CLASSIFICATION OF THE ROCKS. 125 



are well shown in the rocky hill immediately west south-west of 

 Salem and in Nagaramalai near the Chalk hills (Nos. 9*683, 

 9-684, 11*903). The latter rocks are almost always associated with 

 pyroxenite (vide page 26). 



The non-garnetiferous basic forms are composed almost 

 always of pale-green augite, hypersthene, 



Non-garnetiferous forms. . , , , » r 1 • » 



brown-green hornblende, felspar, iron-ores and 

 apatite. Variations in the relative proportions of the first three 

 constituents and in size of grain are frequently observed, but the 

 resemblance in the essential features of the large lenticular masses 

 to those of the small schlieren is so complete that there can be little 

 doubt that the isolated small hills in the Salem-Ahtur valley are 

 composed of rocks related to those in the Shevaroys. 



In the garnetiferous varieties the garnets sometimes attain 



the size of a fist, and are often surrounded by 



Garnetiferous varieties. . . , , . 111 1 e 



large crystals of hornblende and augite, forming 

 patches in the rock having the composition of hornblende-eclogites. 

 Under the microscope the garnets show a very spongy structure 

 through inclusion of blebs and granules of a colourless mineral 

 resembling quartz. Frequently the garnets are seen to be grown, 

 coronal fashion, around the hypersthenes ; in such cases vermiform 



Fig. 2— Hypersthene with corona 0/ spongy garnet, Nagaramalai (No. 11-903). 

 cavities are arranged radially, whilst near the hypersthene the 

 garnet is particularly spongy (fig. 2). In some sections the garnets 



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