236 



ISLAND LIFE. 



[part it. 



Ancient continental islands differ greatly from the preceding 

 in many respects. They are not united to the adjacent continent 

 by a shallow bank, but are usually separated from it by a depth 

 of sea of a thousand fathoms or upwards. In geological structure 

 they agree generally with the more recent islands; like them 

 they possess mammalia and amphibia, usually in considerable 

 abundance, as well as all other classes of animals ; but these are 

 highly peculiar, almost all being distinct species, and many form- 

 ing distinct and peculiar genera or families. They are also well 

 characterised by the fragmentary nature of their fauna, many of 

 the most characteristic continental orders or families being quite 

 unrepresented, while some of their animals are allied, not to 

 such forms as inhabit the adjacent continent, but to others found 

 only in remote parts of the world. This very remarkable set of 

 characters marks off the islands which exhibit them as a 

 distinct class, which often present the greatest anomalies and 

 most difficult problems to the student of distribution. 



Oceanic Islands. — The total absence of warm-blooded terrestrial 

 animals in an island otherwise well suited to maintain them, is 

 held to prove that such island is no mere fragment of any ex- 

 isting or submerged continent, but one that has been actually 

 produced in mid-ocean. It is true that if a continental island 

 were to be completely submerged for a single day and then again 

 elevated, its higher terrestrial animals would be all destroyed » 

 and if it were situated at a considerable distance from land it 

 would be reduced to the same zoological condition as an oceanic 

 island. But such a complete submergence and re-elevation 

 appears never to have taken place, for there is no single island 

 on the globe which has the physical and geological features of a 

 continental, combined with the zoological features of an oceanic 

 island. It is true that some of the coral-islands may be formed 

 upon submerged lands of a continental character, but we have no 

 proof of this ; and even if it were so, the existing islands are to all 

 intents and purposes oceanic. 



We will now pass on to a consideration of some of the more 

 interesting examples of these three classes, beginning with 

 oceanic islands. 



All the animals which now inhabit such oceanic islands must 



