120 



ISLAND LIFE. 



[part I. 



the Alps, and then by the Mediterranean ; whereas in eastern 

 America and Asia the mountain chains run in a north and 

 south direction, and there is nothing to prevent the flora from 

 having been preserved by a southward migration into a milder 

 region. 



Our next two chapters will be devoted to a discussion of the 

 causes which brought about the glacial epoch, and that still 

 more extraordinary climatic phenomenon — the mild climate and 

 luxuriant vegetation of the Arctic zone. If my readers will 

 follow me with the care and attention so difficult and interest- 

 ing a problem requires and deserves, they will find that I have 

 grappled with all the facts which have to be accounted for, and 

 offered what I believe is the first complete and sufficient ex- 

 planation of them. The important influence of climatal changes 

 on the dispersal of animals and plants is a sufficient justification 

 for introducing such a discussion into the present volume. 



