Page:Journal of the Royal Geographical Society of London, Volume 1 (2nd edition).djvu/244

216 naturalists and officers attached to the expedition are placed at our disposal.

There are, however, some points of importance to Physical Geography noticed in the narrative, which it would be improper to pass over. We allude more particularly to the information given of the character and formation of the coral islands which are scattered over the great Southern Pacific Ocean, and which appear to be daily forming new abodes for the roving tribes of those archipelagoes. The observations of Captain Beechey on this subject, illustrated by excellent engravings and diagrams, are of great interest. We shall first briefly notice these observations, and then consider the general views which result from them.

Forster, and other naturalists, have imagined that the polypi of the corals build upwards to a certain height, raising their habitation within a little of the surface of the sea, which gradually throws shells, weeds, sand, small bits of coral, and other things, on the tops of these coral rocks, at last fairly raising them out of the water; but Captain Beechey makes the important observation, that it is the abrupt descent of the external margin which causes the sea to break upon it, and prevents these strips being inundated, and the loose sands, divested of any loose materials, heaped upon them, are rarely elevated more than two feet above the level of the sea.

Those parts of the strip which are beyond the reach of the waves are no longer inhabited by the animals that reared them, but have their cells filled with hard, calcareous matter, and present a brown, rugged appearance. The width of the plain, or strips of dead coral, which came under Captain Beechey's observation, in no instance exceeded half a mile, from the usual wash of the sea to the edge of the lagoon, and in general were only about three or four hundred yards. Beyond these limits, on the lagoon side in particular, where the coral was less mutilated by the waves, them was frequently a ledge two or three feet under water at high tides, and thirty to forty yards in width; after which the sides of the island descended rapidly, apparently by a succession of inclined ledges, formed by numerous columns united at their capitals with spaces between them, in which the sounding lead descended several fathoms. The islands slope on both sides by an almost imperceptible inclination to the first ledge. The entrances to the lagoons generally occur on the leeward side, though they are sometimes situated on a side that runs in the direction of the wind, as at Bow Island. All the points or angles of these islands descend into the sea with less abruptness than the sides, and with more regularity. The wedge-shaped spaces that the meeting of the two sides would form in the lagoon is filled up by the ledges being broader there. In such places, as well as in the narrow part of the lake, the polypi are in greater numbers: they appear