118 GEOLOGY or TRICHINOPOLY, &C. [ClIAP. V. 



greater elevation above tlie Salem plains. Most proLaLly a connection 

 exists between this and the gi-eat rock above described. 



Besides these distinct and probably latest intrusions'^ of granite 

 among the metamorphic rocks^ there are distributed all over the valley 

 of the Cauvery, from Caroor to Trichinopoly^ and beautifully displayed 

 on the numerous bosses and hummocks of quartzo-felspathic gniess of 

 that region, thin strings and veins of granite^ varying from a few inches 

 to a foot in thickness, and of these there are two systems, one of which 

 veiy often crosses the other. In the newer, the walls of the veins are 

 distinctly marked, while in the older the lines of separation are seen with 

 difficulty, these having been obliterated by re-metamorphism. Enclosed 

 fragments of gneiss torn off by the granite during its intrusion are by no 

 means unfrequent. 



* It would appear as if there had been at least three periods of mtrusion of granite in 

 the rocks which now constitute the gneissic series, two of which are apparently much older 

 than the third. 



We have first the two systems of small veins of which those with the scarcely distin- 

 guishable walls are traversed Ijy the more distinct; but these are all so compacted with the 

 traversed rock, so old looking, and so diverted from what would appear to have been their 

 original direction, by the squeezing and folding which the gneiss has undergone, that one can 

 hardly help considering them to have been part of the great system of rocks traversed T)y 

 the apparently later outburst of the Cauvery belt. Tliough the granite of TogamuUay 

 and the Cauvery bank traverses rocks which are permeated by the system of smaller veins, 

 stiU I remember no case of distinct separation between what I take to be the older and newer 

 granite. This, however, could hardly be expected, for the two granites at their junctions 

 Avoixld be so fused together, that any decided separation coidd hardly be made out. Such dif- 

 ferences in the granite would then imply at least two great periods of metamorphism : one 

 when the first scries of granite veias was formed ; the other during the intrusion of the 

 granite of the Cauvery belt, etc. My subsequent observations m Nellore and Cuddapah 

 show that there have indeed been two such periods, but whether these have any connection 

 with the igneous features of Trichinopoly district, etc., is yet to bo made out. In the 

 NeUore and Cuddapah districts is a series of clay slates and quartzites, themselves metamor- 

 phosed, conglemeratic, and ripple marked, which rests unconformably on the older and vawch 

 more altered gneissic rock of South India, — W. K. 



( 34.0 ) 



