518 ISLAND LIFE part it 



would have been increased by the depression of the ocean 

 which must have 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, by the cases 

 of the Azores and Bermuda, how vastly the migratory 

 powers of birds are increased by a stormy atmosphere. 



Migration from North to South has leen 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 hemisphere 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 characteristic of the southern hemisphere appear 

 to have been originally derived from Europe. Thus 

 Eucalyptus and Metrosideros have been determined by 

 Dr. Ettingshausen from their fruits in the Eocene beds of 

 Sheppey, while Pimelea, Leptomeria and four genera of 

 Proteacese 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).^ Then we have such peculiar genera 



^ Sir Joseph Hooker informs me that he considers these identifications 

 worthless, and Mr. Bentham 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 



