CORROSIVE ACTION OF BRINES IN MANITOBA 



461 



horizon in the middle northwestern states and in the western 

 provinces. It is capped by impervious shales, and the water, 

 which circulates under considerable hydrostatic pressure, appar- 

 ently penetrates laterally into Devonian strata, leaches sodium 

 chloride from certain horizons in which the salt has been precipi- 

 tated with the limestone, and reaches the surface where the cover- 

 ing of drift is thin or absent. On an average approximately 430 

 gallons of brine reach the surface per minute during the dry season ; 

 and the salt, if evaporated, would cover the main salt area (200 

 miles by 30 miles) with a coating 2 feet thick in 10,000 years. 



TABLE I 



*From Salt Creek, Salt Point Peninsula, Lake Winnipegosis. Professor M. A. Parker, analyst, 

 t Mean of 77 analyses by W. Dittmar. 



Composition of the brines. — Numerous analyses have been made 

 of the brines. The composition is remarkably uniform, differences 

 occurring only when the brines pass through a considerable depth 

 of glacial drift before reaching the surface. In this case the per- 

 centage of Ca and S0 4 ions is considerably greater than normal. 

 Table I gives the analyses of a typical brine, Dittmar's average 

 of 77 analyses of sea- water being given for comparison. 



The analyses are given in percentages of total solids. The per- 

 centage of salinity in the analysis quoted is somewhat greater than 

 normal, but the percentage values for the constituents vary only 

 slightly from the figures quoted. While on the whole the brine is 

 very similar to sea-water, it is a distinctly purer solution of sodium 

 chloride. The relative percentages of Ca and Mg ions differ in 

 a sense, which may be accounted for by the abstraction of Ca ions 

 by marine organisms. The apparent differences in the carbonate 



