FLIGHT OF PLANTS AND ANIMALS. 431 



Japan and China, three kinds of gingko-trees, for instance, one 

 of them not evidently distinguishable from the Japan 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 genealogies always deal more or less in 

 conjecture ; but we appear to be within the limits of scientific 

 inference when we announce that our existing temperate trees 

 came from the north, and within the bounds of high proba- 

 bility 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 center, 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, when 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 long before 

 its culmination have brought down to our latitudes, 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 occasion- 

 ally 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 and 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 

 can not 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. 



