. Corals and coral islands. Coral reefs and islands; Corals. 1^6 CORALS AND CORAL fSLAXDS. 4<» 10 ratJivnjs. to 20 r"} atoll being freely exposed to the waters of the open sea. When the channels are narrow, or few in number, although the lagoon be of great size and depth (as in Suadiva), there are no ring-formed reefs; where the channels are somewhat broader, the margmal portions of reef, and especially those close to the larger channels, are ring-formed, but the central ones are not so : where they are broadest, almost every reef throughout the atoll is more or less perfectly ring-for
. Corals and coral islands. Coral reefs and islands; Corals. 1^6 CORALS AND CORAL fSLAXDS. 4<» 10 ratJivnjs. to 20 r"} atoll being freely exposed to the waters of the open sea. When the channels are narrow, or few in number, although the lagoon be of great size and depth (as in Suadiva), there are no ring-formed reefs; where the channels are somewhat broader, the margmal portions of reef, and especially those close to the larger channels, are ring-formed, but the central ones are not so : where they are broadest, almost every reef throughout the atoll is more or less perfectly ring-formed. Although their presence is thus contingent on the openness of the marginal channels, the theory of their formation, as we shall hereafter see, is included in that of the parent atolls, of which they form the separate ;' The G?'€at Chagos Bank. — This bank lies about ten degrees south of the Maldives, and is ninety miles long and seventy in its greatest breadth. It is a part of the Chagos Group, in which there are some true atolls, some bare atoll-reefs, and others, like the Great Chagos Bank, that are quite submerged, or nearly so. Its rim is mostly from four to ten fathoms under water. Mr. Darwin confirms the opi- nion of Captain Moresby, that this bank has the character of a lagoon reef, resembling one of the Maldives; and he states, on the evidence of extensive soundings, that, if raised to the surface, it would actually become a coral island, vrith a lagoon. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Dana, James Dwight, 1813-1895. London : Sampson Low, Marston, Low and Searle
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Keywords: ., bookauthordanajame, bookcentury1800, bookdecade1870, bookyear1875
