CHAP. XI.] THE CLASSIFICATION OF ISLANDS. 



2.35 



fragments, and it was long before Mr. Darwin's views obtained 

 general acceptance. Even now the belief still lingers; and 

 we continually hear of old Atlantic or Pacific continents, of 

 "Atlantis" or " Lemuria," of which hypothetical lands many 

 existing islands, although wholly volcanic, are thought to be the 

 remnants. We have already seen that Darwin connected the 

 peculiar geological structure of oceanic islands with the per- 

 manence of the great oceans which contain them, and we have 

 shown that several distinct lines of evidence all point to the same 

 conclusion. We may therefore define oceanic islands, as follows ; 

 — Islands of volcanic or coralline formation, usually far from 

 continents and always separated from them by very deep sea, 

 entirely without indigenous land mammalia or amphibia, but 

 with abundance of birds and insects, and usually with some 

 reptiles. This definition will exclude only two islands which 

 have been sometimes classed as oceanic — New Zealand and the 

 Seychelles. E-odriguez, which was once thought to be another 

 exception, has been shown by the explorations during the Tran- 

 sit of Venus Expedition to be essentially volcanic, with some 

 upraised coralline limestone. 



Continentcd Islands. — Continental islands are always more 

 varied in their geological formation, containing both ancient 

 and recent stratified rocks. They are rarely very remote from 

 a continent, and they always contain some land mammals and 

 amphibia, as well as representatives of the other classes and 

 orders in considerable variety. They may, however, be divided 

 into two well-marked groups — ancient, and recent, continental 

 islands — the characters of which may be easily defined. 



Recent continental islands are always situated on submerged 

 banks connecting them with a continent, and the depth of the 

 intervening sea rarely exceeds 100 fathoms. They resemble the 

 continent in their geological structure, while their animal and 

 vegetable productions are either almost identical with those of the 

 continent, or if otherwise, the difference consists in the presence 

 of closely allied species 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. 



