82 DISTRIBUTION OF CORAL-REEFS. Ch. IV. 



of the Gfalapagos Islands, 1 to the coldness of the cur- 

 rents from the south, but the Grulf of Panama is one 

 of the hottest pelagic districts in the world. 2 In the 

 central parts of the Pacific there are islands entirely 

 free from reefs ; and in some of these cases this appears 

 to be due to recent volcanic action : but the existence 

 of reefs, though scantily developed, and according to 

 Dana, confined to one part of Hawaii (one of the Sand- 

 wich Islands), shows that recent volcanic action does 

 not absolutely 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 navigators that 

 there are no coral-reefs on the west coast of Africa, 3 or 



1 The mean temperature of the surface sea from observations made 

 by the direction of Captain FitzRoy on the shores of the Galapagos 

 Islands, between the 16th of September and the 20th of October, 1835, 

 was 68° Fahr. The lowest temperature observed was 58° *5 at the 

 S."W. end of Albemarle Island ; and on the west coast of this island, it 

 was several times 62° and 63°. The mean temperature of the sea in 

 the Low Archipelago of atolls, and near Tahiti, from similar observa- 

 tions made on board the Beagle, was (although further from the 

 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. 



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



3 It might be concluded, from a paper by Captain Owen (Geograph. 

 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 re- 

 semble those in the West Indies. 



