Age of the Missouri River. — Upliaiii. 85 
fessor Todd finds also in the topography of that region evi- 
dence that in prcglacial time the great tributaries coming from 
the west to join this part of the iMissouri, namely, the Cannon 
Ball river, the Grand and jMoreau rivers, then united, the 
Cheyenne, and the \Miite river, flowed east to the James val- 
ley; and he is inclined to believe that from that valley the 
great stream formed by these affluents passed northeast to the 
Red river of the Xorth and Hudson bay. 
In this view I very heartily concur, as a good confirma- 
tion of it seems to me to be afforded by the contour of the 
Coteau des Prairies, lying between the Minnesota river valley 
and that of the Janies river. Rising ver}^ gradually, without 
definite boundaries southward in Iowa and the southwest 
corner of ^linnesota. this massive highland runs north-north- 
west to a high termination, called the Head of the Coteau, like 
a promontory, between the James valley on the west and the 
continuous and broad ^Minnesota and Red river valleys on the 
east. I attribute this form to preglacial stream erosion, when 
two great rivers here united, flowing northward. The western 
stream may have been the ancient ^lissouri river, while the east- 
ern probably drained the upper part of the Alississippi basin, 
deriving its most eastern and southern waters from parts of 
Wisconsin and the northeast corner of Iowa. According to 
Hershey, the preglacial divide crossed the present course of 
the ^Mississippi somewhere between LaCrosse and Dubuque.* 
The erosion of the present valley of the Missouri river, 
from where it leaves the mountains to the mouths of the Nio- 
brara and James rivers, ranging below the Great Falls from 
one to ten miles in width and from 300 to 600 feet in depth 
cut into the general surface of the plains, may be ascribed 
wholly or chiefly to the work of this great stream since the 
culmination or Kansan stage of the Ice age, probably 50,000 
years or longer ago, when the drift thinly overspreading the 
country along the course of the river was deposited. Only on 
the east side of the river at various places in South Dakota is 
its valley touched by the border of the much later drift sheet 
spread during the moraine-forming Wisconsin stage, near the 
end of the Glacial period. . 
• "The Physiographic Development of the Upper Mississippi Valley," Am. 
Geologist, vol. xx. pp. 246-268, Oct., 1897. 
