1840.] 



of the Great Basaltic District of India. 



65 



in length, extends through the limestone, the strata of which are in some 

 places nearly vertical, but form rounded hills. In others they are capped 

 by sandstone, which exhibits mural precipices of much grandeur, and 

 almost or entirely inaccessible. The strata, for the most part, dip to 

 the N. W., resting on the granite of the Carnatic. This rock is pene- 

 trated by many dikes of greenstone, which have evidently been instru- 

 mental in elevating the stratified rocks to their present singular positions. 

 Little has yet been ascertained regarding the thickness of these strata, 

 which differ much even in the same range of hills. The only minerals 

 they have been ascertained to yield, are varieties of quartz and iron 

 pyrites, the latter of which is so abundant in a few localities, that sul- 

 phur is manufactured from it. At Jumulraudagoo I found the limestone 

 interstratified with muriate of soda ; and it is therefore probable, that the 

 salt diffused through the alluvial soil so extensively as to lender the 

 water of the Pennar brackish duriug the hot season, and the inhabitants 

 independent of the sea-coast for a supply of that article, is derived from 

 this source. 



On emerging from the gorge in the Nulla Mulla range, the Pennar 

 enters the plains of the Carnatic, and near its mouth flows through low 

 hiils of laterite. This deposit rests on the ordinary granite of the Car- 

 natic, with its associated sienites, hornblende schist, quartz rock, and 

 mica slate. It is in a rock composed of a mixture of the last two mine- 

 rals, that the copper-mines of the Nellore district are situated*. In the 

 same neighbourhood, the sandstone and argillaceous limestones are little 

 elevated above the sea, and are continuous with the same rocks on each 

 side of the Kistnah. They are broken through by insulated basaltic 

 hills, in the neighbourhood of which subterranean sounds and frequent 

 local earthquakes are reported to occur ; an assertion I am the more 

 inclined to believe, having myself experienced two slight shocks during 

 a casual visit to the district. 



Having briefly described some of tke more remarkable phenomena 

 exhibited by the southern portion of the great sandstone and argillaceous 

 limestone formations, it will be unnecessary to enter into any detail when 



* The ores are of vai'ious kinds, but the richest is a sulphuret, containing:, according to 

 Mr. Prinsep, 69 per cent, of the pure metal. The copper also occurs in a slate which Mr. 

 Ouchterlonj', of the Madras Engineers, informs me, was considered in Cornwall to be 

 identical with the Killas. If this slate belongs to the " argillaceous limestone" forma- 

 tion, the fact will be of use in determining the relations of that rock to the gneiss, talc 

 slate, and mica schist; a subject on which no observations of any value have yet been 

 made. The primary rocks of this district contain magnetic iron ore and corundum, both 

 Of which occur in the diamond sandstone.. 



