478 THE GEOLOGY OF MINNESOTA. 



( Drift aad contoui 



Drift and contour. 



Glacial striae are very distinct on the quartzyte ledge exposed in sec- 

 tion 29, Adrian, mostly bearing S. 30 E., referred to the true meridian, but 

 in one place, on its southeast portion, bearing S. 20 E. 



The contour of Watonwan and Martin counties is like that which pre- 

 vails generally in the basin of the Minnesota river, and is formed by a 

 slightly undulating or in some portions moderately rolling sheet of till, 

 with massive swells rising in long smooth slopes ten to twenty or thirty 

 feet above the depressions. The gently undulating, smoothed surface of 

 most of this region appears to mark areas over which the ice-sheet moved 

 in a continuous current, and from which it disappeared by melting that 

 was extended at the same time over a wide field. Compared with the thick- 

 ness of the drift, its inequalities of contour in these counties are small, and 

 in an extensive view it seems approximately flat. It is a part of the in- 

 clined plain which rises by an imperceptible slope from the Minnesota river 

 to the Coteau des Prairies. Its rate of ascent toward the southwest, or in- 

 crease in average bight, varies from five to fifteen or twenty feet per mile. 

 This gradual change in altitude is doubtless produced by increase in hight 

 of the bdd-rocks upon which the drift lies as a sheet of somewhat uniform 

 depth, probably varying in these counties from 50 to 150 feet; but the nu- 

 merous small elevations and depressions of the surface appear to be due to 

 the accumulation of different amounts of till by adjoining portions of the 

 moving ice-sheet, without any corresponding unevenness of the underlying 

 rocks. 



Third terminal moraine. The most rolling portion of the drift-sheet in 

 these counties is at the southeast, entering East Chain township from Iowa, 

 and reaching northwestward to Fairmont. It is the continuation of a belt 

 of hilly till, which is connected with the inner or western one of the two 

 terminal moraines that extend from north to south through northern Iowa, 

 passing near Clear Lake and Forest City. This belt, three to six miles or 

 more in width, reaches from the vicinity of Pilot mound in northeastern 

 Hancock county northwestward about forty miles, by Forest City, through 

 western Winnebago county and northeastern Kossuth county in Iowa, and 

 into southeastern Martin county. It attains its greatest hight in the north 

 part of township 98, range 85, Winnebago county, where it is 100 feet 



