366 On the PatcBontology of South America. 



The Neocomian formations are replaced in Europe by the 

 Gault. This member of the cretaceous formation,* so much 

 subdivided, appears to be quite wanting in America ; which is 

 not the case with the chloritic chalks, as a portion of them is 

 found in the Cordilleras of Chili. But then, as I have satisfied 

 myself by comparisons, the Faunas, far from covering immense 

 portions of the earth's surface, appear to be limited in their 

 distribution. They are divided more and more up to the ter- 

 mination of the cretaceous system, which is marked in A me- 

 rica by the first relief of the Chilian system of the CordiIleras,t 

 and by the Gauranian deposit, J which is its immediate re- 

 sult. 



Nature, in fact, ceasing for a time to be in repose, the retreat 

 of the materials again induced vast depressions in the west, 

 whilst a line of dislocation, fifty degrees in length, gives origin 

 to the eastern Cordilleras, therewith producing — as the result 

 of the balancing of the waters upon the then emerged conti- 

 nents, and at the bottom of the maritime basins of America — 

 ferruginous beds, which do not contain any trace of organized 

 bodies. This is the commencement of the tertiary period, an 

 epoch when mammals were yet unknown. A calm then pre- 

 vailed, and the New World exhibited maritime basins and 

 circumscribed continents. After this there appeared, for the 

 first time, numerous mammalia in the midst of a vigorous vege- 

 tation, and the sea was inhabited by marine animals much 

 more diversified than formerly in their forms, but more re- 

 stricted in their faunas. The same species were no longer to be 

 found from one side of the globe to the other ; and the uni- 

 form temperature due to the central heat having lost much of 

 its intensity, the prevailing races of beings were more circum- 

 scribed, and composed, even under the same latitude, and at 

 very inconsiderable distances from each other, local faunas, 

 which Vv'ere often distinct. This, at all events, is the state of 

 matters which is found in the tertiary seas of South America, 

 limited by a simple chain, that of the Cordilleras, which sepa- 

 rates the fauna of the Pacific from that of the Atlantic. At 



♦ See Paleontologie Frangaise (terrains Cretaces), torn i. p. 450 and 639. 

 t Geologic du Voyage dans TAmerique meridionale, p. 272. 

 X lb. page 245. 



