DESCRIPTION OF THE CHIEF TYPES* 



«55 



lowing table gives the average specific gravity of the leading types 

 of hornblende and augite norites : — 



8-752 



8*754 

 9*661 



9-395 

 9*397 

 9*657 

 9*656 

 9'66o 



Hornblende-augite norite 



Augite-norite ........... 



Hornblende-augite norite . . . 



Augite-norite .......... 



jj ... ....... 



>t »........, 



jj *».*....., 



Average specific gravity = 



3*io 



3*09 



3'o8 



3'o85 



3*185 



3*03 



3*1 * 



3*02 



3*o9 



Mineral composition. 



Augite is almost always associated with hypersthene in these 

 norites, and a peculiar greenish-brown variety of hornblende is found 

 to be extremely common. The augite and the 

 hornblende are remarkably uniform in character 

 in all occurrences of the charnockite series, and are almost as charac- 

 teristic as the hypersthene. The amount of opaque iron-ore in the 

 norites always exceeds that in the pyroxenites associated with them. 

 A large quantity of the opaque iron-ore is titaniferous. Sphene 

 is typically absent ; it occurs, however, in a biotite-norite near 

 Pallavaram (No. 9*671), but this rock presents many other excep- 

 tional characters, and is a distinct departure, for some reason not 

 apparent, from the normal type. 



The silica percentage, the specific gravity and the great pre- 

 dominance of labradorite amongst the felspars marks these rocks as 

 distinctly basic, as basic in fact as the augite-norite dykes which cut 

 through them. 



( 37 ) 



