FOREST TREES AND FOREST SCENERY 
find it impossible to live at high alti- 
tudes and on rocky ridges or to subsist 
upon rough, poor soil. Consequently 
we shall find some kinds of trees ex- 
clusive, gregarious only among them- 
selves, while others mingle freely in 
the general concourse. 
Through the persistency, therefore, 
of the vital forces of nature, through 
a suitable climate or situation, through 
the power of adaptation and the deli- 
cate adjustment of many details, the 
vast armies of trees, like migratory 
races, have at last accomplished their 
purpose and found their several homes; 
and to us the varied aspect of the for- 
ests, as we traverse the extended terri- 
tory of our country, is in a manner 
explained. There are stretches of land 
over which the tree growth is dense 
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