REVIEWS. 



The Principles of Economic Geology. By William Harvey 

 Emmons, Ph.D. pp. xviii + 606, with 210 text-figures. New 

 York : McGraw-Hill Book Company, Inc. London : Hill 

 Publishing Co., Ltd. 1918. Price 24.s. net. 

 TN this book the author presents a perspective of the present 

 -*- position of the scientific knowledge of metalliferous and non- 

 metalliferous mineral deposits, with the exception of fuels and oil. 

 However, the amount of space devoted to the non-metalliferous 

 deposits amount to only about 70 pages out of 600, and it is to all 

 intents and purposes a textbook of the geology of metalliferous 

 mining. The first twenty-one chapters of 290 pages are devoted to 

 a discussion of general principles, while the rest of the book is 

 occupied by descriptions of actual occurrences, classified under the 

 headings of the various metals or non-metals. 



This is perhaps scarcely the place to discuss the general question 

 of the rival classifications of ore-deposits, genetic or chemical ; 

 nevertheless it may be allowable to point out that the method here 

 adopted presents many practical advantages, and certainly makes 

 reference easy. A genetic classification, such as has been adopted 

 in most of the larger German books, is perhaps more strictly 

 scientific, but it is certainly confusing to the learner, since it brings 

 together a whole lot of deposits which have little in common from the 

 point of view of the miner and metallurgist, however similar their 

 origin may be. On the other hand, an arrangement by metals 

 groups in one chapter or section deposits that may have been formed 

 in a great variety of ways, and a special difficulty presents itself 

 in the case of ores worked for more than one metal. It is clear 

 that an ideal classification has not yet been evolved, and from the 

 nature of the subject it probably never Avill be. The whole matter 

 is a question of the balancing of advantages and drawbacks, and in 

 our opinion Professor Emmons has acted wisely in choosing as he 

 has done. 



The earlier chapters afford an admirable discussion of the general 

 geological, mineralogical, chemical, and physical principles under- 

 lying the formation of workable mineral deposits. The metalliferous 

 deposits are classified under eight headings, as magmatic 

 segregations, pegmatite deposits, contact-metamorphic deposits, 

 deposits of the deep vein zone, deposits formed at moderate depths by 

 hot solutions, deposits formed at shallow depths by hot solutions, 

 deposits formed at moderate and shallow depths by cold and meteoric 

 solutions, and sedimentary deposits. This subdivision seems some- 

 what elaborate ; it is very doubtf lJ, for example, whether any real 

 distinction can be drawn between pegmatites and veins of the deep 

 zone, and it is well known that certain pegmatite dykes can be 

 followed laterally or vertically into ordinary quartz veins, as indeed 

 is exp)licitly admitted by the author, who also recognizes clearly 



