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. Plere our correlation of Antillean geology with that 
of the continental mammalian deposits fails us completely. 
The supposed Oligocene beds of the Ant illes 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. 
