THE CORROSIVE ACTION OF CERTAIN BRINES 

 IN MANITOBA 1 



R. C. WALLACE 



University of Manitoba, Winnipeg, Canada 



The brines geologically considered. — The Manitoban escarpment 

 consists of a range of hills which fringes on the western side the 

 lake system of which Cedar Lake, Red Deer Lake, Lake Winni- 

 pegosis and Lake Manitoba are the most important members, and 

 extends southward beyond the international boundary line into 

 North Dakota. It reaches, in the Porcupine Mountain, a maximum 

 elevation of 2,500 feet above sea-level. At the foot of the escarp- 

 ment the plain slopes gently eastward from an elevation of 900 

 feet to one of 700 feet. The escarpment is the eastern edge of the 

 Cretaceous shales which extend throughout the western prairies. 

 The shales were uplifted in early Tertiary times, and were eroded 

 from the Red River valley back to the escarpment before the end 

 of the Tertiary period. On this surface of erosion limestones of 

 Paleozoic age are exposed, Ordovician, Silurian, and Devonian 

 strata appearing successively from the edge of the pre-Cambrian 

 shield to the escarpment; while the Dakota sandstone — the lowest 

 member of the Cretaceous series — rests directly on the surface of 

 the Devonian limestones. The basin of the lake system has been 

 carved from Devonian limestones and dolomites. 



At the foot of the escarpment, on the west side of the lakes, a 

 series of salt springs emerges from middle and upper Devonian 

 strata (the Winnipegosan dolomite and Manitoban limestone 

 respectively). 2 These springs follow the base of the escarpment 

 for a distance of 250 miles, but are found in greatest numbers 

 on the west shore of Dawson Bay, at the north end of Lake 



1 Published with the permission of the Directing Geologist, Geological Survey of 

 Canada. 



2 R. C. Wallace, "Gypsum and Brines in Manitoba," Memoir Geol. Surv. Canada 

 (in press) . 



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