This little book consists principally of a series of articles that appeared during 1919 and 1920 in the Arizona Mining Journal (now the Mining Journal), published at Phoenix, Arizona. Each chapter represents one article, and, in most instances, no material changes have been made in these articles, although the last two chapters and the appendices are new and some material has been added to each of the other chapters in order to bring them up to date. The series was originally written for prospectors or miners who are interested in the theoretical aspects of their vocation, and who are honestly seeking to learn the truth. So many mining engineers, geologists, and students of these subjects have, however, commented favorably upon the articles and expressed a desire to obtain them in book form that it is hoped they will prove to have some value to a wider audience than that for which they were originally written. 99 p.