68 THE GLACIAL LAKE AGASSIZ. 



Lac qui Parle counties almost parallel with the Minnesota River, but grad- 

 ually approaching nearer to it and curving north to the mouth of Big Stone 

 Lake. Thence, beneath a veneer of the Cretaceous shales and overl)-ing 

 glacial di'ift, it passes north-northeasterly to the west part of Grrant County, 

 where a well at Herman, 189 feet deep, encountered Archean rocks at a 

 depth of 132 feet. This well first went tln-ough 124 feet of till, and then 

 through 7 or 8 feet of fine-grained, bufi" magnesian hmestone. The remain- 

 ing 57 feet were quartzose granite, with red feldspar, white micaceous 

 quai-tzite, and mica-schist of several varieties.^ 



Farther to the north, through Minnesota, this boundary is more con- 

 jectm-al because of the almost entire absence of exposures of the bed-rocks. 

 Entering the area of Lake Agassiz east of Red Lake, it turns to the north- 

 west and traverses a region wholly di'ift-covered, passing not far west of 

 the Lake of the Woods. 



Noi"th of the international boundary this limit of the Ai-chean area 

 extends a little west of north to the south end of Lake Winnipeg, a few 

 miles east of the mouth of the Red River, and thence, continuing in the 

 same direction, it follows the east shore of Lake Winnipeg along its whole 

 extent to the mouth of the lake. The farther course of this line, accord- 

 ing to the observations of Sir John Richai'dson and later explorations by 

 Dr. Bell and others, of the Geological Survey of Canada, is west-northwest 

 from the mouth of Lake Winnipeg and the west side of Great Playgreen 

 Lake to the south side of Beaver Lake and Lac la Rouge, a distance of 

 275 miles, and thence it cm-ves gradually to the northwest, crossing the 

 Chmx'hill at the north extremity of Isle k la Crosse Lake. 



LOWER SILURIAN FOR>IATIONS. 



In journeying- from south to north along the Red River Valley, the 

 fii'st rock exposures found are Lower Silmian strata, chiefly magnesian 

 limestones, which outcrop in Manitoba at numerous localities 12 to 20 

 miles noi'th-northeast of Winnipeg, and similar outcrops, probably in part 

 of Upper Silurian age, which rise above the general sm-face of drift 5 to 20 

 miles northwesterly from Winnipeg and at about the same distances west of 



'Geol. and Nat. Hist. Survey of Minnesota, Sixth .\nnual Report, for 1877, p. 29; Final Report, 

 Vol. II, 1888, p. 503. 



