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THE POPULAR SCIENCE MONTHLY. 



tory of the surface of our globe, in noting 

 the manifold changes which it has under- 

 gone, 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 num- 

 ber 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 per- 

 missible. 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 " Ap- 

 plied Geology " to meet this want. 



It was a question of no small impor- 

 tance how such a work should be conceived 

 and arranged. On the one hand, it was de- 

 sirable 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 pur- 

 suits, 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 arrange- 

 ment of rock-masses. To one who has al- 

 ready studied geology, these pages will prove 

 a welcome review of certain parts of the sci- 

 ence that bear more directly on the subjects 

 to follow ; for one who has not before en- 

 gaged 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 rela- 

 tive accessibility of valuable substances and 

 deposits is pointed out ; the need of a thor- 

 ough acquaintance with the obtaining geo- 



logical conditions, by those undertaking 

 great architectural or engineering struct- 

 ures, is referred to, and so on. 



The next chapter is devoted to materi- 

 als of construction. This embraces a thor- 

 ough 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 geologi- 

 cal fertilizers, of drainage, and subsoils. 

 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 min- 

 eral 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 geologi- 

 cal 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 im- 

 portant ores receives attention in a separate 

 chapter, and the whole forms a most valu- 

 able resume of the subject. Tables showing 

 the annual production of many of the lead- 

 ing minerals, compiled from the most recent 

 data, will prove of especial interest to manu- 

 facturers. The closing chapters of the book 

 treat of substances adapted to chemical 

 manufacture or use, fictile materials, refrac- 

 tory 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 



