38 W. Upham—Minnesota Valley in the Ice Age. 
the valley just below it by the Whetstone River. Fifteen miles. 
below Big Stone Lake, the Minnesota River flows through a 
marshy lake four miles long and about a mile wide. This may 
be due to the accumulation of alluvium brought into the valley 
by the Pomme de Terre River, which has its mouth about two 
miles below. ‘Twenty-five miles from Big Stone Lake, the 
river enters Lac qti Parle, which extends eight miles with a 
width varying from one-fourth to three-fourths of a mile and a 
maximum depth of twelve feet. This lake, as General Warren 
suggested, has been formed by a barrier of stratified sand and 
silt which the Lac qui Parle River has thrown across the valley. 
He also showed that Lake Pepin on the Mississippi is dammed 
in the same way by the sediment of the Chippewa River; and 
that Lake St. Croix and the last thirty miles of the Minnesota 
River are similarly held as level back-water by the recent de- 
posits of the Mississippi. 
All the tributaries of the Minnesota River have cut deeply 
into the drift, because the main valley has given them the 
requisite slope. The largest of these extend many miles, and 
have their mouths level with the bottomland of the Minnesota 
River. The bluffs of all these valleys are also everywhere 
time with that of the main valley. The short ravines are more 
recent in their origin, and the material that filled their place is 
commonly spread in fan-shaped, moderately sloping banks be- 
low their mouths, which are thus kept at a height from thirty 
to forty feet above the present flood-plain. The road from Fort. 
Ridgely to New Ulm runs along the side of the bluff at the 
only height where a nearly level straight course could be ob- 
tained, being just above these deposits and below the ravines. 
e valleys of the Pomme de Terre and Chippewa Rivers, 75 
to 100 feet deep along most of their course, and one-fourth of 
a mile to one mile in width, were probably avenues of drainage 
from the melting ice-fields in their northward retreat. Between 
these rivers, in the twenty-two miles from Appleton to Monte- 
video, the glacial floods at first flowed in several channels,. 
which are excavated forty to eighty feet below the general level 
of the drift-sheet, and vary from an eighth to a half of a mile 
in width. One of these, starting from the bend of the Pomme 
de Terre River, one and a half miles east of Appleton, extends 
fifteen miles southeast to the Chippewa River near the center of 
Tunsburg. This old channel is joined at Milan station by an- 
other, which branches off from the Minnesota valley, ranning 
four miles east-southeast; it is also joined at the northwest. 
