FOREST GEOGRAPHY AND ARCHZOLOGY. 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 reéntered 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 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 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. 
