434 THE ICE AGE IN NORTH AMERICA. 



and, indeed, to have been connected with Greenland in this 

 or in earlier times. Such a junction, cutting off access of the 

 Gulf Stream to the Polar Sea, would, as some think, other 

 things remaining as they are, almost of itself give glaciation 

 to Europe. Greenland may be referred to, by way of compari- 

 son, as a country which, having undergone extreme glaciation, 

 bears the marks of it in the extreme poverty of its flora, and 

 in the absence of the plants to which its southern portion, 

 extending six degrees below the Arctic Circle, might be entitled. 

 It ought to have trees, and might support them. But, since 

 destruction by glaciation, no way has been open for their re- 

 turn. Europe fared much better, but suffered in its degree 

 in a similar way. 



Turning for a moment to the American Continent for a 

 contrast, we find the land unbroken and open down to the 

 tropic, and the mountains running north and south. The 

 trees, when touched on the north by the on-coming refrigera- 

 tion, had only to move their southern border southward, along 

 an open way, as far as the exigency required ; and there was 

 no impediment to their due return. Then the more southern 

 latitude of the United States gave great advantage over Eu- 

 rope. On the Atlantic border, proper glaciation was felt only 

 in the northern part, down to about latitude 40°. In the in- 

 terior of the country, owing doubtless to greater dryness and 

 summer heat, the limit receded greatly northward in the Mis- 

 sissippi Valley, and gave only local glaciers to the Eocky 

 Mountains ; and no volcanic outbreaks or violent changes of 

 any kind have here occurred since the types of our present 

 vegetation came to the land. So our lines have been cast in 

 pleasant places, and the goodly heritage of forest-trees is one 

 of the consequences. 



The still greater richness of northeastern Asia in arboreal 

 vegetation may find explanation in the prevalence of particu- 

 larly favorable conditions, both ante-glacial and recent. The 

 trees of the Miocene circumpolar forest appear to have found 

 there a secure home ; and the Japanese Islands, to which most 

 of these trees belong, must be remarkably adapted to them. 

 The situation of these islands — analogous to that of Great 

 Britain, but with the advantage of lower latitude and greater 



