22 THE MEANING OF EVOLUTION 



pulled the coral, \\liat at first puzzled him was the 

 fact that so long as he dragged up his coral from 

 depths of a hundred feet or less the coral was alive. 

 Whenever he went to depths of much more than a 

 hundred feet, his coral was always dead, though he 

 was evidently pulling it from situations in which it had 

 grown. Then Darwin remembered the rising Andes, 

 lifting themselves out of the bed of the Pacific. Here 

 was the correlated movement. The bottom of the 

 ocean here was sinking. As it sank it dragged down 

 the corals with it. But the descent was so slow that 

 new corals could build on top of the others fast 

 enough to keep the reef up to the surface of the water. 

 At the rate of growth of coral, this would seem to 

 mean that the bottom could be sinking at a rate of 

 only a few feet a century. But while the reef could 

 keep up to the surface, the rocky island must slowly 

 sink. Darwin inferred that there must be a rocky 

 summit within the lagoon, below the surface of the 

 water. A little sounding soon discovered this island, 

 and the verification of Darwin^s theory of coral reef 

 formation was at hand. The description of this Atoll 

 and of his theory of its formation won for Darwin 

 the esteem of geologists when he later presented it 

 in book form. 



The voyage was continued around the Cape of 

 Good Hope. Pursuing the usual course of sailing 



