132 HUNTING EXTINCT ANIMALS 



be considered as but little older than the directly overlying 

 Patagonian; that is, I would consider them as belonging in 

 the Oligocene epoch instead of in the Cretaceous as Ame- 

 ghino has put them. In fact, from the Cretaceous we know 

 of only the most primitive and smallest of mammals, and 

 placing these beds with their representatives of typically 

 tertiary animals in them, would only be permissible as 

 the result of overwhelming evidence to that effect. 



Following this period of land deposits the country sank 

 again and the inrolling waters deposited over them first 

 the sands with their shallow- water oysters, etc., of the base 

 of the Patagonian. This submergence continued for a long 

 time until the 600 and more feet of Patagonian sands and 

 clays were accumulated. During this time the climate 

 in this section seems to have been much warmer than now, 

 for all the genera and families are typically those adapted 

 to tropical seas. 



Again, the coast rose during the period when the Santa 

 Cruz beds were deposited, a time when there was much 

 volcanic action, for the large part of those beds are com- 

 posed of volcanic dust and ashes. During this time the 

 rivers began cutting away and dissecting the land, and 

 only in favorable places were there any land deposits. 

 In other places it was wholly a story of cutting river valleys 

 and removal of land. This is the second half of the 

 Miocene, and during it the general outlines of the present 

 topography were carved out, the great valleys like those 

 of the Chubut, Chico, Deseado, etc., rivers being then 

 formed, occupied now only by tiny streams all out of pro- 

 portion to the positions they occupy. During this time 

 also the land must have extended considerably farther to 

 the East than the present seacoast. 



This period of elevation was followed during the Pliocene 

 by another sinking, during which the Cape Fairweather 

 and contemporaneous beds, carrying their fauna of shal- 

 low water marine shells, were formed. This submergence 



