Chap. YI.] trichinopoly district — ootatoor group. 



95 



Fic4, 10. Sketch section op xjocks near Olapaudy. 



Jasper. 



Termination of Ootatoor group. 



(a) Arrialoor beds, (o\ o", o'",) Ootatoor beds. o\ Limestone ; o", Grey sand; o'", Shales. 



consisting of gneiss debris, and fragments of oyster shells are intercalated in them. Meanwhile 

 the limestone, concealed for a quarter of a mile beneath the Arrialoor beds, strikes away to the 

 N. E. and close to the grits above mentioned, rests immediately on a small patch of gneiss 

 which protrudes between the shales and grits on one hand and the limestone on the other 

 Beyond this the limestone appears to rest on the shales for about 100 yards, and then again on 

 Local unconformity of shales the gneiss. The limestone is therefore clearly unconformable 

 and limestone. upon the shales ; but I have strong reason to believe that 



this is merely a local unconformity in the Ootatoor beds, and has not any important 

 stratigraphic signification. I have noticed similar shales apparently irregularly intercalated at 

 the base of the limestone at two or three places between Vapoor 

 and Purawoy. The shales sometimes contain nodules of Jasper 

 evidently concretionary. 

 The limestone ridge N. E. of Olapaudy is very narrow : it continues to a point half a mile 

 West of Vylapaudy, and then finally disappears beneath the 

 Arrialoor beds, which are exposed in the little nullah running to 

 the "West of that village. 



To the North of the viUage the flat alluvial plain of the Vellaur commences, and stretches 

 away as far as VerdacheUum, (20 miles to the North-east,) concealing the older rocks. "When 

 the Cretaceous beds re-appear between VerdacheUum and Paroor, the Arrialoor group is the only 

 representative of the series, and no older deposits are exposed imtil we reach the neighbour- 

 hood of Valudayur, which wiU be described further ori . 



Before closing this description I must briefly advert to the little patch of sands, grits, &c., 



which are associated with the boulder-bed of CuUvROodv, and 



Doubtful beds of Cullygoody. a ^^ *.-u ^ fv ^ + <.^, + i i-/ -r 



appear to underlie the coral-reei Imiestone at that locahty. I 



haye already had occasion more than once to refer to these beds, and have briefly mentioned 



the reasons which have induced me to regard them rfs of Ootatoor age. 



These beds are best exposed to the North of the main Cullygoody limestone ridge. Close 

 to the extremity of the ridge the boulder-bed is exposed to a depth of 8 or 10 feet in the bank 

 of the little nullah figured at page 65 (Fig. 6), and resting upon it (and shown to the left of 

 that sketch) are some bands of coarse grit full of a large species of oyster, which is very charac- 

 teristic of these beds. 



Passing to the North in the direction of Malarasure we find the boulder-bed and the associ- 

 ated fossiliferous grits cropping out on the surface, or laid bare 



South of Malarasure. . ... ... «? -i ^ 



m the numerous little water- coui-ses which carry on^ the surface 



drainage. The boulder-bed occurs at the base of the group immediately resting on the gneiss, 



and the grits, the materials of which, like those of the boulder-bed, are derived exclusively 



from the crystalline rocks, project, sometimes in irregular and apparently lenticular masses, 



Sometimes in continuous beds, coursing along the surface of 



the country. I am unable to ofl'er any estimate of the thickness 



of these beds ; the dip, where any is seen, is quite um'eliable and very iiTegular in 



Beds in-egular. 



