FOREST GEOGRAPHY AND ARCHEOLOGY. 231 



accept the supposition of Nordenskjold, that anterior to the 

 Glacial period, Europe was " bounded on the south by an 

 ocean extending from the Atlantic over the present deserts of 

 Sahara and Central Asia to the Pacific," all chance of these 

 American types having" escaped from or reentered Europe 

 from the south and east, is excluded. Europe may thus be 

 conceived to have been for a time somewhat in the condition 

 in which Greenland is now, and indeed to have been con- 

 nected 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, al- 

 most of itself give glaciation to Europe. Greenland may be 

 referred to, by way of comparison, as a country which having 

 undergone extreme glaciation, bears the marks of it in the ex- 

 treme 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 return. Europe fared much bet- 

 ter, 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 therq 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 interior of the country, owing doubtless to greater dry- 

 ness and summer heat, the limit receded greatly northward 

 in the Mississippi Valley, and gave only local glaciers to the 

 Rocky 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. 



