^58 THE OCEAN. 



I come to tlie volcanic formation. The subsidence 

 still goes on ; and, after a while, the water, 13, /3, is 

 level with the summit of the island, which, of course, 

 is now an island no longer ; the growth of the coral 

 has kept pace with the depression, and it is still at 

 the surface, as at S, S ; the more slowly growing 

 species of the interior are still overflowed, and, as the 

 island is submerged in the centre, the water, 6, e, is 

 no longer an annular channel, but a round lagoon ; 

 and thus we have an atoll, as at first described. The 

 subsequent process of elevating and clothing the new 

 islets is a rapid one. Chamisso observes, "As soon 

 as it has reached such a height that it remaiiis 

 almost dry at low-water at the time of ebb, the 

 corals leave off building higher ; sea-shells, frag- 

 ments of coral, sea-hedgehog shells, and their broken- 

 off pricldes, are united by the burning sun, through 

 the medium of the cementing calcareous sand, which 

 has a'risen from the pulverization of the above-men- 

 tioned shells, into one whole or solid stone, which, 

 strengthened by the continual throwing up of new 

 Tiiaterials, gradually increases in thickness, till it at 

 last becomes so high that it is covered only during 

 some seasons of the year by the spring-tides. The 

 heat of the sun so penetrates the mass of stone when 

 it is dry, that it splits in many places, and breaks off 

 in flakes. These flakes, so separated, are raised one 

 upon another by the waves, at the time of high- 

 water. The always-active surf throws blocks of coral 

 (frequently of a fathom in length, and three or four 

 feet thick), and shells of marine animals, between 

 and upon the foundation stones. After this the cal- 



