A. Gray—Forest Geography and Archeology. 191 
comes from a just general view, and not through piecemeal 
suppositions of chances. And I am clear that it is to be found 
y looking to the north, to the state of things at the arctic 
zone,—first, as it now is, and then as it has been. 
North of our forest-regions comes the zone unwooded from 
cold, the zone of arctic vegetation. In this, as a rule, the 
Species are the same round the world; as exceptions, some are 
restricted to a part of the circle. 
The polar projection of the earth down to the northern tropic, 
as here exhibited, shows to the eye—as our maps do not—how 
all the lands come together into one region, and how natural 
it may be for the same species, under homogeneous conditions, 
to spread over it. When we know, moreover, that sea and 
land have varied greatly since these species existed, we may 
well believe that any ocean-gaps, now in the way of equable 
distribution, may have been bridged over. There is now only 
one considerable gap. 
WwW 
kept together at a low level, and made good their retreat, form 
the main body of present arctic vegetation. Those that took to 
the mountains had their line of retreat cut off, and hold their 
positions on the mountain-tops under cover of the frigid climate 
due to elevation. The conditions of these on different conti- 
nents or different mountains are similar, but not wholly alike. 
me species proved better —— to one, some to another, 
ace of the world; where less adapted, or less adaptable, they 
ive perished ; where better adapted, they continue,—with or 
Without some change ;—and hence the diversification of alpine 
lants, as well as the general likeness through all the northern 
emisphere. 
All this exactly applies to the temperate zone vegetation, 
id to the trees that we are concerned with. The clew w 
seized when the fossil botany of the high arctic regions came 
to light; when it was demonstrated that in the times next pre- 
ceding the Glacial period—in the latest Tertiary—from Spitzber- 
gen and Iceland to Greenland and Kamtschatka, a climate like 
that we now enjoy prevailed, and forests like those of New 
