748 TLE OORINALLS OUI GHD OTERO GN 
slopes near the border of the valley. It certainly should not 
be assumed that they have entered the deepest part of the 
channel. 
If the borings at the points named reach the lowest part of 
the channel, we may estimate the rate of descent of the rock 
floor between St. Paul and St. Louis. Between St. Paul and 
Sabula, a distance of 274 miles, the descent is only 57 feet or 2% 
inches per mile. Between Sabula and Fort Madison, a distance 
of about 140 miles, the descent is 64 feet or about 5% inches 
per mile. Between Fort Madison and East St. Louis, a distance 
of about 210 miles, the descent is about 80 feet or 4.57 inches 
per mile. These data indicate much less descent from St. Paul 
to Sabula than below Sabula. We can hardly suppose that a 
much deeper portion of the channel occurs opposite Sabula, for 
the well at this village was sunk in the middle of the valley. It 
seems probable, therefore, that the valley floor has been slightly 
warped, so that its altitude at Sabula is higher, or at St. Paul 
lower, than it was when the stream flowed upon the rock floor. 
To completely demonstrate such a warping, it will be necessary 
to make certain that the low altitude at Fort Snelling and St. 
Paul is not due to local deepening, such as may have been pro- 
duced by glacial water falls, or by subglacial erosion by water or 
ice. At Sabula no such agencies could have been operative. 
The descent in the rock floor, from Sabula to East St. Louis, 
is not markedly different from that of the present stream, being 
145 feet, where the present stream falls 192 feet. If we reduce 
the descent of the present stream at the two rapids to the aver- 
age rate for the river it lessens the difference thirty feet, leaving 
but seventeen feet difference in a distance of about 350 miles, 
t0 Bed of present stream is 380 feet A. T. (G. K. Warren). 
™ Mo. Riv. Com. Rept. for 1890. The low water altitude here given is on the 
Missouri. 
12 Data concerning depth to rock at bridge piers, furnished by Robert Moore, C.E., 
St. Louis, Mo. 
13 In new channel (G. K. Warren). 
4 Low water varies from 267-279 feet A. T. (Gannett). 
5 Tertiary clays set in at bed of river and extend nearly to sea level (Reports on 
Memphis water supply, by J. M. StaFFoRD and LAWRENCE JOHNSON, issued by 
Artesian Water Co. of Memphis). 
