CORAL REEFS 277 



last century both Louis Agassiz and Le Conte had felt 

 the difficulty of applying Darwin's theory of subsidence 

 to the conditions existing along the Straits of Florida. 

 Semper, who in 1863 visited the Pelew Islands, was 

 satisfied that the theory did not offer an explanation of 

 the formation of the coral reefs of that region ; and 

 Murray had returned from the voyage of the Challenger 

 convinced of the fallacy of the conception. Mr. Henry 

 0. Forbes, who visited Keeling Atoll some forty years 

 after Darwin, could not . satisfy himself that there was 

 any proof of subsidence there, or tbat the causes cited by 

 the opponents of Darwin's theory were not sufficient 

 to account for all the phenomena he observed. When 

 Agassiz was in Edinburgh, helping to distribute the 

 collections of the Challenger, he and Murray had many 

 talks on the subject, and Agassiz then expressed his 

 hope of investigating the question for himself. 



During his cruise on the Blake, Agassiz satisfied him- 

 self that Darwin's theory could not account either for 

 the formation of the Florida Reefs, or the Alacran Reef, 

 an atoll-shaped coral growth to the north of Yucatan. 

 For it seemed evident to him that subsidence could not 

 offer a correct explanation for events that had taken 

 place in regions of elevation, or districts that had long 

 remained stationary. He reached the conclusion that the 

 coral reefs of these localities had begun their growths 

 on banks which had been built up by various agen- 

 cies until they had reached a point where the depth was 

 suitable for the growth of corals, and that in this region 

 the coral reefs were a comparatively thin crust resting 

 on such foundations. The accuracy of this view for that 

 district is believed to have now been settled by the ex- 

 aminations of the borings of artesian wells, which show 



