16 THE CANADIAN NATURALIST. [Feb. 



ate of lime to such a solution gives rise, by double decomposition, 

 to sulphate of lime and bicarbonate of magnesia. The former being 

 much the less soluble salt, especially in a strongly saline liquid, is 

 deposited as gypsum ; and subsequently the magnesian carbonate 

 is precipitated in a hydrous form. The effect of this reaction is 

 to eliminate from the sea-water both the sulphuric acid and the 

 magnesia, without the permanent addition to it of any foreign 

 element. 



§ 27. Gypsum may thus be separated from sea-water by 

 two distinct processes, — the one a reaction between sulphate of 

 magnesia and chlorid of calcium, and the other between the same 

 sulphate' and carbonate of lime. The latter, involving a separation 

 of bicarbonate of magnesia, can, as we have seen, only take place 

 when the whole of the chlorid of calcium has been eliminated ; and 

 if we suppose the ancient ocean, unlike the present, to have con- 

 tained more than an equivalent of lime for each equivalent of 

 sulphuric acid, it is evident that a lake or basin of sea-water free 

 from lime-salts could only have been produced by the intervention 

 of carbonate of soda. The action of this must have eliminated the 

 whole of the lime as carbonate, or at least have so far reduced the 

 amount of this base that the sulphates present would be 

 sufficient to separate the remainder by evaporation in the form 

 of gypsum, and still leave in the mother-liquor a quantity of sul- 

 phate of magnesia for reaction with bicarbonate of lime. 



The source of the magnesian carbonate, whose union, under 

 certain conditions, with the carbonate of lime, gives rise to dolo- 

 mite,* may thus be due either to the reaction just described be- 

 tween bicarbonate of lime and solutions holding sulphate of mag- 

 nesia, or to the direct action of carbonate of soda upon waters 

 containing magnesian salts ; but in either case the previous elimi- 

 nation of the incompatible chlorid of calcium must be con- 

 sidered an indispensable preliminary to the production of the 

 magnesian carbonate. 



§ 28. To the three principal sources of mineral matters in 

 mineral waters already enumerated, viz., decaying organic matters, 

 decomposing silicates, and the soluble saline matters in rocks, a few 

 other minor ones must be added. One of these is the oxydation of 

 metallic sulphurets, chiefly iron pyrites, giving rise to sulphate of 



* Silliman's Journal [2] xxviii, 180-186 ; and further, Geol. Survey 

 of Canada, Report for 1859, 214-218. 



