Coral Reefs

Page 85

Another lagoon-island has been discovered ("Naut. Mag." 1839, page 770), in 22 deg 4' S., and 136 deg 20' W. Towards the S.E. part of the group, there are some islands of different formation: ELIZABETH Island is described by Beechey (page 46, 4to edition) as fringed by reefs, at the distance of between two and three hundred yards; coloured red. PITCAIRN Island, in the immediate neighbourhood, according to the same authority, has no reefs of any kind, although numerous pieces of coral are thrown up on the beach; the sea close to its shore is very deep (see "Zool. of Beechey's Voyage," page 164); it is left uncoloured. GAMBIER Islands (see Plate I., Figure 8), are encircled by a barrier-reef; the greatest depth within is thirty-eight fathoms; coloured pale blue. AURORA Island, which lies N.E. of Tahiti close to the large space coloured dark blue in the map, has been already described in a note (page 71), on the authority of Mr. Couthouy; it is an upraised atoll, but as it does not appear to be fringed by living reefs, it is left uncoloured.

The SOCIETY Archipelago is separated by a narrow space from the Low Archipelago; and in their parallel direction they manifest some relation to each other. I have already described the general character of the reefs of these fine encircled islands. In the "Atlas of the 'Coquille's' Voyage" there is a good general chart of the group, and separate plans of some of the islands. TAHITI, the largest island in the group, is almost surrounded, as seen in Cook's chart, by a reef from half a mile to a mile and a half from the shore, with from ten to thirty fathoms within it. Some considerable submerged reefs lying parallel to the shore, with a broad and deep space within, have lately been discovered ("Naut. Mag." 1836, page 264) on the N.E. coast of the island, where none are laid down by Cook. At EIMEO the reef "which like a ring surrounds it, is in some places one or two miles distant from the shore, in others united to the beach" (Ellis, "Polynesian Researches," volume i., page 18, 12mo edition). Cook found deep water (twenty fathoms) in some of the harbours within the reef. Mr. Couthouy, however, states ("Remarks," page 45) that both at Tahiti and Eimeo, the space between the barrier-reef and the shore, has been almost filled up,--"a nearly continuous fringing-reef surrounding the island, and varying from a few yards to rather more than a mile in width, the lagoons merely forming canals between this and the sea-reef," that is the barrier-reef. TAPAMANOA is surrounded by a reef at a considerable distance from the shore; from the island being small it is breached, as I am informed by the Rev. W. Ellis, only by a narrow and crooked boat channel. This is the lowest island in the group, its height probably not exceeding 500 feet. A little way north of Tahiti, the low coral-islets of TETUROA are situated; from the description of them given me by the Rev. J. Williams (the author of the "Narrative of Missionary Enterprise"), I should have thought they had formed a small atoll, and likewise from the description given by the Rev. D. Tyerman and G. Bennett ("Journal of Voyage and Travels," volume i., page 183), who say that ten low coral-islets "are comprehended within one general reef, and separated from each other by interjacent lagoons;" but as Mr. Stutchbury ("West of England Journal," volume i., page 54) describes it as consisting of a mere narrow ridge, I have left it uncoloured. MAITEA, eastward of the group, is classed by Forster as a high encircled island; but from the account given by the Rev. D. Tyerman and G. Bennett (volume i., page 57) it appears to be an exceedingly abrupt cone, rising from the sea without any reef; I have left it uncoloured. It would be superfluous to describe the northern islands in this group, as they may be well seen in the chart accompanying the 4to edition of Cook's "Voyages," and in the "Atlas of the 'Coquille's' Voyage." MAURUA is the only one of the northern islands, in which the water within the reef is not deep, being only four and a half fathoms; but the great width of the reef, stretching three miles and a half southward of the land (which is represented in the drawing in the "Atlas of the 'Coquille's' Voyage" as descending abruptly to the water) shows, on the principle explained in the beginning of the last chapter, that it belongs to the barrier class.

Charles Darwin

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