Chap. X.] valudayur and aerialoor groups — pondicherry. 157 



more rarely conglomeratic, the pebbles, as well as the finer materials, 

 being derived solely from the crystalline rocks. Such a conglomerate 

 is seen in some wells at Pudupakknm, 2 miles from Valudayur, where 

 it is partly consolidated into hard masses of grit, but in most cases 

 the sand is quite soft and easily excavated with the native shovels. 

 In a nullah between Vanoor and Catarakuppum it appears as a hard 

 sandy shale, as usual without any fossils, and to the North, in the neigh- 

 bourhood of Talaveram, there appears to be some calcareous rock, as 

 is evidenced by the great quantity of calcareous debris (kunkur) in 

 the low parts of the soil, which are excavated for lime by the natives. 

 The underlying rock is not visible at this latter place. 



As we ascend to the higher beds, or to. speak more strictly, as 



„. , , , we proceed Eastwards across this strike, the 



Higher beds. 



deposits become finer in grain and more argilla- 

 ceous, but excepting the occasional occurrence of imbedded concre- 

 tions, they are equally unconsolidated with the sands below. An 

 arenaceous clay is seen in the nullah South of Andipaleyara, which, 

 judging from the general direction of the strike, must be below the 

 noduliferous clay shale which occurs to the South. The nodule 



Extent of concretion ^^^^ ^^^ ^^^<^«^ ^^^' t^^^^e are probably more 

 ^^^^^- than one, are not seen North of Royapoothoopak- 



kum, but between this place and Vanoor they may be seen in several 

 wells, and they have been largely used by natives for building rude 

 revetments to their tank bunds, or for paving the sloping rides of the 

 smaller excavated tanks. The limestone of the Arrialoor bottom bed 

 has, however, been more extensively employed for these purposes, being 

 not only more abundant but also far more easy to work. The nodules 

 are again seen in situ, in some field drains to the West of Wattam- 

 polliam, and from some of these I have obtained fossils identical with 

 those of Valudayur ; BacuUtes vacjina is here again the predominating 

 species. The nodules average from 1 to 3 feet in diameter, and. 



