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CHEMICAL DEPOSITS 935 



water flowing into and out of the Tortugas lagoon 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 de- 

 terminations by Dole of the salinity of the water within the Tortugas lagoon 

 and at the southern end of Biscayne Bay show a higher concentration than 

 that in the open sea-water on the outside, indicating 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." 



Johnston and Williamson have recently paid particular attention to 

 tlie solubility-prodnct constant [Ca++] [COg^], the concentration of 

 H0CO3, the effect of temperature on H2CO3 concentration, and the rela- 

 tion of the solubility-product constant to rise in temperature, and say : 



"We believe therefore that the surface layers of the ocean, except in the 

 polar regions and within currents of cold water — in other words, the warmer 

 portions of the ocean — are substantially saturated with CaCOs ; but the truth 

 of this belief can not be regarded as established until trustworthy determina- 

 tions of the several quantities concerned have been made." ^ 



The latest contribution to the subject is by E. C. Wells in an article 

 entitled "The solubility of calcite in sea-water in contact with the atmos- 

 pliere and its variation with temperature." * His experiments were con- 

 ducted witli water from Fowey Rocks Light, Florida, collected between 

 July 19 to 25, 11)15. He says : 



"In other words, sea-water appears to contain so much carbonate that in 

 contact with the atmosphere at 1° 0. it neither has nor acquires an appreciable 

 solvent action on calcite. At higher temperatures it undergoes a slow diminu- 

 tion in its content of carbonates on being agitated in contact with outdoor air." 



The evidence appears to me conclusive that ocean water, except at great 

 depths and probably on the surface in polar regions, is saturated with 

 CaCOg. If this conclusion is granted, it is obvious that any agency that 

 increases the CaCOg concentration or that diminishes the capacity of the 

 water to hold CaCOg in solution will produce precipitation. 



Are there precipitating agencies? There are, and they are both in- 

 organic and organic. Of the inorganic agents there are three, as follows: 

 (1) Increased concentration due to evaporation. (2) Loss of COg into 

 the atmosphere where the CO, content of the atmosphere is below the 

 amount necessary for equilibrium with that of the water. The loss of 

 CO,, under such conditions will be hastened by surface agitation of the 

 water. (3) Loss of CO3 by increase in temperature. Of the organic 



3. Tour. Geol., vol. 24, Dec, 1916, p. 735. 



* Carnegie Inst. Washington Pub. 213, 1917, pp. 316-318. 



LXIX — Bull. Geol. Soc. A.m., Vol. 28, 1916 



