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



Saint Croix river to become joined with the Tertiary Apple river. The 

 Saint Croix, nearly as it exists at the i)resent day, was thus an inherit- 

 ance from the Ice age, beginning as an interglacial river perhaps some 

 40,000 years ago, and again during the linal retreat of the ice-sheet, which 

 here, according to estimates by Professor N. H. Winchell from the rate 

 of recession of the falls of Saint Anthony, was about 8,000 years ago. 



6. The erosion of the valley at the Dalles and for several miles from 

 these gorges, both up and down the river, seems attributable in large 

 part to preglacial streams flowing in opposite directions from a col of the 

 Tertiar}^ and early Quaternary watershed. These stream courses were 

 made continuous by the interglacial Saint Croix. The gorge of the Upper 

 Dalles has undergone further changes by late Glacial and postglacial 

 stream erosion. Its walls have been much riven since the Ice age along 

 the vertical joint planes, but they have suffered only very slight disin- 

 tegration and deca}^ through weathering. 



7. Lakes Saint Croix and Pepin, besides Lac Qui Parle and Big Stone 

 and Traverse lakes, are due to geologically recent and still progressing 

 deposition of alluvium in these valleys, which were deeply eroded by 

 the outflow from the Western Superior glacial lake and from lake 

 Agassiz. The latest and present work of the Saint Croix river in both 

 the Upper and Lower Dalles is to maintain very deep water there, due 

 to the strong eroding current of the stream in times of flood, washing 

 away the sand ahd gravel of its bed in these exceptionally narrow parts 

 of the channel. 



This paper attem})ts to give the broad outlines of the history of the 

 Saint Croix river, and especially of its Upper and Lower Dalles, well 

 known through these two states for their beautiful and even grand 

 scenery. Other parts of the details of erosion in and near the Dalles 

 remain for description and explanation in the following paper. To 

 most visitors in the Interstate park, its })eculiar rock scul})ture to be 

 next considered appears more singular and marvelous than the craggy 

 gorges of the Dalles, the deep river, or the echoes from its cliffs. 



