'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎225] (358/458)

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he older varietof
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Southern
SELENITE OR GYPSUM.
tinguisliable gradations,*—to one great origin actually before us, and of simple ex
planation, than to seek for other agencies now no longer in operation, and of whoso
existence at any time we have no positive proof. It has been already stated that
the rapid formation of kunkur under the surface of the ground is in some of the
districts near Agra a source of serious annoyance to the cultivator. All the shells
and organic remains found in kunkur are recent, and masses of it are found to
penetrate and surround the mangrove roots in the marine blue clay, the wood of
which is still fresh and sound. The theory of the formation of a mineral of such
extensive prevalence, and the very name of which is, strange to say, omitted in
our Home geological indices, seems to be this:—The soil of India everywhere
abounds with lime or fresh water and land shells in a state of extreme comminution :
this is freely taken up by the rain during the earlier part of the monsoon, the solution
being probably assisted by the heat, and the enormous quantity of carbonaceous
matter, the rank growth and rapid decay of vegetables during the rains originate.
When the rains cease, and the heat which follows dries up everything, of course
the lime previously in solution is precipitated, and seeks a nucleus wherever it can
find one. So rapidly does rain-water act on lime in India that a marble slab
exposed to it will in a few days* time lose all its lustre, and in the course of tha
monsoon become corroded, as if acted on by an acid. Fine branches of coral
exposed to it lose in a few days’ time the translucency which adds so greatly to
their beauty, and become dull and opaque as if white-washed : both these I have
made subjects of frequent experiment.
The solvent power of pure water acting on limestone, considerable in itself, is
enormously increased by the presence of carbonic acid. The cementation of the
shells constituting the rocks I have termed littoral concrete, it is obviously effected
by water charged with lime, and is now in progress. I have already adverted to
the singular circumstance of this process proceeding with great vigour and
activity at ono place, while at another close by, similarly situated in all respects,
it should be in entire and absolute abeyance.—See Proceedings of the Society
for April 1851, p. xlviii.
NOTE D, p. 189,
Selenite or Gypsum.— In the small crevices and fissures pervading shales
or aluminous schists, where these are exposed to the air, numberless little crystals,
of selenite are generally found to prevail. I remember, when a very young
chemist, indeed, to have made a large collection of these from a coal seam which
crops out near the Witchlake, St. Andrews, and to have been greatly perplexed
to account for their appearance* The shale specimens from the Indus, recently
presented to the Bombay Geographical Society, by the late Capt*. Christopher, ar<*
pervaded in all directions by beautiful veins of Selenite. In both these cases the
production of the mineral is easily explained: coal shales almost always abound