196 ART. 3. B. KOTO : 



found in large mass, while those of noritic composition are small 

 and intimately mixed in lava-flows, as if forming an integral por- 

 tion of rock components. Hypersthene as compared with diopside 

 has lower melting point and density, and these seem to the writer 

 to be the cause of the later origin and higher level of separation 

 of noritic segregation. 



Another lesson to be learned is, that basic diorite- schists and 

 quartzless gabbros, both being usually considered to be plutonics, 

 may be formed as accessory portions of modern effusives in a 

 comparatively shallow horizon. The only difference observable in 

 comparison with plutonic equivalents is the absence of garnet, 

 which is the geologic barometer, occurring only in deep-seated 

 rocks. 



It is worth while to note in connection with microtinite that 

 the normal chemical composition of the base, or groundmass of 

 rocks of intermediate acidity like andésites, as observed by Teall,^^ 

 greatly resembles that of basic plagioclase. A slight addition of 

 iron to the plagioclase-melt will result in the formation of chemical 

 combinations of the enclaves which are mainly composed of glassy 

 plagioclase or microtine already referred to. From a chemical 

 standpoint there is therefore no coercive ground in the way of 

 explanation on the formation of the microtinite enclaves in our 

 lavas from molten magma. Similar inclusions in sills have been 

 already discussed by some British petrologists."^ 



3) The Ceramicites, Natural Porcelain Ejecta (PL XXII. Fig. 2-8). — 

 By the cordierite- bearing éjecta are hero meant those porcelain-hke 

 projectiles from volcanoes, which contain cordierite as the charac- 



1) ' British Petrography,' p. 42-43. See postea, p. 203. 



2a) J. A. Smythe, ' On Some Inckisions in the Great Whin Sill of Northumberland.' Geol. 

 Mag., 1914, p. 244. 



2'j) Henslop and Smythe, 'The Dyke at Crookdene.' Q.J.G.S., London, 1910, p. 7. 



