298 



GEOLOGICAL SURVEY 



lating the rocks of tke two basins, but these cannot be gone 

 into here. 



The lowest member of the formation in the main or Karnul 

 basin, the Banaganpilly sandstones, includes the true diamond 

 bed, to which so much attention is being devoted at 

 present. The beds where conglomeratic in character have 

 been worked at various places, and at Banaganpilly itself, the 

 capital of the small Native State of that name, they are 

 regularly mined, the demantiferous layer being reached by 

 small shafts sunk to a depth of 15 feet or less. The other 

 workings are open diggings as at Baswapoor, Munnimadagu, 

 Gooraman Konda, and Ramalkota, &c. For details of these 

 mines and the rocks they occur in the reader is referred to Mr. 

 King's Memoir in vol. viii of the Memoirs of the Geological 

 Survey of India, in which the question of the mode of occur- 

 rence and working of diamonds in South India is fully 

 entered into, and from which has been taken most of the 

 recent and reliable information about such diamonds given 

 in the third volume (Economic Geology) of the Manual of 

 the Geology of India and in other recent pamphlets and 

 books by Mr. Ball and others. 



Even where the " diamond bed " has been worked by the 

 native diggers a very large portion has been left un- 

 touched, and very extensive spreads are virgin rock. The 

 exposed area of the Banaganpilly bed is considerable, and a 

 vastly greater area of it is covered up by the overlying 

 limestones and quartzites of the J ammalamadgu and Paneum 

 groups, the thickness of which is not so greats but that it 

 would oif er no serious difficulty to systematic mining. Whe- 

 ther such mining is advisable is a question to be decided by 

 careful "prospecting" or preliminary mining. This too 

 will decide whether mining on a large scale with elaborate 

 machinery in the form of " stone-breakers" for crushing the 

 conglomerate will pay. These are questions to be decided 



