WONDERS OF THE DEEP 77 



and in this way a kind of island is formed down 

 on the ocean bed. 



This is always going on, and thus the low island 

 gradually rises through the addition of further rock 

 material brought to it by the ocean waves and 

 currents, until at last the reef has grown as high 

 as the surface of the water. 



Before long the reef becomes covered with a 

 layer of soil, which is washed on to it by the 

 waves. The seeds which this soil may contain, and 

 those which may be dropped on t® it by the birds, 

 germinate, and not very long after varied forms 

 of tropical and sub-tropical plant life begin to 

 make their appearance, and in this way the coral 

 island, originally quite bare, is clothed with a most 

 luxuriant vegetation. In some instances the original 

 island has completely sunk below the level of the 

 water, leaving the fringe of a reef surrounding a 

 central lagoon. Charles Darwin, one of the most 

 eminent scientists of the nineteenth century, made 

 a special study of the structure and distribution 

 of coral reefs. He has described the lagoon islands, 

 or atolls, as they are called, as " vast rings of 

 coral rock, often many leagues in diameter, here 

 and there surmounted by a low, verdant island, 

 with dazzling white shores, bathed on the outside 

 by the foaming breakers of the ocean ; and on the 

 inside surrounding a calm expanse of water, 

 which, from reflection, is of a bright but pale 

 green colour." He further adds: "The naturalist 

 will feel a deeper astonishment after having 



