42 CORAL-REEFS. 



and I have no doubt it is of general occurrence, although, 

 according to Ehrenberg, the reefs of the Red Sea offer 

 an exception. Chamisso observes that " the red colour 

 of the reef (at the Marshall atolls) under the breakers is 

 caused by a Nullipora, which covers the stone wherever 

 the waves beat ; and, under favourable circumstances, 

 assumes a stalactical form," — a description perfectly applic- 

 able to the margin of Keeling atoll. 1 Although Chamisso 

 does not state that the masses of Nulliporse form points 

 or a mound, higher than the flat, yet I believe that this 

 is the case ; for Kotzebue, 2 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 quite 

 certain are not formed of true coral. 3 Whether a smooth 

 convex mound of Nulliporse, like that which appears as 



1 Kotzebue's First Voyage, vol. iii. p. 142. Near Porto Praya, 

 in the Cape de Verde Islands, some basaltic rocks, lashed by no in- 

 considerable surf, were completely enveloped with a layer of Nulliporse. 

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

 blossomed red ; the layer, however, was of no greater thickness 

 than paper. Another kind, in the form of projecting knobs, grew in 

 the same situation. These Nulliporse are closely related to those 

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



2 Kotzebue's First Voyage, vol. ii. p. 16. Lieut. Nelson, in his 

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

 alludes to the rocky points mentioned by Kotzebue, and infers that 

 they consist of Serpulas, which compose incrusting masses on the reefs 

 of Bermudas, as they likewise do on a sandstone bar off the coast of 

 Brazil (which I have described in London Phil. Journal, Oct. 1841). 

 These masses of Serpulae hold the same position, relatively to the 

 action of the sea, with the Nulliporse on the coral-reefs in Indian 

 and Pacific Oceans. 



3 Captain 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. 



