160 CRETACEOtS ROCKS OF S. INDIA. [pART II. § 2. 



South-east. Beyond this nothing further is seen, the whole of the 

 okler rocks being concealed beneath the thick recent deposit of the 

 Mercanum alluvium. 



This bottom bed of limestone or calcareous sandstone is the only 



Thickness of limestone ^^^^^ ^'o^ky band I have met with in the Arria- 

 at base of group. j^^j, ^^^^ ^f Pondicherry, and this appears to vary 



both in mineral character and thickness. What may be the maximum 

 thickness I have no means of ascertaining, as an entire section is 

 nowhere exposed. The greatest thickness that I have seen either in a 

 native quarry or in a natural out-crop does not exceed 5 or 6 feet, and it 

 is probable that the total thickness is nowhere more than double this 

 amount; to judge from the extent of ground occupied by its out-crop. 

 It has been largely quarried at several places, both for local purposes 

 and for the paving of Pondicherry, for which this stone hasbeen largely 

 used, and the principal supply has been undoubtedly obtained from the 

 neio-hbourhood of Sydrapet, where it occurs within the French territory. 

 The beds which immediately succeed the limestone beds over a 

 horizontal distance of more than half a mile are 

 nowhere exposed, but beyond this soft clays and 

 aro-lllaceous sand are seen in several of the nullahs which carry off the 

 drainage of the high sandstone ridge of the Red Hills. Some of the 

 best sections are those to the East of Ossatary tank, where a consider- 

 able thickness of argillaceous sand occurs, full of the casts of small 

 fossils, both bivalves and univalves, associated with which is a little he- 

 mispherical Bryozoon in great abundance. Both the nature of the 

 deposit and the position of the fossils indicate that the former is an 

 accumulation of comparatively still water, or at least of a sea free from 

 strong and variable currents, and that the shells either lived where 

 they were imbedded, or were drifted but for a short distance. They 

 are never accumulated in nests or lines of false-bedding as in the 

 blocks of the Vanoor limsstone or the limestone beds of the Trichinopoly 



