VII ZOOLOGY OF NORTH AND SOUTH AMERICA 139 



America strongly contrasted with each other. Some few species 

 alone have passed the barrier, and may be considered as 

 wanderers from the south, such as the puma, opossum, kinkajou, 

 and peccari. South America is characterised by possessing 

 many peculiar gnawers, a family of monkeys, the llama, peccari, 

 tapir, opossums, and, especially, several genera of Edentata, the 

 order which includes the sloths, ant-eaters, and armadilloes. 

 North America, on the other hand, is characterised (putting on 

 one side a few wandering species) by numerous peculiar gnawers, 

 and by four genera (the ox, sheep, goat, and antelope) of hollow- 

 horned ruminants, of which great division South America is 

 not known to possess a single species. Formerly, but within 

 the period when most of the now existing shells were living. 

 North America possessed, besides hollow-horned ruminants, the 

 elephant, mastodon, horse, and three genera of Edentata, namely, 

 the Megatherium, Megalonyx, and Mylodon. Within nearly 

 this same period (as proved by the shells at Bahia Blanca) 

 South America possessed, as we have just seen, a mastodon, 

 horse, hollow-horned ruminant, and the same three genera (as 

 well as several others) of the Edentata. Hence it is evident 

 that North and South America, in having within a late geo- 

 logical period these several genera in common, were much more 

 closely related in the character of their terrestrial inhabitants 

 than they now are. The more I reflect on this case, the more 

 interesting it appears : I know of no other instance where we 

 can almost mark the period and manner of the splitting up of 

 one great region into two well-characterised zoological provinces. 

 The geologist, who is fully impressed with the vast oscillations 

 of level which have affected the earth's crust within late periods, 

 will not fear to speculate on the recent elevation of the Mexican 

 platform, or, more probably, on the recent submergence of land 

 in the West Indian Archipelago, as the cause of the present 

 zoological separation of North and South America. The South 

 American character of the West Indian mammals ^ seems to 

 indicate that this archipelago was formerly united to the southern 

 continent, and that it has subsequently been an area of subsidence. 



1 See Dr. Richardson's Report, p. 157; also L'ImtUiit, 1837, p. 253. Cuvier 

 says the kinkajou is found in the larger Antilles, but this is doubtful. M. Gervais 

 states that the Didelphis crancrivora is found there. It is certain that the West 

 Indies possess some mammifers peculiar to themselves. A tooth of a mastodon has 

 been brought from Bahama : Edin. New Phil. Joitni. 1826, p. 395. 



