486 
ISLAND LIFE, 
[part II. 
arisen from such a vast bulk of water being locked up in land- 
ice, and which depression would have produced the same effect 
as a general elevation of all the continents. At this time, too, 
aerial currents would have attained their maximum of force 
in both hemispheres ; and this would greatly facilitate the 
dispersal of all wind-borne seeds as well as of those carried in 
the plumage or in the stomachs of birds, since we have seen 
how vastly the migratory powers of birds are increased by a 
stormy atmosphere. 
Migration from North to South has been long going on. — Now, 
if each phase of colder and warmer mountain-climate — each 
alternate depression and elevation of the snow-line, only helped 
on the migration of a few species some stages of the long route 
from the north to the south temperate regions, yet, during the 
long course of the Tertiary period there might well have arisen 
that representation of the northern flora in the southern hemis- 
phere which is now so conspicuous. For it is very important to 
remark that it is not the existing flora alone that is represented, 
such as might have been conveyed during the last glacial epoch 
only ; but we find a whole series of northern types evidently of 
varying degrees of antiquity, while even some genera character- 
istic of the southern hemisphere appear to have been originally 
derived from Europe. Thus Eucalyptus and Metrosideros have 
been determined by Dr. Ettinghausen from their fruits in the 
Eocene bee's of Sheppey, while Pimelea, Leptomcria and four 
genera of Pioteaceae have been recognised by Professor Heer in 
the Miocene of Switzerland ; and the former writer has detected 
fifty-five Australian forms in the Eocene plant beds of Haring 
(? Belgium ). 1 Then we have such peculiar genera as Pachychla- 
1 Sir Joseph Hooker informs me that he considers these identifications 
worthless, and Mr. Benthain has also written very strongly against the 
value of similar identifications by Heer and Unger. Giving due weight to 
the opinions of these eminent botanists we must admit that Australian 
genera have not yet been demonstrated to have existed in Europe during 
the Tertiary period ; but, on the other hand, the evidence that they did so 
appears to have some weight, on account of the improbability that the 
numerous resemblances to Australian plants which have been noticed by 
different observers should all be illusory; while the well established fact 
of the former wide distribution of many, tropical o,r now restricted types of 
