534 THE GLACIAL LAKE AGASSIZ. 



Lake, concentrated by evaporation without outlet from the water of inflow- 

 ing streams and springs, whicli bring- very small amounts of these salts 

 dissolved from the drift and Cretaceous shale of the adjoining country. 



Much shale gravel and detritus, rich in sulphates, are present in the 

 glacial drift over nearl}' the entire Red River basin, and the percolating 

 rain water found by the fresh artesian wells in the chift of the southern 

 and northern ends of the Red River Valley has acquired minute quantities 

 of alkaline and saline matter. But where its proportion is large, as in the 

 brackish water of the wells from Crookston and Blanchard northward to 

 the edge of Manitoba, it seems impossible that so remarkable difference 

 can be due to diversity in the material of the di'ift, or to longer time and 

 better opportunity afforded to the water for such impregnation wliile perco- 

 lating through porous beds or veins in the di'ift. The saline and alkaline 

 artesian waters of the drift gravel and sand along this central portion of 

 the Red River Valley therefore appear to be received mainly from the 

 same Dakota sandstone which supplies the deep Avells of the James River 

 Valley. 



Several wells in tlie vicinity of Casselton, Blanchard, and ]\Iay^^lle, 

 ranging from 317 to 404 feet in depth, pass tlu-ough the di-ift and enter a 

 very fine white sandstone, probably the Dakota formation, from which they 

 obtain flows of brackish water. About a dozen miles east of Blanchard 

 the drift was found to have a total thickness of 310 feet, below which a 

 boring went 107 feet into exceedingly fine white sandstone, finding, how- 

 ever, no artesian water, apparently because of the very close texture of the 

 rock. The top of the sandstone in these wells is 650 to 575 feet above 

 the sea. If it is the Dakota sandstone, as seems probable and nearly cer- 

 tain, it has an ascent of aboiit 600 feet in 75 miles east from the meridian 

 of Devils Lake and Jamestown, rising in its approach toward the Silurian, 

 Cambrian, and Archean areas of Minnesota and Manitoba. Along a line 

 about 13 miles north of the international boundary the top of the Dakota 

 sandstone ascends eastward from a depth at Deloraine exceeding 156 feet 

 below the sea-level to a depth of only 320 feet below the surface at Morden, 

 where it is encountered 658 feet above the sea.^ The Dakota sandstone 



' J. B. Tyrrell, " Three deep wells in Manitoba," Trans., Roy. Soc. Canada, Vol. IX, Sec. IV, 1891, 

 pp. 91-104. 



