Petrological Abstracts and Reviews 



ALBERT JOHANNSEN 



Adams, Sidney F. "A Microscopic Study of Vein Quartz," 

 Econ. Geol., XV (1920), 623-64. 48 figs, on 8 pis. 

 This study of the microscopic characteristics of vein quartz is con- 

 fined to quartz of hydro thermal origin; magma tic, metamorphic, and 

 replacement quartz are not included. A well illustrated and instructive 

 paper, 



Allen, E, T., and Lombard, Robert H. "A Method for the 



Determination of Dissociation Pressures of Sulphides, and 



Its Application to Covellite and Pyrite," Amer. Jour. Sci., 



XLIII (1917). 175-95- 



A secondary enrichment investigation of the Geophysical Laboratory, 



in which methods and apparatus are described. 



Andersen, Olaf. "On Aventurine Feldspar," Amer. Jour. Sci., 

 '^^ (1915). 351-99- Figs. 13, pis. 3. 

 The Schiller in certain feldspars was determined as being due to 

 oriented, lamellar inclusions of hematite of various shapes and sizes. 

 They originated through the unmixing of an originally homogeneous 

 feldspar which contained iron oxides in solid solution. The lamellae 

 were found always to be oriented after simple crystal forms. 



Backlund, Helge. " Petrogenetische Studien an Taimyrge- 

 steinen," Geol. Fdren. i Stockh. Forhandl., XL (1918), 101-203. 

 Figs. II, map i. 

 This is a petrological study based upon about 500 specimens col- 

 lected by the unfortunate Baron v. Toll in his expedition to Taimyr 

 Peninsula, in northern Asia. The region is made up of gneisses, mica, 

 and other schists, contact hornfeld-like rocks, and three types of granite. 

 Many of the rocks were analyzed, and they are computed into norms 

 and into the Osann system, while under granite the percentage modes 



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