_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.