Chap. VI.] trichinopoly district — ootatoor group. 87 



the latter on the exteiior, and to the depth of some inches, heing produced by wea- 

 thering and the conversion of the iron into a hydrated peroxide. It contains numer- 

 ous shells, chiefly of Pecten, Lima and Ostrea in single valves. Two species of the first- 



^ ., named genus are especially abundant, one a small smooth shell, 



resembhng F. orbicularis, Sow, is one of the most common 



and characteristic shells of the group, the other a Janira, allied to, if not identical with 



Pecten 5-costatus, is no less common, and is one of the shells which ranges through the whole 



of the Cretaceous series of Trichinopoly. 



The limestones are confined to the lower beds of the group, and to the vicinity of the 



Coral-reefs as far North as Cullpaudy and Penangoor. They 

 Beds above limestones. _pt.ii o 



lorm distmct bands, 3 or 4 feet thick, generally not continuous 



for any great distance, and are quarried by the natives chiefly for building the small temples, 



which occur in every village. The beds above the limestones up to the commencement of 



the sands and grits are kunkuriferous clays and shales, with but few fossils ( Inoceramus and 



Annelids.) Between Varagapaudy and Sirgumpoor, and again to the North-west of the latter 



village there is a considerable thickness of gypseous clays and shales (aU imfossiliferous) 



Irregularities of beds at helow the limestone. These rest on the plant-beds with very 

 Sirgumpoor. evident unconformity, and appear to dip beneath some little 



patches of coral-reef limestone which, occur to the North of the Sirgumpoor Nullah, 

 and which are immediately followed by a thick band of the Ootatoor limestone, which 

 crosses the nullah just to the East of the village (page 57). About a mile to the 

 North this limestone band, which has passed into a bed of sand and gravel, appears 

 to lap round over these shales, and to rest on the plant-beds, and finally again passing 

 into limestone, on the coral-reef Kmestone to the South of CuUpaudy. The rmconformity 

 is, however, by no means evident, and from the characteristic mineral character of the 

 bottom shales and their resemblance to those of the Ootatoor beds, I am inclined to 

 regard it as in any case merely a local irregularity, such as I have frequently ob- 

 served elsewhere, and of which we shall meet with many striking examples in the very 

 irregular deposits of a part of the Trichinopoly Group. 



Near Cullpaudy bands of calcareous concretions, from 6 inches to 1 foot in diameter, begin 



to appear in the clays, and Cephalopoda of forms not hitherto 

 Beds East of Cullpaudy. ^ •,-,,■ j ., " m. ,, -««- t-. , , ^ , 



met with, f Ammonites Timotheanus, Mayor; Ftychoceras,^^. } Scaph- 



ites, sp. .'') are sometimes formd enclosed in these. These are the first indications of the rich 

 fauna which becomes so abundant to the North in the neighboui-hood of Maravuttoor and 

 Odium, and the appearance of which is accompanied by a considerable change in the mineral 

 character of the beds. Before proceeding to describe this interesting country, however, I will 

 return to the upper beds of the group in the neighbourhood of Ainaveram. 



The change in mineral character from ochreous clays to grey sand and calcareous grits of 

 Mineral character of Grits, *^^ "PP^^ ^^^^ ^^ "^^^ conspicuous to the West and South-west 

 &c., at Ainaveram. ^f Ainaveram, owing to the dark boulder-like masses of the calca- 



reous bands that mark the out-crop of the latter, ranging above the otherwise smooth surface of 

 the cotton soil, which covers the softer beds sometimes to the thickness of 12 or 14 feet. The 

 grey sands which constitute the mass of the beds, and in which the calcareous bands have 

 been subsequently formed by concretionary action, consist of the minei-als of the gneiss, quartz, 



