of the Clyde Area. 



311 



analyses and norms are very similar and give identical symbols in 

 the American Quantitative Classification. The analysis of innin- 

 morite shows much less lime and more silica, causing its norm to 

 have a more quartzose and alkalic character than that of the Cumbrae 

 type. This is reflected in the symbols for class and rang ; and 

 inninmorite falls into the subrang dacose, but close to tbe border 

 between dacose and the neighbouring subrang tonalose, into which all 

 the other analyses fall. 



Table III. 



Interesting points arise from the consideration of the analyses of 

 average andesite and average hypersthene-andesite. Comparing the 

 two, average hypersthene-andesite has slightly more ferrous iron, 

 magnesia, and lime, but less alkalies than the average andesite. ' 

 Hence, the average hypersthene-andesite is slightly more femic and 

 more calcic than average andesite, as is well shown by the norms 

 and the magmatic symbols (Table III, 5, 6). Furthermore, both 

 averages show about 15 per cent of normative quartz, and fall into 

 the subrang tonalose (II, 4, 3, 4). Hocks with analyses like these 

 should be regarded as dacites according to the classification adopted 

 by Iddings. 1 They would belong to varieties of his shastaite 

 (andesine-dacite), 2 transitional to handaite (labradorite-dacite), devoid 

 of modal quartz. Most of the analyses in this group fall into the 

 subrang tonalose. The rocks called "andesite" by petrographers 

 contain then, on an average, 15 per cent of normative quartz, which, 

 however, rarely appears in the mode, and must exist occult in a fine- 

 textured or glassy base. The term dacite should be restricted to 

 andesitic rocks so rich in excess silica that it appears as quartz in the 

 mode. The average dacite of Daly 3 has 25 per cent of normative 



1 Igneous Bocks, vol. ii, p. 106, 1913. 



2 Ibid., p. 111. 



3 Igneous Rocks and their Origin, 1914, p. 25. 



