150 bulletin: museum of comparative zoology. 



by himself and his assistants dealing more or less directly with these 

 subjects. It can truly be said that he visited, explored, and described 

 with much detail every important coral-reef region of the world, in 

 the Atlantic, Pacific, and Indian Oceans. 



Agassiz's special interest in the coral-island problem was apparently 

 first awakened during his visit to Edinburgh in 1876. I had sketched 

 out a series of papers to be presented to the Royal Society of Edin- 

 burgh during that session, and he heard the first of these read, viz., 

 "The Distribution of Volcanic Debris over the Floor of the Ocean, 

 its Character, Source, and some of the Products of its Disintegration 

 and Decomposition." He became rather enthusiastic about the 

 results arrived at in the paper. Another of these papers dealt with 

 the distribution of carbonate of lime over the floor of the ocean and 

 with coral-reef formations. One of the most striking results of the 

 "Challenger" Expedition was the discovery of enormous numbers of 

 pelagic calcareous Algae, pelagic Foraminifera, and pelagic Mollusca 

 in the surface and sub-surface waters everywhere within tropical and 

 sub-tropical regions, but the dead calcareous shells of these pelagic 

 organisms were not distributed with similar uniformity over the floor 

 of the ocean. In some places they formed Pteropod and Globigerina 

 oozes, but in the very greatest depths not a trace of these shells could 

 be found in the Red Clays which covered the bed of the 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 accumulated. The solvent action was also re- 

 tarded 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 dis- 

 appearance 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 bio- 

 logical, mechanical, and chemical processes everywhere going on in 



