146 HOLLAND: CHARNOCKITE SERIES. 



The mass of rock out of which the remarkable Seven Pagodas' 

 have been hewn in situ is also almost wholly 



Similar large masses. , f . . . , . - .- ... 



made up of quartz (which is crowded with 

 the peculiar acicular inclusions already described) and microper- 

 thitic felspar ; but the evidence for connecting this rock with the 

 charnockite series is confined purely to the similarity in the micros* 

 copic characters of the two principal minerals (No. 9*677). The rock 

 is coarse in grain, and shows slight signs of kaolinization which gives 

 it a dirty-white colour instead of the blue-green of the normal char- 

 nockite. This decomposition which extends to great depths in the 

 rock of the Seven Pagodas, and which enables one at once to distin- 

 guish hand specimens of it from the charnockites of the hill masses 

 further inland, is probably due only to the fact that, being near the 

 coast, it has been submerged below the sea during the limited 

 oscillations of level which are shown to have taken place by the 

 deposition of cretaceous and younger marine beds on the Coroman- 

 del coast. 



The rock of the Seven Pagodas shows on weathered surfaces 

 a very imperfect gneissose structure parallel to the direction of the 

 exposed ridges, and, as Mr. Foote 1 has remarked, parallel to the 

 coast line ; that is, N. 5 E. and S. 5 W. But that this foliation was 

 induced before the complete consolidation of the rock seems almost 

 certain, for the crystals are seen under the microscope to be inter- 

 locked in a complicated way, and the only definite signs of pressure 

 subsequent to consolidation are indicated by the undulose extinctions 

 of the quartz crystals with an occasional granulation of the more 

 delicate intergrowths. 



(2) Intermediate Division. 

 At St. Thomas' Mount and Pallavaram, the norite and the char- 

 nockite form large masses, which whilst being uniform \a composition 

 throughout, are very distinctly marked off from one another. Speci- 

 mens taken from any part of the mass of charnockite will be found 

 to have a specific gravity which never differs greatly from 2*67 



1 Mem s Ceol. Surv. Ind., Vol. X (1871), p. 127, 



( 28 ) 



