448 



ISLAND LIFE 



PART II 



we liave the evidence afforded by geology of wide 

 differences of distribution directly we pass beyond the 

 most recent deposits ; and when we go back to Mesozoic — 

 and still more to Palaeozoic — times, the majority of the 

 groups of animals and plants appear to have had a world- 

 wide range. A large number of our European Miocene 

 genera of vertebrates were also Indian or African, or even 

 American ; the South American Tertiary fauna contained 

 many European types ; while many Mesozoic reptiles and 

 mollusca ranged from Europe and North America to 

 Australia and New Zealand. 



By very good evidence (the occurrence of wide areas of 

 marine deposits of Eocene age), geologists have established 

 the fact that Africa was cut off from Europe and Asia by 

 an arm of the sea in early Tertiary times, forming a large 

 island-continent. By the evidence of abundant organic 

 remains we know that all the types of large mammalia 

 now found in Africa (but which are absent from 

 Madagascar) inhabited Europe and Asia, and many of 

 them also North America, in the Miocene period. At a 

 still earlier epoch Africa may have received its lower types 

 of mammals — lemurs, insectivora, and small carnivora, 

 together with its ancestral struthious birds, and its reptiles 

 and insects of American or Australian affinity ; and at this 

 period it was joined to Madagascar. Before the later 

 continental period of Africa, Madagascar had become an 

 i&land ; and thus, when the large mammalia from the 

 northern continent overran Africa, they were prevented 

 from reaching Madagascar, which thenceforth was enabled 

 to develop its singular forms of low-type mammalia, its 

 gigantic ostrich-like ^pyornis, its isolated birds, its 

 remarkable insects, and its rich and peculiar flora. From 

 it the adjacent islands received such organisms as could 

 cross the sea ; while they transmitted to Madagascar some 

 of the Indian birds and insects which had reached them. 



The method we have followed in these investigations is 

 to accept the results of geological and palseontological 

 science, and the ascertained facts as to the powers of 

 dispersal of the various animal groups ; to take full 

 account of the laws of evolution as affecting distribution, 



