98 CORAL-REEFS. 



many individuals, — first one being broken off or killed by 

 some accident, and then another, and one set of species 

 being replaced by another set with different habits, as the 

 reef rose nearer the surface, or as other changes supervened. 

 The spaces between the corals would become filled up with 

 fragments and sand, and such matter would probably soon 

 be consolidated, for we learn from Lieut. Nelson, 1 that at 

 Bermuda a process of this kind takes place beneath water, 

 without the aid of evaporation. In reefs, also, of the 

 barrier class, we may feel sure, as I have shown, that 

 masses of great thickness have been formed by the growth 

 of the coral ; in the case of Vanikoro, judging only from the 

 depth of the moat between the land and the reef, the wall 

 of coral-rock must be at least 300 feet in vertical thickness. 



It is unfortunate that the upraised coral-islands in the 

 Pacific have not been examined by a geologist. The cliffs 

 of Elizabeth Island, in the Low Archipelago, are eighty feet 

 high, and appear, from Captain Beechey's description, to 

 consist of a homogeneous coral-rock. From the isolated 

 position of this island, we may safely infer that it is an 

 upraised atoll, and therefore that it has been formed by 

 masses of coral, grown together : Savage Island seems, from 

 the description of the younger Forster, 2 to have a similar 

 structure, and its shores are about forty feet high : some of 

 the Cook Islands also appear 3 to be similarly composed. 

 Capt. Belcher, R.N., in a letter which Capt. Beaufort 

 showed me at the Admiralty, speaking of Bow atoll, says, 

 " I have succeeded in boring forty-five feet through coral- 

 sand, when the auger became jammed by the falling in of 

 the surrounding creamy matter." On one of the Maldiva 



1 Geological Transactions, vol. v. p. 113. 



2 Forster's Voyage round the World with Cook, vol. ii. pp. 163, 167. 

 5 Williams's Narrative of Missionary Enterprise, p. 30. 



