268 CORALS AND CORAL LSLANDS. 



the most efficient cause of their absence, both directly, 

 through their fresh waters, and through the detritus they 

 transport and distribute along the shores. It will be observed 

 that this agent, so ineffectual on small islands, is one of vast 

 influence upon larger lands. Mr. Darwin alludes to small 

 patches of coral in the Persian Gulf. Ceylon has some fring- 

 ing reefs. 



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

 purely of coral. Of this character are the Laccadives, Mal- 

 dives, Keehng's, Saya-de-Malha, Almirante, and Cosmoledo. 

 The Chagos Group is of the same character, and the shoal 

 Cargados is probably similar. The Seychelles are small islands 

 with extensive reefs. 



Madagascar has a fringing reef upon its south-western point, 

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

 above : also on the north and eastern shores far down as 

 latitude i8° 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 i6° 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 

 Konfodah. This long continental reef may at first be deemed 

 a little remarkable, after what has been stated about such reefs 

 elsewhere. 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, therefore, an interesting elucidation of the subject 

 under consideration, and confirms the view taken to account 

 for the absence of reefs from many continental 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 occur- 

 ring, are common. 



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

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



