144 CHARLES DARWIN 



lope) 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 ex- 

 isting shells were living, North America possessed, besides 

 hollow-horned ruminants, the elephant, mastodon, horse, and 

 three genera of Edentata, namely, the Megatherium, Megal- 

 onyx, and Mylodon. Within nearly this same period (as 

 proved by the shells at Bahia Blanca) South America pos- 

 sessed, 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 in- 

 habitants 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-char- 

 acterized 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 plat- 

 form, 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. 



When America, and especially North America, possessed 

 its elephants, mastodons, horse, and hollow-horned rumi- 

 nants, it was much more closely related in its zoological 

 characters to the temperate parts of Europe and Asia than 

 it now is. As the remains of these genera are found on 

 both sides of Behring's Straits' and on the plains of Siberia, 



See Dr. Richards9n's Report, p. 157; also L'Institut, 1837, p. 253. 

 Cuvier says the kinkajou is found in the larger Antilles, but this is doubt- 

 ful. M. Gervais states that the Didelphis crancrivora is found there. It 

 is certain that the West Indies possess some mammifers peculiar to them- 

 selves. A tooth of a mastodon has been brought from Bahama; Edin. New 

 Phil. Journ., 1826, p. 395. 



7 See the admirable Appendix by Dr. Buckland to Beechey's Voyage; also 

 the writings of Chamisso in Kotzebue's Voyage. 



