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HISLOP AND HUNTER — NAGPUR. 357
of trap extending over sandstone without being associated with a
second sedimentary formation or volcanic effusion.
Though the three formations are generally connected with each
other, yet it is chiefly the upper one, viz. the overlying trap, that
meets the eye over the face of the country. Leaving out of con-
sideration the very few examples of denudation which have uncovered
the freshwater deposit in the plains, and the equally rare instances
of eruption which have there upheaved it on its edge, it is on the
escarpments of the table-lands that we may be said to gain our whole
knowledge of this department of Nagpur geology. In commencing
our ascent of these steep hills, our attention is attracted by a number
of blocks near the foot, which are easily distinguished from the
masses of basalt among which they have fallen from above. As we
make our way up over the hard, dark, vesicular rock, the blocks in-
crease in number until we come to a friable greyish or bluish-green
zone. We must now move slowly and look narrowly, for a few
5^ards of upward progress may conduct us from the soft amygdaloid,
where fragments are thickly strewed, to a nodular basalt, where not
a trace of them is to be seen. Occasionally the freshwater forma-
tion is so thin that a very little earth or herbage may suffice to hide
it from our sight. But generally the water from the brow of the
hill in the monsoon collects into little rills just at the place where it
leaves the nodular trap, and having now gathered enough of strength
to make an impression on intervening barriers, it proceeds to plough
up the soft deposit, and the still softer subjacent amygdaloid, leaving
an interval between each streamlet, like a talus resting on the harder
vesicular rock below (see fig. 2). The thickness of the overlying
trap on Sitabaldi Hill and the tabulated summits in its immediate
vicinity is from 15 to 20 feet, which agrees very exactly with the
Fig. 2. — Sectional View of one of the Trap Hills near Nagpur.
a. Surface soil. c. Freshwater deposit.
b. Nodular trap (15 to 20ft. thick). d. Soft amygdaloid. e. Hard amygdaloid.
thickness assigned to it by Dr. Voysey at Jillan. On the Western
Ghats, however, according to Colonel Sykes, a stratum of earthy
jasper, which is just our freshwater deposit, was found near Junar
under a thickness of from 300 to 600 feet of basalt*. But it not
unfrequently happens, that in leaving the plain and climbing up a

• Trans. Geol. Soc. 2 ser. vol. iv. p. 419.