336 Pampean Formation. part n. 



there is a thin stratum with a concretionary outline of 

 white hard tosca-rock or marl, which may be considered 

 either as the uppermost bed of the inferior deposits, 

 or the lowest of the Pampean formation; at one time 

 I considered this bed as marking a passage between 

 the two formations ; but I have since become convinced 

 that I was deceived on this point. In the section on 

 the Parana, I did not find any mammiferous remains ; 

 but at two miles distance on the A. Tapas (a tributary 

 of the Conchitas), they were extremely numerous in a 

 low cliff of red Pampean mud with small concretions, 

 precisely like the upper bed on the Parana. Most of 

 the bones were solitary and much decayed; but I saw 

 the dermal armour of a gigantic Edental quadruped, 

 forming a cauldron-like hollow, four or five feet in 

 diameter, out of which, as I was informed, the almost 

 entire skeleton had been lately removed. I found single 

 teeth of the Mastodon Andium, Toxodon Platensis, 

 and JEquus curvidens, near to each other. As this 

 latter tooth approaches closely to that of the common 

 horse, I paid particular attention to its true embedment, 

 for I did not at that time know that there was a similar 

 tooth hidden in the matrix with the other mammiferous 

 remains from Punta Alta. It is an interesting circum- 

 stance, that Prof. Owen finds that the teeth of this 

 horse approach more closely in their peculiar curvature 

 to a fossil specimen brought by Mr. Lyell l from North 

 America, than to those of any other species of Equus. 



The underlying marine tertiary strata extend over a 

 wide area : I was assured that they can be traced in 

 ravines in an east and west line across Entre Rios to 

 the Uruguav, a distance of about 135 miles. In a SE. 

 direction I heard of their existence at the head of the 



1 Lyell's ■ Travels in North America,' vol. i. p. 164, and ' Proc. oi 

 Geolog. Soc' vol. iv. p. 39. 



