16' TRAPS AND INTERTllAPPEAN BEDS 



conclude that the period of their formation differs by a very large portion 

 at least of the time during which the traps accumulated. 



Throughout the middle and higher traps of the Deccan, even to 

 Mahableshwar and the other higher plateaus^ no trace of any sedimen- 

 tary intercalated bed has been found ; all appear confined to the lowest 

 flows, cropping out round the edge of the trap area, or to the highest 

 flows, appearing only at Bombay. 



11. TJieories of formation of the intertrappean heds. — Mr. Hislop, 

 who has perhaps given more attention to the intertrappean rocks than 

 any one else, and to whom we are indebted for the only complete 

 account of the fossils, has proposed the following theory of the formation 

 of these beds."^ He considers that all Central and Western India was an 

 immense lake communicating with the sea to the eastward near 

 Rajamundry ; that in this lake deposits containing remains of animals 

 and plants accumulated ; that these deposits were covered over by trap, 

 and then that a second eruption of trap was injected between the fresh- 

 water bed and the surface of the underlying rock, 



Mr. J. G. Medlicottf showed that this theory was irreconcileable 

 with facts observed by him in the Nerbudda Valley. If it were 

 correct, the lower surface of the sedimentary bed must have been altered, 

 whereas in every instance he had seen the upper surface alone had been 

 changed by the trap flow above it, the under surface remaining un- 

 altered. He says — " In every case within our experience the sedimentary 

 beds have been deposited tranquilly on the previously indurated and 

 moreover previously denudated surface of the trap rock.^^ My own 

 observations, I may say, entirely coincide with Mr. Medlicott's. 



Mr. HislopJ in a later paper considered that both upper and lower 

 traps might be portions of one flow, and brought forward fresh 

 evidence in favor of his views. To enter into these in detail would 



* Quar. Jour. Geol. Soc, Vol. XI, p. 368. 

 t Mem, Geol. Surv. lud., Vol. II, p. 206. 

 J Qnar. Jour. Geol. Soc, Vol, XVI, p. 155, 

 ( 1!^2 ) 



