42 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



free C0 2 be present its concentration must be very slight. However, both 

 Tashiro and Mayer, working independently and pursuing different methods, 

 have shown that calcium carbonate is slightly soluble in Tortugas sea-water 1 

 which remained alkaline to phenolpthalein. Natural sea-water from Tortu- 

 gas, Florida, was found by Professor J. F. McClendon to have a hydrogen-ion 

 concentration of from 8.1 to 8.2 PH. 



Mayer attempted to determine the rate at which sea-water as such can 

 dissolve limestone by placing carefully weighed pieces of Cassis shell in sea- 

 water for one year and then reweighing the shells. The experiments showed 

 that if calcium carbonate does dissolve in natural sea-water, the rate of 

 this solution is so slow that it would take at least 1,000,000 years to dissolve 

 off a layer one fathom thick, and thus the lagoons of atolls which are com- 

 monly 15 to 20 fathoms deep could not have been dissolved out by sea-water 

 as such even if coral limestone dissolves 100 times as fast as a Cassis shell, 

 for most if not all of them are, geologically speaking, of recent formation. 



However, admitting that sea-water is a negligible factor in so far as 

 solution of limestone is concerned, this does not necessarily imply that no 

 appreciable solution of dead coral and limestone takes place in lagoons, for 

 the decomposition of plant and animal organisms which lived over the sur- 

 faces and within the cavities of coral heads may supply a local source of C0 2 

 in the exact positions wherein it may be most effective in causing solution of 

 limestone. In fact, living Annelids (Eunicidae) within the crevices of coral 

 heads are decidedly acid to litmus test, although, as Johnston and Merwin 

 state, this does not necessarily indicate that they dissolve limestone, for, as 

 these authors show, whether sea-water does or does not dissolve CaC0 3 

 depends not only on its temperature and concentration of free C0 2 , but also 

 upon the concentration of calcium already present. 



One might suppose the outpouring of rain-water from the densely forested 

 volcanic shore during the wet season might introduce carbonic acid into the 

 water of the surrounding reef-flats. However, Mayer tested this upon Tutu- 

 ila, Samoa, and Oahu, Hawaiian Islands, in 1917, and found that although 

 the rain is acid of the order io" 5 , the stream and spring waters of these 

 Islands are alkaline having a hydrogen-ion concentration of io -7 . Thus 

 they can not dissolve limestone by reason of their "acidity," and the 

 Murray-Agassiz idea of solution is not supported. 



Dead coral broken off and then washed shoreward from the inner edge 

 of the lithothamnion ridge of Maer Island gradually disappears before it 

 reaches the beach, only a few deeply cavernated dead coral heads being 

 found within 350 feet of the shore, where they lie disintegrating in the calm, 

 warm waters of the shallows. 



'Carl Elschner (1915, The Leeward Islands and the Hawaiian Group, p. 48) rightly states that the solu- 

 bility of calcium carbonate in sea-water is extraordinarily low. 



-Mayer, A. G., Carnegie Inst. Wash. Year Book No. 14, 1915. P- "°i also Proc. National Acad. Sciences, 

 vol. 2, p. 28, 1916. 



