170 On the Granite formation 



easier than hornblende and entumeces very much and bubbles 

 up. In the vicinity of granite hills, a porphyry of black schorl 

 in quartz is also found ; but I am doubtful if it is ever found in 

 granite, the rock being very scarce, and I have only met 

 with it in any quantity a few miles south of Paulcode, and 

 there only, not in situ. 



Dr. Boase* and some other writers have endeavoured to 

 shew, that the brecciated appearance of rocks embedded in 

 granite, are only concretionary varieties separated by segre- 

 gation ; but I conceive that the fact of these fragments being 

 connected with the veins of the granite, and being also 

 intersected by fissures containing granite, and further, from 

 the answering angles of the fragment, these will be received 

 as a sufficient proof of their being true fragments. 



It is pretty generally believed, and stated by most writers 

 on Indian Petrology, that the iron sand from which almost 

 all the iron made in South India is smelted, is derived from 

 the disintegration of trap rocks. But I have in no case ever 

 been able to find iron sand in the vicinity of trap formations, 

 and on the contrary, have constantly found it in the vicinity 

 of granite ranges, particularly near those of euritic granite. 

 I have not been able to determine from what part of the 

 hills it is derived, but I am inclined to believe it is em- 

 bedded in the primary gravel, which forms a part of the 

 structure. This iron sand has been called " iserine" by 

 Dr. Heyne, but it differs in many essentials from that mine- 

 ral, and particularly in being attracted freely by the magnet. 

 To my analysis it gives but. a small proportion of titanium. 

 Dr. Malcolmson (Madras Journal, vol. xii. page 71) states, 

 he was unable to detect titanium in it. In mine it precipita- 

 ted by boiling, and I think there may be two kinds of the 

 iron sand. 



In many granite hills also, small grains of magnetic iron 

 ore may be detected, disseminated through the mass of the 

 * Primary Geology, page 345. 



