1857.] Report on the Progress of the Magnetic Survey. 107 



fresh-water stratum containing only fresh water-shells (Physa, 

 Melania, Unio, &c.) down the Grodavery to Eajahmundry. Near 

 this place occurs a very curious mixture of the unmistakeable fresh- 

 water Physa Prinsepii, with numerous true marine species. 



The lime-stone stratum, with these marine shells, lies like the 

 fresh-water lime-stone of the Deccan between a mass of trap 

 (Dolerite) ; it reposes upon a cellular trap, and is covered by up- 

 wards of 50 feet of nodular trap. It is found at Cateroo, 3 miles 

 from Eajahmundry, and at the Pangadi Hills, 10 miles from the 

 latter place, and is from 2 to 2| feet thick. In some places the 

 rock is quite full of marine shells, which belong to Area, Car- 

 dium, Venus, Cerithium, Turbinella, &c. I also found a large 

 well-preserved nautilus at Pangadi, which will serve to throw 

 some light upon the age of the intertrapian lacustrine and marine 

 formation of India. 



The connection between these strata of Eajahmundry and the 

 merely fresh- water deposits of the Deccan is quite clear ; it seems 

 to have been a deposit probably in a series of great lakes growing 

 brackish to the Eastward. The fresh-water Physa Priusepii, not 

 to be distinguished from the Deccan specimens, lies side by side 

 with Cerithium, Area, and other marine shells. 



The fresh- water intertrapian stratum of the Deccan is from 2 

 to 4 feet thick ; it consists in part of variously coloured marls in 

 part of impure lime-stone. 



In the parts where I had the opportunity of examining it, near 

 Saugor, near Lenni, Nagpore, &c, it generally is covered by globular 

 black trap of from 40 to 70 feet thick only, which seems to have been 

 the most recent of the trap effusions in this part of the country. 

 It rests upon a cellular Amygdaloid or Wacke, into which it some- 

 times graduates, so as to make it impossible to draw any distinct 

 line of separation between the two rocks. I also observed fre- 

 quently quite isolated patches of a very soft cellular Wacke 

 between the fresh-water strata themselves. It seems to me that 

 the fresh-water strata have been deposited at the bottom of lakes 

 covered with volcanic ashes, and it is quite probable that occasional 

 showers of ashes still fell occasionally during the period of the 



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