s 



Geology of the Country 



[July 



face, but they extend their action many inches into the substance of the 

 rock, producing in consequence three, four or more laminae, which, 

 although having decided lines of demarcation, still adhere to the 

 parent rock. 



In this sienitic granite nests of green-stone porphyry are imbedded, 

 as is the case almost in all localities in India, where this rock is found 

 (No. 30). Their decomposition, and consequent falling off, accounts for 

 the cavities we see occasionally on the surface of this rock, at the 

 bottom of which it is not rare to find the remains of the old tenant (the 

 nest of hornblende porphyry) still adhering undecomposed. 



Proceeding west, towards Shamarpilly (just after leaving Golconda- 

 patnam) ; to the left of, and close to, the road, is a little oblong knoll, or 

 rather undulation of the ground, having at the top many blocks, diffe- 

 rent in colour and appearance from the granitic boulders just described. 

 These are of a blackish colour, and covered with large patches of the 

 all-pervading lichens (No. 30). 



They are hornblende rock containing very little felspar — structure 

 semi-foliated, and fracture glimmering. Numerous quartz veins inter- 

 sect it irregularly and in all directions, some of them being nearly a foot 

 thick. They are discernible from a distance on account of the con- 

 trast between their white colour and the black of the rock. In those 

 masses in which the hornblende decays, they are seen projecting 

 above the soil like beds of quartz rock. 



The direction of this dyke-like bed of hornblende rock is N. and S. 

 and its decomposition imparts to the soil in its vicinity a red ferrugi- 

 nous colour, different to that about Golcondapatnam, which is loose, 

 white and sandy, The cause of this colour must be the oxide of iron, 

 which appears to enter largely in the composition of the hornblende ; 

 since, like other primitive green-stones, it affects the magnetic needle. 



Among the rocks, before reaching Bangalore, gneiss seems to pre- 

 dominate. It is composed of the usual minerals, forming regular 

 strata conformable to each other, in some of which at one time the 

 mica, and at others the quartz, predominates, sometimes to the exclusion 

 of the other two minerals (No. 30). The quartz is white and trans- 

 parent, the felspar of a paler hue, and the mica black. 



Bangalore. — In the vicinity of Bangalore, gneiss is seen every 

 where, having veins of quartz, or of foliated felspar, or of both toge- 

 ther, traversing it. It seems to decompose, or to have decomposed, to 

 a great depth, since we see the loam resulting from it very abundant 

 all about Bangalore, and in some places having twenty, or more, feet 

 depth ; such is the case near the bazar behind the Barracks (No. 33), 

 The clay that, is found in this loamy soil is reckoned excellent for tiles, 

 bricks, &c. 



