GEOGRAPHICAL DISTRIBUTION. 315 



On the African coast there are coral reefs at Port Natal, 

 in latitude 30° S. ; and here, owing to the warm currents from 

 the tropical regions, the mean winter temperature of the water 

 is not below 68° F. 



Passing from the Indian to the Atlantic Ocean, we find 

 little or no coral on the west coast of Africa. The islands of 

 Cape St. Ann and Sherboro, south of Sierra-Leone, are de- 

 scribed as coral by Captain Owen, R. N., in the Journal of 

 the Geographical Society (vol. ii., p. 89) ; but this has been 

 since denied. The Island of Ascension, in 7° 56' S., and 14° 

 16' W., must have been bordered by growing coral, as Quoy 

 and Gaymard mention that a bed of coral rock may be seen 

 buried beneath streams of lava. Quoy also states that the 

 corals wmich formed these reefs are no longer found alive, and 

 adds that volcanic eruptions have probably destroyed them. 

 The cold polar currents along the western African coast are the 

 cause of the absence of corals from it, to within six or seven de- 

 grees of the equator ; and these cold waters may at times ex- 

 tend still farther north. The same obstacle to the diffusion of 

 species eastward, mentioned as occurring in the Pacific — that is, 

 westward currents — exists also in the Atlantic, and probably 

 with the same effect. 



On the American shores of the Atlantic, north of the 

 equator, there are few reefs, except in the West Indies. The 

 waters of the Orinoco and Amazon, and the alluvial shores 

 they occasion, exclude corals from that part of the coast. 



In the West Indies, the reefs of Florida (p. 204), Cuba, 

 the Bahamas (p. 213), and of many of the eastern islands are 

 well known. On the east coast of Florida they continue up 

 as far as Cape Florida, in latitude 25° 40' N. ; but the 

 west coast is free from them. There are also said to be patches 

 at intervals along the coast of Venezuela and Guatemala ; but 



