32 THE MEANING OF EVOLUTION 
pulled the coral. What 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 
