Chap. VII.] TRioHixopor.Y i)i>;rRTCT — trichixopoly group. 107 



Chapter VII. — Trichitiopoly Group. 



The Trichinopoly group, the middle sub-division of the Cretaceous 



series, in the Trichinopoly district, is, like the 

 Extent of group. 



Ootatoor group, confined to that district where 

 it occupies a narrow strip of country between the Ootatoor and Arrialoor 

 groups. Its greatest width, 3| miles, is near its Southern extremity, where, 

 overlapping the faulted boundary of the Ootatoor beds, it rests imme- 

 diately on the gneiss, extending down to the alluvial plain of the Cauvery. 

 Its width diminishes gradually as it stretches Northward ; thinning 



out, and not apparently overlapped, until we lose 



Relations to other groups. n • -, 



all trace of it beneath the cotton soil in the North 

 of the district, beyond which we find the Arrialoor group resting on the 

 Ootatoor beds. It is therefore distinctly unconformable to the Ootatoor 

 group, but it is not strikingly so except at its Southern extremity, where 

 the latter group had suffered some disturbance in the interval preced- 

 ing the formation of the Trichinopoly group ; while with respect to the 

 Arrialoor group no decided unconformity of bedding is to be detected, 

 owing possibly to the want of good sections at the junction of the two. 

 The distinction between them rests at present solely on the- evidence of 

 the fossils, coupled with the fact that the Arrialoor beds extend beyond 

 the Trichinopoly group, and rest on the gneiss at both extremities of the 

 latter group. 



The Tricbinopoly beds are, even more characteristically than the 



Ootatoors, the deposits of a shallow sea. As 

 Physical conditions of .r. . 



deposits of Southern part lar JNorth as Uaroodamungalum, the stratification 



presents the greatest irregularity ; an irregu- 

 larity evidently due to the shifting of currents, and yet, owing to the 

 fine and regular lamination of the beds over large areas, most puzzling 

 to the Geologist, who, having followed an apparently regular series of 

 stratified deposits for a distance of a mile or more, suddenly meets with 



