184 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



magnesium chloride remaining in solution. The mother liquor still retains 

 some common salt tog-ether with j^otassium chloride. The first of these is 

 obtained by evaporating until the specific gravity of 1.33 (36°B.) is reached, 

 which causes the deposition of nearly all the common salt; the remaining 

 liquor is then conducted to shallow vats and allowed to cool; this causes 

 the precipitation of the whole of the potassium as the double chloride of 

 potassium and magnesium.*^* 



The succession of chemical precipitates formed when sea water is 

 evaporated has been succinctly described by M. Dieulafait, in the Popular 

 Science Monthly,"^ from which we quote the following: 



First a very weak precipitatiou occurs of carbonate of lime with a trace of strontium, aud of 

 liytlrated sesquioxide of iron, mingled with a slight proportion of manganese. The water then contin- 

 ues to evaporate, but remains perfectly limpid, without forming any other deposit than the one I have 

 mentioned, till it has lost 80 per cent, of its original volume. It then begins to leave an abundant 

 precipitate of perfectly crystallized sulphate of lime with two equivalents of water, or gypsum, iden- 

 tical in geometrical form aud chemical composition with that of the gypsum-beds. This deposit con- 

 tinues until the water has lost 8 per cent, more of its original volume; then all i)recipitation ceases 

 till 2 per cent, more of the original quantity of water has evaporated away. Then a new deposit 

 begins, uot of gypsum, l)ut of chloride of sodium, or sea-salt. » » * The deposition of pure or com- 

 mercial salt continues till the volume of the water has been again reduced by one-half, when a precip- 

 itation of sulphate of magnesia begins to take place with it. This continues, the two salts being de- 

 posited in equal quantities, till only 3 per cent, of the original quantity of water is left. Finally, when 

 the water has been concentrated to 2 percent'., earuallite, or the double chloride of potassium and mag- 

 nesium is deposited. Spontaueoiis evaporation cannot go much further. The residu.al mother-water 

 will uot dry up at the ordiuary temperature even in the hottest regions of the globe ; its chief constit- 

 uent is chloride of magnesium. A body of sea-water, evaijorated naturally, will theu leave a series of 

 deposits in which we will tind, as we dig down, the following minerals in order: deliquescent salts, 

 including chiefly chloride of magnesium ; carnallite, or the double chloride of potassium and magne- 

 sium ; mixed salts, including chloride of sodium aud sulphate of magnesia; sea-salt, mixed with sul- 

 phate of magnesia ; pure sea-salt ; pure gypsum ; weak deposits of carbonate of lime with sesquioxide 

 of iron, etc. 



The correspondence between the succession of salts formed by the 

 evaporation of sea-water, and the succession found in many saline deposits 

 now worked for rock salt, is of great interest, and no doubt explains the 

 genesis of some saline deposits. It is not always necessary, however, in 

 the explanation of the presence of salts in lenticular basins to assume that 

 the deposits commenced with isolated portions of sea- water. On the con- 

 trary the study of inclosed basins indicates that deposits of this nature 

 sometimes result from the long continued concentration of ordinary river- 

 waters. The presence of salt or fresh water mollusks associated with saline 



** Report of Juries: International Exhibition, 1862, Class II, pp. 48-54. 

 «5 October, 188-2. 



