126 ON CORAL AND CORAL REEFS 



If, as we have supposed, the sea could be suddenly 

 withdrawn from around an island provided with a 

 fringing reef, such as the Mauritius, the reef would 

 present the aspect of a terrace, its seaward face, one 

 hundred feet or more high, blooming with the animal 

 flowers of the coral, while its surface would be hol- 

 lowed out into a shallow and irregular moat-like exca- 

 vation. 



The coral mud, which occupies the bottom of the 

 lagoon, and with which all the interstices of the coral 

 skeletons which accumulate to form the reef are filled 

 up, does not proceed from the washing action of the 

 waves alone; innumerable fishes, and other creatures 

 which prey upon the coral, add a very important con- 

 tribution of finely-triturated calcareous matter ; and the 

 corals and mud becoming incorporated together, 

 gradually harden and give rise to a sort of limestone 

 rock, which may vary a good deal in texture. Some- 

 times it remains friable and chalky, but, more often, 

 the infiltration of water, charged with carbonic acid, 

 dissolves some of the calcareous matter, and deposits 

 it elsewhere in the interstices of the nascent rock, thus 

 glueing and cementing the particles together into a 

 hard mass ; or it may even dissolve the carbonate of lime 

 more extensively, and re-deposit it in a crystalline 

 form. On the beach of the lagoon, where the coral 

 sand is washed into layers by the action of the waves, 

 its grains become thus fused together into strata of a 

 limestone, so hard that they ring when struck with a 

 hammer, and inclined at a gentle angle, corresponding 

 with that of the surface of the beach. The hard parts 

 of the many animals which live upon the reef become 

 imbedded in this coral limestone, so that a block may 

 be full of shells of bivalves and univalves, or of sea- 



