1840.] NoUs^ principally Geological^ on Southern India. 133 



and Adrianpatan. It contributes immensely to the fertility of the 

 countries through which it passses ; its waters are conveyed into the 

 fields principally by means of water-courses, and anicuts, constructed 

 at a vast expence by the Hindu princes of Southern India. Two crops 

 of rice are, in general, annually produced on its banks, besides large 

 quantities of most excellent tobacco, sugar-cane, &c. The soil brought 

 down by it is a fine rich clay, produce of the disintegration of the rocks 

 over which it passes, and often mingled with a considerable portion of 

 carbonate of lime, deposited by its waters, and decayed vegetable matter. 

 It is navigated principally by basket-boats, and conveys the produce 

 of Salem, Coimbatoor, and Trichinopoly to the sea. 



Having reached our southern limit, we will now return northerly 

 towards the Tumbuddra, by a different, though almost parallel, route, 

 lying to the east of that just described. 



From Seringapatam to Bangalore the formation is principally gneiss 

 and hornblende schist, penetrated by veins of actynolitic and ehloritic 

 felspar. The rocks in the vicinity of Bangalore are granite, gneiss, 

 and greenstone, in dykes, penetrating them generally in a west to an 

 easterly direction. Tabular masses of a lateritic rock overlie the gneiss, 

 a little to the N. W. of the cantonment. Passing from Bangalore, the 

 geology of which I shall have occasion to notice in a subsequent paper, 

 the road lies in a northerly direction, towards the celebrated stronghold 

 of Nundidroog. 



^undidroog. — Gneiss, with a few clusters and detached hi! Is of granite 

 rising above the undulating level of the table land, are met with. The 

 soil is generally a bluish red, loamy clay, and a quartzy detritus , 

 abounding in ferruginous nodules — debris of the lateritic rock, which 

 is seen on the surface in scattered patches. Near Yellavunkah I ob- 

 served a mass of it covering the surface of the road, and again noticed 

 it near Nundidroog, where it was partially employed, with other stones, 

 in the construction of a bund of a tank. This contained much less 

 quartz than the former, nor was it so porous. A little north from 

 Deonhully, a hill, principally of gneiss in contorted strata, is seen, with 

 a nearly north and south direction. Its southern extremity is crossed, 

 from west to east, by two basaltic greenstone dykes ; the first of which 

 bifurcates on entering the hill from the west: the larger branch pursues 

 its course through the hill without much interruption, and sinks beneath 

 the surface of the soil on the opposite or eastern side. Its breadth ig 

 from 15 to 20 yards. The rock through which it passes, particularly on 

 the left side of the dyke, where it has a scarp of above eight feet high, 

 has the appearance of a channel cut in the rock. The left branch of 



