ALEXANDER AGASSIZ 113 



ocean. It was observed that the thinner and more delicate 

 shells disappeared first from the marine deposits with 

 increasing depth, and only the thicker and more compact 

 shells or their fragments reached the greater depths. These 

 conclusions were verified again and again during the cruise 

 of the ' Challenger,' and subsequently by Agassiz in his 

 expeditions. Evidently the calcareous shells were removed 

 by the solvent action of sea water as they fell towards, or 

 shortly after they reached, the bottom of the ocean. In the 

 shallower depths the majority of the shells reached the 

 bottom before being completely dissolved, and there accumu- 

 lated. The solvent action was also retarded, in these lesser 

 depths, through the sea water in direct contact with the 

 deposit becoming saturated, and therefore unable to take up 

 more lime. The explanations thus given to account for the 

 disappearance of carbonate of lime from deep-sea deposits 

 were then applied to the interpretation of the phenomena of 

 coral atolls and barrier reefs. It was argued that all the 

 characteristic features of atolls and barrier reefs could be 

 explained by a reference to the biological, mechanical, and 

 chemical processes everywhere going on in the ocean without 

 calling in the extensive subsidences demanded by the 

 theories of Darwin and Dana." 



Alexander Agassiz's examination of the coral growths on 

 the coast of Florida in his first cruise in the " Blake," 

 supported by w^hat he had seen of the " Challenger " results, 

 excited an interest which lasted during the remainder of his 

 life, and gave rise to many special expeditions for the 

 purpose of exploring reefs in all parts of the tropical seas. 

 It may be said that the last thirty years of his life were given 

 over to the investigation of coral reef problems. He devoted 

 himseK to accumulating facts, and was on all occasions averse 

 to committing himself to theoretical views. He certainly 

 held that the explanations given by Darwin and Dana of the 

 formation of an atoll could only be of limited application, if 

 even that. And there is no doubt that, as the result of his 



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