in its relations to that of North America. 199 
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 was succeede the “terrace epoch,” as Dana 
names it, “a time of transition towards the present condition, 
bringing the northern part of the continent up to its present 
level, and down to its present cool temperature,”"*—giving the 
arctic flora its present range, and again separating the temperate 
floras of the New and of the Old World to the extent they are 
sup 
podal region affords of itself no presumption that they were orig- 
inated there ;—and that the interchange of plants bet Eastern 
_ Sreater difficulty than does the Arctic flora, the general homo- 
_ Seneousness of which round the world has always been thought 
asenia peltata—To the remarks upon the known range of 
of this species, I have now to add the interesting that it iat) 
_* For the collocation and 
am indebted to the kindness of my friend, Professor Dana. 
