The Marquesas and Isolated Groups.—Beyond the Tuamotu group to the north-east lie the Marquesas showing basic volcanic material deeply dissected and recently so altered by submergence that only fragments of coral are found in the bay-head beaches. The New Zealand-Hawaii zone of great depths is cut between the Equator and lat. io° N. by the low atolls of Christmas, Fanning, Samarang, Palmyra and Barber islands arranged more or less north-west to south-east. East of the eastern Polynesian chains lie Easter island and Sala-y-Gomez island south of the Tropic of Capricorn, and the Galapagos islands on the Equator. All are volcanic in origin and may possibly be compared rather with the oceanic islands of the Atlantic than with the island chains of the rest of the Pacific.
The Hawaiian chain is treated separately. (See HAWAII.) General Physical Geography.—Volcanic islands, commonly called high islands, are widely distributed throughout the area of Oceania except in the extreme eastern parts, where "low islands," coralline atolls, are much more, indeed extraordinarily frequent. The high islands of the Marquesas and the Society (Tahitian) groups are types of extinct volcanic islands. In the long chain of the Solomon islands, in the New Hebrides, in the Tongan group there are still active volcanoes and Hawaii contains the cele brated active crater of Kilauea. In many other places at which only tradition tells of eruption it would hardly be safe to assume that activity might not again burst out. Submarine vents some times break out ; the most remarkable instance of this is that of the so-called Falcon island (lat. 20° 19' S., long. 175° 25' W.), in the Tongan group. In the Pacific Islands Pilot, vol. ii., it is recorded that this was first seen as a breaking reef, from H.M.S. "Falcon," in 1865 ; from the position of this reef smoke was seen to issue, by H.M.S. "Sappho," in 1877; in October 1885 the reef was reported to have taken on the form of an island ; four years later this island was actually surveyed by H.M.S. "Egeria," and found to be 14 miles long north and south, one mile wide, wedge shaped, the highest part, 153 feet above sea-level, being at the south end. It was formed of loose volcanic ashes and cinders, which material was constantly slipping down, as the action of the sea undermined the coast. By 1885 two-thirds of the island had disappeared; and by April 1894 nothing was to be seen where Falcon island had been but a low streak of black rock, invisible at night. But in December of the same year renewed "volcanic
action had formed a new crater, with the result that the island was then fifty feet high, three miles long and one and a half miles broad, the surface being still quite hot. In 1895 the island had again disappeared, its place occupied by a shoal about a hundred yards in extent breaking heavily. In April 1900, the shoal which had been the island was showing about nine feet above water at its northern end." In 1905, as the present writer can testify, the shoal was barely more than a waste, and in 1913 it was officially reported as "non est." In 1926 or 1927 the island, or rather the shoal again appeared, but is said to have disappeared again.
Coral Formations.—Coral reefs, like volcanoes, are dealt with under special articles, but here it must be noted that coral, in one or other of its several forms, is present, not everywhere but more abundantly than in any other ocean, in the Pacific island area, more especially in the eastern portion of that area. The main type-forms in which it appears are as follows : atolls, i.e., rings of coral surrounding a central lagoon ; barrier reefs, i.e., such as front a coast-line or encircle an island or group of islands, leaving a more or less deep channel between it and the shore; and fringing-reefs, i.e., such as are extensions of the shore, gen erally for a short but sometimes for a more considerable distance, and not separated from the shore by any deep water channel.
As to the atolls it must be added that often one or more, or even many, of the highest parts of these may be more or less raised higher than the general sea-level of the ring, so that from a distance these higher parts, especially after vegetation has been attracted to them, may appear from a little distance as distinct islands, and in many cases have been so reported and named.
In other cases, again, what must originally have been atolls have been raised, sometimes more than once, and have thus be come what have been called elevated coral islands; a good example of this is the island of Mare, of the Loyalty group, where there is evidence of three such elevations, so that three former reefs appear as distinct low cliffs, separated from the sea by low and level coast-tracts.