'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎237] (370/458)

LATER1TE.
237
day 9 , that sometimes lithologically speaking, resemble laterite ; and, when that
rock is near, have the appearance of passing into it. I have also observed large
beds in gneiss and hornblende schist, of an impure oxide of iron, assume a cellular
and pish 01 m aspect ; but such must not be mistaken for the.true laterite, nor yet
the beds of re-aggregated gravel derived from the laterite.
“ When we look up from the microscopic view afforded by these slowly
weathering blocks of rock and beds of ore, and cast our eyes upon even the
present extent of larerite over the surface of India, the thickness of its beds, its
flat-topped ranges of hills^ and the gaps effected in their continuity, evidently by
aqueous causes no longer in action, its occasionally imbedding waterworn pebbles
of distant rocks, its often elevated position above the present drainage level of the
country, its beds of lignite and silicified wood, we find no more reason for attri
buting its origin to the weathering of rocks in sitfi, or to their detritus transported
by causes now in action, than for attributing the formation of the older sandstones
to the present disintegration of the granitic and hypogene rocks, of the detritus of
which they were doubtless, as well as the laterite, formed originally.
u The supposed non-fossiliferous character of this rock, which has puzzled
many geologists, and inclined others to the theory of its ancient or volcanic origin,
may in some measure be attributed to its highly ferriferous nature, often approach
ing that of an oxide of iron. It is a general fact, and, as Lyell observes, one not
yet accounted for, that scarcely any fossil remains are preserved in stratified rocks
in which the oxide of iron (derived from the disintegration of hornblende or mica)
abounds : and when we find fossils in the new or old red sandstones of England,
it is in the grey, and usually calcareous beds that they occur. It is well known,
too, that some of the more recent tertiary deposits of Europe are entirely divested
of fossils.
As this singular variety of ferruginous clay and sandstone has not been
mentioned by geological writers on other countries than those l have alluded to,
it may be presumed that laterite either does not exist under this form at all, or hi
such small patches as not to have attracted remark. The question naturally
suggests itself, why this cellular rock should be confined io India, &c. The solu
tion may be in the highly ferriferous nature of the plutonic, trappean, and
hypogene rocks, from which the laterite has confessedly been derived, and in the
supposition of a segregation and subspquent re-arrangement of the different
mineral particles in the substance of the rock itself, by a process in nature a
laboratory, approaching to crystallization, better known than explained or under
stood. If electricity, which is probable, has any share in exciting this movement
and attraction in the mineral particles of the rock, its metallic nature affords a
favorable condition for the active development of this powerful agent. 1 h 0
structure of the rock has received some modification from the action of water, ill
emptying its shells and carrying their contents to the lower parts of the beds.
<£ Age.— Having said thus much to warrant the classification of laterito
among rocks of an aqueous and mechanical origin, I shall proceed to remark that
in age, relatively to other rocks of Southern India, it is older than } he legui an
kunkur, which it underlies, and of more recent origin than the ovei lying tiap,
the shell limestone of Pondicherry, and the diamond sandstone and limestone, on
all of which it is superimposed. It has never been invaded by the dykes o tiap
that penetrate the latter rocks—the hypogene and plutonic rocks,—-fiagments o
all which it sometimes imbeds, but is evidently contemporaneous wit 1 t 10 t >its,
or series of efforts, by which the Western Ghauts Were lifted above the waters ;
since it is seen capping their summits, often shattered into large irregului bloc s,