294 ORIGIN OF LIFE IN AMERICA 



existed, to western North America. I have endeavoured to 

 roughly represent on a map my conception of the geographical 

 conditions then prevailing in North and South America 

 (Fig. 14). Then followed a complete cessation of the migra- 

 tory stream to North America. This must have corresponded 

 with the depression of the Antilles. During the Oligocene 

 Period Professor Osborn recorded a re-establishment of the 

 faunal resemblance of western North America with western 

 Europe. Here our correlation of Antillean geology with that 

 of the continental mammalian deposits fails us completely. 

 The supposed Oligocene beds of the Antilles may really belong 

 to the Eocene Period. Another phase of independent evolu- 

 tion then succeeded this faunal interchange with western 

 Europe. This has been represented on another map (Fig. 16), 

 although I am fully aware of the extreme difficulties and 

 pitfalls connected with such an attempt. Later on, in 

 Miocene times, a fresh invasion occurs from the Old World. 

 This, I think, certainly did not come from the same quarter 

 as the others. We may conclude, therefore, that the land 

 bridge between the Antilles and Europe ceased to exist some 

 time during the Oligocene Period. It is quite possible that 

 long after that time large islands may have marked the former 

 site of the land bridge, while temporary land connections be- 

 tween the Azores and Europe, and between the Canary islands 

 and Africa, may have involved certain fragments of the older 

 trans-Atlantic land connection. 



