IOWA ACADEMY OF SCIENCES. 123 



its present course above Yankton, by the advent of the Wiscon- 

 sin ice- sheet. Now the inference mentioned is this: that if 

 the Missouri v^as so displaced by the Wisconsin advance (and 

 this hypothesis certainly furnishes the best explanation of the 

 known facts), then the James river valley was occupied by the 

 stream previous to that time, at least during the so-called 

 Kansan stage. (Possibly some of its upper tributaries may 

 have discharged to the northeast in pre-glacial times.) If so, 

 we can hardly conceive any sub-glacial till occurring in or west 

 of the axis of that valley or in the Missouri valley above Sioux 

 City. That the James river valley and that of the Missouri 

 river below Yankton, are really identical is indicated by their 

 widths and depths and relations to the drift. If this were not 

 true, then we must believe that both the James valley and the 

 wide Missouri valley below Yankton are of pre-glacial origin 

 to their present depths; that the Missouri was displaced by the 

 Kansan advance; that it must have had another channel below 

 Niobrara or Yankton in that epoch, and that that channel has 

 been so filled that it is unrecognizable, while the Missouri below 

 the latter place has been kept unfilled in some inconceivable way 

 during the recession of the Kansan ice and particularly during 

 the deposition of the loess. If the latter be true, it adds 

 another complication to the problem of the origin of the loess. 

 If the James valley was not a pathway for ice during the 

 Kansan stage, then, if the till in Kansas is really of the Kansan 

 stage, the ice forming it advanced from the Des Moines valley, 

 and the first excavation or the re-excavation of the trough of 

 the lower Missouri is post-Kansan and post-loessial. This the 

 writer urged in his Missouri report,* where he also pointed 

 out an adequate cause for the subsequent great erosion, in the 

 floods of water coming from the whole western margin of the 

 retreating ice-sheet, as well as from the eastern slope of the 

 Rocky Mountains; but he refrains from theorizing further till 

 we have considered other recent observations. We shall find 

 some difficulty with this view. 



II. Old Soil in the Big Sioux T«7fe;/. — Early in September 

 last the writer, with Mr. Bain, of the Iowa Geological Sur- 

 vey, and Mr. Leverett, of the U. S. Geological Survey, visited 

 some instructive localities, near Sioux Falls, which had 

 attracted the attention of the writer; first, in his examination of 



'Missouri Geological Report, Vol. X. 



