128 IOWA ACADEMY OF SCIENCES. 



(kmduslons and Sufj{/e:>itio)i.s. — Prom the data given, we seem 

 justified in concluding that there had been considerable deposi- 

 tion of till over the region of the Big Sioux valley, previous to 

 the occupation of the Altamont moraine of the Wisconsin 

 epoch. The readiest explanation, no doubt, is that the ice 

 sheet spread, at least, over the region mentioned, although it 

 seems not impossible that the comparatively pebbleless till 

 which has been observed at Sioux Falls and east of Canton, 

 may have been deposited by marginal waters, and while 

 occasional bowlders are found they are by no means as numer- 

 ous nor as large as in the Wisconsin till. From the compara- 

 tively drif Lless region ab )ut Garretson and the direction of the 

 striae west of Palisades, we can scarcely doubt that the valley 

 of the Big Sioux was occupied by a lobe of ice but that there 

 were patches east which were comparatively stationary. 



We have not given the subject sufficient study to speak with 

 confidence and yet it seems permissible, at least, to offer a few 

 suggestions which are little more than speculations. 



If we examine the map of tlie region, we shall find that the 

 valley of the James river in South Dakota is separated by a 

 high table land rising over considerable of its surface, to a 

 height of 2,000 feet above the sea. Immediately north of the 

 SoLith Dakota line, the James river makes its nearest approach 

 to the Ked River of the North, the distance being about seventy 

 miles. At that point the divide between the streams is very 

 low and close to the former stream. A cut of twenty to twenty- 

 five feet would probably turn the James river into the Wild 

 Rice and Red rivers. From that jDoint northward, although 

 the divide is about 150 feet above the James, there is no we 1 

 defined ridge, as further south. This brit gs us to a serious 

 objection to the view that the course of the Missouri was down 

 the James river valley, especially while the mass of ice was 

 moving up the Red river valley. Moreover, some have thought 

 that the ancient drainage was once northeast through the 

 valley of the Wild Rice. If such were the case, the difficulties 

 of keeping the James river valley open for pa.ssage of the 

 water while the Red river valley was occupied by ice, would 

 be still more difficult to explain, if not inconceivable. It seems, 

 therefore, more probable that the dividing ridge, which is now 

 so well defined in South Dakota, previous to the W^isconsin 

 epoch, extended further north, possibly as far north as Devil's 

 Lake; though it was narrower and probably lower there than 



