PETROWGICAL ABSTRACTS AND REVIEWS 707 



Shand, S. J. ''The Norite of the Sierra Leone," Geol. Mag., V 

 (1918), 21-23. 

 Describes two norites from Sierra Leone. One an olivine-rich norite, belongs 

 to 2312 (new form) of the reviewer's classification; the other melanocratic, 

 and without olivine, belongs to 3312. 



Shannon, Earl V. "Petrography of Some Lamprophyric Dike 



Rocks of the Coeur d'Alene Mining District, Idaho," Proc. 



U.S. Nat. Museum, LVII (1920), 475-95, pis. 3. 



The various dike-rocks from the Coeur d'Alene district, collected by Ran- 



some, Calkins, and Umpleby, are here classified and described. Among the 



rocks are various minettes, spessartites, and vogesites, and one odinite. From 



the widespread occurrence of these dikes the conclusion is reached that the 



district is underlain by a granitic batholith which is so far down that none of 



the complementary aplite reached the surface. The dikes and ore veins belong 



to substantially the same period. 



Skoetsch, Carl. "Die Einschliisse in den Basalten zwischen 

 Godesberg und Remagen," Centralbl. f. Min., etc., 1921, 



353-63- 

 In this paper are described all the different minerals which have been found 

 in inclusions in the basalts of this region, as well as their mode of origin, and 

 the alterations produced in them by the basaltic magma. 



Smith, W. Campbell. " Riebeckite-Rhyolite from Northern Kordo- 

 fan, Sudan," Mineralog. Mag., XIX (1920), 48-50. 

 Describes a riebeckite-rhyolite from which certain ancient stone imple- 

 ments found at Beraeis are made. Two specimens of tinguaitic dikes from 

 Kadoro, described by Linck, represent the only previously mentioned soda- 

 rich rocks in Kordofan. 



Spangenberg, K. "Die Einbettungsmethode," Fortschr. d. Min. 

 Krist. u. Petr., VII (1920), 397-458. 

 Under "Immersion Methods" are included all those methods for determining 

 refractive indices based upon certain appearances at the contact between a 

 known and an unknown medium. Three groups are discussed: (i) Disap- 

 pearance of the border, (2) Topler's method of inclined illumination (often 

 spoken of as Schroeder van der Kolk's method) ; (3) Becke 's method of raising 

 or lowering the tube of the microscope. A general summary is given of all 

 methods, the reasons for the phenomena are discussed, the relative accuracy 

 shown, and the cause of variation imder different conditions pointed out. 



