GEOGRAPHICAL DISTRIBUTION. 107 



The islands of the Indian Ocean are, to a great extent, purely 

 of coral. Of this character are the Laccadives, Maldives, Keel- 

 ings, Saya-de-Malha, Almirante, and Cosmoledo. The Chagos 

 shoal is of the same character : and the shoal Cargados is proba- 

 bly similar. The Seychelles are small islands with extensive 

 reefs. We remark here the same fact alluded to above, that 

 reefs abound in the open ocean, though absent from the Conti- 

 nental coasts ; and the same reason may apply to both cases. 



Madagascar has a fringing reef upon its southwestern point, 

 according to Mr. Darwin, and on some parts of the coast above ; 

 also on the north and eastern shores far down as latitude 18° S.* 

 The Comoro Islands, between Madagascar and the continent, 

 have large barrier reefs. 



The eastern coast of Africa has narrow reefs extending north 

 with some interruptions from Mozambique, in latitude 16° S., to 

 a short distance from the equator. Corals also abound in the 

 Red Sea, occurring in some parts on both shores, though most 

 frequent on the eastern, from Tor, in the Gulf of Suez, to Kon- 

 fodah. This long continental reef may at first be deemed a little 

 remarkable, after what we have remarked upon such reefs else- 

 where. Yet the surprise is at once set aside by the striking fact 

 that this whole coast, from the isthmus of Suez south, has no 

 rivers, excepting some inconsiderable streams. It affords, there- 

 fore, an interesting elucidation of the subject under consideration, 

 and confirms the view taken to account for the absence of reefs 

 from the China and South Asiatic coasts. It is a fact almost 

 universal, that where there are large fresh water streams, there 

 are earthy or sandy shores ; and where there are no such streams, 

 rocky shores, though not uniformly occurring, are common. 



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. Anne and Sherboro, south of Sierra-Leone, are described as 

 coral by Captain Owen, R.N.f But this has been since denied. 

 The island of Ascension, in 7° 56' S., and 14° 16' W., must 

 have been formerly bordered by growing coral, as Q,uoy and 

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

 beneath streams of lava. Gtuoy also states that the corals which 

 formed these reefs are no longer found alive, and adds that vol- 

 canic eruptions have probably destroyed them. The cold polar 

 currents along the African coast, although generally leaving about 

 fifteen degrees of latitude within the coral-reef seas, may at 

 times close up and reduce it to still narrower limits. The same 

 obstacle to the diffusion of species eastward, mentioned as occur- 

 ring in the Pacific — that is, westerly currents — exists also in the 

 Atlantic, and probably with the same effect. 



* Darwin, op. cit., p. 187. 



f Journal of the Royal Geographical Society, ii, 89. 



