PREHISTORIC BOMBAY. Ill 



North America, covering an area Larger than France and Grreal 

 Britain together, there has probably never been in the history of 

 the world so great an outpouring of lava as that which produced 

 the scries of rocks known to geologists as "the Deccan Traps," to 

 which those of Bombay Island belong. 



Besides the greal depth and area occupied by these rocks, anothei 

 peculiar feature about them is the extreme horizontality and regula- 

 rity of their strata. With the exception of thai dip in which the 

 rocks of Bombay Island partake, and which we have seen to extend 

 over a comparatively small area, the Deccan traps are found to lie 

 in almost exactly horizontal bands, varying in thickness from 8 to 

 200 feet, formed by successive flows of lava. 



This would seem to show that the vents through which the lava 

 was ejected were raised little if at all above the surface of the 

 ground, and that the lava streamed forth in a very liquid state, 

 possibly as molten mud. 



Considering the great area covered by the lava flows, very few of 

 their vents have yet been found. Those which are known, lie princi- 

 pally in the plain of the Concan, and consist for the most part of 

 what are technically known to geologists as "dykes," that is, long- 

 lines or walls of basaltic rock, showing that the lava of which it is 

 formed was ejected from longitudinal cracks or fissures in the earth's 

 crust. This, and the fact that the few crater-like vents yet discov- 

 ered are little more than low hillocks, would seem to confirm the 

 view that the lava flows forming the series of the Deccan traps were 

 poured forth from but slight elevation. 



The position of the known vents would seem to point to the conclu- 

 sion that the scene of the eruptions that produced the Deccau traps 

 was principally in the line of country between the "foot of the west- 

 ern ghauts and the sea. There are, however, in Bombay several 

 places to be noticed presently, which doubtless were the foci of 

 volcanic eruptions later than those which formed the Deccan traps. 

 These, as marking weak spots in the earth's crust, may also have 

 been vents for the earlier eruptions, and others, by subsidence of the 

 land, may now be lying beneath the waters of the harbour and the 

 sea outside. However that may be, it seems pretty clear that much, 

 if not all, of that enormous mass of volcanic rock which we know a 



