244 ISLAND LIFE 



wise, the difference consists in the presence of closely allied 

 specie^ of the same types, with occasionally a very few 

 peculiar genera. They possess in fact all the character- 

 istics of a portion of the continent, separated from it at a 

 recent geological period. 



Ancient continental islands differ greatly from the pre-' 

 ceding in many respects. They are not united to the adja- 

 cent continent by a shallow bank, but are usually separated 

 from it by a depth of sea of several hundreds to more than 

 a thousand fathoms. 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 forming 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 existing 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 sub- 

 merged 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-eleva- 

 tion appears never to have taken place, for there is no 

 single island on the globe Avhich has the physical and geo- 

 logical features of a continental, combined with the zoo- 

 logical features of an oceanic island. It is true that some 

 of the coral-islands may be formed upon submerged lands 



