486 



ISLAND LIFE. 



[part J I. 



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 cr in the stomachs of biids, since we have seen 

 how vastly the migratory powers of birds are increased by a 

 stormy atmosphere. 



Migration from North to South has heen long going on. — Now, 

 if each phase of colder and warmer mountain-climate — each 

 alternate depression and deviation 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 v/e find a wdiole series of northern types evidently of 

 varying degrees of antiquity, while even some genera chara^cter- 

 istic of the southern hemisphere appear to have been originally 

 derived from Europe. Thus Eucalyptus and Metrosicleros have 

 been determined by Dr. Ettinghausen from their fruits in the 

 Eocene bee's of Sheppey, while Firnelea, 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).^ Then we have such peculiar genera as Pachychla- 



1 Sir Joseph Hooker informs me that he considers these identifications 

 worthless, and Mr. Bentharn 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 Lave been noticed by 

 different observers should all be illusory ; while the well established fact 

 of the former wide distribution of niany tropical or now restricted types of 



