164: CRETACEOUS ROCKS OF S. INDIA. [PaRT II. § 2. 



district. It may be further remarked, that the upper fossillferoua 

 zone has not been traced through the Verdachellum area, and that 

 the greater part of the beds there exposed appears to represent 

 a portion of the unfossiliferous central zone of Trichinopolj. The 

 Pondicherry beds above alluded to may be there also in great part 

 a representative of this portion of the formation in which some of 

 the fossils occur locally, including some of the earliest forms of the 

 upper zone fauna. 



The unusual character of the Pondicherry beds tends to bear 



out this supposition, inasmuch as the greater 

 Mineral evidence. 



part of the formation above the bottom lime- 

 stone, and especially the beds exposed to the East of Ossatary 

 tank, are identical with the sandy clays with casts of small 

 fossils which immediately underlie the Megalosaurus bone bed 

 of Trichinopoly, and are intercalated in the lower part of the 

 sand of which the unfossiliferous zone mainly consists. If this 

 be the case, we must infer that to the North of Verdachellum 

 the Arrlaloor formation decreases in thickness much less rapidly 

 than in Trichinopoly. 



The Arrialoor group of Trichinopoly evidently represents a very 



long period of time, a period sufficient to allow 



Lapse of time indicated /> ,i i i ,• ,• , i ^ c 



by change of fauna in of the locai extinction at least 01 an entire 

 ig ei zone. fauna, and its replacement by new forms. It 



would be too much to assert, indeed, that the lower fauna became 

 universally extinct in the interval, but even a local change so entire 

 must require a*long period of time for its accomplishment if unaided 

 by important local changes of physical condition, and of such 

 we have no evidence : and, moreover, the parallelism of the change 

 with that between the white chalk and Moestricht formations of 

 Europe indicates that the change of fauna is cyclical and not episodical 

 in its character. 



