PETROLOGICAL ABSTRACTS AND REVIEWS 643 



and diagenesis. Among the descriptions of the sediments, that on 

 salt deposits is especially detailed, occupying sixteen pages. The crys- 

 talline schists are preceded by chapters on origin and textures. The 

 book is profusely illustrated with photographs, undoubtedly excellent 

 in the originals, but not well reproduced. The book may well serve as 

 a text for students who have a sufficient command of German. 



RosENBUSCH-WuLFiNG. Mikroskopische Physiographic der Min- 

 er alien und Gesteine. Bd. I. Die petrographisch wichtigen 

 Mineralien. Ft. 1. Untersuchungsmethoden. 5th ed., Stutt- 

 gart, 1921. Pp. 252, Figs. 192, and a colored plate. 

 This well-known work again has been revised, enlarged, and prac- 

 tically rewritten by Wiilfing, so that it bears very little resemblance to 

 the third edition of Rosenbusch. The present instalment of the book, 

 which is the first half of the first part, all so far published, deals with 

 methods of preparation, and with general theories of optics. Much 

 new material has been added, and some of the old has been omitted to 

 keep the size of the book within reasonable bounds, but how much has 

 been omitted it is impossible to determine, in many cases, on account 

 of the rearrangement and the appearance of only the first part as yet. 



Following the Introduction, which is somewhat condensed, there is 

 a section on preparation methods. The history of microscopical research, 

 the description of stereographic projection, and the graphical methods 

 and formulas, which followed in the fourth edition, are entirely omitted. 

 Thirty-five pages on the preparation of thin sections come next, instead 

 of being inserted between the chapters on optical principles and optical 

 instruments, a decided improvement in arrangement. Here are given 

 a number of new devices for cutting, grinding, and polishing. The 

 cutting of oriented sections is described in considerable detail, occupying 

 with the instructions for cutting plane surfaces and polishing, some fifteen 

 pages. 



Optical methods are introduced by a general discussion of theories 

 of light. In the preceding edition, following the discussion of the 

 indicatrices, the Fresnel ellipsoid, and uniaxial and biaxial ray and 

 wave surfaces, came a section on lenses, microscopes, and various acces- 

 sories. In the present edition this is omitted, probably to come later, 

 and the discussion of optical phenomena continues unbroken. The 

 same arrangement holds throughout the book. All of the theoretical 

 material is brought together and the determinative methods are omitted, 

 undoubtedly to be collected in the second half. This makes the different 



