34 SCIENCE PROGRESS 



saturation of the minerals present (Geol. Mag. 1917, 4,463-9). 

 This provides the usual five main divisions. He then 

 utilises the double ratio of Or.-Ab.-An., the " colour-ratio " 

 (felsic/mafic ratio), the crystallinity, and the ratios of specific 

 minerals or groups of minerals, in the order named. Like 

 Holmes (Science Progress, July 19 17, 33) he fails to make 

 the ratio between orthoclasic and plagioclasic elements 

 quantitative, since the double ratio of Or.-Ab.-An. provides no 

 data as to the relative amounts of orthoclase and plagioclase 

 present. 



Sargent, H. C, On a Spilitic Facies of Lower Carboniferous 

 Lava-flows in Derbyshire, Quart. Jour. Geol. Soc. 1918,73, pt. 1, 

 11-25. 



Tyrrell, G. W., The Igneous Geology of the Cumbrae 

 Islands, Firth of Clyde, Trans. Geol. Soc. Glasgow, 191 7, 16, 

 244-74. 



Leitch, P. A., and Scott, Dr. A., Notes on the Intrusive 

 Rocks of West Renfrewshire, ibid., 275-89. 



Prof. S. J. Shand describes very fine examples of the granites 

 and gneisses with the peculiar black, glassy veins and dykes, 

 usually known as " trap-shotten gneiss," near Parijs (Orange 

 Free State) (Quart. Journ. Geol. Soc. 191 7, 72, pt. 3, 198-221). 

 He gives the appropriate name of pseudotachylyte to the 

 black injected material. Shand is satisfied that this rock is in 

 truly intrusive relation to its walls. The hypothesis that the 

 pseudotachylyte represents a rock-melt developed within the 

 granite by mechanically produced heat is believed to explain 

 the facts best, but the source of the heat and the mechanism of 

 the intrusive process remain obscure. 



Brouwer's account of the petrography of the interesting 

 alkali rocks of the Transvaal is brought up to date by a paper 

 in which he describes the geological features of these occurrences 

 (Journ. Geol. 191 7, 25, 741-78). The rocks belong to the 

 great Bushveld laccolith, and are held to have been derived 

 by differentiation from the same source as the granites and 

 norites which constitute the main mass of that intrusion. 



The Tertiary volcanic rocks of Mozambique, described by 

 A. Holmes (Quart. Journ. Geol. Soc. 191 7, 72, pt. 3, 222-79), 

 may be divided into an alkalic group consisting of solvsbergite, 

 aegirine-trachyte, phonolite, basalt, etc., and a calcic group of 

 basalts and andesites, thus affording a further illustration of 



