132 CHEMISTRY OF NATURAL WATERS. [IX. 



to the action of these waters the formation of some of the 

 masses of gypsum which appear along the outcrop of the Onon- 

 daga salt-group (Amer. Jour. Sci. (2), VII. 175). That waters 

 like those just mentioned must give rise to sulphate of lime by 

 their action on calcareous rocks is evident ; and some of the 

 deposits of gypsum in this region, as described by good observ- 

 ers, would appear to be thus formed. So far, however, as my 

 personal observations of the gypsums of western Canada have 

 extended, these appear to be in all cases contemporaneous with 

 the shales and dolomites with which they are interstratified, 

 and to have no connection with the sulphuric-acid springs 

 which are so common throughout that region. (Ibid. (2), 

 XXVIII. 365 ; and Geology of Canada, 352.) 



50. We have included in a sixth class the various neutral 

 saline waters in which sulphates predominate, sometimes to 

 the exclusion of chlorides. The bases of these waters are 

 soda, potash, lime, and magnesia ; which are usually found 

 together, though in varying proportions. For the better under- 

 standing of the relations of these sulphated waters, it may be 

 well to recapitulate what has been said about their origin ; 

 and to consider them, from this point of view, under two 

 heads. 



First, those formed from the solution of neutral sulphates 

 previously existing in a solid form in the earth. Strata en- 

 closing natural deposits of sulphates of soda and magnesia, 

 sometimes with sulphate of potash ( 17, 19), afford the 

 most obvious source of these waters. . The frequent occurrence 

 of gypsum, however, points to this salt as a more abundant 

 source of sulphated waters. Solutions of gypsum may in some 

 case exchange their lime for the soda of insoluble silicates, or 

 this salt may be decomposed by solutions of carbonate of soda 

 (7, 19). The decomposition of the sulphate of lime by 

 hydrous carbonate of magnesia, as explained in 21, is doubt- 

 less in many cases the source of sulphate of magnesia, which, 

 more frequently than sulphate of soda, is a predominant element 

 in mineral waters. In connection witli a -uj-rostion made in 

 the section last cited, it may be remarked that I have since 



