0¥ WESTERN AN1> CENTRAL INDIA. 11 



there may be taken as evidence that the lowest traps with which they 

 are intercalated, were poured out, not on the bed of the ocean, but on 

 the sea shore, or in an estuary ; many of the shells met with being 

 clearly estuarine forms, and the association of freshwater species being 

 evidence of the presence of land.''^ With this exception, the only sedi- 

 mentary beds which occur interstratified with the traps from Umurkuntuk 

 to Bombay, and from Gwalior to Belgaum, are distinctly freshwater 

 and, in most instances, lacustrine, no marine organism whatever 

 having as yet been met with in them. With regard to the great mass 

 of the trappean formations, in which sedimentary strata are absent, this 

 very absence of detrital deposits is strong proof of the subaerial accumu- 

 lation of the lava flows. It is also, I think, inconceivable that lava 

 flows beneath water could have preserved their liquidity sufiiciently to 

 be spread out in the thin and enormously extended horizontal beds of 

 which the traps are in great measure composed ; they must necessarily 

 it appears to me, have cooled more rapidly than in the air. 



8. Duration of voleanie period, — Those who have fully appreciated 

 the gradual conviction which has of late years been forced upon the 

 minds of most field geologists, of the enormous periods of time which 

 have been necessary for the accumulation of the various rock masses 

 forming the earth^s crast, will have no difficulty in understandino- that a 

 large division, even of geological time, may very probably have elapsed 

 during the accumulation of the Decean traps. The thickness of these 

 beds cannot be much less than 5,000 feet, perhaps it is considerably 

 more. Upwards of 4,000 feet are seen in the precipitous sides of the 

 valleys below Mahableshwar, Probably considerably more than this is 

 exposed in the Island of Salsette and the neighbouring mainland but 

 the thickness of the section there exposed has not been accurately 



* Quar. Jour, Geol. Soc, Vol. XVI, pp. 176-182. 



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