1840.] Observations on the Fossiliferous beds near PondicJierry. 



41 



The drawing represents the chamber as seen in the section, but the radiat- 

 ed marking is probably owing to crystallization. 

 No. 12 is a cast in limestone of a bivalve shell. 



It is no easy thing to name fossils even to those who are most accus- 

 tomed to geological researches, this department forming in general a 

 separate branch of the science : many of the fossils, however, described 

 in the above lines are of so marked a character, that in those instances 

 where we have ventured to name them with any degree of certainty, we 

 can hardly have been mistaken. I have not neglected either to consult 

 those who were best able to give an opinion on the subject, and have 

 also carefully compared the specimens with the best drawings and au- 

 thorities I could meet with. To Mr. Frederick Burr, I am particularly 

 indebted for the valuable assistance and information he has afforded me. 

 If we do not err therefore very widely from the mark, we have, even oil 

 the information already obtained, very good prima facie evidence that 

 the Pondicherry beds are the equivalents of the upper secondary for- 

 mations of Europe, and the fossils point especially to those of the chalk 

 and greensand. 



It is a well known fact that, during the formation of the cretaceous 

 beds in England, a great quantity of silex held in solution by water 

 must have been poured out ; which, by the process of chemical affinity 

 having collected around various organic nuclei such as corals, sponges 

 and other zoophytes, has formed continuous and extensive layers of flint, 

 interstratified with the chalk, almost every nodule of which contains 

 and derives its shape from the enclosed remains of some organized body 

 in a state of complete petrifaction. We observed no vestige of flints in 

 the limestone at Seedrapett, and all the fossils collected there consist of 

 carbonate of lime, and effervesce freely with acid ; but the vast quantity 

 of silicified wood, in the neighbouring formation of red sand, seems to 

 point to some phenomenon similar to what must have existed during the 

 deposition of the cretaceous beds of Europe.* 



Lieut. Newbold, in the last number of the Journal, suggested that the 

 fossiliferous beds of Pondicherry probably extended into the Verdachel- 

 lum talook of South Arcot. I have made enquiries but have not yet 

 obtained any evidence of this fact. Another interesting question, how- 



* " Flints so commonly enclose the remains of sponges, alcyonia and other zoophytes, 

 that some geologists are of opinion that the nucleus of every nodule was originally an 

 organic body : that this has been the case in most instances is very evident: and in 

 Sussex there are but few flints that do not possess traces of zoophytical organization." 



ManUlVs Geology of Sussex, 144. 



