PART 3.] 
Blauford: Geology of Bombay Presidency. 
91 
occur on the earth’s surface. Another remarkable distinction is the apparent absence, throughout 
a great part of the area, of any foci from which currents of lava could have been poured 
out. Of course cones of loose scoria} would long since have been l'emoved by denudation, 
and nuclei of solid basalt would not easily be recognised amongst flows of similar consti¬ 
tution. Still it is remarkable that so few instances should have been described. Unmistake- 
able nuclei exist in tho lower Narbada valley, some of them, as Metapenai hill south-west 
of Chota Udepiir, consisting of trachyte; and throughout a large tract in the Raj pipla hills 
tho rocks are cut np by immense dykes; but still bettor examples of volcanic foci may bo 
seen in Kachh amongst tho jurassic rocks, one of thorn being tho so-called volcano of 
Dinodar* west of lihuj. Mr. Clark also (Quart. Journ. Geol. Soc., 1869, p. 163,) 
states that a lino of vents exists in the Konkan east of Bombay, and that large 
numbers of dykes occur ; but whilst it is highly probable that there are volcanic foci in this 
direction, it Is doubtful if any large portion of the Deccan traps have flowed from them, for 
tho frequent occurrence (locally, it is true, not universally) of trap dykes, and still more of 
ash-breccia appears to show that centres of eruption must have been scattered widely over 
the country, and it is probable that closer search will show their existence. 
It is evident that the lavas were poured out in a very liquid state, and that they spread 
themselves in wide sheets of small depth over largo areas of country. It is quite possible 
that the more earthy beds which form a very large proportion of the whole may have issued 
in the form of volcanic mud, not necessarily at high temperature. But tho crystalline 
basalts were in all probability poured out as lavas liquified by heat. 
Geologists generally have hitherto explained these peculiar pheuomena by supposing that 
trap rocks similar to those of the Deccan have been poured out at the bottom of the sea, and 
in taking a different view, which I do with some diffidence, I know that I am in opposition 
to all the best authorities and to some at least of my own colleagues. It is considered that 
lavas would preserve their liquidity longer at the bottom of tho sea under the pressure of 
tho water; that they would consequently be spread ovor a largo area; that there would, for 
the same reason, be vesicular structure, but not scoriaceous, and that cones of scorise would 
not bo formed, because tho ashos and fragments blown out from tho crater would be spread 
over the bottom of the sea, 
To this view there is one serious objection, which is, that somo of tho Deccan traps were 
subaerial or poured out in water so shallow that the pressure could not have affected them, 
and that these are undistinguishable from tho mass of tho beds; whilst, on tho other hand, 
thero is no evidence except the single occurrence of marine shells intersti'atified with tho 
basalts near Eajamahindri to show that any portion of them were accumulated beneath the 
sea. In tho case of Rajamabindri there can be no doubt but that somo of the traps are 
submarine, and there can be equally little doubt but that they were poured out in a shallow 
sea or estuary close to land, for tho marine shells found are of littoral or estuary species, not 
of deep water forms, and lreshwator shells arc mixed with them. It is equally clear that 
tho bulk of tho intortrappean sedimentary beds to be presently mentioned, wherever they are 
found from Mundla to Bombay, and from Dewad (Dkawud) in the Rewa Kanta to the Sickel 
hills of Hydrabad, are of freshwater origin, formed in small shallow lakes, and that conse¬ 
quently the greater portion of tho surrounding country, over which tho lava flows were 
poured out, was dry land. 
Another proof that the lowest traps were subaerial is to bo found in tho form of the 
surface on which they rest. This is excessively uneven, valleys upwards of a thousand feet 
deep being found in it in places. This uneven surface can only have resulted from subaerial 
denudation; marine denudation, as has been amply shown, reduces tho area affected by it to 
* The reported eruption of this “ volcano’* in 1819 must be a mistake. There is no trace of any recent igneous 
action on the hill, which is not a volcanic cone, but a nucleus of basaltic rock exposed by denudation. 
