INTERPRETATION OF TOPOGRAPHIC AND GEOLOGIC MAPS INTERPRETATION OF TOPOGRAPHIC AND GEOLOGIC MAPS With Special Reference to Determination of Structure BY C. L. DAKE, Pii. D. Professor of Geology, Missouri Sc/tool of Mines and Metallurgy, liolla. Mo AND J. S. BROWN, Ph. D. Associate Geologist, United States Geological Survey McGRAW-HILL BOOK COMPANY, Inc. NEW YORK AND LONDON 1 9 2 5 S a 5 SV S. 05 Copyright, 1925, b y t h e M cG raw -H ill Book Company, Inc. Copyright renewed 1953 by ELLA F. DAICE & J. S. BROWN PRINTED IN THE UNITED STATES OF AMERICA PREFACE The field of map interpretation is singularly lacking in anything approaching an adequate textbook, largely as a result of the fact that the numerous maps considered essential increase the cost of a text almost prohibitively. The only agency suitably equipped to produce an adequately illustrated treatise on map interpreta­ tion is the Federal Government. Its one essay in this field, Professional Paper 60, “The Interpretation of Topographic Maps,” has never been repeated. This book, though invaluable, contains little information on the reading of structure from contours, and still less on the interpretation of geologic maps. Lack of a suitable text has tended to limit the number and scope of courses in map interpretation, and has in considerable measure deprived the teaching of elementary geology of one of its strongest assets, adequate map illustration. Listing illustrative maps in the general texts is admirable, but, unfortunately, the beginner without laboratory guidance sees only a small fraction of the significant features. A number of small but useful manuals on various phases of map interpretation have appeared, largely in the form of questions, but these manuals demand a skilful instructor to make them of most value. Map interpretation lends concreteness to general and structural geology and has been termed by one of our ablest teachers an “ indoor field course” . It may, in part, wisely replace field studies, with economy in time and money, and has the very real advantage that more of a region or a structure can be visualized a t one time on a map than in the field. For these reasons the authors feel that there is a real place for a treatise of the type herewith presented. The material has been accumulated by the senior author through more than ten years of active teaching of map interpretation. The book was planned vi PREFACE several years ago to include actual maps; but after fruitless conferences with several publishers the plan was abandoned, owing to the expense involved; and it was decided to prepare a text which would refer to the maps of the United States Geological Survey, by way of illustration. It is sincerely hoped that the work will stimulate the general interest in map interpretation, to the end that many more courses will be offered in that subject than now, and that it will help to enrich the illustrative teaching of general and structural geology. The major plan of the work and much of the detail have resulted from the senior author’s experience in teaching map interpretation. The junior author has assisted throughout in the assembling and analysis of illustrative material, and is chiefly responsible for certain minor sections of the text. It is desired, at this point, to express the obligation of thé authors to A. K. Lobeck, of the University of Wisconsin; W. A. Johnston, of the Canadian Geological Survey; W. D. Smith, of the University of Oregon; Frank Leverett, Sidney Paige, N. H. Darton, and G. R. Mansfield, of the United States Geological Survey; and R. C. Tucker, of the West Virginia Geological Survey, for information regarding the geology of certain areas studied by them. They are also indebted to Professors Josiah Bridge and G. A. Muilenburg, of the Missouri School of Mines, for many valuable suggestions; and to Professors Eliot Black- welder, of Stanford University, and D. W. Johnson, of Columbia University, for the inspiration of unexcelled courses in map interpretation. For the fundamental facts of geology and physiography, the authors are indebted to many of our standard texts and reference works. It is, of course, impossible to give adequate individual credit for facts drawn from so great a variety of sources. T he A u t h o r s . H o l l a , M o ., May, 1925. CONTENTS P a o e P r e f a c e ................................................................................................................................................... v I INTRODUCTION......................................................................................................... ** PART I I nterpretation o f T o p o g r a p h ic M a p s ...................................................................... 1 Introductory statem ent.............................................................................. 1 Special features of maps................................................................................... 2 Direction and orientation .......................................................................... 2 Scales.................................................................................................................. 3 Graphic scales ........................................................................................... 3 Fractional scales ....................................................................................... 4 Verbal scales................................................................................................ 5 Methods of representing topography..................................................... 6 Shading......................................................................................................... 6 H a ch u res..................................................................................................... 6 Contours........................................................................................................ 6 Contours and their significance.................................................................. 8 Contour lines............................................................................................... 8 Contour intervals....................................................................................... 8 Depression contours.................................................................................. 10 Contours and land form........................................................................... 11 Numbering of contours............................................................................12 Limits of exactness in reading contours............................................ 14 Drawing topographic profiles...........................................................................17 Describing locations on a m a p ...................................................................18 Conventional symbols (legend)....................................................................... 20 Land forms, their development and recognition............................................ 20 Topography resulting from the work of ground w a ter ............................21 Topography resulting from wind work.........................................................26 Topography resulting from the work of glaciers....................................... 30 Erosional features—-Mountain or Alpine glaciation ...........................30 Depositional features—Continental glaciation .................................... 34 Glacial diversion of drainage.......................................................................38 vii viii CONTENTS P a g e Features resulting from the work of waves.................................................40 Features of submergent shorelines..............................................................42 Features of emergent shorelines.................................................................. 47 Features of neutral shorelines...................................................................... 50 Features of compound shorelines..............................................................52 Abandoned shorelines................................................................................... 53 Features resulting from vulcanism ...............................................................60 Cones and craters.......................................................................................... 60 D ik e s................................................................................................................... 63 Features resulting chiefly from diastrophism ........................................... 65 Features resulting from the work of running w ater ............................... 67 Deposits made by running w ater .............................................................67 Fans, cones, and piedmont alluvial plains ........................................67 Alluvial terraces........................................................................................ 71 Flood-plain featu res ............................................................................... 75 D eltas............................................................................................................. 79 Erosion by running w ater ...........................................................................80 The erosion cycle—its stages.............................................. 81 Criteria for the erosion stages of a single valley.......................... 81 Criteria for the erosion stages of a region.......................................89