GiLACIAL DRIFT AND RIVER DEPOSITS 237 



I'here are two distingiiishable drift sheets in this region, the same as 

 have been generally recognized by Minnesota geologists (see Upham, 6, 

 volume 1, page 580) . These are the Wisconsin and probably the Kansan, 

 as recognized in Iowa. They are best called Old and Young glacial drift, 

 I think, for the present purpose. The Old glacial drift fills, as described, 

 over an uneven surface, but presents apparently a rather uniform upper 

 silrface of its own, in general sloping from west to east. On the north- 

 east side of the Minnesota river the top of this Old drift is at about 890 

 feet above tide. The Eedstone hill therefore stood above the surface of 

 the Old drift, and it was probably on the west side of a wide shallow val- 

 ley. On the Big Cottonwood river, 5 miles west of Eedstone, the Old till 

 rises to about 975 feet above tide. There is, as far as seen, a bed of fine, 

 assorted and stratified, ferruginous, often cemented gravel, at the base of 

 the Old drift. In one place. Just above the mouth of Kalb creek, a small 

 pre-Glacial channel, filled with a thin layer of till under strata of peat 

 and clay with logs of wood, lies beneath the basal gravel bed. Such wood 

 is found also in wells in the central high part of New Ulm city. A few 

 lenses of fresh gravel occur also scattered in the till of the Old drift. 

 While the Old till is dark and compact, as a rule, it is locally leaching to 

 reddish gray color at surface exposures and along water-bearing gravels. 



On the Old drift rests the Young drift, with its rolling upper surface. 

 It has a gravel bed at its base, as a rule, and other sand or gravel patches 

 at the top. Of the two till sheets, the lower contains fresh Cretaceous 

 sand and clay patches occasionally, besides lignite. The upper contains 

 many pieces of a different lignite and has other differences — lighter color, 

 looser texture, etcetera — but it consists so largely of materials of the Old 

 till as to be distinguishable mainly by its superposition. The Young 

 drift is 10 to 100 feet thick. 



Besides the Old and Young glacial drift, there are terrace deposits of 

 gravel, sand, and clay in the river valleys. These deposits have come 

 mainly out of the glacial drift and are, moreover, very closely associated 

 with the same. They are found sometimes in confused relation with 

 them. They were formed, moreover, during the time when the glaciers 

 were yet retreating from the country, and technically they belong to the 

 Glacial or Pleistocene period of the Quaternary age. In the Minnesota 

 valley the terraces were made obvioi^sly by the great river Warren, which 

 formed the outlet to the Glacial lake Agassiz, between the time of retreat 

 of the ice from this region and its disappearance from the north. 



TBE MINNESOTA RIS^ VALLET 



The Minnesota river for many miles above New Ulm has a direct, sim- 

 ple trough-shaped valley, with steep sides 200 feet high and with broad 

 XXIII— Bull. Geol. Soc. Am., Vol. 19, 1907 



