- [Footnote: in corals, and on the other side in the three long-extended
groups or series of Atolls of the Laccadives, the Maldives, and Chagos. The latter series, called by navigators the Chagos-bank, forms a lagoon encircled by a narrow and already much broken, and in great measure submerged, coral reef. The longer and shorter diameters of this lagoon, or its length and breadth, are respectively 90 and 70 geographical miles. Whilst the enclosed lagoon is only from seventeen to forty fathoms deep, the depth of water at a small distance from the outer margin of the coral, (which appears to be gradually sinking), is such, that at half a mile no bottom was found in sounding with a line of 190 fathoms, and, at a somewhat greater distance, none with 210 fathoms. (Darwin, Structure of Coral Reefs, p. 39, 111, and 183.) At the coral lagoon called Keeling-Atoll, Captain Fitz-Roy, at a distance of only two thousand yards from the reef, found no soundings with 1200 fathoms.
"The corals which, in the Red Sea, form thick wall-like masses, are species of Meandrina, Astræa, Favia, Madrepora (Porites), Pocillopora (hemprichii), Millepora, and Heteropora. The latter are among the most massive, although they are somewhat branched. The corals which lie deepest below the surface of the water in this locality, and which, being magnified by the refraction of the rays of light, appear to the eye like the domes or cupolas of a cathedral or other large building, belong, so far as we were enabled to judge, to Meandrina and Astræa." (Ehrenberg, manuscript notices.) It is necessary to distinguish between separate and in part]*
