Geological Speculations. 63 



possessed, besides hollow-horned ruminants, the ele- 

 phant, mastodon, horse, and three genera of Edentata. 

 Within nearly this same period (as proved by the 

 shells at Bahia Blanca) South America possessed a 

 mastodon, horse, hollow-horned ruminant, and the 

 same three genera of Edentata. Hence it is evident 

 that North and South America, in having within 

 a late geological period these several genera in com- 

 mon, were much more closely related in the character 

 of their terrestrial inhabitants than they are now. 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. 



" When America, and especially North America, 

 possessed its elephants, mastodons, horse, and hol- 

 low-horned ruminants, 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 



