CORAL-REEFS. i 1 3 



found in Zetland 1 in Lat. 6o° N, in deep water, and I 

 procured a small species from Tierra del Fuego in Lat. 53 

 S. Capt. Beechey informs me, that branches of pink and 

 yellow coral were frequently brought up from between 20 

 and 25 fathoms off the Low atolls ; and Lieut. Stokes, 

 writing to me from the N.W. coast of Australia, says that a 

 strongly branched coral was procured there from 30 fathoms : 

 unfortunately it is not known to what genera these corals 

 belong. 



Although the limit of depth, at which each particular 

 kind of coral ceases to exist, is far from being accurately 

 known ; yet when we bear in mind the manner in which 

 the clumps of coral gradually became infrequent at about 

 the same depth, and wholly disappeared at a greater depth 

 than 20 fathoms, on the slope round Keeling atoll, on the 

 leeward side of the Mauritius, and at rather less depth, 

 both without and within the atolls of the Maldiva and 

 Chagos Archipelagoes ; and when we know that the reefs 

 round these islands do not differ from other coral forma- 

 tions in their form and structure, we may, I think, conclude 

 that in ordinary cases, reef-building polypifers do not 



living from 92 fathoms. At a greater depth than 90 fathoms off this 

 coral island, the bottom was thickly strewed with joints of Halimeda 

 and small fragments of other Nullipone, but all dead. Captain B. Allen, 

 R.N.j informs me that in the survey of the West Indies it was noticed 

 that between the depth of 10 and 200 fathoms, the sounding lead very 

 generally came up coated with the dead joints of a Halimeda, of which 

 he showed me specimens. Off Pernambuco, in Brazil, in about twelve 

 fathoms, the bottom was covered with fragments dead and alive of 

 a dull red Nullipora, and I infer from Roussin's chart, that a bottom of 

 this kind extends over a wide area. On the beach, within the coral-reefs 

 of Mauritius, vast quantities of fragments of Nulliporse were piled up. 

 From these facts it appears, that these simply organised bodies are 

 amongst the most abundant productions of the sea. 

 1 Fleming's British Animals, genus Caryophyllia. 



873 



