204 CKETAffEOUS ROCKS OF S. TXDIA. [pART III. 



which have existed at least for one or two centuries, and although 

 exposed to the ultimate action of the heat and heavy periodical rains, 

 exhibit in many cases the marks of the chisel and the delicate sharp- 

 ness of ornament, almost as clearly as when turned out from the sculp- 

 tor's hand. Gneiss of this kind prevails to the South of the Cauvery, and 

 also occurs in the northern part of the Trichinopoly district, and in Soutk 

 Arcot ; but in a few spots only, where its presence is indicated by a 

 projecting boss or hillock, most of the gneiss in this part of the country 

 being decomposed to the depth of many feet beneath the even-covering 

 of soil. It is usually of a pale grey fracture, and shows but little trace 

 of foliation. 



Gneiss is used to some extent for metalling the Trichinopoly Trunk 



Road, chiefly in the immediate neighbourhood of 



As road-metalling. m • i • -r-i i i • 



Trichmopoly. Elsewhere the decomposed rock is 



employed, much of which is little better than a friable sandy gravel, 

 except where the ferruginous sub-lateritic form of the same material is 

 obtainable, a metalling which binds well but is scarcely hard enough 

 to stand the great wear and tear to which this road is subject. The 

 anamesite (?) of the dykes which cross the road at several places in the 

 Trichinopoly district, has never been employed, so far as I have observ- 

 ed. It would undoubtedly be the most lasting material procurable, the 

 only question being, how far the increased expense of quarrying and 

 breaking up would be met by its greater durability. 



The only spot at which I have met with crystalline limestone, within 



the limits of my own survey, is in the middle of 

 Crystalline limestone. 



the granitic ridge of Thutchuncoorchy, about two 



miles to the North-east of Cullpolliam, a village on the Madras road. It 



was not worked at this spot, but several bands of a similar rock have 



been noticed by Messrs. King and Foote to the Westward, where they 



are quarried by the natives for building purposes. The stone is too soft 



and pure to withstand the solvent action of rain for any great time. 



