21 (J O.N CORAL ISLANDS. 



15. p. 51. 



On Coral Islands. 



Of all the genera of lythophytes, the madrepore is the 

 most abundant. It occurs most frequently in tropical 

 countries, and decreases in number and variety as we ap- 

 proach the poles. It encircles in prodigious rocks and 

 vast reefs many of the basaltic and other rocky islands in 

 the South Sea and Indian Ocean, and by its daily growth 

 adds to their magnitude. The coasts of the islands in 

 the West Indies, also those of the islands on the east 

 coast of Africa, and the shores and shoals of the Red 

 Sea, are encircled and incrusted with rocks of coral. 

 Several different species of madrepore contribute to 

 form these coral reefs ; but by far the most abundant 

 is the muricated madrepore, madrepora muricata of Lin- 

 naeus. These lithophytic animals not only add to the 

 magnitude of land already existing, but, as Cuvier re- 

 marks, they form whole islands. Dr. Forster, in his Ob- 

 servations made during a Voyage round the World, gives 

 a curious account of the formation of these coral islands 

 in the South Sea. 



All the low isles, he says, seems to me to be a production 

 of the sea, or rather its inhabitants, the polype-like animals 

 forming the lithophytes. These animalcules raise their 

 habitation gradually from a small base, always spreading 

 more and more, in proportion as the structure grows high- 

 er. The materials are a kind of lime mixed with some 

 animal substance. I have seen these large structures in 

 all stages, and of various extent. Near Turtle Island, we 

 found, at a few miles distance, and to leeward of it, a 

 considerable large circular reef, over which the sea broke 

 every where, and no part of it was above water ; it in- 

 cluded a large deep lagoon. To the east and north-gast 



