Chap. VI.] trichinopoly district — ootatoor group. 99 



laminaB, I think we must conclude that all such beds are accumulations of 



boulders previously existing on the land, or remnants of the plant-beds 



which, in the course of gentle depression, have been gradually submerged, 



and covered up by the fine silts of the lower beds.* Throughout this part 



of the formation lime is abundant, principally in the form of calcareous 



., , ,,. . shales, and occasionally of solid limestone : we ma V 

 Abundance of lime m ' "^ •' 



Ootatoor becls. g^jg^ include the lime of the concretions, the Kunkury 



and Chalky infiltrations which abound throughout the group, as an ori- 

 ginal constituent of the rocks, which has been dissolved out of the general 

 mass, and redeposited in the interstices of the clays and shales produced 

 by the shrinking of the mass. Of the absolute proportion of lime we can 

 only form an approximate estimate. The _^5rot^s shales which are abund- 

 antly intercalated throughout the beds, except in the brown Gypseous 

 clays of Ootatoor, contain, according to Mr, Tween's analysis, ^^^ per cent. 

 or not less than two-thirds of their bulk of Carbonate of lime ; but it would 

 be probably much too high an estimate to assume the average percentao-e 

 of lime throughout as anything like this proportion. Even, however if 

 we assume the average of the lime constituents at one-third this amount, 

 or as forming one-fifth of the bulk of the rocks, an estimate which is in 

 all probability rather under than in excess of the truth, this is still re- 

 markable when we consider how few fossils are found in this part of the 

 formation. We must, I think, look to the coral-reefs, which from their 



abundant occurrence along the boundary of the 

 Source of the lime. . 



Ootatoor beds, we have every reason to believe 



were originally dotted thickly over the gneiss sea bottom, as the source 



of the lime so largely intermingled in the fine sediments of the Group. 



The observations of Mr. Dana on the nature of the sediments around 



* Or it may be that they are the debris of the local gneiss, which has frequently a tenden- 

 cy to weather into spheroids. "Were the gneiss so decomposed to be subjected for a short 

 time to a denuding force, the decomposed sandy matri.x would be washed away, and the un- 

 decomposed included masses would form a local accumulation of boulders such as consti- 

 tutes the boulder-beds at the base of the plant-beds and Ootatoor Group. 



