18 W. UPHAM — ICE AND RIVER EROSION IN SAINT CROIX VALLEY 



gested by Mr Elftman, from the Sunrise river b}^ Chisago lake to rejoin 

 the present Saint Croix valley. 



About a sixth part of the Saint Croix basin, lying east and south of 

 Taylors Falls, appears to have been drained during the Tertiary era by 

 a stream coinciding nearly with the Apple river and the lower 30 miles 

 of the Saint Croix river. The large basin and river first described may 

 be called the pregiacial Saint Croix, and the lower small stream may 

 be distinguished as the enlarged pregiacial Ap})le river. 



These Tertiary drainage areas, which by the vicissitudes of the Ice age 

 became united into one stream, the present Saint Croix, I think to have 

 been divided, up to the time of the ice accumulation in the Glacial period, 

 by a watershed of the ver}^ old trapi)ean and Caml)rian rocks, extending 

 from northeast to southwest across the sites of the towns of Saint Croix 

 Falls and Taylors Falls. 



Pleistocene Erosion of the Dalles 



In the twenty-third annual report of the Minnesota Geological Survey 

 for the year 1894 I have stated (on pages 188-190) the evidence that the 

 recession of the ice-sheet during the Buchanan interglacial stage, which 

 succeeded its Kansan stage of maximum area west of the Mississip})i, 

 extended northward be3"ond the site of Barnesville, Minnesota, on the 

 southern part of the great valley plain of the Red river of the North. 

 Probably at that time the ice had been melted away from nearly or quite 

 all of the southern half of Minnesota. That the retreat of the ice-sheet 

 had uncovered the southern third of the Saint Croix basin is shown, in 

 Nessel township, Chisago county, Minnesota, near Rush City, by an in- 

 terglacial Buchanan land surface, with wood and peaty matter, upon a 

 deposit of modified drift that was laid down during the previous retreat 

 of the ice.* Above the wood and peat of this place, and above an ex- 

 tensive plain of the Buchanan modified drift reaching thence several 

 miles eastward, a somewhat uniform mantle of till, 10 to 20 feet deep, 

 was spread during the ensuing Illinoian and lowan glacial readvance. 



We thus know that the district including the Dalles and extending 

 northward at least to Rush City was uncovered from the ice-sheet during 

 the Buchanan stage of the Glacial period. Later the increasing snow- 

 fall again permitted nearly all this basin to be enveloped by the ice of 

 the Illinoian and lowan stages, reaching on the Saint Croix river south- 

 easterly to the conspicuous moraine belts which pass from Saint Paul 

 and Minneapolis northeastward to the northern half of lake Saint Croix 



♦Geology of Minnesota, vol; 2, 1888, pp. 414, 418. 



