380 ON THE GROWTH OF 



Several different tribes of madrepore contribute to form 

 these coral reefs ; but by far the most abundant are those 

 of the genera carophylla, astrea and meandrina. These 

 Hthophytic animals not only add to the magnitude of land 

 already existing, but, according to some naturalists, they 

 form whole islands. Dr Forster, in his Observations made 

 during a Voyage round the World, gives an account of 

 the formation of these coral islands in the South Sea. 



All the low isles, he says, seem to me to be a produc- 

 tion 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 higher. The materials are a kind of lime mixed 

 with some animal substances. 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 included a large deep lagoon. To the 

 east and north-east of the Society Isles, are a great many 

 isles, which in some parts are above water ; in others, 

 the elevated parts are connected by reefs, some of which 

 are dry at low water, and others are constantly under 

 water. The elevated parts consist of a soil formed by a 

 sand of shells and coral rocks, mixed with a light black 

 mould, produced from putrified vegetables, and the dung 

 of sea-fowls ; and are commonly covered by cocoa-nut 

 trees and other shrubs, and a few antiscorbutic plants. 

 The lower parts have only a few shrubs and the above 

 plants ; others still lower, are washed by the sea at high- 

 water. All these isles are connected, and include a la- 

 goon in the middle, which is full of the finest fish ; and 



