624 FRANK LEVERETT 
well records indicate that it was built up from near the level of 
the present river. At Red Wing the filling is 125 feet above the 
river, or 790 feet above sea-level. Its slope is more rapid than the 
fall of the river as far down as the mouth of the Wisconsin River. 
It is there about 70 feet above the river, or 675 feet A.T. At Bagley, 
Wisconsin, 12 miles farther down, the filling is only 60 feet above 
the river, and it maintains a height of 50 to 60 feet above the river 
from there down to about the mouth of the Ohio River. Just above 
the Des Moines rapids, in the vicinity of Fort Madison, the Wis- 
consin filling is exceptionally well preserved at a level 50 to 55 feet 
above the river. 
There were accessions from tributaries at several points, the 
most important being St. Croix, Chippewa, Wisconsin, Rock and 
Illinois rivers. The Illinois is likely to have made a contribu- 
tion of sediment to the lower Mississippi larger than that brought 
down from the upper Mississippi. The Illinois Valley was built 
up at the Wisconsin drift border, at Peoria, 170 feet above the 
present stream. In 175 miles from Peoria to Alton, at the head 
of the American Bottoms on the Mississippi, there is a descent of 
about 160 feet in the surface of the sandy filling of Wisconsin 
age, while the present stream falls only about 25 feet in the same 
distance. Below St. Louis there is sandy filling, which seems 
referable to the Wisconsin glacial drainage, in small remnants in 
recesses of the valley and in the mouths of tributary valleys. Fill- 
ing of this sort is found as far down as the place where the Mis- 
sissippi turns into the gorge near Thebes. The new topographic 
map of the Jonesboro quadrangle brings out terraces at the mouths 
of Dutch Creek and Clear Creek valleys which catch the 38o- 
foot contour. They are 30 feet above the broad flood plain of 
the river. 
DRAINAGE FROM THE GLACIAL LAKES 
The Mississippi Valley was the line of discharge to the Gulf of 
Mexico for several of the great glacial lakes that were developed in 
front of the receding ice border. Lake Agassiz, with a maximum 
area as large as that of all the present Great Laurentian lakes, 
drained into the Mississippi through the Minnesota Valley; Lake 
Duluth, in the Superior Basin, drained through the St. Croix 
