PACIFIC AND BEERING'S STRAIT. 261 



second voyage and visited several of the coral islands, c ** A T p « 



J & ' VIII. 



and was founded, no doubt, upon the experience v — - y— 

 which he had derived upon that voyage. But con- iq 2 6. 

 sidering the extent of some of these islands, it is 

 evident that if this be their form, the lythophites, 

 the animals which construct them, must commence 

 their operations at very great depths, a fact which is 

 doubted by naturalists. The general opinion now 

 is, that they have their foundations upon submarine 

 mountains, or upon extinguished volcanoes, which 

 are not more than four or five hundred feet immersed 

 in the ocean ; and that their shape depends upon the 

 figure of the base whence they spring. It would 

 be immaterial which of these theories were correct, 

 were it not that in the latter instance the lagoon that 

 is formed in all the islands of this description might 

 be occasioned by the shape of the crater alone, 

 whereas, in the former, it must result from the pro- 

 pensity of the coral animals, and this, if true, forms 

 a remarkable and interesting feature in their natural 

 history. Mr. Forster* thought this peculiarity might 

 arise from the instinct of the animalcules forming 

 the reefs, which from a desire to shelter their habi- 

 tation from the impetuosity of the winds, and the 

 power and rage of the ocean, endeavoured to con- 

 struct a ledge, within which was a lagoon entirely 

 screened against the power of the elements, and 

 where a calm and sheltered place was by these 

 means afforded to the animals in the centre of the 

 island. 



Another reason why the consideration of the na- 

 ture of their foundation is not immaterial is, that if 

 the form of the islands arose from the peculiar shape 

 * Forster's Observations, 4to, page 150. 



