228 ESS A YS. 



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. 



