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action of volcanoes, and the working of the small insect usually denominated the coral polypus.

Nature has unquestionably given to that section of the earth a prominent and very characteristic physiognomy, diversified by numerous inequalities on the surface, and distinguished by lofty mountains, the direction of which, from north to south, indicates a striking polarity in their structure. These chains, at the same time, generally present, about the middle of their course, a decided bend from west to east. The best marked among them is that formed by the Ladrone, the Caroline, and the Mulgrave group, and are probably associated, by means of those called St Augustin and some other links, with the archipelago of the Navigators, or that of the Friendly Islands. Even among the Carolines, where the Polynesian series turns due east, the particular masses lie north and south. Another great chain makes its appearance in Luçon, the largest of the Philippines, which passes through the island of Palawan into that of Borneo. The direction of that well-known branch is from north-west to south-east, and bounds on one side the basin of the Chinese Sea. In New South Wales the long line of the Blue Mountains extends to Van Diemen's Land, terminating in immense masses of basalt at South Cape. The fourth great chain takes its commencement at the Andaman and Nicobar Islands, and in its progress gives rise to Sumatra, Java, Timor, and others of less magnitude. It runs in the form of a bow from north-west to southeast, then due east; but it probably passes by Cape Diemen, where it can have no other direction than from north to south.

CHAP. I.

Direction of

the island

chains.

goes.

All the smaller archipelagos of Polynesia, too, lie north The smaller and south, of which New Caledonia and the New He- Archipelabrides form very distinct examples. The group of the Solomon Islands, bending from the south-east to the north-west, is continued in New Ireland and New Hanover. It often happens that the subordinate chains are individually terminated by a larger island than the others of which they are composed. For instance, Ota heite, Owhyhce, and Tierra del Espiritu Santo, are

CHAP L

covery.

found at the extremity of a series, most of which present very contracted limits.

These analogies, if carefully noted, might, it is imagined, have facilitated the progress of discovery, and in particular have contributed to make each archipelago Guide to dis- more easily recognised. By attentively marking the direction of a chain, navigators might have rendered themselves almost certain of discovering new islands; and even now they ought to employ the guidance of a principle which would, in some measure, obviate the hazard occasioned by those immense reefs so common in the Southern Pacific, which, in all probability, follow the direction of chains at the bottom of the ocean. These huge projections make a part of the exterior skeleton of the earth, and radiate like lines from a common centre, or more probably like ribs from the vertebral column of the human figure. At all events, there is a perceptible uniformity in the operation of the law to which these phenomena must be attributed; and when the physical cause is once ascertained, there cannot be any doubt that much practical benefit would result from anticipating its effects, even in cases where there is no other light to direct the judgment.

The volcanic islands.

Among the thousands of islands which shoot up in the South Sea, some rise to a considerable elevation, and generally present a conical form. Many of them are basaltic, often containing in their centres wide tunnels or cavities, and, at other times, round lakes which might be taken for ancient craters. Although the occurrence of volcanic substances has not, on satisfactory evidence, been every where ascertained, there has already been discovered a greater number of volcanoes than in any other part of the world. In the annals of early navigation these are sometimes mentioned as the most splendid appearances in nature; while, on other occasions, they are described with a feeling of unmingled horror. On one place near New Guinea, the flames and smoke rise calmly over a fruitful country; but on the northern verge of the Marians, dreadful torrents of black lava darken the shore

All the low islands seem to have for their base a reef CHAP. L of coral rocks generally disposed in a circular form. The coral The middle space is commonly occupied by a sheet of islands. water, on the margin of which the sand is mixed with pieces of broken coral and other marine productions. These facts have been employed by speculative writers with the view of proving that all the islets must have originated in the labours of the diminutive insect already noticed, and been afterwards enlarged and raised above the surface of the ocean by the accumulation of light substances drifted to them by the action of the waves. It is, however, very remarkable, that among the islands so constituted, some are almost level with the sea, while others are elevated several hundred feet; though on the summits of these last are found masses of coral perforated in the same manner with those found at the water's edge. Now, as the animalcules which raise these submarine habitations cannot live above the face of the deep, it is manifest either that the Pacific has sunk to a lower level, or that the several islands have been raised by an expansive force acting from below. There can be no doubt that the latter agent ought to be assigned as the true cause of the phenomenon.

ous polypes.

It is still a question whether the polypes originate The saxigenthe stoney bodies they inhabit, or whether they find them prepared for their occupation by the hand of nature. Forster, whose experience gives some weight to his opinions on this subject, was inclined to believe that the little creatures actually form the matter which composes the coral masses, and consequently that, by their means, new islands are in a constant process of formation. The great Captain Cook, after a careful investigation of facts, had arrived at the same conclusion. Dalrymple, on the other hand, thinks that these rocks take their rise at the bottom of the sea, from which they are detached by currents or tempests, and thrown on the sandbanks. This, no doubt, may take place in some localities; but the principle most assuredly cannot apply to those reefs which rise like walls in the midst of the ocean. Around New Holland, for example, the

CHAP. I. rocks in question ascend, like perpendicular ramparts, from a very great depth. Such structures, it is obvious, must derive their origin from the animals themselves, unless we attempt to account for them on the grounds of a new hypothesis, which intimates that they may grow in a manner similar to the common seaweed, and that the insects found on them are analogous to those which take up their abode on trees and herbs; a conclusion to which the arborescent appearance of some corals, and the fungous forms of others, are supposed to give a certain degree of countenance.

Operations of By some authors these animalcules are called saxithe polypes. genous, or rock-making, polypes. They are supposed to begin their operations by selecting a suitable spot, such as the summit of a volcano, or the top of a submarine mountain. Having chosen their site, with a reference, it should seem, to an ultimate object, they work with incredible diligence until they reach the surface, above which, as we have already stated, their nature and habits do not permit them to proceed. Mr Lyell remarks, that the circular or oval forms of the numerous coral isles of the Pacific, with the lakes in their centre, naturally suggest the idea that they are nothing more than the crests of submarine volcanoes, having the rims and bottoms of their craters overgrown with coral. This opinion is strengthened by the conical shape of the islands, and the acute angle at which they plunge on all sides into the surrounding ocean. It has also been observed, that although within the circular reefs there is usually The lagoons nothing discernible but a lagoon, the bottom of which is covered with coral, yet within some of these basins, rocks, composed of porous lava and other volcanic substances, rise up, resembling eminences of igneous origin which have been formed in an epoch not beyond the limits of human observation.*

It is stated by Mr Forster that the polypes raise their

Lyell's Principles of Geology (4 vols 12mo, 5th edition, Lond. 1837), vol. iii. pp. 287, 288. Dalrymple's Historical Collection of Voyages and Discovery in the South Pacific Ocean (4to, Lond. 1770), p. 22. `

CHAP. I

reefs.

habitation gradually from a small base, always spreading more and more in proportion as the structure grows higher. The materials, he adds, are a kind of lime mixed with some animal substance. A few miles to the leeward of Turtle Island there was observed a considerable reef, over which the sea broke at all points, The coral and no part of it was entirely under water. East and north-east of the Society group are numerous islets which are only partially raised above the surface; while in some clusters the elevated portions are connected by reefs occasionally dry at ebb-tide. The insects inhabiting these dikes appear as if desirous to shelter their dwelling from the impetuosity of the winds and the rage of the ocean; but as within the tropics the current of air commonly proceeds from one quarter, they, by instinct, endeavour to extend a ledge enclosing a lagoon, which is thereby entirely screened against the power both of the waves and of the breeze. This process, which is not inconsistent with the opinion entertained by Mr Lyell, is generally admitted to be the most probable cause whence have originated those low islands which stud the intertropical latitudes of the Great South Sea.*

islands.

But the High Islands, such as appear decidedly to The high have had an igneous origin, are more important, viewed as the habitations of man, than the coral ridges just described. It has been already remarked that nearly all the regions of the Pacific bear the most unequivocal marks of having been the scene of volcanic action on a vast scale, and that the prevailing features of the larger masses of land confirm the inference which may still be drawn from the imperfect traditions of the people. Some of the isles present volcanoes in a state of activity; others exhibit only the form and altitude which denote a similar origin in remote ages; while a third class display undoubted tokens of having been violently changed by the force of subterranean fire, if not by the more

* Forster's Observations, p. 149-151.

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