Tertiary Formations. 59 



neral similar to that which fills the fissures of the Jura,* where 

 the fact was long ago noticed by M. Brongniart. It is ex- 

 tremely probable that this superficial deposit of reddish earth, 

 which exists also at Rio Janeiro, unites in a continuous man- 

 ner with the great deposit of the Pampas, from which it differs 

 only in the mixture of quartz pebbles derived from the sub- 

 jacent soil. M. Lund, on his part, ascribes the red loam of 

 Brazil to a great irruption of water which, covering all that 

 part of the globe, exterminated the beings which inhabited it. 

 Whatever modification this hypothesis may afterwards receive, 

 it seems to us evident, that, at all events, the extension of the 

 Pampean bed over the mountains of Brazil, if it were com- 

 pletely proved, would overturn the contrary hypothesis which 

 consists in regarding the Pampean loam merely as a deposit, 

 formed tranquilly at the mouth of a great river. Now, this ex- 

 tension of the Pampean formation to the mountains of Brazil, 

 appears to us so much the more probable, because those moun- 

 tains are not the only ones in South America on which traces 

 are met with of the existence of an analogous deposit. The same 

 bed, indeed, presents itself at a much greater height on the 

 flanks of the Bolivian Andes, where it fills small basins at 

 Tariji and at Cochabamba, at a height of about 8400 feet above 

 the ocean, and where it covers the whole great Bolivian Pla- 

 teau, at a mean absolute height of about 13,000 feet. 



The Pampean deposit, occurring in this manner at all heights 

 of the basins, formed of rocks of all epochs, is naturally found 

 in contact with beds of the most different descriptions. On 

 the great Bolivian Plateau, it reposes on the Silurian, Devonian, 

 Carboniferous, andTriassic systems, and likewise on Trachytes; 

 at Cochabamba, on the two first ; at Moxos, on the Guaranian 

 tertiary formation ; and, lastly, in the Pampas, on the Pata- 

 gonian tertiary beds. But, notwithstanding this diversity of 

 the fundamental rocks, wherever it is observed, and whatever 

 may be its height, it invariably forms a horizontal bed, and its 

 composition is fundamentally nearly uniform : in the Pampas 

 it is a reddish loamy bed of great thickness ; at Chiquitos 

 and Moxos it is nearly identical, and on the banks of the Rio- 



* Lund, Coup d'oeil sur les esp^ces 6teintes de mammif eres fossiles du Br^sil, 

 {Annates det Sciences Natvrelles, t. xi. p. 214 and 230 ; 1839.) 



