G. K. Warren— Valley of the Minnesota and Mississippi. 419 
Profiles prepared for publication.— Accompanying this chapter 
are two sheets of longitudinal profiles of the valley from the 
junction of the Minnesota River to the junction of the Ohio. 
The horizontal scale is about eight miles to an inch, and the 
vertical 200 feet to an inch, reduced in publication. The datum 
is the sea-level according to the best determinations, and both 
sides of the valley are given side by side. e parts of the 
banks above low-water are shaded to indicate the strata of dif- 
ferent geological periods, but it must be borne in mind that 
this low-water line does not represent the low-water slope of 
the winding river, but is drawn from point to point along the 
general course of the valley, so as to bring the rocks into their 
proper relative positions. These longitudinal profiles are desig- 
nated as Diagram 2, in two sheets. 
Another sheet, designated as Diagram 8, gives twenty trans- 
verse valley sections, on a larger scale than the profiles: three 
of them on the Minnesota Valley; one on the Mississippi, above 
the junction with the Minnesota; fourteen of them in the valley 
between the Minnesota and the Ohio; one at the mouth of the 
Missouri River, and one at the mouth of the Illinois River. 
These sections are designed to show the extent of our positive 
knowledge of the depth of the bed-rock, and will be described 
in detail in the latter part of this chapter. 
We are mainly indebted for the geological data in these pro- 
files and sections to the report of David Dale Owen, October, 
1851, on the Geological Survey of Wisconsin, Iowa and Minne- 
Sota ; to the report on the Geological Survey of Iowa, by Prof. 
James Hall, Prof. J. D. Whitney and Mr. A. H. Worthen, pub- 
lished in 1858, and the report of Mr. A. H. Worthen, director 
of the Geological Survey of Illinois, published in 1866. 
Method of treating question of depth of bed-rock.—The question 
of depth of the bed-rock beneath the sand that usually forms 
the bed of the river will occupy the remainder of this chapter. 
In presenting my ideas in regard to it, I have thought the 
best order in which I could arrange them would be that in which 
they arose in the rogress of the investigation. It was from 
the first obvious that means and time would not allow of my 
covering such an extended field by actual borings, and that the 
most that could be done was to draw such probable inferences 
as could be done by a study of the rocks visible in the bluffs 
and by an effort to comprehend the manner in which the valley 
was formed. 5 
The consideration of the anomaly presented by Lake Pepin 
lying in the course of the river, and said to have a depth of sixty 
feet near its lower end, was the beginning of thiseffort. If the 
valley in this portion had once been all of this depen. and since 
filled in, then the bed-rock could not be less than sixty feet 
