'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎236] (369/458)

NOTES*
23 a
up by Calder, and put forth by Mr. Conybearo, it must be remarked that, hitherto,
no decided volcanic product has been discovered in laterite, no crater or other
proof of such origin. It is true, it is frequently seen overlying trap rocks ; but it
also overlies granite, hypogene strata, sandstone) and limestone, and in none is it
ever seen as a dyke ; nor are there any signs of forcible intrusion or alteration.
In one hand specimen that fell under my observation, the laterite appeared to
have intruded into and shattered the sandstone ; but in every instance where I
have had an opportunity of seeing veins, if they may be so termed, of the laterite
in other rocks, in situ, they have occurred as deposits from above, into pre
existing chinks of the subjacent rocks, like the conglomerate which fills fissures m
the limestone of Petit Tor; and never injected from below, as is the case with
volcanic rocks.
“ Fragments of trappean, and other rocks, occasionally are imbedded in the
laterite ; as also in the subjacent sandstone, and in other rocks confessedly of
aqueous origin. Cases occur where basalt underlying the trap as at Beder, has the
appearance of passing into it: but this, on minute examination, turns out to be a
confused blending of the debris of both rocks near their junction ; from which dis
tinct and unmixed fragments of either sort could be separated, like bits of granite
from the breccias that are usually found near the junction of the latter with
sandstone. In many localities, however, the line of demarcation between the
laterite and overlying trap is clear and decided.
n Some geologists suppose that laterite is nothing more than granitic, hypogenc,
and trappean rocks weathered in situ* The facts of its imbedding erratic frag,
ments of sandstone, at the Red Hills near Madras, where it rests on granite, and,
its interstratified beds of lignite and silicified wood, militate strongly against this
theory. Besides, nothing is more common in lateritic tracts than to see a hill of
granite, trap, or hypogene rock, capped with a thick crust of laterite ; while the
adjacent hills, composed of an exactly similar rock, and forming a continuation of
the same bed, equally exposed to the action of the weather, are quite bare of
laterite, I have examined many beds of it resting on trap, and amygdaloid inr*
bedding calcedonies, heliotrope, and jasper, but have not hitherto detected in the
upper or middle beds of the former, any fragments of these hard siliceous minerals
which are found to resist successfully the attrition of the most rapid streams of
India, and have been carried by them across the peninsula to the ocean.
“ I have seen laterite, too, resting on limestone, without any traceable lime in
its composition : aud containing veins of manganese, when resting on a trap in
■which hitherto the existence of this mineral has not been detected : facts, proving
that the overlying laterite was not the upper portions of these rocks weathered
in situ.
<s I have often observed, particularly in the Western Ghauts, and on the Malabar
and Concan coasts, where the rains fall heaviest, those granitic, hypogene, and
tnippeau reeks, which contain most iron, weather into ferruginous and colour^
that sometmi
i sn ear, llliv ^
„ gneiss and
isi form aspect
is of re-agg 1
eti we 101
n g blocks
extent of
3 d ranges
causes no
t rocks,
its beds (
s origin tc
>s now in f
resent dis:
iey were <
ii The suppose!
many geologists, i
may in some meas
ingtliat of an oxi
jstaccounted for,
iawhich the oxid
alonnds: and wl
iiisin the grey, ;
too, that some of
of fossils.
<; As tin's sin|
Motioned by ge
'tmay he presurr
s odi small pate'
^gests itself, w
l ' 011 may be iu
Imogens rocks,
^position of
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hwatory, anp n
'«• If electr
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