaeozoic, square-shouldered type. Among
spirifers, the long-winged species (Fig. 392) are very abundant and
Fio. 893.
FIGS. 391-394. DEVONIAN BRACHIOPODS: 891. Spirifer fornacula (after Meek and \VortheiO: a, ven-
tral valve; 6, suture. 392. Spirifer perextensus (after Meek). 393. Orthis Livia: a, dorsal; 6,
side-view. 394. Strophomena rhomboidalis.
characteristic. "We give a few figures of Devonian bivalves, both
brachiopods and lamellibranchs, and a few univalves. It is worthy of
remark that many of these univalves are fresh-water species.
Gephalopods. The characteristic Palaeozoic Cephalopods, or Ortho-
ceratites, continue, but in greatly-diminished numbers and size; but the
Groniatites, a coiled-chambered shell, which seems to be the beginning
of the Ammonite family, are introduced first here. This family, as
already explained, is distinguished by the complexity of the junction of
ANIMALS.
321
FIG. 402.
FIG. 401
FIGS. 395-402. DEVONIAN LAMELLIBRANCHS AND GASTEROPODS: 895. Conocardium trigonale (after
Logan). 896. Aviculopecten parilis (after Meek). 897. Otenopistha antiqua (after Meek). 898.
Lucina Ohioensis (after Meek). 399. Spirorbis omphalodes, enlarged. 400. Spirorbis Arkonensis.
401. Orthonema Newberryi (after Meek). 402. Bellerophon Newberryi (after Meek).
the septa and the shell (suture), and by the dorsal position of the si-
phuncle. In the Goniatites the sutures are not yet very complex.
They are only zigzag. This is shown in the figure.
FIG. 403. Goniatites lamellosus (after Pictet).
322 PALAEOZOIC SYSTEM OF ROCKS.
Crustacea. The very characteristic Palaeozoic order Trilobites is still
abundantly represented, although it has already passed its prime, and is
diminishing' in number and size of species. The Eurypterids introduced
in the Upper Silurian maintain their place through the Devonian.
FIG. 404. FIG. 4U5.
FIGS. 404 and 405. DEVONIAN TBILOBITES : 404. Dalmania punctata, Europe. 405. Phacops Jatifrons,
Europe.
Insects. The earliest insects yet discovered are found in the De-
vonian of Nova Scotia. It is natural that insects should appear along
with forest vegetation, and indeed the insects and the plants are found
in the same strata.
The Devonian insects belong to the Neuroptera (nerve-wing), like
the dragon-fly and ephemera, yet a chirping organ has been detected
which allies them with the crickets, grasshoppers (Orthoptera), etc.
They seem, therefore, to be a connect-
ing link between JVeuropters and Orthop-
ters. An organ adapted to produce
definite kinds of sound to attract their
mates, of course, implies an organ
adapted to appreciate sound. Evident-
ly, therefore, the ear was already some-
406. Wing~of Piatephemera antiqua. what advanced in organization in these
Devonian, America (after Dawson). ,
Fishes. But the grand characteristic of the Devonian age is the
appearance and culmination of the class of fishes. This is a great step
in advance ; for we have here the introduction, not only of a new class,
but a new department (Vertebrata), and the highest of the animal king-
dom. These earliest fishes, as might be expected, however, were far
different from typical fishes of the present day. They belonged wholly
ANIMALS.
323
to the two orders Ganoids (gar-fish, sturgeons, and mud-fishes) and
Placoids (sharks, skates, and rays), and to families of these orders which
are now either wholly or nearly extinct. Appearing first in Uppermost
Silurian and Lower Devonian, few in number and small in size, and of
strangely-uncouth forms in Cephalaspis (Fig. 408) and Pteraspis (Fig.
407), the earliest-known genera, this class soon increased until the
Devonian seas swarmed with them. Probably never in the history of
the earth have fishes existed in greater numbers, variety, and size ; and
certainly never have they been more thoroughly armed for offense and
defense. The Onychodus (agate-toothed Fig. 417), in the Lower De-
vonian of the United States, had jaws eighteen inches long, and teeth
two inches or more long. The animal itself is supposed to have been
twelve to fifteen feet in length. The Dinichthys of Ohio had jaws
twenty-two inches long, and the animal was eighteen feet long. The
Asterolepis (star-scale), described by Hugh Miller, was still more gigan-
tic, being probably twenty to thirty feet in length. The teeth of many
of the Devonian Ganoids were decidedly reptilian in character, i. e.,
long, conical, and fluted at the base, as in many reptiles both living and
extinct. The following figures represent some of the more characteris-
tic Devonian fishes (see also on pages 324 and 325). Of Placoids, on
account of their cartilaginous skeleton and absence of scales, only the
teeth and spines are found. In some of the species these spines were
eighteen inches in length.
Of the fishes above named, some have been so recently discovered,
and so remarkable in character, that they seem to deserve more than a
FIG. 408.
PIGS. 407 and 403. DEVONIAN FISHES Placoderms : 407. Pteraspis. restored by Powrie and Lankaster
(after Dawson). 408. Cephalaspis Lyelli (after Nicholson).
324
PALAEOZOIC SYSTEM OF ROCKS.
bare mention. This is true especially of the Onychodus and the Din-
ichthys, recently discovered in the Devonian of Ohio, and described by
Newberry.
The Onychodus sigmoides was a ganoid fish, twelve to fifteen feet
Fia. 411.
FIG. 412.
FIGS. 409-412. DEVONIAN FISHKS Placoderms : 409. Pterichthys cornutus (after Nicholson). 410.
Coecosteus decipiens (after Owen), tepidoganoide : 411. Holoptychius nobilissimus (after Nichol-
son). 412. Osteolepis (after Nicholson).
ANIMALS.
325
in length, with lower jaw eighteen inches long, set with sharp, conical
teeth, about three-fourths of an inch long, in the usual position. In ad-
dition to these, just at the chin-suture, were set a vertical row of pecul-
Fio. 416.
FIGS. 413-416. DEVONIAN FISHES Lepidoganoids : 413. Glyptolemus Kinairdii (after Nicholson). 414.
Diplacanthus pracilis (after Nicholson). Placoids : 415. Ctenacanthus vetustus, Spine reduced (after
Newberry). 416. Machseracanthus major, Spine reduced (after Newbeny).
iarly-shaped teeth, at least two inches long, pointing forward (Fig.
417 c.) The body was covered with circular imbricated scales an inch in
diameter (Fig. 417 a).
The Dinichthys is the hugest of Devonian fishes yet found in
America, and second only to the Asterolepis of the European Devonian.
According to Newberry, the body of this fish was fifteen to eighteen
feet long and three feet thick. The jawbones, both upper and lower,
are bent, the one downward, the other upward, at the extreme end, and
extended to form two strong, sharp front teeth, above and below, while
behind these the upper margin of the jaw is compressed into a sort of
326 PALEOZOIC SYSTEM OF ROCKS.
knife-edged enameled bone, acting together like shear-blades, or in one
species sharply dentate. The diagram Fig. 418 (in which, however, the
bones are not in natural position) illustrates this structure. Newberry
FIG. 417. Onychodus sigmoides (after Newbcny): a, Scale, natural size; 6, a Tooth, natural size; c, a
Kow of Front Teeth, reduced.
has drawn attention to the -remarkable resemblance of this jaw-structure
to that of the Devonian Coccosteus and the living Lepidosiren, the most
reptilian of all known living fishes. This resemblance is shown in the
accompanying figures (419 and 420).
FIG. 418.-JawsofDinichthysTorrelli, x 5 ' 5 (after Newberry).
FIG. 420. Jaws of Lepidosiren (side-view,
after Newberry).
FIG. 419. Jaws of Dinichthys (side-view,
after Newberry).
Like the Coccosteus (Fig. 410), not only the head but also the whole
fore-part of the body of the Dinichthys, both above and below, was cov-
ered with large protecting plates. The want of scales in the hinder
parts and the cartilaginous condition account for the fact that these
parts have not yet been found.
Among other remarkable fishes found in the Devonian of Ohio may
be mentioned Macropetalichthys (Fig. 421), several species of Coccosteus,
and several of Acanthaspis a genus allied to the Cephalaspis (Fig.
ANIMALS.
327
408). In the Devonian of New York, also, a number of species have
been found.
Ganoids derive their name from the thick, bony, enameled scales
which cover the body, forming an impenetrable coat-of-mail. Now, in
the Devonian Ganoids, as seen in the figures, these scales were some-
times large and imbricated (Fig. 411), sometimes rhomboidal, arranged
in oblique rows and nicely jointed, as in gar-fishes (Lepidosteus and
Polypterus) of the present day (Figs. 412-414), and sometimes large,
immovably soldered polygonal plates (Figs. 409, 410). Sometimes
FIG. 421. Skull of Macropetalichthys
Sullivanti, reduced in size.
FIG. 422. a, Head and fore limb of a
Ceratodus ; 6, Hind limb of same
(after Gunther).
the plates covered only the head (Cephalaspis), sometimes the head
and forward portion of the body, and left the tail free for locomo-
tion (Coccosteus) ; sometimes the whole body seems inclosed almost
immovably in such plates, and the locomotion was effected in great
part by arm-like fins (Pterichthys).
Most of the largest Devonian fishes, as the huge Asterolepis and
the Dinichthys, belonged to the family of Plate-covered Ganoids. It
is to this bony coat-of-mail that we are indebted for the fine preserva-
tion of Devonian Ganoids.
Affinities of Devonian Fishes. Devonian Ganoids may be con-
veniently divided into two sub-orders, viz., Lepido-ganoids (Scale Ga-
noids), or Ganoids proper (Figs. 411-414), and Placo-ganoids (Plate
Ganoids), or Placoderms (Figs. 407-410). The Placoderms are char-
acteristic of the Devonian; the Lepido-ganoids continue in diminish-
ing numbers even to the present time. The Placoderms have no
living near congeners, although the Dinichthys, as just explained,
has some affinities with the Lepidosirens. The nearest living allies
of the Lepido-ganoids are the Polypterus of the Nile, the Lepidos-
teus, or Gar-fish, of North American rivers, the Amia, or mud-fish, of
the same waters, the Lepidosiren of the African and South American
328 PALEOZOIC SYSTEM OF ROCKS.
rivers, and the recently-discovered Ceratodus of Australian rivers, 1 a
genus which ranged in time from the Triassic until now.
The Polypterus and the Ceratodus, especially the latter, have one
very striking reptilian feature, viz., the paired-fins have a scaled lobe,
supported by a many-jointed cartilaginous axis, running down the
centre, and from which the rays come off on each side (Fig. 422). The
FIG. 423.-D'ental Plate of Cestracion Phillippi.
paired-fins in these bear the same relation to the ordinary paired-fin of
fishes which the vertebrated tail-fin does to the ordinary tail-fin (see
next page). It is a true scelidate, or legged fin, and is connected,
through the imperfect limb of the Lepidosiren, with true limbs of am-
phibians. Now, many of the Devonian fishes (Crossopterygians of
Huxley) (Figs. 411 and 413) have this style of fin in a marked degree.
The living Placoid, which most resembles the Devonian Placoids, is
the Cestracion Phillipsi of Australia (Fig. 429). Instead of lancet-
shaped teeth, which characterize most modern sharks, the jaws of the
Cestracion are covered with a broad pavement of rounded plates, much
like a pavement of cobble-stones (Fig. 423). The family of pavement-
toothed sharks are called Cestracionts from this living representative.
The Devonian Placoids were all, or nearly all, Cestracionts.
General Characteristics of Devonian Fishes. Leaving out some
small aberrant orders, fishes may be divided into three orders, viz.,
Teleosts, Ganoids, and Placoids. The Teleosts (perfect bone) comprise
all the ordinary typical fishes. By far the larger number of living fishes
belong to this order. The Ganoids are nearly extinct, but are still
represented by the Polypterus, the Lepidosteus, the Amia, and the Stur-
geon (Accipenser) ; and it is probable that we should include also the Dip-
noi : i. e., Ceratodus, of the Australian rivers, and Lepidosiren, of African
1 These last two genera are by many zoologists put by themselves into a distinct order
of fishes, the Dipnoi ; but they are undoubtedly very closely allied to the early Ganoids.
ANIMALS.
FTG. 427.
FIGS. 424-429. NEAREST LIVING ALLIES OF DEVONIAN FISHES : 424. Ceratodus Fosterii, x fa (after
Gunther). 425. Polypterus. 426. Lepidosiren. 427. Lepidosteus (Gar-Fish). 428. Amia (American
Mud-fish). 429. Cestracion Phillippi (a Living Cestraciont from Australia).
330 PALAEOZOIC SYSTEM OF ROCKS.
and South American rivers. The Placoids (sharks and skates, etc.)
are still abundant, but far less so than the Teleosts.
Now, as already said : 1. The Devonian fishes were all Ganoids and
Placoids, especially the former. There were no ordinary typical fishes
(Teleosts) at all at that time. 2. The Ganoids of the present day have,
some of them, bony skeletons (Lepidosteus), and some cartilaginous skel-
etons (Sturgeon) ; the Devonian Ganoids all had more or less cartilagi-
nous skeletons. Therefore, since all Placoids have cartilaginous skel-
etons, all the fishes of these early times had cartilaginous skeletons.
3. Of Ganoids of the present day, some have the mouth at the end of the
snout (gar-pike), some beneath or on the ventral surface (sturgeons).
FIG. 430. a, Hoinocercal ; 6, Heterocercal.
The same was true in Devonian times. The Lepido-ganoids had ter-
minal mouth ; the Placoderms, ventral mouth ; and, since Placoids all
have ventral mouth, all the Devonian fishes, except the Lepido-ganoids,
had the mouth on the ventral surface. 4. There are two types of fish
tail-fins, differing both in shape and structure. These are the homo-
cereal (even-lobed), found in Teleosts (Fig. 430 a) ; and the heterocercal
(uneven-lobed), found in Placoids (Fig. 4305). In the homocercal, or
even-lobed, the vertebral column terminates abruptly in one or several
large flat bones, from which diverge the fin-rays (Fig. 431 a). In the
heterocercal, or uneven-lobed, the vertical column runs to the extreme
point usually of the upper lobe (Fig. 431 ). Such a tail-fin, therefore,
t
<z
FIG. 431. a, Homocercal (Sword-fish) ; b, Heterocercal (Sturgeon).
is said to be vertebrated ; and this is the better name for this style of
tail, as the structure is more important than shape, and in some cases a
vertebrated tail may be nearly or quite symmetrical, as in Polypterus
(Fig. 425), and Glyptolemus (Fig. 413). Now, while the tails of living
Ganoids are some decidedly vertebrated, and some only slightly so,
ANIMALS. 331
those of Devonian Ganoids are all decidedly vertebrated. And since
Placoids are all vertebrated-tailed, all Devonian fishes are vertebrated-
tailed.
Rank of Devonian Fishes. We have called Teleosts typical fishes.
In Ganoids and Placoids, especially the former, and still more especially
in the Devonian Ganoids, combined with their distinctive fish-charac-
ters, there are other characters which ally them with reptiles, and also
still others which may be termed embryonic. The most important rep-
tilian characters of Ganoids, especially Devonian Ganoids, are : 1. An
external armor of thick bony plates or scales. 2. Large, conical teeth,
with channeled base (Fig. 432 a),
and labyrinthine internal structure, as
shown in section (Fig. 432 b). Some-
times this structure is more complex
than here represented. 3. A some-
what cellular Swim-bladder, in SOme FIG. 432. Structure of a Ganoid Tooth (after
cases freely supplied with blood, open-
ing by a tube into the pharynx, and therefore showing much anal-
ogy to, and in some cases (Ceratodus) acting as, an imperfect lung.
We do not know that this was true of the Devonian Ganoids, but it is
true of their nearest living allies, viz., Polypterus, Lepidosteus, Amia,
and Ceratodus. 4. In many cases, paired fins which were jointed.
Combined with these decidedly reptilian characters are others
which are as decidedly embryonic. The most conspicuous of these
are : 1. The cartilaginous condition of the skeleton, and even the reten-
tion of the embryonic fibrous chorda dorsalis, imperfectly articulated
into a vertebrate column ; and, 2. In the Placoderms, the ventral posi-
tion of the mouth. The vertebrated tail-fin is regarded by some as em-
bryonic, and by others as reptilian.
In Placoids there is a similar combination of reptilian and embry-
onic characters, except in this case the embryonic seem to predominate.
These are, as before 1. The cartilaginous skeleton ; 2. The inferior posi-
tion of the mouth. But also, in addition, 3. The leathery or imperfectly
rayed fins ; 4. The want of an opercle or gill-cover, growing backward
over, and thus covering the gill-slits ; 5. Perhaps the ligamentous in-
stead of bony attachment of the teeth.
On the other hand, the Placoids of the present day at least possess
very high reptilian characters in their reproduction. In all Placoids their
impregnation is internal, and instead of laying great numbers of unim-
pregnated ovules, like most Teleosts, they either lay few large, well-
covered eggs like reptiles and birds (skates and some sharks), or else
their eggs hatch within and they bring forth young alive (ovo-vivip-
arous") like some reptiles; or in some cases there is even an attach-
ment between the yolk-sac of the internally hatched young and the
PALAEOZOIC SYSTEM OF ROCKS.
oviduct of the mother, somewhat similar to that of the placenta to the
uterus of the mammal. The young of Placoids also at first have a kind
of external branchiae like those of amphibian reptiles.
The following schedule shows the combination of characters enu-
merated. It is seen that in Ganoids the reptilian characters, in Placoids
the embryonic characters, predominate. But, on the other hand, the
GANOIDS.
PLACOIDS.
(armor
teeth
reproduction
tail-fin
I Reptilian
Reptilian -
swim-bladder
skeleton
j
paired-fins
mouth
tail fin
fins
V Embryonic
Embryonic
{skeleton
mouth
gills
teeth
J
reptilian characters of Placoids are more decided and higher. The
Lepido-ganoids of Devonian and Carboniferous times were far more
reptilian than existing Ganoids ; hence these have been appropriated
called Sauroid fishes.
Bearing of these Facts on the Question of Evolution. On account
of this combination of connecting and embryonic characters of char-
acters which seem higher and others which seem lower than those of
typical fishes there has been much dispute as to the rank of Ganoids
and Placoids, and especially of Devonian fishes, and therefore as to
their bearing on the question of evolution. The dispute, however, has
been mostly the result of a misconception of the true nature of evolu-
tion. The most fundamental law of evolution is differentiation; i. e.,
is a separation of one generalized form into several specialized forms
a separation of one stem into several branches. The Devonian fishes
are an admirable illustration of this law. The first introduced fishes
were not typical fishes, but Sauroids, i. e., fishes which combined with
their distinctive fish-characters others which allied them with reptiles.
They were the representatives and progenitors of both classes ; from
this common stem diverged two branches, viz., typical fishes on the one
hand, and reptiles on the other. This is but one example of a very
general law, which may be formulated thus : The first introduced of
any class or order were not typical representatives of that class or
order, but connecting links with other classes or orders, the complete
separation of the two or more classes or orders represented being the
result of subsequent evolution. Such connecting links are variously
called connecting types, synthetic types, comprehensive types, com-
bining types, generalized types, etc. We shall find many examples of
such in the course of the history of the organic kingdom.
Suddenness of Appearance. But it is impossible to overlook the
CARBONIFEROUS SYSTEM. 333
comparative suddenness of the appearance of a new class fishes and
a new department vertebrates of the animal kingdom. Observe that
at the horizon of appearance in the uppermost Silurian there is no ap-
parent break in the strata, and therefore no evidence of lost record :
and yet the advance is immense. It is impossible to account for this
unless we admit paroxysms of more rapid movement of evolution
unless we admit that, when conditions are favorable and the time is
ripe for a particular change, it takes place with exceptional rapidity,
perhaps in a few generations.
Reptiles have not yet been found in the Devonian ; Fishes there-
fore were the highest and most powerful animals then living. They
were the rulers of the Devonian seas. The previous rulers, therefore,
viz., Orthoceratites and Trilobites, according to a necessary law, in the
struggle for life, diminish in size and number, and seek safety in a sub-
ordinate position.
SECTION 3. CARBONIFEROUS SYSTEM. AGE OF ACKOGENS AND
AMPHIBIANS.
Retrospect. Before taking up in detail this important and interest-
ing age, it will be instructive to glance back over the ground traversed,
and draw some conclusions.
If we compare, in physical geography, the American with the Eu-
ropean Continent, we find the one marked by simplicity and the other
by complexity of structure. This is true not only of the map-outline,
but also of the profile-outline, or orographic structure. Now, as history
furnishes the key to social and political structure, so geology furnishes
the key to physical structure. The American Continent at least in its
eastern part has developed steadily from the Laurentian nucleus south-
ward and eastward, and probably northward. We have already seen
how the Silurian area was added to the Laurentian, and the Devonian
to the Silurian. It shall be our pleasure, hereafter, to show the con-
tinuance of this steady development throughout the whole geological
history. For our knowledge on this interesting subject we are indebted
almost wholly to Prof. Dana.
In the case of America, the continent thus sketched in outline in
the earliest times has been steadily worked out in detail throughout
all subsequent time ; with some oscillations, true, determining uncon-
formability of strata, rapid changes of physical geography and climate,
and therefore of species, thus marking the great divisions of time, but
on the whole without change of plan or wavering of purpose ; in the
case of Europe, on the contrary, geological history consists of a series
of oscillations so great that it amounts to a successive making and
unmaking of the continent.
334 PALAEOZOIC SYSTEM OP ROCKS.
Hence, nearly all geological problems are expressed in simpler terms,
and are more easily solved here than there. Hence, also, while in Eu-
rope the ages and periods are separated by unconformability of the
rock-system, as well as change in the life-system, in America they are
separated mainly by change in the life-system only.
Subdivisions of the Carboniferous System and Age. The Carbonifer-
ous age is subdivided into three periods, viz. : 1. Sub-Carboniferous;
2. Coal-measures, or Carboniferous proper; 3. Permian.
The sub-Carboniferous was the period of preparation ; the Coal-
measures the period of culmination / the Permian the period of decline
and transition to the Mesozoic. The whole thickness of the carbon-
iferous strata in Nova Scotia is 14,570 feet ; in South Wales it is 14,000
feet, and in Pennsylvania 9,000 feet.
The sub-Carboniferous consists mainly of marine formations ; the
Coal-measures mainly of fresh-water formation the former mainly of
limestone, the latter mainly of sands and clays ; the fossils of the for-
mer are, therefore, mainly marine animals, of the latter mainly fresh-
water and land animals and plants, though marine animals are also
found. In both Europe and America the coal-basins consisting of the
latter are underlaid by the former, which, moreover, outcrop all around,
forming a penumbral margin to the dark areas representing coal-basins
on geological maps (see map, page 278). Between these two, or, rather,
forming the lowest member of the Coal-measures, there is, in many
places, a thick, coarse sandstone, called the millstone grit.
After this general contrast, we will now concentrate nearly our
whole attention upon the Carboniferous period proper ; because in this
middle period culminated all the more striking characteristics of the
age. In speaking of the life-system, however, we will draw from both
sub-Carboniferous and Carboniferous indifferently. The Permian we
shall treat only as a transition to the next era.
Carboniferous Proper Rock-System or Coal- Measures.
The Name. The Carboniferous period is but one of the three peri-
ods of this age. The Carboniferous age is, again, but one of the three
ages of the Palaeozoic era, while the Palaeozoic era is itself but one of
the four great eras, exclusive of the present, of the whole recorded his-
tory of the earth. The Carboniferous period, therefore, is probably not
more than one-thirtieth part of that recorded history. Yet, during that
period were accumulated, and in the strata of that period (Coal-meas-
ures) are still inclosed, at least nine-tenths of all the worked coal, and
probably nearly nine-tenths of all the workable coal in the world. It is
essentially the coal-bearing period. When we remember that every
geological period has its characteristic fossils, by means of which the
formation may be at once recognized by the experienced eye, it is easy
ROCK-SYSTEM OR COAL-MEASURES.
335
to see the importance of this simple fact as a guide to the prospector.
It has been estimated that the money, time, and energy, uselessly ex-
pended in the State of New York in explorations for coal, where any
geologist might be sure there was no coal, would suffice to make a com-
plete geological survey of the State several times over ! The same is
true of Great Britain and many other countries.
Thickness of Strata. Although constituting so small a portion of
the whole stratified crust of the earth, the coal-measures are in some
places of enormous thickness. In Nova Scotia they are 13,000 feet ; in
South Wales, 12,000 feet ; in Pennsylvania, 4,000 feet ; in West Vir-
ginia, over 4,500 feet.
Mode of Occurrence Of Coal. Such being the thickness of the coal-
measures, it is evident that but a small proportion consists of coal. The
coal-measures consist, in fact, of thick strata of sandstone, shales, and
limestone, like other formations ; but in addition to these are inter-
stratified thin seams of coal and beds of iron-ore. Even in the richest
coal-measures, the proportion of coal to rock is not more than as 1 to 50,
and the proportion of iron is still much smaller. In some coal-fields, as,
for example, in the Appalachian, mechanical sediments,
shales, and sand-stones, predominate ; in others, as in the
Western coal-fields, organic sediments or limestone pre-
dominate.
The five kinds of strata mentioned are repeated in
the same coal-basin very many times perhaps 100 or
more, as in the accompanying section ; but, in comparing
one coal-field with another, or in the same coal-field, in
comparing one portion of the series with another, there
is no regular order of succession discoverable. Except
that immediately in contact with the seam beneath, there
is nearly always a thin seam of. fine fire-clay. This con-
stant attendant of a coal-seam is called the under-day.
Again, immediately above, and therefore forming the
roof of the opened seam, there is frequently, though not
so constantly, a shale which, being impregnated with car-
bonaceous matter, is called the black shale or black slate.
These accompaniments are, however, usually too thin to
appear on sections.
In different portions, however, of the same coal-field,
at the same geological horizon, we are apt, to find the Fl
same order. This is the necessary result of the continu-
ity of the strata over the whole basin. If we represent
coal-basins, with their five different kinds of strata, by
reams of variously-colored paper, then, while the order
of succession may be different in the different reams, and
PALAEOZOIC SYSTEM OF ROCKS.
in the upper or lower portion of the same ream, yet at the same level
we find the same order in every portion of the same ream. This is a
test of a field even when separated by denudation into several basins.
It is also a mode of identifying individual coal-seams ; for, if the strata
be continuous, then the seam will have the same accompanying strata
above and below. The great Pittsburg seam has been thus identified,
with great probability, over an area of 14,000 square miles, and, allow-
ing for removal by denudation, over an original area of 34,000 square
miles. Rodgers thinks the original area may have been 90,000 square
miles. 1 This rule for the identification of coal-seams of known value is
often of practical importance; but it must be remembered that the
strata of coal-measures, both the seams and the accompanying shale
and sandstones, like all other strata, thin out on their edges (p. 173).
Nevertheless, there is a most extraordinary continuity in the strata of
the coal-measures.
Plication and Denudation. Coal-bearing strata, like all other strata,
FIG. 434. Panther Creek and Summit Hill Traverse (after Dadow).
were, of course, originally horizontal (p. 173) and continuous, but,
like other strata, they are now found sometimes horizontal and some-
Fio. 435. Nesquehoning Basins (after Dadow).
times dipping at all angles, and folded in the most complex manner. In
the Appalachian region, especially in the anthracite region of Northern
FIG. 436. Illinois Coal-Field (after Dadow).
Pennsylvania, the strata are very much disturbed, and the coal-seams in-
terstratified with them are often nearly perpendicular (Figs. 435 and 437),
1 Phillips, " Geology," p. 217.
COAL-MEASURES.
337
while in Indiana and Iowa the coal-strata are nearly or quite horizontal
(Fig. 436). But, whether horizontal, or gently folded, or strongly pli-
FIG. 437. Section near Nesquehoning (after Taylor).
cated, in all cases denudation has carried away much of the upper por-
tions, leaving them in isolated patches as mountains or basins, as shown
in the map of Northern Pennsylvania (Fig. 439) and in the section
(Fig. 438).
FIG. 433. Section of Appalachian Coal-Field, Pennsylvania, showing Effects of Erosion on Gently-Undu-
lating Strata (after Lesley).
By means of the rule for identifying seams given above, it is often
easy to trace the same seam from one basin to another, or from one
mountain-side to another, with great certainty.
FIG. 439. Map of Anthracite Region of Pennsylvania (after Lesley).
Faults. It is plain, from what has been said above, that there is
an essential difference between a coal-seam and a metalliferous vein.
22
338 PALAEOZOIC SYSTEM OF ROCKS.
Coal-seams are conformable with the strata, and are therefore worked
wholly between the strata. This -would be a comparatively easy matter
if it were not for slips or faults which often occur, and sometimes make
the working unprofitable. In case of a fault, it is important to remem-
ber the rule already given on page 225, viz., that most commonly the
strata on the foot-wall side of the fissure goes upward. In the following
FIG. 440. Section across Yarrow Colliery, showing the Law of Faults (after De la Beche).
section of Yarrow colliery it will be seen that all the slips follow this
law.
Thickness of Seams. Coal-seams vary in thickness from a fraction
of an inch to forty or fifty feet. A workable seam must be at least
three feet thick. A pure, simple seam is seldom more than eight or
ten feet. Mammoth seams, such as occur in the anthracite region of
Pennsylvania, and in Southern France, are produced by the running
together of several seams by the thinning out of the interstratified
shales and sandstones. They are, therefore, almost always compound
seams, i. e., separated by thin partings of clay too thin to form a good
roof or floor, and therefore all worked together.
Number and Aggregate Thickness. In a single coal-field, we have
said, the strata, including the coal-seams, are repeated many times.
In the South Joggins's section, Nova Scotia, there are eighty-one coal-
seams, though most of these are not workable. In North England there
are twenty to thirty seams. In South Wales there are more than 100
seams, seventy of which are worked. In South Lancashire there are
seventy -five seams over one foot thick ; in Belgium 100 seams, and in
Westphalia 117 seams. The aggregate thickness of all the seams in
Lancashire is 150 feet ; in Pottsville, Pennsylvania, 113 feet ; in West-
ern coal-fields, seventy feet.
The thickest and purest are usually near the middle of the series.
Evidently the conditions favorable for the formation and preservation
of coal commenced gradually, even back in the Devonian, reached their
culmination in the middle Coal-measures, and gradually passed away.
This geological day had its morning, its high noon, and its evening.
Coal Areas Of the United States. In no other country are the
coal-fields so extensive as in the United States. The principal coal-
fields are shown on map of Eastern United States, on page 278.
1. Appalachian Coal-Field. This, the greatest coal-field in the
world, commences in Northern Pennsylvania, covers the whole of West-
COAL-MEASURES. 339
ern Pennsylvania and Eastern Ohio, a large portion of West Virginia
and Eastern Kentucky, then passes southward through East Tennessee,
touches the northwest corner of Georgia, and ends in Middle Alabama.
In general terms, it occupied the western slope of the Appalachian
from the confines of New York to Middle Alabama. Its area is at least
60,000 square miles.
2. Central Goal-Field. This covers the larger portion of Illinois,
the southwest portion of Indiana, and the western portion of Kentucky.
Its area is about 47,000 square miles.
3. Western Coal-field. This covers the southern portion of Iowa,
the northern and western portion of Missouri, the eastern portion of
Kansas, and then passes southward through Arkansas into Texas. Its
area is estimated at 78,000 square miles. These two coal-fields are
seen to be connected by sub-Carboniferous. They are probably one im-
mense field separated by erosion.
4. Michigan Coal-field. In the very centre of the State of Mich-
igan there is another coal-field occupying an area of 6,700 square miles.
5. Rhode Island Coal-Field. A small patch of 500 square miles'
area is found in Rhode Island, extending a little into Massachusetts.
6. Nova Scotia and New Brunswick. This is a large area on both
sides of the bay of Fundy. It is estimated at 18,000 square miles.
The following table gives approximately the areas of American
coal-fields of the Carboniferous age :
Appalachian 60)000
Central 47,000
Western 78,000
Michigan 6^00
Rhode Island 500
192,200
Nova Scotia 1 8)0 00
210,200
Of the 190,000 square miles coal-area of the United States, 120,000
square miles is estimated as workable.
Extra-Carboniferous Coal. All the fields mentioned above belong
to the Carboniferous age. But, besides these, the United States is very
rich in coal of other periods. Probably 20,000 to 25,000 square miles
might be added from strata of later times, making in all 150,000 square
miles of workable coal. But of these latter fields we will speak in
their proper places.
Coal-Areas of Different Countries compared. The following table,
taken principally from Dana, exhibits the comparative coal-areas of
the principal coal-producing countries of the world :
340
PALAEOZOIC SYSTEM OF ROCKS.
United States 120,000 to 150,000 square miles.
British America 18,000 "
Great Britain 12,000 "
Spain 4,000 "
France 2,000 "
Germany 1,800 "
Belgium ' 518 "
Europe, estimated 100,000 "
Relative Production of Coal. But if the extent of coal-area repre-
sents approximately the amount of wealth of this kind present in the
strata, the production of coal represents how much of this wealth is
active capital; it represents the development of those industries de-
pendent on coal. In this respect Great Britain is far in advance of all
other countries, as seen by the following table, compiled from the best
sources at hand :
ANNUAL COAL-PRODUCTION IN
MILLIONS OF TONS.
1845.
1864.
1872.
1874.
1875.
Great Britain
31 5
90
123
125
132
United States
4 5
22
50
Germany
46
Belgium
4 9
10
15
* *
France
4 1
10
17
Inspection of the table shows that in the principal coal-producing
countries there is a rapid increase of production. It is believed that, if
the same rate of increase continues, the annual production of Great
Britain will be in thirty years 250,000,000 tons, and the whole work-
able coal will be exhausted in 110 years. 1 As might be expected,
therefore, British statesmen and scientists are casting about with much
anxiety for means by which to promote the more economic use of coal.
Fortunately, our own country is supplied with almost inexhaustible
stores of this source of industrial prosperity.
Origin of Coal, and of its Varieties.
That coal is of vegetable origin is now no longer doubtful. We
will only briefly enumerate the evidences on which is based the present
scientific unanimity on this subject :
1. The remains of an extinct vegetation are found in abundance in
immediate connection with coal-seams ; stumps and roots in the under-
clay, and leaves and stems in the black slate in contact with the seam
and even imbedded in the seam itself. 2. These vegetable remains are
not only associated with the coal-seam, but have often themselves be-
come coal, though still retaining their original form and structure.
1 Armstrong, Nature, vol. vii., p. 291.
ORIGIN OF COAL AND ITS VARIETIES.
341
3. Not only these easily-recognizable imbedded vegetable fragments,
but the imbedding substance also, the whole coal-seam, even the most
structureless portions, and the hardest varieties, such as anthracite,
when carefully prepared in a suitable manner and examined with the
microscope, show vegetable structure. Even the ashes of coal, carefully
examined, show vegetable cells with characteristic markings. The fol-
lowing figures show the results of such examination. 4. A perfect grada-
FIG. 441. Section of Anthracite : a, natural size ; b
and c, magnified (after Bailey).
FIG. 442. Vegetable Structure in Coal
(after Dawson).
tion may be traced from wood or peat, on the one hand, through brown
coal, lignite, bituminous coal, to the most structureless anthracite and
graphite, on the other, showing that these are all different terms of the
same series. In chemical composition, too, the same unbroken series
may be traced. 5. Lastly, the best and most structureless peat, by hy-
draulic pressure, may be made into a substance having many of the
qualities and uses of coal.
We may, with perhaps less confidence, go farther, and say that all
the carbon and hydrocarbon known to us are probably of organic origin.
Carbon probably existed at first only as carbonic acid, and has been re-
duced from that condition only bv organic agency.
Varieties of Coal. The varieties of coal depend upon the purity,
upon the degree of bituminization, and upon the proportion of fixed
and volatile matter.
Varieties depending upon Purity. Coal consists partly of organic
or combustible and partly of inorganic or incombustible matter. On
burning coal, the organic, combustible matter is consumed, and passes
away in the form of gas, while the inprganic, incombustible is left as
ash. Now, the relative proportion of these may vary to any extent.
We may have a coal of only one or two per cent. ash. We may have a
342 PALEOZOIC SYSTEM OF ROCKS.
coal of five, ten, fifteen, twenty per cent, ash ; the coal is now becoming
poor. We may have a coal of thirty or forty per cent, ash ; this is called
bony coal, or shaly coal; it is the valueless refuse of the mines. We may
have a coal of fifty or sixty per cent, ash ; but it now loses the name as
well as the ready combustibility of coal, and is called coaly shale. Fi-
nally, we may have a coal of seventy, eighty, ninety, ninety-five per
cent, ash; and thus it passes, by insensible ' degrees, through black
shale into perfect shale. This passage is often observed in the roof
of a coal-seam.
Now, all vegetable tissue contains incombustible matter, which, on
burning, is left as ash. The amount of ash in vegetable matter is on an
average about one to two per cent. But as, in the process of change
from wood to coal, much of the organic matter is lost (p. 343, et seq.), and
the relative amount of ash is thereby increased, we may say that, if a
coal contains five per cent, or less of ash, it is absolutely pure i. e., its
ash comes wholly from the plants of which it is composed; but if a coal
contains more than ten per cent, ash, it is probably impure i. e., mixed
with mud at the time of its accumulation.
Varieties of Coal depending on the Degree of Bituminization.
The previously-mentioned varieties consist of pure and impure coals;
these consist of perfect and imperfect coals. We find the vegetable
matter, accumulated in different geological periods, in different stages
of that peculiar change called bituminization. Brown coal and lignite
are examples of such imperfect coal. They are always comparatively
modern.
Varieties depending upon the Proportion of Fixed and Volatile
Matter. Coal, even when pure and perfectly bituminized, consists
still of many varieties, having different uses, depending upon the pro-
portion of fixed and volatile matters. These are the true varieties of
coal.
In pure and perfect coal, then, the combustible matter is part fixed
and part volatile. These may be easily separated by heating to red-
ness in a retort. By this means the volatile matter is all driven off,
and may be collected as tar, oil, etc., in condensers, and as permanent
gases in gasometers ; and the fixed matter is left in the retort as coke.
Now, the proportion of these may vary greatly in different coals, and
affect the uses to which the coal is applied. For example, when the
coal consists wholly of fixed carbon, it is called graphite. This is not
usually considered a variety of coal, because it is not readily combusti-
ble ; but it is evidently only the last term of the coal series. Its soft,
greasy feel, and its uses for pencils, as a friction -powder, and as a
material for crucibles, are well known.
When the combustible matter of the coal contains ninety to ninety-
five per cent, fixed carbon, it is called anthracite. This is a hard, brill-
ORIGIN OF COAL AND ITS VARIETIES. 343
iant variety, with conchoidal fracture and high specific gravity. It burns
with almost no flame and produces much heat. It is an admirable coal
for all household purposes, and, with hot blast, may be used in iron-
smelting furnaces.
If the combustible matter contains eighty to eighty-five per cent,
fixed carbon, and fifteen to twenty per cent, volatile matter, it becomes
semi-anthracite or semi-bituminous coal, of various grades. These are
free-burning, rapid-burning coals, producing long flame and high tem-
perature, because they do not cake and clog. They are admirably
adapted for many purposes, but especially for the rapid production
of steam, and therefore for locomotive-engines, and hence are often
called steam-coals.
If the volatile combustible matter rises to the proportion of thirty
to forty per cent., it becomes full bituminous coals, which always burn
with a strong, bright flame, and often cake and form clinkers. This is
perhaps the commonest form of coal, and may be regarded as typical
coal.
If the volatile matter approaches or exceeds fifty per cent., then it
forms highly-bituminous or fat or fusing coals. This variety is espe-
cially adapted to the manufacture of gas and of coke.
Besides these there are several varieties depending on physical
character. Thus cannel or parrot coal is a dense, dry, structureless,
lustreless, highly-bituminous variety, which breaks with a conchoidal
fracture. There may be also some varieties depending upon the kind
of plants of which coal was made, but of this we have no certain evi-
dence.
Origin of these Varieties. There can be little doubt that these,
the true varieties, are produced by slight differences in the nature and
degree of chemical change in the process of bituminization.
It will be seen by the following table, giving approximate formulae,
that vegetable matter and coal of various grades have the same general
composition, except that in the latter case some of the carbon and
much of the hydrogen and oxygen have passed away in the process of
change :
Vegetable matter, cellulose C 3 6H 60 3 o
Bituminous coal C 26 H 10 Oj
Anthracite " C 40 H 8
Graphite " C pure
The excess of the hydrogen and oxygen lost is still better shown in
the following table, in which the constituents are given in proportion-
ate weights instead of equivalents, and the carbon reduced to a con-
stant quantity :
344
PALEOZOIC SYSTEM OF ROCKS.
KINDS OF VEGETABLE MATTER AND COALS.
Carbon.
Hydrogen.
Oxygen.
Cellulose ...
100.00
16.68
133 33
Wood
100.00
12.18
83 0*7
Peat
100.00
9.83
55 67
Lignite
10000
8 37
49 42
10000
6 12
21 23
100.00
2 84
1 74
Graphite " . .
100.00
00
000
Cellulose C s6 H 60 3 o
Decayed C 35 H 56 02 8
More decayed. .Cs^-Aie
Final result. . . .C S1
Now, there are two modes of decomposition to which vegetable
matter may be subjected, viz. : 1. In contact with air; and, 2. Out of
contact with air. The first is partly decomposition, and partly oxida-
tion by the air (eremacausis) ; the second is wholly decomposition.
In Contact With. Air. Under these conditions, the carbon of the
vegetable matter unites with the oxygen of the vegetable matter, form-
ing carbonic acid (CO 2 ); and the hydrogen of the vegetable matter
unites with the oxygen of the air, forming water (H 2 O). Further, it
is evident that for every equivalent of carbon thus lost there are two
equivalents of oxygen and four equivalents of hydrogen lost, so as
always to maintain the same relative propor-
tion of H and O, viz., the proportion forming
water (H a O). The final result of this process
is pure carbon. It is very improbable, how-
ever, that anthracite or graphite is formed in
this way ; for vegetable matter, by aerial de-
cay, falls to powder, it is very probable, however nay, almost cer-
tain that a peculiar substance, pulverulent and retaining vegetable
structure in a remarkable degree, called mineral charcoal, found very
commonly in some stratified coals, has been formed by partial aerial
decay, somewhat as represented in the table. Mineral charcoal has a
high percentage of carbon, with very little hydrogen and oxygen.
Out of Contact with Air. When vegetable matter is buried in
mud or submerged in water, its elements react on each other. Some of
the carbon unites with some of the oxygen, forming carbonic acid (CO a ) ;
some of the carbon unites with some of the hydrogen, forming carbu-
reted hydrogen, or marsh-gas (CHJ ; and some of the hydrogen unites
with some of the oxygen, forming water (H a O). These products are
probably formed in all cases of vegetable decomposition under these
conditions. If, for example, we stir up the mud at the bottom of stag-
nant pools where weeds are growing, the bubbles which rise always
consist of a mixture of C0 2 and CH 4 . In every coal-mine these same
gases are constantly given off; the one being the deadly choke-damp
and the other the terrible fire-damp of the miners. Now, by varying
the relative amounts of these products, it is easy to see how all the
ORIGIN OF COAL AND ITS VARIETIES. 345
principal varieties of bituminous coal maybe formed. I have given
below the approximate composition of typical varieties of bituminous
coal, and of graphite, and constructed formulae expressing the chemical
change by which they are formed :
Vegetable matter cellulose C 36 H 6 o0 3 o l
( 9C0 2 )
Subtract -J 3CH 4 V Ci a H 31 29
( 11H 2 )
And there remain C 24 H 26 = cannel.
Again, vegetable matter
( 7C0 2 )
Subtract 4 3CH 4 J. C 10 H 40 28
( 14H 2
And there remain .
Again, vegetable matter C 38 H6o0 3 o
( 10C0 2 )
Subtract J. 10CH 4 > CaoHsoOso
( 10H 2 )
And there remains Ci 6 = graphite.
The composition of vegetable matter varies considerably. The com-
position of the varieties of coal is differently given by different au-
thorities. Different reactions from those above given might be con-
trived which would give as good results. These reactions, therefore,
are not given as certainly the actual reactions which take place. They
are only intended to show the general character of the changes which
take place in the formation of coal.
Metamorphic Coal. It is probable that bituminous coal is the nor-
mal coal formed by the above process, and that the extreme forms, an-
thracite and graphite, are the result of an after-change produced by
heat. But some geologists go further: they believe that anthracite
has been changed by intense heat sufficient to vaporize the volatile
matters, which then condense in fissures above, as bitumen, petroleum,
etc. ; that, as in art, when bituminous coal is subjected to heat out of
contact with air, the fixed carbon is left as coke, the tarry and liquid
matters are condensed in purifiers, and the permanent gases collected in
gasometers : so in Nature, when beds of bituminous coal are subjected
to intense heat in the interior of the earth, the fixed carbon is left as
1 The composition of wood timber -is usually given as about Ci 2 H 18 8 . I have
taken the formula of cellulose instead, viz., C 6 H 10 5 ; or, taking six equivalents for con-
venience of calculation, C 36 H 6 o0 3 o. I believe this to be much nearer the composition of
vegetable matter of the Coal period than is the formula of hard wood like oak or beech.
All the results may be worked out, however, with equal ease in either formula for vege-
table matter.
34:6 PALAEOZOIC SYSTEM OF ROCKS.
anthracite, the tarry and liquid matters collected in fissures, as bitumen
and petroleum, while the gases escape in burning springs. The process
is of course slow and under heavy pressure, and therefore the residuum
is not spongy like coke. According to this view, anthracite and bitu-
men are necessary correlatives.
There can be no doubt that the graphitic and anthracitic varieties
of coal are always associated with folding and metamorphism of the
strata : 1. In the universally-folded and metamorphic Laurentian rocks
only graphite is found. 2. In Pennsylvania, in the strongly-folded and
highly-metamorphic eastern portion of the field, the coal is anthracite ;
while, as we go westward, and the rocks are less and less metamorphic,
the coal is more and more bituminous, until, when the rocks are hori-
zontal and unchanged, the coal is always highly bituminous. The same
has been observed in Wales : anthracite is always found in metamorphic
regions, and the coal is more and more bituminous as the rocks are less
and less metamorphic. 3. Again, the anthracitic condition of coal may
be sometimes traced to the local effect of trap or volcanic overflows.
In a word, anthracite is metamorphic coal ; and, according to this view,
the same heat which changed the rocks has distilled away the volatile
matters, which may condense above, as bitumen or petroleum.
We have given above the common view. It is partly true and part-
ly erroneous. The true view seems to be as follows :
Anthracite may, indeed, be regarded as metamorphic coal, but it is
not probable that bitumen is its necessary correlative ; it is not prob-
able that the heat of metamorphism is sufficient to produce destructive
distillation. We have already shown (p. 215) that a moderate heat of
300 to 400 Fahr. in the presence of water is sufficient to produce
metamorphism. Such a degree of heat would, doubtless, hasten the
process explained on page 215. The folding and erosion of the rocks,
and the consequent exposure of the edges of the seams, would still
further hasten the process, and bring about anthracitism by facilitating
the escape of the products of decomposition. In all coal-mines CO 2 ,
CH 4 , and H,,O, are eliminated now ; only continue this process long
enough, and anthracite and, finally, graphite is the result. We must
conclude, then, that high heat is not necessary to produce anthracitism ;
for, if it is unnecessary for metamorphism of rocks, much less is it neces-
sary for metamorphism of coal.
Plants of the Coal their Structure and Affinities.
The flora of the coal-measures is the most abundant and perfect of
all extinct florae. Of about 2,500 to 3,000 known fossil species of plants
nearly 700, or about one-fourth, are from the coal-measures. This flora
is peculiarly interesting to the geologist, not only on account of its rela-
tive abundance, but also and chiefly because being the first diversified
PLANTS OF THE COAL. 347
and somewhat highly-organized flora, it is natural to suppose that the
great classes and orders of the vegetable kingdom commenced to diverge
here. We will, therefore, discuss the affinities of these plants some-
what fully.
Where found. The plants of the Coal are found principally : 1. In
the form of stools and roots in their original position in the under-day;
2. Of leaves, and branches, and flattened trunks, on the upper surface
of the coal-seam, and in the overlying black shale; 3. And, finally, in
the form of logs, apparently drift-timber, in the sandstones above the
coal-seam. The black shale overlying the seam is often full of leaves
and fronds of ferns, and of the flattened trunks of other families, in the
most beautiful state of preservation, so that even the finest venation of
the leaves is perfectly distinct. In some cases where the shale is light-
colored, so as to contrast strongly with the jet-black leaves, the effect
on first opening a seam is very striking, and has been compared to the
frescoes on the ceilings of Italian palaces.
Principal Orders. Leaving out some plants of doubtful affinity,
the plants of the Coal may be referred to five orders or families, viz.,
Conifers, Ferns, Lepidodendrids, Sigillarids, and Calamites. It is
usual to refer these last three to the two orders Lycopods and Equisetae;
but they are so peculiar, and their affinities still so doubtful, that we
have preferred to treat them as distinct orders.
All these, as already seen, commenced in the Devonian, as did also
the preservations of their tissues as coal ; but both the vegetation and
the conditions necessary for their preservation culminated in the Coal
period, and therefore we have put off their discussion until now. Con-
trary to our usual custom, we will commence with the highest, viz. :
1. Conifers. These are found mostly in the form of stumps, and logs,
and fruit, and leaves. The logs are found mostly in the sandstones,
and therefore have been supposed, and apparently with good reason, to
be the remains of drift-logs of the highland trees of the times, carried
down by rapid currents. They are known to be conifers by the exoge-
nous structure of the trunk, together with the discigerous tissue of the
wood (Fig. 373 p. 316), and in some cases by the foliage (Fig. 446) and
by the fruit. Several genera have been described, but they all differ
greatly from the ordinary conifers of temperate climates. Their nearest
living congeners seem to be among the tropical family Araucarice (Nor-
folk Island pine), or among the broad-leaved conifers like the Salis-
buria of China (Fig. 444), and the curious Welwitschia of South Africa
(Fig. 443). This last anomalous conifer, with a trunk three or four
feet in diameter, and only one foot high, bears but two strap-shaped
leaves (the original cotyledons) of great size (two or three feet wide
and six feet long), which lasts during its whole life of 100 years
(Maout and Decaisne).
348
PALEOZOIC SYSTEM OF ROCKS.
The Cordaites is now usually referred to the Conifers, 1 though so
anomalous in its foliage. It formed a straight trunk, sometimes sixty
to seventy feet long, clothed atop with long, strap-shaped leaves like
the Dracaena. Fig. 447 is a restoration by Dawson.
Nut-like fruits, called Trigonocarpus, Cardiocarpus, Rhabdocarpus,
etc., found in great numbers in the Coal-measures, are referred to Coni-
FIG. 444 c.
FIGS. 443-445. BBO AD-LEAVED CONIFERS. LIVING CONGENERS or SOME COAL-PLANTS: 443. Wehvitschia
(the whole plant). 444. Salisburia (Ginko) : a, a branch ; 6, section of fruit ; c, a leaf, natural size.
445. Phyllocladus, a branch.
fers. Trigonocarpus is very similar in structure to the nuts of the
Salisburia, the Torreya or California nutmeg, and the yew, or possibly
1 Some place them among Cycads.
PLANTS OF THE COAL.
349
to those of Cycads. Cardiocarpus is strikingly similar to the winged
nut of the Welwitschia. It is believed to be the fruit of Cordaites.
FiQ.,446. Araucarites gracilis, reduced
(after Dawson).
FIG. 44T.-Cordaites (restored by
Dawson).
The anomalous forms called Antholithes are supposed by Newberry
to be the fruit of allies of Cordaites.
Affinities of Carboniferous Conifers. The affinities of the early
Conifers are very obscure, but there is little doubt that they were all re-
markable generalized types. They seem to be allied, on the one hand,
through the Araucariae and the Lepidodendrons, with the Club-mosses;
and on the other, through the broad-leaved yews, such as Salisburia,
Phyllocladus, etc., with the Ferns. The leaf of a Salisburia (Fig. 444)
is dichotomously veined like a fern. A leafy branch of a Phyllocladus
(Fig. 445) is strikingly like that of a Coal-fern, Cyclopteris (Noegge-
rathia). Some of the Conifers of this period differ from all living Coni-
fers, in having a large pith (Fig. 461), and a somewhat loose tissue,
which may be regarded as an embryonic character.
In conclusion, the Conifers of the Coal are undoubted Conifers, but
have a decided alliance with the vascular Cryptogams, viz., with Lyco-
pods, especially the gigantic Lycopods of the Coal, and with Ferns.
2. Ferns. Ferns are the most abundant plants of the Coal period,
both as to individuals and as to variety of species. About one-third to
one-half of all the known species of coal-plants, both in this country
and in Europe, belong to this order. They represent both ordinary
forms, i. e., those with creeping stems, and Tree-ferns, like those now
growing only in warm latitudes (Fig. 463). They are known to be
350
PALEOZOIC SYSTEM OF ROCKS.
ferns by their large complex fronds (Fig. 464), sometimes six to eight
feet long; by the dichotomous venation of their leaves (Fig. 467 a);
FIGS. 448-460. FRUITS OP COAL-PLANTS, PBOBABLT CONIFERS: 44S-450 Triffonooarpon (after New-
berry). 451-458. Cardiocarpon (after Newberry and Dawson). 459, 460. Ehabdocarpon (after
Newberry).
and by the position of their organs of fructification (spore-cases) on the
PLANTS OF THE COAL.
351
under surfaces of the leaves (Figs. 468 and 469). In some localities
these spore-cases are so abundant that the coal seems to be almost
wholly made up of them. The trunks of Tree-ferns are known by the
FIG. 461. Trunk of a Conifer: FIG. 462. Section of same: 5, woody wedges; c, pith and pith-
ed, bark : &, wood ; c, me- rays,
dullary sheath ; d, pith.
large, ragged, ovoid marks left by the falling of the fronds (leaf-scars
Figs. 478 and 479), and by the peculiar arrangement of the vascular
tissue in the cellular in the cross-section. Some coal Tree-ferns had
their large fronds in two vertical ranks (Megaphyton Fig. 464).
. Living Tree-Fern.
F, Q . 464. Megaphyton. a Coal -Fern
restored (after Dawson).
The Ferns of the Coal are, therefore, unmistakably Ferns, yet bota-
nists recognize some features which connect them with other classes.
Caruthers thinks that he finds in the internal structure of the stems of
352
PALEOZOIC SYSTEM OF ROCKS.
FIG. 466.
FIGS. 465-46S. COAL-FERNS : 465. Callipteris Sullivanti (after Lesqnereux). 466. Pecopteris Strongii (after
Lesquereux). 467. Alethopteris Massilonis (after Lesquereux) ; a, same enlarged to show dichotornous
venation. 468. Neuropteris flexuosa, showing spore-cases (after Brongniart).
PLANTS OF THE COAL.
353
o- 471.
FIG. 472.
FIG. 473. FIG. 474.
- . . . . . . .
FIGS. 469-474. COAL-FERNS : 469. Anemopteris oblongata (after Bron^niart). 470. Ortontopteris Wor-
theni (after Lesquereux). 471. Ilymenophyllitis alatus (after Lesquereux). 472. Neuropteris
flexuosa (after Lesquereux). 473. Neuropteris hirsuta (.after Lesquereux). 474. Pecopteris lonchitica
(after Lesquereux).
23
354
PALAEOZOIC SYSTEM OF ROCKS.
FIG. 476.
FIGS. 475-479. COAL-FERNS : 475. Odontopteris gracillitna (after Lesqnereux). 476. Ilymenophvllitis
splendens (after Lesquereux). 477. Leaf-Scars of Palaxmteris, x J i after Dawson). 478. Leaf-Star
of Megaphyton, x | (after Dawson). 479. Caulopteris priineva, showing Leaf-Scars.
Tree-ferns of the Coal two types which are the foreshadowings of the
Monocotyls on the one hand, and the Dicotyls on the other ; and that
therefore they are probably the progenitors, not only of the Tree-ferns
of the present day, but also of the Palms and the foliferous Exogens. 1
The next three orders we will discuss more fully for two reasons :
First, the Conifers were probably mostly highland plants, and only
found their way into the coal-swamps by accident, being in fact
brought down by freshets. The Ferns formed the thick underbrush of
the coal-swamps. Neither of these contributed a very large share to
the material of the coal-seams. The great trees of the coal-swamps,
1 Nature, vol. vi., p. 480, and Scott, American Journal, vol. ix., p. 65.
PLANTS OF THE COAL.
355
and which formed the larger part of the material preserved as coal,
were Lepidodendrids, Sigillarids, and Calamites.
Again, the Conifers and Ferns were unmistakably Conifers and Ferns,
though certainly with characters connecting with other orders and
classes ; but the three orders now about to be discussed combine so
completely the characters of widely-separated classes that there is still
some doubt as to their real place. For that very reason, however, they
are peculiarly interesting to the evolutionist.
3. Lepidodendrids. These are so called from the typical genus
Lepidodendron. We will describe only this genus.
Lepidodendrons are found most commonly in flattened masses rep-
resenting portions of the trunk or branches,
very regularly marked in rhomboidal pattern,
and much resembling the impression of the
scaly surface of a Ganoid fish. The name Le-
pidodendron (scale-tree) is derived from this
fact (Figs. 481-483). These marks are the
scars of the regularly-arracged and crowded
leaves. All portions of the plant, however,
viz., the roots, the trunk, the branches, the
leaves, and the fruit, have been found in abun-
dance. From these the general appearance of
the tree has been approximately reconstructed.
Imagine, then, a tree two to four feet in di-
ameter at base, forty to sixty feet high, with
wide-spreading roots, well adapted for support
on a swampy soil ; the surface of the trunk and
branches regularly marked in rhomboidal pat-
tern, representing the phyllotaxis ; the trunk
dividing and subdividing, but not profusely,
into branches, which are thickly clothed with
scale-like, or spine-like, or needle-like leaves (Figs. 484 and 486), and
terminated by a club-shaped extremity like the terminal cones of some
conifers, or still more like the club-shaped extremities of club-mosses
(Figs. 485, 487, 488) : and we will have a tolerably correct idea of the
Lepidodendron.
The general appearance of the tree is that of an Araucarian conifer,
or of a gigantic club-moss. The fruit, however, turns the scale of affin-
ity in favor of the club-moss ; for the examination of these, which are
found in great abundance, and known under the name olLepidostrobus
(scale - cone), has shown that they bear in the axils of their scales
spores like club-mosses, and not seeds like conifers. Also, like club-
mosses, there are in these plants two kinds of spores 1 microspores and
1 Williamson, Nature, vol. viii., p. 498.
FIG. 480 Restoration of a Lepi-
dodendron, by Dawson.
356
PALEOZOIC SYSTEM OF ROCKS.
macrospores corresponding to stamens and pistils (Fig. 489). This
would again all}- them very closely with conifers. The external ap-
ill
FIG. 486. FIQ.4S5. FIG. 438. FIG. 457.
FIGS. 481-488. LEPIDODEJTDRIDS : 4S1. Lepidodendron modulatum (after Lesqnereux). 482.
dendron diplotigioidcs (after Lesquereux). 483. Lepidodendron politum (after Lesquereux). 4S4.
Lepidodendron corrugatum, branch and loaves (after Dawson). 4S5. Lepidodendron corrugatum,
branch and fruit (after Dawson). 486. Lepidodendron rigens (after Lesquereux). 4M. Lepido-
phloios Acadianus, fruit (after Dawson). 483. Lepidostrobus (after Lesquereux).
PLANTS OF THE COAL.
357
pearance and inflorescence, therefore, indicate that they are Lycopods,
with very strong coniferous affinities.
This conclusion is entirely borne out by the internal structure. Fig.
FIG. 489. Lepidodendron compared with Club-Moss: a, club-moss; ft, a scale enlarged; c. microspores;
d, macrospores ; x, lepidostrobus ; y and 2, the scales containing spores ; m, microspores ; n, ma-
crospores (after Balfour).
490 represents an ideal cross and longitudinal section of the stem of a
Lepidodendron. It is seen that the stem consists of a dense outer bark
or rind, inclosing a great mass of loose
cellular tissue or inner bark, through
the centre of which runs a compara-
tively small fibro-vascular cylinder,
with very distinct pith. Bundles go
from the cylinder outward to form
the venation of the leaves. Now, the
structure of a club-moss is almost the
same, except that the fibro-vascular
cylinder is solid, and there is, there-
FIG. 490. Ide
pith; b, v
l Section of a Lepidodendron: a,
scular cylinder: c, inner bark;
' * ^^
358
PALAEOZOIC SYSTEM OF ROCKS.
fore, no pith. The presence in Lepidodendron of a distinct pith is an
important character, placing it far above modern Lycopods, and allying
it most decidedly with Exogens.
4. Sigillarids. The typical genus of this family is Sigillaria.
These plants are found, like Lepidodendrids, mostly as flattened masses,
wm^rnijm
^'''^^-^'^^r-.^fc 1 :-^- 1
fjm^Km'W
~ nli ^^-s--vi:.'?^----- v
^
FIGS. 401-495. SIOILLARIDS: 491. Sigillaria roticn.ata (after Lesquereux). 492. Siarillaria Grspseri.
493. Sigillaria lievigata (European). 494. Sigillaria obovata (after Lesquereux). 495. Leaf of Sigil-
laria elegans (after Dawson).
which are portions of trunks, but also as roots and leaves. The trunk-
impressions are distinguished from those of Lepidodendrids by longi-
PLANTS OF THE COAL. 359
tudinal ribbings or flutings, ornamented with seal-like impressions
(sigilla, a seal), in vertical rows (Figs. 491-494). Little is known of
their leaves, though they seem to have been similar to those of Lepido-
dendron (Fig. 495).
The best general conception which we can form of the Sigillaria
would represent it as a tall, gently-tapering trunk, longitudinally fluted
like a Corinthian column, and ornamented with seal-like impressions in
vertical ranks, representing the phyllotaxis ; unbranched or else dividing
only into a few large branches, clothed thickly with long, stiffish, taper-
ing leaves. From the base of the trunk extended large, radiating roots,
branching dichotomously and sparsely, with
many long, thread-like rootlets penetrating
the soil below. The stumps of Sigillaria and
Lepidodendrons, with these large, horizontally-
spreading roots and thread-like appendages,
are very common in the underclay, and were
long supposed to be a peculiar plant, and
called Stigmaria, on account of the round
spots (stigma) on their surface. They are
now known to belong to Sigillarids and Le-
pidodendrids, and are either roots or spread-
ing rhizomes (underground branches).
T j.1. e 11 c. /At\n\ j. f FIG. 496. Stigmaria flcoides (after
In the following ngure (497), taken irom Lesquereux).
Dawson, we have attempted to realize the
general appearance of a Sigillaria. Their trunks were sometimes of
prodigious length and diameter. They were probably the largest
trees of the time. In a coal-seam in Dauphin County, Pennsylvania,
flattened stems were found four feet and even five feet in width. Some
of these were exposed for fifty feet, with but little apparent diminution.
One was exposed sixty-five feet, and was estimated to have extended at
least thirty feet more. Another was exposed seventy feet, and was es-
timated to have been eighty to one hundred feet when growing. 1
The Sigillarids are regarded as closely allied to the Lepidodendrids.
Indeed, the two families shade into each other in such wise that there
are many genera the position of which, whether in the one family or in
the other, is doubtful. The typical Sigillaria, however, differs in gen-
eral port from the typical Lepidodendron, chiefly in possessing a more
Palm-like, or Cycas-like, or Dracena-like stem. They are evidently, like
the Lepidodendrids, closely allied to Lycopods, but their alliance with
higher classes is even stronger than that of Lepidodendrids.
The internal structure of the stem entirely confirms this conclusion.
A cross-section (Fig. 498) of a Sigillaria-stem shows a hard external
rind, d, inclosing a great mass of loose, cellular tissue (inner bark),
1 Taylor, "Statistics of Coal," pp. 149, 150; Williamson, Nature, vol. viii., p. 447.
360
PALAEOZOIC SYSTEM OF ROCKS.
c c, through the centre of which runs a comparatively small woody cylin-
der, b b, and in the centre of this again a large pith, a a. From the
woody cylinder go bundles of fibro-vascular tissue, ff, through the cel-
lular tissue of the inner bark, to the leaves, e e. Thus far the descrip-
FIQ. 49T. Restoration of Sigillaria, by Dawsoc.
tion is like the Lepidodendron, except that the woody cylinder is larger
and thicker ; but closer examination shows, in addition, the woody cyl-
inder divided into woody wedges by medullary rays, ff ff, in true ex-
FIG. 498. Ideal Section of a Sipillaria-Stem : a,
woody cylinder; c, inner bark; </, rind; e,
leaves ; /, vascular thread running to the le
medullary rays.
pith; ft,
bases of
FIG. 499. -Cross-Section of
Stem of Cycas.
ogenous style, though the concentric rings characteristic of Exogens
are wanting. Still closer examination with the microscope shows a true
gymnospermous tissue (p. 316, Figs. 373-375); both on cross and longi-
tudinal section. Now, there is no plant living which combines gym-
PLANTS OF THE COAL.
3G1
nospermous tissue with a general stem-structure at all similar to this,
except Cycads (Cycas, Zamia, etc.). For sake of comparison, we have
given (Fig. 499) a cross-section of a Cycas ; the letters represent the
same as in the previous figure. There can be no reasonable doubt, there-
fore, of the close alliance of the Sigillarids with the Cycads* But their
close connection with Lepidodendrids shows an equally close, or closer,
alliance with Lycopods. So thoroughly are they a connecting type that
some paleontological botanists (Dawson) regard them as Cycads with
strong Lycopod affinities, while most regard them as Lycopods with
strong Cycad affinities.
5. Calamites. These are plants having long, slender, tapering, reed-
like stems, jointed and hollow, or else with large pith. The exterior
FIG. 503. FIG. 504.
FIGS. 500-504. -CALAMITES AND THEIR ALLIES: 500. Lower End of Stem of Calamites from Nova Scotia.
501. Lo-rer End of Stem of Calamites cannaeformis. 50'2. Sphenophyllum erosum (after Dawson).
503. Asterophyllites foliosus, England (after Nicholson). 504. Annularia inflata (after Lesquereux).
362 PALEOZOIC SYSTEM OF ROCKS.
surface of the stem is finely striated or fluted, but the striaa are not con-
tinuous nor marked with leaf-scars like the flutings of the Sigillaria, but
are interrupted at the joints in the manner shown in Figs. 5UO and 501.
At the joints are attached in whorls the leaves, which are either scale-
like, or strap-like, or thread-like. Sometimes at the joints of the main
stem come out in whorls thread-like, jointed branches, bearing scale-like
or thread-like leaves. At the lower end of the stem, the joints grow
rapidly smaller and shorter, so that this end was conical. From these
short, rapidly-tapering joints came out the thread-like roots.
What I have said thus far applies word for word to Equisetas ; but
the Equisetae of the present day are small, rush-like plants, never much
thicker than the finger, and seldom more than three or four feet high,
although in South America (Caracas) they grow thirty feet high, but
are very slender ; while Calamites were certainly
two feet or more in diameter, and thirty feet high.
Fig. 505 is an attempt to reconstruct the general ap-
pearance of a Calamite by Dawson.
The internal structure of Calamites still further
removes them from Equisetas ; for they seem to have
had (some of them, at least) a thick, woody cylinder
of exogenous structure and gymnospermous tissue.
And if, as Williamson supposes, 1 many of the striated
jointed stems called Calamites are only casts of the
pith, the stems must have been even much larger than
stated above.
Thus, as Lepidodendrids connected Lycopods with
Conifers, and Sigillarids connected Lycopods with
Cycads, so these connected Equisetas with Conifers.
General Conclusion. The conclusion which we
draw from this examination of Coal plants is: 1. That
they belong to the highest Cryptogams, viz., Vascu-
FIG. 505. Restoration of l ar Cryptogams, and the lowest Phaanogams, viz.,
acaiamite (after Daw- Gymnosperms ; 2. That they were intermediate be-
tween these now widely-separated classes, and con-
nected them closely together. These facts are strictly in accordance
with the law already announced (p. 332), viz., that the earliest repre-
sentatives of any class or order are not typical representatives of that
class or order, but connecting or comprehensive types that is, types
which, along with their distinctive classic or ordinal character, united
others which connected them with other classes or orders. Thus the
now widely-separated classes and orders of organisms, when traced
backward, in time approach each other more and more, and probably
unite in one common stem, although we are seldom able to find the
1 Nature, vol. viii., p. 447.
THEORY OF THE ACCUMULATION OF COAL. 353
point of actual union. Thus, in this case, the now widely-separated
Cryptogams and Phasnogams, when traced backward, approach until in
the Coal they are nearly, if not completely, united. The organic king-
dom may be compared to a tree whose trunk is probably to be found,
if found at all, in the lowest strata ; its main branches begin to separate
in the Palaeozoic, the secondary branches in the Mesozoic, and so the
branching continues until the extreme ramification, but also the flower
and fruit, are found in the fauna and flora of the present day. The
duty of the evolutionist is to trace each bough to its fellow-bough, and
each branch to its fellow-branch, and thus gradually to reconstruct this
tree of life, and determine the law and the cause of its growth.
Theory of the Accumulation of Coal.
There is no question connected with the Carboniferous period con-
cerning which there has been more discussion than the mode in which
coal has been accumulated. There are some things, however, about
which there is little difference of opinion. These we will state first,
and thus narrow the field of discussion.
Presence of Water. That coal has been accumulated in the pres-
ence of water, or at least of abundant moisture, is evident : a. From the
preservation of the organic matter. By aerial decay vegetable matter
is either entirely consumed, or else crumbles into dust. Only in the
presence of water is it preserved and accumulated in larger quantities.
b. The interstratified sand and clays and limestones have, of course,
been deposited like all strata in water, c. The coal itself is not un-
frequently distinctly and finely stratified, d. The plants found in con-
nection with the coal-seams are mostly such as grow in moist ground.
Thus far, then, theorists agree, but from this point opinions diverge,
and until recently have very widely diverged. Some have thought
that coal has accumulated by the growth of plants " in situ" as in
peat-bogs and peat-swamps of the present day. Others have sup-
posed that it has accumulated by driftage of vegetable matter by
rivers, like the rafts now found at the mouths of great rivers of the
present day. According to the one view, a coal-seam is an ancient
peat-swamp; according to the other, it is an immense buried raft.
The one is called the "Peat-bog theory? the other, the ''Estuary or
raft theory."
Recently, however, scientific opinions have converged toward a
common belief. We will not, therefore, discuss these two rival theo-
ries, but simply bring out what is most certain in the present views on
this subject.
1. Coal has been accumulated by growth of vegetation in situ, as
in peat-swamps of the present day. This fact is now demonstrable.
The reasons for believing it are the following : a. The purity of coal.
364
PALEOZOIC SYSTEM OF ROCKS.
The coal of the American coal-fields are, with few exceptions, abso-
lutely pure, i. e., the amount of ash is not greater than would result
from the ash of the plants of which it is composed. The same is true of
coals of most extensive coal-fields everywhere. Now, it has already been
shown (p. 135) that in extensive peat-swamps, like the Great Dismal
Swamp, absolutely pure vegetable accumulations unmixed with sedi-
ment occur ; but in buried rafts or drifted vegetable matter of any kind
there must be a large admixture of mud. b. The preservation of the
most complex and delicate parts of the plant in their natural relations
to each other. Large fronds are spread out and pressed as in a bota-
nist's herbarium. Delicate leaves are preserved with all their finest
venation perfectly visible. This is exactly what we would expect if
they lay where they fell, but is incompatible with driftage by rapid
currents to long distances, c. The position of these perfect specimens
only on the upper part of the seam, as would be the case with the last
fallen leaves, instead of mixed throughout the seam, as would be the
case with drifted matter, d. The presence of stumps with their spread-
ing roots penetrating the underclay exactly as they grew. This is not
an occasional phenomenon, but is found in the underclay of nearly every
coal-seam. In South Wales there are 100 seams of coal, every one of
which is underlaid by clay crowded with roots and sometimes with
stumps. In Nova Scotia there are seventy-six seams, twenty of which
have erect stumps standing in their original position with spreading
roots still penetrating the underclay. The other seams have each its
underclay filled with stigm aria-roots. Besides these seams there are
many dark bands (dirt-beds) indicating old forest -grounds.
The following section (Fig. 506) shows some of these seams and
dirt-beds or forest-grounds, with penetrating roots and erect trunks.
Fig. 507 shows an area of
about one-quarter acre of
surface of the underclay of
an English coal-seam in
which there are seventy-
three stumps in situ. This
last evidence (d) is demon-
strative. Beneath every
coal-seam there is a fossil
soil an ancient forest-
ground.
^Recapitulation. We
may sum up the evidence,
and at the same time make it clearer, by describing a section of a
peat -bog, and comparing with a coal-seam. In such a section we have
always an underclay, on which accumulated the moisture, and on
FIG. 506. Erect Fossil Trees, Coal-Measures, Nova Scotia.
THEORY OF THE ACCUMULATION OF COAL.
365
which grew the original trees of the locality. This underclay is often
full of roots and stumps of
the original growth. Above
this is a fine, structureless,
carbonaceous mass, corre-
sponding to the coal-seam.
On this are the last-fallen
leaves, not yet disorganized,
and the still-growing vege-
tation. Now, imagine this
overwhelmed and buried by
mud or sand, the whole sub-
jected to powerful pressure,
and a slow subsequent pro-
cess Of bituminization ; and FIG. 507.-Ground-Plan of a Fossil Forest, Parkfield Colliery.
we have a complete repro-
duction of the phenomena of a coal-seam with its accompanying under-
clay filled with roots, and its black shale filled with leaf and branch
impressions.
2. Coal has been accumulated at the mouths of rivers, and therefore
in localities subject to floods by the river and incursions by the sea. It
is otherwise impossible to account for the clays and sands (often inclos-
ing drift-timber), and limestones, interstratified with the coal. The phe-
nomena of an individual seam prove the accumulation by growth in
situ; the general phenomena of a coal-basin, with its succession of
strata, prove that this took place at the mouths of rivers. Thus, the
field of discussion is narrowed to very small limits.
We conclude, therefore, that coal has been accumulated in extensive
peat-swamps at the mouths of great rivers, and therefore subject to oc-
casional floodings by the river, and inundations by the sea. That pure
peat may accumulate under these circumstances, is sufficiently proved by
the fact mentioned by Lyell, that over large tracts of ground in the river-
swamp and delta of the Mississippi pure peat is now forming, in spite
of the annual floods; the sediments being all stopped by the thick jungle-
growth surrounding these spots, and deposited on the margins, while
only pure water reaches the interior portions. 1
But if coal has indeed been formed at the mouths of great rivers, we
ought to find at least something analogous to a coal-field in sections of
great river-deltas. And so, indeed, we do. We have seen (p. 130) that
a great river-delta, like that of the Mississippi or the Ganges, consists
of alternate layers of river-sediments (sands and clays) and marine sedi-
ments (limestones), with thin layers of peaty matter, and old forest*
1 Lyell, "Elements of Geology," p. 488.
366 PALAEOZOIC SYSTEM OF ROCKS.
grounds with stumps and roots. It is, in other -words, a coal-field,
though an imperfect one, in the process of formation. It will be remem-
bered, also, that we accounted for this alternation, not by oscillations,
but by the operation of two opposing forces, one depressing (subsi-
dence), the other up-building (river-deposit), with varying success.
When the up-building by river-deposit prevailed, the area was reclaimed,
and became covered with thick jungle vegetation ; when the subsidence
prevailed, it was again covered with water, and buried in river-sediments,
etc. Now and then, when the subsidence was unusually great, the sea
invaded the same area, and limestone was formed. It is substantially
in' this way that coal-fields were probably formed.
Application of the Theory to the American Coal-Fields : a. Appalachian
Coal-Field. A glance at the map (p. 278) will show that, during Carbo-
niferous times, there was high land to the north, east, and west of this
field, and the black area, representing the Coal-measures, was then a
trough, into which, therefore, drained rivers from every side except the
south. This trough was sometimes a coal-swamp, sometimes a lake
emptying southward, sometimes an arm of the sea connecting with the
ocean southward. When it was a coal-marsh, a coal-seam was formed ;
when a lake, sands and clays were deposited by the rivers ; when an
arm of the sea, marine deposits limestones were formed.
This alternation of conditions we explain as follows : There were
three forces at work on this area : 1. A general continental upheaval,
affecting this along with all other parts of the continent ; 2. An up-
building by sedimentary deposit ; 3. A local subsidence. The evidence
of all these is complete. The continental upheaval, as we have already
seen, was unceasing throughout the previous periods, and, as we shall
see, continued throughout the subsequent periods. The up-building by
sediments and the pari passu subsidence are as clearly marked as in
deltas of the present day, by shore-marks , by shalloic-icater fossils, and
especially \>y forest-grounds repeated through several thousand feet of
vertical thickness. The existence of these three forces, therefore, is
not a doubtful hypothesis. Now, the first two would tend to reclaim,
the third to submerge, the area. When the reclaiming forces pre-
dominated, the area became swamp-land, and covered with coal vegeta-
tion, and the river-water, strained through the thick growth, slowly went
southward by a kind of seepage. When the submerging forces pre-
dominated, the area became a lake, and sediments in great quantities
were brought down by the rivers. It is possible, perhaps probable, that
correlative with the more rapid local subsidence which formed the lake
there was also a more rapid elevation of the high lands on all sides, pro-
ducing more torrential river-currents and greater sedimentary deposits.
Now and then, at long intervals, the subsidence would bring the area
below sea-level, and would thus form an interior sea, or mediterranean.
ESTIMATE OF TIME. 367
During such times, limestones would be formed, and marine animals
would be imbedded as fossils.
b. Western Coal-Fields. The Central and Western coal-fields may be
regarded as owe, having been subsequently separated by denudation.
This immensely extensive field may have been, like the Appalachian, a
hollow surrounded on all sides by higher land. If so, the western land
has since been submerged, and covered by more recent deposits. Or it
may have been an extensive jungly flat, bordering a western sea, with
many small rivers with inosculating deltas, flowing westward and seep-
ing through the thick, marshy vegetation. There were here far less
mechanical sediments, because less high land, and far more marine de-
posits, because there was a larger and opener sea ; but, in other re-
spects, the process may be regarded as similar.
Appalachian Revolution. This state of oscillation and incertitude
was cut short bv the Appalachian revolution. At the end of the Coal
period, the sediments which had been so long accumulating in the Appa-
lachian region, until their aggregate thickness had now reached 40,000
feet, at last yielded to the horizontal pressure produced by interior con-
traction of the earth (p. 252), and were crumpled, and mashed, and
thickened up into the Appalachian chain. At the same time the Western
coal-swamps were upheaved sufficiently to become permanent dry land.
This revolution closed the Carboniferous age and the Palseozoic era.
Estimate of Time.
We have already said (p. 264) that it is important that the mind
should become familiarized with the idea of the immense time necessary
to explain geological phenomena. We therefore embrace this oppor-
tunity of making a rough approximative estimate of the Coal period.
The estimate may be made either by taking the whole amount of coal
in a coal-field as the thing to be measured, and the rate at which vigor-
ous vegetation now makes organic matter as the measuring-rod ; or else
by taking the whole amount of sediments in a coal-basin as the thing
to be measured, and the rate of accumulation of sediments by large
rivers as the measuring-rod. We will give both, though the latter is
probably the more reliable.
1. From Aggregate Amount of Coal. A vigorous vegetation as,
for example, an average field-crop or a thick forest makes about 2,000
pounds of dried organic matter per annum per acre, or 200,000 pounds
or 100 tons per century. But 100 tons of vegetable matter pressed to
the specific gravity of coal (1.4), and spread over an acre, would make a
layer less than two-thirds of an inch in thickness. But, according to
Bischof, vegetable matter in changing to coal loses, on an average, four-
fifths of its weight by the escape of C0 2 , CH 4 , and H 2 O (p. 345), only
368 PALAEOZOIC SYSTEM OF ROCKS.
one-fifth remaining. Therefore, vigorous vegetation at present could
make only about one-eighth of an inch of coal, specific gravity 1.4, per
century. To make a layer one foot thick would require nearly 10,000
years. But the aggregate thickness in some coal-basins is 100 feet and
even 150 feet (p. 338). This would require the former near 1,000,000,
the latter 1,400,000 years. It is probable, however, that coal vegeta-
tion was more vigorous than the present vegetation. Our measuring-
rod may be too short ; we will try the other method :
2. From Amount of Sediment. We are indebted to Sir Charles
Lyell for the following estimate of the time necessary to accumulate
the Nova Scotia Coal-measures. This coal-field is selected because the
evidences of river-sediments are very clear throughout. The area of
this coal-basin is given on page 339 as 18,000 square miles ; but the
identity in character of portions now widely separated by seas e. g.,
on Prince Edward's Island, Cape Breton, Magdalen Island, etc. plainly
shows that all these are parts of one original field, which could not
have been less than 36,000 square miles. The thickness at South Jog-
gins is 13,000 feet. At Pictou, 100 miles distant, it is nearly as great.
We will certainly not err on the side of excess, therefore, if we take the
average thickness over the whole area as 7,500 feet. This would give
the cubic contents of the original delta deposit as about 51,000 cubic
miles. Now, the Mississippi River, according to Humphrey and Abbot,
carries to its delta annually sediment enough to cover a square mile
268 feet deep, or nearly exactly one-twentieth of a cubic mile. There-
fore, to accumulate the mass of sediment mentioned above would take
the Mississippi about 1,000,000 years.
It may be objected to this estimate that it is founded on a particu-
lar theory of the accumulation of the Coal-measures. The answer to
this is plain. Any other mode would only extend the time, for this
mode is more rapid than any other. Again, it may be objected that we
have evidence of a very rapid accumulation in stumps and logs and
erect trunks, either bituminized or petrified, and which, therefore, must
have been completely buried before they could decay. The answer is,
that these are only examples of local rapid deposit, and do not at all
affect the general result. Precisely the same happens now in river-
deltas. Again, it maybe objected that the agencies of Nature were far
more energetic then than now. This objection has already been an-
swered on page 264.
We, therefore, return to our estimate with increased confidence
that it is far within limits. But the Coal period, as already said (p.
334), is not more than one-thirtieth of the recorded history of the
earth ; beyond which, again, lies the infinite abyss of the unrecorded.
PHYSICAL GEOGRAPHY AND CLIMATE OF THE COAL PERIOD. 369
Physical Geography and Climate of the Coal Period.
Physical Geography. In the eastern part of the American Conti-
nent the area of land during this period is approximately shown in the
map (p. 278). It included the Laurentian, the Silurian, and Devonian
areas, during the whole age. In the sub-Carboniferous period the sub-
Carboniferous and Carboniferous areas were covered by the sea, but in
fhe Carboniferous period proper the sub-Carboniferous area was land,
and the Carboniferous area, as already seen, was in an uncertain state,
sometimes above and sometimes below the sea-level. It is probable,
also, that the Eastern border-land extended then much beyond the line
of the Tertiary deposits (see map, p. 278), perhaps beyond the present
coast-line, and was partly submerged in the elevation of the Appa-
lachian chain, at the end of the Coal period.
In the Rocky Mountain region there were considerable bodies of
land, mainly in the Basin region, but their limits are not accurately
known.
Again, it is almost certain that all the lands were comparatively
low. None of the great mountain-chains of the continent were yet
formed. It is also probable that the same was true of the other con-
tinents. Nearly all the high mountain-chains are either more recent
in their origin, or else in their principal growth. In general terms,
then, the lands were smaller and lower, and the conditions more
oceanic, than at present.
Climate. The climate of the Coal period was undoubtedly charac-
terized by greater warmth, humidity, uniformity, and a more highly
carbonated condition of the atmosphere, than now obtain. Most of
these characteristics, if not all, are indicated by the nature of the vege-
tation:
1. The icarmth is shown by the existence of a tropical or ultra-
tropical vegetation. Of the present flora of Great Britain about one-
thirty-fifth are Ferns, and none of these Tree-ferns. Of the Coal flora of
Great Britain about one-half were Ferns, and many of these Tree-ferns.
At present in all Europe there are not more than sixty known species
of Ferns : in European Coal-measures there are nearly 350 * species, and
these are certainly but a fraction of the actual number then existing.
That this indicates a tropical climate is shown by the fact that out of
1,500 species of living Ferns known twenty years ago, 1,200, or four-
fifths, were tropical species. The number of known living Ferns is now
about 3,000," but the proportion of tropical species is still probably the
same. Even in the tropics, however, the proportion of Ferns is far less
than in Great Britain during the Coal period. Again, Tree-ferns, arbo-
rescent Lycopods, Cycads, and Araucarian Conifers, are now wholly con-
1 Lesquereux. * Nature, August, 1876.
24
370 PALAEOZOIC SYSTEM OF ROCKS.
fined to tropical or sub-tropical regions. The prevalence of these tropi-
cal families and their immense size, compared with their congeners of the
present day, would seem to indicate not only tropical but wftra-tropical
conditions. And these conditions prevailed not only in the United
States and Europe, but northward to 75 north latitude, for in Mellville
Island have been found coal-strata containing Tree-ferns, gigantic
Lycopods, Calamites, etc.
2. The humidity is indicated by the fact that Tree-ferns and arbo-
rescent Lycopods are most abundant now on islands in the midst of the
ocean ; and further by the great extent of the Coal swamps, and per-
haps also by the general succulence of, or the predominance of cellular
tissue in, the plants of that period.
3. The uniformity is proved by the great resemblance and often
identity of the species in the most widely-separated regions. Accord-
ing to Lesquereux, out of 434 American and 440 European species, 176
are common, and the remainder far less diverse in character than the
species of the two florae at present. Again, in all latitudes, from the
tropics to 75 north latitude, Coal species are extremely similar. Such
uniformity of vegetation shows a remarkable uniformity of climate. From
the earliest times until the present there has been probably a gradual
evolution of continents a gradual differentiation of land and water,
a consequent differentiation of climates, and a corresponding differen-
tiation of faunae and florae.
4. The carbonated condition of the atmosphere is proved by the
large quantity of carbon laid up in the form of coal, the whole of which
was withdrawn from the atmosphere in the form of carbonic acid. It is
also indicated by the nature and the luxuriance of the vegetation. The
proportion of carbonic acid in the atmosphere is now about -fa per cent.
( 20 * o7 ). Now, since carbonic acid is the necessary food of plants, it is
natural to expect that up to a certain limit the increase of atmospheric
carbonic acid would increase the luxuriance of vegetation. Experi-
ments prove that this is true for vascular Cryptogams, but not for
Phaenogams.
We may therefore picture to ourselves the climate of this period as
warm, moist, uniform, stagnant (for currents of air are determined by
difference of temperature), and stifling, from the abundance of carbonic
acid. Such physical conditions are extremely favorable to vegetation,
but unfavorable to the higher forms of animal life.
Cause of this Climate. The moisture and uniformity were the
necessary result of the physical geography already given. They were
due to the wide extent of ocean and the absence of large continents and
high mountains. High mountains are the precipitating points for the
atmosphere points through which it discharges its superabundant
.moisture. As these did not exist, the atmosphere was always highly
PHYSICAL GEOGRAPHY AND CLIMATE OF THE COAL PERIOD. 371
charged. The prevalence of the ocean also, as is well known, produces
uniformity.
The greater warmth of high latitudes is partly explained by the
uniformity. But there is good reason to believe that there was then
a higher mean temperature than now exists. This was probably due
to the constitution of the atmosphere. This may be shown as follows :
The surface-temperature of the earth is now almost wholly due to
external, not to internal, causes. It has been calculated that only one-
twentieth of a degree Fahr. is now due to the latter cause. In going
downward, the heat increases about 1 Fahr. for every 50 to 60 feet,
i. e., the internal heat for every 50 feet of depth increases twenty times
the surface temperature. Now, it has been shown by Fourier and
Hopkins that the same would be true whatever be the surface-tempera-
ture from internal causes. For example, if the surface-temperature
from internal causes be 1, then for every fifty feet of depth the interior
heat would increase 20. If the surface-temperature from internal
causes be 10, then for everv 50 feet of depth the interior heat would
increase 200 a condition of things entirely inconsistent with the
growth of plants, since all the springs would be boiling. We cannot,
therefore, attribute, as many have done, even a few degrees' increase
of mean temperature to causes interior to the earth. In fact, it seems
almost certain that during the whole recorded history of the earth, i. e.,
during the time it has been inhabited by organisms, the surface-tem-
perature of the earth has been almost wholly due to external causes.
Now, the composition of the atmosphere is an external cause, which
greatly affects the surface-temperature, but which has hitherto been
almost wholly neglected. The thorough explanation of this point will
require some discussion of the properties of transparent media in rela-
tion to light and heat.
Many bodies which are transparent to light are opaque to heat.
Such bodies, however, will freely transmit heat, if the heat be accom-
panied with intense light. It is as if the light carried the heat through
with it. Heat thus associated with light is sometimes called light-heat,
while that which is not thus associated is called dark heat. Now, the
bodies spoken of are transparent to light-heat, but opaque to dark heat.
Glass is such a body. If a pane of glass be held between the face and
the sun, the heat passes freely and burns the face, but the same pane
would act as a partial screen before a fire, and as a perfect screen be-
fore a hot, but not incandescent, cannon-ball.
It is in this way we explain the fact that a glass greenhouse, even
in the coldest sunshiny winter's day, becomes insupportably warm if
shut up. The sun-light and heat pass freely through the glass, and
heat the ground, the benches, the flower-pots ; but the light-heat thereby
becomes converted into dark heat, and thus is imprisoned within.
372 PALAEOZOIC SYSTEM OF ROCKS.
Now, the earth and its atmosphere are such a greeenhouse. The light-
heat passes readily through, warms the ground, changes into dark heat,
and is in a measure imprisoned by the partial opacity of the atmosphere
to this kind of heat. The atmosphere is a kind of blanket put about
the earth to keep it warm. So much has long been recognized. But
Tyndall has shown ' that the property of opacity to dark heat in the
case of the atmosphere is due wholly to the small quantity of carbonic
acid and aqueous vapor present ; that oxygen and nitrogen are trans-
parent to dark heat, and, therefore, if the atmosphere consisted only of
these two gases, it would not be heated by radiation from the earth,
and the ground would lose all its heat by radiation during the night,
and become intensely cold like space. In other words, the blanket put
about the earth to keep it warm is woven of carbonic acid and aqueous
vapor.
Now, we have seen that during the Coal period the quantity of car-
bonic acid and aqueous vapor in the air was far greater than now.
The atmosphere was then a double blanket, and therefore kept the
young earth much warmer. We believe that Prof. T. S. Hunt* was
the first to apply this discovery of Tyndall to the explanation of the
climate of the Coal period. E. B. Hunt had previously attributed it to
greater density of the air (Dana, " Manual," p. 353) ; but this is a wholly
different principle. 3
Thus the physical geography explains the humidity and uniformity,
and the greater humidity and the carbonic acid explain the greater
mean temperature. But there is still the carbonic acid to be accounted
for.
The more highly-carbonated condition of the atmosphere must be
attributed to the original constitution of the air. All carbonic-acid-
producing causes, such as animal respiration, combustion, general decay
of organic matter, volcanoes, carbonated springs, etc., only return to the
air what has been previously taken from it. There can be no doubt that
all the carbon in the world, whether in the form of organic matter, or of
coal, or of bitumen, or of carbonates, existed once as carbonic acid in
the air, and has been progressively withdrawn. First immense quanti-
ties were withdrawn and fixed as carbonates, especially as carbonate of
lime (limestone), and the air correspondingly purified. Again, immense
quantities were withdrawn by the luxuriant vegetation of the Coal pe-
riod, and fixed as coal. In this latter method of withdrawal the oxygen
of the carbonic acid is returned, and the oxygenation of the air is in-
1 " Proceedings of the Royal Society," vol. xi., p. 100 ; American Journal, second
series, vol. xxxvi., p. 99.
* " Chemical and Geological Essays," p. 42.
8 According to Buff, "Archives des Sciences," vol. Ivii., p. 293, the opacity to dark heat
of carbonic acid and aqueous vapor has been greatly exaggerated by Tyndall.
IRON-ORE OF THE COAL-MEASURES. 373
creased. We shall see hereafter that the process of purification did not
cease with the Coal period ; for large quantities were again withdrawn
and laid down as coal and lignite in the Jurassic, the Cretaceous, and
Tertiary periods. There can be no doubt that this progressive purifica-
tion of the air, by the withdrawal of superabundant carbonic acid and
returning the pure oxygen, fitted it for the purposes of higher and higher
animals.
Iron- Ore of the Coal- Measures.
We have already stated that the Coal-measures consist of alternat-
ing layers of sandstones, shales, and limestones, containing seams of
coal and bands of iron-ore. We have already discussed the mode of
occurrence, the varieties, and the theory of accumulation of the coal.
We come now to discuss the same points in regard to the iron-ore.
Mode of Occurrence. The mode of occurrence of iron-ore is, in
many respects, like that of coal. Like coal, it is found in seams, which
vary in thickness from a fraction of an inch to forty or fifty feet. Like
coal, these very thick seams are apt to be impure, being largely mixed
with clay. Seams pure enough to work profitably are seldom more
than three or four feet thick. Like coal, the seams are repeated many
times in the same section (Fig. 433, p. 335), but without any discoverable
order of succession. Like coal, the seam is usually underlaid by clay.
Kinds of Ore. The form of iron-ore found in all strata, except those
containing coal, is usually ferric oxide, either hydrated (brown hema-
tite limonite), or anhydrous (red hematite), or else magnetic oxide ;
but in the Coal-measures of this period, and in the Coal-measures of
every other period i. e., in all .strata containing coal, the iron is in
the form of ferrous carbonate. This is usually mixed with clay, and
therefore called clay iron-stone. It is often nodular and mammillated,
and called kidney iron-ore. Sometimes it is mixed intimately with car-
bonaceous matter, and is called black-band ore. This last very valuable
ore is found in Pennsylvania and in Scotland.
The importance of the association of coal and iron in the same strata
cannot be over-estimated. For this reason, the raising of coal and the
manufacture of iron are conducted in connection with each other, and
the smelting-furnaces are often situated at the mouths of the coal-mines.
It is easy to understand, therefore, why Great Britain, the greatest
coal-producing country in the world, should be also the greatest iron-
producing country. Nearly all the iron-ore worked in Great Britain is
taken from her coal-mines. In this country, much iron is made from
the iron carbonates of the coal-mines, but much also from the peroxide
ores found elsewhere, especially in Laurentian strata (p. 273).
The following table gives a comparative view of the annual iron-
production, in tons, of the principal iron-producing countries of the
world. It will be seen that Great Britain makes about half the iron of
374
PALEOZOIC SYSTEM OF ROCKS.
the world. The rapid increase in the production of this great agent of
civilization is also seen.
IRON.
1845.
1856.
1864.
18T1.
1S73.
Great Britain
2 200,000
3 500 000
5 000 000
6 566 000
United States
502,000
1,000,000
1,200,000
2 560 000
France
450,000
1,217,000
1 381 000
1 664 000
World.."
7,000,000
14,485,000
Theory of the Accumulation of the Iron-Ore of the Coal-Measures.
We have already explained (p. 136) how iron-ore is now accumu-
lated by the agency of decaying organic matter. We have also shown
that if the organic matter is consumed in doing the work of accumula-
tion, the iron-ore is left in the form of iron peroxide ; but, if it is accu-
mulated in the presence of excess of organic matter, it retains the form
of ferrous carbonate. We will now give additional evidence, taken
from the occurrence of iron-ore in the strata of the earth, that the same
agency has accomplished the same results in all geological times.
1. Immense beds of iron-ore are found in the strata of all geological
ages ; but, wherever we find them, we find also associated a corre-
sponding amount of strata, decolorized or leached of their iron coloring-
matter. Contrarily, wherever we find the rocks extensively red, we find
also an absence of valuable beds of iron-ore. We are thus led to con-
clude that the iron-ore of iron-beds have been washed out of the strata,
which are thereby left in a decolorized condition.
2. That this has been done by the agency of organic matter is shown
by the fact that, wherever we find evidences of organic matter, whether
in the form of fossils or of coal, we find the sandstones and shales are
white or gray i. e., leached of coloring-matter. Conversely, red rocks
are always barren of fossils or of coal. For example, all the sandstones
of the coal-measures, or of all other strata containing coal, are gray,
while the Old Red sandstone below the coal, and the New Red sandstone
above the coal, and, in fact, all red sandstones, are very poor in fossils
or evidences of organic matter of any kind. Thus, evidences of organic
matter, and the decoloring of the strata, and the accumulation of iron-
ore, are closely associated as cause and effect.
3. In all the strata, whether older or newer, in which there is no
coal, i. e., in which there is no excess of organic matter in a state of
change, the iron-ore is peroxide (ferric oxide) ; while in coal-measures
of all periods, whether Carboniferous, or Jurassic, or Cretaceous, or Ter-
tiary, or in all cases where there is organic matter in excess in a state
of change (not graphite), the iron-ore is in the form of carbonate pro-
toxide, or ferrous carbonate (FeCO 3 ).
IRON-ORE OF THE COAL-MEASURES. 375
Therefore, we conclude that both now and always iron-ore is, and
has been, accumulated by organic agency; again, that both now and
always there are, and have been, three conditions of iron-ore, each as-
sociated with the absence or presence in smaller or larger quantities of
changing organic matter : 1. It may be universally diffused as a color-
ing matter of rocks and soils, and unavailable for industries ; in this
case there has been no organic matter to leach it out and accumulate
it. 2. It may be accumulated as ferric oxide ; in this case there has been
organic matter only sufficient to do the work of accumulation, and was
all consumed in doing that work. 3. It may be accumulated as ferrous
carbonate ; in this case there is excess of organic matter, in' the form
of coal.
This much is certain ; but, as to the exact mode and time of the
leaching and accumulation, there is some difference of opinion. There
are two ways in which the accumulation may have occurred : It may
have accumulated in the coal-marshes during the Coal period, being
then leached out of the surrounding soils, which were therefore left in
a decolorized condition, and in this condition subsequently washed down
as sediments into the coal-marshes. Or, it may have been brought
down as the coloring-matter of red sands and clays ; and afterward,
perhaps after the Coal period, leached out by percolating waters con-
taining organic matter from the coal-beds, carried downward until
stopped by an impervious clav-stratum, and accumulated there. The
former mode is the most probable.
But, in any case, organic matter has been the agent ; and, there-
fore, in this case, as in all other cases, iron-ore is the sign of organic
matter, and the measure of the amount of organic matter consumed in
its accumulation. There are, therefore, three signs of the previous
existence of organisms used by geologists : they are coal, iron-ore, and
fossils.
We cannot dismiss this subject without making one passing reflec-
tion suggested by the mention of these three signs of life :
The organic kingdom is so much matter taken from the atmosphere,
embodied for a brief space in individual living forms, to be again
dissolved by death, and returned to the atmosphere whence it came.
The same material is again taken by the next generation, embodied,
and again returned at its death. The same small quantity of matter in
the atmosphere is embodied and disembodied, again embodied and
disembodied, and thus worked over and over again by constant circula-
tion thousands, yea, millions of times, in the history of the earth.
Now, in this constant circulation of the elements of organic matter,
besides the work done in the fact of circulation itself, viz., the wonderful
but fleeting phenomena of vegetable, animal, vea, of human life, there
was another work, the results of which accumulated from age to age
376 PALEOZOIC SYSTEM OF ROCKS.
a work, too, of the greatest importance to the well-being of the human
race. A portion of this circulating matter, in its course downward
from the organic to the mineral kingdom, stopped half-way, and was
accumulated as great beds of coal reservoirs of stored force. As cir-
culating water descending seaward is stopped and stored in reservoirs
to complete its descent under the control of man, and do his work, so
circulating organic matter descending is stopped and stored, and is
now completing its descent under the control of man, and doing his
work, and thus becomes the great agent of modern civilization.
A second portion of circulating organic elements completes its de-
scent, but in doing so accumulates iron-ore, the second great civilizer of
the human race.
A third portion also completes its descent, but accumulates neither
coal nor iron-ore ; but it accomplishes a work far more subtile and beau-
tiful than either of the others. As each particle of organic matter re-
turns to the atmosphere, it compels a particle of mineral matter to take
its place, thus completely reproducing its form and structure. Thus
fossils are formed, and thus is the history of the organic kingdom self-
recorded. Thus, while the other two portions have subserved the mate-
rial wants of man, this portion has subserved his higher intellectual
wants.
Bitumen and Petroleum.
The origin of bitumen and petroleum is so closely connected with
that of coal, that although not confined to, nor even found principally
in, the Coal-measures, the subject is best taken up in this connection.
It is well known that coal or any organic matter, by suitable distilla-
tion, may be broken up into a great variety of products: some solid, as
coal-pitch; some tarry, as coal-tar; some liquid, as coal-oil; some vola-
tile, as coal-naphtha ; and some gaseous, as coal-gas. Now, we find col-
lected, in fissures beneath the earth, or issuing from its surface, a very
similar series of products: some solid, as asphalt; some tarry, as bitu-
men; some liquid, as petroleum; some volatile, as rock-naphtha ; and
some gaseous, as marsh-gas and carbonic acid of burning springs.
There can be no doubt that these also are of organic origin.
Geological Relations. Bitumen and petroleum are found in all fos-
siliferous rocks, from the lowest Silurian to the uppermost Tertiary, under
certain conditions, among which are the local abundance of organisms
from which these substances are formed, and the absence of great meta-
morphism. The signs of their presence in any locality are iridescent
scums on the water of springs (oil-show), and the issuing of combustible
gases (burning springs). In regard to the first sign, it must be remem-
bered that iridescent scums are produced by many other substances be-
sides petroleum. The second sign is considered the best, although com-
bustible gases may issue from decomposing organic matter of any kind,
BITUMEN AND PETROLEUM.
3T7
or from coal. Some of the burning springs in the oil-region of Ken-
tucky are said to produce a flame twenty to thirty feet long. It is a
curious fact that petroleum is often associated with salt. It is so in
Pennsylvania, in Virginia, and in many other localities.
Oil-Formations. I have said that petroleum and bitumen are found
in all fossiliferous formations, but in each country there are certain for-
mations where it especially abounds : in Europe it is found principally
in the Tertiary ; in Eastern United States it is found almost wholly in
the Palaeozoic, below the Coal-measures ; in California it is found in
the Tertiary.
Principal Oil-Horizons of the United States. In Pennsylvania and
Kentucky oil is found in the Upper Devonian ; in Canada and Michigan,
in the Lower Devonian ; in Western Virginia it is found in the sub-
Carboniferous ; in Ohio, in Lower Coal-measures, though it probably
originates below ; in California it is found in Miocene Tertiary of the
Coast Range, all the way from Los Angeles to Cape Mendocino. These
have been called oil-horizons.
Laws of Interior Distribution. The mode of interior distribution
of petroleum and bitumen is similar to, yet different from, that of
water. Like water, it occurs in. porous strata and collected in fissures
and cavities ; 'like water and with water, it issues in hill-side springs ;
like water and with water, it collects in ordinary wells, or sometimes
spouts in immense quantities from artesian wells. Some of the great
spouting-wells of Pennsylvania, when first opened, yielded 3,000 bar-
rels per day. But, unlike water, there is no perennial large supply ;
the accumulations of ages being exhausted in a few months or a few
years. Unlike water, the force of ejection in great spouting-wells is
not hydrostatic pressure, but the pressure of elastic gases generated
from the petroleum. The great spouting-wells are, therefore, the for-
tunate tappings of reservoirs in large fissures or cavities, which, having
been accumulating for millenniums, are enormously productive, but
378
PALAEOZOIC SYSTEM OF ROCKS.
also rapidly exhausted. In the case of less productive but more per-
manent wells, the oil is contained in more numerous but smaller fissures
and pores. In all cases of collection in large fissures and cavities, these
reservoirs are occupied also by water and gas ; and the three materials
arrange themselves in the order of their relative specific gravities, as in
Figs. 508 and 509.
These facts easily account for the many curious phenomena con-
nected with oil-wells. Thus, if the well a (Fig. 508) taps the reser-
voir, only gas will escape, and oil and water can be gotten only by
pump. But if the well be at b, oil will spout ; and afterward, when the
gas has escaped, oil and water may be pumped. If the well be at c,
then water will spout first and afterward oil. If the cavity be irregu-
lar, with more than one chamber containing compressed gas (Fig. 509),
and the well be at a, then gas will escape first, and afterward oil and
water will spout.
Kinds Of Rocks which bear Petroleum. As already stated, petro-
leum, like water, is found principally in pores and fissures and cavities.
The same kinds of rocks, therefore, which are water-bearing are also
oil-bearing, viz., limestones and sandstones. In Canada it is found in
limestone, in Pennsylvania in sandstone. The intervening shales are
usually barren. In Pennsylvania there are three oil-bearing sandstones,
separated by about 200 feet of intervening shales. If a well reaches
the first sandstone without obtaining oil, the boring is continued to
BKAOYS BEND
the second, or even to the third. Fig. 510 (taken from Lesley) rep-
resents a section through the Pennsylvania oil-regions, showing the
three principal oil-horizons of the United States, viz., the Venango
ORIGIN OF PETROLEUM AND BITUMEN, 379
County (Pennsylvania) horizon with its three sandstones ; the Virginia
sub-Carboniferous horizon above ; and the Canada horizon below.
Petroleum (especially the lighter oils) is found only in horizontal
or gently-folded strata, because strongly-folded and crumpled strata are
always metamorphic, and the heat which produced metamorphism has
also concreted the oil into bitumen or asphalt. Also the outcropping
of the edges of highly-inclined strata favors the escape of gas and
the concretion of the oil. It is hardly probable, therefore, that a light
oil will ever be found in the California oil-region.
In gently-folded strata the most productive portions seem to be
along a line of anticline ; because there we may expect large fissures,
and also, perhaps, because the oil working up on the surface of water
is apt to accumulate under the saddles of the strata.
Origin of Petroleum and Bitumen.
We have seen that the whole petroleum and bitumen series may be
made artificially by destructive distillation of coal. There seems also
to be little doubt that certain organic matters at ordinary temperature,
in presence of abundant moisture, and out of contact of air, will undergo
a species of decomposition or fermentation by which an oily or tarry
substance, similar to bitumen, is formed. In the interior of heaps of
vegetable substance such bituminous matter is often found. Taking
the composition of petroleum as C n H 2n , the reaction by which it is
formed from vegetable matter is expressed in the following :
Cellulose C 3 6H 60 30
Subtract | ! g^ i C 24 H 36 3 o
CiaH S 4 = petroleum.
Or,
Cellulose C 36 H 60 30
Subtract P2CO, ? ...0,^,0,.
C 24 H48 = petroleum.
There are therefore two general theories of the origin of petroleum :
one, that it is produced by the distillation at high temperature of bitu-
minous coal by volcanic heat, the coal being left as anthracite ; the
other, that it is formed at ordinary temperature by a peculiar decompo-
sition of certain organic matters. The evidence in favor of the first
view is the similarity between the artificial and the natural series ; the
objection to it is that the occurrence of petroleum seems to have no
necessary connection with the occurrence below of coal-seams, and also
that petroleum is found mostly in strata which have not been subjected
to any considerable heat.
380 PALAEOZOIC SYSTEM OF ROCKS.
The argument for the other view is the fact that we actually find
fossil cavities in solid limestone containing bitumen, evidently formed
by decomposition of the animal matter. So, also, shales have been
found in Scotland filled with fishes, which have changed into bitumen.
The most probable view seems to be that both coal and petroleum
are formed from organic matter, but of different kinds and under slight-
ly different conditions that coal is formed from terrestrial woody
plants, in the presence of fresh water, while bitumen and petroleum are
formed from more perishable cellular plants and animals, in the presence
of salt-water. We have already noticed the frequent association of
petroleum and salt.
Origin Of Varieties. However formed, there can be no doubt that
the different varieties of this series are formed from one another by a
subsequent process. It is certain that from all varieties CH 4 is con-
stantly passing off, and that the result of this is a slow consolidation.
By this process light oil is changed into heavy oil, heavy oil into bitu-
men, and bitumen into asphalt. Some of the grandest fissure-reservoirs
of oil have thus been changed into solid asphalt. In the upper barren
Coal-measures of West Virginia there is a vein of asphalt four feet
thick, over 3,000 feet long, and of unknown depth. It fills a great
fissure which breaks through the rocks nearly perpendicularly, and out-
crops on the surface.
There are, therefore, two series of substances formed from organic
matter, viz., the coal series and the oil series. In each series the pro-
portion of carbon increases by subsequent change until, perhaps, pure
carbon may be reached. In the coal series we have fat coal, bituminous
coal, semi-anthracite, anthracite, and, finally, graphite. In the oil series
we have light oil, heavy oil, bitumen, asphalt, probably jet, and possi-
bly, finally, diamond: for Liebig has suggested that diamond is most
probably formed by crystallization of carbon from a liquid hydro-carbon,
in which the proportion of carbon is constantly increasing by loss of
CH 4 .
Area of Oil-bearing Strata in the Eastern United States. The
amount of oil in the United States is practically inexhaustible. The
finding of great reservoirs, producing spouting-wells, has always been,
and always will be, very uncertain ; but a moderate return for industry
and capital is certain for an unlimited time. A large portion of the
Palaeozoic basin, including an area of about 200,000 square miles, is un-
derlaid by rocks which are more or less oil-bearing. The eastern por-
tion of the United States is the great oil-bearing, as it is the great
coal-bearing, country of the world.
FAUNA OF THE CARBONIFEROUS AGE.
381
Fauna of the Carboniferous Age.
As heretofore, we will disregard the subdivisions, and treat of the
fauna of the whole age, at least of sub-Carboniferous and Carboniferous,
together. It must be borne in mind, however, that most of the lower
marine animals mentioned are from the sub-Carboniferous, while most of
FIG. 512. FIG. 513.
FIGS 511-513. CARBONIFEROUS CORALS: 511. Lithostrotion Californiense (after Meek). 512. Clisto-
phyllum Gabbi (after Meek). 513. a, Archimedes Wortheni (after Hall) ; 6, Portion of same, enlarged
to show structure.
382
PALAEOZOIC SYSTEM OF ROCKS.
the fresh-water and land animals are from the Coal-measures. We can
notice only what important families are going out, what important fami-
lies are coming in, and a few which are very characteristic.
FIG. 516.
FIG. 518
FIG. 519.
FIGS. 514-520. ECHTNODERMS OF THE CABBONTFEKOTT8 AGE BlosUcls: 514. Pentremitcs Burlingto-
niensis (after Meek). 515. Pentremites gracilis (after Meek). 51 H. Pentremites cervinus (after Hall).
517. Pentremltes pyriformis (after Hall). Crinids: 518. Batoerinus Chrystii (alter Meek). 519.
Scaphiocrinus scalaris (after Meek.) 520. Forbesiocrinus Wortheni (after Meek).
Among corals the same general characteristic Palaeozoic t3?pe (Qua-
dripartita) continues to prevail, though in greatly-diminished variety
of families ; for the Favositidas and Halysitidas have passed away, and
FAUNA OF THE CARBONIFEROUS AGE.
383
only the. Cyathophy Holds, or cup-corals, remain. The most beautiful
and characteristic are the Columnar Lithostrotion (Fig. 511), a polyp-
coral, and the curious corkscrew-like Archimedes (Fig. 513), a Bryozoan.
Among Crinoids, the Cystids no longer exist, for they passed out
with the Silurian, but the Blastids and Crinids increase in number and
FIGS. 521-524 ECHINODERMS or THE CARBONIFEROUS Aa-R Crinid: 521. Zeaorinus elepans Cafter
Hall). EOwnouu and Asteroids: 522. OHgOporns nobilis, x V (after Meek). 523. a, Archicocidaris
Wortheni (after Hall) ; &, Spine of same, natural size. 524. Onyctiaster flexilis (after Meek)
beauty. Also, the free Echinoderms (Echinoids, and Asteroids) begin
to be more abundant.
Among Brachiopods, the straight-hinged or square-shouldered kinds
continue, but pass out almost wholly with this age.
384:
PALAEOZOIC SYSTEM OF ROCKS.
Land and fresh-water shells, as might have been expected, are be-
ginning to be found in great abundance in the Coal-measures. The genus
Pupa, a land air-breathing gasteropod, and the genus Cyclas, a fresh-
FIG. 526.
FIG. 528.
PIGS. 525-528. CAKBCWTFETiors BRAOHIOPODS AND HETEROPODS : 525. Spirifer plenus (after Hall) ;
a, dorsal view ; &, side-view. f>2(>. Chonetes Balmaniana. f>27. Productus punctatus (after Meek).
528. Productus mesialis (after Hall); a, ventral view; 6, side-view.
water bivalve, and the genus Cypris, a little crustacean bivalve, all of
which are still represented by living species, are found.
FAUXA OF THE CARBONIFEROUS AGE.
385
Of course, marine species, both Lamellibranchs and Gasteropods, are
abundant. Some figures of these are given below.
FIG. 530.
FIG. 53L
FIG. 529. FIG. 532.
FIGS. 529-532. CARBONIFEROUS FKESH-WATEK SHELLS : 529. Pupa vetusta (after Dawson) a Land-
Shell; a, natural size; b, enlarged. 5iO. Cypris (after Dawson); a, natural size. 531. Spirobis
(alter Dawson) ; a, natural size. 532. Naiadites (after Dawson).
Among Cephalopods, Orthoceratites still continue, but in diminished
number, variety, and size. Goniatites, introduced in the Devonian, also
FIG. 534.
FIG. 535.
FIGS. 533-536. CARBOXIFEROVS LAMELLIBRANCHS (after Meek) :
risma ventricosa. 535. Aloriszna pleuropistha.
35
FIG. 536.
!. Solenomya anodontoides. 534. Alo-
Astartella" Newberryi.
386
PALAEOZOIC SYSTEM OF ROCKS.
continue, but both may be said to pass out with this age, although a
few seem to pass into the Lower Triassic.
Trilobites and Eurypterids also continue ready to disappear at the
FIGS. 53T-640. CARBONIFEROUS GASTEROPODS (after Meek) : 537. Macrocheilus Newberryi. 588. Pleu-
rotomaria scitula. 539. Euomphaius subquadratus. 540. Bellerophon sublcevis (after Hall).
FIGS. 541, 542. CARBONIFEROUS GONIATITES: 541. Goniatites Lyonl (after Meek) ; a, side-view; 6, end-
view. 542. Goniatites crenistria (European) ; a, side-view ; 6, end-view.
FIG. 543. CARBONIFEROUS CRUSTACEAN : Euproops Dan (after Meek and Worthen).
FAUNA OF THE CARBONIFEROUS AGE.
387
end, but an advance in the Crustacean class is observed in the introduc-
tion here of Limuloids (king-crabs), Fig. 543, and of Macrourans
long-tailed Crustaceans (lobsters, crawfish, shrimps, etc.), Figs. 545-547.
Insects now for the first time seem to be in considerable abundance
and variety. Their appearance in connection with abundant land-vege-
tation seems natural. Nearly all the principal orders of insects are rep-
FIG. 544.
FIG. 546.
FIG. 54T.
FIGS. 544-547. CARBONIFEBOFS CRUSTACEANS : 544. Phillipsia Lodiensis (after Meek and Worthen).
545. Acanthotelson Stiinpsoni (after Meek and Worthen). 546. Palseocarus typus (after Meek
and Worthen). 54T. Anthrapatemon graciiis (after Meek and Worthen).
resented, viz., dragon-flies (Neuropters), Fig. 551 ; grasshoppers, cock-
roaches, etc. (Orthopters), Figs. 549 and 550; spiders and scorpions
(Arachnids), Fig. 548; beetles (Coleopters) and centipedes (Myriapods),
Figs. 552 and 553. About thirty species have been described from the
American Coal-measures, of which eight are Orthopters ; eleven, Neu-
ropters; four, Arachnids; and seven, Myriapods (Scudder).
388
PALAEOZOIC SYSTEM OF ROCKS.
Vertebrates (Fishes). The great Ganoids and Placoids continue in
undiminished or even increased numbers, size, and variety. They are
still the rulers of the seas. Of Placoids, one has been found with dorsal
FIGS. 54S-658. CARBONIFEROUS INSECTS : 548. Eoscorpius earbonarius (after Meek and Worthen). 549.
Blatta Maderw, Wing-case* (after Lesquerenx). 650. Blattina venusta. Wing-cases (after Leg-
qnereux). 551. Miamia Danse (after Scndder). 552. Enphoberia annigera (after Meek and
Worthen). 558. Zylobius sigillarte (after Dawson).
spine eighteen inches long, another with spine three inches broad and
nine and a half inches long, although much of the point is broken off.
Their teeth, too, are beginning to assume more of the character of true
shark's-teeth. They are no longer wholly Cestracionts (Fig. 558), but
also now Hybodonts, having teeth somewhat like modern sharks, but
rounded on the edges (Figs. 560 and 561). Among Ganoids, the
well-protected but sluggishly-moving JPlacoderms have passed away,
FAUNA OF THE CARBONIFEROUS AGE. 389
but the Sauroids continue in increased numbers and size. Bony, enam-
eled scales of the Megalichthys and Holoptychius are found, two to
three inches across; and jaws of the Holoptychius, a foot or more
FIG. 560. FIG. 561. FIG. 559.
FIGS. 554-561. CARBOXTFEBOFS FISHES Placoids : 554. Edestus vorax (after Newberry). 555. Plenrt-
canthus a Ray (after Nicholson). 556. Gyvacanthus (after Nicholson). 557. Ctenacanthus (after
Nicholson). 558. Coehliodus contortua. 559. Petalodus destructor (after Newberry). 560. Clado-
dus spinosus (after Newberry). 561. Orodus mammllare (after Newberry).
390
PALAEOZOIC SYSTEM OF ROCKS.
long, armed with Saurian teeth, two inches in length (Fig. 563). Also,
as we approach the time for the appearance of Reptiles, some of these
FIG. 562.
FIGS. 662, 563. CARBONIFEROUS FISHES Ganoids : 562. Amblypterus macropterus 563 Tooth of
Holoptychius Hibberti, natural size.
Sauroid fishes seem to become still more reptilian in character, while
others become more fish-like.
Reptiles Amphibians. The first known appearance of the class of
Reptiles on the earth was in this age : not yet, however, in as great
numbers or size, or as high in the scale of organization, as in the next
age. The reign of Reptiles had not yet commenced.
The class of Reptiles may be divided into two sub-classes, viz., True
Reptiles and Amphibians. The Amphibians differ so greatly from
other Reptiles, that they are now usually made a distinct class, inter-
mediate between Fishes and True Reptiles. Of these two sub-classes
only the Amphibians are certainly known to have been represented in
the Carboniferous, although probably True Reptiles also existed in the
last portion of this period. Again, Amphibians are subdivided into
four orders, viz.: 1. Tailless Batrachians (Anoura), such as frogs, toads,
etc. ; 2. Tailed Batrachians ( Urodela), such as tritons, salamanders,
sirens, etc.; 3. The rare snake-like forms (Ophiomorpha or Gymno-
phiona); and 4. Labyrinthodonts. Of these, only the Labyrinthodonts
were represented in the Carboniferous. The other three orders still
exist, but the last has been long extinct. The Labyrinthodonts were
very large, often gigantic, reptiles. They were most of them salaman-
driform, with long tail, weak limbs, and sluggish movement. Some
were pisciform, and had paddles instead of feet.
We can only briefly describe a few representatives of the class, and
draw some conclusions.
1. Reptilian Footprints. In the sub-Carboniferous of Pennsylvania,
FAUNA OF THE CARBONIFEROUS AGE.
391
near Pottsville, have been found tracks of a four-footed, crawling ani-
mal, having thick, fleshy feet about four inches long, and making a
stride of about thirteen inches. The impression of a dragging tail is
also visible. The surface of the slab on which the tracks are found is
marked with distinct ripple-bars and rain-prints. "We thus learn,"
says Dana, " that there existed in the region about Pottsville, at that
time, a mud-flat on the border of a body of water ; that the flat was
swept by wavelets, leaving ripple-marks ; that the ripples were still
fresh when a large amphibian walked across the place; that a brief
FIG. 564. Fossil Bain-prints of the Coal Period.
shower of rain followed, dotting with its drops the half-dried mud ;
that the waters again flowed over the flat, making new deposits of de-
tritus, and so buried the records."
Similar tracks have also been found in the Coal-measures of Penn-
sylvania, on a slab affected with sun-cracks (Fig. 565). The reptile
had evidently walked on the cracked and half-dried mud at low tide.
Tracks have also been found in the Coal-measures of Illinois, Indiana,
Kansas, and Nova Scotia, and in the latter place beautiful specimens of
rain-prints (Fig. 564).
There can be little doubt that the reptiles making the tracks men-
tioned above were Labyrinthodonts.
2. Dendrerpeton. In the Coal-measures of Nova Scotia have been
found quite a number of small reptiles, belonging to several genera.
Among these one is especially interesting, on account of the conditions
under which it seems to have been preserved. It is called the Den-
drerpeton tree-reptile (Fig. 566), because it was found by Dawson
and Lyell in sandstone, filling the hollow stump of a Sigillaria (Fig. 567),
along with another small species of reptile, a number of land-shells
pupa, etc. (Fig. 529, p. 385), and a myriapod (Fig. 553, p. 388).
392 PALJSOZOIC SYSTEM OF ROCKS.
The Sigillaria possessed a thick, strong bark, which was more resistant
of decomposition than the cellular interior. Stumps of these trees are
FIG. 565. Slab of Sandstone with Reptilian Footprints, from Coal-measures of Pennsylvania; x J.
often found, consisting only of coaly bark filled with sandstone, evi-
dently deposited within the hollow. These sands are rich repositories
PIG. 566. Jaw of Dendrerpeton Acadeanum, and Section of
Tooth, enlarged (after Dawson).
FIG. 57. Section of Hollow Sigil-
laria Stump, filled with Sand-
stone (after Dawson).
of organic remains. We can easily imagine the circumstances under
which the Dendrerpeton was preserved. A dead Sigillaria tree, rotted
FAUNA OF THE CARBONIFEROUS AGE. 393
to the base and only its hollow stump remaining, stood on the margin
of a coal-swamp; river-floods filled the stump with sand; in the stump
lived and perished a Dendrerpeton ; or else the dead body of the reptile,
together with shells and other organic remains, was floated into the
hollow stump and buried there. This reptile was probably a Labyrintho-
dout, but with strong alliances with true reptiles, especially Lacertians.
3. ArchegOSailTUS (Primordial Saurian). In the Bavarian Coal-
measures has been found the almost perfect skeleton of a reptile, about
three and a half feet long, which combines in a remarkable degree the
characters of Amphibians with those of Ganoid Fishes. It seems to have
been a Labyrinthodont Amphibian, with general form and structure
adapted for a purely aquatic life. It had, certainly in the early stages
of its life, probably throughout life, both gills and lungs, and therefore,
like all the Amphibians of the present day at this stage, or like Perenni-
branchiate Amphibians throughout life, breathed both air and water.
The locomotive organs were paddles, adapted for swimming, not for
walking. The body was covered with imbricated ganoid scales (Fig.
FIG. 568. Archegosaurus.
568, A), and the head with ganoid plates. The structure of the teeth (B)
was also ganoid. The bodies of the vertebras were not ossified nor even
cartilaginous, but retained the early, embryonic, fibrous condition of a
notochord. It was apparently a connecting link between the lowest Pe-
rennibranchiate Amphibians and the Sauroid Fishes (Owen), with, per-
haps, some alliances with the marine Saurians which afterward appeared.
It was so distinct from other Labyrinthodonts that Prof. Owen puts it in
a distinct order, which he calls Ganocephala. The skeleton of this ani-
mal is given above (Fig. 568), with the limbs (C and D) and jaw (E)
of a Proteus a perennibranchiate amphibian for comparison.
4. Eosaurus. In the Coal-measures of Nova Scotia, in 1861, Prof.
Marsh found the vertebrae of what he thinks, with much reason, was a
marine Saurian; an order which is largely developed in the Mesozoic.
But as only the bodies of a few vertebrae have been found, and as the
bi-concavity of these is the chief evidence of marine Saurian affinity,
and as bi-concavity also exists among Labyrinthodonts, Huxley believes
this was also a Labyrinthodont. There is, therefore, still some doubt as
394
PALAEOZOIC SYSTEM OF ROCKS.
to the true affinity of this animal, but the weight of evidence seems in
favor of a marine Saurian. The size of some of the vertebrae was two
and a half inches, indicating a reptile of gigantic dimensions.
Many other genera have been described by authors both in Europe
FIG. 569. Two Vertebrae of Eosaurns Acadiensis (after Dawson).
and America. Among these, Baphetes, Raniceps, Hylerpeton, Hylono-
inus, and Amphibamus from America, and Anthracosaurus, Ophiderpe-
ton, and Apateon from Europe, are best known. The Baphetes and the
Anthracosaurus attained gigantic size.
FIG. 570. Ptyonlus (after Coj
Very recently a large number (thirty-four species referable to seven-
teen genera) of small Amphibians have been brought to light by the
Ohio Survey, and described by Cope. These are all, or nearly all, Laby-
rinthodonts (Stegocephali, Cope). Some of them have the usual broad
FAUNA OF THE CARBONIFEROUS AGE.
395
heads of Amphibians, but a large number are remarkable for their long,
limbless, snake-like forms and pointed heads. These are evidently among
the lowest form of Amphibians, and have strong affinities also with
Ganoid fishes. Figs. 570 and 571 represent two of the Ohio Amphibians.
Some General Observations on the Earliest Reptiles. With the pos-
sible exception of the Eosaurus, all the reptiles of the Carboniferous
were Labyrinthodonts. They are so called on account of the extraordi-
nary labyrinthine structure of their teeth, produced by the intricate
infolding of the surface and of the cavity. The same structure is ob-
served in ganoid teeth, but in a far less degree. The simple infoldings
of Ganoids (Fig. 432, p. 331) become intricate in Labyrinthodonts (Fig.
572).
The Labyrinthodonts were probably the most complete example of a
connecting type which has yet been discovered. First, they were true
FIG. 571. Tuditanus radiatus, x j- (after Cope).
-Section of Tooth of a Labvrinthodont.
Amphibians in the strictest sense, having all of them in the early
stages of their life some throughout life both lungs and gills, and
thus connecting water-breathers with air-breathers. Again, they were
very different from the slimy-skinned Amphibians of the present day, in
being covered, at least partly, with bony scales over the body, and with
closely-fitting bony plates over the head. Again, they differed wholly
from the present Amphibians in having jaws thoroughly armed with very
large and powerful teeth, the structure of which is labyrinthine. All
of these characters connected them with Sauroid fishes which preceded
them, and the great Saurian reptiles which succeeded them. Finally,
they seemed to possess also characters connecting them with several
orders of subsequently-existing reptiles. In the Labyrinthodonts and
Sauroid fishes we can almost find the point of separation of the two
great branches, Reptile and Fish, of the vertebrate stem ; and in the
396 PALAEOZOIC SYSTEM OF ROCKS.
former the commencing differentiation of the several orders of Rep-
tiles.
Some General Observations on the Whole Palaeozoic.
We have defined geology as the history of the evolution of the earth.
Evolution, therefore, is the central idea of geology. It is this idea
alone which makes geology a distinct science. This is the cohesive
principle which unites and gives significance to all the scattered facts
of geology ; which cements what would otherwise be a mere inco-
herent pile of rubbish into a solid and symmetrical edifice. It seems
appropriate, therefore, that at the end of the long and eventful Paleo-
zoic era we should glance backward and briefly recapitulate the evi-
dences of progressive change (evolution), physical, chemical, and vital.
Physical Changes. The Palaeozoic era opened on this continent
with a V-shaped mass of land the Laurentian area to the north;
also, a land-mass of Laurentian rocks, of unknown shape and extent, on
the eastern border, and probably some islands and masses of larger ex-
tent in the Rocky Mountain region. This condition of things is repre-
sented on the map on page 279. Throughout the Palaeozoic era there
was a steady accretion of land to this nucleus by upheaval of contiguous
sea-bottoms ; a steady development of the continent southward (and
perhaps northward) from the northern area, and both eastward and
westward from the eastern border area, until at the end of the Palaeo-
zoic the eastern half of the continent included certainly all the Lau-
rentian, Silurian, Devonian, and Carboniferous areas shown on the map
on page 278, and probably also some on the eastern and western border
of this area, which was subsequently covered by the sea, and is there-
fore now concealed by more recent deposits. The loss of Palaeozoic
land on the eastern border probably took place during the Appalachian
revolution. In the Rocky Mountain region the development was prob-
ably less steady. Unconformity of Carboniferous on Silurian strata
shows extensive land-areas there during Devonian times. Thus it is
seen that the continent was already sketched in the beginning of the
Palaeozoic, and the process of development went on during that era, so
that at the end the outlines of the continent were already unmistakable.
We shall trace the further development hereafter.
Chemical Changes. Progressive changes in chemical conditions are
no less evident. At first, i. e., before the Archaean era before the ex-
istence of life on the earth the atmosphere, as shown by Hunt (" Essays,"
p. 40, et seq.), was loaded with carbonic acid, representing all the car-
bon and carbonates in the world; with sulphuric acid representing all
the sulphur and sulphates ; with hydrochloric acid representing all the
chlorides ; and with aqueous vapor representing all the water in the
world. Of course, such a condition rendered life impossible. From
this primeval atmosphere, by cooling, the strong acids were first pro-
GENERAL OBSERVATIONS ON THE WHOLE PALAEOZOIC. 397
cipitated with the water; and afterward more slowly the carbonic
acid, by the action of this acid upon the primeval silicates, with the
formation of carbonates, especially limestone. All limestones, there-
fore, represent so much carbonic acid withdrawn from the air. This
withdrawal proceeded through the whole Archsean, Silurian, and
Devonian. During the Carboniferous, the purification of the air
was accelerated by the growth of vegetable matter and its preserva-
tion as coal, as already explained, page 344. In this method of with-
drawal the oxygen of the carbonic acid is returned, and the air becomes
more oxygenated.
Progressive Change in Organisms. Corresponding with these
changes, physical and chemical, it is natural to expect changes in spe-
cies, genera, families, etc., of organisms : and such we find. The law of
continuance or geological range of species, genera, families, orders, is
very similar to that of extent or geographical range of the same groups
(p. 157) ; i. e., the laws of distribution in time are similar to those of
distribution in space. The period of continuance (range in time) of
species is, of course, less than that of genera, and that of genera less
than that of families, etc. According to Prof. Hall, there have been in
the Silurian and Devonian ages alone at least thirty complete changes
of species. The changes of genera are, of course, much less numerous,
and those of families still less than those of genera. These general
laws may be illustrated by any Palaeozoic order ; but I select the order
of Trilobites, because they are very numerous, very diversified, and
well studied, and because they came in with the Palaeozoic, continued
throughout the whole era, and then passed away forever.
The following diagram illustrates these laws in the order of Trilo-
bites. It is seen that this order continues through the whole era, com-
mencing in small numbers, reaching its highest development in the
middle Silurian, and declining to the end. But the families are changed
several times. Six groups are given, to show how they come and go
successively. If we should attempt the distribution of genera, the
changes would be much more numerous, and of species still more so.
In the lower portion of the diagram we have attempted to show in a
very general way how the distribution of species of Calymene and
Acidaspis might be represented.
General Comparison of the Fauna of Palaeozoic with that of Neozoic
Times. The greatest change which has ever occurred in the history of
the organic kingdom took place at the end of the Palaeozoic era. As
human history is primarily divided into Ancient and Modern, so the
whole history of the earth may be properly divided into Palaeozoic and
Neozoic times. We wish to contrast broadly the faunas of these two
great divisions of time. In the diagram (p. 399), the vertical line
represents the dividing line between the old and the new time-world.
PAIuEOZOIC SYSTEM OF ROCKS.
In this country it is appropriately called the Appalachian revolution.
On the left is the Palaeozoic, on the right the Neozoic. When families
or orders of animals are placed on one or the other side without mark,
it means that they are the only kind of the contrasted families found
on that side, or nearly so. If the orders or families so placed are
1. Paradoxides
2. Bathyurus, Agnos-
tus, etc
8. Asaphus, Eemo- )
pleurides, Tri- y --
nucleus, etc )
4. Calymene, Acidas- )
pis, etc j
5. Homalonotus, Li-
chas, etc
6. Phillipsia, Griffithides
7. Distribution of ape-)
cies of Calymene, y
etc \
FIG. 578. Diagram illustrating Distribution of Families, etc., in Time.
marked with the sign +, it means that they are the predominant kinds.
For example, among Cephalopods, the Tetrabranchs, or shelled fam-
ily, are the only kinds found in the Palaeozoic ; in the Neozoic, both
families exist, but the Dibranchs or naked ones vastly predominate.
General Picture of Palaeozoic Times.
Perhaps it is not inappropriate to group some of the more impor-
tant facts in a very brief outline-picture of Palaeozoic times. We must
imagine, fhen^wide seas and low continents of small extent; a hot, moist,
still air, loaded with carbonic acid, stifling and unsuited for the life of
warm-blooded animals. If an observer had walked along those early
beaches he would have found cast up, in great numbers, the shells of
Brachiopods ; clinging to the rocks and hiding away among their hollows,
instead of sea-urchins arid star-fishes and crabs, he would have found
GENERAL PICTURE OF PALAEOZOIC TIMES.
399
Palaeozoic times '. Neozoic times.
RADIATA.
|
Corals.
Quadripartita | . .Sexpartita.
Echinoderms.
+ + Stemmed, or Crinoids | . .Free, or Echinoids and Asteriods + +.
Crinoids.
+ Armless, or simple arms I . .Plumose arms.
I
MOLLUSKS.
Bivalves.
+ Brachiopods | . . Lamellibranchs + + .
Brachiopods.
+ Square-shouldered | . .Sloping-shouldered.
Lamellihranchs.
+ Unsiphonated | . . Siphonated + .
Gasteropoda.
Marine | . . Land, fresh-water, and marine.
Marine.
Unbeaked Herbivorous | . . Beaked Carnivorous + .
Cephalopods.
Shelled, or Tetrabranchs I . . Naked, or Dibranchs + 4- .
Shelled.
+ Straight I . . Coiled.
Orthoceratites.
Goniatites.
I Ceratites.
Ammonites.
N a u t i 1 u s.
|
I
ARTICULATA.
Crustacea.
Entomostraca Malacostraca + .
Trilobites.
Limu oids.
Macrourans.
Brachyourans.
VERTEBRATA.
Fishes.
Heterocercals I . . Homocercals + .
Ganoids and Placoids. ... | Teleosts +.
Placoids.
Cestracionts.
Hybodonts.
Squalodonts.
Reptiles.
Amphibians | . . True Reptiles.
crinoids and trilobites. In the open sea he would have found as rulers,
instead of whales and sharks and teleosts and cuttlefish, huge cuirassed
400 ' PALAEOZOIC SYSTEM OF ROCKS.
Sauroids and the straight-chambered Orthoceras. Turning to the land,
he would have seen at first only desolation ; for there were no land-
plants until the Devonian, and almost no land-animals until the Coal.
During the Coal there were extensive marshes, overgrown with great
trees of Sigillaria, Lepidodendron, and Calamites, with dense under-
brush of Ferns, inhabited by insects and amphibians ; no umbrageous
trees, no fragrant flowers or luscious fruits, no birds, no mammals.
These " dim, watery woodlands " are flowerless, fruitless, songless,
voiceless, except the occasional chirp of the grasshopper. If the ob-
server were a naturalist, he would notice, also, the complete absence of
modern types of plants and animals it would be like another world.
This long dynasty was overthrown, this reign of Fishes ended, the
physical conditions described above changed, and the whole fauna and
flora destroyed or transmuted, by the Appalachian revolution. At the
end of the Palceozoic, the sediments which had been so long accumulating
in the Appalachian region at last yielded to the slowly-increasing horizon-
tal pressure, and were mashed and folded and thickened up into the Ap-
palachian chain, and the rocks metamorphosed. In America, this chain
is the monument of the greatest revolution which has taken place in
the earth's history. Similar and very extensive changes in physical
geography must have taken place in other portions of the globe, other-
wise we cannot account for the enormous changes in physical conditions
and fauna and flora. Many of these have been traced, but we cannot
yet trace them as clearly as in America.
Transition from the Palaeozoic to the Mesozoic Permian Period.
The Permian a Transition Period. The Palaeozoic era was closed and
the Mesozoic inaugurated by the Appalachian revolution. All the great
revolutions in the earth's history are periods of oscillations. Such oscil-
lations produce unconformity. They also produce changes of climate,
and therefore of fauna and flora. We find, therefore, that the Mesozoic
rocks are universally, so far as known, unconformable on the Carbonifer-
ous ; and, corresponding with this unconformity, there is a wonderful
change in fauna and flora a change the greatness of which we have at-
tempted to show in the contrast on the preceding page. Now, the older
geologists regarded this change as one of instantaneous destruction and
recreation, because they took no account of a lost interval. But we
have already shown (pp. 179, 280) that in all cases of unconformity
there is such a lost interval, which in some cases is very large. In
order to account for the very great change in the organic world, it is
only necessary to suppose that periods represented by unconformity are
critical periods in the earth's history periods of rapid change in
physical geography, climate, and therefore of rapid change in fauna
and flora, by the passing out of old types and the differentiation of new
PERMIAN PERIOD. 401
types. Unfortunately, in the earth's history, as in human history, it is
exactly these critical periods these periods of change and revolution
the record of which is apt to be lost. In both histories, too, this is
truer the farther back we go. Of the long interval between the Archae-
an and Palaeozoic, not a leaf of record has been yet recovered ; but of
the interval now under discussion many leaves of record have been
recovered. These have been bound together in a separate volume or
chapter and called the Permian. I shall regard the Permian, therefore,
as essentially a transition period ; its rocks were deposited during the
period of commotion ; its fossil types are in a state of change, though
more nearly allied to the Palaeozoic.
From what has just been said, it will be anticipated that the uncon-
formity of the Mesozoic on the Palaeozoic sometimes takes place be-
tween the lowest Mesozoic and the Permian, and sometimes between
the Permian and the Coal. The Permian, therefore, is sometimes con-
formable with the Coal, as, e. g., in this country ; sometimes conform-
able with the Triassic, as in England. It thus allies itself stratigraphi-
cally sometimes with the Palaeozoic, sometimes with the Mesozoic.
Paleontologically it is always more allied to the Palaeozoic. The
English section, and the history of opinion concerning it, admirably il-
lustrate this point. Fig. 574 is an ideal section through the Devonian,
the Coal and Triassic (Lower Mesozoic) of England. Lying uncon-
formably on the eroded surface of the Coal, J, there is seen a continu-
ous and perfectly conformable series of strata, a. This series, more-
over, is lithologically characterized throughout, especially the lower
part, by frequent alternations of Red sandstones, and therefore has been
called New Red sandstone, to distinguish it from the Devonian, which
is often called Old Red sandstone. It is further distinguished through-
out, especially the upper part, by variegated shales, and therefore
called altogether Poikilitic group. It is also distinguished through-
out by the presence of salt, and therefore called the Saliferous group.
Here, then, there were the strongest reasons for regarding the whole
as one group, distinctly separated by unconformity from the underlying
Coal. The line of unconformity was, therefore, naturally believed to
be the line between Palaeozoic and Mesozoic. Unfortunately, the lower
portion is very barren of fossils, and this means of correcting the
stratigraphic conclusion was at first nearly wanting. When fossils
26
402 PALEOZOIC SYSTEM OF ROCKS.
were discovered in sufficient numbers, however, they showed a greater
alliance with the unconformable Coal below than with the conformable
strata above. Thus, if we make the division between Palaeozoic and
Mesozoic on stratigraphical grounds, we would find it between the
Coal and the overlying strata; while, if we make it on paleontological
grounds, we would have to draw the line through the midst of the
conformable strata, a, giving one half to the Palaeozoic and the other
half to the Mesozoic. It is the lower Palaeozoic half which is called the
Permian.
As a broad general fact, therefore, the great commotion which is
called the Appalachian revolution took place, or commenced to take
place, at the end of the Coal period. But the fauna and flora were not
immediately exterminated, but struggled on, maintaining, as it were, a
painful existence under changed conditions, themselves meanwhile
changing, until complete and permanent harmony was reestablished
with the opening of the Mesozoic. If we may use an illustration, the
Appalachian revolution was the death-sentence of Palaeozoic types, but
the sentence was not instantly executed. This transition period, this
period between the sentence and the execution of Palaeozoic types, is
the Permian.
It is well here to draw attention to the fact of this great change of
organisms, the greatest in the whole history of the earth, taking place
FIGS. 575-579.-PERMIAN SHELLS (after Meek) : 575. Eumlcrotis Hawnii. 576. Myalina Permiana.
577. Bakewellia parva. 578. Pleurophorus subcuneatus. 679. A Gasteropod.
in the midst of conformable strata (Fig. 574, a). Evidently the change
must have been comparatively rapid.
We have given the history of change of opinion in regard to the
English section (Fig. 574), because it is a tpye of many discussions and
changes which have occurred and will still occur in geological opinion.
The Permian has been found in the United States, in Kansas, bor-
dering on, and conformable with, the coal of that region (map, p. 278),
and perhaps in other parts of the Plains ; but nothing of importance
or interest has been found in it except a few shells (Figs. 575-579).
PERMIAN PERIOD.
403
Fio. 580. Walchia piniformis (Permian of Europe).
Fra. 682.
Fio. 581. Fio. 583. Fio. 584.
FIGS. 581-584. PERMIAN BRACHIOPODS: 581. Product* horrida. 582. Lingula Credneri. 583. Terebra-
tula elongata. 594. a, 6, Camarophoria globulina (after Nicholson).
FIG. 585. Restoration of Palseoniscus.
Fio. 536. Platysomus gibbosus (Permian of Europe).
404 .MESOZOIC ERA AGE OF REPTILES.
In Europe the flora consists principally of Ferns, Calamites, and
Lepidodendrids, closely allied to those of the Coal, and several species
of Walchia (Fig. 580), Voltzia, Ulmannia, genera of Conifers. In fact,
Conifers are more abundant and varied than in the Coal.
In the fauna, Trilobites and Goniatites are gone, but a few Ortho-
ceratites and a few square-shouldered Brachiopods, such as Productus
(Fig. 581) and Spirifer, are still found, as also are several genera of
Ganoids observed in the Coal (Fig. 585), and some characteristic of this
period (Fig. 586).
Along with Labyrinthodonts, already found in the Coal, are also
found now some Thecodont (socket-toothed) reptiles, allied to Crocodil-
ians, which show a decided advance on the Coal reptiles. Unless we
except the Eosaurus, these are the first true reptiles found. They are
probably the progenitors of the crocodiles, though they have also affini-
ties with the Dinosaurs (Huxley).
CHAPTER IV.
MESOZOIC ERA AGE OF REPTILES.
THE Palaeozoic era, we have seen, was very long, and very diversi-
fied in dominant types, of both animals and plants. It was during this
long era that originated nearly all the great branches, and even sub-
branches, of the organic kingdom. "We have during this era, therefore,
three very distinct ages: an age of Invertebrates, an age of Fishes, and
an age of Acrogens and Amphibians. The Mesozoic was far less long
and far less diversified in dominant types. It consists of only one age,
viz., the age of Reptiles. Never in the history of the earth, before or
since, did this class reach so high a point in numbers, variety of form,
size, or elevation in the scale of organization.
General Characteristics. The general characteristics of the Meso-
zoic era are the culmination of the class of Reptiles among animals, and
of Cycads among plants, and the first appearance of Teleosts (common
osseous fishes), JHrcls, Mammals among animals, and of Palms and
Dicotyls among trees.
Subdivisions. The Mesozoic era is divided into three periods, viz. :
1. Triassic, because of its threefold development where first studied in
Germany; 2. Jurassic, because of the splendid development of its
strata in the Jura Mountains ; 3. Cretaceous, because the chalk of Eng-
land and France belongs to this period.
TRIASSIC PERIOD. 405
f 3. Cretaceous period.
Mesozoic Era. < 2. Jurassic period.
[_ 1. Triassic period.
In this country the Triassic and 'Jurassic are not so distinctly sepa-
rable as they are in Europe, nor as they are from the Cretaceous. They
form, in fact, one series, and if the Mesozoic had been studied first in
this country, the whole would probably have been divided into only two
periods. We shall therefore speak of the Mesozoic of this country as
consisting of two periods, viz., the Jura- Trias and the Cretaceous. On
account of their fuller development in Europe, it will be best to speak,
first, of the Triassic generally ', then of the Jurassic generally, taking our
illustrations mainly from European sources, and then of the Jura-Trias
in America. Also, on account of the comparative poverty of the Trias
in remains, we will dwell much less on this period than on the subse-
quent Jurassic ; for in this latter period culminated all the distinctive
characters of the Reptilian age.
SECTION 1. TRIASSIC PERIOD.
As already stated, the Triassic strata are always unconformable with
the Coal, and the period opens with a fauna and flora wholly and strik-
ingly different from the preceding. In some places, however, there is
found an intermediate series, the Permian, sometimes conformable with
the Coal and unconformable with the Trias, sometimes conformable
with the Trias and unconformable with the Coal. Its fauna and flora
are also to some extent intermediate, though more nearly allied to
those of the Coal. The explanation of this has already been given.
Subdivisions. The subdivisions of the Triassic rocks and period in
several countries are given below:
GERMAN.
FRENCH.
ENGLISH.
3. Keuper.
Marne irise'e.
Variegated marl.
2. Muschelkalk.
Muschelkalk.
Wanting.
1. Bunter Sandstein.
Gres bigan-6.
Upper New Red sandstone.
The flora, of the Trias is very imperfectly known. We find, how-
ever, no longer the great coal-making trees of the Carboniferous Sigil-
larids, Lepidodendrids, and Calamites though Tree-ferns still continue
in abundance. The forest-trees seem to have been principally Tree-
ferns, Cycads, and Conifers, although the last two did not reach their
highest development until the next period. For this reason we will put
off the fuller discussion of them until we come to that period.
406
MESOZOIC ERA AGE OF REPTILES.
FiGfl. 587-689. TBIASSIC CONIFERS AND CYCADS : 587. Voltzia heterophylla. 588. PterophyUum Ja>geri.
539. Podozamites lanceolatns (after Nicholson).
Animals. Among Echinoderms we find no longer
any Cystids and Blastids ; but Crinids^ beautiful lily
EncriniteS) with long plumose arms, are very abundant
(Fig. 590). Among Brachiopods the familiar square-
shouldered forms, including the Spirifer family, the
Strophomena, family, and the Productus family, are
almost if not wholly gone; only a few Spirifers re-
main. Among Cephalopods, we find no longer Ortho-
ceratites or Goniatites, but Ceratites (Fig. 598) take
their place, and Ammonites begin. In Ceratites, the
suture is more complex than in Goniatites, but not
so complex as the subsequent Ammonite. Among
FIG. 590.-Encrinus liliformis.
FIG. 591. Aspidura loricate.
TRIASSIC PERIOD.
407
Crustaceans, we 6nd no longer TriloMtes nor huge Eurypterids, but
Macrourans, which began in the Carboniferous, are now more abundant,
and of more modern forms (Fig. 599).
Fishes. Among fishes, still we find no Teleosts, only Ganoids and
FIGS. 592-597. LAMELLIBRANCHS : 592. Daonella Lommellii. 593. Pecten Valoniensis. 594. Myophpria
lineata. 595. Cardium Rhseticum. 596. Avicula contorta. 597. Avicula socialis (.after Nicholson).
Placoids ; but while the Ganoids are some of them heteroceral or ver-
tebrated-tailed like the Palaeozoic Ganoids, some are only slightly ver-
FIG. 598. Ceratites nodosns.
FIG. 599. Pemphyx Sueurii.
tebrated, and some wholly non-vertebrated-tailed, or homoceral. The
Ceratodus, a remarkable genus of fishes, one species of which still lives
in Australian rivers (Pig. 424, p. 329), is traced back to this period. Being
408
MESOZOIC ERA AGE OF REPTILES.
FIG. 601.
FIG. 602.
FIGS. 600-602. TRIASSTC FISHES : 600. a, Dental Plate of Ceratodus serratus ; 6, Dental Plate of Cer&-
todus altus, Keuper (after Agassiz). 601. Acrodus minimus. 602. Hybodus apicalis (after Agassiz).
FIG. 604.
FIGS. 603. 604. TRIASSIC REPTILES Labyrinthodontx : 603. Mastodonsaurus Jcegeri. 604. Trema-
tosaurus (after Huxley).
TRIASSIC PERIOD.
409
known in a fossil state only by the curious palatal teeth (Fig. 600), it
has heretofore been classed with Placoids. The Placoids are partly
Cestracionts (Fig. 601), and partly Hybodonts (Fig. 602).
Reptiles. This class was represented by Labyrinthodonts, Enalio-
saurs (marine Saurians),Rhynchosaurs (beaked Saurians), and Lacertians
(lizards).
Marine Saurians readied their culmination in the next period, and
we will therefore put off discussion of them until then. Labyrintho-
donts have already been described in connection with the Carbonifer-
ous, where they first occur. They cul-
minated^ however, in the Triassic, and
then became extinct. They reached in
the Triassic gigantic proportions. The
head of the Labyrinthodon (Mastodon-
saurus) Jaegeri (Fig. 603) was more
than three feet long and two feet wide,
and one of the teeth was three and one-
half inches beyond the jaw, and one
and a half inch in diameter at base
(Owen, Figs. 605, 606). Tracks made
by Labyrinthodonts have been found
in England and in Germany, in rocks
FIGS. 605, 606. TBIASSIO REPTILES Labyrinthodonts : 605. Tooth of Labyrinthodon, natural size.
606. Section of same enlarged, showing structure.
of this period. The unknown animal was at first called Cheirotherium
(hand-beast), because of the resemblance of the track to the impression.
of a very fat human hand (Fig. 607). Both the tracks and the skeleton,
show that the hind limbs were much longer than the fore. In the
410
MESOZOIC ERA AGE OF REPTILES.
tracks figured below, the hind-tracks are eight inches and the fore-
tracks about four inches long. Others have been found of much greater
size.
The beaked Saurians, also called Anomodonts (lawless-toothed),
FIG. 607 Tracks of a Cheirotheriuin a Labyrinthodont.
FIG. 608.
FIGS. 608-611. TRTASSIC REPTILES (after Owen) Anomodonts and Theriodonte : 60S. Dieynodon
lacerticeps. 609. Oudenodon Bainii. 610. a b, Lycosaurus. 611. Canine Tooth of Cynodracon,
natural size.
TRIASSIC PERIOD.
411
are peculiar to this period. The most extraordinary of this remarkable
group is the Dicynodon (two-canine-toothed). This was a saurian with
the head and nipping, horny beak of a tortoise, and with two long curved
overhanging canine teeth from the upper jaw (Fig. 608). Several
species have been found, in one of which (the tigriceps) the head was
twenty inches long and eighteen inches wide. They have been found
only in the fresh-water Triassic of South Africa (Karoo beds). Several
other genera of the same order (Anomodonts) have been found in the
same locality. The Oudenodon had a nipping, horny beak (Fig. 609),
without teeth of any kind.
According to Prof. Owen, this remarkable order combined the char-
acters of crocodiles, tortoises, and lizards.
Verv recently from the same South African strata (Karoo beds)
Prof. Owen has described a great number of remarkable reptiles, in-
cluding Lycosaurus, Cynodracon, Tigrisuchus, Cynosuchus, and many
others, which, from some mammalian characters, especially in the teeth,
he calls Theriodonts (beast-tooth). The strata in which they have been
found are usually assigned to the Triassic, but. they may be Permian, as
similar reptiles have been found in the Permian of the Ural. Figs.
510 and 511, taken from Owen, show the characters of these reptiles.
Birds. No Birds have yet been found in the strata of the Triassio
age, unless we except the so-called bird-tracks of the Connecticut Val-
ley sandstone, which we will discuss further on.
FIR. 612,-Tooth of the Microlestes antiquus,
Fio. 613. Myrmecobius fasciatus, Banded Ant-eater of Australia.
Mammals. Remains of two or three small insectivorous Marsupials
have been found in the uppermost Triassic, both of Europe and of the
412 MESOZOIC ERA AGE OF REPTILES.
United States. Figures of a tooth of one of these, Mierolestes antiquus,
are given (Fig. 612), and also a figure of what is regarded as its nearest
living congener (Fig. 613). But as these are found in very small num-
bers in the uppermost Triassic beds, and as similar animals are found
in much greater numbers in the Jurassic, it seems best to regard these
as anticipations, and to put off the discussion of the affinities of the
earliest mammals until we take up that period.
Mammals probably preceded Birds. This is not a little remarkable.
But it must be remembered that Birds are very closely allied to Reptiles,
and may be regarded as a secondary offshoot of the reptilian branch.
Origin of Eock-Salt.
Neither rock-salt nor coal is confined to the rocks of any particular
age. Both have been formed in every age; both are forming now.
But as the subject of the origin of coal-deposits was discussed in con-
nection with that age during which it was accumulated in the greatest
abundance the Carboniferous so the origin of rock-salt is best dis-
cussed in connection with the so-called Saliferous or Triassic.
Age of Rock-Salt. As already stated, rock-salt is found in strata
of all ages, and is forming now. Moreover, there is none which deserves
the name Saliferous to the same extent that the Carboniferous deserves
its name. The salt of Syracuse, New York, is found in the Upper Si-
lurian ; that of Canada, which exists in immense beds 100 feet thick, is
found in the Upper Silurian or Lower Devonian ; that of Pennsylvania
is Upper Devonian ; of Southwest Virginia is sub-Carboniferous ; of
Petite Anse, Louisiana, is uppermost Cretaceous or lowest Tertiary
(Hilgard). In Europe, the English salt-beds are Triassic, the German
beds Triassic and Jurassic ; the celebrated Polish beds at Cracow are
Tertiary.
Mode of Occurrence. Salt occurs in immense beds of pure rock-salt,
or else impregnating strata. It is obtained by direct mining, or else by
boiling down the saline waters either of natural springs or of artesian
wells sunk into the salt-bearing strata. The further explanation of
its mode of occurrence is best and most concisely given by comparing
it with coal.
1. Like coal, it occurs in isolated basins, but these are far more
limited than the great coal-fields. 2. Like coal, it is interstratified with
sands and clays, the whole series repeated often many times. In Ga-
licia, for example, there are found seven salt-beds in the same section.
3. But it differs from coal, in the great thickness of the beds. In Can-
ada the salt-bed is 100 feet thick (Gibson). 1 In Cheshire, England,
there are two beds, one 100 feet, the other 90 feet thick, separated by
thirty feet of shale. At Stassfurt a salt-bed has been penetrated
1 American Journal of Science, vol. v., p. 362, 1873.
ORIGIN OF ROCK-SALT. 413
1,000 feet, and the bottom not yet reached. 1 4. Recollecting the some-
what limited extent of basins, it is evident that salt-beds thin out far
more rapidly than coal. The English salt-beds thin out fifteen feet per
mile. Coal, therefore, lies in extensive sheets, salt in lenticular masses.
5. Coal has its characteristic valuable accompaniment in iron-beds,
salt in beds of gypsum. Thus, as coal-measures consist of repetitions
of sands, clays, occasional limestones, with valuable beds of coal and
iron-ore many times repeated, so salt-measures consist of sands, clays,
and occasional limestones, with valuable beds of salt and gypsum many
times repeated. Gypsum-beds are often entirely separate from salt-
beds, but each salt-bed is apt to be underlaid by gypsum. 6. While
coal-measures are remarkable for the abundance of organic remains,
both vegetable and animal, salt-measures are equally remarkable for
extreme poverty in this respect. The presence of these remains in
the one case, and their absence in the other, are the cause of the dif-
ference in the color of the sandstones. Coal-measure sandstones are
white or gray, being leached of their oxide of iron by organic matter.
Salt-measure sandstones are usually red, the iron being diffused as
coloring-matter.
Theory of Accumulation. We have already seen (p. 73) that salt-
lakes are evaporated residues of river-water or sea-water in dry cli-
mates, and are now, most of them, depositing salt: also, that sea-
water evaporated deposits first gypsum, then salt : also, that these
deposits of salts and gypsum alternate annually with sediments of sand
and clay the salt or gypsum deposit representing the dry season, and
the mechanical deposits representing the season of floods. It is, there-
fore, natural to look in this direction for an explanation of salt and
gypsum deposits to think that salt-basins are dried-up salt-lakes.
But the immense thickness of the beds plainly shows that there must
have been important modifications of this process. It is plain that
the alternations of salt and sedimentary deposit were not annual but
secular.
The conditions under which salt-measures were formed were prob-
ably as follows : Imagine a low, flat coast, with salt lagoons or lakes,
connected periodically with the sea, by changing direction of winds, or
at longer intervals by oscillations of the earth-crust ; and subjected to
hot sun and dry climate, and without contiguous mountains furnishing
abundant sediment. Under these conditions either gypsum alone, or
gypsum first and then salt, might accumulate by deposit indefinitely.
If the water of the lagoon was kept, by periodic fresh supply of sea-
water, just below the saturating point for salt, gypsum only would con-
tinue to deposit; but if the concentration should reach the point of
1 Bischof, " Chemical Geology," vol. i., p. 383.
414 MESOZOIC ERA AGE OF REPTILES.
saturation for salt, then salt would deposit indefinitely, since fresh sup-
plies would come in from the sea.
Something like this is said to take place now, in portions of the
delta of the Indus (Lyell's " Principles "). A low, flat country of 7,000
square miles (Runn of Cutch) is covered by sea-water a portion of
every year by the action of the monsoons, and dry another portion of
every year by the change of wind. Salt seems to be depositing there
without limit. The region is, of course, utterly desolate, and the
lagoon-water almost wholly destitute of life of any kind, vegetable or
animal.
In the deposits of salt-lakes or saturated lagoons we would not
expect to find many animal remains, but the tracks of animals walking
along their muddy shores, as also sun-cracks and rain-prints, would be
found as on other shores. Now, in the strata associated with salt,
although organic remains, as already said, are rare, shore-marks of
all kinds are common.
SECTION 2. JTTEASSIC PERIOD.
This is the culminating period of the Mesozoic era and Reptilian
age. In it all the characteristics of this age reach their highest de-
velopment. We must discuss this somewhat more fully than the last.
The strata belonging to this period are magnificently developed in
the Jura Mountains, and hence the name Jurassic. These mountains
are an admirable illustration of the manner in which ridges and valleys
are formed by the folding of strata (Fig. 614) ; they also abound in
PIG. 614. Section of the Jura Mountains.
fossils of this period. They have always been regarded by geologists,
therefore, as classic ground.
English geologists call the period Oolite (egg-stone), on account
of the abundant occurrence in that country of a peculiar limestone
composed often wholly of small rounded grains like the roe of a fish.
They divide the whole period into three epochs, viz. : 1. Lias; 2.
Oolite proper ; 3. Wealden. They also subdivide the Oolite proper
into Lower, Middle, and Upper Oolite, separated by intervening Oxford
JT7RASSIC PERIOD. 415
and Kimmeridge clays. All these divisions and subdivisions are well
shown in the following section passing from London westward. This
section is interesting not only as exhibiting all the divisions and sub-
divisions of the Oolitic period, but also as showing their conformity
Lower Middle Upper London
Oolite. Oolite. Oolite. Chalk, clay.
Lias. Oxford Clay. Kimmeridge Gault.
Clay.
FIG. 615.
among themselves and with the overlying chalk, and the unconformity
of these with the overlying Tertiary. It also shows how parallel ridges
and intervening hollows are formed by the outcropping of a series of
strata alternately hard and soft.
Origin of Oolitic Limestones. Oolitic limestones are now forming
on coral shores by cementation of rolled and rounded coral-sand grains
(p. 148.) But oolitic grains often contain small foreign particles around
which the limestone is arranged concentrically. In such cases the
rounded grains " seem to have been gathered by attraction, out of the
calcareous mud, round nuclei of previously-solidified matter " (Phillips).
Jurassic Coal-Measures. In the Jurassic times we have reproduced
on a large scale the conditions favorable for luxuriant growth of plants,
and for their accumulation and preservation in the form of coal. Hence
in many countries we have Jurassic coal-fields. To this period belong
the Yorkshire coal of England and the Brora coal of Scotland. To this
or the previous period belong the coal-fields of North Carolina and
Eastern Virginia, and some of the coal-fields of India and China. The
fine coal-measures of New South Wales, Australia, covering an area of
20,000 square miles, have been usually referred to this period, but they
are probably Permian or Carboniferous. Jurassic coal-measures have a
general structure similar to those of the Carboniferous. Like the lat-
ter, they consist of alternations of sands and clays, and occasional lime-
stones, containing seams of coal and beds of iron-ore. The iron-ore too
is of the same kind, viz., day iron-stone. We find here also underclays,
with stumps and roots, and roof-shales filled with leaf-impressions. It
is fair to conclude, therefore, that the mode of accumulation was similar
to that already described, viz., in marshes subject to occasional floods.
Jurassic coal, though perhaps inferior as a general rule to Carbonifer-
ous, is often of good quality, occurring in thick and profitable seams.
Dirt-BedsFossil Forest-Grounds. Coal-seams with their under-
lying clays are fossil swamp-grounds ; dirt-beds are fossil soils or forest-
grounds. The one graduates insensibly into the other, and both are
occasionally found in all strata, from the Devonian upward. In the
416
MESOZOIC ERA AGE OF REPTILES.
Upper Oolite of England, at the Isle of Portland and elsewhere, there
occurs an interesting example of such a fossil forest-ground with the
erect stumps and ramifying roots still in situ, though silicified, and the
logs, also silicified, still lying on the fossil soil (Figs. 616, 617). It is evi-
dent that the sequence of events at this place in Jurassic times was as
follows: 1. The place was sea-bottom, and received sediment which
consolidated into Portland-stone. 2. After being flooded and covered
with river-deposit, it was raised to land and became forest-ground, cov-
ered with trees and other vegetation peculiar to that time, the decaying
FIG. 61 6. -Section In Cliff east of Lul-
worth Cove: a, Dirt-bed.
T 1
FIG. 617. Section in the Isle of Portland :
a L Dirt-bed.
leaves of which accumulated as a rich and thick vegetable mould. 3. It
became flooded with fresh water, and the trees therefore died and rotted
to stumps. 4. The whole ground, with its stumps and logs, became
covered with mud, which hardened into slates. 5. Finally, the whole
was raised into high land, and in the first figure (Fig. 616) tilted at
considerable angle.
Thus, we have here not only an old forest-ground with its vegetable
mould, but also the stumps and logs of the trees which grew there,
still in place ; and closer examination easily detects the kinds of trees
which grew in the forest. They are Cycads and Conifers (Figs. 618-625).
FIG. 618. Zamia spiralis, a living Cycad of Australia.
Still further, there is good reason to believe that the remains of some
of the animals which roamed these forests have been found. Of these
we will speak in their proper place.
PLANTS.
Plants.
417
Although the conditions under which coal was accumulated were
probably similar in all geological periods, yet the kinds of plants out
FIG. 619. Cycas circinalis, x T i 5 , a living Cycad of the Moluccas (after Decaisne).
of which the coal was made varied. As already seen, the principal
coal-plants of the Carboniferous period were vascular Cryptogams. On
the contrary, the principal coal-plants of the Jurassic period were ferns,
FIG. G20.-Stem of Cycadeoidea megalophylla.
Cycads, and Conifers. The Jurassic may be called the age, of Gym-
nosperms, as the Carboniferous was the age of Acrogens. The Gym-
27
418
MESOZOIC ERA AGE OF REPTILES.
nosperms, especially the family of Cycads, reached here their highest
development. This is shown in Fig. 245 on page 270. The leaves (Fig.
621) and short stems of Cycas and Zamia (Fig. 620) are found very
FIG. 621.
FIGS. 621-624. JITRASSIC PLANTS Cycads and Ferns: 621. Pterophyllum comptum (a Cycad). 622.
Hemitelites Brownii (a Fern). 628. Coniopteris Murrayana. 624. Pachypteris lanceolate.
abundantly in connection with the coal-bearing strata. It is probable,
therefore, that the coal is composed largely of these plants. Some
ANIMALS. 419
remains of Jurassic plants are given (Figs. 620-626), and also of living
Cycads (Figs. 618, 619), for comparison.
FIG. 625. FIG
FIGS. 625, 626. JURASSIC PLANTS Conifers : 625. Cone of a Pine. 626. Cone of an Araucaria.
-Animals.
The animals of the Jurassic, both marine, fresh-water, and land,
were very abundant, and have been well preserved. It is impossible,
therefore, in the lower departments, to do more than touch lightly the
most salient points. In the higher departments we will dwell a little
longer.
Corals have assumed now the modern type and style of partitions
(Fig. 627). Among Echinoderms, the Crinids, or plumose-armed Cri-
noids, are very abundant and very beautiful ; in fact, they seem to have
reached their highest point in abundance, diversity, and gracefulness
of form (Figs. 628, 629). But the free forms, Echinoids and Asteroids,
are now equally abundant (Figs. 630-632).
BracMopods are still abundant, though far less so than formerly ;
but they now belong almost wholly to the modern or sloping-shoul-
dered types, such as Terebratula and Rhynchonella. Only a very few
small specimens of the Palaeozoic type linger until the Lias.
Lamellibranchs, or common bivalves, are extremely abundant.
Among the common and characteristic forms are Trigonia, Gryphsea,
and Exogyra, belonging to the oyster family ; and the strangely-shaped
Diceras. It is interesting, also, to observe here the first appearance of
the genus Ostrea (oyster).
Cephalopods. One of the most striking characteristics of the Juras-
sic period is the culmination of the class of Cephalopods in number,
diversity of forms, and, if we except some of the Silurian Orthocera-
tites, in size. They were represented by the Ammonites and the Be-
lemnites, the one belonging to the order of Tetrabranchs, or shelled,
420
MESOZOIC ERA AGE OF REPTILES.
the other to the Dibranchs, or naked Cephalopods. It is important to
observe that the highest order of Cephalopods, the Dibranchs, by far
FIG. 631.
FIG. 623.
FIGS 627-632.-JntA8STC CORALS AND ECHINODERMS : fi-27. Prionastrea ohlonpata. 623. Apiocrinus
Roissianus. (529. Saoeoeoma pectinata (- *~- *"--"' --
Plotii. 632. a 6, Hemicidaris crenukris.
ANIMALS.
421
the most abundantly represented at the present time, were introduced
here for the first time.
FIG. 68T. FIG. 638. FIG. 639. FIG. 640.
FIGS. 633-640. JURASSIC LAMELLIBRANCHS AND BRACHIOPODS OF ENGLAOT) : 638. Astarte excavate.
634. Trigonia clavellata. 635. Ostrea Sowerbyi. 636. Pecten flbrosus. 637. Ostrea Marshii. 638.
Khynchonella varians. 639. Terebratula sphieroldalis. 640. Terebratula digona (after Nicholson).
Ammonites. The Ammonite family, which is distinguished, as already
explained (pp. 306, 320), by the dorsal position of the siphon and the com-
plexity of the suture, is represented in extreme abundance by the type-
FIG. 641. Ammonites Humphreysianus.
genus Ammonites. About 500 species of this genus are known, ranging
in time from the Triassic through the Cretaceous. They are therefore
characteristic of the Mesozoic. They varied extremely in shape, and in
422
MESOZOIC ERA AGE OF REPTILES.
size from half an inch to a yard or more in diameter. Below, and on
page 421, we give figures of some of the most common species.
In the genus Ammonites the distinguishing character of the familv,
viz., the complexity of the suture, reached its highest point. In this
FIGS. 642-645. JUEASSIC CEPHALOPODS Ammonites: 642. Ammonites bifrons. 643. Ammonites mar-
garitanus. 644. Ammonites Jason: a, side-view; b, showing suture. 645. Ammonites cordatns:
a, side-view ; 6, showing suture.
Nautilus.
FIG. 646. Diagram showing the Form of the Suture and the Position of the Siphon in Cephalopods.
ANIMALS.
423
genus, the edge of the septa, which was only plaited in Goniatite, and
lobed in the Ceratite, becomes most elaborately frilled. We give above
(Fig. 646) the form of suture in the type-genera of the different orders
of shelled Cephalopods, the four lower in the order of their first appear-
ance. In each case the suture is supposed to be divided on the ventral
surface and spread out, so that the central part in the figure represents
the dorsal portion, and the two extremities the ventral. In the Ammo-
nite family, which includes the second, third, and fourth, the gradual
evolution of this structure is well shown. The corresponding figures
on the left are sections showing the position of the siphon.
The order in which these several genera appeared, and their contin-
uance, are shown in the diagram (Fig. 656) on page 425.
Belemnites. The Belemnite (^e/Ujitvov, a dart) was nearly allied to
the squid and cuttle-fish of the present day. Like the squid, it had an
internal bone (the pen of the squid),
except that the bone is much larger
and heavier in the Belemnite. It is
this bone, or the lower portion of
it, which is usually fossilized (Figs.
651-654). When perfect it is ex-
panded and hollow at the upper end,
and in the hollow is a small, coni-
FIG. 647. FIG. 648. FIG. 649.
FIGS. 647-649. 64T. Internal Shell of Belemnite (restored by d'Orbigny). 648. The Animal (restored
by Owen). 649. A living Sepia for comparison.
424
MESOZOIC ERA AGE OF REPTILES.
cal, chambered, siphuncled shell, the Phragmocone. Fig. 647, a and >,
shows the perfect bone, and Fig. 651 the upper part broken and the
phragmocone in place. Like the squid, too, it had
an ink-bag, from which it doubtless squirted the
inky fluid to darken the water and escape its enemy.
These ink-bags are often well preserved (Fig. 650),
and the fossil ink has been found to make good pig-
ment (sepia), and drawings of these extinct animals
have actually been made with the fossil ink of their
own ink-bags (Buckland). Belemnites were some of
them of great size, and evidently formidable animals.
The bone of the Belemnites giganteus has been
found two feet long and three to four inches in
FIG. 651. Belemnites Owenii.
diameter at the larger or hollow end. A very perfect specimen of an
allied genus, from the Oalite of England, is shown in Fig. 655.
FIG. 655.
FIGS 652-655 652 Belemnites hastatus. 653. Belemnites unicanaliculatus. 654. Belemnites clavatus.
655. Acanthoteuthis antiquus (after Man tell).
ANIMALS.
425
The following diagram shows the order of succession of families of
the class Cephalopoda :
PALEOZOIC.
NEOZOIC.
MESOZOIC. i CKNOZOIC.
Sil'n. ! Dev'n. i Carb.
Trias.
Juras. j Cret j
Cepha
opods.
i
Shelled or Tetrabranchs.
Naked or Di branch s.
j !
i
!
She
led.
|
Orthoceratites.
1
I Goniatites.
i
.
Ceratites.
i
1 i
A m
m o n i t e s .
N a u
i 1 | U 8.
Na
ked.
j
Belemnites.j
j J
i Sepia.
FIG. 656. Diagram showing Distribution of Cephalopoda in Time.
Crustacea. Crustacea were represented in the Palaeozoic first by
the Trilobites ; then Limuloids ; then, in the last period, by a few Macrou-
rans. In the Triassic the Macrourans became more abundant and of
more modern type. In the Jurassic, the Macrourans continue, with also
many Limuloids, but the former make here a decided approach to the
Brachyourans or true crabs, by the shortening of the tail in some (Fig.
657) ; and the earliest true crab, Palaeinachus a spider-crab has been
found in the Jurassic of England.
Insects. As might be expected from the abundant forest vegeta-
tion, insects have been found in considerable numbers and variety (Figs.
659-663).
Fishes. It will be remembered that the Placoids of the Palaeozoic
were nearly all Cestracionts, or crushing-toothed sharks. The Hybo-
donts, or sharks with teeth pointed, but rounded on the edges, com-
menced in the Carboniferous, or perhaps Devonian, and increased in
the Triassic. Now, in the Jurassic the Cestracionts continue (Fig.
426
MESOZOIC ERA AGE OF REPTILES.
664), but in diminished numbers. The Hybodonts culminate (Fig.
665), and the /Squatodonts, or modern sharks, with lancet-shaped teeth,
commence in small numbers. Rays (Fig. 666), which may be regarded
FIG. 657.
FIGS. 657-659. JUBASSIC CRUSTACEANS AND INSECTS : 657. Kryon arctifonnis, Solenhofen. 658. Eryon
Barrovensis, England. 659. ufischna eximia (Hager).
as among the highest of Placoids, are found in considerable numbers
in the Jurassic.
Ganoids continue, but take on far more modern forms, and have now
in most cases lost the vertebrated structure of the tail-fin, thus fore-
shadowing the Teleosts, which appear in the next period. Among the
ANIMALS. 427
most characteristic Ganoids of this period, and, in fact, of this age, are
FIG. 661.
FIGS. 660-663.-JUEA88IC INSECTS : 660. Libellula. 661. Libellula WestwoodlL 662. Hemerobioides
giganteus. 663. Buprestidium.
FIG. 666.
FIGS. 664-666. JURASSIC FISHES Plac,oids : 664. Tooth of Acrodus nobilis. 665. Hybodus reticula-
tus, Spine and Tooth. 666. Squatina acanthoderma.
428
MESOZOIC ERA AGE OF REPTILES.
the Pycnodonts, a family characterized by a broad, flat body, rhom-
boidal enameled scales, pavement palatal teeth, and persistent noto-
chord (Fig. 667).
FIG. 667. JURASSIC FISHES Ganoid: Tetragonolepis, restored, and Scales of the same.
Reptiles. The huge reptiles which form the distinguishing feat-
ure of this age culminate in the Jurassic period. Their number and
variety are so great that we can only select a few from each order
FIG. 671.
FIGS. 668-671. JURASSIC EEPTILES Ichthyosaurus and Pleeiosaurux : 668. Ichthyosaurus communis,
x T J 5 . (if.!*. Plesiosaunis dolichodoirus, restored, x &,. 670. Vertebrae of Ichthyosaurus and Sec-
tion of same, showing structure. 671. Tooth of Ichthyosaurus, natural size.
for description. They were emphatically rulers in every department
of Nature rulers of the sea, of the land, and of the air. We shall
treat of them under the three heads thus indicated, viz.: 1. Enalio-
ANIMALS. 429
saurs (sea-saurians), or rulers of the sea ; 2. Dinosaurs (huge saurians),
or rulers of the land ; and 3. Pterosaurs (winged saurians), or rulers of
the air. The first were wholly swimming, the second walking, the
third flying, saurians. Intermediate between the first and second was a
fourth order, the Crocodilians, which both swam and crawled.
1. Enaliosaurs. From the immense variety of these we select only
two for description as representative genera, viz., Ichthyosaurus and
Plesiosaurus. Figures of these are given on page 428.
The Ichthyosaurus (fish-saurian} was a huge animal, in some cases
thirty to forty feet in length, with a stout body, short neck, and enor-
mous head, sometimes five feet long, and jaws set with large conical,
striated teeth, sometimes 200 in number. The enormous eyes, some-
times fifteen inches in diameter, were provided with radiating, bony
plates, as are the eyes of birds and some living reptiles, apparently for
adjusting the eye to different distances. The tail was long, and proba-
bly provided terminally with a vertical, Jin-like expansion, unsupported
by rays (Owen). In addition to the powerful fin-tipped tail, the locomo-
tive organs were four short, stout paddles, composed of numerous closely-
united bones, but without distinct toes. These paddles were surrounded
by an expanded, ray-supported web (Fig. 672), which greatly increased
its surface, and therefore its efficiency as swimming-organs (Lyell). The
bodies of the vertebrae were not united by ball-and-socket joint, as in
most living reptiles, but were M-concave (amphiccelous), like those of
fishes (Fig. 670).
672. Paddle-Web of an Ichthyosaurus
That the habits of the creature were predatory and voracious is suffi-
ciently attested by the teeth. It is further proved by the contents of
the stomach, which are sometimes partly preserved. These consist
largely of fish-scales.
From the description given above it is plain that the Ichthyosaurus
combined in a remarkable degree the characters of saurian reptiles with
those of fishes. The vertically expanded tail-tip, the paddles, with sur-
430
MESOZOIC ERA AGE OF REPTILES.
rounding ray-supported web, and the bi-concave vertebral bodies, are
all decided fish characters. In most other respects it was reptilian.
This combination is expressed in the name.
The Plesiosaurus (allied to a saurian) was a less heavy and powerful
animal than the last. It was remarkable for its short, stout, almost
turtle-shaped body ; its long, snake-like neck, consisting of twenty to
forty vertebrae ; its small head ; its short tail, unadapted for powerful
propulsion ; its long' arid powerful paddles, which were its sole swim-
ming-organs ; and its bi-concave vertebral bodies. Sixteen species have
been found in the Jurassic and Cretaceous rocks of Great Britain alone,
and one, _P. dolichodeirus, was twenty-five to thirty feet long (Fig.
669), with paddles six to seven feet long.
FIG. 673.- , Head of a Pliosaurus, greatly reduced ; &, T<
The Pliosaurus (more lizard-like) had the large head and short
neck of the Ichthyosaurus (Fig. 673), with the powerful paddles of the
Plesiosaurus. A perfect paddle of this animal has been found seven feet
long (Fig. 674) ; the animal was probably at least forty feet long.
FIG. 674. Paddle of a Pliosaurus, x 5 \j.
Intermediate between this group and the next inhabiters both
of land and water Crocodilians existed in great numbers, and of great
size. Some, like the Teleosaurus (Fig. 675), were narrow-snouted like
the Gavials of the Ganges, but had arnphicoelous vertebrae like the
Enaliosaurs.
ANIMALS.
431
2. Dinosaurs. These reptiles were the most highly organized in
structure, as they were certainly the hugest in size, which have ever ex-
isted. Though very decided reptiles, they combined certain characters
which allied them strongly with mammals and especially with birds.
Their very large, long, and hollow limb-bones, their strong, massive hip-
bones and sacrum, the latter composed of four to five consolidated ver-
tebrae, allied them with both mammals and birds; while the great elonga-
FIG. 675. Teleosaurus brevidens: a, skull; 5, side-view of snout showing the teeth (after Phillips).
tion backward of the ischium, the massiveness of the hind-legs as com-
pared with the fore-legs, and the possession of only three functional toes
on the hind-foot, which therefore formed a tridactyl track, allied them
still more strongly with birds. On account of this great likeness to
birds in the character of the hind-limbs, they have been called by Prof.
Huxley Ornithoscelida (bird-legged). The following figures (676, 677)
illustrate this bird-like character.
FIG. 676. Pelvis of an Iguanodon (restored by Hulke).
It seems certain that all the Dinosaurs walked with free step, like
quadrupeds, instead of crawling, like reptiles ; and some if not all of
them, had the power of standing and walking on their hind-legs alone,
like birds. The backward elongation of the ischiatic bones seems
evidently connected with the erection of the body on the hind-legs.
We will briefly describe only the most remarkable :
The Iguanodon was a huge herbivorous Dinosaur, found principally
in the Weal den (Upper Jurassic). It takes its name from the form of
432
MESOZOIC ERA AGE OF REPTILES.
its teeth, which are much like those of the Iguana, a living herbivorous
reptile, although in other respects there is little affinity. Fig. 678
Fig. 67T. A, Dromteus; S, Dinosaur; C, Crocodile.
shows the tooth pf the Iguanodon, and Fig. 679 a section of the jaw of
the Iguana, for comparison.
But the difference in size between the living and the extinct reptile
FIG. 678. Tooth of an Iguanodon.
is enormous. The Iguana is from four to six feet long ; the Iguanodon
was certainly thirty feet, perhaps fifty or sixty feet long, and of bulk
ANIMALS.
433
several times greater than that of an elephant. A thigh-bone has been
found fifty-six inches long, twenty-two inches in circumference at the
shaft, and forty-two inches at the condyle. Its habits are supposed to
have been somewhat like those of a hippopotamus. Like this animal,
it wallowed in the mud, and fed on the rank herbage of marshy grounds.
FIG. 679. Section of Jaw of an Iguana, showing the teeth (after Buckland).
The Megalosaur was a somewhat smaller but probably a more for-
midable carnivorous reptile, which lived through the whole Jurassic pe-
riod. Its huge jaws were armed with large, curved, flattened, sabre-like
teeth (Fig. 681). A femur has been found forty-two inches long (Phil-
lips), and a tibia thirty-six inches. The animal was at least thirty
feet long (Owen). Fig. 680 is a restoration of the head of this ani-
mal by Phillips, and Fig. 681 is a tooth of natural size.
FIG. 680. Head of Megalosaurus, x ^ (restored by Phillips).
The Ceteosaur (whale-lizard) was probably the largest reptile in fact,
the largest land-animal which has ever existed. It has been classed
among the Crocodilians, but Prof. Phillips has shown that its true posi-
tion is among the Dinosaurs. A thigh-bone has been found sixty-four
inches long, 27.5 inches in circumference at the shaft, forty-six inches
28
434
MESOZOIC ERA AGE OF REPTILES.
Fio. 681. Megalosaurus
Tooth, natural size (after
Phillips).
FIG. 6S2. Femur of Ceteosaurus,
x jL (after Phillips).
and 44.25 inches in circumference at the two ends, respectively (Fig-.
682). According to Phillips this
animal was at least fifty feet, and
probably from sixty to seventy
feet long, ten feet high when
standing, and of bulk proportion-
ate. It was probably a vegetable
feeder.
The Hylceosaur was another
huge reptile of the same period,
and the Compsognathus a reptile
of smaller size, but of most ex-
traordinary bird-like character,
viz., small head, long, flexible
neck, large and long hind-legs,
and small and short fore-legs.
Ite. 683.-Co mp sognathus (restoration by Wagner). From ^ structurej it must have
walked habitually on its hind-legs alone (Fig. 683).
3. Pterosaurs. These flying reptiles were certainly among the most
extraordinary animals that have ever existed. The order includes sev-
ANIMALS. 435
eral genera, but we will describe only the best known, viz., the Ptero-
dactyl (wing-finger).
The Pterodactyl combined the short, compact body ; the strong
shoulder-girdle, firmly united with the keeled sternum; the short,
aborted tail ; the long, flexible neck, and hollow, air-filled limb-bones,
characteristic of birds with the head, and jaws, and teeth, of a reptile,
FIG. 6S4. Pterodactylus crassirostris.
and the membranous wings of a bat. In the bat, however, the mem-
brane is supported by four fingers, enormously elongated for the pur-
pose, and only one finger is free and clawed ; while in the Pterodactyl
there is only one finger, which is enormously elongated and strength-
ened for the support of the web, and all the others are free and clawed.
FIG. 685. Rhamphorhynchus Bucklandi (restored by Phillips).
The manner in which the web is supposed to have been stretched and
supported is shown in Fig. 684.
Many species have been found ranging in size from two feet to
twenty feet in alar extent. They lived throughout the whole Jurassic
and into the Cretaceous period. In one genus (Rhamphorliynchm,
beak-bill) the anterior portion of the jaws was destitute of teeth, and
probably sheathed with horn like a bird's beak (Fig. 685).
436 MESOZOIC ERA AGE OF REPTILES.
Birds. Until recently, except the doubtful tracks of the Connect-
icut Valley to be mentioned further on, no trace of birds had been
found lower than the Tertiary. But in 1862 bird-bones and beautiful
impressions of bird-feathers were found in the lithographic limestone
(Upper Oolite Jurassic) of Solenhofen. Still later, many remains of
birds were found by Marsh in the Cretaceous of the United States.
These will be described in their proper place.
Thus far the only bird-bones found in the Jurassic are those of the
Archceopteryx (ancient bird) mentioned above. These remains are the
earliest positive proof of the existence of this class; they. are therefore
FIG. 6S6. Archseopteryx macroura, restored (after Owen).
of exceeding interest to the geologist. An examination of the figures
below (Figs. 687, 688) will show that this earliest bird was very differ-
ent from the typical birds of the present day ; that it was, in fact, won-
derfully reptilian. Along with the distinctive bird characters of feet
and limb-bones and pelvis, and especially feathers and feathered wings,
it had the long tail and probably toothed jaws of a reptile. The differ-
ence between the tail of a typical bird and the tail of the Archaeopteryx
is very similar to the difference between a homocercal and a hetero-
cercal tail among fishes. In a typical bird the tail-joints are greatly
shortened and consolidated, so that it is not more than an inch long in
a bird the size of a cock ; and the tail-feathers come out from these in
a radiating manner (Fig. 687, J)). In the Archaeopteryx, on the other
hand, the tail consists of twenty-one long joints ; making the tail of the
skeleton eight or nine inches long, nearly or quite as long as all the
rest of the skeleton ; and to these joints are attached the feathers, one
on each side of each joint (Fig. 687, A). It is a true vertebrated tail.
Another very striking reptilian character is found in the structure
of the hand. In ordinary birds what corresponds to the hand consists
of three fingers, two of which are united, and only one (the thumb) is
ANIMALS.
437
FIG. 687.^!, Tail of Archseopteryx macroura; J3, Vertebrae enlarged; (7, a Feather; Z>, Tail of a Vul-
ture ; E, side-view of the same.
free ; but in this earliest bird the hand consists of four fingers, all sepa-
rate, and two of them terminated with claws.
-A, Fore-limb of Bat; B, Archseopteryx ; <7, Bird; Z>, Pterodactyl, compared. In all a,
scapula; I, humerus ; c, ulna; d, radius ; e, carpus ; /, metacarpus ; g, phalanges.
438
MESOZOIC ERA AGE OF REPTILES.
Mammals. In the same formation and nearly the same horizon in
which we find the dirt-bed and stumps mentioned on page 416 (Upper
Oolite) have been found also in England the remains of fourteen species
of small insectivorous Marsupial mammals, varying in size from that of
a mole to that of a skunk. It would seem, therefore, that we have found
not only an old forest-ground of the Jurassic period, but also the trees
which grew in, and the animals which roamed through, this old forest.
In a somewhat lower bed, the Stonefield slate of England, have been
found four more species ; and still lower in the uppermost Triassic have
been found in all countries taken together two or three other species,
one or two in Europe, and one in the United States making in all about
twenty species of mammals known to have existed in Jurassic times.
FIG. 691.
Fro. 692. FIG. 698.
FIGS. 689-69S. JUKASSIC MAMMALS : 689. Amphitherium Prevostii. 690. Phascolotherium. 691. Am-
phitherium. 692. Triconodon. 693. Plagiaulax.
They were all small Marsupials / and with the exception of one which,
judging by its rodent teeth, was probably a vegetable-feeder, they all
seem to have been insectivorous.
Affinities of the First Mammals. The marsupials differ very great-
ly from ordinary typical mammals, in the fact that in the former there
is no placental attachment between the foetus in utero and the mother.
The foetus, therefore, does not and cannot develop before birth into a
perfect condition fit for independent life. In an imperfect condition it
is born and placed in an abdominal pouch (marsupium), permanently
attached to the teat, and finishes its embryonic development there.
Thus in these animals there are two periods of gestation, one intra-
uterine, very short, and another marsupial, much longer. Marsupial
mammals, therefore, are not truly viviparous, but semi-oviparous, in their
JURA-TRIAS IN AMERICA. 4.39
reproduction, and in this respect allied to birds and reptiles. The class
of Mammals is therefore subdivided into two sub-classes, viz., Placental
or true mammals and Non-placental or semi-oviparous mammals. The
former includes all ordinary mammals ; the latter at present includes
kangaroos, opossums, etc. (Marsupials), and Ornithorhjnchus and
Echidna (Monotremes).
Now the mammals of the Triassio and Jurassic times were wholly
non-placental or semi-oviparous, and therefore approximated the lower
classes of Vertebrates, especially birds and reptiles. The non-pla-
centals are now (with the exception of a few species of opossum found
in America) wholly confined to Australia and the vicinity. In Jurassic
times they were probably very abundant, and spread over all portions
of the earth. Yet they were not rulers of those times ; for they were
wholly unable to contend with the great reptiles. It was essentially
an age of Reptiles. Not only did this class greatly predominate in
number and size, but the reptilian character was strongly impressed on
all the then existing birds and mammals. From the reptilian stem the
bird and mammal branches had not yet so fairly separated that the
connecting links were obliterated.
SECTION 3. JURA-TKIAS us AMERICA.
We have already explained that these two periods are not well sepa-
rated in America. This is partly on account of the poverty of fossils,
and partly on account of the continuity of conditions throughout. It
seems best, therefore, in the present state of knowledge to treat them
together as one period. Doubtless they will be better separated here-
after.
Distribution of Strata. 1. Atlantic Border. Lying in plication-hol-
lows, or denudation-hollows, unconformably on the gneiss (metamorphic
Laurentian or Silurian) of the eastern slope of the Appalachian chain,
are found very remarkable isolated patches of sandstones or sandstones
and shales, which are referred to this period. These patches are strung
along nearly parallel to the chain, and to the coast, from Nova Scotia
to the border of South Carolina. They are represented on the map
(p. 278) by oblique lines. One of them is found in Prince Edward's
Island, another in Nova Scotia ; another is the celebrated Connecticut
River Valley sandstone ; a fourth commences in New Jersey, passes as
a narrow strip through Pennsylvania, Maryland, and into Virginia ; a
fifth and sixth form the Richmond and Piedmont coal-fields of Virginia;
a seventh and eighth, the Dan River and Deep River coal-fields of North
Carolina. As they are isolated, and without contact with any other
formation except the gneiss, on which they lie unconformably, their age
cannot be even conjectured from their stratigraphical relations ; but the
440 MESOZOIC ERA AGE OF REPTILES.
few fossils which they contain seem to refer them either wholly to the
Triassic, or else, more probably, their lower half to the Triassic and
their upper half to the Jurassic of Europe (Hitchcock).
In connection with the more northern patches are found columnar
trap or dolerite ridges, evidently formed by the fissuring of the strata
and the outpouring of igneous matter upon the surface. Mounts Tom
and Holyoke are examples in the Connecticut Valley, the Palisades of
the Hudson in the New Jersey patch ; similar trap-ridges are also very
conspicuous in the Nova Scotia patch.
2. Interior Plains. Rocks of this age seem to be widely distributed
on the eastern slopes of the Rocky Mountains, from the Black Hills
southward, largely covered in the northern parts by Cretaceous, but ex-
posed over wide areas in the region south of the 38th parallel and west
of the 97th meridian, including large portions of Kansas and Indian
Territory, and Northern Texas.
3. Rocky Mountain Region and Pacific Slope. Portions of the
Black Hills, of the Colorado Mountains, and of the Wahsatch range,
consist of these rocks. Outcrops also occur on the slopes of the Uintah
Mountains, and large areas in the plateau region north of Grand Canon,
forming several of the remarkable cliffs of that region, and also large
areas in the valley of the Rio Grande, about Santa Fe, New Mexico.
The auriferous slates of California, both east and west of the Sierra
range, consist of the same.
Life- System.
The characterization of the life-system of the Jura-Trias period in
America is best brought out in connection with a minuter description of
some of the more interesting localities, and of the remarkable records
they contain.
Connecticut River Valley Sandstone. The Strata. This locality has
been made classic ground for the geologist by the indefatigable labors
of the late President Hitchcock, of Amherst. The strata border the
Connecticut River, on both sides, through the whole of Massachusetts
FIG. 694. A Section across the Valley of Connecticut: g, gneiss; 88, sandstone; t, trap ridges.
and Connecticut, forming an irregular area about 110 miles long and 20
miles wide. They consist of red sandstones and shales, dipping somewhat
regularly to the east, at an angle of about 20 to 30, indicating a thick-
ness of at least 5,000 feet (Dana) to 10,000 feet (Hitchcock). The gen-
eral relations of the strata with the intrusive trap and the underlying
gneiss are shown in the accompanying figure (694). The trap is seen to
LIFE-SYSTEM.
441
be mostly conformable with the strata. This regular dipping to the east
throughout the whole series can only be explained by supposing that
at the end of the Jurassic the whole area of previously-horizontal strata
(Fig. 695, A) was lifted into an incline of 20 or more, and afterward
cut away by denudation, as shown in the diagram (Fig. 695, JB).
The whole series of sandstone is very distinctly stratified, and in
many parts beautifully fissile. When these parts are broken open
along their lines of lamination, all kinds of shore-marks are found in the
greatest perfection, viz., ripple-marks, rain-prints, sun-cracks, leaf-
impressions, and tracks of animals. It is evident, therefore, that this
was, throughout, a littoral or shoal-water deposit. But it is at least
5,000 feet thick. Therefore, there must have been subsidence to that
extent. Here, then, we have evidence of rapid deposit (for the mate-
rials are coarse), invasion of interior heat with aqueo-igneous fusion,
subsidence, formation of fissures, and ejection of lava.
Some identifiable fossils, obtained about the middle of the series,
seem to indicate an horizon similar to the Lias, lowest Jurassic ; or to
the Rhastic, uppermost Triassic of England. It is fair to conclude, there-
fore, that this patch represents the whole Jura-Trias period.
The Record. The general redness of the sandstone is sufficient evi-
dence that organic remains are very a
scarce ; and so, indeed, we find it. Two
or three fishes, a few leaves, the most
perfect of which is a species of fern^
Clathopteris and a fir-cone (Fig. 696),
and a few small fragments of thin, hol-
low bones, which may have belonged to
either birds or reptiles, are all that have
been yet found.
But by far the most interesting por-
tion of the record in this locality consists
of tracks. These are partly tracks of
Insects and Crustaceans, and partly of
Reptiles and, possibly, Birds. Some of
** ^"
M2 MESOZOIC ERA AGE OF REPTILES.
those which have been referred to Crustaceans and Insects are shown
in Fig. 697, a, b, c. There lias been found, also, the whole form of one
insect, apparently the larva of an Ephemera (Fig. 698). It is quite
probable that many of the tracks were formed by similar larvae inhabit-
ing the water.
FIG. 698. Larva of an
Ephemera (after Hitch-
cock).
FIG. 697. a, 6, c, Tracks of Insects, Crustacea, or Worms (after Hitchcock).
Reptilian Tracks. By far the larger number of tracks are those of
Reptiles. More than fifty species have been described by Hitchcock.
These vary extremely, both in size and in character. In size, they vary
from the track of a living Triton, a half-inch long, to that of the Oto-
zoum, twenty inches long, and with a stride of three feet. Some had
five toes, some four, and some only three functional toes on the hind-
feet. Again, some had hind and fore feet of nearly equal size, and
evidently walked or crawled in true quadrupedal style. Others had
hind-feet much larger than fore-feet, and were essentially bipedal in
locomotion, only putting down their small fore-feet occasionally ; but
walking bird-like, not hopping kangaroo-like, on their hind-legs. In
connection with the bipedal tracks there have been found what seemed
to be the impression of a dragging tail (Fig. 700) ; but these are so
rare and doubtful that it is generally believed the animals were mostly
long-legged and short-tailed.
The general conclusion from an attentive study of these tracks, in
connection with the findings elsewhere of bones and teeth, is that they
are the tracks mostly of Amphibians of the order of Labyrinthodonts
(four-toed and five-toed, quadruped and biped), but a few were probably
Dinosaurs (three-toed biped). The hugest among them, the Otozoum
Moodii (Fig. 699), was probably a long-legged, biped amphibian, which
stood twelve feet high. The Anomcepus (Fig. 701), on the contrary,
was probably a Dinosaur, which walked often on two legs only, and in
so doing brought the whole tarsus and heel on the ground, in the man-
LIFE-SYSTEM.
443
ner of a kangaroo. In Fig. 700 the mark of a supposed dragging tail
is shown.
Bird-Tracks. Those which have been referred to birds are : 1.
Wholly bipedal, i. e., there is no evidence of fore-feet at all. 2. They
are tridactyl. 3. They have a regular progression in the number of
joints in the tracks, the inner toe having two, the middle toe three,
and the outer toe four joints. Now, in birds the inner toe has three,
the middle toe four, and the outer toe five joints, but the last two joints
FIG. 700.
FIGS 699-701.-REPTILE-TRACKS (after Hitchcock): 699. Otozoum Moodii: a, hind-foot, x T > 5 ; ft, fore-foot,
x ^. 701). Gigantitherium caudatum, x ,V 701. Anounoapus minor, x A: a, hind-foot; &, fore-foot.
in each case make but one division of the track, so that the track is ex-
actly what is given above. The discovery, however, that Dinosaurs
have but three functional toes on the hind-foot, and that they also have
the same number of joints as birds, has greatly shaken confidence in the
ornithic character of these tracks. Only the absence of fore-feet tracks,
therefore, remains. But as many of these early reptiles walked occa-
sionally on two legs, it is not impossible that some of them always
walked thus. It is quite possible, not to say probable, therefore, that
all these tracks are those of Reptiles. Assuming them to be those of
444
MESOZOIC ERA AGE OF REPTILES.
Birds, they varied in size from those of a snipe to those of the great
Brontozoum, eighteen inches long, and with a stride of four feet (Fig.
702). This huge bird, if bird it was,
must have been at least fourteen feet
high (Dana). Such a huge animal must
have been wingless, like the ostrich, etc.,
for its size is far beyond the limit within
which flight is possible.
We have expressed a doubt as to
whether these tracks be those of birds
or reptiles. This is not so strange as it
may at first appear. These two classes
are, indeed, now very widely separated;
but then they were very closely allied.
There were probably animals then liv-
ing which, even if we saw them, might
puzzle us to decide whether to call
them reptilian birds or bird-like rep-
tiles. These tico classes were not yet
fairly disentangled and separated from
each other.
We may easily imagine the circumstances under which these tracks
were formed. During the Jura-Trias period there was in the region
of the Connecticut Valley a shallow inland sea, connected by a narrow
FIG. 702. Track of Brontozoum gigan-
teum, x i (after Hitchcock).
FIG. 703. Portion of a Slab with Tracks of several Species of Brontozoum (after Hitchcock).
outlet with the ocean. Into this the tides flowed and again ebbed,
leaving extensive flats of mud or sand ribbed with ripple-marks. A pass-
LIFE-SYSTEM.
445
ing shower pitted the soft mud, and the sun, coming out again from the
breaking clouds, dried and cracked it. Huge bird-like reptiles, and pos-
sibly reptilian birds, sauntered near the shore-margin in search of food.
The tide came in again with its freight of fine sediments, gently cov-
ered the tracks, and preserved them forever. This occurred constantly
for many ages about the end of the Triassic or the beginning of the
Jurassic period, for the tracks are found near the middle of the series
of strata.
Richmond and North Carolina Coal-Fields. The patches occurring
in Virginia and North Carolina are coal-bearing. They constitute the
Richmond and Piedmont coal-fields of Virginia, and the Deep River
and Dan River coal-fields of North Carolina. Fig. 704 gives a general-
FIG. 704. Section across Richmond Coal-field (after Lyell).
ized section of the Richmond coal-fields, taken from Lyell. The strata
of this field are sandstone and shales, 700 to 800 feet thick, lying in
irregular erosion-hollows of the gneiss. All the phenomena of a coal-
field are here repeated, viz., interstratified seams of coal and beds of
iron-ore, underclays with roots, and roof-shales with leaf-impressions.
There are several seams of coal, the lowest of which is almost in con-
tact with the gneiss. Some of the seams are of great thickness
thirty to forty feet and the coal is very pure. It is probable that
this coal, like that of the Carboniferous times, was formed in a marsh,
which was sometimes converted into a lake. The plants found are
FIG. 705. Dictyopyge, a Ganoid (after EmmonsX
very decidedly Upper Triassic or Lower Jurassic, viz., Cy cads, Conifers,
Equisetae, and Ferns. The animals indicate the same horizon.
The Deep River and Dan River coal-fields of North Carolina are very
similar to those in Eastern Virginia, except that in the Deep River coal-
fields the coal-bearing portion, which seems to correspond with the
whole of the Richmond strata, is underlaid by 3,000 feet of barren sand-
stone. If we call the coal-measures Upper Trias or Lower Juras,
446 MESOZOIC ERA AGE OF REPTILES.
these barren sandstones are certainly Triassic. In the upper portion of
FIG. 710. FIG 711.
FIGS. 706-711. FOSSILS OF NORTH CAROLINA AND RICHMOND COAL-BASINS (after Emmonsl : 706. Walr
chia diffiisus. 707. Podozaraites lanceolatus. 70S. Xeuropteris linsefolia Richmond Coal. 709.
Pecopteris falcatus. 710. Neuropteris. 711. Jaw of Dromatherium sylvestre.
LIFE-SYSTEM.
447
these underlying sandstones, and therefore probably in the Upper Tri-
assic, together with some reptilian teeth, Dr. Emmons found several
jaws of a small Marsupial, similar to the Microlestes found at the same
horizon in English rocks, which he names Dromatherium sylvestre.
This is the only mammal yet found in the Jura-Trias of America. We
give on page 446 figures of the plants and animals of these two basins.
Other Patches. In other patches, especially in New Jersey, Penn-
sylvania, and Nova Scotia, a number of reptilian bones and teeth have
been found. These latter are those of Dinosaurs, and Crocodilians or
Lacertians. The jaw and teeth of a huge reptile, called by Leidy a-
thygnathus (deep jaw), were found in Nova Scotia. The teeth were
four inches long. Cope thinks it may have been a Dinosaur ; Leidy
regards it as Amphibian, while Owen now refers it to his order of
Theriodonts.
?12. FIG. 713. Fio. 714:
FIGS. 712-714. REPTILES : 712. Bathygnathus borealis. reduced (after Dawson); a, fifth tooth natural
size ; 6, cross-section of a tooth. 713. Belodon Carolinensis (after Emmons). 714 Clepsysaurus
Pennsylvanicus (after Emmons).
Interior Plains and Pacific Slope. The Jura-Trias of the interior
plains are singularly deficient in remains of life. The presence of gyp-
sum in many of them furnishes the explanation. These deposits were
probably formed in interior and very salt seas, and these are usually
deficient in life. The two periods are, however, in some places at least,
better separated than on the Atlantic slope, probably because the con-
ditions were more variable. On the slopes of the Black Hills and on
the South Platte River undoubted fossils of the Jurassic period are
found, indicating the existence of an open sea at that place. In New
Mexico Newberry found many beautiful impressions of plants, indicat-
ing the same horizon as in North Carolina and Virginia i. e., Upper
Triassic. Some of these are given below:
On the Pacific coast, marine life, no doubt, abounded, as this was
the margin of an open sea; but the rocks 'here are mostly very highly
metamorphic, and the fossils, therefore, mostly destroyed. Wherever
448,
MESOZOIC ERA AGE OF REPTILES.
FIG 720
FIG. 722.
is. 715-722.-Pi.ANT6 OF THE JuRA-TniA9 (after Newberry) : 715. Branch of Conifer (Braehy-
phyllutn). 716. Branch of Conifer. 717. Conifer. Branch and Fruit. 718. Zamites oceidentalis.
719. Otozamites Macoinbii. 720. Podozamites crassifoiia. 721. Ta'iiiopt. ris rlrirans. '>>. Alethop-
teris Whitneyi.
LITE-SYSTEM.
449
this is not the case, the rocks abound in fossils. In Humboldt County,
Nevada, for example, the strata in some places seem almost wholly
made up of Ceratites Whitneyi (Fig. 727). In the same locality the
Fio. 728. FIG. 724
FIGS. 7-23 and 724. JURASSIC FOSSILS OF UTAH (after Meek) : 723. Belemnites densus. 724. Gryphaea
calceola.
remains of an Enaliosaur (sea-saurian) have been found. On account
of the marine conditions prevalent, the two periods are easily separable
on the Pacific coast.
Physical Geography of the American Continent during the Jura-
Trias Period. During Palaeozoic times the Atlantic shore-line was
certainly farther east than it was subsequently, probably farther east
than it is now (p. 255). At the end of the Palaeozoic occurred the Ap-
FIG. 725. FIG. 727.
FIGS. 725-727,-CALiFORNiA JURA-TRIAS SHELLS: 725. Gryphsea speciosa (after Gabb).
pandicosta (after Gabb). 727. Ceratites Whitneyi (after Gabb).
5. Trigonia
palachian revolution. Coincidently with the up-pushing of the Appa-
lachian chain, the sea-border probably went downward, and the shore-
line advanced westward on the land. During the Jura-Trias the
shore-line to the north was still beyond what it is now, for no Atlan-
tic border deposit is visible ; and along the Middle and Southern States
it was certainly beyond the bounding-line of Tertiary and Cretaceous
(see map, p. 278,) for all the Atlantic deposits of this age have been
covered by subsequent strata ; and yet, probably not much beyond, for
some of these Jura-Trias patches seem to have been in tidal connection
with the Atlantic Ocean. It is. probable, therefore, that the shore-line
was a little beyond the present New England shore-line, and a little
beyond the old Tertiary shore-line of the Middle and Southern Atlantic
States.
29
450 MESOZOIC ERA AGE OF REPTILES.
A little back from this shore-line, and at the foot of the then Appa-
lachian chain, there was a series of old erosion or plication hollows
stretching parallel to the chain. The northern ones had been brought
down to the sea-level, and the tides regularly ebbed and flowed there
then as in the bay of San Francisco, or Puget Sound, at the present
time. In the waters of these bays lived swimming Reptiles, Crocodilian
and Lacertian, and on their flat, muddy shores walked great bird-like
Reptiles, and possibly reptilian Birds. The more southern hollows
seemed to have been above the sea-level, and were alternately coal-
marsh, and fresh-water lake, emptying by streams into the Atlantic.
Since that time the coast has risen 200 or 300 feet, and these patches
are therefore elevated so much above the sea-level.
During the same time the Basin range region, i. e., the region ly-
ing between the Wahsatch and the Sierra ranges, was land; but all
between this and the Palaeozoic area of North America, including the
Plateau region, the eastern Rocky Mountain region, and the region of
the Plains, was covered by a shallow inland sea, with imperfect con-
nection, or none at all, with the ocean, and in which, therefore, gypsum
deposited by evaporation. At least once during Jurassic times this
inland sea became broadly connected with the ocean, so that oceanic
conditions prevailed. The place now occupied by the Wahsatch Moun-
tains was then a marginal sea-bottom, bordering the Basin region con-
tinent. On the west the Pacific shore-line, and therefore the coast -line
of the Basin region continent, was east of the Sierra range, the position
of that range being then also a marginal sea-bottom.
Disturbances which closed the Period. This long Jura-Trias pe-
riod was closed, and the Cretaceous period inaugurated, by the Sierra,
revolution, by which the sediments accumulated along the then Pacific
shore bottom, yielding to the lateral pressure, were mashed together
and swollen up into the Sierra and Cascade ranges, and the coast-line
transferred westward to the other side of these ranges. Coincidently
with this change probably occurred on the Atlantic slope the outbursts
of trap, forming the trap-ridges already spoken of (p. 440). Extensive
changes also occurred at the same time over the whole region of the
inland seas, by subsidence and the inauguration of oceanic conditions,
which continued to prevail during the Cretaceous. There is reason to
believe also that the Wahsatch range, and perhaps also some of the
Basin ranges, commenced to rise at this time. It was essentially a
period of mountain-making in America.
SECTION 4. CRETACEOUS PERIOD.
The most general characteristic of this period is its transitional
character. In it Mesozoic types are passing out, and Cenozoic or
modern types are coming in, and the two types therefore coexist side
CRETACEOUS PERIOD. 451
by side. Nearly everywhere in America, as far as known, the Creta-
ceous lie unconformably on the Jurassic or still lower rocks.
Rock-System Area in America. On the Atlantic border going
southward, we find no Cretaceous rocks until we reach New Jersey.
Here we find a small patch peeping out from under the edge of the
overlying Tertiary, and marked on the map (p. 278) by oblique inter-
rupted lines. This patch passes through New Jersey, Delaware, Mary-
land, to the borders of Virginia. Passing south, we find no continuous
area until we reach Georgia ; yet it underlies the Tertiary in all this
region, as is shown by the fact that the rivers in North and South Caro-
lina cut through the Tertiary and expose the Cretaceous in many places.
The ^{/"-border Cretaceous commences in Western Middle Georgia,
covers all the prairie region of Middle Alabama, the northeastern or
prairie region of Mississippi, then runs northward as a narrow strip
through Tennessee nearly to the mouth of the Ohio. It then disap-
pears beneath the Tertiary to reappear as an area bordering the Gulf
Tertiary on the west side. On the interior plains, the Cretaceous con-
necting with the Gulf-border area stretches northwestward to arctic
regions, occupying nearly the whole of the great, grassy, level Western
Plains called Prairies though much of it is overlaid by the subsequent
Tertiary. In the Rocky Mountain region Cretaceous strata occupy
also large areas in all the Plateau region i. e., the region between
the Eastern range and the Wahsatch range although here also it is
largely overlaid by Tertiary. Recent investigations in Mexico 1 render
it probable that this area stretches also westward through Northern
Mexico to the Pacific. On the Pacific border. Cretaceous strata form a
large part of the Coast ranges, and also in places the lowest western
foot-hills of the Sierra range. Whitney has estimated the thickness of
the Cretaceous rocks in portions of the Coast range as 20,000 feet.
Physical Geography in America. It is not difficult from the Creta-
ceous area just given to reconstruct approximately the physical geog-
raphy. At that time the Atlantic shore-line in all the northern portion
of the continent was farther out or east than now, for the Cretaceous
of this part is all now covered by sea. From New Jersey southward
the shore-line was then farther in or west than now. From Maryland
to Georgia the shore-line, though farther in than now, was farther out
than during the Tertiary, as the Cretaceous is covered by the later de-
posits. The Grulf shore-line was much more extended both northward
and westward than either now or in Tertiary times. From the Gulf there
extended northwestward an immensely wide sea, covering the Plains
region and the Rocky Mountain region as far westward as the Wah-
satch range, and dividing the continent into two continents, an eastern
or Appalachian, and a western or Basin region continent. Probably
1 American Journal of Science, vol. x., p. 386, 1875.
452
MESOZOIC ERA AGE OF REPTILES.
also this sea connected across the region of Mexico with the Pacific,
thus dividing the western continent into two, a northern and a southern.
The Pacific Ocean at that time washed against the foot-hills of the
Sierra range. These facts are represented in the accompanying map.
The probable connection of the Gulf with the Pacific is also indicated.
FIG. 728. Map of North America in Cretaceous Times.
Rocks. The rocks of the Cretaceous period consist of sands, and
clays, and limestones, as in other periods, but, as a whole, are less gener-
ally metamorphic than the older rocks. There is, however, one kind of
rock found in this age in Europe which is so peculiar and so interesting
that it must not be passed over in silence. We refer to the white
chalk of England and France, from which the formation and the period
take their name, " Cretaceous"
Chalk. Chalk is a soft, white, pure carbonate of lime. Scattered
through the soft mass are found very characteristic nodules of pure
flint. These nodules are of various sizes and shapes, sometimes scat-
tered irregularly, sometimes arranged in layers. Often some fossil,
especially a sponge, forms the nucleus around which the aggregation of
the siliceous matter takes place. On account of its extreme softness,
chalk is often sculptured by erosive agencies into fantastic cliffs and
needles (Fig. 729).
Examined with the microscope, chalk is found to be composed largely
of Rhizopod shells, and of Coccoliths and Coccospheres (supposed shells
of uni-celled plants), some perfect, more broken, most of all completely
disintegrated (Fig. 730). The flint-nodules, similarly examined by sec-
CRETACEOUS PERIOD.
453
tion, show spicules of sponge and siliceous shells of Diatoms. Chalk
such as described is found nowhere except in Europe. Figs. 731-734
represent some of the more common Rhizopods found in chalk.
FIG. 729. Chalk-Cliffs witli Flint-Noduk
Origin of Chalk, A material so unique must have been formed
under peculiar conditions. Recent investigations have shown that
FIG. 734.
FIGS. 730-734. FORAMINIFERA OP CHALK: 730. Chalk as seen under the Microscope (after Nicholson).
731. Cuneolina pavonia. 732. Flabellina rugosa. 733. Lituola nautiloides. 734. Chrysalidina gradate
(alter D'Orbigny).
chalk is a deep-sea ooze. In all the deep-sea soundings and dredgings
recently undertaken, it is found that the sea -bottom between the depths
454
MESOZOIC ERA AGE OF REPTILES.
of 3,000 and 20,000 feet, where not too cold, is a white ooze, consisting
wholly of Rhizopod shells (Globigerina, Radiolaria, etc.) and Coccoliths,
Coccospheres, etc., through which are scattered siliceous shells of Dia-
toms. These shells are in every stage of change : some living, or at
least still retaining sarcode ; some perfect, though dead and empty ;
some broken ; most completely disintegrated into an impalpable mud.
From the great abundance of one genus of Rhizopods, this calcareous
mud has been called Globigerina ooze. In deep-sea bottoms, therefore,
chalk is now forming. Also, strange to say, many Sponges, and Star-
fishes, and Echinoids, and Crustaceans, very similar to those formed in
the chalk of Cretaceous times, have been brought up from present deep-
sea bottoms.
FIG. 735. Shells of Living Foraminifera : <?, Orbulina universa, in its perfect condition, showing the
tubular spines which radiate from the surface of the shell ; b, Globigerina bulloides, in its ordinary
condition, the thin hollow spines which are attached to the shell when perfect having been broken off;
c. Textularia variabiiis ; d. Peneroplis planatus ; e, Kotalla concamerata ; /, Cristellaria subarcuatula.
(Fig. a is after Wyville Thomson; the others are after Williamson. All the figures are greatly
enlarged.)
There seems no doubt, therefore, that chalk is a profound sea-bottom
formation. The flint-nodules have been formed by a subsequent process
similar to that which gives rise to other nodules (p. 188). The silica,
which in the ooze was at first scattered, is slowly aggregated into pure
flint-nodules, and the matrix is left in a condition of pure carbonate of
lime.
Extent of Chalk Seas of Cretaceous Times in Europe. Chalk of
CRETACEOUS PERIOD. 455
nearly homogeneous aspect prevails from the north of Ireland through
Middle Europe to the Crimea and Caucasus, 1 a distance of 1,140 miles ;
and, in the other direction, from the south of Sweden to the south of
Bordeaux, a distance of 840 miles (Lyell). It is evident, therefore,
that at that time a very deep sea occupied a large portion of Central
Europe. The white chalk of England and France is about 1,000 feet
thick. When we remember the mode in which it has been formed, this
thickness indicates an almost inconceivable lapse of time.
Cretaceous Coal. Coal is again found in large quantities in rocks of
this period in the United States. The mode of occurrence is similar to
that found in rocks of other periods.
There has been, and still is, much difference of opinion and discussion
among the best observers as to the exact position of the coal or lignites
of the Pacific coast, of the Rocky Mountains, and of the Plains. Some
have been referred to the Cretaceous, some to the Eocene, and some to
the Miocene-Tertiary. With the exception of the last, however, most
or perhaps all the productive fields seem to belong to nearly the same
horizon, which has been called the Great Lignitic formation, and which
by some geologists is regarded as uppermost Cretaceous, by others as
lowermost Eocene. The animal fossils seem to ally the strata with the
Cretaceous, the plants with the Eocene.
The truth is, the Great Lignitic of the West seems to be a transition
between the Cretaceous and the Eocene. While it was depositing, the
changes of physical geography and climate which closed the Cretaceous
and inaugurated the Tertiary had already been accomplished ; but Cre-
taceous types still lingered, ready to disappear. The death-sentence
had been pronounced, but the execution was delayed. In this group,
therefore, Cretaceous and Tertiary forms are more or less mingled.
This is precisely what we might expect ; for in the drying up, by up-
heaval, of the Cretaceous interior sea, marine animals would be gradu-
ally changed into brackish-water and finally into Tertiary fresh-water
animals ; the newly-formed land would be covered with a Tertiary vege-
tation, but the Cretaceous land animals would still continue to hold out
for a while.
Since some of these fields are undoubtedly Cretaceous, it seems best,
in order to avoid repetition, to speak of them all in this connection ; but
as the plants found are entirely different from the Cretaceous plants
to be presently described, and wholly of Tertiary types, it seems best,
until the question is definitely settled, to speak of these under the
Tertiary.
First, on the Plains, just east of the Rocky Mountains, there are
several immense fields: one on the Upper Missouri and Yellowstone,
another about Denver and Marshall, and still another farther south in
1 Favre, " Archives des Sciences," vol. xxxvii., p. 118, et seq.
456
MESOZOIC ERA AGE OF REPTILES.
New Mexico. These coal-fields are supposed to have an aggregate ex-
tent of at least 15,000 square miles. Beyond the limits of the United
States, in the British possessions, are found still other fields (Davvson).
Again, in the Plateau region, between the eastern Rocky Mountain
range and the Wahsatch Mountains, on the Laramie Plains, is found a
very fine field of 5,000 square miles. Again, on the Pacific slope are
several important fields : 1. Monte Diablo and Corral Hollow coal-field,
in California ; 2. Seattle and Bellingham Bay coal-field, of Washing-
ton Territory ; 3. The Nanaimo and Queen Charlotte's Island coal-field,
of British Columbia.
We recapitulate the coal-fields of the United States, and present
them at one view in the following table :
Carboniferous .
Jura-Trias
Cretaceous.
Appalachian
60,000 }
Central
47 000 1
Western
78^000 f
191,700 square miles.
Michigan . . .
6,700 J
' Richmond . . |
170 )
Piedmont . . | "
Deep River. /
500 1
670 square miles
Dan River., j " '
tivv/ j
Western Plains. ...
I Rocky Mountains..
- 20,000
20,000 square miles.
] Monte Diablo, etc..
[ Washington
unknown.
Total 212,370 square miles.
Of which at least 150,000 square miles are workable.
The Cretaceous coals are usually called lignites, but they are really
a very fair coal, and quite different from what usually goes under that
name.
Subdivisions of the Cretaceous. The Cretaceous in America is di-
vided into upper and lower ; in Europe it is divided into upper, middle,
and lower, the chalk being the upper.
Cretaceous . . .
AMERICAN. ENGLISH.
f Upper... .j Upper, or Chalk.
Middle, or Greensand.
Lower, or Lower Geeensand.
Lower. . .
It is probable that the lowermost Cretaceous of Europe is unrepre-
sented in the United States. If so, the reason is evident. The Sierra
revolution was a great event. A gap in the record is the result. Some
of the leaves missing here are recovered in Europe.
Life- System : Plants.
Leaf-impressions are very abundant in the American Cretaceous, and
the most cursory examination reveals at once a type of plants not seen
PLANTS.
457
in any lower rocks, viz., Angiosperms, both Dicotyls and Palms. We
have said that the Sierra revolution at the end of the Jura-Trias pro-
FIG. 73T, FIG. T38. FIG. 739.
FIGS. 736-739. CRETACEOUS PLANTS (after Lesquereux): T36. Liquidamber inteprifolium. 737. Sassafras
Mudgei. 738. Lauras Nebrascensis. 739. Quercus primordialis. All reduced.
duced great change in America. It is probable that a break occurs in
the record here. When the record commences again with the Creta-
4:58
MESOZOIC ERA AGE OF REPTILES.
ceous, we observe a very great difference in the subject matter. The
whole aspect of field and forest must have been different and much more
modern. Nearly all the genera of our modern trees are present, e. g.,
Oaks, Maples, Willows, Sassafras, Dogwood, Hickory, Beech, Poplar,
FIG. 742.
FIGS. 740-743. CBETACEOF 8 PLANTS (after Lesquereux) : 740. Sassafras araliopsis. 741. Sails protese-
folia. 742. Fa^us polyclada. 743. Protophyllum quadratum. All reduced.
Tulip-tree (Liriodendron), Walnut, Sycamore, Sweet^gum (Liquidam-
ber), Laurel, Myrtle, Fig, etc. Out of 130 species of plants found in
the Cretaceous of Nebraska, about 110 species are Dicotyls, and at least
half of these belong to living genera (Lesquereux). And if we include
ANIMALS.
459
the Lignitic in the Cretaceous we may add 200 more species to the
list, but these latter are quite different and Tertiary in type. A few
Palms have also been found in Vancouver's Island.
It is a noteworthy fact that many of the most characteristic Creta-
ceous genera, and those most abundant and varied in species at that time,
are now represented by only one or two species. For example, there
are now only two species of Sassafras ; one species of Plane-tree ; one
of Liriodendron ; and one of Liquidamber. These are evidently the
remnants of an extinct flora.
But if the highest plants, the Dicotyls, are abundant, so are also
the lowest Protophytes or uni-celled plants. Diatoms, Desmids, Cocco-
spheres, are abundant in the chalk of Europe. If they are not found in
America, it is only because deep-sea deposits have not yet been found
there.
Animals.
Protozoa. As already stated, chalk is made up almost wholly of
shells of ForaminiferEe (Rhizopods) and of certain uni-celled plants.
According to Ehrenberg, a cubic inch often contains millions of micro-
scopic organisms. More than 120 species of Foraminifers have been
FIGS. 744, 745. CRETACEOUS SPONGES : 744. Siphonia flcns. 745. Ventriculites simplex.
found in the English chalk alone. Some of these seem to be species
still living in deep seas. These a/e all extremely minute, but some of
larger size are found in the Cretaceous limestone of Texas. Those from
the chalk have already been given.
Sponges are extremely common in the chalk, as they are also in
460
MESOZOIC ERA AGE OF REPTILES.
deep-sea bottoms of the present day. About one hundred have been
found in the chalk.
Echinoderms. The free Echinoderms are now for the first time
in excess of the stemmed. Only very recently, the first Crinoid yet
found in the American Cretaceous has been obtained by Marsh, and
described by Grinnell. The Tfin-
tacrinus socialis (Fig. 746) was
a free Crinoid like the Marsupites
of the English chalk, or the Coma-
tula of the present seas. They
seemed to have lived together in
great numbers in Cretaceous times
in the region of the Uintah Moun-
tains, then a Cretaceous sea. Fig.
746 represents the body ; the arms
were exceedingly numerous and
complex. The Echinoids are es-
FIG. 746.-uintacrinus socialis (after Grinneii). pecially abundant and decidedly
Fio. 749.
FIGS. 747-749. ECUINOIDB or THE CRETACEOUS OF EUROPE: 747. Galerites albogalerus. 748. Discoidea
cylindrica. 749. Goniopygus major.
ANIMALS.
461
modern in type ; and in the chalk some genera are identical with,
and some species very similar to, those recently gotten from deep-sea
ooze. The above are from the European Cretaceous.
FIG.
FIGS. 750-753. CRETACEOUS BEACHIOPODS AND LAMELLIBRANCHS Brachiopods : 750. Terebratula As-
tieriana. Lamellibranchs : 751. Ostrea Idriaensis (after Gabb). 752. Inoceramus dimidius (after
Meek). 753. Exogyra costata (after Owen).
JVToUusks. For the first time Lamdlibranchs are fairly in excess of
Brachlopods. Among the latter the modern family of Terebratulse are
especially conspicuous (Fig. 750). Among the former the most note-
worthy fact is the abundance of the Oyster family Ostrea, Gryphcea,
Exogyra, etc.; and the Avicula family, Avicula, Inoceramus, etc., some
of which are of great size.
462
MESOZOIC ERA AGE OF REPTILES.
Another very strange and characteristic group of shells found here
are the Rudistes or Hippuritidce. In this family one valve is compara-
tively small, and often flat, while the other is enormously deep and
elongated in the shape of a covv's-horn in Hippurites and Radiolites
(Fig. 754), or in the shape of a closely-coiled ram's-horn in Caprinella
and Caprina (Fig. 757). The figures are taken from foreign localities,
but similar forms exist also in this country.
Fio. 754.
FIGS. 754-757. 754. Hippurites Toucasiana, a large individual with two small ones attached fatter
d'Orbipny). 755. Section of a Radiolites cylindriasus, showing structure. 756. Upper Valve of
Eadiolites mammelaris. 757. Caprina adversa (after Woodward).
Among Gasteropoda, the beaked or siphonated kinds are now for
the first time abundant, as in the present seas (Figs. 758-760).
Among Cephalopods the Ammonites and Belemnites still continue
in great numbers and size, but they die out at the end of this period
forever. In the Cretaceous of the "Western Plains some Ammonites have
ANIMALS.
463
been found over three feet in diameter (Dana). This family seemed to
have reached its culmination just before its extinction. But what is
still more remarkable is the introduction of many new genera of very
strange and unexpected forms. These are sometimes partly uncoiled,
FIGS. 75S-760. CRETACEOUS GASTEROPODS : 758. Cyprsea Matthewsonii (after Gabb). 759. Aporrhais
falciforinis (after Gabb). 760. Scalaria billimani (after Lesquereux).
as in Scaphites (boat), Crioceras (ram's-horn), Toxoceras (bow-horn),
Ancyloceras (hook-horn), Hamites (hook); sometimes completely un-
coiled, as in faculties (walking-stick) ; sometimes coiled spirally, like
a Gasteropod, as in Turrulites and Helioceras. Belemnites also con-
tinue, though in diminishing numbers.
FIG. 761. Belemnites impressus (after Gabb).
These strange forms have been likened by Agassiz to death-contor-
tions of the Ammonite family ; and such they really seem to be. From
the point of view of evolution, it is natural to suppose that under the
gradually-changing conditions which evidently prevailed in Cretaceous
times, this vigorous Mesozoic typo would be compelled to assume a
464
MESOZOIC ERA AGE OF REPTILES.
great variety of forms, in the vain attempt to adapt itself to the new
environment, and thus to escape its inevitable destiny. The curve of its
Fro. 768.
Fins 762-768 CRETACEOUS CEPHALOPODS : 762. Ammonites Chicoensis (after Gabb). 763. Scaphites
Kqualis (after Pictet). 764. Crioceras, restored (after Pictet). 765. Heliooeras Kobertinnnsjtafter
Pictet). 766. Ancyloceras percostatus, x J (after Gabb). 767. BacuUtes anceps, x $ (after Wood-
ward). 768. Turnilites catenatus (after D'Orbigny).
ANIMALS.
465
rise, culmination, and decline, reached its highest point just before it
was destroyed. The wave of its evolution crested and broke into
strange forms at the moment of its dissolution.
Among Crustaceans, the Brachyurans, short-tailed Crustaceans
(crabs), which were barely introduced in the Jurassic, are here repre-
sented by several genera.
Vertebrates Fishes. In the development of this class some decided
steps in advance are here recorded. Placoids and Ganoids still con-
no. 771.
FIGS. 769-771. CRETACEOUS FISHES Placoids: 769. Otodus (after Leidy) ; 770. Ptychodns Mortoni
(after Leidy). Teleosts: 771. Portheus moloseus Tooth, natural size (after Cope).
tinue, but Teleosts, or true typical modern fishes, are here introduced
for the first time, and in considerable numbers, and some of gigantic
30
466
MESOZOIC ERA AGE OF REPTILES.
size. These earliest Teleosts were related to salmon, herring, perch,
pike, etc. Beryx, a genus still found in open seas, is found in the Chalk
of Europe and Upper Cretaceous of America. Among Placoids, too,
although the Cestracionts and Hybodonts continue (the latter, however,
passing out with the Cretaceous), the modern type, the true sharks or
FIG. 772.
FIG. 7T4.
FIGS. 772-774. CBETACEOITS FISHES Teleosts: 772. Portheus, restored,
Lewesiensis. 774. Osmeroides ManteUi.
aV (after Cope). 773. Beiyx
Squalodonts, having lancet-shaped teeth, are for the first time abundant.
Above we give figures of Cestraciont and Squalodont teeth, and also a
tooth, natural size, of a gigantic pike, eight feet long, from American
Cretaceous, and a restoration of the same by Cope ; also, two Teleosts
from European Cretaceous.
The Hybodonts were essentially a Mesozoic type ; the Squalodonts
are essentially Tertiary and modern. The two types coexist in the Cre-
ANIMALS. 467
taceous, the former passing out, the latter increasing, and finally dis-
placing the former.
Cope gives ninety-seven species of North American Cretaceous
fishes known in 1875. Of these, if we include the Chimera family, an
aberrant type of Placoids very common in the Cretaceous, forty-jive
were Placoids. The rest are mostly Teleosts, for the Ganoids are rapid-
ly disappearing. In Europe, twenty-five genera of Cycloids and fifteen
of Ctenoids are found in the Cretaceous (Dana).
Reptiles. This class seems to have culminated about the end of the
Jurassic or the beginning of the Cretaceous period. If their remains
are more abundant in the Jurassic in Europe, they are far more abun-
dant in the Cretaceous in America. In fact, we had here in America
during that time an extraordinary abundance and variety of reptilian
life, including all the principal orders already mentioned, viz., Enalio-
saurs, Dinosaurs, Pterosaurs, and Crocodilians, and also a new type, in-
troduced in the Cretaceous for the first time, the Mosasaurs, wholly
marine in habits, but of long, slender, snake-like form, and attaining the
greatest length yet known among reptiles. Turtles were also found in
large numbers and of great size. We can mention only a very few
of the most remarkable of the Cretaceous reptiles.
Among Enaliosaurs Leidy describes one Di'scosaur (Elasmosaur,
Cope) allied to the Plesiosaur, which was fifty feet long, with a neck of
^pww^p***
FIG. 775. Teeth of Hadrosaurus (after Leidy) : a, Pavement of Teeth ; 6 and c, Tooth separated.
sixty vertebras and twenty-two feet long. Among Dinosaurs the Ha-
drosaur from New Jersey was twenty-eight feet long; and, judging
from the huge size of its hind-legs and massiveness of its hips and small
size of its fore-legs, it seems to have been able to stand and walk in the
manner of birds (Fig. 776). This animal was a vegetable-feeder, with
teeth somewhat like those of the Iguanodon, but set in several rows, so
as to form a kind of tessellated pavement (Fig. 775). From the same
468
MESOZOIC ERA AGE OF REPTILES.
locality the Dryptosaurus (Lcelaps), similar to the Megalosaur, and
twenty-four feet long, and the Ornithotarsus (bird-shank), thirty-five
feet long, stood twelve to fifteen feet high when walking
on their hind-legs. The largest of the group is Titanosau-
rus, recently described by Marsh. It was found in Colo-
rado, and was at least fifty feet in length. Among Ptero-
saurs, Marsh has found in the Western Cretaceous the
remains of at least six species; two of which were twenty
to twenty-five feet in alar extent, and another eighteen
feet.
The American Pterosaurs differ from all other known
Pterosaurs in the fact, recently brought to light by Marsh,
that their jaws were entirely toothless, and probably sheathed
with horn, as in birds. They have therefore been placed
by Marsh in a distinct order, Pteranodontia, from the type
genus Pteranodon (winged-toothless). Probably all the
t American Pterosaurs belong to this order. One of them,
P. ingens^ had toothless jaws four feet long, and an ex-
panse of wing of twenty-two feet.
Among the many Chelonians (turtles) found in the
g . Cretaceous of the Western Plains, of the Rocky Mountain
I" region, and of New Jersey, one, the Atlantochelys gigas,
| had a length of nearly thirteen feet, and a breadth across
| the extended flippers of fifteen feet (Cope). The structure
I of this huge turtle was singularly embryonic. The flattened
FIG. 776. Hadrosaurus (restored by Hawkins).
ANIMALS.
469
ribs, which by their coalescence make the greater part of the shell, of
a turtle, were in this species, as in the embryo of modern turtles, not
yet coalesced.
But the most remarkable and characteristic reptiles found in the Cre-
taceous are the Mosasaurs (Pythonomorpha of Cope). The first speci-
men of the order was found in Europe, on the river Meuse, and hence
the name Mosasaurs ; but they seem to have been far more abundant in
FIG. 778.
FIG. 780.
FIGS. 778-781. 778. Head of a Tylosaurus micromus,
x T ' 5 (after Marsh). 780. Tooth of a Mosasaurus,
(Clidastes), x 1 (after Cope).
\ (after Marsh). 779. Paddle of a Lestosaurus,
i (after Leidy). 781. Jaw of an Edestosaurus
America. At least fifty species (Cope) have been found in the Cre-
taceous of New Jersey, the Gulf States, and Kansas. Of these, the
Mosasaurus princeps was sixty to seventy feet long, and Tylosaurus
dyspelor, probably the " longest known reptile, attained a length equal
470 MESOZOIC ERA AGE OF REPTILES.
to the longest whale" (Cope). These reptiles seem to have united the
long, slender form of a snake, and the short, strong, well-fingered pad-
dles of a whale, with the essential characters of a lizard. Another
snake-like character possessed by this order was rows of teeth on the
palatal bones, in addition to those in the jaws ; and a peculiar loose
and movable articulation of the lower jaws, by means of which, when
aided by the recurved teeth, the jaws could act separately like arms, in
dragging down their throats prey which was too large to swallow di-
rectly (Fig. 781). It is these snake-like characters which have pro-
cured for them the family name of Pythonomorpha (Cope).
We give on page 468 a restoration by Cope of one of most slender
forms Edestosaurus and also, on page 469, head and tooth, and pad-
dle and jaw, of other Mosasaurs.
According to Cope, 147 species of reptiles have been described from
the Cretaceous of North America, of which fifty are Mosasaurs, forty-
eight Testudinata (turtles and tortoises), eighteen Dinosaurs, four-
teen Crocodilians, thirteen Sauropterygia (Plesiosaur-like), and four
Pterosaurs At least two more Pterosaurs have been found, making
the whole number now six (Marsh).
In Europe, Iguanodons, Teleosaurs, Ichthyosaurs, Plesiosaurs, and
Pterosaurs still remain, some of the last being twenty-five feet in ex-
panse of wing ; and also a few Mosasaurs were introduced.
Birds. The history of the discovery of the earlier fossil birds is in-
structive. Until 1858, with the exception of the doubtful tracks in
the Connecticut River sandstone, no birds had been found lower than
the Tertiary. In that year the' bones of a bird, probably related to the
gull, was found in the upper greensand of England. In 1862 the won-
derful reptilian bird Archceopteryx macroura, already described (p.
436), was found in the Solenhofen limestone of Germany (Upper Juras-
sic). In 1870 and 1871 Marsh discovered in the Cretaceous of New
Jersey and Kansas sixteen species of birds : five Grallatores (waders),
like the Rail, Snipe, etc. ; five Natatores (swimmers), allied to Cormorants,
Divers, etc. ; and six wonderful Toothed birds, entirely different from
any existing order. These were the most extraordinary birds which
have ever been discovered. Three of them, belonging to the two gen-
era Ichthyornis and Apatornis, were without the horny beak so char-
acteristic of existing birds, but instead had thin, long, slender jaws,
furnished with many sharp, conical teeth, set in sockets, twenty on
each side below, and perhaps as many above (Fig. 782). Their verte-
brae were amphiccelous or bi-concave, as in fishes and many extinct rep-
tiles, but in no modern bird (Fig. 783). Like modern birds, however,
they had a keel on the breast-bone for the attachment of the powerful
muscles of flight. The tail has not been found, but it was possibly
vertebrated, like that of the Jurassic Archaeopteryx, but shorter and not
ANIMALS.
471
so reptilian (Marsh). These birds were about the size of a pigeon, and
were evidently capable of flight. The three other toothed birds had
teeth set in grooves instead of distinct sockets (Fig. 784), and differed
also in having no keel and in having ordinary bird-vertebras (Fig. 785).
FIG. 783.
FIGS. 792-786. ODONTOKNirura (after Marsh) : 782. Lower Jaw of Ichthyornis dispar, x 2. 788. Cervical
Vertebra of same, x 2. 784. Lower Jaw of Hesperornis regalis, x J. 785. Dorsal Vertebra, x J.
766. Tooth of same, x 2.
These were evidently divers, and incapable of flight. Two of them
Hesperornis regalis and Lestornis crassipes were of gigantic size,
being from five to six feet from snout to toe. Below (Fig. 787) we
472
MESOZOIC ERA AGE OF REPTILES.
give a restoration by Marsh of this remarkable bird. In these birds,
therefore, we have the most extraordinary combination of bird charac-
ters with reptilian and fish characters. So extraordinary and excep-
tional is this combination of characters, that Marsh believes he is jus-
tified in placing them not only in new orders Odontotormce (socket-
toothed) and Odontolcce (teeth in groove) but even in a new sub-class
Odontornithes (toothed birds). Yet, exceptional as these characters
may seem, they are just what the law of evolution would lead us to
expect in the earliest birds. As already stated (p. 439), this branch
FIG. 787. Hesperomis regalfc (restored by Marsh).
had not yet been fairly separated from the reptilian stem. It is a note-
worthy fact that these toothed birds lived at the same time and in the
same localities with the toothless Pterosaurs mentioned on page 468.
Mammals. It is a most remarkable fact that although Marsupial
mammals have been found in the Jurassic, and probably existed in con-
siderable numbers then, yet not one has been found in the Cretaceous.
It is certain, however, that they existed at that time, for they are found
in the Tertiary of Europe, and still exist in Australia and elsewhere ;
and it is a well-established law in Paleontology that if a type becomes
CONTINUITY OF THE CHALK. 4.73
extinct it never reappears: Evolution never goes backward: Nature
never repeats herself. It is probable, therefore, that during the Creta-
ceous the Marsupials which doubtless existed had been driven to some
other portion of the earth, where we shall yet find their remains when
our knowledge of the geology of the globe is more complete ; and in
them we shall also probably find the transitions to, or earliest progeni-
tors of, the True mammals of the Tertiary.
Continuity of the Chalk.
It is probable that the deep Atlantic Ocean bottom, where chalk is
now forming, is continuous with the chalk of England and Central
Europe. In other words, in Cretaceous times a deep sea ran from the
mid-Atlantic far into what is now Central Europe, and in the whole of
this deep sea chalk was then formed. At the end of the Cretaceous
period the eastern part was raised and formed a portion of Europe, while
the rest remained as deep-sea bottom, and continued to make chalk until
now. Thus there is no doubt that in the deep Atlantic, off the coast
of Europe, there has been an unbroken continuity of chalk-making
from the Cretaceous times until now. But we have seen (p. 454) that
many of the living deep-sea species are identical with, and nearly all ex-
tremely similar to, those found in the chalk of Cretaceous times. Thus
there has been not only a continuity of chalk-formation, but also to
some extent of the chalk-fauna, to the present time.
These facts were certainly unexpected, but, so far from shaking tha
foundations of geological science, as some have imagined, they are in
perfect accordance with the fundamental principles of geological suc-
cession properly understood ; as we now proceed to show :
1. The facts of identity have been exaggerated. Many of the
Foraminifera only are identical. Among echinoderms the identity
is generic, not specific. 2. In comparing higher with lower species,
we find that the lower species are widely distributed both in space
(geographically) and in time (geologically), and that the continuance
or range in time becomes less and less in proportion as we rise in the
scale. Thus, referring to diagram, Fig. 788, page 476 (under Tertiary),
constructed to illustrate this point, we see that living species of mam-
mals extend back only a little way into the Quaternary, living species of
mollusks back to the beginning of the Tertiary, while living species of
Foraminifera, as we might expect, extend back into the Cretaceous.
3. There is a necessary relation between fauna and external conditions.
Changes in the latter determine corresponding changes in the former.
Now, deep-sea conditions are evidently far less subject to change far
more continuous than shallow-water and land conditions. For this
reason, we should expect deep-sea faunae to change very slowly. 4. But
this cannot affect the geological chronology, because this chronology
474 MESOZOIC ERA AGE OF REPTILES.
rests almost wholly on the remains of shallow-water and land animals.
Chalk is the only profound sea-bottom formation certainly known.. It
is, therefore, wholly exceptional. 5. The reason it is exceptional is
that, as a broad general fact, the present continents have been, through
all geological times, steadily heaved upward out of the ocean, growing
larger and higher ; and, therefore, the successive additions have been
nearly always shallow marginal bottoms and shallow interior seas.
That the exception should occur in Europe rather than in America, too,
is in keeping with the general character of the development of the
European as contrasted with the American Continent. 6. Conversely,
the fact that chalk is so exceptional is proof of the development of
continents as indicated under the last head proof that, as a general
fact, the great inequalities of the earth's crust, which constitute land-
surfaces and sea-bottoms, have remained substantially unchanged in
position from the first, while steadily increasing in vertical dimen-
sions.
General Observations on the Mesozoic.
The Mesozoic, and especially the Jurassic, is characterized by the cul-
mination of two great classes of animals, viz., Cephalopod Mollusks and
Reptiles, and one of plants, the Cycads. This is shown in the diagram
on page 270. The culmination of reptiles is, of course, its most distin-
guishing characteristic. That it was preeminently an age of Reptiles,
may be shown by a comparison of its reptilian fauna with that of the
present day. There are now, on the whole face of the earth, only six
large reptiles over fifteen feet long two in India, one in Africa, three
in America and none over twenty-five feet long. In the Wealden and
Lower Cretaceous of Great Britain alone there were five or six great
Dinosaurs twenty to sixty feet long, ten to twelve Crocodilians and
Enaliosaurs ten to fifty feet long, besides Pterodactyls, turtles, etc.
(Dana). Again, in the Cretaceous of the United States alone the full-
ness of reptilian life was even greater ; for 147 species of reptiles have
been found, most of them of gigantic size. Among these were
fifty species of Mosasaurs, some seventy to eighty feet long; many
huge Dinosaurs, twenty to fifty feet long ; besides Enaliosaurs, Ptero-
saurs, and gigantic turtles (Cope). These are preserved! But the
known fossil fauna of any period is but a fragment of the actual fauna
of that period. Not only did reptiles greatly predominate, but the age
seemed to impress its reptilian character on all other higher animals
existing at that time. The birds were reptilian birds, the mammals
were reptilian mammals. All animals as yet were oviparous (birds and
reptiles) or semi-oviparous (marsupials). It is difficult to imagine the
size of egg produced by an Iguanodon or a Cetiosaurus.
That the climate was then warm and uniform is sufficiently attested
by the character of the fauna and flora. All great reptiles and all Cy-
CENOZOIC ERA AGE OF MAMMALS. 475
cads and Tree-ferns are found now only in tropical or sub-tropical re-
gions. This tropical fauna and flora were substantially similar in all
latitudes in which the strata have been found even as far north as
Spitzbergen (Nordenskiold). 1 During the latter portion of the Creta-
ceous period, as indicated by the abundance of deciduous Dicotyls, the
climate of North America had become cooler, being about 8 or 10
warmer than now.
Disturbance which closed the Mesozoic. The disturbance which
in America closed the Cretaceous period and the Mesozoic era was
a bodily upheaved of the whole western half of the continent, by which
the great interior Cretaceous sea, which previously divided Amer-
ica into two continents, was abolished, and the continent became one.
At the same time the Wahsatch and Uintah Mountains were principally
formed, and the eastern Rocky Mountain range greatly elevated. If
the end of the Jurassic was preeminently a time of mountain-making
(Sierra revolution), the end of the Cretaceous was preeminently a time
of continent-making. The disturbance, as usual with those which close
an era, was probably to some extent oscillatory, i. e., the continent was
probably higher and cooler during the latter part of the Cretaceous than
during the subsequent Eocene. The change of physical geography was
enormous, and the change of climate was doubtless correspondingly
great. We ought to be prepared, therefore, to find, with the opening
of the next era, a very great change in the organisms.
CHAPTER V.
CENOZOIC ERA AGE OF MAMMALS.
THIS deserves the rank of a distinct era, and the corresponding rocks
that of a distinct system, because there is here a great break in the rock-
system, and a still greater break in the life-system. Between the rocks of
the Cretaceous and Tertiary there is, in Europe, universal unconformity.
In America, on the contrary, especially on the Western Plains, there
seems to be in some places a continuous series of conformable rocks con-
necting the two eras (Hayden). The record seems to be continuous.
Yet here, no less than in Europe, there is at a certain horizon a rapid
and most extraordinary change in the life-system. This it seems impos-
sible to explain on the theory of evolution unless we admit periods of
rapid evolution. The reason why there is no general unconformity in
America is, evidently, that the movement here was continental, and not
1 Geological Magazine, November, 1875.
476
CENOZOIC ERA AGE OF MAMMALS.
mere mountain-making and strata-crushing. Such continental move-
ments, however, would produce very great changes in climate, and there-
fore in organic forms. The end of the Jurassic was a period of moun-
tain-making, and therefore of unconformity the end of the Cretaceous,
a time of continent-making, and but little unconformity, but very great
change of climate. Therefore, although the interval lost in America is
far greater at the end of the Jurassic, the change of fauna and flora was
far greater at the end of the Cretaceous.
General Characteristics of the Cenozoic Era. As indicated by the
name, modern history commences here ; modern types were introduced
or became predominant; the present aspect of field and forest commences.
Then, as now, the rulers of the seas were great sharks and whales; the
rulers of the land, mammalian quadrupeds; and the rulers of the air,
birds and bats. Many of the genera and some of the species of both
animals and plants were identical with those still living. The dominant
class becomes now Mammals: Reptiles, therefore, in accordance with a
necessary law, decrease in size and number, and thus find safety in a
subordinate position. In some of these characteristics the Cenozoic era
was anticipated in the Upper Cretaceous, in accordance with the law that
the first beginnings of each age is in the preceding age.
Divisions. The Cenozoic era, or age of Mammals, embraces two
periods, viz. 1. The Tertiary and 2. The Quaternary. In the Ter-
tiary all the mammals are now wholly extinct, but the invertebrate
species are some of them still living, and an increasing percentage of
living species appears as time progresses. In the Quaternary most,
though not all, of the mammalian species are extinct, but most (ninety-
five or more per cent.) of the invertebrate species are living. These
facts are graphically represented in the following diagram, in which
FIG. 788. Diagram illustrating the Relative Duration of Lower and High
the curved ascending lines are the lines of appearance of living species,
and of extinction of extinct species of Foraminifera, of molluscous
shells, and of mammals. In each case the lower shaded space repre-
sents living species appearing in small numbers, and increasing with the
progress of time ; and the upper unshaded or less shaded space, previous
species gradually dying out and -becoming extinct. It is seen that
TERTIARY PERIOD. 477
living species of Foraminifera commenced in the Cretaceous, and very
steadily increased in number ; those of shells commenced in the earliest
Tertiary, and increased somewhat more rapidly ; while those of mammals
commenced only in the Quaternary, and increased correspondingly
rapidly. Also the relative proportion of living and extinct at any
time is shown by comparing the amount of space above and below the
line at that time. Also the relative range in time of low and high
species, and the amount of overlapping of successive faunse, are shown.
The mammalian class probably culminated near the end of the Ter-
tiary or during the Quaternary period.
SECTION 1. TERTIARY PERIOD.
Subdivisions. We have already stated that the general differential
characteristic of this period, as compared with the next, is that all the
mammals, and most of the invertebrates, are extinct ; but of the latter
a percentage, small at first but increasing with the progress of time,
are still living. It is upon this percentage of living shells that Lyell
has based his division of the Tertiary period into three epochs a
Lower, Middle, and Upper Tertiary, or Eocene, Miocene, and Pliocene.
f Pliocene epoch, or Upper Tertiary = 50-90 per cent, living shells.
Tertiary period. -4 Miocene epoch, or Middle Tertiary = 30 per cent, living shells.
L Eocene epoch, or Lower Tertiary = 5-10 per cent, living shells.
These percentages are expressed graphically in the diagram, Fig.
788.
Rock-SystemArea in the United States. On the Atlantic border,
going southward, there is no Tertiary, except a small patch on Martha's
Vineyard, off the coast of Massachusetts, until we reach New Jersey.
From this point southward the Tertiary is a broad strip, about 100 miles
wide, bordering the coast, and shown on the map (p. 278) by the space
shaded with oblique lines running to the right. It constitutes the low-
countries of the Southern Atlantic States. At its junction with the
metamorphic region of the up-countries, there are in nearly all the
rivers cascades which determine the head of navigation. Here, there-
fore, are situated many important towns, e. g., Richmond, Virginia ;
Raleigh, North Carolina ; Columbia, South Carolina ; Augusta, Milledge-
ville, and Macon, Georgia. The same strip of flat lands borders also the
Gulf, expands, in the region of the Mississippi River, northward to the
mouth of the Ohio, and then continues around the western border of
the Gulf. In the Gulf-border region, however, the Tertiary is in con-
tact below with the Cretaceous, instead of with metamorphic Silurian
and Laurentian, as on the Atlantic border. This whole Atlantic-border
and Gulf-border Tertiary is, of course, a marine deposit.
478 CENOZOIC ERA AGE OF MAMMALS.
In the interior, on the Plains and in the Rocky Mountain region,
there are enormous areas of fresh-water deposit, some Eocene, some
Miocene, and some Pliocene, which are of extreme interest.
Among the Eocene basins the most remarkable are : 1. The Green
River basin. 2. The Uintah basins. Both of these are on the east
side of the Wahsatch Mountains, and separated from each other by the
Uintah Mountains, one being north and the other south of that range.
The strata of the Green River basin are 6,000 to 8,000 feet thick. 3.
The San Juan basin (Cope), in the region of the San Juan River, Colo-
rado. Its horizon is the same as the Wahsatch, or lowest Green River
beds, which are the lowest Eocene. This is probably an extension of
the Uintah basin.
Among the Miocene basins the most interesting are : 1. The White
River basin, in Nebraska. 2. The John Day basin, of Oregon. This
latter is 5,000 feet thick, but is largely overlaid by the great lava-
flood of the Northwest. 3. One in Montana, recently discovered by
Grinnell. 1
Of Pliocene basins: 1. Niobrara basin, occupying partly the same
locality as the Miocene White River basin, but far more extensive,
reaching southward far into Texas. 2. In Oregon also there is a
Pliocene basin, occupying partly the same region as the previous Mio-
cene. 3. One recently discovered by Cope on the basin of the Rio
Grande. 4. In connection with the Miocene deposits of Montana, also
Pliocene deposits are found.
All these deposits are imperfectly lithified sand and clays in nearly
horizontal position, and have been worn by erosive agencies in the
most remarkable way, sometimes into knobs and buttes like potato-
hills on a large scale, sometimes into castellated and pinnacled forms,
which resemble ruined cities. These are the " Mauvaises Terres " or
" Bad Lands " of the West (Fig. 789).
On the Pacific coast, a large portion of the Coast ranges from
Southern California to Washington is Tertiary, as are also in many
places the lowest foot-hills of the Sierras.
Physical Geography, From what has been said of the distribution
of the rocks of this age, it is easy to reconstruct in a general way the
physical geography of the American Continent during the early Ter-
tiary period. In the northern part the ^Atlantic shore-line was prob-
ably beyond the present line, for there is no Tertiary deposit visible
there. The shore-line of that time crossed the present shore-line in
New Jersey, then passed along the line of junction of the Tertiary with
the Metamorphic, its waves washing primary shores all along the At-
lantic coasts, as it does now in the northern portion only ; then along
the junction of the same with the Cretaceous. The whole lovv-coun-
1 American Journal of Science, 1876, vol. xi., p. 126.
TERTIARY PERIOD. 479
tries of the Southern Atlantic States and the whole of Florida were then
a sea-bottom. The Gulf of Mexico was far more extensive than now,
FIG. 789. Mauvaises Terres, Bad Lands (after Hayden).
and especially it sent a wide bay northward to the mouth of the Ohio.
The Mississippi River below that point did not then exist.
In the interior, in the region of the Plains and Rocky Mountains,
there were at different times immense fresh-water lakes, the positions of
FIG. TOO. Map of Tertiary Times, showing Outline of Coast and Places of Principal Tertiary Lakes.
480 CENOZOIC ERA AGE OF MAMMALS.
some of which have been already indicated. These lakes drained some
of them into the Mississippi, some into the Colorado, and some into the
Columbia River.
The Pacific shore-line at that time was along the foot-hills of the
Sierra range, and therefore the whole region occupied by the Coast
ranges and the Sacramento and San Joaquin Valleys, and also portions
of Western Oregon, were then a sea-bottom. These facts are roughly
represented on map, Fig. 790. The position of the principal mountain-
chains, e. g., Sierra, Wahsatch, Uintah, the eastern border of the Rocky
Mountains, and Appalachian, is represented, in order the better to lo-
cate the lakes. It will be observed that the continent is nearly finished.
Europe is now remarkable for its inland seas. It was much more so
in Tertiary times.
Many great cities, as, for example, London, Paris, Vienna, are sit-
uated on Tertiary strata, partly because these strata are usually found
on the borders of continents, and partly because they are often found
in the course of great rivers, which once drained lake-basins.
Character of the Rocks. The rocks of this period, along the At-
lantic border and in the interior Plains and Rocky Mountain region, are
mostly imperfectly lithified ; but on the Pacific coast they are not only
of stony hardness, but in many cases completely metamorphic. Much
of the rock in the Coast Chain is scarcely distinguishable from the schists
of the Palaeozoic or still older periods. The reason is evident meta-
morphism is closely connected with mountain-making, and mountain-
making continued until the Tertiary only on the Pacific coast.
Coal. Again, in the Tertiary rocks we find coal, although more
usually in the imperfect condition called lignite. We have already
stated that the Rocky Mountain coal-fields are by many referred to the
Tertiary. We will not repeat these here. But there are others about
which there is as yet no controversy. The Coos Bay coal, of Oregon, is
probably Miocene-Tertiary. Again, Mr. Selwyn, the Geologist of Cana-
da, has reported large fields of coal on the Qu'Appelle and the North
Saskatchewan Rivers, covering an area of 25,000 square miles, a part,
at least, of which he refers to the Tertiary. Much of this coal is of
good quality. It seems most probable, however, that this is of the same
age as the Fort Union coal, concerning the age of which there is so
much discussion.
In Europe also an imperfect coal (lignite) is found in the Miocene in
considerable quantity.
Life- System.
General Remarks. We have already spoken of the great and rapid
change in the life-system between the Cretaceous and the Tertiary, even
where the two series of rocks are continuous and conformable. This
PLANTS. 481
indicates, undoubtedly, a more rapid rate of evolution at that time.
But it also indicates, as one cause of this rapid evolution, a migration
of species brought about by changes in physical geography and climate,
and the imposition of one fauna and flora upon another, and the ex-
termination of one by the other. It is difficult to conceive of these
sudden changes taking place otherwise. We shall speak more fully
of this important point under the Quaternary.
The general character of the life-system of the Tertiary, as already
said, was in the main similar to the present. Nearly all the genera and
many of the species of plants and invertebrate animals were the same
as now, and the difference in aspect would hardly be recognized by the
popular eye ; it was certainly not greater than now exists between dif-
ferent countries. It is only among Mammals that the difference would
be very conspicuous.
Plants.
Among plants, nearly all the genera q/Dicotyls, Palms, and Grasses,
were the same as now, though most of the species are extinct. The gen-
era were the same as now, but not in the same localities. On the con-
trary, the vegetation indicated a much warmer climate than exists now
in the same localities. For example, if we regard the Lignitic as
Eocene-Tertiary, instead of Cretaceous, as do paleontological botanists
generally, then of about 250 species of plants found, a very large pro-
portion were Palms, and many of them of great size ; and among the
Dicotyls many, like Magnolias, indicated a warm climate. Lesquereux
thinks the climate of Fort Union was then similar to that of Florida
and Lower Louisiana now. Again, in Eocene times there were fif-
teen species of Palms in Europe ; and in the Tyrol the flora, according
to Von Ettingshausen, indicated a temperature of 74 to 81 Fahr., and
many of the plants are Australian in type. In the Pliocene, on the
contrary, many European plants were like those in America at the
present time.
During the, Miocene, Europe was covered with evergreens such as
could grow now only in the southernmost part ; and that even as far as
Lapland, and Iceland, and Spitzbergen. It has been estimated that the
Miocene flora indicates a mean temperature of 16 to 20 higher than
now exists in Middle Europe. In America, during the same epoch,
Sequoias almost identical with the Big Tree and Redwood of Califor-
nia ; and Libocedrus, one of them identical with the L. decurrens of
California ; and Magnolias similar to the J/i grandiflora of the South-
ern Atlantic States ; and Taxodium distichum, the cypress of the
swamps of Carolina and Louisiana, all existed in Greenland, and most
of them also in Northern Europe, and Iceland, and Spitzbergen. Heer
estimates the temperature of Greenland in the Miocene as 30 higher
than now.
31
482
CENOZOIC ERA AGE OF MAMMALS.
These facts show not only a warm but a uniform climate, and prob-
ably also a connection in high latitudes between the American and Eu-
ropean Continents. A similar connection, shown also by the vegeta-
tion, probably existed between Alaska and the Asiatic Continent at that
time. Below we give figures of some Dicotyls and Monocotyls of Ameri-
can and European Tertiary.
FIG. 792.
FIG. 793.
FIG. 794.
FIG. 795.
FiG8. 791-796. AMERICAN TERTIARY PLANTS (after Safford and Lesquereux) : 791. Cinnamomum Mis-
sissippiense. 792. Quercus crassinervis. 793. Andromeda vnecinifolite affinis. 794. Carpolithes
irregularis. 795. Fagus ferruginea Nut. 796. Quercus Saffordl.
Another conclusion to be drawn from the foregoing facts is that, in
the race of evolution, Europe seems to have distanced most other coun-
tries. The Australian flora is now only where the European flora was
in Eocene times, and the American flora now where the European was
in the Pliocene. The probable reason is that, in Europe, in these later
geological times, 1 changes of physical geography and climate, and conse-
quent migrations of species, were more frequent, and the struggle for life
1 In Cretaceous times the flora of America seems to have been more advanced than that
of Europe.
PLANTS.
483
more severe. Australia especially, probably on account of its isolation,
has advanced more slowly than most other countries. Many remnants
of extinct faunse and florae exist there still.
FIG. 800.
FIGS. 797-802. PLANTS OP EUROPEAN TERTIARY : 797. Chamaerops Helvetica. 798. Sabal major. T99.
, Single Fruit. 800. Cinna
Leaf, 6, Flower ; c, Seed
.
Platanusaceroides : a, Leaf; 6, Core of a Cluster of Fruits; c, Single Fruit. 800. Cinnamomum poly-
802. Podo-
morphum : a. Leaf; 6, Flower. 801. Acer trilobatum :
gonium Knorrii.
Diatoms. If the highest of plants Dicotyls and Monocotyls were
abundant, probably more abundant than now, so also were the lowest
order of uni-celled plants the Diatoms. Immense deposits, consisting
484
CENOZOIC ERA AGE OF MAMMALS.
wholly of the siliceous shells of these microscopic plants, are found in
the Tertiary. In Europe the Bohemian deposit is celebrated. It is
fourteen feet thick, and every cubic inch of the material, according to
Ehrenberg, contains 40,000,000,000 shells. The Richmond (Virginia)
deposit is equally well known. It is thirty feet thick, and many miles
in extent. Similar deposits are peculiarly abundant in California. They
are found in at least a dozen localities where the Tertiary rocks pre-
vail, as, for example, at San Pablo, in Shasta County, and near Mon-
terey, the last deposit being fifty feet thick.
Some of the more remarkable forms of Diatoms are shown below in
Fig. 803, which is a view under the microscope of the Richmond deposit.
FIG. 803. Microscopic View of Richmond Infusorial Earth (by Ehrenberg).
Deposits of this kind are usually called infusorial earths. They may
often be recognized, even without microscopic examination, by their
soft, chalky consistence, their insolubility in acids, and their extreme
lightness.
Origin of Infusorial Earths. It is well known that mud composed
of diatom shells accumulates at the bottoms of ponds, and lakes, and
sluggish streams. In the deepest parts of Lake Tahoe, where sedi-
ments do not reach, the ooze is composed wholly of infusorial shells. It
ANIMALS. 485
has been shown, also, by Dr. Blake, 1 that the deposits from hot springs
of California and Nevada, even where the temperature is 163 to 174,
abound in Diatoms of the same species as those found in California in-
fusorial earths. It is probable, therefore, that many of these deposits
were made in hot springs and hot lakes, which, judging from the vol-
canic activity of that time, abounded in California then even far more
than now. Dr. Blake thinks the infusorial earths of California are
Miocene.
Animals.
As already stated, among Invertebrates there was a general similarity
to the present fauna. Nearly all the genera, and many of the species,
were identical with those still living. The relation between the various
orders which prevail now, commenced then. The present basis of
adjustment was then established. Then, as now, Brachiopods and
Crinoids were nearly all gone, Echinoderms were nearly all free, and
Bivalves were nearly all Lamellibranchs. Then, as now, naked Ceph-
alopods and short-tailed Crustaceans greatly predominated. A glance
at the following figures of Tertiary shells will show the general resem-
blance to those of the present seas.
In regard to the Invertebrates, there are only three or four points of
sufficient importance to arrest our attention in a rapid survey.
Among Rhizopods, Nummulites (a foraminifer) abounded to an ex-
traordinary degree. Eocene strata, many thousand feet thick, are formed
of these shells. The Nummulitic limestone of the Alps extends east-
ward to the Carpathians, westward to the Pyrenees, and southward into
Africa. It was largely quarried to build the Pyramids of Egypt. It
occurs also extensively in Asia Minor and in the Himalayas.
FIG. 804. Nummulina Isevigata.
This limestone occurs in the Alps 10,000 feet, and in the Himalayas
15,000 feet, above the sea-level. We see, then, the immense changes
which have occurred by mountain-making since the Eocene.
Among bivalve shells, common forms of the present day, such as
the oyster, the clam ( Venus), the scallop-shell (Pecten), etc., were very
numerous, and some of very large size. Oysters especially seemed to
have reached their maximum development in the Tertiary. The Ostrea
1 American Journal of Science, III., vol. iv., p. 148.
486
CENOZOIC ERA AGE OF MAMMALS.
Georgiana (Fig. 806) was ten inches long and four wide ; the Ostrea
Caroliniensis was of equal size, but shorter and broader. A specimen of
the Ostrea Titan of California and Oregon now lies before us, which by
FIG. 808.
Fio. 812.
FIG. 810.
FIGS. 805-S12.-EocE>-K TERTIARY SHELLS: 805. Ostrea selteformis (after Meek). 806. Ostrea Georfii-
ana (after Meek). 807. Pceten nuperum (after Wailes). 803. Anomalocardia MississippiensiB (after
Conrad). 809. Umbrella planulata (after Wailes). 810. Turritella alveata (after Wailes). 811.
Volutalithes dumosa (after Wailes). 812. Volutalithes syinmetrica (after Wailes).
ANIMALS. 487
measurement is thirteen inches long, eight wide, and six thick (Fig. 813),
FIG. 819. FIG. 81T.
FIGS. 81S-S19.-CALiFOR*iA MIOCENE SHELLS (after Gabb) : 813. Ostrea Titan, x ? T . 814. Pecten Cer-
rocensis, x J. S15. Venus pertenuis. 816. Cardium Meekianum. 817. (Jancellana vetusta. 813.
Ficus pyriformis. 619. Ectdnorachnis Breweranus.
4:88
CENOZOIC ERA AGE OF MAMMALS.
and a specimen of JPecten Cerrocensis of California, nine inches across
(Fig. 814). Among univalves also nearly all the forms are familiar.
The illustrations are taken from the Eocene and Miocene. The Pliocene
shells are almost undistinguishable from living shells, except by the
practised eye. It seems useless to give them in an elementary work.
Insects. There are several interesting points connected with this
class which must not be omitted. We have usually found insects abun-
dant in connection with luxuriant vegetation. During the Miocene, phe-
nogamous vegetation was even more abundant than now ; there was also
extreme fullness of insect-life. All orders, even the highest, viz., Lepi-
doptera (butterflies Fig. 821) and Hymenoptera (bees, ants, etc.
Fig. 820), were represented.
In the Miocene of Europe, 1,550 species of insects have been found ;
and of these more than 900 species at CEningen in a stratum only a few
FIG. 820. FIG.
FIGS. 820, 821. INSECTS OF EUROPEAN MIOCENE : 820. a, Pod of Podogonlum Knorrii; Z>, Grass-leaf; c,
Formica lignitum ; d, Ulster coprolithorum. 821. Vanessa Pluto.
feet thick (Lyell). In places the stratum is black with the remains of
insects. The same stratum is also full of leaves of Dicotyls, of which
Heer has described 500 species. Mammalian remains and fishes are also
found in them.
It is interesting to inquire the conditions under which these strata
were formed and filled with these remains. On Lake Superior, at
Eagle Harbor, in the summer of 1844, we saw the white sands of the
beach blackened with the bodies of insects of many species cast ashore.
As many species were here collected in a few days, by Dr. J. L. Le Conte,
as could have been collected in as many months in any other place.
The insects seem to have flown over the surface of the lake; to have
been beaten down by winds and drowned, and then slowly carried
shoreward and accumulated in this harbor, and finally cast ashore by
winds and waves. Doubtless, at CEningen, in Miocene times, there was
an extensive lake surrounded by dense forests ; and the insects drowned
in its waters, and the leaves strewed by winds on its surface, were cast
ashore by its waves. Heer believes also that carbonic-acid emissions
ANIMALS. 489
helped to destroy, and deposits of carbonate of lime to preserve, the
insects.
Among the insects found at (Eningen, Switzerland, and Radoboj,
Croatia, are a great many ants (Fig. 820). In all Europe, there are
now about fifty species of ants. Heer found in the Miocene of CEnin-
gen and Radoboj more than 100 species. 1 And, what is very remark-
able, all of these are winged ants. Ants of the present day are male,
female, and neuter. The males are winged throughout life, and never
live in the nests, but soon perish. The females are also winged until
they are fertilized ; then they drop their wings and live in communi-
ties in a wingless condition ever afterward. The neuters are always
wingless, and therefore always live in nests or in communities. It is
probable that ants at first were only winged males and females, living
in the open air like other insects. The wingless condition and the neu-
tral condition are both connected with their peculiar social habits and
instincts, and have been gradually developed along with the develop-
ment of their habits and instincts. It is probable that all these remark-
able peculiarities, viz., the wingless condition, the neutral condition, the
wonderful instincts, and organized social habits, have been developed
together since the Miocene epoch.
In the fresh-water Miocene of Auvergne, France, there is a remark-
able stratum called indusial limestone, because it is largely composed
of the cast-off hollow cases (indusia) of the caddis-worm or larva of the
caddis-fly (Phryganea], cemented together by carbonate of lime. The
number of these cases is countless. The caddis-worm of the present
day forms for itself a hollow cylindrical case, of bits of stick or pieces
of shell, or sometimes of whole small shells, binding these together by
means of a kind of web. In this hollow cylinder it lives, only put-
ting out the head, and two or three first joints of the body to which the
feet are attached, in walking. When they complete their metamor-
phoses, they leave their shells. Fig. 824 is a recent caddis-worm with
its case of small shells stuck together ; Fig. 823 are indusia of the
Miocene caddis-worm ; and Fig. 822 is the limestone in place, a being
the indusial layer.
In Auvergne, in Miocene times, there existed a shallow lake, in
which carbonate of lime was depositing, as in many lakes of the present
day. In this lake lived myriads of caddis-worms, and their indusia ac-
cumulated for countless generations.
In the Tertiary strata, about the shores of the Baltic, and also in
Sicily, in Asia Minor, and several other localities, usually associated
with lignite, are found masses of amber. This substance is a fossil
resin of several species of Conifer, especially Pinites succinifer. It is
often quite transparent, and inclosed within may be seen, perfectly pre-
1 Pouchet, Popular Science MontUy, June, 18T3.
490
CEN T OZOIC ERA-AGE OF MAMMALS.
served, insects of many kinds. Over 800 species of insects, and frag-
ments of many species of plants, have been found thus inclosed. The
degree of preservation is marvelous ; even the most delicate parts, the
slender legs, the jointed antennae, and the gauzy wings, are perfect.
The manner in which these insects were entangled, inclosed, and pre-
served, may be easily observed even at the present day. The gum
issuing from Conifers is at first in the form of semi-liquid, transparent
tears. Flies, gnats, etc., alighting on these, stick fast, and by the run-
FIGS. 822-S24. 822. Indusial Limestone interstratified with Fresh-Water Marls. 828. A Portion (nat-
ural size) showing the Phryganea Cases. 824. Kecent Larva of a Phryganea, with its Case.
ning down of further exudations are enveloped and preserved forever.
The legs, both in the modern and the fossil resin, are often found
broken by the struggles of the insects to extricate themselves. The in-
sects of the Tertiary, like the plants, show a decided tropical character.
Fishes. The present relation between the three great orders of
Fishes Teleosts, Ganoids, and Placoids was first fairly established in
the Tertiary. Teleosts were first introduced in the Cretaceous, but
ANIMALS.
491
only in the Tertiary did they become very abundant. Ganoids, on the
contrary, became fewer in number ; they sank into their present subor-
dinate position. Among Placoids, the Hybodonts are gone, the Cestra-
cionts are few in number, but the Squalodonts reach their maximum
development, both in number and size. In the marine Tertiary of the
FIG. 829.
FIGS. 625-S29. TERTIAKT Fisms-Pta<50?* : 825. Lamna elegrans (after Atrassiz). 826. Notidanns
primisrenius (after Asrassiz). 827. Carcharorton augustidens (.after Gibbes). 823. Carcharodon
megalodon, x J (after Gibbes). 829. Clupea alta (after Leidy).
492
CENOZOIC ERA AGE OF MAMMALS.
Atlantic border, both Eocene and Miocene, sharks' teeth are found in
immense numbers, and of very great size. Some of the triangular
teeth of the Carcharodon megalodon (Fig. 828) are found six and a
half inches long and six inches broad at the base. The owners of such
teeth must have been fifty to seventy feet long. Some of the more com-
FIGS. 830 631. TERTIARY FISHES Placoids : 880. Rhombus minimus, Lower Eocene. 631. Lebias
cephalotes, Miocene.
mon forms of sharks' teeth of the American Tertiar} r , and Teleosts
from American and European Tertiary, are given above.
Reptiles. The age of Reptiles is past. The huge Enaliosaurs, Dino-
saurs, Mosasaurs, and Pterosaurs, are all extinct. Their class is now rep-
resented by Crocodiles, Turtles, Snakes, and Frogs, though their place
as rulers is supplied by Mammals and Birds. Five species of Snakes,
some of them eight feet long, and nine Crocodilians, have been found in
ANIMALS.
493
the Eocene of Wyoming, and several also in Europe. In the Miocene
of Europe, CEningen, a Salamandroid Amphibian was found four feet
long, and at first mistaken for the skeleton of a man. From this cir-
Pio. 832. Front Portion of the Skeleton of Andrias Scheuchzeri. a Giant Salamander from the Miocene
Tertiary of CEningen, in Switzerland, reduced in size.
cumstance it received its name, Andrias (Fig. 832). The Miocene of the
Himalayas furnishes a gigantic turtle ( Colossochelys Atlas), the cara-
pace of which was twelve feet long and eight feet wide, and seven feet
494 CENOZOIC ERA AGE OF MAMMALS.
high in the roof, and the whole animal was probably twenty feet long.
Over sixty species of Tertiary turtles, and eighteen or twenty species
of crocodiles, have been described from foreign countries (Dana).
The Crocodilians, the highest order of reptiles, first appeared in the
Triassic, but only in generalized forms Staff onolepis, JJelodon, etc.
which closely connected them with the Lizards. From this early form
Huxley has traced with consummate skill the gradual differentiation of
this order, in the position of the posterior nares, the structure of the
head and the form of the vertebral bodies, step by step through the
Jurassic, Cretaceous, to the Tertiary, where the type reached its per-
fection.
Birds. The class of Birds in the Cretaceous was represented only
by the reptilian birds and ordinary water birds. Now, in the Tertiary,
however, the reptilian birds vertebrated-tailed and socket-toothed
have disappeared. The bird-class is fairly differentiated from the rep-
tilian class, and the connecting links destroyed. Birds of all kinds now
appear land-birds as well as water-birds. In America, among land-
birds, woodpeckers, owls, eagles, etc., have been discovered and de-
scribed by Marsh. The number of species found in Europe is much
greater than in America. The Miocene beds of Central France alone
have, according to Milne-Edwards, afforded seventy species. The Mio-
cene birds, like the plants and insects, show a decided tropical charac-
ter. " Parrots and Trogons inhabited the woods ; Swallows built, in
the fissures of the rocks, nests in all probability like those now found
in certain parts of Asia and the Indian Archipelago ; a Secretary-bird,
nearly allied to that of the Cape of Good Hope, sought in the plains the
serpents and reptiles which at that time, as now, must have furnished
its nourishment. Large Adjutants, Cranes, Flamingoes, Palasolodi (birds
of curious forms intermediate between Flamingoes and ordinary Grallas),
and Ibises, frequented the margins of the water where insect-larvae and
mollusks abounded. Pelicans floated on the lakes ; and, lastly, Sand-
grouse and numerous Gallinaceous birds assisted in giving to this or-
nithological population a strange physiognomy which recalls to mind
the descriptions given by Livingstone of certain lakes in Southern
Africa."
Recently a toothed bird has been found in the London clay (Eocene),
and named by O^en Odontopteryx (Fig. 833). But this is not a true
socket-toothed bird. The so-called teeth are only dentations of the
bony edge of the bill.
During the present year (1876) Cope has published the discovery of
a gigantic bird from the lowest Eocene of the San Juan basin. The
Diatryma gigantea, according to Cope, combines the characters of
the Cursores (ostrich family) with those of the extinct Gastornis of the
Paris basin (p. 496). Judging from its foot it was double the size of
ANIMALS. 495
an ostrich. This is the first example of extinct Cursores found in North
America (Cope).
FIG. 833. Skull of Odontopteryx toliapicus, restored (after Owen).
Mammals General Remarks. One of the most noteworthy facts
connected with the first mammals is the apparent suddenness of their
appearance in great numbers. We have already seen small marsupials
quite abundant in the Mesozoic, but no trace of true mammals. In
fact, the existence of these would seem to be incompatible with the
reign of the huge reptiles. But, with the opening of the Eocene, the
earth seems to swarm with mammals. And this is true not only in
Europe, where the unconformity of strata indicates a lost interval at
this point of the history, but also on the Western Plains and Rocky
Mountain region, where the Cretaceous seems to graduate insensibly
into the Tertiary. Upon any theory of evolution this can be accounted
for only by supposing the period between the Cretaceous and Tertiary
to have been one of very great rapidity of change of organic forms
this rapidity of change being the result partly of the pressure of
changed climate, and partly of migration of species and the consequent
struggle for life between different geographical faunae.
True placental mammals not only appear suddenly and in great
numbers, but of nearly all orders, even the highest except man, viz.,
monkeys. These, however, are not typical monkeys, but lemurs, which
may be regarded as a generalized form, connecting monkeys with other
orders. In the oldest Eocene beds (Wahsatch beds of the Green River
and San Juan basins), Cope finds eighty-seven species of vertebrates,
two-thirds of which are mammals. In the Fort Bridger beds of the
Green River basin (Middle Eocene), Marsh finds 150 species of verte-
brates, of which the larger number are mammals, some Herbivora, some
Carnivora, and some Lemurine monkeys. The same species do not
continue through the Tertiary. On the contrary, the mammalian fauna
changes completely several times in the course of that period.
One general characteristic of the early mammalian fauna is the pre-
dominance of Herbivora. Especially is this true of the Cuvierian order
Pachyderms, an order which now includes such diverse forms as ele-
496 CENOZOIC ERA AGE OF MAMMALS.
phant, rhinoceros, hippopotamus, tapir, hog, horse ; and still more
especially is this true of tapir-like Pachyderms. But there is much
reason to believe that the very first Tertiary mammals were far more
generalized in structure than any family of mammals now living.
The Tertiary mammals are of so great interest from the evolution
point of view, that we must dwell upon them somewhat in detail. But
FIG. 834. Tapirus Indicus.
it seems impossible to present selections from the immense mass of
material at hand in an interesting manner, except by taking a few clas-
sic localities from different epochs and different countries, and briefly
describing what has been found in each. We will commence with
some foreign localities, because these were first discovered :
1. Eocene Basin Of Paris. This basin has been made celebrated
by the immortal labors of Cuvier. The discovery in the early portion
of the present century of the rich treasures imbedded in the strata
of this basin, and the consummate skill with which they were worked
up by Cuvier, gave an incredible impulse to geology. Fifty species
of mammals, of which forty species were tapir-like; ten species of
birds, among which one, the Gastornis, was a huge wader as large as an
ostrich ; besides reptiles, fishes, and shells in abundance, were discovered.
In Eocene times the Paris basin seems to have been an estuary full
of shells and fishes, etc., into which the bodies of birds and mammals
were drifted. Among the many remarkable mammals we will select
two as types, viz., the Palceothere and the AnoplotTiere.
The Palseothere, like the Rhinoceros and like some of the earlier
representatives of the horse family, had three hoofed toes on all the
feet. It is usually supposed to have had also the general form and the
short flexible snout of a tapir, 1 and it is with this family that Cuvier
1 The tapir has three toes on the hind-foot, and four on the fore-foot, but the outer
one is small and not functional.
ANIMALS. 497-
supposed it has its nearest alliance. The figure below is Cuvier's resto-
ration, and until recently subsequent discoveries seemed to confirm its
FIG. 835. Restoration of Pateotheriuin magnum (after Owen).
general truthfulness. 1 In 1874, however, the discovery of a complete
skeleton showed that the restoration of Cuvier is far from correct, and
FIG. 836. Palaeotherium magnum (recently-discovered skeleton).
that the neck and limbs were much longer than had been supposed. In
1 Owen, "Paleontology," p. 365.
32
498 CENOZOIC ERA AGE OF MAMMALS.
general form it seems to have been more like the horse family than the
tapirs.
The Anoplothere was a slender and graceful animal without snout,
and possessing only two toes, like ruminants. Most of its characters,
FIG. 637. Anoplotherium commune, restored.
however, allied it to the tapirs. It was, therefore, a remarkable con-
necting link between the tapirs and ruminants.
2. Siwalik Hills, India Miocene. Near the base of the Himalayas
occurs a range of hills which are composed
of fresh-water Miocene strata. They are
jf^^. Hfifl^k extremely rich in vertebrate and especially
^jSgJfej^sji BSk i n mammalian remains, which have been
^BlUH^A thoroughly studied by Falconer. More
AtfMttttdH Wgk than forty species of mammals are de-
^^HH^^H^ scribed from this locality. They are of
{& great variety of forms, both Carnivora and
\.J Herbivora, but the latter are most abun-
yL dant. Among these, perhaps the two
^^ most remarkable are Dinotherium and
FIG. 838. Head of Dinotherinm gigan-
The Dinothere has been found also in
the European Miocene. It was a huge animal, with a skull three feet
long, to which was attached a proboscis. The lower jaw was bent
downward, and carried two long, tusk -like teeth, projecting also down-
ward. The whole height of the head, from the points of these lower
teeth to the top of the cranium, was five feet.
Recently a perfect pelvis has been found, showing the great mas-
siveness of these bones, and showing also, in these huge animals, the
existence of marsupial bones. 1 This strange animal combined, in the
structure of its head, the characters of Elephant, Hippopotamus, Tapir,
and Dugong; but it also had affinities with marsupials. It was the
earliest of Proboscidians.
1 American Journal of Science, II., vol. xxxviii., p. 427.
ANIMALS. 499
The Sivathere was a four-horned antelope, of elephantine size and
some elephantine characters. The four-horned antelope of the present
day lives in the same locality, but is a comparatively small animal, with
two short conical horns from the front part of the frontal bone, and two
somewhat longer ones in the usual place on the back part of the same
bone. The Sivathere, on the other hand, was of elephantine height,
though of slenderer form, with two short conical horns in front, and two
large, palmately branching ones behind. The form of the nose-bones
suggests the existence of a snout. The feet and legs were clearly those
. Head of a Sivatherium giganteum, greatly reduced.
of a Ruminant. . It seems to have combined the characters of a Rumi-
nant and a Pachyderm. The JZramathere was a. similar animal, of
equally gigantic size, found in strata of the same age.
In the same locality were found also three species of Mastodons,
seven species of Elephants, one of them E. ganesu, remarkable for the
prodigious length and size of its tusks ; three species of the Horse fam-
ily ; five species of Rhinoceros ; four to seven species of Hippopotamus,
and three species of hog ; also, Anoplotheres, Camels, Camelopards,
Oxen, Sheep, Antelope, Musk-ox, Monkeys, etc ; also, many Reptiles,
among which were narrow-nosed Crocodiles, like the Gavials now liv-
ing in the Ganges, and the huge Turtle, Colossochelys, already men-
tioned (p. 493).
In the Miocene and Pliocene of Europe are first found remains of
that most destructive of carnivores, the sabre-toothed tiger Machai-
500
CENOZOIC ERA AGE OF MAMMALS.
rodus (Fig. 840). In the Miocene of Europe, also, the first true Mon-
keys were introduced (Flower).
Perhaps it is well to call attention now to the fact that, while the
tapir-like Pachyderms predominate in the Eocene, the huge forms, e. g.,
FIG. 840. A, Skull of Machairodus cultridens, without the lower }aw, reduced in size ; , Canine Tooth
of the same, one-half the natural size. Pliocene, France.
Rhinoceros, Hippopotamus, and Proboscidians, were first introduced
and immediately became abundant in the Miocene.
American Localities. 3. Marine Eocene of Alabama. We select
this as an example of American marine Eocene.
At Claiborne, Alabama, according to Lyell, there
occur no less than 400 species of shells, besides
many JEchinoderms, and abundance of sharks'
teeth. But the most remarkable remains found
there are those of an extinct whale Zeuglodon
cetoides so called from the yoke-like form of
the double-fanged molar teeth, which were six
inches in length (Fig. 841). The skull was long
and pointed (Fig. 842), and set with the double-
fanged teeth behind and conical in front. The
vertebrae, which are in such abundance that they
are used for making fences and even burned by
farmers to rid the fields of them, are, some of
them, eighteen inches long and twelve inches in
diameter (Dana), and the vertebral column has
FIG. 841.-Tooth of a Zeuglo- be6n f Und in P kC6 "^ S6Vent y feet lon S
don cetoides, x f (Lyell). The animal must have been more than
ANIMALS. 501
seventy feet long, and the remains of at least forty individuals have
been found (Lyell).
This animal is peculiarly interesting as the first appearance of the
very distinct order Cetacea. No intermediate links have yet been
found connecting this with other orders of mammals, or with the great
FIG. S42.-Skull of Zeuglodon hydrarchus,
reptiles. And yet, from their large size and marine habits, they are
more likely than land mammals to have been found, if they existed in
earlier or Cretaceous times.
The Atlantic and Gulf border strata are of course all marine, and
therefore contain very few land-animals. It is to the fresh-water ba-
sins of the interior that we must look for a full record of the mam-
A
FIG. 843. Vertebra and Tooth of Zeuglodon cetoides, reduced.
malian fauna of America in Tertiary times. These basins furnish the
fullest and most continuous record of the whole Tertiary which has ever
yet been found. It will be best to take them in the order of their age,
as we can thus best show the evidences, if any, of derivation of the
later from the earlier faunae.
4. Green-River Basin Wahsatch Beds Lower Eocene. About eigh-
ty-seven species of vertebrates have been found by Cope in the San
Juan basin, of which fifty-four are mammals, one bird (Diatryma\
twenty-four reptiles, and eight fishes. A large number of mammals
have also been found in beds of the same horizon in the Green River
basin. These beds have been shown by Marsh to be the equivalent of
the lowest Eocene of England and France, and therefore contain the
502
CEXOZOIC ERA AGE OF MAMMALS.
very earliest known true mammalian fauna. In both countries they are
characterized by the occurrence of the remains of animals of the genus
Coryphodon (peak -tooth), one of the most generalized forms of mammals
both in tooth-structure and in foot-structure yet known. They were
five-toed Ungulates, having the full number of foot-bones unmodified,
and a general structure connecting the more generalized forms of Her-
bivores, such as tapirs, with the more generalized Carnivores, such as
bears (Cope). The genus Coryphodon includes seven or eight Ameri-
FIG. 844. Coryphodon Hamatus (after Marsh) : A, Head, showing form of the brain,
foot; C, Fore-foot, x i.
J; .B, Hind-
Can species. The average size was about that of a tapir; some were
smaller, and some twice as large (Marsh). These generalized forms
have been put into a distinct family called Coryphodontidce by Marsh.
5. Green River Basin Bridger Beds Middle Eocene. From this
wonderful fresh-water deposit there have been described by Marsh,
Cope, and Leidy, 150 species of vertebrates, of which the larger number
are mammals. This shows a marvelous abundance of mammalian life
in this early Tertiary time. The most numerous of these are tapir-like
animals, such as JHyrachyus, Limnohyus (Palceosyops Fig. 846), etc. ;
ANIMALS.
503
but the most formidable are the Dinocerata^ discovered by Marsh, and
placed by him in a new order. The Dinoceras, the type of this family,
was an animal of elephantine size, and armed with both horns and
tusks. Of horns there were three pairs one pair of small ones far in
front on the nasal bones ; another pair of larger ones on the maxillary
FIG. 845. Dinoceras mirabilis, x | (after Marsh) : A, Skull ; , Hind-foot, x J ; C, Fore-foot, x J.
bones, immediately above the canines ; and a third and much larger pair
farther back on the parietals. Besides these formidable weapons, it
was furnished also with powerful pointed tusks eight inches long.
This order includes, according to Marsh, many species belonging to
the genera Dinoceras, Tinoceras, and Uintatherium.
Another extraordinary group of animals discovered by Marsh in the
504
CENOZOIC ERA AGE OP MAMMALS.
same beds has been placed by him in a new order (called Tillodontia).
These animals combine the head of a bear with the incisors of a Ro-
dent and the general characters of Ungulates. The order must be re-
FIG. 846. Limnohyus (Pateo?yops) (after Leidy).
garded, therefore, as a remarkable generalized type. The head and
brain of the Tillotherium are given in Fig. 847.
The first appearance of the horse family (Equidce) is in the Eocene.
First of all in the Lower Green River or Coryphodon beds appears the
FIG. 847. Skull and Brain of Tillotherium fodiens, + J (after Marsh).
Eohippus (earliest horse), a small animal no bigger than a fox, having
three toes on the hind-foot, and four perfect ones on the fore-foot, like the
tapir, and a rudimentary fifth toe ; then in Green River Bridger beds,
the Orohippus (mountain-horse), similar to the last in size, but wanting
the fifth toe.
ANIMALS. 505
Although the Herbivores predominated, there were many mammals
belonging to other orders. For example, there were species allied to
the Cat, Wolf, and Fox ; also, Bats, Squirrels, Moles, and Marsupials ;
also many Monkeys allied to the Lemurs, Marmosets, etc., but more
generalized than any living Lemur.
6. Mauvaises Terres of Nebraska White River Basin Miocene.
From this, the first discovered of the fresh-water basins of the West,
have been collected by Hayden, and described by Leidy, at least
forty different species of mammals, among which twenty-five are Ungu-
lates, eight Carnivores, and most of the remainder Rodents. All of the
species, and many of the families, are entirely different from those
found in the preceding epoch. Although the tapir-like animals still
prevail, the deer, camel, and horse family are also abundant, as seen in
the following schedule :
f Hyena. ]
I lT r rt |f
Panther. J
Rhinoceros family.
Brontotheridae.
Tapir-like animals.
Deer family.
Camel "
Horse "
Rodents.
Turtles.
Among the most remarkable ungulates of this time were the Bron-
totheridce. This family, according to Marsh, includes the Brontotherium,
Menodus (Titanotherium), and several other genera. They were ani-
mals of elephantine size, and armed with at least two horns on the
Carnivores J - Allies.
FIG. 843. Skull of Brontotherium Ingens.
maxillaries. Their nearest allies were the Rhinoceros and the Tapir,
but they had affinities also with the Dinocerata of the Eocene.
The Oreodon is another very remarkable animal, intermediate be-
tween the hog, the deer, and the camel, which at this time inhabited
506
CEXOZOIC ERA AGE OF MAMilALS.
the whole continent from Nebraska to Oregon. A head of one is
shown below.
Rhinoceros.
Elephant.
Mastodon.
Three of the Camel family.
Five of the Horse "
Oreodon.
Deer.
Fox.
Wolf.
Tiger.
Beaver.
Porcupine.
FIG. 649. Oreodon major, x J (after Leidy).
7. Mauvaises Terres Niobrara Basin Pliocene. Nearly in the
same locality as the last, but extending much farther south, occur lake-
deposits of the Pliocene epoch full of mammalian remains ; but these
mammals, though occurring in the same locality, belong to species
entirely different from those of the Miocene. Among the Ungulates
there is a Rhinoceros as large as the Indian
species; an Elephant (E. Americanus) the
same as lived in Quaternary times, as large
as any living ; a Mastodon, but much smaller
than the great mastodon of later times ; and
a large number of species of the Horse and
Camel families, besides other families of Un-
gulates, Carnivores, Rodents, etc., as shown
in the accompanying schedule. Among the
Pliocene horses was one (Protohippus par-
vulus), discovered by Marsh in the Upper
Pliocene of Nebraska, only two feet high. "The large number of
camels and horses gives a decided Oriental character to the fauna "
(Dana). Both the horse and the camel seem to have originated on this,
instead of on the Eastern, continent ; at least the several steps of their
derivation are more abundant and distinct here.
Some General Observations on the Tertiary Mammalian Fauna. 1.
Lartet has shown that the brain-cavity of some of the Tertiary ani-
mals is decidedly smaller relatively than that of their living congeners.
Marsh has, moreover, traced a gradual increase in the relative size of thq
brain from the earliest Eocene to the present time. The brain of the
Coryphodon, Lower Eocene, is not only extremely small in proportion
to the size of the animal, but the higher portion of the brain the cere-
bral lobes is very small in proportion to the cerebellum. The brain
of the Middle Eocene Dinoceras is only about one-eighth the size of a
living Rhinoceros of equal bulk. The brain of the Miocene Brontothere is
larger than that of the Eocene Dinoceras, but much smaller than that of
ANIMALS. 507
the Pliocene Mastodon of nearly the same size. Through the whole line
FIG. 852.
FIGS. 850-852. BRAINS OF CORYPHODON, DINOCERAS, AUD BRONTOTHERTITM, COMPARED (after Marsh) :
850. Corvphodrm. skull and Brain, x i. 851. Dinoceras, Skull and Brain, x . 852. Brontothen-
um, Skull and Brain, x T \.
508
CENOZOIC ERA AGE OF MAMMALS.
of ancestry of the horse the gradually-increasing size of the brain may
be traced step by step.
2. The animals of the Tertiary are nearly all connecting types. As
the Ungulates are the most largely represented, we can best illustrate
the gradual differentiation of modern types in this order.
Cuvier divided all Ungulates (hoofed animals) into two orders, viz.,
Pachyderms and Ruminants. The Pachyderms have always been
acknowledged to be a heterogeneous order, but the Ruminants have
been regarded as one of the most distinct of all mammalian orders.
Their frontal horns in pairs, their hoofs in pairs, the absence of upper
front-teeth, their complex stomachs, and habit of rumination, differ-
entiated them widely from all other animals. But Prof. Owen showed
that this distinction, so clear in zoology, was untenable in paleontology.
He found, in studying extinct Ungulates, that another distinction, viz.,
the foot-structure, was more fundamental and persistent. He therefore
divided all Ungulates into Perissodactyls (odd-toed) and Artiodactyls
(even-toed). A Perissodactyl may have five toes, as in the Corypho-
don and the Elephant ; or three toes, as in the Palseothere, the Rhi-
noceros, and the Tapir; or one toe, as in the Horse. The Artiodactyls
always have their toes in pairs : there may be only two toes, as in
Anoplothere and in Ruminants ; or four, as in the Hog and the Hippo-
potamus. Owen, indeed, made the Elephant, Mastodon, etc., a distinct
CORYPHOOONTIDAE
PRIMAL UNGULATE
FIG. 853. Diagram illustrating the Differentiatiro of the Different Families of Ungulates.
order, under the name of Proboscidians, but these are probably best
regarded as a very distinct offshoot or sub-order of the Perissodactyls.
Now, in earliest Tertiary times the Perissodactyls and Artiodac-
tyls already had diverged from a common stock, probably something
like the Coryphodontidao, although these were doubtless more nearly
ANIMALS. 509
allied to the Perissodactyls. Each of the primary branches then
divided and again divided, until the extreme branch in one direction
became the Horse, and the extreme branch in the other direction the
Ox. In the tree above we have attempted, in a general way, to repre-
sent the differentiation of the several orders of Ungulates. The Cu-
vierian orders, Pachyderms and Ruminants, are indicated by a vinculum.
It is seen at a glance why, by studying living animals alone, the Rumi-
nants seem so distinct.
Genesis of the Horse. In conclusion, it will be interesting and in-
structive to run out one of these branches and show in more detail the
genesis of one of the extreme forms. For this purpose we select the
Horse, because it has been somewhat accurately traced by Huxley and
by Marsh. About thirty-five or forty species of this family, ranging
from the earliest Eocene to the Quaternary, are known in the United
States. The steps of evolution may therefore be clearly traced.
In the lowest part of the Eocene basin ( Coryphodon beds) of Green
River is found the earliest known animal which is clearly referable to
the horse family, viz., the recently-described Eohippus of Marsh. This
animal had three toes on the hind-foot and four perfect, serviceable toes
on the fore-foot; but, in addition, on the fore-foot an imperfect fifth
metacarpal (splint), and possibly a corresponding rudimentary fifth toe
(the thumb), like a dew-claw. Also, the two bones of the leg and fore-
arm were yet entirely distinct. This animal was no larger than a fox.
Next, in the Middle Eocene (Bridger beds), came the Orohippus of
Marsh, an animal of similar size, and having similar structure, except
that the rudimentary thumb or dew-claw is dropped, leaving only four
toes on the fore-foot. Next came, in the Lower Miocene, the Mesohip-
pus, in which the fourth toe has become a rudimentary and useless splint.
Next came, still in the Miocene, the Miohippus of the United States
and nearly-allied Anchithere of Europe, more horse-like than the pre-
ceding. The rudimentary fourth splint is now almost gone, and the
middle hoof has become larger ; nevertheless, the two side-hoofs are
still serviceable. The two bones of the leg have also become united,
though still quite distinct. This animal was about the size of a sheep.
Next came, in the Upper Miocene and Lower Pliocene, the Protohip-
pus of the United States and allied Hipparion of Europe, an animal
still more horse-like than the preceding, both in structure and size.
Every remnant of the fourth splint is now gone ; the middle hoof has
become still larger, and the two side-hoofs smaller and shorter, and no
longer serviceable, except in marshy ground. It was about the size of
the ass. Next came, in the Pliocene, the Pliohippus, almost a complete
horse. The hoofs are reduced to one, but the splints of the two side-
toes' remain to attest the line of descent. It differs from the true horse
in the skull, shape of the hoof, the less length of the molars, and some
510 CEXOZOIC EKA AGE OF MAMMALS.
other less important details. Last comes, in the Quaternary, the mod-
a b c d e f
Pliohippus: Pliocene.
Protohippns : Lower Pliocene.
Miohippus: Miocene.
Mesohippus: Lower Miocene.
Orohippus: Eocene.
FIG. R54. Diagram illustrating Gradual Changes in the Horse Family. Throughout a is fore-foot ;
hind-foot : c, fore-arm ; rf. shank ; e, molar on side-view ; / and g, grinding surface of upper at
lower molars. (Aafter Marsh.)
GENERAL OBSERVATIONS ON THE TERTIARY PERIOD. 5H
ern horse Equus, The hoof becomes rounder, the splint-bones shorter,
the molars longer, the second bone of the leg more rudimentary, and
the evolutionary change is complete.
Similar gradual changes, becoming more and more horse-like, may
be traced in the shape of the head and neck, and especially in the grad-
ually-increasing length and complexity of structure of the grinding-
teeth. All these changes are shown in Fig. 854, for which we are in-
debted to the kindness of Prof. Marsh. The Eohippus is omitted, as
no figures of this have yet been published.
There can be no doubt that if we could trace the line of descent still
farther back we would find a perfect five-toed ancestor. From this
normal number of five, the toes have been successively dropped, ac-
cording to a regular law : first, the thumb, No. 1 ; then the little finger,
No. 5 ; then the index, No. 2 ; and last the ring-finger, No. 4; and the
middle finger, No. 3, only remains. Nos. 2 and 4 are, however, usually
dropped together.
A somewhat similar line of descent has been traced by Cope from
the Miocene Poebrotherium through the Pliocene Procamelus to the
modern camel. It is remarkable that both the horse and the camel seem
to have originated on this continent.
From the earliest and most generalized types, therefore, to the present
specialized types, the principal changes have been, first, from planti-
grade to digitigrade ; second, from short-footed digitigrade to long-footed
digitigrade, i. e., increasing elevation of the heel / third, from five toes
to one toe in the Horse, or two toes in Ruminants ; and, fourth, from
simple omnivorous molars to the complex herbivorous millstones of the
Horse and the Ox.
The change from plantigrade to digitigrade, with increasing eleva-
tion of the heel, when taken in connection with increasing size of the
brain, and therefore presumably with increasing brain-power, shows a
gradual improvement of structure adapted for speed and activity, and a
pari-passu increase of nervous and muscular energy, necessary to work
the improved structure.
3. Not only does the mammalian fauna of the Miocene differ com-
pletely from that of the Eocene, which precedes, and from the Pliocene,
which succeeds it, but there seem to have been at least two distinct
Eocene and two distinct Miocene faunae. Thus there have been many
complete changes in the mammalian fauna in Tertiary times.
General Observations on the Tertiary Period.
We have already seen (p. 452) that during Cretaceous times a wide
sea, occupying the position of the Western Plains and Plateau region,
divided America into two continents, an Eastern and a Western. We
have also seen (p. 475) that at the end of the Cretaceous this sea was
512 CENOZOIC ERA AGE OF MAMMALS.
obliterated by continental upheaval, and the continent became one.
During the Eocene, the eastern portion of the place formerly occu-
pied by this sea was probably dry land, but in the Plateau region
there were great fresh- water lakes, one north of the Uintah Moun-
tains, Green River basin, and one south of the same, and possibly one
in Oregon. There were possibly others yet unknown. At the end of
the Eocene, there was a rise in the Plateau region, which drained the
Eocene lakes, and a corresponding depression in the region of the Plains,
not sufficient to form a sea again, but sufficient to form great Miocene
lakes there. At the end of the Miocene occurred the greatest event of
the Tertiary period, one of the greatest in the history of the American
Continent. At that time the sea-bottom off the then Pacific coast was
crushed together into the most complicated folds (pp. 242, 256), and
swollen up into the Coast Chain, and at the same time fissures were
formed in the Cascade range, with the outpouring of the great lava-
flood of the Northwest, already spoken of (p. 259). Coincidently with
this there was a further letting down of the region of the Plains, and
an extension of the Pliocene lakes southward almost to the Gulf (at-
tended probably with a further rise of the Plateau region). At the
end of the Tertiary, these lakes were in their turn obliterated by the
further upheaval of the continent, which inaugurated the Quaternary.
While this was going on in the western portion of the continent, on
the southeastern and southern border the continent gained, by gradual
rise, nearly all the area shaded as Tertiary. In this direction the con-
tinent was finished with the exception of the larger portion of Florida
and the sea-islands and alluvial flats 1 about the shores of the Southern
Atlantic and Gulf States. These belong to a still later period.
Thus we see that from the end of the Cretaceous to the end of the
Tertiary there was a gradual upheaval of the whole western half of the
continent, by which the axis, or lowest line, of the great interior con-
tinental basin was transferred more and more eastward to its present
position, the Mississippi River. Probably correlative with this up-
heaval of the western half of the continent was the down-sinking of
the mid-Pacific bottom, indicated by coral-reefs (p. 144). Also as a
consequence of the same upheaval the erosive power of the rivers was
greatly increased, and thus were formed those deep canons in the
regions (New Mexico, Colorado, and Arizona) where the elevation was
greatest. Thus the down-sinking of the mid-Pacific bottom, the bodily
upheaval of the Pacific side of the continent, and the down-cutting of
the river-channels into those wonderful canons, are closely connected
with each other.
J In some places about the shores of the Gulf, for reasons which will be explained here-
after, the Quaternary deposits are considerably elevated above the sea-level
QUATERNARY PERIOD. 513
SECTION 2. QUATERNARY PERIOD.
Characteristics. The chief characteristic of the Quaternary is that
it is a period of great and widely-extended oscillations of the earth's
crust in high-latitude regions, attended with great changes of climate.
During this period the class of mammals seem to have culminated.
During this period also man seems to have appeared on the scene. We
do not call it the age of Man, however, because he had not yet estab-
lished his reign. His appearance here is rather in accordance with the
law of anticipation. As already stated, the invertebrate fauna was
almost identical with that still living, but the mammalian fauna was
almost wholly peculiar, differing both from the Tertiary which preceded
and from the present which followed it.
Subdivisions. The Quaternary period is divided into three epochs,
viz. : I. Glacial; II. Champlain; III. Terrace. These epochs are char-
acterized by the direction of the crust-movement, and of the change of
climate. The Glacial epoch is characterized by an upward movement
of the crust in high-latitude regions, until the continents in those
regions stood 1,000 to 2,000 feet above their present height. Large
portions of these regions seem to have been sheeted with ice, and an
arctic rigor of climate extended far into now temperate regions.
The Champlain epoch, on the contrary, is characterized by a down-
ward motion of land-surfaces in the same region until the sea stood
relatively 500 to 1,000 feet above its present level, covering, of course,
much that is now land-surface. It was, therefore, a period of inland
seas. Coincident with this sinking was a moderation of climate, and a
melting of the ice. It was, therefore, also a period of great lakes and
flooded rivers. Over the inland seas and great lakes, loosened masses
of ice floated. It was, therefore, also a period of icebergs.
The Terrace epoch is characterized by the gradual rising again to
the present condition of the continents, and the establishment of the
present condition of climate. It is, in fact, a transition to the pres-
ent era.
Although we call these divisions epochs, yet we must not suppose
that they are equal in length to the epochs of earlier times. As we
approach the present time, and the number and interest of events in-
crease, our divisions of time become shorter and shorter.
It is so difficult to separate these epochs sharply from each other in
all countries, and to synchronize them, that it seems best to treat of the
whole Quaternary period, taking up the epochs successively first in
Eastern North America, as the type or term of comparison, then of the
same on the Pacific coast, and last of the same in Europe.
33
514
CEXOZOIC ERA AGE OF MAMMALS.
Quaternary Period in Eastern North America.
I. Glacial Epoch.
The Materials Drift. Strewed all over the northern part of North
America, over hill and dale, over mountain and valley, covering alike,
in places, all the country rock, Archaean, Palaeozoic, Mesozoic, and Ter-
tiary, to a depth of 30 to 300 feet, and thus largely concealing them
from view, is found a peculiar surface soil or deposit. It consists of a
heterogeneous mixture of clay, sand, gravel, pebbles, subangular stones
of all sizes, unsorted, unstratified, unfossiliferous. The lowest part,
lying in immediate contact with the subjacent country rock, is often a
stiff clay inclosing subangular stones i. e., rock-fragments with the
corners and edges rubbed off. This we will call the " Stony clay " or
^bowlder-clay." It is precisely like the moraine prof onde of a glacier
(p. 53). Lying on the surface of this drift-soil are found many bowl-
FIG. 855. Subangular Stone (after Geikie).
ders of all sizes, often of huge dimensions, sometimes even 100 tons or
more. The imbedded subangular stones are usually marked with
parallel scratches (Fig. 855),
and the large surface-bowlders
are usually angular and un-
scratched. The depth of this
material is greatest in the val-
leys and least on hill and moun-
Fio. 856. Section on Rush Creek, near Mono Lake, tain tops.
It is difficult, nay, impossi-
ble, to give a description of this peculiar deposit, which will apply in
all cases. Sometimes scattered about irregularly through the unstrati-
GLACIAL EPOCH.
515
fied mass are portions which are roughly and irregularly stratified, the
laminaa being often contorted in the most fantastic way (Figs. 856-
858). Sometimes the true stony clay is covered with a more reg-
ularly stratified material, consisting of sand and gravel, apparently sub-
FIG. 857. Section of Orange Sand, Mississippi (after HUgard).
sequently deposited from water. This is particularly the case in the
basin of the Mississippi, as, e. g., in Ohio, Illinois, and Iowa. It is prob-
able, however, that this belongs to the next epoch, Champlain.
We have said that the deposit is peculiar. Nothing resembling it
is found anywhere in tropical or low-latitude countries. In the South-
Fio. 853. Section of Orange Sand, Mississippi (after Hilgard).
era Atlantic States, for instance, the soil is mostly either the insoluble
residue of rocks decomposed in situ, or else consists of neatly-stratified
sands and clays.
Drift-material is not usually represented on geological maps, since
it covers all kinds of country rock ; or else the colors representing the
FIG. 859. Outcropping Eroded Country Eock overlaid by Drift.
various kinds and ages of country rock are simply dotted to indicate the
presence of this surface-material. In sections, of course, it is easily
represented, as in Fig. 859.
The Bowlders. The most casual examination of the great bowlders
516 CENOZOIC ERA AGE OF MAMMALS.
is sufficient in many cases to show that they do not belong to the coun-
try where they now lie, for they are of entirely different material from
the country rock. For example, blocks of granite are found where
there is no granite within many miles, blocks of sandstone on a country
rock of limestone, or vice versa. In many cases it is easy to find the
parent ledge from which these great fragments were torn, and thus to
trace the direction of their transportation. From many observations
of this kind it has been determined that in New England the bowlders
have come usually from the northwest, in Ohio from the north, and in
Iowa from the northeast. In other words, from the highlands of
Canada and a ridge running thence northwestward (Archaean area), the
general direction of travel has been southeast, south, and southwest.
The distance carried may be only a few miles, or may be ten, fifty, one
hundred, or even several hundred miles. In many cases they must have
been carried across valleys 1,000 or 2,000 feet deep, and lodged high
up on the mountain beyond. In many portions of New England and
about Lake Superior the number of fragments, small and great, is so
large as seriously to encumber the soil. Not only the large bowlders,
however, but the whole mass of the material we have been describing,
seem to have been shifted to a greater or less extent. It is for this
reason that the material has been called Drift.
Surface-Rock underlying Drift On removing the drift-covering
the underlying rock is every where polished and planed and scored with
parallel lines, and moutonn'e, precisely like rocks over which a glacier
has passed. We will, therefore, call this surface-appearance " glacia-
tion." We reproduce here from page 52 the roches moutonn'ees of an
ancient glacier in Colorado (Fig. 860). Examinations of the scorings
show that they often pass straight up inclines for considerable distances,
i. e., up one side of a hill, over the top, and down the other side. Their
direction is uninfluenced by smaller inequalities of surface, though they
are thus influenced by the great valleys and mountain-ridges.
The general direction of the scorings corresponds with that of
transportation of the bowlders, showing that they are due to the same
cause. Perfect soil on perfect sound rock always shows that the soil
has not been formed in situ, but has been shifted: the polishing, plan-
ing, scoring, etc., of the rock show that the agent of the shifting has
been ice.
Extent. The general extent of these more conspicuous and char-
acteristic phenomena, viz., the glaciation, the stony clay, and the great
bowlders, is down to about 40 north latitude. The line of southern
limit cuts the Atlantic coast about 40, near New York ; it then bends
a little southward to 38 in Southern Ohio, and then turns a little north-
ward again as it passes west, and finally southward again, along the
Rocky Mountains. Stretching southward of this general limit are
THEORY OF THE ORIGIN OF THE DRIFT.
517
local extensions, usually down valleys. Beyond this the characteristic
phenomena mentioned above are not found, but in the valley of the
Mississippi, and on each side to a considerable distance, a superficial
gravel and pebble deposit, containing northern bowlders called by
FIG. 860. Roches Moutonnees of an Ancient Glacier, Colorado (after Hayden).
Prof. Hilgard " Orange Sand " extends to the shores of the Gulf.
This deposit, however, probably belongs to the early Champlain epoch.
Marine Deposits. Along the northern Atlantic coasts we find no
marine deposits of this time, for the obvious reason that the continent,
in that part, was then more elevated than now ; whatever marine de-
posits were then formed are now covered by the sea. But along the
Southern Atlantic States, coast-deposits of the ordinary kind seem to
have been made continuously, and are still exposed. This shows that
the peculiar and violent phenomena of the North did not reach so far,
and therefore the epochs of the Quarternary period are undistinguish-
able there. The formation of the Peninsula and Keys of Florida,
already explained (p. 149), probably belongs to the Quaternary and the
present.
Theory of the Origin of the Drift.
When the phenomena of the Drift were first observed, they were
supposed to indicate the agency of powerful currents, such as could be
produced only by the most violent and instantaneous convulsions. A
sudden upheaval of the ocean-bed in northern regions was supposed
to have precipitated the sea upon the land, as a huge wave of trans-
518 CENOZOIC ERA AGE OF MAMMALS.
I
lation, which swept from north toward the south, carrying death and
ruin in its course. Hence the deposit was often called Diluvium
(deluge-deposit). Now, however, they are universally ascribed to the
agency of ice acting slowly through great periods of time. Hence the
name Glacial epoch.
As to the manner in which the ice acted, however, opinions have
been more or less divided, some attributing the phenomena to the
agency of land-ice glaciers others to that of drifting icebergs. Ac-
cording to the one, the land during this epoch was greatly raised and
covered with glaciers ; according to the other, the same area was sunk
several thousand feet and swept by drifting icebergs, carried south-
ward by currents, and dropping their load of earth and stones. The
one is called the glacier theory, the other the iceberg theory.
It is probable that both these agencies were at work, either at the
same time or consecutively ; but the decided tendency of science is
toward the recognition of glaciers as the principal agent during this
earliest epoch of the Quaternary. The more the phenomena are stud-
ied, and the more glaciers are studied, especially in polar regions, the
larger is the share attributed to this agency. We will not discuss this
question, but simply give the present condition of science on the
subject.
Statement of the most Probable View. The most probable view
for America, and also for other countries, is, that the Drift, or at least
the most characteristic phenomena of the Drift, viz., the glaciation, the
unsorted bowlder-clay, and in many cases also the great traveled
bowlders, are due to the action of glaciers. They are therefore a land-
deposit, and not a sub-aque.ous deposit. For general proof of this, let
any one study the phenomena of living glaciers, in the Alps and else-
where ; then let him study the appearances left by the recently dead
glaciers of the Sierra ; and then let him study the phenomena of the
Drift, especially the stony clay and the underlying glaciated surfaces.
It will be impossible for him to come to any other conclusion than that
the same agent has been at work in all these. In some cases, viz., in
the valley-extensions of the Drift area, still more conclusive evidence is
found in the existence of distinct terminal moraines.
Objections answered. Many objections have been brought against
this view, which may be compendiously stated as follows : 1. In glacial
regions, like Switzerland, the Himalayas, etc., the glaciers run in all
directions ; but the Drift was carried over wide areas, in a general direc-
tion. Such a general direction is easily accounted for by the action of
icebergs carried by marine currents. 2. The agent of the Drift seems
to have been often uninfluenced by the direction of valleys and ridges
even of considerable size ; thus, for instance, bowlders are carried
across valleys 500 or 1,000 feet deep, and lodged as high up on the
THEORY OF THE ORIGIN OF THE DRIFT. 519
mountain-slope on the other side. This is perfectly consistent with the
action of icebergs drifting over an uneven sea-bottom, but inconsistent
with our usual notions of glacial action. 3. The great distance carried,
sometimes one hundred miles or more, is precisely what we might
expect of icebergs, but difficult to reconcile with our usual notions of
glaciers. 4. Alpine glaciers will not move on a slope of less than 2
or 3, but such a slope, carried several hundred miles, would produce
an incredible elevation of land. A slope of 2| for 200 miles would
produce an elevation of nearly nine miles !
These were unanswerable objections so long as our ideas of glaciers
were confined to those of temperate climates ; but they all find their
complete answer in the phenomena of the polar ice-sheet. Greenland
is 1,200 miles long and 400 or 500 miles wide. This whole area of
over a half-million of square miles is covered 3,000 feet deep with
ice. This ice-mantle moves en masse seaward, moulding itself on
the surface inequalities of the country, and moulding that surface be-
neath itself, producing universal glaciation, and only separating into
distinct glaciers at its margin. In antarctic regions the general ice-
sheet is even still more extensive and thick. Now, it is to such an ice-
mantle that the Drift is to be ascribed, for it moves irrespective of
smaller valleys, in one general direction over great areas, to great dis-
tances, and over a slope of only 1 or even .
Probable Condition during Glacial Times in America. During
Glacial times the Archaean region of Canada seems to have been elevated
1,000 to 2,000 feet above its present level, and covered with 'a general
ice-mantle 3,000 feet to 6,000 feet thick. This ice-sheet moved with
slow glacier motion southeastward, southward, and southwestward, over
New England, New York, Ohio, Illinois, Iowa, etc., regardless of
smaller valleys, glaciating the whole surface, and gouging out lakes in
its course. Northward the ice-sheet probably extended to the poles ; it
was an extension of the polar ice-cap, but its southern limit was about
38 to 40 north latitude, except in the Rocky Mountain region, where,
favored by the elevation, it probably extended considerably farther
south. From its southern margin the ice-sheet stretched out icy fin-
gers, as separate glaciers, down some of the principal valleys. For
example : one great extension stretched southward as the Hudson River
glacier, and its bed may still be traced far out to sea. Another was
the Susquehanna glacier. Those along the eastern coast ran into the
sea and produced icebergs ; but westward over Ohio. Illinois, etc., where
the glaciers did not run into the sea, these separate glaciers must have
produced terminal moraines ; but these have been mostly washed away
by the floods of the Champlain epoch. Some evidences of them, how-
ever, have been observed. Along the eastern slopes of the Rocky
Mountains the evidences of these separate glaciers are very abundant,
520
CENOZOIC ERA AGE OF MAMMALS.
and their lateral and terminal moraines very distinct (Fig. 861). Some
evidences of glaciers have also been detected in the mountains of Vir-
ginia. 1
It is probable that in the valley of the Mississippi the northern ele-
vation extended even to the shores of the Gulf. Prof. Hilgard finds
the evidence of this in the Orange, sand which belongs to this epoch,
FIG. 861. Moraines of Grape Creek, Sangre del Cristo Mou
lo (after Stevenson).
or the beginning of the Champlain, and which indicates torrential cur-
rents, and must have been therefore deposited above sea-level, and yet
in the region of the Mississippi Delta is now several hundred (400) feet
below that level. The evidence is made still more conclusive by the
discovery above the Orange sand of a stump-layer, or old forest-ground,
also several hundred feet below present tide-level.
II. Champlain Epoch.
During the Glacial epoch, as just seen, the whole northern portion
of the continent was elevated 1,000 to 2,000 feet above the present con-
dition ; the polar ice-cap had advanced southward to 40 latitude, with
still farther southward projections favored by local conditions; and an
arctic rigor of climate prevailed over the United States even to the
shores of the Gulf. At the end of this epoch an opposite or downward
movement of land-surface over the same region commenced, and con-
1 American Journal of Science, vol. vi., p. 371 (Stevens).
CHAMPLAIN EPOCH. 521
tinued until a depression of 500 to 1,000 feet below the present level
was attained. This downward movement marks the beginning of the
Champlain epoch. As a necessary consequence, large portions of the
now land were submerged ; it was therefore a time of inland seas.
Another result, or at least a concomitant, was a moderation of the
climate, a melting of the glaciers and a retreat of the margin of the
ice-cap northward. It was therefore a time of flooded lakes and rivers.
Lastly, over these inland seas and great lakes loosened masses of ice
floated as icebergs. It was therefore preeminently a time of iceberg
action.
Evidences Of Subsidence. The evidences of the condition of things
described above are found in old sea-margins, old lake-margins, old
river-terraces, and old flood-plain deposits.
Sea-Margins. Old sea-margins, containing shells and other remains
of living species, are found all along the Northern Atlantic coast, be-
coming higher as we pass northward. In Southern New England the
highest beaches are 40 to 50 feet ; about Boston they are 75 to 100
feet ; in Maine they are 200 feet and upward ; on the Gulf of St.
Lawrence they are 470 feet ; in Labrador 500 feet. In arctic regions
they are in some places 1,000 feet (Dana). The beaches may be traced
up both sides of the St. Lawrence River, and thence around Lake Cham-
plain, where the highest is 393 above tide-level. 1 Upon the beaches
about Lake Champlain have been found abundance of marine shells,
and also the skeleton of a stranded ichale. Evidently there was here
a great inland sea connected with the ocean through the Gulf of St.
Lawrence ; and over this sea icebergs must have floated. This condi-
tion of things has given name to the epoch. In the subsequent reele-
vation of the continent, this salt lake (as it must have been at first)
was gradually rinsed out and freshened by river-water discharged
through the lake and into the St. Lawrence River, as already explained
on a previous page (p. 74).
Flooded Lakes. All the lakes in the region affected by drift show
unmistakable evidences of a far more extended and higher condition
of the waters than now exists. About all these lakes is found a
succession of terraces or old lake-margins. The highest of these marks
the highest water-level, and is the oldest ; the lower ones mark succes-
sive steps in the draining away or drying awav of the waters.
For example, about Lake Ontario successive margins are found up
to 500 feet above the present lake-level ; about Lake Erie, up to 250
feet ; about Lake Superior, up to 330 feet ; and similar margins are
found about Lakes Michigan and Huron. There can be no doubt that
at this time these lakes ran together to form an immense sheet of fresh
water covering the larger portion of Ohio, which according to New-
1 Dana, " Manual," p. 550.
522 CENOZOIC ERA AGE OF MAMMALS.
berry 1 drained southward into the Ohio and Mississippi Rivers, and
on which floated many icebergs loosened from the Canadian glaciers,
and dropping earth and bowlders over Ohio. Hilgard * thinks that the
bursting of this great lake over a barrier across Southern Ohio and Illi-
nois, discharging its waters southward, carried the Orange sand over
that region.
G. M. Dawson 3 finds abundant evidence of a prodigious lake or sea
in British America, extending from the Laurentian axis to the Rocky
Mountains (doubtless connected with the lake previously mentioned),
into which ran glaciers from the Laurentian axis on the one side, and
the Rocky Mountains on the other, forming icebergs which dropped
their debris over the whole area.
Both the elevation of the previous epoch and the subsidence of
this seem to have been greater along the axis of the continent, the val-
ley of the Mississi2)pi, than on the coasts. Hilgard finds evidence in
the Orange-sand deposit, and in the thickness of the subsequent Cham-
plain deposit, of an elevation of 450 feet above the present level, and
a depression of 450 feet (for this is the maximum elevation of the
Champlain deposit above the same level), or an oscillation of 900 feet,
in Louisiana. Farther north it is probably much greater.
River Terraces and Old Flood-Plain Deposits. Nearly all the rivers
in the eastern portion of the continent, over the Drift region, are bor-
dered with high terraces, which have been cut wholly out of an old
flood-plain deposit belonging to the Champlain epoch. In fact, these
rivers show first an elevation, then a depression, and finally a partial re-
elevation ; in other words, all the oscillations of the Quaternary period
are recorded by them.
An examination of the rivers north of the fortieth parallel shows: 1.
An old river-led far deeper and broader than the present ; 2. This deep
and broad river-bed is filled up, often several hundred feet deep, by old
river-deposit; 3. Into this old river-deposit the shrunken stream is
again cutting, but is still far above the bottom of the old river-bed.
This cutting into the old river-deposit produces bluffs and terraces on
each side. It is evident that the great river-bed was gouged out during
the Glacial epoch ; the filling up took place during the Champlain, and
the cutting and terracing during the Terrace epoch.
Fig. 862 is an ideal section across a river-bed in the Drift region, in
which b b is the old river-bed, scooped out during the epoch of eleva-
tion; the dotted line represents the highest level to which the old
river-deposit accumulated, and the shaded portion that part of such
1 Newberry, " Surface Geology."
8 American Journal of Science and Arts, December, 1871.
3 Quarterly Journal of the Geological Society, vol. xxxi., pp. 620, et seq., and " Geology
of the Forty-ninth Parallel," chaps, ix., x.
CHAMPLAIN EPOCH. 523
deposit which still remains. The upper terraces, t , are of course the
oldest, the lower ones being made as the shrunken stream cut deeper
and deeper.
These phenomena are shown in all the river-beds of the Drift region,
but especially by those of the Mississippi basin. Sometimes there is
FIG. 862. Ideal Section across a River-bed in Drift Region : b b 6, old river-bed ; R, the present river , 1 1,
upper or older terraces ; t' t', lower terraces.
only one terrace or bluff ; sometimes there are several, on each side.
The Connecticut River is a good example of the latter, the Mississippi
River of the former.
The Connecticut River is bordered on each side by a succession of
terraces rising one above and beyond the other, composed wholly of
old river-deposit. Beyond this, of course, is the country rock of Jura-
Trias sandstone, covered more or less with drift.
The Mississippi River is bordered on each side by its present flood-
plain deposit, or river-swamps. This, as already said (p. 23), extends
from the mouth of the Ohio River to the head of the delta, a distance of
800 miles, and has an average width of 20 miles. This, its present
flood-plain deposit, is limited on the eastern side by bluffs in some places
200 to 400 feet high, composed of Tertiary strata, capped with an old
river-silt, or Loess, 50 to 70 feet thick, and this, again, covered by a
yellow loam, which extends beyond the limits of the Loess. A layer
of Orange sand separates the Loess from the Tertiary. Patches of the
Loess or bluff-deposit are found also on the western side, showing that
the old flood-plain extended beyond the present flood-plain on both
sides ; but on the west side it has been mostly removed by subsequent
erosion. Beneath the present river swamp-deposit isfotmd, by borings,
a deposit belonging, like the Loess, to the Champlairi epoch, but to an
earlier period, probably an estuary deposit, and called by Hilgard
"Port Hudson" varying in thickness from 30 feet at Memphis to sev-
eral hundred feet in the delta. Beneath this is first the Orange sand
and then the Tertiary.
All these facts are represented in the ideal section of the river and
the strata in its vicinity, given below, constructed from the investiga-
tions of Prof. Hilgard. It is evident that a great trough was hollowed
out in the Tertiary strata during the Glacial epoch, filled with deposit
to the level 1 1 during the Champlain, and again partly cut out during
the Terrace.
524 CENOZOIC ERA AGE OF MAMMALS.
The cause of the flooded condition of the rivers and lakes was part-
ly the depression of the land, by which the sea entered into the old
glacial beds, forming estuaries; partly the smaller angle of slope of the
rivers, by reason of which the waters in their lower parts ran off less
FIG. 863. Ideal Section across Mississippi below Vicksburpr : OS, Orange sand ; PH. Port Hudson,
' te, Loess or old flood-plain d.
>, river-swamp deposit, moder
estuary deposit. Champlain; Is, Loess'or old flood-plain deposit, Champlain; t, loam covering the
Loess, but more extensive ; r
rapidly, and therefore were more swollen, and therefore also deposited
more sediment ; and partly the greater abundance of the water-supply,
from the melting of the glaciers.
III. Terrace Epoch.
At the end of the epoch of subsidence, when the condition of sea
and lakes and rivers was what we have described, there commenced a
movement again in an opposite direction, by which the lands were
slowly brought upward to their present condition a condition, how-
ever, far less elevated than during the Glacial epoch.
Evidences. Sea. The reelevation was not perfectly steady and uni-
form, but stopped, from time to time, sufficiently long for the sea to
make distinct beaches. Below the highest beach, which marks the
maximum depression of the Champlain epoch, and which has already
been described, several other beaches are traceable, which evidently
mark the successive steps of reelevation.
Lakes. Also, the reelevation of the land would bring down the level
of the lakes, partly by change of climate diminishing the water-supply,
and partly by increasing the slope, and thereby increasing the erosive
power, of the discharge-rivers, and thus draining off the lake- waters.
This is well shown on the Canadian lakes, where, in addition to the
highest terrace, already mentioned, which marks the highest flood-level
of the Champlain epoch, are found several lower terraces, which mark
the successive stages of the subsequent depression of the lake-surface.
These distinct beaches would seem to indicate that the rate of draining
away and letting down of the water was not uniform, but had periods
of greater and periods of less rapidity.
Rivers. It is hardly necessary to say that the reelevation would lay
bare the old flood and estuary deposits of the rivers, and the rivers
would immediately commence cutting into these deposits, forming ter-
TERRACE EPOCH. 525
races and bluffs, in number and height depending upon the depth of
the cutting. The Connecticut River has made many of these terraces,
the highest, of course, being the oldest. The Mississippi has apparent-
ly made but one, but this one is very high (Fig. 863). The highest
point of this Champlain deposit, according to Hilgard, is at least 450
feet above tide-level, showing a reelevation and a cutting to that extent
during the Terrace epoch.
History of the Mississippi River. It may be interesting to stop a
moment, and trace, briefly, the history of this great river. During the
Cretaceous period, the Ohio probably ran into the embayment of the
Gulf, represented in Fig. 728 (p. 452) ; but the Mississippi did not yet
exist. The drainage of all that part of the continent was, doubtless,
into the great Cretaceous inter-continental sea. At the beginning of
the Tertiary period, the Mississippi probably commenced to run into
the Tertiary embayment, shown in Fig. 790 (p. 479). The Red and Ar-
kansas, if they then existed, were not tributaries, but separate rivers,
emptying into the same embayment. The Ohio was almost, if not quite,
a separate river also. During the Glacial epoch, the whole embayment
of the Gulf was abolished by elevation. This is clearly demonstrated
by the torrential pebble-deposit (Orange sand), and by the stump-layer
(old forest-ground), found by Hilgard beneath the Port Hudson (Cham-
plain) deposit, on the shores of the Gulf. During the same epoch, bv
reason of this elevation, the great trough, represented in Fig. 863,
was scooped out of the Tertiary strata, 200 to 500 feet deep, either
by a tongue-like extension of the northern ice-sheet, or else, more prob-
ably, by the erosive power of water, favored by the greater slope of the
country southward at that time, and also by the greater water-supply.
During the Champlain epoch, by subsidence this great trough became
an arm of the Gulf, or an estuary, fifty to one hundred miles wide, and
reaching up to the mouth of the Ohio, with extensions up the tribu-
taries ; and this estuary became filled, 200 to 500 feet deep, with sedi-
ments. This deposit was at first estuarian (Port Hudson), and after-
ward river-silt (Loess). During the Terrace epoch, this silt was laid
bare, and the river commenced, and continued to cut, until the bluffs be-
came 200 to 400 feet high. Finally, during the Recent epoch, the river
has again commenced building up by sedimentation, showing thus a
slight depression again, or, at least, a cessation, of the reelevation of
the Terrace epoch. This up-building by sedimentation has continued
up to the present moment, and the deposit (river-swamp and delta de-
posit) has reached, according to Hilgard, a thickness of forty to fifty
feet. Thus the phenomena of the Mississippi distinctly separate the
Terrace from the Recent epoch.
526 CENOZOIC ERA AGE OF MAMMALS.
Quaternary Period on the Western Side of the Continent.
All the most characteristic phenomena of this period, such as gen-
eral glaciation, raised sea-margins, flooded lakes, and flooded rivers,
are abundant and conspicuous on the Pacific side of the continent.
Especially are the evidences of separate ancient glaciers far more per-
fect than on the eastern coast, in fact as perfect as in any part of the
world.
Glaciers. 1 There seems little doubt that during the fullness of
Glacial times an extension of the northern ice-sheet covered the Sierra
Nevada, even to Southern California. From the margins of this ice-
sheet, doubtless, stretched valley-extensions in the form of separate
glaciers into the plains east and west. The direction of motion, and
therefore of transportation, was mainly eastward and westward from
the crest, determined by the mountain-slope; but also partly southward,
determined by northern elevation. The evidence of this condition of
things is yet imperfect. It consists mainly in the general contour-
forms of the surface of the whole higher or granite region of the Sierra
a rounded, billowy appearance, like moutonne rocks on a huge scale.
Following this ice-sheeted condition, we have in the same region
the most perfect and abundant evidences of an epoch of great separate
glaciers, and associated with these are evidences of flooded lakes, into
which the glaciers ran and formed icebergs, and of flooded rivers,
whose swollen currents carried away and redeposited the glacial debris.
This time of great glaciers in California probably corresponds with the
Champlain epoch.
It is impossible to describe all the great ancient glaciers whose
tracks have been traced. They filled all the larger canons, and their
tributaries all the higher and smaller valleys and meadows. Their
tracks are everywhere marked by glaciation and strewed bowlders, and
their terminus at different times by a succession of terminal moraines
and lakelets. We will mention three or four as examples :
1. During the epoch spoken of a great glacier, receiving tributaries
from Mount Hoffman, Cathedral Peaks, Mount Lyell and Mount Clark
groups, filled Yosemite Valley, and passed down Merced Canon. The
evidences are clear everywhere, but especially in the upper valleys,
where the ice-action lingered longest.
2. At the same time tributaries from Mount Dana, Mono Pass, and
Mount Lyell, met at the Tuolumne meadows to form an immense
glacier, which, overflowing its bounds a little below Soda Springs, sent
a branch down the Tenaya Canon to join the Yosemite glacier, while the
main current flowed down the Tuolumne Canon and through Hetch-
1 For a fuller account of the glaciers of the Sierra, and the condition of things dur-
ing the Glacial epoch, see American Journal of Science, vol. iii., p. 325, and vol. x., p. 26.
QUATERNARY PERIOD ON WESTERN SIDE OF CONTINENT. 527
hetchy Valley. Knobs of granite, 500 to 800 feet high, standing in its
pathway, were enveloped and swept over, and are now left round, and
polished, and scored, in the most perfect manner. This glacier was at
least forty miles long and 1,000 feet thick, for its stranded lateral mo-
raine may be traced so high along the slopes of the bounding moun-
tain.
3. The Sierra range on its western side slopes gradually for fifty or
sixty miles ; but on the eastern side it is very precipitous, so that the
plains 5,000 to 7,000 feet below the crest are reached in two or three
miles. In glacial times long and complicated Glaciers with many tribu-
tuaries occupied the western slope, while on the eastern slope innumer-
able short, simple glaciers flowed in parallel streams down the steep in-
cline and out for several miles on the level plain, or even into the waters
of Lake Mono. One of the largest of these took its rise in the snow-
fields about M*mo Pass, flowed down Bloody Cation, and six to seven
miles out on the plain, and evidently into the waters of Lake Mono,
which was then far more extensive and higher than now. Parallel mo-
raines, 300 feet high, formed by the dropping of glacial dkbris oh each
side of the icy tongue, as it ran out on the plain or on the bottom of
the shallow lake, are very conspicuous, as. are also the successive ter-
minal moraines left in the subsequent retreat. Behind these moraines
water has accumulated, forming lakelets.
4. In the fullness of Glacial times Lake Tahoe basin was wholly
occupied by ice, which probably ran out upon the plains of the Basin
region. But in the epoch of great glaciers, of which we are now
speaking, its basin was filled with water, and to a somewhat higher
level than at present ; and into the lake ran many glaciers, whose
tracks are still perfectly distinct. The lakelets and lake-like bay seen
about the southern end of the great lake, and which form so conspicu-
ous a feature of its scenery, were scooped out by these steeply-de-
scending glaciers; and the long parallel debris-ridges bordering the
lakelets, and stretching down to the shores of the great lake, have
been deposited on each side of the glaciers as they ran out into the lake,
doubtless to form icebergs. 1 (See Fig. 864).
During the Terrace epoch these great glaciers of the Sierra retreat-
ed, but not at uniform rate, leaving verv distinct terminal moraines at
the places where their points rested awhile, until they have mostly
retired within the snow-fields which gave them birth. The feeble re-
mains of some of them may still be found hidden away among the
coolest and shadiest hollows of the high Sierra region.
Lake-Margins. About all the great lakes there are terraces or other
evidences of a higher and more extensive condition of their waters.
About Lake Mono there are five or six very distinct terraces, the high-
est of which is 600 to 700 feet above the present lake level. This
1 American Journal of Science, vol. x., p. 126, 1875.
528
CENOZOIC ERA AGE OF MAMMALS.
would carry the lake-waters to the base of the Sierra, and necessitate
the flow of glaciers into them, and the formation of icebergs.
About Great Salt Lake successive terraces have been traced up to
more than 900 feet above the present lake-level. At that time it is
estimated to have contained 400 times its present volume of water ;
and there are some reasons for thinking that it probably once dis-
FIG. 864. Diagram Mnp, showing the Southern End of Lake Tahoe with its Lakelets and Lateral
Moraines.
charged into the Pacific through the Snake and Columbia Rivers, for
the divide between the Salt Lake basin and the Columbia River is only
about 600 feet above the present lake-level. 1 If so, it was then a
fresh, or, at least, a brackish-water lake. About other salt lakes in
this region the same phenomenon is observed. In fact, in all the Basin
1 Dr. Blake, " Proceedings of California Academy of Science," vol. iv., p. 276.
QUATERNARY PERIOD ON WESTERN SIDE OF CONTINENT. 529
region, the valleys between the parallel ranges were then filled with
water (Gilbert).
During the Terrace epoch these lakes were partly drained away,
but still more dried away to lower and lower levels, marked now by
successive terraces. For, if in the East the lakes were mostly drained
away by change of level, in the West they were mostly dried away bj'
change of climate.
Rivers. The rivers, especially in California, mark very distinctly
all the stages of the Quaternary. There are in many parts of Califor-
nia two systems of river-beds, an old and a new. The old belongs to
the later Tertiary and earliest Quaternary ; the new, to the later Qua-
ternary and the present. The change took place during the oscillations
of the Quaternary. The old or dead river-system runs across the pres-
ent drainage-system in a direction far more southerly. This is espe-
cially true of the more northern members of the system. Farther south
the two systems are more nearly parallel, showing less movement in
that region. These old river-beds are filled with Drift-gravel, and often
covered with lava-streams. They will be again referred to and de-
scribed in connection with gold (p. 555). These Drift-gravels probably
represent the Glacial epoch, though Whitney thinks an earlier or Plio-
cene epoch. The present river-system sometimes cuts across, some-
times runs parallel to, the lava-filled beds of the old river-system, and
the beds of the former have in their turn been eroded 2,000 to 3,000
feet in solid rock. In these also have been accumulated immense quan-
tities of gravel and bowlder Drift, evidently brought down from the
FIG. 865. Lava-Stream cut through by Elvers : a, a, basalt; b, &, volcanic ashes ; c, c, Tertiary; d, d,
Cretaceous rocks; R R, direction of the old river-bed; K', B', sections of the present river-beds (from
Whitney).
glacial moraines by the swollen rivers of the Champlain and early Ter-
race epochs. These facts are illustrated by Figs. 865 and 866, in which
R' represents the present river-system, in Fig. 865, cutting across, and
in Fig. 866 running parallel to, the old system It.
FIG. 866. Section across Table Mountain, Tuolumne County, California: Z, lava; G, gravel; S, slate ;
R, old river-bed ; R', present river-bed.
34
530 CENOZOIC ERA AGE OF MAMMALS.
Although it is impossible to synchronize with certainty these events
with the changes in the eastern portion of the continent, yet the order
of sequence is evident ; and that the greater part, if not all, occurred
in the Quaternary, is also evident.
Seas. The boldness of the whole Pacific coast, especially in high
latitudes, indicates, as will be more fully shown hereafter (p. 534), a
previous more elevated condition of the land-surface than now exists.
Demonstrative evidence of the same is also found in elephant-bones
recently discovered on the small island of Santa Rosa, which must then
have been connected with the mainland. 1 This was during the Glacial
epoch. Again, elevated terraces found in many places along the Cali-
fornia coast belong undoubtedly to the Champlain epoch. At San
FIG. 867. Sea-Terraces at San Pedro, California (after Davidson).
Pedro, Lieutenant Davidson finds ten of these, most of them well marked,
rising one above another from sixty-five to 1,200 feet above present sea-
level. 1 At that time the sea not only occupied the bay of San Fran-
cisco, but covered all the flat lands about the bay, including the valleys
of Santa Clara, Napa, and Sonoma ; and thence extending inward,
covered also the whole Sacramento and San Joaquin plains, forming
thus an immense sound 300 miles long and fifty miles wide. In Oregon
Mr. Condon has traced an old sea-margin from the coast up the Colum-
bia River to and beyond the Cascade range. At that time, according to
him, the sea entered the Columbia as a great estuary, spread out over ,
the Willamette Valley as a great sound, and thence up the river.
Puget Sound, with its deep, narrow, complicated channels, was prob-
ably produced by subaerial erosion, at a time of greater land-elevation.
Again, the complicated system of prairies which surrounds its southern
end is evidence of former extension of the sound, and therefore of
an epoch of subsidence, from which reelevation has brought the waters
to their present condition.
On the Thompson River, a branch of Fraser River, British Colum-
bia, beautiful terraces are seen from 50 to 500 feet above the present
level of the river (Lord Milton).
The Quaternary Period in Europe.
In Europe the phenomena were more irregular, the oscillations
more numerous, and perhaps more local, than in America. This is in
1 " Proc. California Academy of Science," vol. v., p. 152. 2 Ibid., Tol. v., p. 90.
THE QUATERNARY PERIOD IN EUROPE.
531
accordance with the general difference in the geological history of the
two continents. Again, in America elevation predominated ; in Europe,
subsidence. Therefore, in America true glacial phenomena predomi-
nated ; in Europe, iceberg phenomena. Nevertheless, the general char-
acter of the phenomena was similar in the two countries. The most
conspicuous and universal effects reach, in Europe, as far as about 50
north latitude.
1. Epoch of Elevation First Glacial Epoch. The Quaternary was
inaugurated in Europe, as in America, by an epoch of elevation, when
the northern portions of that continent stood 1,000 feet or more above
FIG. 868. -Map of Outline of Coast of Western Europe, if elevated 600 Feet (after Lyell).
its present level. The whole of Scandinavia, the whole of Scotland,
and the northern and mountainous portions of England, were ice-sheeted
532
CEXOZOIC ERA AGE OF MAMMALS.
the ice moving from these regions southward, southeastward, and
eastward, producing universal glaciation. The Baltic Sea, the North
Sea, and a wide border about the British Isles, were then land, and swept
over by glaciers. Above we give a map (Fig. 668), from Lyell, showing
what would be the outline of Northwestern Europe, if raised only 600 feet.
Switzerland, at this time, though not ice-sheeted, developed glaciers
on a prodigious scale. Some of these have been traced out with great
care and skill. Especially has this been done for the great Rhone
glacier, by Guyot. At that time a great glacier came down the valley
of the Rhone, emerged on the plains, and filled the whole valley of
Switzerland, fifty miles wide, between the Alps and the Jura, forming
a great mer de glace 50 miles wide, 150 miles long, and 2,000 feet deep.
A figure is given below of this great glacier. The dotted lines show
the direction of motion as determined by bowlders left in the valley or
stranded high up on the slopes of the Jura.
Fio. 869. Map showing the Outline and Course of
Flow of the Great Rhone Glacier (after Lyell).
FIG. 870. Map showing the Lines of DiM* ex-
tending from the Alps into the Plains of the Po
(after Lyell).
Lakes Geneva and Neufchatel were probably scooped out by this
great glacier.
At the same time, also, on the southern slopes of the Alps, long
glaciers stretched out on the plains of Lombardy, as shown by the pro-
digious piles of debris (moraines) still left. Some of these moraines
are 1,500 feet high. Fig. 870 is a map of these lines of debris.
Evidences of glaciers of this time are also found in the Vosges, in
the Pyrenees, and other high mountains of Central Europe.
2. Epoch of Submergence Champlain. Following the epoch of
elevation was an epoch of subsidence, during which the same regions
THE QUATERNARY PERIOD IN EUROPE.
533
which were before most elevated became now most depressed. It is
believed that in Scotland the land was at least 2,000 feet below the
present level. By this depression a great part of Northern Europe was
submerged, and Great Britain was reduced to an archipelago of small
islets. Over the area thus submerged drifted icebergs loosened from
the Scandinavian ice-field.
FIG. 871. Map of the British Isles and Norway, if subsided 1.200 to 2,000 Feet (after Lyell). The lower
shaded portion was not touched by Drift.
At the same time, partly by subsidence, and therefore slackened
water-currents, and partly by moderated climate and melting of glaciers,
there was a flooded condition of rivers and lakes in Middle Europe,
France, Germany, and Switzerland. At the same time, also, the north-
ern portion of Asia and the lake-region of that continent were submerged.
The Caspian Sea, Lake Aral, and other lakes in that region, were prob-
ably then united into one great inland sea, connected either with the
534: CENOZOIC ERA AGE OF MAMMALS.
Black Sea or the then greatly-extended Arctic Ocean, or with both. 1
Either at this time, or more probably during the Glacial epoch, the
Desert of Sahara was submerged.
Evidences of this condition of things are found in old sea-margins,
lake-margins, river-terraces, and flood-plain deposits.
3. Epoch, of Reelevation Second Glacial Epoch Terrace Epoch.
The period of submergence was followed, as in America, by another of
reelevation, as shown by the successive beaches and terraces on sea-
shores, about lakes, and on rivers. But in Europe the reelevation went
much beyond the present level, and brought on a second Glacial epoch,
not, indeed, equal to the first not an ice-sheeted epoch but a reign of
great separate glaciers. During this time Great Britain was again
connected with the continent.
4. Modern Epoch. Afterward the continent again came down to its
present condition, and thus inaugurated the Modern epoch. In Europe,
therefore, the Terrace is more distinctly separated from the present
epoch than in America.
Some General Results of Glacial Erosion.
1. Fiords, We have seen that the phenomena of rivers, in the
region affected by the Drift, show elevation, then subsidence, and then
reelevation to a less height than the first. The first elevation is shown
in their deep, ancient beds; the subsidence, in the filling up of these
with deposit ; the reelevation, in the cutting down into the deposit, and
forming terraces. Now, all these changes are also shown in the phe-
nomena of fiords (Dana).
It will be remembered (p. 35) that the Norway coast is wonderfully
bold and deeply dissected, consisting of high, rocky headlands, separated
by deep inlets running 50 to 100 miles into the country ; and off shore
there is a line of high, rocky isles, evidently the remnants of an old
shore-line. These deep inlets are called in Norway Fiords; and the
name is now used for all such deep inlets separating high headlands.
The coast of Greenland has a precisely similar structure. It, also, con-
sists of bold, rocky headlands, separated by fiords running far into the
country ; and off shore a line of rocky isles 2,000 feet high. In Green-
land these fiords are now occupied by glacial extensions of the general
ice-mantle. The same coast-structure is found on the western side in
high latitudes. The coast of British America and Alaska is also bold
and deeply dissected by fiords; and in Alaska these fiords are now
occupied by great glaciers running down to the sea (Fig. 872).
Now, it seems certain that fiords are deeply-eroded valleys, which
have become half submerged ; and as glaciers are the most powerful of
erosive agents, they are usually half-submerged glacial valleys. These
1 Nature, vol. xiii., p. 74 ; Natural History Magazine, vol. xvii., p. 1*76 ; " Archives des
Sciences," vol. liv., p. 427.
LIFE OF THE QUATERNARY PERIOD. 535
valleys can in most cases be traced as submarine troughs, far out to sea.
In Greenland, for instance, the extension of these troughs, deep below
the present sea-level and far out beyond the reach of the present glaciers,
shows a former more elevated condition; and terraces and recent deposits
up to 500 feet show a subsidence below, and a reelevation to, the present
level. Also, Puget Sound, as already stated, shows the same succession
of changes.
All shores in northern regions are bold and rocky and deeply dis-
sected, and have rocky islets off shore ; in other words, are more or less
PIG. 872. Ideal Section through a Fiord.
affected with fiord-structure. They have been elevated, glacially
eroded, and subsided. It is probable that during the epoch of greatest
elevation a broad continental connection existed between America and
Asia, including the whole area between the Aleutian Isles and Behring
Straits.
2. Glacial Lakes. Lakes are found in all parts of the earth, and are
doubtless due to different agencies, but there can be little doubt that
most of those found in the Drift region are formed by glacial agency.
The whole region which has been affected by glacial agency is thickly
dotted over with lakes, while south of this region there is a comparative
absence of them. In the glacial region of the Sierra Nevada, glacial
lakes are evidently formed in two ways : They are either rock-basins
scooped out by a glacier at some point of its path where the rock is
softer, or where the angle of slope becomes suddenly less ; or else they
are formed by the damming up of waters behind the terminal moraines
left by a retiring glacier. Both of these kinds are very abundant in
the Sierra and other mountain regions. The former are usually high
up the valleys, the latter somewhat lower down. The marshes and
meadows so common in old glacial regions are also often traceable to
the filling up of glacial lakes.
Life of the Quaternary Period.
Plants and Invertebrates. Remains of the life of the Quaternary,
both animal and vegetable, are very numerous, and often very well pre-
536 CENOZOIC ERA-AGE OF MAMMALS.
served. Both the plants and the invertebrate animals are almost wholly
identical with those now living on the earth. We will therefore dis-
miss these with one important remark : The plants and the marine
shells show an arctic climate in now temperate regions. The species
found are still living, but living farther north. There has been a mi-
gration of species northward since Glacial times.
Mammals. But the mammalian fauna of the Quaternary is almost
wholly peculiar. It differs greatly from the Tertiary fauna preceding,
and the present fauna succeeding. The species are, moreover, very
numerous, and many of them of extraordinary size ; for it is the culmi-
nation of the mammalian age. It is necessary, therefore, to describe
some of them, and the conditions under which they were preserved, and
thus to realize in some degree the conditions under which they lived.
We will take our first illustrations from Europe, because the remains are
more numerous and have been more thoroughly studied there.
Mammalian remains of this time are found in Europe 1. In caverns,
where in great numbers they have become entombed ; 2. On beaches
and terraces, where their floating carcasses have become stranded; 3.
In marshes and peat-bogs, where, venturing in search of food, they have
mired and perished ; 4. In ice-cliffs and frozen soils, where they have
been hermetically sealed and preserved to the present time.
1. Bone-Caverns. The richest sources of Quaternary mammalian
remains are undoubtedly bone-caverns. These occur in nearly all coun-
tries, often along the course of streams, but high above the present
stream-level. Their formation and their filling are in some way con-
nected with the floods of the Champlain epoch. They are rich in or-
ganic remains, to a degree which is almost incredible. One of the
most striking peculiarities of these remains is, that they often consist
of a heterogeneous mixture of all kinds, carnivorous and herbivorous,
and all sizes, from the Elephant and Cave-bear on the one hand down to
Rats and Weasels on the other ; sometimes perfect, more often broken,
mingled with earth and gravel, forming unstratified lone-rubbish. An-
other peculiarity of these deposits is that they are often covered
and, as it were, sealed by a stalagmitic crust formed by subsequent
drippings from the roof, and thus preserved against even the suspicion
of disturbance to the present time. We give (p. 537) a section of the
cave of Gailenreuth, with its bone-rubbish and stalagmitic crust.
Among the remains of Herbivores found in bone-caverns, the most
remarkable are those of the Elephant, Rhinoceros, Hippopotamus, the
great Irish Elk, besides Horses and Oxen. Among Carnivores are the
Cave-bear ( Ursus spelceus), larger than, the Grizzly, the Cave-hyena, 1
the Cave-lion, 1 the Sabre-toothed Tiger (Machairodus latidens}, with its
1 These are supposed to be the same species as the African lion and hyena of the
present day, but much larger.
LIFE OF THE QUATERNARY PERIOD.
537
sabre-like tusks, ten inches long, besides smaller animals of the same
order. The remains of the larger Carnivora, especially the Cave-bear
and the Cave-hyena, are the most abundant. The bones of the smaller
Herbivores bear the marks of teeth, as if they had been gnawed. The
skeletons of the large Pachyderms are usually more perfect. In the
Kirkdale Cave, England, the teeth and other parts of 300 individuals of
the Cave-hyena were found. In the Gailenreuth Cave, Franconia, the
538
CENOZOIC ERA AGE OF MAMMALS.
remains of 800 Cave-bears were obtained. In many bone-caves are
found also the bones and rude implements of primeval man. Of these
we will speak more fully hereafter.
FIG. 874.-- Skull of Ursus spelaeus, x J.
FIG. 875. Skull of Hyena spelaea, x J.
Origin of Cave Bone-Rubbish. When it was supposed that the Drift
was caused by a great wave of translation sweeping across the conti-
nent and carrying ruin in its course, the phenomena of bone-caves were
supposed to give countenance to this view. Animals of all sizes and
kinds were supposed to have huddled together in these caves, forgetting
their mutual hostility in the sense of a common danger, and perished
miserably together there.
But at present it is usually believed : 1. That these caves were the
dens of the larger Carnivores, especially the Cave-bear and Cave-hyena,
which dragged their prey there to devour them, and also later the
abodes of men ; 2. That also the floating bodies of large Herbivores, such
as the Elephant, Rhinoceros, etc., were carried into them by the flooded
rivers which then ran at that level ; and 3. That during the Champlain
epoch, when water ran through these caves in large quantities, bones.
and earth were drifted in from above, through fissures and subterranean
LIFE OF THE QUATERNARY PERIOD. 539
passages, and thus found their lodgment in the caves. This last was
probably the principal source of the bone-rubbish in most cases.
Origin of Bone-Caverns. In limestone regions caverns are very
abundant everywhere. They do not seem to be enlarging now ; but
on the contrary to be in most cases filling up either with rubbish or
with stalactitic and stalagmitic deposit. In some cases streams still run
through them. It seems probable that they are mostly due to the ac-
tion of subterranean waters in Champlain times. At that time full
streams ran through and excavated them, partly by erosion, partly by
solution. Gradually, as the Terrace elevation came on, the great
streams into which these cavern tributaries ran cut down their beds to
lower levels, the subterranean waters sought lower levels, and the part
running through the caverns was reduced to drippings; and stalag-
mitic crusts covered the Champlain rubbish and preserved them. Thus,
then, the date of the eaves is Champlain ; of the bone-rubbish is Cham-
plain and early Terrace ; of the stalagmitic crust is later Terrace and
Recent.
2. Beaches and Terraces. On these are found the remains of bodies
which have floated and become stranded. The most abundant of these
are remains of ElepJias primigenius or Mammoth. It is believed that
the bones of 500 individuals have been found on the coast of Norfolk
and Suffolk, and over 2,000 grinders have been dredged up by the
fishermen of the little village of Happesburgh (Woodward). On river-
terraces associated with bones of Quaternary animals have been found
also the rude implements of primeval man. We speak of these more
particularly hereafter.
3. Marshes and Bogs. As might have been anticipated, the re-
mains found in these are mainly those of the larger Herbivores ele-
phants, oxen, stags, etc. It is in these that were found most of the
fine skeletons of the gigantic Irish elk ( Gervus megaceros). This mag-
nificent elk was ten to eleven feet in height to the top of its palmate
antlers, and ten to twelve feet between the antler-tips (Fig. 876).
4. Frozen Soils and Ice Cliffs. As in these have been found the
most perfect specimens of the Mammoth (Elephas primigenius), this
seems to be the proper place to describe the animal.
The genus Elephas ranges in time from about the latter part of
the Miocene to the present. There are about twenty fossil species
known. The genus seems to have reached its maximum development
in the Quaternary. During that period three species inhabited Europe,
viz. : E. antiquus, E. meridionalis, E. primigenius (Lyell), besides
two dwarf species, E. Melitensis, four and a half feet high, and E. Fal-
coneri, three feet high, found in the Quaternary of Malta. Of these,
the largest, the most numerous, and the latest, was the primigenius or
Mammoth. This species roamed in immense herds all over Europe,
540
CENOZOIC ERA AGE OF MAMMALS.
from the shores of the Mediterranean to Siberia, and extended also
over the northern portions of North America. In Siberia the tusks
are so abundant and so well preserved that much of the ivory of com-
merce is gotten from this source.
The Mammoth (Fig. 877) was over twice the bulk and weight of the
largest modern species, and nearly one-third taller. It was thickly cov-
Fia. 876. Skeleton of the Irish Elk (Cervus megaceros), Post-Pliocene, Britain.
ered with a brownish wool, and in parts with long hair ; and was there-
fore well adapted to endure cold. It may seem strange that we should
speak of the hair and wool and the color of an extinct animal ; but
perfectly-preserved specimens have been found sealed in the ice in
Siberia so perfectly preserved that, when first exposed, wolves and
dogs of the present epoch fed on the flesh of this animal belonging to
an extinct fauna. The whole skeleton, with portions of the skin, hair,
wool, hoofs, and eyes of this animal, is now to be found in the museum
at St. Petersburg. The existence of elephants so far north does not
indicate a warm climate, although the Champlain epoch was doubtless
LIFE OF THE QUATERNARY PERIOD.
541
far less rigorous than the Glacial. These elephants were covered with
thick wool, as was also the rhinoceros of Europe.
Quaternary Mammalian Fauna of England. In England alone there
were, in Quaternary times, of Carnivora, the great Cave-bear, the Cave-
hyena, a tiger larger than the Bengal, the Sabre-toothed tiger, as large,
with its flat, curved tusks, eight inches beyond the gums, besides wolves
and lesser Carnivores. Of Herbivores, there were the Mammoth in
herds, two species of rhinoceros, one hippopotamus, the great Irish elk,
three species of oxen, two of them of gigantic size, besides horses,
deer, and other smaller species. Surely this was the culmination of
the Mammalian age in England.
542 CENOZOIC ERA AGE OF MAMMALS.
Mammalian Fauna in North America.
The animals of North America, in Quaternary times, were equallv
abundant ; but the country has been less perfectly explored, and the
collections, therefore, less complete. Bone-caverns, the richest sources
of European collections, are also far more rare.
Among Herbivores^ the most remarkable were the great Mastodon
(M. Americanus) ; two species of elephants, the E. Americanus and the
E. primigenius ; at least two gigantic bisons, one of which was prob-
ably ten feet between the horn-tips ; 1 gigantic horses; gigantic beavers,
one five feet long ; a gigantic stag ( Cervus Americanus}, fully as large
as the Irish elk ; tapirs, peccaries, and a large number of Edentates, an
order now mostly confined to South America, to which belong the sloths
and armadillos. Many of these were also of gigantic size. Carnivores
were not so abundant as in Europe. The most remarkable were a lion
(Felis atrox),as large as the European, and two species of bear ( Ursus
pristinus and amplidens).
Bone-Caves. Caves are found in limestone regions in America
as elsewhere, but they do not seem to have been to the same extent
the dens of Carnivores. In a vertical opening in limestone strata in
Pennsylvania, a kind of cave, mammalian remains have been found be-
longing to thirty-four species, among which were six Edentates, eight
Ungulates, and twelve Rodents. A number have also been found in
the caves of Virginia, and a few in those of Illinois (Cope).
Marshes and Bogs. Most of the remains of large Herbivores have
been found in marshes and bogs. In the Big Bone Lick, Kentucky,
the remains of one hundred mastodons and twenty elephants are said
to have been dug up. Many very perfect skeletons of the great masto-
don have been obtained from marshes in New York, New Jersey, In-
diana, and Missouri. One magnificent specimen was found in a marsh
near Newburg, New York, with its legs bent under the body and the head
thrown up, evidently in the very position in which it mired. The teeth
were still filled with the half-chewed remnants of its food, which con-
sisted of twigs of spruce, fir, and other trees ; and within the ribs, in
the place where the stomach had been, a large quantity of similar mate-
rial was found. In 1866 a very perfect skeleton was found in a bog at
Cohoes, New York.
The Mastodon Americanus (Fig. 878) is probably the largest land-
mammal known. It was twelve to thirteen feet high, and, including
the tusks, twenty-four to twenty-five feet long. It differed from the
1 A specimen of -Bos latifrotis has recently been found in Ohio, the horn-cores of which
were twenty inches around the base, and more than seven feet between the points. Be-
tween the horn-tips must have been at least ten feet.
MAMMALIAN FAUNA IN NORTH AMERICA.
543
elephant chiefly in the character of its teeth. The difference is seen in
Figs. 879, 880, 881. The elephant's tooth, given below (Fig. 880), is
sixteen inches long, and the grinding surface eight inches by four
inches.
FIG. 8T8. Mastodon Americanus (after Owen).
The two genera of Proboscidians, Elephas and Mastodon, appeared
together, or, more probably, the mastodon a little the earlier, in the
FIG. 879. Tooth of Mastodon Americanus.
FIG. 880. Perfect Tooth of an Elephas,
found in Stanislaus County, Cali-
fornia, natural size.
Miocene epoch ; they ranged together through the rest of the Tertiary,
the species, of course, changing several times. At the end of the Ter-
tiary, the mastodon became extinct on the Eastern Continent, but con-
544 CENOZOIC ERA AGE OF MAMMALS.
tinued through the Quaternary, with its companion, the elephant, in
America. At the end of the Quaternary, the mastodon became extinct
wholly, and the elephant in America and Europe, though it still con-
tinues in Asia and Africa. During the Quaternary, therefore, one spe-
cies of mastodon and two species of elephant roamed in herds over
North America from the Gulf to arctic regions. Of the two species of
Fia. 881. Molar Tooth of Mammoth (Elephas primigenius) : a, grinding surface ; b, side-Tiew.
elephant, however, the primigenius was mostly confined to the higher
latitudes, and the Americanus to the southern portions. The latter is
distinguished from the former by less crowded enamel plates in the
grinders and less curved tusks. Of the three genera of Proboscidians
known, the Dinotherium appeared first, then the Mastodon, and last the
Elephant. This is also the order of specialization of teeth-structure.
Among Edentates, a Megatherium, a Megalonyx, and several Mylo-
dons, have been found in North America ; but as their principal home
was in South America, we will describe them
under that head.
River-Gravels. In many portions of the United
States, but especially in California, remains of
mastodon and elephant, and bison, etc., are found
in great numbers in river-gravels. The river-grav-
els of California are spoken of again further on.
Quaternary in South America. A large num-
ber (more than 100) of species of mammals have
been found in the soil of the pampas and in the
caves of Brazil. They are mastodons (different
species from the North American), llamas,
FIG. 682.-Tooth of Machatro- horses, tapirs, rodents, many species of panther-
* (drawn like carnivores, a large sabre-toothed tiger
MAMMALIAN FAUNA IN SOUTH AMERICA.
545
(Machairodus neogceus), with curved, sabre-like tusks twelve inches
long and eight inches beyond the gums (Fig. 882), and especially a
large number of Edentates allied to the sloths and armadillos, but of
gigantic size.
Of the Edentates, the most remarkable, in fact, one of the most
remarkable animals which have ever existed, is the Megatherium (great
beast) Guvieri. The genus Megatherium ranged in Quaternary times
through South America, and into North America as far as the shores
FIG. 833. Megatherium Cuvieri.
of Georgia and South Carolina. At the mouth of the Savannah River
the remains of several individuals of a species of this genus (M. mira-
bilis) have been found. But the largest species and the most perfect
specimens have been found in South America.
The Magatherium Ouvieri, of which we give a figure above, was
larger than a rhinoceros, but was still more remarkable for the clumsy
Fro. 8S4. Lower Jaw of a Megatherium, showing the Gradual Surface of the Teeth (after Owen).
massiveness of its skeleton than for its size. This is especially true of
its hind-legs, hip-bones, and tail. For this reason, it is supposed to
have been able to stand on its hind-legs and tail, while it used its long
35
546
CENOZOIC ERA AGE OF MAMMALS.
free-moving arms, terminated with hands a yard long, to tear down
branches on which it fed. The great skeleton represented above is
eighteen feet long, and its thigh-bones are three times as thick as those
of an elephant. The grinding surface of its molar teeth (it had no
FIG. 885. Claw-Core of a Megalonyx, x J (drawn from a cast of the original).
others) is traversed by triangular ridges admirably adapted to triturate
its coarse food.
Megalonyx (big claw) is the name of another genus of these gigan-
tic sloths, and Mylodon of a third. Both of these genera extended into
North America. In fact, the Megalonyx was first discovered in Green-
FIG. 8S6. Skeleton of Mylodon robnstus, Quaternary. South America.
MAMMALIAN FAUNA OF SOUTH AMERICA AND AUSTRALIA. 547
brier County, Virginia, and named Megalonyx by Thomas Jefferson.
The larger species of Mylodon and Megalonyx were about the size of a
buffalo, or larger.
Of the Armadillos or mailed Edentates, there were several of gi-
gantic size belonging to the genera Glyptodon, Chlamydotherium, and
Pachytherium. The accompanying cut represents one of these eight feet
FIG. 8SV. Skeleton of Glyptodon clavipes, x ^ B , Quaternary, South America.
long, with an invulnerable coat-of-mail. Some species of the genus
Chlamydotherium were much larger one as big as a rhinoceros, and
of Pachytherium as big as an ox (Dana).
Australia. In Australian caves, also, great abundance of remains
has been found, and they show the same prevalence of gigantic spe-
cies. As now, so then, the mammals of Australia were almost all Mar-
supials, but the present species are dwarfs in comparison. The largest
of these was the Diprotodon (two front
teeth), a pachydermoid kangaroo as big
as a rhinoceros. A reduced figure of
the skull, which was three feet long, is
given below.
Among other remarkable species of
marsupials were Macropus (kangaroo)
Titan and M. Atlas, of great size ; Noto-
therium Jfitchelli, as large as a bullock,
and a very remarkable species, supposed by Owen to have been carniv-
orous, and therefore called Thylacoleo (pouched lion) carnifex, as large
as a lion. The striking peculiarity of this animal was the existence of
a broad trenchant premolar, as shown in Fig. 889.
Geographical Fauna of Quaternary Times. We observe, then, that
already the geographical distribution of families was similar to that
which we find at present. Then, as now, Herbivores greatly predomi-
nated in America, while Carnivores were very abundant, and of great
size, in the Eastern Continent. Then, as now, sloths and armadillos
and llamas characterized the fauna of South America, while Marsupials
FIG. 8S8. Skull of Diprotodon Australia,
x i'j, Post-Pliocene, Australia.
548 CENOZOIC ERA AGE OF MAMMALS.
characterized that of Australia. But in each locality the animal life
seems to have been then more abundant, and the species gigantic.
Fio. 889. Thylacoleo, skull reduced (after Flower).
Some General Observations on the Whole Quaternary.
1. Cause Of the Climate. This is confessedly one of the most diffi-
cult questions in geology. There seems to be no doubt that, coincident
with the great changes of climate, there were also great oscillations of
the earth's crust in polar regions ; furthermore, it seems certain that
the intense cold was attended with elevation, and the subsequent mod-
eration of climate with subsidence. This coincidence is itself strong
evidence of a relation of cause and effect. It is generally admitted that
increase in the area and height of polar lands would increase the rigor
of the climate, and decrease of area and height of polar lands would
moderate the climate of northern regions. The amount of this effect
it is impossible to estimate ; but the effect was so enormous and so
wide-spread that the cause, even when supplemented, as it has been,
by changes in the course of oceanic currents such as the Gulf Stream,
has seemed to most physicists and geologists to be insufficient. They
have cast about, therefore, for some other possible cause, external to
the earth itself i. e., cosmical cause to explain it.
The only theory of this kind which seems entitled at the present
time to serious attention is that of Mr. Croll, embraced by Geikie and oth-
er English geologists, which attributes it to the combined influence of
precession of the equinoxes and secular changes in the eccentricity of
the earth's orbit. By the former precession aphelion, or greatest dis-
tance of the- earth from the sun, which is now in summer in our north-
GENERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 549
ern hemisphere, is finally brought around to winter. The effect of this,
it is claimed, would be to make colder winters and warmer summers,
like those now in the southern hemisphere. By the latter, viz., change in
the degree of ellipticity of the orbit, these effects, viz., cold winters and
warm summers, would be increased or decreased according as the ellip-
ticity were increased or decreased. A Glacial epoch is the result of a
coincidence of an aphelion winter with a time of greatest eccentricity.
This theory is still under discussion, and is yet too hypothetical to
justify an elaborate presentation in an elementary work. Suffice it to
say that, if true, one corollary from it would be a recurrence of glacial
conditions with every period of greatest eccentricity. Another would
be the alternation of extreme glacial conditions between the two poles
during each Glacial period (period of greatest eccentricity) with inter-
vals of 26,000 years (cycle of precession). It is hoped that future ob-
servations will test these conclusions. 1
In any case, the coincident oscillations of the earth's crust are unac-
counted for ; and in these oscillations we have, if not a sufficient cause,
at least a true cause, as far as it goes, of the climate.
On any view of the cause of the climate of the Quaternary period, it
seems hardly probable that it is entirely exceptional. Recently, many
geologists, especially Ramsay, have looked for evidences of previous
Glacial periods. Some evidences of this kind have been collected, but
they are far from conclusive. That there have been periods of great
oscillations of the earth's crust, and consequent changes of physical
geography, there can be no doubt. That these were attended with
corresponding oscillations of local climate is also certain. But that
glacial conditions were ever before reached, even in polar regions, seems
more than doubtful. 8 The oscillating temperature of the earth at any
one place, when combined with the gradual cooling of the earth from
early incandescence, might well reach glacial conditions but once. We
may graphically represent this by the diagram on page 550 : Let the
absciss a b represent the course of geological time from early Archaean
times till now, and ordinates upon this, degrees of cold, at any time
and place ; then the curved line a c would represent the cooling of the
earth through all time if the rate were uniformly decreasing (as it
would be if it cooled by radiation only), and the undulating line would
represent the actual oscillating changes of temperature. If g g repre-
1 Among other cosmical causes which have been suggested ought to be mentioned
secular variation in the amount of heat emitted by the sun. Langley (American Journal
of Science and Arts, December, 1875) has modified this view slightly by attributing the
changes of climate to variation in the amount of heat received from the sun ; the variation
being due to change in the absorptive power of the solar atmosphere.
a See " Former Climate of Polar Regions " Nordemkiold, Geological Magazine, Novem-
ber, 1875, p. 525.
550
CENOZOIC ERA AGE OF MAMMALS.
sent the line of glacial conditions such as existed in Quaternary times,
then it is seen that the actual temperature touches this line only once.
ff
FIG. 890. Diagram showing the Secular Increase of Cold, and the Oscillations of Temperature in the
Course of Geological Times.
2. Time involved in the Quaternary Period. There can be no doubt
that the changes of physical geography and climate spoken of were
brought about gradually, and therefore involved long periods of time
so gradually that they might well be unremarked by contemporaneous
man. There are changes by elevation and depression now going on
in various parts of the earth, which are probably as rapid as those of
the Glacial and Champlain epochs. The shores of the Baltic and of
Norway are now rising at an average rate of two and a half feet per
century (p. 129). Continue this process for 800 centuries, and Norway
would attain an elevation equal to that of the Glacial epoch ; and, if
such elevation produces cold, would again be ice-sheeted. Depression,
at similar rate for the same time, would bring about the condition and
climate of the Champlain epoch. Yet these changes are unremarked,
except by the eye of Science. The only difference, if any, between
what is in progress now, and what took place in Glacial times, is the
comparative universality of the oscillations then, and therefore the
greatness of the effect upon climate. It is, of course, impossible to
estimate in years the time of the Glacial and Champlain epochs, unless,
indeed, the theory of Croll be admitted ; but it is not probable that the
estimates given above are exaggerated.
3. The Quaternary a Period of Revolution a Transition between
the Cenozoic and the Modern Eras. We have already seen (pp. 269
and 280) that between the great eras, and perhaps also at other times,
there have been periods of oscillation of the earth's crust, and there-
fore of changes of physical geography, marked by unconformity of
strata ; and changes of climate, marked by apparently abrupt changes
of species. These have been the critical periods of the earth's history
periods of revolution and rapid change. But for that very reason
they are also periods of lost records. We have already spoken of the
lost interval at the end of the Archaean, evidently the greatest of all;
again, of a lost interval at the end of the Palaeozoic, partly recovered
in the Permian, evidently the next greatest ; again, of a lost interval at
the end of the Cretaceous, in a large measure recovered in the Rocky
GENERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 551
Mountain region. There are doubtless many others of less extent.
These periods are always marked by unconformity of the strata and
change in the life-system. The old geologists regarded these changes
as sudden and cataclysmic. All geologists now regard the suddenness
as largely apparent, and the result of lost record.
Now, the Quaternary is also a critical period. It corresponds
with one of the lost intervals ; only, in this case, on account of its near-
ness to us, the record has been recovered. By the study of this period,
therefore, we may hope to solve many problems which have heretofore
puzzled us. Here, for example, we have oscillations of the crust on a
grand scale, producing great changes of physical geography and cli-
mate, and therefore of fauna and flora. Here we have unconformity,
now being produced by sedimentation on old eroded land-surfaces in
all the region affected by the oscillations marine sediments in fiords
and river sediments in old river-channels. But we observe that in this
case these effects have been produced slowly, and that the fauna and
flora have not been suddenly destroyed and suddenly recreated, but
have continued to live throughout, the species gradually changing.
But, what is still more interesting, much light is thrown also on the
hitherto insoluble problem of the mode and the cause of the compara-
tively rapid change of species in these critical periods. The attentive
study of the Quaternary shows that, in addition to the direct effect of
change of climate, one great cause of change of species has been migra-
tion : migration north and south, enforced by change of temperature ;
migration in any direction, permitted by change of physical geography.
This point is so important, that we must explain it somewhat fully.
It will be remembered (p. 481) that in Miocene times Greenland,
Iceland, and Spitzbergen, were covered with a luxuriant temperate
vegetation. The congeners of their vegetation at that time are found
now in California, along the shores of the Southern Atlantic States, and
in Southern Europe. Evidently at that time there was no polar ice-
cap, and therefore no arctic plants. At the end of the Pliocene, the
vegetation shows a climate not greatly differing from the present. It
is probable, therefore, that the cold had increased until an ice-cap had
formed, such as now exists in polar regions, with its accompaniment of
arctic species. As the Glacial epoch came on and culminated, the
polar- ice-cap slowly extended its margin crept slowly southward,
until it reached 40 in America and 50 in Europe and Asia, with local
extensions stretching still farther southward, in the form of separated
glaciers. The southern polar regions were probably similarly affected,
either simultaneously or alternately.
We must not confound this movement southward of the southern
limit of the ice with the current motion of the ice-sheet itself. The
limit of the ice-cap is like the lower limit of a glacier (p. 44). It may
552 CEXOZOIC ERA AGE OF MAMMALS.
be stationary, or advancing or retreating, but the glacial stream flows
ever onward. Again, the motion of a glacial current is slow perhaps
one to three feet per day but the extension or recession of the glacial
limit is far slower, perhaps a few feet per annum. We may thus easily
appreciate the immense time necessary to advance this limit of the ice-
cap to 40 latitude.
At the end of the Glacial and the commencement of the Champlain
epoch a movement of the ice-limit in a contrary direction a retreat
northward commenced and continued, with perhaps some alternate
progressions and regressions, to its present position.
Now, the effect of this advance and retreat of polar ice upon plants
and animals must have been very marked. Temperate plants, inhabit-
ing Greenland in the Miocene, were pushed to the shores of the Gulf.
Arctic plants i. e., those which haunt the margin of perpetual ice
were pushed to Middle United States and to Middle Europe ; and arc-
tic shells were similarly driven southward, slowly, generation after gen-
eration. We say slowly, for otherwise they must have been destroyed.
With the return of temperate conditions, and the retreat of the ice-
cap, these species, both shells and plants, again went northward to their
appropriate place. But the plant species, and some land invertebrate
species, such as insects, had an alternative which the shells had not,
viz., to seek arctic conditions also upward on mountains. Many did
so and were left stranded there. Thus is explained the remarkable fact
that Alpine plant-species in Europe are similar to and largely identical
with those in America ; and both with the present arctic species. This
indicates a former wide distribution of identical arctic species all over
Europe and America, and their subsequent retreat northward into
polar regions, and upward into Alpine isolation. Recently Grote
has observed a similar isolation of Labrador insect-species on Mount
Washington and on the Colorado mountains. 1
There was probably a similar movement, to a less extent, of temper-
ate species. In the Taxodium of the Southern Atlantic and Gulf
swamps, and the Sequoias of California, we doubtless have examples of
species wide-spread in Miocene times, which have been destroyed by
these climatic changes, except in certain limited areas.
But plants and lower species of animals are far less affected by
changes in physical conditions than are the higher species of animals.
This is shown by the wide range both in space and time of the former
as compared with the latter. Under these great changes and enforced
migrations, therefore, plants and invertebrate animal species maintained
their specific characters mostly unchanged, or but slightly changed.
But in the case of mammals destruction or change was inevitable. Both
took place destruction of some and change of the remainder.
1 American Journal of Science, 1875, vol. x., p. 335.
GENERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 553
In America during Quaternary times there was probably a broad
land-connection of North America with South America by the Carib-
bean Sea region ; and certain!}-, as shown by the similarity of plants,
with Northern Asia by the region between the Aleutian Isles and
Behring Straits. Thus migrations were not only enforced by climatic
changes, but permitted by geographical connections with adjacent con-
tinents. Also the great Pliocene lake (p. 478) which separated West-
ern from Eastern North America was abolished, and migrations estab-
lished between the East and West. It is evident that from all these
causes mammalian faunae from widely-different regions were precipitated
upon each other, and struggled together for mastery. Large numbers
of species were destroyed, and the fittest only survived, and these only
under changed forms. It is quite possible that man came to America
with the Asiatic mammalian invasion. If so, his earliest remains in
America may be looked for on the Pacific coast.
Of course, we use the word migrations in its widest sense, as change
of habitat of species as well as of individuals. In the case of plants
and many lower animals, the place of species only moved slowly, from
generation to generation. In the case of mammals there was more de-
cided movement of individuals.
This very important subject has been more closely studied in Europe
than here, although we believe that America is the simplest and best
field for its elucidation. During the Quaternary probably at least four
distinct mammalian faunas struggled together for mastery on European
soil : 1. The Pliocene autochthones. 2. Invasions from Africa, per-
mitted by geographical connection opening a gatevvav through the
Mediterranean, since closed. 3. Invasions from Asia, by opening of a
gateway which has remained open ever since ; with this invasion prob-
ably came man. 4. Invasions from arctic regions. Probably more than
one such invasion took place ; certainly one occurred during the second
Glacial epoch, called on that account the Reindeer period.
The final result of all this struggle was, that the Pliocene autoch-
thones were destroyed ; the southern species were mostlv destroyed or
driven back, with changed forms and diminished size ; the northern spe-
cies, reindeer, glutton, etc., retreated again northward, and the Asiatics
remained in possession of the field, but greatly changed by the strug-
gle. Man was among these, and certainly one of the principal agents
in the change. Speaking more accurately, the present fauna of Europe
may be said to be a product of all these factors ; but the Asiatic inva-
sion seems to be the largest factor.
Thus, then, the gradual progress of evolution, and the causes of the
phenomenon of rapid change of species at critical periods of the earth's
history, may be briefly summarized as follows :
1. A gradual, extremely slow evolution of organic forms under the
554 CENOZOIC ERA AGE OF MAMMALS.
operation of all the forces and factors of evolution known and unknown,
whatever we may conceive these to be. This cause acting alone would
produce gradual changes in time (geological fauna), but without geo-
graphical diversity.
2. This slow evolution takes different directions in different places
and under different physical conditions, and thus gives rise to geo-
graphical faunae and florce. This cause acting alone would produce
extreme geographical diversity, and render determination of synchron-
ism impossible.
3. During critical periods physical changes and consequent migra-
tions^ partly enforced by changes of climate, partly permitted by removal
of barriers, and the precipitation of adjacent faunas and floras upon each
other, and the consequent severe struggle for life, give rise to far more
rapid changes of species, but at the same time to greater geographical
uniformity. This more rapid change of organic forms is produced
partly by severer pressure of external conditions, certainly one factor
of change ; partly by severer struggle for life, certainly another factor
of change ; and doubtless partly also by the mere active operation of
other factors of change, which we do not yet understand. This last
cause tends to produce not only more rapid general evolution, but also
to destroy extreme geographical diversity ; and since it operates on ani-
mals rather more than plants, plant species are more apt to be local,
and are less certainly carried along with the stream of general evolu-
tion, and are, therefore, less reliable in determining geological age than
animals.
Thus, then, regarding the Cenozoic and the Modern as consecutive
eras, and the Quaternary as the transitional, revolutionary, or critical
period between, we see a great, and, if we had lost the Quaternary, an
apparently sudden, change of species. Yet this change, as great as it
is, is not to be compared in magnitude with that which separates the
great eras or even ages from each other. Evidently, therefore, we must
regard the lost interval between the Archaean and Palaeozoic, and that
between the Palaeozoic and Mesozoic, yes, even that between the Meso-
zoic and Cenozoic (as small as this latter is in comparison with the
others), as all of them far greater than the whole Quaternary period ;
or else the forces of evolution must have been far more active in those
earlier times than more recently.
4. Drift 'in Relation to Gold. We have already stated (p. 231) that
gold occurs in two positions, either in quartz-veins intersecting meta-
morphic slates (quartz-mines) or in drift-gravels (placer-mines). The
auriferous slates may be of various ages. In the Appalachian chain,
and in the Ural Mountains, and in Australia, the slate or schist is
metamorphic Silurian. In California it is Jura-Trias. The placer
gold deposits are everywhere Quaternary drift-gravels.
GENERAL OBSERVATIONS OX THE WHOLE QUATERNARY. 555
There has been throughout all geological time a progressive con-
centration of gold, as well as many other metals, in a more and more
available form : 1. It was first disseminated in excessively small quan-
tities, too small to be detected, through the slates, derived doubtless
from the sea, in the waters of which it is detectable in very small quan-
tities. 2. After the upheaval, crumpling, metamorphism, and fissuring
of these slates, the gold was dissolved, and accumulated, along with
silica and metallic sulphides, in these fissures, as auriferous veins. 3.
Atmospheric agencies acting on these outcropping veins dissolved away
the sulphides, and left the gold in a still more available form along the
backs of the veins. 4. Then came the ice-sheet and the glaciers
of the Quaternary, like a plough, cutting away the backs of the
quartz-veins, together with the containing slates, and, like a mill,
grinding all to gravel, and heaping it away in moraines. Some of the
placer-mines are in these moraines, but most of the gold has been
subjected to still another process 5. Lastly, in the Champlain epoch,
the river-floods washed these moraine-heaps down the rivers, sorting
them and depositing where the velocity of the current diminished.
These river-gravels, thus sorted, cradled, panned by the action of cur-
rents, and therefore with the coarse gold near the bottom and high
up the gulches, constitute the richest placer-mines.
The placers of California, however, are of two kinds, viz., the
ordinary or superficial placers, and the deep placers. The superficial
placers are gravel-drifts in the present river-beds. The deep placers
are gravel-drifts in old river-beds. These old river-beds, as already
stated (pp. 238, 529), are in many cases covered up with lava. In some
cases the general direction of the old bed coincides with that of the
present river-system, but more commonly the present river-system cuts
across the old river-system. In all cases, however, it is evident that the
old river-gravels were formed before the lava-flow, and the newer grav-
els after the lava-flow. In all cases also the present river-system has
cut down far below the old beds, in this respect entirely different from
the old river-beds of the eastern portion of the continent.
The following figures are ideal sections altered a little from Whit-
ney's : Fig. 891, of a case in which the old and the present river-beds
are parallel to each other ; Fig. 892, where the latter cut through the
former. In the former case the section is across the lava-flow, as well
as across the river-beds ; in the latter case it is in the direction of the
lava-flow, and therefore of the old river-bed, but across the present
river-bed.
In Fig. 891, which is a section across Table Mountain, in Tuolumne
County, California, L is the lava-cap, 140 feet thick, beneath which is the
old river-bed, R, with its gravel, 6r, now worked by a tunnel, driven
through the rim-slate S. More recent gravels, G', are seen in the pres-
556
CENOZOIC ERA AGE OF MAMMALS.
ent river-beds, R'. In this locality G represents the deep placers, and
G' the superficial placers.
The history of changes shown in these sections is sufficiently
obvious. In the time of the old river-system, R was a river-bed, doubt-
FIG. 891. Section across Table Mountain, Tuolumne County, California : L, lava ; G, gravel ; S, slate ;
Ji, old river-bed ; Jt', present river-bed.
less with a ridge on either side represented by the dotted lines. In
this bed accumulated gravel, containing gold. Then came the lava-
flow, which of course ran down the valley, displacing the river and
FIG. 692. Lava-Stream cut through by Elvers : a, a, basalt; 6, b, volcanic ashes ; c, c, Tertiary; rf, rf,
Cretaceous rocks; It , direction of the old river-bed; Ji\ R', sections of the present river-beds (from
covering up the gravels. The displaced rivers now ran on either side
of the resistant lava, and cut out new valleys, 2,000 feet deep, in the
solid slate, leaving the old lava-covered river-beds and their auriferous
gravels high up on a ridge. In other cases the convulsion which ejected
the lava also changed greatly the general slope of the country, and
therefore the direction of the streams. In such cases of course the
present river-system cuts across the old river-beds and gravels, and
their covering lavas, as shown in Fig. 892.
Age Of the River-Gravels. The age of the old river-gravels is still
doubtful ; that of the newer river-gravels is undoubtedly Champlain
or early Terrace. Below we give a list, taken from Whitney, of the
remains found in these gravels :
Newer placers.
Mastodon.
Elephant.
Bison.
Tapir.
Horse, modern.
Man's works,
f Mastodon. 1
Rhinoceros.
Deep placers. -{ Hippopotamus (ally).
Camel (ally).
[ Horse, extinct species.
Whitney states that the mastodon is not found here, but it has been since found.
PSYCHOZOIC ERA AGE OF MAN RECENT EPOCH 55?
It will be seen that the fauna of the deep placers unite Pliocene
and Quaternary characters, though the Pliocene are the more numer-
ous. The mastodon is distinctively Quaternary, but all the others are
Pliocene. Hence Whitney very naturally places the deep placers in
the uppermost Pliocene, and makes the lava-flow the division-line be-
tween Tertiary and Quaternary. It is not at all impossible, however,
nor even improbable, that many of the Pliocene animals may have lin-
gered on this coast into the Quaternary. In that case we might assign
the deep placers to the earlier Quaternary, and the newer placers to
the later Quaternary. Certain it is that the deep placer-gravels are
similar in all respects to the Quaternary gravels all over the world,
except that, by percolating alkaline waters containing silica, they have
been cemented in some cases into grits and conglomerates. This is
because they are covered with lava which yields both the alkali and
the soluble silica, as already explained (p. 238).
In any case, we have here an admirable illustration of the immensity
of geological times. The whole work of cutting the hard slate-rock
2,000 feet or more has been done since the lava-flow, and therefore
certainly since the beginning of the Quaternary.
CHAPTER VI.
PSYCHOZOIC ERA AGE OF MAN RECENT EPOCH.
Characteristics. The Quaternary, and, indeed, all previous ages,
were reigns of brute force and animal ferocity. A condition of things
prevailed which was inconsistent with the supremacy of man. The age
of man, on the contrary, is characterized by the reign of mind. There-
fore, as was necessary, the dangerous animals decreased in size and
number, and the useful animals and plants were introduced, or else
preserved by man.
Distinctness of this Era. In regard to the distinctness and impor-
tance of this era, there are two views which will probably ever divide
geologists, depending on the two views regarding the relation of man
to Nature. From the purely structural and animal point of view, man
is very closely united with the animal kingdom. He has no department
of his own, but belongs to the vertebrate department, along with quad-
rupeds, birds, reptiles, and fishes. He has no class of his own, but be-
longs to the class Mammalia, along with quadrupeds. Neither has he
an order of his own, but belongs to the order of Primates, along with
monkeys, lemurs, etc. Even a famity of his own, the Hominidce, is
grudgingly admitted by some. But from the psychical point of view it
558 PSYCHOZOIC ERA AGE OF MAN RECENT EPOCH.
is simply impossible to overestimate the space which separates man
from all lower things. Man -must be set off not only against the animal
kingdom, but against the whole of Nature besides, as an equivalent :
Nature the book the revelation and man the interpreter.
So in the history of the earth : from one point of view the era of
man is not equivalent to an era, nor to an age, nor to a period, nor even
to an epoch. But from another point of view it is the equivalent of
the whole geological history of the earth besides. For the history of
the earth finds its consummation, and its interpreter, and its signifi-
cance, in man.
The rocks of this epoch are the present river-deposits, lake-deposits,
sea-deposits, volcanic ejections, etc., already treated of in Part I. The
fauna and flora of this epoch are the species still living on the earth.
These are different from those of the Tertiary, and largely from those
of the Quaternary, times ; but the change, as we have already shown,
has been gradual, not sudden ; man himself being one of the chief agents
of change.
The Change still in Progress Examples of Recent-
ly-Extinct Species. The gradual change of fauna has
been going on through many ages, and is still going
on under our eyes. Many remarkable Quaternary
FIG. 893. Dinornis pig-ant PUS. x ,V (from ft photo- FIG. 894. Aptornis didiformis, x ^ (from a pho-
graph of a skeleton in Christchurch Museum, toprraph of a skeleton in Christchurcu Muse-
New Zealand). urn, New Zealand).
PSYCHOZOIC ERA AGE OF MAN RECENT EPOCH.
559
species have lingered, and become extinct by the agency of man, even
in historic times. Among the most remarkable of these are the huge
wingless birds, the remains of which have been discovered in New Zea-
land and Madagascar, viz., the Dinornis (huge bird), JEpiornls (tall
bird), Palapteryx (old wingless bird), the Solitaire, and the Dodo.
Through the kindness of Mr. C. D. Voy, I am able to give good figures
of the skeletons of several of these extraordinary extinct birds, taken
from photographs (Figs. 893, 894).
FIG. 895. Dinornis elephantopus, r ' 5 (after Owen).
The Dinornis giganteus of New Zealand, and the JEpiornis of
Madagascar, were probably twelve feet high. The tibia of the former
has been found nearly a yard long, and as thick as the tibia of a horse,
and the egg of the latter, well preserved, thirteen inches long and nine
inches in diameter, with a capacity of two gallons. The toe-bones of the
D. elephantopus (Fig. 895) rivaled in size those of an elephant (Owen).
These huge birds must have been capable of making tracks nearly as
large as those of the supposed birds of the Connecticut Valley sandstone
(p. 444). The dodo, a heavy, clumsy bird, of fifty pounds' weight, with
560 P3YCHOZOIC ERA AGE OF MAN RECENT EPOCH.
loose, downy feathers, and imperfect wings, like a new-born chicken,
became extinct only about 150 or 200 years ago. The Apteryx, to
which, of all living birds, the Dinornis, Apatornis, etc., are most nearly
allied, still survives, ready to disappear (Fig. 896).
FIG. 896. Apteryx Australia.
The -50s primigenius, the gigantic ox of Quaternary times, is sup-
posed to be the same as the Urus of Caesar, and therefore became ex-
tinct since Roman times. The aurochs, another Quaternary ox, would
have been now entirety extinct but for the imperial edict which pre-
serves a few in the forests of Lithuania. The lion, the tiger, the bison,
the elephant, and the rhinoceros, and, in fact, all the fiercer and larger
animals, are even now disappearing before the advance of civilized man.
Thus, in passing from geological to present times, we trace rocks
into sediments and soils ; geological agencies into chemical and physical
agencies, now in operation; extinct faunas and florae into the living
fauna and flora ; in a word, geology into chemistry and physics, and
paleontology into zoology and botany.
Now, in this gradual change of fauna, when did man first appear
upon the scene, and what was the character of primeval man ? This
introduces us to two very important but very difficult and obscure sub-
jects.
I. ANTIQUITY OF MAN.
On this interesting subject the three sciences History, Archaeology,
and Geology meet and cooperate ; and the recent rapid advance has
been the result of this union, and especially of the application of geo-
logical methods of research.
Archaeologists have long ago divided the history of human civiliza-
ANTIQUITY OF MAN. 561
tion into three epochs or ages, named, from the materials of which
weapons and tools are made, respectively the Stone age, the Bronze
age, and the Iron age. We are here concerned only with the Stone
age ; the others belong to history.
Closer study has again divided the Stone age into two, viz., the
Palaeolithic (old Stone age) and the Neolithic (newer Stone age).
During the former, only chipped stone implements were used ; while in
the latter polished stone implements were also used. It is principally
with the Palaeolithic that we are here concerned.
Still closer study, in connection with geology, has again divided the
Palaeolithic into an earlier and a later. The earlier, being contempora-
neous with the mammoth, is called the Mammoth age; and the latter,
for similar reasons, the Reindeer age. The mammoth, however, existed
also in this latter age. The former seems to correspond with the Cham-
plain epoch in geology, and the latter with the Terrace of America, or
Second Glacial epoch of Europe. The Neolithic commences the Psycho-
zoic era, or reign of man the period when man had established his
supremacy. The following table expresses these views :
3. Iron age \
2. Bronze age V Psychozoic era.
{Neolithic Domestic animals. )
Paleolithic ^ Reindeer a g e = Terrace or Second Glacial epoch.
' ( Mammoth age = Champlain epoch.
These divisions and their relations to geological epochs have been
established in Europe. They would probably apply also to some parts
of Asia and Africa, for in portions of these old countries man has doubt-
less passed, successively and slowly, through all these stages. But all
these stages are not represented in all countries, nor do they necessarily
correspond to the geological epochs mentioned above. The South-Sea-
Islanders, for example, are still in the Stone age. The American Indians
were in the Stone age only three centuries ago.
The table given above carries man back to the Champlain epoch.
There are some geologists who think they find evidence of a much ear-
lier existence of man. We will, therefore, very rapidly review the evi-
dences of the antiquity of man. In doing so, however, we shall accept
none but thoroughly reliable evidence. There has been recently far too
much eagerness to find facts which overthrow accepted beliefs, and to
accept them on this account alone. We will take up European locali-
ties first, because the subject has been more carefully studied there.
Primeval Man in Europe.
Supposed Miocene Man Evidence unreliable. The earliest period
in the strata of which any supposed evidences of the existence of man
36
562 PSYCHOZOIC ERA AGE OF MAN RECENT EPOCH.
have been found is the Miocene. These evidences, however, are con-
fessedly meagre, and by all careful investigators considered unreliable.
Some flint-flakes, so rough that they may be the result of physical in-
stead of intelligent agencies ; some bones of animals, marked with par-
allel scratches as if scraped, but the scratches may have been produced
by currents, or, as Lyell thinks, by the teeth of Rodents; some more
positive evidences of man's agency, but in strata of more doubtful age,
or else the result of accidental mixture not contemporaneous with the
deposit itself such is, in brief, the evidence. The Miocene man is not
acknowledged by a single careful geologist.
Supposed Pliocene Man. The evidence of the existence of man
during the Pliocene period is, if possible, still more meagre and unre-
liable. M. Hamy thinks he has found undoubted evidence of human
agency in flint implements in Pliocene strata at Savone ; but the con-
temporaneousness of the flints and the deposit is regarded as doubtful.
Again, Palaeolithic implements have been found in Madras in strata sup-
posed by Falconer to be Pliocene ; but more recent investigations make
the strata Quaternary. 1 Of the supposed Pliocene man in California we
will speak further on. Suffice it to say that M. Favre, reviewing the
whole subject up to 1870," and, again, Evans, President of the Geolog-
ical Society of London, reviewing the subject up to 1875, 3 decide that
the existence of Tertiary man is yet unproved.
Quaternary Man Mammoth Age. But of the existence of man in
Europe and America, as early as the middle of the Quaternary period,
there seems to be abundant evidence. We shall select only a few
striking examples :
a. In River-Terraces. In the terraces of the river Spmme, near Abbe-
ville, were found, nearly twenty years ago, by M. Boucher de Perthes,
chipped flint implements, associated with bones of the mammoth, rhi-
noceros, hippopotamus, hyena, horse, etc. The doubts with which the
FIG. 897. Section across Valley of the Somme: 1, peat, twenty to thirty feet thick, resting on
gravel, a 2, lower-level pravels, with elephant-bones and flint implements, covered wHh river-loam
twenty to forty feet thick ; 8, upper-level gravels, with similar fossils covered with loam, in all,
thirty feet thick ; 4, upland-loam, five to six feet thick ; 6, Eocene-Tertiary.
first announcement of these facts was received have been entirely re-
moved by careful examination of the locality by many scientists, both
of France and England.
The findings were in undisturbed gravels, both lower (2) and upper
1 American Journal of Science, 1875, vol. x., p. 232.
8 " Bibliotheque Universelle," " Archives des Sciences," vol. xsxvii., p. 97.
8 American Journal of Science, vol. x., p. 229.
PRIMEVAL MAN IN EUROPE. 5$3
(3), beneath river-loam twenty to thirty feet thick. Supposing that
the upper loam (4) represents the full Champlain flood-deposit, then
3 and 2 represent the later Champlain or early Terrace epoch.
In England, also, at Hoxne, similar flint implements, associated with
bones of extinct animals, were found in strata underlying the higher-
level river-gravels, but overlying the bowlder-drift or true glacial de-
posit. This fixes the age as Champlain. Many other examples of sim-
ilar findings might be cited.
b. Bone-Caves. Engis Skull. In the caves of Belgium and Germany
have been found human bones associated with extinct animals. The
best example is that of the skull found in a cave at Engis, on the banks
of the Meuse, near Liege. Of the great antiquity of this skull there
seems to be no doubt. It was found in bone breccia, associated with
bones of Quaternary, extinct species and living species, beneath a stal-
agmitic crust. This association unmistakably indicates the middle or
latter part of the Quaternary period.
Neanderthal Skull. In a cave at Neanderthal, near Dtisseldorf, was
found a very remarkable human skeleton,which has greatly excited the in-
terest of scientific men. The limb-bones are large, and the protuberances
for muscular attachments very prominent ; the skull very thick, very
low in the arch, and very prominent in the brows. It has been sup-
posed by some to be an intermediate form between man and the ape ;
but, according to the best authority, it is in no respect intermediate, but
truly human. It is probably the skeleton of a man exceptionally mus-
cular in body and low in intelligence. The evidences of antiquity are
FIG. 899. Comparison of Forms of Skulls: ft, Euro-
pean : &, the Neanderthal Man ; c, a Chimpan-
Fia. 80S. Engis Skull, reduced (after Lyell). nee (after Lyell).
far less complete than in the case of the Engis skull, though it proba-
bly belongs to the same epoch. The Engis skull, on the other hand, is
a well-sliaped average human skull. A figure of the Engis skull is
given above (Fig. 898), and a comparison in outline of the Neander-
thal with the ape and European (Fig. 899).
564:
PSYCHOZOIC ERA AGE OF MAN RECENT EPOCH.
Mentone Skeleton. Only a few years ago an almost perfect skele-
ton of a Palaeolithic man was found in a cave at Mentone, near Nice.
It is that of a tall, well-formed man, with average or more than aver-
age-sized skull, and a facial angle of 85. The antiquity of this man is
undoubted, for his bones are associated with those of the cave-lion,
cave-bear, rhinoceros, reindeer, together with living species. The bones
of the skeleton are all in place, surrounded with the implements of the
chase (flint implements), and the spoils of the chase, viz., the bones of
reindeer, perforated teeth of stag, etc. Of the latter, twenty-two lay
about his head. These are supposed to have been worn as a chaplet.
This Quaternary man seems to have laid himself down quietly in his
cave-home and died.
All these, and many more which might be mentioned, belong to
the early Palaeolithic, although the last is possibly a transition to the
next or Reindeer age. They were contemporaneous with the mam-
moth, the rhinoceros, the hippopotamus, the cave-bear, the cave-lion,
the cave-hyena, and other extinct animals ; but the reindeer had not
yet, to any extent, invaded Middle Europe from the north. They seem
to have been savages of the lowest type, living by hunting and dwell-
ing in caves. There is no evidence of agriculture or of domestic ani-
mals. In many cases there have been found some anatomical charac-
ters of a low or animal type, such as flattened shin-bones, very promi-
nent occipital protuberance, less than usual separation between the
temporal ridges, large size of the loisdom teeth, etc. But all these
characters are found now in some savage races, either as racial or
as individual peculiarities. The earliest men yet found are in no
sense connecting links between man and ape. They are distinctively
and perfectly human, and even in many cases
of far better conformation than the lowest types
now living.
Reindeer Age or Later Palaeolithic. Dur-
ing this age man was still associated in
Middle Europe with Quaternary ani-
mals, but also now with arctic
animals, especially the
reindeer. It prob-
ably c o r r e -
sponds with
the Second
Glacial epoch
in Europe,
and the full
beddedTc, layerof "ashes and charcoal eicrht inches thick, with broken, burnt, and TVrrn r>e> pnnn h
gnawed bones of extinct and livinir mammals. uNo h.virth-stones and works of A
Kn,. '.mo. A Section of the Auriirnac Cave: a. vault in which re-mains of seventee
human skeletons were found ; 6, made ground, two feet thick, in which huma
bones and entire bones of extinct and livinp mammals, and works of art, were
art; d, deposit with similar contents ; e, talus washed down from hill above; fg, j n Ampriffl
slab of stone which closed the vault ; / , rabbit-burrow, which led to discovery
PRIMEVAL MAX IN EUROPE.
565
Aurignac Cave. This sepulchral cave and its rich contents were
accidentally discovered by a French peasant. Fig. 900, page 564, is a
diagram section of the cave, taken from Lyell.
On removing the talus, e, a slab of rock,/^, was exposed, covering
the mouth of the cave, a. In this cave were found seventeen human
skeletons of both sexes and of all sizes, together with entire bones of
extinct animals and works of art. Outside of the cave was found a
deposit, c and d, consisting of ashes and cinders, mingled with burnt
and split and gnawed bones of recent and extinct animals, and works
of art. The conclusion reached by M. Lartet is, that this was a family
or tribal burial-place ; that in the cave along with the bodies were
placed funereal gifts in the form of trinkets and food ; and that the
funereal feast was cooked and eaten on the level space in front of
the cave ; and, finally, that carnivorous beasts gnawed the bones left
on the spot. It is evident that the Aurignac men practised religious
rites which indicated a belief in immortality.
The following is a list of the animals the remains of which were
found in and about the cave ; those marked f are either wholly extinct
or extinct in this locality :
FAUNA OF AURIGNAC CAVE.
CARNIVORES.
HERBIVORES.
(Cave-bear
5 or 6
f Mammoth
(Rhinoceros
(Horse
. 2 molars.
. 1
12-15
Brown bear
1
Badger. . .
1 or 2
Polecat
1
f Ass
1
(Cave-lion
Wild-cat
1
1
Hog;
. 1
Sta<r . . .
1
f Cave-hyena
Wolf.
5-6
3
f Irish elk
. 1
3-4
Fox
18-20
f Reindeer
(Aurochs
.10-12
.12-15
Perigord Caves. In Southern France, along the course of the river
Vezere, are found many caves in which are preserved many interesting
relics of man. The Palaeolithic Aquitanians seem to have been some-
what more advanced, and of a more peaceful temper, than the early
Palaeolithic men already described. Although there is no evidence of
agriculture, they lived by fishing as well as by hunting. This is shown
by the number of fishing-hooks of bone found there. They seemed also
to have had a taste and some skill in drawing, for they have left some
drawings of contemporaneous but now extinct animals, especially the
mammoth, the reindeer, and the horse. Fig. 901 is a piece of reindeer-
horn on which is a rude etching of a mammoth.
566 PSYCHOZOIC ERA AGE OF MAN RECEXT EPOCH.
FIG. 901. Drawing of a Mammoth by Contemporaneous Man.
Conclusions. It seems evident that in Europe the earliest men were
contemporaneous with a large number of now extinct animals, and were
a principal agent in their extinction ; that they saw the flooded rivers
of the Champlain epoch, and the great glaciers of the Second Glacial
epoch ; but there is no reliable evidence yet of their existence before or
even during the true Glacial or ice-sheeted epoch. 1
Neolithic Man ; Ref use- Heaps ; Shell- Mounds ; Kitchen- Middens.
In Northern Europe, especially in Denmark, are found shell-mounds
of great size, 1,000 feet long, 200 feet wide, and ten feet high. They
are probably the accumulated refuse of annual tribal feasts. The early
races of men in all countries seem to have had the custom of gathering
in large numbers at stated intervals, and feasting on shell-fish and
other animals, and leaving their remains in large heaps to mark the
spot of assembly. The evidences of a very marked advance are found
in these heaps. The implements are many of them carefully shaped or
else polished by rubbing. There are no longer any remains of extinct
animals, but only of living animals ; and there are now found remains
of at least one domestic animal, viz., the dog, though not yet any evi-
dence of agriculture.
Transition to the Bronze Age Lake Dwellings. In the Swiss,
Austrian, and Hungarian lakes are found abundant evidences of a more
advanced race than any yet mentioned, which had the singular custom
of dwelling in houses constructed on piles in the lakes, and connected
with the land by means of piers or bridges. Similar lake-dwellings are
found now in New Guinea and in South America, and very recently, by
Lieutenant Cameron, in Africa. 8 By means of dredging, a great num-
ber and variety of implements of polished stone and of bronze have
been obtained. Some of these were evidently used for ornament, some
1 Some evidences of Glacial man, which seem somewhat more reliable, have recently
been found in England, but it may be only the Second Glacial epoch.
2 Nature, vol. xiii., p. 202, January, 1876.
PRIMEVAL MAN IN AMERICA. 567
for domestic purposes, some for agriculture ; some were weapons of war,
some fishing-tackle. Many of these are wrought with great skill and
taste. Domestic animals ox, sheep, goat, and dog; cereal grains
wheat and barley ; fruits wild apples, blackberry, etc. ; coarse cloth,
not woven but plaited have also been found. In a word, we have here
all the evidences of communities far .above the state of savagism.
From this time the history of man may be traced, by means of his
remains, through the time of Megalithic structures, through 'the Ro-
man age, step by step, to the present time. But this belongs to the
archaeologist, not the geologist. The Neolithic may be regarded as
the beginning of the Psvchozoic era the connecting link between geol-
ogy and archaeology. The Bronze age and all that follows it belong
clearly to archaeology.
Primeval Man in America.
The facts on this subject are far less numerous and well attested in
America than in Europe. There is, however, undoubtedly a very rich
field for investigation, especially on the Pacific coast.
Supposed Pliocene Man. Several cases are reported of human
bones and works of art having been found in the sub-lava drift de-
scribed on page 555. These cases are none of them thoroughly well
attested, though the evidence is such as to make us suspend our judg-
ment. The best-attested cases are the Calaveras skull mentioned by
Whitney, and the Table Mountain skull reported by C. F. Winslow.
Besides these there are several cases reported of mortars and pestles
found in the sub-lava deposit. Many claim these as evidence of the
existence of man in a somewhat advanced stage of progress (at least
as much so as the Neolithic man of Europe), on the Pacific coast, dur-
ing the Pliocene period. The doubt in regard to this extreme antiquity
of man is of two kinds namely, 1. Doubt as to the pre-lava age of the
remains or works of art, no scientist having seen any of these in situ.
2. Doubt as to the age of the sub-lava drift. It may be not older
than the Champlain (p. 556).
In any case, and whatever be the geological age of the sub-lava
drift, if man should be' undoubtedly found there, it would show an
immense antiquity ; for, since the lava-flow, canons have been cut by
the present rivers 2,000 or 3,000 feet deep in solid slate-rock.
Quaternary Man. Even leaving out the supposed sub-lava-drift
remains, the earliest appearance of man on the American Continent
seems to have been on the Pacific coast, probably as migrants from
Asia. There seems to be no doubt that the works of man have been
found, associated with the remains of animals, both recent and extinct,
in the superficial placer deposits (p. 556). * Among the extinct animals
1 Whitney, " Geological Survey of California," vol. i., p. 252.
568
PSYCHOZOIC ERA AGE OF MAX RECENT EPOCH.
may be mentioned the elephant, the mastodon, and the horse. This
corresponds with the period of primeval man in Europe.
No well-attested evidence of Quaternary man has yet been found
in other parts of the United States. 1 Shell-mounds are abundant on
both the Atlantic and Pacific coasts, but these seem to be of later date
than those of Europe.
Quaternary Man in Other Countries. In India a Palaeolithic imple-
ments, precisely like those found in Europe and elsewhere, were found,
in 1873, associated with extinct species of elephant and hippopotamus
in Quaternary deposits. In the South American bone-caverns human
remains have been found associated with Quaternary animals.
Man, therefore, has been traced back with certainty to the later
Champlain or early Terrace epoch. It is possible that he may be here-
after traced farther to the Glacial or pre-Glacial period. Some confi-
dently expect that he will be traced to the Miocene, but this seems
extremely improbable, for the following reasons :
a. He has been diligently searched for, without success. Now,
while negative evidence is rightly regarded as of little value in geol-
ogy, yet, in this instance, it is undoubtedly of far more than usual
value, because man's works are far more numerous and far more im-
perishable than his bones.
b. Man probably came in with the present mammalian fauna. We
repeat here the diagram illustrating the law of extinction and appear-
T- .E f? T I . .A B Y |j QUATERNARY | RECENT
CRETACEOUS EOCENE [MIOCENE^ [PLIOCENE I&L/IC I CHAM I TER U RECENT
Fio. 902.
ance of species. It is seen that lower species are far less rapidly
changed than higher. Living foraminifers may be traced back into
the Cretaceous ; living shells and other invertebrates to the beginning
of the Tertiary : but living mammals pass out rapidly and disappear in
the Middle Quaternary. Not a single species of mammal now living is
found in the Tertiary. Shall man, the highest of all, be the only ex-
ception ? Man is one of the present mammalian fauna, and came in
with it.
But, again, several distinct mammalian faunae have appeared and
1 Very recently such evidence has been found by Mr. Abbot in New Jersey.
2 American Journal of Science, 1875, vol. x., p. 232.
PRIMEVAL MAN IN AMERICA.
569
disappeared since the beginning of the Miocene. The Miocene mam-
malian fauna is totally different from the Eocene ; the Pliocene total-
ly different from the Miocene ; the Quaternary from the Pliocene ; and
the present from the Quaternary. This is graphically represented in
FIG. 903. Diagram illustrating the Appearance and Extinction of Successive Mammalian Faunae.
the diagram, Fig. 903, in which the alternate shaded and white spaces
represent five consecutive mammalian faunae (there are really more
than five) overlapping each other, but substantially distinct. It seems
in the highest degree improbable that man, a mammal, should survive
the appearance and disappearance of several mammalian faunae. If,
therefore, man should ever be traced to the Miocene, it would probably
be a different species of man the genus Homo, but not the species
Sapiens.
Time since Man appeared. Geology reckons her time in periods,
epochs, etc.; History hers in years. It is impossible to express the
one chronology in terms of the other except in a very rough approxi-
mative way, for want of a reliable common measure. If Mr. Croll's
theory of glacial cold should indeed prove true, then we might hope
to measure man's time on the earth with some degree of accuracy.
But in the absence of confidence in this theory, our only resource is to
use the measure which we have already used on several occasions, viz.,
the effects of causes now in operation. This measure, however, can
give but very rough approximate results.
There is no doubt that very great changes, both in physical geog-
raphy and in the mammalian fauna, have taken place since man ap-
peared. Judging by the rate of changes still in progress, we are natu-
rally led to a conviction of a lapse of time very great in comparison
with that recorded in history. On the other hand, some attempts to
estimate more accurately by means of the growth of deltas in which
have been found implements of the Roman age, the Bronze age, and
the Stone age ; and by the progressive erosion of lake-shores, which is
supposed to have commenced after the Champlain epoch, have led to
very moderate results, viz., 7,000 to 10,000 years. While these results
cannot be received with any confidence, yet it is hoped that many such
will continue to be made.
In conclusion, we may say that we have as yet no certain knowledge
570 PSYCHOZOIC ERA AGE OF MAN RECENT EPOCH.
of man's time on the earth. It may be 100,000 years, or it may be
only 10,000 years, but more probably the former than the latter.
II. CHARACTER or PRIMEVAL MAX.
In regard to the second question, viz., the character of primeval
man, we will make but one remark. We have seen that the earliest
men yet discovered in Europe or America, though low in the scale of
civilization, were distinctively and perfectly human, as much so as any
race now living, and were not in any sense an intermediate link between
man and the ape. Nevertheless, we must not forget that the cradle of
mankind was probably in Asia., Man came to Europe and America
by migration. The intermediate link, if there be any such, must be
looked for in Asia. This question can only be settled by a complete
knowledge of the Quaternary of that country.
In any case, man is the ruler only of the modern era. The presence
of man in Quaternary times must be regarded as an example under the
law of anticipation (p. 267). He only fairly established his supremacy
in the Recent epoch, and therefore the age of man and the Psycho-
zoic era ought to date from that time.
A IIST OF THE PRINCIPAL AUTHORITIES FOR THE ILLUSTRATIONS IN THIS WORK,
AND THE BOOKS FROM WHICH THEY HAVE BEEN TAKEN.
AGASSIZ, L. " Etudes sur les Glaciers " " Poissons Fossiles."
AUTHOR. Am. Jour, of Sci., III., vols. x. and xi. ; also many (about 150)
diagrammatic illustrations throughout this work.
BAILEY, J. TV. Am. Jour, of Sci., II., i.
BRADLEY, F. II. Geological Chart of the U. S.
BRONGNIART, A. " Histoire des V6ge"taux Fossiles."
BUCKLAND, W. " Bridgewater Treatise."
COXRAD, T. A. Jour. Acad. Sci., Philadelphia.
COPE, E. D. Hayden's "U. S. Geog. and Geol. Surv.," vol. ii. "Creta-
ceous Vertebrates ; " Newberry's " Ohio Survey " "Pal. Reptiles of the Coal."
DADDOW, S. H. " Coal, Iron, and Oil."
DANA, J. D. Wilkes's " U. S. Explor. Exped." vol. on " Geology ; " " Man-
ual of Geol."
DAWSON, J. W. " Acadian Geology."
DE LA BECHE, H. " Geological Observer " " Sections and Views of Geo-
logical Phenomena."
D'ORBIGNY, A. " Paleontologie et Geologic."
EMMOXS. E. " Eep. Geol. of K Y. ; " " Rep. Geol. of K C."
FORBES, J. " Alps of Savoy."
FOSTER and WHITNEY. " Rep. on Geol. of L. Supr. District."
GABB, W. M. Whitney's " Geol. Surv. of California."
GEIKIE, A. " Great Ice Age."
GUYOT, A. " Physical Geography."
HALL, J. "Rep. Palaeontology of N. Y.; " "Rep. Geol. of Iowa; " "Rep.
on State Cabinet of K Y."
HAYDEN, F. V. " Rep. Geog. and Geol. Surv. of Terr., 1871-'73," and sev-
eral figures not yet published.
HILGARD, E. W. " Rep. Agric. and Geol. of Miss.," 1860.
HITCHCOCK, E. " Ichnology of Mass.," 1858.
HITCHCOCK, Jr., E. Geol. Map of U. S. in Walker's Statistics of U. S.
HOLMES, W. II. Drawing of Geyser Eruption.
HOWELL, E. E. " U. S. Geog. Surv. by Wheeler," vol. iii. " Geology."
HUXLEY, T. H. " Manual of Anat. of Vertebrates."
JACKSON, W. H. Photograph of Geyser Eruption.
JOHNSTONE, A. K. "Phys. Atlas," last edition.
LEIDY, J. " Cretaceous Reptiles of U. S. ; " "Smithsonian Contributions,"
1865 ; " Fossil Vertebrates of U. S. ; " Hayden's " Geol. Surv. of Terr.," vol. i.
572 LIST OF AUTHORITIES.
LESLEY, J. P. " Manual of Coal and its Topography."
LESQUEEEUS, L. Owen's " Rep. Geol. of Ky. ; " Owen's " Rep. Geol. Ark. ; "
Hayden's " Geog. and Geol. Surv.," vol. vi. ; " Cret. Flora of U. S."
LOGAN, W. " Rep. GeoL Canada."
LTELL, C. "Principles of Geology;" "Elements of Geology;" "An-
tiquity of Man."
MANTELL, G. A. " Fossils of British Museum."
MAOUT and DECAISNE. " General System of Botany."
MAESH, O. C. "Cretaceous Reptiles and Birds, and Tertiary Mammals ;"
Am. Jour, of ScL, 1871-'77.
MEEK and WORTHED. " Geol. Surv. of 111.," vols. ii., iii., iv., v., vi.
MEEK, F. B. Whitney's " Geol. Surv. California," vol. i. ; Newberry's
" Geol. Surv. of Ohio Pal.," vols. i. and ii. ; " Palaeontology of Upper Missouri ; "
"Smithsonian Contributions," 1864.
MURCHISON, R. I. " Siluria."
NEWBERRY, J. S. " Rep. Geol. Surv. of Ohio ; " " Geol. of Macomb Expe-
dition; " " Pacific R. R. Reports," vol. vi.
NICHOLSON, H. A. "Manual of Palaeontology;" "Manual of Zoology;"
"Ancient Life History."
OWEN, D. D. " Rep. Geol. of Wisconsin, Iowa," etc.
OWEN, R. " British Fossil Mammals ; " " Palaeontology."
PACKAED, A. S. Life-Histories.
PHILLIPS, J. " Manual of Geology ; " " Geology of Oxford."
PICTET, F. J. " Traite" de Pale"ontologie."
POWELL, J. W. " Exploration of Colorado River ; " " Geology of Uintah
Mountains."
ROGERS, H. D. " Rep. Geol. of Pennsylvania."
SAFFORD, J. M. " Rep. Geol. of Tennessee."
SCTTDDER, S. H. Worthen's " Rep. Geol. of 111.," vol. iii.
SHAEPE, D. Quar. Jour. Geol. Soc., vol. iii., 1847.
STEVENSON, J. J. "Wheeler's " U. S. Geog. Survey," vol. iii. " Geology."
TAYLOR, R. C. " Statistics of Coal."
TYNDALL, J. " Glaciers of the Alps."
WAILES, B. L. C. " Rep. Agric. and Geol. of Miss.," 1854.
WARD, H. Illustrated Catalogue of Casts.
WHEELEB, G. M. " IT. S. Geog. Surv. west of 100th Meridian."
WHITE, C. A. Wheeler's " U. S. Geog. Surv.," vol. iv. "Palaeontology."
WHITNEY, J. D. " Geol. Surv. of California ; " " Geol. of L. Superior Dis-
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WOODWAED, S. P. " Manual of Mollusca."
WOETHEN. " Geol. Surv. of Illinois."
INDEX.
PAGE
A
Acanthaspis 326
Acanthotelson Stimpsonl 387
Acanthoteuthis antiquus 424
Acephals or Bivalves 301
Acer trilobatum 483
Acervularia Davidson! 319
Acrodus minimus 408
nobilis 427
Acrogens, age of 269, 280
and amphibians, age of 333
Actinoceras 306
^Eschna eximia 426
Agencies, aqueous 9
atmospheric 3
igneous 76
organic
Age of acrogens
amphibians
fishes
invertebrates 282
mammals 475
man 557
mollusks 282
reptiles 404
Ages 269
Agnostus interstrictus 285
Alecto auloporoides 297
Alethopteris Massilonis 352
Whitneyi 448
Alorisma pleuropistha 385
ventricosa 335
Alps 256
Atnblypterus macropterus 890
Ambonychia belli striatus 304
American mud-fish 339
Amia 329
Ammonites bifrons 422
cerdatus 422
Chicoensis 454
Humphreysianus 422
Jason 422
Jurassic 421
margaritanus 422
Ammonite tribe 306
Amphibamus 394
Amphibians, age of 269, 280
Carboniferous 390
133
314
Amphitherium.
Prevostii. .
Amygdaloid....
211
Ancyloceras
percostatus
Andrias Scheuchzeri ,
Andromeda vaccinifolise afflnis
Auemopteris oblongata
Animals of Carboniferous
Cretaceous
DeTonian 319
Jurassic 419
Jura-Trias 442
Permian 402
464
459
Quaternary ............................. 536
Silurian 290
Tertiary 485
Triassic 406
Annelids, Silurian 309
Annularia inflata 361
Anomalocardia Mississippiensis 486
Anomodonts 410
Anomoepus minor 443
Anoplothcrium commune, restored 498
Anon ra 390
Antholites 349
Anthophyllitis Devonicus 318
Anthracite 342
region of Pennsylvania, map of 337
section of, magnified 341
Anthracosaurus 394
Anthrapalasmon gracilis 387
Anticline 177
Antiquity of man 560
Apateon 394
Apatornis 470
Apiocrinua Eoissianus 420
Aporrhais falciformis 463
Appalachian chain 254
coal-field 33S
revolution 400
Apteryx Anstralis 560
Aptornis 558
Arancaria, cone of 419
Araucariae 348
Araucarites gracilis 349
Archan or Eozoic age 269
and Palaeozoic eras, interval between . . 280
574:
INDEX.
Archaean era, time represented by 274
times, physical geography of 274
Archseocidaris 383
Archseopteryx macron ra 470
restored 436
fore-limb of 437
tail, vertebrae, and feather of 437
Archegosaurus 393
Archimedes Wortheni 381
Arenicolites didymus 286
Armadillos 547
Artesian wells 69
Arthrophycus Harlani 289
Articulates 308
Artiodactyls 508
Asaphus gigas 310
Aspidura loricata 406
Astarte excavata 421
Astartella Newberry i 385
Asteria lombricalis 420
Asteroids, Silurian 300
Asterophyllites foliosus 361
latifolia 317
Atlantic Ocean, currents of 39
Atlantochelys gigas 468
PAGE
Belemnites unicanaliculatus 424
Bellerophon Newberryi 321
sublsevis 386
Belodon 494
Carolinensis 447
Beryx Lewesiensis 466
Big Bone Lick 542
Bird, fore-limb of 437
Birds, Cretaceous 470
Jurassic 436
Tertiary 494
gigantic extinct, of New Zealand 558
Bitumen, geological relations of. 376
origin of 376, 379
Blastids, Carboniferous 382
Blatta Maderse 388
Blattina vennsta 388
Bog-iron ore 136
Bone-caverns 536
origin of 539
small 143
Auriferous quartz-veins 231
Aurignac Cave 565
Avicula contorta 407
socialis 407
Trentoneneis 304
Aviculopecten parilis 321
Axes, anticlinal 177
monoclinal 178
synclinal 177
Baculites 463
anceps 464
Badlands 247,478, 479
Bakervillia parva 402
Balanced stones 52
Baphetes 394
Barren Island, section of. 89
Bars 30
Basalt 205
cause of columnar structure of 210
columnar 209
direction of columns of 210
Bat, fore-limb of 437
Bathygnathns borealis 447
Batocrinus Chrystii 382
Beaches and terraces 539
Belemnite, animal, restored 423
Belemnites 423,424
clavatus 424
densns 449
fossil ink-bags of. 424
hastatus 424
Belcmnite-shell, restored 423
Bclemuites impresses 463
ne-caves 542
- human remains in 563
Bone-rubbish, cave, origin of 538
; Bos primigenius 560
j Botanical temperature-regions, in latitude.. 156
vertical 156
| Bowlders 515
of disintegration 6
! Bracliiopod, general description of. 301
! Brachiopods 301
Carboniferous 384
Cretaceous 461
Devonian S20
- Jurassic ............................ 419, 421
- Permian ............................... 403
- Silurian ................................ 303
- structure of ............................ 302
Brachiospongia Roemerana .................. 291
Brachyphyllum, branch of. .................. 448
Brains of coryphodon, dinoceras, and bron-
totherium, compared ...................... 507
Breccia ...................................... 210
Bridgerbeds .............. ................. 502
Brontotheridae .............................. 505
Brontotheriuin .................. ............ 505
- skull and brain of ...................... 507
- ingens, skull of ........... ............. 505
Brontozoum giganteum
Bronze age
- transition to
Buprestidium....
Buthotrephis graciliP ........................ 289
- succnlens .............................. 239
Buttes ...................................... 17
Buttes of the Cross ......................... 16
Calamite, restoration of. 362
Calamites and their allies 361
cannseformis 861
California Miocene shells 487
Caliipteris Sullivanti 852
561
42T
INDEX.
575
PAGE
Camarophoria globulina 403
Canada period 282
Cancellaria vetusta .' . . 487
Canons, how formed 15
Caprina adversa 462
Carboniferous age, echinoderms of. 383
age, fauna of 381
bivalve and univalve shells 385, 386
brachiopods 384
conifers, affinities of 349
crustaceans 386, 387
fishes 388-390
fresh-water shells 385
goniatites 386
insects 388
period proper, rock-system of 334
plants, structure and affinities of. 346
system 280,333
system and age, subdivisions of 334
vertebrates 388
Carcharodon augustidens 491
Cardiocarpon 350
Cardiocarpum Bailey i 318
Cardiocarpns 348
Cardiola interrupts 304
Cardium Hillannm 1S2
Meekianum 487
Rhaeticum 407
Carpolithes irregularis 482
Caryocrinus ornatus 299
Casts of organic remains 194
Catskill period 315
Caulopteris primeva 354
Cave bear 536
Gailenreuth, section of. 537
hyena 536
Caves, limestone 70
Cenozoicera 269,475
divisions of 476
general characteristics of 476
Cephalaspis Lyelli 323
Cephalopods 305
Carboniferous 386
Cretaceous 464
Devonian 320
diagram showing distribution in time. . 425
Jurassic 419
Silurian 307, 308
suture and siphon of, diagrams showing. 422
Ceratites 406
nodosus 407
Whitneyi 449
Ceratodus 328
altus, dental plate of. 408
Fosterii . . 329
serratus, dental plate of 408
structure of limbs of 327
Cervus Americanus
megaceros, skeleton of.
Cestracion Phillips!
Ceteosanrus, femur of 434
Chalk ... 452
PAGE
Chalk cliffs with flint nodules 190
continuity of the 473
foraminifera of 453
origin of. 453
seas of Cretaceous times, extent of, in
Europe 4E4
seen under the microscope 453
Chamaerops Helvetica 483
Champlain 532
epoch 513, 520
Cheirotherinm 419
Chemical effects of subterranean waters 70
Chemung period 315
Chlamydotherium 547
Chlorite-schist 214
Chonetes Dalmaniana 384
Chrysalidina gradata. 453
Cinder-cone, section of 87
Cinnamomum Mississippieuse 482
polymorphnm 483
Cladodus spiuosus 389
Clay, formation of 7
slate 214
Cleavage, association with contorted laminae 183
association with foldings of strata 182
crystalline 180
flag-stone . 180
organic 180
physical theory of 185
planes 181
planes intersecting strata 182
planes cutting through strata 180
slaty 180
5-42
slaty, Sharpe's theory of. 181
Sorby's theory of 185
structure 179
theory, geological application of. 187
Tyndall's theory of 186
Clepsysaurus Pennsylvanicus 447
Clinometer 176
Clisiophyllum Gabbi 381
Club-moss compared with Icpidodendron. . . . 357
Clupea alata 491
Clypeus Plotii 420
Coal areas of different countries compared. 339
areas of the United States 338
basins, Jura-Trias 445
basins, Jura-Trias, fossils of 446
catamites 347
conifers 347
Cretaceous 455
estuary or raft theory of 363
extra-carboniferous 339
fat 343, 352
ferns 347
field, Appalachian 338
field, central 339
field, Michigan 339
field, Nova Scotia and New Brunswick 339
field, Rhode Island 339
field, Richmond and North Carolina. . . 445
field. Western 339
formation, estimate of time in 307
576
INDEX.
PAGE PAGE
Coal, formation of 344 Conocoryphe Kingii 265
fusing 343 Continental form, laws of 168
highly-bituminous 343 Conularia Trentonensis 305
lepidodendrids 347 Copper, veins of 230
measure shale weathering into spheroids 191 Coral, compound, orcorallum 138
measures, iron-ore of. 373 forests, 138
measures, Jurassic 415 growth, conditions of 140
measures, period of. 334 islands 139
measures, plication and denudation of. 336 islands, amount of vertical subsidence. 146
measures, thickness of strata of 335 islands, area of land lost 146
metamorphic 345 islands, crater theory of 143
mode? of occurrence of. 335 islands, rate of subsidence 147
origin of 343 islands, subsidence, geological applica-
origin of, and its varieties 340 tion 148
peat-bog theory of 363 islands, subsidence, theory of. 144
period, cause of climate of 370 islands, subsidence, time revolved 148
period, physical geography and climate 369 polyp 138
plants, fruits of. 350 reef. 139
plants, living congeners of 348 reefs and islands 138
plants, principal orders of 347 reefs, barrier and circular, theories of . . 143
plants, where found 347 reefs, barrier 141
plants of, their structure and affinities 346 reefs, circular 142
relative production of 340 reefs, friniMng 140
seams, faults in 337 j reefs, Florida 149
seams, number and thickness of. 338 I reefs. Pacific 140
seams, thickness of. 338 | Corals, Carboniferous 381
sigillarids 347 cup 292
steam 343 j cyathophylloid 293
theory of the accumulation of 363 | Devonian 319
typical 343 Favositid 293
arieties depending on degree of bitu- Halysitid 293
mi ization 342 Jurassic 419,420
arieties depending upon proportion Silurian 290
of fixed and volatile matter 342 Cordaites 34!
varieties depending upon purity 341 Robbii 311
arieties of 341 Corniferous period 315
vegetable structure in 341 Cormilites serpentarius 309
Coas Range of California 242,256 Coryphodon beds 509
of California, time of formation 512 hamatns, head and feet of. 502
Coccolith? 452 Bkull and brain of 607
Coccospheres 452 Coryphodontid* 502
Coccosteus 326 ! Crepidophyllum Archiaci 319
decipiens 324 | Cretaceous 404,450
Cochliodus contortus 389 animals 451
Comatnla rosacea 298 | area of, in America 451
Compsognathns, restoration of. 434 birds 470
Colorado, canon of. 16 brachiopods 461
Colossochelys Atlas 493 coal 455
Columbia River, falls of. 14 echlnoderms 459.460
Columnaria alreolata 293 fishes 465,466
Columnar structure of rocks 209 gasteropods 46!
Columns, granitic 221 ; lamellibranchs 461
Concretions, limestone 190 life-system of. 45(
Conformable strata 179 mammals 47:
Conifer, branch and fruit of Jura-Trias 448 mollnsks 463
Carboniferous section of trunk of 351 physical geography of, in America
trunk of Carboniferous 351 plants 456-458
Coniferous wood, fossil, section of 316 reptiles 46'
wood, recent, section of 316 rocks of 45:
Conifers, Triassic 406 rock-system of 45]
Coniopteris Mnrrayana 418 spomres 45!
Connecticut River sandstone 440 subdivisions of. 451
Conocardium trigonale 321 vertebrates 465
INDEX.
577
Crinoids, Carboniferous 382, 383
Jurassic 420
living 297
Silurian 300
Triassic 406
Crioceras 463
restored 464
Cristellaria subarcuatula 454
Critical periods ; 400, 551
Crocodile 432
Crossopterygians 328
Crustacea, Devonian 322
Jurassic 425
Silurian 309
Crustaceans, Carboniferous 386,387
Crustacean tracks 285
Cruziana bilobata 289
Ctenacanthus 389
vetustus 325
Ctenopistha antiqua 321
Cuneolina Pavonia 453
Cupriferous veins 230
Cyathophylioid corals 92
Cycadeoidea megalophylla 417
Cyeads, Triassic 406
Cycas circinalis 417
cross-section of stem of 360
Cyclopteris Jacksoni 218
obtusa 317
Cynod racon 411
canine tooth of. 410
Cyprea Matthewsonii 463
Cypris 385
Cyrtolites compressus 305
Dyeri 305
Trentonensis ... 305
Dadoxylon Quangondianum 318
Dalmania liinulurus 312
punctate 322
Daonella Lommellii. . . . v 407
Deltas 24
formation of 26
rate of growth 27
Dendrerpeton 391
Acadeanum. jaw and tooth of 392
Deridrograptus Hallianus 296
Denudation 260
agents of 260
amount of 261
geological time estimated by 264
Deposits, deep-sea shell 155
fresh-water shell 154
from icebergs 66
from wave-action 36
shell 153
Depression of coast of South Atlantic States 130
of deltas of rivers 129
of earth-crust in Pacific Ocean 130
Devonian animals 319
area of, in the United States 315
37
PAGE
320
320
319
Devonian brachiopods
cephalopoda
corals
Crustacea 322
division into periods 315
fishes 322-325
fishes, affinities of. 327
fishes, general characteristics of. 328
fishes, nearest living allies of 329
fishes, rank of. 331
gasteropods 321
insects 323
lamellibranchs 321
land-plants, general remarks on 316
life-system of 315
plants 315-318
physical geography of 315
radiates 320
system 280, 314
trilobites 322
Diamaguetism, apparent, of cleaved slates . . 184
Diatoms of Tertiary 483
Diatryma gigantea 494, 501
Dictyopyge 445
Dicynodon lacerticeps 410
Didymograptus V-fractus 295
Dike, definition of 207
Dikes, age of, how determined 207
effect of, on intersected strata 207
radiating, of volcanoes 87
Dinichthy s 325
jaws of 326
Terrelli 326
Dinoceras mirabilis, skull and feet of. 503
skull and brain of. 507
Dinornis elephantopus 559
giganteus 558
Dinosaurs 429, 431, 432
Dinotherium giganteum, head of 498
Diorite 205
Dip, definition of 175
overturn 176
Diplacanlhus gracilis 325
Diplograptus 295
Diprotodon Australis, skull of 547
Dirt-beds, Jurassic 415
Discoidea cylindrica 460
Dolerite 205
Drift 514
in relation to gold 554
theory of origin of. 517
timber 136
Dromseus 432
Dromatherium sylvestre, jaw of. 446
Earliest reptiles, general observations on. . . 395
Earth, constitution of the interior of 78
crust of the, definition of 166
crust of the, solid thickness of V8
cruet of the, gradual oscillations of. .... 127
crust of the, means of geological obser-
vation of. 166
5T8
INDEX.
PAGE PAGE
Earth, density of the 165 Encrinus liliformis 406
formofthe 164 Engis skull 563
general surface configuration of the 166 Entomostraca 312
Earthquake bridges 118 Eocene basin of Paris 496
determination of focus 124 epoch 477
effect of moon on 126 lower, mammals of 501
epicentrum, determination of 124 marine, of Alabama 500
focus, depth of. 122 middle, mammals of. 502
fissures produced by 118 Tertiary shells 4H6
great sea-wave 119 Eohippns 504
phenomena, explanation of. Ill Eosaurus 393
relation to seasons and atmospheric con- Acadieusis 394
ditions 126 j Eoscorpius carbonarius 388
shocks less severe in mines 118 i Eozofln Canadense 275
shocks more severely felt in mines 117 Equus 510
wave, spherical, determination of Ill | Eras 269
waves, definition of terms 107 I prehistoric 271
waves, their kinds and properties 106 | Erosion, average 10, 263
Earthquakes 104 by glaciers 51
connection with other forms of igneous general 2GO
agency 104 glacial, some general results of. 534
circle of principal destruction of 117 examples of great 12
elevation or depression during 127 ; of continents, rate of 10
frequency of. 104 \ of rain and rivers 9
minor phenomena of, explanation 116 Erosive power of water, law of variation of 11
motion of 116 Eruption of volcanoes 82
originating beneath ocean 119 Eryon arctiformis 426
proximate cause of. 106 Barrovensis 426
soundsof 116 j Estuaries 29
ultimate cause of. 106 deposits in 30
vorticose 114 mode of formation of 29
Earth's interior, constitution of 78 Etna, volcano of. 81
Echinoderms, Carboniferous 382, 383 j Euomphalus subquadratus 386
Cretaceous 459,460 Euphoberia armigera 388
Jurassic 420 EnproOps Danse 386
Silurian 296 Eurypterids, Devonian 322
Triassic 406 Silurian 313
Echinoids and asteroids, Carboniferous 383 Eurypterus remipes 313
Echinorachnis Breweranus 487 Evolution of organic kingdom, illustrated by
Edestosauras (clidastes) restored 468 Devonian fishes 332
jaw of 469 Coal plants 362
Edestusvorax 389 I early reptiles 395
Elephas Americanus 542,543 j early birds 436
antiquus 539 | early mammals 438,506
Falconeri 539 the central idea in geology 396
Melitensi? 539 Exogyra costata 401
mcridionalis 639
primigenins 5:59, 542 p
primigenius, molar tooth of 544
primigenius, skeleton of 541 Fagus ferruginea 482
tooth of 543 polyclada 458
Elevation and depression of earth's crust, Fault, definition of. 174
gradual 127 law of slip in 224
theoriesof 131 Faults 222
Babbage's theory 131 Fauna and flora, geographical definition of. . 155
general theory 132 and flora, continental 159
Herschel's theory 132 and flora, geological 196
gradual, of earth's crust, Greenland... . 129 and flora, cases of local 161
gradual, of earth's crust, Italy 12" first distinct, general remarks on 287
gradual, of earth's crust, Scandinavia.. 129 marine, distribution in latitude 162
gradual, of earth's crust. South America 127 marine, in longitude 162
Elk, Irish 636 marine, special cases 162
Enaliosanrs 428, 429 marine, variation with depth and bottom 162
INDEX.
579
PAGE I PAGE
Fauna, Quaternary mammalian, in North j Ganoids, Carboniferous 390
America 542 Devonian 323
Quaternary mammalian, of England.... 541 Jurassic 428
Favosites hemispherica 319 Gar-fish 327
Ficus pyrifonnis 487 Gas, smoke and flame from volcanoes 85
Felisatrox 542 Gasteropoda, Carboniferous 385,386
Felstone 205 Devonian 321
Fenestella elegans 297 j Cretaceous 463
Ferns, Coal 352-354 Silurian 304, 305
Fingal's Cave 209 j Tertiary 486
Fiord, ideal section through 535 j Gault 415
Fiords, how formed 534 < Geographical distribution of organisms 155
Fire-clay 335 Fauna of Quaternary times 547
Fishes, age of 269, 280, 314 j Geological chronology, manner of construct-
Cretaceous 465,466 I ing 200
Carboniferous 388-390 ( fauna and flora differ more than geo-
Devonian 322-324 graphical 197
Jurassic 425,427,428 period, tested by life-system 196
of Tertiary 490, 491 j period, tested by rock-system 196
Triassic 407, 408 j Geology, definition of 1
Fissures, 221 departments of 2
cause of 221 dynamical 3
Flabellina rugosa 453 historical 266
Flood-plain deposits 22. 522 structural 164
Flora, definition of. 155 German Ocean, tides of. 41
Florida reefs 149 Geyser-eruption, theories of 99
compared with other reefs 152 Geysers, Bunsen's investigations of 100
formation of. 150 | definition of 94
history of changes of. 150 description of. 94
Fold, monoclinal, 178 j Mackenzie's theory of 99
Foliation-structure 214 ' phenomena of eruption of 94
Forarainifera of Chalk 453 of the Yellowstone 9
shells of living 454 Glacial epoch 513, 514
Foraminifers 155 epoch, first 531
Forbesiocrinus Wortheni 382 j epoch, drift-materials of. 514
Forest, fossil, ground-plan of Carboniferous 365 epoch, second 534
Forest-grounds, fossil, Jurassic 416 erosion, some general results of. 534
Formation, geological definition of. ... 179, 196 ' lakes "54, 535
Formica lignitum 488 j scorings 53, 516
Fossils, definition of 191 times in America, probable condition
degrees of preservation of. 191 during 519
distribution in strata 195 j valley, section across 54
nature of, determined by age 196 Glaciation 52, 516
nature of, determined by country Glacier, great RhGne 532
where found 195 i Glaciers as a geological agent 51
nature of, determined by kind of rock 195 ! conditions necessary for 43
primordial, American 285 | definition of 43
primordial, foreign 286 } earth and stones on surface of. 49
stratified rocks classified by means of 199 evidences of former extension of 53
their origin and distribution 190 fissures in 62
Fractures 221 general description of 47
Free crinoid, liviag 298 graphic illustration of 46
Frost, action of 8 | line oflower limit of. 46
Frozen soils and ice-cliffs, mammoth in. ... 539 motion of 44
Fusing-point, not the same for all depths in motion of, and its laws 54
earth 79 j motion of, theories of 57
i physical theory of veins of. 63
Q ramifications of 44
j structure of 60
Gailenrenth Cave, section of 537 transporting power of. 52
Galerites albogalerus 460 veined structure of 62
Ganges, average erosion by 10 Globigerina bulioides 454
Ganocephala 393 I ooze 155
580
INDEX.
Glyptocrinus decadactylns 299
Glyptodon 547
claripes 547
Glyptolemus Kinairdii 325
Giant's Causeway 209
Gigantitherium caudatu m 443
Gneiss 214
decay of 7
Gold, auriferous veins 231, 237
drift in relation to 554
Goniatites, Carboniferous 386
crenistria 386
lamellosus 321
Lyoni 386
Goniopygus major
Gorges, how formed
Granite, decay of
graphic
origin of
syenitic
veins 205
Granitic rocks, chemical composition and
kinds of 2C4
rocks, mode of occurrence of 204
Graptolites 293, 296
Clintonensis 296
Graptolithus Logani 295
Green River Basin, Wahsatch beds 501
River Basin, Bridger beds 502
Greensand 456
Green-stones ... 206
Gryphaea calceola 449
speciosa 449
Gulf Stream, probable agency in formation
of Florida reefs 152
Gymnophiona 390
Gypsum deposited from springs 73
Gyracaiithus 389
PAGE
Huronia 306
Hyalithis primordialis 285
Hybcdus apicalis 408
reticulatus, spine and tooth 427
Hyrachyus 502
Hydrographical basin 10
Hydrozoa, living 294
Silurian 293
Hyena spelaea, skull of. 538
Hylseoeaur 434
Hylerpeton 394
j Hylonomus 394
Hymenocaris vermicauda 286
; Hymenophyllites alatus 353
| splendens 354
Ice, agency of.
floating
Tcuberss as a geological agent
deposits from
formation of
number of
period of
Ice-pillars, formation of
Ichthyocrinus sublajvis
Ichthyornis
dis par
Ichthyosaurus
communi?
Hadrosaurus, restored 468
teeth of 467
Haly sites catenulata : 293
Hamilton period 315
Hamites 463
Helioceras 463
Robertianus 464
Hemerobioides giganteas 427
Hemicidaris crennlaris 420
Hemitelites Brownii 418
Hesperornis regalis, jaw, vertebra, and tooth,
of 471
Heterocrinus simplex 300
Hipparion 509
Hippnrites Toucasiatia 462
Holoptychins Hibberti, tooth of 390
nobilissimus 324
Homocrinus scoparius 300
Hornblende schist 214
Horse family, diagram of gradual changes of 510
genesis of. 509
Horizon, geological 197
paddle, web of
tooth of..
vertebrae of.
Igneous agencies
Iguana, section of jaw of, showing teeth..
Iguanodon
pelvis of.
tooth of
Inachus Kaempferi
Indusial limestone. . .'
Infusorial earth, Richmond..
earths, origin of
Inoceramus dimidins
Insects, Carboniferous
Devonian
Jurassic
43
64
lit 1 ,
66
64
65
513
470
471
429
428
429
428
428
76
432
314
Tertiary
Interior heat of the earth
of earth, increasing temperature of
of earth, rate of increase of temperature
not uniform
Invariable temperature, stratum of
Invertebrates, age of
Irish elk, skeleton of.
Iron age
hat of copper vein
ore of the coal-measures
springs, deposits in
theory of the accumulation of
Islands, coral
mangrove
Isopods
INDEX.
581
PAGE
Jointing, regular, of limestone 220
Joints 181,220
Jupiter Serapis, temple of 128
Jura Mountains, section of 414
Jurassic animals 419
birds 436
cephalopods, ammonites 422
coal-measures 415
corals 420
Crustacea 425
crustaceans and insects 426, 427
echiuoderms 420
fishes 425, 427, 428
fossils of Utah 449
insects 425
lamellibranchs and brachiopods 421
mammals 438
period 404, 414
plants 417,418
plants, cycads, and ferns 418, 419
reptile? 428
Jura-Trias, bird-tracks in 443
distribution of strata of 439
disturbances which closed it 450
ephemera, larva of 442
in America 439
life-system of. 440
of Connecticut Valley 441
on interior plains and Pacific coast. ... 447
plants of 448
tracks, reptilian 442, 443
Kaolin, formation of 7
Kilauea, volcano of 81
Kimmeridge clay 415
King-crabs, larva of 312
Kitchen-middens 560
Labyrinthodon, tooth of
Labyrinthodont, section of tooth of
Labyrinthodonts
Lagoonless islands
Lake-dwellings
Lake-margins
Lakes, alkaline
chemical deposits in
flooded
glacial
salt
Lake Superior, effect of waves on shore of. . .
Tahoe, map of southern end of
Lamellibranchs
Carboniferous
Cretaceous
Devonian
Jurassic 419,
Tertiary.
Lamellibranchs, Triassic 407
Lamination, oblique or cross 173
Lamna elegans
Land-surfaces and sea-bottoms, cause of. .
Laurentian rocks, evidences of life in
system, area of, in North America . . .
system, rocks of
system of rocks
Laurus Nebrascensis
Lava 83
hardened 85
sheets 207
Lead, veins of. 231
Lebias cepbalotes 492
Lepadocrinus Gebhardii 299
Lepidodendrids 355, 356
Lepidodendron 355
compared with club-moss 357
corrugatum 356
diplotigioides 356
Gaspianum 317
ideal section of. 357
modulatum 356
politum 356
rigen? 35d
Lepidoganoids 327
Devonian 324,325
Lepidophloios Acadianus 356
Lepidosiren 327, 329
jaws of 326
Lepidosteus 327, 329
Lestornis crassipes 471
Lestosaurus, paddle of 469
Levees, artificial 23
natural 23
Lias ' 414
Libellula 427
Westwoodii 427
Life-system a test of formation 196
Lime-accumulations 138
Limestone caves 70
concretions 190
decay of 7
indusial 489,490
Limuohyus (Palaeosyops) 502, 504
Limuloids 313
Limulus Moluccanus 314
trilobite stage of 312
young of 312
Lingula acuminata 285
anatina 301
antiqua 285
Credneri 403
Lingulella ferrnginea 286
Liquidamber integrifolium 457
Lisbon earthquake 120
Lithostrotion Californiense 881
Litnites cornu-arietis 308
Graftonensis 308
Lituola nautiloides 453
Londsdalia floriformis 292
Lookout Mountain 247
Lower Helderberg period 282
582
INDEX.
LucinaObioensis....
Lycosaurus ,
PAGE
.... 321
410, 411
Machaeracanthus major 325
Machairodus cultridene 500
latidens 536
neogsens, tooth of 544
Macrocheilus Newberryi 386
Macropetalichthys 326
Sullivanti 327
Macropus Atlas 547
Titan 547
Maelstrom 34
Malacostraca 312
Mammals, age of 269, 475
Cretaceous 472
first, affinities of 438
Jurassic 438
of Tertiary, general remarks on ... 495, 506
Triassic 411,447
Mammoth 539
age 561,562
drawing of, by contemporaneous man. . 566
molar tooth of. 544
skeleton of 541
Man, age of. 269, 557
antiquity of 560
Miocene, supposed 561
Neolithic 566
Pliocene, supposed 561, 567
primeval 538
Quaternary 562
Mangrove Islands 151
Marble 214
Mariacrinns nobilissimus 300
Marly soil, formation of 7
Marshes and bogs, Quaternary mammals
in 539,542
Mastodon Americanus 542
Americanus, tooth of. 543
Mastodonsaurus Jsegeri 408
Manna Loa, volcano of 81
Mauvaises Torres 247, 478, 479
Torres of Nebraska 505
Mechanical agencies of water 9
theory of slaty cleavage, Sharpens 181
Megalonyx, claw-core of. 546
Megalosaurus, head of. 433
tooth of 434
Megaphyton a^l
leaf-scar of 354
Megatherium Cnvieri 545
jaw of 545
mirabilis 545
Melaphyr 205
Menodus 505
Mentone skeleton 564
Mesas 17
Mesozoic animals 406
era 265,404
era, disturbance which closed the 475
PAGE
Mesozoic era, general characteristics of 404
era, subdivisions of 404
general observations on the 474
Metamorphism, agents of. 215
alkali as agent of 216
crushing as cause of heat in 216
explanation of phenomena associated
with 217
genera] 215
215
SIB
816
215
215
51
3SS
211
411
14
225
heat as agent of
local
pressure as agent of
theory of
water as agent of.
Mer de Glace
Miamia Danae
Mica-schist
Microlestes antiquus
Minehaha, falls of.
Mineral veins
Mines, placer
Miocene epoch
man, supposed
of Nebraska
shells, California
Miohippus
Mississippi, delta of
erosion by
flood-plain of.
River, history of
Modern epoch
Modiolopsis solvensis
Mollueks, age of 269,
Monograptus priodon
Mont Blanc glacier region
Monticules
Moraine profonde
terminal, material of
Moraines
in Colorado
lateral
median
Mosasaure
Mosasanrns, tooth of
Mountain-chains, age of
along borders of continents
fissure-eruptions in
general form of, and how produced
metamorphism of
occurrence of fissures, slips, and earth-
quakes in
their structure and origin
theory of origin of
thick sediments of
volcanoes in
Mountain-formation, rate of.
Mountain-forms resulting from erosion
Mountain-origin
Mountain-ranges, parallel
Mountain-sediments, thickness of
Mountain-sculpture
Mountain-structure
Mountains, folding and metamorphism in...
INDEX.
583
Mnrchisonia gracilis 304
Myalina peratennata 402
Myolodon, skeleton of 546
Myophoris lineata 407
Myrmecobius fasciatus 411
N
Naiadites
Nautilus, pearly
pompilius
tribe
Neanderthal skull
Neolithic age
man
Neuropteris
flexuosa 352,
hirsuta
linsefolia
polymorpha
Niagara, falls of, description of
gorge, time necessary to form
period
Nile, flood-plain of
delta of.
Nodular or concretionary structure
Nodules, flattened by pressure .............. 183
flint, in chalk-cliffs .....................
form of. ................................
190
189
- kinds of, found in different strata ...... 189
Norfolk cliffs, effect of waves on ............ 34
Norway, effect of waves on the coast of ..... 35
Notidamus primigenius ..................... 491
Nototherium Mitchelli. . . .................. 547
Nuggets ..................................... 239
Nummulina laevigata ....................... 485
o
Obolella sagittalis
Obsidian
Oceanic agencies, land formed by
currents, geological agency of
theory of
Ocean-waves, effect of
Odontolcse
Odontopteris gracillima
Wortheni
Odontopteryx
toliapicus, restored
Odontornithes
Odontotormae
Oil-bearing strata of the Eastern United
States, area of
Oil-formations
Oil - horizons, principal, of the United
States
Oldhamia antiqua
Olenus macrurus
Oligoporus nobilis
Ondenodon Bainii
Onychaster flexilis
Onychoclus sigmoides
PAGE
OOlite 414
OOlitic limestones, origin of 415
Ooze, deep-sea 453
globigerina 454
Ophiderpeton 394
Ophileta compacta 285
Ophiomorpha 390
Orange sand, Mississippi, section of 515
Orbulina universa 454
Oreodon 505
major 506
Ores 228
metallic, formation of 236
Organic agencies 133
remains, decomposition of, prevented 191
Oganisms, geographical distribution of.... 155
progressive changes in 397
Oriskany period 282
Ormoceras 306
tenufllum 307
Ornithoscelida 431
Orodus mammilare 389
Orohippus 504, 510
Orthis Davidsonii 303
Hicksii 286
Livia 320
Orthoceras 285
Duseri 307
medullare 307
multicameratum 307
restoration of 309
vertebrale 307
Orthoceratite 306
Orthonema Newberryii 321
Orthonota parallela 304
Osmeroides Mautelli 466
Osteolepis 324
Ostrea Caroliniensis 486
Georgiana 485, 486
Idriaensis 461
Marshii 421
selteformis 486
Sowerbyi 421
Titan 486, 487
Otodus 465
Otozamites Macombii 448
Otozoum Moodii 442, 443
Oxford clay 415
Pachyderms 495, 508
Pachypteris lanceolata 418
Pachytherium 547
Palamster Shrefferi 300
PalfEOcarus typus 387
Paleolithic age 561
mammoth age 562
eer age 564
Pateoniscus, restoration of. 403
Palseopteris, leaf-scars of 354
Pateosyops 502
Pateotherium magnum 497
584
INDEX.
PAGE
Palseotherium magnum, restored 497
Placoderms
PAGE
324, 327
era, chemical changes daring
era, fauna of, general comparison of
with that of Neozoic times
era, general observations on
396
397
396
30U
Placoids, Carboniferous
389
465 466
Devonian
Jurassic
323,825
427
491 492
era, physical geography of, on Ameri-
279
280
Plagiaulax
438
346
456
rocks, area of, in the United State?
277
276
Devonian
. 315,317,318
417 418
278
448
times, general picture of
398
Silurian .
289
481-483
483
transition from, to Mesozoic
Paradoxides Bohemicus
400
287
287
496
136
133
133
135
134
135
446
353
352
487
4-21
486
407
407
Tertiary
Platanus aceroides
Plat 6 ' em ra .^ tlqua
403
Peat, alternation of, with pediments
Plesiosaurus
dolichodeirus, restored
430
428
299
402
composition and properties of.
conditions of growth of.
mode of growth of
Pleurocystites squamosns
Pleurotomaria agave
304
304
Pecopteris falcatus
lonchitica
3S6
Pliocene epoch
man, supposed
477
561
510
Pecten cerrocensis
430
head and tooth of.
430
. ..430
Peneroplis planatug
454
297
303
382
382
382
565
508
384
400
403
402
389
192
192
376
378
377
379
380
322
438
387
205
490
348
295
313
419
. B55
Plumbiferous veins
Podogonium Knorrii
231
483,488
448
406,446
327 329
Pentacrinus cap
Pentremites Burlingtoniensis
lanceolatus
Polyzoa, living
Silurian
2%
296,297
205
pyriformis
Perigord caves
Portheus molossus, tooth of.
restored
Primeval man, character of
in America
465
4C6
570
567
561
283
282
h
shells
in Europe
Primordial beach and its fossils..
period
Prionastrea oblongata
Proboscidian ..
420
.. 508
Petroleum, geological relations of.
kinds of rocks which bear
laws of interior distribution of.
403
mcsialis
384
384
origin of varieties of.
Phacops latifrons
300
Protester Sedgw c -
316
Protohippns
parvulus
Protophyllum quadratum
Protozoa, Cretaceous
Silurian
Pseudocrinus bifasciatus
Pseudomonotis Hawnii
510
506
458
459
290,291
2?9
402
317
PhillipsaaLodiensis... .
Phonolite
Phyllocladus
Phyllopods
Psvchozoic era... .
... 2C9, 557
INDEX.
585
Psychozoic era, characteristics of
era, distinctness of.
Pteraspis
Pterichthys cornutus
Pterodactyl, fore-limb of
Pterodactylus crassirostris
Pteropliyllum comptum
Jasgeri
Pteropods, Silurian
Pterosaurs
Pterygotus Anglicus
Gigas
Ptychodus Mortoni
Ptyonius
Pumice
Pupa vetusta
Pnzzuoli, temple of J'ipiter Serapis near. . .
Pythanomorpha
Quaternary, a period of revolution .......... 550
- mammalian fauna of England .......... . 541
- mammalian fauna in North America. . ." 542
- man ................................ 562, 567
- period .................................. 513
- period, cause of climate of ............. 548
-- period, characteristics of. .............. 513
- period in Eastern North America ..... .' 514
- period in Europe ....................... 530
- period in South America ............... 544
- period, mammals of .................... 536
- period, life of the ....................... 595
- period on the western side of the conti-
nent ...................................... 526
- period, plants and invertebrates of.. .. 535
- period, subdivisions of ................. 513
- period, time involved in ................ 550
-- period, general observations on ........ 548
- times, geographical fauna of
Quercus crassinervis
- primordialis
- Saffordi ................................. 482
Quartzite ................................... 214
Quartz veins, auriferous .................... 231
Radiates, Devonian 319
Silurian 290
Radiolites cylindriasus, section of 462
mammelaris 462
Raniceps 394
Ravines, how formed 15
Recent epoch 557
Recently extinct species, examples of 558
Receptaculites formosus 291
Reefs, coral, of Florida 149
coral, of Pacific 140
Refuse-heaps 566
Regelation theory of glaciers, of Tyndall ... 58
Reindeer age 561, 564
Reptiles, age of. 289,404
PAGE
Reptiles, Carboniferous 390
Cretaceous 467
ganoids allied to 331
Jurassic 428
of Tertiary 492
Triassic 408-410
Reptilian footprints, Carboniferous 390
footprints of Jura-Trias 442
Rhabdocarpon 350
Rhabdocarpus 348
Rhamphorhynchus Bucklandi, restored 435
Rhizocrinus Lofotensis 297
Rhombus minimus 492
RhOne, delta of 27
Ripple-marks, how formed 36
River-deposits, age of 27
River-gravels 544
547
482
457
age of 556
Rivers during the Quaternary period 529
winding course of. 21
River-swamp 22
Roches moutonnees 52,517
Rock disintegration 6
Rocking-stones '. 6, 52
Rock-salt, age of 412
mode of occurrence of 412
origin of 412
theory of accumulation of. 413
Rock-system, as a test of a formation 196
Rocks, classes of. 170
consolidation of, cause of 173
definition of 169
extent and thickness of 170
fissure-eruption 205
granitic 203
igneous 202
igneous, classification of. 203
igneous, different modes of classifica-
tion of 211
Laurentian system of 272
metamorphic 213
metamorphic. extent of. on earth-surface 213
metamorphic, origin of 213
metamorphic, position of. 213
metamorphic, principal kinds of 214
stratified, classification of 197
stratified, outline of classification adopt-
ed in this work 201
stratified, comparison of fossils of 199
stratified, have been gradually deposited 172
stratified, kinds of 171
stratified, lithological characters of. ... 198
stratified, more or less consolidated sedi-
ment s 171
stratified, originally nearly horizontal. 173
stratified, or sedimentary..^. 179
stratified, order of superposition of.. . . 198
... 170
n of.
structure common to all 220
trap, mode of occurrence of 203
trappean 205
trappean, general characteristics of .. . 205
trappean, varieties of. 805
586
INDEX.
PAGE
Rocks, unstratified 202 Silurian age, general life-system of. ...
unstratitied, extent on the surface 203 age, physical geography of
unstratified, mode of occurrence of. .... 202 system
unstratified, origin of 202 system, area of, in America 282
volcanic 207 system, character of rocks of 282
Rotalia concamerata 454 system, lower 282
Ruminants 508 system, rocks of 282
Rush Creek, section on 514 system, subdivisions of 282
system, upper 282
g Siphouia ficns 459
Sivatherium 498
Sabal major 483 Siwalik Hills, India, Miocene of 498
Saccocoma pectiuata 420 Slate-rocks, decay of 7
Sal iferous group 401 Slip, law of, in faults 224
Salina period 262 | Soils, depth of 5
Salisburia 348 | how formed 4
Salix proteaefolia 458 j Solenomya anodoutoides 385
Salt-lake, formation of. 74 Sphenophyllum erosum 361
Salt Lake, Utah 73 Sphenothallus angustifolius 2S9
Salt-lakes, deposits in 75 Spirifer 406
Sandstone, Connecticut River 440 Cumberlandise 303
Sandstones, decay of 7 fornacula 320
San Pedro, California, sea-terraces at 530 hysterica 302
Sassafras araliopsis 458 -perextensus 320
Mudgei 457 plenns S84
Scalaria Sillimani 463 striatus 302
Scaphites 463 Spirorbis 385
sequalis 464 Arkonensis 321
Schists .. 214 'omphalodes 321
Scolithns linearis 285 Sponges, Cretaceous 459
Scotland, effect of waves on the coast of. ... 35 j Springs 6f
Scaphiocriims scalaris 382 j carbonated 72
Seas, chemical deposits in 76 | chemical deposits in 71
during the Quaternary period 530 j fissure 6.
Sediments, transportation and distribution I Squatina acanthoderma 427
of.. ]8 ! Stagonolepis 494
Seismome'ters. :::.'...; 122 : St. Anthony, falls of 13
Sepia living 423 I Stegocephali 39-
Serapis, temple of. 128 Stigmaria ficoides 359
Serpentine 214 Stone age W
Shale, black, of coal-measures 335 Btonefield slate *S
Shasta, volcano of. 81 Strata, contorted 17<
Shell-deposits 153 elevated 174
Shell-mounds 536 eroded l.t
Shells, bivalve and univalve, Carbonifer- folded 17^
ous 385,386 inclined 1'-
distorted 181 outcrop of, definition of 177
fresh-water, Carboniferous 385 overturned 171
microscopic, as a rock-forming asrent.. 154 undulating 1
molluscous, as a rock-forming agent... 153 vertical
Permian 402 Stratification 20,1.0
Shore-ice f7 planes 18:
Sierra Nevada 256 Strike, definition of 175
Sigillaria elegans, leaf of 358 Stromatopora conceutrica 29:
Grseseri 358 ruaroea 29(
Isevigata ' 358 Strombodes pentagonus 295
obovata....' 358 Strophomena 4<X
restoration of 360 rhomboidalis 32(
reticulata 358 Structural geology 164
Sigillflria-stem, section of 360 Subangnlar stones 51<
Sigillarids 358 I Sub-Carboniferous period 334
Silica deposited from geysers 94-96 j Submarine banks 4(
deposited from springs 72 | Submergence, epoch of 532
INDEX.
587
PAGE PAGE
Subsidence during the Quaternary, evidence Time eince man appeared 569
of. 521 Times, geological, estimate of. 264
Sulphur deposited from springs 73 Tinoceras 503
Surface-rock underlying drift 515 Titanotherium 505
Syncliiie 177 Tooth, ganoid, structure of 331
Syringopora vesticilata 293 Torreya 348
System, Carboniferous 280 Toxoceras 463
Devonian 280 Trachyte 206
Silurian 280, 282 Transition period 400
Tree-fern, living 351
,n Tree-ferns of Coal period 349
Trees, erect fossil, in coal-measures 364
Table Mountain of California 246 Trematosaurus 408
section of 529, 556 I Trenton period 282
Tseniopteris elegans 448 Triassic conifers and cycaas 406
Tail-fin, heterocercal 330 fishes 407,408
homocercal 330 mammals 411
Talcose schist 214 period 404,405
Tapirus Indicus 496 period, subdivisions of 405
Teleosaurus brevidens 431 reptiles 408-410
Teleosts, Cretaceous 465 Triconodon 438
Tellenomya curta 304 Trigonia clavellata 421
Terebratula Astieriana 461 longa, shell and cast of 194
elonsrata 403 pandicosta 449
flavescens 302 Trigonocarpon, or Trigonocarpus 350
Terrace Canon 250 Trigonocarpus, or Trigonocarpon 348
epoch 513,524 1 Trilobite, larva of 312
epoch in Europe 534 Trilobites, affinities of 312
Terraces, river 522 Devonian 322
sea, at San Pedro, California 530 \ Silurian 309
Tertiary, animals of. 485 i Trocholites Ammonius 308
American localities of. 500 j Tuditanns radiatus 395
birds of 494 I Turritella alveata 486
coal 480 ! Turrulites 463
diatoms of. 483 | catenatus 464
fishes of 490,491 Tylosaurus micromus ... 469
life-system of. 480
mammalian fauna. 495 U
mammalian fauna, general observations Umtacrinus eocialis. ... . . 460
TJintatherium 503
-caro C so SSK^:;: ::: S
period, general observations on 511 | __ how produced '. 281
period, physical geography of 478 ; Undercla of coa] . seam 335
=.*::::::::::::::::::: 481 1S
T^SS ^ riore^nd 8 c a ies:::::::: S
rextulariavariabilis 454 | Ulliidta:!.""!'.!".";".'."'.'."!'.;!".'!; 542
Theca Davidn 286 pristinus....
Theory of coal formation applied to Amer- epelseus 536
ican coai-fieids 36 6 _ spe]Kns i' s ^{ ' oL :^[ ::::::::::::::::: 53 8
Theriodonts 41 0i 411
Thin-crust theory of earth 80 y
Thylacoleo carnifex 547
skull of. 548 Vanessa Pluto 488
Tides, effect of. 32 Vein-stuffs 228, 235
Tiger, sabre-toothed 536 Veins, age of, how determined 229
Tigrisuchus 411 auriferous quartz 231
Tillndonlia 504 auriferous, of California 237
Tillotherium fodiens, skull and brain of. .... 504 cupriferous 230
Time, great divisions and subdivisions of.. . 268 fissure 226
involved in the Quaternary period 550 metalliferous 227
588
INDEX.
Veins, metalliferous, contents of 227
metalliferous, important laws affecting
occurrence andrichness of. 232
metalliferous, ribboned structure of 228
metalliferous, theory of 234
metallifreous, vein-stuffs of
mineral
characteristics of.
irregularities of
of infiltration
of segregation
plumbiferous
pockets in 228
surface-changes of 230
Ventriculites simplex 459
Venus pertenuis 4g7
Vesuvius, section of 88
Viscosity theory of glaciers, of Forbes
Volcanic cone, comparison of, with exoge
nous tree
cone, formation of
cones, kinds of
Volcanic conglomerate
phenomena, subordinate
rocks, decay of
Volcanoes, aqueo-i^neous theory of
chemical theory of
definition of
estimate of ae of
internal fluidity theory of.
mechanical theory of
size, number, and distribution
superheated gas theory of
theory of
Volutalithes dumosa
symmetrica
Voltziaheterophylla...
57
.. 93
406
Vulture, tail of, compared with archseopteryx 437
W
Wahsatch beds
Walchia diffusus
piniformis
Water, chemical agencies of.
mechanical agenies of
comparison of different forms of..
Water-shed
Waters, subterranean
Waves, transporting power of
and tides, examples of action of..
Wealden
Wells, artesian . . .
PAGE
.. 502
.. 446
.. C7
.. 10
.. 414
.. 69
Welwitschia
White River Basin
Winds, action of
Wood, petrified
Worm, marine, trail of
Worms, tracks and borings, Silurian..
Yellowstone Park, springs in
geysers of
Yosemite, falls of
Zamia spiralis
Zamites occidentalis
Zaphrentis bilateralis
Wortheni
Zeacrinus elegans
Zermatt glacier
Zenglodon cetoides. tooth of.
cetoides, vertebrae and tooth of.
hydrarchus, skull of
Zoological temperature-regions
Zylobius sigillarire
416
448
292
319
383
50
500
501
501
158
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