478 



PETROLOGICAL ABSTRACTS AND REVIEWS 



istic ratios derived as follows: Let the atomic proportions of Si, K, Na, Ca, 

 Mg, Fe, be represented by s, k, n, c, m,f. Then 



A- 



MF = 



^ X loo, Sa,=- 



k + n + c + m +f ' k + n 



m+f 



X loo, Ss ^ 



k+n + c + m+f ' k + n + c + m+f 



It is found that in the second edition of Rosenbusch's Gesteinslehre 

 the names of analyzed rocks, with relatively few exceptions, are used in 

 accordance with the following scheme: 



Rosenbusch's syenites are divided into "normal" and "alkali" syenites, 



while his essexite, theralite, and shonkinite and ijolite-missourite families 



fall in the "theralites" and "shonkinites" of the table. 



F. C. Calkins 



HiLLEBRAND. W. F. "The Analysis of Silicate and Carbonate 

 Rocks," Bull. U.S. Geol. Survey No. 422, 1910. Pp. 239. 

 Figs. 27. 



A revision of Bulletin joj. The following are the more important 

 changes and additions. The effect of fine grinding upon the ferrous 

 iron content is discussed in the chapter on the preparation of the sample, 

 and again in the chapter on the determination of ferrous iron. To mini- 

 mize the error due to oxidation the sample may be ground in absolute 

 alcohol. This apparently does not reduce ferric minerals. 



The chapter on water has been rearranged and is introduced by a sec- 

 tion on the role of hydrogen in minerals, in which a provisional classifica- 



