AGENCIES IN DEPOSITION OF CALCIUM CARBONATE 743 



Indeed, there are several facts which point to a parallelism between 

 the amount of lime secreted by organisms and the degree of satura- 

 tion of the sea with respect to CaC0 3 ; thus the animals of the warm 

 seas secrete more lime, on the average, than the same types in cold 

 seas; 1 and, according to Murray, 2 "on the whole, lime at the present 

 time appears to be accumulating toward the equator." These obser- 

 vations directly corroborate the idea that solubility is a significant 

 factor even in the secretion of lime by organisms; that the decreasing 

 abundance of calcareous organisms toward the polar regions is a 

 question not only of the decrease of general vitality (rate of growth 

 and of reproduction) with lowering of temperature, but also of the 

 decreasing capacity 3 of the organism to secrete CaC0 3 from colder 

 sea-water, this being associated with the fact that, though the con- 

 centration of lime is no smaller in the colder water, the degree of 

 unsaturation is greater the colder the sea-water. 



According to Murray, "a limited amount of purely inorganic pre- 

 cipitation does, indeed, take place in coral reefs and some shallow 

 water deposits and in the Black Sea." 4 Now it has been argued 5 

 that chemically precipitated limestones are due to the production 

 of ammonia by decaying organic matter; according to this view such 

 limestones could form only when conditions were such that a long- 

 continued process of persistent decay was possible. According to 

 the view emphasized in the present paper — and, be it noted, this is 

 primarily a chemical, rather than a geological, question — chemical 



1 See citations from the Challenger Reports, in Chamberlin, Jour. Geol., VII 

 (1899), 576-77. 



3 The Depths of the Ocean, p. 180. "In very deep water, even within the tropics, 

 the calcareous shells do not accumulate on the bottom, being apparently removed 

 through the solvent action of sea-water, and with increasing depth the Globigerina 

 ooze passes gradually into another pelagic type, usually Red Clay" (p. 164). 

 "Pteropod ooze is limited to the tropical and subtropical regions, usually in the 

 neighborhood of oceanic islands and on the summits and sides of submarine elevations; 

 it is found in relatively shallow water, and covers a relatively small extent of the 

 ocean floor" (p. 167). 



3 It would be of interest to know if these calcareous organisms could secrete 

 CaC0 3 from colder water kept saturated with calcium carbonate. 



4 The Depths of the Ocean, p. 178. 



5 Most recently by R. A. Daly, Bull. Geol. Soc. Am., XX (1909), 153; in more 

 extended form in Memoir No. 38, Geol. Survey Canada (1912), pp. 643 f. 



