370 On the VaUBontology of Houth America. 



at the surface of the globe, a fauna, which is distinct, but 

 identical in its composition. Thus the Silurian, the Devonian, 

 the Carboniferous, Triassio, Cretaceous, Tertiary, and Diluvian 

 formations, are the same in America as in Europe, and pre- 

 serve the same palaoontological/rtceV*, the same generic forms. 



4. Not only is there the same fades in the extinct fauna 

 of the Old and New World, but some identical species com- 

 mon to both, moreover prove, that they were quite contempo- 

 raneous. 



5. This contemporary existence which is observed at im- 

 mense distances, in the early periods of animalization, and 

 down to the epoch in which the lower cretaceous formations 

 were deposited, appears to depend upon the prevalence of a 

 uniform temperature, and on the shallowness of the oceans, 

 which allowed the living beings not "only to enjoy completely 

 the influence of the external light, a condition quite indis- 

 pensable to their existence, but also to propagate and spread 

 without obstacle, from one locality to another, — circumstances 

 which could no longer occur when, through the influence of 

 inequality of temperature, the cooling of the earth on the one 

 hand, and the elevation of the various systems on the other, 

 together with the corresponding depression of the oceans, many 

 insuperable barriers were presently occasioned to their spread- 

 ing either along the coasts, or in extensive sedimentary de- 

 posits. It is then apparent, that the uniformity of the distribu- 

 tion of the first living beings which flourished upon the globe, 

 was owing as much to the equality of temperature produced by 

 the central heat, as to the shallowness of the seas ; whilst the 

 subdivision of faunas, as we approach the present period, by 

 basins, which become more and more confined, arises from the 

 refrigeration of the earth, from the existence of terrestrial and 

 marine barriers, which presented obstacles to the extension of 

 local faunas. 



6. If faunas are found to have the same points of separa- 

 tion in the New and Old World, and if they agree in the 

 same marked limits as to their palaeontological composition, 

 then we must naturally conclude, that the divisions of forma- 

 tions do not depend upon partial causes, but must have pro- 



