DARWIN AND WALLACE 3 1 



coast. On leaving the Galapagos group, Charles Dar- 

 win writes in his diary the suggestive observation 

 that this little group of rocky islands seems to be one 

 of the greatest centers of creative activity. It was 

 this interesting resemblance of the animals of these 

 islands to each other and to those of the Peruvian 

 coast that finally persuaded Darwin that they were 

 all related and were all descended from those of Peru. 

 For the rest of his life, with an intensity which in- 

 creased with each year, Darwin persisted in a patient 

 search for the possible agencies by which such change 

 could have been brought about. The problem, how- 

 ever, was temporarily eclipsed by a pressing geological 

 question aroused by his visit to the Keeling Atoll. 

 Here his investigation of coral reef formation abso- 

 lutely captivated him. In the case of most coral 

 islands in the Pacific Ocean the reef exists as a circle 

 of coral enclosing a lagoon of water. In the center 

 of this lagoon stands commonly a rocky island. It is 

 plain that this is the foundation on which the coral 

 built. But, in the case of the Atoll, the coral ring was 

 present and so was the internal lagoon, but there was 

 no rocky island. The key to the solution came with 

 an interesting discovery. Darwin began to put down 

 a grappling' iron on the outer side of the reef and 

 to drag up coral. The farther away from the reef he 

 went the deeper was the water from whose bottom he 



