Elements of Geology: A text-book, etc

Front matter

Bibd'seye Tiew of Marble CaSJon from the Vermilion Cliffs, near tiie Motjtii of the Paria. In the distance the Colorado River is seen to turn to the west, where its (forge divides the Twin Plateaus. On the right are seen the Eastern Karbab Displacements appearing as folds, and farther in the distance as faults. ELEMENTS OF a E O L O G T A TEXT-BOOK FOB COLLEGES AND FOR THE GENERAL READER. BY JOSEPH LE CONTE^ AirrnoE of "religion and science," etc., and professor of geologt and natural history IN THE UNIVERSITY OF CALIFORNIA. NEW YORK : D. APPLETON AND COMPANY, 549 AND 551 BEOADWAY. 1878. COPYRIGHT BY D. APPLETON AND COMPANY, 1877. PEEPACE. 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 multiplication 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 interesting to a class of young men, somewhat advanced in general culture and eager for knowledge, but not expecting to become special geologists.

In a word, I have tried to give such knowledge as every thoroughly 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 TREFACE. 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.

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 Survej's, in charge of Prof. Hayden and Lieutenant Wheeler, not only for valuable materials, but also for much personal aid. PAGE CONTENTS. INTRODUCTORY. Definition of Geology, and of its Depabtments 1-2 Geologt, 1 ; Principal Departments, 2 ; Order of Treatment, 2.

Chapter I

Atmospheeio Agencies 3-8 Soils, 4 ; General Explanation, 6 ; Granite, Gneiss, Volcanic Rocks, etc., 7 ; Limestone, 7 ; Sandstones, 7 ; Slate, 7. Mechanical Agencies of the Atmosphere. —Frost, 8 ; Winds, 8.

Chapter II

Aqueous Agencies 9-76 Section 1. Rivers, 9. Erosion of Rain and Rivers, 9 ; Hvdrographical Basin, 10 ; Rate of Erosion of Continents, 10 ; Law of Variation of Erosive Power, 11. Examples 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. Transportation and Distribution of Sediments, 18 ; Experiments, 18 ; Law of Variation, 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.

Ears, 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 ; Geological Agency of Oceanic Currents, 39 ; Submarine Banks, 40 ; Land formed by Ocean Agencies, 42. Section 3. Ice, 43. Glaciers. — Definition, 43 ; Necessary Conditions, 43 ; Ramifications 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; Transportation, 52 ; Deposit— Balanced Stones, 52 ; Material of the Terminal Moraine, CONTENTS. VIII TAGE 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 ; Regelation, 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, 0'_' ; 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 Spring.— Deposits of Carbonate of Lime, 71 ; Explanation, 71 ; Kinds of Materials, 71 ; Deposits of Iron, 72 ; Deposits of Silica, 72 : Deposits of Sulphur and Gypsum, 73. Chemical Deposits 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 70-132 Section 1. Interior Heat of the Earth. — Stratum of Invariable Temperature, 76 ; Increasing Temperature of the Interior of tho Earth, 77 ; Constitution of the Earth's Interior, 78 ; 1. Rate of Increase not uniform, 78 ; 2. Fusing-I'oint not the same for all Depths, 79 ; Astronomical Reasons, 80. Section 2. Volcanoes. — Definition, 81 ; Size, Number, and Distribution, 81 ; Phenomena 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. Theory of Volcanoes, 90 ; Force, 90 ; The Heat, 91 ; Internal Fluidity Theory, 91 ; Objections, 91 ; Chemical Theory, 92 ; Recent 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 ; Bunsen's Investigations, 100 ; Theory of Geyser-Eruption — Principles, 101 ; Application 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 ; Application to Earthquakes, 109 ; Experimental Determination of the Velocity of the Spherical Wave, 111 ; Explanation of Earthquake-Phenomena, 111 ; Vorticose 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 Epicentrum, 124 ; Determination of the Focus, 124 ; Effect of the Moon on Earthquake-Occurrence, 126 ; Relation of Earthquake-Occurrence to Seasons and Atmospheric 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 ; Greenland, 129 ; Deltas of Large Rivers, 129 ; Southern Atlantic States, 1.30 ; Pacific Ocean, 130. Theories of Elevation and Depression, 131 ; Babbage's Theorv, 131 ; Herschel's Theory, 132 ; General Theory, 132. CONTENTS. IX

Chapter IV. Page

Organic Agencies ' . 133-163 Section 1. Vegetable Accumulations.— Peat-Bogs and Peal-Swamps.— Description, 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-Iron Ore, 136. Section 3. Lime Accumulations. — Coral Reefs and Islands. — Interest and Importance, 138 ; Coral Polyp, 138 ; Compound Coral, or Corallum, 138 ; Coral Forests, 138 ; Coral Reef, 139 ; Coral Islands, 139 ; Conditions of Coral-Growth, 140 ; Pacific Reefs, 140 ; Fringing Reefs, 140 ; Barrier Reefs, 141 ; Circular Reefs, or Atolls, 142 ; Small Atolls aud Lagoonless Islands, 143. Theories of Barrier and Circular Reefs, 143 ; Crater Theory, 143 ; Objections, 144 ; Subsidence Theory, 144 ; Proofs, 145 ; Area of Land lost, 146 ; Amount of Vertical Subsidence, 146 ; Rate of Subsidence, 147 ; Time involved, 148 ; Geological Application, 148.

Reefs of Florida, 149 ; Description of Florida, 149 ; General Process of Formation, 150 ; History of Changes, 150 ; Mangrove Islands, 151 ; Florida Reefs compared with other Reefs, 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-Regions, 156 ; Botanical Temperature-Regions in Latitude, 156 ; Further Definition of Regions, 157 ; Zoological Temperature-Regions, 153 ; Continental Fauna and Flora, 159 ; Subdivisions, 160 ; Special Cases, 161 ; Marine Fauna — Distribution in Latitude, 162 ; Distribution in Longitude, 162 ; Depth and Bottom, 162 ; Special Cases, 162.

Chapter I

General Form: and Structure of the Earth .... 16-4-170 1. Form of the Earth, 164. 2. Density of the Earth, 165. 3. Tlie Crust of the Earth, 166 ; Means of Geological Observation, 166. 4. General Surface Configuration of the Earth, 167 ; Cause of Land-Surfaces and Sea-Bottoms, 167 ; Laws of Continental Form, 168. Rocks, 169 ; Classes of Rocks, 170.

Chapter II

Stratified or Sedimentary Rocks 170-202 Section 1. Structure and Position.— Stratification, 170 ; Extent and Thickness, 170 ; Kinds of Stratified Rocks, 171 ; I. Stratified Rocks are more or less Consolidated Sediments, 171 ; Cause of Consolidation, 172 ; II. Stratified Rocks have been gradually deposited, 172 ; III. Stratified Rocks 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 ; Geological Application, 187. Nodular or Concretionary Structure, 188 ; Cause, 188 ; Forms of Nodules, 189 ; Kinds of Nodules found in Different Strata, 189.

Fossils : their Origin and Distribution, 190 ; The Degrees of Preservation are very various, 191 ; Theory of Petrifaction, 192. Distribution of Fossils in the Strata, CONTENTS. X PAOE 195 ; 1. Kind of Rock, 195. 2. The Country where found, 195 ; 3. Tho Age, 196. Section 2. Classification of Stratified Rocks, 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 Surface, 203 ; Classification of Igneous Rocks, 203. 1. Granitic Rocks, 203 ; Chemical 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 Structure, 209 ; Direction of the Columns, 210 ; Cause of Columnar Structure, 210 ; Volcanic Conglomerate and Breccia, 210 ; Amygdaloid, 211. Other Modes of Classification of Igneous Rocks, 21].

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, 211.

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 Laws 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 ofthe 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. Metamorphism of Mountain-Chain3, 257 ; 5. Fissures and Slips, and Earthquakes, 258 ; 6. Fissure-Eruptions, 258 ; 7. Volcanoes, 258.

Chapter III

Primary or Palæozoic System of Rooks and Palæozoic Era . . 276-404 General Description, 276 ; Bocks — Thickness, etc., 276 ; Area in the United States, 277 ; Physical Geography of the American Continent, 279 ; Subdivisions, 280 ; The Interval, 280. Section 1. Silurian System: Age of Invertebrates. — The Rock System, 282; Subdivisions, 282 ; Character of the Rocks, 282 ; Area in America, 282 ; Physical Geography, 283 ; Primordial Beach and its Fossils, 2S3 ; General Remarks on First Distinct Fauna, 287. General Life-System of the Silurian Age, 288. Plants, 290. Animals. — Protozoans, 290 ; Radiates, Corals, 290 ; Hydrozoa, 293 ; Polyzoa, 296 ; Echinoderms, 296 ; Mollusks, 301 ; General Description of a Brachiopod, 301; Lamellibranchs, 304; Gasteropods, 305 ; Cephalopods, 305 ; Articulates, 308 ; Crustacea, 309 ; General Description, 309 ; Affinities of Trilobites, 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 Devonian Age — Plants, 315 ; General Remarks on Devonian Land-Plants, 316. Animals, 319 ; Radiates, 319 ; Brachiopods, 320 ; Cephalopods, 320 ; Crustacea, 322 ; Insects, 322 ; Fishes, 322 ; Affinities of Devonian Fishes, 327 ; General Characteristics of Devonian Fishes, 328 ; Rank of Devonian Fishes, 331 ; Bearing of these Facts on the Question of Evolution, 332 ; Suddenness of Appearance, 332. Section 3. Carboniferous System : Age of Acrogens and Amphibians. — Retrospect, 333 ; Subdivisions of the Carboniferous System and Age, 334. Carboniferous 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, v 338 ; Coal Areas of the United States, 338 ; Extra-Carboniferous Coal, 339 ; Coal, Areas of Different Countries compared, 339 ; Relative Production of Coal, 340.

Origin of Coal and of Us Varieties, 340 ; Varieties of Coal, 341 ; Varieties depending upon Purity, 341 ; Varieties of Coal depending on the Degree of Bituminization, 342 ; Varieties depending upon the Proportion of Fixed and Volatile 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. Conifers, 347 ; Affinities of Carboniferous Conifers, 349 ; 2. Ferns, 349 ; 3. Lepidodendrids, 355 ; 4. Sigillarids, 358 ; 5. Calamites, 361 ; General Conclusion, 362. CONTENTS. XII r.vciE Theory of the Accumulation of Coal, 363; Presence of Water, 363; Application ofthe 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 tho Ac cumulation of the Iron-Ore of the Coal-Measures, 374. Bitumen and Petro leum, 376 ; Geological Relations, 376 ; Oil-Formations, 377 ; Principal Oil- Horizons of the United States, 377 ; Laws of Interior Distiibution, 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, 891 ; 3. Archegosaurus, 393 ; 4. Eosaurus, 393 ; Some General Observations on the Earliest Reptiles, 395. Some General Observations on the Whole Palæo zoic, 396 ; Physical Changes, 396 ; Chemical Changes, 896 ; Progressive Change in Organisms, 397 ; General Comparison of the Fauna of Palæozoic with that of Neozoic Times, 397. General Picture of I'alœozoic Times, 398. Transmis sion from the Palæozoic to the Mesozoic — Permian Period. — The Permian a Tran sition Period, 400.

Chapter IV

Mesozoic Era — Age of Reptiles 404—475 General Characteristics, 404 ; Subdivisions, 404. Section 1. Triassio 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-Beds— Fossil Forest-Grounds, 415. Plants, ill. 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 ; Physical Geography of the American Continent during the Jura-Trias Period, 449 ; Disturbances which closed the Period, 450.

Section 4. Cretaceous Period, 450 ; Rock-System — Area in America, 451 ; Physical 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, iii. Disturbance which closed the Mesozoic, 475.

Chapter V

Cenozoic Era — Age of Mammals 475-557 General Characteristics of the Cenozoic Era, 476 ; Divisions, 476. Section 1. Tertiary Period. — Subdivisions, 477 ; Rock-System— Area 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. XIII 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. Quaternary 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 ofthe Drift, 517; Statement of the most Probable View, 518 ; Objections answered, 518 ; Probable Condition during Glacial Times in America, 519. II. Champlain Epoch, 520 ; Evidences of Subsidence, 521 ; Sea-Margins, 521 ; Flooded Lakes, 521 ; River Terraces and Old Flood-Plain Deposits, 522. III. Terrace Epoch, 524; Evidences—Sea, 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 Europe, 530 ; 1. Epoch of Elevation — First Glacial Epoch, 531 ; 2. Epoch of Submergence— Champlain, 532 ; 3. Epoch of Reelevation— Second Glacial Epoch — Terrace Epoch, 534; 4. Modern Epoch, 534 Some 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 Terraces, 539 ; 3. Marshes and Bogs, 539 ; 4. Frozen Soils and Ice Cliffs, 539 ; Quaternary 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, 550 ; 3. The Quaternary a Period of Revolution — a Transition between the Cenozoic and the Modern Eras, 550 ; 4. Drift in Relation to Gold, 554 ; Age of the River-Gravels, 556.

Chapter VI

Psychozoic Era — Age of Man — Recent Epocn .... 657-570 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 Palæolithic, 564 ; Auri gnac Cave, 565 ; Perigord Caves, 565 ; Conclusions, 566. Neolithic Man — Refuse- Heaps— Shell- Mounds — Kitchen-Middens, 566 ; 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, 509.

II. Character of Primeval Man, 570. INTRODUCTOKY. 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 phenomena of life.

This is physiology. 3. We may study tbe 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. INTRODUCTORY. Principal Departments. — The science of geology, therefore, naturally 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 thc organisms which have successively inhabited its surface. The structure and constitution of tho 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.