[Transcriber's Note: _Text_ and =Text= represent italic and bold text respectively. Subscripts are displayed as an underscore followed by the number or text in braces: SiO_{2}.] * * * * * [Illustration: A Valley with Rocky Ledges cut in the Horizontal Strata, Scotland] THE ELEMENTS OF GEOLOGY BY WILLIAM HARMON NORTON PROFESSOR OF GEOLOGY IN CORNELL COLLEGE GINN & COMPANY BOSTON * NEW YORK * CHICAGO * LONDON Copyright, 1905, 1921, by WILLIAM HARMON NORTON ALL RIGHTS RESERVED 5511 The Atheneum Press GINN & COMPANY PROPRIETORS BOSTON * U.S.A. PREFACE Geology is a science of such rapid growth that no apology is expected when from time to time a new text-book is added to those already in the field. The present work, however, is the outcome of the need of a text-book of very simple outline, in which causes and their consequences should be knit together as closely as possible,--a need long felt by the author in his teaching, and perhaps by other teachers also. The author has ventured, therefore, to depart from the common usage which subdivides geology into a number of departments,--dynamical, structural, physiographic, and historical,--and to treat in immediate connection with each geological process the land forms and the rock structures which it has produced. It is hoped that the facts of geology and the inferences drawn from them have been so presented as to afford an efficient discipline in inductive reasoning. Typical examples have been used to introduce many topics, and it has been the author's aim to give due proportion to both the wide generalizations of our science and to the concrete facts on which they rest. There have been added a number of practical exercises such as the author has used for several years in the class room. These are not made so numerous as to displace the problems which no doubt many teachers prefer to have their pupils solve impromptu during the recitation, but may, it is hoped, suggest their use. In historical geology a broad view is given of the development of the North American continent and the evolution of life upon the planet. Only the leading types of plants and animals are mentioned, and special attention is given to those which mark the lines of descent of forms now living. By omitting much technical detail of a mineralogical and palæontological nature, and by confining the field of view almost wholly to our own continent, space has been obtained to give to what are deemed for beginners the essentials of the science a fuller treatment than perhaps is common. It is assumed that field work will be introduced with the commencement of the study. The common rocks are therefore briefly described in the opening chapters. The drift also receives early mention, and teachers in the northern states who begin geology in the fall may prefer to take up the chapter on the Pleistocene immediately after the chapter on glaciers.