266 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



result of either bacterial or of inorganic agencies). One of the striking 

 features of many shoal-water bottom deposits is the perfection of the pres- 

 ervation of the minute sculpture of foraminiferal shells and alcyonarian 

 spicules. All the facts tend to show that precipitation and not solution is 

 taking place, and it is inconceivable that precipitation and solution could be 

 taking place in the same spot at the same time. 



In order to get more information on the subject, Mr. R. B. Dole kindly 

 undertook, at my request, certain chemical examinations of the waters of the 

 Florida reef tract, and of some samples I collected in the Bahamas. The 

 results of studies he made in 1913 were published in an article entitled "Some 

 chemical characteristics of sea-water at Tortugas and around Biscayne Bay, 

 Florida;" 1 and subsequent studies appear in this volume, pages 299-315. As 

 a part of a discussion of the formation of atoll rims, I summarized in the 

 following words the results obtained up to 1914: 2 



"There are two rival hypotheses for the formation of atolls: one of these 

 attributes them to the submarine solution of the interior of a mass of limestone; 

 the other accounts for them by constructional agencies. In order thoroughly to 

 test the solution hypothesis the results of four lines of investigations were brought 

 to bear upon it, and all are accordant. (1) All the bays, sounds, and lagoons within 

 the Florida reef and key region are filling with sediment; (2) Drew's investigations 

 of denitrifying bacteria show that chemical precipitation of calcium carbonate is 

 taking place in the lagoons; (3) the chemical examination by R. B. Dole of samples 

 of sea-water flowing into and out of the Tortugas lagoon, collected twice daily 

 for a lunar period, show that although both carbonate and bicarbonate radicles are 

 in solution uncombined carbon dioxide is not present, and that the water possesses 

 no capacity for further solution of calcium carbonate by virtue of its content of free 

 carbon dioxide; (4) the determinations by Dole of the salinity of the water within 

 the Tortugas lagoon and at the southern end of Biscayne Bay show a higher con- 

 centration than that in the open sea-water on the outside, indicating that tidal 

 inflow and outflow are not sufficient completely to mix the water in the lagoons 

 with the water of the surrounding sea and that concentration by evaporation is 

 taking place. As the results of these lines of inquiry are so positive, the formation 

 of lagoons by submarine solution may be definitely eliminated from consideration." 



Recently two highly valuable contributions to this subject have ema- 

 nated from the Geophysical Laboratory of the Carnegie Institution. One 

 is entitled "The role of inorganic agencies in the deposition of calcium car- 

 bonate," by John Johnston and E. D. Williamson; 3 the other is "The several 

 forms of calcium carbonate," by John Johnston, H. E. Merwin, and E. D. 

 Williamson. 4 Messrs. Johnston and Merwin have kindly lent me copies of 

 their manuscripts, in advance of publication, and have granted me permis- 

 sion to make such citations as were germane to the subjects here under 

 consideration. 



Johnston and Williamson say that "the titration methods which have 

 usually been employed for the determination of free C0 2 — and to some 



■Carnegie Inst. Wash. Pub. 182, pp. 69-78, 1914. s Jour. Geol., vol. 24, pp. 729-750, 1916. 



2 Jour. Acad. Sci. Wash., vol.4, PP- 27-28, Jan. 19, 1914. 'Am. Jour. Sci., vol. 41, pp., 473-512, 1916. 



