288 PETROLOGICAL ABSTRACTS AND REVIEWS 



unchanged beyond minor additions to bring the work up to date. The 

 treatment of the carbonate rocks is somewhat expanded by a discussion 

 of the marls, and the origin of oolites, and the origin of dolomites. The 

 origin of the oolitic iron ores is also discussed in an additional section. 

 The changes in organic matter by which coal and oil are formed are 

 classified in accordance with Potonie's recent paper. 



Part III. The third part, dealing with the "Crystalline Schists," 

 has been thoroughly revised and brought down to date without any 

 serious modification. Greater emphasis is laid on the chemical composi- 

 tion as an indication of the character of the original rock and here and 

 there the discussion is an application of physical-chemical conclusions 

 to the interpretation of the phenomena. Reference is made to the 

 schistosity developed by crystallization under pressure as described 

 by Riecke and the terminology is modified by the introduction of the 

 terms proposed by Becke. In the descriptive portion no change is 

 made in the systematic treatment, beyond the introduction of a few 

 new names, such as the myrmekite of Sederholm, the astochite- gneiss of 

 Belowsky, and the sagvaudite of Pettersen. 



While the book as a whole is probably the best elementary textbook 

 in descriptive petrography because of the clear style- and comprehensive 

 treatment of the subjects, it must be regarded as falling short of the 

 ideal in the minds of all who find occasion to criticize the continental 

 viewpoint, which has in large measure been developed through the 

 writings and teachings of Rosenbusch. The criticisms against the 

 validity of the dike rocks and the Kern theory are too well known to 

 need restatement. There are, however, numerous inconsistencies in 

 the systematic carrying-out of the underlying views which should be 

 eliminated. For example, the element of age is discarded in the general 

 discussion but frequently appears in the definitions or descriptions 

 of the various rocks. There is likewise ground for criticism in the com- 

 bined use of geological and petrographical criteria in classification which 

 leads to the separating of rock like the keratophyres from the alkali 

 rocks from which they are admittedly indistinguishable in chemical 

 and mineralogical composition and in texture. A third criticism in 

 systematic treatment is that already referred to in the handling of the 

 charnockite and anorthosite series and the relative disregard of the 

 silica content in the chemical discussion by the use of the Osann diagrams. 

 It is a subject for regret that this excellent textbook cannot be trans- 

 lated and still more that there is no equally satisfactory work by an 

 American author. 



Edward B. Mathews 



