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Show 236 ISLAND LIFE. (I'AR'l' II. Ancient continental islands differ greatly from the prec~ding in many respects. They are not united to the adjacent contment 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 isla~ds; h~e them they possess mammalia and amphibia, usually m 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. ~hey are also well characterised by the fragmentary nature of the1~ :auna,. many. of the most characteristic continental orders or families bemg 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 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 h~s 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 OFIAP. XI.] OCEANIC ISLANDS. 237 either themselves have reached them by crossing the ocean, or be the ~escendants of ancestors who did so. Let us then see what are, In fact, the animal and vegetable inhabitants of these islands a~d how far their presence can be accounted for. We will begi~ With the Azores, or Western Islands, because they have been thoroughly w~ll explored by naturalists, and in their peculiarities affo~d ~s a~ Important clue to some of the most efficient means of d1stnbutwn among several classes of animals. |