Coral Reefs

Page 104

and xxv.). There are, however, some ports with deep water, formed by reefs in front of valleys, in the same manner as happens at Mauritius. Captain Beechey, in a letter to me, compares these reefs with those encircling the Society Islands; but there appears to me a marked difference between them, in the less distance at which the Loo Choo reefs lie from the land with relation to the probable submarine inclination, and in the absence of an interior deep water-moat or channel, parallel to the land. Hence, I have classed these reefs with fringing-reefs, and coloured them red.--PESCADORES (west of Formosa). Dampier (volume i., page 416), has compared the appearance of the land to the southern parts of England. The islands are interlaced with coral-reefs; but as the water is very shoal, and as spits of sand and gravel (Horsburgh, volume ii., page 450) extend far out from them, it is impossible to draw any inferences regarding the nature of the reefs.

CHINA SEA.--Proceeding from north to south, we first meet the PRATAS SHOAL (latitude 20 deg N.) which, according to Horsburgh (volume ii., page 335), is composed of coral, is of a circular form, and has a low islet on it. The reef is on a level with the water's edge, and when the sea runs high, there are breakers mostly all round, "but the water within seems pretty deep in some places; although steep-to in most parts outside, there appear to be several parts where a ship might find anchorage outside the breakers;" coloured blue.--The PARACELLS have been accurately surveyed by Captain D. Ross, and charts on a large scale published: but few low islets have been formed on these shoals, and this seems to be a general circumstance in the China Sea; the sea close outside the reefs is very deep; several of them have a lagoon-like structure; or separate islets (PRATTLE, ROBERT, DRUMMOND, etc.) are so arranged round a moderately shallow space, as to appear as if they had once formed one large atoll.-- BOMBAY SHOAL (one of the Paracells) has the form of an annular reef, and is "apparently deep within;" it seems to have an entrance (Horsburgh, volume ii., page 332) on its west side; it is very steep outside.--DISCOVERY SHOAL, also is of an oval form, with a lagoon-like space within, and three openings leading into it, in which there is a depth from two to twenty fathoms. Outside, at the distance (Horsburgh, volume ii., page 333) of only twenty yards from the reef, soundings could not be obtained. The Paracells are coloured blue.--MACCLESFIELD BANK: this is a coral-bank of great size, lying east of the Paracells; some parts of the bank are level, with a sandy bottom, but, generally, the depth is very irregular. It is intersected by deep cuts or channels. I am not able to perceive in the published charts (its limits, however, are not very accurately known) whether the central part is deeper, which I suspect is the case, as in the Great Chagos Bank, in the Indian Ocean; not coloured.--SCARBOROUGH SHOAL: this coral-shoal is engraved with a double row of crosses, forming a circle, as if there was deep water within the reef: close outside there was no bottom, with a hundred fathoms; coloured blue.--The sea off the west coast of Palawan and the northern part of Borneo is strewed with shoals: SWALLOW SHOAL, according to Horsburgh (volume ii., page 431) "is formed, LIKE MOST of the shoals hereabouts, of a belt of coral-rocks, "with a basin of deep water within."--HALF-MOON SHOAL has a similar structure; Captain D. Ross describes it, as a narrow belt of coral-rock, "with a basin of deep water in the centre," and deep sea close outside.--BOMBAY SHOAL appears (Horsburgh, volume ii., page 432) "to be a basin of smooth water surrounded by breakers." These three shoals I have coloured blue.--The PARAQUAS SHOALS are of a circular form, with deep gaps running through them; not coloured.--A bank gradually shoaling to the depth of thirty fathoms, extends to a distance of about twenty miles from the northern part of BORNEO, and to thirty miles from the northern part of PALAWAN.

Charles Darwin

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