ioo CORAL-REEFS. 



in width. The land has the extraordinary breadth of three 

 miles; it consists of parallel ridges of shells and broken 

 corals, which furnish " an incontestable proof," as observed 

 by Cook, 1 "that the island has been produced by accessions 

 from the sea, and is in a state of increase." The land is 

 fronted by a coral-reef, and from the manner in which islets 

 are known to be formed, we may feel confident that the reef 

 was not three miles wide, when the first, or most backward 

 ridge, was thrown up; and, therefore, we must conclude 

 that the reef has grown outwards during the accumulation 

 of the successive ridges. Here then, a wall of coral-rock 

 of very considerable breadth has been formed by the out- 

 ward growth of the living margin, within a period during 

 which ridges of shells and corals, lying on the bare surface, 

 have not decayed. There can be little doubt, from the 

 account given by Capt. Beechey, that Matilda atoll, in the 

 Low Archipelago, has been converted in the space of thirty- 

 four years, from being, as described by the crew of a 

 wrecked whaling vessel, a "reef of rocks" into a lagoon- 

 island, fourteen miles in length, with " one of its sides 

 covered nearly the whole way with high trees." 2 The islets, 

 also, on Keeling atoll, it has been shown, have increased 

 in length, and since the construction of an old chart, several 

 of them have become united into one long islet; but in this 

 case, and in that of Matilda atoll, we have no proof, and 

 can only infer as probable, that the reef, that is the founda- 

 tion of the islets, has increased as well as the islets 

 themselves. 



After these considerations, I attach little importance, as 

 indicating the ordinary and still less the possible rate of 

 outward growth of coral-reefs, to the fact that certain reefs 



1 Cook's Third Voyage, book iii. chap. x. 



2 Beechey's Voyage to the Pacific, chap. vii. and viii. 



