436 TEE ICE AGE IN NORTH AMERICA. 



These questions are answered by an appeal to certain oceanic 

 islands which were outside the influence of continental glacia- 

 tion. According to Wallace, a striking proof of the theory 

 presented by Professor Gray " is found on the Peak of Ten- 

 eriffe, a mountain 12,000 feet high. In the uppermost 4,500 

 feet of this mountain above the limit of trees, Yon Buch 

 found only eleven species of plants, eight of which were 

 peculiar ; but the whole were allied to those found at lower 

 elevations. On the Alps or Pyrenees, at this elevation, 

 there would be a rich flora comprising hundreds of arctic 

 plants ; and the absence of anything corresponding to them 

 in this case, in which their ingress was cut oil by the sea, is 

 exactly what the theory leads us to expect." * 



On both continents, at the close of the Tertiary period, 

 there occurred a remarkable extinction of animals which is 

 doubtless connected with the advance of the continental ice- 

 sheet. Among these we may mention two species of the 

 cat family as large as lions ; four species of the dog family, 

 some of them larger than wolves ; two species of bears ; a 

 walrus, found in Virginia ; three species of dolphins, found 

 in the Eastern States ; two species of the sea-cow, found in 

 Florida and South Carolina ; six species of the horse ; the 

 existing South American tapir ; a species of the South Amer- 

 ican llama ; a camel ; two species of bison ; three species of 

 sheep ; two species of elephants and two of mastodons ; a 

 species of Megatherium, three of Megalonyx, and one of 

 Mylodon — huge terrestial sloths as large as the rhinoceros, or 

 even as large as elephants, which ranged over the Southern 

 States to Pennsylvania, and the Mylodon as far as the Great 

 Lakes and Oregon. f 



This w r ondrous assemblage of animals became extinct upon 

 the approach of the Glacial period, as their remains are all 

 found in post-Pliocene deposits. The intermingling of forms 

 is remarkable. The horses, camels, and elephants which 



* " The Geographical Distribution of Animals," vol. i, p. 43. 

 f Ibid., p. 129. 



