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In a work of this kind, brief and concise statements are necessary in order to confine the volume to its proper size, but the different subjects should receive discussion more or less briefly according to their importance, and the more important subjects should not be neglected while the less important are treated in detail. The latter course not only prevents a book from containing as much useful information as it might otherwise do, but it also makes it extremely misleading to the student, for it gives him an erroneous idea of the relative importance of the different branches of the subject. Thus, in the present volume, the discussion of iron covers 27 pages. Of this number only 18 pages are given to the description of iron deposits proper, while nine pages are given to the enumeration of statistics which might have been condensed into a third of that space. Moreover, the great iron region of the Lake Superior country, which supplies more than two-thirds of the iron ore used in the United States, receives only three pages of treatment. The copper region of the Lake Superior country receives only four page, and the copper and silver region of Butte City, Montana, one of the most celebrated mining localities in the world, receives only two pages; while other much less important subjects receive many pages. Such inequalities might be justifiable if the geology of certain regions were so simple that it could be described in a few words, even though the commercial features might be of great importance. In the instances cited, however, this is not the case.

Economic geology, including both the subject of ore deposits and other subjects which properly belong to this branch of geology, is in much need of accurate geological work and careful discussion. This is especially true in the United States, which is preëminently the mining region of the world; and it is unfortunate that a treatise relating mostly to the ore deposits of this country should have failed to give the subject thorough treatment. The volume, though in some parts it need not be severely criticised, shows in most parts an extremely superficial knowledge of economic geology, and contains many the errors in statements regarding the mineralogical nature of ores and geological nature of ore deposits; it shows a want of knowledge of the commercial features of the various mining industries, and it bears evidence of a lack of the sense of proportion in the amount of space given to different subjects.