THE ORIENTAL MIGRATION. 283 



Many of these plants then, and also some of the 

 animals I have referred to, formed part of the older 

 stream of migration which entered Europe from Asia 

 Minor (vide Fig. 5, p. 117). There were only two 

 courses open to them as they arrived on our continent 

 during earlier Tertiary times. They could either go 

 straight west towards Greece, or in a more northward 

 direction to the newly-formed Alps. As the latter 

 were raised, some of the immigrants were modified 

 so as to adapt themselves to the new surroundings. 

 Others became extinct ; but a great many have per- 

 sisted in the Alps to the present day and exhibit 

 discontinuous distribution, having meanwhile dis- 

 appeared in the intermediate tract between the latter 

 and their original home in Asia. The lowlands of 

 Eastern and Central Europe were either occupied by 

 the sea or by large freshwater lakes, so as effectually 

 to prevent a direct migration northward. 



When the newer migrants arrived from Asia not 

 only had the Alps risen to a lofty, mountain chain 

 acting as an effectual barrier, but Southern Italy and 

 Greece had become disconnected. Some time after, 

 Sicily and Southern Italy also became separated. 

 Meanwhile the stream of migrants which consisted 

 less and less of typically southern forms, emigrants 

 from Central Asia and even Southern Siberia, 

 mingled with the southern forms on their way to 

 Europe, and these now poured across the newly 

 opened plain of Central and Northern Europe. But 

 it was not until some time after this that the Mediter- 



