MUREAY AND NOBLES COUNTIES. 59? 



Drift.] 



lowish color to a depth that varies from ten to twenty-five or thirty feet, 

 below which it is dark bluish. Important differences in its hardness are 

 also noted in the sections of deep wells. How thick this drift-sheet is can 

 only be conjectured, since it has not been passed through in these counties; 

 but from what is known of its depth upon other parts of southern and 

 western Minnesota, it is believed to vary from 100 to 200 feet or more in 

 thickness. Here and there this sheet of till encloses layers of sand and 

 gravel, from which comes the large inflow of water often met with in well- 

 digging. 



Creeks and rivers have excavated valleys in the drift, the deepest being 

 those of Chanarambie, Champepadan and Kanaranzi creeks, and of the Des 

 Moines river. These eroded valleys are 50 to 75 feet deep and generally a 

 half or three-fourths of a mile wide, bordered by bluffs of moderately steep 

 or sometimes quite abrupt slope. Their bottoms are partly till, like the 

 enclosing bluffs ; but much of the lowland adjoining the streams consists 

 of deposits of gravel and sand or fine silt, being part of the alluvium formed 

 during the process of erosion. Its lowest tracts still remain within reach 

 of the high water which is produced by snow-melting in spring or by the 

 largest rains, and these areas of flood-plain are annually increasing in 

 depth by the deposits made during such inundations. 



Modified drift, or beds of gravel, sand and clay, whose formation must 

 be referred to glacial conditions, was not observed in these valleys. The 

 only noteworthy deposit of this kind is that found in Grand Prairie, the 

 most southwest township of Nobles county. Here a plain composed of 

 stratified gravel and sand, but covered by a fertile soil, reaches six miles 

 east from Kanaranzi creek, with a width of about four miles, including the 

 southern two-thirds of this township. This nearly level tract is 20 to 40 

 feet above Kanaranzi creek, to which it supplies a small tributary that has 

 cut a channel of similar depth. The bordering areas of till rise in massive, 

 smooth swells, 40 to 75 feet above this plain. 



Terminal moraines. Foregoing descriptions of the surface features of 

 these counties have called attention to the most important distinction in 

 their deposits of glacial drift or till, namely, the existence of two specially 

 rolling and hilly belts, in part very rough and knolly, with an increased 

 proportion, and sometimes an astonishing abundance, of boulders. The 



