48 Sandstones containing [no. 7, new series. 



cided with an opinion on the age of the sandstones of Central In- 

 dia previously put forward, by Mr. Hislop,* the question seemed 

 so far decided, viz. that the Trivicary sandstones were older than 

 the cretaceous epoch and in all probability Jurassic. 



In December last, the Madras party of the Geological Survey of 

 India, commenced the detailed survey of the South Arcot and Tri- 

 chinopoly Districts, and proceeded in the first place to examine the 

 relations of the Trivicary and Verdoor sandstones in order to gain 

 a distinct knowledge of their relative superposition before tracing 

 out those rocks into other portions of the district. This portion of 

 the work has been now completed, and the result is that the rela- 

 tive superposition of the beds in question proves to be precisely the 

 reverse of that which Mr. Schlagentweit imagined to be the case. 

 As this is a subject of somewhat critical distinction, and will in all 

 probability prove of great importance to the true comprehension of 

 the geology of a large portion of India, it is advisable to state in 

 some detail the grounds upon which the above determination has 

 been arrived at. 



Immediately to the east of the village of Trivicary and stretch- 

 ing thence for a distance, of about half a mile in the direction of 

 Verdoor and Pondicherry, are a series of small irregular sandstone 

 bluffs much eroded by the denuding action of fresh water, and 

 forming a prominent and striking feature in the surrounding land- 

 scape. On near inspection these bluffs are seen to be composed 

 of coarse sandstones much false-bedded and irregularly banded 

 with brilliant tints of lilac, orange, pink, white, &c. ; they are rare- 

 ly conglomeritic, considerable quantities of silicified wood are scat- 

 tered over the surface of the ground, and here and there large 

 masses of the same are seen protruding, from the sandstone in situ. 

 The sandstones are of no great thickness, for so far as can be judged 

 they appear to be nearly horizontal and on their western boundary 

 or towards the village of Trivicary, are seen in several places rest- 

 ing immediately on the crystalline rocks, which everywhere form 

 the bottom rock of the country. The small bluff which bounds this 

 elevated patch of sandstones, is very conspicuous both in its west- 



* Quarterly Journal Geological Society of London, Vol. XI. p. 457. 



