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ON THE CORAL ISLANDS. 



I. THEIR ORIGIN, 



The low islands of the South Sea and Indian Ocean 

 mostly owe their origin to the operations of several 

 species of coral. Their situation with respect to 

 each other, as they often form rows, their union in 

 several places in large groups, and their total ab- 

 sence in otiier parts of the same seas, make us con- 

 clude, that the corals have founded their buildings 

 on shoals in the sea ; or, to speak more correctly, 

 on the tops of mountains lying under water. On 

 the one side as they increase, they continue to 

 approach the surface of the sea, on the other side 

 they enlarge the extent of their work. The larger 

 species of corals, which form blocks measuring 

 several fathoms in thickness, seem to prefer the 

 more violent surf on the external edge of the reef; 

 this, and the obstacles opposed to the continuation 

 of their life, in the middle of a broad reef, by the 

 amassing of the shells abandoned by the animals 

 and fragments of corals, are probably the reason 

 that the outer edge of the reef first approaches 

 the surface. As soon as it has reached such a 

 height, that it remains almost dry at low water, 

 at the time of ebb, the corals leave off building 



