CORAL ISLANDS. 389 



all those reefs, those girdles of madrepore, which are so 

 frequently met with in the South Sea, to the leeward of 

 islands, are shoals depending upon the conformation of 

 the original ground, which will be perceived to belong 

 to it when the direction of the mountains and hills has 

 been attentively observed. It is always where the slopes 

 are gentle, and the sea shallowest, that the greatest masses 

 of madrepores are found. They sprout up if it is calm ; 

 in the contrary case, they form only scattered tufts, be- 

 longing to species which seem to be least affected by the 

 agitation of the waters. 



It has been said, and it is even a matter of general be- 

 lief among mariners, say MM. Quoy and Gaimard, that 

 there occur in the equatorial seas shoals composed of co- 

 rals, which rise from the greatest depths, like walls at the 

 bottom of which the sounding line finds no ground. The 

 fact certainly does exist in so far v* regards the depth 

 spoken of ; and it is this very o*cumstance which is pro- 

 ductive of so much danger to vessels, which, when taken 

 in a calm and carried away by currents, cannot cast anchor 

 in such places. But it is not correct to say that these 

 reefs are entirety formed of madrepores. First, because 

 the species which always form the most considerable banks, 

 such as some meandrinae, certain caryophylleae, but espe- 

 cially the astreae, adorned with the most beautiful and 

 velvety colours, require the influence of light to per- 

 fect them ; because they are not seen to grow beyond a 

 few yards of depth ; and because they cannot consequent- 

 ly be developed at a depth of ten or twelve hundred feet, 

 as they would necessarily be, did they raise the cliffs in 

 question. Besides, these different species of animals 

 would then almost exclusively enjoy the privilege of living 



