FIELD GEOLOGY BY J. H. FARRELL, E. M. MINING GEOLOGIST INCLUDING A GUIDE TO THE SIGHT RECOGNITION OF ONE OR IMPORTANT MINERALS BY ALFRED J. MOSES, E. M., PH. D. PROFESSOR OF MINERALOGY, COLUMBIA UNIVERSITY FIRST EDITION SECOND IMPRESSION MCGRAW-HILL BOOK COMPANY, INC. 239 WEST 39TH STREET, NEW YORK 6 BOUVERIE STREET, LONDON, E. C. 1912 PREFACE 'When 'Omer smote 'is bloomin lyre, KIPLING. Within the last few years the importance of applied, or "practical" geology has received very wide recognition. But while It is freely admitted that the results obtained by specialists in this field are often of inestimable value in the conduct of mining operations, there is no very general understanding of the methods employed in their work. Geological maps are just as necessary as ordinary maps of mine workings, and are not much harder to make when one knows how to go about it. It is the lack of this knowledge which is a serious handicap to many mining men who are naturally keen and intelligent observers, but who fail to record and correlate their observations. They often carry an immense amount of geological data in their minds and make use of it when looking over their mine maps; but such mental pictures lack the graphic quality found only in good geologic maps and sections, which usually meet with instant approval on the part of practical men. Geological literature usually deals with results rather than with the methods of obtaining them, and the terms employed are often of a highly technical nature, so that the text is more or less unintelligible to one who has not had training in the subject. With these ideas in mind I have tried to outline briefly and plainly the means employed in geological mapping, and in the interpretation of geological data. I have also attempted to indicate some lines along which the application of geological theory may be made. The work may be characterized as elemen tary, and no doubt it is from the viewpoint of the trained geologist; but I hope that it will be of some value to those who have had no specialized geological training, or to whom economic work is a new field. The methods of topographic mapping are modified from those of the United States Geological Survey and are adapted to use on the smaller areas comprised by mining properties of average size. I have not attempted to give thorough theoretical discussions, nor have I described all the methods of surface mapping which might find application in such work. My idea is rather to offer a general scheme of procedure which may be modified to suit different cases. The chapters on geologic mapping are the result of several years of experience in the Western mining districts, and are based on notes made when such work was new to me; so that it is to be hoped that they will cover those points which are most important for the beginner to understand. For a part of the material presented I wish to express my thanks to the authors who have allowed me unrestricted use of their work. Professor A. J. Moses' mineralogical tables and descriptions will be appreciated by all who have occasion to refer to them. They are especially valuable for field use in economic work since they include all the most important ore and gangue minerals, and the rock-forming minerals. Professor Joseph W. Roe's paper, "The Application of Descriptive Geometry to Mining Problems," is one of the best and most logical contributions to the subject of geological measurements that has appeared for some time. Mr. S. K. Bradford's paper, "A Portable Assay Outfit for Field Work," treats the subject in a very practical manner and offers a solution to a problem that has vexed many prospectors and exploring geologists. I am indebted to Professor J. F. Kemp of Columbia University for permission to use some of the material in his "Handbook of Rocks," and also for information obtained in some of his courses. I am also indebted to Dr. Charles P. Berkey of Columbia for suggestions and ideas offered in his course in petrography, and |