228 ESSAYS. 
from the Japanese species which alone survives ; that we have 
evidence, not merely of Pines and Maples, Poplars, Birches, 
Lindens, and whatever else characterize the temperate-zone 
forests of our era, but also of particular species of these, so 
like those of our own time and country, that we may fairly 
reckon them as the ancestors of several of ours. Long gene- 
alogies always deal more or less in conjecture ; but we appear 
to be within the limits of scientific inference when we an- 
nounce that our existing temperate trees came from the north, 
and within the bounds of nigh probability when we claim not 
a few of them as the originals of present species. Remains 
of the same plants have been found fossil in our temperate 
region, as well as in Europe. 
Here, then, we have reached a fair answer to the question 
how the same or similar species of our trees came to be so dis- 
persed over such widely separated continents. The lands all 
diverge from a polar centre, and their proximate portions — 
however different from their present configuration and extent, 
and however changed at different times — were once the home 
of those trees, where they flourished in a temperate climate. 
The cold period which followed, and which doubtless came on 
by very slow degrees during ages of time, must have long 
before its culmination brought down to our latitude, with 
the similar climate, the forest they possess now, or rather the 
ancestors of it. During this long (and we may believe first) 
occupancy of Europe and the United States, were deposited in 
pools and shallow waters the cast leaves, fruits, and occasionally 
the branches, which are imbedded in what are called Miocene 
Tertiary or later deposits, most abundant in Europe, from 
which the American character of the vegetation of the period 
is inferred. Geologists give the same name to these beds, in 
Greenland and southern Europe, because they contain the 
remains of identical or very similar species of plants; and 
they used to regard them as of the same age on account of 
this identity. But in fact this identity is good evidence that 
they cannot be synchronous. The beds in the lower latitudes 
must be later, and were forming when Greenland probably 
had very nearly the climate which it has now. 
