736 JOHN JOHNSTON AND E. D. WILLIAMSON 



chemical arguments which have been adduced in favor of this posi- 

 tion. Thus Tolman writes: 1 



As direct evidence that the ocean is not saturated with calcium acid car- 

 bonate, we find (i) of the many hundred bottles of the Challenger's samples 

 of sea-water, from all depths and collected at all temperatures, kept several 

 years, only one or two showed deposit of lime. 2 (2) Sea-shells from the bottom 

 of the Pacific show corrosion and re-solution. 3 The Pteropod shells are not found 

 below fifteen hundred fathoms, and two thousand eight hundred fathoms is the 

 limit for the globigerina ooze. 4 (3) Thoulet found by actual experiment that 

 sea-water will dissolve calcium carbonate from shells, corals, etc. 5 (4) Usiglio, 

 studying the evaporation of the Mediterranean water at Cette, found that no 

 precipitate was formed until the specific gravity of the sea-water increased 

 from 1 .02, the specific gravity of the unevaporated water, to 1 .0503, when the 

 first precipitation begins, composed largely of calcium carbonate with ferric 

 oxide. 6 



Let us now consider these arguments severally. ( 1) That samples 

 of surface water did not deposit CaC0 3 on standing is not good evi- 

 dence one way or the other unless conditions- were carefully con- 

 trolled, for change of temperature or of concentration of C0 2 would 

 influence the result. (2) This shows, of course, that the lower (and 

 colder) layers are not saturated; to this point we revert later. 

 (3) Reference to Thoulet's paper shows that his work proves nothing 

 as to the point in question, for neither the temperature nor the 

 partial pressure of C0 2 was controlled. Indeed, he writes: " In the 

 case of marble .... and of coral, the loss [of weight] in sea-water 

 was negative. This result arises from the fact that small algae 

 appeared .... the weight of which confuses the result." (4) This 

 observation also is no proof, in view of the well-known fact that 

 solutions of calcium carbonate exhibit a great tendency to super- 

 saturation when no solid CaC0 3 is already present; therefore it 

 shows only that, when the density was 1.05, the degree of super- 

 saturation had become so great that precipitation took place. From 



1 C. F. Tolman, Jour. Geol., VII (1899), 604. 



2 Challenger Reports, p. 221. 



3 Jour. Geol., I, 504. 



< Challenger Reports, p. 221. 

 s Comptes rend., CVIII, 753. 

 6 Encyd.Brit.,XXl, 229. 



