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can Science Series

Physics.

By A. L. Kimball, Amherst College.

Chemistry.

By Ira Remsen. President of the Johns Hopkins University.

Geology. _ ^ ^, .

By Thomas C. Chamberlin and Rollin D. Salisbury. Uni-
versity of Chicago.

Physiography.

By Rollin D. Salisbury, University of Chicago.
General Biology.

By William T. Sedgwick, Mass. Institute of Technology, and
Edmund B. Wilson, Columbia University.

Zoology.

By A. S. Packard.

The Human Body.

By H. Newell Martin.

Psychology.

By Willl^lM James.

Ethics.

By John Dewey, Columbia University, and James H. Iufts.
University of Chicago.

Political Economy.

By Francis A. Walker.

Finance.

By Henry C. Adams, University of Michigan.

For full descriptionsof the Advanced, Briefer, and Elemen-
tary Courses published under each topic, see the publishers'
Educational Catalog.

HENRY HOLT AND COMPANY

19 W. 44th St., New York
2461 Prairie Ave.. Chicasro



AMERICAN SCIENCE SRmES




A COLLEG^E^^XT-BOOK

(^OLOGY

JT. ALBERTS COLLEGE LIBRARY



BY

THOMAS C. CHAMBERLIN

AND

ROLLIN D. SALISBURY

Heads of the Departments of Geology and Geography
University of Chicago




NEW YORK
HENRY HOLT AND COMPANY



Copyright, 1909

BY

HENRY HOLT AND COMPANY
-2. YII, '10



R. DONNELLEY & SONS COMPANY
CHICAGO



PREFACE

This text-book on Geolog}^ is intended primarily for college
students who are abeady in possession of the elements of physics,
chemistry, and biolog}'.- It is intended to serve as a basis for a
half-year's work; but by the judicious selection of material to be
presented and omitted, the volume may be used for briefer courses,
and supplemented by the numerous articles and treatises referred
to in the text, it may be made the basis for more extended courses.

In the preparation of the volume it has been the purpose of the
authors to present an outline of the saUent features of geolog};, as
now developed, encumbered as little as possible by technicalities,
and by details whose bearings on the general theme are unimpor-
tant. The attempt has been made to make the book readable,
in the hope that many persons not in colleges or universities may
be interested in following a connected account of the earth's his-
tory, and the means by which that history is recorded and read.

The general plan of the work ha-s been determined by the ex-
perience of the authors as instructors. Little emphasis is laid on
the commonly recognized subdivisions of the science, such as
dynamic geology, stratigraphic geology, physiographic geology, etc.
The treatment proceeds rather from the point of view that the
science is a unit, that its one theme is the history of the earth, and
that the discussions of djmamic geolog}", physiographic geolog}^
etc., apart from their historical bearing, lose much of then* signifi-
cance and interest. The effort has been, therefore, to emphasize
the historical element, even in the discussion of special themes,
such a5 the work of rivers, the work of snow and ice, and the origin
and descent of rocks. This does not mean that phases of geology
other than historical have been neglected, but it means that an
effort has been made to give a historical cast to all phases of the
subject, so far as practicable.



fix



•A^^



iv PREFACE



Throughout the work the central purpose has been not only to
set forth the present status of knowledge, but to present it so that
the student wHl be mtroduced to the methods and sphit of the
science. To this end the worMng methods of the geologist have
been implied as frequently as practicable. To this end also there
has been frankness of statement relative to the hmitation of
knowledge and the uncertamty of many tentative conclusions.
The theoretical and mterpretative elements which enter mto
the general conceptions of geology have been freely used, because
they are regarded as an essential part of the evolution of the science,
because they often help to clear the complete conceptions, and
because they stimulate thought. The aim has been, however,
to characterize h}i)othetical elements as such, and to avoid con-
fusmg the mterpretations based on h}T)othesis, with the statements
of fact and established doctrines. Especial care has been taken
to recognize the uncertam nature of prevalent interpretations when
they are dependent on unverified hypotheses, especially if this
dependence is likely to be overlooked.

In many cases the topics discussed will be found to be presented
in ways differing \videly from those which have become famHiar.
In some cases, fundamentally new conceptions of familiar subjects
are involved; in others, topics not usually discussed in text-books
are stated with some fullness; and m still others, the emphasis
is laid on points which have not commonly been brought into prom-
inence. Whether the authors have been wise in departmg to this
extent from beaten paths, the users of the volume must decide.
Especial attention is dhected to the map work suggested at vari-
ous points'in the text, as on pages 109, 194, 222, 288, 331, 366, 413,
475, 506, 659, 726, 771, and 845. The use of the topographic maps,
folios, and other publications of the United States Geological Sur-
vey, somewhat as suggested, will be of great service in making
the subject real. The reports of the several State Geological
Surveys of the states where this book is used, will also be service-
able. It is suggested that instructors who use the maps and folios
mentioned m the text wtII do well to plan for this work before
reaching the ends of the chapters where mention is made of this
work. The map work should be interwoven with the class-room



PREFACE V

wbrk, rather than added at its close. This adjustment must, of
course, be left to the individual instructor.

In addition to the map work it is hardly necessary to emphasize
the fact that field work is indispensable to the greatest efficiency.
Specific directions for field work, however, even if they were needed,-
are impracticable, since local fields vary so widely.

University of Chicago
May 15, 1909.



ONTENTS



PART I. DYNAMIC AND STRUCTURAL GEOLOGY

CHAPTER I

PRELIMINARY OUTLINE p^^^.

The Eakth in the Solar System 2

The Grand Divisions of the Earth 4

The atmosphere, 4. The hydrosphere, 6. The hthosphere, 7.



CHAPTER II

THE MATERIALS OF THE EARTH AND THEIR ARRANGEMENT

General H

Mantle rock, 11. Solid rock, 12. Stratified rock, 12. Igneous
rock, 13. Metamorphic rock, 14.

Igneous Rocks 1^

Composition of, 23. Classification of, 27. Disruption of, 31.

Sedimentation and Sedimentary Rocks 34

Metamorphism and Metamorphic Rocks 42

Classifications and Nomenclatures 58

Structural Features Common to All Rocks 61

Ore-deposits ^ ^°

Reference List of Important Minerals 74

Reference List of the Commoner Rocks 81



CHAPTER HI

•THE GEOLOGICAL WORK OF THE ATMOSPHERE

Mechanical Work 8^

Dust, 89. Sand, 92. Dunes, 93.

Chemical Work 102

The Atmosphere a Conditioning Agency 103

Summary 109

vii



vm



CONTENTS



CHAPTER IV
LAND WATERS — STREAMS

The Work of Running Water 1^^

Erosive Work of Running Water 114

Beginning of a vaUey, 115. The permanent stream, 117. Modes
of vaUey development, 119. Limits of growth, 121. The de-
velopment of tributaries, 121. The struggle for existence
among valleys and streams, 122. Pkacy, 123. Cycle of erosion
124. General characteristics of topographies developed by river
erosion, 133. Special features resulting from special conditions
of erosion, 133. Rate of degradation, 138.

Analysis of Erosion

Weathering, 140. Transportation, 144. Corrasion, 146. Cor-
rosion (solution, etc.), 148.

Conditions Affecting the Rate of Erosion 149

Effects of Unequal H.^jidness 1^"^

Effect of Ch.^'ges of Level

The Aggradational Work of Running Water 177

Causes of deposition, 177. Location of aUuvial deposits and their
topographic forms, 179.
Stre.oi Terraces

CHAPTER V
GROUND (UNDERGROL^^D) WATER

General Facts ^^"^

Work of Ground-water .= 20-

Chemical, 202. Quantitative importance of solution, 203. De-
position of mineral matter from solution, 205. Mechanical, 206.

Results of the Work of Grol^nd- water 206

Weathering, 206. Caverns, 206. Limestone sinks, 208. Creep,
slumps, and landsHdes, 209. Summary, 210.

9 J 1

Springs "^^^

Mineral matter m solution, 213. Geysers, 213.

21Q
Artesian Wells

CHAPTER VI

THE WORK OF SNOW AND ICE

090

Non-glacial Ice '^■^'^

Gl.'^ciers • ; • • 231

General phenomena of, 236. Size, 237. Movement, 238. Like-
nesses and unhkenesses of glaciers and rivers, 239. Surface
moraines, 242. Debris below surface, 245. Temperature, 245.
Compression and friction as causes of heat, 248. Summary, 249.



CONTENTS ix

The Work of Glaciers 251

Erosion and transportation, 251. Varied nature of glacial debris,
255. Topographic effects of glacial erosion, 256. Positions in
which debris is carried, 258. Wear of drift in transit, 262.

Deposition of Drift

Types of moraines, 266. Distinctive nature of glacial deposits,

267. Glaciated rock surfaces, 268.

272

Glacio-fluvial Work

Icebergs ^^

The Intimate Structure of Glacier Ice ^'o

Development of ice from snow, 275. Structure and arrangement
of crystals in glacier ice, 278. Probable fundamental element in
glacier motion, 280. Auxiliary elements, 282. Corroborative
phenomena, 285. Other views of glacier motion, 286.

CHAPTER VII

THE WORK OF THE OCEAN

General Facts ^89

Processes in Operation in the Sea 292

Diastrophism, 292. Vulcanism, 295. Gradation, 295. Move-
ments of the sea-water, 296. Waves, 297. Work of the waves,
299. Erosion, 299. Wave-erosion and horizontal configura-
tion, 306. Transportation, 308. Deposition by waves, under- .
tow, and shore-currents, 309. Effect of shore-deposition on
coastal configuration, 314. The work of ocean-currents, 315.

Deposits on Ocean-bed • • ^^^

Shallow-water deposits, 317. Chemical and organic deposits in
shallow water, 323. Limestone, 325. Deep-sea deposits, 326.
Contrasted with shallow-water deposits, 326.

CHAPTER VIII

LAKES •

General Facts '^'^'"

Changes taking place in lakes, 332. Lacustrine deposits, 333.
Extinct lakes, 334. Salt lakes, 335. Origin of lake basins, 337.

CHAPTER IX

MOVEMENTS AND DEFORMATIONS OF EARTH'S BODY
(DIASTROPHISM)

Minute and Rapid Movements 338

Earthquakes, 338. The geologic effects of earthquakes, 344.



X CONTENTS

Secular Movements 351

Minor movements, 354. The great periodic movements, 354.
Mountain-folding, 354. Plateau-forming movements, 355.
Continent-forming movements, 356. Extent of the movements,
358. Causes of movements, 360. Original distribution of heat,
361.

CHAPTER X

VULCANISM

Intrusions • ^^"^

Extrusions '^^^

Fissure eruptions, 370. Volcanoes, 371. Distribution of vol-
canoes, 372. Relations of volcanoes, 376. Products of
volcanoes, 377. Formation of cones, 379. Lavas, 383. Vol-
• canic gases, 385. The causes of vulcanism, 388. Modes of
reaching the surface, 391.

CHAPTER XI

STRUCTURAL (GEOTECTONIC) GEOLOGY

Original ^^^

Of sedimentary rocks, 394. Of igneous rocks, 399. Of metamor-
phic rocks, 400. Features arismg from disturbance, 400.



PART II. HISTORICAL GEOLOGY

CHAPTER XII
THE ORIGIN OF THE EARTH

Hypotheses of .^ ^^^

The Laplacian or "Nebular" Hypothesis, 416. The Meteoritic
Hypotheses, 419. The Planetesimal Hypothesis, 420.

CHAPTER XIII

STAGES OF THE EARTH'S HISTORY LEADING TO THE
KNOWN ERAS

Under the Laplacian Hypothesis -426

Under Modification of the Laplacian Hypothesis 430

Under the Planetesimal Hypothesis ,. — 432



CONTENTS XI

CHAPTER XIV

THE ARCHEOZOIC ERA

^ 436

General • •

Conceptions of the earth's composition, 436. Cxeneral character-
istics of the Archean, 440.

Distribution and Local Development of Archean 443

Bearing of the Archean on theories of the origin of the earth, 446.
Earher views of the Archean, 446. Life during the Archeo-
zoic, 447. Duration of the Archeozoic, 447. CUmate, 447.



CHAPTER XV
THE PROTEROZOTC ERA

Formations and Physical History 448

Stratigraphic relations, 448. Subdivisions, 450. Proterozoic
sedimentation, 450. Extent of Proterozoic formations, 453.
- The exposed formations, 453. Geographic relations of the ex-
posed Proterozoic to the Archean, 455.

Proterozoic of the Lake Superior Region -436

The Huronian systems, 457. The Keweenawan system, 460.
General considerations concerning the Lake Superior Protero-
zoic, 467. Sequence of events elsewhere, 470.

Proterozioc Rocks in Other Regions ^''^

Cordilleran region, 472. Eastern part of the United States, 472.
Summary, 473. In other contments, 473.

Life During the Proterozoic Era "4' ^

„ 474

Climate



THE PALEOZOIC ERA

CHAPTER XVI
THE CAIVIBRIAN PERIOD

Formations .\nd Physical History '*' ^

The subdivisions of the Cambrian and their distribution, 476.
Great submergence during the Cambrian, 478. Causes of sub-
mergence, 479. Basis for subdivision of the Cambrian, 481.
Sedimentation in the Cambrian period, 484. Distribution and
outcrops of the Cambrian system, 486. Cambrian in other
continents, 490. Duration of the Cambrian period, 493.



xii CONTENTS

The Life of the Cambrian 494

Plant fossils, 495. Animal fossils, 495. Zoological provinces,
503. The succession of faunas, 504. The abrupt appearance of
the Cambrian fauna, 505.

CHAPTER XVII
THE ORDOVICIAN (LOWER SILURIAN) PERIOD
Formations and Physical History.



507



521



Sedimentation during the Ordovician period, 507. Sections of the
Ordivician, 509. General conditions in the eastern part of the
continent, 510. Igneous rocks, 513. General conditions and
relations of the Ordovician system, 513. Close of period, 515.
Economic products, 517. Foreign Ordovician, 517. Duration
and climate, 520.

Life

Edaphic adaptations, 522. Provincial modifications, 522. Cos-
mopolitan development, 522. Marine Ufe, 523. Land life,
534.

CHAPTER XVIII

THE SILURIAN (UPPER SILURIAN) PERIOD

Formations and Physical Hsitory 536

Silurian of the East, 537. Silurian of the West, 543. Summary,
544. Foreign Silurian, 546.

Silurian Life ^^"

The transition from the Ordovician, 547. The expansional stage
of the Mid-Silurian fauna, 547. Foreign faunas and migrations,
554. The closing restrictional stage, 555.

CHAPTER XIX
THE DEVONIAN PERIOD

Formations and Physical History 559

Devonian of the East, 561. Devonian of the West, 567. Areas
where the Devonian cames to the surface, 569. Close of the De-
vonian, 571. Economic products, 570. Foreign Devonian, 571.
CHmatic conditions, 574.

Devonian Life 574

The marine faunas, 574. Helderberg fauna, 575. Oriskany
fauna, 577. Onondaga fauna, 578. Southern Hamilton fauna,
582. Northwestern Hamilton fauna, 585. Evidence of geo-
graphic connections, 586. Later Devonian (Chemung) fauna,
586. Devonian fauna in the Great Basin area, 587. Life of
land waters, 588. Land life, 592.



CONTENTS xiii

CHAPTER XX

THE MISSISSIPPIAN (EARLY CARBONIFEROUS) PERIOD

Formations and Physical History 596

East of the Great Plains, 597. In the Great Plains, 600. West of
the Great Plains, 600. General considerations, 601. Lower
Carboniferous of other continents, 603. Climate and duration,

606.

The Lite of the Mississippian (Subcarboniferous) 606

Marine faunas, 606. Kinderhook fauna, 607. Osage fauna, 607.
Waverly fauna, 61 L Great Basin fauna, 611. Genevieve (St.
Louis-Kaskaskia) fauna, 613. Evolution of the fishes in the
Mississippian period, 617. Land life of the Mississippian, 619.

CHAPTER XXI
THE PENNSYLVANIAN (UPPER CARBONIFEROUS) PERIOD

Formations and Physical History

Pottsville conglomerate (Millstone grit), 620. Coal measures, 621.
Productive coal-fields, 624. Coal, 630. Extent and relations of
coal-beds, 637. Varieties of coal, 637. Iron ore, 638. Geo-
graphic conditions in the eastern interior, 639. Duration of the
period, 640. Close of the period, 641. Carboniferous forma-
tions in other continents, 641.

Life of the Pennsylv.^jvtian Period

Plant hfe, 643. Climatic implications of the coal-plants, 651.
Land animals, 652. Fresh-water life, 655. Marine hfe, 656.



i^



620



643



CHAPTER XXII
THE PERMIAN PERIOD

Formations and Physical History 680

East of the Mississippi, 660. West of the Mississippi, 660. Corre-
lation, 662. In Europe, 662. Other continents, 666. Permian
glacial formations, 666. Clbse of the Paleozoic era, 668.

Life of the Permian ^^^

Impoverishment of life, 669. Plant life, 669. Land animals, 672.
Fresh- water life, 674. Marine fauna, 674.
Problems of the Permian "^ '



xiv CONTENTS

THE MESOZOIC ERA

CHAPTER XXIII

THE TRIASSIC PERIOD

Formations and Physical History <- 678

Eastern Triassic — Newark series, 678. In the West, 684. On the
Pacific slope, 685. Climatic conditions, 686. Close of the Trias,
687. Foreign Triassic, 687.

Life of the Triassic Period 690

Plant life, 691. Land animals, 691. Marine hfe, 695.

CHAPTER XXIV
THE JURASSIC PERIOD

Formations and Physical History • -• 7C2

Eastern part of the continent, 702. Western interior, 702.
Pacific coast, 705. Thickness, 707. Surface distribution and
position of beds, 707. Close of the Jurassic, 707. Orogenic
movements, 707. Foreign Jurassic, 708. Jurassic coal, 709.
CUmate, 710.

Life of the Period 710

Marine life, 711. Land hfe, 719.

CHAPTER XXV
THE COMANCHEAN (LOWER CRETACEOUS) PERIOD

Introductory 727

Formations and Physical History 728

Atlantic and Gulf Border regions, 728. Texas-Mexico region, 731.
Northern interior, 732. Pacific border, 733. Close of the
Comanchean (Lower Cretaceous) period in North America, 735.
Lower Cretaceous in other continents, 736.

Life "37

Terrestrial vegetation, 737. Land animals, 739. Fresh-water
fauna, 739. Marine faunas, 740. .

. CHAPTER XXVI
THE CRETACEOUS PERIOD

Formations and Physical History 742

Atlantic border region, 742. Eastern Gulf border, 744. Western •
Gulf region, 746. Western interior, 746. Pacific coast, 752.
Close of the period, 752. Upper Cretaceous of other continents;
755. Climate, 759.

Life of the (Upper) Cretaceous 759

Land plants, 759. Land animals, 762. Sea life, 765.



CONTENTS XV

THE CENOZOIC ERA H



CHAPTER XXVII 1

THE EOCENE PERIOD

Formations and Physical History 772

The Eastern coast, 774. The Pacific coast, 774. The Western
interior, 776. The Northwest, 778. General considerations.
778. Close of the Eocene in North America, 780. Eocene in
other continents, 780.

Eocene Life 784

Transition from the Mesozoic, 784. Vegetation, 786. Land ani-
mals, 787. Marine life, 794. Climate, 797.

Oligocene Formations 797

Life of the Oligocene 801

CHAPTER XXVIII

THE MIOCENE PERIOD 4

Formations and Physical History 805 Wl

Altantic coast, 805. GuK coast, 807. Pacific coast, 807. Non-
marine deposits, 811. Igneous activity during the Miocene, 812.
Close of the Miocene, 813. Miocene outside North America, 815.

Life of the Miocene, 818

Land plants, 818. Land animals, 819. Marine hfe, 824. Pro-
vincialism dominant, 824.

CHAPTER XXIX

THE PLIOCENE PERIOD

Formations and Physical History 828

Lafayette formation, 829. Marine Phocene, 835. The Atlantic
coast, 835. The Pacific coast, 835. Crustal movements of the
Phocene, 835. Foreign Pliocene, 840.

Life of the Pliocene 840

Land plants, 840. Land animals, 841. Marine hfe, 845.

CHAPTER XXX
THE PLEISTOCENE OR GLACIAL PERIOD

General 846

Distribution of glaciation, 846. Criteria of glaciation, 849. The
development and thickness of ice-sheets, 861. Stages, in the
history of an ice-sheet, 863.



XVI



CONTENTS



The Work of an Ice-sheet 864

Formations made by the ice-sheets, 864. Fluvio-glacial deposits,
869. Relations of stratified to unstratified drift, 872. Topo-
graphic distribution of stratified drift, 872. Changes in drain-
age effected by glaciation, 873. The succession of ice invasions,
874. The loess, 885. Duration of the glacial period, 890.

The Cause of the Glacial Period 894 •

Hypsometric hypotheses, 895. Astronomic hypotheses, 895.
Atmospheric hypotheses, 898.

Formations Outside the Ice-sheets 899

On the Atlantic and Gulf coasts, 900. In the interior, 904. In
the West, 905. Igneous rocks, 911.

Ch-\nges of Level During the Pleistocene 911

Life of the Pleistocene 9^^

Destructive effects of glaciation, 914. To-and-fro migration, 914.
Climatic adaptations, 915. Land Ufe of the interglacial stages
in glaciated areas, 916. Marine life, 917. The terrestrial Ufe of
the non-glaciated regions, 918. Pleistocene life outside North
America, 920. Man in the glacial period, 922.

CHAPTER XXXI

THE HUMAN OR PRESENT PERIOD

The Present Period Compared With the Pleistocene 931

The end of the glacial period, 931. The end of the deformation
period, 931. The channels on the continental borders, 933.

Life of the Hum.vn Period ^^^

The re-peopling of the glaciated areas, 935. The dynasty of man,
937. Man as a geological agency, 941. Prognostic geology, 942.

Reference Table of the Principal Groups of Plants 944

Reference Table pF the Principal Groups of Animals , 945



LIST OF PLATES

FACES PAGE

I. Dunes in contour 96

II. Streams disappearing in sand, gravel, etc., in an arid region . 120

III. YoutWul valleys, shore of Lake Michigan ...... 121

IV. Map illustrating piracy. Kaaterskill Creek, N. Y. . . 124
V. The widening of the river valley by the meandering of the

stream " 125

VI. Youthful valleys and topography in a region of slight rehef and

in a region of great relief 128

VII. Topographic maturity 132

VIII. Topographic old age 133

IX. Niagara Falls and its surroundings 156

X. Cushetunk and Round mountains, N. J 157

XI. Entrenched meanders. Conodoguinet Creek, Pa. . . . 172
XII. Section of the Cahfornia coast at Oceanside, showing changes

of level of the land 173

Xin. Alluvial fan at the base of mountains. Cucamonga, Cal. . 182

XIV. The Alluvial plain of the Missouri and Big Sioux; S. Dak. 183

XV. Limestone sinks due to ground-water 208

XVI. Glaciers of Glacier Peak, Wash. 236

X v^II. Glaciers and cirques of the Bighorn mountains .... 237

XVIIL An ill-drained plain of glacial drift ; Southern Wisconsin . . 270

XIX. Irregularities of coast developed by erosion and deposition . 303

XX. Shore-line of Marthas Vineyard, Mass 307

XXI, The upper end of Seneca Lake, N. Y 335



GEOLOGY



PART I

THE MATERIALS OF THE EARTH AND
PROCESSES WHICH AFFECT THEM

CHAPTER I
PRELIMINARY OUTLINE

Geology is essentially a history of the earth and its inhabitants.
It treats of rocks and of the agencies and processes which have
been involved in their formation, and from the rocks and their
structures it attempts to make out the various stages through
which the earth and the living things which have dwelt upon it
have passed. It is one of the broadest of the sciences, and brings
under consideration certain phases of other sciences, particularly
astronomy, physics, chemistry, zoology, and botany.

Subdivisions. So broad a science has many subdivisions.
That phase which treats of the outer relations of the earth is Cosmic
or Astronomic Geology; that which treats of the constituent parts
of the earth and its material is Geognosy, of which the most impor-
tant branch is Petrology, the science of rocks. That phase which
deals with the structural arrangement of the rocks is Geotectonic,
or Structural Geology; that which deals with the forces involved
in geologic processes is Dynamic Geology; that which treats of the
face of the earth, or topographic form, is Physiographic Geology;
that which concerns itself with the fossils that have been preserved
in the rocks, and with the faunas and floras that have lived in the
past, constitutes. Paleontologic Geology, or Paleontology. The treat-
ment of the succession of events is Historical Geology, which is

1



2 GEOLOGY

worked out chiefly from the succession of beds of rock formed in the
progress of the ages. .

Besides these general subdivisions, there are special applications
of geologic knowledge which give rise to other terms. Thus Fco-
nomic Geology is concerned with the industrial applications of
geologic knowledge, and Mining Geology, which is a sub-section of
economic geology, with the application of geologic facts and pnn-
ciples to mining. Other simHar subdivisions might be mentioned.

Dominant processes. Three sets of processes, now in operation
on the surface of the earth, have given rise to most of its surface
features. These processes have been designated Diastrophism,
Vulcanism (or Volcanism), and Gradation. Diastrophism includes
aU movements of the outer parts of the lithosphere, whether slow



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