128 LAND MAMMALS IN THE WESTERN HEMISPHERE 



in the latest beds. In the Arctic regions the cold must have 

 been severe, at least during the latter half of the epoch, for 

 in the succeeding Pleistocene we find an Arctic fauna already 

 fully adapted to the extreme severity of present day polar 

 conditions and time was necessary for such an adaptation. 

 In the western interior the climate was not only colder, but 

 also drier than it had been in the Miocene, the desiccation 

 which had begun in the latter epoch becoming progressively 

 more and more marked. 



South America. — The Greater Antilles were larger than 

 at present and Cuba was much extended, especially to the 

 southeastward, and was probably connected with the main- 

 land, not as one would naturally expect, with Yucatan, but 

 with Central America ; this island, it is most likely, was cut 

 off from Hayti. The Isthmian region was considerably broader 

 than it is now and afforded a more convenient highway of 

 intermigration. Costa Rica was invaded by a Pliocene 

 gulf, but it is not yet clear whether this persisted for the whole 

 or only a part of the epoch. In the Argentine province of 

 Entrerios is a formation, the Parana, which is most probably 

 Pliocene, though it may be upper Miocene. This formation 

 is largely marine and shows that the present Rio de la Plata 

 was then a gulf from the Atlantic. A few northern hemisphere 

 mammals in the Parana beds show that the migration had 

 advanced far into South America. A large part of Patagonia 

 was again submerged beneath the sea, which extended to the 

 Andes in places, but just how general the submergence was, 

 it is impossible to say, for the Cape Fairweather formation has 

 been largely carried away by erosion and only fragments of 

 it remain. Along the foothills of the Andes these beds are 

 upturned and raised several thousand feet above the sea-level, 

 a proof that the final upheaval of the southern mountains took 

 place at some time later than the early Pliocene. Continental 

 formations of Pliocene date are largely developed in Argentina ; 

 the Araucanian stage is in two substages, one in the province 



