Reviews 



The Principles of Economic Geology. By W. H. Emmons. New 

 York: McGraw-Hill Book Co., Inc. Pp. 606, with 208 figures. 

 1918. 

 In The Principles of Economic Geology Professor Emmons has 

 aimed to give advanced students of geology a general survey of the 

 science of mineral deposits. The fuels have purposely been omitted, 

 however, as to have treated them adequately would have enlarged the 

 book unduly, and evidently for the same reason the non-metalliferous 

 deposits are somewhat briefly described, receiving but one chapter 

 of the twenty-eight in the book. The volume is thus in essence a con- 

 densed treatise on ore deposits; its central concept is that most ore 

 deposits (except an important group of sedimentary origin) are geneti- 

 cally related to igneous rocks. 



The first chapter consists almost wholly of definitions, such as ore, 

 protore, etc., a necessary groundwork, but it forms a rather heavy 

 introduction to the subject and is likely to dull the interest of students 

 coming fresh to the subject; fortunately the chapter is but three pages 

 long. A suggestive outline of the objects of economic geology, its 

 problems, and its broader relations to petrology and geology would 

 perhaps make a more attractive introduction. The second chapter 

 takes us deep into the subject, namely, the classification of ore 

 deposits. Primary ore deposits are grouped under eight major heads: 



1. Deposits formed by magmatic segregation; consolidated from 

 molten magmas. 



2. Pegmatite veins; deposited by aqueo-igneous magmatic solu- 

 tions. 



3. Contact-metamorphic deposits; deposited in intruded rocks by 

 fluids passing from consohdating intruding rocks. 



4. Deposits of the deep vein zone; formed at high temperature 

 and under great pressure, generally in and along fissures. 



5. Deposits formed at moderate depths by ascending hot solu- 

 tions. 



6. Deposits formed at shallow depths by ascending hot solutions. 



7. Deposits formed at moderate and shallow depths by cold meteoric 

 solutions. 



8. Sedimentary deposits; chemical, mechanical, organic, etc. 



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