REPORT OF THE CHIEF ASTRONOMER 647 



SESSIONAL PAPER No. 25a 



animals living at the surface would, after death, fall to the sea floor, there 

 accumulate and decompose. The rate of decay is in some direct proportion to 

 the temperature. It is in the highest degree probable that the pre-Cambrian 

 polar waters were much warmer than the polar waters are now. Since the bottom 

 temperatures of the whole ocean basin are influenced by polar temperatures, it 

 is fair to conclude that the bottom temperatures of the pre-Cambrian sea were 

 relatively high. Animal carcasses fallen to the sea floor would therefore not be 

 in cold storage but would undergo putrefaction. Both Alexander Agassiz* and 

 Afurrayf hold that putref action takes place even at the present low tempera- 

 tures of the sea bottom. 



During putrefaction ammonium carbonate is given off in large volumes. 

 This powerful alkali has the property of rapidly converting the chloride and 

 sulphate of calcium into precipitated carbonate of calcium. The usual equations 

 for the reactions may be noted : 



CaS0 4 +(NH 4 )„CO..=CaCO,+(NH 4 ),S0 4 

 CaCL +(NH 4 ) 2 C0 3 =CaC(X+2NH 4 Cl 



Both of these reactions are reversible,^: so that new calcium carbonate introduced 

 by rivers into sea water after the original sulphate and chloride had been con- 

 verted, would be first changed to the sulphate or chloride and then finally pre- 

 cipitated. According to Murray, Irvine, and Woodhead the first reaction is that 

 according to which a marine animal secretes calcium carbonate shell or skeleton 

 from sea water; in this case the ammonium carbonate is generated in the decom- 

 position of effete products within the body of the animal. § The chemical 

 process is thus fundamentally the same whether the calcium is abstracted from 

 ocean water through the building of calcareous ' hard parts ' or through the pre- 

 cipitation by decaying carcasses. Both actions are doubtless important at the 

 present time. 



The precipitation probably occurs chiefly in the bottom stratum of the sea 

 water though it would also proceed during the slow subsidence of decaying 

 carcasses of low density. Diffusion and the vertical interchange of water must 

 tend, in a long period, to remove all the calcium salts from the ocean. At length 

 there would remain in solution only a minute quantity of calcium salts brought 

 into the ocean by the short pre-Cambrian rivers and not yet diffused to the 

 bottom stratum. 



Experiment shows that the pure magnesium salts of sea water from which 

 calcium salts have been eliminated are unavailable for the elaboration of car- 

 bonate shells and skeletons by organisms, although the organisms live and thrive 

 in such water. Granting that the essential protoplasmic requirements were, 

 in pre-Cambrian' time, the same as now, experiments thus show the complete 



* Personal communication. 



t Report on the Deep Sea Deposits, Challenger Expedition, 1891, p. 256. 



X Dike hydrochloric acid, most chlorides are practically completely dissociated in 

 dilute aqueous solutions. Analytical Chemistry, by F. P. Treadwell, trans, by W. T. 

 Hall, New York, p. 249, 1905. 



§ Proc. Roy. Soc. Edinburgh. Vol. 16, 1889, p. 324, and Vol. 17, p. 79. 



