50 On the Formation and Growth of Coral Reefs and Islands. 



often encrusted by coral. In various collections, are examples of bottles, 

 npon which very dense corals have colonised themselves ; and there is 

 in the museum of the Bristol Institution, a bottle which was picked up 

 by a diver in Port Royal, Jamaica, to which a dense species of astrea, 

 weighing Mb. 8oz. is adherent. Another specimen of agaricia^ weighing 

 216. 9oz. surrounds a species of oyster, whose age could not be more 

 than two years, and yet it is completely enveloped by this dense coral. 

 And in further proof of the rapidity with which these animals secrete the 

 calcareous matter, we have only to refer to a paper in the Philosophical 

 Transactions, by Capt. Lloyd, who was engaged by liolivar to ascertain 

 the relative levels of the Pacific and Atlantic oceans, and to complete a 

 snrvey of the intervening isthmus of Darien ; wherein he points out the 

 possibility of forming a breakwater across the mouth of Navy Bay, by 

 throwing in coral broken from the adjacent reefs : his attention was called 

 to this by having collected specimens as curiosities, and not being able to 

 carry them away at the time, he returned a short period after, and to his 

 surprise found them permanently soldered to the place whereon he had 

 placed them by their own calcareous deposit. 



We at the same time caution projectors of this kind to take into their 

 mature consideration, whether the foundation might not, by this means, be 

 laid for entirely filling np the harbour, and thus depriving the navy of a port, 

 which it had only intended to make more secure. In fact, the natives of the 

 Polynesian isles have long employed this method for building their jettys, 

 piers, wharfs, fish preserves, &c. At the island of Barabora, a very 

 beautiful pier has thus been formed by the natives, along-side of which a 

 large vessel may lie and discharge, or take in cargo. For a view of this, 

 and much interesting matter respecting these islands, the reader may con- 

 sult Bennet and Tyerman's Mission to the South Sea Islands. 



In a similar manner are vast quantities of shells, &c., encased, fixed, 

 and preserved, either by the hardening of sand, secretion of the calcareous 

 matter before mentioned, or as follows. 



It would appear, that as during the formation of a reef, portions of it 

 become compact, and as dense as any limestone rock; the presumption 

 arises, that w4ien the coral animals die, the animal matter decomposes, 

 and the carbonate of lime, of which tlie coral is composed, will be held in 

 solution , and again, (probably under peculiar circumstances) precipitated 

 of the consistence of paste, entombing shells, corals, fish, &c., which have 

 sufficient animal matter to protect them, by which means they retain their 

 organic form ; in this manner closely resembling the limestones, in which 

 the fossil remains of corals, shells, &c., are so often found ; and, as wc 

 believe, cemented by a paste composed of the lime deri^^ed from their con- 

 geners. 



Among these islands it is not uncommon to see extensive beds, or 

 strata, of particular species of shells, deposited along the shores in the 



