'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎189] (322/458)

lei %freeofi
'Iftnade, aisjsji
to warping
contamii
is most difci'
tub for tie i
rater with tfcl
own or mouldf
een like fineli
i.
him Road anti
s from the
yer clay, covers!'
ing to the de^
urnisliing e®*
abundance, ®;
fates arege'®'
imetimes tlfl;
,ur incto »*
diameter,^
LOWER ALLUVIUM, ^
pearance along the axis of crystallization-it can be rendered beauti
fully distinct by grinding the specimens on their thinnest side, then
polishing them. The selenite plates are always found on edge, and they
5 plit with much ease, with a perfectly smooth and brilliant surface
an d even texture, in the direction of their larger axis, and at right
angles to their plane : this, so far as I have observed, holds uniformly,
and forms a striking contrast to the more extensive deposits of the
same mineral in the deserts of Egypt and of Seinde, where in the great
majority of cases the plates do not break across, but split in the plane
of the plate, or parallel to the plane of the walls of the vein. I have
not met in with any fibrous 01 compact specimens of the mineral of
Bombay; they are plentiful in Scinde and Egypt. The formation of
the selenite, like that of the kunkur, is now in progress, and is very
easily explained. The sulphates of soda and magnesia of the sea salt
decompose the carbonate of lime, and afford carbonate of soda and
magnesia, which at Bombay is washed away by the rains, and sulphate
of lime or selenite remains.*
34:,—In cutting the Town DraiQj vast masses of oyster shells were ex
cavated from the blue clay about five feet under the surface, to the
southward of the Grant Eoad, and nearly opposite the Grant Medical
College; and again in the railway cuttings opposite Parell, and near the
village of Matoonga: they seem identical with those now abounding on
our shores. They are of very large dimensions, and a single mass of
them adhering firmly together was sometimes detached nearly half a
ton in weight. The surface of the ground here is set down by Mr.
Conybeare as about two feet under high water spring tides—so that
the surface of this portion of the Island must a century since have been
liable to occasional submergence.
35.— Lower Alluvium—Yellow Earth.— The cuttings through
the Flats along the line of the railway afford an excellent exhibition of
a third alluvial formation obviously of much older date than the blue
cla r- °f a chesnut brown, or yellowish brown colour, the tint be
coming lighter as we recede from the surface. It is less liable to crack
during the hot weather than the blue clay, especially where regularly
cultivated: in moist, or seldom tilled spots* such as those around the
>culla Schools, it cracks and splits in all directions, the fissures often
* See Note D,, at the end.