'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎208] (341/458)

208
GEOLOGY OF BOMBAY.
Hill, a vast mass of tuffaceous rock, almost white, prevails. Itisf u ||
of veins and cavities usually filled with spar. The cavities are of an
oval or amygdaloidal form, the longer axis in all cases being from N,
E. to S. W., as if the rock, while still in a soft state, had been com
pressed laterally from S. E. to N. W. The cavities are, for the most
part, filled with siliceous spars and veins, and coatings of agate and
chalcedony. The rock blackens very rapidly with the weather, and
its real character is only known when freshly broken. I mistook it,
for a while, for common greenstone. Where it is uniform in texture,
it is cut up for "water troughs and aqueducts, being soft when first
exposed to the air, and hardening afterwards without abrasion or
decay,—in this respect resembling laterite. A purple variety of tuffa,
differing altogether from this, is to be found in the hills between
Sion and Matoonga. The prettily wooded hill, on the base of which
stands the powder Magazine, is composed of it ; and it has here
been well exposed to view by the operations of the quarry-man.
Further to the eastward, white coloured masses, marked with small
oclirey spots like porphyry, are embedded in it; and in detached pieces,
on the seashore, I have found this passing into laterite. After most
careful enquiry I have failed to find the two rocks in contact to
determine the fact, which seems more than probable, that they pass
into each other.—In nearly all these Tuffas beautiful specimens are
found, either of trap which has been disturbed in its viscous state
while cooling, or of sedimentary rock which has been slightly fused
without becoming either jaspideous or having its texture obliterated. I
Lave not been able to determine which of the two is the correct state
of matters, or whether both may not be found occasionally to prevail
1 he rugged masses of Tuffa are occasionally seen coated with this,—
occasionally found running in long thin beds with other rocks .*—hut
the tiap rocks of Bombay would, of themselves, furnish a cabinet, and
the subject of an essay, which could only be properly understood
when lead wdth access to the specimens,—a condition of things attaina
ble only to those who have searched everv quarry and excavation on
the Island.
Lines of Junction*—\t will readily be imagined, from what has been
aheady stated, that very striking appearances are to be met with at all
the lines of junction ; and it is matter of regret that so few opportune
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