7o6 PETROLOGICAL ABSTRACTS AND REVIEWS 



Sederholm, J. J. "On Synantetic Minerals and Related Phe- 

 nomena. (Reaction Rims, Corona Minerals, Kelyphite, Myr- 

 mekite, etc.)," Bull. Comm. Geol. Finlande, No. 48, 1916. Pp. 

 148, pis. 8, figs. 14. 

 Synantetic minerals are those which are characteristic at the contact between 

 two definite minerals in igneous rocks, kelj^Dhite rims being one form. Myrme- 

 kite is appUed to intergrowths of plagioclase and vermicular quartz. In this 

 paper the various forms and the different minerals occurring are discussed in 

 great detail, and the literature is fully summarized. 



Shand, S. J. ''The Pseudotachylyte of Parijs," Quart. Jour. 

 Geol. Soc, LXXII (191 7)', 198-221, pis. 4, figs. 13. 



In the granite from the neighborhood of Parijs, Orange Free State, there 

 occur abundant veins and networks of a dense black rock, to which, from its 

 resemblance to tachylite, the name pseudotachylite is given. Numerous 

 sketch maps and two photographs show the nature of the occurrence in the field, 

 and eight photogravures show the appearance as thin sections. The rock is 

 very opaque, due to innumerable inclusions of very fine black specks of magne- 

 tite. In some of the widest veins there is less magnetite but many polygonal 

 spherulites of dark-brown color in a felt of feldspar-microlites. Several analy- 

 ses are given. The writer concludes that the pseudo-tachylyte originated from 

 the granite itself through melting, which was caused, not by shearing, but by 

 shock or gas-fluxing. 



Shand, S. J. "The Principle of Saturation in Petrography," 

 Geol. Mag., I (1914), 485-93; H (iQ^S). 339-40. 

 Mr. Shand replies to certain critics of his system of classifying rocks on the 

 basis of saturated or unsaturated minerals. (The former minerals are those 

 which are stable in the presence of free silica ynder magmatic conditions, the 

 latter those that are unstable.) 



Shand, S. J. "A System of Petrography," Geol. Mag., IV (191 7), 

 463-69. 

 Gives further ideas as to desirable features in a classification of rocks. 

 Shand proposes the following factors: (i) degree of saturation, giving five 

 divisions; (2) the double ratio of Or-Ab-An, giving about eight famihes within 

 each division; (3) the color ratio, giving from two to ten, but preferably four 

 groups in each family; (4) crystallinity, giving two sub-groups within each 

 group; (5) ratios of specific minerals or groups of minerals, giving the types to 

 which "specific" names wiU be attached; (6) trivial characters of mineralogy 

 and texture, giving varieties. 



