Page:Popular Science Monthly Volume 29.djvu/286

274 of the surface of our globe, in noting the manifold changes which it has undergone, and perhaps, incidentally, studying the flora and fauna that have flourished upon it. Others, however, will regard geology from a different standpoint. Knowledge of the earth's structure, of the location and the occurrence of its various constituents, can be made use of for the interests of man.

A moment's thought of the great number of substances needed by man, for the supply of which he must look to old Mother Earth, will show how closely geological knowledge, applied to this end, is connected with the very progress of the human race. There has been no lack of excellent books devoted to the study of geology as a science, to theoretical geology, if this term be permissible. However, the need has long been felt of some work that would serve as an aid in making a knowledge of the earth's structure available for practical purposes. Professor Williams has written his "Applied Geology" to meet this want.

It was a question of no small importance how such a work should be conceived and arranged. On the one hand, it was desirable to have the treatise of value to the student of geological science; on the other hand, the book was to be made available for a large class in the community whose pursuits, although not exactly calling for a training in geology, yet make a thorough knowledge of some features of this science most desirable. In our opinion, the author has been very successful in meeting this twofold purpose.

The first forty-odd pages of this book are given to a consideration of the rock-forming minerals and their classification; to a description of rocks and the arrangement of rock-masses. To one who has already studied geology, these pages will prove a welcome review of certain parts of the science that bear more directly on the subjects to follow; for one who has not before engaged in the study, a careful perusal of this part is essential to an understanding of the sequel. The economic relations of geological structure are then discussed; the important bearing of structure on the relative accessibility of valuable substances and deposits is pointed out; the need of a thorough acquaintance with the obtaining geological conditions, by those undertaking great architectural or engineering structures, is referred to, and so on.

The next chapter is devoted to materials of construction. This embraces a thorough discussion of building-stones, their properties, strength, and durability. Their geological positions and distribution are considered. Some notes on materials for mortars and cements are added.

Then follow chapters on the relations of geology to agriculture and to health. The former takes up the question of the origin of soils, and their composition; of geological fertilizers, of drainage, and sub-soil's. The latter covers but a few pages and touches on the water-supply of households and communities, and the problems of drainage.

Mineral fuels and geological materials for illumination are taken up in turn. A classification of the coals (with numerous analyses of different kinds) is followed by a review of the geological horizons of mineral fuels; the fuel value of coals, based on their analysis, is explained, and hints are given on the selection of coals adapted to different purposes. The chapter on geological materials for illumination discusses the occurrence of petroleum and the modes of mining and refining this oil.

Next in order comes the consideration of metalliferous deposits. This theme, as is due its importance, occupies a considerable part of the book. Each of the more important ores receives attention in a separate chapter, and the whole forms a most valuable résumé of the subject. Tables showing the annual production of many of the leading minerals, compiled from the most recent data, will prove of especial interest to manufacturers. The closing chapters of the book treat of substances adapted to chemical manufacture or use, fictile materials, refractory substances, ornamental stones, and gems.

From all that has been said, an idea may be formed as to the nature and the scope of this work. A book of this kind must naturally rely to a certain extent on the work done by others. The author's task, in great part, has consisted in collecting and collating material from many sources. But from this it must not be inferred that the