428 G. K. Warren— Valley of the Minnesota and Mississippi. 
turns southwest until the mouth of the Des Moines River is 
passed, and then turns southward again. 
The rock disappears in the bed on passing Keokuk; the 
water then deepens, flowing on a sandy bed, and resumes its 
width of about half a mile between its ordinary banks. On 
tne rapids there are no considerable or permanent islands, but 
as you go above or below, you find them as soon as the rock- 
bed is left. 
arsaw, three miles below the foot of the rapids, the Car- 
boniferous rocks show in the bluffs, and so does the unmodified 
glacial drift, covered with the loess. (See Diagram F.) 
The Mississippi Valley at Warsaw is about eight miles wide; 
part of it a sand terrace, but most of it subject to overflow. 
Proceeding up the Des Moines from the mouth, we leave the 
limestone strata at the point H (Diagram E), and do not meet 
with it again, either in the river bed or bluffs, till we reach the 
int C, where we find it in both places, and thence all along 
up this valley. 
In this distance between H and C the bluffs are only on the 
left bank or north side, and the material appears similar to that 
at Madison or to the loess at Warsaw, shown in Diagram F. If 
we examine the valley of Sugar Creek, we find the bluffs cut 
down as low as on the Des Moines between H and C, and all 
of similar material, clay and sand, but no rock in place. Nor 
could we find on any of the branches between ABC and DEH 
any rock in place or learn of any. ithin these limiting lines 
sese who have dug wells for water find it without reaching 
roc 
At the place marked K on the sand terrace a well fifty feet 
deep encountered no rock, although this was as far down as the 
level of low water in the river. : 
The width of the main valley above Fort Madison is nearly 
the same as below Keokuk, and if we prolong the line of bluff 
between these two places, it will ‘scale a space between them 
where there is no known rock in situ, a which it appears 
recent. It has a thickness of many feet in places. It is 
; Ing ee 
quiet, through which ‘the fine silt dropped. Such conditions 
would exist in salt water, and the silt would prevent the exist- 
* 
