IPISSRGILACIVAIE, WOILILIB IAS (OVD SelB NES SM SSW 2) a le 755 
channel sixty-five feet deeper opposite St. Louis than is yet 
known to us. It is doubtful if the lower end of the Illinois 
Valley has a rock floor as low as at Princeton. Borings in the 
middle of the valley at Beardstown reach rock at an elevation 
seventy-five feet higher than the rock floor at Princeton, though 
nearly 150 miles below Princeton. Several wells have been 
made in Beardstown, and they indicate a quite uniform level of 
the rock floor. It is possible, but hardly probable, that a much 
deeper channel exists at that point. Wells above Beardstown, 
at Pekin and Peoria, though situated in each case within one-half 
mile of the rock bluffs, reach a lower elevation than those at 
Beardstown before entering rock, while at Peru a well which is 
apparently in a small preglacial tributary of the Illinois, several 
miles from the main valley, finds the rock surface at a lower ele- 
vation than the wells at Beardstown. We may have, therefore, 
in this valley, a warping of the rock floor to such a degree that 
the slope has been reversed above Beardstown. 
If we compare the elevation of the rock floor in this portion 
of the Illinois, with that of the Mississippi a few miles to the 
west, we find support for the view that this section of the Illh- 
nois valley is much depressed. The boring at Sabula, Iowa, 65 
miles in direct line from Princeton, apparently tests better than 
any other boring, the limit of excavation in the Mississippi. The 
Sabula boring shows the rock floor to have an elevation 429 feet 
POG O teeteabove that at) Princeton kncase the upper 
Mississippi Valley connected with the valley at Princeton, through 
the Green river basin, its valley floor would have a fall of nearly 
2¥% feet per mile, or six times the rate of fall of the present 
upper Mississippi, and nearly thirty times the fall of the present 
Illinois just below Princeton. 
About 150 miles further down we find no evidence that the 
Illinois and Mississippi differ greatly in the elevation of their 
valley floors. Thus wells at Ft. Madison, on the Mississippi, 
and at Beardstown, on the Illinois, separated by a distance of 
about 60 miles, and in the same relative position as the Sabula 
and Princeton borings, show only 20 feet difference in the alti- 
tude of the rock floor. 
