oeabt.] GEOLOGY OF MINNESOTA. 307 



south toward the equally ancient rocky valley formed by the St. Croix 

 and the Mississippi. 



Morainic accumulations are very extensively developed throughout 

 the State. The most prominent are those of the eastern border of the 

 glacial lobe which extended into central Iowa. This series of moraines 

 enters the State about the center of the eastern boundary, runs south- 

 west wardly to the vicinity of St. Paul and Minneapolis, and then turns 

 and runs southward to the southern limit of the State. The moraines 

 of the western side of this lobe cut across the southwestern coiner of 

 the State. Between these two major terminal moraines are many com- 

 plicated net-works of minor moraines, formed as this great lobe of the 

 glacier receded northward. 



The ''driftless area*' is the only portion of the State that is entirely 

 free from drift. This area, although confined mostly to Wisconsin, 

 covers a considerable territory in the southeastern corner of .Minnesota. 

 Most of Houston and Winona counties and the eastern portions of 

 Wabasha, Olmsted and Fillmore counties are included in this area. 

 Bere the topography is decidedly more rugged than in the adjoining 

 drift -covered areas, and the rocks are exposed in bold outcrops. 26 - 31 



The loess is well developed in the southeastern corner of Minnesota. 

 It covers all of tin; driftless area in the State and extends a short dis- 

 tance west of it, and also northward along the Mississippi nearly to 

 Red \Vin<;\ Outside of the driftless area it is confined chiefly to the 

 river valleys, extending along these much farther west than in the 

 adjoining ground. 



Lake A^ams. 3 *— -This name has been applied by Mr. Warren llpham 

 to a glacial lake which occupied the basin of the Red River of the 

 North and extended over a considerable area in Manitoba. After 

 tin ice sheet had receded beyond the source of the \lvd River, the 

 waters, formed from the melting of the ice, accumulated in a vast inland 

 lake: the high ground to the south was the southern harrier of this 

 lake, while on the north it was bounded by the edge of the retreating 

 ice sheet. When the ice disappeared the present drainage system 

 toward Hudson Bay was established. The area of this lake at the 

 time of its greatest development was greater than that of Lake Supe- 

 rior. In depth it varied much, reaching in some places over 100 feet 

 (123m,). The beaches of hake Agassis are well defined in Minnesota: 

 they enter the western edge of the St at e at Lake Traverse, run east for 

 a short distance, and then north, keeping parallel with the Red River 

 "I the North and usually within 2G (32 km.) miles of it; this northerly 

 direction continues to almost the latitude of ]{vd lake, where it sud- 

 denly turns to the northeast and runs through llvd lake to Rainy lake 

 on the northern border of the State. The outlet of Lake AgftSSiz was 

 the Minnesota River, which is now a small stream Sowing in a gorge 



