84 
IOWA ACADEMY OF SCIENCES. 
with the opening of a temporary course for the Mississippi 
across southeastern Iowa, which occurred at the time the 
Mississippi valley above the rapids was covered by the Labra- 
dor ice field. 
The drainage line referred to leaves the present Mississippi 
at the mouth of the Maquoketa, passes southward along that 
valley (reversed) to Goose Lake channel, and thence to the 
Wapsipinicon valley, coming to that valley a few miles above 
its present mouth. It follows up the Wapsipinicon a few 
miles to the mouth of Mud creek, a southern tributary, which, 
together with a small tributary of Cedar river also called Mud 
creek, furnishes the line of continuation for the old valley to 
tbe Cedar river near the great bend at Moscow. The val- 
ley continues southwest to the Iowa river along the course 
now followed by the Cedar river in its lower twenty-five miles. 
It then passes southward from Columbus Junction to Winfield 
and thence westward to Skunk river at Coppock, opening in 
its westward course two lines, one of which is now utilized by 
Crooked creek. From Coppock the old drainage line follows 
the course of Skunk river southward to Rome, and Cedar 
creek (reversed) to Salem. It there turns southeastward, 
being known as ‘‘Grand valley ” in northern Lee county, and 
joins the Mississippi about six miles west of Ft. Madison, 
nearly opposite the head of the rapids. Its continuation was 
evidently across the rapids into the broad valley below 
Keokuk. 
The altitude of the bottom of this old valley, near the head 
of the rapids, is fully 100 feet above the present stream, but 
connects well with the surface of the valley filling in and 
below the rapids. It is nearly 100 feet lower than at the 
point where it leaves the Iowa valley, seventy-five miles to 
the north. The portion above the point where the Iowa valley is 
crossed has been so modified since the Illinoian stage of glacia- 
tion that very little is known concerning its condition at the 
close of that glacial stage, but the portion south from the Iowa 
valley has been only slightly modified. 
Very little material was deposited on the bed of the 
temporary channel of the Mississippi in the seventy -five miles 
from the Iowa valley to the head of the rapids, but a great 
filling occurred in the broad valley below the rapids, and 
some filling along the rapids, especially at their lower end. 
The valley, which, at the foot of the rapids, had been cut down 
