Chap. X.] valudayur and arrialoor groups — pondicherry. 155 



the majority of the Ammonites that I have seen from Pondicherry are 

 evidently from these or similar limestone nodules, and in only one or 

 two instances have I been able to identify any as certainly from the 

 overlying conglomerate bed. 



The surface of the ground being grassy, or arable land, at only one 

 Character of " Valu- ^^ ^""^^ spots, in little field drains, are these 

 ayur eds. calcareous nodules seen in situ, and here they 



appear to form a band imbedded in soft sandy shale, in which they 

 have been formed by concretionary action. The dip of the strati- 

 fication cannot be ascertained with certainty, but wherever any bed- 

 ding is clearly seen in this group of beds, as in some of the bowries 

 (square wells) around Vanoor, it is either horizontal, or dipping 2° or 

 3° to the South-east, and judging from the strike of the fossiliferous 

 nodule band, it probably coincides with this prevalent structure. 



From what I have above stated, the conclusion at which I arrive 

 Proofs of two distinct respecting the relative ages of the two fossilife- 

 S^°^^^' rous bands is evident. Although no unconformity 



of stratification can be detected, partly because the discordance, if 

 existing locally, must be very small, and partly because the evidence 

 bearing upon this point is very obscure, the facts which remain, viz., 

 the distinctness of the fossils in the two rocks, the divergent relations 

 of the two faunas, as established by comparison with those of the Cre- 

 taceous series of Trichinopoly ; and finally, the occurrence of pebbles 

 of the older rock in a conglomerate of the newer, are quite sufiicient to 

 prove that a long period of time must have elapsed between the forma- 

 tion of the limestone nodule bed and the deposition of the cono-lome- 

 rate rock with Arrialoor fossils. This conclusion first deduced from 

 the comparison of the fossils, and the examination of the rocks of this 

 locality, has been fully borne out on extended examination. The 

 conglomerate bed, though not always presenting itself as a conglo- 

 merate, but more generally as a hard fossiliferous limestone, or 



