'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎207] (340/458)

207
ln S generally l Sf i
are {repjj
Jcasionally s lig|
! tion of tlie
tliem is curious i,
nerally hard, HI
r than theporh
ler and tlie \m\
ranee, before
en split, as if!
► the depth of fc
oftenedbyjr*
ty colour: the l 1
few weehstoft
spots, ex 4 i:
ie finer por^ 1
3 I {# ItbreaM
, all( lcolu^ fel
f the
but
, vyeatheb ®
TRAP AND PSEUDO TRAP ROCKS,
hardly be surpassed as a building stone : near Parell there is a light
blue variety of trap of a soft earthy aspect, which easily yields to the
stonecutter : it looks more like hardened mud than volcanic rock.
It corrodes when exposed to the weather, and is unsuitable for build-*
ing purposes unless under ground. Near the line of railway opposite
Parell, the greenstone assumes a dirty olive brown appearance, and
contains immense nests and veins of calcareous spar, sometimes of very
great beauty. It is hero slightly porphyritio. At the Western base of
Chinchpoogly Hill the greenstone is of a pinkish ochrey hue, and might
be mistaken at a distance for Oolite, or sandstone of the coal forma
tion. It closely resembles the compact felspar of Fifeshire in Scotland.
As a building stone it blackens in the weather, but is not subject to
decay.
Greenstone, Porphyry, and Amygdaloid, are found together in
abundance to the north of the gardens of the Agricultural So
ciety,— near the Baboola Tank,—and to the northward of Parell near
Matoonga. Xhey abound in minerals often of great beauty 5 and
wherever, in fact, the trap and stratified rocks approach each other,
the character of the former becomes vessicular.
3 Trap tufFa.—It is difficult to class and describe our trap tuffas,
diversified and irregular as they are, and presenting themselves mixed
up in the most intricate manner with the more compact of our vol
canic rocks. One of the most prevalent varieties of Tuffa consists of
olive greenish or brownish coloured masses, imbedded in a matrix some
what darker in colour than themselves. It abounds in calcareous
spar in veins and nests. When fresh broken it seems like a plum-pud
ding-stone of uniform hardness and durability ; when exposed to the
weather the matrix is rapidly decomposed, and the rock becomes
cavernous like some varieties of lava ;—the imbedded mass resisting
decay while the matrix disappears. It is to be found from the base of
Nowrojee Hill (see para. 14) to the Chinchpoogly Salt Pans, and is most
conspicuous just opposite “ the Mount,” and along the north side of the
Powder Works compound. Another variety of the trap-tuflfa, pro
bably consisting of this though it diflfers from it in point of aspect,
pievails in the fiats to the eastward of Mr Dickinson's house. The
^bedded masses are whitish, pinkish, greenish, and gray. Where
public road crosses from Sewree to Parell, at the base of Flagstaff