i go 



HOLLAND : S1VAMALAI SERIES. 



the felspar-crystals are almost carmine-red to the naked eye. This 

 is found to be due to innumerable platy, orange-coloured inclusions 

 which, however, are not surrouuded by the peculiar polarizing zone 

 described above. 



A feature worth note in this coarse form of the elaeolite-syenite 

 is the frequent occurrence of a thin film of plagioclase between the 

 elaeolite and the orthoclase (microperthite) crystals. This narrow 

 strip of plagioclase is very varied in thickness, but shows crystallo- 

 graphic parallelism often for very long distances, and a strip at the edge 

 of a microperthitic crystal may even be crystallographically parallel 

 to a zone surrounding an included lump of elaeolite (see fig. 2). 



Fig. 2.— Layer of albite separating elceolite from microperthite. {Magnified 



by 25 diameters, Nicols crossed.) 



The lamellar twinning in these plagioclase strips is very sharply 



defined and shows a maximum angle of about 20 between the 



positions of extinction in alternate lamellae. These strips of 



plagioclase are, in their disposition, comparable to the well-known 



( 22 ) 



