Chap. X.] valudayur and arrialoor groups — pondicherry. 163 



At the same time I am not prepared to assert that no denudation 

 of the Trichinopoly formation preceded the formation of the Arrialoor 

 group, but simply that the evidence obtainable is insufficient to 

 warrant such a conclusion. 



The greater part of the Arrialoor group gives evidence of tranquil 

 Conditions of Arrialoor deposition probably in a sea of no great depth, 

 ^"° ■ for irregular deposits supervene at one point 



(in the case of the bone beds) nearly in the middle of the group, and 

 moderately coarse sands occur at intervals throughout the greater part 

 of the group. 



The same cause, whatever it was that produced the unequal distri- 



Thinning out of de- bution of deposits during the Trichinopoly period, 

 posits towards the North. ,i • , i...,^, 



their great accumulation m the Southern part of 



our area, and their rapid diminution towards the North, continued to 



operate throughout Arrialoor times, so that beds, which, in the North of 



Trichinopoly, have an outcrop of 8 miles in diameter with an averao-e 



dip of between 1° and 2°, are represented near Pondicherry by beds a 



few feet only in thickness. This fact, which is indicated by the 



converging strike of the beds, will tend to 



Intermixture oi lossils. 



explain the concurrence near Pondicherry of 

 fossils characteristic of the higher and lower fossiliferoiis zones of 

 the formation in Trichinopoly. I cannot say whether these fossils were 

 actually intermingled in the same bed, inasmuch as but very few of 

 them were found m situ, and most of them were collected by natives, 

 whose ideas of locality in such matters are not very definite, but their 

 matrix is identical, and I can entertain no doubt that they are all 

 from the limestone at the base of the Arrialoor group. 



With regard to this point it must be observed that only a small 



Eelations of Pondi- proportion of the fauna of the upper zone of 



'^ ^"-^ ^ ^' Trichinopoly occurs at this locality. Intermingled 



with a small proportion also of that of the lower zone In the same 



