P8 Geology of Bangalore, and of [Jan. 



small cavities of a yellow earthy powder, decomposed hornblende, or 

 perhaps iron? Another kind is porphyritic, large, crystals of felspar 

 imbedded, with the same microscopic cavities, this being the rock which 

 Dr. Benza says he is at a loss what to denominate. 



Not far from Seringapatam, are some rocks near the road, about 4 miles 

 before entering the town or rather fort, consisting almost entirely of the 

 red clayey looking felspar, with numerous small cavities of a black shining 

 metallic looking substance, what in decomposition seems to afford theyel- 

 low earthy powder. This is a rock which I should think has at one lime 

 been rather common through Mysore, but has rapidly undergone de- 

 composition, as it appears to contain a good deal of iron. Whilst on the 

 reddish felspar I may mention that there are some gneiss rocks near the 

 gardens of the Horticultural Society, where I have found occasionally 

 some very beautiful specimens — the felspar and quartz of a pinkish tinge, 

 with green streaks and lines, dark green needle-shaped crystals of, I 

 think, epidote, with occasional crystals of kyanite. The next ingredient 

 in the gneiss rocks is the quartz, which is usually of a white colom* or 

 having a very slight blue tinge, generally the first when with felspar, and 

 the last when in veins by itself. The light blue sometimes approaches 

 almost to an amethystine colour — small pieces of rock crystal are some- 

 times picked up, one fine specimen in my possession, containing iron 

 pyrites, was found in some rocks about two miles from the fort. In a 

 small nullah about a mile and a half to the north of the Belfry, and 

 near the boundary hedge of the cantonment, there are large quantities 

 of quartz crystalized into six sided prisms terminated by six sided py- 

 ramids. The hornblende, whir-h is found in beds in this gneiss, is 

 seen in the nullahs decomposing into a greyish or greyish green earth. 



Gneiss is the prevailing rock around Bangalore, and is generally of the 

 common grey colour, with nests and streaks of black mica, large veins 

 of foliated felspar and quartz, and the strata often very much contorted. 

 The process of decomposition is proceeding rapidly, and where a deep 

 ravine exists, this decomposition is well shown — an immense rock will 

 be found retaining its shape, but quite soft and crumbling down on 

 being touched, veins of quartz traversing the soft disintegrated mass 

 in all directions. In digging to any depth, as in forming w^ells, after 

 removing a few feet of a brownish earth, we come upon the gneiss 

 rock in a state of decomposition, forming a white stony earth. In the 

 valleys all around, the felspar decomposes into clay, which is used by 

 the potters and chatty manufacturers. Where a bed or vein of quartz 

 highly ferruginous has existed^ a quartz later! te has been formed, as 

 on the left-hand side on going towards the fort near the Canarese school 



