34 ATOLLS. Ch. I. 



does not state that the masses of Nulliporae form 

 points or a mound, higher than the flat, yet I believe 

 that this is the case ; for Kotzebue, 1 in another part, 

 speaks of the rocks on the edge of the reef ' as visible 

 for about two feet at low-water,' and these rocks we 

 may feel certain are not formed of true coral. 2 

 Whether a smooth convex mound of Nulliporse, like 

 that which appears as if artificially constructed to 

 protect the margin of Keeling Island, is of frequent 

 occurrence round atolls, I know not; but we shall 

 presently meet with it under precisely the same form, 

 on the outer edge of the \ barrier reefs ' which encircle 

 the Society Islands. 



There appears to be scarcely a feature in the 

 structure of Keeling reef, which is not of common, if 

 not of universal occurrence, in other atolls. Thus 



able surf, were completely enveloped with a layer of Nullipora. The 

 entire surface over many square inches, was coloured of a peach-blossom 

 red ; the layer, however, was of no greater thickness than paper. 

 Another kind, in the form of projecting knobs, grew in the same situa- 

 tion. These Nulliporse are closely related to those described on the 

 coral-reefs, but I believe are of different species. 



1 Kotzebue' s First Voyage, vol. ii. p. 16. Lieut. Nelson, in his ex- 

 cellent memoir in the Geological Transactions (vol. ii. p. 105), alludes 

 to the rocky points mentioned by Kotzebue, and infers that they consist 

 of Serpulse, which compose incrusting masses on the reefs of Bermudas, 

 as they likewise do on a sandstone-bar off the coast of Brazil, as de- 

 scribed by me in the London Phil. Journal, Oct. 1841. I have added 

 my description as a short supplement to the present volume. These 

 masses of Serpulse hold the same position, relatively to the action of 

 the sea, with the Nulliporee On the coral-reefs in the Indian and Pacific 

 oceans. 



2 Capt. Moresby, in his valuable paper ' On the Northern Atolls of 

 Maldivas' (Geographical Journal, vol. v.), says that the edges of the 

 reefs there stand above water at low spring tides. 



