PREFACE 



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 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 has 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 dynamic geology, physiographic geology, 

 etc., apart from their historical bearing, lose much of their signifi- 

 cance 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. 



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