144 CRETACEOUS ROCKS OF 8. INDIA. [PaRT II. § 2. 



PART II. § 2. Verdachellum and Pondicheery Areas. 



Chapter IX. — Arrialoor Group in Terdachellum Area. 



Relation of Cretaceous rocks and Cuddalore sandstones. — We have 



Noi-tli of Tricliinopoly ^^^^ i'^ ^^® preceding chapter that, as we pass from 



^^*™*- Ootatoor to the Northern limits of the Trichinopoly 



district, the different groups of fossiliferous rocks successively overlap those 



beneath them, until, at the confines of the Vellaur alluvium, (which 



covers up the whole series for a distance of from 5 to 16 miles,) 



the Arrialoor or highest group rests immediately on the gneiss, and 



occupies an area of not less than 8 miles in width, measured across 



the strike, to where it is covered up by the Cuddalore sandstones. 



These latter rocks occupy the country to the East, and the superficial 



Geology of the stratified rocks, so complicated in the South of the district, 



is here, at its Northern limits, simplified to the superposition of these two 



groups, beneath which the older members of the series are concealed. 



If we now cross the br-oad alluvial plain of the Vellaur and Mani Mukta 



to the high ground in the neighbourhood of Ver- 

 Near Verdachellum. 



dachellum, we find the same two groups of rocks 



emerging from beneath the alluvium, and stretching away to the North, 

 until they again disappear beneath the alluvial deposits of the Guddalum 

 and Puniar. Owing, however, to the gradual overlapping of the Cuddalore 

 sandstones, the area occupied by the Cretaceous rocks in the neighbour- 

 hood of Verdachellum, is much diminished in width, and it is further 

 decreased by two large outliers of the former formations, which at two 

 points entirely overlap the latter and rest immediately upon the gneiss. 

 The Cuddalore sandstones here, as elsewhere, occupy high jungly 



ground, with a thick covering of deep-red sand, 



Exposed by denudation. 



which conceals them everywhere ex sept at their 



scarped boundary. That the deposits at a former period extended across 



the whole area now occupied by the stratified rocks, and that the 



