_AMERICAN SCIENCE SERIES—ADVANCED COURSE_
GEOLOGY
BY
THOMAS C. CHAMBERLIN AND ROLLIN D. SALISBURY
_Heads of the Departments of Geology and Geography, University of Chicago
Members of the United States Geological Survey
Editors of the Journal of Geology_
IN THREE VOLUMES
VOL. I.—GEOLOGIC PROCESSES AND THEIR RESULTS
SECOND EDITION, REVISED
[Illustration]
NEW YORK
HENRY HOLT AND COMPANY
1909
Copyright, 1904,
BY
HENRY HOLT AND COMPANY
PRINTED IN THE U. S. A.
PREFACE.
In the preparation of this work it has been the purpose of the authors
to present an outline of the salient features of geology, as now
developed, encumbered as little as possible by technicalities and
details whose bearings on the general theme are unimportant. In common
with most writers of text-books on geology, the authors believe that
the subject is best approached by a study of the forces and processes
now in operation, and of the results which these forces and processes
are now bringing about. Such study necessarily involves a consideration
of the principles which govern the activities of geologic agencies.
These topics are presented in Volume I, and prepare the way for the
study of the history of past ages, which is outlined in Volume II.
The general plan of the work has been determined by the experience 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 dynamic geology, physiographic geology, etc., apart from their
historical bearing, lose much of their significance and interest.
The effort has, therefore, been to emphasize the historical element,
even in the discussion of special themes, such as 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 the topics
permit.
Throughout the work the central purpose has been not merely to set
forth the present status of knowledge, but to present it in such a way
that the student will be introduced to the methods and spirit of the
science, led to a sympathetic interest in its progress, and prepared to
receive intelligently, and to welcome cordially, its future advances.
Where practicable, the text has been so shaped that the student may
follow the steps which have led to present conclusions. To this end
the working methods of the practical geologist have been implied as
frequently as practicable. To this end also there has been frankness of
statement relative to the limitations of knowledge and the uncertainty
of many tentative conclusions. In these and in other respects, the
purpose has been to take the student into the fraternity of geologists,
and to reveal to him the true state of the development of the science,
giving an accurate and proportionate view of the positive knowledge
attained, of the problems yet unsolved, or but partially solved, and of
solutions still to be attained.
The theoretical and interpretative elements which enter into 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 and complete conceptions, and
because they stimulate thought. The aim has been, however, to
characterize hypothetical elements as such, and to avoid confusing the
interpretations based on hypothesis, with the statements of fact and
established doctrines. Especial care has been taken to recognize the
uncertain nature of prevalent interpretations when they are dependent
on unverified hypotheses, especially if this dependence is likely to be
overlooked. If this shall seem to give prominence to the hypothetical
element, it should also be regarded as giving so much the more emphasis
to that which is really trustworthy, in that it sets forth more frankly
that which is doubtful. Hypothetical and unsolved problems have been
treated, so far as practicable, on the multiple basis; that is,
alternative hypotheses and alternative interpretations are frequently
presented where knowledge does not warrant positive conclusions.
In many cases the topics discussed will be found to be presented in
ways differing widely from those which have become familiar. 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 in still others, the emphasis is laid on points
which have not commonly been brought into prominence. Whether the
authors have been wise in departing to this extent from beaten paths,
the users of the volumes must decide.
The work is intended primarily for mature students, and is designed to
furnish the basis for a year’s work in the later part of the college
course. By judicious selection of material to be presented and omitted,
the volumes will be found useful for briefer courses, and by the use of
the numerous references to the fuller discussions of special treatises,
they may be made the basis for more extended courses than are commonly
given in undergraduate work. The attempt has also been made to make the
volumes readable, in the belief that many persons not in colleges or
universities will be interested in following a connected account of the
earth’s history, and of the means by which that history is recorded and
read. Antecedent elementary courses in geology will not be necessary to
the use of these volumes, though such courses may be helpful.
The arrangement of themes adopted is such as to bring to the fore
processes with which all students are immediately in contact, and
which are available for study at all seats of learning. The commoner
geologic agents, such as the atmosphere and running water, have been
elaborated somewhat more fully than is customary, and the common
rather than the exceptional phases of the work of these agents have
been emphasized, both because of their greater importance and their
universal availability. The text has been so shaped as to suggest field
work in connection with these topics especially, since work of this
sort is everywhere possible.
After the preliminary outline, which is intended to give some idea of
the scope of the science, and of its salient features, and to show the
relations of the special subjects which follow, the order of treatment
is such as to pass from the commoner and more readily apprehended
portions of the subject to those which are less readily accessible and
more obscure. Following the same general conception, the treatment of
the topics is somewhat graded, the earlier chapters being developed
with greater simplicity and fullness, while the later are somewhat more
condensed.
Many acknowledgments are made in the text and foot-notes, but it
is impossible to adequately acknowledge all the sources which have
been drawn upon, since the whole body of literature has been laid
under contribution. The authors especially acknowledge the generous
assistance of Professor J. P. Iddings in connection with the chapter on
The Origin and Descent of Rocks; of Dr. F. R. Moulton, Professor C. S.
Slichter, Professor L. M. Hoskins, Mr. A. C. Lunn, and Mr. W. H. Emmons
in connection with mathematical problems; of Professor C. R. Barnes in
connection with the geologic functions of life; and of Professor Julius
Stieglitz in connection with chemical subjects.
The illustrations have been selected from numerous sources, which are
usually acknowledged in the text. Especial acknowledgment is due to the
U. S. Geological Survey for the use of numerous photographs and maps,
and to Mr. G. A. Johnson, who has made many of the drawings reproduced
in Volume I. The authors are under even larger obligations for
assistance in the preparation of Volume II, for which acknowledgment
will be made in the proper place.
University of Chicago, January, 1904.
CONTENTS.
VOLUME I.
CHAPTER I.
PRELIMINARY OUTLINE.
Subdivisions, 1. Dominant processes, 2.
PAGE
+Astronomic Geology+ 2
The earth as a planet, 2. Its satellite, 3. Dependence on the sun,
4. Meteorites, 4.
+Geognosy+ 5
I. _The Atmosphere_ 5
Mass and extent, 6. Geologic activity, 6. A thermal blanket,
7.
II. _The Hydrosphere_ 7
Oceanic dimensions, 8. Geologic activity, 8. Chief
horizons of activity, 9.
III. _The Lithosphere_ 9
Irregularities, 10. Epicontinental seas, 11. Diversities of
surface, 12. The surface mantle of the lithosphere, 12. The
crust of the lithosphere, 13. The interior, 14. Varieties
of rock in crust, 14. Stratified rocks, 14. Conformability,
15. Relative ages, 15. The crystalline rocks, 16. Four great
sedimentary eras, 17. The Archean complex, 18.
+General Table of Geologic Divisions+ 19