Public domain
[p. iii]
This text-book on Geology is intended primarily for college students who are already in possession of the elements of physics, chemistry, and biology. 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 salient features of geology, as now developed, encumbered as little as possible by technicalities, and by details whose bearings on the general theme are unimportant. 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 history, and the means by which that history is recorded and read.
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 been, therefore, 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 practicable.
[p. iv]
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 will be introduced to the methods and spirit of the science. To this end the working methods of the geologist have been implied as frequently as practicable. . To this end also there has been frankness of statement relative to the limitation of knowledge and the uncertainty of many tentative conclusions.
The theoretical and interpretative elements which enter into the general conceptions of geology have been freely used, because they a,re 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 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.
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 volume must decide.
Especial attention is directed to the map work suggested at various 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 Survey, 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 serviceable. It is suggested that instructors who use the maps and folios mentioned in the text will 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 [p. v] work, 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.