84 CHEMISTRY OF DOLOMITES AND GYPSUMS. [VIII. 



But while some of these saline lakes may be supposed to 

 be basins of sea-water, modified by evaporation either alone 

 or conjoined with the influx of foreign saline matters, others 

 were evidently once fresh-water lakes in which, the loss of 

 water by evaporation being equal to the supply, have grad- 

 ually accumulated the soluble salts of all the rivers and springs 

 flowing into the lake. We may arrive at some notion of the 

 diverse natures of the different saline lakes which would be 

 formed in this way if we suppose the waters of different 

 European rivers to be subjected to evaporation under con- 

 ditions like those of the salt lakes of western Asia. In the 

 waters of the Elbe and Thames chlorides greatly predominate 

 (in the latter with gypsum), with small amounts of magnesian 

 salts, and the evaporation of these waters would give rise to 

 lakes containing a large proportion of common salt. In the 

 Seine, on the contrary, sulphate of lime predominates, while 

 the waters of the Rhine, the Danube, the Arr, and the Arve 

 contain but small amounts of chlorides and large proportions 

 of sulphates of lime and magnesia. 



In other rivers we find alkaline salts. The Loire at Orleans, 

 according to Deville, contains in 100,000 parts, 13.46 of solid 

 matters, of which 35.0 p. c. is carbonate of lime and 30.0 p. c. 

 silica ; while two thirds of the more soluble salts consist of 

 carbonate of soda. In the waters of the Garonne, with as 

 large a proportion of silica and more carbonate of lime, the 

 carbonate of soda equals one fourth of the soluble salts ; while 

 100,000 parts of the water of the Ottawa, according to my 

 analysis, contain 6. 1 1 parts of solid matters, consisting of car- 

 bonate of lime 2.48, carbonate of magnesia 0.69, silica 2.06, 

 sulphates and chlorides of potassium and sodium 0.47, and 

 carbonate of soda 0.41. Silica, although more abundant in 

 alkaline river-waters, is not wanting in waters containing 

 neutral earthy salts like the Seine and the Rhone, of the solid 

 matters of which, according to Deville, it forms respectively 

 10.0 and 13.0 p. c. (Annales de Chimie et de Physique (3), 

 XXIII. 32.) The waters which rise from the lower palaeozoic 

 shales of the St. Lawrence valley are, as I have shown, re- 



