chap, xi.] THE CLASSIFICATION OF ISLANDS. 
235 
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. Rodriguez, 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. 
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 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. 
