﻿448 ON THE BOTANY OF JAPAN. 



probably, to existing species of the United States flora, most of them now inhabiting 

 the region a few degrees farther south. 



If, then, our present temperate flora existed at the close of the glacial epoch, the 

 evidence that it soon attained a high northern range is ready to our hand. For then 

 followed the second epoch of the post-tertiary, called the fluvial by Dana, when the 

 region of the St. Lawrence and Lake Champlain was submerged, and the sea there 

 stood five hundred feet above its present level ; when the higher temperate latitudes of 

 North America, and probably the arctic generally, were less elevated than now, and the 

 rivers vastly larger, as shown by the immense upper alluvial plains, from fifty to three 

 hundred feet above their present beds ; and when the diminished breadth and lessened 

 height of northern land must have given a much milder climate than the present. 



Whatever the cause, the milder climate of the fluvial epoch is undoubted. Its char- 

 acter, and therefore that of the vegetation, is decisively shown, as geologists have re- 

 marked, by the quadrupeds. While the Megatherium, Mylodon, Dicotyles, &c. demon- 

 strate a warmer climate than the present in the Southern and TNIiddle United States, 

 the Elephas primigemus, ranging from Canada to the very shores of the Arctic Ocean, 

 equally proves a temperate climate and a temperate flora in these northern regions. 

 This is still more apparent in the species of the other continent, where, in Siberia, not 

 only the Elephas jmrnigenins, but also a Ehinoceros, roamed northward to the arctic 

 sea-coast. The quadrupeds that inhabited Europe in the same epoch are well known 

 to indicate a warm-temperate climate as far north as Britain, in the middle, if not the 

 later post-tertiary. North America then had its herds of Mastodons, Elephants, Buf- 

 faloes or Bisons of different species, Elks, Horses, Megalonyx, the Lion, &c. ; and, from 

 the relations between this fauna and that of Europe, there is little doubt that the climate 

 was as much milder than the present on this as on the other side of the ocean. All 

 the facts known to us in the tertiary and post-tertiary, even to the limiting line of the 

 drift, conspire to show that the difference between the two continents as to temper- 

 ature was very nearly the same then as now, and that the isothermal lines of the north- 

 ern hemisphere curved in the directions they now do. 



A climate such as these facts demonstrate for the fluvial epoch would again com- 

 mingle the temperate floras of the two continents at Behring's Straits, and earlier — 

 probably through more land than now — by way of the Aleutian and Kurile Islands. 

 I cannot imagine a state of circumstances under which the Siberian Elephant could 

 migrate, and temperate plants could not. 



The fluvial Avas succeeded by the " terrace epoch," as Dana names it, " a time of 

 transition towards the present condition, bringing the northern part of the continent 



