HYDROGRAPHY OF THE EARLY PLEISTOCENE 33 



the South fork of the White river has a wide valley.* Moreover, be- 

 tween that point and the White river there are several miles of canyon 

 in which there are falls. One is near the mouth of Rosebud creek. 



Another peculiarity which should not be overlooked is that the Nio- 

 brara from its present mouth, after following the Missouri for 2 miles, 

 turned to the left between Springfield and Bon Homme and made its 

 way to James river by way of Tabor and Utica. 



Another point is that the Big Sioux joined the Vermilion as indicated. 



In THE EARLY PLEISTOCENE 



Under this head we would include all pre-Wisconsin Pleistocene time, 

 for as yet the differentiation of the Kansan, Iowan, and other epochs has 

 not been made for this region. What we have mapped may be con- 

 sidered as corresponding to the maximum extent of the ice during the 

 Kansan stage. It will be seen that the streams are represented as flow- 

 ing over the same channels as in the Pliocene, but that their size is in- 

 creased. This we believe was true, owing to the drainage from the ice- 

 sheet on the east, and also from an increased rainfall on the west, which 

 we believe would be the logical results of the presence of the ice-sheet. 

 Some may be surprised that the Kansan ice-sheet is not represented as 

 occupying the James River valley, but such we believe was not the con- 

 dition of affairs for the following reasons : 



First, in the numerous borings in the James River valley no distinct 

 evidences have been found of a lower till underlying that deposited by 

 the Wisconsin ice-sheet. 



Second, the new narrow course of the Missouri above Yankton evi- 

 dently follows the margin of the ice-sheet which formed the Altamont or 

 outer moraine, and the chances are strongly against an earlier sheet 

 coinciding so closely in extent with that sheet, as must have been the 

 case if the course of the river was determined by it. If it be suggested 

 that the Kansan extended farther, we would reply that no traces have 

 been found of a channel corresponding to it; and, on the other hand, 

 if it be suggested with more reason that the Missouri for a time may 

 have flowed in a channel which was obliterated or filled by the ice-sheet 

 of the Wisconsin epoch, it is scarcely conceivable that such could have 

 occurred without leaving some trace, at least where it crossed some of the 

 unglaciated portions between the lobes of the ice-sheet of the Wisconsin 

 epoch, and no such traces have been found. On the contrary, all seem 

 to indicate that the Missouri was pushed out of the James River valley 

 by the sheet of the Wisconsin epoch alone. 



* Bulletin 2, South Dakota Geological Survey, p. 128. 



