Since the first edition of the "Principles of Economic Geology" appeared in 1918, great progress has been made in the subject. In the preparation of this, the second edition, it was desired to bring the general treatment and the descriptions of mining districts up to date and at the same time not to increase greatly the size of the book. To do this the descriptions have been cut down where possible and the number of maps and other illustrations has been increased considerably. It is believed that this is desirable because most geologists find maps and sections easier to read and often more illuminating than long descriptions. The number of footnote references has been greatly increased.
The text has been completely reset and rewritten. A few illustrations appearing in the first edition have been retained, but nearly all those appearing in the second edition are new. The number of illustrations is increased from 210 to 329.