80 THE GEOGRAPHY OF MAMMALS 



Burineister, Moreno, and Aineghino. A few words about 

 this branch of the subject may be added. 



The oldest formation containing well-preserved remains 

 of mammals yet investigated is in the neighbourhood of 

 Santa Cruz, in Southern Patagonia, where the deposits are 

 about 200 feet in thickness. The exact age of the Santa 

 Cruz beds it is very difficult to determine, but the best 

 authorities consider that they cannot be of earlier date 

 than the Upper Eocene or Oligocene of Europe. Follow- 

 ing these in point of time, are the so-called " Patagonian " 

 beds of Patagonia and Uruguay, which are probably of 

 Miocene age. The " Araucanian " formation of Ameghino, 

 which is well developed at Monte Hermoso, near Bahia 

 Blanca, in Southern Argentina, seems to correspond 

 approximately with the older European Pliocene. Finally, 

 the later Pliocene is apparently represented by the 

 " Pampas " formation of Argentina and Uruguay. Our 

 knowledge of the extinct mammal-faunas of these beds is 

 mainly due to the efforts of the Argentine palaeontologists 

 just mentioned, but a clear resume" of the work done will be 

 found in a recent number of the Geological Magazine (12). 



In the " Santa Cruz " beds have been found remains of 

 about 120 genera of mammals referable to the following 

 groups : — 



Marsupials. Perissodactyles. Rodents. 



Edentates. Toxodonts. Monkeys. 



Among the Marsupials the most prominent forms in this 

 formation are the Opossums {Dideiphyidm), which are still 

 found all over America, and in Tertiary times appear to 

 have been distributed nearly all over the northern hemi- 

 sphere. But accompanying these are other forms of the 



