Island

Island (A.S. igland, ig, 'island,' and land. Ig is cognate with Icel. ey, Dan. ø, and ultimately with A.S. ed, Gothic ahwa, and Lat. agua, all signifying 'a stream,' 'water.' The s in island crept in through confusion with Fr. isle, derived from Lat. insula), land surrounded by water. The larger masses of land surrounded by water, or parts of them, are Continents (q.v.), and the term island is usually restricted to the smaller. Since Australia has an area of over 3,000,000 sq. m., and (omitting Greenland, which is possibly an ice-bound archipelago) New Guinea, the next island in size, has only 303,000 sq. m., the distinction drawn between continents and islands in the restricted sense is more than verbal. There are few large islands. Borneo, indeed, is little inferior in size to New Guinea; but Madagascar and Sumatra are the only others with an area greater than 100,000 sq. m. Honshū (the main island of Japan) and Great Britain rank next, the latter being sixth in order of size if New Guinea is taken as first. The following table shows the relative mainland area of the largest islands.

Two classes of islands may be distinguished—continental and oceanic. Continental Islands are closely allied by the structure of their rocks to the nearest continental land, from which they are rarely far distant, although sometimes—as in the case of Madagascar and New Zealand—separated by depths exceeding 1000 fathoms. As a rule, continental islands lie to the south and east of the continent with which they are associated. The only exceptions to this rule are islands on the continental shelf—i.e. separated by depths less than 100 fathoms, which have been cut off from the mainland in geologically recent times. With the exception of Madagascar and New Zealand, the separation of which is unusually complete, the plants and animals of continental islands are similar to those on the adjacent continent, and from the slight differences detected the period at which separation took place has sometimes been calculated. Groups of continental islands enclosing seas stretch from the south-east peninsula of each of the northern continents towards the nearest southern continent. The Greek Archipelago points from the Balkan Peninsula towards Africa, the West Indies run from Florida and Yucatan to South America, and the Eastern Archipelago extends from the Malay Peninsula to Australia. These archipelagos represent mountainous tracts of continent which have subsided, or else irregular portions of the submarine plateaus which are undergoing elevation. Professor James Geikie points out in a paper (Scot. Geog. Mag., February 1890) that in past geological epochs groups of great islands occupied the sites of the present continents, and he shows reason for believing that the evolution of continents by the incorporation of islands on the great world ridges is still going on, although accompanied by the formation of new islands through local erosive action on the coasts.

Oceanic Islands rise abruptly from great depths, and show no geological continuity with the continents. They appear above the surface either as (a) Volcanic Islands, usually rugged peaks or vast accumulations of lava nearly as precipitous below the surface as above, or as (b) Coral Islands (q.v.). Numerous submarine mountains have been discovered in different parts of the ocean, which only require moderate elevation or the deposition of sediment or coral growth to appear on the surface as islands. The fauna and flora of oceanic islands like those of Madagascar and New Zealand, which biologically resemble oceanic islands, differ widely from those of the continents, and present many features of unique interest, which have been worked out in detail by Wallace in his Island Life. See GEOGRAPHICAL DISTRIBUTION.

Continental islands have in historical times formed the cradles of great commercial nations, the insular position giving security, and the water border acting at once as a barrier to the less adventurous continental people and as a highway to the bolder islanders, whose closer contact with the sea makes them nations of sailors.—For Floating Islands, see that head; and for the 'Islands of the Blessed' and other fabulous islands, see ANTILLES, ATLANTIS, AVALON, BRENDAN, ELYSIUM, &c.