550

3-rabau

Textbook of

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Public Library Kansas City, Mo.

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DATE OUE

A TEX'f'EQOKiOF GEOLOGY

BY

AMADEUS W. GRABAU S.B., MASS. INST. OF TECHNOLOGY; S.M., S.D., HARVARD PROFESSOR OF PALEONTOLOGY IN THE GOVERNMENT UNIVERSITY OF PEKING, CHINA, AND PALEONTOLOGIST TO THE CHINESE GEOLOGICAL SURVEY FORMERLY LECTURER IN MINERALOGY AND IN GEOLOGY IN TUFTS COLLEGE, PROFESSOR OF MINERALOGY AND GEOLOGY IN THE KENSSELAER POLYTECHNIC INSTITUTE, AND PROFESSOR OF PALAEONTOLOGY IN COLUMBIA UNIVERSITY AUTHOR OF "PRINCIPLES OF STRATIGRAPHY," "GEOLOGY OF THE NONMETALLIC MINERAL DEPOSITS OTHER THAN SILICATES," " NORTH AMERICAN INDEX FOSSILS " (WITH H. W. SHIMER), "GUIDES TO THE GEOLOGY AND PALAEONTOLOGY OF NIAGARA FALLS, OF EIGHTEEN MILE CREEK, AND OF THE SCHOHARIE REGION," ETC., ETC.

PART I GENERAL GEOLOGY

_. C. HEATH & CO, PUBLISHERS BOSTON NEW YORK CHICAGO

COPYRIGHT, 1920, BY D. C. HEATH & Cc 2iO

DEDICATED TO MY FORMER STUDENTS WHO IN THE NEW WORLD AND THE OLD ARE TRANSMITTING, AUGMENTING, AND APPLYING

THE KNOWLEDGE OF THE EARTH SCIENCE IN THE ACQUIRING OF WHICH IT HAS BEEN. MY PRIVILEGE TO AID THEM

PREFACE IN the preparation of this book, I have departed somewhat widely from the prevailing order of treatment in current texts. Instead of beginning with the destruction of rocks, it has seemed more logical to give the student some knowledge of the rocks to be destroyed, and of their character and origin. Instead of treating clastic rocks first and igneous and other non-clastic rocks later, it has seemed more desirable to begin with those rocks from which elastics are largely derived, before -dealing with the elastics themselves. Twenty years of experience as a teacher have convinced me that the average student admitted to courses in geology receives too little instruction in minerals, and although we generally recommend mineralogy as a desirable prerequisite, few teachers can insist upon a preparation in this subject on the part of the student. Yet without a knowledge of at least some minerals the study of rocks is impossible, and few geological phenomena can be adequately understood without at least a general knowledge of the rocks which they affect. Students who are preparing to make geology their life work, will in any case undertake a more extended study of minerals, and they will turn to the excellent textbooks in that science now available, and some of which are listed on page 51. But the great majority of students of geology come to this subject only with the desire to gain some knowledge of the world they live in, of the material of which it is composed, of the forces which have fashioned it, and of the laws which have governed its development. They may do so from a desire to master the secrets of nature for the material benefits to be derived from such a mastery, or for the power which such a knowledge will confer upon them ; or they may undertake the study of the earth, because they wish to broaden their mental horizon and subject themselves to that stimulation of the intellect, that deepening of spiritual perceptions, and that awakening of dormant faculties, which others have found in a sympathetic understanding of, and love for, the out-door world, and which, in its fullest measure, is most frequently vouchsafed to the student of geology. From whatever motive the" student approaches the subject, he should be made to realize that his desires can best be attained, if he keep in mind the maxim of La Rochefoucauld, "Pour Men sawir une chose il faut en sawir les details." Detail does not appeal to the

vi Preface average student, but a knowledge of a certain amount of detail is necessary in any subject, if it is to be well understood, and in geology, as in other sciences, no real understanding of principles and of phenomena is possible without some conscientious devotion to detail. The book

of nature is unsealed only to him who is willing to learn the language in which it is written. I believe that at the ver}^ outset the student of the earth should subject himself to a moderate discipline in the elements of chemistry and mineralogy at least. To those who can not devote the time to separate courses in these sciences, Chapter IV may serve as guide for a series