RELATIONS Ob' KKD AND (,[{\\ DKIFT 11.) 



surfLice roye liigh enou<;h ^o pass over or round tlic inar«2;iM of the ice, or 

 over a low watershed and reach some other route to the sea. 



Tlie relations of the gray drift witli the red are very interesting. Along 

 a central helt the ice-lobes met at their margins. Sometimes the gray 

 till overlies the red, and sometimes the reverse occurs. Tn general tlie 

 gra}" is on top in the central and southern counties, and in the northern 

 the red till, with its modifications, was latest deposited. Sometimes they 

 alternate several times. This complex marginal belt extends roughly, 

 say, from southern Rice countNMiorthward to Minneapolis, thence north - 

 westwardl}'' to Itasca lake, where it turns abruptly eastward, passes 

 through the region of Winnibigoshish lake to the vicinit}^ of Pokegama 

 falls, and thence in general coincides with the Giants range, but leaving 

 that range so as to cross the Pigeon river south of Fowl lake. 



1. Lake Minnesota "^^ 



This lake was first identified and named by Mr Upham.* As de- 

 scribed by him, its outlet was through the Union slough, in Kossuth 

 count\% Iowa, at an elevation above the sea of approximately 1,150 feet. 

 This slough occupies a continuous channel from the most southern 

 headwaters of the Blue Earth river to Buffalo creek, a branch of the Des 

 Moines river, its length being about 8 miles. Its width is from one- 

 eighth to one-fourth of a mile, the enclosing bluffs rising steeply from 

 20 to 30 feet. The surface of the surrounding country is one of undu- 

 lating till. Near the Minnesota boundary line this channel is deeper, 

 and passes by almost imperceptible changes into the channel eroded 

 in the smooth area covered by the lake since the glacial period by the 

 present drainage. 



As will be seen, the area of this lake, which was supposed by Mr 

 Upham to have extended in its greatest extent far toward the northwest, 

 covering nearly all the valley of tlie present Minnesota river as far as 

 Big Stone lake, is here divided into four lakes, each having its individ- 

 ual outlet at a level somewhat different from that through the Union 

 slough. P]ven with this reduction it covered the greater part of Fari- 

 bault, Waseca, and Watonwan counties, and the whole of Blue Earth 

 county, and its depth must have been about 200 feet in the northern 

 part of Blue E]arth county. The ice-barrier to which this lake owed its 

 existence was a fluctuating obstruction, and it must have caused occa- 

 sional important changes in its northern limits. On the plate a dotted 

 line indicates the approximate position of the southern border of the ice 



* On the accompanying plate these lakes are indicated by the numbers here applied to them, 

 t Ninth Anntiai Report of the Minnesota Cieologioal Survey, p. .HI ; final report, vol. i, p. -K'.o. 



