PETROLOGICAL ABSTRACTS AND REVIEWS 629 



Weinschenk-Clark. Petrographic Methods. McGraw-Hill Book 

 Co., New York, 1912. Pp. xxH-396, figs. 371. 



This work is the authorized English translation of the third edition 

 of Weinschenk's Anleitung zum Gebrauch des Polarisationsmikroskops, 

 and the second edition of Die Gesteinsbildenden Mineralien. The English 

 title is rather misleading in that it promises less than is given in the book. 



The translation follows the German text closely enough to be correct, 

 yet is free enough to be easy reading. Part I begins with a description 

 of lenses and microscopes, and gives instructions for testing and adjusting 

 them. The following one hundred pages are devoted to methods of 

 observation in ordinary, and in parallel and convergent polarized light. 

 Many methods are presented, and the phenomena observed and con- 

 clusions to be drawn from them are given, although but little theoretical 

 explanation is attempted. The first part closes with an appendix giving 

 descriptions of rotating, heating, projecting, photographic, and drawing 

 apparatus. 



The second part takes up the cutting of thin sections, the separation 

 of mineral constituents by various chemical and physical means, and 

 methods of micro-chemical investigation, staining, determination of 

 specific gravity, etc. The chapter on the development of rock con- 

 stituents is extremely valuable for beginners, giving excellent figures of 

 various textures (called structures by the translator), and describing 

 intergrowths, inclusions, and so on. The descriptive portion of the book 

 consists of 139 pages with 153 figures, including line drawings of crystal 

 forms and half-tones of thin sections. The descriptions of the various 

 minerals are short but good, and give the principal characteristics. The 

 fact that unusual rock minerals are omitted is to be commended. The 

 methods for the determination of the feldspars are given rather too 

 briefly, however. The volume concludes with 36 pages of tables for the 

 optical determination of minerals. 



The book is well printed on good paper and the cuts have come out 

 fairly well, although, in avoiding the annoying glaze of the paper of the 

 German original, much detail has been lost in the half-tones. The loss 

 here seems greater than the gain. Typographical errors, especially under 

 the illustrations, are numerous. On the whole the book is an excellent 

 one and is extremely well adapted to classes beginning the study of micro- 

 scopical petrography. 



Albert Johannsen 



