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Throughout the region here described these great sheets of volcanic rock
are everywhere approximately horizontal, and constitute a table-land of
3,000 to 4,000 feet in elevation, breaking off in terraced escarpments,
and penetrated by deep river-valleys, of which the Narbudda is the most
important. The foundation rock is sometimes metamorphic schist, or
gneiss, at other times sandstone referred by Hislop to Jurassic age; and
in no single instance has a volcanic crater or focus of eruption been
observed. But outside the central trappean area volcanic foci are
numerous, as in Cutch, the Rajhipla Hills and the Lower Narbudda valley.
The original excessive fluidity of the Deccan trap is proved by the
remarkable horizontality of the beds over large areas, and the extensive
regions covered by very thin sheets of basalt or dolerite.

(_c._) _Geological Age._--As regards the geological age of this great
volcanic series much uncertainty exists, owing to the absence of marine
forms in the inter-trappean beds. One single species, _Cardita
variabilis_, has been observed as occurring in these beds, and in the
limestone below the base of the trap at Dudukur. The _facies_ of the
forms in this limestone is Tertiary; but there is a remarkable absence
of characteristic genera. On the other hand, Mr. Blanford states that
the bedded traps are seen to underlie the Eocene Tertiary strata with
_Nummulites_ in Guzerat and Cutch,[2] which would appear to determine
the limit of their age in one direction. On balancing the evidence,
however, it is tolerably clear that the volcanic eruptions commenced
towards the close of the Cretaceous period, and continued into the
commencement of the Tertiary, thus bridging over the interval between
the two epochs; and since the greater sheets have been exposed
throughout the whole of the Tertiary and Quarternary periods, it is not
surprising if they have suffered enormously from denuding agencies, and
that any craters or cones of eruption that may once have existed have
disappeared.

[1] The Deccan Traps have been described by Sykes, _Geol. Trans._, 2nd
Series, vol. iv.; also Rev. S. Hislop, "On the Geology of the
Neighbourhood of Nagpur, Central India," _Quart. Journ. Geol. Soc._,
vol. x. p. 274; and _Ibid._, vol. xvi. p. 154. Also, H. B. Medlicott and
W. T. Blanford, _Manual of the Geology of India_, vol. i. (1879).

[2] Blanford, _Geology of Abyssinia_,