126 CRETACEOUS ROCKS OF S. INDIA. [PaRT II. § 1. 



and comprising an area of about 200 square miles. In the vicinity of 

 the latter river it is concealed by superficial deposits, (regur and alluvium,) 

 and at Tanjore, 12 miles distant, where the older rocks re-appear to 

 the South of the Cauvery delta, these consist of the Cuddalore sand- 

 stones, a group of doubtful age, but newer than the Cretaceous rocks, 

 upon which they rest in Trichinopoly and South Arcot. It is probable 

 that the Arrialoor beds may be concealed beneath these beds at, or to the 

 East of Tanjore, judging from the strike of the boundary North of the river ; 

 and if so, they may possibly re-appear at some point to the South which 

 has not yet been surveyed. This, however, is at present mere surmise. 



Much of the Arrialoor beds are concealed beneath cotton soil, and 

 sections are even rarer in these beds than in those of the older groups. 



They consist, in great part, of white unfossiliferous 

 Lithological features. 



sands, and green argillaceous sands with casts of 



small fossils in the unconsolidated matrix. Bands of calcareous grit 



and nodular calcareous shales are frequent in the lower beds, and these 



abound in fossils, and similar shales re-appear in some of the higher beds. 



Indeed although there are no very definite boundaries between the, 



sub-divisions of the group, there are in the Arri- 

 Zonal sut-divisions. 



aloor group of Trichinopoly three tolerably well 



defined zones, the lower and uppermost of which are fossiliferous and 

 characterised by distinct faunas, while the middle zone, consisting chiefly 

 of white and grey sands, is almost without fossils. These zones pass 

 into each other in South Arcot, but it will be convenient to observe the 

 distinction in describing the more extensive deposits of Trichinopoly. 



Conglomerates are comparatively of rare occurrence in the group, 

 and, except near its Southern boundary, we do not meet with those fre- 

 quent irregularities of bedding which characterize a large "part of the 

 Trichinopoly group. The dip of the beds is generally very low, the 

 highest (6°) only prevails in the lower beds of the group, where they 

 rest on Trichinopoly beds. Elsewhere dips of 2° and 3° are prevalent, the 



