June 9, 1911] 



SCIENCE 



881 



Now Alexander Agassiz explored anew 

 this region of the earth's surface the fur- 

 thest removed from the shores of conti- 

 nental land, and he found that the same 

 condition of things extended over vast 

 areas of the Pacific Ocean. Here we have 

 almost certainly the region of minimum 

 accumulation on the sea-floor, and recent 

 investigations indicate that there is in these 

 deep deposits more radio-active matter 

 than anywhere else in the solid crust of 

 our planet. A satisfactory and clear un- 

 derstanding of the phenomena has not yet 

 been obtained, but Agassiz 's researches take 

 us a long way on the road to a solution of 

 some exceedingly interesting and impor- 

 tant oceanic problems. 



During the last thirty years of his life, 

 Agassiz became very greatly interested in 

 all coral-reef problems, and organized very 

 many extended expeditions, almost entirely 

 at his own expense, with the view of study- 

 ing coral reefs, coral islands, and upraised 

 coral formations. It would be wearisome 

 to give even an abstract of all the publica- 

 tions by himself and his assistants dealing 

 more or less directly with these subjects. 

 It can truly be said that he visited, ex- 

 plored 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 awak- 

 ened during his visit to Edinburgh in 

 1876. I had sketched out a series of 

 papers to be presented to the Royal So- 

 ciety of Edinburgh 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 re- 

 sults 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 

 Cliallenger expedition was the discovery 

 of enormous numbers of pelagic calcareous 

 algffi, pelagic foraminifera and pelagic 

 mollusea 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 calcare- 

 ous 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 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 ar- 

 gued that all the characteristic features of 

 atolls and barrier-reefs could be explained 

 by a reference to the biological, mechanical 



