Geological papers on western India, including Cutch, Sinde and the south-east coast of Arabia : to which is appended a summary of the geology of India generally / edited for the Government by Henry J. Carter.

Date:: 1857

Credit: Geological papers on western India, including Cutch, Sinde and the south-east coast of Arabia : to which is appended a summary of the geology of India generally / edited for the Government by Henry J. Carter. Source: Wellcome Collection.

168/834 (page 154)

$indurated clay you mention is very probably the result of those muddy eruptions so common, and of such extensive occurrence, in South America. Indeed, I am convinced that the greenstone, basalt, wacke, iron clay or laterite, and the indurated clay, have all a common origin, from the insensible degrees by which they pass the one into the other; and they only differ as to the degree of pressure to which they have been subjected when under fusion.” Again he mentions (Jl. As. Soc. Bengal, Aug. 1833, p. 400), when alluding to the passage of basalt into wacke and then into iron clay, [Laterite?] that the latter takes place “in the space of a few yards.” Dr. Christie (loc. cit.) calls the laterite of Buchanan a “ clay-stone conglomerate” (pp. 462 and 468), and states respecting its position in the district of Dharwar, that it is found “ principally in its western parts, and on the summits of the Ghftts.” Mr. Cole states of a specimen of Laterite from Nellore, given him by the late Dr. Malcolmson, that “it was filled with innumerable minute pebbles of quartz, rarely larger than half the size of a pea, sometimes pellucid, generally much rounded ; together with yellow and ochraceous earths.” These would seem to have been the miliary contents of an amygdaloid,—whether in situ, or in a decomposed or altered rock, or forming foreign substances in a subsequent effusion, I cannot pretend to decide, but I should think the former. Mr. Cole also quotes Mr. Coulthard (As. Ties. vol. xviii.), whose observations appear to favour this supposition, viz. that “ the iron clay about the Sagar district, and which is easy to be met with everywhere there, “ is for the most part amygdaloidal.” Lastly, Mr. Cole himself states of the « Red Hills” at Madras, in the banks (15 feet high) of the old channel, leading into what is termed the lake, that “ they are composed of a dark ferruginous stone, arranged in a stratiform manner, presenting seams or partings, two or more feet asunder, parallel to each other, and nearly horizontal. Vertical fissures intersect the seams at right angles, and thus produce prismatic masses of rock.” The rock is a “ conglomerate,” consisting of nodules of various sizes, imbedded in a “ clayey paste,” which is hard and tenacious : they are “ water-worn,” but present a “considerable angularity of surface, yet still sufficiently rounded to indicate their having undergone attrition’; in size they range from “a filbert to masses a foot or more in diameter. Their fracture exhibits the structure of a coarse-grained sandstone, or grit, of a deep chocolate or claret hue.” “ Small masses of white earth- like lithomarge and mica are sparingly scattered in the sandstone no- dules.” On ascending the hill on the side of the lake, the conglomerate disappears, and changes into the more characteristic laterite, led and cavernous, with “tortuous cavities”; still, however, containing fragments$