CORAL-REEFS. 85 



coldness of the currents from the south, but the Gulf of 

 Panama is one of the hottest pelagic districts in the world. 1 

 In the central parts of the Pacific there are islands entirely 

 free from reefs ; in some few of these cases I have thought 

 that this was owing to recent volcanic action ; but the 

 existence of reefs round the greater part of Hawaii, one of 

 the Sandwich Islands, shows that recent volcanic action 

 does not necessarily prevent their growth. 



In the last chapter I stated that the bottom of the sea 

 round some islands is thickly coated with living corals, 

 which nevertheless do not form reefs, either from insufficient 

 growth, or from the species not being adapted to contend 

 with the breaking waves. 



I have been assured by several people, that there are no 

 coral-reefs on the west coast of Africa, 2 or round the islands 

 in the Gulf of Guinea. This perhaps may be attributed, 

 in part, to the sediment brought down by the many rivers 

 debouching on that coast, and to the extensive mud-banks, 

 which line great part of it. But the islands of St. Helena, 

 Ascension, the Cape Verdes, St. Paul's, and Fernando 

 Noronha, are, also, entirely without reefs, although they 

 lie far out at sea, are composed of the same ancient 

 volcanic rocks, and have the same general form, with those 



equator) 77 '5°, the lowest any day being 76*5°. Therefore we have 

 here a difference of 9*5° in mean temperature, and 18 in extremes; 

 a difference doubtless quite sufficient to affect the distribution of organic 

 beings in the two areas. 



1 Humboldt's Personal Narrative, vol. vii. p. 434. 



2 It might be concluded, from a paper by Capt. Owen {Geography 

 Journ., vol. ii. p. 89), that the reefs off Cape St. Anne and the 



Sherboro' Islands were of coral, although the author states that they 

 are not purely coralline. But I have been assured by Lieut. Holland, 

 R.N., that these reefs are not of coral, or at least that they do not at 

 all resemble those in the West Indies. 



