Geology of South America. 127 



restrlal animals of the extinct fauna, such as the Mylodon, the 

 Megalonyx, the Megatherium, the Platonyx^ the Toxodon^ and 

 the Mastodon, depositing them, along with earthy matters, at 

 all heights, in the terrestrial basins or in the neighbouring 

 seas. Those matters simultaneously transported and deposited 

 on the Plateaux of the Cordilleras to a height of 13,000 feet 

 above the ocean, on the plains of Moxos and Chiquitos, and 

 over the whole bottom of the great basin of the Pampas, consti- 

 tuted the Pampean formation. This Pampean formation, 

 which occurs in horizontal beds at all heights, which is every- 

 where composed of the same loams, and which only contains 

 remains of mammifera, could only have been produced by a 

 general terrestrial cause. M. D'Orbigny believes that he has 

 discovered this cause in one of the soulevements which took 

 place in the Great Cordillera, and which must have produced 

 a sudden displacement of the waters of the ocean ; which latter, 

 moved and agitated with violence, invaded the continents, and 

 destroyed the great terrestrial animals, transporting them tu- 

 multuously to the lowest portions of the continents, or into the 

 bosom of the deep ; and it is evidently to the soulevement of 

 the trachytes alone that the phenomenon can be attributed. 



M. D'Orbigny has remarked that, at some points on the 

 Bolivian Plateau, the trachytic conglomerates appear to cover 

 the Pampean formation, a circumstance which would lead to 

 the belief that they are posterior to that great deposit. This 

 observation coincides with the one noticed above, viz. that the 

 trachytic conglomerates do not appear to be all exactly of the 

 same age. The greater part are contemporaneous with the 

 Pampean formation, but some of them are posterior. In 

 Auvergne, the numerous mammifera of the fauna anterior to 

 that epoch, and which are found at various localities, are en- 

 veloped by trachytic rocks and their conglomerates. We have 

 here an approximation which may not be Avithout its value. 



To this movement may perhaps be referred or compared many 

 facts observed in various parts of the surface of the globe, since we 

 everywhere meet with remains of a terrestrial fauna, now en- 

 tirely extinct ; and because, in a multitude of localities, we 

 find deposits analogous to those of the Pampas, containing 



