166 On the Granite formation 



This is the principal place where it occurs; but in small 

 portions it is common in the Salem district, though not in so 

 firm and solid a state of granitic aggregation as at the Tally- 

 mally. About the sides of this ridge the aggregation of 

 the rock is loose, and the magnetic iron ore is in greater 

 proportion than in the centre blocks, and it can therefore be 

 profitably mined, and the ore extracted from the matrix by 

 pounding and winnowing it ; and it is from this source that 

 the Port Novo Iron Company procure much of their ore. 



A schistous variety of this rock is also found about Kist- 

 nagherry, and in various parts of the Barramahal, among the 

 schistous series, differing from the ferruginous granite prin- 

 cipally in being richer in ore, and being looser in aggre- 

 gation. 



Structure and Aggregation. 



The mode of aggregation of the granite of the district is 

 very variable ; generally it is of a greyish colour, and formed 

 of shining grains like the granite of Aberdeen ; but it is 

 sometimes so fine in grain, as to be almost earthy in fracture, 

 as about Namcull. In other localities it is composed of 

 crystals a few inches in diameter; of this kind a singular 

 variety may be seen near Roycottah, in which the crystalline 

 quartz and felspar radiate apparently from centres three or 

 four inches apart, and in the middle of these centres is a 

 crystalline portion of magnetic iron ore, about half an inch in 

 diameter, with projecting portions partly disseminated into 

 the crystals. 



Near Trippatore, the Yailgherry hills present a continuous 

 formation of porphyritic granite embedding crystals of 

 felspar, about two inches long. The whole mass of these 

 hills, which extend about ten miles in length, is formed of 

 this kind of granite in confused piled round masses, and 

 differing in no other particular in structure or association from 

 other granite hills, except in the instance just mentioned ; 

 the trap and greenstone present occasionally the same por- 



