1840.] 



of the Great Basaltic District of India. 



101 



our Plate, fossil shells are figured, which bear considerable resem- 

 blance to some specimens of Unio from the Sichel Hills, but not suf- 

 ficiently to identify them. They form part of the Dadapoor collection 

 of Sub- Himalayan fossils, so ably investigated by Lieuts. Baker and 

 Durand, and are stated by Mr. Prinsep, in a note, to be identical with 

 specimens collected hy Colonel Burney with the bones of the Mastodon, 

 &c. in Ava. He adds, that they probably belong to the large and thick 

 species of Cijrena noticed by Professor Buckland as occurring in a blue 

 and marly clay near the locality of the fossil bones collected by Mr. 

 Crawford (Geol. Trans., 2nd Series, vol. v.) ; but I found the specimens 

 of these shells in the Society's collection, to differ both from those of 

 the Sub-Himalayahs and of Central India, 

 ^-''''''^r. Pentland, in the same volume of the Geological Transactions, 

 / makes the following observations on Indian tertiary deposits : " How far 

 I " the same formation may be prolonged in a southerly direction along the 



) " peninsulas of Malacca and of Hindoostan it is impossible to say ; al- 



^ " though we possess proofs of its existence at Madras, where it contains 

 " the same species of shells as on the Brahma-putra, and at Pondicherry, 

 " where it envelopes the great masses of silicified wood found near that 



, " city." (p. 394). The formation on which Madras stands is, hov/ever, 

 erroneously referred to the tertiary epoch, being a recent alluvium, accu- 

 mulated by the joint action of the rivers and breakers, and containing 

 the same shells as now inhabit the mud of the salt-water inlets and sea* 

 shore of the Carnatic. 



-j^^ With regard to the age of the silicified wood of Pondicherry, no facts 

 have yet been ascertained which can justify any conclusion. It is, how- 

 ever, to be hoped, that a gentleman familiarly acquainted with the ter- 

 tiary and volcanic rocks of Greece and Italy, will soon communicate 

 positive information regarding the geological relations of the sandstones 

 containing the silicified trees and the fossil shells*, the conical hollows, 

 obsidians, and other indications of volcanic action said to exist in that 

 neighbourhood. 



Relative Age of the Laterite and Trap. 



I shall conclude this paper by one or two remarks on the relative age 

 of the Laterite and Trap. Dr. Babington| and Dr. Christie had observ- 

 ed this rock, both below and above the ghats in the latitudes of Seringa- 



* The shells I have seen differ from those of Cen'ral India, 

 + Geol, Trans,, 1st Series, vol, v., p. 339. 



