360 THE BEAUTIES OF NATURE CHAP. 



feet above the level of the water, and bear 

 generally groups of tufted Cocoa Palms. 



It used to be supposed that these were the 

 summits of submarine volcanoes on which the 

 coral had grown. But as the reef-making 

 coral does not live at greater depths than 

 about twenty-five fathoms, the immense 

 number of these reefs formed an almost 

 insuperable objection to this theory. The 

 Laccadives and Maldives for instance mean- 

 ing literally the " lac of or 100,000 islands," 

 and the " thousand islands" are a series of 

 such atolls, and it was impossible to imagine 

 so great a number of craters, all so nearly of 

 the same altitude. 



In shallow tracts of sea, coral reefs no 

 doubt tend to assume the well-known circular 

 form, but the difficulty was to account for 

 the numerous atolls which rise to the surface 

 form the abysses of the ocean, while the coral- 

 forming zoophytes can only live near the 

 surface. 



Darwin showed that so far from the 

 ring of corals resting on a corresponding 

 ridge of rocks, the lagoons, on the contrary, 



