IOWA ACADEMY OP 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 was 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 Valley . — Early in September 
last the writer, with Mr. Bain, of the Iowa G-eological 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 Keport, Vol. X. 
