CHAr. xr THE CLASSIFICATION OF ISLANDS 243 



part of a continent. This was quite opposed to the 

 opinions of the scientific men of the day, who almost all 

 held the idea of continental extensions, and of oceanic 

 islands being their 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 permanence 

 of the great oceans which contain them, and we have 

 shown that several distinct lines of evidence all point to 

 the same conchision. 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 a fair number 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. Rodriguez, which was once thought to be 

 another exception, has been shown by the explorations 

 during the Transit of Venus Expedition to be essentially 

 volcanic, with some upraised coralline limestone. 



Continental 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 sub- 

 merged 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 other- 



R 2 



