254 PETROLOGICAL ABSTRACTS AND REVIEWS 



BowEN, N. L. ''Differentiation by Deformation," Proc. Nat. 

 Acad. Sci., VI (1920), 159-62. 



Discusses differentiation according to Darwin's theory of fractional 

 crystallization and the squeezing out of the mother liquor. 



BowEN, N. L. "The Sodium-Potassium Nephelites," Amer. Jour. 

 Sci., XLIII (1917), 115-32. Figs. 2. 



While this is strictly a mineralogical paper, it is of importance to 

 petrographers in showing the inaccuracy of calculating nephelite as 

 NaaO • AI2O3 • 6Si02. It is here shown that the molecules NaAlSi04 

 and KALSi04 are fundamental constituents of it, although they may 

 be present in variable amounts. 



Brauns, R. " Skapolithfiihrende Auswiirflinge aus dem Laacher 

 Seegebiet," Neues Jahrb., B.B., XXXIX (1914), 79-125. 

 Pis. 2. 

 Describes seventeen different kinds of scapolite rocks from the 



Laacher Sea region. Numerous analyses are given. 



I 



Braxjns, R. "Der Laacher Trachyt und seine Beziehung zu 

 anderen Gesteinen des Laacher Seegebietes," Neues Jahrb., 

 B.B., XLI (1916), 420-502. Pis. 2. 



This is a very complete study of the Laacher Sea trachyte and 

 related rocks. Twenty-three new analyses are given, all of which are 

 also recast into molecular proportions reduced to 100, and computed 

 according to Osann's system. Nine older analyses are quoted for com- 

 parison. A history of volcanic activity in this region is given, and the 

 following conclusions as to the relationships of the rocks are reached: 

 The white pumice, the Dachsbusch trachyte, and the light Laacher 

 trachyte are so closely related chemically that they are thought to have 

 been derived from the same magma, their differences in habit being 

 due to the action of the inclosed gases. Petrographically they may be 

 designated phonolitic trachytes and trachytic phonoHtes. Further, 

 these rocks are closely related chemically to the adjacent noselite- 

 phonolites, and it is probable that they came from the same magma, 

 their differences being due perhaps to greater differentiation or to 

 assimilation of crystalline schists. The dark Laacher trachyte is more 



