POLYNESIA, or the region of many islands (Gr. poiys, much or many, and pesos, an• island), is the name usually given, with more or less of limitation, to the numerous groups of islands, and sonic few single islands, scattered throughout the great Pacific ocean, between the eastern shores of Asia and the western shores of America. In its widest signification. the term Polynesia might be understood as embracing, besides the groups hereafter to be mentioned, the various islands, large and small, of the Indian archipelago, in one direction; and the vast island of New Holland or Australia, with its dependency of Van Diemen's land, in another. Including these, the whole region has sometimes been called Oceania, and sometimes Australasia—generally, however, in modern times, to the exclusion of the islands in the Indian archipelago, to which cer tain writers have given the name of Malaysia. In proportion, also, as thearea of mari time discovery has become enlarged, it has been thought convenient by some geogra phers to narrow still further the limits of Polynesia to the exclusion of Australia and Van Diemen's laud; while others, again, exclude Papua or New Guinea, New Ireland, Solo mon's isles, the Louisiade group, the New Hebrides, New Caledonia, and certain other groups and single islands. together with New Zealand, front the area of Polynesia. and give to these, in union with Australia, the collective designation of Australasia. To all these, with the exception of New Zealand, French writers have given the name of Mela nesia or the Black, Islands: while a similar name, Kelttnonegia. has been given to them by Prichard and Latham—purely, however, on ethnological grounds, • as we shall pres ently notice.
Thus we have the three geographical divisions of Malaysia, Australasia. and Poly nesia, the last mentioned of which embraces all the groups and single islands not included under the other two. Accepting this arrangement, still the limits between Australasia and Polynesia have not been very accurately defined; indeed, scarcely any two geographers appear to be quite agreed upon the subject; neither shall we pretend to decide in the matter. The following list, however, comprises all the principal groups and single island not previously named as coming under the division of Australasia: viz., 1. North of the equator—The Ladrone or Marian islands. the Pelew islands, the Caroline islands, the Radack and Ralick chains, the Sandwich islands, Gilbert's or Kingstnill's archipelago. and the Galapagos. 2. South of the equator—The Ellice group, the Phoenix and Union groups. the Fiji islands, the Friendly islands, the Navi gator's islands. Cook's or Harvey islands, the Society islands. the Dangerous archi pelago, the Marquesas islands, Pitcairn island, and Easter island.
These islands, which extend from about 20° n. of the equator to about 30° s. of it, are some of them volcanic in their origin, and some of them coraline. The volcanic islands generally rise to a considerable height above the level of the ocean. and are there fore called the high islands, in contradistinction to the coraline or low islands. They consist of basalt and other igneous formations. Of these, the principal are the Friendly islands, one of which, Otaheite or Tahiti, has a mountain rising to the height of 10,000 ft.; the Marquesas islands, also very high; the Samoan or Navigator's islands; and the Sandwich islands, of which Owyhee or Hawaii possesses several bothactive and extinct craters, 13,000, 14,000, and even 16.000 ft. high. The Galapagos group, nearest of all
to South America, are likewise of igneous origin, and have several still active craters. The remaining islands are for the most part of coraline formation.
The coral islands (q.v.) may be distinguished into three classes—namely, atolls or lagoon islands, barrier reefs, and fringing reefs. The atolls are rings of coral reefs, sur rounding a basin of sea-water of considerable depth, which is inclosed within this area. Examples of these are found in the Caroline islands, the Dangerous archipelago, and several other groups. Barrier reefs differ from the atolls chiefly in the fact of their con taining an island in their center, the island being separated from the reef by a body of deep water; the reef is in some instances entirely converted into land, and in others the sea washes over it, except in certain portions which project above the level of the ocean. Barrier reefs occur among the Society islands, the Gambier islands, and many other groups. Fringing reefs are collections of coraline formation, which are found skirting the coasts of an island in the same manner as the barrier reefs, but with out any interior deep water channel. They are found in almost all the groups. From the fact of sonic of these islands being undoubtedly volcanic, it has been argued that all were originally of the same character; those of coraline formation being based upon the crests of submarine volcanoes, over which the coral insects have for an indefinite series of years been engaged in rearing their limestone structures. In opposition to the vol canic theory, Dr. Darwin has propounded one of his own—namely, the theory of subsi dence, which, after mature consideration, he believes to be the only one capable of explaining the various phenomena observable in the coral atolls, barrier reefs, and fring ing reefs of the Pacific. All these he considers as being the production of saxigenous insects, working upward from the foundations of what were originally so many islands, erect above the surface of the ocean, but which duringlong ages have been in a state of gradual subsidence. With respect to the atolls, he states it as his belief, that the lagoon is precisely in the place which the top of a shoal, and, in other cases, the highest part of an island, once occupied. So soon as these have sunk to a depth of from 120 to 180 ft. below the surface, the coral insects (which it is agreed are never found at a lower depth) commence their operations, and these working on in countless myriads, the sunken island, or a portion of it, is in process of time again reared to the level of the surrounding sea. It would take too long to specify all the phenomena upon which Dr. Darwin has based this ingenious theory, especially those connected with what are called the flinging reefs. It must be mentioned. however, that paradoxical as such a theory may seem, it has received the hearty support of no less distinguished a geologist than sir Charles Lyell, who, in the early editions of his Principles of Geology, having held to the volcanic theory, has since abandoned it for that propounded by Dr. Darwin. Nor is this all; for. in the last edition of sir C Lyell's work, we find him mentioning with approval Dr. Darwin's "important generalization that the Pacific and Indian seas, and some of the lands which border.them, might be divided into areas of elevation and areas of subsidence. which occur alternately.