98 li. A. Daly — Limeless Ocean of Pre- Cambrian Time. 



phate and other sulphates acted on by decaying- animal matter 

 as one source of the gas) grew less as time went on, and that 

 the sea-bottom water thereby became gradually sweetened and 

 fit for colonization. The scavenging system once established, 

 it would now be possible for river-borne calcium salts to 

 accumulate in the sea. 



Secondly, it is conceivable that the ancient animal types 

 could elaborate limey structures from even the minute quan- 

 tity of calcium carbonate which sea-water can hold in solution, 

 and that these animals did not then need the sulphate or chlor- 

 ide of calcium for the secretion of calcareous structures. Cal- 

 cium carbonate could not reenter the essential composition of 

 the ocean until the acid radicals freed from the sulphate and 

 chloride (inherited from the Azoic sea) were either destroyed 

 as such or were satisfied by yet stronger bases than lime. The 

 sulphuric acid of the existing seas is being constantly con- 

 verted into insoluble iron sulphide and free sulphur. This 

 reaction takes place best where ferruginous muds are suspended 

 in the water. It would have but limited effects on the floor 

 of the deep sea far from the pre-Cambrian land. Nevertheless, 

 the whole water-body would, through diffusion and marine 

 currents, be in time affected by the reaction and the sul- 

 phuric acid radical of the Eozoic sea would be slowly destroyed. 

 How extensively the radical was replaced by the volcanic 

 emanation of sulphurous gases from the earth's, interior can- 

 not be demonstrated. 



Yet more obscure are the reactions which might have led to 

 the more permanent binding of the sulphuric acid and chlor- 

 ine radicals to magnesium introduced to the sea in the form of 

 the carbonate by the rivers. The chlorine radical freed from 

 calcium chloride might have become in part gradually bound 

 to sodium. 



The utmost efforts of chemists may be unable to determine 

 fully the exact reactions that take place in so complex a solution 

 as sea- water, but it seems fair to grant the possibility of some 

 such rearrangements among the ions of the Eozoic sea-water. 

 Sodium and magnesium salts are the dominant salts in the sea 

 to-day and it is simplest to suppose that they have become so 

 because of a slow evolution of an ocean tending towards a 

 maximum ionic stability. The sulphates are to-day relatively 

 subordinate because of the very extensive precipitation of insol- 

 uble sulphides and carbonates, directly or indirectly through 

 the chemical influences of living or putrefying animals. 



If, finally, the acid radicals became either destroyed as such 

 or permanently bound to bases more powerful than lime, the 

 concentration in the sea-water of calcium carbonate introduced 

 by rivers first became possible. Then and then only might 



