348 Pampean Formation : part n. 



with, eight other still existing Mollusca : it should, 

 moreover, be borne in mind, that a tooth of a pachy- 

 dermatous animal was found with the other remains at 

 Punta Alt a. which Professor Owen thinks almost cer- 

 tainlv belonged to the Alacrauehenia. 



Mr. Lyell l has arrived at a highly important con- 

 clusion with respect to the age of the North American 

 extinct mammifers (many of which are closely allied to, 

 and even identical with, those of the Pampean forma- 

 tion), namely, that they lived subsequently to the period 

 when erratic boulders were transported by the agency 

 of floating ice in temperate latitudes. Xow in the 

 valley of the San Cruz, only fifty miles of latitude south 

 of the spot where the Alacrauchenia was entombed, vast 

 numbers of gigantic, angular boulders, which must 

 have been transported from the Cordillera on icebergs, 

 lie strewed on the plain, at the height of 1,400 feet 

 above the level of the sea. In ascending to this level, 

 several step-formed plains must be crossed, all of which 

 have necessarily required long time for their formation ; 

 hence the lowest or ninety feet plain, with its super- 

 ficial bed containing the remains of the Macrauchenia, 

 must have been formed very long subsequently to the 

 period when the 1,400 feet plain was beneath the sea, 

 and boulders were dropped on it from floating masses 

 of ice. 2 Mr. Ly ell's conclusion, therefore, is thus far 

 confirmed in the southern hemisphere ; and it is the 

 more important, as one is naturally tempted to admit 

 so simple an explanation, that it was the ice-period 

 that caused the extinction of the numerous great 



1 'Geological Proceedings,' vol. iv. p. 36. 



2 It must not be inferred from these remarks, that the ice-action 

 ceased in South America at this comparatively ancient period ; for 

 in Tierra del Fuego boulders were probably transported contempo- 

 raneously with, if not subsequently to, the formation of the ninety 

 feet plain at S. Julian, and at other parts of the coast of Patagonia, 



