52J 256 [October 



980 





VI 



South America as the Source of the Tertiary 



Mammalia 1 



OF the Argentine Territory during the Archaean era there only 

 existed the frame of the massive mountains of the north-west 

 and a few points and islets, which to-day form part of the various 

 isolated mountain chains which rise from the plain of the Pampa, 

 from Salta to Patagonia. 



The oldest fossiliferous deposits of the first Palaeozoic epochs 

 rest on these Archaean rocks : all the organisms are marine. In 

 the latest times of the Palaeozoic era, during the Carboniferous and 

 Permian periods, these small islands served as a nucleus for a 

 greater extension of the land, and then great numbers of terrestrial 

 organisms appeared, of a uniform aspect, precisely as the temperature 

 in all parts of the globe was uniform. 



The deposits of the greater part of the Mesozoic era, with rare 

 exceptions, are found in the Cordillera, where they appear on either 

 side in the form of narrow bands running north and south, proving 

 that then as now the Cordillera of the Andes already existed as a 

 long and narrow land which separated the Atlantic from the Pacific. 

 Both oceans reached the foot of the Cordillera, but in the Atlantic 

 the mountain chains of Tandil, Ventana, Cordoba, San Luis, and 

 various others formed large islands. At this time the geographical 

 differences of temperature began to be felt, causing climatic zones, 

 the most active of the factors which operate in the differentiation of 

 organisms — a differentiation which allows us to determine the rela- 

 tions of the floras and faunas of different regions, and to restore the 

 routes which they followed in their migrations across the lands of 

 other times, which are not the same as those of to-day, furnishing 

 us with the data to reconstruct the ancient connections of the lost 

 continents. 



We have now reached the latest time of the Cretaceous period, 

 the most recent of those which constitute the Mesozoic era. Water 

 predominated in the northern hemisphere, and land in the southern 

 — the reverse of what happens at the present day. The European 



1 Translated by Mrs Smitb Woodward from "La Argentina al travc's de las ultima 

 ('j)ocas geologicas," an address delivered at the inauguration of the University of La 

 Plata, April 18, 1897. (8vo., pp. 35. Buenos Aires : P. E. Coni & Sons, 1897.) 



