12 THE CANADIAN NATURALIST. [Feb. 



ally added to a solution which, like sea-water, contains besides 

 chlorid of sodium, the chlorids and sulphates of calcium and mag- 

 nesium, the greater part of the lime separates as carbonate, carry- 

 ing down with it only from one to three hundredths of carbo- 

 nate of magnesia ; a portion of lime however remaining in solution 

 as bicarbonate. When the chlorid of calcium is wholly decom- 

 posed, the magnesian salt is attacked in its turn, and there finally 

 results a solution in which the whole of the earthy chlorids are 

 replaced by chlorid of sodium. A farther addition of the solution 

 of carbonate of soda gives them the character of alkaline-saline 

 waters ; which moreover contain abundance of earthy carbonates. 



The substitution of neutral carbonate for bicarbonate of soda in 

 the above experiment does not affect the result, except in causing 

 a somewhat larger proportion of magnesia to be thrown down with 

 the carbonate of lime. The resulting liquid still retains large 

 quantities of earthy carbonates in solution.* 



§ 19. In the saline waters just considered, chlorids generally 

 predominate, the sulphates being small in amount, and often 

 altogether wanting. Some exceptions to this are however met 

 with; for apart from waters impregnated with gypsum, whose 

 origin is readily understood, there are others in which sulphate of 

 soda or sulphate of magnesia enter largely. The soda-salt may 

 sometimes be formed by the reaction between solution of gypsum 

 and natriferous silicates referred to in g 7, or by the decompo- 

 sition of gypsum by solution of carbonate of soda ; while in other 

 cases its origin will probably be found in the natural deposits of 

 sulphates, such as glauberite, thenardite, and glauber-salt, which 

 occur in saliferous rocks. A similar origin is probable for many of 

 those springs in which sulphate of magnesia predominates. This 

 salt also effloresces abundantly in a nearly pure form upon certain 

 limestones, and is in some cases due to the action of sulphates 

 from decomposing pyrites upon magnesian carbonate or silicate 

 In by far the greater number of cases, however, its appearance is 

 unconnected with any such process ; and is, according to Mits- 

 cherlich, due to a reaction between dolomite and dissolved gypsum. 



§ 20. In support of this view, it was found by the chemist just 

 named that when a solution of sulphate of lime was made to filter 

 for some time through pulverized magnesian limestone, it was de- 

 composed with the formation of carbonate of lime and sulphate of 



* Geol. Survey of Canada, Report 1853-56, p. 468. 



